Compensation of human variability in pulse oximetry
First Claim
1. A method for compensating for subject-specific variability in an apparatus intended for non-invasively determining the amount of at least two light-absorbing substances in the blood of a subject and provided with emitter means for emitting radiation at a minimum of two different wavelengths and with detector means for receiving the radiation emitted, the method comprising the steps of calibrating the apparatus using a nominal calibration, carrying out initial characterization measurements, said measurements to include measuring radiation received by the detector, based on the characterization measurements, establishing nominal characteristics describing conditions under which the nominal calibration is used, storing reference data indicating the nominal characteristics established, performing in-vivo measurements on a living tissue, wherein radiation emitted through the tissue and received by the detector means is measured, based on the in-vivo measurements and the reference data stored, determining tissue-induced changes in the nominal characteristics, and compensating for subject-specific variation in the in-vivo measurements by correcting the nominal calibration on the basis of the tissue-induced changes.
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Accused Products
Abstract
The invention relates to the calibration of a pulse oximeter intended for non-invasively determining the amount of at least two light-absorbing substances in the blood of a subject. In order to bring about a solution by means of which the effects caused by the tissue of the subject can be taken into account in connection with the calibration of a pulse oximeter, initial characterization measurements are carried out for a pulse oximeter calibrated under nominal conditions. Based on the characterization measurements, nominal characteristics are established describing the conditions under which nominal calibration has been defined, and reference data indicating the nominal characteristics are stored. In-vivo measurements are then performed on living tissue and based on the in-vivo measurements and the reference data stored, tissue-induced changes in the nominal characteristics are determined. Subject-specific variation in the in-vivo measurements is compensated for by correcting the nominal calibration on the basis of the tissue-induced changes.
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Citations
31 Claims
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1. A method for compensating for subject-specific variability in an apparatus intended for non-invasively determining the amount of at least two light-absorbing substances in the blood of a subject and provided with emitter means for emitting radiation at a minimum of two different wavelengths and with detector means for receiving the radiation emitted, the method comprising the steps of
calibrating the apparatus using a nominal calibration, carrying out initial characterization measurements, said measurements to include measuring radiation received by the detector, based on the characterization measurements, establishing nominal characteristics describing conditions under which the nominal calibration is used, storing reference data indicating the nominal characteristics established, performing in-vivo measurements on a living tissue, wherein radiation emitted through the tissue and received by the detector means is measured, based on the in-vivo measurements and the reference data stored, determining tissue-induced changes in the nominal characteristics, and compensating for subject-specific variation in the in-vivo measurements by correcting the nominal calibration on the basis of the tissue-induced changes.
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24. An apparatus for non-invasively determining the amount of at least two light absorbing substances in the blood of a subject, the apparatus comprising
emitter means for emitting radiation at a minimum of two different wavelengths, detector means for receiving said radiation at each of said wavelengths and producing at least two electrical output signals, first signal processing means for processing said output signals and producing a modulation signal for each wavelength, each modulation signal representing the pulsating absorption caused by the arterialized blood of the subject, second signal processing means for applying a predetermined calibration on said modulation signals, whereby transformed modulation signals applicable in the Lambert-Beer model are obtained, memory means for storing reference data indicating nominal characteristics under which said predetermined calibration has been applied, first compensation means, operatively connected to the memory means, for determining tissue-induced changes in the nominal characteristics, second compensation means, operatively connected to the first compensation means, for defining a subject-specific calibration by correcting the predetermined calibration on the basis of the tissue-induced changes, and calculation means, responsive to the second compensation means, for determining said amounts.
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25. A sensor for collecting measurement data for a pulse oximeter intended for non-invasively determining the amount of at least two light absorbing substances in the blood of a subject, the sensor comprising
means for emitting radiation at a minimum of two different wavelengths, means for receiving said radiation at each of said wavelengths and producing at least two electrical output signals, storage means including reference data indicating nominal characteristics describing calibration conditions of the pulse oximeter, said data allowing an apparatus connected to the sensor to determine tissue-induced changes in the nominal characteristics when radiation is emitted through said tissue.
Specification