Who should not go high: chronic disease and work at altitude during construction of the Qinghai-Tibet railroad

Work at high altitude and non-fatal cardiovascular disease associated with unfitness to work: Prospective cohort observation

INTRODUCTION

Mining at high altitude exposes workers to hypoxic environment and cold climate in addition to conventional hazards in mining, but very little is known on how to define fitness to work in prospective candidates with pre-existing conditions. The aim of the current study was to define the incidence of cardiovascular diseases leading to unfitness to work as well as their predictors in a prospective observation.

METHODS

A total of 569 prospective employees (median age 34 (interquartile range (IQR) 28;40) years, 95% men 85% mid-altitude residents) for a high-altitude gold mine in Kyrgyzstan operating at 3800-4500 meters above sea level were screened at pre-employment in 2009-2012 and followed by January 2022. Cox regression was used to quantify the association of baseline demographics and physiological variables with newly diagnosed cardiovascular diseases (CVD) leading to unfitness to work, expressed as hazard ratios (HRs) with 95% confidence intervals (CI).

RESULTS

With 5190 person-years of observation, 155 (27%) workers have left work, of whom 23 had a newly identified CVD leading to unfitness to work (cumulative incidence 4%) with no difference between drivers and other occupations, despite greater blood pressure and body mass index (BMI) in the former at baseline. Age (HR 1.13 (95% CI 1.06;1.22) and BMI (HR 1.18 (95% CI 1.04;1.34)) were associated with a greater chance of having CVD, adjusted for lung function, baseline diagnoses, year of employment and baseline blood pressure. Narrowing the analysis to only men, drivers, smokers and even middle-altitude residents did not change the effect.

CONCLUSION

These findings confirmed high efficacy of pre-employment screening limiting access of workers with advanced conditions to work which later yielded low CVD incidence. In addition to conventional contraindications to work at high altitude, age and high BMI should be considered when a decision is made.

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.

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.

Dose-effect of exercise intervention on heart rate variability of acclimatized young male lowlanders at 3,680 m

This study investigated whether exercise could improve the reduced HRV in an environment of high altitude. A total of 97 young, healthy male lowlanders living at 3,680 m for >1 year were recruited. They were randomized into four groups, of which three performed-low-, moderate-, and high-intensity (LI, MI, HI) aerobic exercise for 4 weeks, respectively. The remaining was the control group (CG) receiving no intervention. For HI, compared to other groups, heart rate (p = 0.002) was significantly decreased, while standard deviation of RR intervals (p < 0.001), SD2 of Poincaré plot (p = 0.046) and the number of successive RR interval pairs that differ by > 50 ms divided by total number of RR (p = 0.032), were significantly increased after intervention. For MI, significantly increase of trigonometric interpolation in NN interval (p = 0.016) was observed after exercise. Further, a decrease in systolic blood pressure (SBP) after high-intensity exercise was found significantly associated with an increase in SD2 (r = - 0.428, p = 0.042). These results indicated that there was a dose effect of different intensities of aerobic exercise on the HRV of acclimatized lowlanders. Moderate and high-intensity aerobic exercise would change the status of the autonomic nervous system (ANS) and decrease the blood pressure of acclimatized lowlanders exposed to high altitude.

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.

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.

UIAA Medical Commission Recommendations for Mountaineers, Hillwalkers, Trekkers, and Rock and Ice Climbers with Diabetes

Hillebrandt, David, Anil Gurtoo, Thomas Kupper, Paul Richards, Volker Schöffl, Pankaj Shah, Rianne van der Spek, Nikki Wallis, and Jim Milledge. UIAA Medical Commission recommendations for mountaineers, hillwalkers, trekkers, and rock and ice climbers with diabetes. High Alt Med Biol. 24: 110-126.-The object of this advice article is not only to give the diabetic mountaineer general guidance but also to inform his or her medical team of practical aspects of care that may not be standard for nonmountaineers. The guidelines are produced in seven sections. The first is an introduction to the guidelines, and the second is an introduction to this medical problem and is designed to be read and understood by diabetic patients and their companions. The third section is for use in an emergency in mountains. The fourth is for rock, ice, and competition climbers operating in a less remote environment. These initial sections are deliberately written in simple language. The fifth and sixth sections are written for clinicians and those with skills to read more technical information, and the seventh looks at modern technology and its pros and cons in diabetes management in a remote area. Sections One and Two could be laminated and carried when in the mountains, giving practical advice.

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.

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.

Healthy worker survival effect at a high-altitude mine: prospective cohort observation

Very little is known about the factors of healthy worker survival effect at high-altitude mines. We conducted this cohort observation of the new hires for a high-altitude gold mine in Kyrgyzstan with the aim to ascertain predictors of survival at work. All new hires in 2009 through 2012 for a high-altitude gold mine (3600–4500 m above sea level) were followed up to January 2022. We tested the association of demographic, physiological predictors and diagnoses at the pre-employment screening with non-survival at work in Cox proportional hazards yielding hazard ratios (HR) with their 95% confidence intervals (CI). The cumulative observation time was 5190 person-years. Blood pressure at pre-employment, lung function, the diagnoses of essential hypertension, chronic obstructive pulmonary disease (COPD) or any other analyzed physiological variables were not associated with non-survival at work. However, smoking (HR 1.55; 95% CI 1.10; 2.17) increased the likelihood of non-survival at work, independent of any diagnosis or lowland residence (HR 1.95; 95% CI 1.31; 2.90). Adjusted for covariates and all diagnoses, having chronic rheumatic fever (HR 10.95; 95% CI 2.92; 33.92), hemorrhoids (HR 1.32; 95% CI 1.01; 3.75), adhesive otitis (HR 1.74; 95% CI 1.05; 2.89) or obesity (HR 1.71; 95% CI 1.01; 2.88) were associated with non-survival at work with time. This prospective observation of new hires for a high-altitude mining operation demonstrated that selected diagnoses, smoking and lowland residence elevated the risk of early exit in prospective workers.

