CA1093158A

CA1093158A - Disposable electrode

Info

Publication number: CA1093158A
Application number: CA271,009A
Authority: CA
Inventors: Jeffrey Berg
Original assignee: Johnson and Johnson
Current assignee: Johnson and Johnson
Priority date: 1976-02-05
Filing date: 1977-02-03
Publication date: 1981-01-06
Also published as: SE7701249L; AU499224B2; IT1077724B; GB1574363A; JPS613506B2; AU2194277A; JPS5295895A; SE433039B; NZ183139A; PH12724A; US4066078A; IN145446B

Abstract

ABSTRACT OF THE DISCLOSURE

An improved combination electrode for use in medical applications requiring monitoring and stimulation, said electrode providing contact with a patient's skin. The electrode comprises a conductive member which can be connected to an external electrical apparatus and an electrically conduc-tive organic polymer plasticized with a polyhydric alcohol for electrically interfacing to the patient's skin being electric-ally and mechanically connected to the conductive member. This electrode, which performs a similar function to the prior art electrodes, eliminates the need for an electrolyte solution, electrode paste or electrode gel. This electrode also adheres to the skin without the use of tape or other securing mediums.

Description

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Ihis invention relates to electrodes and, more parti-cularly, to medical electrodes for providin~ electrical contact with a patient's skin.
Medical electrodes have, in the past, taken many shapes and forms. Principally, they have been shaped according to the use for which they are intended. Electrodes used with monitoring apparatus, such as EKG and EEG machines, commonly have small round contact surfaces, whereas electrodes used with such stimulation apparatus as pain control devices tend to be larger and have rectan~ularly and other conveniently shaped con-tact surfaces. Whether intended for monitoring or stimulation use, a design objective for each electrode group has been, and continues to be, good electrical signal transmission between a patient's skin surface and the electrical cables connected to a particular piece of apparatus. With respect to stimulation and monitoring electrodes, efficient signal transmission across the epidermis conductor interface i5 desirable. Further, with res-pect to stimulation electrodes, effective signal transmission ree of current concentration points or '`hot spots" is also desirable.
Of the electrodes presently available, many offer combination structures including a metallic or otherwise con-ductive support member to which an electrical wire from an asso-ciated apparatus may be attached. In many instances, these electrodes need the addition o~ generous amounts of an electrode paste or gel applied directly to the conductive support member to enhance conductivity across the skin-electrode interface to the point where acceptable operating conditions are achieved.
Other priox art electrodes teach the incorporation of an open cellular skin interface pad secured to a conductive support member. This pad as shown in USP ~o. 3,817,252, is often sponge .:

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material ~hich functions to hold an amount of electroly-te solu-tion in order to enhance conductivity across the skin-pad inter-face. Such an interface pad can be, alternately, saturated with electrode pastes or gels of the type that do run or evaporate as readily as electrolyte solutions.
None of these prior art electrodes offer satisfactory disposable structure, nor do they offer a structure which will maintain constant, efficient and effective electrical trans-mission for long periods of time without the need for addition-al electrode paste, gel or solution. Moreover, there is a ten-dency ~hile using these electrodes, for the electrode gel to se-parate and/or to flow to a non-uniform thickness. Under these conditions, sections of the conductive support member could be exposed to the s~in and local hot spots can result which can cause discomfort if not severe enough to cause burns to the pa-tient's skin .
Prior art electrodes invariably must be secured to the surface of a patient's skin with medical adhesive tape or o-ther securing mediums. Very often an electrode secured in this man-~0 ner will lift off from the skin because of perspiration and/orbecause of movement by the patient, creating a partial or total interruption in the signal transmission, or causing an uneven current density at the electrode-skin interface.
An objective of this invention, therefore, is to pro-vide an electrode with an electroconductive skin-interface subs-trate, which will perform a similar function to, and eliminate the need for, an electrolyte solution, electrode paste or elec-trode gel.
Another objective of this invention is to provide an electrode with a skin-interface substrate having pressure sensitive adhesive properties which will enable the electrode to ~ ~, 3:~5~

