JPH07299149A - Evaluating apparatus for embedded electrode and evaluating method using the same - Google Patents

Abstract

PURPOSE:To estimate a defective move and a location of a defect in an embedded electrode for treatment used by a method wherein a control electrode is placed in a living body near the electrode for treatment and a fine sine wave signal is applied between the electrode for treatment and the control electrode to calculate an electrode impedance from the size and phase of a current flowing through the electrodes and a voltage thereof. CONSTITUTION:A fine sine wave signal is applied between an electrode 2 for treatment having an insulating cover 3 embedded in a living body 1 and a control electrode 4 placed in the living body 1 near the electrode 2 for treatment to calculate an electrode impedance from the value and the phase of a current flowing through the electrodes and a voltage thereof and an evaluation of the electrode 2 for treatment is performed. In the measurement of a frequency characteristic of the electrode impedance, a real number part and an imaginary number part of the impedance which is calculated from a voltage and a current to be applied to the embedded electrode for treatment under a specified frequency are calculated by a computation with a computer to change the frequency sequentially. The real number part and the imaginary number part of the electrode impedance under the frequency changed sequentially are calculated to obtain a locus of the impedance.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to functional electrical stimulation (FES) or therapeutic electrical stimulation (TES) for promoting recovery of functional disorder for the purpose of reconstructing motor paralysis due to stroke or spinal cord injury. In the treatment by
The present invention relates to an apparatus for externally evaluating the state of an electrode embedded near the muscular system and an evaluation method using the apparatus.

[0002]

2. Description of the Related Art Conventionally, functional electrical stimulation (FE) for the purpose of reconstructing motor paralysis due to stroke or spinal cord injury.
S) or therapeutic electrical stimulation (T
In the treatment by ES, etc., electrodes are implanted and placed in the vicinity of the nerve / muscle system in the living body in order to selectively electrically stimulate individual muscles. A typical example of the electrode used here is stainless steel (SUS316
For example, there are 19 fine ropes (diameter: 25 μm) of L) formed in a rope shape, coated with Teflon having a thickness of about 40 μm, and wound in a helical shape.

[0003]

[Problems to be Solved by the Invention] Functional electrical stimulation (FE)
While the treatment by S) has been in full swing, there has not been an effective method to evaluate the percutaneous implantation electrode used here after the implantation. Therefore, it was not possible to determine the movement of the percutaneously embedded electrode, the disconnection in the living body, the poor contact at the terminal, and the like.

Further, not only the above-mentioned percutaneous implantable electrode but also the full implantable functional electrical stimulation (FES) system has the same problem. The present invention changes the impedance of a therapeutic implant electrode from several tens of Hz to several tens of KH.
By using a simple method of measuring in a frequency band up to z, a defect state of a therapeutic implantation electrode in use and a defective portion can be estimated, and an evaluation device for a therapeutic implantation electrode in a living body is used. The purpose is to provide an evaluation method.

[0005]

In order to achieve the above-mentioned object, the present invention provides (A) a device for evaluating an embedded electrode, a therapeutic electrode having an insulating coating embedded in a living body, and the therapeutic electrode. , A reference electrode provided in the living body in the vicinity of, a sine wave power source for applying a minute sine wave signal between the treatment electrode and the reference electrode, a current flowing through the electrode, and an electrode impedance from the magnitude and phase of the voltage. A measuring means for calculating is provided.

(B) In the method for evaluating an embedded electrode, (1) A minute sine is provided between a therapeutic electrode having an insulating coating embedded in a living body and a reference electrode provided in the living body near the therapeutic electrode. A wave signal is applied, the electrode impedance is calculated from the current flowing through the electrode, and the magnitude and phase of the voltage, and the therapeutic electrode is evaluated.

(2) The frequency of the sine wave signal is changed and the frequency characteristic of the electrode impedance is measured. (3) The frequency characteristic of the electrode impedance is measured by
After the voltage applied to the implantable therapeutic electrode under a predetermined frequency and the current vector are separated into a 0-degree component (real part) and a 90-degree component (imaginary part), a predetermined frequency is calculated by a computer. The electrode impedance under the frequency is calculated, the frequency is sequentially changed, the electrode impedance under the frequency that is sequentially changed is calculated, and the impedance locus is obtained.

