Physical Mechanisms of Particle Deposition in the Respiratory Tract

Physical Mechanisms of Particle Deposition in the Respiratory Tract 

Particle deposition in the respiratory system is related to distinct physical mechanisms operating on inhaled particles. The most important of these mechanisms are gravitational sedimentation, impaction by inertial forces, and brownian diffusion (see Fig. 3). Electrostatic forces and interception, the latter being significant only for fibers, are generally less important. In this section the physical mechanisms are briefly introduced. Several excellent overviews are available in the literature (12-14). 

Settling velocities for particles of different sizes are given in Table 1. Gravitational particle displacement becomes more effective than diffusional displacement for spheres larger than 0.5 pm. 

Respirable particles acquire this terminal settling velocity in less than 0.1 ms (13), a fraction of less than 1% of the typical transit time of the airflow in any airway generation of the bronchial tree. For all practical purposes, therefore. 

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