A 52-year-old man with a BMI of 34 kg/m² presents with excessive daytime sleepiness and witnessed apneas during sleep. Polysomnography is performed, and the EEG tracing shows the pattern marked **B** in the diagram — repetitive brief EEG frequency shifts occurring immediately after each cessation of airflow. According to AASM scoring criteria, what is the minimum duration required for each of these EEG events to be classified as a microarousal?
A. ≥10 seconds and <20 seconds
B. ≥3 seconds and <15 seconds
C. ≥15 seconds and <30 seconds
D. ≥1 second and <3 seconds
Explanation
Why ≥3 seconds and <15 seconds is right
By AASM Scoring Manual v3 2023, a microarousal is defined as an abrupt shift in EEG frequency (involving alpha, theta, or frequencies >16 Hz, excluding sleep spindles) that lasts ≥3 seconds and <15 seconds, following ≥10 seconds of stable sleep. In obstructive sleep apnea, these microarousals occur at the termination of apneas and hypopneas as the cortical arousal mechanism restores upper airway tone. This is the precise temporal window that distinguishes a true microarousal from either background EEG noise or a full cortical arousal. The pattern marked B in the diagram represents exactly these repetitive microarousals that characterize OSA on polysomnography.
Why each distractor is wrong
≥1 second and <3 seconds: This duration is too brief and falls below the AASM minimum threshold of 3 seconds. EEG fluctuations of this duration do not meet criteria for a scorable microarousal and would not be counted in the arousal index.
≥10 seconds and <20 seconds: While 10 seconds is the minimum stable sleep duration preceding a microarousal, the microarousal itself must be <15 seconds. Durations ≥15 seconds would constitute a full cortical arousal or stage change, not a microarousal.
≥15 seconds and <30 seconds: This duration exceeds the upper limit of 15 seconds and represents a full arousal or sleep stage change rather than a microarousal. Such events are scored separately and indicate more severe sleep fragmentation.
High-YieldNEET PG
Microarousal = 3–15 seconds of EEG frequency shift after ≥10 seconds stable sleep; longer events = full arousal; shorter events = not scorable.
AASM Scoring Manual v3 2023; Harrison 21e
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