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Lecture 8 - Coggle Diagram
Lecture 8
Drop Foot & the Stimulator Mechanism
Drop foot simulator (Neuroprosthesis)
Symptom
Common in stroke patients
Characterized by lack of dorsiflexion during gait
Lifting of ankle/foot
Result
Foot drags during the swing phase
Leading to an unstable gait & high risk of falls
Clinical & Commercial Success
Effictiveness
One of the most successful neuroprostheses
Clinically & commercially
Patient perceptions
Superior to traditional Ankle-Foot Orthoses (AFOs)
Orthotic Effect
Immediate, measurable improvement in walking speed for patients with progressive (e.g. MS) & non-progressive (e.g. stroke) disorders
Mechanism
Uses a
surface electrode
to electrically stimulate the common peroneal nerve
Timing system
Requires a sensor to detect the phase of gait & trigger stimulation at the correct moment
Therapeutic Effect (Neuroplasticity)
Observed change
Prolonged use (3-12 months) causes a significant increase in corticomuscular excitation
Measurement
Evaluatied by measuring the Motor Evoked Potential (MEP) via EMG after Transcranial Magnetic Stimulation (TMS)
Indications
Increased MEP suggests the connection between the motor cortex & the target muscle (tibialis anterior) is strengthened
Conclusion
Repetitive FES induces neuroplasticity within the CNS, resulting in a lasting therapeutic effect beyond just immediate assistance
FES For Standing
The basis for regular walking
Fundamental for ambulation
Health benefits (SCI patients)
Improve blood circulation
Reduced muscle attrophy
Social & Psychological
Enables face-to-face interactions
Transition from sitting to standing via open-loop control
Limitation
Continuous muscle contraction caused rapid fatigue, reducing stability & endurance
As a result, users still required upper limb support, limiting independence
Transition from sitting to standing via closed-loop control
Improves stability & reduces muscle fatigue
Uses feedback sensors to monitor posture
Controller adjusts stimulation intensity in real time
Turns off or lowers stimulation when not required
Enables more efficient & natural standing control
FES for Walking
About
Foot drop FES
Encourages localized plasticity
Primarily activates peripheral motor neurons
Walking FES
Activates spinal central pattern generator (CPG)
Encourages system-level reorganization
Involved in rhythmic gait generation
Parastep Flexor Withdrawal Reflex Approach
Parastep FES walking is an FDA-approved system
Uses FES to help people w/ paraplegia stand & walk using a walker
Stimulates major leg muscles in a pattern that mimics the CNS's natural walking patterns
Controlled by the user via buttons on the walker handles
Surface Stimulation Systems
Apply electrical currents through electrodes placed on the skin over major muscle groups based on biomechanical data
Used for therapeutic purposes in individuals with motor incomplete SCI
Participants showed improved walking function, including an increase in walking speed
Hybrid FES & Robotic Systems
Goal
Compensate for weak biomechanical movements that FES alone struggles with
Solution
Hybrid systems combining FES w/ passive or active mechanical support
WalkTrainer is an example
Adapts to patient effort
Percutaneous Systems for Complete Paralysis
Individuals with complete SCI achieve successful, walker-supported walking
Electrical Neuromodulation
Goal
Achieve therapeutic outcomes by directly modulating one or more circuits within the CNS
In contrast to FES, which directly activates target muscles
Clinical applications
Various types of neural interfaces (neuroprostheses) have been developed & clinically tested
The type of interface depends on the location & anatomical characteristics of the target nerve
Mechanism of Action
Sensory Nerve Stimulation
Electrical current is applied to sensory nerve fibres
Tuning Parameters
Stimulation is precisely tuned using specific input parameters to elicit desired changes in physiological funtion
Amplitude
Frequency
Duration
Neuroprosthesis for Urinary Incontinence
Overactive Bladder = OAB
2 Main types of incontinence
Stress Incontinence
Urine leakage occurs when intra-abdominal pressure rises
e.g. coughing, laughing
Due to loss of urinal sphincter tone or weakened pelvic floor muscles
Urge Incontinence
Triggered by abnormal signalling btwn bladder & brain
Due to overactivity of parasympathetic (pelvic) nerves
Therapies
Sacral Neuromodulation (SNM)
Continuous stimulation of the S3 nerve roots w/ electrode & generator
Percutaneous Tibial Nerve Stimulation (PTNS)
Indirect modulation of sacral nerve plexus (S2-S4) via stimulation of posterior tibial nerve (leg)
NMES & FES
NeuroMuscular Electrical Stimulation (NMES)
Electrical stimulation that is used to activate motor nerves
Functional Electrical Stimulation (FES)
When NMES is applied to specifically induce an organized, patterned, and functional action, it is called FES
A method of externally controlling muscles when signals from brain can no longer control movement
This can happen after spinal cord injury, stroke, or neurological disease, such as MS
3 Pulse Parameters
Pulse Intensity
Electrical current/voltage
Pulse Duration
Pulses are monophasic or biphasic
Monophasic
Delivers the charge to the tissue without removing the charge from the tissue (all pulses >= 0)
Biphasic
Charge is delivered to the tissue with the removal of a charge
2 types
Symmetric
Asymmetric
Pulse frequency
Mechanisms
Electrode Types
Transcutaneous (surface)
Features
Non-invanse
Placed on skin above target nerve or muscle group
Traditional
Wired to external stimulator
Modern
Adhesive "patch-style" designs with wireless control
Can target
Nerve branch
e.g. Foot drop
Motor point
For efficient muscle activation
Limitations
Requires precise electrode placement
Hard to reach deep muscles
May cause discomfort from skin stimulation
Percutaneous
Features
Fine wires inserted through the skin
Into muscles
Allows deep, selective stimulation
Less discomfort from skin receptors
Sometimes used as a bridge to implants
Limitations
Invasive
Implanted
Features
Fully internal system
Electrodes & stimulator fully internal
Subcutaneous leads connect to chest/abdomen stimulator
Wireless power/control possible
Fewer surface issues
Limitations
Invasive
Requires frequent recharging
Applications
Drop foot stimulator
FES for standing
FES for walking
Spinal Cord Stimulation
FES for Upper limb function
Neruoprosthesis
Replaces or repairs lost function in the nervous system
By interfacing with nerves or brain cells
Through FES
Two main applications
Orthotic FES
Aids movement
e.g. walking in foot drop
Therapeutic FES
Repeated use promotes neural recovery
Research supports long-term motor improvement
FES for Spinal Cord Stimulation
Goal
Invasively or non-invasively activate these spinal cord neural circuits to help individuals w/ SCI partially regain lower-limb function
3 Main Approaches
Epidural Spinal Cord Stimulation (ESCS)
Invasive
Multi-electrode array (16 electrodes) is implanted over the exposed dura (T11-L1 region)
Person with full SCI was able to stand for over 4 mins
Trancutaneous Spinal Cord Stimulation (TSCS)
Non-invasive
Stimulation using surface electrodes over spinal column
To provide a non-surgical method for assisting in standing & walking
Intraspinal Microstimulation (ISMS)
Highly invasive (future potential)