Dilatation of a Medium‐Sized Artery Immediately after Local Changes of Blood Pressure and Flow as Measured by Ultrasonic Technique

The effect of changes in blood pressure and flow on the calibre of the medium‐sized artery has been studied in model experiments with an a‐v fistula on the femoral vessels in dogs, On opening of the fistula a large local fall of blood pressure proximal to the fistula and an increase in flow up to 1000 % has been found. With the use of an ultrasonic technique for measurement of arterial diameter—by which it was possible to measure changes in the diameter in the order of 0.001 mm—we found an immediate increase, in the order of 10 % , in the diameter of the femoral artery on the opening of the a‐v fistula. This increase remained as long as the fistula was patent. The results were identical in 5 dogs. The effect on the diameter of clamping the artery for some time, with consequent removal of the clamp, was examined in 5 dogs. Removal of the clamp itself resulted in only a small and temporary increase in the diameter of the artery. It is concluded that the dilatation of the artery on opening of the fistula must be connected to the sudden increase in flow.