Cardiovascular and hemorheological effects of three modified human hemoglobin solutions in hemodiluted rabbits.

The cardiovascular effects of human albumin (Alb) and three human hemoglobin (Hb) solutions, dextran-benzene-tetracarboxylate Hb, alphaalpha-crosslinked Hb, and o-raffinose-polymerized Hb were compared in anesthetized rabbits undergoing acute isovolemic hemodilution with Hct reduction from 41.4 +/- 2.7 to 28.8 +/- 1.6%. The impact of the vasoconstricting properties of Hb was examined by measuring heart rate (HR), mean arterial pressure (MAP), abdominal aortic, and femoral arterial blood flow, vascular resistance (VR), and aortic distension during the first 3 h after hemodilution. The impact of the hemorheological parameters was assessed by measurements of hemodiluted blood viscosity. In contrast to Alb, the Hb solutions elicited an immediate increase in MAP (20-38%). The effects of Alb and Hb solutions on HR, as well as on aortic and femoral arterial blood flow, were similar. VR decreased with Alb (20-28%) and increased with all three Hb solutions (30-90%), but the MAP and VR rising trends were different with each Hb solution. Aortic distension decreased in Hb groups compared with the Alb group for the first 60 min. The viscosity of hemodiluted blood was similar for all groups at high shear rates but was dependent on the viscosity of the solutions at low shear rates. We conclude that the vasoconstriction elicited by the Hb solutions overrides the vasodilation associated with viscosity changes due to hemodilution and would be the major factor responsible to the cardiovascular changes.