Non-dipping pattern of hypertension and obstructive sleep apnea syndrome

There is growing recognition of cardiovascular consequences of obstructive sleep apnea (OSA). Recurrent episodes of airway obstructions result in hypoxia and hypercapnia increasing sympathetic neural tone, which in turn causes vasoconstriction and marked increases in blood pressure (BP). BP response to OSA may be important in understanding the absence of nocturnal BP fall in the subgroup of hypertensive patients termed 'non-dippers'. Even mild sleep apnea can increase nocturnal BP through different mechanisms including hypoxemia, sympathetic activation, mechanical changes and disruption of normal sleep. Sleep apnea may be an important factor in determining the increased cardiovascular risk in hypertensive non-dippers. Effective treatment of sleep apnea may attenuate neurohumoral and metabolic abnormalities, improve diurnal BP control and conceivably reduce cardiovascular risk. This review examines the evidence linking OSA to non-dipping pattern of hypertension, and discusses potential mechanisms underlying this link. We will review first, prognostic value of nighttime BP; second, the cardiovascular consequences of sleep apnea; third, the evidence for altered diurnal BP profile in sleep apnea; fourth, the mechanisms contributing to both nocturnal and daytime hypertension in sleep apnea; fifth, the benefits of sleep apnea treatment and finally implications for hypertension management.