Impact of non-dipping on cardiovascular outcomes in patients with obstructive sleep apnea syndrome

Obstructive sleep apnea syndrome (OSAS) is a risk factor for cardiovascular events. However, it is unclear how OSAS contributes to the events. We investigated the impact of non-dipping on the incidence of cardiovascular events in a retrospective cohort study comprising 251 patients with OSAS. OSAS was diagnosed by overnight polysomnography and all patients underwent 24-h ambulatory blood pressure monitoring. Non-dipping was diagnosed when reduction in sleep blood pressure was <10% of awake blood pressure. Over a mean 43-month follow-up period, 15 patients (6.0%) developed cardiovascular events including stroke, heart failure, and ischemic heart disease. Significantly higher cardiovascular events were observed in the non-dipping group than those without it by Kaplan-Meier analyses. Cox regression analysis revealed that the presence of non-dipping was significantly and independently associated with the incidence of cardiovascular events (hazard ratio, 3.88; 95% confidence interval, 1.19-17.41; p<0.05), after adjusting for severity of OSAS, and CPAP therapy. Thus, non-dipping was a marker for a poor prognosis in patients with OSAS.