Faradic current Definition .
Faradic current is short duration interrupted direct current with pulse duration of 0.1–1 ms and frequencies between 50–100 Hz, used for the stimulation of innervated muscles. The term faradism was previously used to signify the type of current produced by the first faradic coil and was unevenly alternating current with each cycle consisting of two unequal phases .
Original Faradic Current .
Original faradic current was extensively used in the past. It is a type of current, which can be produced by a faradic coil. It consists of two unequal phases, the first phase is of low intensity and long duration and second phase is of high intensity and short duration. Here, second phase is effective and its duration is one millisecond. Frequency of the original faradic current is 50 cycles per second.
Production .
It is produced on the same principle as that of interrupted direct current. But values of condenser and resistance are low so as to get short duration of impulses and high frequency. An electric pulse generator that produces faradic current has four functional parts in form of power supply, oscillator circuit, modulating circuit and amplifying circuit.
Power supply may be from battery or AC. Oscillator circuit provides short duration pulses of 0.1 to 1 ms with a frequency of 50 to 100 Hz. Modulating circuit gives surged output and amplifying circuit increases the output voltage appropriately.
Interruption and Surging .
Faradic current can be modified by interruption and surging. Hence, the two forms of modified faradic current can be made available for treatment purpose. In case of interrupted faradic current, the output is interrupted at regular intervals. Generally, it is used so as to avoid fatigue of muscles because of higher frequency such as 100 Hz. Surged faradic current is a modification of faradic current characterized by gradual increase in the intensity in such a manner that each impulse reaches higher intensity than that of the preceding one and after peak level it either falls suddenly or gradually.
Surging is also termed as ramping. Surging is obtained automatically in case of modern stimulators by the use of electronic devices. Advantages of surging are that, it avoids fatigue, it does not surprise the patient as current slowly increases over time and not abruptly. Contraction of muscle is similar to physiological/voluntary contraction. Avoid or delay muscle fatigue and avoid elicitation of stretch reflex. It is possible to get various surged durations, frequencies and waveform.
Surged duration is the time taken by impulses to reach peak level of the intensity. That means, if the duration is more, impulses will take more time to reach peak level of intensity. Surged interval is an interval between two surged impulses and the number of surged impulses per unit time is surged frequency. Theoretically, frequency of impulses in surged impulses can be adjusted. Different waveforms such as, sawtooth, triangular and trapezoidal can be made available with surged faradic current.
In sawtooth waveform, the intensity of impulses increases gradually so as to reach peak level and after peak level it falls suddenly. In triangular waveform, the intensity of impulses increases gradually, so as to reach its peak level and after peak level it falls down gradually. In trapezoidal, the intensity of impulses increases gradually so as to reach peak level. At peak level, it remains for sometime and then it falls gradually.
Methods of Application .
Faradic current can be applied by various methods such as motor point stimulation, labile, stabile, nerve conduction method, bath method, under pressure faradism, etc.
1. Motor Point Stimulation .
Motor point stimulation involves stimulation of individual muscle. In this method, an indifferent electrode is placed at the origin of muscle and an active disk electrode (handle/pen electrode) is placed at motor point. With this method almost each and every muscle can be stimulated and thus effect of passive exercise can be given to each and every muscle. However, it is somewhat difficult to stimulate deeply situated muscles with this method.
Advantages of this method are, contraction of individual muscle can be obtained, each and every muscle can be stimulated and isolated muscle contraction can be obtained in the treatment of various conditions, for example, stimulation of abductor hallucis in hallux valgus. However, there are some disadvantages of this method such as, it is tedious, time consuming, trial error method and it is difficult to stimulate deeply situated muscles .
2. Labile Method .
Labile method can be used for stimulation of large muscles with multiple nerve supply for example trunk muscles. Here, an indifferent electrode is placed at the origin of muscle or muscles and an active electrode either disk or small plate electrode is moved over the area to be treated. During this method, current is not usually surged. As the active electrode approaches and leaves the motor point of a muscle, that muscle contracts and relaxes.
3. Nerve Conduction Method .
In nerve conduction method, an indifferent electrode is placed at convenient area and an active electrode to a point at which the nerve trunk is superficial. It will stimulate motor nerve trunk and will cause contractions of all the muscles that it supplies beyond the point of stimulation. Nerve trunk stimulation causes contraction of all muscles innervated by the nerve, that is stimulated. This method is used when it is not possible to use other methods conveniently, for example, in case of wound, splint and edema.
4. Faradic bath Method .
Application of faradic current to the body parts in a tub, tray or tank containing water is termed as bath method of application. Depending upon the placement of electrodes, bath can be of bipolar or unipolar type. In bipolar, both electrodes are kept in the bath and in case of unipolar, only one electrode is kept in the bath while the other one is kept at any convenient part of the body, which is not immersed in the water. Bath method is commonly used for the application of faradic current to the foot and which is often termed as faradic footbath.
Advantages of bath method are that skin resistance is lowered considerably by water and in addition to this, water makes perfect contact with the tissues. Disadvantages of this method of application are that, the current cannot be localized, superficial muscles contract to a greater extent than deeper ones due to the presence of water, chances of electric shock is greater as water can make earthing easily available.
