2. CONTENTS
• Physiological effects of heat
• Indirect effects of heat
• Introduction to SWD
• Methods of application
• Techniques of short wave diathermy
• Therapeutic and physiological uses of SWD
• Dangers of SWD
• Contraindications
3. PHYSIOLOGICAL EFFECTS OF HEAT
• Increased metabolism
• Increased blood supply
• Stimulation of neural receptors
4. • According to Vant Hoff’s law due to increase in temperature there is chemical
reaction
• This causes increased metabolism
• Increased demand of foodstuff and oxygen and increased output of waste products
• This causes dilatation of blood vessels i.e vasodilatation
• Increased blood supply ,so required oxygen ,etc is supplied
• Pain gate theory cause sedative effect
5. INDIRECT EFFECTS OF HEAT
• Muscle tissue : muscle gets relaxed and increased blood supply ensures optimum conditions
for muscle contraction
• General rise in temperature : due to extensive and prolonged heating generalized dilatation
of superficial blood vessels results
• Fall in blood pressure : due vasodilatation , Heat reduced viscosity of blood ,peripheral
resistance is reduced and causes fall in blood pressure .
• Increased activity of sweat glands : reflex stimulation of sweat glands in area exposed to heat
resulting from effect of heat on sensory nerve endings. As heated blood circulates throughout
body it affects centres concerned with regulation of temperature and increased activity of
sweat glands throughout body.
6. INTRODUCTION
• Dia means through, thermy means heat
• SWD is a modality that produces deep heating
via conversion of electromagnetic energy to
thermal energy.
• Frequency of between 107 and 108 Hz
7. • Wavelength of between 30 and 3m
• Commonly used for medical work has frequency 27.12MHz .
• This current is generated in machine circuit ,which is in turn coupled to patient (resonator) circuit which
is used too treat patient
8. MACHINE CIRCUIT
• It consist of two transformers, whose primary coil are connected to source of AC.
• One is step-down transformer and its secondary coil supplies current to the filament heating circuit of
triode valve.
• The other is set-up transformer and connected to anode circuit
• Anode circuit carries the current produced by valve.
• Here it consists of triode valve and oscillator circuit.
• Oscillator circuit consists of condenser and inductor or oscillator coil.
9. • Current of different frequencies are obtained by selecting suitable condensers and
inductances.
• To produce a current of high frequency the capacitances and inductance used must be small
and is made to charge and discharge repeatedly and for obtaining this an Oscillator is
incorporated in to machine circuit along with valve circuit
• Another coil AB lie close to oscillator coil and had one end connected to the grid of the valve
and other through grid leak resistance to the filament
10. PATIENT CIRCUIT
• Also known as resonator circuit
• Circuit is coupled with machine circuit by inductors i.e matching high frequency current is
produced in resonator circuit by EMI
• For this to happen oscillator and resonator circuit must be in resonance with each other
• For condenser field method :electrodes and patients tissues form capacitor ,which depends
on size of electrodes and on distance and material between them
• For cable electrode : it forms inductance which value varies according to its arrangments
11. • When electrodes are arranged in position capacitance of variable condenser is adjusted until
product of inductance and capacitance of resonant circuit equals oscillator circuit.
• When oscillator and resonator circuit are in tune with each other, there is maximum power
transfer to patient circuit.
• Indications that this occurring are :
1) Indicator light on
2) Ammeter shows maximum reading
3) Neon tube will glow
12.
13. WORKING
• The AC from main passes through primary coils of the transformers and EMF is induced in secondary
coils
• An EMF of 20-25volt is set-up in secondary coil of set-down transformer and produces currents through
filament of the valve.
• The filament is heated and thermionic emission takes place and current flows through valve
• The EMF of about 4000volts is induced in the secondary coil of set-up transformer and provided that
anode of valve is positive and filament is negative, current flows in Anode circuit
14. • The electrons flows to filament through anode valve, through oscillator coil in direction C and D and to
transformer back to filament.
