What Is a Polysomnography?
Polysomnography (PSG) is a study or test done while you’re fully
asleep. Your doctor will observe you as you sleep, record data about your sleep
patterns, and identify any sleep disorders. Your doctor will measure the
following during PSG to help chart your sleep cycles:
- brain waves
- skeletal muscle activity
- blood oxygen levels
- heart rate
- breathing rate
- eye movement
PSG registers your body’s shifts between the two stages of sleep,
which are rapid eye movement (REM) sleep, and non-rapid eye movement (non-REM)
sleep. Non-REM sleep is divided into “light sleep” and “deep sleep” phases.
During REM sleep, your brain activity is high, but only your eyes
and breathing muscles are active. This is the stage in which you dream. Non-REM
sleep involves slower brain activity. A person without a sleep disorder will
switch between non-REM and REM sleep about every 90 minutes, experiencing four to
six sleep cycles per night.
Observing your sleep cycles, along with your body’s reactions to
the changes in these cycles, can help identify disruptions in your sleep
Why Do I Need a Polysomnography?
Your doctor can use PSG to diagnose sleep disorders. It often evaluates
for symptoms of sleep apnea, a disorder in which breathing constantly stops and
restarts during sleep. The symptoms of sleep apnea include:
- sleepiness during the day despite having rested
- ongoing and loud snoring
- periods of holding your breath during sleep, which
are followed by gasps for air
- frequent episodes of waking up during the night
- restless sleep
Polysomnography can also help your doctor diagnose the following
- narcolepsy, which involves extreme drowsiness
and “sleep attacks” during the day
- sleep-related seizure disorders
- periodic limb movement disorder or restless leg
syndrome, which involves uncontrolled flexing and extension of the legs while
- REM sleep behavior disorder, which involves
acting out dreams while asleep
- chronic insomnia, which involves having difficulty
falling asleep or remaining asleep
Heart, Lung, and Blood Institute (NHLBI) warns that if sleep disorders go untreated,
they raise your risk of heart disease, high blood pressure, and stroke. There’s
also a link between sleep disorders and an increased risk of injuries related
to falling and car accidents.
How Do I Prepare for a Polysomnography?
To prepare for your PSG, you should avoid consuming alcohol and caffeine
during the afternoon and evening of the test. Alcohol and caffeine can affect sleep
patterns and some sleep disorders. Having these chemicals in your body could
impact your results. You should also avoid taking sedatives.
Remember to discuss any medications you’re taking with your
doctor in case you need to stop taking them before the test.
What Happens During a Polysomnography?
A polysomnography typically takes place at a specialized sleep
center or a major hospital. Your appointment will begin in the evening, about
two hours before your usual bedtime. You’ll sleep overnight at the sleep
center, where you’ll stay in a private room similar to a hotel room. You can
bring whatever is necessary for your bedtime routine, as well as your own
A technician will administer the polysomnography by monitoring
you as you sleep. The technician can see and hear inside your room. You’ll be
able to hear and talk to the technician during the night.
During the polysomnography, the technician will measure your:
- brain waves
- eye movements
- skeletal muscle activity
- heart rate and rhythm
- blood pressure
- blood oxygen level
- breathing patterns, including absence or pauses
- body position
- limb movement
- snoring and other noises
To record this data, the technician will place small sensors
called “electrodes” on your:
The sensors have adhesive patches so they’ll stay on your skin
while you sleep. Elastic belts around your chest and stomach will record your
chest movements and breathing patterns. A small clip on your finger will
monitor your blood’s oxygen level.
The sensors attach to thin, flexible wires that send your data to
a computer. At some sleep centers, the technician will set up equipment to make
a video recording. This will allow you and your doctor to review the changes in
your body position during the night.
It’s likely you won’t be as comfortable at the sleep center as
you would be in your own bed, so you may not fall asleep or stay asleep as
easily as you would at home. However, this usually doesn’t alter the data.
Accurate polysomnography results normally don’t require a full night’s sleep.
When you wake up in the morning, the technician will remove the
sensors. You may leave the sleep center and participate in normal activities
the same day.
What Are the Risks Associated with a
Polysomnography is painless and noninvasive, so it’s relatively
free of risks. You may experience slight skin irritation from the adhesive that
attaches the electrodes to your skin.
What Do the Results Mean?
It may take up to about three weeks to receive the results of
your polysomnography. A technician will compile the data from the night of your
sleep study to graph your sleep cycles. A sleep center doctor will review this
data, your medical history, and your sleep history to make a diagnosis.
If your polysomnography results are abnormal, it may indicate the
following sleep-related illnesses:
- sleep apnea or other breathing disorders
- seizure disorders
- periodic limb movement disorder or other
- narcolepsy or other sources of unusual daytime
To identify sleep apnea, your doctor will review the results of
the polysomnography to look for:
- the frequency of apnea episodes, which occur
when breathing stops for 10 seconds or longer
- the frequency of hypopnea episodes, which occur
when breathing is partially blocked for 10 seconds or longer
With this data, your doctor can measure your results with the apnea-hypopnea index (AHI). An AHI
score lower than 5 is normal. This score, along with normal brain wave and
muscle movement data, usually indicates that you don’t have sleep apnea.
An AHI score of 5 or higher is considered abnormal. Your doctor
will chart abnormal results to show the degree of sleep apnea:
- An AHI score of 5 to 15 indicates mild sleep
- An AHI score of 15 to 30 indicates moderate
- An AHI score greater than 30 indicates severe
What Happens After a Polysomnography?
If you receive a sleep apnea diagnosis, your doctor may recommend
that you use a continuous positive airway pressure (CPAP) machine. This machine
will provide a constant air supply to your nose or mouth while you sleep. A
follow-up polysomnography may determine the right CPAP setting for you.
If you receive a diagnosis of another sleep disorder, your doctor
will discuss your treatment options with you.