U.S. patent number 3,738,369 [Application Number 05/136,329] was granted by the patent office on 1973-06-12 for body organ stimulator function control switch.
This patent grant is currently assigned to General Electric Company. Invention is credited to Theodore P. Adams, David L. Bowers.
United States Patent |
3,738,369 |
Adams , et al. |
June 12, 1973 |
**Please see images for:
( Certificate of Correction ) ** |
BODY ORGAN STIMULATOR FUNCTION CONTROL SWITCH
Abstract
An implantable body organ stimulator such as an electronic
cardiac pacer has a magnetic reed switch and a switch operator
embedded in its encapsulation. The state of the reed switch may be
changed to alter any one of several functional characteristics of
the stimulator with a switch operator which controls the operating
state. The operator comprises a magnet which is movable between two
positions in a guide tube which is adjacent the reed switch. The
magnet may be urged from one position to another with a needle that
enters the interior of the guide tube through an aperture in a
plate that is embedded in the encapsulation. Means are provided in
one embodiment for preventing restoration of the magnet to its
original position.
Inventors: |
Adams; Theodore P. (Wauwatosa,
WI), Bowers; David L. (Wauwatosa, WI) |
Assignee: |
General Electric Company
(Schenectady, NY)
|
Family
ID: |
22472369 |
Appl.
No.: |
05/136,329 |
Filed: |
April 22, 1971 |
Current U.S.
Class: |
607/30; 335/157;
335/170; 335/153; 335/169 |
Current CPC
Class: |
H01H
36/0006 (20130101); A61N 1/37512 (20170801); H01H
36/00 (20130101) |
Current International
Class: |
H01H
36/00 (20060101); A61N 1/375 (20060101); A61N
1/372 (20060101); A61n 001/36 () |
Field of
Search: |
;128/419C,419E,419P,419R,421,422 ;335/153,168,170,157 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Kamm; William E.
Claims
We claim:
1. An implantable body organ stimulator comprising:
a. stimulus signal generator circuit means for producing selectable
signals with different characteristics,
b. enclosure means enclosing said circuit means for permitting said
circuit means to be implanted in body tissue, said circuit means
having output terminals adapted for connecting the same to a body
organ,
c. switch means in said enclosure means and connected in said
circuit, said switch means having stationary contact means and
cooperating contact means operable under magnetic influence to
select signals having particular characteristics,
d. magnetically permeable guide means in said enclosure means and
an instrument receiving passageway therein for providing access to
the interior of said guide means from the exterior of said
enclosure means, said passageway being normally unoccupied by an
instrument when said stimulator is implanted,
e. a magnetic member movable within said guide means between
positions in one of which said element does not influence said
cooperating contact substantially and in another of which it does
influence said contact substantially said member being mechanically
accessible through said passageway,
f. retainer means for releasably retaining said magnetic element in
at least the said one position,
g. means for retaining said magnetic member permanently in said
another position after said member has been moved to said position
where it does influence said cooperating contact,
h. said cooperating contact means of said switch means being
subject to operation by an external magnetic influence and
alternatively under the magnetic influence of said magnetic member
when the latter is moved mechanically by an instrument introduced
through said passageway.
2. The invention set forth in claim 1 including:
a. another retainer means retaining said magnetic member in its
other position and to prevent return of said member to said one
position after said member has been translated.
3. The invention set forth in claim 1 wherein:
a. said guide means is a tubular means and said retainer means is a
tab means depressed at a slant from the wall of said tubular means,
said tab means resilient to allow said magnetic member to be
translated past the tab means and to serve as a retainer means when
said tab means returns to its slanted position.
4. The invention set forth in claim 1 wherein:
a. said guide means is a tubular means in which said magnetic
member is adapted to translate,
b. casing means in said enclosure, said casing means having a
recess for receiving said guide means, and
c. a deformable ring means having a hole therethrough, said ring
means encompassing said tubular guide means and being deformed by
insertion in said recess for grippingly engaging said casing
means.
