Cognitive performance during a simulated climb of Mount Everest: implications for brain function and central adaptive processes under chronic hypoxic stress

A review of methods for assessment of cognitive function in high-altitude hypoxic environments

Hypoxic environments like those present at high altitudes may negatively affect brain function. Varying levels of hypoxia, whether acute or chronic, are previously shown to impair cognitive function in humans. Assessment and prevention of such cognitive impairment require detection of cognitive changes and impairment using specific cognitive function assessment tools. This paper summarizes the findings of previous research, outlines the methods for cognitive function assessment used at a high altitude, elaborates the need to develop standardized and systematic cognitive function assessment tools for high-altitude hypoxia environments.

Impaired Neurological Activity in the Mental Rotation Ability of Tibetan Indigenous Residents After Chronic Exposure to High Altitude

Mental rotation is a core indicator of spatial ability, and a threshold for cognitive impairment may exist at approximately 4,000 m above sea level, but the specific thresholds for the severity of hypoxia in Tibetan indigenous populations in mental rotation ability remain largely unknown. To determine whether a threshold for mental rotation impairment exists in indigenous residents, we related a mental rotation task to inter-individual differences in a range of behavioral performance and neuropsychological characteristics across 51 indigenous Tibetan highlanders and 34 matched controls at three different altitudes (sea level, 2,900 m, and 4,200 m). Analyses of reaction time showed delayed behavioral responses in the 4,200 m altitude group. Further analyses of rotation-related negativity (RRN) revealed that the RRN was significantly more negative and the differences disappeared gradually for different angles among individuals exposed to an altitude of 4,200 m. Moreover, a time-frequency analysis showed significantly enhanced alpha- and beta-band power values for the 4,200 m altitude participants after stimulus presentation. The impairment in mental rotation ability is related to hypoxia and can be attributed to the absence of sufficient cognitive resources, which demonstrates the existence of a threshold for the effects of high altitude on the brain's mental rotation ability. Taken together, our findings have important implications for exploring the altitude threshold for the influence of high-altitude exposure on brain function, as well as for guiding the development of innovative strategies to optimize the response of the organism against chronic hypoxia-induced under extreme environments.

Association between the acceleration of access to visual awareness of grating orientation with higher heart rate at high-altitude

Many studies have indicated a strong relationship between cardiac and brain activities, both of which are sensitive to high-altitude exposure. This study combined a consciousness access task and electrocardiograms (ECG) to uncover conscious awareness in response to high-altitude exposure and its relation to cardiac activity. When compared with the low-altitude groups, the behavioral results showed that the high-altitude participants shortened the time of access to visual awareness of grating orientation, which was accompanied by a faster heart rate, excluding the influence of pre-stimulus heart rate, extent of cardiac deceleration after presenting the stimulus, and task difficulty. Although there were post-stimulation cardiac deceleration and post-response acceleration at both high and low altitudes, a slight increase in heart rate after stimulation at high altitudes may indicate that participants at high altitudes could quickly readjust their attention to the target stimulus. More importantly, the drift diffusion model (DDM) was used to fit the access time distribution of all participants. These results suggest that shorter time at high altitudes might be due to the lower threshold, suggesting that less evidence in high-altitude participants was required to access visual consciousness. The participants' heart rates also negatively predicted the threshold through a hierarchical drift diffusion modeling (HDDM) regression. These findings imply that individuals with higher heart rates at high altitudes have a greater cognitive burden.

Neurodynamics of awareness detection in Tibetan immigrants: evidence from EEG analysis

The psychological effects of long-term exposure to high-altitude environments have attracted great attention. These effects are usually attributed to the diminished cognitive resources due to high-altitude exposure. This study employed electroencephalography (EEG) to investigate the effects of exposure duration on awareness detection tasks. Neither reaction time nor accuracy showed the direct effects of the exposure duration, so did the model indexes obtained from drift diffusion model analysis. However, event-related potentials (ERP) analysis revealed that exposure duration was associated with changes in the visual awareness negativity (VAN) and the late positivity (LP) components, which in turn affected reaction time. Specifically, longer exposure durations were associated with lower VAN and higher LP, resulting in shorter reaction times and greater drift rate. In contrast to previous studies, the reverse relationship between VAN and LP may reflect a compensatory response to the reduced cognitive resources caused by high-altitude exposure. Additionally, increased LP and shorter reaction times with exposure duration may reflect a resistance to the high-altitude environment. We also conducted time-frequency analysis and found that theta power did not vary with exposure duration, suggesting that the reduction in cognitive resources remains stable in these individuals over time. Overall, our study provides new insights into the dynamic effects of high-altitude environments on awareness detection in the presence of reduced cognitive resources.

Cognition and Neuropsychological Changes at Altitude-A Systematic Review of Literature

High-altitude (HA) exposure affects cognitive functions, but studies have found inconsistent results. The aim of this systematic review was to evaluate the effects of HA exposure on cognitive functions in healthy subjects. A structural overview of the applied neuropsychological tests was provided with a classification of superordinate cognitive domains. A literature search was performed using PubMed up to October 2021 according to PRISMA guidelines. Eligibility criteria included a healthy human cohort exposed to altitude in the field (at minimum 2440 m [8000 ft]) or in a hypoxic environment in a laboratory, and an assessment of cognitive domains. The literature search identified 52 studies (29 of these were field studies; altitude range: 2440 m-8848 m [8000-29,029 ft]). Researchers applied 112 different neuropsychological tests. Attentional capacity, concentration, and executive functions were the most frequently studied. In the laboratory, the ratio of altitude-induced impairments (64.7%) was twice as high compared to results showing no change or improved results (35.3%), but altitudes studied were similar in the chamber compared to field studies. In the field, the opposite results were found (66.4 % no change or improvements, 33.6% impairments). Since better acclimatization can be assumed in the field studies, the findings support the hypothesis that sufficient acclimatization has beneficial effects on cognitive functions at HA. However, it also becomes apparent that research in this area would benefit most if a consensus could be reached on a standardized framework of freely available neurocognitive tests.

Sleep loss effects on physiological and cognitive responses to systemic environmental hypoxia

In the course of their missions or training, alpinists, but also mountain combat forces and mountain security services, professional miners, aircrew, aircraft and glider pilots and helicopter crews are regularly exposed to altitude without oxygen supplementation. At altitude, humans are exposed to systemic environmental hypoxia induced by the decrease in barometric pressure (<1,013 hPa) which decreases the inspired partial pressure of oxygen (PIO₂), while the oxygen fraction is constant (equal to approximately 20.9%). Effects of altitude on humans occur gradually and depend on the duration of exposure and the altitude level. From 1,500 m altitude (response threshold), several adaptive responses offset the effects of hypoxia, involving the respiratory and the cardiovascular systems, and the oxygen transport capacity of the blood. Fatigue and cognitive and sensory disorders are usually observed from 2,500 m (threshold of prolonged hypoxia). Above 3,500 m (the threshold for disorders), the effects are not completely compensated and maladaptive responses occur and individuals develop altitude headache or acute altitude illness [Acute Mountain Sickness (AMS)]. The magnitude of effects varies considerably between different physiological systems and exhibits significant inter-individual variability. In addition to comorbidities, the factors of vulnerability are still little known. They can be constitutive (genetic) or circumstantial (sleep deprivation, fatigue, speed of ascent.). In particular, sleep loss, a condition that is often encountered in real-life settings, could have an impact on the physiological and cognitive responses to hypoxia. In this review, we report the current state of knowledge on the impact of sleep loss on responses to environmental hypoxia in humans, with the aim of identifying possible consequences for AMS risk and cognition, as well as the value of behavioral and non-pharmacological countermeasures.

