Medical Conditions and High-Altitude Travel

Retarded astrogliogenesis in response to hypoxia is facilitated by downregulation of CIRBP

The adverse impacts of chronic hypoxia on maternal and infant health at high altitudes warrant significant attention. However, effective protective measures against the resultant growth restrictions and neurodevelopmental disorders in infants and young children are still lacking. This study investigated the neurodevelopment of mice offspring under hypoxic conditions by exposing pregnant mice to a hypobaric oxygen chamber that simulated the hypobaric hypoxia at an altitude of 4000 m until 28 days after delivery. Our findings suggested that prolonged exposure to hypoxia might result in emotional abnormalities and social disorders in offspring. The significant reduction in astrogliogenesis was a characteristic feature associated with neurodevelopmental disorders induced by hypoxia. Further studies demonstrated that cold-induced RNA-binding protein (CIRBP) was a key transcriptional regulator in astrogliogenesis, which downregulated astrocytic differentiation under hypoxia through its crosstalk with the NFIA. Our study emphasized the crucial role of CIRBP in regulating astrogliogenesis and highlighted its potential as a promising target for therapeutic interventions in neurodevelopmental disorders associated with hypoxia.

Emergency Care for High-Altitude Trekking and Climbing

Introduction: High altitude regions are characterized by harsh conditions (environmental, rough terrain, natural hazards, and limited hygiene and health care), which all may contribute to the risk of accidents/emergencies when trekking or climbing. Exposure to hypoxia, cold, wind, and solar radiation are typical features of the high altitude environment. Emergencies in these remote areas place high demands on the diagnostic and treatment skills of doctors and first-aiders. The aim of this review is to give insights on providing the best possible care for victims of emergencies at high altitude. Methods: Authors provide clinical recommendations based on their real-world experience, complemented by appropriate recent studies and internationally reputable guidelines. Results and Discussion: This review covers most of the emergencies/health issues that can occur when trekking or during high altitude climbing, that is, high altitude illnesses and hypothermia, freezing cold injuries, accidents, for example, with severe injuries due to falling, cardiovascular and respiratory illnesses, abdominal, musculoskeletal, eye, dental, and skin issues. We give a summary of current recommendations for emergency care and pain relief in case of these various incidents.

Novel energy optimizer, meldonium, rapidly restores acute hypobaric hypoxia-induced brain injury by targeting phosphoglycerate kinase 1

BACKGROUND

Acute hypobaric hypoxia-induced brain injury has been a challenge in the health management of mountaineers; therefore, new neuroprotective agents are urgently required. Meldonium, a well-known cardioprotective drug, has been reported to have neuroprotective effects. However, the relevant mechanisms have not been elucidated. We hypothesized that meldonium may play a potentially novel role in hypobaric hypoxia cerebral injury.

METHODS

We initially evaluated the neuroprotection efficacy of meldonium against acute hypoxia in mice and primary hippocampal neurons. The potential molecular targets of meldonium were screened using drug-target binding Huprot™ microarray chip and mass spectrometry analyses after which they were validated with surface plasmon resonance (SPR), molecular docking, and pull-down assay. The functional effects of such binding were explored through gene knockdown and overexpression.

RESULTS

The study clearly shows that pretreatment with meldonium rapidly attenuates neuronal pathological damage, cerebral blood flow changes, and mitochondrial damage and its cascade response to oxidative stress injury, thereby improving survival rates in mice brain and primary hippocampal neurons, revealing the remarkable pharmacological efficacy of meldonium in acute high-altitude brain injury. On the one hand, we confirmed that meldonium directly interacts with phosphoglycerate kinase 1 (PGK1) to promote its activity, which improved glycolysis and pyruvate metabolism to promote ATP production. On the other hand, meldonium also ameliorates mitochondrial damage by PGK1 translocating to mitochondria under acute hypoxia to regulate the activity of TNF receptor-associated protein 1 (TRAP1) molecular chaperones.

CONCLUSION

These results further explain the mechanism of meldonium as an energy optimizer and provide a strategy for preventing acute hypobaric hypoxia brain injury at high altitudes.

AQP4- and Kir4.1-Mediated Müller Cell Oedema Is Involved in Retinal Injury Induced By Hypobaric Hypoxia

Hypobaric hypoxia is the main cause of high-altitude retinopathy (HAR). Retinal oedema is the key pathological change in HAR. However, its pathological mechanism is not clear. In this study, a 5000-m hypobaric hypoxic environment was simulated. Haematoxylin and eosin (H&E) staining and electrophysiological (ERG) detection were used to observe the morphological and functional changes in the retina of mice under hypobaric hypoxia for 2-72 h. Toluidine blue staining and transmission electron microscopy were used to observe the morphology of Müller cells in the hypobaric hypoxia groups. The functional changes and oedema mechanism of Müller cells were detected by immunofluorescence and western blotting. The expression levels of glutamine synthetase (GS), glial fibrillary acidic protein (GFAP), aquaporin 4 (AQP4), and inwardly rectifying potassium channel subtype 4.1 (Kir4.1) in Müller cells were quantitatively analysed. This study revealed that retinal oedema gradually increased with prolonged exposure to a 5000-m hypobaric hypoxic environment. In addition, the ERG showed that the time delay and amplitude of the a-wave and b-wave decreased. The expression of GS decreased, and the expression of GFAP increased in Müller cells after exposure to hypobaric hypoxia for 4 h. At the same time, retinal AQP4 expression increased, and Kir4.1 expression decreased. The oedema and functional changes in Müller cells are consistent with the time point of retinal oedema. In conclusion, Müller cell oedema is involved in retinal oedema induced by hypobaric hypoxia. An increase in AQP4 and a decrease in Kir4.1 are the main causes of Müller cell oedema caused by hypobaric hypoxia.

Critical pregnancy at altitude: A look at Latin America

Critical pregnancy at high altitudes increases morbidity and mortality from 2500 m above sea level. In addition to altitude, there are other influential factors such as social inequalities, cultural, prehospital barriers, and lack the appropriate development of healthcare infrastructure. The most frequent causes of critical pregnancy leading to admission to Intensive Care Units are pregnancy hypertensive disorders (native residents seem to be more protected), hemorrhages and infection/sepsis. In Latin America, there are 32 Intensive Care Units above 2500 m above sea level. Arterial blood gases at altitude are affected by changes in barometric pressure. The analysis of their values provides very useful information for the management of obstetric emergencies at very high altitude, especially respiratory and metabolic pathologies.

TRPC4 aggravates hypoxic pulmonary hypertension by promoting pulmonary endothelial cell apoptosis

Pulmonary hypertension (PH) is a devastating disease that lacks effective treatment options and is characterized by severe pulmonary vascular remodeling. Pulmonary arterial endothelial cell (PAEC) dysfunction drives the initiation and pathogenesis of pulmonary arterial hypertension. Canonical transient receptor potential (TRPC) channels, a family of Ca2+-permeable channels, play an important role in various diseases. However, the effect and mechanism of TRPCs on PH development have not been fully elucidated. Among the TRPC family members, TRPC4 expression was markedly upregulated in PAECs from hypoxia combined with SU5416 (HySu)-induced PH mice and monocrotaline (MCT)-treated PH rats, as well as in hypoxia-exposed PAECs, suggesting that TRPC4 in PAECs may participate in the occurrence and development of PH. In this study, we aimed to investigate whether TRPC4 in PAECs has an aggravating effect on PH and elucidate the molecular mechanisms. We observed that hypoxia treatment promoted PAEC apoptosis through a caspase-12/endoplasmic reticulum stress (ERS)-dependent pathway. Knockdown of TRPC4 attenuated hypoxia-induced apoptosis and caspase-3/caspase-12 activity in PAECs. Accordingly, adeno-associated virus (AAV) serotype 6-mediated pulmonary endothelial TRPC4 silencing (AAV6-Tie-shRNA-TRPC4) or TRPC4 antagonist suppressed PH progression as evidenced by reduced right ventricular systolic pressure (RVSP), pulmonary vascular remodeling, PAEC apoptosis and reactive oxygen species (ROS) production. Mechanistically, unbiased RNA sequencing (RNA-seq) suggested that TRPC4 deficiency suppressed the expression of the proapoptotic protein sushi domain containing 2 (Susd2) in hypoxia-exposed mouse PAECs. Moreover, TRPC4 activated hypoxia-induced PAEC apoptosis by promoting Susd2 expression. Therefore, inhibiting TRPC4 ameliorated PAEC apoptosis and hypoxic PH in animals by repressing Susd2 signaling, which may serve as a therapeutic target for the management of PH.

