A non-contact electrocardiogram monitoring system

Abstract

The present invention provides a non-contact electrocardiogram monitoring system, which relates to the technical field of electrocardiogram detection. The system includes a non-contact electrocardiogram sensing electrode, which is used to be arranged on the back of the human body, form a coupling capacitance with the skin on the back of the human body, and collect signals containing electrocardiogram data in a non-contact manner. It also includes a first capacitor connected in parallel with the coupling capacitance. After the coupling capacitance and the first capacitor are connected in parallel, they are connected to an electrocardiogram acquisition circuit through a wire. By connecting a first capacitor in parallel at both ends of the coupling capacitance, the present invention increases the coupling capacitance, reduces the capacitive reactance, and is more conducive to obtaining high-quality electrocardiogram signals. When one contact point of the first capacitor is set on both sides of the neck and the capacitance value is set to 1000 μF, the signal-to-noise ratio of the electrocardiogram signal reaches more than 30 dB, and it has good consistency with the electrocardiogram signal measured by contact.

Description

Technical Field

[0001] The present invention relates to the technical field of electrocardiogram detection, and more particularly, to a non-contact electrocardiogram monitoring system. Background Art

[0002] Currently, the prevalence and mortality of cardiovascular diseases (CVD) in China are on the rise. It is estimated that the mortality rate of cardiovascular diseases accounts for more than 40% of the disease death composition of residents. Electrocardiogram (ECG) is a clinical technical means for diagnosing cardiovascular diseases, which can assist medical staff in identifying the nature and severity of heart lesions and arrhythmias. The electrocardiograph used in traditional electrocardiogram detection is a contact device. Contact electrocardiogram detection requires electrode patches to contact the skin. However, electrode patches are not friendly to patients with sensitive skin, and the most skin-friendly patches on the market can only ensure continuous contact with normal patients for up to 14 days at most. Beyond this time, adverse reactions such as skin rashes will occur. Therefore, in recent years, a non-contact method has been proposed to detect the electrocardiogram signal of the human body, which can detect the electrocardiogram without interference, get rid of the bondage of wire harnesses, and long-term monitor and record electrocardiogram information.

[0003] Existing non-contact electrocardiogram sensing electrodes are mainly composed of electrodes and insulating substrate materials. Using the principle of capacitive coupling, the electrocardiogram signal is coupled from the human skin to the electrode, and the signal is output to the computer terminal for processing through a conditioning circuit. The electrocardiogram signal is transmitted through long-distance ion migration. During the charge transmission process, due to the obstruction of media such as clothes and sheets, charges gradually accumulate on the human epidermis and generate polarization, so that the corresponding opposite charges also accumulate on the electrode surface. When the charges on the skin surface change, the charges on the electrode will also change accordingly. Since the human electrocardiogram signal is a weak electrical signal with a low signal-to-noise ratio, it is easily interfered by external conditions such as different clothing materials, motion artifacts, static electricity, and electromyogram signals on the skin surface, resulting in attenuation due to large impedance during the capacitive coupling process of the electrocardiogram signal. The electrocardiogram signal itself is a weak signal. After attenuation occurs again through capacitive coupling, it will become even weaker, increasing the processing difficulty of the conditioning circuit and digital algorithms, and it is difficult to meet the requirement of stably detecting electrocardiogram signals in medical clinical application scenarios, for example. Summary of the Invention

[0004] The problem to be solved by the present invention is that in the prior art, non-contact electrocardiogram sensing electrodes are prone to attenuation during capacitive coupling, resulting in weaker electrocardiogram signals, thereby increasing the processing difficulty of subsequent conditioning circuits and digital algorithms, and leading to lower detection quality of electrocardiogram signals.

[0005] To solve at least one of the above problems, the present invention provides a non-contact electrocardiogram monitoring system, including non-contact electrocardiogram sensing electrodes, which are used to be arranged on the back of the human body, form a coupling capacitance with the skin of the back of the human body, and collect signals containing electrocardiogram data in a non-contact manner. The system further includes a first capacitor connected in parallel with the coupling capacitance. After the coupling capacitance and the first capacitor are connected in parallel, they are connected to an electrocardiogram acquisition circuit through a wire.

[0006] Preferably, one end of the first capacitor is used to connect to the epidermis of the human body, and the other end is used to connect to the electrocardiogram acquisition circuit.

[0007] Preferably, one end of the first capacitor is used to connect to the neck, armpit or wrist of the human body, and the other end is used to connect to the electrocardiogram acquisition circuit.

[0008] Preferably, the capacitance value of the first capacitor is 1000 μF.

[0009] Preferably, the non-contact electrocardiogram sensing electrode includes a sensitive layer, an insulating layer arranged below the sensitive layer, a reference electrode layer arranged below the insulating layer, and a base layer arranged below the reference electrode layer.

