After an initial consultation with your sleep specialist, you may be referred for a sleep study. A sleep study, or polysomnogram, is a noninvasive, painless test in which sleep patterns and behaviors associated with sleep are recorded.
Polysomnography is considered the “gold standard” test for diagnosing most sleep disorders. The technique or process involves using a polygraph to make a continuous record of various physiological variables during sleep.
During polysomnography, sleep stages and cycles are monitored to identify if or when the sleep patterns are disrupted. The normal process of falling asleep begins with a sleep stage called non-rapid eye movement (NREM) sleep. During this stage, your brain waves slow down considerably and your eyes don't move back and forth rapidly in contrast to later stages of sleep. After an hour or two of NREM sleep, brain activity picks up again 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 in about 90 minutes. The REM stage usually lengthens with each cycle as the night progresses. Sleep disorders can disturb this sleep process.
Data on multiple physiological functions, such as brain wave activity, oxygen level in the blood, heart rate and breathing, and eye and leg movements, are collected through a variety of electrodes and sensors applied to the body surface with paste or tape. Electrodes are placed on the scalp, face, chin, chest, and legs to 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.
Data gathered from the various leads are plotted as a series of waveform tracings. A typical polysomnogram records numerous physiological parameters simultaneously. The results are recorded on a computer, printed out for scoring, and presented to a board-certified physician for interpretation. At a follow-up appointment, the sleep specialist will review the results of the sleep study and, based on the data gathered, discuss any treatment or further evaluation needed.
If the results of the diagnostic polysomnography indicate that the patient has obstructive sleep apnea, then a continuous positive airway pressure (CPAP) device or oral appliance may be prescribed. The purpose of the titration polysomnography is to determine, by trial and error, the optimal settings for the CPAP device, or the oral appliance, to alleviate the sleep apnea or snoring.
At the beginning of the titration study, electrodes and sensors are applied to the body as they were for the diagnostic polysomnography so that the same physiological functions can be recorded.
If CPAP therapy is prescribed, the sleep technologist fits the patient with a CPAP device prior to the sleep study. The CPAP device is designed to gently deliver air into the patient’s airway through a specially designed mask which fits over the nose or mouth, thereby creating enough pressure to keep the airway open during sleep. Throughout the titration study, the sleep technician adjusts the pressure settings to find the optimal setting at which sleep apnea is eliminated.
If an oral appliance is prescribed, the patient arrives at the sleep center with the oral appliance that has been custom fabricated and fitted by his or her dentist. The oral appliance is designed to incrementally advance the mandible until a protrusive position is reached with maximal therapeutic effect. Prior to the sleep study, the sleep technologist verifies that the oral appliance is properly inserted. In a process analogous to CPAP titration, the oral appliance is adjusted manually by trial and error throughout the night to determine the optimal degree of mandibular advancement at which sleep apnea is resolved.
Split Night Study
In some cases, both diagnosis and treatment of a sleep-related breathing problem can be accomplished in a single night's study, rather than two separate studies. The sleep technologist observes obvious signs of sleep apnea during the first few hours of the initial sleep study, ends the diagnostic study, and converts the study into a CPAP titration study. Thus, in a split-night study, both the diagnostic polysomnography 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 is conducted in a similar method as a polysomnogram, but performed during daytime hours. It is used to diagnose narcolepsy or idiopathic hypersomnolence. The test begins two hours after awakening from the overnight polysomnography and consists of four to five attempts at napping scheduled 2 hours apart. During these naps a 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
Like 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.