Abstract
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.
Highlights
Methods for describing the deposition of inhaled particles in the human respiratory tract have received considerable attention in the last twenty years both from theoretical and experimental points of view (Agnew et al, 1984; Bohning et al, 1975; Chan and Lippmann, 1980; Raabe, 1982; Schlesinger et al., 1982; Taulbee and Yu, 1975; Yeh and Schum, 1980; Yu and Taulbee, 1977)
Considerable advances have been made in understanding inhaled particle deposition, there are still many significant unanswered questions, Key Words: lung morphology, dead space, particle deposition including those which relate to the wide variability seen in experimental results
The functional dead space volumes reported in the literature should be reduced by 50 cm3 to predict the thoracic dead space volume to which adult anatomical models should be scaled
Summary
Methods for describing the deposition of inhaled particles in the human respiratory tract have received considerable attention in the last twenty years both from theoretical and experimental points of view (Agnew et al, 1984; Bohning et al, 1975; Chan and Lippmann, 1980; Raabe, 1982; Schlesinger et al., 1982; Taulbee and Yu, 1975; Yeh and Schum, 1980; Yu and Taulbee, 1977). Measurements of the dimensions of individual bronchial segments and of branching and gravity angles on these casts have been used to develop more realistic mathematical models of the bronchial tree (Yeh and Schum, 1980), and these models continue to be used today for predicting deposition of inhaled particles in humans in a variety of theoretical deposition models (Cuddihy et al, 1988; Egan and Nixon, 1985; Xu and Yu, 1986) One aspect of these anatomical models is that they provide an estimate of the bronchial dead space volume (volume of the conducting airways from trachea to terminal bronchioles). For the particle deposition calculations, anatomical models with different dead space volumes were generated using a scaling approach similar to that used by Schum and Yeh (1980) In this method, bronchial airway diameters are assumed to vary as the square root of lung volumes. In our modeling of dead space variation, all tracheobronchial segments are scaled by the same factor
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