Epidemiology of Obstructive Sleep Apnea

Sleep-disturbed breathing, which includes apneas, hypopneas, and oxygen desaturations, occurs in asymptomatic individuals and increases with age. Obstructive apnea is the most frequent type of respiratory disturbance documented by polysomonography, the gold standard test for assessing sleep-disturbed breathing. Many of the prevalence studies done to date have had one or more methodological weaknesses, including selection biases, varying definitions of obstructive sleep apnea, failure to distinguish types of apneas, failure to control for confounding variables, and small sample size. Although there is consensus on the definitions of sleep-disturbed breathing, the appropriate number of apneas and hypopneas for diagnosing clinically significant obstructive sleep apnea is uncertain. While the cutoff of five or more apneas and hypopneas per hour is historically considered abnormal, the origins of this number are vague, and the longevity of those who have this value on polysomnography is not necessarily reduced. This is particularly true among those without symptoms of obstructive sleep apnea syndrome, which include excessive daytime sleepiness, snoring, nocturnal awakenings, and morning headaches. Investigators should be careful to distinguish symptomatic study subjects from asymptomatic subjects, and to exclude central apneas in calculating their estimates. In addition, various studies have used different definitions of sleep apnea syndrome, making comparisons of point estimates difficult. It would be more appropriate for researchers to estimate morbidity and mortality indices with confidence intervals, using several different cutoff points. Subject selection in all studies should follow a two-stage sampling procedure. All subjects with symptoms compatible with obstructive sleep apnea syndrome and a subsample of asymptomatic individuals should be studied with all-night polysomnography. If portable monitoring is used, the validity and reproducibility of this diagnostic method should be assessed. Subjects with significant comorbidity should be excluded from prevalence studies. Factors that clearly increase the risk of sleep-disturbed breathing and obstructive sleep apnea and its related symptoms include age, structural abnormalities of the upper airway, sedatives and alcohol, and probably family history. Although endocrine changes such as growth hormone, thyroid hormone, and progesterone deficiency also have been suggested as risk factors for exacerbating obstructive sleep apnea syndrome, there is minimal epidemiologic evidence to support this. Case-control studies are recommended to assess the relation of endocrine factors to obstructive sleep apnea syndrome in a rigorous fashion. A limited number of mortality studies have suggested decreased survival in persons with the obstructive sleep apnea syndrome, possibly primarily due to vascular-related disease.(ABSTRACT TRUNCATED AT 400 WORDS)