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Chap. 4

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Title: Chap. 4


1
Chap. 4 SENSORY FEEDBACK FOR LOWER LIMB
PROSTHESES
2
Overview
An internal model of the human body is used by
the central nervous system to decide the adequate
motor commands needed to execute movements.
Presence of lesions, such as limb amputation,
induces a mismatch between the output predicted
by the internal model and the movement actually
executed by the body. Thus, a re-organisation of
the motor strategies is needed that induces an
update of the internal model. In prosthetic
subjects rehabilitation can induce the update of
the internal model. If the subject is provided
with some kind of artificial sensory reafference,
it is likely to assume that the process of
updating the internal model can be improved. The
aim of our research is to develop a system
especially designed to provide sensory
biofeedback to lower limb amputee subjects.
  • Biofeedback techniques for rehabilitation of
    lower limb prostheses
  • Role of sensory feedback for the reconstruction
    of the internal model
  • Artificial feedback
  • Auditory, visual, and tactile biofeedbacks
  • Portable device for sensory substitution of the
    ground pressure information in prosthetic foot

3
1. Introduction
  • Internal model by the CNS system for the
    adequate motor commands
  • Limb amputation ? a mismatch between the output
    by the internal model and the movement
  • Reorganization of the motor strategies is needed
    to readapt and update the internal model.
  • Artificial sensory information
  • Biofeedback can help prosthetic subject.
  • Lower limb amputee is lack of pressure
    information by the prosthetic foot on the ground.
  • Artificial biofeedback
  • - induces the location, and the amount of foot
    pressure.
  • - should transmit this information to nervous
    system or sensory substitution.
  • The artificial feedback with the control of
    grasping in upper limb prostheses

4
2. Theories of Movement Control
  • The whole body is involved during the
    locomotion.
  • CNS system has to control the movement and the
    balance.
  • A motor act implies a progressive modification
    of posture.
  • Every posture modification implies a balance
    problem.
  • In other words, CNS has to control movement ?
    posture ? balance
  • Some body segments must be kept stationary
    during movement execution.
  • - For example, a constant head inclination for
    the clear vision of the external world.

5
2.1. Coordination between posture and movement
  • Movement a series of successive postures due
    to a progressive modification of the static
    balance between forces exerted by the agonist
    muscles.
  • Balance point
  • Postural control ? produce the movement
  • ? be ready to move
  • Anticipatory characteristics of postural control
    during movement
  • Action-Perception cycle

To decide the motor program
To provide the relevant command
Programmer
Peripheral receptors
Comparator
Regulator
To provide the relevant command ? Comparison
between the actual and the desired position ?
Identification of the movement completeness and
activation of the succeeding motor act ?
Modificationof the trajectory in case of
inadequacy
6
2.1. Coordination between posture and movement
  • The coordination of a motor act requires the
    control of a great number of DOF.
  • Reduction DOF to use synergies
  • Synergy
  • - The cooordination among different body segments
  • - A specific configuration of muscle activation
    for a specific posture
  • - By sensory input by external disturbance
  • - Or by internal commands for voluntary movements
  • - Not strictly pre-programmed but adapted
  • - Dependent of the support condition
  • - Some basic synergies are innate, and other are
    acquired.

New environments
Old Synergy
New Synergy
Learning process
  • Motor strategy the use of specific synergy or a
    sequence of synergies
  • Choice of the motor strategy higher level
    function by nervous system

7
2.2. Internal model
  • The internal model matches better.
  • Motor commands based on the knowledge of the
    geometry, kinematics and dynamics of the body
    segments of the initial and current state of the
    system
  • Internal model a synthesis of the experience
  • Brain Dual-mode for movement control
  • ? Continuous servo-mechanism
  • - Close-loop by sensory re-afference and
    pre-programmed motor acts
  • - Sensory re-afference build up and update the
    internal model, and choose the most appropriate
    synergies.
  • ? Simulation of the movement to predict the
    consequences and therefore to choose the better
    motor strategy
  • - Use of internal maps, i.e. pool of neurons
    representing external world characteristics
  • - Information from sensory feedback from the
    periphery
  • - Sensory re-afference provides information on
    the actual state of movement execution.

8
2.2. Internal model
  • With changes in environment (i.e. microgravity)
    or the presence of nervous and muscle-skeleton
    apparatus, the internal model becomes inadequate.
  • - Lack of correspondence
  • The internal model matches better.
  • Reorganization of the motor strategies and
    synergies to accomplish a movement.
  • Functional re-education in lower limb
    amputations
  • Rehabilitation program
  • - Aware of new condition
  • - Learn how to use his prosthesis and residual
    functionality
  • - Update of the internal model during
    rehabilitation

9
3. Natural Feedback
  • Sensory receptors neural structures to provide
    information from the external world and from
    within the body
  • Sensory systems
  • - Exteroreceptive sensitive to external stimuli
  • (vision, audition, skin sensation, and chemical
    senses)
  • - Proprioceptive information about the body
    position in space and the relative position of
    body segments to one another
  • - Interoceptive internal events in the body such
    as unconsciousness
  • Somatic sensory system
  • - All three involved.
  • - Tactile sensations by mechanical stimulation
    applied to the body surface
  • - Proprioceptive sensations by mechanical
    displacements of muscles and joints
  • - Perceived at the periphery, and processed and
    relayed to higher level of the nervous system
    through spinal cord or the medulla.

