Note: Descriptions are shown in the official language in which they were submitted.
This invention relates to medical electrodes. More
specifically this invention relates to a bio-electric signal
transmitting pellet that may be used with an electrode for ad-
herence to the skin of a patient to provide conductive contact
between the s~in surface and an electrical conductor,
Temporary body electrodes are required for measuring
bio-electric signals from the skin of a patient for medical
monitoring equipment. Conventionally these electrodes have a
conductive male metallic snap fastener element to which may be
connected a female snap fastener element and an electrical lead
to the monitoring equipment, Medical electrodes presently used
today have a thin base layer between the snap fastener element
and the skin of a patient, This base layer is formed from some
form of conductive material and the electrodes incorporate an
adhesive sheet or strip to hold this conductive layer in position
on the skin of a patient, Many electrodes used today have gel
pads as the conductive layer between the fastener element and the
skin, It has been found, however, that gel pads have some
limitations, especially if the electrode has to remain on the
patient for some time, because the gel is free flowing and can
vary in thickness in the pad when the patient moves, This
variation in thickness of the gel pad can affect the strength
of the bio-electric signal from the skin and hence give an
unstable reading on the monitoring equipment. This variation
in thickness of the gel pad may occur when the snap fastener
element is disconnected and reconnected from the electrical lead
because pressure placed on the pad will tend to squeeze the gel
forcing it out from under the adhesive portion of the electrode,
Furthermore if the gel spills under the adhesive surface or is
smeared onto the skin prior to application of the electrode, the
adhesion of the electrode to the skin may be affected, Another
problem that can occur with gel, is that it dries out, either
~1~4~
during storage or on the skin which has an effect on the signal
resolution.
Other attempts have been made to provide a conductive
layer between the snap fastener connector and the skin. Some of
these include an adhesive pad which has graphite or some other
conductor material incorporated with the adhesive. Other types
of elements have also been tried, none of these, however, have
proved to be completely satisfactory inasmuch as the signal does
not remain consistent over a 2 or 3 day period which is often
required for monitoring purposes. The reasons for this are many,
one such reason is that the conductive layer itself is not a
sufficiently good electrical conductor to monitor minor changes
in bio-electric signals. Another problem that can exist is that
patients who have to wear electrodes for many days are concerned
with irritation of the skin due to the contact between the skin
and the conductive layer.
We have found that a pellet made from a polymer resin,
a humectant, water and in some cases an electrolyte provides a
conductive layer which may be used between the skin and the snap
fastener element of a monitoring electrode. Such a pellet is
flexible but not free flowing, thus it can be used on a curved
portion of the body. It retains its shape and, therefore, has
little variation in thickness due to either mvvement of the body
or connection and disconnection of the electrical lead to the
electrode. Furthermore, the flexible pellet contains a humectant
which retains water in the pellet itself, thus ensuring that the
pellet remains moist and maintains good electrical contact with
the skin. Furthermore, if the pellet is left on the patient's
skin for a long time the water in the pellet may tend to
e~aporate, in which case, the humectant tends to draw water from
the skin of the patient to ensure that the conductive properties
of the pellet are maintained substantially constant at all times.
Using latex type polymer emulsions, humectant, water
and preferrably an electrolyte, it has been found that a solid
flexible conductive pellet of any size and shape can be provided.
The thickness of the pellet may be considerably less than the
conventional type of gel pads used in electrodes available on
the market today, thus the distance between the skin and the snap
fastener element of the electrode is reduced resulting in less
spurious noise in the signal. The electrode may be small so
that it can be used on newborn babies, and does not obstruct
placement of other electrodes or other medical devices such as
tubes and dressings. A small electrode adheres more easily to
curved skin surfaces. Furthermore, a small electrode does not
obstruct examination of a patient's chest area or other medical
procedures such as defibrillation. Precise placement of a small
size of electrode on the skin surface of a patient is an advantage
during stress testing procedures.
The present invention provides a flexible pellet for
transmitting bio-electric signals from a skin surface to an
electrical conductor comprising a polymer resin, a humectant,
and water. In a preferred embodiment an electrolyte is added.
The polymer resin may be a suitable latex type polymer emulsion.
