Effect of hyperbaric oxygenation on intracranial pressure elevation rate in rats during the early phase of severe traumatic brain injury

A review on the neuroprotective effects of hyperbaric oxygen therapy

Hyperbaric oxygen therapy, intermittent breathing of 100% oxygen at a pressure upper than sea level, has been shown to be some of the neuroprotective effects and used therapeutically in a wide range of neurological disorders. This review summarizes current knowledge about the neuroprotective effects of hyperbaric oxygen therapy with their molecular mechanisms in different models of neurological disorders.

Intracranial Pressure Monitoring in Experimental Traumatic Brain Injury: Implications for Clinical Management

Traumatic brain injury (TBI) is often associated with long-term disability and chronic neurological sequelae. One common contributor to unfavorable outcomes is secondary brain injury, which is potentially treatable and preventable through appropriate management of patients in the neurosurgical intensive care unit. Intracranial pressure (ICP) is currently the predominant neurological-specific physiological parameter used to direct the care of severe TBI (sTBI) patients. However, recent clinical evidence has called into question the association of ICP monitoring with improved clinical outcome. The detailed cellular and molecular derangements associated with intracranial hypertension (IC-HTN) and their relationship to injury phenotype and neurological outcomes are not completely understood. Various animal models of TBI have been developed, but the clinical applicability of ICP monitoring in the pre-clinical setting has not been well-characterized. Linking basic mechanistic studies in translational TBI models with investigation of ICP monitoring that more faithfully replicates the clinical setting will provide clinical investigators with a more informed understanding of the pathophysiology of IC-HTN, thus facilitating development of improved therapies for sTBI patients.

Sex Hormones Response to Physical Hyperoxic and Hyperbaric Stress in Male Scuba Divers: A Pilot Study

The use of hyperbaric oxygen plays a significant role in many aspects of medicine. However, there are few studies that analyzed the role of hyperbaric oxygen, in addition to physical exercise, on the endocrine profile. The aim of this study was to compare changes in plasma male sex hormones after hyperbaric physical exercise with different hyperbaric oxygen pre-conditionings. We recruited six healthy, well-trained recreational male divers. Concentrations of prolactin (PRL), follicle-stimulating hormone (FSH), luteotrophic hormone (LH), cortisol, 17-β estradiol (E2), and total testosterone (TT) were measured in venous blood immediately after four different study conditions. Exercise increased PRL and hyperbaric oxygen potentiated this effect. Hyperbaria stimulated the E2 reduction and hyperoxia partially inhibited this reduction. Hyperbaria, but not hyperoxia, stimulated the TT reduction. There were no changes in FSH, LH, and cortisol. The increase in PRL likely reflects a stress response after physical exercise, amplified by hyperbaric oxygen. TT reduction may be interpreted as an acute and transient fertility impairment. Age, blood pressure, and BMI were taken into account as covariates for statistical analyses, and they significantly affected the results, in particular TT. These data open new insight into the role of E2 and PRL in male endocrine adaptive responses.

Aqueous Date Fruit Efficiency as Preventing Traumatic Brain Deterioration and Improving Pathological Parameters after Traumatic Brain Injury in Male Rats

Objective

Following traumatic brain injury, disruption of blood-brain-barrier and consequent brain edema are critical events which might lead to increasing intracranial pressure (ICP), and nerve damage. The current study assessed the effects of aqueous date fruit extract (ADFE) on the aforementioned parameters.

Materials and Methods

In this experimental study, diffused traumatic brain injury (TBI) was generated in adult male rats using Marmarou’s method. Experimental groups include two pre-treatment (oral ADFE, 4 and 8 mL/kg for 14 days), vehicle (distilled water, for 14 days) and sham groups. Brain edema and neuronal injury were measured 72 hours after TBI. Veterinary coma scale (VCS) and ICP were determined at -1, 4, 24, 48 and 72 hours after TBI. Differences among multiple groups were assessed using ANOVA. Turkey’s test was employed for the ANOVA post-hoc analysis. The criterion of statistical significance was sign at P<0.05.

