EFFECTS OF CORONARY AND EXTRAVASCULAR PRESSURE ON INTRAMYOCARDIAL AND EPICARDIAL BLOOD VELOCITY

In open-chest anesthetized dogs phasic coronary blood velocity in an epicardial artery (left anterior descending), a small epicardial artery (within 0.5 cm before penetration into the myocardium) and an intramyocardial artery (septal) were measured during changes in perfusion pressure and extravascular pressure. Circumflex artery diameter was measured during pressure changes to directly assess vascular compliance. At low and normal arterial pressures (< 12586 mm Hg) and during aortic insufficiency, the phasic character of blood flow velocity in the large epicardial arteries was markedly different from that in the small epicardial and septal arteries: there was retrograde systolic blood flow velocity in the septal artery and small epicardial artery, whereas antegrade blood flow velocity persisted in the left anterior descending artery. At pressures > 150/106 mm Hg, the differences in the phasic character of blood flow velocity in the left anterior descending artery from that in the septal artery and small epicardial artery were small and decreased as aortic pressure increased. At pressures > 125 mm Hg, the cross-sectional area change per millimeter of mercury was .apprx. 3 times less than at pressures between 30 and 75 mm Hg, indicating decreased coronary compliance at the higher pressures. Increasing extravascular pressure in the septum (right ventricular hypertension) greatly increased retrograde systolic blood flow velocity in the septal artery (P < 0.05). Right ventricular bypass (0 right ventricular pressure) did not alter the phasic nature of blood flow velocity in the septal artery. Evidently, epicardial capacitance is inversely related to distending pressures. At low and normal arterial pressures epicardial coronary capacitance significantly distorts phasic intramyocardial perfusion and the phasic nature of intramyocardial blood velocity is intimately related to extravascular pressures.