Sleep Studies

	Test Overview
	Health Tools
	Why It Is Done
	How To Prepare
	How It Is Done
	How It Feels
	Risks
	Results
	What Affects the Test
	What To Think About
	References
	Credits

Sleep studies are tests that watch what happens to your body during sleep. The studies are done to find out what is causing your sleep problems. Sleep problems include:

• Sleep apnea, when an adult regularly stops breathing during sleep for 10 seconds or longer. This may be caused by blocked airflow during sleep, such as from narrowed airways. Or it may be caused by a problem with how the brain signals the breathing muscles to work.
• Problems staying awake, such as narcolepsy.
• Problems with nighttime behaviors, such as sleepwalking, night terrors, or bed-wetting.
• Problems sleeping at night (insomnia). This may be caused by stress, depression, hunger, physical discomfort, or other problem.
• Conditions such as periodic limb movement disorder, which is continuous or wild movements of the feet, arms, or legs during sleep.

Sleep studies can also determine whether you have a problem with your stages of sleep. The two stages of sleep are non-rapid eye movement (NREM) and rapid eye movement (REM). Normally, NREM and REM alternate 4 to 5 times during a night's sleep. A change in this cycle may make it hard for you to sleep soundly.

The most common sleep studies are:

• Polysomnogram. This test records several body functions during sleep, including 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, snoring, body muscle movements, and chest and belly movement.
• Multiple sleep latency test (MSLT). This test measures how long it takes you to fall asleep. A video camera is used to record movements during sleep.
• Multiple wake test (MWT). This test measures whether you can stay awake during a time when you are normally awake.

Sleep studies usually are done in a sleep lab. Sleep labs are often located in hospitals.

Should I have a sleep study to diagnose obstructive sleep apnea?

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	Should I have a sleep study to diagnose obstructive sleep apnea?

Sleep studies are done to find sleep problems, including:

• Sleep apnea. For more information, see the topic Sleep Apnea.
• Hypopnea, which is an abnormal decrease in air flow to your lungs.
• Excessive snoring.
• Insomnia.
• Narcolepsy.
• Heart rhythm problems.
• Periodic limb movement disorder.

You likely will be asked to keep a sleep diary for 1 to 2 weeks before your sleep study. Try to follow your normal sleep routine during this time so you will not be too tired or too rested for your sleep test. Do not take any naps for 2 to 3 days before your test. See an example of a sleep diary(What is a PDF document?).

Tell your doctor about any drugs you are taking. You may be asked to stop taking certain drugs, such as sedatives, before your sleep study.

Do not drink or eat any foods with caffeine (coffee, tea, soda pop, chocolate) for 2 to 3 days before your test.

Take a shower or bath before your test, but do not use sprays, oils, or gels on your hair. Do not wear makeup, fingernail polish, or fake nails, because some of the test equipment will be placed on your face and fingers.

Pack a small overnight bag with personal items, such as a toothbrush, comb, favorite pillows or blankets, or a book, to take to the sleep lab. You do not need to wear a hospital gown. You can wear your normal nightclothes.

The sleep lab may send you forms to fill out before the test. These forms will ask about your sleep habits and patterns. The forms may also include questions for the person who sleeps with you; he or she may be aware of sleep habits you do not know you have.

Talk to your doctor about any concerns you have regarding the need for the test, its risks, how it will be done, or what the results will indicate. To help you understand the importance of this test, fill out the medical test information form(What is a PDF document?).

Sleep studies are usually done by a trained sleep lab technician. The studies are usually scheduled for evening and night hours (10 p.m. to 6 a.m.) in a special sleep lab. You will be in a private room, much like a hotel room.

You will need to be at the sleep lab a few hours before the test so the technician can prepare you for the study. You will fill out a questionnaire about your sleep the night before. You will also be asked to fill out another form after the study about your sleep during the study.

Polysomnogram study

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.

Multiple wake test

If a multiple wake test 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.

You will not feel pain during these tests. It may feel odd to be hooked to the sleep study equipment. The sleep lab technician understands that your sleep may not be the same as it is at home because of the equipment. Try to relax and make yourself as comfortable as possible.

After the test, you can shower and shampoo your hair to remove the glue from your body.

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

Sleep studies are tests that watch what happens to your body during sleep to find out what is causing your sleep problems. A polysomnogram (PSG) study checks your brain activity, eye movement, oxygen blood level, 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.

Sleep study results are generally available within 1 to 2 weeks. A family medicine doctor, an internist, a pulmonologist, or a neurologist can review your results at a follow-up visit. The sleep lab technician will not be able to review the results of the study with you.

Normal

Abnormal values

• For a polysomnogram, reduced or blocked air flow to the lungs (RDI value) 5 to 10 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 5 minutes to fall sleep and 2 or more rapid eye movements (REM) during 5 to 6 naps means you may have narcolepsy.
• For a multiple wake 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.

Factors that can interfere with your test or the accuracy of the results include the following:

• You use caffeine, nicotine, alcohol, or sedatives.
• There are changes in your normal activities on the day of the sleep study.
• The electrodes come off during sleep.
• Sleep lab noises keep you awake or keep you from sleeping normally during the sleep study.

• Sleep studies may be done when symptoms of a sleep problem have lasted at least 6 months. Many health conditions can cause abnormal sleep. These include restless legs syndrome, obesity, heart or respiratory diseases, hypothyroidism, depression, and neuromuscular diseases (such as Parkinson's disease).
• A second polysomnographic study may be needed if you were unable to sleep long enough for the test. Also, after your sleep problem has been identified, you may need a second study if your doctor orders treatment such as continuous positive airway pressure (CPAP).
• A split night study is another type of sleep study. During the first half of the night, you are checked for sleep apnea; during the second half of the night, your apnea is treated with breathing aids (such as CPAP) to open your blocked airway.
• Portable sleep study equipment is available for a person to do sleep studies at home. This may be a choice for people who have problems sleeping in a sleep lab. However, home sleep studies may not give the same results as a sleep lab.
• In rare cases, a pH test may be done during a sleep study to see if there is reflux of stomach juices into the esophagus. For a pH test, a small wire is placed in the nose and guided to the lower part of the esophagus.

Other Works Consulted

• Chernecky CC, Berger BJ, eds. (2004). Laboratory Tests and Diagnostic Procedures, 4th ed. Philadelphia: Saunders.

• Fischbach FT, Dunning MB III, eds. (2004). Manual of Laboratory and Diagnostic Tests, 7th ed. Philadelphia: Lippincott Williams and Wilkins.

• Pagana KD, Pagana TJ (2006). Mosby’s Manual of Diagnostic and Laboratory Tests, 3rd ed. St. Louis: Mosby.