CFD simulation of the respiratory cycle

Context

Numerical CFD simulations have enabled us to gain a better understanding of nasal physiology, and in particular of airflow during respiratory cycles. Air, and a fortiori its movements, are not directly observable. The difficult accessibility of the upper respiratory tract makes understanding its flow all the more complicated. Modeling airflow in the nasal passages using CFD numerical tools provides a unique description of this fundamental mechanism of life, as well as quantifying various quantities useful for analyzing respiratory problems or understanding fluid-body interactions.

Objective

This project to simulate human nasal breathing involved the comparison of respiratory parameters between a healthy patient and a patient with a deviated septum. Carried out in partnership with Professor Ludovic De Gabory from CHU de Bordeaux, the objective of the study was to analyze the main flow parameters (pressure, velocity, shear stress, flow distribution, particle residence time) in unsteady flow in all the sinonasal cavities with an accurate 3-dimensional (3D) model and during several respiratory cycles. Results focus on the clinical relevance of understanding normal nasal physiology and the changes attributed to septal deviation.

Nasal wall pressure field during inspiration

Simulation and results

OptiFluides has carried out 3D simulations to simulate airflow over 2 complete breathing cycles. The Navier-Stokes equations for incompressible fluids were solved under transient conditions.

These simulations highlighted the variations in pressure and velocity during the respiratory cycle. Air trajectories were also visualized, demonstrating, for example, the absence of air movement in sinus cavities. We also observed that particle residence time is greater during the expiratory phase than during the inspiratory phase. This is a consequence of the particular shape of the upper respiratory tract, as the same physiological elements do not exert the same function or resistance to flow during each phase. Particle stagnation in the olfactory cleft was also observed, which could be interpreted as an explanation for the phenomenon of olfactory persistence.

These analyses, made possible by CFD modeling, offer a better understanding of the phenomena involved in respiratory cycles, and their possible link with certain pathologies of the ENT sphere, giving rise to an ANR research project and opening the way to the simulation of associated treatments!