Hemodynamic response to normovolemic polycythemia at rest and during exercise in dogs

Very little is known about the influence of polycythemia on oxygen transport during exercise. We studied chronically instrumented dogs trained to run on a treadmill before and after their hematocrit had been increased by isovolemic exchange transfusion with packed red blood cells. With normovolemic polycythemia, cardiac output fell in a linear fashion as hematocrit was increased to 65%, but these changes were balanced by an increasing oxygen content resulting in constant systemic oxygen transport. Oxygen consumption was unchanged both at rest and during exercise after induction of polycythemia. To investigate the effect of polycythemia on oxygen transport further, we measured both mixed venous Po2 and lactate. Mixed venous Po2 increased and lactate remained unchanged both at rest and in exercising polycythemic dogs. Thus, we conclude that, in conscious animals, systemic oxygen transport is well preserved with increasing hematocrit to at least 65%.