Alternate Names : Polysomnography, Rapid Eye Movement Studies, Sleep Studies

Definition

A polysomnograph is a test of sleep cycles and stages through the use of continuous recordings of brain waves (EEG), electrical activity of muscles, eye movement (electrooculogram), respiratory rate, blood pressure, blood oxygen saturation, and heart rhythm and direct observation of the person during sleep.

There are two states of sleep: non-rapid eye movement (NREM) sleep and rapid eye movement (REM) sleep. REM sleep is associated with dreaming and paralysis of body muscles (except for the eye and diaphragm muscles). NREM sleep has four stages distinguishable by EEG waves. REM sleep alternates with NREM sleep approximately every 90 minutes. A person with normal sleep usually has four to five cycles of REM and NREM sleep during a night.