Cardiac output, left coronary artery flow, central aortic blood pressure and myocardial metabolism have been studied in the intact unanesthetized dog during exercise. Cardiac output and left coronary artery flow increase 350 to 400% during moderately severe exercise. The primary mechanical determinant of this increase appears to be cardio-acceleration; the stroke volume and stroke coronary flow contribution is relatively mild. Myocardial oxygen usage increases 300% or more with only a small elevation of the percentage of extraction of oxygen. The large increase of coronary flow in the dog and the significant elevation in hematocrit supply the extra oxygen.

Phasic coronary inflow and its determinants have been studied by means of differential pressure, 1 a constant pressure flowmeter, 2 an orifice meter, 8 a cannulating type of electromagnetic flowmeter, 4 and a differential transformer. 15 All are cumbersome and require the use of anesthetics, surgical trauma, anticoagulants, and insertion of the device into the coronary artery of the open and/or closed chest anesthetized animal. To obviate these difficulties, a miniature electromagnetic flowmeter has been developed and adapted in this laboratory to permit its implantation for weeks on the coronary arteries of the dog. 6 The present communication is concerned with the use of this device in registering the moment-to-moment rate of inflow into the left coronary artery and its major branches, together with myocardial oxygen usage in the resting unanesthetized dog under essentially normal conditions. MethodsThe experiments reported here were done on more than 75 carefully selected healthy mongrel dogs (18 to 27 kg). These dogs underwent two to three months of a rigorous conditioning and training program preparatory to operation and postoperative studies. Each dog was trained to stand or to lie quietly on a pad.The operations were performed under clean conditions. The instruments and drapes were sterilized and the operative field was prepared as in aseptic surgery but no cap, face mask or gloves were worn. With pentobarbital anesthesia

The effect of excitement on phasic aortic pressure and flow, phasic left coronary flow, and myocardial metabolism has been studied in dogs 1–8 weeks after implantation of appropriate flowmeters and other devices. The rapid increase in heart rate and mild increase in blood pressure in the first few seconds tend to maintain coronary flow per minute despite a decrease in stroke cardiac output and coronary flow throughout the cardiac cycle. The main response is a delayed rise in coronary flow per minute resulting from further elevation of heart rate and blood pressure, a moderate increase in stroke cardiac output and a sizeable increase in stroke coronary flow, the latter being divided fairly evenly between systole and diastole. From 60 to 90% of the increase in mean coronary flow arises from the increase in stroke coronary flow, and the remainder from the increased number of heartbeats per minute. Some of the possible mechanisms concerned are discussed.

Page 817: C. R. Rayford, E. M. Khouri, F. B. Lewis and D. E. Gregg, “Evaluation of use of left coronary artery inflow and O2 content of coronary sinus blood as a measure of left ventricular metabolism.” Under methods line 12 should read: After the coronary sinus was carefully dissected, a suture was passed around it for cannulation. The suture was placed distal to the orifices of the coronary veins which drain near the mouth of the coronary sinus (verified at autopsy).

Experiments reported here show that the coronary sinus blood is derived almost entirely from the left coronary artery inflow and is not significantly contaminated with blood from other myocardial territories. The special cannula used for cannulating the coronary sinus permits drainage of all veins which empty into the coronary sinus. In consequence, the percentage of left coronary artery inflow recovered in the coronary sinus is high (usually 80–90%) and reasonably constant during changes in coronary perfusion pressure, aortic constriction, administration of epinephrine or norepinephrine, hemorrhage and reinfusion, induced ventricular fibrillation, and pulmonary artery constriction. The use of the arteriovenous oxygen difference between the arterial and coronary sinus blood in combination with left coronary artery inflow as a precise measure of left ventricular metabolism is validated under these experimental conditions. Submitted on January 29, 1959