The pathology of small airways in chronic airflow limitation

Small airways' disease is an ambiguous term that has been used in three ways: 1. to describe the lesions in the peripheral airways in patients with severe chronic airflow limitation; 2. to describe patients with isolated severe bronchiolitis and 3. to describe patients with mild chronic airflow limitation or the lesions in the small airways of such objects. Emphysema is probably the most important variable in causing chronic airflow limitation. The lesions in the peripheral airways in patients with severe chronic airflow limitation include narrowing and loss of small airways, inflammation, goblet cell metaplasia and intraluminal mucus. The first two lesions are best related to the development of cor pulmonale. In emphysema the peripheral airways are greatly distorted and lack alveolar support, and stenotic areas decrease more in dimension than the rest of the airways. Isolated severe bronchiolitis is best defined in patients with rheumatoid arthritis and causes a characteristic clinical syndrome of rapidly progressive airflow limitation. The most important cause of mild chronic airflow limitation is inflammation of the peripheral airways. This may act by displacing the surface active layer of the airway or, more likely, by inducing muscular hyperactivity. This may result from a direct action on muscle by mediators or may act through a vagally mediated reflex.