Method and apparatus for determining oxygen saturation of blood in body organs

• US 6,594,513 B1
• Filed: 01/12/2000
• Issued: 07/15/2003
• Est. Priority Date: 01/12/2000
• Status: Expired due to Fees

• Current Assignee: Paul D. Jobsis
• Original Assignee: Paul D. Jobsis
• Inventors: Jobsis, Frans F., Jobsis, Paul D.
• Primary Examiner(s): Winakur, Eric F.
• Assistant Examiner(s): KREMER, MATTHEW J
• Application Number:
  US09/481,830
• Time in Patent Office: 1,280 Days
• Field of Search: 600/309-310, 600/316, 600/330, 600/322-326, 600/336, 600/328, 356/39-42
• US Class Current: 600/328
• CPC Class Codes: A61B 5/14553 specially adapted for cerebral tissue

Abstract

A spectrophotometric method and apparatus for determining the degree of oxygen saturation of the hemoglobin in the blood within a body part utilizes differences in light absorption based on differences in extinction coefficients at different wavelengths. Oxygen saturation is determined by utilizing absorption at three or more wavelengths of radiation preferably in the near red and infrared region (NIR) of the spectrum, specifically tailored to two or more components to be detected by the radiation. The first (reference) wavelength is preferably chosen to be at an isosbestic point for the two components, commonly the oxygenated and deoxygenated forms of hemoglobin. The absorption at the isosbestic point is subtracted from the absorption at the other wavelengths. Using these differences in absorption, the amount of each of the components encountered by the light may be determined without determination of pathlength, which would be required to determine the concentration. In order to determine the oxygenation state, i.e. ratio of oxygenated to deoxygentaed blood components, knowledge of the relative amounts suffices. Interference from other light-absorbing components, specifically those that respond to the oxygenation state of the body part (such as cytochrome c oxidase) is in the three wavelength method eliminated by reiterative correction.

Claims

1. A non-invasive, in-vivo, in-situ spectrophotometric method of determining percent oxygen saturation of hemoglobin in blood within a part of a body exhibiting active oxidative metabolism without having to consider changes in optical path length, concentrations of HbO₂ and Hb or degree of light scattering which takes place during such determination, comprising:

(a) selecting electromagnetic radiation of at least three wavelengths to establish at least three selected wavelengths and wherein said at least three selected wavelengths includes a first wavelength which is a reference wavelength, a second wavelength which is a measuring wavelength and a third wavelength which is a measuring wavelength;

(b) irradiating a selected location on said body part with light which at said location includes each of said selected wavelengths each of measured intensity;

(c) measuring the light intensity and calculating the absorbance of each of said selected wavelengths after passing through said body part;

(d) determining the differences between the absorption of light of said reference wavelength and said second and said third wavelengths by subtraction of the absorbance of said reference wavelength from that of said second and third wavelengths;

(e) entering said differences of absorptions of the light of said reference wavelength and said second and third wavelengths in first and second equations derived from differences between relative in-situ determined isosbestic normalized extinction coefficients of Hb and HbO₂ at said reference wavelength and said second and third wavelengths and solving said first and second equations for the amounts of HbO₂ and Hb encountered as distinct from calculated concentrations;

(f) continuously correcting said amounts for absorption contributions of cytochrome c oxidase to said percent oxygen saturation; and

(g) determining tissue oxygen saturation percent as a ratio of the amount of HbO₂ to the total amount of hemoglobin (HbO₂+Hb) times 100.

2. The method of claim 1 wherein said at least three selected wavelengths are selected to be in the region between 600 and 1300 nm.

3. The method of claim 2, wherein the said reference wavelength is at an isosbestic point for oxygenated hemoglobin and deoxygenated hemoglobin of approximately 815 nm.

4. The method of claim 1, further comprising a fourth wavelength in the range of 860-875 nm.

5. The method of claim 1, wherein said step of continuously correcting said amounts is based on determining and entering the extinction coefficient for cytochrome c oxidase into said equations.

6. The method of claim 5, wherein the correction for absorbance contribution of cytochrome c oxidase is performed in a reiterative manner to provide a close approximation of the correction to be applied for determination of tissue oxygen saturation existing during conditions away from normoxia.

7. The method of claim 1, wherein the percent of oxygen saturation of the hemoglobin in the blood is continuously corrected for changes in cytochrome c oxidase by determining the trend of absorbance of cytochrome c oxidase.

