Electrotherapy & Its Instruments

Introduction Electrotherapy is the use of different electric currents to the body to stimulate peripheral nervous system to control pain, cause muscle contraction or to speed healing. It comprises of the application of electrophysical agents (EPAs) for therapeutic purposes. EPAs are applied by microwave diathermy (MWD), shortwave diathermy (SWD), interferential current techniques, transcutaneous electrical nerve stimulation (TENS) etc.

History Franklinism (1750’s)- the medical practice of employing static electricity; Benjamin Franklin developed a ‘Magic Square’ for electric shocks. Galvanism (1790’s)- Luigi Galvani introduced the concept of ‘animal electricity’ (frog electricity); use of direct current in medicine. Faradism (1790’s)- Alessandro Volta created the ‘Voltaic cell’; use of alternating current in medicine begins.

…continued Meanwhile, Guillamo Duchenne used Faradic induction coils to apply currents to muscles 1840’s-60’s. He observed changes in expressions by applying electricity to facial muscles. He was the first to describe muscular dystrophy, a degenerative disorder of muscles. He is, today, known as the father of electrotherapy. Medical induction coil used in England for pain relief in the mid-nineteenth century.

Principles of Electrotherapy Most electrotherapeutic devices are designed electronically as Constant-current- the current output set by the therapist will remain the same; voltage output would change with change in tissue impedance. Constant-voltage- the voltage output set by the therapist will remain the same; there will be change in the current with change in tissue impedance.

A Comparison Impedance of skin fluctuates during treatment, hence in Constant-voltage type device, the current can increase strongly resulting in unpleasant sensation. An advantage of Constant-voltage stimulator is automatic reduction of current when electrode size is reduced. If Constant-current type devices are used in applications where effective area of electrode is changing, there will be a sensation of increased current due to increase in current density. The advantage of the constant-current stimulator is the more consistent level of stimulation.

Stimulation of nerves

Parameters affecting stimulation Rate of rise of the pulse. Current intensity/amplitude Interpulse and intrapulse duration Pulse frequency

Rate of Rise of The Pulse If the rate of rise of the current is very slow it will not provoke a nerve impulse because the ionic balance across the nerve fiber membrane is able to adjust itself, this process is called accommodation. The rate at which accommodation occur is limited so that the threshold may be reached by the slow rising pulses at higher intensity.

The Role of Current Intensity on Physiological Changes If low current density is applied (current intensity /unit area²) to the skin, the nerves transmit touch, temperature and pressure are the first to be stimulated causing mild tapping sensation (sub-sensory level). Higher current densities will affect more sensory nerves causing tingling sensation (sensory level).

…continued Still higher currents will spread to the motor nerves causing muscle contraction; muscle contraction occurs (motor level). Much increase of current density will stimulate pain fibers causing pain (noxious level).

Stimulating Nerve Fibers The amplitude (intensity) of current needed to stimulate a nerve fiber is inversely proportional to its diameter. The larger fibers have a lower electrical resistance. The difference in sensitivity between motor and sensory fibers is due to their different depth; sensory nerves in the skin receive higher current density than deep motor fibers.

Strength duration curve

Pulse frequency A current with lower pulse frequency i.e. 10 pps would meet higher tissue resistance than a current with pulse frequency 1000 pps and would require an increased intensity to overcome the resistance.

Transcutaneous Electrical Nerve Stimulation (TENS) TENS is a method of electrical stimulation which primarily aims to provide a degree of symptomatic pain relief by exciting sensory nerves. The term TENS could represent the use of ANY electrical stimulation using skin surface electrodes which has the intention of stimulating nerves.

Machine Parameters

Mechanism of Action Two main theories- Pain gate mechanism - activation (excitation) of the A beta (Aβ) sensory fibres, and by doing so, reducing the transmission of the noxious stimulus from the ‘c’ fibres, through the spinal cord. Effective range – 80-130 pps.

…continued Endogenous opoid system- stimulation of the A delta (Aδ) fibres which activate the endogenous opoid mechanisms for pain relief (release of opiates such as encephalin). Effective range – 2-5 pps.

Diathermy Application of high-frequency electromagnetic energy to generate heat in body tissues. Heat produced by resistance of the tissue to the passage of the energy. Heating= Current2 X Resistance

Types Two types of diathermy- Shortwave diathermy Microwave diathermy

Shortwave Diathermy Frequency = 27.12 MHz; Wavelength = 11 m

Shortwave diathermy electrodes Capacitor electrodes- a) Air Space Plates b) Pad Electrodes

continued Induction electrodes- a) Cable electrodes b) Drum Electrodes

Heat Distribution

Therapeutic effects of SWD Pain relief: of traumatic pain and rheumatic conditions affecting muscles, ligaments and joints. Muscle spasm: may be reduced directly by SWD. Inflammation: resolution of inflammation as a result of increase blood supply.

Accelerate wound healing: by increase in circulation. Infection: increase circulation and increase white blood cells and antibodies. Fibrosis: increase extensibility of fibrous tissues such as tendons, joint capsule and scars.

Microwave Diathermy Frequency - 2456 MHz or 915 MHz Shorter wavelength than shortwave diathermy Gives superficial heating where most energy is absorbed at the surface of the body.

Microwave Diathermy Directors Large circular field directors – effective diameter is 200mm Small circular field directors – the effective diameter is 100 mm Longitudinal field directors – the effective treatment area is 500mm by 100mm

Therapeutic effects of MWD Relief of pain: treatment of traumatic and rheumatic conditions affecting superficial muscles, ligaments and small superficial joints. Reduce muscle spasm: may be reduced directly by microwave diathermy or may be reduced by relieving of pain. Inflammation: increase in the blood supply will increase venous return from the inflamed area and aids the re-absorption of edema exudates.

Applications of Diathermy Muscle strains Contusions Ligament sprains Tendonitis Osteoarthritis Bursitis Joint contractures Myofacial trigger points Local relaxation Deceased joint stiffness Increased Extensibility of collagen fibers Increased circulation Decrease subacute & chronic pain

SUMMARY Electrotherapy, or the use of electric current for therapeutic purposes, has been in use since the ancient times. Modern techniques include TENS, diathermy and interferential current. Various current parameters determine the degree of stimulation – amplitude, pulse frequency, rate of rise of pulse etc. Electrotherapy has wide applications ranging from pain relief to stimulation of nerves.

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