Blood flow and in vivo apparent viscosity in working and non-working skeletal muscle of the dog after high and low molecular weight dextran.

We studied the effect of high and low molecular weight dextran on blood flow and in vivo apparent viscosity in the vasodilated vascular bed of working and non-working skeletal muscle. In 12 mongrel dogs, the calf muscle of one hindlimb was isolated. Vasodilation was induced either by sciatic stimulation setting the muscle at rhythmic work or by intraarterial infusion of papaverine. Blood flow was measured electromagnetically at different perfusion pressures. In vivo apparent viscosity was calculated by comparing pressure-flow relationship for blood and a reference solution. Viscosity in vitro was determined in a cone-plate viscometer. A hyperviscous state was induced by intravenous infusion of high molecular weight dextran (HMWD). Hemodilution subsequently was produced by administration of low molecular weight dextran (LMWD). After HMWD, blood flow decreased to 30% of control values in the non-working group and to 45% of control values in the working group. After subsequent infusion of LMWD, blood flow returned to 60% of control values in the non-working group and to 70% of control values in the working group. In vivo apparent viscosity increased to values 250% above control in the non-working group and to 120% above control in the working group following HMWD. After subsequent infusion of LMWD in vivo, apparent viscosity decreased, but remained at values 65% above control in the non-working group and 45% above control in the working group. Thus, the flow impairment induced by HMWD was less pronounced in the working muscle, indicating a flow-preserving effect of rhythmic muscle contractions in this state of disturbed blood rheology. In contrast, the flow-improving effect of LMWD by hemodilution was more pronounced in the non-working muscle.