The Sensitivity of an Inhaled Aerosol Tracheobronchial Deposition Model to Input Parameters

Abstract

Mathematical predictions of inhaled particle deposition patterns are widely used for evaluating hazards, modeling respiratory tract physiology and designing aerosol medical procedures. The parameters that are used in aerosol deposition models are physical and biological factors including those associated with the suspended particles, the suspending medium, the gravitational force field, the ventilatory airflow and the respiratory tract airways. It is useful to know how each parameter influences the predicted particle deposition in a calculation; that is, how sensitive the prediction is to a variation in each parameter. With such sensitivity information one a) might better estimate the required accuracy and precision of the input parameters for a calculation, and b) can develop new insights into inhaled particle phenomena in humans. Our sensitivity analysis covered deposition efficiency in the tracheobronchial region only during inspiration. We used a mathematical deposition model published by Yeh and Schum (1980) and our 16 generation airway model (Phalen et al., 1985). The analysis involved varying one model parameter at a time about a pre-selected nominal value. The following parameters were varied: particle diameter; particle density; viscosity of air; acceleration due to gravity; air flow rate; airway lengths; airway radii; airway branch angles; and airway gravity angles. Each analysis was performed for three particle diameters (0.1, 1.0 and 10 micrometers) and two subject ages (2 and 18 years). The results indicated that variations in each of the parameters can produce significant changes in particle deposition, but the most sensitive parameters were particle diameter and density, air flow rate, and airway lengths and radii.