Return to flip book view



 turn up the sound here

















 Treatments can be arranged from as little as $70 per week

Hyperbaric oxygen therapy might improve certainpathophysiological findings in autismDaniel A. Rossignol*University of Virginia, Department of Family Medicine, P.O. Box 800729, Charlottesville, VA 22908, USAReceived 28 September 2006; accepted 28 September 2006Summary Autism is a neurodevelopmental disorder currently affecting as many as 1 out of 166 children in the UnitedStates. Numerous studies of autistic individuals have revealed evidence of cerebral hypoperfusion, neuroinflammationand gastrointestinal inflammation, immune dysregulation, oxidative stress, relative mitochondrial dysfunction,neurotransmitter abnormalities, impaired detoxification of toxins, dysbiosis, and impaired production of porphyrins.Many of these findings have been correlated with core autistic symptoms. For example, cerebral hypoperfusion inautistic children has been correlated with repetitive, self-stimulatory and stereotypical behaviors, and impairments incommunication, sensory perception, and social interaction. Hyperbaric oxygen therapy (HBOT) might be able toimprove each of these problems in autistic individuals. Specifically, HBOT has been used with clinical success in severalcerebral hypoperfusion conditions and can compensate for decreased blood flow by increasing the oxygen content ofplasma and body tissues. HBOT has been reported to possess strong anti-inflammatory properties and has been shownto improve immune function. There is evidence that oxidative stress can be reduced with HBOT through theupregulation of antioxidant enzymes. HBOT can also increase the function and production of mitochondria and improveneurotransmitter abnormalities. In addition, HBOT upregulates enzymes that can help with detoxification problemsspecifically found in autistic children. Dysbiosis is common in autistic children and HBOT can improve this. Impairedproduction of porphyrins in autistic children might affect the production of heme, and HBOT might help overcome theeffects of this problem. Finally, HBOT has been shown to mobilize stem cells from the bone marrow to the systemiccirculation. Recent studies in humans have shown that stem cells can enter the brain and form new neurons,astrocytes, and microglia. It is expected that amelioration of these underlying pathophysiological problems throughthe use of HBOT will lead to improvements in autistic symptoms. Several studies on the use of HBOT in autistic childrenare currently underway and early results are promising.!c2006 Elsevier Ltd. All rights reserved.0306-9877/$ - see front matter!c2006 Elsevier Ltd. All rights reserved.doi:10.1016/j.mehy.2006.09.064Abbreviations: HBOT, hyperbaric oxygen therapy; PDD, pervasive developmental disorder; SPECT, single photon emission comp-uted tomography; PET, positron emission tomography; fMRI, functional magnetic resonance imaging; HIF-1a, hypoxia-inducible fa-ctor-1a; VEGF, vascular endothelial growth factor; IL, interleukin; PMN, polymorphonuclear neutrophil; MCP-1, macrophagechemoattractant protein-1; CSF, cerebral spinal fluid; GFAP, glial fibrillary acidic protein; BDNF, brain derived neurotrophic factor;LNH, lymphoid nodular hyperplasia; TNF-a, tumor necrosis factor-a; IFN, interferon; atm, atmosphere; COX-2, cyclooxygenase-2;SOD, superoxide dismutase; HSP, heat shock protein; SSRI, selective serotonin reuptake inhibitors; CP, cerebral palsy.*Tel.: +1 321 953 0278.E-mail address: dlross7@hotmail.com.Medical Hypotheses (2006) x, xxx–xxxhttp://intl.elsevierhealth.com/journals/mehyPlease cite this article in press as: Rossignol DA, Hyperbaric oxygen therapy might improve certain pathophysiologicalfindings in autism, Med Hypotheses (2006), doi:10.1016/j.mehy.2006.09.064ARTICLE IN PRESS

BackgroundAutism is a neurodevelopmental disorder currentlyaffecting as many as 1 out of 166 children in the Uni-ted States [1] and as many as 1 in 86 in certain areasof England [2]. Over 1.5 million children and adults inthe United States alone are affected with some formof autism [3]. Autism is characterized by impair-ments in soci al interaction, difficulty with communi-cation, and restrictive and repetitive behaviors [4].Traditionally, autism has been considered a highlygenetic disorder, yet the identification of a specificgenetic cause has been elusive despite numerousstudies [5–7]. One recent study has demonstratedthat many children with autism typically have wors-ening of core autistic clinical features with increas-ing age [8]. Moreover, young children diagnosed withPervasive Developmental Disorder (PDD) tend to getworse clinically over time, and almost all are diag-nosed with autism at a later age [9]. According tothese two studies, improvements in core autisticfeatures are uncommon. Therefore, any treatmentthat can improve autistic symptoms demands addi-tional study and implementation.HypothesisRecent analysis has furthered our understanding ofthe underlying pathophysiology of autism that wasnot apparent even several years ago. Novel clinicalfindings in autism have lately been described, includ-ing cerebral hypoperfusion, neuroinflammation andgastrointestinal inflammation, immune dysregula-tion, oxidative stress, relative mitochondrial dys-function, neurotransmitter abnormalities, impaireddetoxification enzymes, dysbiosis, and impaired pro-duction of porphyrins. Many of these findings havebeen correlated with core autistic symptoms. Hyper-baric oxygen therapy (HBOT) might be able to im-prove each of these problems and has been shownto mobilize stem cells from the bone marrow to thesystemic circulation. Recent human studies havedemonstrated that stem cells can enter the brainand form new neurons, astrocytes, and microglia. Itis expected that amelioration of these underlyingpathophysiological problems through the use of HBOTwill lead to improvements in autistic symptoms.Review of the pathophysiology of autismand possible benefits of HBOTCerebral hypoperfusion in autismNumerous independent single photon emissioncomputed tomography (SPECT) and positron emis-sion tomography (PET) research studies have dem-onstrated hypoperfusion to several areas of theautistic brain, most notably the temporal lobes[10–23]. In one study, this hypoperfusion typicallyworsened as the age of the autistic child increased,and become ‘‘quite profound’’ in older childrencompared to younger [11]. The maximal decreasein blood flow in autistic children compared tocontrol children was approximately 8% in anotherstudy [18]. This cerebral hypoperfusion has beencorrelated with many of the core clinical featuresassociated with autism (see Table 1). Repetitive,self-stimulatory, and unusual behaviors includingresistance to changes in routine and environmenthave been correlated with decreased blood flowto the thalamus [13]. ‘‘Obsessive desire for same-ness’’ and ‘‘impairments in communication andsocial interaction’’ have been correlated with de-creased blood flow to the temporal lobes [15].Impairments in processing facial expressions andemotions have been correlated with decreasedblood flow to the temporal lobes and amygdala[24]. Diminished blood flow to the fusiform gyrushas been correlated with difficulty in recognizingfamiliar faces [25]. Decreased language develop-ment [11] and auditory processing [17] have beencorrelated with decreased blood flow to Wernicke’sand Brodmann’s area. Finally, hypoperfusion of thetemporal and frontal lobes has been correlated withdecreased IQ in autistic individuals [20].In addition, not only do autistic individuals havedecreased blood flow at baseline, but w hen autisticchildren attend to a task, they often do not have acompensatory increase in blood flow like typicalTable 1 Selected areas of cerebral hypoperfusion inautism and clinical correlationsArea of cerebralhypoperfusionClinical correlationThalamus Repetitive, self-stimulatory,and unusual behaviors [13]Temporal lobes Desire for sameness and social/communication impairments[15]Temporal lobes andamygdalaImpairments in processingfacial expressions/emotions[24]Fusiform gyrus Difficulty recognizing familiarfaces [25]Wernicke’s andBrodmann’s areasDecreased languagedevelopment and auditoryprocessing problems [11,17]Temporal andfrontal lobesDecreased IQ [20]2 RossignolPlease cite this article in press as: Rossignol DA, Hyperbaric oxygen therapy might improve certain pathophysiologicalfindings in autism, Med Hypotheses (2006), doi:10.1016/j.mehy.2006.09.064ARTICLE IN PRESS

children, and instead sometimes demonstrate de-creased blood flow. Neurotypical children have anincrease in cerebral blood flow as measured byfunctional magnetic resonance imaging (fMRI)when performing a task that requires attention orsensory input; autistic children typically lack thisincrease in blood flow [26]. Control children alsohave an increase in cerebral blood flow when lis-tening to tones and generating sentences; whereasautistic children typically have a decrease in cere-bral blood flow [27]. Upon an auditory stimulation,‘‘normal’’ children have a drop in the left middlecerebral artery resistance index as measured bytranscranial doppler ultrasound (which meansblood flow increases); while autistic children havean increase in resistance index, which causes bloodflow to decrease [28]. These findings might indi-cate that the brain metabolic rate and functionare diminished in autistic children because bloodflow is tightly coupled with these two parameters[29,30].The cause of this cerebral hypoperfusion inautistic individuals is unknown but might be dueto inflammation. One recent study on autopsy brainsamples from autistic individuals described accu-mulation of perivascular macrophages and microg-lia [31], which could be consistent with vasculitis.This accumulation could cause stiffening of thevessel wall and decrease the size of the lumen,leading to decreased cerebral blood flow. Further-more, elevated urinary levels of 8-iso prostane-F2ahave recently been described in some autistic indi-viduals [32]. In some studies, this isoprostane ele-vation has been shown to cause in vivovasoconstriction and increase the aggregation ofplatelets [33]. A more recent study on autistic indi-viduals also demonstrated increased urinary levelsof isoprostane F2a-VI (a marker of lipid peroxida-tion), 2,3-dinor-thromboxane B2(which reflectsplatelet activation), and 6-keto-prostaglandin F1a(a marker of endothelium activation) [34]. Theseelevated markers indicate that some autistic chil-dren have increased platelet aggregation, endothe-lium activation, and vasoconstriction. This isimportant because vasoconstriction can cause de-creased blood flow to the brain, which could re sultin relative hypoxia. Hypoxia has been shown toactivate brain microglia which in turn produceinflammatory mediators, such as Tumor NecrosisFactor-a (TNF-a) and Interleukin-1 (IL-1) [35].Treatment of this inflammation might help restorenormal blood flow. In fact, many inflammatory con-ditions such as lupus, Kawasaki disease, Behc¸et’sdisease, ence phalitis, and Sjo¨gren’s syndrome arecharacterized by cerebral hypoperfusion [36–42],and treatment with anti-inflammatory medicationcan restore normal cerebral blood flow in some ofthese conditions [43,44].Unfortunately, a viscous cycle could ensue as in-creased inflammation could lead to increased cere-bral hypoperfusion (see Fig. 1). This, in turn, canlead to hypoxia. Hypoxia causes an increase in hy-poxia-inducible factor-1a (HIF-1a), which in turncauses an increase in inflammation, including red-ness and swelling of tissues, and the attraction oflymphocytes [45]. HIF-1a is essential for inflamma-tion mediated by myeloid cells [46]. In fact, in onestudy, rats that were null for HIF-1a demonstratedalmost complete inhibition of the inflammatory re-sponse [47]. HIF-1a is also responsible for angio-genesis that is secondary to hypoxia [47,48]. Inaddition, HIF-1a induces Vascular EndothelialGrowth Factor (VE GF), which increases the perme-ability of blood vessels [45] and causes tissue ede-ma. This edema can lead to increased interstitialspace between cells [49] and cause an increase inthe distance that oxygen must diffuse from theblood vessel to the cells and can thus lead to cellu-lar hypoxia [50]. Chronic inflammation is commonlyassociated with the infiltration of polymorphonu-clear neutrophils (PMN’s) and other immune cells,along with the cytokines that are released by thesecells. This causes an increase in local oxygen usagedue to the resultant oxygen requirements of thesenew cells. Yet, at the same time, inflammationcauses reduced oxygen extraction by normal cells[51]. For instance, in one study, elevated markersof inflammation (including IL-6, TNF receptors 1and 2, and high-sensitivity C-reactive protein) werecorrelated with decreased maximum oxygen up-take at peak exercise (VO2max) in patients withknown or suspected coronary artery disease [52].Therefore, inflammation prevents maximal uptakeof oxygen by cells. Inflammation also increases oxi-dative stress and can cause neutrophils to becomemore adherent and attach to vessel walls [53]. Thisinfiltration and increased adherence of inflamma-tory cells can contribute to brain injury by decreas-ing microvascular blood flow, causing thrombosis,and increasing the production of free radicals [54].HBOT and cerebral hypoperfusionHBOT can overcome the effects of cerebral hypop-erfusion (see Table 2) by providing more oxygen tothe brain [55,56], and by causing angiogenesis ofnew blood vessels over time by increasing VEGFlevels [57]. Furthermore, if cerebral hypoperfusionis causing hypoxia that is also driving inflammationthrough the induction of HIF-1a, the oxygenHyperbaric oxygen therapy might improve certain pathophysiological findings in autism 3Please cite this article in press as: Rossignol DA, Hyperbaric oxygen therapy might improve certain pathophysiologicalfindings in autism, Med Hypotheses (2006), doi:10.1016/j.mehy.2006.09.064ARTICLE IN PRESS

delivered by HBOT can improve hypoxia, and thusdownregulate HIF-1a. Hypoxia can lead to apopto-sis [58] regulated by HIF-1a [59]. HBOT has beenshown to inhibit the expression of HIF-1a and itstarget genes [60], and prevent apoptosis [61] byinhibiting proapototic BNIP-1 [60] and by increasingInflammation↑ Oxygen usage by inflammatory cells ↑ Thrombosis ↑ Hypoperfusion ↑ Hypoxia ↑ HIF-1α↑ VEGF ↑ Permeability of blood vessels↑ Tissue edema ↑ Interstitial Space and↓ Distance oxygen can travel ↑ Angiogenesis ↑ 8-isoprostane-F2α,Isoprostane F2α-VI, 6-keto-prostaglandin F1α, and 2,3-dinor-thromboxane B2Vasoconstriction↑ Platelet aggregation↑ Perivascular macrophagesand microglia ↓ Extraction of oxygen by normal cells ↓ Microvascular blood flow Figure 1 Proposed cycle of inflammation and resultant cerebral hypoperfusion in autism.Table 2 Proposed mechanisms of inflammatory-induced cerebral hypoperfusion found in autism and HBOT effectsAutism inflammatory finding Mechanism of hypoperfusion HBOT effect› 8-isoprostane-F2a [32] andisoprostane F2a-VI [34]Vasoconstriction causes decreasedblood flow which leads to decreaseddelivery of oxygen [33]Increases the amount of oxygenin plasma and thus increasesdelivery of oxygen to cells[55,56]› 2,3-dinor-thromboxaneB2[34]Increased aggregation of platelets No effect on plateletaggregation [77]a› 6-keto-prostaglandinF1a[34]Endothelial activation Decreases aggregation of PMN’sto endothelium [66]Cerebral infiltration ofperivascular macrophagesand microglia [31]Vasculitis-like condition Decreases PMN infiltration ininjured areas [54]Cerebral infiltration ofperivascular macrophagesand microglia [31]Increased oxygen usage byinflammatory cells and reduced oxygenextraction by normal cells [51]Increases oxygen in plasma andthus increases delivery ofoxygen to cells [55,56]aIn this study, platelet aggregation decreased slightly after one hyperbaric treatment, but returned to normal with repeatedHBOT.4 RossignolPlease cite this article in press as: Rossignol DA, Hyperbaric oxygen therapy might improve certain pathophysiologicalfindings in autism, Med Hypotheses (2006), doi:10.1016/j.mehy.2006.09.064ARTICLE IN PRESS

the expression of Bcl-2, an inhibitor of apoptosis[62]. Interestingly, Bcl-2 levels in the brains ofsome autistic people are diminished [63].Since the cerebral hypoperfusion in autism islikely secondary to inflammation, HBOT mi ght beespecially helpful because it possesses stronganti-inflammatory properties as will be discussedin detail shortly. Inflam mation is often accompa-nied by PMN infiltration which can decrease micro-vascular blood flow; however, HBOT has beenshown to decrease the infiltration of PMN’s afteran ischemic injury to the brain [54,64,65]. In addi-tion, HBOT inhibits neutrophil attachment to bloodvessel walls [66], reduces leukocyte adherence[67], and increa ses the distance that oxygen cantravel in the interstitial space [68]. HBOT has alsobeen used in cases of vasculitis with good results[69], and with success in disorders characterizedby cerebral hypoperfusion including fetal alcoholsyndrome [70], cerebral palsy [71,72], autism[73], chronic brain injury [74], closed head injury[75], and stroke [76].Neuroinflammation in autismSeveral recent studies have revealed that childrenwith autism have evidence of neuroinflammation[31,78,79]. Marked activation of microglia andastroglia with elevations in IL-6 and macrophagechemoattractant protein-1 (MCP-1) were found inautistic brain samples upon autopsy, along with in-creased proinflammatory cytokines in the cerebralspinal fluid (CSF) of living autistic children [31].Activated microglia have been shown to releaseinflammatory mediators such as IL-1 and TNF-a,and have been implicated as the primary cell typethat controls inflammation-mediated neuronal in-jury [35]. A cell-mediated immune response tobrain tissue in autistic individuals has also been de-scribed [80]. In addition, some autistic childrenhave increased glial fibrillary acidic protein (GFAP)in brain samples [79] and the CSF [81], which is alsoindicative of inflammation and reactive injury.Autoantibodies to neuron-axon filament proteinand GFAP were also increased in the plasma ofautistic individuals compared to control individuals[82]. Autistic children make more serum autoanti-bodies to the brain [83], incl uding IgG and IgMautoantibodies to brain epithelial cells and nucleiwhen compared to typical children [84]. Elevatedserum autoantibo dies to many neuron-specific anti-gens and cross-reactive peptides have been foundin autistic children [85], including antibodies direc-ted against cerebellar Purkinje cells [86], and otherneural proteins (see Table 3) such as myelin basicprotein [85,87,88]. Furthermore, 49% of autisticchildren in one study created serum antibodiesagainst the caudate nucleus, and 18% produced ser-um antibodies to the cerebral cortex [89]. Anotherrecent study demonstrated that autistic children,when compared to control children, developed ser-um autoantibodies to brain derived neurotrophicfactor (BDNF) and had higher levels of serum BDNF.This is important because an elevation of BDNF pre-dicts abnormalities in intellect and social develop-ment [90]. Finally, maternal neuronal antibodiesmight play a role in the development of autism insome children [91].Gastrointestinal inflammation in autismIn addition, some patients with autism havechronic ileocolonic lymphoid nodular hyperplasia(LNH) and enterocolitis characterized by mucosalinflammation of the colon, st omach, and smallintestine [92–94]. These findings might representa ‘‘new variant inflammatory bowel disease’’[93], and have been described as a ‘‘panentericIBD-like disease’’ [95]. As many as 90% of autisticchildren wit h gastrointest inal symptoms haveevidence of ileal LNH, with 68% having moderateto severe ileal LNH [92]. In one study, the gastroin-testinal mucosa was shown to have increasedlymphocytic infiltration and density, crypt cellTable 3 Evidence of neuroinflammation in autismA. Elevated markers of neuroinflammationActivation of microglia and astroglia [31]Brain IL-6 [31]Brain MCP-1 [31]Brian GFAP [79]CSF GFAP [81]B. Elevated serum antibodies to brain proteinsNeuron-axon filament protein [82]GFAP [82]Brain epithelial cells and nuclei [84,83]Myelin basic protein [85,87]Myelin associated glycoprotein [85]Ganglioside [85]Sulfatide [85]Chondroitin sulfate [85]Myelin oligodendrocyte glycoprotein [85]a,h-crystallin [85]Neurofilament proteins [85]Tubulin [85]Cerebellar Purkinje cells [86]Caudate nucleus [89]Cerebral cortex [89]BDNF [90]Hyperbaric oxygen therapy might improve certain pathophysiological findings in autism 5Please cite this article in press as: Rossignol DA, Hyperbaric oxygen therapy might improve certain pathophysiologicalfindings in autism, Med Hypotheses (2006), doi:10.1016/j.mehy.2006.09.064ARTICLE IN PRESS

proliferation, and epithelial IgG deposits mimickingan autoimmune lesion [96]. Another study demon-strated that the gastroin testinal mucosa in autisticindividuals had evidence of increased lymphocytesand proinflammatory cytokines including TNF-a andInterferon-c (IFN-c), and less of the anti-inflamma-tory cytokine IL-10, which is counter-regulatory[97]. Some autistic children also had evidence ofan eosinophilic infiltrate of the gastrointestinalmucosa [98]. Autistic children typically make sig-nificantly more serum antibodies against gliadinand casein peptides resulting in autoimmune reac-tions [99]. More than 25% of autistic individualsmake serum IgG, IgM, and IgA antibodies againstgliadin, which can cross-react with cerebellar pep-tides [86] . Furthermore, when compared to typicalchildren, autistic children produce more proinflam-matory cytokines, including TNF-a, IL-1b, and IL-6[100]. One study has shown that the genetic locifor autism have a propensity to cluster with recog-nized loci for inflammatory diseases [101].Interestingly, children on a gluten and/or caseinfree diet produced less TNF-a in the colonic muco-sa [97], and had less evidence of eosinophilic infil-tration of the mucosa [98]. In addition, the use ofanti-inflammatory treatments might improve autis-tic symptomology [102]. In fact, treatment withcorticosteroids of one child who developed anautoimmune lymphoproliferative syndrom e andsubsequent autism led to object ive improvementsin speech an d developmental milestones [103]. Inanother child with PDD, whose behavior and lan-guage regressed at 22 months of age, treatmentwith corticosteroids ameliorated abnormal behav-iors such as hyperactivity, tantrums, impaired so-cial interaction, echolalia, and stereotypies [104].HBOT and inflammationHBOT has potent anti-inflammatory tissue effects[57] as revealed by several recent animal studies[105,106], with equivalence to diclofenac 20 mg/kg noted in one study [107]. HBOT has been shownto attenuate the production of proinflammatorycytokines including TNF-a [108–111], IL-1[108,112], IL-1b [110,111], and IL-6 [108], and in-crease the production of anti-inflammatory IL-10[113]. HBOT has also been shown to reduce neuro-inflammation in a rat model after traumatic braininjury [65]. HBOT also reduced both inflammationand pain in an animal model of inflammatory pain[114], decreased the symptoms of advanced arthri-tis in rats [115], and attenuated the inflammatoryresponse in the peritoneal cavity caused by in-jected meconium [116]. HBOT has been used in ani-mal studies to improve colitis [105,117–119], andhas been used in humans to achieve remission ofCrohn’s disease [120–124] and ulcerative colitis[125,126] not responding to conventional medica-tions, including corticosteroids. Interestingly, insome studies, the decrease in inflammation withHBOT appeared to be caused by the increased pres-sure, not necessarily by the increased oxygen ten-sion. In one animal study, hyperbaric pressurewithout additional oxygen was shown to decreaseTNF-a levels [127]. In another human study, HBOTat 2 atmosphere (atm) and 100% oxygen, andhyperbaric pressure at 2 atm and 10.5% oxygen(thus supplying 21% oxygen, equal to room air oxy-gen) both showed anti-inflammatory activity byinhibiting IFN-c release, whereas 100% oxygen atroom air pressure (1 atm) actually increased IFN-crelease [128].The anti-inflammatory effect of HBOT might oc-cur through the relief of hypoxia and the down-reg-ulation of HIF-1a [47,60]. HBOT also decreasesProstaglandin E2production [112] which decreasesinflammation because prostglandins increaseinflammation, pain, and edema [57]. In one study,HBOT decreased cyclooxygenase-2 (COX-2) enzymeexpression after transient cerebral ischemia [129].The COX-2 enzyme is responsible for increasedprostaglandin production, leading to increasedinflammation. Blockade of the COX-2 enzyme hasbeen shown to decrease inflammation and cytokinelevels including IL-6 [130]. For these reasons, HBOTmight help amelior ate the inflammation found inautism (see Table 4).Immune function in autismThere is mounting evidence of immune dysregula-tion in autistic individuals (see Table 5), and newresearch is revealing the link between the immunesystem and the nervous system [131]. An increasednumber of autoimmune diseases exist in autisticfamilies compared to control families [132,133]with as much as a 6–8 fold increased incidence[134]. Some researchers believe that autistic chil-dren might have ‘‘an underlying autoi mmune disor-der’’ [135] and that a ‘‘genetic relationship’’ existsbetween autism and immune dysregulation [101].Two early studies revealed that 38% of autistic chil-dren had no detectible Rubella titers despite vacci-nation [136], and 60% produced abnormal serumantibodies to measles hemagglutinin protein whencompared to control children [87]. Autistic individ-uals also make more serum antibodies to Heat6 RossignolPlease cite this article in press as: Rossignol DA, Hyperbaric oxygen therapy might improve certain pathophysiologicalfindings in autism, Med Hypotheses (2006), doi:10.1016/j.mehy.2006.09.064ARTICLE IN PRESS

Shock Protein-90 (HSP -90) [137], which could causeHSP-90 levels to be lower. HSP-90 is a signal trans-ducer which regulates development and cell differ-entiation. In one study, decreased levels of HSP-90allowed natural genetic abnormalities hidden infruit fly populations to suddenly appear [138]. At-tempts to improve the underlying immune defi-ciency in autistic individuals with intravenousimmune globulin have shown promising results[139–141].In addition, several studies have reported abnor-malities in T-lymphocytes, including a decreasednumber of CD4+cells [142] in approximately 35%of autistic individuals [139]. This has led to an al-tered ratio of CD4/CD8 cells with a reduced num-ber of T-helper cells (CD4+CD8") and an increasednumber of suppressor T-cells (CD4"CD8+) in someautistic individuals [143]. One study demonstratedthat treatment with naltrexone increased the num-ber of T-helper inducers and reduced the numberof T-cytotoxic suppressors, resulting in a normali-zation of the CD4/CD8 ratio and improvement ofsymptoms in over half of the autistic children stud-ied [144] . CD4+cells are divided into Th1 and Th2subsets. Th1 cells produce IL-2 and IFN-c and areinvolved in T-cell proliferation, activation of mac-rophages, and cell-mediated immunity includ ingphagocytosis of intracellular pathogens likeviruses. Th2 cells are part of the adaptive immunesystem and produce IL-4, IL-5, IL-6, IL-10, and IL-13. IL-4 is involved in the B-cell production ofIgE. IL-5 stimulates the production of eosinophils,and IL-6 is involved in the production of immuno-globulins. IL-1 and IL-6 are proinflammatory cyto-kines, and IL-10 inhibits Th1 cytokine productionand thus down-regulates the inflammatory re-sponse [145]. Skewing toward Th2 is often seen inallergic responses [146 ]. Interestingly, a history ofallergies in the mother during pregnancy led to agreater than 2-fold elevated risk of autism [147],and children with autism tend to have more foodallergies than control children [148].Some earlier studies demonstrated activation ofthe Th1 system in autistic children with increasedproduction of IL-12 and interf eron when comparedto control children [149,150]. Autistic individualsmake more IFN-c and IL-1 receptor antagonist,which can cause a Th1 skewing [151]. Autistic chil-dren also have increased markers of cell-mediatedTable 4 Effects of HBOT on inflammatory markers and inflammation in autismMarker Classification Autism finding HBOT effectTNF-a Inflammatory › [100,97] fl [111,108,110,109], [127]aIL-1b Inflammatory › [100] fl [111,110]IL-6 Inflammatory › [100,31] fl [108]IL-10 Anti-inflammatory fl [97] › [113]IFN-c Inflammatory › [97] fl [128]bNeuroinflammation › [31,78,79] fl [65]Gastrointestinal inflammation › [92–94] fl [120,125]aHyperbaric pressure without additional oxygen decreased TNF-a.bHyperbaric pressure without additional oxygen also decreased IFN-c.Table 5 Evidence of immunological abnormalities inautismA. Non-neuronal serum antibodies produced inautistic individualsHSP-90 [137]Gliadin [99]Casein [99]Milk butyrophilin [85]Chlamydia pneumoniae [85]Streptococcal M protein [85]Measles hemagglutinin protein [87]B. Cellular, immunoglobulin, and cytokineabnormalities› Serum IgG2 and IgG4 [135]fl Responsiveness of lymphocytes [155]fl Natural killer cells [156]fl Number of total CD4+ cells [143,142]fl Number of T-helper cells (CD4+CD8") [143]› Number of suppressor T-cells (CD4"CD8+) [143]Imbalance of CD4+and CD8+cells [153]› IFN-c [149]› Markers of cell-mediated immunity (urinaryneopterin and biopterin) [152]› IL-4 [154]› IL-5 [154]› IL-12 [149]› IL-13 [154]fl IL-10 [97]› Serum IgE [139,148]fl Serum IgA [139]Hyperbaric oxygen therapy might improve certain pathophysiological findings in autism 7Please cite this article in press as: Rossignol DA, Hyperbaric oxygen therapy might improve certain pathophysiologicalfindings in autism, Med Hypotheses (2006), doi:10.1016/j.mehy.2006.09.064ARTICLE IN PRESS

immunity, a Th-1 function, including elevated uri-nary neopterin and biopterin [152]. Final ly, a cell-mediated immune response to brain tissues inautistic individuals has also been described [80].More recent studies indicate that autistic chil-dren exhibit a shift from Th1 to Th2 T-cell type[135,140], as evidenced by an increased productionof IgE [139,148] and IL-4 producing CD4+T-cells,and lower levels of IL-2 producing CD4+T-cellscompared to control children [153]. Furthermore,about one-third of autistic children in one studydemonstrated IgG subclass deficiency not confinedto the 4 subclasses of IgG [139]. Approximately 5%of autistic individuals have IgA deficiency, which isnormally present in 1 in 700–1000 people, andabout 30-40% have low serum IgA levels [139]. Inspite of these deficiencies, a new study suggeststhat autism is characterized by a heightened im-mune system. This is evidenced by an increasedactivation of both the Th1 and Th2 arms with Th2predominance as indicated by increased IL-4, IL-5and IL-13 when compared to control individuals,without a compensatory increase in IL-10 [154].Shifting from a Th1 to a Th2 T-cell type mightenhance susceptibility to chronic viral infectionsin some autistic individuals [135]. In fact, de-pressed responsiveness of lymphocytes was foundin one study on autistic children [155], and anotherstudy demonstrated a 40% decrease in the numberof natural kill er cells when compared to controlchildren [156]. Therefore, autistic individualsmight have ‘‘enhanced susceptibility to infectionsresulting in chronic viral infections’’ [135].HBOT and immune functionHBOT might be useful in some autoimmune dis-eases [157], and has shown promise in rheumaticdiseases, including lupus and scleroderma [158],and rheumatoid arthritis [159]. HBOT has beenused in animal models to completely suppress auto-immune encephalomyelitis by blocking mononu-clear infiltration and demyelination of the CNS[160], and act ed as an immunosuppressive agentto delay skin allograft rejection [161]. HBOT hasbeen shown to suppress immune responses suchas proteinuria, facial erythema, and lymphadenop-athy in an autoimmune mouse model [162]. In addi-tion, one animal study showed increased survivaland decreased proteinuria, anti-dsDNA antibody ti-ters, and immune-complex deposition in lupus-prone autoimmune mice treated with HBOT [163].HBOT improved symptoms in patients with atopicdermatitis and also decreased IgE immunoglobulinand complement levels [164]. In patients with mul-tiple sclerosis, HBOT produced a significant in-crease in total and helper T-lymphocyte numbersand serum IgA levels [165]. Two other studies dem-onstrated an increase in lymphocyte count, withvariable subset population increases depending onwhich organ (spleen, thymus, or blood) was exam-ined and how much oxygen was given with HBOT[166,167]. HBOT has also been shown to increaseIL-10, the anti-inflam matory interle ukin [113],and induce the production of HSP-90 [168]. Inter-estingly, some of the immunomodulatory effectsof HBOT might be due to the increased pressure,not necessarily the increased oxygen tension[169]. Even low hyperbaric pressures, without addi-tional oxygen, can affect the immune system. Onestudy demonstrated that hyperbaric pressure atjust 20 mmHg (approximately 1.03 atm) can havean effect on the immune system [127]. Based uponthese reasons, HBOT might help improve the im-mune dysregulation found in autistic individuals(see Table 6).Oxidative stress in autismAutistic children have evidence of increased oxida-tive stress including lower serum glutathione levels[170,171]. Some autistic children have increasedred blood cell nitric oxide, which is a known freeradical and toxic to the brain [172]. Of not e, HIF-1a increases the production of nitric oxide [45].Lower serum antioxidant enzyme, antioxidantnutrient, and glutathione levels, as well as higherpro-oxidants have been found in multiple studiesof autistic children [173]. Autistic children haveevidence of increased lipid peroxidation [34,174],including increased malondialdehyde which is amarker of oxidative stress and lipid peroxidation[175]. Decreased activities of certain antioxidantenzymes have also been described in autistic indi-viduals including superoxide dismutase (SOD)Table 6 Effects of HBOT on immune dysregulationin autismMarker Autism finding HBOT effectHSP-90 fl? (due toincreasedantibodies toHSP-90) [137]› [168]Serum IgA fl [139] › [165]Serum IgE › [148,139] fl [164]Lymphocytic activity fl [155] › [166]T-helper cells fl [143] › [165]8 RossignolPlease cite this article in press as: Rossignol DA, Hyperbaric oxygen therapy might improve certain pathophysiologicalfindings in autism, Med Hypotheses (2006), doi:10.1016/j.mehy.2006.09.064ARTICLE IN PRESS

[176], glutathione peroxidase [176], and catalase[174]. Some autistic children also have decreasedactivity of paraoxonase, an antioxidant enzymethat prevents lipid oxidation and also detoxifiesorganophosphates in humans [177]. The gene forHeat Shock Protein 70 (HSP-70), which protectsagainst oxidative stress, was downregulated in mul-tiple cases of autism [178]. Antioxidants such asceruloplasmin [175] and zinc [179] tend to be lowerin autistic patients, and the rat io of copper to zincis abnormal in many autistic children [180]. Fur-thermore, in one study, treatment with antioxi-dants was shown to raise the levels of reduc edglutathione in the serum of autistic children andappeared to improve symptoms [170]. In anotherstudy, the use of antioxidants improved behaviorin some autistic children [181].HBOT and oxidative stressConcerns have been previously raised that HBOTmight increase oxidative stress through the produc-tion of reactive oxygen species [182]. This is a rel-evant concern because of the increased oxidativestress just described in autistic children. However,oxidative st ress from HBOT appears to be less of aconcern at pressures under 2.0 atm [183] which areoften used clinically. Oxidative stress is caused byan imbalance of oxidants and antioxidants. Withlong-term and repeated administration, HBOT be-low 2.0 atm can actually decrease oxidative stress[184–186] by reducing lipid peroxidation [187],and increasing the activity of antioxidant enzymesincluding SOD [185,188], glutathione peroxidase[118], catalase [189], paraoxonase [190], andheme-oxygenase-1 [191–193]. HBOT has also beenshown to increase HSP-70, which protects againstoxidative stress [194,195]. One recent animal studyhas demonstrated that HBOT can suppress oxida-tive stress in brain ti ssues after a stroke [196].HBOT also increases zinc, decreases copper [185],and increases ceruloplasmin levels [197]. Thus,HBOT might help improve the oxidative stressfound in some autistic individuals (see Table 7).Mitochondrial dysfunction in autismLombard hypothesized that autism might be causedby mitochondrial dysfunction [199]. Several recentcase reports supporting this concep t have beenpublished including two autistic children withhypotonia, lactic acidosis and abnormal mitochon-drial enzyme assays on muscle biopsy [200], anautistic child with developmental regression andmitochondrial dysfunction [201], and an autisticchild with mitochondrial dysfunction [202]. A lar-ger case series of 12 children with hypotonia, epi-lepsy, and autism also found mitochondrialdysfunction [203]. Another study on 100 childrenwith autism suggested mild mitochondrial dysfunc-tion as evidenced by red uced carnitine and pyru-vate levels and increased ammonia and alaninelevels [204]. Further research reveals that mito-chondrial point mutations might be the cause ofautism in some people [205]. An association be-tween autism and the mitochondrial aspartate/glu-tamate carrier SLC25A12 gene polymorphism wasrecently described [206] and confirmed [207].Amitochondrial A3243G mutation has also been asso-ciated with autism [208], and both autosomalrecessive and maternally inherited mi tochondrialdefects can cause autism [209]. Some of the morecommon blood abnormalities associated with mito-chondrial dysfunction include elevated aspartateaminotransferase, creatine kinase, and fasting lac-tic acid. In one study of 120 autistic children, 7.2%Table 7 Effects of HBOT on measures of oxidative stress in autismMeasure Classification Autism finding HBOT effectGlutathione peroxidase Antioxidant enzyme fl [176] › [118]Superoxide dismutase Antioxidant enzyme fl [176] › [118,188,185]Heme-oxygenase 1 Antioxidant enzyme ? › [191–193]Catalase Antioxidant enzyme fl [174] › [189]Paraoxonase Antioxidant enzyme; organophosphate detoxification fl [177,198] › [190]HSP-70 Cellular protection against oxidative stress fl [178] › [194,195]Malondialdehyde Marker of oxidative stress and lipid peroxidation › [175] fl [118,185]Ceruloplasmin Antioxidant fl [175] › [197]Glutathione Antioxidant fl [170] › [185]Zinc Antioxidant fl [179] › [185]Copper Metal › [180] fl [185]Hyperbaric oxygen therapy might improve certain pathophysiological findings in autism 9Please cite this article in press as: Rossignol DA, Hyperbaric oxygen therapy might improve certain pathophysiologicalfindings in autism, Med Hypotheses (2006), doi:10.1016/j.mehy.2006.09.064ARTICLE IN PRESS

had a ‘‘definite mitochondrial respiratory chaindisorder’’, and plasma lactate levels were elevatedin 20% of the children [210]. In another study of 159autistic children, compared to 94 control children,autistic children had higher aspartate aminotrans-ferase levels (p = 0.00005), and 47% had elevatedcreatine kinase levels, which might be consistentwith relative mitochondrial dysfunction [201]. Re-cently, mitochondrial abnormalities were discov-ered in a mouse model of Rett Syndrome [211],adisorder classified as a PDD.HBOT and mitochondrial dysfunctionHypoxia can impair mitochondrial function [212].Since only approximately 0.3% of inhaled oxygenis ultimately delivered to the mitochondria [213],increasing the oxygen delivery to dysfunctionalmitochondria by HBOT might aid in improving func-tion [214,215]. In a mouse model with an intrinsicimpairment of mitochondrial complex IV, HBOT at2 atm ‘‘signifi cantly ameliorate[d] mitochondrialdysfunction’’ and delayed the onset of motor neu-ron disease when compared to control mice [215].In animals studies, HBOT increased the amount ofwork done by mitochondria [216], improved mito-chondrial function after brain injury [214], andwas shown to ‘‘protect mitochondria from deterio-ration’’ when compared to normal oxygen andpressure [217]. HBOT also has been shown to in-crease sperm motility by augmenting mitochondrialoxidative phosphorylation in fructolysis-inhibitedsperm cells [218]. HBOT also prevented apoptosisand improved neurological recovery after cerebralischemia by opening mitochondrial AT P-sensitivepotassium chan nels [61]. Finally, HBOT has re-cently been shown to activate mitochondrial DNAtranscription and replication, and increase the bio-genesis of mitochondria in the brains of animals[219]. For these reasons, HBOT might improve therelative mitochondrial dysfunction found in someautistic individuals.Neurotransmitter abnormalities inautismEarly childhood is typified by an increased produc-tion of serotonin when compared to adulthood;however, one study showed that autistic childrensynthesized less serotonin during childhood whencompared to control childre n [220]. Another studydemonstrated lower leve ls of serotonin in bothautistic children and their mothers [221]. Plasmalevels of tryptophan, which is the precursor toserotonin, are lower in autistic children comparedto control children, and are suggestive of a seroto-nergic abnormality [222]. In addition, tryptophanuptake by brain cells as seen on PET scan was lessin autistic children compared to control children[220], and tryptophan depletion can cause a signif-icant increase in autistic behaviors such as ‘‘whirl-ing, flapping, pacing, ban ging and hitting self,rocking, and toe walking’’ [223]. Antibodies againstcerebral serotonin receptors, which preclude thebinding of serotonin, are more common in autisticindividuals when compared to control ind ividuals[224,225]. Selective serotonin reuptake inhibitors(SSRI’s) have been shown to be beneficial for obses-sive and repetitive behaviors [226]. In some stud-ies, SSRI’s including fluoxetine [227], fluvoxamine[226], and escitalopram [228] have shown benefitfor autism.In addition, some autistic children have evi-dence of dopamine overactivity, including higherCSF levels of homovanillic acid, the main metabo-lite of dopamine [229]. Treatment of autistic chil -dren with dopamine agonists has led to worseningof aggression, hyperactivity, and stereotypies[230]. Dopamine antagonists such as pimozide[231] and bromocriptine [232] have shownimprovements in some autistic children.HBOT and neurotransmitterabnormalitiesHBOT has also been shown to reduce the uptake ofserotonin by pulmonary endothelial cells [233,234],and thus might function like an SSRI. In one study,HBOT demonstrated ‘‘antidepress ant-like activ-ity’’ similar to that seen with some SSRI antide-pressants like fluoxetine [235]. In another studyon patients with cluster headaches, HBOT im-proved pain and was shown to act through seroto-nergic pathways [236]. Furthermore, in an animalmodel, HBOT was shown to decrease the releaseof dopamine after cerebral injury [237]. In anotheranimal study, 90% oxygen at room air pressure(1 atm) decreased extracellular dopamine levelsin the brain [238]. Therefore, HBOT might improvethe neurotransmitter imbalances found in someautistic individuals.Toxin exposure in autism and HBOTRecent data has shown that organophosphat e poi-soning can cause atypical autism [239]. Paraoxonase10 RossignolPlease cite this article in press as: Rossignol DA, Hyperbaric oxygen therapy might improve certain pathophysiologicalfindings in autism, Med Hypotheses (2006), doi:10.1016/j.mehy.2006.09.064ARTICLE IN PRESS

is the enzy me responsible for organophosphatedetoxification in humans. In North America, autismhas been associated with variants in the paraoxonasegene which can decrease the activity of this enzymeby 50 percent [177]. This was recently confirmed inanother study that demonstrated reduced activityof paraoxonase in some autistic children [198].HBOT has been shown to increase the activity ofparaoxonase [190], and to prevent a decrease inparaoxonase activity normally seen with a highcholesterol diet [187]. Thus, HBOT might lea d toan improved ability to excrete organophosphatesin some autistic children by upregulating paraoxon-ase activity.Dysbiosis in autismSignificant alterations in intestinal flora, with in-creased amounts of Clostridia bacteria [240–242], and overgrowth of other abnormal bacteria[241], exist in some autistic children when com-pared to control children. In fact, one author hashypothesized that Clostridia infection in the gutmight cause autistic-like symptoms [243]. Further-more, treatment of these abnormal gut bacteriawith antibiotics has led to improvements of autisticsymptoms as measured by a clinical psychologistblinded to the treatment status [244]. Some autis-tic children also have overgrowth of yeast, virus es,and parasites in the gut [245].HBOT and dysbiosisHBOT has been shown to decrease the amount ofabnormal bacteria in the gut and there fore canfunction as an antibiotic [246]. In animal studies,HBOT decreased intestinal bacterial colony countsafter bacteria overgrowth in the distal ileum asso-ciated with bile duct ligation [247]. HBOT is alsobactericidal against many bacteria [248], includingPseudomonas [249,250], Salmonella and Proteus[249], Staphylococcus [251], Mycobacterium tuber-culosis [248], and anaerobic bacteria such asClostridia [252]. In addition, the killing of bacteriaby phagocytic leukocytes is dependent upon oxygen[253], and HBOT has been shown to improve leuko-cyte phagocytic killing of Staphyloccus aureus inanimals [254]. HBOT has also been shown to inhibitthe growth of some yeast [255] and to possess viru-cidal activity against some enveloped viruses [256].HBOT also appears to have an antiviral effectagainst HIV [257]. In an animal model, HBOT im-proved symptoms in a virus-induced leukemia com-pared to a control group [258]. HBOT can also killparasites, including Leishmania amazonens is[259]. Thus HBOT might lead to an improvementin the dysbiosis found in some autistic children byreducing counts of abnormal pathogens.Porphyrin production in autism andHBOTChildren with autism might have impaired produc-tion of some porphyrins [260] which are involvedin the synthesis of heme, which carries oxygen inthe body. Therefore, the ability to deliver oxygenon hemoglobin could be compromised in someautistic children [261], and HBOT might help over-come this by increasing the amount of oxygen dis-solved in plasma.Stem cells and HBOTRecently, HBOT at 2.0 atm was shown to mobilizestem/progenitor cells from the bone marrow of hu-mans into the systemic circulation. Elevations werefound in the number of colony-forming cells asdemonstrated by an increase in the number ofCD34+cells by 8-fold after 20 HBOT sessions[262]. Since stem cells are also produced in thebrain, this gives rise to the possibility of neuropoi-esis [263], which might aid in reversing chronicneurodegenerative dis orders. Furthermore, in twohuman case reports, female bone-marrow-trans-plant patients received cells from male donors.On autopsy of these females, staining for the maleY-chromosome in their brains demonstrated thatmale donor stem cells from the bone marrow hadcrossed into the brain and formed new neuron s,astrocytes, and microglia [264,265].Additional HBOT and future studyconsiderationsHBOT pressure considerationsPrevious studies have shown improvements ofsymptoms in children with autism and cerebralpalsy (CP) at hyperbaric pressures of 1.3 atm withor without additional oxygen [72,73,266]. The useof HBOT in children appears generally safe, evenat pressures up to 2.0 atm for 2 h per day for 40sessions [267]. Many of the potential benefit s ofHBOT as des cribed above were found in studies athigher hyperbaric pressures. Further study is neces-Hyperbaric oxygen therapy might improve certain pathophysiological findings in autism 11Please cite this article in press as: Rossignol DA, Hyperbaric oxygen therapy might improve certain pathophysiologicalfindings in autism, Med Hypotheses (2006), doi:10.1016/j.mehy.2006.09.064ARTICLE IN PRESS

sary to determine if these benefits also hold true atthe lower hyperbaric pressures (1.3–1.5 atm) com-monly being utilized for autistic individuals and toestablish the optimal hyperbaric pressure for aut-ism and related disorders.HBOT oxygen concentration considerationsAs described above, in one study, the decrease ininflammation with HBOT appeared to be causedby the increased pressure, not necessarily by theincreased oxygen tension. In this human study,both HBOT and hyperbaric pressure demonstratedanti-inflammatory activity by inhibiting IFN-c re-lease, whereas 100% oxygen at room air pressure(1 atm) actually increased IFN-c release [128]. Fur-ther study is needed to verify this finding, to deter-mine if this phen omenon equally applies to theother noted benefits of HBOT, to better understandthe mechanisms of action of HBOT, and to deter-mine the optimal oxygen concentration for use inautistic individuals.HBOT session count considerationsThe number of HBOT sessions needed to producefull clinical improvements is unclear. In one studycombining the use of SPECT and HBOT, an averageof 70 treatments was needed to show a significantincrease in cerebral blood oxygenation and metab-olism in patients with chronic neurological disor-ders including CP, stroke, and traumatic braininjury. Of note, the rate of improvement in cere-bral blood oxyg enation and metabolism was moreprofound during the last 35 HBOT sessions whencompared to the first 35 [74]. In another study ofchildren with CP using HBOT at 1.7 atm, serialfunctional measurements after 40 and 80 HBOTsessions showed continuing objective improve-ments including a decrease in the total time of cus-todial care and improved gross motor function. Atthe end of 80 treatments, children in the studywere continuing to improve, and the authors notedthat the optimal number of treatments could notbe determined as it appeared that further HBOTsessions would yield additional improvements[268]. Further study is needed to clarify the opti-mal number of HBOT sessions for autisticindividuals.Pathophysiology as a primary acceptancecriterion for HBOTHBOT has been used by the Navy since 1943 for airembolism and decompression sickness, two indica-tions that are widely accepted. However, no pro-spective, double-blind, placebo-controlled trialshave been performed on these 2 indications;rather, the use of HBOT is justified based uponthe underlying pathophysiology of these 2 condi-tions and the mechanism of action of HBOT [68].The use of HBOT for autism is considered ‘‘off-la-bel’’ [269]. However, examining the pathophysiol-ogy of autism continues to indicate that HBOTmight be effective for treating autism [270]. Sev-eral studies on the use of HBOT in autism are cur-rently underway and early results are promising.It is hoped that a clearer understanding of the po-tential benefits of HBOT in treating the commonsymptoms of autism will spur other researchers toinvestigate the use of HBOT in autistic individuals.ConclusionsNumerous studies of autistic individuals have re-vealed evidence of cerebral hypoperfusion, neuro-inflammation and gastrointestinal inflammation,immune dysregulation, oxidative stress, relativemitochondrial dysfunction, neurotransmitterabnormalities, impaired detoxification of toxins,dysbiosis, and impaired production of porphyrins.HBOT has been shown to increase oxygen deliveryto hypoperfused or hypoxic tissues, decreaseinflammation and oxidative stress, and increasethe production of mitochondria and the numberof circulating stem cells. HBOT might also improvethe immune dysfunction, neurotransmi tter abnor-malities, and dysbiosis specifically found in autisticindividuals. Further studies are necessary to testthis hypothesis and are currently underway. Thepossible effects of HBOT on autism are summarizedin Table 8.Table 8 Summary of the proposed HBOT effects onthe pathophysiology found in autismProblem AutismfindingHBOTeffectCerebral perfusion fl›Neuroinflammation inflammation ›flGastrointestinal inflammation ›flImmune dysregulation ›flOxidative stress ›flMitochondrial function fl›Neurotransmitter abnormalities ›flDetoxification enzyme function fl›Dysbiosis ›flPorphyrin production fl›Circulating stem cells ›12 RossignolPlease cite this article in press as: Rossignol DA, Hyperbaric oxygen therapy might improve certain pathophysiologicalfindings in autism, Med Hypotheses (2006), doi:10.1016/j.mehy.2006.09.064ARTICLE IN PRESS

