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.