CA2097857A1 - Fes method improvements - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

The motor function of a partially or completely paralyzed muscle is restored by implanting a nerve electrode, e.g. a cuff electrode, for sensing electrical signals from a sensory nerve which innervates a part of the body which is phy-siologically related to the partially or completely paralyzed muscle, stimulating the paralyzed muscle by means of a muscle stimulator, sensing by means of said nerve electrode an electrical signal from the sensory nerve, producing a further control signal for reactivating the muscle stimulator dependent on the electrical signal sensed after the expiration of a predetermined period of time after the stimulation of the muscle, and restimulating the paralyzed muscle in response to said further control signal. The electrical signal is amplified, band-pass-filtered, and optionally rectified and bin-integrated when producing said further control signal. The bin-integration is performed by means of an integrator having an adjustable integration period, said integrator being synchronized with the muscle stimulator. A secure grip of an object through FES of a partially or completely paralyzed muscle which is involved in holding the object, is obtained by detecting the start of a slip of the object from the ENG signal from the nerve electrode and immediately upon detection of the start of a slip producing or modifying a control signal for activating a muscle stimulator stimulating the paralyzed muscle. The start of the slip is detected automatically as an event that exceeds a predetermined threshold value in that the ENG
recorded from the sensory nerve is processed using analog or digital circuitry, and a low pass-filtered version of the ENG, delayed by a number of samples, is subtracted from the actual electrical signal sensed, thereby removing unrelated background activity from the signal.

Description

20~78~7 FES METHOD IMPROVBMENTS

The present invention relate~ to FES method im~xovement~. I~
one aspect, the pre~ent invention ~elate~ ~o a no~el Rrinciple ~or r~coxdi~ and using natur~1 sensory nexve a~tivity from pe~ipheral nerve~ ln a system ~or functiona~
electrical stlmula~ion (FE~) wherein the artifac~ ~ignal generated by muscle stimulation i~ minimize~. In another aspect, the invention relates to the utilization of a specific slip-related ~ignal ~or providing a secure grip o~
a~ object throu~h FES os a p~r~ical~y or com~letely paralyzed muscle which i8 involved in holding the object.

GE~ERAL BA~KGRo~D

It i6 po6~ible to 6timulate paxalysed muscles electrically and in this way make paralysed limb~ perform functional lS moveme~ts. T~is tec~nique, called functional electri~al stimulation (FES), has been known for de~ade~ and se~eral research grou~s worldwide are currently in~olved in developing the techniqus. The research i~ dire~ted more and more towardfi the development of implantable sy~tem~ tha~ use alo~ed-loop co~trol, since moat pr~viou~ system~ ~ave su~f~ed from practical and co~metlcal problems becau6e of the external equipment a~d ~he dif~iculk control of stlmulated m~le~. To de~elop ~uch 6ystems, it i~ ne~essary to develop ~nsorg that are ~uitable ~or long-term imp~an~tion. Some necessary fe~ture~ of such ~enso~s a~e biocompatibili~y, reliability, durab~lity and small size.
~ry faw artificial sensor~ have these ~eatures.

For a ha~d-grasp prosthesis or foot-drop pxosthesis, nerve cuf f elec~rode~ might be implanted on lndi~idual nerves in 30 the hand or foot. ~h~3 aign~ expected to tell when a~
object }~as co~ltact with the ski~ (for example in the fins~ers, the nerve ~ig~al response when the object slips, and in the foot a~ impact between the sole a~d the ground surface). The ~i~n~ n thus in a hand-grasp prosthesis be used f or i . e .

2~7~7 updating the stimulation intensity if a ~rasped object ~tarts to 61ip and also to detect the minimum stimulation intensity necessary for holding an object, and in the ~oot the ner~e signal can be u~ed to activate the ankle dorsiflexor muscle at the appropriate time du~ing ~ step-cycle.

Human ~kin, joints and mu~cle~ a~e equipped wi~h numerous se~sors t~at e~able us to sense our ~urrounding~ ~nd the st~te of our body. If this info~m~tio~ can be reliably recorded, it i9 pos~ible to use these _~O~ Lnn~ ~ to provide feedback si~nals to an F~S system. The technic~l problem~ of recording the information have been ~ub~tantlal because of the small size o~ the nerve fibre~ and the low amplitude of the ~i~n~ hat i~ to be recorded compared to the noi~e introduced b~ ~timulation o~ ~u~ ne~r~y.

US Pate~t 4,750,499 by J.A. Ho~fer de~cribed an FES Yystem for p~tially re~toring th~ motor ~un~ion of ~ per~on h~ving p~r~lyzed mucles, said method comprising implantin~ a ~orce sensor ~ompxi~ing a nerve electrode for ~ensing electrical signals pri~ily f~o~ ~ech~noreceptors ~s~ociated with a 2~ ~eripheral sen~ory nerve that supp].ie6 glabrous ~kin of the pex~on ha~ing the paralyzed mu6cle~;, 6ensing electrical sign~ls ~ia ~aid force sen~or, proclucing an alectrical c~n~ol ~ign~l ~or actl~atin~ a mu~cle stimulator i~ response to the electrical ~ignal~ sen6ed by ~aid ~erve el~ctrode, ~nd ~5 6tlmulating the p~r~lyzed ~usc~le~ in ~ccor~n~e with s~id contxol ~i~nal. In a practical implementation of this ~ystem artifact6 ~uch ~ stimulation arti~acts and mus~}e respon~e~
du~ to the ~timulation will, however, be supe~imposed on the electro~euro~ram (ENG) ~ignal. If the nerve cuff electro~e must be located in clo~e pro~imity to ~timulated mu6cle, a~
may often be the c~e, th~ EN~ ~ignal will most l~kely be so disturbed ~hat the proposed sy~tem can not function. ~ ~

In an ~t~empt to xeduce the noi~e introduced by 6timulation ~ :
of muscles nearby, Knaflitz ~nd ~exletti ~ ) have developed ~ de~ice which eature~ the following: a) a ;:: . :
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20g78~37 ~'hybxid" outpu~ stage, op~ical isol~tion of both ~he ~timulation output stage and o~ the inp~t ampllfie~ stage, monophasic or bipha~ timulation output, artif~ot ~uppres~ion obtai~ed by slew rate limiting in the isolated ~tage and signal bl~nking i~ the ~round re~erred stage, and ~i~gle and double differential de~ection o~ the myoelectrlc sig~al.~ Howe~er, this hae not been a useful approach as the ~witche~ in mo~ ~a~es created more noi~e than ~ras removed when applied to the high gain ~10000~) ampl~fiers used in theix ~tudy.

DESt::RIPTION OF ~IE INVEN~IO~

A main aspect of the pre~ent invention relate~ to a method for a~ lea~t partially restoring the motor fun~tion of a partially or completel~ p~ralyz~d mu~cle, said method comprising implanting a nerve electrode for ~e~ing electrical signals from ~ ~en~ory ner~e which innervate~ a part of the body which i6 physiologically rel~ted ~o the partially or completely paralyzed muscle, stimulating ~he paralyzed muscle by means of a mus~le stimulator, ~en~in;T by mean~ of said ~er~e electrode an electrical signal from the sensory nerve, producing a furthe~ control ~ign~l for reac~ivati~ the muscle ~tl~ulator depende~t on the electrical signal sensed after the expiration of a predetermined period of time after the stimula~ion o~ the muscle, and rest~mulating the p~ralyzed muscle in response ~o ~aid furth~r control ~ignal.

An importan~ ~eature of ~he present inve~tion is that dur~ng predetermined period o~ time after the ~timulation o~ the muscle or muscle~, esRentially no electrical ~ignal i8 sensed ~rom the sensory nerve, i.e. the further control signal for reactivatin~ the muscle ~timulator i~ dependent on~y on the electrical signal sensed after the expiration of a pre~
determined period of time ~fter the stim~lation o~ the muscle or ffl~scles~ The objective of thi~ is to a~oid or minimi~e th~
artifact cont~mination ~y the electromyo~ram (EMG) on the EN~

2~978~7 signal. Examples on how this can be aco~pli~hed are described in more detail in the followiny.

T~e invention ~an al~o be de~cribed a~ a FES ~ystem for at least partially restoring the rnotor function of a hum~n 5 having ~t least one partially or ~ompletely paralyze~ muscle, ~aid system compr~sing a stimulator mean~3 ~or stimulating the p~ral~r2;ed m~scle or mu6cles ~ ~n impla:ntable ner~re electrode for s~n~ing elec~rical ~ignals from a sen~ory nerve whi~h innerv~te~ a part o~ the bod~ which i~ phy~iologicRlly 10 ~elated to the partially or c:ompletely paralyzed nuscle or muscle~, and control means re~ponsive to ~he electrical s~gnal~ sens~d ~ro~n said se~sory ner~e a~ter the expiration of a pre-detennined p~riod of time after the ~tir~ulation of 'che mu~cle or mu~cle~ ~or produci~g a ~urthe~ control signal for re-activating said stimulator mean~.

In a presently preferred embodiment, the invention relate~ to a FES ~ystem as described above w~e~ei~ said con~rol m~ans 20 compri~es means for amplifying, band-pasE~-filtering, and optionally reatifying and bln-integrating the sensed electri-cal signal and means for producing said further control ~ig-nal in response to ~aid bin-integrat~d electxical sig~al. As an example, the bin-inte~ration in ~he FBS sys~em according to the inve~tion can be performed ~ mean~ of an integrator having an adjustable integration period, ~aid integrator being synchronized wi~h ~he s~imulator means.

More than on~ par~ially ox completely paraly~ed muscle can be stimulalted by the method ox ~ES ~ystem o~ the invention, In a particular e~bodiment whi~h i6 described in more detail in Example 1, the recordin~ cu~ was placed on the tibial ner~e ~nd the ~o~r plan~Ar~lexor muscles were s~imul~ed in turn by the co~p~ter. T~e present ~n~ention thu~ ~lso provides ~
method ~or at lea~t partially re~tori~ the motor ~unction of :
~evexal paxtially or compleSely p~ralyzed muscles, said method comprising impl~nting a nerve electrode for senslng ~,. . .,: i , 2~7~7 electrical sig~ om a sensory nerve which innervate~ a part of the body which i~ ph~siologic~lly related to the parti~lly or completely par~lyzed mu~les, stimul~ting one of the paralyzed musc~e~ by means o~ a musc~e ~timulator, 5 ~en~ing by means of s~id nerve electrode an electric~l signal from the ~n~oxy nerve, producing a further con~rol ~ign~l ~o~ ~eactivating ~nother muscle ~timulator ~ependent on ~e electrical 6ig~al sensed after ~he expiratlon of a pre-determi~ed period of ~ime ~ft~r the stimulation of ~hè
muscle, and restimulatin~ another paralyzed mu~cle ~n response to said further control ~isnal. In an alternative em~odiment, ~everal partially or completely paralyzed muscles may be stimulated 6imultaneou31~, the further control ~i~nal for reactiva~in~ the muscle gtimulator or mus~le stimulators bein~ depe~dent on the electrical ~ignal sen~ed after the expiration of a predete~mined period of tim~ after the first stim~l~tion of the mu6cle6. In further embodiments, the method may compri~e more than one nerve electrode coupled to one or ~everal mu6cle ~timulator~, i.e. the method may com-prise the ~ombination o~ two or moxe ~S system~ o~ theinvention workin~ to~ether i~dependently or integrated e.g.
by mean of a computer in an appropriate way.

