Sleep Apnea (cont.)
Siamak T. Nabili, MD, MPH
Siamak T. Nabili, MD, MPH
Dr. Nabili received his undergraduate degree from the University of California, San Diego (UCSD), majoring in chemistry and biochemistry. He then completed his graduate degree at the University of California, Los Angeles (UCLA). His graduate training included a specialized fellowship in public health where his research focused on environmental health and health-care delivery and management.
In this Article
How is obstructive sleep apnea diagnosed and evaluated?
History and physical examination
Obstructive sleep apnea can be diagnosed and evaluated by subjective (perceived or biased) and objective (factual, based on empirical data) methods. An example of a subjective method that measures the effects of obstructive sleep apnea on patients is the Epworth Sleepiness Scale.
The Epworth Sleepiness Scale is a self-report test that establishes the severity of sleepiness. A person rates the likelihood of falling asleep during specific activities. Using the scale from 0 to 3 below, the risk of dozing can be ranked from the chart below.
0 = Unlikely to fall asleep
After ranking each category, the total score is calculated. The range is 0 to 24, with higher scores suggesting greater sleepiness.
Breaking it down further, excessive daytime sleepiness is greater than 10. Primary snorers usually have a score less than 10, and individuals with moderate to severe sleep apnea usually have a score greater than 16. Self-reported, subjective measures such as the Epworth Sleepiness Scale usually are combined with a thorough medical history. The history includes questions about:
Next a physical examination is performed to examine the areas of possible airway collapse.
The primary objective test for obstructive sleep apnea is polysomnography, also referred to as a sleep study. This test measures different physical and physiological parameters while a subject is asleep. During attended polysomnography, a technician observes a person sleeping and monitors recording equipment in the setting of a sleep laboratory. A typical polysomnography test includes:
The EEG (electroencephalogram) monitors brain waves and can be used to determine the level of sleep or wakefulness. It is helpful for determining if an event (respiratory or limb movement) disrupts the level of sleep.
An EOG (electro-oculogram) measures eye movements using sticker electrodes placed next to each eye. During REM sleep (dreaming sleep), the eyes typically move from side-to-side. This measurement can help determine the duration of REM sleep.
An EMG (electromyogram) measures muscle movements. Frequently, an additional monitor is placed on the chin to measure muscle relaxation (tone). During stage 1-4 sleep there is a baseline muscle tone; however, during REM sleep all muscles relax. The EMG also helps to determine the duration of REM sleep. An EMG of the legs can be used to detect "restless legs syndrome" or periodic leg movements during sleep.
Oral and nasal airflow can be measured by several different methods to help determine the size and frequency of breaths during sleep. Chest and abdominal movements occur with each attempt to breathe and can be used to distinguish between central sleep apnea and obstructive sleep apnea. (During central sleep apnea, the signal to take a breath is not given, so the muscles do not attempt to take a breath. During obstructive sleep apnea, the muscles attempt to take a breath, but no air moves.)
Measurement of the loudness of snoring can be used to quantify snoring. (Sometimes a measurement is needed to convince someone that they have a snoring problem.) It can also be used to measure changes after treatments for snoring.
Oximetry is used to measure the decreases in oxygen in the blood during apneas and hypopneas.
The video monitor is most helpful for detecting movement disorders, parasomnias, or seizures during sleep. (Often a patient will not remember sleepwalking, sleep talking, or other parasomnias, so a video is helpful to review the events with the patient.)
After polysomnography is completed the data are analyzed by a board certified sleep specialist. The number of apneas, hypopneas, leg movements, and desaturations as well as sleep levels are all recorded in a formal report, and a diagnosis is made.
Although the primary objective test for obstructive sleep apnea is the sleep study (polysomnography); other tests for obstructive sleep apnea include the:
Multiple Sleep Latency Test
For someone who reports being sleepy during the day, it is sometimes helpful to measure how sleepy they are. Also, after treatment of sleep problems the doctor may want to measure improvement in daytime sleepiness. Sleepiness can be measured with a Multiple Sleep Latency Test (MSLT).
Basically, the MSLT measures how fast someone falls asleep during the day. It must be done after an overnight sleep study (polysomnography), which documents adequate opportunity for sleep the night before. The test is composed of four to five naps that last 20 minutes and are spaced2 hours apart. The person is instructed to try and fall asleep. The average time to fall asleep is calculated for all four or five tests. Normal time would be greater than 10 minutes to fall asleep. Excessive sleepiness is less than 5 minutes to fall asleep.
Maintenance of Wakefulness Test
The Maintenance of Wakefulness Test (MWT) also measures daytime sleepiness. The person in this test is instructed to try to stay awake. This is repeated for four 40-minute sessions 2 hours apart. Not falling asleep in all four tests is the strongest objective measure of no daytime sleepiness.
Some agencies use these tests to ensure that their employees are not excessively sleepy while at work. Specifically, airline pilots and truck drivers who have sleepiness need to be tested. This is done for public safety and work productivity. Unfortunately, there is no test that will guarantee that someone will not fall asleep at his or her job or while driving.
Severity levels in obstructive sleep apnea
Obstructive sleep apnea can be categorized as mild, moderate, or severe. This stratification assists in determining the direction of treatment. For example, some treatments that are excellent for mild sleep apnea nearly always will fail for severe sleep apnea.
The severity level is measured with polysomnography. In one grading scale using the apnea-hypopnea index, mild obstructive sleep apnea is 5 to 15 events per hour, moderate obstructive sleep apnea is 15 to 30 events per hour, and severe obstructive sleep apnea is more than 30 events per hour.
Reviewed by Jay W. Marks, MD on 9/25/2012
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