WO1999032032A1 - Non-invasive device for electromyographic measurements - Google Patents

Non-invasive device for electromyographic measurements Download PDF

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Publication number
WO1999032032A1
WO1999032032A1 PCT/FR1998/002837 FR9802837W WO9932032A1 WO 1999032032 A1 WO1999032032 A1 WO 1999032032A1 FR 9802837 W FR9802837 W FR 9802837W WO 9932032 A1 WO9932032 A1 WO 9932032A1
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WIPO (PCT)
Prior art keywords
electrodes
signals
housing
groups
amplification
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PCT/FR1998/002837
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French (fr)
Inventor
Jean-Yves Hogrel
Jacques Duchene
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Association Francaise Contre Les Myopathies
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Application filed by Association Francaise Contre Les Myopathies filed Critical Association Francaise Contre Les Myopathies
Priority to EP98962540A priority Critical patent/EP1041928A1/en
Priority to JP2000525030A priority patent/JP2001526074A/en
Priority to CA002312879A priority patent/CA2312879A1/en
Publication of WO1999032032A1 publication Critical patent/WO1999032032A1/en

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    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/24—Detecting, measuring or recording bioelectric or biomagnetic signals of the body or parts thereof
    • A61B5/25—Bioelectric electrodes therefor
    • A61B5/279—Bioelectric electrodes therefor specially adapted for particular uses
    • A61B5/296—Bioelectric electrodes therefor specially adapted for particular uses for electromyography [EMG]
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/24—Detecting, measuring or recording bioelectric or biomagnetic signals of the body or parts thereof
    • A61B5/316—Modalities, i.e. specific diagnostic methods
    • A61B5/389—Electromyography [EMG]

