An in vitro assessment of the flow characteristics of spiral-ridged and smooth-walled JJ ureteric stents

Objective To assess drainage through spiral-ridged and smooth-walled JJ ure teric stents (designed to ensure upper tract drainage) and thus determine w hether drainage preferentially occurs around rather than through the spiral -ridged stent, promoting renal flow and potentially facilitating the passag e of urinary stone fragments. Materials and methods A mechanical ureteric model was constructed to mimic the funnel characteristics of the renal pelvis. A motor pump was used to he lp simulate respiratory and skeletal movement, resulting in differential mo tion between the intraluminal stent and the surrounding ureteric wall. Tube s of varying internal diameters were used to simulate different sizes of me ter. Flow rates of standard 7 F smooth-walled stents were compared with 7 F spiral-ridged stents with and without occluded lumens, and with and withou t standardized excursions. Results Extraluminal flow (mean rates) with and without movements simulatin g respiratory excursions were significantly higher with the spiral stent fo r all stent diameters evaluated. All flow rates increased as the ureteric d iameter increased. Total flow past the spiral stent was significantly great er than flow with the smooth-walled stent under all conditions tested. Rows measured around the spiral stent under conditions of excursion were the hi ghest of all categories, 20-fold higher than in smooth-walled, closed, stat ionary stents. Conclusion Spiral-ridged JJ stents provided substantially greater flow in t his in vitro model. Extraluminal flow was markedly increased with the spira l-ridged configuration. The difference in flow rates was more pronounced at the smaller pseudo-ureteric tube diameters, simulating dimensions found in clinical practice. The flow rate also was increased when the central lumen remained open, and was greater still when there was dynamic excursion with respiratory movements.