The influence of erythrocyte concentration upon the pressure-flow relationships in the dog's hind limb.

Since alterations in cell-plasma ratios are of paramount importance in the assessment of periplieral resistance, a study of pressure-flow relations was made in which blood having wide hematocrit values was perfused through a dog's hind limb in which collateral circulation has been excluded. When vessels were moderately dilated by denervation, the relative apparent viscosity was not affected by the perfusion pressure. When, however, the vessels were maximally dilated after a preceding period of anoxia, the relative apparent viscosity was found to become greater as perfusion pressure was progressively reduced. The in vivo relative apparent viscosity did not significantly exceed that of plasma until the erythrocyte concentration reached 30 per cent.