Resistive index - An experimental study of acute complete unilateral ureteral obstruction

RATIONALE AND OBJECTIVES. To study the effects of acute complete unilateral ureteral obstruction (UUO) and release on porcine renal resistive index (RI). METHODS. Under general anesthesia, UUO was induced in six pigs. RI was measured bilaterally at predetermined intervals for 4 hours of UUO and 1 hour of release. Additionally, measures of renal blood flow (RBF), glomerular filtration rate (GFR), arterial blood pressure, renal vascular resistance (RVR), and ipsilateral renal intrapelvic pressure (IPP) were obtained. RESULTS. UUO and resultant progressive IPP increase caused prompt and significant ipsilateral RI elevation, and contralateral RI decrease. Concomitantly, ipsilateral RVR increased significantly while RBF and GFR declined, both significantly. Release of obstruction saw an almost immediate normalization of ipsilateral RI, RVR and RBF while ipsilateral GFR assumed 80% of baseline value 15 minutes postobstruction. Throughout the experiment, ipsilateral RI correlated significantly with changes in IPP, GFR, RBF, and RVR with correlation coefficients of 0.844, -0.851, -0.898, and 0.836 respectively (P < 0.001). CONCLUSIONS. UUO causes a divergent RI response that is instantly reversed upon release. IPP seems to be the principal effector of these changes in the early phases of UUO.