Some examples of suitable polymer resins include acrylic, acryl;c
esters, methacrylic acid ester, vinyl acetate, acrylic ester-
acrylonitrile copolymer, ethylene-vinyl acetate copolymer, vinyl
chloride-ethylene-vinyl acetate terpolymer or mixtures thereof.
These examples in no way limit the range of polymer resins suit-
able for inclusion in pellets of the present invention. Polymer
resin may be in the approximate range of about 50-70% by weight
of the pellet. Suitable humectants include but are not limited
to, glycerine, triethanolamine, urea, sorbitol or mixtures
thereof, and be in the approximate range of about 10-25~ by
weight of the pellet. The electrolyte may include metal halides,
60~i
nitrates and sulfates such as sodium chloride, potassium chloride,
ammonium nitrate, sodium bromide, potassium iodide, silver
chloride, magnesium sulfate; other suitable electrolytes include
ammonium acetate, sodium citrate, ammonium citrate, zinc citrate
and mixtures thereof, or other suitable electrolyte materials
and may be in the approximate range of about 1-10% by weight of
the pellet, and the water may be in the approximate range of
about 10-25% by weight of the pellet.
In another embodiment there is provided a skin con-
tacting electrode for measuring bio-electric signals comprising
a flexible foam sheet having an aperture therethrough, the sheet
having an adhesive coated lower surface for contacting the skin,
an electrical terminal extending through the aperture in the
sheet, the terminal being secured to the sheet and having a sub-
stantially flat lower contact surface, an electrical conductive
flexible pellet on the lower contact surface of the terminal,
the pellet having a skin contacting surface extending flush or
beyond the lower surface of the sheet, the pellet adapted to
transmit bio-electric signals from the skin to the lower contact
surface of the terminal, the pellet comprising a polymer resin,
a humectant, water, and preferably an electrolyte.
In drawings which illustrate embodiments of the
invention,
Fig. 1 is a vertical cross sectional view of one
embodiment of an electrode incorporating the bio~electric signal
transmitting pellet of this invention.
Fig. 2 is an exploded view of the components of the
electrode shown in Fig. 1.
Figs. 3 and 4 are vertical cross sectional views of
other embodiments of an electrode incorporating the bio-electric
signal transmitting pellet of the present invention.
Fig. 5 is an isometric view of an electrode attached
1 ~ ~ 160~;
to the skin of a patient.
Fig. 6 is an isometric view of a triangular shaped
electrode that may be used with a bio-electric signal trans-
mitting pellet of the present invention.
Fig. ~ is an isometric view of an oval shaped elect
rode showing aeration holes in the foam sheet.
Bio-electric signal transmitting pellets of the
present invention are composed of polymer resin, a humectant,
water and in some cases an electrolyte. The polymer resin may
be selected from a variety of suitable latex type polymer
emulsions such as an aqueous emulsion of acrylic esters or
acrylic ester - acrylonitrile copolymer. Suitable polymer
emulsions include acrylic - PLEX 4871D (Trade mar~ of Rohm GmbH
Chemische Fabrik), methacrylic acid ester - ROHAFLOC KF-400 (Trade
mark of Rohm GmbH Chemische Fabrik), vinyl acetate - C191-103 (Trade
mark of Borden Chemicals), epoxy - EC9722 (Trade mark of Borden
Chemicals), acrylic ester -acrylonitrile copolymer - DL3260
(Trade mark of Reichhold Chemicals Inc.), ethylene-vinyl acetate
copolymer - AIRFLEX 400 (Trade mark of Air Products and Chemicals
Inc.), and vinyl chloride-ethylene-~inyl acetate terpolymer -
AIRFLEX 456 (Trade mark of Air Products and Chemicals Inc.).
This list covers only a few of the polymer resins suitable for
inclusion in pellets of the present invention. The polymer resin
in the pellet is preferably in the approximate range of about 50
to 70% by weight of the pellet.
