Patent ID: 8515514

Claim:
A method for compensating for subject-specific variability in a pulse oximeter intended for non-invasively determining in in-vivo measurement the amount of at least two light-absorbing substances in the blood of a subject and provided with emitters for emitting radiation at a minimum of two different wavelengths and with a detector for transforming the radiation received into an electrical output signal, the method comprising the steps of measuring a detector output signal when living tissue of the subject is present between the emitters and the detector in a sensor, wherein the detector output signal depends on the tissue, reading from a memory a nominal calibration comprising nominal extinction matrix E kl 0 , reading from the memory nominal characteristics describing conditions under which the nominal calibration has been done, the nominal characteristics comprising: nominal values for a calculation defining tissue-induced correction to the nominal extinction matrix E kl 0 due to light transmission through living tissue, nominal values for a calculation defining temperature-induced corrections to the nominal extinction matrix E kl 0 due to wavelength shifts caused by changes in emitter temperatures, establishing values for both calculations for the sensor on the living tissue of the subject using the detector output signal, forming a subject-specific calibration by correcting the nominal extinction matrix E kl 0 with both calculations with the established values, solving hemoglobin fractions using the corrected nominal extinction matrix in a Lambert-Beer model.