Acute Mountain Sickness, Hypoxia, Hypobaria and Exercise Duration each Affect Heart Rate

Abstract

In this study, we quantified the changes in post-exercise resting heart rate (HR_rst) associated with acute mountain sickness (AMS), and compared the effects of hypobaric hypoxia (HH) and normobaric hypoxia (NH) on HR_rst. We also examined the modulating roles of exercise duration and exposure time on HR_rst. Each subject participated in 2 of 6 conditions: normobaric normoxia (NN), NH, or HH (4 400 m altitude equivalent) combined with either 10 or 60 min of moderate cycling at the beginning of an 8-h exposure. AMS was associated with a 2 bpm higher HR_rst than when not sick, after taking into account the ambient environment, exercise duration, and SpO₂. In addition, HR_rst was elevated in both NH and HH compared to NN with HR_rst being 50% higher in HH than in NH. Participating in long duration exercise led to elevated resting HRs (0.8–1.4 bpm higher) compared with short exercise, while short exercise caused a progressive increase in HR_rst over the exposure period in both NH and HH (0.77–1.2 bpm/h of exposure). This data suggests that AMS, NH, HH, exercise duration, time of exposure, and SpO₂ have independent effects on HR_rst. It further suggests that hypobaria exerts its own effect on HR_rst in hypoxia. Thus NH and HH may not be interchangeable environments.

Key words

altitude - normobaric - hypobaric - cardiovascular

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