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

Closing the loop: autonomous intelligent control for hypoxia pre-acclimatization and high-altitude health management

Hypobaric hypoxia at high altitudes threatens the health of high-altitude residents. The development of effective methods to guarantee the safety of frequent human activities in high-altitude locations is therefore needed. Pre-acclimatization at sea level is an effective approach to mitigate subsequent altitude sickness for rapid ascent, which offers a viable substitute to on-site acclimatization, minimizes the associated risks that are linked to prolonged exposure in high-altitude environments and can be personalized to individual hypoxic responses. Another critical aspect to prevent long-term physical damage is personalized health management at high altitudes, which is enabled by the emerging technologies of wearable sensors, the Internet of Medical Things and artificial intelligence. In this review, we outline the progress in pre-acclimatization and high-altitude health management, as well as the understanding of physiological mechanisms under hypoxia, highlighting the important role that is played by wearable sensors and physiological closed-loop control systems in developing intelligent personalized solutions. We also discuss the challenges and prospects of deploying autonomous intelligent monitoring and control in high-altitude health management.

Oxygen saturation and acute mountain sickness during repeated altitude exposures simulating high-altitude working schedules

This study aimed to quantify the effect of two consecutive prolonged, intermittent exposures to high and very high altitudes on oxygen saturation (SpO2) and acute mountain sickness (AMS). For this, healthy lowlanders (N = 21), aged 18-30 years, underwent two 7-day sojourns at the ALMA observatory, Chile (6 h/day at 5050 m, 18 h/day at 2900 m), separated by 1-week at 520 m. SpO2 (pulse oximetry) and AMS severity (AMSc, Environmental Symptom Questionnaire cerebral score) diagnosing AMS (AMSc ≥ 0.7) were assessed daily at both altitudes. The study was registered at www.ClinicalTrials.gov: NCT02730143. SpO2 at 2900 m and 5050 m on arrival was mean ± SD 93.6 ± 0.5% and 79.9 ± 1.0% (P < 0.05 between altitudes), whereas the AMSc scores were 0.43 ± 0.08 and 0.97 ± 0.11 (P < 0.05 between altitudes), respectively. At 2900 m during a 7-day intermittent hypoxic exposure, SpO2 increased by a mean (95% CI) 0.3 %/day (0.1;0.4) and by 0.9 %/day (0.4;1.3) at 5050 m. Similarly, AMSc decreased by 0.05 points/day (0.01;0.08) at 2900 m and by 0.16 points/day (0.11;0.21) at 5050 m. During the second sojourn (vs. 1st sojourn), day 1, SpO2 at 2900 m was unchanged but higher at 5050 m by 2.9% (0.6;5.3). AMSc was lower at 2900 m and 5050 m by 0.37 (0.16;0.59) and 0.37 (0.11;0.63) (P < 0.05 both comparisons vs 1st sojourn), respectively. Acclimatization with the 2nd sojourn increased SpO2 at 2900 m by 0.3%/day (0.1;0.4) and 5050 m by 0.5%/day (0.1;0.8). AMSc remained unchanged with acclimatization at 2900 m but decreased at 5050 m by 0.08 points/day (0.04;0.11). In conclusion, in healthy lowlanders, a 7-day intermittent hypobaric hypoxic exposure improved SpO2 and AMS severity at 2900 m, with larger improvements at 5050 m. During a second identical sojourn, initial AMS severity was reduced despite comparable SpO2 at 2900 m compared to the 1st sojourn. No further acclimatization effects were observed in SpO2 but in AMS symptoms at 2900 m. In contrast, re-exposure to 5050 m showed higher initial SpO2 and lower AMSc values with further improvement with intermittent re-exposures. These findings highlight altitude-dependent acclimatization patterns and confirm pre-conditioning's effectiveness in preventing AMS.

