Effects of treatment of obstructive sleep apnea on circadian hemodynamics

INTRODUCTION: The role of obstructive sleep apnea syndrome (OSAS) in the etiology of daytime hypertension is still an issue of debate, which is fed by the high prevalence of the syndrome in hypertensive patients. In this study the anti-hypertensive effect of short-term treatment of obstructive sleep apnea with nasal continuous positive airway pressure (nCPAP) was assessed. PATIENTS AND METHODS: In eight patients with documented OSAS (mean apnea index 62 apneas/h), two 24-h continuous finger blood pressure registrations (Portapres) were performed. At baseline and after 3 weeks of treatment with nCPAP. Ten hypertensive control subjects were studied. Stroke volume (SV), cardiac output (CO) and total peripheral resistance (TPR) were assessed by pulse contour analysis. RESULTS: Hemodynamics were highly reproducible in the controls. nCPAP therapy improved apnea-activity in all OSAS patients. This was associated with a reduction of nighttime systolic (SBP), mean arterial (MAP) and diastolic blood pressure (DBP). Treatment also reduced daytime MAP by -11 mm Hg (ranging from -27 to 1; P < 0.05), and DBP by -7 mm Hg (-24 to 3; P < 0.05). CO was significantly increased in daytime by 9% (-4 to 25; P < 0.05), whereas TPR was reduced by -15% (-34 to 3; P < 0.05). CONCLUSIONS: Treatment of OSAS caused a reduction in daytime MAP and DBP, associated with a reduction of vascular resistance. These findings are consistent with the hypothesis of a reduced sympathetic outflow at night after therapy of obstructive sleep apnea, carrying over to the day.