Sympathetic nervous signal sensing system and method

Abstract

A sympathetic nerve signal sensing system is disclosed. The system includes an electrode pair, a high input impedance receiving circuit, a differential circuit, and a post-processing circuit. The electrode pair is disposed on a subject and includes a first electrode configured to receive a first signal and a second electrode configured to receive a second signal. The high input impedance receiving circuit includes a first follower configured to receive the first signal and output a third signal, and a second follower configured to receive the second signal and output a fourth signal. The differential circuit is configured to differentially process the third and fourth signals to generate a fifth signal. The post-processing circuit is configured to filter the fifth signal using a first filter frequency band to output a sympathetic nerve signal.

Description

[Technical Field]

[0001] This invention relates to a sympathetic nerve signal sensing system and method; particularly to a non-contact sympathetic nerve signal sensing system and method. [Previous Technology]

[0002] Sympathetic nerve activity (SNA) signals are a crucial indicator for monitoring or measuring conditions such as anxiety or emotional stress. In clinical applications, microneurography is the standard procedure for directly measuring SNA signals. However, microneurography is an invasive measurement method, making it difficult to apply in long-term or wearable applications. While non-invasive measurement methods, such as measuring heart rate variability (HRV) using electrode patches, exist for SNA assessment, these methods still require contact with the skin. Contact electrode patches can easily cause psychological resistance from the subject, especially when used for assessing anxiety or emotional stress. In some cases, operators may even use conductive adhesives or other media to assist with electrode patch application, which not only increases discomfort for the subject but also poses risks of cleaning or allergic reactions.

[0003] In view of the above-mentioned deficiencies in the prior art, non-invasive and non-contact SNA measurement methods will be the focus of development in this field. [Summary of the Invention]

[0004] One of the objectives of this invention is to provide a non-contact sympathetic nerve signal sensing system and method.

[0005] One specific embodiment of the present invention provides a sympathetic nerve signal sensing system. The sympathetic nerve signal sensing system includes an electrode pair, a high input impedance receiving circuit, a differential circuit, and a post-processing circuit. The electrode pair is disposed outside the sympathetic nerve signal source of the subject and includes a first electrode configured to receive a first signal and a second electrode configured to receive a second signal. The high input impedance receiving circuit is coupled to the electrode pair and includes a first follower configured to receive the first signal and output a third signal substantially equal to the first signal, and a second follower configured to receive the second signal and output a fourth signal substantially equal to the second signal. The differential circuit is coupled to the high input impedance receiving circuit. The differential circuit is configured to differentially process the third and fourth signals to generate a fifth signal. The post-processing circuit is coupled to the high input impedance receiving circuit. The post-processing circuit is configured to filter the fifth signal using a first filter frequency band to output a sympathetic nerve signal.

[0006] One specific embodiment of the present invention provides a method for sensing sympathetic nerve signals. The method includes: setting electrodes outside a sympathetic nerve signal source of a subject; wherein the electrode pair includes: a first electrode configured to receive a first signal and a second electrode configured to receive a second signal; receiving the first signal and outputting a third signal substantially equal to the first signal using a high input impedance receiving circuit, and receiving the second signal and outputting a fourth signal substantially equal to the second signal; differentially processing the third signal and the fourth signal using a differential circuit to generate a fifth signal; and a subsequent processing circuit filtering the fifth signal using a first filtering frequency band to output a sympathetic nerve signal.

[0007] As described above, the high input impedance receiving circuit can effectively cancel out the equivalent impedance generated by various media (e.g., skin, muscle, air, clothing, or hair) between the sympathetic nerve signal source and the electrode pair. The follower within the high input impedance receiving circuit can provide high input impedance and low output impedance, thus achieving impedance isolation between the electrode pair and the rest of the circuit. This further reduces crosstalk between the electrode pair and the rest of the circuit.

[0008] In one embodiment, it further includes a negative impedance circuit coupled between the electrode pair and the high input impedance receiving circuit; wherein the negative impedance circuit is configured to provide a negative impedance value approximately equal to the negative of the equivalent impedance of the sympathetic nerve signal source to the electrode pair to the inputs of the first follower and the second follower.

[0009] In one embodiment, it further includes: a controller coupled between the post-processing circuit and the negative impedance circuit; wherein the controller is configured to adjust the negative impedance value of the negative impedance circuit according to at least signal parameters of the sympathetic nerve signal.