Definitions

  • the invention relates to the non-invasive evaluation of the neuromuscular system of living beings by surface electromyography.
  • the measurement is carried out by receiving signals at the electrodes resulting from a muscular contraction caused either voluntarily, or by mechanical or electrical stimulation.
  • Surface electromyography consists of detecting, record and process the myoelectric signal received, the precursor of the muscle contraction obtained.
  • This technique aims to identify certain neurological or muscular diseases whose physiological characteristics can result in the deviation of certain signal parameters: amplitudes, signal frequencies or propagation velocities of muscular action potentials.
  • certain pathologies are characterized by preferential degenerations of one type of fiber compared to another.
  • Duchenne muscular dystrophy causes selective damage to so-called fast fibers.
  • Such modifications condition the measured average values of speed of propagation of the myoelectric signal.
  • muscle fibers are only activated if the stress is greater than a certain threshold at their neuromuscular junction.
  • the fibers are grouped into functional units, the motor unit which groups together all of the fibers innervated by the same motor neuron.
  • the motor unit action potential is equal to the sum of the elementary muscular action potentials of each of its component fibers.
  • the myoelectric signal received at the electrode results from the spatial and temporal summation of the signals of all the motor units recruited.
  • Signal measurement is affected by the anatomical and functional properties of the muscle studied and by the control patterns of the central or peripheral nervous system.
  • the complexity of the electromyographic signal has given rise to multiple measurement and processing protocols, without any protocol or any attempt at modeling allowing, until now, a reliable and reproducible analysis of the characteristics of the signal allowing an understanding and an identification of the physiological reality of the muscle.
  • Another method is based on an indirect evaluation from spectral parameters, such as the average frequency or the median frequency, supposed to be linearly correlated to the conduction speed.
  • spectral parameters such as the average frequency or the median frequency
  • Such a method is described in the article by Lindstrôm et al. published in the journal Electromyography, vol. 10, pages 341 to 356, 1970 or in the article by Stulen FB and De Luca of the review IEEE Trans. Biomed. Eng. , flight. 28, pages 515 to 523, 1981.
  • Experimental studies have shown the limits of this type of relationship, the spectral parameters being dependent on several factors other than the speed of propagation of the muscular action potential.
  • the anisotropy of the muscle and tissue properties located between the signal source and the detection zone leads to variations in the spectral content of the signal and in the estimation of the conduction speed.
  • the electrodes are arranged in groups for each of which the signals transmitted by the electrodes are, after amplification, combined by weighted summation into a single signal, equivalent to the signal supplied by a spatial filter whose characteristics are determined by the factors of weighting of the electrode signals and by the geometric distribution of the electrodes in the group. It has been shown that one of the most interesting arrangements consists in forming groups of five electrodes arranged in a cross with a central electrode and four peripheral electrodes and in applying to the electrode signals a weighting factor equal to 4 (or - 4). for the central electrode and at - 1 (or at + 1) for each peripheral electrode, which corresponds to a double spatial differentiation of the surface distribution of potential in two orthogonal directions, i.e.
  • the number of "Laplacian" groups of electrodes is relatively high, for example 16 or more, or even 64, and the neighboring groups have electrodes in common to reduce the total number electrodes and size.
  • the signals picked up by the electrodes are preamplified, applied to a bandpass filter, then amplified and digitized to be recorded in an information processing system equipped with software performing high-pass filtering, spatial filtering of the type indicated above and an evaluation of the resulting signals. It has also been proposed to use in these systems larger groups of electrodes, comprising for example 9 electrodes arranged in a square matrix, in order to perform isotropic spatial filtering which is more efficient in terms of the spatial resolution of the detection.
  • the large number of electrodes (32 in some systems, 128 in others) is, on the one hand, an advantage because it allows all of the electrodes to be placed on a muscular zone without seeking great precision , and then to select, by examining the spatially filtered signals, the electrode groups best placed with respect to the motor units examined.
  • This large number of electrodes is also a drawback because of the surface occupied by all of the electrodes and the large number of amplifiers and high-pass or band-pass filters associated with the electrodes.
  • the computer processing of the signals from the electrodes does not make it possible to have directly exploitable signals in real time and, in general, all the means of acquisition and processing of the signals are complex and can only be used by experienced specialists. Another consequence of this complexity is that, if these systems are of certain interest as as apparatus laboratory or research tools, they are not at all suited to routine use in hospitals.
  • the object of the invention is in particular to overcome this drawback by proposing a non-invasive system of electromyographic measurements, which makes it possible to have information of a quality comparable to that which can be obtained with the aforementioned multielectrode systems, and which is simple and compact enough to be portable and usable by medical personnel who are not very specialized but of course trained in this technique, for example in a hospital environment for monitoring pathologies or the effects of a therapeutic treatment.
  • the electromyographic measurement device with surface electrodes comprises at least one group of electrodes and means of spectral filtering and amplification with weighted summation carrying out spatial filtering of the signals transmitted by the electrodes, and is characterized in that that the aforementioned means of spectral filtering and amplification with weighted summation consist of circuits mounted with the electrodes in a housing of which one face carrying the electrodes forms a detection face, the device also comprising means for connecting this housing to supply means, amplification means and data processing means.
  • the device according to the invention makes it possible to obtain in real time, at the output of the aforementioned box, signals which have been spatially filtered on site and which are directly exploitable, for example by viewing on a cathodic screen, unlike known multielectrode systems in which the spatially filtered signals are only available in deferred time at the output of the computer processing means.
  • This device can comprise, depending on the applications for which it is intended, a single group of electrodes, or two or three groups of electrodes, or more, each group being associated with spectral filtering and spatial filtering circuits contained in the housing. cited above.
  • the number of groups of electrodes remains small, so that the dimensions of the housing containing the electrodes and the associated spectral filtering and spatial filtering circuits remain as small as possible so that the detection face of this housing can be applied to a muscular area of reduced surface, not comprising tendon and innervation regions liable to disturb detection and measurement.
  • the other elements of the device can be integrated in another case having dimensions sufficiently small to be easily transportable.
  • the data processing system may be an independent portable microcomputer connectable to a box containing the supply circuits and an oscilloscope or other similar means for viewing the spatially filtered signals.
  • the dimensions of the electrodes and the distances between electrodes are advantageously determined as a function of the characteristics of the muscle to which they will be applied, the diameters of the electrodes varying between 1 and 4 mm approximately, the distance between electrodes being preferably substantially equal to 2.5 times the diameter of an electrode.
  • the ends of the electrodes intended to be applied to the skin are preferably sawtooth, in order to improve the quality of the contact with the skin and therefore the quality of the signals transmitted by the electrodes.
  • the spatially filtered signals are themselves subjected to an additional differential amplification, making it possible to improve the quality of the resulting signals, either by verifying that the common mode has been completely eliminated, or by eliminating more completely the common mode present in the signals transmitted by the electrodes and due to the presence of non-propagated activities in the zone examined.
  • means are provided for validating the location of the electrodes relative to an underlying muscular zone, these validation means comprising means for spectral analysis in real time of the spatially filtered signals, making it possible to determine the median frequencies or the average frequencies of these signals and compare them with each other to validate a measurement when the median frequency or the average frequency of the signal of a central group of electrodes is less than or substantially equal to the median frequencies or the average frequencies of the signals of the neighboring groups, respectively. Thanks to these characteristics, the device according to the invention is particularly well suited to the clinical monitoring of neuromuscular pathologies. It also applies to any area of muscle monitoring in which at least one surface electrode is used, for example in biomechanics, physiology and sports medicine.
  • the invention allows clinical monitoring of neuromuscular function in response to short- or medium-term stresses to which the muscular system may be subject, for example fatigue, treatment, rehabilitation, hypokinesia.
  • FIGS. 1a and 1b respectively represent the configuration of the detection face of a housing and the shape of the electrodes of the device according to the invention in an exemplary embodiment with three groups of electrodes;
  • FIG. 2 represents an alternative embodiment of an electrode,
  • FIG. 3 diagrammatically represents an electronic circuit board of the detection unit,
  • FIG. 4 diagrammatically represents the processing chain for the captured signals,
  • Figure 5 shows a visualization of muscle action potentials obtained using the device according to the invention.
  • a set of electrodes and associated circuits for spectral filtering and spatial filtering is contained in a housing 1 of small dimensions, one face of which comprises a plate 2 of electrically insulating material on which appear from the ends of the electrodes E intended to be applied to the skin of a patient at the level of a muscular zone to be studied.
  • the electrodes E are here eleven in number and are arranged in a matrix configuration in three rows comprising respectively three, five and three electrodes to form three groups L1, L2 and L3, each group comprising a central electrode E1, E2, E3 respectively and four electrodes located equidistant from the central electrode, these four electrodes being aligned two by two with the central electrode in perpendicular directions, the assembly forming a cross.
  • the central group of electrodes L2 has two electrodes in common, respectively (E2, El), and (E2, E3), with each of the other two groups L1 and L3.
  • An electrode E is shown diagrammatically in perspective in FIG. 1b, and comprises a cylindrical tube 3 connected to a support disc 4 at one end, this disc 4 being the detection end and appearing on the detection face 2 of the housing 1.
  • L electrode E can be made of any electroconductive material and for example of gilded copper or in a gold-silver alloy -copper in the following respective proportions: 75%, 20% and 5%.
  • Gold has excellent resistance to external agents (acidity, sweat, ...) and excellent safety compared to the skin and is stiffened by the addition of silver or any other electroconductive metal having the desired mechanical properties. Copper facilitates electrical transmission with the electronic circuit shown schematically in Figure 3.
  • the cylindrical tube 3 of the electrode may have a diameter of 2 millimeters and the head 4 a diameter of 4 millimeters, the tube coming to be inserted directly into the electronic circuit.
  • the diameter of the electrode heads can vary between approximately 1 and 4 millimeters, the distance between electrodes being between 2.5 and 10 millimeters approximately and preferably being substantially equal to 2.5 times the diameter of the electrode.
  • the heads of the electrodes E have a diameter of 2 millimeters, the distance between the electrodes is 5 millimeters, the dimensions of the detection surface 2 are 3 cm ⁇ 2 cm, and the external dimensions of the housing 1 are approximately 6 cm x 4 cm x 2 cm.
  • the head 4 of the electrode E has an application face on the skin which is not flat, but in "sawtooth" shape, in order to improve the quality of the contact between the electrode and the skin.
  • the electrodes E are carried by a printed circuit board RI, for example made of glass fibers - epoxy coming to connect to an amplification circuit VI, the plate RI and the circuit VI being shown side by side in FIG. 3.
  • a printed circuit board RI for example made of glass fibers - epoxy coming to connect to an amplification circuit VI, the plate RI and the circuit VI being shown side by side in FIG. 3.
  • each electrode E is connected to amplification means 5 via a connector K and a high-pass filter 6 conventionally constituted by a circuit of the type RC. Filtering at 6 Hz is provided, to overcome the effects of polarization of the electrodes.
  • the amplification means 5 comprise, for all of the electrodes E, three operational amplifiers 7 with high input impedance, each operational amplifier 7 being associated with a group L1, L2 or L3 respectively of electrodes so that the signals transmitted by the electrodes of this group are amplified with a weighting factor which is equal to + 4 (or - 4) for the central electrode and - 1 (or + 1) for each of the four peripheral electrodes.
  • These circuits are made in CMOS-CMS technology or etched in the form of ASIC and the operational amplifiers 7 have a linear gain equal to 100 and a common mode rejection rate close to 100 dB.
  • the on-site amplification of the signals transmitted by the electrodes makes it possible to increase the signal / noise ratio, the signals picked up having a low level, typically of the order of 50 ⁇ V at 1 rav.
  • the housing 1 containing the aforementioned electrodes and circuits has three output channels including each transmits the output signal from an operational amplifier 7, two input channels for supplying these amplifiers and one channel connected to a reference electrical conductor.
  • a non-magnetic shielding of the housing is obtained by coating the internal faces of the housing with a copper foil or the like, connected to the reference electrical conductor.
  • the detection unit 1 is connected to a power supply unit 9 which further transmits the output signals from the unit 1 to an isolated amplifier stage 10 whose output is connected to an oscilloscope 11 or other analog signal display means, and to a device 12 for acquiring and processing digital data.
  • the connections are made using shielded cables of the BNC type.
  • the device 12 can be a microcomputer of the PC type or the like with a video screen for viewing the signals.
  • the device according to the invention is used in the following way:
  • the detection face of the housing 1 is applied directly to the skin, without the addition of contact gel, in a muscle area to be examined.
  • the spatially filtered signals of the three groups of electrodes are displayed on the screen of the oscilloscope 11. A visualization of these three signals S1, S2 and S3 is shown in FIG.
  • a recording of the signals for a period of a few seconds makes it possible to obtain a distribution of the speeds of propagation of the detectable muscular action potentials brought into play during the effort.
  • the recording is extended over a necessarily longer period.
  • the invention has provided a certain number of means making it possible to verify this location and this orientation.
  • the real-time visualization of the signals on the oscilloscope screen makes it possible to verify an approximate location and the orientation of the groups of electrodes on the muscle fibers. For this, we check the direction of propagation of the action potentials (validation of the location of the electrodes in relation to the neuromuscular junctions) and the amplitude of the action potentials (validation of the alignment of the electrodes according to the muscle fibers).
  • a frequency analysis of the spatially filtered signals makes it possible to validate the location of the electrodes, to accept or reject the measurements made with these electrodes.
  • the average or median frequencies of the signals transmitted by the electrodes or those of the spatially filtered signals vary according to the location of the electrodes, in the same direction as the estimates of the propagation speeds (the mean frequency of the signal being the statistical mean of the spectral power density of the signal, its median frequency being that which divides the surface of the spectrum into two equal parts).
  • the method for validating the location of the electrodes therefore consists, according to the invention, in determining the average or median frequencies of the spatially filtered signals of the three groups of electrodes, to compare them and to validate the localization when the average or median frequency of the signal of the central group is lower or equal to the average or median frequencies of the signals of the two other groups of electrodes.
  • the average frequencies of the signals can be calculated from the Fourier transforms of these signals.
  • the invention is not limited to the exemplary embodiments which have been described and shown. It is in particular possible to use more than three groups of electrodes in the device according to the invention, or else a single group of electrodes for the detection of muscular activity, or two groups of electrodes for the determination of propagation of muscle action potentials.
  • the groups of electrodes can be supplemented to each comprise nine electrodes with a square matrix arrangement (analogous to that which can be seen in FIG. 1a as regards the central electrode E2, surrounded by eight other electrodes).
  • the weighting coefficients of the electrode signals can then be - 12 (or + 12) for a central electrode, + 2 (or - 2) for the four electrodes closest to the central electrode, and + 1 (or - 1) for the other four electrodes (as described in the article published in "IEEE Transactions and Biomedical Engineering", Vol. 44, No. 7, July 1997, by C. Disselhorst-Klug, J. Silny and G. Rau).
  • the invention can also be used in an NMR (Nuclear Magnetic Resonance) type tunnel in order to quantify the parameters of the electromyography: the variation of the electromyographic parameters, speed of propagation or spectral analysis of the muscle action potential, is then correlated. to the kinetics of metabolic parameters, such as the concentration of hydrogen ions or of phosphate-bound ions (adenosine di or tri-phosphate, inorganic phosphate, phosphocreatine, ...), provided by NMR spectroscopy. It is thus possible to study the influence of metabolic parameters on electromyographic parameters, and to deduce correlations with physiological measurements relating to certain pathologies, for example during muscle fatigue.
  • NMR Nuclear Magnetic Resonance
  • this measurement system can be used in place of any system of surface electrodes, whether they are floating or dry, in particular in the fields of biomechanics and ergonomics, the dimensions of the electrodes and the number of Laplacian signals measured then being adapted as a function of the desired use, generally using one to three groups of electrodes.

