Role of the vagus in control of cardiac output in the unanesthetized dog

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Abstract
This study is based on 145 cardiac output determinations by the indocyanine green dye-dilution technique in 10 trained, unanesthetized dogs. The response of each animal to 1-norepinephrine was studied before and after bilateral cervical vagotomy. Prior to vagotomy the dog responds to this catecholamine with an increase in arterial pressure and hematocrit. The dog''s cardiac output was studied after the hematocrit had stabilized and while the arterial pressure was elevated. There was, at this time, a significant decrease in heart rate, but no significant change in cardiac output. After vagotomy the dog had an elevated heart rate, an elevated cardiac output, an a decreased stroke volume. He responded to norepinephrine with a more pronounced increase in arterial pressure, which was associated with an increase in hematocrit, no significant change in heart rate, and an increase in stroke volume and cardiac output. The vagi are important in regulating cardiac output and that this regulation, in turn, plays a role in the control of arterial pressure.