Optical monitoring of tissue viability using reflected spectroscopy in vivo

Only few techniques that could provide real-time continuous multiparametric physiological data have been developed. Therefore, experimental and clinical monitoring devices for organ and tissue viability evaluation are still lacking. In this study, we present the new concept of tissue vitality defined as a product of a few parameters monitored in real-time by a combined measurement of tissue blood flow and volume as well as the oxidation reduction state of the mitochondria. The hypothesis behind the new approach is that in order to evaluate in real-time tissue vitality, it is necessary to monitor both microcirculatory blood flow and volume as well as the intracellular O₂ balance as reflected in the mitochondrial redox state. Using a multisite and multiparametric monitoring system we were able to compare responses monitored in real-time from 4 different organs (brain, liver, kidney and testis) or 4 different locations in the same organ. The principles of the multichannel NADH redox state system were previously described, while the laser Doppler flowmeter used is commercially available. We have built a unique 4 channel bundle of optical fibers used for light transmission between the monitored organs and the measuring system. Rats and gerbils were monitored under various pathological situations such as hypoxia, ischemia, hyperoxia and hypercapnia and the correlation between tissue blood flow and NADH redox state was calculated. We believe that by using the suggested monitoring system and the development of the appropriate algorithm for better data analysis, a new era in tissue real-time monitoring will unfold under experimental and clinical conditions.