Home » Electrotherapy; Low Frequency Currents
Galvanic current


It is an interrupted direct current also called long duration current having more than 1 ms up to 300 ms or 600 ms. But the commonly used duration is 100 ms duration requires a frequency of 30 pulses/ min. If the duration increases the frequency must be reduced. The interval between the impulses should never be of shorter duration than the impulses themselves.
Pulse duration ≤ Interval duration
t 1 ≤ t 2

Physiological effects:

                               Types of Denervated muscle fibers

Neurotmesis (complete denervation)
Axonotmesis (partial denervation)
Neurapraxia (compression of nerve)

The intensity and duration of impulses in galvanic current is adequate so that it can cause a sluggish worm like contraction. When current is applied it produces sensory stimulation resulting in the feeling stabbing or burning sensation. It increases blood circulation causing erythema (redness) of the skin. Stimulation of motor nerve with such current produces contraction of the muscle supplied by that nerve.

Therapeutic effect and use:

There has been confusion over the therapeutic use of electrical stimulation for denervated muscles for the last many years. The purpose of such current is to maintain the muscles in as healthy state as possible to prevent the complication by electrically artificial contraction. Skeletal muscles have greater power of regeneration. When the muscles are denervated the following changes will occur.
  • Loss of voluntary contraction and reflex activities
  • Atrophy: Resulting in fibrosis
  • Fibrillization: Spontaneous contraction
There are considerable literatures concerning the effects of electrics stimulation. In 1987 Spieloloz concluded that it will retard the muscle atrophy and degeneration but can not prevent it completely. In 1983 Devis provide evidences that all the denervated muscle fibers must be activated to produce isometric contractions. And isometric contractions are more effective than isotonic contractions and the regular contraction should commence (start or begin or cause to start) as soon as possible.
In short value of electrical stimulation for denervated muscle is not proven and its application to gain muscle power what may be small benefits are obtain but not justified. If some of the motor units (motor end plate + motor nerve + muscle fibers) are intact galvanic current is the choice of treatment.
Interrupted direct current is still recommended for the treatment of Axonotmesis and Neurotmesis nerve repair is to be taken.

Contra – indications:

  • Cardiac pacemakers and Arrhythmias
  • Hemorrhagic condition
  • Thrombosis and thrombophlebitis (inflammation of wall of vein)
  • Early tendon transfer and repair
  • Pregnancy: On pelvic, low back and abdomen
  • Unconscious patient
  • Recent radiotherapy
  • Carotid sinus
  • Child with mental disturbance
  • Malignancy
  • Infected wound and skin lesion

Under:
TENS (Transcutaneous Electrical Nerve Stimulation)


It is the application of low frequency pulsed rectangular current through skin to reduce pain. A small battery machine is used to generate a current having specific stimulatory effect.

Parameters of TENS:

Pulse shape: Rectangular
Pulsed width: Measured in microseconds and often 100 μs or 200 μs
Pulse frequency: As low as 2 Hz and as high as 600 Hz but usually fixed i.e. 150 Hz.
Pulse intensity: Vary from 0 – 60 mA.
  1. High TENS: High frequency and low intensity
Frequency 100 – 500 Hz
Pulse width 100 – 500 μs
Intensity 5 – 30 mA
  1. Low TENS: Low frequency and high intensity
Frequency 1 -5 Hz
Pulse width 100 – 250 μs
Intensity more than 30 mA
Electrode placement:
  • Area of greater intensity of pain/near
  • Trigger or motor point

Advantages of TENS:

  • It is non – invasive, portable and non addictive.
  • It is cheaper than regular analgesics.
  • It has few contraindications and precautions
  • It has changeable battery and electrodes.
Disadvantages of TENS:
  • Number of patients fails to tolerate the electrical stimulation.
  • Skin irritation may occur due to allergic reaction.
  • Chemical burn is also a disadvantage of TENS.

Indications of TENS:

  • Chronic pain syndrome
  • Phantom limb pain
  • Reflex sympathetic dystrophy
  • Post operative conditions
  • Obstetric pain

Contra indications:

  • Continuous TENS may result some electrolytic reaction below the skin
  • Pacemakers
  • First three month of pregnancy
  • Hemorrhagic conditions
  • Open wounds
  • Carotid sinus
  • Over mouth
  • Near eyes

Treatment method:

A patient may have a single daily treatment of 40 min duration. Portal TENS can be used continuously for 24 hrs.

