Hypoxia-related altitude illnesses

Accelerating healing at high altitudes: Oxygen and bFGF delivery through nanoparticle-loaded gel dressings

High altitude environment is mainly characterized by low oxygen. Due to persistent hypoxia, nonhealing wounds are common in high-altitude areas. Moreover, Basic fibroblast growth factor (bFGF) is a versatile biologically active substance that has crucial impact on wound healing. Given the limited availability of atmospheric oxygen and reduced blood oxygen saturation in high-altitude area, and the challenge that arises from direct oxygen and bFGF delivery to wounds through the traumatized vascular structure, it necessitates an innovative solution for local and permeable delivery of oxygen and bFGF. In this study, we present a strategy that involves revamping traditional gel-based wound dressings through the incorporation of nanoparticles encapsulating oxygen and bFGF, engineered to facilitate the localized delivery of dissolved oxygen and bFGF to wound surfaces. The prospective evaluation of this delivery technique's therapeutic impacts on epithelial, endothelial and fibroblasts cells can be materialized. Further experiment corroborated these effects on a high-altitude wounds' murine model. Given its biocompatibility, efficacy, and utility, we posit that NOB-Gel exhibits remarkable translational potential for managing and hastening the healing process of an array of clinical wounds, more so for wounds inflicted at high altitudes.

Intertwined regulators: hypoxia pathway proteins, microRNAs, and phosphodiesterases in the control of steroidogenesis

Oxygen sensing is of paramount importance for maintaining cellular and systemic homeostasis. In response to diminished oxygen levels, the hypoxia-inducible factors (HIFs) orchestrate various biological processes. These pivotal transcription factors have been identified as key regulators of several biological events. Notably, extensive research from our group and others has demonstrated that HIF1α exerts an inverse regulatory effect on steroidogenesis, leading to the suppression of crucial steroidogenic enzyme expression and a subsequent decrease in steroid levels. These steroid hormones occupy pivotal roles in governing a myriad of physiological processes. Substantial or prolonged fluctuations in steroid levels carry detrimental consequences across multiple organ systems and underlie various pathological conditions, including metabolic and immune disorders. MicroRNAs serve as potent mediators of multifaceted gene regulatory mechanisms, acting as influential epigenetic regulators that modulate a broad spectrum of gene expressions. Concomitantly, phosphodiesterases (PDEs) play a crucial role in governing signal transduction. PDEs meticulously manage intracellular levels of both cAMP and cGMP, along with their respective signaling pathways and downstream targets. Intriguingly, an intricate interplay seems to exist between hypoxia signaling, microRNAs, and PDEs in the regulation of steroidogenesis. This review highlights recent advances in our understanding of the role of microRNAs during hypoxia-driven processes, including steroidogenesis, as well as the possibilities that exist in the application of HIF prolyl hydroxylase (PHD) inhibitors for the modulation of steroidogenesis.

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.

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.

Effects of acute exposure to hypoxia on sleep structure in healthy adults: A systematic review

The sleep quality of lowlanders in hypoxic environments has become increasingly important with an increase in highland and alpine activities. This study aimed to identify the effects of acute exposure to hypoxia on the sleep structure of lowlanders and to analyze the changes in sleep indicators at varying levels of hypoxia. This review was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Twenty-three studies were screened and included in the quantitative analysis. The results showed that acute exposure to hypoxia reduced sleep quality in lowlanders. Post-sleep arousal events and the percentage of N1 were significantly increased, whereas total sleep time, sleep efficiency, and the percentage of N3 and rapid eye movement sleep were significantly decreased in hypoxic environments. Acute exposure to hypoxia had the greatest negative impact on wakefulness after sleep onset (WASO). In addition, a larger decrease in sleep efficiency and higher increase in the percentages of N1 and WASO were observed when lowlanders were exposed to higher levels of hypoxia. This study clarifies the quantitative effects of acute hypoxic exposure on sleep in lowlanders based on original studies and explains the sleep disorders faced by lowlanders in hypoxic environments.

Contrast-free dynamic susceptibility contrast using sinusoidal and bolus oxygenation challenges

Deoxygenation-based dynamic susceptibility contrast (dDSC) MRI uses respiratory challenges as a source of endogenous contrast as an alternative to gadolinium injection. These gas challenges induce T2*-weighted MRI signal losses, after which tracer kinetics modeling was applied to calculate cerebral perfusion. This work compares three gas challenges, desaturation (transient hypoxia), resaturation (transient normoxia), and SineO2 (sinusoidal modulation of end-tidal oxygen pressures) in a cohort of 10 healthy volunteers (age 37 ± 11 years; 60% female). Perfusion estimates consisted of cerebral blood flow (CBF), cerebral blood volume (CBV), and mean transit time (MTT). Calculations were computed using a traditional tracer kinetics model in the time domain for desaturation and resaturation and in the frequency domain for SineO2. High correlations and limits of agreement were observed among the three deoxygenation-based paradigms for CBV, although MTT and CBF estimates varied with the hypoxic stimulus. Cross-modality correlation with gadolinium DSC was lower, particularly for MTT, but on a par with agreement between the other perfusion references. Overall, this work demonstrated the feasibility and reliability of oxygen respiratory challenges to measure brain perfusion. Additional work is needed to assess the utility of dDSC in the diagnostic evaluation of various pathologies such as ischemic strokes, brain tumors, and neurodegenerative diseases.

The cardiovascular system at high altitude: A bibliometric and visualization analysis

BACKGROUND

When exposed to high-altitude environments, the cardiovascular system undergoes various changes, the performance and mechanisms of which remain controversial.

AIM

To summarize the latest research advancements and hot research points in the cardiovascular system at high altitude by conducting a bibliometric and visualization analysis.

METHODS

The literature was systematically retrieved and filtered using the Web of Science Core Collection of Science Citation Index Expanded. A visualization analysis of the identified publications was conducted employing CiteSpace and VOSviewer.

RESULTS

A total of 1674 publications were included in the study, with an observed annual increase in the number of publications spanning from 1990 to 2022. The United States of America emerged as the predominant contributor, while Universidad Peruana Cayetano Heredia stood out as the institution with the highest publication output. Notably, Jean-Paul Richalet demonstrated the highest productivity among researchers focusing on the cardiovascular system at high altitude. Furthermore, Peter Bärtsch emerged as the author with the highest number of cited articles. Keyword analysis identified hypoxia, exercise, acclimatization, acute and chronic mountain sickness, pulmonary hypertension, metabolism, and echocardiography as the primary research hot research points and emerging directions in the study of the cardiovascular system at high altitude.

CONCLUSION

Over the past 32 years, research on the cardiovascular system in high-altitude regions has been steadily increasing. Future research in this field may focus on areas such as hypoxia adaptation, metabolism, and cardiopulmonary exercise. Strengthening interdisciplinary and multi-team collaborations will facilitate further exploration of the pathophysiological mechanisms underlying cardiovascular changes in high-altitude environments and provide a theoretical basis for standardized disease diagnosis and treatment.

