Association of arterial oxygen saturation and acute mountain sickness susceptibility: a meta-analysis

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.

Evaluation of colour vision impairment during acute hypobaric hypoxia in aviation medicine: a randomized controlled trial

The digitization of aircraft cockpits places high demands on the colour vision of pilots. The present study investigates colour vision changes upon acute exposure to hypobaric hypoxia. The digital Waggoner Computerized Color Vision Test and the Waggoner D-15 were performed by 54 healthy volunteers in a decompression chamber. Respective altitude levels were sea level, 10,000 or 15,000 ft for exposure periods of 15 and 60 min, respectively. As for 60 min of exposure a significant decrease in colour perception was found between subjects at 15,000 ft as compared to the control group as well as between subjects at 15,000 ft as compared to subjects at 10,000 ft. No significant difference was found in the comparison within the 15,000 ft groups across time points pre-, peri-, and post-exposure. Thus, pilots appear to experience only minor colour vision impairment up to an exposure altitude of 15,000 ft over 60 min of exposure.

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.

The changes of electroencephalography in mountaineers on Mount Jade, Taiwan: An observational study

BACKGROUND

The diagnosis of acute mountain sickness, which lacks a reliable and objective diagnostic tool, still depends on the clinical symptoms and signs and remains a major threat and unpredictable disease affecting millions of mountaineers.

OBJECTIVES

To record electroencephalography signals with small, convenient, wireless equipment and to test whether electroencephalography parameters, which are more sensitive and reliable markers, could predict the symptoms of acute mountain sickness.

METHODS

Twenty-five participants were enrolled and separated into two groups to climb Mount Jade in Taiwan. We collected electrocardiography signals and arterial oxygen saturation data at ground, moderate (2,400 m), and high altitude (3,400 m). A spectral analysis of the electrocardiography was performed to assess the study subjects' electroencephalography activity at different frequencies (α, β, θ, δ) and the mean power frequency of electrocardiography. The clinical symptoms and Lake Louise Acute Mountain Sickness scores of the subjects were recorded for comparison.

RESULTS

A significant change in the δ power of electroencephalography was recorded in subjects ascending from the ground to a high altitude of 3,400 m in a 4-day itinerary. In addition, between the two groups of subjects with and without acute mountain sickness (Lake Louise Acute Mountain Sickness scores < 3 and ≥ 3), the δ power of electroencephalography at the fronto-parietal 1 and parietal 3 electrodes at moderate altitude as well as the changes of δ power and mean power frequency of electrocardiography over parietal 4 at high altitude showed a significant difference. At moderate altitude, the increasing δ power of electroencephalography at the parietal 4 electrode was related to the headache symptom of acute mountain sickness before ascending to high altitude.

CONCLUSION

At moderate altitude, the δ power increase of electroencephalography at the P4 electrode could be a predictor of acute mountain sickness symptoms before ascending to high altitude. Thus, electroencephalography had the potential to identify the risk of acute mountain sickness.

The Role of Hypoxia-Inducible Factor in the Mechanisms of Aging

Aging is accompanied by a reduction in the oxygen delivery to all organs and tissues and decrease in the oxygen partial pressure in them, resulting in the development of hypoxia. The lack of oxygen activates cell signaling pathway mediated by the hypoxia-inducible transcription factor (HIF), which exists in three isoforms - HIF-1, HIF-2, and HIF-3. HIF regulates expression of several thousand genes and is a potential target for the development of new drugs for the treatment of many diseases, including those associated with age. Human organism and organisms of laboratory animals differ in their tolerance to hypoxia and expression of HIF and HIF-dependent genes, which may contribute to the development of inflammatory, tumor, and cardiovascular diseases. Currently, the data on changes in the HIF expression with age are contradictory, which is mostly due to the fact that such studies are conducted in different age groups, cell types, and model organisms, as well as under different hypoxic conditions and mainly in vitro. Furthermore, the observed discrepancies can be due to the individual tolerance of the studied organisms to hypoxia, which is typically not taken into account. Therefore, the purpose of this review was to analyze the published data on the connection between the mechanisms of aging, basal tolerance to hypoxia, and changes in the level of HIF expression with age. Here, we summarized the data on the age-related changes in the hypoxia tolerance, HIF expression and the role of HIF in aging, which is associated with its involvement in the molecular pathways mediated by insulin and IGF-1 (IIS), sirtuins (SIRTs), and mTOR. HIF-1 interacts with many components of the IIS pathway, in particular with FOXO, the activation of which reduces production of reactive oxygen species (ROS) and increases hypoxia tolerance. Under hypoxic conditions, FOXO is activated via both HIF-dependent and HIF-independent pathways, which contributes to a decrease in the ROS levels. The activity of HIF-1 is regulated by all members of the sirtuin family, except SIRT5, while the mechanisms of SIRT interaction with HIF-2 and HIF-3 are poorly understood. The connection between HIF and mTOR and its inhibitor, AMPK, has been identified, but its exact mechanism has yet to be studied. Understanding the role of HIF and hypoxia in aging and pathogenesis of age-associated diseases is essential for the development of new approaches to the personalized therapy of these diseases, and requires further research.

