# Patent

## Title
Nerve cuff with pocket for leadless stimulator

## Abstract

An extravascular nerve cuff that is configured to hold a leadless, integral, implantable microstimulator. The nerve cuff may include a cuff body having a pocket or pouch for removably receiving the implantable device within. The nerve cuff can be secured around the nerve such that the electrodes of the device are stably positioned relative to the nerve. Furthermore, the nerve cuff drives the majority of the current from the stimulation device into the nerve, while shielding surrounding tissues from unwanted stimulation.

## Background
CROSS REFERENCE TO RELATED APPLICATION
This application claims the benefit under 35 U.S.C. §119 of U.S. Provisional Patent Application No. 61/185,494, filed on Jun. 9, 2009, titled “NERVE CUFF WITH POCKET FOR LEADLESS STIMULATOR”.


INCORPORATION BY REFERENCE
All publications and patent applications mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication or patent application was specifically and individually indicated to be incorporated by reference.
FIELD OF THE INVENTION
The present invention relates generally to implantable neural stimulators, and more specifically to a nerve cuff with a pocket for removably receiving an active leadless stimulation device, and methods of stimulating a nerve using such nerve cuff.
BACKGROUND OF THE INVENTION
Implantable electrical stimulation devices have been developed for therapeutic treatment of a wide variety of diseases and disorders. For example, implantable cardioverter defibrillators (ICDs) have been used in the treatment of various cardiac conditions. Spinal cord stimulators (SCS), or dorsal column stimulators (DCS), have been used in the treatment of chronic pain disorders including failed back syndrome, complex regional pain syndrome, and peripheral neuropathy. Peripheral nerve stimulation (PNS) systems have been used in the treatment of chronic pain syndromes and other diseases and disorders. Functional electrical stimulation (FES) systems have been used to restore some functionality to otherwise paralyzed extremities in spinal cord injury patients.
Typical implantable electrical stimulation systems can include a system with one or more programmable electrodes on a lead that are connected to an implantable pulse generator (IPG) that contains a power source and stimulation circuitry. However, these systems can be difficult and/or time consuming to implant, as the electrodes and the IPG are usually implanted in separate areas and therefore the lead must be tunneled through body tissue to connect the IPG to the electrodes. Also, leads are susceptible to mechanical damage over time as they are typically thin and long.
Recently, small implantable neural stimulator technology, i.e. microstimulators, having integral electrodes attached to the body of a stimulator has been developed to address the disadvantages described above. This technology allows the typical IPG, lead and electrodes described above to be replaced with a single device. Elimination of the lead has several advantages including reduction of surgery time by eliminating, for example, the need for implanting the electrodes and IPG in separate places, the need for a device pocket, tunneling to the electrode site, and strain relief ties on the lead itself. Reliability is therefore increased significantly, especially in soft tissue and across joints because active components, such as lead wires, are now part of the rigid structure and are not subject to the mechanical damage due to repeated bending or flexing over time.
However, the leadless integral devices tend to be larger and more massive than the electrode/lead assemblies, making it difficult to stably position the device in the proper position in respect to a nerve. Without device stability, the nerve and/or surrounding muscle or tissue can be damaged due to movement of the assembly.
There remains a need for a leadless integral device that is stably positioned on the nerve, and can provide for removal and/or replacement of the stimulation device with relative ease.
SUMMARY OF THE INVENTION
Described herein are extravascular nerve cuffs for securing a leadless, integral, implantable device to a nerve. The nerve cuff typically includes a pouch or pocket. The cuff electrode configuration of the stimulation device allows the device to be stably positioned proximate a nerve, such as the vagus nerve. Furthermore, the cuff electrode configuration also has the characteristics of driving most of the current into the nerve, while shielding surrounding tissues from unwanted stimulation. Methods of securing a leadless microstimulator using such nerve cuffs are also described herein, as well as methods of stimulating a nerve using microstimulators secured using such cuffs.
There are numerous advantages to using leadless cuffs with a microstimulator, including a decrease in encapsulation (e.g., to about 100 microns) compared to systems without leadless cuffs, since there is less “tugging” on the leadless cuff. Furthermore, leadless cuffs, which may securely attach to a nerve and hold a microstimulator in position, may allow a microstimulator to be modified or replaced while maintaining the same positioning relative to the nerve.
