Changes in Heart Rate on Intravenous Infusion in Dogs with Chronic Cardiac Denervation. ∗

Abstract

Discussion and conclusions

In all cases, an increase in heart rate resulted from intravenous infusion of fluid into dogs with chronic cardiac denervation, the increments ranging from 4 to 31 beats per minute. In those cases in which it was measured, right atrial pressure increased; in individual experiments, the increase in pressure was proportional to the volume infused. In the experiments with dextran, the maximal increase in right atrial pressure preceded the maximal increase in heart rate by intervals ranging from 4 to 54 minutes. Part of this wide variation was explained by the fact that the peak of the increase in rate often was approached so slowly that it was difficult to locate it precisely in relation to the time axis. In the experiments with saline, there was a clearly defined lag of 2 1/2 minutes in the example shown in Fig. 1, but in the others the small degree of cardiac acceleration made it impossible to decide if a lag was present. Similarly, a lag between the maximal increase in venous pressure and the maximal increase in heart rate has been reported by Coleridge and Linden(5) in a study of the Bainbridge reflex in intact anesthetized dogs.

When exercised, dogs with cardiac denervation achieve a maximal heart rate in 90 to 100 seconds. An increase in the transmural atrial pressure, due to an increase in depth of respiration and in return of blood to the heart, might be expected to develop early in exercise and to be sustained throughout the period of work. In the experiments shown in Fig. 1 and 2, the maximal transmural atrial pressures were achieved in 15 seconds and 15 minutes, respectively, but the corresponding maxima in heart rates did not occur until 2 1/2 and 45 minutes later, at which times the transmural pressures had declined considerably from their maximal values.