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Apparatus for measuring hemoglobin concentration and oxygen saturation thereof

  • US 5,149,503 A
  • Filed: 03/02/1990
  • Issued: 09/22/1992
  • Est. Priority Date: 07/24/1987
  • Status: Expired due to Term
First Claim
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1. An apparatus for measuring a degree of oxygen saturation in blood, comprising:

  • source means for emitting light at a first and second wavelength (λ

    1, λ

    2), with a difference of a degree of extinction between oxygenated hemoglobin and carbomonoxy hemoglobin being comparatively large at said first wavelength and small at said second wavelength;

    first light-irradiating means having a first light-irradiating portion, and being coupled to said source means for alternately irradiating blood with light of said first or second wavelength (λ

    1, λ

    2);

    second light irradiating means having a second light-irradiating portion, and being coupled to said source means for constantly irradiating the blood with light of said second wavelength λ

    2 ;

    detecting means, arranged such that the distance from the detecting means to said first light-irradiating means and the distance from the detecting means to said second light-irradiating means differ, for detecting intensities (I1, I2, I3) of light reflected from the blood irradiated with the light from each of the first and second light-irradiating portions of said first and second light-irradiating means corresponding to their wavelength;

    memory means for storing an Hb calibration curve;

    arithmetic means for calculating a reflected-light intensity ratio function g(Hb'"'"') of blood having a reference value (Hb'"'"') of hemoglobin concentration by reference to said Hb calibration curve stored in said memory means;

    first corrective value calculating means for calculating a first corrective value (X) based on both a reflected-light intensity ratio (I2 /I3)s) from a blood with known hemoglobin concentration and said reflected-light intensity ratio function, according to an equation X=g(Hb'"'"')×

    (I2 /I3)/(I2 /I3)s, to correct a ratio (I2 /I3) of detected reflected-light intensity (I2) due to irradiation with light of said second wavelength produced by said first light-irradiating means versus detected reflected-light intensity (I3) due to irradiation with light of said second wavelength produced by said second light-irradiating means;

    second corrective values calculating means for calculating a second corrective value (C1) based on said first corrective value (X), the reflected-light intensity (I3) of light from the second light-irradiating means detected continuously by said detecting means, and a constant value (C0), according to an equation C1 =C0 ×

    (I3

    (X);

    reflected-light intensity ratio correcting means for correcting to remove an influence of hematocrit value and for calculating a corrected reflected-light intensity ratio (Rs) based on said second corrective value (C1), a reflected-light intensity ratio (I1 /I2) of the detected reflected-light intensity (I1) of light of said first wavelength produced by the first light-irradiating means versus detected reflected-light intensity (I2) of light of said second wavelength produced by the first light-irradiating means, according to an equation Rs =(I1 -C1)/(I2 -C1); and

    oxygen saturation degree calculating means for calculating the degree of oxygen saturation in blood based on a correlation function (f(x)) using the corrected reflected light intensity ratio (Rs) outputted by said reflected light intensity ratio correcting means.

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