Electrotherapy Effects and Indications

Effects, Indications and Contraindications of Electrotherapy

• Pain Relief: TENS and IFC are preferred devices.
• Muscle Re-education: NMES, Russian stimulation for disuse atrophy, muscle strengthening, relaxation of muscle spasm, increase range of motion, increase circulation, decrease chronic edema, and orthotic substitution (FES).
• Tissue Healing: DC for drug delivery (iontophoresis) and denervated muscle stimulation. HVPC for decreasing acute edema and wound healing.
• Contraindications: Pacemaker (potentially other implanted devices), malignancy, seizure disorder, cardiac arrhythmia, over a pregnant uterus (except during labor and delivery).
• Safety: Avoid transcerebral, transthoracic, or anterior neck electrode placement. Refer to “Spotlight on Safety” pg. 644 for safe operation guidelines.

Muscle and Nerve Cell Excitation

• The resting membrane potential (RMP) is negative due to the inside of the cell being more negative at rest.
• An impulse causes a change in ion concentration, making the inside more positive (depolarization).
• This only occurs if the RMP is below threshold.
• Absolute Refractory Period: No amount of stimulation will evoke an action potential.
• Relative Refractory Period: A suprathreshold stimulation is necessary to evoke an action potential.
• For an action potential to be evoked, the amplitude, duration, and rise time of the stimulus must be sufficient to overcome the threshold of the nerve or muscle membrane.
• The impulse (action potential) propagates along the nerve fiber until it synapses with another nerve or the motor end plate of a muscle.
• Action potentials are all or none based on whether the stimulus reaches threshold.
• Conductors: Nerve, muscle, motor points, trigger points.
• Insulators: Adipose, scar tissue.
• Speed of conduction: Faster if fibers are myelinated (large); slower if unmyelinated.
• Conduction slows with extreme or prolonged ice, pressure, and anoxia.
• Motor point: The anatomic place where the nerve enters the muscle.
• Motor unit: The motor nerve and the muscle fibers it innervates. Small units have a low ratio (e.g. 1:5) for fine motor control, while large units have a high ratio (1:100 or more) for force production.
• Voluntary contractions: Small motor units are recruited before large units resulting in gradual contraction. The reverse happens with E-stim.

Principles of Electricity

• Current: The flow of electrically charged particles from one place to another. Measured in amps, milliamps, or microamps.
• Voltage: A measure of electromotive force. Measured in volts or millivolts.
• Resistance: The ability of a material to oppose the flow of ions. Measured in ohms.
• Ohm's Law: Current in a conductor varies proportionally to voltage and inversely proportionally to resistance. (I = V/R)
• Constant Current Devices: Current does not vary regardless of changes in resistance. Advantage: consistent physiological response. Disadvantage: Current concentrates in the remaining contact area if part of the electrode loses contact or dries out.
• Constant Voltage Devices: Voltage does not vary, but current increases or decreases as resistance changes. Disadvantage: quality of the response changes with resistance changes and may not be as effective or comfortable.
• Strength-Duration Curve: Correlates with the amplitude and duration of the pulse. The area of a pulse (S x D) = charge. Vertical axis: Strength; Horizontal axis: Pulse duration. Shortest pulse duration: HVPC; Longest pulse duration: DC.
• Relationship between Strength and Duration: Inverse. Shorter pulses require higher amplitude to reach threshold, while longer pulses need less amplitude to reach the same nerve threshold.
• Sequence of activation with E-stim: Sensory, motor, pain.
• Expected response if duration remains constant and amplitude increases: Sensory: buzzing/tingling. Motor: weak contraction that becomes stronger as more motor units are recruited. Pain: Higher intensity.
• Muscle membranes have a much higher threshold than nerve membranes.

Waveforms of Therapeutic Current

• Monophasic: Pulses above or below the 0 line for the entire time. Current flows in one direction. Produces a polarity effect.
• Biphasic: Pulses above and below the 0 line. Changes direction. Produces a polarity effect only if unbalanced.
• Polarity: Electron flow in one direction results in one electrode being (+) and the other (-). Therapeutic applications with polarity from greatest to least effect: Iontophoresis, denervated muscle (DC), acute edema (HVPC), NMES (pulsed current: biphasic asymmetrical unbalanced).
• Balanced waveform: All electrodes are equal. No polarity effect.

