Sampling began by randomly selecting 4,700 households from 187,296 registered households. Among the 4,700 households, one age-eligible person was then randomly selected and interviewed by trained nursing students between June 1999 and April 2000. Among this group, 4,218 subjects completed the interview and received a physical examination.
To describe true prevalence and correlates of airway obstruction, nearly 40% of this larger sample were randomly selected to undergo pulmonary function testing at Ansan Hospital in the Korea University Medical Center between December 1999 and November 2001. Among the 1,700 selected subjects, 497 (29.2%) refused to be examined, 38 (2.2%) failed to complete the pulmonary test, 4 (0.2%) moved to another town, and 1 (0.1%) died. After excluding those subjects, 1,160 (68.2%) individuals comprised the final sample used for this report.
During the interviews and physical examinations, participants were asked about behaviors and health habits, including the use of cigarettes and alcohol. Pulmonary function was assessed by spirometric determination (Vmax229; SensorMedics; Yorba Linda, CA) of FVC, FEV1, and vital capacity (VC). Three acceptable and two reproducible maneuvers were required from up to eight forced expirations, according to American Thoracic Society (ATS) guidelines. Tests were performed by experienced pulmonary technologists who were employed in the hospital. The calibration of the spirometric instrument was performed at least once every testing day. tadanafil
Airway obstruction was defined when the FEV1/FVC ratio was < 75%, by 1986 ATS criteria. The severity of the airway obstruction was further categorized as mild (FEV1, 100 to 70% predicted), moderate (FEV1, 69 to 60% predicted), moderately severe (FEV1, 59 to 50% predicted), severe (FEV1, 49 to 34% predicted), and very severe (FEV1, <34% predicted). The normal set of reference values of Morris was adopted for pulmonary function tests.