Adaptive calibration for pulse oximetry
First Claim
1. A method of calibrating a pulse oximeter comprising:
- selecting a probe having an emitter, a detector, and a pathlength between the emitter and detector;
measuring transmission of light through a tissue of interest with the probe;
compiling a database of measured values characterizing the transmission of light through such a tissue;
formulating a value for a parameter kDC as a function of at least one of the measured values, wherein kDC is determined based only on empirical data; and
incorporating the parameter kDC into a calibration equation for determining a value for SpO2, wherein the calibration equation includes using kDC as a multiplier for a value determined from the measured values.
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Abstract
A method for calibrating a pulse oximeter device and an apparatus incorporating the method and a system for utilizing the method. The method is based on modeling light propagation in tissue at two wavelengths, typically, one in the red and one in the infrared range of the spectrum. A formula is derived relating the arterial oxygen saturation to a ratio R commonly measured by standard pulse oximeters. A specific parameter is identified and utilized in the calibration of the oximeter. This parameter is formulated in terms of the DC signals measured by the pulse oximeter at the two wavelengths. An empirical method for estimating this parameter based on experimental data is also described.
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Citations
26 Claims
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1. A method of calibrating a pulse oximeter comprising:
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selecting a probe having an emitter, a detector, and a pathlength between the emitter and detector;
measuring transmission of light through a tissue of interest with the probe;
compiling a database of measured values characterizing the transmission of light through such a tissue;
formulating a value for a parameter kDC as a function of at least one of the measured values, wherein kDC is determined based only on empirical data; and
incorporating the parameter kDC into a calibration equation for determining a value for SpO2, wherein the calibration equation includes using kDC as a multiplier for a value determined from the measured values. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. A method of performing optical blood oximetry comprising:
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measuring the transmission of light through tissue;
determining at least one DC value based upon the transmission of light measurements;
selecting a calibration parameter kDC based upon the determined DC value, wherein the calibration parameter is determined based only on empirical data; and
estimating SaO2 based upon the selected calibration parameter by using the calibration parameter as a multiplier for a value determined from the measuring step. - View Dependent Claims (12, 13, 14, 15)
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16. A method of performing optical blood oximetry comprising:
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measuring the transmission of light through tissue;
determining at least one DC value based upon the transmission of light measurements;
selecting a calibration parameter kDC based upon the determined DC value, wherein kDC includes a partial derivative Dr value; and
estimating SaO2 based upon the selected calibration parameter.
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17. A method of performing optical blood oximetry comprising:
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(a) measuring the transmission of light through tissue;
(b) determining at least one DC value based upon the transmission of light measurements by performing the steps including;
(1) quantifying an AC value based upon the transmission of light, (2) calculating a Ratio R, and (3) relating R to the calibration parameter that accounts for background absorption and scattering of light including determining a partial derivative Dr value, and using the Dr value to relate R to the calibration parameter;
(c) selecting a calibration parameter kDC based upon the determined DC value; and
(d) estimating SaO2 based upon the selected calibration parameter.
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18. A method of performing optical blood oximetry comprising:
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(a) measuring the transmission of light through tissue;
(b) determining at least one DC value based upon the transmission of light measurements by performing the steps including;
(1) quantifying an AC value based upon the transmission of light, including estimating a partial derivative Dr value, (2) calculating a Ratio R, and (3) relating R to the calibration parameter that accounts for background absorption and scattering of light;
(c) selecting a calibration parameter based upon the determined DC value; and
(d) estimating SaO2 based upon the selected calibration parameter.
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19. A physiological condition measuring device comprising:
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light generating means;
light detecting means, wherein an optical path having pathlength is defined between the light generating means and the light detecting means; and
a processing system that measures light incident upon the light detecting means and returns a solution determined from a calculation that includes multiplying (1) a value determined from the measured light and (2) a calibration parameter kDC that is based only on empirical data. - View Dependent Claims (20, 21, 22, 23, 24)
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25. An apparatus for determining oxygen saturation of hemoglobin in arterial blood using signals received from a probe, the signals being indicative of the light absorption of arterial blood, which has pulsatile and non-pulsatile components, at two or more light wavelengths, the apparatus comprising:
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means responsive to the signals received from the probe;
means for convening the signals received into data;
memory means for storing the data;
computing means for calculating parameters from the data; and
means for relating the calculated parameters to a predicted arterial oxygen saturation, that includes (1) selecting a calibration parameter kDC based upon the non-pulsatile components, wherein the calibration parameter is determined based only on empirical data, and (2) estimating oxygen saturation based upon (a) the selected calibration parameter and (b) the calculated parameters, wherein estimating the oxygen saturation includes using the calibration parameter as a multiplier for the calculated parameters.
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26. A system for performing pulse oximetry comprising:
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a probe including at least one light source for transmitting light and at least one detector for detecting the transmitted light;
a processing system in communication with the probe so as to receive signals from the probe, wherein the processing system (a) determines data corresponding to
1) first variables indicative of the optical parameters of a tissue being probed based on the received signals and
2) second variables related to a parameter kDC that is determined based only on empirical data and that accounts for the scattering and absorption of light by the tissue, and (b) determines an estimate of oxygen saturation by performing a calculation that includes multiplying the first variables by the second variables.
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Specification