The humectant may be glycerine, triethanolamine, urea,
sorbitol and mixtures thereof. This list does not limit the
range of suitable humectants. The approximate range of humectant
is about 10 to 25% by weight of the pellet. The electrolyte is
normally incorporated into the polymer resin in the approximate
range of up to about 10% by weight of the total pellet. Examples
of suitable electrclytes include metal halides, nitrates and
0~
sulfates such as sodium chloride, potassium chloride, sodium
bromide, potassium iodide, ammonium nitrate, silver chloride,
magnesium sulfate and the like. Other suitable electrolyte
materials include ammonium acetate, sodium citrate, ammonium
citrate, zinc citrate and the like. Those skilled in the art
can obtain a conductive medium using any one or more of the
above-mentioned electrolytes or mixtures thereof. Many other
suitable electrolytes may be employed. The water may be dis-
tilled, de-ionized or plain tap water. The range of water is
normally in the approximate range of about 10 to 25% by weight
of the pellet.
Preferred ranges of formulations are as follows,
polymer resins about 55 to 65% by weight of the pellet, humectant
about 15 to 20% by weight of the pellet, electrolyte about 2 to
5% by weight of the pellet, and water about 15 to 20% by weight
of the pelletO
In some cases it has been found that no electrolyte
is required in the pellet, but in such cases, higher amounts of
humectant and water are required. In one example, 50% by weight
polymer resin, 25% by weight humectant and 25% by weight water
were formed into a satisfactory pellet. The mixture is formed
into whatever shape of pellet is desired. In one embodiment the
pellets are substantially flat, and may be any shape, round,
square, triangular as required for the electrode. In other
embodiments the pellets may have one flat surface for contact
with the terminal and a curved surface for contacting the skin
of a patient.
~ eferring now to the drawings, one embodiment of an
electrode is shown in Figs. 1 and 2 wherein a flexible foam sheet
10 having a large aperture 11 therein has an adhesive composition
on its lower surface 12. The adhesive composition is any one of
a number of adhesives used for attachment of the sheet 10 to the
6~)~
skin of a patient. A stud 13 of a two part electrical male
snap fastener element terminal for connection to a female snap
fastener elelnent attached to an electrical lead. The eyelet 14
of the terminal has a post 15 which extends upwards into an
aperture on the underneath of the stud 13 and sandwiches a
flexible sheet 16 therebetween. The eyelet 14 of the terminal
is made from a hard plastic material and is silver plated with
a silver chloride coating. The silver chloride coating on the
eyelet 14 extends to a substantially flat lower contact sur-
face 17 which is contained within the large aperture 11 of the
flexible foam sheet 10. The flexible sheet 16 sandwiched be-
tween the stud 13 and the eyelet 14 of the electrical terminal
has an adhesive on its lower surface which adheres to the top
surface of the flexible foam sheet 10.
A bio-electric signal transmitting pellet 18 of the
present invention is provided within the aperture 11 of the
flexible foam sheet 10. The pellet 18 illustrated is shown in
the shape of a round disc. In some cases other shapes, such as
square pellets, are suitable especially if they are cut from
sheets. The pellet 18 is in contact with the flat lower con-
tact surface 17 of the eyelet 14 of the terminal, and is sub-
stantially the same area as the eyelet 14 of the terminal. The
skin contacting surface 19 of the pellet 18 is flush or extends
beyond the lower surface 12 of the foam sheet 10. The electrical
conductive pellet 18 is shown as being substantially flat and
flexible. It retains its shape in normal use and provides a
consistent reproducible stab-e signal with little or no drift in
the baseline. The skin contacting surface 19 of the pellet 18
preferably extends in the order of from 1 to 50 thousands of an
inch beyond the adhesive lower surface 12 of the foam sheet 10.
Fig, 3 illustrates another embodiment of an electrode
which does away with the sheet 16 and sandwiches the flexible
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6()6
foam sheet 10 between the stud 13 and the eyelet 14 of the two
part terminal. The electrical conductive pellet 18 is located
on the substantially flat lower contact surface 17 of the eyelet
14 of the terminal. As can be seen, the skin contacting sur-
face 19 of the pellet 18 extends beyond the lower surface 12 of
the flexible foam sheet 10, This lower surface 12 of the foam
sheet 10 has an adhesive coating thereon to ensure that the
sensing element stays in contact with the skin of a patient.
