Neuroprosthetics Neuroprosthetics

Motor ProsthesesMotor Prostheses

BackgroundBackground

Damage to the Central Nervous System Damage to the Central Nervous System (CNS) can result in sensory loss, muscle (CNS) can result in sensory loss, muscle contraction, cognitive problems, loss of contraction, cognitive problems, loss of motor control & biological function lossmotor control & biological function loss

Treatments include – drugs, physical Treatments include – drugs, physical therapy, surgery & rehab (+ future – therapy, surgery & rehab (+ future – neural regeneration)neural regeneration)

Also possible – Neural Motor Prosthesis Also possible – Neural Motor Prosthesis

DefinitionDefinition

Motor Prosthesis (MP) is a device that Motor Prosthesis (MP) is a device that electrically stimulates nerves electrically stimulates nerves innervating a series of muscles for innervating a series of muscles for restoring functional movement or restoring functional movement or biological function.biological function.

Here we look at how electrical Here we look at how electrical stimulation can be used to overcome stimulation can be used to overcome motor and functional lossmotor and functional loss

Clinical ApplicationsClinical Applications

Spinal cord injurySpinal cord injury

Brain injuryBrain injury

Diseases that effect neural functionDiseases that effect neural function

Spinal Cord InjurySpinal Cord Injury

Greatest level of success in this areaGreatest level of success in this area Usually caused by car or diving accident (UK)Usually caused by car or diving accident (UK) Severance or compression of cord by a Severance or compression of cord by a

fractured bone & tissue swellingfractured bone & tissue swelling Mobile areas of vertebral column are most Mobile areas of vertebral column are most

susceptiblesusceptible Paraplegia – paralysis of the lower Paraplegia – paralysis of the lower

extremetiesextremeties Tetraplegia – paralysis of upper & lower ext.Tetraplegia – paralysis of upper & lower ext.

Spinal Cord InjurySpinal Cord Injury

Muscle Atrophy – degeneration of muscle Muscle Atrophy – degeneration of muscle tissue due to loss of neuronal inputtissue due to loss of neuronal input

Muscles to be stimulated need Muscles to be stimulated need strengthening regime prior to introductionstrengthening regime prior to introduction

Second level + higher injuries – loss of Second level + higher injuries – loss of ability of brain stem to control breathingability of brain stem to control breathing

Cervical + lumbar level lesions – loss of Cervical + lumbar level lesions – loss of bladder, bowel & sexual functionsbladder, bowel & sexual functions

Brain InjuryBrain Injury Many different disorders result – Many different disorders result –

cognitive and sensory not issue herecognitive and sensory not issue here Use of MP can be hindered by cognitive Use of MP can be hindered by cognitive

problemsproblems But MP can be used for motor relearningBut MP can be used for motor relearning Stroke – blood vessel in brain is blocked Stroke – blood vessel in brain is blocked

or ruptured – loss of blood flow to an areaor ruptured – loss of blood flow to an area Result is neuronal deathResult is neuronal death Most common is stroke in one motor Most common is stroke in one motor

area, resulting in paralysis in one side area, resulting in paralysis in one side (opposite)(opposite)

Brain InjuryBrain Injury StrokeStroke also causes – hyperreflexia, muscle also causes – hyperreflexia, muscle

spasticity, muscle atrophyspasticity, muscle atrophy

Cerebral Palsy (CP)Cerebral Palsy (CP) – occurs shortly after – occurs shortly after birthbirth

Caused by accident, infection (meningitis or Caused by accident, infection (meningitis or enchepalitis) or brain asphyxsiaenchepalitis) or brain asphyxsia

All these lead to neuronal deathAll these lead to neuronal death Result is difficult to perform motor tasks – Result is difficult to perform motor tasks –

spastic CP – muscles permanently contracted spastic CP – muscles permanently contracted

DiseasesDiseases

Some lead to neuronal death, some to loss Some lead to neuronal death, some to loss of the myelin sheath around neurons thus of the myelin sheath around neurons thus preventing action potential conduction and preventing action potential conduction and some affect the generation or release of some affect the generation or release of neurotransmittersneurotransmitters

Only first type can benefit from prosthetics Only first type can benefit from prosthetics – do not affect nerves going to muscles– do not affect nerves going to muscles

MP generates action potentials in nerves to MP generates action potentials in nerves to cause muscle contractions cause muscle contractions

So use in MS & MND very limited at present So use in MS & MND very limited at present

Motor Prosthesis DesignMotor Prosthesis Design

Stimulus delivery systemStimulus delivery system – electrode – electrode + wires for stimulation+ wires for stimulation

Control unitControl unit – interpret user – interpret user commands, convert info into muscle commands, convert info into muscle stimulationsstimulations

