Autonomic activity during human sleep as a function of time and sleep stage JOHN TRINDER, JAN KLEIMAN, MELINDA CARRINGTON, SIMON SMITH, SIBILAH BREEN, NELLIE TAN and YOUNG KIM Department of Psychology, University of Melbourne, Parkville, VIC, 3010, Australia Accepted in revised form 13 June 2001; received 3 January 2001 INTRODUCTION Numerous studies have recorded human blood pressure (BP) and heart rate (HR) over 24 h, showing reductions during the nyctohemeral phase (e.g. Bevan et al. 1969; Mancia et al. 1983; Furlan et al. 1990; Parati et al. 1990). The periods of reduced cardiac activity have been shown to coincide with the occurrence of sleep (Bristow et al. 1969; Smyth et al. 1969). Further, barore¯ex sensitivity increases during sleep (Smyth et al. 1969; see also Lombardi and Parati, 2000 for a review of this literature). More recently, constant routine studies have indicated that the fall in HR during sleep is partly attributable to the circadian system (Burgess et al. 1997; Kerkhof et al. 1998). In contrast, the fall in BP is entirely because of the in¯uence of sleep (Kerkhof et al. 1998). Studies that have speci®cally investigated sleep in humans have con®rmed that there is a fall in BP and HR during non- rapid eye movement (NREM) sleep as compared with relaxed wakefulness. Blood pressure may also be lower in slow wave sleep (SWS) than stage 2. During rapid eye movement (REM) Correspondence: Dr John Trinder, Department of Psychology, Univer- sity of Melbourne, Parkville, VIC., 3010, Australia. Tel.: +613 8344 6365; fax: +613 93476618; e-mail: j.trinder@psych.unimelb.edu. au J. Sleep Res. (2001) 10, 253±264 SUMMARY While there is a developing understanding of the in¯uence of sleep on cardiovascular autonomic activity in humans, there remain unresolved issues. In particular, the eect of time within the sleep period, independent of sleep stage, has not been investigated. Further, the in¯uence of sleep on central sympathetic nervous system (SNS) activity is uncertain because results using the major method applicable to humans, the low frequency (LF) component of heart rate variability (HRV), have been contradictory, and because the method itself is open to criticism. Sleep and cardiac activity were measured in 14 young healthy subjects on three nights. Data was analysed in 2-min epochs. All epochs meeting speci®ed criteria were identi®ed, beginning 2 h before, until 7 h after, sleep onset. Epoch values were allocated to 30-min bins and during sleep were also classi®ed into stage 2, slow wave sleep (SWS) and rapid eye movement (REM) sleep. The measures of cardiac activity were heart rate (HR), blood pressure (BP), high frequency (HF) and LF components of HRV and pre-ejection period (PEP). During non-rapid eye movement (NREM) sleep autonomic balance shifted from sympathetic to parasympathetic dominance, although this appeared to be more because of a shift in parasympathetic nervous system (PNS) activity. Autonomic balance during REM was in general similar to wakefulness. For BP and the HF and LF components the change occurred abruptly at sleep onset and was then constant over time within each stage of sleep, indicating that any change in autonomic balance over the sleep period is a consequence of the changing distribution of sleep stages. Two variables, HR and PEP, did show time eects re¯ecting a circadian in¯uence over HR and perhaps time asleep aecting PEP. While both the LF component and PEP showed changes consistent with reduced sympathetic tone during sleep, their pattern of change over time diered. KEYWORDS blood pressure, heart rate, sympathetic nervous system, parasympa- thetic nervous system, sleep onset, vagal tone Ó 2001 European Sleep Research Society 253