What are low frequency currents?

Currents with frequency ranges from 50 to 100 HzPrimary use is to stimulate nerves & musclesVarious currents in this category are used for physiotherapeutic treatmentsCommonly used are

Direct currentFaradic current

Faradic current: Short duration Less than 10 msec Stimulate denervated muscles Repetition more (50-100 Hz)

Direct current: Long duration More than 10 msec Stimulate innervated muscles Repetition rate shorter (30Hz)

Faradic Type Currents

•Short duration interrupted direct current with a pulse duration of 0.02 to 1 ms and frequency of 50 – 70 Hz.

•The current is normally surged, ranging from 4 – 30 surges per minute with varying rest period.

•Faradic type and original faradic currents are muscle stimulating currents acting directly on nerve fibres. (used to stimulate the muscle with intact nerve supply)

1. Stimulation of sensory nerves:minimal; feels prickling sensation; causes vasodilatation of

superficial blood vessels > reddening under the active electrode.

2. Stimulation of motor nerves: stimulation causes muscle contraction; surged to allow the

muscle relaxation > surge gradually increase and decrease > contraction similar to voluntary contraction; changes taking place within the muscle is similar to voluntary contraction =>↑ metabolism, ↑ O and food stuff up take, ↑ output of waste products => ↑ blood supply to the muscle; muscle contraction and relaxation causes pumping effect on veins and lymphatic vessels => ↑ venous and lymphatic return

3. No stimulation of denervated muscles4. Ionic movement in intracellular and extracellular tissue

fluids: faradic alter the permeability of the cell membrane hence

reduce the swelling by accelerating the movement of tissue fluid. It also causes arteriolar dilatation which removes all metabolites and waste products.

Physiological effects

Facilitation of muscle contraction when inhibited by pain: pain inhibits the transmission of impulses to the motor units at anterior

horn cells and stimulation ↓ inhibition & ↑ transmission of voluntary impulses and induce relaxation to antagonists.

Re-education of muscle action: restore the sense of movement if unable to contract a muscle voluntarily.

Active contraction should be attempted with stimulationTraining a new muscle action: need after tendon transplant or other reconstruction of muscles which

required to perform different action; Active contraction should be attempted with stimulation with concentrating on the movement

Neuropraxia of a motor nerve: nerve is stimulated below the site of the lesion to contract the muscles.Venous and lymphatic drainage: pumping action of alternate contraction & relaxation of muscles & joint

movements ↑ venous and lymphatic returnReduce formation and loosening of adhesions: adhesion formation by the effusion is prevented by the movements;

stimulation contract muscles if active exercise is impossible.

Indications

A

– Skin lesions– Infection– Inflammation– Thrombosis– Marked loss of skin

sensation– Active TB or cancer– Cardiac pace makers– Unreliable patients– Superficial metals

Contraindications

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Preparation of the apparatus

Operator should test the apparatus by attaching leads & electrodes to the terminals holding the two electrodes in a moistened hand Current turned up until a mild prickling sensation is experienced 7 a muscle contraction is producedIf the surging is automatic the duration & frequency of the surge should also be tested

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Preparation of the apparatusThe active electrode may be a disc electrode or a small lint pad with a flat plate electrode This is preferable for large muscle like quadriceps & gluteiA flat plate electrode & lint pad are used for an indifferent electrode to complete the circuitPad should contain at least eight layers of lint so that they are thick enough to make good contact with the tissueThey should be folded evenly with no creases & soaked in warm 1% salineTap water can be used but in addition of salt reduces the wetting solutionElectrodes should be 1cm smaller & to reduce the danger of coming contacted with the skinCorners of the electrode should be roundedBecause points may become bent & dig into the pad

Long duration I.D.C.• Unidirectional currents with long durations, interrupted

at regular intervals are given directly to muscles aiming to reduce, prevent or reverse the course of muscle atrophy. It has the ability to regrowth and repair the nerve.

• Pulse duration: Specific pulse duration varying from 100 – 2000 ms. 1 -100 ms are taken as either long or short duration pulses.

• Pause duration: It should be at least 2-3 times as long as that of the pulse duration.

• Frequency: Generally from 5 – 10 Hz, depending on the pulse duration.

• As muscle tissue is less excitable than the nerves greater electric charge is needed.

Production of interrupted direct currentThis is produced by modification in the form of interruption in direct

current where current is made to flow & seized at regular intervalsThis production of IDC involves1.Source of IDC 2.Transistor3.Potential divider4.Timer circuit

Which is needed to provide therapeutic D.C is a steady unidirectional voltageA means of regulating the voltage applied to the tissue via terminals marked positive & negative & means of measuring current flowThe mains voltage is rectified & reduced & a potential divider is placed in parallel with the patientMoving the control can alter this dividerWith potential divider at zero no voltage is applied so that no current will flowThe milliameter in series with the patient will indicate zero current flow

Effects of electrical stimulation on denervated muscles

Reduction of denervation atrophy: early stimulation retard the denervation atrophy due to the contractions of muscles. It normalise the rate of glycogen synthesis and enhance the role of carbohydrate oxidation. It assists to protect the bone density and systemic functioning if the large muscles are paralysed.

Utilisation of substances: electrically produced contractions and relaxations of muscles use the substrates that come to the area due to increased blood supply.

Increase venous and lymphatic return: pumping effect increase the venous and lymphatic circulation. Otherwise accumulation of tissue fluid in fascial planes and in and around muscles can cause contractures in muscles and soft tissues.

Working hypertrophy: in a partial damage of a nerve, some of the muscles supplied by the nerve escape damage and get disuse atrophy but stimulation will produce working hypertrophy of these muscles.

Time: Stimulation should start in early stage because maximal atrophy occurs in the first 3 months.

Pulse duration: Neuropraxia – 100 ms rectangular pulsesAxonotmesis – 100 -600 ms triangular or trapezoidal pulsesAxonotmesis and neurotmesis – 100 – 2000 ms triangular or saw tooth pulsesRegeneration – do not use faradic type currents with maximal contractions. Continue using long duration pulses.

Type of contraction and frequency of treatment:20 -30 isometric contractions at least twice a day or 90 -200 contractions daily.Important to have a rest phase between contractions (1 -2 min.).If 90 -200 contractions are used, there should be 1 -2 min. interval between groups of 30 contractions.

Long time treatment should be given for about 1 -2 years until the patient get voluntary contractions.

Selection of treatment for denervated muscles

1. Gross oedema2. Pain3. Scar tissues and contractures4. Skin lesions5. Lack of pain sensation6. Active TB or cancer7. Over cardiac pacemakers8. Thrombosis and

thrombophlebiltis9. Unreliable patients10.Superficial metal11.Infections12.Transthoracic or neck

currents

Contraindications

Muscle damage: excessive stimulation can damage the denervated muscleShocksBurns

Dangers

Method of application – Monopolar technique (for

small muscles):• Active electrode

(cathode) on the muscle belly slightly distally. Inactive electrode (anode) is kept away from the muscle on the opposite side of the part.

– Bipolar technique (for large muscles):• two electrodes on the

either end of the muscle belly, cathode is generally placed at the distal end.

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