Sleep apnea and cardiovascular risk.

Sleep apnea is evident in approximately 10% of adults in the general population, but in certain cardiovascular diseases, and in particular those characterized by sodium and water retention, its prevalence can exceed 50%. Although sleep apnea is not as yet integrated into formal cardiovascular risk assessment algorithms, there is increasing awareness of its importance in the causation or promotion of hypertension, coronary artery disease, heart failure, atrial arrhythmias, and stroke, and thus, not surprisingly, as a predictor of premature cardiovascular death. Sleep apnea manifests as two principal phenotypes, both characterized by respiratory instability: obstructive (OSA), which arises when sleep-related withdrawal of respiratory drive to the upper airway dilator muscles is superimposed upon a narrow and highly compliant airway predisposed to collapse, and central (CSA), which occurs when the partial pressure of arterial carbon dioxide falls below the apnea threshold, resulting in withdrawal of central drive to respiratory muscles. The present objectives are to: (1) review the epidemiology and patho-physiology of OSA and CSA, with particular emphasis on the role of renal sodium retention in initiating and promoting these processes, and on population studies that reveal the long-term consequences of untreated OSA and CSA; (2) illustrate mechanical, autonomic, chemical, and inflammatory mechanisms by which OSA and CSA can increase cardiovascular risk and event rates by initiating or promoting hypertension, atherosclerosis, coronary artery disease, heart failure, arrhythmias, and stroke; (3) highlight insights from randomized trials in which treating sleep apnea was the specific target of therapy; (4) emphasize the present lack of evidence that treating sleep apnea reduces cardiovascular risk and the current clinical equipoise concerning treatment of asymptomatic patients with sleep apnea; and (5) consider clinical implications and future directions of clinical research and practice.