United States Patent [19]
`Davey et al.
`
`[54] MAGNETIC NERVE STIMULATOR FOR
`EXCITING PERIPHERAL NERVES
`
`[75]
`
`Inventors: Kent R. Davey, New Smyrna Beach,
`Fla.; Charles Epstein. Atlanta, Ga.
`
`[73] Assignee: Neotonus, Inc.. Marietta, Ga.
`
`(21] Appl. No.: 345,572
`
`Nov. 28, 1994
`[22] Filed:
`Int. Cl.6
`....................................................... A61N 1./0t
`[51]
`[52] U.S. CI. ................................................................ 600/13
`[58] Field of Search ....................... 600/9-15; 607/48-52
`
`[56]
`
`References Cited
`
`U.S. PATENf DOCUMENfS
`
`7/1990 Cadwell .................................... 600/15
`4,940,453
`5,066,272 11/1991 Eaton et al ............................... 600/14
`5,156,587 10/1992 Montone ................................... 600/13
`
`FOREIGN PATENT DOCUMENTS
`3930930 10/1990 Germany ····················••n••······· 600/13
`OTHER PUBLICATIONS
`
`K. Davey and Lanbo Luo, Toward Functional Magnetic
`Stimulation Theory (PMS) and Experiment, submitted to
`IEEE Transactions on Biomedical Engineering. (submitted
`in Jul. 1993).
`K.R. Davey, et al., An Alloy-Core Electromagnet for Tran(cid:173)
`scranial Brain Stimulation, J. Qin. Neurophysiol vol. 6, No.
`4, p. 354.
`C.M. Epstein et al., Localizing the Site of Magnetic Brain
`Stimulation in Humans, Neurology, vol. 40, pp. 666-670.
`S.M.Hersch et al., Biological Consequence of Transcranial
`Magnetic Stimulation on the Mouse, Society for Neuro(cid:173)
`science Abstracts. vol. 16. 551.7.
`J.D. Weissman et al., Magnetic Brain Stimulation and Brain
`Size: Relevance to animal studies, vol. 85, pp. 215-219.
`
`111111111 Olll 111111111111110111111111101111111111111101
`US005725471A
`[lll Patent Number:
`[45] Date of Patent:
`
`5,725,471
`Mar. 10, 1998
`
`P.P.Brodak et al .. Magnetic Stimulation of the Sacral Roots,
`Neuroourology and Urodynamics, vol. 12, pp. 533-540.
`T. Kujirai et al., The Effect of Transcranial Magnetic Stimu(cid:173)
`lation on Median Nerve Somatosensory Evoked Potentials,
`electroencephalography and clinical Neurophysiology, vol.
`89. p. 227-234.
`Y. Omura, et al. Basic Electrical Parameters for Safe and
`Effective Therapeutics
`.
`.
`.
`, Accupuncture and
`Electro-Therapeutics Res .• Int., J., vol. 12, pp. 201-225.
`R.W. Gulch and 0. Lutz, Influence of Strong Static Mag(cid:173)
`netic Fields on Heart Muscle Contraction. Phys. Med. Biol.,
`vol. 31, No. 7, pp. 763-767.
`J. Bucking et al., The Influence of a Strong Magnetic Field
`on Muscular Contration, (Rad. ?) and Environ. Biophy., vol.
`11, pp. 79-85.
`"Mangetic Brain Stipulation and Brain Size: Relevance to
`Animal Studies," by J.D. Weissman, C.M. Epstein and K.R.
`Davey; Electroencephalography and clinical Neurophysiol(cid:173)
`ogy 85 (1992) 215-219.
`
`Primary &aminer-John P. Lacyk
`Attorney. Agent, or Firm-Levisohn. Lerner, Berger &
`Langsam
`
`[57]
`
`ABSTRACT
`
`A magnetic nerve stimulator system is comprise of a core of
`highly saturable material with a coil winding. A thyrister
`capacitive discharge circuit pulses the device. A rapidly
`changing magnetic field is guided by the core, preferably
`vanadium permendur. For task specific excitation of various
`nerve groups, specially constructed cores allow for excita(cid:173)
`tion of nerves at deeper levels with higher efficiency than is
`possible with air-core stimulators. Among the applications
`possible with this invention are treatment of incontinence,
`rehabilitation of large muscle groups in the leg and arm. and
`excitation of abdominal wall muscle groups to aid in weight
`loss and metabolic rate increase. A C-shape is employed for
`focussing the stimulation as desired.
`
`44 Claims, 4 Drawing Sheets
`
`L.iminot i ans
`
`4
`
`5
`
`\
`\
`\
`
`/
`
`___ ,,.,.
`
`/
`
`/
`
`\.
`
`' .....
`
`' ' --
`
`-------
`----------
`
`Allergan EX1068
`Page 1
`
`

