Sleep Studies

What is polysomnography?

“Polysomnography” is the term used for an overnight study administered by a sleep technologist at the sleep clinic. It is considered the “gold standard” test for diagnosing sleep apnea. Most people normally go through four to six sleep cycles during the night, cycling between NREM and REM sleep approximately every 90 minutes. The purpose of polysomnography is to trace events that occur during each sleep cycle so as to detect any abnormalities that may impede the normal sleep process.

In a typical polysomnography, information is gathered in much the same way as a polygraph is used for a lie detector test.  The sleep technologist attaches various electrodes and sensors to your body through which data on your brain wave activity, oxygen levels in the blood, heart rate and breathing, and eye and leg movements, are recorded while you sleep. In a separate room from where you sleep, the sleep technologist observes you while you sleep and monitors the recording data as it is being collected.

If the sleep technologist determines after the diagnostic polysomnography that you have sleep apnea and would benefit from PAP therapy, he or she will recommend a second polysomnography, called a titration polysomnography, to determine the optimal settings to set your PAP device to alleviate the sleep apnea. During the second sleep study, the settings on the PAP device are adjusted by trial-and-error to find the right pressure that helps keep your airway open while you sleep.  Titration polysomnography is similar to diagnostic polysomnography in that the same physiological functions are observed and recorded.  However, in the titration study, the patient uses a PAP device while sleeping.

If during the first few hours of the diagnostic polysomnography, sufficient data are collected to diagnose sleep apnea, the sleep technologist may ask you to wear the PAP device during the remainder of the sleep study so that the optimal settings for use of the PAP device may be determined. When both a diagnostic and titration polysomnography are performed on the same night, the study is called a “split-night” study. For the sleep technologist to convert the diagnostic polysomnography into a titration polysomnography on the same night, obvious signs of sleep apnea must be observed during the first few hours of the sleep study so that there is enough time during the night to effectively titrate the device.

What happens during the overnight sleep study at the sleep clinic?

The sleep study usually begins in late evening and ends at about 6:00 AM the next morning.   Once you arrive at the sleep clinic for your scheduled study, a sleep technologist will welcome you and show you to your private bedroom.  

You may bring items you use for your bedtime routine, and you can sleep in your own nightclothes. The room where the sleep study is conducted is similar to a hotel room; it is dark and quiet during the sleep study. You don't share the room with anyone else. The room has a video camera, so that the sleep technologist can see what's happening in the room when the lights are out, and an audio system, so that he or she can talk to you and hear you from the monitoring area outside your room.

After you change into your sleepwear, the sleep technologist will explain the procedure and what to expect during the night. The technician will prepare you for the study by placing electrodes and sensors on your head, chest, and legs. The areas where the sensors will be attached are cleaned and the electrodes are attached with special gels and paste. Elastic belts with sensors will be placed around your chest and abdomen. Airflow sensors will be placed under your nose and a finger clip will be applied to monitor your oxygen levels. All of the sensors are connected to a small portable box that transmits signals to the sleep monitoring and recording equipment that is in the nearby control room.

If the sleep study is a titration polysomnography, the sleep technologist will fit you with a PAP mask and explain how the PAP device works or, alternatively, deliver an oral appliance to you with instruction on its use.

During the sleep study, every attempt is made to allow for a normal night’s sleep.  You wear your own sleepwear and can bring your favorite pillow, book or magazine. Showers and basic toiletries are available for your use in the morning. A trained sleep technologist is available to explain the procedure, operate the diagnostic equipment and is stationed all night in an adjacent control room to both monitor the sleep recording and ensure your comfort and well-being. If you need assistance, you can talk to him or her through the monitoring equipment. The technologist can come into the room to detach the wires if you need to get up during the night.

In the morning when the sleep study is completed, the sensors are removed, and you may leave the sleep center. You're given an appointment for a follow-up visit with your doctor or the sleep specialist.

What happens after the sleep study?

Once your sleep study is performed, a board-certified physician will interpret the results of your study usually within 48 hours. A detailed report of the sleep study will be compiled with treatment recommendations. At the follow-up appointment the findings of your sleep study will be reviewed with you and a treatment plan discussed. Your doctor will continue to meet with you as needed to ensure that your sleep disorder is resolved.

What is involved with home sleep apnea tests?

In certain circumstances when there is a high likelihood that the patient has moderate-to-severe obstructive sleep apnea and the patient has no significant medical conditions other than the suspected obstructive sleep apnea, the sleep specialist may order a home sleep apnea test instead of an overnight study at the sleep clinic.

If a home sleep apnea test is indicated, the patient is given portable diagnostic equipment to take home to wear overnight while he or she is sleeping. Once the test is completed, the equipment is returned to the sleep clinic where the test results are scored and interpreted by board-certified sleep specialists.

In some cases, a follow-up overnight sleep study at the sleep clinic may be necessary if the test results are unclear; there is insufficient data to make a diagnosis; another sleep-related disorder is suspected; or the test results indicate that the patient does not have obstructive sleep apnea even though clinical symptoms of the medical condition persist.

What other diagnostic tests are available?

Patients who experience excessive daytime sleepiness or who fall asleep at inappropriate times may be candidates for a Multiple Sleep Latency Test (MSLT) or Maintenance of Wakefulness Test (MWT). The MSLT is designed to measure how long it takes a person to fall asleep during the course of a day. The MWT tests a person's ability to stay awake for a designated period of time, usually 20 minutes.

The MSLT and MWT are performed during daytime hours and are used to diagnose narcolepsy or idiopathic hypersomnolence. The MSLT begins two hours after awakening from a diagnostic polysomnography; it consists of four to five attempts at napping scheduled 2 hours apart. During these naps, the sleep technologist monitors the patient’s sleep/wake patterns. The test measures how quickly the person falls asleep during regular waking hours as well as the kind of sleep experienced during the naps.

Similar to the multiple sleep latency test, the maintenance of wakefulness test provides an objective measurement of the degree of daytime sleepiness. The MWT measures the ability of a person to resist sleep when instructed to remain awake for 20 minutes. It is a daytime study which usually begins two hours after awakening and involves a series of tests at set intervals throughout the day. However, unlike the MSLT, the patient is instructed to stay awake during the nap.