Clinical Implications for Exercise at Altitude Among Individuals With Cardiovascular Disease: A Scientific Statement From the American Heart Association

An increasing number of individuals travel to mountainous environments for work and pleasure. However, oxygen availability declines at altitude, and hypoxic environments place unique stressors on the cardiovascular system. These stressors may be exacerbated by exercise at altitude, because exercise increases oxygen demand in an environment that is already relatively oxygen deplete compared with sea‐level conditions. Furthermore, the prevalence of cardiovascular disease, as well as diseases such as hypertension, heart failure, and lung disease, is high among individuals living in the United States. As such, patients who are at risk of or who have established cardiovascular disease may be at an increased risk of adverse events when sojourning to these mountainous locations. However, these risks may be minimized by appropriate pretravel assessments and planning through shared decision‐making between patients and their managing clinicians. This American Heart Association scientific statement provides a concise, yet comprehensive overview of the physiologic responses to exercise in hypoxic locations, as well as important considerations for minimizing the risk of adverse cardiovascular events during mountainous excursions.

Blood Pressure Response in Miners Exposed to Chronic Intermittent Hypoxia in Chile

Introduction: Limited information is available on blood pressure (BP) behavior in workers exposed to chronic intermittent hypoxia (CIH), and even less is known regarding effects of CIH on 24-h ambulatory BP in those affected by arterial hypertension at sea level (SL). The aims of this study were to assess clinic and 24-h ambulatory BP at SL and at high altitude (HA; 3,870 m above SL) in workers exposed to CIH, and to compare BP response to HA exposure between normotensive and hypertensive workers.

Methods: Nineteen normotensive and 18 pharmacologically treated hypertensive miners acclimatized to CIH were included, whose work was organized according to a “7 days-on−7 days-off” shift pattern between SL and HA. All measurements were performed on the second and seventh day of their HA shift and after the second day of SL sojourn.

Results: Compared to SL, 24-h systolic BP (SBP) and diastolic BP (DBP) increased at HA [+14.7 ± 12.6 mmHg (p < 0.001) and +8.7 ± 7.2 mmHg (p < 0.001), respectively], and SBP nocturnal fall decreased consistently (−4.1 ± 9.8%; p < 0.05) in all participants, with hypertensives showing higher nocturnal DBP than normotensives (p < 0.05) despite the current therapy. Also, heart rate (HR) nocturnal fall tended to be reduced at HA. In addition, the 24-h SBP/DBP hypertension threshold of ≥130/80 mmHg was exceeded by 39% of workers at SL and by 89% at HA. Clinic HR, SBP, and DBP were significantly higher on the second day of work at HA compared with SL, the increase being more pronounced for SBP in hypertensives (p < 0.05) and accompanied by, on average, mild altitude sickness in both groups. These symptoms and the values of all cardiovascular variables decreased on the seventh day at HA (p < 0.05) regardless of CIH exposure duration.

Conclusion: Long history of work at HA according to scheduled CIH did not prevent the occurrence of acute cardiovascular changes at HA during the first days of exposure. The BP response to HA tended to be more pronounced in hypertensive than in normotensive workers despite being already treated; the BP changes were more evident for 24-h ambulatory BP. Twenty-four-hour ABP monitoring is a useful tool for an appropriate evaluation of BP in CIH workers.

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.

[Blood pressure and high altitude: physiological response and clinical management]

High altitude is an extreme environment that challenges human beings exposed because of work, recreational activities, or habitat. Exposure to hypobaric hypoxia results in physiological adaptations in response to the geography and the associated extreme environmental conditions. These acclimatization responses can be diverse and result from evolutionary changes and comorbidities. In this context, this review aims to identify the available evidence on the effects of high altitude on blood pressurefrom the physiological to clinical aspects at rest and during exerciseand the underlying mechanisms and possible clinical implications of acute and chronic intermittent hypoxia.

Polysaccharide from Potentilla anserina L ameliorate pulmonary edema induced by hypobaric hypoxia in rats

High-altitude pulmonary edema (HAPE) is a life-threatening disease occurs in hypobaric hypoxia (HH) environment, which could be treated by Dexamethasone, but might cause side-effects. Potentilla anserina L polysaccharide (PAP) holds promising physiological and pharmacological properties which could be beneficial for HAPE treatment. In our study, the anti-hypoxia effect of PAP was firstly investigated through anti-normobaric hypoxia test and anti-acute hypoxia test. Then we established a model of HAPE and measured the lung water content, pathological changes and MDA, NO, SOD, GSH concentrations in lung tissues. We also evaluated the protein and mRNA levels of pro-inflammatory cytokines (IL-1β, IL-6, TNF-α, VEGF, NF-κB and HIF-1α) by ELISA kits, RT-PCR and Western blotting. As expected, PAP could dramatically reduce the lung water content, alleviate lung tissue injury, and inhibit MDA and NO production, it also promote SOD activity and GSH expression. In addition, it has been found that PAP blocked the NF-κB and HIF-1α signaling pathway activation, inhibited the generation of downstream pro-inflammatory cytokines. Therefore, PAP provides great potential in HAPE treatment mainly through suppression of oxidative stress and inflammatory suppression.

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.

[Heart Patients and Exposure to Altitude]

Overall, heart patients should be advised individually with respect to their tolerance of altitudes. However, the historical reflex that altitude 'per se' is bad for heart patients should become a thing of the past. Adequately treated and stable patients can usually go up to an altitude of 2500 m without any restrictions. Higher altitudes are also possible for a large number of patients, but may require an adaptation of the medication and further clarification. This is especially the case when physical work is to be performed at great heights.

Cardiovascular Risk Is Increased in Miner's Chronic Intermittent Hypobaric Hypoxia Exposure From 0 to 2,500 m?