[0010] Preferably, the non-contact electrocardiogram monitoring system further includes a conductive fabric, which is connected to the first capacitor, and the conductive fabric is integrated on a pillow and used to contact and connect with the neck of the human body.

[0011] Preferably, there are two pieces of the conductive fabric, and the two pieces of the conductive fabric are integrated on the same side edge of the pillow and arranged at intervals. The two pieces of the conductive fabric are respectively used to contact and connect with both sides of the neck of the human body.

[0012] Preferably, the distance between the two pieces of the conductive fabric is 3 cm, and the width of each piece of the conductive fabric is 5 cm.

[0013] Preferably, the non-contact electrocardiogram monitoring system further includes an Ag / Agcl wet electrode. One end of the Ag / Agcl wet electrode is connected to the first capacitor, and the other end is used to connect to the epidermis of the human body.

[0014] Preferably, the non-contact electrocardiogram monitoring system further includes a voltage follower, which is arranged on the circuit after the coupling capacitance and the first capacitor are connected in parallel.

[0015] The advantages of the present invention compared with the prior art are as follows:

[0016] By connecting a first capacitor in parallel across both ends of the coupling capacitor, the present invention increases the coupling capacitor, reduces the capacitive reactance, and improves the coupling ability for electrocardiogram (ECG) signals, thus being more conducive to obtaining high-quality ECG signals. Compared with the prior art methods such as increasing the effective area of the coupling capacitor, using materials with high dielectric constants, and reducing the thickness of sheets and hospital gowns, the present invention can select a parallel capacitor with an appropriate capacitance value as needed, without generating more noise, and has strong operability. Moreover, verified by experiments of the present invention, significant effects have been achieved. The signal-to-noise ratio of the ECG signals collected by the monitoring system of the present invention reaches above 30 dB, has good consistency with the ECG signals collected by the contact measurement system, the average heart rate error within 20 minutes is within 2%, and the detection rate of R waves is above 97%. Description of the Drawings

[0017] Figure 1 Schematic diagram of non-contact capacitive coupling in an embodiment of the present invention;

[0018] Figure 2 Schematic diagram of non-contact parallel-capacitor coupling in an embodiment of the present invention;

[0019] Figure 3 Equivalent model of an Ag / AgCl wet contact electrode in an embodiment of the present invention;

[0020] Figure 4 Equivalent model of a capacitive-coupling non-contact electrode in an embodiment of the present invention;

[0021] Figure 5 Equivalent model of a parallel-capacitor non-contact electrode in an embodiment of the present invention;

[0022] Figure 6 Equivalent circuit of capacitive coupling for non-contact ECG acquisition in an embodiment of the present invention;

[0023] Figure 7 Equivalent circuit of parallel capacitor for non-contact ECG acquisition in an embodiment of the present invention;

[0024] Figure 8 Physical diagram of the parallel-capacitor circuit in an embodiment of the present invention;

[0025] Figure 9 Schematic diagram of parallel capacitors under different conditions in an embodiment of the present invention;

[0026] Figure 10 Schematic diagram of the human body part with multi-point parallel capacitors in an embodiment of the present invention;

[0027] Figure 11 Waveform of multi-point parallel-capacitor ECG acquisition in an embodiment of the present invention;

[0028] Figure 12It is the average signal-to-noise ratio curve graph of collecting electrocardiogram signals by paralleling 45 kinds of capacitance values in the embodiment of the present invention;

[0029] Figure 13 It is the waveform of collecting electrocardiogram by the contact method of Ag / Agcl wet electrode and conductive fabric at the neck in the embodiment of the present invention;

[0030] Figure 14 It is the waveform of collecting electrocardiogram signals by the electrode and the electrode plus the paralleled capacitor in the embodiment of the present invention;

[0031] Figure 15 It is the comparison of electrocardiogram waveforms between the monitoring system and the reference system in the embodiment of the present invention. Specific Embodiments

[0032] To make the above objects, features and advantages of the present invention more obvious and understandable, the following specifically describes the embodiments of the present invention in conjunction with the accompanying drawings.

[0033] Non-contact electrocardiogram monitoring is a technology that uses the principle of capacitive coupling to extract heart signals through clothes and sheets. Among them, the coupling capacitor is an important factor affecting the signal-to-noise ratio of non-contact electrocardiogram. Increasing the coupling capacitor can improve the coupling ability of electrocardiogram signals (ECG).

