Airflow obstruction in bronchiectasis: correlation between computed tomography features and pulmonary function tests

Background-An obstructive defect is usual in bronchiectasis, but the pathop hysiological basis of airflow obstruction remains uncertain. High resolutio n computed tomographic (CT) scanning now allows quantitation of static morp hological abnormalities, as well as dynamic changes shown on expiratory CT scans. The aim of this study was to determine which static and dynamic stru ctural abnormalities on the CT scan are associated with airflow obstruction in bronchiectasis. Methods-The inspiratory and expiratory features on the CT scan of 100 patie nts with bronchiectasis undergoing concurrent lung function tests were scor ed semiquantitatively by three observers. Results-On univariate analysis the extent and severity of bronchiectasis, t he severity of bronchial wall thickening, and the extent of decreased atten uation on the expiratory CT scan correlated strongly with the severity of a irflow obstruction; the closest relationship was seen between decreased for ced expiratory volume in one second (FEV,) and the extent of decreased atte nuation on the expiratory CT scan (R-s = -0.55, p<0.00005). On multivariate analysis bronchial wall thickness and decreased attenuation were consisten tly the strongest independent determinants of airflow obstruction. The exte nt of decreased attenuation was positively associated with the severity of bronchial wall thickness, but was not independently Linked to gas transfer levels. Endobronchial secretions seen on CT scanning had no functional sign ificance; the severity of bronchial dilatation was negatively associated wi th airflow obstruction after adjustment for other morphological features. Conclusions-These findings indicate that airflow obstruction in bronchiecta sis is primarily Linked to evidence of intrinsic disease of small and mediu m airways on CT scanning and not to bronchiectatic abnormalities in large a irways, emphysema, or retained endobronchial secretions.