Airway Dimensions at Inspiratory and Expiratory Multisection CT in Chronic Obstructive Pulmonary Disease: Correlation with Airflow Limitation

Abstract

To analyze the relationship between airflow limitation and airway dimensions from the third to the fifth generation of bronchi in patients with chronic obstructive pulmonary disease (COPD) by using inspiratory and expiratory multisection computed tomography (CT). This retrospective study was approved by the institutional review board, which waived the need for informed consent. The study included 50 patients with COPD who underwent both inspiratory and expiratory 64-detector CT. In each patient, mean values of airway luminal areas from the third to the fifth generation of three bronchi (right B1, right B10, and left B3) were measured at inspiratory CT (IA3, IA4, and IA5) and expiratory CT (EA3, EA4, and EA5). To evaluate the change of the airway luminal area between inspiration and expiration, the ratio of expiratory to inspiratory airway luminal area in each generation was calculated (EA3/IA3, EA4/IA4, and EA5/IA5). Correlations between airway dimensions and pulmonary function test results were evaluated. The correlation coefficients between airway luminal area measured at expiratory CT and the forced expiratory volume in 1 second (FEV(1)) were higher than those for inspiratory CT and improved as the airway size decreased from the third to the fifth generation (IA3, r = .02; IA4, r = .18; IA5, r = .26; EA3, r = .09; EA4, r = .40; EA5, r = .63). EA5/IA5 had the highest correlations with FEV(1) (r = .72, P < .001). There were no significant correlations between EA3/IA3 and pulmonary function test results. Airway lumen measured at expiratory CT was more closely related to expiratory airflow measurements than was lumen measured at inspiratory CT. In addition, the changes of airway luminal area between inspiration and expiration were strongly related to airflow limitation.