`

`U.S. Patent
`
`Mar. 10, 1998
`
`Sheet 1 of 4
`
`5,725,471
`
`<.O
`'
`\
`-..J
`
`'
`~
`' "' ~
`' \
`
`en
`C
`
`0 -
`0
`C
`,.,
`E
`_J
`
`-
`
`' \
`
`/
`
`_,,,,
`/
`
`\
`
`\
`\
`\
`\
`\
`I
`J
`I
`I
`I
`I
`I
`I
`
`/
`
`/
`
`/
`
`-~
`
`/
`
`•
`
`I
`
`\
`\
`\
`\
`\
`\
`\
`l
`I
`f
`I
`I
`I
`I
`I
`I
`I
`I
`
`Allergan EX1068
`Page 2
`
`

`

`U.S. Patent
`
`Mar. 10, 1998
`
`Sheet 2 of 4
`
`5,725,471
`
`18
`
`12
`
`16
`
`2
`
`14
`
`FIG.2
`
`AG.3
`
`20
`
`Allergan EX1068
`Page 3
`
`

`

`U.S. Patent
`
`Mar. 10, 1998
`
`Sheet 3 of 4
`
`5,725,471
`
`22
`
`I - - - - - - - - ... -
`
`F/04
`
`0
`
`30
`
`FIG.7
`
`Allergan EX1068
`Page 4
`
`

`

`U.S. Patent
`
`Mar. 10, 1998
`
`Sheet 4 of 4
`
`5,725,471
`
`F/G.5
`
`28
`
`FJG.6
`
`Allergan EX1068
`Page 5
`
`

