CA1152570A

CA1152570A - Biomedical electrode

Info

Publication number: CA1152570A
Application number: CA000347778A
Authority: CA
Inventors: Franklin C. Larimore
Original assignee: Minnesota Mining and Manufacturing Co
Current assignee: 3M Co
Priority date: 1979-03-21
Filing date: 1980-03-17
Publication date: 1983-08-23
Also published as: AU538413B2; IT8020791A0; IT1131006B; GB2045088B; DE3010754A1; FR2451747B1; JPH0175408U; FR2451747A1; AU5662180A; GB2045088A

Abstract

ABSTRACT
An essentially dry, disposable biomedical electrode is disclosed com-prising a body conformable, electrically conductive extensible interfacing member, an extensible backing member, having a hole therethrough, adhered to one side of the interfacing member and a reusable low profile one-piece electrically conductive connector adhered to the top surface of the inter-facing member. In an alternative embodiment the backing member does not have a hole but partially covers the connector to which it is adhered thereby securing the connector.

Description

~5z~7~ File No 915,550 BIOMEDICAL ELECTRODE

This invention relates to disposable electrodes, often termed "biomedical" electrodes, for establishing an electrical connection between the skin of the human anatomy and an electromedical apparatus, such as a high impedance electromyograph, electrocardiograph, electrical neurostimulator for pain relief, and the like. More particularly it relates to so called "dry" bioelectrodes which do not require the use of messy creams or gels to enhance conductivity between ~he skin and the electrode plate.
A variety of disposable biomedical electrodes are known in the art. Generally, they comprise a metallic electrode plate adapted for connection to a lead wire which is, in turn, attached to the electromedical apparatus. Typically, a paste, cream, or gel which contains ionic material is relied upon to conduct the electric current and improve the electrical connection between the skin of the patient and the electrode plateO
An adhesive tape is commonly used to adhere the entire apparatus to the skin. Examples of electrodes of this general type are described in U.S. Patents 3,587,565 and 3,805,769.
The conductive pastesJ creams, or yels used in these prior art biomedical electrodes are unpleasant to use, sloppy, and often irritating to the skin particularly when the skin is cleaned and abraded prior to application ,.~, 31Ll~iiZ~

-2--of the electrode. Since these electrodes all contain water as the major ingredient to solvate the ions present and function as a medium through which the solvated ions migrate, they require elaborate packaging to prevent loss of water prior to use. Furthermore, they leave a residue on the skin after removal of the electrode which requires cleanup. A further disadvantage of the electrodes of the conductive paste, cream, and gel types is that they develop an overpotential in defibrillation procedures unless the surface of the electrode plate is of expensive silver/silver chloride.
To overcome many of the problems associated with so called ~wetU electrodes, biomedical electrodes having an integrally formed metal snap connector have been proposed whlch utilize "dry" conductive material. U.S.
Patents ~,008,721 and 3,911,906 disclose biomedical electrodes utilizing adhesives impregnated with conductive particles. These adhesives serve the dual purpose of enhancing conductivity with the skin and securing the electrode to the skin. Although avoiding the sloppiness and packaging problems associated with gels and pastes, such electrodes generally do not provide satisfactory electrical connection to the skin because the presence of the conductive filler results in a high signal-to-noise ratio and is deleterious to adhesion. Generally, the use of nonhomogeneous conductive formulations in bio-electrodes has been found to give rise to noisy electrical ~ Z570 signals. It is speculated that dispersed metal or salt particles in a binder matrix form a discontinuous, electrically conductive path which develops ran-dom, nonuniform electrical fields between particles which causes noise.
A further disadvantage associated with most prior art disposable electrodes is their relatively high cost due to a larger extent to the metal snap connector. Since the connector is permanently attached to the electrode it must be discarded after one use along with the electrode.
The biomedical electrode according to the present invention of~ers several advantages over the previously described biomedical electrodes. The present electrode by virtue of its dry conductive material eliminates messy gels, creams or pastes. Also, the biomedical electrode of the present inven-tion may be manufactured at a lower cost because the rigid snap fastener which is an integral part of the prior art electrode has been eliminated and a flexible reusable connector provided instead.
According to the present invention, there is provided a dry biomedical electrode for establishing electrical contact between the epidermal layer of the skin of a mammal and an external electromedical device comprising: a body conformable, electrically conductive, extensible interfacing member having an adherent top surface and a lower body contacting surface adherent to the skin; at least one body conformable, one-piece electrically conductive connector having a substantially flat electrical impulse distribution/
receiving portion having a flat lower surface adapted for electrical contact with 2E~7~

