High altitude exposure impairs sleep patterns, mood, and cognitive functions

EEG and fNIRS datasets based on Stroop task during two weeks of high-altitude exposure in new immigrants

Maintaining sufficient cerebral oxygen metabolism is crucial for human survival, especially in challenging conditions such as high-altitudes. Human cognitive neural activity is sensitive to fluctuations in oxygen levels. However, there is a lack of publicly available datasets on human behavioural responses and cerebral dynamics assessments during the execution of conflicting tasks in natural hypoxic environments. We recruited 80 healthy new immigrant volunteers (males, aged 20 ± 2 years) and employed the Stroop cognitive conflict paradigm. After a two-week exposure to both high and low-altitudes, the behavioural performance, prefrontal oxygen levels, and electroencephalography (EEG) signals were recorded. Comparative analyses were conducted on the behavioural reaction times and accuracy during Stroop tasks, and statistical analyses of participants' prefrontal oxygen levels and EEG signals were performed. We anticipate that our open-access dataset will contribute to the development of monitoring devices and algorithms, designed specifically for measuring cerebral oxygen and EEG dynamics in populations exposed to extreme environments, particularly among individuals suffering from oxygen deficiency.

Elevating understanding: Linking high-altitude hypoxia to brain aging through EEG functional connectivity and spectral analyses

High-altitude hypoxia triggers brain function changes reminiscent of those in healthy aging and Alzheimer's disease, compromising cognition and executive functions. Our study sought to validate high-altitude hypoxia as a model for assessing brain activity disruptions akin to aging. We collected EEG data from 16 healthy volunteers during acute high-altitude hypoxia (at 4,000 masl) and at sea level, focusing on relative changes in power and aperiodic slope of the EEG spectrum due to hypoxia. Additionally, we examined functional connectivity using wPLI, and functional segregation and integration using graph theory tools. High altitude led to slower brain oscillations, that is, increased δ and reduced α power, and flattened the 1/f aperiodic slope, indicating higher electrophysiological noise, akin to healthy aging. Notably, functional integration strengthened in the θ band, exhibiting unique topographical patterns at the subnetwork level, including increased frontocentral and reduced occipitoparietal integration. Moreover, we discovered significant correlations between subjects' age, 1/f slope, θ band integration, and observed robust effects of hypoxia after adjusting for age. Our findings shed light on how reduced oxygen levels at high altitudes influence brain activity patterns resembling those in neurodegenerative disorders and aging, making high-altitude hypoxia a promising model for comprehending the brain in health and disease.

Dose-effect of exercise intervention on heart rate variability of acclimatized young male lowlanders at 3,680 m

This study investigated whether exercise could improve the reduced HRV in an environment of high altitude. A total of 97 young, healthy male lowlanders living at 3,680 m for >1 year were recruited. They were randomized into four groups, of which three performed-low-, moderate-, and high-intensity (LI, MI, HI) aerobic exercise for 4 weeks, respectively. The remaining was the control group (CG) receiving no intervention. For HI, compared to other groups, heart rate (p = 0.002) was significantly decreased, while standard deviation of RR intervals (p < 0.001), SD2 of Poincaré plot (p = 0.046) and the number of successive RR interval pairs that differ by > 50 ms divided by total number of RR (p = 0.032), were significantly increased after intervention. For MI, significantly increase of trigonometric interpolation in NN interval (p = 0.016) was observed after exercise. Further, a decrease in systolic blood pressure (SBP) after high-intensity exercise was found significantly associated with an increase in SD2 (r = - 0.428, p = 0.042). These results indicated that there was a dose effect of different intensities of aerobic exercise on the HRV of acclimatized lowlanders. Moderate and high-intensity aerobic exercise would change the status of the autonomic nervous system (ANS) and decrease the blood pressure of acclimatized lowlanders exposed to high altitude.

The Effect of High-Altitude Hypoxia on Neuropsychiatric Functions

Liu, Bo, Minlan Yuan, Mei Yang, Hongru Zhu, and Wei Zhang. The effect of high-altitude hypoxia on neuropsychiatric functions. High Alt Med Biol. 25:26-41, 2024. Background: In recent years, there has been a growing popularity in engaging in activities at high altitudes, such as hiking and work. However, these high-altitude environments pose risks of hypoxia, which can lead to various acute or chronic cerebral diseases. These conditions include common neurological diseases such as acute mountain sickness (AMS), high-altitude cerebral edema, and altitude-related cerebrovascular diseases, as well as psychiatric disorders such as anxiety, depression, and psychosis. However, reviews of altitude-related neuropsychiatric conditions and their potential mechanisms are rare. Methods: We conducted searches on PubMed and Google Scholar, exploring existing literature encompassing preclinical and clinical studies. Our aim was to summarize the prevalent neuropsychiatric diseases induced by altitude hypoxia, the potential pathophysiological mechanisms, as well as the available pharmacological and nonpharmacological strategies for prevention and intervention. Results: The development of altitude-related cerebral diseases may arise from various pathogenic processes, including neurovascular alterations associated with hypoxia, cytotoxic responses, activation of reactive oxygen species, and dysregulation of the expression of hypoxia inducible factor-1 and nuclear factor erythroid 2-related factor 2. Furthermore, the interplay between hypoxia-induced neurological and psychiatric changes is believed to play a role in the progression of brain damage. Conclusions: While there is some evidence pointing to pathophysiological changes in hypoxia-induced brain damage, the precise mechanisms responsible for neuropsychiatric alterations remain elusive. Currently, the range of prevention and intervention strategies available is primarily focused on addressing AMS, with a preference for prevention rather than treatment.

Nitronyl Nitroxide Ameliorates Hypobaric Hypoxia-Induced Cognitive Impairment in Mice by Suppressing the Oxidative Stress, Inflammatory Response and Apoptosis

Abundant investigations have shown that hypobaric hypoxia (HH) causes cognitive impairment, mostly attributed to oxidative stress, inflammation, and apoptosis. HPN (4'-hydroxyl-2-subsitiuted phenylnitronyl nitroxide) is an excellent free radical scavenger with anti-inflammatory and anti-apoptotic activities. Our previous study has found that HPN exhibited neuroprotective effect on HH induced brain injury. In the present study, we examined the protective effect and potential mechanism of HPN on HH-induced cognitive impairment. Male mice were exposed to HH at 8000 m for 3 days with and without HPN treatment. Cognitive performance was assessed by the eight-arm radical maze. The histological changes were assayed by Nissle staining. The hippocampus cell apoptosis was detected by Tunnel staining. The levels of inflammatory cytokines and oxidative stress markers were detected. The expression of oxidative stress, inflammation-related and apoptosis-related proteins was determined by western blot. HPN administration significantly and mitigated HH induced histological damages and spatial memory loss with the evidence of decreased working memory error (WME), reference memory error (RME), total errors (TE) and total time (TT). In addition, HPN treatment significantly decreased the content of H2O2 and MDA, increased the levels of SOD, CAT, GSH-Px and GSH, and inhibited the synthesis of TNF-α, IL-1β and IL-6. Moreover, HPN administration could down-regulate the expression of NF-κB, TNF-α, Bax, and cleaved caspase-3 and up-regulate the expression of Nrf2, HO-1 and Bcl-2. The number of apoptotic cells was also significantly decreased in the hippocampus of mice in the HPN group. There results indicate that HPN improve HH-induced cognitive impairment by alleviating oxidative stress damage, suppressing inflammatory response and apoptosis and may be a powerful candidate compound for alleviating memory loss induced by HH.

Acute mountain sickness predicts the emotional state of amateur mountaineers

Research on amateur mountaineers is scarce, and this study aims to delve into the emotional experiences of ten amateur mountaineers during their ascent using the "Befindlichkeitsskala" (BFS) and Lake Louise Acute Mountain Sickness scoring system (LLS). These subjects were exposed to altitudes of 3140 m, 4300 m, and 5276 m, respectively. We found that LLS scores were negatively correlated with positive emotions (β = -27.54, p < 0.05) and positively correlated with negative emotions (β = 21.97, p < 0.05). At an altitude of 4300 m, individuals with AMS exhibited significant differences in depression, anger, excitement, and inactivity compared to climbers without AMS. Upon returning to 3140 m after completing the climb, significant differences were observed in emotions such as happiness, calmness, anger, excitement, and depression. Throughout the three-day climb, noteworthy differences emerged in activity, happiness, calmness, inactivity, positive emotions (p < 0.01), negative emotions, and overall emotional scores (p < 0.05). Our study suggests a decline in the emotional well-being of amateur climbers with increasing altitude, highlighting AMS as a pivotal predictive factor for emotional experiences while climbing.

