Definition: The constant direct current which is sometimes known as constant galvanism is a unidirectional current of unvarying intensity.

Physiological Effects

The tissues of the body are the conductors of electricity because the tissue fluid contains ions and so are electrolytes. Consequently the current which passes through the body is convection current, consisting of two way migration of ions. The conductivity of different tissues varies according to the amount of fluid that they contain: muscle, with a good blood supply, being a good conductor, while fat is a poor conductor. The epidermis has a high resistance, about 1000 ohms, as it contain little fluid and the superficial layers do not readily absorb moisture. The resistance of underlying tissues is much less than that of skin, so the current spreads considerably once it has passed through the skin, and the current density, and therefore the effects, are much greater in the superficial tissues than in the deep tissues. The physiological effects of constant D.C. are due to two way migration of ions.

1- Vasodilatation: Erythema of skin is observed when the pads are removed after treatment, especially at cathode, and indicates that current causes vasodilatation. This undoubtedly takes place in the superficial tissues, but it seems unlikely that there is any appreciable effect in the deep tissues. There are several theories as to the cause of vasodilatation:

a- It may be due to the moving ions stimulating the sensory nerve endings and so causing the reflex dilatation of blood vessels.
b- Irritation of the cells may cause the liberation of “H” substance. This produces the triple response of dilatation of capillaries, by direct effect, dilatation of arterioles by axon reflex, local edema due to increased permeability of capillary walls.
c- Vasodilatation may be due to the mechanical action of the moving ions bombarding the walls of blood vessels.

As a result of vasodilatation there is increased blood supply to the superficial tissues, which produces the sensation of warmth experienced during the treatment. There is no direct production of heat in the tissues as the intensity of current that can be tolerated is not sufficient for this purpose.

2- Polar Effects: These are effects produced in tissues immediately under the electrodes and differ at anode and cathode.

a- Electrotonus: Electrotonus is the effect upon nerve conductivity and excitability and can be demonstrated in the laboratory with gastrocnemius muscle and sciatic nerve of the frog. Electrical stimulation of nerve produces a muscle contraction, but if at the same time if the constant D.C. is applied with one electrode between the point of stimulation and the muscle, the strength of contraction is modified. If anode is applied, the strength of contraction is reduced as anode has the effect of decreasing the conductivity of nerve. The cathode has the opposite effect of increasing the conductivity of nerve, and so the contraction of muscle.

Anelectrotonus is the decreased excitability and conductivity of nerve in the region of anode, catelectrotonus the increased excitability and conductivity of nerve in the region of cathode. Both are due to the development of potential difference across the plasma membranes of axons of nerve as the current passes. The P.D. developed under anode augments the normal resting P.D. and so make it difficult for the impulse to pass, while that under cathode reduces the resting P.D. and increases the conductivity.

While these effects can be demonstrated in the laboratory it seems doubtful whether they can occur in the living body, as increase in P.D. on one side of axon is accompanied by a reduction on the other side. At the same time clinical evidence indicates that the effect is produced to some extent. There is no other explanation of the relief of pain that follows treatment with anodal galvanism and further evidence is provided by the greater erythema produced at the cathode and reduced at the anode, so that there is greater reflex vasodilatation at the former than at the latter.

b- Electrophoresis: When a current is passed through a non living semi solid electrolyte such as gelatin, there is increase in fluid at cathode and a decrease at anode. The former is known as cataphoresis, the latter as anaphoresis. Various explanations of the effects have been given, but it is thought to be due to the movement of positively charged colloidal particles which are present in the electrolytes and to which water molecules adhere. When a P.D. is applied, the colloidal particles which considerably larger than the ions, migrate slowly away from anode and towards cathode, carrying water molecules with them and bringing about the redistribution of the fluid. In the living tissues, the continued circulation of the fluids must to a large extent counteract this effect, but there appears to be some reduction in the fluid present in the superficial tissues underlying the anode, and increase at the cathode.

