External defibrillator

Abstract

The present invention belongs to the technical field of medical devices, and particularly relates to an external defibrillator. An external defibrillator includes a DC power supply and a pair of defibrillation electrodes; between the DC power supply and the pair of defibrillation electrodes, there is also included a series connection of: a resistance reduction circuit, connected to the DC power supply, reducing the internal resistance of the DC power supply to a preset power supply internal resistance; an impedance matching circuit, connected to the resistance reduction circuit, matching the power supply internal resistance with the transthoracic impedance of the human body, and having a defibrillation voltage output terminal; an electrode switching circuit, respectively connected to the defibrillation voltage output terminal or the defibrillation electrodes, switching the connection relationship between the impedance matching circuit and the defibrillation electrodes. The present invention does not need to measure the transthoracic impedance, can adjust the defibrillation current according to the transthoracic impedance, indirectly compensate the transcardiac current, so that the transcardiac current reaches the expected value, is suitable for various defibrillation electrodes, and reduces the complexity of the design.

Description

Technical Field

[0001] The present invention belongs to the technical field of medical devices, and particularly relates to an external defibrillator. Background Art

[0002] An external defibrillator is a device that applies an electrical pulse through electrodes to the skin of a patient (external electrodes) to achieve electrical defibrillation of the heart. It is used for first aid of patients with ventricular fibrillation, ventricular tachycardia, and suspected cardiac arrest.

[0003] The principle of electrical defibrillation is to apply a strong electrical pulse to the heart within an extremely short time, causing most cardiac self-regulating cells to depolarize simultaneously within a short time, inactivating all possible reentry channels, allowing the sinoatrial node to resume its dominant position and control the heartbeat, and restoring sinus rhythm.

[0004] "The 2000 International Guidelines on Cardiopulmonary Resuscitation and Emergency Cardiovascular Care" states: "Defibrillation relies on successfully selecting an appropriate energy to generate an effective current passing through the heart (transcardiac current) to achieve defibrillation, while causing minimal electrical damage to the heart. If the energy and current are too small, a single shock cannot terminate the arrhythmia; while if the energy and current are too large, it may cause functional or morphological damage to the heart. Selecting an appropriate current can also reduce the number of repeated shocks, thereby reducing myocardial damage."

[0005] The key factor for successful defibrillation is the transcardiac current, and energy is only a means to generate the current. The average transcardiac current is the effective component of defibrillation. The higher the average transcardiac current, the greater the success rate of defibrillation. The peak transcardiac current is the main component that damages myocardial function. The higher the peak transcardiac current or the too large average transcardiac current, the more severe the degree of myocardial damage.

[0006] The defibrillation waveform is a key factor affecting the success rate of defibrillation, mainly including the phase, shape, pulse width, peak-to-average ratio, etc. of the waveform. The biphasic wave has two phases in sequence: the first phase is the positive phase, and the current flows from the positive electrode to the negative electrode; the second phase is the negative phase, and the current flows reversely between the positive and negative electrodes. By clearing the residual charge of the first phase through the reverse second-phase current, the recurrence rate of ventricular fibrillation after defibrillation can be reduced.

[0007] The latest research data shows that: "The effective time of the current for terminating ventricular fibrillation does not exceed 12 milliseconds. A current greater than 12 milliseconds has no meaning for improving the defibrillation effect, but instead increases the degree of myocardial function damage and leads to the recurrence of ventricular fibrillation."

[0008] Impedance compensation technology means that the defibrillator adjusts the parameters during the discharge process according to the measured transthoracic impedance of the patient to improve the success rate of defibrillation and achieve personalized defibrillation. The main problems of this method are as follows: 1. The measurement of transthoracic impedance must be completed after the defibrillator is charged. Therefore, it is only suitable for defibrillation electrode pads and not for defibrillation electrode plates, while defibrillation electrode plates are still the most popular defibrillation method. 2. The measurement of transthoracic impedance and the defibrillation pulse delivery are carried out at different times, resulting in poor real-time performance. 3. Measuring transthoracic impedance increases the complexity of the circuit, and the more complex the circuit, the worse the reliability. Summary of the Invention

[0009] Aiming at the technical problem in the prior art that impedance compensation requires measuring transthoracic impedance to adjust the parameters during the discharge process, the present invention aims to provide an external defibrillator that can achieve dynamic adjustment without measuring transthoracic impedance.

[0010] An external defibrillator includes a DC power supply and a pair of defibrillation electrodes;

[0011] Between the DC power supply and the pair of defibrillation electrodes, there is also a series connection of:

[0012] A resistance reduction circuit, connected to the DC power supply, reducing the internal resistance of the DC power supply to a preset power supply internal resistance;

[0013] An impedance matching circuit, connected to the resistance reduction circuit, matching the power supply internal resistance with the transthoracic impedance of the human body, and having a defibrillation voltage output terminal;

[0014] An electrode switching circuit, respectively connected to the defibrillation voltage output terminal or the defibrillation electrodes, switching the connection relationship between the impedance matching circuit and the defibrillation electrodes.

