Contribution of Hypoxic Exercise Testing to Predict High-Altitude Pathology: A Systematic Review

Can acute high-altitude sickness be predicted in advance?

In high-altitude environments, the oxygen and air density are decreased, and the temperature and humidity are low. When individuals enter high-altitude areas, they are prone to suffering from acute mountain sickness (AMS) because they cannot tolerate hypoxia. Headache, fatigue, dizziness, and gastrointestinal reactions are the main symptoms of AMS. When these symptoms cannot be effectively alleviated, they can progress to life-threatening high-altitude pulmonary edema or high-altitude cerebral edema. If the risk of AMS can be effectively assessed before people enter high-altitude areas, then the high-risk population can be promptly discouraged from entering the area, or drug intervention can be established in advance to prevent AMS occurrence and avoid serious outcomes. This article reviews recent studies related to the early-warning biological indicators of AMS to provide a new perspective on the prevention of AMS.

Establishing a prediction model of severe acute mountain sickness using machine learning of support vector machine recursive feature elimination

Severe acute mountain sickness (sAMS) can be life-threatening, but little is known about its genetic basis. The study was aimed to explore the genetic susceptibility of sAMS for the purpose of prediction, using microarray data from 112 peripheral blood mononuclear cell (PBMC) samples of 21 subjects, who were exposed to very high altitude (5260 m), low barometric pressure (406 mmHg), and hypobaric hypoxia (VLH) at various timepoints. We found that exposure to VLH activated gene expression in leukocytes, resulting in an inverted CD4/CD8 ratio that interacted with other phenotypic risk factors at the genetic level. A total of 2286 underlying risk genes were input into the support vector machine recursive feature elimination (SVM-RFE) system for machine learning, and a model with satisfactory predictive accuracy and clinical applicability was established for sAMS screening using ten featured genes with significant predictive power. Five featured genes (EPHB3, DIP2B, RHEBL1, GALNT13, and SLC8A2) were identified upstream of hypoxia- and/or inflammation-related pathways mediated by microRNAs as potential biomarkers for sAMS. The established prediction model of sAMS holds promise for clinical application as a genetic screening tool for sAMS.

Assessment of Psychological and Social Fitness in Healthy Adults Permanently Living at Very High Altitude

BACKGROUND

Environmental factors of high altitude, especially hypobaric hypoxia, may directly and persistently affect human physical and mental health. Our study was designed to assess the psychological and social fitness in healthy adults permanently living at very high altitude, i.e., an average elevation of 3650 m.

METHODS

In our observational study, 320 participants were included, among which 218 (68.1%) had resided in such a setting for more than 20 years. Participants underwent 138 assessments, including the Self-Rating Anxiety Scale (SAS), Symptom Check List 90 (SCL-90) and the Evaluation Scale of Human Adaptation Capability (ESHAC). SAS (20 items) and SCL-90 (90 items) were used to assess psychological fitness, and the ESHAC (28 items) was used to assess social fitness. Pearson analysis was used to assess correlations and Logistic regression analysis was performed to determine independent influencing factors.

RESULTS

The highest SAS score was 80 and the mean score was 43.26 ± 8.88, which was higher than the norm in China (p < 0.001). Sixty (18.8%) participants showed anxiety symptoms and 14 (4.4%) had moderate or severe anxiety. The average score of SCL-90 was 140.88 ± 44.77, and 96 (30.0%) participants showed SCL-90 scores ≥160. Compared with the norm, significant differences were shown in eight of the nine SCL-90 factor scores, i.e., somatization, obsessive-compulsive, depression, anxiety, hostility, phobic anxiety, paranoid ideation, and psychoticism. The average score of ESHAC was 19.92 ± 4.54, and 114 (35.6%) participants did not reach the qualifying standard. Significant correlations were observed between the SAS score, SCL-90 total and factor scores, and ESHAC scores. The Logistic regression analysis showed that being born at very high altitude was an independent influencing factor (AOR = 2.619; 95% CI, 1.629-4.211; p < 0.001) after controlling for other factors.

CONCLUSION

Permanently living at very high altitude can influence the psychological and social fitness of healthy adults.

The HMOX2 polymorphism contributes to the carotid body chemoreflex in European sea-level residents by regulating hypoxic ventilatory responses

This study investigates whether a functional single nucleotide polymorphism of HMOX2 (heme oxygenase-2) (rs4786504 T>C) is involved in individual chemosensitivity to acute hypoxia, as assessed by ventilatory responses, in European individuals. These responses were obtained at rest and during submaximal exercise, using a standardized and validated protocol for exposure to acute normobaric hypoxia. Carriers of the ancestral T allele (n = 44) have significantly lower resting and exercise hypoxic ventilatory responses than C/C homozygous carriers (n = 40). In the literature, a hypoxic ventilatory response threshold to exercise has been identified as an independent predictor of severe high altitude-illness (SHAI). Our study shows that carriers of the T allele have a higher risk of SHAI than carriers of the mutated C/C genotype. Secondarily, we were also interested in COMT (rs4680 G > A) polymorphism, which may be indirectly involved in the chemoreflex response through modulation of autonomic nervous system activity. Significant differences are present between COMT genotypes for oxygen saturation and ventilatory responses to hypoxia at rest. In conclusion, this study adds information on genetic factors involved in individual vulnerability to acute hypoxia and supports the critical role of the ≪ O2 sensor ≫ - heme oxygenase-2 - in the chemosensitivity of carotid bodies in Humans.