Clinical aspects of mucus and mucous plugging in asthma.

Abnormalities in the production and transport of airway secretions play an important role in the pathophysiology of asthma, especially during acute exacerbations of the disease. The synthesis of mucus becomes disordered, and other constituents of airway contents, including eosinophils and shed bronchial epithelial cells, contribute to the abnormal sputum that is produced. Altered viscoelastic properties of asthmatic mucus lead to impaired mucus transport rates. In addition, ciliary function may be directly inhibited by factors within the secretions. The consequence of these derangements is often widespread plugging of small bronchi and bronchioles. Occasionally, segmental or subsegmental atelectasis develops, but in most series radiographically visible atelectasis is uncommon. A rare complication is mucoid impaction of the bronchi, in which a central masslike opacity on chest radiograph is the manifestation of a large mucous plug in a major bronchus. A hypersensitivity reaction to fungi has been implicated in the formation of at least some mucoid impactions. A variety of pharmacological and other methods have been used in attempts to modify abnormal airway secretions and to promote their clearance, but none is of proven benefit. The development of effective therapies will probably require a better understanding of the regulation of normal mucociliary transport and of the disturbances that occur in asthma.