adhere to the skin without the use of tape or other securing mediums.
Another objective of this invention is to provide an adhesive substrate that has hlgh tack so that minimal pressure is needed to apply it to the skin but is such that it can also be easily separable from the skin upon removal without any noticeable residue.
A further objective i5 to provide an electrode with a non~ uid skin-interface substrate which is a film or sheet, which will maintain a uniform thickness and will not separate to expose sections of a conductive ~support member to the skin.
An even further objective is to provide an electrode having a s~in-interfacesubstrate which will not decompose or dry out under long periods of use.
According to the invention, there is provided an elec-trode providing electrical contact with a patient's s~cin com-prising:
a conductive member connectable to an external electri-cal apparatus and ~O means for electrically interfacing to said patlent's s~in being electrically and mechanically connected to said con-ductive member, said interfacing means consisting essentially of an electrically conductive organic polymer plasticized with a polyhydric alcohol.
The medical electrode of khe invention is suitable cor stimulation and monitoring applications, and includes an elec-trically conductive member capable of being connected to extern-al electro-medical apparatus. This conductive member may be a pliable sheet of material preferably having connected thereto a medium for securing positive electrical connection between 3~5~

the conductive member and the external electro-medical appara-tus. Attached to the underside of the conductive member and ex-tending away from the electrical connection is an electrically conductive skin-interface substrate material preferably in the form of a film. This material must have adhesive properties so that it will adhere to the skin of a patient.

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Preferably, this material also has plastic and hydrophilic properties. A suitable combination of the aforementioned adhesive, plastic and hydrophilic properties is provided by an adhesive composi~ion which comprises an electrically con-ductive organic polymer plasticizea with a polyhydric alcohol~
Suitable electrically conduc~ive organic polymers include 1) polymers or copolymers derived from the polymerization of an ester of an ~ olefinically unsatura~ed carboxylic acid and an alcohol having a terminal quaternary ammonium group, and 2) sulfated cellulose esters. The pref~rred polyhydric alcohol plasticizer is glycerolO
m e novel features of this invention as well as the invention itself, both as to its organization and method of operation, will best be understood from the following des-cription taken in connection with the accompanying drawings in which like characters refer to like parts, and in which:
Figure 1 shows a perspective view of the electrode, Figure 2 shows a cross section in side elevation through the electrode of Figure 1-Figure 3 shows a plan elevation cross section through the skin-interfacing film of the electrode of Figure 1.
Medical electrodes are intended for usage as efficient and efective signal transmission mediums between a patient's skin and an electro-medical apparatus. Primary to ~heir oper-ation is a uniform conductivity through the elec~rode itself and a uniform conductivity across the electrode-skin inter-face. Uniform conductivity through an electrode is most o~ten interrupted by a non-uniformity in the electrode material~
Uniform conductivity across the electrode-skin interface is ~0 most often interrupted by a separation of some or all of the electrode interfacing material in contact with a patient's skin.

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The electrode at hand is intended to be disposable.
It is also intended to have adhesive properties sufficient to be self-adhering to a patient's skin for approximately 48-120 hours~ However, it should contain sufficient flexibility and elasticity to move as a patient's skin moves while returning to original shape when permitted. Additionally, it is intended to provide uniform conductivity with even current densities of approximately 30 microamperes per square millimeter when subjected to a stimulus of about 10-50 milliamperes at 10-350 cycles per second having a pulse duration of about 50-1000 microseconds. This elec~rode is intended to be easily handled, non-irritating to a patient's skin, and sterilizable.
The electrode configuration is shown in Eigure 1. A
conductive member 11 is cut, stamped or otherwise shaped out of a piece of conductive material which, in the principal em-bodiment, is aluminum foil. The shape ~o which this conduct-ive member 11 formed will depend upon the particular applica-tion in which it is to be used. The shape is sometimes round, but most commonly as shown in figure 1, this member 11 is ~0 rectangularly shaped. A convenient size for many applications is ~rom about 1~1/2 inches by abou~ 8 inches in size. Alter-nately, other metallic foils, conductive polymers, graphitized or metalized cloth or wire mesh may be used. For each material material, an appropriate strength and thickness is ~o be cho-sen to yield a pliable, yet sufficiently strong member 11.
When the conductive member 11 is of aluminum foil, it usually is of 1-10 mil thickness.
Secured to the outer surface of the conductive mem-ber 11 is a connector 13 for providing a medium to which ex-ternal signal cables may be attached for electrically commu-nicating with the conductive member 11. This connector 13 ~3~

