RU2175523C1 - Pulse oximeter - Google Patents

Abstract

FIELD: medical equipment, applicable for noninvasive variation of saturation of arterialized blood with oxygen in the conditions of continuous monitoring. SUBSTANCE: the pulse dosimeter has a source of radiation in the red radiation bend, connected to the first current source, source of radiation in the infra-red radiation band, connected to the second current source, photodetector made in the form of a photodiode, and an electric signal converter, connected to the photodetector, DC voltage amplifier, whose input is connected to the output of the electric signal converter made in the form of a voltage-to-voltage converter, series-connected first synchronous detector, whose first input is connected to the output of the DC voltage amplifier, the first high-pass filter and the first AC voltage amplifier, series-connected second synchronous detector, whose first input is connected to the output of the DC voltage amplifier, the second high-pass filter and the second AC voltage amplifier, as well as an antiphase pulse shaper at a frequency of 200 to 2000 Hz, whose first output is connected to the control input of the first synchronous detector, and the second output - to the control input of the second synchronous detector, and connected with its output to the indicator, and with its first and second inputs - to the outputs of the first and second AC voltage amplifiers, respectively, of the function computation unit. In addition, use is made of a reference voltage driver with "Amplitude of currents", "Balance of currents" and "″α″" regulators, as well as an adjustable AC voltage source at a frequency of 1 to 2 Hz and a switch with the respective couplings. EFFECT: provision of check-up of pulse oximeter in the process of manufacture and service. 2 cl, 7 dwg

Description

 The invention relates to medical equipment and can be used for non-invasive measurement of arterial blood oxygen saturation in continuous monitoring mode.

 One of the important diagnostic and prognostic indicators in anesthesiology, intensive care and intensive care is the degree of saturation of the circulating blood with oxygen, which is characterized by a saturation coefficient.

 To determine the saturation coefficient by a non-invasive method, pulse oximeters are used, the principle of which is based on spectrometry of the tissues of the finger or earlobe.

 Known pulse oximeters comprise a red radiation source connected to the first current source, an infrared radiation source connected to the second current source, and a photodetector connected to the amplification path [1]. The task of the amplification path is the formation of four signals: constant components of the red and infrared channels and variable components of the red and infrared channels. In this case, the amplifier must satisfy very high technical requirements, in particular, the amplifier must have a large dynamic range (of the order of 600 dB according to [1]), should have, as a rule, a system for automatically adjusting the gain and radiation power of radiation sources, and should provide high stability the ratios of the variables and the constant components of the red and infrared signals.

 The fulfillment of these requirements is very difficult, which leads to a sharp decrease in the accuracy of determining the saturation coefficient. The complexity of the equipment used complicates its maintenance and increases its price.

 Known pulse oximeter described in [2, p. 16, fig. 1]. This pulse oximeter contains a red radiation source connected to the first current source, an infrared radiation source connected to the second current source, a photodetector made in the form of a photodiode connected to an electric signal converter, made in the form of a current-voltage converter . To perform measurements with a pulse prototype oximeter, it is necessary to have an amplification path with high technical characteristics specified in the description of the analogue [1].

где S - коэффициент сатурации, A $\genfrac{}{}{0ex}{}{\text{Hb}}{\text{λ1}}$ и A $\genfrac{}{}{0ex}{}{\text{Hb}}{\text{λ2}}$ - коэффициенты экстинкции восстановленного гемоглобина на длинах волн излучения, соответственно в красном и инфракрасном диапазонах излучения, ΔV_λ1 и ΔV_λ2 - двойные амплитуды переменного напряжения на выходах, соответственно, первого и второго усилителей напряжения переменного тока,

