Diathermy Units

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.