Pulmonary Function Test

Spirometry (Vmax 22; Sensor-Medics, Yorba Linda, CA, USA) was conducted by trained technicians, following guidelines outlined by the American Thoracic Society/European Respiratory Society for standardizing pulmonary function tests at the time of cohort enrollment.¹³ Spirometry test produced forced expiratory volume in 1 second (FEV₁; maximum volume exhaled during the first second of expiration as a measurement of large airway obstruction), forced expiratory flow 25% to 75% (FEF 25–75%; mean forced expiratory flow in the middle half of forced vital capacity as a measurement of middle to small airway obstruction), peak expiratory flow (PEF; maximum flow obtained as a measurement of large airway function), and forced vital capacity (FVC; the volume of air forcefully exhaled after maximal inhalation). An “acceptable spirometry curve” was defined as that which shows the start of the test and expiration ≥6 seconds, shows greatest differences between the 2 measurements of FEV₁ and FVC <150 mL. A test that produced two acceptable spirometry curves was considered valid and included for analysis. Subjects were categorized as having “obstructive” pulmonary function if the ratio of FEV₁ to FVC (FEV₁/FVC) was below 70% according to the Global Initiative for Chronic Obstructive Lung Disease (GOLD) criteria.¹⁴ The severity of airflow limitation was determined according to the same criteria, using FEV₁. GOLD criteria state that in individuals with FEV1/FVC below 70%, decreasing FEV₁ indicates more severe obstruction (GOLD1 FEV₁ 80 or above, GOLD2 50–79, GOLD3 30–49, and GOLD4 FEV₁ below 30). Subjects were considered to have normal pulmonary function if FEV₁/FVC ≥70% and FVC ≥80% predicted. Patients identified to have COPD following the spirometry test were directed to consult with pulmonologists for prescriptions of appropriate inhalers.