Spirometry reference values after inhalation of 200 μg of Salbutamol

OBJECTIVE: The criteria for disease severity established by the Global Initiative for Chronic Obstructive Lung Disease are based on forced expiratory volume in I second (FEV) expressed as a percentage of the predicted value after application of a bronchodilator. This study aims to determine postbronchodilator spirometry reference values. SUBJECTS AND METHODS: A cluster sample of subjects aged 40 years or over was chosen to be representative of the metropolitan areas of 5 Latin American cities (Sao Paulo, Mexico City, Montevideo, Santiago, and Caracas). Spirometry was performed on 5183 subjects following the recommendations of the American Thoracic Society before and after inhalation of 200 mu g of salbutamol. Multiple linear regression equations were fitted for the postbronchodilator spirometric values-FEV1, forced expiratory volume in 6 seconds (FEV6), peak expiratory flow rate, forced vital capacity (FVC), FEV1/FEV6, FEV1/FVC and forced expiratory flow between 25% and 75% of vital capacity (FEF25-75). These were adjusted for sex, age, and height in 887 asymptomatic subjects with no history of lung disease. RESULTS: The postbronchodilator reference values for FEV, FEV1/FVC, and FEV1/FEV6 were on average 3% higher than those obtained before bronchodilation. This apparently small difference caused an upward shift in the 5th percentile (lower limit of normal) of the predicted values. When prebronchodilation instead of postbronchodilation reference values were used, 3.2% of the results for airflow obstruction in our population of over-40-year-olds were false negatives. CONCLUSIONS: The reported reference values are more appropriate for postbronchodilator spirometry and make it possible to reduce the number of misclassifications.