Short wave diathermy

       The diathermy means, 'through heating' or producing deep heating directly in the tissues of the body. 

        Externally applied sources of heat like hot towels, infrared lamps and electric heating pads often produce discomfort and skin burns long before adequate heat has penetrated to the deeper tissues.

         But with the diathermy technique, the subject's body becomes a part of the electrical circuit and the heat is produced within the body and not transferred through the skin.

         The heating of the tissues is carried out by high frequency alternating current which generally has a frequency of 27.12 MHz and wavelength of 11m. The short wave diathermy machine consists of 2 main circuits.

                      * Oscillating circuit - which produces a high frequency current.

                      * Patient circuit - which is connected to the oscillating circuit.

  There are several ways of regulating intensity of current supplied to the patient from a shortwave diathermy machine. This can be done by either

 

                          * Controlling the anode voltage

                          * Controlling the filament of heating current

                          * Adjusting the grid bias by change of grid leak resistance R1 or

                          * Adjusting the position of the resonator coil with respect to the oscillator coil.

Simplified circuit diagram of a short 

wave diathermy unit

     Methods of applying electrodes in shortwave diathermy treatment,

                                * Condenser method

                                * Inductive method

                                * Inductive heating by a coil housed in a drum

Condenser method

       One means of applying shortwave diathermy is through the condenser method. In this, the treatment site is placed between two electrodes functioning as capacitor plates. Monitoring of patient movement is required, because movement can affect the amplitude of the heat concentration being applied.

Inductive diathermy

        Inductive SWD units contains coils which creates a magnetic field. This field projects forward into the body and generates a circular, electric field within the target tissue. Typically, the coils are confined to flexible cables or within a rigid drum.

Although most short-wave diathermy machines have an output power control, yet there is no induction of the amount of converted and absorbed heat within the body tissues. Therefore, the intensity of treatment is dependent on the subjective sensation of warmth felt by the patient.