InfEflaence of Hyp oxid on the Pdmonmy Cimddztion of Nonmmotized Dogs’

hypercapnia) were first described in 1882 by Openchowski (I) who found that “the pressure in the pulmonary artery during asphyxiation may rise to 65 mm Hg. ” In 1942 Beyne (2) observed that pulmonary as well as systemic hypertension occurred in dogs when alveolar oxygen tension fell below 70 mm Hg. He suggested that the increased pressure observed was to be attributed to a rise in cardiac output which represented “a useful and fortunate reaction of adaptation. ” He based this conclusion on the fact that pressures did not rise during hypoxia in perfusion experiments at constant inflow into the pulmonary vessels. In 1946 Von Euler and Liljestrand (3) induced pulmonary hypertension in the cat by administering low oxygen mixtures. These authors did- not measure flow, but nevertheless postulated that the increased pulmonary artery pressure observed was due to a vasoconstriction of the pulmonary vessels induced locally by low oxygen tension. More recent studies of the pulmonary hypertension induced by low oxygen have approached this problem under a great variety of conditions. At least four types of experiments have been reported: I) The isolated lung or heart lung preparatio