Why it’s done

Polysomnography monitors your sleep stages and cycles to identify if or when your sleep patterns are disrupted and why.

The normal process of falling asleep begins with a sleep stage called non-rapid eye movement (NREM) sleep. During this stage, your brain waves, as recorded by electroencephalography (EEG), slow down considerably. Your eyes don’t move back and forth rapidly during NREM, in contrast to later stages of sleep.

After an hour or two of NREM sleep, your brain activity picks up again, and rapid eye movement (REM) sleep begins. Most dreaming occurs during REM sleep.

You normally go through multiple sleep cycles a night, cycling between NREM and REM sleep in about 90 minutes. Sleep disorders can disturb this sleep process.

Your doctor may recommend polysomnography if he or she suspects you have:

• Sleep apnea or another sleep-related breathing disorder. In this condition, your breathing repeatedly stops and starts during sleep.
• Periodic limb movement disorder. In this sleep disorder, you involuntarily flex and extend your legs while sleeping. This condition is sometimes associated with restless legs syndrome.
• You experience overwhelming daytime drowsiness and sudden attacks of sleep in this condition.
• REM sleep behaviour disorder. This sleep disorder involves acting out dreams as you sleep.
• Unusual behaviours during sleep. Your doctor may perform this test if you do unusual activities during sleep, such as walking, moving around a lot or rhythmic movements.
• Unexplained chronic insomnia. If you consistently have trouble falling asleep or staying asleep, your doctor may recommend polysomnography.

Risks

Polysomnography is a non-invasive, painless test. The most common side effect is skin irritation caused by the adhesive used to attach test sensors to your skin.

How you prepare

You may be advised to avoid drinks or food containing alcohol or caffeine during the afternoon and evening before polysomnography. Alcohol and caffeine can change your sleep patterns, and they may make symptoms of some sleep disorders worse.

Napping in the afternoon before a sleep study is discouraged. You’ll usually be asked to bathe or shower before your sleep study. But don’t put on lotions, gels, colognes or makeup before the test, as these can interfere with the use of the electrodes.

What you can expect during polysomnography

You arrive at the sleep center or hospital in the afternoon for polysomnography and stay overnight. You may bring items you use for your bedtime routine, and you can sleep in your own nightclothes.

After you get ready for bed, one of the technologists will place sensors on your scalp, temples, chest and legs using a mild adhesive, such as glue or tape. The sensors are connected by wires to a computer, but the wires are long enough to let you move around in bed. A small clip is placed on your finger or ear to monitor the level of oxygen in your blood.

While you sleep, the computer records your:

• Brain waves
• Eye movements
• Heart rate
• Breathing pattern
• Blood oxygen level
• Body position
• Chest and abdominal movement
• Limb movement
• Snoring and other noise you may make as you sleep

Although you probably won’t fall asleep as easily or sleep as well at the sleep center/hospital as you do at home, this usually doesn’t affect the test results. A full night’s sleep isn’t required to obtain accurate polysomnography results.

After polysomnography

In the morning, the sensors are removed, and you may leave the sleep center/hospital. You can return to your usual activities after polysomnography.

Results

The measurements recorded during polysomnography provide a great deal of information about your sleep patterns.

For example:

• Brain waves and eye movements during sleep can help your health care team assess your sleep stages and identify disruptions in the stages that may occur due to sleep disorders such as narcolepsy and REM sleep behaviour disorder.
• Heart and breathing rate changes and changes in blood oxygen that are abnormal during sleep may suggest sleep apnea.
• Frequent leg movements that disrupt your sleep may indicate periodic limb movement disorder.
• Unusual movements or behaviours during sleep may be signs of REM sleep behaviour disorder or another sleep disorder.

The information gathered during polysomnography is evaluated by a polysomnography technologist, who uses the data to chart your sleep stages and cycles. Based on the data gathered, your doctor will discuss any treatment or further evaluation that you may need.