- коэффициент экстинкции оксигемоглобина на длинах волн, соответственно, в красном и инфракрасном диапазонах излучения.Also known pulse oximeter [3]. This pulse oximeter contains a red radiation source connected to the first current source, an infrared radiation source connected to the second current source, a photodetector made in the form of a photodiode, and an electrical signal converter connected to the photodetector, a DC voltage amplifier the input of which is connected to the output of the electric signal converter, made in the form of a voltage-voltage converter, connected in series the first synchronous detector, the first input of which is connected to the output of the DC voltage amplifier, the first high-pass filter and the first AC voltage amplifier, connected in series with the second synchronous detector, the first input of which is connected to the output of the DC voltage amplifier, the second high-pass filter and the second amplifier AC voltage, as well as an antiphase pulse shaper with a frequency of (200-2000) Hz, the first output of which is connected to the control input of the first synchronous detector ora, and the second output - to the control input of the second synchronous detector, and its output connected to the indicator, and its first and second input - to the outputs, respectively, first and second AC voltage amplifiers function calculating unit

where S is the saturation coefficient, A $\genfrac{}{}{0ex}{}{\text{Hb}}{\text{λ1}}$ and A $\genfrac{}{}{0ex}{}{\text{Hb}}{\text{λ2}}$ - extinction coefficients of the restored hemoglobin at radiation wavelengths, respectively, in the red and infrared radiation ranges, ΔV _λ1 and ΔV _λ2 are double amplitudes of the alternating voltage at the outputs, respectively, of the first and second AC voltage amplifiers,

- the extinction coefficient of oxyhemoglobin at wavelengths, respectively, in the red and infrared ranges of radiation.

 In the first embodiment of the pulse oximeter according to the patent [3], the electric signal converter is made in the form of a voltage-voltage converter, and the DC voltage amplifier has a linear characteristic.

 In the second embodiment of the pulse oximeter according to the patent [3], the electric signal converter is made in the form of a current-voltage converter, and the DC voltage amplifier is made with a logarithmic conversion characteristic.

 The disadvantage of all considered pulse oximeters, including the oximeter according to the patent [3], is the impossibility of their verification during manufacturing and operation, which leads to a decrease in the accuracy of measurement of the saturation coefficient. The decrease in measurement accuracy is due to both a change in the parameters of the elements and blocks included in the pulse oximeter, and a deviation from the nominal wavelengths of the radiation sources in the red and infrared radiation ranges.

 The problem solved by the invention is the ability to verify the pulse oximeter in the manufacturing process and operation.

где S - коэффициент сатурации,

- коэффициенты экстинкции восстановленного гемоглобина на длинах волн излучения, соответственно, в красном и инфракрасном диапазонах излучения, α = ΔV_λ1/ΔV_λ2, ΔV_λ1и ΔV_λ2 - двойные амплитуды переменного напряжения на выходах, соответственно, первого и второго усилителей напряжения переменного тока,

- коэффициент экстинкции оксигемоглобина на длинах волн, соответственно, в красном и инфракрасном диапазонах излучения, дополнительно введены формирователь опорных напряжений с регуляторами "Амплитуда токов", "Баланс токов" и ″α″, а также регулируемый источник переменного напряжения частотой (1-2) Гц и коммутатор, при этом первый и второй выходы формирователя опорного напряжения подключены, соответственно, к первому и второму входам коммутатора, первый и второй управляющие входы которого соединены, соответственно, с первым и вторым выходами формирователя противофазных импульсов частотой (200-2000) Гц, первый и второй выходы коммутатора подключены к управляющим входам, соответственно, первого источника тока и второго источника тока, выход регулируемого источника переменного напряжения частотой (1-2) Гц подключен к входу ″α″ формирователя опорных напряжений, упомянутый блок вычисления функции выполнен в виде последовательно соединенных мультиплексора, аналого-цифрового преобразователя и микропроцессора, при этом первый и второй входы мультиплексора являются, соответственно, первым и вторым входами упомянутого блока вычисления функции, третий и четвертый входы мультиплексора соединены с выходами первого и второго синхронных детекторов, соответственно, управляющие входы аналого-цифрового преобразователя и мультиплексора соединены с первым и вторым управляющими выходами микропроцессора.This problem is solved in that in a pulse oximeter containing a radiation source in the red radiation range connected to the first current source, an infrared radiation source connected to the second current source, a photodetector made in the form of a photodiode, and an electrical signal converter connected to the photodetector, a DC voltage amplifier, the input of which is connected to the output of the electric signal converter, made in the form of a voltage-voltage converter connected in series to the first synchronous detector, the first input of which is connected to the output of the DC voltage amplifier, the first high-pass filter and the first AC voltage amplifier, connected in series to the second synchronous detector, the first input of which is connected to the output of the DC-voltage amplifier, second high-pass filter and a second AC voltage amplifier, as well as an antiphase pulse generator with a frequency of (200-2000) Hz, the first output of which is connected to the control at the input of the first synchronous detector, and the second output to the control input of the second synchronous detector, and connected to its output to the indicator and its first and second inputs to the outputs of the first and second AC voltage amplifiers, respectively, the function calculation unit

