Sleep disorders, nocturnal blood pressure, and cardiovascular risk: A translational perspective

Cardiovascular disease (CVD) represents the first cause of death globally. The nighttime is generally a period of relative protection from CVD events such as myocardial infarction, sudden cardiac death, and stroke, at least compared to the early morning period. The nighttime also generally entails lower values of arterial blood pressure (ABP) and heart rate (HR) and higher cardiac parasympathetic modulation. These day-night cardiovascular rhythms are ultimately driven by circadian molecular oscillators in the hypothalamic suprachiasmatic nucleus and in peripheral cells, including those in the heart, blood vessels, and kidneys. The wake-sleep states are intermediate mechanisms of circadian cardiovascular regulation, with non-REM sleep decreasing ABP and HR and increasing cardiac parasympathetic modulation at the beginning of the night. Obstructive sleep apnea, insomnia, and the restless legs syndrome have high prevalence in the general population and may increase nighttime cardiovascular activity and CVD risk. CVD risk is better predicted by ABP values during nighttime sleep than during daytime wakefulness. Higher nighttime values of ABP and HR increase cardiac work and vessel wall stress. During the night, circadian rhythms may enhance cardiac responses to hypertrophic stimuli, increase vascular smooth muscle Rho kinase activity and contractility, decrease endothelial nitric oxide production and vascular responses to vasodilators, and increase circulating monocytes with the potential to infiltrate atherosclerotic plaques. Together, these factors configure a "perfect storm" scenario that may make increased cardiovascular activity during the night a final common mechanism linking sleep disorders to CVD risk.