Blood rheology and systemic oxygen transport.

The interrelationship between systemic oxygen transport and hematocrit, has been studied under various conditions, while the influence of plasma viscosity on oxygen transport and tissue oxygenation has not entirely been explored. In experiments in dogs the plasma viscosity was increased either by isovolemic hemodilution with 6% hydroxyethyl starch (HES) 200/0.62, or 6% dextran-70, or by infusion of dextran-500 in a volume equivalent to 4% of blood volume from baseline to 3 mPa.s. Cardiac output and regional blood flow were assessed by means of radioactive labelled microspheres and local tissue oxygenation by means of pO2 multiwire surface electrodes. In normotensive healthy animals elevated plasma viscosity did neither jeopardize systemic nor regional blood flow; local tissue oxygenation of skeletal muscle remained unchanged or was even improved. We conclude that among the rheological factors influencing oxygen transport, the hematocrit plays the predominant role, while plasma viscosity is of minor importance.