Computed tomographic measures of airway morphology in smokers and never-smoking normals

Abstract

Bronchial wall area percent (WA% = 100 × wall area/total bronchial cross sectional area) is a standard computed tomographic (CT) measure of central airway morphology utilized in smokers with chronic obstructive pulmonary disease (COPD). Although it provides significant clinical correlations, the range of reported WA% is narrow. This suggests limited macroscopic change in response to smoking or that remodeling proportionally affects the airway wall and lumen dimensions such that their ratio is preserved. The objective of this study is to assess central airway wall area (WA), lumen area (Ai), and total bronchial area (Ao) from CT scans of 5,179 smokers and 92 never smoking normal subjects. In smokers, WA, Ai, and Ao were positively correlated with forced expiratory volume in 1 s (FEV1) expressed as a percent of predicted (FEV1%), and the WA% was negatively correlated with FEV1% (P < 0.0001 for all comparisons). Importantly, smokers with lower FEV1% tended to have airways of smaller cross-sectional area with lower WA. The increases in the WA% across GOLD stages of chronic obstructive pulmonary disease (COPD) can therefore not be due to increases in WA. The data suggest two possible origins for the WA% increases: 1) central airway remodeling resulting in overall reductions in airway caliber in excess of the decreased WA or 2) those with COPD had smaller native airways before they began smoking. In both cases, these observations provide an explanation for the limited range of values of WA% across stages of COPD.

Keywords: chronic obstructive pulmonary disease; computed tomographic scan; lumen; wall area.

Fig. 1.

Left: the mean wall area (WA), total bronchial area (Ao), and WA percent (WA%) of RB1 for men and women, respectively. Right: the same measures for RB10 in men and women. Data includes airway morphology of never-smokers, smokers with normal lung function (“at risk”), and smokers with a range of disease severity (GOLD 1, 2, 3, and 4). Values on the y-axis are either in mm² (WA and Ao) or a % (WA%).

Fig. 2.

Axial images of a smoker with normal lung function (A) and GOLD 4 chronic obstructive pulmonary diseas (COPD; B). Note the airways highlighted by the white arrows. A: the lumens (Ai) and Ao are larger. B: the Ao is reduced with a resulting smaller Ai and WA.