Effects of skin surface cooling and heating on autonomic nervous activity and baroreflex sensitivity in humans

The influence of skin surface cooling and heating on heart rate variability (HRV), blood pressure variability (BPV), and baroreflex sensitivity (BRS) were studied in 11 healthy supine volunteers in air temperatures of 18 degrees C (cool), 24 degrees C (mild), 48 degrees C (warm), and 60 degrees C (hot) in a styrene foam chamber. The high-frequency component of HRV (HFRR) decreased and the ratio of low- to high-frequency components, LFRR/HFRR, increased with skin surface heating. Therefore, a suppression of cardiac vagal nervous activity and an enhancement of cardiac sympathetic nervous activity can be caused by skin surface heating. The low-frequency component of BPV (LFSBP), i.e. the fluctuations of the Mayer waves, increased with skin surface heating. The responses between the very low-frequency components of HRV (VLFRR) and systolic BPV (VLFSBP) to thermal skin stimulation were different, although these variables both were considered to be indicators of the thermoregulatory vasomotor control or renin-angiotensin system. Baroreflex sensitivity (BRS) did not increase with skin surface heating, at least in humans.