RATIONALE:
To evaluate the relative contributions of quantitative CT (QCT) measures of emphysema, air trapping, and airway wall thickening and narrowing, to airflow obstruction in cigarette smokers with and without chronic obstructive lung disease (COPD).
METHOD:
2000 cigarette smokers participating in the COPDGene study were evaluated, 818 subjects were excluded because of missing QCT. Thirona Lung Quantification software was used to extract QCT measures from inspiratory and expiratory CT scans for each subject, including emphysema (%LAA-950, defined as the percentage of low attenuation areas (LAA) below -950HU in inspiratory scans), gas trapping (%LAA-856, defined as the percentage of LAA below -856HU in expiration), and an index score for airway wall thickening and/or narrowing (Pi10, defined as the root of the wall area of a hypothetical airway of 10-mm internal perimeter). The evaluated spirometry measures included the ratio of forced expiratory volume in 1 second (FEV1) and forced vital capacity (FVC), and the predicted percentage of FEV1 (FEV1%-predicted).
QCT measures were correlated to FEV1/FVC and FEV1%-predicted using Pearson correlation. In addition, multiple linear regression analysis was used to evaluate the predicted value of the QCT measures on both FEV1/FVC and FEV1%-predicted. For these models, the spirometry measures were log10-transformed to ensure a distribution of residuals closer to normal.
RESULTS:
The 1183 subjects were divided over GOLD stagesChar16 0 to 4:478, 100, 279, 143 and 47. 136 subjects were unclassified by GOLD. %LAA-950, %LAA-856, and Pi10 correlated significantly with both FEV1/FVC (p<0.0001, r= -0.758, r=-0.829, and r=-0.423, respectively) and FEV1%-predicted (p<0.0001, r= -0.628, r=-0.728, and r=-0.547, respectively). In the regression model for FEV1/FVC, the combination of the three QCT measures accounted for 74.5% of the variation in FEV1/FVC, with a relative contribution of 68.7% for %LAA-856, 3.1% for Pi10, and 2.6% for %LAA-950. In the regression model for FEV1%-predicted, the combination of the three QCT measures accounted for 65.8% of the variation in FEV1%-predicted, with a relative contribution of 52.9% for %LAA-856, 11.6% for Pi10, and 1.3% for %LAA-950.
CONCLUSION:
Gas trapping and airway wall thickening and/or narrowing are the major contributors to airflow obstruction in cigarette smokers.