Health Encyclopedia

Polysomnography

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 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.

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

Blood oxygen levels
Body position
Brain waves (EEG)
Breathing rate
Electrical activity of muscles
Eye movement, breathing rate
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 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 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 electrodes are recorded while you are awake (with your eyes closed) and during sleep. The time taken to fall asleep is measured as well as the time to enter REM sleep.

Monitors to record your heart rate and breathing will be attached to your chest. These also must remain in place during 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.

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:

Excessive daytime sleepiness
Hypersomnia
Insomnia
Narcolepsy
Obstructive sleep apnea and other breathing difficulties during sleep
Periodic limb movements disorder (frequent movements of the legs during sleep)
REM behavior disorder (a condition where dreams are physically ”acted out”)

Normal Values

A normal test result shows usual or normal patterns of brain waves and muscle movements during sleep, without frequent breathing problems.

What abnormal results mean

Abnormal results may confirm a suspected sleep disorder. For example, episodes of stopped breathing during sleep is called sleep apnea. See: Obstructive sleep apnea

References

Collop NA, Anderson WM, Boehlecke B, Claman D, Goldberg R, Gottlieb DJ, et al. Clinical guidelines for the use of unattended portable monitors in the diagnosis of obstructive sleep apnea in adult patients. Portable Monitoring Task Force of the American Academy of Sleep Medicine. J Clin Sleep Med. 2007 Dec 15;3(7):737-47.

Ahmed M, Patel NP, Rosen I. Portable monitors in the diagnosis of obstructive sleep apnea. Chest. 2007 Nov;132(5):1672-7.

Patel NP, Ahmed M, Rosen I. Split-night polysomnography. Chest. 2007 Nov;132(5):1664-71.

Patil SP, Schneider H, Schwartz AR, Smith PL. Adult obstructive sleep apnea: pathophysiology and diagnosis. Chest. 2007 Jul;132(1):325-37.

Review Date:9/12/2008
Reviewed By:Allen J. Blaivas, DO, Pulmonary, Critical Care, and Sleep Medicine, Department of Veteran Affairs, VA New Jersey Health Care System, East Orange , NJ . Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.

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