Heterogeneity of treatment effect: the case for individualising oxygen therapy in critically ill patients

Oxygen therapy is ubiquitous in critical illness but oxygenation targets to guide therapy remain controversial despite several large randomised controlled trials (RCTs). Findings from RCTs evaluating different approaches to oxygen therapy in critical illness present a confused picture for several reasons. Differences in both oxygen target measures (e.g. oxygen saturation or partial pressure) and the numerical thresholds used to define lower and higher targets complicate comparisons between trials. The duration of and adherence to oxygenation targets is also variable with consequent substantial variation in both the dose and the dose separation. Finally, heterogeneity of treatment effects (HTE) may also be a significant factor. HTE is defined as non-random variation in the benefit or harm of a treatment, in which the variation is associated with or attributable to patient characteristics. This narrative review aims to make the case that such heterogeneity is likely in relation to oxygen therapy for critically ill patients and that this has significant implications for the design and interpretation of trials of oxygen therapy in this context. HTE for oxygen therapy amongst critically ill patients may explain the contrasting results from different clinical trials of oxygen therapy. Individualised oxygen therapy may overcome this challenge, and future studies should incorporate ways to evaluate this approach.

Nocturnal pulse oxygen saturation dynamics at simulated high altitude: Predictive value for acute mountain sickness in healthy men born pre-term

The physiological sequelae of pre-term birth might influence the responses of this population to hypoxia. Moreover, identifying variables associated with development of acute mountain sickness (AMS) remains a key practically significant area of altitude research. We investigated the effects of pre-term birth on nocturnal oxygen saturation (S p O 2 ${{S}_{{\mathrm{p}}{{{\mathrm{O}}}_{\mathrm{2}}}}}$ ) dynamics and assessed the predictive potential of nocturnalS p O 2 ${{S}_{{\mathrm{p}}{{{\mathrm{O}}}_{\mathrm{2}}}}}$ -related metrics for morning AMS in 12 healthy adults with gestational age < 32 weeks (pre-term) and 12 term-born control participants. Participants spent one night at a simulated altitude of ∼4200 m (normobaric hypoxia; fraction of inspired O2 = 0.141), with nocturnalS p O 2 ${{S}_{{\mathrm{p}}{{{\mathrm{O}}}_{\mathrm{2}}}}}$ and heart rate recorded continuously at the fingertip using pulse oximetry and with morning AMS assessed using the Lake Louise scale. Pre-term and term-born participants had similar nocturnal meanS p O 2 ${{S}_{{\mathrm{p}}{{{\mathrm{O}}}_{\mathrm{2}}}}}$ (mean ± SD; 77% ± 3% vs. 77% ± 4%; P = 0.661), minimumS p O 2 ${{S}_{{\mathrm{p}}{{{\mathrm{O}}}_{\mathrm{2}}}}}$ (median[IQR]; 67[4]% vs. 69[5]%; P = 0.223), relative time spent withS p O 2 ${{S}_{{\mathrm{p}}{{{\mathrm{O}}}_{\mathrm{2}}}}}$  < 80% (72% ± 29% vs. 70% ± 27%; P = 0.879) and mean heart rate (79 ± 12 vs. 71 ± 7 beats/min; P = 0.053). However, the increase inS p O 2 ${{S}_{{\mathrm{p}}{{{\mathrm{O}}}_{\mathrm{2}}}}}$ between the two halves of the night was blunted with prematurity (-0.12% ± 1.51% vs. 1.11% ± 0.78%; P = 0.021). Moreover, the cumulative relative desaturation-based hypoxic 'load' was higher with prematurity (32[26]%min/h vs. 7[25]%min/h; P = 0.039), underpinned by increased desaturation frequency (69[49] vs. 21[35] counts/h; P = 0.009). MeanS p O 2 ${{S}_{{\mathrm{p}}{{{\mathrm{O}}}_{\mathrm{2}}}}}$ , minimumS p O 2 ${{S}_{{\mathrm{p}}{{{\mathrm{O}}}_{\mathrm{2}}}}}$ , morningS p O 2 ${{S}_{{\mathrm{p}}{{{\mathrm{O}}}_{\mathrm{2}}}}}$ and relative time spent withS p O 2 ${{S}_{{\mathrm{p}}{{{\mathrm{O}}}_{\mathrm{2}}}}}$  < 80% predicted AMS incidence better than a random classifier exclusively in the pre-term group, with no other variables predictive of AMS in the two groups separately or combined. Overall, pre-term birth might alter nocturnalS p O 2 ${{S}_{{\mathrm{p}}{{{\mathrm{O}}}_{\mathrm{2}}}}}$ dynamics and influence AMS prediction in severe hypoxia.

