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What To Expect During a Sleep Study

Sleep studies are painless. The polysomnogram (PSG), multiple sleep latency test (MSLT), and maintenance of wakefulness test (MWT) usually are done at a sleep center.

The room the sleep study is done in may look like a hotel room. A technician makes the room comfortable for you and sets the temperature to your liking.

Most of your contact at the sleep center will be with nurses or technicians. They can answer questions about the test itself, but they usually can't give you the test results.

During a Polysomnogram

Sticky patches with sensors called electrodes are placed on your scalp, face, chest, limbs, and a finger. While you sleep, these sensors record your brain activity, eye movements, heart rate and rhythm, blood pressure, and the amount of oxygen in your blood.

Elastic belts are placed around your chest and belly. They measure chest movements and the strength and duration of inhaled and exhaled breaths.

Wires attached to the sensors transmit the data to a computer in the next room. The wires are very thin and flexible. They are bundled together so they don't restrict movement, disrupt your sleep, or cause other discomfort.

The image shows the standard setup for a polysomnogram. In figure A, the patient lies in a bed with sensors attached to the body. In figure B, the polysomnogram recording shows the blood oxygen level, breathing event, and rapid eye movement (REM) sleep stage over time.  

The image shows the standard setup for a polysomnogram. In figure A, the patient lies in a bed with sensors attached to the body. In figure B, the polysomnogram recording shows the blood oxygen level, breathing event, and rapid eye movement (REM) sleep stage over time.

If you have signs of sleep apnea, you may have a split-night sleep study. During the first half of the night, the technician records your sleep patterns. At the start of the second half of the night, he or she wakes you to fit a CPAP (continuous positive airway pressure) mask over your nose and/or mouth.

A small machine gently blows air through the mask. This creates mild pressure that keeps your airway open while you sleep.

The technician checks how you sleep with the CPAP machine. He or she adjusts the flow of air through the mask to find the setting that's right for you.

At the end of the PSG, the technician removes the sensors. If you're having a daytime sleep study, such as an MSLT, some of the sensors might be left on for that test.

Parents usually are required to spend the night with their child during the child's PSG.

During a Multiple Sleep Latency Test

The MSLT is a daytime sleep study that's usually done after a PSG. This test often involves sensors placed on your scalp, face, and chin. These sensors record brain activity and eye movements. They show various stages of sleep and how long it takes you to fall asleep. Sometimes your breathing is checked during an MSLT.

A technician in another room watches these recordings as you sleep. He or she fixes any problems that occur with the recordings.

About 2 hours after you wake from the PSG, you're asked to relax and try to fall asleep in a dark, quiet room. The test is repeated four or five times throughout the day. This is because your ability to fall asleep changes throughout the day.

You get 2-hour breaks between tests. You need to stay awake during the breaks.

The MSLT records whether you fall asleep during the test and what types and stages of sleep you have. Sleep has two basic types: rapid eye movement (REM) and non-REM. Non-REM sleep has three distinct stages. REM sleep and the three stages of non-REM sleep occur in regular cycles throughout the night.

The types and stages of sleep you have during the day can help your doctor diagnose sleep disorders such as narcolepsy, idiopathic hypersomnia, and other sleep disorders that cause daytime tiredness.

During a Maintenance of Wakefulness Test

This sleep study usually is done the day after a PSG, and it takes most of the day. Sensors on your scalp, face, and chin are used to measure when you're awake and asleep.

You sit quietly on a chair in a comfortable position and look straight ahead. Then you simply try to stay awake for a period of time.

An MWT typically includes four trials lasting about 40 minutes each. If you fall asleep, the technician will wake you after about 90 seconds. There usually are 2-hour breaks between trials. During these breaks, you can read, watch television, etc.

If you're being tested as a requirement for a transportation- or safety-related job, you may need a drug-screening test before an MWT.

During a Home-Based Portable Monitor Test

If you're having a home-based portable monitor test, you'll need to set up the equipment at home before you go to sleep.

When you pick up the equipment at the sleep center or your doctor's office, someone will show you how to use it. In some cases, a technician will come to your home to help you prepare for the study.

During Actigraphy

You don't have to go to a sleep center for this test. An actigraph is a small device that's usually worn like a wristwatch. You can do your normal daily routine while you wear it. You remove it while bathing or swimming.

The actigraph measures your sleep–wake behavior over 3 to 14 days and nights. Results give your doctor a better idea about your sleep habits, such as when you sleep or nap and whether the lights are on while you sleep.

Your doctor may ask you to keep a sleep diary while you wear an actigraph. You can find a sample sleep diary in the National Heart, Lung, and Blood Institute's "Your Guide to Healthy Sleep."

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March 29, 2012 Last Updated Icon

The NHLBI updates Health Topics articles on a biennial cycle based on a thorough review of research findings and new literature. The articles also are updated as needed if important new research is published. The date on each Health Topics article reflects when the content was originally posted or last revised.