Cardiovascular Indicators of Systemic Circulation and Acute Mountain Sickness: An Observational Cohort Study

Background: Acute high-altitude (HA) exposure results in blood pressure (BP) and cardiac function variations in most subjects, some of whom suffer from acute mountain sickness (AMS). Several previous studies have found that cardiovascular function indicators are potentially correlated with AMS.

Objectives: This study aims to examine HA-induced cardiovascular adaptations in AMS patients and compare them with healthy subjects. It also aims to investigate the relationship between cardiovascular function indicators and AMS, as well as to provide some insightful information about the prevention and treatment of AMS.

Methods: Seventy-two subjects were enrolled in this cohort study. All the subjects ascended Litang (4,100 m above sea level). They were monitored by a 24-h ambulatory blood pressure (ABP) device and underwent echocardiography examination within 24 h of altitude exposure. The 2018 Lake Louise questionnaire was used to evaluate AMS.

Results: Acute mountain sickness group consisted of more women (17 [60.7%] vs. 10 [22.7%], p = 0.001) and fewer smokers (5 [17.9%] vs. 23 [52.3%], p = 0.003). Compared with subjects without AMS, subjects with AMS had lower pulse pressure (PP) (daytime PP, 45.23 ± 7.88 vs. 52.14 ± 4.75, p < 0.001; nighttime PP, 42.81 ± 5.92 vs. 49.39 ± 7.67, p < 0.001) and lower effective arterial elastance (Ea) (1.53 ± 0.24 vs. 1.73 ± 0.39, p = 0.023). Multivariate regression indicated that female sex (OR = 0.23, p = 0.024), lower daytime PP (OR = 0.86, p = 0.004), and lower Ea (OR = 0.03, p = 0.015) at low altitude (LA) were independent risk factors for AMS. Combined daytime PP and Ea at LA had a high predictive value for AMS (AUC = 0.873; 95% CI: 0.789–0.956). Correlation analysis showed that AMS-induced headache correlated with daytime PP (R = −0.401, p < 0.001) and nighttime PP at LA (R = −0.401, p < 0.001).

Conclusion: Our study demonstrated that AMS patients had a lower PP and Ea at LA. These baseline indicators of vasodilation at LA were closely associated with AMS, which may explain the higher headache severity in subjects with higher PP at LA.

Accuracy and Reliability of Commercial Wrist-Worn Pulse Oximeter During Normobaric Hypoxia Exposure Under Resting Conditions

Purpose: The present study analyzed peripheral blood oxygen saturation (S_pO₂) and heart rate (HR) measurements taken on the Garmin fēnix® 5X Plus watch, comparing them to measurements taken on a standard medical-grade pulse oximeter during normobaric hypoxia exposure under resting conditions. Methods: Thirteen women (mean ± SD: Age 20 ± 1 years, height 165 ± 5 cm, mass, 67 ± 9 kg) and ten men (mean ± SD: Age 21 ± 3 years, height 177 ± 6 cm, mass 78 ± 11 kg) sat inside a customized environmental chamber while the fraction of inspired oxygen (F_IO₂) was adjusted to simulate altitudes of 12,000; 10,000; 8,000; 6,000; and 900 ft. The novel commercial device (Garmin fēnix®) and a medical-grade pulse oximeter (Nonin® 7500) were used to measure S_pO₂ and HR in triplicate at each simulated altitude. Bland-Altman analyses were used to assess differences between methods. Results: Bland-Altman analysis indicated 3.3% bias for S_pO₂ measurements taken on the Garmin fēnix® at 12,000 ft of simulated altitude (limits of agreement: -1.9-8.6%). Mean differences in S_pO₂ measurements were smaller at the remaining simulated altitudes, where bias measurements ranged from 0.7% to 0.8%. The Garmin fēnix® also underestimated heart rate, but those discrepancies were minimal (bias measurements at all simulated altitude exposures were < 1.0 bpm). Conclusions: With the exception of readings taken at 12,000 ft of simulated altitude, the Garmin fēnix® exhibits minimal overestimation of S_pO₂ and minimal underestimation of HR during simulated altitude exposure. These data suggest the Garmin fēnix® watch may be a viable method to monitor S_pO₂ and HR under most ambient environmental conditions.

