Prevention of high-altitude pulmonary edema by nifedipine

Acute mountain sickness prediction: a concerto of multidimensional phenotypic data and machine learning strategies in the framework of predictive, preventive, and personalized medicine

Background

Acute mountain sickness (AMS) is a self-limiting illness, involving a complex series of physiological responses to rapid ascent to high altitudes, where the body is exposed to lower oxygen levels (hypoxia) and changes in atmospheric pressure. AMS is the mildest and most common form of altitude sickness; however, without adequate preparation and adherence to ascent guidelines, it can progress to life-threatening conditions.

Aims

Due to the multi-factorial predisposition of AMS among individuals, identifying AMS biomarkers before high altitude exposure from multiple dimensions (e.g., clinical, metabolic, and proteomic markers) and integrating them to build an AMS predictive model enables early diagnosis and personalized interventions, which allows targeted allocation of medical resources, such as prophylactic medications (e.g., acetazolamide) and supplemental oxygen, to those who need them most and prevention of unnecessary complications. Consequently, predicting AMS utilizing biomarkers from multidimensional phenotypic data before high-altitude exposure is essential for the paradigm change in high-altitude medical research from currently applied reactive services to the cost-effective predictive, preventive, and personalized medicine (PPPM/3PM) in primary (reversible damage to health and targeted protection against health-to-disease transition) and secondary (personalized protection against disease progression) care.

Methods

To this end, this study recruited 83 Han Chinese male volunteers and obtained clinical, proteomic, and metabolomic profiles for analysis before they ascended to high altitudes. The Mann-Whitney U test was used to identify clinical features distinguishing AMS from non-AMS. The proteomic and metabolomic features were concatenated and clustered to find co-expression modules associated with AMS. A machine learning model, Mutual Information-radial kernel-based Support Vector Machine-Recursive Feature Elimination (MI-radialSVM-RFE) was employed for biomarkers selection and AMS prediction. A molecular docking technique was used to select molecular biomarkers that can bind with Traditional Chinese Medicine (TCM) ingredients.

Results

Among 83 participants, 66 were selected for detailed analysis after quality control steps. Six protein-metabolite co-expression modules were identified as significantly associated with AMS. The MI-radialSVM-RFE model selected 12 biomarkers (two clinical features: systolic blood pressure (SBP) and peak expiratory flow (PEF); six proteins: Acyl-CoA synthetase long-chain family member 4 (ACSL4), immunoglobulin kappa variable 1D-16 (IGKV1D-16), coagulation factor XIII B subunit (F13B), prosaposin (PSAP), poliovirus receptor (PVR), and multimerin-2 (MMRN2); and four metabolites: 2-Methyl-1,3-cyclohexadiene, calcitriol, 4-Acetamido-2-amino-6-nitrotoluene, and 20-Hydroxy-PGE2) for the AMS prediction model. The model exhibited excellent predictive performance in both training (n = 66) and validating cohorts (n = 24) with AUCs of 0.97 and 0.94, respectively. Additionally, molecular docking analysis suggested PSAP and ACSL4 proteins as potential molecular targets for AMS prevention.

Conclusion and expert recommendations

This study advances high-altitude medicine by developing a predictive model for AMS using clinical, proteomic, and metabolomic data. The identified biomarkers linked to energy metabolism, immune response, and vascular regulation offer insights into AMS mechanisms. High-altitude predictive approaches should focus on implementing biomarker-driven risk screening using clinical, proteomic, and metabolomic data to identify high-risk individuals before high-altitude exposure. Preventive measures should prioritize pre-acclimatization protocols, tailored nutritional strategies and interventions guided by biomarker profiles, and lifestyle adjustments, such as maintaining mitochondrial health through proper nutritional strategies.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13167-025-00404-9.

Comparative effects of pharmacological interventions for the prevention of acute mountain sickness: A systematic review and Bayesian network meta-analysis

BACKGROUND

Acute Mountain Sickness (AMS), the most prevalent high-altitude illness, necessitates effective preventive measures due to rising sudden high-altitude exposure from tourism and occupational activities. Current Pharmacological prophylaxis lack robust comparisons, dose optimization, and confounder-adjusted analysis.

METHODS

This network meta-analysis (NMA) included 28 randomized controlled trials (RCTs), evaluated healthy individuals with a rapid ascent to >2500 m, compared 13 drugs for AMS incidence, severe AMS (SAMS) incidence, Lake Louise Score (LLS), peripheral oxygen saturation (SpO2), and pulmonary artery pressure (PAP). Quality was evaluated using Cochrane Risk of Bias tools and CINeMA (Confidence in Network Meta-Analysis) for evidence grading. Network meta-regression adjusted for ascent altitude and exposure duration to identify "time" windows or "height" windows.

RESULTS

250 mg BID acetazolamide (OR = 0.31, 95 %CI: 0.20-0.47) demonstrated a 5-day preventive efficacy window, while 375 mg BID acetazolamide (OR = 0.31, 95 %CI: 0.18-0.54) showed a shorter 3-day window. 4 mg BID dexamethasone (OR = 0.29, 95 %CI: 0.16-0.54) and 600 mg TID ibuprofen (OR = 0.44, 95 %CI: 0.3-0.64) also significantly reduced AMS incidence. No pharmacological interventions reduced SAMS incidence. After altitude adjustment, sildenafil (40 mg TID; MD = -1.11, 95 %CI: 2.01-0.25) attenuated altitude-induced PAP elevation.

CONCLUSION

Moderate-dose acetazolamide (125-250 mg BID) effectively prevents AMS with a longer prophylactic window compared to high-dose regimens (375 mg BID). There is no pharmacological intervention to prevent SAMS and no high-quality evidence to prevent high-altitude-induced PAP elevation. Our findings delineate the efficacy duration of acetazolamide across doses, while underscoring the imperative for robust clinical trials to advance the evidence base.

Protective effects of Tanshinone IIA preconditioning against hypobaric hypoxia-induced lung injury in a rat model

Tanshinone IIA (Tan-IIA), derived from Salvia miltiorrhiza, has been used in traditional Chinese medicine to treat cardiovascular diseases and pulmonary hypertension. This study investigates the potential of Tan-IIA preconditioning as a protective strategy against hypoxia-induced lung injury. Male Sprague-Dawley rats (200 ± 25 g) were divided into four groups: normoxia, normoxia with Tan-IIA, hypobaric hypoxia, and hypobaric hypoxia with Tan-IIA. Tan-IIA was administered intraperitoneally at doses of 10, 20, and 40 mg/kg body weight one hour before exposure to hypobaric hypoxia (simulated altitude of 25,000 feet for 48 h). Pulmonary edema was assessed by measuring transvacuolar leakage of sodium fluorescein dye and lung water content. Exposure to hypoxia triggered redox imbalances, inflammation, and changes in levels of nitric oxide (NOx), endothelin- 1, and Na/K ATPase, which contributed to pulmonary edema. Tan-IIA preconditioning, particularly at 20 mg/kg, was effective in reversing these disturbances. Tan-IIA modulated the expression of key signaling molecules, including c-Jun N-terminal kinase (JNK), extracellular signal-regulated kinase (ERK), and p38, as well as downstream activator protein- 1 (AP- 1) subunits (Jun and Fos), thus reducing inflammation. Its protective effects were partly due to increased NO levels and decreased endothelin, which lowered pulmonary vasoconstriction and permeability, respectively. Additionally, enhanced Na/K ATPase expression via hypoxia-inducible factor- 1 (HIF- 1) and AP- 1 pathways promoted alveolar fluid clearance, while interactions between nuclear factor erythroid 2-related factor 2 (Nrf2) and c-Jun highlighted the anti-oxidative properties of Tanshinone IIA. These findings demonstrate that Tanshinone IIA preconditioning protects against hypoxia-induced lung injury by mitigating pulmonary leakage. This highlights its potential therapeutic application in hypoxic lung conditions.

Global research trends and emerging hotspots in acute high altitude illness: a bibliometric analysis and review (1937-2024)

INTRODUCTION

Acute High Altitude Illness (AHAI) includes conditions such as Acute Mountain Sickness (AMS), High Altitude Cerebral Edema (HACE), and High Altitude Pulmonary Edema (HAPE), which result from rapid ascent to altitudes exceeding 2,500 m. Although interest in AHAI research has been growing, a systematic and comprehensive analysis of global research trends remains lacking.

