The study was a subproject in a Specialized Center of Research in the Cardiopulmonary Disorders of Sleep. Frequent sleep-related respiratory disturbances (SRRD) have been recognized to occur in as many as 70 percent of elderly and 15 percent of middle-aged subjects. Although it is widely agreed that subjects with obvious daytime sleepiness that occurs in association with severe obstructive sleep apnea (Respiratory disturbance indices (RDI) >30) benefit from treatment of their sleep disorders; there is no consensus (and a paucity of data) regarding treatment benefits in subjects with a less profound disorder. Rational utilization of health care resources for diagnosis and treatment of sleep apnea requires assessment of whether adverse health effects occur as a consequence of mild or moderate levels of SRRD, and whether any such health effects may be reversible with treatment.