8. The method of claim 1, wherein the reference wavelength is at an isosbestic point for oxygenated hemoglobin and deoxygenated hemoglobin of approximately 815 nm.

9. The method of claim 1, wherein said reference wavelength is in the range of 810-820 nm, said first measuring wavelength is in the range of 750-785 nm, and said second measuring wavelength is in the range of 895-925 nm.

10. The method of claim 1 wherein said at least three selected wavelengths comprises four wavelengths and includes first and second reference wavelengths on opposite sides of an isosbestic point of said hemoglobin.

11. A non-invasive, in-vivo, in-situ spectrophotometric method of determining the percent oxygen saturation of the hemoglobin in the blood within a part of the body exhibiting active oxidative metabolism without having to consider changes in the optical path length, concentrations of HbO₂ and Hb or degree of light scattering which takes place during such determination, comprising:

(a) selecting electromagnetic radiation of at least three wavelengths to establish at least three selected wavelengths and wherein said at least three selected wavelengths includes a first wavelength which is a reference wavelength, a second wavelength which is a measuring wavelength and a third wavelength which is a measuring wavelength;

(b) irradiating a selected location on said body part with light which at said location includes each of said selected wavelengths each of measured intensity;

(c) measuring the light intensity and calculating the absorbance of each of said selected wavelengths after passing through said body part;

(d) determining the differences between the absorption of light of said reference wavelength and said second and said third wavelengths by subtraction of the absorbance of said reference wavelength from that of said second and third wavelengths;

(e) entering said differences of absorptions of the light of said reference wavelength and said second and third wavelengths, in first and second equations derived from differences between relative in-situ determined isosbestic normalized extinction coefficients of Hb and HbO₂ at said reference wavelength and said second and third wavelengths and solving said first and second equations for the amounts of HbO₂ and Hb encountered as distinct from calculated concentrations;

(f) continuously correcting said amounts for absorption contributions of cytochrome c oxidase to said percent oxygen saturation based on determining and entering the extinction coefficient for cytochrome c oxidase into said equations and performing said correction in a reiterative manner to provide a close approximation of the correction to be applied for determination of tissue oxygen saturation existing during conditions away from normoxia; and

(g) determining tissue oxygen saturation percent as a ratio of the amount of HbO₂ to the total amount of hemoglobin (HbO₂+Hb) times 100.

12. A non-invasive, in-vivo, in-situ spectrophotometric method of determining the percent oxygen saturation of the hemoglobin in the blood within a part of the body exhibiting active oxidative metabolism without having to consider changes in the optical path length, concentrations of HbO₂ and Hb or degree of light scattering which takes place during such determination, comprising:

(a) selecting electromagnetic radiation of at least three wavelengths to establish at least three selected wavelengths and wherein said at least three selected wavelengths includes a first wavelength which is a reference wavelength, a second wavelength which is a measuring wavelength and a third wavelength which is a measuring wavelength;

(b) irradiating a selected location on said body part with light which at said location includes each of said selected wavelengths each of measured intensity;

(c) measuring the light intensity and calculating the absorbance of each of said selected wavelengths after passing through said body part;

(d) determining the differences between the absorption of light of said reference wavelength and said second and said third wavelengths by subtraction of the absorbance of said reference wavelength from that of said second and third wavelengths;

(e) entering said differences of absorptions of the light of said reference wavelength and said second and third wavelength, in first and second equations derived from differences between relative in-situ determined isosbestic normalized extinction coefficients of Hb and HbO₂ at said reference wavelength and said second and third wavelengths and solving said first and second equations for the amounts of HbO₂ and Hb encountered as distinct from calculated concentrations;

(f) continuously correcting said amounts for absorption contributions of cytochrome c oxidase to said percent oxygen saturation;

(g) continuously correcting the percent of oxygen saturation of the hemoglobin in the blood for changes in cytochrome c oxidase by determining the trend of absorbance of cytochrome c oxidase; and

(h) determining tissue oxygen saturation percent as a ratio of the amount of HbO₂ to the total amount of hemoglobin (HbO₂+Hb) times 100.

