THE RENAL VASCULAR-RESPONSE TO ACUTELY ELEVATED INTRAPELVIC PRESSURE - RESISTIVE INDEX MEASUREMENTS IN EXPERIMENTAL URINARY OBSTRUCTION

Purpose: To assess the accuracy of resistive index (RI) in the diagnosis of obstruction. Materials and Methods: The time course of RI and its relationship to intrapelvic pressure were measured in 6 dogs following unilateral obstruction. Results: Changes in RI 1) occurred as early as 1/2 hour after acute obstruction, 2) only reached diagnostic sensitivity after 3 to 4 hours, 3) accurately diagnosed obstruction whenever the RI ratio between the kidneys exceeded 1.15 and 4) were uninfluenced by alterations in intrapelvic pressure. Conclusions: Because RI more closely reflects changes in renal blood flow than pelvic pressure, it can accurately diagnose acute obstruction but only after several hours. Diagnostic accuracy in chronic obstruction may be influenced by these physiologic relationships.