Influence of ischemia and hypoxia on breathing in ducks.

We examined the influence of whole and lower body hypoxia and lower body ischemia on breathing in White Pekin ducks, Anas platyrhynchos, excluding pathways involving the carotid bodies. Carotid body denervated birds breathing 10 or 5% O2 developed a tachypnea after a latency of 30-100 s. The tachypnea was more pronounced with the more severe hypoxia, resulting in almost a doubling of minute ventilation (VE). Occlusion of the abdominal aorta in unanesthetized ducks produced immediate development of hypertension. Ventilation was unaffected for the 1st min; a tachypnea then developed rapidly and persisted for the duration of the occlusion resulting in a 25% increase in VE. After thoracic spinal section, all ventilatory responses to occlusion were eliminated. Experimental perfusion of the brain and single intact carotid body in unanesthetized ducks with hyperoxic blood during low O2 breathing (6-9% O2) resulted in tachypnea, also after a considerable latency. These results suggest that severe hypoxia can affect breathing in birds via pathways other than those involving the carotid bodies.