Correlation between hematological indicators in acclimatized high-altitude individuals and acute mountain sickness

Background

The impact of acute mountain sickness (AMS) on individuals ascending to plateaus, soon after exposure to high altitudes, is well-documented. However, the specific relationship between AMS and alterations in blood parameters remains unclear.

Methods

A total of 40 healthy volunteers were recruited. Following their arrival at an altitude of 3,300 m, an AMS questionnaire survey was administered 48 h later. Based on the AMS scores obtained, participants were categorized into three groups: non-AMS, mild AMS, and moderate/severe AMS (encompassing both moderate and severe cases). Blood routine tests were performed on all groups at 3-, 7-, and 30-days post-arrival at the plateau, with blood oxygen saturation tests conducted at 3 and 30 days after rapidly entering the plateau.

Results

In the current investigation, a total of 40 participants were stratified into non-AMS (n = 24), mild-AMS (n = 8), and moderate/severe-AMS (n = 8) cohorts subsequent to rapid ascension to an altitude of 3,300 m. The incidence of AMS in this study was 40%. Noteworthy elevations in red blood cells (RBC), hemoglobin (Hb), and hematocrit (HCT) levels were noted at the 3-day mark post-ascent across all delineated groups. By the 7th day, the moderate/severe-AMS cohort displayed sustained increments in Hb and HCT levels, whereas solely HCT levels rose in the mild-AMS and non-AMS cohorts. Upon reaching the 30-day milestone, the moderate/severe-AMS group demonstrated a reduction in RBC, Hb, and HCT levels, while only HCT levels decreased in the mild-AMS and non-AMS groups. Furthermore, it was observed that all groups exhibited notable reductions in oxygen saturation (SpO2) at 3 days post-ascent, followed by a partial recovery at 30 days, albeit remaining below baseline levels. The correlation analysis results indicated that RBC, Hb, and HCT exhibited a positive correlation with the severity of AMS after a 7-day acclimatization period at high altitude. Conversely, SpO2 demonstrated a negative correlation with the severity of AMS following the same duration at high altitude. The findings of the study suggest a strong association between alterations in RBC, Hb, and HCT levels and AMS, particularly among individuals in the moderate/severe-AMS category who displayed more significant fluctuations in these parameters.

Conclusion

Individuals suffering from moderate to severe AMS demonstrated increased levels of RBC, Hb, and HCT, as well as reduced SpO2, indicating a greater need for oxygen adaptation to high-altitude hypoxia. These findings emphasize the physiological adjustments to high altitudes and their potential implications for the treatment of AMS.

Pulse oximetry for the prediction of acute mountain sickness: A systematic review

Acute mountain sickness (AMS) causes serious illness for many individuals ascending to high altitude (HA), although preventable with appropriate acclimatisation. AMS is a clinical diagnosis, with symptom severity evaluated using the Lake Louise Score (LLS). Reliable methods of predicting which individuals will develop AMS have not been developed. This systematic review evaluates whether a predictive relationship exists between oxygen saturation and subsequent development of AMS. PubMed, PubMed Central, MEDLINE, Semantic Scholar, Cochrane Library, University of Birmingham Library and clinicaltrials.gov databases were systematically searched from inception to 15 June 2023. Human studies involving collection of peripheral blood oxygen saturation (S p O 2 ${{S}_{{\mathrm{p}}{{{\mathrm{O}}}_{\mathrm{2}}}}}$ ) from healthy lowlanders during ascent to HA that evaluated any relationship betweenS p O 2 ${{S}_{{\mathrm{p}}{{{\mathrm{O}}}_{\mathrm{2}}}}}$ and AMS severity were considered for eligibility. Risk of bias was assessed using a modified Newcastle-Ottawa Tool for cohort studies (PROPSPERO CRD42023423542). Seven of 980 total identified studies were ultimately included for data extraction. These studies evaluatedS p O 2 ${{S}_{{\mathrm{p}}{{{\mathrm{O}}}_{\mathrm{2}}}}}$ and AMS (via LLS) in 1406 individuals during ascent to HA (3952-6300 m). Risk of bias was 'low' for six and 'moderate' for one of the included studies. Ascent profiles andS p O 2 ${{S}_{{\mathrm{p}}{{{\mathrm{O}}}_{\mathrm{2}}}}}$ measurement methodology varied widely, as did the statistical methods for AMS prediction. Decreasing oxygen saturation measured with pulse oximetry during ascent shows a positive predictive relationship for individuals who develop AMS. Studies have high heterogeneity in ascent profile and oximetry measurement protocols. Further studies with homogeneous methodology are required to enable statistical analysis for more definitive evaluation of AMS predictability by pulse oximetry.

