Elsevier

Clinical Neurophysiology

Volume 113, Issue 9, September 2002, Pages 1517-1521
Clinical Neurophysiology

Age difference in heart rate changes associated with micro-arousals in humans

https://doi.org/10.1016/S1388-2457(02)00189-XGet rights and content

Abstract

Objectives: Heart rate (HR) is known to change in association to micro-arousals (MA) during sleep. The aim of the present study was to evaluate the effect of age on HR variations associated with MA.

Methods: Thirty-two healthy subjects underwent one night of polysomnographic recording. They were divided into two groups of 16 subjects according to age i.e. young (20–35 years) and middle-aged (50–65 years). The R-R intervals were calculated for 11 heart beats (10 intervals) before and 15 heart beats after the onset of MA.

Results: HR changes associated with MA were characterized by a tachycardia followed by a bradycardia in both young- and middle-aged subjects. However, middle-aged subjects showed a significant reduction in the amplitude of both tachycardia and bradycardia as compared to young subjects.

Conclusions: This study revealed an age-related reduction in the amplitude of the HR changes associated with MA. These results may reflect a decline in parasympathetic functions and a higher risk of cardiovascular diseases with advancing age.

Introduction

The American Sleep Disorders Association (ASDA) has defined a micro-arousal (MA) as an abrupt shift in electroencephalographic (EEG) frequency, which may include theta, alpha and/or frequencies greater than 16 Hz. This shift generally contrasts with the background EEG activity and must last between 3 and 10 s to be scored (ASDA, 1992). Usually, subjects are unaware of MA but when they occur frequently, MA can be a major cause of excessive daytime sleepiness (Bonnet and Arand, 1996).

Recently, Sforza et al. (2000) have studied heart rate (HR) changes associated with MA in 27 healthy adults (19–55 years). These authors have found that MA was associated with a tachycardia followed by a bradycardia. Detailed analyses of the HR changes showed that the tachycardia started before EEG signs of MA. Using spectral analysis, Bonnet and Arand (1997) also observed that the increase in HR generally begins before the onset of visually detected EEG arousal in young adults.

An age-related difference in these MA-related cardiac variations has been observed (Noda et al., 2000). In a study of EEG arousals at the termination of sleep apneas/hypopneas in 13 middle-aged (40–60 years) and 10 elderly (60–77 years) patients with obstructive apnea syndrome (OSAS), the authors observed a higher cardiac activation associated with arousals in middle-aged patients in comparison to elderly patients. However, sleep apnea is known to affect autonomic sympathetic and parasympathetic activities and to possibly increase risk for cardiovascular diseases (Narkiewicz and Somers, 2001, Leung and Bradley, 2001). Therefore, the reduction in the HR activation following the EEG arousals associated with sleep apnea/hypopnea in elderly patients could be due either to the effect of repetitive hypoxia in OSAS or to normal age-related changes in cardiac activation. The present study was aiming at evaluating the age-related differences in HR changes associated with MA in a population of subjects without sleep disorders.

Section snippets

Population

Sixteen young adults (mean age: 24.6, range: 20–35 years, 8 men and 8 women) and 16 middle-aged subjects (mean age: 54.8, range: 50–65 years) matched for gender were included in this study. None of the subjects were taking medication reported to influence cardiovascular functions or sleep architecture. In addition, they were all free of sleep complaints and cardiovascular diseases. All subjects signed a consent form and the study was approved by the hospital committee.

Polysomnographic recordings

All subjects underwent one

Results

As shown in Table 1, no between-group difference was found for MA indices. Young and middle-aged subjects showed similar MA indices for the entire night (10.25±3.92 and 11.69±4.46 respectively, ns) and for stage 2 sleep separately (11.44±5.3 and 9.64±4.77 respectively, ns). In young and in middle-aged subjects, MA were associated with significant HR changes (F(25, 375)=19.04, P<0.001, Fig. 1a and F(25, 375)=12.3, P<0.001, Fig. 1b, respectively). In young subjects, planned comparisons showed an

Discussion

Results of the present study showed that MA are associated with a tachycardia starting prior to the onset of MA and followed by a bradycardia; these changes lasting at least 20 R-R intervals. In young subjects, HR changes began 5 R-R intervals before EEG signs of MA. In middle-aged subjects, HR changes began only 1 R-R interval before MA. The early tachycardia observed in young subjects suggests that HR changes are not an autonomic response to MA but rather a primary event that may contribute

Acknowledgements

This research was supported by the Canadian Institutes of Health Research (grant to J.M. and studentship to M.M.) and by the National Sciences and Engineering Research Council (studentship to N.G.). The authors are grateful to Dominique Petit, PhD, for reviewing the manuscript. The authors also thanks Gaétan Poirier, MSc, and Jean Paquet, PhD, for helping with the analyses and statistics.

References (18)

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