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

Neuroprotective Effects of Qi Jing Wan and Its Active Ingredient Diosgenin Against Cognitive Impairment in Plateau Hypoxia

Background/Objectives: High-altitude environments have a significant detrimental impact on the cognitive functions of the brain. Qi Jing Wan (QJW), a traditional herbal formula composed of Angelica sinensis, Astragalus membranaceus, and Rhizoma Polygonati Odorati, has demonstrated potential efficacy in treating cognitive disorders. However, its effects on cognitive dysfunction in plateau hypoxic environments remain unclear. Methods: In this study, acute and chronic plateau cognitive impairment mouse models were constructed to investigate the preventive and therapeutic effects of QJW and its significant active ingredient, diosgenin (Dio). Behavioral experiments were conducted to assess learning and memory in mice. Morphological changes in hippocampal neurons and synapses were assessed, and microglial activation and inflammatory factor levels were measured to evaluate brain damage. Potential active ingredients capable of crossing the blood-brain barrier were identified through chemical composition analysis and network database screening, followed by validation in animal and brain organoid experiments. Transcriptomics analysis, immunofluorescence staining, and molecular docking techniques were employed to explore the underlying mechanisms. Results: QJW significantly enhanced learning and memory abilities in plateau model mice, reduced structural damage to hippocampal neurons, restored NeuN expression, inhibited inflammatory factor levels and microglial activation, and improved hippocampal synaptic damage. Transcriptomics analysis revealed that Dio alleviated hypoxic brain damage and protected cognitive function by regulating the expression of PDE4C. Conclusions: These findings indicate that QJW and its significant active ingredient Dio effectively mitigate hypoxic brain injury and prevent cognitive impairment in high-altitude environments.

Preoperative hypoxic biomarkers and postoperative delirium in patients with obstructive sleep apnea

PURPOSE

Postoperative delirium (POD) in patients with obstructive sleep apnea (OSA) is associated with increased mortality and healthcare costs. In this study, we investigated the association of OSA risk, serum biomarkers for central nervous ischemia (S100B and NSE), and POD.

METHODS

After research ethics approval, patients completed the STOP BANG assessment before undergoing elective surgery. Blood was drawn for S100B and NSE measurement, and cognitive performance was tested using the Montreal Cognitive Assessment (MoCA) at study admission and postoperatively at discharge. Delirium assessment was performed using the Nursing Delirium Screening Scale (NuDESC) and the Confusion Assessment Method (CAM).

RESULTS

One hundred twenty-four enrolled patients were separated into three OSA-risk groups based on STOP BANG score testing (low risk, n = 22; intermediate risk, n = 67; high risk, n = 35). Preoperative NSE values increased with OSA risk (NSE in ng/ml; mean [range]; low risk: 15.6 [9.2-44.3]; intermediate risk: 21.8 [7.6-114.1]; high risk: 29.2 [10.1-151]; p = 0.039). Postoperative MoCA and NuDESC assessments were not different between the OSA-risk groups. We found a decreasing incidence for POD with increasing OSA risk (positive CAM: low risk: 18.1%, intermediate risk: 12.0%; high risk: 11.5%, p = 0.043). However, this was no longer detectable in a complete case analysis. In patients with POD, postoperative ischemic biomarker values were not different between OSA-risk groups.

CONCLUSION

We found a trend of decreasing POD incidence with increasing OSA risk, which was not robust in a complete case analysis. Our results possibly support the phenomenon of hypoxic preconditioning.

Longitudinal assessment of retinal and visual pathway electrophysiology and structure after high altitude exposure

