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Hypopnea (sometimes spelled hypopnœa) is a medical term for a disorder which involves episodes of overly shallow breathing on the order of 30-50% of normal respiration or an abnormally low respiratory rate. This differs from apnea in that there remains some flow of air. Hypopnea events may happen while asleep or while awake.

During sleep, hypopnea is classed as a sleep disorder. With moderate to severe hypopnea, sleep is disturbed such that patients may get a full night's sleep but still not feel rested because they did not get the right kind of sleep. The disruption in breathing may cause a drop in blood oxygen level, which may, in turn, disrupt the stages of sleep.

Hypopneas may be obstructive in nature which means that the airway has closed to some extent. Hypopneas may also be "central" in nature where the airway is completely open. Continuous Positive Airway Pressure can be used to alleviate obstructive hypopneas but will not help if the hypopneas are central in nature.

A hypopnea is scored as a central hypopnea only if none of the following conditions are present.

  • Snoring during the event
  • An increase in the flatting of the nasal pressure flow or PAP flow signal
  • Paradoxical breathing (The chest wall moves in during inhale and out during exhale)

The above requirements are from the AAST website from an article entitled "Scoring Obstructive Hypopnea VS Central Hypopnea."

Daytime hypopnea events are mostly limited to those with severely compromised respiratory muscles, as occurs in some neuromuscular diseases. Similarly, daytime hypopnea can also cause a drop in blood oxygen level."

Apnea: 80% to 100% reduction in airflow for >= 10 seconds
Hypopnea: 50% to 80% reduction in airflow for >= 10 seconds
Flow Limitation: <50% reduction in airflow for >= 10 seconds

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