Airway wall response to deep inspiration in COPD

Background: Protective effects of deep inspiration (DI) fail in chronic obstructive pulmonary disease (COPD). It is unknown if this reflects abnormal properties of the airway wall. Aim: To determine if the response of the airway wall to stretch is abnormal in COPD. Methods: Subjects undergoing lung surgery (65±3y) had lung function assessed before surgery and a bronchial segment was dissected from resected lung tissue for in vitro study. Subjects with COPD had a post-bronchodilator FEV1/FVC ratio and FEV1 below lower limit of normal. Response to DI was assessed from maximal and partial (M/P) flow ratio. In bronchial segments, bronchodilation to simulated DI was measured from the change in airway volume after a transient stretch. Wall dimensions were measured on fixed airways. Results: The M/P ratio positively correlated with FEV1/FVC (%predicted, p=0.002, r=0.72) and was reduced from 0.87±0.14 (mean±SE) in the control group (n=9) to 0.50±0.08 in the COPD group (n=7, P=0.047). An M/P ratio of <1 indicated that the dominant effect of DI was bronchoconstriction, and the lower ratio in the COPD group reflected greater constriction. Bronchodilation (%volume) to DI in vitro positively correlated with M/P ratio in vivo (p=0.03, r=0.53). However the magnitude of bronchodilation to DI was not different between groups (p=0.42). Airway wall thickness was not related to M/P ratio (p=0.61) or bronchodilation (p=0.96) and was not different between groups (p=0.81). Conclusion: A DI produces bronchoconstriction in subjects not undergoing bronchial challenge, which is greater in subjects with COPD. While the intrinsic response of the airway wall to stretch contributes to the respiratory effect of DI, it is not different in subjects with COPD.