Blood constituent measuring device and method

• US 4,407,290 A
• Filed: 04/01/1981
• Issued: 10/04/1983
• Est. Priority Date: 04/01/1981
• Status: Expired due to Fees

• Current Assignee: BOC Group BV (Linde Plc)
• Original Assignee: Bion Technologies, Inc. (Bion Environmental Technologies, Inc.)
• Inventors: Wilber, Scott A.
• Primary Examiner(s): Apley, Richard J.
• Assistant Examiner(s): Yanulis, George
• Application Number:
  US06/250,956
• Time in Patent Office: 916 Days
• Field of Search: 128/632, 128/633, 128/634, 128/653, 128/654, 128/663, 128/665, 128/666, 128/667, 356/39, 356/40, 356/41, 356/42, 364/416, 364/417
• US Class Current: 600/330
• CPC Class Codes: A61B 5/14551 for measuring blood gases
• CPC Class Codes: G01N 21/3151 using two sources of radiation of different wavelengths G01N21/33 - G01N21/39 take precedence

Abstract

A non-invasive blood constituent measuring device and method are disclosed for measuring changes in blood thickness of predetermined blood constituents relative to total change in blood thickness at a test area to thereby determine the concentration of such constituents in the blood in a living body, which measured constituents may be, for example, hemoglobin and oxyhemoglobin to enable determination of oxygen saturation of blood. The device includes a plurality of light emitting diodes operationally controlled by timing circuitry for sequentially emitting light at different predetermined wavelengths toward a blood containing tissue sample, such as an ear lobe. A linear sensor receives emitted light passing through the sample and a train of AC modulated pulses indicative thereof is formed and then the signal representative of the light received from each emitter is scaled so that the DC components of each are normalized to a predetermined reference level with the pulse train being divided into channels at a decoder where remaining DC offset is removed and the DC component in each channel is then removed at a low pass filter, after which the AC signals in each channel are multiplexed and converted to a digital signal indicative of changes in the thickness of blood constituents for processing in a digital processor to determine therefrom the saturation of the measured blood constituents. A test unit is also included for testing operation of the device by introducing known AC modulated test signals into the circuitry.

Claims

1. A blood constituent measuring device, comprising:

electromagnetic energy emitting means for emitting electromagnetic energy at a plurality of predetermined wavelengths through a blood-containing sample at a test area;

sensing means for receiving electromagnetic energy from said sample at said plurality of wavelengths;

signal producing means connected with said sensing means to produce output signals responsive to electromagnetic energy received by said sensing means at said plurality of wavelengths;

normalizing means for receiving said output signals from said signal producing means and scaling the same so that the DC components are normalized; and

processing means for receiving said output signals from said normalizing means and producing an output indicative of changes in the thickness of preselected constituents of blood relative to the total change in blood thickness.

2. The device of claim 1 wherein said processing means includes means for separating said output signals into separate channels each of which is related to a different one of said plurality of wavelengths of electromagnetic energy emitted by said electromagnetic energy emitting means.

3. The device of claim 2 wherein said device includes timing means connected with said electromagnetic energy emitting means, normalizing means and processing means for controlling separation of said input signals into said separate channels at said processing means and for causing scaling of said output signals.

4. The device of claim 3 wherein said timing means causes said electromagnetic energy emitting means to be sequentially energized for predetermined time periods to cause a train of pulses to be produced by said signal producing means as said output signals coupled to said normalizing means.

5. The device of claim 1 wherein said output signals from said signal producing means include AC and DC components, and wherein said normalizing means includes means for providing a signal proportional to the quotient of the AC component and DC component.

6. A blood constituent measuring device, comprising:

timing means;

first and second light emitting diodes connected with said timing means to cause light to be sequentially emitted at different wavelengths toward a test area;

photodiode means for receiving light from said light emitting diodes after said light has passed through said test area, said test area being adapted to receive a tissue sample having blood moving therein;

current to voltage converting means connected with said photodiode means to produce a train of AC modulated pulses when light is received at said photodiode means from said light emitting diodes;

normalization means connected with said current to voltage converting means to receive said train of pulses therefrom and normalize said pulses by scaling said pulse developed by light from each of said light emitting diodes so that the average component of each of said pulses developed by light from one of said light emitting diodes is equal to the average component from each of said pulses developed by light from the other of said light emitting diodes;