Abstract

The invention concerns a device for electromyographic measurements with surface electrodes, comprising at least a group of electrodes (E) and spectral filtering means and weighted summation amplifying means producing a spatial filtering of signals transmitted by the electrodes. The invention is characterised in that said spectral filtering and weighted summation amplifying means consist of circuits (6, 5) mounted with the electrodes (E) in a housing (1) whereof one surface bearing the electrodes (E) forms a sensing surface (2), the device further comprising means for connecting said housing to powering means (9), amplifying means (10) and data processing means (12).

Description

Dispositif non invasif de mesures électromyographiques Non-invasive device for electromyographic measurements
L'invention concerne l'évaluation non invasive du système neuromusculaire des êtres vivants par électromyographie de surface.The invention relates to the non-invasive evaluation of the neuromuscular system of living beings by surface electromyography.
Actuellement, les seuls systèmes électromyographiques de détection reconnus pour l'évaluation clinique des pathologies neurologiques ou neuromusculaires sont de type invasif et sont mis en oeuvre à l'aide d'aiguilles détectrices qui pénètrent au sein du muscle étudié. Outre la douleur, le traumatisme et le risque d'infection qui résultent de ce type d'intervention, les systèmes invasifs présentent 1 ' inconvénient de ne permettre que des mesures ponctuelles très sélectives, sans possibilité de réelle évaluation d'une zone musculaire donnée. Il est par ailleurs impossible de faire le suivi clinique d'une pathologie avec ces systèmes. Pour éviter ces inconvénients et permettre une mesure suffisamment précise sur une étendue plus large, il s'est développé des techniques non invasives d ' électromyographie de surface utilisant des électrodes dites flottantes, qui nécessitent un gel de contact, ou des électrodes dites sèches. Ces électrodes de surface nécessitent habituellement une préparation de la surface de la peau (rasage, légère abrasion et dégraissage) .Currently, the only electromyographic detection systems recognized for the clinical evaluation of neurological or neuromuscular pathologies are of the invasive type and are implemented using detecting needles which penetrate the studied muscle. In addition to the pain, trauma and risk of infection that result from this type of intervention, invasive systems have the drawback of allowing only very selective punctual measurements, without the possibility of real evaluation of a given muscle area. It is also impossible to follow a pathology clinically with these systems. To avoid these drawbacks and allow a sufficiently precise measurement over a wider area, non-invasive surface electromyography techniques have been developed using so-called floating electrodes, which require a contact gel, or so-called dry electrodes. These surface electrodes usually require preparation of the skin surface (shaving, light abrasion and degreasing).
La mesure est effectuée par réception au niveau des électrodes de signaux résultant d'une contraction musculaire provoquée soit volontairement, soit par stimulation mécanique ou électrique. L' électromyographie de surface consiste à détecter, enregistrer et traiter le signal myoélectrique reçu, précurseur de la contraction musculaire obtenue.The measurement is carried out by receiving signals at the electrodes resulting from a muscular contraction caused either voluntarily, or by mechanical or electrical stimulation. Surface electromyography consists of detecting, record and process the myoelectric signal received, the precursor of the muscle contraction obtained.
Cette technique vise à identifier certaines maladies neurologiques ou musculaires dont les caractéristiques physiologiques peuvent se traduire par la déviation de certains paramètres du signal : amplitudes, fréquences du signal ou vitesses de propagation des potentiels d'action musculaires. Ainsi, certaines pathologies sont caractérisées par des dégénérescences préférentielles d'un type de fibre par rapport à un autre. Par exemple, la myopathie de Duchenne entraîne une atteinte sélective des fibres dites rapides. De telles modifications conditionnent les valeurs moyennes mesurées de vitesse de propagation du signal myoélectrique.This technique aims to identify certain neurological or muscular diseases whose physiological characteristics can result in the deviation of certain signal parameters: amplitudes, signal frequencies or propagation velocities of muscular action potentials. Thus, certain pathologies are characterized by preferential degenerations of one type of fiber compared to another. For example, Duchenne muscular dystrophy causes selective damage to so-called fast fibers. Such modifications condition the measured average values of speed of propagation of the myoelectric signal.
De façon générale, les fibres musculaires ne sont activées que si la sollicitation est supérieure à un certain seuil au niveau de leur jonction neuromusculaire. Les fibres sont regroupées en unités fonctionnelles, l'unité motrice qui regroupe l'ensemble des fibres innervées par le même neurone moteur. Le potentiel d'action d'unité motrice est égal à la somme des potentiels d'action musculaires élémentaires de chacune des fibres qui la composent. Le signal myoélectrique reçu au niveau de l'électrode résulte de la sommation spatiale et temporelle des signaux de toutes les unités motrices recrutées. La mesure du signal est affectée par les propriétés anatomiques et fonctionnelles du muscle étudié et par les schémas de contrôle du système nerveux central ou périphérique. De plus, lors de la mesure, il y a superposition des signaux électriques des unités motrices activées. La complexité du signal électromyographique a donné naissance à de multiples protocoles de mesure et de traitement, sans qu'aucun protocole ni aucune tentative de modélisation ne permettent, jusqu'à présent, une analyse fiable et reproductible des caractéristiques du signal permettant une compréhension et une identification de la réalité physiologique du muscle.Generally, muscle fibers are only activated if the stress is greater than a certain threshold at their neuromuscular junction. The fibers are grouped into functional units, the motor unit which groups together all of the fibers innervated by the same motor neuron. The motor unit action potential is equal to the sum of the elementary muscular action potentials of each of its component fibers. The myoelectric signal received at the electrode results from the spatial and temporal summation of the signals of all the motor units recruited. Signal measurement is affected by the anatomical and functional properties of the muscle studied and by the control patterns of the central or peripheral nervous system. In addition, during the measurement, there is a superposition of electrical signals from the activated motor units. The complexity of the electromyographic signal has given rise to multiple measurement and processing protocols, without any protocol or any attempt at modeling allowing, until now, a reliable and reproducible analysis of the characteristics of the signal allowing an understanding and an identification of the physiological reality of the muscle.
Il est connu de mesurer la vitesse de conduction du potentiel d'action musculaire par mesure du temps de propagation de ce potentiel à l'aide d'au moins trois électrodes de mesure. Cette méthode conduit généralement à une surestimation difficilement quantifiable de la vitesse de conduction, qui peut s'expliquer en partie par la présence d'activités non propagées sur toute la zone couverte par le système d'électrodes.It is known to measure the conduction speed of the muscular action potential by measuring the propagation time of this potential using at least three measurement electrodes. This method generally leads to an overestimation of the conduction speed which is difficult to quantify, which can be explained in part by the presence of non-propagated activities over the entire area covered by the electrode system.
Une autre méthode est basée sur une évaluation indirecte à partir de paramètres spectraux, tels que la fréquence moyenne ou la fréquence médiane, supposés être linéairement corrélés à la vitesse de conduction. Une telle méthode est décrite dans l'article de Lindstrôm et al. paru dans la revue Electromyography, vol. 10, pages 341 à 356, 1970 ou dans l'article de Stulen F.B. et De Luca de la revue IEEE Trans. Biomed. Eng . , vol. 28, pages 515 à 523, 1981. Des études expérimentales ont montré les limites de ce type de relation, les paramètres spectraux étant dépendants de plusieurs facteurs autres que la vitesse de propagation du potentiel d'action musculaire. L ' anisotropie des propriétés musculaires et des tissus localisés entre la source du signal et la zone de détection conduit à des variations dans le contenu spectral du signal et dans l'estimation de la vitesse de conduction. Afin d'améliorer la mesure du signal, il a été proposé, par exemple dans le document de H. Reucher et al, paru dans le journal IEEE Trans . Biomed. Eng. , vol. 34, pages 98 à 113, 1987, de réaliser un filtrage spatial à l'aide d'un système multiélectrodes et d'une sommation pondérée des signaux qui sont transmis par les électrodes.Another method is based on an indirect evaluation from spectral parameters, such as the average frequency or the median frequency, supposed to be linearly correlated to the conduction speed. Such a method is described in the article by Lindstrôm et al. published in the journal Electromyography, vol. 10, pages 341 to 356, 1970 or in the article by Stulen FB and De Luca of the review IEEE Trans. Biomed. Eng. , flight. 28, pages 515 to 523, 1981. Experimental studies have shown the limits of this type of relationship, the spectral parameters being dependent on several factors other than the speed of propagation of the muscular action potential. The anisotropy of the muscle and tissue properties located between the signal source and the detection zone leads to variations in the spectral content of the signal and in the estimation of the conduction speed. In order to improve the measurement of the signal, it has been proposed, for example in the document by H. Reucher et al, which appeared in the journal IEEE Trans. Biomed. Eng. , flight. 34, pages 98 to 113, 1987, to perform spatial filtering using a multielectrode system and a weighted summation of the signals which are transmitted by the electrodes.
