Numerical and experimental study of expiratory flow in the case of major upper airway obstructions with fluid–structure interaction

Abstract

This study deals with the numerical prediction and experimental description of the flow-induced deformation in a rapidly convergent-divergent geometry which stands for a simplified tongue, in interaction with an expiratory airflow. An original in vitro experimental model is proposed, which allows measurement of the deformation of the artificial tongue, in condition of major initial airway obstruction. The experimental model accounts for asymmetries in geometry and tissue properties which are two major physiological upper airway characteristics. The numerical method for prediction of the fluid-structure interaction is described. The theory of linear elasticity in small deformations has been chosen to compute the mechanical behaviour of the tongue. The main features of the flow are taken into account using a boundary layer theory. The overall numerical method entails finite element solving of the solid problem and finite differences solving of the fluid problem. First, the numerical method predicts the deformation of the tongue with an overall error of the order of 20%, which can be seen as a preliminary successful validation of the theory and simulations. Moreover, expiratory flow limitation is predicted in this configuration. As a result, both the physical and numerical models could be useful to understand this phenomenon reported in heavy snorers and apneic patients during sleep. r

Simulation of Pharyngeal Airway Interaction with Air Flow Using Low‐Re Turbulence Model

“…Following the approach of Chouly and coworkers [2], a simplified three-dimensional flow configuration representing the pharyngeal airway is illustrated in Figure 1.…”

“…Therefore, in order to close the RANS equations (1) and (2), only the turbulent viscosity is required, which is determined by using 2 unknowns, that is, turbulent kinetic energy k and turbulent rate of dissipation ω. The principle behind SST k-ω model is to blend the original k-ω and k-ε together such that, near the wall, the accuracy and robustness of the k-ω model is captured, while away from the wall (i.e., free stream or free shear regions), the accuracy of the k-ε is captured.…”

“…Collapse of the human pharyngeal airways during sleep has serious health complications with an estimated 10% of snorers being at risk to obstructive sleep apnoea [1,2]. These episodes of partial or full cessation of breathing per hour, influence the quality of sleep, reduce brain oxygen saturation and have been linked to hypertension and heart failures [1].…”

“…On the subject of obstructive sleep apnoea, Chouly et al [2,13] and Van Hirtum et al [14] developed an asymptotic Navier-Stokes equation coupled with linear elastic shell elements to model flow-induced deformation of a simplified tongue subjected to expiratory flow. The collapse of the tongue onto the pharyngeal wall was also simulated via in-vitro experiments to validate their model assumptions and numerical results.…”

“…The coupling between a two-dimensional, quasisteady, laminar, incompressible fluid flow with a shell model developed by Chouly et al [2] was successful in obtaining efficient real-time results and was validated using pressurised latex in their experiments. Indeed, based on Reynolds Number, the flow is expected to be within the laminar (Re < 2000) or transitional (2000 < Re < 10000) regime.…”