`

`1
`MAGNETIC NERVE STIMULATOR FOR
`EXCITING PERIPHERAL NERVES
`
`BACKGROUND OF THE INVENTION AND
`DESCRIPTION OF THE PRIOR ARf
`
`5,725,471
`
`5
`
`2
`without undue additional skin irritation. A contribution
`offered by the present invention is the ability to achieve
`higher levels of focusing of the magnetic field and thus
`stimulation within the patient. Commensurate with this
`greater level of focusing comes some flexibility in the
`number of possible applications that might be targeted. Also
`accompanying the higher degree of focus is a higher level of
`power efficiency. Typically, the devices being designed by
`the methods outlined in this invention reduce the magnetic
`reluctance path by a factor of two. This reluctance reduction
`10 translates into a diminution of the current by the same factor
`and a fourfold reduction in power loss.
`Magnetic stimulation of neurons has been heavily inves(cid:173)
`tigated over the last decade. Almost all magnetic stimulation
`work has been done in vivo. The bulk of-the magnetic
`stimulation work has been in the area of brain stimulation.
`Cohen has been a rather large contributor to this field of
`research (See e.g., T. Kujirai. M. Sato. J. Rothwell. and L.
`G. Cohen, 'The Effects of Transcranial Magnetic Stimula(cid:173)
`tion on Median Nerve Somatosensory Evoked Potentials",
`Journal of Clinical Neurophysiology and Electro
`20 Encephalography, Vol. 89, No. 4, 1993, pps. 227-234.) This
`work has been accompanied by various other research
`efforts including that of Davey, et al. (See. K. R. Davey, C.
`H. Cheng, C. M. Epstein "An Alloy-Core Electromagnet
`for Transcranial Brain Stimulation", Journal of Clinical
`25 Neurophysiology, Volume 6, Number 4. 1989. p.354); and
`that of Epstein, et al. (See, Charles Epstein, Daniel
`Schwartzberg, Kent Davey, and David Sudderth, "Localiz(cid:173)
`ing the Site of Magnetic Brain Stimulation in Humans",
`Neurology, Volume 40. April 1990, pps. 666-670). The bulk
`30 of all magnetic stimulation research attempts to fire nerves
`in the central nervous system.
`The present invention differs in a number of respects from
`previous research and efforts. First, the present invention has
`primary applicability to the peripheral nervous system.
`35 although it can be employed to stimulate nerves in the
`central nervous system as well. Second, and more
`importantly, the previous nerve stimulation work is domi(cid:173)
`nated almost exclusively by air core coils of various shapes
`and sizes. The present invention. as will be discussed. relates
`to the use of a core of a highly saturable material, preferably
`40 vanadium permendur. Among the air core stimulators are
`circles, ovals, figure eights, and D shaped coils. The coils are
`normally excited by a capacitive discharge into the winding
`of the core of these coils. This exponentially decaying field
`has a time constant typically in the neighborhood of 100
`microseconds. Typical target values for the magnetic field
`peak happen to be near two Tesla. J. A. Cadwell is perhaps
`the leader among those who are now using and marketing
`these air core stimulators. Among his primary patents is U.S.
`Pat. No. 4,940.453 entitled "Method and Apparatus for
`so Magnetically Stimulating Neurons" Jul. 10, 1990. There are
`a number of power supplies all of which operate on a basic
`capacitive type discharge into a number of air core coils
`which are sold with his units. Various shaped coils are being
`explored at this time. One such coil is a cap shaped device
`which fits over the motor cortex (K. Krus, L. Gugino, W.
`Levy, J. Cadwell, and B. Roth 'The use of a cap shaped coil
`for transcranial stimulation of the motor cortex", Journal of
`Neurophysiology, Volume 10. Number 3, 1993, pages
`353-362).
`Some efforts are being given to various circuits used to
`60 fire these air core coils. H. Eton and R. Fisher offer one such
`alternative in their patent "Magnetic Nerve Stimulator" U.S.
`Pat. No. 5,066,272 Nov. 19, 1991. They suggest the use of