where S is the saturation coefficient,

are the extinction coefficients of the reduced hemoglobin at the radiation wavelengths, respectively, in the red and infrared radiation ranges, α = ΔV _λ1 / ΔV _λ2 , ΔV _λ1 and ΔV _λ2 are the double amplitudes of the alternating voltage at the outputs, respectively, of the first and second AC voltage amplifiers,

- extinction coefficient of oxyhemoglobin at wavelengths, respectively, in the red and infrared ranges of radiation, an additional voltage shaper with regulators "Amplitude of currents", "Balance of currents" and ″ α ″, as well as an adjustable source of alternating voltage with frequency (1-2) are additionally introduced Hz and a switch, while the first and second outputs of the reference voltage driver are connected, respectively, to the first and second inputs of the switch, the first and second control inputs of which are connected, respectively, with the first and second output Ami of the generator of antiphase pulses with a frequency of (200-2000) Hz, the first and second outputs of the switch are connected to the control inputs, respectively, of the first current source and the second current source, the output of an adjustable AC source with a frequency of (1-2) Hz is connected to the input voltage reference shaper, said function calculation unit is made in the form of a series-connected multiplexer, an analog-to-digital converter and a microprocessor, while the first and second inputs of the multiplexer are, respectively but, first and second inputs of said arithmetic function unit, third and fourth multiplexer inputs connected to outputs of the first and second synchronous detectors, respectively, control inputs of the analog-to-digital converter and multiplexer are connected to first and second control outputs of the microprocessor.

 In addition, in the proposed pulse oximeter, the reference voltage driver can contain two operational amplifiers, a resistive voltage divider, three resistive adjustable voltage dividers and two feedback resistors, while the first output of the resistive adjustable voltage divider is connected to the DC bus, and its second output to the zero potential bus, the output of the first resistive adjustable voltage divider is connected to the midpoint of the resistive voltage divider, resistive div a voltage divider, second and third resistive adjustable voltage dividers are connected between the inverting inputs of the first and second operational amplifiers, the midpoint of the second resistive adjustable divider is connected to the DC bus, the middle point of the third resistive adjustable voltage divider is the input ″ α ″ of the reference voltage shaper, the first resistor feedback is connected between the output of the first operational amplifier and its inverting input, the second feedback resistor is on between the output of the second operational amplifier and its inverting input, the first, second, and third adjustable resistive voltage dividers are, respectively, the regulators "Amplitude of currents", "Balance of currents" and ″ α ″, the outputs of the first and second operational amplifiers are, respectively, the first and second outputs of the reference voltage driver.

The essence of the invention is illustrated by drawings, which depict:
in FIG. 1 is a functional diagram of a pulse oximeter,
in FIG. 2 is a functional block diagram of the calculation function (1),
in FIG. 3 - an example of the concept of the background,
in FIG. 4 is a diagram of a voltage-voltage converter,
in FIG. 5 is a diagram explaining the formation of current signals at the outputs of the first and second current sources,
in FIG. 6 is a timing diagram of the signals at the outputs of the antiphase pulse generator, synchronous detectors and AC voltage amplifiers,
in FIG. 7 - timing diagrams of the signals at the control inputs and outputs of the switch.

