What a sleep study involves

Why sleep studies are done

Sleep studies help diagnose obstructive sleep apnea, central sleep apnea, narcolepsy, periodic limb movements and some unusual behaviors during sleep. The National Heart, Lung, and Blood Institute describes them as painless tests that show how much and how well you sleep and whether a disorder is disrupting it.

For most midlife adults, the question is sleep apnea. A study confirms whether it is present, which type it is and how severe it is, which guides treatment.

Home test or sleep lab?

Your clinician decides which test fits. MedlinePlus explains that a home test is mainly an option when sleep apnea is the main concern. You wear a small device for one night, sometimes two. People with significant heart or lung disease, or a suspected different sleep disorder, often need a sleep center instead.

• Home sleep apnea test: sleeps in your own bed; measures breathing, airflow, effort and oxygen; does not measure brain waves, so it estimates sleep time
• In-lab polysomnography: full set of sensors, a technician monitoring overnight, and the ability to detect a wider range of disorders
• Titration study: an in-lab night used to find the right CPAP pressure, sometimes combined with a diagnostic night

What happens at a sleep center

You typically arrive about two hours before your usual bedtime and sleep in a private bedroom, MedlinePlus notes. A technician attaches removable sensors to your scalp, face, near your eyelids, chest, legs and a finger. Belts around the chest and abdomen track breathing effort, a small sensor under the nose measures airflow, and a clip on your finger monitors oxygen.

The sensors record brain waves, eye movements, muscle activity, heart rhythm, breathing and oxygen levels throughout the night. Many centers also record video to capture movements. You can move and turn over, and the technician can help if a sensor slips or you need to get up.

How to prepare

MedlinePlus advises avoiding sleep medicines, alcohol and caffeine before the test unless your sleep specialist says otherwise, because they change how you sleep.

• Follow your normal routine as much as possible the day of the test
• Avoid alcohol and caffeine beforehand, and skip daytime naps
• Ask your clinician before stopping any regular medication; do not take sleep aids unless told to
• Wash and dry your hair, and skip oils, lotions and hair products that can loosen sensors
• Bring comfortable sleepwear, your usual pillow if you like, and anything you need for the morning

Will I be able to sleep?

Almost everyone worries about this. Most people sleep less well than at home, but usually well enough to get a useful result. The study does not need a perfect night, and technicians are used to people taking a while to drift off. If too little sleep is recorded, a repeat study may be arranged.

A few things help: keep to your usual bedtime routine, bring a book or something familiar, and tell the technician if the room feels too warm or cold. For a home test, follow the setup instructions carefully and put the device on just before bed, since a sensor that falls off early is one reason a home study may need to be repeated.

Reading your results

The study counts apneas, pauses in breathing lasting at least 10 seconds, and hypopneas, partial reductions in breathing of similar length. Divided by hours of sleep, these give the apnea-hypopnea index (AHI). MedlinePlus lists an adult AHI below 5 as normal; 5 to 14 as mild; 15 to 29 as moderate; and 30 or more as severe.

Your report will also show how low your oxygen dropped, how long you spent in each sleep stage, how often you woke and whether events were worse on your back or during REM sleep. A sleep specialist interprets these together with your symptoms and history; the AHI alone does not tell the whole story.

What happens next

If you have sleep apnea, NHLBI lists treatment options including CPAP and other airway pressure devices, custom oral appliances, positional therapy, weight loss, hypoglossal nerve stimulation and surgery. For adults with obesity and moderate to severe obstructive sleep apnea, a weight-loss medication is also FDA-approved for this use.

If your study is normal but you are still exhausted, that is useful information too. It points your clinician toward other causes, such as insomnia, thyroid problems, anemia, depression, medications or hormone changes.

Don't wait for the test if…

If you are falling asleep while driving, stop driving drowsy and tell your clinician, as this can make testing more urgent. Seek emergency care for chest pain, fainting or severe breathlessness.