Electrical Stimulation Lecture Notes

Electrical Stimulation: Introduction

• Electrical stimulation (e-stim) involves using electrical current to stimulate nerves or nerve endings that innervate muscles under the skin.
• It can be applied superficially or directly into muscles to enhance muscle function.
• The basic premise is that stimulating a peripheral nerve will transmit excitation along the nerve to the motor end plates, causing muscle contraction.
• Patients with central nervous system abnormalities but intact peripheral nerve function (e.g., post-stroke) may benefit.
• Current flows from one electrode, through the skin and tissues, to the second electrode, causing nerve depolarization.
• The negative electrode is the active electrode (cathode), and the positive electrode is the indifferent electrode (anode).

Terminology

• ES (Electrical Stimulation): General term for any type of electrical stimulation.
• TENS (Transcutaneous Electrical Nerve Stimulation): Applied across the skin for analgesic effect, without causing muscle contraction. Parameters are set for pain relief.
• NMES (Neuromuscular Electrical Stimulation): Stimulates peripheral nerves to cause sensory, motor, or noxious responses.
• TES (Therapeutic Electrical Stimulation): Parameters set to cause muscle contraction, aiming to improve movements.
• FES (Functional Electrical Stimulation): Used in time with attempted voluntary contraction to complete functional movements and tasks.

Benefits and Evidence

• Benefits patients with upper motor neuron lesions (stroke, MS, incomplete spinal cord injury, CP).
• Possible benefits:
  • Strengthening muscles or preventing disuse atrophy.
  • Maintaining or improving joint range of motion.
  • Facilitating voluntary movements.
  • Reducing oedema (through muscle pumping).
  • Decreasing spasticity or increasing activity of opposing muscle groups (adjunct to botulinum toxin).
• FES can induce plastic changes at a cortical level.
• FES creates a stronger contraction and may offer better outcomes compared to passive electrical stimulation because it trains dexterity and coordination.

Evidence of Effectiveness

• Small to moderate benefits for improving strength with electrical stimulation, but methodological issues exist in trials.
• Stroke Foundation guidelines: Electrical stimulation may improve strength after stroke (weak recommendation).
• Electrical stimulation may be used for walking, in addition to other therapies.
• Harlett et al. (2015) systematic review:
  • FES improves upper/lower limb activity compared to placebo or training alone.
  • Significant improvement in walking speed of 0.08 meters per second with FES compared to training alone.
  • High risk of bias in many trials due to lack of blinding.

Further Considerations for Stroke

• Spasticity: Low to very low quality evidence suggests electrical stimulation may be used.
• Swelling: Not commonly used clinically for swelling in stroke.
• Lack of consensus on optimal dosage, patient groups, treatment parameters, timing, or duration.
• Electrical stimulation is commonly used clinically due to being cheap, easy to use, and having few negative aspects.

Multiple Sclerosis

• Evidence for FES in MS includes improved gait speed, cost-effectiveness, quality of life, and possibly benefits for falls, spasm, and spasticity.
• Fatigue is a consideration: repeated muscle contractions can contribute to excessive fatigue.

Types of Stimulation

• Cyclic Stimulation: Repeatedly activates the muscle at a set duty cycle; used for shoulder subluxation and oedema. Machine cycles between on and off phase.
• Hand Switch Triggered Devices: On/off phases are manually controlled, allowing timing of contractions during activity.
• EMG Triggered Devices: EMG signal from a target muscle exceeding a threshold triggers electrical stimulation, augmenting movement. Requires some voluntary contraction.
• Pressure Triggered Devices: Pressure switch (e.g., in shoe) times muscle activation with gait.

Channel Selection

• Single Channel Devices: Use one pair of electrodes.
• Multichannel Devices: Use two or more pairs of electrodes simultaneously to stimulate multiple muscle groups; more common in the upper limb.
• Alternating or Synchronous Modes: Allow for reproduction of agonist/antagonist or synergistic muscle activity.
• Alternating Mode: Prevents problems associated with muscle imbalances; delay time between channel changeover can assist with voluntary movement.
• Synchronous Channel Mode: Reproduces synergistic muscle activity; useful for functional activities.

Precautions

• Circulatory insufficiency or poor blood pressure control.
• History of autonomic dysreflexia (T6 spinal cord injury or above): can cause a rise in blood pressure elicited by a noxious stimulus below the level of the lesion.
• Risk of dissemination (spreading current to unwanted muscles).
• Potential for exacerbation of existing conditions (e.g., cancer, infections, tuberculosis).
• Uncontrolled epilepsy.
• Challenges in communication, cognition, or behaviour.
• Broken skin or wounds; care needed with dry, cracked, flaky, or fragile skin.
• Sensory loss: Sharp/blunt test needed to determine if patient can feel the current.

