Biological electrode

A low-impedance biological electrode device for establishing electrical connection between the human body and electrical recording or stimulating apparatus without the use of conducting fluids, such as, gels, pastes and electrolytes, comprising, a substantially planar relatively thin electrode body, having as the electrically conducting connecting unit contacting the human body, a plurality of individual longitudinally extending strands, fibers, or filaments of conducting material embedded in a pressure-sensitive or solvent-activated adhesive which serves to bond the strands together in a composite connecting unit and to bond the connecting unit on one side to said electrode body and on the other side or interface to the human body, a modification being the use of strands cross-oriented with respect to the longitudinal strands, as exemplified by woven conductive material, the connecting unit being provided with a transverse bus bar in the form of metal foil in electrical contact with an electrical connecting element for conducting current from the connecting unit in contact with the human body to the electrical recording or stimulating apparatus.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
Electro-medical electrodes for establishing electrical connection between 
an animal body, specifically the human body, and an electrical recording 
device. 
2. Description of the Prior Art 
In the prior medical art it has been a well known practice to attach 
electrodes to the skin to provide contact and through which electrical 
signals are transmitted between the anatomy and electromedical apparatus. 
U.S. Pat. to Baum, No. 3,187,745 and Berman, No. 3,085,577 are exemplary 
of such electrodes, employed in the art of electrocardiography wherein 
electrical heart signals are received, and the U.S. Pat. to Alderman, No. 
2,872,926, is exemplary of an electrode employed in the art of 
electroencephalography wherein electrical brain signals are received. The 
signals, in either event, are suitably recorded or charted and are a 
measure of a body function or functions under known conditions, such as 
rest, exercise, mental stress, intensive care and the like. Also, with the 
advent of space travel and radio monitoring, or with the use of small 
portable electromedical recording devices, it is now possible to 
biologically monitor body functions of pilots under conditions encountered 
in fulfilling their missions. The importance of maintaining a low 
resistance contact with the anatomy is well recognized and the patents 
referred to are exemplary of obtaining the desired results by utilizing 
electrolytes, electroconductive gels, pastes and/or adhesives through 
which an electric signal is transmitted. Other pertinent U.S. Pat. Nos. 
are 2,555,037; 2,985,172; 3,170,459; 3,474,775; 3,475,213; 3,565,059; 
3,607,788; 3,710,782; 3,713,435; and 3,911,906. The U.S. Pat. to Howell, 
No. 2,943,628 is exemplary of another approach wherein contact is made 
with metal foil surrounded by a pressure sensitive adhesive. 
As the art referred to has advanced, certain improvements appear desirable, 
including the need for more rapid and expedient application of the 
electrodes and simplification of their construction, together with its 
attendant reduction of cost. Additionally, a light weight electrode is 
desirable to minimize or obviate inertial movement relative to a 
predetermined position on the skin. 
Prior art biological electrodes for electrocardiography are not capable of 
rapid attachment to the body and rapid removal therefrom, are not 
non-irritating, transparent to medical x-rays, or easily removed by 
dissolution of adhesive or by peeling. The adhesive used with prior art 
biological electrodes, such as gelled pads, has a tendency to dry out 
during storage or use, and in some cases serves as a nutrient for 
bacteria. 
While others have taught the incorporation of conducting particles into 
electrode surfaces, the absence from their teaching of several critical 
elements prevented them from disclosing products of practical utility. A 
satisfactory biological electrode must exhibit at least two required 
properties; (1) it must provide a high electrical conductivity through the 
skin, and (2) it must have enough adhesive strength to remain securely in 
place on the patient. It has been found that the use of particles of 
conventional geometry, i.e., "fine powder carbon" (Reinhold U.S. Pat. No. 
3,911,906), silver flakes or their metal particles (Burton U.S. Pat. No. 
4,008,721), and carbon black (Johnson U.S. Pat. No. 3,474,775), results in 
pressure sensitive electrodes which may have one, but never both of the 
above properties. Prior electrodes having satisfactory conductivity did 
not have enough adhesive strength, and increasing the adhesive content to 
cure this defect resulted in lowering the conductivity to an 
unsatisfactory level. 
Stow U.S. Pat. No. (3,475,213) overcome part of the problem with the use of 
particles having a "substantial thickness in relation to their width and 
length", typically "spheres or granules". While solving part of the 
problem, particles of this geometry still leave conductivity across the 
face of the electrode so low as to require a conductive backing material. 
This backing material would typically be a metal foil, and would not lend 
itself well to the skin "breathability" or conformability desirable in a 
biological electrode. 