may be a conductive swaged snap fastener 13, as shown in the accompanying drawings, which is available commercially. This fastener 13 is riveted or otherwise mechanically and elec-trically attached to the conductive member 11, extending per-pendicularly from the outer surface of this member 11.
Abutting the inner surface of the conductive membex 11 is an electrically conductive skin-interface substrate 15.
This substrate lS is a layer of material being typically a film or sheet which will be described below.
The conductive substrate 15 is shaped correspondingly to the conductive member 11. When constructed in combination with a rectangular member 11, the substrate 15 is also rect-angular. The film thickness of this substrate 15 is uniform throughout, however, this uniform film may be of various thick-nesses. A range of 1/64-1/4 inches is eommon. With the lesser film thicknesses, the substrate 15 coats the surface of the conduetive member 11 to its edges, while with greater film thicknesses, the substrate 15 can ~e extended beyond the edges of the conduc~ive member 11 as illustrated in figures 1 and

2. ~his extension beyond the edges of the conductive member 11 provides an extra measure of security from the conduetive member 11 eoming into direct eontact with a patient's skin, as well as serving to reduce curling of the edges,of the con-duetive member 11. As will be diseussed below, the substrate 15 is a film or sheet having adhesive properties, thus when it is brought into contact with the eonductive member 11, it will adhere to that member 11 providing elec~rical connection with it.
A diffusion screen 17, figure 2 may be used in elee-trode configurations where a greater thickness substrate 15 film is used. This diffusion screen 17, while not a necessary ~3~SI~

part of the electrode, will tend to further distribute current densities throughout the substrate 15 which can result in a more uniform density of current at the substrate 15 surface in contact with a patient's skinO ~ further advantage to the use of this screen 17 is that it acts to reenforce and strengthen the substrate 15.
~ he screen 17 is positioned midway through the thick-ness of the substrate 15, in alignment with the conductive member 11, and is of a size to extend completely under the conductiv~ member 11. The screen 17, figure 3, can be a meta~, such as 316 stainless steel, or a metalized fabric of the type ~hich is flash vaporized with aluminum particles, Typically, this screen can be of a size having 4-1/2 to 13 courses per inch.
In operation, the electrode is applied with the subs-trate 15 in direct contact with the skin. me adhesive proper-ties of the substrate 15 eliminate the necessity for tape or other securing mediums to hold ~he elec~rode in continuous con~
tact with the skin. me swaged fastener 13, or other suitable ~0 connector, receives electrical signals from an external appa-ratus. m ese signals are conducted into the conductive mem-ber 11 which in ~urn directly conducts them into the substrate 15. In this manner, current densities are uniformly distri-buted over the area of the substrate 15 in contact with the conductive member 11 and, in turn, are uniformly transmitted to the skin surface in contact with the substrate 15~
Primary to the unique structure of the electrode for eliminating the n~ed for added electrode paste~, gels or elec-trolyte solutions, and for eliminating the need for securing mediums to hold the electrode in plac~, is the composition and structure of the substrate 15 material, enabling it to possess . .

