Background. Changes in the tone of the autonomic nervous system during sleep occur and characterize individual
sleep stages and probably also sleep cycles. The spectral analysis of the heart rate variability (SA HRV) is a tool for
exact assessment of autonomic nervous activity giving us precise information on the activity of the autonomic nervous
system – on its sympathetic and parasympathetic component.
Methods and Results. All night polysomnographic recording was performed in 11 healthy subjects, during which
the SA HRV was carried out. The total spectral power of the heart rate variability and relative values of its individual
components were evaluated: the very low frequency component (VLF), the low frequency component (LF), and high
frequency component (HF). The absolute value of the RR-interval duration was assessed. The LF spectral band in
normalized units was significantly higher during REM sleep than in non-REM sleep. On the other hand, the HF
spectral band in normalized units was significantly higher during non-REM sleep compared to REM sleep. The
LF/HF ratio, which reflects the sympathovagal balance, had a maximal value during REM sleep and reached its
minimum in non-REM sleep. A gradual lengthening of the RR-interval and lowering of the LF/HF ratio during night
Conclusions. The SA HRV showed to be a sensitive method for detection of activity of the autonomic nervous system
during sleep. The sympathovagal balance was shifted to prevailing sympathetic activity in REM sleep. On the
contrary, during non-REM sleep this balance was shifted towards prevailing parasympathetic influence. A gradual
increase of parasympathetic influence during night was also observed.
autonomic nervous system, sleep, heart rate variability.