Interrupted Direct Current

Interrupted direct current Definition .

Interrupted direct current is also known as modified direct current or interrupted galvanic current. Interrupted direct current is commonly used for stimulation of denervated muscles and for electrodiagnostic purpose. It is a modified type of direct current characterized by commencement and cessation of the current flow at regular intervals. In other words, it is a current, whose flow stops and starts at regular intervals. Impulse duration ranges between 0.01 m/s to 3,000 m/s and the frequency vary as per the pulse duration and the interval selected between them.

For instance, if the impulse duration is 100 millisecond, then the frequency is 30 cycles per second. The pulses used in interrupted direct current can be called long-durated and short-durated pulses. Long-durated pulses are those whose duration is more than 10 millisecond and short-durated are those whose duration is less than 10 millisecond. Various waveforms of interrupted direct current, such as sawtooth, triangular, depolarized, trapezoidal and rectangular can be used in clinical applications.

Production of Interrupted direct current .

Interrupted direct current for the treatment can be availed from battery or electricity operated stimulator. Electronic muscle stimulator works on multivibrator or flip-flap circuit .

Physiological and Therapeutic Effects of Interrupted direct current .

Physiological effects of interrupted direct current are stimulation of sensory nerves, stimulation of motor nerves, effect of muscle contraction, increased metabolism, effect on denervated muscle and chemical effect.

Sensory Nerve Stimulation .

When interrupted direct current is applied to the body, there is feeling of stabbing or burning sensation as a result of stimulation of sensory nerves. Stimulation of sensory nerves also causes reflex vasodilation of superficial blood vessels leading to reddening of the skin or erythema.

Motor Nerve Stimulation .

Interrupted direct current stimulates motor nerves and if intensity is sufficient then it will cause contraction of muscles supplied by it. It produces very brisk contraction followed by immediate relaxation of innervated muscles but sluggish contraction of denervated muscles occur, if impulse duration is adequate. Sluggish contraction means worm-like slow contraction and relaxation .

Since interrupted direct current can produce the contractions of denervated muscles, it is commonly used in the treatment of peripheral nerve injuries to stimulate the muscles, so as to prevent or minimize the possibility of atrophy, degeneration and fibrosis of muscles following denervation (remember it with FAD: fibrosis, atrophy and degeneration). However, it should be remembered that therapeutic electrical stimulation does not accelerate the rate of regeneration following peripheral nerve injuries or neuropathies.

Effect on Denervated Muscle .

Following denervation, muscles undergo various changes. These changes include paralysis, flaccidity, atrophy, decreased muscle weight, decreased muscle protein, decreased sarcoplasm, decrease in number of muscle fibers, replacement by fibrous and adipose tissues, and degeneration. Stimulation of denervated muscle  improves its nutrition by increasing blood supply.

Further on, blood supply is increased due to muscle contractions, as a result of pumping effect. As a result of electrical stimulation, nutrition of muscles is improved and this in turn retards atrophy, degeneration and fibrosis. For this purpose, electrical stimulation can be applied to produce 90 contractions of each muscle every day.  But this is controversial, various trends followed are 10 to 30 contractions, 30 to 300 contractions per day or three times per week. I personally feel that these variations are as per the convenience of the therapist and patients.

Chemical Effect .

Very negligible amount of chemicals are formed when interrupted direct current is applied since there is pause or rest in between any two impulses. As the muscles contract and relax, they exert a pumping action on veins and lymphatic vessels lying within and around them.

The valves in these vessels direct the fluid towards the heart. If muscle contraction is strong and moreover, if there is joint movement then, both of these exert a pumping effect on vessels leading to increased venous and lymphatic return.

Pole Used for Stimulation .

Usually cathode is used as an active electrode, but sometimes a greater response can be obtained to anode and hence, it should be decided on the basis of clinical situation and as per the response to these poles in denervated muscles.

 

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