AcknowledgementThe author thanks Mr. Michael Haynes for reviewingthis manuscript and offering editorial advice.References[1] Singh N. (contact). Press release: CDC launches ‘‘Learnthe signs. Act early.’’ Campaign. http://www.cdc.gov/od/oc/media/pressrel/r050222.htm. February 22, 2005[accessed 9.5.06].[2] Baird G, Simonoff E, Pickles A, et al. Prevalence ofdisorders of the autism spectrum in a population cohort ofchildren in South Thames: the special needs and autismproject (SNAP). Lancet 2006;368(9531):210–5.[3] Shaul M. (contact). GAO-05-220. United States Govern-ment Accountability Office. Report to the chairman andranking minority member, subcommittee on human rightsand wellness, committee on government reform, house ofrepresentatives. Special education: children with autism.http://www.gao.gov/new.items/d05220.pdf. January2005 [accessed 9.5.06].[4] Kanner L. Autistic disturbances of affective contact.Nervous Child 1943;2:217–50.[5] London EA. The environment as an etiologic factor inautism: a new direction for research. Environ HealthPerspect 2000;108(S3):401–4.[6] Baird G, Cass H, Slonims V. Diagnosis of autism. BMJ2003;327(7413):488–93.[7] Klauck SM. Genetics of autism spectrum disorder. Eur JHum Genet 2006;14(6):714–20.[8] Charman T, Taylor E, Drew A, Cockerill H, Brown JA, BairdG. Outcome at 7 years of children diagnosed with autismat age 2: predictive validity of assessments conducted at 2and 3 years of age and pattern of symptom change overtime. J Child Psychol Psychiatry 2005;46(5):500–13.[9] Lord C, Risi S, DiLavore PS, Shulman C, Thurm A, Pickles A.Autism for 2 to 9 years of age. Arch Gen Psychiatry2006;63(6):694–701.[10] Ryu YH, Lee JD, Yoon PH, Kim DI, Lee HB, Shin YJ.Perfusion impairments in infantile autism on technetium-99m ethyl cysteinate dimer brain single-photon emissiontomography: comparison with findings on magnetic reso-nance imaging. Eur J Nucl Med 1999;26(3):253–9.[11] Wilcox J, Tsuang MT, Ledger E, Algeo J, Schnurr T. Brainperfusion in autism varies with age. Neuropsychobiology2002;46(1):13–6.[12] Chiron C, Leboyer M, Leon F, Jambaque I, Nuttin C, SyrotaA. SPECT of the brain in childhood autism: evidence for alack of normal hemispheric asymmetry. Dev Med ChildNeurol 1995;37(10):849–60.[13] Starkstein SE, Vazquez S, Vrancic D, et al. SPECT findingsin mentally retarded autistic individuals. J Neuropsychia-try Clin Neurosci 2000;12(3):370–5.[14] Mountz JM, Tolbert LC, Lill DW, Katholi CR, Liu HG.Functional deficits in autistic disorder: characterization bytechnetium-99m-HMPAO and SPECT. J Nucl Med1995;36(7):1156–62.[15] Ohnishi T, Matsuda H, Hashimoto T, et al. Abnormalregional cerebral blood flow in childhood autism. Brain2000;123(Pt9):1838–44.[16] George MS, Costa DC, Kouris K, Ring HA, Ell PJ. Cerebralblood flow abnormalities in adults with infantile autism. JNerv Ment Dis 1992;180(7):413–7.[17] Boddaert N, Zilbovicius M. Functional neuroimaging andchildhood autism. Pediatr Radiol 2002;32(1):1–7.[18] Zilbovicius M, Boddaert N, Belin P, et al. Temporal lobedysfunction in childhood autism: a PET study. Am JPsychiatry 2000;157(12):1988–93.[19] Kaya M, Karasalihoglu S, Ustun F, et al. The relationshipbetween 99mTc-HMPAO brain SPECT and the scores of reallife rating scale in autistic children. Brain Dev2002;24(2):77–81.[20] Hashimoto T, Sasaki M, Fukumizu M, Hanaoka S, Sugai K,Matsuda H. Single-photon emission computed tomographyof the brain in autism: effect of the developmental level.Pediatr Neurol 2000;23(5):416–20.[21] Gillberg IC, Bjure J, Uvebrant P, Vestergren E, Gillberg C.SPECT (single photon emission computed tomography) in31 children and adolescents with autism and autism-likeconditions. Eur Child Adolesc Psychiatry 1993;2(1):50–9.[22] Boddaert N, Chabane N, Belin P, et al. Perception ofcomplex sounds in autism: abnormal auditory corticalprocessing in children. Am J Psychiatry 2004;161(11):2117–20.[23] Ito H, Mori K, Hashimoto T, et al. Findings of brain99mTc-ECD SPECT in high-functioning autism-3-dimensional ste-reotactic ROI template analysis of brain SPECT. J MedInvest 2005;52(1–2):49–56.[24] Critchley HD, Daly EM, Bullmore ET, et al. The functionalneuroanatomy of social behaviour: changes in cerebralblood flow when people with autistic disorder processfacial expressions. Brain 2000;123(Pt11):2203–12.[25] Pierce K, Haist F, Sedaghat F, Courchesne E. The brainresponse to personally familiar faces in autism: findings offusiform activity and beyond. Brain 2004;127(Pt12):2703–16.[26] Allen G, Courchesne E. Differential effects of develop-mental cerebellar abnormality on cognitive and motorfunctions in the cerebellum: an fMRI study of autism. Am JPsychiatry 2003;160(2):262–73.[27] Muller RA, Behen ME, Rothermel RD, et al. Brain mappingof language and auditory perception in high-functioningautistic adults: a PET study. J Autism Dev Disord1999;29(1):19–31.[28] Bruneau N, Dourneau MC, Garreau B, Pourcelot L, LelordG. Blood flow response to auditory stimulations in normal,mentally retarded, and autistic children: a preliminarytranscranial Doppler ultrasonographic study of the middlecerebral arteries. Biol Psychiatry 1992;32(8):691–9.[29] Fox PT, Raichle ME. Focal physiological uncoupling ofcerebral blood flow and oxidative metabolism duringsomatosensory stimulation in human subjects. Proc NatlAcad Sci USA 1986;83(4):1140–4.[30] Parri R, Crunelli V. An astrocyte bridge from synapse toblood flow. Nat Neurosci 2003;6(1):5–6.[31] Vargas DL, Nascimbene C, Krishnan C, Zimmerman AW,Pardo CA. Neuroglial activation and neuroinflammation inthe brain of patients with autism. Ann Neurol2005;57(1):67–81.[32] Ming X, Stein TP, Brimacombe M, Johnson WG, LambertGH, Wagner GC. Increased excretion of a lipid peroxida-tion biomarker in autism. Prostaglandins Leukot EssentFatty Acids 2005;73(5):379–84.[33] Pratico D, Lawson JA, Rokach J, FitzGerald GA. Theisoprostanes in biology and medicine. Trends EndocrinolMetab 2001;12(6):243–7.[34] Yao Y, Walsh WJ, McGinnis WR, Pratico D. Altered vascularphenotype in autism: correlation with oxidative stress.Arch Neurol 2006;63(8):1161–4.Hyperbaric oxygen therapy might improve certain pathophysiological findings in autism 13Please cite this article in press as: Rossignol DA, Hyperbaric oxygen therapy might improve certain pathophysiologicalfindings in autism, Med Hypotheses (2006), doi:10.1016/j.mehy.2006.09.064ARTICLE IN PRESS

[35] Lu DY, Liou HC, Tang CH, Fu WM. Hypoxia-induced iNOSexpression in microglia is regulated by the PI3-kinase/Akt/mTOR signaling pathway and activation of hypoxia induc-ible factor-1a. Biochem Pharmacol 2006. doi:10.1016/j.bcp.2006.06.038, in press.[36] Ichiyama T, Nishikawa M, Hayashi T, Koga M, Tashiro N,Furukawa S. Cerebral hypoperfusion during acute Kawa-saki Disease. Stroke 1998;29(7):1320–1.[37] Huang WS, Chiu PY, Tsai CH, Kao A, Lee CC. Objectiveevidence of abnormal regional cerebral blood flow inpatients with systemic lupus erythematosus on Tc-99mECD brain SPECT. Rheumatol Int 2002;22(5):178–81.[38] Postiglione A, De Chiara S, Soricelli A, et al. Alterations ofcerebral blood flow and antiphospholipid antibodies inpatients with systemic lupus erythematosus. Int J Clin LabRes 1998;28(1):34–8.[39] Lass P, Krajka-Lauer J, Homziuk M, et al. Cerebral bloodflow in Sjo¨gren’ssyndrome using 99Tcm-HMPAO brainSPET. Nucl Med Commun 2000;21(1):31–5.[40] Caca I, Nazaroglu H, Unlu K, Cakmak SS, Ari S, Sakalar YB.Color Doppler imaging of ocular hemodynamic changes inBehc¸et’s disease. Jpn J Ophthalmol 2004;48(2):101–5.[41] Wakamoto H, Ohta M, Nakano N, Kunisue K. SPECT in focalenterovirus encephalitis: evidence for local cerebralvasculitis. Pediatr Neurol 2000;23(5):429–31.[42] Nishikawa M, Matsubara T, Yoshitomi T, Ichiyama T,Hayashi T, Furukawa S. Abnormalities of brain perfusion inechovirus type 30 meningitis. J Neurol Sci 2000;179(S1–2):122–6.[43] Mathieu A, Sanna G, Mameli A, et al. Sustained normal-ization of cerebral blood-flow after iloprost therapy in apatient with neuropsychiatric systemic lupus erythemat-osus. Lupus 2002;11(1):52–6.[44] Liu FY, Huang WS, Kao CH, Yen RF, Wang JJ, Ho ST.Usefulness of Tc-99m ECD brain SPECT to evaluate theeffects of methylprednisolone pulse therapy in lupuserythematosus with brain involvement: a preliminaryreport. Rheumatol Int 2003;23(4):182–5.[45] Nathan C. Immunology: oxygen and the inflammatory cell.Nature 2003;422(6933):675–6.[46] Cramer T, Yamanishi Y, Clausen BE, et al. HIF-1a IsEssential for Myeloid Cell-Mediated Inflammation. Cell2003;112(5):645–57.[47] Cramer T, Johnson RS. A novel role for the hypoxiainducible transcription factor HIF-1a: critical regulation ofinflammatory cell function. Cell Cycle 2003;2(3):192–3.[48] Ryan HE, Lo J, Johnson RS. HIF-1a is required for solidtumor formation and embryonic vascularization. EMBO J1998;17(11):3005–15.[49] Lu G, Qian X, Berezin I, Telford GL, Huizinga JD, Sarna SK.Inflammation modulates in vitro colonic myoelectric andcontractile activity and interstitial cells of Cajal. Am JPhysiol 1997;273(6 Pt 1):G1233–45.[50] Ishii Y, Ushida T, Tateishi T, Shimojo H, Miyanaga Y.Effects of different exposures of hyperbaric oxygen onligament healing in rats. J Orthop Res 2002;20(2):353–6.[51] Harrison DK, Abbot NC, Carnochan FM, Beck JS, James PB,McCollum PT. Protective regulation of oxygen uptake as aresult of reduced oxygen extraction during chronic inflam-mation. Adv Exp Med Biol 1994;345:789–96.[52] Van de Veire NR, De Winter O, Philippe J, et al. Maximumoxygen uptake at peak exercise in elderly patients withcoronary artery disease and preserved left ventricularfunction: the role of inflammation on top of tissueDoppler-derived systolic and diastolic function. Am HeartJ2006;152(2):297e.1–7.[53] Suematsu M, Schmid-Schonbein GW, Chavez-Chavez RH,et al. In vivo visualization of oxidative changes in micro-vessels during neutrophil activation. Am J Physiol1993;264(3Pt2):H881–91.[54] Miljkovic-Lolic M, Silbergleit R, Fiskum G, Rosenthal RE.Neuroprotective effects of hyperbaric oxygen treatmentin experimental focal cerebral ischemia are associatedwith reduced brain leukocyte myeloperoxidase activity.Brain Res 2003;971(1):90–4.[55] Sheffield PJ, Davis JC. Application of hyperbaric oxygentherapy in a case of prolonged cerebral hypoxia followingrapid decompression. Aviat Space Environ Med 1976;47(7):759–62.[56] Neubauer RA, James P. Cerebral oxygenation and therecoverable brain. Neurol Res 1998;20(Suppl. 1):S33–6.[57] Al-Waili NS, Butler GJ. Effects of hyperbaric oxygen oninflammatory response to wound and trauma: possiblemechanism of action. Scientific World J 2006;6:425–41.[58] Banasiak KJ, Xia Y, Haddad GG. Mechanisms underlyinghypoxia-induced neuronal apoptosis. Prog Neurobiol2000;62(3):215–49.[59] Carmeliet P, Dor Y, Herbert JM, et al. Role of HIF-1alphain hypoxia-mediated apoptosis, cell proliferation andtumour angiogenesis. Nature 1998;394(6692):485–90.[60] Ostrowski RP, Colohan AR, Zhang JH. Mechanisms ofhyperbaric oxygen-induced neuroprotection in a rat modelof subarachnoid hemorrhage. J Cereb Blood Flow Metab2005;25(5):554–71.[61] Lou M, Chen Y, Ding M, Eschenfelder CC, Deuschl G.Involvement of the mitochondrial ATP-sensitive potassiumchannel in the neuroprotective effect of hyperbaricoxygenation after cerebral ischemia. Brain Res Bull2006;69(2):109–16.[62] Wada K, Miyazawa T, Nomura N, et al. Mn-SOD and Bcl-2expression after repeated hyperbaric oxygenation. ActaNeurochir Suppl 2000;76:285–90.[63] Fatemi SH, Stary JM, Halt AR, Realmuto GR. Dysregulationof reelin and Bcl-2 proteins in autistic cerebellum. JAutism Dev Disord 2001;31(6):529–35.[64] Atochin DN, Fisher D, Demchenko IT, Thom SR. Neutrophilsequestration and the effect of hyperbaric oxygen in a ratmodel of temporary middle cerebral artery occlusion.Undersea Hyperb Med 2000;27(4):185–90.[65] Vlodavsky E, Palzur E, Soustiel JF. Hyperbaric oxygentherapy reduces neuroinflammation and expression ofmatrix meralloproteinase-9 in the rat model of traumaticbrain injury. Neuropathol Appl Neurobiol 2006;32(1):40–50.[66] Thom SR. Effects of hyperoxia on neutrophil adhesion.Undersea Hyperb Med 2004;31(1):123–31.[67] Zamboni WA, Roth AC, Russell RC, Graham B, Suchy H,Kucan JO. Morphologic analysis of the microcirculationduring reperfusion of ischemic skeletal muscle and theeffect of hyperbaric oxygen. Plast Reconstr Surg1993;91(6):1110–23.[68] Williams RL. Hyperbaric oxygen therapy and the diabeticfoot. J Am Podiatr Med Assoc 1997;87(6):279–92.[69] Efrati S, Bergan J, Fishlev G, Tishler M, Golik A, Gall N.Hyperbaric oxygen therapy for nonhealing vasculiticulcers. Clin Dermatol, in press. doi:10.1111/j.1365-2230.2006.02240.x.[70] Stoller KP. Quantification of neurocognitive changesbefore, during, and after hyperbaric oxygen therapy in acase of fetal alcohol syndrome. Pediatrics 2005;116(4):e586–91.[71] Montgomery D, Goldberg J, Amar M, et al. Effects ofhyperbaric oxygen therapy on children with spastic diple-14 RossignolPlease cite this article in press as: Rossignol DA, Hyperbaric oxygen therapy might improve certain pathophysiologicalfindings in autism, Med Hypotheses (2006), doi:10.1016/j.mehy.2006.09.064ARTICLE IN PRESS

gic cerebral palsy: a pilot project. Undersea Hyperb Med1999;26(4):235–42.[72] Collet JP, Vanasse M, Marois P, et al. Hyperbaric oxygenfor children with cerebral palsy: a randomised multicentretrial. Lancet 2001;357(9256):582–6.[73] Heuser G, Heuser SA, Rodelander D, Aguilera O, Uszler M.Treatment of neurologically impaired adults and childrenwith ‘‘mild’’ hyperbaric oxygenation (1.3 ATM and 24%oxygen). In: Joiner JT, editor. Hyperbaric oxygenation forcerebral palsy and the brain-injured child. FlagstaffArizona: Best Publications; 2002. p. 109–15.[74] Golden ZL, Neubauer R, Golden CJ, Greene L, Marsh J,Mleko A. Improvement in cerebral metabolism in chronicbrain injury after hyperbaric oxygen therapy. Int JNeurosci 2002;112(2):119–31.[75] Rockswold GL, Ford SE, Anderson DC, Bergman TA,Sherman RE. Results of a prospective randomized trialfor the treatment of severely brain-injured patients withhyperbaric oxygen. J Neurosurg 1992;76(6):929–34.[76] Nighoghossian N, Trouillas P, Adeleine P, Salord F.Hyperbaric oxygen in the treatment of acute ischemicstroke. Stroke 1995;26:1369–72.[77] Ersoz G, Ocakcioglu B, Bastug M, Ficicilar H, YavuzerS. Platelet aggregation and release function in hyper-baric oxygenation. Undersea Hyperb Med 1998;25(4):229–32.[78] Pardo CA, Vargas DL, Zimmerman AW. Immunity, neuro-glia and neuroinflammation in autism. Int Rev Psychiatry2005;17(6):485–95.[79] Laurence JA, Fatemi SH. Glial fibrillary acidic protein iselevated in superior frontal, parietal and cerebellarcortices of autistic subjects. Cerebellum 2005;4(3):206–10.[80] Weizman A, Wiezman R, Szekely GA, Wijsenbeek H, LivniE. Abnormal immune response to brain tissue antigen inthe syndrome of autism. Am J Psychiatry 1982;139(11):1462–5.[81] Ahlsen G, Rosengren L, Belfrage M, et al. Glial fibrillaryacidic protein in the cerebrospinal fluid of children withautism and other neuropsychiatric disorders. Biol Psychi-atry 1993;33(10):734–43.[82] Singh VK, Warren R, Averett R, Ghaziuddin M. Circulatingautoantibodies to neuronal and glial filament proteins inautism. Pediatr Neurol 1997;17(1):88–90.[83] Singer HS, Morris CM, Williams PN, Yoon DY, Hong JJ,Zimmerman AW. Antibrain antibodies in children withautism and their unaffected siblings. J Neuroimmunol2006;178(1–2):149–55.[84] Connolly AM, Chez MG, Pestronk A, Arnold ST, Mehta S,Deuel RK. Serum autoantibodies to brain in Landau-Kleffner variant, autism, and other neurologic disorders.J Pediatr 1999;134(5):607–13.[85] Vojdani A, Campbell AW, Anyanwu E, Kashanian A, Bock K,Vojdani E. Antibodies to neuron-specific antigens inchildren with autism: possible cross-reaction with enceph-alitogenic proteins from milk, Chlamydia pneumoniae andStreptococcus group A. J Neuroimmunol 2002;129(1–2):168–77.[86] Vojdani A, O’Bryan T, Green JA, et al. Immune responseto dietary proteins, gliadin and cerebellar peptides inchildren with autism. Nutr Neurosci 2004;7(3):151–61.[87] Singh VK, Lin SX, Newell E, Nelson C. Abnormal measles-mump-rubella antibodies and CNS autoimmunity in chil-dren with autism. J Biomed Sci 2002;9(4):359–64.[88] Singh VK, Warren RP, Odell JD, Warren WL, Cole P.Antibodies to myelin basic protein in children with autisticbehavior. Brain Behav Immun 1993;7(1):97–103.[89] Singh VK, Rivas WH. Prevalence of serum antibodies tocaudate nucleus in autistic children. Neurosci Lett2004;355(1–2):53–6.[90] Connolly AM, Chez M, Streif EM, et al. Brain-derivedneurotrophic factor and autoantibodies to neural antigensin sera of children with autistic disorders, Landau-Kleffnersyndrome, and epilepsy. Biol Psychiatry 2006;59(4):354–63.[91] Dalton P, Deacon R, Blamire A, et al. Maternal neuronalantibodies associated with autism and a language disor-der. Ann Neurol 2003;53(4):533–7.[92] Wakefield AJ, Ashwood P, Limb K, Anthony A. Thesignificance of ileo-colonic lymphoid nodular hyperplasiain children with autistic spectrum disorder. Eur J Gastro-enterol Hepatol 2005;17(8):827–36.[93] Uhlmann V, Martin CM, Sheils O, et al. Potential viralpathogenic mechanism for new variant inflammatorybowel disease. J Clin Pathol: Mol Pathol 2002;55(2):84–90.[94] Furlano RI, Anthony A, Day R, et al. Colonic CD8 andgamma delta T-cell infiltration with epithelial damage inchildren with autism. J Pediatr 2001;138(3):366–72.[95] Balzola F, Barbon V, Repici A, et al. Panenteric IBD-likedisease in a patient with regressive autism shown for thefirst time by the wireless capsule enteroscopy: anotherpiece in the jigsaw of this gut-brain syndrome? Am JGastroenterol 2005;100(4):979–81.[96] Torrente F, Ashwood P, Day R, et al. Small intestinalenteropathy with epithelial IgG and complement deposi-tion in children with regressive autism. Mol Psychiatry2002;7(4):375–82.[97] Ashwood P, Anthony A, Torrente F, Wakefield AJ. Spon-taneous mucosal lymphocyte cytokine profiles in childrenwith autism and gastrointestinal symptoms: mucosalimmune activation and reduced counter regulatory inter-leukin-10. J Clin Immunol 2004;24(6):664–73.[98] Ashwood P, Anthony A, Pellicer AA, Torrente F, Walker-Smith JA, Wakefield AJ. Intestinal lymphocyte populationsin children with regressive autism: evidence for extensivemucosal immunopathology. J Clin Immunol 2003;23(6):504–17.[99] Vojdani A, Pangborn JB, Vojdani E, Cooper EL. Infections,toxic chemicals and dietary peptides binding to lympho-cyte receptors and tissue enzymes are major instigators ofautoimmunity in autism. Int J Immunopathol Pharmacol2003;16(3):189–99.[100] Jyonouchi H, Sun S, Le H. Proinflammatory and regulatorycytokine production associated with innate and adaptiveimmune responses in children with autism spectrumdisorders and developmental regression. J Neuroimmunol2001;120(1–2):170–9.[101] Becker KG, Freidlin B, Simon RM. Comparative genomicsof autism, Tourette syndrome and autoimmune/inflam-matory disorders. http://www.grc.nia.nih.gov/branches/rrb/dna/pubs/cgoatad.pdf. April 23, 2003 [accessed9.26.06].[102] Wakefield AJ, Puleston JM, Montgomery SM, Anthony A,O’Leary JJ, Murch SH. Review article: the concept ofentero-colonic encephalopathy, autism and opioid recep-tor ligands. Aliment Pharmacol Ther 2002;16(4):663–74.[103] Shenoy S, Arnold S, Chatila T. Response to steroid therapyin autism secondary to autoimmune lymphoproliferativesyndrome. J Pediatr 2000;136(5):682–7.[104] Stefanatos GA, Grover W, Geller E. Case study: cortico-steroid treatment of language regression in pervasivedevelopmental disorder. J Am Acad Child Adolesc Psychi-atry 1995;34(8):1107–11.Hyperbaric oxygen therapy might improve certain pathophysiological findings in autism 15Please cite this article in press as: Rossignol DA, Hyperbaric oxygen therapy might improve certain pathophysiologicalfindings in autism, Med Hypotheses (2006), doi:10.1016/j.mehy.2006.09.064ARTICLE IN PRESS

[105] Akin ML, Gulluoglu BM, Uluutku H, et al. Hyperbaricoxygen improves healing in experimental rat colitis.Undersea Hyperb Med 2002;29(4):279–85.[106] Luongo C, Imperatore F, Cuzzocrea S, et al. Effects ofhyperbaric oxygen exposure on a zymosan-induced shockmodel. Crit Care Med 1998;26(12):1972–6.[107] Sumen G, Cimsit M, Eroglu L. Hyperbaric oxygen treat-ment reduces carrageenan-induced acute inflammation inrats. Eur J Pharmacol 2001;431(2):265–8.[108] Weisz G, Lavy A, Adir Y, et al. Modification of in vivo andin vitro TNF-alpha, IL-1, and IL-6 secretion by circulatingmonocytes during hyperbaric oxygen treatment in patientswith perianal Crohn’s disease. J Clin Immunol 1997;17(2):154–9.[109] Yang ZJ, Bosco G, Montante A, Ou XI, Camporesi EM.Hyperbaric oxygen reduces intestinal ischemia-reperfu-sion-induced TNF-alpha production and lung neutrophilsequestration. Eur J Appl Physiol 2001;85(1–2):96–103.[110] Benson RM, Minter LM, Osborne BA, Granowitz EV.Hyperbaric oxygen inhibits stimulus-induced proinflam-matory cytokine synthesis by human blood-derivedmonocyte-macrophages. Clin Exp Immunol 2003;134(1):57–62.[111] Yang Z, Nandi J, Wang J, et al. Hyperbaric oxygenationameliorates indomethacin-induced enteropathy in rats byModulating TNF-alpha and IL-1beta production. Dig Dis Sci2006;51(8):1426–33.[112] Inamoto Y, Okuno F, Saito K, et al. Effect of hyperbaricoxygenation on macrophage function in mice. BiochemBiophys Res Commun 1991;179(2):886–91.[113] Buras JA, Holt D, Orlow D, Belikoff B, Pavlides S, ReenstraWR. Hyperbaric oxygen protects from sepsis mortality viaan interleukin-10-dependent mechanism. Crit Care Med2006;34(10):2624–9.[114] Wilson HD, Wilson JR, Fuchs PN. Hyperbaric oxygentreatment decreases inflammation and mechanical hyper-sensitivity in an animal model of inflammatory pain. BrainRes 2006;1098(1):126–8.[115] Warren J, Sacksteder MR, Thuning CA. Therapeutic effectof prolonged hyperbaric oxygen in adjuvant arthritis of therat. Arthritis Rheum 1979;22(4):334–9.[116] Tokar B, Gundogan AH, Ilhan H, Bildirici K, Gultepe M,Elbuken E. The effects of hyperbaric oxygen treatment onthe inflammatory changes caused by intraperitonealmeconium. Pediatr Surg Int 2003;19(9–10):673–6.[117] Rachmilewitz D, Karmeli F, Okon E, Rubenstein I, BetterOS. Hyperbaric oxygen: a novel modality to ameliorateexperimental colitis. Gut 1998;43(4):512–8.[118] Gulec B, Yasar M, Yildiz S, et al. Effect of hyperbaricoxygen on experimental acute distal colitis. Physiol Res2004;53(5):493–9.[119] Gorgulu S, Yagci G, Kaymakcioglu N, et al. Hyperbaricoxygen enhances the efficiency of 5-aminosalicylic acid inacetic acid-induced colitis in rats. Dig Dis Sci 2006;51(3):480–7.[120] Takeshima F, Makiyama K, Doi T. Hyperbaric oxygen asadjunct therapy for Crohn’s intractable enteric ulcer. AmJGastroenterol1999;94(11):3374–5.[121] Colombel JF, Mathieu D, Bouault JM, et al. Hyperbaricoxygenation in severe perineal Crohn’s disease. Dis ColonRectum 1995;38(6):609–14.[122] Nelson Jr EW, Bright DE, Villar LF. Closure of refractoryperineal Crohn’s lesion: integration of hyperbaric oxygeninto case management. Dig Dis Sci 1990;35(12):1561–5.[123] Lavy A, Weisz G, Adir Y, Ramon Y, Melamed Y, Eidelman S.Hyperbaric oxygen for perianal Crohn’s disease. J ClinGastroenterol 1994;19(3):202–5.[124] Brady 3rd CE, Cooley BJ, Davis JC. Healing of severeperineal and cutaneous Crohn’s disease with hyperbaricoxygen. Gastroenterology 1989;97(3):756–60.[125] Buchman AL, Fife C, Torres C, Smith L, Aristizibal J.Hyperbaric oxygen therapy for severe ulcerative colitis. JClin Gastroenterol 2001;33(4):337–9.[126] Gurbuz AK, Elbuken E, Yazgan Y, Yildiz S. A differenttherapeutic approach in patients with severe ulcerativecolitis: hyperbaric oxygen treatment. South Med J2003;96(6):632–3.[127] Shiratsuch H, Basson MD. Differential regulation of mono-cyte/macrophage cytokine production by pressure. Am JSurg 2005;190(5):757–62.[128] Granowitz EV, Skulsky EJ, Benson RM, et al. Exposure toincreased pressure or hyperbaric oxygen suppresses inter-feron-c secretion in whole blood cultures of healthyhumans. Undersea Hyperb Med 2002;29(3):216–25.[129] Yin W, Badr AE, Mychaskiw G, Zhang JH. Down regulationof COX-2 is involved in hyperbaric oxygen treatment in arat transient focal ischemia model. Brain Res 2002;926(1–2):165–71.[130] Anderson GD, Hauser SD, McGarity KL, Bremer ME, IsaksonPC, Gregory SA. Selective inhibition of cyclooxygenase(COX)-2 reverses inflammation and expression of COX-2and interleukin 6 in rat adjuvant arthritis. J Clin Invest1996;97(11):2672–9.[131] Ashwood P, Van de Water J. A review of autism and theimmune response. Clin Dev Immunol 2004;11(2):165–74.[132] Sweeten TL, Bowyer SL, Posey DJ, Halberstadt GM,McDougle CJ. Increased prevalence of familial autoimmu-nity in probands with pervasive developmental disorders.Pediatrics 2003;112(5):e420.[133] Valicenti-McDermott M, McVicar K, Rapin I, Wershil BK,Cohen H, Shinnar S. Frequency of gastrointestinal symp-toms in children with autistic spectrum disorders andassociation with family history of autoimmune disease. JDev Behav Pediatr 2006;27(Suppl. 2):S128–36.[134] Comi AM, Zimmerman AW, Frye VH, Law PA, Peeden JN.Familial clustering of autoimmune disorders and evalua-tion of medical risk factors in autism. J Child Neurol1999;14(6):388–94.[135] Croonenberghs J, Wauters A, Devreese K, et al. Increasedserum albumin, gamma globulin, immunoglobulin IgG, andIgG2 and IgG4 in autism. Psychol Med 2002;32(8):1457–63.[136] Stubbs EG. Autistic children exhibit undetectable hemag-glutination-inhibition antibody titers despite previousrubella vaccination. J Autism Child Schizophr 1976;6(3):269–74.[137] Evers M, Cunningham-Rundles C, Hollander E. Heat shockprotein 90 antibodies in autism. Mol Psychiatry2002;7(Suppl. 2):S26–8.[138] Queitsch C, Sangster TA, Lindquist S. Hsp90 as a capacitorof phenotypic variation. Nature 2002;417(6889):618–24.[139] Gupta S, Aggarwal S, Heads C. Dysregulated immunesystem in children with autism: beneficial effects ofintravenous immune globulin on autistic characteristics. JAutism Dev Disord 1996;26(4):439–52.[140] Gupta S. Immunological treatments for autism. J AutismDev Disorder 2000;30(5):475–9.[141] Plioplys AV. Intravenous immunoglobulin treatment ofchildren with autism. J Child Neurol 1998;13(2):79–82.[142] Denney DR, Frei BW, Gaffney GR. Lymphocyte subsets andinterleukin-2 receptors in autistic children. J Autism DevDisord 1996;26(1):87–97.[143] Warren RP, Margaretten NC, Pace NC, Foster A. Immuneabnormalities in patients with autism. J Autism Dev Disord1986;16(2):189–97.16 RossignolPlease cite this article in press as: Rossignol DA, Hyperbaric oxygen therapy might improve certain pathophysiologicalfindings in autism, Med Hypotheses (2006), doi:10.1016/j.mehy.2006.09.064ARTICLE IN PRESS

