Previous studies in healthy individuals have documented that traditional autonomic measures, such as mean heart
rate and blood pressure, demonstrate characteristic changes
during sleep, and have established differences between
non-rapid eye movement (NREM) and rapid eye movement (REM) sleep.6-8 More recently, several studies utilizing HRV analysis have confirmed differences between
NREM and REM sleep in sympathovagal activity.
There appears to be consensus that compared to waking,
NREM sleep is characterized by a decreased LF/HF ratio
suggesting vagal predominance, while REM sleep is associated with an increased LF/HF ratio indicating sympathetic dominance.9-13 Sleep-related changes in the individual
LF and HF bands generating the described alterations in
LF/HF ratio have been less consistent. For example,
Vaughn et al. found an increase in the LF component during REM sleep, while others have instead reported
decreased HF band power as the main cause of the increased LF/HF ratio during REM.