Hypoxic preacclimatization combining intermittent hypoxia exposure with physical exercise significantly promotes the tolerance to acute hypoxia

Background: Both hypoxia exposure and physical exercise before ascending have been proved to promote high altitude acclimatization, whether the combination of these two methods can bring about a better effect remains uncertain. Therefore, we designed this study to evaluate the effect of hypoxic preacclimatization combining intermittent hypoxia exposure (IHE) and physical exercise on the tolerance to acute hypoxia and screen the optimal preacclimatization scheme among the lowlanders. Methods: A total of 120 Han Chinese young men were enrolled and randomly assigned into four groups, including the control group and three experimental groups with hypoxic preacclimatization of 5-day rest, 5-day exercise, and 3-day exercise in a hypobaric chamber, respectively. Main physical parameters for hypoxia acclimatization, AMS incidence, physical and mental capacity were measured for each participant in the hypobaric chamber simulated to the altitude of 4500 m in the effect evaluation stage. The effect was compared between different schemes. Results: During the effect evaluation stage, SpO2 of the 5-day rest group and 5-day exercise group was significantly higher than that of the control group (p = 0.001 and p = 0.006, respectively). The participants with 5-day rest had significantly lower HR than the controls (p = 0.018). No significant differences of AMS incidence were found among the four groups, while the proportion of AMS headache symptom (moderate and severe vs. mild) was significantly lower in the 3-day exercise group than that in the control group (p = 0.002). The 5-day exercise group had significantly higher VO2max, than the other three groups (p = 0.033, p < 0.001, and p = 0.023, respectively). The 5-day exercise group also had significantly higher digital symbol and pursuit aiming test scores, while shorter color selection reaction time than the control group (p = 0.005, p = 0.005, and p = 0.004, respectively). Conclusion: Hypoxic preacclimatization combining IHE with physical exercise appears to be efficient in promoting the tolerance to acute hypoxia. Hypoxia duration and physical exercise of moderate intensity are helpful for improvement of SpO2 and HR, relief of AMS headache symptoms, and enhancement of mental and physical operation capacity.

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.

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.

Efficacy of Sildenafil on healthy humans in high‑altitude hypoxia at rest and during exercise: A meta‑analysis

The current meta-analysis aimed to fully evaluate the efficacy of Sildenafil in healthy humans at different altitudes, focusing on echocardiographic and hemodynamic parameters. Relevant studies were retrieved from the Cochrane, Embase and PubMed databases. Odds ratios (OR) were determined for dichotomous data and weighted mean differences with 95% confidence intervals (CIs) for continuous data. A total of 16 RCTs were included in the current meta-analysis. Short-term treatment with Sildenafil significantly elevated resting heart rate (P<0.01) at altitudes <4,000 meters. No significant differences in heart rate were observed between the Sildenafil and placebo groups at rest and during exercise at an altitude of >4,000 meters (P>0.05). Sildenafil improved resting cardiac output at an altitude of >5,000 meters (P<0.01) and exercising arterial oxygen saturation at <4,000 meters (P<0.01). Sildenafil reduced resting pulmonary artery systolic pressure (PASP) at altitudes >4,000 meters (P<0.01) and exercising PASP at altitudes >5,000 meters (P<0.01). Therefore, Sildenafil efficacy in healthy humans with high-altitude hypoxia is related to altitude and rest or exercise.

Nanocurcumin attenuates pyroptosis and inflammation through inhibiting NF-κB/GSDMD signal in high altitude-associated acute liver injury

Exposure to a hypobaric hypoxic environment at high altitudes can lead to liver injury, and mounting evidence indicates that pyroptosis and inflammation play important roles in liver injury. Curcumin (Cur) can inhibit pyroptosis and inflammation. Therefore, our purpose here was to clarify the mechanism underlying the protective effect of nanocurcumin (Ncur) and Cur in a rat model of high altitude-associated acute liver injury. Eighty healthy rats were selected and exposed to different altitudes (6000 or 7000 m) for 0, 24, 48, or 72 h. Fifty normal healthy rats were divided into normal control, high-altitude control, salidroside (40 mg/kg [Sal-40]), Cur (200 mg/kg [Cur-200]), and Ncur (25 mg/kg [Ncur-25]) groups and exposed to a high-altitude hypobaric hypoxic environment (48 h, 7000 m). Serum-liver enzyme activities (alanine transaminase, aspartate transaminase, and lactate dehydrogenase were detected and histopathology of liver injury was evaluated by hematoxylin and eosin staining, and inflammatory factors were detected in liver tissues by enzyme-linked immunosorbent assays. Pyroptosis-associated proteins (gasdermin D, gasdermin D N-terminal [GSDMD-N], pro-Caspase-1, and cleaved-Caspase-1 [cleaved-Casp1]) and inflammation-associated proteins (nuclear factor-κB [NF-κB], phospho-NF-κB [P-NF-κB], and high-mobility group protein B1 [HMGB1]) levels were analyzed by immunoblotting. Ncur and Cur inhibited increased serum-liver enzyme activities, alleviated liver injury in rats caused by high-altitude hypobaric hypoxic exposure, and downregulated inflammatory factors, including tumor necrosis factor-α, interleukin (IL)-1β, IL-6, and IL-18, in rat liver tissues. The level of P-NF-κB, GSDMD-N, cleaved-Casp1, and HMGB1 in rat liver tissues increased significantly after high-altitude exposure. Ncur and Cur downregulated P-NF-κB, GSDMD-N, cleaved-Casp-1, and HMGB1. Ncur and Cur may inhibit inflammatory responses and pyroptosis in a rat model of high altitude-associated acute liver injury.

Impression life with pulmonary hypertension: clinically relevant characteristics and quality of life among patients in Gansu, China

BACKGROUND

The adverse effects of pulmonary arterial hypertension (PAH) on physical, emotional, and health-related quality of life (HRQoL) remain primarily unrecognized, especially in resource-limited settings.

OBJECTIVES

This study aims to characterize the HRQoL of patients with PAH in this area and also identify the potential role of clinically relevant characteristics, including the 6-min walk distance test (6MWD), WHO-Functional Classification (WHO-FC), and mental health in the occurrence of lowering quality of life.

DESIGN

This was a cross-sectional observational study.

METHODS

Inpatients with PAH were chosen from a tertiary hospital located in Gansu province, China. All participants were interviewed face-by-face by using questionnaires, including items from the 36-Item Short Form Health Survey (SF-36), the self-rating anxiety scale, and the self-rating depression scale. Data on demographic and clinically relevant characteristics, including WHO-FC and 6MWD, were also collected by tracing medical recorders. Multiple linear regression analysis was used to determine the association between demographic, clinically relevant characteristics data, and physical component summary (PCS) or mental component summary (MCS) in SF-36.

RESULTS

Of the 152 participants, SF-36 differed significantly from Chinese norms in all eight domains, with role-physical (21.55 ± 9.87) less than one-third of the norm (88.79 ± 28.49). Multiple linear regression results showed that the factors with the greatest impact on PCS were anxiety scores (β = -0.22, p = 0.001), followed by WHO-FC (β = -0.16, p = 0.014) and 6MWD (β = 0.15, p = 0.036). The factors with the greatest impact on MCS were WHO-FC (β = -0.30, p < 0.001), followed by anxiety (β = -0.23, p = 0.001) and depression scores (β = -0.16, p = 0.013).

CONCLUSION

HRQoL was substantially reduced among PAH patients in the resource-limited area, mainly the physiological functions. WHO-FC and anxiety scores were independently associated with both PCS and MCS in SF-36. Clinicians should make reasonable rehabilitation programs and plans for patients according to their cardiac function grade and the severity of clinical symptoms. In addition, psychological interventions should also be taken, especially for those with anxiety symptoms, so as to improve their HRQoL.

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.

Prevalence and Determinants of Delay in Time-to-Diagnosis for Pulmonary Arterial Hypertension Patients in Gansu China: A Observational Cohort Study

Current studies of patients with pulmonary arterial hypertension (PAH) have shown a significant diagnostic delay. However, the causes and risk factors for this delay are not been well explored in Chinese population. This study aimed to assess the status of diagnostic delay in patients with PAH in China. Additionally, we identified factors associated with the delay. Demographic and clinical data were collected from 153 PAH patients admitted to three tertiary hospitals in Gansu, China, from March 2020 to October 2022. Based on the recorded date, the diagnostic delay was divided into patient delay and health system delay. For analysis, we divided diagnostic delay into 2 groups (≤3 years and >3 years). Factors associated with delay were identified by binary logistic regression. The median diagnostic delay was 3 years (IQR: 0.25-5.88). Binary logistic regression analysis showed that male (OR = 2.48, 95% CI: 1.10-5.58), those with junior high school or below (OR = 3.65, 95% CI: 1.36-9.78), living far away from the tertiary hospital (OR = 2.66, 95% CI: 1.14-6.18), initially visit hospital before 2018 (OR = 3.82, 95% CI: 1.68-8.71), and visit hospital at county level or below (OR = 3.80, 95% CI: 1.42-10.18) were risk factor for diagnostic delay (>3 years). Despite increased awareness, most patients with PAH in Gansu, China still experienced a delay in diagnosis of more than 3 years. Male sex, lower educational background, and being away from tertiary hospitals are risk factors for delay. Furthermore, factors impacting time-to-diagnosis and its impact should be continuously evaluated as therapeutic strategies continue to evolve and improve.

