Glossary of Sleep-related terms

Respiratory Disturbance Index (RDI)(Apnea/Hypopnea Index)

The frequency of abnormal respiratory events per hour of sleep. These events are classified as Apneas or Hypopneas. Apnea is when breathing (airflow) stops for 10 seconds or more. Hypopnea is a partial blockage of airflow resulting in arousal and a possible drop in oxygen level. An RDI of 45 would indicate that the patient is experiencing complete or partial airflow blockage 45 times per hour.1