Pressure-Flow Relationship of the Coronary System

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Abstract
In the coronary system of perfused dog hearts, the logarithm of flow was a linear function of the arterial perfusing pressure both when the ventricles were beating and fibrillating. Flow at all pressures was less during fibrillation. When the hearts were replaced by artificial fixed resistances, a similar logarithmic relationship was found but with a considerably different slope. This was due to decreases in the apparent viscosity of blood at higher pressures, changes which were actually measured by comparing the flow of blood with that of saline under these conditions. Apparent viscosity also decreased with the value of the fixed resistance so that, on the basis of these 2 variables, the extreme conditions under which blood could have the properties of a solid or a true soln. could be indicated. Changes of vol. of the coronary system with pressure were also measured and the effect of these on flow, both directly and indirectly by affecting apparent viscosity, was pointed out. The possible role of the vol. changes in modifying the massaging action of the myocardial contraction was also noted. All these factors, and probably more, contributed to the logarithmic pressure-flow-relationship.