Epidemiology, Risk Factors, and Genetics of High-Altitude–Related Pulmonary Disease

Whole-exome sequencing in searching for novel variants associated with the development of high altitude pulmonary edema

BACKGROUND

High altitude pulmonary edema (HAPE) is a high-altitude idiopathic disease with serious consequences due to hypoxia at high altitude, and there is individual genetic susceptibility. Whole-exome sequencing (WES) is an effective tool for studying the genetic etiology of HAPE and can identify potentially novel mutations that may cause protein instability and may contribute to the development of HAPE.

MATERIALS AND METHODS

A total of 50 unrelated HAPE patients were examined using WES, and the available bioinformatics tools were used to perform an analysis of exonic regions. Using the Phenolyzer program, disease candidate gene analysis was carried out. SIFT, PolyPhen-2, Mutation Taster, CADD, DANN, and I-Mutant software were used to assess the effects of genetic variations on protein function.

RESULTS

The results showed that rs368502694 (p. R1022Q) located in NOS3, rs1595850639 (p. G61S) located in MYBPC3, and rs1367895529 (p. R333H) located in ITGAV were correlated with a high risk of HAPE, and thus could be regarded as potential genetic variations associated with HAPE.

CONCLUSION

WES was used in this study for the first time to directly screen genetic variations related to HAPE. Notably, our study offers fresh information for the subsequent investigation into the etiology of HAPE.

Hyperbaric oxygen preconditioning for prevention of acute high-altitude diseases: Fact or fiction?

Acute high-altitude diseases, including acute mountain sickness (AMS), high-altitude cerebral edema (HACE), and high-altitude pulmonary edema (HAPE), have been recognized as potentially lethal diseases for altitude climbers. Various preconditioning stimuli, including hyperbaric oxygen (HBO), have been proposed to prevent acute high-altitude diseases. Herein, we reviewed whether and how HBO preconditioning could affect high-altitude diseases and summarized the results of current trials. Evidence suggests that HBO preconditioning may be a safe and effective preventive method for acute high-altitude diseases. The proposed mechanisms of HBO preconditioning in preventing high-altitude diseases may involve: 1) protection of the blood-brain barrier and prevention of brain edema, 2) inhibition of the inflammatory responses, 3) induction of the hypoxia-inducible factor and its target genes, and 4) increase in antioxidant activity. However, the optimal protocol of HBO preconditioning needs further exploration. Translating the beneficial effects of HBO preconditioning into current practice requires the "conditioning strategies" approach. More large-scale and high-quality randomized controlled studies are needed in the future.

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

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

Time Domains of Hypoxia Responses and -Omics Insights

The ability to respond rapidly to changes in oxygen tension is critical for many forms of life. Challenges to oxygen homeostasis, specifically in the contexts of evolutionary biology and biomedicine, provide important insights into mechanisms of hypoxia adaptation and tolerance. Here we synthesize findings across varying time domains of hypoxia in terms of oxygen delivery, ranging from early animal to modern human evolution and examine the potential impacts of environmental and clinical challenges through emerging multi-omics approaches. We discuss how diverse animal species have adapted to hypoxic environments, how humans vary in their responses to hypoxia (i.e., in the context of high-altitude exposure, cardiopulmonary disease, and sleep apnea), and how findings from each of these fields inform the other and lead to promising new directions in basic and clinical hypoxia research.

Qi-Long-Tian formula extract alleviates symptoms of acute high-altitude diseases via suppressing the inflammation responses in rat

Background

Chinese Yunnan Province, located in the Yunnan–Guizhou Plateau, is a famous tourist paradise where acute high-altitude illness common occurs among lowland people visitors due to non-acclimatization to the acute hypobaric hypoxia (AHH) conditions. Traditional Chinese medicine, such as Qi-Long-Tian (QLT) formula, has shown effectiveness and safety in the treatment of acute high-altitude diseases. The aim of this study was to clarify the therapeutic mechanisms of this traditional formula using a rat model in a simulated plateau environment.

Methods

Following testing, lung tissue samples were evaluated by hematoxylin–eosin staining and for biochemical characteristics. mRNA-Seq was used to compare differentially expressed genes in control rats, and in rats exposed to AHH and AHH with QLT treatment.

Results

Inflammation-related effectors induced following QLT treatment for AHH included MMP9 and TIMP1, and involved several phosphorylation signaling pathways implicated in AHH pathogenesis such as PI3K/AKT and MAPK signaling.

Conclusion

This study provides insights into the major signaling pathways induced by AHH and in the protective mechanisms involved in QLT formula activity.

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

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

The impact of physical fitness and body mass index in children on the development of acute mountain sickness: A prospective observational study

Background

Acute mountain sickness (AMS) is commonly found among people traveling above 2500 m. We investigated whether the occurrence of AMS is related to differences in individual physical fitness and BMI in subjects 11–13 years of age.

Methods

This study was conducted at Xue Mountain, Taiwan (elevation of 3886 m) between June 13, 2011 and June 17, 2011. Subjects were asked to ascend from Taipei City (25 m) to the summit (3886 m) over 3 days and 2 nights. Gender, age, weight, height, and fitness index (determined using a 3-minute step test) were recorded at sea level before ascent. The Lake Louise AMS score was used to record symptoms and diagnose AMS.

Results

A total of 179 subjects (mean age: 11.8 years; 102 males, 77 females) were included in the analysis. A total of 44.7% of subjects were diagnosed with AMS. Male gender (p = 0.004) and elevated body mass index (BMI) (p < 0.001) were each associated with the development of AMS. However the physical fitness index was comparable in subjects with and without AMS (67.8 ± 10.1 vs. 68.0 ± 9.3, p = 0.9).

