Cold lungs, warm heart? Temperature effects on the oxygen‐hemoglobin dissociation curve of bar‐headed geese

Abstract

Bar‐headed geese accomplish the extraordinary feat of migrating over the Himalayas, where oxygen (O2) levels are only ½ −1/3 that at sea‐level. It is well known that hemoglobin (Hb) of this species has enhanced O2 affinity, assisting O2 loading in this hypoxic environment. As temperature at these altitudes is extremely low and bar‐headed geese cross the mountains when air temperatures are at daily minima, we hypothesized that enhanced temperature effects may be beneficial for O2 loading (if these birds decrease temperature at the blood/gas barrier) and O2 unloading at the exercising muscle. Using the mixing technique on whole‐blood, preliminary evidence suggests that the O2‐Hb curve temperature coefficient of bar‐headed geese is higher than that of other birds near baseline CO2 (4%) and more interestingly, is highest when CO2 is high (7%) (e.g. at locomotory muscle). This should enhance unloading of O2 to exercising tissues, where temperature and CO2 levels will be near their maxima. At low CO2 (1%) (e.g. as may be experienced at the blood/gas barrier due to the enhanced hypoxic ventilatory response in this species) the temperature coefficient is lowest, suggesting that decreased temperature may not further enhance O2 loading. This finding parallels that of the diving emperor penguin in its analogous environment, as its air sac temperature is not decreased despite extremely low ambient temperatures. NSF Funded