Fig. 2. (A) A sequence of absorption spectra A(
) was obtained from the heart region of haemoglobin (Hb)-rich (above) and Hb-poor (below) animals during a normoxic/anoxic transition experiment. While progressing from the oxygenated to the deoxygenated state, Hb changed its absorbance characteristics, and this can be followed by the disappearance of the maxima at 540 and 576 nm and by the appearance of a broad peak around 560 nm. Note that, because of the difference in Hb concentration, the spectra of the two groups are scaled differently. In addition, the spectra have been displaced vertically by a constant factor to demonstrate better the changes in absorbance. Because of the lower Hb concentration, the spectra of Hb-poor animals appeared to be tilted to the right, which indicates the presence of non-Hb components with higher absorbances in the shorter wavelength range. Moreover, the unequal spacing of spectra reflects fluctuations in the optical properties of the body region analyzed, which were caused by slight body movements of the animal. These effects made it impossible to use reference spectra of purified Hb solutions for the determination of Hb saturation. Instead, in vivo spectra, Ho() and Hd() for oxy-Hb and deoxy-Hb, respectively, obtained under normoxic and anoxic conditions were used for spectral comparisons that permitted the determination of Hb oxygen-saturation and (B) the calculation of corrected absorption spectra A'() by applying equations 1 and 2 (see text for details).
