Prediction of regional myocardial blood flow in dogs

Three indices of regional coronary flow were tested to determine if a good correlation between calculated driving pressure and flow could be found. Four different myocardial depths were examined. All three indexes were based on subtraction of a backpressure to flow. The first assumed backpressure to be equal to ventricular pressure; the second assumed backpressure to be twice ventricular pressure; and the third index assumed backpressure to be zero and thus was simply coronary pressure. Only the index that used left ventricular pressure as the backpressure to flow exhibited proportionality for the subendocardial samples. Similarly, only coronary pressure yielded a good fit for the subepicardial samples. Although subendocardial flow was always in proportion to the index, the index was poor at predicting the absolute value of that flow. The usefulness of such a directional predictor of subendocardial perfusion was illustrated by examining the phase shift resulting from partial occlusion of a coronary artery. The index predicted that subendocardial flow would be lower when coronary pressure was reduced by partially occluding the coronary vessel than when it was presented with an equivalent steady pressure. Microsphere measurements confirmed this prediction. We conclude that an index that assumes ventricular pressure to be the backpressure to flow is an accurate predictor of relative changes in subendocardial perfusion.