Lecture 17Lecture 17Dimitar Stefanov

Functional Neural Stimulation for Movement Restoration (FNS)

•FNS activates paralyzed skeletal muscles by using an electronic stimulator, which delivers trains of pulses to neuromuscular structures.

•The basic phenomenon of the stimulation is a contraction of muscle due to the controlled delivery of electric charge to neuromuscular structures.

FES systems is applied to restoration of:1. Goal-oriented movements (movements at hand or arm);2. Cyclic movements (walking and standing movements).

The time delay between muscle stimulation and muscle activation is called the neural dynamics.

Non-linear relationship between input activation and generated joint torque (depends on the joint angle, the joint velocity and acceleration).

Limb dynamics – depends on the mass and inertia characteristics of the limb, damping, elasticity, stiffness.

Block diagram of FNS model

Upper extremity FESA./ Classification, regarding the part of the upper limb, which will be stimulated:a./ FES of hand motions;b./ FES of elbow motions;c./ FES of shoulder motions.

B./ Classification, regarding the source of control signals to trigger or regulate the FES patterns:

1. Shoulder control (Buckett et al., 1988);2. Voice control (Handa at al., 1982; Nathan&Ohry, 1990);3. Respiratory control (Hoshimiya et al., 1989);4. Joystick control (Peckham&Keith, 1992)5. Position transducers (Prochazka, 1993;

Rebersek&Vodovnik, 1973).

C./ Classification, regarding the number of the channels for FES patterns:

1. Systems with one- or two channels;2. Multi channels systems.

D./ Classification of the systems, regarding the type of the electrodes:

1. FES systems based on surface electrodes (transcutaneous electrodes);

2. FES systems based on implanted electrodes (percutaneous electrodes);

3. FES systems based on implantable stimulators.

Review of some systems for FES:

1963 (Long&Mascirelli) – the first grasping system (prehension and release); a spring for hand closure and electrical stimulation for of the the thumb extensor for release.

1984 (Rudel at al.) simple two-channel stimulation system and a shoulder activated position transducer (sliding potentiometer); at the neutral position of the potentiometer –stimulation pulses stop;

First FES clinic - in Sendai (Japan) – many persons are implanted with up to 30 intramuscular electrodes – mainly for therapy, not to assist in grasping.

Review of some systems for FES (continue):

Japanese FES systems for functional grasping, activated by voice or suck&puff interface; use of pre-programmed EMG-based stimulation patterns; applied to subjects with lack of natural grasping and elbow movements.

1989 – Ben Gurion University, Israel (Nathan) – voice controlled multichannel surface electrode system; 12 bipolar stimulation channels; control of elbow, wrist and hand function; surface stimulation (doesn’t allow dexterity while grasping); problem – need of everyday mounting and fitting of the system.

Institut fuer Biokibernetic, Karlsruhe, Germany –recording of the EMG of weak muscle; amplifying the EMG and stimulation the same muscle; special means to prevent the positive feedback (Hollaender at al., 1987);

Review of some systems for FES (continue):

The Case Western Reserve University (CWRU) – fully implantable system; hand opening/closing, selection of the grasp, proportional control of palmar and lateral grip; joystick for control of the stimulation signals; preprogrammed control; joystick, activated by the contralateral shoulder. The movement of the joystick activates preprogrammed sequence of stimulation (the palmar grip starts from the extended fingers and thumb, followed by movement of the thumb and after that by fingers flexion); 1992 – (Peckham&Keith), surgically modification of the grasp (pining some joints and fixation of some tendons); two modes: grasp and hold, potentiometer for control of the grip and additional EMG signal for to hold the hand closed; application at home for daily living tasks.

The Cleveland FES Center includes: Cleveland VA Medical Center, MetroHealth Medical Center, Case Western Reserve University, and Edison BioTechnology Center.

Some projects of the Cleveland FES Center

http://feswww.fes.cwru.edu/projects/index.htm#briefs

Implantable Stimulation, Telemetry, and Transducer System for Neural Control

The transducer, implanted in the wrist, allows the individual to control grasp opening and closing through voluntary movement of the wrist.

Under development – new version of stimulator; up to sixteen channels of stimulation, one implanted joint angle transducer and two channels of myoelectric signal transduction.

Myoelectric signal obtained from arm or neck muscles will be used to control various features of the grasp and/or arm movements.

EEG-based Controller for FNS Hand Grasp Systems (P. Hunter Peckham); Persons with C5 - C6 level spinal cord injury.

http://feswww.fes.cwru.edu/projects/phprsf.htm

Bionic glove (University of Alberta, CA, Arthur Prochazka), 1997; Neuromotion Inc.,

http://www.ualberta.ca/~aprochaz/hpage.html

Hand opening and closing stimulator for C5-C6 quadriplegic people

Self-adhesive electrodes over certain muscles; elastic glove over the electrodes; tightening the glove causes electrical contact with the electrodes; user's wrist movements are sensed by a transducer control a microprocessor based stimulator.