10
3.1. Tactile sensation
  • Mechanoreceptors
  • - Slowly adapting mechanoreceptors continuously
    responding
  • - Rapidly adapting mechanoreceptors respond only
    at the onset of the stimulus
  • Two rapidly adapting mechanoreceptors
  • - Meissner corpuscle in the paillae of the
    corium of the hand and foot, front of the
    forearm, the skin of the lips and the mucous
    membrane of the tip of the tongue
  • - Pacini corpuscle in subcutaneous positions at
    palm of the hand and the sole of the foot
  • Two slowly adapting mechanoreceptors
  • - Merkel receptors in the papillae and
    epithelium of the skin of man and animals,
    especially the skin area with no hair
  • - Ruffini corpuscle subcutaneous tissue of human
    finger

11
3.2. Preprioceptive sensation
  • Preprioception
  • - Sense of balance, primarily by the vestibular
    apparatus
  • - Sense of stationary position of the limbs
  • - Sense of limb movement (kinethesia)
  • Sense of the limb position and movement by
    peripheral receptors
  • Peripheral receptors
  • - Mechanoreceptors located in the joint capsules
  • - Cutaneous mechanoreceptors
  • - Mechanoreceptors located in the muscle and
    transducing muscle stretch
  • - A receptor in each spindle responds to an
    increase of muscle length and transmits to the
    spinal cord.
  • - The Glogi tendon organs stretch receptor
    responding to an increase in tension rather than
    length, measuring forces, and sending impuses to
    the spinal cord.

12
4. Artificial Feedback
  • Natural prosthesis
  • - Replaces the peripheral part of the damaged
    system and connected to CNS.
  • - Blind subjects with an array of microelectrodes
    implanted in cerebral cortex.
  • Substitutive prosthesis
  • - Uses a different sensory system for
    non-producible system.
  • - Navigation system with the obstacle avoidance
    for the blind.
  • - Auditory and tactile signals to the subject.

13
4. Artificial Feedback
  • For an amputee
  • - Foot pressure might be the only information
    that can be reasonably measured.
  • Natural and substitutive solutions to create
    artificial feedback for the blind

Nervous pathway
Pressure sensors
CNS
Natural prosthesis
Visual, Auditory, Tactile
Substitutive prosthesis
14
5. Center of Pressure
  • Maintaining balance is the most important for
    lower limb amputees, especially at the beginning
    of rehabilitation.
  • Balance when the ground projection of the body
    CM lies inside the support surface.
  • CM position
  • - Not directly detectable.
  • - Must be reconstructed through the internal
    model using muscle-tendon receptors and the
    cutaneous receptors of the foot sole.
  • ? Provides CNS with signals and can be used to
    obtain the position of CP.

5.1. Instrumentation for CP evaluation
  • CP the point of application of the vertical
    component of the resulting ground reaction force
  • Need to measure the intensity of ground reaction
    forces on the foot surface

15
5.1.1. Force plates
  • Measure the forces and the moments during the
    stance phase
  • Vertical, anterior-posterior, medial-lateral
    components
  • Piezoelectric when stressed, electric charge
    generated
  • Resistive sensors
  • Optical systems
  • Deformable metals
  • Strain-gauge
  • KISTLER force plates
  • - Quartz transducers
  • - No power supply required.
  • - Special charge amplifier and low noise coaxial
    cables required to convert the charge
    proportional to the applied load.
  • - More sensitive and greater force range than
    strain-gauge type
  • - Drift
  • AMTI force plates
  • - Stain-gauges (load cells)
  • - No drift

16
5.1.2. Sensorized insoles
  • Few sensors placed in specific zone or in a
    matrix form
  • Matrix sensors 60 - 960 sensors
  • F-Scan system
  • - Flexible and trimmable sensor with 960 sensing
    locations
  • - High-speed data communication
  • - peak force vs. time, pressure vs. time, peak
    pressure vs. time, and pressure profile
  • - Advantage Successive gait cycle
  • - Disadvantage Movement hindrance due to cables
  • Data communications
  • - Cable
  • - Data logger A/D converter carried with the
    subjects
  • - Telemetry only a limited number of data
    transferred