The effects of sleep deprivation, acute hypoxia, and exercise on cognitive performance: A multi-experiment combined stressors study

INTRODUCTION

Both sleep deprivation and hypoxia have been shown to impair executive function. Conversely, moderate intensity exercise is known to improve executive function. In a multi-experiment study, we tested the hypotheses that moderate intensity exercise would ameliorate any decline in executive function after i) three consecutive nights of partial sleep deprivation (PSD) (Experiment 1) and ii) the isolated and combined effects of a single night of total sleep deprivation (TSD) and acute hypoxia (Experiment 2).

METHODS

Using a rigorous randomised controlled crossover design, 12 healthy participants volunteered in each experiment (24 total, 5 females). In both experiments seven executive function tasks (2-choice reaction time, logical relations, manikin, mathematical processing, 1-back, 2-back, 3-back) were completed at rest and during 20 min semi-recumbent, moderate intensity cycling. Tasks were completed in the following conditions: before and after three consecutive nights of PSD and habitual sleep (Experiment 1) and in normoxia and acute hypoxia (FIO2 = 0.12) following one night of habitual sleep and one night of TSD (Experiment 2).

RESULTS

Although the effects of three nights of PSD on executive functions were inconsistent, one night of TSD (regardless of hypoxic status) reduced executive functions. Significantly, regardless of sleep or hypoxic status, executive functions are improved during an acute bout of moderate intensity exercise.

CONCLUSION

These novel data indicate that moderate intensity exercise improves executive function performance after both PSD and TSD, regardless of hypoxic status. The key determinants and/or mechanism(s) responsible for this improvement still need to be elucidated. Future work should seek to identify these mechanisms and translate these significant findings into occupational and skilled performance settings.

Sleep at high altitude: A bibliometric study and visualization analysis from 1992 to 2022

Background

As an important monitoring index for adaptation to hypoxia, sleep may reflect the adaptive state of the body at high altitudes. The literature has shown a link between altitude and sleep problems, and sleep changes have become a common problem for individuals at high altitudes, negatively impacting their physical and mental health. As research on high-altitude sleep has gained attention in recent years, the publishing volume has increased worldwide, necessitating a more comprehensive understanding of this field. This manuscript evaluates the key themes and emerging trends in high-altitude sleep over the past few decades and predicts future research directions.

Methods

Articles related to high-altitude sleep published from 1992 to 2022 were retrieved from the Web of Science Core Collection, and the relevant literature characteristics were extracted after the screening. Then, bibliometric analyses and visualizations were performed using Microsoft Excel, CiteSpace, VOSviewer, and an online analysis platform (http://bibliometric.com).

Results

A total of 1151 articles were retrieved, of which 368 were included in the analysis, indicating a gradually increasing trend. The United States, Switzerland, and China have made significant contributions in this field. Bloch KE from the University of Zurich was determined to be the most productive and academically influential author in this field. The highest-yielding journal was High Altitude Medicine & Biology. Initially, altitude training was the primary research topic. Currently, research focuses on sleep disorders and sleep apnea. In the coming years, keywords such as "sleep quality," "prevalence," and "obstructive sleep apnea" will attract more attention.

Conclusion

Our findings will assist scholars to better understand the intellectual structure and emerging trends in this field. Future developments in high-altitude sleep research are highly anticipated, particularly in terms of sleep quality at high altitudes and its associated prevalence. This research is also crucial for the improvement and treatment of symptoms during nocturnal sleep in patients with chronic hypoxia due to cardiopulmonary diseases at high altitudes.

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.

Mechanism, prevention and treatment of cognitive impairment caused by high altitude exposure

Hypobaric hypoxia (HH) characteristics induce impaired cognitive function, reduced concentration, and memory. In recent years, an increasing number of people have migrated to high-altitude areas for work and study. Headache, sleep disturbance, and cognitive impairment from HH, severely challenges the physical and mental health and affects their quality of life and work efficiency. This review summarizes the manifestations, mechanisms, and preventive and therapeutic methods of HH environment affecting cognitive function and provides theoretical references for exploring and treating high altitude-induced cognitive impairment.

The Effect of Ultrahigh Altitude on the Mental Health of Civil Servants in Western China Based on Propensity Score Matching

Wang, Luyao, Bo Zhou, Chenghui Yang, Shuya Pan, Yulan Huang, and Jinyu Wang. The effect of ultrahigh altitude on the mental health of civil servants in western China based on propensity score matching. High Alt Med Biol. 24:193-200, 2023. Objective: This study aims to analyze the net effect of ultrahigh altitude on the mental health of civil servants in western China after adjusting for sociodemographic factors. Methods: A cross-sectional study was performed to survey the mental health of 2,939 civil servants working at an altitude of more than 1,500 m in 13 areas of the Tibetan Qiang Autonomous Prefecture of Ngawa using the Insomnia Severity Index Questionnaire, 7-item Generalized Anxiety Disorder Scale, and Patient Health Questionnaire-9. Ultrahigh altitude refers to an area above 3,500 m above sea level, which may have an impact on the sleep and mood of residents. Therefore, our research was divided into two groups based on altitude (ultrahigh altitude >3,500 m; high altitude = 1,500-3,400 m). Propensity score matching (PSM) was used to control for sociodemographic factors and compare the differences in mental health between the two groups. Results: After kernel matching, the mean bias of the covariates was reduced from 21.6 to 1.8. The severity of insomnia, depression, and anxiety in civil servants at ultrahigh altitudes was still significantly greater than that in civil servants at high altitudes after controlling for sociodemographic factors, and the average treatment effects on the treated were 1.39, 1.35, and 0.80, respectively; the results were significant (α < 0.01). PSM regression analysis further showed that for every 100 m increase in altitude, the severity of anxiety, depression, and insomnia increased by 0.042 points (p < 0.001), 0.063 points (p < 0.001), and 0.070 points (p < 0.001), respectively, all of which were higher than those obtained with ordinary least squares regression. Conclusion: Ultrahigh altitude significantly increases the severity of insomnia, depression, and anxiety after adjusting for sociodemographic factors.

Isolated high altitude psychosis, delirium at high altitude, and high altitude cerebral edema: are these diagnoses valid?

Psychosis is a psychopathological syndrome that can be triggered or caused by exposure to high altitude (HA). Psychosis can occur alone as isolated HA psychosis or can be associated with other mental and often also somatic symptoms as a feature of delirium. Psychosis can also occur as a symptom of high altitude cerebral edema (HACE), a life-threatening condition. It is unclear how psychotic symptoms at HA should be classified into existing diagnostic categories of the most widely used classification systems of mental disorders, including the Diagnostic and Statistical Manual of Mental Disorders (DSM-V) and the International Statistical Classification of Diseases and Related Health Problems (ICD-11). We provide a diagnostic framework for classifying symptoms using the existing diagnostic categories: psychotic condition due to a general medical condition, brief psychotic disorder, delirium, and HACE. We also discuss the potential classification of isolated HA psychosis into those categories. A valid and reproducible classification of symptoms is essential for communication among professionals, ensuring that patients receive optimal treatment, planning further trips to HA for individuals who have experienced psychosis at HA, and advancing research in the field.

The Brain at High Altitude: From Molecular Signaling to Cognitive Performance

The brain requires over one-fifth of the total body oxygen demand for normal functioning. At high altitude (HA), the lower atmospheric oxygen pressure inevitably challenges the brain, affecting voluntary spatial attention, cognitive processing, and attention speed after short-term, long-term, or lifespan exposure. Molecular responses to HA are controlled mainly by hypoxia-inducible factors. This review aims to summarize the cellular, metabolic, and functional alterations in the brain at HA with a focus on the role of hypoxia-inducible factors in controlling the hypoxic ventilatory response, neuronal survival, metabolism, neurogenesis, synaptogenesis, and plasticity.

