Evaluation of changes in central airway dimensions, lung area and mean lung density at paired inspiratory/expiratory high-resolution computed tomography

The aim of this study was to improve the understanding of interdependencies of dynamic changes in central airway dimensions, lung area and lung density on HRCT. The HRCT scans of 156 patients obtained at full inspiratory and expiratory position were evaluated retrospectively. Patients were divided into four groups according to lung function tests: normal subjects (n=47); obstructive (n=74); restrictive (n=19); or mixed ventilatory impairment (n=16). Mean lung density (MLD) was correlated with cross-sectional area of the lung (CSAL), cross-sectional area of the trachea (CSAT) and diameter of main-stem bronchi (DB). The CSAL was correlated with CSAT and DB. MLD correlated with CSAL in normal subjects (r=−0.66, p<0.0001) and patients with obstructive (r=−0.62, p<0.0001), restrictive (r=−0.83, p<0.0001) and mixed ventilatory impairment (r=−0.86, p<0.0001). The MLD correlated with CSAT in the control group (r=−0.50, p<0.0001) and in patients with obstructive lung impairment (r−0.27, p<0.05). In patients with normal lung function a correlation between MLD and DB was found (r=−0.52, p<0.0001). CSAL and CSAT correlated in the control group (r=0.67, p<0.0001) and in patients with obstructive lung disease (r=0.51, p<0.0001). The CSAL and DB correlated in the control group (r=0.42, p<0.0001) and in patients with obstructive lung disease (r=0.24, p<0.05). Correlations for patients with restrictive and mixed lung disease were constantly lower. Dependencies between central and peripheral airway dimensions and lung parenchyma are demonstrated by HRCT. Best correlations are observed in normal subjects and patients with obstructive lung disease. Based on these findings we postulate that the dependencies are the result of air-flow and pressure patterns.