Patent Application
20230181079
The present invention relates to a body electrode for recording electrophysiological signals from a body. In particular the invention relates to a shielded body electrode providing a contact between the shield and the skin of the body.
Electrodes applied on the skin surface of a subject, e.g. a human, can be used to record electrophysiological signals produced e.g. by the heart, i.e. an electrocardiogram (ECG), by the brain, i.e. an electroencephalogram (EEG), by the eyes, i.e. an electroretinogram (ERG) and/or an electrooculogram (EOG). The quality of such a recording is limited by the performance of the used electrodes. The electrodes may be subject for different disturbances that in turn give rise to disturbances in the output of the recorded electrophysiological signals. One such disturbance is caused by electrostatic fields surrounding the body electrode. The electrostatic fields may give rise to electrostatic induction which may cause disturbances. Such disturbances may create signal amplitudes that can be many times the size of the electrophysiological signal to be recorded, and hence may deteriorate accurate recording of electrophysiological signals. Electrostatic fields can be generated by e.g. clothes, electrode cable movements, objects in the surrounding etc. The signals from electrostatic induced disturbances has a frequency content overlapping the electrophysiological signals which makes it difficult to use conventional soft—and hardware filters to remove it from the recording.
US7993167B2 discloses an ECG lead set which is shielded against electrostatic disturbances by an electrical shield. The electrical shield is covered by a nonconductive cover and is electrically connected to the shield of the coaxial cable of the lead set.
JP2013022150A discloses an electrostatic induction noise suppressor device for a bioelectrode, and a method for suppressing electrostatic induction noise in a biological signal detected by a biological electrode. The electrostatic induction noise suppressing device has a discharge part for discharging a charging charge of the charging part to the living body via a connecting part for electrically connecting the charging part and the body surface.
In the prior art there is a need for an improved electrostatic protection of a body electrode, and to improve the quality of a recording of electrophysiological signals from body electrodes by minimizing the influence caused by electrostatic fields.
The object of the invention is to provide a body electrode that overcomes at least some of the drawbacks of prior art. This is achieved by the body electrode as defined in claim 1, the body electrode arrangement as defined in claim 17 and the measurement system as defined in claim 18.
According to one aspect of the invention a body electrode for electrophysiological signal monitoring is provide. The body electrode is during used arranged to be attached to the skin of a subject, and comprises:
According to one embodiment of the invention the skin contact element is formed from the layered shield structure and the ion conducting layer is a continuous layer including the skin contact element.
According to one embodiment the layered shield structure of the body electrode further comprises an ion-conducting layer, and the ion-conducting layer of the skin contact element is arranged to be connected with the ion-conducting layer of the layered shield structure.
According to one embodiment of the invention the layered shield structure comprises an ionic conducting layer arranged below the electrically conducting shield and the layered shield structure covers at least the electrically conducting compartment, the connector and the transducer element.
According to one embodiment of the invention the skin contact element is a wire-like structure extending from the electrical shield layer on the outer peripheral of the collar and over at least a portion of the skin facing surface of the body electrode.
According to one embodiment of the invention the layered shield structure further comprises at least one flap arranged to during use spatially overlap with a lead shield.
According to one embodiment of the invention at least one of the materials in the layers of the skin contact element differs from the materials in the layers of the transducer element.
According to one embodiment of the invention the potential difference Udiff, between the transducer element and the electrically conducting layer is lower than 30 mV.
According to embodiments of the invention the electrically conducting layers of the body electrode and/or the skin contact element is provided as a layer comprising an ion carrier material comprising an ion solution or to which an ion solution may be provided before use. Thereby the electrically conducting layer(s) functions as both the electrically conducting layer and the ion conducting layer.
According to one embodiment of the invention the ion conducting layer comprises a polymer matrix and a water-soluble salt. The polymer matrix may comprise a hydrogel.
According to one embodiment of the invention the electrically conducting layer comprises a carbon-based polymer material and the ion conducting layer comprises an acrylic material.
According to one embodiment of the invention the ion conducting layer is adhesive. The ion conducting layer may be provided as an adhesive layer that is arranged to, during use, also fastens the skin contact element to the skin.