(4) The frequency of the sine wave signal is 10 ¹
-10 ⁴ Hz. (5) The frequency of the sine wave signal is 10 ¹ to 10 ⁴ Hz, and the electrode impedance Z is over this frequency range.
When (Ω) exhibits a low value in the vicinity of 10 ² to 10 ³ Ω, both the metal electrode and the insulating coating of the therapeutic electrode are estimated to be normal. (6) The frequency of the sine wave signal is 10 ¹ to 10 ⁴ Hz, and the electrode impedance Z (Ω) is 10 ¹ to 10 ² H.
When the z has a large value in the vicinity of 10 ⁶ to 10 ⁷ Ω in the low frequency band and exhibits a change that is almost inversely proportional to the frequency in the high frequency band of 10 ³ to 10 ⁴ Hz, the insulation coating of the therapeutic electrode is normal. However, it is presumed that the metal electrode has a wire break.

(7) The frequency of the sine wave signal is from 10 ¹ to
When it is 10 ⁴ Hz and the electrode impedance Z (Ω) changes with an intermediate value between claims 6 and 7, it is presumed that the embedded electrode has a disconnection in both the metal electrode and the insulating coating.

[0010]

According to the present invention, the treatment electrode (2) having the insulating coating (3) embedded in the living body (1) and the living body (1) near the treatment electrode (2) are provided. Since a minute sine wave signal is applied between the reference electrodes (4), the electrode impedance is calculated from the magnitude and phase of the current flowing in the electrodes and the voltage, and the therapeutic electrode (2) is evaluated. It is possible to measure the quality of the percutaneously embedded electrode or the completely embedded electrode by a simple method.

Further, the frequency characteristics of the electrode impedance can be measured by changing the frequency of the applied sine wave signal, the movement of the treatment electrode (2), the treatment electrode (2) in the living body (1). ) Insulation failure or contact failure at the terminal can be reliably evaluated. Furthermore, since the reference electrode is embedded in the living body in the vicinity of the therapeutic electrode, it is less affected by noise from the external atmosphere and is more reliable than when the reference electrode is formed on the skin surface. It is possible to measure the impedance of the therapeutic electrode having high efficiency.

[0012]

Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a configuration diagram of an implantable therapeutic electrode evaluation apparatus according to an embodiment of the present invention. In this figure, reference numeral 1 is a living body to be treated by functional electrical stimulation (FES), and a therapeutic metal electrode 2 having an insulating coating 3 is percutaneously embedded in the living body 1. On the other hand, the reference electrode 4 is also embedded in the living body 1 near the metal electrode 2.

Therefore, the terminal A of the metal electrode 2 and the reference electrode 4
A power source that outputs a minute sine wave signal is connected between the terminals B of 1 and the impedance Z of the electrode on the living body side between the terminals A and B is obtained by an impedance measuring device. That is, a minute sinusoidal voltage is applied from the outside of the living body 1, and the electrode impedance is calculated from the current flowing through the electrode and the magnitude and phase of the voltage.

Further, the frequency of the sine wave signal is changed to obtain the frequency characteristic of the electrode impedance. That is, as shown in FIG. 3, the frequency characteristic of the electrode impedance is measured by measuring the voltage applied to the therapeutic implant electrode under a predetermined frequency f ₁ and the real part R _{1 of the} impedance Z calculated from the current and The imaginary part X ₁ is the computer 11
Was calculated by the calculation, it is changed sequentially frequency, a real part R _2, R ₃ ... R _n of successively changed frequency f _2, f ₃ ... electrode impedance under f _n, the imaginary part X _2, X ₃ ... X
_The impedance locus can be obtained by calculating _n .
The obtained data can be stored in the memory 12 or can be displayed on the screen by the display device 13.

Although not shown, the frequency characteristic data to be sampled is stored in advance in the memory as reference data for each failure state of the therapeutic electrode, and the frequency characteristic data obtained by the measurement is referred to. The data to be processed may be collated by the computer 11, and if the results of the collation are the same or similar, it may be presumed to be the defective state of the therapeutic electrode corresponding thereto.

