Electrode Placement in Electrical Stimulation

Electrode Placement

• Importance: proper electrode placement is crucial for effective electrical stimulation
• Factors to consider:
  • Muscle belly vs. tendon vs. nerve
  • Proximity to target muscle or nerve
  • Avoiding bony prominences and sensitive areas
• Types of electrodes:
  • Surface electrodes (e.g. self-adhesive pads, carbon electrodes)
  • Insertional electrodes (e.g. needle electrodes, fine wire electrodes)
  • Implantable electrodes (e.g. epidural, cortical)

Stimulation Waveforms

• Types of waveforms:
  • Monophasic (single polarity)
  • Biphasic (alternating polarity)
  • Polyphasic (multiple polarity changes)
• Parameters to adjust:
  • Pulse width (duration)
  • Pulse amplitude (intensity)
  • Frequency (rate of stimulation)
  • Duty cycle (ratio of stimulation to rest time)

Muscle Contraction

• Mechanisms:
  • Direct muscle stimulation (DMS)
  • Indirect muscle stimulation (IMS) via nerve stimulation
• Types of muscle contractions:
  • Isometric (constant length)
  • Isotonic (constant force)
  • Eccentric (lengthening)
  • Concentric (shortening)
• Applications:
  • Muscle strengthening and rehabilitation
  • Muscle relaxation and spasticity management

Pain Modulation

• Mechanisms:
  • Gate control theory (activation of inhibitory neurons)
  • Endogenous opioid release
  • Descending pain modulation (brainstem-mediated)
• Applications:
  • Chronic pain management
  • Post-operative pain relief
  • Pain management in rehabilitation settings

Nerve Conduction

• Mechanisms:
  • Action potential generation and propagation
  • Saltatory conduction (jumping between nodes of Ranvier)
• Applications:
  • Nerve conduction studies (NCS) for diagnosis and monitoring
  • Nerve stimulation for muscle contraction and pain modulation
  • Neuroprosthetics and neural interfaces

Electrode Placement

• Proper electrode placement is crucial for effective electrical stimulation
• Factors to consider when placing electrodes include:
  • Targeting the muscle belly, tendon, or nerve
  • Proximity to the target muscle or nerve
  • Avoiding bony prominences and sensitive areas
• Three types of electrodes are used:
  • Surface electrodes (e.g. self-adhesive pads, carbon electrodes)
  • Insertional electrodes (e.g. needle electrodes, fine wire electrodes)
  • Implantable electrodes (e.g. epidural, cortical)

Stimulation Waveforms

• Three types of waveforms are used in electrical stimulation:
  • Monophasic (single polarity)
  • Biphasic (alternating polarity)
  • Polyphasic (multiple polarity changes)
• Four parameters can be adjusted to customize stimulation:
  • Pulse width (duration)
  • Pulse amplitude (intensity)
  • Frequency (rate of stimulation)
  • Duty cycle (ratio of stimulation to rest time)

Muscle Contraction

• Muscle contraction can occur through:
  • Direct muscle stimulation (DMS)
  • Indirect muscle stimulation (IMS) via nerve stimulation
• Four types of muscle contractions can occur:
  • Isometric (constant length)
  • Isotonic (constant force)
  • Eccentric (lengthening)
  • Concentric (shortening)
• Applications of muscle contraction include:
  • Muscle strengthening and rehabilitation
  • Muscle relaxation and spasticity management

Pain Modulation

• Pain modulation occurs through:
  • Gate control theory (activation of inhibitory neurons)
  • Endogenous opioid release
  • Descending pain modulation (brainstem-mediated)
• Applications of pain modulation include:
  • Chronic pain management
  • Post-operative pain relief
  • Pain management in rehabilitation settings

Nerve Conduction

• Nerve conduction involves:
  • Action potential generation and propagation
  • Saltatory conduction (jumping between nodes of Ranvier)
• Applications of nerve conduction include:
  • Nerve conduction studies (NCS) for diagnosis and monitoring
  • Nerve stimulation for muscle contraction and pain modulation
  • Neuroprosthetics and neural interfaces

Electrode Placement

• Electrodes for TENS are placed on the skin surface, typically 1-2 cm apart
• EMG electrodes are placed on the skin surface or inserted into muscle tissue to record muscle activity
• Intramuscular stimulation involves inserting electrodes directly into muscle tissue

Muscle Contraction

Depolarization and Recruitment

• Electrical stimulation causes muscle fibers to depolarize, leading to muscle contraction
• Stimulation recruits muscle fibers to contract, increasing force production

Stimulation Frequency

• Stimulation frequency affects muscle contraction force and speed
• Low frequency (1-20 Hz) produces slow, low-force contractions
• High frequency (20-100 Hz) produces fast, high-force contractions

Stimulation Waveforms

Monophasic, Biphasic, and Triphasic

• Monophasic waveforms consist of a single pulse of electrical energy with anodal (positive) or cathodal (negative) polarity
• Biphasic waveforms consist of alternating pulses of anodal and cathodal polarity
• Triphasic waveforms combine anodal, cathodal, and neutral phases

Pulse Duration

• Pulse duration varies from 50-500 μs and affects stimulation efficacy and comfort

Pain Modulation

Gate Control Theory and Endogenous Opioids

• Electrical stimulation activates large-diameter nerve fibers, "closing the gate" to pain transmission
• Stimulation releases endogenous opioids, reducing pain perception

Conditioned Pain Modulation

• Repeated stimulation can lead to long-term pain modulation and reduced pain sensitivity

Nerve Conduction

Action Potential and Conduction Velocity

• Electrical stimulation generates action potentials in nerve fibers
• Conduction velocity is the speed of action potential propagation, affected by fiber type and stimulation parameters

Fiber Recruitment

• Stimulation recruits nerve fibers in order of size, from largest to smallest diameter
• Reverse recruitment occurs when stimulation recruits smaller fibers first, depending on stimulation parameters

Learn about the importance and factors to consider for proper electrode placement in electrical stimulation, including different types of electrodes.