Polysomnography is a comprehensive recording of the biophysiological changes that occur during sleep. It is usually performed at night, when most people sleep, though some labs can accommodate shift workers and people with circadian rhythm sleep disorders and do the test at other times of day. The PSG monitors many body functions including brain (EEG), eye movements (EOG), muscle activity or skeletal muscle activation (EMG) and heart rhythm (ECG) during sleep. After the identification of the sleep disorder sleep apnea in the 1970s, the breathing functions respiratory airflow and respiratory effort indicators were added along with peripheral pulse oximetry.

Polysomnograms are used to monitor a patient’s sleep stages and cycles to determine the presence of disturbances that can be attributed to sleep disorders. PSGs use a variety of equipment that monitors brain activity, muscle activity, breathing activity, and more to get a comprehensive interpretation of what disorder (if any) the patient is suffering from.