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A Low-Light Television System For The In Vivo Measurement Of Oxidative Metabolism As Indicated By NADH Fluorescence

In 1962 Chance demonstrated the feasibility of monitoring intramitochondrial NADH levels in vivo. NADH serves as an indicator of oxidative metabolism because it fluoresces at 475 nm while its oxidized form NAD+ does not fluoresce significantly. We have designed a long focal length television fluorometer for the direct measurement of NADH fluorescence in the operating room on a practical basis. It enables a comparison of simultaneous metabolic changes in several anatomic areas. The 30-cm working distance of the system permits metabolic measurements to be made with a minimum of interference with normal operating procedures and other instrumentation. The tissue is illuminated at 360 nm by a mercury arc lamp, and the resulting fluorescence is monitored by a television system. Fluorescence variations are then analyzed by video densitometric techniques to localize metabolic changes that occur on a regional basis. Intravenous sodium fluorescein provides a reference fluorescence at 529 nm to compensate for the absorption of the ultraviolet excitation light by the hemoglobin in the blood. The difference between the fluorescence at 475 nm and 529 nm represents a corrected NADH fluorescence signal related to local oxidative metabolism. By employing this system in conjunction with other instrumentation, we have demonstrated a strong correlation among NADH fluorescence, oxygen consumption, and potassium kinetics in exposed cerebral cortex. Additionally, some effects of ischemia on NADH fluorescence were studied in both cortex and myocardium.