Contraindications

• Pregnancy, especially over the abdomen.
• In-built electrical devices (e.g., pacemakers).
• Lower motor neuron lesion, which would include damage to the nerves in limbs or nerve root in those with spinal cord injury below T12, unless there is some incomplete connection.
• Polio, motor neuron disease, Guillain Barre syndrome (depending on recovery).
• Ankle fusion (if considering dorsiflexers).

Communication and Consent

• Explain the procedure, expectations, and sensations to the patient.
• Check sharp/blunt discrimination.
• Ask if they can feel something and if they feel anything else.
• Instruct the patient not to move or touch equipment.
• Use consent questions: Do you understand? Do you have any questions? Are you happy to proceed?

Treatment Parameters

• Waveform
• Pulse duration (microseconds)
• Frequency (Hertz)
• Pulse amplitude (millivolts or milliamps)
• Ramp up and ramp down time
• On and off time
• Intensity, threshold and fall time

Waveform

• Represents amplitude and direction of current flow over time.
• Pulsed Current: Intermittent current flow interrupted by periods of no current flow.
  • Monophasic: Current flows in one direction only; polarity does not change; rectangular waveform.
  • Biphasic: Bidirectional flow of current with two distinct phases.
    • Symmetrical: Two identical phases with equal and opposite current flow; no net charge accumulation.
    • Asymmetrical: Polarity changes but phases are not the same.
      • Balanced: Charge in each phase is equal and opposite; no net charge accumulation.
      • Unbalanced: Phases have different amounts of charge; net balance of charge on the skin.
• Biphasic asymmetrical pulse current is the most common type used in portable NMES units.
• Symmetrical biphasic pulse currents are the most comfortable and preferred to stimulate large muscle groups.

Pulse Duration

• Time elapsed from when the current leaves the zero line until it returns back to baseline, includes all phases of a biphasic current.
• Adjust for individual comfort.
• Shorter pulse width means increased comfort due to decreased average current.
• Common settings: 200-300 microseconds.
• Shorter pulse duration is preferable because it's easier to discriminate between sensory, motor, and pain nerves.
• Examples:
  • 70-80 microseconds: superficial muscles of the face
  • 70-90 microseconds: superficial muscles of the hand
  • 200-350 microseconds: muscles of the leg
  • 150-300 microseconds: muscles of the arm
• The shorter the pulse duration, the more superficial the treatment received, and the greater amplitude required to activate the nerve fibres.

Frequency

• Number of pulses delivered per second (Hertz).
• Machines allow a range from 2 Hz to 200 Hz.
• Must be enough to cause a tetanic contraction of the muscle.
• 1-20 Hz: Series of single twitches.
• One hertz, you will feel one twitch per second. At 10 Hz, you will feel a tremor of the muscle as 10 twitches per second occur.
• 35-50 Hz: Muscle contracts continuously (tetanic contraction); affects Type IIa and some IIb fibers.
• For preventing atrophy or targeting slow-twitch fibers, use 30-35 Hz.
• Higher frequencies (above 100 Hz) have little additional effect because pulses occur in the refractory period.

Ramp Up and Ramp Down Time

• Ramp Up Time: Time for stimulating current to reach set amplitude (1-2 seconds).
• Ramp Down Time: Time for stimulating current to return to zero intensity (1-2 seconds).
• Ramp up causes gradual excitation of nerve fibers, increasing comfort.
• Electrical stimulation machines have a range of about 0.3 to 9.9 seconds for ramping.
• Ramp down allows gradual unexcitation of nerve fibres and slow release or lowering of the part.

On and Off Time

• On Time: Time the patient is receiving a stimulus.
• Off Time: Rest time; should be at least as long as the on time, or longer.
• If a patient is likely to fatigue easily, then longer off times are needed.
• A guide is off time between each train of pulses is commonly double the on time because the parotid muscles need greater time for recovery.
• Duty Cycle: Ratio of on time to the sum of on and off time.

Threshold

• Relevant to triggered devices.
• Set the threshold to encourage the patient to work as hard as possible voluntarily.
• EMG-triggered: encourage maximal activation before the device triggers.
• Pressure, positional or outcome-based options: encourage the most activity available from the patient before the device would trigger and assist them.