Over the past 40 years, mining activities in Chile have relocated miners who normally live at sea level to work at high altitudes. This results in a form of chronic intermittent hypobaric hypoxia (CIHH) characterized by alternating periods of work at high altitude and rest periods at sea level. Previous studies performed in our laboratory showed that aerobic capacity is reduced at 3,800 m, even when oxygen content is maintained. Our study aimed to determine the corporal composition, food intake, maximum oxygen uptake, and concentration of high sensitivity C reactive protein (hsCRP) in an acclimatized miner population that work from 0 to 2,500 m with CIHH exposure over 4 years. All miners recruited for our study were operators of heavy trucks with CIHH for over 4 years (shiftwork 7*7 days), and our experimental population was composed of 54 miners at sea level, 61 at 1,600 m, and 38 at 2,500 m. All evaluations were performed on the 3rd or 4th day of diurnal shiftwork. To determine corporal composition, we measured weight and height (to calculate body mass index, BMI), skinfolds (to calculate body fatty, BF), and waist circumference (WC); maximal aerobic capacity was evaluated using a ramp-incremental cycling to exhaustion protocol and a venous blood sample before the exercise test to measure (hsCRP) via an ELISA test. We found higher values of BMI, BF, and WC, in the miners' population but observed no significant difference between populations. We found a decrease in VO₂ of 11.6% at 1,600 m and 25.9% at 2,500 m compared to miners at sea level. An increase in (hsCRP) at 1,600 and 2,500 m regards sea level. We observed a high prevalence of overweight and obese subjects, which was related to the ad libitum availability of food and low physical activity (sedentarism). We found that work capacity was maintained despite a decreased VO₂ max at moderate altitude. However, overweight and obesity support an increased risk of cardiometabolic disease in miner's which is unrelated to altitude. In contrast, an increased hsCRP level could be associated with increased inflammatory mechanisms at 1,600 and 2,500 m.

Does intermittent exposure to high altitude increase the risk of cardiovascular disease in workers? A systematic narrative review

OBJECTIVE

Several working groups (eg, miners, flight crews and soldiers) are subjected to chronic intermittent hypoxic exposure. The cardiovascular implications have been studied but not systematically reviewed with focus on possible negative health implications. The aim of the present review was to systematically evaluate the hypothesis that intermittent hypoxic exposure causes cardiovascular stress detrimental to health in workers.

DESIGN

Systematic review.

DATA SOURCES

Electronic database search of PubMed, Scopus and Web of Science up to April 2020.

ELIGIBILITY CRITERIA

Studies of workers ≥18 years repeatedly subjected to months to years of irregular intermittent hypoxia, lasting from a few hours (eg, flight crews), one or a few days (eg, soldiers), or several days to weeks (eg, miners working at high altitude), written in English and evaluating the effect of intermittent hypoxia on cardiovascular disease were included. Animal studies, books, book chapters, personal communication and abstracts were excluded. The primary outcome measure was changes in standardised mortality ratio.

DATA EXTRACTION AND SYNTHESIS

Two independent reviewers extracted data and assessed risk of bias using the Cochrane Collaboration's tool.

RESULTS

119 articles were identified initially, 31 of which met the inclusion criteria. Of these, 17 were retrospective cohort mortality studies (irregular short-term intermittent hypoxia), and 14 studies were observational (long-term intermittent hypoxia). The population of irregular short-term intermittent hypoxia users (flight crew) showed a lower mortality by cardiovascular disease. Long-term intermittent hypoxia over several years such as in miners or soldiers may produce increased levels of cardiac disorders (12 studies), though this is probably confounded by factors such as obesity and socioeconomic status.

CONCLUSION

This systematic narrative review found that cardiovascular disease mortality in flight crews is lower than average, whereas miners and soldiers exposed to intermittent hypoxia experience increased risks of cardiovascular diseases. The impact of socioeconomic status and lifestyle appears of importance.

PROSPERO REGISTRY NUMBER

CRD42020171301.

Effect of Synbiotics on Amelioration of Intestinal Inflammation Under Hypobaric Hypoxia

Khanna, Kunjan, Kamla Prasad Mishra, Sudipta Chanda, Lilly Ganju, Shashi Bala Singh, and Bhuvnesh Kumar. Effect of synbiotics on amelioration of intestinal inflammation under hypobaric hypoxia. High Alt Med Biol. 22:32-44, 2021. Aim: High-altitude exposure alters the gastrointestinal (GI) system, which may be a cause of hypobaric hypoxia (HH)-induced microbial dysbiosis. Therefore, we investigated the effect of a combination of beneficial bacteria and nondigestible fiber popularly known as "synbiotics" (Syn) to mitigate intestinal inflammation and microbial dysbiosis post-HH exposure. Methods: Syn, that is, a combination of probiotics and prebiotics, was given to male Sprague-Dawley rats 3 days prior and along with the HH exposure to assess its effect on mucosal barrier injury and inflammation. Changes in the gut microbiota and functional analysis were assessed using 16S rRNA and whole-genome sequencing (WGS) analysis. Results: Syn treatment significantly improved mucosal barrier injury in terms of decreased serum fluorescein isothiocyanate dextran from 96.1 ± 7.95 μg/ml in HH-alone group to 38.35 ± 4.55 μg/ml in HH + Syn group (p < 0.01) and decreased serum zonulin levels, that is, from 134.7 ± 19.05 ng/ml (HH alone) to 64.02 ± 7.33 ng/ml (HH + Syn) (p < 0.05), along with improvement in the intestinal villi under HH exposure. Levels of proinflammatory cytokines and chemokines significantly reduced upon Syn treatment, indicating attenuation of inflammation and immune cell migration. Syn treatment significantly reduced Th17 biased immune response preventing interleukin (IL)-17-induced inflammatory response with 8.1 ± 0.5 ng/mg protein in HH exposure group, while treatment with Syn in HH-exposed group reduced IL-17 levels to 2.01 ± 0.3 ng/mg protein (p < 0.001). Analysis of 16S rRNA showed significant (p < 0.05) alterations in Deferribacteres, Firmicutes, and Verrucomicrobia at the phylum levels, whereas Prevotella, Paenibacillus, Clostridium, Turicibacter, Bacillus, Anoxybacillus, Enterococcus, SMB53, Mucispirillum, Allobaculum, and Lactococcus were significantly altered (p < 0.05) in abundance at the genus level. WGS analysis revealed improvement in GI health by regulating functional pathways post-Syn treatment. Conclusion: Our findings indicate that Syn treatment improves intestinal barrier function and curtailed inflammation in the HH-exposed rat models, proving it to be a promising potential countermeasure for HH-induced gut problems.