[144] Scifo R, Cioni M, Nicolosi A. Opioid-immune interactions inautism: behavioural and immunological assessment duringa double-blind treatment with naltrexone. Ann Ist SuperSanita 1996;32(3):351–9.[145] Moore KW, de Waal Malefyt R, Coffman RL, O’Garra A.Interleukin-10 and the interleukin-10 receptor. Annu RevImmunol 2001;19:683–765.[146] Ngoc PL, Gold DR, Tzianabos AO, Weiss ST, Celedon JC.Cytokines, allergy, and asthma. Curr Opin Allergy ClinImmunol 2005;5(2):161–6.[147] Croen LA, Grether JK, Yoshida CK, Odouli R, Van de WaterJ. Maternal autoimmune diseases, asthma and allergies,and childhood autism spectrum disorders: a case–controlstudy. Arch Pediatr Adolesc Med 2005;159(2):151–7.[148] Lucarelli S, Frediani T, Zingoni AM, et al. Food allergy andinfantile autism. Panminerva Med 1995;37(3):137–41.[149] Singh VK. Plasma increase of interleukin-12 and inter-feron-gamma: Pathological significance in autism. J Neu-roimmunol 1996;66(1–2):143–5.[150] Stubbs G. Interferonemia and autism. J Autism Dev Disord1995;25(1):71–3.[151] Croonenberghs J, Bosmans E, Deboutte D, Kenis G, MaesM. Activation of the inflammatory response system inautism. Neuropsychobiology 2002;45(1):1–6.[152] Messahel S, Pheasant AE, Pall H, Ahmed-Choudhury J,Sungum-Paliwal RS, Vostanis P. Urinary levels of neopterinand biopterin in autism. Neurosci Lett 1998;241(1):17–20.[153] Gupta S, Aggarwal S, Rashanravan B, Lee T. Th1- and Th2-like cytokines in CD4+ and CD8+ T cells in autism. JNeuroimmunol 1998;85(1):106–9.[154] Molloy CA, Morrow AL, Meinzen-Derr J, et al. Elevatedcytokine levels in children with autism spectrum disorder.J Neuroimmunol 2006;172(1–2):198–205.[155] Stubbs EG, Crawford ML. Depressed lymphocytes respon-siveness in autistic children. J Autism Child Schizophr1977;7(1):49–55.[156] Warren RP, Foster A, Margaretten NC. Reduced naturalkiller cell activity in autism. J Am Acad Child AdolescPsych 1987;26(3):333–5.[157] Xu X, Yi H, Kato M, et al. Differential sensitivities tohyperbaric oxygen of lymphocyte subpopulations of nor-mal and autoimmune mice. Immunol Lett 1997;59(2):79–84.[158] Wallace DJ, Silverman S, Goldstein J, Hughes D. Use ofhyperbaric oxygen in rheumatic diseases: case report andcritical analysis. Lupus 1995;4(3):172–5.[159] Lukich VL, Poliakova LV, Sotnikova TI, Belokrinitskii DV.Hyperbaric oxygenation in the comprehensive therapy ofpatients with rheumatoid arthritis. FIZIOL ZH 1991;37(5):55–60.[160] Warren J, Sacksteder MR, Thuning CA. Oxygen immuno-suppression: modification of experimental allergicencephalomyelitis in rodents. J Immunol 1978;121(1):315–20.[161] Erdmann D, Roth AC, Hussmann J, et al. Skin allograftrejection and hyperbaric oxygen treatment in immune-histoincompatible mice. Undersea Hyperb Med1995;22(4):395–9.[162] Saito K, Tanaka Y, Ota T, Eto S, Yamashita U. Suppressiveeffect of hyperbaric oxygenation on immune responses ofnormal and autoimmune mice. Clin Exp Immunol1991;86(2):322–7.[163] Chen SY, Chen YC, Wang JK, et al. Early hyperbaricoxygen therapy attenuates disease severity in lupus-proneautoimmune (NZB X NZW) F1 mice. Clin Immunol2003;108(2):103–10.[164] Olszanski R, Pachut M, Sicko Z, Sztaba-Kania M, WilkowskaA. Efficacy of hyperbaric oxygenation in atopic dermatitis.Bull Inst Marit Trop Med Gdynia 1992;43(1–4):79–82.[165] Nyland H, Naess A, Eidsvik S, Glette J, Matre R, Hordnes C.Effect of hyperbaric oxygen treatment on immunologicalparameters in multiple sclerosis. Acta Neurol Scand1989;79(4):306–10.[166] Lee AK, Hester RB, Coggin JH, Gottlieb SF. Increasedoxygen tensions modulate the cellular composition of theadaptive immune system in BALB/c mice. Cancer Biother1993;8(3):241–52.[167] Lee AK, Hester RB, Coggin JH, Gottlieb SF. Increasedoxygen tensions influence subset composition of thecellular immune system in aged mice. Cancer Biother1994;9(1):39–54.[168] Thom SR, Bhopale V, Fisher D, Manevich Y, Huang PL,Buerk DG. Stimulation of nitric oxide synthase in cerebralcortex due to elevated partial pressures of oxygen: anoxidative stress response. J Neurobiol 2002;51(2):85–100.[169] van den Blink B, van der Kleij AJ, Versteeg HH, Pep-pelenbosch MP. Immunomodulatory effect of oxygen andpressure. Comp Biochem Physiol A Mol Integr Physiol2002;132(1):193–7.[170] James SJ, Cutler P, Melnyk S, et al. Metabolic biomarkersof increased oxidative stress and impaired methylationcapacity in children with autism. Am J Clin Nutr2004;80(6):1611–7.[171] James SJ, Melnyk S, Jernigan S, et al. Metabolic endophe-notype and related genotypes are associated with oxida-tive stress in children with autism. Am J Med Genet Part B,in press. doi:10.1002/ajmg.b.30366.[172] Sogut S, Zoroglu SS, Ozyurt H, et al. Changes in nitricoxide levels and antioxidant enzyme activities may have arole in the pathophysiological mechanisms involved inautism. Clin Chim Acta 2003;331(1–2):111–7.[173] McGinnis WR. Oxidative stress in autism. Altern TherHealth Med 2004;10(6):22–36.[174] Zoroglu SS, Armutcu F, Ozen S, et al. Increased oxidativestress and altered activities of erythrocyte free radicalscavenging enzymes in autism. Eur Arch Psychiatry ClinNeurosci 2004;254(3):143–7.[175] Chauhan A, Chauhan V, Brown WT, Cohen I. Oxidativestress in autism: increased lipid peroxidation and reducedserum levels of ceruloplasmin and transferrin – theantioxidant proteins. Life Sci 2004;75(21):2539–49.[176] Yorbik O, Sayal A, Akay C, Akbiyik DI, Sohmen T.Investigation of antioxidant enzymes in children withautistic disorder. Prostaglandins Leukot Essent Fatty Acids2002;67(5):341–3.[177] D’Amelio M, Ricci I, Sacco R, et al. Paraoxonase genevariants are associated with autism in North America, butnot in Italy: possible regional specificity in gene-environ-ment interactions. Mol Psychiatry 2005;10(11):1006–16.[178] Purcell AE, Jeon OH, Zimmerman AW, Blue ME, Pevsner J.Postmortem brain abnormalities of the glutamate neuro-transmitter system in autism. Neurology 2001;57(9):1618–28.[179] Yorbik O, Akay C, Sayal A, Cansever A, Sohmen T, CavdarAO. Zinc status in autistic children. J Trace Elem Exp Med2004;17(2):101–7.[180] Adams JB, Holloway C. Pilot study of a moderate dosemultivitamin/mineral supplement for children with autis-tic spectrum disorder. J Altern Complement Med2004;10(6):1033–9.[181] Dolske MC, Spollen J, McKay S, Lancashire E, Tolbert L. Apreliminary trial of ascorbic acid as supplemental therapyHyperbaric oxygen therapy might improve certain pathophysiological findings in autism 17Please cite this article in press as: Rossignol DA, Hyperbaric oxygen therapy might improve certain pathophysiologicalfindings in autism, Med Hypotheses (2006), doi:10.1016/j.mehy.2006.09.064ARTICLE IN PRESS

for autism. Prog Neuropsychopharmacol Biol Psychiatry1993;17(5):765–74.[182] Alleva R, Nasole E, Di Donato F, Borghi B, Neuzil J,Tomasetti M. alpha-Lipoic acid supplementation inhibitsoxidative damage, accelerating chronic wound healing inpatients undergoing hyperbaric oxygen therapy. BiochemBiophys Res Commun 2005;333(2):404–10.[183] Wada K, Miyazawa T, Nomura N, Tsuzuki N, Nawashiro H,Shima K. Preferential conditions for and possible mecha-nisms of induction of ischemic tolerance by repeatedhyperbaric oxygenation in gerbil hippocampus. Neurosur-gery 2001;49(1):160–7.[184] Yatsuzuka H. Effects of hyperbaric oxygen therapy onischemic brain injury in dogs. Masui 1991;40(2):208–23.[185] Ozden TA, Uzun H, Bohloli M, et al. The effects ofhyperbaric oxygen treatment on oxidative and antioxi-dants levels during liver regeneration in rats. Tohoku J ExpMed 2004;203(4):253–65.[186] Yasar M, Yildiz S, Mas R, et al. The effect of hyperbaricoxygen treatment on oxidative stress in experimentalacute necrotizing pancreatitis. Physiol Res 2003;52(1):111–16.[187] Kudchodkar BJ, Wilson J, Lacko A, Dory L. Hyperbaricoxygen reduces the progression and accelerates theregression of atherosclerosis in rabbits. ArteriosclerThromb Vasc Biol 2000;20(6):1637–43.[188] Gregorevic P, Lynch GS, Williams DA. Hyperbaric oxygenmodulates antioxidant enzyme activity in rat skeletalmuscles. Eur J Appl Physiol 2001;86(1):24–7.[189] Nie H, Xiong L, Lao N, Chen S, Xu N, Zhu Z. Hyperbaricoxygen preconditioning induces tolerance against spinalcord ischemia by upregulation of antioxidant enzymes inrabbits. J Cereb Blood Flow Metab 2006;26(5):666–74.[190] Sharifi M, Fares W, Abdel-Karim I, et al. Usefulness ofhyperbaric oxygen therapy to inhibit restenosis afterpercutaneous coronary intervention for acute myocardialinfarction or unstable angina pectoris. Am J Cardiol2004;93(12):1533–5.[191] Speit G, Dennog C, Eichhorn U, Rothfuss A, Kaina B.Induction of heme oxygenase-1 and adaptive protectionagainst the induction of DNA damage after hyperbaricoxygen treatment. Carcinogenesis 2000;21(10):1795–9.[192] Rothfuss A, Radermacher P, Speit G. Involvement ofheme-oxygenase-1 (HO-1) in the adaptive protection ofhuman lymphocytes after hyperbaric oxygen (HBO) treat-ment. Carcinogenesis 2001;22(12):1979–85.[193] Rothfuss A, Speit G. Investigations on the mechanism ofhyperbaric oxygen (HBO)-induced adaptive protectionagainst oxidative stress. Mutat Res 2002;508(1–2):157–65.[194] Dennog C, Radermacher P, Barnett YA, Speit G. Antiox-idant status in humans after exposure to hyperbaricoxygen. Mutat Res 1999;428(1–2):83–9.[195] Shyu WC, Lin SZ, Saeki K, et al. Hyperbaric oxygenenhances the expression of prion protein and heat shockprotein 70 in a mouse neuroblastoma cell line. Cell MolNeurobiol 2004;24(2):257–68.[196] Ostrowski RP, Tang J, Zhang JH. Hyperbaric oxygensuppresses NADPH oxidase in a rat subarachnoid hemor-rhage model. Stroke 2006;37(5):1314–8.[197] Moak SA, Greenwald RA. Enhancement of rat serumceruloplasmin levels by exposure to hyperoxia. Proc SocExp Biol Med 1984;177(1):97–103.[198] Pasca SP, Nemes B, Vlase L, et al. High levels ofhomocysteine and low serum paraoxonase 1 arylesteraseactivity in children with autism. Life Sci 2006;78(19):2244–48.[199] Lombard J. Autism: a mitochondrial disorder? Med Hypoth-eses 1998;50(6):497–500.[200] Filipek PA, Juranek J, Smith M, et al. Mitochondrialdysfunction in autistic patients with 15q inverted dupli-cation. Ann Neurol 2003;53(6):801–4.[201] Poling JS, Frye RE, Shoffner J, Zimmerman AW. Develop-mental regression and mitochondrial dysfunction in a childwith autism. J Child Neurol 2006;21(2):170–2.[202] Clark-Taylor T, Clark-Taylor BE. Is autism a disorder offatty acid metabolism? Possible dysfunction of mitochon-drial b-oxidation by long chain acyl-CoA dehydrogenase.Med Hypotheses 2004;62(6):970–5.[203] Fillano JJ, Goldenthal MJ, Rhodes CH, Marin-Garcia J.Mitochondrial dysfunction in patients with hypotonia,epilepsy, autism, and developmental delay: HEADD syn-drome. J Child Neurol 2002;17(6):435–9.[204] Filipek PA, Juranek J, Nguyen MT, Cummings C, Gargus JJ.Relative carnitine deficiency in autism. J Autism DevDisord 2004;34(6):615–23.[205] Graf WD, Marin-Garcia J, Gao HG, et al. Autism associ-ated with the mitochondrial DNA G8363A transferRNA(Lys) mutation. J Child Neurol 2000;15(6):357–61.[206] Ramoz N, Reichert JG, Smith CJ, et al. Linkage andassociation of the mitochondrial aspartate/glutamatecarrier SLC25A12 gene with autism. Am J Psychiatry2004;161(4):662–9.[207] Segurado R, Conroy J, Meally E, Fitzgerald M, Gill M,Gallagher L. Confirmation of association between autismand the mitochondrial aspartate/glutamate carrierSLC25A12 gene on chromosome 2q31. Am J Psychiatry2005;162(11):2182–4.[208] Pons R, Andreu AL, Checcarelli N, et al. MitochondrialDNA abnormalities and autistic spectrum disorders. JPediatr 2004;144(1):81–5.[209] Lerman-Sagie T, Leshinsky-Silver E, Watemberg N, Lev D.Should autistic children be evaluated for mitochondrialdisorders? J Child Neurol 2004;19(5):379–81.[210] Oliveira G, Diogo L, Grazina M, et al. Mitochondrialdysfunction in autism spectrum disorders: a popula-tion-based study. Dev Med Child Neurol 2005;47(3):185–99.[211] Kriaucionis S, Paterson A, Curtis J, Guy J, MacLeod N, BirdA. Gene expression analysis exposes mitochondrial abnor-malities in a mouse model of Rett Syndrome. Mol Cell Biol2006;26(13):5033–42.[212] Magalha˜es J, Ascensa˜o A, Soares JMC, et al. Acute andsevere hypobaric hypoxia increases oxidative stress andimpairs mitochondrial function in mouse skeletal muscle.J Appl Physiol 2005;99:1247–53.[213] Lane N. Oxygen: the molecule that made the world.Oxford University Press; 2002. p. 166–7.[214] Daugherty WP, Levasseur JE, Sun D, Rockswold GL,Bullock MR. Effects of hyperbaric oxygen therapy oncerebral oxygenation and mitochondrial function follow-ing moderate lateral fluid-percussion injury in rats. JNeurosurg 2004;101(3):499–504.[215] Dave KR, Prado R, Busto R, et al. Hyperbaric oxygentherapy protects against mitochondrial dysfunction anddelays onset of motor neuron disease in Wobbler mice.Neuroscience 2003;120(1):113–20.[216] Boveris A, Chance B. The mitochondrial generation ofhydrogen peroxide: general properties and effect ofhyperbaric oxygen. Biochem J 1973;134(3):707–16.[217] Gosalvez M, Castillo Olivares J, De Miguel E, Blanco M,Figuera D. Mitochondrial respiration and oxidative phos-phorylation during hypothermic hyperbaric hepatic pres-ervation. J Surg Res 1973;15(5):313–8.18 RossignolPlease cite this article in press as: Rossignol DA, Hyperbaric oxygen therapy might improve certain pathophysiologicalfindings in autism, Med Hypotheses (2006), doi:10.1016/j.mehy.2006.09.064ARTICLE IN PRESS

[218] Bar-Sagie D, Mayevsky A, Bartoov B. Effects of hyperbaricoxygenation on spermatozoan motility driven by mito-chondrial respiration. J Appl Physiol 1981;50(3):531–7.[219] Gutsaeva DR, Suliman HB, Carraway MS, Demchenko IT,Piantadosi CA. Oxygen-induced mitochondrial biogenesisin the rat hippocampus. Neuroscience 2006;137(2):493–504.[220] Chugani DC, Muzik O, Behen M, et al. Developmentalchanges in brain serotonin synthesis capacity in autisticand nonautistic children. Ann Neurol 1999;45(3):287–95.[221] Connors SL, Matteson KJ, Sega GA, Lozzio CB, Carroll RC,Zimmerman AW. Plasma serotonin in autism. PediatrNeurol 2006;35:182–6.[222] Croonenberghs J, Delmeire L, Verkerk R, et al. Peripheralmarkers of serotonergic and noradrenergic function inpost-pubertal, caucasian males with autistic disorder.Neuropsychopharmacology 2000;22(3):275–83.[223] McDougle CJ, Naylor ST, Cohen DJ, Aghajanian GK,Heninger GR, Price LH. Effects of tryptophan depletionin drug-free adults with autistic disorder. Arch GenPsychiatry 1996;53(11):993–1000.[224] Todd RD, Ciaranello RD. Demonstration of inter- andintraspecies differences in serotonin binding sites byantibodies from an autistic child. Proc Natl Acad Sci,USA 1985;82(2):612–6.[225] Singh VK, Singh EA, Warren RP. Hyperserotoninemia andserotonin receptor antibodies in children with autism butnot mental retardation. Biol Psychiatry 1997;41(6):753–5.[226] McDougle CJ, Naylor ST, Cohen DJ, Volkmar FR, HeningerGR, Price LH. A double-blind, placebo-controlled study offluvoxamine in adults with autistic disorder. Arch GenPsychiatry 1996;53(11):1001–8.[227] Hollander E, Phillips A, Chaplin W, et al. A placebocontrolled crossover trial of liquid fluoxetine on repetitivebehaviors in childhood and adolescent autism. Neuropsy-chopharmacology 2005;30(3):582–9.[228] Owley T, Walton L, Salt J, et al. An open-label trial ofescitalopram in pervasive developmental disorders. J AmAcad Child Adolesc Psychiatry 2005;44(4):343–8.[229] Gillberg C, Svennerholm L. CSF monoamines in autisticsyndromes and other pervasive developmental disordersof early childhood. Br J Psychiatry 1987;151:89–94.[230] Young JG, Kavanagh ME, Anderson GM, Shaywitz BA,Cohen DJ. Clinical neurochemistry of autism and associ-ated disorders. J Autism Dev Disord 1982;12(2):147–65.[231] Ernst M, Magee HJ, Gonzalez NM, Locascio JJ, RosenbergCR, Campbell M. Pimozide in autistic children. Psycho-pharmacol Bull 1992;28(2):187–91.[232] Simon-Soret C, Borenstein P. A trial of bromocriptine inthe treatment of infantile autism. Presse Med1987;16(26):1286 [in French].[233] Fisher AB, Block ER, Pietra G. Environmental influences onuptake of serotonin and other amines. Environ HealthPerspect 1980;35:191–8.[234] Block ER, Stalcup SA. Depression of serotonin uptake bycultured endothelial cells exposed to high O2 tension. JAppl Physiol 1981;50(6):1212–9.[235] Sumen-Secgin G, Cimsit M, Ozek M, Eroglu L. Antidepres-sant-like effect of hyperbaric oxygen treatment in forced-swimming test in rats. Methods Find Exp Clin Pharmacol2005;27(7):471–4.[236] Di Sabato F, Rocco M, Martelletti M, Giacovazzo M.Hyperbaric oxygen in chronic cluster headaches: influenceon serotonergic pathways. Undersea Hyperb Med1997;24(2):117–22.[237] Yang Z, Camporesi C, Yang X, et al. Hyperbaric oxygen-ation mitigates focal cerebral injury and reduces striataldopamine release in a rat model of transient middlecerebral artery occlusion. Eur J Appl Physiol 2002;87(2):101–7.[238] Adachi YU, Watanabe K, Higuchi H, Satoh T, Vizi ES.Oxygen inhalation enhances striatal dopamine metabolismand monoamineoxidase enzyme inhibition prevents it: amicrodialysis study. Eur J Pharmacol 2001;422(1-3):61–8.[239] Worth J. Paraoxonase polymorphisms and organophos-phates. Lancet 2002;360(9335):802–3.[240] Finegold SM, Molitoris D, Song Y, et al. Gastrointestinalmicroflora studies in late-onset autism. Clin Infect Dis2002;35(Suppl. 1):S6–S16.[241] Song Y, Liu C, Finegold SM. Real-time PCR quantitation ofClostridia in feces of autistic children. Appl EnvironMicrobiol 2004;70(11):6459–65.[242] Parracho HM, Bingham MO, Gibson GR, McCartney AL.Differences between the gut microflora of children withautistic spectrum disorders and that of healthy children. JMed Microbiol 2005;54(Pt 10):987–91.[243] Bolte ER. Autism and Clostridium tetani. Med Hypotheses1998;51(2):133–44.[244] Sandler RH, Finegold SM, Bolte ER, et al. Short-termbenefit from oral vancomycin treatment of regressive-onset autism. J Child Neurol 2000;15(7):429–35.[245] Cave S. Autism in children. Int J Pharmaceut Compd2001;5(1):18–9.[246] Knighton DR, Halliday B, Hunt TK. Oxygen as an antibiotic.The effect of inspired oxygen on infection. Arch Surg1984;119(2):199–204.[247] Akin ML, Erenoglu C, Dal A, Erdemoglu A, Elbuken E,Batkin A. Hyperbaric oxygen prevents bacterial transloca-tion in rats with obstructive jaundice. Dig Dis Sci2001;46(8):1657–62.[248] Gottlieb SF. Effect of hyperbaric oxygen on microorgan-isms. Annu Rev Microbiol 1971;25:111–52.[249] Bornside GH, Pakman LM, Ordonez Jr AA. Inhibition ofpathogenic enteric bacteria by hyperbaric oxygen:enhanced antibacterial activity in the absence of carbondioxide. Antimicrob Agents Chemother 1975;7(5):682–7.[250] Clark JM, Pakman LM. Inhibition of pseudomonas aerugin-osa by hyperbaric oxygen: II. Ultrastructural changes.Infect Immun 1971;4(4):488–91.[251] Bornside GH. Enhancement of antibiotic activity againststaphylococcus aureus by exposure to hyperbaric oxygen.Appl Microbiol 1967;15(5):1020–4.[252] Unsworth IP, Sharp PA. Gas Gangrene. An 11-year reviewof 73 cases managed with hyperbaric oxygen. Med J Aust1984;140(5):256–60.[253] Babior BM. Oxygen-dependent microbial killing by phago-cytes: Part I. N Engl J Med 1978;298(12):659–68.[254] Mader JT, Brown GL, Guckian JC, Wells CH, Reinarz JA. Amechanism for the amelioration by hyperbaric oxygen ofexperimental staphylococcal osteomyelitis in rabbits. JInfect Dis 1980;142(6):915–22.[255] Arao T, Hara Y, Suzuki Y, Tamura K. Effects of high-pressure gas on yeast growth. Biosci Biotechnol Biochem2005;69(7):1365–71.[256] Baugh MA. HIV: reactive oxygen species, enveloped virusesand hyperbaric oxygen. Med Hypotheses 2000;55(3):232–238.[257] Reillo MR, Altieri RJ. HIV antiviral effects of hyperbaricoxygen therapy. J Assoc Nurses AIDS Care 1996;7(1):43–5.[258] Libet B, Siegel BV. Response of a virus-induced leukemia inmice to high oxygen tension. Cancer Res 1962;22(6):737–742.[259] Arrais-Silva WW, Collhone MC, Ayres DC, de Souza SoutoPC, Giorgio S. Effects of hyperbaric oxygen on LeishmaniaHyperbaric oxygen therapy might improve certain pathophysiological findings in autism 19Please cite this article in press as: Rossignol DA, Hyperbaric oxygen therapy might improve certain pathophysiologicalfindings in autism, Med Hypotheses (2006), doi:10.1016/j.mehy.2006.09.064ARTICLE IN PRESS

amazonensis promastigotes and amastigotes. Parasitol Int2005;54(1):1–7.[260] Nataf R, Skorupka C, Amet L, Lam A, Springbett A, LatheR. Porphyrinuria in childhood autistic disorder: implica-tions for environmental toxicity. Toxicol Appl Pharmacol2006;214(2):99–108.[261] Haley BE, Small T. Interview with Dr. Boyd E. Haley:biomarkers supporting mercury toxicity as the majorexacerbator of neurological illness, recent evidence viathe urinary porphyrin tests. Medical Veritas 2006;3:921–34.[262] Thom SR, Bhopale VM, Velazquez OC, Goldstein LJ, ThomLH, Buerk DG. Stem cell mobilization by hyperbaricoxygen. Am J Physiol Heart Circ Physiol 2006;290(4):H1378–86.[263] Steindler DA, Pincus DW. Stem cells and neuropoiesis inthe adult human brain. Lancet 2002;359(9311):1047–54.[264] Mezey E, Key S, Vogelsang G, Szalayova I, Lange GD, CrainB. Transplanted bone marrow generates new neurons inhuman brains. Proc Natl Acad Sci USA 2003;100(3):1364–69.[265] Cogle CR, Yachnis AT, Laywell ED, et al. Bonemarrow transdifferentiation in brain after transplan-tation: a retrospective study. Lancet 2004;363(9419):1432–7.[266] Marois P, Vanasse M. Hyperbaric oxygen therapy andcerebral palsy. Dev Med Child Neurol 2003;45(9):646–8.[267] Ashamalla HL, Thom SR, Goldwein JW. Hyperbaric oxygentherapy for the treatment of radiation-induced sequelaein children: the University of Pennsylvania experience.Cancer 1996;77(11):2407–12.[268] Waalkes P, Fitzpatrick DT, Stankus S, Topolski R. Adjunc-tive HBO treatment of children with cerebral anoxicinjury. Army Med Dept J 2002(April–June):13–21.[269] Feldmeier JJ, editor. Hyperbaric oxygen 2003: indicationsand results: the hyperbaric oxygen therapy committeereport. Kensington, MD: Undersea and Hyperbaric MedicalSociety; 2003.[270] Rossignol DA, Rossignol LW. Hyperbaric oxygen therapymay improve symptoms in autistic children. Med Hypoth-eses 2006;67(2):216–28.20 RossignolPlease cite this article in press as: Rossignol DA, Hyperbaric oxygen therapy might improve certain pathophysiologicalfindings in autism, Med Hypotheses (2006), doi:10.1016/j.mehy.2006.09.064ARTICLE IN PRESS

Hyperbaric oxygen therapy may improvesymptoms in autistic childrenDaniel A. Rossignola,b,*, Lanier W. RossignolaBlue Ridge Medical Cent er, 4038 Thomas Ne lson Highway, Arrington, VA 22922, USAbUniversity of Virginia, P.O. Box 800729, Charlottesville, VA, USAReceived 26 January 2006; accepted 7 February 2006Summary Autism is a neurodevelopmental disorder that currently affects as many as 1 out of 166 children in theUnited States. Recent research has discovered that some autistic individuals have decreased cerebral perfusion,evidence of neuroinflammation, and increased markers of oxidative stress. Multiple independent single photonemission computed tomography (SPECT) and positron emission tomography (PET) research studies have revealedhypoperfusion to several areas of the autistic brain, most notably the temporal regions and areas specifically related tolanguage comprehension and auditory processing. Several studies show that diminished blood flow to these areascorrelates with many of the clinical features associated with autism including repetitive, self-stimulatory andstereotypical behaviors, and impairments in communication, sensory perception, and social interaction. Hyperbaricoxygen therapy (HBOT) has been used with clinical success in several cerebral hypoperfusion syndromes includingcerebral palsy, fetal alcohol syndrome, closed head injury, and stroke. HBOT can compensate for decreased blood flowby increasing the oxygen content of plasma and body tissues and can even normalize oxygen levels in ischemic tissue. Inaddition, animal studies have shown that HBOT has potent anti-inflammatory effects and reduces oxidative stress.Furthermore, recent evidence demonstrates that HBOT mobilizes stem cells from human bone marrow, which may aidrecovery in neurodegenerative diseases. Based upon these findings, it is hypothesized that HBOT will improvesymptoms in autistic individuals. A retrospective case series is presented that supports this hypothesis.!c2006 Elsevier Ltd. All rights reserved.BackgroundOverview of autismAutism is a neurodevelopmental disorder currentlyaffecting as many as 1 out of 166 children in theUnited States [1] that is characterized by impair-ments in social interaction, difficulty with commu-nication, and restrictive and repetitive behaviors[2]. It affects children from all socioeconomicand ethnic backgrounds [3]. Autism was considered0306-9877/$ - see front matter!c2006 Elsevier Ltd. All rights reserved.doi:10.1016/j.mehy.2006.02.009Abbreviations: SPECT, single photon emission computedtomography; PET, positron emission tomography; HBOT, hyp-erbaric oxygen therapy; MRI, magnetic resonance imaging;ATA, atmosphere absolute; CP, cerebral palsy; SOD, superox-ide dismutase.*Corresponding author. Tel.: +1 434 263 4000; fax: +1 434 2634160.E-mail addresses: dlross7@hotmail.com (D.A. Rossignol),dlross7@hotmail.com (L.W. Rossignol).Medical Hypotheses (2006) x, xxx–xxxhttp://intl.elsevierhealth.com/journals/mehyARTICLE IN PRESS

a rare condition before the 1990’s with a preva-lence of approximately 1 in 2500 children [4]. How-ever, according to the US Department ofDevelopmental Services, the prevalence of autismspectrum disorders increased 556% from 1991 to1997 [5]. Autism is now more common than child-hood cancer, cerebral palsy, Down’s syndrome, spi-na bifida, or cystic fibrosis [6,7]. In addition,autism is found throughout the globe and the prev-alence worldwide is increasing 3.8% per year [8].Autism is an incompletely understood disorder[3,5], but new clinical research is beginning to un-ravel some of its mysteries.Overview of hyperbaric oxygen therapyHyperbaric oxygen therapy (HBOT) involves inhal-ing 100% oxygen at greater than one atmosphereabsolute (ATA) in a pressurized chamber [9]. HBOThas been used successfully in humans at varyingpressures to treat a range of conditions. Many clin-ical applications of HBOT are at higher pressures(over 2.0 ATA) including treatment of decom pres-sion sickness, arterial gas embolism, carbon mon-oxide poisoning [10], amyotrophic lateral sclerosis[11], and complex regional pain syndrome [12].However, HBOT has also been used at lower pres-sures (1.5 ATA or less) with clinical success in con-ditions including fetal alcohol syndrome [13] andischemic brain injury [14]. HBOT at 1.5 ATA wasutilized in a prospective trial of 168 patients withclosed head trauma with a significant reduction inmortality (32% versus 17%) [15].HBOT has been shown to increase the oxygencontent of plasma [16] and body tissues [17] andcan even normalize oxygen levels in ischemic tissue[18]. In fact, the amount of oxygen delivered byHBOT at 3.0 ATA and 100% oxygen is able to keeptissue viable even without oxygen input from circ u-lating hemoglobin [17]. In rat models, HBOT hasbeen shown to reduce the effects of hypoxia andischemia on the neonatal brain [19]. Human studiesdemonstrate that HBOT causes mild vasoconstric-tion resulting in decreased blood flow [20,21] butat the same time causes increased oxygen deliveryand levels in target tissues [16,17,20]. By causingmild vasoconstriction, HBOT can reduc e edema inischemic tissue [22] including the brain [20,2 3],which results in lowering intracranial pressure [20].HBOT is generally considered safe [17] at oxygenpressures below 3.0 ATA and with treatment dura-tions of less than 120 min [10,13,24]. The use ofHBOT in children appears generally safe, even atpressures of 2.0 ATA for 2 hours per day for up to40 sessions [25]. The most common side effect ofHBOT is middle ear barotrauma, which occurs inapproximately 2% of patients. The incidence ofsuch barotrauma is decreased with pseudoephed-rine treatment before HBOT. Less common side ef-fects in desce nding order include sinus squeeze,serous otitis, claustrophobia, and reversible myo-pia. Seizures may occur infrequently in about0.01–0.03% of patients [9].HypothesisMultiple studies have revealed that autism is a neu-rodegenerative disease characterized by cerebralhypoperfusion, neuroinflammation, and increasedoxidative stress. HBOT helps overcome hypoperfu-sion, has potent anti-inflammatory effects and re-duces oxidative stress. Furthermore, HBOTmobilizes stems cells from human bone marrow.Therefore, HBOT will improve symptoms of autism.Improving cerebral hypoperfusion inautismEvidence of decreased cerebral blood flow inautism and possible mechanisms ofhypoperfusionEven in the pre sence of normal magnetic resonanceimaging (MRI) findings, focal areas of decreasedcerebral blood flow occur in children with autism[26]. Multiple independent single photon emissioncomputed tomography (SPECT) and positron emis-sion tomography (PET) research studies have dem-onstrated hypoperfusion to several areas of theautistic brain, most notably the temporal lobes[26–39]. Several studies show that reduced bloodflow to the temporal regions and other brain areascorrelates with many of the clinical findings associ-ated with autism including repetitive, self-stimula-tory and stereotypical behaviors, and impairmentsin communication, sensory perception, and socialinteraction [27,29,31,39–42]. Furthermore, a cor-relation between decreased IQ and hypoperfusionof the temporal and frontal lobes has been de-scribed in autistics [36].The cause of this decreased blood flow is notknown but may be secondary to changes in cerebralarterial resistance. Under normal conditions, cere -bral blood flow increases when local brain tissuemetabolic rate and functioning increases [43,4 4].However, this response may be reversed in autisticchildren. One of the first studies measuring cere-bral blood flow in autistic children utilized trans-cranial Doppler ultrasound and showed decreased2 Rossignol and RossignolARTICLE IN PRESS

blood flow and concomitantly increased middlecerebral arterial resistance upon auditory stimula-tion. Conversely, control neurotypical and men-tally re tarded children showed opposite results[45].The mechanism of this abnormal change in cere-bral arterial resistance in autistic children is un-known. However, several studies have shown thatastrocytes can regulate cerebral blood flow. Astro-cytes can directly cause arteriole vasoconstrictionthrough a calcium mechanism [46] and arteriolevasodilatation through a cyclooxyg enase medium[47]. Neurons, astrocytes, and vascular cells com-pose a functional unit that maintains proper bloodflow and oxygenation for the brain [48]. Neuralactivity normally causes increased cerebral bloodflow thus delivering increased oxygen [44]. How-ever, a recent study found evidence of neuroin-flammation and astroglial activation in autism[49]. It is possible that astroglial inflammationmay affect the control of blood flow regulated byastrocytes and lead to the abnormal changes incerebral artery resistance and hypoperfusion seenin some autistic children.Furthermore, inflammation is a known cause ofdecreased blood flow and sev eral inflammatoryconditions have associated cerebral hypoperfusionincluding lupus [50,51], Sjo¨gren’s syndrome [52],Behc¸et’s disease [53], viral encephalitis [54,55],and acute Kawasaki disease [40]. One SPECT studyof 27 children with echovirus meningitis demon-strated decreased cerebral blood flow in 74% ofthe children [55] and two recent SPECT studie s re-vealed impaired cerebral perfusion in 81% of pa-tients with Sjo¨gren’s syndrome [52]. In one SPECTstudy of patients with systemic lupus erythemato-sus, 59% had evidence of cerebral hypoperfusion[51]. Furthermore, treatment of the inflammati onfound in lupus with iloprost [56] and methylpred-nisolone [57] normalized cerebral blood flow onfollow-up SPECT scans. It is conceivable that thecerebral hypoperfusion found in autistic childrenmay be triggered by neuroinflamm ation and there-fore may be reversible with anti-inflammatorymodalities.Zones of the autistic brain affected bydecreased blood flow and symptomcorrelationsCerebral hypoperfusion may play a role in some ofthe more unusual characteristics of autistic behav-ior. Diminished blood flow to the thalamus hasbeen correlated with the autistic clinical featuresof repetitive, self-stimu latory, and unusual behav-iors including resistance to changes in routine andenvironment [29]. Hypoperfusion of the temporallobes has also been linked with increased autismsymptom profile scores including ‘‘obsessive desirefor sameness’’ and ‘‘impairments in communica-tion and social interaction’’ [31]. Another studyon ‘‘high functioning’’ autistics demonstrated de-creased blood flow to areas of the temporal lobeand amygdala, which was correlated with clinicalimpairments in processing facial expressions andemotions [42]. This was confirmed by a recentstudy of autistics demonstrating diminished bloodflow to the ‘‘fusiform face area’’ responsible forrecognizing familiar faces [58].In addition, decreased perfusion of the temporallobes is a consistent finding in many studies ofautistic children. Two larger controlled studies(21–23 autistic children) using SPECT and PETscans confirmed significant bitemporal hypoperfu-sion [31,34]. In both of these studies, the controlgroup was mentally retarded; therefore, the hyp-operfusion could not be attributed to mental retar-dation alone [33,34]. Another SPECT study of 31autistic children, 16 of whom had epilepsy, alsodemonstrated reduction of cerebral bloo d flow tothe temporal lobes. Of note, cerebral blood flowwas not different between those with and withoutepilepsy, suggesting that epilepsy itself was notassociated with hypoperfu sion in these individuals[37]. A more recent PET study of 11 autistic chil-dren rev ealed dimini shed blood flow to the lefttemporal area, including Wernicke’s area (whichis involved in language comprehension) and Brod-mann’s area 21 (involved in auditory processingand language), when compared to age-matchedmentally retarded children [39]. Interestingly, anassociation between temporal lobe abnormalities[59] and the subsequent development of secondaryautism has been described in tuberous sclerosis[60], infantile spasms [61], herpes simplex enceph-alitis [62,63], and an acute encephalopathic illnessin children [64] .The relative amount of cerebral hypoperfusionin autistic children can vary by age. In one study,hypoperfusion of the prefrontal and left temporalareas worsened and became ‘‘quite profound’’ asthe age of the autistic child increased. This dimin-ished perfusion correlated with decreased lan-guage development. The authors concluded thathypoperfusion ‘‘subsequently prevents develop-ment of true verbal fluency and development inthe temporal and frontal areas associated withspeech and communication’’ [27].Hypoperfusion of the temporal and other brainregions has been correlated with many of the clin-ical findings associated with autism including self-Hyperbaric oxygen therapy may improve symptoms in autistic children 3ARTICLE IN PRESS

stimulatory behaviors and impairments in commu-nication, sensory perception, and social interaction[33,34]. This diminished bloo d flow may be medi-ated by neuroinflammation. Further studies onthe effects of inflammation on blood flow in theautistic brain are needed, especially studies involv-ing the temporal lobes where hypoperfusion iscommon. Whatever the cause of the hypoperfu -sion, the possibility exists that the enhancementof oxygen delivery to the brain accomplished byHBOT may improve some of the symptoms foundin autistic children.The use of HBOT in cerebral hypoperfusiondisordersThe oxygen delivered by HBOT can reverse hypoxiain brain tissues caused by hypoperfusion [65,66].Cerebral hypoperfusion causes hypoxia, which trig-gers electrical failure in brain cells. Worsening hy-poxia then eventually results in ion pump failure,which ultimately leads to cell death [67]. Cells thathave electr ical failure but retain ion pump abilityhave been described as ‘‘idling’’ because they re-main alive but non-functional [68]. SPECT studieshave confirmed the presence of these ‘‘idlingcells,’’ which surround areas of focal ischemiaand comprise what is termed the ‘‘ischemic pen-umbra’’ [69]. Restoration of oxygenation, some-times even years after the ischemic insult, cansalvage these cells, which may explain why theacute findings of a stroke are poor predictors ofultimate clinical outcomes [67].Even thoug h HBOT causes decreased cere bralblood flow through vasoconstriction [70], it simul-taneously causes increased cerebral oxygen tension[20] and may accelerate brain recovery from ische-mia [71] . In one case report, 80 sessions of HBOT at1.5 ATA increased oxyg enation to the ischemicpenumbra on SPECT scans and significantly im-proved cognitive and motor function in a patientwith an ischemic brain injury from a near drowningepisode 12 years earlier [14]. Another study ofthree patients with brain injuries showed areas of‘‘dormant’’ neurons in the ischemic penumbra onSPECT scans prior to the commencement of HBOTat 1.5 ATA. All three patients had improvement inthe oxygenation of these areas as seen on post-HBOT SPECT scans, which was correlated with clin-ical improvement [65].HBOT has been used with clinical effectivenessin some cerebral hypoperfusion disorders includinglupus [72] and traumatic midbrain syndrome [73],and may be beneficial in acute ischemic stroke[74] and acute myocardial infarction [16]. In addi-tion, HBOT has been used in several studies on chil-dren with cerebral palsy (CP). Some children withCP due to perinatal asphyxia have focal areas ofcerebral hypoperfusion on SPECT scans [75]. Signif-icant clinical improvements were found in onestudy of child ren with CP after 20 sessions of HBOTat 95% oxygen and 1.75 ATA [76].Other studies using HBOT in cerebral hypoperfu-sion disorders have been performed at lower pres-sures (1.5 ATA or less). Stoller recently reported onone pediatric case of fetal alcohol syndrome,which is considered ‘‘irreversible and incurable’’[13] and is characterized by cerebral hypoperfusionon SPECT studies [77]. Using HBOT at 1.5 ATA, thechild had statistically significant improvements inverbal, memory, reaction time, impulse control,and visual motor scores [13]. In addition, Heuseret al. [78] treated a four year old autistic childusing lower pressure HBOT at 1.3 ATA and reported‘‘striking improvement in behavior including mem-ory and cognitive functions’’ after only ten ses-sions. Furthermore, the child had improvement ofcerebral hypoperfusion as measured by pre-HBOTand post-HBOT SPEC T scans [78]. These case re-ports are notable because they demonstrate thatsome ‘‘irreversible’’ and permanent neurologicalconditions can have clinical improvements withHBOT.The number of HBOT sessions needed to producefull clinical improvements from cerebral hypoper-fusion or ischemia is unclear. In one study combin-ing the use of SPECT and HBOT, an average of 70treatments was needed to show a significant in-crease in cerebral blood oxygenation and metabo-lism in patients with chronic neurologicaldisorders including CP, stroke, and traumatic braininjury. Of note, the rate of improvement in cere-bral blood oxygenation was more profound duringthe last 35 treatments compared to the first 35[79]. In addi tion, reports from some HBOTresearchers indicate that younger patients tendto have improvements more quickly than older pa-tients [79]. Therefore, older patients may needmore treatments.Since many autistic children experience at leasta mild degree of cerebral hypoperfusion, this de-creased blood flow could lead to an element ofbrain hypoxia. Multiple SPECT studies have shownevidence of relative brain hypoxia in certain cere-bral hypoperfusion syndromes, including autism[78], which improved after HBOT [14,65,78,79]. Itis certainly plausible that the increased oxygendelivery by HBOT could overcome any hypoxiacaused by hypoperfusion and thus lead to improve-ments in the symptoms of autistic children.4 Rossignol and RossignolARTICLE IN PRESS

Improving neuroinflammation in autismEvidence of neuroinflammation in autismRecent studies reveal that autism is characterizedby neuroinflammation. Autopsy brain samples ofautistic patients demonstrate an active neuroin-flammatory process in the middle frontal gryus,anterior cingulate gryus, and cere bellar hemi-spheres including increased microglial and astrog-lial activation and increased proinflammatorycytokines. Furthermore, cereb rospinal fluid ob-tained from living autistic patients also ‘‘showed aprominent proinflammatory profile’’ [49]. Previousstudies of autistic children have shown circulatingserum autoantibodies to brain elements includingneuron-axon filament protein and glial fibrillaryacidic protein [80], the caudate nucleus, cerebralcortex and cerebellum [81,82] and neuron-specificantigens including myelin basic protein [83,84].Inflammation in autistic children is not limitedto the brain. When compared to typical children,autistic children make significantly more serumantibodies against gliadin and casein peptides[85], produce more pro-inflammatory cytokines[86], and have an imbalance of CD4+and CD8+cells[87]. Furthermore, some patients with autism havemucosal inflammation of the stomach, small intes-tine and colon characterized by ile o-colonic lym-phoid nodular hyperplasia [88]. In these children,the gastrointestinal mucosa has evidence of proin-flammatory cytokines [89], increased lymphocyticdensity, and epithelial IgG deposits mimicking anautoimmune lesion [90].Several different therapies have been employedin treating the inflamma tion found in autistic chil-dren with some clinical success, including intrave-nous immune globulin [91]. Further research isneeded to clarify the role of inflam mation in aut-ism and to investigate potential therapies [92].However, HBOT may be useful in decr easing inflam-mation found in autistic patients and may therebyimprove symptoms.HBOT use in inflammatory conditionsSeveral animal studies have revealed that HBOT haspotent anti-inflammatory tissue effects [93,94]with equivalence to diclofenac 20 mg/kg noted inone study using HBOT at 2.4 ATA and 100% oxygen[95]. HBOT has also been shown to decrease thesymptoms of advanced arthritis in rats [96] andattenuates the inflammatory response in the perito-neal cavity caused by injected meconium [97]. Inaddition, one animal study using HBOT at 2.5 ATAshowed increased survival and decreased protein-uria, anti-dsDNA antibody titers, and immune-com-plex deposition in lupus-prone autoimmune mice[98]. Furthermore, HBOT has been used in animalstudies to improve colitis [93]. Interestingly, thirtysessions of HBOT at 2.0 ATA has been used in hu-mans to achieve remission of ulcerative colitis notresponding to conventional therapies [99]. Thismay be relevant in autistic children given the higherprevalence of gastrointestinal mucosal inflamma-tion described previously. Given the results of thesestudies, it is certainly plausible that HBOT can de-crease both neuroinflammation and gastrointestinalinflammation in autistic children and therebypotentially lead to improvements in symptoms.Improving oxidative stress in autismEvidence of increased oxidative stress inautismRecent studie s have shown that autistic childrenhave evidence of increased oxidative stress includ-ing lower serum glutathione levels [100]. Sogutet al. [101] demonstrated that autistic childrenhad incre ased red blood cell nitric oxide, which isa known reactive free radical and is toxic to thebrain [101]. James et al. [100] recently showedthat total serum glutathione levels were 46% lowerand oxidized glutathione was 72% higher in autisticchildren when compared to neurotypical controls.This was reflected in a lower redox ratio of reducedglutathione to oxidized glutathione, which presum-ably led to decreased antioxidant ability in theseautistic children [100]. Lower serum antioxidantenzyme, antioxidant nutrient, and glutathione lev-els, as well as higher pro-oxidants have been foundin multiple studies of autistic children [102]. Fur-thermore, treatment with anti-oxidants has beenshown to raise the levels of reduced glutathionein the serum of autistic children and appears to im-prove symptoms [100]. It is speculated that treat-ment with hyperbaric oxygen may also helpreduce oxidative stress in autistic children.The effect of HBOT on oxidative stressMultiple studies have shown neutral effects on oxi-dative stress with HBOT use [103]. In one study onhorse platelets, measures of oxidative stress werenot increased after HBOT; in fact, a rise in the anti-oxidant enzyme superoxide dismutase (SOD) wasfound 24 h after HBOT without a fall in glutathionelevels [104]. In another study on dogs, following18 min of complete cerebral ischemia, HBOT atHyperbaric oxygen therapy may improve symptoms in autistic children 5ARTICLE IN PRESS