[0010] In one embodiment, it further includes: a controller coupled between the post-processing circuit and the negative impedance circuit; wherein the post-processing circuit is further configured to filter the fifth signal at a second filtering frequency band to output an electrocardiogram signal; and wherein the controller is configured to adjust the negative impedance value of the negative impedance circuit according to at least signal parameters of the electrocardiogram signal.

[0011] As described above, a negative impedance value is provided through the negative impedance circuit to reduce the equivalent impedance difference between the sympathetic nerve signal source and the electrode pair. Therefore, the electrode pair of the present invention further improves the accuracy of the sympathetic nerve signal through compensation by the negative impedance circuit without contacting the subject's skin. Furthermore, in one embodiment, the negative impedance of the negative impedance circuit can be further adjusted according to the feedback of the measurement signal to achieve the best compensation effect.

Implementation Method

[0025] Any reference to elements referred to herein by names such as "first," "second," etc., does not generally limit the number or order of these elements. Rather, these names are used herein as a convenient way to distinguish two or more elements or instances of elements. Therefore, it should be understood that the names "first," "second," etc., in the claim do not necessarily correspond to the same names in the written description. Furthermore, it should be understood that references to first and second elements do not imply that only two elements can be used or that the first element must precede the second element. The terms "comprising," "including," "having," "containing," etc., as used herein are open-ended, meaning that they include but are not limited to.

[0026] The term “coupled” is used herein to refer to a direct or indirect electrical coupling between two structures. For example, in one example of indirect electrical coupling, one structure may be coupled to another structure via a passive element such as a resistor, capacitor, or inductor.

[0027] In this invention, the terms "exemplary" and "for example" are used to mean "serving as an example, instance, or illustration." Any implementation or aspect described herein as "exemplary" or "for example" is not necessarily to be construed as preferred or advantageous over other aspects of the invention. The terms "about" and "approximately" as used herein with respect to specified values ​​or characteristics are intended to mean within a certain value (e.g., 10%) of the specified value or characteristic.

[0028] Referring to Figure 1, there may be various media (e.g., skin 12 or clothing 13) between the sympathetic nerve signal source 11 of the subject 10 (e.g., the heart of the subject 10) and the electrode pair 20. These media will have different equivalent impedances (Zeq) due to their different conductivity or dielectric constant. Therefore, when the electrode pair 20 acquires sympathetic nerve-related signals from the subject 10 in a non-contact manner, it will be affected by the equivalent impedance (Zeq) and the input impedance (Zin) of the device itself. Therefore, the present invention provides a sympathetic nerve signal sensing system with high input impedance (Zin).

[0029] Please refer to FIG2, which illustrates a sympathetic nerve signal sensing system 100 according to a specific embodiment of the present invention. The sympathetic nerve signal sensing system 100 includes an electrode pair 110, a high input impedance receiving circuit 120, a differential circuit 130, and a post-processing circuit 140. The electrode pair 110 is disposed outside (e.g., on the chest or back) of the subject 10's sympathetic nerve signal source (e.g., the sinoatrial node) and includes a first electrode 111 configured to receive a first signal S1 and a second electrode 112 configured to receive a second signal S2. The high input impedance receiving circuit 120 is coupled to the electrode pair 110 and includes a first follower 121 configured to receive the first signal S1 and output a third signal S3 substantially equal to the first signal S1, and a second follower 122 configured to receive the second signal S2 and output a fourth signal S4 substantially equal to the second signal S2. Differential circuit 130 is coupled to high input impedance receiving circuit 120. Differential circuit 130 is configured to differentially process the third signal S3 and the fourth signal S4 to generate a fifth signal S5. Post-processing circuit 140 is coupled to high input impedance receiving circuit 120. Post-processing circuit 140 is configured to filter the fifth signal S5 using a first filter band BP1 to output a sympathetic nerve signal AS.

