not finished MT3 Lecture 16: Implanted Walking Assist Systems for Foot Drop Flashcards
Explain slide 20 schematic b
The longer you pull, the longer the hook electrode and the saline and you get a longer recorded AP. because you get a longer stretch of receptive pathway
What is the reason for wanting to use fairly long (30mm) nerve cuffs to record nerve activity?
The amplitude of the signal recorded depends non-linearly on the length of the cuff. The longer the nerve cuff, the greater the nerve signal amplitude that can be recorded. To obtain maximal signal amplitudes, a cuff of length comparable to the wavelength of the action potential source should be used. As the cuffs are placed on large myelinated axons, a 30mm long cuff is appropriate.
if you make the cuff half he length of the action potential, you’ll get the largest ap?
Compare 3 methods of closing nerve cuffs
A: self-coiling variable lumen. connective tissue will invade the coil it if the cuff is not sutured shut. connective tissue bridge –> electrical shunting. cuff can flip itself open and nerve can come out of it if its not held together by sutures
He used B - suturing
- requires good seal, otherwise current leakage pathway. not good for stimulation or recording. signal can be contaminated as well
C: improved cuff closure method (he made this)
- two ends of cuff are interlocked. monofilament suture is placed in each interlocking mechanism to keep it closed. quicker than tying sutures.
slide 22
student of Dr. Hoffer:
measure response of ___
recorded tibial nerve activity
- discussed experimental set up and objective of study
- skin receptors would generate AP that would travel up tibial nerve.
built in natural sensor that can track the stance phase using a nerve cuff
skin indentation doesn’t follow force linearly.
as the skin gets squeezed, you get less and less change in skin indentation for similar amounts of force increase
nerve responds vigorously with low level of force change
when you slowly ramp down the force, the skin adapts but not very much,
you see that the nerve does not really respond very much to small changes in force decline. will respond vigorously when weight comes off
skin receptors are made to respond to changes from 0 to something
lays foundation to build prosthetic device to use this set up as a sensor
remember 2nd midterm about a runner…suddenly lost sensation in one toe.
- compression neuropathy from pounding impact on ground
- can’t feel anything on toe. feels like there’s a hole in the shoe
- lost all sensation towards the tip of the toe
- why did he think there was a hole in the shoe? cortically, suddenly, there was a lost in input
- remember ot review lecture 5 - and what happens to the cortex when something is not arriving
- the foot is like the hand
- remember to review that hand lecture.
why did the sensation go away evne though theres no repair of the peripheral nerve yet since its so slow
cortically, the sensation there is a hole went awya. silent synapse. cutaneous branch of tibial nerve that was not damaged will take over the cortex area
Restoration of use of paralyzed muscles using sensory nerve signals for state control of FES assisted walking
purpose: develop FES assisted walking system by paralyzing cat extensor and trying to apply stimulation when you “estimate” gait via recording of radial and median nerve EMG
proximal median blocking cuff: has a catheter that came out of the animal. This cuff allowed for the injection of short acting anesthetic directly into nerve and paralyze the nerve and leg lower to this nerve
distal median and radial recording cuff
- records nerve activity
proximal radial cuff: also recorded nerve actvitiy
results (before paralysis):
- nice EMG bursts - you can tell when they start and end. provides markers of start and end of stance and swing phase
- you can see early onset sharp peak in median and ulnar nerve that mark the stance and swing phase
- temporarily paralyzed the extensors of the upper limb by blocking nerve activity with anesthetic. this will cause the wrist to yield. the cat doesn’t place their wrist down when they walk (they tip toe). when you block activity to extensors, you ahve this yielding of the wrist. blocked motor but not sensory
applied electrical activity to assist cats gait based on gathering palmaris longus activity before paralysis.
Neurostep patents
Neurocuff:
4 channel cuff
* modular 4-channel design
* easy opening and secure closing
* thin flexible walls
- current flows through 2 reference electrodes (sink).
why did the cuffs have ridges? allowed for nice snug fit at time of implant that provided insulation while allowing for some swelling (edema - 1 week later) typical postoperative of the implantation and allow the nerve to grow into the cuff w/o compression (encapsulation in thin layer of connective tissue at 6-12 months) )(squeeze from all sides = compression; squeeze from some parts = allow it to change shape)
each of these electrodes would record or stimulate a portion of the nerve
Neurocuff benefits
- improved stimulation and sensory recording selectivity (each set records from a specific portion of nerve)
Lecture 32 - subuv noise amplifier technology
Requirements:
noise level less of a microvolt
power consumption less than 12 mW @ 5V
- since it must be on all the time
neurostep pilot study
- Study approved by Health Canada and five
research institutions. - Carried out in Vancouver, Jun 2003 to Feb 2004.
