What is obstructive sleep apnea (OSA)?

Obstructive sleep apnea (OSA) is the most common form of apnea and occurs when airflow through the nose or mouth is blocked. The blockage can be caused by several things, including narrowing of the airway by excess tissue (typically as a result of obesity), enlarged tonsils or a large uvula (the small fleshy pendulum of tissue that hangs from the soft palate at the back part of the roof of the mouth).

If air cannot easily flow into or out of the nose or mouth, it's more difficult to breathe. The increased effort of breathing causes a suction force in the upper part of the airway that causes it to collapse further. This can result in heavy snoring or a pause in airflow, which creates low levels of oxygen and increased levels of carbon dioxide in the blood, which in turn may wake a person from sleep or cause an arousal. With each abrupt change from deep sleep to light sleep, a signal goes from the brain to the upper airway muscles to open the airway; normal breathing resumes, often with a loud snort or gasp.

While that arousal is only a brief disturbance in sleep that does not last long enough to be considered an awakening, it can still contribute to sleep disruption. Frequent arousals, although necessary for breathing to restart, prevent restorative, deep sleep. Drinking alcohol or taking sleeping pills increases the frequency and duration of breathing pauses by sedating the brain and preventing the arousal.

Several different types of sleep-related breathing disorders exist, but the most common is obstructive sleep apnea. People with this condition might wake hundreds of times a night, whether they are conscious of it or not, because of a lack of oxygen caused by a complete or partial blocking of the upper airway by some physical obstruction.

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