Optical assessment of intravascular and intracellular parameters related to tissue viability

Tissue viability represents the balance between O₂ supply and demand. In our previous paper (Mayevsky et al; Proc.SPIE 6083 : z1-z10, 2006) the HbO₂ was added to the multiparametric tissue spectroscope (Mayevsky et al J.Biomedical Optics 9:1028-1045,2004). This parameter provides relative values of microcirculatory blood oxygenation (MC-HbO₂) evaluated by the 2 wavelength reflectometry principle. The advantage of this approach as compared to pulse oximetry is that the measurement is not dependent of the existence of the pulse of the heart. Also in the MC-HbO₂ the information is collected from small vessels providing O₂ to the mitochondria as compared to the pulse oximeter indicating blood oxygenation by the respiratory and cardiovascular systems. In the present study we compared the level of blood oxygenation measured by the pulse oximeter to that measured by the CritiView in the brain exposed to various systemic and localized perturbations of O₂ supply or demand. We exposed gerbils to anoxia, hypoxia, ischemia and terminal anoxia. In addition we measured mitochondrial NADH (surface fluorometry), tissue reflectance, tissue blood flow (laser Doppler flowmetry) from the same site of MC-HbO₂ measurement. A clear connection was found between the two blood oxygenation parameters only when systemic perturbations were used (anoxia, hypoxia and terminal anoxia). Under local events (ischemia) the MC-HbO₂ was responsive while the systemic oxygenation was unchanged. We concluded that MC-HbO₂ has a significant value in interpretation of tissue energy metabolism under pathophysiological conditions.