Vagal withdrawal during hot flashes occurring in undisturbed sleep

Abstract

Little is known about the impact of hot flashes on cardiac autonomic regulation, particularly vagal control. Therefore, we assessed the cardiac autonomic profile associated with physiological hot flashes occurring in undisturbed sleep. Eleven perimenopausal women (45-56 y) had overnight laboratory recordings of polysomnography, electrocardiography, and skin conductance. Eighteen hot flashes that occurred in stable non-rapid eye movement sleep undisturbed by arousals were analyzed. Heart rate variability measures were obtained for three consecutive 2-minute windows starting from 4 minutes before (baseline and preflash periods) to 2 minutes after the onset of hot flashes (hot flash period). Heart rate increased by, on average, 4 beats/minute with the occurrence of a hot flash compared with both baseline (P < 0.001) and preflash (P < 0.001). High-frequency power was reduced, reflecting a decrease in vagal activity, at the onset of a hot flash compared with baseline (P < 0.001) and preflash (P < 0.001). There was no change in sympathovagal balance with the onset of a hot flash. The magnitude of the hot flash (ie, skin conductance amplitude) was associated with increased heart rate (r = 0.78, P < 0.001) and decreased vagal tone (r = -0.56, P = 0.014). Physiological hot flashes per se, recorded during undisturbed sleep periods and independent of any arousals, are associated with increased heart rate and decreased cardiac autonomic vagal activity. These data support the hypothesis that the parasympathetic branch of the autonomic nervous system is involved in the cardiac response to a hot flash.