[0034] As Figure 1 shown, it is a non-contact capacitive coupling schematic diagram. A non-contact electrocardiogram sensing electrode is arranged between the human body and the mattress. Electrodes are placed at different parts of the human body and connected to the positive and negative poles of the galvanometer of the electrocardiograph through lead wires. This circuit connection method for recording electrocardiograms is called an electrocardiogram lead. Currently, single-lead, 12-lead, etc. are commonly used. In this embodiment, the single-lead method is adopted. Therefore, it is only necessary to place electrodes at two positions on the human body. As Figure 1 shown, V E1 and V E2 are the electrocardiogram signals of the human body, and C ECG1 and C ECG2 are the coupling capacitors formed between the back skin of the human body and the electrodes.

[0035] Equation (1) is the relationship between capacitance and area, distance, etc., and is also called the determinant of capacitance, which expresses the relationship between capacitance and several parameters related to the capacitance size. According to Equation (1), it can be known that increasing the dielectric constant, increasing the effective area of the capacitor, and reducing the distance between the capacitor plates can all increase the capacitance value. Specifically for the coupling capacitor involved in this embodiment, generally increasing the coupling capacitor can adopt materials with a high dielectric constant, increasing the effective area of the coupling capacitor, and reducing the electrode distance between the human skin and the electrode to form a coupling capacitor. Among them, C E is the coupling capacitor; ε 0 is the vacuum permittivity; ε ris the dielectric constant of the material; A is the effective area of the coupling capacitor; d is the thickness of the cotton sheet plus the hospital gown used in the hospital.

[0036]

[0037] However, the method of increasing the coupling capacitor by increasing the effective area of the coupling capacitor has the problem of introducing more noise due to the too large electrodes; and using materials with high dielectric constants has certain limitations in increasing the coupling capacitor; d is difficult to be greatly reduced in practical applications.

[0038] Please refer to Figure 2 As shown, a non-contact electrocardiogram monitoring system according to an embodiment of the present invention realizes the purpose of increasing the coupling capacitor by connecting a first capacitor in parallel at both ends of the coupling capacitor. The system includes non-contact electrocardiogram sensing electrodes (hereinafter also simply referred to as electrodes), and the non-contact electrocardiogram sensing electrodes are used to be arranged on the back of the human body to form a coupling capacitor C between the electrodes and the skin of the back of the human body. ECG1 、C ECG2 , the electrodes collect signals containing electrocardiogram data in a non-contact manner, and further include a first capacitor C P connected in parallel with the coupling capacitor. The coupling capacitor and the first capacitor are connected in parallel and then connected to an electrocardiogram acquisition circuit through a wire. It should be noted that Figure 2 shows that two electrodes are respectively placed at two positions on the back of the human body to couple electrocardiogram signals at different positions. Among them, ECG1 is the electrocardiogram signal at the upper part of the back of the human body in Figure 2 , C ECG1 is the corresponding coupling capacitor, and ECG2 is the electrocardiogram signal at the lower part of the back of the human body in Figure 2 , C ECG2 is the corresponding coupling capacitor. In this embodiment, a first capacitor is coupled at both ends of each coupling capacitor. The so-called both ends of the coupling capacitor are the two poles of the coupling capacitor. That is, a first capacitor C ECG1 is coupled at both ends of C p1 , and a first capacitor C ECG2 is coupled at both ends of C p2 . Since they are all first capacitors, therefore Figure 2 C p1 and C p2 are both represented by C p .

[0039] Suppose there are two capacitors C 1 and C 2 connected in parallel, then the total capacitance of the two capacitors connected in parallel can be calculated by Equation (2),

[0040] C = C 1 + C 2 (2);

[0041] Among them, in formula (2), C represents the equivalent capacitance of two parallel capacitors C 1 and C 2 .

[0042] According to formula (3), increasing the capacitance can reduce the capacitive reactance,

[0043]

[0044] In formula (3), X C is the capacitive reactance, C is the capacitance value, ω is the angular frequency, and f is the signal frequency.

[0045] Therefore, in this embodiment, by connecting a first capacitor in parallel at both ends of the coupling capacitor, the coupling capacitor is increased, the capacitive reactance is reduced, which is more conducive to obtaining high-quality electrocardiogram signals.

[0046] It should be noted that the contact point between the electrode plate of the first capacitor and the human body should theoretically be within the effective area of the coupling capacitor. It can be understood that the real effective signal is the heart, and the heart needs to reach the electrode plate through the skin including the dermis and epidermis. Since the skin has a resistance effect, the effective area of the coupling capacitor is actually located within the epidermis. However, considering the actual application, the actual contact point between the first capacitor and the human body should not be selected within the effective area of the coupling capacitor, because this will increase the distance between the upper and lower plates of the coupling capacitor. And from formula (1), it can be seen that increasing the distance between the upper and lower plates will reduce the capacitance value of the coupling capacitor. Therefore, the selection of the contact point between the first capacitor and the human body should meet the following two points: First, the contact point only plays the role of a reference potential; second, the parallel first capacitor has no electrocardiogram signal or extremely weak electrocardiogram signal. In this embodiment, the actually selected contact point is located outside the human epidermis. It can be understood that there is a section of epidermis layer between it and the theoretical contact point within the effective area of the coupling capacitor.