A ~uitable nerve electrode for se~ing electrical signal~
from a se~o~y nerve can be e.g. a cuff electrode implanted 25 around a peripheral se~ory nerve. In such a cuff elect~ode, which may be a split cuff or a 6piral cuff elec:trode, the ~tability of th~ re~orded ~ig~al i.~ s~able enough to be used i~ a FES sys~em. Also othe~ ~uitable nerve electrodes such as intrafa~cicular ox in~neural electrode ~Hoffer and ~aug-land, 1~92) m~ be used in the meth~d or FEs system ~ ~heinvention.

In ~ presently pre~erre~ ~mbodime~t, the method according to :~
t~e in~en~on i~ ~ method wh~rein the electrical si~nal i8 ampli~ied, band-pass-fil~ered, and optionally rectified and bin-int~grated when producing 6aid further control ~i~nal.

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2~g7~7 The bin-inte~r~ n can be performed b~ mean~ o~ an inte-grator having an adjustable integration period, said lnte-grato~ being syn~hroni~ed with the ~uscle ~timul2tor or ~uscle stimulator~. The sensed electrical signal i~ generally S inte~rated i~to a single ~alue to produce the ~urther control slg~al .

Within the ~cope of the prese~t invention are al~o msthods w~erein the EMG artiact i~ minimized by other ~ethod~ such as subtra~ting the EM~ nal recorded ~y other, ne~r~y e~ec-0 trodes ~rom the ENG sign~l prior to the proce~ing b~ themethod of the i~ention. By the use of ~ch fuxther methods for artifact suppre~Rion, the predetermined time period during which essenti~lly no ele~t~ ignal i8 6en~ed ~rom the æen60ry nerve can be mi~i~ized.

~n a presently pre~erred embodime~t, the p~rt of the body innervated by the eensory ner~ compriæe~ a skin area.
However, it i~ contemplated that the method of the i~ve~tlo~
will alæo be u~e~ul when t~e part of the body innervated by the ~en~ory ner~e compri~es ne~ve~ f~om proprioceptors æuch as muæcu~ar spindles, Golgi tendon organ~ or join~ recep~or~.

The m~cle ~timul~tion ~a~ be ~ompli~h~d by any suitable muscle ~timulator. ~or a re~lew, ~ee e . ~ nes a~d Creery, 1~90. ~lso other stimulator~ with appropriate ~eatures can be uæed in the method of the invention. .

6enerally, for hu~an application~ it i8 pre~ently pr~ferred that the ætimulation signals should ~e genera~ed ~ ~
~regue~cy o~ about 5-50 E~z, more preferably about 10-20 Hz.
The ~cle re~timul~tion provided by the further stimulation ~on~ol ~i~nal can be ~axied e.g. by ad~us~ing the amplitude of the stimulation pul~e~. Al~o~ ~he pulse wid~h o~ the ~timul~ion pulse~ c~n be ~aried. Ini ~he presently pre$erred embodiment~, the pul~e width of the ~ti~ulatio~ipulses i3 i~
the magnitude of about 100 - 300 microseconds, su~h as ~50 -~0 micros~conds, e.y. 200 microsecond~. Al~o the fre~ue~cy ,''` ` :` : . ' `: ~ ' ' '`. :
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, 2~9~7 of the ~ti~ul~tion o~ the mu3cle or muscle~ ma~ be varied~
~owe~ex, i~ a simplified embodiment of the method of the in~ention, the frequency of the stimulatiôn of the m~scle or mu~cles is sub~tantially con~tant.

Based upon th~ information in the present ~pecifi~ation a~d claim~ will be within the skill of th~ pe~son skilled in ~he art to determine a suitable prede~ermined period of time after the ~timulation of the mu~cle du~ing whi~h e~entiall~
no electrical ~ign~l should be ~ensed from the sensory nerve.
0 Thl~ pe~iod will of course ~ary depending on the diagnosi~ of the patient, the particular paralyzed m~cle or muscles which are ~timulated, the distance and orientation ~e~ween the nerve electrade and the mu6cle stimulator, ~he ~ype o* the ~timulation el~ctrode~, the maximum current neede~ for stimulation e~c. ~enerally, the period i~ cont~pla~ed to ~e about 3-10 ms or in certain circumstance~ ~ven 1~8 or more after the stimulation of the ~uscle. ~s a starting poin~, it is proposed that the time period i~ set to be about 5-7 ms.

Example 1 describes a cat model ~.o validate reduction of ~0 artifact~ by th~ m~thod of the inv~3ntion, and ~xample ~
de~cribes a ~imple F~S system ~or correction o~ footdrop in a hemiplegic spasti~ male.

The techni~ue used in the present lnvention i~ ~hown ~hema-tically in Figur~ lA. A n~rve electrode ~uch ~ a tripolar cu~f elect~ode, i~ implanted on a ~e~30xy nerve t~at innex-~ates the part of the body of interest, e.g. skin, joint(s) ox mu~cle~) or a combination the~eof. ~ dif~ere~tial amplifier (AMP), with high common-mode reJection and a gain between o.I million and 1 million, a~plifies the ~ignal recorded from the ~en~er and the two connected end-ele~trodea. The amplifier has ~ bandwidth from ~00 Hz to 10 kHz, comparabl~ to the bandwidth of the nerve ~i~nal. Thi~
~ignal i~ then rectified in a ful~-wave act~ve rectifier (R~iI). When nearby mus~les are ~timulated, this signal una~oidab}y cont~i~s large peaks o~ stimulation a~ti~acts ~if ~ . , .

^ 8 2097~7 sur~ace ~timulation is ~sed, t~e ~timulation pul~e~ will t~pically have an amplitude of 100 v, whereas the recorded ne~v~ ~ignal is ln the order of 1 ~V~.

After ampIif~cation of the signal from the nerve cu~f ele~- :
trode, further proces~ing i5 ne~e~sary to remove noise ~nd artifact~, produce a ~ignal t~at ~epresen~s the over~ll acti~ity in the ~er~e, and change that siynal into a cont~ol ~igmal to the ~timulator. An ~xample of a ~ircuit to do thi~
h~ been implemented for a portable ~oot-drop corre~tion system, ~ased on analog components.

The circuit consi6ts of the followin~ parts as shown in the block diagxam (Fi~ure ls):

HP-filter Thi~ high-pass filter is m~inly nece~ary ~ecause of ~ossible offset voltages ~rom the ampli~ier ~ha~ supplies the cir~uit with information from the electrode. However, ~in~e ~ere mi~ht be some ~nintended muscle acti~ity in the recorded ~ignal, the cutof~ ~re~uency has been set high, to approximately 600 Hz.

~0 Active rectifier Af~er the hig~-pass ~ilter, the ~ignal is now without DC
off~et and i~ then full-wave rectified, a~ the first stage of producing an envelope of the nerve ~ al. The recti~ier is acti~e, i.e. it doe~ not lose inform~tio~ beca~se o~ ~ diode-~oltage drop for negati~e ~alues, as would a p~iverecti:Eier.

Bin-inte~.r~tor with timing circuit In ~he pre~ent embodiment the bin-integ~ator is the key part o~ the arSi~act remo~al sche~e. It ~on~ists of an int~grator 30 that can be re~et, as controlled by an external IB2376B~ /AS/lg93o6o4 ::

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2~7~;~7 synchroni~ation signal and the timer circuit ~eing part o~
the integ~at~r. When a muscle i~ electrically stimulated, the stimulator gen~s a sy~chroniza~ion signal to the bin-integrator. Thi~ nal is high for t~pically 100 ~8 duri~y each stimulus. D~rin~ thi6 time, ~he i~p~ to the integrator ia di~conne~ed by U4~ (see Figure lC), re~ulting in the value on the output of the i~tegrator being kept constant.
When the synchronization signal end~, it ~ta~ts a timer (U3A
on the circuit diagram) (Fi~ure lC) tha~ short-circuit~ the capacitor i~ the integrator (C3). The tim~r i8 ad~u~table up to 27 ms. During thi~ p~riod, that i~ adjustable in du~ation b~ P~, the integrator i~ reset, and thus ignores the signal.
The timer is norm~lly adjusted to time ou~ ri~ht a~ter stimu lation arti~cts that contaminate the si~nal have ~ied out.
Then the integrator ~tart8 to integrate during a perlod which the ~ignal contain8 only neu~al i~formation wi~hout artifacts until a new synchronization ~ign~l appears from the ~timula-tor. ~uring the time the integrator outpu~ i8 kept con~tant, the switches U4~ ~nd U4D co~ec~ it to the hold-circuit made up by C4 and U2C, ~hereby ~oring the fin~l value of the inte~ration. The ~equence o~ the~e values is ~s~ally re~exred to as the recti~ied, bin-integrate~l ENG, or jus~ E~G, and i8 a direct mea~ure of the overall activity ~n the nerve.

~ndpa~s filter 25 It is nece~sary to process further the RE~-ENG ~o produce a cc~ntrol signal for the stimulator. In the present em~odiment, the fir~t step is band-pa~ filtering to produce a ~ooth signal that woul~ reflect overall change~ in the nerve activity rather than ~he absolute ~ctivity. ~his is done by ca~cadin~ tw~ pa~Bive first order ~ilte~ - a lQwpass section (R10 ~nd ~7) with ~ ~utof~ f~equency of ~pproxim~tely 20 Hz, and a highpa6s ~ection (~5 and R~0) ~et at approximately 1 H~. An inverting amplifler with gain = lo then ~ollows ~ecause o~ loss o~ signal amplitude in ~he passi~e ~ilte~s.

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lo 2897~7 Acti~e rec~ifier ~sually the astest change~ in nexve ac~i~it~ are increases (as when the heel ~trikes the floor), but sometimes ~
decrease could gi~e ~he most p~ominent peak in ~he highpass fil~ered ox differentiated nerve activity. To increa~e detection reliability, both the positi~e an~ negative peak are used for detection by rectifying the si~nal firet. ~ain, the rectifier i~ a~tive in order no~ to lose infoxma~ion because o~ diode-~oltaye drops.

Comparator After highpas~ filtering and rectification, heel-s~ik~ o~n now be detected by simple thresh~ld detectio~.

