Evaluation of Coronary Vasoregulation Through Controlling Regional Myocardial Flow

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The intrinsic pattern of myocardial perfusion is determined by coronary vascular tone. Since the most principal sites of coronary vascular tone are the arterioles, the evaluation of coronary circulation on a microscopic level is indispensable to understand the coronary vasoregulatory function. In this study, we applied a newly developed nitric oxide (NO) microsensor to measure the concentration of vascular tissue NO,which plays an essential role in regional myocardial flow regulation. Furthermore, we visualized the spatial pattern of within-layr myocardial perfusion by digital-radiography combined with a molecular deposition technique. The analysis of myocardial perfusion pattern gives valuable information on the coronary vasoregulation because its characteristics of hierarchical structure are reflected in myocardial perfusion pattern. The experimental results were summarized as follows.The No sensor was inserted into the vascular media of the isolated canine femoral artery, perfused w … More ith a Krebs-Henseleit solution. NO concentration in the vascular media increased linearly with perfusion flow rate (flow shear stress on the vascular wall) and also with administration of a substrate of NO synthase, L-arginine. NO production, i. e., measured current was attenuated by perfusing a solution containing an inhibitor of NO synthase, N^<omega>-nitro-L-arginine. It is thus shown that the new NO sensor has satisfactory performance for a selective measurement of NO in the vascular media.Microregional myocardial flows are more uniform and continuous at high O_2 consuming or low O_2 supply states. There were transmural differences in a regional flow correlation in the left ventricular myocardium, which may be due to the higher O_2 consumption in the subendocardium. Since the regional flow correlation in the subepicardium was increased to a similar level observed in the subendocardium during hypoxia, the subepicardium will allow heterogeneous flow patterns in normoxia, but not anymore in hypoxia in comparison with the subendocardium. Less