Surgery: light – thermal – and electrical application – Light – thermal – and electrical application – Electrical energy applicator
Reexamination Certificate
2001-08-21
2003-07-29
Layno, Carl (Department: 3762)
Surgery: light, thermal, and electrical application
Light, thermal, and electrical application
Electrical energy applicator
Reexamination Certificate
active
06600956
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to nerve electrodes, and more particularly to an improved circumferential neural (circumneural) electrode assembly for implantation on and electrical stimulation of selected nerve tissue of a patient, the electrode assembly providing reduced nerve constriction, improved tissue compatibility, and reduced current spread, and being configured and fabricated for ease of implantation.
Circumneural electrodes are generally designed to encompass a portion of a nerve longitudinally to permit electrical stimulation of the nerve. The stimulation may be intended to modulate electrical signals or impulses normally carried by the nerve. Alternatively or additionally, the nerve electrode may be used for sensing electrical signals carried by the nerve. The required installation of the electrode on a nerve for such purposes presents a considerable number of design problems. To provide mechanical stability of the electrode relative to the nerve, and in recognition that the nerve can move relative to the surrounding tissue, a structure that encompasses the nerve is desirable. This type of structure also provides efficiency in minimizing or optimizing the distance between the stimulating electrode and the nerve body. Nerves, however, are sensitive and easily damaged or traumatized by abrasion or stresses caused by subjection to mechanical forces.
From a mechanical perspective, an ideal peripheral nerve electrode has a structure strong enough to resist tensile forces arising from the attached conductor cable, but pliant enough to prevent tension, compression or constriction of the nerve. Tensile forces acting on the electrode should be minimized to prevent excess nerve constriction or to prevent the electrode from dislodging from the nerve. In addition, circumferential electrodes should be designed to fit closely against the nerve, and yet minimize constriction of the nerve attributable to swelling of the nerve inside the electrode structure.
Adverse mechanical forces can be attributable to constriction of the nerve by the circumneural electrode, or to a pull on or torque transmitted to the electrode (and thus, to the nerve) by a lead wire. Or the nerve may atrophy as a consequence of lack of nutritional fluid exchange owing to the close proximity of the electrode. Previously popular cuff electrodes have lost appeal because of their stiffness that often causes nerve damage.
Present-day nerve electrodes have been found difficult to install on the nerve using common surgical tools. In particular, many designs do not lend themselves to placement using endoscopic tools. Also, difficulty is encountered in explanting the electrode, because of tissue in-growth.
U.S. Pat. No. 4,573,481 discloses an implantable helical electrode assembly with a configuration having one or more flexible ribbon electrodes. Each ribbon electrode is partially embedded in aperipheral surface of an open helical dielectric support matrix adapted to be threaded or wrapped around a selected nerve or nerve bundle during surgical implantation of the electrode assembly. The resiliency of the assembly allows it to expand in the event of swelling of the nerve. The electrode's expansion characteristic conceptually allows for implantation on a range of nerve sizes. Its resiliency also allows fluid exchange between the helical coils, and mechanical compliance at its ends. But the electrode is difficult to install on the nerve because the helical configuration must first be unraveled and then re-formed about the nerve. In addition, the open structure of the electrode allows for wide current spread between the anode and cathode, which can cause adverse muscle or external tissue stimulation. Further, this electrode is one of those that is difficult to explant or remove from the nerve due to tissue in-growth into the helical structure. Lastly, the complex spiral shape of the electrode renders it difficult to manufacture, lending it to neither automated manufacturing or molding methods.
An improvement in electrode design is disclosed in U.S. Pat. No. 4,920,979, where a flexible electrode-supporting matrix has two oppositely directed helical portions centrally joined and with free outer ends. The helical portions extend circumferentially at least one turn and up to as much as about two turns. A thin, flexible conductive ribbon is secured to the inner surface to provide multiple electrodes on one or both portions, and a connecting electrical cable couples the electrode array to an electronics package for stimulation and/or sensing. The central passage through the helical portions accommodates a pair of pins that extend from the respective closed legs of a tweezer-like installation tool. When the pins are inserted through the central passage and the legs of the tweezers are opened, the helical portions are spread open to allow the assembly to be slipped over the nerve with the two open-sided portions restrained in a direction generally perpendicular to the length of the nerve. Upon release by withdrawing the pins of the installation tool, the two end portions return to a helical shape to encircle the nerve with their electrode portions conductively contacting the nerve surface. This arrangement simplifies electrode installation and reduces nerve trauma during implantation. However, the particular design exhibits poor mechanical retention properties that render the electrode structure easily dislodged from the nerve during implant.
Thus, the availability of these and other circumneural helical or spiral electrodes has not eliminated problems in installation of the electrode on the nerve or in attachment of the lead wire to the electrode assembly. Conflicting design goals of maximizing mechanical strength for fatigue resistance while minimizing spring constant to allow compliance with the nerve and its movement, must be addressed. It is desirable to improve the strength, durability, flexibility and fatigue resistance of the electrode assembly itself, and as well, to improve the mechanical strength of the electrical connection between the lead conductor and the electrode assembly.
In another prior art implantable lead for nerve stimulation, the lead body comprises an MP35N (cobalt chromium alloy) electrical coil conductor having a helical or spiral electrode assembly at its distal end. The conductor has a biocompatible electrically insulative sheath, and a lead connector at its proximal end for insertion into a mating electrical connector of the implanted signal generator. The electrode assembly includes one or more single turn platinum spiral electrical stimulation ribbon conductors with a 90% platinum/10% iridium alloy wire reinforcing component in the weld between the conductor coil and the ribbon electrode. The ribbon conductor is molded in a silicone elastomer insulating material so that the conductor portion is bonded to the insulation but exposed at the underside of the spiral. An integral anchor tether is employed to retain the implanted electrode in place without undue flexing, thereby substantially reducing the possibility of fatigue and fracture of the electrode or the weld connection to the conductor coil.
In the latter prior art design, heat treating of the platinum ribbon stimulating electrode surface makes the platinum material soft and ductile, creating vulnerability of the ribbon electrode to damage during implantation if subjected to excessive manipulation or improper handling. If the electrode helix is overly stretched by the surgeon during installation of the electrode on the nerve, it may be deformed to an extent that affects its performance and long term reliability as a nerve-stimulating electrode. The tether reduces the magnitude of repetitive, small force loads on the lead connection to the electrode after implantation, but the possibility of mechanical fatigue at the weld joint remains.
The assignee of the invention disclosed in the present application owns several improvement patents covering nerve electrodes, including U.S. Pat. Nos. 4,979,511; 5,21
Kollatschny Shawn D.
Maschino Steve E.
Blank Rome LLP
Cyberonics, Inc.
Layno Carl
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