CN113693583A - Transthoracic impedance measurement circuit and defibrillator - Google Patents
Transthoracic impedance measurement circuit and defibrillator Download PDFInfo
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- 238000002847 impedance measurement Methods 0.000 title claims abstract description 36
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- A61B5/00—Measuring for diagnostic purposes; Identification of persons
- A61B5/05—Detecting, measuring or recording for diagnosis by means of electric currents or magnetic fields; Measuring using microwaves or radio waves
- A61B5/053—Measuring electrical impedance or conductance of a portion of the body
- A61B5/0531—Measuring skin impedance
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- A61N1/32—Applying electric currents by contact electrodes alternating or intermittent currents
- A61N1/38—Applying electric currents by contact electrodes alternating or intermittent currents for producing shock effects
- A61N1/39—Heart defibrillators
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61N—ELECTROTHERAPY; MAGNETOTHERAPY; RADIATION THERAPY; ULTRASOUND THERAPY
- A61N1/00—Electrotherapy; Circuits therefor
- A61N1/18—Applying electric currents by contact electrodes
- A61N1/32—Applying electric currents by contact electrodes alternating or intermittent currents
- A61N1/38—Applying electric currents by contact electrodes alternating or intermittent currents for producing shock effects
- A61N1/39—Heart defibrillators
- A61N1/3904—External heart defibrillators [EHD]
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Abstract
The invention discloses a transthoracic impedance measuring circuit and a defibrillator, wherein the transthoracic impedance measuring circuit comprises: the device comprises at least two electrode plates, an alternating current constant current source, a voltage detection circuit and a main control circuit; the main control circuit controls the alternating current constant current source to apply an alternating current constant current signal to the object to be detected through the electrode plates, the voltage at two ends of the object to be detected is detected through the voltage detection circuit, and finally the transthoracic impedance of the object to be detected is calculated through the ohm law. The invention utilizes the characteristic of capacitance of direct current isolation and alternating current isolation to eliminate the influence of equivalent capacitance component in transthoracic impedance of an object to be measured, directly measures the equivalent resistance component in the transthoracic impedance, and is beneficial to improving the real-time performance and the accuracy of the transthoracic impedance measurement.
Description
Technical Field
The invention relates to the technical field of medical instruments, in particular to a transthoracic impedance measuring circuit and a defibrillator.
Background
In modern clinical medicine, the defibrillator is widely used for treating sudden cardiac arrest, can effectively convert malignant arrhythmia into normal sinus rhythm, and saves the life of a patient. The defibrillation success rate depends on whether the defibrillation energy and the defibrillation waveform of the defibrillation signal are proper or not, and the transthoracic impedance of the patient directly influences the defibrillation energy and the defibrillation waveform of the signal to be defibrillated, so the transthoracic impedance of the patient needs to be detected in real time in the defibrillation process, and then the defibrillation voltage, current and duration are continuously adjusted according to the transthoracic impedance, so that each defibrillation parameter is guaranteed to meet the requirements.
The cell is used as the basic structural unit of human biological tissue, and consists of cell membrane and intracellular and extracellular fluids, wherein the cell membrane has selective permeability, the intracellular fluid has conductivity, the extracellular fluid can be regarded as electrolyte, and when the biological tissue is excited by direct current or low-frequency alternating current, the current avoids the cell membrane and mainly passes through the extracellular fluid. The body impedance equivalent circuit can therefore be viewed as a series-parallel network of resistors and capacitors, where the equivalent resistive component is the transthoracic impedance measurement we need.
At present, a measuring circuit which can eliminate the influence of equivalent capacitance components and directly detect the equivalent resistance components in the transthoracic impedance of a human body is lacked.
Disclosure of Invention
The invention mainly aims to provide a transthoracic impedance measuring circuit, which aims to eliminate the influence of capacitance components and directly measure the transthoracic impedance of a human body.
To achieve the above object, the present invention provides a transthoracic impedance measurement circuit, comprising:
the at least two electrode plates are used for being electrically connected with an object to be detected;
the alternating current constant current source is connected with the electrode plate and is used for outputting an alternating current constant current signal to the electrode plate;
the voltage detection circuit is connected with the electrode plate and is used for detecting the voltage of the electrode plate and outputting a corresponding voltage detection signal;
the main control circuit is connected with the alternating current constant current source and the voltage detection circuit respectively, and is used for determining the transthoracic impedance value of the object to be detected according to the voltage detection signal and the current value of the alternating current constant signal.
In one embodiment, the frequency value of the alternating current constant current signal is greater than or equal to 60 kilohertz.
In one embodiment, the current value of the ac constant current signal is less than 1 ma.
In one embodiment, the ac constant current source comprises:
the constant current source is used for outputting a direct current constant current signal;
and the input end of the inverter circuit is connected with the constant current source, and the output end of the inverter circuit is connected with the electrode plate.