A Breathtaking Lift: Sex and Body Mass Index Differences in Cardiopulmonary Response in a Large Cohort of Unselected Subjects with Acute Exposure to High Altitude

Vignati, Carlo, Massimo Mapelli, Benedetta Nusca, Alice Bonomi, Elisabetta Salvioni, Irene Mattavelli, Susanna Sciomer, Andrea Faini, Gianfranco Parati, and Piergiuseppe Agostoni. A breathtaking lift: sex and body mass index differences in cardiopulmonary response in a large cohort of unselected subjects with acute exposure to high altitude. High Alt Med Biol 00:000-000, 2021. Background: Every year, thousands of people travel to high altitude and experience hypoxemia. At high altitude, the partial pressure of oxygen decreases. The aim of this observational study was to determine if there is a relationship between anthropometric features and basic cardiorespiratory variables, including oxygen saturation (SpO₂), heart rate (HR), and blood pressure (BP), following acute exposure to high altitude. Materials and Methods: At the 3,466 m top of a cableway station, we installed an automated system for measuring peripheral SpO₂, HR, BP, height, weight, and body mass index (BMI). Results: Between January and October 2020, out of 4,874 volunteers (age 39.9 ± 15.4 years, male 54.4%), 3,267 provided complete data (1,808 cases during winter and 1,459 during summer). SpO₂ was 86.8% ± 6.8%. At multivariable analysis, SpO₂ was significantly associated with age, sex, season, BMI, and HR but not with BP. We identified 391 (12%) subjects with SpO₂ ≤80%: they were older, with a higher BMI and HR but without sex or BP differences. Finally, winter season was associated with greater frequency of SpO₂ ≤80% (13.3% vs. 10.3%, p = 0.008). Conclusion: Our data show that high BMI, older age, and male sex were associated with greater degrees of hypoxemia following exposure to high altitude, particularly during the winter.

Physiological responses during ascent to high altitude and the incidence of acute mountain sickness

Acute mountain sickness (AMS) occurs when there is failure of acclimatisation to high altitude. The aim of this study was to describe the relationship between physiological variables and the incidence of AMS during ascent to 5300 m. A total of 332 lowland‐dwelling volunteers followed an identical ascent profile on staggered treks. Self‐reported symptoms of AMS were recorded daily using the Lake Louise score (mild 3–4; moderate‐severe ≥5), alongside measurements of physiological variables (heart rate, respiratory rate (RR), peripheral oxygen saturation (SpO₂) and blood pressure) before and after a standardised Xtreme Everest Step‐Test (XEST). The overall occurrence of AMS among participants was 73.5% (23.2% mild, 50.3% moderate–severe). There was no difference in gender, age, previous AMS, weight or body mass index between participants who developed AMS and those who did not. Participants who had not previously ascended >5000 m were more likely to get moderate‐to‐severe AMS. Participants who suffered moderate‐to‐severe AMS had a lower resting SpO₂ at 3500 m (88.5 vs. 89.6%, p = 0.02), while participants who suffered mild or moderate‐to‐severe AMS had a lower end‐exercise SpO₂ at 3500 m (82.2 vs. 83.8%, p = 0.027; 81.5 vs. 83.8%, p < 0.001 respectively). Participants who experienced mild AMS had lower end‐exercise RR at 3500 m (19.2 vs. 21.3, p = 0.017). In a multi‐variable regression model, only lower end‐exercise SpO₂ (OR 0.870, p < 0.001) and no previous exposure to altitude >5000 m (OR 2.740, p‐value 0.003) predicted the development of moderate‐to‐severe AMS. The Xtreme Everest Step‐Test offers a simple, reproducible field test to help predict AMS, albeit with relatively limited predictive precision.

