A Numerical Study Of Airway Resistance And Particle Deposition In Normal And Asthmatic Lungs

Abstract

Rationale: Computational fluid dynamics (CFD) has become a popular tool for studying particle deposition in the lungs because they can be used to track individual particle motion and quantify particle deposition in a region of interest. In the study, we apply a high-fidelity CFD model together with CT image based airway models to study airway resistance and particle deposition in both normal and asthmatic lungs. The objective of this study is to investigate numerically the effect of constricted airways, as in the asthmatic lung, on airway resistance and particle deposition. Methods: Two human airway models are constructed from CT volumetric images. One subject is normal, and the other is asthmatic. The subject-specific physiologically realistic flow boundary condition is derived based on air volume difference between two CT lung images of the same human subject. Because turbulent laryngeal jet is induced at the glottal constriction in the trachea, a large eddy simulation (LES) technique is adopted to capture turbulent-transitional-laminar flows in the central airways. A constant inspiratory flow rate of Q=3.42×10 -4 m 3 /s is imposed at the inlets of the two airway models. In order to understand the characteristics of deposition of pharmaceutical aerosols or bacteria in both models, particle transport simulations are performed on LES-predicted air flow fields. Particle size of 2.5 µm is considered. Airway resistances R = Δp/Q, where Δp is the pressure drop and the unit of R is Pa/(m 3 /s), for various generations of airway segments in both models are shown in Table 1 for comparison. Results: The result shows significant pressure drop (~ 200 Pa) and airway resistance (~7420 Pa/(m 3 /s)) in the asthmatic lung, especially in the right upper lobe (RUL) and the left lower lobe (LLL). It is found that local high pressure drop is associated with local high air speed due to constricted airways. Figure 4 shows that particles tend to be deposited in the RUL and LLL. The color contours of air speed in figure 3 show that that local airway constriction induces high air speed and increases particle deposition in the constricted regions and at their downstream bifurcations. Conclusion: The obstructed airways can induce high airway resistance and subsequently increase particle deposition in the constricted regions and at their downstream bifurcations. Particle deposition Pressure drop (Δp) and Resistance (Q/Δp)