U.S. patent number 3,735,766 [Application Number 05/135,069] was granted by the patent office on 1973-05-29 for optional unipolar-bipolar body organ stimulator.
This patent grant is currently assigned to General Electric Company. Invention is credited to David L. Bowers, John E. Mohalski.
United States Patent |
3,735,766 |
Bowers , et al. |
May 29, 1973 |
OPTIONAL UNIPOLAR-BIPOLAR BODY ORGAN STIMULATOR
Abstract
A body organ stimulator such as an electronic cardiac stimulator
has the customary connector for attaching intra-cardiac catheter
leads or myocardial leads to operate the stimulator in a bipolar
mode. Set in the resin encapsulation of the stimulator or in an
adapter is an indifferent electrode plate which connects internally
of the device with one of the connector terminals. The plate in the
stimulator or the adapter is dipped in medical grade silicone
sealant. An insulating label or strip is then superposed over the
sealant coated plate and it is dipped and cured again. At the time
of implantation, the physician has the option of stripping the
label to expose the plate so the stimulator may be operated in the
unipolar mode or leave the strip in place for operation in the
bipolar mode.
Inventors: |
Bowers; David L. (Wauwatosa,
WI), Mohalski; John E. (Milwaukee, WI) |
Assignee: |
General Electric Company
(Schenectady, NY)
|
Family
ID: |
22466383 |
Appl.
No.: |
05/135,069 |
Filed: |
April 19, 1971 |
Current U.S.
Class: |
607/36;
D24/168 |
Current CPC
Class: |
A61N
1/37512 (20170801) |
Current International
Class: |
A61N
1/375 (20060101); A61N 1/372 (20060101); A61m
001/36 () |
Field of
Search: |
;128/404,405,419E,419P,419R,421,422,2.6G,2.1E,417,418,DIG.4 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Kamm; William E.
Claims
We claim:
1. A body-implantable organ stimulator comprising:
a. stimulus signal generating means having at least one output
terminal which is adapted to be connected to a body organ and
having another output terminal,
b. indifferent electrode means and an insulating support therefor
and including means for connecting said electrode means to said
other output terminal for receiving a signal therefrom, and
c. insulating means adapted to adhere over said indifferent
electrode means sealingly with said insulating support and to
jointly cover the entire conductive area thereof, said insulating
means being optionally removable to activate said indifferent
electrode means and to expose the same to a conductive medium.
2. The invention set forth in claim 1 wherein:
a. said insulating support for said indifferent electrode means
comprises a material encapsulating said generating means, said
indifferent electrode means being set in said material,
b. said insulating means being a membrane means which covers the
said indifferent electrode means.
3. The invention set forth in claim 2 wherein said insulating means
comprises:
a. a first layer of rupturable membrane material on said
indifferent electrode,
b. flexible strip means adhered as a protective means to said first
membrane layer substantially in congruence with said indifferent
electrode means, and
c. a second layer of rupturable membrane material on said strip
means.
4. The invention set forth in claim 3 wherein:
a. said first and second layers are comprised of silicone
rubber.
5. The invention set forth in claim 3 wherein:
a. said flexible strip means is comprised of polyester film which
is roughened on at least the one side thereof which interfaces with
said first membrane layer.
6. The invention set forth in claim 1 wherein:
a. said indifferent electrode means comprises a conductive
stainless steel plate.
7. A body-implantable organ stimulator comprising:
a. stimulus signal generating means having at least two output
terminals,
b. a connector means having at least two terminals which are
supplied from the aforesaid output terminals, said connector means
being adapted to connect with insulated leads that supply an
organ,
c. insulating material encapsulating said generating means and a
part of said connector means,
d. an indifferent electrode means set in the external surface of
said encapsulating material and connected with at least one of said
output terminals inside of said encapsulating material, and
e. insulating means adapted to separably adhere to said indifferent
electrode means and to cover said electrode means, said insulating
element being optionally removable to activate said indifferent
electrode means.
8. The invention set forth in claim 7 wherein:
a. said insulating means comprises a rupturable membrane.
9. The invention set forth in claim 7 wherein:
a. said insulating means comprises at least two flexible films
laminated together, and
b. a silicone rubber membrane is on said indifferent electrode to
which membrane said laminated insulating films adhere.
