Disease of the airways in chronic obstructive pulmonary disease

The pathological hallmarks of chronic obstructive pulmonary disease (COPD) are inflammation of the small airways (bronchiolitis) and destruction of lung parenchyma (emphysema). The functional consequence of these abnormalities is airflow limitation. Airway abnormalities and emphysema interact in a complex fashion in the development of airflow limitation in COPD. In an attempt to improve understanding of the role of the airways in COPD, the morphological counterparts of airflow limitation, the cellular inflammatory infiltrate in the airways and the relationship between emphysema type and airway abnormalities are reviewed. Significant correlation between airway remodelling and functional measurements are found in earlier stages of COPD. In advanced COPD, airflow limitation is reflected by airway narrowing, airway deformity and extent of emphysema. The cellular inflammatory infiltrate is mainly composed of neutrophils in early stages of COPD. However, the presence of CD8+ T-cells seems to differentiate smokers with COPD from smokers that would not develop the disease. The inflammatory changes and remodelling found in the airways and their contribution to airflow obstruction might be modulated by the type of emphysema smokers develop, with centrilobular emphysema showing more severe inflammatory changes and narrower airways than panlobular emphysema. In conclusion, the degree of airway involvement in chronic obstructive pulmonary disease can vary greatly for the same degree of airflow obstruction, depending on the type of emphysema smokers develop. If the underlying lung abnormalities in chronic obstructive pulmonary disease vary, as the evidence suggests, the study of cigarette-induced lung disease as a single entity will further delay understanding of chronic obstructive pulmonary disease.