Health-related quality of life and its changes of the Tibetan population in China: based on the 2013 and 2018 National Health Services Surveys

OBJECTIVE

Health-related quality of life (HRQoL) was an important health outcome measure for evaluating an individual's overall health status. However, there was limited in the literature on HRQoL and its long-term changes of the Tibetan population. This study aimed to assess HRQoL of Tibetan and its changes over time, and explore the differences in HRQoL for residents at different altitudes.

DESIGN

Data for the cross-sectional study were extracted from the fifth and sixth waves of the National Health Services Surveys which were conducted in 2013 and 2018. A multistage stratified cluster random sampling strategy was used to select representative participants.

SETTING

Tibet Autonomous Region in China.

PARTICIPANTS

This study recruited 14 752 participants in 2013 and 13 106 participants in 2018, and after excluding observations with missing values for key variables, 10 247 in 2013 and 6436 in 2018 were included in the study analysis.

PRIMARY AND SECONDARY OUTCOME MEASURES

The EQ-5D-3L was used to measure participants' HRQoL.

RESULTS

The mean health state utility scores of the participants were 0.969±0.078 and 0.966±0.077 in 2013 and 2018, respectively. Pain/discomfort was the most frequently prevalent issue reported in 18.1% and 17.9% of the participants in 2013 and 2018, respectively. Tibetans living 3500-4000 m altitude had the best HRQoL. Age, sex, employment status, educational attainment, chronic disease and weekly physical exercise were influencing factors associated with HRQoL.

CONCLUSIONS

The HRQoL of the Tibetan population was lower than the general Chinese population, and decreased over time between 5 years. There were differences in HRQoL among Tibetan at different altitudes, with residents living at 3500-4000 m having the best quality of life. More attention should be paid to those Tibetans who are older, female, unemployed and without formal education.

Prevalence and risk factors of stroke in high-altitude areas: a systematic review and meta-analysis

OBJECTIVE

The primary objective of this study is to investigate the prevalence and risk factors of stroke in high-altitude areas through a comprehensive systematic review and meta-analysis.

DESIGN

This study adopts a systematic review and meta-analysis design.

DATA SOURCES

A thorough search was conducted on databases including PubMed, Web of Science, Embase, Cochrane Library, MEDLINE and SCOPUS, covering the period up to June 2023.

ELIGIBILITY CRITERIA

Studies reporting the prevalence of stroke in high-altitude areas and exploring related risk factors were included, regardless of whether they involved clinical samples or the general population. Studies with incomplete, outdated or duplicate data were excluded.

DATA EXTRACTION AND SYNTHESIS

We performed eligibility screening, data extraction and quality evaluation of the retrieved articles. Meta-analysis was employed to estimate the prevalence and risk factors of stroke in high-altitude areas. The Newcastle-Ottawa Scale was used to assess the risk of bias.

RESULTS

A total of 17 studies encompassing 8 566 042 participants from four continents were included, with altitudes ranging from 1500 m to nearly 5000 m. The pooled prevalence of stroke in high-altitude areas was found to be 0.5% (95% CI 0.3%-7%). Notably, the prevalence was higher in clinical samples (1.2%; 0.4%-2.5%) compared with the general population (0.3%; 95% CI 0.1%-0.6%). When considering geographic regions, the aggregated data indicated that stroke prevalence in the Eurasia plate was 0.3% (0.2%-0.4%), while in the American region, it was 0.8% (0.4%-1.3%). Age (OR, 14.891), gender (OR, 1.289), hypertension (OR, 3.158) and obesity (OR, 1.502) were identified as significant risk factors for stroke in high-altitude areas.

CONCLUSIONS

The findings of this study provide insights into the pooled prevalence of stroke in high-altitude areas, highlighting variations based on geographic regions and sampling type. Moreover, age, gender, hypertension and obesity were found to be associated with the occurrence of stroke.

PROSPERO REGISTRATION NUMBER

CRD42022381541.

High Altitude Pulmonary Edema, High Altitude Cerebral Edema, and Acute Mountain Sickness: an enhanced opinion from the High Andes - La Paz, Bolivia 3,500 m

Traveling to high altitudes for entertainment or work is sometimes associated with acute high altitude pathologies. In the past, scientific literature from the lowlander point of view was primarily based on mountain climbing. Sea level scientists developed all guidelines, but they need modifications for medical care in high altitude cities. Acute Mountain Sickness, High Altitude Pulmonary Edema, and High Altitude Cerebral Edema are medical conditions that some travelers can face. We present how to diagnose and treat acute high altitude pathologies, based on 51 years of high altitude physiology research and medical practice in hypobaric hypoxic diseases in La Paz, Bolivia (3,600 m; 11,811 ft), at the High Altitude Pulmonary and Pathology Institute (HAPPI - IPPA). These can occasionally present after flights to high altitude cities, both in lowlanders or high-altitude residents during re-entry. Acute high altitude ascent diseases can be adequately diagnosed and treated in high altitude cities following the presented guidelines. Treating these high-altitude illnesses, we had no loss of life. Traveling to a high altitude with sound medical advice should not be feared as it has many benefits. Nowadays, altitude descent and evacuation are not mandatory in populated highland cities, with adequate medical resources.

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.

High-altitude cerebral edema manifesting as T2/FLAIR hyperintensity and microbleeds in the white matter on MRI brain

High-altitude cerebral edema is a rare type of acute mountain illness characterized by consciousness disruption and truncal ataxia. Here we discuss a 40-year-old nondiabetic, nonsmoker male who went on a tour to Nanga Parbat. On returning home, the patient developed symptoms of headache, nausea, and vomiting. His symptoms worsened with time and he developed lower limb weakness and shortness of breath. Later, he underwent a computerized tomography chest scan. On the basis of CT scan findings, the doctors decided that the patient was suffering from COVID-19 Pneumonia despite having negative COVID-19 PCR tests multiple times. Later, the patient presented to our hospital with similar complaints. MRI of the brain revealed T2/fluid-attenuated inversion recovery hyperintense and T1 hypointense signals in the bilateral semioval centrum, posterior periventricular white matter, and corpus callosum genu, body, and splenium. These abnormal signals were discovered to be more evident in the corpus callosum's splenium. Moreover, susceptibility-weighted imaging revealed micro hemorrhages in the corpus callosum. This verified the diagnosis that the patient is suffering from high-altitude cerebral edema. Within 5 days, his symptoms resolved and he was discharged with full recovery.