Superoxide dismutase 1-modified dental pulp stem cells alleviate high-altitude pulmonary edema by inhibiting oxidative stress through the Nrf2/HO-1 pathway

High-altitude pulmonary edema (HAPE) is a deadly form of altitude sickness, and there is no effective treatment for HAPE. Dental pulp stem cells (DPSCs) are a type of mesenchymal stem cell isolated from dental pulp tissues and possess various functions, such as anti-inflammatory and anti-oxidative stress. DPSCs have been used to treat a variety of diseases, but there are no studies on treating HAPE. In this study, Sprague-Dawley rats were exposed to acute low-pressure hypoxia to establish the HAPE model, and SOD1-modified DPSCs (DPSCsHiSOD1) were administered through the tail vein. Pulmonary arterial pressure, lung water content (LWC), total lung protein content of bronchoalveolar lavage fluid (BALF) and lung homogenates, oxidative stress, and inflammatory indicators were detected to evaluate the effects of DPSCsHiSOD1 on HAPE. Rat type II alveolar epithelial cells (RLE-6TN) were used to investigate the effects and mechanism of DPSCsHiSOD1 on hypoxia injury. We found that DPSCs could treat HAPE, and the effect was better than that of dexamethasone treatment. SOD1 modification could enhance the function of DPSCs in improving the structure of lung tissue, decreasing pulmonary arterial pressure and LWC, and reducing the total lung protein content of BALF and lung homogenates, through anti-oxidative stress and anti-inflammatory effects. Furthermore, we found that DPSCsHiSOD1 could protect RLE-6TN from hypoxic injury by reducing the accumulation of reactive oxygen species (ROS) and activating the Nrf2/HO-1 pathway. Our findings confirm that SOD1 modification could enhance the anti-oxidative stress ability of DPSCs through the Nrf2/HO-1 signalling pathway. DPSCs, especially DPSCsHiSOD1, could be a potential treatment for HAPE. Schematic diagram of the antioxidant stress mechanism of DPSCs in the treatment of high-altitude pulmonary edema. DPSCs can alleviate oxidative stress by releasing superoxide dismutase 1, thereby reducing ROS production and activating the Nrf2/HO-1 signalling pathway to ameliorate lung cell injury in HAPE.

Urinary proteomics for noninvasive monitoring of biomarkers of chronic mountain sickness in a young adult population using data-independent acquisition (DIA)-based mass spectrometry

Different populations exhibit varying pathophysiological responses to plateau environments. Therefore, it is crucial to identify molecular markers in body fluids with high specificity and sensitivity to aid in determination. Proteomics offers a fresh perspective for investigating protein changes linked to diseases. We utilize urine as a specific biomarker for early chronic mountain sickness (CMS) detection, as it is a simple-to-collect biological fluid. We collected urine samples from three groups: plains health, plateau health and CMS. Using DIA's proteomic approach, we found differentially expressed proteins between these groups, which will be used as a basis for future studies to identify protein markers. Compared with the healthy plain population, 660 altering proteins were identified in plateau health, which performed the resistance to altitude response function by boosting substance metabolism and reducing immune stress function. Compared to the healthy plateau population, the CMS group had 140 different proteins identified, out of which 8 were potential biomarkers for CMS. Our study has suggested that CMS may be closely related to increased thyroid hormone levels, oxidative damage to the mitochondria, impaired cell detoxification function and inhibited hydrolase activity. SIGNIFICANCE: Our team has compiled a comprehensive dataset of urine proteomics for AMS disease. We successfully identified differentially expressed proteins between healthy and AMS groups using the DIA proteomic approach. We discovered that 660 proteins were altered in plateau health compared to the healthy plain population, resulting in a heightened resistance to altitude response function by boosting substance metabolism and reducing immune stress function. Additionally, we pinpointed 140 different proteins in the AMS group compared to the healthy plateau population, with 8 showing potential as biomarkers for AMS. Our findings suggest that the onset of AMS may be closely linked to increased thyroid hormone levels, oxidative damage to the mitochondria, impaired cell detoxification function and inhibited hydrolase activity.

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.

Investigating Sea-Level Brain Predictors for Acute Mountain Sickness: A Multimodal MRI Study before and after High-Altitude Exposure

BACKGROUND AND PURPOSE

Acute mountain sickness is a series of brain-centered symptoms that occur when rapidly ascending to high altitude. Predicting acute mountain sickness before high-altitude exposure is crucial for protecting susceptible individuals. The present study aimed to evaluate the feasibility of predicting acute mountain sickness after high-altitude exposure by using multimodal brain MR imaging features measured at sea level.

MATERIALS AND METHODS

We recruited 45 healthy sea-level residents who flew to the Qinghai-Tibet Plateau (3650 m). We conducted T1-weighted structural MR imaging, resting-state fMRI, and arterial spin-labeling perfusion MR imaging both at sea level and high altitude. Acute mountain sickness was diagnosed for 5 days using Lake Louise Scoring. Logistic regression with Least Absolute Shrinkage and Selection Operator logistic regression was performed for predicting acute mountain sickness using sea-level MR imaging features. We also validated the predictors by using MR images obtained at high altitude.

RESULTS

The incidence rate of acute mountain sickness was 80.0%. The model achieved an area under the receiver operating characteristic curve of 86.4% (sensitivity = 77.8%, specificity = 100.0%, and P < .001) in predicting acute mountain sickness At sea level, valid predictors included fractional amplitude of low-frequency fluctuations (fALFF) and degree centrality from resting-state fMRI, mainly distributed in the somatomotor network. We further learned that the acute mountain sickness group had lower levels of fALFF in the somatomotor network at high altitude, associated with smaller changes in CSF volume and higher Lake Louise Scoring, specifically relating to fatigue and clinical function.

CONCLUSIONS

Our study found that the somatomotor network function detected by sea-level resting-state fMRI was a crucial predictor for acute mountain sickness and further validated its pathophysiologic impact at high altitude. These findings show promise for pre-exposure prediction, particularly for individuals in need of rapid ascent, and they offer insight into the potential mechanism of acute mountain sickness.

The Intersection of Geriatrics, Climate Change, and Wilderness Medicine: Education is Critical

According to the US Census, for the first time in history, older adults are projected to exceed the number of children by 2035. These seniors are headed to the outdoors in increasing numbers and face unique risks. They benefit from careful pre-event evaluation planning to maintain their health in wilderness environments. Climate change is affecting all of us, but seniors are considered an especially vulnerable group. This vulnerability needs to be addressed not only when older adults head into the wilderness but also when the wilderness "comes to them" in areas where wilderness medicine and disaster medicine overlap. Education of both providers and patients is vital. This article aims to discuss the special needs of older adults/seniors /elders (defined as those over 65 unless otherwise indicated) in the wilderness as well as the vulnerability of older adults to climate change, both during planned wilderness activities and when the wilderness "comes to them" because of climate change, and to identify opportunities for education and adaptation of patients and education of physicians and wilderness and disaster responders to care for these older patients. The PubMed and Google Scholar Database search engines were utilized to review relevant English language publications between 2000 and 2023 that addressed individuals over 65 and explored the overlap of geriatrics (aged over 65), wilderness and disaster medicine, and climate change and create a perspective summary. Because of increased numbers of older adults heading into the wilderness for outdoor activities or having wilderness thrust upon them due to climate change, cross training of all specialties including the fields of emergency, geriatrics, wilderness medicine, and disaster medicine is needed in collaboration with other organizations and search and rescue. Response agencies must recognize that training in wilderness medicine provides a background for practitioners working in dangerous and remote settings and ought to seek out individuals with such skills when placing responders in the field. Climate change is making these intersections and the need for this education more urgent with time.