According embodiments of the invention the transducer element comprises Ag/AgCl. A matching skin contact may be provided by
There is an advantage with the invention that the potential difference, as given by the Udiff value can be reduced and/or stabilized. A reduced and/or stabilized Udiff value may result in reduced disturbances during an electrophysiological measurement. To match the electrical potential characteristics of the transducer element and the skin contact element by the design of the body electrode has advantages over applying filtering or signal processing at a later stage since the disturbances otherwise caused may be similar to the signal variations to be detected.
A further advantage with the invention is that there is no openings/holes present that may allow electrostatic fields to penetrate through the shield structure and reach the conducting compartment where it may cause disturbances.
According to one aspect of the invention a body electrode arrangement is provided comprising least one body electrode an indifferent body electrode and a hub device. Each of the body electrodes comprises a transducer element that during use is connected to a measuring device via a signal conductor. In the body electrode each of the body electrodes comprises a layered shield structure comprising an electrically conducting layer and an electrically dissipative layer. An isolated lead is arranged to pass the hub device and electrically connect the electrically conducting layers of the each of the body electrodes and the indifferent body electrode provides a skin contact element that is arranged to be in electrical contact with the isolated lead.
According to one embodiment the indifferent body electrode comprises a transducer element utilized as a skin contact element and the isolated lead is connected to the transducer element of the indifferent electrode.
According to one embodiment the indifferent electrode is a body electrode comprising a skin contact element as described above, and wherein the skin contact element of the indifferent electrode is connected to the isolated lead.
There is an advantage with the invention that one body electrode function as a skin contact element. Then the other body electrodes do not need to comprise a skin contact element.
According to one aspect of the invention a measurement system is provided comprising a body electrode according to the above aspects of the invention. The measurement system comprises means configured to:
According to one aspect of the invention a measurement system is provided connected to the body electrode arrangement described above and further comprises means configured to:
Terms such as “top”, “on top”, “bottom”, upper“, lower”, “below”, “above” etc. are used merely with reference to the geometry of the embodiment of the invention shown in the drawings and/or during normal operation of the described device and system and are not intended to limit the invention in any manner. The aim of a body electrode is to receive and record electrophysiological signals from a body. The signals are recorded by a transducer element and transmitted to various medical instruments. Such recordings may be disturbed by electrostatic induction surrounding the body electrode. Electrostatic induction may be caused by changing electrostatic fields surrounding the body electrode. Such electrostatic fields can for example be generated by clothing or other covers, electrode cable movements, the surrounding environment etc. Disturbances at the interface between the electrolyte medium and the skin may cause changes of the potential at the interface which may result in disturbances in the recorded electrocardiogram, wherein “potential” refers to an electric potential and/or an electrochemical potential, typically measurable with a common voltmeter and/or oscilloscope. Disturbances may be reduced and/or stabilized using a body electrode according to the invention.
A body electrode according to the invention is schematically illustrated in
The body electrode 100 further comprises a layered shield structure 120 arranged so that it forms at least part of the free surface 103. The layered shield structure 120 comprises an electrostatic dissipative layer 112 and an electrically conducting layer 113, with the dissipative layer 112 on top of the electrically conducting layer 113 as seen from the collar 104.
According to one embodiment the layered shield structure 120 is arranged so that it covers at least the transducer element 106, the connector 106, the lead 110 and the conductive compartment 108.
In one embodiment the connector 106 is arranged on top of the transducer element 105, in such case there may be no lead 110 and the layered shield structure 120 may be arranged so that it covers at least the connector 106, the transducer element 105, and the conductive compartment 108.
In an embodiment illustrated in
According to one embodiment an aggregate 130 comprising a body electrode 100 and a lead connector 106′ comprising a layered shield structure is provided, wherein the layered shield structures of the lead connector 106′ and the body electrode 100 forms a unified electrical shield structure.
