Nonuniform distribution of microspheres in blood flowing through a medium-size artery

Suspensions of rigid microspheres, varying from 7.5 to 80 μ diameter, were injected into the left ventricle or ascending aorta of five anesthetized rabbits. After injection, an exposed branch of the femoral artery was frozen ultrarapidly, then removed; after histologic preparation, serial cross sections were studied microscopically. The radial distribution of the spheres within the vessel lumen was uneven, with a progressively decreasing concentration peripherally. This appeared to be proportional to sphere diameter and extended too far in from the periphery to be explained by entrance effect only. Microspheres of 7.5 to 10 μ diameter had the radial distribution which most closely approached that of erythrocytes in these same arteries.