Predictive Capacity of Pulmonary Function Tests for Acute Mountain Sickness

Small, Elan, Nicholas Juul, David Pomeranz, Patrick Burns, Caleb Phillips, Mary Cheffers, and Grant S. Lipman. Predictive capacity of pulmonary function tests for acute mountain sickness. High Alt Med Biol. 22: 193-200, 2021. Background: Pulmonary function as measured by spirometry has been investigated at altitude with heterogenous results, though data focused on spirometry and acute mountain sickness (AMS) are limited. The objective of this study was to investigate the capacity of pulmonary function tests (PFTs) to predict the development of AMS. Materials and Methods: This study was a blinded prospective observational study run during a randomized controlled trial comparing acetazolamide, budesonide, and placebo for AMS prevention on White Mountain, CA. Spirometry measurements of forced expiratory volume in one second (FEV₁), forced vital capacity (FVC), and peak expiratory flow were taken at a baseline altitude of 1,250 m, and the evening of and morning after ascent to 3,810 m. Measurements were assessed for correlation with AMS. Results: One hundred three participants were analyzed with well-matched baseline demographics and AMS incidence of 75 (73%) and severe AMS of 48 (47%). There were no statistically significant associations between changes in mean spirometry values on ascent to high altitude with incidence of AMS or severe AMS. Lake Louise Questionnaire scores were negatively correlated with FVC (r = -0.31) and FEV₁ (r = -0.29) the night of ascent. Baseline PFT had a predictive accuracy of 65%-73% for AMS, with a receiver operating characteristic of 0.51-0.65. Conclusions: Spirometry did not demonstrate statistically significant changes on ascent to high altitude, nor were there significant associations with incidence of AMS or severe AMS. Low-altitude spirometry did not accurately predict development of AMS, and it should not be recommended for risk stratification.

Differences in Tolerance to Hypoxia: Physiological, Biochemical, and Molecular-Biological Characteristics

Hypoxia plays an important role in the development of many infectious, inflammatory, and tumor diseases. The predisposition to such disorders is mostly provided by differences in basic tolerance to oxygen deficiency, which we discuss in this review. Except the direct exposure of different-severity hypoxia in decompression chambers or in highland conditions, there are no alternative methods for determining organism tolerance. Due to the variability of the detection methods, differences in many parameters between tolerant and susceptible organisms are still not well-characterized, but some of them can serve as biomarkers of susceptibility to hypoxia. At the moment, several potential biomarkers in conditions after hypoxic exposure have been identified both in experimental animals and humans. The main potential biomarkers are Hypoxia-Inducible Factor (HIF)-1, Heat-Shock Protein 70 (HSP70), and NO. Due to the different mechanisms of various high-altitude diseases, biomarkers may not be highly specific and universal. Therefore, it is extremely important to conduct research on hypoxia susceptibility biomarkers. Moreover, it is important to develop a method for the evaluation of organisms' basic hypoxia tolerance without the necessity of any oxygen deficiency exposure. This can contribute to new personalized medicine approaches' development for diagnostics and the treatment of inflammatory and tumor diseases, taking into account hypoxia tolerance differences.

The Role of Salivary miR-134-3p and miR-15b-5p as Potential Non-invasive Predictors for Not Developing Acute Mountain Sickness

Background

Acute mountain sickness (AMS) is a crucial public health problem for high altitude travelers. Discriminating individuals who are not developing (AMS resistance, AMS−) from developing AMS (AMS susceptibility, AMS+) at baseline would be vital for disease prevention. Salivary microRNAs (miRNAs) have emerged as promising non-invasive biomarkers for various diseases. Thus, the aim of our study was to identify the potential roles of salivary miRNAs in identifying AMS− individuals pre-exposed to high altitude. Moreover, as hypoxia is the triggering factor for AMS, present study also explored the association between cerebral tissue oxygenation indices (TOI) and AMS development after exposed to high altitude, which was the complementary aim.