Utility of hypoxic modalities for musculoskeletal injury rehabilitation in athletes: A narrative review of mechanisms and contemporary perspectives

Recent evidence suggests that different hypoxic modalities might accelerate the rehabilitation process in injured athletes. In this review, the application of hypoxia during rehabilitation from musculoskeletal injury is explored in relation to two principles: (1) facilitating the healing of damaged tissue, and (2) mitigating detraining and inducing training adaptations with a reduced training load. Key literature that explores the underlying mechanisms for these themes is presented, and considerations for practice and future research directions are outlined. For principle (1), passive intermittent hypoxic exposures might accelerate tissue healing through angiogenic and osteogenic mechanisms. Experimental evidence is largely derived from rodent research, so further work is warranted to establish whether clinically meaningful effects can be observed in humans, before optimal protocols are determined (duration, frequency, and hypoxic severity). Regarding principle (2), a hypoxia-related increase in the cardiometabolic stimulus imposed by low-load exercise is appealing for load-compromised athletes. As rehabilitation progresses, a variety of hypoxic modalities can be implemented to enhance adaptation to energy-systems and resistance-based training, and more efficiently return the athlete to competition readiness. While hypoxic modalities seem promising for accelerating musculoskeletal injury rehabilitation in humans, and are already being widely used in practice, a significant gap remains regarding their evidence-based application.

Incidence and risk factors of acute mountain sickness during ascent to Hoh Xil and the physiological responses before and after acclimatization

OBJECTIVES

Ascending to altitudes >2500 m may lead to acute mountain sickness (AMS).

METHODS

The demographics, height, weight, body mass index (BMI), smoking, and alcohol consumption of 104 healthy controls were collected in Chengdu (500 m). Heart rate (HR), saturation of pulse oxygen (SpO2), and AMS-related symptoms were collected in Hoh Xil (4200 m). A headache with Lake Louise score ≥3 was defined as AMS.

RESULTS

The incidence of AMS was 60.58%. AMS group had a lower SpO2 and higher HR than non-AMS group. Alcohol consumption seemed a risk factor for AMS. There was no difference in the BMI, age, height, weight, and smoking between AMS and non-AMS groups. The most common AMS symptom was headache, followed by dyspnea, insomnia, dizziness, lassitude, and anorexia. Women were prone to suffer from dizziness. The value of SpO2 and HR was improved both in AMS and non-AMS groups after hypoxia acclimatization, and the value showed greater improvement in AMS group. Oxygen therapy decreased the AMS-induced tachycardia, which had no any effect on SpO2 and symptom alleviating time.

CONCLUSION

Lower SpO2 and higher HR following exposure to high altitude were associated with AMS susceptibility. The anthropometric data changes were larger in AMS group than non-AMS group before and after hypoxia acclimatization.

