Sleep apnea is a condition in which breathing stops and starts during sleep. It is usually associated with snoring. Snoring is a sign that the upper airway calibre has narrowed to a critical degree. If the narrowing becomes too severe it promotes closure of the airway resulting in an apnea. An apnea is arbitrarily defined as a cessation of airflow that lasts at least ten seconds. A hypopnea is defined as a significant reduction in airflow lasting at least ten seconds and usually associated with a decline in a person's oxygen level.
Untreated, apnea can greatly affect daytime functioning. Rarely, the only daytime hint of the nocturnal turmoil may be a sense of having slept poorly. But far more often, the person is aware in many ways that all is not right. Awakening is often accompanied by a fierce headache, which lessens in an hour or two. But the person may remain irritable and forgetful, often finding it difficult to concentrate for the rest of the day. Interest in sex may wane, and the person may become depressed.
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.