Sleep Studies


Procedure overview

Photograph of a woman undergoing a sleep study

What is a Sleep Study?

Sleep is a state of relative unconsciousness and stillness of the voluntary muscles. The stages of sleep range from light to deep and each one has specific characteristics that can be measured. A sleep study also known as a polysomnogram consists of a number of medical tests performed at the same time during sleep. The tests measure specific sleep characteristics and helps diagnose sleep disorders.

The basic recordings may include:

  • Electroencephalography (EEG): Measures brain wave activity.
  • Electrooculogram (EOG): Measures eye movement.
  • Electromyography (EMG): Measures muscle movement.
  • Other recordings. An electrocardiogram (ECG) may be used to capture electrical activity of the heart; video recordings may also be part of the procedure.

Sleep studies generally take place in a sleep lab during a person's 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.

In addition to polysomnograms, multiple sleep latency tests (MSLT) and multiple wake tests (MWT) may be performed. MSLT's measure how long it takes to fall asleep, while MWT's measure whether you can stay awake during specified times.

Doctors trained in sleep medicine evaluate test results to determine a course of action and resolve sleep related issues. A trained sleep technician will be with you in the sleep lab during the testing period.

What can be measured in a sleep study?

Various body activities and indicators may be measured during a sleep study. Measurements may include:

  • 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.

Reasons for the procedure

Various conditions can cause difficulty with sleep. Common reasons for a sleep study include:

Sleep terrors (nightmares during non-dream stages of sleep), sleep walking or talking, and rapid eye movement disorders are less common conditions that may also require a sleep study for accurate diagnosis and treatment.

Before the procedure

  • Your doctor will explain the procedure to you and offer the opportunity to ask questions that you might have.
  • You may be asked to restrict your sleep before the study, avoiding naps for example.
  • Notify your doctor of all medications (prescription and over-the-counter) and herbal supplements that you are taking, as 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 complete ahead of time. Do your best to provide the most accurate responses.
  • Showering before going to the sleep lab may be helpful; however, avoid using lotion or oil on your skin because the electrodes may not adhere to the skin.
  • You may be encouraged 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 medical condition, your doctor may request other specific preparation.

During the procedure

A sleep study is generally performed on an outpatient basis at night. Procedures may vary depending on your condition and your doctor's practices.

Generally, a sleep study (polysomnography) follows this process:

  1. You will be asked to remove any jewelry or other objects that may interfere with the procedure.
  2. You will be asked to 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, which measures the oxygen level in the blood vessels, and air flow monitors, which measure breathing, will be applied to the finger and face, respectively.
  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 begin before you fall asleep.
  7. For multiple sleep latency testing (MSLT), short nap periods will be assigned at intervals.
  8. For multiple wake testing (MWT), you will be asked to try and stay awake for certain periods of time.
  9. When the study has been completed, the electrodes and other devices will be removed.

Online resources

The content provided here is for informational purposes only, and was not designed to diagnose or treat a health problem or disease, or replace the professional medical advice you receive from your doctor. Please consult your health care provider with any questions or concerns you may have regarding your condition.

American Academy of Family Physicians

American Academy of Sleep Medicine

American Board of Sleep Medicine

American Lung Association

National Heart, Lung, and Blood Institute (NHLBI)

National Institutes of Health (NIH)

National Library of Medicine

National Sleep Foundation

For more information on sleep disorders and sleep studies, call 314.747.9355 or 877.747.9355 or email us.