`two capacitors--0ne to capacitively discharge into the coil
`of interest. and a second to recover the charge from the
`65 inductive energy resident in the coil. The circuit used in the
`present invention accomplishes the same objective with a
`single capacitor.
`
`15
`
`A nerve cell can be excited in a number of ways. but one
`direct method is to increase the electrical charge within the
`nerve. thus increasing the membrane potential inside the
`nerve with respect to the surrounding extracellular fluid
`One class of devices that falls under the umbrella of Func(cid:173)
`tional Electrical Stimulation (FES) realizes the excitation of
`the nerves by directly injecting charges into the nerves via
`electrodes which are either placed on the skin or in vivo next
`to the nerve group of interest. The electric fields necessary
`for the charge transfer are simply impressed via the wires of
`the electrodes.
`FES is accomplished through a mechanism which
`involves a half-cell reaction. Electrons flow in wires and
`ions fl.ow in the body. At the electro-electrolytic interface, a
`half-cell reaction occurs to accomplish the electron-ion
`interchange. Unless this half-cell reaction is maintained in
`the reversible regime, necrosis will result-partially because
`of the oxidation of the half-cell reaction and partially
`because of the chemical imbalance accompanied by it.
`The advantage of FES is that the stimulation can usually
`be accomplished from extremely small electrodes with very
`modest current and voltage levels. The disadvantage
`however, is that it involves half-cell reactions. Most reha(cid:173)
`bilitation programs using FES place the electrodes directly
`on the skin. A conductive gel or buffering solution must be
`in place between the electrodes and the skin surface. Long
`term excitation of nerve or muscle tissue is often accompa(cid:173)
`nied by skin irritation due to the current concentration at the
`electrode/skin interface. This problem is especially aggra(cid:173)
`vated when larger excitation levels are required for more
`complete stimulation or recruitment of the nerve group.
`By contrast, magnetic stimulation realizes the electric
`fields necessary for the charge transfer by induction. Rapidly
`changing magnetic fields induce electric fields in the bio(cid:173)
`logical tissue; when properly oriented. and when the proper
`magnitude is achieved, the magnetically induced electric
`field accomplishes the same result as realized by FES. that
`of transferring charge directly into the nerve to be excited.
`When the localized membrane potential inside the nerve
`rises with respect to its normal negative ambient level of 45
`approximately -90 millivolts (this level being sensitive to
`the type of nerve and local pH of the surrounding tissue), the
`nerve "fires."
`The present invention is especially targeted at applica(cid:173)
`tions that are not suited for the use of implanted electrodes.
`The invention is preferred for use in those situations where
`stimulation can be achieved noninvasively. In those appli(cid:173)
`cations which include incontinence and rehabilitation of
`muscle groups as well as potential weight loss treatment, the
`desired excitation levels using FES often fall outside of what
`might be considered comfortable limits. That is, the electri(cid:173)
`cal current that ideally would be injected through the skin to
`excite the muscle groups of interest often leads to some skin
`irritation with time. Even in applications where this is not
`the case, the mandatory use of gels and direct electrode/skin
`placement is inconvenient and is often resisted by the
`patient.
`Magnetic excitation. on the other hand, has the attractive
`feature of not requiting electrode skin contact. Thus. stimu(cid:173)
`lation can be achieved through the clothing that is being
`worn. This overcomes the objection of inconvenience and
`preservation of a patient's dignity. Secondly, because there
`is no direct contact. stronger excitation levels can be realized
`
`55
`
`Allergan EX1068
`Page 6
`
`