5. The invention set forth in claim 4 including:
a. an indifferent electrode plate means supported on said enclosure
means,
b. said tubular guide means being mechanically and electrically
connected to said plate means and being electrically connected to
said switch means and one of said output terminals, whereby to
provide alternate conductive paths to an organ from either said one
terminal or said indifferent electrode plate means.
6. The invention set forth in claim 1 including:
a. an electrode plate means supported on said enclosure means and
having said instrument receiving passageway therein, and
b. a gas permeable elastomeric plug is in said passageway, which
plug is adapted for being penetrated by an instrument for
translating said magnetic member,
c. said electrode plate means being connected to one of said output
terminals and to said switch means whereby said switch means
provides alternate conductive paths to either said one terminal or
said electrode plate means.
7. The invention set forth in claim 1 wherein:
a. said guide means is a tubular means and said magnetic member is
in said tubular means
b. said retainer means comprising a viscous substance occupying
substantially the space in said tubular means that is not occupied
by said magnetic member, said viscous substance retaining said
member in its initial position and flowing past said magnetic
member when it is translated mechanically whereby to retain said
member in its translated position.
8. The invention set forth in claim 1 including:
a. a cylindrical magnetic shield surrounding said guide means
coextensively with said magnetic member for preventing said member
from being moved by magnetic influence and for compelling said
member to be mechanically moved when said member is in one
position.
9. A body implantable organ stimulator which has optionally
selective operating characteristics, comprising:
a. stimulus signal generator circuit means for producing selectable
signals with different characteristics, said circuit means having
output terminals adapted for connecting to a body organ and
enclosure means for permitting said stimulator to be implanted in
body tissue,
b. a magnetic reed switch connected in said circuit and operable
from a first switching state to a second switching state to cause
the stimulator to have different operating characteristics,
c. an electrode plate means associated with said stimulator and
connected to one of said output terminals, said plate means having
an aperture,
d. casing means and a tubular guide means therein mechanically and
electrically connected to said plate means and electrically
connected to said reed switch, said guide means being aligned with
said aperture,
e. a magnetic member for operating said reed switch translatable in
said guide means from a first position where the magnetic field is
not effectively coupled with said reed switch to a second position
where it is effectively coupled therewith to transfer said reed
switch to its second state,
f. means for magnetically shielding said magnetic member when it is
in its first position,
g. means at opposite ends of said tubular means for retaining said
magnetic member in one or the other of its positions, and
h. a viscous substance substantially occupying the space within
said tubular means that is not occupied by said magnetic
member.
10. An implantable body organ stimulator which has optionally
selective operating characteristics, comprising: switching
a. stimulus signal generator circuit means for producing selectable
signals with different characteristics, said circuit means having
output terminals adapted for connecting to a body organ and
enclosure means for permitting said stimulator to be implanted in
body tissue,
b. a magnetic reed switch that is connected in said circuit and
operable from a first switching state to a second switching state
to cause the stimulator to have different operating
characteristics,
c. an electrode plate means associated with said stimulator and
connected to one of said output terminals, said plate means having
an aperture,
d. casing means and a tubular guide means therein mechanically and
electrically connected to said plate means and electrically
connected to said reed switch, said guide means being aligned with
said aperture, said tubular guide means having an axially disposed
resilient tab means projecting radially inwardly thereof,
e. a magnetic member for operation said reed switch translatable in
said guide means from a first position where its field is not
effectively coupled with said reed switch to a second position
where its field is effectively coupled, said tab means retaining
said magnetic member in its first position,
f. said resilient tab means being deflected by said magnetic member
when the member is translated under the influence of an instrument
admitted through said aperture and said tab means returning to its
undeflected position to retain said magnetic member in its second
position.
11. The invention set forth in claim 10 wherein:
a. weld means constitute said electrical connection of said tubular
guide means at one end to said plate means,
b. said casing means being diametrally enlarged in the vicinity of
said weld means to provide a recess thereabout,
c. a deformable ring member in said recess jointly engaging said
guide means and said casing means, and
d. conductive sealant means occupying at least a part of said
recess and being in contact with said casing means, said guide
means and said plate means.
