Loss of Small Airways Before Emphysema May Explain COPD

The narrowing and disappearance of small airways before the onset of emphysematous destruction, which is marked by the onset and spread of lesions and holes in the lung, may explain the increased peripheral airway resistance reported in chronic obstructive pulmonary disease (COPD), according to a recent study published in the New England Journal of Medicine.

The study used multidetector computed tomography (CT) to compare the number of small airways (measuring 2.0mm to 2.5mm in diameter) in patients with various stages of COPD, as judged by scoring on the Global Initiative for Chronic Obstructive Lung Disease (GOLD) scale. MicroCT was used to measure the extent of emphysema, the number of terminal bronchioles per milliliter of lung volume and the minimum diameters and cross-sectional areas of terminal bronchioles. Both isolated lungs removed from patients with COPD who underwent transplantation and donor lungs were examined.

According to researchers, samples from the isolated lungs of patients with severe COPD who underwent lung transplantation showed significant reductions in the total cross-sectional area and numbers of terminal bronchioles. Furthermore, analysis revealed that the narrowing and loss of terminal bronchioles occurred before the onset of emphysematous destruction.

In samples from patients with COPD, as compared with control samples, the number of small airways was reduced for those participants who were categorized as GOLD stages one through four. Authors of the study note that they could not determine whether the reduction in the number of small airways that was observed by CT analysis was a true reduction or simply a narrowing to the point at which the airways were no longer visible.

They add: “Despite these limitations, the microCT results extend earlier reports by showing that there is both widespread narrowing and loss of smaller conducting airways before the onset of emphysematous destruction in both centrilobular and panlobular emphysema phenotypes of COPD.”

Research for this study was funded by the National Heart, Lung, and Blood Institute, the Canadian Institute of Health Research–Thoracic Imaging Network of Canada, the Canadian Collaborative Innovative Research Fund, GlaxoSmithKline, and the Lavin Family Supporting Foundation.