Aims: This study hypothesized that the sleep-wake cycle is the major determinant factor affecting blood pressure (BP) dipping in rats and that the sympathovagal imbalance during quiet sleep is associated with the degree of BP fall.
Methods: Polysomnographic recording was performed by telemetry on freely moving Wistar–Kyoto rats over 24 h. Active waking and quiet sleep stages were scored using electroencephalogram and electromyogram. BP dipping was assessed as the percentage decline in SBP from dark active waking to light quiet sleep. About 38% of the rats were classified as dippers (>10% dip) and 62% as nondippers (<10% dip).
Results: Among the dipper rats, as compared to dark active waking, the R-R interval and high-frequency power of heart rate variability (a cardiac vagal index) were increased, whereas low-frequency power of blood pressure variability [(BLF), a vascular sympathetic index)] was decreased in light quiet sleep. The sleep-wake cycle rather than the light-dark cycle played the major role in determining BP dipping. The light-dark change in R-R interval, BLF during dark active waking, and baroreflex sensitivity indices during quiet sleep were significantly lower among nondipper rats than among dipper rats. Correlation analysis revealed that BLF during dark active waking as well as high-frequency power of heart rate variability and baroreflex sensitivity indices during light quiet sleep were correlated with the BP dipping percentage.
Conclusion: This study confirms that the sleep-wake cycle is more important than the light-dark cycle in determining BP dipping. Moreover, lower baroreflex control and parasympathetic activity during quiet sleep as well as lower sympathetic activity during active waking are associated with reduced BP dipping.
aInstitute of Brain Science
bSleep Research Center
cBrain Research Center
dFaculty of Medicine, School of Medicine, National Yang-Ming University
eDepartment of Education and Research, Taipei City Hospital, Taipei, Taiwan
*Terry B.J. Kuo and Chun-Yu Chen contributed equally to the writing of this article.
Correspondence to Cheryl C.H. Yang, PhD, Sleep Research Center and Institute of Brain Science, National Yang-Ming University, No. 155, Sec. 2, Li-Nong St., Taipei 11221, Taiwan. Tel: +886 2 28267058; fax: +886 2 28273123; e-mail: firstname.lastname@example.org
Abbreviations: BLF, low-frequency power of blood pressure variability; BP, blood pressure; BrrA, baroreflex sensitivity of ascending MAP-RR pairs; BrrD, baroreflex sensitivity of descending MAP-RR pairs; EEG, electroencephalogram; MAP, mean arterial pressure; NREM, nonrapid eye movement
Received 11 October, 2013
Revised 29 November, 2013
Accepted 29 November, 2013
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