Timer In the present example, ~ timer that ~tart~ at heel-~trike and time~ out a~ter a time that corresponds to the duration o~ the stance ph~se h~ been emplo~ed. In this way the inform~tio~ obtained when She heel hits ~he floor has been used. The timer control~ a tranæistor that rwitches the st~mul~tor on and off (whi~h iB a commercially available 20 unit). The stimulator is turned on when the timer ru~s out (estimat~d time of foot lift~ ~nd off when the heel hits the floor Iwhich then initiate~ a new c~cle). The timer i~ :
adjus~able up to 2.7 ~. This system might ~e modified to use the inormation obtained when the heel i8 lifted fxo~ the floor.

T~e analo~ c~rcu~t described abo~e i~ ba~ed on a digital implement~tion, uising al di~ital 6ignal proces60r tDSP) (TMS
320C35) placed on a plug-in ~rd in a I~M-~ompa~i~le peF~-ona compute~ The sircuit wa~ thus implemented as a~ ~nalog 30 circui~ as at tha~ time it di~ not seem practi~ally possible ::~
to make a ~m~ll DSP ~ard ~or a porta~le ~nit. It i~
contempl~ted, however, that in the near ~uture it will be 18~37~iEII.001/AS/1493Q~; 04 ,: ~ : ::: : ` : ~: , . .
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2 ~ 7 pos~ible ~o ad~pt a~ existing portable DSP æ~tem that will be able to perform t~e same function and other functlon~
well.

The circuit presen~ed ~n Fi~ure lC is implemented using ~tan-dard analog componentS. However, the size can be dra~t~cally reduced by using 6urface mou~ted componentS (SMD), as the present inventor~ have done with the amplifiers th~t have been ~onstruc~ed. Furthermore, there seem to ~e no m~jo~
problems in implementin~ a digital version on a custom-desi~ned chip (ASIC) that would include bo~h the ampli~ler~or t~e neural ~i~nal~, the electronics ~escribe~ here for control of a s~imulator, and th~ s~imulator itself. This ha~
been done by others for more 8~ mple stimulators (~ee e.g.
~gnes and Creery), which has made it po~ible to mount all the Compo~e~ts inside a biocompati~le case and im~lant thiS
in the body. ~ .

In ~ummary, ~o remove the ar~i~act~ described above, t~e recti~ied ~ignal i~ thu~ bin-integrated in su~h a w~y th~t : ~:
the noise-free signal in-betwee~ stimuli i8 integrat~d into a ~in~le value by means of a ~witched integrator and sample-and-hold circuit con~rolled by the ~timulation or alte~native an~log or digital methods a~ described above.
Co~a~ina~io~ by s~imulation axti~acts wa~ ~educed by ~ampling the ENG only durin~ periods in-bet~een artifacts.
The resul~lng 3ignal, w~ich correspo~d~ to the smoot~ed en~elope v~ She nerve signal, or in oSher words, the o~erall a~tivity in the ner~e is then processe~ (~OGIC), after which it can be used as a feedback ~iqn~l for the ~timul~tor :
~STIM).

Anoth~r method f~r suppre~sion o~ a stimulation artif~ct could be to blank i~ out by ~i~her di~onneoting or shor~-cir~uiting the recording electrode during and for ~ome time after the sti~ulu~ pxi~ciple thi~ would wo~k if ~oi~ele~s ~witches we~e available. Howe~ex, ln e~perime~ts pe~foxmed by the present inventors with currently a~ailable switches, 1~376~.~SIASI~3~

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lZ 2 ~ 5 7 these proved to be una~ceptable becaus~ o~ ad~itional switching no~e. The metho~ of the invention only ~equires tha~ the ~irst stage of amplification has a short recovery-ti~e a~ter eYe~tual SatUration. It ia con~empl~ted tha~ a recovexy-time in the range o~ 0-~ m~ will ~e pre~erred, ~ut reco~e~y-times up to about 5-7 ms or even more will be acc~pt~ble - depending on the ~equency o~ ~u~cle stimulation.

Due to ~he larger distanceY that can be obtained between stimu~ation electrode~ and a nerve cuff electrode it can be expected that in human FES systems, th~ arti~act problem~ ma~
be smaller than thoYe presented i~ the cat model ~see Example 1~. On the other hand, human muscles can ~e larger than ca~
muscle6, and the numb~r of mu~cle~ ~i~ulated in a F~S system o~ the invention may be much larger than fou~, which may in-crease the number of artifacts. Ho~ever, as long as there i at least 10 ~ between any two ~timuli, it should be posstble to ~ample noise-free ENG. This ca~ be obtained if group~ of ~us~les axe stimulated ~i~ulta~eou~ly rather than ~n a random or time-distributed manner. In hu~n applications, it i~ also likely that the stimulation frequency will be lower than the 25 Hz per muscle uYed fo~ the cat expe~iment~, thereby leaving longer artifact-free periocls between the consee~tive ~timuli.

25 Among several restorative application~ that can be envi~ion- :
ed, ~wo, in par~ r, ~o~ld in prin~iple be implemented readily~ con~rol of ha~d fun~ion i~ ~uadriple~ic or hemi-plegic per~on~, and control o~ stance and g~it in paraplegic or hemiple~i~ pe~on3.

Elec~rical 6timulation of the pe~oneal ner~e, used for cor-reGtion o a drop-~oo~ ha~ ~ecome an ~ bli~hed therapeutic -~
a~d fu~tion~l method. The ~timulation i6 applied during the swing ph~se of the ~ffected leg and prevent~ drop-~oot, so the patient walks faster and more securel~ The use of the ~5 natural tactile inform~tion recorded f~o~ ner~e~ suppl~ing ~ fi~ A~1~3~

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13 2~7~7 the foo~ can make it po~sib~e for ~he pa~ient to walk without wires running from an exte~nal heel cont~ct sen~or to the stimul~tor. using the distin~t peak th~t appear~ i~ the sur ENG ~i~nal at heel - contact and the method of the invention, it h~ ~e~n possible to cont~ol a drop-foot ~timulator dur~g w~lking (see Ex~mple 2). The di~in~ neural peaks are contemplated to relate to p~essure changes on the skin and a~sociated stre~che~ of the ~kin mechanorece~o~ in the ~kin area ~hat ~ innerv~ted by the ~ural ~erve.

10 The hum~n fingertip has ~ great capabi~ity to detect slips between an objeat a~d the surface of the skin. ~urface fea-ture~ protruding a few micrometers from the 3ur~Ace of an object can be di~criminated whe~ ~troked alon~ the surfa~e of the skin a~d small sli~s invol~i~g onl~ ~ p~rt of the ~kin :~
surface in contact with ~n object held in a precision grip can be d~tected ~Johansson and We~tling, 1~87). T~i~
capabili~y ori~inate~ from the large number of low threshold mechanore~eptors in the ~kin of the fingertips (as many a~
241 units/cm2 (Johansson and Vallbo, 1979)). The infGrmation ~rom these receptors is importa~t for the control of preci6ion grip; if the ~kln i~ anae~thetized, the ~b~e~t be~ome~ ina~pable o~ ~dequately adjus~ing the grip ~orce to the weight ~nd surface structure o~ an objec~ (Joh~n~on ~nd Westling, 1984).

During p~ecision ~asks, normal subjects u~ually produ~ g~ip force~ ~re~y greater than the minimum force required to hold a~ objec~ (Johans~on and Westlin~ 87), which is determ~ned by both the weight of the object and the fric~ional prop-er~ies of the sur~ace in cont~ct with the f inger8. If the ~0 grip force is insufficient and thQ object ~tarts to 81ip, mo~t low-~hre~hold merchanorecep~ive ~ni~ re~pond with ~harp bursts of ~cti~it~. Slips may happen if the grip force ch~nge~; a~ ~ oonseqlle~e of ~h~ngin~ joint angles or f~ti~e, if the weigh~ of ~he object increases (e.g. a coffee c~p ~hat gets filled) or if the frictional coefficient decreases (e.g.
caused by per6piration). In normal human subjects it has been 18:Z376i31.0011AS/19~3~

: ' : :: : ~ : .: :
: . , ~.::: :.:: ~ :

- , . , :
,. ' ' 14 ~978~7 shown that a ahort-latency spinal reflex of cutaneou6 oxigin is usually elicited by ~uch a ælip, ~o that withln 80 ms of the ~tart o~ a slip, th~ grip force increases and the objec~
is held set;:urely again (,Johansson and Westl:Lng, 1987). This rapid corr~ctive re~pon~e iS automatic, ~nd doe~ not i~olve conscious particip~tion by th~ 8u~j ect~. The re~lex ~ction i~
quite powerful, to the extent tha~ sub; ects often cann~t voluntarily relea~e their grip slowl~ ~o let an ob~ect fall, be~ause the reflex tends to interfere ~ohans~o~ a~d Westling, 1~87).

The cumulatlve activi~y of cutaneous merchanoreceptor~ can bç
reco~ded with a nerve cuff electrode (reviewed by Hoffer, lggO) and is pre~umed ~o be adeguate ~or feedback control of a sy~tem for ~un~tional electri~al ~timul~tion (~ES). The relation ~etween the electroneurogram (ENG) o~tained from a nerve cuff implanted on a sen~ory ner~e and the ~orce applied perpendicularly on the sk~n innervated by the ner~ wa~
identified, but contained ~ome inherent ~on-li~earities tha~
made it difficult to use the EN~ for estimation o the ~0 perpendicular skin contact force. The sen~i~ivity of t~e cutaneou~ mechanoreceptorQ to ~lip~ occur~i~g betwee~ the skin and an ob~ect ~uggests that the ENG may contain a different, and possibly ~rery u~eful, kind of infor~nation other that ju~t information about per~endi~ula~ co~tact force. The possibility o~ e~tracting 81ip ~elated information from the ENG recorded with a ~erve cu~f electro~e and its pos~ible applica~ion in an FES system for hand grasp is a central feature of the present invention. Wi~h rellable Qllp in~ormation available, an FES 8y~tem impleme~ting ~
r~ iGial gxipping re~lex~ should enable a par~lysed ha~d to hold an obje~t with onl~r the neces~ary force and maintain a good grip ev~n if the muscle~; fatigue, if skin~to-object ~iction ~ ges o~ i~ the weight of ~he obj e~t c:h~n~es . A
di~erent version of a~ H~r~i~icial gripping re~lex" ha3 prevlou~ly been imple~ented ~or the control o~ prosthetic hand6, where the incipient slip o~ an ob; ec~ bei~ held by ~n ',:, - ~' ~ ` i :: :
.. . . .
.~. , , : .
:. :
, ., : : . : .

~7~
amputee in a pro~thetic hand wa~ measured and u6ed to c~ntrol the force o~ prehension (Colman and Salisbur~, 1967).

