Electrical Stimulation Flashcards
What is the ‘Triad’ in EStim?
The patient, the therapist and the machine.
What are the roles of biophysical agents?
- Control pain, oedema, inflammation
- Facilitate tissue healing
- Reeducate lost or impaired motor function
- Control symptoms to facilitate other physiotherapeutic interventions: ROM, Manual Therapy, Muscle Strengthening, Motor Re-education.
What are the specific roles of biophysical agents that apply to neurorehabilitation?
- Control Pain
2. Reeducate lost or impaired motor function
What are the Types of Electrical Modalities?
- Sensory level stimulation:
- TENS: Transcutaneous electrical nerve stimulation is used for pain control and management. - Motor level stimulation:
-NMES: neuromuscular electrical stimulation: muscle re-education, muscle strengthening.
(No active contraction)
-FES: functional electrical stimulation: muscle substitution.
(Functional active movement performed during EStim- ideal in neurorehab).
What are the Therapeutic effects of ESTIM?
- Decrease or control pain
- Decrease muscle spasms
- Increase force/function
- Electrodiagnosis
For what conditions or problems is EStim indicated?
- Musculoskeletal problems: sports injuries and traumatic/overuse injuries.
- Neurological Problems:
- Chronic Pain
- Muscle weakness or loss of function
- Muscle re-education
- Spasticity management - Other: Wound Healing and Obstetrics.
Review of Electric Currents and Action Potentials:
1) Overview
2) What is the basis for nerve communication?
3) What is the baseline polarization of the cell membrane?
1) Depolarization of a cell membrane creates an AP that get propagated down a muscle or nerve to generate a stimulus for movement or sensation.
2) Movement of ions across the cell membrane via sodium and potassium channels creased at depolarization that initiates an AP.
3) The inside is more negatively charged than the outside by (-60 to -90 mV)
What is the sequence of nerve depolarization?
Resting: All channels closed. When an adequate stimulus arrives (such as EStim):
1. Na channels open and Na flows in.
- RMP reaches +30 mV, K channels open and permeability to Na decreases.
- Membrane repolarizes and Ap is propagated down the neuron.
How can an action potential be propagated down a neuron?
Depolarization in one area of a neuron stimulates propagation down an axon by causing adjacent intracellular potentials to reach threshold and activate Na channels.
Absolute Refractory Period: Time during which another stimulus given to a neuron will not stimulate the neuron.
Relative Refractory Period: Time during which a stronger then normal stimulus is needed to elicit an AP.
-During relative refractory period the nerve can be excited by a graded (increasing) stimulation. This is the mechanism for propagating AP along myelinated nerve fibres.
- How are muscles stimulated by neurons?
2. What is excitation-contraction coupling?
- Neurons synapse at the muscle and release Ach, which is responsible for depolarization of the muscle membrane by activating Na channels.
- Neural excitation causes Ach release which elicits AP in muscle. It is the excitation of the muscle (AP) that causes changes in the cell resulting in contraction (coupling of excitation AP to muscular contraction):
- Muscle AP reaches SR via transverse tubular system.
- The SR releases Ca2+ which binds to troponin.
- Troponin binds to tropomyosin.
- Allowing interaction b/w actin and myosin.
What are the steps for: A. Initiation of muscle contraction?
B. Relaxation.
A.
- Neuron sends impulse releasing ACh.
- Ca2+ ions are released and actin exposes active sites.
- Myosin cross bridges attaches to actin and sarcomeres shorten.
- Muscle shortens and contracts.
B.
- AP stops.
- Ca 2+ pumped back into SR by Ca2+ activated ATPsae.
- Troponin inhibition ceases
- Actin-myosin interaction stops.
- How does the activation phase compare to the contraction-relaxation phase?
What happens when a muscle is:
1. maximally stimulated once?
- Second neural impulse occurs after muscle has relaxed?
- Second neural impulse occurs before the muscle has relaxed?
- Subsequent impulse occurs during the contraction time of the first?
- Activation=5ms more rapid than the contraction-relaxation phase 100ms.
- Twitch is produced
- A second twitch is produced.
- Partial summation
- Tetanic contraction
Basically to get a tetanic contraction you have to have temporal summation where a subsequent neural impulse occurs during the activation phase of the first. (see diagram).
20 Hz lots of impulses, 40 Hz tetanic contraction.
W/ increase in frequency there may be a small increase in force, but once tetany has been achieved, this increase is negligible.
- What is rate coding?
- What sort of relationship is the force-frequency relationship?
- What frequency is needed for max titanic contraction?
- What are lower frequencies needed for?
- What happens with higher frequencies?
- The frequency of the EStim current selected in order to generate a certain amount of force.
- Sigmoidal.
- 30-80 Hz needed for max titanic contraction.
- Lower frequency required to produce tension under voluntary action b/c you do not want to override the active contraction of the muscle. This frequency depends on the muscle, lower frequency for endurance muscles and higher frequency for faster twitch muscles.
Soleus 11 Hz vs Biceps 30 Hz - Higher rate coding leads to higher fatigue.
What types of Estim machines can PTs use?
- Portable devices (NMES)
2. Multifunctional machines (multi-stim unit (Us, NMES)
- What types of electrodes can be used?
2. Where should the electrodes be placed?
- Self-adhesive pre-gelled, carbon rubber (add conductive medium), metal electrodes (sponge and water).
- The farther apart the deeper the current, the closer you get to the nerve. So it depends on what you are trying to stimulate. Muscle: Put them closer together. Never: Farther Apart.