CONTENT

A total of 3,214 articles and reviews published from 1937 to 2024 were retrieved from the Web of Science Core Collection. Bibliometric tools, including CiteSpace and VOSviewer, were applied to thoroughly assess publication trends, collaborative networks among authors, institutional contributions, and keyword co-occurrence patterns. The dataset represents the contributions of over 11,758 authors across 86 countries and 3,378 institutions, reflecting the significant growth of this research domain.

SUMMARY AND OUTLOOK

Our findings highlight the increasing scholarly attention to AHAI research, with the United States leading in publication numbers. Emerging research themes include cellular activation, oxidative stress, risk factors, and hypobaric hypoxia. This is the first systematic bibliometric review of AHAI literature, offering a detailed roadmap of research hotspots, potential collaborations, and key future directions. These findings provide a valuable reference for researchers aiming to explore gaps and build on the existing knowledge in high-altitude medicine.

Proof of concept study - alternative pharmacoprophylaxis for high-altitude pulmonary edema: A hospital-based randomized controlled trial

Background

High-altitude pulmonary edema (HAPE) is noncardiogenic pulmonary edema caused by exaggerated hypoxic pulmonary vasoconstriction and abnormally high pulmonary artery pressure. Some patients who develop HAPE have more chances to develop HAPE again on reinduction to high altitude (HA). This was a pilot project to look for a suitable drug (acetazolamide, nifedipine, or tadalafil) that could be used prophylactically in HAPE patients on reinduction to HA. The study incorporated a randomized, double-blind, placebo-controlled trial.

Method

One hundred and twenty serving personnel/previously healthy lowlanders, inducted to HA, thirty in each group, with history of one episode of clinically and radiologically diagnosed mild-to-moderate HAPE, were randomly distributed in the nifedipine, acetazolamide, tadalafil, and placebo groups. On discharge, all the patients were sent on leave for 4 weeks, after descent, to their homes, and they had to report to transit camp before reascent, where they were given either of the three medications or the placebo, then they were inducted to HA.

Result

HAPE, on reascent, did not develop in patients, given any of the three medications but developed in four patients in the placebo group.

Conclusion

Hence, a fully conscious person with mild-to-moderate HAPE could be effectively managed at altitude if the appropriate expertise and facilities are available and may be reinducted with any of the three drugs, if exigency exists. Trial Registry No.: CTRI/2022/03/041543.

Eleutheroside B Pretreatment Attenuates Hypobaric Hypoxia-Induced High-Altitude Pulmonary Edema by Regulating Autophagic Flux via the AMPK/mTOR Pathway

High-altitude pulmonary edema (HAPE) is a life-threatening disease, and autophagy deficiency is implicated in the pathogenesis of HAPE. Eleutheroside B (EB), which is the main bioactive component of Acanthopanax senticosus, exhibits various pharmacological activities. Our previous research demonstrated that autophagic structures were widely found in the ultrastructure of lung tissue in HAPE rats. However, whether EB regulates autophagy deficiency in HAPE remains unknown. This study aimed to investigate the protective effects of EB on hypobaric hypoxia-induced HAPE and explore the underlying molecular mechanism of regulating autophagy. The rat model of high-altitude pulmonary edema was replicated using a hypobaric hypoxic chamber. Rats were pretreated with EB or in combination with chloroquine or compound C. The pulmonary edema was assessed by the lung wet/dry ratio, total protein concentration in bronchoalveolar lavage fluid, and histological analysis. Inflammation and oxidative stress were measured using commercial biochemical kits. Autophagy and autophagic flux were evaluated by western blotting, transmission electron microscopy, and adeno-associated virus-mRFP-GFP-labeled tandem fluorescence LC3. The AMPK/mTOR signaling pathway was detected by western blotting. EB alleviated hypobaric hypoxia-induced pulmonary edema, hypoxemia, acid-base imbalance in the blood, inflammation, and oxidative stress in a dose-dependent manner. EB restored impaired autophagic flux by activating the AMPK/mTOR signaling pathway. However, chloroquine or compound C abolished eleutheroside B-mediated autophagy flux restoration. EB has the potential to restore impaired autophagic flux in the lung of hypobaric hypoxia-induced HAPE rats, which could be attributed to the activation of AMPK/mTOR signaling pathway.

Prevention, Diagnosis, and Treatment of Acute Altitude Illness

This JAMA Clinical Guidelines Synopsis summarizes the Wilderness Medical Society’s 2024 recommendations on prevention, diagnosis, and treatment of acute altitude illness.

Acute Coronary Syndrome at Altitude: Diagnostic Dilemma on Aconcagua Using Point-of-Care Ultrasound

At the Plaza de Mulas medical tent, located at 4300 m (14,100 ft) along the Normal Route to the 6960 m (22,837 ft) summit of Aconcagua in Argentina, a Korean male in his 50s with no known medical conditions presented with lightheadedness and shortness of breath. He had taken sildenafil and acetazolamide that morning without improvement. Vital signs on arrival were notable for oxygen saturations in the high 60s with basilar crackles on lung auscultation, concerning for high altitude pulmonary edema. The patient was started on oxygen via nasal cannula and given dexamethasone. History was limited secondary to language barriers, but on review of systems the patient noted mild chest pressure. Bedside cardiac echocardiogram was performed, which revealed a septal wall motion abnormality. The patient was therefore given aspirin and clopidogrel and was flown to a lower trailhead, where he was met by local Emergency Medical Services. A 12-lead electrocardiogram revealed an anterior ST-elevation myocardial infarction, and the patient was taken emergently to the catheterization lab in Mendoza and underwent stent placement with a full recovery.

Evaluation of Crocetin as a Protective Agent in High Altitude Hypoxia-Induced Organ Damage

Crocetin is an aglycone of crocin naturally occurring in saffron and has been proved to have antioxidant, anti-inflammatory, and antibacterial activities. In this experiment, the protective effect of crocetin on vital organs in high-altitude hypoxia rats was studied. Crocetin was prepared from gardenia by the alkaline hydrolysis method, and its reducing ability and free radical scavenging ability were tested. The in vitro anti-hypoxia vitality was studied on PC12 cells. The anti-hypoxic survival time of mice was determined in several models. The acute hypoxic injury rat model was established by simulating the hypoxic environment of 8000 m-high altitude for 24 h, and the anti-hypoxia effect of crocetin was evaluated by intraperitoneal injection with the doses of 10, 20, and 40 mg/kg. The water contents of the brain and lung were determined, and the pathological sections in the brain, lung, heart, liver, and kidney were observed by HE staining. The levels of oxidative stress (SOD, CAT, H2O2, GSH, GSH-Px, MDA) and inflammatory factors (IL-1β, IL-6, TNF-α, VEGF) in rat brain, lung, heart, liver, and kidney tissues were detected by ELISA. The results indicated that crocetin exhibited strong reducing ability and free radical scavenging ability and could improve the activity of PC12 cells under hypoxia. After intraperitoneal injection with crocetin, the survival time of mice was prolonged, and the pathological damage, oxidative stress, and inflammation in rats' tissue were ameliorated. The protective activity of crocetin on vital organs in high-altitude hypoxia rats may be related to reducing oxidative stress and inhibiting inflammatory response.

Adapting nitric oxide: A review of its foundation, uses in austere medical conditions, and emerging applications

Nitric oxide was first identified as a novel and effective treatment for persistent pulmonary hypertension of the newborn (PPHN), and has since been found to be efficacious in treating acute respiratory distress syndrome (ARDS) and pulmonary hypertension. Physicians and researchers have also found it shows promise in resource-constrained settings, both within and outside of the hospital, such as in high altitude pulmonary edema (HAPE) and COVID-19. The treatment has been well tolerated in these settings, and is both efficacious and versatile when studied across a variety of clinical environments. Advancements in inhaled nitric oxide continue, and the gas is worthy of investigation as physicians contend with new respiratory and cardiovascular illnesses, as well as unforeseen logistical challenges.

