Assessment of optimal balloon size for rupture of the ureteropelvic junction and mid-ureter in a porcine model

Mechanical characteristics of the ureter and clinical implications

The ureteric wall is a complex multi-layered structure. The ureter shows variation in passive mechanical properties, histological morphology and insertion forces along the anatomical length. Ureter mechanical properties also vary depending on the direction of tensile testing and the anatomical region tested. Compliance is greatest in the proximal ureter and lower in the distal ureter, which contributes to the role of the ureter as a high-resistance sphincter. Similar to other human tissues, the ureteric wall remodels with age, resulting in changes to the mechanical properties. The passive mechanical properties of the ureter vary between species, and variation in tissue storage and testing methods limits comparison across some studies. Knowledge of the morphological and mechanical properties of the ureteric wall can aid in understanding urine transport and safety thresholds in surgical techniques. Indeed, various factors alter the forces required to insert access sheaths or scopes into the ureter, including sheath diameter, safety wires and medications. Future studies on human ureteric tissue both in vivo and ex vivo are required to understand the mechanical properties of the ureter and how forces influence these properties. Testing of instrument insertion forces in humans with a focus on defining safe upper limits and techniques to reduce trauma are also needed. Last, evaluation of dilatation limits in the mid and proximal ureter and clarification of tensile strength anisotropy in human specimens are necessary.

Radial Dilation of Ureteral Balloons: Comparative in Vitro Analysis

BACKGROUND AND PURPOSE

The dynamics of ureteral balloon expansion may differ with increasing extrinsic compressive forces and inflation pressures. This study compared the ability of ureteral balloons to expand under different conditions.

MATERIALS AND METHODS

The balloons tested were the Cook Accent, Ascend, Ascend AQ, and Pursuit; the Bard 195503 and UroForce; and the Boston Scientific Microvasive UroMax Ultra. When available, multiple balloon diameters and lengths were tested. With a guidewire in place, the balloon tip was secured by elevated vise grips on either side of the balloon. A string was wrapped around the balloon center once, and incremental increases in load were added (2 g, 42 g, 82 g, 122 g) to represent increasing extrinsic compression. The balloon was inflated with contrast medium, and circumference changes were measured at increments of 2 atm up to burst pressure. Balloons were tested in triplicate for each weight.

RESULTS

The majority of the balloons were unable to reach 90% of their expected diameter with larger constrictive loads (122 g) at low inflation pressure (4 atm). The only balloons that achieved a diameter at 4 atm that was at least 90% of the expected diameter with a coefficient of variance (CV) of <10% at all radial loads were the Pursuit 6 mm x 4 cm (98.2 +/- 2.2%; CV 7.88%), UroMax Ultra 7 mm x 4 cm (97.5 +/- 1.4%; CV 5.94%), and the UroMax Ultra 7 mm x 6 cm (101 x 1.2%; CV 7.67%). At inflation burst pressure, the balloons able to maintain a diameter at or above 100% of expected with a CV of <5% at burst pressure were the Ascend AQ 4 mm x 4 cm (116 +/- 1.0%; CV 3.34%) and the Pursuit 6 mm x 4 cm (108 +/- 2.0%; CV 4.53%).

CONCLUSION

Reaching maximum inflation diameter at low pressures in the face of increasing extrinsic compression may help minimize the risk of ureteral injury. Reliable expansion to maximum diameter even with higher extrinsic compressive forces is another important characteristic of ureteral balloons. Balloon material, configuration, and dimensions may contribute to differences in dilation properties.