[Several hemodynamic indices during human breathing of oxygen under excess pressure].

The paper gives the experimental findings on the pattern and value of circulation changes in ten test subjects exposed to oxygen breathing at positive pressure of 20 mm Hg. The major parameters of central circulation were registered by the method of radioactive label (I131) dilution. During the exposure the test subjects showed an average 27% decrease in the cardiac output as compared with the control level. The test subjects who were pretrained to the exposure displayed a smaller reduction of cardiac output. It is suggested that the circulation changes found under the experimental conditions were mainly induced by peripheral changes rather than by the cardiac function. It is concluded that the reduction of cardiac output is associated with a decrease of the venous return to the heart caused by the diminished circulating blood volume and by the increased total peripheral resistance.