Recommendations for Women in Mountain Sports and Hypoxia Training/Conditioning

The (patho-)physiological responses to hypoxia are highly heterogeneous between individuals. In this review, we focused on the roles of sex differences, which emerge as important factors in the regulation of the body's reaction to hypoxia. Several aspects should be considered for future research on hypoxia-related sex differences, particularly altitude training and clinical applications of hypoxia, as these will affect the selection of the optimal dose regarding safety and efficiency. There are several implications, but there are no practical recommendations if/how women should behave differently from men to optimise the benefits or minimise the risks of these hypoxia-related practices. Here, we evaluate the scarce scientific evidence of distinct (patho)physiological responses and adaptations to high altitude/hypoxia, biomechanical/anatomical differences in uphill/downhill locomotion, which is highly relevant for exercising in mountainous environments, and potentially differential effects of altitude training in women. Based on these factors, we derive sex-specific recommendations for mountain sports and intermittent hypoxia conditioning: (1) Although higher vulnerabilities of women to acute mountain sickness have not been unambiguously shown, sex-dependent physiological reactions to hypoxia may contribute to an increased acute mountain sickness vulnerability in some women. Adequate acclimatisation, slow ascent speed and/or preventive medication (e.g. acetazolamide) are solutions. (2) Targeted training of the respiratory musculature could be a valuable preparation for altitude training in women. (3) Sex hormones influence hypoxia responses and hormonal-cycle and/or menstrual-cycle phases therefore may be factors in acclimatisation to altitude and efficiency of altitude training. As many of the recommendations or observations of the present work remain partly speculative, we join previous calls for further quality research on female athletes in sports to be extended to the field of altitude and hypoxia.

Wilderness Medical Society Clinical Practice Guidelines for the Prevention, Diagnosis, and Treatment of Acute Altitude Illness: 2024 Update

To provide guidance to clinicians about best practices, the Wilderness Medical Society (WMS) convened an expert panel to develop evidence-based guidelines for prevention, diagnosis, and treatment of acute mountain sickness, high altitude cerebral edema, and high altitude pulmonary edema. Recommendations are graded based on the quality of supporting evidence and the balance between the benefits and risks/burdens according to criteria put forth by the American College of Chest Physicians. The guidelines also provide suggested approaches for managing each form of acute altitude illness that incorporate these recommendations as well as recommendations on how to approach high altitude travel following COVID-19 infection. This is an updated version of the original WMS Consensus Guidelines for the Prevention and Treatment of Acute Altitude Illness published in Wilderness & Environmental Medicine in 2010 and the subsequently updated WMS Practice Guidelines for the Prevention and Treatment of Acute Altitude Illness published in 2014 and 2019.

High altitude hypoxia and oxidative stress: The new hope brought by free radical scavengers

Various strategies can be employed to prevent and manage altitude illnesses, including habituation, oxygenation, nutritional support, and medication. Nevertheless, the utilization of drugs for the prevention and treatment of hypoxia is accompanied by certain adverse effects. Consequently, the quest for medications that exhibit minimal side effects while demonstrating high efficacy remains a prominent area of research. In this context, it is noteworthy that free radical scavengers exhibit remarkable anti-hypoxia activity. These scavengers effectively eliminate excessive free radicals and mitigate the production of reactive oxygen species (ROS), thereby safeguarding the body against oxidative damage induced by plateau hypoxia. In this review, we aim to elucidate the pathogenesis of plateau diseases that are triggered by hypoxia-induced oxidative stress at high altitudes. Additionally, we present a range of free radical scavengers as potential therapeutic and preventive approaches to mitigate the occurrence of common diseases associated with hypoxia at high altitudes.

High-Altitude Pulmonary Edema in Women: A Scoping Review-UIAA Medical Commission Recommendations

Pichler Hefti, Jacqueline, Dominique Jean, Alison Rosier, Mia Derstine, David Hillebrandt, Lenka Horakova, Linda E. Keyes, Kastė Mateikaitė-Pipirienė, Peter Paal, Marija Andjelkovic, Beth Beidlemann, and Susi Kriemler. High-altitude pulmonary edema in women: a scoping review-UIAA Medical Commission Recommendations. High Alt Med Biol. 24:268-273, 2023. Background: High-altitude pulmonary edema (HAPE) can occur >2,500-3,000 m asl and is a life-threatening medical condition. This scoping review aims to summarize the current data on sex differences in HAPE. Methods: The International Climbing and Mountaineering Federation (UIAA) Medical Commission convened an international author team to review women's health issues at high altitude. Pertinent literature from PubMed and Cochrane was identified by keyword search combinations (including HAPE), with additional publications found by hand search. The primary search focus was for original articles that included minimum one woman and at least a rudimentary subgroup analysis. Results: The literature search yielded 7,165 articles, 416 of which were relevant for HAPE, and 7 of which were ultimately included here. Six were case series, consistently reporting a lower HAPE prevalence in women. The one retrospective case-control study reported male HAPE prevalence at 10/100,000 and female at 0.74/100,000. No studies were identified that directly compared sex differences in the prevalence of HAPE. No published data was found for topics other than epidemiology. Conclusions: Few studies and associated methodological limitations allow few conclusions to be drawn. Incidence of HAPE may be lower in women than in men. We speculate that besides physiological aspects, behavioral differences may contribute to this potential sex difference.

New strategy for rational use of antihypertensive drugs in clinical practice in high-altitude hypoxic environments

High-altitude hypoxic environments have critical implications on cardiovascular system function as well as blood pressure regulation. Such environments place patients with hypertension at risk by activating the sympathetic nervous system, which leads to an increase in blood pressure. In addition, the high-altitude hypoxic environment alters the in vivo metabolism and antihypertensive effects of antihypertensive drugs, which changes the activity and expression of drug-metabolizing enzymes and drug transporters. The present study reviewed the pharmacodynamics and pharmacokinetics of antihypertensive drugs and its effects on patients with hypertension in a high-altitude hypoxic environment. It also proposes a new strategy for the rational use of antihypertensive drugs in clinical practice in high-altitude hypoxic environments. The increase in blood pressure on exposure to a high-altitude hypoxic environment was mainly dependent on increased sympathetic nervous system activity. Blood pressure also increased proportionally to altitude, whilst ambulatory blood pressure increased more than conventional blood pressure, especially at night. High-altitude hypoxia can reduce the activities and expression of drug-metabolizing enzymes, such as CYP1A1, CYP1A2, CYP3A1, and CYP2E1, while increasing those of CYP2D1, CYP2D6, and CYP3A6. Drug transporter changes were related to tissue type, hypoxic degree, and hypoxic exposure time. Furthermore, the effects of high-altitude hypoxia on drug-metabolism enzymes and transporters altered drug pharmacokinetics, causing changes in pharmacodynamic responses. These findings suggest that high-altitude hypoxic environments affect the blood pressure, pharmacokinetics, and pharmacodynamics of antihypertensive drugs. The optimal hypertension treatment plan and safe and effective medication strategy should be formulated considering high-altitude hypoxic environments.

Heat, Cold, and Environmental Emergencies in Athletes

With the increase in outdoor events, there is an inevitable rise in climate-related environmental emergencies. Heat exposure can place athletes at risk for life-threatening heatstroke which requires emergent diagnosis and rapid in-field management. Cold exposure can lead to hypothermia, frostbite, and other nonfreezing injuries that require prompt evaluation and management to minimize morbidity and mortality. Altitude exposure can lead to acute mountain sickness or other serious neurologic or pulmonary emergencies. Finally, harsh climate exposure can be life-threatening and require appropriate prevention and event planning.

A comprehensive review of natural products with anti-hypoxic activity

Natural products exhibit substantial impacts in the field of anti-hypoxic traetment. Hypoxia can cause altitude sickness and other negative effect on the body. Headache, coma, exhaustion, vomiting and, in severe cases, death are some of the clinical signs. Currently, hypoxia is no longer just a concern in plateau regions; it is also one of the issues that can not be ignored by urban residents. This review covered polysaccharides, alkaloids, saponins, flavonoids, peptides and traditional Chinese compound prescriptions as natural products to protect against hypoxia. The active ingredients, effectiveness and mechanisms were discussed. The related anti-hypoxic mechanisms involve increasing the hemoglobin (HB) content, glycogen content and adenosine triphosphate (ATP) content, removing excessive reactive oxygen species (ROS), reducing lipid peroxidation, regulating the levels of related enzymes in cells, protecting the structural and functional integrity of the mitochondria and regulating the expression of apoptosis-related genes. These comprehensive summaries are beneficial to anti-hypoxic research and provide useful information for the development of anti-hypoxic products.

