Three-Dimensional Numerical Simulations of Peristaltic Contractions in Obstructed Ureter Flows

Abstract

Ureteral peristalsis can be considered as a series of waves on the ureteral wall, which transfers the urine along the ureter toward the bladder. The stones that form in the kidney and migrate to the ureter can create a substantial health problem due to the pain caused by interaction of the ureteral walls and stones during the peristaltic motion. Three-dimensional (3D) computational fluid dynamics (CFD) simulations were carried out using the commercial code ansys fluent to solve for the peristaltic movement of the ureter, with and without stones. The effect of stone size was considered through the investigation of varying obstructions of 5%, 15%, and 35% for fixed spherical stone shape. Also, an understanding of the effect of stone shape was obtained through separate CFD calculations of the peristaltic ureter with three different types of stones, a sphere, a cube, and a star, all at a fixed obstruction percentage of 15%. Velocity vectors, mass flow rates, pressure gradients, and wall shear stresses were analyzed along one bolus of urine during peristalsis of the ureteral wall to study the various effects. It was found that the increase in obstruction increased the backflow, pressure gradients, and wall shear stresses proximal to the stone. On the other hand, with regard to the stone shape study, while the cube-shaped stones resulted in the largest backflow, the star-shaped stone showed highest pressure gradient magnitudes. Interestingly, the change in stone shape did not have a significant effect on the wall shear stress at the obstruction level studied here.

A three‐dimensional (3D) two‐way coupled fluid‐structure interaction (FSI) study of peristaltic flow in obstructed ureters

“…Previously, although Najafi et al did carry out a detailed comparative study on ureters with and without obstructions, they only considered the fluid domain. In this paper, the flow is primarily driven due to the deformation in the structural domain.…”

“…High shear stresses and pressure gradient values were observed near the location of the obstruction. Previous studies also demonstrated a similar kind of behavior . There was a slight increase in the calculated volume flow rate compared to 2D axisymmetric studies conducted previously, including the previous works of the current authors, even though the average flow rate was comparable.…”

“…There was a slight increase in the calculated volume flow rate compared to 2D axisymmetric studies conducted previously, including the previous works of the current authors, even though the average flow rate was comparable. The mass flow rate reported in Figure shows that backflow tendencies and mass flow rate values at inlet were similar to the work of Najafi et al…”

“…The reference pressure for the flow domain is chosen to be 130 Pa, with open boundary conditions incorporated on both ends of the ureter, which implies that the flow is solely driven by the peristaltic mechanics. Again, the same properties were also used to model the flow domain in previous studies . A no‐slip boundary condition is assumed on the ureter wall.…”

“…High concentration of minerals in the urine can crystallize and form kidney stones obstructing the ureter flow path . Obstruction in the urine flow path can cause urine backflow, which is an unwanted phenomenon and can lead to various complications such as urinary tract infections . Another problem related to renal caculi or ureterolithiasis is the rupture of the ureter wall, which might require in some cases, surgical interventions .…”