In one embodiment of the invention, the nerve cuff generally includes a cuff body or carrier, made of a flexible material such as a medical-grade soft polymeric material (e.g., SilasticTM or TecothaneTM) forming a cuff or sleeve, having a pocket or pouch defined therein for removably receiving a leadless stimulation device. The leadless stimulation device is positioned within the pocket or sleeve such that the electrodes of the device are positioned proximate the nerve to be stimulated. The pocket can be defined by the space between the stimulation device and an inner surface of the cuff body or can comprise a pouch-like structure attached to the cuff body for containing the stimulation device. The nerve cuff can be coupled to the nerve, a surrounding sheath that contains the nerve, or both depending on the desired level of stability.
The nerve cuff can be implanted by first dissecting the nerve, such as the vagus nerve, from its surrounding sheath, wrapping the nerve cuff around the nerve, coupling or suturing the nerve cuff to one of either the nerve or the sheath and inserting the stimulation device within the pocket or pouch of the cuff body such that the stimulation device is proximate the nerve.
For example, described herein are nerve cuffs for securing a leadless microstimulator in stable communication with a nerve. A nerve cuff may include: a cuff body having a channel extending within the length of the cuff body for passage of a nerve; a pocket within the cuff body, configured to removably hold the leadless microstimulator; and an elongate opening slit extending the length of the cuff body configured to be opened to provide access to the pocket.
The nerve cuff may also include an internal electrical contact within the cuff body. For example, the internal electrical contact may be configured to electrically couple the microstimulator and the nerve. In some variations, the nerve further includes an external electrical contact on the outer surface of the cuff body configured to couple with the microstimulator.
In some variations, the cuff body comprises shielding configured to electrically isolate the microstimulator within the nerve cuff. The cuff body may be of uniform thickness, or it may have a non-uniform thickness. For example, the cuff body may have a thickness between about 5 and about 20 mils.
In some variations, the outer surface of the nerve cuff is substantially smooth and atraumatic. The nerve outer surface of the nerve cuff may be rounded and/or conforming. For example, the body may conform to the region of the body into which the cuff and/or microstimulator are implanted.
In some variations, the channel comprises a support channel configured to support the nerve within therein, to prevent pinching of the nerve.
The elongate opening slit may extend the length of the cuff body in an interlocking pattern. In some variations, the slit extends along the side of the cuff body, adjacent to the channel. In other variations, the slit extends along the top of the cuff body, opposite to the channel.
The nerve cuff may also include one or more attachment sites in the elongate opening slit configured to help secure the slit closed. For example, the attachment sites may be holes or passages for a suture.
In some variations, the cuff body is formed of a flexible and biocompatible polymer (e.g., a polymeric biocompatible material such as a silicone polymer.
Also described herein are nerve cuffs for securing a leadless microstimulator in stable communication with a nerve, comprising: an insulating cuff body having a nerve channel extending within the length of the cuff body for passage of a nerve, wherein the cuff body electrically isolates the microstimulator within the cuff body; a conductive surface within the nerve channel configured to engage one or more electrical contacts on the microstimulator; a pocket within the cuff body, configured to removably hold the leadless microstimulator; and an elongate opening slit extending the length of the cuff body configured to be opened to provide access to the pocket.
As mentioned above, the nerve cuff may include one or more external electrical contact on the outer surface of the cuff body configured to couple with the microstimulator.
In some variations, the nerve cuff body has a uniform thickness; in other variations, the nerve cuff body has a non-uniform thickness. The cuff body may have a thickness between about 5 and about 20 mils.
The outer surface of the nerve cuff may be substantially smooth and atraumatic. For example, the outer surface of the nerve cuff may be contoured.
In some variations, channel through the nerve cuff comprises a support channel configured to support the nerve within therein, to prevent pinching of the nerve.
In some variations, the elongate opening slit extends the length of the cuff body in an interlocking pattern. For example, the interlocking pattern may be a zig-zag pattern, or a sinusoidal pattern.
Also described herein are methods of implanting a leadless microstimulator in communication with a vagus nerve, the method comprising: exposing a vagus nerve; opening a slit of a nerve cuff having a nerve cuff body, wherein the slit opens along the length of the nerve cuff body; placing the nerve cuff around the vagus nerve so that the nerve is within a channel extending the length of nerve cuff; inserting a leadless microstimulator within a pocket in the nerve cuff; and securing the slit of the nerve cuff closed so that the leadless microstimulator is in electrical communication with the nerve and electrically isolated within the nerve cuff body.