[0030] The electrode pair 110 can be disposed on the outside of the sympathetic nerve signal source of the subject 10 through a mounting structure. For example, the mounting structure can be attached to the outside of the subject 10's chest or back (e.g., on clothing) using a strap or Velcro. Alternatively, the electrode pair 110 can be disposed on or inside a structure such as a mattress or chair back, allowing the subject 10 to sit or lie down, thus placing the electrode pair 110 close to the subject 10 on the outside of the sympathetic nerve signal source. The first electrode 111 and the second electrode 112 can be configured according to conventional electrodes for measuring electrocardiogram signals. Alternatively, the first electrode 111 and the second electrode 112 can be disposed on the skin at the shortest distance from the sinoatrial region of the subject 10's heart. It should be noted that the present invention is not limited to the type of medium between the electrode pair 110 and the skin. In one embodiment, the medium between the electrode pair 110 and the skin can be air, a braided fabric, a conductor wire braid, or a dielectric material (e.g., PDMS). In one embodiment, the first electrode 111 and the second electrode 112 may be flexible capacitive electrodes. In this embodiment, the electrode pair 110 may be made of polymer foam and wrapped with an outer layer of conductive textile. The flexible capacitive electrodes can conform to the curvature of the body, thereby significantly reducing the gap between the electrode pair 110 and the subject 10, and can fit snugly to stabilize the dielectric state between the electrode pair 110 and the skin.

[0031] The high input impedance receiving circuit 120 is composed of a first follower 121 and a second follower 122. The first follower 121 and the second follower 122 correspond to the first electrode 111 and the second electrode 112, respectively. The first follower 121 and the second follower 122 can be composed of any high input impedance amplifier, transistor circuit, instrumentation amplifier, or other components. The first follower 121 and the second follower 122 are preferably configured with high input impedance and low output impedance, so that a large voltage drop ratio can be obtained from the electrode pair and the voltage can be provided to the next stage circuit. Therefore, the output signal of the first follower 121 (i.e., the third signal S3) can be approximately equal to the first signal S1 from the first electrode 111, and the output signal of the second follower 122 (i.e., the fourth signal S4) can be approximately equal to the second signal S2 from the second electrode 112.

[0032] The differential circuit 130 may be constructed, for example, by components such as an instrumentation amplifier or a low-noise amplifier. The differential circuit 130 differentially processes the third signal S3 and the fourth signal S4 provided by the high input impedance receiving circuit 120. This allows the difference signal (i.e., the fifth signal S5) between the third signal S3 and the fourth signal S4 to be captured and amplified.

[0033] The post-processing circuit 140 can be a filter circuit, or a signal processing circuit integrating a filter circuit and a signal amplification circuit. The filter circuit can be a bandpass filter, or an equal circuit composed of a high-pass filter and a low-pass filter. The filtering frequency band of the filter circuit (i.e., the upper and lower limits of the bandpass filter) can be selected according to the frequency band of interest (ROI). In the application of the sympathetic nervous system, the filtering frequency band can be selected according to the frequency of the commonly used sympathetic nerve signal AS in medicine. In one embodiment, the first filtering frequency band BP1 for the sympathetic nerve signal AS is 500~1000 Hz. After the fifth signal S5 is filtered by the post-processing circuit 140, the frequency band signals other than the first filtering frequency band BP1 can be excluded, thereby retaining the sympathetic nerve signal AS of the subject 10.

[0034] In one embodiment, the sympathetic nerve signal AS of the subject 10 can be transmitted to the back-end device 150 via communication. As shown in FIG3, the sympathetic nerve signal sensing system 100 may further include the back-end device 150. The back-end device 150 is configured to receive the sympathetic nerve signal AS and perform at least one signal processing on the sympathetic nerve signal AS. The back-end device 150 is, for example, an electronic device such as a computer, tablet computer, or smartphone. The back-end device 150 can acquire the sympathetic nerve signal AS from the post-processing circuit 140 via physical wiring, for example, a data acquisition system (DAQ). On the other hand, the post-processing circuit 140 may also include an analog-to-digital converter module or a wireless communication module to achieve wireless communication coupling with the back-end device 150. The back-end device 150 can perform signal post-processing using software methods (e.g., instruction sets edited in a programming language) or hardware methods (e.g., signal processing elements such as averagers or integrators). The at least one signal processing step is, for example, averaging, integration, accumulation, or rectification. In one specific embodiment, the sympathetic nerve signal AS can be rectified to obtain the absolute value signal |AS| of the sympathetic nerve signal AS. Then, within a specific time window of seconds (e.g., 100 ms), the sum of the sympathetic nerve signal AS is represented as an integrated sympathetic nerve signal. Finally, the integrated sympathetic nerve signal can be averaged over a specific time unit of seconds to obtain an averaged sympathetic nerve signal value. However, the post-processing method is not limited to this.