The change of attention network functions and physiological adaptation during high-altitude hypoxia and reoxygenation

Previous studies have not reached a definitive conclusion regarding the effect of high-altitude hypoxia and reoxygenation on attention. To clarify the influence of altitude and exposure time on attention and the relations between physiological activity and attention, we conducted a longitudinal study to track attention network functions in 26 college students. The scores on the attention network test and physiological data, including heart rate, percutaneous arterial oxygen saturation (SpO₂), blood pressure, and vital capacity in pulmonary function measurement, were collected at five time-points: two weeks before arriving at high altitude (baseline), within 3 days after arriving at high altitude (HA3), 21 days after arriving at high altitude (HA21), 7 days after returning to sea level (POST7) and 30 days after returning to sea level (POST30). The alerting scores at POST30 were significantly higher than those at baseline, HA3 and HA21; the orienting scores at HA3 were lower than those at POST7 and POST30; the executive control scores at POST7 were significantly lower than those at baseline, HA3, HA21, and POST30; and the executive control scores at HA3 were significantly higher than those at POST30. The change in SpO₂ during high-altitude acclimatization (from HA3 to HA21) was positively correlated with the orienting score at HA21. Vital capacity changes during acute deacclimatization positively correlated with orienting scores at POST7. Attention network functions at the behavioral level did not decline after acute hypoxia exposure compared with baseline. Attention network functions after returning to sea level were improved compared with those during acute hypoxia; additionally, alerting and executive function scores were improved compared with those at baseline. Thus, the speed of physiological adaptation could facilitate the recovery of orienting function during acclimatization and deacclimatization.

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.

The Effects of High-Altitude Mountaineering on Cognitive Function in Mountaineers: A Meta-Analysis

BACKGROUND

Nowadays, with the convenience of international traveling and driven by many individuals' fond dreams of challenging high-altitude exercises, high-altitude mountaineering is becoming increasingly popular worldwide. Therefore, we performed a meta-analysis to determine the effects of high-altitude mountaineering on cognitive functions in mountaineers before and after climbing.

METHODS

After a thorough electronic literature search and selection, eight studies were included in this meta-analysis, and the conducted test cycles ranged from 8 to 140 days. Eight variables were included in this meta-analysis: the Trail-Making Test (TMB), Digit Span-Forward (DSF), Digit Span-Backward (DSB), Finger Tapping Test-Right (FTR) Finger Tapping Test-Left (FTL), Wechsler Memory Scale Visual (WMSV), the Aphasia Screening Test (Verbal Items) (AST-Ver), and the Aphasia Screening Test (Visual Motor Errors) (AST-Vis). The effect sizes (ES) and forest plots of these eight variables were generated.

RESULTS

Five variables (TMB, ES = 0.39; DSF, ES = 0.57; FTR, ES = 0.50; FTL, ES = 0.16; WMSV, ES = 0.63) out of eight were significantly improved after high-altitude mountaineering, whereas the ES values of DSB, AST-Ver, and AST-Vis did not show significant improvement after climbing.

CONCLUSION

Despite two limitations, namely, methodological issues inherent in the meta-analysis and the inability to explain high heterogeneity between studies, this study is the first meta-analysis that has attempted to specify and compare the cognitive functions of mountaineers before and after high-altitude mountaineering. Furthermore, as a short-term plateau exercise, high-altitude mountaineering has no significant negative impacts on the cognitive functions of climbers. Future research is needed for a long period of high-altitude mountaineering.

Night-Time Heart Rate Variability during an Expedition to Mt Everest: A Case Report

Mt Everest has been gaining popularity from casual hiking athletes, climbers, and ultra-endurance marathon runners. However, living and sleeping at altitude increases the risk of injury and illness. This is because travel to high altitudes adversely affects human physiology and performance, with unfavourable changes in body composition, exercise capacity, and mental function. This is a case report of a climber who reached the summit of Mt Everest from the north side. During his 40-day expedition, we collected sleep quality data and night-time heart rate variability. During the night inside the tent, the air temperature ranged from -12.9 to 1.8 °C (-5.8 ± 4.9 °C) and the relative humidity ranged from 26.1 to 78.9% (50.7 ± 16.9%). Awake time was 17.1 ± 6.0% of every sleep-time hour and increased with altitude (r = 0.42). Sleep time (r = -0.51) and subjective quality (r = 0.89) deteriorated with altitude. Resting heart rate increased (r = 0.70) and oxygen saturation decreased (r = -0.94) with altitude. The mean NN, RMSSD, total power, LF/HF, and SD1 and SD2 were computed using the NN time series. Altitude reduced the mean ΝΝ (r = -0.73), RMSSD (r = -0.31), total power (r = -0.60), LF/HF ratio (r = -0.40), SD1 (r = -0.31), and SD2 (r = -0.70). In conclusion, this case report shows that sleeping at high altitudes above 5500 m results in progressively reduced HRV, increased awakenings, as well as deteriorated sleep duration and subjective sleep quality. These findings provide further insight into the effects of high altitude on cardiac autonomic function and sleep quality and may have implications for individuals who frequently spend time at high altitudes, such as climbers.

Women's mood at high altitude. sexual dimorphism in hypoxic stress modulation by the tryptophan-melatonin axis

Sexual (and gender)-dimorphism in tolerance to hypobaric hypoxia increasingly matters for a differential surveillance of human activities at high altitude (HA). At low altitudes, the prevalence of anxiety and depression in women has already been found to double when compared with men; it could be expected to even increase on exposure to HA. In purposefully caring for the health of women at HA, the present work explores the potential involvement of the tryptophan (Trp)-melatonin axis in mood changes on exposure to hypobaric hypoxia. The present work highlights some already known anxiogenic effects of HA exposure. Hypoxia and insomnia reduce serotonin (5-HT) availability; the latter defect being expressed as failure of brown adipose tissue (BAT) activation and mood disorders. Rapid eye movement (REM) sleep organization and synapsis restoration that are additionally affected by hypoxia impair memory consolidation. Affective complaints may thus surge, evolving into anxiety and depression. Sex-related differences in neural network organization and hormonal changes during the menstrual cycle, and certainly also during the life cycle, underscore the possibility of 5-HT-related mood alterations, particularly in women on HA exposure. The mean brain rate of 5-HT synthesis at sea level is already 1.5-fold higher in males than in females. sexual dimorphism also evidences the overexpression effects of SERT, a 5-HT transporter protein. Gonadal and thyroid hormones, as influenced by HA exposure, further modulate 5-HT availability and its effects in women. Besides caring for adequate oxygenation and maintenance of one's body core temperature, special precautions concerning women sojourning at HA should include close observations of hormonal cycles and, perhaps, also trials with targeted antidepressants.

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.

Physical and mental health at high altitude of individuals doing yogic practices

Objectives

There is an increase trend in the past few years, in the number of people traveling to high altitude for recreational activities such as pilgrims, mountaineering, and climbing and for occupational purposes such as defense and mining which have resulted in increasing in hypoxia conditions and anxiety-related medical problems at high altitude. As it is known that mental stress affects brain and heart functions, a recent research performed on Sudarshan Kriya Yoga (SKY) further validated the effectiveness of SKY on participants (practicing SKY) as compared to control after quantifying mental stress. To study the physiological effect of SKY advance breathing technique when immediately ascends to high altitude, we wanted to study the level of stress and mental well-being of lowlanders at high altitude.

Materials and Methods

It is an interventional study performed at high altitudes, with low landers as participants where their biochemical and psychological parameters are being assessed.

Results

The result for biochemical parameter cholesterol, triglycerides, low-density lipoproteins (LDLs), high-density lipoproteins (HDLs), very low-density lipoproteins, LDL-HDL ratio, and cholesterol-HDL ratio showed a significant decrease in the pre- and post-analyses values with P ≤ 0.001. Acute mountain sickness (AMS), Warwick-Edinburgh Mental Well-being Scale, and State and Trait Anxiety Inventory (STAI) also show a decreasing trend with significant result in AMS, mental well-being, and non-significant in STAI p value is P = 0.016, P = 0.055, and P = 0.125, respectively.

Conclusion

We observed positive outcome both in for biochemical and stress-related parameters with SKY advance program practitioners who have rapidly ascend to high altitude.

