A model of stepwise isovolaemic blood exchange in anaesthetised, spontaneously breathing rats to evaluate the oxygen transport efficiency of artificial oxygen carriers.

Our research pursues the production of hypo-oncotic artificial oxygen carriers, based on artificial covalently cross-linked hyperpolymeric mammalian haemoglobins. To evaluate their in vivo efficiency in oxygen delivery to the tissue we developed a small animal model of stepwise isovolaemic blood exchange in anaesthetised, spontaneously breathing rats. With the aid of a two-way respiratory micro valve for small animals the overall oxygen uptake by the tissue of the animal can be determined. Measurements of oxygen contents in arterial and mixed venous blood and of some further blood parameters together with known oxygen-binding characteristics of artificial and native oxygen carriers, permits the determination of the way the two oxygen carriers contribute to the overall oxygen uptake. These so-called partial oxygen net to transport rates (i.e. partial oxygen uptakes), related to the corresponding intravascular mass flow of the transporters, are characteristic measures of the efficiency of the oxygen transporter, the so-called oxygen transport quality. Other biological indicators for an adequate oxygen supply are oxygen-dependent changes of ventilation, cardiac output, heart rate, and systemic vascular resistance. The performance of artificial oxygen carriers is elucidated by a comparison with experimental results from the analogous treatment of rats with non oxygen-transporting plasma expanders.