[0035] In one embodiment, the post-processing circuit 140 may have multiple filtering frequency bands for sympathetic nerve-related bioelectrical signals BS (e.g., electromyography signals or electrocardiogram signals). Referring to Figure 4, the post-processing circuit 140 is further configured to filter the fifth signal S5 using a second filtering frequency band BP2 to output an electrocardiogram signal. The second filtering frequency band BP2 corresponding to the electrocardiogram signal is, for example, 0.05~150 Hz. It should be noted that Figure 4 is only an example, and the post-processing circuit 140 may have multiple filtering frequency bands, for example, filtering both electrocardiogram signals and electromyography signals (25~500 Hz) simultaneously.

[0036] In one embodiment, the sympathetic nerve signal sensing system 100 may further include a bias resistor 160. Specifically, referring to FIG5, the bias resistor 160 is coupled between the input terminal of the first follower 121 and the ground terminal GND, and coupled between the input terminal of the second follower 122 and the ground terminal GND. The main function of the bias resistor 160 is to discharge static charge in the clothing 13 or skin 12 to the ground terminal GND. In a specific embodiment, the bias resistor 160 may have a resistance value greater than 624 kΩ. The resistance value of the bias resistor 160 can be selected to satisfy the effect of eliminating static electricity and avoid affecting the frequency response of the overall circuit. For example, the bias resistor 160 and the clothing 13 or skin 12 form an equivalent loop of a high-pass filter, causing an impact during the measurement of the sympathetic nerve signal AS. The impact during measurement is, for example, that the high-frequency signal is introduced to the ground terminal GND through the bias resistor 160, but is not limited thereto.

[0037] In one embodiment, the sympathetic nerve signal sensing system 100 may further include an AC coupling circuit 170. Specifically, referring to FIG6, the AC coupling circuit 170 is coupled between the high input impedance receiving circuit 120 and the differential circuit 130. The AC coupling circuit 170 is configured to eliminate the DC components of the third signal S3 and the fourth signal S4 to retain the AC components (S3', S4'). The AC coupling circuit 170 is positioned after the high input impedance receiving circuit 120 and before the differential circuit 130. The AC coupling circuit 170 is primarily used to eliminate the DC offset in the third signal S3 and the fourth signal S4. In one specific embodiment, the cutoff frequency of the AC coupling circuit 170 is designed to be 0.03 Hz. This further reduces DC signal interference when measuring the sympathetic nerve signal AS, avoiding errors in the interpretation of heart rhythm signals or other signals.

[0038] Based on the above embodiments, the present invention proposes a specific circuit architecture diagram. Referring to Figure 7, the AC coupling circuit 170, composed of an ungrounded resistor and capacitor, serves as a high-pass filter to eliminate DC components. Two high-impedance voltage followers can be used as an output stage between the AC coupling circuit 170 and the differential circuit 130 to avoid signal attenuation. The post-processing circuit 140 is a band-pass filter and amplifier circuit composed of a Butterworth low-pass filter and a Butterworth high-pass filter. It should be noted that the circuit architecture shown in Figure 7 is intended to illustrate the feasibility of implementing the present invention and is not intended to limit the circuit architecture of the present invention.

[0039] In one embodiment, the sympathetic nerve signal sensing system 100 may further include a common-mode electrode 181 and its corresponding circuitry 182 (e.g., a right foot drive circuit). Specifically, referring to FIG8, the common-mode electrode 181 may be positioned at any suitable location to receive signals common to the ground electrode and / or the second electrode 112. For example, the common-mode electrode 181 may be positioned outside the sympathetic nerve signal source of the subject 10 and integrated with the electrode pair as an integrated patch. The common-mode electrode 181 is configured to receive a common-mode signal common to the first signal S1. The differential circuitry 130 is further configured to differentially process the common-mode signal with the third signal S3 and the fourth signal S4, respectively. The common-mode electrode 181 and its corresponding circuitry 182 are used to reduce common-mode interference of biosignals. For example, common-mode signals affected by external electromagnetic waves (e.g., ambient electromagnetic waves or alternating current electromagnetic waves) of the subject 10 may be eliminated. Please refer to Figure 9 for the specific circuit architecture of this embodiment. It should be noted that the circuit architecture shown in Figure 9 is intended to illustrate the feasibility of implementing the present invention and is not intended to limit the circuit architecture of the present invention.

