[Mucociliary drainage of the respiratory tract].

Mechanical cleansing of the airways is related, on the one hand, to the amount and physicochemical qualities of the mucus and, secondly, to ciliary activity. Mobilisation of mucus is ensured by polarisation and coordination of ciliary movements. The speed of the mucosal "conveyor belt" depends, amongst other things, on th frequency of ciliary beating movements. The latter may be modified by various physiological factors including temperature, carbon dioxide, cations, pH, certain chemical mediators, in particular acetylcholine, but also by numerous harmful agents present in the air, such as irritant pollutants, viruses or bacterial toxins. This action may result in pathological states. It has also been possible to demonstrate changes in mucociliary drainage due to a certain number of iatrogenic factors. Thus, from a certain concentration upwards, general anesthetics (barbiturates, halothane) and local anesthetics (Xylocaine) have a depressant effect. Similarly, anticholinergic agents are capable of slowing mucosal transport by acting at one and the same time on ciliary activity and the secretion of mucus. Certain pharmaceutical preparations with a local action are cilio-inhibitory either by virtue of their excessively acid pH or, and more often, because preservatives are poorly selected or are present in excessive amounts. Finally, hyperoxia is capable of inducing slowing in the mucosal "conveyor belt", the degree of which depends upon the levels of oxygen and the duration of exposure. By contrast, it is possible to stimulate drainage of the airways by action on the properties of the mucus (mucolytic agents) or on ciliary motility, using pharmacological agents, such cholinergic and adrenergic drugs, in particular beta adrenergic agonists (salbutamol, terbutaline).