Description
BACKGROUND OF THE INVENTION
The present invention relates to electric body organ stimulators
such as electronic cardiac pacers. The most prevalent current
practice is for manufacturers to provide stimulators in which the
operating characteristics such as output voltage and current, pulse
energy, pulse rate and pulse width are fixed. Unfortunately, the
physiological requirements of some patients may dictate that one or
more of these characteristics by something other than a standard or
fixed value. This has compelled manufacturers to make and stock a
variety of stimulators with different characteristics in order to
meet the requirements of different classes of patients. This
situation is problematical for hospitals and cardiologists too
because they are compelled to stock a variety of stimulators in
order to be sure of having the right type on hand when needed. It
is readily apparent that having to make and stock a limited number
of models or styles of stimulators would be beneficial to patients,
manufacturers, hospitals, and physicians from the economic as well
as the medical point of view.
Some progress has been made in improving the versatility of
stimulators. One approach has been to incorporate a magnetic reed
switch in the stimulator. The switch is variously connected in the
electronic circuitry to switch capacitors, inductors, resistors or
other circuit elements and thereby change the functional
characteristics of the stimulator. The patient or the physician or
both were provided with a permanent magnet that could be placed in
proximity with the stimulator over intervening body tissue and the
magnetic reed switch would respond by changing states in which case
a functional characteristic, usually stimulus pulse rate, was
changed. Moreover, on a subsequent occasion, the magnet could be
applied again to restore the reed switch and the functional
characteristic to its original state. Experience has taught,
however, that it is usually undesirable to adapt a stimulator for
being switched back and forth between functional states because
such switching might be done by the patient to his disadvantage. It
is preferred at the time of implantation that the physician
determine those functional characteristics which are appropriate to
the particular patient and then set the stimulator to operate and
remain in the most desirable state or mode. On the other hand, it
is advantageous to enable the physician to test various modes of
operation at the time of implantation in order to determine the
best operating mode for the patient. This suggests the need for a
switch operator which will permit performing test switching but
which can be locked in a fixed state after the best operating mode
is determined. Heretofore, no suitable switch operator has been
available that could operate reliably in the body environment.
Requirements of a switch operator for use in body organ stimulators
is that it be reliable, durable, compact, inexpensive, not subject
to inadvertent operation or tampering, not adversely affected by
body fluids and that it be adapted for effective sterilization. In
addition, it must permit test switching of the functional
characteristics of the stimulator by the physician and not the
patient.
SUMMARY OF THE INVENTION
It is a general object of this invention to overcome the
above-noted disadvantages by providing a body organ stimulator with
a function selection switch operator.
A further object of this invention is to provide a switch operator
which is compact, reliable from the mechanical and electrical point
of view, subject to effective sterilization and can be switched
either before, during or after implantation by the physician.
Other more specific objects are to provide a switch operator which
has at least two states either of which may be established as a
stable state at the option of the physician at the time of
implantation or sometime after implantation with minimum discomfort
to the patient. A corollary to this object is to provide an
operator which is adapted for remote magnetic operation and which
will latch in a stable state.
How the foregoing and other more specific objects are achieved will
appear from time to time throughout the course of the description
of illustrative embodiments of the invention which will be set
forth hereinafter.
In general terms, the new switch operator may be characterized as a
casing having a magnet holder or magnet guide tube inside of and
substantially coextensive with the casing. There is a permanent
magnet inside of the guide tube. In one embodiment, the permanent
magnet is retained in one position or state by silicone grease with
which the guide tube is filled. When the magnet is shifted
manually, it passes through the grease and is magnetically retained
thereby in a second stable position in the guide tube. In another
embodiment, the magnet may be shifted past resilient tabs which are
mechanically urged out of the way by the magnet to permit its
passage and which spring back behind it to preclude restoration of
the magnet to its original position, thereby making the switch
unidirectional. In both embodiments there is a reed switch outside
of the casing which is in one state or another depending on whether
the magnet is shifted. The magnet is accessible for being shifted
with a needle which is admitted through a small aperture in an
indifferent electrode plate which forms part of the stimulator. All
parts are of materials which will not be adversely affected by body
fluids or other chemicals likely to be encountered in stimulator
applications.
