Autonomic Nervous System Activity and Menopausal Symptoms
thesisposted on 05.11.2016, 00:00 by Lauren L. Drogos
Hot Flashes (HFs) occur in up to 75% of women transitioning through menopause. Previous research suggests objective HFs may shift the balance between the calming branch (parasympathetic) and the ‘fight or flight’ branch (sympathetic) of the autonomic nervous system (ANS) through withdrawal of calming activity. There is limited evidence about the effect of HFs on the ‘fight or flight’ branch of the ANS. Independent of ANS changes, HFs are associated with decreased cardiovascular health (CVH). The link between CVH and the physiology of HFs is not understood. Here we investigate differences in ANS function between women with frequent or infrequent self-reported and objectively detected HFs. Participants included 40 midlife women (Mean age = 52.1) from a parent study investigating associations between menopausal symptoms and cognition: half reported frequent HFs (>30 per week) and half reported infrequent HFs (<7 per week). HFs were assessed with objective monitoring and subjective reporting. Parasympathetic activity was assessed with variability in heart rate (HRV), which was validated against expected changes with posture (laying, sitting, and standing). Sympathetic (fight or flight) activity was measured using salivary alpha-amylase, which was validated by the expected drop after awakening. HRV changed across body position (p<0.05) but not between self-reported or objective HF group (p’s>0.40). At thirty minutes after wake, women with objective HFs had an attenuated awakening response of salivary alpha-amylase compared to women without objective HFs (β=0.71, SE= 0.32, p=0.03, d=0.73). The total number of objective HFs was the best predictor of area under the curve and awakening response of sAA. Our findings support a state shift in autonomic balance towards increased ‘fight or flight’ activation with objective, but not self-reported, HFs. In addition, we found evidence that objective HFs have a dose-dependent relationship with sympathetic activity. Finally, our findings suggest that withdrawal of parasympathetic activity occurs transiently during objective HFs, but not during a validated posture challenge. Overall, our data provide evidence that objective hot flashes are associated with a shift in the balance between the sympathetic and parasympathetic branches of the autonomic nervous system; specifically, towards increased sympathetic tone with increased frequency of objective HFs.