• The electron form in CD will induce EMF in coil AB in direction that electrons will move to grid of valve
making it negative thus blocking the flow of electrons from filament
• This will lead to dying of current in anode circuit. This reduction in current will lead to self-induced
EMF.
• According to Lenz law, this EMF will try to prevent fall in current by offering resistance to flow of
current.
15. • This will charge condenser X(positive) and Y(negative) polarity opposite to earlier one.
• Now when self-induced EMF totally dies away, condensers again discharges through oscillator
coil, but in opposite direction(D to C).
• Flow of current from D to C induce an EMF in AB such that electrons move from A to B and
grid loses its negative charge and anode current flows again.
• This sequence continues and each time condenser charges and discharges through oscillator
circuit leading to production of high frequency current(SWD).
16. GRID LEAK
• When the current flows across the valve some electrons are caught on the grid and grid leak
is provided to enable these electrons to escape back to the filament.
• The resonator coil lies within the varying magnetic field set up around the oscillatory coil, so
provided that two circuit are in resonance high frequency current in induced in it.
• The current is similar to that in the oscillator circuit and is supplied to patient
17. PRINCIPLES OF DIATHERMY
• Before injury, the dipole molecules of the body tissue are arranged on the basis of polarity
• When the tissue is damaged the dipoles distribution become irregular and deviates from
polarity based arrangement .
• Under the influence of an electric field , they rotate according to the polarity of their charge
in the direction of the field lines and get rearranged and tends to acquire its previous stage
of polarity
18. • As the subcutaneous layer is fatty , direct delivery of heat to the deep layers of tissue is not possible
• Diathermy involves uneven and uncontrolled delivery of heat therefore sometimes instead of the
target tissue , surrounding tissue gets affected
• Diathermy uses an electric current to produce heat deep inside a targeted tissue. It can reach areas as
deep as two inches from the skin’s surface
• The diathermy machine does not apply heat directly to the body. Instead, the current from the machine
allows the body to generate heat from within the targeted tissue
• As the heat increases, it promotes blood flow. • It can also help improve flexibility in stiff joints and
connective tissue
19. TYPES OF DIATHERMY
• SHORT WAVE DIATHERMY
• LONGWAVE DIATHERMY
• MICROWAVE DIATHERMY
• ULTRASOUND DIATHERMY
• LASER DIATHERMY
20. METHODS OF APPLICATIION
• Two methods of application :
1) capacitor/ condenser field
2) Inductothermy (cable ) method
21. CAPACITOR FIELD METHOD
• Electrodes are placed on each side of part to be treated ,separated
from skin by insulating material. Uses the patient’s tissues as a part of
the circuit.
• Electrodes acts as plates of capacitor ,while patient tissue with
insulating material form dielectric
• .
22. • The electrodes act as the plates of the capacitor, while the pts tissue together with the insulating
material which separate them from the electrodes for the dielectric.
• When the current is applied, rapidly alternating charges are setup on the electrodes & gives rise to a
rapidly alternating electric field b/w them.
• The electric field also influences the material which lies within it
23. INDUCTION (CABLE) METHOD
• In this method a thick, insulated cable is used for treatment
purposes.
• Electric field or magnetic field or both are achieved by the
use of cable method Current flowing within the coil produces
a rotating magnetic field
24. • THE ELECTROSTATIC FIELD: is produced at the end of the cable & effects are similar when the current is
applied by a condenser method.
• THE MAGNETIC FIELD : varies as the current oscillates & an EMF is produced by electromagnetic
induction
• Thus, the electric field influences the material that lies b/w the plates; this causes the oscillation of the
ion, distortion of the molecules & rotation of dipoles.
• This causes production of heat in the tissues by electric filed of SWD, which is the primary function of
SWD.
• The heat production is an accordance with joule’s law (Q=I2 RT) , but depends upon the distribution of
the electric field
25.