Results

Brain water content in ADFE-treated groups was decreased in comparison with the TBI+vehicle group. VCS at 24, 48 and 72 hours after TBI showed a significant increase in ADFE groups in comparison with the TBI+vehicle group. ICP at 24, 48 and 72 hours after TBI, was decreased in ADFE groups, compared to the TBI+vehicle. Brain edema, ICP and neuronal injury were also decreased in ADFE group, but VCS was increased following on TBI.

Conclusion

ADFE pre-treatment demonstrated an efficient method for preventing traumatic brain deterioration and improving pathological parameters after TBI.

Hyperbaric oxygen therapy for traumatic brain injury: bench-to-bedside

Traumatic brain injury (TBI) is a serious public health problem in the United States. Survivors of TBI are often left with significant cognitive, behavioral, and communicative disabilities. So far there is no effective treatment/intervention in the daily clinical practice for TBI patients. The protective effects of hyperbaric oxygen therapy (HBOT) have been proved in stroke; however, its efficiency in TBI remains controversial. In this review, we will summarize the results of HBOT in experimental and clinical TBI, elaborate the mechanisms, and bring out our current understanding and opinions for future studies.

Trending autoregulatory indices during treatment for traumatic brain injury

Our goal is to use automatic data monitoring for reliable prediction of episodes of intracranial hypertension in patients with traumatic brain injury. Here we test the validity of our method on retrospective patient data. We developed the Continuous Hemodynamic Autoregulatory Monitor (CHARM), that siphons and stores signals from existing monitors in the surgical intensive care unit (SICU), efficiently compresses them, and standardizes the search for statistical relationships between any proposed index and adverse events. CHARM uses an automated event detector to reliably locate episodes of elevated intracranial pressure (ICP), while eliminating artifacts within retrospective patient data. A graphical user interface allowed data scanning, selection of criteria for events, and calculating indices. The pressure reactivity index (PRx), defined as the least square linear regression slope of intracranial pressure versus arterial BP, was calculated for a single case that spanned 259 h. CHARM collected continuous records of ABP, ICP, ECG, SpO2, and ventilation from 29 patients with TBI over an 18-month period. Analysis of a single patient showed that PRx data distribution in the single hours immediately prior to all 16 intracranial hypertensive events, significantly differed from that in the 243 h that did not precede such events (p < 0.0001). The PRx index, however, lacked sufficient resolution as a real-time predictor of IH in this patient. CHARM streamlines the search for reliable predictors of intracranial hypertension. We report statistical evidence supporting the predictive potential of the pressure reactivity index.

Decompressive craniectomy reduces white matter injury after controlled cortical impact in mice

Reduction and avoidance of increases in intracranial pressure (ICP) after severe traumatic brain injury (TBI) continue to be the mainstays of treatment. Traumatic axonal injury is a major contributor to morbidity after TBI, but it remains unclear whether elevations in ICP influence axonal injury. Here we tested the hypothesis that reduction in elevations in ICP after experimental TBI would result in decreased axonal injury and white matter atrophy in mice. Six-week-old male mice (C57BL/6J) underwent either moderate controlled cortical impact (CCI) (n=48) or Sham surgery (Sham, n=12). Immediately after CCI, injured animals were randomized to a loose fitting plastic cap (Open) or replacement of the previously removed bone flap (Closed). Elevated ICP was observed in Closed animals compared with Open and Sham at 15 min (21.4±4.2 vs. 12.3±2.9 and 8.8±1.8 mm Hg, p<0.0001) and 1 day (17.8±3.7 vs. 10.6±2.0 and 8.9±1.9 mm Hg, p<0.0001) after injury. Beta amyloid precursor protein staining in the corpus callosum and ipsilateral external capsule revealed reduced axonal swellings and bulbs in Open compared with Closed animals (32% decrease, p<0.01 and 40% decrease, p<0.001 at 1 and 7 days post-injury, respectively). Open animals were also found to have decreased neurofilament-200 stained axonal swellings at 7 days post-injury compared with Open animals (32% decrease, p<0.001). At 4 weeks post-injury, Open animals had an 18% reduction in white matter volume compared with 34% in Closed animals (p<0.01). Thus, our results indicate that CCI with decompressive craniectomy was associated with reductions in ICP and reduced pericontusional axonal injury and white matter atrophy. If similar in humans, therapeutic interventions that ameliorate intracranial hypertension may positively influence white matter injury severity.