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the desired physical, chemical and electrical properties.
Substrate 15 is a sheet or film of an electrically conductive organic polymer plasticized with a polyhydric al-cohol, preferably glycerol.
One example of an electrically conductive organic polymer which is suitable for use in substrate 15 is a hydro-colloidal material disclosed in U.50 Paten~ No. 4,111,992 issued September 5, 1978, inventor Michael Rosenberger~ mese hydrophilic random interpolymers have a capacity for absorbing and retaining large amounts, for example 10-1~5 times their own weight, of water. me cross-linked random hydrophylic inter-polymer compositions useful as components in substrate 15 may be prepared in accordance with the methods described in the above mentioned copending application. m e composition of the random hydrophilic interpolymers may be the same as the com-positions disclosed in U.S. Patent No. 4,111,992, tha~ is, the interpolymers may comprise: (A) from about 10 par~s by weight to about 90 parts by weight of an ester of an of,~ -olefinical-ly unsaturated carboxylic acid and a monohydric or polyhydric ~0 alcohol having a terminal quaternary ammonium group, and (B) correspondingly, from about 90 parts by weight to about 10 parts by weight of at least one ~ olefinically unsaturated comonomer, and (C) at least 0.02 parts by weight of a cross-lin~ing agent comprising a difunctional monomer.
In addition to the aforementioned interpolymer compo-sitions it is also possib e to use as the polymeric component of substrate 15 random interpolymers which include 100 parts by weight of an ester of an ~ olefinically unsaturated carboxylic acid and a monohydric or polyhydric alcohol having terminal quaternary ammonium group and at least 0.~ parts by weight of a difunctional cross-linking agent. The latter ~ .

3~58 mentioned random interpolymers are similar in composition to the first mentioned random interpolymer, except, of courseO
that the latter clas~ of polymers does no~ include the ~
olefinically unsaturated comonomers which are found in the first class of interpolymers. Both classes of polymer compo-sitions can be prepared by the method outlined in U.S0 Patent ~o. 4,111,992.
In accordance with this aspect of the inventionS the random interpolymer esters form a colloidal dispersion or suspen~ion in water. Glycerol or another polyhydric alcohol is added to the continuous phase to enhance plastici~y and hydrophilicity~ This form of the substrate 15 may be prepared by casting the hydrocolloidal material, described above, into shallow trays -Eor dryingO Heating to 120F for a given period of time, depending upon concentration and composition will hasten the formation of the hydrocolloid into an elas~ic and plastic film or sheet. m e thickness of this film or sheet is determined by the concentration of solids and the depth of pool of the hydrocolloidal material cast.
The composition and processing yields a material of su~ficient thickness to be a sheet and not a ~ilm of material.
me physical integrity of a sheet of material, wi~h its shape re~ention and elasticity, is desirable to the electrode structure and operation.
While as previously mentioned, the above disclosed interpolymers will absorb large amounts of wa~er, they are not completely insoluble in water due to the fact that they contain at least 0~02 parts by weight per 100 part~ of monomer of a difunctional cross-linking agent.
A second example of an electrically conductive organic polymer suitable for use in preparing substrate 15 is an al-~ . . .. .. .

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kali salt of a sulfated cellulose ester. The sulfated cellu-lose ester may be prepared as set forth in U.S. 3,897,782 issued August 5, 1975, inventor Deger C~ Tunc, The sulfated cellulose ester is selected from the group consisting of alkali cellulose ester sulfates wherein the acyl group comprises from 1 to 6 carbon atoms; more pre-ferably the acyl group comprises from 1 to 4 carbon atoms.
Examples of these resins are such alkali cellulose ester sulfates as sodium, potassium or lithium cellulose aceta~e sulfate, sodium, potassium or lithium cellulose ace-tate-butyrate sul~ate, sodium cellulose propionate sulfate and potassium cellulose butyrate sulate.
It has been discovered that these resins exhibit the unusual properties of retaining their tensile strength in salt solutions such as body fluids while readily dispersing in tap water~ It has further been discovered that these unique pro-perties are a function o~ the degree of sulfate gubsti~ution which expresses the average number of sulfate groups per anhydroglucose unit of the cellulosic ester. In general, by reducing this factor in a particular resin it will exhibit decreasing dispersibility in water and increasing strength in salt solutions. A moxe detailed discussion of this composi~ o tion may be obtained from a reading of the Body Fluid Barrier Filmspatent disclosure referenced above.
The substrate 15 compositions exhibit a tackiness which can be increased as the glycerol concentration i5 in-creased. As water and/or salt water is absorbed the surface of the substrate material 15 softens. As a result, the subs~
trate 15 will flow into pores and other irxegularities in the skin, creating a mechanical-interlock bond with ~he skin in addition to the already present adhesive bond. The bonding - - . .