The present invention, which is described hereinafter, takes advantage of 
the unique geometry of fibers used with a "soft" (deformable on a 
microscopic scale) adhesive to solve the problems not addressed by the 
prior art. In contrast to the particles used by Stow, fibers have a high 
length-to-thickness (diameter) ratio, and thus a single fiber may make 
physical and electrical contact with the many other fibers that may cross 
it anywhere along its length. This property of fibers provides a very high 
conductivity at low fiber concentrations in the adhesive, thus permitting 
the construction of an electrode having good adhesive strength, good 
electrical properties, and no foil backing. The particles mentioned in the 
prior art, on the other hand, can make contact with only a few other 
particles, and then only in the confines of a non-linear geometry, 
resulting in the limitations already discussed. 
For use as a biological electrode, conductivity through the electrode is 
important, but is not enough in itself; the electrode surface must provide 
for high conductivity to the skin and into the body. Fibers imbedded in a 
rigid or semirigid binder might have excellent electrical properties 
throughout the electrode, but would not be able to provide the many 
necessary skin contacts to make a usable biological electrode interface. 
To facilitate good contact between the skin and fibers, the adhesive or 
binder in the electrode must be soft enough at the time of application to 
allow the adhesive to "flow" out of the way of the fibers, permitting as 
many fibers as possible to make direct contact with the skin. The adhesive 
then fills in any available voids provided by skin and fiber 
irregularities to provide for firm holding strength. The result is a 
series of microscopic hills (fibers) for conductivity, with adhesive in 
the valleys for holding strength. Thus the combination of fibers and the 
required type adhesive is important. 
The above desired properties for the electrode of the present invention are 
obtained in one of two ways: (1) combining fibers with a soft, pressure 
sensitive adhesive, or (2) combining fibers with a solvent activated 
adhesive that is soft upon application to the skin, but becomes more rigid 
upon drying. For optimum properties, the fibers should have a very small 
diameter (.apprxeq.0.0003") and as high a length to diameter ratio as 
possible (preferably greater than 1500) for the following reasons. The 
small diameter of a fiber allows for more fibers per unit area of 
electrode surface, and thus better electrical properties. The greater the 
length of the fibers involved, the fewer fiber ends will be present on the 
electrode surface, resulting in less skin irritation to the patient. 
Unacceptable skin irritations and itching has been observed when 0.0003" 
diameter fibers are used in lengths much shorter than one-half inch, but 
very little irritation when longer fibers are used. Accordingly, fibers 
less than 0.0003" in diameter and at least one-half inch in length are 
preferred. 
SUMMARY OF THE INVENTION 
A low-impedance biological electrode device for establishing electrical 
connection between the human body and electrical recording or stimulating 
apparatus without the use of conducting fluids, such as, gels, pastes and 
electrolytes, comprising, a substantially planar relatively thin electrode 
body, having as the electrically conducting connecting unit contacting the 
human body, a plurality of individual longitudinally extending strands, 
fibers, or filaments of conducting material embedded in a 
pressure-senstive or solvent-activated adhesive which serves to bond the 
strands together in a composite connecting unit and to bond the connecting 
unit on one side to said electrode body and on the other side or interface 
to he human body, a modification being the use of strands cross-oriented 
with respect to the longitudinal strands, as exemplified by woven 
conductive material, the connecting unit being provided with a transverse 
bus bar in the form of a metal foil in electrical contact with an 
electrical connecting element for conducting current from the connecting 
unit in contact with the human body to the electrical apparatus. 
The electrode is of laminated construction with the conducting connection 
unit having its interface which contacts the body covered with a plastic 
release cover which itself may be covered with a paper backing. A bus bar 
in the form of aluminum foil is adhesevely secured across one end of the 
conducting unit. A plastic strip is provided between the foil and the 
outer release strip. An electrical connecting plug is secured to the body 
to connect the foil to the appropriate electrical instrument. The strands 
of the conducting unit may be provided with an adhesive supporting 
backing. A gauze strip may be secured to the backing or to the fibers 
themselves and a final lamination of sponge rubber constitutes the other 
face of the electrode body. A preferred adhesive for securing the strands 
of the conducting unit together is plasticized polyvinylpyrrolidone.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The invention will now be described with reference to the accompanying 
drawing in which like numbers represent the parts. 
Referring to FIG. 1, the numeral 10 represents the electrode of the 
invention attached to the patient and connected by electrical connections 
12 to an electrical instrument 14, such as an electrosurgery device. 
Referring to FIG. 2, the electrode 10 is shown as a substantially planar, 
relatively thin structure, having an electrical connector 36 mounted in 
one end thereof. 
