Histopathology of the small airways: Similarities and differences between ageing and COPD

Age-related lung function decline is associated with small airway closure and gas trapping. The mechanisms which cause these changes are not fully understood. It has been suggested that COPD is caused by accelerated ageing. We have investigated pathological changes in the small airways during ageing, and evaluated whether the same or different processes exist in COPD. Histopathology and immunohistochemistry were used to examine small airway remodelling in healthy ageing, and then compare to age matched COPD patients. Ageing was associated with reduced alveolar attachment numbers (rho= -0.4 p = 0.049), increased epithelial area (rho = 0.5 p = 0.01), greater luminal narrowing due to epithelial expansion (rho = 0.5 p = 0.04) and increased alveolar septal neutrophils (rho = 0.6 p = 0.005). Compared to age matched controls, COPD small airways had 31% less alveolar attachments per airway (p = 0.02) and significantly more alveoalr septal neutrophils (p = 0.0007). Increased airway wall thickness was a feature of COPD but was not related to ageing in non-smokers. Alveolar attachment loss, accompanied by alveolar septum neutrophilic inflammation, and increased luminal narrowing due to epithelial expansion are major features of small airway remodelling during ageing. These features can explain the increased small airway narrowing and closure during ageing. Alveolar attachment loss is accelerated in COPD, likely due to increased neutrophilic inflammation.