In an embodiment the lead connector 106′ may be a clip-on, or clamp, connector type that is arranged to be clamped onto the connector 106 of the body electrode 100. Such connector types are known in the art. The layered shield structure of such a clip-on connector would typically be in the form of two parts that during mounting would open up to receive the connector 106. After mounting, and the two parts of the layered shield structure is closed and electrically connected again forming a unified connector shield without any holes or openings. Alternatively, the two parts of the layered shield structure of the lead connector 106′ are arranged to overlap in the closed position.
In one embodiment the connector 106 is arranged at a distance from transducer element 105 and connected with an electrical lead 110.
The body electrode 100 further comprises a skin contact element 115 that at least during use of the body electrode 100 comprises an ion conducting layer 114′ and an electrically conducting layer 113′ as schematically illustrated in the in the enlarged view of Figure le. The skin contact element 115 may further, according to embodiments of the invention, be provided with an electrostatic dissipative layer 112′. The layered structure is relevant for all variants of the skin contact element 115, for example the embodiments described with reference to
According to one embodiment depicted in
In an alternative embodiment, schematically illustrated in
In yet another embodiment, schematically illustrated in
The skin contact element 115; 115′; 115″ is in contact with the skin during use of the body electrode 100. The skin contact element 115; 115′; 115″ is in electrical contact with the electrically conducting layer 114. In that way, the skin contact element 115; 115′; 115″ enables charge transfer between the layered shield structure 120 and the skin during use of the body electrode 100.
The materials and the thickness of the layers, i.e. the electrically conducting layer 114′ and the ion conducting layer of the skin contact element 115; 115′; 115″ are selected so that the electrical potential of the skin contact element 115; 115′; 115″ matches the electrical potential of the transducer element 105 comprised in the conductive compartment 108. That the electrical potentials are matching should herein be understood as that the potential difference, Udiff, between the electrical shield layer 113 and the transducer element 105 is kept lower than 30 mV, or lower than 20 mV, or lower than 15 mV, or lower than 10 mV, or lower than 7 mV, or lower than 5 mV during use of the body electrode.
The layered shield structure 120 comprising the electrically conducting layer 113 and the electrostatic layer 112 may be arranged at a distance from the transducer element 105 so that the transducer element 105 and the layered shield structure 120 are not in contact at least during use of the body electrode 100. Furthermore, the layered shield structure 120 may be comprehensive so that it does not comprise any openings/holes larger than 1.5×0.5 mm.
The electrostatic dissipative layer 112 is arranged on top of the body electrode 100 forming at least part of the free surface 103. The electrically dissipative layer 112 may for example comprise a polymer, an elastomer, a woven or non-woven textile or a mixture thereof. The electrostatic dissipative layered shield structure 112 preferably have a surface resistivity of 105-1011 Ohms per square.
The electrically conducting layer 113 is arranged underneath the electrostatic dissipative layer 112. The electrically conducting layer 113 may have a surface resistivity that is equal or less than 10−1-103 Ohms per square. The electrically conducting layer 113 may comprise: a metal, an electrically conducting carbon paint, a carbon-based polymer, an electrically conducting polymer or an ionic polymer. The electrically conducting layer 113 may alternatively comprise a material, referred to as an ion carrier, that can be loaded with an ion solution for example a woven or non-woven material that comprises an ion solution e.g. a liquid containing water-soluble salts, or a mixture thereof. The electrostatic dissipative layer 112 and the electrically conducting shield layer 113 are in contact with each other so that charge can drain from the electrostatic dissipative layer 112 to the electrically conducting shield layer 113.
The skin contact element 115; 115′; 115″ comprises an ion conducting layer 114′ and an electrically conducting layer 113′ and is in electrical contact with the layered shield structure 120. The ion conducting layer 114′ may for example be a liquid gel and a water-soluble salt or a hydrogel with a water-soluble salt, or a polymer matrix and a water-soluble salt or a polymer matrix that is both ion-conducting and electrical conducting. A water-soluble salt should be understood as a salt having an aqueous solubility of at least 100 g/1000 ml water at 25° C., e.g. NaCl, KCl and CaCl2. with concentrations of for example 3 g salt per 97 g of water equal to 3% by mass. The ion conducting layer may also comprise an acrylic material.