In some variations, the step of securing the opening slit of the nerve cuff closed comprises securing the slit so that the leadless microstimulator engages an internal electrical contact within the nerve cuff body. The leadless microstimulator may engage an internal electrical contact configured to provide circumferential stimulation around the nerve within the channel.
The step of securing may comprise suturing the slit closed. In some variations, the slit may be self-closing. For example, there may be enough tension in the cuff to keep it closed by itself. In some variations, dissolvable sutures may be used to keep it closed until the body encapsulates it.
The method may also include the step of testing the microstimulator to confirm electrical communication with the nerve.
In some variations, the step of placing the nerve cuff comprises placing an oversized nerve cuff around the vagus nerve.
Also described herein are methods of implanting a leadless microstimulator in communication with a vagus nerve including the steps of: exposing a vagus nerve; opening a slit of a nerve cuff having a nerve cuff body, wherein the slit opens along the length of the nerve cuff body; placing the nerve cuff around the vagus nerve so that the nerve is within a channel extending the length of nerve cuff; inserting a leadless microstimulator within a pocket in the nerve cuff so that the microstimulator communicates with one or more internal electrical contacts within the nerve cuff; and closing the slit of the nerve cuff so that the nerve is in electrical communication with the one or more internal electrical contact.
In some variations, the leadless microstimulator and the internal electrical contact is configured to provide circumferential stimulation around the nerve within the channel. The step of closing may include the step of securing the slit of the nerve cuff closed. For example, the step of closing may comprise suturing the slit closed. The step of placing the nerve cuff may comprise placing an oversized nerve cuff around the vagus nerve.
The above summary of the invention is not intended to describe each illustrated embodiment or every implementation of the present invention. The figures and the detailed description that follow more particularly exemplify these embodiments.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view depicting a nerve cuff with stimulation device implanted proximate a nerve, according to an embodiment of the invention.
FIG. 1A is a top view depicting the implanted nerve cuff with stimulation device of FIG. 1;
FIG. 1B is a top view depicting the implanted nerve cuff with stimulation device according to an alternative embodiment of the invention;
FIG. 2 is a front view depicting an implanted nerve cuff with strain relief according to an embodiment of the invention;
FIG. 3 is a front view depicting an implanted nerve cuff with suture holes according to an embodiment of the invention;
FIG. 4 is an open view depicting the nerve cuff with suture holes of FIG. 3;
FIG. 5 is a top view depicting a closing device for the implanted nerve cuff of FIG. 1;
FIG. 6 is a perspective view depicting marsupializaton of the stimulation device within a pocket of the nerve cuff of FIG. 1;
FIG. 7A is a top view depicting a nerve cuff having a conforming shield according to an embodiment of the invention.
FIG. 7B is a front view of the nerve cuff of FIG. 7a. 
FIG. 8A is a top view depicting an open nerve cuff according to an embodiment of the invention;
FIG. 8B is a front view of the nerve cuff of FIG. 8a; and
FIG. 8C is a top view depicting the nerve cuff of FIG. 8 in a closed configuration.
FIGS. 9A and 9B show side views through a section of the cuff body wall, indicating uniform and varying thicknesses, respectively.
FIGS. 10A-10D illustrate one variation of a nerve cuff as described herein. FIG. 10A shows an end view, FIG. 10B is a side perspective view, FIG. 10C is a side view, and FIG. 10D is a longitudinal section through the device attached to a nerve, showing internal features including a microstimulator.
FIGS. 11A-11D illustrate another variation of a nerve cuff. FIG. 11A shows an end view, FIG. 11B is a side perspective view, FIG. 11C is a side view, and FIG. 11D is a longitudinal section through the device attached to a nerve, showing internal features including a microstimulator.
FIG. 12 shows one variation of a microstimulator that may be used in the nerve cuffs described herein.
FIG. 13A shows a perspective view of another variation of a microstimulator that may be used as described herein. FIGS. 13B and 13C are end and bottom views, respectively, of the microstimulator shown in FIG. 13A.
FIGS. 14 A and 14B illustrate side and end views, respectively of another variation of a nerve cuff.
FIGS. 15A-15C show top, side and sectional views, respectively of a nerve cuff such as the one shown in FIG. 14A, attached to a nerve. FIG. 15D is a section though the middle of a nerve cuff with a microstimulator secured there.
FIG. 16 is an internal end view of a microstimulator similar to the ones shown in FIGS. 14A-15D.
FIG. 17 is a sectional view showing the inside of another variation of a nerve cuff.
FIG. 18 is a side perspective view of the top-opening nerve cuff shown in FIG. 17.
FIG. 19 is a side perspective view of a side-opening nerve cuff.
FIG. 20 is a transparent view of the bottom of a nerve cuff, showing the nerve channel.
FIG. 21 is a side view of another variation of a nerve cuff.
FIGS. 22A-22H illustrate steps for inserting a nerve cuff such as the nerve cuffs described herein.
FIG. 23 shows an equivalent circuit modeling current loss when the nerve cuff is only loosely arranged over the nerve.



