Oxygen transport in chicken embryos under hypothermal exposure

Fertile hens' eggs incubated for 16 days at 38 degrees C were abruptly exposed to a temperature of 30 degrees C for 2 h and then determinations of blood gas parameters and the O2 dissociation curve were performed. In addition, O2 uptake was measured. Under hypothermal exposure the O2 dissociation curve showed a marked leftward shift in accordance with the increase in pH. The O2 saturation in arterialized blood of the allantoic vein reached almost 100%, and the blood S(O2) of the allantoic artery also increased up to about 50% in contrast with about 20% in normothermal controls. The blood flow rate through the chorioallantoic capillary plexus seemed to be almost identical with that of normothermal embryos. Because of the increased O2 affinity and the decreased O2 consumption, the systemic venous O2 reserve should be raised by hypothermal exposure. In connection with this conjecture, the redistribution of blood flow and O2 quantity by hypothermal exposure were calculated using the same circulation model as used in normothermal embryos. The result came closer to fetal lambs than to normothermal embryos.