0020 Heart Rate Variability Changes During Sleep in Postmenopausal Women

Abstract Introduction Young women present a lower risk of cardiovascular disease (CVD) than age-matched men, but this risk steeply increases at menopause. Heart rate variability (HRV) has been proposed as a marker of cardiovascular health, which changes with circadian phase and menopause. We aim to understand the changes in the circadian variation of HRV that occurs in postmenopausal women. Methods Eight healthy PMW (54.8±3.4 years, one taking hormones) and 12 healthy young women (YW; 25.8±3.4 years) in their mid-follicular phase were enrolled. Participants were healthy sleepers. After a regular 8-h sleep schedule at home for ≥2 weeks, participants entered the laboratory. After a baseline nocturnal sleep period, they underwent a 48-h (PMW) or 72-h (YW) ultradian sleep-wake cycle procedure (USW) consisting of alternating 60-min wake and nap opportunities. Sleep was polysomnographically recorded. EKG recordings were used to calculate HRV parameters: heart rate (HR), SDNN, RMSSD, HF. Circadian parameters (mesor, amplitude, phase) were calculated by fitting a cosinor to HRV parameters during the first 24 naps of the USW. Linear mixed-effects models were used for between-group comparisons. Results During the hourly analysis of the baseline sleep period, PMW presented lower SDNN, RMSSD and HF compared to YW (p≤0.025), with no differences in HR. PMW also had lower SDNN, RMSSD, and HF throughout N2, N3, REM sleep, and wake epochs (p≤0.013). During the USW procedure, YW showed a significant circadian variation of HR during NREM sleep and wake, and HF during NREM sleep (p≤0.010), whereas these variations were not significant in PMW. Both groups presented a significant circadian variation of SDNN in NREM sleep and wake (p≤0.037), with no differences in amplitude or phase. PMW also presented a lower mesor of SDNN, RMSSD and HF (p≤0.024). Conclusion The lower HRV (SDNN) and parasympathetic activity (RMSSD and HF) during the sleep of PMW is consistent with the increased risk of developing CVD after menopause. Furthermore, the dampened circadian variation of HR and HF in PMW suggest a weakened circadian regulation of the cardiovascular system. This could be a mechanism involved in the increased CV risk after menopause, although this would require further investigation. Support (if any) Canadian Institutes of Health Research.