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Two models of increased coronary resistance with normal epicardial arteries. A. The increased resistance to flow (R2), which could be either a fixed anatomic or a functional defect, is at the arteriolar level. B. The increased resistance to flow (R3) is at the intramural prearteriole. P1 and P2 = pressures proximal and distal to the abnormal resistance, respectively; R1 = the normally responsive subepicardial arteriole [80]. Refer to text for a detailed explanation.
