Regional blood flow and oxygenation of the rabbit heart subjected to acute coronary occlusion — effect of phenoxybenzamine

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Abstract
The effect of phenoxybenzamine (2 mg/kg) on subepicardial (EPI) and subendocardial (ENDO) blood flow and oxygenation was determined in ischemic and non-ischemic areas of hearts subjected to acute coronary occlusion in 24 pentobarbital-anesthetized open-chest New Zealand white rabbits. Ten minutes after occlusion, blood flow measured with radioactive microspheres was 57% lower in the occluded region compared to the non-occluded area. There were no EPI vs. ENDO differences at this time. Phenoxybenzamine was then administered and one hour after occlusion, flow in all areas was significantly reduced. Flow in the occluded area fell to a lesser extent than in the non-occluded area. ENDO flows were lower than EPI in both areas. After occlusion, relative tissue PO2 fell significantly in the affected area. No other changes were significant. Phenoxybenzamine lowered relative tissue PO2 in the occluded ENDO but had no other effect. This indicates that the relationship of O2 supply to consumption is preserved in the heart after phenoxybenzamine except in the occluded ENDO. In this region, the fall in relative tissue PO2 indicates that the reduction in flow is large compared to any change in metabolism. The reduction in this relationship may be due to reduced perfusion pressure for collateral flow and/or “coronary steal”.