Methods

In this study, 124 healthy men were recruited, and were exposed at simulated high altitude of 4,500 m. Salivary miR-134-3p and miR-15b-5p were measured at baseline (200 m). AMS was diagnosed based on Lake Louise Scoring System at 4,500 m. The measurements of physiological parameters were recorded at both the altitudes.

Results

Salivary miR-134-3p and miR-15b-5p were significantly up-regulated in AMS− individuals as compared to the AMS+ (p < 0.05). In addition, the combination of these miRNAs generated a high power for discriminating the AMS− from AMS+ at baseline (AUC: 0.811, 95% CI: 0.731−0.876, p < 0.001). Moreover, the value of cerebral TOIs at 4,500 m were significantly higher in AMS− individuals, compared to AMS+ (p < 0.01).

Conclusion

Our study reveals for the first time that salivary miR-134-3p and miR-15b-5p can be used as non-invasive biomarkers for predicting AMS− individuals pre-exposed to high altitude.

Transcriptional profiling in the livers of rats after hypobaric hypoxia exposure

Ascent to high altitude feels uncomfortable in part because of a decreased partial pressure of oxygen due to the decrease in barometric pressure. The molecular mechanisms causing injury in liver tissue after exposure to a hypoxic environment are widely unknown. The liver must physiologically and metabolically change to improve tolerance to altitude-induced hypoxia. Since the liver is the largest metabolic organ and regulates many physiological and metabolic processes, it plays an important part in high altitude adaptation. The cellular response to hypoxia results in changes in the gene expression profile. The present study explores these changes in a rat model. To comprehensively investigate the gene expression and physiological changes under hypobaric hypoxia, we used genome-wide transcription profiling. Little is known about the genome-wide transcriptional response to acute and chronic hypobaric hypoxia in the livers of rats. In this study, we carried out RNA-Sequencing (RNA-Seq) of liver tissue from rats in three groups, normal control rats (L), rats exposed to acute hypobaric hypoxia for 2 weeks (W2L) and rats chronically exposed to hypobaric hypoxia for 4 weeks (W4L), to explore the transcriptional profile of acute and chronic mountain sickness in a mammal under a controlled time-course. We identified 497 differentially expressed genes between the three groups. A principal component analysis revealed large differences between the acute and chronic hypobaric hypoxia groups compared with the control group. Several immune-related and metabolic pathways, such as cytokine-cytokine receptor interaction and galactose metabolism, were highly enriched in the KEGG pathway analysis. Similar results were found in the Gene Ontology analysis. Cogena analysis showed that the immune-related pathways were mainly upregulated and enriched in the acute hypobaric hypoxia group.

Physiological Responses in Humans Acutely Exposed to High Altitude (3480 m): Minute Ventilation and Oxygenation Are Predictive for the Development of Acute Mountain Sickness

The importance of arterial oxygen saturation for the prediction of acute mountain sickness (AMS) is still a matter of debate. Reasons for discrepancies may result from varying laboratory or field conditions and their interactions. Thus, we analyzed data from our prior high-altitude studies, including participants of a broad range of age of both sexes (20 males and 20 females, aged between 20 and 67 years) under strictly standardized conditions of pre-exposure and acute exposure to real high altitude (3480 m). A set of resting cardiovascular, respiratory, hematological, and metabolic variables were recorded at high altitude (Testa Grigia, Plateau Rosa, 3480 m; Swiss-Italian boarder) after performing pretests at low altitude (Innsbruck, 600 m, Austria). Our analyses indicate that (1) smaller changes in resting minute ventilation (VE) and a larger decrease of peripheral oxygen saturation (SpO₂) during the first 3 hours of acute exposure to high altitude were independent predictors for subsequent development of AMS (90% correct prediction), (2) there are no differences of responses between sexes, and (3) there is no association of responses with age. Considering the independent effects of both responses (VE and SpO₂) may be of clinical/practical relevance. Moreover, the presented data derived from a broad age range of both sexes might be of interest for comparative purposes.

Increased Cytokines at High Altitude: Lack of Effect of Ibuprofen on Acute Mountain Sickness, Physiological Variables, or Cytokine Levels

Lundeberg, Jenny, John R. Feiner, Andrew Schober, Jeffrey W. Sall, Helge Eilers, and Philip E. Bickler. Increased cytokines at high altitude: lack of effect of ibuprofen on acute mountain sickness, physiological variables or cytokine levels. High Alt Med Biol. 19:249-258, 2018.

