Spirometry was performed using a portable computerized pulmonary function system (FERRARIS KOKO, Louisville, CO, USA), according to the American Thoracic Society . FVC and FEV1 were measured in litres (L), and the FEV1/FVC calculated. Measurements were obtained before and 20 minutes after being given a metered 400 μg dose of fenoterol as a bronchodilator. The FVC and FEV1 values were also expressed as a percentage of reference values .