In the drawings are indicated:
1 - radiation source in the red radiation range,
2 - the first current source,
3 - radiation source in the infrared range of radiation,
4 - a second current source,
5 - photodetector,
6 - voltage-voltage converter,
7 - DC voltage amplifier,
8 - the first synchronous detector,
9 - the first high-pass filter,
10 is a first AC voltage amplifier,
11 is a second synchronous detector,
12 is a second high-pass filter,
13 is a second AC voltage amplifier,
14 - shaper antiphase pulses,
15 - indicator
16 is a function calculation unit,
17, 18 - isolation capacitors,
19, 20 - resistors of CR-chains,
21 - shaper of the reference voltage,
22 is an adjustable source of alternating voltage,
23 - switch
24 - multiplexer,
25 - analog-to-digital Converter,
26 - microprocessor,
27 - the first operational amplifier,
28 is a second operational amplifier,
29, 30 - series-connected first and second resistors forming a resistive voltage divider,
31 - a third resistor forming a first resistive adjustable voltage divider,
32, 33, 34 - series-connected fourth, fifth, sixth resistors forming a second resistive adjustable voltage divider,
35 is a seventh resistor forming a third resistive adjustable voltage divider,
36 is a first feedback resistor,
37 - second feedback resistor,
38 is the third operational amplifier,
39 is a third feedback resistor,
40 - fourth feedback resistor,
41 - waveform at the first output of the driver 14,
42 - waveform at the second output of the driver 14,
43 - waveform at the output of the synchronous detector 8,
44 - waveform at the output of the synchronous detector 11,
45 - waveform at the output of amplifier 10,
46 - waveform at the output of the amplifier 13,
t is the time axis
U is the axis of stresses.

 The pulse oximeter (see Fig. 1) contains a radiation source 1 connected to the first current source 2, a radiation source 3 connected to the second current source 4, a photodetector 5 connected to the voltage-voltage converter 6.

 Sources 1 and 3 of the radiation are made in the form of LEDs. The radiation wavelength of source 1 lies in the red emission range and is, for example, (650 ± 10) nm. The radiation wavelength of source 3 lies in the infrared range and is, for example, (940 ± 15) nm.

 The photodetector 5 is made in the form of a photodiode. The wavelength range of the light signals received by the photodetector 5 should overlap the wavelength range in which the wavelengths emitted by the signal sources 1 and 3 lie.

 The converter 6 is made in the form of a voltage-voltage converter, for example, according to the circuit shown in FIG. 4. In particular, the converter 6 is made on the third operational amplifier 38, covered by negative feedback using a divider connected between the output of the third operational amplifier 38 and the zero potential bus and formed by the third and fourth feedback resistors 39 and 40. Between the connection point of the feedback resistors communication 39 and 40 and the inverting input of the third operational amplifier 38 includes a photodetector 5, made in the form of a photodiode. Converter 6 can also be implemented according to other known voltage-voltage converter circuits.

 The pulse oximeter also contains a DC voltage amplifier 7, the input of which is connected to the output of the electric signal converter 6, serially connected to a first synchronous detector 8, the first input of which is connected to the output of amplifier 7, a first high-pass filter 9 and a first AC voltage amplifier 10, in series connected by a second synchronous detector 11, the first input of which is connected to the output of the amplifier 7, a second high-pass filter 12 and a second AC voltage amplifier 13.

 Identical high-pass filters 9 and 12 can be made according to various well-known schemes, including in the form of simple separation CR-chains on passive elements 17, 19 and 18, 20 (see Fig. 1). The lower limit of the passband of the filters 9 and 12 is chosen based on and from the lowest possible heart rate of the patient. Typically, the lower limit of the passband of filters 9 and 12 is tenths of a hertz.

 Amplifiers 10 and 13 of AC voltage should provide amplification of the variable component signals at the outputs of synchronous detectors 8 and 11 in the frequency range of the patient’s heartbeat, that is, a sufficient frequency range from fractions of a hertz to units of hertz is sufficient.

 The first output of the antiphase pulse shaper 14 is connected to the first control input of the switch 23 and the control input of the first synchronous detector 8. The second output of the shaper 14 is connected to the second control input of the switch 23 and the control input of the second synchronous detector 1. The shaper 14 can be made, for example, in the form the simplest multivibrator. In addition, the shaper 14 can be made in the form of a frequency divider of the clock pulses of the microprocessor 26, which is part of the unit 16. The pulse repetition rate at the output of the shaper 14 is (200-2000) Hz. At a lower pulse repetition rate at the output of the shaper 14, the accuracy of determining the saturation coefficient is reduced due to time quantization errors. With an increase in the pulse frequency, the requirements for the technical characteristics of radiation sources 1, 3 and synchronous detectors 8 and 11 increase.

