Improved oxygenation of ischemic myocardium by hemodilution with stroma-free hemoglobin solution.

Experiments were conducted in anesthetized open-chest dogs subjected to occlusion of the left anterior descending coronary artery for three hours. The oxygenation of myocardial tissue was monitored by a polarographic technique capable of recording simultaneously the oxygen tension (Po2) of myocardial tissue and electrograms. Ischemic injury was monitored by means of ST-segment elevations on myocardial and epicardial electrograms. The volume of the myocardial infarct was measured at the end of each experiment by incubation of transverse slices of left ventricle in a solution of nitroblue tetrazolium and by separation of the unstained (ischemic) from the stained (normal) portions. In one group of dogs, hemodilution was performed after 15 minutes of ischemia by exchanging blood with a stroma-free hemoglobin solution (from a hematocrit reading of 45 +/- 3 percent to 23 +/- 2 percent). Changes occurring in this group were compared with those occurring in dogs that did not undergo hemodilution, underwent hemodilution with dextran 75, or were transfused with whole blood. Hemodilution with hemoglobin reduced aortic and left ventricular filling pressures while increasing coronary blood flow, increased myocardial Po2 from 2 +/- 2 mm Hg to 8 +/- 2 mm Hg (P less than 0.005), lowered the ST-segment elevation of both myocardial and epicardial electrograms, and reduced the volume of the myocardial infarct. These effects were unmatched by hemodilution with dextran or infusion of whole blood.