Positive Psychological Changes at High Altitude Shown by the Low Landers after the Yoga Intervention—Sudarshan Kriya Yoga (SKY)

Background

Immediate assent to high altitude affects the cognitive performance and mood of an individual, which is followed by depression and anxiety. It also affects the sleep quality, general health, and happiness quotient of an individual. Sudarshan Kriya Yoga (SKY) is a cyclical breathing technique, which has been proven successful in managing stress, depression, anxiety, and helps in the improvement of sleep quality.

Purpose

The current study was to understand the role of SKY meditation on psychological parameters, happiness quotient of low landers at high altitude (Leh).

Methods

It is a two-armed pre–post study with experimental and control group both are lowlanders, and their psychological parameters are being assessed when they immediately assent to high altitude (Leh). There are two groups experimental group (SKY) was from AOL SKY–AMP and has prior SKY meditation experience. The control group does not have any yoga or meditation experience. SKY–AMP is a 4 days protocol done at high altitude by the SKY group. Both groups reach Leh through air mode transportation.

Results

Oxford Happiness Questionnaire (OHQ) showed a significant result in the SKY group with P ≤ .001, whereas it is nonsignificant in the control group. We also observed anthropometric and physiological changes in the participants showing significant effects on weight, BMI, waist circumference, hip circumference, and blood pressure; with no significant effect in the control group. It is one of the first studies done with both two groups, where yoga and meditation are done at high altitude and then seen the changes in the groups at physical and psychological level.

Conclusion

Yogic practices can be helpful in having positive psychological change in the lowlanders at high altitude.

Effect of simultaneous exercise and cognitive training on executive functions, baroreflex sensitivity, and pre-frontal cortex oxygenation in healthy older adults: a pilot study

Aging is characterized by cognitive decline affecting daily functioning. To manage this socio-economic challenge, several non-pharmacological methods such as physical, cognitive, and combined training are proposed. Although there is an important interest in this subject, the literature is still heterogeneous. The superiority of simultaneous training compared to passive control and physical training alone seems clear but very few studies compared simultaneous training to cognitive training alone. The aim of this pilot study was to investigate the effect of simultaneous exercise and cognitive training on several cognitive domains in healthy older adults, in comparison with either training alone. Thirty-five healthy older adults were randomized into one of three experimental groups: exercise training, cognitive training, and simultaneous exercise and cognitive training. The protocol involved two 30-min sessions per week for 24 weeks. Cognitive performance in several domains, pre-frontal cortex oxygenation, and baroreflex sensitivity were assessed before and after the intervention. All groups improved executive performance, including flexibility or working memory. We found a group by time interaction for inhibition cost (F_(2,28) = 6.44; p < 0.01) and baroreflex sensitivity during controlled breathing (F_(2,25) = 4.22; p = 0.01), the magnitude of improvement of each variable being associated (r = -0.39; p = 0.03). We also found a decrease in left and right pre-frontal cortex oxygenation in all groups during the trail making test B. A simultaneous exercise and cognitive training are more efficient than either training alone to improve executive function and baroreflex sensitivity. The results of this study may have important clinical repercussions by allowing to optimize the interventions designed to maintain the physical and cognitive health of older adults.

The interplay of hypoxic and mental stress: Implications for anxiety and depressive disorders

Adequate oxygen supply is essential for the human brain to meet its high energy demands. Therefore, elaborate molecular and systemic mechanism are in place to enable adaptation to low oxygen availability. Anxiety and depressive disorders are characterized by alterations in brain oxygen metabolism and of its components, such as mitochondria or hypoxia inducible factor (HIF)-pathways. Conversely, sensitivity and tolerance to hypoxia may depend on parameters of mental stress and the severity of anxiety and depressive disorders. Here we discuss relevant mechanisms of adaptations to hypoxia, as well as their involvement in mental stress and the etiopathogenesis of anxiety and depressive disorders. We suggest that mechanisms of adaptations to hypoxia (including metabolic responses, inflammation, and the activation of chemosensitive brain regions) modulate and are modulated by stress-related pathways and associated psychiatric diseases. While severe chronic hypoxia or dysfunctional hypoxia adaptations can contribute to the pathogenesis of anxiety and depressive disorders, harnessing controlled responses to hypoxia to increase cellular and psychological resilience emerges as a novel treatment strategy for these diseases.

Executive Functions and Mood States in Athletes Performing Exercise Under Hypoxia

Hypoxia can impair cognitive performance, whereas exercise can enhance it. The effects of hypoxia on cognitive performance during exercise appear to be moderated by exercise duration and intensity and by severity and duration of hypoxia and cognitive task. In normal individuals, exercise under hypoxia can evoke adverse post-exercise mood states, such as tension and fatigue. However, little is known about the effects of hypoxia during exercise in trained athletes. The purpose of this study was to investigate how hypoxia affected executive functions and mood states, assessed, respectively, during and post-exercise and to explore the role of motivation moderators, such as inhibition and activation systems (BIS-BAS). Two different sessions of exercise in normoxia and hypoxia (FiO2 13%), each lasting 18 min, were randomly assigned in a counterbalanced order and administered to seventeen male athletes. During exercise bouts, participants performed a mental task (BST) aimed to produce cognitive interference and suppression. Reaction times and accuracy of responses were recorded. After 5 min, all participants completed two questionnaires assessing mood states (ITAMS) and incidence of symptoms potentially related to hypoxia (AMS-C). The results show that hypoxia impairs cognitive performance in terms of slower reaction times, but a high BAS attenuates this effect. Participants with high BAS show an equivalent cognitive performance under hypoxia and normoxia conditions. No effects were found on mood states. Further research is required to investigate the role of BAS, cognitive abilities, and mood states in prolonged hypoxic conditions.

Hypoxia Differentially Affects Healthy Men and Women During a Daytime Nap With a Dose-Response Relationship: a Randomized, Cross-Over Pilot Study

Context: The use of daytime napping as a countermeasure in sleep disturbances has been recommended but its physiological evaluation at high altitude is limited. Objective: To evaluate the neuroendocrine response to hypoxic stress during a daytime nap and its cognitive impact. Design, Subject, and Setting: Randomized, single-blind, three period cross-over pilot study conducted with 15 healthy lowlander subjects (8 women) with a mean (SD) age of 29(6) years (Clinicaltrials identifier: NCT04146857, https://clinicaltrials.gov/ct2/show/NCT04146857?cond=napping&draw=3&rank=12). Interventions: Volunteers underwent a polysomnography, hematological and cognitive evaluation around a 90 min midday nap, being allocated to a randomized sequence of three conditions: normobaric normoxia (NN), normobaric hypoxia at FiO2 14.7% (NH15) and 12.5% (NH13), with a washout period of 1 week between conditions. Results: Primary outcome was the interbeat period measured by the RR interval with electrocardiogram. Compared to normobaric normoxia, RR during napping was shortened by 57 and 206 ms under NH15 and NH13 conditions, respectively (p < 0.001). Sympathetic predominance was evident by heart rate variability analysis and increased epinephrine levels. Concomitantly, there were significant changes in endocrine parameters such as erythropoietin (∼6 UI/L) and cortisol (∼100 nmol/L) (NH13 vs. NN, p < 0.001). Cognitive evaluation revealed changes in the color-word Stroop test. Additionally, although sleep efficiency was preserved, polysomnography showed lesser deep sleep and REM sleep, and periodic breathing, predominantly in men. Conclusion: Although napping in simulated altitude does not appear to significantly affect cognitive performance, sex-dependent changes in cardiac autonomic modulation and respiratory pattern should be considered before napping is prescribed as a countermeasure.

Objective sleep assessments for healthy people in environmental research: A literature review

To date, although many studies had focused on the impact of environmental factors on sleep, how to choose the proper assessment method for objective sleep quality was often ignored, especially for healthy subjects in bedroom environment. In order to provide methodological guidance for future research, this paper reviewed the assessments of objective sleep quality applied in environmental researches, compared them from the perspective of accuracy and interference, and statistically analyzed the impact of experimental type and subjects' information on method selection. The review results showed that, in contrast to polysomnography (PSG), the accuracy of actigraphy (ACT), respiratory monitoring-oxygen saturation monitoring (RM-OSM), and electrocardiograph (ECG) could reach up to 97%, 80.38%, and 79.95%, respectively. In terms of sleep staging, PSG and ECG performed the best, ACT the second, and RM-OSM the worst; as compared to single methods, mix methods were more accurate and better at sleep staging. PSG interfered with sleep a great deal, while ECG and ACT could be non-contact, and thus, the least interference with sleep was present. The type of experiment significantly influenced the choice of assessment method (p < 0.001), 85.3% of researchers chose PSG in laboratory study while 82.5% ACT in field study; moreover, PSG was often used in a relatively small number of young subjects, while ACT had a wide applicable population. In general, researchers need to pay more attention at selection of assessments in future studies, and this review can be used as a reliable reference for experimental design.

