Modulation of the Sympatho-Vagal Balance during Sleep: Frequency Domain Study of Heart Rate Variability and Respiration

Sandra Werner,Sergio Cerutti,Geoffrey Viardot,Ramona Cabiddu,Anna M Bianchi

doi:10.3389/fphys.2012.00045

Abstract

Sleep is a complex state characterized by important changes in the autonomic modulation of the cardiovascular activity. Heart rate variability (HRV) greatly changes during different sleep stages, showing a predominant parasympathetic drive to the heart during non-rapid eye movement (NREM) sleep and an increased sympathetic activity during rapid eye movement (REM) sleep. Respiration undergoes important modifications as well, becoming deeper and more regular with deep sleep and shallower and more frequent during REM sleep. The aim of the present study is to assess both autonomic cardiac regulation and cardiopulmonary coupling variations during different sleep stages in healthy subjects, using spectral and cross-spectral analysis of the HRV and respiration signals. Polysomnographic sleep recordings were performed in 11 healthy women and the HRV signal and the respiration signal were obtained. The spectral and cross-spectral parameters of the HRV signal and of the respiration signal were computed at low frequency and at breathing frequency (high frequency, HF) during different sleep stages. Results attested a sympatho-vagal balance shift toward parasympathetic modulation during NREM sleep and toward sympathetic modulation during REM sleep. Spectral analysis of the HRV signal and of the respiration signal indicated a higher respiration regularity during deep sleep, and a higher parasympathetic drive was also confirmed by an increase in the coherence between the HRV and the respiration signal in the HF band during NREM sleep. Our findings about sleep stage-dependent variations in the HRV signal and in the respiratory activity are in line with previous evidences and confirm spectral analysis of the HRV and the respiration signal to be a suitable tool for investigating cardiac autonomic modulation and cardio-respiratory coupling during sleep.

Highlights

Cardiac automaticity is intrinsic to various pacemaker tissues, it is well established that the heart rate variability (HRV), i.e., the oscillation in the interval between consecutive heart beats (RR intervals), is under the control of the autonomic nervous system (ANS), the main regulation circuit of internal body functions (Pagani et al, 1986; Vanderlei et al, 2009)
A similar trend is followed by the respirogram power spectral density (PSD), which show an increase in the high frequency (HF) component during non-rapid eye movement (NREM) sleep, with the characteristic peak progressively becoming more pronounced as sleep deepness increases, and decreases during rapid eye movement (REM) sleep, when a less pronounced and more widely distributed peak can be observed
The cross-spectra between the tachogram and the respirogram show an increase in the synchronization between the two signals during NREM periods, which reaches its highest value during sleep stage N3, and a decrease during the REM period, when synchronization is hardly visible

Summary

Introduction

Cardiac automaticity is intrinsic to various pacemaker tissues, it is well established that the heart rate variability (HRV), i.e., the oscillation in the interval between consecutive heart beats (RR intervals), is under the control of the autonomic nervous system (ANS), the main regulation circuit of internal body functions (Pagani et al, 1986; Vanderlei et al, 2009). The study of the HRV represents one of the most reliable and widely used tools to investigate the cardiac autonomic modulation (Task Force of the European Society of Cardiology and the North American Society of Pacing and Electrophysiology, 1996). By analyzing the HRV in the time and in the frequency domains, information about autonomous activity can be obtained; three main spectral components can be identified on the HRV signal spectrum: very low frequency (VLF: 0.01–0.04 Hz), low frequency (LF: 0.04–0.15 Hz), and high frequency (HF: 0.15–0.4 Hz) components. Physiological interpretation of the VLF component has not been completely elucidated yet (Task Force of the European Society of Cardiology and the North American Society of Pacing and Electrophysiology, 1996), but it seems to be related to slow regulation mechanisms that cannot be studied in the time intervals typically considered for the spectral analysis of the HRV signal

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