Noninvasive device for photoelectrically measuring the property of arterial blood

• US 4,694,833 A
• Filed: 03/13/1986
• Issued: 09/22/1987
• Est. Priority Date: 02/19/1982
• Status: Expired due to Term

• Current Assignee: Minolta Camera Kabushiki Kaisha
• Original Assignee: Minolta Camera Kabushiki Kaisha
• Inventors: Hamaguri, Kenji
• Primary Examiner(s): Howell, Kyle L.
• Assistant Examiner(s): Hanley, John C.
• Application Number:
  US06/839,433
• Time in Patent Office: 558 Days
• Field of Search: 128/633, 128/634, 128/665, 128/666, 356/41
• US Class Current: 600/330
• CPC Class Codes: A61B 5/14551 for measuring blood gases
• CPC Class Codes: G01J 1/1626 Arrangements with two photodetectors, the signals of which are compared
• CPC Class Codes: G01J 2001/161 Ratio method, i.e. Im/Ir
• CPC Class Codes: G01N 21/314 with comparison of measurements at specific and non-specific wavelengths dual wavelength spectrometry G01J3/427
• CPC Class Codes: G01N 2201/1245 Averaging several measurements

Abstract

A noninvasive device for photoelectrically measuring a property of arterial blood is provided. Light that contacts living tissue with arterial blood is converted into a pair of electrical signals. The electrical signals are processed to provide information of the amplitude of the measured signals and are further processed to produce a final output signal that is substantially a square function of a ratio between the electrical signals representative of the amplitudes.

Claims

1. A noninvasive device for photoelectrically measuring a property of arterial blood in living tissue comprising:

means for generating a source light and causing said light to enter into living tissue, such that the light generating means remains outside the living tissue and only the generated light passes into the living tissue;

means for photoelectrically measuring the intensity of the source light emerging from the living tissue after contact with the arterial blood therein, at a pair of separate wavelengths, to produce a pair of electrical signals, respectively, each signal including an alternating-current component and a direct-current component;

means for calculating information from said pair of electric signals representative of the relative amplitude of the alternating-current component compared to the direct-current component for each of the measured wavelengths and for producing first and second calculated outputs, respectively, each output representing a respective said relative amplitude;

means for obtaining a final output signal according to a function containing the square of a ratio between the first and second calculated outputs and containing no terms of first order in said ratio; and

means for indicating the property of the arterial blood in response to the final output.

2. The invention of claim 1, wherein said obtaining means includes means for approximating the linear function of the square of the ratio as a joint combination of a plurality of linear functions of the ratio.

3. The invention of claim 1, wherein said approximating means includes means for selecting one of the plurality of linear functions for use in approximating, the one selected being dependent upon the level of the ratio.

4. The invention of claim 1, wherein the obtaining means includes a microprocessor and an associated digital memory circuit.

5. The invention of claim 1, wherein the obtaining means includes means for previously storing various values for the final output signal in relation to a variety of possible combinations of values for the first and second calculated outputs, and means for searching a specific value for the final output signal in accordance with a specific combination of values for the first and second calculated outputs actually obtained by the calculating means.

6. A noninvasive device for photoelectrically measuring a property of arterial blood in living tissue comprising:

means for providing a source light to enter into living tissue from the outside thereof;

means for photoelectrically measuring the intensity of the source light emerging from the living tissue after contact with the arterial blood contained therein, at a predetermined pair of wavelengths within the source light, and for producing a pair of electrical signals respectively representing the intensity at each wavelength;

means for generating information representative of the relative variation in amplitude of each of the electric signals with respect to a reference level;

means for obtaining a final output signal according to a function containing the square of a ratio between the information from said generating means for the first of the pair or wavelengths and that for the second pair thereof and containing no terms of first order in said ratio; and

means for indicating the property of the arterial blood in response to the final output signal.

7. The invention of claim 6, wherein said obtaining means includes means for approximating the linear function of the square of the ratio as a joint combination of a plurality of linear functions of the ratio.

8. The invention of claim 6, wherein said approximating means includes means for selecting one of the plurality of linear functions for use in approximating, the one selected being dependent upon the level of the ratio.

9. The invention of claim 6, wherein the obtaining means includes a microprocessor and an associated digital memory circuit.

10. The invention of claim 6, wherein the obtaining means includes means for previously storing various values for the final output signal in relation to a variety of possible combinations of values for the first and second calculated outputs, and means for searching a specific value for the final output signal in accordance with a specific combination of values for the first and second calculated outputs actually obtained by the calculating means.

11. A noninvasive device for photoelectrically measuring a property of arterial blood in living tissue comprising:

means for generating a source light and causing said light to enter into living tissue, such that the light generating means remains outside the living tissue and only the generated light passes into the living tissue;

means for photoelectrically measuring the intensity of the source light emerging from the living tissue after contact with the arterial blood therein, at a pair of separate wavelengths, to produce a pair of electrical signals, respectively, each signal including an alternating-current component and a direct-current component;

means for calculating information from said pair of electric signals representative of the relative amplitude of the alternating-current component compared to the direct-current component for each of the measured wavelengths and for producing first and second calculated outputs, respectively, each output representing a respective said relative amplitude;

means for obtaining a final output signal according to a function having a variable which is the ratio between the first and second calculated outputs and which contains at least one second order term of said variable and no first order terms in said variable; and

means for indicating the property of the arterial blood in response to the final output.

12. The invention of claim 11, wherein said obtaining means includes means for approximating the linear function of the square of the ratio as a joint combination of a plurality of linear functions of the ratio.

13. The invention of claim 11, wherein said approximating means includes means for selecting one of the plurality of linear functions for use in approximating, the one selected being dependent upon the level of the ratio.

14. The invention of claim 11, wherein the obtaining means includes a microprocessor and an associated digital memory circuit.

15. The invention of claim 11, wherein the obtaining means includes means for previously storing various values for the final output signal in relation to a variety of possible combinations of values for the first and second calculated outputs, and means for searching a specific value for the final output signal in accordance with a specific combination of values for the first and second calculated outputs actually obtained by the calculating means.

16. A noninvasive device for photoelectrically measuring a property of arterial blood in living tissue comprising:

means for providing a source light to enter into living tissue from the outside thereof;

means for photoelectrically measuring the intensity of the source light emerging from the living tissue after contact with the arterial blood contained therein, at a predetermined pair of wavelengths within the source light, and for producing a pair of electrical signals respectively representing the intensity at each wavelength;

means for generating information representative of the relative variation in amplitude of each of the electric signals with respect to a reference level;

means for obtaining a final output signal according to a function having a variable which is the ratio between the information from said generating means for the first of the pair of wavelengths and that for the second of the pair thereof and which contains at least one second order term of said variable and no first order terms of said variable; and

means for indicating the property of the arterial blood in response to the final output signal.

17. The invention of claim 16, wherein said obtaining means includes means for approximating the linear function of the square of the ratio as a joint combination of a plurality of linear functions of the ratio.

18. The invention of claim 16, wherein said approximating means includes means for selecting one of the plurality of linear functions for use in approximating, the one selected being dependent upon the level of the ratio.

19. The invention of claim 16, wherein the obtaining means includes a microprocessor and an associated digital memory circuit.

20. The invention of claim 16, wherein the obtaining means includes means for previously storing various values for the final output signals in relation to a variety of possible combinations of values for the first and second calculated outputs, and means for searching a specific value for the final output signal in accordance with a specific combination of values for the first and second calculated outputs actually obtained by the calculating means.