FAST WAVELENGTH SCANNING REFLECTANCE SPECTROPHOTOMETER FOR NONINVASIVE DETERMINATION OF HEMOGLOBIN OXYGENATION IN HUMAN SKIN

Oxygen saturation of hemoglobin (HbSO(2)) in skin vessels may be deter mined with photometric methods. However, the optical complexity of the skin makes quantitative measurements difficult. A possible approach i s the analysis of reflectance spectra using the two-flux theory of Kub elka and Munk. The final equation of this theory which describes the t ransformation between absorbed and reflected light has been approximat ed by a hyperbola. Based on this approximation we evaluated skin spect ra obtained from the forearm of 23 healthy subjects with a fast scanni ng reflection photometer (Oxyscan) applying visible light (535-620 nm) . The hyperbola was used in a multicomponent analysis in which the mea sured spectrum is recalculated using reference spectra of oxygenated a nd deoxygenated hemoglobin (gaussian least-square method). A crucial r equirement for the evaluation is the subtraction of the individual ski n spectrum, obtained by clearing a spot of skin of hemoglobin exerting external pressure. At rest HbSO(2) was in the range between 42 and 89 % (mean +/- SD: 72.9 +/- 12.2%). Pharmacological and thermal generatio n of hyperemia combined with respiration of pure oxygen raised the val ues to 86-100% (97.9 +/- 4.6%). This was in good agreement with capill ary ex vivo analysis yielding 96-100% (98.7 +/- 0.4%). Under arterial occlusion HbSO(2) fell below 30% (14.5 +/- 7.8%). Our method allows ra pid determinations of absolute HbSO(2) values in the skin. The evaluat ion error is estimated to be between 5% for oxygenated and 10% for deo xygenated values.