Ou~ e~perimental m~del of a h~nd ~aspang and lifting an object was the foot of an an~es~hetized cat pressin~ ag~inst 5 an objec~ that would slide down if the force exerted by ~he ~oot was in~u~icien~ to hold the object in place. The fox~e wa~ p~od~ced ~y stimulation of the plantar~lexor muscle~ vi~
intramuscular electrodes, u~ing a c~mputer controlled FES
s~tem. Slip i~formation extracted fxom ~he tibial ENG wa~
u3ed to compensate for slip occurring in two d~ff~ren~
experimental situations: When mu~cle ac~ivatlon declane~ a~d the grip force ~ell below ~he minimu~ level re~uired for a secure grip or when the weight of th~ object increased suddenly while being held with a constant grip force, ~au8ing 15 the obj ect to move .

The findings made in connection wit~ these experimen~s gave rise to another important main aspect o~ the prese~t inventlon. This a~pect of the ~nve~tlon relates to a met~od ~or pro~iding a sec~e ~rip of an objec~ through FES o~ a partially or completely paralyzed muscle which is involved in holdin~ the obj ect, compri~ing implanting a nerve electrode ~or ~e~n~ing electrical signals ~rom a sensory nerve which innerYates a part o~ the bod~
which i~ phy~iologically related to the partially or completely paraly~d m~Rcle, detec~ing the s~art of a slip o~ the obje~t from the ENG
si~nal from the nerve electrode, and immediately upon detection of ~he ~tar~ o~ a slip producing or modifying a control signal for activating a muscle ~timulator and ~timulating the paralyæed mu~cle in respons~ to gai~ control ~ignal.

:

16 ~9~7 ~he ~tart o~ the slip ma~r, e . g ., be caused by an ex~xnal change in the load or wei~ht o~ the object, or ~y an in~ernal d~sturba~ce such as fa~ , or it may be c~used ~y ~ chans~e in the frictional coefficien~ of the ~kin, such a~ due to sweating.

As will ~e expl~ined in greater detail in the following, the start o~ the slip is pre~erably detected ~utomatically a~ an event that exceeds a predetermined threshold value, A
6uitable way of doin~ t~ig is whe~e the ENG recorded from the sensory nerve is processed u~ing analog or digital circuitry, arld a ~ilte~ed version of the ENG is subtr~cted from the actu~l electri~al ~ignal sen6ed, thereby removing unrelated background a~ti~ity ~rom ~he signal, the res~lting ~lcu~ted signal being ident~fied ~s a signal related to the start of a slip if it exceeds a predetermined ~alue. The fi~tered version of the ENG, ~uch as a low pa~s-filtered ~ersio~, is suitably delayed by a number of samples and then subtracted from the act~al ~ignal ~en6ed. The actual signal which may or 20 may not represe~t a "start of sl~p-related signal", ~
suitably ~n unfilte~d ~ignal or ~ ~ignal which has been :
subjected to filtering wlth a shorter time constant than the first-mentioned filtered ver~ion.

Fur~her de~ails concerning thi~ aspect of the invention are given in below:

Sig~als from cutaneou~ mechanorec~ptor~ were recorded with a nerv~ cuff electrode implanted on the tibial nerve of cats.
The~e ~lgnals ~an be rel2ted to the perpe~dicular ski~
co~tact ~orce appl~ed on the central footpad. The sig~al~ can also be recorded during functional electrical stimulation ~ES) and th2ref~re may be u~ed a~ ~eedback ~or an FES s~stem appropriate for restoring motor ~unctions ln patient6 paraly~ed ~y, for example, a ~pinal cord injury or ~troke.

. .. . . . . , . . .. , .. . ~ , .. .. . . . ~ .. . .. .. . . .. . ~. .. ... . .

17 2~97~7 Example ~ describes how slip-related information wa~ derived from the cu~aneous electroneurogram (EN¢). This inormation was used in ~n ~vent-driven contxoller ~or pre~ision grip that allowed the FES system to compensate ~or unexpected 5 61ips between an object and the skin. In thi~ way an "a~ti~i-cial gripping reflex~ was implemented that comp~nsated auto-matlcally for internal change~ tigue) and external pertur-ba~ion~ lincreased load, changing frlctlonal coefficient).
Thls control acheme proved to be ~o~ust, and is presumed to be applicable ~or restoration of precision grip in paraly~ed humanfi using FES.

The info~mation recorded with a nerve cuff elec~rode implan~ed on a cutaneous nexve can be used reliably for ~eedba~ ~o~t~ol i~ a ~ES sy~tem. This appro~ch could havP
dlrect applications for the restora~ion of preci~ion gr~p ln spinal cord inju~ed patient~ (e.g. C4-C6 ~uadriple~ic;, where i~ could ~e u~ed ~o i~plement a~ "artific~al gripping ~eflex' zimilar to the natural ~ripping re~lex that 1~ prese~t 1 normal h~man~.

The ~ em of the invention reliably detected slips from the re~orded ENG, in ~ituations where t~he slips occurred either because of decreasi~g ~rip force or be~au~e in increased load force. The grip wa~ ~ully regained by i~suing a pul~e doublet to each of the four muscle~, combined with a 25-30% increase in ~he duration o~ ~ubsequent pul~es. The reaulting grip ~orce clo~ely re~embled th~t o ~u~ane when ad~usting to a ~udder~ increa~e i~ load force (~oh~nsson and Westling, 198~) by increasing rapidly to a high value and the ~et~lin~ at a value ~omewh~t high than b~fore the load ~hange. ~he time 30 ~etween the obje~t fir~t started to move and ~lip detection was in ~he range o~ 50 to 100 m~. Typically, for ~lip8 cauaed by ou~ "fatigue" p~r~digm, the object moved less than 3 mm before it w~ c~ught, and for ~lips caused by a ~udden increase in load the object moved lesa than 4 mm befoxe it W~S c~ugh~. The method proved ~o be equally robust in ~11 three c~t~ u~ed in thi~ ~tudy.

. _ . . .. . .

.' : .: -., , ' .'' ': ~ . .'. ., :
'` ' ' ' :'. ' ,' .' ', ' ' ' ' : , ` 18 2~7~7 Only one pa~a~eter (the threshold v~lue) i~ the slip det~c-tion algorithm needed initial adjustment at ~ach da~ o~
experiment, although it did ~ot need any ~urther change~ for ~he ~st bf the recording ~e~qion (that usually l~ted 4-6 hour~ he threshold ~a~eter could be increas~d ~y more t~an 50~ of its optimal value wi~hout ~eriously effecti~g the detection of 81ips. Once ~et, the thre~hold value ~eeded no other ~d~ustment durlng the re~t of th~ experimen~ that day.

The increme~t in the ~timulat~on intensi~y after ~lip w~s set to 25-30~ in the pres~nt experiment~, whic~ proved necessary and sufficient to ~ecure the ~rip i~ these specific ~itu-ations. In a clinical FES system, the optimal value of thi~
factor will depend not only on the inst~ntaneou~ recruitment curre for the stimula~ed muscle~s), but also on the rea~ons 15 for ~lips, e.g~ how the weight of the obje~t ha~ changed, how ~ :
strong a per~urbation was, as well as a number of other factors, æuch as the frayility of the object. It is antici-pated that this value ma~ be easil~ ad~ustable by the usex, to ~it the exact condi~lons of his/her muscles, ~emperament, and FES system.

In additio~ to e~abli~g an FES sy~tem to compensate for declining grip for~e or external perturbations, slip informa-tion may also be used for an initial determination of the optimal sti~ulation i~tensity, and thus a~oid causing muscle fatigue ~rom using unnece~sarily strong stimulation. The sti~ulatio~ ~chem~ shown in Fig. ~, i.e., a ~lowly decreasing intensity co~bi~ed with slip detec~ion and compensation, ~toma~ic~lly determine~ ~he minim~m ne~ess~xy intensit~ ~o hold an object and to adjust to Qlowly varying load change6, ~0 or i~ may just be used initially to de~ermine a suitable in~en~ity that i~ ~hen held constant unl~s and unti~ other ~ occur.

In the intact human, infoxmatio~ from ski~ re~eptors is es~ential for the regula~ion of force duri~g p~e~isio~ grip.
Visual cues s~ch as ~ize, material a~d surface structure play : . . . ' ' " ' ' ' . . . ;, ., ' ,, ' ' `: ~ , '' ' . " ~ ~'' ` ` , ~ , ' , ' ' ~ 19 2~7~
a role in deciding the ini~ial f~rce~ when gripping and lifting an object, but for the s~eady-state holding pha~e, the ~oma~o~e~ory i~o~matio~ ~rom the skin effectively defines the necessary force wi~h no app~rent relation to pre-lift visual cues. The ra~ult~ repo~ted hexe suggest that an FES system for precision grip in paralysed human~ could u6e the same cutaneous afferent in~ormation a~ the intact organism ~nd implement a slmilar ~ontrol strategy, thereby adj4sting the ~rip for~e automatically to the weight and surface ~tru~ture of ~he objeGt in hand in the form of an "ar~ificial gripping ref l~x " .

In paraly~ed humans, tactile information ari~ing from the th~mb, index and~or middle fingers could be recorded with nerve cuff electrodes, either from the palmar ~taneous branch of t~e med~an nerve p~o~imal to the wri~t, or from individual internal digital nerve branches in the hand.
Experimen~s with a nerve cu~f implanted on the median ner~e of a monkey (Milner et al., 1~1) have produced ~G -~ignal~
d~ring perturbation~ of p~ecision grip that closely re~bmble ~0 those repre~ented in the cat experiment~ by the pre~ent inventor6 sug~esting that the median nerve may be a ~uitable ~ource of the de~ired signal.

~or the restoration of gait and ~tance 1n per~o~ i~paired by paraplegia or ~troke, cutaneou~ feedback information 2~ originating from mechanoreceptor~ in th2 601e~ of the fe~t could be recorded with nerve cuff electrodes implanted on the internal and external plantar branche~ of the po~te~ior ti~ial nerve, and the ~ural ~e~ve. The ~ibial nerve branches contain afferent~ ~xom the medial and lateral aspects of the 30 ball of the foot, ~nd the su~l nerve contain3 affexent~ fro~
the ~eel. To avoid me~hanical damage to the ner~es or cuff electrodes, the ele~trodes wo~ld ~e~t he installed proximal to the ankle, rather than in the foot.

I~ st~oke patients who ma~ require o~ly electricsl ~timula-kion o~ ~he pe~oneal nerve to control ankle dorsiflexion 209~ 7 during t~e ~wing phas~, a ~i~gle ~ural or tibial nerve cuff w~uld ba ~uf~icient to monitor whether or not the ~ected ~oot i5 ~upporting wel~ht. Recording~ frvm the sural nerve in man (Slnk~2r et al., 1991) hae demon trated a di~tlnct peak in ~he nerve ~ignal at ~oot contact. In paxtially or oo~pl~t~
par~lçgi~ ~atients, wher~ the coordlnated activation o~ both legs must be re6tored, three cuf~ recording electrodes in each leg would provide in~orm~tion on mediolateral and anteropo~ter~or welgh~ di~tri~ution on each leg, as well a~
on timing of foot contact and inter-limb load dl~txibution, con~idered e~ential for ~u~cessful restora~lon o~ g~it with ~ES. although ~u~h lnformation ~an be obtained with external preQsure sensor~ placed inside shoes, inherent problem~ of calibration, ~echanical and electrical dri~t, lead breakage, and ~en~itivity to en~ironmental factors like moiature and temperature, th~t afect external tr~n~ducers, would be avoided i~ nerve c~$f electr4des were used. Becau~e sati~-~actory re~toration of gait often cannot b~ achieved u~ing F~S alone, individual ~ol~t~on~ ~re likely to involve F~S-ba~ed hybrid sy6tem~ tailored to the epecific pattern of~e~60rimotor def~c~t pre~ented by each patient.

