US3654933A

US3654933A - Implatable electrode

Info

Publication number: US3654933A
Application number: US776348A
Authority: US
Inventors: Norman R Hagfors
Original assignee: Medtronic Inc
Current assignee: Medtronic Inc
Priority date: 1968-11-18
Filing date: 1968-11-18
Publication date: 1972-04-11
Anticipated expiration: 1989-04-11
Also published as: DK132105C; NL147331B; DK132105B; SE364872B; NL6917338A; JPS4836280B1; FR2023550A1; FR2023550B1

Abstract

An improved electrode for implantation into a body including one or more electrical conductor leads adapted to be connected to a source of electrical signal, and one or more flexible electrodes attached to the leads, so that the electrodes may be bent around the portion of the body to which they are to make electrical contact. The leads and the portion of the electrode not to be in contact with the body are encapsulated in a substance substantially inert to body fluids and tissue.

Description

United States Patent Hagfors [451 Apr. 11, 1972 1 1 IMPLATABLE ELECTRODE 3,279,468 10/1966 Le Vine 1 28/410 [72] lnventor: Norman R. Hagfors, Minneapolis, Minn. 52 22 47 [73] Assignee: Medtronic Inc., Minneapolis, Minn. Re26,809 3/197 flagfofs 3/ 18 R 6,8 0 Filed: Nov. 18 1968 e2 1 3/1970 Schwartz et al 128/418 2 l 1 App]. No: 776,348 FOREIGN PATENTS OR APPLICATIONS 106,662 9/1924 Switzerland 1 28/410 I I a 4 I I s i s a s a i I a 4 s I s I I a l a a I n u I I I a v n a p I I a o I I I I e v I u a I I I I A. Assistant mine xy e 128/419 D16 Attorney-Lew Schwartz and Donald R. Stone 57 ABSTRACT [56} References Cited 1 An improved electrode for implantat1on mm a body lncluding UNITED STATES PATENTS one or more electrical conductor leads adapted to be connected to a source of electrical signal, and one or more flexi- 298511 72 8 I L 52 1 ble electrodes attached to the leads, so that the electrodes may 3405 J15 1 ag ors 18 be bent around the portion of the body to which they are to 3142115 I l 1/1969 Schwartz et "128/418 make electrical contact. The leads and the portion of the elec- 2118415 I 1 12/1939 Bagno et "128/21 x trode not to be in contact with the body are encapsulated in a 2,187,928 1/1940 Barcroft 1 28/404 X Substance Substantially inert to body fluids and tissue 3,157,181 11/1964 McCarty ..128/404 3,216,424 1 1/1965 Chardack 128/418 35 Claims, 14 Drawing Figures PATENTEDAPR 11 I972 3,654,933

sum 1 0r 2 r 15 r 14 F1155 11 INVEN'IOR.

11/084440 e Mrarazs IMPLATABLE ELECTRODE BACKGROUND OF THE INVENTION Implantable electro-medical devices are now well known in the art. The structure of the electrodes which connect the electrical signals from an implantable device to a desired portion of the body, has been found to be highly important to those skilled in the art. For example, two electrode structures particularly adaptable to connect to nerves are shown and described in U.S. Pat. application Ser. No. 12,981, filed Dec. 10, 1965, by Seymour 1. Schwartz et al., now U.S. Pat. No. Re. 26,810 and assigned to the assignee of this invention; and, U.S. Pat. No. Re. 26,809, issued Mar. 3, 1970, having the same inventor as this application, and assigned to the assignee of this invention.

A review of the above mentioned application and patent will indicate that numerous advantages and disadvantages arise from the structure selected for the implantable electrode. For example, the structure should be one which avoids traumatizing the portion of the body to which it is to be connected, a particular electrode structure may be preferable as providing greater current density to a greater depth in the portion of the body to be stimulated, and a guarded electrode structure may be preferred to prevent excess leakage current from stimulating portions of the body adjacent to that portion it is desired to stimulate. These are just a few of the problems involved in the structure of implantable electrodes.

The apparatus of this invention overcomes particular prior art problems by providing a structure which is capable of atraumatic connection to nerves or other portions of the body of various sizes, while providing a permanent connection to the portion of the body, and providing an improved current density through the portion of the body to which it is connected, as well as other various advantages.

