Functional impairment in emphysema: contribution of airway abnormalities and distribution of parenchymal disease

Abstract

Objective: The aim of this study was to identify ancillary morphologic features on high-resolution CT that modify airflow obstruction and gas transfer levels in individuals with emphysema.

Materials and methods: The extent of emphysema on high-resolution CT was quantified by density masking in 101 patients. CT scans were evaluated for airway abnormalities (bronchial wall thickness, extent of bronchiectasis, bronchial dilatation, and evidence of small airways disease) and disease heterogeneity (uniformity, core-rind distribution, craniocaudal distribution, and lung texture). Stepwise regression analysis was used to determine CT features that influenced forced expiratory volume in 1 sec (FEV1) and the single-breath diffusing capacity for carbon monoxide (Dlco) for a given extent of emphysema.

Results: The extent of emphysema using automated estimation was 28.4% +/- 12.3% (mean +/- SD). On univariate analysis the extent of emphysema correlated strongly with FEV1 (R = -0.63, p < 0.0005) and Dlco (R = -0.63, p < 0.0005) levels. Stepwise regression analysis revealed that bronchial wall thickness and the extent of emphysema were the strongest independent determinants of FEV1 (model R2 = 0.49; p = 0.002 and < 0.001, respectively); the extent of bronchiectasis and degree of bronchial dilation did not separately influence FEV1 levels. The only morphologic features linked to Dlco levels on multivariate analysis were increasingly extensive emphysema and a higher proportion of emphysema in the core region (model R2 = 0.45; p < 0.001 and 0.002, respectively).

Conclusion: The important additional CT abnormalities in individuals with emphysema that influence FEV1 and Dlco levels irrespective of disease extent are bronchial wall thickness and core-rind heterogeneity, respectively. These observations have implications for the accurate functional assessment of patients considered for lung volume reduction surgery.