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 ain 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 ofmeasuring 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 Ekl0,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 Ekl0 due to light transmission through living tissue,nominal values for a calculation defining temperature-induced corrections to the nominal extinction matrix Ekl0 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 Ekl0 with both calculations with the established values,solving the hemoglobin fractions using the corrected nominal extinction matrix in a Lambert-Beer model.
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Accused Products
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.
33 Citations
16 Claims
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1. A method for compensating for subject-specific variability in a pulse oximeter intended for non-invasively determining ain 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 Ekl0, 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 Ekl0 due to light transmission through living tissue, nominal values for a calculation defining temperature-induced corrections to the nominal extinction matrix Ekl0 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 Ekl0 with both calculations with the established values, solving the hemoglobin fractions using the corrected nominal extinction matrix in a Lambert-Beer model. - View Dependent Claims (2, 3, 4, 5, 12)
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6. 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 a light transmission 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 from a memory nominal calibration comprising transformations used to transform in-vivo measurement signals to the corresponding signals in the Lambert-Beer tissue model, reading from the memory nominal characteristics describing conditions under which the nominal calibration has been done, the nominal characteristics comprising: -
nominal values for functional light transmissions FLT defining light transmission for each emitter through tissue at nominal conditions, establishing tissue values for the functional light transmissions FLT using the detector output signals, forming subject-specific calibration transformations using the change between the nominal values and the tissue values of the functional light transmissions FLT and the nominal calibration transformations, solving the hemoglobin fractions using the corrected calibration transformations. - View Dependent Claims (7, 8, 9, 10, 11)
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13. 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
a sensor attached to the pulse oximeter, for receiving an output signal at at least two distinct wavelengths, a signal processing part for extracting AC and DC signals for each wavelength output signal, each wavelength signal representing the transmission of light through tissue of the subject, and a memory, a calculation means for calculating the amount of at least two light absorbing substances in the blood of a subject, a control and measurement unit for controlling operation of the pulse oximeter, wherein the pulse oximeter comprises an extinction coefficient compensation block operatively connected to the signal processing part and to the memory for reading nominal extinction matrix Ekl0 and nominal calibration characteristics responsive to the tissue average characteristics of a population of subjects, said block comprising calculation means adapted to correct the nominal extinction matrix Ekl0 for the sensor on living tissue of a subject, responsive to the tissue characteristics of the individual subject, the extinction coefficient compensation block being further operatively connected to the sensor and to the memory for reading nominal calibration characteristics describing the temperature behaviour of sensor emitters, the calculation means being further adapted to correct the nominal extinction matrix Ekl0 for the temperature of the sensor emitters on living tissue of an individual subject, a temperature determining block, wherein the calculation means of the extinction coefficient compensation are further adapted to establish tissue values for the functional light transmissions FLT using the DC signals, establish temperature values for the emitters in a sensor, form a subject-specific calibration by correcting the nominal extinction matrix Ekl0 using the change between the nominal values and tissue values of the functional light transmissions FLT, the temperature values of the emitters and the nominal transformations, and a hemoglobin fraction calculation unit comprising means solving the hemoglobin fractions using the corrected nominal extinction matrix in accordance with the Lambert-Beer model.
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15. 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
a sensor attached to the pulse oximeter, for receiving an output signal at at least two distinct wavelengths and controlling operation of the sensor, a signal processing part for extracting AC and DC signals for each wavelength output signal, each wavelength signal representing the transmission of light through tissue of the subject, and a memory, a calculation means for calculating the amount of at least two light absorbing substances in the blood of a subject, wherein the pulse oximeter comprises, a transformation compensation block operatively connected to the signal processing part and to the memory for reading nominal transformations obtained for a population of subjects and used to transform in-vivo measurement signals to the corresponding signals in the Lambert-Beer model and nominal values for functional light transmissions FLT defining light transmission for each emitter through average tissues of the population of subjects, said block comprising calculation means adapted to establish tissue values for the functional light transmissions FLT using the DC signals, form a subject-specific calibration by correcting the nominal transformations using the change between the nominal values and tissue values of the functional light transmissions FLT, and a hemoglobin fraction calculation unit connected to the extinction coefficient compensation block and the calibration values compensation block, said unit comprising means for solving the hemoglobin fractions using the corrected subject-specific calibration transformations to transform the in-vivo measurement signals to the corresponding signals in the Lambert-Beer model.
Specification