Polysomnography (sleep study)
Polysomnography, also called “sleep study”, is a test used to diagnose sleep disorders. Polysomnography records your brain waves, the oxygen level in blood, heart rate and breathing, as well as eye and leg movements during the study.
Polysomnography usually is done at a sleep disorders unit within a hospital or at a sleep center. Patient is asked to come to the sleep center in the evening for polysomnography so that the test can record night time sleep patterns. Polysomnography is occasionally also done during the day to accommodate shift workers who habitually sleep during the day.
In addition to helping diagnose sleep disorders, polysomnography may be used to help adjust treatment plan if already diagnosed with a sleep disorder.
Why it's done
Polysomnography monitors sleep stages and cycles to identify if or when 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, brain waves, as recorded by electroencephalography (EEG), slow down considerably.
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, brain activity picks up again, and rapid eye movement (REM) sleep begins. Most dreaming occurs during REM sleep.
One normally goes through four to six sleep cycles a night, cycling between NREM and REM sleep in about 90 minutes. REM stage usually lengthens with each cycle as the night progresses. Sleep disorders can disturb this sleep process.
Polysomnography monitors sleep stages and cycles to identify if or when sleep patterns are disrupted.
Polysomnography is recommended when following are suspected:-
- Sleep apnoea or another sleep-related breathing disorder. In this condition, 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.
- Narcolepsy. Experiencing overwhelming daytime drowsiness and sudden attacks of sleep in this condition.
- REM sleep behaviour disorder. This sleep disorder involves acting out dreams as one sleeps.
- Unusual behaviours during sleep. In case of unusual activities during sleep, such as walking, moving around a lot or rhythmic movements.
- Unexplained chronic insomnia. If one consistently has trouble falling asleep or staying asleep.
Polysomnography is a non-invasive, painless test. Complications are rare. The most common side effect is skin irritation caused by the adhesive used to attach test sensors to the skin. Napping the afternoon before the sleep study is usually discouraged.
How to Prepare for the test
No eating, drinking alcohol or anything with caffeine during the afternoon and evening before polysomnography. Alcohol and caffeine can change the sleep patterns, and they may make symptoms of some sleep disorders worse.
What can be Expected
Reach the sleep center in the evening for polysomnography carrying items for use for bedtime routine (including own nightclothes) and stay overnight in a single room with its own bathroom. The room is similar to a hotel room, and it's dark and quiet during the test.
The room has a video camera, so the polysomnography technologists monitoring can see what's happening in the room when the lights are out. It also has an audio system, so they can talk to you and hear you from their monitoring area outside the room.
After being ready for bed, one of the technologists places sensors on 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 one move normally in bed. A small clip also is placed on finger or ear to monitor the level of oxygen in blood.
While you sleep, a technologist monitors the following:
All of these measurements are recorded on a continuous graph.
- Brain waves
- Eye movements
- Heart rate
- Breathing pattern
- Blood oxygen level
- Body position
- Limb movement
- Snoring and other noise you may make as you sleep
Monitoring is done by the technician throughout the night. If assistance is needed, patient can talk to the technician through the monitoring equipment. Wires can be detached if there is a need to get up during the night.
During the study, the technologist may also try using a positive airway pressure (PAP) machine for sleep apnea. This is a device that consists of a tight-sealing nosepiece through which a gentle stream of air is delivered to enhance breathing.
An opportunity is provided to try on a PAP device before the sleep study begins so that you are not surprised by it if tried later in the night. If necessary, oxygen also may be used during the study to bolster breathing.
Although one probably won't fall asleep as easily or sleep as well at the sleep center as one does at home, this usually doesn't affect the test results. A full night's sleep isn't required to obtain accurate polysomnography results.
In the morning, the sensors are removed, leave the sleep center and return to usual daily activities.
The measurements recorded during polysomnography provide a great deal of information about the sleep patterns. For example:
The information gathered during polysomnography is evaluated first by a polysomnography technologist, who uses the data to chart sleep stages and cycles. Then that information is reviewed by sleep center doctor.
- Brain waves and eye movements during sleep can help in assessment of sleep stages and identify disruptions in the stages that may occur due to sleep disorders such as narcolepsy and REM sleep behavior disorder.
- Heart and breathing rate changes and changes in blood oxygen that are abnormal during sleep may suggest sleep apnea.
- Correct settings for PAP or oxygen in case same is being considered for home use.
- Frequent leg movements that disrupt sleep may indicate periodic limb movement disorder.
- Unusual movements or behaviors during sleep may be signs of REM sleep behavior disorder or another sleep disorder.
It may take up to two weeks to receive the results of polysomnography. At a follow-up appointment, doctor reviews the results and discuss any treatment or further evaluation that may be needed.