Pulmonary function

At both sites, we measured spirometry using standardized equipment (Vitalograph® Pneumotrac, Model 6800, Ennis, Ireland), which met equipment and procedure requirements of the American Thoracic Society/European Respiratory Society (ATS/ERS) spirometry standards [9]. A certified respiratory physiologist performed pre-bronchodilator spirometry on all participants and a post-bronchodilator spirometry on all those meeting criteria for obstruction by the American Thoracic guidelines. The spirometers had been factory calibrated before use in our study, and the technicians checked daily calibration with a 3-L syringe. We were interested in the lung function (forced expiratory volume in 1 s (FEV₁)) and the forced vital capacity (FVC). We included two acceptable trials if the best values were within 200 mL of one another and participants who had a ratio of FEV₁ to FVC less than 0.7 were subjected to a post-bronchodilator test using four puffs (360 μg) of Albuterol (Ventolin, GSK, Philadelphia PA). Spirometry was then repeated after 10 min. COPD was defined as a ratio of FEV₁ to FVC < 0.7 [10].