For hand control application~, the tactile feedback recorded ~rom the median nerve or from ~ts ~ranche8 would regulate the ~utput of a portable mulsi~hannel FES ~ystem to control ~e~eral type~ o~ grip by stimulating for~arm and hand muscles via, e.~., permanently lmplanted ep~my~ial electrode~. To a~old ri3ks associated wi~h tran~out~neou~ pa~sage of lead~, it would be pref~rabl~ that both the nerve ~ecoxding and the musclQ etimulation information would be telemetered acros~
the ~kin. The command ~ignal~ for the FES ~y~tem would be generated by the user, u~ing unaffected motor functionc. In initial application~, regu~atory feedback would be lmplemen~ed to uae slip ln o~mation to automatlcally update the ~timulation parameter~. To also implement continuou~
~5 regulatory feedback, app~opriate algorithm~ would have to be avallable to extract momen~-to-moment informa~ion on grip force or other xele~ant p~rameter, fro~ the ~NG ~ignal.

1~2376BI.~OIIAS119~306 0~

~` 21 2097~7 The principle of the present lnvention may also be useful in other ~pplications where physiologic~l sig~ls must ~e sampled during stimulation o~ nearb~ muscles, e.~. in FES
systems USiXl~ the EMG from int~ct or partially int~ct muscle~
or ENG from e~i~ere~t nerves a~ a means to ~o~trol the stimu-~ator or prothesis.

It i~ evident that ~he two abo~e main aspec~s o~i the i~vention can be used independently or combined in o~der to impro~e FES methods.

': ' ` ': '~ ':, :', : .: ` , ' ' , . : ~: , 2~ 2~97~7 LEGEND ~O F~GURES:

Figure 1.

A) Principle for recordin~ a~d using natural sensory nerve acti~ity from peripheral nerves in a sy~tem for functional neuromu~cular stimulation. Figure shows as an example a ~ystem for restor~tion of upper limb fu~ction, but the principle would be similar for lowe~ limb.
1. Telemetxic coupling between i~pl~nted and ex~ernal equipment 10 ~. Implanted stimulator 3. Shoulder position ~enso~

4. Stimulation ele~txode~

5. External portable control units and batterie~
AMP: Amplifier for the ne~ral ~i~nal 15 ~BI; ~e~tifier ~ bin-integrator (see Figure lB) ~OGIC: Extr~ction of information and generation of control signal STIM: S~i~ula~or ~) Block dia~x~m o~ the artifact ~uppression technique and met~od to co~t~ol a foo~drop stimu]Lator. The fir~t par~, tha~
corresponds to the RBI unit in ~i~ure lA, i~ where ~he axtifact~ in the neural signal are ~uppressed. It consists of the highpass fil~er, rectifier ~nd bin-integrator ~see text for de~ail6). The second par~ peci~ic to the ~oot-dro~
prosthe~is application, and gene~ates a control signal for the stimula~or based on the artifa~t free ne~ve ~ign~l. Thi6 ~-- part corrsponds to the LOGI~ uni~ in Figure lA, ~nd con~ist~
o~ the band-pass ilter, rectifier, comparator and timer ~see text for det~il~).

C) ~xample of how the ~y~tem in Fig~re lB can be implemanted using standard analog elec~ronics. The p~rt~ separated ~y d~shed lines corr~pond to the blocks in Figure lB. The : ~ . :, ;;, . .
. .

23 2~97~
circuit here has bee~ used in a port~ble ~tem ~or footdrop correction. See text for detailed description of the circuit.

Figure Z.

R~w ~i~nal recorded ~xom the ~ibial nerve cuff while nearby ~uscle~ were ti~ulat~d. Four sweeps o~ data are shown ~uperimposed. ~n the top trace, the b~ndwid~h was 65 Hz - 10 kHz, and the EM~ ~olleys were clearly present, wh~re~s in the bot~om ~race, the signal was high-pass filtered at lOOo Ez and the EMG pickup was pra~ti~lly removed. ~orizontal bar~
lo show the period~ duxi~g which the ner~e cuff signal w~s bin-integrated ~d ~mpled by the computer.
AS - amplifier saturation TO = Temporary tape o~erload due to saturation Figure 3.

Veri~icatio~ of the a~ti~act removal method, The solid ~xa~es ~how ~he force (top3 and normal rectified, bin-integrat~d E~G
(bottom) during st~mulation of the four cal~ muscles in a cat model under anaestesia. ~h~ da6hed traces ~how a similar trial, with the tibial nerv~ blocked distal to the recordin~
cuff.

Figure 4.

~e~tified ~nd bin-inte~ted (RBI) hum~n ~ural ner~e cuf~
reco~ding~ while tapping with a finger on the ~kin within the innervation area o~ the nerve. In the ~op trace, ~o elec- :
trical sti~lation is applied and the ner~e signal is no~
dis~urbed ~y artifactL~ ~hs middl~ trac~ shows the dist~r~ed ~ .
nerved signal when a 100 Hz stimulation is applied ne~t to the nerve without ar~ifact suppre~sion. The bottom ~ra~e shows ~he ~erve sig~l du~i~g e~e ~ame 100 Hz, but wlth artifact suppression.

... .. .

' ' ' .~ , ' , . . ' .' ' ' ' ' ~ ' ' " ~ ~ " '. ' . ' ' I ~

~ '. ', . ~, , . ~ , , 24 ~ 7 8 5 7 Figure 5.

Diagxam of elect~odes implanted in cat hindli~b and apparatu~
u~ed to measure ~eural respon~e~ during grip. The cat was under anesthesi~. The limb was fixed at the ankle malleoli and knee with atx~a~ic, cupped clamps. Forcas ~ere produced by F~S via electrodes implanted in the ~our ankl~ dorsiflexor ~u~cles (MG, LG, Sol and Pl; not ~ re shown). ENG acti~ity in the tibi~l ner~e was recorded wi~h a tripolar nerve cuff electrode. ~hen the plantarflexor muscles were stimulated the paw moved (curved arrow until the footp~d pressed against an object ~hat could slide vertically along a low~riction hearing. It wa~ covered with fine sandpaper o~ t~e s~rfa~e contacted by t~e ca~'s footpad, and contained two ~orce transducers to measuxe vertical (load) force a~d horizontol (g~ip) f~rce, as well a~ a linear po~ition transducer to measure vextical position.

`` 2s 2097~7 RE FEREN~ES

P.grles, W. F., MacCreery, r). E~., editor~, "Neural Prosthesis~
ln: dFundamerltal Studies~, Printice Hall, New ~er~ , USA, l9gO .
CoL~a~. ~.B., I,l. Salisbur5r, A~ ol. Eng. S, pp~ SOS-~ll, 19~7.

tior~o~, A.~, }1, F~rssb~rg, R.S. Johansson, ~:;. ~cs~ Ylsul~ d~ cues ~ ~e progr~nF, of ~an~p~lla~e fo~ces du~g prec~s~on ~p," ~p. Br~;n Rcs., 83, ~p. 477-482~ 1~91.
Haugl~nd, l~X., ~A. Hoffer, T. Sin~ "Ski~ contactforce i~f~a~o~ i~ elec~D~ ~aphic sigr ~s ~:co~d by imp~ted ~lerve ~uff clec~dcs," JEEE rransaclzoAs on Biom~. En~., (sub~tted concu~ iiy).

Ra~glantl~ ~, J~. Hoffer, ~'Senso~y aervc s~nals ~ecorW by ~lg~nud cuff c~cctrodc~
duAslgfi~on~l e~ ic~l s~a~on of ~imb D:uscks,"lEEE ~oc~o ls on~iorr~d. ~ng., tsu~il~;a COD~n~ty), ~cr; JA., "TcchDiqucs to ~udy spinql-co~, p~ripheral n~. ~nd mu~cle activitS~ iA f~ely m3~ ~a~s," NcuromcJfsod~, Yol. 15. pp. 6~ 1990.

J.A., ~u~land ~ ~nd Li, T~ Obta3~:ng skin ~ontact fos~e info~o~ ~m irt~plantcd n~e cuff~ecording el~e~od~s, Pro~. IF~E L-ng. fn M~d, d~Biol. 30c, Inr~. ~or~ 928-g~g, ~8~.

~o~e~, J~., Hau~ltnd~ ~ and Sin~, T. Fun~o~al resrora~on of ~ecision ~ip usl~ slip ~forma~n ob~ed f~ pesiphe~l ne~ve~eco~n~s. ~roc. Ann. ~ tl. Co~. IE~E Eng. in ~fcd ~ Biot. Soc. 13:~96-~g7, lg91.

Hoffer, ~A. and~laugland, M. Si~ls f~o~ tact;lg sens~rs in ~3abrous s}~n sl~itable for resPring :
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Hof~cr, J.A., N. Sugano, (~.E. I,Deb, W.B. M~ks, hq.;l. O'I~ono~an, C.A. Pratt, "C~t ~indlimb a~o20neumns dus;n~ 10con~ation. II. ~om~ tivîty pattent8t~ 30~ , of ~e~uop~ys. ~al, S7, ~o. 2, 3~p. 53~-553, ~eb. 1987.
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.: ~ : : . . : . ~ : : . , : . . . : .

:.: . . . :: : . , ,: ::
i . .: - ~: ~ I :: . . .

26 2~g78~7 Joh~ssDa, ~s., A~. 'It~o, "T~ sensibiliy i ~c human band: ~el~e a~d absol~
der~si~ies o~ pes ~f me~hano~ecep~e ur~iTs in gl~brous skin~"J. P~ ol. (Lond~ 2815, pp. ~83-300, l9~g.

nsson, RS., G. Wes~ng, "~ s of ~labrous s~n ~eprors ~nd sensorlmolor ma~y in au~oma~c c0~ f pr~isio~ ~p ~heJ~ ng rouE h~ ar n~ore slippay obje~ tas~
Res.~ 36, PF~ ~S0-5~4, lg84.