5. Faradism Under Pressure .
Faradism under pressure method is used in the treatment of edema to increase the venous and lymphatic drainage from the edematous area. Here, the faradic current is applied along with an elastic bandage such as elastocrepe bandage and the body part, which is to be treated, is kept elevated during treatment. This form of treatment is applied for 15 to 20 minutes only.
6. Faradism to Pelvic Floor Muscles .
Here, the active electrode is placed in the perineal region or rectum or vagina and an indifferent electrode over lumbosacral region. This method of application can be used in prolapse of pelvic organs, stress, incontinence, etc.
Physiological Effects of original faradic and faradic type of current .
Physiological effects of original faradic and faradic type of current are stimulation of sensory nerves, stimulation of motor nerves, effect of muscle contraction, increased metabolism, effect on denervated muscle and chemical effect.
1. Stimulation of Sensory Nerves .
When faradic type of current is applied to the body, then there is a feeling of mild prickling sensation as a result of stimulation of sensory nerves. Stimulation of sensory nerves also causes reflex vasodilation of superficial blood vessel leading to reddening of the skin or erythema.
2. Stimulation of Motor Nerves .
Faradic type of current stimulates motor nerves and if intensity is sufficient, then it will cause contraction of muscles supplied by it. As stimulations are repeated 50 times per second or more, it produces tetanic contraction. If this type of contraction is continued for more than a short period of time, then muscle fatigue is produced and hence the current is surged or interrupted in order to give relaxation. Advantage of surging is that the strength of contraction increases gradually in such a manner that it is similar to voluntary contraction.
3. Chemical Effect .
Very negligible amount of chemicals are formed when faradic current is applied, as the pulse duration is too small.
4. Effect on Denervated Muscle .
Faradic current is never used for stimulation of denervated muscle. Since the intensity of current required producing a contraction of denervated muscle with a faradic current is usually too great to be tolerable for treatment purposes. Therefore, faradic current is not satisfactory for stimulation of denervated muscles.
5. Effect of Muscle Contraction .
Electrical stimulation of muscles by faradic current increases metabolism and pumping effect of muscles. Metabolism is a collective process, which consists of physical, chemical, anabolic and catabolic changes in the body tissues by which living state of body is maintained. As a result of muscle contraction due to electrical stimulation, metabolism is increased. Increased metabolism increases demand for oxygen and foodstuff and as a result of it, there is an increase in the output of waste products including metabolites.
These metabolites cause dilation of capillaries and arterioles and increase the blood supply to the muscle. As the muscle contracts and relaxes, it exerts a pumping action on veins and lymphatic vessels lying within and around them. The valves in this vessel direct the fluid towards the heart. If muscle contraction is strong and joint movement is also there then, both of these exert a pumping effect on vessels leading to increased venous and lymphatic return.
Therapeutic Effect of Faradic Current .
Faradic current is primarily used to produce contraction of normally innervated muscles and current, usually surged so as to get contractions, which resembles or is similar to voluntary contractions.
1. Facilitation of Muscle .
Muscle contraction can be facilitated by faradic type of current. The facilitation effect of faradic current can be used when a patient is unable to produce a muscle contraction or finds difficulty in doing so. Muscle contraction may be inhibited as a result of trauma, inflammation, pain and surgery, etc. (you can remember this with a word TIPS).
Here, faradic current stimulation is used in assisting voluntary contraction, for example, faradic stimulation of the quadriceps following meniscectomy. The patient should be encouraged to attempt voluntary contraction at the same time so as to get voluntary control by minimizing inhibition.
2. Muscle Re-education .
Muscle action can be re-educated, if voluntary muscle action is lost as a result of prolonged disease or incorrect use. For instance, re-education of abductor hallucis in hallux valgus. Here, the current is applied in such a way that it produces the abduction of the great toe.
3. New Muscle Action .
After tendon transplantation or other reconstruction operations, faradic current can be used for training of new muscle action. Muscle is stimulated so as to produce new action or movement. During stimulation, the patient should attempt to perform voluntary contraction. Once the patient is able to perform new movement actively without electric stimulation, then electric stimulation is discontinued.
4. Motor Nerve Neurapraxia .
Faradic stimulation to the paralyzed muscles can be applied following neurapraxic lesion of the motor nerve. Electrical stimulation can be given till voluntary control is developed. However, electrical stimulation may not be needed in neurapraxia as recovery takes place without any marked changes in the muscle tissue.
5. Blood Supply .
Faradic current can cause reflex vasodilation and hence, can be used for increase in blood supply in conditions where heat treatment may not be a safe choice. For this purpose, sensory level intensity is applied with bath method of application.
6. Effect on Edema .
Faradic current can be used in the treatment of edema for improving venous and lymphatic drainage. Faradism under pressure method of faradic current application can be used for this purpose.
Uses of Faradic Current .
Faradic current can be used in the treatment of muscle inhibition, edema, incontinence, hallux valgus, Bell’s palsy (neurapraxic lesion), metatarsalgia, postural flat-feet, after tendo-achilles surgery, after knee surgeries, rheumatoid arthritis, tendon transplantation, later stages of peripheral nerve injuries, chilblain, muscle spasm, pain relief by counter-irritation etc.
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