Circadian variation of heart rate variability during different sleep stages

Abstract

Introduction Heart rate (HR) and heart rate variability (HRV) have been shown to be influenced by the circadian system during wakefulness and to be affected by sleep. The aim of the present study was to assess the effects of sleep stages on the circadian variation of HRV. Materials and methods Fifteen healthy subjects (12 men, 3 women in follicular phase; mean age ± SD: 24.6 ± 4.5 years) entered the laboratory for an 8-h baseline nocturnal sleep episode during which sleep disorders were ruled out. Upon awakening, they underwent a 72-h ultradian sleep–wake cycle (USW) procedure consisting of 60-min wake episodes in dim light ( 10 lux) alternating with 60-min nap opportunities in darkness. HR was monitored, high and low frequencies (HF, LF), and the LF:HF ratio were calculated as indexes of HRV. Core body temperature (CBT) and polysomnographic sleep recordings were collected throughout the experiment.Circadian phase was determined based on CBT min (0°) and HRV data was analyzed based on circadian phase and its corresponding sleep stage using non-linear mixed models. Results A significant circadian rhythm was observed for HR during each sleep stage (P = 0.002); for HF power during each sleep stage (P = 0.05) except REM sleep; for LF power during each sleep stage (P = 0.02) except slow wave sleep (SWS) and REM sleep; and for the LF:HF ratio only during wake epochs during naps and REM sleep (P = 0.003).During stage 2 sleep and SWS, HR minimum occurred at the beginning of the night, advanced relative to the CBT minimum (P ⩽ 0.03).During REM sleep, HR was maximal around the time of habitual awakening (10:13 ± 0:42).The acrophase of HF and LF power rhythms measured during sleep was aligned with CBT min.There was a trend for the HF power acrophase during SWS to be advanced relative to the CBT min (P = 0.07).The acrophase of the LF:HF ratio during REM sleep occurred in the early morning, significantly advanced compared to that of wake episodes (P 0.001). Conclusion A significant circadian rhythm in parasympathetic cardiac modulation was observed during non-REM sleep with an acrophase around 02:00.Sympathovagal cardiac balance also followed a circadian pattern during REM sleep, with maximal sympathetic cardiac dominance occurring in the early morning.The temporal relationship between sleep stage-specific circadian rhythms in HRV and the diurnal distribution of adverse cardiovascular events lends support to the theory that autonomic balance modulates cardiovascular risks throughout the day. Acknowledgements Research was supported by the Canadian Institutes of Health Research (CIHR). P. Boudreau was supported by Institut de recherche Robert-Sauve en sante et en securite du travail (IRSST).