Conclusions

This study shows that both BMI and male gender were associated with the development of AMS in 11–13 year old children. Physical fitness was not associated with the occurrence of AMS.

Electronic supplementary material

The online version of this article (doi:10.1186/s12887-015-0373-0) contains supplementary material, which is available to authorized users.

Rate of ascent and acute mountain sickness at high altitude

OBJECTIVE

To examine the effect of ascent rate on the induction of acute mountain sickness (AMS) in young adults during a climb to Jiaming Lake (3350 m) in Taiwan.

DESIGN

Prospective, nonrandomized.

SETTING

Climb from 2370 to 3350 m.

PARTICIPANTS

Young adults (aged 18 to 26 years) (N = 91) chose to participate in either the fast ascent (3 days; n = 43) or slow ascent (4 days; n = 48) group (1 and 2).

ASSESSMENT OF RISK FACTORS

Two criteria were used to define AMS. A Lake Louise score ≥3 and Lake Louise criteria [in the setting of a recent gain in altitude, the presence of headache and at least 1 of gastrointestinal discomfort (anorexia, nausea, or vomiting), fatigue or weakness, dizziness or lightheadedness, or difficulty sleeping].

MAIN OUTCOME MEASURES

Heart rate, blood oxygen saturation (SaO2), and symptoms of AMS were monitored each morning and evening.

RESULTS

Baseline characteristics were similar between groups, except for significant differences in history of alcohol consumption (P = 0.009) and climbing experience above 3000 m (P < 0.001). The incidence of AMS was not associated with the rate of ascent. Acute mountain sickness was most prevalent in group 1 on day 2 in the evening and in group 2 on day 3 in the evening. In both groups, AMS correlated with the initial reduction in SaO2. Body mass index (BMI) >24 kg/m was identified as a significant risk factor for AMS.

CONCLUSIONS

The development of AMS was closely associated with an initial reduction in SaO2. A BMI >24 kg/m also contributed to the occurrence of AMS.

CLINICAL RELEVANCE

These findings indicate that factors other than ascent rate should be considered when trying to ameliorate the risk of AMS.

Chinese herbal medicine for acute mountain sickness: a systematic review of randomized controlled trials

Objectives. We aimed to assess the current clinical evidence of Chinese herbal medicine for AMS. Methods. Seven electronic databases were searched until January 2013. We included randomized clinical trials testing Chinese herbal medicine against placebo, no drugs, Western drugs, or a combination of routine treatment drugs against routine treatment drugs. Study selection, data extraction, quality assessment, and data analyses were conducted according to Cochrane standards. Results. Nine randomized trials were included. The methodological quality of the included trials was evaluated as low. Two trials compared prescriptions of Chinese formula used alone with Western drugs. A meta-analysis showed a beneficial effect in decreasing the score of AMS (MD: −2.23 [−3.98, −0.49], P = 0.01). Only one trial compared prescriptions of Chinese formula used alone with no drugs. A meta-analysis showed a significant beneficial effect in decreasing the score of AMS (MD: −6.00 [−6.45, −5.55], P < 0.00001). Four trials compared Chinese formula used alone with placebo. A meta-analysis also showed a significant beneficial effect in decreasing the score of AMS (MD: −1.10 [−1.64, −0.55], P < 0.0001). Two trials compared the combination of Chinese formula plus routine treatment drugs with routine treatment drugs. A meta-analysis showed a beneficial effect in decreasing the score of AMS (MD: −5.99 [−11.11, −0.86], P = 0.02). Conclusions. No firm conclusion on the effectiveness and safety of Chinese herbal medicine for AMS can be made. More rigorous high-quality trials are required to generate a high level of evidence and to confirm the results.

Preservation of TSPO by chronic intermittent hypobaric hypoxia confers antiarrhythmic activity

Abnormal activation of mitochondrial translocator protein (TSPO) contributes to arrhythmogenesis during cardiac metabolic compromise; however, its role in the antiarrhythmic activities of chronic hypoxia adaptation remains unclear. Our results demonstrated that 80% of normoxic rats developed ischaemic VF, whereas this condition was seldom observed in rats with 14 days of chronic intermittent hypobaric hypoxia (CIHH). TSPO stimulation or inhibition affected the arrhythmias incidence in normoxic rats, but did not change the CIHH-mediated antiarrhythmic effects. Abrupt and excessive elevation of TSPO activity was positively linked to ischaemic VF, and CIHH preserved TSPO activity during ischaemia. The preservation of TSPO activity by CIHH also contributed to the maintenance of intracellular Ca homeostasis. These results suggest that the blunt sensitivity of TSPO to ischaemic stress may be responsible for the antiarrhythmic effects by CIHH.

The athlete and high altitude

Expanding athlete participation in high-altitude environments highlights the importance for a sports physician to have a good understanding of the high-altitude illness (HAI) syndromes: acute mountain sickness (AMS), high-altitude cerebral edema (HACE), and high-altitude pulmonary edema (HAPE). All may occur in the setting of acute altitude exposure higher than 2500 m; incidence and severity increases as altitudes or ascent rates increase. Once HAI is recognized, proven therapies should be instituted to alleviate symptoms and avert the possibility of critical illness. Allowing for acclimatization is the best strategy for preventing HAI. Acetazolamide and dexamethasone are additional preventive measures for AMS/HACE; nifedipine, salmeterol, and phosphodiesterase inhibitors are useful in preventing HAPE. Along with the immediate hazards of HAI with altitude exposure, the sport physician also should be familiar with altitude/hypoxic training practices used by athletes to enhance fitness and performance.