PT PAP 101: Electric Currents in Physiotherapy

PT PAP 101: Application of Direct and Alternative Current in Physiotherapy

• Course: PT PAP 101
• Topic: Application of Direct and Alternative current in Physiotherapy
• Date: December 25, 2024

Objectives

• Students will differentiate between direct and alternative currents.
• Students will understand electric conduction properties in the human body.
• Students will correlate Ohm's law to therapeutic current.
• Students will know methods for reducing skin resistance.
• Students will know the therapeutic benefits of direct and alternative currents.

Classification of Electric Currents

• Direction of flow:
  • Alternating current (AC): Flows in both directions.
  • Direct current (DC): Flows in one direction.
• Frequency:
  • Low frequency: 50-100 Hz (e.g., IDC, Faradic, galvanic, sinusoidal, TENS).
  • Medium frequency: 100-4000 Hz (e.g., interferential currents).
  • High frequency: >1 MHz (e.g., SWD, MWD, UST).
• Voltage:
  • Low voltage: <100 Volts
  • High voltage: >100 Volts

Concept of Electrotherapy Application

• Every living cell has a membrane potential (approximately -70 mV) with the inside of the cell being negative.
• Cell membrane potential relates directly with cell membrane transport mechanisms, particularly ion movement.
• Changes in membrane potential influence ion movement.

Electrotherapy Application Principle

• Sufficient energy can alter membrane behavior.
• Smaller energy levels can "tickle" the membrane, inducing excitement and cellular excitement.
• These processes are fundamental for graded and action potentials, with voltage changes across the membrane.

Low Frequency Current

• Alternating current with frequency 0-1000 Hz.
• Actions:
  • Stimulates nerves and muscles.
  • Produces muscle contractions and relaxation.

Types of Low Frequency Current

• Faradic current
• Galvanic current
• Sinusoidal current
• Dynamic current

What are Low Frequency Currents?

• Used primarily to stimulate nerves and muscles.
• Various currents exist in this frequency range.
• Commonly used:
  • Direct current: Longer duration (>10 msec), stimulates innervated muscles, repetition rate is faster (30 Hz).
  • Faradic current: Shorter duration (<10 msec), stimulates denervated muscles, repetition rate is slower (50-100 Hz).

Dynamic Current

• Low frequency current
• Can be semi-wave or full-wave sinusoidal
• 50-100 Hz frequency
• Combination of frequency and strength plus constant galvanic current creates modulations.
• Modulations have varying effects, like analgesic effects and sympathetic blockade.

Sinusoidal Current

• Alternating current with 50 Hz frequency.
• 10 ms pulse duration.
• Sine wave form.

Effect of Sinusoidal Current

• Effects are similar to faradic current (though possible differences exist).
• Marked sensory stimulation; more marked improvement of circulation.
• More painful, due to the longer stimulation time.

Therapeutic Effect of Direct Current

• Sensory changes (tingling, prickling, mild irritation, itching).
• Localized erythema (with prolonged stimulation).
• Pain relief.
• Acceleration of healing.
• Stimulates denervated nerves.
• Could lead to tissue destruction with high current densities.

Ohm's Law

• Current in a circuit is directly proportional to voltage and inversely proportional to resistance.
• Resistance depends on skin epidermis; larger cross-sectional area reduces resistance.

Alternating Current

• Bidirectional flow of electrons.
• No true positive/negative poles.
• Examples: Interferential stimulation, premodulated currents, pain relief, neuromuscular stimulation.

Practical Tips to Decrease Skin Resistance

• Decrease distance between electrodes.
• Increase electrode size.
• Minimize air electrode interface.
• Use electrode gel or moisten electrodes.
• Pre-warm skin.

Conductor

• Substance that transports electrical charge.

Higher Conductance Materials

• Silver, Copper
• Electrolyte Solutions
• Blood cells (high ionic content)
• Inner skin layer
• Nerves
• Muscle fibers
• Cell membranes

Low Conductance Materials

• Air, Wood, Glass, Rubber
• Bone
• Cartilage
• Tendons
• Ligaments
• Outer skin layer (keratinized epithelium acts as an insulator)

Frequency (in Hz)

• Direct current (DC)/ Galvanic
• Interrupted direct current (faradic current)
• Transcutaneous electrical nerve stimulation (TENS)
• High-voltage pulsed current (HVPC)
• Didynamic current
• Interferential current
• Russian current
• Shortwave diathermy (SWD)
• Ultrasound (US)
• Individual twitch (<20 Hz)
• Spinal pain modulation (60-120 Hz)
• Supra-spinal pain modulation (≤20 Hz)

Effect of Electrical Stimulation

• Musculoskeletal system: Muscle excitation, contraction, increase in muscle strength/endurance, increased muscle blood flow, muscle fiber hypertrophy.
• Wound healing: Increased capillary permeability and blood flow, macrophage/leucocyte and fibroblast/osteoblast activities, bactericidal effects, reduced edema.
• Pain perception: Modulation of pain perception through central and peripheral mechanisms.

High Frequency Current (HFC)

• Mechanism: Transformation of absorbed electrical energy into heat (Joule's law).
• Heat production depends on the application method.

Mechanism of Heat Production Using HFC

• Capacitors: Store electrical energy in an electric field between plates.
• Induction field: Strength of magnetic field depends on current through conductor.
• Eddy currents: Generated by changing magnetic fields; circulate in closed loops.

Summary

• Low frequency currents for muscle and nerve stimulation.
• Medium frequency currents for muscle re-education, pain relief, edema drainage.
• High frequency currents for deep heat production.