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

• Current Assignee: Terumo Kabushiki Kaisha (Terumo Corporation)
• Original Assignee: Terumo Kabushiki Kaisha (Terumo Corporation)
• Inventors: Honda, Hiroaki, Kohno, Hiromasa, Nudeshima, Masahiro
• Primary Examiner(s): Warden, Robert J.
• Assistant Examiner(s): Blythe, Stephanie
• Application Number:
  US07/460,057
• Time in Patent Office: 935 Days
• Field of Search: 356/39, 356/40, 356/41, 356/42, 356/445, 356/448, 422/82.05, 422/82.11, 436/66, 436/68, 436/164, 435/808
• US Class Current: 422/82.05
• CPC Class Codes: A61B 5/0059 using light, e.g. diagnosis by transillumination, diascopy, fluorescence A61B5/0093, A61B5/1455, A61B5/02416 and A61B5/0261 take precedence
• CPC Class Codes: A61B 5/14557 specially adapted to extracorporeal circuits
• CPC Class Codes: G01N 2021/3144 for oxymetry
• CPC Class Codes: G01N 21/3151 using two sources of radiation of different wavelengths G01N21/33 - G01N21/39 take precedence
• CPC Class Codes: Y10S 435/808 Optical sensing apparatus

Abstract

A light beam having a first wavelength (λ₁) is applied to the blood from a first light radiation section, while a light beam having a second wavelength (λ₂) is applied from second and third light radiation sections different in positions from the first radiation section and from each other to the blood and the respective reflected-light intensity (I₁, I₂, I₃) is detected. A first correction value (X) for correcting the reflected-light intensity ratio (I₂ /I₃) is calculated by a first correction value operation section (40) and a second correction value (C₁) is calculated by a second correction value operation section (42) by use of this first correction value and the reflected-light intensity (I₃). The reflected-light intensity ratio (I₁ /I₂) is corrected by use of this second correction value and an oxygen saturation in the blood is operated based on correlation function by use of the corrected reflected-light intensity ratio (R_s). The reflected-light intensity ratio (I₂ /I₃) is corrected by the coefficient of correction thus operated and the hemoglobin concentration in the blood is operated based on correlation function by use of the reflected light intensity ratio thus corrected.

Claims

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 (R_s) 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 R_s =(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 (R_s) outputted by said reflected light intensity ratio correcting means.

2. An apparatus for measuring a degree of oxygen saturation according to claim 1, wherein said memory means stores a reference correlation function h(x) as said Hb calibration curve:

wherein

space="preserve" listing-type="equation">h(x)=b.sub.2 x.sup.2 +b.sub.1 x+b.sub.0

and where x=I₂ /I₃, and b₀, b₁ and b₂ are constant values.

3. An apparatus for measuring a degree of oxygen saturation according to claim 1, wherein said second corrective means calculates said second value C₁ by using an equation:

space="preserve" listing-type="equation">C.sub.1 =C.sub.0 ×

(I.sub.3)×

(X)

where C₀ is a constant value.

4. An apparatus for measuring a degree of oxygen saturation according to claim 1, wherein said oxygen degree calculating means calculates the degree of oxygen saturation in blood based on the correlation function f(x):

space="preserve" listing-type="equation">f(x)=a.sub.3 R.sub.s.sup.3 +a.sub.2 R.sub.s.sup.2 +a.sub.1 R.sub.s +a.sub.0

where a₀, a₁, a₂ and a₃ are constant values.

5. An apparatus for measuring a degree of oxygen saturation according to claim 1, wherein each of said first and second light-irradiating means includes an optical fiber for transmitting light from said source means respectively to said first and second light-irradiating portions, each of said first and second light-irradiating portions comprising an end face of said optical fiber.

6. An apparatus for measuring a degree of oxygen saturation according to claim 1, wherein said detecting means includes a photodetector, and a light-transmitting portion for transmitting light from a photodetecting portion to said photodetector, said photodetecting portion comprising an end face of an optical fiber which forms the light-transmitting portion.

7. An apparatus for measuring hemoglobin concentration in blood, comprising:

source means for emitting light at a specific wavelength (λ

₂), with a difference of a degree of extinction between oxygenated hemoglobin and carbomonoxy hemoglobin being comparatively small;

first and second light-irradiating means having first and second light-irradiating portions, respectively, and being coupled respectively to said source means for irradiating blood with light of said specific wavelength (λ

₂) from different directions;

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

corrective coefficient calculating means for calculating a corrective coefficient (A) based on a ratio of a ratio (I₁ /I₂) of the reflected-light intensity (I₁) of light from said first light-irradiating means to the reflected-light intensity (I₂) of light from said second light-irradiating means to a ratio ((I₁ /I₂)_s) of intensities of reflected-light from a blood with known hemoglobin concentration irradiated by said first and second light-irradiating means, according to an equation A=((I₁ /I₂)_s /(I₁ /I₂));

reflected-light intensity ratio correcting means for multiplying a reflected-light intensity ratio (I₁ /I₂) by said corrective coefficient (A) to obtain a corrected reflected-light ratio (R_s); and

hemoglobin concentration calculating means for calculating the hemoglobin concentration in blood based on a correlation function h(R_s) using the corrected reflected-light intensity ratio (R_s) outputted by said reflected light intensity ratio correcting means.

8. An apparatus for measuring a hemoglobin concentration according to claim 7, wherein each of said first and second light-irradiating means has different light-irradiating portions for irradiating the blood with light from said source means from different directions.

9. An apparatus for measuring a hemoglobin concentration according to claim 7, wherein said corrective coefficient calculating means includes memory means for storing an inverse function g(HB), and arithmetic means for calculating a reflected-light intensity ratio ((I₁ /I₂)_s) from blood with known hemoglobin concentration using both the inverse function g(Hb) and a reference value of hemoglobin concentration.

10. An apparatus for measuring a hemoglobin concentration according to claim 7, wherein said reflected-light intensity ratio correcting means calculates said corrected reflected-light intensity ratio (Rs) according to an equation:

space="preserve" listing-type="equation">Rs=A×

(I.sub.1 /I.sub.2)={(I.sub.1 /I.sub.2).sub.s /(I.sub.1 /I.sub.2)}×

(I.sub.1 /I.sub.2).

11. An apparatus for measuring a hemoglobin concentration according to claim 7, wherein said hemoglobin concentration calculating means calculates the hemoglobin concentration in blood based on the correlation function:

space="preserve" listing-type="equation">H(Rs)=-4.55 R.sub.s.sup.2 +37.8 R.sub.s -4.91.

12. An apparatus for measuring a hemoglobin concentration according to claim 7, wherein said detecting means includes a photodetector, and a light-transmitting portion for transmitting light from a photodetecting portion to said photodetector, said photodetecting portion comprising an end face of an optical fiber which forms the light-transmitting portion.