MECHANISMS FOR INCREASED BLOOD-FLOW RESISTANCE DUE TO LEUKOCYTES

Despite the small number of leukocytes relative to erytkrocytes in the circulation, leukocytes contribute significantly to organ blood flow resistance. The present study was designed to investigate whether inte ractions between leukocytes and erythrocytes affect the pressure-flow relationship in a hemodynamically isolated rat gracilis muscle. At con stant arterial flow rate, arterial pressure was increased significantl y when relatively few physiological counts of leukocytes were added to a suspension containing erythrocytes at physiological hematocrits. Ho wever, the arterial pressure after perfusion of similar numbers of iso lated leukocytes without erythrocytes was only slightly increased. An increase in resistance was also observed when leukocytes were replaced with 6-mu m microspheres. We propose a new mechanism for increasing t he hemodynamic resistance that involves hydrodynamic interactions betw een leukocytes and erythrocytes. In the presence of larger and less de formable leukocytes, erythrocytes move through capillaries more slowly than without leukocytes. Therefore erythrocytes are displaced from th eir axial positions. Slowing and radial displacement of erythrocytes s erve to increase the relative apparent viscosity attributable to eryth rocytes, thereby causing a significant elevation of organ blood flow r esistance.