Dispersion of inhaled particles in the human lungs

A theoretical model of the dispersion of inhaled particles in the human respiratory tract is proposed. The model takes into account the contributions of air flow, Brownian motion, and gravitational settling, but neglects the effect of inertia of the particles. The dispersion is analyzed by dividing the respiratory tract into five zones according to the aerodynamic characteristics. The dispersion in each zone is described by a response curve at the outlet of the zone for a step input of aerosols at the inlet of that zone. Calculations for a single breath of 450 and 1980 ml of aerosols (as a step input to the mouth) over a period of 4 and 6 sec, respectively, were carried out using the proposed model, and the results were compared with the experimental curves for the distribution of half-micron particles in exhaled air reported in the literature. The model predicts that for larger breaths, Brownian motion and gravitational settling of half-micron particles are the major factors controlling the dispersion of inhaled particles.