Partial Pressure of Arterial Oxygen in Healthy Adults at High Altitudes: A Systematic Review and Meta-Analysis

Importance

With increasing altitude, the partial pressure of inspired oxygen decreases and, consequently, the Pao2 decreases. Even though this phenomenon is well known, the extent of the reduction as a function of altitude remains unknown.

Objective

To calculate an effect size estimate for the decrease in Pao2 with each kilometer of vertical gain among healthy unacclimatized adults and to identify factors associated with Pao2 at high altitude (HA).

Data Sources

A systematic search of PubMed and Embase was performed from database inception to April 11, 2023. Search terms included arterial blood gases and altitude.

Study Selection

A total of 53 peer-reviewed prospective studies in healthy adults providing results of arterial blood gas analysis at low altitude (<1500 m) and within the first 3 days at the target altitude (≥1500 m) were analyzed.

Data Extraction and Synthesis

Primary and secondary outcomes as well as study characteristics were extracted from the included studies, and individual participant data (IPD) were requested. Estimates were pooled using a random-effects DerSimonian-Laird model for the meta-analysis.

Main Outcomes and Measures

Mean effect size estimates and 95% CIs for reduction in Pao2 at HA and factors associated with Pao2 at HA in healthy adults.

Results

All of the 53 studies involving 777 adults (mean [SD] age, 36.2 [10.5] years; 510 men [65.6%]) reporting 115 group ascents to altitudes between 1524 m and 8730 m were included in the aggregated data analysis; 13 of those studies involving 305 individuals (mean [SD] age, 39.8 [13.6] years; 185 men [60.7%]) reporting 29 ascents were included in the IPD analysis. The estimated effect size of Pao2 was -1.60 kPa (95% CI, -1.73 to -1.47 kPa) for each 1000 m of altitude gain (τ2 = 0.14; I2 = 86%). The Pao2 estimation model based on IPD data revealed that target altitude (-1.53 kPa per 1000 m; 95% CI, -1.63 to -1.42 kPa per 1000 m), age (-0.01 kPa per year; 95% CI, -0.02 to -0.003 kPa per year), and time spent at an altitude of 1500 m or higher (0.16 kPa per day; 95% CI, 0.11-0.21 kPa per day) were significantly associated with Pao2.

Conclusions and Relevance

In this systematic review and meta-analysis, the mean decrease in Pao2 was 1.60 kPa per 1000 m of vertical ascent. This effect size estimate may improve the understanding of physiological mechanisms, assist in the clinical interpretation of acute altitude illness in healthy individuals, and serve as a reference for physicians counseling patients with cardiorespiratory disease who are traveling to HA regions.

Three rare presentations of high-altitude pulmonary edema at a high-altitude clinic in the Everest region (4371 m): A case series

Diagnosis of HAPE can be challenging when the presentation deviates from usual natural history. Point of care ultrasonography serves as a great diagnostic tool in such settings. An umbrella treatment could be beneficial during such scenarios.

Molecular Mechanisms of High-Altitude Acclimatization

High-altitude illnesses (HAIs) result from acute exposure to high altitude/hypoxia. Numerous molecular mechanisms affect appropriate acclimatization to hypobaric and/or normobaric hypoxia and curtail the development of HAIs. The understanding of these mechanisms is essential to optimize hypoxic acclimatization for efficient prophylaxis and treatment of HAIs. This review aims to link outcomes of molecular mechanisms to either adverse effects of acute high-altitude/hypoxia exposure or the developing tolerance with acclimatization. After summarizing systemic physiological responses to acute high-altitude exposure, the associated acclimatization, and the epidemiology and pathophysiology of various HAIs, the article focuses on molecular adjustments and maladjustments during acute exposure and acclimatization to high altitude/hypoxia. Pivotal modifying mechanisms include molecular responses orchestrated by transcription factors, most notably hypoxia inducible factors, and reciprocal effects on mitochondrial functions and REDOX homeostasis. In addition, discussed are genetic factors and the resultant proteomic profiles determining these hypoxia-modifying mechanisms culminating in successful high-altitude acclimatization. Lastly, the article discusses practical considerations related to the molecular aspects of acclimatization and altitude training strategies.

Severe Respiratory Failure Developing in the Course of High-Altitude Pulmonary Edema in an Alpinist with COVID-19 Pneumonia: A Case Report

Pigoń, Katarzyna, Ryszard Grzanka, Ewa Nowalany-Kozielska, and Andrzej Tomasik. Severe respiratory failure developing in the course of high-altitude pulmonary edema in an alpinist with COVID-19 pneumonia: a case report. High Alt Med Biol. 23:372-376, 2022.-The case of a 38-year-old Polish alpinist, evacuated from base camp (4,200 m) under Lenin's Peak due to severe high-altitude pulmonary edema (HAPE) and symptoms of acute mountain sickness/high-altitude cerebral edema (HACE), is presented. Starting the expedition, the man was asymptomatic and had a negative COVID-19 molecular test. After a few days of trekking, he developed typical HAPE and HACE. After evacuation to the hospital in Bishkek, a diagnosis of acute bronchopneumonia was made by computed tomography (CT) imaging. A COVID-19 test was not performed at that time. After returning to Poland, a complete noninvasive cardiac and pulmonary assessment disclosed no pathology. The initial chest CT reassessment was read as demonstrating the densities typical for COVID-19 pneumonia, and a SARS-CoV-2 antibody test corroborated the diagnosis. Pre-existing lung disease increases the risk of developing HAPE. In the era of the COVID-19 pandemic, people traveling at a high altitude and unaware of the infection are at particular risk.

Mean corpuscular haemoglobin concentration (MCHC): a new biomarker for high-altitude pulmonary edema in the Ecuadorian Andes

Ascent to high altitude (> 3000 m height above sea level or m.a.s.l) exposes people to hypobaric atmospheric pressure and hypoxemia, which provokes mountain sickness and whose symptoms vary from the mild acute mountain sickness to the life-threatening, high-altitude pulmonary edema (HAPE). This study analysed the risk factors underlying HAPE in dwellers and travellers of the Ecuadorian Andes after sojourning over 3000 m height. A group of HAPE patients (N = 58) was compared to a NO HAPE group (N = 713), through demographic (ethnicity, sex, and age), red blood cell parameters (erythrocytes counts, hematocrit, median corpuscular volume, median corpuscular haemoglobin, and median corpuscular haemoglobin concentration (MCHC)), altitude (threshold: 3000 m.a.s.l.), and health status (vital signs) variables. Analysis of Deviance for Generalised Linear Model Fits (logit regression) revealed patterns of significant associations. High-altitude dwellers, particularly children and elder people, were HAPE-prone, while women were more tolerant of HAPE than men. Interestingly, HAPE prevalence was strongly related to an increment of MCH. The residence at middle altitude was inversely related to the odds of suffering HAPE. Ethnicity did not have a significant influence in HAPE susceptibility. Elevated MCHC emerges like a blood adaptation of Andean highlanders to high altitude and biomarker of HAPE risk.

An update on environment-induced pulmonary edema – “When the lungs leak under water and in thin air”

Acute pulmonary edema is a serious condition that may occur as a result of increased hydrostatic forces within the lung microvasculature or increased microvascular permeability. Heart failure or other cardiac or renal disease are common causes of cardiogenic pulmonary edema. However, pulmonary edema may even occur in young and healthy individuals when exposed to extreme environments, such as immersion in water or at high altitude. Immersion pulmonary edema (IPE) and high-altitude pulmonary edema (HAPE) share some morphological and clinical characteristics; however, their underlying mechanisms may be different. An emerging understanding of IPE indicates that an increase in pulmonary artery and capillary pressures caused by substantial redistribution of venous blood from the extremities to the chest, in combination with stimuli aggravating the effects of water immersion, such as exercise and cold temperature, play an important role, distinct from hypoxia-induced vasoconstriction in high altitude pulmonary edema. This review aims at a current perspective on both IPE and HAPE, providing a comparative view of clinical presentation and pathophysiology. A particular emphasis will be on recent advances in understanding of the pathophysiology and occurrence of IPE with a future perspective on remaining research needs.

