Mechanisms of Respiratory Stimulation During Hemorrhage

The immediate effects of severe hemorrhage on respiratory rate and amplitude were determined in dogs before and after bilateral vagotomy and isolation of the carotid sinuses. The animals were anesthetized with morphine (3 mg/kg) intramuscularly and sodium pentobarbital (15 mg/kg) intravenously. The sino-aortic denervated animals showed no respiratory responses to 1–2 mg of sodium cyanide. Most of the animals showed immediate respiratory stimulation in response to hemorrhage before denervation, and in a large percentage of these the stimulation still could be elicited by hemorrhage after sino-aortic denervation. The rapid onset of the stimulation in the denervated animals and the fact that slow withdrawal of blood to produce a certain level of hypotension caused less stimulation than rapid withdrawal would indicate that decreased blood flow through the respiratory center may not be the basis for the response.