[0015] As a preferred solution, the DC power supply uses a 15V disposable battery.

[0016] As a preferred solution, the resistance reduction circuit uses a resistance reduction capacitor;

[0017] The DC power supply is grounded through the resistance reduction capacitor.

[0018] As a preferred solution, the resistance reduction capacitor is composed of at least one of a high-frequency low-resistance capacitor or a super capacitor in parallel.

[0019] As a preferred solution, the impedance matching circuit includes:

[0020] A switch compensation signal terminal;

[0021] An oscillator, with two output terminals being switch pulses with a phase difference of 180°;

[0022] At least one group of impedance matching components, and each group of the impedance matching components includes:

[0023] A dual-channel driver, with two input ends respectively connected to two output ends of the oscillator, and two enable ends both connected to the switch compensation signal end;

[0024] A transformer, with a primary tap on the primary side, and the primary tap is connected to the DC power supply;

[0025] A first NMOS transistor, with the gate connected to an output end of the dual-channel driver, the source grounded, and the drain connected to one end of the primary side of the transformer;

[0026] A second NMOS transistor, with the gate connected to the other output end of the dual-channel driver, the source grounded, and the drain connected to the other end of the primary side of the transformer;

[0027] The secondary sides of the transformers in multiple groups of the impedance matching components are connected in series and then connected to the defibrillation voltage output end through a voltage doubler rectification circuit.

[0028] As a preferred solution, the first NMOS transistor and the second NMOS transistor adopt N-channel insulated gate field effect transistors with a drain-source on-resistance less than 1 mΩ.

[0029] As a preferred solution, the voltage doubler rectification circuit is a voltage doubler rectification circuit composed of multiple rectification capacitors and multiple rectification diodes;

[0030] The rectification capacitors adopt chip capacitors.

[0031] As a preferred solution, the oscillator includes:

[0032] A power switch driver, with two output ends respectively connected to two input ends of the dual-channel driver;

[0033] A timing capacitor, with one end grounded and the other end connected to the timing capacitor input end of the power switch driver;

[0034] A first timing resistor, with one end connected to the power supply input end and the other end connected to the timing capacitor discharge end of the power switch driver;

[0035] A second timing resistor, with one end connected to the timing capacitor input end and the other end connected to the timing capacitor discharge end.

[0036] As a preferred solution, the power switch driver adopts a push-pull MOSFET power switch driver with a dead time compensation function and a built-in oscillator, and the power switch driver adopts a power switch driver with an oscillation frequency of 200 kHz and a dead time of 150 ns.

[0037] As a preferred solution, the electrode switching circuit employs two single-pole double-throw electronic switches, with one single-pole double-throw electronic switch corresponding to one defibrillation electrode;

[0038] The common terminal of the single-pole double-throw electronic switch is connected to the corresponding defibrillation electrode, the normally closed terminal of the single-pole double-throw electronic switch is grounded, and the normally open terminal of the single-pole double-throw electronic switch is connected to the defibrillation voltage output terminal.

[0039] As a preferred solution, the power switch driver uses a PWM controller chip;

[0040] The external defibrillator further includes a closed-loop compensation circuit, and the closed-loop compensation circuit includes:

[0041] Two defibrillation voltage sampling resistors, which are connected in series and have one end connected to the defibrillation voltage output terminal and the other end grounded;

[0042] A defibrillation current sampling resistor, which is connected in series with a load resistor, and the load resistor is the equivalent resistor of the human body;

[0043] A first voltage follower, with the non-inverting input terminal connected to the common terminal of the two defibrillation voltage sampling resistors and the inverting input terminal connected to the output terminal;

[0044] A second voltage follower, with the non-inverting input terminal connected to one end of the defibrillation current sampling resistor and the inverting input terminal connected to the output terminal;

[0045] A non-inverting adder, with the non-inverting input terminal connected to the output terminal of the first voltage follower through a third resistor, the non-inverting input terminal connected to the output terminal of the second voltage follower through a fourth resistor, the inverting input terminal connected to the output terminal through a fifth resistor, the inverting input terminal grounded through a sixth resistor, and the resistances of the third resistor, the fourth resistor, the fifth resistor, and the sixth resistor are the same;

[0046] An error amplifier, with the non-inverting input terminal connected to the preset voltage terminal, the inverting input terminal connected to the output terminal of the non-inverting adder, and the output terminal connected to the error signal input terminal of the PWM controller chip.

[0047] As a preferred solution, the PWM controller chip controls the voltage at the output terminal of the non-inverting adder to be equal to the preset voltage provided by the preset voltage terminal;

[0048] The compensation method of the closed-loop compensation circuit adopts the following formula:

[0049] V SET =(kV DF +R S I DF )

[0050]

[0051] Among them, R1 and R2 are two of the defibrillation voltage sampling resistors, and R S is the defibrillation current sampling resistor, V SET is the preset voltage provided by the preset voltage terminal, and V DF is the defibrillation voltage provided by the defibrillation voltage output terminal, and I DF is the defibrillation current;

[0052] After k and R S are fixed, the defibrillation current I SET is changed by changing the preset voltage V DF .