The Prevalence and Risk Factors of High-Altitude Pulmonary Hypertension Among Native Tibetans in Sichuan Province, China

Gou, Qiling, Rufeng Shi, Xin Zhang, Qingtao Meng, Xinran Li, Xi Rong, Zhabu Gawa, Nage Zhuoma, and Xiaoping Chen. The prevalence and risk factors of high-altitude pulmonary hypertension among native Tibetans in Sichuan Province, China. High Alt Med Biol. 21:327-335, 2020. Background: Studies evaluating the prevalence and risk factors of high-altitude pulmonary hypertension (HAPH) are lacking. Objective: To determine the prevalence of HAPH and its correlated factors among highlanders living 3200 m above sea level in Ganzi Tibetan Autonomous Prefecture, Sichuan Province, China. Methods: This was a single-center, cross-sectional study involving 1129 subjects (mean age 46.6 ± 14 years, 39% men). In native Tibetans, HAPH was defined as a mean pulmonary artery pressure >30 mmHg as measured by transthoracic echocardiography. Results: HAPH had a crude prevalence of 6.2% and was more prevalent in men than in women (8.6% vs. 4.6%, p = 0.005). Elderly adults were more likely to develop HAPH than young adults (odds ratio [OR] = 5.308, 95% confidence interval [CI] = 2.562-10.993). Highlanders with HAPH had more severe metabolic abnormalities (including elevated blood pressure, blood glucose, blood lipids, BMI, etc., p < 0.05) and significantly increased hemoglobin and hematocrit levels (p < 0.01). In multivariate logistic regression analysis, independent risk factors for HAPH were metabolic syndrome (OR = 3.128, 95% CI = 1.110-8.818), age (>60 years vs. <40 years) (OR = 2.924, 95% CI = 1.282-6.669), and decreased SpO₂ (OR = 1.072 per 1-unit decrease; 95% CI = 1.010-1.136). Conclusion: It could be concluded that HAPH was prevalent among 6.2% of native Tibetans in Sichuan Province, China. Increasing age, metabolic syndrome, and decreased SpO₂ were independent predisposing factors for HAPH.

Polysaccharide extracted from Potentilla anserina L ameliorate acute hypobaric hypoxia-induced brain impairment in rats

High altitude cerebral edema (HACE) is a high altitude malady caused by acute hypobaric hypoxia (AHH), in which pathogenesis is associated with oxidative stress and inflammatory cytokines. Potentilla anserina L is mainly distributed in Tibetan Plateau, and its polysaccharide possesses many physiological and pharmacological properties. In the present study, the protective effect and potential treatment mechanism of Potentilla anserina L polysaccharide (PAP) in HACE were explored. First, we measured the brain water content and observed the pathological changes in brain tissues, furthermore, malondialdehyde (MDA), nitric oxide (NO), superoxide dismutase (SOD), and glutathione (GSH) were evaluated by kits. Finally, the protein contents and mRNA expressions of pro-inflammatory (IL-1β, IL-6, TNF-α, vascular endothelial cell growth factor [VEGF], NF-κB, and hypoxia inducible factor-1 α [HIF-1α]) were detected by ELISA kits, RT-PCR, and western blotting. The results demonstrated that PAP reduced the brain water content, alleviated brain tissue injury, reduce the levels of MDA and NO, and increased the activity of SOD and GSH level. In addition, PAP blocking the NF-κB and HIF-1α signaling pathway activation inhibited the generation of downstream pro-inflammatory cytokines (IL-1β, IL-6, TNF-α, and VEGF). Therefore, PAP has a potential to treat and prevent of HACE by suppression of oxidative stress and inflammatory response.

Alterations to cardiac morphology and function among high-altitude workers: a retrospective cohort study

OBJECTIVES

Exposure to high altitude can affect human health, including the development of adverse cardiovascular effects. This study aimed to investigate alterations in cardiac morphology and function in high-altitude workers and to identify risk factors associated with cardiac abnormalities.

METHODS

A retrospective cohort study was conducted with 286 Qinghai-Tibetan Railroad maintenance workers. Participant data were collected from company personnel records. Data on echocardiography and diagnosis of cardiac abnormalities were extracted from participants' medical records. Time-to-event analysis was used to investigate the risk of cardiac abnormalities among participants with different baseline characteristics and identify risk factors associated with cardiac abnormalities that developed as a result of working at high altitude.

RESULTS

A total of 173 participants had developed cardiac abnormalities during the follow-up period. The most common cardiac abnormality was right atrial enlargement, followed by left ventricular diastolic dysfunction and tricuspid regurgitation. Among participants with cardiac abnormalities, the median follow-up time was 17 months. Compared with participants who were younger than 20 years and working at altitude <4000 m, participants older at employment and working at extremely high altitude were more likely to develop cardiac abnormalities. Nearly 40% of the participants who worked at altitude <4000 m remained without cardiac abnormalities during the follow-up period.

CONCLUSIONS

Over 60% of participants developed cardiac abnormalities after working at high altitude, predominantly right heart enlargement and left ventricular diastolic dysfunction. Age at employment and workplace altitude were significant risk factors for cardiac abnormalities. Enhanced regular physical examinations are recommended for high-altitude workers.

The prognostic value of altitude in patients with heart failure with reduced ejection fraction

Objective:

It is well known that the altitude may affect the cardiovascular system. However, there were a few data related to the effect of altitude on the adverse outcome in patients with heart failure with reduced ejection fraction (HFREF). The aim of the present study was to investigate the role of intermediate high altitude on the major adverse cardiovascular outcome in patients with HFREF.