10. The invention set forth in claim 7 wherein said insulating
means comprises:
a. a first thin layer of rupturable sealant deposited on said
encapsulating material and said indifferent electrode means,
b. an insulating strip means adhered to said indifferent electrode
means through the agency of said first layer of sealant, and
c. a second thin layer of rupturable sealant deposited over said
first layer and said insulating strip means.
11. The invention set forth in claim 7 wherein:
a. said indifferent electrode means comprises a conductive
stainless steel plate.
12. An implantable electric body organ stimulator that is
characterized by being operable in either bipolar or unipolar
modes, comprising:
a. a stimulus signal generator and an insulating encapsulation
enclosing said generator,
b. connector means accessible from the exterior of said
encapsulation and having at least two terminals which are connected
with said generator to receive stimulus signals therefrom and which
are adapted to connect with leads for stimulating an organ in the
bipolar mode,
c. an indifferent electrode set in said encapsulation at least a
part of said indifferent electrode being subject to exposure for
contacting body tissue and said indifferent electrode being
connected with at least one of said terminals, and
d. an insulating element adhesively engaged with said indifferent
electrode to insulate and inactivate said electrode when operation
in the bipolar mode is desired, said element being removable when
operation in the unipolar mode is desired.
13. An implantable body organ stimulator comprising:
a. a stimulus pulse generator having first and second output
terminals and first and second connector means connected
respectively with said terminals,
b. an insulating enclosure for said pulse generator, said connector
means being exposed through said enclosure to enable connecting
organ connectable lead means thereto,
c. lead means including a third connector means for coupling with
said output terminal connector means, said lead means including at
least one conductor extending from said third connector means and
connecting with said first connector means when coupled and an
organ engaging conductive electrode element attached to said
conductor, said conductor having insulation thereon,
d. another indifferent electrode element connected with said second
connector means,
e. insulation means covering the entire conductive area of said
indifferent electrode element, a portion of said insulation means
being optionally separable from the remainder thereof to expose
said indifferent electrode element for enabling contact with body
tissue.
14. The invention set forth in claim 13 wherein:
a. said separable portion of said insulation means comprises
rupturable membrane means.
Description
BACKGROUND OF THE INVENTION
Although the invention is pertinent to various types of
body-implantable electric organ stimulators, it will be discussed
primarily in connection with an electronic cardiac stimulator which
shall hereafter be called a stimulator for brevity.
The pulse or stimulus signal generating circuitry in a stimulator
is usually encapsulated in resin along with batteries. A suitable
connector extends from the encapsulation. The connector usually has
two terminals although certain prior stimulators which have a
built-in indifferent electrode employ a one-terminal connector. At
the time of implantation, suitable flexible conductive leads are
attached to the organ which is to be stimulated and to the
stimulator connector. Various types of leads are used. One type has
two conductor elements and a connector on one end that couples with
the stimulator connector. The other end of the conductors are bared
and adapted for suturing directly into the myocardium in which case
stimulating pulse current from the stimulator flows through active
tissue between the bared ends. The leads just described are
commonly called myocardial leads.
Intra-cardiac catheter leads are another type. This type usually
has two flexible concentric conductors which are insulated from
each other and terminate at one end in a stimulator connector and
at the other end in a pair of metal terminals which are spaced
apart and insulated from each other. Leads of this type extend from
the stimulator through a blood vessel to the interior of the heart.
Current pulses which flow between the exposed terminals stimulate
the heart.
When leads of the types described above are used, the operating
mode is characterized as bipolar because both poles or terminals of
the stimulus signal generator are connected directly on or near the
heart. Sometimes, however, unipolar stimulation is physiologically
indicated or preferred by the physician. Unipolar stimulation
implies connecting only one of the output terminals from the
stimulus signal generator directly to the heart and using as the
other terminal a large area metal plate, called an indifferent
electrode, which is implanted at some distance from the heart,
usually in subcutaneous tissue, providing a return conductive path
from the heart to the stimulator by way of the indifferent
electrode.
Some presently available stimulators have an indifferent electrode
plate embedded in the insulating encapsulation so that the plate
will contact body tissue when the stimulator is implanted. With
this arrangement the stimulator will operate in the unipolar mode
if it is used in conjunction with an appropriate single conductor
lead. If bipolar stimulation is indicated for a particular patient,
however, the unipolar type of stimulator just described cannot be
used since the indifferent electrode would be exposed and active.
Thus, it is evident that up to this time manufacturers have had to
provide one type of stimulator having no exposed electrode plate
and another with such a plate in order to fulfill the physician's
requirements and needs in all cases.