26. SELECTION /PLACEMENT OF ELECTRODES
• Types of electrodes
1) Spacing of electrodes
2) Positioning of electrodes (coplanar, contraplanar, Monoplanar,crossfire)
3) Size of electrodes
27. FACTORS INFLUENCE FIELD DISTRIBUTION IN S.W.D
Spacing :
• allows the lines of force in the electrostatic field to
• diverge before entering the tissues. This prevents
• concentration of heat in the superficial tissues and
• ensures more heating through the part.
28. • Spacing provided by:
1. wrapping flexible pads in towel.
2. flat felt spacing pads
between pad electrode and skin
3. air when using space plate
Normal spacing
• even field distribution.
Increased spacing
• Deep field concentration.
Decreased spacing
• superficialconcentration
29. Electrode size:
• if the electrodes are too small than the diameter of treated part line of force will be
concentrated superficially.
• If the electrodes are markedly larger the line of force will be lost in the air.
• Ideally, the electrodes should be slightly larger than the area treated.
• To concentrate heat on one aspect of the part the electrode should be unequal in size
(smaller one placed over the area where concentration of heat is required)
• You can produce concentration of heat by using equal size electrodes but with unequal
spacing (25 mm over concentrated area and more than 30 mm on other electrode).
30. THERAPEUTIC VARIATION IN THE
FIELD DISTRIBUTION
• Coplanar application to structures on one aspect of the body. If the spacing is less than 25 mm more
concentration in the treat superficial tissue.
• The distance between adjacent ends must be greater than the sum of skin electrode distance (A+B)
otherwise the line of force Will pass directly between Electrodes rather than tissues
31. • Contra planar Applications
• Two flexible pads, two space plates or flexible pad with a space plate are used.
• It is essential to put a cotton towel between the two limbs to any absorb
perspiration
32. • Cross-fire application:
• For the treatment of sinuses,space plates positioned after
half diagonally,of treatment time the positions are
alternate.
• this ensures that the all the sinses membranesare heated.
• Care must be taken to avoid direct placement over the eye
uterinedisorders such as dysmenrrohea.
33. PHYSIOLOGICAL EFFECTS
• Increased metabolism
• Increased blood supply
• General rise in temperature
• Fall in blood pressure
• Increased activity of sweat glands
34. THERAPEUTICAL EFFECTS
1) Effect on Inflammation
• Assist in removal of Waste Products
• All these effects bring about resolution of inflammation
2) Effect on Bacterial Infection
• Inflammation is normal response of Body to bacteria
• Heating the tissue auguments these changes so reinforces body's normal mechanism to of dealing with
infecting organisms
• Ex. Boils,
35. 3) Reducing Healing time
• Increased Blood supply
• More Nutritive Material
• More O2 supply
4) Relief of Pain
• Sedative Effect
• Removal of Waste Products
• Resolution of Inflammation
• Counter irritation
36. 5) Effect on Muscle Tissue
• Muscle relaxation
• Relief of Muscle Spasm
38. DANGERS
• Burns due to following reason :
• Concentration of electric field
• Excess current
• Impaired blood flow
• Hypersensitive skin
• Leads touching skin
• 1. Scalds
• 2. Electric shock
• 3. Overdose
• 4. Precipitation of gangrene
• 5. Faintness
• 6. Giddiness
39. CONTRAINDICATIONS
• Metal implants or metal
• jewelry (be aware of body
• piercings)
• Cardiac pacemakers
• Ischemic areas
• Peripheral vascular disease
• Perspiration and moist dressings: The water collects and concentrates the heat.
40. • Tendency to hemorrhage, including menstruation.
• Pregnancy
• Fever
• Sensory loss
• Cancer
• Deep X ray
• Tumours
• Unreliable patients
41. • Areas of particular sensitivity:
• – Epiphyseal plates in children
• – The genitals
• – Sites of infection
• – The abdomen with an
• implanted intrauterine device
• (IUD)
• – The eyes and face
• – Application through the skull