2.0 ATA reduced brain damage without increasingoxidative stress [105]. Furthermore, in a rat modelof reperfusion, HBOT exte nded skin flap life with-out evidence of oxidative stress [106] .In addition, numerous studies have shownimprovements in oxidative stress with HBOT includ-ing increased production of antioxidants and antiox-idant enzymes and decreased markers of oxidativestress such as malondialdehyde [105,107,108]. Animprovement in the survival rate of skin flaps andan increase in SOD levels were found in one studywhen rats were exposed to hyperbaric oxygen at2.0 ATA [109 ]. In another study, HBOT at 2.5 ATA in-duced the production of antioxidants and decreasedmalondialdehyde levels in rats [107]. Furthermore,in a study of rats with pancreatitis, HBOT at 2.5ATA decreased oxidat ive stress markers includingmalondialdehyde, and increased the levels of theanti-oxidant enzymes glutathione peroxidase andSOD [108]. HBOT has also been shown to acutel yraise the levels of reduced glutathione in the plasmaand lymphocytes of some humans after just onetreatment session at 2.5 ATA [110]. Finally, ische-mia-reperfusion injuries usually cause oxidativestress through decreases in glutathione levels andactivities of catalase and SOD. However, in one ratstudy of ischemia, pretreatment with 1–3 doses ofHBOT caused an increase in liver glutathione andSOD levels and protected against liver injury; con-trol animals not receiving HBOT actually had dropsin glutathione and anti-oxidant enzyme levels andhad concomitant liver damage [111].HBOT, reactive oxygen species, andanti-oxidantsConcerns have been raised that HBOT may cause in-creased oxidative stress through the production ofreactive oxygen species [112]. This concern is con-troversial as studies have shown mixed results.Contrary to the studi es discussed previously, sev-eral studies using HBOT at 2.5 ATA or greater havefound evidence of increased oxidative stress [113–115]. Support for this higher pressure effect wasfound in one study, which demonstrated that HBOTat 2.0 ATA increased SOD levels whereas HBOT at3.0 ATA caused SOD levels to decr ease, presumablybecause the SOD had to neutralize more free radi-cals at the 3.0 ATA pressure [116]. Thus, from anoxidative stress and SOD production standpoint,there might be an optimal HBOT pressure, whichfalls somewhere below 2.5 ATA.Along a similar line of thought, some authorshave speculated that a limited quantity of re activeoxygen metabolites may actually have beneficialeffects in the human body [117–119]. The produc-tion of small amounts of oxygen radicals may con-fer protection from future hypoxia and this effecthas been termed ‘‘ischemic tolerance.’’ In one ani-mal study, pre-treatment with HBOT at 2.0 ATAprior to an ischemia insult induce d ischemic toler-ance whereas pre-treatment at 3.0 ATA did not,possibly because this higher pressure may havegenerated too many oxygen radicals [116].Nevertheless, many studies demonstrate thatHBOT lowers oxidative stress. Furthermore, oxida-tive stress appears to be less of a concern at pres-sures under 2.0 ATA, which are often used clinically[116]. In spite of this, therapies to raise glutathi-one levels [100] and the use of antioxidants [120]may be beneficial in patients with conditions of in-creased oxidative stress before HBOT is contem-plated. Several antioxidant supplements havebeen found to attenuate oxidative stress inducedby high pressure HBOT including a-lipoic acid[112], melatonin [121], N-acetylcysteine[111,122], vitamin E [123], riboflavin [124], sele-nium [123,124], and glutathione [125]. Based uponthese findings, a combination of antioxidants andHBOT may help reduce oxidative stress in autisticchildren and lead to improvements in symptoms.Improving stem cell mobilization inautismRecently, HBOT at 2.0 ATA and 100% oxygen for 2 hwas shown to mobilize stem/progenitor cells fromthe bone marrow of humans. Elevations were foundin the number of colony-forming cells as demon-strated by an increase in the number of CD34+cellsby almost 2-fold [126]. This finding is relevant be-cause autism and hypoxic brain injuries are consid-ered by many to be permanent conditio ns.However, new research is revealing that evenlong-standing brain disorders ma y be partiallyreversible [13,14]. Recently, stem cells have beenisolated in the adult brain. This leads to the possi-bility of neuropoiesis, or regrowth, of certain braincells. A possible scenario for inducing brain repairthrough the use of existing mature brain stem cellshas been described and is dependent on an intactvascular supply and ade quate oxygen [127], bothof which can be enhanced by HBOT.Testing the hypothesisThere is a strong possibility that HBOT could playan integral role in improving brain disorders associ-ated with hypoxia, hypoperfusion, inflammation,6 Rossignol and RossignolARTICLE IN PRESS

and/or oxidative stress, including autism, throughthe improvement of oxygen supply, decreasedinflammation and oxidative stress, and/or therecruitment of new stem cells (see Table 1). Thisin turn should lead to improved clinical outcomes.Some physicians have begun using HBOT in autisticchildren and anecdotal reports indicate that HBOThas improved symptoms in autistic children includ-ing enhancements in socialization, language, andrepetitive behaviors [78,128]. A recent retrospec-tive case series also indicates that low pressureHBOT may improve symptoms in autistic children(see Appendix A). Further resear ch in this area,including HBOT trials in autistic patients, is ur-gently needed to test this hypothesis.AcknowledgmentsThe authors thank the following for reviewing thismanuscript and offering advice: Dr. John Battiston,Dr. Bentley Calhoun, Mr. Michael Haynes, Dr. Eliza-beth Mumper, Dr. David Slawson, and Dr. Kyle VanDyke. Written consent was obtained from the chil-dren’s parent(s) for publication of case series data.The authors have two autistic sons who partici-pated in the case series.Appendix A. Low pressure hyperbaricoxygen therapy1improves symptoms inautistic children: A retrospe ctive caseseriesBackgroundSince low pressu re HBOT (under 1.5 ATA) improvedsymptoms in some patients with cerebral hypoper-fusion disorders [13–15,65], it was hypothesizedthat low pressure HBOT would also help autism, adisease in which cerebral hypoperfusion is an inte-gral component [31,32]. Recently, evidence hasaccumulated that low pressure hyperbaric therapyat 1.3 ATA and less than 100% delivered oxygen mayimprove symptoms in some diseases associat edwith cerebral hypoperfusion. For instance, onestudy using hyperbaric therapy at 1.3 ATA and roomair demonstrated clinical improvements in somechildren with CP [129,130], a disease shown tohave evidence of diminished cerebral blood flow[75]. Furthermore, one case report indicated‘‘striking improvement’’ in a 4 year old child withautism aft er using hyperbaric therapy for 10 ses-sions at 1.3 ATA and room air. The child also hadimprovement of cerebral hypoperfusion as mea-sured by pre-HBOT and post-HBOT SPECT scans[78]. Base d upon these findings, it was hypothe-sized that low pressure HBOT would improve symp-toms of autism. A retrospective case series wasexamined to evaluate this hypothesis. A review ofthe medical literature was performed using MED-LINE and Google Scholar and no clinical studieswere found on the use of HBOT in autistic children.MethodsThis study is a retrospective analysis of 6 au tisticchildren who underwent low-pressure HBOT. All 6children had a prior diagnosis of autism (DSM-IV299.00) by an outside physician and none of thechildren had previously received HBOT. In the nor-mal course of treatment, parent-rated scales wereobtained pre-treatment and post-treatment. TheUniversity of Virginia Institutional Review Boardfor Health Sciences Research approved our retro-spective examination of cases in this study andfor the use of this data for publication.Informed consent was obtained from eachchild’s parent(s) prior to starting HBOT. All 6 chil-dren started and 5 completed 40 1 h sessions oflow pressure HBOT at 1.3 ATA and 28–30% oxygen(after adjustment for the pressure effect) over athree month period. One child (Child C) only fin-ished twenty-five sessions due to scheduling con-flicts and was included in the analysis. All 6children were taking multiple antioxidant supple-ments before starting HBOT. Children were allowedto continue all current therapies and to add newones during HBOT. The characteristics of the chil-dren, including age and sex, are found in Table 2.A low pressure hyperbaric chamber was used.Room air mixed with oxygen from an oxygenconcentrator was pumped into the pressurizedTable 1 Summary of HBOT use in autismAutism HBOT. Cerebral perfusion m Perfusion to brain tissuem Inflammation . Inflammationm Oxidative stress . Oxidative stressNeurodegenerativediseasem Stem cells1Hyperbaric oxygen therapy (HBOT) normally refers to inhal-ing 100% oxygen at greater than 1 ATA in a pressurized chamber[9]. However, for the purposes of this case series, the treatmentwith hyperbaric pressure at 1.3 ATA augmented with 28–30%oxygen is referred to as HBOT. Hyperbaric pressure at 1.3 ATAand room air is simply termed hyperbaric therapy.Hyperbaric oxygen therapy may improve symptoms in autistic children 7ARTICLE IN PRESS

chamber, resulting in a final chamber oxygen con-centration of 28–30% by direct oximetry measure-ment using a Moxy!oxygen monitor and afteradjustment for the pressu re effect. Multiple ran-dom oximetry measurements were taken on differ-ent treatment days to verify the consistency of thechamber oxygen concentration, which uniformlyremained 28–30%. Parent rated pre-treatmentscores and post-treatment scores were calculatedfor each subject (see Table 2) using the AutismTreatment Evaluation Checklist (ATEC), ChildhoodAutism Rating Scale (CARS), and Social Responsive-ness Scale (SRS). ATEC is a scoring system of verbalcommunication, sociability, sensory/cognitiveawareness, and health/autistic behaviors publishedby the Autism Research Institute [131]. CARS is awidely used scale for screening and diagnosing aut-ism and has been shown to correlate very well withthe DSM-IV criteria for autism diagnosis [132]. SRSis a recently validated test of interpersonal behav-ior, communication, and stereotypical traits inautism [133].ResultsLow pressure HBOT was well tolerated by all 6 chil-dren with no adverse effects noted. More dramaticimprovements were found in children age 4 andunder when compared to those in the older group(Table 3).ATEC score resultsThe average improvement in all children on ATECwas 22.1% (p = 0.0538) ( Fig. 1). ATEC scores im-proved by 31.6% in the younger group comp aredto 8.8% in the older group (Fig. 2).Table 2 Patient characteristics and scoresaChild Age Sex ATEC beforeHBOTATEC afterHBOTCARS beforeHBOTCARS afterHBOTSRS beforeHBOTSRS afterHBOTA 2 M 40 22 21 17 98 44B 4 M 91 55 37.5 30 154 110Cb3 M 75 64 45 38 135 121D 7 M 35 32 27 25 94 62E 6 F 88 80 41.5 39.5 139 121F 7 F 24 22 23 22 54 67aDeclining scores indicate improvement on these scales.bReceived only 25 HBOT treatments.Table 3 Average score changesaby ageAge ATEC beforeHBOTATEC afterHBOTCARS beforeHBOTCARS afterHBOTSRS beforeHBOTSRS afterHBOT4 and under 68.7 47.0 34.5 28.3 129.0 91.75 and older 49.0 44.7 30.5 28.8 95.7 83.3All children 58.8 45.8 32.5 28.6 112.3 87.5aDeclining scores indicate improvement on these scales.020406080100Before HBOT After 40 HBOTScoreChild AChild BChild CChild DChild EChild FFigure 1 ATEC scores for all children.020406080Before HBOT After 40 HBOTScoreAge Under 5Age Over 5Figure 2 ATEC scores by age.8 Rossignol and RossignolARTICLE IN PRESS

CARS score resultsThe average improvement in all children on CARSwas 12.1% (p = 0.0178) (Fig. 3). CARS improved18.0% in the younger group and 5.6% in the oldergroup (Fig. 4).SRS score resultsThe average improvement in all children on SRSwas 22.1% (p = 0.0518) (Fig. 5). SRS improved28.9% in the younger group and 13.0% in the oldergroup (Fig. 6).DiscussionAutism is characterized, in part, by decreasedcerebral blood flow [31,32]. Low pressure HBOThas been used in some cerebral hypoperfusionconditions including CP. Recently, a study demon-strated that some children with CP had clinicalimprovements using hyperbaric therapy at 1.3ATA. In this study, 111 patien ts with CP and a his-tory of hypoxia in the perinatal period had statis-tically significant clinical improvements in grossmotor function, memory, attention, and languageproduction after hyperbaric therapy. One groupreceived lower pressure hyperbaric therapy at1.3 ATA and room air while the other group wasgiven higher pressure HBOT at 1.75 ATA and100% oxygen. Interestingly, the improvements insymptoms were statistically equivalent in thetwo groups [129]. Most of the improvements con-tinued for 3 months after treatment and some ofthe children from the study began walking, speak-ing, and sitting for the first ti mes in their lives[130]. However, it must be noted that this studywas controversial, as children in the lower pres-sure group improved equally with children in thehigher pressure group. However, based on thesefindings, it was hypothesized that low-pressureHBOT could potentially improve symptoms inautistic children.This case series suggests that low pressure HBOTmay indeed be beneficial in the treatment of aut-ism. An interesting finding from this case serieswas that the younger children had more significantimprovements in clinical outcome scores than theolder children. This is congruent with reports fromsome HBOT researchers indicating that younger pa-tients tend to have improvements more quicklythan older patients [79]. This effect may be par-tially explained by the findings of a previous study,which showed that autistic children aged 3–4 yearsexperience diminished frontal lobe blood flow com-pared to age-matched neurotypical children [41]. Itis possible that HBOT in younger autistic childrencan improve cerebral oxygenation and thus over-come the effects of hypoperfusion and aid thesechildren in ‘‘catching up’’ with their neurotypical01020304050Before HBOT After 40 HBOTScoreChild AChild BChild CChild DChild EChild FFigure 3 CARS scores for all children.010203040Before HBOT After 40 HBOTScoreAge Under 5Age Over 5Figure 4 CARS scores by age.020406080100120140160180Before HBOT After 40 HBOTScoreChild AChild BChild CChild DChild EChild FFigure 5 SRS scores for all children.020406080100120140Before HBOT After 40 HBOTScoreAge Under 5Age Over 5Figure 6 SRS scores by age.Hyperbaric oxygen therapy may improve symptoms in autistic children 9ARTICLE IN PRESS

peers. Furthermore, the younger children in thiscase series may have had less overall hypoperfusionto surmount because decreased cerebral blood flowto areas associated with communication has beenshown to worsen with increasing age in autisticchildren [27]. It is likely that the older children inthis case series need more than 40 HBOT sessionsto show further improvements, especially sincesome HBOT researchers have noted that 50–80HBOT sessions are typically needed to show signif-icant clinical gains [79]. In addition, the chamberwas augmented with only 28–30% oxygen inst eadof 100% oxygen. It is possible that the children inthis case series may have experienced moreimprovements if 100% oxygen and/or a higher pres-sure had been used. These speculations certainlywarrant further testing.This case series did have several inherent limi-tations. Children were allowed to continue allother therapies for autism and also add new ones,such as supplements. Therefore, other therapiescould have contributed to the some of the clinicalgains. Parents were not blinded to the fact thattheir children received HBOT and eva luation ofthe children was through parent-rated scales,either of which could lead to bias. There was noplacebo or control group. Thus, the improvementscould have been due merely to the naturaldevelopment of the children, although none ofthe parents reported their child as undergoingdevelopmental spurts of similar or greater magni-tude in the recent past. Finally, this series lackedpower because the sample size was small. Despitethese limitations, the analysis of this case seriessuggests substantial clinical benefits were pro-duced, and therefore, this hypothesis needs tobe tested in a formal prospective study.ConclusionsHBOT has been shown to increase oxygen deliveryto hypoperfused or hypoxic tissues, decreaseinflammation and oxidative stress, and mobilizestem cells from human bone marrow. The mecha-nism of clinical improvements in ATEC, CARS, andSRS scores in the children studied may be second-ary to increased oxygenation of underpe rfusedareas of the autistic brain, reduced neuroinflam-mation, decreased oxidative stress, or a combina-tion of these. This case series suggests that lowpressure HBOT improves symptoms in autistic chil-dren. Further research in this area, including HBOTtrials in autistic patients, using observers blindedto the intervention, is now needed to test thishypothesis.References[1] Singh N (contact). Press release: CDC launches ‘‘Learn thesigns. Act early.’’ Campaign, http://www.cdc.gov/od/oc/media/pressrel/r050222.htm; February 22, 2005[accessed 21.01.06].[2] Kanner L. Autistic disturbances of affective contact.Nervous Child 1943;2:217–50.[3] Rapin I. Autism. N Engl J Med 1997;337(2):97–104.[4] Wing L, Potter D. The epidemiology of autistic spectrumdisorders: is the prevalence rising? Ment Retard Dev DisabilRes Rev 2002;8(3):151–61.[5] Stokstad E. New hints into the biological basis of autism.Science 2001;294:34–7.[6] Muhle R, Trentacoste SV, Rapin I. The genetics of autism.Pediatrics 2004;113:472–86.[7] Centers for Disease Control and Prevention. How commonis autism spectrum disorder? www.cdc.gov/ncbddd/aut-ism/asd_common.htm; February 17, 2005 [accessed21.01.06].[8] Gillberg C, Wing L. Autism: not an extremely raredisorder. Acta Psychiatr Scand 1999;99(6):399–406.[9] Feldmeier JJ. Chairman and Editor. Hyperbaric oxygen2003: indications and results: the hyperbaric oxygentherapy committee report. Kensington, MD: Underseaand Hyperbaric Medical Society; 2003.[10] Leach RM, Rees PJ, Wilmshurst P. ABC of oxygen:hyperbaric oxygen therapy. BMJ 1998;317:1140–3.[11] Steele J, Matos LA, Lopez EA, et al. A phase 1 safety studyof hyperbaric oxygen therapy for amyotrophic lateralsclerosis. ALS 2004;5:250–4.[12] Kiralp MZ, Yildiz S, Vural D, Keskin I, Ay H, Dursun H.Effectiveness of hyperbaric oxygen therapy in the treat-ment of complex regional pain syndrome. J Int Med Res2004;32:258–62.[13] Stoller KP. Quantification of neurocognitive changesbefore, during, and after hyperbaric oxygen therapy in acase of fetal alcohol syndrome. Pediatrics 2005;116:586–91.[14] Neubauer RA, Gottlieb SF, Miale A. Identification ofhypometabolic areas in the brain using brain imaging andhyperbaric oxygen. Clin Nucl Med 1992;17(6):477–81.[15] Rockswold GL, Ford SE, Anderson DC, Bergman TA,Sherman RE. Results of a prospective randomized trialfor the treatment of severely brain-injured patients withhyperbaric oxygen. J Neurosurg 1992;76(6):929–34.[16] Shandling AH, Ellestad MH, Hart GB, et al. Hyperbaricoxygen and thrombolysis in myocardial infarction: the‘‘HOT MI’’ pilot study. Am Heart J 1997;134:544–50.[17] Gill AL, Bell CAN. Hyperbaric oxygen: its uses, mechanismsof action and outcomes. Q J Med 2004;97:385–95.[18] Ackerman NB, Brinkley FB. Oxygen tensions in normal andischemic tissues during hyperbaric therapy. JAMA1966;198(12):1280–3.[19] Calvert JW, Yin W, Patel M, et al. Hyperbaric oxygenationprevented brain injury induced by hypoxia-ischemia in aneonatal rat model. Brain Res 2002;951:1–8.[20] Sukoff MH, Ragatz RE. Hyperbaric oxygenation for thetreatment of acute cerebral edema. Neurosurgery1982;10(1):29–38.[21] Bird AD, Telfer AB. Effect of hyperbaric oxygen on limbcirculation. Lancet 1965;13:355–6.[22] Nylander G, Lewis D, Nordstrom H, Larsson J. Reduction ofpostischemic edema with hyperbaric oxygen. Plast Rec-onstr Surg 1985;76(4):596–603.10 Rossignol and RossignolARTICLE IN PRESS

[23] Veltkamp R, Siebing DA, Sun L, et al. Hyperbaric oxygenreduces blood-brain barrier damage and edema aftertransient focal cerebral ischemia. Stroke 2005;36:1679–83.[24] Nuthall G, Seear M, Lepawsky M, Wensley D, Skippen P,Hukin J. Hyperbaric oxygen therapy for cerebral palsy:two complications of treatment. Pediatrics 2000;106(6):E80.[25] Ashamalla HL, Thom SR, Goldwein JW. Hyperbaric oxygentherapy for the treatment of radiation-induced sequelaein children: the University of Pennsylvania experience.Cancer 1996;77(11):2407–12.[26] Ryu YH, Lee JD, Yoon PH, Kim DI, Lee HB, Shin YJ.Perfusion impairments in infantile autism on technetium-99m ethyl cysteinate dimer brain single-photon emissiontomography: comparison with findings on magnetic reso-nance imaging. Eur J Nucl Med 1999;26(3):253–9.[27] Wilcox J, Tsuang MT, Ledger E, Algeo J, Schnurr T. Brainperfusion in autism varies with age. Neuropsychobiology2002;46:13–6.[28] Chiron C, Leboyer M, Leon F, Jambaque I, Nuttin C, SyrotaA. SPECT of the brain in childhood autism: evidence for alack of normal hemispheric asymmetry. Dev Med ChildNeurol 1995;37(10):849–60.[29] Starkstein SE, Vazquez S, Vrancic D, et al. SPECT findingsin mentally retarded autistic individuals. J Neuropsychia-try Clin Neurosci 2000;12:370–5.[30] Mountz JM, Tolbert LC, Lill DW, Katholi CR, Liu HG.Functional deficits in autistic disorder: characterization bytechnetium-99m-HMPAO and SPECT. J Nucl Med1995;36(7):1156–62.[31] Ohnishi T, Matsuda H, Hashimoto T, et al. Abnormalregional cerebral blood flow in childhood autism. Brain2000;123:1838–44.[32] George MS, Costa DC, Kouris K, Ring HA, Ell PJ. Cerebralblood flow abnormalities in adults with infantile autism. JNerv Ment Dis 1992;180(7):413–7.[33] Boddaert N, Zilbovicius M. Functional neuroimaging andchildhood autism. Pediatr Radiol 2002;32:1–7.[34] Zilbovicius M, Boddaert N, Belin P, et al. Temporal lobedysfunction in childhood autism: a PET study. Am JPsychiatry 2000;157:1988–93.[35] Kaya M, Karasalihoglu S, Ustun F, et al. The relationshipbetween 99mTc-HMPAO brain SPECT and the scores of reallife rating scale in autistic children. Brain Dev2002;24:77–81.[36] Hashimoto T, Sasaki M, Fukumizu M, Hanaoka S, Sugai K,Matsuda H. Single-photon emission computed tomographyof the brain in autism: effect of the developmental level.Pediatr Neurol 2000;23:416–20.[37] Gillberg IC, Bjure J, Uvebrant P, Vestergren E, Gillberg C.SPECT (single photon emission computed tomography) in31 children and adolescents with autism and autism-likeconditions. Eur Child Adolesc Psychiatry 1993;2(1):50–9.[38] Boddaert N, Belin P, Chabane N, et al. Perception ofcomplex sounds: abnormal pattern of cortical activation inautism. Am J Psychiatry 2003;160:2057–60.[39] Boddaert N, Chabane N, Belin P, et al. Perception ofcomplex sounds in autism: abnormal auditory corticalprocessing in children. Am J Psychiatry 2004;161:2117–20.[40] Ichiyama T, Nishikawa M, Hayashi T, Koga M, Tashiro N,Furukawa S. Cerebral hypoperfusion during acute Kawa-saki disease. Stroke 1998;29:1320–1.[41] Zilbovicius M, Garreau B, Samson Y, et al. Delayedmaturation of the frontal cortex in childhood autism. AmJ Psychiatry 1995;152(2):248–52.[42] Critchley HD, Daly EM, Bullmore ET, et al. The functionalneuroanatomy of social behaviour: changes in cerebralblood flow when people with autistic disorder processfacial expressions. Brain 2000;123:2203–12.[43] Fox PT, Raichle ME. Focal physiological uncoupling ofcerebral blood flow and oxidative metabolism duringsomatosensory stimulation in human subjects. Proc NatlAcad Sci USA 1986;83:1140–4.[44] Parri R, Crunelli V. An astrocyte bridge from synapse toblood flow. Nat Neurosci 2003;6(1):5–6.[45] Bruneau N, Dourneau MC, Garreau B, Pourcelot L, LelordG. Blood flow response to auditory stimulations in normal,mentally retarded, and autistic children: a preliminarytranscranial Doppler ultrasonographic study of the middlecerebral arteries. Biol Psychiatry 1992;32:691–9.[46] Mulligan SJ, MacVicar BA. Calcium transients in astrocyteendfeet cause cerebrovascular constrictions. Nature2004;431:195–9.[47] Zonta M, Angulo MC, Gobbo S, et al. Neuron-to-astrocytesignaling is central to the dynamic control of brainmicrocirculation. Nat Neurosci 2003;6(1):43–50.[48] Iadecola C. Neurovascular regulation in the normal brainand in Alzheimer’s disease. Nat Rev Neurosci 2004;5:347–60.[49] Vargas DL, Nascimbene C, Krishnan C, Zimmerman AW,Pardo CA. Neuroglial activation and neuroinflammation inthe brain of patients with autism. Ann Neurol2005;57:67–81.[50] Huang WS, Chiu PY, Tsai CH, Kao A, Lee CC. Objectiveevidence of abnormal regional cerebral blood flow inpatients with systemic lupus erythematosus on Tc-99mECD brain SPECT. Rheumatol Int 2002;22:178–81.[51] Postiglione A, De Chiara S, Soricelli A, et al. Alterations ofcerebral blood flow and antiphospholipid antibodies inpatients with systemic lupus erythematosus. Int J Clin LabRes 1998;28:34–8.[52] Lass P, Krajka-Lauer J, Homziuk M, et al. Cerebral bloodflow in Sjo¨gren’s syndrome using 99Tcm-HMPAO brainSPET. Nucl Med Commun 2001;21:31–5.[53] Caca I, Nazaroglu H, Unlu K, Cakmak SS, Ari S, Sakalar YB.Color Doppler imaging of ocular hemodynamic changes inBehc¸et’s disease. Jpn J Ophthalmol 2004;48:101–5.[54] Wakamoto H, Ohta M, Nakano N, Kunisue K. SPECT in focalenterovirus encephalitis: evidence for local cerebralvasculitis. Pediatr Neurol 2000;23:429–31.[55] Nishikawa M, Matsubara T, Yoshitomi T, Ichiyama T,Hayashi T, Furukawa S. Abnormalities of brain perfusion inechovirus type 30 meningitis. J Neurol Sci 2000;179:122–6.[56] Mathieu A, Sanna G, Mameli A, et al. Sustained normal-ization of cerebral blood-flow after iloprost therapy in apatient with neuropsychiatric systemic lupus erythemat-osus. Lupus 2002;11:52–6.[57] Liu FY, Huang WS, Kao CH, Yen RF, Wang JJ, Ho ST.Usefulness of Tc-99m ECD brain SPECT to evaluate theeffects of methylprednisolone pulse therapy in lupuserythematosus with brain involvement: a preliminaryreport. Rheumatol Int 2003;23:182–5.[58] Pierce K, Haist F, Sedaghat F, Courchesne E. The brainresponse to personally familiar faces in autism: findings offusiform activity and beyond. Brain 2004;127:2703–16.[59] Bachevalier J. Medial temporal lobe structures andautism: a review of clinical and experimental findings.Neuropsychologia 1994;32(6):627–48.[60] Bolton PF, Griffiths PD. Association of tuberous sclerosis oftemporal lobes with autism and atypical autism. Lancet1997;349:392–5.Hyperbaric oxygen therapy may improve symptoms in autistic children 11ARTICLE IN PRESS

[61] Chugani HT, Da Silva E, Chugani DC. Infantile spasms. III.Prognostic implications of bitemporal hypometabolism onpositron emission tomography. Ann Neurol 1996;39(5):643–9.[62] Gillberg C. Brief report: onset of age 14 of a typicalautistic syndrome. A case report of a girl with herpessimplex encephalitis. J Autism Dev Disord 1986;16(3):369–75.[63] Ghaziuddin M, Tsai LY, Eilers L, Ghaziuddin N. Briefreport: autism and herpes simplex encephalitis. J AutismDev Disord 1992;22(1):107–13.[64] DeLong GR, Bean SC, Brown FR. Acquired reversibleautistic syndrome in acute encephalopathic illness inchildren. Arch Neurol 1981;38(3):191–4.[65] Neubauer RA, James P. Cerebral oxygenation and therecoverable brain. Neurol Res 1998;20(Suppl. 1):S33–6.[66] Sheffield PJ, Davis JC. Application of hyperbaric oxygentherapy in a case of prolonged cerebral hypoxia followingrapid decompression. Aviat Space Environ Med 1976;47(7):759–62.[67] Astrup J, Symon L, Siesjo BK. Thresholds in cerebralischemia—the ischemic penumbra. Stroke 1981;12(6):723–5.[68] Neubauer RA, Gottlieb SF, Kagan RL. Enhancing ‘‘idling’’neurons. Lancet 1990;335(8688):542.[69] Olsen TS, Larsen B, Herning M, Skriver EB, Lassen NA.Blood flow and vascular reactivity in collaterally perfusedbrain tissue. Evidence of an ischemic penumbra in patientswith acute stroke. Stroke 1983;14(3):332–41.[70] Jacobson I, Harper AM, McDowall DG. The effects ofoxygen under pressure on cerebral blood-flow and cere-bral venous oxygen tension. Lancet 1963;18:549.[71] Kapp JP, Phillips M, Markov A, Smith RR. Hyperbaricoxygen after circulatory arrest: modification of postische-mic encephalopathy. Neurosurgery 1982;11(4):496–9.[72] Wallace DJ, Silverman S, Goldstein J, Hughes D. Use ofhyperbaric oxygen in rheumatic diseases: case report andcritical analysis. Lupus 1996;5(1):84.[73] Holbach KH, Wassmann H, Kolberg T. Improved revers-ibility of the traumatic midbrain syndrome using hyper-baric oxygen. Acta Neurochir (Wien) 1974;30(3–4):247–56.[74] Nighoghossian N, Trouillas P, Adeleine P, Salord F.Hyperbaric oxygen in the treatment of acute ischemicstroke. Stroke 1995;26:1369–72.[75] Kao CH, Wang SJ, Yeh SH. The relationship among thequantitative perfusion-defect indices in Tc-99m HMPAObrain SPECT, IQ test, and involved extremities in childrenwith cerebral palsy due to perinatal asphyxia. Clin NuclMed 1994;19(4):309–13.[76] Montgomery D, Goldberg J, Amar M, et al. Effects ofhyperbaric oxygen therapy on children with spastic diple-gic cerebral palsy: a pilot project. Undersea Hyperb Med1999;26(4):235–42.[77] Riikonen R, Salonen I, Partanen K, Verho S. Brain perfusionSPECT and MRI in foetal alcohol syndrome. Dev Med ChildNeurol 1999;41:652–9.[78] Heuser G, Heuser SA, Rodelander D, Aguilera O, Uszler M.Treatment of neurologically impaired adults and childrenwith ‘‘mild’’ hyperbaric oxygenation (1.3 ATA and 24%oxygen). In: Joiner JT, editor. Hyperbaric oxygenation forcerebral palsy and the brain-injured child. FlagstaffArizona: Best Publications; 2002. p. 109–15.[79] Golden ZL, Neubauer R, Golden CJ, Greene L, Marsh J,Mleko A. Improvement in cerebral metabolism in chronicbrain injury after hyperbaric oxygen therapy. Int JNeurosci 2002;112:119–31.[80] Singh VK, Warren R, Averett R, Ghaziuddin M. Circulatingautoantibodies to neuronal and glial filament proteins inautism. Pediatr Neurol 1997;17(1):88–90.[81] Singh VK, Rivas WH. Prevalence of serum antibodies tocaudate nucleus in autistic children. Neurosci Lett2004;355:53–6.[82] Vojdani A, O’Bryan T, Green JA, et al. Immune responseto dietary proteins, gliadin and cerebellar peptides inchildren with autism. Nutr Neurosci 2004;7(3):151–61.[83] Singh VK, Lin SX, Newell E, Nelson C. Abnormal measles-mumps-rubella antibodies and CNS autoimmunity in chil-dren with autism. J Biomed Sci 2002;9:359–64.[84] Vojdani A, Campbell AW, Anyanwu E, Kashanian A, Bock K,Vojdani E. Antibodies to neuron-specific antigens inchildren with autism: possible cross-reaction with enceph-alitogenic proteins from milk, Chlamydia pneumoniae andStreptococcus group A. J Neuroimmunol 2002;129:168–77.[85] Vojdani A, Pangborn JB, Vojdani E, Cooper EL. Infections,toxic chemicals and dietary peptides binding to lympho-cyte receptors and tissue enzymes are major instigators ofautoimmunity in autism. Int J Immunopathol Pharmacol2003;16(3):189–99.[86] Jyonouchi H, Sun S, Le H. Proinflammatory and regulatorycytokine production associated with innate and adaptiveimmune responses in children with autism spectrumdisorders and developmental regression. J Neuroimmunol2001;120:170–9.[87] Gupta S, Aggarwal S, Rashanravan B, Lee T. Th1- and Th2-like cytokines in CD4+and CD8+T cells in autism. JNeuroimmunol 1998;85:106–9.[88] Wakefield AJ, Ashwood P, Limb K, Anthony A. Thesignificance of ileo-colonic lymphoid nodular hyperplasiain children with autistic spectrum disorder. Eur J Gastro-enterol Hepatol 2005;17:827–36.[89] Ashwood P, Anthony A, Torrente F, Wakefield AJ. Spon-taneous mucosal lymphocyte cytokine profiles in childrenwith autism and gastrointestinal symptoms: mucosalimmune activation and reduced counter regulatory inter-leukin-10. J Clin Immunol 2004;24(6):664–73.[90] Torrente F, Ashwood P, Day R, et al. Small intestinalenteropathy with epithelial IgG and complement deposi-tion in children with regressive autism. Mol Psychiatry2002;7:375–82.[91] Gupta S. Immunological treatments for autism. J AutismDev Disord 2000;30(5):475–9.[92] Zimmerman AW. Commentary: immunological treatmentsfor autism: in search of reasons for promising approaches.J Autism Dev Disord 2000;30(5):481–4.[93] Akin ML, Gulluoglu BM, Uluutku H, et al. Hyperbaricoxygen improves healing in experimental rat colitis.Undersea Hyperb Med 2002;29(4):279–85.[94] Luongo C, Imperatore F, Cuzzocrea S, et al. Effects ofhyperbaric oxygen exposure on a zymosan-induced shockmodel. Crit Care Med 1998;26(12):1972–6.[95] Sumen G, Cimsit M, Eroglu L. Hyperbaric oxygen treat-ment reduces carrageenan-induced acute inflammation inrats. Eur J Pharmacol 2001;431:265–8.[96] Warren J, Sacksteder MR, Thuning CA. Therapeutic effectof prolonged hyperbaric oxygen in adjuvant arthritis of therat. Arthritis Rheum 1979;22(4):334–9.[97] Tokar B, Gundogan AH, Ilhan H, Bildirici K, Gultepe M,Elbuken E. The effects of hyperbaric oxygen treatment onthe inflammatory changes caused by intraperitonealmeconium. Pediatr Surg Int 2003;19:673–6.[98] Chen SY, Chen YC, Wang JK, et al. Early hyperbaricoxygen therapy attenuates disease severity in lupus-prone12 Rossignol and RossignolARTICLE IN PRESS

autoimmune (NZB X NZW) F1 mice. Clin Immunol2003;108:103–10.[99] Buchman AL, Fife C, Torres C, Smith L, Aristizibal J.Hyperbaric oxygen therapy for severe ulcerative colitis. JClin Gastroenterol 2001;33(4):337–9.[100] James SJ, CutlerP, Melnyk S, et al. Metabolic biomarkers ofincreased oxidative stress and impaired methylation capac-ity in children with autism. Am J Clin Nutr 2004;80:1611–7.[101] Sogut S, Zoroglu SS, Ozyurt H, et al. Changes in nitricoxide levels and antioxidant enzyme activities may have arole in the pathophysiological mechanisms involved inautism. Clin Chim Acta 2003;331:111–7.[102] McGinnis WR. Oxidative stress in autism. Altern TherHealth Med 2004;10(6):22–36.[103] Feldmeier J, Carl U, Hartmann K, Sminia P. Hyperbaricoxygen: does it promote growth or recurrence of malig-nancy? Undersea Hyperb Med 2003;30(1):1–18.[104] Shaw FL, Handy RD, Bryson P, Sneyd JR, Moody AJ. Asingle exposure to hyperbaric oxygen does not causeoxidative stress in isolated platelets: no effect on super-oxide dismutase, catalase, or cellular ATP. Clin Biochem2005;38:722–6.[105] Yatsuzuka H. Effects of hyperbaric oxygen therapy onischemic brain injury in dogs. Masui 1991;40(2):208–23.[106] Zamboni WA, Roth AC, Russell RC, Nemiroff PM, Casas L,Smoot EC. The effect of acute hyperbaric oxygen therapyon axial pattern skin flap survival when administeredduring and after total ischemia. J Reconstr Microsurg1989;5(4):343–7.[107] Ozden TA, Uzun H, Bohloli M, et al. The effects ofhyperbaric oxygen treatment on oxidative and antioxi-dants levels during liver regeneration in rats. Tohoku J ExpMed 2004;203:253–65.[108] Yasar M, Yildiz S, Mas R, et al. The effect of hyperbaricoxygen treatment on oxidative stress in experimentalacute necrotizing pancreatitis. Physiol Res 2003;52:111–6.[109] Kaelin CM, Im MJ, Myers RA, Manson PN, Hoopes JE. Theeffects of hyperbaric oxygen on free flaps in rats. ArchSurg 1990;125(5):607–9.[110] Dennog C, Radermacher P, Barnett YA, Speit G. Antiox-idant status in humans after exposure to hyperbaricoxygen. Mutat Res 1999;428:83–9.[111] Yu SY, Chiu JH, Yang SD, et al. Preconditioned hyperbaricoxygenation protects the liver against ischemia-reperfu-sion injury in rats. J Surg Res 2005;128:28–36.[112] Alleva R, Nasole E, Di Donato F, Borghi B, Neuzil J,Tomasetti M. a-Lipoic acid supplementation inhibits oxi-dative damage, accelerating chronic wound healing inpatients undergoing hyperbaric oxygen therapy. BiochemBiophys Res Commun 2005;333(2):404–10.[113] Dennog C, Gedik C, Wood S, Speit G. Analysis of oxidativeDNA damage and HPRT mutations in humans after hyper-baric oxygen treatment. Mutat Res 1999;431:351–9.[114] Benedetti S, Lamorgese A, Piersantelli M, Pagliarani S,Benvenuti F, Canestrari F. Oxidative stress and antioxi-dant status in patients undergoing prolonged exposure tohyperbaric oxygen. Clin Biochem 2004;37:312–7.[115] Chavko M, Harabin AL. Regional lipid peroxidation andprotein oxidation in rat brain after hyperbaric oxygenexposure. Free Radic Biol Med 1996;20(7):973–8.[116] Wada K, Miyazawa T, Nomura N, Nawashiro H, Shima K.Preferential conditions for and possible mechanisms ofinduction of ischemic tolerance by repeated hyperbaricoxygenation in gerbil hippocampus. Neurosurgery2001;49:160–7.[117] Hink J, Jansen E. Are superoxide and/or hydrogen peroxideresponsible for some of the beneficial effects of hyperbaricoxygen therapy? Med Hypotheses 2001;57(6):764–9.[118] Barja G. Oxygen radicals, a failure or a success ofevolution? Free Radic Res Commun 1993;18(2):63–70.[119] McCord JM. The evolution of free radicals and oxidativestress. Am J Med 2000;108:652–9.[120] Patel V, Chivukula IV, Roy S, et al. Oxygen: from thebenefits of inducing VEGF expression to managing the riskof hyperbaric stress. Antioxid Redox Signal 2005;7(9-10):1377–87.[121] Pablos MI, Reiter RJ, Chuang JI, et al. Acutely adminis-tered melatonin reduces oxidative damage in lung andbrain induced by hyperbaric oxygen. J Appl Physiol1997;83:354–8.[122] Pelaia P, Rocco M, De Blasi RA, et al. Assessment of lipidperoxidation in hyperbaric oxygen therapy: protective roleof N-acetylcysteine. Minerva Anestesiol 1995;61(4):133–9.[123] Hollis AL, Butcher WI, Davis H, Henderson RA, Stone WL.Structural alterations in retinal tissues from rats deficientin vitamin E and selenium and treated with hyperbaricoxygen. Exp Eye Res 1992;54(5):671–84.[124] Boadi WY, Thaire L, Kerem D, Yannai S. Effects of dietaryfactors on antioxidant enzymes in rats exposed to hyper-baric oxygen. Vet Hum Toxicol 1991;33(2):105–9.[125] Weber CA, Duncan CA, Lyons MJ, Jenkinson SG. Depletionof tissue glutathione with diethyl maleate enhanceshyperbaric oxygen toxicity. Am J Physiol 1990;258(6 Pt 1):L308–12.[126] Thom SR, Bhopale VM, Velazquez OC, Goldstein LJ, ThomLH, Buerk DG. Stem cell mobilization by hyperbaricoxygen. Am J Physiol Heart Circ Physiol 2005; in press.[127] Steindler DA, Pincus DW. Stem cells and neuropoiesis inthe adult human brain. Lancet 2002;359:1047–54.[128] Harch PG, Small T. Interview with Dr. Paul Harch: theapplication of hyperbaric oxygen therapy in chronicneurological conditions. Medical Veritas 2005;2:637–46.[129] Collet JP, Vanasse M, Marois P, et al. Hyperbaric oxygenfor children with cerebral palsy: a randomised multicentretrial. Lancet 2001;357:582–6.[130] Marois P, Vanasse M. Letter to the editor: ‘‘Hyperbaricoxygen therapy and cerebral palsy’’. Dev Med Child Neurol2003;45:646–8.[131] Autism Research Institute. Autism Treatment EvaluationChecklist (ATEC) Internet Scoring Program, http://www.autismeval.com/ari-atec/ [accessed 25.01.06].[132] Rellini E, Tortolani D, Trillo S, Carbone S, Montecchi F.Childhood autism rating scale (CARS) and autism behaviorchecklist (ABC) correspondence and conflicts with DSM-IVcriteria in diagnosis of autism. J Autism Dev Disord2004;34(6):703–8.[133] Constantino JN, Davis SA, Todd RD, et al. Validation of abrief quantitative measure of autistic traits: comparison ofthe social responsiveness scale with the autism diagnosticinterview-revised. J Autism Dev Disord 2003;33(4):427–33.Hyperbaric oxygen therapy may improve symptoms in autistic children 13ARTICLE IN PRESS



                                                                                                                                                                                                                                                                                                                                                                                                                                        

                                                                                                                                                                                                                                                                                                                                                                                                                                                    

                                                                                                                                                                                                                                                                                                

           

                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             

                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       

                                                                                                                                                                                                                                                                                                                                                                                                                                         

                                                                                                                                                                                                                                                                                                                                                 

                                                                                                                                                                                                                                                                                                                                                                               

                                                                                                                                                                                                                                                                                                                                                 

                                                                                                                                                                                                                                                                              

