Definition & Overview

Polysomnography is a medical test primarily used for the diagnosis of sleeping disorders. It’s designed to record brain wave activity, blood oxygen levels, breathing and heart rate as well as eye and leg movements while the patient is asleep. It can detect any disruptions to normal sleep patterns helping doctors to diagnose any abnormalities so a targeted treatment plan can be formulated.

Who Should Undergo and Expected Results

Polysomnography is recommended for patients who are suspected of having sleep disorders, such as:

  • Sleep apnoea, or when a patient stops breathing during sleep
  • Periodic limb movement disorder, or when a patient flexes and extends his legs involuntarily during sleep
  • Narcolepsy, or when a person experiences extreme drowsiness and sudden sleepiness during the day
  • REM sleep behaviour disorder, or when a patient acts out dreams during sleep
  • Chronic insomnia, or difficulty falling asleep or staying asleep throughout the night

Polysomnography can also be recommended to patients who experience the following symptoms:

  • Difficulty falling asleep
  • Frequent sleep disruptions
  • Breathing problems during sleep
  • Involuntary movements during sleep
  • Feeling extremely sleepy during the day
  • Snoring
  • Making abnormal noises during sleep
  • Making abnormal muscle activities such as twitching the eyes
  • Holding the breath during sleep, then gasping or snorting out

A polysomnography monitors the patient’s sleeping patterns throughout all stages of sleep and records the patient’s:

  • Brainwaves
  • Heart rate
  • Blood oxygen level
  • Breathing pattern
  • Eye movements
  • Body or limb movements

How is the Procedure Performed?

Polysomnography is a routine diagnostic test performed in special sleep centres or sleep disorders unit of a hospital. It is usually scheduled at night so the patient’s nighttime sleep patterns can be properly observed. To easily fall asleep for the test, patients are advised against napping on the afternoon prior to the sleep study and to refrain from consuming anything that contains caffeine or alcohol, as both can have an effect on the sleep patterns and may aggravate the symptoms the patient is experiencing.

During the actual test, the patient is asked to sleep alone in a dark and quiet room equipped with a video camera and an audio system. Throughout the test, sensors are attached to the patient’s scalp, temple, legs, and chest. The data provided by the sensors tend to differ depending on what kind of sleep study is being performed, which could be:

  • Diagnostic overweight PSG
  • Diagnostic daytime multiple sleep latency test
  • Two-night evaluation PSG and CAP titration
  • Split-night PSG with CAP titration

To ensure the efficacy and results of the test, practitioners used a combination of several different tests and equipment, such as:

  • EEG or electroencephalogram
  • EMG or electromyogram
  • EOG or electrooculogram
  • EKG or electrocardiogram
  • Snoring microphone
  • Nasal airflow sensor

If sleep apnoea is strongly suspected, the patient may also be hooked to a positive airway pressure or PAP machine to enhance his breathing during sleep.

On the morning following the sleep study, the patient is discharged and advised to come back for a scheduled follow-up visit where the results of the test are discussed.

In some cases, the polysomnography is followed by another sleep-related diagnostic test called the multiple sleep latency test or MSLT, especially if daytime sleepiness is an issue for the patient. An MSLT test is capable of recording the number and length of naps that a person takes within a single day.

Possible Risks and Complications

Polysomnography is a safe diagnostic test that causes little to no pain and discomfort to the patient. It is non-invasive and not associated with any serious risks to health. The most common side effect reported is skin irritation arising from the adhesive used to attach sensors to the body during the test.


  • Armon C., “Polysomnography.” Medscape.

  • Rohling L., Blankvoort C., Mattern-Coren E., De Weerd A., “Medical technology assessment of polysomnography, type 2: Full PSG at home.”

  • Beck S., Marcus C. “Pediatric polysomnography.” Sleep Med Clin. 2009; 4(3): 393-406.

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