In one embodiment, the voltage detection circuit further includes:
the input end of the signal processing circuit is connected with the voltage detection circuit, and the output end of the signal processing circuit is connected with the main control circuit;
the signal processing circuit is used for converting the voltage detection signal into a smooth direct current signal and outputting the smooth direct current signal to the main control circuit.
In one embodiment, the signal processing circuit includes:
a differential amplification circuit for differentially amplifying the voltage detection signal;
the band-pass filter circuit is connected with the output end of the differential amplification circuit and is used for performing band-pass filtering on the voltage detection signal after differential amplification;
the rectifying circuit is connected with the output end of the band-pass filter circuit and is used for converting the voltage detection signal in an alternating current form into the voltage detection signal in a direct current form;
and the peak detection circuit is used for acquiring the peak value of the voltage detection signal in a direct current form and outputting the peak value to the main control circuit.
The main control circuit is also used for determining the transthoracic impedance value of the object to be detected connected with the electrode slice according to the peak value of the voltage detection signal.
In an embodiment, the transthoracic impedance measurement circuit further comprises:
a reference load connected in series with the electrode plates;
a first input end of the switching circuit is connected with the electrode plate, a second input end of the switching circuit is connected with the reference load, and an output end of the switching circuit is respectively connected with the alternating current constant current source and the voltage detection circuit;
the main control circuit is also used for determining the transthoracic impedance value of the object to be detected according to the voltage detection signal of the reference load, the resistance of the reference load and the alternating current constant current signal.
In one embodiment, the switching circuit is a double pole double throw relay.
In an embodiment, the transthoracic impedance measurement circuit further comprises:
and the input end of the defibrillation protection circuit is connected with the electrode plate, and the output end of the defibrillation protection circuit is connected with the voltage detection circuit.
The invention also provides a defibrillator, which comprises the transthoracic impedance measuring circuit and a defibrillation device;
the defibrillation device adjusts the defibrillation energy and the defibrillation waveform of the output defibrillation signal according to the transthoracic impedance value detected by the transthoracic impedance measuring circuit.
The technical scheme of the invention utilizes the characteristic of 'direct-alternating-current isolation' of the capacitor, outputs an alternating current constant current signal to the object to be detected through the electrode plate by the alternating current constant current source, and detects the voltage at two ends of the object to be detected by the voltage detection circuit. At the moment, the current of the alternating current constant current signal is known, the voltage at two ends of the object to be measured is known, and the transthoracic impedance of the object to be measured can be calculated through ohm's law. At this time, the impedance of the equivalent capacitance component is 0, that is, the loss generated by the equivalent capacitance component is 0, relative to the ac constant current source, and therefore the transthoracic impedance obtained by the test at this time is completely the equivalent resistance component. The method and the device have the advantages that the equivalent resistance component in the transthoracic impedance is directly measured, the influence of the equivalent capacitance component is eliminated, the accuracy of transthoracic impedance measurement is improved due to the fact that the equivalent capacitance component can be eliminated, the instantaneity of transthoracic impedance measurement is improved due to the fact that the equivalent resistance component is directly measured, and the success rate of the defibrillator is improved.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the structures shown in the drawings without creative efforts.
FIG. 1 is a circuit diagram of a transthoracic impedance measurement circuit in accordance with an embodiment of the present invention;
FIG. 2 is a circuit diagram of an embodiment of an AC constant current source of the transthoracic impedance measurement circuit of the present invention;
FIG. 3 is a circuit diagram of one embodiment of a voltage detection circuit of the transthoracic impedance measurement circuit of the present invention;
FIG. 4 is a circuit diagram of an embodiment of a differential amplifier circuit of the transthoracic impedance measurement circuit of the present invention;
FIG. 5 is a circuit diagram of one embodiment of a bandpass filter circuit of the transthoracic impedance measurement circuit of the present invention;
FIG. 6 is a circuit diagram of one embodiment of a rectifying circuit of the transthoracic impedance measurement circuit of the present invention;
FIG. 7 is a circuit diagram of one embodiment of a peak detector circuit of the transthoracic impedance measurement circuit of the present invention;
FIG. 8 is a circuit diagram of another embodiment of a transthoracic impedance measurement circuit of the present invention;
fig. 9 is a circuit diagram of an embodiment of a defibrillation protection circuit of the transthoracic impedance measurement circuit of the present invention.
