Computational Simulation of Urinary System

Abstract

The aim of the present study is to create a computational model of the ureteral system that accurately mimics its dynamic functionality. This model will be able to replicate the peristaltic movement of the ureter for a variety of physiological conditions. The objective of this research was met using our in-house fluid solid interaction model, known as coupled Cgles-Y-code in which the moving boundaries between the solid and fluid domain were replicated using a novel immersed boundary method. First, a comprehensive literature review on ureteral physiology was conducted with a focus on the anatomy of the ureter and theories behind mechanisms of ureteral peristaltic function in various physiological and pathological conditions. Next, the nonlinear tensile properties of the ureteral wall were integrated into the Y-code using the equivalent strain method and the resulting model was compared with a model with linear tensile properties. It was shown that the implementation of nonlinear tensile properties was more accurate and more closely matched the behaviour of the native ureteral wall. Next, the development of more anatomically accurate ureter model geometry was presented along with a variety of approaches to optimise the mesh resolution for this complex model. A new algorithm was then developed in order to model the Intra-Abdominal Pressure (IAP) into the Y-code. Next, two separate contraction models, constant radial and time-window-frame, were introduced. It was observed that a use of the time-window-frame contraction model coupled with the IAP algorithm exhibited a better agreement with the existing clinical data than the constant radial contraction model. Finally, a comprehensive study was conducted on the urodynamic responses when different pathological conditions are modelled. The results from using a linear tensile model, replicating an unhealthy condition, showed a high level of shear stress around the contraction lumen and a higher urine velocity in vicinity of the contraction region. In another scenario, a highly depressed amplitude of peristalsis, known to be a consequence of taking vasodilators, was simulated. It was shown that an inefficient contraction can increase the possibility of continuous reflux during the propagation of peristalsis.