CHANGES IN THE CORONARY CIRCULATION FOLLOWING INCREASED AORTIC PRESSURE, AUGMENTED CARDIAC OUTPUT, ISCHEMIA AND VALVE LESIONS

Abstract

Records of the rates of flow and of the total inflow into the left coronary artery of dogs were taken with the orifice meter together with the aortic and peripheral coronary pressures under different dynamic conditions. During both systole and diastole the total and intramural flows increase following aortic compression, blood transfusion, ischemia and only during systole in aortic insufficiency, while in diastole of the latter the intramural flow decreases and the total flow increases. The pressure differentials follow the direction of the metered flows but they provide only a qualitative measure of flow. These differential pressure changes may be less than, greater than or the same as the flow alterations. The latter finding permits certain deductions: (1) that changes, especially during diastole, in the ratio of intramural flow to differential pressure indicate alterations in size of the available coronary bed, and (2) that changes in systolic peripheral coronary pressure reflect changes in extravascular compression or support. Calculations indicate that following increase of cardiac work through simple elevation of aortic pressure the available coronary bed becomes smaller while in ischemia and in augmented cardiac work due to increased cardiac output the bed increases, because in the former the diastolic flow increases less than the pressure differential while in the latter the reverse is true. Furthermore the minute flow per mm. Hg. aortic pressure decreases with aortic compression and increases with augmented venous return. In elevation of aortic pressure, augmented cardiac output, aortic stenosis and aortic insufficiency, but not ischemia, the extravascular support is presumably increased as evidenced by the increased peripheral coronary systolic pressure. Failure of extravascular compression to rise concomitantly with the aortic systolic pressure is in part responsible for the augmentation of systolic flow in these conditions and its converse for the reduction of flow in aortic stenosis.