Brain structure and neurocognitive function in two professional mountaineers during 35 days severe normobaric hypoxia

BACKGROUND

Animal studies have elicited therapeutic potential of severe ambient hypoxia for neurodegenerative diseases. However, uncertainties exist relative to individual (mal-)adaption mechanisms of the brain to hypoxia. To investigate the effects of hypoxia on cognitive performance and cerebral morphology, two healthy professional mountaineers (participants A and B) conducted a 35-day study with 14 consecutive days of exposure to oxygen concentrations between 8% and 8.8%.

METHODS

Participants were examined at seven time points by cerebral magnetic resonance imaging (MRI) and at 27 time points by a test battery covering a spectrum of cognitive domains. Blood neuron specific enolase and neurofilament light chain levels were analyzed before, during and after hypoxia.

RESULTS

While cognitive performance was largely unaffected by hypoxic conditions, morphological MRI changes were evident. White matter volumes increased (max.: A: 4.3% ± 0.9%; B: 4.5% ± 1.9%) while grey matter volumes (A: -1.5% ± 0.8%; B: -2.5% ± 0.9%) and cerebrospinal fluid volumes (A: -2.7% ± 2.4%; B: -5.9% ± 8.2%) decreased. Furthermore, the number (A: 11 to 17; B: 26 to 126) and volumes (A: 140%; B: 285%) of white matter hyperintensities increased in hypoxia but had returned to baseline after a 3.5-month recovery phase. Diffusion weighted imaging of the white matter indicated cytotoxic edema formation. Biochemical markers of brain injury remained grossly negative.

DISCUSSION

Severe sustained normobaric hypoxia was tolerated in highly selected individuals which may pave the way for future translational studies of the therapeutic potential of hypoxia in neurodegenerative diseases.

Acute mountain sickness and sleep disturbances differentially influence cognition and mood during rapid ascent to 3000 and 4050 m

The impact of acute mountain sickness (AMS) and sleep disturbances on mood and cognition at two altitudes relevant to the working and tourist population is unknown. Twenty unacclimatized lowlanders were exposed to either 3000 m (n = 10; 526 mmHg) or 4050 m (n = 10; 460 mmHg) for 20 h in a hypobaric chamber. AMS prevalence and severity was assessed using the Environmental Symptoms Questionnaire (ESQ) and an AMS‐C score ≥ 0.7 indicated sickness. While sleeping for one night both at sea level (SL) and high altitude (HA), a wrist motion detector was used to measure awakenings (Awak, events/h) and sleep efficiency (Eff, %). If Eff was ≥85%, individuals were considered a good sleeper (Sleep+). Mood and cognition were assessed using the Automated Neuropsychological Assessment Metric and Mood Scale (ANAM‐MS). The ESQ and ANAM‐MS were administered in the morning both at SL and after 20 h at HA. AMS severity (mean ± SE; 1.82 ± 0.27 vs. 0.20 ± 0.27), AMS prevalence (90% vs. 10%), depression (0.63 ± 0.23 vs. 0.00 ± 0.24) Awak (15.6 ± 1.6 vs. 10.1 ± 1.6 events/h), and DeSHr (38.5 ± 6.3 vs. 13.3 ± 6.3 events/h) were greater (p < 0.05) and Eff was lower (69.9 ± 5.3% vs. 87.0 ± 5.3%) at 4050 m compared to 3000 m, respectively. AMS presence did not impact cognition but fatigue (2.17 ± 0.37 vs. 0.58 ± 0.39), anger (0.65 ± 0.25 vs. 0.02 ± 0.26), depression (0.63 ± 0.23 vs. 0.00 ± 0.24) and sleepiness (4.8 ± 0.4 vs. 2.7 ± 0.5) were greater (p < 0.05) in the AMS+ group. The Sleep− group, compared to the Sleep+ group, had lower (p < 0.05) working memory scores (50 ± 7 vs. 78 ± 9) assessed by the Sternberg 6‐letter memory task, and lower reaction time fatigue scores (157 ± 17 vs. 221 ± 22), assessed by the repeated reaction time test. Overall, AMS, depression, DeSHr, and Awak were increased (p < 0.05) at 4050 m compared to 3000 m. In addition, AMS presence impacted mood while poor sleep impacted cognition which may deteriorate teamwork and/or increase errors in judgement at HA.

Cognitive impairment caused by hypoxia: from clinical evidences to molecular mechanisms

Hypoxia is a state of reduced oxygen supply and excessive oxygen consumption. According to the duration of hypoxic period, it can be classified as acute and chronic hypoxia. Both acute and chronic hypoxia could induce abundant neurological deficits. Although there have been significant advances in the pathophysiological injuries, few studies have focused on the cognitive dysfunction. In this review, we focused on the clinical evidences and molecular mechanisms of cognitive impairment under acute and chronic hypoxia. Hypoxia can impair several cognitive domains such as attention, learning and memory, procession speed and executive function, which are similar in acute and chronic hypoxia. The severity of cognitive deficit correlates with the duration and degree of hypoxia. Recovery can be achieved after acute hypoxia, while sequelae or even dementia can be observed after chronic hypoxia, perhaps due to the different molecular mechanisms. Cardiopulmonary compensatory response, glycolysis, oxidative stress, calcium overload, adenosine, mitochondrial disruption, inflammation and excitotoxicity contribute to the molecular mechanisms of cognitive deficit after acute hypoxia. During the chronic stage of hypoxia, different adaptive responses, impaired neurovascular coupling, apoptosis, transcription factors-mediated inflammation, as well as Aβ accumulation and tau phosphorylation account for the neurocognitive deficit. Moreover, brain structural changes with hippocampus and cortex atrophy, ventricle enlargement, senile plaque and neurofibrillary tangle deposition can be observed under chronic hypoxia rather than acute hypoxia.

Self-Selected Motivational Music Enhances Physical Performance in Normoxia and Hypoxia in Young Healthy Males

Humans exposed to hypoxia are susceptible to physiological and psychological impairment. Music has ergogenic effects through enhancing psychological factors such as mood, emotion, and cognition. This study aimed to investigate music as a tool for mitigating the performance decrements observed in hypoxia. Thirteen males (mean ± SD; 24 ± 4 years) completed one familiarization session and four experimental trials; (1) normoxia (sea level, 0.209 FiO₂) and no music; (2) normoxia (0.209 FiO₂) with music; (3) normobaric hypoxia (∼3800 m, 0.13 FiO₂) and no music; and (4) normobaric hypoxia (0.13 FiO₂) with music. Experimental trials were completed at 21°C with 50% relative humidity. Music was self-selected prior to the familiarization session. Each experimental trial included a 15-min time trial on an arm bike, followed by a 60-s isometric maximal voluntary contraction (MVC) of the biceps brachii. Supramaximal nerve stimulation quantified central and peripheral fatigue with voluntary activation (VA%) calculated using the doublet interpolation method. Average power output (W) was reduced with a main effect of hypoxia (p = 0.02) and significantly increased with a main effect of music (p = 0.001). When combined the interaction was additive (p = 0.87). Average MVC force (N) was reduced in hypoxia (p = 0.03) but VA% of the biceps brachii was increased with music (p = 0.02). Music reduced subjective scores of mental effort, breathing discomfort, and arm discomfort in hypoxia (p < 0.001). Music increased maximal physical exertion through enhancing neural drive and diminishing detrimental mental processes, enhancing performance in normoxia (6.3%) and hypoxia (6.4%).

