THE INFLUENCE OF SHORT PERIODS OF INDUCED ACUTE ANOXIA UPON PULMONARY ARTERY PRESSURES IN MAN

Abstract

Pulmonary hypertension was rapidly induced in human subjects by breathing 10% O2 in N for short periods of time, while there was only a very slight rise in the systemic blood pressure. The pulmonary pressure increases occurred rapidly when the subject was changed from breathing air (21% O2) to the 10% O2 mixture. A maximal rise in pulmonary artery pres- sure was present after 2-4 mins. and this was maintained as long as the subject was kept on the 10% O2, 15 to 20 mins. When the low O2 breathing was discontinued the pulmonary artery pressure returned rapidly to normal. The rise in pulmonary artery pressure due to acute anoxia was not the result of an increase in cardiac output, for the latter (detd. by the direct Fick method and the cardiac catheterization technique) was slightly decreased. Pulmonary vascular resistance was almost doubled during anoxia, while the systemic peripheral resistance increased only slightly. The low O2 breathing also produced hyperventilation with an increased CO2 output, a lowering of the arterial pCO2, an increase in pH and a decrease in O2 consumption.