title: Physiologic effects of increasing hemoglobin concentration in left-to-right shunting in infants with ventricular septal defects.
abstract: We studied the acute effects of increasing hemoglobin concentration and hematocrit on the pulmonary and systemic circulations of nine infants with large left-to-right shunts. After isovolemic exchange transfusion, which was designed to raise hemoglobin but keep blood volume constant, a consistent rise in systemic and pulmonary vascular resistances occurred. This rise was comparable to those previously found in isolated circulations showing a linear relation between hematocrit and loge of the vascular resistance. These changes in resistance were accompanied by decreases in systemic and pulmonary blood flow and a marked decline in left-to-right shunt. Despite the decrease in systemic blood flow, there was no decline in systemic oxygen transport, and there may have been a marginal decrease in left ventricular stroke work. These observations help explain why the newborn with a large ventricular septal defect and a high hemoglobin concentration does not have clinical signs of a large left-to-right shunt, and also suggest that the postnatal decline in hematocrit has a substantial role in the normal fall in pulmonary vascular resistance after birth.
mesh_terms: D001775:Blood Circulation; D001810:Blood Volume; D005078:Exchange Transfusion, Whole Blood; D006321:Heart / Q000503:physiopathology; D006343:Heart Septal Defects; D006345:Heart Septal Defects, Ventricular / Q000097:blood / Q000503:physiopathology*; D006400:Hematocrit; D006439:Hemodynamics; D006454:Hemoglobins / Q000032:analysis; D006801:Humans; D007223:Infant; D008954:Models, Biological; D010100:Oxygen / Q000097:blood; D010101:Oxygen Consumption; D011652:Pulmonary Circulation; D014655:Vascular Resistance
chemical_list: D006454:Hemoglobins; D010100:Oxygen