Optical device
A method for monitoring blood oxygen saturation (SO 2 ) includes the steps of calculating an estimate of SO 2 in the blood and correcting the estimate by a scaling factor. A preferred embodiment of the method includes the steps of transmitting light containing a plurality of wavelengths into the blood; measuring a remitted spectrum over the plurality of wavelengths; calculating a measured blood absorption spectrum from the remitted spectrum; estimating local rates of change in the measured blood absorption spectrum at a plurality of the wavelengths; and calculating the estimate of SO 2 as a function of absolute values of the local rates of change of the measured blood absorption spectrum.
1. A method for SO 2 monitoring, comprising the steps of:
calculating an estimate of SO 2 in blood to be monitored;
correcting said estimate of SO 2 in blood by a scaling factor;
transmitting light containing a plurality of wavelengths into the blood;
measuring a remitted spectrum over the plurality of wavelengths;
calculating a measured blood absorption spectrum from the remitted spectrum;
estimating local rates of change in the measured blood absorption spectrum at a plurality of the wavelengths, including at least one isobestic wavelength; and,
calculating the estimate of SO 2 as a function of absolute values of the local rates of change of the measured blood absorption spectrum.
2. The method for SO 2 monitoring according to claim 1 , wherein before said step of calculating the estimate of SO 2, further comprising the steps of:
removing effects of light scattering from the measured blood absorption spectrum;
calculating an area under the measured blood absorption spectrum after said step of removing effects of light scattering; and,
normalizing the measured blood absorption spectrum by the area under the measured blood absorption spectrum determined during said step of calculating.
3. The method for SO 2 monitoring according to claim 1 , further comprising the step of applying a Kubelka Monk transformation to the measured blood absorption spectrum.
4. The method for SO 2 monitoring according to claim 1 , wherein the step of calculating the estimate of SO 2 comprises the steps of:
computing a hemoglobin index value as a function of absolute values of the local rates of change of the measured blood absorption spectrum between a plurality of pairs of isobestic points, whereby the hemoglobin index value is independent of blood oxygenation;
computing an oxygenation parameter as a function of absolute values of the local rates of change of the measured blood absorption spectrum between a plurality of isobestic points and at least one non-isobestic point, whereby the oxygenation parameter is dependent on blood oxygenation;
normalizing the oxygenation parameter by the hemoglobin index value; and,
estimating SO 2 as a measure of the level of the normalized oxygenation parameter relative to a predetermined fully deoxygenated reference value and a fully oxygenated reference value.