While the invention is amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and will be described in detail. It should be understood, however, that the intention is not to limit the invention to the particular embodiments described. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the invention are directed to a retaining device, such as a carrier or cuff, which positions active contacts, i.e. electrodes, of a stimulation device against the targeted nerve directing the current from the electrodes into the nerve. The retaining device also inhibits or prevents the current from flowing out to the surrounding tissue.
Referring to FIG. 1, one example of a nerve cuff 100 adapted for holding a stimulation device is coupled to a nerve 102. Nerve 102 can comprise any nerve in the human body targeted for therapeutic treatment, such as, for example, the vagus nerve. Nerve cuff adapter 100 generally comprises an outer carrier or cuff 104 body that can comprise any of a variety of medical grade materials, such as, for example, SilasticTM brand silicone elastomers, or TecothaneTM polymer.
In general, a nerve cuff including a cuff 104 body having (or forming) a pouch or pocket 106 for removably receiving an active, implantable stimulation device 108 having one or more integrated, leadless electrodes 110 on a surface of stimulation device 108 proximate nerve 102. As illustrated in FIGS. 1 and 1A, nerve cuff 100 wraps around nerve 102 such that electrodes 110 are positioned proximate nerve 102.
Contacts or electrodes 110 can be positioned directly against nerve 102, as illustrated in FIG. 1A, or in close proximity to nerve 102, as illustrated in FIG. 1B. Referring specifically to FIG. 1B, close proximity of electrodes 110 and nerve 102 will leave a gap or space 112 that may naturally be filled with fluid or connective tissue. In one embodiment of the invention, electrodes 110 and/or the inner surface of cuff body 104 can include optional steroid coatings to aid in reducing the local inflammatory response and high impedance tissue formation.
In one embodiment, the pocket 106 for containing the stimulation device 108 is defined by the open space between the nerve 102 and the inner surface of the cuff body 104. Stimulation device 108 can be passively retained within pocket 106 by the cuff body 104, or can be actively retained on cuff body with fastening means, such as, for example, sutures. In other embodiments, pocket 106 can comprise a pouch-like structure attached to cuff body 104 into which stimulation device 108 can be inserted. Stimulation device 108 can be passively retained within a pouch-like pocket by simply inserting the device 108 into the pocket or can be actively retained with fastening means. A pouch-like pocket can be positioned either in the interior or on the exterior of cuff body 104. Pouch-like pocket 106 and/or cuff body 104 can include access openings to allow electrodes to be positioned directly proximate or adjacent to nerve 102.
Cuff body 104 can have a constant thickness or a varying thickness as depicted in FIGS. 9A and 9B. The thickness of cuff body 104 can be determined to reduce the palpable profile of the device once the stimulation device is inserted. In one embodiment, the thickness of cuff body can range from about 1 to about 30 mils, or from about 5 to about 20 mils. In one embodiment shown in FIG. 9B, cuff 104 can have a greater thickness at a top and bottom portion of the cuff and a smaller thickness in a middle portion where the stimulation device is contained.
A key obstacle to overcome with implanting stimulation devices proximate nerves or nerve bundles is attaching a rigid structure that makes up the stimulation device along a fragile nerve in soft tissue. In one embodiment of the invention, this issue is resolved by encasing nerve 102 and device 108 in a cuff body 104 that comprises a low durometer material (e.g., SilasticTM or TecothaneTM) as described above, that conforms around nerve 102. Further, as illustrated in FIG. 2, cuff body 104 can comprise strain reliefs 114 on its ends that reduce or prevent extreme torsional rotation and keep nerve 102 from kinking Strain reliefs 114 can coil around nerve 102, and are trimmable to a desired size, such as the size of nerve 102. Further, strain relief 114 can be tapered. In some variations, the lateral ends of the nerve cuff, forming the channel into which the nerve may be place, are tapered and have a tapering thickness, providing some amount of support for the nerve. In some variations, the channel through the nerve cuff in which the nerve may sit, is reinforced to prevent or limit axial loading (e.g., crushing) of the nerve or associated vascular structures when the nerve is within the cuff.
Given the design or architecture of cuff body 104, any vertical movement of cuff body 104 on nerve 102 is not critical to electrical performance, but can result in friction between device 108 and nerve 102 that could potentially damage nerve 102. For that reason, device 108 should readily move up and down nerve 102 without significant friction while being sufficiently fixated to nerve 102 so that eventually connective tissue can form and aid in holding device 108 in place. The challenge is stabilizing device 108 so that it can be further biologically stabilized by connective tissue within several weeks.
Nerve cuff 100 should not be stabilized to surrounding muscle or fascia that will shift relative to the nerve. Therefore, referring to FIGS. 3 and 4, nerve cuff 100 can further comprise connection devices, such as suture holes or suture tabs, for coupling and stabilizing cuff body 104 with device 108 to at least one of the nerve bundle or nerve 102, and the surrounding sheath that contains nerve 102. In one embodiment of the invention, for example, as shown in FIG. 3, cuff body 104 can comprise suture holes 116 that can be used with sutures to couple cuff 104 body with device 108 to the surrounding nerve sheath. In an alternative embodiment of the invention, shown in FIG. 4, suture tabs 118 with suture holes 116 extend from one or both sides of cuff body 104.
Several stabilizing mechanisms can be used, including suture tabs and holes, staples, ties, surgical adhesives, bands, hook and loop fasteners, and any of a variety of coupling mechanisms. FIGS. 3 and 4, for example, illustrates suture tabs and holes that can be fixed to the surrounding sheath with either absorbable sutures for soft tissue or sutures demanding rigid fixation.
FIG. 5 illustrates sutures 120 that clamp or secure cuff body 104 with device 108 to a surgeon-elected tension. Sutures 120 can be tightened or loosened depending on the level of desired stability and anatomical concerns. As shown in FIG. 5, a gap 122 can be present so long as cuff adapter 100 is sufficiently secured to nerve 102, with a limit set to a nerve diameter to prevent compression of the vasculature within nerve 102. Surgical adhesives (not shown) can be used in combination with sutures 120 on surrounding tissues that move in unison with the neural tissue.