Retinal microvasculature is a potential biomarker for acute mountain sickness

Increased cerebral blood flow resulting from altered capillary level autoregulation at high altitudes leads to capillary overperfusion and then vasogenic cerebral edema, which is the leading hypothesis of acute mountain sickness (AMS). However, studies on cerebral blood flow in AMS have been mostly restricted to gross cerebrovascular endpoints as opposed to the microvasculature. This study aimed to investigate ocular microcirculation alterations, the only visualized capillaries in the central neural system (CNS), during early-stage AMS using a hypobaric chamber. This study found that after high altitude simulation, the optic nerve showed retinal nerve fiber layer thickening (P=0.004-0.018) in some locations, and the area of the optic nerve subarachnoid space (P=0.004) enlarged. Optical coherence tomography angiography (OCTA) showed increased retinal radial peripapillary capillary (RPC) flow density (P=0.003-0.046), particularly on the nasal side of the nerve. The AMS-positive group had the largest increases in RPC flow density in the nasal sector (AMS-positive, Δ3.21±2.37; AMS-negative, Δ0.01±2.16, P=0.004). Among multiple ocular changes, OCTA increase in RPC flow density was associated with simulated early-stage AMS symptoms (beta=0.222, 95%CI, 0.009-0.435, P=0.042). The area under the receiver operating characteristics curve (AUC) for the changes in RPC flow density to predict early-stage AMS outcomes was 0.882 (95%CI, 0.746-0.998). The results further confirmed that overperfusion of microvascular beds is the key pathophysiologic change in early-stage AMS. RPC OCTA endpoints may serve as a rapid, noninvasive potential biomarker for CNS microvascular changes and AMS development during risk assessment of individuals at high altitudes.

A bibliometric analysis of the studies in high-altitude induced sleep disturbances and cognitive impairment research

Background: The two main symptoms at high altitude, sleep abnormalities and cognitive impairments, interact with each other. These two dysfunctions are also closely related to systemic multisystem diseases, including cerebrovascular diseases, psychiatric disorders, and immune regulatory diseases. Purpose: To systematically analyze and visualize research on sleep disturbances and cognitive impairment at high altitudes using a bibliometrics method, and to determine future research directions by analyzing research trends and the latest hotspots. Methods: Publications from 1990 to 2022 on sleep disturbances and cognitive impairment at high altitudes were retrieved from the Web of Science. Using the R Bibliometrix software and Microsoft Excel, all data were examined statistically and qualitatively. For network visualization, the data were later exported into VOSviewer 1.6.17 and CiteSpace 6.1.R6. Results: A total of 487 articles in this area were published from 1990 to 2022. In this period, there was an overall increase in the number of publications. The United States has shown considerable importance in this sector. Bloch Konrad E was the most prolific and valuable author. The most prolific journal was High Altitude Medicine & Biology, and it has been the first choice for publishing in this field in recent years. Analysis of keyword co-occurrences suggested that research interest in the clinical manifestations of sleep disturbances and cognitive impairment caused by altitude hypoxia was mainly focused on "acute mountain-sickness," "insomnia," "apnea syndrome," "depression," "anxiety," "Cheyne-strokes respiration," and "pulmonary hypertension." The mechanisms of disease development related to "oxidative stress," "inflammation," "hippocampus," "prefrontal cortex," "neurodegeneration," and "spatial memory" in the brain have been the focus of recent research. According to burst detection analysis, "mood" and "memory impairment," as terms with high strength, are expected to remain hot topics in the coming years. High-altitude-induced pulmonary hypertension is also in the emerging stage of research, and the treatments will continue to receive attention in the future. Conclusion: More attention is being focused on sleep disturbances and cognitive impairment at high altitudes. This work will serve as a useful reference for the clinical development of treatments for sleep disturbances and cognitive impairment induced by hypobaric hypoxia at high altitudes.

Withaferin A Enhances Mitochondrial Biogenesis and BNIP3-Mediated Mitophagy to Promote Rapid Adaptation to Extreme Hypoxia

Rapid adaptation to extreme hypoxia is a challenging problem, and there is no effective scheme to achieve rapid adaptation to extreme hypoxia. In this study, we found that withaferin A (WA) can significantly reduce myocardial damage, maintain cardiac function, and improve survival in rats in extremely hypoxic environments. Mechanistically, WA protects against extreme hypoxia by affecting BCL2-interacting protein 3 (BNIP3)-mediated mitophagy and the peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α)-mediated mitochondrial biogenesis pathway among mitochondrial quality control mechanisms. On the one hand, enhanced mitophagy eliminates hypoxia-damaged mitochondria and prevents the induction of apoptosis; on the other hand, enhanced mitochondrial biogenesis can supplement functional mitochondria and maintain mitochondrial respiration to ensure mitochondrial ATP production under acute extreme hypoxia. Our study shows that WA can be used as an effective drug to improve tolerance to extreme hypoxia.

Changes in the Gut Microbiota of Rats in High-Altitude Hypoxic Environments

This study was conducted to investigate the effects of high-altitude hypoxic environments on the gut microbiota. Male Sprague-Dawley rats were randomly divided into three groups, namely, the plain, moderate-altitude hypoxic, and high-altitude hypoxic groups. On the 3rd, 7th, 15th, and 30th days of exposure, fecal samples were collected and analyzed via 16S rRNA gene sequencing technology. Fecal microbiota transplantation (FMT) experiments were also performed. The results showed significant differences between the gut microbiota structure and diversity of rats in the high-altitude hypoxic group and those of rats in the other groups. Further, compared with that of rats in the plain group, the gut microbiota of rats in the two hypoxic groups showed the most significant changes on day 7. Furthermore, the gut microbiota of the rats in the FMT groups exhibited changes and became increasingly similar to those of the rats in the hypoxic groups. We also identified the phylum Firmicutes, genus Akkermansia, and genus Lactobacillus as the core microbiota under hypoxic conditions. Phenotypic analysis indicated a decrease in the proportion of aerobic bacteria and an increase in that of anaerobic bacteria, possibly owing to the high-altitude hypoxic environment. Additionally, functional analysis showed significant differences between the different groups with respect to different metabolic pathways, including carbohydrate metabolism, energy metabolism, glycan biosynthesis, and metabolism. These findings indicated significant changes in gut microbiota structure and diversity under high-altitude hypoxia, establishing a foundation for further research on the pathogenesis and development of diseases, as well as drug metabolism, under high-altitude hypoxia. IMPORTANCE In this study, we investigated the effects of high-altitude hypoxic environments with low oxygen levels on the gut microbiota characteristics of rats. We observed that high-altitude hypoxia is an important environmental factor that can affect gut microbiota structure and diversity, thereby affecting homeostasis in the host intestinal environment. These findings provide a basis for further studies on disease initiation and development, as well as drug metabolism, in high-altitude hypoxic environments.

Effects of Acute Exposure and Acclimatization to High-Altitude on Oxygen Saturation and Related Cardiorespiratory Fitness in Health and Disease

Maximal values of aerobic power (VO₂max) and peripheral oxygen saturation (SpO₂max) decline in parallel with gain in altitude. Whereas this relationship has been well investigated when acutely exposed to high altitude, potential benefits of acclimatization on SpO₂ and related VO₂max in healthy and diseased individuals have been much less considered. Therefore, this narrative review was primarily aimed to identify relevant literature reporting altitude-dependent changes in determinants, in particular SpO₂, of VO₂max and effects of acclimatization in athletes, healthy non-athletes, and patients suffering from cardiovascular, respiratory and/or metabolic diseases. Moreover, focus was set on potential differences with regard to baseline exercise performance, age and sex. Main findings of this review emphasize the close association between individual SpO₂ and VO₂max, and demonstrate similar altitude effects (acute and during acclimatization) in healthy people and those suffering from cardiovascular and metabolic diseases. However, in patients with ventilatory constrains, i.e., chronic obstructive pulmonary disease, steep decline in SpO₂ and V̇O₂max and reduced potential to acclimatize stress the already low exercise performance. Finally, implications for prevention and therapy are briefly discussed.