C-Introduction of Ions into the Tissues or Iontophoresis: When a constant D.C. is passed through the body, there are two way migrations of ions in the tissues and also in solution containing the pads. Consequently there is interchange of ions between the tissues and the pads. Positive ions are repelled by the anode and pass from pad to tissues under this electrode, while at cathode they are attracted from tissues to pad. Similarly negative ions move from pad to the tissues under the cathode and from tissue to pad under anode. Thus ions contained in the pads are repelled into the tissues under the electrode bearing the same charge as the ions, and the current can be used to introduce ions into the tissues, treatment being known as medical ionization or iontophoresis.

d- Chemical Effects: When a direct current is passed through an electrolyte, chemical changes take place at the electrodes. If the current is applied to the body with metal electrodes with direct in contact with the tissues, the tissues are involved in the chemical reactions and are destroyed. There is coagulation of tissues at the anode, while at cathode they tend to liquefy. When pads are used the chemicals are formed between the pads and electrodes, but should the pad be of insufficient thickness the acid formed at anode and alkali formed at cathode soak through to the skin and cause destruction of the tissues. The chemical effects are utilized in the treatment called surgical ionization or surgical iontophoresis, but are also responsible for the burns which are liable to occur with direct current.

Summary of reactions at anode and cathode
Cathode Anode
Attraction of (+) ions Attraction of (-) ions
Alkaline reaction by formation of NaOH Acid reaction by formation of HCL
Decreased density of protein (sclerolytic) Increased density of protein (sclerotic)
Increased nerve excitability via hypo polarization Decreased nerve excitability via hyper polarization

Therapeutic Effects and Uses

The effects of constant direct current are confined to superficial tissues. So it is of limited therapeutic value, but the following may me utilized:

Counter Irritation: This is most evident at cathode. The moving ions irritate the superficial sensory nerve endings, which have been rendered more excitable by catelectrotonus, and the marked stimulation of these nerves appears to reduce impulses reaching the brain from the underlying structures. Pain due to lesion of deeper structures is relieved and the method may be used in the treatment of chronic lesions such as osteoarthritis, chronic rheumatoid arthritis, and stiff joints following injury, tennis elbow, and tenosynovitis. It is most likely to be effective for lesions of superficial structures such as wrist, knee and ankle joints. The constant D.C. alone is rarely an adequate treatment, but may be used to relieve pain as a preliminary to active exercise.

Anodal Galvanism: Under the anode there appears to be relief of pain and muscle spasm, probably due to anelectrotonus, and a reduction of recently exuded fluid, probably due to anaporesis. As stated previously, it seems unlikely that these effects can be produced due to any appreciable extent in the body, yet recent injuries such as ankle sprains, do seem to derive benefit from the treatment. It can, however, be effective only for a limited period before organization of the exuded fluid occurs.

Methods of Application

Contra planar: The pads are applied opposite aspect of the structure to be treated, the most suitable surfaces being chosen. For instance, when treating the knee joint the pads are usually placed on medial and lateral aspect, avoiding the irregular anterior and posterior surfaces.

The effects of constant D.C. are confined to the superficial tissues, so to obtain the maximum effects the pads should be as large as possible. Care must, however, be taken that the pads are not placed too close to each other, or the current may concentrate between them.

When the structure being treated is equidistant from the surfaces to which the pads are applied, both pads should be of same size. When the structure is near to one surface than to the other the active electrode, which is as large as practicable, is placed on the nearer surface, with a large directing electrode opposite. The intensity of current passing through both pads is the same, so the current density, and therefore the sensory stimulation, is less under larger pad than under smaller one. Thus undue sensory stimulation under directing electrode, which might limit the total current tolerated, is avoided. The principal effect of current, when applied in this way, is probably counter irritation. So cathode is placed on the more painful aspect.

A current density of 2 milliampere per square inch of pad is desirable and the treatment usually lasts for 20 to 30 minutes. Both the intensity and the duration of the treatment must, however, be determined by the tolerance of the patient’s skin, which varies considerably in different individuals. Treatment is usually applied on alternate days, as the skin tends to become sore with more frequent applications.

Cathodal Galvanism: The cathode is applied over the effected structure and the circuit completed with a much larger anode elsewhere on the body. The active pad may be large, covering as much of the effected structure as possible, or when the lesion is localized; a small pad may be used.

The indifferent pad should be appreciably larger than the active, so that the current density under it is low, otherwise the sensory stimulation in this area may limit the total current that can be applied. A high current density is desirable and when the active pad is small 2 milliampere per square inch or more may be tolerated. Although if a large active pad is used it is not as rule possible to apply so high a current density. The duration of treatment is usually 20 to 30 minutes, but both this and the intensity of current must be determined by the patient tolerance. The treatment is usually applied on alternate days.

The principal effect is counter irritation, and theoretically a large pad should be most satisfactory because of the widespread effects, but it often proves less effective than the contra planar method, possibly because the patient tends to tolerate a higher current density with the latter.

