THE PRESSURE-FLOW RELATION IN SKELETAL-MUSCLE PERFUSED ERYTHROCYTE SUSPENSIONS

In spite of numerous investigations of erythrocyte theology, there is limited information about the influence of erythrocyte suspensions on whole organ pressure-flow relationships, In this study, we present who le organ pressure-flow curves for resting vasodilated gracilis muscle of the rat, in which the microanatomy and vessel properties have been determined previously, For pure erythrocyte suspensions from donor rat s, the organ resistance increases only mildly with perfusion time (les s than a 5% shift over a one-hour perfusion time), while in contrast, erythrocyte suspensions containing leukocytes show an increases of res istance near 100% over a period of 25 min. Variation in pressure-flow curves in the muscle at the same arterial hematocrit between different rats is less than 15%. The pressure-flow relation for pure erythrocyt e suspensions depends on hematocrit, Shear thinning is exhibited at hi gh hematocrits, while Newtonian behavior is approached at arterial hem atocrits below 15%. The whole organ apparent viscosity for pure erythr ocyte suspensions (normalized by cell-free plasma resistance) is a non -linear function of hematocrit; at physiological pressures, it reaches values comparable to those of apparent viscosities measured in rotati onal viscometers or in in vitro tube flow (diameters greater than 0.8 mm), The apparent viscosities estimated from. the whole organ experime nts tend to be higher than those measured in straight tubes under in v itro conditions, The pressure-flow curves for pure erythrocyte suspens ions are shifted towards lower pressures than the curves for mixed sus pensions of erythrocytes at the same hematocrit and with leukocytes at physiological cell counts, These acute experiments show that pure ery throcyte suspensions yield highly reproducible resistances in the skel etal muscle microcirculation with dilated arterioles. Relative apparen t viscosities measured in vivo are higher than those measured in strai ght glass tubes of comparable dimesions.