Numerical Simulations of Peristalsis in Unobstructed Human Ureters

Urine is transported from the kidney to the urinary bladder through the ureter by peristalsis and pressure gradients. The contractile force acting on the ureter wall has drawn considerable interest in the field of biomechanics. Backflow of urine from bladder to the kidney can occur due to failure of the ureterovesical (ureteral-bladder) junction or blockage in the ureter passage because of recurrent urinary tract infection and also due to formation of stone in kidney. To understand the nature of the flow as well as its effect on the ureter wall, two-way fluid-solid interaction (FSI) modeling of the ureter peristaltic flow at different pressure is required. A transient 2D axisymmetric numerical calculation of ureteral wall peristalsis and urine flow is performed with a fully-coupled monolithic solver using an arbitrary Lagrangian-Eulerian (ALE) method. The ureter is assumed to be a circular tube with successive compression waves traveling downstream. The incompressible Navier-Stokes equations are solved to calculate the laminar flow of urine. The ureter wall is modeled as a non-linear hyper-elastic, nearly incompressible material, by curve fitting the biaxial test data of a human ureter, obtained from literature. Displacement due to peristalsis on ureteral wall is created with a compressive force having a Gaussian bell-curve variation along the length of the ureter, and a certain wavelength specified according to the data found from previous studies. It is observed that, as the compression wave travels from the abdominal part of the ureter towards to the pelvis, it is more likely for urine reflux to occur due to the failure of the ureteropelvic junction rather than the ureterovesical junction.Copyright © 2016 by ASME