 The outputs of the amplifiers 10 and 13 are connected, respectively, to the first and second inputs of the block 16 for calculating the function (1), the output of which is connected to the indicator 15.

 Block 16 is made in the form of series-connected multiplexer 24, analog-to-digital converter 25 and microprocessor 26. In this case, the first and second inputs of multiplexer 24 are, respectively, the first and second inputs of the function calculation unit 26, the third and fourth inputs of multiplexer 26 are connected to the outputs of the first and second synchronous detectors 8 and 11, respectively (Fig. 2).

 The indicator 15 may be a dial indicator, a digital display, a personal computer monitor, and the like.

 The pulse oximeter also contains a driver of 21 reference voltages with regulators "Amplitude of currents" ("Amplitude 1"), "Balance of currents" ("Amplitude 1") and ″ α ″, as well as an adjustable source 22 of alternating voltage with a frequency of (1-2) Hz . In this case, the first and second outputs of the driver 21 of the reference voltage are connected, respectively, to the first and second inputs of the switch 23, the first and second outputs of which are connected to the control inputs, respectively, of the first current source 2 and the second current source 4. The output of the adjustable source 22 of an alternating voltage with a frequency of (1-2) Hz is connected to the input ″ α ″ of the driver 21 of the reference voltage (Fig. 1, 5).

 The voltage reference driver 21 (see FIG. 3) includes, in particular, the first and second operational amplifiers 27 and 28, a resistive voltage divider, three resistive adjustable voltage dividers and two feedback resistors 36 and 37. The resistive voltage divider is made on series-connected precision first and second resistors 29 and 30. The first resistive adjustable voltage divider is made on the third resistor 31. The second resistive voltage divider is made on the fourth, fifth, and sixth resistors 32, 33, and 34 connected in series. Third resistive an adjustable voltage divider is made on the seventh resistor 35. Resistors 31, 33 and 35 are potentiometers.

 The first terminal of the first adjustable voltage divider is connected to the DC bus, and its second terminal is connected to the zero potential bus. The output of the first adjustable voltage divider is connected to the midpoint of the resistive voltage divider. The resistive voltage divider, the second and third adjustable voltage dividers are connected between the inverting inputs of the first and second operational amplifiers 27 and 28. The midpoint of the second adjustable divider is connected to the DC bus. The midpoint of the third adjustable voltage divider is the input "″ α ″ ″ of the driver 21 of the reference voltage. A first feedback resistor 36 is connected between the output of the first operational amplifier 27 and its inverting input, a second feedback resistor 37 is connected between the output of the second operational amplifier 28 and its inverting input. The first, second and third adjustable resistive voltage dividers are, respectively, the regulators "Amplitude of currents", "Balance of currents" and ″ α ″. The outputs of the first and second operational amplifiers 27 and 28 are, respectively, the first and second outputs of the driver 21 of the reference voltage.

 In the General case, the voltage reference driver can be performed according to other schemes, for example, using a microprocessor and a digital-to-analog converter.

 The adjustable source of alternating voltage 22 may be an analog generator of infra-low frequency (1-2) Hz with adjustable voltage amplitude from zero to a predetermined value.

 Shaper 21 reference voltages and an adjustable source 22 of alternating voltage can be constructed according to other schemes that ensure the formation of these voltages, including using microprocessors and a digital-to-analog converter.

 The proposed pulse oximeter works as follows.

 In operating mode, the voltage at the output of the regulated source 22 is set equal to zero. The regulators "Amplitude of currents", "Balance of currents" and ″ α ″ are in their working positions, established when calibrating the pulse oximeter.