Reversal of neurovascular coupling in the default mode network: Evidence from hypoxia

Local changes in cerebral blood flow are thought to match changes in neuronal activity, a phenomenon termed neurovascular coupling. Hypoxia increases global resting cerebral blood flow, but regional cerebral blood flow (rCBF) changes are non-uniform. Hypoxia decreases baseline rCBF to the default mode network (DMN), which could reflect either decreased neuronal activity or altered neurovascular coupling. To distinguish between these hypotheses, we characterized the effects of hypoxia on baseline rCBF, task performance, and the hemodynamic (BOLD) response to task activity. During hypoxia, baseline CBF increased across most of the brain, but decreased in DMN regions. Performance on memory recall and motion detection tasks was not diminished, suggesting task-relevant neuronal activity was unaffected. Hypoxia reversed both positive and negative task-evoked BOLD responses in the DMN, suggesting hypoxia reverses neurovascular coupling in the DMN of healthy adults. The reversal of the BOLD response was specific to the DMN. Hypoxia produced modest increases in activations in the visual attention network (VAN) during the motion detection task, and had no effect on activations in the visual cortex during visual stimulation. This regional specificity may be particularly pertinent to clinical populations characterized by hypoxemia and may enhance understanding of regional specificity in neurodegenerative disease pathology.

Mental fatigue independent of boredom and sleepiness does not impact self-paced physical or cognitive performance in normoxia or hypoxia

This study investigated the individual and combined effects of mental fatigue (MF) and hypoxia (HYP) on physical and cognitive performance. Fifteen males (24 ± 3 years) completed one familiarization session and six experimental trials, including: 1) normoxia (0.209 FiO₂) and no MF; 2) normoxia (0.209 FiO₂) with MF; 3) mild normobaric HYP (0.13 FiO₂) and no MF; 4) mild normobaric HYP (0.13 FiO₂) with MF; 5) severe normobaric HYP (0.10 FiO₂) and no MF; 6) severe normobaric HYP (0.10 FiO₂) with MF. Each condition included a 15-min self-paced time trial, followed by a 60-s isometric maximal voluntary contraction of the biceps brachii. MF was induced using a 16-min individualized cognitive test prior to exercise performance. Following each time trial, participants performed the Tower of Hanoi cognitive test. A main effect of HYP was observed on average power output, oxygen consumption and muscle oxygenation (P ≤ 0.004), with no effect of MF (P ≥ 0.599). Voluntary activation of the biceps brachii was also reduced in HYP (68.42 ± 5.64%, P = 0.039). No effect of MF or HYP was observed on cognitive performance (P ≥ 0.138). HYP impacted physical performance, whilst MF had no effect on self-paced physical or cognitive performance.

Influence of Acetazolamide on Hand Strength and Manual Dexterity During a 30-h Simulated High Altitude Exposure

INTRODUCTION

High altitude missions pose significant challenges to Warfighter medical readiness and performance. Decreased circulating oxygen levels cause a decrease in exercise performance and can cause debilitating symptoms associated with acute mountain sickness, especially with rapid ascent. Acetazolamide (AZ) is known to minimize symptoms of acute mountain sickness, but it is unknown whether this medication alters hand strength and manual dexterity during altitude exposure.

MATERIALS AND METHODS

Ten male volunteers (22 ± 4 yr, 75.9 ± 13.7 kg, 174.9 ± 9.3 cm) participated in two separate 30 h simulated altitude exposures (496 mmHg, equivalent to 3,500 m, 20°C, 20% RH) in a hypobaric chamber. Participants were given either a placebo or 250 mg of AZ twice daily for 3.5 d (2 sea-level [SL] days + the 30 h altitude exposure) in a randomized, single-blind, crossover design. During SL and both altitude (ALT) exposures, hand function tests were performed, including hand grip and finger pinch strength tests, as well as the Purdue Pegboard (PP) and magazine loading tests to assess manual dexterity. Paired T tests and two-way repeated measure analysis of variance were used as appropriate to evaluate the effects of AZ and ALT. The value of p < 0.05 was accepted for statistical significance.

RESULTS

There were no influences of acute ALT exposure or AZ treatment on hand strength (eg, grip strength; SL: 39.2 ± 5.5 kg vs. ALT: 41.5 ± 6.9 kg, p > 0.05) or dexterity (eg, PPassembly; placebo: 35.5 ± 5.3 vs. AZ: 34.3 ± 4.6, p > 0.05) in our volunteers. Two dexterity tests (PPsum and magazine loading) showed improvements over time at ALT, regardless of treatment, where scores were improved after 10 h of exposure compared to at 1 h (eg, magazine loading: 56 ± 12 vs. 48 ± 10, p < 0.001). This pattern was not seen in the PPassembly test or any strength measurements.

CONCLUSIONS

Our results suggest that 500 mg/d of AZ does not influence hand strength or manual dexterity during a 30 h exposure to 3,500 m simulated ALT. Acute ALT exposure (1 h) did not influence dexterity or strength, although some measures of dexterity showed improvements as exposure time increased. We conclude that use of AZ to optimize medical readiness at ALT is unlikely to impair the Warfighter's ability to complete mission tasks that depend on hand function.

Acute aerobic exercise impairs aspects of cognitive function at high altitude

Hypoxia-mediated cognitive dysfunction can be transiently mitigated by exercise in a laboratory-based setting. Whether this effect holds true in the context of high altitude hypoxia has not been determined. We investigated the effect of acute aerobic exercise on cognitive function (CF) at low (1400m) and high altitude (4240m). Fifteen volunteers (24.1±3.5yrs; 9 females) exercised for 20-min at 40-60% of their heart rate reserve at low and high altitude. CF was assessed before and 10-min after exercise using a tablet-based battery of executive function tests. A sea-level control group (n=13; 24.2±2.4 years; 9 females) performed time-matched CF tests to assess the contribution of a learning effects due to repeated testing. Measures of resting CF were unaffected by ascent to high altitude. Following high altitude exercise, performance significantly worsened on the digit symbol substitution task - a test of processing speed, working memory, and visuospatial attention (z=0.01 vs. -0.59, p=0.02, η²=0.35). No effect was found on other measures of CF following exercise. There was no association between changes in peripheral oxygen saturation and changes in CF following high altitude exercise (r=0.22, p=0.44), but higher hemoglobin concentration at high altitude was associated with a decline in CF following exercise at high altitude (r=-0.65, p=0.02). Acute aerobic exercise performed at high altitude impairs some aspects of CF, whereas other CF tests remain unchanged. The strong ecological validity of this study warrants attention and follow-up investigations are needed to better characterize selective impairment of CF with high altitude exercise.

The Impact of Environmental Stress on Cognitive Performance: A Systematic Review

OBJECTIVE

In this review, we detail the impact of environmental stress on cognitive and military task performance and highlight any individual characteristics or interventions which may mitigate any negative effect.

BACKGROUND

Military personnel are often deployed in regions markedly different from their own, experiencing hot days, cold nights, and trips both above and below sea level. In spite of these stressors, high-level cognitive and operational performance must be maintained.

METHOD

A systematic review of the electronic databases Medline (PubMed), EMBASE (Scopus), PsycINFO, and Web of Science was conducted from inception up to September 2018. Eligibility criteria included a healthy human cohort, an outcome of cognition or military task performance and assessment of an environmental condition.

RESULTS

The search returned 113,850 records, of which 124 were included in the systematic review. Thirty-one studies examined the impact of heat stress on cognition; 20 of cold stress; 59 of altitude exposure; and 18 of being below sea level.

CONCLUSION

The severity and duration of exposure to the environmental stressor affects the degree to which cognitive performance can be impaired, as does the complexity of the cognitive task and the skill or familiarity of the individual performing the task.

APPLICATION

Strategies to improve cognitive performance in extreme environmental conditions should focus on reducing the magnitude of the physiological and perceptual disturbance caused by the stressor. Strategies may include acclimatization and habituation, being well skilled on the task, and reducing sensations of thermal stress with approaches such as head and neck cooling.

