The overnight sleep study or polysomnography (PSG) is the "gold-standard" for diagnosing sleep apnea. It is a comprehensive recording of the biophysiological changes that occur during sleep. The PSG monitors many body functions including brain (EEG), eye movements (EOG), muscle activity (EMG), heart rhytm (ECG) during sleep, respitory air flow and blood oxygen levels (pulse oximetry).
PSG is used to diagnose or rule out many types of sleep disorders including narcolepsy, restless legs syndrome. REM behavior disorder, parasomnias and sleep apnea.
The following shows a polysomnography being performed on a patient:
Below is an example of a polysomnographic record (30 seconds). An EEG is highlighted by a red box. Eye movements are highlighted the red line.