`

`5,725,471
`
`5
`
`10
`
`3
`Some stimulation research is being performed on the
`peripheral nervous system (See e.g .• Paul Maccabee, V.
`Amassian. L. Eberle. and R. Cracco. "Magnetic Coil Stimu(cid:173)
`lation of Straight and Bent Amphibian and Mammalian
`Peripheral Nerve in vitro: Locus of Excitation. " Journal of
`Physiology. Volume 460, Januar 1993, pages 201-219.) The
`bulk of Maccabee's work is however targeted for cranial
`excitation. The applications of the present invention focus
`on the peripheral nervous system although it can be used on
`the central nervous system. as well.
`SUMMARY OF THE INVENTION
`Magnetic stimulation of peripheral nerves has the advan(cid:173)
`tages of convenience and threshold variability over compet(cid:173)
`ing FES systems. An advance of the present invention over
`competing magnetic nerve stimulators is in the. use of a
`magnetic core of highly saturable material, and in the design
`of the magnetic core stimulator itself.
`An objective of the present invention is to "fire" a coil
`having about a 100 microsecond characteristic decay time,
`fifteen times per second. The system must be reasonably
`efficient and reliable to fire at such a high repetition rate.
`This rate is necessary to keep the muscle groups more or less
`continuously stimulated.
`The exact stimulation frequency will be varied somewhat
`depending on the requirements of the application. Some(cid:173)
`times muscle groups will need to be excited for a five second
`period. followed by rest for a five second period and then be
`stimulated continuously for another five seconds and then
`rest again. While they are being stimulated, it is desirable to
`have the muscle groups continuously excited. This require(cid:173)
`ment dictates the necessity of continuing to pulse the cores 30
`at a repetition rate of 15 Hz. Because of the large currents
`involved during any given firing of the core, it is necessary
`to make the cores as efficient as possible. It is desirable to
`focus the magnetic field into the region targeted for stimulus
`to the exclusion of surrounding regions. The specially
`designed cores offered by this invention realize that
`focusability, whereas the air core coils used by the prior art
`do not.
`The simplest core that might be selected would be that of
`a "C" shaped core. The span of the "C" must be carefully
`chosen; the span affects both the penetration depth and the
`magnitude of the field. Possibly of more importance is the
`construction of the core. The best cores are constructed from
`thin laminate, highly saturable material. A typical core might
`be wound using two mil stock of vanadium perrnendur. A
`long ribbon of such material is wound on a mandrel ( e.g. a 45
`mandrel of wood or plastic) for the radius, thickness and
`depth desired. Each side of the ribbon is coated with a thin
`insulative coating to electrically isolate it from its neighbor.
`A generic core that might be used at various locations around
`the body might span an angle of about 210°. Once the ribbon
`has been wound on the mandrel to the desired dimensions.
`it is dipped in epoxy to freeze its position. Once the epoxy
`has dried, the mandrel is removed and the core may be cut
`for the span of angle desired. The cut may destroy the
`electrical isolation of adjacent laminations. Each cut must be
`finely ground so that it is smooth, and then a deep etch
`performed. The deep etch is performed by dipping each of
`the cut ends in an acid bath. This causes the cut ends to
`delarninate slightly, but maintains the electrical isolation of
`the laminations. Failure to perform this deep etch seems to
`result in considerable eddy current loss and heating at the cut
`ends of the core. Following the deep etch, the ends are
`brushed with epoxy to maintain the shape and structural
`integrity of the core. The final step of the construction is to
`wind a coil of insulated wire about the core. A typical
`inductance for a core of this type is about 20 µH. The present
`invention. however, may be practiced at other inductances or
`magnetic field strengths. as well.
`
`4
`In the simplest configuration, each core has only one