A more detailed description of embodiments of the invention will
now be set forth in reference to the drawings.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a plan view of a body implantable stimulator in which
some of the parts that are essential to explaining the invention
are shown in dashed lines;
FIG. 2 is a view of the right side of FIG. 1;
FIG. 3 is a schematic diagram of a stimulator in which the
invention is incorporated;
FIG. 4 is an assembly view of one version of the new switch
operator and an associated switch, some of the parts being shown in
section;
FIG. 5 is an exploded view of the assembly shown in FIG. 4;
FIG. 6 is a plan view of a locking element; and
FIG. 7 depicts in section an alternative embodiment of the switch
operator.
DESCRIPTION OF A PREFERRED EMBODIMENT
A typical implantable stimulator in which the invention may be
incorporated is shown in FIG. 1. This may be an electronic cardiac
pacer, for instance. The shape of the stimulator is determined by
an insulating medium 10 in which a battery and the electronic
components of the device are encapsulated. The battery is shown as
a dashed line circle 11 to which rigid conductors 12 and 13 are
suitably attached. Conductors 12 and 13 are rigid and serve to
deliver electric power to a printed circuit board 14 and to support
the same prior to encapsulation of the whole unit. The electronic
circuitry which usually comprises a pulse timing circuit and a
pulse generating circuit is not shown in detail but it will be
understood to be encompassed in the broken line rectangle
identified by the reference numeral 15. Mounted on printed circuit
board 14 is a connector assembly generally indicated by the numeral
16 and having one part 17 embedded in encapsulation 10 and another
part 18 extending therefrom.
As can bee seen in FIG. 2, part 18 of connector assembly 16 is
cylindrical and surrounds an insulating block 19 in which there are
two output terminals comprising connector pin sockets 20 and 21. As
shown in FIG. 1, sockets 20 and 21 are connected to printed circuit
board 14 by means of conductors 24 and 25. Conductor 25 connects
with the printed circuit board by means of a jumper 26 which
junctions with 25 at 27. An extension of conductor 25, namely 28,
connects at junction 27 and to the casing of the new switch
operator which is generally designated by numeral 31. The details
of the switch operator will be described later. Adjacent operator
31 is a reed switch which has one conductor 32 connecting with
conductor 28 and operator 31. Two conductors 34 and 35 connect the
reed switch to printed circuit board 14 in this example.
In this device, electric pulses at a suitable width, repetition
rate and energy are delivered from pulse generator 15 and its
associated circuit board 14 to pin sockets 20 and 21 by way of
conductors 24 and 25. The output characteristics or other functions
of the pulse generator are changed by operation of reed switch 33
with operator 31 as will be described more fully hereinafter. Note
also in FIGS. 1 and 2 that in the side of encapsulation 10 there is
embedded a metal plate 36 which serves as an optionally usable
indifferent electrode. The same signal which is applied to pin
socket 20 by way of conductors 25 and 26 is also applied to
indifferent electrode 36 by reason of it being connected with
operator 31 by way of conductor 28.
In some cases indifferent electrode plate 36 may be covered with an
insulating strip 37 as can be seen in FIG. 2. This strip is adhered
to electrode plate 36 and is capable of being peeled off by the
implanting physician to expose the indifferent electrode and
activate it if desired for unipolar stimulation Indifferent
electrode 36 is only exposed and activated and in contact with body
tissue if the preferred treatment of the patient is to stimulate
with a single conductor lead extending from connector 16 to the
organ which is to be stimulated as is true of the unipolar mode. In
such case, the connector of the single conductor lead, not shown,
would join with the pin socket 21 which is fed from the printed
circuit board through conductor 24 and current would flow from the
end of the lead through the organ and return through body tissue to
the indifferent electrode plate 36. The return circuit to the pulse
generator is completed through the casing of switch operator 31 and
conductor 28, as is evident in FIG. 1. If, instead of the unipolar
mode of stimulation just described bipolar stimulation is desired
by the physician, the plastic insulating strip 37 is permitted to
remain in place and a two-conductor lead, not shown, is connected
between connector 16 and the organ which is to be stimulated.