Dans ce système, les électrodes sont disposées en groupes pour chacun desquels les signaux transmis par les électrodes sont, après amplification, combinés par sommation pondérée en un signal unique, équivalent au signal fourni par un filtre spatial dont les caractéristiques sont déterminées par les facteurs de pondération des signaux des électrodes et par la répartition géométrique des électrodes dans le groupe. Il a été montré qu'une des dispositions les plus intéressantes consiste à former des groupes de cinq électrodes agencées en croix avec une électrode centrale et quatre électrodes périphériques et à appliquer aux signaux des électrodes un facteur de pondération égal à 4 (ou - 4) pour l'électrode centrale et à - 1 (ou à + 1) pour chaque électrode périphérique, ce qui correspond à une double différentiation spatiale de la distribution superficielle de potentiel dans deux directions orthogonales, c'est-à-dire à la fonction de transfert d'un filtre de Laplace bidimensionnel . On améliore ainsi, en particulier, la résolution spatiale de la détection. Dans les systèmes connus de ce type, le nombre de groupes "laplaciens" d'électrodes est relativement élevé, par exemple de 16 ou davantage, voire même de 64, et les groupes voisins ont des électrodes en commun pour réduire le nombre total d'électrodes et l'encombrement. Les signaux captés par les électrodes sont préamplifiés, appliqués à un filtre passe-bande, puis amplifiés et numérisés pour être enregistrés dans un système de traitement de l'information équipé d'un logiciel réalisant un filtrage passe-haut, un filtrage spatial du type indiqué ci -dessus et une évaluation des signaux résultants. Il a également été proposé d'utiliser dans ces systèmes des groupes plus importants d'électrodes, comprenant par exemple 9 électrodes agencées en une matrice carrée, pour réaliser un filtrage spatial isotropique plus performant au niveau de la résolution spatiale de la détection.In this system, the electrodes are arranged in groups for each of which the signals transmitted by the electrodes are, after amplification, combined by weighted summation into a single signal, equivalent to the signal supplied by a spatial filter whose characteristics are determined by the factors of weighting of the electrode signals and by the geometric distribution of the electrodes in the group. It has been shown that one of the most interesting arrangements consists in forming groups of five electrodes arranged in a cross with a central electrode and four peripheral electrodes and in applying to the electrode signals a weighting factor equal to 4 (or - 4). for the central electrode and at - 1 (or at + 1) for each peripheral electrode, which corresponds to a double spatial differentiation of the surface distribution of potential in two orthogonal directions, i.e. to the function of transfer of a two-dimensional Laplace filter. This improves, in particular, the spatial resolution of the detection. In known systems of this type, the number of "Laplacian" groups of electrodes is relatively high, for example 16 or more, or even 64, and the neighboring groups have electrodes in common to reduce the total number electrodes and size. The signals picked up by the electrodes are preamplified, applied to a bandpass filter, then amplified and digitized to be recorded in an information processing system equipped with software performing high-pass filtering, spatial filtering of the type indicated above and an evaluation of the resulting signals. It has also been proposed to use in these systems larger groups of electrodes, comprising for example 9 electrodes arranged in a square matrix, in order to perform isotropic spatial filtering which is more efficient in terms of the spatial resolution of the detection.
Dans ces systèmes, le grand nombre d'électrodes (32 dans certains systèmes, 128 dans d'autres) est, d'une part, un avantage car il permet de poser l'ensemble des électrodes sur une zone musculaire sans rechercher une grande précision, et de sélectionner ensuite, par examen des signaux filtrés spatialement, les groupes d'électrodes les mieux placés par rapport aux unités motrices examinées. Ce grand nombre d'électrodes est d'autre part un inconvénient en raison de la surface occupée par l'ensemble des électrodes et du nombre important d'amplificateurs et de filtres passe-haut ou passe- bande associés aux électrodes. En outre, le traitement informatique des signaux des électrodes ne permet pas de disposer en temps réel de signaux directement exploitables et, de façon générale, l'ensemble des moyens d'acquisition et de traitement des signaux est complexe et ne peut être utilisé que par des spécialistes confirmés. Une autre conséquence de cette complexité est que, si ces systèmes présentent un intérêt certain en tant qu'appareils de laboratoire ou outils de recherche, ils ne sont pas du tout adaptés à un ' usage de routine en milieu hospitalier.In these systems, the large number of electrodes (32 in some systems, 128 in others) is, on the one hand, an advantage because it allows all of the electrodes to be placed on a muscular zone without seeking great precision , and then to select, by examining the spatially filtered signals, the electrode groups best placed with respect to the motor units examined. This large number of electrodes is also a drawback because of the surface occupied by all of the electrodes and the large number of amplifiers and high-pass or band-pass filters associated with the electrodes. Furthermore, the computer processing of the signals from the electrodes does not make it possible to have directly exploitable signals in real time and, in general, all the means of acquisition and processing of the signals are complex and can only be used by experienced specialists. Another consequence of this complexity is that, if these systems are of certain interest as as apparatus laboratory or research tools, they are not at all suited to routine use in hospitals.
L'invention a notamment pour but de pallier cet inconvénient en proposant un système non invasif de mesures électromyographiques, qui permet de disposer d'informations d'une qualité comparable à celle que l'on peut obtenir avec les systèmes multiélectrodes précités, et qui est suffisamment simple et compact pour être portable et utilisable par du personnel médical peu spécialisé mais bien entendu formé à cette technique, par exemple en milieu hospitalier pour le suivi de pathologies ou des effets d'un traitement thérapeutique. Le dispositif de mesures électromyographiques à électrodes superficielles selon l'invention, comprend au moins un groupe d'électrodes et des moyens de filtrage spectral et d'amplification à sommation pondérée réalisant un filtrage spatial des signaux transmis par les électrodes, et est caractérisé en ce que les moyens précités de filtrage spectral et d'amplification à sommation pondérée sont constitués par des circuits montés avec les électrodes dans un boîtier dont une face portant les électrodes forme une face de détection, le dispositif comprenant également des moyens de connexion de ce boîtier à des moyens d'alimentation, des moyens d'amplification et des moyens de traitement de données. Le dispositif selon l'invention permet d'obtenir en temps réel, en sortie du boîtier précité, des signaux qui ont été filtrés spatialement sur site et qui sont directement exploitables, par exemple par visualisation sur un écran cathodique, au contraire des systèmes multielectrodes connus dans lesquels les signaux filtrés spatialement ne sont disponibles qu'en temps différé en sortie des moyens de traitement informatique.The object of the invention is in particular to overcome this drawback by proposing a non-invasive system of electromyographic measurements, which makes it possible to have information of a quality comparable to that which can be obtained with the aforementioned multielectrode systems, and which is simple and compact enough to be portable and usable by medical personnel who are not very specialized but of course trained in this technique, for example in a hospital environment for monitoring pathologies or the effects of a therapeutic treatment. The electromyographic measurement device with surface electrodes according to the invention comprises at least one group of electrodes and means of spectral filtering and amplification with weighted summation carrying out spatial filtering of the signals transmitted by the electrodes, and is characterized in that that the aforementioned means of spectral filtering and amplification with weighted summation consist of circuits mounted with the electrodes in a housing of which one face carrying the electrodes forms a detection face, the device also comprising means for connecting this housing to supply means, amplification means and data processing means. The device according to the invention makes it possible to obtain in real time, at the output of the aforementioned box, signals which have been spatially filtered on site and which are directly exploitable, for example by viewing on a cathodic screen, unlike known multielectrode systems in which the spatially filtered signals are only available in deferred time at the output of the computer processing means.
Ce dispositif peut comprendre, selon les applications auxquelles il est destiné, un seul groupe d'électrodes, ou deux ou trois groupes d'électrodes, ou davantage, chaque groupe étant associé à des circuits de filtrage spectral et de filtrage spatial contenus dans le boîtier précité.This device can comprise, depending on the applications for which it is intended, a single group of electrodes, or two or three groups of electrodes, or more, each group being associated with spectral filtering and spatial filtering circuits contained in the housing. cited above.
Il est préférable, dans la plupart des cas, que le nombre de groupes d'électrodes reste peu élevé, de façon que les dimensions du boîtier contenant les électrodes et les circuits associés de filtrage spectral et de filtrage spatial restent aussi faibles que possible pour que la face de détection de ce boîtier puisse être appliquée sur une zone musculaire de surface réduite, ne comprenant pas de régions tendineuses et d'innervation susceptibles de perturber la détection et la mesure.It is preferable, in most cases, that the number of groups of electrodes remains small, so that the dimensions of the housing containing the electrodes and the associated spectral filtering and spatial filtering circuits remain as small as possible so that the detection face of this housing can be applied to a muscular area of reduced surface, not comprising tendon and innervation regions liable to disturb detection and measurement.
