Heart rate variability during high heat stress: a comparison between young and older adults with and without Type 2 diabetes

Am J Physiol Regul Integr Comp Physiol. 2016 Oct 1;311(4):R669-R675. doi: 10.1152/ajpregu.00176.2016. Epub 2016 Aug 10.


We examined whether older individuals with and without Type 2 diabetes (T2D) experience differences in heart rate variability (HRV) during a 3-h exposure to high heat stress compared with young adults. Young (Young; n = 22; 23 ± 3 yr) and older individuals with (T2D; n = 11; 59 ± 9 yr) and without (Older; n = 25; 63 ± 5 yr) T2D were exposed to heat stress (44°C, 30% relative humidity) for 3 h. Fifty-five HRV measures were assessed for 15 min at baseline and at minutes 82.5-97.5 (Mid) and minutes 165-180 (End) during heat stress. When compared with Young, a similar number of HRV indices were significantly different (P < 0.05) in Older (Baseline: 35; Mid: 29; End: 32) and T2D (Baseline: 31; Mid: 30; End: 27). In contrast, the number of HRV indices significantly different (P < 0.05) between Older and T2D were far fewer (Baseline: 13, Mid: 1, End: 3). Within-group analyses demonstrated a greater change in the Young group's HRV during heat stress compared with Older and T2D; the number of significantly different (P < 0.05) HRV indices between baseline and End were 42, 29, and 20, for Young, Older, and T2D, respectively. Analysis of specific HRV domains suggest that the Young group experienced greater sympathetic activity during heat stress compared with Older and T2D. In conclusion, when compared with young, older individuals with and without T2D demonstrate low HRV at baseline and less change in HRV (including an attenuated sympathetic response) during 3 h high heat stress, potentially contributing to impaired thermoregulatory function.

Keywords: autonomic response; heart rate variability; heat stress; hyperthermia; sympathetic nervous system.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Aging*
  • Body Temperature
  • Body Temperature Regulation*
  • Diabetes Mellitus, Type 2 / physiopathology*
  • Female
  • Heart Rate*
  • Heat-Shock Response*
  • Humans
  • Male
  • Middle Aged
  • Reproducibility of Results
  • Sensitivity and Specificity
  • Sympathetic Nervous System / physiology*
  • Young Adult

Grants and funding