Toward the modeling of mucus draining from human lung: role of airways deformation on air-mucus interaction

Abstract

Chest physiotherapy is an empirical technique used to help secretions to get out of the lung whenever stagnation occurs. Although commonly used, little is known about the inner mechanisms of chest physiotherapy and controversies about its use are coming out regularly. Thus, a scientific validation of chest physiotherapy is needed to evaluate its effects on secretions. We setup a quasi-static numerical model of chest physiotherapy based on thorax and lung physiology and on their respective biophysics. We modeled the lung with an idealized deformable symmetric bifurcating tree. Bronchi and their inner fluids mechanics are assumed axisymmetric. Static data from the literature is used to build a model for the lung's mechanics. Secretions motion is the consequence of the shear constraints apply by the air flow. The input of the model is the pressure on the chest wall at each time, and the output is the bronchi geometry and air and secretions properties. In the limit of our model, we mimicked manual and mechanical chest physiotherapy techniques. We show that for secretions to move, air flow has to be high enough to overcome secretion resistance to motion. Moreover, the higher the pressure or the quicker it is applied, the higher is the air flow and thus the mobilization of secretions. However, pressures too high are efficient up to a point where airways compressions prevents air flow to increase any further. Generally, the first effects of manipulations is a decrease of the airway tree hydrodynamic resistance, thus improving ventilation even if secretions do not get out of the lungs. Also, some secretions might be pushed deeper into the lungs; this effect is stronger for high pressures and for mechanical chest physiotherapy. Finally, we propose and tested two a dimensional numbers that depend on lung properties and that allow to measure the efficiency and comfort of a manipulation.

New insights into the mechanisms controlling the bronchial mucus balance

“…Regarding the interaction between the airflow and the mucus layer, recent studies have shown that the airflow in the airways is able, in some conditions, to displace the mucus [ 15 , 16 ]. Actually, the airflow applies a stress on the mucus layer; if this stress is high enough, the airflow is able to drag the mucus and to make it move.…”

“…Four potential mechanisms controlling (actively or passively) the volume of mucus in an airway can be highlighted: the mucociliary transport, often mentioned as being the main mechanism of control [ 14 ], mass exchange between the mucus and the epithelium or the submucosal glands, the interaction between the mucus and the airflow in the lungs [ 15 , 16 ] and the water exchange between mucus and inhaled or exhaled air (evaporation/condensation) [ 17 ].…”

Towards bioinspiredin vitromodels of intestinal mucus

“…88 Physiological mucus models include all the mucus components like lipids, proteins, DNA and cell debris, that contribute to mucus properties, such as mesh size, viscoelastic behaviour and net charge. 89,90 For instance, samples of physiological mucus scraped from the jejunum of pigs and piglets show a reduction of their LVR extension and storage modulus (G 0 ) values at any strain and a decrease of viscosity at a given shear rate when treated with DNAse. 37 These observations are corroborated by the evidence that in the airway mucus, the presence of DNA from neutrophils during inammation leads to increased viscosity, which may contribute to the pathophysiology of severe disease like cystic brosis.…”

ANSYS‐MATLAB co‐simulation of mucus flow distribution and clearance effectiveness of a new simulated cough device

“…Bronchial secretion is a kind of non‐Newtonian fluid that mainly consists of water and macromolecular constituents . The most specific part of bronchial secretion is mucus which is approximately 30 μm thick .…”