Quantitative emphysema assessment of pulmonary function impairment by computed tomography in chronic obstructive pulmonary disease.
Objective: The objective of this study was to determine the capability of quantitative emphysema by computed tomography (CT) to assess pulmonary function impairment in a population of current smokers with and without airflow limitation.
Methods: Seventy-six subjects (30 normal smokers; 8 with mild obstruction; 17 with moderate obstruction; 13 with severe obstruction; 8 with very severe obstruction) underwent CT examinations and pulmonary function tests. For the quantitative assessment, percentages of low attenuation volume (%LAVs) of whole lung, right lung, left lung, and each lobe were obtained. Computed tomography measurements were related to lung function (forced expiratory volume in 1 second [FEV1], ratio of FEV1 to forced vital capacity, diffusing capacity for carbon monoxide [DLCO], ratio of residual volume to total lung capacity [RV/TLC]) by multivariate linear regression analysis.
Results: Quantitative CT measurements of emphysema were moderately, negatively correlated to airflow limitation (FEV1 and ratio of FEV1 to forced vital capacity) (r = -0.68 to -0.52, P < 0.001). Except for right middle and lower lobes, all the quantitative CT measurements showed moderate, negative correlations with diffusing capacity (DLCO) (r = -0.63 to -0.54, P ≤ 0.001) and weak to moderate correlations with RV (RV/TLC) (r = 0.36-0.41, P < 0.01). As compared with control samples, the %LAV of whole lung, right lung, left lung, and each lobe was increased in patients with GOLD stages 2, 3, and 4 disease (P < 0.05), and the % LAV of whole lung, right lung and right upper lobe was increased in patients with GOLD stage 1 (P < 0.05).
Conclusions: Pulmonary function results, particularly DLCO and RV/TLC, were primarily affected by the % LAV of the upper lobes. Quantitative CT measurements of emphysema provides a morphological method to investigate lung function impairment in patients with chronic obstructive pulmonary disease.