Atypical neurological symptoms at high altitude: a systematic literature review

BACKGROUND

Acute Mountain Sickness (AMS) is a prevalent and potentially debilitating condition affecting individuals who participate in high-altitude journeys, mostly above 2500 m. The main symptoms of AMS, listed in the Lake Louise Symptom score used to diagnose AMS, are headache, dizziness, nausea, and fatigue. However, mountaineering can also be associated with other neurological disturbances. Most records related to neurological disorders associated with high-altitude medicine focus on AMS and its typical neurological symptoms indicated in official criteria. Other conditions related to acute exposure to high altitudes are high-altitude headaches (HAH), which usually precede AMS and high-altitude cerebral oedema (HACE), which can be a complication of AMS or appear independently.

METHODS

This review aimed to describe studies that included atypical neurological symptoms, which appear during acute exposure to high altitudes and are not mentioned in the criteria of AMS or HACE. Four databases, PubMed, Embase, Web of Science, and Medline Ultimate, were screened. PROSPERO registration ID for this review is CRD420250654251.

FINDINGS

Studies that met our inclusion criteria presented symptoms related to well-known conditions, such as stroke, deep cerebral vein thrombosis, seizures, or transient neurological dysfunctions. Moreover, cranial nerve palsies, olfactory threshold impairment, multiple sclerosis worsening, or speech, memory, and sensation disturbances were described in patients at high altitudes.

CONCLUSIONS

This review shows that high altitude may be an inducing factor in other neurological disturbances besides AMS, HAH, and HACE symptoms. The growing popularity of high-altitude stays should be associated with increasing knowledge about the unusual neurological symptoms that may occur.

Is Smoking Associated with the Risk of Acute Mountain Sickness? A Systematic Review and Meta-Analysis

Background: Controversy remains in the association between smoking and the risk of acute mountain sickness (AMS). Therefore, a systematic review of the existing literature may help clarify this association. Methods: We conducted a systematic search of PubMed, Embase, and Cochrane Library from database inception up to October 19, 2021. Both unadjusted and adjusted relative risks (RRs) and 95% confidence intervals (CIs) were calculated to compare the risk of AMS in the smoking and nonsmoking groups. Meta-regression was conducted to explore the factors causing heterogeneity of the studies, and subsequent stratified analysis was performed to present the pooled RR in different subgroups. Publication bias was assessed using funnel plots. Results: A total of 28 eligible articles (31 studies) were included. The pooled unadjusted and adjusted RRs were 0.88 (95% CI: 0.78-1.01) and 0.87 (95% CI: 0.77-0.99), respectively, using random-effect models. Publication bias was observed owing to restrictions on the sample size. The ascending altitude and sex composition of the study population were likely sources of heterogeneity according to meta-regression. Studies on participants with an ascending altitude of over 3,500 m or composed of both males and females reported a slight but not significant protective effect of smoking on the risk of AMS, with high heterogeneity. Conclusions: Smoking had no significant effect on AMS risk in this meta-analysis. Current studies showed high heterogeneity and included little information on quantitative exposure to smoking (i.e., dose and frequency); thus, the results require careful explanation.

Prevalence of burnout among military personnel in the plateau region of China: a cross-sectional survey

OBJECTIVES

The geographical environment and military activities in the plateau area pose potential work-related stressors for military personnel, leading to burnout which is an external manifestation of internal energy exhaustion caused by stress. Without countermeasures, this can result in serious military problems. This study aims to examine the association between burnout and occupational stressors among military personnel stationed in the plateau area of China.

MATERIAL AND METHODS

A stratified randomized cluster sampling survey was conducted among 2026 military personnel from 6 different troops stationed in the plateau area of China. The Chinese Maslach Burnout Inventory-General Survey(MBI-GS in Chinese) was administered from March 2022 to December 2023, and data were analyzed using SPSS version 25.

RESULTS

A total of 2026 military personnel participated in the survey. The mean overall burnout score was 3.37 ± 0.73, with emotional exhaustion at 2.69 ± 0.89, depersonalization at 3.58 ± 0.92, and professional achievement at 3.81 ± 0.85 levels respectively reported by participants on average scale scores ranging from zero to six. Severe level of burnout was reported by 43.2% of participants while medium level of burnout was reported by 54 .3%. Age, education level, length of military service, and household income were identified as important factors influencing burnout.