High altitude (HA) exposure induces impairments in visual function. This study was designed to dynamically observe visual function after returning to lowland and elucidate the underlying mechanism by examining the structure and function of retina and visual pathway. Twenty-three subjects were recruited before (Test 1), and one week (Test 2) and three months (Test 3) after their return from HA (4300 m) where they resided for 30 days. The clock task was used to assess visual cognition; and pattern-reversal visual evoked potential (p-VEP) and full-field electroretinogram (ff-ERG) were employed to record electrophysiological responses of retinal cells; optical coherence tomography (OCT), color doppler imaging (CDI) and magnetic resonance imaging(MRI) were used to measure structures of retina and visual pathway. In Test 2 vs. Test 1, there was increased reaction time during angle task; the amplitudes of scotopic 3.0 cd·s/m2 and scotopic 10.0 cd·s/m2 ERG a-wave and scotopic 3.0 cd·s/m2 oscillatory potential in the right eye were significantly decreased, all of which were negatively correlated with the increased reaction time during the angle task. In Test 3 vs. Test 1, there were decreased amplitude of scotopic 10.0 cd·s/m2 a-wave in the right eye and increased velocity of ophthalmic artery and ocular perfusion pressure in bilateral eyes. The VEP and visual pathway structures remained normal throughout the entire test. HA exposure caused damage to rod and cone responses in both outer and inner retina. After returning to sea level, the damaged visual cell functions gradually recovered over time, coinciding with an increase in the ocular perfusion.

The Effects of Nocturnal Hypoxemia on Cognitive Performance in Andean Highlanders

Background: Many Andean highlanders exposed to chronic hypoxemia are susceptible to excessive erythrocytosis (EE) and chronic mountain sickness (CMS). Nocturnal hypoxemia is more marked than diurnal hypoxemia and includes sustained and intermittent components. The potential for cognitive impairments related to nocturnal hypoxemia in this population has not been extensively studied, but improved understanding may provide opportunities for the prevention of long-term effects of EE and CMS. Methods: To examine this relationship, 48 participants residing permanently at 4,340 m completed an overnight sleep study and a battery of cognitive function tests that examined a broad range of cognitive domains. Results: Greater nocturnal hypoxemia was associated with longer reaction times on Balloon Analogue Risk Task (BART) (p < 0.01) and Emotion Recognition Test (ERT) (p < 0.01). Longer completion times of Trail Making Task were also associated with increased nocturnal hypoxemia (p = 0.03). Increased hematocrit was similarly associated with longer reaction times on the ERT (p = 0.01) and the BART (p = 0.01). Conclusion: Overall, our results showed that increased nocturnal hypoxemia and higher hematocrit were associated with impairments in cognitive performance in individuals residing permanently at high altitude.

Cognitive performance during exposure to moderate normobaric hypoxia after sleep restriction: Relationship to physiological and stress biomarkers

INTRODUCTION

Exposure to moderate levels of simulated hypoxia has subtle cognitive effects relative to ground level, in healthy individuals. However, there are few data on the cognitive consequences of the combination of hypoxia and partial sleep deprivation, which is a classic military or civilian operational context. In this study, we tested the hypothesis that exposure to moderate hypoxia while sleep-restricted impairs several domains of cognition, and we also assessed physiological parameters and salivary concentrations of cortisol and alpha-amylase.

METHOD

Seventeen healthy males completed two sessions of cognitive tests (sustained attention using the PVT psychomotor vigilance task and executive functions using the Go-NoGo inhibition task and N-Back working memory task) after 30 min (T + 30') and 4 h (T + 240') of exposure in a normobaric hypoxic tent (FIO2 = 13.6 %, ≃ 3,500 m) (HY). This was completed after one night of sleep restriction (3 a.m. to 6 a.m. bedtime, SRHY) and one night of habitual sleep (10 p.m. to 6 a.m. bedtime, HSHY) (with cross-over randomization). The two nights sleep architecture and physiological parameters (oxygen saturation (SpO2) and heart rate (HR) during T + 30' and T + 240'sessions were analyzed. Salivary cortisol and alpha-amylase (sAA) concentrations were analyzed before hypoxia, after the T + 30' and T + 240' cognitive sessions, and after leaving the hypoxic tent.

