VALIDATION OF MINIATURE ULTRASONIC TRANSIT-TIME FLOW PROBES FOR MEASUREMENT OF RENAL BLOOD-FLOW IN RATS

This study validates the accuracy of miniature ultrasonic transit-time flow probes for measuring renal blood flow (RBF) in the rat. Probes f or 1-mm and 2-mm vessels were calibrated ex vivo using excised arterie s at varying flow rates and hematocrit (Hct). Correlation between meas ured and true flow rates for the 2-mm probe were identical (r = 1.0) a t both normal and subnormal Hct values. Correlation for the 1-mm probe was high (r = 0.994) at normal Hct, but varied at both high flow rate s and subnormal Hct values. In vivo correlation of RBF measurements us ing the 1-mm probe with the clearance and extraction of p-aminohippuri c acid showed a high correlation (r = 0.84; n = 72, P < 0.0001) over a wide range of flow rates (0.5-21 ml/min) and Hct (36-74%). Zero flow levels remained steady, averaging -0.2 +/- 0.2 ml/min during occlusion in the living animal and -0.1 +/- 0.3 ml/min after exsanguination. Th is study shows that the ultrasonic transit-time flowmeter (1-mm and 2- mm probes) is a reasonably accurate and reliable method with which to measure RBF in the anesthetized, acute-instrumented rat.