A Step Test to Evaluate the Susceptibility to Severe High-Altitude Illness in Field Conditions

Hermand, Eric, Léo Lesaint, Laura Denis, Jean-Paul Richalet, and François J. Lhuissier. A step test to evaluate the susceptibility to severe high-altitude illness in field conditions. High Alt Med Biol. 25:158-163, 2024.-A laboratory-based hypoxic exercise test, performed on a cycle ergometer, can be used to predict susceptibility to severe high-altitude illness (SHAI) through the calculation of a clinicophysiological SHAI score. Our objective was to design a field-condition test and compare its derived SHAI score and various physiological parameters, such as peripheral oxygen saturation (SpO2), and cardiac and ventilatory responses to hypoxia during exercise (HCRe and HVRe, respectively), to the laboratory test. A group of 43 healthy subjects (15 females and 28 males), with no prior experience at high altitude, performed a hypoxic cycle ergometer test (simulated altitude of 4,800 m) and step tests (20 cm high step) at 3,000, 4,000, and 4,800 m simulated altitudes. According to tested altitudes, differences were observed in O2 desaturation, heart rate, and minute ventilation (p < 0.001), whereas the computed HCRe and HVRe were not different (p = 0.075 and p = 0.203, respectively). From the linear relationships between the step test and SHAI scores, we defined a risk zone, allowing us to evaluate the risk of developing SHAI and take adequate preventive measures in field conditions, from the calculated step test score for the given altitude. The predictive value of this new field test remains to be validated in real high-altitude conditions.

Altitude illnesses

Millions of people visit high-altitude regions annually and more than 80 million live permanently above 2,500 m. Acute high-altitude exposure can trigger high-altitude illnesses (HAIs), including acute mountain sickness (AMS), high-altitude cerebral oedema (HACE) and high-altitude pulmonary oedema (HAPE). Chronic mountain sickness (CMS) can affect high-altitude resident populations worldwide. The prevalence of acute HAIs varies according to acclimatization status, rate of ascent and individual susceptibility. AMS, characterized by headache, nausea, dizziness and fatigue, is usually benign and self-limiting, and has been linked to hypoxia-induced cerebral blood volume increases, inflammation and related trigeminovascular system activation. Disruption of the blood-brain barrier leads to HACE, characterized by altered mental status and ataxia, and increased pulmonary capillary pressure, and related stress failure induces HAPE, characterized by dyspnoea, cough and exercise intolerance. Both conditions are progressive and life-threatening, requiring immediate medical intervention. Treatment includes supplemental oxygen and descent with appropriate pharmacological therapy. Preventive measures include slow ascent, pre-acclimatization and, in some instances, medications. CMS is characterized by excessive erythrocytosis and related clinical symptoms. In severe CMS, temporary or permanent relocation to low altitude is recommended. Future research should focus on more objective diagnostic tools to enable prompt treatment, improved identification of individual susceptibilities and effective acclimatization and prevention options.

Potential therapeutic effects of traditional Chinese medicine in acute mountain sickness: pathogenesis, mechanisms and future directions

Background and objectives

Acute mountain sickness (AMS) is a pathology with different symptoms in which the organism is not adapted to the environment that occurs under the special environment of high altitude. Its main mechanism is the organism's tissue damage caused by acute hypobaric hypoxia. Traditional Chinese medicine (TCM) theory focuses on the holistic concept. TCM has made remarkable achievements in the treatment of many mountain sicknesses. This review outlines the pathogenesis of AMS in modern and traditional medicine, the progress of animal models of AMS, and summarizes the therapeutic effects of TCM on AMS.

Methods

Using the keywords "traditional Chinese medicine," "herbal medicine," "acute mountain sickness," "high-altitude pulmonary edema," "high-altitude cerebral edema," "acute hypobaric hypoxia," and "high-altitude," all relevant TCM literature published up to November 2023 were collected from Scopus, Web of Science, PubMed, and China National Knowledge Infrastructure databases, and the key information was analyzed.

Results

We systematically summarised the effects of acute hypobaric hypoxia on the tissues of the organism, the study of the methodology for the establishment of an animal model of AMS, and retrieved 18 proprietary Chinese medicines for the clinical treatment of AMS. The therapeutic principle of medicines is mainly invigorating qi, activating blood and removing stasis. The components of botanical drugs mainly include salidroside, ginsenoside Rg1, and tetrahydrocurcumin. The mechanism of action of TCM in the treatment of AMS is mainly through the regulation of HIF-1α/NF-κB signaling pathway, inhibition of inflammatory response and oxidative stress, and enhancement of energy metabolism.