Proteomic and Morphological Profiling of Mice Ocular Tissue During High-altitude Acclimatization Process: An Animal Study at Lhasa

Purpose

High-altitude environment mainly with hypobaric hypoxia could induce pathological alterations in ocular tissue. Previous studies have mostly focused on sporadic case reports and simulated high-altitude hypoxia experiments. This aim of this study was to explore the proteomic and morphological changes of ocular tissue in mice at real altitude environment.

Methods

In this study, mice were flown from Chengdu (elevation: 500 m) to Lhasa (elevation: 3600 m). After exposure for 1day, 3, 6, 10, 20, 30, and 40days, the mice were euthanatized to obtain blood and ocular tissue. Serological tests, ocular pathological examinations, integral ocular proteomics analysis, and Western blot were conducted.

Results

We focused on acute phase (1–3 days) and chronic phase (>30 days) during high-altitude acclimatization. Serum interleukin-1 was increased at 3 days, while superoxide dismutase, interleukin-6, and tumor necrosis factor-α showed no statistical changes. H&E staining demonstrated that the cornea was edematous at 3 days and exhibited slower proliferation at 30 days. The choroid showed a consistently significant thickening, while there existed no noticeable changes in retinal thickness. Overall, 4073 proteins were identified, among which 71 and 119 proteins were detected to have significant difference at 3 days and 40 days when compared with the control group. Functional enrichment analysis found the differentiated proteins at 3 days exposure functionally related with response to radiation, dephosphorylation, negative regulation of cell adhesion, and erythrocyte homeostasis. Moreover, the differential profiles of the proteins at 40 days exposure exhibited changes of regulation of complement activation, regulation of protein activation cascade, regulation of humoral immune response, second-messenger-mediated signaling, regulation of leukocyte activation, and cellular iron homeostasis. Interestingly, we found the ocular proteins with lactylation modification were increased along high-altitude adaptation.

Conclusion

This is the first work reporting the ocular proteomic and morphological changes at real high-altitude environment. We expect it would deep the understanding of ocular response during altitude acclimatization.

Experiencing Urban Green and Blue Spaces in Urban Wetlands as a Nature-Based Solution to Promote Positive Emotions

Green and blue spaces are nature-based solutions (NBSs) that evoke positive emotions of experiencers therein. There is an impetus to optimize wetland forest landscapes by planning the geographical arrangement of metrics that promote positive emotion. The facial expressions of nature experiencers in photos, downloaded from social media databases with landscape metrics, were evaluated for emotions and given scores. Happy and sad scores were rated by FireFACE v1.0 software and positive response index (PRI) was calculated as happy score minus sad score. Spatial areas and tree height were evaluated from Landsat 8 images and digital model maps, respectively. Visitors at middle and senior ages smiled more frequently in southern parts than in northern parts, and females had higher happy scores and PRI than males. Both green- and blue-space areas had positive relationships with PRI scores, while blue spaces and their area to park area ratios had positive contributions to happy scores and PRI scores in multivariate linear regression models. Elevation had a negative relationship with positive facial emotion. Overall, based on spatial distributions of blue-space area and elevation, regional landscape was optimized so people perceived more happiness in wetlands around Zhejiang and Shanghai, while people in wetlands of Jiangxi and Hubei showed more net emotional expressions.

Individual Variation Exists Within the Psychological Response to Hypoxic Bed Rest: A Retrospective Analysis

Individual variation is of interest to Space Agency's, which cannot be explored with astronauts due to anonymity. We retrospectively analysed data collected throughout three projects (LunHab: 10-day male, PlanHab: 21-day male, and FemHab: 10-day female) to elucidate the potentially masked individual variation in the psychological responses to bed rest. The Profile of Mood State (POMS) and Positive and Negative Affect Schedule (PANAS) - instruments used to asses psychological state - and Lake Louise Mountain Sickness (LLMS) scores were collected prior to, following and throughout three interventions: 1: normoxic bed rest 2: hypoxic bed rest and 3: hypoxic ambulatory confinement. Total Mood Disturbance (TMD) was calculated from the POMS results, positive affect (PA), and negative affect (NA) from PANAS. The three instruments were included in a latent class mixed model. TMD, NA, and LLMS were included in a four-class model, with each class representing a specific type of response (Class 1: descending, Class 2: flat, Class 3: somewhat flat, Class 4: ascending). Responses for PA were assigned to only two classes (Classes 1 and 2). 54.55% or 24 participants were included in Class 2 (TMD, NA, and LLMS), where the responses did not change and neither hypoxia or activity level had a significant effect on emotional state. The remaining participants were allotted to Class 1, 3, or 4, where hypoxia was a significant covariate, while activity (bed rest) was significant only for class 3. For PA, 84.09% or 37 participants were assigned to class 2 indicating a significant effect of hypoxia on the participants responses with no effect of physical activity. Class 1 participants (n = 7) were not affected by hypoxia, however, physical activity improved their PA. Participants undergoing confinement, hypoxia and bed rest do not exhibit a uniform emotional response and may be categorised into 2-4 distinct classes. These results indicate significant individual emotional responses, that may be masked and underreported by traditional statistical approaches like means ± SD. The emotional state of our participants is a complex construct likely influenced by past experiences and different coping mechanisms which allowed some to adapt to the experimental environment more readily.

The Effect of Chronic Intermittent Hypobaric Hypoxia on Sleep Quality and Melatonin Serum Levels in Chilean Miners

High-altitude mining is an important economic resource for Chile. These workers are exposed to chronic intermittent hypobaric hypoxia (CIHH), which reduces their sleep quality and increases the risk of accidents and long-term illnesses. Melatonin, a hormone produced by the pineal gland, is a sleep inducer that regulates the circadian cycle and may be altered in populations subjected to CIHH. This work aimed to assess the relationship between altitude, sleep quality, and plasma melatonin concentrations in miners with CIHH exposure. 288 volunteers were recruited from five altitudes (0, 1,600, 2,500, 3,500, and 4,500 m). All volunteers worked for 7 days at altitude, followed by 7 days of rest at sea level. We performed anthropometric assessments, nocturnal oximetry, sleep quality and sleepiness surveys, and serum melatonin levels upon awakening. Although oxygen saturation progressively decreased and heart rate increased at higher altitudes, subjective perception of sleep quality was not significantly different, and sleepiness increased in all groups compared to population at sea level. Similarly, melatonin levels increased at all assessed altitudes compared to the population at sea level. These data confirm that sleep disturbances associated with CIHH increase morning melatonin levels. Therefore, this hormone and could potentially serve as a biomarker of sleep quality.

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.

Optimism and Health Self-Perception-Related Differences in Indigenous Kiwchas of Ecuador at Low and High Altitude: A Cross-Sectional Analysis

Ortiz-Prado, Esteban, Katherine Simbaña-Rivera, Diego Duta, Israel Ochoa, Juan S. Izquierdo-Condoy, Eduardo Vasconez, Kathia Carrasco, Manuel Calvopiña, Ginés Viscor, and Clara Paz. Optimism and health self-perception-related differences in indigenous Kiwchas of Ecuador at low and high altitude: a cross-sectional analysis. High Alt Med Biol 00:000-000, 2021. Background: Living at high altitude causes adaptive responses at every physiological and molecular level within the human body. Emotional and psychological short- or long-term consequences, including mood changes, higher mental overload, and depression prevalence, as well as increased risk to commit suicide have been reported among highlanders. The objective of this report is to explore the differences in self-reported dispositional optimism and health perception among sex-, age-, and genotype-controlled indigenous Kiwcha natives living at two different altitudes. Methods: A cross-sectional analysis of the comparison of means of subscales and summary scores of the 36-item short-form health survey (SF-36) self-reported questionnaire and the Life Orientation Test-Revised was conducted among 219 adults Kiwchas living at low (230 m) and high altitude (3,800 m) in Ecuador. Results: High-altitude dwellers presented lower scores in all the studied dimensions of SF-36 and the total score. Differences were found for the role limitation sphere due to vitality (p = 0.005), mental health (p = 0.002), and social functioning (p = 0.005). In all the cases, participants living at low altitudes scored higher than those living at high altitudes. Lowland women were more optimistic than their high-altitude counterparts. Conclusions: We observe that populations located at high altitudes have more unfavorable self-reported health states. Although our results depict the existence of significant differences in the health status of indigenous peoples living at different altitudes, further studies are needed to explain in depth the sociodemographic and/or environmental factors that might underlie these differences.

