Model-based investigation of gas exchange in pulmonary capillaries due to various scenarios of lung abnormalities and treatments -

Abstract

Lung diseases (IRDS, lung obstructive diseases, apnea, lung interstitial emphysema, etc.) are a serious threat to human beings of all ages and typically lead to malfunctioning of the respiratory system that could cause death. The physical mechanisms behind clinical therapies that rely on various modalities of lung ventilation such as high frequency oscillatory ventilation (HFOV), are not yet fully understood. This is, in part, due to the limitations associated with in vivo measurements. The aim of this work is to present a physically-based lung model to investigate the effect of lung abnormalities and treatment scenarios on exchange of gases with the blood. This model builds on a previous model to accurately predict exchanges of oxygen and carbon dioxide with blood in the pulmonary capillaries. The previous model couples lung mechanics, gas transport in the airways and the alveoli, and blood oxygenation through diffusion of gases across the alveolar membrane. However, it was built for the purpose of studying the effect of Bubble CPAP on preterm infants. The current model will enhance the previous one by estimating lung parameters over a span of height, age, gender, and body weight to cover a wide variety of individuals. Not only the model will be generalized, it will also add the distribution of carbon dioxide in the respiratory system, improve the numerical cost of the solution by efficiently coupling the air and blood side, and implement the dissociation curves to relate concentrations and partial pressures of gases in blood through the binding property of hemoglobin. Unlike lumped models in literature, the model takes into account the dynamics of the spatial distribution of respiratory gases in the airways and within individual alveoli, which leads to more accurate prediction of gases transport. Gas exchange is investigated with the variation of respiration frequency, pressure amplitude, tissue compliance, and airway resistance. The results show altered gas exchange in the case of lung abnormalities, justifie