Red Cell Interactions with the Microcirculation

We have measured RBC velocity profiles for mammalian arterioles and venules from high-speed cinematographic motion pictures. Measurements were made at 320× and 400× optical magnification over an averaging time period of 10 ms. In vivo profiles are uniformly nonsymmetrical, the RBCs exhibit rotation, and they frequently deviate sidewise from the overall axial direction of motion. In general, this is more pronounced on the venous side. Since all of the profiles are time variant and the average values are synchronous with the midstream velocity, individual RBC velocities will vary about the average. Profiles become more blunted in vessels with smaller diameters. In vessels below 16 μm diameter, the velocity gradients between adjacent RBCs are quite small; for large vessels, recognizable profiles develop and become fully developed in blood vessels above 30 μm in diameter. This blunting is further affected by the midstream velocity and the local hematocrit; when the velocity is reduced below 1.2 mmls and/or an increased hematocrit is present, the profile becomes more blunted.