Dr. Stephen Schendel
Plastic, Maxillofacial and Sleep Surgery

society logo

Polysomnography Sleep Test

Polysomnography Sleep Test - Palo Alto, CA


A sleep test monitors and studies you while you sleep (or try to sleep). There are two types of sleep:

  • Rapid eye movement (REM) sleep
  • Non-rapid eye movement (NREM) sleep

You dream during REM sleep. The muscles of your body do not move during REM sleep, but your eyes and lungs do move. NREM sleep has four stages distinguishable by EEG waves. REM sleep alternates with NREM sleep approximately every 90 minutes. A person with normal sleep usually has four to five cycles of REM and NREM sleep during a night.

A sleep study measures your sleep cycles and stages by recording the following information:

  • Blood oxygen levels
  • Body position
  • Brain waves (EEG)
  • Breathing rate
  • Electrical activity of muscles
  • Eye movement, breathing rate
  • Heart rate

How the Test is Performed

The most common type of sleep study is performed in a special sleep center. You will be asked to arrive about 2 hours before your normal bedtime and will sleep in a bed at the center. So that you are comfortable, many of the rooms are modeled after a standard hotel room. In most cases the sleep study takes place during the night. The health care provider will place electrodes (don’t worry, they only monitor the electrical waves produced by the brain and do not give you an electric shock) on your chin, scalp and the outer edge of your eyelids. These must remain in place while you sleep.

Signals from electrodes are recorded while you are awake (with your eyes closed) and during sleep. The time taken to fall asleep is measured as well as the time to enter REM sleep.

Monitors to record your heart rate and breathing will be attached to your chest. These also must remain in place during sleep. A specially trained health care provider will directly observe you while you sleep and note any changes in your breathing or heart rate. The number of times that you either stop breathing or almost stop breathing will be measured. In some sleep study centers, a video camera records your movements during sleep.

How to Prepare

In order to get an accurate measurement of your sleep habits we ask that you do not take any sleeping medication. You also need to avoid drinking any type of alcohol or beverage that contains caffeine (this does include tea, decaffeinated coffee and certain waters). You need to be able to fall asleep naturally.

The test is done to diagnose possible sleep disorders, including:

  • Excessive daytime sleepiness
  • Hypersomnia
  • Insomnia
  • Narcolepsy
  • Obstructive sleep apnea and other breathing difficulties during sleep
  • Periodic limb movements disorder (frequent movements of the legs during sleep)
  • REM behavior disorder (a condition where dreams are physically ”acted out”)

Normal Results?

A normal test result shows usual or normal patterns of brain waves and muscle movements during sleep, without frequent breathing problems.

What Abnormal Results Mean?

Abnormal results may confirm a suspected sleep disorder. For example, an episode of stopped breathing during sleep is called sleep apnea.