Tremor suppression system, based on FES (A. Prochazka).

Restoration of standing and walking

Ljubljana, Slovenija (Bajd, 1982, Gracanin, 1967)

Single-channel stimulation system – applicable to special group of patients with incomplete spinal cord injury who can perform limited walking without FES system.Multichannel system (1989) –FES system with at least four channels; oriented to patients with complete spinal cord injury, who have preserved upper-body control; stimulation of the quadriceps locks the knee. Swing phase – by movement of the upper part of the body and using of rolling walker; hand- or foot switches are used for flexion-extension alternation. The Parastep Functional Electrical Stimulation SystemInvented by Daniel Graupe (University of Illinois at Chicago, EECS Dept.), produced by Sigmedics, Inc. of Northfield, IL.

The user controls the stimulation through switches on the handgrips of the walker or through a keypad on the stimulator unit; standing and sitting, taking right steps, taking left steps, and increasing and decreasing the electrical current.

http://feswww.fes.cwru.edu/standingsystem/index.html

Cleveland FES center

Implantable standing FES systems

Studies that include investigational devices for human use are registered with the Food and Drug Administration (FDA).

Eight channel fully implantable system.

Remotely controlled wireless microstimulators

BIONAdvanced Bionics Corporation http://www.advancedbionics.com/products_frame.asp

The muscle wasting that afflicts many stroke patients can lead to serious complications such as thrombosis in bedridden patients.

Gerald Loeb, a biomedical engineer at the University of Southern California

2 millimetres in diameter; can be injected directly into a muscle using a 12-gauge needle; once in place they are activated by a radio signal from a coil worn by the patient; deliver a pulse of 30 milliamps for about 0.5 milliseconds.

http://www.newscientist.com/ns/19991211/newsstory1.html

•Devised in a cylindrical shape with a stimulation electrode on each end, the microelectrodes contain their electronics in a hermetic glass capsule. •Their physical dimensions are 2 mm in diameter and 16 mm in length. •The electrodes are made of an activated iridium disk and an oxidized sintered tantalum slug which also serves as a power storage capacitor. •The challenge of making the micro-stimulator consists of building a miniature, temperature sensitive electronic assembly and enclosing it into a slightly larger hermetic capsule made of high temperature glass.• A custom CMOS chip, a rectifying diode and a chip resistor are mounted on a miniature two-sided printed circuit board, 0.18 mm thick. •The components are connected by gold wire bonds and 0.15 mm wide gold-plated copper traces.

CUSTOM SILICON CHIP TECHNOLOGY FOR IMPLANTABLE FES MICROSTIMULATORS Primoþ Strojnik, Joseph Schulman, Philip Troyk,Gerald Loeb, and Paul Meadows http://www.bme.med.ualberta.ca/~fes/ifess/page/p21.htm http://www.dinf.org/resna96/page116.htm

•The chip-PC board assembly is sandwiched between two ferrite half-cylinders. •Two layers (200 turns) of 25 m insulated copper wire wound on the ferrite represent a self-resonating receiving coil.• The ends are attached to the PC board.• A layer of a glob-top epoxy secures the components and the bond wires. •Building the hermetic package involves making hermetic glass bead to metal seals to make electrode feed-throughs, creating contacts on the inside of the feed-through, and making a glass bead to glass capsule final seal. •A miniature spring coil maintains a reliable connection between the inside feed-through contacts and the electronic assembly. •Hermeticity better than 1x10^-10 atm-cc/s was achieved in sealing the microstimulators.

CUSTOM SILICON CHIP TECHNOLOGY FOR IMPLANTABLE FES MICROSTIMULATORS Primoþ Strojnik, Joseph Schulman, Philip Troyk,Gerald Loeb, and Paul Meadows http://www.bme.med.ualberta.ca/~fes/ifess/page/p21.htm http://www.dinf.org/resna96/page116.htm

•The BION produces asymmetric biphasic constant-current pulses.

•The BION receives power as well as stimulation commands via magnetic link from an external coil that is worn by the patient.

•An amplitude modulated 2 MHz carrier powers and transfers stimulation data to the micro-stimulator and provides the basic clock for the digital part of the micro-stimulator circuitry.

•The microstimulators are addressable. One coil can control up to 255 uniquely addressable BIONs.

http://www.biontech.org/about/what_is_a_bion_01.html

Problems, which limit the effectiveness of the FES systems:•Fast fatigue•Reduced torques generated through FES in comparison with central nervous system control•Osteoporosis and stress fractures.

Hybrid Assistive systems (HAS)Integration of two assistive systems: FES system and external mechanical orthosis.

Advantages:1. Partial mechanical support2. Parallel operation of the biological and mechanical system3. Sequential operation of the biological and the mechanical system.