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1 Institute of Neuroscience, Tzu Chi University, Hualien 970, Taiwan; Department of Neurology, Tzu Chi Buddhist General Hospital, Hualien 970, Taiwan; Department of Physiology, Tzu Chi University, Hualien 970, Taiwan
2 Department of Physiology, Tzu Chi University, Hualien 970, Taiwan; Institute of Neuroscience, Tzu Chi University, Hualien 970, Taiwan
3 Institute of Neuroscience, Tzu Chi University, Hualien 970, Taiwan; Department of Physiology, Tzu Chi University, Hualien 970, Taiwan
4 Department of Neurology, Koo Foundation Sun Yat-Sen Cancer Center, Taipei 112, Taiwan
* To whom correspondence should be addressed. E-mail: cchyang{at}mail.tcu.edu.tw.
The role of the autonomic nervous system in spontaneous hypertension during each stage of the sleep-wake cycle remains unclear. The present study attempted to evaluate the differences in cardiac autonomic modulations among spontaneously hypertensive rats (SHR), normotensive Wistar-Kyoto rats (WKY), and Sprague-Dawley rats (SD) across the sleep-wake cycles. Continuous power spectral analysis of electroencephalogram, electromyogram and heart rate variability were performed in unanesthetized free moving rats during daytime sleep. Frequency domain analysis of the stationary R-R intervals (RR) was performed to quantify the high-frequency power (HF), low-frequency power (LF) to HF ratio (LF/HF), and normalized LF (LF%) of heart rate variability. WKY and SD had similar mean arterial pressure, which is significantly lower than that of SHR during active waking, quiet sleep, and paradoxical sleep. As compared with WKY and SD, SHR had lower HF but similar RR, LF/HF, and LF% during active waking. During quiet sleep, SHR developed higher LF/HF and LF% in addition to lower HF. SHR ultimately exhibited significantly lower RR accompanied with higher LF/HF and LF% and lower HF during paradoxical sleep as compared with WKY. We concluded that significant cardiac sympathovagal imbalance with an increased sympathetic modulation occurred in SHR during sleep although it was less evident during waking.
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