CONCLUSION

This study highlights a relatively high prevalence of burnout among military personnel stationed in plateau areas necessitating attention towards their occupational health particularly focusing on working hours and economic aspects so as to formulate effective policies and implement intervention measures that strengthen career development for soldiers deployed in such regions.

Influence of Smoking and Alcohol Habits on Symptoms of Acute Mountain Sickness on Mount Fuji: A Questionnaire Survey-Based Pilot Study

Horiuchi, Masahiro, Satomi Mitsui, and Tadashi Uno. Influence of smoking and alcohol habits on symptoms of acute mountain sickness on Mount Fuji: a questionnaire survey-based pilot study. High Alt Med Biol 00:000-000, 2024. Background: Acute cigarette smoking or alcohol intake would cause opposing vasculature effects that may influence acute mountain sickness (AMS). The present study aimed to investigate the effects of smoking and alcohol consumption behaviors, and acute smoking and consuming alcohol during ascent on AMS on Mount Fuji. Methods: This questionnaire survey study included 887 participants who climbed Mount Fuji and obtained information regarding sex, age, and smoking and alcohol habits, including behavior during ascent. Results: AMS prevalence was 45% for all participants. A univariate analysis revealed that younger participants (20-29 years) were associated with increased AMS prevalence (effect size [ES] = 0.102, p = 0.057) and severity (ES = 0.18, p = 0.01). A prediction model using multiple logistic regression indicated that several factors influenced AMS risk: younger age (p = 0.001), daily smoking habits (p = 0.021), no smoking (p = 0.033), or alcohol consumption during ascent (p = 0.096). Alcohol consumption during ascent had no effect on the increased AMS risk in younger participants (20-29 years), while alcohol consumption during ascent increased AMS risk for middle-age participants (50-59 years). Conclusion: Younger individuals are more likely to experience AMS. Smoking habits are associated with an increased AMS risk. It may be recommended that middle-aged climbers should ascend without consuming alcohol.

Gastrointestinal syndrome encountered during a train voyage to high altitudes: A 14-day survey of 69 passengers in China

BACKGROUND

The diagnosis and evaluation of the severity of acute mountain sickness (AMS) continue to be problematic due to a lack of consensus on the inclusion of symptoms in a scoring system. Recent investigations highlight the significance of gastrointestinal symptoms in identifying this condition. However, the specific gastrointestinal symptoms associated with AMS have not been thoroughly elucidated in previous studies, and the underlying risk factors remain inadequately comprehended.

METHODS

This study aimed to investigate the characteristics, trends, and risk factors related to gastrointestinal symptoms encountered during train travel to high altitude. A total of 69 passengers, specifically all with medical backgrounds, were surveyed 6 times over a period of 14 days.

RESULTS

The daily incidence of abdominal discomfort was higher than non-gastrointestinal symptoms within 14 days. Gastrointestinal symptoms demonstrated a greater prevalence, longer duration, and increased risk compared to non-gastrointestinal symptoms, such as headaches. The symptoms of abdominal distension and bowel sound hyperaction were found to be prevalent and persistent among patients diagnosed with AMS, exhibiting a high incidence rate. Gender, age, body mass index (BMI), smoking habits, and alcohol consumption were identified as risk factors associated with the occurrence and duration of gastrointestinal symptoms.

CONCLUSION

This study suggests that gastrointestinal symptoms are more common and persistent when traveling to the plateau by train. These symptoms should be taken into consideration in the further diagnosis and prevention of AMS. Therefore, this study provides a significant theoretical foundation for the prevention and treatment of AMS.

Can acute high-altitude sickness be predicted in advance?

In high-altitude environments, the oxygen and air density are decreased, and the temperature and humidity are low. When individuals enter high-altitude areas, they are prone to suffering from acute mountain sickness (AMS) because they cannot tolerate hypoxia. Headache, fatigue, dizziness, and gastrointestinal reactions are the main symptoms of AMS. When these symptoms cannot be effectively alleviated, they can progress to life-threatening high-altitude pulmonary edema or high-altitude cerebral edema. If the risk of AMS can be effectively assessed before people enter high-altitude areas, then the high-risk population can be promptly discouraged from entering the area, or drug intervention can be established in advance to prevent AMS occurrence and avoid serious outcomes. This article reviews recent studies related to the early-warning biological indicators of AMS to provide a new perspective on the prevention of AMS.