[0053] The positive and progressive effects of the present invention are as follows: The present invention uses an external defibrillator and has the following advantages:

[0054] 1. Adjust the defibrillation current according to the transthoracic impedance, indirectly compensate the transcardiac current, and make the transcardiac current reach the expected value. When the transthoracic impedance is low, the defibrillation current is appropriately increased, and when the transthoracic impedance is high, the defibrillation current is appropriately decreased to ensure that enough current flows through the heart. The present invention does not need to measure the transthoracic impedance and can achieve real-time dynamic adjustment, which is suitable for various defibrillation electrodes and reduces the complexity of the design.

[0055] 2. The DC power supply provides a low-voltage power supply to supply energy to the defibrillator; the resistance reduction circuit reduces the internal resistance of the low-voltage power supply to the micro-ohm level; the impedance matching circuit matches the internal resistance of the power supply with the transthoracic impedance of the human body, so that the transthoracic impedance of the human body passes through the defibrillation current; the electrode switching circuit obtains a defibrillation waveform of a fixed pulse width biphasic wave by switching the connection relationship between the impedance matching circuit and the defibrillation electrode.

[0056] 3. The external defibrillator of the present invention has a simple structure, small size and light weight, and is suitable for disposable defibrillation applications and wearable defibrillation applications. Brief Description of the Drawings

[0057] Figure 1 is a connection schematic diagram of the present invention;

[0058] Figure 2 is a schematic diagram of an open-loop compensation circuit of the present invention;

[0059] Figure 3 is Figure 2 the compensation signal and defibrillation waveform diagram corresponding to the circuit schematic diagram of;

[0060] Figure 4 is the diagram of defibrillation current varying with transthoracic impedance;

[0061] Figure 5 is the diagram of defibrillation voltage varying with transthoracic impedance;

[0062] Figure 6 Graph of defibrillation power varying with transthoracic impedance;

[0063] Figure 7 Schematic diagram of a closed-loop compensation circuit according to the present invention. Detailed implementation manners

[0064] In order to make the technical means, creative features, achieved purposes and functions of the present invention easy to understand, the present invention will be further described below with reference to specific illustrations.

[0065] In the present invention, when describing an external defibrillator:

[0066] 1. The defibrillation current refers to the current flowing through the defibrillation electrodes during the cardiac shock discharge.

[0067] 2. The transthoracic current refers to the current flowing through the heart during the cardiac shock discharge.

[0068] 3. The defibrillation voltage refers to the potential difference between the two defibrillation electrodes during the cardiac shock discharge.

[0069] 4. The defibrillation waveform refers to the curve of the defibrillation current varying with time during the cardiac shock discharge.

[0070] 5. The transthoracic impedance refers to the equivalent impedance between the two defibrillation electrodes. Since the capacitive reactance component is very small, the transthoracic impedance can be equivalent to a resistance. The transthoracic impedance ranges from 25Ω to 175Ω. The factors determining the transthoracic resistance impedance include: the size of the electrode pads, the interface between the defibrillator and the skin, the number of defibrillations and the time interval, the respiratory phase, the distance between the electrodes (determined by the size of the chest), and the pressure of the defibrillator on the skin. The transthoracic impedance is the only variable in defibrillation.

[0071] Refer to Figure 1 , an external defibrillator, comprising a DC power supply 1, a resistance reduction circuit 2, an impedance matching circuit 3, an electrode switching circuit 4, and a pair of defibrillation electrodes 5 connected in sequence.

[0072] The DC power supply 1 provides a low-voltage power supply. The DC power supply 1 of the present invention preferably uses a 15V disposable battery. Since the internal resistance of the disposable battery is in the order of ohms, it can provide an instantaneous current in the order of amperes.

[0073] The resistance reduction circuit 2 is connected to the DC power supply 1. The resistance reduction circuit 2 reduces the internal resistance of the DC power supply 1 to a preset power supply internal resistance, for example, reduces it to the order of micro-ohms. After passing through the resistance reduction circuit 2, the low-voltage power supply can provide an instantaneous current in the order of kiloamperes.

[0074] Refer to Figure 2, the resistance reduction circuit 2 uses a resistance reduction capacitor C1, and the DC power supply 1 is grounded through the resistance reduction capacitor C1. The resistance reduction capacitor C1 is preferably composed of at least one of a high-frequency low-resistance capacitor or a super capacitor connected in parallel. The function of the high-frequency low-resistance capacitor is to reduce the internal resistance of the DC power supply 1, and the function of the super capacitor is to provide sufficient charge during the pulse delivery. The larger the resistance reduction capacitor C1, the smaller the voltage drop across the resistance reduction capacitor C1 during the discharge process, the smaller the peak-to-average ratio of the defibrillation current, the better the defibrillation effect, and the smaller the myocardial damage.

[0075] The impedance matching circuit 3 is connected to the resistance reduction circuit. The impedance matching circuit 3 matches the internal resistance of the power supply with the transthoracic impedance of the human body, so that the transthoracic impedance of the human body allows the defibrillation current to flow through. The impedance matching circuit 3 has a defibrillation voltage output terminal, and the defibrillation voltage output terminal outputs a defibrillation voltage V DF .

