Polysomnography is a sleep study. This test records certain body functions as you as you sleep, or try to sleep. Polysomnography is used to diagnose sleep disorders.
Sleep study; Polysomnogram; Rapid eye movement studies; Split night polysomnography; PSG
How the Test is Performed
There are two states of sleep:
- Rapid eye movement (REM) sleep. Most dreaming occurs during REM sleep. Under normal circumstances, your muscles, except for your eyes and breathing muscles, do not move during this stage of sleep.
- Non-rapid eye movement (NREM) sleep. NREM has three stages that can be detected by brain waves (EEG).
REM sleep alternates with NREM sleep about every 90 minutes. A person with normal sleep usually has four to five cycles of REM and NREM sleep during a night.
A sleep study measures your sleep cycles and stages by recording:
- Air flow in and out of your lungs as you breathe
- The level of oxygen in your blood
- Body position
- Brain waves (EEG)
- Breathing effort and rate
- Electrical activity of muscles
- Eye movement
- Heart rate
Polysomnography can be done either at a sleep center or in your home.
AT A SLEEP CENTER
Full sleep studies are usually done at a special sleep center.
- You will be asked to arrive about 2 hours before bedtime.
- You will sleep in a bed at the center. Many sleep centers have comfortable bedrooms, similar to a hotel.
- The test is usually done at night so that your normal sleep patterns can be studied. If you are a night shift worker, many centers can perform the test during your normal sleep hours.
- Your health care provider will place electrodes on your chin, scalp, and the outer edge of your eyelids. You will have monitors to record your heart rate and breathing attached to your chest. These will remain in place while you sleep.
- The electrodes record signals while you are awake (with your eyes closed) and during sleep. The test measures the amount of time it takes you to fall asleep and how long it takes you to enter REM sleep.
- A specially-trained health care provider will observe you while you sleep and note any changes in your breathing or heart rate.
- The test will record the number of times that you either stop breathing or almost stop breathing.
- There are also monitors to record your movements during sleep. Sometimes a video camera records your movements during sleep.
You may be able to use a sleep study device in your home instead of at a sleep center to help diagnose sleep apnea. You either pick up the device at a sleep center or a trained therapist comes to your home to set it up.
Home testing may be used when:
- You are under the care of a sleep specialist
- Your sleep doctor thinks you have obstructive sleep apnea
- You do not have other sleep disorders
- You do not have other serious health problems, such as heart disease or lung disease
How to Prepare for the Test
Whether the test is at a sleep study center or at home, you prepare the same way. Unless directed to do so by your doctor, do not take any sleep medicine and do not drink alcohol or caffeinated beverages before the test. They can interfere with your sleep.
Why the Test is Performed
- Daytime sleepiness (falling asleep during the day)
- Loud snoring
- Periods of holding your breath while you sleep, followed by gasps or snorts
- Restless sleep
Polysomnography can also diagnose other sleep disorders:
- Periodic limb movements disorder (moving your legs often during sleep)
- REM behavior disorder (physically "acting out" your dreams during sleep)
A sleep study tracks:
- How often you stop breathing for at least 10 seconds (called apnea)
- How often your breathing is partly blocked for 10 seconds (called hypopnea)
- Your brain waves and muscle movements during sleep
Most people have short periods during sleep where their breathing stops or is partly blocked. The Apnea-Hypopnea Index (AHI) is the number of apnea or hypopnea measured during a sleep study. AHI results are used to diagnose obstructive sleep apnea.
Normal test result show:
- Few or no episodes of stopping breathing. An AHI of less than 5 is considered normal.
- Normal patterns of brain waves and muscle movements during sleep.
What Abnormal Results Mean
Test results above 5 may mean you have sleep apnea:
- 5 - 15 is mild sleep apnea
- 15 - 30 is moderate sleep apnea
- More than 30 is severe sleep apnea
To make a diagnosis and decide on treatment, the sleep specialist must also look at:
- Other findings from the sleep study
- Your medical history and sleep-related complaints
- Your physical exam
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