Stimulating signals are then delivered from pulse generator 15
across the ends of the leads which are in contact with the
organ.
Before discussing the new switch operator in detail, its general
applicability to implantable stimulators will be discussed in
connection with the schematic diagram of a stimulator shown in FIG.
3. In this case, the encapsulating resin may be considered as being
within the boundaries of dash-dot line 10. The output terminals 20
and 21 are schematically represented as extending out of the
encapsulation. Within encapsulation 10 there is generally some form
of timing and signal generating circuit which is marked 40 in FIG.
3. Output signals from circuit 40 are delivered to output terminals
20 and 21. The parameters of the signal generator such as output
voltage, output current, output signal energy, pulse width, pulse
amplitude and pulse repetition rate are dependent on the choice of
circuit elements as is well known to skilled electronic circuit
designers. Any one of the parameters mentioned can usually be
changed by appropriate selection of or switching of inductors,
capacitors, resistors, or active elements such as transistors.
Thus, any circuit elements such as those just mentioned may be
connected with conductors such as 34 and 35 to a reed switch 38 or
any appropriate magnetically operable switch. One or more reed
switches 33 and one or more operators 31 may be present to allow
alteration of one or more of the above-mentioned parameters. One
parameter on which the physician usually desires some choice is
stimulating pulse energy. Stimulating with the lowest energy pulses
to which the heart will respond but still provide an adequate
margin of safety is usually preferred both for physiological
reasons an to extend battery life.
The signal generator 40 may be adapted to produce output signals at
two different energy levels such as thirty or sixty microjoules.
This may be achieved by incorporating a voltage doubler circuit and
a voltage tripler circuit, neither of which is shown, in the signal
generator 40. A lead such as 35 may be brought out from the voltage
doubler and connected to one contact of reed switch 33 and another
lead 34 from the tripler may be connected to the other contact of
the reed switch. A lead 41 may interconnect the common reed of the
reed switch 33 to a line which supplies output terminal 21 and is
in common with the voltage doubler and tripler circuits. Thus, when
reed switch 33 is in one position or state, low energy signals may
be applied to output terminal 21, and when it is in the other
state, high energy signals may be applied. Note also that the reed
switch 33 may be connected to switch operator 31 and to indifferent
electrode plate 36 so that when the latter is activated and
terminal 21 is not in use, either high or low energy stimulation
will be available, by virtue of operating reed switch 33, for the
unipolar mode as was true in connection with operating in the
bipolar mode. In this particular example, reed switch 33 is under
the control of operator 31. The state of the operator, and hence
the reed switch, may be changed by inserting a thin narrow
instrument such as needle 42 through an aperture 43 in indifferent
electrode plate 36 which is sealingly engaged with the operator 31
as will be described.
In FIG. 4, one embodiment of the new switch operator 31 is shown
assembled and in section. An exploded view of the operator is shown
in FIG. 5. The operator is adapted to mount next to any suitable
surface such as indifferent electrode plate 36. The construction
and steps involved in assembling the operator will be considered in
connection with FIGS. 5 and 6 concurrently.
Operator 31 comprises a tubular guide or magnet holder 50 which has
a flared end 51 and is preferably made of non-magnetic stainless
steel. Intermediate the ends of the guide are two resilient tabs 52
and 52' which are depressed inwardly and serve as magnet retainer
means. There is a clearance space such as 53 contiguous with each
tab so that the tabs 52 and 52' are free to spring radially
outwardly and to return to the position in which they are shown. A
cylindrical permanent magnet 54 is inserted in guide 50 as shown in
FIG. 4. The flared end 51 of guide 50 is then placed against plate
36 surrounding aperture 43. The flared part 51 is spot-welded to
plate 36 at four circumferentially spaced apart points two of which
55 and 56 being visible in FIG. 4. A silicone plug 57 haVing a
conically shaped body and a mushroom shaped head may be inserted in
aperture 43 of electrode plate 36. Plug 57 prohibits contaminants
from entering switch operator 31 but it is permeable to the gas
which is used for sterilizing the stimulator. Thus, even though
switch operator 31 is otherwise totally enclosed as will appear,
its interior is accessible to sterilizing gas.
