Electrochemically reversible silver-silver chloride electrode for detecting bioelectric potential differences generated by human muscles and organ

Day, J. L.

Lippitt, M. W., Jr.

English

NASA Technical Reports Server

Jan. 7,1969 
Filed D ~ G .  31, 1964 
J. L. DAY ETAL 3,420,223 
ELECTRODE FOR BIOLOGICAL RECORDING 
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3,420,223 
ELECTRODE FOR BIOLOGICAL RECORDING 
Joe L. Day and Maxwell W. LipFitt, Jr., Houston, Tex., 
assignors to the United States of America as repre- 
sented by the Administrator of the National Aero- 
nautics and Space Administration 
Filed Dec. 31, 1954, Ser. No. 422,864 
U.S. CI. 128-2.06 7 Claims 
Int. C1. A61b 5/04 
ABSTRACT O F  THE DISCLOSURE 
An electrode for detecting potential differences generat- 
ed by parts of the human body comprising an electro- 
chemically reversible silver chloride anodized silver disk 
which contacts the skin through an electrode paste on one 
face of the disk. A lead wire is soldered to the opposite 
face end this connection is then coated with an epoxy 
resin to preclude contact of it with the paste in order to 
prevent spurious electrical activity which would spoil 
the quality of the signal. 
The invention described herein was made by em- 
ployees of the United States Government and may be 
manufactured and used by or for the Government for 
governmental purposes without the payment of any 
royalties thereon or therefor. 
This invention relates to instrumentation for measur- 
ing the bioelectrical potentials of living animal bodies 
and more particularly to  an improved electrode for de- 
tecting potential dserences generated by the heart, brain, 
and other parts of the human body. 
Due to the planned exploration of outer space medical 
science has been summoned to  further investigate the ef- 
fects on the human body of unusual physical conditions 
caused by such factors as high speeds, elevated tempera- 
tures, and extremely rapid acceleration. In addition to 
this preexploratory research, it is desirable to monitor 
certain functions of the human body while an astronaut 
or pilot is engaged in his normal operational functions. 
One method of accomplishing these objectives is by 
utilization of the phenomeca of bioelectric potentials. 
By accurately measuring the minute potential generated 
by the muscles and organs of a living body, a scientist 
or physician can accurately translate these electrical 
parameters into meaningful biological and physiological 
characteristics. 
The use of electrode systems for sensing bioelectric 
potentials on a living body has long been known to medi- 
cal science. Both the clinician and medical investigator 
have been plagued, however, by unsatisfactory electrode 
devices which produce inconsistent and inaccurate wave- 
forms. Most prior art electrodes have been found unsuit- 
able for extended or repeated usage not only because of 
their general design which causes localized skin irrita- 
tion, but also because of deterioration of the electrode 
proper. Due to the electrochemically irreversible nature 
of their construction, the use of prior art electrodes on 
any thing other than a substantially static body in- 
troduces severe artifact into waveform readings. Use on 
active physical subjects is additionally discouraged by 
reason of the relatively fragile connection of the lead 
wire to the electrode plate. Further, it has been found 
that considerable electro-chemical noise results from the 
manner in which this connection has been made. There- 
fore, the instant invention is directed to an improved 
electrode device for use with electrocardiograms, electro- -  
enceuhalograms. imnedance Dneumoarams. and other de- - - I _  - ,  
vices measuring bioelectric potentials of a living body. 70 contact the upper surface 37 also. This is doni in order to 
The present electrode is found to substantially eliminate reduce the current density, it being known that a reduc- 
spurious electrical activity during operation thereby pro- tion in the current density reduces the rate of deteriora- 
2 
ducing accurate and reliable waveforms. More specifi- 
cally, due to an improved electrode plate consisting of 
an electro-chemically reversible silver chloride anodized 
silver disk, the present invention, when used in conjunc- 
5 tion with any electrode paste containing sufficient 
chloride ions, detects the smallest of potentials while 
minimizing electro-chemical artifact. An additional ad- 
vantage of the snbject invention resides in its durable 
and highly insulative comtruction which thereby allows 
10 use during active physical movements while simultane- 
ously eliminating sources of electro-chemical noise. Also, 
due to the improved construction and design of the elec- 
