Shortwave Diathermy (SWD)

Shortwave Diathermy (SWD)

• SWD uses oscillating high-frequency non-ionizing electromagnetic energy to produce deep heat within tissues, similar to broadcast radio waves.

Types of SWD Generators

• Induction field generators and capacitive field generators are the two types of SWD generators
• The type of SWD application depends on the generator
• EM field induction places the patient in the electromagnetic field produced by the equipment.
• A capacitive field SWD unit uses the patient's tissues in the actual electrical circuit, also called a condenser field
• The tissues' resistance to energy flow generates heat.
• Induction generators produce the most heat within the muscle layer directly beneath the coil
• Capacitive generators affect tissues under each plate and selectively heat adipose tissue and bone
• Because heating with capacitive SWD depends highly on water content, it is not recommended for patients with thick adipose tissue layers
• Patient's tissues are placed between two electrodes when using capacitive SWD
• Two insulated plates/electrodes are placed on each side of the site that is being treated
• When an alternating current is applied to the circuit, the plates will always have opposite electrical charges, creating a strong electrical force between them
• The flow of electrical energy passes through the tissues in a series circuit, which acts as an electrical resistor and produces frictional heating
• Tissues that present the most electrical resistance, such as adipose tissue, produce the most heat.
• Capacitive SWD heats the body on each side, unlike the inductive technique

Modes of Application

• Shortwave diathermy is delivered in either continuous or pulsed forms
• Continuous SWD increases subcutaneous tissue temperature but is generally limited to chronic conditions
• The output may also be pulsed, allowing use with some acute and subacute conditions, preventing tissue temperatures from increasing too fast or too high
• Friction caused by the passage of energy through the tissue produces heat
• The total amount of power (measured in watts) and the ratio between the length of the "ON" pulse and the duration of the "OFF" cycle determine how much heating occurs
• Non-thermal effects occur when a low average intensity, short pulse duration, and low duty cycle are used, even though heat is still generated

Effects of SWD

• Non-thermal SWD changes the way that ions bind to the cell membrane, altering cellular function
• Increased microvascular perfusion
• Activation of fibroblast growth factors
• Increased macrophage activity
• Assist in tissue healing
• Promotes edema reduction
• Thermal effects lead to the primary advantage of shortwave diathermy being the relatively large volume and depth of tissue it can heat
• Shortwave diathermy can increase intramuscular temperatures by 4°C to 5°C
• SWD heating characteristics are similar to those of ultrasound, but because of the larger amount of tissue heated, the heat is retained three times longer following the treatment than with ultrasound

Cellular Level Effects

• Increased delivery and concentration of white blood cells (WBC)
• Improved chondrocyte proliferation
• Increased cell membrane permeability assists in the removal of cellular debris and metabolic toxins that may have collected in the area
• Primary pain relief with SWD application stems from decreased muscle spasm, reduction of adhesions and contractures, and increased blood flow
• As a thermal modality, SWD causes vasodilation, increasing blood flow, capillary filtration, capillary pressure, and oxygen perfusion
• Deep heating characteristics stimulate increased fibroblastic activity, increased collagen deposition, and new capillary growth deeper in the tissues than superficial heating agents

Contraindications and Precautions

• Acute inflammation
• Ischemia
• Hemorrhage
• Questions regarding the suitability of SWD for the condition being treated should be referred to the patient's physician
• The intensity for thermal treatments is based on patient feedback
• Diminished capacity to feel heat, interpret sensations, and/or communicate with the clinician
• Individuals who are pregnant, or may be pregnant
• Individuals who have a cardiac pacemaker or other implanted electronic device should not be permitted within 50 feet (15 m) of the unit while output is being generated
• Metal within the output field
• Active deep vein thrombosis or thrombophlebitis
• Active infection
• Cancerous tumors
• Diathermy unit EMF can disrupt the pacemaker's rhythm and overheat the implanted metal
• Shortwave diathermy applied through the skull using capacitive plates, trans cerebral application, should be performed with extreme caution
• Contact lenses must be removed before application of SWD to the face or head, or both
• Application of SWD to the female pelvic region (including use of vaginal electrodes), abdomen, and lumbar spine may increase menstrual flow
• Application of SWD to these regions during pregnancy or suspected pregnancy is an absolute contraindication
• Remove moist dressings, adhesive tape, and skin creams before treatment