6- Direct Current_2

7/30/2019 6- Direct Current_2

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Lecture VI

Dr. Amal HM. Ibrahim

Professor of Physical Therapy

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Direct current (DC) is a unidirectionalflow of electrons through a conductor for1 sec or longer or current passing

continuously in the same direction withthe same intensity. It is known as galvaniccurrent or constant current

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The current can be modulated bythree means first, reversed DC in

which the current flow for 1 sec ormore in one direction then reversed

for 1sec or more.

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Second, interrupted DC, in which thecurrent is flow for 1 sec up to 60 sec, thecurrent switch off for some seconds and

then starts again. This type is used to causetwitch contraction of denervated muscles.

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Third modulation is surged DC or rampingDC in which the current is rising graduallyand falling gradually over 1 second or longer,

the term ramp up and ramp down are usedrespectively.

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Direct current passes to the

tissues through two electrodescovered with wet pads, wetsponge, water bath or bath with

suitable solution. The DCcurrent will changed toconvection current in the wet

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At positive electrode (anode), an acid isformed and at the negative electrode

(cathode) an alkaline is formed causingchemical damage or burn. The magnitude ofchemical damage depends on current

density (the current intensity per unit area)and time of application.

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The current in any circuit is directlyproportional to the voltage and

inversely proportional to the resistance.The major resistance facing any currentapplied to the tissues is the epidermis

(impedance of the skin).

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Direct current has been used for a periodof 10 to 30 minutes. The current densitymust be kept at the level that does notcause tissue damage or discomfort to thepatient. Commonly the range of dose is

between 0.33mA/cm and 0.5mA/cm.

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1- Sensory irritation and hyperemia

Direct current causes mild tingling orprickling sensation. More current leadingto erythema of the skin under theelectrodes (the effect is marked under thecathode, negative electrode).

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2- Sedation and relief pain

Direct current is thought to reduce

nerve conduction velocity by usinglow dosage as 0.3mA for a longperiod, about 30 minutes. Also DC

can relief pain through inhibition ofpain receptors through pain gatetheory.

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3- Enhance wound healing

Application of DC current for 2 hours three times

daily accelerates healing of various kinds of wounds.First put the negative electrode (cathode) over thewound for 3 days and the positive electrode (anode)about 25 cm away from the wound. The total current

used could be varied between 0.2 and 1mA, so thecurrent density for most ulcers would be very low.

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3- Enhance wound healing

The mechanism by DC suggested that an antibacterialeffect accelerate healing, increased circulation and thegrowth and repair may account for.

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Factors affecting healing

Factors known to delay healing are divided into generaland local:

1- General: age, protein deficiency, low vitamin Clevel, steroids and NSAIDs (inhibitory effect),temperature (lower healing rate when colder).

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Factors affecting healing

Factors known to delay healing are divided into general

and local: 2- Local: poor blood supply/ ischemia, adhesion to bone

or other underlying tissues, continued inflammation,drying of the wound, excessive movements.

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4- Tissue destruction

It is the caustic effect of DC current applied through a

fine needle (cathode) as active electrode leading toliquefaction and a large moist pad (anode) as dispersiveelectrode lead to coagulation of proteins. This effect isused in destruction of unwanted tissues as warts or

removal of unwanted hair.

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5-Anodal galvanism (Electrophoresis)

Electrophoresis is the using ofanodal galvanism for treatment oflocal edema (drying effect)

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6- Electrotonus

Application of sub-threshold nerve stimulus

does not cause actionpotential but it affects theirmembrane potential. Thenegative electrode

(cathode) causes localdepolarization. The positiveelectrode (anode) causesthe reverse-hyper-polarization.

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7- Iontophoresis

Iontophoresis is the use of direct current to driving

topically applied substances in the form of ionsacross biological membrane for therapeuticpurposes.

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When DC used for pain relief therecommended dosage differ according to thepolarity used. When use cathode (activeelectrode), the current density used between0.5-0.8mA/cm2 for 10-20 minutes. If theanode is used (active electrode), lowercurrent density between 0.15-o.25mA/cm2for 15-30 minutes.

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1. Chemical burn or damage of the treatedtissues as a result of high current density, lowskin resistance (presence of cuts abrasions oruneven pressure), and touch of metal part ofelectrode to the skin.

2. Shock can occur if the circuit is broken

suddenly.

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Iontophoresis is a specific therapy byusing direct current to introduce

ionized drugs across biologicalmembrane for therapeutic purposes.It is sometimes called ion transfer.

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If a direct current is applied to theelectrolyte, convection current will flow. Thepositive charged ions will move toward theanode electrode.

The drug must be in ionic form (has acharge) it can be travel in either direction

depending on the polarity applied.

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The tissues are continuous electrolyte with thesolution of the wet pad or sponge which contain theionized drug. The negative charged ions will drift awayfrom the negative electrode and pass through the skin

and into the tissues and the same will happen to thepositive charged ions.

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The effects of Iontophoresis are either local

in the skin (under active electrode) orsystemic by disseminated through the tissuefluids.

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The effects of Iontophoresis depend on:

1- Current density which is limited by patienttolerance (should not exceed 0.2mA/cm+).

2- Time of application (20 to 30 minutes).

3- The concentration of ions in the solutionbetween 1 to 2%.

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The effects of Iontophoresis depend on:

4- Presence of some ions like zinc or silver form precipitateswhich are insoluble and may limit penetration.

The effect of Iontophoresis therapy depends also on themedication to be introduced. The therapist should be fullyinformed of the effect, side effect, indications andcontraindications of applied medications before treatmentbegins.

