Lung Defense Mechanisms: Their Importance in Respiratory Care

The type and extent of respiratory-system damage produced by airborne or bloodborne noxious agents depend upon four major factors: the chemical and physical quality of the agent, the quantity inhaled, the site of deposition in the respiratory system, and the rate of clearance from that site. A high degree of interdependence among these factors is noted. Large inert particles are filtered out in the upper airway and may never reach the tracheobronchial tree or peripheral airspaces. Smaller, more chemically reactive particles provide greater hazard to the respiratory system, as they may reach the peripheral airspaces, where clearance is slower and less effective. Noxious gases are particularly hazardous because of their ability to deposit deep in the respiratory system and to produce extensive tissue damage. Viable agents such as bacteria, viruses, and fungi provide other threats to lung integrity-multiplication, tissue invasion, and immune stimulation. The interaction between pre-existing lung disease and immunosuppression, combined with multiple noxious-agent exposure, provides a framework upon which a given patient's respiratory disease may be understood. Respiratory care may be applied either as a preventive measure to forestall further tissue damage or as a therapeutic approach to reverse the respiratory-system damage already present.