Case study - ex firefighter:
* Subject was a 70-yr-old male, 3 yr post-stroke,
with foot drop and severe hypotonia.
* Managed with a knee brace in addition to AFO (prevented hyperextension of the knee but also caused pain)
* Could only walk 5-10 m without fatiguing.
* Required a cane and contact guard assistance.
- right foot was good foot
Surgically implanted neurostep system
- A single 6-cm longitudinal incision in the posterior thigh was required.
- The Common Peroneal (CP) and Tibial nerves were cleared over 6 cm.
* measure circumference of nerve to determine cuff size
* cuffed both nerves
Nerve circumferences were measured using a flexible silicone ruler.
Appropriately sized NeurocuffsTM were selected.
- The Neurocuff closing suture was sealed with a cautery tip.
The nerves were protected with a Teflon® heat shield strip. - control unit was implanted in subcutaneous pocket in medial thigh . and incision was closed.
neurostep was turned on or off with a telemetry programming interface or a magnet (patient was given magnet)
- stimulation of channels 1 and 3 (out of 4 channels) gave the best combination of moving the foot forward and not everting or inverting. foot could be lifted enough for walking! :D.
results: disuse atrophy in the
paralyzed muscles was reversed and ankle
around day 30 we suddenly got substantial force around 50 N
electrical exercising protocol to build up of strength of very atrophied dorsiflexor muscles until suddenly he started producing substantial force. a week later you still got force but slightly yess (not sure why). 50 days later you got larger forces. substantial forces for walking
measured fatigue resistance as well (time to reach 70% of initial averaged force)
- done by stimulating every second or two and monitored force production
- 30 days in: took a minute to decline to 70%.
With application of NeurostepTM stimulation, fatigue resistance in
the ankle dorsiflexors also improved markedly during the 2nd month.
also on day 21, recorded tibial nerve signals during walking
slide 41: spending more time on right foot which was good foot. left foot had longer swing phase since it was weaker.
What did the subject say was the benefits of the neurostep?
- 5 weeks after implant, he no longer needed a knee brace.
- 10 weeks after implant, his gait had improved markedly.
- 6 months after implant, he regularly walked the length of his driveway and back
(250m) without fatiguing. - His balance control was greatly improved.
- Using Exercise Mode at home proved very useful. if you apply magnet for 30s, it will switch to exercise mode where it will turn automatically turn on and off periodically. helps to strengthen muscle
- The nerve stimulation was never painful, nor unpleasant. he liked the tingling as it proved that it was on and working
- He was appreciative of how much using the device had improved his mobility,
balance and lifestyle. - The battery ran out after 8 months; patient’s condition slowly deteriorated.
What happened after the battery ran out?
therapeutic effect, could still walk for a bit but then he slowly deteriorated as muscle atrophied due to lack of drive
unfortunately device didn’t get commercially approved so he never got a new one
however he went to alberta and stein fitted him for an external FES. not as convenient. old device was still in there but did not interfere with external FES
slide 44
What are the rquirements for nerve dimensions to place cuff?
answer: distance between natural separation level of 2 branches of sciatic nerve inside the thigh and the axis of the knee
there is this length of nerve that is available.
cannot separate connective tissue too close to knee joint as nerve must bend around knee
cuff must be placed high. if too far distal (and near knee joint) will cause loss of function
study: measured in 33 subjects the distance between natural separation point and axis of knee joint
knee to branch separatin level (SK) could vary between 5cm to more than 15cm
as a safety precaution, minimum should be 9cm to put a 3cm cuff.
only half the people tested would be eligible for nerve cuff. probably to establish eligibilty for cuff do an MRI to determine separatin level. taller people you would expect them to have a large separation level (but not confirmed).
where can you find neurostep?
CE mark approval in europe. although they didn’t market it
