Airway dimensions in asthma and COPD in high resolution computed tomography: can we see the difference?

Airway remodeling in asthma and COPD results in bronchial wall thickening. The thickness of the bronchial wall can be measured in high-resolution computed tomography. The objectives of the study were to assess the bronchial lumen and wall dimensions in asthma and COPD patients, in relation to disease severity, and to compare the airway dimensions in patients with asthma and COPD.

Ten asthma subjects and 12 COPD subjects with stable, mild to moderate disease were investigated. All subjects underwent chest high-resolution computed tomography (window level - 450 Hounsfield units, window width 1,500 Hounsfield units). Cross-sections of bronchi (external diameter 1.0-5.0 mm) were identified on enlarged images. The following variables were measured: external and internal diameter, wall area, lumen area, total airway area, the percentage of airway wall area, wall thickness, and the ratio of wall thickness to external diameter. Separate sub-analyses were performed for airways with external diameter ≤ 2.0 mm and external diameter > 2.0 mm.

We measured 261 and 348 cross-sections of small airways in subjects with asthma and COPD, respectively. There was a significant difference in wall thickness and wall area, which were both greater in asthmatics than in COPD patients. In bronchi with external diameter > 2.0 mm, all measured parameters were significantly higher in asthma than COPD. In individual asthmatics the airway wall thickness was similar in all the assessed bronchi, while in COPD it was related to the external airway diameter.

Our results indicate that bronchial walls are thicker in asthmatics than in patients with COPD. It seems that airway wall thickness and the lumen diameter in patients with asthma are related to disease severity. There is no such a relationship in COPD patients. High-resolution computed tomography may be a useful tool in the assessment of airway structure in obstructive lung disease.