Wall shear stress distribution in a compliant airway tree

TL;DR

This study develops a mathematical model to analyze how airflow-induced shear stress distributes in a compliant airway tree, revealing factors influencing mucus movement and implications for chest physiotherapy effectiveness.

Contribution

The paper introduces a comprehensive model accounting for airway compliance, air inertia, and tree structure to predict shear stress distribution in the lungs.

Findings

Shear stress distribution depends on airway deformation dynamics and air inertia.

Maximum shear stress location and amplitude are influenced by airflow and tissue pressure.

Tuning airflow and tissue pressure can potentially control air-mucus interactions during therapy.

Abstract

The airflow in the bronchi applies a shear stress on the bronchial mucus, which can move the mucus. The air--mucus interaction plays an important role in cough and in chest physiotherapy (CP). The conditions under which it induces a displacement of the mucus are still unclear. Yet, the air--mucus interaction justifies common technics of CP used to help the draining of the mucus in prevalent diseases. Hence, the determination of the distribution of the shear stress in the lung is crucial for understanding the effects of these therapies and, potentially, improve their efficiency. We develop a mathematical model to study the distribution of the wall shear stress (WSS) induced by an air flow exiting an airway tree. This model accounts for the main physical processes that determines the WSS, more particularly the compliance of the airways, the air inertia and the tree structure. We show that the WSS distribution in the tree depends on the dynamics of the airways deformation and on the air inertia. The WSS distribution in the tree exhibits a maximum whose amplitude and location depend on the amount of air flow and on the "tissue" pressure surrounding the airways. To characterize the behavior of the WSS at the tree bifurcations, we derive new analytical criteria related to the airway size reduction in the bifurcations. Our results suggest that a tuning of the airflow and of the tissue pressure during a CP maneuver might allow to control, at least partially, the air--mucus interaction in the lung.