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Sleep Study

What is a sleep study?

The stages of sleep range from light to deep. Each stage has characteristics that can be measured. A sleep study is a number of tests done at the same time during sleep. The tests measure specific sleep characteristics and help to diagnose sleep disorders. A sleep study may also be called polysomnogram.

The basic recordings done during a sleep study may include:

  • Electroencephalography (EEG). This measures brain wave activity.
  • Electrooculogram (EOG). This measures eye movement.
  • Electromyography (EMG). This measures muscle movement.
  • Other recordings. An electrocardiogram (ECG) may be used to record electrical activity of the heart. Video recordings may also be made of you while you sleep.

Sleep studies generally take place in a sleep lab during your normal sleeping hours. The goal is to record brain and body activity that occurs during sleep so that sleep disorders can be diagnosed and treated.

During a sleep study, the following may be measured:

  • Eye movement. The number of eye movements and their frequency or speed.
  • Brain activity. The electrical currents of the brain.
  • Limb movement. The number and intensity of movements.
  • Breathing patterns. The number and depth of respirations.
  • Heart rhythm. The electrical activity of the heart.
  • Oxygen saturation. The percentage of oxygen in the blood.
  • Acid/base balance of the stomach. The amount of acid secreted during sleep.
  • Sleep latency. The time it takes to fall asleep.
  • Sleep duration. The period of time a person stays asleep.
  • Sleep efficiency. The ratio of the total time asleep to the total time in bed.

In addition these tests may be done:

  • Multiple sleep latency tests (MSLT) measure how long it takes to fall asleep
  • Multiple wake tests (MWT) measure whether you can stay awake during specified times.

Doctors trained in sleep medicine evaluate test results to treat sleep issues. A trained sleep technician will be with you in the sleep lab during the testing period.

Why might I need a sleep study?

Common reasons for a sleep study include:

  • Excessive snoring
  • Sleep apnea (periods where the breath stops)
  • Daytime sleepiness
  • Insomnia (inability to sleep)
  • Narcolepsy (sudden onset of sleep)
  • Restless legs syndrome (condition causing uncomfortable leg sensations)

Nightmares during nondream stages of sleep (sleep terrors), sleep walking or talking, and rapid eye movement disorders are less common conditions that may also require a sleep study.

There may be other reasons for your healthcare provider to recommend a sleep study.

What are the risks of a sleep study?

There are no known risks for a sleep study other than possible skin irritation due to the attachment of the electrodes to the skin.

How do I get ready for a sleep study?

  • Your doctor will explain the procedure and you can ask questions.
  • You may be asked to limit your sleep before the study, avoiding naps for example.
  • Tell your doctor of all medicines (prescription and over-the-counter) and herbal supplements that you are taking. They may alter test results.
  • Avoid caffeine-containing products for several days before the testing as they may cause you to take longer to fall asleep.
  • Sedatives are not allowed during the sleep study as they can alter results.
  • A sleep questionnaire or diary may be given to you (and your bed partner, if applicable) to fill out ahead of time. Do your best to give true responses.
  • Showering before going to the sleep lab may be helpful. But, avoid using lotion or oil on your skin because the electrodes may not stick to the skin.
  • You may be urged to bring your own pajamas and pillow.
  • If needed, you may be able to shower and dress for work the morning after the sleep study.
  • Based on your condition, your doctor may ask for other preparation.

What happens during a sleep study?

A sleep study is generally done on an outpatient basis at night. Procedures may vary based on your condition and your provider's practices.

Generally, a sleep study follows this process:

  1. You will need remove any jewelry or other objects that may interfere with the procedure.
  2. You will change into pajamas or a hospital gown.
  3. Small metal discs, or electrodes, will be positioned on your head and body for EEG, ECG, EOG, and EMG cables.
  4. Pulse oximetry measures the oxygen level in the blood vessels through a small clip placed on your finger. Air flow monitors measure breathing.
  5. The temperature of the room may need to be maintained at a certain level, but blankets can be adjusted as needed.
  6. Lights will be turned off and monitoring will start before you fall asleep.
  7. For multiple sleep latency testing (MSLT), short naps will be assigned at intervals.
  8. For multiple wake testing (MWT), you will be asked to try and stay awake for certain periods.
  9. When the study is complete, the electrodes and other devices will be removed.

What happens after a sleep study?

You won't need any special care after a sleep study. Results may take several days. However, your provider may give you other instructions after the procedure, based on your situation.

Next steps

Before you agree to the test or the procedure make sure you know:

  • The name of the test or procedure
  • The reason you are having the test or procedure
  • The risks and benefits of the test or procedure
  • When and where you are to have the test or procedure and who will do it
  • When and how will you get the results
  • How much will you have to pay for the test or procedure
Online Medical Reviewer: MMI board-certified, academically affiliated clinician
Online Medical Reviewer: Nelson, Gail A., MS, APRN, BC
Date Last Reviewed: 11/12/2013
© 2000-2015 The StayWell Company, LLC. 780 Township Line Road, Yardley, PA 19067. All rights reserved. This information is not intended as a substitute for professional medical care. Always follow your healthcare professional's instructions.
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