RERA (Respiratory Effort-Related Arousal)

A Respiratory Effort-Related Arousal (RERA) is a breathing event where respiratory effort increases progressively over a sequence of breaths due to airway narrowing, but the airflow reduction does not meet the criteria for apnea (complete cessation) or hypopnea (significant reduction with oxygen drop). The sequence ends when the brain triggers a brief cortical arousal to restore normal airflow.

RERAs are significant because they fragment sleep without being counted in the standard AHI metric. A person with an AHI of 2 (normal) but a RERA index of 15 per hour is experiencing substantial sleep disruption. RERAs are a hallmark of Upper Airway Resistance Syndrome (UARS), where the airway is narrow enough to increase breathing effort and cause arousals but not narrow enough to produce the apneas and hypopneas that AHI measures.

True RERA scoring requires EEG to detect cortical arousals. AirwayLab estimates RERA-like events from the flow waveform by identifying sequences of 3 to 15 consecutive breaths with progressively worsening NED scores, terminated by a recovery breath (sudden NED drop). This provides a useful estimate of respiratory effort arousals from SD card data alone.