Polysomnography is a sleep study. A sleep study monitors you as you sleep, or try to sleep.
There are two states of sleep:
- Rapid eye movement (REM) sleep
- Non-rapid eye movement (NREM) sleep
REM sleep is associated with dreaming. Your body muscles (except your eyes and lungs) do not move during this stage of sleep.
NREM sleep has four stages that can be detected by brain electrical activity (EEG) waves.
REM sleep alternates with NREM sleep approximately every 90 minutes. A person with normal sleep usually has four to five cycles of REM and NREM sleep during a night.
A sleep study measures your sleep cycles and stages by recording the following information:
- Air flow in and out of the lungs during breathing
- Blood oxygen levels
- Body position
- Brain waves (EEG)
- Breathing effort and rate
- Electrical activity of muscles
- Eye movement
- Heart rate
Sleep study; Polysomnogram; Rapid eye movement studies
How the test is performed
The most common type of sleep study is performed at a special sleep center. You will be asked to arrive about 2 hours before bedtime. You will sleep in a bed at the center. Many sleep centers have rooms that are similar to hotel rooms, so that you are in a comfortable bedroom. The test is often done during the night so that your normal sleep patterns can be studied.
The health care provider will place electrodes on your chin, scalp, and the outer edge of your eyelids. These must remain in place while you sleep.
Signals from the electrodes are recorded while you are awake (with your eyes closed) and during sleep. The time it takes you to fall asleep is measured, as well as the time it takes you to enter REM sleep.
Monitors to record your heart rate and breathing will be attached to your chest. These also must remain in place while you sleep. A specially trained health care provider will directly observe you while you sleep and note any changes in your breathing or heart rate. The number of times that you either stop breathing or almost stop breathing will be measured.
In some sleep study centers, a video camera records your movements during sleep.
Portable sleep study devices that can be used in the home instead of at a sleep center are available to help diagnose sleep apnea. You should not use these devices unless you have been evaluated by a sleep specialist.
How to prepare for the test
Do not take any sleeping medication and do not drink alcohol or caffeine-containing beverages before the test.
Why the test is performed
The test is done to diagnose possible sleep disorders, including obstructive sleep apnea (OSA). Often, OSA is suspected because of the following symptoms:
- Daytime sleepiness (falling asleep during the day)
- Loud snoring
- Periods of breath holding, followed by gasps or snorts
- Restless sleep
- Periodic limb movements disorder (frequent movements of the legs during sleep)
- REM behavior disorder (a condition in which people physically "act out" their dreams)
A normal test result shows usual or normal patterns of brain waves and muscle movements during sleep, without frequent breathing problems.
What abnormal results mean
A sleep study keeps track of:
- How often you stop breathing completely for at least 10 seconds (called apnea)
- How often your breathing is partly blocked for 10 seconds (called hypopnea)
Results are most often reported using the Apnea-Hypopnea Index (AHI), which can be used to diagnose obstructive sleep apnea.
- 5 - 15 is mild sleep apnea
- 15 - 30 is moderate sleep apnea
- More than 30 is severe sleep apnea
The sleep specialist must also look at other findings from the sleep study and the history and physical exam to make the diagnosis and decide on treatment. A sleep study can also help diagnose narcolepsy.
Patel NP, Ahmed M, Rosen I. Split-night polysomnography. Chest. 2007 Nov;132(5):1664-71.
Patil SP, Schneider H, Schwartz AR, Smith PL. Adult obstructive sleep apnea: pathophysiology and diagnosis. Chest. 2007 Jul;132(1):325-37.
Epstein LJ, Kristo D, Strollo PJ Jr. Adult Obstructive Sleep Apnea Task Force of the American Academy of Sleep Medicine. Clinical guideline for the evaluation, management, and long-term care of obstructive sleep apnea in adults. J Clin Sleep Med. 2009;5:263-276.
Cao M. Advances in narcolepsy. Med Clin N Am. 2010;94:541-555.
Denis Hadjiliadis, MD, Assistant Professor of Medicine, Division of Pulmonary, Allergy and Critical Care, University of Pennsylvania, Philadelphia, PA. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.
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