Conclusion

The main pathogenesis of AMS is unclear. Still, TCM formulas and components have been used to treat AMS through multifaceted interventions, such as compound danshen drip pills, Huangqi Baihe granules, salidroside, and ginsenoside Rg1. These components generally exert anti-AMS pharmacological effects by inhibiting the expression of VEGF, concentration of MDA and pro-inflammatory factors, down-regulating NF-κB/NLRP3 pathway, and promoting SOD and Na + -K + -ATPase activities, which attenuates acute hypobaric hypoxia-induced tissue injury. This review comprehensively analyses the application of TCM in AMS and makes suggestions for more in-depth studies in the future, aiming to provide some ideas and insights for subsequent studies.

Serum vascular endothelial growth factor is a potential biomarker for acute mountain sickness

Background: Acute mountain sickness (AMS) is the most common disease caused by hypobaric hypoxia (HH) in high-altitude (HA) associated with high mortality when progressing to high-altitude pulmonary edema (HAPE) and/or high-altitude cerebral edema (HACE). There is evidence for a role of pro- and anti-inflammatory cytokines in development of AMS, but biological pathways and molecular mechanisms underlying AMS remain elusive. We aimed to measure changes in blood cytokine levels and their possible association with the development of AMS.

Method: 15 healthy mountaineers were included into this prospective clinical trial. All participants underwent baseline normoxic testing with venous EDTA blood sampling at the Bangor University in United Kingdom (69 m). The participants started from Beni at an altitude of 869 m and trekked same routes in four groups the Dhaulagiri circuit in the Nepali Himalaya. Trekking a 14-day route, the mountaineers reached the final HA of 5,050 m at the Hidden Valley Base Camp (HVBC). Venous EDTA blood sampling was performed after active ascent to HA the following morning after arrival at 5,050 m (HVBC). A panel of 21 cytokines, chemokines and growth factors were assessed using Luminex system (IL-1β, IL-2, IL-4, IL-6, IL-8, IL-10, IL-12p40, IL-1ra, sIL-2Rα, IFN-γ, TNF-α, MCP-1, MIP-1α, MIP-1β, IP-10, G-CSF, GM-CSF, EGF, FGF-2, VEGF, and TGF-β1).

Results: There was a significant main effect for the gradual ascent from sea-level (SL) to HA on nearly all cytokines. Serum levels for TNF-α, sIL-2Rα, G-CSF, VEGF, EGF, TGF-β1, IL-8, MCP-1, MIP-1β, and IP-10 were significantly increased at HA compared to SL, whereas levels for IFN-γ and MIP-1α were significantly decreased. Serum VEGF was higher in AMS susceptible versus AMS resistant subjects (p &lt; 0.027, main effect of AMS) and increased after ascent to HA in both AMS groups (p &lt; 0.011, main effect of HA). Serum VEGF increased more from SL values in the AMS susceptible group than in the AMS resistant group (p &lt; 0.049, interaction effect).

Conclusion: Cytokine concentrations are significantly altered in HA. Within short interval after ascent, cytokine concentrations in HH normalize to values at SL. VEGF is significantly increased in mountaineers suffering from AMS, indicating its potential role as a biomarker for AMS.

Establishing a prediction model of severe acute mountain sickness using machine learning of support vector machine recursive feature elimination

Severe acute mountain sickness (sAMS) can be life-threatening, but little is known about its genetic basis. The study was aimed to explore the genetic susceptibility of sAMS for the purpose of prediction, using microarray data from 112 peripheral blood mononuclear cell (PBMC) samples of 21 subjects, who were exposed to very high altitude (5260 m), low barometric pressure (406 mmHg), and hypobaric hypoxia (VLH) at various timepoints. We found that exposure to VLH activated gene expression in leukocytes, resulting in an inverted CD4/CD8 ratio that interacted with other phenotypic risk factors at the genetic level. A total of 2286 underlying risk genes were input into the support vector machine recursive feature elimination (SVM-RFE) system for machine learning, and a model with satisfactory predictive accuracy and clinical applicability was established for sAMS screening using ten featured genes with significant predictive power. Five featured genes (EPHB3, DIP2B, RHEBL1, GALNT13, and SLC8A2) were identified upstream of hypoxia- and/or inflammation-related pathways mediated by microRNAs as potential biomarkers for sAMS. The established prediction model of sAMS holds promise for clinical application as a genetic screening tool for sAMS.

