IN-VIVO OXIMETRY USING EPR AND INDIA INK

Recent advances in electron paramagnetic resonance (ERR) oximetry have established the use of the particulate materials fusinite and lithium phthalocyanine (LiPc) as probes for measurement of oxygen tensions in tissues in vivo with a sensitivity and accuracy that is relevant for studying pathophysiological processes. India ink, another potentially very useful new probe for EPR oximetry, shares the critical properties of fusinite and LiPc and has the additional advantage of already havi ng been widely used clinically with no apparent toxicity. The line wid th is particularly sensitive to changes in oxygen tension of less than 30 mmHg; in this range the line broadening/unit of pO(2) is much grea ter than that of fusinite and LiPc. Over the range of biological condi tions that can occur in vivo, the response of the EPR spectrum of Indi a ink to pO(2) is independent of pH, oxidants, reductants, and the nat ure of the medium. In this paper we describe the relevant properties o f India ink and its use to measure pO(2) in vivo in experimental anima ls and a human subject.