Use of a single13C NMR resonance of glutamate for measuring oxygen consumption in tissue

A kinetic model of the citric acid cycle for calculating oxygen consumption from13C nuclear magnetic resonance (NMR) multiplet data has been developed. Measured oxygen consumption (MV˙o2) was compared with MV˙o2predicted by the model with13C NMR data obtained from rat hearts perfused with glucose and either [2-13C]acetate or [3-13C]pyruvate. The accuracy of MV˙o2measured from three subsets of NMR data was compared: glutamate C-4 and C-3 resonance areas; the doublet C4D34 (expressed as a fraction of C-4 area); and C-4 and C-3 areas plus several multiplets of C-2, C-3, and C-4. MV˙o2determined by set 2(C4D34 only) gave the same degree of accuracy as set 3(complete data); both were superior to set 1(C-4 and C-3 areas). Analysis of the latter suffers from the correlation between citric acid cycle flux and exchange between α-ketoglutarate and glutamate, resulting in greater error in estimating MV˙o2. Analysis of C4D34 is less influenced by correlation between parameters, and this single measurement provides the best opportunity for a noninvasive measurement of oxygen consumption.