Which statement best describes the Respiratory Disturbance Index?

• A. It measures the number of apneas per hour
• B. It measures the number of hypopneas per hour
• C. It measures respiratory disturbances per hour during sleep
• D. It measures the duration of respiratory events

Answer: (C)

RDI describes the total number of respiratory disturbances that occur per hour of sleep. It captures apneas, hypopneas, and respiratory effort-related arousals (RERAs), counting how many events disrupt breathing per hour rather than focusing on a single type or on how long each event lasts. This broader counting approach is why it best describes the Respiratory Disturbance Index. Counting only apneas or only hypopneas provides a narrower view, and measuring duration would address how long events last rather than how often they occur per hour.