What Are Sleep Studies?

Sleep studies allow doctors to measure how much and how well you sleep. They also help show whether you have sleep problems and how severe they are.

Sleep studies are important because untreated sleep disorders can increase your risk for high blood pressure, heart attack, stroke, and other medical conditions. People usually aren't aware of their breathing and movements while sleeping. They may never think to talk to their doctors about sleep- and health-related issues that may be linked to sleep problems.

Doctors can diagnose and treat sleep disorders. Talk to your doctor if you feel tired or very sleepy while at work or school most days of the week. You also may want to talk to your doctor if you often have trouble falling or staying asleep, or if you wake up too early and aren't able to get back to sleep. These are common signs of a sleep disorder.

Doctors can diagnose some sleep disorders by asking questions about your sleep schedule and habits and by getting information from sleep partners or parents. To diagnose other sleep disorders, doctors also use the results from sleep studies and other medical tests.

Sleep studies can help doctors diagnose:

• Sleep-related breathing disorders (such as sleep apnea)
• Sleep-related seizure disorders
• Parasomnias (such as sleepwalking)
• Narcolepsy
• Insomnia
• Circadian (ser-KA-de-an) rhythm disorders.

You can find more information on sleep and sleep disorders in the National Heart, Lung, and Blood Institute's "Your Guide to Healthy Sleep."

Types of Sleep Studies

Four common sleep studies are used to help diagnose sleep-related problems:

• Polysomnogram (pol-e-SOM-no-gram), or PSG
• Multiple sleep latency test, or MSLT
• Maintenance of wakefulness test, or MWT
• Actigraphy

Polysomnogram

A PSG is usually done while you stay overnight at a sleep center. A PSG records brain activity, eye movements, heart rate, and blood pressure.

It also records the amount of oxygen in your blood, how much air is moving through your nose while you breathe, and chest movements that show whether you're making an effort to breathe. In some cases, breathing sounds, including snoring, also are recorded.

PSG results are used to help diagnose:

• Insomnia
• Sleep-related breathing disorders (such as sleep apnea)
• Narcolepsy (PSG and MSLT results will be reviewed together)
• Sleep-related seizure disorders
• Parasomnias (such as sleepwalking)

Your doctor also may use a PSG to find the right setting for you on a continuous positive airway pressure (CPAP) machine. CPAP is the most common treatment for sleep apnea.

A CPAP machine uses a small pump to gently supply air to your nose or mouth through a special mask. The right setting involves adding just enough extra air to create mild pressure that keeps your airways open while you sleep.

If your doctor thinks that you have sleep apnea, he or she may schedule a split-night sleep study. During the first half of the night, your sleep will be checked without a CPAP machine. This will show if you have sleep apnea and how severe it is.

If the PSG shows signs that you have sleep apnea, you will use a CPAP machine during the second half of the split-night study. A technician checks your breathing using the PSG and adjusts the flow of air through the CPAP mask to find the correct setting for you.

A PSG also helps doctors:

• Adjust CPAP settings after weight loss or gain
• Recheck your sleep if symptoms return despite treatment with CPAP
• Find out how well surgery has worked to correct a sleep-related breathing problem.

Multiple Sleep Latency Test

This daytime sleep study measures how sleepy you are. It's typically done the day after a PSG. You relax in a quiet room for about 30 minutes while a technician checks your brain activity.

The MSLT records whether you fall asleep during the test and what types and stages of sleep you're having. Sleep has two basic types: rapid eye movement (REM) and non-REM. REM sleep and non-REM sleep occur in patterns throughout the night.

The types and stages of sleep can help your doctor diagnose sleep disorders such as narcolepsy, idiopathic hypersomnia, and circadian rhythm disorders.

The test is repeated three or four times throughout the day. This is because your ability to fall asleep also changes throughout the day.

Maintenance of Wakefulness Test

This daytime sleep study measures your ability to stay awake and alert. It's usually done the day after a PSG and takes most of the day.

Results may be used to show whether your inability to stay awake is a public or personal safety concern or to check your response to treatment.

Actigraphy

This sleep study is done while you go about your normal daily routine. It doesn't require an overnight stay at the sleep clinic.