Commercially available stimulators which do not have an integral
indifferent electrode plate may be converted to the unipolar mode
with a suitable adapter. Available adapters customarily comprise
two conductive leads each of which terminates at a corresponding
end in a connector which mates with the connector on the
stimulator. The distal tip of one lead is attached to or in contact
with the interior of the heart. The other lead terminates in an
exposed metal plate constituting an indifferent electrode which is
usually implanted in body tissue in proximity with the stimulator.
Thus, stimulating current flows from the distal tip of the lead and
returns through body tissue to the indifferent electrode and the
stimulator.
It should be evident from the foregoing discussion that
manufacturers must make and inventory a variety of stimulators,
adapters and other accessories to fulfill the diverse needs of the
physician and patient. It is also necessary for hospitals to keep
the various types of these devices on hand lest a patient remain
untreated while a specialized device is awaiting delivery.
SUMMARY OF THE INVENTION
An object of the present invention is to overcome the above-noted
disadvantages by providing a body organ stimulator which is adapted
for optional use in either the bipolar or unipolar operating modes
without employing any adapter or other special accessories.
Another object of the invention is to enable a manufacturer to
reduce the number of types of body organ stimulators and adapters
that are in production by making types of stimulators and adapters
that are originally adapted for bipolar stimulation and which can
be readily converted by the user for unipolar stimulation.
A more specific object of this invention is to equip stimulators
and adapters with an indifferent electrode, for unipolar
stimulation, which may be maintained in an inactive state if
desired so that immediately before implantation, or even after, the
stimulator may be converted from bipolar to unipolar or from
unipolar to bipolar operation.
A more specific object of this invention is to incorporate in or at
a remote location from the stimulator an indifferent electrode
which is covered and insulated by an adhesive but removable strip
or insulating membrane which may remain in place for bipolar
stimulation but can be removed for unipolar stimulation.
In general terms, one concept involves embedding an indifferent
electrode in the form of a metal plate in the surface of the
resinous material in which the electronic components of the
stimulator are encapsulated. An insulating adhesive membrane
sealant coating is applied to the plate and to give added strength
to the membrane an insulating strip is applied to the adhesive
membrane sealant. Then another coating of sealant is applied to
help retain the protective strip. To convert the stimulator to
unipolar operation, the user merely peels off the strip or rubs off
the membrane coating covering the plate, thereby exposing the
indifferent electrode plate and rendering it active. Another
concept is to have the indifferent electrode at a remote location
in the body to apply an insulating membrane or strip to the
electrode.
How the foregoing and other more specific objects of the invention
are achieved will appear from time to time throughout the course of
the ensuing more detailed description of a preferred embodiment of
the invention taken in conjunction with the drawings.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a plan view of a body organ stimulator incorporating the
invention;
FIG. 2 is a view of the right side of FIG. 1;
FIG. 3 is a plan view of the internal components of the stimulator
shown in the preceding figures before the components are
encapsulated, some of the components being represented
schematically;
FIG. 4 is a vertical cross section taken on a line corresponding
with 4--4 in FIG. 1;
FIG. 5 is a magnified view of a partial cross section of the
stimulator taken on a line corresponding with 5--5 in FIG. 4;
FIG. 6 is a plan view of an intra-cardiac catheter electrode which
exemplifies electrodes with which the new stimulator may be
used;
FIG. 7 is an isolated plan view of the insulating element or
removable strip which is used to maintain the indifferent electrode
in an inactive state; and
FIG. 8 is a magnified cross section of the insulating element shown
in the preceding figure.
DESCRIPTION OF A PREFERRED EMBODIMENT
The configuration shown in FIG. 1 is that of a cardiac stimulator
which typifies stimulators in which the invention may be
incorporated. The internal components of the stimulator are in a
resinous encapsulation 10 which is conventional. The encapsulation
10 serves as electrical insulation and as a body fluid impervious
barrier. The battery pack subassembly for furnishing electric power
to the encapsulated electronic components of the stimulator is
represented by the broken line marked 11. The battery pack is also
in an encapsulation. There will be a further discussion of the
battery pack 11 later in reference to FIG. 3.
Extending from the battery pack through the encapsulation are a
pair of battery terminal extensions 12 and 13 which also serve as
supporting posts for a printed circuit board 14. The electronic
components of the stimulus signal generating means are not shown in
detail but it will be understood that they are mounted on printed
circuit board 14 and are encompassed in the space which is defined
by the dash-dot rectangle 15.
