Alveolar Deposition of Fibers in Rodents and Humans

Alveolar deposition fractions (respirability) of inhaled fibers in rats, hamsters, and humans were calculated based on previously developed deposition models. Because of differences in airway size and ventilation condition, humans were found to have a greater deposition fraction than rodents. Nevertheless, the deposition curve (alveolar deposition fraction vs fiber aerodynamic diameter) for all species has a similar shape which exhibits two peak deposition values. Increasing the aspect ratio or decreasing the mass density of the fiber shifts the deposition curve to lower aerodynamic diameters and reduces the values of peak deposition. For fiber aerodynamic diameters greater than 3.5 microns and aspect ratios greater than 10, rodents were found to have no alveolar deposition, whereas the human deposition remains appreciable.