Resetting Proteostasis of CIRBP with ISRIB Suppresses Neural Stem Cell Apoptosis under Hypoxic Exposure

Neurological disorders are often progressive and lead to disabilities with limited available therapies. Epidemiological evidence implicated that prolonged exposure to hypoxia leads to neurological damage and a plethora of complications. Neural stem cells (NSCs) are a promising tool for neurological damage therapy in terms of their unique properties. However, the literature on the outcome of NSCs exposed to severe hypoxia is scarce. In this study, we identified a responsive gene that reacts to multiple cellular stresses, marked cold-inducible RNA-binding protein (CIRBP), which could attenuate NSC apoptosis under hypoxic pressure. Interestingly, ISRIB, a small-molecule modulator of the PERK-ATF4 signaling pathway, could prevent the reduction and apoptosis of NSCs in two steps: enhancing the expression of CIRBP through the protein kinase R- (PKR-) like endoplasmic reticulum kinase (PERK) and activating transcription factor 4 (ATF4) axis. Taken together, CIRBP was found to be a critical factor that could protect NSCs against apoptosis induced by hypoxia, and ISRIB could be acted upstream of the axis and may be recruited as an open potential therapeutic strategy to prevent or treat hypoxia-induced brain hazards.

International society of sports nutrition position stand: tactical athlete nutrition

This position stand aims to provide an evidence-based summary of the energy and nutritional demands of tactical athletes to promote optimal health and performance while keeping in mind the unique challenges faced due to work schedules, job demands, and austere environments. After a critical analysis of the literature, the following nutritional guidelines represent the position of the International Society of Sports Nutrition (ISSN).

General Recommendations

Nutritional considerations should include the provision and timing of adequate calories, macronutrients, and fluid to meet daily needs as well as strategic nutritional supplementation to improve physical, cognitive, and occupational performance outcomes; reduce risk of injury, obesity, and cardiometabolic disease; reduce the potential for a fatal mistake; and promote occupational readiness.

Military Recommendations

Energy demands should be met by utilizing the Military Dietary Reference Intakes (MDRIs) established and codified in Army Regulation 40-25. Although research is somewhat limited, military personnel may also benefit from caffeine, creatine monohydrate, essential amino acids, protein, omega-3-fatty acids, beta-alanine, and L-tyrosine supplementation, especially during high-stress conditions.

First Responder Recommendations

Specific energy needs are unknown and may vary depending on occupation-specific tasks. It is likely the general caloric intake and macronutrient guidelines for recreational athletes or the Acceptable Macronutrient Distribution Ranges for the general healthy adult population may benefit first responders. Strategies such as implementing wellness policies, setting up supportive food environments, encouraging healthier food systems, and using community resources to offer evidence-based nutrition classes are inexpensive and potentially meaningful ways to improve physical activity and diet habits. The following provides a more detailed overview of the literature and recommendations for these populations.

Poor Knowledge of Acute Mountain Sickness in Latin American Medical Students

INTRODUCTION

Acute altitude exposure is a common event in Latin America that can result in mild to severe altitude illness. Medical students from some Latin American countries receive little information on this topic. Our aim was to determine the knowledge and incidence of acute mountain sickness (AMS), as well as the methods used to prevent AMS among medical students attending the Pan-American Student Meeting in Cusco, Peru, a city at high altitude (3400 m).

METHODS

We conducted a cross-sectional study on medical students attending a conference. Participants completed a questionnaire on the day of registration that collected demographic data and investigated students' knowledge of AMS, its prophylaxis, and their personal experience of symptoms.

RESULTS

A total of 840 students attended the meeting. Two hundred eighty-eight returned surveys, 51 from high altitude locations. Respondent age was 23±3 y (mean±SD), and 72% were female. Thirty-two percent had basic knowledge about symptoms of AMS. Headache was recognized as a symptom by 79%. Knowledge of AMS prophylaxis was reported by 70%. Coca leaf products and dimenhydrinate were mentioned by 30 and 16%, respectively, whereas acetazolamide was recognized by only 10% of participants. AMS incidence was 42%. Prophylactic measures were adopted by 47% of the participants in our study. Thirty-six percent used dimenhydrinate and 27% used coca tea. Less than 1% used acetazolamide as recommended.

CONCLUSIONS

We found poor knowledge of AMS and effective prophylaxis among medical students from several South American countries traveling to 3400 m.

Clinical characteristics and mortality associated with COVID-19 at high altitude: a cohort of 5161 patients in Bogotá, Colombia

Background

There are few data on the clinical outcomes of patients with coronavirus disease 2019 (COVID-19) in cities over 1000 m above sea level (masl).

Objectives

To describe the clinical characteristics and mortality of patients with COVID-19 treated at a high complexity hospital in Bogotá, Colombia, at 2640 masl.

Methods

This was an observational study of a cohort including 5161 patients with confirmed COVID-19 infection from 19 March 2020 to 30 April 2021. Demographic data, laboratory values, comorbidities, oxygenation indices, and clinical outcomes were collected. Data were compared between survivors and nonsurvivors. An independent predictive model was performed for mortality and invasive mechanical ventilation (IMV) using classification and regression trees (CART).

Results

The median cohort age was 66 years (interquartile range (IQR) 53–77), with 1305 patients dying (25%) and 3856 surviving (75%). The intensive care unit (ICU) received 1223 patients (24%). Of 898 patients who received IMV, 613 (68%) of them perished. The ratio of partial pressure arterial oxygen (PaO₂) to fraction inspired oxygen (FiO₂), or the P/F ratio, upon ICU admission was 105 (IQR 77–146) and 137 (IQR 91–199) in the deceased and survivors, respectively. The CART model showed that the need for IMV, age greater than 79 years, ratio of oxygen saturation (SaO₂) to FiO₂, or the S/F ratio, less than 259, and lactate dehydrogenase (LDH) greater than 617 U/L at admission were associated with a greater probability of death.

Conclusion

Among more than 5000 patients with COVID-19 treated in our hospital, mortality at hospital discharge was 25%. Older age, low S/F ratio, and high LDH at admission were predictors of mortality.

Salidroside attenuates high altitude hypobaric hypoxia-induced brain injury in mice via inhibiting NF-κB/NLRP3 pathway

Salidroside (Sal), an active ingredient from Rhodiola crenulate, has been reported to exert neuroprotection in cerebral injury from hypobaric hypoxia (HH) at high altitude. However, it remains to be understood whether its protective effects are related to inflammation suppression. In the present work, we aimed to reveal the mechanism of Sal attenuating HH-induced brain injury in mice caused by an animal hypobaric and hypoxic chamber. Our results provided that Sal could attenuate HH-evoked pathological injury and oxidative stress response by decreasing the content of ROS and MDA, and elevating the activities of SOD and GSH-Px. Sal treatment could partly enhance the energy metabolism, evidenced by increasing the activities of Na⁺-K⁺-ATPase, Ca²⁺-Mg²⁺-ATPase, ATP, SDH, HK and PK, while decreasing the release of LDH and LD. Meanwhile, Sal administration reversed the degradation of tight junction proteins ZO-1, Occludin and Claudin-5. Further, the increased levels of TNF-α, IL-1β and IL-6 were confined with Sal administration under the HH condition. Importantly, Sal could downregulate the proteins expression of p-NF-κB-p65, NLRP3, cleaved-Caspase-1 and ASC. Sal also decreased the protein expression of iNOS and COX2 with the increased CD206 and Arg1 expression. Taken together, these data provided that the inhibited NF-κB/NLRP3 pathway by Sal could attenuate HH-induced cerebral oxidative stress injury, inflammatory responses and the blood brain barrier (BBB) damage, attributing to the improved energy metabolism and the microglial phenotype of anti-inflammatory M2. The findings suggested that Sal was expected to be a promising anti-inflammatory agent for high altitude HH-induced brain injury.

