Shortwave Diathermy

1. Shortwave Diathermy Prof. Dr. Gehan Mosaad

2. At the end of the lecture the student should be able to • Define short wave diathermy and know its types • Discuss the mechanism of heat production by SWD • Understand methods and techniques of SW application • Identify factors affecting field distribution • Know the precautions of using SWD

3. Shortwave Diathermy • SWD is a means of producing therapeutic heat in the tissues by the use of radio waves of high frequency. • Shortwave radiation is within the radiofrequency range( 3kHz to 300MHz and wavelengths of 1 m to 100 km). • SWD machine used by physiotherapy utilize the frequency of 27.12 MHz and wavelength of 11 meter. • There are two types of SWD • Continuous shortwave • Pulsed shortwave

4. Heat Production by SWD • Any living tissue consists of three types of molecules: • Charged molecules • Dipolar molecules • Non polar molecules • All of three types will influence the conductivity and hence the heating produced by SWD

5. Heat Production by SWD (cont) Passing a current of sufficient intensity at a high frequency increases the internal kinetic energy of matter causes heating and increase temperature in the material. SWD produces heat through tissue by: • Vibration of charged molecules (ions and certain proteins) • Rotation of dipolar molecules (water and some proteins) • Distortion of non-polar molecules (fat cells)

6. Molecular reaction to high frequency alternating current

7. Methods of shortwave application • Capacitive method By using: • Air space plates • Pad electrodes. • Inductive method By using: • Cables • Drums.

8. Capacitive method • A high-frequency a alternating electric current flows from one plate to the other through the patient. • The patient is part of the electric circuit connecting the two electrodes. • Area to be treated is placed between electrodes and becomes part of external circuit. • As the current flows through the tissue, it causes oscillation of charged particles and thus increases tissue temperature.

9. Capacitive method 1- Air Space Plates • They aremetal plates encased in a plastic housing. • Metal plates can be adjusted 3cm within guard.

10. Capacitive methodAir Space Plates

11. Capacitive method 2- Pad Electrodes • They are malleable metal covered with a thin layer of rubber • They must have uniform contact pressure on the body • Towels are used to prevent burns

12. Inductive method • The tissues are placed in the electromagnetic field by the use of an insulated cable or coil electrode which is available in two forms cable and drum electrodes. 1- The cable electrodes • Theyare bundles of plastic-coated wires • The cable may be wrapped around the extremity or coiled flat like a pancake and placed on the skin. • When an alternating electric current flows through these wires, eddy currents are induced inside the limb. • Patient placed in a magnetic field NOT part of a circuit

13. Cable Electrodes The cable is wrapped around the extremity The cable is coiled flat like apancake and placed on the skin

14. Inductive method(cont.) 2- Drum electrodes • A drum applicator is made of a flat spiral coil inside a plastic housing. • The drum is placed directly over the area being treated, and the flow of alternating electric current in the coil produces a magnetic field, which in turn induces eddy currents within the tissues. • Diathermy devices with drum applicators may have one or two drums or a single drum that can be bent to the area being treated.

15. Drum electrode A drum applicator is made of flat spiral coil inside a plastic housing

16. Inductive method (cont.) • Whenhigh frequency alternating current (AC)flowsin the inductive coil produces magnetic field perpendicular to the coil which in turn produces eddy current inside the tissue. • These induced electric currents cause charged particles in the tissue to oscillate that leads to an elevation in tissue temperature • The amount of heat generated in the tissue is affected by the strength of the magnetic field that reaches the tissue and by the strength and intensity of the induced eddy current.

17. Inductive method (cont.) • The strength of magnetic field is affected by the distance of tissue from the applicator according to inverse square law. • Thestrength of the induced eddy currents is determined by: - strength of the magnetic field in the area - electrical conductivity of the tissue in the area. • The electrical conductivity of tissue depends primarily on - tissue type - frequency of the signal being applied.

18. Inductive method (cont.) • Metals and tissues with a high water and electrolyte content, such as muscle or synovial fluid, have high electrical conductivity, whereas tissues with a low water content, such as fat, bone, and collagen, have low electrical conductivity. • Thus, inductive coils can heat both deep and superficial tissues, but they produce the most heat in tissues with the highest electrical conductivity

19. The drum is placed directly over the area being treated • May use more than one drum depending on treatment area • Toweling is important • The cable is arranged in a pancake shape • Towel between skin and coil • Spacing between turns in coil must be at least 3cm and maintained by using rubber or wooden spacer.

20. Techniques of application of SWD I. Positioning of electrode in capacitive method • Contraplanner technique: It is used to treat structure on the two aspect of the body. Two electrodes are placed on opposite sides of the part being treated e.g. joint. • Co-planner technique: It is used to treat structure on one aspect of the body .Two electrodes are placed on the same line together of the part being treated e.g. back.

21. Techniques of application of SWD (cont.) The distance between electrodes must be greater than sum of skin electrode distance, other wise the line of force passes between the electrodes rather than through the tissue • Cross fire technique The position of electrodes is contra planner technique. But, half of treatment time, the electrodes are placed anterior and posterior to the treated area and the second half of time, the electrodes are repositioned, lateral and medial to the treated area, e.g. pelvis.

22. Techniques of application of SWD (cont.) II. Shape of electrode in inductive method. In case of cable electrode • wrapped around the extremity • coiled flat like a pancake and placed on the skin

23. Factors affecting field distribution Capacitive Electrodes 1- Spacing of electrode: - Normal spacing Uniform field - Closely spaced Superficial heating - Far spaced Deep heating - Unequal spacing Superficial heat under closer one 2- Size of electrode: - Electrode is little larger than the part Uniform field - Electrode is too bigger than the part Heat loss - Electrode is too smaller than the part Superficial heat - Electrode are of unequal size Superficial heat under smaller one

24. Factors affecting field distribution (cont.) 3- Position of electrode relative to the tissue - Electrode parallel to skin surface Uniform field - The distance between electrodes less than the combined skin electrode distances Most of field passes through air space - Electrode isn't parallel to skin surface Superficial heat under closest part of electrode

25. Factors affecting field distributionCapacitive Electrodes

26. Precautions • Electronic or magnetic equipment in the field The SWD device should be isolated from these devices. Because the treatment field may interfere with such equipments as computers. It is recommended that the leads and applicators of diathermy devices be at least 3 m, and preferably 5 m, from other equipments. • Obesity Diathermy should be used with caution in obese patient because it may heat fat excessively, especially capacitive plate. • Copper bearing intra-uterine contraceptive devices Diathermy should be used with caution with patient using copper-bearing intrauterine contraceptive device.

27. When Should Diathermy Be Used? • If the skin or some underlying soft tissueis tender and is unable to tolerate pressure. • When the treatment goal is to increase tissue temperatures in a large area. • In areas where subcutaneous fat is thick and deep heating is required.

28. Case study Case 1 MS is a 50-year-old female. She has been diagnosed with adhesive capsulitis of the right shoulder and has been referred to physical therapy. She complains of shoulders stiffness. The objective exam reveals restricted right shoulder active and passive range of motion. Case 2 AB is a 24-year-old male, football player who suffered from left ankle inversion sprain approximately 48 hours ago. He complains of moderate pain and swelling at the lateral ankle.

29. Thank You