Sleep Testing, Polysomnography, and Diagnostic Assessment
What you must know
Polysomnography (PSG) records EEG, EOG, EMG (chin and legs), ECG, airflow, respiratory effort, oxygen saturation, and body position. Home sleep apnea testing (HSAT) is appropriate for adults with high pretest probability of moderate-severe OSA without significant comorbidity; it is not appropriate for suspected central apnea, OHS, severe cardiopulmonary disease, or pediatric patients.
Staging rules: N1 = low-amplitude mixed-frequency EEG, slow eye movements; N2 = spindles/K-complexes; N3 = ≥20% slow waves (0.5-2 Hz, >75 µV); R = low-amplitude mixed-frequency EEG, rapid eye movements, lowest chin EMG. Arousals require ≥3 seconds of EEG shift. Desaturation is typically ≥3% or ≥4% depending on the scoring rule.
Traps
- Using HSAT in a patient with heart failure or suspected OHS.
- Confusing the AASM recommended vs acceptable hypopnea rules.
- Missing that positional and REM-related OSA may be underestimated on HSAT.
- Forgetting that total sleep time (not time in bed) is the denominator for AHI.
Rule of thumb
"PSG is the gold standard; HSAT is a screening shortcut for uncomplicated suspected OSA."
Worked example
A 45-year-old with snoring, witnessed apneas, no cardiopulmonary disease, and BMI 31 is a good HSAT candidate. If the HSAT is negative but suspicion remains, proceed to in-lab PSG.