Chronic Exposure to High Altitude: Synaptic, Astroglial and Memory Changes

Long-term operations carried out at high altitude (HA) by military personnel, pilots, and astronauts may trigger health complications. In particular, chronic exposure to high altitude (CEHA) has been associated with deficits in cognitive function. In this study, we found that mice exposed to chronic HA (5000 m for 12 weeks) exhibited deficits in learning and memory associated with hippocampal function and were linked with changes in the expression of synaptic proteins across various regions of the brain. Specifically, we found decreased levels of synaptophysin (SYP) (p < 0.05) and spinophilin (SPH) (p < 0.05) in the olfactory cortex, post synaptic density−95 (PSD-95) (p < 0.05), growth associated protein 43 (GAP43) (p < 0.05), glial fibrillary acidic protein (GFAP) (p < 0.05) in the cerebellum, and SYP (p < 0.05) and PSD-95 (p < 0.05) in the brainstem. Ultrastructural analyses of synaptic density and morphology in the hippocampus did not reveal any differences in CEHA mice compared to SL mice. Our data are novel and suggest that CEHA exposure leads to cognitive impairment in conjunction with neuroanatomically-based molecular changes in synaptic protein levels and astroglial cell marker in a region specific manner. We hypothesize that these new findings are part of highly complex molecular and neuroplasticity mechanisms underlying neuroadaptation response that occurs in brains when chronically exposed to HA.

The interactive effects of acute exercise and hypoxia on cognitive performance: A narrative review

Acute moderate intensity exercise has been shown to improve cognitive performance. In contrast, hypoxia is believed to impair cognitive performance. The detrimental effects of hypoxia on cognitive performance are primarily dependent on the severity and duration of exposure. In this review, we describe how acute exercise under hypoxia alters cognitive performance, and propose that the combined effects of acute exercise and hypoxia on cognitive performance are mainly determined by interaction among exercise intensity and duration, the severity of hypoxia, and duration of exposure to hypoxia. We discuss the physiological mechanism(s) of the interaction and suggest that alterations in neurotransmitter function, cerebral blood flow, and possibly cerebral metabolism are the primary candidates that determine cognitive performance when acute exercise is combined with hypoxia. Furthermore, acclimatization appears to counteract impaired cognitive performance during prolonged exposure to hypoxia although the precise physiological mechanism(s) responsible for this amelioration remain to be elucidated. This review has implications for sporting, occupational, and recreational activities at terrestrial high altitude where cognitive performance is essential. Further studies are required to understand physiological mechanisms that determine cognitive performance when acute exercise is performed in hypoxia.

Living High and Feeling Low: Altitude, Suicide, and Depression

After participating in this activity, learners should be better able to:• Assess epidemiologic evidence that increased altitude of residence is linked to increased risk of depression and suicide• Evaluate strategies to address hypoxia-related depression and suicidal ideation ABSTRACT: Suicide and major depressive disorder (MDD) are complex conditions that almost certainly arise from the influences of many interrelated factors. There are significant regional variations in the rates of MDD and suicide in the United States, suggesting that sociodemographic and environmental conditions contribute. Here, we review epidemiological evidence that increases in the altitude of residence are linked to the increased risk of depression and suicide. We consider the possibility that chronic hypobaric hypoxia (low blood oxygen related to low atmospheric pressure) contributes to suicide and depression, which is suggested by animal models, short-term studies in humans, and the effects of hypoxic medical conditions on suicide and depression. We argue that hypobaric hypoxia could promote suicide and depression by altering serotonin metabolism and brain bioenergetics; both of these pathways are implicated in depression, and both are affected by hypoxia. Finally, we briefly examine treatment strategies to address hypoxia-related depression and suicidal ideation that are suggested by these findings, including creatine monohydrate and the serotonin precursors tryptophan and 5-hydroxytryptophan.

Neuronal and vascular deficits following chronic adaptation to high altitude

We sought to understand the mechanisms underlying cognitive deficits that are reported to affect non-native subjects following their prolonged stay and/or work at high altitude (HA). We found that mice exposed to a simulated environment of 5000 m exhibit deficits in hippocampal learning and memory accompanied by abnormalities in brain MR imaging. Exposure (1-8 months) to HA led to an increase in brain ventricular volume, a reduction in relative cerebral blood flow and changes in diffusion tensor imaging (DTI) derived parameters within the hippocampus and corpus callosum. Furthermore, neuropathological examination revealed significant expansion of the neurovascular network, microglia activation and demyelination within the corpus callosum. Electrophysiological recordings from the corpus callosum indicated that axonal excitabilities are increased while refractory periods are longer despite a lack of change in action potential conduction velocities of both myelinated and unmyelinated fibers. Next generation RNA-sequencing identified alterations in hippocampal and amygdala transcriptome signaling pathways linked to angiogenesis, neuroinflammation and myelination. Our findings reveal that exposure to hypobaric-hypoxia triggers maladaptive responses inducing cognitive deficits and suggest potential mechanisms underlying the adverse impacts of staying or traveling at high altitude.

High altitude with monotonous environment has significant impact on mood and cognitive performance of acclimatized lowlanders: Possible role of altered serum BDNF and plasma homocysteine level

BACKGROUND

Monotony resulting due to the wilderness, sparse population and isolation from society could adversely affect human physiology and cause mood alterations. Thus, observations need to be conducted in order to elucidate the possible role of circulating biomarkers in inducing altered mood and cognitive performance following prolonged exposure to high altitude (HA) with persistent monotonous environment.

OBJECTIVE

The present study aimed towards investigating the impact of monotonous environment in remote HA on mood and cognitive performance of human volunteers and its correlation with serum brain derived neurotrophic factor (BDNF) and plasma homocysteine level.

METHODS

The present study was conducted on male lowlander participants who had normal social life prior to induction in HA environment. Baseline data was acquired at altitude ≤240 m mean sea level (MSL). Thereafter, the participants were inducted to an altitude of 4500-4800 m MSL. After acclimatization to HA, the participants were assigned as acclimatized low landers (ALL). Longitudinal follow up was conducted after 8 months of high altitude induction on acclimatized low landers (8ALL). Further, to study the effect of monotony, the participants were randomly assigned into different group sizes during their further stay of 4 months in HA viz. ≤5 (12ALL ≤ 5) and ≥10 (12ALL ≥ 10). Mood and cognitive performance of the participants were assessed by standard self-administered questionnaires. Serum BDNF and plasma homocysteine were estimated and their correlation with mood and cognition were determined.

RESULTS

The findings showed significantly low serum BDNF in 12ALL ≤ 5 group when compared to baseline, 8ALL and 12AL ≥ 10 groups. Alleviated serum BDNF was associated with increased prevalence of mood alterations in HA with persistent monotonous environment. Participants of 12ALL ≥ 10 group showed significantly higher cognitive performance as compared to 12ALL ≤ 5 group which was associated with reduced plasma homocysteine level.

LIMITATIONS

Total registered volunteers during baseline study were not available during the entire period of this study. The second limitation was exclusion of participants with medical history of severe head injuries, chronic diseases in family and extreme baseline serum profile. Third limitation of the study was to exclude the participants detected with MCI after 8 months of HA induction for negating the role of hypobaric hypoxia on mood and cognition.

CONCLUSION

The study advocated that ALLs of 12ALL ≤ 5 group have increased prevalence of depressive trait and cognitive impairment which was correlated with reduced serum BDNF and augmented plasma homocysteine level as compared to participants of 12ALL ≥ 10 group having better social interaction with improved cognition and mood. The basic findings of the present study revealed that prolonged HA stay after physiological acclimatization should be regulated by proper social interaction involving normal group size to avoid detrimental effect of monotony and its significant impact on circulatory biomarkers.

