Sleep studies are tests that record what happens to your body during sleep. The studies are done to find out what is causing your sleep problems.
Sleep studies can also determine whether you have a problem with your stages of sleep. The two main types 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.
Common sleep studies
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. It also determines whether you enter REM sleep.
- Maintenance of wakefulness test (MWT). This test measures whether you can stay awake during a time when you are normally awake.
If your doctor thinks that you may have shift work sleep disorder or another problem with your body's internal clock (circadian rhythm), you may have a test called actigraphy. For this test, you wear a device on your wrist that looks like a watch. The device measures your movement during sleep and when you are awake. It helps your doctor learn what times during the day you are active and what times you are sleeping.
Sleep studies usually are done in a sleep lab. But sleep studies also can be done with portable equipment you use at home.
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Why It Is Done
Sleep studies are done to find sleep problems, including:
- Sleep apnea, when an adult regularly stops breathing during sleep for 10 seconds or longer.
- Excessive snoring.
- Problems staying awake, such as narcolepsy.
- Problems with nighttime behaviors, such as sleepwalking, night terrors, bed-wetting, or REM behavior disorders (RBD).
- Conditions such as periodic limb movement disorder, which is repeated muscle twitching of the feet, arms, or legs during sleep.
- Seizures that occur at night (nocturnal seizures).
How To Prepare
You may be asked to keep a sleep diary ( What is a PDF document? ) 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.
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.
You may be asked to avoid food or drinks with caffeine for a day or two 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.
If the sleep study will be done in a sleep lab, pack a small overnight bag with personal items, such as a toothbrush, comb, favorite pillows or blankets, or a book, to take along. 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 mean. To help you understand the importance of this test, fill out the medical test information form ( What is a PDF document? ).
How It Is Done
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. But if you usually sleep during the day, your test will be done during the hours you normally sleep. You will be in a private room, much like a hotel room. For portable sleep monitoring, you will use equipment at home that records information about you while you sleep.
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.
For a polysomnogram (PSG) study, small pads or patches 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.
How It Feels
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. Hair conditioner may help get the glue out of your hair.
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 record 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.
The results of your sleep study should be available within 1 to 2 weeks. The sleep lab technician will not be able to review the results with you. Your sleep study will be read by a sleep medicine specialist. Your doctor can review your results at a follow-up visit.
Brain activity ( electroencephalogram, or EEG):
Eye movement (electrooculogram, or EOG):
Slow eye movements are present at the start of sleep and change to rapid eye movements during REM sleep.
Muscle movement ( electromyogram, or EMG):
No leg jerking or other abnormal muscle movement is present.
Blood oxygen (O2) level (oximetry):
Blood O2 level (oximetry) is greater than 90%. footnote 1
Heart rate and rhythm ( EKG, ECG):
Heart rate and rhythm are normal. No heart rate changes ( arrhythmias), such as an abnormally slow or fast heart rate, are noted.
Breathing effort (respiratory disturbance index, or RDI):
No reduced air flow (hypopnea) or blocked air flow (apnea) to the lungs is found.
Chest and belly movements:
The chest and belly move normally throughout the study.
Audio and video recordings:
Sleep is restful and not disturbed. Night terrors, sleepwalking, and sleep talking do not occur.
Excessive snoring or abnormal snoring patterns are not present.
Airflow through the mouth and nose is not blocked.
Taking 10 to 20 minutes to fall asleep is normal.
Being awake for about 40 minutes is normal.
- 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 40 minutes is considered abnormal. This means you have severe daytime sleepiness. People who have narcolepsy also may have abnormal test results.
What Affects the Test
Reasons you may not be able to have the test or why the results may not be helpful 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.
What To Think About
- 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 polysomnogram 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.
- 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.
Current as of: June 9, 2019
Author: Healthwise Staff
Medical Review: Anne C. Poinier, MD - Internal Medicine
Adam Husney, MD - Family Medicine
E. Gregory Thompson, MD - Internal Medicine
Hasmeena Kathuria, MD - Pulmonology, Critical Care Medicine, Sleep Medicine
Current as of: June 9, 2019