The role of chronic bronchitis in the pathogenesis of chronic obstructive pulmonary disease.

Emphysema and a variety of lesions directly involving the conducting airways constitute the morphologic basis of air-flow obstruction in chronic obstructive pulmonary disease (COPD). Traditionally, inflammation and hypertrophy of the mucus-secreting elements within the central airways (chronic bronchitis), manifest clinically by chronic cough and recurrent bouts of purulent sputum expectoration due to infection, were held to be important in the development of COPD. While chronic cough and purulent bronchitis contribute to the morbidity associated with established COPD, epidemiologic studies suggest that neither is an independent factor in its causation. Furthermore, structure-function studies indicate that lesions in the distal bronchial tree (peripheral airways disease) are functionally more important than central airways disease in the genesis of air-flow obstruction. The severity of peripheral airways increases with advancing age, but it is only weakly related to the history of cigarette use. Other causes of peripheral airways disease have not been clearly elucidated, but a role for viruses, and certain other infectious agents, has been suggested by experimental animal studies.