Polysonography, also called a sleep study, is a test used to diagnose sleep disorders. It records brain waves (EEG), the oxygen level in the blood, heart rate and breathing, as well as eye and leg movements. The test is performed throughout the night or during the day for shift workers. Together with the sleep history, the results of the sleep study are used to diagnose over 80 sleep disorders. The most common being obstructive sleep apnea.