SUMMARY OF THE INVENTION Briefly described, the apparatus of this invention comprises one or more flexible electrodes connected to leads which are adapted to be connected to a source of electrical signal. The flexibility of the electrodes enables them to be wrapped around, for example, a portion of a nerve to be stimulated. Thus a greater surface contact area is provided between the electrode and the nerve, and the connection can be properly fitted to avoid trauma. The leads and the portion of the electrode not to be in contact with the nerve are encased in a substance substantially inert to body fluids and tissue. A guarded electrode configuration may be used with the apparatus of this invention, in which case it is preferable to have the surface area of the electrode being guarded equal to the combined surface area of the guarding electrodes. This will provide an improved current density.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a two-electrode configuration of the apparatus of this invention;

FIG. 2 is a second perspective view of the configuration of FIG. 1 as shown in its preferred form prior to connection;

FIG. 3 is a perspective view of a three-electrode, guarded electrode configuration of the apparatus of this invention;

FIG. 4 is another perspective view of the configuration of FIG. 3 shown in its preferred form prior to connection;

FIG. 5 is a perspective view showing the apparatus of this invention after connection to a portion of a body;

FIG. 6 is a top-plane view of a variation of a guarded electrode configuration of the apparatus of this invention;

FIG. 7 is a copy of an equipotential line plot of the apparatus of this invention shown in FIG. 1;

FIG. 8 is a copy of an equipotential line plot of a prior art two-electrode configuration;

FIG. 9 is a copy of an equipotential line plot for the apparatus of FIG. 3;

FIG. 10 is a copy of an equipotential line plot wherein the center or guarded electrode is not twice the surface area of the guarding electrodes;

FIG. 11 is a copy of an equipotential line plot for a prior art three-electrode, guarded electrode configuration;

FIG. 12 is a copy of an equipotential line plot for the apparatus of FIG. 6;

FIG. 13 is a perspective view of a variation of the apparatus of this invention involving a two-electrode, guarded electrode configuration, and

FIG. 14 is another perspective view of the apparatus of FIG. 13 shown in the preferred form prior to connection.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Throughout the FIGS. of the drawing the same number has been used to indicate the same or similar part of the apparatus, though the embodiments themselves may vary.

Referring first to FIGS. 1 and 2, there is seen a pair of electrical conductor leads 10 and 11, which are adapted to be connected to a source of electrical signal. An electrode 12 is connected to lead 10, while another electrode 13 is connected to lead 11. Electrodes l2 and 13 are shown in the preferred embodiment of FIG. 1 as generally rectangular, flat pieces of metal, which are flexible. If desired,

flexible electrodes

12 and 13 can be position retaining, that is, of a material that will hold any position or shape to which it is flexed.

Leads

10 and 11 are encapsulated in a substance 14 substantially inert to body fluids and tissue.

Electrodes

12 and 13 are partially encapsulated in substance 14, leaving exposed those surfaces which will make contact with a portion of the body. A pair of

tabs

15 and 16 extend from substance 14 in the manner shown in FIG. 1, for a purpose to be described below.

FIG. 2 shows the embodiment of FIG. 1 in a shape which has been found preferable for the manufacture of nerve electrodes. In FIG. 2,

electrodes

12 and 13 and the associated portion of substance 14 are shown in a curved state to make it easy to hook the electrodes around a nerve, whereafter additional bending of

electrodes

12 and 13 is completed. To achieve the form of FIG. 2, substance 14 is preferably semicured while the structure is held in the position shown in FIG.

Referring now to FIG. 5, it can be seen that the apparatus of FIGS. 1 and 2 is attached to a portion of the body, here shown as a representative drawing of a nerve 20, by bending electrodes l2 and 13 around nerve 20. In FIG. 5 it can be seen that when the attachment of

electrodes

12 and 13 is completed.

tabs

15 and 16 will have met, at which time they are preferably joined by sutures such as 21, and the unneeded portions of

tabs

15 and 16 are then cut off.

Referring now to FIGS. 3 and 4, there are again shown leads l0 and 11 encapsulated in a substance 14, the substance 14 having extending

tabs

15 and 16. A pair of

electrodes

22 and 24 are here shown connected to lead 10 while a single electrode 23 is shown connected to lead 11.