Secured to printed circuit board 14 is an electric connector
assembly which is generally designated by the reference numeral 16.
One part 17 of connector assembly 16 is embedded in resinous
encapsulating material 10 and another tubular part 18 extends
therefrom. As can be seen in FIG. 2, inside of exposed tubular
extension 18 is an insulating block 19 in which there are two small
connector pin sockets 20 and 21. These connector pin sockets are
optionally available for connecting either single or double
conductor organ attachment leads to the stimulator as will be
described shortly hereinafter in reference to FIG. 6.
The electrical conductors for delivering electric stimulus signals
from the printed circuit board mounted stimulus signal generator 15
to the output terminals comprising connector pin sockets 20 and 21
may be seen most clearly in FIG. 3 where these conductors are
represented schematically by dashed lines. In this figure, the
battery pack 11, printed circuit board 14, conducting supporting
posts 12 and 13 and connector assembly 16 are shown in solid
outline. The rectangle 15 in which the electronic components are
encompassed is shown in dash-dot lines. A conductor 24, shown in
dashed lines, makes one of the connections between printed circuit
board 14 and a connector pin socket 20 within connector assembly
16. A conductor comprising sections 25 and 26 makes another
connection from printed circuit board 14 to the other pin 21 in
connector assembly 16. Thus, one may see that stimulating signals
may be delivered from signal generator 15 to each of the connected
output terminal sockets 20 and 21. When two conductor attachment
leads are coupled between the connector 16 and the organ, the
stimulator will function in the bipolar mode as it is called with
both active conductor ends terminated in the organ which is to be
stimulated.
Involved with unipolar pacing is another conductor 27 which
junctions at 28 with conductor 26 and also connects with a
conductive supporting post 29. Post 29 connects with a contact
element 30 which is represented by two concentric circles in FIG.
3. Contact element 30 connects with an indifferent electrode
constituting a metal plate 37, see FIG. 2, as will be discussed in
detail a little later. The battery pack 11 shown in FIG. 3
comprises four batteries 31, 32, 33 and 34 whose electrical
connections are omitted for the sake of clarity. The batteries are
in a resin encapsulation 35 from which conductors 12, 13 and 29
extend. After battery pack 11 is attached to printed circuit board
14 and after electronic components 15 and the connector assembly 16
are in place, the unit shown in FIG. 3 is placed in a mold, not
shown, and molded into encapsulating material 10 so that the final
product has the configuration shown in FIGS. 1 and 2.
An indifferent electrode comprising a thin stainless steel plate 37
is also embedded in the surface of encapsulation 10 shown in FIG.
2. As will be described, indifferent electrode plate 37 is only
active when the unipolar stimulating mode is desired. For the
present, it is sufficient to observe that on the inside of plate 37
there is a contact pin assembly 36 which inserts into cylindrical
contact element 30 and makes a sound electrical connection
therewith. Other suitable means for making a connection between
plate 37 and printed circuit board 14 and its associated signal
generating circuitry 15 may also be employed as long as the plate
is electrically connected with an output terminal of the stimulus
signal generator and to one of the terminals or pin sockets in
connector assembly 16.
Refer now to FIG. 4 which shows in cross section the stainless
steel indifferent electrode plate 37 embedded in a surface of
encapsulating material 10. In accordance with a preferred
embodiment of the invention, when construction of the stimulator
has been advanced to this point, it is dipped in a silicone rubber
compound which is characterized by curing or vulcanizing in air.
The ordinary medical grade room temperature vulcanizing silicone
compound which is now commonly used in connection with making
implantable stimulators is a suitable material for dipping as just
described. A coating of silicone material 38 about ten to twenty
mils thick remains on the object. This coating does not feel tacky
when touched but any thin lightweight object can be made to adhere
to it, at least temporarily, by merely pressing the object against
coating 38. Note that silicone rubber coating layer 38 covers plate
37 without any discontinuities. This coating 38 is sufficient to
insulate the plate 37 but does not have the strength to resist
tearing when sharp objects come in contact such as medical
instruments.
After the first coating of silicone rubber 38 is deposited as
described above and while it is still viscous and uncured, an
insulating element in the form of a laminated plastic label 39,
which is used as a protective shield against tearing, is pressed
against that part of coating 38 which overlays plate 37 and the
assembly is dipped again in the self-curing silicone rubber
compound. This forms an outer layer or coating 40 for holding the
label in position and covering the entire stimulator except tubular
extension 18 of connector 16 which is not coated by the first or
second dips.