Repetitive long-term hyperbaric oxygen treatment (HBOT) administered after experimental traumatic brain injury in rats induces significant remyelination and a recovery of sensorimotor function

Cells in the central nervous system rely almost exclusively on aerobic metabolism. Oxygen deprivation, such as injury-associated ischemia, results in detrimental apoptotic and necrotic cell loss. There is evidence that repetitive hyperbaric oxygen therapy (HBOT) improves outcomes in traumatic brain-injured patients. However, there are no experimental studies investigating the mechanism of repetitive long-term HBOT treatment-associated protective effects. We have therefore analysed the effect of long-term repetitive HBOT treatment on brain trauma-associated cerebral modulations using the lateral fluid percussion model for rats. Trauma-associated neurological impairment regressed significantly in the group of HBO-treated animals within three weeks post trauma. Evaluation of somatosensory-evoked potentials indicated a possible remyelination of neurons in the injured hemisphere following HBOT. This presumption was confirmed by a pronounced increase in myelin basic protein isoforms, PLP expression as well as an increase in myelin following three weeks of repetitive HBO treatment. Our results indicate that protective long-term HBOT effects following brain injury is mediated by a pronounced remyelination in the ipsilateral injured cortex as substantiated by the associated recovery of sensorimotor function.

[Hyperbaric oxygen therapy and inert gases in cerebral ischemia and traumatic brain injury]

Cerebral ischemia is a common thread of acute cerebral lesions, whether vascular or traumatic origin. Hyperbaric oxygen (HBO) improves tissue oxygenation and may prevent impairment of reversible lesions. In experimental models of cerebral ischemia or traumatic brain injury, HBO has neuroprotective effects which are related to various mechanisms such as modulation of oxidative stress, neuro-inflammation or cerebral and mitochondrial metabolism. However, results of clinical trials failed to prove any neuroprotective effects for cerebral ischemia and remained to be confirmed for traumatic brain injury despite preliminary encouraging results. The addition of inert gases to HBO sessions, especially argon or xenon which show neuroprotective experimental effects, may provide an additional improvement of cerebral lesions. Further multicentric studies with a strict methodology and a better targeted definition are required before drawing definitive conclusions about the efficiency of combined therapy with HBO and inert gases in acute cerebral lesions.

Study of cell apoptosis in the hippocampus and thalamencephalon in a ventricular fluid impact model

The aim of this study was to investigate the apoptosis of nerve cells in the hippocampal and thalamencephalon regions using a rabbit model of ventricular fluid impact. The results for the study demonstrated a variety of pathophysiological changes in the rabbit model, while changes in the hippocampal and thalamencephalon regions were observed under a light microscope following hematoxylin and eosin (H&E)/terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining. Among the mild, moderate and severe injury groups, there were significant differences in the mortality rate and in the changes in vital signs and consciousness recovery time following trauma. Furthermore, H&E staining showed that pathological changes, such as hemorrhage and necrosis, occurred in the hippocampal and thalamencephalon regions at an early stage subsequent to trauma, while TUNEL staining showed that neuronal apoptosis occurred in the various injury groups. In traumatic brain injuries, the impact caused by cerebrospinal fluid moving with a certain energy results in marked damage to the contralateral periventricular structures and may generate a series of pathophysiological changes.

Effect of melatonin on intracranial pressure and brain edema following traumatic brain injury: role of oxidative stresses

BACKGROUND AND AIMS

Traumatic brain injury (TBI) is one of the main causes of brain edema and increased intracranial pressure (ICP). In the clinic it is essential to limit the development of ICP after TBI. In the present study, the effects of melatonin on these parameters at different time points and alterations of oxidant factors as one of the probable involved mechanisms have been evaluated.

