Analysis and characterization of diffusive flows and movement of the human acinar region: An experimentally validated CFD model

This paper presents a study of the gas exchanges at the alveolar level to define the respiratory capacity of a subject. A numerical multidimensional approach is proposed for the prediction of the diffusive flows of gases (oxygen and carbon dioxide) in the alveoli accounting for the gas exchange phenomena including the surface variation due to the alveoli motion. The overset mesh technique is used to reproduce a realistic surface variation during inspiration and expiration and simulate the expansion and retraction of the alveolar sac. A gas-exchange model is implemented to predict the gas distribution in the alveolar sac wall by assigning a gas flow function through the membrane. The numerical analysis enables to evaluate the flow field within the single alveoli in terms of total and partial pressure of the considered alveolar gases, as well as the species distribution due to the diffusive flows. The predictive capabilities of the numerical model are addressed by comparing the calculations with the values obtained by means the mobile metabolic system K5 from COSMED. An experimental campaign on a set of healthy subjects is used to evaluate the diffusive flows through the membrane and a good agreement between the numerical results and the experimental measurements is found. These evaluations are suitable for the characterization of the breathing capacity in physiological or pathological conditions; therefore, the proposed model can be used as a valid support for bioengineering studies in terms of respiratory gas exchange prediction.