Notoginsenoside R1 treatment facilitated Nrf2 nuclear translocation to suppress ferroptosis via Keap1/Nrf2 signaling pathway to alleviated high-altitude myocardial injury

High-altitude myocardial injury (HAMI) represents a critical form of altitude illness for which effective drug therapies are generally lacking. Notoginsenoside R1, a prominent constituent derived from Panax notoginseng, has demonstrated various cardioprotective properties in models of myocardial ischemia/reperfusion injury, sepsis-induced cardiomyopathy, cardiac fibrosis, and myocardial injury. The potential utility of notoginsenoside R1 in the management of HAMI warrants prompt investigation. Following the successful construction of a HAMI model, a series of experimental analyses were conducted to assess the effects of notoginsenoside R1 at dosages of 50 mg/Kg and 100 mg/Kg. The results indicated that notoginsenoside R1 exhibited protective effects against hypoxic injury by reducing levels of CK, CK-MB, LDH, and BNP, leading to improved cardiac function and decreased incidence of arrhythmias. Furthermore, notoginsenoside R1 was found to enhance Nrf2 nuclear translocation, subsequently regulating the SLC7A11/GPX4/HO-1 pathway and iron metabolism to mitigate ferroptosis, thereby mitigating cardiac inflammation and oxidative stress induced by high-altitude conditions. In addition, the application of ML385 has confirmed the involvement of Nrf2 nuclear translocation in the therapeutic approach to HAMI. Collectively, the advantageous impacts of notoginsenoside R1 on HAMI have been linked to the suppression of ferroptosis via Nrf2 nuclear translocation signaling.

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

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

Low- and moderate-intensity aerobic exercise improves the physiological acclimatization of lowlanders on the Tibetan plateau

This study investigates whether exercise as a strategy for improving physical fitness at sea level also offers comparable benefits in the unique context of high altitudes (HA), considering the physiological challenges of hypoxic conditions. Overall, 121 lowlanders who had lived on the Tibetan Plateau for >2 years and were still living at HA during the measurements were randomly classified into four groups. Each individual of the low-intensity (LI), moderate-intensity (MI), and high-intensity (HI) groups performed 20 sessions of aerobic exercise at HA (3680 m) over 4 weeks, while the control group (CG) did not undergo any intervention. Physiological responses before and after the intervention were observed. The LI and MI groups experienced significant improvement in cardiopulmonary fitness (0.27 and 0.35 L/min increases in peak oxygen uptake [V ˙ $\dot{\mathrm{V}}$ O2peak], both p < 0.05) after exercise intervention, while the hematocrit (HCT) remained unchanged (p > 0.05). However, HI exercise was less efficient for cardiopulmonary fitness of lowlanders (0.02 L/min decrease inV ˙ $\dot{\mathrm{V}}$ O2peak, p > 0.05), whereas both the HCT (1.74 %, p < 0.001) and glomerular filtration rate (18.41 mL/min, p < 0.001) increased with HI intervention. Therefore, LI and MI aerobic exercise, rather than HI, can help lowlanders in Tibet become more acclimated to the HA by increasing cardiopulmonary function and counteracting erythrocytosis.

Ceramide-1-phosphate alleviates high-altitude pulmonary edema by stabilizing circadian ARNTL-mediated mitochondrial dynamics

INTRODUCTION

High-altitude pulmonary edema (HAPE) is a severe and potentially fatal condition with limited treatment options. Although ceramide kinase (CERK)-derived ceramide-1-phosphate (C1P) has been demonstrated to offer protection against various pulmonary diseases, its effects on HAPE remain unclear.

OBJECTIVES

Our study aimed to investigate the potential role of CERK-derived C1P in the development of HAPE and to reveal the molecular mechanisms underlying its protective effects. We hypothesized that CERK-derived C1P could protect against HAPE by stabilizing circadian rhythms and maintaining mitochondrial dynamics.

METHODS

To test our hypothesis, we used CERK-knockout mice and established HAPE mouse models using a FLYDWC50-1C hypobaric hypoxic cabin. We utilized a range of methods, including lipidomics, transcriptomics, immunofluorescence, Western blotting, and transmission electron microscopy, to identify the mechanisms of regulation.

RESULTS

Our findings demonstrated that CERK-derived C1P played a protective role against HAPE. Inhibition of CERK exacerbated HAPE induced by the hypobaric hypoxic environment. Specifically, we identified a novel mechanism in which CERK inhibition induced aryl hydrocarbon receptor nuclear translocator-like (ARNTL) autophagic degradation, inducing the circadian rhythm and triggering mitochondrial damage by controlling the expression of proteins required for mitochondrial fission and fusion. The decreased ARNTL caused by CERK inhibition impaired mitochondrial dynamics, induced oxidative stress damage, and resulted in defects in mitophagy, particularly under hypoxia. Exogenous C1P prevented ARNTL degradation, alleviated mitochondrial damage, neutralized oxidative stress induced by CERK inhibition, and ultimately relieved HAPE.

CONCLUSIONS

This study provides evidence for the protective effect of C1P against HAPE, specifically, through stabilizing circadian rhythms and maintaining mitochondrial dynamics. Exogenous C1P therapy may be a promising strategy for treating HAPE. Our findings also highlight the importance of the circadian rhythm and mitochondrial dynamics in the pathogenesis of HAPE, suggesting that targeting these pathways may be a potential therapeutic approach for this condition.

Symposium review: high altitude travel with pulmonary vascular disease

Pulmonary arterial hypertension and chronic thromboembolic pulmonary hypertension are the main precapillary forms of pulmonary hypertension (PH) summarized as pulmonary vascular diseases (PVD). PVDs are characterized by exertional dyspnoea and oxygen desaturation, and reduced quality of life and survival. Medical therapies improve life expectancy and physical performance of PVD patients, of whom many wish to participate in professional work and recreational activities including traveling to high altitude. The exposure to the hypobaric hypoxic environment of mountain regions incurs the risk of high altitude adverse events (AEHA) due to severe hypoxaemia exacerbating symptoms and further increase in pulmonary artery pressure, which may lead to right heart decompensation. Recent prospective and randomized trials show that altitude-induced hypoxaemia, pulmonary haemodynamic changes and impairment of exercise performance in PVD patients are in the range found in healthy people. The vast majority of optimally treated stable PVD patients who do not require long-term oxygen therapy at low altitude can tolerate short-term exposure to moderate altitudes up to 2500 m. PVD patients that reveal persistent severe resting hypoxaemia (S p O 2 ${{S}_{{\mathrm{p}}{{{\mathrm{O}}}_{\mathrm{2}}}}}$  <80% for >30 min) at 2500 m respond well to supplemental oxygen therapy. Although there are no accurate predictors for AEHA, PVD patients with unfavourable risk profiles at low altitude, such as higher WHO functional class, lower exercise capacity with more pronounced exercise-induced desaturation and more severely impaired haemodynamics, are at increased risk of AEHA. Therefore, doctors with experience in PVD and high-altitude medicine should counsel PVD patients before any high-altitude sojourn. This review aims to summarize recent literature and clinical recommendations about PVD patients travelling to high altitude.

