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Why it's done
By Mayo Clinic staffPolysomnography monitors your sleep stages and cycles to identify if or when your sleep patterns are disrupted and why.
The normal process of falling asleep begins with a sleep stage called non-rapid eye movement (NREM) sleep. During this stage, your brain waves, as recorded by electroencephalography (EEG), slow down considerably. Your eyes don't move back and forth rapidly during NREM, in contrast to later stages of sleep. After an hour or two of NREM sleep, your brain activity picks up again, and rapid eye movement (REM) sleep begins. Most dreaming occurs during REM sleep.
You normally go through four to six sleep cycles a night, cycling between NREM and REM sleep in about 90 minutes. Your REM stage usually lengthens with each cycle as the night progresses. Sleep disorders can disturb this sleep process. Polysomnography monitors your sleep stages and cycles to identify if or when your sleep patterns are disrupted.
Your doctor may recommend polysomnography if he or she suspects you have:
- Sleep apnea or another sleep-related breathing disorder — your breathing repeatedly stops and starts during sleep.
- Periodic limb movement disorder — you involuntarily flex and extend your legs while sleeping. This sleep disorder is sometimes associated with restless legs syndrome.
- Narcolepsy — you experience overwhelming daytime drowsiness and sudden attacks of sleep.
- REM sleep behavior disorder — you act out dreams as you sleep.
- Unusual behaviors during sleep — you do unusual activities during sleep, such as walking, moving around a lot or rhythmic movements.
- Unexplained chronic insomnia — you consistently have trouble falling asleep or staying asleep.
- Behrouz J, et al. Polysomnography. Clinics in Chest Medicine. 2010;31:287.
- Overnight sleep study. American Academy of Sleep Medicine. http://yoursleep.aasmnet.org/ArticlePrinterFriendly.aspx?id=12&DType=4. Accessed Sept. 2, 2011.
- Sleep cycles. American Academy of Sleep Medicine. http://www.sleepeducation.com/sleepcycles.aspx. Accessed Sept. 3, 2011.
- Your guide to healthy sleep. National Heart, Lung, and Blood Institute. http://www.nhlbi.nih.gov/health/public/sleep/healthy_sleep.htm. Accessed Sept. 3, 2011.
- What are sleep studies? National Heart, Lung, and Blood Institute. http://www.nhlbi.nih.gov/health/health-topics/topics/slpst/. Accessed Sept. 1, 2011.
- Sleep studies. American Thoracic Society. http://patients.thoracic.org/information-series/en/resources/sleep-studies.pdf. Accessed Sept. 1, 2011.
- St. Louis EK, et al. The nervous system. In: Bope ET, et al. Conn's Current Therapy. Philadelphia, Pa.: Saunders Elsevier; 2011. http://www.mdconsult.com/books/page.do?eid=4-u1.0-B978-1-4377-0986-5..00008-9--sc9000&isbn=978-1-4377-0986-5&sid=1201926766&uniqId=279535098-3#4-u1.0-B978-1-4377-0986-5..00008-9--s9180. Accessed Sept. 2, 2011.
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