Hot flashes and cardiac vagal control

OBJECTIVE: The understanding of the physiology of hot flashes is incomplete. The autonomic nervous system has been hypothesized to play a role in hot flashes but has received limited empirical attention. Furthermore, emerging research has linked hot flashes to cardiovascular risk. Reduced high-frequency heart rate variability (HF-HRV), an index of vagal control of heart rate, has been associated with cardiovascular events. We hypothesized that decreases in HF-HRV would occur during hot flashes relative to periods before and after hot flashes. METHODS: Thirty perimenopausal and postmenopausal women aged 40 to 60 years reporting four or more hot flashes per day underwent laboratory hot flash provocation testing, with electrocardiogram and measurement of sternal skin conductance. Hot flashes were reported and identified from sternal skin conductance. HF-HRV was estimated using spectral analysis of the heart rate time series. The 5-minute interval during the hot flash period was compared with that during two nonflash periods before and after the hot flash via mixed-effects models. RESULTS: HRV was significantly decreased during hot flashes relative to periods before (b = 0.18, SE = 0.05; P = 0.0001) and after (b = 0.16, SE = 0.05; P = 0.002) physiologically measured hot flashes, controlling for age, race, education, task condition, menopause status, task, hypertension status, diabetes status, physical activity, body mass index, smoking, and anxiety. Findings were unchanged when considering self-reported hot flashes. CONCLUSIONS: Significant decreases in cardiac vagal control occurred during hot flashes, which may help shed light on the physiology of hot flashes. The autonomic nervous system may deserve greater attention in understanding the mechanisms linking hot flashes to cardiovascular risk.