Influence of wall surface on the flow of blood through endothelial-lined glass tubes

It has been proposed that the presence of endothelial cells lining small vessels decreases resistance to microcirculatory blood flow. Results of previous investigations have been inconclusive when fibrin-coated glass tubes were used to approximate the endothelial layer. Estimates of the decrease in apparent viscosity for blood flow in these tubes have ranged from near-zero to 50% when compared to flow in unlined glass tubes. The present study was devised to determine the effect of endothelial cell layer on blood flow in vessels under in vitro conditions in which pressure--flow relationships can be monitored precisely. Monolayers of human endothelial cells were grown over the major portion of the inner surface of glass tubes (I.D. = 1130 microns, length = 7.5 cm), and differential pressure and flow in the tubes were measured for plasma and suspensions of erythrocytes in plasma. Controls of phosphate buffer solution and culture medium were used to calculate inner diameters for both tube types. Results show statistically insignificant differences between apparent viscosities calculated from pressure-flow data in unlined and endothelial cell-lined tubes. These data indicate that the presence of endothelial lining does not have a marked influence on apparent viscosity of either blood or plasma when flowing through tubes of this diameter.