Effects on Cognitive Functioning of Acute, Subacute and Repeated Exposures to High Altitude

Objective: Neurocognitive functions are affected by high altitude, however the altitude effects of acclimatization and repeated exposures are unclear. We investigated the effects of acute, subacute and repeated exposure to 5,050 m on cognition among altitude-naïve participants compared to control subjects tested at low altitude.

Methods: Twenty-one altitude-naïve individuals (25.3 ± 3.8 years, 13 females) were exposed to 5,050 m for 1 week (Cycle 1) and re-exposed after a week of rest at sea-level (Cycle 2). Baseline (BL, 520 m), acute (Day 1, HA1) and acclimatization (Day 6, HA6, 5,050 m) measurements were taken in both cycles. Seventeen control subjects (24.9 ± 2.6 years, 12 females) were tested over a similar period in Calgary, Canada (1,103 m). The Reaction Time (RTI), Attention Switching Task (AST), Rapid Visual Processing (RVP) and One Touch Stockings of Cambridge (OTS) tasks were administered and outcomes were expressed in milliseconds/frequencies. Lake Louise Score (LLS) and blood oxygen saturation (SpO₂) were recorded.

Results: In both cycles, no significant changes were found with acute exposure on the AST total score, mean latency and SD. Significant changes were found upon acclimatization solely in the altitude group, with improved AST Mean Latency [HA1 (588 ± 92) vs. HA6 (526 ± 91), p < 0.001] and Latency SD [HA1 (189 ± 86) vs. HA6 (135 ± 65), p < 0.001] compared to acute exposure, in Cycle 1. No significant differences were present in the control group. When entering Acute SpO₂ (HA1-BL), Acclimatization SpO₂ (HA6-BL) and LLS score as covariates for both cycles, the effects of acclimatization on AST outcomes disappeared indicating that the changes were partially explained by SpO₂ and LLS. The changes in AST Mean Latency [ΔBL (−61.2 ± 70.2) vs. ΔHA6 (−28.0 ± 58), p = 0.005] and the changes in Latency SD [ΔBL (−28.4 ± 41.2) vs. ΔHA6 (−0.2235 ± 34.8), p = 0.007] across the two cycles were smaller with acclimatization. However, the percent changes did not differ between cycles. These results indicate independent effects of altitude across repeated exposures.

Conclusions: Selective and sustained attention are impaired at altitude and improves with acclimatization.The observed changes are associated, in part, with AMS score and SpO₂. The gains in cognition with acclimatization during a first exposure are not carried over to repeated exposures.

Adenosine A2A receptor involves in neuroinflammation-mediated cognitive decline through activating microglia under acute hypobaric hypoxia

Hypobaric hypoxia (HH) at high altitudes leads to a wide range of cognitive impairments which can handicap human normal activities and performances. However, the underlying mechanism is still unclear. Adenosine A_2A receptors (A_2ARs) of the brain are pivotal to synaptic plasticity and cognition. Besides, insult-induced up-regulation of A_2AR regulates neuroinflammation and therefore induces brain damages in various neuropathological processes. The present study was designed to determine whether A_2AR-mediate neuroinflammation involves in cognitive impairments under acute HH. A_2AR knock-out and wild-type male mice were exposed to a simulated altitude of 8000 m for 7 consecutive days in a hypobaric chamber and simultaneously received behavioral tests including Morris water maze test and open filed test. A_2AR expression, the activation of microglia and the production of TNF-α were evaluated in the hippocampus by immunohistochemistry and ELISA, respectively. Behavioral tests showed that acute HH exposure caused the dysfunction of spatial memory and mood, while genetic inactivation of A_2AR attenuated the impairment of spatial memory but not that of mood. Double-labeled immunofluorescence showed that A_2ARs were mainly expressed on microglia and up-regulated in the hippocampus of acute HH model mice. Acute HH also induced the accumulation of microglia and increased production of TNF-α in the hippocampus, which could be markedly inhibited by A_2AR inactivation. These findings indicate that microglia-mediated neuroinflammation triggered by A_2AR activation involves in acute HH-induced spatial memory impairment and that A_2AR could be a new target for the pharmacotherapy of cognitive dysfunction at high altitudes.

Effects of Dietary Nitrate Supplementation on Physiological Responses, Cognitive Function, and Exercise Performance at Moderate and Very-High Simulated Altitude

Purpose: Nitric oxide (NO) bioavailability is reduced during acute altitude exposure, contributing toward the decline in physiological and cognitive function in this environment. This study evaluated the effects of nitrate (NO3−) supplementation on NO bioavailability, physiological and cognitive function, and exercise performance at moderate and very-high simulated altitude.

Methods:Ten males (mean (SD): V˙O2max: 60.9 (10.1) ml·kg⁻¹·min⁻¹) rested and performed exercise twice at moderate (~14.0% O₂; ~3,000 m) and twice at very-high (~11.7% O₂; ~4,300 m) simulated altitude. Participants ingested either 140 ml concentrated NO3−-rich (BRJ; ~12.5 mmol NO3−) or NO3−-deplete (PLA; 0.01 mmol NO3−) beetroot juice 2 h before each trial. Participants rested for 45 min in normobaric hypoxia prior to completing an exercise task. Exercise comprised a 45 min walk at 30% V˙O2max and a 3 km time-trial (TT), both conducted on a treadmill at a 10% gradient whilst carrying a 10 kg backpack to simulate altitude hiking. Plasma nitrite concentration ([NO2−]), peripheral oxygen saturation (SpO₂), pulmonary oxygen uptake (V˙O2), muscle and cerebral oxygenation, and cognitive function were measured throughout.

Results: Pre-exercise plasma [NO2−] was significantly elevated in BRJ compared with PLA (p = 0.001). Pulmonary V˙O2 was reduced (p = 0.020), and SpO₂ was elevated (p = 0.005) during steady-state exercise in BRJ compared with PLA, with similar effects at both altitudes. BRJ supplementation enhanced 3 km TT performance relative to PLA by 3.8% [1,653.9 (261.3) vs. 1718.7 (213.0) s] and 4.2% [1,809.8 (262.0) vs. 1,889.1 (203.9) s] at 3,000 and 4,300 m, respectively (p = 0.019). Oxygenation of the gastrocnemius was elevated during the TT consequent to BRJ (p = 0.011). The number of false alarms during the Rapid Visual Information Processing Task tended to be lower with BRJ compared with PLA prior to altitude exposure (p = 0.056). Performance in all other cognitive tasks did not differ significantly between BRJ and PLA at any measurement point (p ≥ 0.141).

Conclusion: This study suggests that BRJ improves physiological function and exercise performance, but not cognitive function, at simulated moderate and very-high altitude.

Caudwell Xtreme Everest: A prospective study of the effects of environmental hypoxia on cognitive functioning

Background

The neuropsychological consequences of exposure to environmental hypobaric hypoxia (EHH) remain unclear. We thus investigated them in a large group of healthy volunteers who trekked to Mount Everest base camp (5,300 m).

Methods

A neuropsychological (NP) test battery assessing memory, language, attention, and executive function was administered to 198 participants (age 44.5±13.7 years; 60% male). These were studied at baseline (sea level), 3,500 m (Namche Bazaar), 5,300 m (Everest Base Camp) and on return to 1,300 m (Kathmandu) (attrition rate 23.7%). A comparable control group (n = 25; age 44.5±14.1 years; 60% male) for comparison with trekkers was tested at/or near sea level over an equivalent timeframe so as to account for learning effects associated with repeat testing. The Reliable Change Index (RCI) was used to calculate changes in cognition and neuropsychological function during and after exposure to EHH relative to controls.