Anodal Galvanism: The anode is applied over the area to be treated and the circuit completed with a larger cathode elsewhere on the body. The latter should be at some distance from the anode, in order that it shall not interfere with anodal effects, and should be larger than the anode so that patient is not unduly conscious of it, though as a low current density is used it is not likely to limit the intensity of the current that can be applied. The treatment is found to be most effective if a low current density, ¼ to ½ milliampere per square inch of pad, is applied for 40 to 60 minutes. As the current density is low and the treatment effective for only a small period, the skin usually tolerates daily application.

Technique of Treatment

Preparation of the apparatus: The source of current is a cell battery or apparatus which uses the main supply, the former being advisable for the treatment of any part of the head.

The apparatus must be tested before applying current to the patient. Leads are attached to the terminals and held with the free ends, in a bowl of tap water. The control is turned up and the needle of milliampere meter watched to ensure that the regulation of the current is even.

The control should be turned up at least as far as will be required for the treatment, or faults, in the potential divider may pass undetected. Tap water is used as it has a fairly higher resistance and so the current cab turned well up without passing excess current through the milliamperemeter.

The shunt of meter should be tested and the polarity can be checked by observing the bubbles of hydrogen formed at the cathode. The polarity is rarely incorrectly marked but is easily checked in the course of other test. The operator may then test the current on himself, as for faradism, and if he is not familiar with the apparatus it is advisable to test the shunts to ensure that the current is not broken when the switch is moved from one position to another.

Pads similar to those for faradism are required, but they must be at least half an inch in thickness for a treatment of average intensity and the duration, in order that chemicals formed at the electrodes shall not soak through the skin. Sixteen thicknesses of lint or eight of Turkish toweling, evenly folded with no creases or raw edges, are suitable. The pads are soaked in 1 percent saline, care being taken that the salt is fully dissolved as other wise it mat cause concentration of the current. The electrodes are half an inch smaller all round than the pads, with rounded corners.

Preparation of the patient: The skin is washed and abrasions protected as for faradism, but in addition skin sensation must be tested at first attendance to ensure that the patient will be able to detect any concentration of the current. The test may be made by a blunt object and cotton wool.

Application of the pads and the electrodes: The skin is moistened with the saline and the pads and electrodes are applied, cares being taken that no metal comes in contact with the tissue. The electrodes are covered with jaconet, half an inch larger all round than the pads, and bandaged firmly in position. The whole of both pads must be covered by the bandage it is advisable to bandage the leads away from the skin. If the surface is irregular, hollows may be padded with white wool soaked in saline, or brown wool may be placed over the hollows, on the top of pads and electrodes, in order to exert extra pressure in these areas and maintain even contact between the pad and the skin.

Application of the current: The patient is warned that he will experience a prickling sensation as the current is increased, which will gradually passes off and be replaced by a sensation of warmth, also that he must report any discomfort or concentration of current. The current is turned up slowly, taking about 5 minutes to reach the maximum, in order to allow time for the skin resistance to fall. It will be noticed that during this period the pointer of milliamperemeter continues to move up when the control is stationary, due to the fall in resistance which occurs as the ions enter the skin. When the current is first applied the ions pass mainly through the hair follicles and ducts of the sweat glands, where the resistance is less than that of the intervening epidermis. The prickling sensation experienced at this stage is thought to be due to stimulation of the sensory nerve endings at the bases of hair follicles. The continued passage of current results in ions entering the epidermis and reducing its resistance, so that the distribution of current becomes more even. The prickling passes off and the sensation of warmth is due to the increased blood supply.

Throughout the treatment the operator should be within the call of the patient and should inspect the meter at frequent intervals. If the needle goes up after it has stabilized, the situation must be investigated. It may be due to the bandage becoming damp and forming a short circuit between the pads, or the skin may be breaking down with the development of burn. If the patient reports discomfort, especially at one spot, the current must be turned down and the area examined.

At the conclusion of treatment the current must be reduced slowly and turned off. The skin is washed to remove any chemicals that may have soaked through the pads, dried and powdered, or a soothing cream such as glycol jelly may be applied. The skin should be evenly red under the cathode, while erythema under anode is less marked and may be uneven.

The intensity of the current and the duration and the frequency of the treatment have been considered with the method of application. At the first attendance it is usual to apply rather less current, and for a shorter time, than on subsequent sessions, in order to ensure that there is no adverse reaction of the skin. A record should be kept of size and position of pads, the intensity of current, the duration of treatment and skin reaction at each attendance.

Treatment in Baths

The advantages and disadvantages of applying the current in baths, and the method of arranging the treatment is described as under.

