JP2001526074A - Non-invasive device for electromyographic measurements - Google Patents

Abstract

(57) Abstract: The present invention relates to an apparatus for electromyography having a surface electrode, wherein the surface electrode generates at least a group of electrodes (E), spatial filtering means, and spatial filtering of a signal transmitted by the electrode. Weighted sum amplification means. According to the present invention, the spatial filtering and the weighted meter amplifying means comprise circuits (6, 5) attached to the electrodes (E) of the housing (I), and one surface of the housing (I) supporting the electrodes (E) is Forming a sensing surface (2), the device is further characterized in that it comprises means for connecting said housing to biasing means (9), amplifying means (10) and data processing means (12).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD OF THE INVENTION

The present invention relates to non-invasive analysis of the neuromuscular system of living tissue by surface electromyography.

[0002]

[Prior art]

At present, for clinical medical analysis of neurological or neuromuscular disorders, electromyographic detection systems are only invasive and are performed by a detector needle inserted into the muscle to be studied. ing. In addition to pain, the risk of trauma and infection resulting from this type of intervention makes invasive systems a very selective, limited measurement that does not allow actual analysis of a given muscle area Is given. In addition, clinical follow-up of the disease with these systems is not possible.

To avoid these drawbacks and to allow sufficiently accurate measurements over a wider range, non-invasive surface electromyographic procedures using so-called floating electrodes have been developed, which consist of contact gels or so-called Requires dry electrodes. These surface electrodes usually require a pre-treatment of the skin surface (shaving, mild polishing, degreasing).

[0004] Measurements are made by receiving at the electrodes spontaneous or signals resulting from muscle contractions caused by mechanical or electrical stimulation. Surface EMG consists of detecting, recording, and processing the received EMG signals, which are indicative of muscle contraction.

[0005] This procedure is designed to identify certain neurological or muscular disorders, whose physiologic properties depend on certain parameters of the signal, such as the amplitude, the signal frequency, or the speed of propagation of the muscle action potential. May cause change. Thus, some diseases are characterized by the selective degradation of one type of fiber over another. For example, Duchenne muscular dystrophy undergoes a selective attack, so-called rapid fiber. Such altered state adjusts the average measurement of the propagation speed of the electromyographic signal.

[0006] Generally, muscle fibers are only activated when stimulation exceeds a certain threshold at their neuromuscular junction. The fiber is assembled into a functional unit. The motor unit that assembles all the fibers is interposed by the same motor nerve. The operating potential of the motor unit is equal to the sum of the muscle actions of the elements of each fiber that make up it.

[0007] Electromyographic signals received at the electrodes result from the spatial and temporal sum of the signals from all of the reinforced motor units. The measurement of the signal is influenced by the anatomical and functional properties of the muscle under consideration and by the central and peripheral nervous system control connections. Furthermore, when the measurement is performed, the electrical signal of the energized motor unit is superimposed. The complexity of electromyographic signals has given rise to a number of measurement and processing protocols without any protocol or modeling that has traditionally allowed reliable and reproducible analysis of the properties of the signal, an understanding of the physiological reality of muscles and Enable identification.

[0008] It is known to measure the conduction velocity of a potential acting on a muscle by measuring the propagation time of this potential with three or more measuring electrodes. This method creates quantitative difficulties in overestimating the conduction velocity, which is partially explained by the presence of non-propagating activities in the entire area covered by the electrode system.

Another approach is based on indirect estimates based on spectral parameters, such as average or intermediate frequencies, that are considered to be directly linearly correlated with conduction velocity. Such a method is described in the literature (IEEE TRANS. Biomed. ENG. 28, 515-52).
3 (1981)). Experimental studies have shown the constraints of this type of relationship. Spectral parameters depend on several factors other than the conduction velocity of the muscle action potential. Muscle properties and localized tissue anisotropy between the signal source and the detection area result in changes in the spectral content of the signal and the evaluation of the conduction velocity.