`winding. The winding is excited by an exponentially decay(cid:173)
`ing pulse with a characteristic time of about 20 µs. The
`actual signal has a ringing period of about that time within
`an envelope that is exponentially decaying so that only two
`to three cycles are ever witnessed by the coil current. The
`excitation is repeated on a period of about 15-20 Hz. As
`stated above, the repetition cycle of these patterns will be
`varied according to the application. The circuit usually
`consists of a transformer which feeds into a full wave
`rectifier bridge. The bridge voltage charges the capacitor; the
`charge on the capacitor is triggered with a silicon control
`rectifier to drive current into the coil. The return charge
`coming back through the coil the second time is fed through
`the diode back into the capacitor to prepare the circuit for the
`15 second phase of excitation.
`There are three principal target applications for this
`invention-incontinence, muscle rehabilitation, and weight
`control treatment For the treatment of incontinence, it is
`necessary to stimulate the pelvic floor muscles. Such a
`20 stimulation is achieved by concentrating and focusing mag(cid:173)
`netic flux directly up the vaginal cavity. One suitable core
`capable of realizing this objective is constructed by com(cid:173)
`bining two individual "C" cores each spanning an angle of
`about 210°. The legs of the cores are brought together in a
`25 central region. The common central leg of the two "C" cores
`is wound by a coil and the return path for the flux is split
`between the two "C"s. The cores themselves fit proximally
`and distally on a saddle upon which the patient sits during
`treatment.
`The second area of potential application is in the reha-
`bilitation of muscles. The primary muscle groups targeted
`are the thigh, calf, biceps. and triceps. The geometry is
`similar for all these applications, and thus a cylindrical
`extension around the muscle is used. Although one solution
`for this problem is a simple "C" core and coil which is
`moved around by the discretion of the patient. a more
`suitable stimulator resembles the tubular shape motors used
`in electromechanics to propel a secondary member down a
`tube. Here the geometry would necessarily require a hinged
`tubular shape having recesses or slots which would run
`40 azimuthally around the muscle group to be stimulated. The
`coils of the stimulator fits in these recesses or slots and the
`surrounding structure would again be a laminated vanadium
`composite. If the structure were fitted with two or three coils,
`they could be stimulated in a phased arrangement
`Such an excitation would have the effect of kneading the
`muscle tissue group along its longitudinal axis. This par(cid:173)
`ticular excitation pattern may be instrumental in more fully
`recruiting larger muscle groups such as the hamstring group
`in the leg. Full recruitment or stimulation of the nerve group
`50 would be advantageous to long term rehabilitation. Prelimi(cid:173)
`nary experiments with the device indicate that excitations at
`the frequencies mentioned accomplish exercise of the
`muscles at a higher efficiency and rate than could be
`accomplished through normal means.
`Another area of potential application is that of assisting in
`weight loss management. As with muscle rehabilitation, one
`alternative is to simply use a handheld unit moved over
`multiple areas of the body. One particularly difficult group to
`stimulate might be the abdominal wall. A possible method
`for realizing excitation of this group would resemble a chest
`60 plate that might be hinged to the side of a chair in which the
`patient sits. The chest plate would contain a two or three
`phase arrangement of coils backed by the laminated vana(cid:173)
`dium cores constructed in the manner dictated above. The
`cores would be spaced to drive the flux deeply within the
`65 abdominal muscle group. Both in muscle rehabilitation and
`in weight loss management. the phasing of the coils can be
`alternated with time to give the effect of a back and forth
`
`35
`
`55
`
`Allergan EX1068
`Page 7
`
`

