arousal index
Polysomnographic measure calculating the number of arousals per hour of sleep, indicating sleep fragmentation severity.
Full Definition
The arousal index is a quantitative measure derived from polysomnography that calculates the total number of arousals divided by the total sleep time in hours. Arousals are brief awakenings or shifts to lighter sleep stages lasting 3-15 seconds that fragment sleep continuity without necessarily causing full consciousness. The arousal index provides an objective assessment of sleep fragmentation and sleep quality, with normal values typically below 15 arousals per hour in healthy adults, though this increases with age. Elevated arousal indices are associated with various sleep disorders including sleep apnea, periodic limb movement disorder, and other conditions that disrupt sleep architecture. The measure helps clinicians assess sleep quality and the potential impact of treatments on sleep consolidation.
In Context
- "The arousal index of 45 per hour indicated severe sleep fragmentation requiring treatment." — Sleep study report
- "CPAP therapy reduced the arousal index from 38 to 12 events per hour." — Treatment efficacy report