Muscle movement against cuff adapter 100 can also transfer undesired stresses on nerve 102. Therefore, in an embodiment of the invention, low friction surfaces and/or hydrophilic coatings can be incorporated on one or more surfaces of cuff body 104 to provide further mechanisms reducing or preventing adjacent tissues from upsetting the stability of nerve cuff 100.
FIG. 6 illustrates a nerve cuff 100 with a stimulator device removably or marsupially secured within pocket or pouch 106 of cuff body 104. By the use of reclosable pouch 106, active stimulator device 108 can be removed or replaced from cuff body 104 without threatening or endangering the surrounding anatomical structures and tissues. Device 108 can be secured within cuff body 104 by any of a variety of securing devices 124, such as, for example, sutures, staples, ties, zippers, hook and loop fasteners, snaps, buttons, and combinations thereof. Sutures 124 are shown in FIG. 6. Releasing sutures 124 allows access to pouch 106 for removal or replacement of device 108. Not unlike typical cuff style leads, a capsule of connective tissue can naturally encapsulate nerve cuff 100 over time. Therefore, it will most likely be necessary to palpate device 108 to locate device 108 and cut through the connective tissue capsule to access sutures 124 and device. The removable/replaceable feature of nerve cuff 100 is advantageous over other cuff style leads because such leads cannot be removed due to entanglement with the target nerve and critical vasculature.
As discussed supra, compression of nerve 102 must be carefully controlled. Excess compression on nerve 102 can lead to devascularization and resulting death of the neural tissue. Compression can be controlled by over-sizing or rightsizing nerve cuff 100, so that when pocket sutures 124 are maximally tightened, the nerve diameter is not reduced less that the measured diameter. Cuffs formed from SilasticTM or TecothaneTM materials are relatively low cost, and therefore several sizes can be provided to the surgeon performing the implantation of nerve cuff 100 to better avoid nerve compression.
Miniature stimulators, such as device, are still large enough to be felt and palpated by patients as are state-of-the-art commercial cuff systems. Referring to FIG. 7, to avoid such palpation, nerve cuff 100 can further comprise a protecting shield 126 conforming to the shape of the anatomical structures, such as in the carotid sheath. In this embodiment, nerve cuff 100 is secured around the vagus nerve, while isolating device 108 from contact with both the internal jugular vein (IJV) 132, and common carotid artery 134. Shield 126 then further isolates device 108 from other surrounding tissues. It is critical to minimize the profile of the entire cuff adapter 100 while maintaining the compliance of such materials as SilasticTM or TecothaneTM. In one embodiment of the invention, protective shield 126 is formed from a PET material, such as Dacron®, optionally coated with SilasticTM or TecothaneTM forming a thin and compliant structure that will allow for tissue separation when required.
When a nerve does not provide sufficient structural strength to support nerve cuff adapter 100, collateral structures can be included in or on cuff body 104. Because of a high degree of anatomical variance such a scheme must demand the skill of the surgeon to utilize a highly customizable solution. FIG. 8a illustrates a variable size nerve cuff 100 with a wrappable retainer portion 128 extending from cuff body 104. As shown in FIG. 8c, cuff body 104 is secured around nerve 102, while retainer portion 128 is secured around the sheath or other surrounding anatomical structures, such as the IJV 132 and/or carotid artery 134. As shown in FIG. 8b, wrappable retainer portion 128 can include securing devices 130, such as suture holes, for securing the entire nerve cuff 100 around the desired anatomical structures. This configuration allows for access to device 108 through pocket 106 as in previous embodiments, while adapting to a multitude of anatomical variations to obtain the desired stability of nerve cuff 100 on nerve 102.
FIGS. 10A-10D illustrate a variation of a nerve cuff that includes a cuff body forming a channel (into which a nerve may be fitted) and an slit formed along the length of the nerve cuff body. In this example, the nerve cuff body also includes a pocket region within the cuff body positioned above the nerve channel. The top of the body (opposite from the nerve channel) includes a long slit 1003 along its length forming on opening. The cuff body may be along the slit by pulling apart the edges, which may form one or more flaps. In the example shown in FIG. 10A, the slit may be split open to expose the inside of the nerve cuff and allow the nerve to be positioned within the internal channel, so that the cuff is positioned around the nerve. The same split may be used to insert the microcontroller as well. In some variations a separate opening (slit or flap) may be used to access the pocket or pouch for the microcontroller.
FIG. 10B shows a perspective view of the nerve cuff holding a microcontroller after it has been inserted onto a nerve (e.g., the vagus nerve). FIG. 10C shows a side view of the same. FIG. 10D shows a section though the view of FIG. 10C, illustrating then nerve within the channel formed through the nerve cuff, and a microstimulator held snugly within the nerve cuff so that the microstimulator is in electrical communication with the nerve via a shared surface between the two. In some variations, as discussed below, the microstimulator is held in a separate, possibly isolated, compartment and electrical contact with the nerve is made by one or more internal leads that couple the microstimulator with the nerve through an internal contact.
The exemplary cuff shown in FIGS. 10A-10D has a conformal configuration, in which the wall thickness is relatively constant, as can be seen from the sectional view in FIG. 10D. In contrast, FIGS. 11A-11D illustrate a variation of a nerve cuff in which the wall thickness varies along the perimeter. This non-uniform thickness may effectively cushion the device relative to the surrounding tissue, even as the patient moves or palpitates the region. This may have the added benefit of preventing impingement of the nerve. Similarly, the variable thickness may enable smooth transitions and help conform the cuff to the surrounding anatomy.
For Example, FIG. 11A shows an end view (with exemplary dimensions illustrated). It should be noted that in any of the figures or examples provided herein, the dimensions shown or described are for illustration only. In practice the dimensions may be +/− some percentage of the values shown (e.g., +/−5%, 10%, 15%, 20%, 25%, 30%, 40%, 50%, etc.). The section through the device shown in FIG. 11D illustrates the non-uniform thickness of the walls.
