Hemodynamic responses to acute hematocrit and blood volume alterations in rats.

Previous investigations of polycythemia in rodents failed to delineate the effects of the increased hematocrits from the effects of possible changes in blood volume. The hemodynamic responses of anesthetized rats to acutely produced increases in hematocrit and blood volume were therefore studied in this experiment. Acute isovolumetric polycythemia decreased O2 transport from a control value of 44.9 to 35.1 ml/min/kg 60 min after the exchange-transfusion. However, the high venous O2 content (over 12 Vol.-%) following the production of isovolumetric polycythemia suggested that there was still sufficient oxygen available to the tissues. Hypervolemia significantly modified the response to acute polycythemia. When hematocrit was maintained at a constant level, acute hypervolemia increased O2 transport (to 54.6 ml/min/kg after 60 min), and when acute hypervolemia and polycythemia were induced simultaneously, O2 transport was transiently increased (to 57.5 ml/min/kg after 15 min) and then returned to a value similar to the control level.