Evaluation of myocardial blood flow heterogeneity by using molecular deposition technique and fractal analysis

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The goal of this study was to evaluate microheterogeneity of myocardial blood flow and a functional zone of vascular control, and their dependency on arterial oxygen tension (PO_2). We introduced a new method of imaging myocardial blood flow with highest spatial resolution so far, and succeeded to visualize regional blood flow of the rabbit left ventricle during normoxic and hypoxic states. We injected ^3H-labeled desmethylimipramine into the left ventricle of the anesthetized rabbit heart (n=12) , and imaged myocardial blood flow distribution using digital-radiography with highest resolution of 0.01 mm^2. The image was quantitated ; we computed the coefficient of variation (CV) and the correlation between adjacent regional fows (C_A). CV was resolution dependent ; with increasing resolution ranging from 0.01 mm^2 to 1 mm^2, CV increased in both normoxic and hypoxic states (p<0.001). At all resolution, CV was larger during normoxia(PO_2=97<plus-minus>20 mmHg)than hypoxia (PO_2=26<plus-minus>5 mmHg)(p<0.001) , while C_A was smaller in normoxia than in hypoxia(p<0.001). In the normoxic state, C_A of the deep myocardial layr is larger than that of superficial myocardial layr (p<0.001). The hypoxic perfusion resulted in no difference in C_A between the myocardial layrs. We conclude as followings : 1) The heterogeneity of myocardial blood flow increased with measurement resolution, and there is surprising microheterogeneity at resolution of 0.01 mm^2.2) In response to decreased arterial PO_2, the heterogeneity of blood flow decreased regardless of spatial resolution, and the functional zone of vascular control enlaged as evaluated by C_A. The latter suggests that the main site of vascular control shifts toward larger arteriole during the hypoxic state.