DIATHERMY
What is DIATHERMY?
• The use of non-ionizing
ionizing electromagnetic
energy from the radio-frequency
radio
spectrum
as therapeutic agent
Types of Diathermy
 Long wave
- longest wavelength 300 – 30 m
- most penetrating
- no longer utilized due to high potential of
causing burns and interference with radio
transmissions
 Shortwave
 Microwave
SHORTWAVE DIATHERMY
Superficial and
deep heating
modality
Frequency
- 27.12 MHz
Wavelength
- 11 m
Method of Heat
Transfer
- Conversion
Manner of Delivery
- continuous
- pulsed
Continuous vs Pulsed SWD
PULSED SWD
 Pulse Repetition Rate (PRR)
- 15 to 800 Hz
 Pulse Duration (PD)
- 25 to 400 microseconds
 Peak Pulse Power (PPP)
- 100 to 1000 watts
 Duration
- 20 minutes (5-15
15 acute; 10-20
10
chronic)
Calculating Mean Power in PSWD
1. Cycle Duration = 1000 / PRR
2. % cycle SWD delivered =
(PD x 100) / Cycle Duration
3. Mean Power delivered =
PPP x % cycle SWD
SHORTWAVE
DIATHERMY UNIT
HEAT PRODUCTION
• Dependent on:
SPECIFIC ABSORPTION RATE
Tissue conductivity
charged molecules
dipolar molecules
non--polar molecules
Electrical field magnitude
Charged Molecules
Ions and certain
proteins
Molecules are
accelerated along
lines of electric force
Most
Most efficient way of
heat production
+
-
+
-
+
-
+
-
Dipolar Molecules
Water and some
proteins
Positive pole of the
molecule aligns itself
to the negative pole
of the electric field
(vice versa)
Moderately
Moderately efficient
Non-Polar Molecules
• Fat cells
• Electron cloud is distorted but negligible
heat is produced
• Least efficient heat production
Clinical Implication !
• Blood, having high ionic content, is a
good conductor
 vascular tissues as well
• Metal and sweat are good conductors 
if metal implants and sweat are present
within the electric field, may cause burn
SHORTWAVE DIATHERMY
Condenser
Field
Induction
Field
CONDENSER FIELD
• Patient’s tissues are used as DIELECTRIC
between the conducting electrodes
• Oscillation and rotation of the molecules of
the tissues produces heat
• Either flexible metal plates (malleable) or rigid
metal discs can be used as electrodes
• Can be applied in 3 ways: contraplanar,
coplanar, or longitudinal
Ways of Application
Contraplanar
- aka Transverse positioning
- plates are on either side of the limb
Ways of Application
Coplanar
- plates parallel with the longitudinal
section of the body part; same side
Ways of Application
Longitudinal
- plates are placed at each end of the limb
In what way should
SWD be applied?
• No conclusive evidence as to the technique of
application that will produce the most effect
on the heated tissue (Kitchen and Bazin, 1996)
GUIDELINES !
Electrodes should be:
Equal in size
Slightly
Slightly larger than the area treated
Equidistant
Equidistant and at right angles to the
skin surface
INDUCTION FIELD
• Patient is in the electromagnetic field or
the electric circuit  produce strong
magnetic field  induce electrical
currents within the body (EDDY currents)
• Utilizes either an insulated cable or an
inductive coil applicator
Arrangement of Inductive Coil
Monode: coil
arranged in one plane
Hinged Diplode:
permits electrode to
be positioned at
various angles around
the three sides of the
body part, or in one
plane
Which is more effective: condenser or induction field?