INTRODUCTION

There is no consensus on the role of inflammation in high-altitude acclimatization.

AIMS

To determine the effects of a nonsteroidal anti-inflammatory drug (ibuprofen 400 mg every 8 hours) on blood cytokines, acclimatization, acute mountain sickness (AMS, Lake Louise Score), and noninvasive oxygenation in brain and muscle in healthy volunteers.

MATERIALS AND METHODS

In this double-blind study, 20 volunteers were randomized to receive ibuprofen or placebo at sea level and for 48 hours at 3800 m altitude. Arterial, brain, and leg muscle saturation with near infrared spectroscopy, pulse oximetry, and heart rate were measured. Blood samples were collected for cytokine levels and cytokine gene expression.

RESULTS

All of the placebo subjects and 8 of 11 ibuprofen subjects developed AMS at altitude (p = 0.22, comparing placebo and ibuprofen). On arrival at altitude, the oxygen saturation as measured by pulse oximetry (S_pO₂) was 84.5% ± 5.4% (mean ± standard deviation). Increase in blood interleukin-1β (IL-1β), interleukin-6 (IL-6), interleukin-8 (IL-8), interleukin-10 (IL-10), tumor necrosis factor-α (TNF-α), and granulocyte-macrophage colony-stimulating factor (GM-CSF) levels occurred comparably in the placebo and ibuprofen groups (all not significant, univariate test by Wilcoxon rank sum). Increased IL-6 was associated with higher AMS scores (p = 0.002 by Spearman rank correlation). However, we found no difference or association in AMS score and blood or tissue oxygenation between the ibuprofen and placebo groups.

CONCLUSIONS

We found that ibuprofen, at the package-recommended adult dose, did not have a significant effect on altitude-related increases in cytokines, AMS scores, blood, or tissue oxygenation in a population of healthy subjects with a high incidence of AMS.

Exploration of Acute Phase Proteins and Inflammatory Cytokines in Early Stage Diagnosis of Acute Mountain Sickness

Wang, Chi, Hui Jiang, Jinyan Duan, Jingwen Chen, Qi Wang, Xiaoting Liu, and Chengbin Wang. Exploration of acute phase proteins and inflammatory cytokines in early stage diagnosis of acute mountain sickness. High Alt Med Biol. 19:170-177, 2018.

BACKGROUND

Early diagnosis of acute mountain sickness (AMS) is currently based on personal appreciation of the severity of symptoms. A more objective method to diagnose AMS is required. Inflammatory cytokines and acute phase proteins have been reported to be different at high altitude.

METHODS

A total of 104 male soldiers rapidly ascending from Beijing (20-60 m) to Germu, Qinghai (3200 m), were divided into AMS group and non-AMS group according to the Lake Louis Score system. Blood pressure, pulse rate, and oxygen saturation were measured. Forty-nine blood samples were collected before and on the 3rd day after ascending to the high altitude. Serum haptoglobin (Hp), transferrin (Tf), and complement C3 were detected by immune scattered nephelometry, whereas serum interleukin-1beta (IL-1β), IL-6, and tumor necrosis factor-α (TNF-α) were detected by chemical luminescence immunity analyzer. The sensitivity, specificity, and receiver operating characteristic curve were evaluated. Youden index with the maximum value was used to determine cutoff values of each parameter. Logistic regression was performed to determine the diagnostic efficiency of combination of three cytokines.

RESULTS

Differences of physical indexes between AMS group and non-AMS group were of no statistical significance. In AMS group, serum Tf significantly increased while Hp decreased when compared with non-AMS group. Serum IL-1β, IL-6, and TNF-α were higher in the AMS group than in the non-AMS group. The cutoff values for Tf, Hp, IL-1β, IL-6, and TNF-α were 263.5 mg/dL, 119.35 mg/dL, 6.2 pg/mL, 15.05 pg/mL, and 18.35 pg/mL, respectively. Area under the curve (AUC) of combining three cytokines together was higher than AUC of each cytokine separately.

CONCLUSIONS

Acute phase proteins and inflammatory cytokines (IL-1β, IL-6, and TNF-α) show significant changes between the AMS group and the non-AMS group. Combination of inflammatory cytokines or acute phase proteins improves the specificity for diagnosis of AMS. This might provide objective indexes for scanning and screening individuals susceptible to AMS in the early stage of rapid ascending.