Pathophysiology and Therapy of High-Altitude Sickness: Practical Approach in Emergency and Critical Care

High altitude can be a hostile environment and a paradigm of how environmental factors can determine illness when human biological adaptability is exceeded. This paper aims to provide a comprehensive review of high-altitude sickness, including its epidemiology, pathophysiology, and treatments. The first section of our work defines high altitude and considers the mechanisms of adaptation to it and the associated risk factors for low adaptability. The second section discusses the main high-altitude diseases, highlighting how environmental factors can lead to the loss of homeostasis, compromising important vital functions. Early recognition of clinical symptoms is important for the establishment of the correct therapy. The third section focuses on high-altitude pulmonary edema, which is one of the main high-altitude diseases. With a deeper understanding of the pathogenesis of high-altitude diseases, as well as a reasoned approach to environmental or physical factors, we examine the main high-altitude diseases. Such an approach is critical for the effective treatment of patients in a hostile environment, or treatment in the emergency room after exposure to extreme physical or environmental factors.

High-Altitude Pulmonary Edema in Colorado Children: A Cross-Sectional Survey and Retrospective Review

Kelly, Timothy D., Maxene Meier, Jason P. Weinman, Dunbar Ivy, John T. Brinton, and Deborah R. Liptzin. High-altitude pulmonary edema in Colorado children: a cross-sectional survey and retrospective review. High Alt Med Biol. 23:119-124, 2022. Introduction: Few studies of high-altitude pulmonary edema (HAPE) are specific to the pediatric population. The purpose of this investigation was to further characterize the radiographic patterns of pediatric HAPE, and to better understand ongoing risk following an initial pediatric HAPE episode. Methods: This study uses both a retrospective chart review and cross-sectional survey. Pediatric patients with HAPE at a single quaternary referral center in the Rocky Mountain Region were identified between the years 2013 and 2020. Patients were eligible if they presented with a clinical diagnosis of HAPE and had a viewable chest radiograph (CXR). Surveys were sent to eligible patients/families to gather additional information relating to family history, puberty, and HAPE recurrence. Results: Forty-two individuals met criteria for clinical diagnosis of HAPE with a viewable CXR. A majority of CXRs (24/42, 57.1%) demonstrated predominant right-sided involvement. Similarly, 24 CXRs (24/42, 57.1%) demonstrated predominant upper lobe involvement. Twenty-one (21/42, 50%) surveys were completed. A minority of individuals went on to experience at least one other HAPE episode (8/19, 42.1%). Conclusion: The most common radiographic pattern seen in pediatric HAPE is pulmonary edema that favors the right lung and upper lobes. After an initial HAPE presentation, some children will experience additional HAPE episodes.

Hypoxia and hemorheological properties in older individuals

Hypoxia is caused by insufficient oxygen availability for the organism leading to reduced oxygen delivery to tissues and cells. It has been regarded as a severe threat to human health and it is indeed implicated in pathophysiological mechanisms involved in the development and progression of many diseases. Nevertheless, the potential of controlled hypoxia interventions (i.e. hypoxia conditioning) for improving cardio-vascular health is gaining increased attention. However, blood rheology is often a forgotten factor for vascular health while aging and hypoxia exposure are both suspected to alter hemorheological properties. These changes in blood rheology may influence the benefits-risks balance of hypoxia exposure in older individuals. The benefits of hypoxia exposure for vascular health are mainly reported for healthy populations and the combined impact of aging and hypoxia on blood rheology could therefore be deleterious in older individuals. This review discusses evidence of hypoxia-related and aging-related changes in blood viscosity and its determinants. It draws upon an extensive literature search on the effects of hypoxia/altitude and aging on blood rheology. Aging increases blood viscosity mainly through a rise in plasma viscosity, red blood cell (RBC) aggregation and a decrease in RBC deformability. Hypoxia also causes an increase in RBC aggregation and plasma viscosity. In addition, hypoxia exposure may increase hematocrit and modulate RBC deformability, depending on the hypoxic dose, i.e, beneficial effect of intermittent hypoxia with moderate dose vs deleterious effect of chronic continuous or intermittent hypoxia or if the hypoxic dose is too high. Special attention is directed toward the risks vs. benefits of hemorheological changes during hypoxia exposure in older individuals, and its clinical relevance for vascular disorders.

Effects of acetazolamide on pulmonary artery pressure and prevention of high altitude pulmonary edema after rapid active ascent to 4,559 m

Acetazolamide prevents acute mountain sickness (AMS) by inhibition of carbonic anhydrase. Since it reduces acute hypoxic pulmonary vasoconstriction (HPV), it may also prevent high-altitude pulmonary edema (HAPE) by lowering pulmonary artery pressure. We tested this hypothesis in a randomized, placebo-controlled, double-blind study. Thirteen healthy, non-acclimatized lowlanders with a history of HAPE ascended (<22h) from 1,130 to 4,559m with one overnight stay at 3,611m. Medications started 48h before ascent (acetazolamide: n=7, 250mg 3x/d; placebo: n=6, 3x/d). HAPE was diagnosed by chest radiography, and pulmonary artery pressure by measurement of right ventricular to atrial pressure gradient (RVPG) by transthoracic echocardiography. AMS was evaluated with the Lake Louise Score (LLS) and AMS-C Score. Incidence of HAPE was 43% vs. 67% (acetazolamide vs. placebo, p=0.39). Ascent to altitude increased RVPG from 20±5 to 43±10mmHg (p<0.001) without a group difference (p=0.68). Arterial PO₂ fell to 36±9mmHg (p<0.001) and was 8.5mmHg higher with acetazolamide at high altitude (p=0.025). At high altitude, the LLS and AMS-C score remained lower in those taking acetazolamide (both p<0.05). Although acetazolamide reduced HAPE incidence by 35%, this effect was not statistically significant, and considerably less than reductions of about 70-100% with prophylactic dexamethasone, tadalafil, and nifedipine performed with the same ascent profile at the same location. We could not demonstrate a reduction in RVPG compared to placebo treatment despite reductions in AMS severity and better arterial oxygenation. Limited by a small sample size, our data do not support recommending acetazolamide for prevention of HAPE in mountaineers ascending rapidly to over 4,500m.

Association of variants m.T16172C and m.T16519C in whole mtDNA sequences with high altitude pulmonary edema in Han Chinese lowlanders

Background

High altitude pulmonary edema (HAPE) is a hypoxia-induced non-cardiogenic pulmonary edema that typically occurred in un-acclimatized lowlanders, which inevitably leads to life-threatening consequences. Apart from multiple factors involved, the genetic factors also play an important role in the pathogenesis of HAPE. So far, researchers have put more energy into the nuclear genome and HAPE, and ignored the relationship between the mitochondrion DNA (mtDNA) variants and HAPE susceptibility.

Methods

We recruited a total of 366 individuals including 181 HAPE patients and 185 non-HAPE populations through two times. The first time, 49 HAPE patients and 58 non-HAPE individuals were performed through whole mtDNA sequences to search the mutations and haplogroups. The second time, 132 HAPE patients and 127 non-HAPE subjects were collected to apply verifying these mutations and haplogroups of mtDNA with the routine PCR method.

Results

We analyzed and summarized the clinical characteristics and sequence data for the 49 HAPE patients and 58 non-HAPE individuals. We found that a series of routine blood indexes including systolic arterial blood pressure (SBP), heart rate (HR), white blood cell (WBC), and C-reactive protein (CRP) in the HAPE group presented higher and displayed significant differences compared with those in the non-HAPE group. Although the average numbers of variants in different region and group samples were not statistically significant (P > 0.05), the mutation densities of different regions in the internal group showed significant differences. Then we found two mutations (T16172C and T16519C) associated with the HAPE susceptibility, the T16172C mutation increased the risk of HAPE, and the T16519C mutation decreased the HAPE rating. Furthermore, the two mutations were demonstrated with 132 HAPE patients and 127 non-HAPE individuals. Unfortunately, all the haplogroups were not associated with the HAPE haplogroups.

