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Short-wave diathermy. By Abdullah Radwan. General consideration. A high frequency current may be defined as the current that alternate with a high frequency of oscillations of a million or more per second.
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Short-wave diathermy By Abdullah Radwan
General consideration • A high frequency current may be defined as the current that alternate with a high frequency of oscillations of a million or more per second. • When applied to the human tissue, the extremely short impulse of each oscillation can not cause any ionic movement or electrochemical reaction and so, do not stimulate sensory or motor nerves. • When an electric current is passing through a conductor there will be collision between the electrons flow and atoms of the conductor, where these electrons lose their kinetic energy and create thermal energy.
Cont., • The production of heat is not specific for high frequency currents alone but, any electric current can heat the tissues. • Low frequency currents are not suitable for tissue heating, because their electrolytic or polarity effects will cause tissue destruction at the intensity which would cause appreciable heating.
There are 3 methods of high frequency tissue heating:- • The oldest method: is long wave diathermy, obsolete now. • It employed oscillations of frequency of one million per second. • It was applied through bare metal electrodes placed in direct contact with the skin or mucous membranes. • It was produced by obsolete spark gap apparatus.
2. The present method: is short wave diathermy. • It has replaced the old method, i.e. long wave diathermy. • It employs oscillations from 10-100 million per sec. • It is routinely applied through a spacing of air or rubber. • It is produced by tube apparatus.
3. Microwave diathermy: • It employs oscillation of 3000 millions per second. • It is used by forcing a single beam of electromagnetic energy from some distance to the region to be treated. • It is produced by a magnetron (صمام مفرغ) oscillator.
Production of short wave diathermy • The high frequency short wave diathermy is produced by two circuits: 1. an oscillating circuit which is made of: • a source of current, • a condenser, • a coil, and, • a vacuum glass triode valve (sometimes, two or more valves are used). 2. a resonating circuit in which the patient is put. It is made of: • a coil, • a variable condenser and, • an ammeter. • It must be made in resonance with the oscillating circuit by a variable condenser, the capacity of which is varied till complete tuning is obtained, and when resonance of both circuits is at its maximum the patient feels the best heat.
The frequencies allowed for short wave diathermy are: • 13.66 megacycles • 27.33 megacycles and, • 40.98 megacycles • The wave length corresponding the allowed frequencies are: • 22, meters • 11, meters and, • 7.5 meters respectively. • The wave length is determined by the formula: • ג = V/N where ג (wavelength), V (light velocity), and N (frequency of oscillation). • Most of diathermy machines operate at a frequency of 27.33 megacycles and hence a wavelength of 11 meters. • The usual out-put amperage of short wave apparatus varies between 15- 25 amperes.
Physiological effects of short wave diathermy • The main physiological effects of diathermy are due to raising of the temperature along the course of its passage. • The heat produced during diathermy treatment is directly proportional to: • Square of current strength, • Resistance of the conductor, • Time of treatment and, • Size of electrodes. The physiological effects are generally classified into: • Local effects, • General effects.
I. Local effects • Increased local circulation with production of local hyperemia. • Increased phagocytic activity. • Resolution of chronic inflammation as a result of increased blood supply increased venous return from the area which helps absorption of oedema & exudate. • Increased local metabolism. • Pain relief by the marked sedative effect on the sensory nerves. • Reduction of muscle spasm by heating relaxation by the marked soothing effect on motor nerves. • Increased sweat gland activity with perspiration. • Promotion of healing due to increased blood supply to the area. • Control of chronic infection by increased circulation increased white cells & antibodies reinforcement of blood defense mechanisms. • Increased extensibility of fibrous tissues such as tendons, joints, capsules &scar.
II. General effects • Vasodilatation with subsequent increase in the circulation rate, pulse rate and reduction of the blood pressure. • Increase in the phagocytic activities. • Increase in the rate, depth and volume of respiration per minute. • Increase in the sweat gland activity with subsequent perspiration. • Increase in the volume and alkalinity of urine. • Increase in the general metabolism in the form of activation of all metabolic processes. • Increased local immunity.
Indications of SWD: • Subacute and chronic traumatic conditions. • Acute, subacute, and chronic inflammatory lesions e.g. conjunctivitis, bronchitis, and skin infections as folliculitis,…. • Acute, subacute and chronic rheumatic conditions as RA, OA, fibrositis,….. • Painful conditions as neuralgia, sciatica,… • Promotes healing in wounds and superficial ulcers,… • Preliminary to other lines of ttt as exercises,…
Contra-indications of SWD: • Malignancy as heat will increase metabolism increases the rate of growth. • Haemorrhage will be increased due to vasodilatation. • Venous thrombosis or phlebitis. • Ischemic tissues development of gangrene. • Pregnancy & menstruation. • Metal in tissues concentrate heat destruction of tissues. • Disturbed skin sensation. • Unreliable patients like small children, defective mentality & unconscious patient. • Tuberculous joints increased rate of infection joint damage. • Hypersensitivity to heat. • Patients with decompensate cardiac, hepatic or renal diseases. • Blood pressure abnormalities.
Advantages of SWD: • Simple operation of the machine. • Comfortable to the patient. • Heat can be applied to superficial & deep structures as required. • Undue skin heat can be avoided. • Many different varieties of application are available.
Disadvantages (Hazards) of SWD: • Accurate measurement of the amount of heat received by the patient is not possible. • Deep tissue burn (and superficial burns) can occur due to: • Concentration of electric field. • Excess current. • Hypersensitive skin. • Impaired circulation. • Leads touching the skin. • Overdosage increases symptoms especially pain. • Precipitation of gangrene in areas of impaired circulation. • Electric shock if contact with the apparatus circuit is made. • Faintness due to rapid rise from bed after extensive treatment (decreased cerebral blood flow). • Giddiness if applied to the head due to its effect on the semicircular canals. • Damage of the equipment.
Dosage • Till the present time, it is not possible to measure the high frequency current flow through the body of the patient, so that, the dosimetry still depends largely on the patient’s subjective feeling of warmth which is relative. • Acute inflammatory conditions: 10 min of low intensity short wave can be given daily or on alternate days. • Chronic inflammatory conditions: 15- 20 min of high intensity short wave daily or on alternate days. • Deep seated lesions: 30 min may be given.
Technique of application • Condenser field technique: The part of the patient to be treated is placed between two condenser plates. 3 modification of this technique are available: • Condenser plates are enclosed in rigid plastic material to provide proper spacing between body surface and condenser plates. • The condenser plates are covered by a glass envelope. • The condenser plates are flexible and are enclosed in rubber or plastic materials called condenser pads.
II. Induction coil application: • The coil is enclosed in a flexible plastic container which can be moulded as required to fit different parts of the body and can be shaped to any desired form. • Special care should be taken to insure that the cable turns don’t cross each other.
Instructions of application • Remove clothes from the treated part of the patient and inspect this part before and after ttt. • Test patient sensations by hot or cold test tubes. • Any wet bandages or dressings should be replaced by dry ones. • All metallic objects should be removed from the field of ttt because they lead to concentration of electric energy with possibility of burning tissues.
Cont., 5.Patient should be placed on wooden chair or no metallic parts, and use mattresses without metals. 6. Patient should be placed in a comfortable posture with minimal or no movement during ttt. Little movement of the patient during ttt may change the circuit impedance and current flow may be greatly increased and possible burn may occur. 7. Patient should be informed that he will receive mild pleasant sensation of heat and any burning or unpleasant sensation should be noted at once. • Turning the patient circuit should be done at low output level then adjusted to the desired level. • Let the patient rest after ttt for enough time till the skin cooled off especially in bad weather or aged persons.