Wearable physiological sensors and real-time algorithms for detection of acute mountain sickness

This is a minireview of potential wearable physiological sensors and algorithms (process and equations) for detection of acute mountain sickness (AMS). Given the emerging status of this effort, the focus of the review is on the current clinical assessment of AMS, known risk factors (environmental, demographic, and physiological), and current understanding of AMS pathophysiology. Studies that have examined a range of physiological variables to develop AMS prediction and/or detection algorithms are reviewed to provide insight and potential technological roadmaps for future development of real-time physiological sensors and algorithms to detect AMS. Given the lack of signs and nonspecific symptoms associated with AMS, development of wearable physiological sensors and embedded algorithms to predict in the near term or detect established AMS will be challenging. Prior work using [Formula: see text], HR, or HRv has not provided the sensitivity and specificity for useful application to predict or detect AMS. Rather than using spot checks as most prior studies have, wearable systems that continuously measure SpO2 and HR are commercially available. Employing other statistical modeling approaches such as general linear and logistic mixed models or time series analysis to these continuously measured variables is the most promising approach for developing algorithms that are sensitive and specific for physiological prediction or detection of AMS.

Hypoxia augments LPS-induced inflammation and triggers high altitude cerebral edema in mice

High altitude cerebral edema (HACE) is a life-threatening illness that develops during the rapid ascent to high altitudes, but its underlying mechanisms remain unclear. Growing evidence has implicated inflammation in the susceptibility to and development of brain edema. In the present study, we investigated the inflammatory response and its roles in HACE in mice following high altitude hypoxic injury. We report that acute hypobaric hypoxia induced a slight inflammatory response or brain edema within 24h in mice. However, the lipopolysaccharide (LPS)-induced systemic inflammatory response rapidly aggravated brain edema upon acute hypobaric hypoxia exposure by disrupting blood-brain barrier integrity and activating microglia, increasing water permeability via the accumulation of aquaporin-4 (AQP4), and eventually leading to impaired cognitive and motor function. These findings demonstrate that hypoxia augments LPS-induced inflammation and induces the occurrence and development of cerebral edema in mice at high altitude. Here, we provide new information on the impact of systemic inflammation on the susceptibility to and outcomes of HACE.

Association between smoking and the risk of acute mountain sickness: a meta-analysis of observational studies

BACKGROUND

People rapidly ascending to high altitudes (>2500 m) may suffer from acute mountain sickness (AMS). The association between smoking and AMS risk remains unclear. Therefore, we performed a meta-analysis to evaluate the association between smoking and AMS risk.

METHODS

The association between smoking and AMS risk was determined according to predefined criteria established by our team. Meta-analysis was conducted according to the PRISMA guidelines. We included all relevant studies listed in the PubMed and Embase databases as of September 2015 in this meta-analysis and performed systemic searches using the terms "smoking", "acute mountain sickness" and "risk factor". The included studies were required to provide clear explanations regarding their definitions of smoking, the final altitudes reached by their participants and the diagnostic criteria used to diagnose AMS. Odds ratios (ORs) were used to evaluate the association between smoking and AMS risk across the studies, and the Q statistic was used to test OR heterogeneity, which was considered significant when P < 0.05. We also computed 95% confidence intervals (CIs). Data extracted from the articles were analyzed with Review Manager 5.3 (Cochrane Collaboration, Oxford, UK).

RESULTS

We used seven case-control studies including 694 smoking patients and 1986 non-smoking controls to analyze the association between smoking and AMS risk. We observed a significant association between AMS and smoking (OR = 0.71, 95% CI 0.52-0.96, P = 0.03).

CONCLUSIONS

We determined that smoking may protect against AMS development. However, we do not advise smoking to prevent AMS. More studies are necessary to confirm the role of smoking in AMS risk.

Influence of Acute Normobaric Hypoxia on Hemostasis in Volunteers with and without Acute Mountain Sickness

INTRODUCTION

The aim of the present study was to investigate whether a 12-hour exposure in a normobaric hypoxic chamber would induce changes in the hemostatic system and a procoagulant state in volunteers suffering from acute mountain sickness (AMS) and healthy controls.