The reference numbers illustrate:
| reference numerals | Name (R) | Reference numerals | Name (R) |
| 10 | |
312 | Band- |
| 20 | AC constant |
313 | Rectifying |
| 30 | |
314 | |
| 40 | Master control circuit | Q1～Q5 | First to |
| 21 | Constant current source | R1～R26 | First to twenty- |
| 22 | Inverter circuit | U1～U11 | First to eleventh |
| 31 | Signal processing circuit | D1～D8 | First to |
| 311 | Differential amplifier circuit | C1～C5 | First to fifth capacitors |
The implementation, functional features and advantages of the objects of the present invention will be further explained with reference to the accompanying drawings.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
It should be noted that all the directional indicators (such as up, down, left, right, front, and rear … …) in the embodiment of the present invention are only used to explain the relative position relationship between the components, the movement situation, etc. in a specific posture (as shown in the drawing), and if the specific posture is changed, the directional indicator is changed accordingly.
In the present invention, unless otherwise expressly stated or limited, the terms "connected," "secured," and the like are to be construed broadly, and for example, "secured" may be a fixed connection, a removable connection, or an integral part; can be mechanically or electrically connected; they may be directly connected or indirectly connected through intervening media, or they may be connected internally or in any other suitable relationship, unless expressly stated otherwise. The specific meanings of the above terms in the present invention can be understood by those skilled in the art according to specific situations.
In addition, the descriptions related to "first", "second", etc. in the present invention are only for descriptive purposes and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one such feature. In addition, technical solutions between various embodiments may be combined with each other, but must be realized by a person skilled in the art, and when the technical solutions are contradictory or cannot be realized, such a combination should not be considered to exist, and is not within the protection scope of the present invention.
The invention provides a transthoracic impedance measuring circuit.
In one embodiment of the invention. Referring to fig. 1, the transthoracic impedance measurement circuit includes:
at least two electrode plates 10 for electrically connecting with an object to be measured;
the alternating current constant current source 20 is connected with the electrode plate 10, and the alternating current constant current source 20 is used for outputting an alternating current constant current signal to the electrode plate 10;
the voltage detection circuit 30 is connected with the electrode plate 10, and the voltage detection circuit 30 is used for detecting the voltage of the electrode plate 10 and outputting a corresponding voltage detection signal;
the main control circuit 40 is connected to the ac constant current source 20 and the voltage detection circuit 30, and the main control circuit 40 is configured to determine a transthoracic impedance value of the object to be detected according to the voltage detection signal and the current of the ac constant current source 20.
The number of the electrode sheets 10 is not limited, and may be set according to actual requirements.
The ac constant current source 20 may be an integrated ac constant current source chip, or may be built up by using discrete components, which is not limited herein.
The voltage detection circuit 30 may be any type of ac signal detection circuit, for example, an average detection circuit, which performs half-wave or full-wave rectification on an ac signal by constructing an ac-dc conversion circuit, and then obtains a relatively smooth dc signal by using an integration circuit for a pulsating dc signal outputted by rectification, where the amplitude of the dc signal is a half-wave rectified average value or a full-wave rectified average value of the signal to be detected, and then the relationship between the half-wave rectified average value or the full-wave rectified average value of the signal to be detected and an effective value is used to calculate the effective value of the signal to be detected. For another example, the peak detection circuit performs half-wave or full-wave rectification on the alternating current signal through the constructed alternating current-direct current conversion circuit, then uses the charging capacitor to keep the peak value of the pulsating direct current signal output by rectification, so as to obtain a relatively gentle direct current signal, the amplitude of the direct current signal is the peak value of the alternating current signal to be detected, and then uses the relation between the peak value and the effective value of the signal to be detected to calculate the effective value of the signal to be detected.
The master control circuit 40 may be a Micro Control Unit (MCU) or other type of controller, and is not limited thereto.
The transthoracic impedance of the subject to be measured includes an equivalent capacitance component and an equivalent resistance component. Through test research, the equivalent capacitance component is the interference quantity, and the equivalent resistance component is the quantity to be tested in the defibrillation work.
The technical scheme of the invention utilizes the characteristic of 'direct current isolation and direct current isolation' of the capacitor, an alternating current constant current signal is output to an object to be detected through the electrode plate 10 by the alternating current constant current source 20, and the voltage at two ends of the object to be detected is detected by the voltage detection circuit 30. At the moment, the current of the alternating current constant current signal is known, the voltage at two ends of the object to be measured is known, and the transthoracic impedance of the object to be measured can be calculated through ohm's law. At this time, the impedance of the equivalent capacitance component is 0 with respect to the ac constant current source 20, that is, the loss generated by the equivalent capacitance component is 0, and therefore, the transthoracic impedance obtained by the test at this time is completely the equivalent resistance component. The method and the device have the advantages that the equivalent resistance component in the transthoracic impedance is directly measured, the influence of the equivalent capacitance component is eliminated, the accuracy of transthoracic impedance measurement is improved due to the fact that the equivalent capacitance component can be eliminated, the instantaneity of transthoracic impedance measurement is improved due to the fact that the equivalent resistance component is directly measured, and the success rate of the defibrillator is improved.
In an embodiment of the invention, a frequency value of the ac constant current signal is greater than or equal to 60 khz.
