faradic currents

8/11/2019 Faradic currents

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Faradic Current

Faradic current is a short-duration interrupted current, with a pulse

duration ranging from 0.1 and 1 msec and a frequency of 50 to 100 Hz.

Faradic currents are always surged for treatment purposes to produce a

near normal tetanic-like contraction and relaation of muscle. !urrent

surging means the gradual increase and decrease of the peak intensity.

Forms of faradic current:

"ach represents one impulse#

$ %n surged currents, the intensity of the successi&e impulses increases

gradually, each impulse reaching a peak &alue greater than the preceding

one then falls either suddenly or gradually.

$ 'urges can (e ad)usted from * to 5-second surge, continuously or (y

regularly selecting frequencies from + to 0 surges minute.

$ est period /pause duration should (e at least * to times as long as

that of the pulse to gi&e the muscle the sufficient time to reco&er /regain

its normal state.

$ he most comforta(le pulse is either 0.1-msec pulse, with a frequency

of 20 Hz or 1-msec pulse with a frequency of 50 Hz.

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Physiological effects of faradic current:

1. Stimulation of sensory nerves: %t is not &ery marked (ecause of the

short duration. %t causes refle &asodilatation of the superficial (lood

&essels leading to slight erythema. he &asodilatation occurs only in the

superficial tissues.

2. Stimulation of the motor nerves: %t occurs if the current is of a

sufficient intensity, causing contraction of the muscles supplied (y the

ner&e distal to the point of stimulus. 3 suita(le faradic current applied to

the muscle elicits a contraction of the muscle itself and may also spread

to the neigh(oring muscles. he character of the response &aries with the

nature and strength of the stimulus employed and the normal or

pathological state of muscle and ner&e. he contraction is tetanic in type

(ecause the stimulus is repeated 50 times or more sec4 if this type is

maintained for more than a short time, muscle fatigue occurs. 'o, the

current is commonly surged to allow for muscle relaation i.e. “when the

current is surged, the contraction gradually increases and decreases in

strength in a manner similar to voluntary contraction”.

3. Stimulation of the nerve is due to producing a change in the semi-

permeaility of the cell memrane: his is achie&ed (y altering the

resting mem(rane potential. hen it reaches a critical ecitatory le&el,

the muscle supplied (y this ner&e is acti&ated to contract.

!. "aradic currents will not stimulate denervated muscle: he ner&esupply to the muscle (eing treated must (e intact (ecause the intensity of

current needed to depolarize the muscle mem(rane is too great to (e

comforta(ly tolerated (y the patient in the a(sence of the ner&e.

#. $eduction of swelling and pain: %t occurs due to alteration of the

permea(ility of the cell mem(rane, leading to acceleration of fluid

mo&ement in the swollen tissue and arterial dilatation. 6oreo&er, it leads

to increase meta(olism and get red of waste products.

*



%. &hemical changes: he ions mo&e one way during one phase of the

current4 and in the re&erse direction during the other phase of the current

if it is alternating. %f the two phases are equal, the chemicals formed

during one phase are neutralized during the net phase. %n faradic current,

chemical formation should not (e great enough to gi&e rise to a serious

danger of (urns (ecause of the short duration of impulses.

Indications:

1. "acilitation of muscle contraction inhiited y pain: 'timulation must

(e stopped when good &oluntary contraction is o(tained.

2. 'uscle re-education: 6uscle contraction is needed to restore the sense

of mo&ement in cases of prolonged disuse or incorrect use4 and in muscle

transplantation. (he rain appreciates movement not muscle actions, so

the current should (e applied to cause the mo&ement that the patient is

una(le to perform &oluntarily.

3. (raining a new muscle action: 3fter tendon transplantation, muscle

may (e required to perform a different action from that pre&iously carried

out. ith stimulation (y faradic current, the patient must concentrate with

the new action and assist with &oluntary contraction.

7. hen a ner&e is se&ered, degeneration of the aons takes place after

se&eral days. 'o, for a few days after the in)ury, the muscle contraction

may (e o(tained with faradic current. %t should (e used to eercise themuscle as long as a good response is present (ut must (e replaced (y

modified direct current as soon as the response (egins to weaken.

#. )mprovement of venous and lymphatic drainage: %n edema and

gra&itational ulcers, the &enous and lymphatic return should (e

encouraged (y the pumping action of the alternate muscle contraction and

relaation.



%. *revention and loosening of adhesions: 3fter effusion, adhesions are

lia(le to form, which can (e pre&ented (y keeping structures mo&ing with

respect to each other. Formed adhesions may (e stretched and loosened

(y muscle contraction.

+. *ainful nee syndromes: 3fter trauma, there is inhi(ition of muscle

contraction, leading to muscle atrophy. For eample, after knee surgery

e.g. menisectomy, there should (e no gross effusion of the knee as it

causes difficulty in o(taining the motor point of the muscles.

. )nhiition of uadriceps contraction y pain: 3s in rheumatoid

arthritis, su(luation of patella, chondromalicia patellae and chronic

effusion of the knee.

Contraindications:

/ Sin lesions: he current collects at that point causing pain.

/ &ertain dermatological conditions: 'uch as psoriasis, tinea and eczema.

$ 3cute infections and inflammations.

$ hrom(osis.

$ 8oss of sensation.

$ !ancer.

$ !ardiac pacemakers.

$ 'uperficial metals.

(he mechanism of pain inhiition and muscle spasm:

9ain has an inhi(itory effect on the large anterior horn cells.

'timulation of the afferent ner&e fi(ers decreases this inhi(ition and

influences the alpha motor neurons. 'u(sequently, facilitation of

transmission of impulses to the etrafusal fi(ers follows with inhi(ition

of the antagonists, allowing a more natural sequence of mo&ements.

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&ontrolled muscle contraction:

'er&o-mechanism is the integration of neural circuits in the spinal

le&el and the higher centers. &ontrolled muscle contraction results from:

$ "citation of the small efferent fi(ers, which cause contraction of the

intrafusal fi(ers.

$ 'tretching of muscle spindle, which sends information to the anterior

horn cells, recruiting the motor unit, leading to muscle contraction.

$ %nhi(ition of the anterior horn cells supplying the antagonistic groups.

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faradic currents

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