The effect of dead space on inhaled particle deposition

Mathematical models which have been developed to predict the deposition of particles in the conducting airways of the lung require simplified anatomical models of the dimensions and geometry of the bronchial airways. In order to produce valid deposition predictions, the computed volumes of the conducting airways must be realistic in comparison to anatomical dead space. This requirement must be met even as the developing lung grows to maturity and then undergoes aging. The effect of these age-related changes on predicted particle deposition efficiencies has not been well studied. Numerous authors have suggested that differences in lung volumes (total lung capacity, functional residual capacity, dead space and tidal volume) may account for significant variations between predicted or observed particle deposition but no general age-specific relationship has been proposed. New models are proposed to describe changes in dead space as functions of age and body size, and methods to adjust existing anatomical models to various dead space predictions are given. Also, the effect of these modifications to anatomical models on particle deposition efficiencies are simulated for a variety of breathing patterns for models scaled to represent young children, adults, and aged persons.