said interfacing member and means for connection to said electromedical device at an upper surface thereof, said connector being releasably adherent to said top surface of said interfacing member; and an extensible bac~ing member adhered to said connector and at least a portion of said top surface of said interfacing member whereby said connector is retained in electrical contact with said interfacing member.
The invention will now be described in greater detail with reference to the accompanying drawings, in which:
FIGURE 1 is a perspective view of the biomedical electrode of the present invention;
FIGURE 2 is an enlarged cross-sectional view of the biomedical electrode of FIGURE 1 through line 2-2;
FIGURE 3 is a perspective view of the interfacing member and attached backing of the biomedical electrode of the present invention;
FIGURE 4 is a cross-sectional view of the biomedical electrode of FIGURE 3 through line 4-4;

31 ~S~57~J

FIGURE ~ is a perspective view of an alternative and preferred embodiment of the electrode of the present invention;
FIGURE 6 is a fragmented side view of the biomedical electrode of FIGURE 5;
FIGURE 7 is an end view of the biomedical electrode of FIGURE 6;
and FIGURE 8 is a side view of a second alternative embodiment of the electrode of the present invention.
Referring to the drawing wherein like reference characters designate like or corresponding elements and referring particularly to FIGURE 1, the biomedical electrode 10 is comprised of a one piece electrically conductive reusable connector 16 and a body conformable, electrically conductive inter-facing member 11 having a top surface and a lower body contacting surface adherent to the skin.
Interfacing member 11 preferably exhibits extensibility which is similar to skin. Extensibility is used herein to mean the ability of a material to stretch when a force is applied in a manner similar to skin, i.e. up to 50%, and substantially returned to its prestretched condition when the force is removed. The preferred interfacing member 11 is comprised of a carrier portion 12, coated with an electrically conductive adhesive 13.
Carrier portion 12 may be comprised of a mat s~

of separate fibers bonded together, e.g. a nonwoven web, which is body conformable and extensible. The fibers may be polyester, nylon or a cellulosic derivative, e.g., rayon, paper, etc. Carrier portion 12 may also be of a 5 woven structure if the weave allows for the needed extensibility and adhesive impregnation. The ability of a woven or nonwoven structure to allow for impregnation of the conductive adhesive enables the adhesive 13 to conduct the electrical impulse evenly throughout the interfacing 10 member 11. It has been unexpectedly found carrier portion 12 may be made of a film, such as cellophane, for certain types of electrode, e.g., receiving electrode. The prefer-red material for carrier portion 12 is Crystex~ paper tissue, manufactured by Crystal Paper Co., ~iddletown, 15 Ohio. Carrier portion 12 imparts a measure of mechanical strength to the construction and may be omitted if the conductive adhesive layer 13 has sufficient strength and extensibility to maintain integrity during use. One group of adhesives which have been found to exhibit this 20 integrity is plasticized natural gums, e.g., karaya, carageenen, guar.
Adhesive 13 not only should be electrically conductive but should exhibit sufficient tack to releasably adhere to both the skin and reusable connector 25 16.
The preferred adhesive 13 is comprised of 75:25 butyl acrylate-acrylic acid copolymer neutrali~ed to 95 ~ ~ra ~/e ~r ,4 .

, ~5257~

mole percent with methyl diethanolamine to which 20 parts/100 parts copolymer and 30 parts/100 parts copolymer of a water soluble plasticizer and a water soluble tackifier respectively are added as described in U.S.
5 Patent 3,065,770. The resultant adhesive composition preferably is coated onto both sides of said carrier scrlm 12 at 9,2 micrograms/cm2 (dry basis) to form the interfacing member 11.
It is contemplated that other polymeric 10 adhesives such as those disclosed in U.S. Patents 4,125,110, 4,066,078, 4,067,342, 3,911,906, 4,054,714 and

3,994,302 may be utilized in interfacing members of the present invention.
Af f ~c~
- -~ptionally attached to the top surface of 15 interfacing member 11 is a backing member 14 which in the embodiment of FIGURES 1-4 has a hole 15 therethrough which allows access to the top surface of the interfacing member 11. The backing member 14 acts to maintain the integrity of the interfacing member 11 by covering all of its 20 surface except the hole 15 when the biomedical electrode 10 is positioned on the wearer. Backing member 14 must exhibit sufficient extensibility to be compliant with interfacing member 11 after electrode 10 is placed on the wearer. The preferred material for backing member 14 is a 25 vinyl foam tape sold under the trade name of Microfoam Tape, 3M Company, St~ Paul, Minnesota 55101. Other suitable materials include a compressed polyurethane foam ~S2~7~

