Abstract
BackgroundInvestigating the responses of autonomic nervous system (ANS) in hypoxia may provide some knowledge about the mechanism of neural control and rhythmic adjustment. The integrated cardiac and respiratory system display complicated dynamics that are affected by intrinsic feedback mechanisms controlling their interaction. To probe how the cardiac and respiratory system adjust their rhythms in different simulated altitudes, we studied heart rate variability (HRV) in frequency domain, the complexity of heartbeat series and cardiorespiratory phase synchronization (CRPS) between heartbeat intervals and respiratory cycles.MethodsIn this study, twelve male subjects were exposed to simulated altitude of sea level, 3000 m and 4000 m in a hypobaric chamber. HRV was assessed by power spectral analysis. The complexity of heartbeat series was quantified by sample entropy (SampEn). CRPS was determined by cardiorespiratory synchrogram.ResultsThe power spectral HRV indices at all frequency bands depressed according to the increase of altitude. The SampEn of heartbeat series increased significantly with the altitude (P < 0.01). The duration of CRPS epochs at 3000 m was not significantly different from that at sea level. However, it was significantly longer at 4000 m (P < 0.01).ConclusionsOur results suggest the phenomenon of CRPS exists in normal subjects when they expose to acute hypoxia. Further, the autonomic regulation has a significantly stronger influence on CRPS in acute hypoxia. The changes of CRPS and HRV parameters revealed the different regulatory mechanisms of the cardiac and respiratory system at high altitude.
Highlights
Investigating the responses of autonomic nervous system (ANS) in hypoxia may provide some knowledge about the mechanism of neural control and rhythmic adjustment
These findings suggest that hypoxia-induced changes in cardiac rhythm may be a threat for the health of people exposed to hypoxic environment
Hypoxia led to increasing resting heart rate (HR) and respiratory rate (RespR) accompanied with decreasing SpO2 (Table 1)
Summary
Investigating the responses of autonomic nervous system (ANS) in hypoxia may provide some knowledge about the mechanism of neural control and rhythmic adjustment. Moderate altitude could increase the incidence of cardiac arrhythmia in healthy older people [4]. Kujanik et al [5] reported the occurrence of supraventricular and ventricular extrasystoles was proportional to the altitude in acute hypoxia in healthy older man. These findings suggest that hypoxia-induced changes in cardiac rhythm may be a threat for the health of people exposed to hypoxic environment
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