Evaluation of change in blood flow by contrast-enhanced power Doppler imaging during norepinephrine-induced renal vasoconstriction

We evaluated the changes in flow induced by intrarenal infusion of norepine phrine by an ultrasonographic contrast agent and power Doppler imaging. Hyp operfusion was induced in dogs (N = 5) by infusing norepinephrine directly into the renal artery for 30 min at doses of 0.7 mu g/kg/min, 1.0 mu g/kg/m in, and 1.9 mu g/kg/min. Contrast agent injections were made before and aft er each infusion of norepinephrine. The transit of contrast agent through t he kidney and color enhancement were measured by computer analysis of power Doppler images. Mean transit time and effective renal plasma flow were mea sured. The effective renal plasma flow decreased by 29%, 30%, and 64%, resp ectively, with the increasing doses of norepinephrine. Paralleling this cha nge, the mean transit time, which corresponds to reduction in renal blood f low, increased by 26%, 43%, and 77%, respectively, from the preinfusion val ue. Regression analysis shows renal blood flow to decrease exponentially wi th norepinephrine dose. Renal blood flow changes measured by contrast-enhan ced imaging correlated closely with the effective renal plasma flow measure ments. Computer analysis of contrast-enhanced power Doppler images allowed measurement of renal blood flow. This technique may be useful in assessing renal perfusion during pharmacologic and other therapeutic interventional p rocedures.