Heart rate and blood pressure variability, and baroreflex sensitivity, during heat exposure in persons with type 2 diabetes and hypertension

The autonomic nervous system regulates cardiovascular homeostasis during stressors such as heat, but the effects of type 2 diabetes (T2D) with hypertension on such responses are unclear. Twenty male participants (10 with type 2 diabetes and hypertension and 10 age-matched healthy controls; mean ages 64 ± 4.14 and 63 ± 5.42 years) underwent a 90-minute whole-body heat exposure at 40 °C and 50% relative humidity. Heart rate variability (HRV), baroreflex sensitivity (BRS), and blood pressure variability (BPV) were assessed before, during and after the heat exposure. Heat exposure increased heart rate in both groups but this response was less in T2D (5.43 bpm; ~ 7% increase) versus controls (13.96 bpm; ~ 22% increase; p = 0.014). Similarly, reductions in HRV indices to heat stress were generally smaller in magnitude among participants with T2D. For example, high-frequency power (HF RR) decreased by 31.21 ms² (~54.5% reduction) in T2D because of heat exposure, compared with a reduction of 179.35 ms² (~74% reduction) in controls (p = 0.038). Further, LF BRS decreased by 1.07 ms/mmHg (~25% reduction) vs. 3.96 ms/mmHg (~51% reduction) (p = 0.021), HF BRS by 1.58 ms/mmHg (~35% reduction) vs. 4.15 ms/mmHg (~62% reduction) (p = 0.034), and mean BRS by 1.18 ms/mmHg (~26% reduction) vs. 4.16 ms/mmHg (~58% reduction) (p = 0.010) in those with T2D versus controls, respectively. Low-frequency power (LF RR), LF/HF ratio and BPV parameters also showed smaller (though nonsignificant) changes in T2D. Overall, combined T2D and hypertension produced blunted autonomic responses to short-term heat exposure, potentially increasing vulnerability to temperature extremes.