Partial ureteral obstruction: Role of renal resistive index in stages of obstruction and release

Objectives. To study the changes in renal resistive index (RI) and renal function before and after release of different grades of partial unilateral ureteral obstructions. Methods. Ten dogs were subjected to right partial ureteral obstruction. Grade 1 (mild) obstruction was applied to 5 dogs (group A) and grade 5 (moderate and severe) obstruction was applied to the other 5 dogs (group B). Obstruction was maintained for 8 weeks, followed by release of obstruction. All dogs were subjected to excretory urography, technetium-99m mercaptoacetyltriglycine diuretic renography with calculation of half-time drainage (T-1/2), and bilateral renal Doppler ultrasonography before the start of the experiment, after 8 weeks of obstruction, and every 2 weeks during the 8 weeks after release of obstruction. Results. In both groups, after induction of right ureteral obstruction, there was a dramatic decrease of effective renal plasma flow (ERPF), increase of RI, and increase of T-1/2 Of the right kidney. Relief of obstruction was associated with normalization of T-1/2, reversal of RI, and recovery of ERPF to near basal values. No correlation was found between ERPF at the end of the recovery period and the functional parameters (T-1/2, RI, or ERPF) of the obstructed kidney before release of obstruction. Conclusions. (1) Unilateral partial ureteral obstruction produces an elevation of RI and T-1/2 and a fall in ERPF of the corresponding kidney. (2) After relief of obstruction, renal function is regained with associated reversal of RI. (3) Functional parameters (T-1/2, RI, or ERPF) of the obstructed kidney do not predict the recovery of ERPF after release of obstruction. (4) Rapid reversal of a previously elevated RI is an early indicator of recoverability of renal function after relief of ureteral obstruction. (C) 1997, Elsevier Science Inc. All rights reserved.