The role of autonomic and baroreceptor reflex control in blood pressure dipping and nondipping in rats.

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.

Suppressing cardiac vagal modulation and changing sleep patterns in rats after chronic ischemic stroke injury.

Chronic autonomic function and sleep architecture changes in patients post-stroke are not well understood. Using wireless polysomnographic recordings, this study aimed to investigate the long-term effects on sleep patterns and autonomic function in free moving rats after middle cerebral artery occlusion (MCAO). The sleep pattern and heart rate variability (HRV) of Wistar-Kyoto rats (WKY) were analyzed. After 7-10days, the rats were divided into two groups: an MCAO group (n=8) and a sham surgery group (n=8). Compared with shams, MCAO rats showed decreased accumulated quiet sleep (QS) time over 24h during the 3rd week. The time percentage, duration and delta power of QS were also significantly decreased in the MCAO group during the dark period. Compared with baseline, there were significant increases in the parasympathetic-associated HRV measures in the sham group, including the total power (TP), high frequency power (HF) and lower frequency power (LF), throughout the post-operative weeks (primarily the 2nd and 3rd weeks), reflecting a developmental increase of parasympathetic modulation; the normalized LF and the LF-HF ratio were unaffected. In great contrast, however, most of the HRV measures in the MCAO group were not significantly changed. Therefore, this study showed that the long-term effects of ischemic stroke injury involve retardation of the establishment of parasympathetic enhancement and disturbance of the normal sleep-wake cycle.