In order to diagnose certain sleep-related disorders, a sleep study may be indicated. A sleep study is a noninvasive, painless test in which sleep patterns and behaviors associated with sleep are recorded. Sleep Centers of Texas offers both overnight sleep studies at its sleep clinics in San Antonio and Ennis as well as home sleep apnea tests which are performed in the patient’s home.


What sleep studies are conducted overnight at the sleep clinics?

The most common sleep study administered by sleep technologists at the sleep clinic is called “polysomnography.” Most individuals normally go through four to six sleep cycles during the night, cycling between non-rapid eye movement (NREM) and rapid eye movement (REM) sleep every 90 to 110 minutes. The purpose of polysomnography is to trace the events that occur during the individual’s sleep cycles in order to detect any abnormalities that may impede the normal sleep process.

There are three types of polysomnography studies:

  • Diagnostic Polysomnography: The purpose of this sleep study is to diagnose or rule out any sleep-related disorder.
  • Titration Polysomnography: If sleep apnea is diagnosed and PAP therapy or oral appliance therapy is prescribed, a second sleep study, the titration polysomnography, is conducted to determine the optimal settings on the PAP device or oral appliance to eliminate the sleep apnea.
  • Split-Night Study: A split-night study is a combination diagnostic and titration study. The first half of the sleep study is conducted to diagnose sleep apnea. If midway through the night sufficient data has been collected to establish a definitive diagnosis of sleep apnea, then CPAP titration is started to determine the optimal settings on the CPAP device to eliminate the sleep apnea.


How does polysomnography work?

In a typical polysomnography, information is gathered in much the same way as a polygraph collects data for a lie detector test. The sleep technologist attaches various electrodes and sensors to your scalp, face, chin, chest, finger and legs to record multiple biological functions during sleep, such as brain wave activity, eye movement, leg movement, muscle tone, heart rate, airflow, breathing effort, snoring and oxygen levels in your blood. In a separate room, the sleep technologist observes you while you sleep and monitors the recording data as it is being collected. Additionally, a record of the sleep study is made via an audiovisual recording.


How does a diagnostic polysomnography differ from a titration polysomnography?

The purpose of the initial polysomnography is to diagnose sleep-related disorders. If the results of the diagnostic polysomnography indicate that the patient has sleep apnea, then the sleep specialist may recommend PAP therapy or oral appliance therapy to treat the disorder. In order to establish the optimal settings for the PAP device or oral appliance to be used, a follow-up titration polysomnography is necessary to determine, on a trial-and-error basis, the optimal settings for the device.

The titration polysomnography is similar to the diagnostic polysomnography in that the same biological functions are monitored and recorded; however, during the second polysomnography the patient wears a CPAP device or oral appliance while sleeping.


Can sleep studies be performed in the patient’s home rather than at the sleep clinic?

In certain circumstances, the sleep specialist may order a home sleep apnea test instead of an overnight study at the sleep clinic. A home sleep study is a simplified version of an overnight, attended sleep study. It is only used though to diagnose or rule out obstructive sleep apnea. Other sleep-related disorders cannot be diagnosed with a home sleep apnea test.

If a home sleep apnea test is indicated, the patient is given the equipment to take home with him or her to use overnight while sleeping. Before going to sleep, the patient secures the sensors on his or her body. Through these sensors, information is recorded while the patient sleeps on his or her airflow, snoring, breathing effort, heart rate and oxygen levels. In the morning, the sensors are removed and all items and equipment are returned to the sleep clinic so that the data can be downloaded and analyzed.

In some cases, a follow-up overnight sleep study at the sleep clinic may still be necessary if the test results are unclear; there is insufficient data to make a diagnosis; or another sleep-related disorder is suspected. If the home sleep apnea test does not find obstructive sleep apnea even though symptoms of sleep apnea are apparent, a diagnostic polysomnography at the sleep clinic will be necessary to rule out other reasons for hypersomnia.


What other diagnostic tests are performed at the sleep clinic?

In addition to overnight studies, two other sleep studies are conducted in the daytime at the sleep clinic: Multiple Sleep Latency Test (MSLT) and Maintenance of Wakefulness Test (MWT).

Patients who experience excessive daytime sleepiness or who fall asleep at inappropriate times may be candidates for a MSLT or 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 resist sleep and stay awake for a designated period of time. During these studies, the sleep technologist monitors the patient’s sleep/wake patterns. The MSLT and MWT 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 testing, the patient is asked to relax and try to fall asleep. The test measures how quickly the person falls asleep during regular waking hours as well as the kind of sleep experienced during the naps.

The MWT also provides an objective measurement of the degree of daytime sleepiness. However, instead of measuring the patient’s ability to fall asleep, the MWT measures the patient’s ability to stay awake for defined period of time under sleep-inducing circumstances. The MWT may be done following overnight polysomnography, but it doesn't necessarily have to follow polysomnography. The MWT measures the person’s ability to resist sleep and stay awake when instructed to remain awake for 20 minutes.

The MWT is based on the idea that, in some cases, the patient’s ability to stay awake may be more important than his or her ability to fall asleep. The test is generally used to determine whether an individual’s inability to stay awake is a public or personal safety concern. It is also commonly used to document treatment of a sleep-related disorder for the Department of Motor Vehicles or for an employer.


What happens after the sleep study?

Once your sleep study is finished, a board-certified physician will interpret the results of your study usually within 48 hours. A detailed report of the sleep study is 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-related disorder is resolved.