As described above, movement of the therapeutic metal electrode, disconnection of the therapeutic metal electrode in the living body, without removing the state of the electrode in the living body from the frequency characteristics of the electrode impedance,
It is possible to evaluate poor insulation of the therapeutic metal electrode or poor contact at the terminal. Hereinafter, these evaluation methods will be described in detail. An equivalent circuit between terminals A and B in FIG. 1 is represented as in FIG. Here, Rs is a series resistance of the therapeutic metal electrode 2 itself and a resistance due to a living tissue between the therapeutic metal electrode 2 and the reference electrode 4. Further, Re and Ce are the real part and the imaginary part of the interface impedance of the conductive part 2a of the metal electrode to be evaluated, and are parameters that depend on the surface area. Figure 1
Then, the impedance of the electrode system viewed from the terminals AB, that is, the impedance Z measured by the electrode impedance measuring device 5 including the sine wave power source 6 for applying the minute sine wave signal shown in FIG. When expressed by an equation, Z = R−jX (1), and the real part and the imaginary part are as follows.

R = Rs + Re / [1+ (ωCeRe) ² ] ... (2) X = ωCeRe ² / [1+ (ωCeRe) ² ] ... (3) Here, from the real part of the formula (1) to the therapeutic metal electrode 2 The effective resistance represented by the distance L ₁ between the reference electrode 4 and the reference electrode 4 and the surface area of the electrode exposed portion, and the change in the reactance can be known from the imaginary part.

Hereinafter, each mode of three typical types of therapeutic metal electrodes will be described based on the equation (1). When there is no disconnection in the therapeutic metal electrode Since there is no change in the electrode itself, Re and Ce are constant and there is no change in DC resistance Rs.

[0019] If there is movement of the therapeutic metal electrode 2, if there is a change in [Delta] L ₁ at a distance L ₁ in FIG. 1, it appears as a change in ΔRs DC resistance Rs proportionally. That is, since ΔRs∝ΔL ₁ , the change amount of the real part R of the impedance is ΔR ΔR∝ΔL ₁ (regardless of frequency) (4), and the change of the therapeutic metal electrode 2 appears in the change of the real part of the impedance.

When the insulation coating is normal and only the therapeutic metal electrode 2 is broken (in the case of FIG. 4) As shown in FIG. 4, when the treatment metal electrode 2 is broken only in the insulation coating 3, The conductive electrical connection with the tissue is lost, the terminals A and B are open, and the resistance value becomes infinite. However, in reality, since there is a line capacitance Cs formed between the living tissue and the metal electrode, the terminal A
Between −B, the line capacitance Cs is not connected but is connected. Therefore, the magnitude of impedance | Z |
Is approximately | Z | = 1 / ωCs
(5), which is represented by a simple function of the angular frequency ω.

On the other hand, the relationship between the length L ₃ of the therapeutic metal electrode 2 and the line capacitance Cs is approximately Cs∝L ₃ as shown in FIG. By obtaining the capacitance per contact, the length L ₃ of the electrode from the size of the line capacitance Cs to the disconnection point can be estimated.

When both the therapeutic metal electrode and the insulating coating are broken (in the case of FIG. 5) When the insulating coating 3 shown in FIG. 1 is broken as shown in FIG. The surface area in contact with the tissue will be significantly reduced. Therefore, the value of Ce is greatly reduced and the value of Re is significantly increased. Therefore, at low frequencies, | Z | ≈Re from the above equation (2), and at high frequencies, Z≈Rs−jX≈Rs−j / ωCe from the above equation (3).

In the above cases, and, the frequency dependence of the impedance magnitude | Z | is summarized as shown in FIG. Hereinafter, specific experimental examples will be described. As shown in FIG. 1, a small sinusoidal voltage is applied from the outside of the living body 1 between the therapeutically embedded electrode, which is the electrode to be measured, and the reference electrode in two patients who have electrodes embedded in their lower limbs for training or functional reconstruction. Then, calculate the electrode impedance from the current flowing through the electrode, the magnitude and phase of the voltage, and then change the frequency of the sine wave signal to obtain the frequency characteristic of the electrode impedance. It shows in FIG.

