Abstract
Abstract
The purpose of this study was to test the hypothesis that under reduced flow conditions, spatial heterogeneity (segment-to-segment variability) of myocardial blood flow would be inversely proportional to the rate of perfusion and that vasoconstriction would alter this relationship in anesthetized open-chest dogs. A carotid-left circumflex coronary artery shunt was created. Coronary blood flow determinations employed the radioactive microsphere technique. Fifty tissue samples were obtained from the affected left ventricle, including subepicardial and subendocardial samples. The coefficient of variation (CV = 100 x SD/mean), an index of spatial heterogeneity, was computed. Flows were obtained under three separate conditions: control, a 50% flow reduction in the circumflex artery, and vasopressin infusion, in which the administered dose reduced circumflex artery flow by 50%. The within-animal CV increased from a control of 18 + 9 to 45 + 25 with partial occlusion and 46 + 18 with vasopressin. No significant differences in CV were found between the two reduced flow conditions. A significant linear relationship between CV and mean coronary flow was found (r = 0.51, P < 0.001) over the entire range of flows studied (CV = −0.34∗flow + 50.91) for control, 50% occlusion, and vasopressin treatment. The correlation was significantly improved (r = 0.69) using the equation CV = (1319.06/flow) + 4.44. Thus, the relative heterogeneity of coronary blood flow increased with reductions in coronary blood flow, regardless of the means of flow reduction.
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