Effect of exertional vs. passive heat stress on diurnal rhythms of hemodynamic parameters and parasympathetic modulation of cardiac function
Abstract
Previously, we demonstrated that the addition of exercise to exposure to high ambient temperatures (Ta), leading to increased core temperature (Tc), exaggerates alterations in autonomic nervous system function for several hours into recovery. Here we tested the hypothesis that this stress combination impairs diurnal fluctuations (DF) in hemodynamic and cardiac autonomic parameters. Rats were exposed to an Ta of 39°C while resting (HS‐C) or exercising on a running wheel (HS‐EX). Once Tc reached 41.5°C, the exercise protocol was stopped in HS‐EX and Ta was reduced to 25°C in both groups. Tc and systolic BP (SBP) were recorded telemetrically. Before the protocol, DF were apparent in Tc (+0.68±0.08°C), HR (+34±4 bpm), SBP (+6±4 mmHg), and relative high frequency spectral power of HR (HFHR, +6.4±1.5%). On the night and day following the experimental day, DF were preserved for Tc and HR in both groups. DF in SBP were preserved in HS‐C but not in HS‐EX. DF in HFHR were lost in both groups, suggesting that heat stress impairs cardiac autonomic function independent of the activity level. In conclusion, the lack of DF in SBP following heat exposure in HS‐EX but not in HS‐C suggests that the combination of heat stress and exercise causes greater cardiovascular impairment than heat stress alone, even with the same increase in Tc and shorter exposure to heat stress. (Supported by USAMRMC; author views not official US Army or DoD policy)
Document Details
- Document Type
- Pub Defense Publication
- Publication Date
- Apr 01, 2010
- Source ID
- 10.1096/fasebj.24.1_supplement.804.2
Entities
People
- Frederick O. Liaboe
- Harald M Stauss
- Kevin C. Kregel
- Lisa R. Leon
Organizations
- United States Army Medical Research and Development Command
- United States Army Research Institute of Environmental Medicine
- University of Iowa