In the embodiment, the frequency value of the alternating current constant current signal is set to be greater than or equal to 60 kilohertz, so that the alternating current constant current signal can directly pass through the equivalent capacitance component without loss, and the transthoracic impedance obtained by testing is completely the equivalent resistance component.
In an embodiment of the present invention, a current value of the ac constant current signal is less than 1 ma to improve safety.
In an embodiment of the present invention, referring to fig. 2, the ac constant current source 20 includes:
a constant current source 21 for outputting a direct current constant current signal;
and the input end of the inverter circuit 22 is connected with the constant current source 21, and the output end of the inverter circuit 22 is connected with the electrode plate 10.
The constant current source 21 may be the constant current source shown in fig. 2, or may be another constant current source. The inverter circuit 22 may be the inverter circuit 22 shown in fig. 2, or may be another inverter circuit, which is not limited herein.
Referring to fig. 2, the first operational amplifier U1 compares the reference voltage with the voltage at the two ends of the second resistor R2, and when the voltage at the two ends of the second resistor R2 is not equal to the reference voltage, adjusts the voltage output to the first MOS transistor Q1 through the first resistor R1, and further adjusts the drain-source resistance between the drain and the source of the first MOS transistor Q1, and finally makes the voltage at the two ends of the second resistor R2 equal to the reference voltage, so that the current flowing through the second resistor R2 is constant, and at this time, the current value I of the constant current signal provided by the constant current source is equal to the reference voltageDPCan be obtained by the following formula:
wherein, V0 is the voltage value of the reference voltage, and R2 is the resistance value of the second resistor R2.
The reference voltage V0 is adjustable voltage, and the current value I of the constant current signal provided by the constant current source can be adjusted by adjusting the voltage value of the reference voltageDPThe size of (2).
With continued reference to fig. 2, an H-bridge circuit composed of a second MOS transistor Q2, a third MOS transistor Q3, a fourth MOS transistor Q4, and a fifth MOS transistor Q5 is provided at the output terminal of the constant current source (the drain of the first MOS transistor Q1). The second MOS transistor Q2 and the fifth MOS transistor Q5 form an upper arm of the H-bridge circuit, and the third MOS transistor Q3 and the fourth MOS transistor Q4 form a lower arm of the H-bridge circuit. The upper and lower bridge arms can be controlled to be alternately conducted by outputting a PWM signal through the main control circuit 40 or other circuits, so that a dc constant current signal provided by the constant current source 21 can be converted into an ac constant current signal and output to the object to be measured connected to the electrode plate 10.
In an embodiment of the present invention, referring to fig. 3, the voltage detection circuit 30 includes:
the input end of the signal processing circuit 31 is connected with the voltage detection circuit 30, and the output end of the signal processing circuit 31 is connected with the main control circuit 40;
the signal processing circuit 31 is configured to convert the voltage detection signal into a smooth dc signal and output the dc signal to the main control circuit 40.
It can be understood that, taking the main control circuit 40 as a micro control unit as an example, the voltage detection signal is an ac signal, and the micro control unit cannot directly receive the ac signal. In this embodiment, the signal processing circuit 31 converts the voltage detection signal from an ac signal to a corresponding smooth dc signal, so that the micro control unit can receive and process the voltage detection signal.
Further, with continued reference to fig. 3, the signal processing circuit 31 includes:
a differential amplification circuit 311 for differentially amplifying the voltage detection signal;
a band-pass filter circuit 312, connected to the output end of the differential amplifier circuit 311, for performing band-pass filtering on the voltage detection signal after differential amplification;
a rectifying circuit 313, connected to an output end of the band-pass filter circuit 312, for converting the voltage detection signal in an ac form into the voltage detection signal in a dc form;
and a peak detection circuit 314, configured to obtain a peak value of the voltage detection signal in a direct current form, and output the peak value to the main control circuit 40.
The peak value of the voltage detection signal of the main control circuit 40 determines the transthoracic impedance value of the object to be measured connected to the electrode sheet 10.
The present embodiment differentially amplifies the differential voltages V1 and V2 on at least two electrode pads 10 by a differential amplifier and outputs a differentially amplified voltage V3. Interference signals such as myoelectric signals generated by the object to be detected are filtered by a band-pass filter, only the differential amplification voltage V3 is reserved, and the filtered signals are marked as filtering signals V4. The ac filtered signal V4 is half-wave or full-wave rectified by the rectifier circuit 313 to become a pulsating dc signal V5. Then, the peak value of the pulsating direct current signal is obtained by the peak value detection circuit 314, and a relatively gentle direct current signal V6 is obtained and output to the main control circuit 40, wherein the amplitude of the gentle direct current signal is the peak value of the differential amplification voltage V3.
