A method for continuous recording in vivo of blood oxygen tension

A catheter-type Po 2 electrode has been developed which permits the polarographic continuous recording of the blood oxygen tension in vivo. The electrodes have the size of ordinary cardiac catheters and yield continuous Po 2 tracings in the animal over several hours, with a standard deviation of less than 3%. Model experiments assessed the dependency of the polarographic readings on temperature and showed that static pressure was without effect, but pulsatile pressure caused mechanical deflections depending on the rate of pressure change, and the readings became constant with linear velocities of more than 8–10 cm/sec. In experiments with anesthetized dogs, the readings were calibrated on arterial blood samples analyzed in an in vitro polarograph. With changing inspiratory o 2 concentrations, the time for reaching a new equilibrium was found to be 3–4 minutes. The course of the alveolar-arterial o 2 gradient was studied over the whole range of inspiratory o 2 concentrations. The value of this gradient in the higher o 2 ranges permitted the estimation of venous admixture in the anesthetized dog; the average was 5.5% of the cardiac output. Submitted on February 20, 1959