The coronary circulation

THE experiments described here were performed with a method, the details of which have been given in earlier communications (1, 2). The method consists in establishing a perfusion of a large branch of a coronary artery at constant pressure, and in measuring the inflow of blood into the perfused artery by a hot-wire anemometer and a continuous method of registration. The separation of the coronary circulation in the perfused area from the systemic circulation enabled us to study the changes in the coronary blood flow which follow variations of the aortic pressure and of the output of the heart, in so far as these variations affect the strength of the cardiac contractions (3). It is obvious that, since in these experiments the coronary system is supplied with blood from two independent sources, we can investigate the effects of various agencies either by their direct administration to the perfused area, or by their administration to the rest of the cardiac muscle through the coronary supply of the aortic origin. In view of the contradictions which exist as regards the effect of temperature on the coronary circulation, we carried out a series of experiments with the object of separating the effects due to the direct influence of temperature on the coronary blood vessels from those which may be produced indirectly as the result of changes in the strength of contraction and in the rate of the heart beat.