Polysomnography

Polysomnography (PSG) is a comprehensive diagnostic test used to study sleep and diagnose sleep disorders. It combines multiple physiological signals recorded during sleep, including brain activity measured by electroencephalography (EEG), eye movements recorded by electrooculography (EOG), and muscle tone assessed by electromyography (EMG), typically from the chin. Additional measurements commonly include heart rate and rhythm (electrocardiography, ECG), oxygen saturation via pulse oximetry, nasal and oral airflow, respiratory effort using belts around the chest and abdomen, and sometimes body position, snoring, and limb movements.

This test is usually performed in a sleep laboratory with overnight monitoring, though portable home systems may be used in selected cases. The patient is wired with sensors and sleeps while signals are recorded. A sleep specialist later scores the data in 30-second epochs to determine sleep stages: non-rapid eye movement stages N1, N2, N3 and rapid eye movement (REM) sleep, along with arousals and awakenings. The recording also helps identify breathing abnormalities such as obstructive or central sleep apnea, hypopneas, periodic limb movements, and other sleep-related events.

PSG is the basis for diagnosing many disorders and is often followed by targeted tests such as the multiple sleep latency test (MSLT) or maintenance of wakefulness test (MWT) to evaluate daytime sleepiness, especially in suspected narcolepsy. Home sleep apnea testing may substitute PSG for some suspected obstructive sleep apnea cases, but PSG remains the gold standard for comprehensive assessment.