RESULTS

Sustained attention (RT and number of lapses in the PVT) and executive functions (Go-NoGo and 1-Back and 2-Back parameters, as inhibition and working memory signatures) were impaired in the SRHY condition compared to HSHY. SpO2 and HR were higher after 4 h compared with 30 min of hypoxia in the HSHY condition, while only HR was statistically higher in the SRHY condition. In SRHY, salivary AA concentration was lower and cortisol was higher than in HSHY. A significant increase in sAA concentration is observed after the cognitive session at 4 h of hypoxia exposure compared to that at 30 min, only in the SRHY condition. There are significant positive correlations between reaction time and the corresponding heart rate (a non-invasive marker of physiological stress) for the executive tasks in the two sleep conditions. This was not observed for salivary levels of sAA and cortisol, respective reliable indicators of the sympathoadrenomedullary system and the hypothalamic-pituitary adrenocortical system.

CONCLUSION

Exposure to moderate normobaric hypoxia (≃ 3500 m / ≃ 11,500 ft simulated) after a single night of 3-hour sleep impairs cognitive performance after 30 min and 4 h of exposure. The key determinants and/or mechanism(s) responsible for cognitive impairment when exposed to moderate hypoxia with sleep restriction, particularly on the executive function, have yet to be elucidated.

Effects of long-term exposure to high-altitude on episodic memory: The moderating role of daytime dysfunction

Chronic exposure to high-altitude hypoxic environments may influence short-term memory and working memory. However, its impact on long-term memory, specifically episodic memory, remains understudied. In this study, we systematically investigated the effects of long-term exposure to high altitude (3650 m) on episodic memory, including item memory and source memory. Moreover, we examined the moderating role of daytime dysfunction on the relationship between altitude and episodic memory. In total, 97 participants were enrolled in the study: 49 were from the high-altitude (HA) group, comprising those born and raised in low altitude (LA) areas (< 500 m) and had migrated to HA for 2∼3 years after turning 18; and 48 were from the LA group, who had never lived at high altitudes. Episodic memory was evaluated using a what-when-where task, whereas daytime dysfunction was measured by the Pittsburgh Sleep Quality Index. For item memory, hit rate and correct rejection rate were significantly lower in the HA group relative to the LA group. For source binding memory, the performance in what-where binding and what-when-where binding were decreased in the HA group, but the what-when binding did not differ between the two groups. Furthermore, the effects of altitude on hit rate, what-where binding, and what-when-where binding were significantly pronounced in individuals with higher levels of daytime dysfunction. These findings suggest that long-term exposure to high-altitude hypoxic environments influences episodic memory performance, including item recognition and source-binding memory. Specifically, spatial source memory is affected by high-altitude exposure, whereas temporal source memory remains unaffected. Moreover, these results highlight the importance of considering sleep quality, especially good daytime function, in maintaining optimal episodic memory function following chronic exposure to high altitudes.

[Identification of Differences in Brain Functions at Varied Degrees of Acclimatization to High Altitudes Based on Resting-State Electroencephalogram Signals]

Objective

To explore the differences in brain functions between individuals with good acclimatization to high altitudes and those with poor acclimatization based on microstate and functional connectivity analysis of resting-state electroencephalogram (EEG) activities.

Methods

A total of 44 residents exposed to the high-altitude environment of 3650 m above sea level were enrolled. They were divided into two groups according to their findings for the high-altitude acclimatization index (AAI), with 22 in the good acclimatization group and 22 in the poor acclimatization group. The good acclimatization group had 10 males and 12 females of the mean age of (20.48±2.09) years. Among them, 10 were Tibetans, and 12 were Han Chinese. The poor acclimatization group consisted of 18 males and 4 females, with a mean age of (18.90±1.25) years. Among them, 7 were Tibetans, and 15 were Han Chinese. The K-means clustering algorithm was used to classify EEG microstates into four categories of A, B, C, and D. The average duration, coverage, occurrence frequency, and transition probabilities between microstates were compared. Coherence analysis (COH) was performed to assess the strength of brain network connectivity.

Results

Compared to the good acclimatization group, the poor acclimatization group exhibited a longer duration, higher occurrence frequency, and coverage of microstate C. The coverage of microstate D was also higher, while the occurrence frequency and coverage of microstate B were lower. The poor acclimatization group showed a decrease in transitions from microstate B to A or D, while transitions from C to B or D, and those from D to A or C increased, showing statistically significant differences between the groups (P<0.05). In the α, β, δ, and θ frequency bands, the poor acclimatization group had higher COH strength in regions such as the frontal and occipital lobes, showing symmetrical functional connectivity between the left and right hemispheres.

