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(Polysomnogram; Overnight Sleep Study; Rapid Eye Movement Studies)

Pronounced: Pol-ee-som-NAH-grah-fee

En Español (Spanish Version)


Polysomnography is a study of sleep cycles and behavior, usually done all night long in a sleep center. This study involves observing a person at sleep while continuously charting brain waves, muscle activity, breathing, eye movements, and heart rhythms.

Parts of the Body Involved

Polysomnography tracks a variety of processes in the body.

  • Special sensors, called electrodes, placed on the head show brain wave patterns which can be used to determine what stages of sleep or wakefulness a person is in.
  • Electrodes track muscle movement or tension in your legs, diaphragm (large breathing muscle), or eyes.
  • Breathing monitors on the nose, mouth, or chest can tell when breathing stops, airflow is low, or oxygen levels change.
  • Monitors track heart rate and rhythms.
  • A clip on the finger monitors the color of blood, which helps indicate its oxygen level. A blood pressure cuff monitors blood pressure.

Monitored Breathing

Sleep monitor apnea

© 2008 Nucleus Medical Art, Inc.

Reasons for Procedure

This study allows doctors to track the different stages of sleep, called nonrapid eye movement (NREM) sleep and rapid eye movement (REM) sleep, which is associated with dreaming. The test can track other characteristics and events such as

  • The number of times you awaken
  • Sleepwalking
  • Nightmares
  • Periodic limb movement disorder
In addition, the study can evaluate sleeping disorders. These include:

  • Trouble falling or staying asleep ( insomnia )
  • Breathing that stops during sleep (apnea)
  • A problem with falling asleep suddenly during the day ( narcolepsy )

A sleep study may also be done to help set up treatment for sleep-related breathing disorders or to show why a treatment is not working.

Risk Factors for Complications During the Procedure

There are no known risks associated with this study.

What to Expect

  • Wash your hair, but do not use any sprays, oils, or conditioners.
  • The night of the test, eat dinner as you normally would.
  • Do not drink alcohol or caffeinated beverages or take any sleeping aids before the test.
  • Bring any medications you are taking. When making the appointment for the sleep study, ask whether you should keep taking them in the days before the test.
  • Bring comfortable pajamas and a bathrobe to wear.
  • Arrive a couple of hours ahead of time or as instructed.


Anesthesia is not used during this study.

Description of the Procedure

You will arrive in the evening and have time to become comfortable in a room where you will sleep alone. A technologist attaches electrodes to your head, legs, and chest. Signals from these sensors travel through wires to a computer where they show what stages of sleep or wakefulness you are in. Other monitors are placed around your chest, near your nose and mouth, and on your finger. You will be able to read or relax until your bedtime. Although you will be able to move and turn over during sleep, the technologist may ask you to try sleeping in a certain position for a part of the night. Before lights are turned out, the technologist will test the sensors to be sure they are working. The technologist will also observe you by video during the night in case sensors come loose or need to be removed for you to go to the bathroom. The technologist may come in during the night to check on or fix sensors. You can communicate with this person by an intercom.

After Procedure

In the morning, the technologist will test and remove the sensors and clean your skin where electrodes were attached. In most cases, you will then be free to go home, to work, or to your hospital room. In some instances, your doctor may ask for an additional test for Narcolepsy known as The Multiple Sleep Latency Test (MSLT). In this case, you will stay for part of the next day during which you will be asked to nap for up to 20 minutes every 2 hours. The technician will measure the time it takes you to fall asleep and the time it takes you to go into Rapid Eye Movement (REM) sleep which is a test for the severity of sleepiness and an indicator of Narcolepsy.

How Long Will It Take?

The study lasts about 10 to 12 hours.

Will It Hurt?


Possible Complications

If you did not sleep well, you may be tired. But other than that, there are no complications. It is common not to sleep well away from home, but this will not affect your test results.

Average Hospital Stay

You will spend the night at the sleep center.

Postoperative Care



Results from this test may come immediately, but usually within two weeks. The technologist reviews the data, charting your sleep stages and noting any abnormal breathing or leg movements. A doctor reviews the results to determine the cause of your sleep problem.

Call Your Doctor If Any of the Following Occurs

There should be no side effects or complications from the study.


American Academy of Sleep Medicine

American Sleep Apnea Association

National Sleep Foundation


Better Sleep Council Canada

Canadian Sleep Society


Culebras, A. Sleep disorders In: Gilman S, editor. MedLink Neurology. San Diego: MedLink Corporation. Available at www.medlink.com. Accessed May 31, 2008.

Medical encyclopedia: polysomnogram. MedlinePlus website. Available at: http://www.nlm.nih.gov/medlineplus/ency/article/003932.htm . Accessed September 1, 2005.

Montagna P. Periodic limb movements. In: Gilman S, editor. MedLink Neurology . San Diego: MedLink Corporation. Available at www.medlink.com. Accessed March 20, 2007.

Overnight sleep study. American Academy of Sleep Medicine website. Available at http://www.sleepeducation.com/Topic.aspx?id=12 . Accessed September 1, 2005.

Polysomnography test (PSG). University of Iowa Virtual Hospital website. Available at http://www.vh.org/adult/patient/neurology/polysomnographytest/index.html . Accessed September 1, 2005.

What is polysomnography? Available at American Association of Respiratory Care website. http://www.yourlunghealth.org/basic_information/diagnostic_tests/polysomnography/index.cfm . Accessed September 1, 2005.

Last reviewed May 2008 by J. Thomas Megerian, MD, PhD, FAAP

Please be aware that this information is provided to supplement the care provided by your physician. It is neither intended nor implied to be a substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with any questions you may have regarding a medical condition.

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