The actigraph is a simple device that's usually worn like a wristwatch. The doctor may ask you to wear the device for several days—except when bathing or swimming.

This test gives 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.

Who Needs a Sleep Study?

If you often feel very tired during the day—even though you spent enough time in bed to be well rested—talk to your doctor. This is a common sign of a sleep disorder. A number of sleep disorders can disrupt your sleep, leaving you sleepy during the day.

Other common signs of sleep disorders include the following.

• It takes you more than 30 minutes to fall asleep at night.
• You awaken often during the night and then have trouble falling back to sleep, or you awaken too early in the morning.
• You feel sleepy during the day and fall asleep within 5 minutes if you have an opportunity to nap, or you fall asleep at inappropriate times during the day.
• Your bed partner claims you snore loudly, snort, gasp, or make choking sounds while you sleep, or your partner notices your breathing stops for short periods.
• You have creeping, tingling, or crawling feelings in your legs that are relieved by moving or massaging them, especially in the evening and when you try to fall asleep.
• You have vivid, dreamlike experiences while falling asleep or dozing.
• You have episodes of sudden muscle weakness when you're angry, fearful, or when you laugh.
• You feel as though you can't move when you first wake up.
• Your bed partner notes that your legs or arms jerk often during sleep.
• You regularly feel the need to use stimulants to stay awake during the day.

Describe your signs and symptoms to your doctor. It's important to note how tired you feel and whether your signs and symptoms affect your daily routine. Early signs of sleep disorders aren't easy to detect during routine visits. There are no blood tests for sleep disorders, and the doctor isn't watching you sleep.

If you've had a sleep disorder for a long time, it may be hard for you to notice its impact on your daily routine. Using a sleep diary, such as the one found in "Your Guide to Healthy Sleep," may be helpful.

Your doctor can decide whether you need a sleep study. A sleep study allows your doctor to observe sleep patterns and to diagnose a sleep disorder, which can then be treated.

Certain medical conditions have been linked to sleep disorders. These include heart failure, coronary artery disease, obesity, diabetes, high blood pressure, and stroke or transient ischemic attack (TIA, or "mini-stroke"). If you have one of these conditions, talk with your doctor about whether it would be helpful to have a sleep study.

What To Expect Before a Sleep Study

Before a sleep study, your doctor may ask you about your sleep habits and whether you feel well rested and alert during the day.

You may be asked to keep a sleep diary or sleep log. You will record information such as when you went to bed, when you woke up, how many times you woke up during the night, and more. You can find an example of a sleep diary in "Your Guide to Healthy Sleep."

What To Bring With You

Depending on what type of sleep study you're having, you may need to bring:

• Notes from your sleep diary or sleep log. These may be helpful to your doctor.
• Pajamas and a toothbrush for overnight sleep studies.
• A comfortable pillow.
• A book or something to do between testing periods if you're having a multiple sleep latency test or a maintenance of wakefulness test (MWT).

How To Prepare

You may need to stop or limit the use of tobacco, caffeine, and stimulants before having a sleep study. Your doctor may ask you about alcohol, medicines, or other substances that you take and about allergies that you have.

You may routinely take medicine that affects your sleep patterns. If so, a sleep specialist will help you plan how to take it during and possibly before the test.

You should try to sleep well the night before you have an MWT, because you will have to try to stay awake during this test. If you're being tested as a requirement for a transportation- or safety-related job, you may be asked to take a drug-screening test.

What To Expect During a Sleep Study

Sleep studies are painless. Parents can go with their children to a sleep study.

The polysomnogram (PSG), multiple sleep latency test (MSLT), and maintenance of wakefulness test (MWT) are usually 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. You can ask them any questions that you may have about the sleep study.

During a Polysomnogram

Sticky patches called sensors are placed on your scalp, face, chest, limbs, and a finger. While you sleep, these devices 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 abdomen. They measure chest movements and the strength and duration of each exhaled breath.

Wires attached to the sensors transmit the data to a computer in the next room. The wires are very thin and flexible and are bundled together to minimize discomfort. You will be able to roll in any direction.

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

The technician also helps keep you comfortable and disconnects the equipment if you need to go to the bathroom.

