Hypopnea is defined as a 30-50% decrease in airflow that lasts longer than 10 seconds, a decrease in respiratory movements or a decrease in oxygen saturation (O2 saturation) in the blood, or awakenings resulting from this. RDI (Respiratory Disturbance Index) or apnea-hypopnea index (AHI), the most commonly used value in determining the severity of respiratory arrest during sleep, is the sum of the apnea and hypopnea numbers occurring in one hour.