Both nerve cuff variations shown in FIGS. 10A-10D and FIGS. 11A-11D are substantially rounded or conforming, and have non-traumatic (or atraumatic) outer surfaces. As mentioned, this relatively smooth outer surface may enhance comfort and limit encapsulation of the nerve cuff within the tissue.
As can be seen from FIGS. 10D and 11D, the microstimulator typically rests above (in the reference plane of the figure) the length of the nerve when inserted into the nerve cuff. In some variations, the microstimulator includes a contoured outer surface onto which one or more contacts (for contacting the nerve or an internal conductor within the nerve cuff) are positioned. For example, FIG. 12 illustrates one variation of a microstimulator 1201. In this example, the microstimulator includes one or more contacts on its outer surface with which to provide stimulation to a nerve. FIG. 13A shows another variation of a microstimulator 1301 in which the outer surface (the bottom in FIG. 13A) is curved to help form a channel surrounding the nerve when the microstimulator is inserted into the nerve cuff. FIG. 13B shows an end view, illustrating the channel concavity 1303 extending along the length of the microstimulator, and FIG. 13C shows a bottom view, looking down onto the channel region. In practice, the microstimulator shown may be placed within the nerve cuff and be held in position at least partially around the nerve. Thus, the microstimulator may help protect the nerve, which may lie within this channel. As mentioned above, and described in greater detail below, it is not necessary that the nerve lie against the contacts, as current may be conducted to the nerve from within the nerve cuff, which may be insulated sufficiently to prevent excessive leak or spillover of the current even when the cuff is oversized and only loosely surrounds the nerve. Furthermore, the nerve cuff may include one or more internal contacts allowing the current from the microstimulator to be distributed to the nerve via one or more internal contacts or leads, including circumferentially around the nerve.
FIGS. 14A and 14B show another variation of a nerve cuff. In this example, the slit forming the opening is positioned on the upper surface (opposite to the nerve channel) along the length of the device. The slit is formed in an interlocking pattern. In FIG. 14a, the slit forms a zig-zag pattern, although other interlocking patterns may be used. For example, a sinusoidal or square-wave pattern may be used. The interlocking pattern may distribute the strain of closing the cuff around the nerve and microstimulator, and may make it easier to close the cuff once it has been positioned and the microstimulator has been inserted. FIG. 14B shows an end view of the same cuff shown in FIG. 14A.
FIGS. 15A-15C show a similar cuff to the one shown in FIG. 14A from top and side views, connected to a nerve. In these example, the nerve extends through the internal channel and out the openings (which may be oval shaped, as shown in FIG. 14B) at either end. In FIG. 15C, a section through the length of the device shows that the microstimulator is positioned in the pouch (cavity) above the nerve. The microstimulator maybe held in place by the walls of the cuff. A conforming microstimulator (such as the one shown in FIG. 13A-13C) may be used, as illustrated in the cross-sectional view shown in FIG. 15D. The contacts 1503 of the conforming microstimulator are positioned on the bottom of the device.
As mentioned briefly above, in some variations of the nerve cuff, the inner surface of the cuff body includes one or more internal contacts configured to couple with the microstimulator held within the pouch, and transmit any applied energy to the nerve (or receive energy from the nerve) positioned within the channel through the nerve cuff. The internal lead may be positioned so that it applies current to the underside (along the bottom region of the channel), or around the sides of the nerve as it sits within the channel. In some variations the internal conductor or lead is configured around the channel so that the nerve may be circumferentially stimulated, optimizing the applied stimulation. FIG. 17 is a long section though a nerve cuff, showing the inside of the cuff, and illustrates a variation of a nerve cuff having an internal lead 1703 that may apply stimulation to the underside of the nerve. This internal lead may be formed of any biocompatible conductive material, including medals, conductive plastics, or the likes. The internal lead may include exposed electrode surfaces 1703 for making contact with the nerve. Electrodes may be active contacts, also formed of any appropriate conductive material (e.g., metals, conductive polymers, braided materials, etc.). In some variations, the internal lead is coated or treated to help enhance the transfer of energy between the microstimulator and the nerve. Circumferential stimulation or conduction around the lead may reduce the impedances and assure uniform cross-sectional stimulation of the nerve bundle.
FIG. 19 shows another variation of a nerve cuff as described herein. In this example, the nerve cuff includes slit 1903 along one side of the device, adjacent to the nerve channel, which can be opened (e.g., by pulling apart the flaps or sides of the cuff) to expose nerve channel and the pocket for the microstimulator.
Many of the nerve cuff variations described herein may be opened and positioned around the nerve, for example, by splitting them open along a slit or hinge region. The device may be configured so that they have sufficient resiliency to close themselves, or remain closed if the edges of the slit region are brought together. Thus, the device may have a shape memory property that encourages them to close. In some variations, as already mentioned, it may be useful to hold them closed, at least temporarily, once they have been positioned over a nerve and the microstimulator has been positioned within the pocket. Thus, the device may include one or more closure elements. For example, the device may include a suture hole or passage for suturing the device closed. In some variations the nerve cuff includes a button or other fastener element. In some variations, as illustrated in FIGS. 6 and 18, the device may be sutured close with a dissolvable suture. A few weeks or months after insertion, the nerve cuff may be encapsulated or engulfed by the surrounding tissue, and will be held closed by this encapsulation. Thus, the dissolvable sutures merely keep the cuff closed for initial anchoring before biointegration and encapsulation occurs.
