Age-related scaling for aerosol and vapor deposition in the upper airways of humans.

Several theoretical models have been proposed in recent years to calculate age-related respiratory tract deposition of aerosols in humans. A critical factor in these models is the assumption about deposition in the airways above the trachea. In those models in which upper airway deposition is considered, a scaling factor, related to another airway dimension (usually tracheal diameter), is used to calculate an upper-airway dimension which determines inertial deposition. The paper reviews present knowledge of upper airway dimensions and airflow and proposed an age-related relationship for the critical nasal dimension, the nasal orifice. Relative inertial parameters for breathing at rest are obtained as a function of age from 1 mo to adulthood and compared to previous assumptions. The use of dimensionless parameters for predicting age-related deposition of diffusing particles and vapors is considered, and suggested experimental studies are proposed to supply needed information for age-related dosimetry of the entire respiratory tract.