Impact of altitude on the dosage of indoor particulates entering an individual's small airways

The complexity of indoor particulate exposure intensifies at higher altitudes owing to the increased lung capacity that residents develop to meet the higher oxygen demands. Altitude variations impact atmospheric pressure and alter particulate dynamics in ambient air and the human respiratory tract, complicating particulate inhalation. This study assessed the fraction of PM2.5 and PM10 entering small airways. This assessment covered an altitude range from 400 m above sea level to 3650 m, and an in vitro respiratory tract model was used. The experimental results confirmed that with increasing altitude, the penetration fractions of PM2.5 and PM10 significantly increased from 0.133 ± 0.031 and 0.141 ± 0.045 to 0.404 ± 0.159 and 0.353 ± 0.132, respectively. Additionally, the computational fluid dynamics simulation results revealed that among particles with sizes of 0.1 to 10 µm, the 7.5-μm particles exhibited the most substantial reduction in deposition in the upper airway, displaying a decrease of 6.27%. Our findings underscore the health risks faced by low-altitude residents during acclimatization to higher altitudes, as they experience heightened exposure to particulate matter sources.

[Cerebral oxygen metabolism and brain electrical activity of healthy full-term neonates in high-altitude areas: a multicenter clinical research protocol]

Further evidence is needed to explore the impact of high-altitude environments on the neurologic function of neonates. Non-invasive techniques such as cerebral near-infrared spectroscopy and amplitude-integrated electroencephalography can provide data on cerebral oxygenation and brain electrical activity. This study will conduct multiple cerebral near-infrared spectroscopy and amplitude-integrated electroencephalography monitoring sessions at various time points within the first 3 days postpartum for healthy full-term neonates at different altitudes. The obtained data on cerebral oxygenation and brain electrical activity will be compared between different altitudes, and corresponding reference ranges will be established. The study involves 6 participating centers in the Chinese High Altitude Neonatal Medicine Alliance, with altitude gradients divided into 4 categories: 800 m, 1 900 m, 2 400 m, and 3 500 m, with an anticipated sample size of 170 neonates per altitude gradient. This multicenter prospective cohort study aims to provide evidence supporting the impact of high-altitude environments on early brain function and metabolism in neonates.

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

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

Adaptation to Living at High Altitude in Patients with COPD. Comparative Study of Exercise Capacity and Ventilatory Variables between Patients Residing at High and Low Altitudes in the Andes

González-García, Mauricio and Luis Ernesto Téllez. Adaptation to living at high altitude in patients with COPD. Comparative study of exercise capacity and ventilatory variables between patients residing at high and low altitudes in the Andes. High Alt Med Biol. 00:000-000, 2024. Introduction: Although some variables related to oxygen transport and utilization such as ventilation, pulmonary vascular responses to hypoxia, heart rate (HR), cardiac output, hemoglobin (Hb), and oxygen saturation (SpO2) are used to compare adaptation to altitude between populations, peak oxygen consumption (VO2) constitutes an integrative measure of total oxygen transport that may reflect successful adaptation to altitude. We designed this study to make a direct comparison of VO2 in a cardiopulmonary exercise test (CPET) between chronic obstructive pulmonary disease (COPD) patients residing at high altitude (Bogotá, Colombia: 2,640 m) (COPD-HA) and those living at low altitude (Bucaramanga, Colombia: 959 m) (COPD-LA). Methods: All patients performed a CPET with measurements of VO2, minute ventilation (VE), HR, oxygen pulse (VO2/HR), ventilatory equivalents (VE/VCO2), and SpO2. Unpaired T-test or Mann-Whitney U test were used for comparisons between COPD-HA and COPD-LA. Results: We included 71 patients with COPD, 53 COPD-HA, and 18 COPD-LA. There were no differences between groups in age, sex, or forced expiratory volume in 1 second. The means ± SD of Hb, g/dl was slightly higher in COPD-HA (15.9 ± 1.9 vs. 14.7 ± 1.8, p = 0.048), without differences in VO2, % pred (71.6 ± 17.9 vs. 69.0 ± 17.0, p = 0.584), VO2/HR, % pred (92.1 ± 22.0 vs. 89.7 ± 19.8, p = 0.733) or VE/MVV, % (75.5 ± 14.1 vs. 76.5 ± 14.3, p = 0.790) at peak exercise between groups. Median (IQR) of VE/VCO2 nadir [38.0 (37.0-42.0) vs. 32.5 (31.0-39.0), p = 0.005] was significantly higher, and SpO2, % at rest [88.0 (86.0-91.0) vs. 95.0 (94.0-96.0), p < 0.001] and at peak exercise [84.0 (77.0-90.0) vs. 93.0 (92.0-95.0), p < 0.001] were significantly lower in COPD-HA. Conclusions: Despite higher desaturation at rest and during exercise in COPD-HA, there were no differences in VO2 peak between COPD-HA and COPD-LA, suggesting a potential altitude adaptation in those patients chronically exposed to hypoxia.

Effect of furosemide in the treatment of high-altitude pulmonary edema

BACKGROUND

High-altitude pulmonary edema (HAPE) refers to the onset of breathlessness, cough, and fever at rest after arriving at high altitudes. It is a life-threatening illness caused by rapid ascent to high altitudes. Furosemide is controversial in HAPE treatment but is routinely used in China. Further research is needed to assess its efficacy and impact on HAPE management and prognosis. The aim of this study is to determine the effectiveness of furosemide for HAPE.

METHODS

A retrospective was conducted to analysis of patients with HAPE admitted to the People's Hospital of Shigatse City from January 2018 to September 2023. Patients were divided into furosemide group and non-furosemide group for further analysis. Clinical variables including demographic information, comorbidities, vital signs, inflammatory markers, biochemical analysis, CT severity score and prognostic indicators were collected.

RESULTS

A total of 273 patients were enrolled, with 209 patients in the furosemide group and 64 patients in the non-furosemide group. The furosemide group showed a significantly decrease in CT severity scores compared to the non-furosemide group. Subgroup analysis showed that the longer the duration of furosemide use, the more pronounced the improvement in lung CT severity scores. But there were no significant differences in length of hospital stay and in-hospital mortality between the two groups.

CONCLUSION

Furosemide helps alleviate pulmonary edema in HAPE patients, but further research is needed to clarify its impact on prognosis.

High altitude retinopathy: An overview and new insights

High altitude retinopathy (HAR) is a common ocular disorder that occurs on ascent to high altitude. There are many clinical symptoms, retinal vascular dilatation, retinal edema and hemorrhage are common. These usually do not or slightly affect vision; rarely, severe cases develop serious or permanent vision loss. At present, the research progress of HAR mainly focuses on hemodynamic changes, blood-retinal barrier damage, oxidative stress and inflammatory response. Although the related studies on HAR are limited, it shows that HAR still belongs to hypoxia, and hypobaric hypoxia plays an aggravating role in promoting the development of the disease. Various studies have demonstrated the correlation of HAR with acute mountain sickness (AMS) and high-altitude cerebral edema (HACE), so a deeper understanding of HAR is important. The slow ascent rates and ascent altitude are the key to preventing any altitude sickness. Research on traditional chinese medicine (TCM) and western medicine has been gradually carried out. Further exploration of the pathogenesis and prevention strategies of HAR will provide better guidance for doctors and high-altitude travelers.

