Apparatus and technique for the quantitative measurement of oxygen tension in living tissues

A method is described for the quantitative measurement of oxygen tension in tissue using flush-ended gold and platinum electrodes in conjunction with a transistor amplifier. A circuit is also given for automatic recording. The difficulties involved are noted and the techniques used to surmount these problems described. A satisfactory method was devised to grind electrodes with reproducible ends. The variables involved in biological systems were overcome by the use of several electrodes. Suitable apparatus was designed to calibrate the electrodes against known mixtures of oxygen in nitrogen and 5% $\text{CO}_{2}$. The medium used for this purpose was an artificial extracellular fluid (A.E.F.) which was maintained at physiological pH by the $\text{CO}_{2}$. The oxygen cathode gave a current directly proportional to oxygen tension and had a temperature coefficient of 2% per 1 degrees C. The current voltage curve showed no plateau with flush-type electrodes unless these were large or coated with collodion. Addition of the normal concentration of protein did not significantly alter the current. More than 2% of added protein reduced the current, whole blood had little effect, and haemoglobin exerted an effect comparable with its protein value. Glutathione reduced the current. The problem of diffusion of oxygen on to a flush type of electrode was examined theoretically and conclusions were tested by experiment: (a) by using compressed cotton wool and A.E.F. as a diffusion medium; (b) by comparison of flush-ended and recessed electrodes in vivo and in rats' limbs perfused with calibration fluid and M/1000-NaCN at 0 to 2 degrees C. The oxygen consumption of the flush-type electrode was calculated and found to be negligible compared with that of the block of tissue which formed its diffusion zone. The extrapolation from calibration conditions to conditions in vivo is therefore valid. Using this information it has been possible to express diffusion current measurements found in tissue in terms of oxygen tension.