Leads

22, 23 and 24 extend generally parallel, and leads 22 and 24 are in current guarding relation to lead 23. The advantages of a current guarding embodiment are described in U.S. Pat. No. Re. 26,809, mentioned above. FIG. 4 shows a configuration of this second preferred embodiment similar to that of FIG. 2 and achieved in the same manner and for the same purposes as those described above in the discussion of FIG. 2. The embodiment of FIGS. 3 and 4 is connected to a portion of the body, such as nerve 20 in FIG. 5, in the same manner described above for the connection of the embodiment of FIGS. 1 and 2.

Referring again to FIGS. 3 and 4, it can be seen that electrode 23 is of greater width than either of

electrodes

22 and 24. Preferably, the width of

electrodes

22 and 24 is substantially equal, and the width of electrode 23 is approximately twice that of either of

electrodes

22 and 24. This improvement results in a greater current density through the portion of the body to receive the electrical signal, such as nerve 20 in FIG. 5. This effect will be more fully described below.

Referring now to FIG. 6, there is seen a variation of the guarded electrode embodiment of the apparatus of this invention. In this embodiment, leads l0 and 11 are again connected, respectively, to a pair of parallel extending

electrodes

12 and 13. A U-shaped electrode 18 is at least partially encapsulated in substance 14 such that leads 12 and 13 extend into the open end of U-shaped member 18 and are parallel to and substantially in the same plane as member 18.

FIGS. 7 through 12 constitute copies of equipotential line plots of the apparatus of this invention and of various prior art electrode configurations, the plots actually taken by the inventor of the apparatus of this invention. FIGS. 7 through 12 represent cross sections of the electrodes as they would appear when connected to a portion of the body, such as nerve 20 in FIG. 5.

Referring first to FIG. 7, the two-electrode configuration of FIG. 1, it can be seen that

electrodes

12 and 13 appear on opposite sides of the portion of the body to which they are attached. FIG. 8 is an equipotential line plot of a prior art twoelectrode configuration such as that of the patent application of Seymour I. Schwartz et al. described above. The electrodes herein are denoted 12 and 13, and it can be seen that they appear on only one side of the portion of the body to which they are attached. A review of the equipotential line plots of FIGS. 7 and 8, recognizing that current is normal to the equipotential lines, makes apparent that the plot of FIG. 7 has a greater density of equipotential lines, with less curvature,

' located in the central portion between

electrodes

12 and 13.

The plot of FIG. 8 indicates very few equipotential lines limited to the space between electrodes 12' and 13, and shows more equipotential lines extending external to the entire configuration than does the plot of FIG. 7. It thus becomes apparent that the concentration of current in the nerve such as 20 is much improved by the use of the apparatus of this invention as depicted by FIG. 7.

FIGS. 9, and 11 are equipotential line plots for various three-electrode configurations. FIG. 9 represents an equipotential line plot for apparatus such as that shown in FIGS. 3 and 4. FIG. 10 represents an equipotential line plot for a configuration similar to that shown in FIGS. 3 and 4, but where the guarded electrode 23 is not of greater width than the guarding

electrodes

22 and 24. FIG. 11 is an equipotential line plot for a prior art guarded electrode configuration such as that shown in US. Pat. No. Re. 26,809, described above.

In FIG. 11, the three electrodes are denoted 22", 23" and 24". It can be seen that guarded electrode 23" has the greater amount of equipotential lines surrounding it, but that very few equipotential lines extend through the portion of the body to which the electrode is connected. Further, the shape of the equipotential lines surrounding electrode 23" indicate that they contribute little current to the longitudinal direction of the portion of the body being stimulated.

Reference to the equipotential line plot of FIG. 10 indicates an improvement in the number of equipotential lines flowing vertically, as shown in the diagram, through the portion of the body to be stimulated. This advantage is achieved through the fact that electrodes 22, 23' and 24' appear on opposite sides of the portion of the body to which they are connected. However, reference to FIG. 9 indicates a by far greater number of equipotential lines which are comparatively evenly spaced and extend vertically through the portion of the body being stimulated. This much improved result is due to the surface area of guarded electrode 23 being approximately double that of either of the two guarding

electrodes

22 and 24. It is thus apparent that the type of structure obtainable with the flexible electrodes of this invention allows a greatly improved current density and distribution in the portion of the body to be stimulated over the prior art configurations, as may be seen by comparing the prior art equipotential line plot of FIG. 11 to that of the plot of FIG. 10 and FIG. 9. It is also apparent that the apparatus of FIG. 3 of the drawing is preferred in that it gives the most favorable equipotential line plot as shown in FIG. 9.

