Age-related differences in the mechanism of nondipping among patients with obstructive sleep apnea syndrome.

The frequency of nondipper (those lacking the normal drop in nocturnal blood pressure [BP]) is high in patients with obstructive sleep apnea syndrome (OSAS). The objective of this study is to investigate age-related differences in the nocturnal BP profile of patients with OSAS. The study subjects included 214 patients with polysomnography-diagnosed OSAS. The status of dipper or nondipper was determined by 24-hour ambulatory BP measurements. We divided the subjects into three groups by age (younger, middle-aged, and elderly) and compared the frequency and sleep profiles of nondippers in the different age groups. The prevalence of nondippers was significantly higher in the elderly OSAS group than in the younger and middle-aged OSAS groups (69% vs. 45%, 47%; P < .05). In the younger OSAS group, nondippers, when compared with dippers, were characterized by higher apnea-hypopnea index (AHI, 48.2 ± 27.1 vs. 37.4 ± 23.0 times/h, P < .05), whereas in the middle-aged and elderly OSAS groups, the AHI of nondippers was almost identical to that of dippers. On the other hand, in the elderly OSAS group, nondippers, when compared with dippers, had shorter periods of slow wave sleep as measured by nonrapid eye movement stage 3-4, whereas nondippers and dippers in the other two age groups were not different in terms of slow wave sleep. These results indicate age-related differences in major mechanisms leading to nondipping. Severe apnea causes nondipping only in young OSAS patients, whereas disturbance of sleep quality plays a more important role in elderly OSAS patients.