Definition: Diathermy is the treatment process by which cutting, coagulation of tissues are obtained.
· Application of high-frequency electromagnetic energy
· Used to generate heat in body tissues
· Heat produced by resistance of tissues
· Also used for non-thermal effects
· Treatment can be controlled easily.
· Use of appropriate electrodes permit the heat to be localized only in the region to be treated.
· Amount of heat that is to be delivered can be adjusted accurately.
· Inter lying tissues, muscles, bones, internal organs, etc, can be provided with heat by using high frequency
Physiologic Responses To Diathermy
· Not capable of producing depolarization and contraction of muscles
· Wavelengths too short
Physiologic Effects Are Those of Heat In General
· Tissue temperature increase
· Increased blood flow (vasodilation)
· Increased venous and lymphatic flow
· Increased metabolism
· Changes in physical properties of tissues
· Muscle relaxation
Doses are not precisely controlled thus the amount of heating cannot be accurately measured
Heating= Current2 X Resistance
Types of diathermy
· Shortwave diathermy
· Ultrasonic diathermy
· Microwave diathermy
· Surgical diathermy
1. SHORTWAVE DIATHERMY
· Power supply powers radio frequency oscillator (RFO)
· RFO provides stable drift-free oscillations at given frequency
· Power amplifier generate power to drive electrodes
· Output resonant tank tunes in the patient for maximum power transfer
• Power output should provide energy to raise tissue temp to therapeutic range (40-45 deg c) (80-120 watts)
• Should exceed sar-specific absorption rate (rate of energy absorbed /unit area of tissue mass)
• Generates both an electrical and a magnetic field
• Capacitor electrodes
• Inductor electrodes
• Selection of appropriate electrodes can influence the treatment
1.1 Capacitor Electrodes
· Create stronger electrical field than magnetic field
· Ions will be attracted or repelled depending on the charge of the pole
• Electrical field is the lines of force exerted on charged ions that cause movement from one pole to another
• Center has higher current density than periphery
• Patient is between elec trodes and becomes part of circuit
• Tissue is between electrodes in a series circuit arrangement
• The tissue that offers the greatest resistance to current flow develop s the most heat
• Fat tissue resists curre nt flow
• Thus fat is heated in a n electrical field
• Typical with capacitor electrodes
Air Space Plates
• Two metal plates surroounded by plastic guard
• Can be moved 3cm within guard
• Produce high-frequency oscillating current
• When overheated discharges to plate of lower potential
• Area to be treated is pllaced between electrodes becoming part of circuit
• Sensation of heat in direct proportion to distance of electrode from skin
• Closer plate generates more surface heat
• Parts of body low in subcutaneous fat best treated
• Greater electrical field
• Patient part of circuit
• Must have uniform contact (toweling)
• Spacing equal to cross-sectional diameter of pads
• Part to be treated should be centered
• Increasing the spacing will increase the depth of penetration but will decrease the current density
1.2 Induction Electrodes
Creates a stronger magnetic field than electrical field. A cable or coil is wrapped circumferentially around an extremity or coiled within an electrode
· Passing current through a coiled cable creates a magnetic field by inducing eddy currents (small circular electrical fields) that generate heat
· Patient in a magnetic field not part of a circuit
· Tissues in a parallel arrangement
· Greatest current flow through tissue with least resistance
· Tissue high in electrolytic content respond best to a magnetic field
Toweling is essential
Pancake coil must have 6” in center then 5-10cm spacing between turns
One or more monopolar coils rigidly fixed in a housing unit
May use more than one drum depending on area treated.
2. ULTRASONIC DIATHERMY
· It is used for curing the diseases of peripheral nervous system, skeletal muscle system and skin ulcers.
· It is adopted when the short wave treatment has failed and it helps to achieve the localization of heart to the affected part.
· The heating effect is produced in the tissues by the absorption of ultrasonic energy. The absorption effect is similar to that of a micro massage.
· It is better than the manual massage because the micro massage provides a greater depth of massage without causing any pain to the patient.
· Piezo-electric transducer is excited by the high frequency alternating current produced by the Rf oscillator.
· Ultrasonic wave from the piezo electric transducer is used for the purpose of treatment.
· It can be applied in continuous mode or pulse mode.
· Frequency range of 800 KHz to 1MHz is suitable for the ultrasonic method of treatment
3. MICROWAVE DIATHERMY
· In this method the tissues are heated by the absorption of microwave energy. The frequency used is about 2450 MHz.
· Better results are obtained by the microwave method and it is more advantageous than the short wave method.
· There is no pad electrodes and flexible cable.
· Microwave is transmitted into body and treat directly from the direction of unit.
· Microwaves are produced with the help of magnetron
· Proper cooling arrangements are made for the purpose of cooling the magnetron
· Necessary precautions should be taken during this method of treatment
· Excessive dosage causes skin burns and the skin should be dry as the waves are rapidly absorbed by water.
· Patients with implanted pacemaker should not undergo this treatment
· There are possibilities of over heating
· Care should be taken while the treatment is made near the eyes.
4. SURGICAL DIATHERMY
· Logic board is the main part of the unit which produces the necessary waveforms for cutting, coagulation and hemostasis modes of operation.
· An astable multivibrator generates 500 kHz square pulses. The output from this oscillator is divided into a number of frequencies using binary counters.
· These frequencies are used as system timing signals, A frequency of 250 KHz provides a split phase signal to drive output stages on the power output board.
· Frequency of 250 Hz is used for cutting , after the high power amplification by push pull amplifier.
· The output of the push pull amplifier is given to a transformer so that the voltage is stepped up and the output signal from the unit is well isolated.
· The isolator switch provides an isolated switching control between the active hand switch and the rest of the unit.
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