[0076] Referring to Figure 2 , the impedance matching circuit 3 is preferably composed of a transformer and its accessory circuit, and the accessory circuit refers to Figure 2 the components other than the resistance reduction capacitor C1 in

[0077] The switch compensation signal terminal is Figure 2 the ON / OFF terminal in

[0078] The two output terminals of the oscillator are switch pulses with a phase difference of 180°. Referring to Figure 2 , the oscillator preferably includes a power switch driver IC1, a timing capacitor C2, a first timing resistor R7, and a second timing resistor R8.

[0079] The two output terminals of the power switch driver IC1 are respectively connected to the two input terminals of each dual-channel driver in the impedance matching component. As Figure 2As shown, there are two sets of impedance matching components, and each set of impedance matching components has a dual driver, namely dual driver IC2 and dual driver IC3. One output terminal (OUTA terminal) of the power switch driver IC1 is respectively connected to one input terminal (INA terminal) of the dual driver IC2 and one input terminal (INA terminal) of the dual driver IC3. The other output terminal (OUTB terminal) of the power switch driver IC1 is respectively connected to the other input terminal (INB terminal) of the dual driver IC2 and the other input terminal (INB terminal) of the dual driver IC3. The voltage input terminal (VDD terminal) of the power switch driver IC1 is connected to the power supply input terminal, and the power supply input terminal provides a +12V DC power supply. The ground terminal (GND terminal) and the current sampling input terminal (CS terminal) of the power switch driver IC1 are both grounded.

[0080] One end of the timing capacitor C2 is grounded, and the other end of the timing capacitor C2 is connected to the timing capacitor input terminal (CT terminal) of the power switch driver IC1.

[0081] One end of the first timing resistor R7 is connected to the power supply input terminal, and the power supply input terminal provides a +12V DC power supply. The other end of the first timing resistor R7 is connected to the timing capacitor discharge terminal (DIS terminal) of the power switch driver IC1.

[0082] One end of the second timing resistor R8 is connected to the timing capacitor input terminal (CT terminal), and the other end of the second timing resistor R8 is connected to the timing capacitor discharge terminal (DIS terminal).

[0083] In the present invention, an oscillator is constituted by the power switch driver IC1, the timing capacitor C2, the first timing resistor R7 and the second timing resistor R8. Among them, the power switch driver IC1 is a push-pull MOSFET power switch driver IC1 with a built-in oscillator having a dead time compensation function. The power switch driver IC1 is preferably the UCC28089 chip. This series of chips is a push-pull MOSFET power switch driver with a built-in oscillator having a dead time compensation function, and its driving ability is 0.5A. The UCC28089 chip has a low start-up current.

[0084] The timing capacitor C2, the first timing resistor R7 and the second timing resistor R8 are used to determine the oscillation frequency and the dead time. In the present invention, the oscillation frequency is preferably 200kHz, the dead time is 150ns, and the OUTA terminal and the OUTB terminal of the power switch driver IC1 output two switching pulses with a phase difference of 180° and a frequency of 100kHz.

[0085] The impedance matching components can be set to one set or multiple sets according to needs. It is preferably set to multiple sets, and more preferably set to two sets as Figure 2 shown. Figure 2Taking the two sets of impedance matching components shown as an example, it includes a dual-channel driver IC2, a dual-channel driver IC3, a transformer T1, a transformer T2, a first NMOS transistor Q1, a first NMOS transistor Q3, a second NMOS transistor Q2, a second NMOS transistor Q4, and a voltage doubling rectifier circuit. Taking one set of impedance matching components as an example, its circuit connection relationship is as follows:

[0086] One input terminal (INA terminal) of the dual-channel driver IC2 is connected to an output terminal (OUTA terminal) of the oscillator, and the other input terminal (INB terminal) of the dual-channel driver IC2 is connected to an output terminal (OUTB terminal) of the oscillator. The two enable terminals (ENA terminal and ENB terminal) of the dual-channel driver IC2 are both connected to the ON / OFF terminal (switch compensation signal terminal). One output terminal (OUTA terminal) of the dual-channel driver IC2 is connected to the gate of the first NMOS transistor Q3, and the other output terminal (OUTB terminal) of the dual-channel driver IC2 is connected to the gate of the second NMOS transistor Q4. The voltage input terminal (VDD terminal) of the dual-channel driver IC2 is connected to the power supply input terminal, and the power supply input terminal provides a +12V DC power supply. The ground terminal (GND terminal) of the dual-channel driver IC2 is grounded.

[0087] The dual-channel driver IC2 and the dual-channel driver IC3 preferably adopt the UCC27528 dual-channel driver, and the dual-channel driver IC2 and the dual-channel driver IC3 can respectively increase the current of the switching pulses output by the oscillator to 5A.

