Different Mechanisms of Airway Hyperresponsiveness between Exercise and Methacholine-Induced Bronchoconstriction in Chronic Asthma

Purpose: The aim of this study was to explore the different mechanisms of exercise-(EIB) and methacholine-(MIB) induced bronchoconstriction in patients with chronic asthma. Methods: We measured the FEV1, recovery time (RT), and AUC 0-60 min (area under the curve from 0 to 60 min after exercise in FEV1) in 41 asthmatics, who received exercise and methacholine challenge tests. Results: Among these asthmatics, 12 asthmatics had EIB and 29 had no EIB. The recovery time was prolonged (109.2 ±26.5 min, n= 11, p＜0.001) and AUC 0-60 min was larger (1201.0 ± 70.0 % ‧min, p＜0.0001) in the EIB group, compared to the non-EIB group (RT : 36.9±5.9 min; AUC : 328.0 ± 28.0 %·min, respectively, n=28). There was no difference in AUC and RT after methacholine-induced bronchoconstriction between the EIB and non-EIB groups (1136.0 ± 115.8 versus 1121.0 ± 122.7 %．min, p= 0.936; 111.5 ± 14.2 versus 106.0 ± 14.3 min, p=0.757 ). There was no significant correlation between the magnitude of AUC induced by exercise test or methacholine challenge (r= 0.24) Conclusion: We suggested that there were different mechanisms between EIB and MIB. The delayed bronchodilation in the EIB asthmatic subjects was probably related to presence of bronchoconstrictors.