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Sleep studies are tests that record what happens to your body during sleep. The studies are done to find out what's causing your sleep problems.
Sleep studies can also find out if 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.
Sleep studies usually are done in a sleep lab. But they also can be done with portable equipment you use at home.
Common sleep studies
The most common sleep studies are:
This test records several body functions during sleep, such as 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.
A special type of polysomnogram can be done at home. This test may record different functions than a study done in a sleep lab.
- Multiple sleep latency test (MSLT).
This test measures how long it takes you to fall asleep. It also finds out if you enter REM sleep.
- Maintenance of wakefulness test (MWT).
This test measures to see if 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.
Why It Is Done
Sleep studies are done for people who say that sleep isn't restful or that they are tired all day. These studies can help find sleep problems, such as:
- Sleep apnea. This means that an adult regularly stops breathing during sleep for 10 seconds or longer.
- Excessive snoring.
- Problems staying awake, such as narcolepsy.
- Problems with nighttime behaviors. These include sleepwalking, night terrors, bed-wetting, and REM behavior disorders (RBD).
- Conditions such as periodic limb movement disorder. This 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 for 1 to 2 weeks before your sleep study. Try to follow your normal sleep routine during this time so you won't be too tired or too rested for your sleep test. Don't 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 don't use sprays, oils, or gels on your hair. Don't 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, a comb, favorite pillows or blankets, or a book, to take along. You don't need to wear a hospital gown. You can wear your normal nightclothes.
If you will have portable sleep monitoring, your doctor will explain how to use the equipment at home.
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.
How It Is Done
Sleep 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'll be in a private room, much like a hotel room. For portable sleep monitoring, you'll use equipment at home that records information about you while you sleep.
You'll 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 form 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.
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.
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. They should not make it hard to sleep. At the start 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 as it should. 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.
There are different ways the test may be done. You may sleep all night while the equipment records your sleep information. Or you may be monitored for half the night and then if you have sleep apnea, you may wear a mask that's 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're ready and the equipment is working right, 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.
Portable sleep monitoring
If you will have portable sleep monitoring, your doctor will explain how to use the monitoring equipment at home. You'll 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 see how often the leg moves while you sleep.
Multiple sleep latency test
If a multiple sleep latency test (MSLT) is being done, you'll need to stay at the sleep lab overnight and part of the next day. During this test, you will take naps every 2 hours starting the morning after your nighttime sleep test. You will be given 20 minutes to fall asleep. If you take a nap, you'll 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'll 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.
How long the test takes
- You will stay in the sleep lab overnight. For some tests, you will also stay part of the next day.
How It Feels
You won't 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 you can.
Your skin may be red or itchy from the glue used with the electrodes. There are no other risks with sleep studies.
The results of your sleep study should be ready within 1 to 2 weeks. The sleep lab technician won't 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):
Sleep time, stages of sleep (NREM and REM), and awake time are normal. No abnormal brain activity (such as a seizure) is noted.
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. Other sleep disorders, such as periodic limb movement disorder, may be found.
- 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.
Current as of: October 26, 2020
Author: Healthwise Staff
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: October 26, 2020
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