trode it may be used over extended periods of t h e  of 
up to 28 days or more without fear of appreciable dete- 
15 rioration of the electrode or irritation by the wearer. 
Additional features of this invention and a more com- 
plete understanding of the nature of its use may be had 
upon examination of the following detailed description, 
claims, and accompanying drawings wherein like numer- 
20 als denote like parts in the various views and wherein: 
FIG. 1 is a perspective view of the preferred electrode 
of the invention; 
FIG. 2 is a cross section of the electrode of FIG. 1 
along the axis 2-2 thereof; 
FIG. 3 is a perspective view of the electrode of FIG. 1 
having the electrode disk displaced from the housing SO 
as to show the interior thereof; 
FIG. 4 is a perspective view of a modified electrode in 
accordance with the invention; 
FIG. 5 is a cross section of the electrode of FIG. 4 
along the axis 5--5 thereof; and 
FIG. 6 is a perspective view of the modified electrode 
in which the housing is displaced from the electrode and 
rotated 180" so as to show the internal recess in the 
With reference to FIG. 1 there is shown the electrode 
housing 3 which is made from a generally soft, non- 
allergenic, non-toxic, and electrically non-conductive 
material such as silicone rubber (Silastic), natural rub- 
40 ber, neoprene, vinyl, or other similar material. The hous- 
ing though shown to be of annular, frusto-conical form 
may take numerous configurations without departing 
from the essence of the invention noted hereinafter. 
Extending from a side of the annular housing and in- 
45 tegrally forming a part thereof is a strain relief protuber- 
ance 5 having a longitudinal aperture 7 extending there- 
through to the central bore 9 which is disposed normally 
to it in the housing. The strain relief maintains the lead 
wire 15 in a substantially linear plane in the length which 
50 is proximate to its connection with the electrode plate 19. 
It thereby serves to  reduce the possibility of accidental 
fracture of the soldered connection 38. Since the wire 
could, however, be rotationally twisted around its own 
longitudinal axis during active use, a double connection 
65 means to the electrode plate is provided by means of a 
tie-down 23 which is discussed hereinafter. The preferred 
housing additionally embodies a circumferential groove 
25 which extends around bore 9 of the housing at a point 
which is approximately midway between its upper surface 
Disposed within the groove is the electrode plate or 
disk 19 which is made from jeweler's fine grade silver. 
Although the disk may vary in size in accordance with the 
size of the housing, it may generally be approximately .75 
65 inch in diameter and approximately .030 inch thick. The 
disk is provided with a plurality of holes as best shown at 
33 (FIG. 3 )  extending therethrough the function of which 
is to permit electrode paste, when applied to the bottom 
surface 35 of the disk. to seeD therethrough so as to 
25 
30 
35 bottom thereof. 
60 27 and its lower surface 31. 
the plate. Care must be taken-to cover all of the com- 
pound metal junction formed by the solder wire and elec- 
trode plate since if any is left exposed there will occur, 
by reason of the electrolytic nature of the paste, a battery 
action which will produce spurious electrical activity, thus 
spoiling the signal quality. Properly applied insulation 
effectively precludes this possibility. After the epoxy has 
cured, the disk is degreased and washed thoroughly again 
with deionized water. It is then placed in a cell with a 
silver chloride and is anodized in an 0.10 normal sodium 
chloride solution for 20 minutes to a current density of ap- 
proximately 3 milliamps per square centimeter this being 
based on the total surface of the active electrode area. 
A smooth, even coat of silver chloride is thus produced 
on the silver disk. It is important that the disk not be 
touched with fingers or metal thereafter. The load wire 
15, discussed above, is then dressed down flat across the 
major dimension of the plate and is secured by means of 
a tie-down knot, also as explained above. A drop of 
cement is applied to  the knot to maintain it. 
Electrode plates fabricated in accordance with the 
above procedure may be re-used repeatedly and are found 
by reason of their silver chloride coating to be electro- 
chemically reversible when used in conjunction with an 
electrode paste containing sufficient chloride ions to per- 
mit active interchange between both the electrode plate 
and paste. Although various electrode pastes may be used 
in conjunction with the subject invention, the paste de- 
scribed in copending application Ser. No. 422,088, filed 
