METHOD FOR NONINVASIVE DETERMINATION OF HEMOGLOBIN AND OXYGEN CONCENTRATIONS IN THE BLOOD

Abstract

The invention applies to the analysis of the chemical composition of materials and can be used primarily in diagnostic medical equipment for noninvasive determination of hemoglobin and oxygen concentrations contained in the blood.

The method proposes to alternately irradiate the biological tissue with optical radiation of the first, second, and third wavelength ranges, including 700 nm, 880 nm, and 960 nm, respectively, receive the reflected optical radiation, convert it to an electrical signal, determine the concentration of hemoglobin based on the sum of the electrical signals obtained by irradiating with optical radiation of the first and second ranges, which is reduced by a value determined by the electrical signal obtained upon irradiation with optical radiation of the third range, and determine the concentration of oxygen based on the difference between the electrical signals obtained by irradiating with optical radiation of the second and first ranges, which is reduced by a value determined by the electrical signal obtained by irradiating with optical radiation of the third range.

The invention provides a reduction in the error of determining the concentrations of hemoglobin and oxygen that stems from the presence of water in the biological tissue under study.

Claims

1. (canceled)

2. (canceled)

3. (canceled)

4. (canceled)

5. A method for noninvasive determination of the hemoglobin concentration in blood, including: alternate irradiation of the biological tissue in any sequence with optical radiation of the first wavelength range, including 700 nm, optical radiation of the second wavelength range, including 880 nm, and optical radiation of the third wavelength range, including 960 nm, reception of the optical radiation diffusely reflected by the biological tissue, conversion of the received optical radiation into an electrical signal, and determination of the hemoglobin concentration in blood based on the sum of the electrical signals obtained when the biological tissue is irradiated with optical radiation of the first and second wavelength ranges, which is reduced by a value determined by the electrical signal obtained under irradiation of the biological tissue with optical radiation of the third wavelength range.

6. A method according to claim 5, wherein the hemoglobin concentration in the blood is determined using the experimentally obtained calibration curve between the concentration of hemoglobin and the resulting total electrical signal U.sub.TOT=U.sub.1+U.sub.2−, where U.sub.1, U.sub.2, and U.sub.3 are the electrical signals obtained by irradiating biological tissue with optical radiation of the first, second, and third wavelength ranges, respectively; .sub.13 and .sub.23 are coefficients obtained in advance by processing the known characteristics of the relative spectral sensitivity of the optical radiation receiver used in the measurement and the water absorption spectrum in the first, second, and third wavelength ranges, respectively.

7. A method according to claim 6, wherein the described coefficients, obtained by processing the known characteristics of the relative spectral sensitivity of the optical radiation receiver used in the measurement and the water absorption spectrum in the first, second, and third wavelength ranges, are calculated in advance according to the following expressions: .sub.13=.sub.3S.sub.3/.sub.1/S.sub.1 and .sub.23=.sub.3S.sub.3/.sub.2/S.sub.2, where .sub.1, .sub.2, and .sub.3 are the average values of the water absorption coefficients in the first, second, and third wavelength ranges, respectively; S.sub.1, S.sub.2, and S.sub.3 are the average values of the relative spectral sensitivity of the optical radiation receiver in the first, second, and third wavelength ranges, respectively.

8. A method for noninvasive determination of the oxygen concentration in blood, including: alternate irradiation of the biological tissue in any sequence with optical radiation of the first wavelength range, including 700 nm, optical radiation of the second wavelength range, including 880 nm, and optical radiation of the third wavelength range, including 960 nm, reception of the optical radiation diffusely reflected by the biological tissue, conversion of the received optical radiation into an electrical signal, and determination of the oxygen concentration in blood based on the difference between the electrical signals obtained when the biological tissue is irradiated with optical radiation of the second and first wavelength ranges, which is reduced by a value determined by the electrical signal obtained under irradiation of the biological tissue with optical radiation of the third wavelength range.

