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 patterns.
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 sleep disorders:
- 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 asleep
- REM sleep behavior disorder, which involves acting out dreams while asleep
- chronic insomnia, which involves having difficulty falling asleep or remaining asleep
The National 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.
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.
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 pajamas.
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.
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.
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 movement disorders
- narcolepsy or other sources of unusual daytime fatigue
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 apnea.
- An AHI score of 15 to 30 indicates moderate sleep apnea.
- An AHI score greater than 30 indicates severe sleep apnea.
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.