Evaluation of Potential for Nature-Based Recreation in the Qinghai-Tibet Plateau: A Spatial-Temporal Perspective

Nature-based recreation (NBR) is an important cultural ecosystem service providing human well-being from natural environments. As the most concentrated and high-quality wilderness in China, the Qinghai-Tibet Plateau (QTP) has unique advantages for NBR. In this study, we designed an integrated nature-based recreation potential index (INRPI) based on four aspects: nature-based recreation resources, landscape attractiveness, recreation comfort and opportunity, and recreation reception ability. A combination of the analytic hierarchy process (AHP) and entropy evaluation method was adopted to assess the NBR potential in the QTP from 2000 to 2020. The research shows that: (i) The INRPI for the QTP decreases gradually from southeast to northwest and increases slightly from 2000 to 2020. (ii) The INRPI displays a pronounced difference on either side of the Qilian-Gyirong line. The areas with very high and high potentials mainly distributed in the southeast of the line, while areas with very low and low potentials distributed in the northwest. (iii) The construction of protected areas effectively improves NBR potential. Areas of INRPI at diverse levels within protected areas obviously increased in 2020. (iv) Increasing altitude has a notable effect on INRPI, and 3000 m is a critical dividing line for the NBR in the QTP. These findings can contribute to decision-makers in guiding rational use and spatial planning of natural land and promoting sustainable recreational development.

Biological Effect of Quercetin in Repairing Brain Damage and Cerebral Changes in Rats: Molecular Docking and In Vivo Studies

This study examined the protective effect of quercetin against high-altitude-induced brain damage in rats. A molecular docking study was performed to investigate the potential effect of quercetin in reducing brain damages through its ability to target the oxidative stress enzymes. Biomarker assessment screening assays were also performed then followed by in vivo studies. Three groups of rats were divided into the control group, an untreated animal model group with induced brain damage, and finally, the quercetin treated group that received quercetin dose equal to 20 mg/kg of their body weights. Molecular docking studies and biomarker assessment screening assays proved the potential effect of quercetin to affect the level of representative biomarkers glutathione (GSH), glutathione reductase (GR), glutathione-S-transferase (GST), glutathione peroxidase (GPx), superoxide dismutase (SOD), catalase (CAT), and malondialdehyde (MDA). Additionally, the protective effect of quercetin against high altitude, low pressure, and low oxygen was also investigated by exploring the brain histopathology of experimental rats. Brain damage was observed in the untreated animal model group. After treatment with quercetin, the cerebral edema in the brain tissues was improved significantly, confirming the protective effects of quercetin. Therefore, quercetin can be used as a natural food additive to protect from the highaltitude-induced brain damage.

Gut microbiota imbalance mediates intestinal barrier damage in high-altitude exposed mice

The environmental conditions in high-altitude areas can induce gastrointestinal disorders and changes in gut microbiota. The gut microbiota is closely related to a variety of gastrointestinal diseases, although the underlying pathogenic mechanisms are not well-identified. The present study aimed to investigate the regulatory effect of high altitude on intestinal dysfunction via gut microbiota disturbance. Forty C57BL/6J mice were divided into four groups: one plain control group (CON) and three high-altitude exposure groups (HAE) (altitude: 4000 m a.s.l.; oxygen content: 12.7%; 1-, 2- and 4-week exposure). Another set of 40 mice was divided into two CON and two HAE subgroups. Antibiotic cocktails were administered to one CON and HAE groups and autoclaved water was administered to the second CON and HAE groups for 4 weeks, respectively. In the fecal microbiota transplantation experiment, there were four transplantation groups, which received, respectively: phosphate-buffered saline for 2 weeks, feces from CON for 2 weeks, feces from HAE-4W for 2 weeks, and HAE-4W for 4 weeks. Hematoxylin and eosin staining, periodic acid-Schiff staining, a terminal deoxynucleotidyl transferase dUTP nick end labeling assay and a quantitative reverse transcriptase-polymerase chain reaction were applied to detect changes in intestinal cellular structure, morphology, apoptosis and intestinal inflammatory response. Fecal microbiota was analyzed using 16S rDNA amplicon sequencing. A high-altitude environment changed the ecological balance of gut microbiota in mice and caused damage to the intestinal structure and mucosal barrier. Interestingly, similar damage, which was inhibited by antibiotic cocktails at high altitude, was observed in mice transplanted with fecal microbiota from HAE. A high-altitude environment contributes to dyshomeostasis of gut microbiota, thereby impairing the intestinal mucosal barrier, eventually inducing and exacerbating intestinal damage.

A Sports Nutrition Perspective on the Impacts of Hypoxic High-Intensity Interval Training (HIIT) on Appetite Regulatory Mechanisms: A Narrative Review of the Current Evidence

High-intensity interval training (HIIT) and low-oxygen exposure may inhibit the secretion of appetite-stimulating hormones, suppress appetite, and inhibit dietary intake. Physiological changes affecting appetite are frequent and include appetite hormone (ghrelin, leptin, PYY, and GLP-1) effects and the subjective loss of appetite, resulting in nutritional deficiencies. This paper is a narrative review of the literature to verify the HIIT effect on appetite regulation mechanisms and discusses the possible relationship between appetite effects and the need for high-intensity exercise training in a hypoxic environment. We searched MEDLINE/PubMed and the Web of Science databases, as well as English articles (gray literature by Google Scholar for English articles) through Google Scholar, and the searched studies primarily focused on the acute effects of exercise and hypoxic environmental factors on appetite, related hormones, and energy intake. In a general normoxic environment, regular exercise habits may have accustomed the athlete to intense training and, therefore, no changes occurred in their subjective appetite, but there is a significant effect on the appetite hormones. The higher the exercise intensity and the longer the duration, the more likely exercise is to cause exercise-induced appetite loss and changes in appetite hormones. It has not been clear whether performing HIIT in a hypoxic environment may interfere with the exerciser’s diet or the nutritional supplement intake as it suppresses appetite, which, in turn, affects and interferes with the recovery efficiency after exercise. Although appetite-regulatory hormones, the subjective appetite, and energy intake may be affected by exercise, such as hypoxia or hypoxic exercise, we believe that energy intake should be the main observable indicator in future studies on environmental and exercise interventions.

Uncovering the Metabolic Mechanism of Salidroside Alleviating Microglial Hypoxia Inflammation Based on Microfluidic Chip-Mass Spectrometry

Microglia are the main immune cells in the brain playing a critical role in neuroinflammation, and numerous pieces of evidence have proved that energy metabolism is closely associated with inflammation in activated microglia. Salidroside (Sal) isolated from Tibetan medicine Rhodiola crenulate can inhibit microglial hypoxia inflammation (HI). However, whether the inhibition is due to the intervening energy metabolic process in microglia is not clear. In this work, the hypoxic microenvironment of BV2 microglial cells was simulated using deferoxamine (DFO) in vitro and the change of cell metabolites (lactate, succinate, malate, and fumarate) was real-time online investigated based on a cell microfluidic chip-mass spectrometry (CM-MS) system. Meanwhile, for confirming the metabolic mechanism of BV2 cells under hypoxia, the level of HI-related factors (LDH, ROS, HIF-1α, NF-κB p65, TNF-α, IL-1β, and IL-6) was detected by molecular biotechnology. Integration of the detected results revealed that DFO-induced BV2 cell HI was associated with the process of energy metabolism, in which cell energy metabolism changed from oxidative phosphorylation to glycolysis. Furthermore, administration of Sal treatment could effectively invert this change, and two metabolites of Sal were identified: tyrosol and 4-hydroxyphenylacetic acid. In general, we illustrated a new mechanism of Sal for reducing BV2 cell HI injury and presented a novel analysis strategy that opened a way for real-time online monitoring of the energy metabolic mechanism of the effect of drugs on cells and further provided a superior strategy to screen natural drug candidates for HI-related brain disease treatment.