[0088] The primary side of the transformer T1 has a primary tap, and the primary tap is connected to the DC power supply 1. The secondary sides of the transformers T1 in multiple sets of impedance matching components are connected in series and then connected to the defibrillation voltage output terminal through a voltage doubling rectifier circuit. Through the design of multiple transformers in multiple sets of impedance matching components of the present invention, such as the transformers T1 and T2, the turns ratio of each transformer can be reduced. For example, if the primary side of the transformer is selected to be 1 turn, the voltage per turn is 15V, which can balance the iron loss and magnetic loss of the transformer and also reduce the distributed capacitance of the transformer. For example, the number of turns of the secondary side of the transformer is 40 turns, so that the no-load voltage of the secondary side is 600V output. After the two secondary sides of the transformers are connected in series and output 1200V, after voltage doubling rectification, the defibrillation voltage V DF = 2400V. The impedance of the primary side output circuit includes: the internal resistance of the resistance-reducing capacitor C1, the on-resistance of each switching transistor, and the internal resistance of the transformer. The overall design makes the output impedance of the circuit about 50Ω.

[0089] The gate of the first NMOS transistor Q3 is connected to an output terminal (OUTA terminal) of the dual-channel driver IC2, the source of the first NMOS transistor Q3 is grounded, and the drain of the first NMOS transistor Q3 is connected to one end of the primary side of the transformer T1.

[0090] The gate of the second NMOS transistor Q4 is connected to another output terminal (OUTB terminal) of the dual-channel driver IC2. The source of the second NMOS transistor Q4 is grounded, and the drain of the second NMOS transistor Q4 is connected to the other end of the primary side of the transformer T1.

[0091] The first NMOS transistor Q3 and the second NMOS transistor Q4 are N-channel insulated-gate field-effect transistors with a drain-source on-resistance less than 1 mΩ.

[0092] The voltage-doubling rectifier circuit is a voltage-doubling rectifier circuit composed of multiple rectifier capacitors and multiple rectifier diodes. The rectifier capacitors are chip capacitors. Specifically, as Figure 2 shown, taking two groups of impedance matching components as an example, the voltage-doubling rectifier circuit includes a third rectifier capacitor C3, a fourth rectifier capacitor C4, a fifth rectifier capacitor C5, a sixth rectifier capacitor C6, a first rectifier diode D1, a second rectifier diode D2, a third rectifier diode D3, and a fourth rectifier diode D4.

[0093] The third rectifier capacitor C3, the fourth rectifier capacitor C4, the fifth rectifier capacitor C5, and the sixth rectifier capacitor C6 are connected in series in sequence, with one end connected to the defibrillation voltage output terminal and the other end grounded. The first rectifier diode D1, the second rectifier diode D2, the third rectifier diode D3, and the fourth rectifier diode D4 are connected in series in sequence, with the negative terminal connected to the defibrillation voltage output terminal and the positive terminal grounded.

[0094] Both ends of the secondary side of the transformer T1 are respectively connected to the common terminal of the third rectifier capacitor C3 and the fourth rectifier capacitor C4, and the common terminal of the first rectifier diode D1 and the second rectifier diode D2.

[0095] The common terminal of the fourth rectifier capacitor C4 and the fifth rectifier capacitor C5 is short-circuited with the common terminal of the second rectifier diode D2 and the third rectifier diode D3.

[0096] Both ends of the secondary side of the transformer T2 are respectively connected to the common terminal of the fifth rectifier capacitor C5 and the sixth rectifier capacitor C6, and the common terminal of the third rectifier diode D3 and the fourth rectifier diode D4.

[0097] Since the third rectifier capacitor C3, the fourth rectifier capacitor C4, the fifth rectifier capacitor C5, and the sixth rectifier capacitor C6 only discharge during the dead time, very small chip capacitors can be selected to reduce the volume of the device.

[0098] The electrode switching circuit 4 is respectively connected to the defibrillation voltage output terminal or the defibrillation electrode 5 to switch the connection relationship between the switching impedance matching circuit 3 and the defibrillation electrode 5.

[0099] The electrode switching circuit 4 preferably uses two single-pole double-throw electronic switches, and one single-pole double-throw electronic switch corresponds to one defibrillation electrode 5. The common terminal of the single-pole double-throw electronic switch is connected to the corresponding defibrillation electrode 5, the normally closed terminal of the single-pole double-throw electronic switch is grounded, and the normally open terminal of the single-pole double-throw electronic switch is connected to the defibrillation voltage output terminal to reduce the patient leakage current.

[0100] Referring to Figure 3 , the two electrodes can be respectively referred to as the first electrode and the second electrode. When the normally open terminal of the switch on the first electrode is closed and the normally closed terminal of the switch on the second electrode is closed, the first phase of the defibrillation pulse is output. When the normally closed terminal of the switch on the first electrode is closed and the normally open terminal of the switch on the second electrode is closed, the second phase of the defibrillation pulse is output.