Methods:

Patients with HFREF admitted to the outpatient clinics at the first center at sea level and the second center at 1890 m were prospectively enrolled in the study. HFREF was defined as symptoms/signs of heart failure and left ventricular ejection fraction <40%. The major adverse cardiac outcome (MACE) was defined as all-cause death, stroke, and re-hospitalization due to heart failure. The median follow-up period of the study population was 27 months.

Results:

The study included 320 (58.55% male, mean age 65.7±11.2 years) patients. The incidence of all-cause death was 8.5%, stroke 6.1%, re-hospitalization due to decompensated heart failure 34.3%, and MACE 48.9%. In Kaplan-Meier analysis, patients with HFREF living at high altitude had more MACE (71.1% vs. 25.3%, log rank p=0.005) and presented with more stroke (11.3% vs. 2.1%, log rank p=0.001) and re-hospitalization due to heart failure (65.1% vs. 20.1%, log rank p<0.001) rates than those at low altitude in the follow-up; however, the rate of all-cause death was similar (9.4% vs. 8.1%, log rank p=0.245).

Conclusion:

In the present study, we demonstrated that the intermediate high altitude is the independent predictor of MACE in patients with HFREF. High altitude may be considered as a risk factor in decompensating heart failure.

Clinical recommendations for high altitude exposure of individuals with pre-existing cardiovascular conditions: A joint statement by the European Society of Cardiology, the Council on Hypertension of the European Society of Cardiology, the European Society of Hypertension, the International Society of Mountain Medicine, the Italian Society of Hypertension and the Italian Society of Mountain Medicine

Take home figure

Ventilatory parameters at rest after months of stay at 3300 m: A comparison between acclimatized lowlanders and natives at Leh

Background

Increased pulmonary ventilation helps lowlanders and natives to maintain arterial oxygenation at high altitudes. Natives of Ladakh have been shown to have similar ventilatory parameters as Tibetans at 3300 m. But there is limited literature comparing these parameters in Ladakhi natives with acclimatized lowland sojourners.

Methods

End-tidal carbon dioxide partial pressure (EtCO₂), blood oxygen saturation (SpO₂) and hemoglobin concentration (Hb) were measured in 276 participants, 126 native highlanders (NHL - 40 females, 86 males) and 150 acclimatized lowlanders (ALL - 60 females, 90 males).

Results

EtCO₂ was greater in the NHL compared to the ALL, (33.8 ± 3.3 vs 31 ± 2.5 mmHg) although SpO₂ was lower (90.9 ± 2.4 vs 91.7 ± 2.3%). When grouped by sex, NHL males had significantly greater EtCO₂ than NHL females, ALL males and ALL females. Hb and calculated arterial oxygen content was similar in Ladakhis and acclimatized lowlanders, although greater in males compared to females. Systemic blood pressure, heart rate and the proportion of hypertensives was significantly greater in the ALL.

Conclusion

Native Ladakhis, have a significantly greater resting EtCO₂ (especially in males) and lower SpO₂ than acclimatized lowlanders. Blood Hb concentration and oxygen content is, however, similar in natives and acclimatized lowlanders of the same sex.

Association between homocysteine level and blood pressure traits among Tibetans: A cross-sectional study in China

Studies on hypertension (HTN) in Tibetans who live in high altitude areas are less and whether total homocysteine level (tHcy) is associated with blood pressure (BP) levels or HTN status in Tibetans is unknown.A total of 1486 Tibetans with complete information from a cross-sectional survey conducted in Lhasa Chengguan County of Tibet were included in this study. Demographic data, self-reported history of disease, and life styles were collected using a questionnaire. Blood tHcy, creatinine, fasting plasma-glucose, total cholesterol, triglycerides, and BP were measured with equipment.The median tHcy level of the whole population was 14.60 (13.17-16.50) μmol/L, and the prevalence of HTN was 26.99%. Regression models, adjusted for possible covariates, showed that an average increase of 1 lnHcy (log transformation of tHcy level) was associated with an increase of 3.78 mmHg of systolic BP (SBP, P = .011) and 3.02 mmHg of diastolic BP (DBP, P = .003). The prevalence of HTN, levels of SBP and DBP in the third (OR for HTN: 1.60, P = .026; β for SBP: 3.41, P = .004; β for DBP: 2.57, P = .002) and fourth (OR for HTN: 2.19, P < .001; β for SBP: 5.08, P < .001; β for DBP: 3.09, P < .001) quartile of tHcy level were higher than those in the first quartile.THcy is associated with BP levels and HTN status among Tibetans. Both HTN management and tHcy level should be paid more attention in Tibetans.

Determining the Operating Costs of a Medical Surveillance Program for Copper Miners Exposed to High Altitude-Induced Chronic Intermittent Hypoxia in Chile Using a Combination of Microcosting and Time-Driven Activity-Based Costing

BACKGROUND

Copper mining installations in Chile use a large number of workers who do their jobs at high altitudes, exposing them to the conditions of chronic intermittent hypobaric hypoxia. The Chilean Safety Association implements the surveillance program.

OBJECTIVE

This organization, under the sponsorship of the Chilean Superintendency of Social Security, was interested in determining the costs involved in this program to support its decision-making processes and to improve its performance.

METHODS

Direct operating costs of the Hypoxia Medical Surveillance Program were determined through on-site surveys applied to the organization's local agencies in charge. The microcosting method was used, quantifying personnel costs, consumables, and equipment and overhead costs. Time-driven activity-based costing was partially adapted for the allocation of personnel and equipment costs. Costs concerning activities, groups of activities and items, and average cost per exposed worker were determined.

RESULTS

The annual costs of the program were $127 299.58. The highest costs corresponded to the assessment activities, which were $89 192.13, representing 60.06% of the total. The labor factor costs were $77 568.50, which represents 60.93% of the total. The average cost per worker in the program is $21.17.