                                                                                 View publication statsView publication stats

RE V I E W Open AccessHyperbaric oxygen treatment in autismspectrum disordersDaniel A Rossignol1*, James J Bradstreet2,3, Kyle Van Dyke4, Cindy Schneider5, Stuart H Freedenfeld6,Nancy O’Hara7, Stephanie Cave8, Julie A Buckley9, Elizabeth A Mumper10and Richard E Frye11AbstractTraditionally, hyperbaric oxygen treatment (HBOT) is indicated in several clinical disorders include decompressionsickness, healing of problem wounds and arterial gas embolism. However, some investigators have used HBOT totreat individuals with autism spectrum disorders (ASD). A number of individuals with ASD possess certainphysiological abnormalities that HBOT might ameliorate, including cerebral hypoperfusion, inflammation,mitochondrial dysfunction and oxidative stress. Studies of children with ASD have found positive changes inphysiology and/or behavior from HBOT. For example, several studies have reported that HBOT improved cerebralperfusion, decreased markers of inflammation and did not worsen oxidative stress markers in children with ASD.Most studies of HBOT in ch ildren with ASD examined changes in behaviors and reported improvements in severalbehavioral domains although many of these studies were not controlled. Although the two trials employing acontrol group reported conflicting results, a recent systematic review noted several important distinctions betweenthese trials. In the reviewed studies, HBOT had minimal adverse effects and was well tolerated. Studies which useda higher frequency of HBOT sessions (e.g., 10 sessions per week as opposed to 5 sessions per week) generallyreported more significant improvemen ts. Many of the studies had limitations which may have contributed toinconsistent findings across studies, including the use of many different standardized and non-standardizedinstruments, making it difficult to directly compare the results of studies or to know if there are specific areas ofbehavior in which HBOT is most effective. The variability in results between studies could also have been due tocertain subgroups of children with ASD responding differently to HBOT. Most of the reviewed studies relied onchanges in behavioral measurements, which may lag behind physiological changes. Additional studies enrollingchildren with ASD who have certain physiological abnormalities (such as inflammation, cerebral hypoperfusion, andmitochondrial dysfunction) and which measure changes in th ese physiological parameters would be helpful infurther defining the effects of HBOT in ASD.Keywords: Hyperbaric oxygen treatment, Autism, Oxidative stress, Inflammation, BehaviorIntroductionHyperbaric oxygen treatment (HBOT) involves inhalingup to 100% oxygen at a pressure greater than one at-mosphere (atm) in a pressurized chamber [1]. HBOT isindicated in several clinical disorders include decom-pression sickness, healing of problem wounds, arterialgas embolism and carbon monoxide poisoning [2].Treatment with HBOT for these disorders uses higherpressures (over 2.0 atm). Higher pressure HBOT hasbeen shown to increase the oxygen content of plasma[3] and body tissues [4] and may normalize oxygen levelsin ischemic tissues [5].As compared to treatment with HBOT for many clas-sical indications, HBOT used at lower pressures (e.g. 1.3to 1.5 atm and oxygen at 24 to 100%) has started to beinvestigated to treat certain neurological disorders, someof which are considered to have few efficacious treat-ments. For example, recent studies have investigatedlower pressure HBOT for traumatic brain injury (TBI) inboth animal models [6-10] and humans [11-23]. In a re-cent prospective trial of 16 patients with TBI, HBOT at1.5 atm/100% oxygen (40 hourly treatments over 30 days)* Correspon dence: rossignolmd@gmail.com1Rossignol Medical Center, 3800 West Eau Gallie Blvd., Melbourne, FL 32934,USAFull list of author information is available at the end of the articleMEDICAL GAS RESEARCH© 2012 Rossignol et al.; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the CreativeCommons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, andreproduction in any medium, provided the original work is properly cited.Rossignol et al. Medical Gas Research 2012, 2:16http://www.medicalgasresearch.com/content/2/1/16

resulted in significant improvements in their neuro-logical exam, IQ, memory, post-traumatic stress symp-toms, depression, anxiety and quality of life. Patie ntsalso displayed objective improvements in brain perfusionmeasured by pre- and post-HBOT single photon emis-sion computed tomography (SPECT) scans [17]. Thehuman studies of TBI also include a controlled retro-spective review and a controlled prospective clinical trial[15,18]. Larger multicenter trials are ongoing in attemptto confirm these controlled clinical studies [24].Other neurological disorders have been reported toimprove with lower pressure HBOT; one investigatorreported significant improvements in IQ for a 15 yearold child who had fetal alcohol syndrome using HBOTat 1.5 atm/100% oxygen for 73 sessions [25]. Someinvestigators have reported that HBOT possessesneuroprotective effe cts [8,26,27]. Interestingly, oxygensupplementation has recently been reported to enhancecognition [17]. For example, in several double-blindstudies of healthy young adults, the use of supplemen-tary oxygen, when compared with room air, significantlyenhanced memory [28], cognitive performance, word re-call and reaction time for 24 hours [29], as well as atten-tion and picture recognition [30].Autism spectrum disorders (ASD) are a heterogeneousgroup of neurodevelopmental disorders that are defined bybehavioral observations and are characterized by impair-ments in communication and social interaction along withrestrictive and repetitive behaviors [31]. ASD includes aut-istic disorder, Asperger syndrome, and pervasive develop-mental disorder-not otherwise specified (PDD-NOS). Anestimated 1 out of 110 individuals in the United States iscurrently affected with an ASD [32]. The etiology of ASDis unclear at this time. Although several genetic syn-dromes, such as Fragile X and Rett syndromes, have beenassociated with ASD, empirical studies have estimated thatgenetic syndromes only account for 6-15% of ASD cases[33]. Therefore, the majority of ASD cases are not due to asimple single gene or chromosomal disorder. Althoughmany of the cognitive and behavioral features of ASD arethought to arise from dysfunction of the central nervoussystem (CNS), evidence from many fields of medicine hasdocumented multiple non-CNS physiological abnormal-ities associated with ASD [34-37], suggesting that, in someindividuals, ASD arises from systemic, rather than organspecific, abnormalities. Specifically, in recent decades, re-search and clinical studies in ASD have implicated physio-logical and metabolic systems that transcend specificorgan dysfunction, such as cerebral hypoperfusion, im-mune dysregulation, inflammation, oxidative stress, andmitochondrial dysfunction [38,39]. In this context, ASDmay arise from, or at least involve, systemic physiologicalabnormalities rather than being a purely CNS disorder, atleast in a subset of individuals with ASD [40].To date, ASD has few efficacious treatments. AppliedBehavioral Analysis (ABA) is a form of behavioral ther-apy which has been reported to lead to improvements insome children with ASD. ABA treats the behavioralmanifestations of ASD. Studies of ABA generally observechildren with ASD over a period of one to two years.Lovaas first reported that ABA resulted in significantgains in IQ and behavioral problems over a 2 year periodof time in some children with A SD [41]. Researchersfrom the Wisconsin Early Autism Project observed simi-lar behavioral and IQ improvements with ABA after4 years of observations [42]. However, only modest gainswere detected using ABA compared to ecle ctic therapyby researchers in Norway when children were observedfor only one year [43]. Therefore, behavioral therapiestypically require long time periods to cause behavioraland cognitive changes in children with ASD.Some treatments for ASD target physiological abnor-malities that have been reported in some children. How-ever, very few of these types of treatments have beencritically evaluated. Starting around 2005, some investi-gators speculated that HB OT may be useful in improv-ing behavioral and physiological abnormalities found insome children with ASD [44-48]. This manuscript willreview the current evidence for HBOT as a treatmentfor ASD. First, the effects of HBOT on phy siological ab-normalities in children with ASD will be reviewed. Sec-ondly, the effects on aut istic behaviors will be discussed.Finally, potential adverse effects of HBOT in A SD andlimitations of studies will be re viewed.The effects of HBOT on physiological abnormalities inASDCerebral hypoperfusion in ASD and the effects of HBOTA number of studies have reported cerebral hypoperfusionin individuals with ASD compared to controls as measuredby positron emission tomography (PET), SPECT or func-tional magnetic resonance imaging (fMRI) [49-51]. Thishypoperfusion has been correlated with certain autisticbehaviors such as repetitive behaviors [52], desire forsameness [53], impairments in processing facial expres-sions and emotions [54], and decreased language develop-ment [55]. Furthermore, lower cerebral perfusion has beensignificantly correlated with increasing age in children withASD [55] and with more severe autistic behaviors [56].It is possible that HBOT could improve cerebral perfusionin ASD. Several studies have reported significant improve-ments in cerebral perfusion with the use of HBOT at lowerpressures (i.e., 1.3 to 1.5 atm), as measured by pre- and post-HBOT SPECT scans in several neurological conditions, in-cluding TBI and chronic brain injury [16,17,19,22]. Inaddition, cerebral perfusion has been shown to change inchildren with ASD after treatment with HBOT. For example,several case reports have demonstrated improvements inRossignol et al. Medical Gas Research 2012, 2:16 Page 2 of 13http://www.medicalgasresearch.com/content/2/1/16

cerebral perfusion, as measured by pre- and post-treatmentSPECT scans, with the use of HBOT at 1.3 atm/24% oxygen,including one child with ASD who received 1 hour of HBOTper day for 10 consecutive days [57] and two children withASD wh o rec e i ved 40–80 treatments [58]. Behavioralimprovements were observed in these children as well.Figure 1a-b demonstrates the pre- and post-HBOT SPECTscans in one child from this latter case report [58].Kinaci et al. reported on the cerebral perfusion effects ofHBOT at 1.5 atm/100% oxygen for 50 sessions at 60minutes per day in 108 children with ASD [59]. At baseline,all 108 patients had normal MRI scans and decreased tem-poral lobe perfusion as measured by SPECT scans, while88% had decreased frontal lobe perfusion and 61% haddecreased perfusion to other brain areas. Post-treatmentHBOT SPECT scans demonstrated that 82.4% of thepatients had an improvement in temporal lobe perfusion,85.3% improved in frontal lobe perfusion, and 75.8% hadimprovements in perfusion to other brain areas. Behavioralimprovements were also observed in these children.Figure 1 SPECT scan images in a 12 year old boy with autism (a) before and (b) after 80 sessions of HBOT at 1.3 atm. Legend: minus 2(green) to minus 4 (blue) standard deviations indicate the magnitude of regional hypofunctioning (hypoperfusion). White arrows indicateimprovement in deeper cortical hypoperfusion patterns. Red arrows on sagittal slices show the midline cerebellum hypoperfusion andimprovements after HBOT. Yellow arrows on the “underside” view show the temporal lobe hypoperfusion with improvements after HBOT.Pictures courtesy of J. Michael Uszler, MD. Credit: Permission for use of figure from Hyperbaric Oxygen for Neurological Disorders granted by BestPublishing Company, Palm Beach Gardens, FL.Rossignol et al. Medical Gas Research 2012, 2:16 Page 3 of 13http://www.medicalgasresearch.com/content/2/1/16

Strengths of this study included objective measurements(SPECT imaging), evaluations by clinicians, and a largersample size than other studies.Inflammation in ASD and the effects of HBOTRecent studies support the notion that some individualswith ASD manifest neuroinflammation, immune dysregula-tion and/or gastrointestinal inflammation. A recent reviewreported that 416 publications implicated inflammation orimmune abnormalities in ASD, including 65 publications ofneuroinflammation and 31 publications of gastrointestinalinflammation [38]. A number of studies suggest that thegastrointestinal inflammation reported in some childrenwith ASD has characteristics similar to inflammatory boweldisease (IBD) [60-63]. Furthermore, several studies havereported abnormal inflammatory markers in some childrenwith ASD. For example, elevations in TNF-alpha [64-67]and neopterin (a marker of activation of the cellular im-mune system) [68-70] have been reported in several studiesof children with ASD.Treatment with HBOT has been shown to possess potentanti-inflammatory properties in both animal [71-73] andhuman studies [74-78]. HBOT has been reported to de-crease the production of pro-inflammatory cytokines (in-cluding TNF-alpha, interferon-gamma, IL-1 and IL-6) inboth animal [79,80] and human studies [78,81] as well as in-crease counter-inflammatory IL-10 levels [82]. In one study,HBOT also decreased neopterin levels [83]. Furthermore , arecent systematic review reported improvements in studiesthat used HBOT in IBD [84]. The effect of HBOT on redu-cing inflammation may be mediated through a pressure-related effect and not necessarily by the oxygen delivered.For example, one human study reported a reduction ininterferon-gamma production by lymphocytes with HBOTat 2.0 atm/10.5% oxygen but an increase in interferon-gamma with 100% oxygen delivered at 1.0 atm [78].Two prospective studies have examined the effects ofHBOT on biomarkers of inflammation in children withASD [85,86]. In the first study, 12 children received HBOTat 1.3 atm/24% oxygen and 6 children received HBOT at1.5 atm/100% oxygen. Biomarkers were measured beforeand after 40 HBOT sessions [85]. C-reactive protein (a gen-eral marker of inflammation) dropped in the overall studypopulation (p = 0.021). Children who had the highest C-reactive protein levels showed the largest decrease. Behav-ioral improvements were also observed in these children.In the second study, plasma cytokine levels, includingsome associated with inflammation, were measured be-fore and after 80 HBOT sessions delivered at 1.5 atm/100% oxygen over a 20 week period in 10 children withASD [86]. Behavioral improvement s were observed inthese children, but the study reported no significantchanges in cytokines during the study. However, theauthors noted that none of the children had abnormalcytokine levels at the beginning of the study, making itless likely that a significant change could be observed.Furthermore, since cerebrospinal fluid (CSF) cytokineabnormalities have been reported in some children withASD [64,87,88], the authors noted that CSF cytokinescould have changed. However, CSF cytokines were notmeasured in the study. Further studies of HBOT in chil-dren with ASD who have abnormal cytokines and mar-kers of inflammation are warrante d to investigate thesefindings in more depth.In addition to these two studies, one of the authors(DAR) has observed a decrease in urinary neopterinlevels after HBOT in some children. For example, onechild with ASD who was treated with HBOT at 1.5 atm/100% oxygen for 40 treatments over 1 month had a dropin urinary neopterin, measured immediately before start-ing HBOT and immediately after stopping, from 768 to391 μmol/mol creatinine, respectively. Another childwith ASD who had significant eczema and bowel inflam-mation with abdominal distension had resolution of ec-zema, chronic di arrhea and abdominal distension withHBOT at 1.5 atm/100% oxygen for 40 treatments over1 month [58]. See Figure 2a-b for pre- and post-HBOTpictures of this child.Mitochondrial dysfunction in ASD and the effects of HBOTSome individuals with ASD manifest evidence of mito-chondrial dysfunction [34,89]. A recent review articlereported that 145 publications implicated mitochondrialdysfunction in ASD [38]. Although treatments for mito-chondrial dysfunction remain relatively limited [34], inter-est has recently increased in using HBOT as a potentialtreatment. Both animal and human studies have examinedthe effects of HBOT on mitochondrial function. Severalanimal models have reported improvements in mitochon-drial function with HBOT [90-96]. For example, in oneFigure 2 6 year old boy with autism who received HBOT at1.5 atm. Before HBOT, physical exam reveals distendedabdomen (a) with chronic diarrhea. After HBOT, patient hasimprovements in distended abdomen (b) and bowel movements.Figure use with parental permission. Credit: Permission for use offigure from Hyperbaric Oxygen for Neurological Disorders grantedby Best Publishing Company, Palm Beach Gardens, FL.Rossignol et al. Medical Gas Research 2012, 2:16 Page 4 of 13http://www.medicalgasresearch.com/content/2/1/16

study of rats with normal mitochondrial function, HBOTincreased the production of ATP in muscle tissue com-pared to a control group [97]. A recent study of rat hippo-campus reported that HBOT increased mitochondrialbiogenesis and autophagy through, in part, an increasedproduction of reactive oxygen species (ROS). Through thisprocess, new healthy mitochondrial were produced andold dysfunctional mitochondrial were destroyed. Thisstudy also found increased activation of mitochondrialDNA transcription and replication with HBOT [98]. In arecent controlled study of 69 patients with severe TBI,HBOT at 1.5 atm/100% oxygen significantly increasedbrain oxygen levels, increased cerebral blood flow, anddecreased CSF lactate levels (high CSF lactate is a markerof mitochondrial dysfunction). In this study, HBOT alsoimproved brain metabolism and mitochondrial functioncompared with both room air treatment and 100% oxygengiven at normobaric pressure [18]. Although one investiga-tor has reported improvements using HBOT in childrenwith concomitant mitochondrial disease and ASD [99], noclinical studies have been published to date examining theeffects of HBOT on mitochondrial function in individualswith ASD; further study in this area is needed.Oxidative stress in ASD and the effects of HBOTMultiple studies have reported evidence of oxidative stress inchildren with ASD [36,100-102]. A recent review articlereported that 115 publications implicated oxidative stress inASD [38] . Sinc e some chi l d r e n with ASD hav e evide nce ofelevated oxidative stress [38,100], some investigators haveexpressed concern that HBOT could increase oxidative stressin this subset of children [85].Theoretically,HBOTmightincrease oxidative stress through the augmented productionof ROS from the high concentration of oxygen [103]. Thismay occur because increased oxygen delivery to mitochon-dria can increase ROS production. However, HBOT hasbeen shown to upregulate the production of antioxidantenzymes such as superoxide dismutase [104,105], glutathi-one peroxidase [106], catalase [107], paraoxonase [108] andheme-oxygenase 1 [109,110]. This increase in antioxidantenzyme levels has been termed “conditioning” and can pro-tect against damage caused by ROS [44,111]. Interestingly,increasing ROS may be a potential mechanism of action ofHBOT because ROS play an important role in cellular sig-naling and in triggering certain metabolic pathways [112].Furthermore, as previously discussed, a slight increase inROS produced by HBOT may be beneficial as these ROS ap-pear to augment mitochondrial biogenesis [98].Two studies have reported measurements of oxidativestress markers before and after HBOT in children with ASD[85,113]. In the first study, HBOT was administered daily at1.3 atm to 48 children with ASD, and superoxide dismutase(SOD), catalase and glutathione peroxidase levels were mea-sured before starting HBOT and after 1 day and 32 days ofHBOT [113]. SOD was 4.5-fold and 4.7-fold higher at 1 and32 days after starting HBOT, respectively. Mean catalaseincreased by 1.9-fold after 1 day and after 32 days was 90%of the initial level before beginning HBOT. Finally, meanglutathione peroxidase increased by 1.4-fold after 1 day andafter 32 days was 1.2-fold higher than before beginningHBOT. The effects of HBOT on these antioxidant enzymesmay be an example of conditioning as previously discussed.In the second prospective study, 12 children with ASDreceived HBOT at 1.3 atm/24% oxygen and 6 childrenreceived HBOT at 1.5 atm/100% oxygen. Biomarkerswere measured before and after 40 HBOT session s [85].Behavioral improvements were observed in these chil-dren and plasma oxidized glutathione levels did not sig-nificantly change at 1.3 atm (p = 0.557) or 1.5 atm(p = 0.583). Since oxidized glutathione is exported fromcells when intracellular level s exceed the redox capacity[114], this finding suggests that intracellular oxidativestress did not significantly worsen with HBOT at thesetwo commonly used lower HBOT pressures in ASD[85].The effects of HBOT on behavioral measurements in ASDThe majority of treatment studies using HBOT in chil-dren with ASD have measured behavioral rather thanphysiological parameters. These behavioral studies canbe divided into those with and without control children.Studies lacking control childrenSeveral case studies have reported behavioral improve-ments in individuals with ASD from treatment withHBOT. The first published report of the use of HBOT inan individual with ASD was in 1994 [115]. In this report,treatment with HBOT resulted in improvements in moodand social interactions in a three year old child with ASD.The number of treatments and other HBOT parameterswere not reported. In 2002, Heuser et al. reported a “strik-ing improvement” in behavior, memory, social interaction,verbalizations and cognitive functioning in a 4 year oldboy with ASD after HBOT treatment at 1.3 atm/24% oxy-gen for 10 consecutive days [57]. Another investigatorobserved significant objective improvements in coloringskills (see Figure 3a-d) as well as speech and self-help skillsin a 17 year old child with ASD using HBOT at 1.5 atm/100% oxygen for 20 sessions [116]. Burke noted improve-ments in 2 children with ASD using HBOT at 1.3 atm/28% oxygen, including improvements in communication,aggressiveness and social interaction [117]. Another reportnoted objective improvements in one child with ASD inhandwriting (Figure 4a-b) after 40 treatments with HBOTat 1.3 atm/24% oxygen, as well as improvements in finemotor skills, bowel function, language and communication[58]. One investigator reported improvements in language,social interaction and overall cognition in a 3 year old boyRossignol et al. Medical Gas Research 2012, 2:16 Page 5 of 13http://www.medicalgasresearch.com/content/2/1/16

with ASD using HBOT at 1.3 atm/24% oxygen for 40 treat-ments. This child also had chronic diarrhea and had thefirst normal bowel movement in his life with HBOT treat-ment [99]. In another report, 23 patients with ASD hadvarious improvements in social interaction, language andrepetitive behaviors with HBOT at 1.5 atm [47]. Finally,one prospective study of 20 children with ASD reportedimprovements in communication, social interaction andstereotypical behaviors after 20 HBOT sessions at 1.5 atm/100% oxygen [118].The first published case-series to examine the effects ofHBOT in 6 children with ASD administered HBOT at1.3 atm/28% oxygen (1 hour treatments for 40 treatments)[119]. Improvements were reported on the Autism Treat-ment Evaluation Checklist (ATEC), the Childhood AutismRating Scale (CARS) and the Social Responsiveness ScaleFigure 3 Coloring book pages from 17 year old girl with autism: (a) before beginning HBOT at 1.5 atm/100% oxygen; (b) after oneweek of HBOT (5 sessions at one hour each), she is beginning to create patches of color to fill in a space; (c) after 3 weeks of HBOT(about 15 hours of HBOT), she uses correct colors for Winnie the Pooh and Eyore, and the foliage except for the tree trunk; and (d)after 5 weeks of HBOT (20 hours of HBOT), she begins to respect borders and boundaries and even outlines the inner border withcolor. After 6 months, her coloring abilities remained stable. Pictures courtesy of Carol L. Henricks, MD. Credit: Permission for use of drawingsgranted by the Journal of American Physicians and Surgeons.Rossignol et al. Medical Gas Research 2012, 2:16 Page 6 of 13http://www.medicalgasresearch.com/content/2/1/16

(SRS). More significant improvements were observed inchildren under age 5 compared to those older.A follow-up prospective study examined the effects ofHBOT in 18 children with ASD [85]. Twelve childrenwere treated at 1.3 atm/24% oxygen and 6 were treated at1.5 atm/100% oxygen. Hyperbaric sessions were 45 min-utes in duration for 40 total sessions. As previously noted,markers of oxidative stress and inflammation were mea-sured. Pre- and post-HBOT parent-rated SRS and ATECindicated significant improvements in each group, includ-ing motivation, speech, and cognitive awareness (p < 0.05for each). Strengths of this study included the prospectivenature and the use of objective measurements (oxidativestress and inflammatory markers). One group of investiga-tors criticized this study, stating that significant improve-ments were only observed when both groups (1.3 atm and1.5 atm) were combined [120]; however, the improvementswere indeed significant for each group individually [85].One small, prospective case series of 3 children withASD using a multiple baseline design reported no signifi-cant improvements (compared to baseline) after 27–40HBOT treatments at 1.3 atm/88% oxygen. The treatmentswere 1 hour in duration, 5 days per week. However, onechild had an increase in spontaneous communication andanother child had a decrease in problem behaviors withHBOT and an immediate increase in problem behaviorswhen HBOT was stopped [121]. These improvementswere felt by the authors to be unrelated to HBOT butcould not necessarily be explained by other factors.Strengths of this study included the prospective nature,the multiple baseline design (including a baseline prior toinitiating HBOT), as well as evaluations by therapists andvideotaping.Another prospective study from Thailand reported theeffects of HBOT at 1.3 atm/100% oxygen for 10 sessions(one session per week) in 7 children with ASD [122].Significant improvements (p < 0.001 for each) wereobserved in social interaction, fine motor and eye-handcoordination, language, gross motor skills and self-helpscores. Strengths of this study included the prospectivenature and the objective measurements of self-help andmotor skills by therapists.A large, retrospective study from Turkey using HBOTat 1.5 atm/100% oxygen for 50 sessions at 60 minutesper day reported pre- and post-HBOT ATEC scores [59].As previously noted, improvements in cerebral perfusionwere observed on pre- and post-HBOT SPECT scans. Asrated by clinicians/therapists for 54 children with ASD,improvements were observed in speech/language/com-munication in 79%, sociability in 85.5%, sensory/cogni-tive awareness in 87%, and health/physical/behavior in75.2%. Strengths of this study included objective mea-surements (SPECT imaging), eval uations by clinicians,and a larger sample size than other studies.One prospective study using a multiple baseline designexamined the effects of HBOT at 1.3 atm/24% oxygenfor 40 treatme nts in 16 children with ASD treated overan average of 56 days [123]. The mean frequency oftreatments was 4.78 sessions per week with a range of2.46 to 7.0 sessions. No consistent positive or negativeeffects were observed. The authors noted that the studyused an observational technique which may not havebeen sufficient to measure changes in certain areas, suchas attention and memory, and that the numbe r of treat-ments per week was about half as other studies whichreported improvements using similar HBOT parametersin children with ASD. Strengths of this study includedthe multiple baseline design (including a baseline priorto initiating HBOT), as well as evaluations by therapistsand videotaping.Finally, a more recent prospective study in 10 childrenwith ASD measured the effects of HBOT at 1.5 atm/100%oxygen for 1 hour per day, 5 days per week for 80 treat-ments (completed over 20 weeks, with a 4 week break be-tween the 40thand 41sttreatment) on several behavioralscales as rated by parents and clinicians [86]. As previouslynoted, cytokine markers were measured before and afterHBOT. Significant improvements were observed as mea-sured by parent-rated ABC in irritability, lethargy, hyper-activity and overall scores (p = 0.02 or less for each). Onthe parent-rated PDD Behavior Inventory (PDD-BI), sig-nificant improvements were observed in sensory problems,specific fears, and aggressiveness (p = 0.006 or less foreach). Overall, parents reported improvements in eye con-tact, imitation, language, tantrums, gastrointestinal pro-blems and eczema. A significant improvement of 2 points(corresponding to “much improved”) was observed on theclinician-rated CGI-I scale in all 10 children. Strengths ofthis study included the prospective nature, evaluations byclinicians, and objective measurements (cytokine levels).Figure 4 Handwriting in a 6 year old boy (a) before and (b)after 40 HBOT sessions at 1.3 atm. Pictures courtesy of JamesNeubrander, MD. Credit: Permission for use of figure from HyperbaricOxygen for Neurological Disorders granted by Best PublishingCompany, Palm Beach Gardens, FL.Rossignol et al. Medical Gas Research 2012, 2:16 Page 7 of 13http://www.medicalgasresearch.com/content/2/1/16

Studies with control chil drenIn a recent systematic review published in Medical GasResearch, Ghanizadeh reviewed two randomized, double-blind, controlled trials using HBOT in children with aut-ism [124]. The first study investigated the effects of HBOTat 1.3 atm/24% oxygen for 40 treatments, utilizing 2 treat-ments per day, 5 days per week, over 4 weeks in 33 chil-dren with autistic disorder compared to 29 controlchildren with autistic disorder who received slightly pres-surized room air (1.03 atm and 21% oxygen) [125]. Com-pared to the control group, significant improvements wereobserved in the treated children on the clinician-ratedCGI scale and the parent-rated CGI and ATEC scales inoutcomes including overall functioning, receptive lan-guage, social interaction, eye contact and sensory/cognitiveawareness. Of the children completing more than 1 HBOTsession, one child dropped out of the study after ninetreatment sessions because asthma symptoms worsened,but this was not felt to be related to the treatment.Ghanizadeh noted that six other children dropped out ofthe study (four before the study began and two before fin-ishing one full treatment). In this study, six medical cen-ters participated and the findings did not significantlydiffer across centers. Strengths of this study included eva-luations by blinded clinicians and parents (only the HBOTtechnician was aware of group assignment), an assessmentof blinding (which was adequate), an intention-to-treatanalysis (children finishing more than 1 HBOT sessionwere included in the analysis), the prospective nature, theuse of a control group, and the use of 6 centers (whichmay have minimized potential biases associated with a sin-gle site study).Several criticisms of this study [125] arose in the com-ments se ctions of BMC Pediatrics and by other authors[120,123]. One criticism was the claim that the effect oftreatment was determin ed by anintragroup analysis ofthe treatment group alone, and not by anintergroupanalysis of the treatment compared to the control group;however, the analysis was indeed anintergroup analysiswhere the effects of treatment were compared betweenthe two groups. The authors noted that a typographicalerror in the manuscript may have contributed to someconfusion as ± SEM (standard error of the mean) wasused when all of the reported values were actually ± SD(standard deviation). Another criticism was that the ef-fect size of the treatment was probably small; however,the effect sizes were calculated as moderate to large(0.55 for the ATEC sensory/cognitive awareness sub-scale; 1.0 for physician-rated CGI score for overall func-tioning; and 0.62 for parent-rated CGI score for overallfunctioning [126]).In the second controlled study, 18 children with autismwere treated with HBOT at 1.3 atm/24% oxygen for 80 ses-sions (completed within 15 weeks) and compared to 16children treated with placebo (free air-flow through achamber at ambient pressure). Both groups received inten-sive ABA therapy and no significant changes werereported using several different behavioral scales [120].Ghanizadeh [124] noted that twelve participants (26% ofthe children entering the study) withdrew from the study.It was not noted if these participants were in the treatmentgroup or the control group or when they dropped out ofthe study; the scores from these 12 children were notincluded in the final analyses. Ghanizadeh [124] alsoobserved that the number of patients in each groupwas small and that both groups showed some improve-ments during the study. Furthermore, it was noted byGhanizadeh [124] that since both groups received inten-sive ABA therapy during the trial, one explanation for thelack of efficacy observed is that HBOT did not add signifi-cant therapeutic effects to intensive ABA. Strengths of thisstudy included the prospective nature, the use of a controlgroup and evaluation by blinded assessors.Ghanizadeh [124] reported several important distinc-tions between these two controlled trials [120,125] whichmight help account for the different outcomes, includingthe number of participants, potential differences in diagno-ses, different age ranges of the study participants, differentoutcome assessors, possible differences in demographicsand autism severity, multicenter [125] vs. single center trial[120], assessment of blinding in one study [125] but not inthe second [120], and the intensity of treatments with onestudy providing a mean of 10 hours of hyperbaric treat-ments per week [125] and the other study providing, onaverage, about 5 hours per week [120]. Ghanizadeh alsonoted that one [120] of the studies had a relatively highdropout rate which may have affected the results of thestudy. Although the other controlled study had 7 childrendrop out of the study, 4 dropped before starting the studyand two before finishing one treatment session [125].Moreover, Ghanizadeh noted that for one of the studies[120], there was no assessment of blinding efficacy asdescribed in other HBOT studies [127,128].Adverse effects of HBOT in ASDMost studies did not report any significant adverseevents using HBOT in individuals with ASD. Some stud-ies specifically noted there were no adverse events[85,119]. One study reported no adverse effects exceptfor transient tinnitus in one child which resolved withinone week [122]. Ano ther study reported several non-serious adverse events, including ear discomfort (4 chil-dren), ear infections (2 children) and for 1 child ea ch:hyperactivity, increased vocal sensitivity, increased sen-sory needs, insomnia, fatigue, dehydration, irritability,mouthing of objects, and a seizure [86]. One of the con-trolled studies reported that one child in the treatmentgroup develope d both urinary frequency (urinalysis wasRossignol et al. Medical Gas Research 2012, 2:16 Page 8 of 13http://www.medicalgasresearch.com/content/2/1/16

normal) and a skin rash that the treating physicianthought was yeast-related. Another child in the treat-ment group had worsening of asthma symptoms afternine treatment sessions and was removed from thestudy; a third child had anxiety and dropped out of thestudy before finishing one full treatment. In the con trolgroup, one child developed abdominal distension anddiarrhea during the study and another child had worsen -ing of eczema [125]. The other controlled study reportedno adverse events in the treatment group but reportedthat one of the children in the control group developedhyponatremia and the acute onset of seizures and wasremoved from the study [120]. In a recent systematic re-view, Ghanizadeh highlighted that the use of HBOT inchildren with ASD was associated with minimal adverseevents.Limitations of the reviewed studiesMany of the reviewed studies suffered from limitations, in-cluding the lack of control children, an open-label design,a small number of participants, a retrospective design andthe use of parent-rated scales. Indeed, there were only twocontrolled studies that did not suffer from these types oflimitations. These limitations may have contributed to in-consistent findings across studies. In addition, some stud-ies used measurements or obser vational techniques whichmay not have been sufficient to measure changes in cer-tain areas, such as attention and memory [123]. Thereviewed studies also utilized many different standardizedand non-standardized instruments, making it difficult todirectly compare the results of studies or to know if thereare specific areas of behavior in which HBOT is most ef-fective. None of the studies reported measurements of thelong-term effects of HBOT beyond the study period, so itis not known if any of the reported improvements werelong lasting.Most of the reviewed studies relied on changes in behav-ioral measurements, which may lag behind physiologicalchanges. Based on previous studies of ABA therapy in chil-dren with ASD, it is not likely that substantial changes inbehavior will be detectable over short observation periods,i.e., less than one year. In fact, studies on ABA therapy re-port substantial changes over periods from 1 to 4 years[41-43]. Given the complex requirements of brain develop-ment, it is likely that the observed physiological and neuroi-maging changes observed in children with ASD usingHBOT precede developmental and intellectual improve-ments. In fact, the studies which examined physiologicalchanges with HBOT, especially changes in cerebral perfu-sion, reported substantial changes which were oftenobserved over short periods of time. Although many of thereviewed studies reported behavioral improvements insome children with ASD, none of the studies lasted morethan several months. This time period is probably ofinsufficien t length to quantify the impact of HBOT on de-velopment. Additional studies examining the long term ef-fect of HBOT in individuals with ASD are warranted.Most studies reported improvements with HBOT inphysiological abnormalities and/or behavioral outcomesof children with ASD; however, two studies from thesame group of researchers did not find any notableimprovements [120,123], and a third small studyreported minimal improvements [121]. The variability inresults between studies could have been due to certainsubgroups of children with ASD responding differentlyto HBOT [123]. For example, it is possible that child renwith abnormal cytokines, higher inflammatory markers,cerebral hypoperfusion or mitochondrial dysfunctionmay be more likely to demonstrate improvements. How-ever, many of the behavioral studies did not measurechanges in bioche mical varia bles (such as markers of in-flammation or oxidative stress). One behavioral studymeasured changes in cytokine levels, but all of the chil-dren treated with HBOT had normal cytokine levels,making it unlikely that a significant change in cytokineswould be observed [86]. Additional studies enrollingchildren with ASD who have certain physiological ab-normalities (such as inflammation or cerebral hypoper-fusion) and which measure changes in thesephysiological parameters would be helpful in investigat-ing this further.Studies which used a higher frequency of HBOT ses-sions (e.g., 10 sessions per week as opposed to 5 sessionsper week) generally reported more significant improve-ments. This appears to be consistent with studies inother neurological conditions such as traumatic brain in-jury [17] where studies using a higher mean number ofHBOT sessions per month (e.g., 40 treatments within aone month period) generally reported more significanteffects. Additional studies are needed to look at variousHBOT parameters (pressure and oxygen levels) in chil-dren with ASD to help determine optimal treatmentparameters.ConclusionsHBOT at the pressures commonly used in children withASD (up to 1.5 atm/100% oxygen) has been reported toimprove cerebral perfusion, decrease markers of inflam-mation and not worsen oxidative stress markers. Moststudies of HBOT in children with ASD reportedimprovements in several behavioral domains althoughmany of these studies were not controlled. Although thetwo trials employing a control group reported conflictingresults, a recent systematic review noted several import-ant distinctions between these trials. Collectively, thereviewed studies indicate that the use of HBOT in chil-dren with ASD is associated with minimal adverseevents and is well tolerated. We conclude that HBOT isRossignol et al. Medical Gas Research 2012, 2:16 Page 9 of 13http://www.medicalgasresearch.com/content/2/1/16

a safe and potentially effective treatment for childrenwith ASD but that further studies are warranted. Futurestudies would be wise to use standardized behavioralmeasurement tools and physiological biomarkers in acontrolled study design. Targeting ASD subgroups thatpossess specific physiological abnormalities with HBOTmay be a potentially fruitful method for determiningwhich ASD individuals would benefit from treatmentwith HBOT.Competing interestsDAR, CS, SHF, NO, SC, JAB and EAM treat individuals with hyperbarictreatment in their clinical practices and derive revenue from this. KVD worksat a hyperbaric center and recommends HBOT, but does not derive revenuefrom hyperbaric treatments. JJB prescribes hyperbaric treatment but doesnot derive revenue from this. DAR and EAM have previously receivedresearch funding from the International Hyperbarics Association (IHA) for twostudies of hyperbaric treatment in children with autism [85,125] and CSpreviously received research funding from the IHA for one of these studies[125]. JAB has previously received research funding from the IHA for onestudy of hyperbaric treatment in children with autism and their parents. EAMhas received hyperbaric chambers and financial support from OxyHealth LLCfor remodeling the Rimland Center, a center for mentoring cliniciansinterested in learning how to care for children with autism spectrumdisorders. DAR and KVD are medical advisors (unpaid) for IHA. REF declaresthat he has no competing interests.Authors' contributionsDR conceived the study and wrote the initial draft. All remaining authorsedited the paper for content and suggested changes. All authors read andapproved the final manuscript.Author details1Rossignol Medical Center, 3800 West Eau Gallie Blvd., Melbourne, FL 32934,USA.2International Child Development Resource Center, 104 Colony Park Dr.Suite 600, Cumming, GA 30040, USA.3Southwest College of NaturopathicMedicine, Department of Pediatrics, Tempe, AZ, USA.4Wisconsin IntegrativeHyperbaric Center, 6200 Nesbitt Road, Fitchburg, WI 53719, USA.5Center forAutism Resear ch and Education, 4045 East Union Hills Drive, Suite 116,Phoenix, AZ 85050, USA.6Stockton Family Practice, Stockton Center forHealth Care, 56 South Main Street, Suites A & B, Stockton, NJ 08559, USA.7Center for Autism & Integrative Health, 3 Hollyhock Lane, Wilton, CT 06897,USA.8Cypress Integrative Medicine, 10562 South Glenstone Place, BatonRouge, LA 70810, USA.9Pediatric Partners of Ponte Vedra, 5270 Palm ValleyRoad, Ponte Vedra Beach, FL 32082, USA.10The Rimland Center, 2919Confederate Ave, Lynchburg, VA 24501, USA.11Department of Pediatrics,Arkansas Children’s Hospital Research Institute, University of Arkansas forMedical Sciences, Little Rock, AR 72202, USA.Received: 29 March 2012 Accepted: 19 May 2012Published: 15 June 2012References1. Feldmeier JJ, Chairman and Editor: Hyperbaric ox ygen 2003: indications andresults: the hyperbaric oxygen therapy committee report. Kensington, MD:Undersea and Hyperbaric Medicine Society; 2003.2. Leach RM, Rees PJ, Wilmshurst P: Hyperbaric oxygen therapy. BMJ 1998,317(7166):1140–1143.3. Shandling AH, Ellestad MH, Hart GB, Crump R, Marlow D, Van Natta B,Messenger JC, Strauss M, Stavitsky Y: Hyperbaric oxygen and thrombolysisin myocardial infarction: the "HOT MI" pilot study. Am Heart J 1997, 134(3):544–550.4. Gill AL, Bell CN: Hyperbaric oxygen: its uses, mechanisms of action andoutcomes. QJM 2004, 97(7):385–395.5. Ackerman NB, Brinkley FB: Oxygen tensions in normal and ischemictissues during hyperbaric therapy. Studies in rabbits. JAMA 1966, 198(12):1280–1283.6. Wang GH, Zhang XG, Jiang ZL, Li X, Peng LL, Li YC, Wang Y: Neuroprotectiveeffects of hyperbaric oxygen treatment on traumatic brain injury in the rat. JNeurotrauma 2010, 27(9):1733–1743.7. Palzur E, Zaaroor M, Vlodavsky E, Milman F, Soustiel JF: Neuroprotective effect ofhyperbaric oxygen therapy in brain injury is mediated by preservation ofmitochondrial membrane properties. Brain Res 2008, 1221:126–133.8. Henninger N, Kuppers-Tiedt L, Sicard KM, Gunther A, Schneider D, Schwab S:Neuroprotective effect of hyperbaric oxygen therapy monitored by MR-imaging after embolic stroke in rats. Exp Neurol 2006, 201(2):316–323.9. Harch PG, Kriedt C, Van Meter KW, Sutherland RJ: Hyperbaric oxygen therapyimproves spatial learning and memory in a rat model of chronic traumaticbrain injury. Brain Res 2007, 1174:120–129.10. Vlodavsky E, Palzur E, Soustiel JF: Hyperbaric oxygen therapy reducesneuroinflammati on and expression of matrix metalloproteinase-9 in the ratmodel of traumatic brain injury. Neuropathol Appl Neurobiol 2006, 32(1):40–50.11. Wright JK, Zant E, Groom K, Schlegel RE, Gilliland K: Case report: Treatment of mildtraumatic brain injury with hyperbaric oxygen. Undersea Hyperb Med 2009, 36(6):391–399.12. Eovaldi B, Zanetti C: Hyperbaric oxygen ameliorates worsening signs andsymptoms of post-traumatic stress disorder. Neuropsychiatr Dis Treat 2010,6:785–789.13. Lv LQ, Hou LJ, Yu MK, Ding XH, Qi XQ, Lu YC: Hyperbaric oxygen therapyin the management of paroxysmal sympathetic hyperactivity aftersevere traumatic brain injury: a report of 6 cases. Arch Phys Med Rehabil2011, 92(9):1515–1518.14. Stoller KP: Hyperbaric oxygen therapy (1.5 ATA)intreatingsportsrelatedTBI/CTE: two case reports. Med Gas Res 2011, 1(1):17.15. Sahni T, Jain M, Prasad R, Sogani SK, Singh VP: Use of hyperbaric oxygen intraumatic brain injury: Retrospective analysis of data of 20 patientstreated at a tertiary care centre. Br J Neurosurg 2011, 26(2):207.16. Harch PG, Fogarty EF, Staab PK, Van Meter K: Low pressure hyperbaricoxygen therapy and SPECT brain imaging in the treatment of blast-induced chronic traumatic brain injury (post-concussion syndrome) andpost traumatic stress disorder: a case report. Cases J 2009, 2:6538.17. Harch P, Andrews SR, Fogarty E, Amen DG, Pezzullo JC, Lucarini J, Aubrey C, TaylorDV, Staab P, Van Meter K: APhaseIStudyofLowPressureHyperbaricOxygenTherapy for Blast-Induced Post Concussion Syndrome and Post TraumaticStress Disorder. JNeurotrauma2012, 29(1):168–185.18. Rockswold SB, Rockswold GL, Zaun DA, Zhang X, Cerra CE, Bergman TA, Liu J: Aprospective, randomized clinical trial to compare the effect of hyperbaric tonormobaric hyperoxia on cerebral metabolism, intracranial pressure, and oxygentoxicity in severe traumatic brain injury. JNeurosurg2010, 112(5):1080–1094.19. Shi XY, Tang ZQ, Xiong B, Bao JX, Sun D, Zhang YQ, Yao Y: Cerebral perfusionSPECT imaging for assessment of the effect of hyperbaric oxygen therapyon patients with postbrain injury neural status. Chin J Traumatol 2003, 6(6):346–349.20. Shi XY, Tang ZQ, Sun D, He XJ: Evaluation of hyperbaric oxygen treatment ofneuropsychiatric disorders following traumatic brain injury. Chin Med J (Engl)2006, 119(23):1978–1982.21. Hardy P, Johnston KM, De Beaumont L, Montgomery DL, Lecomte JM, Soucy JP,Bourbonnais D, Lassonde M: Pilot case study of the therapeutic potential ofhyperbaric oxygen therapy on chronic brain injury. JNeurolSci2007, 253(1–2):94–105.22. Golden ZL, Neubauer R, Golden CJ, Greene L, Marsh J, Mleko A: Improvement incerebral metabolism in chronic brain injury after hyperbaric oxygen therapy.Int J Neurosci 2002,112(2):119–131.23. Golden Z, Golden CJ, Neubauer RA: Improving neuropsychological functionafter chronic brain injury with hyperbaric oxygen. Disabil Rehabil 2006, 28(22):1379–1386.24. Helms A, Evans AW, Chu J, Sahgal A, Ostrowski R, Sosiak T, Wolf G, Gillett J,Whelan H: Hyperbaric oxygen for neurologic indications–actio n plan formulticenter trials in: stroke, traumatic brain injury, radiation encephalopathy&statusmigrainosus.Undersea Hyperb Med 2011, 38(5):309–319.25. Stoller KP: Quantif ica tio n of neurocognitive changes before, during, and afterhyperbaric oxygen therapy in a case of fetal alcohol syndrome. Pediatrics2005, 116(4):586–591.26. Matchett GA, Martin RD, Zhang JH: Hyperbaric oxygen therapy andcerebral ischemia: neuroprotective mechanisms. Neurol Res 2009, 31(2):114–121.27. Huang L, Obenaus A: Hyperbaric oxygen therapy for traumatic braininjury. Med Gas Res 2011, 1(1):21.Rossignol et al. Medical Gas Research 2012, 2:16 Page 10 of 13http://www.medicalgasresearch.com/content/2/1/16

