Reactive hyperemia characteristics of the myocardium

Blood flow before and after occlusion of cannulated left circumflex coronary arteries of anesthetized open-chest dogs was studied using a continuously recording rotameter. Five- to one hundred and eighty-second occlusion periods were performed. Flow in excess of control flow (reactive hyperemia), peak flow, and duration of reactive hyperemia increased in magnitude following occlusions up to approximately 2 minutes. Flow debts estimated from control flows before occlusion were almost always overpaid. Series of 30-second occlusions showed that the reactive hyperemic blood flow responses were uniform in the same dog. In 15 dogs, the effect of drugs on myocardial reactive hyperemia was variable, isoproterenol, levarterenol and epinephrine usually did not alter or increased, while Pitressin decreased, reactive hyperemic blood flow. It is concluded that the myocardial response to anoxia is a reproducible phenomenon, increases with lengthening periods of anoxia, is variably affected by drugs and that the estimated flow debt for myocardial anoxia is overpaid.