[0101] Referring to Figure 2 , after power-on, the power supply input terminal provides a +12V DC power supply, and the oscillator starts to work. When the ON / OFF terminal is at a high level, the dual-channel driver IC2 and the dual-channel driver IC3 have output signals, the first NMOS transistor Q1 and the second NMOS transistor Q2 alternately switch, the first NMOS transistor Q3 and the second NMOS transistor Q4 alternately switch, and alternating magnetic fields are generated in the cores of the transformers T1 and T2, so that an AC voltage is generated in the secondary coil. After being rectified and filtered by the voltage doubler rectifier circuit, the defibrillation voltage V is output at the defibrillation voltage output terminal. DF Referring to Figure 3 , this voltage can directly generate a defibrillation current on the transthoracic impedance of the human body after passing through the electrode switching circuit 4. When the ON / OFF terminal is at a low level, the output of the defibrillation voltage V DF stops, the defibrillation current is zero, and the defibrillation is paused or ended.

[0102] Referring to Figure 1 , the external defibrillator may further include a control circuit 6, and the control circuit 6 is respectively connected to the DC power supply 1, the impedance matching circuit 3 and the electrode switching circuit 4. The control circuit 6 is used to control the power supply state of the DC power supply 1, the control circuit 6 is used to control the on / off state of the switching compensation signal of the impedance matching circuit 3, and the control circuit 6 is used to control the switching state of the electrode switching circuit 4.

[0103] Referring to Figure 4 , the greater the transthoracic impedance, the smaller the defibrillation current. Referring to Figure 5 , the higher the defibrillation voltage, the greater the defibrillation current. Referring to Figure 6 , the relationship among the defibrillation current, the defibrillation voltage and the transthoracic impedance follows Ohm's law.

[0104] The relationship between the defibrillation current, the transthoracic current, and the transthoracic impedance is that after the transthoracic impedance shunts the defibrillation current, the remaining current is the transthoracic current. The smaller the transthoracic impedance, the more the shunting, and the smaller the transthoracic current. The larger the transthoracic impedance, the less the shunting, and the larger the transthoracic current. Due to the shunting effect of the transthoracic impedance, only about 5% of the defibrillation current can pass through the heart to form the transthoracic current.

[0105] The present invention compensates the defibrillation current according to the transthoracic impedance, indirectly compensates the transthoracic current, and makes the transthoracic current reach the expected value. Specifically, for a low transthoracic impedance with more shunting, the defibrillation current is appropriately increased, and for a high transthoracic impedance with less shunting, the defibrillation current is appropriately decreased. For example, when the transthoracic impedance is 25Ω, the defibrillation current compensation is 30A, and when the transthoracic impedance is 175Ω, the defibrillation current compensation is 10A. Then the compensation relationship is:

[0106]

[0107] where, I DF is the defibrillation current, in units of A; V SET is the preset voltage, in units of V; k is the transthoracic resistance compensation factor, dimensionless; R TTI is the transthoracic impedance, in units of Ω; R S is the defibrillation current sampling resistance, in units of Ω.

[0108] Let V SET = 5V, R TTI = 25Ω, I DF = 30A; R TTI = 175Ω, I DF = 10A, and substitute into Equation (1). The values of k and R S can be obtained. k = 1 / 450, R S = 1 / 9Ω.

[0109] Then,

[0110]

[0111] where, V DF is the defibrillation voltage, in units of V; R O is the compensation resistance, in units of Ω.

[0112] The defibrillation discharge time constant τ = (R TTI + R O )·C, and the compensation resistance R O will increase the time constant and reduce the peak-to-average ratio of the defibrillation current.

[0113] It can be seen from Equation (2) that: as long as the defibrillation voltage is set at V DF = 2250V, R O = 50Ω, the above goals can be achieved.

[0114] Is actually equivalent to a voltage source with an internal resistance of R O and an open-circuit voltage of V DF Adjust V DF That is, I can be adjusted proportionally DF Changing R O Can change I DF With V DF And R TTI The variation relationship among the three. There is no feedback during discharge, so it is open-loop compensation.

[0115] Substitute

[0116]

[0117] Into Equation (1) to get:

[0118] V SET = kV DF + R S I DF (3)

[0119] When k = 0, the defibrillation voltage has no effect on the defibrillation current, in a constant current state. When k > 0, the defibrillation voltage will affect the defibrillation current. The higher the defibrillation voltage, the smaller the defibrillation current. At low transthoracic impedance, the defibrillation voltage is low and the defibrillation current increases. The defibrillation current is automatically adjusted according to the expected law with the transthoracic impedance. There is no term for transthoracic impedance in the above formula, so it is not necessary to measure the transthoracic impedance.

[0120] Based on the above principle, the external defibrillator of the present invention realizes an open-loop compensation method without detecting transthoracic impedance by building a circuit connection diagram such as Figure 1 And Figure 2 As shown in Figure 3 , when the transthoracic impedance ranges from 25Ω to 175Ω, the defibrillation current can be adjusted according to different transthoracic impedances to indirectly compensate the transcardiac current and make the transcardiac current reach the expected value.

[0121] In Equation (3) of the above open-loop compensation method, after k and R S Are fixed, changing V SET Can change the defibrillation current I DF . V SET Remains unchanged during the defibrillation pulse delivery, which can be automatically given by the defibrillator or set by the user. This method has negative feedback during discharge, so it is closed-loop compensation.

