Effects of bronchodilators on dynamic hyperinflation following hyperventilation in patients with COPD

BACKGROUND AND OBJECTIVE: The present study was performed to examine the occurrence of dynamic hyperinflation following hyperventilation in COPD patients and former smokers without COPD, and the efficacy of short-acting anticholinergic agents (SAAC) and beta2-agonists (SABA) for lung hyperinflation following metronome-paced hyperventilation in COPD. METHODS: Fifty-nine patients with COPD, 20 ex-smokers without COPD and 20 healthy subjects who had never smoked were examined for dynamic hyperinflation by metronome-paced hyperventilation with respiratory rate increasing from 20 to 30 and 40 tidal breaths/min. Dynamic hyperinflation was evaluated as the decrease in inspiratory capacity (IC) following hyperventilation, and the effects of SAAC and SABA on dynamic hyperinflation were assessed. RESULTS: COPD patients showed a significant increase in end-expiratory lung volume and a decrease in IC following hyperventilation, and ex-smokers without COPD also showed mild but significant dynamic hyperinflation. Multiple stepwise linear regression analysis revealed that the carbon monoxide transfer coefficient (DLco/VA) and RV/TLC were significant and independent determinants of dynamic hyperinflation in COPD. Treatment with SAAC and SABA significantly increased IC at each respiratory rate, independently of the increases in FEV1. Furthermore, SABA significantly inhibited the decrease in IC due to hyperventilation. CONCLUSIONS: These findings suggest that lung hyperinflation following hyperventilation may be a useful method for detecting dynamic hyperinflation observed not only in patients with COPD but also in ex-smokers without COPD, and both SAAC and SABA are effective in reducing dynamic hyperinflation in COPD.