Modeling Deposition of Inhaled Particles - Aerosols: Measurement, Dosimetry, and Health Effects - page 89

Bifurcation normal
Vortex
centers
FIGURE 5.2 Image of a CFD simulation of secondary velocity currents in the eighth generation of a bifur-
cating airway, using FLUENT 6.0.
CFPD methods have been used to examine the effects of complex low patterns on particle
motion and deposition in the respiratory system. An example of such low patterns in a model air-
way is shown in Figure 5.2. Martonen and Guan 54,55 performed linked luid dynamics and particle
motion studies that examined the effects of tumors on the deposition of particles in an idealized
two-dimensional (2D) airway bifurcation. In recent years, as desktop computing capabilities have
increased, many three-dimensional (3D) simulation studies have been performed. These studies can
be categorized into three groups: (1) studies in idealized bifurcations, (2) studies in physiologically
realistic (data-driven) bifurcating lung airways, and (3) studies in models of extrathoracic airways.
5.3.1.4.1 CFPD Studies in Idealized Bifurcations
In these types of studies, CFPD is used to examine airlow and particle deposition in smooth-
walled, tubular airway systems having regular (usually symmetric) branching angles. An example
of a CFPD simulation in a multiply bifurcating idealized airway (performed in FLUENT) is shown
in Figure 5.3. Zhang et al., 56-59 Comer et al., 53,60 Longest et al., 61,62 and Martonen et al. 18,63 have all
performed CFPD studies aimed at predicting particle deposition in idealized bifurcating airways or
networks. Zhang et al. 64 have also considered idealized representations of tumors within the airways.
5.3.1.4.2 CFPD Studies in Physiologically Realistic Bifurcating Airways
As available computing resources have grown, it has become easier to generate 3D morphological
models of the lung airways from medical images. As this capability has grown, more and more CFD
studies are being performed to study the airlow and particle deposition in bifurcating networks
developed from images of real human lungs. Studies have been performed in the trachea and upper
airways 65 and in more complicated networks involving several airway generations, 66-68 and in mod-
els representative of asthmatic lungs. 69
5.3.1.4.3 CFPD Studies in the Extrathoracic Airways
Much of the recent work being done in CFPD is in simulations of particle deposition in the extratho-
racic airways. The extrathoracic airways, such as the mouth, throat, and larynx, have very irregular
geometries, and, thus, generalizing low and deposition patterns in these areas is more dificult than