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and, concommitantly, the electrical transmission of the elec-trode are enhanc~d as it "ages" in contact with the sk.in.
The flow condition eliminates air spaces between the skin and the substrate 15 to greatly reduce the impedance across the interface. mis in ~urn greatly reduces the heat normally created at this interface. While the surface portion of the substrate 15 will flow, the greater portion of its mass will remain intact. Thus, ~he material resis~s separation or the development of irregular thicknesses. As a result, two heat and/or burn producing conditions, i.e. a high resistance across the interface due to an air layer which creates high temperatures over the entire interface, and ~he physical con~
tact of the conductive member 11 dîrectly to the skin creating a shunt of the current to a small area and generating extreme temperatures in that area, are avoided~
A secondary electrical effect is also improved as the electrode "ages". Present during the operation of all elec-trodes is a battery effect created at the skin interface due to the capacitance across this interface. ~his battery effect causes some current to tend to circle backward towards its source of flow creating eddy currents. With this elec-trode of the invention, as water and body salts are absorbed into the electrode subs~rate, the interface area becomes more ionically, i.e., electrically, homogenous thus reducing the battery effect and any resulting eddy currents.
The electrode may be packaged for llse in a sealed sterilized envelope of any of a number of sui~able materials such as polyethylene. A release paper of the waxed or plas-tic coated type can be used to protect the substrate 15 be-~0 fore application ~o a skin surface.

Since many changes and many embodiments could b~ made ~3~

to the above-described invention without departing from the scope thereof, it is intended that all matter contained in the above description be interpreted as illustrative and not in the limiting sense.

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Claims

The embodiments of the invention in which an exclu-sive property or privilege is claimed are defined as follows:

1. An electrode providing electrical contact with a patient's skin comprising:
a conductive member connectable to an external elec-trical apparatus, and adhesive means for electrically interfacing to said patient's skin being electrically and mechanically connected to said con-ductive member, said interfacing means consisting essentially of an electrically conductive organic polymer plasticized with a polyhydric alcohol.

2. The electrode of claim 1 wherein said interfacing means is of sufficient thickness to constitute a sheet of material.

3. An electrode providing electrical contact with a patient's skin comprising:
a conductive member connectable to an external elec-trical apparatus, and adhesive means for electrically interfacing to said patient's skin being electrically and mechanically connected to said con-ductive member, said interfacing means comprising an electrical-ly conductive organic polymer plasticized with a polyhydric al-cohol, said electrically conductive organic polymer being an ester of an ?,.beta. olefinically unsaturated carboxylic acid and a monohydric or polyhydric alcohol having a terminal quaternary ammonium group.

4. An electrode providing electrical contact with a patient's skin comprising:

a conductive member connectable to an external elec-trical apparatus; and adhesive means for electrically interfacing to said patient's skin being electrically and mechanically connected to said con-ductive member, said interfacing means comprising an electrical-ly conductive organic polymer plasticized with a polyhydric al-cohol, said electrically conductive organic polymer being a sulfated cellulose ester.

5. The electrode of claim 1 wherein said polyhydric alcohol is glycerol.

6. The electrode of claim 1 wherein said interfacing means is an adhesive sheet adherent to said conductive member.

7. The electrode of claim 1 wherein said interfacing means is an adhesive film adherent to said conductive member.

8. The electrode of claim 6 wherein said adhesive sheet contains a diffusion screen located within said sheet and in alignment with said conductive member.

9. The electrode of claim 7 wherein said film is pliable and hydrophilic.

10. The improved electrode of claim 6 wherein said sheet is pliable and hydrophilic.

11. The improved electrode of claims 1, 3 or 4, where-in said interfacing means is further characterized as providing uniform conductivity with even current densities of approximate-ly 30 microamperes per square millimeter when subjected to a stimulus of about 10-50 milliamperes at 10-350 cycles per second having a pulse duration of about 50-1000 microseconds.