Results

Overall, attention, verbal ability and executive function declined in those exposed to EHH when the performance of the control group was taken into account (RCI .05 to -.95) with decline persisting at descent. Memory and psychomotor function showed decline at highest ascent only (RCI -.08 to -.56). However, there was inter-individual variability in response: whilst NP performance declined in most, this improved in some trekkers. Cognitive decline was greater amongst older people (r = .42; p < .0001), but was otherwise not consistently associated with socio-demographic, mood, or physiological variables.

Conclusions

After correcting for learning effects, attention, verbal abilities and executive functioning declined with exposure to EHH. There was considerable individual variability in the response of brain function to sustained hypoxia with some participants not showing any effects of hypoxia. This might have implications for those facing sustained hypoxia as a result of any disease.

Effects of Mood States and Anxiety as Induced by the Video-Recorded Stroop Color-Word Interference Test in Simple Response Time Tasks on Reaction Time and Movement Time

Mood states and anxiety might alter performance in complex tasks whereas in more simple tasks such as stimulus-response, high anxiety could provoke bias in mechanisms of attention leading to better performances. We investigated the effects of anxiety, tension, and fatigue induced by the video-recorded Stroop Color-Word Interference Test on either reaction or movement time. 61 subjects performed a visual and an auditory response-time test in Control and Anxiogenic conditions during which heart rate was measured. Tension and anxiety states were assessed using self-evaluation. Analysis showed auditory response time was improved for both reaction and movement times in the Anxiogenic condition. These data suggest that the increased attention underlying anxiety and mood responses could have favored auditory response time by leading subjects to process stimuli more actively. In addition, state-anxiety and tension could have influenced muscular tension, enhancing the movement time in the auditory task.

Association of Cognitive Performance with Time at Altitude, Sleep Quality, and Acute Mountain Sickness Symptoms

OBJECTIVE

It is well documented that cognitive performance may be altered with ascent to altitude, but the association of various cognitive performance tests with symptoms of acute mountain sickness (AMS) is not well understood. Our objective was to assess and compare cognitive performance during a high-altitude expedition using several tests and to report the association of each test with AMS, headache, and quality of sleep.

METHODS

During an expedition to Mount Everest, 3 cognitive tests (Stroop, Trail Making, and the real-time cognitive assessment tool, an in-house developed motor accuracy test) were used along with a questionnaire to assess health and AMS. Eight team members were assessed pre-expedition, postexpedition, and at several time points during the expedition.

RESULTS

There were no significant differences (P >.05) found among scores taken at 3 time points at base camp and the postexpedition scores for all 3 tests. Changes in the Stroop test scores were significantly associated with the odds of AMS (P <.05). The logistic regression results show that the percent change from baseline for Stroop score (β = -5.637; P = .032) and Stroop attempts (β = -5.269; P = .049) are significantly associated with the odds of meeting the criteria for AMS.

CONCLUSIONS

No significant changes were found in overall cognitive performance at altitude, but a significant relationship was found between symptoms of AMS and performance in certain cognitive tests. This research shows the need for more investigation of objective physiologic assessments to associate with self-perceived metrics of AMS to gauge effect on cognitive performance.

The Impact of Different Environmental Conditions on Cognitive Function: A Focused Review

Cognitive function defines performance in objective tasks that require conscious mental effort. Extreme environments, namely heat, hypoxia, and cold can all alter human cognitive function due to a variety of psychological and/or biological processes. The aims of this Focused Review were to discuss; (1) the current state of knowledge on the effects of heat, hypoxic and cold stress on cognitive function, (2) the potential mechanisms underpinning these alterations, and (3) plausible interventions that may maintain cognitive function upon exposure to each of these environmental stressors. The available evidence suggests that the effects of heat, hypoxia, and cold stress on cognitive function are both task and severity dependent. Complex tasks are particularly vulnerable to extreme heat stress, whereas both simple and complex task performance appear to be vulnerable at even at moderate altitudes. Cold stress also appears to negatively impact both simple and complex task performance, however, the research in this area is sparse in comparison to heat and hypoxia. In summary, this focused review provides updated knowledge regarding the effects of extreme environmental stressors on cognitive function and their biological underpinnings. Tyrosine supplementation may help individuals maintain cognitive function in very hot, hypoxic, and/or cold conditions. However, more research is needed to clarify these and other postulated interventions.

Strain variation in the adaptation of C57Bl6 and BALBc mice to chronic hypobaric hypoxia

The interplay of environmental and genetic factors may lead to a spectrum of physiological and behavioral outcomes. How environmental stress factors interact with the diverse mouse genomes is still poorly understood and elucidating the underlying interactions requires specific stress models that can target integrated physiological systems. Here, we employ behavioral tests and whole-body plethysmography to examine the effects of 12 weeks of simulated high altitude (HA) exposure on two inbred mouse strains, BALBc and C57Bl6. We find that HA induced- weight loss recovers at significantly different rates in these two strains. Even at 12 weeks, however, both strains fail to reach body weight levels of controls. Performance on two motor tasks, rotarod and treadmill, improve with HA exposure but more prominently in BALBc mice. Whole-body plethysmography outcomes indicate that compensation to chronic HA includes increased respiratory frequencies and tidal volumes in both strains. However, the effects on tidal volume are significantly greater in BALBc mice and showed a biphasic course. Whole- body metabolic rates are also increased in both strains with prolonged HA exposure, but were more pronounced in BALBc mice suggestive of less successful adaptation in this strain. These adaptations occur in the absence of gross pathological changes in all major organs. Together these results indicate that chronic HA exposure results in environmental stressors that impact the specific physiological responses of BALBc more than C57Bl6 mice. Thus, these strains provide a promising platform for investigating how genetic backgrounds can differentially reinforce the effects of long-lasting environmental stressors and their potential to interact with psychological stressors.

Domain specific changes in cognition at high altitude and its correlation with hyperhomocysteinemia

Though acute exposure to hypobaric hypoxia is reported to impair cognitive performance, the effects of prolonged exposure on different cognitive domains have been less studied. The present study aimed at investigating the time dependent changes in cognitive performance on prolonged stay at high altitude and its correlation with electroencephalogram (EEG) and plasma homocysteine. The study was conducted on 761 male volunteers of 25-35 years age who had never been to high altitude and baseline data pertaining to domain specific cognitive performance, EEG and homocysteine was acquired at altitude ≤240 m mean sea level (MSL). The volunteers were inducted to an altitude of 4200-4600 m MSL and longitudinal follow-ups were conducted at durations of 03, 12 and 18 months. Neuropsychological assessment was performed for mild cognitive impairment (MCI), attention, information processing rate, visuo-spatial cognition and executive functioning. Total homocysteine (tHcy), vitamin B12 and folic acid were estimated. Mini Mental State Examination (MMSE) showed temporal increase in the percentage prevalence of MCI from 8.17% on 03 months of stay at high altitude to 18.54% on 18 months of stay. Impairment in visuo-spatial executive, attention, delayed recall and procedural memory related cognitive domains were detected following prolonged stay in high altitude. Increase in alpha wave amplitude in the T3, T4 and C3 regions was observed during the follow-ups which was inversely correlated (r = -0.68) to MMSE scores. The tHcy increased proportionately with duration of stay at high altitude and was correlated with MCI. No change in vitamin B12 and folic acid was observed. Our findings suggest that cognitive impairment is progressively associated with duration of stay at high altitude and is correlated with elevated tHcy in the plasma. Moreover, progressive MCI at high altitude occurs despite acclimatization and is independent of vitamin B12 and folic acid.