[0122] Since Equation (3) above is only a summation relationship, it is very easy to use an analog circuit to achieve real-time dynamic adjustment of the defibrillation current. The circuit schematic diagram of the closed-loop compensation is as shown in Figure 7 .

[0123] When the power switch driver IC1 uses a PWM controller chip, such as the UC3825 controller chip, the present invention can implement a closed-loop compensation method. At this time, the present invention further includes a closed-loop compensation circuit. Referring to Figure 7 the closed-loop compensation circuit includes a defibrillation voltage sampling resistor R1, a defibrillation voltage sampling resistor R2, a defibrillation current sampling resistor R S , a first voltage follower U1, a second voltage follower U2, a non-inverting summer U3, a third resistor R3, a fourth resistor R4, a fifth resistor R5, a sixth resistor R6, an error amplifier U4, and a preset voltage terminal.

[0124] The defibrillation voltage sampling resistor R1 and the defibrillation voltage sampling resistor R2 are connected in series. The non-common end of the defibrillation voltage sampling resistor R1 is connected to the defibrillation voltage output terminal, and the defibrillation voltage output terminal outputs a defibrillation voltage V DF . The non-common end of the defibrillation voltage sampling resistor R2 is grounded. The voltage at the common end of the defibrillation voltage sampling resistor R1 and the defibrillation voltage sampling resistor R2 is V1.

[0125] The defibrillation current sampling resistor R S is connected in series with the load resistor, and the load resistor is the equivalent resistance of the human body. The current flowing through the defibrillation current sampling resistor R S is the defibrillation current I DF . The non-grounded end voltage of the defibrillation current sampling resistor R S is V3.

[0126] The non-inverting input terminal of the first voltage follower U1 is connected to the common end of the defibrillation voltage sampling resistor R1 and the defibrillation voltage sampling resistor R2, and the inverting input terminal of the first voltage follower U1 is connected to the output terminal of the first voltage follower U1. The voltage at the output terminal of the first voltage follower U1 is V2.

[0127] The non-inverting input terminal of the second voltage follower U2 is connected to one end of the defibrillation current sampling resistor R S , and the inverting input terminal of the second voltage follower U2 is connected to the output terminal of the second voltage follower U2. The voltage at the output terminal of the second voltage follower U2 is V4.

[0128] The non-inverting input terminal of the non-inverting summer U3 is connected to the output terminal of the first voltage follower U1 through the third resistor R3, the non-inverting input terminal of the non-inverting summer U3 is connected to the output terminal of the second voltage follower U2 through the fourth resistor R4, the inverting input terminal of the non-inverting summer U3 is connected to the output terminal of the non-inverting summer U3 through the fifth resistor R5, the inverting input terminal of the non-inverting summer U3 is grounded through the sixth resistor R6, and the resistances of the third resistor R3, the fourth resistor R4, the fifth resistor R5, and the sixth resistor R6 are the same. The voltage at the output terminal of the non-inverting summer U3 is V5.

[0129] The non-inverting input terminal of the error amplifier U4 is connected to the preset voltage terminal, the inverting input terminal of the error amplifier U4 is connected to the output terminal of the in-phase adder U3, and the output terminal of the error amplifier U4 is connected to the error signal input terminal of the PWM controller chip. The preset voltage provided by the preset voltage terminal is V SET , and the output terminal voltage of the error amplifier U4 is V6.

[0130] Refer to Figure 7 , V DF is the defibrillation voltage, I DF is the defibrillation current, the resistor R1 and the resistor R2 are defibrillation voltage sampling resistors, and the sampling voltage V1 = kV DF , the transthoracic resistance compensation factor

[0131] The resistor R S is the defibrillation current sampling resistor, and the voltage V3 = R S I DF .

[0132] The first voltage follower U1 and the second voltage follower U2 are used to reduce the influence of the subsequent circuit on the sampling V1 and V3.

[0133] Since the resistance values of the third resistor R3, the fourth resistor R4, the fifth resistor R5, and the sixth resistor R6 are the same, then V5 = (V1 + V3) = (kV DF + R S I DF )

[0134] V6 is the error signal, which is used to compensate the defibrillation discharge circuit. The error signal V6 is sent to the PWM controller chip. Under the control of the PWM controller chip, through the opposite trend change, the deep negative feedback compensation will make V5 = V SET , and achieve V SET = (kV DF + R S I DF )

[0135] After k and R S are fixed, the defibrillation current I SET is changed by changing the preset voltage V DF . This closed-loop compensation method does not require measuring the transthoracic impedance and can achieve real-time dynamic adjustment.

[0136] The basic principles, main features and advantages of the present invention have been shown and described above. Those skilled in the art should understand that the present invention is not limited by the above embodiments. What is described in the above embodiments and the specification only illustrates the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed. The scope of protection claimed by the present invention is defined by the appended claims and their equivalents.