METHODS

Albino N-Mary rats were divided into five groups of sham, TBI, TBI + vehicle, TBI + Mel5 and TBI + Mel20. Brain injury was induced by Marmarou method. Melatonin was injected i.p. at 1, 24, 48 and 72 h after brain trauma. Brain water and Evans blue dye contents as well as oxidant/antioxidant factors were measured 72 h after TBI. ICP and neurological scores were determined at -1, 1, 24, 48 and 72 h post-TBI.

RESULTS

Brain water and Evans blue dye contents in melatonin-treated groups decreased as compared to the TBI + vehicle group (p <0.001). Veterinary coma scale (VCS) at 24, 48 and 72 h after TBI showed a significant increase in melatonin groups (TBI + Mel5: p <0.01 and TBI + Mel20: p <0.001) in comparison to the TBI + vehicle group. ICP at 24, 48 and 72 h after TBI decreased in melatonin groups as compared to the TBI + vehicle group (p <0.001). Superoxide dismutase and glutathione peroxidase activities showed a significant increase, whereas malondialdehyde level in these groups was significantly lower in melatonin groups in comparison to the TBI + vehicle group (p <0.001).

CONCLUSION

Melatonin decreases brain edema, BBB permeability and ICP, but increases VCS after TBI. These effects are probably due to inhibition of oxidative stress.

A prospective, randomized Phase II clinical trial to evaluate the effect of combined hyperbaric and normobaric hyperoxia on cerebral metabolism, intracranial pressure, oxygen toxicity, and clinical outcome in severe traumatic brain injury

OBJECT

Preclinical and clinical investigations indicate that the positive effect of hyperbaric oxygen (HBO2) for severe traumatic brain injury (TBI) occurs after rather than during treatment. The brain appears better able to use baseline O2 levels following HBO2 treatments. In this study, the authors evaluate the combination of HBO2 and normobaric hyperoxia (NBH) as a single treatment.

METHODS

Forty-two patients who sustained severe TBI (mean Glasgow Coma Scale [GCS] score 5.7) were prospectively randomized within 24 hours of injury to either: 1) combined HBO2/NBH (60 minutes of HBO2 at 1.5 atmospheres absolute [ATA] followed by NBH, 3 hours of 100% fraction of inspired oxygen [FiO2] at 1.0 ATA) or 2) control, standard care. Treatments occurred once every 24 hours for 3 consecutive days. Intracranial pressure, surrogate markers for cerebral metabolism, and O2 toxicity were monitored. Clinical outcome was assessed at 6 months using the sliding dichotomized Glasgow Outcome Scale (GOS) score. Mixed-effects linear modeling was used to statistically test differences between the treatment and control groups. Functional outcome and mortality rates were compared using chi-square tests.

RESULTS

There were no significant differences in demographic characteristics between the 2 groups. In comparison with values in the control group, brain tissue partial pressure of O2 (PO2) levels were significantly increased during and following combined HBO2/NBH treatments in both the noninjured and pericontusional brain (p < 0.0001). Microdialysate lactate/pyruvate ratios were significantly decreased in the noninjured brain in the combined HBO2/NBH group as compared with controls (p < 0.0078). The combined HBO2/NBH group's intracranial pressure values were significantly lower than those of the control group during treatment, and the improvement continued until the next treatment session (p < 0.0006). The combined HBO2/NBH group's levels of microdialysate glycerol were significantly lower than those of the control group in both noninjured and pericontusional brain (p < 0.001). The combined HBO2/NBH group's level of CSF F2-isoprostane was decreased at 6 hours after treatment as compared with that of controls, but the difference did not quite reach statistical significance (p = 0.0692). There was an absolute 26% reduction in mortality for the combined HBO2/NBH group (p = 0.048) and an absolute 36% improvement in favorable outcome using the sliding dichotomized GOS (p = 0.024) as compared with the control group.

