Sleep apnea is an obstructive disorder characterized by repeated episodes of partial or complete cessation of breathing during sleep. These episodes may be classified as obstructive, central or mixed apnea. Obstructive apnea is the absence of airflow despite an effort to breathe. Central apnea is the absence of airflow due to a lack of ventilatory effort. Mixed apnea begins with the central component of no effort to breathe, followed by a lack of airflow despite the fact that the patient is trying to breathe. Apneas or partial cessations of breathing during sleep are considered clinically significant if they last at least 10 seconds, although they usually last for 20 to 30 seconds and can last for more than a minute.
Most episodes of sleep apnea are caused when the throat airway collapses. Muscles relax during sleep and may cause a narrowing of the upper airway during inspiration, hence snoring. This narrowing of the airway also leads to increased respiratory effort and causes the individual to partially awaken. The arousal restores the muscle tone of the upper airways, allowing the individual to fall back to sleep. In sleep apnea, the cycle of sleep and arousal may be repeated throughout the night. Substances that relax muscles, such as alcohol and tranquilizers (benzodiazepines), tend to exacerbate sleep apnea.
