FLUCTUATIONS IN AUTONOMIC NERVOUS ACTIVITY DURING SLEEP DISPLAYED BY POWER SPECTRUM ANALYSIS OF HEART-RATE-VARIABILITY

Objective: The use of an efficient noninvasive method to investigate the autonomic nervous system and cardiovascular control during sleep. Background: Beat-to-beat heart rate variability displays two main components: a low-frequency (LF) one representing sympathetic and parasympathetic influence and a high-frequency (HF) component of parasympathetic origin. Sympathovagal balance can be defined as LF/HF ratio. Methods/design: We reviewed normal, standardly staged all-night polysomnograms from 10 healthy children aged 6 to 17 years. Recorded 256-second traces of heart rate and respiration were sampled. Power spectra of instantaneous heart rate and respiration were computed using a fast Fourier transform method, Results: The study revealed a decrease in LF during sleep, with minimal values during non-REM slow-wave sleep and elevated levels similar to those of wakefulness during REM, HF increased with sleep onset, reaching maximal values during slow-wave sleep, and behaved as a mirror image of LF, LF/HF ratio displayed changes similar to those in LF. Conclusion: The sympathetic predominance that characterizes wakefulness decreases during non-REM sleep, is minimal in slow-wave sleep, and surges toward mean awake levels during REM sleep, The autonomic balance is shifted toward parasympathetic predominance during slow-wave sleep. This noninvasive method used to outline autonomic activity achieves results that are in complete agreement with those obtained with direct invasive tools.