Definition of Sleep apnea:

Sleep apnea is a condition characterized by episodes of stopped breathing during sleep.

See also: Sleep disorders

Causes, incidence, and risk factors:

In normal conditions, the muscles of the upper part of the throat keep this passage open to allow air to flow into the lungs. These muscles usually relax during sleep, but the passage remains open enough to permit the flow of air. Some individuals have a narrower passage, and during sleep, relaxation of these muscles causes the passage to close, and air cannot get into the lungs. Loud snoring and labored breathing occur. When complete blockage of the airway occurs, air cannot reach the lungs.

For reasons that are still unclear, in deep sleep, breathing can stop for a period of time (often more than 10 seconds). These periods of lack of breathing, or apneas, are followed by sudden attempts to breathe. These attempts are accompanied by a change to a lighter stage of sleep. The result is fragmented sleep that is not restful, leading to excessive daytime drowsiness.

Older obese men seem to be at higher risk, though as many as 40% of people with obstructive sleep apnea are not obese. Nasal obstruction, a large tongue, a narrow airway and certain shapes of the palate and jaw seem also to increase the risk. A large neck or collar size is strongly associated with obstructive sleep apnea. Ingestion of alcohol or sedatives before sleep may predispose to episodes of apnea.

The classic picture of obstructive sleep apnea includes episodes of heavy snoring that begin soon after falling asleep. The snoring proceeds at a regular pace for a period of time, often becoming louder, but is then interrupted by a long silent period during which no breathing is taking place (apnea). The apnea is then interrupted by a loud snort and gasp and the snoring returns to its regular pace. This behavior recurs frequently throughout the night.

During the apneas, the oxygen level in the blood falls. Persistent low levels of oxygen (hypoxia) may cause many of the daytime symptoms. If the condition is severe enough, pulmonary hypertension may develop leading to right-sided heart failure or cor pulmonale.