Oxygen saturation of hemoglobin (HbSO₂) in skin vessels may be determined with photometric methods. However, the optical complexity of the skin makes quantitative measurements difficult. A possible approach is the analysis of reflectance spectra using the two-flux theory of Kubelka and Munk. The final equation of this theory which describes the transformation between absorbed and reflected light has been approximated by a hyperbola. Based on this approximation we evaluated skin spectra obtained from the forearm of 23 healthy subjects with a fast scanning reflection photometer (Oxyscan) applying visible light (535-620 nm). The hyperbola was used in a multicomponent analysis in which the measured spectrum is recalculated using reference spectra of oxygenated and deoxygenated hemoglobin (gaussian least-square method). A crucial requirement for the evaluation is the subtraction of the individual skin spectrum, obtained by clearing a spot of skin of hemoglobin exerting external pressure. At rest HbSO₂ was in the range between 42 and 89% (mean ± SD:72.9 ± 12.2%). Pharmacological and thermal generation of hyperemia combined with respiration of pure oxygen raised the values to 86-100% (97.9 ± 4.6%). This was in good agreement with capillary ex vivo analysis yielding 96-100% (98.7 ± 0.4%). Under arterial occlusion HbSO₂ fell below 30% (14.5 ± 7.8%). Our method allows rapid determinations of absolute HbSO₂ values in the skin. The evaluation error is estimated to be between 5% for oxygenated and 10% for deoxygenated values.

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Abstract. This publication reports the derivation and the implementation of a simulation model that describes non-resonant photoacoustic gas sensors. The photoacoustic effect is modelled in detail for the successive steps of radiation emission, stimulation of molecules, collisional relaxation processes and finally the pressure formation in a closed gas cell. The photoacoustic effect offers great potential in the development of selective, miniaturized gas sensor systems. We verify and discuss the results of our model assuming typical parameters and values in indoor CO 2 sensing applications. We set up a sensor system for experimental verification of the simulated data and discuss the results. The results of the simulation model are in good accordance with the experimental data and can therefore be used as a novel and efficient tool for the development of non-resonant photoacoustic gas sensor systems.