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Diathermy Units

Types of diathermy · Shortwave diathermy · Ultrasonic diathermy · Microwave diathermy · Surgical diathermy

DIATHERMY UNITS

 

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

 

Advantages:

 

·        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

·        Analgesia

 

Diathermy Heating

 

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

 

SWD Electrodes

 

         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

Pad Electrodes

 

         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

 

Cable Electrode

 

Two arrangements:

Pancake coils

 

Wraparound coils

Toweling is essential

 

Pancake coil must have 6” in center then 5-10cm spacing between turns

 

Drum Electrode

One or more monopolar coils rigidly fixed in a housing unit

 

May use more than one drum depending on area treated.

Toweling important.

 

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

 

Precautions

 

·        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.

Disadvantages

 

·        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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