`

`5,725,471
`
`s
`"kneading" stimulation pattern. The rationale behind weight
`management is that the firing of these muscle groups
`requires the uptake of adenosine triphosphate; this energy
`expenditure is being artificially induced by the magnetic
`stimulator.
`In summary. it is noted that there are a number of ways to
`more efficiently stimulate various muscle groups within the
`body. The key to these more efficient techniques revolves
`around using high saturation thin laminate material to con(cid:173)
`struct these cores and thereby drive and focus the flux into
`the regions desired. A simple "C" type core achieves a
`reluctance advantage of at least a factor of two over con(cid:173)
`ventional cores. By using multiple cores connected at a
`center leg, a single focus site can be achieved with the return
`path disbursed in two or more areas so as to discourage
`excitation when the field is returned. In other applications.
`multiphased coils that actually enclose the tissue of interest
`can be excited so as to roll or knead muscle groups direc(cid:173)
`tionally with time. Certain wrapping applications may be
`more instrumental for higher recruitment of injured muscle
`groups.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 is a plan view of a "C" shaped core stimulator with
`the toroidal coil field winding wrapped around the core. The
`field lines ( dotted) indicate the depth of penetration and
`focusing of the stimulation.
`FIG. 2 is a schematic of the electrical circuit used to
`stimulate the coil winding.
`FIG. 3 is a top plan view of a core stimulator configuration
`used in the treatment of incontinence; the core is designed to
`fit underneath a saddle shaped cushion in which the patient
`sits during treatments.
`FIG. 4 is a perspective view of a core stimulator (wrapped
`around a patient's leg) used to massage muscles in the leg
`for rehabilitation purposes. The tubular core is hinged on
`one side and is designed to fold around the leg.
`FIG. 5 is a perspective view of a half section of the core
`stimulator used for arm or leg muscle rehabilitation; wind(cid:173)
`ings of different phases are placed in adjacent recesses or
`slots, cut into the core. FIG. (j is an end view of the leg or
`arm stimulator. The winding going from one section to the
`next is taken out in a long fold to allow for ease of opening
`of the core units for facilitating placement around the leg or
`arm.
`FIG. 7 is a schematic perspective view of a hinged
`multiphased stimulator designed to conform around the
`torso of the patient
`
`10
`
`30
`
`6
`which can be produced by the core. The characteristic
`magnetic fields in the cores have strengths in the range of
`two Tesla. The laminate material must be constructed of a
`highly saturable material. Preferably. vanadium permendur
`5 is used. This material carries a high field density. In this
`application, high saturation is more important than high
`permeability. A winding or coil 4 is then wrapped around the
`core in such a way as to drive the flux through the cut ends
`5. The field lines (j give an indication of the depth of
`penetration and degree of focusing expected with such a
`core.
`FIG. 2 shows an electrical circuit used to "fire" the core
`and coil of FIG. 1. A normal 120 volt, 60 Hz signal excites
`the circuit at 7. A transformer 8 amplifies the voltage up to
`about 1-3 kV. This high voltage AC signal is then fed into
`15 a full wave rectifier bridge 10. The signal from the rectifier
`bridge is then passed through a diode 12 to charge a
`capacitor 14. The purpose of all the electrical components to
`the left or upstream of the capacitor is to simply put charge
`into the capacitor: The energy residing in the circuit which
`20 will be pumped into the stimulator core is one-half C (the
`capacitance value) times the voltage squared When thyrister
`}(j is triggered with a small control voltage pulse, current
`flows through the thyrister and into the core 2. Most of this
`energy goes back into the capacitor 14, recharging it in the
`25 opposite polarity from its initial charge. The reverse charged
`capacitor 14 immediately discharges again through the
`stimulator coil 2 through diode 18, connected in parallel.
`Theoretically, all of this energy should pass into capacitor 14
`to recharge it according to its initial polarity. In practice, of
`course. this LC circuit has some loss, and the thyrister l(j
`does not shutoff immediately. Two to three exponentially
`decaying ring cycles of this L circuit are witnessed in
`practice before current of core 2 is completely shut off. After
`shutoff, the capacitor charges through diode 12 as it did
`initially. It continues to charge until thyrister l(j is triggered
`35 again.
`Different stimulation/rest cycles are employed for differ(cid:173)
`ent tasks. In the treatment of incontinence, one such stimu(cid:173)
`lation cycle might be five seconds on, five seconds off.
`During the five seconds which are characterized as "on",
`40 thyrister l(j would continuously be pulsed 15 times per
`second. These stimulation montages can be altered accord(cid:173)
`ing to the requirements and goal of the stimulation protocol.
`The circuit shown is a preferred embodiment for the
`practice of this invention but other circuit designs (such as
`45 a dual capacitor arrangement or so forth) may be used to fire
`the coil as well, as will be apparent to those skilled in the art.
`Moreover, whereas the magnetic field produced by this
`embodiment pulses at approximately 20-50 kHz, variations
`in that frequency may be practiced as well.
`Shown in FIG. 3 is a dual "C" core type arrangement
`suitable for the treatment of incontinence. The individual
`"C''s comprising this core each span an angle of about 220°.
`The cores 20 are placed end to end in a W type arrangement
`The winding 4 is wrapped around the common center leg of
`the two cores. The cut ends of these cores are designed to be
`55 flush with the lower side of a saddle cushion 21 in which the
`patient sits. The primary flux is driven up the common
`central core into the vaginal cavity. This flux is returned
`through the posterior and anterior arms of the "W'. Because
`the return flux is much lower in magnitude, no stimulation
`occurs except at the vaginal floor near the center leg of the
`HW''t.
`FIG. 4 shows a core stimulator suitable for exciting leg
`and arm muscle groups. In this configuration the cores 22
`would constitute a tubular type shroud into which a leg 24
`or an arm would be inserted. Although the "C" core of FIG.
`1 would be suitable for this task. its geometry is difficult to
`achieve a homogenous and controlled stimulus of this
`
`so
`
`DEfAil..ED DESCRIPTION OF THE
`INVENTION AND THE PREFERRED
`EMBODIMENT
`As shown in FIG. 1. a "C" shaped core is capable of
`stimulating various peripheral nerve groups throughout the
`body. The core 2 is constructed by winding two to four mil
`laminations of a highly saturable material on a mandrel; the
`number of laminations required will be dictated by the
`thickness and depth of the core desired This closed loop
`spool of laminations is removed from the mandrel and
`coated with epoxy to give the unit structural integrity. The
`closed loop is then cut to give the length and angle of the "C'' 60
`shape, as desired. A deep acid etch is then performed on the
`cut edges. The cut edges are soaked in an acid bath which
`causes the epoxy to dissolve resulting in a slight delamina(cid:173)
`tion of the core in the vicinity of the cut. Epoxy is then
`brushed on the etched ends to prevent further delamination. 65
`This procedure is necessary to prevent eddy currents from
`flowing in the core. This would diminish the effective B field
`
`Allergan EX1068
`Page 8
`
`