Command interfaceCommand interface – records signals – records signals generated by user & converts into generated by user & converts into commands for the MPcommands for the MP

Stimulus Delivery SystemStimulus Delivery System

All MPs operate by electrical stimulation of All MPs operate by electrical stimulation of nerves to elicit a muscle contraction – three nerves to elicit a muscle contraction – three methods exist for thismethods exist for this

Surface electrodesSurface electrodes – on surface of skin over – on surface of skin over point where nerve & muscle joinpoint where nerve & muscle join

Require conductive adhesives or pad for Require conductive adhesives or pad for contactcontact

Low cost & noninvasiveLow cost & noninvasive Not all muscles can be activated (those nearest Not all muscles can be activated (those nearest

skin) & Large power due to large voltages (80V) skin) & Large power due to large voltages (80V) to drive current across skin impedanceto drive current across skin impedance

Stimulus Delivery SystemStimulus Delivery System

Percutaneous ElectrodesPercutaneous Electrodes – Inserted – Inserted through skin with needle near motor point through skin with needle near motor point of muscle of muscle

Single or multiple wire strandsSingle or multiple wire strands Barbed at the end to ensure anchoringBarbed at the end to ensure anchoring Power requirements much reducedPower requirements much reduced Skin irritation + infection can occurSkin irritation + infection can occur Stress on wires at interface – poss Stress on wires at interface – poss

breakagebreakage

Stimulus Delivery SystemStimulus Delivery System

Implanted Electrodes Implanted Electrodes – implanted in body– implanted in body EpimysialEpimysial – platinum-iridium disk in a silicon – platinum-iridium disk in a silicon

pad, sutured near muscle motor point pad, sutured near muscle motor point IntramuscularIntramuscular – inserted with needle, – inserted with needle,

stainless steel with umbrella anchorstainless steel with umbrella anchor Nerve CuffNerve Cuff – Platinum-iridium bands that – Platinum-iridium bands that

encircle the nerve to the muscleencircle the nerve to the muscle AdvantagesAdvantages – highly selective (not nerve – highly selective (not nerve

cuff), less powercuff), less power Disadvantage Disadvantage – Invasive, surgery for – Invasive, surgery for

placement and replacement placement and replacement

Control UnitControl Unit

Consists of command processor & control Consists of command processor & control processorprocessor

Command ProcessorCommand Processor – interprets user – interprets user generated signals to operate various motor generated signals to operate various motor prosthesis functionsprosthesis functions

E.g. System state (on/off), activation pattern E.g. System state (on/off), activation pattern selectionselection

Control ProcessorControl Processor – converts signals from – converts signals from command processor into actual functioncommand processor into actual function

Decides specific muscle stimulations requiredDecides specific muscle stimulations required

Command InterfaceCommand Interface

Records user generated signals to Records user generated signals to operate the MPoperate the MP

Examples EMG, Voice, switches, Examples EMG, Voice, switches, respirationrespiration

Use least number of input channelsUse least number of input channels Reduce amount of noise (SNR)Reduce amount of noise (SNR) Transition rate is importantTransition rate is important Performance reliabilityPerformance reliability Interface must be cheap, simple and Interface must be cheap, simple and

invisible invisible

Cardiac PacemakerCardiac Pacemaker

Implanted device that delivers electrical Implanted device that delivers electrical impulses to cardiac tissue to control heart impulses to cardiac tissue to control heart contractions contractions

Stimulus via lead wires and electrodes on Stimulus via lead wires and electrodes on heart surface or in heart musclesheart surface or in heart muscles

Electrodes have to withstand movementElectrodes have to withstand movement Platinum alloy for biological compatibility – Platinum alloy for biological compatibility –

avoiding corrosionavoiding corrosion IPG – Implanted Pulse Generator – IPG – Implanted Pulse Generator –

Titanium package Titanium package

Foot StimulatorsFoot Stimulators

First used for correction of footdrop – First used for correction of footdrop – inability to lift foot during swing in walking inability to lift foot during swing in walking (toes do not clear the ground)(toes do not clear the ground)

Liberson (1961) stimulated peroneal Liberson (1961) stimulated peroneal nerve using surface electrodes – resulted nerve using surface electrodes – resulted in dorsiflexion of foot (toes avoided in dorsiflexion of foot (toes avoided ground)ground)

Switch on sole of shoe – closed when Switch on sole of shoe – closed when liftedlifted

Hand StimulatorsHand Stimulators

For those with cervical level injury at 4For those with cervical level injury at 4thth and and 55thth levels levels

Electrical stimulation combined with hand & Electrical stimulation combined with hand & wrist splintwrist splint