Any of the nerve cuffs described herein may also include one or more external leads or contacts facing the outside of the nerve cuff body, which may be used to stimulate tissues outside of the nerve cuff, and not just the nerve within the channel through the cuff. FIG. 21 illustrates one variation of a nerve cuff having external leads. In this example, the nerve cuff includes two external contacts 2103 that are connected (through the wall of the nerve cuff body) to the microstimulator held within the nerve cuff pocket. Such external leads may be used for sensing in addition to (or instead of) stimulation. For example, these electrical contacts may be used to sense other physiological events such as muscle stimulation and/or cardiac function. These signals can be applied to aid synchronization of target nerve stimulation to minimize artifacts of target stimulation. Such signals may be too faint for reliable remote sensing, however the position of the microstimulator (insulated within the housing of the nerve cuff) may allow accurate and reliable sensing.
A nerve may sit within a supported channel through the nerve cuff. As illustrated in FIG. 20, the channel 2003 may be formed having generally smooth sides, so as to prevent damage to the nerve and associated tissues. In some variations the nerve channel though the cuff is reinforced to prevent the cuff from pinching the device or from over-tightening the device when closed over the nerve. Supports may be formed of a different material forming the nerve cuff body, or from thickened regions of the same material. Although multiple sizes of nerve cuff may be used (e.g., small, medium, large), in some variations, an oversized nerve cuff may be used, because the insulated cuff body will prevent leak of current from the microstimulator to surrounding tissues.
In general, the nerve cuff body may be electrically insulating, preventing leakage of charge from the microstimulator during operation. In some variations the nerve cuff includes shielding or insulation sufficient to electrically insulate the microstimulator within the nerve cuff body. Shielding material may particularly include electrically insulative materials, including polymeric insulators.
It may be shown mathematically using an equivalent circuit of the microstimulator, as shown in FIG. 23, that the current from a microstimulator is not appreciably passed out of even a loosely applied nerve cuff. This allows for the use of oversized nerve cuffs, rather than requiring rigorous sizing, or risking constricting the nerve.
For example, assuming a nerve with a cross section of Narea is surrounded by a column of fluid Farea enclosed by the nerve cuff, where contacts on the inside the microstimulator are spaced Espacing apart (center to center) and have a width Ewidth and circle around the column of fluid and nerve Edegrees, it can be shown that the current will leak out the ends through a distance between the center of the electrode and the end of the nerve cuff that is defined by a distance Dguard.
The electrical model (illustrated in FIG. 23) consists of a current source that drives through DC isolation capacitors (Ciso2 optional), through the capacitance of each electrode (Cdl1 and Cdl2). From the electrodes, the current passes through either path RS or Rlp1+Rb+Rlp2. Where as a portion of the current passing through Rs provides useful work and the current passing through Rlp1+Rb+Rlp2 passes outside of the device and may cause undesirable effects.
If the nerve has a tight fit, then all the current passing through Rs would contribute towards stimulation, but only a portion of the current can activate the nerve in the case of a loose fit. Based on this model, it can be shown that (assuming that the nerve and fluid columns form an ellipse defined by the major and minor axis a and b, and the pulse width is short and capacitances are large) just the real impedance and efficiency can be estimated.
The electrode surface area is determined to estimate the complex portion of the impedance: Farea=π*aF*bF and Narea=π*aN*bN.
Assuming the impedance of the cuff contained fluid and nerve has a similar conductance p and electrodes are spaced at Espacing then the real resistance of the conduction volume is: Rworking=Espacing*ρ/Farea, where the wasted resistance that should be maximized is calculated by: Rwasted=2*Dguard*ρ/Farea+Rbulk, where Rbulk is defined as the free field resistance between the two ends of the cuff.
So the efficiency (η) of the real current delivered in the POD is Rwasted/(Rworking+Rwasted), and for the case of an undersized nerve assuming the conductivity of tissue and the fluid column is about equivalent then the stimulation efficiency is defined as ηT=η*Narea/Farea.
Methods of Insertion
In operation, any of the devices described herein may be positioned around the nerve, and the microstimulator inserted into the nerve cuff, in any appropriate manner. FIGS. 22A-22H illustrate one variation of a method for applying the nerve cuff around the nerve and inserting a microstimulator. In this example, the patient is prepared for application of the nerve cuff around the vagus nerve to hold a microstimulator device securely relative to the nerve (FIG. 22A). An incision is then made in the skin (≈3 cm) along Lange's crease between the Facial Vein and the Omohyoid muscle (FIG. 22B), and the Sternocleidomastoid is retracted away to gain access to the carotid sheath (FIG. 22C). The IJV is then reflected and ≦2 cm of the vagus is dissected from the carotid wall.
In some variations, a sizing tool may be used to measure the vagus (e.g., diameter) to select an appropriate microstimulator and cuff (e.g., small, medium, large). In some variations of the method, as described above, an oversized cuff may be used. The nerve cuff is then placed under the nerve with the opening into the nerve cuff facing the surgeon (FIG. 22D), allowing access to the nerve and the pocket for holding the microstimulator. The microstimulator can then be inserted inside cuff (FIG. 22E) while assuring that the microstimulator contacts capture the vagus, or communicate with any internal contacts/leads. The nerve cuff may then be sutured shut (FIG. 22F). In some variations, the microstimulator may then be tested (FIG. 22G) to confirm that the device is working and coupled to the nerve. For example, a surgical tester device, covered in a sterile plastic cover, may be used to activate the microstimulator and perform system integrity and impedance checks, and shut the microstimulator off. If necessary the procedure may be repeated to correctly position and connect the microstimulator. Once this is completed and verified, the incision may be closed (FIG. 22H).
The invention may be embodied in other specific forms without departing from the essential attributes thereof; therefore, the illustrated embodiments should be considered in all respects as illustrative and not restrictive. The claims provided herein are to ensure adequacy of the present application for establishing foreign priority and for no other purpose.