Les autres éléments du dispositif (circuit d'alimentation, écran de visualisation, système de traitement de données) peuvent être intégrés dans un autre boîtier ayant des dimensions suffisamment réduites pour être aisément transportable. Eventuellement, le système de traitement de données peut être un micro-ordinateur portable indépendant et connectable à un boîtier contenant les circuits d'alimentation et un oscilloscope ou autre moyen analogue de visualisation des signaux filtrés spatialement . Dans le dispositif selon l'invention, les dimensions des électrodes et les distances entre électrodes sont avantageusement déterminées en fonction des caractéristiques du muscle sur lequel elles seront appliquées, les diamètres des électrodes variant entre 1 et 4 mm environ, la distance entre électrodes étant de préférence sensiblement égale à 2,5 fois le diamètre d'une électrode . Les extrémités des électrodes destinées à être appliquées sur la peau sont de préférence en dents de scie, pour améliorer la qualité du contact avec la peau et donc la qualité des signaux transmis par les électrodes. Selon une autre caractéristique de l'invention, les signaux filtrés spatialement sont eux-mêmes soumis à une amplification différentielle supplémentaire, permettant d'améliorer la qualité des signaux résultants, soit en vérifiant que le mode commun a été complètement éliminé, soit en- éliminant plus complètement le mode commun présent dans les signaux transmis par les électrodes et dû à la présence d'activités non propagées dans la zone examinée . Selon une autre caractéristique de l'invention, des moyens sont prévus pour valider la localisation des électrodes par rapport à une zone musculaire sous-jacente, ces moyens de validation comprenant des moyens d'analyse spectrale en temps réel des signaux filtrés spatialement, permettant de déterminer les fréquences médianes ou les fréquences moyennes de ces signaux et de les comparer entre elles pour valider une mesure quand la fréquence médiane ou la fréquence moyenne du signal d'un groupe central d'électrodes est inférieure ou sensiblement égale aux fréquences médianes ou aux fréquences moyennes respectivement des signaux des groupes voisins. Grâce à ces caractéristiques, le dispositif selon l'invention est particulièrement bien adapté au suivi clinique des pathologies neuromusculaires. Il s'applique également à tout domaine de suivi musculaire dans lequel on utilise au moins une électrode de surface, par exemple en biomécanique, en physiologie et en médecine sportive.The other elements of the device (power supply circuit, display screen, data processing system) can be integrated in another case having dimensions sufficiently small to be easily transportable. Optionally, the data processing system may be an independent portable microcomputer connectable to a box containing the supply circuits and an oscilloscope or other similar means for viewing the spatially filtered signals. In the device according to the invention, the dimensions of the electrodes and the distances between electrodes are advantageously determined as a function of the characteristics of the muscle to which they will be applied, the diameters of the electrodes varying between 1 and 4 mm approximately, the distance between electrodes being preferably substantially equal to 2.5 times the diameter of an electrode. The ends of the electrodes intended to be applied to the skin are preferably sawtooth, in order to improve the quality of the contact with the skin and therefore the quality of the signals transmitted by the electrodes. According to another characteristic of the invention, the spatially filtered signals are themselves subjected to an additional differential amplification, making it possible to improve the quality of the resulting signals, either by verifying that the common mode has been completely eliminated, or by eliminating more completely the common mode present in the signals transmitted by the electrodes and due to the presence of non-propagated activities in the zone examined. According to another characteristic of the invention, means are provided for validating the location of the electrodes relative to an underlying muscular zone, these validation means comprising means for spectral analysis in real time of the spatially filtered signals, making it possible to determine the median frequencies or the average frequencies of these signals and compare them with each other to validate a measurement when the median frequency or the average frequency of the signal of a central group of electrodes is less than or substantially equal to the median frequencies or the average frequencies of the signals of the neighboring groups, respectively. Thanks to these characteristics, the device according to the invention is particularly well suited to the clinical monitoring of neuromuscular pathologies. It also applies to any area of muscle monitoring in which at least one surface electrode is used, for example in biomechanics, physiology and sports medicine.
De façon générale, l'invention permet le suivi clinique de la fonction neuromusculaire en réponse à des sollicitations à court ou moyen terme dont le système musculaire peut être l'objet, par exemple fatigue, traitement, rééducation, hypokinésie.In general, the invention allows clinical monitoring of neuromuscular function in response to short- or medium-term stresses to which the muscular system may be subject, for example fatigue, treatment, rehabilitation, hypokinesia.
D'autres caractéristiques et avantages de l'invention apparaîtront à la lecture de la description qui suit faite en référence aux dessins annexés dans lesquels : les figures la et lb représentent respectivement la configuration de la face de détection d'un boîtier et la forme des électrodes du dispositif selon l'invention dans un exemple de réalisation à trois groupes d'électrodes ; la figure 2 représente une variante de réalisation d'une électrode, la figure 3 représente schématiquement une carte de circuits électroniques du boîtier de détection, la figure 4 représente schématiquement la chaîne de traitement des signaux captés, - la figure 5 représente une visualisation de potentiels d'action musculaires obtenue à l'aide du dispositif selon l'invention.Other characteristics and advantages of the invention will appear on reading the following description made with reference to the appended drawings in which: FIGS. 1a and 1b respectively represent the configuration of the detection face of a housing and the shape of the electrodes of the device according to the invention in an exemplary embodiment with three groups of electrodes; FIG. 2 represents an alternative embodiment of an electrode, FIG. 3 diagrammatically represents an electronic circuit board of the detection unit, FIG. 4 diagrammatically represents the processing chain for the captured signals, - Figure 5 shows a visualization of muscle action potentials obtained using the device according to the invention.
Dans un exemple non limitatif de réalisation de l'invention, un ensemble d'électrodes et de circuits associés de filtrage spectral et de filtrage spatial est contenu dans un boîtier 1 de faibles dimensions dont une face comporte une plaque 2 de matière électriquement isolante sur laquelle apparaissent des extrémités des électrodes E destinées à être appliquées sur la peau d'un patient au niveau d'une zone musculaire à étudier.In a nonlimiting example of embodiment of the invention, a set of electrodes and associated circuits for spectral filtering and spatial filtering is contained in a housing 1 of small dimensions, one face of which comprises a plate 2 of electrically insulating material on which appear from the ends of the electrodes E intended to be applied to the skin of a patient at the level of a muscular zone to be studied.
Les électrodes E sont ici au nombre de onze et sont disposées dans une configuration matricielle en trois rangées comprenant respectivement trois, cinq et trois électrodes pour former trois groupes Ll, L2 et L3 , chaque groupe comprenant une électrode centrale El, E2 , E3 respectivement et quatre électrodes situées à égale distance de l'électrode centrale, ces quatre électrodes étant alignées deux à deux avec l'électrode centrale dans des directions perpendiculaires, l'ensemble formant une croix. Le groupe central d'électrodes L2 a deux électrodes en commun, respectivement (E2, El), et (E2, E3), avec chacun des deux autres groupes Ll et L3.The electrodes E are here eleven in number and are arranged in a matrix configuration in three rows comprising respectively three, five and three electrodes to form three groups L1, L2 and L3, each group comprising a central electrode E1, E2, E3 respectively and four electrodes located equidistant from the central electrode, these four electrodes being aligned two by two with the central electrode in perpendicular directions, the assembly forming a cross. The central group of electrodes L2 has two electrodes in common, respectively (E2, El), and (E2, E3), with each of the other two groups L1 and L3.
Une électrode E est représentée schématiquement en perspective en figure lb, et comprend un tube cylindrique 3 relié à un disque support 4 à une extrémité, ce disque 4 étant l'extrémité de détection et apparaissant sur la face de détection 2 du boîtier 1. L'électrode E peut être réalisée en une matière électroconductrice quelconque et par exemple en cuivre doré ou dans un alliage or-argent -cuivre dans les proportions respectives suivantes : 75 %, 20 % et 5 %. L'or présente une excellente résistance aux agents externes (acidité, sueur, ...) et une excellente innocuité par rapport à la peau et est rigidifié par l'addition d'argent ou de tout autre métal électroconducteur ayant les propriétés mécaniques voulues. Le cuivre facilite la transmission électrique avec le circuit électronique représenté schématiquement en figure 3.An electrode E is shown diagrammatically in perspective in FIG. 1b, and comprises a cylindrical tube 3 connected to a support disc 4 at one end, this disc 4 being the detection end and appearing on the detection face 2 of the housing 1. L electrode E can be made of any electroconductive material and for example of gilded copper or in a gold-silver alloy -copper in the following respective proportions: 75%, 20% and 5%. Gold has excellent resistance to external agents (acidity, sweat, ...) and excellent safety compared to the skin and is stiffened by the addition of silver or any other electroconductive metal having the desired mechanical properties. Copper facilitates electrical transmission with the electronic circuit shown schematically in Figure 3.