[0040] As described above, the high input impedance receiving circuit 120 can effectively cancel the equivalent impedance generated by various media between the sympathetic nerve signal source and the electrode pair. The follower within the high input impedance receiving circuit 120 can provide high input impedance and low output impedance, thus achieving impedance isolation between the electrode pair and the remaining circuitry. This further reduces crosstalk between the electrode pair and the remaining circuitry. Furthermore, signal measurement quality can be further improved through other circuit configurations, such as the bias resistor 160, AC coupling circuit 170, or common-mode electrode 181 in the embodiments. It should be noted that the above embodiments can be implemented individually or in combination, and the present invention is not limited to any particular embodiment.

[0041] In one embodiment, the sympathetic nerve signal sensing system 100 may further include a negative impedance circuit 190. Specifically, referring to FIG10, the negative impedance circuit 190 is coupled between the electrode pair and the high input impedance receiving circuit 120; wherein the negative impedance circuit 190 is configured to provide a negative impedance value approximately equal to the negative of the equivalent impedance from the signal source of the sympathetic nerve signal AS to the electrode pair to the inputs of the first follower 121 and the second follower 122. In this embodiment, in addition to utilizing the high input impedance receiving circuit 120 to reduce the proportion of influence of skin or clothing on signal reception, the impedance mismatch problem caused by the dielectric value between skin, clothing, air, or other electrode pairs and the sympathetic nerve signal source can also be reduced by the negative impedance circuit 190 disposed between the electrode pair and the high input impedance receiving circuit 120. The negative impedance value of the negative impedance circuit 190 can be preset. For example, when the wearing environment of the test subject 10 is uniform (e.g., uniform clothing, uniform wearing distance, etc.), the preset negative impedance value can reduce the operator's operational difficulty. On the other hand, the negative impedance value of the negative impedance circuit 190 can be adjustable. For example, the negative impedance circuit 190 has adjustable active or passive components, and the electrical characteristics (e.g., resistance, capacitance, or inductance) of the active or passive components can be adjusted by control signals or mechanical rotation. The adjustable negative impedance circuit 190 can be used to adjust the signal-to-noise ratio according to different usage scenarios.

[0042] In one embodiment, the negative impedance circuit 190 can adjust its negative impedance value based on at least one signal parameter of the sympathetic nerve signal AS. Specifically, referring to FIG11, the sympathetic nerve signal sensing system 100 further includes a controller 195. The controller 195 is coupled between the post-processing circuit 140 and the negative impedance circuit 190. The controller 195 is configured to adjust the negative impedance value of the negative impedance circuit 190 based on at least one signal parameter of the sympathetic nerve signal AS. For example, the controller 195 can adjust the negative impedance value of the negative impedance circuit 190 based on the measured signal parameters of the sympathetic nerve signal AS (e.g., amplitude, baseline level, spectrum, or signal-to-noise ratio). In one specific embodiment, the controller 195 can use whether the baseline level of the sympathetic nerve signal AS is greater than a baseline threshold (e.g., defined as 30 μV). When the baseline level is less than the baseline threshold, the controller 195 adjusts the negative impedance value of the negative impedance circuit 190 or issues a warning to allow the operator to make adjustments.

