The lung mucosa: a critical environmental battleground

The entirety of the lung mucous membrane and epithelial surface are exposed to the environment; react to noxious environmental gases, vapors, and particles; and are under physiologic and humoral mediator control. In recent years much information has been gained regarding the mucous membrane of the tracheobronchial tree, its physiology, and its reaction to environmental hazards. The pharmacologic control of secretion, ciliary beat rate, and net mucus flow governs both the clearance of mucus and the clearance of particles. The physiologic factors that govern this clearance mechanism can be influenced by pharmacologic agents in patients with lung disease and presumably also in patients with purely environmental injury. The effects of ozone on lung function, lung compliance, and airway resistance have been well documented in adults and children. Environmental ozone also alters mucous membrane function, increasing mucociliary secretion rate and peripheral lung clearance. The speed-up in clearance implies an increase in mucous gland secretion, which may act unfavorably when ciliary beat is damaged, glandular hypertrophy is present, or flow-limiting segments exist, as is usually the case in bronchial asthma and chronic obstructive pulmonary disease. Thus, whereas the consequences of ozone may be modest for a normal, healthy individual, they presumably increase hazards for the individual with lung disease or damage. For this reason, efforts should be made to control or limit damage by ozone or other environmental inhalants in such individuals. This goal may be facilitated by a wider knowledge of the pharmacologic control of the mucous membrane.