Portal vein blood flow measurements using pulsed Doppler and electromagnetic flowmetry in dogs: a comparative study.

Comparative measurements of portal vein blood flow were performed at laparatomy in anesthetized dogs using either a pulsed Doppler echo system or electromagnetic flowmeters. Three hundred four simultaneous determinations were obtained under baseline conditions and during vasopressin and glucagon infusions. In each dog, serial triplicate measurements were taken within 10 min of each other. In all the cases, flow changes induced by vasoactive drugs followed the same direction regardless of the method used. Portal vein blood flow as measured by electromagnetic flowmetry ranged from 85 to 1570 ml/min. Portal vein blood flow values obtained with Doppler and electromagnetic flowmeters were not significantly different (609 +/- 335 vs. 600 +/- 370 ml/min; p = NS) and were highly correlated (r = 0.918, p less than 0.001). The difference between values obtained by the two techniques was -3 +/- 159 ml/min or -1.0% +/- 21.2% (mean +/- SD). This difference was not influenced by the portal vein diameter but increased slightly as a function of the angle of insonation. When considering the mean of triplicate measurements, we also found a highly significant correlation between data obtained by the two techniques (r = 0.934, p less than 0.001; n = 63). The mean difference was 11 ml/min, but limits of agreement between these methods were -267 and +239 ml/min. This relative discrepancy was explained by a coefficient of variation higher in Doppler measurements than in electromagnetic measurements (10.9% vs. 5.9%). These data demonstrate that under our experimental conditions, Doppler flowmetry is probably not an ideal method to measure absolute portal vein blood flow values, and that more sophisticated equipment is needed to improve its reproducibility and accuracy. In humans, however, this method might be a useful tool to assess the direction of portal flow changes in the same individual.