Polysomnography is a study or test done while a person is fully asleep. You will be observed while you sleep so that your doctor can record data about your sleep patterns and identify any sleep disorders. Your doctor will measure your brain waves, blood oxygen levels, heart and breathing rates, and eye movement during polysomnography to help chart your sleep cycles.
Polysomnography registers your body’s shifts between the two stages of sleep: rapid eye movement (REM) sleep and non-rapid eye movement (non-REM) sleep. 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 is characterized by 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.
Polysomnography is used to diagnose sleep disorders. It is often is used to evaluate symptoms of sleep apnea, a disorder in which your 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, followed by gasps for air
- restless sleep
Polysomnography can also be used to diagnose the following sleep disorders:
- narcolepsy (extreme drowsiness and “sleep attacks” during the day)
- sleep-related seizure disorders
- periodic limb movement disorder or restless leg syndrome (uncontrolled flexing and extension of the legs while asleep)
- REM sleep behavior disorder (acting out dreams while asleep)
- chronic insomnia (difficulty falling asleep or remaining asleep)
The National Heart, Lung, and Blood Institute warns that if left untreated, sleep disorders can raise your risk for heart disease, high blood pressure, and stroke. Sleep disorders have also been linked to an increased risk of injuries related to falling and car accidents.
A polysomnography is conducted at a specialized sleep center. Your appointment will begin in the evening, about two hours before your usual bedtime. You will sleep overnight at the sleep center, where you will stay in a private room similar to a hotel room. You will be able to bring whatever is necessary for your bedtime routine, as well as your own pajamas.
A polysomnography is usually administered by a technician, who will monitor you while you sleep. The technician can see and hear inside your room and you will be able to hear and talk to the technician during the night.
During the polysomnography, the technician will measure your:
- brain waves
- eye movements
- heart rate and rhythm
- blood pressure
- blood oxygen level
- breathing patterns
- body position
- limb movement
- snoring and other noises
To record this data, the technician will place small sensors, called electrodes, on your scalp, temples, chest, and legs. The sensors have adhesive patches so they will 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 oxygen level.
The sensors are attached 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 that occurred during the night.
Chances are that 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 being measured. 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 is relatively risk free. You may experience slight skin irritation from the adhesive that attaches the electrodes to your skin.
To prepare for your polysomnography, you will probably be asked to avoid drinking alcohol and eating or drinking anything that contains caffeine during the afternoon and evening of the test. Since sleep patterns and some sleep disorders can be affected by alcohol and caffeine, having these chemicals in your body could impact your results. You will also be asked to avoid taking sedatives.
Remember to discuss any medications you are taking with your doctor in case you need to stop taking them before the test.
It may take up to two weeks for you 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 physician will review this data, along with your medical history and sleep history in order 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, the results of the polysomnography are reviewed for:
- frequency of apnea (instances when breathing stopped for 10 seconds or longer)
- frequency of hypopnea (instances when breathing was partially blocked for 10 seconds or longer)
With this data, your results can be measured using the Apnea-Hypopnea Index (AHI). An AHI score lower than five is normal. This score, along with normal brain wave and muscle movement data, usually indicates that you do not have sleep apnea.
Abnormal results are usually indicated by an AHI score of five or higher. Abnormal results are charted to show degrees of sleep apnea:
- mild sleep apnea: AHI score of 5 to 15
- moderate sleep apnea: AHI score of 15 to 30
- severe sleep apnea: AHI score higher than 30
If you are diagnosed with sleep apnea, your physician may recommend that you use a continuous positive airway pressure (CPAP) machine. This machine will provide a constant air supply to your nose and/or mouth while you sleep. A follow-up polysomnography may be recommended to determine the right CPAP setting for you.
If you are diagnosed with another sleep disorder, your doctor will discuss the treatment options with you.