Compensation of human variability in pulse oximetry
First Claim
1. 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 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 tissue, reading a nominal calibration and nominal calibration characteristics from a memory, establishing values for the same nominal characteristics for the sensor on living tissue of the subject using the detector output signal, calculating changes in the nominal calibration characteristics induced by the living tissue, forming a subject-specific calibration by correcting the nominal calibration with the changes, solving the hemoglobin fractions using the corrected nominal calibration.
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Abstract
The invention relates to a method of calibrating a pulse oximeter, in which the effects caused by tissue of a subject can be taken into account. A detector output signal is measured when living tissue of the subject is present between emitters and the detector in a sensor. Nominal calibration and nominal calibration characteristics are read from a memory, whereupon values for the same nominal characteristics for the sensor on living tissue of the subject are established using the detector output signal. Then, changes in the nominal calibration characteristics induced by the living tissue are calculated and a subject-specific calibration is formed by correcting the nominal calibration with the changes. Finally, the hemoglobin fractions are solved using the corrected nominal calibration. The invention also relates to a pulse oximeter having pre-stored data in a memory comprising data of initial characterization measurements, data of nominal characteristics describing calibration conditions under which a predetermined calibration of the apparatus has been applied, and data of nominal calibration and nominal calibration characteristics. An extinction coefficient compensation block is operatively connected to the first signal processing means and to the memory for reading data, said block comprising first calculation means adapted to correct the nominal characteristics of the sensor on living tissue of the subject. A transformation compensation block is operatively connected to the first signal processing means for receiving the DC signals and to the memory for reading data, said block comprising second calculation means adapted to correct the transformation values based on the changes in the DC signals induced by tissue of the subject. Alternatively, said data may be stored in the sensor part of the pulse oximeter.
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Citations
28 Claims
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1. 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 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 tissue, reading a nominal calibration and nominal calibration characteristics from a memory, establishing values for the same nominal characteristics for the sensor on living tissue of the subject using the detector output signal, calculating changes in the nominal calibration characteristics induced by the living tissue, forming a subject-specific calibration by correcting the nominal calibration with the changes, solving the hemoglobin fractions using the corrected nominal calibration.
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17. A pulse oximeter for non-invasively determining in in-vivo measurement the amount of at least two light absorbing substances in the blood of a subject, the pulse oximeter having an interface to a sensor for receiving an output signal at at least two distinct wavelengths and controlling operation of the sensor, the pulse oximeter further comprising
signal processing means for extracting AC and DC signals for each wavelength, each wavelength signal representing the absorption caused by the blood of the subject, pre-stored data in a memory, comprising data of initial characterization measurements, data of nominal characteristics describing calibration conditions under which a predetermined calibration of the apparatus has been applied, and data of nominal calibration and nominal calibration characteristics, an extinction coefficient compensation block operatively connected to the first signal processing means, and to the memory for reading data, said block comprising first calculation means adapted to correct the nominal characteristics of the sensor on living tissue of the subject, a transformation compensation block operatively connected to the first signal processing means for receiving the DC signals and to the memory for reading data, said block comprising second calculation means adapted to correct the transformation values based on the changes in the DC signals induced by tissue of the subject, and a hemoglobin fraction calculation unit connected to the extinction coefficient compensation block and the calibration values compensation block, said unit comprising means for applying the corrected nominal characteristics and the corrected nominal calibration values in solving the hemoglobin fractions.
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21. A sensor for collecting measurement data for 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, the sensor comprising
at least one light emitter for emitting light at a minimum of two different wavelengths, a light detector for receiving said light at each of said wavelengths and producing an electrical output signal indicating the received light at the said wavelengths, a pulse oximeter readable memory data pre-stored in the memory, comprising data of initial characterization measurements, data of nominal characteristics describing calibration conditions under which a predetermined calibration of the pulse oximeter has been establihed, and data of nominal calibration values, wherein said data allows the pulse oximeter connected to the sensor to determine tissue-induced changes in the nominal characteristics when light is propagated through said tissue.
Specification