Le tube cylindrique 3 de l'électrode peut avoir un diamètre de 2 millimètres et la tête 4 un diamètre de 4 millimètres, le tube venant s'insérer directement dans le circuit électronique. De façon générale et en fonction du type de muscle à étudier, le diamètre des têtes d'électrode peut varier entre environ 1 et 4 millimètres, la distance entre électrodes étant comprise entre 2,5 et 10 millimètres environ et étant de préférence sensiblement égale à 2,5 fois le diamètre de l'électrode.The cylindrical tube 3 of the electrode may have a diameter of 2 millimeters and the head 4 a diameter of 4 millimeters, the tube coming to be inserted directly into the electronic circuit. Generally and depending on the type of muscle to be studied, the diameter of the electrode heads can vary between approximately 1 and 4 millimeters, the distance between electrodes being between 2.5 and 10 millimeters approximately and preferably being substantially equal to 2.5 times the diameter of the electrode.
Dans l'exemple de réalisation de la figure la, les têtes des électrodes E ont un diamètre de 2 millimètres, la distance entre électrodes est de 5 millimètres, les dimensions de la surface de détection 2 sont de 3 cm x 2 cm, et les dimensions extérieures du boîtier 1 sont de 6 cm x 4 cm x 2 cm environ.In the embodiment of FIG. 1a, the heads of the electrodes E have a diameter of 2 millimeters, the distance between the electrodes is 5 millimeters, the dimensions of the detection surface 2 are 3 cm × 2 cm, and the external dimensions of the housing 1 are approximately 6 cm x 4 cm x 2 cm.
Dans la variante représentée en figure 2, la tête 4 de l'électrode E a une face d'application sur la peau qui n'est pas plane, mais en "dents de scie", pour améliorer la qualité du contact entre l'électrode et la peau.In the variant shown in FIG. 2, the head 4 of the electrode E has an application face on the skin which is not flat, but in "sawtooth" shape, in order to improve the quality of the contact between the electrode and the skin.
Dans le boîtier 1, les électrodes E sont portées par une plaque de circuit imprimé RI, par exemple en fibres de verre - époxy venant se connecter à un circuit d'amplification VI, la plaque RI et le circuit VI étant représentés côte à côte en figure 3. Au moyen de ce circuit imprimé, chaque électrode E est connectée à des moyens d'amplification 5 via un connecteur K et un filtre passe-haut 6 constitué de façon classique par un circuit du type RC. Un filtrage à 6 Hz est prévu, pour s'affranchir des effets de polarisation des électrodes. Alternativement, notamment lorsqu'on s'intéresse uniquement à la propagation du signal, on peut utiliser un filtrage à 70-80 Hz environ pour minimiser les effets du réseau de distribution électrique (à une fréquence de 50 Hz en Europe et de 60 Hz aux Etats-Unis d 'Amérique) et aussi pour éliminer tout artefact de mouvement. Les moyens d'amplification 5 comprennent, pour l'ensemble des électrodes E, trois amplificateurs opérationnels 7 à haute impédance d'entrée, chaque amplificateur opérationnel 7 étant associé à un groupe Ll, L2 ou L3 respectivement d'électrodes de telle sorte que les signaux transmis par les électrodes de ce groupe soient amplifiés avec un facteur de pondération qui est égal à + 4 (ou - 4) pour l'électrode centrale et - 1 (ou + 1) pour chacune des quatre électrodes périphériques. Ces circuits sont réalisés en technologie CMOS-CMS ou gravés sous forme d'ASIC et les amplificateurs opérationnels 7 ont un gain linéaire égal à 100 et un taux de réjection en mode commun proche de 100 dB .In the housing 1, the electrodes E are carried by a printed circuit board RI, for example made of glass fibers - epoxy coming to connect to an amplification circuit VI, the plate RI and the circuit VI being shown side by side in FIG. 3. By means of this printed circuit, each electrode E is connected to amplification means 5 via a connector K and a high-pass filter 6 conventionally constituted by a circuit of the type RC. Filtering at 6 Hz is provided, to overcome the effects of polarization of the electrodes. Alternatively, especially when we are only interested in the propagation of the signal, we can use filtering at around 70-80 Hz to minimize the effects of the electrical distribution network (at a frequency of 50 Hz in Europe and 60 Hz in United States of America) and also to eliminate any movement artifacts. The amplification means 5 comprise, for all of the electrodes E, three operational amplifiers 7 with high input impedance, each operational amplifier 7 being associated with a group L1, L2 or L3 respectively of electrodes so that the signals transmitted by the electrodes of this group are amplified with a weighting factor which is equal to + 4 (or - 4) for the central electrode and - 1 (or + 1) for each of the four peripheral electrodes. These circuits are made in CMOS-CMS technology or etched in the form of ASIC and the operational amplifiers 7 have a linear gain equal to 100 and a common mode rejection rate close to 100 dB.
L'amplification sur site des signaux transmis par les électrodes permet d'augmenter le rapport signal/bruit, les signaux captés ayant un niveau faible, typiquement de l'ordre de 50 μV à 1 rav.The on-site amplification of the signals transmitted by the electrodes makes it possible to increase the signal / noise ratio, the signals picked up having a low level, typically of the order of 50 μV at 1 rav.
Le boîtier 1 contenant les électrodes et les circuits précités comporte trois voies de sortie dont chacune transmet le signal de sortie d'un amplificateur opérationnel 7, deux voies d'entrée pour l'alimentation de ces amplificateurs et une voie reliée à un conducteur électrique de référence. Un blindage amagnétique du boîtier est obtenu au moyen d'un revêtement des faces internes du boîtier par une feuille de cuivre ou analogue, raccordée au conducteur électrique de référence.The housing 1 containing the aforementioned electrodes and circuits has three output channels including each transmits the output signal from an operational amplifier 7, two input channels for supplying these amplifiers and one channel connected to a reference electrical conductor. A non-magnetic shielding of the housing is obtained by coating the internal faces of the housing with a copper foil or the like, connected to the reference electrical conductor.
Comme représenté schématiquement en figure 4, le boîtier de détection 1 est connecté à un boîtier 9 d'alimentation électrique qui transmet de plus les signaux de sortie du boîtier 1 à un étage amplificateur isolé 10 dont la sortie est reliée à un oscilloscope 11 ou autre moyen analogue de visualisation des signaux, et à un dispositif 12 d'acquisition et de traitement de données numériques. Les liaisons sont réalisées au moyen de câbles blindés du type BNC. Typiquement, le dispositif 12 peut être un micro-ordinateur du type PC ou analogue avec un écran vidéo pour la visualisation des signaux.As shown diagrammatically in FIG. 4, the detection unit 1 is connected to a power supply unit 9 which further transmits the output signals from the unit 1 to an isolated amplifier stage 10 whose output is connected to an oscilloscope 11 or other analog signal display means, and to a device 12 for acquiring and processing digital data. The connections are made using shielded cables of the BNC type. Typically, the device 12 can be a microcomputer of the PC type or the like with a video screen for viewing the signals.
Le dispositif selon l'invention est utilisé de la façon suivante :The device according to the invention is used in the following way:
La face de détection du boîtier 1 est appliquée directement sur la peau, sans addition de gel de contact, au niveau d'une zone musculaire à examiner. Après mise sous tension du dispositif, les signaux filtrés spatialement des trois groupes d'électrodes sont visualisés sur l'écran de l'oscilloscope 11. Une visualisation de ces trois signaux SI, S2 et S3 est représentée en figure 5 dans le cas d'un effort isométrique du biceps et montre la propagation d'un potentiel d'action musculaire (mesuré en mV) dans le temps (mesuré en millisecondes) correspondant à un pic sur les courbes Cl, C2 et C3 , ce pic passant de la position PI sur la courbe Cl (correspondant au signal SI du groupe d'électrodes Ll)-, aux positions P2 puis P3 sur les courbes C2 et C3 correspondant aux signaux S2 et S3 des groupes d'électrodes L2 et L3 respectivement. De ce déplacement et de sa durée, on peut déduire une première valeur de la vitesse de propagation d'un potentiel d'action musculaire.The detection face of the housing 1 is applied directly to the skin, without the addition of contact gel, in a muscle area to be examined. After powering up the device, the spatially filtered signals of the three groups of electrodes are displayed on the screen of the oscilloscope 11. A visualization of these three signals S1, S2 and S3 is shown in FIG. 5 in the case of an isometric effort of the biceps and shows the propagation of a muscular action potential (measured in mV) over time (measured in milliseconds) corresponding to a peak on the curves Cl, C2 and C3, this peak passing from the position PI on the curve Cl (corresponding to the signal SI of the group of electrodes Ll) -, to the positions P2 then P3 on the curves C2 and C3 corresponding to the signals S2 and S3 of the electrode groups L2 and L3 respectively. From this displacement and its duration, a first value can be deduced from the speed of propagation of a muscular action potential.
Un enregistrement des signaux pendant une durée de quelques secondes permet d'obtenir une distribution des vitesses de propagation des potentiels d'action musculaires détectables mis en jeu au cours de l'effort. En étude de fatigabilité, l'enregistrement se prolonge sur une durée nécessairement plus importante.A recording of the signals for a period of a few seconds makes it possible to obtain a distribution of the speeds of propagation of the detectable muscular action potentials brought into play during the effort. In a fatigability study, the recording is extended over a necessarily longer period.
Comme les résultats obtenus dépendent beaucoup de la localisation et de l'orientation des groupes d'électrodes par rapport aux fibres musculaires, l'invention a prévu un certain nombre de moyens permettant de vérifier cette localisation et cette orientation.As the results obtained depend very much on the location and the orientation of the electrode groups with respect to the muscle fibers, the invention has provided a certain number of means making it possible to verify this location and this orientation.