Referring to FIG. 3, the outer release strip 18 of suitable plastic is 
shown peeled back to expose the conducting connection unit indicated 
generally at 20. The release strip protects the adhesive surface of unit 
20 until the electrode is ready for use. The connecting unit 20 is 
comprised of individual strands, fibers, or filaments 22, the majority of 
which are supported in a substantially planar orientation. These fibers or 
strands extend longitudinally over or through the length of the electrode 
body 10. The terms "over" and "through" mean that the fibers are supported 
throughout the unit including on its surface. Preferably, some of the 
fibers extend the entire length of the unit to provide a large area of 
coverage over the skin, although it is not required that any of the fibers 
do this. The fibrous strands or filaments are preferably made of graphite, 
such as, carbon yarn or other carbonized fiber, although they may be 
metallic fibers, knits and woven screens. The terms "fibers", "strands" 
and "filaments" are used interchangeably herein. If woven metallic or 
graphite screens are used, they will include fibers oriented transversely 
of the longitudinal fibers and they are referred to herein as being 
"cross-oriented", this term including any angular orientation of the 
transverse fibers with the longitudinal fibers. The fibers are secured 
together by a pressure sensitive or agent-activated adhesive, which forms 
the fibers into a composite units and serves to bind them on one side to 
the electrode and on the other side to the human body. By "agent-activated 
adhesive" is meant a composition which is made adhesive by means of an 
additive, such as, a solvent or one causing a chemical reaction. The 
adhesive must be sufficiently soft so that upon application of the 
electrode it will spread or "flow" away from the fibers or strands near 
the surface of the unit 20 to permit direct contact of the strands or 
fibers with the skin when the adhesive "sets", as the adhesives used are 
not conductive and one purpose of the invention is to avoid the use of 
conductive adhesives and like materials. The adhesive then fills in any 
voids between skin and fibers, including those formed by fiber and skin 
irregularities, to provide for firm holding strength. The resulting bond 
comprises a series of exposed microscopic hills (fibers) for conductivity, 
and valleys filled with adhesive for holding strength. The result is 
produced by the critical combination of properly planar oriented fibers 
and adhesive. The covering strip or insulator 24 of suitable plastic for 
the bus bar 26 is shown peeled back to expose the bus bar overlying one 
end of the conductive filaments 22 of connecting unit 20 and in electrical 
connection with a plug 16. In the preferred construction an aluminum foil 
26 is used for the bus bar and is positioned transversely entirely across 
one end of the connecting unit 20 in electrical contact therewith. 
Referring to FIGS. 4, 5 and 6, the laminated structure of the electrode 
will now be described starting with the centrally located connecting unit 
20 and proceeding in each direction. Proceeding toward the bottom of the 
electrode, the next layer as shown in the figures is the bus bar 26 over 
which is centrally positioned the circular flange constituting the base 27 
of the electrical plug 16. The next succeeding layer is the plastic strip 
or cover 24 for protecting the bus bar 26 extending only far enough 
longitudinally of the connecting unit to perform this function. The final 
layer constituting the bottom of the electrode and covering the adhesive 
interface of the electrode and the cover 24 is the release strip 18. 
An outer protective backing 28 of paper may be provided to protect the 
entire laminated structure. Proceeding in the other direction from the 
connecting unit 20, the conductive filaments 22 which are clearly 
illustrated in FIGS. 5 and 6 as being contiguous may be reinforced with an 
upper backing layer of adhesive covering 30. To this covering, or to the 
strands if no covering is used, a layer 32 of ordinary surgical gauze may 
be secured by a suitable adhesive for extra strength. An outer top 
covering 34, preferably of sponge rubber, is adhesively secured over the 
gauze layer to complete the laminated electrode structure. 
An electrical connector 36 is provided for electrical connection to the 
electrical plug 16 as shown in FIGS. 2 and 4. Connector 36 is used to 
connect the plug 16, and in turn the connecting unit 20, with apparatus 
14. 
The pressure-sensitive or solvent-activated tacky adhesive used to bind the 
conducting filaments 22 together into a composite unit is an important 
feature of the invention as explained above. The preferred active 
ingredient of the adhesive is polyvinylpyrrolidone sold commercially under 
the trade name "PLASDONE K29-32". Other materials which may be used are a 
nitrocellulose base material sold commercially as "DUCO 5458", siloxane, 
vinyl acetate, acrylate, or other such type organic polymer. The adhesive 
mixture is compounded by mixing with the active agent a plasticizer such 
as dioctyl phthalate, camphor, glycerin, or other equivalent plasticizer 
and, alternatively, a conventional tackifier, such as, "IGE CO-210". A 
suitable solvent for the solvent-activated adhesive is alcohol. Other 
conventional solvents may be used. The polyvinylpyrrolidone base adhesive 
can be formulated as a solvent activated or a pressure sensitive adhesive, 
and this is the preferred type adhesive for forming the adhesive matrix of 
strands and adhesive having the property of spreading or "flowing" upon 
application of unit 20 to permit direct contact of the fibers or strands 
with the skin. Other adhesive compositions may be used, such as some of 
those disclosed in the above-cited patents. 