Claims

1. An external defibrillator, comprising a DC power supply and a pair of defibrillation electrodes; It is characterized in that Between the DC power supply and the pair of defibrillation electrodes, there is also included a series connection of: A resistance reduction circuit, connected to the DC power supply, reducing the internal resistance of the DC power supply to a preset power supply internal resistance; An impedance matching circuit, connected to the resistance reduction circuit, matching the power supply internal resistance with the transthoracic impedance of the human body, and having a defibrillation voltage output terminal; An electrode switching circuit, respectively connected to the defibrillation voltage output terminal or the defibrillation electrodes, switching the connection relationship between the impedance matching circuit and the defibrillation electrodes; The impedance matching circuit includes: A switch compensation signal terminal; An oscillator, with two output terminals being switch pulses with a phase difference of 180°; At least one group of impedance matching components, and each group of the impedance matching components includes: A dual-channel driver, with two input terminals respectively connected to the two output terminals of the oscillator, and two enable terminals both connected to the switch compensation signal terminal; A transformer, having a primary tap on the primary side, and the primary tap is connected to the DC power supply; A first NMOS transistor, with the gate connected to one output terminal of the dual-channel driver, the source grounded, and the drain connected to one end of the primary side of the transformer; A second NMOS transistor, with the gate connected to the other output terminal of the dual-channel driver, the source grounded, and the drain connected to the other end of the primary side of the transformer; The secondary sides of the transformers in multiple groups of the impedance matching components are connected in series and then connected to the defibrillation voltage output terminal through a voltage multiplier rectifier circuit; The oscillator includes: A power switch driver, with two output terminals respectively connected to the two input terminals of the dual-channel driver; A timing capacitor, with one end grounded and the other end connected to the timing capacitor input terminal of the power switch driver; A first timing resistor, with one end connected to the power supply input terminal and the other end connected to the timing capacitor discharge terminal of the power switch driver; A second timing resistor, with one end connected to the timing capacitor input terminal and the other end connected to the timing capacitor discharge terminal; The power switch driver uses a PWM controller chip; The external defibrillator further includes a closed-loop compensation circuit, and the closed-loop compensation circuit includes: Two defibrillation voltage sampling resistors, connected in series, with one end connected to the defibrillation voltage output terminal and the other end grounded; A defibrillation current sampling resistor, connected in series with a load resistor, and the load resistor is the equivalent resistor of the human body; A first voltage follower, with the non-inverting input terminal connected to the common terminal of the two defibrillation voltage sampling resistors, and the inverting input terminal connected to the output terminal; A second voltage follower, with the non-inverting input terminal connected to one end of the defibrillation current sampling resistor, and the inverting input terminal connected to the output terminal; A non-inverting adder, with the non-inverting input terminal connected to the output terminal of the first voltage follower through a third resistor, the non-inverting input terminal connected to the output terminal of the second voltage follower through a fourth resistor, the inverting input terminal connected to the output terminal through a fifth resistor, the inverting input terminal grounded through a sixth resistor, and the resistances of the third resistor, the fourth resistor, the fifth resistor, and the sixth resistor are the same; An error amplifier, with its non-inverting input terminal connected to a preset voltage terminal, its inverting input terminal connected to the output terminal of the in-phase adder, and its output terminal connected to the error signal input terminal of the PWM controller chip; The PWM controller chip controls the voltage at the output terminal of the in-phase adder to be equal to the preset voltage provided by the preset voltage terminal; The compensation method of the closed-loop compensation circuit adopts the following formula: ； Among them, and are two of the defibrillation voltage sampling resistors, is the defibrillation current sampling resistor, is the preset voltage provided by the preset voltage terminal, is the defibrillation voltage provided for the defibrillation voltage output terminal, is the defibrillation current; After and are fixed, the defibrillation current is changed by changing the preset voltage . .

2. The external defibrillator according to claim 1, characterized in that, The DC power supply uses a 15V disposable battery.

3. The external defibrillator according to claim 1, characterized in that, The resistance reduction circuit uses a resistance reduction capacitor; The DC power supply is grounded through the resistance reduction capacitor.

4. The external defibrillator according to claim 3, wherein The resistance reduction capacitor is composed of at least one of a high-frequency low-resistance capacitor or a super capacitor connected in parallel.

5. The external defibrillator according to claim 1, characterized in that, The first NMOS transistor and the second NMOS transistor use N-channel insulated gate field effect transistors with a drain-source on-resistance less than 1mΩ; The voltage-doubling rectifier circuit is a voltage-doubling rectifier circuit composed of multiple rectifier capacitors and multiple rectifier diodes, and the rectifier capacitors use chip capacitors.

6. The external defibrillator according to claim 1, characterized in that, The power switch driver uses a push-pull MOSFET power switch driver with a dead-time compensation function and a built-in oscillator, and the power switch driver uses a power switch driver with an oscillation frequency of 200kHz and a dead time of 150ns.

7. The external defibrillator according to claim 1, characterized in that, The electrode switching circuit uses two single-pole double-throw electronic switches, and one single-pole double-throw electronic switch corresponds to one defibrillation electrode; The common terminal of the single-pole double-throw electronic switch is connected to the corresponding defibrillation electrode, the normally closed terminal of the single-pole double-throw electronic switch is grounded, and the normally open terminal of the single-pole double-throw electronic switch is connected to the defibrillation voltage output terminal.

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