When it's time for you to sleep, the room will be dark and quiet.

If you show 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 continuous positive airway pressure (CPAP) mask over your nose and mouth.

The mask is connected to a small machine that gently blows air through the mask. This creates mild pressure that keeps your airways 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 helps you out of bed and removes the sensors. If you're having a daytime sleep study, such as an MSLT, some of the sensors may be left on for that test.

During a Multiple Sleep Latency Test

The MSLT is a daytime sleep study that's usually done after a PSG. Sensors on your scalp, face, and chin usually are used for this test. These sensors record brain activity. They show various stages of sleep and how long it takes you to fall asleep. Sometimes your breathing also is checked during an MSLT.

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

Starting 1.5 to 3 hours after you wake from the PSG, you're asked to relax in a quiet room for about 30 minutes. The test is repeated three or four 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 four distinct stages. REM sleep and the four stages of non-REM sleep occur in patterns throughout the night.

The types and stages of sleep can help your doctor diagnose a sleep disorder such as narcolepsy, idiopathic hypersomnia, or a circadian rhythm disorder.

During a Maintenance of Wakefulness Test

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

You sit quietly on a bed 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 are usually 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 the MWT.

During an Actigraph Test

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

The actigraph measures your sleep–wake behavior over 3 to 7 days. 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.

You may be asked to keep a sleep diary while you wear the actigraph.

What To Expect After a Sleep Study

Once the sensors are removed after a polysomnogram, multiple sleep latency test, or maintenance of wakefulness test, you can go home. If you used an actigraph to measure your sleep–wake behavior, you return it to your doctor's office.

You won't receive a diagnosis right away. Your primary care doctor or sleep specialist will review the results of your sleep study or sleep studies. He or she will use your medical history, your sleep history, and the test results to make a diagnosis.

It may take a couple of weeks to get the results of your sleep study. Usually, your doctor, nurse, or sleep specialist will explain the test results and work with you and your family to develop a treatment plan.

What Do Sleep Studies Show?

Sleep studies allow doctors to watch sleep patterns and note sleep-related problems that patients don't know or can't describe during routine office visits. These studies are needed to diagnose certain sleep disorders, such as narcolepsy and sleep apnea.

After the sleep study, your doctor will get the results. The results will include information that the sleep technician records about sleep and wake times, sleep stages, abnormal breathing, the amount of oxygen in your blood, and any movement during sleep.

Your doctor will use your sleep study results and your medical and sleep histories to make a diagnosis and create a treatment plan.

Results From a Polysomnogram

Polysomnogram (PSG) results are used to help diagnose:

• Insomnia
• Sleep-related breathing disorders, such as sleep apnea
• Narcolepsy (PSG and multiple sleep latency test (MSLT) results will be reviewed together)
• Sleep-related seizure disorders
• Parasomnias (such as sleepwalking)

If you have sleep apnea, your doctor also may use a PSG to find the right setting for you on a continuous positive airway pressure (CPAP) machine. A CPAP machine uses a small pump to gently supply air to your nose or mouth through a special mask. The right setting involves adding just enough extra air to create mild pressure that keeps your airways open while you sleep.

A PSG also helps doctors:

• Adjust CPAP settings after weight loss or gain
• Recheck your sleep if symptoms return despite treatment with CPAP
• Find out how well surgery has worked to correct a sleep-related breathing problem.

For sleep-related breathing disorders, such as sleep apnea, technicians use a PSG to record the number of abnormal breathing events. These include either pauses in breathing or dips in the level of oxygen in your blood.

In adults, when the number of events is 10 or more per hour, treatment may be needed. Children who have one to three events per hour also may need treatment.

Results From a Multiple Sleep Latency Test

MSLT results are used to help diagnose narcolepsy, idiopathic hypersomnia, and circadian rhythm disorders.

For narcolepsy, technicians study how quickly you fall asleep. The MSLT also shows how long it takes you to reach different types and stages of sleep. Sleep has two basic types: rapid eye movement (REM) and non-REM. Non-REM sleep has four distinct stages. REM sleep and the four stages of non-REM sleep occur in patterns throughout the night.