[0047] In some of these embodiments, as Figure 1 shown, the non-contact electrocardiogram sensing electrode includes a sensitive layer, an insulating layer disposed below the sensitive layer, a reference electrode layer disposed below the insulating layer, and a base layer disposed below the reference electrode layer.

[0048] In this embodiment, the sensitive layer, the insulating layer, the reference electrode layer, and the base layer are sequentially disposed from top to bottom and are respectively connected by an adhesive layer. Below the non-contact electrocardiogram sensing electrode is a mattress, and below the mattress is a shielding layer. In this embodiment, the non-contact electrocardiogram sensing electrode and a bedsheet are sequentially laid on the mattress. After a patient wearing a hospital gown lies on the mattress, based on the principle of capacitive coupling, the electrocardiogram signal is coupled from the human skin to the electrode.

[0049] To facilitate comparison of the differences between this embodiment and the prior art, Figures 3 - 5Respectively shown are the equivalent models of the Ag / AgCl wet contact electrode, capacitive coupled non-contact electrode, and the parallel capacitive non-contact electrode in this embodiment for electrocardiogram acquisition. Among them, Figures 3 - 5 in Figures 3 - 5 , Dermis is the dermis, epidermis is the epidermis, gel is the gel, dielectric layer is the dielectric layer, electrode is the electrode, and Parallel capacitor is the parallel capacitor. The dermis layer is equivalent to a resistor R d , while the epidermis layer can be regarded as a resistor R e and a capacitor C e in parallel. In the dielectric layer, the skin-electrode interface can be regarded as a resistor R E and a capacitor C E in parallel ( Figure 4 ). There is a section of epidermis layer between the actual contact point and the theoretical contact point within the effective area of the coupling capacitor, which can also be regarded as a resistor R e-e and a capacitor C e-e in parallel, and it forms a parallel capacitor with the first capacitor C p ( Figure 2 , Figure 5 ). It should be understood that during the equivalent process, since there are differences between the actual contact point and the theoretical contact point of the added first capacitor in contact with the human body, the actual contact point is the contact point used during actual application. It can be understood that it is impossible to set the contact point inside the human epidermis. Therefore, due to the presence of a section of epidermis layer between the actual contact point and the theoretical contact point within the effective area of the coupling capacitor, and this section of epidermis layer can be equivalent to a resistor R e-e and a capacitor C e-e in parallel, which is briefly recorded as the epidermis layer equivalent capacitor. Therefore, the capacitor connected in parallel at both ends of the coupling capacitor is actually composed of the series connection of the first capacitor and the epidermis layer equivalent capacitor.

[0050] In some of these embodiments, the non-contact electrocardiogram monitoring system further includes a voltage follower, and the voltage follower is arranged on the circuit after the coupling capacitor and the first capacitor are connected in parallel.

[0051] The setting of the voltage follower can prevent the attenuation of the electrocardiogram signal during the coupling transmission process, satisfy the impedance matching of the front and rear stages, and improve the resistance of the electrode to external noise and artifacts, so as to extract weak electrocardiogram signals through clothes and sheets.

[0052] Figure 6 is the capacitive coupling equivalent circuit for non-contact electrocardiogram acquisition, Figure 7It is the equivalent parallel - capacitor circuit for non - contact electrocardiogram acquisition. In a circuit with resistance, inductance, and capacitance, the obstruction to the current in the circuit is called impedance. Impedance is commonly denoted by Z and is a complex number. The real part is called resistance, and the imaginary part is called reactance, which consists of capacitive reactance and inductive reactance. Therefore, the impedance of a parallel combination of a resistor and a capacitor can be expressed as

[0053] After transformation, we get

[0054] where jω can be replaced by s, j is the imaginary unit, and ω is the angular frequency. Then the impedance of a parallel combination of a resistor and a capacitor can be expressed as:

[0055]

[0056] Z s 、Z coupling and Z in represent the impedance of the skin, the coupling capacitor, and the voltage follower respectively. Then Z s 、Z coupling and Z in are as shown in Eqs. (4) - (6).

[0057]

[0058]

[0059]

[0060] where Rin and Cin in Eq. (6) are the resistance and capacitance of the voltage follower.

