Polysomnography, also known as a sleep study, is a detailed test used to diagnose sleep disorders. This procedure records brain waves, oxygen level in the blood, heart rate and breathing, as well as leg and eye movements of the patient during the study.

Polysomnography is usually conducted at a sleep centre or sleep disorders unit within a hospital. It’s usually done at night, rarely during the day to accommodate shift workers who normally sleep during the day. Further, this study also helps to start or modify a treatment plan if a person has been already diagnosed with a sleep disorder.
Polysomnography/Sleep Study

Why It’s Done?

Polysomnography evaluates the sleep stages and cycles to determine if or when a person’s sleep schedules are disrupted and why.

There are various types of home sleep apnea test devices using different patterns of sensors. They usually record breathing rate, airflow, oxygen levels and heart rate. One type also provides information on blood vessel tone.

The normal process of falling asleep starts with a sleep stage- non-rapid eye movement (NREM) sleep. During this stage, brain waves slow down remarkably and are recorded by electroencephalography (EEG). The patients’ eyes don’t move back and forth quickly during NREM when compared to later stages of sleep. After an hour or two of NREM sleep, brain activity picks up again and rapid eye movement (REM) sleep starts, and most dreaming happens during REM sleep.

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A person generally goes through multiple sleep cycles at night, cycling between NREM and REM sleep in about 90 minutes. Sleep disorders can impede this sleep method.

The healthcare provider may suggest polysomnography if he or she suspects a person may have the following condition:

  • Sleep apnea or another sleep-related breathing disorder
  • Periodic limb movement disorder
  • Narcolepsy
  • REM sleep behaviour disorder
  • Unusual behaviours during sleep
  • Unexplained chronic insomnia

How To Prepare For the Study?

The doctor will explain in detail about the procedure to the patient. Some of the things to be taken care of include:

Before The Procedure:

Refrain from eating or drinking any caffeinated beverages and restrict alcohol, particularly in the afternoon and evening before the test. Consuming alcohol and caffeine may alert the patient’s sleep schedule and can make sleep disorders symptoms worse.

The patient is asked to wear night clothes, while the test is performed. The patient is advised not to wear any tight clothes as these may interfere with the patient's sleep.

The patient is asked to come to the sleep centre and stay overnight.

The study room would be very calm and dark, to aid the patient fall asleep quickly.

The study room will also have a rest room attached to and it is not shared with others, to avert any kind of disturbance.

This room is installed with a camera to watch all the movements of the patient precisely after the lights are turned off.

The sleep specialist carefully evaluates the body reactions and the sleep cycles of the patient.

The room is also installed with an audio system, for the patient to speak with a sleep specialist in case of any doubt.

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During The Procedure:

When the patient is about to sleep, the technician connects electrodes on the patient’s temple, scalp, legs, and chest with help of adhesive tapes. These electrodes are linked to long wires which are further connected to a computer. The wires attached are very long and do not cause any hindrance while sleeping.

A small clip-like device is also connected to the patient’s ear or finger, to constantly monitor the oxygen supply in the blood.

While the patient is asleep, the following parameters are recorded by the technician:

  • Breathing cycle (respiration)
  • Heart rate
  • Level of oxygen in the blood
  • Brain waves
  • Muscle tone
  • Leg Movements
  • Eye movements
  • Body positions
  • Any noises like snoring while sleeping

These parameters are carefully evaluated throughout the night and recorded on a graph.

In case of any emergency, the patent can alert the sleep technician immediately for assistance.

The patient is connected to positive airway pressure (PAP) machine, and this is used mainly for patients with sleep apnea, which is a breathing disorder associated with sleep. In this condition, the breathing of the patient stops and begins frequently.

PAP machine comprises a nosepiece that aids in providing a mild air stream to the patient to help boost the breathing process while sleeping. Generally, patients undergoing tests with the PAP machine would be asked to try the machine once before the study begins so that patient does not feel any discomfort when the machine is used during the night. The patient may not be able to sleep easily, while in the study room as compared to at home. Although, a lesser duration of sleep or discomfort in the sleep during the test would not largely impact test results in any way.

After The Procedure:

When the patient wakes up the next morning, the electrodes attached are removed and the patient is allowed to go home in the morning and resume daily routine normally. The patient is asked to visit the doctor for a review.

The healthcare provider assesses the graph of the body reactions and sleep cycles of the patient cautiously and finds out any interferences in the sleep schedule.

When the patient wakes up the next morning, the electrodes or the test sensors attached to the body are removed. The patient is allowed to go home in the morning and the patient can resume routine activities normally. The technician interprets and analyses the results of the patient and hands them to the doctor.


The doctor diagnoses and evaluates any sleep disorders in the patient based on the graphs obtained and the sleep cycles of the patient.

The doctor would discuss the results of the study in detail with the patient. If any abnormal behavioural changes in the sleep schedule of the patient are observed in the report, then the doctor may recommend medications or decide on a treatment plan. A normal study indicates no or very few signs of episodes of stopped breathing and normal patterns of muscle and eye movements and brainwaves during sleep.

Whereas abnormal study results indicate abnormal brain waves and muscle movements that cause sleep disorders. Abnormalities and findings noted from the test include:

Eye movements and brain waves measured, while the patient is asleep help the doctor check the impediments in the sleep schedule of the patient, which can be a marker of multiple abnormalities related to sleep. Some of the sleep abnormalities, which can be diagnosed from eye movements and brain waves are REM-related sleep disorders and narcolepsy.

The result can indicate the oxygen level required by the patient during sleep, thus the doctor can determine the treatment plan accordingly.

The heart rate changes and the variations in the breathing rate can be a sign of sleep apnea.

Other behaviours observed during the study may be a result of multiple conditions and problems related to the sleep

Issues observed with limb or leg movements can be a sign of limb-based disorders in the patient.