The Measurement of pO2 by O2 Electrode in the Presence of Changing pCO2

Studies on the transport of O2 and CO2 in the alveoli and blood have focused on simultaneous measurements of the two gases with classical instruments; an interaction between the two gases has been assumed (see Bohr Effect and Rahn-Otis Plot). Nevertheless, of late years with wide use of the Kimmich-Kreuzer Oxygen Electrode in liquids and gases, the measurements have included oxygen alone. These small (2mm) polarographic catheter electrodes have been used in both physiologic and bioengineering applications. Within a particular range of polarization voltage, the electrode current is limited by O2 diffusion across a membrane; i.e., at a constant polarization voltage, current is linearly related to pO2. Since it is often the case that measurements of pO2 are taken while pCO2 is changing, CO2 effects on the electrode current should be known and corrected for. In the present experiments, electrical currents at 5% and 21% O2 with varying amounts of CO2 were measured. Polarograms (a plot of current v. voltage) made in the presence and absence of CO2 were compared. The pO2 measurement is significantly affected by CO2 at 21% O2, but not a 5% O2; i.e., the O2 value changed with different CO2 levels. These results are particularly interesting since the electrode membrane is a physical model of the alveolar membrane