The adhesives serve not only to bond the conductive strands into a 
composite unit, but they also serve to bond the connecting unit 20 on one 
side into the electrode and to bond the unit 20 on its other side to the 
human body when applied thereto after removal of release strip 18. 
The composition of the pressure sensitive organic adhesive or the 
solvent-activated adhesive can vary within fairly wide limits to provide 
an adhesive having the desired properties to permit maximum contact 
between conducting fibers and the skin, as discussed above. The conductive 
fibers in the composite electrical connecting unit 20 comprise about 10-90 
percent by volume and preferably 40-50 percent by volume of the unit. The 
adhesive should have a cone penetration range of 0.5-10 cm. as determined 
by the ASTM test procedure D-217. The bond strength of the adhesive should 
range from 0.25-10 lb/inch as tested against stainless steel by ASTM test 
method D-903, the preferred range being 0.5-2.5 lb/inch width. The surface 
resistivity of the conductor/adhesive composite should be in the range of 
less than five ohms/sq. cm. Also the bus bar 26 should extend transversely 
of the consolidated strands and should extend entirely across the strands 
for the most effective transfer of electrical current. 
In operation, the body area to which the electrode is to be applied is 
properly cleaned. The release strip 18 is then peeled off and if a 
pressure sensitive adhesive is used the electrode is applied to the arm or 
other body area by contacting the body area with the adhesively coated 
strands and applying pressure. If a solvent-activated adhesive is used, an 
activating solvent, such as alcohol, is applied to the adhesive before 
applying it to the body area. The receptacle 36 leading to the electrical 
recording instrument 14 is then inserted over the plug 16 and recordings 
noted. 
Comparative tests were made with the electrode of the invention 
incorporating the novel conducting connecting unit 20 and with 
conventional electrodes using conducting gels and electrolytes, and the 
results are set forth in the following examples: 
EXAMPLE 1 
An electrode was prepared by placing graphite yarns in parallel, 
unidirectional, substantially planar orientation on an aluminum foil strip 
to serve as a bus bar, followed by impregnating the layup with a presure 
sensitive adhesive having the following composition: 
______________________________________ 
Polyvinylpyrrolidone (PLASDONE K 29-32) 
10 grams 
Tackifier (IGE CO-120) 15 grams 
Solvent (Denatured alcohol) 15 grams 
______________________________________ 
The wet fibers were covered with a polyethelene film so that the composite 
could be rolled to compress the assembly. The polyethelene was removed, 
adhesive was dried, and electrical attachment was made by applying 
sufficient pressure of the contacting surface against the skin to insure 
that the adhesive "flowed" or spread away from the surface fibers to 
permit their direct contact with the skin. The adhesive then fills in any 
voids between skin and fibers, including those formed by fiber and skin 
irregularities, to provide for firm holding strength. The electrode was 
evaluated by placement on the right upper arm of a patient using its 
adhesive for attachment. For comparative purposes, a commercial dispersive 
electrode with pre-gelled electrolyte was placed in a comparable location 
on the left arm of the patient. Electrosurgical power was applied across 
the pair of electrodes. In the range of 130-150 watts the gelled electrode 
caused considerable stimulative sensation and some heating. In contrast, 
the conductive adhesive electrode of the invention produced no stimulation 
with a comparable amount of heating. 
EXAMPLE 2 
An electrode was prepared as in Example 1, except that the aluminum foil 
was used only in the form of a narrow strip perpendicular to the direction 
of the graphite fibers at the end where the electrical connector was 
attached. This pressure-sensitive electrode was applied and tested by the 
same tests used in Example 1 to 150 watts of electrosurgical coagulation 
power without adverse patient reaction. In contrast, the gelled electrode 
caused reaction at 135 watts. 
Other successful tests giving comparable results to those of Examples 1 and 
2, were made using metallic fibers, and knits and woven screens of 
metallic fibers and graphite fibers. Successful tests were also made using 
an electrode incorporating the conductive connecting unit 20 having 
conducting fibers impregnated with solvent activated adhesives in which 
the active agent was vinyl acetate, acrylate or other equivalent type 
organic polymers. Others which are operative are nitrocellulose and 
siloxane. 
It was found that the electrodes as described above, using the operative 
combination of fibers and adhesive, and particularly those using the 
polyvinylpyrrolidone adhesive combination with the fibers, strands or 
filaments, were easily attached and removed and conformed accurately with 
the human body. As the Examples show, more efficient power dissipation 
without pain or heat development than with conventional electrosurgery 
pads using gels and electrolytes was obtained. It was found that the 
adhesive did not dry out during storage or during use. It was also found 
that the adhesive was not a nutrient for bacteria. The adhesive contained 
in the connecting unit 20 was non-irritating and the electrode was found 
to be transparent to medical x-rays. The impedance of the electrode was 
comparable to that of conventional electrodes using conductive gels, 
pastes, and electrolytes.