sold under the trade name of Scott Felt*, Scott Foam Division, Scott Paper Company, Eddystone, Pennsylvania or a closed cell polyethylene foam, sold under the trade name of Volara*, Voltex Corporation, Lawrence, Massachusetts.
For the present invention, a body conformable, one-piece electrically conductive connector 16 connects the interfacing member 11 to the electro-medical device. Reusable connector 16 is comprised of a substantially flat electrical impulse distribution/receiving portion having a flat lower surface adapted to fit within hole 15 of backing member 14 in electrical contact with the interfacing member 11. Connector 16 also is provided with an upper surface having an adapter 1~ for connection to the connector lead of the electromedical device ~not shown). The connector is preferably made of a carbon impregnated silicone rubber, SE 760Q, General Electric Company, Waterford, New York. Other suitable carbon impregnated polymeric materials include plasticized polyvinyl chloride, epichlorohydrin rubber, polyurethane * Trade marks Z5~6~

molding compound, polytetra1~orethylene and a polymer of ethylene-propylene-diene (e.g EPDM rubber).
Referring to FIGURE 4, an optional release liner 17 may be attached to the lower surface of the interfacing member 11 in order to preserve its adhesive character until ready for use. Such release liners are well known to the art.
To use the biomedical electrode assembly of the present invention, the release liner 17 is removed and the electrode is placed on the desired surface of the skin.
Prior to placing the electrode to the skin, the skin or the lower surface of the interfacing member 11 may be wetted with water to optimize the adherence and conduc-tivity of the adhesive. The connector, which has been previously attached to the lead of the electromedical device, is then releasably adhered to the upper surface of the interfacing member 11 through hole 15. When the monitoring or stimulation is complete the connector is removed and preserved while the disposable portion constituted by the interfacing member 11 and the attached backing 14 may be discarded.
~ eferring to Figures 5 through 8, alternative embodiments 20 and 30 may be made without departing from the spirit of the present invention. The alternative embodiments 20 and 30 are also comprised of an optional release liner 17, an interfacing member 11 and an optional backing mem~er 14A. Connectors 21 and 31 of embodiments ~5~5~

20 and 30 respectively likewise comprise a one piece construction having means for connection with an e~ternal electromedical device 18 and a flat electrical impulse distribution/receiving portion -for electrical contact with interfacing member 11.
Connectors 21 and 31 differ from connector 16 of electrode 10 in that they are elongated rather than circular. It has been found that in certain use situations movement of the patient may cause the connector 16 of embodiment 10 to become separated from interfacing member 11. By over-laying a portion of backing 14A on the top surface of connector 21 or 31 this problem is substantially eliminated.
In order to facilitate the placement of connector 21 or 31, an additional double sided release liner ~no~ shown) may be placed between a portion of the backing member 14 and the interfacing member 11. This double sided release liner may then be removed and connector 21 or 31 positioned on interfacing member 11 as shown in Figure 5 or 8. Backing member 14A is then positioned so as to releasably adhere to at least a portion of the top surface of connector 21 or 31 and interfacing member 11 so as to insure electrical contact between connector 21 or 31 and interfacing member 11.
It is contemplated that electrode 20 can be supplied as shown in Figure 5 and the connector may be discarded along with the remainder of the electrode after the initial use or removed, if desired and reused.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A dry biomedical electrode for establishing electrical contact between the epidermal layer of the skin of a mammal and an external electromedical de-vice comprising: a body conformable, electrically conductive, extensible inter-facing member having an adherent top surface and a lower body contacting surface adherent to the skin; at least one body conformable, one-piece electrically conductive connector having a substantially flat electrical impulse distribution/receiving portion having a flat lower surface adapted for electrical contact with said interfacing member and means for connection to said electromedical device at an upper surface thereof, said connector being releasably adherent to said top surface of said interfacing member; and an extensible backing member adhered to said connector and at least a portion of said top surface of said interfacing member whereby said connector is re-tained in electrical contact with said interfacing member.

2. The dry biomedical electrode in accordance with claim 1 wherein said connector consists of a carbon impregnated polymeric material selected from a group consisting of silicone rubber, plasticized polyvinyl chloride, epichloro-hydrin rubber, polytetrafluoroethylene, or a polymer of ethylene-propylene diene.

3. A dry biomedical electrode in accordance with claim 1 or 2 wherein said interfacing member is comprised of a carrier portion having an electrically conductive adhesive coating said top surface and said lower body contacting surface.