lthough descriptions of sleep-disordered breathing (SDB) have been ound in medical and nonmedical literature for centuries, most of our urrent knowledge about this condition has been obtained in the past 30 ears. SDB—snoring, limited respiratory flow leading to arousals or xihemoglobin desaturations (hypopneas), or complete cessation of irflow (apneas)—are common and occur in up to 20% of the population. f accompanied by symptoms, SDB has been classified into 3 general ategories: obstructive sleep apnea (OSA) syndromes, central sleep apnea CSA) syndromes, and sleep-related hypoventilation/hypoxemia synromes. OSA is the most common of the 3 groups and its prevalence epends on the diagnostic definition used; using the most conservative efinition of apnea-hypopnea index, AHI, 5 with excessive daytime leepiness, 2%-6% of the population have OSA. CSA syndromes are less common in the general population and their xact prevalence is unknown. CSA is more common in patients with ongestive heart failure (CHF) and chronic opioid use. Coexistence of SA and central apnea activity, the latter typically revealed on attempts o correct obstructive events, is termed complex sleep apnea. Finally, besity-hypoventilation syndrome is a disorder combining obesity (body ass index 30 kg/m) with evidence of daytime hypercapnia (PaCO2 5 mm Hg).