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 through these stages about 4 to 6 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 may be done if your sleep is not restful or if you are tired all day. These studies can help find sleep problems, such as:
- Sleep apnea.
- 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).
- Ongoing problems that have not responded to treatment.
How To Prepare
You may be asked to keep a sleep diary 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 on the day of 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 during the afternoon or evening before your test.
If the sleep study will be done in a sleep lab, you will be asked to shower or bathe before your test. Don't use sprays, oils, or gels on your hair. Don't wear makeup, fingernail polish, or fake nails. Take a small overnight bag with personal items, such as a toothbrush, a comb, favorite pillows or blankets, and a book. You can wear your own 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. If you have a bed partner, they may also be asked questions. They 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 before the test so the technician can prepare you for the study. You may fill out a form about your sleep the night before. You may 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 your movements 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 will help you and your doctor decide on follow-up studies or treatment. Your results may include information about:
- Your blood oxygen (O2) level.
- Your heart rate and rhythm.
- The amount of times your breathing stops per hour.
- Snoring and the airflow from your nose and mouth.
- How fast you fall asleep.
- How long you stay asleep and how much time you're awake.
- Movement of your chest, belly, arms, and legs while you sleep.
- How active you are while you're asleep.
Your doctor may recommend treatment based on the results of your test. You may need an additional study to make sure the treatment is working.
Current as of: March 1, 2022
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