CONCLUSIONS

In this Phase II clinical trial, in comparison with standard care (control treatment) combined HBO2/NBH treatments significantly improved markers of oxidative metabolism in relatively uninjured brain as well as pericontusional tissue, reduced intracranial hypertension, and demonstrated improvement in markers of cerebral toxicity. There was significant reduction in mortality and improved favorable outcome as measured by GOS. The combination of HBO2 and NBH therapy appears to have potential therapeutic efficacy as compared with the 2 treatments in isolation. CLINICAL TRIAL REGISTRATION NO.: NCT00170352 (ClinicalTrials.gov).

Shedding light on mitochondrial function by real time monitoring of NADH fluorescence: I. Basic methodology and animal studies

Normal mitochondrial function in the process of metabolic energy production is a key factor in maintaining cellular activities. Many pathological conditions in animals, as well as in patients, are directly or indirectly related to dysfunction of the mitochondria. Monitoring the mitochondrial activity by measuring the autofluorescence of NADH has been the most practical approach since the 1950s. This review presents the principles and technological aspects, as well as typical results, accumulated in our laboratory since the early 1970s. We were able to apply the fiber-optic-based NADH fluorometry to many organs monitored in vivo under various pathophysiological conditions in animals. These studies were the basis for the development of clinical monitoring devices as presented in accompanying article. The encouraging experimental results in animals stimulated us to apply the same technology in patients after technological adaptations as described in the accompanying article. Our medical device was approved for clinical use by the FDA.

Brain tissue oxygen monitoring and hyperoxic treatment in patients with traumatic brain injury

Cerebral ischemia is a well-recognized contributor to high morbidity and mortality after traumatic brain injury (TBI). Standard of care treatment aims to maintain a sufficient oxygen supply to the brain by avoiding increased intracranial pressure (ICP) and ensuring a sufficient cerebral perfusion pressure (CPP). Devices allowing direct assessment of brain tissue oxygenation have showed promising results in clinical studies, and their use was implemented in the Brain Trauma Foundation Guidelines for the treatment of TBI patients in 2007. Results of several studies suggest that a brain tissue oxygen-directed therapy guided by these monitors may contribute to reduced mortality and improved outcome of TBI patients. Whether increasing the oxygen supply to supraphysiological levels has beneficial or detrimental effects on TBI patients has been a matter of debate for decades. The results of trials of hyperbaric oxygenation (HBO) have failed to show a benefit, but renewed interest in normobaric hyperoxia (NBO) in the treatment of TBI patients has emerged in recent years. With the increased availability of advanced neuromonitoring devices such as brain tissue oxygen monitors, it was shown that some patients might benefit from this therapeutic approach. In this article, we review the pathophysiological rationale and technical modalities of brain tissue oxygen monitors, as well as its use in studies of brain tissue oxygen-directed therapy. Furthermore, we analyze hyperoxia as a treatment option in TBI patients, summarize the results of clinical trials, and give insights into the recent findings of hyperoxic effects on cerebral metabolism after TBI.

Hyperbaric oxygenation improves locomotor ability by enhancing neuroplastic responses after cortical ablation in rats

OBJECTIVE

To investigate whether hyperbaric oxygenation (HBO) can improve the recovery of motor functions in rats after suction ablation of the right sensorimotor cortex.

METHODS

The experimental paradigm implies the following groups: Control animals (C), Control + HBO (CHBO), Sham controls (S), Sham control + HBO (SHBO), Lesion group (L), right sensorimotor cortex was removed by suction, Lesion + HBO (LHBO). Hyperbaric protocol: pressure applied 2.5 atmospheres absolute, for 60 minutes, once a day for 10 days. A beam walking test and grip strength meter were used to evaluate the recovery of motor functions. Expression profiles of growth-associated protein 43 (GAP43) and synaptophysin (SYP) were detected using immunohistochemistry.

RESULTS

The LHBO group achieved statistically superior scores in the beam walking test compared to the L group. Additionally, the recovery of muscle strength of the affected hindpaw was significantly enhanced after HBO treatment. Hyperbaric oxygenation induced over-expression of GAP43 and SYP in the neurons surrounding the lesion site.

