Continuous measurement and recording of relevant normal and abnormal physiological activities during sleep: A recording of polysomnography has several physiological variables, both directly and indirectly related to the state and stages of sleep, to determine all possible biological causes of sleep disorders.

Usually, respiration, oxygen saturation, body position, and other factors are also measured during the polysomnography; including, the brain, eye movements, muscle or skeletal muscle motions, and heart rhythms.