Surface electrode for finger extensionSurface electrode for finger extension Flexion by using spring between thumb and Flexion by using spring between thumb and

middle/index fingersmiddle/index fingers Increase in stimulation causes extension, as Increase in stimulation causes extension, as

current decreases so spring returns fingercurrent decreases so spring returns finger

Limitations of MPsLimitations of MPs

DenervationDenervation – Charge needed to – Charge needed to drive muscles directly is large, drive muscles directly is large, causing tissue heating. MPs not good causing tissue heating. MPs not good if nerves damagedif nerves damaged

Muscle SpasticityMuscle Spasticity – Action potentials – Action potentials spontaneously active, overriding any spontaneously active, overriding any possible MP actionpossible MP action

Limited FeedbackLimited Feedback available – usually available – usually limited to visual + auditory. limited to visual + auditory. Cognitive stress on userCognitive stress on user

Commercially AvailableCommercially Available

Estimated there will be over 100,000 Estimated there will be over 100,000 MPs in use by 2010MPs in use by 2010

Upper ExtremityUpper Extremity Lower ExtremityLower Extremity Organ SystemsOrgan Systems

Upper Extremity MPsUpper Extremity MPs

Bionic GloveBionic Glove – augments grasp using – augments grasp using surface electrodes for finger movementssurface electrodes for finger movements

Handmaster SystemHandmaster System – Electrodes mounted – Electrodes mounted in a brace, so easier to use – fingers againin a brace, so easier to use – fingers again

AutoMoveAutoMove – surface electrodes but control – surface electrodes but control signals augment muscle movementssignals augment muscle movements

Freehand SystemFreehand System – Implanted system: – Implanted system: Stimulator in chest – works with palmar Stimulator in chest – works with palmar grasp (glass) and lateral grasp (pencil)grasp (glass) and lateral grasp (pencil)

Lower Extremity MPsLower Extremity MPs

Mostly for footdrop or standing for Mostly for footdrop or standing for paraplegics (limited success with walking)paraplegics (limited success with walking)

Odstock, MicroFES & FootlifterOdstock, MicroFES & Footlifter – use – use surface electrodes for foot & knee flexion surface electrodes for foot & knee flexion

Parastep SystemParastep System – restores standing & – restores standing & walking (about 1,000 recipients) – six walking (about 1,000 recipients) – six electrodes follow pattern of stimulationelectrodes follow pattern of stimulation

Organ System ProsthesesOrgan System Prostheses

Stimulation of sacral nerves to control Stimulation of sacral nerves to control bladder & urethral contraction bladder & urethral contraction

VOCAREVOCARE – two (implanted) electrode pairs, – two (implanted) electrode pairs, user controlled – problem in loss of erection user controlled – problem in loss of erection – not so acceptable with males– not so acceptable with males

Quik-Coff Quik-Coff – surface electrodes on abdominal – surface electrodes on abdominal wall – help coughing – user activatedwall – help coughing – user activated

Atrostim & T154Atrostim & T154 – implanted devices – implanted devices stimulate phrenic nerve to restore stimulate phrenic nerve to restore respirationrespiration

New Clinical ApplicationsNew Clinical Applications

Current technology requires intact motor Current technology requires intact motor nerve to muscle for muscle contractionnerve to muscle for muscle contraction

Device needed where myelin sheath has Device needed where myelin sheath has degenerated – no action potentials – nerve degenerated – no action potentials – nerve regeneration so MP can workregeneration so MP can work

Neural regeneration in spinal cord – MPs Neural regeneration in spinal cord – MPs guide growth for regenerated nerves and guide growth for regenerated nerves and maintain muscle strengthmaintain muscle strength

Use MP to block unwanted signals for CP Use MP to block unwanted signals for CP

Technology DevelopmentTechnology Development

Drive towards implanted technologyDrive towards implanted technology Multichannel stimulation via RF linkMultichannel stimulation via RF link Modular implanted systems that Modular implanted systems that

communicate – limited need for wirescommunicate – limited need for wires Power/battery requirements – biofuel Power/battery requirements – biofuel

cells, make use of body chemistrycells, make use of body chemistry Think & respond system to replace Think & respond system to replace

externally generated control signalsexternally generated control signals

Final WordsFinal Words

Present MPs mainly limited to use Present MPs mainly limited to use where nerve fibres to muscle link is where nerve fibres to muscle link is OK – e.g. spinal cord injuryOK – e.g. spinal cord injury

Exciting area of development for Exciting area of development for implant technologyimplant technology

Have only considered therapy here – Have only considered therapy here – not nervous system extension or not nervous system extension or supergrip!! supergrip!!

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Emerging TechnologiesEmerging Technologies