On chemoreceptor control of ventilatory responses to CO2 in unanesthetized ducks

Using cross perfusion between pairs of animals we examined the effects of increases in arterial CO2 tension (Paco2) at pulmonary, carotid body, and central chemoreceptors on ventilation in unanesthetized, spontaneously breathing White Pekin ducks. By adjusting the level of inspired CO2 of either the experimental or donor animals it was possible to manipulate Paco2 at any one or combination of the receptor groups. Stimulation of central chemosensitive areas alone was three to four times more effective in increasing both frequency and minute ventilation (Ve) than stimulation of the carotid bodies alone. Increases in tidal volume were small in both instances. Increasing PCO2 in the pulmonary circulation of an innervated lung, independent of changes in Paco2 at the carotid body or head, had no effect on VE. We conclude that central chemoreceptors play the major role in a steady-state response of awake ducks to CO2 while the carotid bodies play a smaller but still significant role. The intrapulmonary chemoreceptors play no role in the response per se although their inhibition by high airway CO2 causes marked effects on the pattern of breathing