Sleep Studies

After reviewing data from the clinical evaluation, the sleep specialist may recommend further diagnostic testing in the form of a sleep study, or polysomnography. A sleep study is a noninvasive, painless test in which sleep patterns and behaviors associated with sleep are observed and recorded.


Diagnostic Polysomnography

Polysomnography is considered the “gold standard” in diagnostic testing for most sleep disorders. The technology involves recording various physiological variables simultaneously during sleep through the use of a polygraph.

Sleep is divided into several stages beginning with non-rapid eye movement (NREM) sleep. During this stage, brain waves slow down and the eyes move back and forth more slowly than in later stages of sleep. After an hour or two of NREM sleep, brain activity picks up and rapid eye movement (REM) sleep begins. Most dreaming occurs during REM sleep.

Most people normally go through four to six sleep cycles during the night, cycling between NREM and REM sleep approximately every 90 minutes. The REM stage usually lengthens with each cycle as the night progresses. Sleep disorders can disturb this process.

During polysomnography, data on various physiological functions are gathered from various leads, which are electrodes and sensors applied to the patient's body with paste or tape. The information collected from these leads is then plotted as a series of waveform tracings on a computer which is located in a separate room where sleep technologists observe the patient as he or she sleeps. A typical polysomnogram records multiple physiological parameters simultaneously.

The physiological functions monitored during polysomnography generally include brain wave activity, oxygen level in the blood, heart rate, breathing, eye movements and leg movements. The electrodes placed on the scalp, face, chin, chest, and legs monitor brain waves, heart activity and body movements during sleep. An elastic belt is placed around the abdomen to record respirations. Two thin wires are placed near the nose and mouth to record air flow during breathing. The oxygen content of the blood is measured non-invasively with a simple clip on the index finger. Audiovisual recordings are also made.

Once the test results are recorded on the computer, they are printed out for scoring and forwarded to a board-certified physician for review and interpretation. During the follow-up appointment, the sleep specialist reviews the results of the sleep study with the patient, discusses the diagnosis and presents various treatment options.

Titration Polysomnography

If obstructive sleep apnea is diagnosed and either positive airway pressure (PAP) therapy or oral appliance therapy prescribed, a second polysomnography called a titration polysomnography is scheduled and performed to determine the optimal settings at which to set the PAP device or oral appliance to alleviate the sleep apnea.

At the beginning of the titration study, electrodes and sensors are applied to the body as they were for the diagnostic polysomnography and the same physiological functions are observed and recorded. Additionally, though, the patient also wears either a PAP device or uses an oral appliance during the sleep study.

Throughout the titration polysomnography, the sleep technologist monitors the patient for signs of sleep apnea and adjusts the settings on the PAP device or oral appliance accordingly to alleviate the apneic episodes. Through a process of trial and error, the sleep technologist eventually is able to determine the optimal settings at which to set the PAP device or oral appliance so that the patient's airway remains open throughout sleep.

Split Night Study

In some cases, both diagnosis and treatment of a sleep-related breathing disorder can be accomplished in a single night's study, rather than in two separate studies. The sleep technologist observes obvious signs of sleep apnea during the first few hours of the sleep study, ends the diagnostic study, and converts the study into a PAP titration study. Thus, in a split-night study, both diagnostic and titration polysomnography are done in the same night.


Multiple Sleep Latency Test

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, which is performed during daytime hours, is used to diagnose narcolepsy or idiopathic hypersomnolence. The test begins two hours after awakening from the overnight 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.

Maintenance of Wakefulness Test

Similar to the multiple sleep latency test (MSLT), the maintenance of wakefulness test (MWT) 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" opportunities.

The patient is placed in a quiet room with dim lighting and asked to stay awake. The test is generally used to diagnose narcolepsy as well as to determine whether an individual’s inability to stay awake is a public or personal safety concern.

Contact Us

Sleep Centers of Texas
7839 Interstate 10 West
San Antonio,TX 78230-4779

Phone: 210.520.8333
Fax: 210.520.8335


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