Centre for Study and Treatment of Circadian Rhythms, Douglas Mental Health University Institute, Department of Psychiatry, McGill University, Montreal, Quebec, Canada.
Chronobiol Int. 2012 Jul;29(6):757-68. doi: 10.3109/07420528.2012.674592.
Morning hours are associated with a heightened risk of adverse cardiovascular events. Recent evidence suggests that the sleep-wake cycle and endogenous circadian system modulate cardiac function in humans and may contribute to these epidemiological findings. The aim of the present study was to investigate the interaction between circadian and sleep-wake-dependent processes on heart rate variability (HRV). Fifteen diurnally active healthy young adults underwent a 72-h ultradian sleep-wake cycle (USW) procedure (alternating 60-min wake episodes in dim light and 60-min nap opportunities in total darkness) in time isolation. The present study revealed a significant main effect of sleep-wake-dependent and circadian processes on cardiac rhythmicity, as well as a significant interaction between these processes. Turning the lights off was associated with a rapid increase in mean RR interval and cardiac parasympathetic modulation (high-frequency [HF] power), whereas low-frequency (LF) power and sympathovagal balance (LF:HF ratio) were reduced (p ≤ .001). A significant circadian rhythm in mean RR interval and HRV components was observed throughout the wake and nap episodes (p ≤ .001). Sleep-to-wake transitions occurring in the morning were associated with maximal shifts towards sympathetic autonomic activation as compared to those occurring during the rest of the day. Namely, peak LF:HF ratio was observed in the morning, coincidental with peak salivary cortisol levels. These results contribute to our understanding of the observed increase in cardiovascular vulnerability after awakening in the morning.
早晨与不良心血管事件风险增加有关。最近的证据表明，睡眠-觉醒周期和内源性昼夜节律系统调节人类的心脏功能，并可能导致这些流行病学发现。本研究旨在探讨昼夜节律和睡眠-觉醒依赖过程对心率变异性（HRV）的相互作用。15 名日间活动的健康年轻成年人在时间隔离下接受了 72 小时超昼夜睡眠-觉醒周期（USW）程序（在暗光下交替进行 60 分钟的清醒期和在全黑环境下进行 60 分钟的小睡机会）。本研究揭示了睡眠-觉醒依赖过程和昼夜节律过程对心脏节律性的显著主要影响，以及这些过程之间的显著相互作用。关灯后，平均 RR 间期和心脏副交感神经调节（高频[HF]功率）迅速增加，而低频（LF）功率和交感神经-副交感神经平衡（LF:HF 比）降低（p ≤ .001）。在清醒和小睡期间，观察到平均 RR 间期和 HRV 成分的显著昼夜节律（p ≤ .001）。与白天其他时间相比，早晨发生的睡眠-觉醒转换与最大的交感神经自主激活相关。即，清晨观察到 LF:HF 比的峰值，同时观察到唾液皮质醇水平的峰值。这些结果有助于我们理解早晨醒来后心血管脆弱性增加的原因。
