Pulmonary circulation and oxygen transport in lambs at high altitude.

The oxygen transport and pulmonary hemodynamics of lambs native to low altitude were evaluated in Denver and on Mount Evans (12,700 ft.). Because the Hb-O2 dissociation curve is placed well to the right of most other mammals, markedly depressed arterial O2 saturations (59%) occurred at high altitude. However, the lambs adapted remarkably well and showed normally rapid growth. The mixed venous Po2 was relatively well maintained, primarily by a narrowing of the A-V Po2 gradient to 11 mm Hg. Despite the marked hypoxemia, elevation of the pulmonary artery pressure was not a consistent finding, and when it occurred it was neither marked nor sustained.