A plan view of insulating element or label 39, which is comprised
of two thin plastic lamina, is shown in FIG. 7 and a cross section
thereof is shown in FIGS. 4, 5, 7 and 8. Insulating element 39
should have substantially the same shape and size as indifferent
electrode plate 37 in which case element 39 will be substantially
congruent with plate 37 when the insulating element is properly
placed on the first silicone coating 38. The margins of insulating
element 39 may, however, extend beyond the margins of plate 37 if
desired. It should be evident from inspection of FIG. 4 that the
inner and outer silicone coatings 38 and 40 plus the intervening
laminated plastic insulating element 39 will prevent conduction
between plate 37 and body tissue in the event the unit is implanted
in the body in this condition. When the coatings 38 and 40 and
insulating element 39 are intact as shown in FIG. 4, electric
stimulating energy can only be delivered from the stimulator
through one or the other or both of the output terminals 20 and 21
within connector assembly 16. Of course, any one of the elements
38, 39 or 40 alone could insulate plate 37. Indifferent electrode
plate 37 would remain inactive in any case.
As indicated by the legend on the insulating element or the label
39, in FIG. 7, the label is only intended to be removed when
unipolar pacing is desired. To direct the user's attention to this
capability, a corner 41 of the element is shaded as shown. To
remove the label 39, the user may insert the tip of a scalpel at
the edge of the shaded area to raise the element 39 sufficiently to
allow gripping its corner with the fingers or other suitable
instruments and tearing it off. As will be explained, the
properties of the insulating element or label 39 are such that the
layer of silicone rubber 38 which intervenes between the label and
plate 37 peels off with the label as does that area of the outer
coating 40 which is congruent with the label. The resin provides a
good bonding surface for the silicone coating and makes a clean
parting line between the plate and resin during removal. In other
words, when the label 39 is removed, the two silicone coatings 38
and 40 will remain with the label 39 and the electrode plate 37
will be exposed and substantially clear of any silicone coating or
insulating material. If any residual fragments of coating remain,
they can be rubbed off or picked off easily with a knife blade,
spatula, or the like. When indifferent electrode plate 37 is
exposed in this manner, of course, the stimulator is adapted for
operation in the unipolar mode when it comes in contact with body
tissue.
FIG. 5 shows a magnified cross section taken through indifferent
electrode plate 37 and the various insulating layers which are
disposed upon it at completion of the manufacturing process. This
general construction has already been described. However, it is
important to note that the plastic laminate label 39 which is shown
alone in cross section in FIG. 8 is comprised of two individual
plastic film layers 39' and 39". The bottom of layer 39", it should
be noted, is roughened to improve its adhesive properties with
respect to silicone layer 38 on which it is adhered. The degree of
roughening is not particularly important but it should be
sufficient to remove any signs of glossiness from the surface which
interfaces with the silicone coating 38 that is on metal plate 37.
The metal plate 37 is smooth and free of surface marks which could
cause adhering of the silicone rubber. Because the lower surface of
lamina 39" is roughened, its adhesion to silicone coating 38 is
better than the adhesion between the silicone coating 38 and plate
37 in which case the coating 38 will remain with the laminated
insulating element or label 39 rather than stick to the plate when
the label is peeled off. Moreover, if the physician has reason for
wanting to replace the label 39 for reinsulating indifferent
electrode 37 he may do so by pressing the label back into position
over the plate 37 and the silicone rubber coating 38 which adheres
to the label will again effect adhesion and a seal between the
label and plate 37.
The lamina 39' and 39" comprising the label 39 have been made of
polyester film each about three mils thick in a commercial
embodiment. Dupont's Mylar is a suitable material although any
non-toxic flexible inert material with good moisture and electrical
insulating properties may be used. The top lamina 39' has been made
of clear Mylar and the legend which appears in FIG. 7 has been
printed directly on the backside of lamina 39' or on its interface
42 with lamina 39". After the legend is printed on the bottom side
of lamina 39', that side is coated with adhesive and the lower
lamina 39" is pressed onto it. By constructing the insulating label
39 in this manner, the legend is made easy to read and there is
further assurance that if either the ink or the adhesive between
the lamina is even slightly toxic there will be no danger of toxic
material ever coming into contact with body tissue. Of course, the
ink and adhesives used in the label 39 are chosen from materials
which are non-toxic in the light of present knowledge and
experimental testing.