Anxiety as a Risk Factor for Acute Mountain Sickness Among Young Chinese Men After Exposure at 3800 M: A cross‒sectional Study

Purpose

We aimed to explore whether anxiety is a risk factor for acute mountain sickness [AMS] in a young Chinese male population.

Patients and Methods

A total of 143 young Chinese men with a median age of 23 years (IQR, 21-25) were employed in the present study, and they were divided into the AMS+ and AMS- groups according to the Lake Louise AMS score [AMS-S] after exposure at 3800 m for two days. Participants' pulse oximeter saturation [SpO2] and heart rate [HR] were measured. AMS was evaluated using the AMS-S. The anxiety and sleep quality of the subjects were assessed using the Zung Self-Rating Anxiety Scale [SAS] and the Athens Insomnia Scale [AIS], respectively. Outcomes were analysed using Spearman's partial correlation and logistic regression analysis.

Results

After two days of exposure at 3800 m, the overall prevalence of AMS was 54% in the whole group. The HR was significantly higher in the AMS+ group than in the AMS- group, as well as the SAS score and AIS score. A converse pattern was observed for SpO2. A significant difference was observed for the change in SAS and AIS score between the AMS+ and AMS- groups. Correlation analysis showed that AMS-S was positively correlated with SAS score, AIS score, HR, ΔSAS score, ΔAIS score, and ΔHR but negatively correlated with SpO2. AIS score was positively correlated with SAS score. After logistic regression analysis was adjusted for HR, SpO2, ΔAIS and ΔHR, SAS score (OR=1.446, 95% CI 1.200-1.744, p<0.001), AIS score (OR=1.216, 95% CI 1.033-1.432) and ΔSAS score (OR=1.158, 95% CI 1.012-1.327) were identified as independent risk factors for AMS.

Conclusion

The present study suggests that anxiety is a risk factor for AMS among young Chinese men, and poor sleep quality may partially mediate the association.

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.

Healthy worker survival effect at a high-altitude mine: prospective cohort observation

Very little is known about the factors of healthy worker survival effect at high-altitude mines. We conducted this cohort observation of the new hires for a high-altitude gold mine in Kyrgyzstan with the aim to ascertain predictors of survival at work. All new hires in 2009 through 2012 for a high-altitude gold mine (3600–4500 m above sea level) were followed up to January 2022. We tested the association of demographic, physiological predictors and diagnoses at the pre-employment screening with non-survival at work in Cox proportional hazards yielding hazard ratios (HR) with their 95% confidence intervals (CI). The cumulative observation time was 5190 person-years. Blood pressure at pre-employment, lung function, the diagnoses of essential hypertension, chronic obstructive pulmonary disease (COPD) or any other analyzed physiological variables were not associated with non-survival at work. However, smoking (HR 1.55; 95% CI 1.10; 2.17) increased the likelihood of non-survival at work, independent of any diagnosis or lowland residence (HR 1.95; 95% CI 1.31; 2.90). Adjusted for covariates and all diagnoses, having chronic rheumatic fever (HR 10.95; 95% CI 2.92; 33.92), hemorrhoids (HR 1.32; 95% CI 1.01; 3.75), adhesive otitis (HR 1.74; 95% CI 1.05; 2.89) or obesity (HR 1.71; 95% CI 1.01; 2.88) were associated with non-survival at work with time. This prospective observation of new hires for a high-altitude mining operation demonstrated that selected diagnoses, smoking and lowland residence elevated the risk of early exit in prospective workers.

Chronic Intermittent Hypobaric Hypoxia (4600 M) Attenuates Pulmonary Vasodilation Induced by Acetylcholine or Sodium Nitroprusside

Moraga, Fernando A., Giselle Miranda, Vasthi López, Carmen Vallejos, and Daniel Silva. Chronic intermittent hypobaric hypoxia (4600 M) attenuates pulmonary vasodilation induced by acetylcholine or sodium nitroprusside. High Alt Med Biol. 19:149-155, 2018.

BACKGROUND

Previous studies performed in rats exposed to chronic intermittent hypobaric hypoxia (CIHH), at a simulated altitude of 4600 m, showed reduced nitric oxide (NO) production, increased arginase activity, and increased oxidative stress. However, studies on vascular function are scarce. Our aim was to measure plasma nitrate and nitrite (NOx) concentration and study pulmonary vascular function in rats exposed to CIHH in the presence of potassium chloride (KCl), acetylcholine (Ach), and sodium nitroprusside (SNP).

