Imaging epicardial oxygen.

Measurements of oxygen concentration and metabolic status in the heart are important to understanding the mechanisms that control cardiac respiration and its response to changing workload and substrate delivery. This paper presents images, recorded from a perfused rat heart, that reveal regional changes in concentrations of epicardial oxygen and of mitochondrial NADH in response to local ischemia, heterogeneous perfusion, and barbiturate inhibition. A fluorescence/ phosphorescence imaging system was developed to acquire digital images of oxygen concentration and NADH fluorescence from the epicardium of perfused hearts. The oxygen imaging technique is based upon quenching of Pd(II) meso-tetra(p-sulfonatophenyl)porphin phosphorescence by dissolved oxygen. Images of oxygen and NADH fluorescence provided complimentary information about oxygen supply and demand in the heart. The utility of two-dimensional measurements of the mitochondrial bioenergetic status is illustrated by the comparison of gradients for NADH and oxygen across the boundary separating locally ischemic tissue from normoxic epicardium. Images of oxygen concentration provide a powerful means for studying the dynamics of regional oxygen supply/ demand relationships in cardiac muscle.