The Effect of High-Altitude Hypoxia on Neuropsychiatric Functions

Liu, Bo, Minlan Yuan, Mei Yang, Hongru Zhu, and Wei Zhang. The effect of high-altitude hypoxia on neuropsychiatric functions. High Alt Med Biol. 25:26-41, 2024. Background: In recent years, there has been a growing popularity in engaging in activities at high altitudes, such as hiking and work. However, these high-altitude environments pose risks of hypoxia, which can lead to various acute or chronic cerebral diseases. These conditions include common neurological diseases such as acute mountain sickness (AMS), high-altitude cerebral edema, and altitude-related cerebrovascular diseases, as well as psychiatric disorders such as anxiety, depression, and psychosis. However, reviews of altitude-related neuropsychiatric conditions and their potential mechanisms are rare. Methods: We conducted searches on PubMed and Google Scholar, exploring existing literature encompassing preclinical and clinical studies. Our aim was to summarize the prevalent neuropsychiatric diseases induced by altitude hypoxia, the potential pathophysiological mechanisms, as well as the available pharmacological and nonpharmacological strategies for prevention and intervention. Results: The development of altitude-related cerebral diseases may arise from various pathogenic processes, including neurovascular alterations associated with hypoxia, cytotoxic responses, activation of reactive oxygen species, and dysregulation of the expression of hypoxia inducible factor-1 and nuclear factor erythroid 2-related factor 2. Furthermore, the interplay between hypoxia-induced neurological and psychiatric changes is believed to play a role in the progression of brain damage. Conclusions: While there is some evidence pointing to pathophysiological changes in hypoxia-induced brain damage, the precise mechanisms responsible for neuropsychiatric alterations remain elusive. Currently, the range of prevention and intervention strategies available is primarily focused on addressing AMS, with a preference for prevention rather than treatment.

Cardiovascular physiology and pathophysiology at high altitude

Oxygen is vital for cellular metabolism; therefore, the hypoxic conditions encountered at high altitude affect all physiological functions. Acute hypoxia activates the adrenergic system and induces tachycardia, whereas hypoxic pulmonary vasoconstriction increases pulmonary artery pressure. After a few days of exposure to low oxygen concentrations, the autonomic nervous system adapts and tachycardia decreases, thereby protecting the myocardium against high energy consumption. Permanent exposure to high altitude induces erythropoiesis, which if excessive can be deleterious and lead to chronic mountain sickness, often associated with pulmonary hypertension and heart failure. Genetic factors might account for the variable prevalence of chronic mountain sickness, depending on the population and geographical region. Cardiovascular adaptations to hypoxia provide a remarkable model of the regulation of oxygen availability at the cellular and systemic levels. Rapid exposure to high altitude can have adverse effects in patients with cardiovascular diseases. However, intermittent, moderate hypoxia might be useful in the management of some cardiovascular disorders, such as coronary heart disease and heart failure. The aim of this Review is to help physicians to understand the cardiovascular responses to hypoxia and to outline some recommendations that they can give to patients with cardiovascular disease who wish to travel to high-altitude destinations.

Injuries and medical emergencies among international travellers

BACKGROUND

Tropical infectious diseases and vaccine-preventable emergencies are the mainstay of pre-travel consultations. However, non-communicable diseases, injuries and accidents that occur during travel are not emphasized enough in these settings.

METHODS

We performed a narrative review based on a literature search of PubMed, Google Scholar, UpToDate, DynaMed and LiSSa and on reference textbooks and medical journals dedicated to travel, emergency and wilderness medicine. Relevant secondary references were extracted. We also aimed to discuss newer or neglected issues, such as medical tourism, Coronavirus Disease 2019, exacerbations of co-morbidities associated with international travel, insurance coverage, health care seeking abroad, medical evacuation or repatriation and tips for different types of travellers' emergency medical kits (personal, group, physician handled).

RESULTS

All sources reviewed led to the selection of >170 references. Among epidemiological data on morbidity and deaths while abroad, only retrospective data are available. Deaths are estimated to occur in 1 in 100 000 travellers, with 40% caused by trauma and 60% by diseases, and <3% linked to infectious diseases. Trauma and other injuries acquired during travel, such as traffic accidents and drowning, can be reduced by up to 85% with simple preventive recommendations such as avoiding simultaneous alcohol intake. In-flight emergencies occur on 1 in 604 flights on average. Thrombosis risk is two to three times greater for travellers than for non-travellers. Fever during or after travel can occur in 2-4% of travellers, but in up to 25-30% in tertiary centres. Traveller's diarrhoea, although rarely severe, is the most common disease associated with travel. Autochthonous emergencies (acute appendicitis, ectopic pregnancy, dental abscess) can also occur.

CONCLUSIONS

Pre-travel medicine encounters must include the topic of injuries and medical emergencies, such as the risk-taking behaviours and foster better planning in a comprehensive approach along with vaccines and infectious diseases advices.

A novel clinical prediction scoring system of high-altitude pulmonary hypertension

Background

High-altitude pulmonary hypertension (HAPH) is a common disease in regions of high altitude where performing right heart catheterization (RHC) is challenging. The development of a diagnostic scoring system is crucial for effective disease screening.

Methods

A total of 148 individuals were included in a retrospective analysis, and an additional 42 residents were prospectively enrolled. We conducted a multivariable analysis to identify independent predictors of HAPH. Subsequently, we devised a prediction score based on the retrospective training set to anticipate the occurrence and severity of HAPH. This scoring system was further subjected to validation in the prospective cohort, in which all participants underwent RHC.

Results

This scoring system, referred to as the GENTH score model (Glycated hemoglobin [OR = 4.5], Echocardiography sign [OR = 9.1], New York Heart Association-functional class [OR = 12.5], Total bilirubin [OR = 3.3], and Hematocrit [OR = 3.6]), incorporated five independent risk factors and demonstrated strong predictive accuracy. In the training set, the area under the curve (AUC) values for predicting the occurrence and severity of HAPH were 0.851 and 0.832, respectively, while in the validation set, they were 0.841 and 0.893. In the validation set, GENTH score model cutoff values of ≤18 or >18 points were established for excluding or confirming HAPH, and a threshold of >30 points indicated severe HAPH.

Conclusions

The GENTH score model, combining laboratory and echocardiography indicators, represents an effective tool for distinguishing potential HAPH patients and identifying those with severe HAPH. This scoring system improves the clinical screening of HAPH diseases and offers valuable insights into disease diagnosis and management.

Effects of acetazolamide combined with remote ischemic preconditioning on risk of acute mountain sickness: a randomized clinical trial

BACKGROUND

We aimed to determine whether and how the combination of acetazolamide and remote ischemic preconditioning (RIPC) reduced the incidence and severity of acute mountain sickness (AMS).

METHODS

This is a prospective, randomized, open-label, blinded endpoint (PROBE) study involving 250 healthy volunteers. Participants were randomized (1:1:1:1:1) to following five groups: Ripc (RIPC twice daily, 6 days), Rapid-Ripc (RIPC four times daily, 3 days), Acetazolamide (twice daily, 2 days), Combined (Acetazolamide plus Rapid-Ripc), and Control group. After interventions, participants entered a normobaric hypoxic chamber (equivalent to 4000 m) and stayed for 6 h. The primary outcomes included the incidence and severity of AMS, and SpO2 after hypoxic exposure. Secondary outcomes included systolic and diastolic blood pressure, and heart rate after hypoxic exposure. The mechanisms of the combined regime were investigated through exploratory outcomes, including analysis of venous blood gas, complete blood count, human cytokine antibody array, ELISA validation for PDGF-AB, and detection of PDGF gene polymorphisms.