Cognitive Impairment and Its Associated Factors in Older Adults Living in High and Low Altitude Areas: A Comparative Study

BACKGROUND

Cognitive impairment is a major health concern in older adults. Few studies have examined the association between environmental factors and cognitive impairment, especially in high altitude areas. In this study, the prevalence of cognitive impairment in older adults living in high altitude was compared with those living in low altitude areas.

METHODS

This was a comparative study conducted at Qinghai (high altitude group), and Guangzhou (low altitude group), China. Cognition, depressive symptoms and quality of life (QOL) were assessed using the Montreal Cognitive Assessment (MoCA), Patient Health Questionnaire (PHQ-9) and WHO Quality of Life brief version-WHOQOL-BREF, respectively.

RESULTS

Altogether, 644 older adults (207 in Qinghai and 437 in Guangzhou) completed the assessment. The prevalence rate of cognitive impairment was 94.7% (95% CI: 91.6-97.7%) in older adults living in the high altitude area, while the corresponding figure was 89.2% (95% CI: 86.3-92.1%) in the low altitude area. After controlling for covariates, the high altitude group appeared more likely to have cognitive impairment (OR = 2.92, 95% CI: 1.23-6.91, P = 0.015) compared with the low altitude group. Within the high altitude group sample, multinomial logistic regression analysis revealed that older age (aged 74 and above) was significantly associated with higher risk of severe cognitive impairment (OR = 3.58, 95%CI: 1.44-8.93, P = 0.006), while higher education level (secondary school and above) was associated with decreased risk of moderate cognitive impairment (OR = 0.43, 95%CI: 0.22-0.85, P = 0.006). Within the high altitude group, QOL did not differ significantly between normal/mild, moderate and severe cognitive impairment subgroups across physical [F _{(1, 207)} = 1.83, P = 0.163], psychological [F _{(1, 207)} = 1.50, P = 0.225], social [F _(1,207) = 2.22, P = 0.111] and environmental domains [F _(1,207) = 0.49, P = 0.614].

CONCLUSION

This study found that cognitive impairment was more common among older adults living in the high altitude area. Regular screening and appropriate interventions should be provided to older adults in need.

Sleep-Induced Hypoxia under Flight Conditions: Implications and Countermeasures for Long-Haul Flight Crews and Passengers

PURPOSE

Recuperation during sleep on board of commercial long-haul flights is a safety issue of utmost importance for flight crews working extended duty periods. We intended to explore how sleep and blood oxygenation (in wake versus sleep) are affected by the conditions in an airliner at cruising altitude.

METHODS

Healthy participants' sleep was compared between 4-h sleep opportunities in the sleep laboratory (n = 23; sleep lab, ie, 53 m above sea level) and in an altitude chamber (n = 20; flight level, ie, 753 hPa, corresponding to 2438 m above sea level). A subgroup of 12 participants underwent three additional conditions in the altitude chamber: 1) 4-h sleep at ground level, 2) 4-h sleep at flight level with oxygen partial pressure equivalent to ground level, 3) 4-h monitored wakefulness at flight level. Sleep structure and blood oxygenation were analysed with mixed ANOVAs.

RESULTS

Total sleep time at flight level compared to in the sleep laboratory was shorter (Δ mean ± standard error -11.1 ± 4.2 min) and included less N3 sleep (Δ -17.6 ± 5.4 min), while blood oxygenation was decreased. Participants spent 69.7% (± 8.3%) of the sleep period time but only 13.2% (± 3.0%) of monitored wakefulness in a hypoxic state (<90% oxygen saturation). Oxygen enrichment of the chamber prevented oxygen desaturation.

CONCLUSION

Sleep - but not wakefulness - under flight conditions induces hypobaric hypoxia which may contribute to impaired sleep. The results caution against the assumption of equivalent crew recovery in-flight and on the ground but hold promise for oxygen enrichment as a countermeasure. The present results have implications for flight safety and possible long-term consequences for health in crews.

Sleep, short-term memory, and mood states of volunteers with increasing altitude

PURPOSE

This study sought to identify the changes and potential association between sleep characteristics and short-term memory, and mood states among volunteers at different altitudes and times.

METHOD

A total of 26 healthy volunteers were recruited from the PLA General Hospital, and we conducted a longitudinal prospective survey for over 1 year from November 2019 to April 2021. First, we collected demographic data, sleep parameters by overnight polysomnography (PSG), short-term memory by digit span test, and mood states by completing a questionnaire with a brief profile of mood states among participants in the plain (53 m). Then, we continuously followed them up to collect data in the 3rd month at an altitude of 1,650 m (on the 3rd month of the 1-year survey period), the 3rd month at an altitude of 4,000 m (on the 6th month of the 1-year survey period), and the 9th month at an altitude of 4,000 m (on the 12th month of the 1-year survey period). Multiple linear regression analysis was used to construct models between sleep parameters and short-term memory, and mood states.

RESULTS

The prevalence of sleep apnea syndrome (SAS) significantly increased with rising elevation (P < 0.01). The apnea-hypopnea index (AHI), the mean apnea time (MAT), the longest apnea time (LAT), and the duration of time with SaO₂ < 90% (TSA90) were increased (P < 0.05), and the mean pulse oxygen saturation (MSpO₂), the lowest pulse oxygen saturation (LSpO₂), and heart rate were significantly decreased with increasing altitude (P < 0.05). Digit span scores were decreased with increasing altitude (P < 0.001). A negative mood was more severe and a positive mood increasingly faded with rising elevation (P < 0.001). Additionally, linear correlation analysis showed that higher AHI, LAT, and MAT were strongly associated with a greater decline in short-term memory (in the 3rd and 9th month at an altitude of 4,000 m, respectively: r _s = -0.897, -0.901; r _s = -0.691, -0.749; r _s = -0.732, -0.794, P < 0.001), and also were strongly associated with more severe negative mood (in the 3rd month at altitudes of 1,650 m and 4,000 m, respectively: r _s = 0.655, 0.715, 0.724; r _s = 0.771, 0.638, 0.737, P < 0.000625). Multiple linear regression pointed out that AHI was a significant predictor of negative mood among people at different altitudes (in the 3rd month at an altitude of 1,650 m: TMD = 33.161 + 6.495*AHI; in the 3rd month at an altitude of 4,000 m: TMD = 74.247 + 1.589*AHI, P < 0.05).

CONCLUSION

SAS developed easily in high altitudes, most often in CSA (central sleep apnea, CSA). The sleep, short-term memory, and negative mood were significantly more damaged with elevation in volunteers. Sleep parameters were closely associated with short-term memory and mood states in volunteers at high altitudes; the higher the sleep parameters (AHI, LAT, and MAT) scores, the more significant the mood disorders and the more obvious impairment of short-term memory. AHI was a critical predictor of the negative mood of volunteers at different altitudes. This study provides evidence that could help with the prevention and control of sleep disorder, cognitive disorder, and negative mood among populations with high altitudes.

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.