Conclusion

The good and poor high-altitude acclimatization groups exhibit different neural mechanisms in terms of microstates and functional connectivity. There are significant differences between individuals with good acclimatization and those with poor acclimatization regarding visual information processing, interference resistance, brain network stability, and coherence.

A narrative review of periodic breathing during sleep at high altitude: From acclimatizing lowlanders to adapted highlanders

Periodic breathing during sleep at high altitude is almost universal among sojourners. Here, in the context of acclimatization and adaptation, we provide a contemporary review on periodic breathing at high altitude, and explore whether this is an adaptive or maladaptive process. The mechanism(s), prevalence and role of periodic breathing in acclimatized lowlanders at high altitude are contrasted with the available data from adapted indigenous populations (e.g. Andean and Tibetan highlanders). It is concluded that (1) periodic breathing persists with acclimatization in lowlanders and the severity is proportional to sleeping altitude; (2) periodic breathing does not seem to coalesce with poor sleep quality such that, with acclimatization, there appears to be a lengthening of cycle length and minimal impact on the average sleeping oxygen saturation; and (3) high altitude adapted highlanders appear to demonstrate a blunting of periodic breathing, compared to lowlanders, comprising a feature that withstands the negative influences of chronic mountain sickness. These observations indicate that periodic breathing persists with high altitude acclimatization with no obvious negative consequences; however, periodic breathing is attenuated with high altitude adaptation and therefore potentially reflects an adaptive trait to this environment.

Ferroptosis pathways: Unveiling the neuroprotective power of cistache deserticola phenylethanoid glycosides

ETHNOPHARMACOLOGICAL RELEVANCE

Cistanche deserticola is a kind of parasitic plant living in the roots of desert trees. It is a rare Chinese medicine, which has the effect of tonifying kidney Yang, benefiting essence and blood and moistening the intestinal tract. Cistache deserticola phenylethanoid glycoside (PGS), an active component found in Cistanche deserticola Ma, have potential kidney tonifying, intellectual enhancing, and neuroprotective effects. Cistanche total glycoside capsule has been marketed to treat vascular dementia disease.

AIM OF THE STUDY

To identify the potential renal, intellectual enhancing and neuroprotective effects of PGS and explore the exact targets and mechanisms of PGS.

MATERIALS AND METHODS

This study systematically investigated the four types of pathways leading to ferroptosis through transcriptome, metabolome, ultrastructure and molecular biology techniques and explored the molecular mechanism by which multiple PGS targets and pathways synergistically exert neuroprotective effects on hypoxia.

RESULTS

PGS alleviated learning and memory dysfunction and pathological injury in mice exposed to hypobaric hypoxia by attenuating hypobaric hypoxia-induced hippocampal histopathological damage, impairing blood‒brain barrier integrity, increasing oxidative stress levels, and increasing the expression of cognitive proteins. PGS reduced the formation of lipid peroxides and improved ferroptosis by upregulating the GPX-4/SCL7A311 axis and downregulating the ACSL4/LPCAT3/LOX axis. PGS also reduced ferroptosis by facilitating cellular Fe2+ efflux and regulating mitochondrial Fe2+ transport and effectively antagonized cell ferroptosis induced by erastin (a ferroptosis inducer).

CONCLUSIONS

This study demonstrated the mechanism by which PGS prevents hypobaric hypoxic nerve injury through four types of ferroptosis pathways, achieved neuroprotective effects and alleviated learning and memory dysfunction in hypobaric hypoxia mice. This study provides a theoretical basis for the development and application of PGS.