For example, in order to improve the measurement of the q-method signal described in the literature (IEEE TRANS. Biomed. ENG. 34, 98-113, 1987), a signal transmitted by a multi-electrode system is called. Spatial filtering by the weighted sum of

In this system, the electrodes are arranged in groups, for each of which the signals transmitted by Ii are weighted after amplification and summed into a unique signal, which is determined by the weighting factor of the signal of the electrodes and by the electrodes in the group. Equal to the signal output by the spatial filter whose characteristics are determined by the geometric distribution of One of the most useful devices is to form a group of five electrodes in a cross with one central electrode and four peripheral electrodes, and to apply an electrode signal with a weighting factor equal to 4 (or -4) to the central electrode. A structure is shown that supplies an electrode signal with a weighting factor equal to -1 (or +1) to each peripheral electrode, which corresponds to a spatial difference of twice the surface distribution of the potential in two orthogonal directions. That is, it corresponds to the transfer function of a two-dimensional Laplace filter. Thus, in particular, the spatial resolution of the detection is improved.

In known systems of this type, the number of Laplace groups of electrodes is relatively high, for example 16 or more, some 64. Neighboring groups have common electrodes, reducing overall electrode count and congestion. The signal captured by the electrodes is pre-amplified and supplied to a band-pass filter, which is further amplified, digitized and recorded in an information processing system, which includes a high-pass filter, the aforementioned spatial filter,
And software for analyzing the resulting signal. In these systems, a larger group of electrodes is used, for example nine, which are arranged in a square matrix, suggesting that they provide more efficient spatial filtering at the level of detector resolution.

[0013] In these systems, a large number of electrodes (32 or 128 depending on the system) is available, on the one hand, so that a set of electrodes can be placed in the area of the muscle without the need for high accuracy. The determined signals make it possible to best arrange the group selected for the motor unit to be tested. On the other hand, many electrodes have the disadvantage that the surface occupied by the electrodes is large, and that many amplifiers and filters are required. Furthermore, the processing of the information of the electrode signals is not directly available in real time.
In general, the complete set of signal acquisition and processing means is complex and can only be used by experienced persons. While these systems are valuable in the lab, they are not suitable for routine use in hospitals.

[0014]

[Problems to be solved by the invention]

It is an object of the present invention to provide a simple and compact, having information quality comparable to that obtained with the aforementioned non-invasive EMG measurement system, without the drawbacks of the aforementioned non-invasive EMG measurement system. Non-invasive EMG measurement that can be used by people without special training (of course, those who are well versed in this technology) can also be used to monitor diseases in environments such as hospitals, and are effective for treatment Is to provide a system.

[0015]

[Means for Solving the Problems]

The present invention relates to an electromyography having a surface electrode comprising one or more groups of electrodes and a spatial filtering and amplifying means having a weighted sum for performing spatial filtering of the signal transmitted by the electrodes. In the apparatus, the spatial filtering and amplifying means having the weighted sum is constituted by a circuit mounted by electrodes in the housing;
The one surface carrying the electrodes forms a detection surface, and the device is also characterized by means for connecting the housing to power supply means, amplification means and data processing means.

The device according to the invention makes it possible to obtain in real time a signal at the output of the aforementioned housing, the signal being spatially filtered and the spatially filtered signal being, as in known devices, In contrast to being available only for a delayed time at the output of the information processing device, it can be displayed directly on the screen of the cathode ray tube.

The device can be used with a single group of electrodes or two or three electrode groups, depending on the application for which it was designed, each group containing a spectral and spatial filter housed in the aforementioned housing. Associated with the circuit.

In the most preferred case, the number of electrode groups is kept small, so that the size of the housing containing the electrodes and the spectral and spatial filter circuits is kept as small as possible. This is because the sensing surface of the housing must be able to be applied to small surface areas that do not constitute muscle and innervation areas so as not to disturb the detection and measurement.

The other elements of the device (power supply circuit, visible screen, data processing system) are integrated in another small volume housing for easy transport. The data processing system may also be a stand-alone portable computer, which may be connected to a power circuit and a housing containing an oscilloscope or other visual means.

In the device of the present invention, the size of the electrodes and the distance between the electrodes can be determined as a function of the characteristics of the muscle applied. For example, the diameter of the electrode is about 1 to 4 mm, and the distance between the electrodes is about 2.5 times the diameter of the electrode.

The tip of the electrode designed to be applied to the skin is preferably tooth-shaped to improve the contact with the skin, thereby improving the quality of the signal transmitted by the electrode.

According to another characteristic of the invention, the spatially filtered signal is subjected to additional differential amplification, to check that the common mode has been completely eliminated, or to be transmitted by the electrodes. Improving the quality of the resulting signal by more completely eliminating common modes present in certain signals, the common modes being due to the presence of activity that has not been propagated to the area under test.

