Computer simulations of particle deposition in the developing human lung.

An age-dependent theoretical model has been developed to predict PM dosimetry in children's lungs. Computer codes have been written that describe the dimensions of individual airways and the geometry of branching airway networks within developing lungs. Breathing parameters have also been formulated as functions of subject age. Our computer simulations suggest that particle size, age, and activity level markedly affect deposition patterns of inhaled air pollutants. For example, the predicted lung deposition fraction is 38% in an adult but is nearly twice as high (73%) in a 7-month-old for 2-micron particles inhaled during heavy breathing. Tracheobronchial (TB) and pulmonary (or alveolated airways, P) deposition patterns may also be calculated using the model. Due to different clearance processes in the TB and P airways (i.e., mucociliary transport and macrophage action, respectively), the determination of compartmental dose is important for PM risk assessment analyses. Furthermore, the results of such simulations may aid in the setting of regulatory standards for air pollutants, as the data provide a scientific basis for estimating dose delivered to a designated sensitive subpopulation (children).