Therapeutic Currents

• Direct Current (DC): Constant flow of electrons in one direction for more than 1 second.
• Alternating Current (AC): Continuous flow, current changing from positive to negative. Sinusoidal.
• Pulsatile: Non-continuous flow of electrons delivered in pulses in one direction (monophasic) or both directions (biphasic).
• Biphasic: Can be balanced (no polarity effect) or unbalanced (mild polarity effect).

Electrodes

• Monopolar Arrangement: Two electrodes of unequal size. One electrode is more active (smaller) and current density is greater under the smaller electrode. Used for DC (denervated muscle, iontophoresis) and HVPC (optional).
• Bipolar Arrangement: Paired electrodes of equal size. Current density is equally distributed.
• Quadripolar Arrangement: Four electrodes of equal size, channels intersect to surround the painful area. Current density is equal in all electrodes.

Other Considerations

• Longitudinal electrode placement along a muscle increases conduction. Ideal for muscle contraction.
• Placing electrodes from the same channel farther apart causes the current to go deeper.
• Ideally, electrodes from the same circuit should be positioned at least one electrode width apart.
• The patient may experience more sensation under one electrode if it is over a motor point or trigger point, not in full contact, or smaller than the others.
• Electrode care: No bathing, sleeping with electrodes on. Store on acetate when not in use. Replace if they don't adhere to skin.

Parameters of Electrical Stimulation

• Amplitude: The magnitude of current. controls intensity.
• Pulse Duration: The amount of time to deliver a pulse. Measured in microseconds.
• Rise Time: The time it takes for current to move from zero to peak intensity within a pulse.
• Frequency: The number of pulses per second. 1-10 pps: Motor twitch. 35-50 pps: Tetanized muscle contraction. 75-150 pps: Sensory response.
• Modulation: Any alteration in amplitude, duration, or frequency. Used to prevent accommodation.
• Duty Cycle: On: Off time. Longer off times for patients with neuromuscular conditions or high intensity contractions. Shorter off times for intentional fatigue or once the patient has adapted to E-stim.

Devices

Transcutaneous Electrical Nerve Stimulation (TENS)

• Biphasic, balanced waveform; bipolar placement. Used for pain relief.
• Gate Control Theory: High frequency, short duration pulses, sensory response only. Relief is fast but short-lasting.
• Endorphin Theory: Low frequency, long duration pulses, motor twitch. Relief is slower but lasts longer.
• Brief Intense TENS: High frequency, long duration pulses, strong paresthesia or motor response. For painful procedures.

Interferential Current (IFC)

• Biphasic balanced waveform, sinusoidal.
• Used for pain relief.
• The intersection of 2 currents with different frequencies produces beats (bps).
• Electrode placement: Quadripolar (ALWAYS) or Bipolar (Premodulated).
• Unique Parameters: Sweep: Modulates frequency. Scan: Modulates amplitude.

Neuromuscular Electrical Stimulation (NMES)

• Biphasic, symmetrical or asymmetrical waveform.
• Used to activate innervated muscles.
• Russian Stimulation: Biphasic balanced, AC current delivered in bursts. Often used for strengthening in a clinic setting.
• Amplitude: F+ tetanized muscle contraction. Adjusted and progressed as tolerated.
• Pulse Duration: Typically high (300 microseconds).
• Frequency: 25-50 pps for smooth contraction. 50 pps is more comfortable and fatiguing than 25 pps.
• Duty Cycle: Varying on:off times.
• Ramp Time: Gradually increase amplitude for comfort.
• Treatment time: 10-20 contractions, at least 3 times a week.
• Electrodes: One over motor point, the other parallel to muscle fibers. Larger electrodes are more comfortable.

Iontophoresis

• Direct current (DC) to deliver drugs into the body.
• Dosage: 40-80 mA-min.
• Procedure: Ensure no allergy, clean skin, polarity set to drug, saturate active pad with ion solution.
• DC is also used to stimulate denervated muscles to maintain viability.

High Volt Pulsatile Current (HVPC)

• Monophasic pulses of very short duration.
• Therapeutic applications: Wound healing and reducing acute edema. Usually monopolar, but can be bipolar.

Biofeedback

• Not electrical stimulation, but a good substitute if E-stim is contraindicated or poorly tolerated.
• Indications: Muscle relaxation or muscle re-education.