Cognitive performance in high-altitude climbers: a comparative study of saccadic eye movements and neuropsychological tests

Impairment of cognitive performance during and after high-altitude climbing has been described in numerous studies and has mostly been attributed to cerebral hypoxia and resulting functional and structural cerebral alterations. To investigate the hypothesis that high-altitude climbing leads to cognitive impairment, we used of neuropsychological tests and measurements of eye movement (EM) performance during different stimulus conditions. The study was conducted in 32 mountaineers participating in an expedition to Muztagh Ata (7,546 m). Neuropsychological tests comprised figural fluency, line bisection, letter and number cancellation, and a modified pegboard task. Saccadic performance was evaluated under three stimulus conditions with varying degrees of cortical involvement: visually guided pro- and anti-saccades, and visuo-visual interaction. Typical saccade parameters (latency, mean sequence, post-saccadic stability, and error rate) were computed off-line. Measurements were taken at a baseline level of 440 m and at altitudes of 4,497, 5,533, 6,265, and again at 440 m. All subjects reached 5,533 m, and 28 reached 6,265 m. The neuropsychological test results did not reveal any cognitive impairment. Complete eye movement recordings for all stimulus conditions were obtained in 24 subjects at baseline and at least two altitudes and in 10 subjects at baseline and all altitudes. Measurements of saccade performances showed no dependence on any altitude-related parameter and were well within normal limits. Our data indicates that acclimatized climbers do not seem to suffer from significant cognitive deficits during or after climbs to altitudes above 7,500 m. We demonstrated that investigation of EMs is feasible during high-altitude expeditions.

Neuropsychological Functioning Associated with High-Altitude Exposure

This article focuses on neuropsychological functioning at moderate, high, and extreme altitude. This article summarizes the available literature on respiratory, circulatory, and brain determinants on adaptation to hypoxia that are hypothesized to be responsible for neuropsychological impairment due to altitude. Effects on sleep are also described. At central level, periventricular focal damages (leuko-araiosis) and cortical atrophy have been observed. Frontal lobe and middle temporal lobe alterations are also presumed. A review is provided regarding the effects on psychomotor performance, perception, learning, memory, language, cognitive flexibility, and metamemory. Increase of reaction time and latency of P300 are observed. Reduced thresholds of tact, smell, pain, and taste, together with somesthetic illusions and visual hallucinations have been reported. Impairment in codification and short-term memory are especially noticeable above 6,000 m. Alterations in accuracy and motor speed are identified at lower altitudes. Deficits in verbal fluency, language production, cognitive fluency, and metamemory are also detected. The moderating effects of personality variables over the above-mentioned processes are discussed. Finally, methodological flaws found in the literature are detailed and some applied proposals are suggested.

Cortical Sensorimotor Interactions During the Expectancy of a Go/No-Go Task: Effects of Painful Stimuli

The intent of this electroencephalography study was to investigate the competition between cortical nociceptive and cognitive-motor processes preceding sensorimotor interactions. Sensorimotor expectancy processes to painful stimulation and motor go/no-go demands were indexed over primary sensorimotor and midline cortical areas by contingent negative variation (CNV). Before the sensorimotor interaction, CNV was observed over midline posterior and bilateral central areas. Early expectancy of painful stimulation and the go/no-go task induced an evident midline posterior CNV. During the late expectancy period. CNV extended to the right central area contralateral to the stimulation. These findings suggest a sequential activation of midline posterior and primary sensorimotor areas contralateral to the painful stimulation as a reflection of the enhanced nociceptive processes preceding painful sensorimotor interactions.

Working in permanent hypoxia for fire protection-impact on health

OBJECTIVES

A new technique to prevent fires is continuous exchange of oxygen with nitrogen which leads to an oxygen concentration of between 15% and 13% in the ambient air. This paper reviews the effect of short-term, intermittent hypoxia on health and performance of people working in such atmospheres.

METHODS

We reviewed the effect of ambient air hypoxia on human health in the literature using Medline, as well as reference lists of articles and handbooks. Articles were assessed from the perspective of working conditions in fire-protected rooms.

RESULTS

Oxygen reduced to 15% and 13% in normobaric atmospheres is equivalent to the hypobaric atmospheres found at 2,700 and 3,850-m altitudes. When acutely exposed, a healthy person responds within minutes to hours with increased ventilation, stimulation of the sympathetic system, increased heart rate, increased pulmonary-circulation resistance, reduced plasma volume, and stimulation of erythropoesis. Acute mountain sickness occurs frequently at these oxygen partial pressures, but the full syndrome is rare if continuous exposure is limited to 6 h. Mood, cognitive, and psychomotor functions may be mildly impaired in these conditions, but data are inconclusive. Persons suffering from cardiac, pulmonary, or hematological diseases should consult a specialist in order for their individual risk to be assessed, and medical screening for any of these diseases is strongly recommended prior to exposure.

CONCLUSION

Preliminary evidence suggests that working environments with low oxygen concentrations to a minimum of 13% and normal barometric pressure do not impose a health hazard, provided that precautions are observed, comprising medical examinations and limitation of exposure time. However, evidence is limited, particularly with regard to workers performing strenuous tasks or having various diseases. Therefore, close monitoring of the health problems of people working in low oxygen atmospheres is necessary.

Doppler study of middle cerebral artery blood flow velocity and cerebral autoregulation during a simulated ascent of Mount Everest

OBJECTIVE

To explore cerebral hemodynamics in 8 healthy volunteers in a hypobaric chamber up to the altitude of Mount Everest after a progressive stepwise decompression to 8,848 m.

METHODS

Physiological, clinical, and transcranial Doppler data were collected after at least 3 days at 5,000, 6,000, and 7,000 m and within 4 hours of reaching 8,000 m and returning to sea level.

RESULTS

Three subjects were excluded at 8,000 and 8,848 m because of acute neurological deficits. Heart rate increased; mean arterial pressure remained stable; PaO2 and PaCO2 decreased with altitude; hemoglobin (Hb) and hematocrit (Ht) increased; arterial O2 content decreased over 6,000 m; middle cerebral artery blood flow velocity (MCAv) increased only during acute exposure to 8,000 m; and the corresponding pulsatility (PI) and resistivity indices (RI) decreased over 5,000 m. PI and RI correlated with heart rate. The transient hyperemic response (THR) of MCAv to common carotid compression was depressed at 8,000 m.

CONCLUSIONS

At 8,000 m, the increase in MCAv seemed to reflect the normal hemodynamic response to acute hypoxia. The decrease of THR at this altitude could be an indication of impaired cerebral autoregulation. The role of impaired cerebral autoregulation in the genesis of acute neurologic deficits, observed at 8,000 m and above in 3 subjects, remains speculative.

Operation Everest III (Comex'97): the effect of simulated sever hypobaric hypoxia on lipid peroxidation and antioxidant defence systems in human blood at rest and after maximal exercise

Eight subjects were placed in a decompression chamber for 31 days at pressures from sea level (SL) to 8848 m altitude equivalent. Whole blood lipid peroxidation (LP) was increased at 6000 m by a mean of 23% (P<0.05), at 8000 m by 79% (P<0.01) and at 8848 m by 94% (P<0.01). (All figures are means.) Two days after return to sea level (RSL), it remained high, by 81% (P<0.01), while corresponding erythrocyte GSH/GSSG ratios decreased by 31, 46, 49, 48%, respectively (each P<0.01). Erythrocyte SOD and plasma ascorbate did not change significantly. At sea level, maximal exercise induced a 49% increase in LP (P<0.01), and a 27% decrease in erythrocyte GSH/GSSG ratio relative to resting values (P<0.05). At 6000 m, the LP was enhanced further from 23 (P<0.05) to 66% (P<0.01), and after RSL from 81 (P<0.01) to 232% (P<0.01), while pre-exercise GSH/GSSG ratios did not change significantly. Exercise did not change plasma ascorbate relative to sea level or to 6000 m, but decreased after RSL by 32% (P<0.01). These findings suggest that oxidative stress is induced by prolonged hypobaric hypoxia, and is maintained by rapid return to sea level, similar to the post-hypoxic re-oxygenation process. It is increased by physical exercise.