[0043] In one embodiment, the negative impedance circuit 190 can adjust its negative impedance value based on at least one signal parameter of the bioelectrical signal associated with the sympathetic nerve signal AS. For example, referring to FIG12, the sympathetic nerve signal sensing system 100 further includes a controller 195 coupled between the post-processing circuit 140 and the negative impedance circuit 190. The post-processing circuit 140 is further configured to filter the fifth signal S5 at a second filtering frequency band BP2 to output a bioelectrical signal (e.g., an electrocardiogram signal). The controller 195 is configured to adjust the negative impedance value of the negative impedance circuit 190 based on at least one signal parameter of the output bioelectrical signal (e.g., amplitude, baseline level, spectrum, or signal-to-noise ratio). Specifically, the adjustment can be based on a known or signal-to-noise ratio of bioelectrical signal. For example, the various states of the electrocardiogram signal (e.g., waveforms such as PQRS) can determine the corresponding possible sympathetic nerve signal AS. Since both the electrocardiogram (ECG) signal and the sympathetic nerve signal AS are received by the electrode pair and processed and filtered by the negative impedance circuit 190 and other circuits, the ECG signal can be used as a basis for adjustment. When the negative impedance value of the negative impedance circuit 190 is adjusted so that the signal parameters such as the signal-to-noise ratio or baseline level of the ECG signal reach the expected quality, the sympathetic nerve signal AS can also obtain better signal quality by adjusting the negative impedance value of the negative impedance circuit 190.

[0044] The negative impedance circuit 190 provides a negative impedance value to reduce the equivalent impedance difference between the sympathetic nerve signal source and the electrode pair. Therefore, the electrode pair of the present invention, without contacting the skin of the subject 10, further improves the accuracy of the sympathetic nerve signal AS through compensation by the negative impedance circuit 190. Furthermore, in the above embodiment, the negative impedance of the negative impedance circuit 190 can be further adjusted according to the feedback of the measurement signal to achieve the best compensation effect.

[0045] The prior description of the invention is provided to enable those skilled in the art to make or practice the invention. Various modifications to the invention will be apparent to those skilled in the art, and the general principles defined herein can be applied to other variations or embodiments can be combined with or implemented individually without departing from the spirit or scope of the invention. Therefore, the invention is not intended to be limited to the examples described herein, but is accorded the widest scope consistent with the principles and novel features of the invention herein. [Simplified Explanation of the Diagram]

[0012] The accompanying drawings presented in this invention are intended to help describe various embodiments of the invention. However, to simplify the drawings and / or highlight what the drawings are intended to present, known structures and / or elements in the drawings may be drawn in a simple schematic manner or presented in an omitted manner. On the other hand, the number of elements in the drawings may be singular or plural. The accompanying drawings presented in this invention are only for illustrating these embodiments and not for limiting them.

[0013] Figure 1 illustrates a schematic diagram of the resistance measurement of the present invention.

[0014] Figure 2 illustrates a block diagram and measurement schematic diagram of a sympathetic nerve signal sensing system in one embodiment of the present invention.

[0015] Figure 3 illustrates a schematic diagram of a sympathetic nerve signal sensing system including a back-end device in one embodiment of the present invention.

[0016] Figure 4 illustrates a schematic diagram of a sympathetic nerve signal sensing system having multiple filter frequency bands in one embodiment of the present invention.

[0017] Figure 5 illustrates a schematic diagram of a sympathetic nerve signal sensing system including a bias resistor in one embodiment of the present invention.

[0018] Figure 6 illustrates a schematic diagram of an AC coupling circuit included in a sympathetic nerve signal sensing system according to an embodiment of the present invention.

[0019] Figure 7 illustrates the circuit architecture of the sympathetic nerve signal sensing system in one embodiment of the present invention.

[0020] Figure 8 illustrates a schematic diagram of a sympathetic nerve signal sensing system including a common-mode electrode in one embodiment of the present invention.

[0021] Figure 9 illustrates the circuit architecture of the sympathetic nerve signal sensing system in one embodiment of the present invention.

[0022] Figure 10 illustrates a schematic diagram of a sympathetic nerve signal sensing system including a negative impedance circuit in one embodiment of the present invention.

[0023] Figure 11 illustrates a schematic diagram of a sympathetic nerve signal sensing system including a controller to adjust a negative impedance circuit in one embodiment of the present invention.

[0024] Figure 12 illustrates a schematic diagram of a sympathetic nerve signal sensing system including a controller to adjust a negative impedance circuit in one embodiment of the present invention.