CONCLUSIONS

The partial adaptation of the time-driven activity-based costing method in combination with the microcosting method provides a suitable solution to determine the total costs of running a healthcare program of this kind. The information generated by this study will aid in the decision-making and management processes of the Hypoxia Medical Surveillance Program.

Relation of Patent Foramen Ovale to Acute Mountain Sickness

Over 50% of patients who rapidly ascend to extreme altitudes develop various symptoms known as acute mountain sickness (AMS), which rarely can be life threatening. It is unclear why some patients are more susceptible to AMS than others. Our objective was to determine whether patent foramen ovale (PFO) is a risk factor for AMS. Subjects who had hiked to altitudes above 10,000' (∼3,000 meters) on the John Muir Trail in California were recruited. Participants completed a questionnaire and 2-physician adjudication was performed in regard to AMS status. A transcranial Doppler with agitated saline contrast injection was performed to evaluate the presence or absence of PFO. The primary outcome was the development of AMS. From 2016 to 2018, 137 hikers were recruited into the study. There was a higher prevalence of PFO in hikers with AMS 15 of 24 (63%) compared with hikers without AMS 44 of 113 (39%); p = 0.034. In the multivariate model, the presence of a PFO significantly increased the risk for developing AMS: odds ratio 4.15, 95% confidence intervals 1.14 to 15.05; p = 0.030. In conclusion, hikers with a PFO had significantly higher risk of developing AMS relative to hikers without a PFO. Clinicians should consider PFO a risk factor in patients who plan to hike to high altitudes.

Pulmonary vascular dysfunction in metabolic syndrome

Metabolic syndrome is a critically important precursor to the onset of many diseases, such as cardiovascular disease, and cardiovascular disease is the leading cause of death worldwide. The primary risk factors of metabolic syndrome include hyperglycaemia, abdominal obesity, dyslipidaemia, and high blood pressure. It has been well documented that metabolic syndrome alters vascular endothelial and smooth muscle cell functions in the heart, brain, kidney and peripheral vessels. However, there is less information available regarding how metabolic syndrome can affect pulmonary vascular function and ultimately increase an individual's risk of developing various pulmonary vascular diseases, such as pulmonary hypertension. Here, we review in detail how metabolic syndrome affects pulmonary vascular function.

Hypobaric birth room may prevent intraventricular hemorrhage in extremely low birth weights infants

In the early postnatal period, intraventricular hemorrhage may develop in infants with extremely low birth weights due to hemodynamic instability. One of the most significant factors in intraventricular hemorrhage development is fluctuations in the cerebral blood flow due to left-to-right shunting as a result of patent ductus arteriosus, and such cases most frequently develop intraventricular hemorrhage within the first 72 h. The frequency of intraventricular hemorrhage may be reduced through the prevention of fluctuations in the cerebral blood flow in this time frame. Based on our hypothesis, we recommend that extremely low birth weight infants should be delivered and monitored in hypobaric rooms for the first three days after birth, as this may reduce left-to-right shunting as a result of patent ductus arteriosus by preventing the rapid drops seen in pulmonary pressure after birth. A more stable hemodynamic status may be achieved by increasing the cerebral blood flow during an acute term in a hypobaric environment. Gradual transition to the normobaric status at the end of the third day may prevent the long-term negative effects of hypobaric conditions.

The effects of respiratory inhaled drugs on the prevention of acute mountain sickness

BACKGROUND

Acute mountain sickness (AMS) is common in high-altitude travelers, and may lead to life-threatening high-altitude cerebral edema (HACE) or high-altitude pulmonary edema (HAPE). The inhaled drugs have a much lower peak serum concentrations and a shorter half-life period than oral drugs, which give them a special character, greater local effects in the lung. Meanwhile, short-term administration of inhaled drugs results in almost no adverse reactions.

METHODS

We chose inhaled ipratropium bromide/salbutamol sulfate (combivent, COM), budesonide (pulmicortrespules, BUD), and salbutamol sulfate (ventolin, VEN) in our study to investigate their prophylactic efficacy against AMS. Since COM is a compound drug of ipratropium bromide and salbutamol sulfate, to verify which part of COM plays a role in the prevention of AMS, we also tested VEN in our experiment.

RESULTS

In our study, Lake Louise scores (LLS) in the COM (1.14 ± 0.89 vs 1.91 ± 1.23, P < .05) and BUD (1.35 ± 0.94 vs 1.91 ± 1.23, P < .05) groups were both significantly lower than the placebo group at 72 hours. There were no significant differences in LLS scores among the 4 groups at 120 hours. The incidence of AMS in the COM group was significantly reduced at 72 hours (16.7% in COM group vs 43.4% in placebo group, P < .05) after exposure to high-altitude. There were no significant differences in AMS incidences at 120 hours among the 4 groups.

CONCLUSION

The prophylactic use of COM could prevent AMS in young Chinese male at 72 hours after high-altitude exposure. BUD also could reduce LLS but not prevent AMS at 72 hours. Ipratropium bromide maybe the effective drug in COM work on the prevention of AMS alone.

Exposure and Exercise Training in Hypoxic Conditions as a New Obesity Therapeutic Modality: A Mini Review

Obesity is an important health problem caused by positive energy balance. Generally, low calorie dietary intake combined with regular exercise is the most common modality to lose bodily fat in obese people. Although this is the first modality of choice for obesity treatment, it needs to be applied to obese patients for at least 12 weeks or more and it does not provide consistent results because it is difficult to suppress increased appetite due to exercise. Recently, many researchers have been applying hypoxic conditions for the treatment of obesity, as many studies show that people residing in high altitudes have a lower percentage of body fat and fewer obesity-related illnesses than people living at sea level. Hypoxic therapy treatment, including hypoxic exposure or hypoxic exercise training, is recommended as a way to treat and prevent obesity by suppression of appetite, increasing basal metabolic rate and fat oxidation, and minimizing side effects. Hypoxic therapy inhibits energy intake and appetite-related hormones, and enhances various cardiovascular and metabolic function parameters. These observations indicate that hypoxic therapy is a new treatment modality for inducing fat reduction and promoting metabolic and cardiovascular health, which may be an important and necessary strategy for the treatment of obesity. As such, hypoxic therapy is now used as a general medical practice for obesity treatment in many developed countries. Therefore, hypoxic therapy could be a new, practical, and useful therapeutic modality for obesity and obesity-related comorbidities.

