Overnight Sleep Study

One of the methods used to diagnose sleep disorders is an overnight sleep study. If you are scheduled for an overnight sleep study your referring doctor will provide you with instructions about how to prepare for this evaluation. It's important that you don't take any sleeping medication, alcohol, or caffeine-containing beverages before the study.

A sleep study, also known as a polysomnogram, is a combination of procedures that test a patient's sleep cycles and stages. It consists of continuous recordings of brain waves using an electroencephalogram, eye movement using an electrooculogram, electrical activity of muscles, blood oxygen saturation, respiratory rate and heart rhythm, along with direct observation of the sleeping person.

During the overnight sleep study, electrodes will be placed on your scalp, the outer edge of your eyelids, and on your chin. Instruments will record your movements, the time it takes you to fall asleep, and other factors. You also will be videotaped while you are sleeping.


Polysomnography is a sleep study. A sleep study monitors you as you sleep, or try to sleep.
There are two states of 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 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:

Alternative Names
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 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.

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:

Normal Values
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
Abnormal results may confirm a suspected apnea.