Dans un premier temps, la visualisation en temps réel des signaux sur l'écran de l'oscilloscope permet de vérifier une localisation approximative et l'orientation des groupes d'électrodes sur les fibres musculaires. Pour cela, on vérifie la direction de propagation des potentiels d'action (validation de la localisation des électrodes par rapport aux jonctions neuromusculaires) et l'amplitude des potentiels d'action (validation de l'alignement des électrodes selon les fibres musculaires) .First, the real-time visualization of the signals on the oscilloscope screen makes it possible to verify an approximate location and the orientation of the groups of electrodes on the muscle fibers. For this, we check the direction of propagation of the action potentials (validation of the location of the electrodes in relation to the neuromuscular junctions) and the amplitude of the action potentials (validation of the alignment of the electrodes according to the muscle fibers).
Dans un deuxième temps, une analyse fréquentielle des signaux filtrés spatialement permet de valider la localisation des électrodes, pour accepter ou rejeter les mesures faites avec ces électrodes .Secondly, a frequency analysis of the spatially filtered signals makes it possible to validate the location of the electrodes, to accept or reject the measurements made with these electrodes.
On a en effet constaté que les calculs des vitesses de propagation des potentiels d'action donnent souvent des valeurs trop élevées, ce qui peut résulter d'une part de la présence d'un mode commun sur l'ensemble des électrodes utilisées, ce mode commun étant dû lui-même à la présence d'activités non propagées, et d'autre part des propriétés non homogènes et anisotropiques des muscles et des tissus situés entre les muscles et la surface de détection. L'analyse des variations d'un certain nombre de paramètres de 1 ' électromyographie de surface en fonction de la localisation des électrodes, a montré que l'on pouvait définir une localisation pour laquelle on obtient des valeurs minimales des estimations des vitesses de propagation (valeurs minimales moyennes pour toutes les conditions de contraction) . Pour déterminer cette localisation particulière, on utilise le fait que les fréquences moyennes ou médianes des signaux transmis par les électrodes ou celles des signaux filtrés spatialement varient en fonction de la localisation des électrodes, dans le même sens que les estimations des vitesses de propagation (la fréquence moyenne du signal étant la moyenne statistique de la densité spectrale de puissance du signal, sa fréquence médiane étant celle qui partage la surface du spectre en deux parties égales) .It has indeed been observed that the calculations of the propagation velocities of the action potentials often give values that are too high, which may result on the one hand from the presence of a common mode on all of the electrodes used, this mode common being itself due to the presence of non-propagated activities, and on the other hand inhomogeneous and anisotropic properties of the muscles and tissues located between the muscles and the detection surface. The analysis of the variations of a certain number of parameters of the surface electromyography as a function of the location of the electrodes, showed that one could define a location for which one obtains minimum values of the estimates of the propagation velocities ( mean minimum values for all contraction conditions). To determine this particular location, we use the fact that the average or median frequencies of the signals transmitted by the electrodes or those of the spatially filtered signals vary according to the location of the electrodes, in the same direction as the estimates of the propagation speeds (the mean frequency of the signal being the statistical mean of the spectral power density of the signal, its median frequency being that which divides the surface of the spectrum into two equal parts).
Le procédé de validation de la localisation des électrodes consiste donc, selon l'invention, à déterminer les fréquences moyennes ou médianes des signaux filtrés spatialement des trois groupes d'électrodes, à les comparer entre elles et à valider la localisation quand la fréquence moyenne ou médiane du signal du groupe central est inférieure ou égale aux fréquences moyennes ou médianes des signaux des deux autres groupes d'électrodes. Les fréquences moyennes des signaux peuvent être calculées à partir des transformées de Fourier de ces signaux. Un programme simple d'analyse spectrale en temps réel permet de valider ou de rejeter, par comparaison entre trois valeurs de fréquence, une mesure effectuée au moyen du dispositif selon l'invention.The method for validating the location of the electrodes therefore consists, according to the invention, in determining the average or median frequencies of the spatially filtered signals of the three groups of electrodes, to compare them and to validate the localization when the average or median frequency of the signal of the central group is lower or equal to the average or median frequencies of the signals of the two other groups of electrodes. The average frequencies of the signals can be calculated from the Fourier transforms of these signals. A simple program of spectral analysis in real time makes it possible to validate or reject, by comparison between three frequency values, a measurement carried out by means of the device according to the invention.
Bien entendu, l'invention n'est pas limitée aux exemples de réalisation qui ont été décrits et représentés. Il est notamment possible de mettre en œuvre plus de trois groupes d'électrodes dans le dispositif selon l'invention, ou bien un seul groupe d'électrodes pour la détection de l'activité musculaire, ou deux groupes d'électrodes pour la détermination de la propagation des potentiels d'action musculaire.Of course, the invention is not limited to the exemplary embodiments which have been described and shown. It is in particular possible to use more than three groups of electrodes in the device according to the invention, or else a single group of electrodes for the detection of muscular activity, or two groups of electrodes for the determination of propagation of muscle action potentials.
Il est également possible d'effectuer une nouvelle différentiation sur les signaux filtrés spatialement, obtenus en sortie du boîtier de détection. Cette nouvelle différentiation permet d'améliorer la qualité des signaux obtenus, grâce à une élimination plus poussée du mode commun et une comparaison aux signaux obtenus précédemment .It is also possible to carry out a new differentiation on the spatially filtered signals obtained at the output of the detection unit. This new differentiation makes it possible to improve the quality of the signals obtained, thanks to a further elimination of the common mode and a comparison with the signals obtained previously.
Par ailleurs, les groupes d'électrodes peuvent être complétés pour comprendre chacun neuf électrodes à disposition matricielle carrée (analogue à celle que l'on peut voir en figure la en ce qui concerne l'électrode centrale E2 , entourée de huit autres électrodes) . Les coefficients de pondération des signaux des électrodes peuvent alors être de - 12 (ou + 12) pour une électrode centrale, de + 2 (ou - 2) pour les quatre électrodes les plus proches de l'électrode centrale, et de + 1 (ou - 1) pour les quatre autres électrodes (comme décrit dans l'article publié dans "IEEE Transactions and Biomédical Engineering", Vol. 44, n° 7, July 1997, par C. Disselhorst-Klug, J. Silny et G. Rau) .Furthermore, the groups of electrodes can be supplemented to each comprise nine electrodes with a square matrix arrangement (analogous to that which can be seen in FIG. 1a as regards the central electrode E2, surrounded by eight other electrodes). The weighting coefficients of the electrode signals can then be - 12 (or + 12) for a central electrode, + 2 (or - 2) for the four electrodes closest to the central electrode, and + 1 (or - 1) for the other four electrodes (as described in the article published in "IEEE Transactions and Biomedical Engineering", Vol. 44, No. 7, July 1997, by C. Disselhorst-Klug, J. Silny and G. Rau).
L'invention peut aussi être utilisée dans un tunnel de type RMN (Résonance Magnétique Nucléaire) afin de quantifier les paramètres de 1 ' électromyographie : la variation des paramètres électromyographiques, vitesse de propagation ou analyse spectrale du potentiel d'action musculaire, est alors corrélée à la cinétique de paramètres métaboliques, tels que la concentration en ions hydrogêne ou en ions liés au phosphate (adénosine di ou tri-phosphate, phosphate inorganique, phosphocréatine, ... ), fournis par la spectroscopie RMN. Il est ainsi possible d'étudier l'influence des paramètres du métabolisme sur les paramètres électromyographiques, et d'en déduire des corrélations avec des mesures physiologiques relevant de certaines pathologies, par exemple lors de la fatigue musculaire. Hormis les applications de l'invention dans le domaine clinique, ce système de mesure peut être utilisé à la place de tout système d'électrodes de surface, qu'elles soient flottantes ou sèches, notamment dans les domaines de la biomécanique et de l'ergonomie, les dimensions des électrodes et le nombre de signaux laplaciens mesurés étant alors adaptés en fonction de l'utilisation souhaitée, en mettant en oeuvre de façon générale de un à trois groupes d'électrodes. The invention can also be used in an NMR (Nuclear Magnetic Resonance) type tunnel in order to quantify the parameters of the electromyography: the variation of the electromyographic parameters, speed of propagation or spectral analysis of the muscle action potential, is then correlated. to the kinetics of metabolic parameters, such as the concentration of hydrogen ions or of phosphate-bound ions (adenosine di or tri-phosphate, inorganic phosphate, phosphocreatine, ...), provided by NMR spectroscopy. It is thus possible to study the influence of metabolic parameters on electromyographic parameters, and to deduce correlations with physiological measurements relating to certain pathologies, for example during muscle fatigue. Apart from the applications of the invention in the clinical field, this measurement system can be used in place of any system of surface electrodes, whether they are floating or dry, in particular in the fields of biomechanics and ergonomics, the dimensions of the electrodes and the number of Laplacian signals measured then being adapted as a function of the desired use, generally using one to three groups of electrodes.

