STUDIES ON THE EFFECT OF CARDIAC IRREGULARITY ON THE CIRCULATION II. THE ESTIMATION OF CARDIAC OUTPUT IN DOGS SUBJECT TO ARTIFICIAL AuRIcumAR FIBRILLATION

In preceding papers (1, 2, 3) we have reported observations upon the rate of blood flow in regular and irregular tachycardias in normal unanesthetized dogs. In those experiments the values for the relative blood flow were obtained by calculating the ratio of the oxygen removed from each liter of blood by the tissues curing the artificial rhythm to the oxygen removed during the normal rhythm, the ratio during the normal period being placed at 100. We did not estimate the oxygen consumption because of the reaction of untrained unan-esthetized animals to the procedures used in measuring it. We did not wish to anesthetize the animals because of the secondary changes that accompany anesthesia. Because of the undesirable effect of morphine on the respiration and in slowing the heart rate we decided against its use. We have also performed a few experiments on trained unanes-thetized dogs. In these we have been able to measure the oxygen consumption and calculate the minute volume output of the heart (Fick's method). The results in these experiments agreed so closely with the calculations made of the relative blood flow that it seemed useless to accumulate a larger amount of data on the minute volume output of the heart under these conditions than is here presented. METHODS All the dogs were trained to breathe in a Benedict spirometer before they were used in these experiments for 20 to 30 minutes a day for 10 days to 2 weeks. At the end of this time they lay quietly on the board during metabolism tests withou