It is not imperative to the function of the new stimulator that the
label for insulating the indifferent electrode be laminated. It
could just as well be a single layer of flexible or relatively
inflexible impervious insulating material and it could be opaque if
desired. The illustration of the invention will suggest to those
skilled in the stimulator art that various means may be used for
concealing or electrically isolating the indifferent electrode with
an insulating element that is held in place with a rupturable
adhesive membrane sealant. It will be evident to those skilled in
the art that an indifferent electrode in an adapter may also be
provided with removable insulation similarly to the manner just
discussed in respect to an electrode in the stimulator.
A lead assembly that will serve as a basis for describing how the
new stimulator may be used is shown in FIG. 6 and is indicated
generally by the numeral 45. The leads here depicted comprise an
elongated flexible conductor assembly 46 which may take many forms
but in this case comprises two electrically isolated coaxial
conductors, not shown, which are electrically insulated from each
other and surrounded by insulation in a well-known manner. The
proximal end of the conductor assembly terminates in a self-sealing
connector 47 which may be plugged into the connector assembly 16 of
the stimulator. The distal end of the conductor assembly terminates
in a metal tip 48 which is spaced from a metal ferrule 49. The
metal tip and ferrule are separated by an insulating section 50.
The distal end of the conductor assembly having the tip and ferrule
may terminate in one of the chambers of the heart in connection
with cardiac stimulation. Current delivered by the stimulator flows
between the tip 48 and ferrule 49 and any tissue or blood that
intervenes between them for the purpose of conducting current
through the organ and stimulating it. The lead assembly of FIG. 6
may be joined with connector assembly 16 of the stimulator for
operation in the bipolar stimulating mode if insulating element or
label 39 is intact with indifferent electrode plate 37. A suitable
converter, not shown, may also be used to facilitate connecting a
single conductor organ lead to a two-terminal connector such as
16.
Lead assemblies very similar to that shown in FIG. 6 are also
provided with a single conductor terminating in a single conductive
tip such as tip 48. Usually, single conductor lead assemblies are
adapted for use as a cathode; in other words, they must be
connected to the negative terminal of the stimulator since the
leads of some manufacturers are made of materials that will be
seriously eroded by electrolytic action if they are used as an
anode. The single conductor type of lead must cooperate with an
indifferent electrode which is made available either through being
built into the stimulator or as part of an adapter as mentioned
when discussing the background of the invention. In the present
example, only the negative of the connector pins 20 or 21 in
stimulator connector assembly 16 is electrically connected with the
single conductor in the lead assembly shown in FIG. 6 and the
indifferent electrode 37 is activated by removing the label 39 from
over it as described above. Hence, after implantation, the
indifferent electrode 37 will be in conductive contact with body
tissue and in an active state for unipolar stimulation. As
mentioned earlier, the ability to convert the stimulator from
bipolar to unipolar operation enables the manufacturer to produce
only one style of stimulator for making these operating modes
available and the user is required to stock only the one style
without sacrificing the ability to provide either or both modes of
stimulation on short notice, such as during stimulator
implantation.
Those versed in the art will appreciate that types of organ
stimulating leads other than that in FIG. 6 may also be used with
the new stimulator design. In addition, those skilled in the art
will appreciate that in certain cases the bipolar electrodes and
the indifferent electrode may be used at the same time and that in
other cases, particularly in experimental or precautionary implants
the stimulator may be implanted with the indifferent electrode
concealed and in readiness for activation on a propitious occasion
by gaining access for peeling off the insulating element or label
by way of minor surgery under local anesthesia. The indifferent
electrode may also have forms other than a plate. For instance, it
could be one or more pins, a ring, a sleeve, or a metallic casing
that houses the electronics and batteries. Rupturable adhesive
sealants other than self-curing single component silicone systems
can also be used as long as they approximate the properties of
medical grade silicones such as body compatibility, fluid
impermeability, good electrical insulation, pliability,
adhesiveness without permanent bonding and rupturability within
limits. The invention is applicable to any type of indifferent
electrode whether it is associated directly with or located
remotely from the stimulator.
Although a preferred embodiment of the invention has been described
in considerable detail, it should be understood that such
description is illustrative rather than exclusive, for the
invention may be variously embodied and is to be limited in scope
only by interpretation of the claims which follow.
* * * * *