Sleep apnea classification

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Saarah T. Alkhairy, M.D.


There are three types of sleep apnea: obstructive, central, and mixed. The majority of patients have obstructive sleep apnea (OSA). Individuals of untreated sleep apnea stop breathing repeatedly during the night usually for a minute or longer, during their sleep. Most of the time, these individuals are unaware of these episodes because the episodes don't trigger an awakening. Obstructive sleep apnea results from the narrowing or total blockage of the airway. In central sleep apnea, there is failure of the central nervous system to send appropriate signals to the muscles of respiration. These signals control the individual's breathing. It is also possible for an individual to have a combination of these two types, referred to as mixed apnea.


Sleep apnea can be classified into three categories:

Obstructive Sleep Apnea (OSA)

  • The majority of the three forms
  • It results from either the narrowing or total blockage of the respiratory airway which occurs when the soft tissue at the back of the throat collapses during sleep
  • OSA may be classified into three classes based on the severity of the disease[1]:
  • The severity of the disease is assessed by the Apnea Hypopnea index (AHI), which combines apneas and hypopneas
  • Apneas are defined as breathing pauses lasting 10 seconds
  • Hypopneas are defined as events lasting 10 seconds in which there is continued breathing but ventilation is reduced by at least 50% from the previous baseline during sleep
  • None/Minimal OSA: AHI < 5
  • Mild OSA: AHI = 5-14: Patients may either be asymptomatic or may complain of sleepiness when they are sedentary. The daytime sleepiness often does not impair the patients' quality of life.
  • Moderate OSA: AHI = 15-29: Patients are usually symptomatic.
  • Severe OSA: AHI ≥ 30: Patients' symptoms are severe enough to interfere with daily activities. They may fall asleep during activities that require attention (e.g. driving)

Central Sleep Apnea

  • The brain is unable to send appropriate signals to the muscles that control breathing due to the instability of the respiratory center
  • It is referred to as idiopathic central sleep apnea when an underlying etiology cannot be identified
  • Cheyne-Stokes breathing is a subtype of breathing in central sleep apnea, which is defined as periodic breathing with recurrent episodes of apnea that alternate with episodes of rapid breathing
  • In Cheyne-Stokes breathing, apnea episodes occur during sleep and during wakefulness

Mixed Apnea/Complex Sleep Apnea


  1. Loscalzo, Joseph; Longo, Dan L.; Fauci, Anthony S.; Dennis L. Kasper; Hauser, Stephen L (2011). Harrison's Principles of Internal Medicine, 18th Edition. McGraw-Hill Professional. ISBN 0-07-174889-X.

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