3Oha~s50n, ~.S., ~. ~es~ing, "Siga~ls in ~d~e ~ffere~ e fingers eliciPng ~p~l~e rno~
~sponses d~g pre~ grip," E;~p. Bra~ ~es, 6~. pp. 141~154, 1~87.
Joh~sso~. RS.. C;. Wes~ing, "Pn~gramm~d ~sd ~ggered ~e~n~ id loa~ ~ge8 d~ g prcc~sic n ~ip," E~p. Br~in R~s., 71, pp. 7~-86, 1988.

l~ilncr, T~., C~ Dug~s, N. Pic8$d, A. SInltb "~usaneous ~ nt acti~ n the meti~n ~e . . .
dun~g ~aspnng in thcpr~a~c,~aln~cs., 548, pp. æ8 ~41, l~gl.

Si~ ugl~d, M., Haase, J. and ~of~e~, J.A. Whole senso~ ve re~s 1~ hu~
-~n app~icadon f~rne~al p~s~eses. P~oc. Ann. ~ntl. Co~ E; Eng. in ~ed. ~ Bisl. Soc.
900~ 91.
~P1lbO~ A.B., R~. Joha~s~on, '~p~es of sutancous ~cc~anor~ep~r~ he hu~Dan hand rcla~ oucb sensa~on," H~n Ncuro~o~. 3~ 14, S~ger Verlag, l9~A

Wcs~ling, ~ RS. ~oh~sson, "Rcsponses in glabsous sldn mechanorec~s d~ p~slon ~p fn h~mans," E~p. br~in re~carch, N~. 66, pp. 128-140, 1987.
Zaj~c, E:~.. ~L. ~oung, '~schar~o prop~cs of hindlisllb moto~curons L~ d~brate ca~ during ~ ~ :
~ocomo~o~ ~nduced by mese~ceph2~ic s~mu~a~on", Jour~ of ~europhysiology, vol. 43, pp.
1221-1~35, May 1980~.
. . .

~, : , : ,~

;,: . . , : : . :

--` 2~8~

EXAMPLl~S

MINIMIZING ~ G~AR'rIFAt:~T SIGNAI GENERATEr) BY MUSC~E
~:TIMU~TION I~ A CAT E~CPERI?~ilT

5 ~_ In ~at~ which were surgic~lly ane~thetized, a 30-40 mm long, 2.2 mm I.~. silicone rubber cu~$ with 3 circumfer&ntial ~tainle~ steel wire electrodes (Cooner A~ 631) wa~ impla~ted on t~e le~t ~ibial ne~v~, 2-4 cm proximal to the ankle joint.
A scia~ic ner~e recording cuff, 20 mm long, 4 mm I.D. with three stainless steel wire electrodes, was implanted in the mid-thigh region. Leads from the cuffs and other lmplanted device~ coursed 0ubcu~aneou~1y to a~ external connector mounted on the cat'~ back a~ described in ~offer, 1~0. A~ter :L5 6urgery, catq were ~ive~ analgesics (Acepromazine Male~te ~nd subcut~neous Morphine, 0.10 mg/kg) for at least ~4 hr.
Recording sessions ~tarted 4-7 day~ after implantation.

Nerve blocking cuffs:

To exclude the participation of motor activity in the ENG
~0 recorded from the tibial nerve during walkin~, in several cats a blocking cuff 8 mm long, was placed on the tlbi~
nerve, b~tween the ti~ial and sciatic recording ~u~s. ~xonal condu~tion w~ blocke~d by infusing lidocairle sodium solution (~), via a catheter that 1~3d to the bloclcing cu:E:E from a :
25 ~ort in the external connector. The conduction block was :
asse~sed from the pr~gre~si~e reduction of the compound action ~otential xecorded by the s~iatic ner~e cu~f, e~oked by stimulation o~ the tibial ner~e at the distal r~cording cu~. Usually, the tibial nerve was completely blocked after 30 20-30 mix~ute~. ~t ~che end o e~L~h expe~im~nt the block wa6 rever~ed wi~ usion of norma~ ~aline solution. . .

'. , . , ' : ': '. '.':'~ ~ ' "' i '. ' ~ " ' ::

2~ 2~97~7 ~n o~hex cat3, a tibial nerve blocking cuff wa~ placed dis~al to the tibial nerve re~ording ~uff in order to identify the contributions fro~ footpad ~erents, and the pre~ence in the recording cuff ~i~nal o~ any artifacts cau~ed by the ~timuli s a~d/o~ compound EMG potent~al~ d~ri~g FES of nearby mu~sley.

ata ~ollection:

~ average once per week during a 1-3 mo~ths period, each cat w~s anaesthetized with halothane g~s, the left ~oot wa~
shaved, remaining hair was removed with depilatoxy cream, ~nd ~he leg was s~cured at the ~nkle malleoli ~nd knee with two pair~ of cup~ed holders. In the first series o~ experime~t~, a servo-controlled motor wa~ u~ed ~o pu~h perpendicularly on the ~entral footpad with ~ 1 cm di~c~6haped probe, ~pplied fo~ces were monitored by a ~ries tran~du~ex, The ~osition and compli~n~e of the motor were electronically re~ulated with posi~ion, veloci~y and ~or~e f~edback. Control 8igna were generated with ~n IBM-compatihle l386 computer. ~e tibial E~G wa8 analog-rectified ancl bin-~ntegrated i~ 1-lo ms bi~ ak PSI-l). ENG, m~tor position ~nd forc~ d~ta were ~:
digitized on-line (100 Hz/channel) with the same computer.

Removal o~ arti~c~
Two ~teps are used to reduçe the ~mplitude of arti~act~ from near~ mus~le activity (EMG) in the nerve ~ctivity ~ENG
si~nal): 1) High-p~g~ filtering and 2) ~ynchronization of 6ampling and stimula~ion.

) The freq~ency di~t~ibution~ of ENG and EM~ re~orded by tripolar nerve cuf~ electrodes are largely ~on-over-lapping. Most o~ the E~G could th~r&~ore ~e ~extracted~
from the cuff signal by filtering the ~ignal w~th a ~harp hiyh-pa66 analog filter at 1~00 ~z (Ithaco model 4302, set at 80 ds/decad2).

~) Bec~use the times of 6timulation were k~ow~ a~d both the ~timulatlon artlfa~t a~d the EMG CAPs were limited in 8~376~ 1~306 P4 - 29 2~978~7 ~ime, it was pc~6~ible to reduce th~ arti~ac~ pickup ~ub-stantially ~ only u~lng the cuff ~i~nal at the end of the inter-pul~e int~rval, i.e. the sa~pling wa5 locked to the ~timula~lon, resulting in a ~ampling frequency of loo Hz.

Figure 2 ~hows 4 superimposed recording~ o~ the cuff signal durlng FES. Each record wa~ 40 m~ long and thus included 4 ~timuli. The four tra~es were ~yn~hronized to the time ~f stimulation of the soleus muscle. Each tim~ a muscle was stimul~ted ~abelled 'Stiml), the fi~t event in the ~uff signal w~ the ~timulation axtifact, ~howing up ~ a narrow spike that would vary in ampl$tude depending on the ~timulation inten~ity and the ~uscle that wa~ ~timulated.
This was followed by the compound EMG volley fxom the ~timulated mu~cle, ~howing up a3 a ~lower, large ~mplitud0 wave in the cuff ~ignal (la~elled EIN). T~e shape of this ~MG
bur~t depended on the stimulus in~ensity and ~he mu~cle being ~timula~ed, but ~ otherwise very repeatable, The neural ~ignal itself wa~ the hi~er-frequency signal, 5 ~V in amplitude, onto which the artif~ct~ wer~ ~dded.

Th~ data in Fi~ure ~ were obtai~ed by record$ng the cu~
signal on an FM ~ape re~order while~ the co~pute~ c~ntrolled the stimulation intensity using external foxce feed~ack, as de~cribed above. The signal was then replayed and ~ample~ at a high rate t20 kHz) to produc~ the. ~igure. For large po~itive arti~act amplitude~, the amplifter satuxated (marked AS) and for la~e ~egative amplltudes, the t~pe record~r overloaded (marked TO) ca~ g th~ nal to be zero during the overload.
The effecti~ of filteri~g ~an be seen by comparing tihe top a~d bottom tra~es in Figure 2. In the top panel, filtered b~tween ~5 ~z and ~O k~z, the pickup of the EMG volley ~howed up very clearly. In the hottom panel, the same ~ignal wa~ ur~her high-pa~ filtered at 1 kHz, and the EM~ çontamination wa~
3S laryely removed.

I~37~x.~ ~306~

2~78~7 The ~timul~tion artifacts were bla~ed out by sampling the BNG ~nl~ durin~ period~ _ -between artifact~. Periods of artifacts are normally e~ily located by visuel inspection of he ~NG-signal since remain~ o~ stimulus-related EMG, direct stimula~io~ ar~i~act~ and amplifi~r r~covery are ~ynchronized ~o the stimul~tion, which i8 no~ ~e case for the ENG. ~he bin was defined so that none o~ the~e ~rti~act~ we~e apparent within the window. Instead, we used a re~ti~ier/integra~or (B~k RBI-l) that had an adjustable inte~r~tion period a~d was reset in synchrony wi~h an external clock. Thi~ clock was supplied by the ~tlmulator, and it was thus pos~ible to integrate the E~G signal in bin~ that las~ed 3-4 ~ and that included only data from the la~t pa~ of each inter-stimulus interval (~o~izontal bars in Figure 2~. The ENG in eac~ o~
15 the~e periods was ~ectified an~ in~egrated, resulting in a sin~le value ~or each bin that was sampled just before a new stimulation pulse was elicited.

The ~alidlty of thi~ method of noise or artifa~ suppre~sion WAS demonstrated by the ~ollowing ~xperiment. ~he muscle~
20 were first stimulated to generate a force profile show~ by the ~olid trace in Fig~re 3, top panel. Thi6 gavç rise to the ~NG signal shown by the ~olid trac~3 in Pigure 3, bo~tom panel. Wi~hout changing the setup, conduction in the ne~ve was th~n blocked with infusion of 0.4 ml lidocaine to the blocking cuff. A~ter approximately half an hour, the ENG
~ignal recorded from ~he tibi~l nerve was insensitive to touching a~d squeezing o the ~oot, demonstrati~g that afferent conduction wa~ completely blo~ked. The -~timulation was then repeated and a similar force profile was generated, (shown by the dashed line in Figure 3, top pan~l). The sampled cuf f ~ignal was ~ow redu~ed to the ~lat dashed line in ~igure 3, bottom p~nel, i.e. containing ~either E~G, nor s~imulation artifacts or EMG. Since ~he only difference w~s the blocking o~ the ~ex~e distal to the reco~ding cu~f, thi~
experiment showed that for the unblocked ner~e, the sampling method removed all introduGed artifacts and only ~ampled ENG
~c~i~it~.

