Introducing additional side holes to enhance flow pathways in ureteral stents

Abstract

Ureteral stents, which are hollow tubes placed in the ureter to ensure the continuous flow of urine from the kidney to the bladder, continue to face complications despite advancements in their design and coatings. The stent placement not only reduces or stop ureter peristalsis, but also prevents the closure of the ureterovesical junction (UVJ). During voiding, the increase in intravesical pressure, creates a pressure gradient that leads the urine to ascend the ureter, a condition known as vesicoureteral reflux (VUR). VUR can lead bacteria up the ureter until the kidney, promoting biofilm formation and raising the risk of kidney infection. Additionally, VUR results in increased renal pressure, damaging the kidney. Conversely, reflux can aid in clearing crystalline particles and diminishing encrustation in the side holes and in the distal side of the stent. This study explores how adding side holes to the extremities of the stent affects urine flow through the stent and side holes during VUR.

A stented ureter model equipped with eight equidistant side holes, plus two at each extremity, was constructed using the COMSOL Multiphysics software, as depicted in Figure 1A. To simulate VUR, a pressure gradient of 20Pa was imposed between the bladder and the kidney, and no slip boundary condition was applied. The pressure difference induced the reflux phenomenon, mimicking the clinical scenario commonly observed in patients with ureteral stents. Measurements of flux through the side holes and the flow dynamics within the stent lumen were quantified.

Adding side holes to a stent reduces luminal flow at both ends, as less fluid enters or exits through the end openings (Figure 1B). Conversely, these side holes increase flow through themselves compared to stents without such additions (Figures 1C and 1D). Consequently, with the added side holes, reflux occurs predominantly along the ureter since the outflow trough the main extremity of the stent is almost zero, potentially lowering renal pelvis pressure. In stents without extra side holes, only the distal and proximal holes are active. With additional side holes, these become passive, while those near the renal pelvis turn active, enhancing the overall flow.

The addition of side holes to the stent extremities significantly alters fluid dynamics. It decreases flow through the stent's ends while enhancing flow through the side holes themselves. This modification likely shifts reflux patterns along the ureter, with potential benefits reducing the renal pelvis pressure, and increasing the washout of encrusted particles on side holes.