Conclusions

We provided evidence of differences in mtDNA polymorphism frequencies between HAPE and non-HAPE Han Chinese. Genotypes of mtDNA 16172C and 16519C were correlated with HAPE susceptibility, indicating the role of the mitochondrial genome in the pathogenesis of HAPE.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12890-021-01791-1.

Beneficial Extracardiac Effects of Cardiovascular Medications

Cardiovascular diseases are the most common cause of death worldwide, with cardiovascular medications being amongst the most common medications prescribed. These medications have diverse effects on the heart, vascular system, as well as other tissues and organ systems. The extra cardiovascular effects have been found to be of use in the treatment of non-cardiovascular diseases and pathologies. Minoxidil is used to manage systemic hypertension with its well-known side effect of hirsutism used to treat alopecia and baldness. Sildenafil was originally investigated as a treatment option for systemic hypertension; however, its side effect of penile erection led to it being widely used for erectile dysfunction. Alpha-1 blockers such as terazosin are indicated to treat systemic hypertension but are more commonly used for benign prostatic hyperplasia and post-traumatic stress disorder. Beta blockers are the mainstay treatment for congestive heart failure and systemic hypertension but have been found useful to help in patients with intention tremors as well as prophylaxis of migraines. Similarly, calcium channel blockers are indicated in medical expulsion therapy for ureteric calculi in addition to their cardiovascular indications. Thiazides are commonly used for treating systemic hypertension and as diuretics. Thiazides can cause hypocalciuria and hypercalcemia. This side effect has led to thiazides being used to treat idiopathic hypercalciuria and associated nephrolithiasis. Spironolactone is commonly utilized in treating heart failure and as a diuretic for edema. It's well described anti-androgen side effects have been used for acne vulgaris and hirsutism in polycystic ovarian syndrome. This review article discusses how the various extracardiovascular effects of commonly used cardiovascular medications are put to use in managing non-cardiovascular conditions.

Mitochondrial DNA mutations contribute to high altitude pulmonary edema via increased oxidative stress and metabolic reprogramming during hypobaric hypoxia

High altitude pulmonary edema (HAPE) is experienced by non-acclimatized sea level individuals on exposure to high altitude hypoxic conditions. Available evidence suggests that genetic factors and perturbed mitochondrial redox status may play an important role in HAPE pathophysiology. However, the precise mechanism has not been fully understood. In the present study, sequencing of mitochondrial DNA (mtDNA) from HAPE subjects and acclimatized controls was performed to identify pathogenic mutations and to determine their role in HAPE. Hypobaric hypoxia induced oxidative stress and metabolic alterations were also assessed in HAPE subjects. mtDNA copy number, mitochondrial oxidative phosphorylation (mtOXPHOS) activity, mitochondrial biogenesis were measured to determine mitochondrial functions. The data revealed that the mutations in Complex I genes affects the secondary structure of protein in HAPE subjects. Further, increased oxidative stress during hypobaric hypoxia, reduced mitochondrial biogenesis and mtOXPHOS activity induced metabolic reprogramming appears to contribute to mitochondrial dysfunctions in HAPE individuals. Haplogroup analysis suggests that mtDNA haplogroup H2a2a1 has potential contribution in the pathobiology of HAPE in lowlanders. This study also suggests contribution of altered mitochondrial functions in HAPE susceptibility.

High-altitude illnesses: Old stories and new insights into the pathophysiology, treatment and prevention

Areas at high-altitude, annually attract millions of tourists, skiers, trekkers, and climbers. If not adequately prepared and not considering certain ascent rules, a considerable proportion of those people will suffer from acute mountain sickness (AMS) or even from life-threatening high-altitude cerebral (HACE) or/and pulmonary edema (HAPE). Reduced inspired oxygen partial pressure with gain in altitude and consequently reduced oxygen availability is primarily responsible for getting sick in this setting. Appropriate acclimatization by slowly raising the hypoxic stimulus (e.g., slow ascent to high altitude) and/or repeated exposures to altitude or artificial, normobaric hypoxia will largely prevent those illnesses. Understanding physiological mechanisms of acclimatization and pathophysiological mechanisms of high-altitude diseases, knowledge of symptoms and signs, treatment and prevention strategies will largely contribute to the risk reduction and increased safety, success and enjoyment at high altitude. Thus, this review is intended to provide a sound basis for both physicians counseling high-altitude visitors and high-altitude visitors themselves.

Pulmonary Hypertension in Acute and Chronic High Altitude Maladaptation Disorders

Alveolar hypoxia is the most prominent feature of high altitude environment with well-known consequences for the cardio-pulmonary system, including development of pulmonary hypertension. Pulmonary hypertension due to an exaggerated hypoxic pulmonary vasoconstriction contributes to high altitude pulmonary edema (HAPE), a life-threatening disorder, occurring at high altitudes in non-acclimatized healthy individuals. Despite a strong physiologic rationale for using vasodilators for prevention and treatment of HAPE, no systematic studies of their efficacy have been conducted to date. Calcium-channel blockers are currently recommended for drug prophylaxis in high-risk individuals with a clear history of recurrent HAPE based on the extensive clinical experience with nifedipine in HAPE prevention in susceptible individuals. Chronic exposure to hypoxia induces pulmonary vascular remodeling and development of pulmonary hypertension, which places an increased pressure load on the right ventricle leading to right heart failure. Further, pulmonary hypertension along with excessive erythrocytosis may complicate chronic mountain sickness, another high altitude maladaptation disorder. Importantly, other causes than hypoxia may potentially underlie and/or contribute to pulmonary hypertension at high altitude, such as chronic heart and lung diseases, thrombotic or embolic diseases. Extensive clinical experience with drugs in patients with pulmonary arterial hypertension suggests their potential for treatment of high altitude pulmonary hypertension. Small studies have demonstrated their efficacy in reducing pulmonary artery pressure in high altitude residents. However, no drugs have been approved to date for the therapy of chronic high altitude pulmonary hypertension. This work provides a literature review on the role of pulmonary hypertension in the pathogenesis of acute and chronic high altitude maladaptation disorders and summarizes current knowledge regarding potential treatment options.

Effect of losartan on performance and physiological responses to exercise at high altitude (5035 m)

Objective

Altitude-related and exercise-related elevations in blood pressure (BP) increase the likelihood of developing pulmonary hypertension and high-altitude illness during high-altitude sojourn. This study examined the antihypertensive effect and potential exercise benefit of the angiotensin II receptor antagonist losartan when taken at altitude.

Methods

Twenty participants, paired for age and ACE genotype status, completed a double-blinded, randomised study, where participants took either losartan (100 mg/day) or placebo for 21 days prior to arrival at 5035 m (Whymper Hut, Mt Chimborazo, Ecuador). Participants completed a maximal exercise test on a supine cycle ergometer at sea level (4 weeks prior) and within 48 hours of arrival to 5035 m (10-day ascent). Power output, beat-to-beat BP, oxygen saturation (SpO₂) and heart rate (HR) were recorded during exercise, with resting BP collected from daily medicals during ascent. Before and immediately following exercise at 5035 m, extravascular lung water prevalence was assessed with ultrasound (quantified via B-line count).

Results

At altitude, peak power was reduced relative to sea level (p<0.01) in both groups (losartan vs placebo: down 100±29 vs 91±28 W, p=0.55), while SpO₂ (70±6 vs 70±5%, p=0.96) and HR (146±21 vs 149±24 bpm, p=0.78) were similar between groups at peak power, as was the increase in systolic BP from rest to peak power (up 80±37 vs 69±33 mm Hg, p=0.56). Exercise increased B-line count (p<0.05), but not differently between groups (up 5±5 vs 8±10, p=0.44).

Conclusion

Losartan had no observable effect on resting or exercising BP, exercise-induced symptomology of pulmonary hypertension or performance at 5035 m.

