CT Air Trapping Is Independently Associated with Lung Function Reduction over Time

PURPOSE: We aimed to study the association between lung function decline and quantitative computed tomography (CT) air trapping. MATERIALS AND METHODS: Current and former heavy smokers in a lung cancer screening trial underwent volumetric low-dose CT in inspiration and expiration. Spirometry was obtained at baseline and after 3 years. The expiratory to inspiratory ratio of mean lung density (E/I-ratio(MLD)) was used to quantify air trapping. CT emphysema was defined as voxels in inspiratory CT below −950 Hounsfield Unit. Linear mixed modeling was used to determine the association between CT air trapping and lung function. RESULTS: We included 985 subjects with a mean age of 61.3 years. Independent of CT emphysema, CT air trapping was significantly associated with a reduction in forced expiratory volume in one second (FEV(1)) and the ratio of FEV(1) over the forced vital capacity (FEV(1)/FVC); FEV(1) declines with 33 mL per percent increase in CT air trapping, while FEV(1)/FVC declines 0.58% per percent increase (both p<0.001). CT air trapping further elicits accelerated loss of FEV(1)/FVC (additional 0.24% reduction per percent increase; p = 0.014). CONCLUSION: In a lung cancer screening cohort, quantitatively assessed air trapping on low-dose CT is independently associated with reduced lung function and accelerated decline of FEV(1)/FVC.