Respiratory flow in obstructed airways

doi:10.1016/j.jbiomech.2005.10.009

Journal of Biomechanics

Volume 39, Issue 15, 2006, Pages 2743-2751

https://doi.org/10.1016/j.jbiomech.2005.10.009 Get rights and content

Abstract

Chronic obstructive pulmonary disease (COPD) is one of the most common diseases in human community. The COPD always results in inflammation that leads to narrowing and obstruction of the airways. The obstructive airways have significant effect on respiratory flow. In order to understand the flow phenomenon in such obstructive airways, four three-dimensional four-generation lung models based on the 23-generation model of Weibel [1963. Morphometry of the Human Lung. Springer, Academic Press, Berlin, New York] are generated. The fully three-dimensional incompressible laminar Navier–Stokes equations are solved using computational fluid dynamics (CFD) solver on unstructured tetrahedral meshes. Therein, a symmetric four-generation airway model is served as the reference, the other three models are considered to be obstructed at each generation, respectively. The calculation results show that the obstructive airway has significant influence on the air flow in both up- and down-stream airways and it even results in flow separation in the conjunction region. The re-circulation cell blocks the air from entering the downstream branches. This may be the reason why COPD patients should breathe gently, and this also provides some valuable information for medicine powder deposition.

Introduction

Chronic obstructive pulmonary disease (COPD) is one of the most common diseases in the world and it is caused by blocking of the airways in the lung which invariably results from heavy smoking and inhalation of pollutants of various kinds. Numerous studies have been carried out on this topic and the typical model is a symmetric bifurcation airway. However, chronic bronchitis is an inflammation of the bronchi which alters the branching configuration significantly.

The inflamed bronchi are no longer symmetric or regular asymmetric airways. From previous studies (Liu et al., 2002, Liu et al., 2003), the flow rate and secondary flow pattern in human lung are quite sensitive to the tube diameter and bifurcation configuration. The flow characteristics of the asymmetric airway are totally different from that of the symmetric one. Therefore, obstructions in airways could significantly alter the velocity distribution, air flow rate, and pressure distribution.

Most of the early studies focused on the flow and deposition in a symmetric bifurcation model under symmetric flow conditions. From these studies (Schroter and Sudlow, 1969; Pedley et al., 1977; Isabey and Chang, 1981; Snyder and Olson, 1989; Zhao and Lieber, 1994), skewed velocity profiles and two symmetric eddies in the two-generation experimental bifurcation flow models were found.

Detailed air/particle transport phenomena as well as local deposition patterns and surface densities of deposited particle in bifurcating airways are difficult to obtain experimentally. Consequently, computational fluid dynamics (CFD) simulation is an alternative and an effective tool to acquire such information and enhance understanding of this difficult problem. Several multi-dimensional simulations have been carried out to study bifurcation flow and particle transport in the upper respiratory tract, the bronchial airways and the acinar region of the lung (Martonen et al., 1994; Balashazy et al., 1999; Lee et al., 2000; Comer et al., 2001; Darquenne, 2001; Liu et al., 2002; Hegedus et al., 2004; and Miguel et al., 2004). These studies have provided additional detailed information of particle behavior in the lung airways and showed that this behavior is inherently linked to the fluid flow patterns within the airways. However, all the studies only considered a straight smooth airway, i.e. the effect of obstruction was ignored.

In this study, we are concerned with the three-dimensional flow in four-generation obstructed bifurcation airways. A symmetric four-generation airway model is served as the reference, and the other three models are considered to be obstructed at either the second generation or the third generation airways. The objective is to investigate the influence of obstructed airway on the flow pattern, air flow rate and pressure drop.

Section snippets

Numerical method

A schematic view of the four-generation models adopted in this study is shown in Fig. 1. The bold solid lines indicate a symmetric model, which is constructed based on the fifth to eighth generations of the 23-generation model of Weibel (1963). The diameter of each generation is equal to that of the fifth to eighth in the model of Weibel (1963), respectively. The bifurcation angle is 70°. Detailed geometric parameters are tabulated in Table 1. In order to study the effect of COPD on bifurcation

Results and discussion

To thoroughly investigate the effect of COPD on bifurcation flow, five Reynolds numbers, 300, 600, 900, 1200 and 1500, are selected to simulate the respiratory flow, where the Reynolds number is defined as $Re = ρ UD / μ$ , in which ρ is the air density, U is the mean inlet velocity, D is the diameter of the inlet tube, and μ is the dynamic viscosity.

Conclusions

The effect of COPD on respiratory flow is numerically studied on four different four-generation models. The fully three-dimensional incompressible laminar Navier–Stokes equations are solved by a CFD solver. The numerical calculation leads to the following conclusions:

(1)
The obstructed airway alters the flow field significantly, a strong separation region exists behind the “throat” at higher Reynolds number. In a bifurcation airway, the obstruction may generate re-circulation both upstream and

Acknowledgements

Support given by the Research Grants Council of the Government of the HKSAR under Grant No. PolyU 5273/04E PolyU and by the Hong Kong Polytechnic University under Central Research Grant Nos. A-PG08 and G-T677 is gratefully acknowledged.

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Respiratory flow in obstructed airways

Abstract

Introduction

Section snippets

Numerical method

Results and discussion

Conclusions

Acknowledgements

Journal of Aerosol Science

Respiratory Physiology & Neurobiology

Journal of Aerosol Science

Journal of Biomechanics

Journal of Biomechanics

Journal of Hazardous Materials B

Respiratory Physiology