Comparative aspects of oxygen transport in animals with hemoglobin of high (llama) and low (sheep) affinity for oxygen.

he llama's hemoglobin has a very high affinity Tfor oxygen. Pm in the llama is about 23 mm Hg versus about 27 mm Hg in man and 41 mm Hg in sheep (Hb type B ) . This property of the hemoglobin molecule facilitates oxygen uptake in the lungs, but could hinder oxygen release at the tissue level. We have studied the oxygen transport system in awake, unsedated llamas in the standing position at sea level and after five and ten weeks at 3420 meters: at rest breathing air and under acute hypoxia, acute hyperoxia and exercise. We have also compared the oxygen transport in the llama with that of homozygous sheep (Hb type B ) at a PB of 629-637 mm Hg and after acute exposure to three levels of simulated altitudes: PB 535, 435, and 335 mm Hg. Exposure to 3420 meters produced a significant decrease in Pa02 (P<0.025) from 87 to 51-53 mm Hg, but SaOz remained above 92 percent. An average increase in hemoglobin concentration from 10.6 to 11.8 g/100 ml was enough to maintain CaO2 unchanged. The llama tolerate+ chronic hypoxia (3420 m ) with no change in Q, (Ca-CV)02, or systemic oxygen transport ( Q x CaOz), while operating in the middle steep portion of the Hb-02 curve. No change in the position of the Hb-02 dissociation curve was found: Pso was 22.7 mm Hg at sea level and 23.7 mm Hg at altitude. The llama possesses very effective mechanisms of oxygen extraction: its coefficient of oxygen utilization ( (Ca02-Cm2) ICa02) is about 50 percent greater than in man. Under conditions of acute hypoxia (low 0 2 inhalation-PI@ 65 to 75 mm Hg), the coefficient of 0 2 utilization rose even further while