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DEEP HEAT
Deep heat is produced when energy is converted into heat as it passes through body tissues.
Energy sources include
(1) High-Frequency currents ( Shortwave Diathermy )
(2) Electromagnetic Radiation ( Microwave Diathermy )
(3) High-Frequency Sound ( Ultra Sonography )
The temperature distribution in the tissues heated by any of these modalities results from the pattern of relative heating, which is the amount of energy converted to heat at any given location.
The practitioner should choose a heating modality that produces the highest temperature at the site of concern without exceeding the temperature tolerance at the affected site or in tissues above or below that site.
The temperature rise depends on the properties of the tissue, including the specific heat, thermal conductivity, and the length of time that the heating modality is applied.
The temperature rise and distribution of heat that are associated with these modalities are superimposed on the physiologic temperature distribution in the tissues prior to diathermy application. Usually, the superficial temperature is low at the skin surface and higher at the core.
The physiologic effects of temperature occur at the site of the application and in distant tissue. The local effects are caused by the elevated temperature response of cellular function by direct and reflex action.
Locally, there is a rise in blood flow with associated capillary dilatation and increased capillary permeability. Initial tissue metabolism increases, and there may be changes in the pain threshold. Distant changes from the heated target location include reflex vasodilatation and a reduction in muscle spasm (as a result of skeletal muscle relaxation).
Vigorous heating produces the highest temperature at the site where the therapeutic result is desired. The tissue undergoes a rapid temperature rise, with the temperature coming close to the tolerance level.
Vigorous heating is used for chronic conditions that require deep structures, such as large joints, to be heated. When acute inflammatory processes are occurring, deep heating requires extreme care, because it can obscure inflammation.
Local tissue temperature is maintained during mild heating, the primary effect being the production of a higher temperature at a site distant from the heating modality's application.
Reflex vasodilatation occurs when the rise in temperature is slow for short periods, such as during a subacute process. With the proper application, superficial and deep heating methods can accomplish mild heating.
The best method for large-area deep heating is shortwave diathermy.
SUMMARY
The therapeutic effects of deep heating modalities are usually produced by the conversion of applied energy into heat as the energy penetrates tissue. Because the temperature distribution varies significantly across different modalities, the clinician should use the appropriate modality for the condition at hand.
To provide the greatest therapeutic effect, the temperature rise generated by the modality should be the maximum increase that the patient can tolerate. For a specific localized pathology, the deep heating modality that is selected must produce a maximum temperature elevation at the site of the pathology.
The following areas are treated selectively by the listed modalities:
v The application of microwave radiation or of shortwave diathermy with capacitor plates, at a frequency of 2456 MHz, can provide selective heat to deep subcutaneous tissue and superficial muscle.
v Shortwave diathermy with an induction coil applicator, administered at 27 MHz, can heat superficial muscle.
v Microwave diathermy administered at 915 MHz can selectively, but thoroughly, heat muscle.
v Ultrasonography administered at a frequency of 0.8-1 MHz preferentially heats joints, ligaments, tendons, tendon sheaths, fibrous scars, nerve trunks, and myofascial interfaces. Ultrasonography is especially useful for heating joints that have a thick layer of overlying soft tissues that shortwave diathermy or microwave diathermy cannot penetrate.
v Shortwave diathermy with internal electrodes, administered at 27 MHz, can provide selective heat for pelvic organs in cases of chronic pelvic inflammatory disease and can be employed for the management of coccygeal muscle spasms (such as those of the urogenital diaphragm).
DEEP HEATING MODALITIES
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