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.