Abstract

The Bar-headed Goose (Anser indicus) has been observed flying at altitudes up to 9200 m during its semi-annual migration across the Himalayas, suggesting that this species may possess unique adaptations to hypoxia. Therefore, Bar-headed geese and individuals of a comparison species (Pekin Duck — Anas platyrhynchos forma domestica) were subjected to progressive hypoxia corresponding to altitudes up to 11,580 m. After 15 min exposure to each level of hypoxia, tidal volume, respiratory frequency, and levels of O2 and CO2 in arterial and venous blood were determined. In separate experiments the dissociation curve and Bohr effect factor were determined for each species also. The Bar-headed Goose showed a lower resting normoxic level of resting ventilation than the Pekin Duck, as well as a threshold of ventilatory increase in response to hypoxia and maximum ventilation at lower levels of inspired oxygen. After five weeks of acclimatization at 5640 m, both species showed hyperventilation under normoxic conditions, threshold of ventilatory increase, and level of maximum ventilation at lower levels of inspired oxygen than prior to acclimatization. Both species show about the same partial pressures of O2 and CO2 in arterial and venous blood under normoxic conditions. During progressive hypoxia, the Bar-headed Goose is able to maintain only marginally higher partial pressures of O2 in arterial and venous blood, but O2 content is much greater than that observed in the Pekin Duck. This is primarily due to the relatively greater affinity of Bar-headed Goose hemoglobin for O2. Acclimatization produces polycythemia, increased hemoglobin levels, and a large rightward shift in the dissociation curve for the Pekin Duck, while none of these changes were observed in the Bar-headed Goose.

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