Diffusion Deposition of Small-sized Particles in the Bronchial Tree

Abstract

The deposition pattern of radioactive aerosols (AMD = 0.2–0.4 μm) has been studied in a plastic model of the upper bronchial tree, whose geometry corresponded with the dichotomous lung model of WEIBEL. The deposition probabilities w in the different bronchial regions for inspiration and expiration were measured as function of air-flow rate v in the range of 0.1–50 l./min. In addition radioautographs were prepared to study the fine structure of the deposition pattern. The measured w-values can be approximated by the relation w = k, a−n (n > 0), where k is a characteristic factor for each generation and nearly equal for inspiration and expiration. The slope-coefficient n amounts to 0.65 ± 0.07 for all bronchial generations. The results indicate that deposition due to turbulent diffusion plays an important role in the trachea and larger bronchi. With increasing depth in the bronchial tree, however, the measured ra-values approach the theoretical values, calculated with the theory of Gormley et al. for diffusion in a laminar air stream.