Might a high hemoglobin mass be involved in non-cardiogenic pulmonary edema? The case of the chronic maladaptation to high-altitude in the Andes

Exposure to hypoxic environments when ascending at high altitudes may cause life-threatening pulmonary edema (HAPE) due to a rapid accumulation of extracellular fluid flooding in the pulmonary alveoli. In Andeans, high-altitude adaptation occurs at the expense of being more prone to chronic mountain sickness: relative hypoventilation, excess pulmonary hypertension, and secondary polycythemia. Because HAPE prevalence is high in the Andes, we posit the hypothesis that a high hemoglobine mass may increase HAPE risk. In support of it, high intrapulmonary hypertension along with hyperviscosity produced by polycytemia may enhance sear forces and intravascular hemolysis, thus leading to increased acellular hemoglobin and the subsequent damage of the alveolar and endothelial barrier. It is proposed to investigate the relationship between the vaso-endothelial homeostasis and erythropoiesis in the maladaptation to high altitude and HAPE. This research is especially important when reentry HAPE, since rheologic properties of blood changes with rapid ascent to high altitudes.

The role of hypoxia-induced modulation of alveolar epithelial Na+- transport in hypoxemia at high altitude

Reabsorption of excess alveolar fluid is driven by vectorial Na⁺-transport across alveolar epithelium, which protects from alveolar flooding and facilitates gas exchange. Hypoxia inhibits Na⁺-reabsorption in cultured cells and in-vivo by decreasing activity of epithelial Na⁺-channels (ENaC), which impairs alveolar fluid clearance. Inhibition also occurs during in-vivo hypoxia in humans and laboratory animals. Signaling mechanisms that inhibit alveolar reabsorption are poorly understood. Because cellular adaptation to hypoxia is regulated by hypoxia-inducible transcription factors (HIF), we tested whether HIFs are involved in decreasing Na⁺-transport in hypoxic alveolar epithelium. Expression of HIFs was suppressed in cultured rat primary alveolar epithelial cells (AEC) with shRNAs. Hypoxia (1.5% O₂, 24 h) decreased amiloride-sensitive transepithelial Na⁺-transport, decreased the mRNA expression of α-, β-, and γ-ENaC subunits, and reduced the amount of αβγ-ENaC subunits in the apical plasma membrane. Silencing HIF-2α partially prevented impaired fluid reabsorption in hypoxic rats and prevented the hypoxia-induced decrease in α- but not the βγ-subunits of ENaC protein expression resulting in a less active form of ENaC in hypoxic AEC. Inhibition of alveolar reabsorption also caused pulmonary vasoconstriction in ventilated rats. These results indicate that a HIF-2α-dependent decrease in Na⁺-transport in hypoxic alveolar epithelium decreases alveolar reabsorption. Because susceptibles to high-altitude pulmonary edema (HAPE) have decreased Na⁺-transport even in normoxia, inhibition of alveolar reabsorption by hypoxia at high altitude might further impair alveolar gas exchange. Thus, aggravated hypoxemia might further enhance hypoxic pulmonary vasoconstriction and might subsequently cause HAPE.

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.

No Relevant Analogy Between COVID-19 and Acute Mountain Sickness

Berger, Marc Moritz, Peter H. Hackett, and Peter Bärtsch. No relevant analogy between COVID-19 and acute mountain sickness. High Alt Med Biol. 21:315-318, 2020.-Clinicians and scientists have suggested therapies for coronavirus disease-19 (COVID-19) that are known to be effective for other medical conditions. A recent publication suggests that pathophysiological mechanisms underlying acute mountain sickness (a syndrome of nonspecific neurological symptoms typically experienced by nonacclimatized individuals at altitudes >2500 m) may overlap with the mechanisms causing COVID-19. In this short review, we briefly evaluate this mistaken analogy and demonstrate that this concept is not supported by scientific evidence.

COVID-19 Lung Injury and High-Altitude Pulmonary Edema. A False Equation with Dangerous Implications

Amid efforts to care for the large number of patients with coronavirus disease (COVID-19), there has been considerable speculation about whether the lung injury seen in these patients is different than acute respiratory distress syndrome from other causes. One idea that has garnered considerable attention, particularly on social media and in free open-access medicine, is the notion that lung injury due to COVID-19 is more similar to high-altitude pulmonary edema (HAPE). Drawing on this concept, it has also been proposed that treatments typically employed in the management of HAPE and other forms of acute altitude illness—pulmonary vasodilators and acetazolamide—should be considered for COVID-19. Despite some similarities in clinical features between the two entities, such as hypoxemia, radiographic opacities, and altered lung compliance, the pathophysiological mechanisms of HAPE and lung injury due to COVID-19 are fundamentally different, and the entities cannot be viewed as equivalent. Although of high utility in the management of HAPE and acute mountain sickness, systemically delivered pulmonary vasodilators and acetazolamide should not be used in the treatment of COVID-19, as they carry the risk of multiple adverse consequences, including worsened ventilation–perfusion matching, impaired carbon dioxide transport, systemic hypotension, and increased work of breathing.

Oxygen availability in a HAPE-positive and a HAPE-negative woman before and during a visit to 3480 meters

BACKGROUND

Testing the hypoxic ventilatory response (HVR) at low-altitude helps to detect those who do not hyperventilate appropriately in hypoxia but might not necessarily predict the HVR and the risk to develop acute mountain sickness (AMS) at high altitude. However, a low HVR seems to be particularly prevalent in individuals susceptible to high-altitude pulmonary edema (HAPE+). In this short communication, we assessed differences in physiological parameters in two comparable women before and 3 hours after exposure to 3,480 meters. One woman had a (clinically diagnosed) history of high-altitude pulmonary edema (HAPE+) while the other did well at previous exposures to high altitude (HAPE-).

METHODS

Heart rate, blood pressure, ventilation, arterial blood gas variables, arterial haemoglobin saturation, haemoglobin concentration, arterial oxygen content and delta plasma volume were measured or calculated before and after arrival at high altitude.

RESULTS

At high altitude, plasma volume decreased in the HAPE- woman which in turn increased haemoglobin concentration. Ventilation was elevated in the HAPE- but not in the HAPE + woman. Arterial oxygen content fell in the HAPE + while it was preserved in the HAPE- woman. This resulted from lower peripheral oxygen saturation (-35%), lower haemoglobin concentration (-12%) and lower arterial partial pressure of oxygen (-59%) in the HAPE+.

CONCLUSION

Considerable haemoglobin desaturation and lack of haemoconcentration were characteristics of the HAPE + woman when exposed to high altitude, while the higher arterial oxygen content in the HAPE- woman was related to both haemoconcentration and hyperventilation (and associated haemoglobin saturation).

Impaired pulmonary gas exchange efficiency, but normal pulmonary artery pressure increases, with hypoxia in men and women with a patent foramen ovale

NEW FINDINGS

What is the central question of this study? Do individuals with a patent foramen ovale (PFO⁺ ) have a larger alveolar-to-arterial difference in P O 2 ( A - a D O 2 ) than those without (PFO^- ) and/or an exaggerated increase in pulmonary artery systolic pressure (PASP) in response to hypoxia? What is the main finding and its importance? PFO⁺ had a greater A - a D O 2 while breathing air, 16% and 14% O₂ , but not 12% or 10% O₂ . PASP increased equally in hypoxia between PFO⁺ and PFO^- . These data suggest that PFO⁺ may not have an exaggerated acute increase in PASP in response to hypoxia.

ABSTRACT

Patent foramen ovale (PFO) is present in 30-40% of the population and is a potential source of right-to-left shunt. Accordingly, those with a PFO (PFO⁺ ) may have a larger alveolar-to-arterial difference in P O 2 ( A - a D O 2 ) than those without (PFO^- ) in normoxia and with mild hypoxia. Likewise, PFO is associated with high-altitude pulmonary oedema, a condition known to have an exaggerated pulmonary pressure response to hypoxia. Thus, PFO⁺ may also have exaggerated pulmonary pressure increases in response to hypoxia. Therefore, the purposes of the present study were to systematically determine whether or not: (1) the A - a D O 2 was greater in PFO⁺ than in PFO^- in normoxia and mild to severe hypoxia and (2) the increase in pulmonary artery systolic pressure (PASP) in response to hypoxia was greater in PFO⁺ than in PFO^- . We measured arterial blood gases and PASP via ultrasound in healthy PFO⁺ (n = 15) and PFO^- (n = 15) humans breathing air and 30 min after breathing four levels of hypoxia (16%, 14%, 12%, 10% O₂ , randomized and balanced order) at rest. The A - a D O 2 was significantly greater in PFO⁺ compared to PFO^- while breathing air (2.1 ± 0.7 vs. 0.4 ± 0.3 Torr), 16% O₂ (1.8 ± 1.2 vs. 0.7 ± 0.8 Torr) and 14% O₂ (2.3 ± 1.2 vs. 0.7 ± 0.6 Torr), but not 12% or 10% O₂ . We found no effect of PFO on PASP at any level of hypoxia. We conclude that PFO influences pulmonary gas exchange efficiency with mild hypoxia, but not the acute increase in PASP in response to hypoxia.