At this time, the main control circuit 40 may calculate the effective value of the differential amplified voltage V3 according to the relationship between the peak value and the effective value of the differential amplified voltage V3, and then calculate the effective value of the voltage at the two ends of the object to be detected connected to the electrode pad 10 according to the effective value of the differential amplified voltage V3 and the amplification factor of the differential amplifying circuit 311, and may calculate the transthoracic impedance of the object to be detected by ohm's law according to the effective value of the voltage at the two ends of the object to be detected and the current value of the ac constant current signal.
In an embodiment of the invention, referring to fig. 4, the differential amplifier circuit 311 includes a third resistor R3, a fourth resistor R4, a fifth resistor R5, a sixth resistor R6, a seventh resistor R7, an eighth resistor R8, a second operational amplifier U2, a third operational amplifier U3, a fourth operational amplifier U4, a fifth operational amplifier U5, and a sixth operational amplifier U6.
Specifically, the non-inverting input terminal of the second operational amplifier U2 is connected to the differential voltage V1, and the inverting input terminal of the second operational amplifier U2 is connected to the output terminal to form an input buffer/follower, where the input impedance of the buffer is infinite and the output impedance is small, so that a later-stage circuit can obtain a large voltage. Similarly, the third operational amplifier U3 also forms an input buffer/follower.
The fourth operational amplifier U4, the fifth operational amplifier U5, and the sixth operational amplifier U6 further form a differential amplifier circuit 311:
the non-inverting input end of a fourth operational amplifier U4 is connected with the output end of a second operational amplifier U2, the inverting input end of a fourth operational amplifier U4 is connected with one end of a third resistor R3, the other end of the third resistor R3 is connected with the output end of a fourth operational amplifier U4, and the output end of a fourth operational amplifier U4 is connected with one end of a fourth resistor R4;
the non-inverting input end of the fifth operational amplifier U5 is connected with the output end of the third operational amplifier U3, the inverting input end of the fifth operational amplifier U5 is connected with one end of a sixth resistor R6, the other end of the sixth resistor R6 is connected with the output end of the fifth operational amplifier U5, and the output end of the fifth operational amplifier U5 is connected with one end of a seventh resistor R7;
an inverting input terminal of the fourth operational amplifier U4 is connected to one terminal of an eighth resistor R8, and the other terminal of the eighth resistor R8 is connected to an inverting input terminal of the fifth operational amplifier U5.
The other end of the fourth resistor R4 is connected to the inverting input terminal of the sixth operational amplifier U6, and the other end of the seventh resistor R7 is connected to the non-inverting input terminal of the sixth operational amplifier U6.
The resistance of the third resistor R3 is equal to the resistance of the sixth resistor R6, and the resistance of the fourth resistor R4 is equal to the resistance of the seventh resistor R7.
In this way, the output voltage V of the sixth operational amplifier U6OUTCan be obtained by the following formula:
wherein, R3 is the resistance of the third resistor R3, R4 is the resistance of the fourth resistor R4, R5 is the resistance of the fifth resistor R5, and R8 is the resistance of the eighth resistor R8.
The present embodiment amplifies the differential voltage V1 and the differential voltage V2 into the differential amplified voltage V3 through the differential amplifying circuit 311, so that the signal processing circuit 31 can better process the differential amplified voltage V3, and the main control circuit 40 can receive the voltage detection circuit 30 with a proper voltage value.
Referring to fig. 5, the band pass filter includes: a ninth resistor R9, a tenth resistor R10, an eleventh resistor R11, a twelfth resistor R12, a thirteenth resistor R13, a seventh operational amplifier U7, a first capacitor C1, and a second capacitor C2.
One end of a ninth resistor R9 is connected to the differential amplification voltage V3, the other end of the ninth resistor R9 is connected to one end of a first capacitor C1, the other end of the first capacitor C1 is connected to the non-inverting input end of a seventh operational amplifier U7, the non-inverting input end of the seventh operational amplifier U7 is connected to one end of a twelfth resistor R12, and the other end of the twelfth resistor R12 is grounded; the inverting input end of the seventh operational amplifier U7 is connected with one end of an eleventh resistor, the other end of the eleventh resistor R11 is connected with the output end of the seventh operational amplifier U7, the inverting input end of the seventh operational amplifier U7 is also connected with one end of a tenth resistor R10, and the other end of the tenth resistor R10 is grounded;
an output end of the seventh operational amplifier U7 is connected with one end of a thirteenth resistor R13, the other end of the thirteenth resistor R13 is connected with a common end of a first capacitor C1 and a ninth resistor R9, and one end of a second capacitor C2 is connected with a common end of a first capacitor C1 and a ninth resistor R9; the other terminal of the second capacitor C2 is connected to ground. The output of the seventh operational amplifier U7 outputs a filtered signal V4 in which the differentially amplified signal V3 is filtered.
