A sleep study (or polysomnogram) is similar to an EEG or electrocardiogram but makes 16 different measurements of the brain and body while one is asleep. This test is not invasive. The test begins at night when you go to sleep and lasts to the morning as would a normal night of sleep.
Your brain and body function vary differently during sleep than during the day. Even if your heart, breathing, and brain activity are completely normal during the day, they may be different or abnormal during sleep. The only way to determine the nature of the sleep problem is to take a variety of measurements during sleep.
Prepare yourself for your night in the sleep laboratory as if you were going to spend the night in a hotel. Bring with you everything you would need to spend the night away from home, including pajamas. Most patients who come for a sleep study find that they sleep about the same as they would at home.
Electrodes are placed on different parts of your body to provide information to the computer to measure up to 16 different body functions at the same time. These include:
- Brain waves or EEG. Six electrodes are attached to the scalp. Measurement of brain waves allows determination of the different and specific stages of sleep.
- Eye movements. Two or three electrodes attached with tape near the right and left eyes help to determine specific sleep stages.
- Muscle activity. Usually two or three electrodes attached with tape to the chin or under the chin measure muscle tone and activity. This plays a large role in determining the sleep stage throughout the night.
- Electrocardiogram. Usually three electrodes are attached with tape to the upper chest to record heart rhythm and activity.
- Leg movements. A small belt or cuff is placed around each ankle to record leg movements. Occasionally, two electrodes are attached with tape to the lower legs to measure leg muscle activity.
- Breathing. Breathing is measured in several ways. First, a sensor is attached with tape to the upper lip to measure air flow. Second, lightweight belts are placed around the chest and abdomen to measure how much effort is made to breathe. These belts are not tight or restrictive. They are sensitive to the motion of breathing.
- Oxygen levels in the blood. A sensor is attached to one of the fingers or ear with tape to measure the oxygen levels in the blood.
- Other sensors. Depending on the particular problem, other types of sensors may be used.