Blood pressure effects of CPAP in nonresistant and resistant hypertension associated with OSA: A systematic review of randomized clinical trials

Obstructive sleep apnea (OSA) is a rather common chronic disorder, associated with increased prevalence of hypertension. The pathophysiological mechanisms for hypertension in OSA are at least in part linked to intermittent hypoxia developed during nightly hypopneas and apneas. Hypoxemia stimulates sympathetic overactivity, systemic inflammation, oxidative stress, and endothelial dysfunction. However, it appears that intermittent hypoxemia is not the only factor in the development of hypertension in OSA. Supplemental oxygen therapy that improved oxyhemoglobin saturation to similar levels to those achieved with CPAP treatment did not reduce BP. In this scenario, it could be proposed that hypoxemia acts as a trigger of sympathetic overdrive, which when set is the main factor in the development of hypertension in OSA. This review appraises evidence provided by randomized controlled trials on the BP-lowering effectiveness of continuous positive airway pressure (CPAP) treatment of OSA patients with nonresistant and resistant hypertension. It suggests that CPAP treatment is more effective in treating resistant hypertension than nonresistant hypertension. A possible explanation is that sympathetic overactivity and altered vascular reactivity in OSA could be more severe in resistant hypertension than in nonresistant hypertension. An intricate interaction among compliance, adherence, and their interaction with demographic characteristics, genetic factors, and comorbidities of the population included might explain the differences found between trials on their influence over the antihypertensive effectiveness of CPAP. Further long-term trials are needed in hypertensive OSA patients to assess whether CPAP treatment in OSA patients consistently restores physiological nocturnal BP fall and adjusts resting and circadian heart rate.