Abstract
Background: The autonomic nervous system (ANS) is crucial for acclimatization. Investigating the responses of acute exposure to a hypoxic environment may provide some knowledge of the cardiopulmonary system’s adjustment mechanism.Objective: The present study investigates the longitudinal changes and recovery in heart rate variability (HRV) in a young healthy population when exposed to a simulated plateau environment.Methods: The study followed a strict experimental paradigm in which physiological signals were collected from 33 healthy college students (26 ± 2 years, 171 cm ± 7 cm, 64 ± 11 kg) using a medical-grade wearable device. The subjects were asked to sit in normoxic (approximately 101 kPa) and hypoxic (4,000 m above sea level, about 62 kPa) environments. The whole experimental process was divided into four stable resting measurement segments in chronological order to analyze the longitudinal changes of physical stress and recovery phases. Seventy-six time-domain, frequency-domain, and non-linear indicators characterizing rhythm variability were analyzed in the four groups.Results: Compared to normobaric normoxia, participants in hypobaric hypoxia had significantly lower HRV time-domain metrics, such as RMSSD, MeanNN, and MedianNN (p < 0.01), substantially higher frequency domain metrics such as LF/HF ratio (p < 0.05), significantly lower Poincaré plot parameters such as SD1/SD2 ratio and other Poincaré plot parameters are reduced considerably (p < 0.01), and Refined Composite Multi-Scale Entropy (RCMSE) curves are reduced significantly (p < 0.01).Conclusion: The present study shows that elevated heart rates, sympathetic activation, and reduced overall complexity were observed in healthy subjects exposed to a hypobaric and hypoxic environment. Moreover, the results indicated that Multiscale Entropy (MSE) analysis of RR interval series could characterize the degree of minor physiological changes. This novel index of HRV can better explain changes in the human ANS.
Highlights
As is well known, acute exposure to a plateau environment tends to activate a series of stress responses
The calculation of RMSSD was more stable compared to pNN50, which usually reflects abrupt changes in the RR interval and is a high-frequency component of heart rate variability (HRV; Ciccone et al, 2017); as shown in Table 3, there was no significant difference in pNN50 changes (p = 0.816)
Similar to pNN50, SDSD, CVNN, and CVSD reflect the high-frequency variance components of heart rate estimated from short time course measurements (Stein, 2002; Shaffer and Ginsberg, 2017), were positively correlated with each other
Summary
Acute exposure to a plateau environment tends to activate a series of stress responses. It manifests headache, insomnia, appetite loss, dyspnea, or even can be developed as acute mountain sickness. Evidence suggests that this acute hypoxia may cause systemic metabolic imbalances and increase cardiovascular disease risks (Riley and Gavin, 2017; Parati et al, 2018). Acute hypoxia tends to activate sympathetic mechanisms regulating the cardiovascular system, such as increased heart rate, cardiac output, and blood pressure (Perini et al, 1996; Vigo et al, 2010), and may cause hyperventilation of the respiratory system (Woods et al, 2008). Investigating the responses of acute exposure to a hypoxic environment may provide some knowledge of the cardiopulmonary system’s adjustment mechanism
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
