Validation of a flow-differential technique for the recording of splenic blood-volume changes to vasoactive agents.

Splenic blood-volume changes to norepinephrine were determined in the anesthetized cat by recording the integral of the difference between splenic arterial flow and splenic venous flow (flow-differential technique) with ultrasonic transit-time flowmeters, and the changes recorded with this technique were compared with those recorded with an independent technique, the gravimetric method. Norepinephrine (0.003-0.3 microgram/min/kg of body weight) induced dose-related decreases in splenic volume, and the values recorded by the flow-differential technique were not significantly different from those recorded with the gravimetric technique. The values recorded by the two methods were highly correlated (r = 0.86). The slope of the line plotting the relation between the two methods was close to unity (0.97 +/- 0.12), and the intercept of the line was close to zero (-0.46 +/- 1.6 ml). The results suggest that the recording of the flow differential between splenic arterial flow and splenic venous flow with ultrasonic transit time flowmeters is a valid method for the recording of splenic blood-volume changes to vasoactive agents.