NONINVASIVE MONITORING OF THE REDOX STATE OF CYTOCHROME-OXIDASE IN LIVING TISSUE USING NEAR-INFRARED LASER LIGHTS

A triple wavelength spectrophotometric method was developed to monitor changes in the concentrations of oxygenated and deoxygenated hemoglobin, and in the redox state of cytochrome oxidase in living tissue. Three wavelengths of an NIR (near-infrared) laser beam were used to monitor hemoglobin (780, 805 and 830 nm) and cytochrome (cyt.) oxidase (780, 790 and 830 nm). Algorithms for calculating changes in the concentrations of oxidized cyt. oxidase (aa3), and oxygenated and deoxygenated hemoglobin were developed using NIR spectral analysis of these chromatophores. To assess the ability of these algorithms to measure independent changes in the concentration of oxy-, deoxyhemoglobin and oxidized cyt. oxidase in tissue, experiments involving a fluorocarbon (FC-43) exchange transfusion at very low hematocrits were conducted in anesthetized rats. The observed data indicate that FC-43 circulation at FiO2 1.0 can supply sufficient oxygen to the rat brain to maintain the oxidation state of mitochondrial oxidase (cyt.aa3) near pre-exchange levels. The relationships between changes in oxidized cyt. oxidase and oxyhemoglobin content in response to variations in FiO2 of inspired gas were then examined in the rat brain. These results also confirmed the ability of the triple wavelength algorithms to distinguish changes in the oxidized copper band of cyt.aa3 from those in absorption by oxy- and deoxyhemoglobin. NIR monitoring of skeletal muscle to determine the redox state of cyt. oxidase was performed in a few human cases and the results indicated that these observations can increase our understanding of the process of oxygen transport to tissues.