The transducer element 105 may for example be a silver/sliver chloride type.
The body electrode 100 may for example be in the form of a square with a side of 25-55 mm and having a collar of 0.5-3 mm in thickness. Or the body electrode 100 may have the shape of a circle with a diameter of 25-55 mm and a collar of 0.5-3 mm in thickness. For such body electrodes the layered shield structure may be in the form of a circle having a diameter of 15-25 mm or in the shape of a square having a side of 15-25 mm
For such body electrodes as described above the area of the skin contact element 115, 115′, 115″ or 215 may be between 4 mm2 and 100 mm2
The skin contact element 115 may additionally be in the form of single strand wire for example comprising silver, the single strand wire may have a surface contacting part being 10-30 mm long and 0.1-1 mm in diameter.
In one embodiment of the invention, schematically illustrated in
The body electrode 200 further comprises a conductive compartment 208 which in the direction parallel to the skin facing surface 202 is limited by the wall 204a of the collar 204, the conductive compartment 208 comprises an electrolyte medium 209 at least during use of the body electrode 200. The body electrode 200 further comprises a layered shield structure 220 arranged on the free surface 203 so that it forms at least part of the free surface 203. The layered shield structure 220 comprises an electrostatic dissipative layer 212, an electrically conducting layer 213, and an ion conducting layer 214. The dissipative layer 212 is arranged on top off the electrically conducting layer 213 on the side that faces away from the free surface 203. The ion conducting layer 214 is arranged in contact with the electrically conducting layer 213 on the side that faces away from the free surface 203. The ion conducting layer 214 is arranged to be in contact with the skin 201 via a skin contact element 215 formed by the layered shield structure 220.
According to one embodiment illustrated in
The ion conducting layer 214; 314 may comprise an ionic gel, semi-gel or a hydrogel. According to one embodiment the ion conducting layer 214; 314 is in the form of an adhesive. The adhesive ion conducting layer 214; 314 may in this embodiment serve several functions: as the ion conducting material providing the electrical connection to the skin during use, to adhere the skin contact element 215 to the skin and to adhere the electrical shield layer 213 to the underlying parts of the body electrode 200.
The body electrode 100; 200 may also comprise an additional layer that is adhesive and arranged at the skin facing surface 102; 202 to attach the body electrode 100; 200 to the skin 101.
The body electrode 100; 200 may additionally comprise additional layers for example additional shields, e.g. electrical and/or electrostatic dissipative, at least partly surrounding electrical parts of the body electrode 100; 200, such the lead 110; 210, and/or connector 106; 206, etc.
According to one embodiment of the invention there may be an aggregate arrangement 517 comprising several body electrodes 500, such as five body electrodes for example, and a hub device 518. Each body electrode 500 comprises a layered shield structure 120 comprising an electrically conducting layer 113 and an electrically dissipative layer 112, and a lead connector 106′ covered by a layered shield structure. Such an embodiment is schematically illustrated in
According to one embodiment of the aggregate arrangement 517 one of the body electrodes is an indifferent electrode 521, that has a different function and/or design than the other body electrodes. The indifferent electrode 521 is provides a skin contact element for the aggregate arrangement 517.
According to one embodiment the indifferent body electrode 521 comprises a transducer element utilized as a skin contact element and the isolated lead 519 is connected to the transducer element of the indifferent electrode 521.
According to one embodiment the indifferent body electrode 521 the indifferent electrode is a body electrode 100, 200, 400 as described above, with its skin contact element 115; 115′; 115″ connected to the isolated lead 519.
According to one embodiment of the aggregate arrangement 517 at least one of the body electrodes 100 comprises a skin contact element 115 and is used to contact the skin during use of the aggregate arrangement 517. In such an embodiment the skin contact element 115 may be connected to the other body electrodes 100 via the isolated lead 519.
