The effects of volume infusion were examined in cardiac autotransplants to determine the role of cardiac innervation in the Bainbridge reflex. In autotransplantation the atria are transected ventral to the vena cavae and pulmonary veins. The remaining atria ("host") are innervated. The autotransplanted atria and ventricles ("donor") are extrinsically denervated. Host and donor heart rate, arterial pressure, aortic flow, and, in several experiments, venous pressure were monitored. Sixteen volume infusions (saline or 6% dextran) of 300 to 800 cc were given to five unanesthetized animals. In three additional experiments infusions were given after atropine, 2 mg, and propranolol, 1 mg/kg.
In all of these animals, volume infusion was accompanied by a small change in donor rate and a consistent increase in the host rate. The venous pressure, when measured, increased 7 cm H2O, the aortic pressure mean change was +3 mm Hg, and the cardiac output increased 0.2 L/min. Atropine and propranolol both attenuated the host rate response to infusion.
A venous pressure rise distributed equally to innervated and denervated portions of the same heart resulted in an increase only in the innervated portion. It is concluded that local stretch does not appear to be responsible for the tachycardia in the intact animal.
- © 1971 American Heart Association, Inc.