28. Moss MC, Scholey AB: Oxygen administration enhances memoryformation in healthy young adults. Psychopharmacology (Berl) 1996, 124(3):255–260.29. Scholey AB, Moss MC, Neave N, Wesnes K: Cognitive performance,hyperoxia, and heart rate following oxygen administration in healthyyoung adults. Physiol Behav 1999, 67(5):783–789.30. Moss MC, Scholey AB, Wesnes K: Oxygen administration selectivelyenhances cognitive performance in healthy young adults: a placebo-controlled double-blind crossover study. Psychopharmacology (Berl) 1998,138(1):27–33.31. APA: Diagnostic and statistical manual of mental disorders. 4th edition.Washington, DC: American Psychiatric Association; 1994.32. Rice C: Prevalence of autism spectrum disorders - Autism andDevelopmental Disabilities Monitoring Network, United States, 2006.MMWR Surveill Summ 2009, 58(10):1–20.33. Schaefer GB, Mendelsohn NJ: Genetics evaluation for the etiologicdiagnosis of autism spectrum disorders. Genet Med 2008, 10(1): 4–12.34. Rossignol DA, Frye RE: Mitochondrial dysfunction in autism spectrumdisorders: a systematic review and meta-analysis. Mol Psychiatry 2011, 17(3):290–314.35. Buie T, Campbell DB, Fuchs GJ 3rd, Furuta GT, Levy J, Vandewater J,Whitaker AH, Atkins D, Bauman ML, Beaudet AL: Evaluation, diagnosis, andtreatment of gastrointestinal disorders in individuals with ASDs: aconsensus report. Pediatrics 2010, 1:S1–18. 125 Suppl.36. James SJ, Melnyk S, Jernigan S, Cleves MA, Halsted CH, Wong DH, Cutler P,Bock K, Boris M, Bradstreet JJ, et al: Metabolic endophenotype and relatedgenotypes are associated with oxidative stress in children with autism.Am J Med Genet B Neuropsychiatr Genet 2006, 141(8):947–956.37. Ashwood P, Krakowiak P, Hertz-Picciotto I, Hansen R, Pessah I, Van de WaterJ: Elevated plasma cytokines in autism spectrum disorders provideevidence of immune dysfunction and are associated with impairedbehavioral outcome. Brain Behav Immun 2010, 25(1):40–45.38. Rossignol DA, Frye RE: A review of research trends in physi ologicalabnormalities in autism spectrum disorders: immune dysregulation,inflammation, oxidative stress, mitochondrial dysfunction andenvironmental toxicant exposures . Mol Psychiatry 2011, 17(4):389–401.39. Ming X, Brimacombe M, Chaaban J, Zimmerman-Bier B, Wagner GC:Autismspectrum disorders: concurrent clinical disorders. J Child Neurol 2008, 23(1):6–13.40. Herbert MR: Autism: a brain disorder or a disorder that affects the brain.Clinical Neuropsychiatry 2005, 2(6):354–379.41. Lovaas OI: Behavioral treatment and normal educational andintellectual functioning in young autistic children. J Consult ClinPsychol 1987, 55(1):3–9.42. Sallows GO, Graupner TD: Intensive behavioral treatment for childrenwith autism: four-year outcome and predictors. Am J Ment Retard 2005,110(6):417–438.43. Eikeseth S, Smith T, Jahr E, Eldevik S: Intensive behavioral treatment atschool for 4- to 7-year-old children with autism. A 1-year comparisoncontrolled study. Behav Modif 2002, 26(1):49–68.44. Rossignol DA: Hyperbaric oxygen therapy might improve certainpathophysiological findings in autism. Med Hypotheses 2007, 68(6):1208–1227.45. Buckley JA: How mild hyperbaric oxygen therapy works and why it isgood for our children. Medical Veritas 2005, 2:647.46. Stoller KP, Small T: Interview with Dr. Kenneth P. Stoller: Hyperbaricoxygen therapy (HBOT), Autism, Aspartame and Mercury. Medical, Veritas2006, 3(1):957–966.47. Harch PG, Small T: Interview with Dr Paul Harch: the application ofhyperbaric oxygen therapy in chronic neurological conditions. MedicalVeritas 2005, 2(2):637–646.48. Rossignol DA, Small T: Interview with Dr. Dan A. Rossignol: hyperbaricoxygen therapy improves symptoms in autistic children. Medical Veritas2006, 3:1–4.49. Zilbovicius M, Boddaert N, Belin P, Poline JB, Remy P, Mangin JF, Thivard L,Barthelemy C, Samson Y: Temporal lobe dysfunction in childhood autism:a PET study. Positron emission tomography. Am J Psychiatry 2000, 157(12):1988–1993.50. Zilbovicius M, Garreau B, Tzourio N, Mazoyer B, Bruck B, Martinot JL,Raynaud C, Samson Y, Syrota A, Lelord G:Regional cerebral blood flow inchildhood autism: a SPECT study. Am J Psychiatry 1992, 149(7):924–930.51. Boddaert N, Zilbovicius M: Functional neuroimaging and childhoodautism. Pediatr Radiol 2002 , 32(1):1–7.52. Starkstein SE, Vazquez S, Vrancic D, Nanclares V, Manes F, Piven J, Plebst C:SPECT findings in mentally retarded autistic individuals. J NeuropsychiatryClin Neurosci 2000, 12(3):370–375.53. Ohnishi T, Matsuda H, Hashimoto T, Kunihiro T, Nishikawa M, Uema T, SasakiM: Abnormal regional cerebral blood flow in childhood autism. Brain2000, 123(Pt 9):1838–1844.54. Critchley HD, Daly EM, Bullmore ET, Williams SC, Van Amelsvoort T,Robertson DM, Rowe A, Phillips M, McAlonan G, Howlin P, et al: Thefunctional neuroanatomy of social behaviour: changes in cerebral bloodflow when people with autistic disorder process facial expressions. Brain2000, 123(Pt 11):2203–2212.55. Wilcox J, Tsuang MT, Ledger E, Algeo J, Schnurr T: Brain perfusion inautism varies with age. Neuropsychobiology 2002, 46(1):13–16.56. Gendry Meresse I, Zilbovicius M, Boddaert N, Robel L, Philippe A, Sfaello I,Laurier L, Brunelle F, Samson Y, Mouren MC: Autism severity and temporallobe functional abnormalities. Ann Neurol 2005, 58(3):466–469.57. Heuser G, Heuser SA, Rodelander D, Aguilera O, Uszler M: In Treatment ofneurologically impaired adults and children with “mild” hyperbaric oxygenation(1.3 atm and 24 % oxygen). In Hyperbaric oxygenation for cerebral palsy andthe brain-injured child. Edited by Joiner JT. Flagstaff, Arizona: BestPublications; 2002.58. Rossignol DA: The use of hyperbaric oxygen therapy in autism . InHyperbaric oxygen for neurological disorders. Edited by Zhang JH. Flagstaff,AZ: Best Publishing Company; 2008:209–258.59. The effects of hyperbaric oxygen therapy in children with autism spectrumdisorders: [http://archive.rubicon-foundation.org/xmlui/handle/123456789/9163].60. Ashwood P, Anthony A, Pellicer AA, Torrente F, Walker-Smith JA, WakefieldAJ: Intestinal lymphocyte populations in children with regressive autism:evidence for extensive mucosal immunopathology. J Clin Immunol 2003,23(6):504–517.61. Balzola F, Barbon V, Repici A, Rizzetto M, Clauser D, Gandione M,Sapino A: Panenteric IBD-like disease in a patient with regressiveautism shown for the first time by the wireless capsule enteroscopy:another piece in the ji gsaw of this gut-brain syndrome? Am JGastroenterol 2005, 100(4):979–981.62. Furlano RI, Anthony A, Day R, Brown A, McGarvey L, Thomson MA, DaviesSE, Berelowitz M, Forbes A, Wakefield AJ, et al: Colonic CD8 and gammadelta T-cell infiltration with epithelial damage in children with autism. JPediatr 2001, 138(3):366–372.63. Torrente F, Ashwood P, Day R, Machado N, Furlano RI, Anthony A, DaviesSE, Wakefield AJ, Thomson MA, Walker-Smith JA: Small intestinalenteropathy with epithelial IgG and complement deposition in childrenwith regressive autism. Mol Psychiatry 2002, 7(4):375–382. 334.64. Chez MG, Dowling T, Patel PB, Khanna P, Kominsky M: Elevation of tumornecrosis factor-alpha in cerebrospinal fluid of autistic children. PediatrNeurol 2007, 36(6):361–365.65. Ashwood P, Anthony A, Torrente F, Wakefield AJ: Spontaneous mucosallymphocyte cytokine profiles in children with autism andgastrointestinal symptoms: mucosal immune activation and reducedcounter regulatory interleukin-10. J Clin Immunol 2004, 24(6):664–673.66. Li X, Chauhan A, Sheikh AM, Patil S, Chauhan V, Li XM, Ji L, Brown T, MalikM: Elevated immune response in the brain of autistic patients. JNeuroimmunol 2009, 207(1–2):111–116.67. Jyonouchi H, Sun S, Le H: Proinflammatory and regulatory cytokineproduction associated with innate and adaptive immune responses inchildren with autism spectrum disorders and developmental regression.J Neuroimmunol 2001, 120(1–2):170–179.68. Messahel S, Pheasant AE, Pall H, Ahmed-Choudhury J, Sungum-Paliwal RS,Vostanis P: Urinary levels of neopterin and biopterin in autism. NeurosciLett 1998, 241(1):17–20.69. Sweeten TL, Posey DJ, McDougle CJ: High blood monocyte counts andneopterin levels in children with autistic disorder. Am J Psychiatry 2003,160(9):1691–1693.70. Messahel S, Pheasant AE, Pall H, Kerr AM: Abnormalities in urinary pterinlevels in Rett syndrome. Eur J Paediatr Neurol 2000, 4(5):211–217.71. Akin ML, Gulluoglu BM, Uluutku H, Erenoglu C, Elbuken E, Yildirim S, CelenkT: Hyperbaric oxygen improves healing in experimental rat colitis.Undersea Hyperb Med 2002, 29(4):279–285.Rossignol et al. Medical Gas Research 2012, 2:16 Page 11 of 13http://www.medicalgasresearch.com/content/2/1/16

72. Luongo C, Imperatore F, Cuzzocrea S, Filippelli A, Scafuro MA, Mangoni G,Portolano F, Rossi F: Effects of hyperbaric oxygen exposure on azymosan-induced shock model. Crit Care Med 1998, 26(12):1972–1976.73. Sumen G, Cimsit M, Eroglu L: Hyperbaric oxygen treatment reducescarrageenan-induced acute inflammation in rats. Eur J Pharmacol 2001,431(2):265–268.74. Abbot NC, Beck JS, Carnochan FM, Gibbs JH, Harrison DK, James PB, LoweJG: Effect of hyperoxia at 1 and 2 ATA on hypoxia and hypercapnia inhuman skin during experimental inflammation. J Appl Physiol 1994, 77(2):767–773.75. Takeshima F, Makiyama K, Doi T: Hyperbaric oxygen as adjunct therapyfor Crohn's intractable enteric ulcer. Am J Gastroenterol 1999, 94(11):3374–3375.76. Nelson EW Jr, Bright DE, Villar LF: Closure of refractory perineal Crohn'slesion. Integration of hyperbaric oxygen into case management. Dig DisSci 1990, 35(12):1561–1565.77. Lavy A, Weisz G, Adir Y, Ramon Y, Melamed Y, Eidelman S: Hyperbaricoxygen for perianal Crohn's disease. J Clin Gastroenterol 1994, 19(3):202–205.78. Granowitz EV, Skulsky EJ, Benson RM, Wright J, Garb JL, Cohen ER, SmithlineEC, Brown RB: Exposure to increased pressure or hyperbaric oxygensuppresses interferon-gamma secretion in whole blood cultures ofhealthy humans. Undersea Hyperb Med 2002, 29(3):216–225.79. Yang Z, Nandi J, Wang J, Bosco G, Gregory M, Chung C, Xie Y, Yang X,Camporesi EM: Hyperbaric oxygenation ameliorates indomethacin-induced enteropathy in rats by modulating TNF-alpha and IL-1betaproduction. Dig Dis Sci 2006, 51(8):1426–1433.80. Inamoto Y, Okuno F, Saito K, Tanaka Y, Watanabe K, Morimoto I, YamashitaU, Eto S: Effect of hyperbaric oxygenation on macrophage function inmice. Biochem Biophys Res Commun 1991, 179(2):886–891.81. Weisz G, Lavy A, Adir Y, Melamed Y, Rubin D, Eidelman S, Pollack S:Modification of in vivo and in vitro TNF-alpha, IL-1, and IL-6 secretion bycirculating monocytes during hyperbaric oxygen treatment in patientswith perianal Crohn's disease. J Clin Immunol 1997, 17(2):154–159.82. Buras JA, Holt D, Orlow D, Belikoff B, Pavlides S, Reenstra WR:Hyperbaricoxygen protects from sepsis mortality via an interleukin-10-dependentmechanism. Crit Care Med 2006, 34(10):2624–2629.83. Altinel O, Demirbas S, Cakir E, Yaman H, Ozerhan IH, Duran E, Cayci T, AkgulEO, Ersoz N, Uysal B, et al: Comparison of hyperbaric oxygen and medicalozone therapies in a rat model of experimental distal colitis. Scand J ClinLab Invest 2011, 71(3):185–192.84. Rossignol DA: Hyperbaric oxygen treatment for inflammatory boweldisease: a systematic review and analysis. Med Gas Res 2012, 2(1):6.85. Rossignol DA, Rossignol LW, James SJ, Melnyk S, Mumper E: The effects ofhyperbaric oxygen therapy on oxidative stress, inflammation, andsymptoms in children with autism: an open-label pilot study. BMC Pediatr2007, 7(1):36.86. Bent S, Bertoglio K, Ashwood P, Nemeth E, Hendren RL: Brief Report:Hyperbaric Oxygen Therapy (HBOT) in Children with Autism SpectrumDisorder: A Clinical Trial. J Autism Dev Disord 2011, .87. Vargas DL, Nascimbene C, Krishnan C, Zimmerman AW, Pardo CA:Neuroglial activation and neuroinflammation in the brain of patientswith autism. Ann Neurol 2005, 57(1):67– 81.88. Ashwood P, Van de Water J: A review of autism and the immuneresponse. Clin Dev Immunol 2004, 11(2):165–174.89. Frye RE, Rossignol DA: Mitochondrial dysfunction can connect the diversemedical symptoms associated with autism spectrum disorders. PediatrRes 2011, 69(5):41–47.90. Dave KR, Prado R, Busto R, Raval AP, Bradley WG, Torbati D, Perez-PinzonMA: Hyperbaric oxygen therapy protects against mitochondrialdysfunction and delays onset of motor neuron disease in Wobbler mice.Neuroscience 2003, 120(1):113–120.91. Boveris A, Chance B: The mitochondrial generation of hydrogen peroxide.General properties and effect of hyperbaric oxygen. Biochem J 1973, 134(3):707–716.92. Daugherty WP, Levasseur JE, Sun D, Rockswold GL, Bullock MR: Effects ofhyperbaric oxygen therapy on cerebral oxygenation and mitochondrialfunction following moderate lateral fluid-percussion injury in rats. JNeurosurg 2004, 101(3):499–504.93. Gosalvez M, Castillo Olivares J, De Miguel E, Blanco M, Figuera D:Mitochondrial respiration and oxidative phosphorylation duringhypothermic hyperbaric hepatic preservation. J Surg Res1973, 15(5):313–318.94. Bar-Sagie D, Mayevsky A, Bartoov B: Effects of hyperbaric oxygenation onspermatozoan motility driven by mitochondrial respiration. JApplPhysiol1981, 50(3):531–537.95. Lou M, Chen Y, Ding M, Eschenfelder CC, Deuschl G: Involvement of themitochondrial ATP-sensitive potassium channel in the neuroprotectiveeffect of hyperbaric oxygenation after cerebral ischemia. Brain Res Bull2006, 69(2):109–116.96. Calvert JW, Zhang JH: Oxygen treatment restores energy status followingexperimental neonatal hypoxia-ischemia. Pediatr Crit Care Med 2007, 8(2):165–173.97. Kurt B, Kurt Y, Karslioglu Y, Topal T, Erdamar H, Korkmaz A, Turkozkan N, Yaman H,Odabasi Z, Gunhan O: Effects of hyperbaric oxygen on energy production andxanthine oxidase levels in striated muscle tissue of healthy rats. JClinNeurosci2008, 15(4):445–450.98. Gutsaeva DR, Suliman HB, Carraway MS, Demchenko IT, Piantadosi CA:Oxygen-induced mitochondrial biogenesis in the rat hippocampus.Neuroscience 2006, 137(2):493–504.99. Van Dyke K: Hyperbaric oxygen therapy (HBOT) for autism: Anintroduction. Autism File 2009, 33:5–6.100. Chauhan A, Chauhan V: Oxidative stress in autism. Pathophysiology 2006,13(3):171–181.101. Chauhan A, Chauhan V, Brown WT, Cohen I: Oxidative stress in autism:increased lipid peroxidation and reduced serum levels of ceruloplasmin andtransferrin–the antiox ida nt proteins. Life Sci 2004, 75(21):2539–2549.102. James SJ, Cutler P, Melnyk S, Jernigan S, Janak L, Gaylor DW, Neubrander JA:Metabolic biomarkers of increased oxidative stress and impairedmethylation capacity in children with autism. Am J Clin Nutr 2004, 80(6):1611–1617.103. Alleva R, Nasole E, Di Donato F, Borghi B, Neuzil J, Tomasetti M: alpha-Lipoic acid supplementation inhibits oxidative damage, acceleratingchronic wound healing in patients undergoing hyperbaric oxygentherapy. Biochem Biophys Res Commun 2005, 333(2):404–410.104. Ozden TA, Uzun H, Bohloli M, Toklu AS, Paksoy M, Simsek G, Durak H,Issever H, Ipek T:The effects of hyperbaric oxygen treatment on oxidantand antioxidants levels during liver regeneration in rats. Tohoku J ExpMed 2004, 203(4):253–265.105. Gregorevic P, Lynch GS, Williams DA: Hyperbaric oxygen modulatesantioxidant enzyme activity in rat skeletal muscles. Eur J Appl Physiol2001, 86(1):24–27.106. Gulec B, Yasar M, Yildiz S, Oter S, Akay C, Deveci S, Sen D: Effect of hyperbaricoxygen on experimental acute distal colitis. Physiol Res 2004, 53(5):493–499.107. Nie H, Xiong L, Lao N, Chen S, Xu N, Zhu Z: Hyperbaric oxygen preconditioninginduces tolerance against spinal cord ischemia by upregulation ofantioxidant enzymes in rabbits. JCerebBloodFlowMetab2006, 26(5):666–67 4.108. Sharifi M, Fares W, Abdel-Karim I, Koch JM, Sopko J, Adler D: Usefulness ofhyperbaric oxygen therapy to inhibit restenosis after percutaneouscoronary intervention for acute myocardial infarction or unstable anginapectoris. Am J Cardiol 2004, 93(12):1533–1535.109. Speit G, Dennog C, Eichhorn U, Rothfuss A, Kaina B: Induction of hemeoxygenase-1 and adaptive protection against the induction of DNAdamage after hyperbaric oxygen treatment. Carcinogenesis 2000, 21(10):1795–1799.110. Rothfuss A, Radermacher P, Speit G: Involvement of heme oxygenase-1(HO-1) in the adaptive protection of human lymphocytes afterhyperbaric oxygen (HBO) treatment. Carcinogenesis 2001, 22(12):1979–1985.111. Rothfuss A, Speit G: Investigations on the mechanism of hyperbaric oxygen(HBO)-induced adaptive protection against oxidative stress. Mutat Res 2002,508(1–2):157–165.112. Thom SR: Oxidative stress is fundamental to hyperbaric oxygen therapy.J Appl Physiol 2009, 106(3):988–995.113. Audhya T: Autism Research Institute Garden Grove Think Tank Meeting,2007. In Adjustment of SOD, GPO & catalase activity in RBC of normal andautistic children during hyperoxia. Garden Grove, CA:; 2007.114. Dickinson DA, Forman HJ: Glutathione in defense and signaling: lessons fromasmallthiol.Ann N Y Acad Sci 2002, 973:488–504.115. Anonymous: Little Michael's development had stopped--It was called"childhood autism" until hyperbaric oxygen therapy!. Hyperbaric OxygenReport 1994, 1(1):1–3.Rossignol et al. Medical Gas Research 2012, 2:16 Page 12 of 13http://www.medicalgasresearch.com/content/2/1/16

116. Henricks CL: Ani’s story: A case study in late improvement in neurologicfunction after hyperbaric oxygenation therapy. J Amer Physicians Surg2010, 15(3):94–95.117. Burke C: Hyperbaric Oxygen Therapy. Supertwins Magazine 2007, 17(2):1–2.118. Treating children with autism using hyperbaric oxygen therapy: [http://www.hyperbaricmedicinecenter.com/images/pdf/autism_study.pdf].119. Rossignol DA, Rossignol LW: Hyperbaric oxygen therapy may improvesymptoms in autistic children. Med Hypotheses 2006, 67(2):216–228.120. Granpeesheh D, Tarbox J, Dixon DR, Wilke AE, Allen MS, Bradstreet JJ:Randomized trial of hyperbaric oxygen therapy for children with autism.Research Autism Spectrum Disorders 2010, 4:268–275.121. Lerman DC, Sansbury T, Hovanetz A, Wolever E, Garcia A, O'Brien E, AdedipeH: Using behavior analysis to examine the outcomes of unproventherapies: An evaluation of hyperbaric oxygen therapy for children withautism. Behavior Analysis in Practice 2009, 1(2):50–58.122. Chungpaibulpatana J, Sumpatanarax T, Thadakul N, Chantharatreerat C,Konkaew M, Aroonlimsawas M: Hyperbaric oxygen therapy in Thai autisticchildren. J Med Assoc Thai 2008, 91(8):1232–1238.123. Jepson B, Granpeesheh D, Tarbox J, Olive ML, Stott C, Braud S, Yoo JH,Wakefield A, Allen MS: Controlled Evaluation of the Effects of HyperbaricOxygen Therapy on the Behavior of 16 Children with Autism SpectrumDisorders. J Autism Dev Disord 2011, 41(5):575–588.124. Ghanizadeh A: Hyperbaric oxygen therapy for treatment of children withautism, a systematic review of randomized trials. Med Gas Res 2012, 2(1):13.125. Rossignol DA, Rossignol LW, Smith S, Schneider C, Logerquist S, Usman A,Neubrander J, Madren EM, Hintz G, Grushkin B, et al: Hyperbaric treatmentfor children with autism: a multicenter, randomized, double-blind,controlled trial. BMC Pediatr 2009, 9:21.126. Cohen J: Statistical power analysis for the behavioral sciences (second edition).Hillsdale, NJ: Lawrence Erlbaum Associates; 1988.127. Clarke D: Effective patient blinding during hyperbaric trials. UnderseaHyperb Med 2009, 36(1):13–17.128. Clarke RE, Tenorio LM, Hussey JR, Toklu AS, Cone DL, Hinojosa JG, Desai SP,Dominguez Parra L, Rodrigues SD, Long RJ, et al: Hyperbaric oxygentreatment of chronic refractory radiation proctitis: a randomized andcontrolled double-blind crossover trial with long-term follow-up. Int JRadiat Oncol Biol Phys 2008, 72(1):134–143.doi:10.1186/2045-9912-2-16Cite this article as: Rossignol et al.: Hyperbaric oxygen treatment inautism spectrum disorders. Medical Gas Research 2012 2:16 .Submit your next manuscript to BioMed Centraland take full advantage of: • Convenient online submission• Thorough peer review• No space constraints or color figure charges• Immediate publication on acceptance• Inclusion in PubMed, CAS, Scopus and Google Scholar• Research which is freely available for redistributionSubmit your manuscript at www.biomedcentral.com/submitRossignol et al. Medical Gas Research 2012, 2:16 Page 13 of 13http://www.medicalgasresearch.com/content/2/1/16

BioMed CentralPage 1 of 15                       BMC PediatricsOpen AccessResearch articleHyperbaric treatment for children with autism: a multicenter, randomized, double-blind, controlled trialDaniel A Rossignol*1, Lanier W Rossignol1, Scott Smith1, Cindy Schneider2, Sally Logerquist2, Anju Usman3, Jim Neubrander4, Eric M Madren5, Gregg Hintz6, Barry Grushkin7 and Elizabeth A Mumper8Address: 1International Child Development Resource Center, Melbourne, FL, USA, 2Center for Autism Research and Education, Phoenix, AZ, USA, 3True Health Medical Center, Naperville, IL, USA, 4Edison, NJ, USA, 5Princess Anne Medical Associates, Virginia Beach, VA, USA, 6Therapeutic Pathways, East Troy, WI, USA, 7Biognosys, Nanuet, NY, USA and 8Rimland Center, Lynchburg, VA, USAEmail: Daniel A Rossignol* - rossignolmd@gmail.com; Lanier W Rossignol - dlross7@hotmail.com; Scott Smith - scott@icdrc.org; Cindy Schneider - cschneider@center4autism.org; Sally Logerquist - logerquist@cox.net; Anju Usman - anju0@yahoo.com; Jim Neubrander - drneubrander@drneubrander.com; Eric M Madren - emmadren@yahoo.com; Gregg Hintz - therapeuticpathways@yahoo.com; Barry Grushkin - bgrushkin2@cs.com; Elizabeth A Mumper - drmumper@rimlandcenter.com* Corresponding author AbstractBackground: Several uncontrolled studies of hyperbaric treatment in children with autism havereported clinical improvements; however, this treatment has not been evaluated to date with acontrolled study. We performed a multicenter, randomized, double-blind, controlled trial to assessthe efficacy of hyperbaric treatment in children with autism.Methods: 62 children with autism recruited from 6 centers, ages 2–7 years (mean 4.92 ± 1.21),were randomly assigned to 40 hourly treatments of either hyperbaric treatment at 1.3 atmosphere(atm) and 24% oxygen ("treatment group", n = 33) or slightly pressurized room air at 1.03 atm and21% oxygen ("control group", n = 29). Outcome measures included Clinical Global Impression(CGI) scale, Aberrant Behavior Checklist (ABC), and Autism Treatment Evaluation Checklist(ATEC).Results: After 40 sessions, mean physician CGI scores significantly improved in the treatmentgroup compared to controls in overall functioning (p = 0.0008), receptive language (p < 0.0001),social interaction (p = 0.0473), and eye contact (p = 0.0102); 9/30 children (30%) in the treatmentgroup were rated as "very much improved" or "much improved" compared to 2/26 (8%) of controls(p = 0.0471); 24/30 (80%) in the treatment group improved compared to 10/26 (38%) of controls(p = 0.0024). Mean parental CGI scores significantly improved in the treatment group comparedto controls in overall functioning (p = 0.0336), receptive language (p = 0.0168), and eye contact (p= 0.0322). On the ABC, significant improvements were observed in the treatment group in totalscore, irritability, stereotypy, hyperactivity, and speech (p < 0.03 for each), but not in the controlgroup. In the treatment group compared to the control group, mean changes on the ABC totalscore and subscales were similar except a greater number of children improved in irritability (p =0.0311). On the ATEC, sensory/cognitive awareness significantly improved (p = 0.0367) in thetreatment group compared to the control group. Post-hoc analysis indicated that children over agePublished: 13 March 2009BMC Pediatrics 2009, 9:21 doi:10.1186/1471-2431-9-21Received: 20 January 2009Accepted: 13 March 2009This article is available from: http://www.biomedcentral.com/1471-2431/9/21© 2009 Rossignol et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

  2009, :21 http://www.biomedcentral.com/1471-2431/9/21Page 2 of 15                       5 and children with lower initial autism severity had the most robust improvements. Hyperbarictreatment was safe and well-tolerated.Conclusion: Children with autism who received hyperbaric treatment at 1.3 atm and 24% oxygenfor 40 hourly sessions had significant improvements in overall functioning, receptive language, socialinteraction, eye contact, and sensory/cognitive awareness compared to children who receivedslightly pressurized room air.Trial Registration: clinicaltrials.gov NCT00335790BackgroundAutistic Disorder (autism), along with Asperger syndromeand pervasive developmental disorder–not otherwisespecified (PDD-NOS), comprise a spectrum of neurode-velopmental disorders (collectively termed autism spec-trum disorders or ASD) that are characterized byrestrictive and repetitive behaviors along with impair-ments in communication and social interaction [1]. Thenumber of children diagnosed with ASD has increasedover the last decade [2-4] and ASD currently affects asmany as 1 out of 150 individuals in the United States(U.S.) [5]. ASD is generally considered a "static" neurolog-ical disorder [6] without any known cure. The use ofhyperbaric treatment in children with ASD has increasedin recent years [7] and traditionally involves inhaling upto 100% oxygen at a pressure greater than one atmosphere(atm) in a pressurized chamber [8]. Most typical indica-tions for hyperbaric treatment involve the use of hyper-baric pressures above 2.0 atm. Higher atmosphericpressures are generally required to treat conditions such ascarbon monoxide poisoning and to improve wound heal-ing [8,9]. However, improvements have been observed viatreatments with 95–100% oxygen and hyperbaric pres-sures of 1.5–2.0 atm for some chronic neurological condi-tions, including autism [7], fetal alcohol syndrome [10],cerebral palsy [11,12], and chronic or traumatic braininjury [13-16]. Furthermore, improvements in some ofthese conditions, including autism [7,17] and cerebralpalsy [12], have been observed with the use of hyperbaricpressures of 1.3 atm and oxygen levels of 21–24%. In onestudy, significant improvements were observed in chil-dren with autism with the use of hyperbaric treatment atboth 1.5 atm/100% oxygen and 1.3 atm/24% oxygen; nei-ther hyperbaric protocol worsened markers of oxidativestress and both reduced C-reactive protein (a marker ofinflammation) [7]. Rationales for the use of hyperbarictreatment in autism include decreasing inflammation [18-20], improving cerebral hypoperfusion [21,22], and mod-ulating immune dysregulation [23-25], all reported asproblems in some individuals with autism [26-34]. Sev-eral case reports [21,22] and three uncontrolled studiesenrolling between 6 and 18 children with autism[7,17,35] have reported clinical improvements withhyperbaric treatment at 1.3 atm. However, to our knowl-edge, the efficacy of hyperbaric treatment in children withautism has not been evaluated to date with a controlledstudy. Given this background, we decided to study theeffects of hyperbaric treatment in children with autismusing 1.3 atm and 24% oxygen compared to near-placebohyperbaric conditions (slightly pressurized room air at1.03 atm and 21% oxygen).Hyperbaric treatment for children is generally regarded assafe, even at pressures of 2.0 atm and 100% oxygen fortwo hours per day [36]. In descending order, the mostcommon side effects observed during hyperbaric treat-ment are barotrauma (2% incidence), sinus squeeze,serous otitis, claustrophobia, reversible myopia, and newonset seizure (which occurs in 1–3 per 10,000 treatments)[8]. In children with autism, the use of hyperbaric treat-ment using pressures up to 1.5 atm and 100% oxygen hasbeen shown to be safe and well-tolerated [7,17].MethodsStudy DesignThis was a prospective, randomized, double-blind, con-trolled trial involving treatment in parallel groups for 4weeks. Active treatment was hyperbaric treatment at 1.3atm and 24% oxygen for 40 sessions lasting 1 hour eachat pressure ("treatment group"), whereas the control treat-ment consisted of slightly pressurized room air at 1.03atm and 21% oxygen for 40 sessions lasting 1 hour eachat pressure ("control group"). Comparison of the clinicaleffects of parallel treatments for 4 weeks was the primaryobjective of this study. The number of treatments (40 ses-sions) and the overall treatment period (4 weeks) werechosen because these were previously shown to be safe intwo other studies of hyperbaric treatment in children withautism [7,17].Participants: Eligibility Criteria and RecruitmentThis study was approved by the Liberty InstitutionalReview Board and enrolled children, 2 to 7 years of age,who had a diagnosis of Autistic Disorder and had not pre-viously received any type of hyperbaric treatment. All chil-dren met the DSM-IV criteria for Autistic Disorder [1] andthis diagnosis was also corroborated by psychologistsusing the Autism Diagnostic Interview–Revised (ADI-R)and the Autism Diagnostic Observation Schedule(ADOS). Children with PDD-NOS, Asperger syndrome,

  2009, :21 http://www.biomedcentral.com/1471-2431/9/21Page 3 of 15                       seizure disorder, current ear infection, uncontrolledasthma, inability to equalize ear pressure, fragile X syn-drome, and ongoing treatment with chelation medicationwere excluded from participation in this study. Writteninformed consent was obtained from the parents and,when possible, the child. Sixty-six children were evaluatedfor inclusion in the study from six clinics throughout theU.S. Four children were excluded from participationbecause the diagnosis of Autistic Disorder could not becorroborated by ADI-R and ADOS. Therefore, the recruit-ment process yielded 62 eligible participants, who wererandomized as depicted in Figure 1.InterventionsThe active treatment was hyperbaric treatment at 1.3 atmand 24% oxygen in a monoplace hyperbaric chamber for60 minutes at this pressure per session (this length of timedid not include approximately 10–15 minutes for pressur-ization and depressurization). Oxygen flowing at 10 litersper minute from an oxygen concentrator was mixed withroom air and pumped into the chamber following a pro-tocol previously described [7]. This resulted in a finalchamber oxygen concentration of approximately 24% asmeasured by an oxygen monitor. This treatment was giventwice a day separated by a minimum of 4 hours, 5 days perweek, for 4 consecutive weeks, for a total of 40 treatmentsper child.Control treatment consisted of slightly pressurized roomair (1.03 atm and 21% oxygen) in a monoplace hyper-baric chamber for 60 minutes at this pressure per session(this length of time did not include approximately 10–15minutes for pressurization and depressurization). Thistreatment was given twice a day separated by a minimumof 4 hours, 5 days per week, for 4 consecutive weeks, for atotal of 40 treatments per child. For blinding purposes,Consolidated Standards of Reporting Trials (CONSORT) flow diagramFigure 1Consolidated Standards of Reporting Trials (CONSORT) flow diagram.66 children assessed4 excluded: not Autistic Disorder62 randomized33 assigned hyperbaric therapy29 assigned control group4 dropped out 3 dropped out29 completed study,30 analyzed 26 completed study, 26 analyzed

  2009, :21 http://www.biomedcentral.com/1471-2431/9/21Page 4 of 15                       participants underwent a brief compression to 1.1 atm atthe beginning of each treatment. The chamber was thenslowly decompressed from 1.1 to 1.03 atm where the pres-sure stayed for the remainder of the treatment. No oxygenwas added to the chamber and thus the chamber was pres-surized with room air (approximately 21% oxygen). Thechildren in the control group remained in the chamber forthe same length of time as children in the treatmentgroup. At the end of each treatment, the pressure wasslowly increased to 1.1 atm over about 5 minutes andthen the chamber was depressurized. Procedures weredeveloped and applied to mimic, for the control group,the experience of hyperbaric treatment at 1.3 atm, andthereby to keep participants and parents unaware of thenature of the intervention. These procedures includedcovering control switches, inflating and deflating thechambers to simulate pressure changes, and masking thesounds from the chambers. To further mask the groupassignments, the equipment (including chambers) usedfor the control group was indistinguishable from theequipment used for the treatment group. Moreover, thesame type of equipment was used at each study site. Apressure of 1.03 atm (with increases to 1.1 atm for severalminutes at the beginning and at the end of the treatment)was chosen for the control group because this pressurerepresented the lowest that could be applied and stilleffectively simulate hyperbaric treatment at 1.3 atm. Toverify its effectiveness, prior to beginning the study, thispressure protocol was tested in six adult individuals whowere randomly and repeatedly exposed to both the treat-ment group pressure (1.3 atm) and the control grouppressure (1.03 atm with short increases to 1.1 atm) andnone of these individuals were able to reliably distinguishbetween the two pressures. At each study site, the primaryinvestigator (DAR) visited and trained each hyperbarictechnician to ensure that the same protocol was followedto minimize variances between study sites. An analysisperformed after the study was finished demonstrated nosignificant differences (p = ns) between the six study sitesfor age, initial autism severity, and initial and final scoreson all of the scales used in this study (this analysis can befound in the results section).Initial screening for this study included medical historytaking and a physical examination by one of the studyphysicians. This included examination of the ears andtympanic membranes. Throughout each treatment, chil-dren were closely monitored by a hyperbaric technicianfor any signs of ear pain or other problems, and parentswere instructed on how to recognize ear pain in theirchild. In both groups, in order to facilitate treatments, aparent or primary caretaker accompanied the child intothe chamber as it was deemed that the children were tooyoung to enter and remain in the chamber alone for theduration of each treatment. Children finishing more thanone full session were included in the final analysis in anintention-to-treat manner. Daily treatment logbooks foreach child were maintained by the hyperbaric technicianand any side effects during treatment were recorded. Atthe end of the study, all children assigned to the controlgroup were offered 40 hyperbaric treatments at the treat-ment pressure (1.3 atm and 24% oxygen) if the parentsdesired (all parents chose this option; treatments wereprovided without charge). During the study period, chil-dren in both groups were not allowed to begin any newtherapies or stop any current therapies, including medica-tions and nutritional supplementation. At the onset of thestudy, the use of nutritional supplements, medications,and applied behavioral analysis (ABA) therapy was simi-lar in both the treatment and control groups (p = ns), seeTable 1.Randomization and AllocationFrom the 62 children who were enrolled in the study, 33were randomly allocated to the treatment group and 29were randomly allocated to the control group. To achievethis allocation, a random allocation sequence (1:1) wasgenerated and stratified on both the participant's group(treatment or control) and center, and this sequence wasequilibrated every eight patients. The allocation sequenceremained concealed to all investigators, study partici-pants, parents, nursing staff, and all other clinic staff. Theonly person at each center who was aware of the groupassignment for each particular child was the hyperbarictechnician, who had no input in the evaluation (outcomemeasures) of the child. The hyperbaric technician was spe-cifically instructed not to discuss the treatment nature orgroup assignments with anyone else in the clinic, includ-ing participants, parents, psychologists, and physicians. Itwas not possible to blind the hyperbaric technician due tothe nature of the study (the technician had to know thegroup assignment in order to adjust the chamber to thecorrect pressure for treatment). However, all individualsinvolved in evaluating the child (parents, physicians, andpsychologists) remained blinded to the group assignmentfor each child throughout the entire study period. Inhyperbaric treatment studies, the study is considered dou-ble-blinded if the study participants and the evaluators ofoutcome measures are both blinded to group assignment(as they were in this study), even though the hyperbarictechnician is aware of the assignment [37,38]. After thestudy was completed, parents in both groups were sur-veyed to determine the effectiveness of the blinding proc-ess, and there was no significant difference betweengroups in their ability to determine which group theirchild had been assigned (p = ns).Outcome measuresThe primary outcome measures were changes comparedto baseline observed after 4 weeks (40 sessions) of treat-

  2009, :21 http://www.biomedcentral.com/1471-2431/9/21Page 5 of 15                       ment, in parallel groups, on (1) Aberrant Behavior Check-list–Community (ABC) total score and subscale scores,based on the parent's or primary caretaker's rating, (2)Autism Treatment Evaluation Checklist (ATEC) total scoreand subscale scores, based on the parent's or primary care-taker's rating, and (3) Clinical Global Impression–Improvement (CGI) scale for changes in overall function-ing and subscales, as rated by the parent or primary care-taker and also as rated separately by the treating physician(without knowledge of the parental ratings).Previous studies of hyperbaric treatment in children withautism have utilized the ABC and/or ATEC [7,17]. TheABC is a 58-item questionnaire that assesses communica-tion, reciprocal social interaction, play, and stereotypicalbehaviors [39]. It is used to evaluate the effectiveness ofmedications and other therapeutic interventions and isscored from 0 ("not at all a problem") to 3 ("problem issevere in degree"). For this study, a total score was calcu-lated as well as scores in 5 subscales: irritability, socialwithdrawal (also termed lethargy), stereotypy, hyperactiv-ity, and inappropriate speech. The ABC was administeredimmediately prior to beginning the study (to determinebaseline scores) and immediately after finishing 40 ses-sions. Lower scores on the ABC indicate lower autismseverity.The ATEC is a questionnaire developed by the AutismResearch Institute to evaluate treatment efficacy in indi-viduals with autism. It consists of four subscales: Speech/Language/Communication, Sociability, Sensory/Cogni-tive Awareness, and Health/Physical/Behavior. The scoresare weighted according to the response and the corre-sponding subscale. The higher the subscale and totalscores, the more impaired the subject. A split-half reliabil-ity analysis on 1,358 checklists indicated high internalconsistency among the questions within each subscale[40]. The ATEC is designed to allow evaluators to assessTable 1: Initial characteristics of children in the treatment and control groupsTreatment Control Comparison between groups (p-value)Age 4.97 ± 1.29 4.86 ± 1.13 0.7288*Male 30/33 22/29 0.1672**Use of nutritional supplements 23/33 20/29 0.9999**Use of medications 16/33 10/29 0.3915**Applied Behavioral Analysis Therapy 15/33 11/29 0.733**ABC Total Score 55.2 ± 28.7 53.3 ± 24.0 0.7843*ABC Irritability 13.2 ± 9.5 12.2 ± 7.9 0.6714*ABC Social Withdrawal 10.5 ± 6.9 11.2 ± 6.9 0.7048*ABC Stereotypy 7.5 ± 4.9 6.2 ± 4.7 0.3205*ABC Hyperactivity 20.7 ± 9.9 20.1 ± 8.2 0.8279*ABC Speech 3.4 ± 3.1 3.6 ± 3.6 0.8567*ATEC Total Score 75.3 ± 19.5 75.6 ± 21.0 0.9592*ATEC Speech/Language/Communication 16.3 ± 5.0 15.9 ± 6.1 0.7958*ATEC Sociability 17.4 ± 6.6 17.8 ± 6.2 0.849*ATEC Sensory/Cognitive Awareness 18.1 ± 5.2 19.6 ± 5.6 0.3676*ATEC Health/Physical/Behavior 23.5 ± 11.5 22.4 ± 8.3 0.72*** Chi-square test with Yates' correction or Fisher's exact test.* Student's t test

  2009, :21 http://www.biomedcentral.com/1471-2431/9/21Page 6 of 15                       outcomes of certain treatments commonly used in indi-viduals with autism. In this study, scores were calculatedfor the total score and the four separate subscales. TheATEC was administered immediately prior to beginningthe study (to determine baseline scores) and immediatelyafter finishing 40 sessions. Due to an administrationerror, the baseline ATEC was not performed at one of thestudy centers, and thus data was available for analysis for23 children in the treatment group and 21 children in thecontrol group.Scores for the CGI scale were obtained immediately after40 sessions. The CGI scale gives an impression of globalchanges in certain areas for each child compared to base-line [41]. A total score for change in overall functioningwas rated by a parent or primary caregiver and separatelyby the treating physician (the same physician who ini-tially evaluated the child) using the following ratings: 1("very much improved"), 2 ("much improved"), 3 ("min-imally improved"), 4 ("no change"), 5 ("minimallyworse"), 6 ("much worse"), and 7 ("very much worse").Children who received a score of "very much improved"or "much improved" on the physician CGI overall func-tioning score were considered to be "good responders" totreatment. Data was also collected from parents and phy-sicians as to whether or not there were improvements inthe following CGI subscales: receptive language, expres-sive language, sleep pattern, attention span, activity level,bowel movement pattern, self-stimulatory behavior,social awareness/alertness, social interaction, play skills,self-injurious behavior, eye contact, mood, anxiety level,aggression, general health, gross motor skills, and finemotor skills.AnalysisAll data were prospectively collected and analyzed usingStatsDirect statistical software (version 2.7.2) and are pre-sented as mean ± SEM (standard error of the mean). Dataanalysis was based on an intention-to-treat approach onall participants who finished more than one treatment orcontrol session.Power CalculationsBecause this was the first controlled study of its kind,power calculations were based on the closest comparablestudy that had outcome data available at the time of thisstudy design [17]. Analysis of this data demonstrated amedium to large effect size, depending on the scale exam-ined (Cohen's d = 0.44 to 0.77) [42]. Using the most con-servative effect size (d = 0.44), a power calculation usingG*Power 3 [43] indicated that a total sample of 43 chil-dren would achieve a power of 80% with alpha set at 0.05(two-tailed).Planned ComparisonsPlanned group comparisons were performed on the pri-mary outcome measures. The normal distribution of datawas checked using the Kolmogorov-Smirnov test. Inparameters with normal distribution, comparisons wereanalyzed using the Student's t test. When normality wasnot present and equal variance could not be assumed,nonparametric tests (Mann-Whitney and Wilcoxonsigned rank tests) were used. The Pearson's chi-square (2)test with Yates' correction or the Fisher's exact test (whensubgroups contained less than 10 children) was applied toassess differences in the percentage of children respond-ing to treatment in each group. In all analyses, a p-valueless than 0.05 (two-tailed) was considered significant.ResultsStudy SampleThe flow of participants throughout the study is depictedin Figure 1. This study consisted of 52 boys and 10 girls,which is consistent with the male/female ratio observed inchildren with autism [44]. The mean age of all childrenwas 4.92 ± 1.21 years and was similar (p = ns) in the treat-ment group (4.97 ± 1.29 years) and the control group(4.86 ± 1.13 years), see Table 1. There were more girls inthe control group compared to the treatment group, butthis difference was not significant (p = ns). Initial ABC andATEC scores were similar in both groups (p = ns). At theonset of this study, the use of nutritional supplements,medications, and applied behavioral analysis (ABA) ther-apy was similar in both groups (p = ns), see Table 1. One-way analysis of variance (ANOVA) demonstrated no sig-nificant differences (p = ns) between the six centers thatparticipated in this study for: age, initial autism severity,initial ABC total scores, final ABC total scores, initialATEC total scores, final ATEC total scores, physician CGIscores, or parental CGI scores.Attrition rates during the study were low (see Figure 1). Inthe treatment group, two children dropped out of thestudy prior to beginning any treatments due to an illness(one with otitis media, the other with bronchitis).Another child dropped out before finishing one full treat-ment due to anxiety in both the child and the parent.Finally, one child was removed from the study after ninesessions because asthma symptoms worsened (neither theparents nor the treating physician felt that the hyperbarictreatments contributed to the increased asthma symp-toms, but the child was removed from the study as a pre-caution); this child's scores performed at time of drop-outshowed mild improvements in behavior (as separatelyranked by both the physician and the parents) and thesescores were included in the intention-to-treat analysis.The inclusion or exclusion of this child's scores had no sig-nificant effect on the statistical analysis. The remaining 29children completed all 40 hyperbaric treatment sessions

  2009, :21 http://www.biomedcentral.com/1471-2431/9/21Page 7 of 15                       at 1.3 atm and 24% oxygen. Therefore, data from 30 chil-dren were analyzed in the treatment group.In the control group, two children dropped out of thestudy prior to beginning any treatments (one because of adeath in the family, the other because of the time commit-ment). One child dropped out prior to finishing one fulltreatment due to parental claustrophobia. The remaining26 children finished all 40 sessions at 1.03 atm and 21%oxygen.Outcome MeasuresPhysician Clinical Global Impression (CGI) ScaleAfter 40 sessions, the mean physician CGI score forchange in overall functioning compared to baseline signif-icantly improved (p = 0.0008) by 1.13 points in the treat-ment group (2.87 ± 0.78, score of 4 = "no change")compared to 0.38 points in the control group (3.62 ±0.75), see Figure 2. Furthermore, 9/30 (30%) children inthe treatment group had a "very much improved" or"much improved" rating compared to 2/26 (7.7%) in thecontrol group (p = 0.0471). An improvement on the CGIscale (score of 1, 2, or 3) was noted in 24/30 (80%) chil-dren in the treatment group compared to 10/26 (38%) inthe control group (p = 0.0024). Conversely, 16/26 (62%)children in the control group had a "no change" or "min-imally worse" score (CGI score of 4 or 5) compared to 6/30 (20%, all 6 had a score of 4) in the treatment group (p= 0.0024). In the control group, two children received ascore of 5 ("minimally worse"), whereas none receivedthis score in the treatment group (p = 0.211). No childreceived a score worse than 5 in either group. Examinationof the physician CGI subscales demonstrated that morechildren improved in the treatment group compared tothe control group in receptive language (p < 0.0001),social interaction (p = 0.0473), and eye contact (p =0.0102); a trend towards improvement was also observedin activity level (p = 0.0545).Parental Clinical Global Impression (CGI) ScaleThe mean parental CGI score for change in overall func-tioning compared to baseline significantly improved (p =0.0336) by 1.30 points in the treatment group (2.70 ±0.81, score of 4 = "no change") compared to 0.83 pointsin the control group (3.17 ± 0.73), see Figure 2. A "verymuch improved" or "much improved" rating wasAbsolute change compared to baseline on the mean CGI overall functioning score in the treatment and control groups as rated separately by physicians and parentsFigure 2Absolute change compared to baseline on the mean CGI overall functioning score in the treatment and con-trol groups as rated separately by physicians and parents. * p < 0.001; ** p < 0.05.

