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Changes in heart rate variability following acclimation to heat
A Frank1, M Belokopytov, D Moran
1Heller Institute of Medical Research, Sheba Medical Center, Tel Hashomer, Israel.
Summary
Heat acclimation in healthy individuals led to increased sympathetic tone and adaptive cardiovascular changes. This suggests peripheral factors play a key role in regulating cardiac function during heat exposure.
Area of Science:
- Environmental Physiology
- Cardiovascular Physiology
Background:
- Heat acclimation is crucial for individuals exposed to high temperatures.
- Understanding sympatho-vagal balance is key to explaining cardiovascular adaptation to heat.
Purpose of the Study:
- To investigate changes in sympatho-vagal balance during heat acclimation.
- To explore the role of cardiac autonomic regulation in cardiovascular adaptation to heat.
Main Methods:
- Eight healthy individuals underwent a 10-day heat acclimation protocol (40°C, 40% RH).
- Analysis of heart rate variability (R-R intervals) in time and frequency domains was performed on days 1 and 10.
- Physiological parameters including rectal temperature, heart rate, and sweat rate were monitored.
Main Results:
- Typical heat acclimation responses were observed: reduced rectal temperature and heart rate, increased sweat rate.
- A decrease in final heart rate on day 10 was accompanied by an increase in sympathetic tone.
- Heart rate variability analysis indicated shifts in sympatho-vagal balance.
Conclusions:
- Heat acclimation induces adaptive cardiovascular changes, including altered sympatho-vagal balance.
- Increased sympathetic tone during heat acclimation suggests a role in cardiovascular adaptation.
- Peripheral factors appear more critical than intrinsic cardiac factors in controlling cardiac function during heat exposure.