RU2152030C1 - Pulsating oximeter - Google Patents

Abstract

FIELD: medical engineering. SUBSTANCE: device has infrared radiation source connected to the first power supply source, infrared radiation source connected to the second power supply source, photodetector designed as photodiode, and current-to-voltage converter, direct-current voltage amplifier which input is connected to electric signal converter output designed as voltage- to-voltage converter, the first synchronous detector the first input of which is connected to constant current voltage amplifier output, the first high frequency filter and the first alternating current voltage amplifier are connected in series. The second synchronous detector, the first input of which is connected to constant current voltage amplifier output, the second high frequency filter and the second alternating current voltage amplifier are connected in series. The first output of opposite phase pulse shaper of 200-2000 Hz frequency has its first output connected to control input of the first power supply source and to control input of the first synchronous detector, its second output being connected to control input of the second power supply source and to control input of the second synchronous detector, and also connected to indicator unit with its output and with its first and second inputs to the outputs of the first and the second alternating current voltage amplifiers, respectively. Function calculation unit is also available. Another version of the device has current-to-voltage converter and voltage converter with log-log characteristic instead of voltage-to-voltage converter and constant current voltage amplifier. EFFECT: enhanced accuracy in measuring oxygen saturation of arterial blood in noninvasive mode. 2 cl, 4 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: the constant components of the red and infrared channels, and the 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.

 Also known pulse oximeter described in [2, p. 16, fig. 1] and adopted as a prototype of the proposed group of inventions. This pulse oximeter contains a radiation source in the red range of radiation connected to the first current source, a radiation source in the infrared range of radiation 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 indicated in the description of the analogue [1].

 The objective of the invention is the creation of a simple pulse oximeter with increased accuracy in determining the coefficient of saturation.

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. Значения этих коэффициентов известны и зависят только от длин волн в красном и инфракрасном диапазонах излучения.The specified problem in the first embodiment of the invention is solved in that in a pulse oximeter containing a radiation source in the red radiation range connected to the first current source, a radiation source in the infrared radiation range connected to the second current source, a photodetector made in the form of a photodiode, and a converter electrical signal, a voltage converter with a logarithmic conversion characteristic is introduced, the input of which is connected to the output of the current-voltage converter, in series with a single first synchronous detector, the first input of which is connected to the output of a voltage converter with a logarithmic conversion characteristic, a first high-pass filter and a first AC voltage amplifier, connected in series with a second synchronous detector, the first input of which is connected to a voltage converter with a logarithmic conversion characteristic, a second upper filter frequencies and a second AC voltage amplifier, as well as an antiphase pulse generator 200 -2000 Hz, the first output of which is connected to the control input of the first current source and the control input of the first synchronous detector, and the second output - to the control input of the second current source and the control input of the second synchronous detector, and connected by its output to the indicator and its first and second inputs - to the outputs of the first and second AC amplifiers, respectively, the function calculation 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 reduced 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 of the first and second alternating current amplifiers,

the extinction coefficient of oxyhemoglobin at wavelengths, respectively, in the red and infrared ranges of radiation. The values of these coefficients are known and depend only on wavelengths in the red and infrared ranges of radiation.

 The specified task in the second embodiment of the invention is solved in that in a pulse oximeter containing a radiation source in the red radiation range connected to the first current source, a radiation source in the infrared radiation range connected to the second current source, a photodetector made in the form of a photodiode, and a converter current-voltage connected to the photodetector, a voltage converter with a logarithmic conversion characteristic is introduced, the input of which is connected to the output of the current-voltage converter a series-connected first synchronous detector, the first input of which is connected to the output of a voltage converter with a logarithmic conversion characteristic, a first high-pass filter and a first AC voltage amplifier, serially connected to a second synchronous detector, the first input of which is connected to a voltage converter with a logarithmic conversion characteristic, a second high-pass filter and a second AC voltage amplifier, as well as a phase shaper pulses with a frequency of 200-2000 Hz, the first output of which is connected to the control input of the first current source and the control input of the first synchronous detector, and the second output - to the control input of the second current source and the control input of the second synchronous detector, and connected by its output to the indicator and its the first and second inputs - to the outputs of the first and second AC voltage amplifiers, respectively, the unit for calculating the function (1).

The essence of the invention is illustrated by drawings, which depict:
in FIG. 1 is a functional diagram of a device according to the first embodiment,
in FIG. 2 is a schematic diagram of a voltage-to-voltage converter,
in FIG. 3 - time charts,
in FIG. 4 is a functional diagram of a device according to the second embodiment.

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 calculation unit,
17, 18 - isolation capacitors,
19, 20 - resistors of CR-chains,
21 is an operational amplifier
22, 23 - feedback resistors,
24 - waveform at the first output of the shaper 14,
25 - waveform at the second output of the driver 14,
26 - waveform at the output of the synchronous detector 8,
27 - waveform at the output of the synchronous detector 11,
28 - waveform at the output of amplifier 10,
29 - waveform at the output of the amplifier 13,
t is the time axis
U is the stress axis,
30 - current-voltage converter,
31 - voltage converter with a logarithmic conversion characteristic.

