Heart rate variability in menopausal hot flashes during sleep

Objective: The aim of this study was to determine if heart rate variability changes during hot flashes recorded during sleep. Methods: This study was performed in a university medical center laboratory with 16 postmenopausal women demonstrating at least four hot flashes per night. Polysomnography, heart rate, and sternal skin conductance to indicate hot flashes were recorded in controlled, laboratory conditions. Results: For the frequency bin of 0 to 0.15 Hz, spectral power was greater during waking compared with non-rapid eye movement sleep and less during stages 3 and 4 compared with stages 1 and 2. Power was greater during hot flashes compared with subsequent periods for all hot flashes. Power was greater during hot flashes compared with preceding and subsequent periods for those recorded during stage 1 sleep. For waking hot flashes, power in this band was higher before hot flashes than during or after them. Conclusions: These data are consistent with our theory of elevated sympathetic activation as a trigger for menopausal hot flashes and with previous work on heart rate variability during the stages of sleep.