Sleep Evaluation and Diagnostic Testing
Polysomnography fundamentals
In-lab PSG records EEG, EOG, EMG, ECG, airflow, respiratory effort, oxygen saturation, and body position. Scoring follows AASM rules: hypopnea requires a 30% or greater drop in airflow with 3% desaturation or an arousal; apnea requires 90% or greater airflow reduction for at least 10 seconds. The apnea-hypopnea index (AHI) is events per hour of sleep.
Home sleep apnea testing and actigraphy
Home sleep apnea testing (HSAT) uses limited channels and is appropriate for adults with high pretest probability of moderate-to-severe OSA without significant cardiopulmonary comorbidity. It underestimates events because it measures time in bed, not sleep time, and cannot reliably diagnose central apnea, hypoventilation, or mild OSA. Actigraphy estimates sleep-wake patterns from movement over days to weeks; it is useful for circadian assessment and insomnia but is not a diagnostic test for apnea.
Traps
- HSAT negative result in high suspicion should prompt in-lab PSG.
- MSLT requires prior overnight PSG and adequate sleep before testing; it measures sleep-onset REM periods for narcolepsy.
- Maintenance of wakefulness test measures ability to stay awake, not sleepiness per se.
- Central vs obstructive events hinge on effort: absent effort suggests central.
Rule of thumb
Use the test that matches the question: PSG for comprehensive diagnosis, HSAT for straightforward OSA, actigraphy for circadian/insomnia patterns, MSLT for central hypersomnia.