MODELING [O-15]OXYGEN TRACER DATA FOR ESTIMATING OXYGEN-CONSUMPTION

The most direct measure of oxidative tissue metabolism is the conversi on rate of oxygen to water via mitochondrial respiration. To calculate oxygen consumption from the analysis of tissue residue curves or outf low dilution curves after injection of labeled oxygen one needs realis tic mathematical models that account for convection, diffusion, and tr ansformation in the tissue. A linear, three-region, axially distribute d model accounts for intravascular convection, penetration of capillar y and parenchymal cell barriers (with the use of appropriate binding s paces to account for oxygen binding to hemoglobin and myoglobin), the metabolism to [O-15]water in parenchymal cells, and [O-15]water transp ort into the venous effluent. Model solutions fit residue and outflow dilution data obtained in an isolated, red blood cell-perfused rabbit heart preparation and give estimates of the rate of oxygen consumption similar to those obtained experimentally from the flow times the arte riovenous differences in oxygen contents. The proposed application is for the assessment of regional oxidative metabolism in vivo from tissu e O-15-residue curves obtained by positron emission tomography.