Background: The assessment of bronchodilator-induced change in forced vital capacity (FVC) is dependent on forced expiratory time (FET) in subjects with airflow limitation. Limited information is available on the concurrent responses of FVC, forced expiratory volume in six seconds (FEV6), and FET in the bronchodilation test among patients with obstructive airways disease or in the general population. The aim of this study was to assess the changes in FEV6, FVC, and FET, and their relationships in a standardized bronchodilation test in the general population.
Methods: We studied bronchodilation response in a general adult population sample of 628 individuals (260 men, 368 women) with flow-volume spirometry. The largest FVC, the corresponding FET and the largest FEV6 both at the baseline and after 0.4 mg of inhaled salbutamol were selected for analysis.
Results: After administration of salbutamol FEV6 decreased on average -13.4 (95% CI -22.3 to -4.5) ml or -0.2% (-0.4% to 0.0%) from the baseline. The 95th percentile of change in FEV6 was 169.1 ml and 5.0%. FVC decreased on average -42.8 (-52.4 to -33.3) ml or -1.0% (-1.2% to -0.7%). Concurrently FET changed on average -0.2 (-0.4 to 0.0) seconds or 0.4% (-1.4% to 2.3%). There were four subjects with an increase of FVC over 12% and only one of these was associated with prolonged FET after salbutamol. Changes in FEV6 and FVC were more frequently positive in subjects with reduced FEV1/FVC in baseline spirometry.
Conclusion: In general adult population, both FEV6 and FVC tended to decrease, but FET remained almost unchanged, in the bronchodilation test. However, those subjects with signs of airflow limitation at the baseline showed frequently some increase of FEV6 and FVC in the bronchodilation test without change in FET. We suggest that FEV6 could be used in assessment of bronchodilation response in lieu of FVC removing the need for regulation of FET during bronchodilation testing.