Measurement of RBC deformation and velocity in capillaries in vivo

Red blood cells (RBC) become deformed while flowing through capillaries. We captured images of blood flow in capillaries and of RBC in the rat mesentery using a high-speed camera at 2000 frames/s and then directly measured and estimated the deformation and velocity of RBC in a non-uniform capillary. The distribution of the capillary diameter was determined by image processing. We applied a deformation index and simple modeling to observe RBC deformation in capillaries. The average capillary diameter was approximately 6.2 μm, and the average velocity of RBC was about 1.85 mm/s. The average deformation index of RBC in the capillary was about 1.55. The present results showed that RBC in capillaries generally assume a specific shape depending on external forces such as the velocity of the blood flow and capillary diameter in vivo.