Test Overview
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 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.
- Problems sleeping
during the day because you work at night or do rotating shift work. This sleep
problem is called shift work sleep disorder.
- Conditions such as
periodic limb movement disorder, which is
repeated muscle twitching 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. 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. Sleep
labs are often located in hospitals. But sleep studies also can be
done with portable equipment you use at home.
Sleep Apnea: Should I Have a Sleep Study?
Why It Is Done
Sleep studies are done to find sleep
problems, including:
- Sleep apnea. For more information, see the
topic
Sleep Apnea.
- Excessive
snoring.
- Insomnia.
- Narcolepsy.
- Heart rhythm
problems.
- Periodic limb movement disorder.
- Shift
work sleep disorder or other
circadian rhythm problems.
How To Prepare
You will probably 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.
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.
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.
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.
Risks
Your skin may be red or itchy from the glue used
with the electrodes. There are no other risks with sleep studies.
Results
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.
Sleep study results are
generally available within 1 to 2 weeks. A
sleep medicine specialist, family medicine doctor,
internist, or pulmonologist 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
Polysomnogram (PSG) study | 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: | Blood O2 level is greater than
90%. |
|---|
| 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): | Reduced air flow (hypopnea) or no
air flow (apnea) to the lungs occurs fewer than 5 times in 1 hour. |
|---|
| 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. |
|---|
| Snoring monitor: | Excessive snoring or abnormal
snoring patterns are not present. |
|---|
| Airflow monitors: | Airflow through the mouth and
nose is not blocked. |
|---|
Multiple sleep latency test (MSLT) | Sleep onset: | Taking 10 to 20 minutes to
fall asleep is normal. |
|---|
Maintenance of wakefulness test (MWT) | Sleep onset: | Being awake for about 25
minutes is normal. |
|---|
Abnormal values
- 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 25 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.
- 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. But 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.
References
Other Works Consulted
- Chernecky CC, Berger BJ (2008). Laboratory Tests and Diagnostic Procedures, 5th ed. St. Louis:
Saunders.
- Collop NA, et al. (2007). Clinical
guidelines for the use of unattended portable monitors in the diagnosis of
obstructive sleep apnea in adult patients. Journal of Clinical Sleep Medicine, 3(7): 737–747.
- Fischbach FT, Dunning MB III, eds. (2009).
Manual of Laboratory and Diagnostic Tests, 8th ed.
Philadelphia: Lippincott Williams and Wilkins.
- Pagana KD, Pagana TJ (2010). Mosby’s Manual of Diagnostic and Laboratory Tests, 4th ed. St. Louis: Mosby.
Credits
| By | Healthwise Staff |
|---|
| Primary Medical Reviewer | Anne C. Poinier, MD - Internal Medicine |
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| Specialist Medical Reviewer | Mark A. Rasmus, MD - Pulmonology, Critical Care Medicine, Sleep Medicine |
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| Last Revised | June 17, 2011 |
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