Objectives: To define an exact pressure-flow correlation in the upper urinary tract using an improved measurement method, to quantitatively characterize the degree of postrenal obstruction and to find a simple way of calculating it in everyday urological practice.
Methods: The data of 112 cases were included in the analysis. The dynamic method of a multistep, constant pressure perfusion study was used to precisely measure a wide range of pressure-flow dependences. Values of established parameters measuring the degree of obstruction were compared: the intrapelvic pressure, the ureteral opening pressure and the newly introduced 'obstruction coefficient'.
Results: Pressure-flow relations can be best presented by a parabolic curve described by the simple formula Y = AX(2) + B. Depending on the degree of obstruction, the shape of this curve can be characterized by a single number, that we defined as the 'obstruction coefficient'. Computer-based evaluation software for the easy calculation of this coefficient is presented here and freely available on demand. The Whitaker-test, the ureteral opening pressure, and the 'obstruction coefficient' showed significant correlation proving that the latter was clinically applicable in measuring the degree of obstruction.
Conclusion: Calculation of the 'obstruction coefficient' enables us to exactly define the degree of upper urinary tract obstruction and to safely monitor for a long period conditions inhibiting ureteric passage.