Referring now to FIG. 12, there is shown an equipotential line plot for the apparatus of FIG. 6, a variation of the guarded electrode configuration. Here again, the equipotential line plot achieved by having

electrodes

12, 13 and 18 on both sides of the portion of the body being stimulated is seen to be preferable to that of the prior art guarded electrode configuration of FIG. 11.

Referring now to FIGS. 13 and 14 there is yet another variation of the apparatus of this invention, this variation comprising a two-electrode, guarded configuration. In FIG. 13 there is shown a pair of

leads

50 and 51. Lead 50 has an extending portion 52 which acts as an electrode such as electrode 12 of FIG. 1, except that extending portion 52 is curved in a generally U-shape as shown in FIGS. 13 and 14. Lead 51 has an extending portion 53 which acts as electrode 13 in FIG. 1, except that electrode 53 extends into the U-shape formed by electrode 52. Leads 50 and 51 are encapsulated in substance 14 having extending

tabs

15 and 16, while the extending

portion comprising electrodes

52 and 53 are partially encapsulated in substance 14, having exposed those areas adapted to be connected to the portion of the body. FIG. 14 shows the structure of FIG. 13 in the form preferable prior to connection, which is for the purposes and achieved in the manner described above for the apparatus of FIG. 2.

Again referring to FIGS. 13 and 14 it should be recognized that the highly

flexible leads

50 and 51, which terminate in

electrodes

52 and 53, are of a different design than coiled leads l0 and 11 of FIG. 1, and that the use of

leads

50 and 51 is unique in implantable electrodes. Each of

leads

50 and 51 comprises a plurality of non-overlapping, helically wound, electrical conductor lines. The lines are wound around an electrically insulating core. In addition, each of the lines comprises a single electrical conductor strip which is helically wound on a separate electrically insulating core. The use of this type of lead in an implantable electrode offers a greater flexibility and durability than leads previously used in the prior art.

From the above description it will be apparent that the apparatus of this invention offers significant advantages over the prior art, and it should be recognized that the embodiments described above are the preferred embodiments but that other configurations may be used without departing from the scope of this invention.

That which is claimed is:

1. Electrode apparatus for implantation in the body comprising: electrical conductor lead means adapted to be connected to a source of electrical current; flexible electrode means connected to said lead means, said flexible electrode means including means for being bent to adjustably substantially completely encircle and electrically contact the portion of the body to receive the electrical signal; and said lead means and a portion of said electrode means being encapsulated in an electrically insulating substance substantially inert to body fluids and tissue.

2. The apparatus of claim 1 in which said substance includes: portions of said substance encapsulating said electrode means which extend in opposite directions when said electrode means are not bent and which are adapted to meet for joining when said electrode means are bent to generally encircle the portion of the body, for holding said electrode means in contact with the portion of the body.

3. The apparatus of claim 1 including: a pair of said lead means; and a pair of said flexible electrode means, each connected to a different one of said lead means.

4. The apparatus of claim 3 in which said pair of flexible electrodes each comprise a generally rectangular flat strip of flexible metal.

5. The apparatus of claim 4 in which said flexible metal is position retaining.

6. The apparatus of claim 3 in which said pair of flexible electrode means extend generally parallel.

7. The apparatus of claim 6 including: U-shaped electrical conductor means at least partially encapsulated in said substance and mounted so that said parallel pair of flexible electrode means extend parallel to and in substantially the plane of and through the open end of said U-shaped means.

8. The apparatus of claim 1 including: a pair of lead means; a pair of said flexible electrode means, both connected to a first one of said pair of lead means; a third of said flexible electrode means connected to a second one of said pair of lead means; and said pair of flexible electrode means mounted for current guarding said third flexible electrode means.

9. The apparatus of claim 8 in which the surface area of said third flexible electrode is approximately equal to the combined surface area of said pair of flexible electrodes.

10. The apparatus of claim 8 in which: each of said flexible electrode means comprise a generally rectangular flat strip of flexible metal.

