High Frequency currents and its types PDF

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Summary

High frequency currents and its types.Especially details on short wave diathermy with its physiological and therapeutic effects and uses...

Description

High Frequency Currents Definition: A high frequency current is a current which alternates so rapidly that it does not stimulate motor or sensory nerves. • Frequency: • Frequency is >6000Hz

APPLICATIONS: This treatment can be applied directly or indirectly • To the skin and can be used to heat ,stimulate or sanitise the skin The machine use a high frequency current that alternates over 100,000 cycles per seconds. • A high frequency machine will have an on/off switch and an intensity control.

MODALITIES: o Ultrasound o diathermy o Short wave diathermy. o Infrared rays o Ultraviolet rays o Laser

Shortwave diathermy: Shortwave diathermy (SWD) is use of high frequency electromagnetic waves of the frequency between 107 and 108 Hz and a wavelength between 30m and 3 m to generate heat in the body tissues .it provides deepest heat available to the physiotherapist. The therapeutically used frequencies and wavelength are 27.12MHz and 11 m (commonly). The less common frequencies and wavelength are 40.68MHz and 7.5m and 13.56 MHz and 22m.

Principles: It is not possible to produce high frequency currents by some mechanical device which produces sufficient rapid movements. This type of current can only be produced by discharging a condenser through an inductance of low-ohmic resistance. If a current of very high frequency is required, the capacitance and inductance should be small and if a current of low frequency is required the capacitance and inductance should be large. This is the mechanism of production of high frequency current.

Construction: The system consists of two circuits: 1. The machine circuit 2. The patient circuit

Methods of Applications: The transfer of electrical energy to the patient tissues occurs either by electrostatic field or electromagnetic field. Therefore, two methods of applications are used: 1. Condenser/capacitor field method 2. Cable method Capacitance depends upon:   

The size of electrodes The distance between electrodes The tissues between the electrodes

Tuning of circuit: When electrodes are arranged in position with the patient body, the capacitance of variables capacity is adjusted until the product of inductance and capacitance of resonator circuit is equal to that of oscillator circuit.thus when resonator and oscillator circuit are tune with each other there is transfer of maximum energy into patient's body parts.

Capacitor Field Method The electrodes are placed on each side of the part being treated. The electrodes are separated by the skin by means of an insulating material. The electrodes act as the plates of the capacitor, while the patient's tissues together with the insulating material which separates them from the electrodes for the dielectric. When the current is applied, rapidly alternating charges are setup on the electrodes and gives rise to a rapidly alternating electric field between them. The electric field also influences the material which lies within it.

Cable Method or Inductothermy In this method, a thick insulated cable is used for treatment purposes. Electric field or magnetic field or both are achieved by the use of cable method. When the high frequency current oscillates in the cable, a varying electrostatic field is set up between its ends and a varying magnetic field around its center. The cable is coiled around the patient's body and is separated from the patient's body by a layer of insulating material.

Physiological effects:     

Effects on metabolism of the body Effects due to increase blood supply Effects of heat on the nervous tissues Effects of heat on the muscular tissues Effects of heat on the sweat glands.

(1) Effects on metabolism of the body As the van't Hoff's statement states that "any chemical change which is capable of being accelerated is accelerated by the rise in temperature. The metabolism of body itself is accelerated both the anabolism as well as catabolism is enhanced, the oxygen supply to tissue is increased and thus the heating of damage tissues is accelerated.

(2) Effects due to increase blood supply The heat has a direct effect on blood vessels.it cause vasodilation of vessels in the area of heating. When there is generalized vasodilation, the peripheral resistance is reduced. heat also reduced viscosity of the blood and thus there is generalized fall in the blood pressure.

(3) Effects of heat on the nervous system Heat alters conduction in nervous tissues.it produces a sense of sedation .perception of pain is also reduced as it enhances the pain threshold.high frequency current does not stimulate motor or sensory nerves.the shorter the impulse of current ,the less is the effect on the nervous system.

(4) Effects of heat on muscular tissue Increased blood supply provides optimal environment for the muscles to contract .it provides fresh nutrients,oxygen and removes the waste products faster.thus efficacy of muscle is increased.

(5) Effects of heat on sweat glands The heat has an effects on sweat glands as well. As heated blood is circulated throughout the body,it stimulates the centers for regulation of sweat gland. The production of sweat gland is increased and thus there is increased elimination of waste products.

Therapeutic effects:

     

Effects on inflammation Effects in bacterial infections Relief of pain Effects on muscle tissue Traumatic condition Reducing healing time

(1)Effect on inflammation The dilation of arterioles and capillaries results in an increased flow of blood to the area which increased supply of oxygen and nutritive material. This increased flow of blood increase antibodies and white blood cells these effects help to bring about resolution of inflammation.

(2) Effect in bacterial infections Inflammation is normal response of tissue to the presence of bacteria, the principal features being vasodilation, exudation of fluid into tissue and an increase in concentration of white blood cell and antibodies in the area.

(3)Effect on relief of pain Mild degree of heating is found to be effective in relieving pain. Presumably as a result of sedative side effects.

(4)Effect on muscle tissue The heating induce muscle relaxation, so short wave diathermy may be used for the relief of muscle spasm associated with inflammatory and trauma, usually as a preliminary in conduction with movements.

(5)Effect on traumatic condition The beneficial effect of shortwave diathermy on traumatic lesion is similar to those produced in inflammation. The exudation of fluid and increased flow of blood through the area assist in removal of waste products.

(6) Effect on reducing healing time: To promote the healing of wound or injured tissue, an increased blood supply to tissue may be of benefit, provided that the vascular responses to heat to tissue are normal.

Dangers of Shortwave Diathermy

1. Burns    

Concentration of electric field Excess current Impaired blood flow Hypersensitive skin Leads touching skin

2.Scalds 3. Electric shock 4. Overdose 5.Precipitation of gangrene 6. Faintness 7.Giddiness...