Impact of 2 days of staging at 2500-4300 m on sleep quality and quantity following subsequent exposure to 4300 m

The impact of 2 days of staging at 2500-4300 m on sleep quality and quantity following subsequent exposure to 4300 m was determined. Forty-eight unacclimatized men and women were randomly assigned to stage for 2 days at one of four altitudes (2500, 3000, 3500, or 4300 m) prior to assessment on the summit of Pikes Peak (4300 m) for 2 days. Volunteers slept for one night at sea level (SL), two nights at respective staging altitudes, and two nights at Pikes Peak. Each wore a pulse oximeter to measure sleep arterial oxygen saturation (sSpO2 , %) and number of desaturations (DeSHr, events/hr) and a wrist motion detector to estimate sleep awakenings (Awak, awakes/hr) and sleep efficiency (Eff, %). Acute mountain sickness (AMS) was assessed using the Environmental Symptoms Questionnaire and daytime SpO2 was assessed after AMS measurements. The mean of all variables for both staging days (STG) and Pikes Peak days (PP) was calculated. The sSpO2 and daytime SpO2 decreased (p < 0.05) from SL during STG in all groups in a dose-dependent manner. During STG, DeSHr were higher (p < 0.05), Eff was lower (p < 0.05), and AMS symptoms were higher (p < 0.05) in the 3500 and 4300 m groups compared to the 2500 and 3000 m groups while Awak did not differ (p > 0.05) between groups. At PP, the sSpO2 , DeSHr, Awak, and Eff were similar among all groups but the 2500 m group had greater AMS symptoms (p < 0.05) than the other groups. Two days of staging at 2500-4300 m induced a similar degree of sleep acclimatization during subsequent ascent to 4300 m but the 2500 m group was not protected against AMS at 4300 m.

Effects of changes in end-tidal PO2 and PCO2 on neural responses during rest and sustained attention

Impairments of cognitive function during alterations in arterial blood gases (e.g., high-altitude hypoxia) may result from the disruption of neurovascular coupling; however, the link between changes in arterial blood gases, cognition, and cerebral blood flow (CBF) is poorly understood. To interrogate this link, we developed a multimodal empirical strategy capable of monitoring neural correlates of cognition and CBF simultaneously. Human participants performed a sustained attention task during hypoxia, hypercapnia, hypocapnia, and normoxia while electroencephalographic (EEG) activity and CBF (middle and posterior cerebral arteries; transcranial Doppler ultrasound) were simultaneously measured. The protocol alternated between rest and engaging in a visual target detection task that required participants to monitor a sequence of brief-duration colored circles and detect infrequent, longer duration circles (targets). The target detection task was overlaid on a large, circular checkerboard that provided robust visual stimulation. Spectral decomposition and event-related potential (ERP) analyses were applied to the EEG data to investigate spontaneous and task-specific fluctuations in neural activity. There were three main sets of findings: (1) spontaneous alpha oscillatory activity was modulated as a function of arterial CO2 (hypocapnia and hypercapnia), (2) task-related neurovascular coupling was disrupted by all arterial blood gas manipulations, and (3) changes in task-related alpha and theta band activity and attenuation of the P3 ERP component amplitude were observed during hypocapnia. Since alpha and theta are linked with suppression of visual processing and executive control and P3 amplitude with task difficulty, these data suggest that transient arterial blood gas changes can modulate multiple stages of cognitive information processing.

Alterations in the gut microbiota contribute to cognitive impairment induced by the ketogenic diet and hypoxia

Many genetic and environmental factors increase susceptibility to cognitive impairment (CI), and the gut microbiome is increasingly implicated. However, the identity of gut microbes associated with CI risk, their effects on CI, and their mechanisms remain unclear. Here, we show that a carbohydrate-restricted (ketogenic) diet potentiates CI induced by intermittent hypoxia in mice and alters the gut microbiota. Depleting the microbiome reduces CI, whereas transplantation of the risk-associated microbiome or monocolonization with Bilophila wadsworthia confers CI in mice fed a standard diet. B. wadsworthia and the risk-associated microbiome disrupt hippocampal synaptic plasticity, neurogenesis, and gene expression. The CI is associated with microbiome-dependent increases in intestinal interferon-gamma (IFNg)-producing Th1 cells. Inhibiting Th1 cell development abrogates the adverse effects of both B. wadsworthia and environmental risk factors on CI. Together, these findings identify select gut bacteria that contribute to environmental risk for CI in mice by promoting inflammation and hippocampal dysfunction.

Methamphetamine exacerbates pathophysiology of traumatic brain injury at high altitude. Neuroprotective effects of nanodelivery of a potent antioxidant compound H-290/51

Military personnel are often exposed to high altitude (HA, ca. 4500-5000m) for combat operations associated with neurological dysfunctions. HA is a severe stressful situation and people frequently use methamphetamine (METH) or other psychostimulants to cope stress. Since military personnel are prone to different kinds of traumatic brain injury (TBI), in this review we discuss possible effects of METH on concussive head injury (CHI) at HA based on our own observations. METH exposure at HA exacerbates pathophysiology of CHI as compared to normobaric laboratory environment comparable to sea level. Increased blood-brain barrier (BBB) breakdown, edema formation and reductions in the cerebral blood flow (CBF) following CHI were exacerbated by METH intoxication at HA. Damage to cerebral microvasculature and expression of beta catenin was also exacerbated following CHI in METH treated group at HA. TiO2-nanowired delivery of H-290/51 (150mg/kg, i.p.), a potent chain-breaking antioxidant significantly enhanced CBF and reduced BBB breakdown, edema formation, beta catenin expression and brain pathology in METH exposed rats after CHI at HA. These observations are the first to point out that METH exposure in CHI exacerbated brain pathology at HA and this appears to be related with greater production of oxidative stress induced brain pathology, not reported earlier.

Oxygen Enrichment Mitigates High-Altitude Hypoxia-Induced Hippocampal Neurodegeneration and Memory Dysfunction Associated with Attenuated Tau Phosphorylation

Cai, Jing, Junyong Ruan, Xi Shao, Yuanjun Ding, Kangning Xie, Chi Tang, Zedong Yan, Erping Luo, and Da Jing. Oxygen enrichment mitigates high-altitude hypoxia-induced hippocampal neurodegeneration and memory dysfunction associated with attenuated tau phosphorylation. High Alt Med Biol 00:000-000, 2021. Background: Brain is predominantly vulnerable to high-altitude hypoxia (HAH), resulting in neurodegeneration and cognitive impairment. The technology of oxygen enrichment has proven effective to decrease the heart rate and improve the arterial oxygen saturation by reducing the equivalent altitude. However, the efficacy of oxygen enrichment on HAH-induced cognitive impairments remains controversial based on the results of neuropsychological tests, and its role in HAH-induced hippocampal morphological and molecular changes remains unknown. Therefore, this study aims to systematically investigate the effects of oxygen enrichment on the memory dysfunction and hippocampal neurodegeneration caused by HAH. Materials and Methods: Fifty-one male Sprague-Dawley rats were equally assigned to three groups: normal control, HAH, and HAH with oxygen enrichment (HAHO). Rats in the HAH and HAHO groups were exposed to hypoxia for 3 days in a hypobaric hypoxia chamber at a simulated altitude of 6,000 m. Rats in the HAHO group were supplemented with oxygen-enriched air, with 12 hours/day in the hypobaric hypoxia chamber. Results: Our results showed that oxygen enrichment improved the locomotor activity of HAH-exposed rats. The Morris water maze test revealed that oxygen enrichment significantly ameliorated HAH-induced spatial memory deficits. Oxygen enrichment also improved morphological alterations of pyramidal cells and the ultrastructure of neurons in the hippocampal CA1 region in rats exposed to acute HAH. Tau hyperphosphorylation at Ser396, Ser262, Thr231, and Thr181 was also significantly attenuated by oxygen enrichment in HAH-exposed rats. Conclusions: Together, our study reveals that oxygen enrichment can ameliorate HAH-induced cognitive impairments associated with improved hippocampal morphology and molecular expression, and highlights that oxygen enrichment may become a promising alternative treatment against neurodegeneration for humans ascending to the plateau.

Hypoxia and brain aging: Neurodegeneration or neuroprotection?

The absolute reliance of the mammalian brain on oxygen to generate ATP renders it acutely vulnerable to hypoxia, whether at high altitude or in clinical settings of anemia or pulmonary disease. Hypoxia is pivotal to the pathogeneses of myriad neurological disorders, including Alzheimer's, Parkinson's and other age-related neurodegenerative diseases. Conversely, reduced environmental oxygen, e.g. sojourns or residing at high altitudes, may impart favorable effects on aging and mortality. Moreover, controlled hypoxia exposure may represent a treatment strategy for age-related neurological disorders. This review discusses evidence of hypoxia's beneficial vs. detrimental impacts on the aging brain and the molecular mechanisms that mediate these divergent effects. It draws upon an extensive literature search on the effects of hypoxia/altitude on brain aging, and detailed analysis of all identified studies directly comparing brain responses to hypoxia in young vs. aged humans or rodents. Special attention is directed toward the risks vs. benefits of hypoxia exposure to the elderly, and potential therapeutic applications of hypoxia for neurodegenerative diseases. Finally, important questions for future research are discussed.