[0061] Assume that the closed - loop current of the heart signal is I. For the Figure 6 capacitive - coupling equivalent circuit of non - contact electrocardiogram acquisition, according to Kirchhoff's voltage law, Eq. (7) is obtained

[0062]

[0063] Eq. (7) can be simplified to Eq. (8);

[0064]

[0065] According to Eq. (8), a higher Z in or a lower Z coupling is more likely to obtain an output similar to the heart signal. According to Eqs. (6) and (8), a voltage follower with a high - input resistance and a low - input capacitance can greatly enhance the signal resolution and approach the real electrocardiogram signal. In addition, according to Eqs. (5) and (8), the material properties of non - conductive fabrics also directly affect the measurement of non - contact electrocardiogram signals.

[0066] According to Equation (5), increasing the coupling capacitance C E can reduce the impedance Z coupling , and according to Equation (8), reducing the impedance Z of the coupling capacitance coupling can increase the output voltage. Thus, it can be seen that a larger coupling capacitance is an important factor for obtaining high-fidelity non-contact electrocardiogram signals.

[0067] According to Figure 7 , Z p is the impedance of the first capacitor, as shown in Equation (9). For the parallel capacitor equivalent circuit of non-contact electrocardiogram acquisition in Figure 7 , Equation (10) is obtained from Kirchhoff's voltage law and simplified to Equation (11). According to Equations (2), (9), and (11), it can be known that the method of using parallel capacitors in this embodiment can obtain electrocardiogram signals close to the real ones.

[0068]

[0069]

[0070]

[0071] The capacitance value of the coupling capacitor is one of the key factors affecting the quality of electrocardiogram signals. In some embodiments, to explore the relationship between increasing the coupling capacitance and the acquisition effect of non-contact electrocardiogram signals, a parallel capacitor circuit as shown in Figure 8 is designed. This circuit has a total of 45 capacitors with different capacitance values, and the specific parameters are shown in Table 1. There are two capacitors with each capacitance value, which are respectively connected in parallel to the upper and lower electrodes as shown in Figure 9 ; one end of the first capacitor is connected to the signal input end, and the other end is connected to the human epidermis. Figure 9 In

[0072] Table 1 Capacitance values of parallel capacitors

[0073]

[0074]

[0075] To further verify whether connecting capacitors in parallel at both ends of the coupling capacitor is truly effective, this embodiment uses an LCR digital bridge to measure the capacitance and impedance. Under the condition that the measurement frequency is 40 Hz and the dielectric layers of the coupling capacitors are both the patient gown and the bedsheet, first verify whether connecting capacitors in parallel at both ends of the silver sheet electrode is truly effective, as shown in Figure 9(a), Figure 9 (as shown in (b)); secondly, verify whether the parallel capacitor on the effective coupling capacitor formed between the fabric electrode and the human back is real and effective, such as Figure 9 (d), Figure 9 (as shown in (e)); finally, verify whether the parallel capacitor is real and effective with the neck as one end contact point of the parallel capacitor, such as Figure 9 (as shown in (f)).

[0076] Figure 9 (a) shows measuring the capacitance under the condition of separating clothes and sheets between two silver electrodes, Figure 9 (b) shows measuring the capacitance under the condition of separating clothes and sheets between two silver electrodes and paralleling a 1 mF capacitor, Figure 9 (c) is directly measuring the capacitance of a 1 mF capacitor, Figure 9 (d) shows measuring the capacitance under the condition of separating clothes and sheets between the human back and the electrode patch, Figure 9 (e) shows measuring the capacitance under the condition of separating clothes and sheets between the human back and the electrode patch and paralleling a 1 mF capacitor, Figure 9 (f) shows measuring the capacitance under the condition of separating clothes and sheets between the human neck and the electrode patch and paralleling a 1 mF capacitor.

[0077] Table 2 shows the capacitance and impedance values measured under Figure 9 different conditions. From Figure 9 (e) and Figure 9 (f), it can be seen that one end of the parallel capacitor does not need to be connected to the epidermis of the human back directly opposite to the effective coupling capacitor. With the neck as one end contact point, the capacitance and impedance do not differ much.

[0078] Table 2 Measurement of Capacitance - Impedance

[0079]

[0080] In order to obtain the best position of the contact point between the first capacitor and the human body, in some embodiments, as Figure 10 shown, select 8 contact points on the human epidermis, which are: cheek, neck, armpit, waist, wrist, thigh, calf, instep, and use the Ag / Agcl wet electrode as the contact method for connecting one end of the parallel capacitor to the human epidermis.

[0081] Under the same conditions, conduct the experiment of parallel capacitors at different positions on the human body for 5 subjects (Subjects 1 - 5 in Table 4), and select the test results of 8 positions on the body of one subject at 10 - second intervals for display, as Figure 11 shown, where Figure 11 (a) - Figure 11(h) respectively represent the waveforms of parallel - capacitor electrocardiogram acquisition at 8 points on the cheek, neck, armpit, waist, wrist, thigh, calf, and instep. The average signal - to - noise ratio and standard deviation of the waveforms at the 8 points with a 10 - s time interval are calculated respectively, and the results are shown in Table 3. From the waveform diagram and signal - to - noise ratio of the electrocardiogram signal, it can be seen that the electrocardiogram signals collected at the contact points of the neck, armpit, and wrist have better QRS complexes, P waves, and T waves, and high - quality electrocardiogram signals are obtained.

