Computational analysis of obstructive disease and cough intensity effects on the mucus transport and clearance in an idealized upper airway model using the volume of fluid method

Abstract

This study provides a quantitative analysis to investigate the effects of cough intensity and initial mucus thickness on the mucus transport and clearance in a mouth-to-trachea airway geometry using an experimentally validated Volume of Fluid (VOF) based multiphase model. In addition, the accuracy of simplifying mucus as Newtonian fluid is also quantified by the comparisons of mucus transport and clearance efficiencies with the simulations using realistic shear-thinning non-Newtonian fluid viscosities as a function of shear rate. It proves that the VOF model developed in this study can capture air–mucus interface evolution and predict the mucus transport behaviors driven by the expiratory cough waveforms. Numerical results show that noticeable differences can be identified between the simulations using simplified Newtonian fluid and the realistic non-Newtonian fluid viscosity models, which indicates that an appropriate non-Newtonian fluid model should be applied when modeling mucus transport to avoid the possible inaccuracy induced by the Newtonian fluid simplification. Furthermore, the results also indicate that an intense cough can enhance the mucus clearance efficiency in chronic obstructive pulmonary disease (COPD) upper airways. Additionally, although higher mucus clearance efficiency is observed for severe COPD conditions with a thicker mucus layer, there is a possibility of mucus accumulation and obstruction in the upper airway for such a COPD condition if the cough is not strong enough, which will possibly cause further breathing difficulty. The VOF model developed in this study can be further refined and integrated with discrete phase models to predict the mucus clearance effect on inhaled particles explicitly.