arousalindex

ArousalIndex, or AI, is a metric used in sleep medicine to quantify how frequently arousals occur during sleep. An arousal is a brief shift in electroencephalographic (EEG) activity toward faster frequencies, lasting at least three seconds and usually following a period of stable sleep. The arousal index is defined as the number of such arousals per hour of sleep.

Measurement and calculation are typically based on overnight polysomnography, which records EEG, EOG, and EMG signals. Sleep technicians score arousals according to standardized criteria (such as those from the American Academy of Sleep Medicine). AI is calculated by dividing the total number of scored arousals by the total sleep time in hours. This yields a time-normalized measure of sleep fragmentation.

Clinical use and interpretation vary with age and context but generally, a higher AI indicates greater sleep fragmentation and poorer sleep maintenance. It is used to assess sleep quality in a range of conditions, including obstructive sleep apnea, periodic limb movement disorder, insomnia with objective arousals, and restless legs syndrome. Treatments that improve sleep continuity, such as continuous positive airway pressure (CPAP) for sleep apnea, often reduce AI.

Limitations include variability in arousal scoring between criteria sets, differences in sleep stage distribution, and comorbid conditions that affect EEG activity. AI should be interpreted alongside other sleep metrics, such as the apnea-hypopnea index, sleep efficiency, and oxygen desaturation, to provide a comprehensive assessment of sleep health.