Polysomnogram

Definition

A polysomnograph is a test of sleep cycles and stages through the use of continuous recordings of brain waves (EEG), electrical activity of muscles, eye movement (electrooculogram), breathing rate, blood pressure, blood oxygen saturation, and heart rhythm and direct observation of the person during sleep.

There are two states of sleep: non-rapid eye movement (NREM) sleep and rapid eye movement (REM) sleep. REM sleep is associated with dreaming and paralysis of body muscles (except for the eye and diaphragm muscles). NREM sleep has four stages distinguishable by 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.

How the test is performed

Polysomnograms are usually conducted in a sleep study center. You will lie on a bed in the test center. The test may be carried out during the night so that normal sleep patterns can be reproduced. Electrodes are placed on the chin, the scalp, and the outer edge of the eyelids in preparation for the test.

Characteristic patterns from the electrodes are recorded while you are awake with your eyes closed and during sleep. The time taken to fall asleep is measured as well as the time to enter REM sleep. Sometimes the movements of a person during sleep are recorded by video camera.

How to prepare for the test

Do not take any sleeping medication and do not drink alcohol or caffeine-containing beverages before the test.

How the test will feel

Electrodes will be placed on the skin and scalp. Monitors to record heart rate and breathing rate will be attached to the chest. Sometimes other test to determine breathing disorders during sleep are also performed.

Why the test is performed

The test is performed to evaluate possible sleep disorders, such as insomnia, hypersomnia, excessive daytime sleepiness, obstructive sleep apnea, narcolepsy, breathing difficulties during sleep, behavior disturbances during sleep, or other sleep disorders.

Normal Values

Usual or normal patterns of brain waves and muscle movements during sleep.

What abnormal results mean

Abnormal results may confirm a suspected sleep disorder.

What the risks are

The risks are negligible as long as the tests and equipment are appropriately supervised.

Special considerations

Sleep studies may be applied to other disorders.

Illustrations

Sleep studies

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