Cardiac receptors evoke ventilatory response with increased venous PCO2 at constant arterial PCO2

The effects of elevated venous PCO2 and denervation of the cardiac ventricles on ventilation were studied in 20 anesthetized open-chest unidirectionally ventilated White Leghorn cockerels. Venous PCO2 was increased by insufflating the gut with high CO2 while recording changes in the amplitude of the sternal movements. Arterial blood gases were held constant by unidirectionally ventilating the lungs with gas flows approximately five times the animal's resting minute volume. Insufflating the gut with 90% N2-10% O2 did not change the level of ventilation, whereas with 90% CO2-10% O2 the amplitude of sternal movement increased 500% above that with no gut gas flow. Exchange of N2 for the CO2 was followed by a rapid reduction of ventilatory movements to control levels. Arterial blood gases remained constant during gut gas insufflation, whereas mixed venous PCO2 increased and mixed venous pH decreased when high CO2 was given to the gut. Cutting the middle cardiac nerves, which primarily innervate the ventricles of the heart, reduced the ventilatory response to CO2 gut insufflation by 67%. Sympathetic denervation of the thoracic viscera did not change the responses. It appears that, in the chicken, increasing the mixed venous PCO2 while holding the arterial blood gases constant alters ventilation by an afferent system located in the venous circulation or in the right ventricle which is sensitive to changes in PCO2.