RESULTS

The combination of acetazolamide and RIPC exhibited powerful efficacy in preventing AMS, reducing the incidence of AMS from 26.0 to 6.0% (Combined vs Control: RR 0.23, 95% CI 0.07-0.70, P = 0.006), without significantly increasing the incidence of adverse reactions. Combined group also showed the lowest AMS score (0.92 ± 1.10). Mechanistically, acetazolamide induced a mild metabolic acidosis (pH 7.30 ~ 7.31; HCO3- 18.1 ~ 20.8 mmol/L) and improved SpO2 (89 ~ 91%) following hypoxic exposure. Additionally, thirty differentially expressed proteins (DEPs) related to immune-inflammatory process were identified after hypoxia, among which PDGF-AB was involved. Further validation of PDGF-AB in all individuals showed that both acetazolamide and RIPC downregulated PDGF-AB before hypoxic exposure, suggesting a possible protective mechanism. Furthermore, genetic analyses demonstrated that individuals carrying the PDGFA rs2070958 C allele, rs9690350 G allele, or rs1800814 G allele did not display a decrease in PDGF-AB levels after interventions, and were associated with a higher risk of AMS.

CONCLUSIONS

The combination of acetazolamide and RIPC exerts a powerful anti-hypoxic effect and represents an innovative and promising strategy for rapid ascent to high altitudes. Acetazolamide improves oxygen saturation. RIPC further aids acetazolamide, which synergistically regulates PDGF-AB, potentially involved in the pathogenesis of AMS.

TRIAL REGISTRATION

ClinicalTrials.gov NCT05023941.

Moderate altitude exposure impacts host fasting blood glucose and serum metabolome by regulation of the intestinal flora

Moderate altitude exposure has shown beneficial effects on diabetes incidence but the underlying mechanisms are not understood. Our study aimed to investigate how the human gut microbiome impacted the serum metabolome and associated with glucose homeostasis in healthy Chinese individuals upon moderate-altitude exposure. Faecal microbiome composition was assessed using shotgun metagenomic sequencing. Serum metabolome was acquired by untargeted metabolomics technology, and amino acids (AAs) and propionic acid in serum were quantified by targeted metabolomics technology. The results indicated that the moderate-altitude exposed individuals presented lowered fasting blood glucose (FBG) and propionic acid, increased circulating L-Glutamine but decreased L-Glutamate and L-Valine, which correlated with enriched Bacteroidetes and decreased Proteobacteria. Additionally, the silico causality associations among gut microbiota, serum metabolome and host FBG were analyzed by mediation analysis. It showed that increased Bacteroides ovatus (B. ovatus) and decreased Escherichia coli (E. coli) were identified as the main antagonistic species driving the association between L-Glutamate and FBG in silico causality. Furthermore, the high-fat diet (HFD) fed mice subjected to faecal microbiota transplantation (FMT) were applied to validate the cause-in-fact effects of gut microbiota on the beneficial glucose response. We found that microbiome in the moderate-altitude exposed donor could predict the extent of the FBG response in recipient mice, which showed lowered FBG, L-Glutamate and Firmicutes/Bacteroidetes ratio. Our findings suggest that moderate-altitude exposure targeting gut microbiota and circulating metabolome, may pave novel avenues to counter dysglycemia.

Acute Mountain Sickness and High Altitude Cerebral Edema in Women: A Scoping Review-UIAA Medical Commission Recommendations

Derstine, Mia, Dominique Jean, Beth A. Beidleman, Jacqueline Pichler Hefti, David Hillebrandt, Lenka Horakova, Susi Kriemler, Kasté Mateikaité-Pipiriené, Peter Paal, Alison Rosier, Marija Andjelkovic, and Linda E. Keyes. Acute mountain sickness and high altitude cerebral edema in women: A scoping review-UIAA Medical Commission recommendations. High Alt Med Biol. 24:259-267, 2023. Background: Acute mountain sickness (AMS) and high-altitude cerebral edema (HACE) are illnesses associated with rapid ascent to altitudes over 2,500 m in unacclimatized lowlanders. The aim of this scoping review is to summarize the current knowledge on sex differences in the epidemiology, pathophysiology, symptomatology, and treatment of AMS and HACE, especially in women. Methods and Results: The UIAA Medical Commission convened an international author team to review women's health issues at high altitude and to publish updated recommendations. Pertinent literature from PubMed and Cochrane was identified by keyword search combinations (including AMS, HACE, and high altitude), with additional publications found by hand search. The primary search focus was for articles assessing lowland women sojourning at high altitude. Results: The literature search yielded 7,165 articles, 37 of which were ultimately included. The majority of publications included did not find women at increased risk for AMS or HACE. There was extremely limited sex-specific data on risk factors or treatment. Conclusions: There is a limited amount of data on female-specific findings regarding AMS and HACE, with most publications addressing only prevalence or incidence with regard to sex. As such, general prevention and treatment strategies for AMS and HACE should be used regardless of sex.

Hypoxia and the Aging Cardiovascular System

Older individuals represent a growing population, in industrialized countries, particularly those with cardiovascular diseases, which remain the leading cause of death in western societies. Aging constitutes one of the largest risks for cardiovascular diseases. On the other hand, oxygen consumption is the foundation of cardiorespiratory fitness, which in turn is linearly related to mortality, quality of life and numerous morbidities. Therefore, hypoxia is a stressor that induces beneficial or harmful adaptations, depending on the dose. While severe hypoxia can exert detrimental effects, such as high-altitude illnesses, moderate and controlled oxygen exposure can potentially be used therapeutically. It can improve numerous pathological conditions, including vascular abnormalities, and potentially slows down the progression of various age-related disorders. Hypoxia can exert beneficial effects on inflammation, oxidative stress, mitochondrial functions, and cell survival, which are all increased with age and have been discussed as main promotors of aging. This narrative review discusses specificities of the aging cardiovascular system in hypoxia. It draws upon an extensive literature search on the effects of hypoxia/altitude interventions (acute, prolonged, or intermittent exposure) on the cardiovascular system in older individuals (over 50 years old). Special attention is directed toward the use of hypoxia exposure to improve cardiovascular health in older individuals.

Challenges in the management of high-altitude illnesses and emergencies in Bhutan and Nepal

Many popular tourist attractions and trekking routes in Bhutan and Nepal are situated between 3000 and 6000 m in elevation. High-altitude emergencies are becoming more common and medical providers must be aware of the practical and medical issues in managing these disorders. We reflect on the challenges in providing high-altitude emergency medical services in Bhutan and Nepal.

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.

Mechanisms underlying the health benefits of intermittent hypoxia conditioning

Intermittent hypoxia (IH) is commonly associated with pathological conditions, particularly obstructive sleep apnoea. However, IH is also increasingly used to enhance health and performance and is emerging as a potent non-pharmacological intervention against numerous diseases. Whether IH is detrimental or beneficial for health is largely determined by the intensity, duration, number and frequency of the hypoxic exposures and by the specific responses they engender. Adaptive responses to hypoxia protect from future hypoxic or ischaemic insults, improve cellular resilience and functions, and boost mental and physical performance. The cellular and systemic mechanisms producing these benefits are highly complex, and the failure of different components can shift long-term adaptation to maladaptation and the development of pathologies. Rather than discussing in detail the well-characterized individual responses and adaptations to IH, we here aim to summarize and integrate hypoxia-activated mechanisms into a holistic picture of the body's adaptive responses to hypoxia and specifically IH, and demonstrate how these mechanisms might be mobilized for their health benefits while minimizing the risks of hypoxia exposure.

Surgical masks and filtering facepiece class 2 respirators (FFP2) have no major physiological effects at rest and during moderate exercise at 3000-m altitude: a randomised controlled trial

BACKGROUND

During the COVID-19 pandemic, the use of face masks has been recommended or enforced in several situations; however, their effects on physiological parameters and cognitive performance at high altitude are unknown.