People who fall asleep in less than 5 minutes or quickly reach REM sleep may need treatment for a sleep disorder.

Results From a Maintenance of Wakefulness Test

Maintenance of wakefulness test (MWT) results may be used to show whether your inability to stay awake is a public or personal safety concern. This study also is used to show how well treatment is working.

Results From an Actigraph Test

Actigraph 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. This study also is used to help diagnose circadian rhythm disorders.

What Are the Risks of Sleep Studies?

Sleep studies are painless. There is a small risk of skin irritation from the sensors. The irritation will go away once the sensors are removed.

Although the risks of sleep studies are minimal, these studies take time (at least several hours). If you're having a daytime sleep study, bring a book or something to entertain yourself with during the test.

Key Points

• Sleep studies allow doctors to measure how much and how well you sleep. They also help show whether you have sleep problems and how severe they are.
• Sleep studies are important because untreated sleep disorders can increase your risk for high blood pressure, heart attack, stroke, and other medical conditions. People usually aren't aware of their breathing and movements while sleeping. They may never think to talk to their doctors about sleep- and health-related issues that may be linked to sleep problems.
• Sleep studies can help doctors diagnose sleep-related breathing disorders (such as sleep apnea), sleep-related seizure disorders, parasomnias (such as sleepwalking), narcolepsy, insomnia, and circadian rhythm disorders.
• Four common sleep studies are used to help diagnose sleep-related problems: polysomnogram (PSG), multiple sleep latency test (MSLT), maintenance of wakefulness test (MWT), and an actigraph test.
  • A PSG is an overnight sleep study that records brain activity, eye movements, heart rate, and blood pressure. It also records the amount of oxygen in your blood, how much air is moving through your nose while you breathe, and chest movements that show whether you're making an effort to breathe. In some cases, breathing sounds, including snoring, also are recorded. Your doctor also may use a PSG to find the right setting for you on a continuous positive airway pressure (CPAP) machine.
  • An MSLT is a daytime sleep study that measures how sleepy you are. It records brain activity to show various stages of sleep. It also shows how long it takes you to fall asleep.
  • An MWT is a daytime sleep study that measures your ability to stay awake. Results may be used to show whether your inability to stay awake is a public or personal safety concern or to assess your response to treatment.
  • The actigraph sleep study measures sleep–wake behavior while you go about your normal routine. 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. The actigraph is a small device that's usually worn like a wristwatch.
• If you often feel very tired during the day, talk to your doctor. This is a common sign of a sleep disorder. Other common signs of sleep disorders are listed in "Who Needs a Sleep Study."
• Certain medical conditions have been linked to sleep disorders. These include heart failure, coronary artery disease, obesity, diabetes, high blood pressure, and stroke or transient ischemic attack (TIA, or "mini-stroke"). If you have one of these conditions, talk with your doctor about whether it would be helpful to have a sleep study.
• Sleep studies are painless. The PSG, MSLT, and MWT studies are usually done in a sleep center. The room the study is done in may look like a hotel room. You don't have to go to a sleep center for an actigraph test. You wear the device while you go about your normal daily routine.
• After the sleep study, your doctor will get the results. The results will include information about sleep and wake times, sleep stages, abnormal breathing, the amount of oxygen in the blood, and any movement during sleep.
• Your doctor will study the results and use them and your medical and sleep histories to make a diagnosis and help develop a treatment plan. You may not get the diagnosis until a few weeks after the sleep study.
• The risks of sleep studies are minimal. There is a small risk of skin irritation from the sensors. The irritation will go away once the sensors are removed.

Links to Other Information About Sleep Studies

NHLBI Resources

• Insomnia (Diseases and Conditions Index)
• Narcolepsy (Diseases and Conditions Index)
• Restless Legs Syndrome (Diseases and Conditions Index)
• Sleep Apnea (Diseases and Conditions Index)
• Sleep Disorders Information
• "Your Guide to Healthy Sleep"

Non-NHLBI Resources

• Idiopathic hypersomnia (MedlinePlus)
• Sleep Studies (MedlinePlus)

Clinical Trials

• Current Research (ClinicalTrials.gov)