Reduced capacity of autonomic and baroreflex control associated with sleep pattern in spontaneously hypertensive rats with a nondipping profile

OBJECTIVE: Ambulatory blood pressure (BP) monitoring with a lack of nocturnal BP fall (BP nondipping) has been reported to be more prevalent among hypertensive populations and is a risk factor for cardiovascular disease than in patients with dipping pattern. However, its underlying mechanism is not fully understood. This study hypothesized that spontaneously hypertensive rats (SHRs) with a nondipping profile have an exaggerated disruption of both autonomic functioning and sleep compared with Wistar-Kyoto rats (WKYs) with a nondipping profile. METHODS: Continuous power spectral analysis of electroencephalogram, electromyogram, and cardiovascular variability was performed in WKYs and SHRs over 24 h. BP dipping was assessed as the percentage decline in SBP from dark active waking to light quiet sleep (lQS). According to the human definition of BP dipping (10%), we divided WKYs and SHRs into dipper and nondipper groups individually. RESULTS: Of the four groups, both parasympathetic activity and baroreflex sensitivity in sleep were the lowest in the SHR nondippers. Compared with the WKY nondippers, the SHR nondippers spent more time awake and less time asleep during the light period and the opposite during the dark period. Moreover, they showed more interruptions and a lower delta power percentage of lQS. Correlation analysis revealed that baroreflex sensitivity during lQS was correlated with the BP dipping percentage in SHRs. CONCLUSION: SHR nondippers exhibit poor sleep quality and impaired autonomic functioning to a greater degree than do SHR dippers and WKY nondippers, which may account for a higher cardiovascular risk in this population.