Alaska Sleep Education Center

What is a Polysomnogram Test?

Posted by Kevin Phillips

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on Aug 13, 2015 10:10:00 AM

Man getting a polysomnography.

If you suspect you have a sleep disorder and are looking to get it treated, chances are you'll have to have a polysomnogram (PSG) test performed to properly diagnose your disorder.

But what exactly is a polysomnogram test? How is it conducted? And what can it tell you about your sleep troubles?

What is a Polysomnogram?

Simply put, a PSG is both a research tool used for studying sleep and a diagnostic tool used to determine sleep disorders.

pegs are usually performed overnight either at a hospital or at a sleep clinic, under the supervision of a sleep technician. The facilities usually have the look and feel of a comfortable hotel room rather than a sterile hospital room.

Polysomnograms are used to monitor a patient's sleep stages and cycles to determine the presence of disturbances that can be attributed to sleep disorders. PSGs use a variety of equipment that monitors brain activity, muscle activity, breathing activity, and more to get a comprehensive interpretation of what disorder (if any) the patient is suffering from.

How is a PSG Conducted?

First, the patient needs to schedule a sleep study. This can be achieved either by discussing concerning symptoms with your primary care provider or having a consultation with a sleep specialist (usually by contacting a local sleep clinic). Our website is full of information on the steps to take to get a sleep study.

In most cases, you will be asked to arrive at the Sleep Clinic around 7 p.m. at night. This gives the sleep technician plenty of time to get you caught up on any necessary paperwork, walk you through the procedure, get you hooked up to the equipment, get the equipment calibrated, and finally, allow you some downtime to prepare for sleep.

Patients are encouraged to show up to the test already having eaten dinner, bring comfortable clothing to sleep in, as well as bring clothing to change into the next morning.

Patients will have their own comfortable room to sleep in during the night while a technician monitors the data from an adjacent room. Video and audio surveillance allow the patient and technician to communicate during the night.

Patients are usually aroused from the test around 6 a.m. and discharged by 7 a.m.

What disorders are being diagnosed in a Polysomnogram?

PSGs are used to diagnose a large variety of sleep disorders using a large variety of equipment. Typical sleep disorders diagnosed by a PSG are:


CPAP titration tests are also held overnight. They usually follow a PSG from a previous night and are used to determine appropriate oxygen pressure levels for controlling sleep apnea events.

PSGs are occasionally performed during the day. Patients with certain circadian rhythm disorders in which their typical bedtime is during the day, may want a PSG test administered during their normal sleep schedule.

Sleep disorders such as narcolepsy and idiopathic hypersomnia (IH) may be conducted during the day in a variation of a PSG test. Two typical daytime tests include the multiple sleep latency test (MSLT) and the maintenance of wakefulness test (MWT).

MSLTs are generally used to distinguish between narcolepsy and IH.

MWTs are usually administered either to see if previously prescribed treatments for certain sleep disorders are successful, or if one's ability to stay awake in a certain occupation is a concern.

Insomnia is rarely tested by a PSG and is usually diagnosed by a simple consultation in discussing sleep troubles. However, if the insomnia is chronic with unexplained causes, a PSG might be used to help rule out any other underlying sleep disorder.

What equipment is used in a PSG?

Because there are so many sleep disorders that manifest with many different symptoms, a variety of monitoring equipment is used during a PSG. These include:

  • EEG (electroencephalography) electrodes to measure electrical brain activity. 8 electrodes are placed on the skin of the scalp to measure three main areas of the brain: frontal, central, and occipital (back).

    • EEGs help determine what stage of sleep a patient is in. There are four stages of sleep: Non-rapid eye movement (Non-REM)  stages 1-3 and rapid eye movement (REM). Stages 1 &2 of Non-REM are considered light sleep. Stage 3 is considered slow-wave (deep) sleep. And REM sleep is where the brain becomes very active and dreams likely occur.
  • EOG (electrooculography) electrodes to measure eye movement. 2 leads are used and placed one on the outside of each eye.

    • EOGs also help determine stages of sleep based on eye movements. During REM sleep eye movement increases substantially.
  • EMG (electromyography) electrodes to measure muscle activity. This usually includes 2 electrodes placed on the chin (one above jawline, one below), and one on each leg near the shin.

  • EMGs can help diagnose sleep-related movement disorders such as RLS, PLMD, and bruxism, and also REM behavior disorder.

  • EKG/ECG (electrocardiography) electrodes to measure the electrical activity of the heart. This usually includes 2-3 leads on the chest.

  • 2 Belts are used to measure respiratory effort. One around the chest and one around the diaphragm. These belts measure respiratory effort based on the expansion and contraction of the belts. 

  • A nasal cannula/pressure transducer is fitted in the nostrils to measure changes in inhalation and exhalation, and the rate of breathing.

  • A Pulse oximeter is placed on a patient's finger to measure blood oxygen saturation levels. Pulse oximeters are very helpful in diagnosing sleep-related breathing disorders such as sleep apnea in which the blood oxygen saturation typically drops during apnea/hypopnea events.

    • nasal cannulas, pulse oximeters, and respiratory belts work together to help diagnose sleep apnea based on the amount of air actually coming in versus the amount of effort the body makes in getting the air into the body. Dips in blood oxygen saturation are also strong indicators of sleep-related breathing disorders.
  • A sound probe may be used to detect the volume of snoring and can be helpful in differentiating between apnea events (partial or complete cessation of breathing) and hypopnea events (slow or shallow breathing).

  • A patient may also be monitored on a closed-circuit video system and audio device. This allows the sleep technician to monitor the patient's behaviors and movements during sleep, as well as allow communication between patient and tech from different rooms.

For a complete look at the various components used in a PSG check out the video from ERS Education below


Results of a PSG

In the morning the technician will wake the patient from sleep and remove all of the monitoring equipment.

Sleep technicians will score the PSG test by reviewing 30-second "epochs" of data. The technician's scoring gets passed onto a board-certified sleep specialist for review. Results often take between 7-10 days to get back to the patient.

  • Brain waves and eye movements help specialists determine what stages of sleep the patient reached, how long the cycles were, and the duration of each stage. This information helps clue the professional to identify disruptions in various sleep stages that help pinpoint a disorder.

  • Leg movements during sleep help determine sleep stages, as muscle atonia usually occurs during REM. This can also help diagnose RBD, which is physical activity occurring during REM, when the body is supposed to be immobilized. It also helps determine the presence of movement disorders and distinguish between them such as RLS vs PLMD.

  • Chin movements can help diagnose bruxism.

  • Breathing irregularities help diagnose sleep-related breathing disorders.

  • Heart rhythms and blood oxygen levels are also strong indicators of sleep-related breathing disorders.

The sleep specialist's diagnosis is usually sent to the referring primary care physician with specific recommendations for treatments.

If you live in Alaska and are ready to have a polysomnography test to help diagnose your disorder, contact the Alaska Sleep Clinic for a free 10-minute phone consultation with a sleep educator.

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Topics: sleep study

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