12. The improved electrode of claims 1, 3 or 4, where-in said interfacing means is a non-liquid adhesive substrate effective to adhere the electrode to skin, said substrate being easily separable from the skin upon removal without any notice-able residue.

13. An electrode providing electrical contact with a patient's skin comprising:
a conductive member including means for connection to an external electrical apparatus, and means for electrically interfacing to said patient's skin being electrically and mechanically connected to said con-ductive member, said interfacing means being a non-liquid adhesive subs-trate which is easily separable from the skin upon removal with-out any noticeable residue and which consists essentially of an electrically conductive organic polymer plasticized with a poly-hydric alcohol with said organic polymer being derived from an ester of an ?,.beta. -olefinically unsaturated carboxylic acid and a monohydric or polyhydric alcohol having a terminal quaternary ammonium group.

14. The electrode of claim 13, wherein said interfacing means is of sufficient thickness to constitute a sheet of material.

15. The electrode of claim 13, wherein said polyhydric alcohol is glycerol.

16. The electrode of Claim 13, wherein said interfacing means is an adhesive sheet adherent to said conductive member.

17. The electrode of claim 13, wherein said interfacing means is an adhesive film adherent to said conductive member.

18. The electrode of claim 16, wherein said adhesive sheet contains a diffusion screen located within said sheet and in alignment with said conductive member.

19. The electrode of claim 17, wherein said film is pliable and hydrophilic.

20. The improved electrode of claim 16, wherein said sheet is pliable and hydrophilic.

21. The electrode of claim 1 wherein said interfacing means is further characterized as providing uniform conductivity with even current densities of approximately 30 microamperes per square millimeter when subjected to a stimulus of about 10-50 milliamperes at 10-350 cycles per second having a pulse duration of about 50-1000 microseconds.

22. The electrode of claim 13, wherein said plastic-ized organic polymer comprises (A) from about 10 parts by weight to about 90 parts by weight of an ester of an ?,.beta. -olefinically unsaturated carboxylic acid and a monohydric or polyhydric al-cohol having a terminal quaternary ammonium group, and (B) correspondingly, from about 90 parts by weight to about 10 parts by weight of at least one ?,.beta. -olefinically unsaturated comonomer, and (C) at least 0.02 parts by weight of a cross-linking agent comprising a difunctional monomer.

23. An electrode providing electrical contact with a patient's skin comprising:
a conductive member including means for connection to an external electrical apparatus, and means for electrically interfacing to said patient's skin being electrically and mechanically connected to said con-ductive member, said interfacing means being a non-liquid adhesive subs-trate which is easily separable from the skin upon removal with-out any noticeable residue and which consists essentially of an electrically conductive organic polymer plasticized with a poly-hydric alcohol, said organic polymer comprising a sulfated cellulose ester.

24. The electrode of claim 23, wherein said sulfated cellulose ester is an alkali cellulose ester sulfate wherein the acyl group comprises from 1 to 6 carbon atoms.

25. The electrode of claim 23, wherein said inter-facing means is further characterized as providing uniform con-ductivity with even current densities of approximately 30 micro-amperes per square millimeter when subjected to a stimulus of about 10-50 milliamperes at 10-350 cycles per second having a pulse duration of about 50-1000 microseconds.

26. An electrode providing electrical contact with a patient's skin comprising:
a conductive member including means for connection to an external electrical apparatus; and adhesive means for electrically interfacing to said patient's skin being electrically and me-chanically connected to said conductive member, said interfacing means consisting essentially of an electrically conductive or-ganic polymer plasticized with a polyhydric alcohol with said organic polymer including quaternary ammonium groups.

27. An electrode providing electrical contact with a patient's skin comprising:
a conductive member including means for connection to an external electrical apparatus; and adhesive means for electrically interfacing to said patient's skin being electrically and me-18 .

mechanically connected to said conductive member, said inter-facing means consisting essentially of an electrically conduct-ive organic polymer plasticized with a polyhydric alcohol with said organic polymer including sulfate groups.