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

Area of Science:

• Environmental Physiology
• Altitude Medicine
• Exercise Physiology

Background:

• Post-exercise resting heart rate (HRrst) is a key physiological indicator.
• Understanding factors influencing HRrst is crucial for assessing physiological stress.
• Hypobaric hypoxia (HH) and normobaric hypoxia (NH) present different environmental challenges.

Purpose of the Study:

• To quantify changes in post-exercise resting heart rate (HRrst) related to acute mountain sickness (AMS).
• To compare the effects of hypobaric hypoxia (HH) and normobaric hypoxia (NH) on HRrst.
• To examine the influence of exercise duration and exposure time on HRrst.

Main Methods:

• Subjects underwent 2 of 6 conditions: normobaric normoxia (NN), NH, or HH (4,400m equivalent).
• Exercise consisted of 10 or 60 minutes of moderate cycling at the start of an 8-hour exposure.
• HRrst was measured post-exercise, with AMS, SpO2, exercise duration, and exposure time analyzed.

Main Results:

• AMS was associated with a 2 bpm higher HRrst compared to not being sick, independent of environmental factors.
• Both NH and HH elevated HRrst compared to NN, with HH showing a 50% greater increase than NH.
• Longer exercise duration (60 min) resulted in higher HRrst (0.8–1.4 bpm) than shorter duration (10 min).

Conclusions:

• AMS, NH, HH, exercise duration, exposure time, and SpO2 independently affect HRrst.
• Hypobaria exerts a distinct effect on HRrst in hypoxic conditions.
• Normobaric hypoxia and hypobaric hypoxia are not interchangeable environments for physiological assessment.