Dispersion of indicator measured from microvessels of cat mesentery.

The indicator-dilution method was used to investigate blood flow in the microvascular network of the mesenteric membrane of the cat by replacing the normal blood flow into the mesenteric artery with a dextran-saline solution for a finite period of time. The dilution of the dextran-saline bolus as it flowed downstream was measured in a selected arteriole and its adjacent venule with a microphotometric system. Based on an in vitro calibration study done on glass capillary tubes, the measured optical density was converted to the hematocrit. The dilution curve for a finite injection and for a step injection, the mean transit time (MTT), and the appearance time for the arteriole and the venule were computed. The dispersion found in the arterial system, a network of diverging branches, was reasonably well simulated by the dispersion in a parabolic flow system. However, the dispersion found in the venules, where the irregular capillary blood flow converges, was considerably skewed from that in a parabolic system. A wide distribution of MTT was found for the arterioles and the venules, and there was considerable overlap in the MTT distribution for these two groups. This finding cannot be simulated by a network with a parallel arrangement. The difference in MTT for pairs of arterioles and venules was distributed over a narrow range, probably indicating shunt flow in the mesenteric microvascular network.