11. The apparatus of claim 10 in which said flexible metal is position retaining.

12. The apparatus of claim 10 in which: the width of said pair of flexible electrodes is equal; and the width of said third flexible electrode is approximately twice the width of one of said pair of flexible electrodes.

13. The apparatus of claim 10 in which: all said flexible electrode means extend generally parallel; and said third flexible electrode means is mounted between said pair of flexible electrode means.

14. The apparatus of claim 1 in which: said lead means comprise a plurality of electrical conductor lines wound in a nonoverlapping, helical pattern around an electrically insulating core; said lines each comprising a single electrical conductor strip helically wound around a separate electrically insulating core; and said flexible electrode means comprise an extending portion ofsaid lead means.

15. The apparatus of claim 14 in which: one of said flexible electrode means is U-shaped; and the other of said flexible electrode means extends parallel to and in substantially the plane of and through the open end of said U-shape of said one flexible electrode, so that said one flexible electrode means is in current guarding relation to said other flexible electrode means.

16. In implantable electrode apparatus having electrical conductor lead means connected to a plurality of electrode means, the lead means adapted to be connected to a source of electrical current such that at least one of the electrode means is of opposite electrical polarity to at least another of the electrode means, the improvement comprising: the electrode means including means for selective flexing to substantially completely encircle and electrically connect to a portion of a body such that at least portions of electrode means of opposite electrical polarity are on opposite sides of the portion of the body.

17. Electrode apparatus for implantation in the body comprising: electrical conductor lead means adapted to be connected to a source of electrical current; flexible electrode means connected to said lead means, and including bend area means for bending to adjustably substantially completely encircle the portion of the body to receive the electrical signal; said lead means and a portion of said electrode means being encapsulated in an electrically insulating substance substantially inert to body fluids and tissue; and at least a portion of said bend area means not encapsulated in said substance.

18. The apparatus of claim 17 in which said substance includes: portions of said substance encapsulating said electrode means which extend in opposite directions when said bend area means are not bent for joining when said bend area means are bent to generally encircle the portion of the body, for holding said electrode means in contact with the portion of the body.

19. The apparatus of claim 17 including: a pair of said lead means; and a pair of said flexible electrode means, each connected to a different one of said lead means.

20. The apparatus of claim 19 in which said pair of flexible electrodes each comprise a generally rectangular flat strip of flexible metal having a bend area portion not encapsulated in said substance.

21. The apparatus of claim 20 in which said flexible metal is position retaining.

22. The apparatus of claim 19 in which said pair of flexible electrode means extend generally parallel.

23. The apparatus of claim 22 including U-shaped electrical conductor means at least partially encapsulated in said substance and mounted so that said parallel pair of flexible electrode means extend parallel to and in substantially the plane of and through the open end of said U-shaped means.

24. The apparatus of claim 17 including: a pair of lead means; a pair of said flexible electrode means, both connected to a first one of said pair of lead means; a third of said flexible electrode means connected to a second one of said pair of lead means; and said pair of flexible electrode means mounted for current guarding said third flexible electrode means.

25. The apparatus of claim 24 in which the surface area of said third flexible electrode is approximately equal to the combined surface area of said pair of flexible electrodes.

26. The apparatus of claim 24 in which: each of said flexible electrode means comprise a generally rectangular flat strip of flexible metal having a bend area portion not encapsulated in said substance.

27. The apparatus of claim 26 in which said flexible metal is position retaining.

28. The apparatus of claim 26 in which: the width of said pair of flexible electrodes is equal; and the width of said third flexible electrode is approximately twice the width of one of said pair of flexible electrodes.

29. The apparatus of claim 26 in which: all said flexible electrode means extend generally parallel; and said third flexible electrode means is mounted between said pair of flexible electrode means.

30. The apparatus of claim 17 in which: said lead means comprise a plurality of electrical conductor lines wound in a non-overlapping, helical pattern around an electrically insulating core; said lines each comprising a single electrical conductor strip helically wound around a separate electrically insulating core; and said flexible electrode means comprise an extending portion of said lead means.

31. The apparatus of claim 30 in which: one of said flexible electrode means is U-shaped; and the other of said flexible electrode means extends parallel to and in substantially the plane of and through the open end of said U-shape of said one flexible electrode, so that said one flexible electrode means is mounted for providing current guarding to said other flexible electrode means.

