Blood-flow distribution at branches of arterial microvessels in the frog mesentery

Abstract

The blood-flow distribution was studied in 49 bifurcations of arterial trunks 25.7 μ in diameter into branches 0.9 μ in diameter in the mesentery ofR. temporaria. The flow was calculated as the product of the linear velocity of blood flow and the area of cross-section of the vessel. The linear velocity was measured by impulse digital chronometry of the erythrocyte transit time, and the geometry of the bifurcation was studied in intravital photographs. The asymmetrical structure of the bifurcation was established: One branch had a lumen 2.2 times greater than the other, and a smaller angle of turn (29° and 59°). The flow into branch I was 3 times greater than the flow into branch II, as the result of its larger lumen and the greater linear velocity of the blood flow. According to calculations, the specific resistance of turn of the branch was negligible compared with the total resistance to its blood flow; hence it follows that the angle of turn of the branches is not an important regulator of the blood volume flowing through it. The correlation found experimentally between the blood flow in the branches, their radius, and their angle of turn is well described by equations of an “optimal” model of vascular ramification.