Claims

REVENDICATIONS
1. Dispositif de mesures électromyographiques à électrodes superficielles, comprenant au moins un groupe d'électrodes (E) et des moyens de filtrage spectral et d'amplification à sommation pondérée réalisant un filtrage spatial des signaux transmis par les électrodes, caractérisé en ce que les moyens précités de filtrage spectral et d'amplification à sommation pondérée sont constitués par des circuits1. Electromyographic measurement device with surface electrodes, comprising at least one group of electrodes (E) and means of spectral filtering and amplification with weighted summation carrying out spatial filtering of the signals transmitted by the electrodes, characterized in that the aforementioned means of spectral filtering and amplification with weighted summation consist of circuits
(6, 5) montés avec les électrodes (E) dans un boîtier(6, 5) mounted with the electrodes (E) in a housing
(1) dont une face portant les électrodes (E) forme une face de détection (2) , le dispositif comprenant également des moyens de connexion de ce boîtier à des moyens (9) d'alimentation, des moyens (10) d'amplification et des moyens (12) de traitement de données .(1) of which one face carrying the electrodes (E) forms a detection face (2), the device also comprising means for connecting this housing to supply means (9), amplification means (10) and data processing means (12).
2. Dispositif selon la revendication 1, caractérisé en ce qu'il comprend également des moyens, tels par exemple qu'un oscilloscope (11) ou un écran vidéo ou analogue, de visualisation en temps réel des signaux de sortie du boîtier (1) .2. Device according to claim 1, characterized in that it also comprises means, such as for example an oscilloscope (11) or a video screen or the like, for real-time display of the output signals of the housing (1) .
3. Dispositif selon la revendication 1 ou 2, caractérisé en ce que les électrodes (E) sont agencées de façon compacte en deux groupes ayant des électrodes communes, pour délivrer des signaux permettant la détermination de la propagation des potentiels d'action musculaire. 3. Device according to claim 1 or 2, characterized in that the electrodes (E) are arranged compactly in two groups having common electrodes, to deliver signals allowing the determination of the propagation of the muscular action potentials.
4. Dispositif selon la revendication 1 ou 2, caractérisé en ce que les électrodes sont agencées de façon compacte en au moins trois groupes (Ll, L2 et L3 ) ayant deux à deux des électrodes communes.4. Device according to claim 1 or 2, characterized in that the electrodes are arranged compactly in at least three groups (L1, L2 and L3) having two by two of the common electrodes.
5. Dispositif selon la revendication 4, caractérisé en ce qu'il comprend des moyens d'amplification différentielle des signaux filtrés spatialement obtenus en sortie du boîtier (1) .5. Device according to claim 4, characterized in that it comprises means for differential amplification of the spatially filtered signals obtained at the output of the housing (1).
6. Dispositif selon l'une des revendications précédentes, caractérisé en ce que le boîtier de détection (1) comprend un blindage interne amagnétique raccordé à une électrode de référence.6. Device according to one of the preceding claims, characterized in that the detection unit (1) comprises an internal non-magnetic shield connected to a reference electrode.
7. Dispositif selon l'une des revendications précédentes, caractérisé en ce que le circuit (6) de filtrage spectral dans le boîtier (1) est un filtre passe-haut, ayant une fréquence de coupure sensiblement égale à 6 Hz ou à 70-80 Hz environ.7. Device according to one of the preceding claims, characterized in that the circuit (6) of spectral filtering in the housing (1) is a high-pass filter, having a cut-off frequency substantially equal to 6 Hz or 70- 80 Hz approximately.
8. Dispositif selon l'une des revendications précédentes, caractérisé en ce que les électrodes ont des extrémités de détection en dents de scie.8. Device according to one of the preceding claims, characterized in that the electrodes have sawtooth detection ends.
9. Dispositif selon l'une des revendications précédentes, caractérisé en ce que les circuits du boîtier (1) sont du type CMOS-CMS ou ASIC.9. Device according to one of the preceding claims, characterized in that the circuits of the housing (1) are of the CMOS-CMS or ASIC type.
10. Dispositif selon l'une des revendications précédentes, caractérisé en ce que la distance entre électrodes est comprise entre 2,5 et 10 millimètres environ et est de préférence sensiblement égale à 2,5 fois le diamètre d'une électrode. 10. Device according to one of the preceding claims, characterized in that the distance between electrodes is between 2.5 and 10 millimeters approximately and is preferably substantially equal to 2.5 times the diameter of an electrode.
11. Dispositif selon l'une des revendications précédentes, caractérisé en ce qu'il comprend des moyens d'analyse spectrale en temps réel des signaux filtrés spatialement, permettant de déterminer les fréquences médianes ou les fréquences moyennes de ces signaux et de les comparer entre elles pour valider une mesure quand la fréquence médiane ou la fréquence moyenne du signal d'un groupe central d'électrodes est inférieure ou sensiblement égale aux fréquences médianes ou aux fréquences moyennes des signaux des groupes voisins d'électrodes. 11. Device according to one of the preceding claims, characterized in that it comprises means of spectral analysis in real time of the spatially filtered signals, making it possible to determine the median frequencies or the average frequencies of these signals and to compare them between they are used to validate a measurement when the median frequency or the average frequency of the signal of a central group of electrodes is less than or substantially equal to the median frequencies or the average frequencies of the signals of the neighboring groups of electrodes.
PCT/FR1998/002837 1997-12-22 1998-12-22 Non-invasive device for electromyographic measurements WO1999032032A1 (en)

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EP98962540A EP1041928A1 (en) 1997-12-22 1998-12-22 Non-invasive device for electromyographic measurements
JP2000525030A JP2001526074A (en) 1997-12-22 1998-12-22 Non-invasive device for electromyographic measurements
CA002312879A CA2312879A1 (en) 1997-12-22 1998-12-22 Non-invasive device for electromyographic measurements

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FR9716272A FR2772588B1 (en) 1997-12-22 1997-12-22 NON-INVASIVE DEVICE FOR ELECTROMYOGRAPHIC MEASUREMENTS, PROCESS FOR VALIDATION OF THESE MEASUREMENTS AND USE OF SUCH A DEVICE

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CA2312879A1 (en) 1999-07-01

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