Sources 1, 3 of radiation and a photodetector 5 are installed on the finger or earlobe using known devices. At the outputs of the reference voltage driver 21, constant voltages U ₁ and U ₂ are generated, which are supplied to the first and second inputs of the switch 23. The synchronized pulse sequences S ₁ and S ₂ shifted relative to one another in time arrive at the first and second control inputs of the switch 23. And as a result, at the outputs of the switch 23, pulse sequences N ₁ and N ₂ are shifted relative to one another in time with pulse amplitudes U ₁ and U ₂ . Pulse sequences N ₁ and N ₂ then go to the inputs of the first and second current sources 2 and 4, which produce currents I ₁ and I ₂ , the instantaneous values of which are proportional to the amplitudes of the pulses U ₁ and U ₂ . Sources 1 and 3 alternately form luminous fluxes in the red and infrared ranges, which, passing through the object under study, cause a current in the photodetector circuit 5, which is proportional at each moment of time to the radiation intensity. The signal generated at the output of converter 6 is amplified by amplifier 7 and then fed to the inputs of synchronous detectors 8 and 11, which are synchronized by pulses from pulse former 14 to their control inputs and to control inputs of switch 23. A signal is generated at the output of synchronous detector 8, proportional to the natural logarithm of the light flux passing through the object under study in the red range of radiation, and at the output of the synchronous detector 11 in the infrared range. The variable signal components extracted by filters 9 and 12 and amplified by amplifiers 10 and 13 are fed to the first and second inputs of function calculation unit 16 (1), the third and fourth inputs of which receive signals from the outputs of synchronous detectors 8 and 11. The signals received at the first and the second inputs of the multiplexer 24, synchronized by the control signal from the second control output of the microprocessor 26, are converted by an analog-to-digital converter 25, synchronized by the control signal from the first control output of the microprocessor 26, into a sequence of digital samples that are entered into the microprocessor 26 and are used to calculate the values of α and the saturation coefficient S. At the output of the microprocessor 26, a digital signal is generated that carries information about the saturation coefficient, which is displayed on the indicator 15. Moreover, due to the logarithmic conversion characteristic in the proposed device amplitude the variable signal components are little dependent on the thickness of the tissue of the finger or earlobe, while maintaining information about the pulse volume of oxidized and restored new hemoglobin.

When adjusting or checking the metrological characteristics of the pulse oximeter, a filter with specified absorption characteristics in the red and infrared wavelength ranges is installed instead of living tissue in the space between the radiation sources 1, 3 and the photodetector 5. At the output of an adjustable source of alternating voltage 22, a predetermined amplitude Δ U of harmonic infra-low-frequency voltage with a frequency of 1-2 Hz is set. At the first and second outputs of the driver 21 of the reference voltage generated two constant voltage U ₁ and U ₂ with pulsating components ΔU ₁ and ΔU ₂ .

The output signals of the driver 21 of the reference voltage are supplied to the first and second inputs of the switch 23, at the output of which the pulse sequences N ₁ and N ₂ shifted relative to one another are generated with pulse amplitudes U ₁ and U ₂ with pulsating components ΔU ₁ and ΔU ₂ . Pulse sequences N ₁ and N ₂ then go to the inputs of the first and second current sources 2 and 4, which generate currents I ₁ + ΔI ₁ and I ₂ + ΔI ₂ , the instantaneous values of which are proportional to the pulse amplitudes U ₁ + ΔU ₁ and U ₂ + ΔU ₂ (Fig. 5, 7).

Metrological verification of the basic error of the proposed pulse oximeter is reduced to setting verified values of the saturation coefficients using the regulators "Amplitude of currents", "Balance of currents" and ″ α ″ and comparing the readings of the saturation coefficients with their set values in the operating range of light absorption coefficients, which are set at help filters with known characteristics. At the same time, rotating the resistor 31 engine ("Amplitude of currents"), simultaneously changing the voltage values U ₁ and U ₂ and, therefore, the amplitudes of the currents I ₁ and I ₂ , rotating the resistor engine ("Current balance"), changing the voltage ratio U ₁ / U ₂ and the ratio of the amplitudes of the currents I ₁ / I ₂ . Rotating the resistor engine 35 (″ α ″), the ratio of the pulsating voltage components ΔU ₁ / ΔU ₂ and the ratio of the amplitudes of the currents ΔI ₁ / ΔI _{2 are} changed.

