Quantitative evaluation of optical reflection spectra of blood-free perfused guinea pig brain using a nonlinear multicomponent analysis.

After developing a blood-free perfused preparation of the guinea pig brain a nonlinear multicomponent analysis (NLMCA) of the reflection spectra of the brain surface was worked out by which the redox state of cytochrome aa3, c, and b could be evaluated quantitatively and almost continuously. The NLMCA allowed to simulate the tissue reflection spectra in such a way that only a small statistical error remained between the recorded and the computed spectra. Using redox states of cytochrome aa3 and c as an intracellular oxygen probe it was found that in order to supply the guinea brain with sufficient oxygen by a saline medium equilibrated with 95% oxygen and 5% CO2 the temperature had to be reduced to 18-20 degrees C. At this temperature cytochrome aa3 was 95% oxidized.