Contrast medium, blood, and saline were injected at various rates into the hepatic arteries of 10 dogs, and the flow rate was continuously monitored by an electromagnetic flow probe. The flow rate was significantly increased following injection of all three materials at rates which were below the preinjection blood flow rate. However, the increase in hepatic artery flow rate did not begin until three to six seconds after the beginning of injection. At injection rates above the preinjection blood flow rate, the flow rate increased simultaneously with the injection of contrast medium and blood. Saline was not injected at these rates. The level of increase in flow rate was not significantly different regardless of the material injected or the rate of injection. The maximum flow rate was achieved at a similar interval from the beginning of injection of each of the substances, but the return of the flow rate to baseline levels was significantly longer after injection of contrast medium than after injection of blood.
These findings are consistent with the well known vasodilatation properties of contrast medium, but the mechanism of the flow rate changes following injection of blood and saline is unclear. These findings suggest that measurements of arterial blood flow rate that rely on the intraarterial injections are inaccurate unless the flow measurements are made within the first three seconds of injection and unless the injection rate is below the baseline flow rate in the injected artery.