The body electrode 100; 200; 400 will during use exhibit potential differences between different parts, as schematically illustrated by the equivalent circuit of
Udiff=Ush-Uel 1
Udiff should preferably be small, i.e. close to or at 0, and remain stable, i.e. constant during use of the body electrode 100; 200, and in particular during the presence of the electrostatic field causing the disturbance. A constant and/or small Udiff value may result in an electrophysiological recording with at least a reduced amount of disturbances and/or a reduced amplitude of the disturbances. Constant shall be interpreted as to include small variations, such as a 10% variation, or a 5% variation or shall be interpreted as to include small variations in the potential such as a 10 mV variation, or a 6 mV variation or a 3 mV variation. The variation can be assessed during a time period, such as for example 1 min when the body electrode is subjected to electrostatic field disturbances. Udiff may remain at a value that enables that a signal-to-noise ratio between the recorded electrophysiological signal and a noise signal, e.g. induced by an electrostatic field, is not higher than 45 dB, or not higher than 40 dB.
The potential difference between the transducer element 105; 205 and the skin contact element 115; 115′; 115″; 215, i.e. Udiff, may tested in a test equipment schematically illustrated in
The measurement instrument probes may preferably be selected depending on/in respect to the material under test specifically certain shielding material which is appreciated by a person skilled in the art. For example, regular/standard stainless steel measuring instrument probes may typically be selected for electronic conducting material, e.g. metals. For ionic conducting materials a reference Ag/AgCl electrode can be used as probes, stainless steel probes or other probes having insufficient electrical/electrochemical stability may introduce measurement errors. For electron conducting material being fragile i.e break upon mechanical impact from regular stainless steel probes or materials in other ways inappropriate to use regular stainless steel probes as the ones described above, such as for example a thin layer structure with a layer thickness of 10-50 μm, it may be beneficial to use a probe comprising of a stable Ag/AgCl transducer element and an electrolyte medium comprised of Cl—ions, e.g. NaCl.
For measurement probes having a stable electrochemical potential this should be deduced from the measured Udiff, i.e if an Ag/AgCl electrode has been used with an electrochemical potential of 15 mV, 15 mV should be deduced from the measured Udiff.
A constant Udff may be achieved by a constant and/or stable Ush and/or Udiff value. Such a stable value for Uel may be achieved by a transducer element 105; 205 comprising a metal, e.g. Ag, coated with a metal salt with a low aqueous solubility, e.g. AgCl, which hereinafter will be referred to as a standard type of transducer element. A stable Ush value may be achieved by a skin contact element 115; 115′; 115″; 215 comprising a metal, e.g. Ag, coated with a metal salt, e.g. AgCl and an ion conducting layer 114; 214; comprising a salt, e.g a water-soluble salt such as NaCl, KCl or CaCl2.
According to one embodiment wherein the transducer element is of standard type. The skin contact element comprises silver metal Ag with a conductive medium comprising a gel or hydrogel with at least 0.6% by mass of a chloride salt i.e. NaCl, KCl and CaCl2.
According to one embodiment wherein the transducer element is of standard type and the electrolyte medium comprises a gel or hydrogel with at least 0.6% by mass of a chloride salt i.e. NaCl, KCl or CaCl2, the electrically conductive layer of the skin contact element comprises silver (Ag).
According to one embodiment wherein the transducer element is of standard type. The skin contact element comprises silver Ag coated with AgCl with a conductive medium comprising a gel or hydrogel with at least 0.6% by mass of a chloride salt i.e. NaCl, KCl and CaCl2.
According to one embodiment wherein the transducer element is of standard type and the conductive layer of the skin contact element comprises carbon coated with an acrylic polymer matrix wherein the polymer matrix (ion conductive layer) may serve as both electric conductive and ion conductive.
According to one embodiment wherein the transducer element is of standard type and the skin contact element comprises carbon coated with an electric conducting acrylic polymer matrix and a water-soluble salt with at least 0.6% by mass of a chloride salt i.e. NaCl, KCl and CaCl contained in the polymer matrix.
According to one embodiment wherein the transducer element is of standard type, the electrolyte medium comprises a gel or liquid with at least 0.6% by mass of a chloride salt i.e. NaCl, KCl and CaCl2. and the skin contact element comprises an ionic conductive layer containing a gel or liquid with at least 0.6% by mass of a chloride salt i.e. NaCl, KCl and CaCl2.