[0082] Table 3 Signal - to - noise ratio of electrocardiogram signals collected by parallel - capacitor at 8 points

[0083]

[0084] Table 4 Physical characteristic parameters of 10 subjects

[0085]

[0086] For convenient application, the selection of the contact point should also consider the following two points: First, the selection of the contact point should not interfere with the human body's sleep and be able to ensure that it can be in contact with the human body after lying down. Second, Ag / AgCl wet electrodes are not used to avoid discomfort to the human body during long - term electrocardiogram monitoring and are not applicable to patients with various skin burns. Therefore, in some preferred embodiments, the system further includes a conductive fabric electrode, and one end of the first capacitor is connected to the human neck through the conductive fabric electrode. In the application example, a conductive fabric material identical to the sensitive layer of the non - contact electrocardiogram sensing electrode is selected to replace the Ag / AgCl wet electrode, and it is integrated on the side edge of the pillow so that both sides of the human neck can be in contact with it when lying down. The selection of integrating the conductive fabric on the side edge of the pillow in this embodiment has the following advantages: First, as known above, both sides of the neck can be used as the contact points for one end of the parallel capacitor, and high - quality electrocardiogram signals can be obtained. Second, the flexible conductive fabric can meet the comfort of sleep. Finally, considering people's sleep habits, they always like to lie in bed with the pillow as a reference, ensuring that the human neck can be in contact with the side edge of the pillow during sleep.

[0087] Therefore, in this embodiment, the neck (or called the throat) is finally determined as the contact point for one end of the parallel capacitor. That is, one end of the first capacitor is used to connect to the human neck, and the other end is connected to the non - contact electrocardiogram sensing electrode.

[0088] In some of these embodiments, relevant experiments are also carried out on the optimal capacitance in parallel at the neck and the influence of the gradual increase in the capacitance value of the parallel capacitor on the electrocardiogram signal quality. Select the parallel capacitor C pThe capacitance value ranges from 10 pF to 2,700 μF, with a total of 45 commonly used capacitance values for capacitors. The specific parameters are shown in Table 1. For 5 subjects (Subjects 2, 3, 6, 9, and 10 in Table 4), Ag / AgCl wet electrodes are used at the neck as the contact method for one end of the parallel capacitor to connect with the human epidermis, and the capacitance value of the parallel capacitor is gradually increased to collect electrocardiogram signals. For the electrocardiogram signals collected for each capacitance value capacitor, 7 waveforms are selected to calculate the average signal-to-noise ratio, and the plotted curve is as shown in Figure 12 shown.

[0089] From the curve of the signal-to-noise ratio, it is found that under the same conditions, as the capacitance value of the parallel capacitor gradually increases, the average signal-to-noise ratio of the electrocardiogram signals collected by the 5 subjects shows an upward trend. When the parallel capacitor C p is greater than 1,000 μF, the signal-to-noise ratio of the electrocardiogram signal does not show an obvious upward trend. Combining with Equation (12), where R bias is the bias resistor and C E is the coupling capacitor, it can be seen that too large a parallel capacitor will affect the response time τ of the monitoring system.

[0090] τ = R bias (C E + C p ) (12);

[0091] Therefore, to ensure that the monitoring system has an appropriate response time and obtains high-quality electrocardiogram signals, the capacitance value of the optimal parallel capacitor selected at the neck is 1,000 μF.

[0092] In summary, in this embodiment, one contact point of the parallel capacitor is set on both sides of the neck, and the optimal capacitance value of the parallel capacitor is 1,000 μF.

[0093] In practical applications, two conductive fabrics placed on PDMS materials are integrated on the side edges of the pillow. Since the neck circumference widths of most people are between 10 - 14 cm, the middle distance between the two conductive fabrics is set to 3 cm, and the width is set to 5 cm. Two contact methods, namely Ag / AgCl wet electrodes and conductive fabrics on the pillow, are used to conduct a test comparison at the necks of 5 subjects (Subjects 2, 3, 6, 9, and 10 in Table 4). The test results of one subject are as shown in Figure 13 shown. Among them, Figure 13 (a) is the waveform of the electrocardiogram collected by the conductive fabric contact method, Figure 13 (b) is the waveform of the electrocardiogram collected by the Ag / AgCl wet electrode contact method, Figure 13 (c) is the waveform of the electrocardiogram collected by disconnecting the electrode input under the conductive fabric contact method, Figure 13 (d) is the waveform of the electrocardiogram collected by disconnecting the electrode input under the Ag / AgCl wet electrode contact method.