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1- Local Anesthesia

Using drugs like lignocaine or procaine will causelocal coetaneous anesthesia for about 14.5 minutes,increased if we add adrenaline, (infiltration cause

anesthesia about 22.2min and topical applicationabout 2.1 min). Local anesthesia has been usedtherapeutically in the treatment of herpes zosterand trigeminal neuralgia. Sometimes used inphysiotherapy department and with patient who

are sensitive to hypodermic injections for ear andeye surgery.

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2-Treatment of idiopathic hyperhidrosis (excessivesweating)

Glycopyronium bromide administered by Iontophoresis hasbeen recommended as simple, safe and effective treatment ofexcessive sweating. Hyperhidrosis usually affects palms, solesand axilla whose exocrine glands innervated by sympatheticsystem. The effect of Glycopyronium bromide(anticholinergic agent), lasts a variable length of time. Abed

and Morgan 1974, found a mean of 33.7 days for the palm and47.2 days for the soles of foot. It was suggested that fewpatients need repeated treatment every 4 to 6 weeks

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3-Application of vasodilators

Histamine is a vasodilator has been administeredby Iontophoresis for a variety of disorders.

Histamine Iontophoresis is used for arthritis,enhance wound healing and improve the viabilityof skin grafts.

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4- Application of inorganic cations

Inorganic cations carry a positive charge and aredelivered from the anode. Zinc has been used inthe treatment of patients with ischemic ulcers to

promote healing and prevent infection. SilverIontophoresis has also been used with some successin the treatment of patients with rheumatoidarthritis. Copper Iontophoresis has been used totreat chronic fungal infections of the feet.Magnesium Iontophoresis has been used to treatpatients with sub deltoid bursitis.

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5- Application of inorganic anions

Inorganic anions are administered under thecathode. Acetic acid Iontophoresis has been

described the treatment of patient with calciumdeposits around the shoulder and myositisossificans affecting quadriceps femoris muscle.Iodide iontophoresis has been used as useful in the

management of problems related to scar tissue andrelease of scar adhesion of tendon to bone.

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6- Application of antibiotics

Application of antibiotics by iontophoresis hasbeen used for treatment of ear chondritis following

burn injury and non healing ulcers.

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7-Application of anti-inflammatory drugs

Iontophoresis has been used to treat tendonitis andbursitis. The advantages of these methods are pain

less and sterility of the treatment. Thedisadvantages are being very expensive and timeconsuming.

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8- Relief of chronic pain (neurogenic pain)

Iontophoresis has been used and recommended forthe treatment of chronic pain syndromes, like

patient suffering from post-herpetic neuralgia andchronic pain in terminal cancer.

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In addition to the general principles of application

Ensure the drug is under the correct electrode (positivecharged ions under anode and negative charged ions

under cathode). Most of ions used are positive exceptacetate, chloride, iodide and salicylate which arenegatively charged.

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The treatment time and dose is variable, that if theeffect of treatment is inadequate you can continuefor longer time.

The initial dose for hyperhidrosis should be low:1.125mA for 3min for a 30cm2.

For other iontophoretic treatment the dosage isabout 0.05mA/cm2 for 20 to 30min.

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Systemic effects can occur, especially with large areas

application, in form of headaches, abdominal pain, ormild dryness of the mouth.

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1. Pregnancy.

2. Cardiovascular disorders especially with histamineiontophoresis.

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The circuit must be closed.

The dispersive electrode must be larger 2.5 than the

active electrode for muscle and nerve stimulation.The both electrodes are equal in size for sensorystimulation.

.

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The dispersive electrode (indifferent or

inactive) should preferably be positionedopposite to the active electrode, or at adistance about 25cm away from active

electrode.

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Cover the electrodes with pads oflint, gauze or sponge.

The electrode is slightly smaller1cm than the pad to avoidelectrode skin touch.

The pads must be thick enough(about 1cm after compression).

.

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Good fixation of the electrodes using bandage forirregular skin surface to avoid higher resistance of

some points. Prefer to treat extremities by immersing in water

bath.

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Explain the nature of treatment and feeling tothe patient.

Decrease skin resistance by wetting, warming, orwashing the skin.

Increase intensity slowly and dont switch on oroff with switch above zero.

Avoid electrical stimulation over areas with lowresistance like cuts and abrasions to avoiduneven skin resistance.

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Practical application of direct current In addition to the general principles of application

Prepare the patient, examine and test the treatedarea.

Warn the patient to report any painful sensation toavoid the risk of chemical burn.

Avoid application over cuts and abrasions to avoidchemical burn.

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Practical application of directcurrent

If a water bath is used for extremities, theelectrodes clipped to the side of the container.The size of this electrode does not matter but itshould be situated well away from the immersed

part. If one electrode is used in the bath it calledmonopolar bath and if both electrodes are used itcalled bipolar bath.

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Warn patient not to give his limb away from thebath during treatment to avoid shock.

Cover the untreated area close to the surface of

the water by cream or oil to avoid the passing ofcurrent through the tissues and cause burningsensation.

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The meter may show sudden little increasewithout the control being move due to loweringof the skin resistance. You should turn thecontrol down slowly and examine the area toavoid chemical burn.

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Practical application of direct current For enhance wound healing, measure the wound

size (by transparent) to calculate the currentdensity and to evaluate the rate of healing. Theulcer may be packed with gauze soaked in sterilesaline to allow adequate conduction of the current.

The electrodes wrapped in saline soaked gauze andfixed to the wound by strap or bandage.

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Practical application of direct current Apply the cathode as active electrode for the first

three days for its bacterio-cidal effect if the wound is

infected and the anode should be of the same size orlarger than cathode and placed on the nearest area.After three days we use anode as active electrode andcathode as dispersive electrode. If the wound is notinfected we start treatment with anode as active

electrode. The current should not cause musclecontraction and might applied each day for 2-4hours.

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6- Direct Current_2