A cylindrical casing 58, preferably of non-magnetic stainless
steel, constitutes the exterior of the switch operator 31 assembly.
Casing 58 is enlarged diametrally at its end 59 to create a recess
and there are annular shoulders 60 and 61 within the recess. A reed
switch 33 is in proximity with casing 58. It has a flexible lead 62
which is welded at 63 to casing 58. The welding of the reed switch
lead 62 is accomplished before the reed switch and casing 58 are
encapsulated. To secure the glass body of reed switch 33 against
casing 58 prior to encapsulation, a thin shrinkable plastic sleeve
64 is used. Reed switch 63 is provided with two stationary contacts
66 and 67 which might be connected to conductors 34 and 35 leading
to the signal generator 40 as shown in FIG. 3.
It is contemplated that in most cases, casing 58 and its associated
reed switch 33 will be encapsulated in the same encapsulation that
holds the other electronic circuit components of the stimulator
prior to the insertion of guide tube 50, its magnet 54 and plate 36
to which the guide tube is attached. The enlarged portion 59 of
casing 58 must, in the last analysis, have good electrical
continuity with the circuit including reed switch 33, casing 58,
guide tube 50 and plate 36. Casing 58 should also be mechanically
secure with respect to guide tube 50 when the latter is inserted
within the former.
To enhance the mechanical and electrical integrity of the device, a
split ring 69 is provided. This ring is initially flat as can be
seen in FIGS. 5 and 6. In a commercial embodiment the ring is about
9 mils thick and has an unstressed outside diameter about 50 mils
greater than the largest inside diameter of enlarged portion 59 on
casing 58. The ring as may be seen in FIG. 6 is slotted at 70 and
has an inside hole 71 whose initial diameter is about 2 mils less
than the outside diameter of guide tube 50. Split ring 69 serves as
a means for locking casing 58 to guide tube 50. During assembly,
ring 69 is inserted in the enlarged portion 59 on casing 58 and
then the guide tube 50 is inserted in the hole 71 of split ring 69,
continuing into the bore of casing 58. When the face of the ring 69
strikes shoulder 60 in the casing, the oversize ring is caused to
flex and curve as shown in FIG. 4. The inner and outer edges of the
ring then make firm gripping contact with the inside of the casing
and the outside of the guide tube. Prior to insertion of guide tube
50 into casing 58 as just described, a quantity of conductive
plastic material 73 is deposited around the flared end 51 of guide
tube 50 and the indifferent plate 36. This conductive material
occupies most of the recess within the enlarged casing portion 59
and further assures positive and lasting electric continuity from
reed switch 33 to indifferent electrode plate 36, by virtue of the
conductive material contacting guide tube 50, casing 58, split ring
69, and plate 36.
When switch operator 31 and plate 36 are assembled as shown in FIG.
4 and encapsulated in resin 10, for instance, plate 36 will remain
exposed from the outside of the stimulator. If a magnet of adequate
strength is brought in proximity with the stimulator, reed switch
33 will change its contact state. A change of switch state may
correspond with a change in output energy or in some other
functional characteristic of the stimulator. For instance,
stimulators are usually set by the manufacturer to operate in the
low energy mode. At the time of implantation, the physician may
desire to have a choice as to whether the particular patient should
be stimulated with high or low energy. Thus, after the
implantations is completed except for closing the incision where
the stimulator is located, the patient will be stimulated with low
energy pulses. The physician may then want to determine whether
high energy stimulation is indicated in the particular case. He may
do so by bringing a magnet, not shown, of suitable strength in
proximity with the stimulator and thereby cause reed switch 33 to
change its state and temporarily, at least, cause stimulation in
the high energy mode. If the final decision is for high energy
stimulation, the physician may insert needle 42 through silicone
rubber plug 57 and force magnet 54 down guide tube 50 past tabs 52
and 52'. As the magnet 54 travels it deflects spring tabs 52 and
52' and passes them. Thereafter the tabs spring inwardly again as
shown in FIG. 4 and serve as a latch or retainer means to
positively prevent magnet 54 from returning to the position in
which it is initially shown. When magnet 54 is positioned at the
left end of guide tube 50, it, of course, is magnetically coupled
with reed switch 33 and influences it to switch to another state
which corresponds with high energy stimulation. The magnet
continues to influence the reed switch for the life of the
stimulator. If tabs 52 and 52' are omitted the magnet 54 will be
movable bidirectionally.