Claims

1. A sympathetic nerve signal sensing system, comprising: an electrode pair disposed outside a sympathetic nerve signal source of a subject, including: A first electrode, configured to receive a first signal; And a second electrode configured to receive a second signal; A high input impedance receiving circuit, coupled to the electrode pair, includes: a first follower configured to receive the first signal and output a third signal approximately equal to the first signal; and a second follower configured to receive the second signal and output a fourth signal approximately equal to the second signal; a differential circuit coupled to the high input impedance receiving circuit, wherein the differential circuit is configured to differentially process the third signal and the fourth signal to generate a fifth signal; and a post-processing circuit coupled to the high input impedance receiving circuit, wherein the post-processing circuit is configured to filter the fifth signal using a first filter band to output a sympathetic nerve signal; wherein the high-pass cutoff frequency of the first filter band is 500 Hz or higher. A negative impedance circuit is coupled between the electrode pair and the high input impedance receiving circuit; wherein the negative impedance circuit is configured to provide a negative impedance value to the inputs of the first follower and the second follower, which is approximately equal to the negative of the equivalent impedance of the sympathetic nerve signal source to the electrode pair; and a controller is coupled between the post-processing circuit and the negative impedance circuit; wherein the post-processing circuit is further configured to filter the fifth signal with a second filtering frequency band to output an electrocardiogram (ECG) signal; and wherein the controller is configured to adjust the negative impedance value of the negative impedance circuit according to at least one signal parameter of the ECG signal.

2. The sympathetic nerve signal sensing system as claimed in claim 1, further comprising: a common-mode electrode configured to receive a common-mode signal sharing the same mode as the first signal; and wherein the differential circuit is further configured to perform the differential processing on the common-mode signal with the third signal and the fourth signal, respectively.

3. The sympathetic nerve signal sensing system as described in claim 1 further comprises: a back-end device configured to receive the sympathetic nerve signal and perform at least one signal processing on the sympathetic nerve signal.

4. The sympathetic nerve signal sensing system as described in claim 1, wherein the post-processing circuit is further configured to filter the fifth signal with a second filter band to output an electrocardiogram signal.

5. The sympathetic nerve signal sensing system as claimed in claim 1, further comprising: an AC coupling circuit coupled between the high input impedance receiving circuit and the differential circuit; wherein the AC coupling circuit is configured to eliminate the DC component of the third signal and the fourth signal.

6. The sympathetic nerve signal sensing system as described in claim 1, further comprising: a bias resistor coupled between the input terminal and the ground terminal of the first follower.

7. The sympathetic nerve signal sensing system as claimed in claim 1, wherein the controller is configured to further adjust the negative impedance value of the negative impedance circuit based on at least one signal parameter of the sympathetic nerve signal.

8. The sympathetic nerve signal sensing system as described in claim 1, wherein the first filter frequency band is selected from 500 to 1000 Hz.

9. A method for sensing sympathetic nerve signals, comprising: setting an electrode on the outside of a sympathetic nerve signal source of a subject; The electrode pair includes: A first electrode configured to receive a first signal and a second electrode configured to receive a second signal; A high-input-impedance receiving circuit receives the first signal and outputs a third signal approximately equal to the first signal, and receives the second signal and outputs a fourth signal approximately equal to the second signal; a differential circuit performs differential processing on the third and fourth signals to generate a fifth signal; a post-processing circuit filters the fifth signal using a first filtering frequency band to output a sympathetic nerve signal; wherein the high-pass cutoff frequency of the first filtering frequency band is above 500 Hz; a negative impedance circuit provides a negative impedance value approximately equal to the negative of the equivalent impedance of the sympathetic nerve signal source to the electrode pair to the input terminal of the high-input-impedance receiving circuit; the post-processing circuit filters the fifth signal using a second filtering frequency band to output an electrocardiogram (ECG) signal; and a controller adjusts the negative impedance value of the negative impedance circuit according to at least one signal parameter of the ECG signal.

10. The sympathetic nerve signal sensing method as described in claim 9, further comprising: setting a common-mode electrode; wherein the common-mode electrode is configured to receive a common-mode signal that is in the same mode as the first signal; and further performing differential processing on the common-mode signal with the third signal and the fourth signal respectively using the differential circuit.

11. The sympathetic nerve signal sensing method as described in claim 9 further comprises: receiving the sympathetic nerve signal with a back-end device and performing at least one signal processing on the sympathetic nerve signal.

12. The sympathetic nerve signal sensing method as described in claim 9 further includes: using an AC coupling circuit to eliminate the DC component of the third signal and the fourth signal.

13. The sympathetic nerve signal sensing method as described in claim 9, wherein the first filter frequency band is selected from 500 to 1000 Hz.

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