BACKGROUND: Although there are improvements of clinical symtoms after bronchodilator inhalation in COPD patients, it has been noted that there was no increase of FEV1 in some cases. FEV1 did not reflect precisely the improvement of ventilatory mechanics after bronchodilator inhalation in these COPD patients. The main pathophysiology of COPD is obstruction of airway in expiratory phase but in result, the load of respiratory system is increased in inspiratory phase. Therefore the improvement of clinical symptoms after bronchodilator inhalation may be due to the decrease of inspiratory load. So we performed the study which investigated the effect of bronchodilator on inspiratory response of vetilatory mechanics in COPD patients. METHODS: In 17 stable COPD patients, inspiratory and expiratory forced flow-volume curves were measured respectively before bronchodilator inhalation. l0mg of salbutamol solution was inhaled via jet nebulizer for 4 minutes. Forced expiratory and inspiratory flow-volume curves were measured again 15 minutes after bronchodilator inhalation. RESULTS: FEV1, FVC and FEV1/FVC% were 0.92 +/-0.34L(38.3+/- 14.9% predicted), 2.5+/-0.81L (71.1 +/-21.0% predicted) and 43.1+/-14.5% respectively before bronchodilator inhalation. The values of increase of FEV1, FVC and PIF(Peak Inspiratory Flow) were 0.15 +/-0.13L(relative increase: 17.0%), 0.58+/-0.38 L(29.0%) and 1.0+/-0.56L/sec(37.5%) respectively after bronchodilator inhalation. The increase of PIF was twice more than FEV1 in average(p<0.001). The increase of PIF in these patients whose FEV1 was not increased after bronchodilator inhalation were 35.0%, 44.0% and 55.5% respectively. CONCLUSION: The inspiratory parameter reflected improvement of ventilatory mechanics by inhaled bronchodilater better than expiratory parameters in COPD patients.