Modes of TENS:

a.    Conventional TENS:

It is the most commonly used mode of TENS. It can be used for both Acute and Chronic pain.
Mechanism of Action:
Stimulation of large diameter through pain gate control theory
  • Frequency 100 – 150 Hz
  • Intensity 12 – 30 mA
  • Pulse width 50 – 80 µs

b.   Acupuncture like mode:

Mechanism of Action:
The stimulation of small diameter nerve fibers to release endogenous opiods  
Parameters:
  • Frequency 1 -5 Hz
  • Intensity above 30 mA
  • Pulse duration 150 – 300 µs

c.    Burst mode:

This mode has characteristics of both high and low TENS. The pain control is through both routes.
Parameters:
  • Frequency 50 – 100 Hz but the frequency is delivered in packets of 1 – 4 Hz
  • Pulse duration of 50 – 100 µs
  • Intensity below 30 mA

d.   Brief intense TENS:

It has rapid onset but for short term. Clinician used it for wound debridment, joint mobilization and contracture.
  • Frequency 80 – 150 Hz
  • Pulse duration 50 – 250 µs
  • Intensity according to tolerance of patient

Under:
Pain modulation


Pain is unpleasant sensation of the body. The receptors of pain are called nociceptors. Nociceptors are present all over the body especially skin (subcutaneously). Any physical, thermal and mechanical pressure stimulates the nociceptors.
The impulses are carried by two types of neuron; Primary or 1st order neuron and Secondary or 2nd order neuron.

1st order neuron:

Primary afferent fibers transmit impulses from the sensory receptors to dorsal horn of spinal cord.

2nd order neuron:

2nd order afferent fibers carry sensory impulses from the dorsal horn of the spinal cord to the brain.
  • A α and A β are large diameter (myelinated) nerve fibers.
  • A Δ and C fibers are the small diameter (unmyelinated) nerve fibers.

The impulses from spinal cord to the brain are carried by Dorsal spinothalamic tract, spinoreticular tract and spinocephalic tract.

Pain Gate Control Theory:

This theory was suggested by Pat wall and Melazak in 1965.
Afferent input is mainly through posterior root of spinal cord and all afferent information must pass through synapses in the Substantia Gelatinosa and Nucleus Propius of the posterior horn.

Mechanism:

It was suggested that pain to pass through this gate, there must be unopposed passage for nociceptive information arriving at the synapse. However if the gate is concurrently receiving the impulses produce by the stimulation of large diameter fiber (thermoceptors, mechanoceptors). Then this traffic predominates with the resultant presynaptic inhibition of the small diameter nociceptive information. Many physiotherapeutic agents causing stimulation of the endings connected to the large diameter nerve fibers. The use of Manipulation, TENS, Interferential therapy, Heat, Massage, Ice, Vibration and Movements can produce reduction of pain by closing the pain gate.

Under:
Iontophoresis


The therapeutic techniques involving the introduction of ion into the body tissue through patient’s skin is called Iontophoresis.

Principle:

Place the ions under the electrode with the same charge i.e. negative ions placed under cathode and positive ions under anode. The electrode under which ions are placed is called active electrode. Iontophoresis is used for hyperhydrosis (excessive sweating).

Use of tape water:

The use of tape water produces no side effect but the ions in it may not inhibit sweating sufficiently. So an anticollinerfic compound in distilled water is recommended. The hands and feet may be affected and require treatment but no attempt should be made to treat the hands and feet on the same day. There should be elapse of several days in their treatment.

Apparatus:

  1. Source of direct current
  2. Shallow plastic tray
  3. Foot or arm bath for cathode
  4. Two lint pads to cover electrodes
  5. Anti-cholinergic compound solution
  6. Distilled water

Methods of application:

Hands:

The shallow plastic tray is placed on arm bath table and patient sit along its side. The active electrode is placed in the plastic tray (anode) and is covered with one of the lint pads, the pads should be minimum 8 layers thick so that they make good contact with the tissues and the electrodes. The tray may also contain 0.05 % solution of anti – cholinergic compound glycopyronium in distilled water. The hand is placed in the tray and the electrode is connected to the positive terminal.

Feet:

One of the feet is placed in a few cm water in a foot bath and the lint pads covered electrode (cathode) which is connected to the negative terminal and slowly increased to the desired effect for desired time.

Dosage:

The dosage is based on the size of the patient and skin tolerance. For an average Adult the dosage is 12mA for 12 min and half of this treatment for child. The need to repeat the treatment varies with each patient. Some patients have relief for month after treatment and some patients require a repeat less than 4 – 6 weeks.

Precautions of Iontophoresis:

  • Care about skin abrasion
  • Open wounds
  • Remove the rings
  • Thickness of pads (minimum 8 layers)
  • Warm the patient

Side effects:

Anti – cholinergic compound act as sympathomimatic (increases heart rate, respiratory rate)

Ions which are used for different conditions:

Ions
Source
Condition
Concentration
Acetateˉ
Acetic acid
Deposition of Ca over tendon e.g. tendonitis
2 -5 %
Chlorideˉ
Sodium chloride
Adherent scars
2 %
Copper +
CuSO4
Fungal infestation e.g. allergic rhinitis
2 %
Dexamethasone phosphate ˉ
Dexa Na2PO3
Inflammation
0.5 %
Iodine ˉ
Iodex (potassium Iodide)
Scar mobilization
5 %
Lidocane +
Lidocane
Local anesthetic
5 %
Magnesium+
MgSO4
Muscle relaxant, vasodilatation, oedema reduction
2 %
Salicylate ˉ
Na Sal (Na2S2O3)
Inflammation, pain management
2 %
Zinc +
ZnO
Dermal ulcer
20 %
Glycopyronium Bromide ˉ
Cholinergic compound + distilled water
Hyperhydrosis
20 %
Calcium+
CaCl2
Mycospasm (tremors)
2 %

Under:
Faradic Type of current


The short duration interrupted direct current with pulse duration 0.1 – 1 ms and frequency in between 50 – 100 Hz, used for the stimulation of innervated muscles is called faradic type of current. The current produced by faradic coil is called multivibrator current (producing tetanic contraction).

