Electricity in Electrotherapy

1. Definition

2. Basic Physics of Electricity (Relevant to Electrotherapy)

2.1 Atom and Charge

• Every atom has a nucleus (protons = positive charge) surrounded by electrons (negative charge).
• Ions are charged particles formed when atoms gain or lose electrons - these carry current through biological tissues.
• Living tissue is an electrolyte medium: rich in Na⁺, K⁺, Ca²⁺, Cl⁻ ions that conduct electricity.

2.2 Electric Current (I)

• The flow of charged particles (electrons in metal, ions in tissue) through a conductor.
• Unit: Ampere (A) - in therapy, milliamperes (mA) and microamperes (µA) are used.
• Formula: I = Q / t (charge per unit time)

2.3 Voltage / Potential Difference (V)

• The driving force that pushes current through tissue.
• Unit: Volt (V)
• Higher voltage = greater ability to push current through high-resistance tissue.

2.4 Resistance (R) and Impedance (Z)

• Resistance (DC): opposition to current flow. Unit: Ohm (Ω)
• Impedance (AC): total opposition to AC flow (includes capacitive reactance of cell membranes).
• Skin has high impedance; deeper tissues (muscle, nerve) have lower impedance.
• Ohm's Law: V = I × R

2.5 Power (P)

• P = V × I (Watts)
• Relevant for heat produced during high-frequency therapy (diathermy).

2.6 Frequency (f)

• Number of cycles per second. Unit: Hertz (Hz)
• This is one of the most important parameters in electrotherapy:
  • Low frequency (< 1000 Hz): nerve and muscle stimulation
  • Medium frequency (1,000 - 100,000 Hz): deeper penetration, less skin resistance
  • High frequency (> 100,000 Hz): heat production (diathermy)

2.7 Waveform

• Monophasic (DC): current flows in one direction only
• Biphasic (AC): current alternates direction
• Pulsed: interrupted bursts of mono- or biphasic current

2.8 Pulse Parameters

3. Types of Therapeutic Electricity (Current Types)

3.1 Direct Current (DC) - Galvanic Current

• Continuous, unidirectional flow of current.
• No change in polarity.
• Historically called galvanic current (after Luigi Galvani).
• Effects:
  • Chemical effects at electrodes (electrolysis)
  • Ion migration through tissues
  • Stimulates denervated muscle (requires long pulse duration: 10-300 ms)
• Therapeutic uses:
  • Iontophoresis - drives charged drug molecules through the skin using polarity
  • Stimulation of denervated muscles (peripheral nerve injuries)
  • Wound healing (promotes cell migration)
  • Chronic pain (low-intensity)

3.2 Alternating Current (AC)

• Current reverses direction periodically in a sinusoidal or other wave pattern.
• No net ion migration.
• Types by frequency:
  • Low-frequency AC (Faradic current, 50-100 Hz): muscle stimulation with intact nerve supply
  • Medium-frequency AC (1,000-10,000 Hz): less skin resistance, deeper penetration
  • High-frequency AC (>100,000 Hz): produces heat (diathermy, shortwave)
• Therapeutic uses:
  • Muscle strengthening and re-education (EMS)
  • Pain relief (TENS)
  • Deep heating (diathermy)
  • Interferential therapy (uses two medium-frequency AC beams)

3.3 Pulsed Current

• Interrupted bursts of DC or AC - current flows for brief intervals then stops.
• Can be monophasic pulsed (modified DC) or biphasic pulsed (modified AC).
• Most modern clinical devices use pulsed current.
• Sub-types:
  • Surged faradic: intensity surges up and down - resembles voluntary muscle contraction
  • Interrupted galvanic: DC interrupted repeatedly - used for denervated muscle
  • High-voltage pulsed current (HVPC): twin peaks, microsecond pulses - wound healing and edema

4. Common Electrotherapy Modalities and How They Work

4.1 TENS - Transcutaneous Electrical Nerve Stimulation

• Current type: Pulsed biphasic
• Frequency: 2-150 Hz
• Mechanism:
  • High-frequency TENS (Conventional): activates large-diameter Aβ fibers → Gate Control Theory (closes the pain gate in the dorsal horn)
  • Low-frequency TENS (Acupuncture-like): activates Aδ/C fibers → releases endorphins and enkephalins
• Uses: Chronic and acute pain, back pain, arthritis, neuropathic pain, labor pain