MATERIALS AND METHODS

37 healthy participants were passively exposed to 12.6% FiO2 (simulated altitude hypoxia of 4,500 m). AMS development was investigated by the Lake Louise Score (LLS). Prothrombin time, activated partial thromboplastin time, fibrinogen, and platelet count were measured and specific methods (i.e., thromboelastometry and a thrombin generation test) were used.

RESULTS

AMS prevalence was 62.2% (LLS cut off of 3). For the whole group, paired sample t-tests showed significant increase in the maximal concentration of generated thrombin. ROTEM measurements revealed a significant shortening of coagulation time and an increase of maximal clot firmness (InTEM test). A significant increase in maximum clot firmness could be shown (FibTEM test).

CONCLUSIONS

All significant changes in coagulation parameters after exposure remained within normal reference ranges. No differences with regard to measured parameters of the hemostatic system between AMS-positive and -negative subjects were observed. Therefore, the hypothesis of the acute activation of coagulation by hypoxia can be rejected.

Diagnosis and prediction of the occurrence of acute mountain sickness measuring oxygen saturation--independent of absolute altitude?

PURPOSE

Commercialization of trekking tourism enables untrained persons to participate in trekking tours. Because hypoxia is one of the main purported triggers for acute mountain sickness (AMS), pulse oximetry, which measures arterial oxygen saturation (SPO2), is discussed to be a possible and useful tool for the diagnosis of AMS. The purpose of this study was to evaluate possible associations between SPO2 values and the occurrence of AMS.

METHODS

In 204 trekkers, SPO2 values (pulse oximetry) were measured and the Lake Louise Self-assessment Score (LLS) was administered over the first 7 days of their trekking tours.

RESULTS

During treks at altitudes of 2500-5500 m in Nepal, India, Africa, and South America, 100 participants suffered from mild AMS, 3 participants suffered from severe AMS, and 9 participants reported both mild and severe AMS. The lowest mean SPO2 was 85.5 (95 % confidence interval (CI), 83.9-86.1 %) on day 5. SPO2 and LLS exhibited a weak to moderate negative correlation for all days of the study (ρ ranging from -0.142 to -0.370). Calculation of time-shifted associations of 24 and 48 h resulted in the disappearance of most associations. Susceptibility to headaches (odds ratio (OR) 2.9-7.2) and a history of AMS (OR 2.2-3.1) were determined to be potential risk factors for the development of AMS.

CONCLUSION

Since there is no strong altitude-independent association between AMS and SPO2 during the first week of high-altitude adaptation, the implementation of pulse oximetry during trekking in order to detect and predict AMS remains questionable.

Variants of the low oxygen sensors EGLN1 and HIF-1AN associated with acute mountain sickness

Two low oxygen sensors, Egl nine homolog 1 (EGLN1) and hypoxia-inducible factor 1-α inhibitor (HIF-1AN), play pivotal roles in the regulation of HIF-1α, and high altitude adaption may be involved in the pathology of acute mountain sickness (AMS). Here, we aimed to analyze single nucleotide polymorphisms (SNPs) in the untranslated regions of the EGLN1 and HIF-1AN genes and SNPs chosen from a genome-wide adaptation study of the Han Chinese population. To assess the association between EGLN1 and HIF-1AN SNPs and AMS in a Han Chinese population, a case-control study was performed including 190 patients and 190 controls. In total, thirteen SNPs were genotyped using the MassARRAY® MALDI-TOF system. Multiple genetic models were tested; The Akaike's information criterion (AIC) and Bayesian information criterion (BIC) values indicated that the dominant model may serve as the best-fit model for rs12406290 and rs2153364 of significant difference. However, these data were not significant after Bonferroni correction. No significant association was noted between AMS and rs12757362, rs1339894, rs1361384, rs2009873, rs2739513 or rs2486729 before and after Bonferroni correction. Further haplotype analyses indicated the presence of two blocks in EGLN1; one block consists of rs12406290-rs2153364, located upstream of the EGLN1 gene. Carriers of the "GG" haplotype of rs12406290-rs2153364 exhibited an increased risk of AMS after adjustments for age and smoking status. However, no significant association was observed among HIF-1AN 3'-untranslated region (3'-UTR) polymorphisms, haplotype and AMS. Our study indicates that variants in the EGLN1 5'-UTR influence the susceptibility to AMS in a Han Chinese population.