What is polysomnography?

If your symptoms and signs suggest that you may be having a sleep disorder, your sleep doctor, who should be a certified sleep specialist, will suggest a sleep study called polysomnography (PSG) or polysomnogram to confirm the diagnosis. It is the most accurate method to diagnose a sleep disorder like sleep apnea.

Good sleep is essential for good health. Sleeplessness is a health hazard over the long term with serious consequences. It is therefore necessary that you get the required hours of sleep every night.

PSG measures a number of physical and physiological activities while you are asleep. It also monitors your sleep stages and patterns to see if there is any disruption in your sleep cycle during sleep.

Polysomnography, also referred to as nocturnal polysomnography, is the most common sleep study, which also records your breathing and muscle movements when you are sleeping. 


Polysomnography is an overnight procedure and is painless. It is usually done at a sleep center overnight where you may have to spend about 6 hours. But it may be done during the day for night shift workers who usually sleep in the daytime.

The polysomnography (PSG) equipment is called a polysomnogram. Surface electrodes are put on your scalp, face, chest, and limbs. They send signals of the brain and muscle activity to a measuring machine, which records the signal digitally.

Belts are wrapped around your chest and abdomen to record your breathing. PSG records various physiological activities such as brain activity, heart rate, heart rhythm, and blood pressure, the results of which help the doctor to arrive at a diagnosis of your sleep disorder. It may also be used to plan your treatment.

What polysomnography records and tells us

The polysomnography sleep test records the physiological activities of your brain and body during your sleep.

It will record your AHI (apnea-hypopnea index), ECG, EEG, EOG, EMG, stages of sleep, the magnitude of snoring, body movement, oxygen saturation, pulse rate, and information about your breathing.

  • An electroencephalogram(EEG) measures brain activity in the form of brain waves, which shows whether your sleep consists of all stages of the sleep cycle or whether it is disturbed. Disruptions in sleep stages may suggest narcolepsy or REM sleep behavior disorder.
  • Electro-ocular gram(EOG) records eye movements. This helps to determine the presence of the sleep stage, particularly the REM sleep stage, during which the eye movements are very characteristic.
  • The electromyogram (EMG) studies muscle activity such as face twitches, teeth grinding, and leg movements. This helps to determine if REM sleep is present during sleep. Frequent leg movements may indicate a periodic limb disorder such as restless leg syndrome, which is a sleep disorder because these movements often disrupt your sleep.
  • The nasal airflow sensor measures airflow in and out of the lungs while you are asleep.
  • The snoring microphone measures the snoring activity. Very loud snoring is indicative of sleep apnea.
  • A pulse oximeter measures the percentage of oxygen (saturation) in the hemoglobin of your blood. It is a small, lightweight device that painlessly wraps around your finger and the procedure is non-invasive. Low oxygen levels may indicate sleep apnea.

The sleep specialist evaluates the results of all these sleep study tests to diagnose a sleep disorder that may be present.

Indications for polysomnography – Why you do it

Your doctor will advise polysomnography to diagnose the presence (or absence) of the following sleep disorders and conditions.

  • Sleep apnea
  • Restless leg syndrome -This is a condition in which you involuntarily flex and extend your lower limbs in your sleep.
  • Narcolepsy – This condition is associated with extreme daytime drowsiness.
  • Chronic insomnia is a sleepless long-lasting disorder where its causes need to be identified and diagnosed
  • An unusual activity during sleep such as sleepwalking or performing other complex behaviors while asleep.
  • A REM sleep disorder where you act out your dreams.


Polysomnography is a non-invasive test in which surface electrodes are used. Complications are rare and may consist of slight skin irritation at the site where the electrodes are placed.

Instructions to follow before the procedure

  • Avoid beverages and foods that contain alcohol or caffeine from the afternoon before the night of the study. Both can change your sleep patterns and can worsen your sleep disorder symptoms if present.
  • Do not have an afternoon siesta on the day of the study.
  • Take a bath before the sleep study.
  • Do not use any deodorant, gel, or colognes before going for the test. They may interfere with the sensitivity of the electrodes.


The results that are obtained during the sleep study provide a great deal of information about your sleep patterns. For example:

  • Brain waves and eye movements during sleep can help assess your sleep stages and identify any disruptions in the stages. These disruptions are typical of narcolepsy or REM sleep behavior disorder.
  • Changes in heart and breathing rate and blood oxygen may suggest sleep apnea.
  • Frequent leg movements 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 a few days or weeks to get your results. The information obtained during PSG is evaluated is reviewed by your sleep center provider.

Based on the data gathered, your healthcare provider will discuss any treatment or further evaluation that you may need.