Sympathetic cardiac stimulating fibers in the vagi

¹ Institute of Physiology, Faculty of Medicine, University of Chile Santiago, Chile

The cardiac effects obtained by the stimulation of the vagus nerve were studied in the isolated heart preparation of cats, perfused with Tyrode's solution according to Langendorff's technique. High cervical stimulation of the vagus produced slight or no positive inotropic and chronotropic effects in the atropinized heart. Excitation of the thoracic portion produced intense cardiac stimulation. The cardiac stimulating effect is not influenced by supra- or infranodose vagotomy. Complete cervical and upper thoracic sympathectomy abolished vagal cardiac stimulation. It is concluded that sympathetic fibers that join the vagal trunk at the lower cervical and, perhaps, upper thoracic level, are responsible for the positive chrono and inotropic effects obtained when stimulating the intact or degenerated vagus nerve.

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