Functional electrical stimulation (FES) Flashcards
What is FES used for?
Activating muscles
How does FES activate the muscle?
Electrodes are placed on the skin above the muscles. Then trains of electrical signals are sent through the muscle. The muscle motor nerves are activated, in turn activating the muscle
What gets activated first, nerves or muscles? Why?
Nerves, because they have a lower threshold
Which of the following is depolarised? Cathode or Anode?
Cathode
What is the effect of having unequal size of anode/cathode?
Makes current more or less dense, increasing precision.
Name one side effect of too high current
Skin burns
Explain the effect of higher amplitude or width of the pulses
Both lead to a stronger nånting
Explain “balanced asymmetric bipolar”
The compensating pulse is smaller (in amplitude) but longer in time to not activate the nerves under the anode side, eller nåt
True or false?
Larger pulse = larger contraction of muscle
False
Why are different motor units activated after each other?
So that the total tension in the muscle is “quite smooth”
How does FES activate the muscle in comparison to how the brain does?
Brain: Smaller motor units first
Electrical stimulation: Large motor units first, the same motor unit with every part, need higher frequencies
What is the biggest drawback of FES?
Fatigue. The muscle can no longer produce movement after ish 20 sec
What kind of control system is usually used for FES, and why?
Open loop, due to the complexity of the human body
How can FES be used for spinal cord injury specifically?
The potentials produced by the brain can be used in the affected body part, but signals must go around non-functioning body parts.
What are matrix electrodes used for?
Increase selectivity. For example, allowing to extend only one specific finger, for example, pointing with the index finger
What are the challenges with controlling muscle? Explain the specific issues for the following methods:
1. PID controller
2. Inverse plant model
Non-linearity and time invariant due to muscle fatigue
1. Poor results since the method is developed for linear systems
2. Some aspects cannot be reversed due to non-linearity
What frequencies does the brain vs FES use for activation?
Brain: 6-8Hz
FES: 20-40Hz
What is used to solve the issue with controlling muscle fatigue?
An adaption mechanism in the closed loop to direct model and inverse model
What is the primary target for nerve-muscle stimulation using FES?
Muscle nerves
What is the primary target for reflex simulation using FES?
Cutaneous sensory nerves
What is FET?
Therapy in which Paretic patients are asked to exercise functional tasks assisted
with a neural prosthesis that controls the opening, grasping, holding, and releasing
functions.
What does FET control (upper limb)?
The flexor and extensor
muscles
How often is FET done?
Daily, 30-minutes long sessions, during
three consecutive weeks.
What does FET control (lower limb)?
Targets Nociceptive Withdrawal Reflex to control Hip flexion, Dorsi-flexion, Inversion, Plantar flexion (tror jag man kan formulera det)