According to another feature of the invention, means are provided for establishing the position of the electrodes with respect to the area located below the muscle, these means for the validation being provided in real time of the spatially filtered signal. Determining the intermediate or average frequency of these signals, wherein the intermediate or average frequency of the signals of the central group of the electrodes is less than or approximately equal to the intermediate or average frequency of the signals of the adjacent group. Sometimes it is possible to compare them and validate the measurement.

As a result of these properties, the device according to the invention is particularly well suited for clinical tracking of neuromuscular diseases. It is also applicable in the field of muscle monitoring where at least one surface electrode is used, for example in biomechanics, physiology, sports medicine.

In general, the present invention allows for clinical tracking of neuromuscular function in response to short or intermediate duration stimuli experienced by the muscular system, such as fatigue, treatment, retraining, motor impairment, and the like.

[0026]

BEST MODE FOR CARRYING OUT THE INVENTION

Other features and advantages of the present invention will become apparent from the following description with reference to the accompanying drawings. In a non-limiting embodiment of the present invention, a set of electrodes and associated spectral and spatial filtering circuits are included in a small space housing 1, the surface of which is a plate 2 of an electrically insulating material. , On which the tips of the electrodes E designed to be applied to the patient's skin at the level of the muscle area to be studied emerge.

Here, the electrodes E have the number 11 and are arranged in a matrix structure of three rows, each comprising 3, 5, 3 electrodes, whereby three groups L1,
L2, L3, each group comprises a center electrode E1, E2, E3, four electrodes are equidistantly spaced from the center electrode, these four electrodes being perpendicular to each other around the center electrode. 2x2 aligned in the direction, forming a whole cloth.
The central group of electrode L2 has two common electrodes (E2, E1) and (E2, E3), respectively, having two other groups L1, L3, respectively.

The electrode E is shown schematically in perspective in FIG. 1 b and comprises a cylindrical tube 3 connected at one end to a support disk 4, which disk 4 has a detection end And can be seen on the detection surface 2 of the housing 1. The electrodes E are made of any electronically conductive material, for example gold-plated copper or a gold-silver-copper alloy in the proportions of 75%, 20% and 5%, respectively. Gold has good resistance to external media (acids, sweat ...) and good harmlessness to the skin, adding silver or any other electronically conductive metal with the desired mechanical properties More robust. Copper helps the electrical conductivity of the electronic circuit shown schematically in FIG.

The cylindrical tube 3 of the electrode has a diameter of 2 mm, the head 4 has a diameter of 4 mm, and the tube is inserted directly into the electronic circuit. Typically, as a function of the type of muscle studied, the diameter of the electrode head may be varied between about 1 and 4 millimeters, and the distance between the electrodes is comprised between about 2.5 and 10 millimeters. , About 2.5 times the diameter of the electrode.

In the embodiment shown in FIG. 1a, the head of the electrode E has a diameter of 2 millimeters, the distance between the electrodes is 5 millimeters and the dimensions of the detection surface are 3 cm × 2.
cm and the external dimensions of the housing are about 6 cm x 4 cm x 2 cm.

In the variant shown in FIG. 2, the head 4 of the electrode E has an application surface on the skin, which is not flat to improve the quality of contact between the electrode and the skin, but has a “sawtooth” Shape ".

In the housing 1, the electrodes E are supported by a printed circuit plate 1 made for example of fiberglass-epoxy, connected to the amplifier circuit V 1,
1 and V1 are shown side by side in FIG. By means of this printed circuit, each electrode E is connected to the amplifier means 5 by means of a connector K and a high-pass filter 6 which is constructed in a standard manner by means of an RC type circuit. 6 to discharge the polarization effect of the electrodes
A device for Hz filtering is created. Instead, use filtering at about 70-80 Hz (frequency 50 Hz in Europe, 60 Hz in the United States) to minimize the effects of the electrical distribution network, especially when signal propagation alone is a problem, and to remove moving artifacts. Can be removed.

The amplifier means 5 of the set of electrodes E comprises three operational amplifiers 7 of high input impedance, each operational amplifier 7 being transmitted by a group of electrodes L1, L2, L3, respectively, and the electrodes of this group. Are associated with a group of types that are amplified by a weighting factor equal to +4 (or -4) at the center electrode and -1 (or +1) at each of the four surrounding electrodes. These circuits are CMOS-C
Constructed in MS technology or etched in the form of an ASIC, the operational amplifier 7 has a linear gain equal to 100 and a rejection level in a common mode close to 100 dB.

