Displacement of alveolar macrophages in air space of human lung.

The role of alveolar macrophages in the process of the human lung clearance is summarised. Three patterns of alveolar macrophage (AM) displacement on the surface of alveolus are distinguished depending on the loading of the surface with insoluble deposits, i.e. directional, directional with small stochastic noise and purely random. The physical analysis is presented of chemotactic movement and hydrodynamical effects on the residence time of AMs in a geometrical model of the human alveolus. The calculation of exit times from the alveolus is also presented. Calculations show that simultaneous passive and active displacement of AMs loaded with particles reduces exit time of the macrophage by 85%, compared to the case of purely directional movement. When active transport is reduced, due to AM overloading, exit time is determined by the passive transport rate. For reduced surfactant activity, the exit time of AM from the alveolus is the function of its chemotactic activity only and is inversely proportional to AM mobility. The exit time of AMs tends towards infinity when both mechanisms of clearance decay.