METHODS

Thirty male Wistar rats were divided into two groups: A control group (normoxia (N), n = 10) and a CIHH group (2N × 2H × 30 days, n = 20). CIHH exposure was performed in a hypobaric chamber at 428 Torr (4600 m). Noninvasive systolic blood pressure (SBP), heart rate, and body weight (BW) were measured. Blood samples were obtained to measure NOx levels and hematocrit (Hct). CIHH animals that gained BW and presented a Hct <20% and maintained SBP were classified as tolerant, and animals that lost >30% of their BW, increased Hct and SBP >20% were classified as intolerant. Animals were sacrificed and small pulmonary arteries (SPA) were obtained to perform concentration-response curves to KCl, Ach, and SNP.

RESULTS AND CONCLUSIONS

Intolerant rats (30%) had decreased NOx levels. SPA had a larger vasocontraction response to KCl and a lower dilation response to SNP in the SPA compared to tolerant and control animals. In addition, SPA had a lower dilatation response to Ach compared with the control. Together, these results show that CIHH alters endothelium-dependent vasodilation.

Relationship between Smoking and Acute Mountain Sickness: A Meta-Analysis of Observational Studies

Aims

Previous epidemiological investigations of the relationship between smoking and acute mountain sickness (AMS) risk yielded inconsistent findings. Therefore, a meta-analysis of observational studies was performed to determine whether smoking is related to the development of AMS.

Methods

Searches were performed on PubMed, Scopus, Embase, and Web of Science for relevant studies that were published before November 2016 reporting smoking prevalence and AMS. Two evaluators independently selected studies, extracted data, and assessed study quality. The pooled relative risks (RRs) and 95% confidence intervals (CIs) were obtained using random-effects models. Subgroup analyses were performed according to the type of participant, altitude, and study design.

Results

A total of 11 observational studies involving 7,106 participants, 2,408 of which had AMS, were eligible for inclusion in this meta-analysis. The summary RR for AMS comparing smokers to nonsmokers was 1.02 (95% CI: 0.83 to 1.26). Specific analyses for altitude, type of participant, and study design yielded similar results. There was significant heterogeneity for all studies (Q = 37.43; P < 0.001; I² = 73%, 95% CI: 51% to 85%). No publication bias was observed (Egger's test: P = 0.548, Begg's test: P = 0.418).

Conclusions

The meta-analysis indicates that no difference was found in AMS risk with regard to smoking status.

Is Smoking a Predictor for Acute Mountain Sickness? Findings From a Meta-Analysis

AIM

Studies of the potential association between cigarette smoking and acute mountain sickness (AMS) have reached contradictory conclusions. Our aim was to perform a meta-analysis of studies across a range of populations to ascertain better the true relationship between cigarette smoking and AMS.

MATERIALS AND METHODS

We used the PRISMA protocol to identify and screen eligible studies of smoking and AMS. Databases including Pubmed and Google Scholar were searched, using the terms "smoking" and "acute mountain sickness." We conducted a meta-analysis of the selected studies in order to evaluate causal inference, evaluate potential biases, and investigate possible sources of heterogeneity across studies.

RESULTS

We identified 3907 publications, of which 29 were eligible for inclusion by reporting smoking status and AMS. Of these, eight publications were excluded because they were duplicative or were lacking quantitative data. The 21 studies analyzed included 16 566 subjects. These fell into two groups: occupational/military (n = 8) or volunteers/trekkers/mixed (n = 13). Study heterogeneity was high (X (2) = 55.5, P < .001). Smoking was not statistically associated with increased risk of AMS: pooled OR = 0.88 (95% CI = 0.74-1.05). Stratification yielded similar risk estimates among the occupational/military studies versus all others and studies at relatively higher and lower altitudes.

CONCLUSIONS

Overall, smoking was not statistically significantly associated with AMS: there is no consistent effect of cigarette smoking acting as either a protective factor against or a risk factor for AMS.

IMPLICATIONS

This is the first quantitative assessment of published studies on smoking and AMS, which shows smoking to be neither a risk, nor protective. Studies specifically focusing on smoking as a risk factor, should guide further research on this issue. Although all smokers should be strongly advised to quit, studies on risk factors for AMS focusing on other exposures could shed light on the full range of risks for AMS.