Wherein, the center frequency f of the band-pass filter circuit 312pCan be calculated by the following formula:
wherein, R9, R12 and R13 are resistance values of the ninth resistor R9, the twelfth resistor R12 and the thirteenth resistor R13, respectively, and C1 and C2 are capacitance values of the first capacitor C1 and the second capacitor C2, respectively. In this embodiment, the center frequency f of the band-pass filter circuit 312 can be set by selecting appropriate resistance and capacitance parameterspThe filtered signal V4 is output for differentially amplifying the frequency of the signal V3 so as to filter out interference signals (e.g., myoelectric signals) other than the differentially amplified signal V3.
Referring to fig. 6, the rectifying circuit 313 includes: a fourteenth resistor R14, a fifteenth resistor R15, a sixteenth resistor R16, a seventeenth resistor R17, an eighteenth resistor R18, a nineteenth resistor R19, a twentieth resistor R20, an eighth operational amplifier U8, a ninth operational amplifier U9, a first diode D1 and a second diode D2.
One end of a fourteenth resistor R14 is connected to the filtered signal V4, the other end of the fourteenth resistor R14 is connected to the inverting input terminal of the eighth operational amplifier U8, the inverting input terminal of the eighth operational amplifier U8 is connected to one end of a fifteenth resistor R15, the other end of a fifteenth resistor R15 is connected to the anode of the first diode D1, the cathode of the first diode D1 is connected to the output terminal of the eighth operational amplifier U8, the output terminal of the eighth operational amplifier U8 is connected to the anode of the second diode D2, the cathode of the second diode D2 is connected to one end of a sixteenth resistor R16, and the other end of the sixteenth resistor R16 is connected to the inverting input terminal of the eighth operational amplifier U8.
The common end of the fifteenth resistor R15 and the first diode D1 is connected with one end of a seventeenth resistor R17, and the other end of the seventeenth resistor R17 is connected with the inverting input end of a ninth operational amplifier U9;
the common end of the sixteenth resistor R16 and the second diode D2 is connected with one end of a nineteenth resistor R19, and the other end of the nineteenth resistor R19 is connected with the non-inverting input end of a ninth operational amplifier U9;
the inverting input end of the ninth operational amplifier U9 is connected with one end of an eighteenth resistor R18, and the other end of the eighteenth resistor R18 is connected with the output end of the ninth operational amplifier U9;
the non-inverting input terminal of the ninth operational amplifier U9 is connected to one end of the twentieth resistor R20, and the other end of the twentieth resistor R20 is grounded.
The output of the ninth operational amplifier U9 outputs a pulsating dc signal V5. For convenience of calculation, the resistance values of the fourteenth resistor R14, the fifteenth resistor R15, the sixteenth resistor R16, the seventeenth resistor R17, the eighteenth resistor R18, the nineteenth resistor R19 and the twentieth resistor R20 are all equal. The pulsating direct current signal V5 can be obtained by the following formula:
wherein, R17 and R18 are the resistances of the seventeenth resistor R17 and the eighteenth resistor R18, respectively.
In the embodiment, the full-wave rectification circuit 313 is built to rectify the filtered signal V4 into the pulsating direct-current signal V5, so that peak detection/mean detection can be performed subsequently, and the main control circuit 40 can acquire a voltage detection signal in a direct-current form.
Referring to fig. 7, the peak detector circuit 314 includes: a twenty-first resistor R21, a twenty-second resistor R22, a tenth operational amplifier U10, an eleventh operational amplifier U11, a third capacitor C3, a third diode D3, and a fourth diode D4.
The non-inverting input end of a tenth operational amplifier U10 is connected to the pulsating direct current signal V5, the inverting input end of a tenth operational amplifier U10 is connected to the anode of a third diode D3, the cathode of the third diode D3 is connected to the output end of a tenth operational amplifier U10, the output end of the tenth operational amplifier U10 is connected to the anode of a fourth diode D4, the cathode of the fourth diode D4 is connected to the non-inverting input end of an eleventh operational amplifier U11, the non-inverting input end of the eleventh operational amplifier U11 is connected to one end of a twenty-second resistor R22 and one end of a third capacitor C3, and the other end of the twenty-second resistor R22 and the other end of the third capacitor C3 are grounded;
an inverting input terminal of the eleventh operational amplifier U11 is connected to one end of the twenty-first resistor R21, and the other end of the twenty-first resistor R21 is connected to an inverting input terminal of the tenth operational amplifier U10; an inverting input terminal of the eleventh operational amplifier U11 is connected to the output terminal. The output end of the eleventh operational amplifier U11 outputs a smooth direct current signal V6; v6 can be obtained by the following formula:
V6＝V5-Vd；
vd is the forward voltage drop of the third diode D3 and the fourth diode D4;
in this embodiment, the peak detection is performed on the pulsating dc signal V5, and the peak signal is stabilized to form a smooth dc signal V6, which is output to the main control circuit 40, so that the main control circuit 40 can obtain the peak signal of the voltage at the two ends of the object to be measured according to the smooth dc signal V6 and the inverse operation of the processing process of the signal processing circuit 31, obtain the effective value of the voltage at the two ends of the object to be measured according to the relationship between the peak signal and the effective value of the voltage at the two ends of the object to be measured, and further obtain the transthoracic impedance of the object to be measured according to the effective value of the voltage at the two ends of the object to be measured and the effective value of the ac constant current signal.
