Role of the Autonomic Nervous System in the Circulatory Response to Acutely Induced Anemia in Unanesthetized Dogs *

Abstract

The role of the autonomic nervous system in the circulatory adaptation to acutely induced isovo-lemic anemia was evaluated by comparing the responses of 7 intact unanesthetized dogs with the responses of 8 dogs which had been subjected to chronic total cardiac denervation. After the induction of severe isovolemic anemia, produced by the exchange of dextran for blood, cardiac output rose markedly in both groups of animals. The rise was significantly greater, however, in the intact dogs than in the cardiac denervated animals. In the intact dogs the increase in cardiac output stemmed predominantly from a rise in heart rate, elevations in stroke volume playing a less important role. In contrast, in the cardiac denervated dogs, the increase in cardiac output tended to be more the result of an augmentation in stroke volume. In an additional 4 dogs, catecholamine depletion was produced by prior administration of reserpine. These dogs responded in a fashion similar to the cardiac denervated animals in respect to the changes in cardiac index, heart rate, and stroke volume that occurred during anemia, but they displayed smaller increases in cardiac output and in heart rate than the intact dogs. From these results it is concluded that an intact autonomic nervous system is necessary for the total circulatory response to anemia. In the absence of a functioning autonomic nervous system, the organism appears to fall back on what may be looked upon as a reserve mechanism for the augmentation of cardiac output[long dash]the elevation of stroke volume.