Update on the roles of distal airways in COPD.

This review is the summary of a workshop on the role of distal airways in chronic obstructive pulmonary disease (COPD), which took place in 2009 in Vence, France. The evidence showing inflammation and remodelling in distal airways and the possible involvement of these in the pathobiology, physiology, clinical manifestations and natural history of COPD were examined. The usefulness and limitations of physiological tests and imaging techniques for assessing distal airways abnormalities were evaluated. Ex vivo studies in isolated lungs and invasive measurements of airway resistance in living individuals have revealed that distal airways represent the main site of airflow limitation in COPD. Structural changes in small conducting airways, including increased wall thickness and obstruction by muco-inflammatory exudates, and emphysema (resulting in premature airway closure), were important determinants of airflow limitation. Infiltration of small conducting airways by phagocytes (macrophages and neutrophils), dendritic cells and T and B lymphocytes increased with airflow limitation. Distal airways abnormalities were associated with patient-related outcomes (e.g. dyspnoea and reduced health-related quality of life) and with the natural history of the disease, as reflected by lung function decline and mortality. These data provide a clear rationale for targeting distal airways in COPD.