There may be more trouble with snoring than the usual one of keeping one's spouse awake, a University of Illinois researcher cautions. As more research is done, it becomes apparent that heavy snoring often is associated with a cessation of breathing during sleep known as apnea, said Dr. Melvin Lopata, chief of the pulmonary section at the University of Illinois Medical Center. "We are finding apnea in more and more cases where people have no symptoms other than their heavy snoring." Patients with extreme apnea may stop breathing altogether when asleep, resuming oxygen intake only when they awake. Such people may fall asleep and awaken hundreds of times each night. When they get up in the morning they do not feel well rested. Such people may not realize that they have apnea and can be diagnosed only by spending the night sleeping in a laboratory where machines monitor their breathing, oxygen intake and other physical functions. "As more physicians and patients become aware of what apnea is, we find more cases of it," Lopata said. "Snoring occurs when there is a narrowing of the upper air passageway. Typically, apnea occurs when there is a complete blockage. It may be a matter of degree. "We don't know yet if a majority of heavy snorers have some degree of apnea, but it does seem to be at least a significant number of them. The real question is the long-range significance. Will the heavy snorer today go on to suffer pronounced apnea in the future? We wonder if the heart problems and personality changes associated with apnea will develop in these people."