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

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

INTRODUCTION

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

AIMS

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

MATERIALS AND METHODS

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

RESULTS

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

CONCLUSIONS

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

High-Altitude-Induced alterations in Gut-Immune Axis: A review

High-altitude sojourn above 8000 ft is increasing day by day either for pilgrimage, mountaineering, holidaying or for strategic reasons. In India, soldiers are deployed to these high mountains for their duty or pilgrims visit to the holy places, which are located at very high altitude. A large population also resides permanently in high altitude regions. Every year thousands of pilgrims visit Holy cave of Shri Amarnath ji, which is above 15 000 ft. The poor acclimatization to high altitude may cause alteration in immunity. The low oxygen partial pressure may cause alterations in gut microbiota, which may cause changes in gut immunity. Effect of high altitude on gut-associated mucosal system is new area of research. Many studies have been carried out to understand the physiology and immunology behind the high-altitude-induced gut problems. Few interventions have also been discovered to circumvent the problems caused due to high-altitude conditions. In this review, we have discussed the effects of high-altitude-induced changes in gut immunity particularly peyer's patches, NK cells and inflammatory cytokines, secretary immunoglobulins and gut microbiota. The published articles from PubMed and Google scholar from year 1975 to 2017 on high-altitude hypoxia and gut immunity are cited in this review.

Relationship of altitude mountain sickness and smoking: a Catalan traveller's cohort study

OBJECTIVES

The aim of this study is to analyse the relationship between smoking and altitude mountain sickness in a cohort of travellers to 2500 metres above sea level (masl) or higher.

SETTING

Travel Health Clinic at the Hospital Universitari de Bellvitge, in Barcelona, Spain.

PARTICIPANTS

A total of 302 adults seeking medical advice at the travel clinic, between July 2012 and August 2014, before travelling to 2500 masl or above, who agreed to participate in the study and to be contacted after the trip were included. Individuals who met the following criteria were excluded: younger than 18 years old, taking carbonic anhydrase inhibitors for chronic use, undergoing treatment with systemic corticosteroids and taking any medication that might prevent or treat altitude mountain sickness (AMS) prior to or during the trip. The majority of participants were women (n=156, 51.7%). The mean age was 37.7 years (SD 12.3). The studied cohort included 74 smokers (24.5%), 158 (52.3%) non-smokers and 70 (23.2%) ex-smokers. No statistical differences were observed between different sociodemographic characteristics, constitutional symptoms or drug use and smoking status.

OUTCOMES

The main outcome was the development of AMS, which was defined according to the Lake Louise AMS criteria.

RESULTS

AMS, according to the Lake Louise score, was significantly lower in smokers; the value was 14.9%, 95% CI (6.8 to 23.0%) in smokers and 29.4%, 95% CI (23.5 to 35.3%) in non-smokers with an adjusted OR of 0.54, 95% CI (0.31 to 0.97) independent of gender, age and maximum altitude reached.

CONCLUSIONS

These results suggest that smoking could reduce the risk of AMS in non-acclimated individuals. Further studies should be performed in larger cohorts of travellers to confirm these results. Despite the results, smoking must be strongly discouraged because it greatly increases the risk of cardiorespiratory diseases, cancer and other diseases.

Physiological Changes to the Cardiovascular System at High Altitude and Its Effects on Cardiovascular Disease

Riley, Callum James, and Matthew Gavin. Physiological changes to the cardiovascular system at high altitude and its effects on cardiovascular disease. High Alt Med Biol. 18:102-113, 2017.-The physiological changes to the cardiovascular system in response to the high altitude environment are well understood. More recently, we have begun to understand how these changes may affect and cause detriment to cardiovascular disease. In addition to this, the increasing availability of altitude simulation has dramatically improved our understanding of the physiology of high altitude. This has allowed further study on the effect of altitude in those with cardiovascular disease in a safe and controlled environment as well as in healthy individuals. Using a thorough PubMed search, this review aims to integrate recent advances in cardiovascular physiology at altitude with previous understanding, as well as its potential implications on cardiovascular disease. Altogether, it was found that the changes at altitude to cardiovascular physiology are profound enough to have a noteworthy effect on many forms of cardiovascular disease. While often asymptomatic, there is some risk in high altitude exposure for individuals with certain cardiovascular diseases. Although controlled research in patients with cardiovascular disease was largely lacking, meaning firm conclusions cannot be drawn, these risks should be a consideration to both the individual and their physician.

Obesity as a Conditioning Factor for High-Altitude Diseases

Obesity, a worldwide epidemic, has become a major health burden because it is usually accompanied by an increased risk for insulin resistance, diabetes, hypertension, cardiovascular diseases, and even some kinds of cancer. It also results in associated increases in healthcare expenditures and labor and economic consequences. There are also other fields of medicine and biology where obesity or being overweight play a major role, such as high-altitude illnesses (acute mountain sickness, hypoxic pulmonary hypertension, and chronic mountain sickness), where an increasing relationship among these two morbid statuses has been demonstrated. This association could be rooted in the interactions between obesity-related metabolic alterations and critical ventilation impairments due to obesity, which would aggravate hypobaric hypoxia at high altitudes, leading to hypoxemia, which is a trigger for developing high-altitude diseases. This review examines the current literature to support the idea that obesity or overweight could be major conditioning factors at high altitude.

Assessing agreement of blood pressure-measuring devices in Tibetan areas of China: a systematic review

BACKGROUND

The validity of blood pressure (BP)-measuring tools at very high altitudes is uncertain. Therefore, the objective of this review was to examine the degree of agreement of BP-measuring devices in Tibet.

