Variation in axial velocity profile of red cells passing through a single capillary

We have used an analysis of the velocity of individual red cells as the cells pass through a capillary in order to estimate the variability in cross-sectional area of the capillary lumen available for flow along the length of the vessel. The purpose of the study was to determine if there were irregularities of sufficient magnitude and frequency to support Secomb's hypothesis that local constrictions in the capillary lumen could hinder blood flow at low driving pressure, due to the energy required to deform red cells as they pass through the constriction. All capillary segments analyzed to date, in both rat and frog, have shown regions where the velocity of individual cells is consistently faster or slower than that of the mean velocity of all other cells in the same segment. There are approximately two constrictions per 100 microns in the rat and one per 100 microns in the frog. On average these constrictions appear to reduce the cross-sectional area by 30% in the rat and 16% in the frog. These results provide evidence in support of Secomb's hypothesis. In addition, our results from one bifurcation indicate that the capillary lumen increases in cross-sectional area as one moves from the parent vessel to the region of the bifurcation. Downstream of the bifurcation the lumen rapidly decreases in area by 45 to 54%. Thus a red cell must undergo even greater deformation as it passes through a capillary bifurcation than it will in most other sections of the capillary network.(ABSTRACT TRUNCATED AT 250 WORDS)