Respiratory_disturbance_index
The respiratory disturbance index (RDI)—or respiratory distress Index—is a formula used in reporting polysomnography (sleep study) findings. Like the apnea-hypopnea index (AHI), it reports on respiratory distress events during sleep, but unlike the AHI, it also includes respiratory-effort related arousals (RERAs).[1] RERAs are arousals from sleep that do not technically meet the definitions of apneas or hypopneas, but do in some way disrupt breathing during sleep and cause respiratory symptoms that may cause an arousal.
A RERA is characterized by increasing respiratory effort such as dyspneas (and thus decreasing esophageal pressures) for 10 seconds or more leading to an arousal from sleep, but one that does not fulfill the criteria for a hypopnea or apnea.[2]