Fast Wavelength Scanning Reflectance Spectrophotometer for Noninvasive Determination of Hemoglobin Oxygenation in Human Skin

Abstract

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.

Is mean blood saturation a useful marker of tissue oxygenation?

“…These S mb O 2 values are similar to other ORS studies of normal healthy human skin, which identified that the saturation of hemoglobin in dermal vessels was greater in acral skin of the extremities compared with proximal sites. For example, Caspary and colleagues reported mean(SD) oxygen saturation of 65(11.9)% for volar forearm and 90(3.9)% for tip of index finger (4), whereas others report mean oxygen saturations of 72.9(12.2)% for lateral forearm (33). All studies were performed with a skin temperature of 26 -31°C, although unfortunately the researchers did not specify the source-detector spacings.…”

“…Spectra ranging from 470 to 1,120 nm are acquired in 0.05 s, processed by use of a custom-written Windows-based software package, and analyzed by using MatLab (The MathWorks, Natick, MA). The protocol was designed to replicate the experimental technique suggested by Merschbrock and colleagues (33) in which reflectance spectra are obtained specifically from the blood volume in the skin and not the surrounding interstitium. Initially a reference spectrum is taken with pressure applied to the probe sufficient to occlude the superficial blood vessels.…”

“…The development over the last 30 years of noninvasive optical techniques such as optical reflectance spectroscopy (ORS) (2,18,22,33) and near-infrared spectroscopy (NIRS) (7, 23) has significantly advanced our understanding of the hemodynamics of the cutaneous (1, 20), muscle (36), cerebral (11,13,29,48), and gastrointestinal (15, 38) microcirculation. Furthermore, mean blood saturation (S mb O 2 ) and tissue oxygen index (TOI) derived by ORS and NIRS, respectively, evoke a concept that we can also measure the oxygen delivery to the tissue.…”

Effect of an oxygen pressure injection (OPI) device on the oxygen saturation of patients during dermatological methyl aminolevulinate photodynamic therapy

“…To minimize the effect of other absorbers in the tissue, a reference spectrum was initially taken by applying pressure to the probe sufficiently to occlude the superficial blood vessels. Subtracting this reference spectrum from the subsequent recorded blood-filled spectra produced a spectrum that could be attributed to absorption and scattering by blood alone and not the surrounding interstitium [21,22]. Due to the heterogeneity of the microvasculature and photosensitizer localization the oxygen saturation measurement was taken at the same point within the lesion on each occasion.…”

Principal component model of multispectral data for near real-time skin chromophore mapping

“…Occlusion experiments were chosen as the behavior of blood volume and blood oxygenation over time is well known, which is ischemia during, and reactive hyperemia after occlusion. 4,8,29,30 All volunteers signed a consent form approved by the Institutional Review Board of the Eunice Kennedy Shriver National Institute of Child Health and Human Development under the Protocol No. 08-CH-0001.…”