METHODS

Eight healthy participants (four females) rested and exercised (cycling, 1 W/kg) while wearing no mask, a surgical mask or a filtering facepiece class 2 respirator (FFP2), both in normoxia and hypobaric hypoxia corresponding to an altitude of 3000 m. Arterialised oxygen saturation (SaO2), partial pressure of oxygen (PaO2) and carbon dioxide (PaCO2), heart and respiratory rate, pulse oximetry (SpO2), cerebral oxygenation, visual analogue scales for dyspnoea and mask's discomfort were systematically investigated. Resting cognitive performance and exercising tympanic temperature were also assessed.

RESULTS

Mask use had a significant effect on PaCO2 (overall +1.2 ± 1.7 mmHg). There was no effect of mask use on all other investigated parameters except for dyspnoea and discomfort, which were highest with FFP2. Both masks were associated with a similar non-significant decrease in SaO2 during exercise in normoxia (-0.5 ± 0.4%) and, especially, in hypobaric hypoxia (-1.8 ± 1.5%), with similar trends for PaO2 and SpO2.

CONCLUSIONS

Although mask use was associated with higher rates of dyspnoea, it had no clinically relevant impact on gas exchange at 3000 m at rest and during moderate exercise, and no detectable effect on resting cognitive performance. Wearing a surgical mask or an FFP2 can be considered safe for healthy people living, working or spending their leisure time in mountains, high-altitude cities or other hypobaric environments (e.g. aircrafts) up to an altitude of 3000 m.

Environmental and behavioral regulation of HIF-mitochondria crosstalk

Reduced oxygen availability (hypoxia) can lead to cell and organ damage. Therefore, aerobic species depend on efficient mechanisms to counteract detrimental consequences of hypoxia. Hypoxia inducible factors (HIFs) and mitochondria are integral components of the cellular response to hypoxia and coordinate both distinct and highly intertwined adaptations. This leads to reduced dependence on oxygen, improved oxygen supply, maintained energy provision by metabolic remodeling and tapping into alternative pathways and increased resilience to hypoxic injuries. On one hand, many pathologies are associated with hypoxia and hypoxia can drive disease progression, for example in many cancer and neurological diseases. But on the other hand, controlled induction of hypoxia responses via HIFs and mitochondria can elicit profound health benefits and increase resilience. To tackle pathological hypoxia conditions or to apply health-promoting hypoxia exposures efficiently, cellular and systemic responses to hypoxia need to be well understood. Here we first summarize the well-established link between HIFs and mitochondria in orchestrating hypoxia-induced adaptations and then outline major environmental and behavioral modulators of their interaction that remain poorly understood.

Sex-related Differences in Loop Gain during High-Altitude Sleep-disordered Breathing

Rationale: Central sleep apnea (CSA) is pervasive during sleep at high altitude, disproportionately impacting men and associated with increased peripheral chemosensitivity. Objectives: We aimed to assess whether biological sex affects loop gain (LGn) and CSA severity during sleep over 9-10 days of acclimatization to 3,800 m. We hypothesized that CSA severity would worsen with acclimatization in men but not in women because of greater increases in LGn in men. Methods: Sleep studies were collected from 20 (12 male) healthy participants at low altitude (1,130 m, baseline) and after ascent to (nights 2/3, acute) and residence at high altitude (nights 9/10, prolonged). CSA severity was quantified as the respiratory event index (REI) as a surrogate of the apnea-hypopnea index. LGn, a measure of ventilatory control instability, was quantified using a ventilatory control model fit to nasal flow. Linear mixed models evaluated effects of time at altitude and sex on respiratory event index and LGn. Data are presented as contrast means with 95% confidence intervals. Results: REI was comparable between men and women at acute altitude (4.1 [-9.3, 17.5] events/h; P = 0.54) but significantly greater in men at prolonged altitude (23.7 [10.3, 37.1] events/h; P = 0.0008). Men had greater LGn than did women for acute (0.08 [0.001, 0.15]; P = 0.047) and prolonged (0.17 [0.10, 0.25]; P < 0.0001) altitude. The change in REI per change in LGn was significantly greater in men than in women (107 ± 46 events/h/LGn; P = 0.02). Conclusions: The LGn response to high altitude differed between sexes and contributed to worsening of CSA over time in men but not in women. This sex difference in acclimatization appears to protect females from high altitude-related CSA. These data provide fundamental sex-specific physiological insight into high-altitude acclimatization in healthy individuals and may help to inform sex differences in sleep-disordered breathing pathogenesis in patients with cardiorespiratory disease.

Active ascent accelerates the time course but not the overall incidence and severity of acute mountain sickness at 3,600 m

Acute mountain sickness (AMS) typically peaks following the first night at high altitude (HA) and resolves over the next 2-3 days, but the impact of active ascent on AMS is debated. To determine the impact of ascent conditions on AMS, 78 healthy Soldiers (means ± SD; age = 26 ± 5 yr) were tested at baseline residence, transported to Taos, NM (2,845 m), hiked (n = 39) or were driven (n = 39) to HA (3,600 m), and stayed for 4 days. AMS-cerebral (AMS-C) factor score was assessed at HA twice on day 1 (HA1), five times on days 2 and 3 (HA2 and HA3), and once on day 4 (HA4). If AMS-C was ≥0.7 at any assessment, individuals were AMS susceptible (AMS+; n = 33); others were nonsusceptible (AMS-; n = 45). Daily peak AMS-C scores were analyzed. Ascent conditions (active vs. passive) did not impact the overall incidence and severity of AMS at HA1-HA4. The AMS+ group, however, demonstrated a higher (P < 0.05) AMS incidence in the active vs. passive ascent cohort on HA1 (93% vs. 56%), similar incidence on HA2 (60% vs. 78%), lower incidence (P < 0.05) on HA3 (33% vs. 67%), and similar incidence on HA4 (13% vs. 28%). The AMS+ group also demonstrated a higher (P < 0.05) AMS severity in the active vs. passive ascent cohort on HA1 (1.35 ± 0.97 vs. 0.90 ± 0.70), similar score on HA2 (1.00 ± 0.97 vs. 1.34 ± 0.70), and lower (P < 0.05) score on HA3 (0.56 ± 0.55 vs. 1.02 ± 0.75) and HA4 (0.32 ± 0.41 vs. 0.60 ± 0.72). Active compared with passive ascent accelerated the time course of AMS with more individuals sick on HA1 and less individuals sick on HA3 and HA4.NEW & NOTEWORTHY This research demonstrated that active ascent accelerated the time course but not overall incidence and severity of acute mountain sickness (AMS) following rapid ascent to 3,600 m in unacclimatized lowlanders. Active ascenders became sicker faster and recovered quicker than passive ascenders, which may be due to differences in body fluid regulation. Findings from this well-controlled large sample-size study suggest that previously reported discrepancies in the literature regarding the impact of exercise on AMS may be related to differences in the timing of AMS measurements between studies.

High-altitude cerebral hypoxia promotes mitochondrial dysfunction and apoptosis of mouse neurons

Introduction

Neuronal cell death is an important factor in the pathogenesis of acute high-altitude cerebral hypoxia; however, the underlying molecular mechanism remains unclear. In this study, we tested if high-altitude hypoxia (HAH) causes neuronal death and mitochondrial dysfunction using various in vivo and in vitro approaches.

Methods

Acute high-altitude cerebral hypoxia was induced by hypobaric hypoxia chamber in male mice. we explored the mechanisms of neuronal cell death using immunofluorescence, western blotting, transmission electron microscopy, and flow cytometry. Next, mitochondrial function and morphology were observed using Jc-1 staining, seahorse assay, western blotting, MitoTracker staining, and transmission electron microscopy. Moreover, open field test, elevated plus test, and Morris water maze were applied for animal behavior.