  2009, :21 http://www.biomedcentral.com/1471-2431/9/21Page 8 of 15                       observed in 9/30 (30%) children in the treatment groupcompared to 4/26 (15%) in the control group (p =0.2238). Furthermore, 27/30 (90%) children had animprovement on the CGI scale (score of 1, 2, or 3) in thetreatment group compared to 19/26 (73%) in the controlgroup (p = 0.1616). A score of "no change" or "minimallyworse" (CGI score of 4 or 5) was reported in 3/30 (10%,all scored 4) in the treatment group versus 7/26 (27%) inthe control group (p = 0.1616). One child received a scoreof 5 ("minimally worse") in the control group comparedto none in the treatment group (p = 0.4643). No childreceived a score worse than 5 in either group. Examinationof the parental CGI subscales demonstrated that morechildren improved in the treatment group compared tothe control group in receptive language (p = 0.0168) andeye contact (p = 0.0322).Examination of the mean CGI score for change in overallfunctioning in the treatment group as rated by the physi-cians compared to the parental ratings demonstrated thatthere was no significant difference (p = 0.4716). A signifi-cant correlation existed between the physician and paren-tal CGI scales for the treatment group (r = 0.60, p =0.0005). However, parents of children in the controlgroup were significantly more likely to rate an improve-ment on the CGI score for change in overall functioningthan were physicians (p = 0.0245) and therefore the cor-relation between the physician and parental CGI scaleswas not significant (r = 0.27, p = 0.1819).Aberrant Behavior Checklist (ABC) ScoresIn the treatment group, the ABC total score significantlyimproved after 40 sessions (p = 0.0118), see Additionalfile 1. Improvements in ABC subscales were also observedin the treatment group for irritability (p = 0.0147), stere-otypy (p = 0.0124), hyperactivity (p = 0.0211), andspeech (p = 0.0155). No significant improvements wereobserved in the control group on the ABC total score orany of the ABC subscales (p = ns). Analysis of changes inthe ABC total score and subscale scores between the treat-ment and control groups demonstrated no significantchanges (p = ns), although there was a trend towardsimprovement in the treatment group for irritability (p =0.0976, see Figure 3) and 20/30 (67%) children in thetreatment group had an improvement in irritability com-pared to 9/26 (35%) in the control group (p = 0.0311).Autism Treatment Evaluation Checklist (ATEC) ScaleIn the treatment group, significant improvements wereobserved on the ATEC scale in total score (p = 0.002),sociability (p = 0.0009), sensory/cognitive awareness (p =0.0017), and health/physical/behavior (p = 0.0446), seeAdditional file 2. In the control group, ATEC improve-ments were found in total score (p = 0.0385) and sociabil-ity (p = 0.0134). Analysis of changes in ATEC total scoreand subscale scores between the treatment and controlgroups showed a significant improvement in sensory/cog-nitive awareness in the treatment group (p = 0.0367), seeFigure 4. Non-significant improvements in the treatmentgroup compared to the control group were observed in theother ATEC subscales (p = ns).Analysis by age and autism severityBecause we had previously observed that both youngerchildren and children who had higher initial autism sever-ity improved more robustly with hyperbaric treatment at1.3 atm [7,17], two separate sub-analyses of the effects ofage and initial autism severity on the outcome scales usedin this study were performed to determine if a subgroupcould be identified that had a better response to hyper-baric treatment.AgePost-hoc analysis of children in the treatment group dem-onstrated a better improvement on the ABC total score inchildren who were over age 5 compared to those age 5 andunder (p = 0.0482). Comparison of children who wereover age 5 in the treatment and control groups demon-strated that children in the treatment group had signifi-cantly better improvements on the ABC in irritability (p =0.0149), social withdrawal (p = 0.0086), and stereotypy(p = 0.0434). There was no significant difference in ABCscores between the treatment and control groups for chil-dren age 5 and younger (p = ns). When examining theATEC scale, comparison of children who were over age 5between the treatment and control groups demonstratedthat children in the treatment group had significantly bet-ter improvements in sociability (p = 0.0095) and sensory/cognitive awareness (p = 0.0384). No significant differ-ence between the two groups was observed for childrenage 5 and younger on the ATEC scale (p = ns). No signifi-cant age effect (p = ns) was observed between the treat-ment and control groups on the parental or physician CGIscales.Autism severityPost-hoc analysis of children in the treatment group dem-onstrated that those who had an initial ADOS score belowthe 50th percentile for all children (less initial autismseverity) had similar improvements in ABC total scoreand subscales compared to children with an initial ADOSscore above the 50th percentile (p = ns). However, com-parison of children in the treatment group and the controlgroup who had an initial ADOS score below the 50th per-centile (less autism severity) demonstrated that the chil-dren in the treatment group had significantly betterimprovements in ABC irritability (p = 0.0348) and ABCstereotypy (p = 0.0359). There was no significant differ-ence in ABC scores between the treatment and controlgroups for children with an initial ADOS score above the

  2009, :21 http://www.biomedcentral.com/1471-2431/9/21Page 9 of 15                       50th percentile (p = ns). When examining the ATEC scale,comparison of children in the treatment group and thecontrol group with an initial ADOS score below the 50thpercentile demonstrated a significantly better improve-ment in the treatment group in sociability (p = 0.0333).No significant difference between groups was observed forchildren with an initial ADOS score above the 50th percen-tile (p = ns). No significant effect (p = ns) was observed forautism severity between the treatment and control groupson the parental or physician CGI scales.Adverse events and toleranceHyperbaric treatment in this study was safe and well-tol-erated. In the treatment group, one child developed bothurinary frequency (urinalysis was normal) and a skin rashthat the treating physician thought was yeast-related. Aspreviously described, one child had worsening of asthmasymptoms after nine treatment sessions and was removedfrom the study, and another child had anxiety anddropped out of the study before finishing one full treat-ment. None of the children in the treatment groupreceived a score worse than 4 ("no change") on the physi-cian or parental CGI for change in overall functioning. Inthe control group, one child developed abdominal disten-sion and diarrhea during the study, but was able to com-plete the study. Another child in the control group hadworsening of eczema during the study. No other adverseevents including barotrauma or seizures were observed ineither group.DiscussionTo our knowledge, this trial represents the first controlledstudy of hyperbaric treatment in children with autism.Previous studies examining this treatment in autism havedescribed improvements that could have been due, inpart, to a participation (placebo) effect. The results ofuncontrolled studies in autism should be interpreted withcaution, especially since some randomized, double-blind,placebo-controlled studies in individuals with autismhave reported relatively high improvement rates in theplacebo group. For example, one prospective study com-paring a single dose of IV secretin to a placebo found that30% of the children receiving the placebo had a signifi-cant improvement immediately after the infusion [45].Another prospective study comparing daily treatmentwith amantadine to a placebo over a 4-week period founda mean placebo response rate of 37% [46]. In the currentstudy, 80% of children in the hyperbaric treatment groupChanges compared to baseline on the ABC total score and subscales (percentage change) in the treatment and control groupsFigure 3Changes compared to baseline on the ABC total score and subscales (percentage change) in the treatment and control groups. *** p < 0.1.

  2009, :21 http://www.biomedcentral.com/1471-2431/9/21Page 10 of 15                       had an improvement on the CGI scale for change in over-all functioning as rated by blinded physicians; however,38% of children in the control group were also rated asimproved. This 38% improvement rate in the controlgroup may have occurred because these children receiveda very low level of hyperbaric pressure (1.03 atm withshort increases to 1.1 atm), and therefore, strictly speak-ing, this pressure did not represent a true placebo-controlgroup. Hyperbaric pressure as low as 20 mmHg (approxi-mately 1.03 atm) has been shown to decrease in vitro pro-inflammatory cytokine release (including IL-1beta) fromhuman monocytes and macrophages [47]. Some childrenwith ASD have elevations in certain pro-inflammatorycytokines, including IL-1beta [32,48]. Therefore, some ofthe improvements observed in the control group couldhave been due to the slight hyperbaric pressure received.Because the control group experienced pressure condi-tions closer to those of the treatment group than a trueplacebo (e.g., 1.00 atm and 21% oxygen) would have pro-vided, the difference in clinical outcomes between thetreatment and control groups may have been less signifi-cant than what would have been observed with a placebo.However, a true placebo could not have been used withthis study design because some degree of hyperbaric pres-sure was needed to mimic hyperbaric treatment at 1.3atm, otherwise blinding of the group assignment wouldhave not been possible. A pressure of 1.03 atm (with shortincreases to 1.1 atm) was chosen for the control groupbecause testing performed prior to the study indicatedthat this pressure was the lowest that could be given andstill effectively simulate, from the perspective of theblinded parents and children, hyperbaric treatment at 1.3atm. The blinding procedure in this study appeared to beadequate because there was no significant differencebetween the two groups in the ability of parents to cor-rectly guess the group assignment of their child. Further-more, 73% of parents of children in the control grouprated their child as improved on the CGI scale which alsosuggests that the blinding procedure was adequate,because if parents thought that their child was in the con-trol group, they probably would have been less likely torate an improvement after treatment. In the hyperbarictreatment group, parental CGI scores significantly corre-lated with physician CGI scores (r = 0.60, p = 0.0005)which strengthens the CGI results in this group. In thecontrol group, the parents were significantly more likelyChanges compared to baseline on the ATEC total score and subscales (percentage change) in the treatment and control groupsFigure 4Changes compared to baseline on the ATEC total score and subscales (percentage change) in the treatment and control groups. ** p < 0.05.

  2009, :21 http://www.biomedcentral.com/1471-2431/9/21Page 11 of 15                       to rate their child as improved on the CGI scale comparedto the physicians (p = 0.0245) and therefore the parentaland physician CGI scales did not significantly correlate (r= 0.27, p = 0.1819). This finding further suggests that theblinding procedure was adequate in this study and alsodemonstrates evidence of a participation effect in the con-trol group.In this trial, the use of hyperbaric treatment at 1.3 atm waswell-tolerated and confirmed previous reports of safety.This study also demonstrated clinical improvements thatwere similar to previous uncontrolled studies of hyper-baric treatment in children with autism [7,17,21,22,35].The findings of this study are significantly strengthenedbecause of the presence of a control group which previoushyperbaric treatment studies in autism lacked, and alsobecause of the use of six separate centers which shouldhave minimized potential bias, especially since there wereno significant differences between study sites in age, ini-tial autism severity, and initial and final scores on all ofthe scales used in this study. In this current trial, signifi-cant improvements were observed in several domainswith the use of hyperbaric treatment at 1.3 atm and 24%oxygen compared to slightly pressurized room air, includ-ing overall functioning, receptive language, social interac-tion, eye contact, and sensory/cognitive awareness. Thereason for these different areas of improvement is notclear. The mechanism of action of hyperbaric treatment inautism is not entirely known, although it may act bydiminishing gastrointestinal and cerebral inflammationand by improving immune dysregulation and cerebralhypoperfusion [24]. Multiple studies have reported thatthese problems are relatively common in children withautism [26-34].Cerebral hypoperfusion, especially of the temporal lobes,is a very common finding in children with autism com-pared to typically-developing children, affecting up to75% [28,49]. This hypoperfusion is an indirect measure ofdiminished brain activity [28] because cerebral bloodflow is normally tightly coupled to brain metabolic rateand function [50,51]. Several studies have reported thatthe anatomical location of cerebral hypoperfusion signif-icantly correlates with certain autistic behaviors [24]. Forexample, in a study of 30 individuals with autism com-pared to 14 non-autistic individuals, hypoperfusion of thethalamus as measured by Single Photon Emission Com-puted Tomography (SPECT) was observed in the autismgroup and significantly correlated (r = 0.42, p < 0.01) withrepetitive behaviors and unusual sensory interests [52]. Inanother SPECT study of 23 children with autism com-pared to 26 non-autistic children, hypoperfusion of theright medial temporal lobes was found in the autismgroup and was correlated with obsessive desire for same-ness (p < 0.001), and hypoperfusion of the medial pre-frontal cortex and anterior cingulate gyrus was associatedwith impairments in social interaction and communica-tion (p < 0.001) [27]. Furthermore, two SPECT studies inindividuals with autism have reported that cerebralhypoperfusion significantly worsens with increasing age[53,54]. In one of these studies, hypoperfusion of brainareas that controlled speech (left temporal lobe and fron-tal areas) significantly worsened with increasing age (p <0.001) and was associated with deficits in language for-mation and "subsequently prevent [ed] development oftrue verbal fluency and development in the temporal andfrontal areas associated with speech and communication"[54]. Furthermore, in another study of 45 children withautism, children with the highest degree of left temporallobe hypoperfusion, as measured by Positron EmissionTomography (PET), also had the most severe autisticbehavior [55].The cause of cerebral hypoperfusion in children withautism is not known. Several studies have describedapparent vascular-associated cerebral inflammation inchildren with autism compared to controls includingperivascular macrophage and microglia accumulation inpost-mortem autistic brain samples [33] as well as thepresence of serum IgM and IgG autoantibodies that bindto small blood vessels in the brain in about 30% of chil-dren [26,56]. These findings could be consistent with acerebral vasculitis [24]. Elevated urinary levels of 8-iso-prostane-F2 have also been reported in some childrenwith autism [57]. In some studies, this isoprostane eleva-tion has been shown to cause in vivo vasoconstriction andincrease the aggregation of platelets [58]. Furthermore,elevations in 2,3-dinor-thromboxane B2 (associated withincreased platelet activation) and 6-keto-prostaglandinF1 (a marker of endothelium activation) have beendescribed in some children with autism [59]. Theseinflammatory-related findings could contribute to the cer-ebral hypoperfusion described in autism [24].Cerebral hypoperfusion is associated with hypoxia [24]and several studies in children with ASD have reportedevidence of cerebral hypoxia, as measured by a reductionin brain Bcl-2 and an increase in brain p53 [60-63]. Ele-vated p53 is induced by hypoxia [64] and a decrease inBcl-2 is associated with increased apoptosis provoked byhypoxia [65]. Hypoxia leads to higher brain concentra-tions of hypoxia-inducible factor 1 (HIF-1) [66]. Anincrease in HIF-1 causes an increase in inflammation,including redness and swelling of tissues, and the attrac-tion of lymphocytes [66]. HIF-1 is essential for inflam-mation mediated by myeloid cells [67]. In fact, in onestudy, rats that were null for HIF-1 demonstrated almostcomplete inhibition of the inflammatory response [68].HIF-1 is responsible for angiogenesis that is secondary tohypoxia [68,69] and also induces Vascular Endothelial

  2009, :21 http://www.biomedcentral.com/1471-2431/9/21Page 12 of 15                       Growth Factor (VEGF), which increases the permeabilityof blood vessels [66] and causes tissue edema. Evidence ofcerebral edema in 19 children with autism compared to20 typically-developing children was suggested by onerecent T2-magnetic resonance imaging (MRI) study [70].This edema can lead to increased interstitial spacebetween cells [71] and cause an increase in the distancethat oxygen must diffuse from blood vessels to reach braincells and can thus lead to cellular hypoxia [72]. Inflamma-tion is also associated with blood-brain barrier distur-bances which can further increase cerebral edema [24].Chronic inflammation is commonly associated with theinfiltration of polymorphonuclear neutrophils and otherimmune cells, along with the cytokines that are releasedby these cells. This causes an increase in local oxygenusage due to the elevated oxygen requirements created bythese newly infiltrated cells. Yet, at the same time, inflam-mation causes reduced oxygen extraction by normal cells[73]. For instance, in one study, elevated markers ofinflammation (including IL-6, tumor necrosis factorreceptors 1 and 2, and high-sensitivity C-reactive protein)were significantly correlated with decreased maximumoxygen uptake at peak exercise (VO2max) in patients withknown or suspected coronary artery disease [74]. There-fore, inflammation prevents maximal uptake of oxygen bycells. Inflammation also increases oxidative stress and cancause neutrophils to become more adherent and attach tovessel walls [75]. This infiltration and increased adherenceof inflammatory cells can contribute to brain injury bydecreasing microvascular blood flow, causing thrombosis,and increasing the production of free radicals [76]. Hyper-baric treatment can overcome the effects of cerebralhypoperfusion and hypoxia by: increasing the plasmaoxygen tension which transfers more oxygen into tissue,including the brain [77,78], decreasing cerebral edema[79], inhibiting the expression of HIF-1 and its targetgenes [80], and by causing angiogenesis over time [18].Several case reports in children with autism havedescribed improved cerebral perfusion after hyperbarictreatment at 1.3 atm, as measured by post-hyperbarictreatment SPECT scans compared to pre-hyperbaricSPECT scans [21,22]. If the hypoperfusion in childrenwith autism is related to cerebral inflammation, thenhyperbaric treatment could potentially improve cerebralperfusion by decreasing this inflammation [24]. Hyper-baric treatment possesses strong anti-inflammatory prop-erties [18-20] and has been shown to significantlydecrease neuroinflammation [81] as well as cerebraledema and blood-brain barrier damage in animal models[79]. At 1.3 atm, hyperbaric treatment decreased a markerof inflammation (C-reactive protein) in one study of chil-dren with autism [7]. It is unknown if any of the improve-ments observed in this study were mediated through animprovement in cerebral hypoperfusion and/or a decreasein cerebral inflammation as this study was not designed toexamine these possibilities. However, since cerebralhypoperfusion is relatively common [28,49] and can bediffuse in location in children with autism [82,83], andthe anatomical location of hypoperfusion significantlycorrelates with certain autistic behaviors [27,52,54], thenimproving hypoperfused brain areas with hyperbarictreatment could account for the different areas ofimprovement observed in this study.Our previous studies suggested children who wereyounger and those who had higher initial autism severityresponded more robustly to hyperbaric treatment [7,17].However, these studies were small and uncontrolled, andthus we analyzed these two parameters (age and autismseverity) in this study with a post-hoc analysis. An inter-esting finding from this current study was that childrenwho were over age 5 had significantly better improve-ments on the ABC total score with hyperbaric treatment at1.3 atm compared to younger children (p = 0.0482).Given the fact that older children with autism generallyhave a higher degree of cerebral hypoperfusion comparedto younger children [53,54] and that hyperbaric treatmentcan improve cerebral hypoperfusion [21,22], these factorscould have accounted for the age findings observed in thisstudy. Additional studies examining the use of hyperbarictreatment in children with autism that also incorporateSPECT or PET scans to measure changes in cerebral bloodflow might be helpful in further delineating these possi-bilities. Moreover, children who had lower initial autismseverity also had the most improvements with hyperbarictreatment in this study. The reason for this finding is notknown, but may be due to greater levels of oxidative stressand other metabolic problems recently described in chil-dren with higher autism severity compared to those withlower severity [84].Because this study was not designed to measure the long-term outcomes of hyperbaric treatment in children withautism, additional studies are needed to determine if thesignificant improvements observed in this study lastbeyond the study period. It is possible that ongoing treat-ments would be necessary to maintain the improvementsobserved, but this study was not designed to examine thatpossibility. Our clinical observations in children withautism suggest that additional hyperbaric treatmentsbeyond 40 total sessions can lead to additional improve-ments; however, further studies are needed to formallyvalidate these observations. Recently, several companieshave started producing and marketing portable hyper-baric chambers that are approved by the U.S. Food andDrug Administration (FDA) for home use and are able tosupply the hyperbaric treatment parameters used in thisstudy. Therefore, the widespread and long-term use of thispotential treatment is feasible and not necessarily costly

  2009, :21 http://www.biomedcentral.com/1471-2431/9/21Page 13 of 15                       (on a per treatment basis). Finally, this study was notdesigned to determine if higher hyperbaric treatmentparameters (higher atmospheric pressure and oxygen lev-els, which can only be provided in a clinic setting) wouldlead to better or more long-lasting results. Additionalstudies are needed to investigate that possibility.ConclusionGiven the positive findings of this study, and the shortageof proven treatments for individuals with autism, parentswho pursue hyperbaric treatment for their child withautism can be assured that it is a safe treatment modalityat the pressure used in this study (1.3 atm), and that itmay improve certain autistic behaviors. Further studiesare needed by other investigators to confirm these find-ings; we are aware of several other planned or ongoingstudies of hyperbaric treatment in children with autism.However, in light of the positive results of this study andthose of several previous studies [7,17,21,22,35], the useof hyperbaric treatment appears to be a promising treat-ment for children with autism.AbbreviationsABA: Applied Behavioral Analysis; ABC: Aberrant Behav-ior Checklist; ADI-R: Autism Diagnostic Interview-Revised; ADOS: Autism Diagnostic Observation Schedule;ASD: Autism Spectrum Disorder; ATEC: Autism TreatmentEvaluation Checklist; atm: atmosphere; CGI: Clinical Glo-bal Impression; FDA: Food and Drug Administration;HIF-1: Hypoxia-Inducible Factor 1; IHA: InternationalHyperbarics Association; MRI: Magnetic Resonance Imag-ing; ns: not significant; PDD-NOS: pervasive developmen-tal disorder-not otherwise specified; PET: PositronEmission Tomography; SPECT: Single Photon EmissionComputed Tomography; U.S.: United States; VEGF: Vas-cular Endothelial Growth Factor.Competing interestsDAR, LWR, SS, CS, AU, JN, EMM, and EAM treat individ-uals with hyperbaric treatment in their clinical practicesand derive revenue from hyperbaric treatment. DAR,LWR, and EAM had previously received research fundingfrom the International Hyperbarics Association for an ear-lier study of hyperbaric treatment in autism [7]. EAM hasalso received hyperbaric chambers and financial support(unrelated to this study) from OxyHealth LLC for remod-eling the Rimland Center, a center for mentoring clini-cians interested in learning how to care for children withautism spectrum disorders. The remaining authors (SL,GH, and BG) declare that they have no competing inter-ests.Authors' contributionsDAR, LWR, and EAM conceived of the study and the studydesign. DAR, SS, CS, AU, JN, EMM, and EAM performedinitial physical exams on the children and were responsi-ble for completing the physician CGI scales. SL and GHperformed psychological testing on the children includingADOS and ADI-R. DAR and BG performed the statisticalanalysis. All authors read and approved the final manu-script.Additional materialAcknowledgementsThe authors thank Glenna Osborne, Helen Yoo, Evelyn Kung, and Scott Allen for providing psychological testing for some of the children in this study and also thank Mr. Michael Haynes for reviewing this manuscript and offering editorial advice. We are grateful for the work of Shannon Kenitz of the International Hyperbarics Association (IHA) for an unrestricted grant which funded this study, which included use of hyperbaric chambers and funding for all hyperbaric technician salaries during the study. The IHA had no involvement in the study design, collection, analysis, interpretation of data, writing of the manuscript, or in the decision to submit the manuscript for publication. All treatments and study evaluations were performed with-out charge to all participants. We especially thank the parents and children in our study for their participation. This data was presented, in part, at the Undersea and Hyperbaric Medical Society (UHMS), Gulf Coast Chapter Annual Scientific Meeting, Nashville, Tennessee, September 1, 2007.Note in proofDuring the proofing stage of the final manuscript pdf, the authors realized that some data from the ADOS testing was inadvertently omitted and the editors were notified. ADOS was used to confirm the diagnosis of autism and to determine if a change in diagnosis occurred during the study. Com-parison of pre- and post-ADOS performed by blinded assessors demon-strated no significant change in autism diagnosis between the two groups (p = ns).References1. APA: Diagnostic and statistical manual of mental disorders.4th edition. Washington, DC: American Psychiatric Association;1994. 2. Chakrabarti S, Fombonne E: Pervasive developmental disordersin preschool children. JAMA 2001, 285(24):3093-3099.3. Bertrand J, Mars A, Boyle C, Bove F, Yeargin-Allsopp M, Decoufle P:Prevalence of autism in a United States population: theAdditional File 1Table 2. Changes on the ABC scale and subscales in the treatment and control groups (lower scores denote improvement). # Wilcoxon signed rank tests. ## Mann Whitney test.Click here for file[http://www.biomedcentral.com/content/supplementary/1471-2431-9-21-S1.doc]Additional File 2Table 3. Changes on the ATEC scale and subscales in the treatment and control groups (lower scores denote improvement). # Wilcoxon signed rank tests. ## Mann Whitney test.Click here for file[http://www.biomedcentral.com/content/supplementary/1471-2431-9-21-S2.doc]

  2009, :21 http://www.biomedcentral.com/1471-2431/9/21Page 14 of 15                       Brick Township, New Jersey, investigation. Pediatrics 2001,108(5):1155-1161.4. Baird G, Charman T, Baron-Cohen S, Cox A, Swettenham J, Wheel-wright S, Drew A: A screening instrument for autism at 18months of age: a 6-year follow-up study. J Am Acad Child AdolescPsychiatry 2000, 39(6):694-702.5. Rice C: Prevalence of autism spectrum disorders–autism anddevelopmental disabilities monitoring network, 14 sites,United States, 2002. MMWR 2007, 56:12-28.6. Muhle R, Trentacoste SV, Rapin I: The genetics of autism. Pediat-rics 2004, 113(5):e472-486.7. Rossignol DA, Rossignol LW, James SJ, Melnyk S, Mumper E: Theeffects of hyperbaric oxygen therapy on oxidative stress,inflammation, and symptoms in children with autism: anopen-label pilot study. BMC Pediatr 2007, 7(1):36.8. Feldmeier JJ, Chairman and Editor: Hyperbaric oxygen 2003: indi-cations and results: the hyperbaric oxygen therapy commit-tee report. Kensington, MD: Undersea and Hyperbaric MedicineSociety; 2003. 9. Leach RM, Rees PJ, Wilmshurst P: Hyperbaric oxygen therapy.BMJ 1998, 317(7166):1140-1143.10. Stoller KP: Quantification of neurocognitive changes before,during, and after hyperbaric oxygen therapy in a case of fetalalcohol syndrome. Pediatrics 2005, 116(4):e586-591.11. Montgomery D, Goldberg J, Amar M, Lacroix V, Lecomte J, LambertJ, Vanasse M, Marois P: Effects of hyperbaric oxygen therapy onchildren with spastic diplegic cerebral palsy: a pilot project.Undersea Hyperb Med 1999, 26(4):235-242.12. Collet JP, Vanasse M, Marois P, Amar M, Goldberg J, Lambert J, Las-sonde M, Hardy P, Fortin J, Tremblay SD, et al.: Hyperbaric oxygenfor children with cerebral palsy: a randomised multicentretrial. HBO-CP Research Group. Lancet 2001,357(9256):582-586.13. Rockswold GL, Ford SE, Anderson DC, Bergman TA, Sherman RE:Results of a prospective randomized trial for treatment ofseverely brain-injured patients with hyperbaric oxygen. JNeurosurg 1992, 76(6):929-934.14. Golden ZL, Neubauer R, Golden CJ, Greene L, Marsh J, Mleko A:Improvement in cerebral metabolism in chronic brain injuryafter hyperbaric oxygen therapy. Int J Neurosci 2002,112(2):119-131.15. Hardy P, Johnston KM, De Beaumont L, Montgomery DL, LecomteJM, Soucy JP, Bourbonnais D, Lassonde M: Pilot case study of thetherapeutic potential of hyperbaric oxygen therapy onchronic brain injury. J Neurol Sci 2007, 253(1–2):94-105.16. Shi XY, Tang ZQ, Sun D, He XJ: Evaluation of hyperbaric oxygentreatment of neuropsychiatric disorders following traumaticbrain injury. Chin Med J (Engl) 2006, 119(23):1978-1982.17. Rossignol DA, Rossignol LW: Hyperbaric oxygen therapy mayimprove symptoms in autistic children. Med Hypotheses 2006,67(2):216-228.18. Al-Waili NS, Butler GJ: Effects of hyperbaric oxygen on inflam-matory response to wound and trauma: possible mechanismof action. Scientific World Journal 2006, 6:425-441.19. Buchman AL, Fife C, Torres C, Smith L, Aristizibal J: Hyperbaricoxygen therapy for severe ulcerative colitis. J Clin Gastroenterol2001, 33(4):337-339.20. Takeshima F, Makiyama K, Doi T: Hyperbaric oxygen as adjuncttherapy for Crohn's intractable enteric ulcer. Am J Gastroen-terol 1999, 94(11):3374-3375.21. Heuser G, Heuser SA, Rodelander D, Aguilera O, Uszler M: Treat-ment of neurologically impaired adults and children with"mild" hyperbaric oxygenation (1.3 atm and 24% oxygen). InHyperbaric oxygenation for cerebral palsy and the brain-injured childEdited by: Joiner JT. Flagstaff, Arizona: Best Publications; 2002. 22. Rossignol DA: The use of hyperbaric oxygen therapy inautism. In Hyperbaric oxygen for neurological disorders Edited by:Zhang JH. Flagstaff, AZ: Best Publishing Company; 2008:209-258. 23. Granowitz EV, Skulsky EJ, Benson RM, Wright J, Garb JL, Cohen ER,Smithline EC, Brown RB: Exposure to increased pressure orhyperbaric oxygen suppresses interferon-gamma secretionin whole blood cultures of healthy humans. Undersea HyperbMed 2002, 29(3):216-225.24. Rossignol DA: Hyperbaric oxygen therapy might improve cer-tain pathophysiological findings in autism. Med Hypotheses2007, 68(6):1208-1227.25. Weisz G, Lavy A, Adir Y, Melamed Y, Rubin D, Eidelman S, Pollack S:Modification of in vivo and in vitro TNF-alpha, IL-1, and IL-6secretion by circulating monocytes during hyperbaric oxy-gen treatment in patients with perianal Crohn's disease. JClin Immunol 1997, 17(2):154-159.26. Connolly AM, Chez MG, Pestronk A, Arnold ST, Mehta S, Deuel RK:Serum autoantibodies to brain in Landau-Kleffner variant,autism, and other neurologic disorders. J Pediatr 1999,134(5):607-613.27. Ohnishi T, Matsuda H, Hashimoto T, Kunihiro T, Nishikawa M, UemaT, Sasaki M: Abnormal regional cerebral blood flow in child-hood autism. Brain 2000, 123(Pt 9):1838-1844.28. Zilbovicius M, Boddaert N, Belin P, Poline JB, Remy P, Mangin JF, Thi-vard L, Barthelemy C, Samson Y: Temporal lobe dysfunction inchildhood autism: a PET study. Positron emission tomogra-phy. Am J Psychiatry 2000, 157(12):1988-1993.29. Jyonouchi H, Sun S, Itokazu N: Innate immunity associated withinflammatory responses and cytokine production againstcommon dietary proteins in patients with autism spectrumdisorder. Neuropsychobiology 2002, 46(2):76-84.30. Torrente F, Ashwood P, Day R, Machado N, Furlano RI, Anthony A,Davies SE, Wakefield AJ, Thomson MA, Walker-Smith JA, et al.:Small intestinal enteropathy with epithelial IgG and comple-ment deposition in children with regressive autism. Mol Psy-chiatry 2002, 7(4):375-382.31. Ashwood P, Anthony A, Torrente F, Wakefield AJ: Spontaneousmucosal lymphocyte cytokine profiles in children withautism and gastrointestinal symptoms: mucosal immuneactivation and reduced counter regulatory interleukin-10. JClin Immunol 2004, 24(6):664-673.32. Jyonouchi H, Geng L, Ruby A, Zimmerman-Bier B: Dysregulatedinnate immune responses in young children with autismspectrum disorders: their relationship to gastrointestinalsymptoms and dietary intervention. Neuropsychobiology 2005,51(2):77-85.33. Vargas DL, Nascimbene C, Krishnan C, Zimmerman AW, Pardo CA:Neuroglial activation and neuroinflammation in the brain ofpatients with autism. Ann Neurol 2005, 57(1):67-81.34. Chez MG, Dowling T, Patel PB, Khanna P, Kominsky M: Elevation oftumor necrosis factor-alpha in cerebrospinal fluid of autisticchildren. Pediatr Neurol 2007, 36(6):361-365.35. Chungpaibulpatana J, Sumpatanarax T, Thadakul N, ChantharatreeratC, Konkaew M, Aroonlimsawas M: Hyperbaric oxygen therapy inThai autistic children. J Med Assoc Thai 2008, 91(8):1232-1238.36. Ashamalla HL, Thom SR, Goldwein JW: Hyperbaric oxygen ther-apy for the treatment of radiation-induced sequelae in chil-dren. The University of Pennsylvania experience. Cancer1996, 77(11):2407-2412.37. Annane D, Depondt J, Aubert P, Villart M, Gehanno P, Gajdos P,Chevret S: Hyperbaric oxygen therapy for radionecrosis ofthe jaw: a randomized, placebo-controlled, double-blind trialfrom the ORN96 study group. J Clin Oncol 2004,22(24):4893-4900.38. Clarke RE, Tenorio LM, Hussey JR, Toklu AS, Cone DL, Hinojosa JG,Desai SP, Dominguez Parra L, Rodrigues SD, Long RJ, et al.: Hyper-baric oxygen treatment of chronic refractory radiation proc-titis: a randomized and controlled double-blind crossovertrial with long-term follow-up. Int J Radiat Oncol Biol Phys 2008,72(1):134-143.39. Aman MG, Singh NN, Stewart AW, Field CJ: The aberrant behav-ior checklist: a behavior rating scale for the assessment oftreatment effects. Am J Ment Defic 1985, 89(5):485-491.40. Autism Treatment Evaluation Checklist (ATEC): Reliabili-ties and Score Distributions 2000 [http://www.autism.com/ari/atec/atec_report.htm].41. Guy W: Clinical Global Impression. 1976 [http://www.servier.com/App_Download/Neurosciences/Echelles/CGI.pdf]. Rockville,MD42. Cohen J: Statistical power analysis for the behavioral sciences.second edition. Hillsdale, NJ: Lawrence Erlbaum Associates; 1988. 43. Faul F, Erdfelder E, Lang AG, Buchner A: G*Power 3: A flexiblestatistical power analysis program for the social, behavioral,and biomedical sciences. Behavior Research Methods 2007,39:175-191.44. Fombonne E: Epidemiology of autistic disorder and other per-vasive developmental disorders. J Clin Psychiatry 2005, 66(Suppl10):3-8.

