Sleep Study


Procedure overview

What is a sleep study?

Sleep is a state of relative unconsciousness and stillness of the voluntary muscles (muscles that are controlled at will). The stages of sleep range from light to deep and each 1 has specific characteristics that can be measured. A sleep study consists of a number of medical tests performed at the same time during sleep. The tests measure specific sleep characteristics and help to diagnose sleep disorders. A sleep study may also be referred to as a polysomnogram.

The term "polysomnogram" indicates that there are multiple tests in a sleep study. Breaking the word into parts, "poly" means many, while "somno" means sleep and "gram" means recording many sleep recordings. The basic recordings may include:

  • Electroencephalography (EEG). This measures brain wave activity.

  • Electrooculogram (EOG). This measures eye movement.

  • Electromyelography (EMG). This 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.

Photograph of a woman undergoing a sleep study

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 and whether there are episodes of shallow breathing (hypopneas) or episodes of breathing cessations (apneas). 

  • Heart rhythm and rate. 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.

  • Arousals. Going from deeper to lighter stages of sleep or awakening, associated with limb movements or changes in breathing. 

Reasons for the procedure

Various conditions can cause difficulty with sleep. 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)

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

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

Risks of the procedure

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

Before the procedure

  • The sleep clinic 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 the sleep clinic 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 should not be used during the sleep study as they can alter results. But if you typically use a prescribed or over-the-counter sleep medication, or if you have insomnia, check with the sleep clinic doctor about taking your medication so that you will sleep adequately during the study.

  • 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, the sleep clinic 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 the sleep clinic 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.

After the procedure

Generally, no special care is required after a sleep study and results may take several days. However, the sleep clinic doctor may give you additional or alternate instructions after the procedure, depending on your particular situation.

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 health care provider. Please consult your health care provider with any questions or concerns you may have regarding your condition.

This page contains links to other websites with information about this procedure and related health conditions. We hope you find these sites helpful, but please remember we do not control or endorse the information presented on these websites, nor do these sites endorse the information contained here.

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

National Institute of Neurological Disorders and Stroke