first and second decoding means connected with said normalizing means and said timing means to receive said normalized train of pulses and produce separate outputs in first and second separated channels with the signal in said first channel being developed from light from said first light emitting diode and the signal in said second channel being developed from light from said second light emitting diode;

first and second low pass filter means connected with said first and second decoding means in said first and second channels so that said first low pass filter means receives said signal from said first decoding means and said second low pass filter means receives said signal from said second decoding means;

voltage reference generator means connected with said first and second low pass filter means to supply a DC voltage to said first and second low pass filter means;

first and second integrator means connected with said first and second low pass filter means to receive said pulses therefrom;

first multiplexing means connected with said first and second integrator means and said normalization means;

second multiplexing means connected with said first and second low pass filter means to receive said output therefrom and provide a multiplexed output;

analog to digital converter means connected with said second multiplexing means; and

digital processing means connected with said analog to digital converter means and responsive to inputs therefrom providing an output indicative of changes in the thickness of preselected constituents of blood relative to the total change of blood thickness in the tissue sample at said test area.

7. A blood constituent measuring device, comprising:

light emitting means for emitting light through a blood-containing sample;

light sensing means for receiving light from said sample at said plurality of wavelengths;

signal producing means connected with said light sensing means to produce output signals responsive to light received by said light emitting means at said plurality of wavelengths; and

processing means including a processor for receiving said output signals from said signal producing means and producing an output indicative of oxygen saturation of blood in said tested sample, said processor determining said oxygen saturation thereof through measurement of blood thickness changes of said sample at said test area and using the relationship ##EQU13## where the constants X₁ . . . X_2m are chosen for the particular constituent for determining changes in the thickness of preselected constituents of blood relative to the total change in the thickness of blood in the sample in the test area and R(λ

₁) . . . R(λ

_m) is the ratio of the AC to DC components of received light at the respective frequency.

8. The device of claim 7 wherein said processing means includes means to separate said output signals received from said signal producing means into different channels, and wherein said device includes timing means connected with said light emitting means and said processing means whereby said output signals received by said signal processings means are separated into channels according to wavelengths of emitted light causing said output signal to be produced at said signal producing means.

9. The device of claim 7 wherein said device includes normalizing means connected with said signal producing means and said processing means to scale said output signals received from said signal producing means to normalize said output signals so that the DC components are equal prior to coupling of said output signals to said processing means.

10. A blood thickness change measuring device, comprising:

electromagnetic energy emitting means for emitting electromagnetic energy at a blood-containing sample to be tested;

sensing means for receiving electromagnetic energy from said sample;

signal producing means connected with said sensing means to produce output signals having an AC and a DC component with said output signals being produced responsive to electromagnetic energy received by said sensing means;

normalizing means for receiving said output signals from said signal producing means and scaling said signals so that the DC components of each are equal; and

processing means for receiving said output signals from said normalizing means and responsive thereto producing an output indicative of blood thickness changes in said tested sample.

11. The device of claim 10 wherein said electromagnetic energy emitting means emits electromagnetic energy at a plurality of predetermined wavelengths at said sample, wherein said sensing means receives electromagnetic energy at said plurality of wavelengths and produces output signals indicative thereof, and wherein said processing means includes signal separation means for dividing said output signals received from said sensing means into a plurality of channels equal in number to said plurality of wavelengths of electromagnetic energy emitted by said electromagnetic energy emitting means and producing an output signal in each of said channels indicative of electromagnetic energy emitted from a different one of each of said plurality of wavelengths of electromagnetic energy emitted by said electromagnetic energy emitting means.

12. The device of claim 11 wherein said device includes timing means connected with said electromagnetic energy emitting means and said processing means so that said timing means causes said electromagnetic energy emitting means to be sequentially energized for predetermined time periods to cause a train of pulses to be produced by said signal producing means as the output signal therefrom.

13. A method for indicating the relative amounts of predetermined blood constituents in a blood-containing sample, said method comprising:

directing electromagnetic energy at a plurality of wavelengths through a sample to be tested;

collecting electromagnetic energy from said sample at said plurality of wavelengths and forming electronic signals indicative thereof;

normalizing said electronic signals by scaling the DC components with respect to each other; and

processing said signals after said signals have been normalized to indicate from the measured change in thickness of said predetermined blood constituents relative to the total change in blood thickness, the amount of said constituents in the blood-containing sample tested.

14. The method of claim 13 wherein normalizing of said electronic signals includes dividing the AC component of each signal by the DC component and multiplying by a predetermined constant.

