Muscle oxygenation measurement in humans by noninvasive optical spectroscopy and Locally Weighted Regression |
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Authors: | Lorilee S.L. Arakaki Kenneth A. Schenkman Wayne A. Ciesielski Jeremy M. Shaver |
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Affiliation: | 1. Department of Pediatrics, University of Washington, Box 356320, Seattle, WA 98195, USA;2. Department of Anesthesiology, University of Washington, Box 356540, Seattle, WA 98195, USA;3. Eigenvector Research, Inc., 3905 West Eaglerock Dr., Wenatchee, WA 98801, USA |
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Abstract: | We have developed a method to make real-time, continuous, noninvasive measurements of muscle oxygenation (Mox) from the surface of the skin. A key development was measurement in both the visible and near infrared (NIR) regions. Measurement of both oxygenated and deoxygenated myoglobin and hemoglobin resulted in a more accurate measurement of Mox than could be achieved with measurement of only the deoxygenated components, as in traditional near-infrared spectroscopy (NIRS). Using the second derivative with respect to wavelength reduced the effects of scattering on the spectra and also made oxygenated and deoxygenated forms more distinguishable from each other. Selecting spectral bands where oxygenated and deoxygenated forms absorb filtered out noise and spectral features unrelated to Mox. NIR and visible bands were scaled relative to each other in order to correct for errors introduced by normalization. Multivariate Curve Resolution (MCR) was used to estimate Mox from spectra within each data set collected from healthy subjects. A Locally Weighted Regression (LWR) model was built from calibration set spectra and associated Mox values from 20 subjects using 2562 spectra. LWR and Partial Least Squares (PLS) allow accurate measurement of Mox despite variations in skin pigment or fat layer thickness in different subjects. The method estimated Mox in five healthy subjects with an RMSE of 5.4%. |
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Keywords: | Mox, muscle oxygenation NIR, near infrared NIRS, near-infrared spectroscopy LWR, Locally Weighted Regression MCR, Multivariate Curve Resolution PLS, Partial Least Squares Aobs, total absorbance summed across all wavelengths B, effective path length Eo and Ed, total absorptivities summed across all wavelengths of the oxygenated and deoxygenated species, respectively Co and Cd, concentrations of oxygenated and deoxygenated species, respectively RMSECV, root mean squared error of cross-validation PCs, principal components RMSE, root mean square error |
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