Some
Some studies argue that inductive diathermy
produces greater increase in temperature of
deeper tissues compared to
condenser/capacitive technique
Any
Any deep effects following capacitive
technique requires considerable increase in
superficial tissue temperature
THERAPEUTIC EFFECTS
(continuous and pulsed)
Increase
Increase blood flow
Assist
Assist in resolution of inflammation
Increase
Increase extensibility of deep collagen
tissue
Decrease
Decrease joint stiffness
Relieve
Relieve deep muscle pain and spasm
INDICATIONS
Soft tissue healing
- conflicting evidence as regards
effectiveness of SWD
- controlled animal studies revealed
insignificant results as well as trials
involving human subjects (Kitchen and
Bazin, 1996); to date, no studies in the
treatment setting was conducted
INDICATIONS
• Recent ankle injuries
- inconclusive results following three
double-blind
blind protocols (Kitchen and Bazin)
INDICATIONS
Pain Syndromes
- Pulsed SWD may
provide better
pain relief in some
musculoskeletal
conditions (neck
and back) than
SWD
A. Nerve Regeneration
- studies were done on cats
and rats
- PSWD induced
regeneration of axons,
acceleration and recovery of
nerve conduction
B. Osteoarthritis
- no established effect
C. Post-operative
Post
MICROWAVE
DIATHERMY
Superficial and deep heating
Frequency: 300 MHz to 300 GHz
Wavelength: 1m to 1mm
Therapeutic Parameters:
A. 122.5 mm – 2456 MHz
B. 327 mm – 915 MHz
C. 690 mm – 433.9 MHz
Dosage: acute 5 to 15 minutes
MICROWAVE DIATHERMY APPARATUS
How is microwave produced?
Direct
Direct current (DC) is shunted to the cathode in
the magnetron valve
Release
Release of electrons from the cathode to the
multi-cavity
cavity anode valve
Electrons
Electrons oscillate at predetermined frequency
High
High frequency alternating current is
transmitted along a coaxial cable
Coaxial
Coaxial cable transmits energy to a director
Fate of Microwave
 Absorbed
- energy is taken up by the material
 Transmitted
- pass through the material without being
absorbed
 Refracted
- direction of propagation is altered
 Reflected
THERAPEUTIC EFFECTS
• Increased blood flow or circulation to the
area
• Increased tissue temperature
• Increased metabolism
• Facilitate relaxation
• Increased pain threshold
• Decreased blood viscosity
INDICATIONS
• Soft tissue injury
• Mobilization
• Pain relief
CONTRAINDICATIONS
• Pacemakers
• Metal implants
• Impaired
sensation
• Pregnancy
• Hemorrhage
• Ischemic Tissue
• Testicles and eyes
Malignant CA
Active TB
Fever
Thrombosis
X-ray exposure
Uncooperative
patient
• Areas of poor
•
•
•
•
•
•
PRECAUTIONS
• Operator should observe caution when
handling the machine: same
contraindications apply
Production of Microwave:
- Produced by high frequency current and have
same frequency as the currents which
produce them
- Not produced by Oscillators/ Vacuum tube
valves / Solid state devices
Magnetron:
- Consists of cylindrical cathode surrounded by
an anode structure with cavities opening into
the cathode Anode space by means of slot.
• O/P energy is derived from the resonator
system by means of a coupling loop forced
into one of the cavities.
• The energy picked up on the coupling loop is
carried out of the magnetron on the central
conductor of a co-axial
axial o/p tube throgh a glass
seal to the director
• Director has radiating element of antenna
• Electrical current transformed to antenna &
emits EM radiation. Then a reflector which
direct energy to the patient.
Components of Microwave Diathermy
• Main supply voltage
• Interference Suppression filter( Bypass the
high frequency pick up generated by
Magnetron)
• Fan motor connected with power supply (
Used to cool magnetron)
Delay Circuit
• Magnetron has to warmup for 3 to 4 minutes
before power may be delivered from it
• Delay ckt – connects the anode supply to the
magnetron after this time elapse
• Lamp lights up after 5 minutes – For indicates
that apparatus is ready to use
Magnetron Circuit
• Filament heating voltage is obtained directly from the
secondary winding of the transformer
• Cathode circuit contains suppression filters
• Anode supply may be DC or AC.
• DC voltage from full wave rectifier followed by voltage
doubler circuit
• A high wattage variable resistance in series controls current
applied to the anode circuit
• AC voltage is applied to the anode of the
through series connected thyrotron sothat AC
voltages of both tubes are equal in phase.