15. A method for determining the relative amounts of predetermined blood constituents in a blood-containing sample, the method comprising:

sequentially directing light at at least two different wavelengths through a sample to be tested;

collecting light from said sample and developing therefrom a pulse train indicative of received light at both of said wavelengths;

normalizing the pulses from said pulse train by scaling said pulses so that the average components of said pulses are equal;

separating the pulses of said pulse train into first and second channels with the pulses in said first channel being indicative of light emitted at one wavelength and the pulses in the second channel being indicative of light emitted at the other wavelength of said two different wavelengths;

then multiplexing said signals in each channel;

converting said multiplexed signals to digital signals; and

digitally processing said signals to provide an indication of the amount of each predetermined constituent in the blood of said sample.

16. The method of claim 15 wherein digital processing is carried out using the relationship ##EQU14## where X₁ . . . x_2m are constants chosen for the particular constituent and R(λ

₁) . . . R(λ

_m) are the ratios of the AC and DC components of the light at the respective wavelengths.

17. A method for determining the relative amounts of predetermined blood constituents in a blood-containing sample at a test area, said method comprising:

directing light at at least two wavelengths at a blood-containing sample at a test area;

collecting light from the sample and developing electronic signals in digital form indicative of light collected at the two wavelengths of light directed to the sample; and

processing the electronic signals in a digital processor to provide an output indicative of the relative amounts of said predetermined blood constituents through measurement utilizing the relationship ##EQU15## where X₁ . . . X₂ are chosen for the particular constituent.

18. A method for determining the relative amounts of predetermined blood constituents in a blood-contain sample at a test area, said method comprising:

positioning a blood-containing sample at a test area;

directing light at the sample at the test area and collecting therefrom the light at at least two different wavelengths;

developing electronic signals with respect to light collected at the two different wavelengths;

normalizing the electronic signals developed from each of the two different wavelengths so that the DC components are equal;

simultaneously sampling the normalized electronic signals developed from each of the two different wavelengths;

calculating from the samples the Δ

AC for each signal where Δ

AC equals the algebraic difference between two consecutive samples of one signal;

calculating an estimate of the relative amount of each constituent by the equation, ##EQU16## where X₁ . . . X_2m are constants chosen for the particular constituent and wavelength and R(λ

₁) . . . R(λ

_m) are the ratios of the AC and DC components of the respective wavelength;

calculating weighting factors which are functions of the magnitude of the Δ

AC'"'"'s and also the difference between the estimate and the final calculation of the relative amount of each constituent;

multiplying the appropriate weighting factors by the estimates of each of said constituents;

accumulating a number of weighting factors and an equal number of weighting factors multipled by the estimates of each of said constituents;

performing a final calculation of relative amounts of each constituent by dividing accumulated products by accumulated weighting factors; and

19. A method for determining oxygen saturation of blood, said method comprising:

directing electromagnetic energy at a plurality of wavelengths toward a sample to be tested for oxygen saturation of blood;

collecting electromagnetic energy from said sample at said plurality of wavelengths and forming electronic signals indicative thereof;

normalizing said electronic signals by scaling the DC components of each to a predetermined reference level; and

processing said signals after said signals have been normalized to indicate the percentage of oxygen saturation of blood in said sample.

20. The method of claim 19 wherein signals formed from collected electromagnetic energy are processed in a plurality of channels equal in number to the plurality of wavelengths of emitted electromagnetic energy with an output from each of said channels being utilized to determine the percentage of oxygen saturation of blood in the sample.

21. The method of claim 20 wherein said processing of said signals includes determining changes in blood thickness containing oxyhemoglobin relative to total change in blood thickness to enable said indication of the percentage of oxygen saturation of blood.

22. The method of claim 20 wherein said electromagnetic energy is emitted sequentially at said different wavelengths so said electromagnetic energy is collected to form a train of pulses as said electronic signals.

23. The method of claim 19 wherein normalizing of said electronic signals includes dividing the AC component of each signal by the DC component and multiplying by a predetermined constant.