13. A non-invasive, in-vivo, in-situ spectrophotometric method for calculating oxygen saturation of the hemoglobin in the blood in tissue of a body organ exhibiting active oxidative metabolism without having to consider changes in the optical path length, concentrations of HbO₂ and Hb or scattering which takes place during such determination, comprising:

(a) establishing a source of multiple and at least three wavelengths of light and at least one of which is substantially at an isosbestic point of oxy- and deoxy-hemoglobin;

(b) contacting a selected location on said organ with said light to cause said light to be selectively either reflected from or passed through said organ and when passed through said organ being of sufficient intensity to pass both through said organ as well as through any skin and bone in the path of said light;

(c) prior to contacting said organ with said light, mixing said multiple wavelengths of light such that said tissue at said location receives light of each of said wavelengths homogenously;

(d) creating signals representative of the absorption by the tissue for each of the wavelengths;

(e) processing said signals by subtracting the absorbance by the tissue for the wavelength at said isosbestic point from the absorbance of each of the other wavelengths to establish for each other wavelength a difference between such absorbances;

(f) processing signals representative of said differences and determining from the differences the oxygen saturation of the hemoglobin in the blood in the tissue; and

(g) during said processing continuously correcting said amounts for absorption contributions of cytochrome c oxidase to said percent oxygen saturation in a reiterative manner.

14. A non-invasive, in-vivo, in-situ spectrophotometric apparatus for calculating oxygen saturation in the hemoglobin in blood in tissue of a body organ exhibiting active oxidative metabolism independent of changes in optical path length, concentration of HbO₂ and Hb and scattering, comprising:

(a) a plurality of light sources located externally of the organ and providing multiple and at least three wavelengths of light and at least one of which is at an isosbestic point of hemoglobin;

(b) means for mixing said wavelengths of light to provide a beam of light containing each of said wavelengths;

(c) means for receiving said beam of light and contacting said organ with said light to cause said light to be selectively either reflected from or passed through said organ and when passed through said organ being of sufficient intensity to pass both through said organ as well as through any skin and bone in the path of said light;

(d) means for comparing the absorbance by the tissue for each of the said three wavelengths after being passed through the organ and creating signals representative of such absorbance;

(e) means for processing said signals by subtracting the absorbance by the tissue for the wavelength at said isosbestic point from the absorbance of each of the other wavelengths to establish for each other wavelength a difference between such absorbances;

(f) means for continuously correcting said processing by reiterative calculation for the relative tissue absorptions associated with said wavelengths for the absorption contribution of cytochrome c oxidase; and

(g) means for processing signals representative of said differences and determining from the differences the oxygen saturation of the blood in the tissue.

15. A non-invasive, in-vivo, in-situ spectrophotometric method of determining the percent of oxygen saturation of the hemoglobin in the blood within a part of the body exhibiting active oxidative metabolism without having to consider changes in the optical path length, concentrations of HbO₂ and Hb or scattering which takes place during such determination, comprising:

(a) selecting electromagnetic radiation of three wavelengths, one of said wavelengths being at an isosbestic point of hemoglobin;

(b) irradiating a selected location on the tissue comprising said body part with light which at said location includes light of each of said selected wavelengths;

(c) determining the relative absorptions of each of said wavelengths by said body part tissue;

(d) adjusting by reiterative calculation the relative tissue absorptions associated with said wavelengths for contributions to said absorptions by cytochrome c oxidase;

(e) processing signals representative of said absorptions and adjustment; and

(f) utilizing said processing to calculate the percent oxygen saturation of the hemoglobin in the blood within said body part.

16. A non-invasive, in-vivo, in-situ spectrophotometric method of determining the percent of oxygen saturation of the hemoglobin in the blood within a part of the body exhibiting active oxidative metabolism without having to consider changes in the optical path length, concentrations of HbO₂ and Hb or scattering which takes place during such determination, comprising:

(a) selecting electromagnetic radiation of three wavelengths, one of said wavelengths being at an isosbestic point of hemoglobin;

(b) irradiating a selected location on the tissue comprising said body part with light which at said location includes light of each of said selected wavelengths;

(c) determining the relative absorptions of each of said wavelengths by said body part tissue;

(d) adjusting by reiterative calculation the relative tissue absorptions associated with said wavelengths for contributions to said absorptions by cytochrome c oxidase;

(e) processing signals representative of said absorptions and adjustment; and

(f) utilizing said processing to calculate the percent oxygen saturation of the hemoglobin in the blood within said body part.