Obstructive sleep apnea

Repeated occlusion of the upper airway during sleep results in the obstructive sleep apnea syndrome. Affected individuals may experience excessive daytime sleepiness, intellectual impairment, and personality changes, and their risk of cerebrovascular accidents, ischemic heart disease, and severe respiratory failure is increased.

Sleep apnea is defined as total or partial cessation of nasal or oral airflow during sleep. Occlusion of the upper airway despite continued respiratory muscle activity is characteristic of obstructive sleep apnea. This is in contradistinction to central apnea, in which airflow ceases because of a lack of respiratory effort (due to an absent respiratory drive).

Apnea refers to total cessation of airflow for more than 10 seconds, whereas hypopnea usually refers to a 50% decrease in airflow, also for more than 10 seconds. The apnea or hypopnea index indicates the number of such events per hour of sleep (averaged for the total sleep time).

The occurrence of more than five episodes of apnea an hour identifies the sleep apnea syndrome, although this definition may not apply to an older population. Obstructive sleep apnea is considered mild if the apnea-plus-hypopnea index (AHI) is 6 to 20; moderate if the AHI is 21 to 50; and severe if the AHI is more than 50.

Obstructive sleep apnea affects about 1% of the population and is being recognized as a major cause of sleep disorders and daytime sleepiness. Although originally thought of as benign, the condition is now associated with increased mortality and morbidity from cardiovascular or cerebrovascular disease, arrhythmias, and automobile accidents.

Obstructive sleep apnea is accompanied by increased morbidity and mortality from cardiovascular and cerebrovascular disease. Daytime sleepiness due to the disorder may also be a factor in a higher incidence of automobile accidents in these patients.

The primary event in the pathogenesis of obstructive sleep apnea is occlusion of the upper airway as a result of approximation of the posterior tongue and palate to the pharyngeal walls. This usually occurs at the level of the velopharyngeal airway but also may occur at the hypopharyngeal airway. Instances of apnea are more frequent during rapid eye movement (REM) sleep and are characterized by inhibition of the upper airway muscles and airway collapse.

Asphyxia develops, with resolution only when brief arousal to a lighter stage of sleep restores upper airway muscle tone and patency. This sequence of events may be repeated several times and cause fragmented sleep. Daytime sleepiness results predominantly from this fragmentation, although nighttime hypoxemia may be a contributing factor.

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