Changes in Cardiac Output During the Transition From Closed to Open A-V Fistula in the Unanesthetized Dog

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Abstract
In an unanesthetized dog the sudden opening of a unilateral femoral arteriovenous fistula is followed by a rapid increase in both heart rate and stroke volume. The increase in stroke volume and heart rate was much larger when the average of the first 2 heart strokes rather than the average of 10 heart strokes before and after opening the fistula was considered. The increase in cardiac output which takes place on suddenly opening an A-V fistula is regarded as a series of cardiodynamic responses to the fall in systemic blood pressure. Results from atropinizing or bilaterally vagotomizing a group of dogs demonstrated that the vagi are essential to the heart in its response by increase of rate to opening an arteriovenous fistula. The limited number of dogs studied with cardiac sympathectomy permits one merely to suggest that the accelerator nerves to the heart do not play a major role in the immediate heart rate increase accompanying the opening of an A-V fistula.

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