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 three stages distinguishable by EEG waves. REM sleep alternates with NREM sleep approximately every 90 minutes. A person with normal sleep usually has three to four 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 sleep in a bed in the test center. The test may be carried out during the night or during the day so that normal sleep patterns can be reproduced. Electrodes are placed on the chin, the scalp, the outer edge of the eyelids and the legs in preparation for the test. These electrodes will monitor activities such as brain waves, muscle movements, eye movements, breathing, snoring, heart rate and leg movements during sleep. An airflow detector is also placed below the nose. All of these electrodes and monitors are temporary and can be disconnected during the night to allow you to use the bathroom.
Characteristic patterns from the electrodes are recorded while you are awake with your eyes closed and during sleep. The time it takes for you to fall asleep is measured, as well as the time it takes for you to get into REM sleep. The patient will be recorded by video camera.
The test is performed to evaluate possible sleep disorders, such as insomnia, hypersomnia, excessive daytime sleepiness, obstructive sleep apnea, narcolepsy, breathing difficulties, behavior disturbances during sleep, or other sleep disorders.
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