Pathophysiology of the small airways.

This review describes, in some detail, the normal structure of the small airways, how this structure is achieved during the development of the bronchial tree from embryogenesis to adulthood, and how the structure determines the function of the airways at different ages and in disease. We then describe the structural abnormalities in small airways in chronic obstructive pulmonary disease (COPD) and their relationship with the disordered pulmonary function found in this disease, as an example of the mechanisms leading to airflow limitation in diseased airways. We address the pathology of small airways in different stages of COPD, summarizing the structural abnormalities associated with the progressive deterioration of pulmonary function from smokers with normal lung function to smokers with severe COPD. The importance of the elastic recoil in the normal and abnormal function of the airways is also highlighted.