Obstructive sleep apnea overview


 * Associate Editor(s)-In-Chief: Kashish Goel, M.D.

Obstructive sleep apnea (OSA) is not only much more frequent than central sleep apnea, it is a common condition in many parts of the world. If studied carefully in a sleep lab by polysomnography, approximately 1 in 5 American adults has at least mild OSA. Since the muscle tone of the body ordinarily relaxes during sleep, and since, at the level of the throat, the human airway is composed of walls of soft tissue, which can collapse, it is easy to understand why breathing can be obstructed during sleep. Although many individuals experience episodes of obstructive sleep apnea at some point in life, a much smaller percentage of people are afflicted with chronic severe obstructive sleep apnea.

Normal sleep/wakefulness in adults has distinct stages numbered 1 to 4, REM sleep, and wake. The deeper stages (3 to 4) are required for the physically restorative effects of sleep and in pre-adolescents are the focus of release for human growth hormone. Stages 2 and REM, which combined are 70% of an average person's total sleep time, are more associated with mental recovery and maintenance. During REM sleep in particular, muscle tone of the throat and neck, as well as the vast majority of all skeletal muscles, is almost completely attenuated, allowing the tongue and soft palate/oropharynx to relax, and in the case of sleep apnea, to impede the flow of air to a degree ranging from light snoring to complete collapse. In the cases where airflow is reduced to a degree where blood oxygen levels fall, or the physical exertion to breathe is too great, neurological mechanisms trigger a sudden interruption of sleep, called a neurological arousal. These arousals may or may not result in complete awakening, but can have a significant negative effect on the restorative quality of sleep. In significant cases of obstructive sleep apnea, one consequence is sleep deprivation due to the repetitive disruption and recovery of sleep activity. This sleep interruption in stages 3 and 4 (also collectively called slow-wave sleep), can interfere with normal growth patterns, healing, and immune response, especially in children and young adults.

Many people experience elements of obstructive sleep apnea for only a short period of time. This can be the result of an upper respiratory infection that causes nasal congestion, along with swelling of the throat, or tonsillitis that temporarily produces very enlarged tonsils. The Epstein-Barr virus, for example, is known to be able to dramatically increase the size of lymphoid tissue during acute infection, and obstructive sleep apnea is fairly common in acute cases of severe infectious mononucleosis. Temporary spells of obstructive sleep apnea syndrome may also occur in individuals who are under the influence of a drug (such as alcohol) that may relax their body tone excessively and interfere with normal arousal from sleep mechanisms.