Quantitative emphysema assessment of pulmonary function impairment by computed tomography in chronic obstructive pulmonary disease

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.

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.

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).

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.