According to a further aspect of the above embodiment wherein the polymer matrix is an adhesive adhering to a substantially flat surface which could be a skin surface.
According to one aspect of the invention a measurement system 880, schematically illustrated in
According to one embodiment the device for electrophysiological measuring 881 comprises an electric potential equalization circuit 882 and is used with one or more body electrodes 800 which are shielded by layered shield structure 820 comprising an electrical and an electrically dissipative layer but not provided with a skin contact element.
According to one embodiment the device for electrophysiological measuring 881 comprises an electric potential equalization circuit 882 and is used with the body electrodes 100, 200, 400 described with reference to
The measurement part 884 may have input characteristics typically required for an electrophysiological differential amplifier, such as used in equipment for electrophysiological signal recording and/or monitoring. The measurement part 884 preferably has a gain equal to 1 and is preferably an amplifier of a so called voltage follower type, i.e. with gain equal to one, having suitable input characteristic such as input impedance, typically in the order of 10-100 MOhm, and an input off-set current, typically in the order of 5-50 nA. The feedback part 883 may be based on an operational amplifier. The electric potential equalization circuitry operates to actively bring the electrical potential difference between the layered shield structure 820 and/or connector shield 806′, and the transducer element 805 down and towards a zero level.
The measurement system 800 system according to the invention is via the electric potential equalization circuitry configured to record a signal received by a transducer element 805 of a body electrode 800 and perform process the signal according to the continuous main steps of:
The method is capable of delivering a Udiff that is should be lower than 30 mV, or lower than 20 mV, or lower than 15 mV, or lower than 10 mV, or lower than 7 mV, or lower than 5 mV.
In one embodiment an aggregate arrangement 517 comprising an indifferent electrode 521 used as a skin contact element may be provided with a device for electrophysiological measuring 881. In such embodiment the measurement part 884 measures the electric potential via the indifferent electrode and the feedback part 883 provides the connector shields 806′ of the other body electrodes 500 with an electric potential, based on the measured electric potential from the indifferent electrode.
All embodiments, variants and examples may be combined with each other unless stated otherwise.
Implementation example:
For an ECG recording of diagnostic quality, it is desirable with a reduction of electrostatic noise in the order of a 100 times reduction in amplitude. In line with the above described embodiment a ECG body electrode was produced and tested. The outer shape of a body electrode used was a square with a 33 mm side. A shield structure was a circular electrode shield with a diameter of 25 mm. The body surface contacting electrode (transducer element) area was 18 mm in diameter, the transducer element/electrode conductive medium interface was of silver/silver chloride with a conductive hydrogel with at least 2% by mass sodium chloride as the electrode conductive medium. There was a collar surrounding the electrically conducting electrode portion and with a thickness of 1.5 mm. The skin contact element was a 0.3 mm diameter single strand wire 30 mm long made of silver which during use was in contact with the body surface. A connector shield overlapped a cable, i.e. lead, shield with at least 5 mm. The cable shield was connected electrically to a shielding circuit of an amplifier. The body electrode shield and the connector shield were not electrically connected with the cable shield. There were no holes or openings in the shield structure, formed by the electrode shield and connector shield, larger than a rectangle with sides 1.5 mm×0.5 mm. The device/body surface impedance was approximately 50 kOhm, for frequency range 6-100 Hz. The air room temperature was 22 degree Celsius and the relative humidity was 50%. The potential difference between the shield structure and the transducer element, i.e. Udiff, was measured to maximum 20 mV DC with a change, peak to peak, of maximum 2 mV per minute. With the same device described but without any electric potential equalization arrangement, i.e. said body surface contact element, and without the shield structure, disturbances on the electrophysiological signal of up to 2 mV amplitude is observed. With devices according to embodiments herein, electrostatic disturbance impact was below 0.01 mV in amplitude.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2050287-8 | Mar 2020 | SE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/SE2021/050197 | 3/5/2021 | WO |