4.2 Interferential Current Therapy (IFC)

• Current type: Two medium-frequency AC currents (e.g., 4,000 Hz and 4,100 Hz)
• Mechanism: The two currents intersect in tissue and create a beat frequency (100 Hz in this example). This low-frequency interference current penetrates deeply with minimal skin resistance.
• Uses: Deep pain, inflammation, muscle spasm, postoperative pain, joint injuries

4.3 Neuromuscular Electrical Stimulation (NMES) / EMS

• Current type: Pulsed biphasic or faradic
• Mechanism: Depolarizes motor nerve → muscle contraction. Prevents disuse atrophy.
• Uses: Muscle weakness, post-surgical rehabilitation, stroke rehabilitation, prevention of DVT

4.4 Functional Electrical Stimulation (FES)

• Specialized NMES that activates muscles in a coordinated sequence to restore function.
• Uses: Foot drop, spinal cord injury, hemiplegic gait

4.5 Iontophoresis

• Current type: DC (galvanic)
• Mechanism: Uses polarity of DC to drive ionized drug molecules through the skin. Positive drugs are pushed in under the positive electrode (anode), negative under cathode.
• Uses: Local anti-inflammatory drug delivery (dexamethasone), antibiotics, calcium for muscle spasm

4.6 Shortwave Diathermy (SWD)

• Current type: High-frequency AC (~27.12 MHz)
• Mechanism: Oscillating electric field causes molecular vibration and ionic oscillation → generates deep heat within tissues
• Uses: Deep muscle and joint heating, chronic arthritis, muscle spasm, pre-exercise warming

4.7 Transcranial Direct Current Stimulation (tDCS)

• Current type: Weak DC (1-2 mA)
• Mechanism: Modulates resting membrane potential of cortical neurons (anodal = excitatory, cathodal = inhibitory)
• Uses: Neurological rehabilitation, stroke, chronic pain modulation, research

4.8 Microcurrent Electrical Therapy (MET)

• Current type: DC at microampere level (< 1 mA, usually 10-500 µA)
• Mechanism: Mimics the body's own bioelectric currents → promotes ATP synthesis and protein synthesis at cellular level
• Uses: Wound healing, tissue repair, facial rehabilitation

5. Importance of Current Parameters in Treatment

6. Clinical Uses of Electrotherapy

Pain Management

• Acute and chronic musculoskeletal pain (TENS, IFC)
• Neuropathic pain, sciatica, back pain
• Post-operative pain
• Arthritis, tendinitis, bursitis

Muscle Rehabilitation

• Prevent disuse atrophy after injury or surgery (EMS)
• Re-educate muscles after nerve injury (faradic/NMES)
• Improve strength and endurance
• Restore function in neurological patients (FES for foot drop, stroke)

Wound Healing and Tissue Repair

• Microcurrent, HVPC - promote cell migration and angiogenesis
• Iontophoresis for local drug delivery into wounds
• Reduce edema (HVPC)

Neurological Conditions

• Stroke rehabilitation (FES, tDCS, NMES)
• Spinal cord injury (FES)
• Peripheral nerve injury (galvanic to denervated muscle)
• Cerebral palsy (reducing spasticity)

Circulatory and Inflammatory Conditions

• Reduce inflammation and swelling (IFC, TENS)
• Improve local blood circulation
• Lymphedema management

Orthopedic Conditions

• Fracture healing (PEMF - pulsed electromagnetic field)
• Ligament and tendon injuries
• Pre-surgical conditioning, post-surgical recovery

7. Contraindications (Safety Summary)

• Cardiac pacemakers or implanted electronic devices
• Over the chest or heart
• Pregnancy (abdomen/lower back)
• Active malignancy in treatment area
• Thrombosis or active bleeding
• Skin infections, open wounds (except specific wound-healing protocols)
• Impaired sensation in the treatment area (risk of burns)
• Epilepsy (transcranial stimulation)

Summary Table