Dec. 29, 1964, now abandoned, also identified as NASA 
Case No. 1181, has been found particularly suitable for 
uses described herein. The above ionic interchange is 
based on the well-known Nernst effect in which a metal, 
anodized with one of its slightly soluble salts, (in this case 
silver chloride), in contact with a solution containing the 
anion (chloride) of the anodized coating, sets up a re- 
action in which the slightly soluble salt provides a stable 
concentration of silver ions at the interface, as well as 
saturation of the electrolyte. This in turn permits the 
passage of current carried by the chloride ion, which is 
the common ion of the silver chloride-sodium system. The 
silver ions are provided by the silver metal which anodic- 
ally forms the silver chloride. The silver chloride permits 
passage of current between similar electrodes by the above 
process, thus greatly minimizing polarization and creat- 
3,420,223 
3 4 
tion caused by electrolytic processes over extended periods ing a reversible electrode. In this manner the electro- 
of time. The disk is attached to the lead wire 15 by means chemical noise normally associated with prior art elec- 
of a soldered connection 38 proximate to the edge there- trodes is substantially eliminated even when the electrode 
of. The wire is arranged to extend across a major dimen- is used on a physically active subject. 
sion of the disk to the opposite side where it is attached Although the electrode structure described above (with 
by means of a second more flexible means such as tie- respect to FIGS. 1 thru 3)  embodies a housing of flexible 
down 23 which extends around the wire and through each material, it is readily apparent that the silver-silver chlo- 
of two holes 41 on either side thereof. These holes may ride electrode disk may, with feasibility be utilized in 
be made with a No. 58 drill whereas apertures 33 should other types of housings. Thus in FIGS. 4 thru 6 there 
be somewhat larger. It is thus seen that by soldering the is shown a housing 3A of methylmethacrylcate (Lucite) 
wire to the disk at a point opposite or removed from the which has a cylindrical recess 9A extending into the hous- 
tie-down connection that movement of the wire with re- ing from the bottom surface 31A thereof. Since the hous- 
spect to  the disk at the soldered point is substantially ing 3A is not open at both ends the disk 19A, as best 
eliminated except for movement which could be trans- shown in FIG. 6, is not drilled with a plurality of holes 
mitted by rotational twisting of the wire itself. It is found 15 therein, since to do so would preclude effective cleaning 
however that this latter motion is substantially reduced of the top surface 37A of the electrode. The disk how- 
because of the resistance to  twisting effected by the rela- ever is constructed, from its electro-chemical aspect, in 
tively small diameter of the strain relief longitudinal aper- the same manner as the electrode disk of FIG. 1 described 
ture 7. It may be noted in this regard that this aperture, above. As shown in FIG. 5, the lead wire 15 extends 
shown in FIG. 2 is somewhat exaggerated in size but that 20 through a housing aperture IA-1 and is laid across a 
in normal construction the walls of the aperture will be major dimension of the disk in groove 51 to an edge 
in intimate contact with the wire throughout. The anodized thereof which opposes the entry edge. The soldering and 
electrode plate 19, to which the wire is solder&, is prepared epoxy coating of the 'lead wire are accomplished in the 
in accordance with the following procedure. same manner as previously explained. A tie-down con- 
After the plate or disk is cut to the desired size, cleaned, 25 nection is not necessary because the inflexible material 
sanded, and washed in deionized water, the soldered con- from which the housing is made precludes bending of the 
nection is cleaned with an appropriate solvent such as an lead wire at its entry into the aperture 7A. After the 
alcohol and then coated with an epoxy resin 39 or other wire is threaded through the aperture and into groove 
effective insulation which will preclude contact of it with 51 in the housing at the base of recess 9 therein, the elec- 
sn trode disk is affixed in the housing with an euoxv resin "" 
35 
40 
45 
50 
5.5 
60 
65 
70 
75 
39 or other suitable adhesive in permanent manner. 
The electrodes fabricated in accordance with the 
preceding description may undergo continuous and re- 
peated use without suffering structural failures of the lead 
wire. Although the reversibility of the electrode plate 
deteriorates, thus causing spurious potential rise over a 
period of time, the electrodes of the type initially de- 
scribed may be disassembled, cleaned, and reanodized as 
