Response patterns to bronchodilator and quantitative computed tomography in chronic obstructive pulmonary disease

Background: Patients with chronic obstructive pulmonary disease (COPD) show different spirometric response patterns to bronchodilator, such that some patients show improvement principally in expiratory flow (forced expiratory volume in 1s; FEV ₁), whereas others respond by improvement of lung volume (forced vital capacity; FVC). The mechanisms of these different response patterns to bronchodilator remain unclear. We investigated the associations between bronchodilator responsiveness and quantitative computed tomography (CT) indices in patients with COPD. Methods: Data on a total of 101 patients with stable COPD were retrospectively analysed. Volume and flow responses to bronchodilator were assessed by FVC and FEV ₁ changes before and after inhalation of salbutamol (400μg). Volumetric CT was performed to quantify emphysema, air trapping and large airway thickness. Emphysema was assessed by the volume fraction of the lung under -950Hounsfield units (HU; V ₉₅₀) at full inspiration and air trapping by the ratio of mean lung density (MLD) at full expiration and inspiration. Airway wall thickness and wall area percentage (WA%; defined as wall area/[wall area+lumen area]×100), were measured near the origin of right apical and left apico-posterior bronchus. Results: Among quantitative CT indices, the CT emphysema index (V _{950 insp}) showed a significant negative correlation with postbronchodilator FEV ₁ change (R=-0·213, P=0·004), and the CT air-trapping index correlated positively with postbronchodilator FVC change(R=0·286, P≤0·001). Multiple linear regression analysis showed that CT emphysema index had independent association with postbronchodilator FEV ₁ change and CT air-trapping index with postbronchodilator FVC change. Conclusion: The degrees of emphysema and air trapping may contribute to the different response patterns to bronchodilator in patients with COPD.