Relationships of personality traits with performance in reaction time, psychomotor ability, and mental efficiency during a 31-day simulated climb of Mount Everest in a hypobaric chamber'

Exposure to chronic hypoxia induces behavioral and mood disturbances and alterations in cognitive functions. We examined the relationships of personality traits, including trait-anxiety, with performance in binary visual reaction time, psychomotor ability, and mental efficiency, using the psychological database of the 'Everest-Comex 97' experiment, which consisted in a 31-day simulated climb in a hypobaric chamber from sea level to 8,848 m altitude. Analysis yielded a significant positive correlation between the climbers' mean reaction time at hypoxic conditions and preclimb scores on trait-anxiety (as assessed by Spielberger's State-Trait Anxiety Inventory) and further significant negative correlations with both Factor A (reserved-outgoing) and Factor G (expedient-conscientious) of the Cattell Sixteen Personality Factor Questionnaire. In contrast, no significant correlation was found between the climbers' mean psychomotor performance and mental efficiency with personality traits, including anxiety. These findings agree with those of previous studies: (i) anxiety could mediate stimulus-response tasks but not more complex tasks requiring strategic processes, (ii) individuals with personality traits such as 'reserved' and 'expedient' could have slight advantages in processing information on stimulus-response tasks. Limitations in study design are also discussed.

Relationships between mood states and performances in reaction time, psychomotor ability, and mental efficiency during a 31-day gradual decompression in a hypobaric chamber from sea level to 8848 m equivalent altitude

High altitude is characterized by hypoxic environmental conditions that may induce a set of pathological disorders, known as acute mountain sickness. In addition to the physiological symptoms, exposure to high altitude may also produce adverse changes in motor skills, mental efficiency, and mood states, including anxiety. In the present study, we investigated the relationships between mood states, including anxiety, and performance changes in reaction time, psychomotor ability and mental efficiency in eight climbers participating in the 'Everest-Comex 97', a 31-day gradual decompression in a hypobaric chamber from sea level to 8848 m equivalent altitude. Tests of visual reaction time, manual dexterity, and number ordination were used; anxiety responses and mood states were assessed using the Spielberger State-Trait Anxiety Inventory (STAI) and the 'Profile of Mood States' (POMS), respectively. A significant positive correlation was found between the climbers' performance in reaction time and changes in state-type anxiety levels, suggesting that anxiety could lead to an improved reaction time. In addition, significant negative correlations were also found between the climbers' performance in psychomotor ability, mental efficiency, and reaction time, and several POMS factors, including Tension, Hostility, Confusion, and Fatigue. Overall, these data indicate, in agreement with previous studies, that anxiety may favour, or at least not alter, the processes of information of relatively simple tasks, such as reaction time, and further suggest that adverse changes in moods could modulate performance negatively.

Physiological profile of middle-aged and older climbers who ascended Gasherbrum II, an 8035-m Himalayan peak

BACKGROUND

The purpose of this study was to investigate the physiological characteristics of a group of middle-aged and older Japanese climbers who ascended Gasherbrum II, an 8035-m peak in the Karakoram Range of the Himalayas.

METHODS

Body composition, cardiac structure, and respiratory gas exchange during exercise were estimated in eight climbers with differing levels of experience (seven men and one woman, aged 54 to 63 years) 6 months before their expedition.

RESULTS

Using supplementary O2, the four experienced climbers ascended beyond Camp 4 (7400 m) without showing any health problems and were able to attempt the summit. In contrast, the others, who had minimal experience at extreme altitude, suffered from altitude sickness on the way to Camp 4. Body mass index values were relatively high, but their low percentage of body fat (14.9%-21.4%) was indicative of the climbers' substantial lean body weight. Cardiac structures were generally normal, although three experienced male climbers had borderline hypertension and eccentric hypertrophy of the left ventricle. Peak VO2 ranged from 30.9 to 45.6 ml/kg/min, and no significant relationship between fitness level and the success or failure of the ascent was evident.

CONCLUSIONS

Even sexagenarians are capable of safely climbing 8000-m peaks with supplementary O2. An exceptionally high fitness level, as is seen in elite older athletes, does not appear to be required. What is essential, however, is moderate fitness, good health, and extensive experience.

Color discrimination under chronic hypoxic conditions (simulated climb "Everest-Comex 97")

Hypoxia is known to alter visual functions. In the present study, the effects of chronic hypobaric hypoxia upon visual color discrimination were studied in 8 subjects participating in a simulated climb from sea level (PO2 = 210 hPa) to 8,848 m (PO2 = 70 hPa) over a 31-day period of confinement in a decompression chamber ('Everst-Comex 97'). During these investigations, the subjects were required to discriminate between colors of different hue in the red, blue, and green ranges. Alterations in color discrimination increased slightly but significantly as altitude increased. Impairments occurred mainly in the red and blue ranges. In addition, our results further indicate that color discrimination would be affected only when a minimum threshold of difference between color stimuli is not present. Methodological and physiological implications are discussed.

A study of mood changes and personality during a 31-day period of chronic hypoxia in a hypobaric chamber (Everest-Comex 97)

High altitudes of more than 3,000 meters produce physiological disorders and adverse changes in mood states. In the present study, we report analyses of mood states and personality traits in eight experienced climbers participating in a 31-day period of confinement in hypobaric chamber and gradual decompression from sea level to 8,848 m (Experiment 'Everest-Comex 97'). The subjects were tested at 5,500 m and 6,500 m on Day 13, 5,000 m and 6,500 m on Day 24, and 8,000 m and 8,848 m altitude on Days 27 and 31. Adverse changes in mood states, such as Vigor and Fatigue, occurred at 8,000 m and 8,848 m, which were significantly correlated with cerebral altitude symptomatology. In addition, a significant negative correlation was found between Fatigue and Factor C, which is a personality measure of emotional stability. We suggest that individuals with low emotional stability could be more sensitive to environmental stressors than more emotionally stable subjects who face reality.

An anxiety, personality and altitude symptomatology study during a 31-day period of hypoxia in a hypobaric chamber (experiment 'Everest-Comex 1997')

Extreme environmental situations are useful tools for the investigation of the general processes of adaptation. Among such situations, high altitude of more than 3000 m produces a set of pathological disorders that includes both cerebral (cAS) and respiratory (RAS) altitude symptoms. High altitude exposure further induces anxiety responses and behavioural disturbances. The authors report an investigation on anxiety responses, personality traits, and altitude symptoms (AS) in climbers participating in a 31-day period of confinement and gradual decompression in a hypobaric chamber equivalent to a climb from sea-level to Mount Everest (8848 m altitude). Personality traits, state-trait anxiety, and AS were assessed, using the Cattell 16 Personality Factor questionnaire (16PF), the Spielberger's State-Trait Anxiety Inventory (STAI), and the Lake Louise concensus questionnaire. Results show significant group effect for state-anxiety and AS; state-anxiety and AS increased as altitude increased. They also show that state-type anxiety shows a similar time-course to cAS, but not RAS. Alternatively, our results demonstrate a significant negative correlation between Factor M of the 16PF questionnaire, which is a personality trait that ranges from praxernia to autia. In contrast, no significant correlation was found between personality traits and AS. This suggests that AS could not be predicted using personality traits and further support that personality traits, such as praxernia (happening sensitivity), could play a major role in the occurrence of state-type anxiety responses in extreme environments. In addition, the general processes of coping and adaptation in individuals participating in extreme environmental experiments are discussed.