desired, while the electrode of FIGS. 4 thm 6 may be 
cleaned and anodized without disassembling. 
In applying the electrode of the subject invention to the 
skin, a piece of tape (or other adhesive) having adhesive 
on both sides and conforming to the shape of the bottom 
surface 31 of the electrode is applied thereto. After the 
tape is applied to the electrode, the protective covering 
on the remaining adhesive surface is left intact until the 
recess of the electrode is filled with electrode paste. The 
skin is then lightly swabbed with acetone to remove skin 
oils and desiccate the skin so as to improve the adhesion. 
After removing the protective covering on the tape, the 
electrode is firmly pressed to the skin. In using the elec- 
trode of FIG. 1 the area within the housing above plate 
19 is filled with electrode paste to a point just below top 
surface 27 of the housing. A small piece of silicone tape 
is then applied across the area so as to retain the paste 
therein. The upper area should not be overfilled since 
to do so would preclude effective adhesion of the tape. 
An additional piece of appropriate surgical tape approxi- 
mately 3 inches by 3 inches is then applied across the 
entire electrode so as to prevent frictional contact of it 
against the clothing of the subject. The electrode of FIG. 
4 is applied in the same manner as described above ex- 
cept for the elimination of the electrode paste in the upper 
surface and the small piece of silicone tape thereover. 
While there have been shown, described, and pointed 
out in two different embodiments the fundamental novel 
features of the invention, it should be understood that 
various omissions, substitutions, or changes in the shape, 
electrode plate-housing tie-down connection means, and 
other details of the device illustrated and its operation 
may be made by those skilled in the art without depart- 
ing from the spirit and scope of the invention as described 
herein and in the following claims. 
Having thus described the invention, what is claimed 
as new and is desired to be secured by Letters Patent is: 
3,420,223 
6 
4. The voltage detection device as recited in claim 3 1. A voltage detection device for use on a living animal 
wherein said second means comprises a string affixing the 
a housing of flexible material having a lower body con- lead to the plate. 
5. The voltage detection device as recited in claim 4 
a bore having internal walls which extend through the 5 wherein said electrode plate has a plurality of holes there- 
through for allowing an electrolytic paste to be freely 
said walls having electrode support means thereon a p  applied to both surfaces thereof. 
wherein said electrode plate has a plurality of holes there- 
5 
body during active physical exertion comprising: 
tacting surface and an upper surface: 
housing to each of said surfaces; 
Proximately midway between said lower and upper 6. The voltage detection device as recited in claim 1 
engaged 10 through for allowing an electrolytic paste to be freely 
surfaces; 
by said electrode support means; 
an electrical lead having an end portion disposed across 
the surface of said metal plate and in abctting rela- 
tion thereto; 
first means fusing the end of said electrical lead to 
the plate adjacent a first edge portion thereof, and 
second means fixedly holding said lead to said plate 
adjacent an edge portion remote from said first edge 
portion so as to thereby preclude movement of the 
lead at said first edge portion; and 
an insulating medium covering said first connection 
means so as to preclude introduction of extraneous 
electrical signals into the lead. 
2. The voltage detection device as recited in claim 1 
wherein said electrically conductive metal plate is made 
cf a fine grade silver sheet material having a coating of 
silver chloride thereon. 
an electrically conductive plate 
to both snrfaces thereof* 
7. The voltage detection device as recited in claim 1 
wherein said insulating means comprises a coating of 
15 
20 
25 
epoxy resin. 
2,943,628 
3,085,577 
3,170,459 
3,216,424 
3,295,515 
References Cited 
UNITED STATES PATENTS 
7/1960 Howell _ _ _ _ _ _ _ _ _ _ _ _ _  1 2 8 4 1 8  
4/1963 Berman et al. _ _ _ _ _ _ _ _  128-218 
211965 Phipps et al. _ _ _ _ _ _ _ _  128-2.06 
1111965 Chardock _ _ _ _ _ _ _ _ _ _ _  1 2 8 4 1 8  
1/1967 Kahn _ _ _ _ _ _ _ _ _ _ _ _ _ _  128-2.06 
OTHER REFERENCES 
Auslegeschrift, application No. 1,108,820, German 
7/15/ 1961. 
WILLIAM E. KAMM, Primniy Examiner. 3. The voltage detection device as recited in claim 2 wherein said insulating means comprises a coating of 
epoxy resin. 30 


Electrode for biological recording

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