Sleep Testing, Monitoring, and Diagnostic Procedures
Polysomnography and scoring
PSG records EEG, EOG, EMG (chin and legs), ECG, airflow, respiratory effort, oxygen saturation, and body position. Scoring uses AASM rules: sleep onset is the first epoch of any sleep stage; stage transitions follow specific rules (e.g., N2 continues until an arousal, transition to N3, or wake). Arousals require an abrupt EEG frequency shift ≥3 seconds. Leg movements are scored by duration (0.5–10 s) and periodicity. ECG monitoring identifies arrhythmias, and transcutaneous CO2 or end-tidal CO2 is used in pediatrics or suspected hypoventilation.
MSLT, MWT, actigraphy, and home testing
MSLT consists of 4–5 naps at 2-hour intervals after an overnight PSG; it measures mean sleep latency and SOREMPs. MWT assesses the ability to stay awake and is used for safety-of-life determinations (e.g., commercial drivers, narcolepsy monitoring). Actigraphy estimates sleep-wake patterns over days and is useful for circadian assessment and insomnia; it is not a substitute for PSG for apnea. Home sleep apnea testing (HSAT) is appropriate for adults with high pretest probability of moderate-to-severe OSA without significant comorbidity; it is not appropriate for children, complex comorbidity, or suspected central apnea.
Traps: using HSAT in a patient with heart failure or COPD (underestimates severity, misses central events); interpreting MSLT after inadequate sleep; and assuming actigraphy measures sleep stages-it estimates rest-activity, not architecture.
Rule of thumb: HSAT underestimates AHI because it typically scores time in bed rather than total sleep time and may miss hypopneas.
Worked example: A patient with witnessed apneas, no comorbidity, and high pretest probability is a reasonable HSAT candidate; a child or a patient with heart failure is not.