Adaptation and altitude sickness: A 40-year bibliometric analysis and collaborative networks

Introduction

We analyze the scientific production and collaboration networks of studies based on adaptation and altitude diseases in the period 1980-2020.

Methods

The publications were extracted from journals indexed in Scopus. The bibliometric analysis was used to analyze the scientific production, including the number of annual publications, the documents, and the characteristics of the publications. With the VOSviewer software, the analysis of collaborative networks, productivity of the countries, as well as the analysis of the co-occurrence of keywords were visualized.

Results

15,240 documents were registered, of which 3,985 documents were analyzed. A significant trend was observed in the number of publications (R ²: 0.9847; P: < 0.001), with annual growth of 4.6%. The largest number of publications were original articles (77.8%), these published more frequently in the journal "Altitude Medicine and Biology". The largest number of countries were from Europe and Asia; however, the largest collaboration network was with the United States. Of the countries with high altitudes, China and Peru ranked first in scientific productivity. The research priorities were on the adaptation mechanism (37.1%), mainly anoxia and respiratory function. Acute mountain sickness (18.4%) and pulmonary edema (14.7%) were the most reported diseases. Of the top 10 institutions, "University of Colorado" and "Universidad Peruana Cayetano Heredia" contributed more than 100 publications.

Conclusions

Scientific production on adaptation and altitude illnesses continues to grow. The United States and United Kingdom present collaborative networks with high-altitude countries. The research is aimed at studying the mechanisms of adaptation to altitude and acute mountain sickness.

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.

Using machine learning to determine the correlation between physiological and environmental parameters and the induction of acute mountain sickness

Background

Recent studies on acute mountain sickness (AMS) have used fixed-location and fixed-time measurements of environmental and physiological variable to determine the influence of AMS-associated factors in the human body. This study aims to measure, in real time, environmental conditions and physiological variables of participants in high-altitude regions to develop an AMS risk evaluation model to forecast prospective development of AMS so its onset can be prevented.

Results

Thirty-two participants were recruited, namely 25 men and 7 women, and they hiked from Cuifeng Mountain Forest Park parking lot (altitude: 2300 m) to Wuling (altitude: 3275 m). Regression and classification machine learning analyses were performed on physiological and environmental data, and Lake Louise Acute Mountain Sickness Scores (LLS) to establish an algorithm for AMS risk analysis. The individual R² coefficients of determination between the LLS and the measured altitude, ambient temperature, atmospheric pressure, relative humidity, climbing speed, heart rate, blood oxygen saturation (SpO₂), heart rate variability (HRV), were 0.1, 0.23, 0, 0.24, 0, 0.24, 0.27, and 0.35 respectively; incorporating all aforementioned variables, the R² coefficient is 0.62. The bagged trees classifier achieved favorable classification results, yielding a model sensitivity, specificity, accuracy, and area under receiver operating characteristic curve of 0.999, 0.994, 0.998, and 1, respectively.

Conclusion

The experiment results indicate the use of machine learning multivariate analysis have higher AMS prediction accuracies than analyses utilizing single varieties. The developed AMS evaluation model can serve as a reference for the future development of wearable devices capable of providing timely warnings of AMS risks to hikers.

