2 At the end of the lecture the student should be able to Define short wave diathermy and know its typesDiscuss the mechanism of heat production by SWDUnderstand methods and techniques of SW applicationIdentify factors affecting field distributionKnow the precautions of using SWD
3 Shortwave DiathermySWD 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( 3 kHz to 300 MHz and wavelengths of 1 m to 100 km).SWD machine used by physiotherapy utilize the frequency of MHz and wavelength of 11 meter.There are two types of SWDContinuous shortwavePulsed shortwave
4 Heat Production by SWDAny living tissue consists of three types of molecules:Charged moleculesDipolar moleculesNon polar moleculesAll 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 methodBy using:Air space platesPad electrodes.Inductive methodCablesDrums.
8 Capacitive method A high-frequency a alternating electric current flows from one plate to the other throughthe patient.The patient is part of the electriccircuit connecting the two electrodes.Area to be treated is placed betweenelectrodes and becomes part of external circuit.As the current flows through the tissue,it causes oscillation of charged particlesand thus increases tissue temperature.
9 Capacitive method 1- Air Space Plates They are metal plates encased in a plastic housing.Metal plates can be adjusted 3cm within guard.
11 Capacitive method 2- Pad Electrodes They are malleable metal covered with a thin layer of rubberThey must have uniform contact pressure on the bodyTowels are used to prevent burns
12 Inductive methodThe 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 electrodesThey are bundles of plastic-coated wiresThe 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 a pancake and placed on the skin
14 Inductive method(cont.) 2- Drum electrodesA 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 A drum applicator is made of flat spiral coil inside a plastic housing Drum electrodeA drum applicator is made of flat spiral coil inside a plastic housing
16 Inductive method (cont.) When high frequency alternating current (AC) flows in 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 temperatureThe 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.The strength 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 May use more than one drum depending on treatment area The drum is placed directly over the area being treatedMay use more than one drum depending on treatment areaToweling is importantThe cable is arranged in a pancake shapeTowel between skin and coilSpacing 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 methodContraplanner technique:It is used to treat structure on the two aspect of the body. Twoelectrodes 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 .Twoelectrodes are placed on the same line together of the partbeing 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 tissueCross fire techniqueThe 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 electrodewrapped around the extremitycoiled 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 one2- 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 heatunder 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 distribution Capacitive 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.ObesityDiathermy should be used with caution in obese patient because it may heat fat excessively, especially capacitive plate.Copper bearing intra-uterine contraceptive devicesDiathermy 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 tissue is 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 studyCase 1MS 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 2AB 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.