Elsevier

Clinical Neurophysiology

Volume 114, Issue 11, November 2003, Pages 2146-2155
Clinical Neurophysiology

A study of the dynamic interactions between sleep EEG and heart rate variability in healthy young men

https://doi.org/10.1016/S1388-2457(03)00215-3Get rights and content

Abstract

Objective: We investigated the interactions between heart rate variability and sleep electroencephalogram power spectra.

Methods: Heart rate and sleep electroencephalogram signals were recorded in 8 healthy young men. Spectral analysis was applied to electrocardiogram and electroencephalogram recordings. Spectral components of RR intervals were studied across sleep stages. The cross-spectrum maximum was determined as well as coherencies, gains and phase shifts between normalized high frequency of RR intervals and all electroencephalographic frequency bands, calculated over the first 3 NREM-REM cycles.

Results: RR intervals increased from awake to NREM and decreased during REM. Normalized low frequency decreased from awake to NREM and increased during REM while normalized high frequency evolved conversely. Low to high frequency ratio developed in opposition to RR intervals. Coherencies between normalized high frequency and power spectra were high for all bands. The gain was highest for delta band. Phase shift between normalized high frequency and delta differed from zero and modifications in normalized high frequency preceded changes in delta by 41±14°.

Conclusions: Our study demonstrates that: (1) all electroencephalographic power bands are linked to normalized high frequency; (2) modifications in cardiac vagal activity show predominantly parallel changes and precede changes in delta band by a phase shift corresponding to a lead of 12±5 min.

Introduction

Numerous cardiovascular events occur during nocturnal sleep (Vanoli et al., 1995, Lavery et al., 1997, Peled et al., 1999, Crasset et al., 2001); indeed, cardiovascular control is markedly affected by nocturnal sleep (Mancia, 1993, Somers et al., 1993). Spectral analysis has been applied to the electroencephalogram (EEG) signal to define 5 spectral frequency bands (delta, theta, alpha, beta and sigma) that characterize sleep in detail (Aeschbach and Borbely, 1993), and can be applied to the RR interval (RRI, the time between two successive R waves of the QRS signal on the electrocardiogram (ECG)) also, to assess changes in cardiac autonomic control (Akselrod et al., 1981, Vanoli et al., 1995). In healthy subjects, heart rate decreases during non-rapid-eye-movement (NREM) sleep and increases during rapid-eye-movement (REM) sleep (Somers et al., 1993, Cajochen et al., 1994, Task Force of the European Society of Cardiology and the North American Society of Pacing and Electrophysiology, 1996, Crasset et al., 2001). In addition, in healthy humans, heart rate displays low-frequency (LF) oscillations – a marker of sympathetic predominance (Pagani et al., 1986) that increase during REM sleep (Zemaityte et al., 1986, Berlad et al., 1993, Vanoli et al., 1995, Bonnet and Arand, 1997) – and faster oscillations of the respiratory frequency (high frequency, HF), a marker of vagal activity that predominate during NREM sleep (Zemaityte et al., 1986, Berlad et al., 1993, Vanoli et al., 1995, Bonnet and Arand, 1997).

Limited data are available on the dynamic interactions between sleep EEG and RRI variability (Charloux et al., 1998, Otzenberger et al., 1998, Ehrhart et al., 2000, Brandenberger et al., 2001). In particular, no information exists on which frequency band in the EEG signal is most related to the cardiac autonomic control during sleep; and little is known about the time series interactions between EEG dynamics and heart rate variability (HRV) during the night (Otzenberger et al., 1998, Ehrhart et al., 2000, Brandenberger et al., 2001).

The investigation of dynamic interactions between the spectral power bands of sleep EEGs and the HF or LF bands of HRV may contribute to a better understanding of the physiological mechanisms underlying the interactions between sleep and cardiac autonomic control.

Section snippets

Subjects

Eight young adult males aged between 18 and 23 years (mean 20.5 years) participated in the study. They were paid student volunteers, studying at the Sleep Laboratory of the ULB-Erasme Hospital. All subjects were healthy, with no current or past somatic, psychiatric, or sleep pathologies such as apnea-hypopnea syndrome, periodic legs movement syndrome, parasomnia and snoring. None had a family history of mental disorders. The participants reported a regular sleep-wake schedule and no current or

Sleep characteristics

The mean duration of NREM sleep was 357±29 min (71±4%) and of REM sleep was 109±15 min (22±3%), while the mean duration of the awake stage was 38±19 min (7±4%). The sleep efficiency was 86±7%. These results were in line with our previously reported normal values (Linkowski et al., 1989). The mean duration of the first 3 NREM-REM cycles was 323±71 min (Table 1).

RRI variability during sleep (Fig. 3)

RRI increased during the shift from the awake stage to NREM sleep and decreased during REM sleep, while the LFnu decreased during the

Discussion

Interest in the interactions between cardiac activity and sleep is growing. Indeed, a large number of cardiovascular events occur during the night (Lavery et al., 1997, Crasset et al., 2001). This study investigates the dynamic interactions between heart rate variability and EEG power spectrum across the first 3 NREM-REM cycles of nocturnal sleep in healthy young men.

Heart rate changes during sleep have also been studied in order to determine if this could provide a new basis for sleep staging.

Acknowledgements

We thank Bernard Jacques for technical assistance and all the other members of the sleep laboratory for their active participation. Research reported in this paper was supported by the Erasmus Foundation, the Foundation for cardiac surgery, the Marc Hurard Foundation, Pfizer and Astra Zeneca (Belgium). M.D. is a Research Associate of the National Fund for Scientific Research (Belgium).

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