Results

Results revealed that HAH disrupted mitochondrial function and promoted neuronal apoptosis and necroptosis both in HT-22 cells and in mouse hippocampal neurons. Moreover, the mitochondrial membrane potential and adenosine triphosphate production decreased in neurons after HAH, while oxidative stress and mitochondrial fission increased. Behavioral studies suggested that HAH induced anxiety-like behavior and impaired spatial memory, while it had no effect on athletic ability.

Discussion

These findings demonstrated that HAH promotes mitochondrial dysfunction and apoptosis of mouse neurons, thus providing new insights into the role of mitochondrial function and neuronal cell death in acute high-altitude cerebral hypoxia.

Flying to high-altitude destinations: Is the risk of acute mountain sickness greater?

BACKGROUND

Altitude sojourns increasingly attract individuals of all ages and different health statuses due to the appeal of high-altitude destinations worldwide and easy access to air travel. The risk of acute mountain sickness (AMS) when flying to high-altitude destinations remains underemphasized. Thus, this review aims to evaluate the altitude-dependent AMS incidence depending on the mode of ascending, e.g. by air vs terrestrial travel.

METHODS

A literature search was performed to identify the observational studies assessing AMS incidence after acute ascent of primarily healthy adults to real high altitude. In addition, placebo arms of interventional trials evaluating the prophylactic efficacy of various drugs have been separately analysed to confirm or refute the findings from the observational studies. Linear regression analyses were used to evaluate the altitude-dependent AMS incidence.

RESULTS

Findings of 12 observational studies, in which the AMS incidence in 11 021 individuals ascending to 19 different altitudes (2200-4559 m) was evaluated, revealed an impressive 4.5-fold steeper increase in the AMS incidence for air travel as compared with slower ascent modes, i.e. hiking or combined car and/or air travel and hiking. The higher AMS incidence following transportation by flight vs slower means was also confirmed in placebo-treated participants in 10 studies of drug prophylaxis against AMS.

CONCLUSIONS

Due to the short time span in going from low to high altitude, reduced acclimatization likely is the main reason for a higher AMS risk when travelling to high-altitude destinations by flight. To avoid frustrating travel experiences and health risks, appropriate and timely medical advice on how to prepare for air travel to high altitude is of vital importance. Effective preparation options include the use of modern pre-acclimatization strategies and pharmacological prophylaxis by acetazolamide or dexamethasone, or even considering alternate itineraries with more gradual ascent.

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.

Remote ischemic preconditioning improves spatial memory and sleep of young males during acute high-altitude exposure

OBJECTIVE

The high-altitude hypoxia environment will cause poor acclimatization in a portion of the population. Remote ischemic preconditioning（RIPC）has been demonstrated to prevent cardiovascular and cerebrovascular diseases under ischemic or hypoxic conditions. However, its role in improving acclimatization and preventing acute mountain sickness (AMS) at high altitude has been undetermined. This study aims to estimate the effect of RIPC on acclimatization of individuals exposed to high altitude.

METHODS

The project was designed as a randomized controlled trial with 82 healthy young males, who received RIPC training once a day for 7 consecutive days. Then they were transported by aircraft to a high altitude (3680 m) and examined for 6 days. Lake Louise Score(LLS) of AMS, physiological index, self-reported sleep pattern, and Pittsburgh Sleep Quality Index（PSQI）score were applied to assess the acclimatization to the high altitude. Five neurobehavioral tests were conducted to assess cognitive function.

RESULTS

The result showed that the RIPC group had a significantly lower AMSscore than the control group (2.43 ± 1.58 vs 3.29 ± 2.03, respectively; adjusted mean difference-0.84, 95% confidence interval-1.61 to -0.06, P = 0.036). and there was no significant difference in AMS incidence between the two groups (25.0% vs 28.57%, P = 0.555). The RIPC group performed better than the control group in spatial memory span score (11[9-12] vs 10[7.5-11], P=0.025) and the passing digit (7[6-7.5] vs 6[5-7], P= 0.001). Spatial memory was significantly higher in the high-altitude RIPC group than in the low-altitude RIPC group (P＜0.01). And the RIPC group obtained significantly lower self-reported sleep quality score (P = 0.024) and PSQI score (P = 0.031).

CONCLUSIONS

The RIPC treatment improved spatial memory and sleep quality in subjects exposed to acute hypoxic exposure and this may lead to improved performance at high altitude.

Low-dose of caffeine alleviates high altitude pulmonary edema via regulating mitochondrial quality control process in AT1 cells

Backgrounds: High-altitude pulmonary edema (HAPE) is a life-threatening disease without effective drugs. Caffeine is a small molecule compound with antioxidant biological activity used to treat respiratory distress syndrome. However, it is unclear whether caffeine plays a role in alleviating HAPE.

Methods: We combined a series of biological experiments and label-free quantitative proteomics analysis to detect the effect of caffeine on treating HAPE and explore its mechanism in vivo and in vitro.

Results: Dry and wet weight ratio and HE staining of pulmonary tissues showed that the HAPE model was constructed successfully, and caffeine relieved pulmonary edema. The proteomic results of mice lungs indicated that regulating mitochondria might be the mechanism by which caffeine reduced HAPE. We found that caffeine blocked the reduction of ATP production and oxygen consumption rate, decreased ROS accumulation, and stabilized mitochondrial membrane potential to protect AT1 cells from oxidative stress damage under hypoxia. Caffeine promoted the PINK1/parkin-dependent mitophagy and enhanced mitochondrial fission to maintain the mitochondria quality control process.

Conclusion: Low-dose of caffeine alleviated HAPE by promoting PINK1/parkin-dependent mitophagy and mitochondrial fission to control the mitochondria quality. Therefore, caffeine could be a potential treatment for HAPE.

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.

Transcription factors and potential therapeutic targets for pulmonary hypertension

Pulmonary hypertension (PH) is a refractory and fatal disease characterized by excessive pulmonary arterial cell remodeling. Uncontrolled proliferation and hypertrophy of pulmonary arterial smooth muscle cells (PASMCs), dysfunction of pulmonary arterial endothelial cells (PAECs), and abnormal perivascular infiltration of immune cells result in pulmonary arterial remodeling, followed by increased pulmonary vascular resistance and pulmonary pressure. Although various drugs targeting nitric oxide, endothelin-1 and prostacyclin pathways have been used in clinical settings, the mortality of pulmonary hypertension remains high. Multiple molecular abnormalities have been implicated in pulmonary hypertension, changes in numerous transcription factors have been identified as key regulators in pulmonary hypertension, and a role for pulmonary vascular remodeling has been highlighted. This review consolidates evidence linking transcription factors and their molecular mechanisms, from pulmonary vascular intima PAECs, vascular media PASMCs, and pulmonary arterial adventitia fibroblasts to pulmonary inflammatory cells. These findings will improve the understanding of particularly interactions between transcription factor-mediated cellular signaling pathways and identify novel therapies for pulmonary hypertension.

Pregnancy and Exercise in Mountain Travelers

ABSTRACT

Pregnant women are traveling to high altitude and evidence-based recommendations are needed. Yet, there are limited data regarding the safety of short-term prenatal high-altitude exposure. There are benefits to prenatal exercise and may be benefits to altitude exposure. Studies evaluating maternofetal responses to exercise at altitude found the only complication was transient fetal bradycardia, a finding of questionable significance. There are no published cases of acute mountain sickness in pregnant women, and data suggesting an increase in preterm labor are of poor quality. Current recommendations across professional societies are overly cautious and inconsistent. Non-evidence-based restrictions to altitude exposure can have negative consequences for a pregnant women's physical, social, mental, and economic health. Available data suggest that risks of prenatal travel to altitude are low. Altitude exposure is likely safe for women with uncomplicated pregnancies. We do not recommend absolute restrictions to high altitude exposure, but rather caution and close self-monitoring.