High altitude-induced pulmonary hypertension in normal cattle.

• Elevation of the pulmonary arterial pressure is known to occur during hypoxia in a number of mammalian species. The mechanisms involved in the production of this hypertension are, however, not clearly understood. Most previous investigations have been concerned with the effect of short periods of severe hypoxia upon the pulmonary circulation. The effects of mild, prolonged hypoxia are less well documented. Eotta et al. reported an increase in the pulmonary arterial pressure and resistance, polycythemia, and hypervolemia in both temporary and permanent human residents of Moraeocha, Peru (altitude 14,900 feet). They suggested that the pulmonary hypertension might relate to the observed increase in hematocrit and blood volume rather than to a direct effect of hypoxia on the pulmonary vasculature. It has been known for many years that a small percentage of cattle residing at high altitude develops right heart failure. In 1915, Glover and Newsom described a syndrome of right heart failure with venous distention, weakness, dyspnea on exertion, diarrhea, and edema of the dependent portions of the neck and thorax occurring in cattle pastured in the high mountain valleys of Colorado. Hypertrophy and dilatation of the right ventricle, passive congestion of the liver, hydrothorax, and ascites were found at necropsy. The edema present in the pectoral