Surging:

The process of giving relaxation to the tetanic contraction produced by faradic current is called surging.

     i.        Trapezoidal surging:

The impulses increases and decreases gradually forming trapezoidal shape

   ii.        Triangular surging:

The impulses increases and decreases gradually forming triangular shape

  iii.        Saw Tooth:

The impulses increases gradually but suddenly fall.

Physiological effects of faradic type of current (low frequency current):

It stimulates the intact nerve by producing change in the permeability of the cell membrane altering the testing potential of the membrane. When the resting potential of the cell membrane reaches the excitatory level, the muscle supplied by the nerve contracts. Along with motor supply the current also produces sensory stimulation of nerve.
The skin provides 3200Ω and epidermis 1000 Ω, deep fascia, fats having different ions. When it passes through them it may cause chemical burn. To reduce this effect, the resistance is reduced to appropriate measures.

a)   Sensory effects (sensory nerve stimulation):

By applying the faradic type of current, there is mild prickling sensation. There is also mild erythema (redness) of the skin due to vasodilatation of superficial vessels.

b)   Motor effects (motor nerve stimulation):

The faradic current stimulates the motor nerve, if the faradic current is of sufficient intensity having 50 Hz frequency and 0.1 – 1ms shortest duration it will produce tetanic contraction. The tetanic contraction causes muscle fatigue. So to avoid this current is surged to allow muscular relaxation.

c)   Effect on muscle contraction:

Faradic current causes muscle contraction similar to the normal muscle. Contraction and relaxation of muscles produce pumping action which increases blood supply to the muscles as a result of increased demand and supply of oxygen and nutrition.
Sufficient muscular contraction and relaxation causes pumping effect on venous and lymphatic vessels which leads to removal of waste products.

d)   Effect on denervated muscles:

For the stimulation of denervated muscles, the impulse required is more than 1 ms which can not be tolerated by the patient. So, faradic current is short duration current with sufficient intensity, which cannot stimulate the denervated muscles.

Indications of faradic type of current:

1)   Facilitation of muscle contraction:

 When the muscle is unable or difficult to contract then we use stimulation by faradic current. The muscle contraction is integrated by complex process throughout the spinal cord level or higher center.
Excitation of the small efferent nerve causes contraction of intrafusal muscle fibers.
Stretching of muscle spindle stimulates the primary nerve endings and sends information to the anterior horn cells of the spinal cord.
When contraction of agonist occurs, at the mean time relaxation of antagonist occurs.

2)   Re – education of muscle action:

Inability to contract a muscle voluntarily may be as a result of prolong disuse and incorrect pattern. The nerve has the power of accommodation, the current which rises or falls suddenly is more effective and initiating an impulse than one which changes slowly.

3)   Stimulation of nerve:

When a sensory nerve is stimulated, the downward traveling impulse has no effect while the upward traveling impulse is appreciated to reach the conscious level of brain.
When the motor nerve is stimulated, the upward traveling impulse in unable to pass the 1st synapse (N/N) while the downward traveling impulse passes to the muscles causing contraction

4)   Effect of frequency stimulation:

When a single stimulus is applied per second, it will produce a sudden brisk contraction followed by immediate relaxation. Increasing the frequency to 20 Hz or above will produce tetanic contraction because there is no time for relaxation.

5)   Strength of contraction:

It depends on number of motor units activated and rate of change of current. If the intensity of current rises suddenly, there will be no time for accommodation which results in sudden brisk contraction but if the current rises slowly, greater time will be required for accommodation i.e. trapezoidal, triangular current.

6)   Oedema reduction:

Alternative contraction and relaxation (pumping action) of the muscle causes lymphatic and venous drainage (return) so reduces the oedema. This process is called faradism under pressure.

Under:
Low frequency currents


These are short duration currents having pulse duration ranging from 0.1 – 1 ms.

Types of low frequency currents:

     i.        Direct current:

a)   Constant direct current:

These are unidirectional flow of electrons towards the positive pole. The therapeutic use of unidirectional flow of currents is to introduce medication into the body tissues called Iontophoresis.

b)   Interrupted direct current:

If the continuous unidirectional current is interrupted, it gives rise to series of pulses or phases of unidirectional current.

   ii.        Alternating current:

In alternating current the electrons are constantly changing the direction. Electrons in the alternating current always move from negative pole to positive pole. This is used to reduce edema and relief of pain.

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