Respiratory sensitivity to carbon dioxide in cross-circulated dogs

Abstract

The effect of CO₂ on ventilation was studied in cross-circulated dogs. In these experiments the recipient dog's head was perfused exclusively by arterial blood from the donor dog through anastomoses of the common carotid arteries of the donor to the vertebral arteries of the recipient. The carotid arteries of the recipient dog, as well as its muscles in the neck, were tied. The injection of lipiodol and latex did not reveal leakage from the recipient's head to its body or vice versa. Ventilation and arterial Pco₂ of both dogs were determined before, during, and after the inhalation of carbon dioxide of 3, 5, and 7% with 20% oxygen and balance nitrogen by the donor for 20 min or more. The sensitivity of the respiratory centers of both dogs to Pco₂ was similar, as indicated by the regression lines relating ventilation in both dogs as a function of arterial Pco₂ of the donor dog only. The blood of the recipient's body was hypocapnic when its head was receiving hypercapnic blood. The sensitivity coefficient in both dogs was similar to that of decerebrate dogs during CO₂ inhalation. It is inferred that the central CO₂ chemoreceptors can account for all the ventilatory response to CO₂ inhalation.