For a polysomnogram (PSG) study, small metal discs called electrodes will be placed on your head and body with a small amount of glue and tape. (The glue washes off easily after the test.) The electrodes record your brain activity, eye movement, oxygen and carbon dioxide blood levels, heart rate and rhythm, breathing rate and rhythm, the flow of air through your mouth and nose, the amount of snoring, body muscle movements, and chest and belly movements. Soft elastic belts will be placed around your chest and belly to measure your breathing. Your blood oxygen levels will be checked by a small clip (oximeter) placed either on the tip of your index finger or on your earlobe.

The electrodes, elastic belts, and oximeter are designed to be as comfortable as possible and should not make it hard to sleep. At the beginning of the test, you will be asked to do things such as blink your eyes, move your legs, and hold your breath. This is done to make sure the equipment is working correctly. Polysomnogram recording equipment and video monitors will record your movements and activities while you sleep. The technician will be in a separate room checking the recordings.

If you have sleep apnea, you may wear a mask that is connected to a continuous positive airway pressure (CPAP) machine. The mask fits over your nose or over your nose and mouth. The mask over the nose is used most often. The CPAP machine delivers air or extra oxygen. This increases the air pressure in your throat so your airway is more open when you breathe in. When you are ready and the equipment is working correctly, the lights will be turned off, and you can go to sleep. For most polysomnogram studies, you will need to spend at least 6 hours overnight in the sleep lab.

Multiple sleep latency test If a multiple sleep latency test (MSLT) is being done, you will need to stay at the sleep lab overnight and part of the next day. During this test, you will take naps every 2 hours beginning the morning after your nighttime sleep test. You will be given 20 minutes to fall asleep. If you take a nap, you will be woken up after 15 minutes. Between naps, you try to stay awake. The amount of time it takes for you to fall asleep for the naps and the sleep patterns during the naps will be recorded using most of the same equipment used during the polysomnographic studies.

Maintenance of wakefulness test (MWT) If an MWT is done, you will need to stay at the sleep lab overnight and part of the next day. You will try to stay awake without napping during the day. The information will be recorded with most of the same equipment used during the polysomnographic study.

Portable sleep monitoring If you will have portable sleep monitoring, your doctor will explain how to use the monitoring equipment at home. You will need to sleep with short tubes in your nose and a cap on your finger that connect to a small monitor. The monitor records information while you sleep, such as your breathing pattern and blood oxygen level. You may also wear a device that records sounds you make, and a band around a leg to check how often the leg moves while you sleep.

Your skin may be red or itchy from the glue used with the electrodes. There are no other risks with sleep studies.

For a polysomnogram, reduced or blocked air flow to the lungs (RDI value) that occurs more than 5 times in 1 hour may mean you have sleep apnea.

For a multiple sleep latency test (MSLT), taking an average of 5 to 10 minutes to fall asleep means you have mild to moderate daytime sleepiness. An average of less than 5 minutes to fall asleep means you have severe daytime sleepiness. An average of less than 8 minutes to fall sleep along with 2 or more rapid eye movements (REM) during 5 to 6 naps means you may have narcolepsy.

For a maintenance of wakefulness test (MWT), falling asleep in less than 25 minutes is considered abnormal. This means you have severe daytime sleepiness. People who have narcolepsy also may have abnormal test results.