METHODS

We conducted electronic searches in Medline, Embase, Cinahl, Cochrane Library, Global Health Library and the ISI Web of Science. Randomised and observational studies were considered for inclusion. The methodological characteristics of included studies were assessed using the Quality Assessment of Diagnostic Accuracy Studies-2 criteria. Our primary outcome was the difference in mean BP measurements between the new device and the gold standard.

RESULTS

We identified three eligible studies, out of which two with a total of 162 participants were included. The studies differed in their methodology. One study reported significantly higher systolic blood pressure (SBP) measurement with electronic sphygmomanometer (Omron) compared with mercury sphygmomanometer (mean difference 5.8±4.7 mm Hg; p<0.001), with no significant difference in diastolic blood pressure (DBP) measurement (0.4±3.9 mm Hg; p=0.23). The second study reported mean differences of 1.0±5.9 mm Hg and -3.1±4.6 mm Hg for SBP and DBP, respectively.

CONCLUSION

The limited evidence from published studies suggests that automated (Omron) BP monitors show a high degree of agreement for DBP when compared against mercury sphygmomanometer at high altitudes. However, the degree of such agreement for SBP is not consistent. Few studies assessing the validity of automated BP monitors at high altitudes have been conducted, and they differ in design and methodology. Further research assessing the suitability of BP-measuring instruments at high altitudes is therefore warranted.

Protective effects of puerarin on acute lung and cerebrum injury induced by hypobaric hypoxia via the regulation of aquaporin (AQP) via NF-κB signaling pathway

OBJECTIVE

Hypobaric hypoxia, frequently encountered at high altitude, may lead to lung and cerebrum injury. Our study aimed to investigate whether puerarin could exert ameliorative effects on rats exposed to hypobaric hypoxia via regulation of aquaporin (AQP) and NF-κB signaling pathway in lung and cerebrum.

MATERIALS AND METHODS

40 Sprague Dawley rats were divided into four groups (normal control group, hypobaric hypoxia group, puerarin group and dexamethasone group). Wet/dry ratio, blood gas, pathological changes of lung and cerebrum and spatial memory were observed in each group. Inflammatory cytokines in bronchoalveolar lavage fluid (BALF) were determined with ELISA and expression of AQP1, AQP4, NF-κB signaling pathway in lung and cerebrum with western blot RESULTS: Puerarin showed significant preventative effects on tissue injury and behavioral changes, as evidenced by histopathological findings and Morris water maze. In addition, levels of inflammatory cytokines in BALF decreased in the two preventative groups compared with those of hypobaric hypoxia group. AQP in lung and cerebrum increased under the condition of hypobaric hypoxia while was down regulated in both two preventative groups. NF-κB and IκB was also inhibited by puerarin.

CONCLUSION

Our study suggested that lung and cerebrum injury, increased inflammatory cytokines in BALF and increased AQP1, AQP4 and NF-κB signaling pathway occurred under the condition of hypobaric hypoxia. Moreover, puerarin could prevent lung and cerebrum injury of rats exposed to hypobaric hypoxia via down-regulation of inflammatory cytokines, AQP1 and AQP4 expression and NF-κB signaling pathway.

High altitude-related hypertensive crisis and acute kidney injury in an asymptomatic healthy individual

BACKGROUND

High-altitude exposure causes a mild to moderate rise in systolic and diastolic blood pressure. This case report describes the first documented case of a hypertensive crisis at altitude, as well as the first report of the occurrence of acute kidney injury in the context of altitude-related hypertension.

CASE PRESENTATION

A healthy, previously normotensive 30-year old, embarked on a trek to Everest Base Camp (5300 m). During his 11-day ascent the subject developed increasingly worsening hypertension. In the absence of symptoms, the individual initially elected to remain at altitude as had previously been the plan. However, an increase in the severity of his hypertension to a peak of 223/119 mmHg resulted in a decision to descend. On descent he was found to have an acute kidney injury that subsequently resolved spontaneously. His blood pressure reverted to normal at sea level and subsequent investigations including a transthoracic echocardiogram, cardiac magnetic resonance imaging, renal ultrasound, and urinary catecholamines were normal.

CONCLUSION

This report challenges the view that transient rises in blood pressure at altitude are without immediate risk. We review the evidence that altitude induces hypertension and discuss the implications for the management of hypertension at altitude.

Evidence for and Against Genetic Predispositions to Acute and Chronic Altitude Illnesses

MacInnis, Martin J., and Michael S. Koehle. Evidence for and against genetic predispositions to acute and chronic altitude illnesses. High Alt Med Biol. 17:281-293, 2016.-Humans exhibit marked variation in their responses to hypoxia, with susceptibility to acute and chronic altitude illnesses being a prominent and medically important example. Many have hypothesized that genetic differences are the cause of these variable responses to hypoxia; however, until recently, these hypotheses were based primarily on small (and sometimes anecdotal) reports pertaining to apparent differences in altitude illness susceptibility between populations, the notion that a history of altitude illness is indicative of subsequent risk, the heritability of hypoxia-related traits, and candidate gene association studies. In the past 5 years, the use of genomic techniques has helped bolster the claim that susceptibility to some altitude illnesses is likely the result of genetic variation. For each of the major altitude illnesses, we summarize and evaluate the evidence stemming from three important characteristics of a genetic trait: (1) individual susceptibility and repeatability across assessments, (2) biogeographical differences and familial aggregation, and (3) association(s) with genetic variants. Evidence to support a genetic basis for susceptibilities to acute mountain sickness (AMS) and high-altitude cerebral edema (HACE) is limited, owing partially to the subjective and unclear phenotype of AMS and the rarity and severity of HACE. In contrast, recent genomic studies have identified genes that influence susceptibility to high-altitude pulmonary edema, chronic mountain sickness, and high-altitude pulmonary hypertension. The collection of more individual, familial, and biogeographical susceptibility data should improve our understanding of the extent to which genetic variation contributes to altitude illness susceptibility, and genomic and molecular investigations have the potential to elucidate the mechanisms that underpin altitude illness susceptibility.