9. A method according to claim 8, wherein the oxygen concentration in the blood is determined using the experimentally obtained calibration curve between the concentration of oxygen in the blood and the resulting residual electrical signal U.sub.DIFF=U.sub.2−U.sub.1−U.sub.3(.sub.13+.sub.23), where U.sub.1, U.sub.2, and U.sub.3 are the electrical signals obtained by irradiating biological tissue with optical radiation of the first, second, and third wavelength ranges, respectively; .sub.13 and .sub.23 are coefficients obtained in advance by processing the known characteristics of the relative spectral sensitivity of the optical radiation receiver used in the measurement and the water absorption spectrum in the first, second, and third wavelength ranges, respectively.

10. A method according to claim 9, wherein the described coefficients, obtained by processing the known characteristics of the relative spectral sensitivity of the optical radiation receiver used in the measurement and the water absorption spectrum in the first, second, and third wavelength ranges, are calculated in advance according to the following expressions: .sub.13=.sub.3S.sub.3/.sub.1/S.sub.1 and .sub.23=.sub.3S.sub.3/.sub.2/S.sub.2, where .sub.1, .sub.2, and .sub.3 are the average values of the water absorption coefficients in the first, second, and third wavelength ranges, respectively; S.sub.1, S.sub.2, and S.sub.3 are the average values of the relative spectral sensitivity of the optical radiation receiver in the first, second, and third wavelength ranges, respectively.

Description

BRIEF DESCRIPTION OF DRAWING

[0022] FIG. 1 shows the block diagram of the device that provides the best way to implement the claimed method for noninvasive determination of hemoglobin and oxygen concentrations in the blood, where t is the block of light-emitting diodes (LEDs). 2—the optical receiver, 3—the amplifier, 4—the analog-to-digital converter, 5—the controller, 6—the display unit, and 7 is the biological tissue.

[0023] FIG. 2 shows the absorption spectra for oxyhemoglobin, deoxyhemoglobin, and water in the wavelength range from 600 nm to 1100 nm.

PREFERRED EMBODIMENT OF THE INVENTION

[0024] A device that provides the best way to implement the claimed method of noninvasive determination of hemoglobin and oxygen concentrations in blood comprises a series connected optical radiation receiver 2, amplifier 3, analog-digital converter 4, controller 5 and display unit 6, and also an LED unit 1 connected to output of the controller 5.

[0025] The LED unit 1 comprises at least one LED configured to emit optical radiation in a first wavelength range (680-720 nm), including 700 nm, for example LED L-132XHT by Kingbright, at least one LED with emission in the second wavelength range (860-900 nm), including 880 nm, for example LED BL-314IR by BetLux, and at least one LED with emission in the third wavelength range (940-980 nm), including 960 nm, for example LED TSUS4400 by Vishay.

[0026] A photodiode sensitive to optical radiation in the wavelength range from 570 to 1100 nm, for example photodiode BPW34 by Vishay, is used as the optical radiation receiver 2.

[0027] The optical radiation receiver 2 and the LEDs of the LED unit 1 are mounted on a common base (not shown in FIG. 1) that is pressed against the biological tissue 7, and the LEDs are arranged around the optical radiation receiver 2.

[0028] A precision operational amplifier, for example AD8604 by Analog Devices, can be used as the amplifier 3.

[0029] A high-speed analog-to-digital converter of a large bit width (from 12 bits), for example an analog-to-digital converter AD7655 by Analog Devices, can be used as the analog-to-digital converter 4.

[0030] The controller 5 can be any microcontroller having the necessary resources to control an external analog-to-digital converter and sufficient speed, for example ATXmega128A4U by Atmel, equipped with permanent and operative memory devices.

[0031] The device that implements the proposed method of noninvasive determination of hemoglobin and oxygen concentrations in the blood works as follows.

[0032] To determine the hemoglobin and oxygen concentrations in the blood, the base with the optical radiation receiver 2 and the LEDs of the LED unit 1 is pressed against the biological tissue 7 under study.

