Objective: To test the hypothesis that sleep-related breathing disorder (SRBD) is associated with increasing severity of cardiovascular risk markers.
Design: A cross-sectional study of sleep laboratory patients.
Setting: University Hospital Sleep Disorders Centre.
Patients: We studied 591 patients referred for a sleep study, all of them without a history of systemic hypertension.
Interventions: Clinical interview, two unattended sleep studies, and assessment of office blood pressure, cholesterol concentration, alcohol and nicotine consumption and daytime blood gases.
Main outcome measure: Post-hoc analysis of different cardiovascular risk markers: mean blood pressure, pulse pressure, and the type and grade of systemic hypertension.
Results: Patients were classified as normotensive (blood pressure < 140/90 mmHg, n = 228) or hypertensive (blood pressure ≥ 140/90 mmHg, n = 363) according to office blood pressure measurements. Mixed (systolic and diastolic) hypertension was the most common type of hypertension (n = 182), followed by isolated diastolic hypertension (n = 101), borderline isolated systolic hypertension (n = 70), and isolated systolic hypertension (n = 10). The frequency of mixed hypertension increased with SRBD activity (P < 0.05) and respiratory disturbance index (RDI; the number of breathing disorders per hour of estimated sleep time) was increased in those with mixed hypertension compared with those with normotension (24.8 compared with15.7;t test:P < 0.01). In hypertensive patients classified as having grades 1–3 of hypertension (n = 265, 80 and 18, respectively), there was a progressive increase in RDI (18.9, 27.2 and 30.3, respectively, P < 0.01). Mean blood pressure increased significantly with RDI. Pulse pressure increased significantly with age (P < 0.001), but was unrelated to the degree of SRBD.
Conclusion: We conclude that mean blood pressure and the severity of hypertension, but not pulse pressure, increase with the severity of the SRBD.