 Thus, the present invention allows for the verification of the pulse oximeter in the manufacturing process and operation.

 Industrial applicability of the invention is determined by the fact that a device based on it can be made on the basis of the above description and drawings and used for non-invasive measurement of arterial blood oxygen saturation in continuous monitoring mode.

Sources of information
1. Sterlin Yu.G. Specific problems in the development of pulse oximeters. Medical Technology, 1993, N 6, p. 26-30.

 2. Orlov A.S. Determination of the degree of saturation of circulating blood with oxygen by the amplitude of the pulse wave. Medical Technology, 1992, N 5, p. 16-17.

 3. RF patent N 2152030, IPC G 01 N 33/49, publ. 06/27/2000 (prototype).

Claims (2)

1. A pulse oximeter containing a radiation source in the red radiation range connected to the first current source, an infrared radiation source connected to the second current source, a photodetector made in the form of a photodiode, and an electrical signal converter connected to the photodetector, a voltage amplifier DC, the input of which is connected to the output of the electrical signal converter, made in the form of a voltage-voltage converter, connected in series a second synchronous detector, the first input of which is connected to the output of the DC voltage amplifier, the first high-pass filter and the first AC voltage amplifier, connected in series with the second synchronous detector, the first input of which is connected to the output of the DC voltage amplifier, the second high-pass filter and the second amplifier AC voltage, as well as an antiphase pulse shaper with a frequency of 200 - 2000 Hz, the first output of which is connected to the control input of the first synchronous detector torus, and the second output to the control input of the second synchronous detector, and connected to its outputs to the indicator and its first and second inputs to the outputs of the first and second AC voltage amplifiers, respectively, the function calculation unit

where S is the saturation coefficient;

- extinction coefficients of reduced hemoglobin at radiation wavelengths, respectively, in the red and infrared radiation ranges;

- double amplitudes of the alternating voltage at the outputs of the first and second amplifiers of the AC voltage, respectively;
t

- the extinction coefficient of oxyhemoglobin at wavelengths, respectively, in the red and infrared ranges of radiation,
characterized in that it further comprises a voltage shaper with regulators "Amplitude of currents", "Balance of currents" and "α", as well as an adjustable source of alternating voltage with a frequency of 1 - 2 Hz and a switch, while the first and second outputs of the voltage shaper are connected respectively, to the first and second inputs of the switch, the first and second control inputs of which are connected respectively to the first and second outputs of the antiphase pulse generator with a frequency of 200 - 2000 Hz, the first and second outputs of the switch are connected to the control inputs of the first current source and the second current source, the output of an adjustable AC voltage source with a frequency of 1 - 2 Hz is connected to the input "α" of the reference voltage driver, the mentioned function calculation unit is made in the form of series-connected multiplexer, analog-to-digital converter and microprocessor wherein the first and second inputs of the multiplexer are respectively the first and second inputs of said function calculation unit, the third and fourth inputs of the multiplex ra connected to outputs of the first and second synchronous detectors, respectively, control inputs of the analog-to-digital converter and a multiplexer connected respectively with the first and second control outputs of the microprocessor.  2. The pulse oximeter according to claim 1, characterized in that the reference voltage generator comprises two operational amplifiers, a resistive voltage divider, three resistive adjustable voltage dividers and two feedback resistors, while the first output of the first resistive adjustable voltage divider is connected to a constant voltage bus and its second output is with a zero potential bus, the output of the first resistive adjustable voltage divider is connected to the midpoint of the resistive voltage divider, the resistive d voltage divider, the second and third resistive adjustable voltage dividers are connected between the inverting inputs of the first and second operational amplifiers, the midpoint of the second resistive adjustable divider is connected to the DC bus, the middle point of the third resistive adjustable voltage divider is the input "α" of the reference voltage shaper, the first resistor feedback is connected between the output of the first operational amplifier and its inverting input, the second feedback resistor is on between the output of the second operational amplifier and its inverting input, the first, second, and third resistive adjustable voltage dividers are, respectively, the regulators "Amplitude of currents", "Balance of currents" and "α", the outputs of the first and second operational amplifiers are respectively the first and second outputs of the shaper reference stresses.

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