Is it Possible for Individuals with Pre-Existing Mental Disorders to Perform Mountain Sports at High Altitude-First Evidence from a Pilot Cross-Sectional Questionnaire Study

Gstir, Claudia, Timo Schurr, Roxana Ehlers, Johannes Burtscher, Barbara Sperner-Unterweger, and Katharina Hüfner. Is it possible for individuals with pre-existing mental disorders to perform mountain sports at high altitude-First evidence from a pilot cross-sectional questionnaire study. High Alt Med Biol. 00:00-00, 2024. Introduction: Mountain sports at high altitude (HA) are gaining increasing popularity, but little is known about the effect of such activities on mental health, despite a great prevalence of mental disorders. Methods: Data were collected using an online self-report questionnaire assessing mental and somatic disorders in individuals performing mountain sports at HA (>2,500 m above sea level [ASL]) as well as their symptom change. Nonparametric tests were used for analyses. Results: 251 individuals without pre-existing disorders (noD), 34 with somatic disorders (somaD), and 38 with mental disorders (mentalD; mainly depressive, eating, and anxiety disorders) participated in this study. Overall, 44.7% of the mentalD group compared with 14.7% of somaD experienced ameliorated symptoms during mountain sports at HA, while 2.6% and 8.8%, respectively, reported a worsening (χ2[2] =8.13, p = 0.017). People in the mentalD compared with somaD group significantly less frequently inform tour partners (41.9% vs. 90.9%; χ2[2]=16.69, p < 0.001) about their condition or consult their physician (2.6% vs. 26.5%; χ2[1]=8.53, p = 0.003) regarding their plans to perform mountain sports at HA. 14.5% of all participants reported mental symptoms at 2,500-3,500 m ASL, 23.5% between >3,500-5,500 m ASL and 31.8% >5,500 m ASL. Conclusion: Individuals with mental disorders often report improved mental health during mountain sports at HA, possibly due to a combination of physical activity, the alpine natural environment, and/or moderate hypoxia. The fact that tour partners and physicians are rarely informed shows the need to reduce the stigma of mental disorders in the mountain sports community. The study was prospectively registered with the German Clinical Trials Registry (DRKS00024949).

The effects of long-term high-altitude exposure on cognition: A meta-analysis

Long-term high altitudes (HA) exposure's impact on cognition has yielded inconsistent findings in previous research. To address this, we conducted a meta-analysis of 49 studies (6191 individuals) to comprehensively evaluate this effect. Moderating factors such as cognitive task type, altitude (1500-2500 m, 2500-4000 m, and above 4000 m), residential type (chronic and lifelong), adaptation level and demographic factors were analyzed. Cognitive tasks were classified into eight categories: perceptual processes, psychomotor function, long-term memory, working memory, inhibitory control, problem-solving, language, and others. Results revealed a moderate negative effect of HA on cognitive performance (g = -.40, SE =.18, 95% CI = -.76 to -.05). Psychomotor function and long-term memory notably experience the most pronounced decline, while working memory and language skills show moderate decreases due to HA exposure. However, perceptual processes, inhibitory control, and problem-solving abilities remain unaffected. Moreover, residing at altitudes above 4000 m and being a HA immigrant are associated with significant cognitive impairment. In summary, our findings indicate a selective adaptation of cognitive performance to HA conditions.

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.

Exercise performance reduction and preventive measures in highland sports

The plateau is a special environment with low pressure, low oxygen, low temperature, and high ultraviolet radiation. The exercise performance of people on the plateau is generally reduced, which seriously affects the life and health of people living in the plateau and entering the plateau. In recent years, the prevention and treatment of injury caused by high altitude hypoxia has attracted wide attention. It has shown that the higher the altitude with the longer the duration of exercise, the faster the stationing, the greater the impact on people's sports performance. Rapid entry into the plateau and long-term stay in the plateau have an impact on people's explosive power, endurance and fine operation. Advances in medical technology enable various prevention methods to be used to acclimate to high altitude environments. However, in vitro intervention methods are costly, easy to rebound and possess limited effects. Therefore, drug prevention and treatment is obviously a more economical choice. Chemical drugs increase the efficiency of high altitude exercise by improving the ischemic and hypoxic symptoms of the heart and brain, increasing lung ventilation and arterial oxygenation capacity, and accelerating the elimination of adverse product accumulation after exercise. Single Chinese medicine, Chinese patent medicine, and compound preparations can improve exercise performance by promoting body metabolism, improving muscle endurance, enhancing immunity, and other mechanisms. Traditional Chinese medicine has unique advantage and application prospect in improving plateau sports performance damage.

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.