• Definition

    Polysomnography is a sleep study. A sleep study monitors you as you sleep, or try to sleep.

    There are two states of sleep:

    • Rapid eye movement (REM) sleep
    • Non-rapid eye movement (NREM) sleep

    REM sleep is associated with dreaming. Your body muscles (except your eyes and lungs) do not move during this stage of sleep.

    NREM sleep has four stages that can be detected by brain electrical activity (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.

    A sleep study measures your sleep cycles and stages by recording the following information:

    • Air flow in and out of the lungs during breathing
    • Blood oxygen levels
    • Body position
    • Brain waves (EEG)
    • Breathing effort and rate
    • Electrical activity of muscles
    • Eye movement
    • Heart rate

    Alternative Names

    Sleep study; Polysomnogram; Rapid eye movement studies

    How the test is performed

    The most common type of sleep study is performed at a special sleep center. You will be asked to arrive about 2 hours before bedtime. You will sleep in a bed at the center. Many sleep centers have rooms that are similar to hotel rooms, so that you are in a comfortable bedroom. The test is often done during the night so that your normal sleep patterns can be studied.

    The health care provider will place electrodes on your chin, scalp, and the outer edge of your eyelids. These must remain in place while you sleep.

    Signals from the electrodes are recorded while you are awake (with your eyes closed) and during sleep. The time it takes you to fall asleep is measured, as well as the time it takes you to enter REM sleep.

    Monitors to record your heart rate and breathing will be attached to your chest. These also must remain in place while you sleep. A specially trained health care provider will directly observe you while you sleep and note any changes in your breathing or heart rate. The number of times that you either stop breathing or almost stop breathing will be measured.

    In some sleep study centers, a video camera records your movements during sleep.

    Portable sleep study devices that can be used in the home instead of at a sleep center are available to help diagnose sleep apnea. You should not use these devices unless you have been evaluated by a sleep specialist.

    How to prepare for the test

    Do not take any sleeping medication and do not drink alcohol or caffeine-containing beverages before the test.

    Why the test is performed

    The test is done to diagnose possible sleep disorders, including obstructive sleep apnea (OSA). Often, OSA is suspected because of the following symptoms:

    • Daytime sleepiness (falling asleep during the day)
    • Loud snoring
    • Periods of breath holding, followed by gasps or snorts
    • Restless sleep
    • Narcolepsy
    • Periodic limb movements disorder (frequent movements of the legs during sleep)
    • REM behavior disorder (a condition in which people physically "act out" their dreams)