Experimental variations in renovascular resistance in normal man as detected by means of ultrasound.

The pulsatility index (PI) of blood flow velocities has been reported to vary with changes in peripheral vascular resistance. Since blood flow velocities can easily be detected with the Echo-Color-Doppler technique in interlobar arteries of normally positioned kidneys, we tried in six healthy volunteers to estimate pharmacological induced variations in renal plasma flow (RPF) and renovascular resistance (RVR) by means of PI measurements. In this study no significant correlation between the absolute values of PI and RVR was found. In order to correct PI for different blood pressure-inputs to the renal artery, PI was divided by the pulsatility of the systemic arterial pressure, i.e. the 'blood pressure index' [BPI = (SAD-DAP)/MAP)], resulting in the 'velocity blood-pressure index' (VBI = PI/BPI), which was significantly correlated with RVR (r = 0.54, P less than 0.01). The pharmacological induced changes of RPF and RVR (delta RPF, delta RVR) were also correlated to the respective changes of PI and VBI (delta PI, delta VBI), with the highest significance when delta VBI was plotted against delta RVR (r = 0.83, P less than 0.0001). VBI, i.e. the pulsatility index of blood flow velocities as corrected for the pulsatility of the driving force, may be a tool for noninvasive assessment of changes in RVR and thereby of importance for the diagnosis and follow-up of renovascular diseases.