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Predictions of inter- and intra-lobar deposition patterns of inhaled particles in a five-lobe lung model

Abstract Objective To develop a stochastic five-lobe lung model and to compute particle deposition fractions in the five lobes, considering anatomical as well as ventilatory asymmetry. Materials and methods The stochastic five-lobe lung model was derived from an existing stochastic model for the whole lung, which implicitly contains information on the lobar airway structure. Differences in lobar ventilation and sequential filling of individual lobes were simulated by a stochastic lobar ventilation model. Deposition fractions of inhaled unit density particles in the five lobes were calculated by an updated version of the Monte Carlo deposition code Inhalation, Deposition, and Exhalation of Aerosols in the Lung (IDEAL). Results Simulations for defined exposure and breathing conditions revealed that the two lower lobes receive higher deposition and the two upper lobes lower deposition, compared to the average deposition for the whole lung. The resulting inter-lobar distribution of deposition fractions indicated that the non-uniform lung morphometry is the dominating effect, while non-uniform ventilation only slightly enhances the lobar differences. The relation between average lobe-specific deposition fractions and corresponding average values for the whole lung allowed the calculation of lobe-specific deposition weighting factors. Discussion Comparison with limited deposition measurements for upper vs. lower (U/L) and left vs. right (L/R) lobes revealed overall agreement between experimental and theoretical data. Calculations of the L/R deposition ratio for inhaled aerosol boli confirmed the hypothesis of Möller et al. that the right lung is less able to expand at the end of a breath because of the restrictive position of the liver.