Impact of High Altitude on Cardiovascular Health: Current Perspectives

Globally, about 400 million people reside at terrestrial altitudes above 1500 m, and more than 100 million lowlanders visit mountainous areas above 2500 m annually. The interactions between the low barometric pressure and partial pressure of O2, climate, individual genetic, lifestyle and socio-economic factors, as well as adaptation and acclimatization processes at high elevations are extremely complex. It is challenging to decipher the effects of these myriad factors on the cardiovascular health in high altitude residents, and even more so in those ascending to high altitudes with or without preexisting diseases. This review aims to interpret epidemiological observations in high-altitude populations; present and discuss cardiovascular responses to acute and subacute high-altitude exposure in general and more specifically in people with preexisting cardiovascular diseases; the relations between cardiovascular pathologies and neurodegenerative diseases at altitude; the effects of high-altitude exercise; and the putative cardioprotective mechanisms of hypobaric hypoxia.

Toxic Metabolic Encephalopathy in Hospitalized Patients with COVID-19

Background

Toxic metabolic encephalopathy (TME) has been reported in 7–31% of hospitalized patients with coronavirus disease 2019 (COVID-19); however, some reports include sedation-related delirium and few data exist on the etiology of TME. We aimed to identify the prevalence, etiologies, and mortality rates associated with TME in severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)-positive patients.

Methods

We conducted a retrospective, multicenter, observational cohort study among patients with reverse transcriptase–polymerase chain reaction-confirmed SARS-CoV-2 infection hospitalized at four New York City hospitals in the same health network between March 1, 2020, and May 20, 2020. TME was diagnosed in patients with altered mental status off sedation or after an adequate sedation washout. Patients with structural brain disease, seizures, or primary neurological diagnoses were excluded. The coprimary outcomes were the prevalence of TME stratified by etiology and in-hospital mortality (excluding comfort care only patients) assessed by using a multivariable time-dependent Cox proportional hazards models with adjustment for age, race, sex, intubation, intensive care unit requirement, Sequential Organ Failure Assessment scores, hospital location, and date of admission.

Results

Among 4491 patients with COVID-19, 559 (12%) were diagnosed with TME, of whom 435 of 559 (78%) developed encephalopathy immediately prior to hospital admission. The most common etiologies were septic encephalopathy (n = 247 of 559 [62%]), hypoxic-ischemic encephalopathy (HIE) (n = 331 of 559 [59%]), and uremia (n = 156 of 559 [28%]). Multiple etiologies were present in 435 (78%) patients. Compared with those without TME (n = 3932), patients with TME were older (76 vs. 62 years), had dementia (27% vs. 3%) or psychiatric history (20% vs. 10%), were more often intubated (37% vs. 20%), had a longer hospital length of stay (7.9 vs. 6.0 days), and were less often discharged home (25% vs. 66% [all P < 0.001]). Excluding comfort care patients (n = 267 of 4491 [6%]) and after adjustment for confounders, TME remained associated with increased risk of in-hospital death (n = 128 of 425 [30%] patients with TME died, compared with n = 600 of 3799 [16%] patients without TME; adjusted hazard ratio [aHR] 1.24, 95% confidence interval [CI] 1.02–1.52, P = 0.031), and TME due to hypoxemia conferred the highest risk (n = 97 of 233 [42%] patients with HIE died, compared with n = 631 of 3991 [16%] patients without HIE; aHR 1.56, 95% CI 1.21–2.00, P = 0.001).

Conclusions

TME occurred in one in eight hospitalized patients with COVID-19, was typically multifactorial, and was most often due to hypoxemia, sepsis, and uremia. After we adjustment for confounding factors, TME was associated with a 24% increased risk of in-hospital mortality.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12028-021-01220-5.

Analysis of the characteristics of sleep in patients with patent foramen ovale complicated with obstructive sleep apnea

PURPOSE

Analyzing sleep quality and sleep structure in patients with patent foramen ovale (PFO) complicated with obstructive sleep apnea (OSA) and the interaction between OSA and PFO in sleep.

METHODS

We compared patients with PFO complicated with OSA, patients with simple PFO, and controls. Pittsburgh Sleep Quality Index was used to compare sleep quality and polysomnography was used to compare sleep structure of the three groups.

RESULTS

Compared with the control group (n = 62), PFO with OSA (n = 48) and simple PFO (n = 61) groups had more frequent occurrence of poor sleep quality (χ² = 89.901; p < 0.001). These two groups also showed decreased sleep efficiency (p < 0.010), lower percentages of REM sleep, and reduced N3 sleep (p < 0.050). The N2 sleep was prolonged (p < 0.010). The nocturnal lowest SpO₂ was lower and the oxygen desaturation index was higher (p < 0.50). Compared with the simple PFO group, the poor sleep quality was more frequent in the PFO with OSA group; sleep latency (p < 0.001) was prolonged; wake after sleep onset (p < 0.001) and arousal times (p = 0.031) were increased; and sleep micro-arousal index (p = 0.037), periodic leg movement index (p = 0.024), and apnea hypopnea index (p < 0.001) were higher in the PFO with OSA group.

CONCLUSION

Patients with PFO and OSA have poor sleep quality with changes in sleep stage and high occurrence rate of sleep disorders. OSA further deteriorates sleep quality and alters sleep structure in patients with PFO.

Class switching of carbonic anhydrase isoforms mediates remyelination in CA3 hippocampal neurons during chronic hypoxia

Chronic exposure to hypoxia results in cerebral white matter hyperintensities, increased P300 latency, delayed response and impairment in working memory. Despite burgeoning evidence on role of myelination in nerve conduction, the effect of chronic hypoxia on myelination of hippocampal neurons has been less studied. The present study provides novel evidence on alterations in myelination of hippocampal CA3 neurons following chronic hypoxic exposure. Sprague Dawley rats exposed to global hypobaric hypoxia simulating altitude of 25,000 ft showed progressive demyelination in CA3 hippocampal neurons on 14 days followed by remyelination on 21 and 28 days. The demyelination of CA3 neurons was associated with increased apoptosis of both oligodendrocyte precursor cells (OPCs) and mature oligodendrocytes (OLs), peroxidation of myelin lipids, and nitration induced reduced expression of Carbonic Anhydrase II (CAII). Prolonged hypoxic exposure of 21 and 28 days on the other hand resulted in peroxisome proliferator-activated receptor alpha (PPARα) induced upregulation of Carbonic Anhydrase IV (CAIV) expression in mature oligodendrocytes through iNOS mediated mechanisms along with reduction in lipid peroxidation and remyelination. Inhibition of carbonic anhydrase activity on the other hand prevented remyelination of CA3 neurons. Based on these findings we propose a novel iNOS mediated mechanism for regulation of myelination in hypoxic hippocampal neurons through class switching of carbonic anhydrases.

The Possible Importance of Glutamine Supplementation to Mood and Cognition in Hypoxia from High Altitude

Hypoxia induced by low O₂ pressure is responsible for several physiological and behavioral alterations. Changes in physiological systems are frequent, including inflammation and psychobiological declines such as mood and cognition worsening, resulting in increased reaction time, difficulty solving problems, reduced memory and concentration. The paper discusses the possible relationship between glutamine supplementation and worsening cognition mediated by inflammation induced by high altitude hypoxia. The paper is a narrative literature review conducted to verify the effects of glutamine supplementation on psychobiological aspects. We searched MEDLINE/PubMed and Web of Science databases and gray literature by Google Scholar for English articles. Mechanistic pathways mediated by glutamine suggest potential positive effects of its supplementation on mood and cognition, mainly its potential effect on inflammation. However, clinical studies are scarce, making any conclusions impossible. Although glutamine plays an important role and seems to mitigate inflammation, clinical studies should test this hypothesis, which will contribute to a better mood and cognition state for several people who suffer from problems mediated by hypoxia.