Improved model for myocardial diffuse reflectance spectra by including mitochondrial cytochrome aa3, methemoglobin, and inhomogenously distributed RBC

The aim of this study was to compare a previously used light transport model (I) comprising the chromophores hemo- and myoglobin, fat, and water, with two extended models, where the chromophores of cytochrome aa3, methemo- and metmyoglobin are added (model II), and in addition, accounting for an inhomogenous hemoglobin distribution (model III). The models were evaluated using calibrated diffuse reflectance spectroscopy measurements on the human myocardium. Model II proved a significantly better spectral fitting, especially in the wavelength ranges corresponding to prominent absorption characteristics for the added chromophores. Model III was significantly better than model II and displayed a markedly higher tissue fraction and saturation of hemo- and myoglobin. The estimated tissue chromophore fractions, saturation and oxidation levels, were in agreement with other studies, demonstrating the potential of diffuse reflectance spectroscopy measurements for evaluating open heart surgery. However, the choice of chromophores and vessel packaging effects in the light transport model has a major effect on the results.