Vagal Withdrawal During Hot Flashes Occurring in Undisturbed Sleep

SRI Authors: Ian M. Colrain, Fiona C Baker, Massimiliano de Zambotti

Abstract

Objective

Little is known about the impact of hot flashes on cardiac autonomic regulation, in particular vagal control. Thereby, we assessed the cardiac autonomic profile associated with physiological hot flashes occurring in undisturbed sleep.

Methods

Eleven perimenopausal women (45 to 56 years) had overnight laboratory recordings of polysomnography, electrocardiography, and skin conductance. 18 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-min windows starting from 4 min before (baseline and pre-flash periods) to 2 min after the onset of hot flashes (hot flash period).

Results

Heart rate increased by, on average, 4 beats per minute with the occurrence of a hot flash compared to both baseline (p < 0.001) and pre-flash (p < 0.001). High frequency power was reduced, reflecting a decrease in vagal activity, at the onset of a hot flash compared to baseline (p < 0.001) and pre-flash (p < 0.001). There was no change in sympathovagal balance with the onset of a hot flash. The magnitude of the hot flash, i.e. 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).

Conclusions

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.

Keywords: Hot flash, sleep, autonomic activity, hot flush, heart rate variability, menopause

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