THE EFFECT OF THE EXTRAVASCULAR SUPPORT OF THE VENTRICLES ON THE FLOW IN THE CORONARY VESSELS

Abstract

A method is described for measuring total coronary inflow and coronary sinus outflow in a completely denervated heart-lung of isolated heart prep. in which the coronary arteries are perfused with blood at constant pressure and all other variables are controlled. Expts. show that changes in heart rate alone do not appreciably alter the rate of the total coronary blood flow. The rate of total coronary blood flow varies directly with the coronary per-fusion pressure, other conditions being constant. When all other variables are kept constant, the total coronary inflow is decreased by raising the mean pressure within the heart cavities and thus the mean intramuscular tension within their walls. Decreasing these pressures increases the total coronary inflow. This change in coronary inflow can be effected by varying the pressures and tensions of each side of the heart alone. When the mean pressure of the heart cavities is changed, the rate of sinus outflow varies in a direction opposite to the total coronary inflow, so that the ratio between the 2 varies widely. Changes in sinus outflow depend almost entirely on changes in pressure in the rt. side of the heart, the pressures in the It. side having little effect. The coronary sinus outflow may persistently exceed the total coronary inflow when the mean pressure in the heart cavities and the mean intramuscular tension of their walls are high relative to the coronary perfusion pressure; changes in the pressure in the rt. heart are more effective than in the lt. in this regard. The significance of these findings is discussed. The coronary sinus outflow cannot be used as a measure of the total coronary flow. Significant passive changes in the calibre of the coronary vessels are produced by altering the extravascular tension in the heart walls and this factor as well as variations in the aortic pressure must be ruled out before changes in coronary inflow can be ascribed to active changes in the tone of the muscles in the coronary vessel walls.