Regional Differences Exist in Elastic Wall Properties in the Ureter

Abstract

According to classical mechanical theory, the passive elastic properties of a distensible tube are important for the resistance to flow. The aim was to study luminal dimensions under pressure loading and the tension-strain distribution of the ureter in anaesthetized pigs by means of impedance planimetry. Stepwise inflation of an intraluminal balloon in which the cross-sectional area (CSA) and pressure were measured provided the distension stimulus in the ureteropelvine junction, in the mid-ureter and in the intramural part of the ureter at the ureterovesical junction. The circumferential tension-strain distributions were computed from steady state values of these measurements. The CSA always reached equilibrium within the two-minute distension period. The steady state pressure-CSA curves were nonlinear and differed between the three measuring points (p < 0.001). The most pronounced difference was found between the ureteropelvine junction and the two other measuring points. At the lowest applied pressure of 1 kPa the steady state CSA was 15.4 ± 1.1, 16.6 ± 1.1, and 19.9 ± 1.9 mm² in the intramural part, middle part and ureteropelvine junction, respectively. At the maximum pressure the figures were 41.9 ± 2.9, 47.0 ± 2.7, and 73.1 ± 8.2 mm² for the three locations, respectively. The circumferential tension-strain distributions were nonlinear with an exponential-like behaviour. The tension-strain curve obtained from the ureteropelvine junction was translated to the right compared to the curves obtained from the two other measuring points (p < 0.05) indicating that the ureteropelvine junction was more compliant than the two other locations.

Key-words:

• impedance planimetry
• stiffness
• tension-strain distribution