Low Frequency Currents

1. Low Frequency Currents

2. What are low frequency currents? Currents with frequency ranges from 50 to 100 Hz Primary use is to stimulate nerves & muscles Various currents in this category are used for physiotherapeutic treatments Commonly used are Direct current Faradic 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)

3. 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)

4. Physiological effects • 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 muscles • 4. 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.

5. Indications • 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 stimulation • Training 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 return • Reduce formation and loosening of adhesions: • adhesion formation by the effusion is prevented by the movements; stimulation contract muscles if active exercise is impossible.

6. Contraindications • Skin lesions • Infection • Inflammation • Thrombosis • Marked loss of skin sensation • Active TB or cancer • Cardiac pace makers • Unreliable patients • Superficial metals A

7. 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 produced • If the surging is automatic the duration & frequency of the surge should also be tested to

8. Preparation of the apparatus • The 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 & glutei • A flat plate electrode & lint pad are used for an indifferent electrode to complete the circuit • Pad should contain at least eight layers of lint so that they are thick enough to make good contact with the tissue • They should be folded evenly with no creases & soaked in warm 1% saline • Tap water can be used but in addition of salt reduces the wetting solution • Electrodes should be 1cm smaller & to reduce the danger of coming contacted with the skin • Corners of the electrode should be rounded • Because points may become bent & dig into the pad %

9. 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.

10. Production of interrupted direct current • This is produced by modification in the form of interruption in direct current where current is made to flow & seized at regular intervals • This production of IDC involves • Source of IDC • Transistor • Potential divider • Timer circuit • Which is needed to provide therapeutic D.C is a steady unidirectional voltage • A means of regulating the voltage applied to the tissue via terminals marked positive & negative & means of measuring current flow • The mains voltage is rectified & reduced & a potential divider is placed in parallel with the patient • Moving the control can alter this divider • With potential divider at zero no voltage is applied so that no current will flow • The milliameter in series with the patient will indicate zero current flow

11. 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.

12. Selection of treatment for denervated muscles • Time: • Stimulation should start in early stage because maximal atrophy occurs in the first 3 months. • Pulse duration: • Neuropraxia – 100 ms rectangular pulses • Axonotmesis – 100 -600 ms triangular or trapezoidal pulses • Axonotmesis and neurotmesis – 100 – 2000 ms triangular or saw tooth pulses • Regeneration – 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.

13. Contraindications • Gross oedema • Pain • Scar tissues and contractures • Skin lesions • Lack of pain sensation • Active TB or cancer • Over cardiac pacemakers • Thrombosis and thrombophlebiltis • Unreliable patients • Superficial metal • Infections • Transthoracic or neck currents

14. Dangers Muscle damage: excessive stimulation can damage the denervated muscle Shocks Burns

15. 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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