An alternative switch operator embodying the principles of the one
just described is shown in FIG. 7 and is generally designated by
the reference numeral 31'. Parts which are similar to those
described in connection with the previous embodiment will be given
the same reference numeral except that a prime mark will be added.
Thus, the reed switch is marked 33' and the plastic sleeve which
surrounds it and holds it to the operator is marked 64'. The
stationary contacts of the reed switch are marked 66' and 67'.
Silicone plug 57' which may be operated by a needle 42' have their
counterparts in the previous embodiment as does the indifferent
electrode plate 36'.
Operator 31' also has a slidable magnet 54' which is in a magnet
holder or guide tube 80 which is given a different reference
numeral because of its structural dissimilarity with its
counterpart in the previous embodiment. Guide tube 80 is preferably
non-magnetic stainless steel and has a part of its outer surface
length diametrally reduced such as at 81 extending to its right end
in FIg. 7. The reduced portion 81 is surrounded by a cylindrical
shell 82 of magnetic material which constitutes a magnetic shield
for magnet 54'. Shield 82 has a flange 83 which is spot-welded at
101 to electrode plate 36' and then electrically and mechanically
bonded with conductive epoxy resin 100 to the guide tube 80 and
outer tube 88.
A ring-shaped magnetic keeper 84 is placed within cylindrical
magnetic shield 82 and there is another magnetic keeper 85 fit
within the internally shouldered left end 86 of the guide tube 80.
Magnet 54', therefore, will adhere to one keeper 84 or the other 85
depending upon which keeper the magnet is in contact with
originally. A space 86 is filled with silicone grease to serve as
magnet position retainer means in this embodiment. The bore of
guide tube 80 is somewhat larger than the outside diameter of
magnet 54' in which case the grease will flow along the sides of
the magnet and occupy the space which it formerly occupied when the
magnet is urged to the left in FIG. 7 by inserting the needle
42'.
When the magnet 54' is in the position in which it is shown in FIG.
7, it has no influence on magnetic reed switch 33'. When magnet 54'
is shifted to the left, however, the shielding effect of shield 82
is removed and the magnet causes the reed switch to change states.
The magnet is kept in the operative position under the influence of
the silicone grease and by magnetic attraction with keeper 85 which
is retained in place by an end cap 87 and is preferably made of
magnetic stainless steel. The end cap fits tightly within guide
tube 80 and is further secured in place and sealed by conductive
epoxy resin which is spread on its periphery before insertion.
Guide tube 80 is surrounded by an outer cylindrical sleeve 88 which
fits tightly around guide tube 80 and is secured thereto with epoxy
resin at the interfaces of these elements. Sleeve 88 is preferably
stainless steel of a non-magnetic type. One flexible lead 62' from
the reed switch may be welded as at 63' to the outside of outer
cylindrical sleeve 88. The cylindrical interspace 89 surrounding
magnetic shield 82 may also be filled with conductive epoxy resin
so that there is good electric continuity from the reed switch to
the keeper plate 36' by way of the switch operator assembly.
As described earlier, during assembly magnetic shield 82 is first
spot-welded to electrode plate 36' and magnetic keeper ring 84 is
inserted within shield 82 as shown. The whole assembly shield 82
and plate 36 are inserted into cavity 89 with epoxy placed on the
outside surface of shield 82 and 83. Before assembly, parts 80 and
88 are usually previously embedded in a resinous insulating
material such as encapsulation 10. Before final assembly, movable
magnet 54' is inserted within guide tube 80 which has been filled
to a suitable depth with silicone grease. Upon assembly, the magnet
will adhere to keeper ring 84. Conductive epoxy resin is used
between interfaces of all the metal parts to avoid relying on press
fits and to augment electric continuity of the operator.