[0033] When the device is turned on, the LEDs of the LED unit 1 do not emit the optical radiation. The electrical signal from the optical radiation receiver 2. determined by its dark current, is amplified by the amplifier 3 and converted by the analog-to-digital converter 4 into a digital code, which enters the controller 5 and is stored in its operative memory device.

[0034] Then, the signals from the controller 5 initiate alternate energy supply of ihe LEDs of the LED unit 1. The sequence in which the LEDs are switched are not important for the proposed method.

[0035] For example, when a voltage is applied to a LED of the LED unit 1 that is configured to emit optical radiation in the first wavelength range of 680-720 nm, this LED emits optical radiation of the indicated wavelength range towards the biological tissue 7. A portion of this radiation is absorbed, predominantly by deoxynemogiobin. and a part diffusely reflects and gets to the optical radiation receiver 2, which converts this part of the optical radiation into an electrical signal, determined, to a greater extent, by the concentration of deoxyhemoglobin in the biological tissue 7 and, to a lesser extent, by oxyhemoglobin and water (see FIG. 2). This electrical signal is amplified by the amplifier 3 and. after conversion by the analog-to-digital converter 4 into a digital code, enters the controller 5. In order to account for the measurement error that stems from the dark current of the optical radiation receiver 2. the controller 5 subtracts from the digital code that it has received from the analog-to-digital converter 4 a digital code corresponding to the electric signal from the dark current of the optical radiation receiver 2 (the latter code is stored in the main memory). Then, the controller 5 records this difference, corresponding to the electric signal u.sub.1, to the main memory, and this signal is mainly determined by the concentration of deoxyhemoglobin in the examined biological tissue 7.

[0036] Then, the previously turned-on LED turns off, and voltage is applied, for example, to a LED of the LED unit 1 configured to emit optical radiation in the second range with wavelengths of 860-900 nm. This LED emits optical radiation of the indicated wavelength range in the direction of the biological tissue 7. Similarly, the optical radiation receiver 2 converts the diffusely reflected optical radiation into an electrical signal, which is determined predominantly by the oxyhemoglobin concentration in the biological tissue 7 and, to a lesser extent, by deoxyhemoglobin and water (see FIG. 2). This electrical signal is amplified by the amplifier 3 and, after conversion by the analog-to-digital converter 4 into a digital code, enters the controller 5. In order to account for the measurement error that stems from the dark current of the optical radiation receiver 2, the controller 5 subtracts from the digital code that it has received from the analog-to-digital converter 4 a digital code corresponding to the electric signal from the dark current of the optical radiation receiver 2 (the latter code is stored in the main memory). Then, the controller 5 records this difference, corresponding to the electric signal u.sub.2, to the main memory, and this signal is mainly determined by the concentration of oxyhemoglobin in the examined biological tissue 7.

[0037] Then, the previously turned-on LED turns off, and voltage is applied to a LED of the LED unit 1 configured to emit optical radiation in the third range with wavelengths of 940-980 nm. This LED emits optical radiation of the indicated wavelength range in the direction of the biological tissue 7. Similarly, the optical radiation receiver 2 converts the diffusely reflected optical radiation into an electrical signal, which is determined predominantly by the concentration of water in the biological tissue 7 and, to a lesser extent, by oxyhemoglobin and deoxyhemoglobin (see FIG. 2). This electrical signal is amplified by the amplifier 3 and, after conversion by the analog-to-digital converter 4 into a digital code, enters the controller 5. In order to account for the measurement error that stems from the dark current of the optical radiation receiver 2, the controller 5 subtracts from the digital code that it has received from the analog-to-digital converter 4 a digital code corresponding to the electric signal from the dark current of the optical radiation receiver 2 (the latter code is stored in the main memory). Then, the controller 5 records this difference, corresponding to the electric signal u.sub.3, to the main memory, and this signal is mainly determined by the concentration of water in the examined biological tissue 7.

