[Defence capacities of the respiratory tract]

The defenses of the lung against inhaled gases and particles include aerodynamic filtration mechanisms of the tracheobronchial tree, mechanical clearance and local detoxification. Cough, mucociliary transport, alveolo-bronchiolar fluid flow and clearance to lymph and blood participate in the mechanical excretory mechanisms whereas phagocytosis, immunologic and secretory mechanisms, and tissue reaction represent in-situ detoxification. Impaired mucociliary transport causes obstruction of the airways, the pathophysiologic hallmark of chronic nonspecific lung diseases. The clearance of diseases airways is not easy. It may be accomplished either by changing primarily the physicochemical properties of the mucus or by stimulating ciliary activity. By means of doublebind-crossover studies in patients with stable chronic nonspecific lung diseases, it is shown how drugs which presumably improve the clearance of diseased airways do affect the various physicochemical properties of the tracheobronchial mucus.