:: Section 6
Regional deposition is of more interest because it's more relevant in assessing the potential hazard of inhaled particles and the effectiveness of therapeutic delivery. The deposition fraction in the three regions can be approximated by the following equations.
For the Head Airways,
For the Tracheobronchial region,
For the Alveolar region,
The largest particles are removed by settling and impaction in the Head Airways. Ultrafine particles less than 0.01 μm can also have significant deposition in this region due to their high diffusivity. In the Tracheobronchial region, impaction and settling are important for particles larger than 0.5 μm although the overall deposition fraction in this size range is quite small. This is because the majority has been removed in the preceding head airways. Ultrafine particles also have a high deposition efficiency in this region due to their rapid Brownian motion. Particles entering the Alveolar region have high deposition efficiency no matter they are larger or small: settling for large particles and diffusion for small particles. As see in the figure, Alveolar deposition is not significant whenever head airways and tracheobronchial airways deposition is high. Again, these two rapid cleared regions are very important in protecting the more vulnerable alveolar region from irritating or harmful particles.