Purpose: To determine if quantitative CT estimates of lung parenchymal overinflation and airway dimensions in smokers with a normal FEV1 can predict the rapid decline in FEV1 that leads to COPD.
Methods: Study participants (n=143; age 45~72yrs; 54% male) were part of a lung cancer screening trial, had a greater than 30 pack years smoking history and a normal FEV1 and FEV1/FVC at baseline (FEV1: 99.4±12.8% (SD), range: 80.2~140.7%; FEV1/FVC: 77.9±4.4 (SD), range: 70.0~88.0%). An inspiratory, multislice CT scan was acquired for each subject at baseline. Custom software was used to measure airway lumen and wall dimensions; the percentage of the lung inflated beyond a predicted maximal lung inflation, the lower attenuation lung area with an X-ray attenuation lower than –950HU; and the size distribution of the overinflated lung areas and the lower attenuation was described using a cluster analysis. Multiple regression analysis was used to test the hypothesis that these CT measurements combined with other baseline characteristics might identify those who would develop an excessive annual decline in FEV1.
Results: The annual change in FEV1%predicted was -2.3±4.7 (SD) with a range from -23.0 to +8.3%. Multiple regression analysis revealed that the annual change in FEV1%predicted was significantly associated with baseline percent overinflated lung area measured on quantitative CT, FEV1%predicted, FEV1/FVC, and gender.
Conclusion: Quantitative CT scan evidence of overinflation of the lung predicts a rapid annual decline in FEV1 in smokers with normal FEV1.