SHORTWAVE DIATHERMY
This deep heat modality involves the therapeutic application of high-radiofrequency electrical currents. The electromagnetic field is usually at a radio frequency of 27.12 MHz (λ = 11.06 m).
Hyperemia, sedation, and analgesia are the basic physiologic effects. The reduction in muscle spasm resulting from muscle relaxation is caused by an increased vascular supply to the treated area. A transverse technique is applied to treat a larger anatomic area, with the primary concentration at the midpoint between electrodes.
Proper application and tuning are required for this modality. The patient's electrical impedance becomes part of the impedance of the patient's own circuit. The patient's circuit must be set to resonance, so the patient's circuit frequency is equal to that of the machine.
The patient should feel only a comfortable heat. For therapeutic benefit, the tissue temperature should be elevated to between 40º and 45° C. Continuous supervision and observation of the patient are required. The treatment time is usually 20-30 minutes.
At clinically relevant energies, shortwave diathermy can increase subcutaneous fat temperature by 15° C and muscle temperature by 4-6° C at a depth of 4-5 cm. Patients should be placed on a wooden table or chair when shortwave diathermy is applied.
One means of applying shortwave diathermy is through the condenser method. In this, the treatment site is placed between 2 electrodes functioning as capacitor plates.
Monitoring of patient movement is required, because movement can affect the amplitude of the heat concentration being applied. Another technique, the inductive coil method, involves coil applicators that selectively heat superficial musculature (unless these applicators are used on joints with minimal overlying soft tissue, resulting in selective heating of the joint).
Inductively coupled units use induced eddy currents to heat tissue, especially tissue, such as muscle, with high water content. Units joined to provide aggregate capacity use electrical fields to heat tissue with low water content, such as fat. Self-adjusting resonators minimize the positioning effect.
Felt or plastic spacers should be used with the condenser method. When the condenser or inductive coil method is applied, a towel should be used to absorb perspiration, thereby avoiding localized heat concentration. The patient must be instructed to remain motionless.
The output of the machine should be adjusted to a desired level so that movement does not change the impedance circuit and increase current flow (which would mean a greater risk of a dose increase and resultant burns).
The shortwave diathermy unit should be tuned to low power as per patient tolerance, and the meter readings should be properly documented. Heating localization depends on the coupling of radio waves to the patient.
APPLICATIONS
The following problems can be treated with shortwave diathermy, depending on the individual condition of each patient and the desired treatment goals:
Inflammation (joint or tissue)
Pain/spasm
Sprains/strains
Tendinitis
Tenosynovitis
Bursitis
Rheumatoid arthritis
Periostitis
Capsulitis
CONTRAINDICATIONS
Malignancy
Sensory loss
Tuberculosis
Metallic implants or foreign bodies
Pregnancy
Application over moist dressings
Ischemic areas or arteriosclerosis
Thromboangiitis obliterans
Phlebitis
Cardiac pacemakers
Contact lenses
Metal-containing intrauterine contraceptive devices
Metal in contact with skin (eg, watches, belt buckles, jewelry)
Use over epiphyseal areas of developing bones
Active menses
Note: In addition, extreme care must be used with pediatric or geriatric patients.
The literature is not clear on the amount of heating that occurs in the case of metal surgical clips; in addition, the effect of shortwave diathermy on actual bony growth plates is not known with certainty.
The most common complication of shortwave diathermy is the development of burns, which may be caused by a number of factors, including the following
Faulty equipment
Improper technique
Inadequate patient supervision
Inappropriate positioning of the patient