Circulatory responses to high altitude in the cat and rabbit

Cats were taken from Denver (5,200 ft.) to Mt. Evans (14,150 ft.) anticipating that this degree of hypoxia would induce pulmonary hypertension. Rabbits were included for comparison with the cat. All cats died without developing pulmonary hypertension or right heart failure, and in spite of arterial and mixed venous O2 tensions maintained well above those of the rabbit. Presumably the cat's failure to survive was not a failure of oxygen transport to the arterial blood, or to the systemic capillaries. Paradoxically, five of eight rabbits survived despite poor arterial blood oxygenation. The rabbits developed marked polycythemia associated with modest right ventricular hypertension and dilatation.