Real-time in-vivo measurement of myoglobin oxygen saturation

摘要

A method for determining myoglobin oxygen fractional saturation in vivo in muscle tissue and intracellular oxygen tension (pO. sub.2), typically in the presence of hemoglobin, is provided. The method comprises measuring the absorption spectrum of the tissue using spectrographic equipment known to the art, including equipment for non- invasively taking spectroscopic measurements of tissue, or adaptations of such equipment to provide the preferred measurements described herein, or using spectrographic equipment specifically designed as described herein for use in non-invasive measurements of reflectance spectra. The measured spectrum is corrected for light scattering effects, such as by taking the second derivative of the data, or by using other means which are known to the art. Myoglobin fractional oxygen saturation is calculated from the measured spectrum employing calibration coefficients that are themselves calculated from application of multivariate analysis to a calibration set created from the second derivatives of absorption spectra. The calibration set spectra preferably representing absorbances of (1) a range of concentrations of hemoglobin (wherein a range of concentrations of oxyhemoglobin and deoxyhemoglobin are present), (2) one concentration of myoglobin (preferably selected to match the concentration of myoglobin in the target muscle tissue) with varying relative amounts of oxy- and deoxymyoglobin and (3) a range of concentrations of scattering agents to mimic scattering encountered in target tissue. The range of concentrations of oxy- and deoxyhemoglobin and the relative amounts of oxy- and deoxymyoglobin represented in calibration set spectra span the range of concentrations of these species encountered in the target tissue. Sample tissue spectra are preferably measured in the visible, the near- infrared or both wavelength ranges. Diffuse reflectance spectroscopy is the preferred method for obtaining spectral data. A partial least squares (PLS) method is preferably used to calculate calibration coefficients from the calibration set which in turn are used to calculate myoglobin oxygen saturation from the measured data. Other means known to the art may also be used. Measured myoglobin oxygen saturation determinations can be used to calculate intracellular oxygen tension, if accurate p50 values at appropriate physiologic pH and temperature for myoglobin-oxygen dissociation are available. An improved method of accurate determination of myoglobin-oxygen dissociation curves under physiologically relevant conditions is also provided.