A specific example of evaluation of this frequency characteristic will be shown below. (1) When there is no disconnection of the therapeutic metal electrode: The curves shown in FIG. 7 show normal contraction without disconnection because muscle contraction was recognized by electrical stimulation from the stimulator and desired movement was obtained. It is a characteristic of the electrode that is considered to be a perfect electrode.

Here, the magnitude of the impedance of the electrode |
The difference in Z | is considered to be due to the difference in the length L ₂ of the embedded electrode and the distance L ₁ between the electrode tip and the reference electrode. These correspond to ′ in FIG. That is, in this mode, the electrode impedance Z (Ω) is 10 ² to 10 ⁴ over the frequency range of 10 ¹ to 10 ⁴ Hz.
It exhibits a low value in the vicinity of 10 ³ Ω, and it is estimated that both the metal electrode and the insulating coating of the therapeutic electrode are normal.

(2) When the insulation coating is normal and only the therapeutic metal electrode is broken: The characteristic curve in FIG. 7 is an electrode in which no muscle contraction due to electrical stimulation is observed, and the impedance | Z | characteristic is a function of frequency. And the line capacitance C _S between the living tissue and the metal electrode
It is thought to be due to the characteristics. Furthermore, the magnitude of the impedance at low frequencies is very large, the contact between the electrode and the living tissue is extremely small, and the disconnection occurs almost only in the insulating coating film (state in FIG. 4). Considered equal. These correspond to those shown in FIG.

That is, in this mode, the electrode impedance Z (Ω) exhibits a large value in the vicinity of 10 ⁶ to 10 ⁷ Ω in the low frequency band of 10 ¹ to 10 ² Hz, and 10 ³
In the high frequency band of -10 ⁴ Hz, the change is almost inversely proportional to the frequency, and it is estimated that the therapeutic electrode has a normal insulating coating but the metal electrode has a wire break. (3) Metallic electrode for treatment and electrode with insulation coating disconnected The characteristic curve shown in FIG. 7 is an electrode in which muscle contraction due to electrical stimulation is not recognized, like the therapeutical metal electrode of the characteristic curve. Compared with the magnitude of the impedance | Z | of a normal therapeutic metal electrode (characteristic curve shown in FIG. 7), the value is one digit or more larger. This is because the insulation coating 3 is broken along with the therapeutic metal electrode 2 (state of FIG. 5), and the electrical contact with the living tissue is significantly reduced, so that the magnitude of impedance is increased.
It is assumed that the state is sufficiently smaller than the characteristic curve shown in FIG. This corresponds to that shown in FIG.

That is, in this mode, the electrode impedance Z (Ω) exhibits an intermediate value between the above (1) and (2), and it is presumed that the metal electrode and the insulating coating are broken. In addition, although the evaluation of the transcutaneous implantable electrode is described in the above embodiment, it is needless to say that the present invention can be similarly applied to not only the transdermal implantable electrode but also a complete implantable functional electrical stimulation (FES) system.

[0029]

As described above in detail, according to the present invention, the following effects can be obtained. (1) It is possible to accurately evaluate the implantable therapeutic implant electrode without removing the implantable therapeutic implant electrode in the living body.

(2) In particular, a minute sine wave signal is applied between the therapeutic electrode having an insulating coating embedded in the living body and a reference electrode provided in the living body in the vicinity of the therapeutic electrode, and the electrode is applied. Since the electrode impedance was calculated from the current and voltage magnitude and phase flowing through the electrode, and the implantable therapeutic electrode was evaluated, the quality of the percutaneous implantable electrode or the completely implantable electrode can be measured by a simple method. it can.

Further, the frequency characteristics of the electrode impedance can be measured by changing the frequency of the applied sinusoidal signal, and the implantation treatment electrode can be moved, the implantation treatment electrode in the living body, and the implantation treatment electrode can be measured. It is possible to reliably evaluate poor insulation or poor contact at terminals. Furthermore, since the reference electrode is provided in the living body in the vicinity of the therapeutic electrode, it is less affected by noise from the external atmosphere and is more reliable than when the reference electrode is formed on the skin surface. It is possible to measure the impedance of the therapeutic electrode having high efficiency.

