Moderate normovolaemic haemodilution increases regional myocardial blood flow but has no effect on experimental infarct size

Regional myocardial blood flow was measured with radioactive microspheres before and 1, 3, 6, and 12 h after occlusion of the left anterior descending coronary artery (LAD) in anaesthetized cats. In one group of cats, 1 h after LAD occlusion, moderate normovolaemic haemodilution was started with a dextran 40 solution, which reduced the haematocrit by 20-25% throughout the rest of the experiment. In the other group, the haematocrit was kept at the original level. Infarct size was measured planimetrically 12 h after the coronary ligation, using the tetrazolium staining technique for disclosing the ischaemic myocardium. Haemodilution increased blood flow in the non-ischaemic myocardium and in the so-called 'border zone' comprising both normal, and ischaemic tissue. However, in the severely ischaemic myocardium dependent on collateral blood flow, where there was no admixture of non-ischaemic myocardium, the blood perfusion was not significantly affected by the haemodilution. After 12 h of ischaemia the infarct size in the control group was fully comparable with that in the haemodiluted group: 28 +/- 3 and 27 +/- 4 (percentage of the left ventricle, mean +/- SEM), respectively.