  2009, :21 http://www.biomedcentral.com/1471-2431/9/21Page 15 of 15                       45. Sandler AD, Sutton KA, DeWeese J, Girardi MA, Sheppard V, BodfishJW: Lack of benefit of a single dose of synthetic human secre-tin in the treatment of autism and pervasive developmentaldisorder. N Engl J Med 1999, 341(24):1801-1806.46. King BH, Wright DM, Handen BL, Sikich L, Zimmerman AW, McMa-hon W, Cantwell E, Davanzo PA, Dourish CT, Dykens EM, et al.:Double-blind, placebo-controlled study of amantadinehydrochloride in the treatment of children with autistic dis-order. J Am Acad Child Adolesc Psychiatry 2001, 40(6):658-665.47. Shiratsuch H, Basson MD: Differential regulation of monocyte/macrophage cytokine production by pressure. Am J Surg 2005,190(5):757-762.48. Jyonouchi H, Sun S, Le H: Proinflammatory and regulatorycytokine production associated with innate and adaptiveimmune responses in children with autism spectrum disor-ders and developmental regression. J Neuroimmunol 2001,120(1–2):170-179.49. Boddaert N, Chabane N, Barthelemy C, Bourgeois M, Poline JB,Brunelle F, Samson Y, Zilbovicius M: [Bitemporal lobe dysfunc-tion in infantile autism: positron emission tomographystudy]. J Radiol 2002, 83(12 Pt 1):1829-1833.50. Fox PT, Raichle ME: Focal physiological uncoupling of cerebralblood flow and oxidative metabolism during somatosensorystimulation in human subjects. Proc Natl Acad Sci USA 1986,83(4):1140-1144.51. Parri R, Crunelli V: An astrocyte bridge from synapse to bloodflow. Nat Neurosci 2003, 6(1):5-6.52. Starkstein SE, Vazquez S, Vrancic D, Nanclares V, Manes F, Piven J,Plebst C: SPECT findings in mentally retarded autistic individ-uals. J Neuropsychiatry Clin Neurosci 2000, 12(3):370-375.53. Kaya M, Karasalihoglu S, Ustun F, Gultekin A, Cermik TF, Fazlioglu Y,Ture M, Yigitbasi ON, Berkarda S: The relationship between99mTc-HMPAO brain SPECT and the scores of real life rat-ing scale in autistic children. Brain Dev 2002, 24(2):77-81.54. Wilcox J, Tsuang MT, Ledger E, Algeo J, Schnurr T: Brain perfusionin autism varies with age. Neuropsychobiology 2002, 46(1):13-16.55. Gendry Meresse I, Zilbovicius M, Boddaert N, Robel L, Philippe A,Sfaello I, Laurier L, Brunelle F, Samson Y, Mouren MC, et al.: Autismseverity and temporal lobe functional abnormalities. AnnNeurol 2005, 58(3):466-469.56. Connolly AM, Chez M, Streif EM, Keeling RM, Golumbek PT, KwonJM, Riviello JJ, Robinson RG, Neuman RJ, Deuel RM: Brain-derivedneurotrophic factor and autoantibodies to neural antigens insera of children with autistic spectrum disorders, Landau-Kleffner syndrome, and epilepsy. Biol Psychiatry 2006,59(4):354-363.57. Ming X, Stein TP, Brimacombe M, Johnson WG, Lambert GH, Wag-ner GC: Increased excretion of a lipid peroxidation biomar-ker in autism. Prostaglandins Leukot Essent Fatty Acids 2005,73(5):379-384.58. Pratico D, Lawson JA, Rokach J, FitzGerald GA: The isoprostanesin biology and medicine. Trends Endocrinol Metab 2001,12(6):243-247.59. Yao Y, Walsh WJ, McGinnis WR, Pratico D: Altered vascular phe-notype in autism: correlation with oxidative stress. Arch Neu-rol 2006, 63(8):1161-1164.60. Fatemi SH, Halt AR, Stary JM, Realmuto GM, Jalali-Mousavi M:Reduction in anti-apoptotic protein Bcl-2 in autistic cerebel-lum. Neuroreport 2001, 12(5):929-933.61. Fatemi SH, Halt AR: Altered levels of Bcl2 and p53 proteins inparietal cortex reflect deranged apoptotic regulation inautism. Synapse 2001, 42(4):281-284.62. Fatemi SH, Stary JM, Halt AR, Realmuto GR: Dysregulation of Ree-lin and Bcl-2 proteins in autistic cerebellum. J Autism Dev Disord2001, 31(6):529-535.63. Araghi-Niknam M, Fatemi SH: Levels of Bcl-2 and P53 are alteredin superior frontal and cerebellar cortices of autistic sub-jects. Cell Mol Neurobiol 2003, 23(6):945-952.64. Graeber TG, Peterson JF, Tsai M, Monica K, Fornace AJ Jr, Giaccia AJ:Hypoxia induces accumulation of p53 protein, but activationof a G1-phase checkpoint by low-oxygen conditions is inde-pendent of p53 status. Mol Cell Biol 1994, 14(9):6264-6277.65. Shimizu S, Eguchi Y, Kamiike W, Itoh Y, Hasegawa J, Yamabe K,Otsuki Y, Matsuda H, Tsujimoto Y: Induction of apoptosis as wellas necrosis by hypoxia and predominant prevention of apop-tosis by Bcl-2 and Bcl-XL. Cancer Res 1996, 56(9):2161-2166.66. Nathan C: Immunology: Oxygen and the inflammatory cell.Nature 2003, 422(6933):675-676.67. Cramer T, Yamanishi Y, Clausen BE, Forster I, Pawlinski R, MackmanN, Haase VH, Jaenisch R, Corr M, Nizet V, et al.: HIF-1alpha isessential for myeloid cell-mediated inflammation. Cell 2003,112(5):645-657.68. Cramer T, Johnson RS: A novel role for the hypoxia inducibletranscription factor HIF-1alpha: critical regulation of inflam-matory cell function. Cell Cycle 2003, 2(3):192-193.69. Ryan HE, Lo J, Johnson RS: HIF-1 alpha is required for solidtumor formation and embryonic vascularization. EMBO J1998, 17(11):3005-3015.70. Hendry J, DeVito T, Gelman N, Densmore M, Rajakumar N, PavloskyW, Williamson PC, Thompson PM, Drost DJ, Nicolson R: Whitematter abnormalities in autism detected through transverserelaxation time imaging. Neuroimage 2006, 29(4):1049-1057.71. Lu G, Qian X, Berezin I, Telford GL, Huizinga JD, Sarna SK: Inflam-mation modulates in vitro colonic myoelectric and contrac-tile activity and interstitial cells of Cajal. Am J Physiol 1997,273(6 Pt 1):G1233-1245.72. Ishii Y, Ushida T, Tateishi T, Shimojo H, Miyanaga Y: Effects of dif-ferent exposures of hyperbaric oxygen on ligament healingin rats. J Orthop Res 2002, 20(2):353-356.73. Harrison DK, Abbot NC, Carnochan FM, Beck JS, James PB, McCol-lum PT: Protective regulation of oxygen uptake as a result ofreduced oxygen extraction during chronic inflammation. AdvExp Med Biol 1994, 345:789-796.74. Van de Veire N, De Winter O, Philippé J, De Buyzere M, Bernard D,Langlois M, Gillebert T, De Sutter J: Maximum oxygen uptake atpeak exercise in elderly patients with coronary artery dis-ease and preserved left ventricular function: the role ofinflammation on top of tissue Doppler-derived systolic anddiastolic function. Am Heart J 2006, 152(2):e291-297.75. Suematsu M, Schmid-Schonbein GW, Chavez-Chavez RH, Yee TT,Tamatani T, Miyasaka M, Delano FA, Zweifach BW: In vivo visuali-zation of oxidative changes in microvessels during neu-trophil activation. Am J Physiol 1993, 264(3 Pt 2):H881-891.76. Miljkovic-Lolic M, Silbergleit R, Fiskum G, Rosenthal RE: Neuropro-tective effects of hyperbaric oxygen treatment in experi-mental focal cerebral ischemia are associated with reducedbrain leukocyte myeloperoxidase activity. Brain Res 2003,971(1):90-94.77. Sheffield PJ, Davis JC: Application of hyperbaric oxygen therapyin a case of prolonged cerebral hypoxia following rapiddecompression. Aviat Space Environ Med 1976, 47(7):759-762.78. Neubauer RA, James P: Cerebral oxygenation and the recover-able brain. Neurol Res 1998, 20(Suppl 1):S33-36.79. Veltkamp R, Siebing DA, Sun L, Heiland S, Bieber K, Marti HH, NagelS, Schwab S, Schwaninger M: Hyperbaric oxygen reduces blood-brain barrier damage and edema after transient focal cere-bral ischemia. Stroke 2005, 36(8):1679-1683.80. Ostrowski RP, Colohan AR, Zhang JH: Mechanisms of hyperbaricoxygen-induced neuroprotection in a rat model of subarach-noid hemorrhage. J Cereb Blood Flow Metab 2005, 25(5):554-571.81. Vlodavsky E, Palzur E, Soustiel JF: Hyperbaric oxygen therapyreduces neuroinflammation and expression of matrix metal-loproteinase-9 in the rat model of traumatic brain injury.Neuropathol Appl Neurobiol 2006, 32(1):40-50.82. Hashimoto T, Sasaki M, Fukumizu M, Hanaoka S, Sugai K, Matsuda H:Single-photon emission computed tomography of the brainin autism: effect of the developmental level. Pediatr Neurol2000, 23(5):416-420.83. Boddaert N, Zilbovicius M: Functional neuroimaging and child-hood autism. Pediatr Radiol 2002, 32(1):1-7.84. Geier DA, Kern JK, Garver CR, Adams JB, Audhya T, Nataf R, GeierMR: Biomarkers of environmental toxicity and susceptibilityin autism. J Neurol Sci 2008 in press.Pre-publication historyThe pre-publication history for this paper can be accessedhere:http://www.biomedcentral.com/1471-2431/9/21/prepub

The Science Journal of the Lander The Science Journal of the Lander College of Arts and Sciences College of Arts and Sciences Volume 13 Number 2 Spring 2020 - 2020 Is Hyperbaric Oxygen Therapy Effective For Treating Autism? Is Hyperbaric Oxygen Therapy Effective For Treating Autism? Malky Meyer Touro College Follow this and additional works at: https://touroscholar.touro.edu/sjlcas Part of the Biology Commons, and the Pharmacology, Toxicology and Environmental Health Commons Recommended Citation Recommended Citation Meyer, M. (2020). Is Hyperbaric Oxygen Therapy Effective For Treating Autism?. The Science Journal of the Lander College of Arts and Sciences, 13(2). Retrieved from https://touroscholar.touro.edu/sjlcas/vol13/iss2/10 This Article is brought to you for free and open access by the Lander College of Arts and Sciences at Touro Scholar. It has been accepted for inclusion in The Science Journal of the Lander College of Arts and Sciences by an authorized editor of Touro Scholar. For more information, please contact touro.scholar@touro.edu.

65AbstractAutism spectrum disorder (ASD) is characterized as a developmental disability caused by abnormalities in brain function. Studies -available research.Is Hyperbaric Oxygen Therapy Effective For Treating Autism?Malky MeyerMalky Meyer graduated in January 2020 with a Bachelor of Science degree in Biology. She will attend Touro Bayshore Physician Assistant program.IntroductionAutism spectrum disorder (ASD) is a neurodevelopmen-communication and social interaction across multiple contexts and restricted repetitive patterns of behavior, interests, or activities,” (APA, 2013). ASD includes autistic disorder, pervasive developmental disorder, and Asperger syndrome. Approximately 1 out of 110 people in the United States are currently affected by ASD (Rice, 2006). The cause of ASD is unclear. Although several genetic syndromes, such as Fragile X and Rett syndromes, have been linked with ASD, the majority of ASD cases are not due to a simple single gene or chromosomal disorder; studies have estimated that genetic syndromes only ac-count for 6-15% of ASD cases (Schaefer & Mendelsohn, 2008). Recently, research and clinical studies in ASD have linked physiological abnormalities, such as cerebral hy-dysfunction and immune dysregulation (Rossignol & Frye, 2012). With this perspective, ASD may consist of physio-logical irregularities rather than merely a CNS disorder (Herbert, 2005). Treating ASD is not a simple matter; there are a limited number of treatments. The behavioral aspects of ASD are manageable with the help of behavior-has been proven to lead to advances in certain children with ASD. In two years, ABA brought about remarkable children with ASD (Lovaas, 1987). After four years, ABA researchers at the Wisconsin Early Autism project found & Graupner, 2005). Conversely, researchers in Norway found that eclectic therapy (a form of psychotherapy) was successful in the treatment of children with ASD who were observed for only one year. The results proved to supersede the effective outcomes of ABA (Eikeseth, et al., 2002). When it comes to cognitive and behavioral transformations in children with ASD, behavioral thera-pies are not an ideal approach, as they are quite time de-manding. Additional treatments for ASD that aim to treat physiological irregularities have been conveyed, yet, a majority of these forms of treatments have not been crit-ically assessed. However, many studies were performed to test the effects of HBOT to treat the physiological ab-normalities possessed by people with ASD, many of which have shown promising results.MethodsThe research incorporated in this paper was retrieved from original research papers and scholarly articles ob-tained through Touro College’s library of databases, such        were also used to acquire data. The articles chosen were critically assessed, compared, and analyzed to evaluate if hyperbaric oxygen therapy is effective for treating autismHistory of Hyperbaric ChambersHyperbaric air or “air under pressure” is a medical treat-ment that dates back over 150 years. In 1662, a British physician created a sealed chamber in which the air was compressed and decompressed using valves and oxygen. This was extraordinary;it preceded the discovery of oxygen and was utilized as a treatment for respiratory diseases (Clarke, 2008). The idea of employing pressur-ized environments developed further in 1879, when the French surgeon, Fontaine, built a pressurized mobile op-erating room. He observed that inhaled nitrous oxide treated in an increased pressure environment were not as cyanotic as those treated in standard conditions. Additionally, his patients experienced improved oxygen-ation (Fontaine, 1879). In the early 1900’s, Dr. Orville Cunningham, a professor of anesthesia, found a greater improvement in heart disease victims when they resided

66Malky Meyercloser to sea level than when they were living at higher altitudes. Later, hyperbaric chambers were utilized by the military, in the 1940’s, to treat deep-sea divers who expe-rienced decompression sickness. In the 1950’s, physicians         steered to its use for carbon monoxide poisoning in the 1960’s. Since then, over 10,000 clinical trials and case studies have been achieved for several other health-relat-ed purposes, with the great majority reporting successful outcomes (Ohnishi, et al. 2000).Hyperbaric oxygen therapy (HBOT)Hyperbaric oxygen therapy (HBOT) is the medical use of oxygen in a pressurized environment, and involves breathing 100% oxygen while inside a hyperbaric cham-ber that exhibits pressures greater than sea level (1 at-mosphere). The increased pressure permits oxygen to dissolve and saturate the blood plasma (autonomous of hemoglobin), which yields an extensive array of valuable physiological and cellular outcomes. This noninvasive therapy is the most reliable way to provide ample oxygen to all organs of the body. The standard treatment lasts for 60-90 minutes, during which the patient lies down and breathes regularly (Feldmeier, 2003). The use of hy-perbaric oxygen treatment (HBOT) was implemented as a treatment method for numerous clinical disorders. It has been proven in several clinical studies to enhance the body’s inherent ability to regenerate and repair. It is used as a therapy to facilitate the healing process in both chronic and acute disorders. Decompression sickness, stroke victims, arterial gas embolism, healing of wounds, severe carbon monoxide poisoning and smoke inhalation are only some of the common uses of HBOT. However, in 2005, researchers began to consider using HBOT to improve behavioral and physiological abnormalities found in individuals with ASD (Leach, et al. 1998). This paper will evaluate the current data on treating ASD with HBOT. First, the effects of HBOT on physiological irregularities in children with ASD will be evaluated. Then, the effects on autistic behaviors will be examined. Finally, the appar-ent contrary effects of HBOT in ASD and restrictions of studies will be assessed.Cerebral Hypoperfusion in ASD and the Effects of HBOT     -ological abnormalities possessed by individuals with ASD. Positron emission tomography (PET) and single-photon emission computed tomography (SPECT) were used in studies to discern hypoperfusion exhibited in the brains of people with ASD versus normal healthy brains (Bjørklund, et al. 2018). Both PET and SPECT scans are types of nu-clear imaging tests that utilize radioactive tracers to cre-ate three-dimensional images. However, they differ in the radiotracers used. Studies have proven these scans to be           (Amen, et al. 2011; NIH CC, 2002). Common autistic behaviors such as need for consistency (Ohnishi, et al. 2000), habitual behaviors (Starkstein, et al. 2000), disability in processing emotions and facial expressions (Critchley, et al. 2000), and delayed language development (Wilcox, et al. 2002), are linked to hypoperfusion. Moreover, hy-poperfusion is related with increasing age in children with ASD (Wilcox, et al. 2002). It is possible that HBOT could improve cerebral hypoperfusion in ASD. Numerous stud-ies were completed that evaluated the effects of HBOT to treat various neurological disorders, such as chronic brain injury and traumatic brain injury. The results of the SPECT scans were evaluated before and after the deliv-ery of HBOT at low pressures (1.3 to 1.5 atm). These        (Golden, et al. 2002). Histograms correlated to the pre and post SPECT scans were analyzed with a widely used medical images software called Osirix DICOM. Results       beneath the cerebral cortex in the central area of white matter, known as the centrum ovale. The pre-HBOT im-ages displayed a larger array of counts in the histograms than in the post-HBOT. The narrower range of counts in the post-HBOT corresponded to the increase of perfu-sion to the lacking areas. The effectiveness was studied through many areas in addition to SPECT: physical exam, symptoms, and psychological measurement (Harch, et al. 2012). Moreover, numerous case studies have reported enhancements in cerebral perfusion after HBOT treat-ment. One study involved a child with ASD who received one hour of HBOT at 1.3 atm and 24% oxygen per day for ten days (Heuser, et al. 2002). The SPECT scans revealed increased perfusion. However, the effects of ten treat-ments only lasts several months. For longer lasting effects (6-18 months) more treatments are necessary (20-60 treatments). Behavioral improvements were detected in this child including cognitive and memory functions. The child became sympathetic, started to point and articulate, and interact with others. Another child with ASD, who received 40 treatments of HBOT at 1.3 atm and 24% oxygen, also presented behavioral improvements, such motor skills (Rossignol, 2008).Another study involved 108 children with ASD who

67Is Hyperbaric Oxygen Therapy Effective For Treating Autism?experienced decreased perfusion in their temporal lobes as measured by SPECT scans (Kinaci, et al. 1970). They received HBOT at 1.5 atm with 100% oxygen for an hour a day for 50 days. After their treatments, SPECT scans revealed that 82.40% showed improvements in their temporal lobes, 85.26% in their frontal lobes, and 75.75% in other areas. Furthermore, clinicians did an Autism Treatment Evaluation Checklist (ATEC) on 54 of the in-in Sociability, 79% in Speech/Language/Communication, 75.2% in Health/Physical/Behavior, and 87% in Sensory/Cognitive Awareness. This study revealed major improve-ments in the physical, behavioral and cerebral perfusion of children with ASD after HBOT (Kinaci, et al. 1970). This study is reliable due to the large sample size, unbiased SPECT imaging, and therapist assessments.Oxidative Stress in ASD and the Effects of HBOTproduction of reactive oxygen species (free radicals) and antioxidant defenses. Some children with ASD experience oxidative stress. Some researchers believe that HBOT in-directly causes an increase in oxidative stress due to the from the elevated oxygen levels (Alleva, et al. 2005). Therefore, they are reluctant to use HBOT on children with ASD, since some of them already have elevated oxi-dative stress levels (Rossignol, et al. 2007). A contributing factor to their increased oxidative stress levels might be due to the excessive amounts of oxygen supply to their cell’s mitochondria, which can escalate the production of ROS. In contrast, HBOT has proven to upregulate antiox-issues found in children with ASD such as glutathione peroxidase, superoxide dismutase (Gulec, et al. 2004), and catalase (Nie, et al. 2006). The antioxidant enzyme level increase can protect against harm initiated by ROS (Rossignol, 2007). Additionally, minor elevations in ROS created by HBOT can be advantageous, as they increase mitochondrial biogenesis (Gutsaeva, et al. 2006).        on oxidative stress in children with autism (Audhya, -ministering HBOT at 1.3 atm daily to 48 children with autism. Catalase, glutathione peroxidase and superoxide dismutase (SOD) levels were screened before beginning HBOT and again after day 1 and day 32 of HBOT (Audhya, 2007). Results demonstrated a 1.9-fold increase of the -provement after 32 days. Glutathione peroxidase showed a 1.4-fold increase after 1 day and a 1.2-fold increase after 32 days from the initial HBOT. Finally, a 4.5-fold increase of SOD was observed after 1 day and a 4.7-fold increase after 32 days of starting HBOT. The results of HBOT on antioxidant enzymes can be considered conditioning. The second study involved 18 autistic children from ages 3-16. This open label, prospective study included ad-ministering 40 treatments of HBOT, with 24% oxygen, at 1.3 atm, to 12 children, and 100% oxygen at 1.5 atm to 6 children. Blood markers were taken before and after 40 treatments (Rossignol, et al. 2007). Researchers noticed dramatic improvements in speech, socialization, GI func-tion, and strength. The effects persisted months after the      -es were seen in plasma-oxidized glutathione levels. This proves that oxidative stress markers did not worsen be-cause oxidized glutathione is transported from within the cells when intracellular levels surpass the redox capacity (Dickinson and Forman, 2002). However, the intracellu-lar oxidative stress levels in the children with ASD did not diminish with the lower HBOT pressures (Rossignol, et al. 2007). The open-label nature of this study and the two diverse treatment groups (one group who received 24% oxygen at 1.3 atm versus the other group who re-ceived 100% oxygen at 1.5 arm), as well as the absence of a control group, are some of the limitations of this study. Nonetheless, the prospective nature of this study strengthens it.     immune dysregulation as supported by recent studies. indicators in children with ASD. For instance, increases in Tumor Necrosis Factor-alpha (TNF-alpha) (Chez, et al. 2007), and neopterin (cellular immune system activation marker) (Messahel, et al. 1998), were related in studies of children with ASD. Additionally, studies showed that children with ASD, who reported having gastrointestinal            cytokines (including TNF-alpha, IL-1 and IL-6) (Weisz, et levels were reported after HBOT (Buras, et al. 2006). Moreover, improvements in IBD were reported in a systematic review that used HBOT (Rossignol 2012). A study reported a decrease in production of interfer-on-gamma by lymphocytes with HBOT at 2.0 atm/10.5% oxygen, but an increase in interferon-gamma with 100%

68Malky Meyeroxygen administered at 1.0 atm (Granowitz, et al. 2002). Therefore, it is concluded that the result of HBOT on       -sure-related component and not particularly on the de-livery of oxygen. Unfortunately, a series of recurring events can cause -bral hypoperfusion. This may cause hypoxia, which leads to production of HIF-1a (hypoxia-inducible factor-1alpha)       fundamental in the innate immune system, as it triggers    in children with ASD were inspected in two prospective        given 40 treatments of HBOT at 1.3 atm/24% oxygen and 6 children who were given HBOT at 1.5 atm/100% oxygen. Biomarkers were measured before and after the treatments by testing the participants’ blood specimens taken before and after the treatments (Rossignol, et al. 2007). Improvements were seen in C-reactive proteins       -creased in the total study population (p=0.021). The most levels of C-reactive proteins prior to the study. These children also showed behavioral improvements. SRS (Social Responsiveness Scale), ABC-C (Aberrant Behavior Checklist – Community), and ATEC (Autism Treatment were used to calculate the scores for each child before and after their treatments. The second study measured plasma cytokine levels, in-HBOT. Ten children with ASD participated in this 20 week study with 80 sessions of HBOT given to them at 1.5 atm/100% oxygen (Bent, et al. 2012). Although the study     -tions were observed in cytokines. Yet, the authors men-tioned that none of the children actually had irregular cytokine levels prior to the study, so notable variations could not be seen. In another study, a child with ASD who suffered from -      -ments of HBOT at 1.5 atm and 100% oxygen over the course of a month (Rossignol 2008).Mitochondrial Dysfunction in ASD and the Effects of HBOTMitochondrial dysfunction is observed in some people with ASD (Rossignol & Frye, 2011; Frye & Rossignol, 2011). HBOT is considered a possible treatment for mitochon-drial dysfunction, although treatments for this condition are minimal (Rossignol & Frye, 2011). The outcomes of HBOT on mitochondrial dysfunction were measured in various studies. In a controlled study HBOT at 1.5 atm and 100% oxygen was administered to 69 patients who obtained severe traumatic brain injury (TBI), within 24 hours of in-         and reduced CSF lactate levels (elevated CSF lactate is an indicator of mitochondrial dysfunction). Results also showed improvements in mitochondrial function and brain metabolism after contrasting both room air treat-ment of 21% oxygen and 100% oxygen given at normal pressure (1 atm) (Rockswold, et al. 2010).HBOT can make more electron transport chains in mitochondria. In 2008, a study was conducted on healthy rat tissue (Kurt, et al. 2008). HBOT was done on the rat and the tissues were looked at before and after the treat-ment. Results showed that the mitochondria were work-through physical exercise. During exercise, the cells are stressed and mitochondria are making more electron transport chains. Similarly, with HBOT, the cells are slight-ly stressed and they make more electron transport chains       oxidative stress. Furthermore, a study was conducted in 2006, which showed it is possible to increase the number of mito-chondria in the brain cells of rats. This phenomenon is called mitochondrial biogenesis (Gutsaeva et al. 2006). This was not demonstrated in humans, because it would require risky brain biopsies to be performed on patients. This can be one possible mechanism as to why HBOT is working. Although these results seem promising, no clin-ical studies were performed to test the effects of HBOT on mitochondrial dysfunction in children with ASD. Behavioral Measurements in ASD and the Effects of HBOTMost of the studies performed using HBOT for chil-dren with ASD have inquired behavioral rather than physiological factors. In a current systematic review, two double-blind, arbitrary, controlled trials were re-viewed regarding the use of HBOT in children with ASD of giving 33 children with ASD, 40 treatments of HBOT with 24% oxygen at 1.3 atm, which included 2 treatments each day for 5 days a week, over the course of 4 weeks. This study was performed in comparison to 29 control

69Is Hyperbaric Oxygen Therapy Effective For Treating Autism?children with ASD who were given room air that was slightly pressurized (1.03 atm/21% oxygen) (Rossignol, et al. 2009). Noteworthy improvements were detected in the treated children on the ATEC scales (questionnaire that measures changes in severity of ASD in response to treatment) by the caregiver, as well as on the CGI scales (Clinical Global Impression rating scales: measures the severity of symptoms, treatment response and the effec-tiveness of treatments) by the clinicians and parents. The results showed improvements in language, eye contact, cognitive attentiveness and overall functioning. Strengths of this study comprise of the involvement of 6 medical centers (which limited possible biases correlated to a    clinicians and the use of a control group.The second study examined the outcome of giving 18 children with ASD, 80 treatments of HBOT with 24% ox-ygen at 1.3 atm, within a 15 week duration. These results were compared to 16 children who were treated with a pressure. Subsequently, ABA therapy was given to both -ious behavioral scales (Granpeesheh, et al. 2010). These undesirable results can be attributed to the fact that rig-orous ABA therapy was given during the administration of HBOT which did not seem successful (Ghanizadeh, 2012). On the other hand, this study is reliable because of the blinded evaluators as well as the control group. The contrasting results can be ascribed to the discrepancies among the two controlled trials (Ghanizadeh, 2012). For example, the age and quantity differences of the partici-pants, as well as the magnitude of treatments. One study delivered 10 hours of HBOT per week (Rossignol, et al. 2009). While the other study provided 5 hours per week (Granpeesheh, et al. 2010). There were also probable dis-tinctions in ASD severity.Antagonistic Properties of HBOT in ASDAmong the many studies performed, minimal unfavorable outcomes were reported of HBOT usage for people with autism. One study stated that “HBOT was safely admin-istered to autistic children and all participants were able events” (Rossignol, et al. 2007). A different study informed minor antagonistic effects, including 4 kids with earaches, 2 kids with otitis media and other individuals who were autonomously affected with insomnia, seizures, lethargy,       2012). In a controlled study, one of the participants ex-perienced frequent urination and a skin rash which the doctor attributed to yeast as the causing factor. Other       child who experienced regressing symptoms of asth-ma after several HBOT treatments. The physicians did not think the two were related, but removed the child as a safeguard. Another child withdrew from the study before completing it due to anxiety. One participant in the control group experienced diarrhea and abdominal swelling, yet still completed the experiment. In addition, another control group participant experienced wors-ening of pre-existing eczema. Seizures or barotrauma, however, were not detected in neither the treatment nor control groups (Rossignol, et al. 2007). In a study per-formed on the effects of HBOT in Thai autistic children, it was reported in the data analysis that “there was no serious adverse effect in any case and tinnitus was a mild side effect in one case and it went away in one week” (Chungpaibulpatana, et al. 2008). According to the FDA, “patients receiving HBOT are at risk of suffering an injury that can be mild (such as sinus pain, ear pressure, painful joints) or serious (such as paralysis, or air embolism). Since hyperbaric chambers (FDA commissioner, 2013) .Restrictions of the Studies PerformedMost of the studies performed contain restraints that contribute to the erratic results among them, including the retrospective approaches, the absence of control participants and the minimal amount of participants. Moreover, the open trials increase bias, as both the par-ticipants and the researchers are aware which treatment is being given. However, two of the controlled studies did not contain these restraints. Furthermore, other studies         -ness (Jepson, et al. 2011). Unfortunately, the long-term effects of HBOT are unknown because once the study was complete researchers did not follow up on the long-lasting effects. Additionally, a majority of the studies       -     therapy in individuals with autism is only effective when done over a substantial period of time. For example, ABA      over a one to four year duration (Lovaas, 1987; Sallows & Graupner, 2005). in autistic children treated with HBOT to be observed before intellectual and developmental enhancements due to the intricacies of brain maturation. Studies have found 

70Malky Meyer    of the studies noted behavioral enhancements in sever-al children with autism, the studies only persisted for a few months. This short duration of time is not enough Further studies are necessary to investigate the long last-ing results of HBOT in people with autism. Many studies noted behavioral and physiological ad-vances when treating autistic children using HBOT. Yet, noteworthy developments were not found when re-searchers from a common group performed two studies (Granpeesheh, et al. 2010; Jepson, et al. 2011), and insig- (Lerman, et al. 2009). The inconsistent outcomes among the studies may be attributed to the autistic children’s opposing responses to HBOT (Jepson, et al. 2011). To illustrate, children who possess certain physiological ab-normalities such as mitochondrial dysfunction, cerebral display improvements. Nevertheless, most of the studies performed to test behavioral aspects did not analyze the chemical aspects such as levels of oxidative stress or in--participants already had regular cytokine levels prior to their HBOT treatment (Bent, et al. 2011).Further investigation is required including participants   -ities and which analyze variations in these physiological Noteworthy improvements were related in studies which administered HBOT sessions more frequently. This also seemed true in studies that used HBOT to treat patients with traumatic brain injuries, (Harch, et al. 2012). More studies, however, are needed to analyze several HBOT factors, such as the ideal oxygen and pressure limits re-quired to treat patients with ASD.HBOT in Thailand-termine the effects of HBOT to treat autistic children and whether it is safe or not (Chungpaibulpatana, et al. 2008). The study included 7 Thai autistic children who received 10 sessions of HBOT once a week at 1.3 atm. Before and development 2. Fine motor and Eye-hand coordination 3. Language development 4. Gross motor development 5. Self - help skills” (Chungpaibulpatana, et al. 2008). Results children who displayed progress while 25% showed no reaction to the treatment.FDA ApprovalAlthough HBOT is currently being used as a treatment method to treat various disorders in Thailand such as          the FDA to cure or be successful in the treatment of au-tism, cancer, or diabetes (FDA, 2013). However, the FDA did approve the use of HBOT for several other condi-tions. These include “treatment of air or gas embolism (dangerous ‘bubbles’ in the bloodstream that obstruct circulation), carbon monoxide poisoning, decompression sickness (‘the bends’), and thermal burns (caused by heat DisadvantagesDr. Paul Claus, medical director of Mayo Clinic’s Hyperbaric and Altitude Medicine Program, relates risk factors of HBOT. The increased oxygen of the chamber facility. Therefore, necessary precautions are taken. The patients are required to remove their street clothes since cotton blend clothing instead. Additionally, the treatments are quite expensive; they are approximately $1,500 an hour in most hospital settings (Claus, 2017). However, if more studies are done documenting improvements of HBOT, then hopefully the cost will be covered by the healthcare system or insurance companies to further Conclusion“There is no one-answer for many questions but there are many answers for one question. Multiple factors are the possible causes of autism. The curative factors may be from multidisciplinary approaches,” (Chungpaibulpatana, et al. 2008). Numerous studies have demonstrated that HBOT is an effective treatment for children with autism. The pressures utilized during treatment with HBOT (1.5 atm/100% oxygen maximum) are proven to improve the common physiological abnormalities in individuals with ASD; such as, cerebral hypoperfusion, oxidative stress, in-studies that targeted the behavioral measurements in ASD also showed positive results even though most of those studies did not use control groups. The two studies that did utilize control groups however related opposing outcomes. However, multiple crucial variations between the trials were noted. Taken together, the studies imply that the use of HBOT in children with autism correlates

71Is Hyperbaric Oxygen Therapy Effective For Treating Autism?with marginal antagonistic effects and is handled well. In       treatment for kids with autism. However, additional stud-ies are necessary before it can become an internationally accepted treatment method. Future studies should be -logical abnormalities within the various ASD subdivisions -ciency and determine which people can gain from HBOT treatment. Furthermore, why don’t the hospitals in Thailand publish anything regarding their routine HBOT usage? They value intellectual property not academic publications. If it were not more clinically effective than the use of HBOT would not be used regularly and its   studies performed, overall, the use of hyperbaric oxygen therapy appears to be a promising treatment for children with ASD.ReferencesAlleva R, Nasole E, Di Donato F, Borghi B, Neuzil J, Tomasetti M. Alpha-Lipoic acid supplementation inhibits oxidative damage, accelerating chronic wound healing in patients undergoing hyperbaric oxygen therapy. Biochem Biophys Res Commun. 2005;333(2):404–410. doi: 10.1016/j.bbrc.2005.05.119. Amen, D. G., Trujillo, M., Newberg, A., Willeumier, K., Tarzwell, R., Wu, J. C., & Chaitin, B. (2011, July 28). Brain SPECT Imaging in Complex Psychiatric Cases: An Evidence-Based, Underutilized Tool. Retrieved from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3149839/.American Psychiatric Association. (2013). Diagnostic and statistical manual of mental disorders. Washington, D.C.Ashwood P, Anthony A, Pellicer AA, Torrente F, Walker--tions in children with regressive autism: evidence for extensive mucosal immunopathology. J Clin Immunol. 2003;23(6):504–517. Audhya T. Adjustment of SOD, GPO & catalase activity in RBC of normal and autistic children during hyperoxia.Garden Grove, CA; 2007. Autism Research Institute Garden Grove Think Tank Meeting, 2007.Bent S, Bertoglio K, Ashwood P, Nemeth E, Hendren RL. Brief Report: Hyperbaric Oxygen Therapy (HBOT) in Children with Autism Spectrum Disorder: A Clinical Trial. J Autism Dev Disord. 2012 Jun;42(6):1127-32. doi: 10.1007/s10803-011-1337-3.Bjørklund, Geir, et al. “Cerebral Hypoperfusion in Autism Spectrum Disorder.” Acta Neurobiologiae Experimentalis, U.S. National Library of Medicine, 2018, https://www.ncbi.nlm.nih.gov/pubmed/29694338.Buras JA, Holt D, Orlow D, Belikoff B, Pavlides S, Reenstra WR. Hyperbaric oxygen protects from sepsis mortality via an interleukin-10-dependent mechanism. Crit Care Med. 2006;34(10):2624–2629. doi: 10.1097/01.CCM.0000239438.22758.E0.Chez MG, Dowling T, Patel PB, Khanna P, Kominsky M. Elevation of tumor necrosis factor-alpha in cerebrospinal 365. doi: 10.1016/j.pediatrneurol.2007.01.012.Chungpaibulpatana J, Sumpatanarax T, Thadakul N, Chantharatreerat C, Konkaew M, Aroonlimsawas M. Hyperbaric oxygen therapy in Thai autistic children. J Med Assoc Thai. 2008;91(8):1232–1238. https://www.ncbi.nlm.nih.gov/pubmed/18788696.Clarke, D. (2008). History of Hyperbaric Therapy. In T. S. Neuman & S. R. Thom (Eds.), Physiology and Medicine of Hyperbaric Oxygen Therapy (1st ed., pp. 3-23). Philadelphia: Saunders. Retrieved from ClinicalKey.Claus, P. Mayo Clinic Radio: Hyperbaric oxygen therapy. 2017. https://newsnetwork.mayoclinic.org/discussion/mayo-clinic-radio-hyperbaric-oxygen-therapy/.Cramer T, Yamanishi Y, Clausen BE, et al. HIF-1a Is 2003;112(5):645–57. Critchley HD, Daly EM, Bullmore ET, Williams SC, Van Amelsvoort T, Robertson DM, Rowe A, Phillips M, McAlonan G, Howlin P. et al.The functional neuroanat-omy of social behaviour: changes in cerebral blood expressions. Brain. 2000;123(Pt 11):2203–2212.Oxygen Therapy: Don’t Be Misled.” U.S. Food and Drug Administration, FDA, 23 Aug. 2013, https://www.fda.gov/consumers/consumer-updates/hyperbaric-oxygen-therapy-dont-be-misled.Dickinson DA, Forman HJ. Glutathione in defense and signaling; lessons from a small thiol. Ann N Y Acad Sci. 2002;973:488–504. doi: 10.1111/j.1749-6632.2002.tb04690.x. Eikeseth S, Smith T, Jahr E, Eldevik S. Intensive be-havioral treatment at school for 4- to 7-year-old children with autism. A 1-year comparison con-trolled study. Behav Modif. 2002;26(1):49–68. doi: 10.1177/0145445502026001004. Feldmeier JJ, Chairman and Editor. Hyperbaric oxygen

72Malky Meyer2003: indications and results: The hyperbaric oxygen therapy committee report. Kensington, MD: Undersea and Hyperbaric Medicine Society; 2003. Fontaine JA. Emploi chirurgical de l’air comprime. Union Med. 1879;28:445.Frye RE, Rossignol DA. Mitochondrial dysfunction can connect the diverse medical symptoms associated with autism spectrum disorders. Pediatr Res. 2011;69(5):41–47. doi: 10.1203/PDR.0b013e318212f16b.Ghanizadeh A. Hyperbaric oxygen therapy for treat-ment of children with autism, a systematic review of randomized trials. Med Gas Res. 2012;2(1):13. doi: 10.1186/2045-9912-2-13.Golden ZL, Neubauer R, Golden CJ, Greene L, Marsh J, Mleko A. Improvement in cerebral metabo-lism in chronic brain injury after hyperbaric oxygen therapy. Int J Neurosci. 2002;112(2):119–131. doi: 10.1080/00207450212027. Granowitz EV, Skulsky EJ, Benson RM, Wright J, Garb JL, Cohen ER, Smithline EC, Brown RB. Exposure to increased pressure or hyperbaric oxygen sup-presses interferon-gamma secretion in whole blood cultures of healthy humans. Undersea Hyperb Med. 2002;29(3):216–225.Granpeesheh D, Tarbox J, Dixon DR, Wilke AE, Allen MS, Bradstreet JJ. Randomized trial of hyperbaric oxygen therapy for children with autism. Research Autism Spectrum Disorders. 2010;4:268–275. doi: 10.1016/j.rasd.2009.09.014.Gulec B, Yasar M, Yildiz S, Oter S, Akay C, Deveci S, Sen D. Effect of hyperbaric oxygen on experimental acute distal colitis. Physiol Res. 2004;53(5):493–499. Gutsaeva DR, Suliman HB, Carraway MS, Demchenko IT, Piantadosi CA. Oxygen-induced mitochondrial biogenesis in the rat hippocampus. Neuroscience. 2006;137(2):493–504. doi: 10.1016/j.neuroscience.2005.07.061Harch P, Andrews SR, Fogarty E, Amen DG, Pezzullo JC, Lucarini J, Aubrey C, Taylor DV, Staab P, Van Meter K. A Phase I Study of Low Pressure Hyperbaric Oxygen Therapy for Blast-Induced Post-Concussion Syndrome and Post Traumatic Stress Disorder. J Neurotrauma. 2012;29(1):168–185. doi: 10.1089/neu.2011.1895.Herbert MR. Autism: a brain disorder or a disor-der that affects the brain. Clinical Neuropsychiatry. 2005;2(6):354–379. Heuser G, Heuser SA, Rodelander D, Aguilera O, Uszler M. In: Treatment of neurologically impaired adults and children with “mild” hyperbaric oxygenation (1.3 atm and 24 % oxygen). In Hyperbaric oxygenation for cerebral palsy and the brain-injured child. Joiner JT, editor. Flagstaff, Arizona: Best Publications; 2002.Jepson B, Granpeesheh D, Tarbox J, Olive ML, Stott Evaluation of the Effects of Hyperbaric Oxygen Therapy on the Behavior of 16 Children with Autism Spectrum Disorders. J Autism Dev Disord. 2011;41(5):575–588. doi: 10.1007/s10803-010-1075-y.Kinaci, et al. “The Effects of Hyperbaric Oxygen Therapy In Children With Autism Spectrum Disorders.” Rubicon Research Repository, Undersea and Hyperbaric Medical Society, 1 Jan. 1970, http://archive.rubicon-foundation.org/xmlui/handle/123456789/9163.Kurt, B., Kurt, Y., Karsliolu, Y., Topal, T., Erdamar, H., Korkmaz, A., … Günhan, O. (2008, April). Effects of hyperbaric oxygen on energy production and xanthine oxidase levels in striated muscle tissue of healthy rats. https://www.ncbi.nlm.nih.gov/pubmed/18280739Leach RM, Rees PJ, Wilmshurst P. Hyperbaric oxygen therapy. BMJ. 1998;317(7166):1140–1143. doi: 10.1136/bmj.317.7166.1140. Lerman DC, Sansbury T, Hovanetz A, Wolever E, Garcia A, O’Brien E, Adedipe H. Using behavior analysis to examine the outcomes of unproven therapies: An eval-uation of hyperbaric oxygen therapy for children with autism. Behavior Analysis in Practice. 2009;1(2):50–58.Lovaas OI. Behavioral treatment and normal educational and intellectual functioning in young autistic children. J Consult Clin Psychol. 1987;55(1):3–9.Messahel S, Pheasant AE, Pall H, Ahmed-Choudhury J, Sungum-Paliwal RS, Vostanis P. Urinary levels of neopterin and biopterin in autism. Neurosci Lett. 1998;241(1):17–20. doi: 10.1016/S0304-3940(97)00976-2.cell. Nature 2003;doi: 10.1038/422675aNie H, Xiong L, Lao N, Chen S, Xu N, Zhu Z. Hyperbaric oxygen preconditioning induces tolerance against spinal cord ischemia by upregulation of antioxidant enzymes in rabbits. J Cereb Blood Flow Metab. 2006;26(5):666–674. doi: 10.1038/sj.jcbfm.9600221. NIH CC: National Institutes of Health Clinical Center (CC). (2002, December 10). PET Scan to Study Brain Control of Human Movement. Retrieved from https://clinicaltrials.gov/ct2/show/NCT00001324.

73Is Hyperbaric Oxygen Therapy Effective For Treating Autism?Ohnishi T, Matsuda H, Hashimoto T, Kunihiro T, Nishikawa M, Uema T, Sasaki M. Abnormal regional cere-9):1838–1844. Rice C. Prevalence of autism spectrum disorders - Autism and Developmental Disabilities Monitoring Network, United States, 2006. MMWR Surveill Summ. 2009;58(10):1–20.Rockswold SB, Rockswold GL, Zaun DA, Zhang X, Cerra CE, Bergman TA, Liu J. A prospective, randomized clinical trial to compare the effect of hyperbaric to normobaric hyperoxia on cerebral metabolism, intracra-nial pressure, and oxygen toxicity in severe traumatic brain injury. J Neurosurg. 2010;112(5):1080–1094. doi: 10.3171/2009.7.JNS09363.Rossignol, DA, RE Frye. “A review of research trends in physiological abnormalities in autism spectrum disorders: mitochondrial dysfunction and environmental toxicant exposures.” Molecular psychiatry vol. 17,4 (2012): 389-401. doi:10.1038/mp.2011.165Rossignol DA, Frye RE. Mitochondrial dysfunction in autism spectrum disorders: a systematic review and meta-analysis. Mol Psychiatry. 2011;17(3):290–314.Rossignol DA. In: Hyperbaric oxygen for neurological disorders. Zhang JH, editor. Flagstaff, AZ: Best Publishing Company; 2008. The use of hyperbaric oxygen therapy in autism; pp. 209–258.Rossignol DA. “Hyperbaric oxygen therapy may im-prove symptoms in autistic children.” Med Hypotheses. Volume 67, Issue 2, 2006, Pages 216-228. https://doi.org/10.1016/j.mehy.2006.02.009Rossignol DA. Hyperbaric oxygen therapy might im-Med Hypotheses. 2007;68(6):1208–1227. doi: 10.1016/j.mehy.2006.09.064.-matory bowel disease: a systematic review and analysis. Med Gas Res. 2012;2(1):6. doi: 10.1186/2045-9912-2-6. Rossignol DA, Rossignol LW, James SJ, Melnyk S, Mumper E. The effects of hyperbaric oxygen therapy on with autism: an open-label pilot study. BMC Pediatr. 2007;7(1):36. doi: 10.1186/1471-2431-7-36.Rossignol DA, Rossignol LW, Smith S, Schneider C, Logerquist S, Usman A, Neubrander J, Madren EM, Hintz G, Grushkin B. et al.Hyperbaric treatment for children with autism: a multicenter, randomized, double-blind, controlled trial. BMC Pediatr. 2009;9:21. doi: 10.1186/1471-2431-9-21.Sallows GO, Graupner TD. Intensive behavioral treat-ment for children with autism: four-year outcome and predictors. Am J Ment Retard. 2005;110(6):417–438. doi: 10.1352/0895-8017(2005)110[417:IBTFCW]2.0.CO;2.Schaefer GB, Mendelsohn NJ. Genetics evaluation for the etiologic diagnosis of autism spectrum dis-orders. Genet Med. 2008;10(1):4–12. doi: 10.1097/GIM.0b013e31815efdd7.Starkstein SE, Vazquez S, Vrancic D, Nanclares V, retarded autistic individuals. J Neuropsychiatry Clin Neurosci. 2000;12(3):370–375. doi: 10.1176/appi.neuropsych.12.3.370. Weisz G, Lavy A, Adir Y, Melamed Y, Rubin D, Eidelman S, IL-1, and IL-6 secretion by circulating monocytes during hyperbaric oxygen treatment in patients with perianal Crohn’s disease. J Clin Immunol. 1997;17(2):154–159. doi: 10.1023/A:1027378532003.Wilcox J, Tsuang MT, Ledger E, Algeo J, Schnurr T. Brain perfusion in autism varies with age. Neuropsychobiology. 2002;46(1):13–16. doi: 10.1159/000063570.