Polysomnography is a study of sleep cycles and sleep behavior. It is usually done in a sleep center overnight. This study involves observing a person at sleep while continuously charting brain waves (EEG), muscle activity (EMG), breathing, eye movements, and heart rhythms.

Monitored Breathing

Sleep monitor apnea
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Reasons for Test

This study can evaluate sleeping problems, such as:

  • Trouble falling or staying asleep (insomnia)
  • Breathing that stops during sleep (apnea)
  • A problem with falling asleep suddenly during the day (narcolepsy)
  • Nightmares and sleepwalking
  • Problems with arm or leg movement during sleep

What to Expect

Prior to Test

  • 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 medicines 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.
  • Make sure to arrive to the test on time.

Description of Test

You will arrive in the evening. You will be given time to become comfortable in the room where you will sleep. Electrodes will be attached to your head, legs, and chest. 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, you may be asked to try to sleep in a certain position for a part of the night. Before the 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. This will be done 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 or fix sensors. An intervention to assist with sleep, such as continuous positive airway pressure (CPAP) may be started midway through the night.

In some instances, your doctor may ask for an additional test for narcolepsy. The test is known as The Multiple Sleep Latency Test (MSLT). You will need to stay for part of the next day. You will be asked to nap for up to 20 minutes every two hours. The time it takes you to fall asleep and the time it takes you to go into rapid eye movement (REM) sleep will be measured.

After Test

In the morning, your sensors will be removed. In most cases, you will then be free to go home.

After the procedure, be sure to follow your doctor's instructions.

How Long Will It Take?

About 10-12 hours

Will It Hurt?



Results from this test may come immediately. They are most often available 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

There should be no side effects or complications from the study. Call your doctor if you have any concerns.

In case of emergency, CALL 911.