Autonomic activity during human sleep as a function of time and sleep stage

Abstract

While there is a developing understanding of the influence of sleep on cardiovascular autonomic activity in humans, there remain unresolved issues. In particular, the effect of time within the sleep period, independent of sleep stage, has not been investigated. Further, the influence 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 specified criteria were identified, beginning 2 h before, until 7 h after, sleep onset. Epoch values were allocated to 30‐min bins and during sleep were also classified 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 effects reflecting a circadian influence over HR and perhaps time asleep affecting PEP. While both the LF component and PEP showed changes consistent with reduced sympathetic tone during sleep, their pattern of change over time differed.

Reduced parasympathetic activity during sleep in the symptomatic phase of severe premenstrual syndrome

“…Landen et al (12) used 24-h ECG recordings for their time domain HRV measures, and 10-min ECG recordings when subjects were awake for frequency domain HRV measures. Total variance of HRV depends on the length of the recording period (10) and there are differences in HRV measures between waking and sleeping hours (30) and according to sleep stages (22). By using a 24-h recording period that combined wake and sleep periods, menstrual phase differences in time-domain HRV variables in the women with PMDD may have been masked in the study by Landen et al (12).…”

“…The analyses were conducted using software developed at the University of Melbourne (22). During initial analyses of the ECG, R waves were detected using an automated algorithm, allowing inter-beat interval to be calculated by the program.…”

“…Power spectrum analysis of HRV was conducted to determine activity in the high frequency (HF) and low frequency (LF) bands according to published guidelines (10) and following procedures used in a previous study (22). Periods of stable sleep were analysed in 2 minute epochs (see below for criteria used to identify epochs).…”

“…Power within the LF and HF bands was quantified by the absolute integrated power in arbitrary units. Peak frequency of the high frequency band (HFfr), which is a measure of respiratory rate (22), was also calculated.…”

“…However, sleep is not a uniform state with regard to cardiovascular activity. NREM sleep is characterized by lower heart rate, and a higher HF power component of HRV compared with wakefulness (22). These changes are reversed during REM sleep; thus heart rate is higher, whereas HF power is lower, compared with NREM sleep (22).…”