17
5.1.3. Telemetric acquisition of CP
  • On-line computing of the CP position during
    movement is essential.
  • Recently developed prototype (Instituto
    Superiore di Sanita, Italy)
  • - Matrix of 64 pressure sensitive sensors
  • - Analog signal processing by a small sized
    resistive circuit
  • - CP position in x-y coord and the vertical GRF
    displayed in real-time.
  • - Analog output from the insole directly control
    biofeedback devices
  • - Insole output connected to a small A/D
    converter at a frequency of 60Hz
  • - By telemetry, digital output transmitted in 7
    bytes records to the serial port of PC.
  • - Applied for the visual and auditory biofeedback

18
5.2. Normal trajectory of CP during walking
  • Gait cycle
  • - Stance phase
  • - Swing phase
  • Normal Gait
  • ? CP lies on the medial-posterior heel,
  • ? moves through the mid-foot region,
  • ? continues towards the forefoot, crossing the
    metatarsal heads
  • ? terminates in the region of the great and 2nd
    toe.
  • Area of CP trajectories during successive steps

19
5.2. Normal trajectory of CP during walking
  • Area of CP trajectories during successive steps

20
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6. Visual and Auditory Feedback
6.1. Visual feedback
  • Visual biofeedback showing CP position on a
    screen
  • Left and right foot images with reference areas
  • Points outside the reference area in different
    color
  • - information on the deviation from the desired
    performance
  • Display of both CP trajectory and the movement
    in visual feedback
  • - difficulty in watching the screen and
    simultaneously correcting his mistakes during the
    initial phase of re-education
  • Visual representation of CP movement is more
    useful to the physiotherapists
  • On-line trajectory of CP position can better
    understand how to instruct the subject.

23
6.2. Acoustic feedback
  • Acoustic feedback by using sounds to be aware of
    the CP distance from the reference area.
  • Different sound for deviations from the
    reference area
  • Acoustic biofeedback simple tones or recorded
    sounds
  • - Complex messages confuses the subject.
  • Avoid instantaneous correction only if the
    subject leaves the reference area for at least
    50ms.
  • Advantage
  • - does not employ the sensory pathways for
    movement control
  • - The simple message makes the task easier.
  • Disadvantages
  • - too noisy

24
7. Tactile and Proprioceptive Biofeedback
  • Tactile and proprioceptive feedback for
    artificial limbs
  • a. Direct neural stimulation
  • b. Transcutaneous stimulation
  • c. Mechanical vibrators
  • Only a few studies in lower limb prostheses.
  • Kawamura et al.
  • - Surface electrocutaneous signals to provide
    foot sole pressure information
  • - Four independent tape switches on the sole of
    the prosthetic foot drive four surface electrodes
    on the thigh in above-knee amputees.
  • - Detection of prosthesis knee angle
  • Direct peripheral nerve stimulation by Cliiper
    et al.
  • - Four Pt-Ir electrodes inserted in the sciatic
    nerve of patients
  • - The frequency of electrical stimulation was
    modulated by the bending moment through the
    strain gauges on the pylon of the prosthesis.

25
7. Tactile and Proprioceptive Biofeedback
  • Sabolich and Ortega (1994)
  • - Noninvasive system with transcutaneous
    electrical stimulation to sense organs at the
    socket-limb interface.
  • - Two pressure transducers in the sole of the
    artificial foot
  • - Send tingling signals to the amputees residual
    limb.
  • - Some benefits in weight distributions, step
    length, and stance time

26
8. A Portable Device for Tactile Stimulation
8.1. The system
  • Mechanical tactile stimulation for artificial
    sensory feedback
  • Components Two FSR sensors, a circuit, and two
    small eccentric DC motors
  • FSR sensors ideal for touch control,
    inexpensive, thin (gt0.15mm),
  • durable (107 actuations) and environmentally
    resistant
  • The box (circuit and power supply) 220g

27
8.1. The system
  • Two eccentric motors from the mobile phone
  • For BK amputees, two vibrators on the thigh in
    anterior and posterior positions to maintain the
    spatial correspondence of with three sensors.
  • Four-sensors-four-corresponding-stimulators
  • Limitations
  • - Spatial discrimination ability in tactile
    stimulation
  • - Constant conscious effort from the subject

28
8.2. Rehabilitation protocol
  • Sensory feedback on the pressure by artificial
    foot on any surface
  • (automobile clutch, brake, or bicycle pedals)
  • Rehabilitation protocol
  • - Step I. Orthostatic exercises to obtain static
    balance
  • - Step II. Walk inside the parallel bars
  • - Step III. Walk with some auxilliary devices
    such as crutches
  • - Step IV. Walk without any auxilliary devices
  • Experiments
  • - Motion analysis with ELITE system
  • - F-Scan and Video-controller
  • Main goal of the experiment
  • - to quantify the advantage of the tactile
    sensory feedback in reducing the duration of the
    rehabilitation process in amputees

29
9. Conclusions
  • The sensation of the ground pressure of
    artificial foot
  • - important in control and coordination of
    walking, running, and doing other activities
  • CNS needs sensory re-afference in order to
    update and maintain the internal model for
    appropriate strategies
  • Process of updating the internal model for an
    amputee with some kind of artificial sensory
    information
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