In an embodiment of the present invention, referring to fig. 8, the transthoracic impedance measurement circuit further includes:
a reference load connected in series with the electrode sheet 10;
a first input end of the switching circuit is connected with the electrode plate 10, a second input end of the switching circuit is connected with the reference load, and an output end of the switching circuit is respectively connected with the alternating current constant current source 20 and the voltage detection circuit 30;
the main control circuit 40 is further configured to determine a transthoracic impedance value of the object to be measured according to the voltage detection signal of the reference load, the resistance of the reference load, and the ac constant current signal.
The reference load may be a high precision, robust load.
The switching circuit can be a double-pole double-throw relay, the relay is a mechanical switch, compared with an electronic switch such as an MOS (metal oxide semiconductor) tube, the switching of the relay is physically switching, so that the reference load and the object to be measured cannot influence the measurement of each other when the voltage at two ends of the object to be measured and the voltage at two ends of the reference load are switched and measured.
Referring to fig. 8, the reference load may be the second resistor R2 described above. Of course, in other embodiments, the switching circuit may be another type of switching circuit, and the reference load may be a load separately provided from the constant current source.
In this embodiment, two first fixed contacts of the double-pole double-throw relay are respectively connected to the two electrode plates 10, two second fixed contacts of the double-pole double-throw relay are respectively connected to two ends of the second resistor R2, and two moving contacts of the double-pole double-throw relay are connected to the signal processing circuit 31/main control circuit 40. By controlling the double-pole double-throw relay, the voltages of the second resistor R2 and the two ends of the object to be measured can be measured respectively. Since the current flowing through the second resistor R2 is identical to the current flowing through the object to be measured, the following formula can be obtained:
wherein, V8 and V7 are voltages at two ends of the object to be tested, V10 and V9 are voltages at two ends of a second resistor R2, R2 is a voltage value of the second resistor R2, and R is a voltage value of the second resistor R2PIs the transthoracic impedance of the subject to be tested.
The second resistor R2 can be a high-precision low-drift resistor, and since V8 and V7, and V10 and V9 are obtained by processing and detecting the same signal processing circuit 31, and both measurements are subject to the same error loss, the embodiment can avoid the error caused by the signal processing circuit 31, thereby greatly improving the measurement precision of the transthoracic impedance.
In an embodiment of the present invention, the transthoracic impedance measurement circuit further includes:
and the input end of the defibrillation protection circuit is connected with the electrode plate 10, and the output end of the defibrillation protection circuit is connected with the voltage detection circuit 30.
Referring to fig. 9, the defibrillation protection circuit may include a twenty-third resistor R23, a twenty-fourth resistor R24, a twenty-fifth resistor R25, a twenty-sixth resistor R26, a fourth capacitor C4, a fifth capacitor C5, a fifth diode D5, a sixth diode D6, a seventh diode D7, and an eighth diode D8.
Specifically, one end of the fourth capacitor C4 is connected to one of the two electrode plates 10, the other end of the fourth capacitor C4 is connected to one end of a twenty-fifth resistor R25, the other end of the twenty-fifth resistor R25 outputs a differential voltage V1, one end of the twenty-third resistor R23 is connected to a common end of the fourth capacitor C4 and the twenty-fifth resistor R25, and the other end of the twenty-third resistor R23 is grounded;
one end of a fifth capacitor C5 is connected with the other of the two electrode plates 10, the other end of the fifth capacitor C5 is connected with one end of a twenty-sixth resistor R26, the other end of the twenty-sixth resistor R26 outputs a differential voltage V2, one end of a twenty-fourth resistor R24 is connected with the common end of the fifth capacitor C5 and the twenty-sixth resistor R26, and the other end of the twenty-fourth resistor R24 is grounded;
the anode of the fifth diode D5 is connected to the negative pole of the safety voltage, and the cathode of the sixth diode D6 is connected to the positive pole of the safety voltage; the cathode of the fifth diode D5 is connected to the anode of the sixth diode D6, and the common terminal of the fifth diode D5 and the sixth diode D6 is connected to the common terminal of the fourth capacitor C4 and the twenty-fifth resistor R25.
The anode of the seventh diode D7 is connected to the negative pole of the safety voltage, and the cathode of the eighth diode D8 is connected to the positive pole of the safety voltage; the cathode of the seventh diode D7 is connected to the anode of the eighth diode D8, and the common terminal of the seventh diode D7 and the eighth diode D8 is connected to the common terminal of the fifth capacitor C5 and the twenty-sixth resistor R26.