CONCLUSIONS

Data presented suggest that hyperbaric oxygen therapy can intensify neuroplastic responses by promoting axonal sprouting and synapse remodelling, which contributes to the recovery of locomotor performances in rats. This provides the perspective for implementation of HBO in clinical strategies for treating traumatic brain injuries.

Neuroprotective effects of hyperbaric oxygen treatment on traumatic brain injury in the rat

This study was designed to evaluate the potential benefits of hyperbaric oxygen (HBO) in the treatment of traumatic brain injury (TBI). The right cerebral cortex of rats was injured by the impact of a 20-g object dropped from a predetermined height. The rats received HBO treatment at 3 ATA for 60 min after TBI. Neurological behavior score, brain water content, neuronal loss in the hippocampus, and cell apoptosis in brain tissue surrounding the primary injury site were examined to determine brain damage severity. Three and six hours after TBI, HBO-treated rats displayed a significant reduction in brain damage. However, by 12 h after TBI, the efficacy of HBO treatment was considerably attenuated. Furthermore, at 24, 48, and 72 h after TBI, the HBO treatment did not show any notable effects. In contrast, multiple HBO treatments (three or five times in all), even when started 48 h after TBI, remarkably reduced neurology deficit scores and the loss of neuronal numbers in the hippocampus. Although multiple treatments started at 48 h significantly improved neurological behaviors and reduced brain injury, the overall beneficial effects were substantially weaker than those seen after a single treatment at 6 h. These results suggest that: (1) HBO treatment could alleviate brain damage after TBI; (2) a single treatment with HBO has a time limitation of 12 h post-TBI; and (3) multiple HBO treatments have the possibility to extend the post-TBI delivery time window. Therefore, our results clearly suggest the validity of HBO therapy for the treatment of TBI.

Effect of sex steroid hormones on brain edema, intracranial pressure, and neurologic outcomes after traumatic brain injury

Recent studies have reported that estrogen and progesterone have a neuroprotective effect after traumatic brain injury (TBI); however, the mechanism(s) for this effect have not yet been elucidated. The aim of the present study was to investigate the role of sex steroid hormones on changes in brain edema, intracranial pressure (ICP), and cerebral perfusion pressure (CPP) after TBI in ovariectomized (OVX) rats. In this study, 50 female rats were divided into 5 groups: control (intact), sham, and 3 TBI groups consisting of vehicle, estrogen (1 mg/kg), and progesterone (8 mg/kg). TBI was induced by the Marmarou method, and the hormones were injected i.p. 30 min after TBI. ICP was measured in the spinal cord, and CPP was calculated by subtracting the mean arterial pressure (MAP) from ICP. The results revealed that brain water content after TBI was lower (p < 0.001) in the estrogen and progesterone groups than in the vehicle group. After trauma, ICP was significantly higher in TBI rats (p < 0.001). The ICP in the estrogen and progesterone groups decreased at 4 and 24 h after TBI compared with vehicle (p < 0.001 and p < 0.05, respectively). The CPP in the estrogen and progesterone groups increased after 24 h compared with vehicle (p < 0.001). Also after TBI, the neurological score (veterinary coma scale) was significantly higher than vehicle at 1 h (p < 0.01) and 24 h (p < 0.001) in the group treated with estrogen. In conclusion, pharmacological doses of estrogen and progesterone improved ICP, CPP, and neurological scores after TBI in OVX rats, which implies that these hormones play a neuroprotective role in TBI.

Protective effect of hyperbaric oxygen therapy on experimental brain contusions

BACKGROUND

We evaluated the effect of hyperbaric oxygen therapy (HBO) on experimental brain contusions in rats using magnetic resonance imaging (MRI).

