Asymmetry in sympathetic and vagal activities during sleep-wake transitions

Study Objectives: To explore the role of autonomic nervous system in initiation of sleep-wake transitions. Design: Changes in cardiovascular variability during sleep-wake transitions of adult male Wistar-Kyoto rats on their normal daytime sleep were analyzed. Interventions: A 6-h daytime sleep-wakefulness recording session was performed. Measurements and Results: Electroencephalogram and electromyogram (EMG) signals were subjected to continuous power spectral analysis, from which mean power frequency of the electroencephalogram (MPF) and power of the EMG were quantified. Active waking (AW), quiet sleep (QS), and paradoxical sleep (PS) were defined every 8 s according to corresponding MPF and EMG power. Continuous power spectral analysis of R-R intervals was performed to quantify its high-frequency power (HF, 0.6-2.4 Hz), low-frequency power (0.06-0.6 Hz) to HF ratio (LF/HF). MPF exhibited two phases of change during AW-QS and QS-AW transitions: a slowly changing first phase followed by a rapidly changing second phase. HF increased linearly with the decrease of MPF during the first phase of AW-QS transition whereas LF/HF increased linearly with the increase of MPF during the first phase of QS-AW transition. However, the LF/HF was not correlated with the HF. The MPF and HF exhibited only a rapidly changing phase during QS-PS transition. The LF/HF declined transiently during the QS-PS transition, followed by a sustained increase in PS. Conclusions: The parasympathetic activity before falling asleep and the sympathetic activity before waking up change coincidentally with EEG frequency, and may respectively contain the messages of sleeping and waking drives.