Electric Stimulation in Physical Therapy

Electric Stimulation in Physical Therapy

• Electric Stimulation (ES) is the application of therapeutic electrical currents to excitable tissues. ES aims to generate muscle contraction, stimulate sensory nerves for pain control, and create electrical fields for injury healing.
• Basic Physics of Electrotherapy: All matter contains atoms with charged particles called ions. The net movement of electrons constitutes an electrical current.
• Electrical Potentials: A difference in electrical potential creates an electrical current.
  • A battery has a higher potential at one terminal compared to the other, resulting in a flow of charges from the higher to lower potential.
• Current Flow requires a source of energy and a conducting pathway.
  • Conductors offer little resistance to current flow.
    • Metals like copper, gold, and silver, along with electrolyte solutions, have free electrons and facilitate conductivity.
  • Insulators resist current flow.
    • Air, wood, and glass have fewer free electrons and limit conductivity.
• Current Intensity (Ampere, mA, µA): Measures the movement of electrons per second.
  • 1 Ampere = 1 Coulomb per second.
  • 1 milliampere (mA) = 1/1000th of an Ampere.
  • 1 microampere (µA) = 1/1,000,000th of an Ampere.
• Ohm's Law: Relates current, voltage, and resistance. Current intensity is directly proportional to voltage and inversely proportional to resistance.
• Factors Affecting Resistance:
  • Material Composition: High water content reduces impedance and improves conductivity (e.g., nerve and muscle). Bone, fat, tendons, and fascia have lower water content and act as insulators.
  • Body Temperature: Increased temperature promotes conductivity by increasing surface salt content and moisture.
  • Injury and Disease: Resistance decreases in open wounds and abrasions.
• Minimizing Impedance:
  • Cleaning the skin with alcohol removes dirt and body oils.
  • Removing excess hair reduces impedance.
  • Warming the area before stimulation increases conductivity.
• Electrical Current Parameters:
  • Horizontal Axis (X): Represents time or duration (millisecond-microsecond).
  • Vertical Axis (Y): Represents magnitude or intensity (milliampere-microampere).
  • Isoelectric Zero: Demarcation between positive and negative charge, where no net charge exists.
• Waveform: Visual representation of the current pulse.
  • Shape, Amplitude (strength), and Duration (length of time) are key characteristics of the waveform.
• Current Direction (Polarity):
  • Direct Current (DC): Constant direction, positive or negative, monopolar.
    • Can cause electrolysis (breakdown of water molecules) due to constant polarity.
  • Alternating Current (AC): Rapidly changes direction, positive and negative, multidirectional.
    • Minimizes risk of electrolysis and chemical reactions due to rapid switching.
    • Reduces skin impedance, improving tissue stimulation efficiency.
• Current Intensity and Nerve Fiber Diameter:
  • Lower Intensity: Stimulates thicker, large-diameter nerves (e.g., motor nerves).
  • Higher Intensity: Stimulates thinner, small-diameter nerves (e.g., sensory nerves).
• Pulse Duration and Nerve Fiber Diameter:
  • Longer Pulse Duration: Stimulates thicker fibers.
  • Shorter Pulse Duration: Stimulates thinner fibers.
• Amplitude (Peak Amplitude): Refers to the depth of current penetration.
  • High peak amplitude penetrates deeper into the tissues.
• Rate of Rise and Decay of Pulse:
  • Rise Time: How quickly the pulse reaches its maximum amplitude in each phase.
  • Decay Time: How quickly the pulse returns to baseline from its peak.
  • Faster rise time promotes excitability in nervous tissue due to the "accommodation phenomenon" (nerve fibers becoming less responsive to sustained stimulation).

Electrotherapy Waveform Parameters

• Direction/Polarity: Positive or negative.
• Shape: Rectangular, triangular, sinusoidal, etc.
• Duration: Time the current flows in one cycle.
• Intensity: Magnitude or strength of the current.
• Frequency: Number of pulses delivered per second (Hz).
• Burst Frequency: Number of bursts delivered per second.

Types of Electrical Currents

• Low Frequency (1-1000 Hz):
  • Stimulates both sensory and motor nerves.
  • Examples: Faradic current, Diadynamic current, High Voltage Pulsed Stimulation (HVPS), Transcutaneous Electrical Nerve Stimulation (TENS), Microcurrent.
• Medium Frequency (1000-10,000 Hz):
  • Primarily stimulates sensory and motor nerves through modulation.
  • Examples: Interferential currents, Russian currents.
• High Frequency (>10,000 Hz):
  • Does not stimulate sensory or motor nerves.
  • Primarily produces thermal effects.
  • Examples: Shortwave diathermy, microwave, ultrasound.

Key Considerations for Stimulation

• Action Potential: The mechanism by which electrical stimulation triggers nerve and muscle responses.
  • Involves changes in membrane potential due to movement of ions (sodium and potassium).
• Pulse Duration: Length of time the current flows in one cycle.
• Frequency: Number of pulses delivered per second.
• Burst Frequency: Number of bursts delivered per second.

This quiz covers the fundamentals of electric stimulation in physical therapy, focusing on the application of therapeutic electrical currents and the physics behind electrotherapy. Understand the role of electrical potentials, current flow, and the materials that facilitate or resist this flow. Test your knowledge about how electric stimulation can help in therapeutic settings.