Lung volume vs air flow: a match for shear stresses distribution in the bronchial tree

Chest physiotherapy is used to extract mucus excess from the lung. Two main types of techniques have been based on air-mucus interaction: high air flows applied at standard lung volumes; low air flows at small lung volumes. Both are hypothesized to bring shear stress high enough to overcome mucus yield stress. However, no full understanding of the underlying biophysics involved exists as today.Our goal is to reach scientific insights on how the shear stress behaves in the bronchial tree for these two different approaches of chest physiotherapy.We developped a mathematical model to compute the quasi-static shear stress in the airway tree accounting for air inertia and a mean lung’s tissue pressure. A model of compliant bronchi in a symmetric tree was used as lung’s model (Lambert & al., 1982, J. Appl Physiol Respir Environ Exerc Physiol 52(1):44-56).Our model is able to mimic different configuration. Standard mucus (yield stress 1 Pa) can be mobilized in the entire tree by using low and moderate air flows (0.1 to 2 L/s). For cystic fibrosis case (yield stress 15 Pa), it can be mobilized from 12th generation to trachea by using moderate and strong air flows (2 to 10 L/s). When mucus obstructs a bronchus, we observe a pressure saturation distal to the occlusion and a drop in shear stress occurs.Our results allow to analyse responses of a wide range of air flow rates and tissue pressures, mimicking different CP techniques. we show that depending to these two core ...
Source: European Respiratory Journal - Category: Respiratory Medicine Authors: Tags: Respiratory function technologists/scient. Source Type: research