In-situ amplification of the signal transmitted by the electrodes makes it possible to increase the signal / noise ratio, and the signal captured has a low level, typically of the order of 50 μV to 1 mV.

The housing 1 containing the electrodes and circuits described above has three output channels, each transmitting the output signal of an operational amplifier 7, and two output channels for supplying these amplifiers.
It has one input channel and one channel connected to the reference electrical conductor.

The non-magnetic shielding of the housing is obtained by covering the inside of the housing with a copper sheet or the like connected to a reference electrical conductor.

As shown schematically in FIG. 4, the detection housing 1 is connected to a power supply housing 9, which also transmits the output signal from the housing 1 to a separate amplifier stage 10 whose output is an oscilloscope. 11 or other similar means for signal visualization and a device 12 for digital data acquisition and processing. The link is made by a shielded cable of the BNC type. Typically, device 12 may be a microcomputer, such as a PC type, having a video screen for signal visualization.

The device according to the invention is used in the following way. The detection surface of the housing 1 is provided directly on the muscle area to be tested, without adding a contact gel. After the voltage is applied to the device, the spatially filtered signals from the three groups of electrodes are visualized on an oscilloscope screen 11. The visualization of these three signals S1, S2, S3 in the case of biceps isometric action is shown in FIG. 5 and corresponds to the peaks of the curves C1, C2, C3 (measured in milliseconds).
5 shows the propagation of the working potential (measured in mV) of the muscle over time, the peak of which is from the position P1 on the curve C1 (corresponding to the signal S1 of the electrode group L1), Position P on curve C2 corresponding to each of S3
2 to P3 on curve C3. From the displacement and the period, the initial value of the propagation speed of the muscle action potential is deduced.

The recording of the signal for a few seconds makes it possible to obtain a distribution of the velocity of propagation of the detectable muscle working potential involved during the operation. In fatigue studies, this record is extended for as long as necessary.

Since the results obtained are highly dependent on the position and orientation of the electrode group with respect to the muscle fibers, the invention provides a certain number of means making it possible to establish this position and orientation.

In the first stage, real-time visualization of the signal on the oscilloscope screen makes it possible to ensure the approximate position and orientation of the electrode groups on the muscle fibers. For this purpose, the direction of propagation of the operating potential (confirmation of the electrode position with respect to the neuromuscular junction) and the amplification of the operating potential (confirmation of the alignment of the electrodes with respect to the muscle fibers) are established.

In the second stage, a frequency analysis of the spatially filtered signal makes it possible to ascertain the position of the electrodes in order to accept or reject the measurements made at these electrodes.

In practice, the calculation of the speed of propagation of the operating potential often gives very high values, which meanwhile that a common mode due to the presence of unpropagated activity exists in the set of electrodes used. And, on the other hand, was observed to result from non-uniform anisotropy identification of muscle and tissue located between the muscle and the detection surface. Analysis of the change of a certain number of parameters in the surface electromyogram as a function of the position of the electrode can limit the position at which the minimum value of the evaluation of the propagation velocity (average minimum value in all situations of atrophy) was obtained Is shown.

To determine this particular position, the average or intermediate frequency of the signal transmitted by the electrode, or the average or intermediate frequency of the spatially filtered signal, is equivalent to evaluating the speed of propagation, Use the fact that varies as a function of position (the average frequency of the signal is a statistical average of the spectral density of the signal strength, the intermediate frequency separating the surface area of the spectrum into two equal parts) .

The validation process for the positioning of the electrodes, therefore, according to the invention, determines the average or intermediate frequency of the spatially filtered signal from the three groups of electrodes,
When the average or intermediate frequency of the signals of the central group is less than or equal to the average or intermediate frequency of the signals of the two other groups of electrodes, and comparing them to confirm the position. The average frequency of the signals can be calculated from the Fourier transform of these signals. A simple program for real-time spectral analysis makes it possible to compare or reject these frequency values and to confirm or reject them by means of measurements made by the device according to the invention.

Accordingly, the present invention is not limited to the illustrated and illustrated example embodiments. In particular, it is possible to use more than three groups of electrodes in the device according to the invention, or one electrode for the detection of muscle activity, or two groups of electrodes for determining the propagation of muscle working potential.