High altitude is associated with pTau deposition, neuroinflammation, and myelin loss

Mammals are able to adapt to high altitude (HA) if appropriate acclimation occurs. However, specific occupations (professional climbers, pilots, astronauts and other) can be exposed to HA without acclimation and be at a higher risk of brain consequences. In particular, US Air Force U2-pilots have been shown to develop white matter hyperintensities (WMH) on MRI. Whether WMH are due to hypoxia or hypobaria effects is not understood. We compared swine brains exposed to 5000 feet (1524 m) above sea level (SL) with 21% fraction inspired O₂ (FiO₂) (Control group [C]; n = 5) vs. 30,000 feet (9144 m) above SL with 100% FiO₂ group (hypobaric group [HYPOBAR]; n = 6). We performed neuropathologic assessments, molecular analyses, immunohistochemistry (IHC), Western Blotting (WB), and stereology analyses to detect differences between HYPOBAR vs. Controls. Increased neuronal insoluble hyperphosphorylated-Tau (pTau) accumulation was observed across different brain regions, at histological level, in the HYPOBAR vs. Controls. Stereology-based cell counting demonstrated a significant difference (p < 0.01) in pTau positive neurons between HYPOBAR and C in the Hippocampus. Higher levels of soluble pTau in the Hippocampus of HYPOBAR vs. Controls were also detected by WB analyses. Additionally, WB demonstrated an increase of IBA-1 in the Cerebellum and a decrease of myelin basic protein (MBP) in the Hippocampus and Cerebellum of HYPOBAR vs. Controls. These findings illustrate, for the first time, changes occurring in large mammalian brains after exposure to nonhypoxic-hypobaria and open new pathophysiological views on the interaction among hypobaria, pTau accumulation, neuroinflammation, and myelination in large mammals exposed to HA.

Contribution of Hypoxic Exercise Testing to Predict High-Altitude Pathology: A Systematic Review

Altitude travelers are exposed to high-altitude pathologies, which can be potentially serious. Individual susceptibility varies widely and this makes it difficult to predict who will develop these complications. The assessment of physiological adaptations to exercise performed in hypoxia has been proposed to help predict altitude sickness. The purpose of this review is to evaluate the contribution of hypoxic exercise testing, achieved in normobaric conditions, in the prediction of severe high-altitude pathology. We performed a systematic review using the databases PubMed, Science Direct and Embase in October 2021 to collect studies reporting physiological adaptations under hypoxic exercise testing and its interest in predicting high-altitude pathology. Eight studies were eligible, concerning 3558 patients with a mean age of 46.9 years old, and a simulated mean altitude reaching of 5092 m. 597 patients presented an acute mountain sickness during their altitude travels. Three different protocols of hypoxic exercise testing were used. Acute mountain sickness was defined using Hackett’s score or the Lake Louise score. Ventilatory and cardiac responses to hypoxia, desaturation in hypoxia, cerebral oxygenation, core temperature, variation in body mass index and some perceived sensations were the highlighted variables associated with acute mountain sickness. A decision algorithm based on hypoxic exercise tests was proposed by one team. Hypoxic exercise testing provides promising information to help predict altitude complications. Its interest should be confirmed by different teams.

Blood Flow and Respiratory Gas Exchange in the Human Placenta at Term: A Data Update

Reliable measurements using modern techniques and consensus in experimental design have enabled the assessment of novel data sets for normal maternal and foetal respiratory physiology at term. These data sets include (a) principal factors affecting placental gas transfer, e.g., maternal blood flow through the intervillous space (IVS) (500 mL/min) and foeto-placental blood flow (480 mL/min), and (b) O₂, CO₂ and pH levels in the materno-placental and foeto-placental circulation. According to these data, the foetus is adapted to hypoxaemic hypoxia. Despite flat oxygen partial pressure (pO₂) gradients between the blood of the IVS and the umbilical arteries of the foetus, adequate O₂ delivery to the foetus is maintained by the higher O₂ affinity of the foetal blood, high foetal haemoglobin (HbF) concentrations, the Bohr effect, the double-Bohr effect, and high foeto-placental (=umbilical) blood flow. Again, despite flat gradients, adequate CO₂ removal from the foetus is maintained by a high diffusion capacity, high foeto-placental blood flow, the Haldane effect, and the double-Haldane effect. Placental respiratory gas exchange is perfusion-limited, rather than diffusion-limited, i.e., O₂ uptake depends on O₂ delivery.