A Comparison of Blood Viscosity Measured In Vitro and in a Vascular Bed

Abstract

DJOJOWGITO,A. M., B. FOLKOW, B. UBERG and S. W. WHITE. A comparison of blood viscosity measured in vitro and in a vascular bed. Acta physiol. scand. 1970. 78. 70-84.Blood viscosity in vivo ("apparent viscosity") and its variations with flow rate was analyzed in the maximally dilated calf muscle vascular bed of the cat by comparing pressure-flow relationships for blood and a Newtonian fluid (dextran-Tyrode) over a flow range between 60 and 0.2 ml/min x 100 g tissue. Viscosity in vitro for the same perfusates was measured in a cone-plate viscometer.-Apparent viscosity was much lower (approximately 50 76 ) than iii vitro values at high shear rates, with less variation between animals. I t increased with decreased flow but was as a maximum only doubled, which occurred at flows around 0.5 ml/min x 100 g. Since such small flows normally occur in constricted vessels with higher flow velocities than at maximal dilatation, the range of viscosity changes with flow in the intact circulation is probably decidedly smaller. The steep rise of viscosity in vitro at quite low shear rates had no counterpart in vivo; in fact, viscosity then tended to fall again. The discrepancies between blood viscosity in vivo and in vitro seem to be related to vascular dimensions, favour-

Capillary Transport in Relation to Perfusion Pressure and Capillary Flow in Hyperemic Dog Skeletal Muscle in Shock

“…The reduction in the maximal value of PSp is consistent with the re duction of CFC seen in cat skeletal muscle, both in hemorrhagic shock [6] and in induced RBC aggregation [9]. There may thus be a reduction of PSp by vessel obstruction.…”

“…It is, therefore, important to fix the vascular bed in a state of maximal vasodilation for comparison of the exchange in control and shock at different levels of perfusion pressure and flow. This point has been stressed, for example, by Djojosugito et al [9] and by Lundgren and Mellander [11]. In the present study, vasodilation was induced by adding papaverine to the injectate, found in other experiments to give the same vasodilation as muscular work combined with ischemia [4].…”

“…With return towards higher flows and perfusion pressures, PSp returned to the same level as before reduction. This reduction of PSp probably signified a more inhom ogeneous distribution of flow through capillaries at low pressures and flows [12,13], rather than a reduction of the open capillary bed, as CFC was unchanged down to a perfusion pressure 20 mm Hg during similar experimental conditions [9].…”

Limited hemodilution in hemorrhagic shock in dogs: Effects on central hemodynamics and the microcirculation in skeletal muscle

“…From intravital microscopic observation [6,23,25] as well as findings from in vivo studies on isolated vascular beds [5,16,21], excessive red cell aggregation in posteapillary vessels, decreased deformation of slowly moving red cells and complete obstruction of vessels from stagnant clumped red cells have been reported. On the other hand studies from in vitro flow devices suggest, that decreasing the flow velocity and increasing the hematocrit leads to a tremendous increase in viscous resistance of blood [11,37,39].…”

Rheological properties of human erythrocytes and their influence upon the “Anomalous” viscosity of blood

“…It is very unlikely that this question can be answered adequately from the analysis of pressure-flow curves obtained in entire organs. The presently available data are equivocal [1,39,46]. The presence of a positive intercept in pressure-flow curves (zero flow at finite pressure) which is customarily related to critical closure of small blood vessels (BuI~TON [21 ]) may at least in part be related to the rheological properties of red cell aggregates.…”