Exposure to High-Altitude Environment is Associated with Drug Transporters Change: miR-873-5p-Mediated Alteration of Function and Expression Levels of Drug Transporters under Hypoxia

Hypoxia is the main characteristic of a high-altitude environment, affect ing drug metabolism. However, so far, the mechanism of miRNA involved in the regulation of drug metabolism and transporters under high-altitude hypoxia is still unclear. This study aims to investigate the function s and expression levels of multidrug resistance protein 1 ( MDR1 ), m ultidrug resistance-associated protein 2 ( MRP2 ), breast cancer resistance protein ( BCRP ) , peptide transport 1 (PEPT1), and organic anion-transporting polypeptides 2B1 (OATP2B1) in rats and Caco-2 cells after exposure to high - altitude hypoxia. The protein and mRNA expression of MDR1 , MRP2, BCRP, PEPT1, and OATP2B1 were determined by Western blot and qPCR. The function s of MDR1 , MRP2, BCRP, PEPT1, and OATP2B1 were evaluated by determining the effective intestinal permeability and a bsorption rate constants of their specific substrates in rats under high-altitude hypoxia , and uptake and transport studies were performed on Caco-2 cells . To screen the miRNA associated with hypoxia, Caco-2 cells were examined by high throughput sequencing . We observed that the miR-873-5p was significantly decreased under hypoxia and might target MDR1 and pregnane X receptor ( PXR). To clarify whether miR-873-5p regulates MDR1 and pregnane X receptor (PXR) under hypoxia, Caco-2 cells were transfected with mimics or inhibitors of miR-873-5p and negative control (NC). The function and expression of drug transporters were found to be significantly increased in rats and Caco-2 cells under hypoxia. We found that miR-873-5p regulated MDR1 and PXR expression. Herein, it is shown that miRNA may affect the expression of drug transporter and nuclear receptor under hypoxia. Significance Statement This study explores if alterations to the microRNAs, induced by high-altitude hypoxia, can be translated to altered drug transporters. Among miRNAs, which show a significant change in a hypoxic environment, miR-873-5p can act on the MDR1 gene; however, there are multiple miRNAs that can act on the PXR. We speculate that the miRNA-PXR-Drug transporter axis is important in the physiological disposition of drugs. The results of this study are anticipated to be helpful for rational pharmaceutical use in high - altitude environments .

GLOBAL REACH 2018: intra-arterial vitamin C improves endothelial-dependent vasodilatory function in humans at high altitude

High altitude-induced hypoxaemia is often associated with peripheral vascular dysfunction. However, the basic mechanism(s) underlying high-altitude vascular impairments remains unclear. This study tested the hypothesis that oxidative stress contributes to the impairments in endothelial function during early acclimatization to high altitude. Ten young healthy lowlanders were tested at sea level (344 m) and following 4-6 days at high altitude (4300 m). Vascular endothelial function was determined using the isolated perfused forearm technique with forearm blood flow (FBF) measured by strain-gauge venous occlusion plethysmography. FBF was quantified in response to acetylcholine (ACh), sodium nitroprusside (SNP) and a co-infusion of ACh with the antioxidant vitamin C (ACh+VitC). The total FBF response to ACh (area under the curve) was ∼30% lower at high altitude than at sea level (P = 0.048). There was no difference in the response to SNP at high altitude (P = 0.860). At sea level, the co-infusion of ACh+VitC had no influence on the FBF dose response (P = 0.268); however, at high altitude ACh+VitC resulted in an average increase in the FBF dose response by ∼20% (P = 0.019). At high altitude, the decreased FBF response to ACh, and the increase in FBF in response to ACh+VitC, were associated with the magnitude of arterial hypoxaemia (R² = 0.60, P = 0.008 and R² = 0.63, P = 0.006, respectively). Collectively, these data support the hypothesis that impairments in vascular endothelial function at high altitude are in part attributable to oxidative stress, a consequence of the magnitude of hypoxaemia. These data extend our basic understanding of vascular (mal)adaptation to high-altitude sojourns, with important implications for understanding the aetiology of high altitude-related vascular dysfunction. KEY POINTS: Vascular dysfunction has been demonstrated in lowlanders at high altitude (>4000 m). However, the extent of impairment and the delineation of contributing mechanisms have remained unclear. Using the gold-standard isolated perfused forearm model, we determined the extent of vasodilatory dysfunction and oxidative stress as a contributing mechanism in healthy lowlanders before and 4-6 days after rapid ascent to 4300 m. The total forearm blood flow response to acetylcholine at high altitude was decreased by ∼30%. Co-infusion of acetylcholine with the antioxidant vitamin C partially restored the total forearm blood flow by ∼20%. The magnitude of forearm blood flow reduction, as well as the impact of oxidative stress, was positively associated with the individual severity of hypoxaemia. These data extend our basic understanding of vascular (mal)adaptation to high-altitude sojourns, with important implications for understanding the aetiology of high altitude-related changes in endothelial-mediated vasodilatory function.

Fasting promotes acute hypoxic adaptation by suppressing mTOR-mediated pathways

Rapid adaptation to a hypoxic environment is an unanswered question that we are committed to exploring. At present, there is no suitable strategy to achieve rapid hypoxic adaptation. Here, we demonstrate that fasting preconditioning for 72 h reduces tissue injuries and maintains cardiac function, consequently significantly improving the survival rates of rats under extreme hypoxia, and this strategy can be used for rapid hypoxic adaptation. Mechanistically, fasting reduces blood glucose and further suppresses tissue mTOR activity. On the one hand, fasting-induced mTOR inhibition reduces unnecessary ATP consumption and increases ATP reserves under acute hypoxia as a result of decreased protein synthesis and lipogenesis; on the other hand, fasting-induced mTOR inhibition improves mitochondrial oxygen utilization efficiency to ensure ATP production under acute hypoxia, which is due to the significant decrease in ROS generation induced by enhanced mitophagy. Our findings highlight the important role of mTOR in acute hypoxic adaptation, and targeted regulation of mTOR could be a new strategy to improve acute hypoxic tolerance in the body.

Hypoxic Exercise Exacerbates Hypoxemia and Acute Mountain Sickness in Obesity: A Case Analysis

Acute mountain sickness (AMS) is a common syndrome characterized by headache, dizziness, loss of appetite, weakness, and nausea. As a major public health issue, obesity has increased in high altitude urban residents and intermittent commuters to high altitudes. The present study investigated acute hypoxic exposure and hypoxic exercise on hypoxemia severity and AMS symptoms in a physically active obese man. In this case analysis, peripheral oxygen saturation (SpO₂) was used to evaluate hypoxemia, heart rate (HR) and blood pressure (BP) were used to reflect the function of autonomic nervous system (ANS), and Lake Louise scoring (LLS) was used to assess AMS. The results showed that acute hypoxic exposure led to severe hypoxemia (SpO₂ = 72%) and tachycardia (HRrest = 97 bpm), and acute hypoxic exercise exacerbated severe hypoxemia (SpO₂ = 59%) and ANS dysfunction (HRpeak = 167 bpm, SBP/DBP = 210/97 mmHg). At the end of the 6-h acute hypoxic exposure, the case developed severe AMS (LLS = 10) symptoms of headache, gastrointestinal distress, cyanosis, vomiting, poor appetite, and fatigue. The findings of the case study suggest that high physical activity level appears did not show a reliable protective effect against severe hypoxemia, ANS dysfunction, and severe AMS symptoms in acute hypoxia exposure and hypoxia exercise.

Irbesartan ameliorates chronic mountain sickness in a rat model via the cholesterol metabolism: An iTRAQ -based proteomics analysis

OBJECTIVE

To study the effects of irbesartan on pulmonary artery lesions in a rat model with chronic mountain sickness (CMS) and identify the biomarkers involved.

METHODS

In this study, we used a rat model of CMS to evaluate the therapeutic effect of irbesartan by measuring pulmonary artery pressure and evaluating the histopathology of the pulmonary artery. We also used proteomics technology to identify differentially expressed proteins (DEPs) in the serum and performed bioinformatics analysis. Results were then verified by enzyme linked immunosorbent assay (ELISA) and immunohistochemistry (IHC).

RESULTS

Irbesartan treatment induced a significant decrease (P < 0.05) in the pulmonary artery pressure of CMS rats. Histopathological and electron microscope further confirmed that high altitude hypoxia induced changes in the structure of the pulmonary artery tissue and caused ultrastructural lesions. Proteomics analysis identified 40 DEPs; bioinformatics analysis further revealed that the cholesterol metabolism pathway plays a crucial role in the occurrence of CMS. ELISA and IHC verified that several DEPs (Apo-A1, Apo-C1, Apo-E, IGF-1, Profilin1, and Col1a1) represent critical biological markers in pulmonary artery disease caused by CMS.