[0094] Figure 13 The average signal-to-noise ratios of (a) and (b) are 35.066dB and 38.075dB respectively. It can be seen that the quality of the ECG signal obtained by the conductive fabric is slightly worse than that by the Ag / Agcl wet electrode contact method, but the characteristics of the ECG signals of the conductive fabric and Ag / Agcl wet electrode contact methods are approximately the same. The main reason for this is that when the human body lies down, the neck will rub against the conductive fabric and introduce noise, resulting in slightly poor quality of the collected ECG signal. Figure 13 (c) and (d) disconnect the input of the non-contact ECG sensing electrode, that is, there is no coupling capacitor, only the first capacitor and DRL are retained, and the waveforms of the ECG signals are measured under the two contact modes. There is a very weak ECG signal at the neck, with a lot of noise. It has also been processed by digital filtering, but the baseline drift is still serious. It can be seen that the contact point at the neck is only used as a reference potential point to increase the coupling capacitor and a contact point where the first capacitor is connected in parallel with the coupling capacitor.

[0095] In some of the embodiments, in order to illustrate that the non-contact ECG monitoring system of this embodiment can improve the quality of collecting ECG signals, experiments were conducted on collecting ECG signals with electrodes and electrodes plus parallel capacitors. The results are as follows: Figure 14 As shown, Figure 14 (a) shows the waveform of the ECG signal collected only using non-contact ECG sensing electrodes. Figure 14 (b) shows the waveform of the ECG signal collected after the first capacitor is connected in parallel. Five subjects (subjects No. 2, 3, 6, 9, and 10 in Table 4) wore hospital gowns and collected ECG signals through the bed sheets. When the capacitor is not connected in parallel, the ECG signal collected by non-contact is shown in Figure 2. Figure 14 (a) As shown. The monitoring system of this embodiment selects the contact mode of integrated conductive fabric on the pillow, the capacitance of the parallel capacitor is 1000μF, and the collected ECG signal is as follows Figure 14 (b) As shown in the test results, it is found that when the capacitor is not connected in parallel, the ECG signal waveform is extremely unstable, noisy and has serious baseline drift; but when the capacitor is connected in parallel, the monitoring system of this embodiment obtains a clear ECG signal waveform.

[0096] To verify the correlation between the system under the applied conditions and the standard contact - monitored electrocardiogram (ECG) signals, some embodiments conducted synchronous comparison tests between contact and non - contact methods. According to the single - lead measurement standard revised by the American Academy of Sleep Medicine, Ag / AgCl wet electrodes were attached to the corresponding positions on the human body (reference system). Electrocardiogram signal monitoring tests were carried out on 5 subjects (subjects No. 2, 3, 6, 7, and 8 in Table 4) for 20 minutes each. The monitoring system of this embodiment and the reference system were run simultaneously, and the collected electrocardiogram signal data was stored. Electrocardiogram waveforms with a 10 - s time interval at the same time were selected for display respectively. The results are as Figure 15 shown, where Figure 15 (a) represents the electrocardiogram waveform diagram of the system described in this embodiment, Figure 15 (b) represents the electrocardiogram waveform diagram of the reference system. It was found that under the conditions of the system, compared with the electrocardiogram signals collected by non - contact and contact methods, except for a small amount of noise interference, there was no difference, and the two had good consistency.

[0097] Each interval of the electrocardiogram signal can be used to diagnose the heart. The PR interval is the atrioventricular excitation conduction time and is used for the diagnosis of atrioventricular block; the QRS interval is the left and right ventricular contraction time and is used for the diagnosis of ventricular hypertrophy or intraventricular conduction block; the QT interval is the ventricular depolarization time and is used for the diagnosis of arrhythmia; the RR interval is the cardiac cycle and is used for calculating the heart rate. The feature extraction algorithm was used to Figure 15 calculate the average values and standard deviations of the PR, QRS, QT, and RR intervals for the non - contact and contact waveforms with a 10 - s time interval respectively. The results are shown in Table 5, Figure 5 where ECGpro represents the electrocardiogram signal interval of the monitoring system of this embodiment, ECGref represents the electrocardiogram signal interval of the reference system, standard represents the standard interval, and variation represents the variation rate. The results show that compared with all intervals of non - contact and contact methods, all variations are within 6.0%, and all intervals are consistent with the standard interval.

[0098] Table 5 Comparison of electrocardiogram signal intervals between the monitoring system of this embodiment and the reference system

[0099]

[0100] The feature extraction algorithm was used to calculate the average heart rate per minute and the average heart rate for 20 minutes of the two monitoring systems respectively. The average heart rate error of the two monitoring systems for 20 minutes was within 2%, and the detection rate of R waves was above 97%.

