Myocardial Blood Flow and Oxygen Uptake During Acute Red Cell Volume Increments

The role of red cell mass in the regulation of coronary blood flow and myocardial oxygen consumption has been examined after acute transfusion of sedimented red cells. Patients with substantial blood-loss anemia had a lower than normal left ventricular oxygen uptake, despite a high myocardial blood flow at rest. A 50% rise of hematocrit reduced coronary flow markedly. Although systemic arterial pressure, cardiac output, and left heart work rose, myocardial oxygen consumption was unchanged. Red cell transfusion of normovolemic dogs resulted in a decrease of both myocardial flow and oxygen uptake associated with an elevation of time-tension index and left ventricular work, accelerated isometric contraction and prolonged systole. There was no evidence of ischemia or change of left ventricular hemodynamic parameters that would account for the reduced myocardial blood flow and oxygen uptake. These findings, in the presence of an increased oxygen carrying capacity and extraction, would appear to be related principally to enhanced blood viscosity.