Intensity

• Needs to be sufficient to create a contraction.
• Settings depend on the patient's sensation and skin resistance.
• Higher intensity recruits more motor units but can spread to unwanted muscles and cause faster fatigue.
• Machines are generally limited to less than 50 milliamps.
• A wider pulse duration may allow for a lower amplitude which can lead to a more patient comfort.
• Ask the patient to tell you when they can first feel something (sensory information).
• Turn up the intensity slowly looking for the desired muscle contraction and continuing to ask the patient about their comfort.
• Do not tune up the intensity during an off period, or when the device is in ramping phase.

Skin Preparation

• Check for broken areas of skin.
• Decrease skin's impedance by:
  • Shaving/cutting hair.
  • Washing area with warm, soapy water or alcohol wipe.
  • Ensuring skin is clean and dry.
• Check skin condition below electrodes after use.

Electrodes

• Self-Adhesive Electrodes:
  • Pre-gelled, convenient, but lose adhesive quality with repeated use.
  • Uneven distribution can increase the risk of an electrical burn and increase patient discomfort.
  • Cannot be used between patients.
  • Wipe with alcohol gel to extend life and improve adherence.
• Carbon Rubber Electrodes:
  • Used with electrode-specific gel and held in place with tape/straps.
  • Can be used many times and cleaned between patients.
  • Electrode sponges moistened with tap water may be used to couple carbon rubber electrodes to the skin.
  • Secure firmly to avoid uneven current distribution.
  • The Bioness now also uses a felt based type electrode and again this is only to be able to be used with one patient at a time.

Electrode Size and Placement

• Size: Selected based on the size of the target muscle and the required depth and spread of the current.
  • Larger electrodes promote deeper current penetration.
  • 5x5 cm: medium-sized muscles (forearm, calf, shoulder).
  • 5x10 cm or 10x10 cm: larger muscles (quadriceps, hamstrings, glutes).
• Placement: Where the strongest, most comfortable contraction is felt/observed; generally over the anticipated motor point and distal to this point in the same muscle.
• If electrodes are close together, there will be a superficial flow of current.
• If the electrodes are further apart, there will be a deeper flow of current.
• If a sub optimal response is achieved then we move the electrode, only moving one at a time.
• If limited response, improve skin preparation and check stimulation parameters.
• Increase contact of the electrode to the skin by applying more pressure using tape strapping or bandages.

Dosage

• No known set recommendations are backed by evidence in scientific literature.
• Strengthening: reasonable to work more so to fatigue.
• Glenohumeral subluxation: low-level cyclic stimulation over a longer time.
• Short and few sessions are known to be ineffective.

Common Parameter Settings

• Movement Reeducation and Muscle Strengthening:
  • Frequency: 35-50 Hz (tetanic contraction).
  • Pulse Width: 200-300 microseconds.
  • Ramp Up/Down Time: applied to the specific situation and patient.
  • Biphasic Waveforms.
• Recommended Time:
  • Movement re education: 15-20 minutes per day
  • Muscle strengthening: 30 minutes two to three times a day.
  • Intensity or amplitude should be high enough to cause a muscle contraction but remain comfortable.

Electrode Placement Examples

• Quadriceps: Large electrodes over VMO and proximal vastus lateralis; avoid rectus femoris.
• Hamstrings: Video demonstration.
• Tibialis Anterior/Dorsiflexion: Motor point or muscle belly in the more proximal tibialis anterior or nerve at the corner of the fibula head and within tibialis anterior muscle.
• Shoulder Subluxation: Electrodes on supraspinatus and posterior deltoid, frequency of 30 Hz, a pulse width of two fifty microseconds, a longer on time of thirty seconds, and an off time of only five seconds, still with a ramp of one second up and down at the biphasic wave form, but with treatment starting at one hour a day and working up to as much as six hours a day for this condition.
• Extension of Wrist and Fingers: Video demonstration.
  • The negative electrode of the asymmetric waveform is placed over the finger extension motor point but enlarged to allow activation of wrist extensors.
  • Positive electrode remains over the tendinous portion of the forearm.

NeuroTrack Device

• Dual channel device with customizable settings (program 15).
• Understanding how the device works and being able to adjust the settings is essential to obtain accurate stimulation and muscle contraction.

L 300 GO Bioness System

• FES system capable of timing electrical stimulation with the gait cycle.
• Accelerometer triggered; available with thigh and calf cuff (quads, hamstrings, tibialis anterior).
• System components will appear as green squares on the leg illustration.
• Wetting the cloth electrode, just run it under the cap.
• Turn on the binus.
• You'll see the green flashing light.
• Then hold the minus and the plus button down together.
• You'll see it flashing different colors.
• Then you're gonna turn on the MyBindness app, and the buy MyBindness app will come up like this, and then you'll hit pair.
• The L 300 GO is specifically designed to meet clinician and home user needs through innovative product features and expanded configurations.