A further embodiment of an electrode is shown in Fig. 4
wherein a one part stud 13A is provided with a sheet 16 adhering
to the top of the flat portion of the stud 13A. The flexible
foam sheet 10 is the same as shown in Fig. 1, but the pellet 18
has a flat surface for contacting the lower contact surface 17
of the stud 13A and a curved surface for contact with the skin
of a patient.
Fig. 5 illustrates an electrode 20 attached to the
ar~ 21 of a patient with a snap fastener connector 22 having
an electrical lead 23 thereon which leads to a monitoring device.
The shape of electrodes may be round as illustrated in Fig. 2,
substantially square with rounded edges as illustrated in Fig. 5,
triangular with rounded edges as illustrated in Fig. 6, or oval
as shown in Fig. 7. Almost any desired shape of electrodes may
be made, Fig. 7 shows an added feature for electrodes which
include a number of aeration holes 30 in the foam sheet 10
surrounding the stud 13 and the sheet 16. The aeration holes
30 aid in aerating the skin under the electrode. In general
the size of the electrodes of the present invention may be made
smaller than those presently available today. When packaged
the electrodes have a protective film or release sheet extending
over the adhesive surface of the foam sheet 10 protecting the
electrical conductive pellet 18 therein. The electrodes are
packaged in a sealed envelope to avoid evaporation of water from
11'~'~6~
the pellet 18 durin~ storage. It has been found that if the
pellet 18 does dry out, then in view of the humectant material
contained therein it re-absorbs water when a drop or more is
added, allowin~ the pellet 18 to retain its conductive properties.
EXAMPLES
~ atches of material were made for forming into bio-
electric signal transmitting pellets from the following formu-
lations:
Percentages
1. Borden C191-103 60
Glycerine 17.5
Ammonium Nitrate 5
Water 17.5
2. Borden EC9722 62.2
Urea 8.6
Magnesium Sulfate 4.2
Water 25,0
3. Rohm Rohafloc KF-400 50
Glycerine 25
Water 25
4. Air Products Airflex 456 70
Triethanolamine 12
Zinc Citrate 6
Water 12
5. Airflex 100 HS 60
Urea 20
Ammonium Acetate 5
Water 15
6. Rohafloc KF 400 15
Reichhold DL-3260 45
Triethanolamine 17
Sodium Sulfate 2.5
Water 20.5
7. Rohafloc KF 400 4
Reichhold DL-3260 56
Glycerine 15
Potassium Chloride 5
Water 20
8. Reichhold DL-3260 60
Glycerine 17
` Sodium Chloride 5
Water 18
9. Reichhold DL-3260 55
Urea 10
Potassium Nitrate 10
Water 25
6(:)t;
10. Borden EC 97~2 62.5
Triethanolamine 10
Urea 10
Ammonium Chloride 2.5
Water 15
11. Reichhold DL-3260 60
Glycerine 17.5
Zinc Citrate 2.5
Sodium Chloride 2.5
Water 17.5
12. Borden EC 9722 60
Sorbitol 15
Potassium Chloride 5
Water 20
13. Airflex 456 70
Sorbitol 10
Potassium Chloride 4
Water 16
14. Borden C191-103 52.4
Sorbitol 7.1
Glycerine 7.1
Magnesium Sulfate 9.5
Water 23.9
15. Airflex 456 60
Rohafloc KF-400 5
Triethanolamine 15
Sodium Chloride 6
Water 14
16. PLEX 4871D 55
Glycerine 15
Potassium Chloride 2.5
Water 17.5
The formulations were formed into pellets approximately
1/16 inch thick. Some of the pellets were made into round discs,
some were made into square pellets. In each case the area of the
pellet was about the same as the lower contact surface of a snap
fastener terminal. Electrodes were prepared similar to those
shown in the drawings and tested for conductivity. All the
samples were satisfactory, and performed as well or better than
present day commercially available electrodes.
Although the invention has been described by reference
to specific materials forming the conductive pellets and specific
electrode designs, it is not intended that the invention be
limited thereby but that modifications to the above-described
invention are intended to be included as falling within the
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11~41;06
broad scope and spirit of the invention,
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