Attenuated pulmonary pressor response to hypoxia in bar-headed geese

We determined the pulmonary pressor response during hypoxia in bar-headed geese (Anser indicus), a species that flies at altitudes up to 9,000 m, and Pekin ducks (Anas platyrhynchos), a non-flyer. Mean pulmonary arterial blood pressure (PAP) and arterial O2 partial pressure (PaO2) were measured in unanesthetized birds acutely exposed to 21, 10, 5, and, in geese only, 4% O2. PAP in geese did not change as PaO2 was reduced from 95 to 46 Torr and rose only 3 mmHg when PaO2 was reduced to 28 Torr. The same PaO2 decline in ducks (99 to 29 Torr) resulted in an 11-mmHg rise in PAP. The data suggest that very little or no increase in pulmonary vascular resistance occurs in these geese during hypoxia. This bird may provide a unique model in which to study pulmonary vascular control mechanisms.