CONCLUSIONS

Irbesartan significantly improved pulmonary artery damage in a rat model of CMS possibly by impacting on the cholesterol metabolism pathway and by reducing damage to vascular endothelial cells. Irbesartan also inhibited the expression levels of IGF-1, Profilin1 and Col1a1 to relieve pulmonary artery pressure and improve lung function by inhibiting vascular remodeling. Several proteins were identified as potential biomarkers of CMS, including Apo-A1, Apo-C1, Apo-E, IGF-1, Profilin1, and Col1a1.

Impact of High Altitude on Cardiovascular Health: Current Perspectives

Globally, about 400 million people reside at terrestrial altitudes above 1500 m, and more than 100 million lowlanders visit mountainous areas above 2500 m annually. The interactions between the low barometric pressure and partial pressure of O2, climate, individual genetic, lifestyle and socio-economic factors, as well as adaptation and acclimatization processes at high elevations are extremely complex. It is challenging to decipher the effects of these myriad factors on the cardiovascular health in high altitude residents, and even more so in those ascending to high altitudes with or without preexisting diseases. This review aims to interpret epidemiological observations in high-altitude populations; present and discuss cardiovascular responses to acute and subacute high-altitude exposure in general and more specifically in people with preexisting cardiovascular diseases; the relations between cardiovascular pathologies and neurodegenerative diseases at altitude; the effects of high-altitude exercise; and the putative cardioprotective mechanisms of hypobaric hypoxia.

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.

The Use of Pulse Oximetry in the Assessment of Acclimatization to High Altitude

Background: Finger pulse oximeters are widely used to monitor physiological responses to high-altitude exposure, the progress of acclimatization, and/or the potential development of high-altitude related diseases. Although there is increasing evidence for its invaluable support at high altitude, some controversy remains, largely due to differences in individual preconditions, evaluation purposes, measurement methods, the use of different devices, and the lacking ability to interpret data correctly. Therefore, this review is aimed at providing information on the functioning of pulse oximeters, appropriate measurement methods and published time courses of pulse oximetry data (peripheral oxygen saturation, (SpO₂) and heart rate (HR), recorded at rest and submaximal exercise during exposure to various altitudes. Results: The presented findings from the literature review confirm rather large variations of pulse oximetry measures (SpO₂ and HR) during acute exposure and acclimatization to high altitude, related to the varying conditions between studies mentioned above. It turned out that particularly SpO₂ levels decrease with acute altitude/hypoxia exposure and partly recover during acclimatization, with an opposite trend of HR. Moreover, the development of acute mountain sickness (AMS) was consistently associated with lower SpO₂ values compared to individuals free from AMS. Conclusions: The use of finger pulse oximetry at high altitude is considered as a valuable tool in the evaluation of individual acclimatization to high altitude but also to monitor AMS progression and treatment efficacy.

Low Stroke Volume Index in Healthy Young Men Is Associated with the Incidence of Acute Mountain Sickness after an Ascent by Airplane: A Case-Control Study

Background

The aims of this study were to explore the characteristics of left ventricular (LV) functional changes in subjects with or without acute mountain sickness (AMS) and their associations with AMS incidence.

Methods

A total of 589 healthy men were enrolled and took a trip from Chengdu (500 m, above sea level (asl)) to Lhasa (3700 m, asl) by airplane. Basic characteristics, physiological data, and echocardiographic parameters were collected both at Chengdu and Lhasa, respectively. AMS was identified by the Lake Louise Questionnaire Score.

Results

The oxygen saturation (SpO₂), end-systolic volume index, end-diastolic volume index (EDVi), stroke volume index (SVi), E-wave velocity, and E/A ratio were decreased, whereas the heart rate (HR), ejection fraction, cardiac index (CI), and A-wave velocity were increased at the third day after arrival, as evaluated by an oximeter and echocardiography. However, AMS patients showed higher HR and lower EDVi, SVi, CI, E-wave velocity, and E/A ratio than AMS-free subjects. Among them, SVi, which is mainly correlated with the changes of EDVi and altered LV filling pattern, was the most valuable factor associated with AMS incidence following receiver-operator characteristic curves and linear and Poisson regression. Compared with subjects in the highest SVi tertile, subjects in the middle SVi tertile showed higher multivariable Incidence Rate Ratios (IRR) for AMS with higher incidences of mild headache and gastrointestinal symptoms, whereas subjects in the lowest SVi tertile showed even higher multivariable IRR with higher incidences of all the symptoms.

Conclusions

This relatively large-scale case-control study revealed that the reduction of SVi correlated with the altered LV filling pattern was associated with the incidence and clinical severity of AMS.

Altitude, Acute Mountain Sickness, and Acetazolamide: Recommendations for Rapid Ascent

Toussaint, Claudia M., Robert W. Kenefick, Frank A. Petrassi, Stephen R. Muza, and Nisha Charkoudian. Altitude, acute mountain sickness, and acetazolamide: recommendations for rapid ascent. High Alt Med Biol. 22:5-13, 2021. Background: Sea level natives ascending rapidly to altitudes above 1,500 m often develop acute mountain sickness (AMS), including nausea, headaches, fatigue, and lightheadedness. Acetazolamide (AZ), a carbonic anhydrase inhibitor, is a commonly used medication for the prevention and treatment of AMS. However, there is continued debate about appropriate dosing, particularly when considering rapid and physically demanding ascents to elevations above 3,500 m by emergency medical and military personnel. Aims: Our goal in the present analysis was to evaluate and synthesize the current literature regarding the use of AZ to determine the most effective dosing for prophylaxis and treatment of AMS for rapid ascents to elevations >3,500 m. These circumstances are specifically relevant to military and emergency medical personnel who often need to ascend rapidly and perform physically demanding tasks upon arrival at altitude. Methods: We conducted a literature search from April 2018 to February 2020 using PubMed, Google Scholar, and Web of Science to identify randomized controlled trials that compared AZ with placebo or other treatment with the primary endpoint of AMS incidence and severity. We included only research articles/studies that focused on evaluation of AZ use during rapid ascent. Results: Four doses of AZ (125, 250, 500, and 750 mg daily) were identified as efficacious in decreasing the incidence and/or severity of AMS during rapid ascents, with evidence of enhanced effectiveness with higher doses. Conclusions: For military, emergency medical, or other activities involving rapid ascent to altitudes >3,500 m, doses 500-750 mg/day within 24 hours of altitude exposure appear to be the most effective for minimizing symptoms of AMS.

Mortality in Different Mountain Sports Activities Primarily Practiced in the Summer Season-A Narrative Review

Millions of people engage in mountain sports activities worldwide. Although leisure-time physical activity is associated with significant health benefits, mountain sports activities also bear an inherent risk for injury and death. However, death risk may vary across various types of mountain sports activities. Epidemiological data represent an important basis for the development of preventive measures. Therefore, the aim of this review is to compare mortality rates and potential risk factors across different (summer) mountain sports activities. A comprehensive literature search was performed on the death risk (mortality) in mountain sports, primarily practiced during the summer season, i.e., mountain hiking, mountain biking, paragliding, trekking, rock, ice and high-altitude climbing. It was found that the death risk varies considerably between different summer mountain sports. Mortality during hiking, trekking and biking in the mountains was lower compared to that during paragliding, or during rock, ice or high-altitude climbing. Traumatic deaths were more common in activities primarily performed by young adults, whereas the number of deaths resulting from cardiovascular diseases was higher in activities preferred by the elderly such as hiking and trekking. Preventive efforts must consider the diversity of mountain sports activities including differences in risk factors and practitioners and may more particularly focus on high-risk activities and high-risk individuals.