[0101] In summary, in this embodiment, by connecting a first capacitor in parallel at both ends of the coupling capacitor, the purpose of increasing the coupling capacitor and reducing the equivalent impedance is achieved. Under the condition of the same parallel capacitor, eight contact points of the human body from top to bottom at one end of the parallel capacitor are selected, and combined with the actual application, the best contact points are finally determined to be both sides of the neck, and the signal-to-noise ratio of the electrocardiogram signal can reach more than 30 dB. To determine the best capacitor for the best contact points, capacitors with 45 capacitance values are connected in parallel at the contact points on the neck, and combined with the system response time, the capacitance value of the best capacitor is determined to be 1000 μF. When continuously increasing the coupling capacitor, the signal-to-noise ratio of the electrocardiogram signal of this system can be increased from about 10 dB to more than 30 dB. Under the conditions of the best contact points and the best capacitor, the signal-to-noise ratios of 5 subjects can all reach more than 33 dB. Using a flexible conductive fabric to replace the contact method of the Ag / AgCl wet electrode and integrating it on the side edge of the pillow meet the actual application requirements. Under the same conditions, the signal-to-noise ratio of the same subject under the two contact methods differs by about 3 dB. Only the first capacitor is used in both contact methods, and a very weak electrocardiogram signal is measured, further confirming that the neck contact points can be used as the contact points at one end of the parallel capacitor to increase the coupling capacitor. Comparing the electrode and the electrode with a parallel capacitor, it is found that the monitoring system of this embodiment can obtain high-quality electrocardiogram signals without increasing the effective area of the coupling capacitor and the dielectric constant of the intermediate medium. The electrocardiogram signals measured by the non-contact and contact methods have good consistency. Compared with all the intervals of the non-contact and contact methods, all the changes are within 6.0%, and all the intervals are consistent with the standard intervals. The average heart rate error of the two monitoring systems within 20 minutes is within 2%, and the detection rate of the R wave is above 97%.

[0102] Although the present disclosure is disclosed as above, the protection scope of the present disclosure is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present disclosure, and these changes and modifications will all fall within the protection scope of the present invention.

Claims

1. A non-contact electrocardiogram monitoring system, characterized in that, it includes non-contact electrocardiogram sensing electrodes, the non-contact electrocardiogram sensing electrodes are used to be arranged on the back of the human body, form a coupling capacitance with the skin of the back of the human body, collect signals containing electrocardiogram data in a non-contact manner, and also include a first capacitor connected in parallel with the coupling capacitance. One end of the first capacitor is used to be connected to the human epidermis, and the other end is used to be connected to the electrocardiogram acquisition circuit. After the coupling capacitance and the first capacitor are connected in parallel, they are connected to the electrocardiogram acquisition circuit through a wire.

2. The non-contact electrocardiogram monitoring system according to claim 1, characterized in that, one end of the first capacitor is used to be connected to the neck, armpit or wrist of the human body, and the other end is used to be connected to the electrocardiogram acquisition circuit.

3. The non-contact electrocardiogram monitoring system according to claim 1, characterized in that, the capacitance value of the first capacitor is 1000 μF.

4. The non-contact electrocardiogram monitoring system according to claim 1, characterized in that, the non-contact electrocardiogram sensing electrode includes a sensitive layer, an insulating layer arranged below the sensitive layer, a reference electrode layer arranged below the insulating layer, and a base layer arranged below the reference electrode layer.

5. The non-contact electrocardiogram monitoring system according to claim 1, characterized in that, it further includes a conductive fabric, the conductive fabric is connected to the first capacitor, and the conductive fabric is integrated on the pillow for contact connection with the neck of the human body.

6. The non-contact electrocardiogram monitoring system according to claim 5, characterized in that, the conductive fabric includes two pieces, and the two pieces of conductive fabric are integrated on the same side edge of the pillow and arranged at intervals, and the two pieces of conductive fabric are respectively used for contact connection with both sides of the neck of the human body.

7. The non-contact electrocardiogram monitoring system according to claim 6, characterized in that, the distance between the two pieces of conductive fabric is 3 cm, and the width of each piece of conductive fabric is 5 cm.

8. The non-contact electrocardiogram monitoring system according to claim 1, characterized in that, it further includes an Ag / Agcl wet electrode, one end of the Ag / Agcl wet electrode is connected to the first capacitor, and the other end is used to be connected to the human epidermis.

9. The non-contact electrocardiogram monitoring system according to claim 1, characterized in that, it further includes a voltage follower, and the voltage follower is arranged on the circuit after the coupling capacitance and the first capacitor are connected in parallel.

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