[NCIt Definition]: A disorder characterized by recurrent episodic disruptions of breathing during sleep. It is caused by the intermittent relaxation of pharyngeal muscles leading to the narrowing or complete blockage of the upper airway. This results in compensatory arousal from sleep to breathe again. An anatomically narrow airway from body habitus or enlarged pharyngeal structures may also predispose to obstruction. Clinical presentation usually includes snoring, daytime sleepiness, difficulty concentrating and fatigue. Clinical course may progress to chronic hypoxemia with cardiovascular and cerebrovascular sequelae.

[MSH Definition]: A disorder characterized by recurrent apneas during sleep despite persistent respiratory efforts. It is due to upper airway obstruction. The respiratory pauses may induce HYPERCAPNIA or HYPOXIA. Cardiac arrhythmias and elevation of systemic and pulmonary arterial pressures may occur. Frequent partial arousals occur throughout sleep, resulting in relative SLEEP DEPRIVATION and daytime tiredness. Associated conditions include OBESITY; ACROMEGALY; MYXEDEMA; micrognathia; MYOTONIC DYSTROPHY; adenotonsilar dystrophy; and NEUROMUSCULAR DISEASES. (From Adams et al., Principles of Neurology, 6th ed, p395)

[HPO Definition]: A condition characterized by obstruction of the airway and by pauses in breathing during sleep occurring many times during the night. Obstructive sleep apnea is related to a relaxation of muscle tone (which normally occurs during sleep) leading to partial collapse of the soft tissues in the airway with resultant obstruction of the air flow. [HPO:probinson]