24. A method for determining oxygen saturation of blood, comprising:

sequentially directing light at at least two different wavelengths at a sample to be tested for oxygen saturation of blood;

collecting light from said sample and developing therefrom a pulse train indicative of received light at both of said wavelengths;

normalizing the pulses of said pulse train by scaling said pulses so that the average components of said pulses are equal;

separating the pulses of said pulse train into first and second channels with the pulses in said first channel being indicative of light emitted at one wavelength and the pulses in the second channel being indicative of light emitted at the other wavelength of said two different wavelengths;

then multiplexing said signals in each channel;

converting said multiplexed signals to digital signals; and

digitally processing said signals to provide an indication of oxygen saturation in the blood of said sample.

25. A method for determining blood thickness changes, said method comprising:

directing electromagnetic energy toward a blood-containing sample at a test area;

collecting electromagnetic energy from the sample at the test area and providing from the collected electromagnetic energy electronic signals having a DC and an AC component;

normalizing the electronic signals by scaling the signals so that the DC components are equal; and

processing the normalized electronic signals to provide an output indicative of blood thickness changes in the sample tested.

26. The method of claim 25 wherein electromagnetic energy is emitted at a sample at a plurality of predetermined wavelengths, and wherein electromagnetic energy is collected with respect to the plurality of wavelengths of emitted electromagnetic energy and electronic signals developed with respect to each of said wavelengths with each of said electronic signals thus developed being normalized by scaling said signals.

27. The method of claim 26 wherein said electromagnetic energy is emitted in bursts and said electronic signals are pulses each of which is normalized by scaling.

28. The method of claim 25 wherein normalizing of said electronic signals includes dividing the AC component of each signal by the DC component and multiplying by a predetermined constant.

29. An apparatus for measuring at least one constituent of blood in tissue comprising means for selectively passing light of a plurality N of wavelengths through said tissue, wherein N is at least equal to the number of constituents to be measured, means for sensing said light and producing a plurality of signals corresponding to the attenuation of said light at the respective wavelengths, means for adjusting the average levels of said signals to be equal to each other or to a determined quantity, and data processing means responsive to said adjusted signals for determining the quantity of said constituents.

30. The apparatus of claim 29 wherein said means for passing light through said tissue comprises a plurality of separate light emitters and means for sequentially energizing the said emitters, and said means for sensing said light and producing signals comprises photosensitive means, whereby the output of said photosensitive means comprises alternate sequences of pulses corresponding to the respective separate light emitters.

31. The apparatus of claim 30 wherein one of said emitters emits light in the infrared region and another of said emitters emits light in the red region.

32. The apparatus of claim 30 wherein said means for adjusting comprises an operational transconductance amplifier means having first and second inputs, low pass filter means applying signals from said photosensing means to one of said inputs, and means directed upon the signals from said photosensitive means to the other input of said transconductance amplifier means, and intergrator means connected to control the transconductance of said amplifier means by the time integral of the signal output of the transconductance amplifier means.

33. The apparatus of claim 29 wherein said means responsive to said adjusted signals comprises data processing means for solving the expression;

##EQU17## for Δ

L^A.sbsp.1 through Δ

L^A.sbsp.m, wherein K(λ

)^A.sbsp.1 . . . K(λ

)^A.sbsp.m are the attenuation coefficients of blood at the respective wavelengths with the ^A.sbsp.1 . . . ^A.sbsp.m indicating the associated quantities relating to different attenuating substances, and Δ

I(λ

) and I(λ

) are the varying and constant components respectively of the input signals to the data processing means, at the respective wavelengths.

34. The method of measuring one or more determined constituents of blood, comprising sensing the attenuation of light passing through tissue containing the blood at a plurality of different wavelengths at least equal in number to the number of said constituents to be determined, to produce a quantity at each wavelength corresponding to the portion of the variation of attenuation divided by the average attenuation, calculating the quantity of each said constituent indicated at each wavelength, and determining the quantity of each said constituents by summing the quantities determined thereof at each wavelength.

35. The method according to claim 34 wherein said step of calculating the quantity of each said constituent comprises solving the relationship;

##EQU18## for Δ

L^A.sbsp.1 through Δ

L^A.sbsp.m, which represent the quantities of constituents 1 . . . m, wherein K(λ

)^A.sbsp.1 . . . K(λ

)^A.sbsp.m are the attenuation coefficients of blood at the respective wavelength λ

which relates to the different attenuating substances designated A₁ -A_m, and the quantity ##EQU19## corresponding to said quotient at each respective wavelength.

36. The method of claim 35 further comprising solving the relationship;

##EQU20## for determining the percentage concentration %A_m of each constituent, and Δ

L is the sum of the quantities of the various constituents.