EFFECTS OF VISCOSITY, ISCHEMIA, CARDIAC OUTPUT AND AORTIC PRESSURE ON CORONARY BLOOD FLOW MEASURED UNDER A CONSTANT PERFUSION PRESSURE

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Abstract
The effects of several altered circulatory conditions on coronary flow was studied during perfusion of the coronary artery with blood under a constant head of pressure. In elevation of blood pressure and increased cardiac output following augmented venous return, the coronary bed receives an increased blood supply because, although the aortic pressure rises, the peripheral coronary pressure fails to rise as much. The increase of flow which actually occurs is generally somewhat greater than that predicted from the differential pressures. In addition, the reduction in viscosity of the perfusate by substitution of Locke''s soln. for blood causes an unexpectedly large increase of flow[long dash]-amounting at times to 300-400% of the rate observed with blood. Also, a period of ischemia of the coronary bed greatly increases the flow during the initial period of restored circulation. Such flow augmentations are suggested by the concomittant slight decrease in peripheral coronary pressure, but the method of differential pressures fails to indicate the magnitude of the flow change. Peripheral coronary pressure curves can accurately represent the time relations of the change of flow to the aortic pressure variations but do not indicate the magnitude of the change in resistance to flow under various circulatory conditions; hence the flow itself is underestimated.

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