The effects of mild normovolemic hemodilution on regional flow, oxygenation, and small vessel blood content in the rabbit heart subjected to acute coronary occlusion.

The effect of mild hemodilution (hematocrit, 19%) on ischemic and nonischemic regions of myocardium during acute coronary occlusion was studied in 41 pentobarbital-anesthetized, open-chest New Zealand white rabbits. Blood flow in the control area determined with radioactive microspheres was unaffected by occlusion and increased 61.8% following hemodilution. The endo/epi ratio remained at about 1.0. Occlusion decreased flow in the affected region to 41% of the control myocardium, and endo/epi ratio decreased significantly to 0.76. Hemodilution raised flow in this area 84.3%. Occlusion increased small vessel blood content (a measure of open capillary density) in the ischemic region significantly. Hemodilution further significantly increased this volume in the occluded area, although the increase in the control region was not significant. Relative tissue pO2, measured polarographically, declined significantly following occlusion in the affected area. Isovolemic hemodilution did not affect relative O2 tension in either area. The data indicate that during mild hemodilution, the O2 supply-demand status of both the occluded and nonoccluded myocardial regions is maintained.