Faradic current

A faradic type of current is a short-duration interrupted direct current with a pulse duration of 0.1 -1 ms and frequency of 50 -100 Hz (hertz). faradic current is used for stimulation of the innervated muscle. It consists of two unequal phases:

• Low-intensity long duration current.
• High-intensity short duration current.

Modified faradic current

Faradic-type currents always surge for treatment purposes to produce a normal tetanic-like contraction and relaxation muscle. the current surges so that the intensity of successive impulses increases gradually, each impulse reaching a peak value greater than the preceding one, then falls, either suddenly or gradually.In the original faradic coil, the current was surged by hand but in the modern stimulator, an electronic device is used .surged current means gradual increase and gradual decrease of the peak intensity.

TYPES OF FARADIC CURRENT

• Trapezoidal faradic current

Impulse increase slowly maintained there for some time and decreases gradually forming the trapezoidal shape.

• Triangular faradic current

The impulse increases gradually but suddenly falls.

• Rectangular faradic current

Impulse increase rapidly maintained there for some time and then it will gradually fall.

NERVE TRANSMISSION  

In a normal nerve, there is a difference in the concentration of ions inside and outside the nerve. Due to this, there is a difference of potential called the potential difference between the inside and outside of the nerve.Nerve remains in two states

1. Resting-state.
2. Stimulation state.

  PHYSIOLOGICAL EFFECT OF FARADIC TYPE CURRENT

• Stimulation of sensory nerves.

When a current of faradic type is applied to the body, a mild pricking sensation is experienced. This is due to stimulation of the sensory nerve and is not very marked because the stimuli are of fairly short duration. The sensory stimulation causes a reflex vasodilation of the superficial blood vessel so that there is a slight reddening of the skin ( erythema ) . The vasodilation is generally confined to the superficial tissue and is of little practical importance.

• Stimulation of motor nerve.

A current of the faradic type stimulation the motor nerves and, if the current is of sufficient intensity, cause contraction of the muscles which they supply. because the stimuli are repeated 50 per second or more, the contraction is tetanic. If this type of contraction is maintained for more than a short period of time, muscle fatigue is produced, so the current commonly surges to allow for muscle relaxation.

• Stimulation of denervated muscle.

The current required to produce a contraction of denervated muscle with an impulse lasting for 1 ms is usually too great to be tolerated for treatment purposes. The faradic type of current is therefore not satisfactory for the stimulation of denervated muscles.

Indication of Faradic current.

• Facilitation of muscle contraction: when the patient is unable to perform voluntary action, electric stimulation is given to assist the musculature contraction.
• Re-education of muscle: As a result of long illness if a muscle doesn’t perform its function or forgets its function, then electric stimulation is given to act and the so that it can resume its function, and the phenomenon is called ‘Muscular re-education. during muscular re-education, when the stimulation is given, the patient is asked to perform the contraction himself too.
• Neuropraxia of motor nerve: Injury to a nerve is called neuropraxia, and the impulse originating from the brain is unable to pass across the site of the lesion and thus unable to reach the muscle which results in reduced muscular contraction.

Pumping action: the alternating contraction and relaxation result in the pumping action which results in increased venous and lymphatic return.

Contraindications of faradic current.      

• Skin lesion
• Infection
• Inflammation
• Thrombosis
• Marked loss of skin sensation
• Active tuberculosis or cancer
• Cardiac pacemaker
• Thrombophlebitis
• Unreliable patient
• Superficial metal

REFERENCES :Clayton’s electrotherapy  – Introduction, physiological effects of faradic current.Virendra kr. Khokkar  – Indication and contra-Indication of faradic current  .Jag Mohan Singh of electrotherapy – nerve transmission