tailieunhanh - THERAPY FOR MUCUS-CLEARANCE DISORDERS_2

The thought of mucus disturbs many people. Mucus is beneficial as the first defense of the airways. The mucus lining traps inhaled particles and allows them to be cleared from the airway by cilia and cough. The mucus layer also prevents dehydration and desiccation of the airway surface and provides a nutrient milieu for the ciliated epithelium. Mucus can also be quite bad. Airway mucus retention due to hypersecretion or poor mucus clearance is a characteristic of many airway diseases including cystic fibrosis, chronic bronchitis, bronchiectasis, and asthma. Mucus retention is thought to lead to airway obstruction, atelectasis, and tissue destruction by entrapping inflammatory mediators. It promotes microbial. | 11 Mucokinetic Agents and Surfactant ANTONIO ANZUETO University of Texas Health Science Center San Antonio Texas . BRUCE K. RUBIN Wake Forest University School of Medicine Winston-Salem North Carolina . I. Introduction In healthy individuals airway secretions constitute a bi-layer with a periciliary fluid interposed between the epithelium and the mucous gel. In the airways mucus is usually cleared by the airflow and ciliary interaction. Effective cough clearance requires high flow velocity to detach the sputum from the epithelium and to mobilize secretions so that they can be expectorated. For the mucus to slide on top of the epithelium there is a need for a complex of phospholipidprotein compound similar to the alveolar surfactant to be present 1 . Mucoki-netic agents improve the cough clearance of mucus by increasing airflow or by altering the sputum epithelium interface by reducing mucus adhesiveness. In this chapter we discuss the role of surfactant in sputum clearance its antiinflammatory activity and the role of surfactant supplementation in improving mucus clearance in some conditions . chronic bronchitis and cystic fibrosis. We will also review the effect of bronchodilators 02 agonists and methylxanthines in mucus clearance. II. Surfactant Composition and Metabolism Pulmonary surfactant is a complex mixture of phospholipids and proteins that creates a unique interface separating gas and liquids at the alveolar cell surface Copyrighted Material 307 308 Anzueto and Rubin reducing surface tension and maintaining lung volumes at end expiration. Surfactant has effects on surface tension not only in the alveolus where it is produced by Type II cells but also in the bronchi and probably in the entire airway 1 2 . Airway surfactant consists of phospholipids that represent 80-90 of the mass 3 . In the lung phosphatidylcholine 70-80 and phosphatidylglycerol 10 are the most common phospholipid constituents. Lesser amounts of phosphatidylserine neutral .