QUANTITATIVE RELATION BETWEEN REACTIVE HYPEREMIA AND THE MYOCARDIAL ISCHEMIA WHICH IT FOLLOWS

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Abstract
The quantitative effect on coronary flow of different periods of myocardial ischemia was observed in an isolated prep, of the dog heart with fibrillating ventricles. Blood-flow through the fore-limb of the same animals was studied simultaneously under the same conditions. In this prep, coronary flow was detd. by active changes in the coronary vessels. In the heart, correlation of the components of the ischemic periods with those of the subsequent hyper-emic periods and analysis of the relationships found, led to the following conclusions: The coronary blood supply is greater than that necessary to meet myocardial needs. The hyperemia due to the ischemia is more than adequate to make up for the myocardial deficit acquired. The cause of the hyperemia is apparently an easily diffusible dilator substance which is destroyed in the presence of O2. The degree of hyperemia not only varies with the duration of the ischemia and hence with the accumulation of the dilator substance, but also with the responsiveness of the coronary vessels to this substance. The coronary vessels are decidedly more reactive to ischemia than are the limb vessels. The importance of reactive hyperemia as a mechanism operating to compensate for any inadequacies in coronary flow in the intact animal is emphasized, and the bearing of these data on reactive hyperemia in other vascular beds is suggested.

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