• The amount of the current through the
magnetron /output power can be varied by
shifting the phase of the control grid voltage
with respect to the phase of the anode
voltage
• Phase shift can be achieved – By using
capacitor resistor network.
Safety circuit
• Fuse(500 mA) in the anode supply circuit
• Large self inductance coils in primary supply–
supply For
considerable interference
• Due to small dimensions – cores become saturatedto avoid that coils are split up in such a way that no
magnetization
• Duration of irradiation – 10 to 25 minutes.
• Skin should be dry as these waves are absorbed by
water.
Electrotherapy
i-tt curve
• First stimulated with long impulses ( first 1s pulse
duration then 0-05ms)
• For each impulse duration the current intensity is
adjusted until the stimulation threshold has been
exceeded.
• So the current intensity has to be achieved to keep
threshold value
• Impulse Duration(1000-300
300-100-10-3-1-0.05ms)
Chronaxie Period:
Minimum duration of impulse that will
produce a response with a current of double
of the rheobase
Rheobase:
Minimum intensity of current that will
produce a response if the stimulus is of finite
duration
Galvanic current
• Steady flow of direct current
• Movement of ions and their collection at the
skin areas lying beneath the electrodes
• Bright red coloration due to increased blood
flow
• For atonic Paralysis, for treatment of
disturbance in blood flow, iontophoresis
• Current intensity – 0.3 to 0.5 ma/sq.cm
• Duration : 10-20 minutes
Faradic current
• Sequence of pulses with defined shape & current
intensity
• Pulse duration – 1minute
minute triangular waves with
interval 20 minutes
• Acts upon muscle tissue and upon the motor nerves
to produce muscle contractions
• No ion transfer & No chemical effect
• Treatment of muscle weakness after immobilization
and disuse atrophy & functional paralysis treatment
Surging current
• Peak current increases & decreases
rhythmically & the rate of increase and
decrease of peak amplitude is slow
• Surge rate: 6-60 surges / minute
• Ratio of interval to the duration of surging is
varied
• For the treatment of spasm and pain
Exponentially progressive
current
• For the treatment of severe paralysis
• Possibility of providing selective stimulation
• Slope of the exponential pulse is varied
Biphasic Stimulation
• Stimulating pulse is followed by a pulse of
opposite polarity of 1/10th amplitude & 1o
times the width
• Neutralize the polarization of the electrodes
Multivibrators role in Functional
Electrical simulation
• M1 – Set basic stimulus Frequency. Variable rate MV – Trigger M2
• M2 Monostable MV – sets the pulse widthwidth Provide an interrupted
Galvonic output (Rate and duration can be controlled
• M4 – Astable MV- produces short duration faradic current
• M3 – Faradic current modulated at the frequency set by M1M1 output
is surged faradic ( Slow rate of increase and decrease in intensity)
• By integrating the output of M2 interrupted galvanic pulses – can
be modified to have an exponential rise and fall
• Galvonic current – By suitably tapping the DC
supply
• Selector switch to emitter follower stage – To
Low impedance constant voltage output
• Floating type – isolated from earth
• Isolation transformer or RF Coupling
Different types :
Constant voltage / constant current type
Advantages of Constant current
Therapy
• Current flow is constant irrespective of the
patients resistance
• Distortion free
• Avoids irradiating stimulatory sensation
between electrodes by keeping electrodes
firmly to the skin and in one position
Interferrential Current therapy
• Fixed Frequency – 4000 Hz
• Second adjustable Frequency: 4001 – 4400 Hz
• By Heterodyning Interference frequency is
created
• Concentrated at the point of intersection
between the electrodes
• Current perfuse over the greater depth and
over a larger volume of tissue then other
forms of electrical therapy
• At interferential range ( 4000Hz) – Rsistance is
80 times lower at 50 Hz(in conventional
system)
• So current crosses the skin easily with less
stimulation
• Tolerable – Dosage can be increased
• To deep structures
Equipment Details
• 2 Channel + 4 electrodes ( In Quad Polar
arrangement
• Each channel – Sinusoidal symmetrical a.c at
high Frequency (2000-- 5000Hz)
• Both undergone constructive and Destructive
Interference