Effects of coronary and extravascular pressure on intramyocardial and epicardial blood velocity.

In open-chest anesthetized dogs we measured 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) during changes in perfusion pressure and extravascular pressure. Circumflex artery diameter was also measured during pressure changes to directly assess vascular compliance. At low and normal arterial pressures (less than 125/86 mmHg) 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 greater than 150/106 mmHg, 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 greater than 125 mmHg, the cross-sectional area change per millimeter of mercury was approximately three times less than at pressures between 30 and 75 mmHg, 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 less than 0.05). However, right ventricular bypass (0 right ventricular pressure) did not alter the phasic nature of blood flow velocity in the septal artery. From these results we confirmed that epicardial capacitance is inversely related to distending pressures.(ABSTRACT TRUNCATED AT 250 WORDS)