How small airway disease relates to emphysema in COPD explant lungs

The relationship between small airway disease and emphysema in COPD remains debated: does one precede the other, or do they evolve independently? To address this, Thibo Verheyen, PhD student at the Antwerp University, quantified small airway disease and compared lung function in COPD patients with and without emphysema.

Emphysema was defined as ≥5% of a lung lobe with CT attenuation values below –950 Hounsfield units. Patients underwent pulmonary function testing and in vivo CT, followed by lobectomy (mostly for lung cancer). Lobes were processed and analyzed using micro-CT, allowing visualization down to the alveolar level. We assessed terminal and transitional bronchiole counts, wall thickness, alveolar attachments, and airway
circularity.

When comparing emphysema to non-emphysema groups, no significant differences were found in pulmonary function parameters (FEV1, FEV1/FVC ratio, DLCO, TLC, RV) or in small airway measures. However, strong correlations emerged between emphysema percentage on CT and micro-CT measures (airway counts, attachments, wall thickness) as well as diffusion capacity and lung volumes.

These findings suggest that a 5% emphysema cutoff may be insufficiently sensitive. In addition, evidence of small airway disease in non-emphysema lungs supports the hypothesis that small airway loss precedes emphysema development in COPD.