[0038] Then, the considered processes of sequential switching of the LEDs of the LED unit 1, initiated by the signals from the controller 5, are repeated multiple times, each time followed by conversion of the reflected optical radiation into an electrical signal by the optical radiation receiver 2 and processing of the obtained digital codes by the controller 5. As a result, digital values of the electrical signals u.sub.1, u.sub.2, and u.sub.3 are accumulated in the main memory of the controller 5, which are statistically processed by the controller 5 for filtering the random measurement errors. This processing results in the average numerical values U.sub.1, U.sub.2, and U.sub.3 of the electrical signals u.sub.1, u.sub.2, and u.sub.3. respectively, which are stored in the main memory of the controller 5. Based on the obtained average numerical values U.sub.1, U.sub.2, and U.sub.3 of the electrical signals, the controller 5 calculates the total electric signal according to the following expression:

U.sub.TOT=U.sub.1+U.sub.2−

[0039] where U.sub.1, U.sub.2, and U.sub.3 are the average numerical values of the electrical signals obtained by exposing the biological tissue 7 to optical radiation of the first, second, and third wavelength ranges, respectively;

[0040] .sub.13, .sub.23 are coefficients obtained in advance by processing the known characteristics of the relative spectral sensitivity of the optical radiation receiver 2 and the water absorption spectrum in the first, second, and third wavelength ranges, respectively, which are stored in the main memory of the controller 5.

[0041] Based on the obtained average numerical values U.sub.1, U.sub.2, and U.sub.3 of the electrical signals, the controller 5 calculates the residual electric signal according to the following expression:

U.sub.DIFF=U.sub.2−U.sub.1−,

[0042] where U.sub.1, U.sub.2, and U.sub.3 are the average numerical values of the electrical signals obtained by exposing the biological tissue 7 to optical radiation of the first, second, and third wavelength ranges, respectively;

[0043] .sub.13, .sub.23 are coefficients obtained in advance by processing the known characteristics of the relative spectral sensitivity of the optical radiation receiver 2 and the water absorption spectrum in the first, second, and third wavelength ranges, respectively, which are stored in the main memory of the controller 5.

[0044] The above-mentioned coefficients, which are stored in the main memory of the controller 5, are determined in advance by processing the known characteristics of the relative spectral sensitivity of the optical radiation receiver 2 and the water absorption spectrum in the first, second, and third wavelength ranges, according to the following expressions:

.sub.13=.sub.3S.sub.3/.sub.1/S.sub.1,

.sub.23=.sub.3S.sub.3/.sub.2/S.sub.2,

[0045] where .sub.1, .sub.2, and .sub.3 are the average values of the water absorption coefficients in the first, second, and third wavelength ranges, respectively;

[0046] S.sub.1, S.sub.2, and S.sub.3 are the average values of the relative spectral sensitivity of the optical radiation receiver 2 in the first, second, and third wavelength ranges, respectively.

[0047] The controller 5 determines the concentration of hemoglobin in the blood using the calibration curve between the concentration of hemoglobin and the resulting total electrical signal U.sub.TOT. The calibration curve has been experimentally obtained in advance and is stored in the main memory of the controller 5.

[0048] The controller 5 determines the concentration of oxygen in the blood using the calibration curve between the concentration of oxygen and the resulting residual electrical signal U.sub.DIFF. The calibration curve has been experimentally obtained in advance and is stored in the main memory of the controller 5.

[0049] The obtained hemoglobin and oxygen concentrations in the blood are transferred from the controller 5 to the display unit 6, which displays these values to the device operator.

INDUSTRIAL APPLICABILITY

[0050] The authors of the present invention have developed and tested a prototype device that provides the proposed method of noninvasive determination of hemoglobin and oxygen concentrations in the blood The tests of the prototype device showed, firstly, its operability and, secondly, the possibility of achieving the technical result, consisting in increasing the accuracy of determination of hemoglobin and oxygen concentrations by 10-12% reduction of the measurement error due to the presence of water in the biological tissue under study.