VENTILATORY RESPONSE TO CO2 IN BIRDS .1. MEASUREMENTS IN UNANESTHETIZED DUCK

Ventilation and blood gases were measured in unanesthetized ducks at various levels of inspired CO2 partial pressure ((PICO). Ventilation was markedly augmented with increasing PICO, whereas arterial and mixed venous PCO stayed essentially constant up to a PICO of about 20 torr and changed only slightly between that and the highest level tested (35 torr). After carbonic anhydrase had been blocked, blood PCO was elevated at all levels of PICO but the ventilatory response to increases in PICO were attenuated. The response to CO2 in the normal bird (before administration of acetazolamide) shows similarities to that in mammals. Qualitative differences between both classes of vertebrates after blockade of carbonic anhydrase may, however, suggest differences in their systems that control ventilation. © 1978.