Acetazolamide, Nifedipine and Phosphodiesterase Inhibitors: Rationale for Their Utilization as Adjunctive Countermeasures in the Treatment of Coronavirus Disease 2019 (COVID-19)

Effective treatments for Coronavirus Disease 2019 (COVID-19) outbreak are urgently needed. While anti-viral approaches and vaccines are being considered immediate countermeasures are unavailable. The aim of this article is to outline a perspective on the pathophysiology of COVID-19 in the context of the currently available clinical data published in the literature. This article appreciates clinical data published on COVID-19 in the context of another respiratory illness - high altitude pulmonary edema (HAPE). Both conditions have significant similarities that portend pathophysiologic trajectories. Following this potential treatment options emerge. Both COVID-19 and HAPE exhibit a decreased ratio of arterial oxygen partial pressure to fractional inspired oxygen with concomitant hypoxia and tachypnea. There also appears to be a tendency for low carbon dioxide levels in both as well. Radiologic findings of ground glass opacities are present in up to 86% of patients with COVID-19 in addition to patchy infiltrates. Patients with HAPE also exhibit patchy infiltrates throughout the pulmonary fields, often in an asymmetric pattern and CT findings reveal increased lung markings and ground glass-like changes as well. Widespread ground-glass opacities are most commonly a manifestation of hydrostatic pulmonary edema. Similarly, elevated fibrinogen levels in both conditions are likely an epiphenomenon of edema formation rather than coagulation activation. Autopsy results of a COVID-19 fatality revealed bilateral diffuse alveolar damage associated with pulmonary edema, pro-inflammatory concentrates, and indications of early-phase acute respiratory distress syndrome (ARDS). HAPE itself is initially caused by an increase in pulmonary capillary pressure and induces altered alveolar-capillary permeability via high pulmonary artery hydrostatic pressures that lead to a protein-rich and mildly hemorrhagic edema. It appears that COVID-19 and HAPE both discretely converge on ARDS. In light of this, a countermeasure that has been shown to be effective in the analogous condition of HAPE is Acetazolamide. Acetazolamide has a myriad of effects on different organ systems, potently reduces hypoxic pulmonary vasoconstriction, improves minute ventilation and expired vital capacity. Other therapeutics to consider that are also directed towards decreased pulmonary pressure include Nifedipine and Phosphodiesterase inhibitors. This review describes COVID-19 in parallel to HAPE. Deranged respiratory parameters that are present in both conditions are highlighted. The utilization of medications found to be effective in HAPE, for the treatment of COVID-19, is proposed. Given the medical emergency of a growing contagion and the thousands of lives at stake, expedient attempts to improve survival are needed. Acetazolamide, Nifedipine and Phosphodiesterase inhibitors may be potential countermeasures.

The unknown known: non-cardiogenic pulmonary edema in amlodipine poisoning, a cohort study

Context: Amlodipine is the most common calcium channel blocker (CCB) on the Swedish market, and poison center (PC) consultations for amlodipine overdoses are increasing. The clinical picture is dominated by vasodilation with relative preservation of cardiac function. CCBs selectively dilate vessels on the afferent side of the capillary network which, in states of preserved or increased blood flow may lead to edema formation, including non-cardiogenic pulmonary edema (NCPE). This complication has been considered rare in CCB poisoning. In this cohort study of nineteen amlodipine poisonings with high amlodipine blood levels, the incidence and clinical significance of NCPE in severe amlodipine poisoning are explored.Methods: During 2017-2018 the Swedish PC prospectively encouraged the gathering of blood samples in amlodipine poisonings with symptoms requiring treatment with inotropes or vasopressors. Samples were sent by mail to the Forensic Toxicology Division at the Swedish National Board of Forensic Medicine for screening and quantification of relevant toxicants. Patients with blood amlodipine levels >0.25 µg/mL were included in a cohort whose case details were gathered from medical records and PC-case notes with a special focus on signs of NCPE.Results: Nineteen patients met the blood amlodipine inclusion criteria. Four (21%) died and one patient was treated with VA-ECMO. Nine patients developed NCPE defined as a need for positive pressure ventilation (PPV) while having an echocardiographically normal left ventricular function.Conclusion: In this prospective cohort study of consecutive and analytically confirmed significant amlodipine poisonings NCPE was a common finding occurring in 47% of the whole cohort and in 64% of patients who did not go on to develop complete hemodynamic collapse.

Genetic Predisposition to High-Altitude Pulmonary Edema

Background: Exaggerated pulmonary arterial hypertension (PAH) is a hallmark of high-altitude pulmonary edema (HAPE). The objective of this study was therefore to investigate genetic predisposition to HAPE by analyzing PAH candidate genes in a HAPE-susceptible (HAPE-S) family and in unrelated HAPE-S mountaineers. Materials and Methods: Eight family members and 64 mountaineers were clinically and genetically assessed using a PAH-specific gene panel for 42 genes by next-generation sequencing. Results: Two otherwise healthy family members, who developed re-entry HAPE at 3640 m during childhood, carried a likely pathogenic missense mutation (c.1198T>G p.Cys400Gly) in the Janus Kinase 2 (JAK2) gene. One of them progressed to a mild form of PAH at the age of 23 years. In two of the 64 HAPE-S mountaineers likely pathogenic variants have been detected, one missense mutation in the Cytochrome P1B1 gene, and a deletion in the Histidine-Rich Glycoprotein (HRG) gene. Conclusions: This is the first study identifying an inherited missense mutation of a gene related to PAH in a family with re-entry HAPE showing a progression to borderline PAH in the index patient. Likely pathogenic variants in 3.1% of HAPE-S mountaineers suggest a genetic predisposition in some individuals that might be linked to PAH signaling pathways.

High-altitude illness: Management approach

In high altitudes, usually above 2500 m, travelers are faced with decreased partial pressure of oxygen along with decreased barometric pressure. High-altitude illness, a syndrome of acute mountain sickness, high-altitude cerebral edema and high-altitude pulmonary edema, occurs due to the hypobaric hypoxia when there is inadequate acclimatization. This review provides detailed information about pathophysiology, clinical features, prevention and treatment strategies for high-altitude illness according to the current literature.

The Hen or the Egg: Impaired Alveolar Oxygen Diffusion and Acute High-altitude Illness?

Individuals ascending rapidly to altitudes >2500 m may develop symptoms of acute mountain sickness (AMS) within a few hours of arrival and/or high-altitude pulmonary edema (HAPE), which occurs typically during the first three days after reaching altitudes above 3000-3500 m. Both diseases have distinct pathologies, but both present with a pronounced decrease in oxygen saturation of hemoglobin in arterial blood (SO₂). This raises the question of mechanisms impairing the diffusion of oxygen (O₂) across the alveolar wall and whether the higher degree of hypoxemia is in causal relationship with developing the respective symptoms. In an attempt to answer these questions this article will review factors affecting alveolar gas diffusion, such as alveolar ventilation, the alveolar-to-arterial O₂-gradient, and balance between filtration of fluid into the alveolar space and its clearance, and relate them to the respective disease. The resultant analysis reveals that in both AMS and HAPE the main pathophysiologic mechanisms are activated before aggravated decrease in SO₂ occurs, indicating that impaired alveolar epithelial function and the resultant diffusion limitation for oxygen may rather be a consequence, not the primary cause, of these altitude-related illnesses.