As in connection with the previous embodiment, the patient's
response to different stimulus energy levels may be tested by
placing a suitably strong test magnet, not shown, in proximity with
the reed switch 33' to cause it to switch and the stimulator to
respond by delivering signals of different energy level. When the
test magnet is removed, the reed switch returns to its original
state. If low stimulating energy is indicated for the particular
patient, magnet 54' be allowed to remain in the position in which
it is shown. If high energy stimulation is indicated, a needle 42'
will be perforated through silicone plug 57' and the magnet 54'
will be shifted through grease 86 which will transpose and
contribute toward holding the magnet in its operative position in
cooperation with keeper 85. It should be appreciated that one of
the purposes for occupying the interior of guide tube 80 with
silicone grease is to provide an impediment for shifting of magnet
54' in the event the stimulator is subjected to a mechanical shock
which would be sufficient to move the magnet 54'. Also the grease
will occupy the space surrounding the magnet in the guide tube 80,
reducing the chance of body fluid entrapment. Unless magnet 54' is
moved a considerable distance from keeper 84 by use of needle 42',
the magnet will always return to its rest position against the
keeper. Of course, the end cap 87 adjacent the other keeper 85 may
be provided with a perforation that would enable shifting the
magnet 54' to its original position once it was switched to the
left. If the silicone grease is omitted, the magnet 54' can be
shifted bidirectionally with an external magnet. Such modification
is usually not advantageous when the operator is used in a
stimulator to accomplish the purposes hereinabove discussed.
In summary, both embodiments of the new operator have a sealed
chamber in which a magnet is disposed for unidirectional movement
by application of a manual force. The magnet will be retained in
one chosen state or the other in either embodiment. The operator is
adapted to cooperate with a switch which is also entirely sealed
and not subject to deterioration by oxidation or permeation by
fluids from the body or even possibly from a leaky battery. How the
operator may be modified to make it bidirectional has been
discussed. The device is useful in cardiac stimulators as well as
other body organ stimulators. Although emphasis has been placed on
controlling stimulus energy levels with the new operator, it will
be understood that various other functional characteristics of the
stimulator may be controlled or selected likewise.
Equipping stimulators with a means for controlling the stimulus
energy levels has some additional advantages which have not been
mentioned heretofore. For instance, if low energy mode is chosen
initially, that energy may be inadequate for stimulation when the
batteries are near depletion. On the other hand, it may be that the
attending physician is aware of impending failure of the stimulator
because of battery depletion although it may be impossible for the
convenience of the patient or because of inability to make a
hospital reservation to replace the stimulator power supply
immediately. An emergency situation can easily be avoided in those
cases where the low energy mode is in effect, since the physician
can extend the life of the stimulator for a reasonable period by
switching it to the high energy state, possibly at the expense of a
slightly lower stimulus pulse rate. This can be achieved by
locating the switch assembly behind electrode plate 36 or 36' under
an X-ray fluoroscope so a needle may be inserted through the tissue
and perforate the silicone plug to transfer the magnet and hence
switch the stimulator to the high energy mode. The residual battery
capacity will usually be sufficient to stimulate the patient at the
increased energy and at an acceptable rate until replacement of the
stimulator is possible.
Another important advantage of the invention described above is
that it enables the manufacturer to maintain good quality control
by getting better data on the life of the stimulator when operated
in either the high energy or low energy mode but not both. This
results from the fact that the magnetic switch operator cannot be
shifted back to its original state in which case the manufacturer
upon receipt of a returned stimulator will know the mode of
operation which the stimulator has been in and will be able to make
a judgment as to whether its life was appropriate for that mode.
Moreover, a different warranty period is applicable to each
mode.
Although embodiments of the invention have been described in detail
such description is to be considered illustrative rather than
limiting, for the invention may be variously embodied and is to be
limited only by the claims which follow.
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