Sleep Study (Polysomnography)

What It Is

A sleep study measures what happens in the body during sleep. In a sleep lab, a technologist places sensors on the scalp, face, chest, legs, and finger, and monitors the recordings through the night from another room.

The recordings show the stages of sleep and whether breathing pauses, drops in oxygen, unusual movements, or heart rhythm changes occur. Doctors use this information, along with symptoms and history, to evaluate sleep disorders.

A home sleep apnea test uses fewer sensors and is done in a person's own bed. It focuses on breathing and oxygen and is used in selected situations, mainly when obstructive sleep apnea is suspected.

Common Terminology

Polysomnography (PSG)

A detailed overnight sleep study that records many body signals at once.

Apnea

A pause in breathing during sleep lasting at least about 10 seconds.

Hypopnea

A period of shallow or reduced breathing during sleep, usually with a drop in oxygen or a brief awakening.

Apnea-hypopnea index (AHI)

The average number of apneas and hypopneas per hour of sleep, used to describe the severity of sleep apnea.

EEG

Electroencephalogram; a recording of brain wave activity used to identify sleep stages.

REM sleep

Rapid eye movement sleep, the stage in which most vivid dreaming occurs.

CPAP titration

A sleep study in which CPAP air pressure is adjusted to find a setting that keeps the airway open.

Pulse oximetry

A sensor, usually on a finger, that estimates the oxygen level in the blood.

Why It Is Done

A sleep study may be done to help evaluate:

• Suspected obstructive sleep apnea, especially with loud snoring, observed breathing pauses, or daytime sleepiness.
• Excessive daytime sleepiness, including possible narcolepsy (often with a daytime nap test called an MSLT).
• Unusual behaviors during sleep, such as acting out dreams or sleepwalking.
• Periodic limb movements or other movement problems during sleep.
• Fitting and adjusting CPAP or other breathing treatment.

How It Is Performed

This is a general description of an in-lab study:

• The person arrives in the evening and sleeps in a private room set up like a bedroom.
• A technologist attaches small sensors to the scalp, face, chest, and legs, plus belts around the chest and belly and a clip on a finger.
• Sensors record brain waves, eye movements, muscle activity, heart rhythm, breathing, airflow, and oxygen levels.
• A camera and microphone often record sleep position and snoring.
• In a split-night study, CPAP may be started partway through the night if significant sleep apnea is seen.
• A home test uses a small portable device with fewer sensors that the person puts on at bedtime.

Before the Procedure

Before a sleep study, in general:

• The sleep center usually provides instructions about the day of the test.
• People are often asked to avoid caffeine and alcohol and to skip naps on the day of the study.
• Clean, dry hair and skin without oils or lotions help sensors stick well.
• Bringing comfortable sleepwear and usual bedtime items can make the night easier.
• The care team typically reviews current medicines and gives guidance about them.

Recovery Overview

After the study:

• Sensors are removed in the morning, and most people can return to normal activities right away.
• Any adhesive or paste on the skin and hair washes off.
• Many people sleep less well than usual in the lab, and technologists are used to this.
• A sleep specialist reviews the recordings, and results are typically discussed at a follow-up visit.

Risks and When Complications May Be Discussed

A sleep study is noninvasive and generally very low risk. Things that may come up include:

• Mild skin irritation from adhesives or sensor paste.
• Difficulty sleeping in an unfamiliar place, which can affect the recording.
• Home tests can sometimes miss or underestimate sleep apnea, so an in-lab study may be suggested afterward.
• If a home device stops recording or falls off, the test may need to be repeated.

Questions to Ask a Healthcare Professional

General questions people often find useful to bring to an appointment:

• Is an in-lab study or a home sleep apnea test more appropriate, and why?
• What should be done about usual medicines on the night of the study?
• What happens if sleep does not come easily during the test?
• What does the apnea-hypopnea index mean in general terms?
• How long will it take to get results?
• If a sleep disorder is found, what treatment options are generally discussed?

Sources

This guide was written in plain language from the following authoritative references.

1. Polysomnography — MedlinePlus (U.S. National Library of Medicine)
2. Sleep Studies — National Heart, Lung, and Blood Institute (NHLBI)
3. Sleep Apnea — MedlinePlus (U.S. National Library of Medicine)

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