MATERIALS AND METHODS

Ten Sprague-Dawley rats were investigated at 24 h and 72 h after controlled cortical impact injury. One hour after trauma, 5 rats were treated for 60 min with 100% oxygen at 2.5 absolute atmosphere (ATA), 5 were kept at normobaric room air. MRI was performed longitudinally at 24 h and 72 h after injury. Lesion volume was determined in T2 weighted MRI scans. Relative apparent diffusion coefficient (ADC) changes were calculated in comparison to the contralateral side.

RESULTS

Following HBO, T2 lesion volume was smaller at 24 h versus controls (63.1 +/- 16.5 mm3 vs. 87.4 +/- 13.8 mm3, p < 0.05), and decreased further at 72 h (46.8 +/- 17.8 mm3 vs. 92.5 +/- 13.1 mm3, p < 0.01). At 24 h, the mean relative ADC change in the lesion area decreased from + 26.8 +/- 2.3% in controls to + 2.3 +/- 12.2% in HBO animals (p < 0.01). At 72 h, the HBO effect on relative ADC values was less when compared to 24 h.

DISCUSSION

A 60-minute exposure to hyperbaric oxygen starting 1 h after impact injury significantly attenuated lesion growth and relative increase of ADC values within the contused area for up to 72 h. Thus, a "single-shot" HBO treatment seems to have long-lasting neuroprotective effects on the contused brain and its penumbra.

Hyperbaric oxygen therapy and cerebral ischemia: neuroprotective mechanisms

INTRODUCTION

Numerous studies have demonstrated a protective effect of hyperbaric oxygen therapy in experimental ischemic brain injury, and many physiological and molecular mechanisms of hyperbaric oxygen therapy-related neuroprotection have been identified.

METHODS

Review of articles pertaining to hyperbaric oxygen therapy and cerebral ischemia in the National Library of Medicine and National Institutes of Health database, emphasizing mechanisms of hyperbaric oxygen therapy-related neuroprotection.

RESULTS

Hyperbaric oxygen therapy has been shown to ameliorate brain injury in a variety of animal models including focal cerebral ischemia, global cerebral ischemia, neonatal hypoxia-ischemia and subarachnoid hemorrhage. Small human trials of hyperbaric oxygen therapy in focal ischemia have not shown benefit, although one trial of hyperbaric oxygen therapy before cardiopulmonary bypass demonstrated improved neuropsychological and inflammatory outcomes with hyperbaric oxygen therapy. Hyperbaric oxygen therapy is associated with improved cerebral oxygenation, reduced blood-brain barrier breakdown, decreased inflammation, reduced cerebral edema, decreased intracranial pressure, reduced oxidative burden, reduced metabolic derangement, decreased apoptotic cell death and increased neural regeneration.

CONCLUSION

On a molecular level, hyperbaric oxygen therapy leads to activation of ion channels, inhibition of hypoxia inducible factor-1alpha, up-regulation of Bcl-2, inhibition of MMP-9, decreased cyclooxygenase-2 activity, decreased myeloperoxidase activity, up-regulation of superoxide dismutase and inhibition of Nogo-A (an endogenous growth-inhibitory factor). Ongoing research will continue to describe the mechanisms of hyperbaric oxygen therapy-related neuroprotection, and possibly expand hyperbaric oxygen therapy use clinically.

Hyperbaric oxygen and cerebral physiology

Hyperbaric oxygen (HBO) therapy is defined by the Undersea and Hyperbaric Medical Society (UHMS) as a treatment in which a patient intermittingly breathes 100% oxygen under a pressure that is greater than the pressure at sea level [a pressure greater than 1 atmosphere absolute (ATA)]. HBO has been shown to be a potent means to increase the oxygen content of blood and has been advocated for the treatment of various ailments, including air embolism, carbon monoxide poisoning, wound healing and ischemic stroke. However, definitive established mechanisms of action are still lacking. This has led to uncertainty among clinicians, who have understandingly become hesitant in regard to using HBO therapy, even in situations where it could prove beneficial. Therefore, this review will summarize the literature regarding the effects of HBO on brain oxygenation, cerebral blood flow and intracranial pressure in both the healthy and injured brains, as well as discuss how changes in these three factors can impart protection.