Flow characteristics of 3 unique ureteral stents: Investigation of a Poiseuille flow pattern

Purpose: The pattern of flow in the stented ureter (intraluminal and/or ext ra luminal) has only been defined for the standard pigtail stent. No data a re available on stent flow for any specialty stents. To our knowledge we pr esent the first investigation characterizing the type of flow through a ste nt (Poiseuille versus nonPoiseuille flow). Materials and Methods: Flow was measured in an unstented ureter, a standard 7Fr double pigtail stent and the 7/3Fr Tail dagger stent, 7Fr Spirastent d ouble dagger and 14/7Fr endopyelotomy stent using a previously developed st ent flow model. In vitro pressure flow studies were also done in nonfenestr ated 14/7Fr, Tail and standard 7Fr stents. These stents were infused at a c onstant flow rate of 2 to 10 mi. per minute with monitoring of the correspo nding pressure gradients. Resistance to flow was determined for these stent s using pressure flow plots and Poiseuille's law. Results: In vivo the 7Fr pigtail, 14/7Fr endopyelotomy and 7/3Fr Tail stent s had statistically similar flow rates. Flow through each of these stents e xceeded the flow through an unstented ureter. The Spirastent had the least flow in all categories tested. There was no correlation of Poiseuille flow parameters measured in vitro for nonfenestrated stents with in vivo stent f low. Conclusions: In stented ureters fluid drains through and around the stent r egardless of its design. The flow characteristics of these 3 specialty sten ts were not predictable according to lumen or stent size. In vitro Poiseuil le's flow did not correlate with in vivo stent flow.