Treatment of sleep apnea with CPAP lowers central and peripheral blood pressure independent of the time-of-day: a randomized controlled study

BACKGROUND Obstructive sleep apnea (OSA) is a risk factor for hypertension and randomized controlled trials have shown that OSA treatment with continuous positive airway pressure (CPAP) reduces peripheral blood pressure and arterial stiffness. Arterial stiffness is known to augment central aortic blood pressure independent of peripheral brachial blood pressure. Currently, it is unclear whether the reduction in blood pressure with CPAP is similar between central and peripheral sites. It is also unknown whether there are any time-of-day influences on central blood pressure changes after CPAP. METHODS Thirty-eight patients received therapeutic and sham CPAP in random order for 8 weeks each with an intervening 1-month washout. Peripheral and central blood pressure and arterial stiffness (augmentation index and time to reflection) were measured by pulse wave analysis at end-of-treatment visits. Measurements were taken in the afternoon (~2 pm) and the next morning (~9 am). RESULTS Compared to sham, CPAP significantly reduced central systolic (mean difference: -4.1mm Hg; P = 0.003), central diastolic (-3.9mm Hg; P = 0.0009), peripheral systolic (-4.1mm Hg; P = 0.004), and peripheral diastolic (-3.8mm Hg; P = 0.001) blood pressure. These effects were not influenced by time-of-day. Time to reflection was improved with CPAP compared to sham (3.7ms; P = 0.01). There was no overall difference in augmentation index however when examined by time-of-day, a modest reduction with CPAP was observed in the morning (-2.5%; P = 0.03) but not in the evening (0.12%; P = 0.91). CONCLUSION CPAP reduces both central and peripheral blood pressure independent of the time-of-day. In contrast, modest improvements in conduit arterial stiffness after CPAP may only occur in the morning.