Alternative names: Sleep study; Polysomnogram; Rapid eye movement studies; Split night polysomnography; PSG; OSA – sleep study; Obstructive sleep apnea – sleep study; Sleep apnea – sleep study
Definition: Polysomnography is a sleep study. This test records certain body functions as you sleep or try to sleep. Polysomnography is used to diagnose sleep disorders.
How the Test is Performed
There are two stages 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 most often 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 centre or in your home.
AT A SLEEP CENTRE
Full sleep studies are most often done at a special sleep centre.
- You will be asked to arrive about two hours before bedtime.
- You will sleep in a bed at the centre. Many sleep centres have comfortable bedrooms, similar to a hotel.
- The test is most often done at night so that your normal sleep patterns can be studied. If you are a night shift worker, many centres 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 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 centre to help diagnose sleep apnea. You either pick up the device at a sleep centre 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 centre 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 behaviour 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 five is considered normal.
- Normal patterns of brain waves and muscle movements during sleep.
What Abnormal Results Mean
In adults, test results above five may mean you have sleep apnea:
- five to 15 is mild sleep apnea
- 15 to 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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