Types of Sleep Apnea
Scientists have distinguished three types of sleep apnea: obstructive sleep apnea, central sleep apnea, and mixed sleep apnea. However, since all three types of apnea may have similar symptoms and signs, a sleep apnea study is needed to tell the difference among them.
Obstructive Sleep Apnea Syndrome
Obstructive Sleep Apnea (OSA) is the most common type. During OSA efforts to breathe continue but air cannot flow in or out of the patient's nose or mouth. The patient snores heavily and has frequent arousals (abrupt changes from deep sleep to light sleep) without being aware of them.
OSA occurs when the throat muscles and tongue relax during breathing and partially block the opening of the airway. When the muscles of the soft palate at the base of the tongue and the uvula (the small conical fleshy tissue hanging from the center of the soft palate)relax and sag, the airway becomes obstructed making breathing labored and noisy. Airway narrowing may also occur due to being overweight, possibly because of the associated increases in the amount of tissue in the airway.
Central Sleep Apnea
The reduction in oxygen and increase in carbon dioxide which occur during apnea cause arousals. With each arousal, a signal is sent to the upper airway muscles to open the airway; breathing is resumed with a loud snort or gasp. Although arousals serve as a rescue mechanism and are necessary for a patient with apnea, they interrurupt sleep, and the patient ends up with less restorative and deep sleep than normal individuals.
Central Sleep Apnea occurs less frequently than obstructive apena. There is no airflow in or out of the airways because efforts to breathe have stopped for short periods of time. In central apnea, the brain temporarily fails to send the signals to the diaphragm and the chest muscles that maintain the breathing cycle. It is present more often in the elderly than in younger people but often goes unrecognized.
In central apnea, there is periodic loss of rhythmic breathing movements. The airway remains open but air does not pass through the nose or mouth because activity of the diaphragm and the chest muscles stops. Patients with central apnea may not snore and they tend to be more aware of their frequent awakenings than those with obstructive apnea.
Mixed Sleep Apnea
In mixed apnea, a period of central apnea is followed by a period of obstructive apnea before regular breathing resumes. People with mixed apnea frequently snore.
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Swanson, Jennifer. Sleep Disorders Sourcebook. Detroit, Michigan: Omnigraphics, Inc., 1999: 175-176.