Comparisons of measurements of pO2 in tissue in vivo by EPR oximetry and microelectrodes.

Abstract

Polarographic micro-electrode measurements are very useful for measuring pO2 in vivo, especially for measurements of the variation of pO2 within a tumor (1,2,8). This method has several advantages, including: it is the only direct method currently in extended use in the clinical setting; it can provide data on microscopic heterogeneity; and it is fairly widely available. While the micro-electrode method has become a type of “gold standard” for measurement of pO2 in tissues, it has some limitations and disadvantages: it can be technically difficult; it has limited resolution at the very low levels of pO2 that are important for many clinically relevant processes; and it can perturb the tissues significantly, especially when used in repeated studies to monitor pO2 in tissues over time. Repeated measurements are especially desirable to follow the effect on tissue pO2 after treatment with some drugs (e.g. anti-cancer drugs and anesthetics) and radiation, the effects of acute and chronic ischemia, and changes in respiratory factors. Electron paramagnetic resonance (EPR) oximetry appears to offer some complimentary advantages for such studies: it can monitor pO2 continuously and/or repeatedly at the exactly the same localized area in tissue in vivo without the need for anesthesia; it can resolve small differences in pO2 even at the very low levels that occur pathophysiologically; and it can be used in a variety of settings.