IU376EX.0011AS1199306 04 31 2~78~7 EXAMPLE ~

FOOTDROP PROSTHESI~ ~N A H~MIP~E~IC SPASTIC MALE

For the footdrop prosthe~i~, the neural ~ignal from the sural nerve can be u~ed ~or detection of foot-contact.
S Hi~hpa~s-filtering at 1 Hz followed by rectiEicat~on and threshold ~omparison reliably detects when ~he hebl touche~
the floor during walking. Thi~ h~s been u~ed ~o ~witch on and off a commercially available peroneal stimulato~ lKDC 200~A) a~d in ~his way, replaci~g the usual heel-switch ~at mu~t be mounted in the shoe with the ~atural sensors in the 6kin of the ~oot.

In the present example, the sural nerve in a 35 year old hemiple~ic ~pastic male subject with a drop foo~ was instrumentecl with a ~ripolar whole nerve cuff electrode 15 approximately 7 cm proximal and 3 cm pos~erior of the ~atsral malleolus of the right ank~e joint. A cli~ical examination had xevealed tha~ the ~atient had an Achille~ tendon con-tracture and tremor ~round the ankle j oint. ~he subject gave his con~ent and the ~tudy wan approved by the Local Ethioal Committee.

Surgical procedure The surgery was performe~ during lo~al ~naesthesia. To pre~ent compres~ion-neuropathy a~oci~t~d wlth post-surg~cal oedema, it was ensured that the inner dlameter o~ the cuff ~.
wa~ more tha~ 3~ la~ger ~han the ner~e diame~ex. The th~ee Teflon-coated multi~t~nd ~tainless steel l~ad out wixes ~ooner Wire Company, ~5A) from the ~uff elec~rode we~e put through ~he skin approxir~a~ely 25 ~m abo~re ~he la~eral malleolu~3, The rlerve cu~ was placed so that the nerre was 30 neither pulled xlor tor~ed by 'che wires. Thls make~ the long-tenn prognosis of a nerve prepa~a'cion excellent.

ls237~;~lAsll~3o6 o~

32 2~7~S7 Nerve cuff electrode confiquration The nerve cuff recording ~lectrode consisted o~ an insulating cuff (silioone tubing) cont~ining thr~e circumferential metal electrodey (~lexible 40-str~nd stainle~s ~teel wir~, ~e~lon-co~ted~, placed around pa~t of the sural nerve. The de~ign,fabxica~ion and surgical implan~atlon of nerve cuff r~cording electrodes have been reviewed in detail elsewhere (~o~er, lg90). The in~ulating cuff ~erve6 to re~ol~e the sm~ll act1on currents gener~ted by nerve fibres, by constraining the current ~low within a long, narrow resi~ti~e path. In this applic~tion, the ~uff wa~ 3 cm lon~ ~nd had an inner di~met~r of 2.5 mm.

eural ~e~ g~Sion_and s~imulation The leads ~rom the implanted nerve cuff electrode ~ere con-nected to a dif~erential ENG ampli~ier with a high common mode rejection. The ~r~n~cutaneous ~timulat~on was m~de by means of a reference electrode abo~e the tibiali~ a~terior muscle and an ac~lve ele~trode above ~he common perone~l nerve just distal to th~ br~nching off of the ~uperficial ~O peroneal nerve.

The neural amplifierrwas ba~ery-~upplied a~d optlcally isolated ~rom the mai~s ~o increase the common mode rejection and to reduce the risk to the gubj~ct. To further reduce noise pick-ups, an external ref~rence electrode wa~ placed b~twee~ the stimulation elec~ode~ And the nerve ~uff electxode. T~e ~eural signa~ wa~ fourth-order b~nd pass filtered from 0.7 to 10 kH~ (Kron-Hite, model 3750). This would red~ce remai~i~g pick-up of 50 Hz from the m~ins, if any, and the EMG from ~eigh~ouring mus~les to a negligible level. ~he bandwidth of th~ record~d neural ~ignal ran~ed ~ro~ 0.2 to 3.0 kHz.

1~376EX.WI/AS/1~306 W

`~ 33 2~97~7 and wlthou~ removal o~ arti~act~ ~xom_ ~he nerve ~iqnal The ~ural nerve activit~ in a human Eubject was r~cord~d while tapping with a ~inger on the skin w$thi~ the inner vation ~rea o~ ~he nexve. Fig. 4 (top) ~hows the ampli~ed, recti~ied and integ~ted (RBI) nerve si~nal without an el~ctrical Qtimulation. A ~lear peak in the ~erve signal was observed when the finger touched the skin. Fig. 4 (middle) show~ the RBI sural nerve activity when an electric~l ~timu-lation every lO ms (100 Hz) was applied ~ex~ to the nerve.
The electrical 6timulation eli~ited an a~tion pote~ial in .
the nerve r~cordings approximately 2 m~ after the st~mulation ~i~h a duratio~ of approximately 2 ms (not ~hown). Fig. 4 ~middle) shows how thi~ unwa~ted ~ignal incr~ased the xecorded activity making it ~ery difficult to detect thenerve re~pon~es caused by the finger-tapping. Applying the ~rtif~ct suppression techni~ue by samplin~ the nerve signal in a window from 5 to 1~ ms after each stimulation, the art~-facts ~ere removed and the ~erve ~esponses to the finger-tapping were again reco~nized in the cuff electrode recor-dings tfig. 4 (bottom)). The ~ecti~ied and integrated nerve signal in each of the sampled periods after a stimulatio~
re~ulted in ~ single ~alue ~or each bin that was ~ampled ~us~
be~ore a new stimulation pul~e was elicited. The artifact ::
~5 suppression is made exactly as desGribed for the cat data in Exampl~

Slip-detection and ~ompensation in a eat model of human position grip The hindlimb of anaestheti~ed cat~ was used as an experime~t~l ~odel for the paralysed human limb, with the central footpad as a mod~1 gla~rou~ skin. Three cat6 (4-~ kg) were chroni~lly implan~ed using asep~ic technig~es, ~ :
l R~37~ A~ g93 o6 o~l ~

' j : ' ' ' ' .................................... : ' ' ' " . '~ ' ", ~ . , , ~ , , ' :

, ~4 2~7~7 ~ollowing the procedure~ and guidelines described in ~xample 1.

Bipolar intramus~ular stimulation elec~rodes were im~lanted in each o~ ~our ankle extensor muscles: Medi~l a~d lateral ga~trocnemius (~G, LG), ~oleu6 (Sol~ an~ plant~ris (Pl). The electrodes ~onsisted of two Teflon coated, 40-~tr~nd ~tain-les~ ~teel wire~ (Cooner 634), with the e~d~ dein~ulated for 15 mm, and ~ere in~ert~d in the muscle diagon~lly to the fibres, about 2 cm ~part in the proximal part of the muscle (see Fig. 5). Bipolar ~timulati~n electrodes were used, rather than monopolar with respect to a common ~ro~nd, because of the higher 6electivity attained~

A tripolar nerve recording cu~ ~30 mm long, 2.2 mm I.D.) was implanted on the tibial nerve, distal to the mu~cular branches; and 4-5 ~m above the ankle. A~ this level, the tibial nerve contains mainly Affere~t fibre~, mo~tly from the plantar Yur~açe of the foot and the ~ootpads, and the cuff could ~e implan~ed without obstxuc~ing the blood ~upply to ~he nerve or causing mechanical damage to t~e nerve.

The cats recovered for at least 3 days ater ~urgery ~efore the first experiment was performed, in order for the implanted devlce~ to sta~ilize wlthin the l~g. At the begi~ning of each recording session, ~he cat was a~ae~thetized with an intr~enous injection of Thiopentothal (8-10 mg/kg) throu~h a catheter implanted in a superficial jugular vein, intubated and maintained under anae~thesia with Halothane in a mixture of nitrou~ o~ide and oxygen.

To remove sen~oxr affe~ent ~ontribution~ from hair receptors in ~he skin surrounding the centxal footpad, prior to ea~h experiment the ~oot was sha~ed ~nd treated with ~epila~ory cream, followed by ~ thorough wash and application of moisturizing cre~m.

Ig~376BX.WI/A~/19930C 04 ~

:

`` 35 2~3~7~7 During an experiment, the cat waE~ supported ~y a heated sling, with the implanted hindlimb fixed by two pairs of cupped claTnps pressed around ~he an1~le ~nd knee jOlnt8 (~ig.
5). This allowed the a~kle joint mo~re and did 3lot do ~erious 5 damage to the 3}cin. The ankle and knee angles were 100. The foot huny Yertically w~exl ~o~ ~imulated. When the ankle extensor mll~3cles were ~timulated, the ~ootpad p~l~hecl horizontally again~t a ~e6t object that could s~ide ve~tically with low fri~ion alo~ two bars, and that would fall if held by ~he foot.

I~:? analogy to the precisios~ ~rip experimenta by Westling and Johansson ~19~7), th~ o~ject w~s equi~ed with force aensor~
that mea~ured the horizontal grip force ~nd the vertical lo~d ~orce by means of strai~-gauge force transducers ~Revere, FT50). T~e vertical position of the object wa~ measured with a m~ch~nical linear po~ition transducer (W~ters, LRT-S-lOOB) (Fig. 5). ~ravity caused a constan~ downwards pull of 1.4 ~, since the object weighed abou~ 140 grams. The ~urface of the obj ect was 600 grit sandpaper .

~0 The s~imulator we uaed for F~g ~as the same a~ in ~xample 1, produced rectangular monopha~ic co:n~tant current pul8es with a fl~ed ~mplitude for ea~h channel. Pulse widths were independently controlled for each of the fo~r muacles between û and 255 ~lS, in s~eps of l~s, by a '386 computer via a parallel po~t. Each muacle was 6timulated at a fixed frequenc~ o~ 25 Hz, i.e. with interpulae intervals of 40 ms.
To re~uce ~orce rip~le ~au8ed by unfused tetani, the four muscles were ~timulated se~uentially, so that o~e of the muscles wa~ ~timulated every lO ma, giving ~n ~ggr~gate stimulation frequency of 1~ Hz, e.g. the ~me a~ de~cxibed in E~ample l.

The ENG si~nal xecoxded from the tibial nerve was filtered :~
~lk-lo kHz bandpass), rec~ified ~nd bin-integrated (in one 3 ms bin every 10 ms) be~ore sampling. This procedure ~a~ used :~
3$ to cancel out the pickup o~ artifacts as de~cribed in Example 1~2376EX.0011AS/1~9~06 04 . :: ,: . ` . ` , : : .
~': ~ ~ : .' : , : ` :

~~` 36 2~7~
1, ~nd also allowed the u~e of a l~wer ~amplin~ fre~uenc~
(100 H ) that the ~requency necessary to sample the raw E~G
~20 kH~. The bin-integrator and sampling were ~ynchronized to the delivery of stimulation pulses by the com~uter. In khis way the EN~ envelope ~a~ ~mpled at the sa~e $requency as th~ ~ggregate ~timulation rate (100 ~z). In the following the term llE~Gll will ~efer to the envelope of the ENG rat~er that to the raw ENG, since o~ly the envelope w~ ~pled ~or feedback purpo~e~.

lo Resul t~

To investiga~e slip-related info~matio~ contained in ~he E~
~ign~l, the following initial experiments were done: The four plantarflexvr mu~cles ~ere stimulated with a train of pul~e~
o~ constant width, thus generating a force that was approximately const~nt. The pulse width wa~ chosen 80 that the generated fo~ce was not suf~lcient for the foot to hold the ob~ect in place. Uhder these condition~, the ob~ect had to be partially ~upported by the e~perimenter, who ~ould thus allow it to fall by relea~i~g it~ ~upport in ~m~ll 8teps, each step cau~in~ a slip betwe~n the pa~ and the object as de~cri~ed in Hof~er and Haugland ".~92.

