Arousal (Cortical / Respiratory)

A cortical arousal is a brief shift in brain wave activity lasting at least 3 seconds, detected by EEG, that indicates a partial awakening from sleep. Arousals do not necessarily mean the person wakes up consciously. They are brief disruptions to sleep architecture that can occur dozens of times per hour without the sleeper being aware.

Respiratory arousals are specifically triggered by breathing events: apneas, hypopneas, RERAs, or flow limitation. The brain detects increased respiratory effort or reduced oxygen and triggers a brief awakening to restore normal breathing. While this is a protective mechanism, frequent arousals fragment sleep and prevent the brain from spending sufficient time in restorative deep sleep stages.

Important context from research: Dr. Avram Gold's work suggests that flow limitation itself may drive symptoms through the limbic and HPA axis stress response, independently of cortical arousals. This means that counting arousals alone may miss the full picture of how sleep-disordered breathing affects daytime functioning. AirwayLab presents arousal estimates alongside primary flow limitation metrics for this reason.