## Claims

1. A nerve cuff for enclosing a leadless microstimulator, the microstimulator having a body with electrodes integrally attached thereto, in stable communication with a nerve, the nerve cuff comprising:
a cuff body having a channel extending within the length of the cuff body for passage of a nerve;
a pocket within the cuff body, configured to removably hold the leadless microstimulator; and
an elongate opening slit extending the length of the cuff body configured to be opened to provide access to the pocket and the channel, and configured to be closed around the pocket and channel, enclosing the cuff body around the nerve.

2. The nerve cuff of claim 1, further comprising an internal electrical contact within the cuff body.

3. The nerve cuff of claim 2, wherein the internal electrical contact is configured to electrically couple the microstimulator and the nerve.

4. The nerve cuff of claim 1, further comprising an external electrical contact on the outer surface of the cuff body configured to couple with the microstimulator.

5. The nerve cuff of claim 1, wherein the cuff body comprises shielding configured to electrically isolate the microstimulator within the nerve cuff.

6. The nerve cuff of claim 1, wherein the cuff body has a uniform thickness.

7. The nerve cuff of claim 1, wherein the cuff body has a non-uniform thickness.

8. The nerve cuff of claim 7, wherein the cuff body has a thickness between about 5 and about 20 mils.

9. The nerve cuff of claim 1, wherein the outer surface of the nerve cuff is substantially smooth and atraumatic.

10. The nerve cuff of claim 1, wherein the outer surface of the nerve cuff is rounded.

11. The nerve cuff of claim 1, wherein the channel comprises a support channel configured to support the nerve within therein, to prevent pinching of the nerve.

12. The nerve cuff of claim 1, wherein the elongate opening slit extends the length of the cuff body in an interlocking pattern.

13. The nerve cuff of claim 1, wherein the slit extends along the side of the cuff body, adjacent to the channel.

14. The nerve cuff of claim 1, further comprising attachment sites in the elongate opening slit configured to help secure the slit closed.

15. The nerve cuff of claim 1, wherein the cuff body is formed of a flexible and biocompatible polymer.