Previous research has found that cardiac parasympathetic nervous system (PN
S) activity increases and cardiac sympathetic nervous system (SNS) activity
decreases during night-time sleep. This study aimed to examine in greater
detail the time course of these changes in cardiac autonomic nervous system
(ANS) activity. In the week prior to the experimental night, nine subjects
maintained a constant sleep-wake schedule and experienced an adaptation ni
ght. Each subject's experimental night consisted of 2 h of presleep wakeful
ness, followed by a night of sleep, commencing at each subject's normal sle
ep onset time. One hundred and twenty beat blocks of presleep wakefulness a
nd stable Stage 2 non-rapid eye movement (NREM) sleep across the night were
selected. SNS activity was assessed using pre-ejection period, the amplitu
de of the T-wave in the ECG and the 0.1 Hz peak from the spectral analysis
of the EGG. PNS activity was assessed using respiratory sinus arrhythmia (s
pectral analysis). Heart rate and respiratory rate were also measured. The
results indicated a progressive decrease in SNS activity throughout sleep a
nd a rise in PNS activity during the first half of the normal sleep period.
The changes in PNS activity were similar, while the changes in SNS activit
y were altered, compared with a previous study in which stage of sleep was
not controlled. This indicates a likely sleep stage influence on SNS activi
ty, but not on cardiac PNS activity. These results are consistent with the
concept of a primarily circadian, but not sleep, influence on PNS activity,
and primarily a sleep, but not circadian, influence on SNS activity.