Optical spectroscopic imaging for non-invasive evaluation of tissue oxygenation

Altered rates of oxygen delivery and uptake between and possibly within different organs occur during critical illness. The mechanisms governing this heterogeneity are as yet not fully understood and techniques directed at being able to map the course of oxygen to the mitochondria to produce ATP, the main molecule needed to drive energy requiring processes in the cell, would give valuable information about the mechanisms underlying organ dysfunction during disease. Oxidative phosphorylation occurring in the mitochondria is the main site for the production of ATP in mammalian cells. Metabolic substrates, ADP and Pi, and O2 are the ingredients needed to produce ATP. Due to the central role of oxidative phosphorylation in the metabolism of the cell, much attention has been directed at developing non-invasive techniques to measure intermediates of the oxidative phosphorylation in tissue as an indication of the metabolic state of tissue. One such method enables mapping the distribution of tissue hypoxia by use of a fluorescence technique based on the measurements reduced nicotine amide dinucleotide (NADH). NADH is situated at the high-energy side of the respiratory chain and during tissue hypoxia accumulates in concentration because less NADH is oxidized to NAD+. Excitation of NADH by 366 nm light produces, unlike NAD+, fluorescence at 460 nm light. Previously, however, producing images of NADH fluorescence distribution in tissue has been limited to saline perfused in vitro models. We recently undertook to develop an NADH videoflurometer sensitive enough to NADH fluorescence in vivo (Ince C, Bruining HA (1991) Optical Spectroscopy for the measurement of tissue hypoxia.(ABSTRACT TRUNCATED AT 250 WORDS)