Mechanisms of sleep-disordered breathing: causes and consequences

Obstructive sleep apnea (OSA) is very common in the general population and is characterized by ineffective inspiratory efforts against a collapsed upper airway during sleep. Collapse occurs mainly at the level of the velopharynx and oropharynx due to a combination of predisposing anatomy and the withdrawal of pharyngeal dilator activity during sleep. Central sleep apnea (CSA) is a manifestation of chemoreflex control instability, leading to periods of inadequate respiratory drive sufficient to trigger breathing, usually alternating with periods of hyperventilation. While both forms of apnea are the result of differing pathophysiology, it has become increasingly clear that OSA and CSA often coexist in the same patient, the existence of one can predispose to the other, and that the two are not as distinct as previously thought. Both OSA and CSA exert a number of acute deleterious effects including intermittent hypoxia, arousals from sleep, and swings in negative intrathoracic pressure, which in turn lead to chronic physiologic consequences such as autonomic dysregulation, endothelial dysfunction, and cardiac remodeling. These underlying pathophysiological mechanisms provide a framework for understanding why OSA and CSA may predispose to cardiovascular diseases like ischemic heart disease and stroke.