 The pulse oximeter according to the first embodiment (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 electric signal converter 6.

 Sources 1 and 2 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 perceived by the photodetector 5 of the light signals should overlap the wavelength range in which lie the wavelengths emitted by the signal sources 1 and 3.

 The converter 6 is made in the form of a voltage-voltage converter, for example, according to the circuit shown in FIG. 2. The Converter 6 can be performed according to other known schemes of the Converter voltage - voltage.

 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 the amplifier 7, the first high-pass filter 9 and the first AC voltage amplifier 10, in series connected to a second synchronous detector 11, the first input of which is connected to the output of an 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 known schemes, including in the form of the simplest dividing 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 control input of the first current source 2 and the control input of the first synchronous detector 8. The second output of the shaper 14 is connected to the control input of the second current source 4 and the control input of the second synchronous detector 11. The shaper 14 can be performed, for example, in the form of a simple multivibrator. When using digital devices for processing and recording the results as part of the pulse oximeter, the shaper 14 can be made, for example, in the form of a frequency divider of the clock pulses of these devices. 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 may be made in the form of an analog or digital computing device. In the latter case, block 16 may comprise a series-connected multiplexer, the first and second inputs of which are respectively the first and second inputs of block 16, an analog-to-digital converter, and a microprocessor.

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

 The proposed pulse oximeter works as follows.

 Sources 1, 3 of radiation and a photodetector 5 are installed on the finger or earlobe using known devices. Sources 1 and 3 alternately form light fluxes in the red and infrared ranges, which, passing through the object under study, cause a current in the circuit of the photodetector 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 radiation sources 1 and 3. In this case, a signal is generated at the output of the synchronous detector 8, which is proportional to the natural logarithm of the light flux passing through the object under investigation in the red emission range due to the new implementation of the converter 6, and in the infrared range at the output of the synchronous detector 11. The variable signal components extracted by filters 9 and 12 and amplified by amplifiers 10 and 13 are fed to the inputs of function calculation unit 16 (1), at the output of which an analog or digital signal is generated that carries information about the saturation coefficient. Due to the logarithmic characteristic of the conversion in the proposed device, the amplitudes of the variable component signals depend little on the thickness of the tissue of the finger or earlobe, while maintaining information about the pulse volume of oxidized and reduced hemoglobin.

 The pulse oximeter in the second embodiment differs from the oximeter in the second in that it contains a current-voltage converter 30 and a voltage converter 31 with a logarithmic conversion characteristic. The operation of the device according to the second embodiment occurs similarly to the operation of the oximeter according to the first embodiment. In this case, the same result is achieved.

 Thus, the proposed invention can simplify the pulse oximeter while improving the accuracy of determining the coefficient of saturation.

 The industrial applicability of the inventions is determined by the fact that devices based on them 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.

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 electric signal converter connected to the photodetector, characterized in that a DC voltage amplifier is introduced into it, the input of which is connected to the output of the electric signal converter, made in the form of a voltage - voltage converter secondly connected 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 filter frequencies 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 the input of the first current source and the control input of the first synchronous detector, and the second output to the control input of the second current source and the control input of the second synchronous detector, and connected by its output to the indicator and its first and second inputs to the outputs of the first and second AC voltage amplifiers, respectively current function calculation 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 reduced hemoglobin at radiation wavelengths, respectively, in the red and infrared radiation ranges;
ΔV _λ1 and ΔV _λ2 are the double amplitudes of the alternating voltage at the output of the first and second AC voltage amplifiers, respectively;

the extinction coefficient of oxyhemoglobin at wavelengths, respectively, in the red and infrared ranges of radiation. 2. 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 a current-voltage converter connected to the photodetector, different the fact that a voltage converter with a logarithmic conversion characteristic is introduced into it, the input of which is connected to the output of the current-voltage converter, serially connected by a first synchronous detector, the first input of which is connected to the output of a voltage converter with a logarithmic conversion characteristic, a first high-pass filter and a first AC voltage amplifier connected in series with a second synchronous detector, whose first input is connected to a voltage converter with a logarithmic conversion characteristic, a 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 the output of which is connected to the control input of the first current source and the control input of the first synchronous detector, and the second output to the control input of the second current source and the control input of the second synchronous detector, and connected by its input to the indicator and its first and second inputs to the outputs of the first and second AC voltage amplifiers function calculation 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 reduced hemoglobin at radiation wavelengths, respectively, in the red and infrared radiation ranges;
ΔV _λ1 and ΔV _λ2 are the double amplitudes of the alternating voltage at the outputs of the first and second AC voltage amplifiers, respectively;

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

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