The fourth capacitor C4 and the fifth capacitor C5 are used for filtering out the direct current component of the voltage at the two ends of the object to be measured. The fifth to eighth diodes D8 are high-voltage fast diodes, and the differential voltages V1 and V2 are clamped, so that the differential voltages V1 and V2 are smaller than the safety voltage. Therefore, when the defibrillator works, the high voltage applied to the object to be tested can not damage the signal processing circuit 31 and the main control circuit 40, and the protective effect is achieved.
The invention also provides a defibrillator, which comprises the transthoracic impedance measuring circuit and a defibrillation device; the specific structure of the transthoracic impedance measurement circuit refers to the above embodiments, and since the defibrillator adopts all the technical solutions of all the above embodiments, at least all the beneficial effects brought by the technical solutions of the above embodiments are achieved, and no further description is given here. The defibrillation device adjusts the defibrillation energy and the defibrillation waveform of the output defibrillation signal according to the transthoracic impedance value detected by the transthoracic impedance measuring circuit.
The above description is only an alternative embodiment of the present invention, and not intended to limit the scope of the present invention, and all modifications and equivalents of the present invention, which are made by the contents of the present specification and the accompanying drawings, or directly/indirectly applied to other related technical fields, are included in the scope of the present invention.
Claims (10)
1. A transthoracic impedance measurement circuit, comprising:
the at least two electrode plates are used for being electrically connected with an object to be detected;
the alternating current constant current source is connected with the electrode plate and is used for outputting an alternating current constant current signal to the electrode plate;
the voltage detection circuit is connected with the electrode plate and is used for detecting the voltage of the electrode plate and outputting a corresponding voltage detection signal;
the main control circuit is connected with the alternating current constant current source and the voltage detection circuit respectively, and is used for determining the transthoracic impedance value of the object to be detected according to the voltage detection signal and the current value of the alternating current constant signal.
2. The transthoracic impedance measurement circuit of claim 1 wherein said ac constant current signal has a frequency value of 60 khz or greater.
3. The transthoracic impedance measurement circuit of claim 1 wherein the ac constant current signal has a current value of less than 1 ma.
4. The transthoracic impedance measurement circuit of claim 1 wherein said ac constant current source comprises:
the constant current source is used for outputting a direct current constant current signal;
and the input end of the inverter circuit is connected with the constant current source, and the output end of the inverter circuit is connected with the electrode plate.
5. The transthoracic impedance measurement circuit of claim 1 wherein said voltage detection circuit further comprises:
the input end of the signal processing circuit is connected with the voltage detection circuit, and the output end of the signal processing circuit is connected with the main control circuit;
the signal processing circuit is used for converting the voltage detection signal into a smooth direct current signal and outputting the smooth direct current signal to the main control circuit.
6. The transthoracic impedance measurement circuit of claim 5 wherein said signal processing circuit comprises:
a differential amplification circuit for differentially amplifying the voltage detection signal;
the band-pass filter circuit is connected with the output end of the differential amplification circuit and is used for performing band-pass filtering on the voltage detection signal after differential amplification;
the rectifying circuit is connected with the output end of the band-pass filter circuit and is used for converting the voltage detection signal in an alternating current form into the voltage detection signal in a direct current form;
the peak detection circuit is used for acquiring the peak value of the voltage detection signal in a direct current form and outputting the peak value to the main control circuit; the main control circuit is also used for determining the transthoracic impedance value of the object to be detected connected with the electrode slice according to the peak value of the voltage detection signal.
7. The transthoracic impedance measurement circuit of claim 1, wherein the transthoracic impedance measurement circuit further comprises:
a reference load connected in series with the electrode plates;
a first input end of the switching circuit is connected with the electrode plate, a second input end of the switching circuit is connected with the reference load, and an output end of the switching circuit is respectively connected with the alternating current constant current source and the voltage detection circuit;
the main control circuit is also used for determining the transthoracic impedance value of the object to be detected according to the voltage detection signal of the reference load, the resistance of the reference load and the alternating current constant current signal.
8. The transthoracic impedance measurement circuit of claim 7 wherein said switching circuit is a double pole double throw relay.
9. The transthoracic impedance measurement circuit of claim 1, wherein the transthoracic impedance measurement circuit further comprises:
and the input end of the defibrillation protection circuit is connected with the electrode plate, and the output end of the defibrillation protection circuit is connected with the voltage detection circuit.
10. A defibrillator comprising the transthoracic impedance measurement circuit of claims 1-9 and a defibrillation apparatus;
the defibrillation device adjusts the defibrillation energy and the defibrillation waveform of the output defibrillation signal according to the transthoracic impedance value detected by the transthoracic impedance measuring circuit.
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