It is also possible to further distinguish the spatially filtered signal obtained at the output of the detection housing. This further distinction makes it possible to improve the signal quality obtained by a more effective reduction of the common mode and a comparison with the previously obtained signal.

Furthermore, the electrodes are provided so as to comprise nine electrodes, each arranged in a square matrix (similar to the matrix seen in FIG. 1a, in which the center electrode E2 is surrounded by eight other electrodes). Groups may be supplemented. (C. Disse
lhorst-Klug, J.Silny and G.Rau IEEE Transactons and Biomedical Engineer
ing, Volume 44, No. 7, as described in the article published in July 1997)
The weighting factors of the signals from the electrodes are -12 (or +12) for the center electrode, +2 (or -2) for the four electrodes closest to the center electrode, and +1 (or -1) for the other four electrodes.

The invention may also be used in NMR (nuclear magnetic resonance) tunnels to determine the amount of electromyographic parameters, ie changes in electromyographic parameters, velocity of propagation of muscle working potentials or spectral analysis. Correlation with the movement of metabolic parameters such as the concentration of hydrogen ions or ions linked to phosphates (adenosine, di- or triphosphates, inorganic phosphates, phosphocreatine) by NMR spectroscopy. Thus, it is possible to study the effects of metabolic parameters on electromyographic parameters and to deduce from that study correlations with physiological measurements arising from certain diseases such as, for example, muscle fatigue.

As is evident from the use of the invention in the clinical field, this measurement system can be used in place of any system of surface electrodes, whether floating or dry, especially in the field of biomechanics and ergonomics The dimensions of the electrodes and the number of Laplace signals measured are typically employed as a function of the desired use by using one to three groups of electrodes.

[Brief description of the drawings]

FIG. 1 shows the structure of the detection surface of the housing and the formation of the electrodes of a device having three groups of electrodes according to the invention.

FIG. 2 is a diagram illustrating an alternative embodiment of an electrode.

FIG. 3 is a schematic diagram of a potential circuit map of a detection housing.

FIG. 4 is a schematic diagram of a processing sequence of a captured signal.

FIG. 5 is a diagram showing visualization of muscle action potentials obtained by the device according to the present invention.

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Claims (11)

[Claims] 1. An electromyogram having a surface electrode comprising one or more groups of electrodes and spatial filtering and amplifying means having a weighted sum for performing spatial filtering of signals transmitted by the electrodes. In a measuring device, the spatial filtering and amplifying means having the weighted sum comprises a circuit mounted by electrodes in a housing, one surface of which supports the electrodes forms a detection surface, and the device also comprises: An electromyogram measurement apparatus, comprising: a power supply unit; and a unit for connecting the housing to the amplification unit and the data processing unit. 2. Apparatus according to claim 1, comprising visual means, such as an oscilloscope or a video screen, for observing the signal from the output of the housing in real time. 3. The device according to claim 1, wherein the electrodes are compactly arranged in two groups having a common electrode and output a signal which allows the determination of the propagation of the potential of the muscular action. 4. Apparatus according to claim 1, wherein the electrodes are compactly arranged in three or more groups sharing a paired common electrode. 5. The apparatus according to claim 4, further comprising means for differentially amplifying the spatially filtered signal obtained at the output of the housing. 6. The device according to claim 1, wherein the detection housing comprises an internal non-magnetic shield connected to the reference electrode. 7. The spatial filtering circuit in the housing may be about 6 Hz or 70-8.
Apparatus according to any of the preceding claims, having a cutoff frequency approximately equal to 0 Hz. 8. The device according to claim 1, wherein the electrode has a toothed detection end. 9. Apparatus according to claim 1, wherein the circuit of the housing is of the CMOS-CMS or ASIC type. 10. The device according to claim 1, wherein the distance to the electrodes is in the range of about 2.5 to 10 mm, preferably approximately equal to 2.5 times the diameter of the electrodes. 11. When the center frequency or the average frequency of the signals of the electrodes of the central group is less than the center frequency or the average frequency of the signals of the electrodes of the neighboring group
It comprises means for real-time spectral analysis of the spatially filtered signal, which makes it possible to compare between them and to determine the median or average frequency of these signals to validate the measurement Apparatus according to any one of the preceding claims.