Characterization of the near infrared absorption spectra of cytochrome aa 3 and haemoglobin for the non-invasive monitoring of cerebral oxygenation

Abstract

Near infrared (IR) spectroscopy can give continuous, direct information about cerebral oxygenation in vivo by providing signals from oxygenated and deoxygenated haemoglobin and cytochrome aa 3 . Due to a lack of precise spectral information and uncertainties about optical path length it has previously been impossible to quantify the data. We have therefore obtained the cytochrome aa 3 spectrum in vivo from the brains of rats after replacing the blood with a fluorocarbon substitute. Near infrared haemoglobin spectra were also obtained, at various oxygenation levels, from cuvette studies of lysed human red blood cells. Estimates of optical path length have been obtained. The data were used to construct an algorithm for calculating the changes in oxygenated and deoxygenated haemoglobin and oxygenated cytochrome aa 3 in tissue from changes in near IR absorption.