`

`5,725,471
`
`5
`
`8
`(e) capacitor means connected to said diode;
`(f) a thyristor connected to said capacitor means, said
`thyristor connected to said stimulator coil; and
`(g) a second diode connected to said capacitor means, said
`second diode also being connected to said stimulator
`coil.
`S. A magnetic nerve stimulator as claimed in claim 7,
`wherein said capacitor means comprises a single capacitor.
`9. A magnetic nerve stimulator as claimed in claim 1,
`10 wherein the decay time of said coil is about one hundred
`(100) microseconds.
`10. A magnetic nerve stimulator as claimed in claim l,
`wherein said coil generates a magnetic field at least about
`fifteen ( 15) times per second.
`11. A magnetic nerve stimulator as claimed in claim 1,
`15 wherein said core defines an arc of approximately two
`hundred ten (210) degrees.
`12. A magnetic nerve stimulator as claimed in claim 1,
`wherein said core comprises a ribbon of said saturable
`material coated with a thin insulative coating.
`13. A magnetic nerve stimulator as claimed in claim 12,
`20 wherein said ribbon is further provided with an epoxy
`coating.
`14. A magnetic nerve stimulator as claimed in claim 3,
`wherein the ends of said core are smoothly ground.
`15. A magnetic nerve stimulator as claimed in claim 1,
`25 further comprising at least two approximately C shaped
`cores, said two C-shaped cores being held closely together
`to form a common leg, and wherein said coil is wrapped
`around a portion of said common leg.
`16. A magnetic nerve stimulator as claimed in claim 1,
`wherein two of said cores are provided, said cores being
`
`3° C-shaped, and wherein said magnetic nerve stimulator fur(cid:173)
`
`7
`muscle group. As shown in FIG. S, each section of the
`stimulator 22 is comprised of two half shells 26. Recesses or
`slots 27 are cut into the half shells to allow placement of
`coils which will be wound preferentially within the shells.
`The individual windings of the shell 26 are aligned in such
`a way as to create a magnetic field which is preferentially
`along the axis of the arm or the leg. Adjacent recesses or
`slots of the stimulator 22 will contain different phases. A two
`or three phase arrangement is used to excite a traveling
`magnetic field which moves down and up the axis of the
`arm/leg. This winding arrangement is not unlike that used in
`tubular motors to realize an axial traveling wave. One edge
`of the two common halves constituting the stimulator 22
`must act as a hinge. The winding electrically connecting the
`two halves is simply accomplished by bringing the wire
`down as an extension 28 as suggested in FIG. 6. The extra
`length of winding associated with the extension 28 guaran(cid:173)
`tees the needed flexibility of the stimulator to hinge and
`wrap around the patient's arm or leg.
`FIG. 7 suggests yet another alternative embodiment suit(cid:173)
`able for the stimulation of abdominal muscles. Here the
`stimulator 30 is hinged to a chair into which the patient sits.
`The stimulator then folds around the patient's abdomen
`during treatment The stimulator 30 is again constructed of
`laminated highly permeable, highly saturable material. Mul(cid:173)
`tiple windings are laid in recesses or slots which are cut into
`the core. The windings are designed to drive flux into the
`abdomen and cause a contraction of the abdominal wall
`muscle group. Again the windings can be phased to cause a
`directional massaging of this muscle group.
`Having described this invention with regard to certain
`specific embodiments, it is to be understood that the descrip(cid:173)
`tion is not meant as a limitation since further modifications
`may now suggest themselves to those skilled in the art and
`it is intended to cover such modifications as fall within the
`scope of the appended claims.
`I claim:
`1. A magnetic nerve stimulator comprising:
`(a) an arc shaped core spanning an angle ofless than three
`hundred sixty degrees (360°), said arc shaped core
`comprising vanadium permendur;
`(b) a stimulator coil, said coil at least partially wrapped
`around said core; and
`(c) electric current means connected to said stimulator
`coil to create a current flow in said stimu