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(Circulation. 2005;112:849-854.)
© 2005 American Heart Association, Inc.

Hypertension

Sleep-Related Changes in Cardiovascular Neural Regulation in Spontaneously Hypertensive Rats

Terry B.J. Kuo, MD, PhD; Cheryl C.H. Yang, PhD

From the Institute of Neuroscience (T.B.J.K., C.C.H.Y.) and Department of Physiology (T.B.J.K., C.C.H.Y.), Tzu Chi University, and Department of Neurology (T.B.J.K.), Tzu Chi Buddhist General Hospital, Hualien, Taiwan.

Correspondence to Cheryl C.H. Yang, PhD, Department of Physiology, Tzu Chi University, No. 701, Chung Yang Rd, Section 3, Hualien 970, Taiwan. E-mail cchyang{at}mail.tcu.edu.tw

Received September 3, 2004; revision received March 14, 2005; accepted April 11, 2005.

Background— Sleep has significant effects on cardiovascular neural regulation. The aim of this study is to explore the possible change in sympathetic vasomotor activity and baroreflex sensitivity associated with spontaneous hypertension during each stage of the sleep-wake cycle.

Methods and Results— Polysomnographic analysis was performed in freely moving spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto rats (WKY) during their normal daytime sleep. Continuous spectral analyses of electroencephalogram and electromyogram were performed to define active waking, quiet sleep, and paradoxical sleep. Low-frequency power of the arterial pressure variability (BLF) was quantified to provide an index of sympathetic vasomotor activity. Spontaneous baroreflex sensitivity was assessed (1) by the slopes of the regression lines of the mean arterial pressure and R-R intervals pairs that ascended (BrrA) or descended (BrrD) successively and (2) by the magnitudes of the arterial pressure and R-R intervals transfer functions in the high-frequency (BrrHF) or low-frequency (BrrLF) ranges. SHR had significantly higher mean arterial pressure during each of the sleep-wake states. Although the values of BLF, BrrA, BrrD, BrrHF, and BrrLF in SHR did not differ from those of WKY during active waking, SHR had a significantly higher BLF and lower BrrA, BrrD, BrrHF, and BrrLF compared with WKY during quiet sleep and paradoxical sleep.

Conclusions— SHR had enhanced sympathetic vasomotor activity but attenuated baroreflex sensitivity during sleep although each phenomenon was not evident when awake.

Key Words: baroreceptors • blood pressure • nervous system, autonomic • hypertension • sleep

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