How a Polysomnography Sleep Study Works

A polysomnography sleep study records your brain, breathing, oxygen, heart and movement all at once while you sleep overnight in a lab. A trained technologist watches over you, and a sleep doctor reads the results. The test is painless and non-invasive (nothing goes inside your body).

What is polysomnography?

Polysomnography (PSG) is a full overnight sleep study. It is done in a sleep lab. It is the most detailed and accurate test for finding sleep problems.

A trained sleep technologist watches over you all night. Special equipment records what your body does while you sleep. Most insurance plans cover it. To confirm your plan, please check with our office at (512) 931-1575.

What does the study measure?

A PSG records many things in your body at the same time:

• Brain waves (EEG, or electroencephalogram) — Show your stages of sleep. These are light sleep (N1 and N2), deep sleep (N3), and dream sleep (REM).
• Eye movements (EOG, or electrooculogram) — Help spot dream sleep (REM).
• Muscle activity (EMG, or electromyogram) — In the chin and legs.
• Heart (ECG, or electrocardiogram) — Heart rate and rhythm.
• Breathing effort — How your chest and belly move as you breathe.
• Airflow — Air moving in and out of your nose and mouth.
• Pulse oximetry — A clip on your finger that checks the oxygen in your blood.
• Snoring microphone — Records how loud you snore and how often.
• Body position sensor — Tracks how you lie all night.
• Video — Records your movements and actions during sleep.

Myth: A sleep study only counts how many times you stop breathing. Fact: A sleep study measures much more than breathing. It gives a full picture of your sleep stages, brain activity, heart and movements.

What problems can this test find?

It can find many sleep problems, not just sleep apnea:

• Obstructive sleep apnea (OSA) — When your throat gets blocked during sleep.
• Central sleep apnea — When your brain does not send the signal to breathe.
• Periodic limb movement disorder (PLMD) — When your legs or arms jerk often in sleep.
• REM sleep behavior disorder — When you act out your dreams.
• Narcolepsy — When used together with a daytime nap test (MSLT).
• Seizures at night — Fits caused by bursts of brain activity during sleep.
• Parasomnias — Unusual actions in sleep, like sleepwalking or sleep terrors.

How are the results scored?

After your study, a registered sleep technologist goes through the data. They mark every change in sleep stage. They also mark every breathing problem, leg movement and brief wake-up (arousal) during the night. Then a board-certified sleep doctor reads the results and makes a diagnosis.

Key numbers in your report include:

• Total sleep time — How long you really slept.
• Sleep efficiency — The share of your time in bed that you spent asleep.
• Sleep architecture — How your night was split between the stages of sleep.
• AHI (Apnea-Hypopnea Index) — How many times per hour your breathing stopped or got shallow.
• Oxygen nadir — Your lowest oxygen level of the night.
• PLM index — How many leg movements you had per hour.
• Arousal index — How many brief wake-ups you had per hour.

When is this test advised?

Your doctor may want you to have a sleep study in the lab when:

• A home test was unclear — A home sleep test did not give a clear answer. Or it was normal, but your doctor still strongly suspects a problem.
• The problem may be complex — A more complex sleep problem may be present, like narcolepsy, unusual sleep actions or seizures.
• You have serious health problems — Examples are heart failure, COPD (a long-term lung disease) or a disease of the nerves and muscles.
• You need a CPAP titration — This is a night to find the right air pressure for your CPAP machine.
• Treatment needs checking — Your doctor needs to check how well your treatment works.