Bifurcating airway model

Fig. 38 Schematic of geometry of the triple bifurcation airway model (Mazaheri and Ahmadi )...

Zhang, Z., Kleinstreuer, C., and Kim, C.S. (2001b). Flow Structure and Particle Transport in a Triple Bifurcation Airway Model. J. Fluid Eng. Trans. ASME, Vol. 123, pp. 320-330. 

Kim CS, Iglesias AJ. Deposition of inhaled particles in bifurcating airway models 1. Inspiratory deposition. J Aerosol Med 1989 2 1-14. 

Kim CS, Fisher DM, Lutz DJ, Gerrity TR. Particle deposition in bifurcating airway models with varying airway geometry. J Aerosol Sci 1994 25 567-581. 

The air stream velocity profile downstream of a bifurcation is asymmetrical. The peak velocity occurS near the inner wall of the daughter branches in the plane of the bifurcation (Olson, et al., 1973). We observed this skewed distribution and unsteady flow when the velocity was measured near the open end of recently bifurcated airways for this model cast (Sussman, et al., 1985). 

Zhao Y, Brunskill CT, Lieber BB. Inspiratory and expiratory steady-flow analysis in a model symmetrically bifurcating airway. Trans ASME 1997 199 52-58. 

Effects of airflow and turbulence on particle deposition in the lung were examined by Chan et al. using the airflow measurements in hollow casts and airway bifurcation models. Heyder et al. measured total and regional aerosol depositions through the mouth and the nose. Experimental studies for inspiratory particle depositions in single and double bifurcation airways were reported by Johnston and Schroter, Kim and Iglesias, Kim et al., and Kim and Fisher. ... 

Airflow and capture efficiency in a triple bifurcation airway was also studied by Zhang et al., where they used a three-dimensional model. They assumed laminar flow condition and used commercial software to study the airflow structure and particle transport pattern in the lung. They also showed that the parficle depositions in the first bifurcation and first and second bifurcation are comparable with the earlier suggested correlations under laminar flow conditions. 

The estimated number of tubes in each airway generation depends on the bifurcation model used in describing the tracheobronchial tree. Though bronchial bifurcations are asymmetric, symmetric models, exemplified by Weibel, or asymmetric models, such as one suggested by Horsfield, can... 

The size of the fibrous particles that appear to induce disease in the animal models is compatible with the measured respiratory range in humans (Lipp-man, 1977). Most particulate deposition takes place not in the upper or conducting portion of the airways but in the alveolar region of the pulmonary tree (the respiratory unit). Some surface deposition may occur at bifurcations in the bronchial tree, but the actual amount at each location is influenced by anatomy, specific to the species—probably to an individual—as well as the variety of fiber. A large proportion of airborne particulates are rejected as part of the normal clearance mechanisms in animals, but in humans clearance mechanisms may be compromised by smoking, for example. We are unaware of any experiments on fiber toxicity using smoking rats ... 

Fractals have fascinating properties that are present in many natural objects and had not been incorporated in previous models of nature (5, 6). If any small piece of a fractal is magnified, it appears similar to a larger piece. This property is called self-similarity and is illustrated by the fractal in Figure 2. Self-similarity can occur only if structures at a small scale are related to structures at a larger scale. Fractal objects include the repeated bifurcations of the airways in the lung (7), the distribution of blood flow in the ever-smaller vessels in the heart (8), and the ever-finer infoldings of cellular membranes (9). 

Weibel and Raabe et al. have shown that the structure of human bronchial airways can be approximated as a network of repeatedly bifurcating tubes. The bifurcations are generally asymmetric. In most computer models, however, symmetric conditions are assumed. 

In this chapter, fundamentals of particle transport, deposition, and removal were reviewed, and some of their biomedical applications were described. Particular attention was given to recent advances in computational modeling of nano and microparticle transport and deposition in human airways. Transport and deposition processes in lung bifurcations, nose and oral passages, as well as in alveolar cavities were discussed. Rheological properties of blood are also discussed, and sample simulation results are presented. The presented results showed the following ... 

Ahmadi and McLaughlin describe biomedical applications of particle transport and deposition. Special attention is given to recent advances in the use of computational models for predicting the transport, dispersion, and deposition of particles in the human airway passages. These include airflow and particle transport in the nose, oral airways, lung bifurcation, and alveolar cavities. In addition, an overview of advances in blood flow simulations in various arteries is presented. 

Heistracher T, Hofmann W. Physiologically realistic models of bronchial airway bifurcations. J Aerosol Sci 1995 26 497-509. 

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