The Gold Standard of Sleep Testing
Polysomnography (PSG) is a comprehensive overnight sleep study conducted in a sleep laboratory. It's the most detailed and accurate test available for diagnosing sleep disorders. A trained sleep technologist monitors you throughout the night while sophisticated equipment records your body's activity during sleep.
What Polysomnography Measures
A PSG simultaneously records multiple body functions during sleep:
- Electroencephalogram (EEG) — Brain wave activity to identify sleep stages (N1, N2, N3, and REM sleep)
- Electrooculogram (EOG) — Eye movements to detect REM sleep
- Electromyogram (EMG) — Muscle activity in the chin and legs
- Electrocardiogram (ECG) — Heart rate and rhythm
- Respiratory effort — Chest and abdominal movement during breathing
- Nasal/oral airflow — Air movement through the nose and mouth
- Pulse oximetry — Blood oxygen saturation levels
- Snoring microphone — Records snoring intensity and patterns
- Body position sensor — Tracks sleeping position throughout the night
- Video recording — Captures movements and behaviors during sleep
What Conditions PSG Can Diagnose
- Obstructive sleep apnea (OSA)
- Central sleep apnea
- Periodic limb movement disorder (PLMD)
- REM sleep behavior disorder
- Narcolepsy (in combination with MSLT)
- Nocturnal seizures
- Parasomnias (sleepwalking, sleep terrors)
How Results Are Scored
After your study, a registered polysomnographic technologist scores the data, identifying every sleep stage transition, breathing event, leg movement, and arousal throughout the night. A board-certified sleep medicine physician then interprets the results and provides a diagnosis.
Key metrics in your report include:
- Total sleep time — How long you actually slept
- Sleep efficiency — Percentage of time in bed spent sleeping
- Sleep architecture — Distribution of sleep stages
- AHI (Apnea-Hypopnea Index) — Number of breathing events per hour
- Oxygen nadir — Lowest oxygen level recorded
- PLM index — Number of leg movements per hour
- Arousal index — Number of arousals per hour
When Is PSG Recommended?
Your doctor may recommend an in-lab PSG when:
- A home sleep test was inconclusive or negative despite strong clinical suspicion
- Complex sleep disorders are suspected (narcolepsy, parasomnias, seizures)
- You have significant medical conditions (heart failure, COPD, neuromuscular disease)
- A CPAP titration is needed
- Evaluation of treatment effectiveness is required
Myth vs. Fact
Myth: A sleep study is just about counting how many times you stop breathing.
Fact: Polysomnography measures far more than breathing — it provides a complete picture of your sleep architecture, neurological activity, cardiac function, and movement patterns.
Key Takeaways
- Polysomnography is the most comprehensive sleep test available
- It simultaneously measures brain waves, breathing, oxygen, heart rhythm, and movement
- PSG can diagnose a wide range of sleep disorders beyond sleep apnea
- Results are scored by trained technologists and interpreted by sleep physicians
- The test is painless, non-invasive, and typically covered by insurance