32. Electrode apparatus for implantation in the body comprising: electrical conductor lead means adapted to be connected to a source of electrical current; flexible wraparound electrode means connected to said lead means, said electrode means including means for forming an adjustable configuration adapted to substantially encircle and electrically contact different-sized portions of the body to receive the electrical currents; and electrically insulating, flexible means substantially inert to body fluids and tissue encapsulating said lead means and a portion of said electrode means.

33. Electrode apparatus for implantation in the body comprising: electrical conductor lead means adapted to be connected to a source of electrical current; flexible wraparound electrode means connected to said lead means, said electrode means including means for forming an adjustable configuration adapted to substantially encircle and electrically contact different-sized portions of the body to receive the electrical current and for confining and concentrating sufficient current density to a selected portion of the body without adversely affecting said portion of the body, and electrically insulating, flexible means substantially inert to body fluids and tissue encapsulating said lead means and a portion of said electrode means.

34. Electrode apparatus for implantation in the body comprising: electrical conductor lead means adapted to be connected to a source of electrical current; flexible, wraparound, substantially elongated electrode means connected to said lead means, said electrode means including means for forming an adjustable configuration adapted to substantially encircle and electrically contact different-sized portions of the body to receive the electrical current; electrically insulating, flexible, means substantially inert to body fluids and tissue encapsulating said lead means and all of said electrode means except for that portion of said electrode means adapted to contact a portion of the body; and generally oppositely extending tab means connected to the portion of said insulating means encapsulating said electrode means. said tab means for fastening together for assisting in retaining said electrode means in a desired configuration.

35. Electrode apparatus for implantation in the body comprising: electrical conductor lead means adapted to be connected to a source of electrical current; flexible, wraparound, substantially elongated electrode means connected to said lead means, said lead means comprising at least two separate electrical conductors and said electrode means comprising at least two separate electrodes; electrically insulating, flexible means substantially inert to body fluids and tissue encapsulating said lead means and all of said electrode means except for a portion of said electrode means adapted to contact a portion of the body; said encapsulating means extending beyond said electrode means and defining oppositely extending integral tab means; said portion of said electrode means adapted to contact a portion of the body defining an elongated area of exposed electrode surface comprising a major portion of the length of said electrode means and further defining an elongated area of reduced thickness in cross section, substantially less than the thickness of areas immediately adjacent opposite ends of said electrode means, said area of reduced thickness defining an elongated portion of greater flexibility than the areas immediately adjacent thereto, and further providing a bend area means for forming an adjustable configuration adapted to substantially encircle different-sized portions of the body to receive the electrical current, such that when said bend area is bent around a portion of the body the areas of greater thickness and said tab means will lie substantially to one side of said portion of the body.

Claims

5. The apparatus of claim 4 in which said flexible metal is position retaining.

14. The apparatus of claim 1 in which: said lead means comprise a plurality of electrical conductor lines wound in a non-overlapping, helical pattern around an electrically insulating core; said lines each comprising a single electrical conductor strip helically wound around a separate electrically insulating core; and said flexible electrode means comprise an extending portion of said lead means.

33. Electrode apparatus for implantation in the body comprising: electrical conductor lead means adapted to be connected to a source of electrical current; flexible wraparound electrode means connected to said lead means, said electrode means including means for forming an adjustable configuration adapted to substantially encircle and electrically contact different-sized portions of the body to receive the electrical current and for confining and concentrating sufficient current density to a selected portion of the body without adversely affecting said portion of the body; and electrically insulating, flexible means substantially inert to body fluids and tissue encapsulating said lead means and a portion of said electrode means.

34. Electrode apparatus for implantation in the body comprising: electrical conductor lead means adapted to be connected to a source of electrical current; flexible, wraparound, substantially elongated electrode means connected to said lead means, said electrode means including means for forming an adjustable configuration adapted to substantially encircle and electrically contact different-sized portions of the body to receive the electrical current; electrically insulating, flexible, means substantially inert to body fluids and tissue encapsulating said lead means and all of said electrode means except for that portion of said electrode means adapted to contact a portion of the body; and generally oppositely extending tab means connected to the portion of said insulating means encapsulating said electrode means, said tab means for fastening together for assisting in retaining said electrode means in a desired configuration.