Epidemiology of Sleep Apnea Syndrome

BACKGROUND: The Sleep Apnea Syndrome consists of sleep-induced disturbances of breathing and breathing-induced disturbances of sleep. Symptoms of pathologic sleepiness and, less commonly, frequent awakenings and light sleep reflect the fragmentation of sleep by repeated respiration-related arousals. Snoring, intermittent choking, and nocturnal dyspnea reflect varying degrees of upper airway obstruction associated with Sleep Apnea Syndrome. Observations of breathing during sleep show varying combinations and degrees of periodic breathing, apneas, and hypoxemia. In more severe cases, cardiovascular complications, including systemic and pulmonary hypertension and cardiac arrhythmias, occur. The clinical spectrum thus varies from the asymptomatic patient, to one with chronic cardiac and respiratory failure who is at risk of sudden death. Most patients are disabled by varying degrees of pathologic sleepiness. The rapid increase of clinical activity with the Sleep Apnea Syndrome created an urgent need for a more complete description of this condition. Clinical descriptions were derived from case series of severely afflicted patients. Limited epidemiologic data, however, indicated that symptoms and objective manifestations of Sleep Apnea Syndrome occurred commonly in the population. It was unknown whether subjects with these findings were unrecognized patients, premorbid individuals at risk, or normal subjects with no special impairments. There was a need to define the frequency of signs and symptoms of Sleep Apnea Syndrome in the general population, and to determine the health effects related to these findings. DESIGN NARRATIVE: Subjects were recruited from a previous survey, the Belen Health Study, conducted from July 1984 through November 1985. Based on the data of the earlier survey, 421 subjects were identified for recruitment and 275 actually participated. The Belen Health Study questionnaire included items directed at Sleep Apnea Syndrome. Subjects for the sleep study were selected based on responses to the initial questionnaire. For the sleep study, an additional questionnaire was used, as well as new techniques of home monitoring of breathing during sleep, and polysomnography to define the prevalence of symptoms and manifestations of Sleep Apnea Syndrome. An assessment of the health effect of Sleep Apnea Syndrome was made by reference to the demographic, socio-economic, and health data from the Belen Health Study. Diagnostic criteria and the utility of home monitors for clinical diagnosis were also determined.