What are the respiratory metrics used in assessing obstructive sleep apnea (OSA)?

Updated: Sep 24, 2019
  • Author: Wendy M Smith, MD; Chief Editor: Arlen D Meyers, MD, MBA  more...
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Hypopneas are episodes of abnormally shallow breathing as defined by a 50-75% decrease in airflow. Some definitions require an oxygen desaturation of 2–4% or EEG arousal due to partial airway closure. Airway obstruction should last a minimum of 10 seconds in adults and 8 seconds in children (≥4 y).

Apneas are defined as 90% or greater decrease in airflow for 10 seconds or longer. [48]

The apnea-hypopnea index (AHI) is the sum of the number of apneic and hypopneic episodes per hour of sleep.

The respiratory disturbance index (RDI) is equal to the average number of respiratory disturbances per hour. It is similar to the AHI; however, it also includes respiratory events that do not technically meet the definitions of apneas or hypopneas but do disrupt sleep (as measured by cortical arousal) .

Respiratory event–related arousals (RERAs) are events characterized by increasing respiratory effort for 10 seconds or longer, leading to an arousal from sleep; these events do not fulfill the criteria for a hypopnea or apnea. They can be measured with esophageal manometry.

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