The ~harp bursts of ~G activit~ that signalled when ~lip8 occurred were typical ~or all e~perime~ts and f~r all cat~
used in thi6 ~tudy. Slip-~el~ted burs~s were di ti~ct eno~gh from the backgxound ENG to be detected wi~h great ~u~acy, and very early in the sl~p phase.

The sharp bur~ts.o~ ~NG activit~ that ~ignalled when ~lips occurred werf3 ~pical ~or all experime~t.q and for all cats u~ed in this ~t~d~. Slip-relaSed burst~ we~e dl~in~ enoguh 30 from the ~ack~round E~ to be detected with great accuracy, and very early in the slip phase.

lR~ nnllA~ nftn~ ~

37 2~97~57 A. Detect1on of sli~

Sinçe ~lip~ were accompanied by ENG bur~t~, they could be detected comparing the di~eren~ial E~G to ~ th~eshold ~alue.
Simple dif~erentiation, through, calcula~ed a~ the dif~erence ~e~ween the present ~Ç v~l~e and an old ENG ~alue, pro~ed too noi~y. In~tead~ a "slip detec~ion" ~ignal waa calculated by subtrac~ing d lo~-pass ~iltered (time con~tant = 0. 28) ve~ion of ~he F~NG ~l~nal dela~ed by 20 sample~ (20Q~) from the ~unfilte~ed' E~G, thereby remo~ing the b~ckground activity from the ENG. The 'unfiltexed~ ENG al~o needed some ~i~tering to reduce no~e, but thi~ was done with a ~orter time con~tant (0. 07s). The set of time constant~, ~ela~ and threshold value save the most sensitive and robu~t ~lip detection were ~ou~d by trial and error.

Implementation of the d~tection algorithm wa~ done in C
(Tur~o-C 2.0, Borla~d), and the filt~rs were i~plemented a~
~irst order auto-regressi~e (AR) ilters, which are computa-ti~nally ~ery ~imple. ~he algorithm to detect slip is show~
below:

repeat (this loop xu~ a~ 100 Hz) Update 20 samples o~ old E~G v~l~e~ :
Sample new ENG v~lue Background~G~BackgroundEN~*a+OldENG* (l.a~
SlipENG-SlipEN¢~b+NewENG*(1-b) SlipDetect-Slip~NG-B~Ckgr~UndENG
if SlipDetect~Thxe~hold then ~iqnal that ~ ~lip o~curred e~d The constants a a~d b were de~ermined from the time constants di~cussed abo~e (for O=~.2~ a=0.~51 and n,o . 07s--~
~Y0.867). Within the al~o~thm, the mu~cle stimulation inten-sitie6 were also determined and pulse~ were ~ ed by the computer, as de~cribed below.

18Z376~X.~I/AS/19~306 04 38 2097~57 B. Increase of force after slip A~ ~oon as a slip was detected, the fo~c:e was in~rea~ed as fast as po~3ible to reesta~ ;h a secure grip of the object hefore it moved out of reach. This was done by one of the ~ollowing two di~exen~ method~ By introduoing immediate-ly a single, closely ~paced pair o~ stimula~ion ~ulses (~dou-blet") to each of the four mu~cle~. ~his i~ a technique thatis also u~ed by the central nervous system i;n ~o~rnal çondi-tion~ ~nd can cause t~e force to not only increa~e rapidly, but al~o remain high for a prolonged period afte~ an extra pul~e. The ~ime be~ween the two pul~e~ was set to 5 ms. 2).
By increasin~ the pulse width ~arkedly for a ~hort period after the 61ip, in order to recrult ~o~e mo~or units~

Once the gr~p wa.s re-establishad, it w~s maintaimed by incre-~ing the pul~e width moderately (rel~tive to the original PW). ~i~h ~his approach, the grip force change~ cloaely resembled those seen in hum~n~ d~rlng the ad~ustment to ~udden increases in load force (~ohansson and Westling, 1988).

Because the ENG was sampled at 100 H~, a maximum of 10 ms could elapse b~tween ~he detec~ion of a slip ~om the ~NG and the response from the controlle~. Since the ENG w~s ~a~pled jwst before each stimulus pulse wa~ elicited, ~he fastest response ~o a detected ~lip wa~ determined only by ~he time it took to do the calculations (le3s th~n 1 ms). The main delay in the ~lip detection was caused by the low-pass f il-tering of the EN~ that wa~ necessary to remove ~alse detec-tions caused by normal variations in the ENG. The time-con-stant for thiæ ~ilte~ wa~ 70m~, as de~ribed a~ovQ. The delay 30 fxs~m ~he monl~nt the object first started to slide dow~ un~il the ~lip w~ detected w~R betwee~ 50 to 100 ms, ~ut ~aried considera~ly.

doublet pulse caused the next ENG sample to contain addi- -tional stimulus artifact, but this wa~ not a problem, becau~e t~2376~X,OOl/AS/19~3~ 04 ` ~g 20978~7 once the controlle~ was switched i~to "~lip comperlsation mode", it did no~ req~ire or expe~t ~lid ~ample~ fo~ the ne~t 300 m~. Thls p~evented e~xoneo~ detec~ions o~ ~lip during rapid in increase~ in stimulation intensity, which predictably gave ri~e ~o ph~sic EN~ burst~ ~hat could resemble t~o~e caused ~y a 81ip.

The stimulation ~lgorithm in~luded an ~utomatic ~hut-o~f o~
stimulation in the ob~ect dropped ou~ or rang~, determined by monitoring the signal from the vertical position transducer.

lo C. Te~t o~ closed-l~oP_slip com~en~ation controller Two set~ of expe~iments were done~

1) In experiments that ~ lated progressive "~atigue" in the stimulaa~ed muscles, the stimulation ~tarted at ~ le~el higher that the minimum nese~ y to hold the object. The inten~ity of sti~lation was then decrea~ed at a constant ra~e, until the ~or~e became in~ufficient to hold the object, whiah then ~t~rted to alip. De~ection of the ~lip triggered the control-ler to lncrease the intensity and gra~p the object a~
detailed ln the preceding ~ectiOn, i.e~. an llartificial grip-ping reflexll was ellcl~ed. ~he in~en~ty of ~timulation wa~~hen slowly decreased at the same rate as prior to khe slip.

2) In experime~t~ ~hat ~odeled the response to lncrea~es ln external load, the st~mulation inte~sity was held constant at a le~el ~ufficient for the foot to hold the object. After a fi~ed time, an extra load wa~ dropped o~ the object, causing the obiect to ~lip and start to ~11. The ~artificial reflex loop" cau~ed th~ slip information obtained from the neur~l ~ign~l to increase the ~timulation inten-~ity and thu~ o the ~rip foxce, in orde~ to ~atah the object before it fell~

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Claims (17)

1. A method for at least partially restoring the motor unction of a partially or completely paralyzed muscle, said method comprising implanting a nerve electrode for sensing electrical signals from a sensory nerve which innervates a part of the body which is physiologically related to the partially or completely paralyzed muscle stimulating the paralyzed muscle by means of a muscle stimu-lator sensing by means of said nerve electrode an electrical signal from the sensory nerve producing a further control signal for reactivating the muscle stimulator dependent on the electrical signal sensed after the expiration of a predetermined period of time after the stimulation of the muscle, and restimulating the paralyzed muscle in response to said further control signal.

2. A method according to claim 1 wherein the nerve electrode is a nerve cuff electrode.

3. A method according to claim 1 or 2 wherein the electrical signal is amplified, band-pass-filtered, and optionally rectified and bin-integrated when producing said further control signal.

4. A method according to claim 3 wherein the bin-integration is performed by means of an integrator having an adjustable integration period, said integrator being synchronized with the muscle stimulator.

5. A method according to any of claims 1-4 wherein the part of the body is innervated by the sensory nerve comprises a skin area.

6. An FES system for at least partially restoring the motor function of a human having at least one partially or com-pletely paralyzed muscle, said system comprising:

a stimulator means for stimulating the paralyzed muscle or muscles an implantable nerve electrode for sensing electrical signals from a sensory nerve which innervates a part of the body which is physiologically related to the partially or completely paralyzed muscle or muscles, and control means responsive to the electrical signals sensed from said sensory nerve after the expiration of a predetermined period of time after the stimulation of the muscle for producing a further control signal for reactivating said stimulator means.

7, An FES system according to claim 6, wherein said control means comprises means for amplifying, band-pass-filtering, and optionally rectifying and bin-integrating the sensed electrical signal and means for producing said further control signal in response to said bin-integrated electrical signal.

8. An FES system according to claim 7, wherein the bin-integration is performed by means of an integrator having an adjustable integration period, said integrator being syn-chronized with the stimulator means.

9. A method for providing a secure grip of an object through FES of a partially or completely paralyzed muscle which is involved in holding the object, comprising implanting a nerve electrode for sensing electrical signals from a sensory nerve which innervates a park of the body which is physiologically related to the partially for completely paralyzed muscle, detecting the start of a slip of the object from the ENG
signal from the nerve electrode, and immediately upon detection of the start of a slip producing or modifying a control signal for activating a muscle stimulator and stimulating the paralyzed muscle in response to said control signal.

10. A method according to claim 9, wherein the start of the slip is caused by an external change in the load or weight of the object.

11. A method according to claim 9, wherein the start of the slip is caused by an internal disturbance such as fatigue.

12. A method according to claim 9, wherein the start of the slip i caused by a change in the frictional coefficient of the skin, such as due to sweating.

13. A method according to any of claims 9-12, wherein the start of the slip is detected automatically as an event that exceeds a predetermined threshold value.

14. A method according to claim 13, wherein the ENG recorded from the sensory nerve is processed using analog or digital circuitry, and a filtered version of the ENG is subtracted from the actual electrical signal sensed, thereby removing unrelated background activity from the signal, the resulting calculated signal being identified as a signal related to the start of a slip if it exceeds a predetermined value.

15. A method according to claim 14, wherein the filtered version of the ENG is delayed by a number of samples and then subtracted from the actual signal sensed.

16. A method according to claim 14 or 15, wherein the filtered version is a low-pass filtered version.

17. A method according to any of claims 9-16 wherein the actual signal is an unfiltered signal or a signal which has been subjected to filtering with a shorter time constant than the version subtracted.