THE MEASUREMENT OF OXYGEN IN-VIVO USING EPR TECHNIQUES

The measurement of pO(2) in vivo using EPR has some features which hav e already led to very useful applications and this approach is likely to have increasingly wide and effective use. It is based on the effect of oxygen on EPR spectra which provides a sensitive and accurate mean s to measure pO(2) quantitatively. The development of oxygen-sensitive paramagnetic materials which are very stable, combined with instrumen tal developments, has been crucial to the in vivo applications of this technique. The physical basis and biological applications of in vivo EPR oximetry are reviewed, with particular emphasis on the use of EPR spectroscopy at 1 GHz using particulate paramagnetic materials for the repetitive and non-invasive measurement of pO(2) in tissues. In vivo EPR has already produced some very useful results which have contribut ed significantly to solving important biological problems. The charact eristics of EPR oximetry which appear to be especially useful are ofte n complementary to existing techniques for measuring oxygen in tissues . These characteristics include the capability of making repeated meas urements from the same site, high sensitivity to low levels of oxygen, and non-invasive options. The existing techniques are especially usef ul for studies in small animals, where the depth of measurements is no t an overriding issue. In larger animals and potentially in human subj ects, non-invasive techniques seem To be immediately applicable to stu dy phenomena very near the surface (within 10 mm) while invasive techn iques have some very promising uses. The clinical uses of EPR oximetry which seem especially promising and likely to be undertaken in the ne ar future are long-term monitoring of the status and response to treat ment of peripheral vascular disease and optimizing cancer therapy by e nabling it to be modified on the basis of the pO(2) measured in the tu mour.