Download Short Wave Diathermy

High-Frequency Currents
The concept of producing heat deep within the tissues, beyond the
reach of infrared and other forms of superficial heat is appreciated by
physical therapists. Currents with oscillations greater than 1000 Hz
(cycles / second) are termed high-frequency currents. Generally, this type
of currents used to generate heat is in the megacycle range. Most
commonly utilized high-frequency currents are found with:
* Short wave diathermy.
* Microwave diathermy.
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Short Wave Diathermy
Short wave diathermy has been a viable modality in physical
therapy for many years. Originally, it was utilized for musculoskeletal
conditions which require increased circulation and other benefits of
thermal increase. Moreover, short wave diathermy has proven an
effective modality in the management of non-orthopedic conditions such
as pulmonary, urologic and gynecological conditions.
Physics:
Heat generation through short wave diathermy depends on the
molecular activity within the tissue exposed. Differential heating is noted
within bone, muscle and fat because of the different densities of these
tissues. It should be noted that the more-dense tissue naturally becomes
warmer than the less-dense one. Actually, the shorter the wavelength or
the higher the frequency is, the greater the penetration will be.
Administration of short wave diathermy for medical purposes
occurs through three wavelengths: 7, 11 and 22 meters, in terms of
frequencies: 45, 27 and 13 mega cycles. The most common models of
short wave diathermy units are in the 22-meter band.
Physiological effects:
The principal effect of short wave diathermy on the body is the
production of heat in the tissues due to the rise of temperature.
1. Increased metabolism:
Heating tissues accelerates chemical changes such as metabolism,
so oxygen and food staffs are used up. As there is increased metabolism,
there will be increased output of waste products.
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2. Increased blood supply:
As a result of increased output of waste products such as
metabolites, which act on the walls of the capillaries and arterioles, these
tissues dilate. In addition, heat has direct effect on blood vessels, causing
vasodilatation. Heat also produces stimulation of superficial nerve
endings, causing reflex dilatation of the arterioles. Vasodilatation
increases blood flow through the area, so that the necessary oxygen and
nutritive materials are supplied and waste products are removed.
3. General rise of temperature:
As blood passes through the heated tissues, it also becomes heated
and carries the heat to other body parts. As a result, heat reduces the
excitability of nerves, provided that heat is not excessive. Furthermore,
rise of temperature induces muscle relaxation and increases the efficiency
of muscle action.
4. Fall in blood pressure:
The generalized vasodilatation reduces the peripheral resistance to
blood flow. Heat also reduces blood viscosity, which helps in the
reduction of blood pressure.
5. Increased activity of sweet glands:
If a general rise of temperature occurs, there will be increased
activation of the sweet glands.
Indications:
1. For chronic and mild conditions:
- Myositis and arthritis.
- Pelvic inflammation.
- Otitis media.
- Bronchitis.
- Sinusitis.
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2. As an adjunctive modality:
Short wave is also used with other procedures such as
iontophoresis to enhance local absorption.
Contraindications:
1. Acute inflammatory conditions or hemorrhage: Heating of the tissues
by diathermy causes dilatation of blood vessels. So, it shouldn’t be
employed immediately after an injury or in any case where hemorrhage
has recently occurred or may occur, such as gastric or intestinal diseases
associated with ulceration. It shouldn’t be applied on the abdomen or
pelvis during menstruation.
2. Venous thrombosis or phlebitis: Application of short wave diathermy
may aggravate the inflammatory process.
3. Arterial diseases: Diathermy shouldn’t be applied to parts which have
defective blood supply.
4. Pregnancy: Diathermy shouldn’t be applied to the abdomen or pelvis
during pregnancy.
5. Metals in the tissues: Diathermy causes concentration of electric field
in the metal, which may precipitate burns.
6. Loss of skin sensation: It is safer to avoid the application of diathermy
to cases where there is loss of skin sensation.
7. Tumors: Short wave diathermy shouldn’t be applied to areas of
malignant growth.
8. X-ray therapy: X-ray therapy devitalizes the tissues, rendering them
more susceptible to damage. So, short wave diathermy shouldn’t be
applied to areas recently exposed to therapeutic doses of X-rays.
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Treatment procedures:
1. Electrodes:
Types:
a) Condenser field method:
Electrodes are placed on each side of the treated part, separated
from the skin by an insulating material. The electrodes act as plates of a
condenser, while the patient’s tissues form the dielectric. When the
current is applied rapidly, alternating charges are set up on the electrodes,
causing a rapidly alternating electric field between them. The electric
field influences the materials which lie within it and produces heat.
b) Cable method:
The cable is coiled in relation to the patient’s skin but separated
from it by a layer of insulating material. As high-frequency currents
oscillate in the cable, an electric field is set up between its ends and a
magnetic field around its center. These fields affect the tissues that lie
within them.
Electrode arrangement:
* Contraplanar technique:
It is the most satisfactory technique, especially for the treatment of
deeply-placed structures. The electrodes are then placed over the opposite
aspects of limbs, so that the electric field is directed through deep tissues.
 Coplanar technique:
In this technique, electrodes are placed side by side on the same
aspect of the part, provided there is an adequate distance between them.
The distance between the two electrodes should be more than the total
width of spacing. In this method, the heat is more superficial and suits
certain areas such as the spine, where one electrode is placed over the
dorsal region, while the other placed over the lumbar one.
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 Cross fire technique:
In this technique, half of the treatment period is given with the
electrodes in one position and then they are moved to be at right angle to
that obtained during the first part of the treatment. For example, for the
knee joint, during the first half of the session, the electrodes are placed on
the medial and lateral aspects of the knee. On the opposite, during the
second half of the session, the electrodes are transferred to the anterior
and posterior aspects of the knee.
 Monopolar technique:
The active electrode is placed over the site of the lesion, while the
indifferent one is applied to some distant part of the body. This method is
used for very superficial lesions (face and sinuses).
2. Preparation of the patient:
- Treatment should be on a couch, chair or a table, which must be
wooden and free from metals.
- Do not allow the target area to be hidden by clothes to avoid unwanted
irritation or burn.
- The skin must be dry.
- Metal objects such as earrings and necklaces, tight straps or elastic
supports should be removed.
- The patient must be comfortable and the part to be treated should be
fully supported.
- Skin sensation must be tested before treatment starts.
3. Monitoring the treatment:
- The apparatus should be earthen.
- Before starting treatment, all meters of the apparatus should be on zero
position (the starting position).
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- Select the power level according to the patient’s condition.
- Increase the intensity gradually till the desired heating level is reached.
- Now, the patient should feel mild sensation of warmth, which continues
throughout the session.
- Immediately check for any complaint of hot sensation.
- The physical therapist should remain within call of the patient during
the whole treatment period.
- At the end of treatment, the control knobs are returned to zero position,
current switched off and the electrodes removed.
4. Duration of treatment:
Treatment time may vary between 10 and 30 minutes, depending
on the patient’s condition. Frequency of treatment is usually twice
weekly, while daily treatment is not contraindicated when needed. When
treatment is within a limited space such as the sinuses or the face,
excessive treatment should be avoided.
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