DIASTOLIC-SYSTOLIC DIFFERENCES IN CORONARY BLOOD-FLOW - EFFECT OF STENOSIS AND TACHYCARDIA IN THE ANESTHETIZED DOG

Blood flow in the left coronary artery is lower in the systole than in the diastole. This difference is attenuated in the presence of severe stenosis, which affects the flow more during the diastole than during the systole. Some explanations have been suggested: epicardial vasodi latation distal to the stenosis, a decrease in myocardial contractilit y and impairment of the intramyocardial pump effect. The present inves tigation in anaesthetized dogs showed that, in the presence of severe stenosis, the attenuation of the diastolic-systolic coronary flow diff erences occurs together with distal vasodilatation in the epicardial l ayers of the myocardium. ?his attenuation may be even greater if furth er vasodilatation is induced by increasing the heart rate. No evidence of reduced myocardial contractility was observed. In addition, it was found that the onset of the systolic rise of the coronary blood press ure below the stenosis occurs before that of the aortic blood pressure . This finding may serves as evidence for the role played by the intra myocardial pump mechanism in causing the systolic reduction of coronar y flow. Since this mechanism is believed to propel some blood back int o the aorta during the systole, the impairment of this retrograde flow caused by the stenosis could also account for the reduction of the di astolic-systolic flow differences.