Water makes perfect contact with the tissues, the encumbrance of pads and electrodes are avoided, and prolonged soaking reduces the resistance of the skin. Prepare the patient and apparatus as described previously. Position the patient in sitting on a plinth with the back well supported and the feet on the stool which is covered with a plastic sheet. This position may have to be adapted for older patients or patients with a history of dizziness, but has the advantage that the physiotherapist is able to sit to manipulate the control of the machine and at the same time observe the muscle contraction achieved. Place the patient foot in the bath containing enough warm water. The position of electrodes is adjusted according to the individual requirement of the area to be treated. As for example, for the treatment of feet, place two electrodes transversely across the bottom of the bath, one under the heel and the other under the forefoot. A suitable duration and intensity of current is selected. Intensity is increased gradually and according to the tolerance of the patients.

Precautions: When treatment is applied in baths, the danger of burn is rather less than when pads and electrodes are used, as any chemical which may be formed dissolve in water and so diluted. Burns could occur, however, if metal contact with the tissue, so rings etc must be removed and the patient warned not to touch the electrodes. Breaks in the skin are protected with petroleum jelly, as they would cause discomfort due to the concentration of current.

The danger of shock is greater than with pads and electrodes. In addition the patient should be warned not to take the limb out of the bath during the treatment, as this would break the circuit and cause a shock.

The control is turned up and very slowly, as owing to the low skin resistance; the slight variation in EMF causes an appreciable variation in the intensity of the current. The patient’s sensation is the main guide to the intensity of the current that should be applied.

Uses of Bath Treatment: Treatment in bath is satisfactory where a wide spread effect is required but the method is not suitable for a localized application. It is of most use for the application of current to an irregular area such as the hand and foot, but as the limb must be dependent it is not suitable for the treatment of the swollen areas. In some cases a monopolar bath may conveniently be used as an indifferent electrode.

Dangers and Precautions

Electric Shock: Electric shock is one of the dangers associated with the application of constant D.C.

Electrolytic Burns: Burns produced by the constant D.C. may be electrolytic of chemical burns. The tissue is destroyed and the burn appears as a grey spot, surrounded by a reddened area. As tissue is destroyed, the healing is by second intention and is liable to be slow. The area should be kept dry and care must be taken that it does not become infected. The burn is usually protected with dry sterile gauze and healing can be hastened by the application of infra red or ultraviolet.

Burns are most liable to occur if the current is applied with metal in contact with the tissue, as the tissues are involved in directly in chemical actions. This may occur if the electrode, clip or the end of lead projects over the edge of the pad, if there are small places of metal on the pad, which might have been dropped when trimming the lead and electrode, if there are metal objects, such as rings, in contact with the tissues, or if there is metal embedded in the tissues, e.g. a plated fracture.

Concentration of current may also cause a burn, as more chemicals are formed in the area of concentration than elsewhere. This may be due to break in the skin, to the presence of undissolved salt on the pad, to pads of uneven thickness, or with creases or raw edges, or pads that are unevenly damp. It may be due to electrode being bent cracked or much smaller than the pad or to the pads too closer to each other, so that current concentrates between them.

If the pads are too thin for the intensity and the duration of the treatment, chemicals may soak through to the skin, or if the pads have not been properly washed after a previous treatment and still contains some chemicals, the same thing may occur. If the patient has not received adequate warning of the current that he will experience, he may tolerate too much current, or fail to report any concentration of current. If the skin sensation is defective in the area to which the current is applied, excessive current or concentration may pass undetected. Application of liniment may render the skin more susceptible to damage, and so it is wiser not to apply the current in the areas on which liniment has recently been used.

Galvanic Rash: A rash may be produced on the skin as a result of constant D.C; individuals with sensitive skin are liable to show this reaction. This type of rash varies in different cases; it may red like nettle rash, or small white spots or minute blisters may appear. The skin should be washed and soothing cream may be applied. This is better than the powder, as the skin tends to become dry and chapped with repeated application of the current

Giddiness: This is liable to occur if the current is passed through the region of semicircular canals, particularly when the intensity is being varied, e.g. in treatment of ear or mandibular joints. When applying currents to these areas the patient must be fully supported, the current increased and decrease very slowly, and the operator at hand throughout the treatment.


The current must not be applied to the followings:

1- Anesthetic areas of the skin
2- Hypersensitive skin
3- Breaks in the skin
4- Metal embedded in the tissues
5- Application of liniment
6- It is impossible to give a satisfactory treatment