A Numerical Investigation of Urine Bolus Transportation in the Ureter Using a Mathematical Model Constructed Based on Clinical Morphometric Data during Peristalsis

One of the major abnormalities in the urinary system is vesicoureteral reflux which may allow toxins and bacteria from the bladder to infect and hamper kidney function, thus leading to dialysis or in the critical cases, kidney transplantation. A quantitative analysis to characterize urine flow will further aid our understanding of the ureter and also aid in the design of flow aided devices such as valves and stents to correct reflux conditions.

A numerical simulation with fluid-structure interactions (FSI) was introduced and solved to perform the ureteral flow analysis. The incompressible Navier-Stokes equations were used as the governing equations for the fluid and a non-linear hyperelastic model was utilized for the compliant wall. The finite element equations for both the structure and the fluid were solved by the Newton-Raphson iterative method.

Recirculation regions formed upside of urine central jet, adjacent to the bolus peak. Separation occurred in the urine flow, behind the moving bolus and ureteropelvic reflux began from that location and extended to the upstream and ureteral inlet. The maximum luminal pressure occurred in the back of bolus during peristalsis. The maximum volumetric flow rate resulted from isolated bolus transportation was measured to be 0.92 mlit/min.

Effect of the vital function of ureteropelvic junction in prevention of reflux is inevitable, especially in the beginning of peristaltic wave propagation because of presence of fluid inertial forces. As the future work, we suggest that Patient-specific modeling of ureteral mechanics will be valuable to identify crucial disease conditions and will further aid our understanding of the ureter and also aid in the design of flow aided devices such as valves and stents to correct reflux conditions.