Types of Adult Sleep Apnea

by Food and Drug Administration (FDA)

(Page 3 of 3)

In all cases of sleep apnea some part of the respiratory system narrows, impairing oxygen intake. Lowered blood oxygen levels then trigger the brain to prompt the intake of breath. The sleeper gasps, jump-starting the breathing process — until the next halt. But doctors distinguish three variations on this theme:

Obstructive Sleep Apnea: The typical person suffering from this most common and severe form of apnea is an overweight male between 35 and 50 who usually has a small jaw, a small opening to the airway at the back of the throat, and a large tongue or tonsils. During sleep, the muscles of the soft palate and at the base of the tongue and the uvula (the "punching bag" structure hanging in the throat) relax and sag, blocking the airway, which collapses. As breathing stops, the diaphragm and chest muscles strain until the block is literally uncorked, and a noisy gasp — the snore — is taken. When breathing stops, blood oxygen levels fall, forcing the heart to work harder. As a result, blood pressure rises, and the heartbeat may even become irregular. Obstructive sleep apnea is made worse by drinking alcohol or taking tranquilizers, antihistamines, or sleeping pills.

Central Sleep Apnea: In this rarer form of the disorder, the airway remains open, but the diaphragm and chest muscles temporarily fail. The dropping blood oxygen levels signal the brain, which prompts the person to awaken and gasp in a breath. Because the airway is typically open, this apnea sufferer does not snore loudly but does have daytime sleepiness. Central sleep apnea is more common among people over 60, and is often seen in nursing homes and among the ill.

Mixed Apnea: Some people experience long periods of obstructive sleep apnea interspersed with brief periods of central sleep apnea.

Sleep Lab — First Step to Treatment

Sleep apnea is often treatable. Many sufferers don't know this, however, because only 10 to 25 percent of cases are ever diagnosed. This is either because the person is unaware of the snoring or does not know that loud snoring is a symptom of apnea.

Can sleep apnea really be dangerous, if you can have it and not even know it?

"I believe to some extent we have oversold [sleep apnea's] life-threatening nature. I see people in here who have had sleep apnea for 20 years. Are they dying? Only indirectly, because sleep apnea contributes to hypertension, accidents, sleepiness, and psychological problems," says John Shepard, M.D., director of the Sleep Disorders Clinic of the Mayo Clinic in Rochester, Minn.

A definitive diagnosis of sleep apnea requires a visit to one of the country's 142 sleep laboratories. Here, a variety of tests are conducted while the patient sleeps, and physiological measurements are correlated to body movements. The entire procedure is called polysomnography.

The patient arrives at the sleep lab about an hour before bedtime. If he or she normally drinks alcoholic beverages, the usual amount is consumed at the usual time, so that observations match the patient's customary experience. A technician then places dime-sized sensors on different parts of the person's body. These measure heart rate, brain wave patterns, muscle activity, leg and arm movements, and eye movements, which indicate the stage of sleep.

An elastic band holding gauges is strapped around the chest and abdomen to track movements of the muscles involved in breathing. A light mask covering the mouth and nose measures the respiratory rate, which monitors the frequency of apneic episodes. Finally, a test called oximetry measures dips in arterial oxygen saturation, the hallmark of sleep apnea.

"In oximetry, a probe is clipped onto the finger or the ear. There is a light source. The light goes through the lobe or finger, and the refraction of the light is proportional to the [amount of] oxygen in the arterioles of the blood," says Martin Scharf, Ph.D., director of the Center for Research in Sleep Disorders in Cincinnati.

The automated scanners of the sleep lab produce a readout of each measurement, and these can be displayed next to one another so that one symptom or sign is easily correlated with another. For example, cessation of breathing usually coincides with a dip in oxygen saturation, and both tend to occur when the patient is sleeping on his or her back.

A night in a sleep lab is often followed by a daytime multiple sleep latency test, which monitors a series of two-hour naps. This test distinguishes between sleep apnea and narcolepsy, in which a person falls asleep very suddenly during the day. Scharf uses the nap test to quantify a patient's report of sleepiness, and to back up polysomnography. "I see people who drive a lot, and have a history of falling asleep, like truck drivers. I won't say 'you're cured' until I repeat the multiple sleep latency test and show they're not sleepy," he says.

Some sleep labs also study the architecture of the nose and throat, using x-rays and fiber-optic endoscopes (lights on flexible wires snaked into narrow body cavities) to picture upper airway structures.

Video cameras are beginning to be used to do the work of technicians, allowing polysomnography to move from a specialized lab setting to a typical hospital ward and even to a physician's office. Physiological data are superimposed on the video of the sleeping patient.

About the Author

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