[Brief description of drawings]

FIG. 1 is a block diagram of an evaluation device for an implantable therapeutic electrode showing an embodiment of the present invention.

FIG. 2 is an equivalent circuit at the time of evaluating a therapeutic embedded electrode showing an example of the present invention.

FIG. 3 is a block diagram of a measuring device of an evaluation device for an implantable therapeutic electrode according to an embodiment of the present invention.

FIG. 4 is a diagram showing a disconnection state of only a therapeutic embedded electrode.

FIG. 5 is a diagram showing a disconnection state of a therapeutic embedded electrode and an insulating coating.

FIG. 6 is a frequency characteristic schematic diagram in evaluation of an implantable electrode for treatment showing an example of the present invention.

FIG. 7 is a specific frequency characteristic diagram in evaluation of a therapeutic embedded electrode showing an example of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Living body 2 Treatment metal electrode 3 Insulation coating 4 Reference electrode 5 Electrode impedance measuring device 6 Sine wave power supply 10 Measuring device 11 Computer 12 Memory 13 Display device

Claims (8)

[Claims] 1. A therapeutic electrode having an insulating coating embedded in a living body, (b) a reference electrode provided in the living body in the vicinity of the therapeutic electrode, and (c) the therapeutic electrode. A sine wave power supply that applies a minute sine wave signal between the reference electrodes,
(D) A device for evaluating an embedded electrode, which comprises a current flowing through the electrode and a measuring means for calculating the electrode impedance from the magnitude and phase of the voltage. 2. A small sinusoidal signal is applied between (a) a therapeutic electrode having an insulating coating embedded in a living body and a reference electrode provided in the living body near the therapeutic electrode, and (b). An embedded electrode evaluation method for evaluating a therapeutic electrode by calculating an electrode impedance from the magnitude and phase of a current flowing through the electrode and the voltage. 3. The embedded electrode evaluation method according to claim 2, wherein the frequency characteristic of the electrode impedance is measured by changing the frequency of the sine wave signal. 4. The frequency characteristic of the electrode impedance is measured by measuring a voltage applied to the implantable therapeutic electrode under a predetermined frequency and a vector of a current and a 0 degree component (real part).
And the 90-degree component (imaginary part) are separated, the electrode impedance under a predetermined frequency is calculated by a computer calculation, the frequency is sequentially changed, and the electrode impedance under the sequentially changed frequency is calculated. The method for evaluating an embedded electrode according to claim 3, wherein the impedance locus is obtained. Frequency of claim 5 wherein said sinusoidal signal 10 ¹ to 10
^The method for evaluating an embedded electrode according to claim 3, wherein the frequency is ⁴ Hz. Wherein the frequency of the sinusoidal signal 10 ¹ to 10
^{It is 4} Hz, and when the electrode impedance Z (Ω) exhibits a low value in the vicinity of 10 ² to 10 ³ Ω over this frequency range, both the metal electrode and the insulating coating are presumed to be normal for the therapeutic electrode. Evaluation method of embedded electrodes. Frequency of wherein said sinusoidal signal 10 ¹ to 10
⁴ Hz, electrode impedance Z (Ω) is 10 ¹ ~
In the case where a large value in the vicinity of 10 ⁶ to 10 ⁷ Ω is exhibited in the low frequency band of 10 ² Hz and a change substantially inversely proportional to the frequency is exhibited in the high frequency band of 10 ³ to 10 ⁴ Hz, the insulation coating of the therapeutic electrode is The method for evaluating an embedded electrode according to claim 4, wherein it is estimated that the metal electrode is normal but has a wire break. Frequency of wherein said sinusoidal signal 10 ¹ to 10
5. The embedded electrode according to claim 4, wherein the embedded electrode is presumed to have a break in both the metal electrode and the insulating coating when the electrode impedance Z (Ω) changes at a frequency of ⁴ Hz and exhibits an intermediate value between the aforementioned claims 6 and 7. Electrode evaluation method.