What is DIATHERMY?
The use of non-ionizing electromagnetic energy
from the radio-frequency spectrum as
SHORTWAVE DIATHERMY: means of producing therapeutic heat in the tissues by the use of radio waves of high frequency.
CONVERSIVE HEATING: a relatively uniform heating produced by the conversion of electrostatic or electromagnetic fields into heat within the tissues.
ELECTROSTATIC FIELD: is set up between two electrodes by the application of a current to the electrodes.
ELECTROMAGNETIC FIELD: is set up around the loops of a coil through which a current is passing.
A CONDENSER/CAPACITOR: consists of two metal plates separated by an insulator. It stores electrical energy.
A DIELECTRIC: is the insulating (non – conducting) material between the metal plates of a condenser.
The CONDENSER FIELD METHOD: uses the patient in the circuit as part of a condenser, so that the electrostatic field is set up in the tissues.
INDUCTOTHERMY: the patient’s tissues are placed in the
The shortwave diathermy machines used by physiotherapists utilize the frequency of 27.12MHZ and a wavelength of 11m. Shortwave diathermy is produced from two main circuits:
The machine circuit, which produces high frequency current and amplifies its intensity.
The patient circuit, which is coupled (connected) to the machine circuit by inductors (electrodes & electrical leads). This transfers electrical energy to the patient in the form of electrostatic or
electromagnetic field.
In the condenser field method, electrostatic field is created by including the patient’s part / tissue as part of a condenser.
In this method two electrodes are applied to the part, with spacing between the electrode and the skin.
Electrodes are condenser plates and the patient’s tissues together with the spacing are dielectric of the condenser.
In the inductothermy method, a thick insulated cable is used to complete the circuit from the machine.
The cable is coiled around the tissues but separated by spacing. Two electric fields are set up in this method.
Firstly the electromagnetic field is set up around the center of the cable and secondly, the electrostatic field is set up between its ends.
These fields will be concentrated in the tissues.
Superficial and
deep heating
modality
Frequency
- 27.12 MHz
Wavelength
- 11 m
Method of Heat
Transfer
- Conversion
Manner of Delivery
- continuous
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
Calculating Mean Power in PSWD
1.
Cycle Duration = 1000 / PRR
2.
% cycle SWD delivered =
(PD x 100) / Cycle Duration
HEAT PRODUCTION
Dependent on:
SPECIFIC ABSORPTION RATE
Tissue conductivity
charged molecules dipolar molecules
Charged Molecules
Ions and certain
proteins
Molecules are
accelerated along lines
of electric force
Most efficient way of
-Dipolar Molecules
Water and some
proteins
Positive pole of the
molecule aligns itself to
the negative pole of the
electric field (vice versa)
Moderately efficient heat
Non-Polar Molecules
Fat cells
Electron cloud is distorted but negligible heat is
produced
! Clinical Implication !
Blood, having high ionic content, is a good
conductor
vascular tissues as well
Metal and sweat are good conductors
if
SHORTWAVE DIATHERMY
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
Ways of Application
Contraplanar
- aka Transverse positioning
Ways of Application
Coplanar
Ways of Application
Longitudinal
In what way should SWD be applied?
GUIDELINES
Electrodes should be:
Equal in size
Slightly larger than the area treated
Equidistant and at right angles to the skin
INDUCTION FIELD
Patient is in the electromagnetic field or the
electric circuit
produce strong magnetic
field
induce electrical currents within the
body (EDDY currents)
Arrangement of Inductive Coil
Monode: coil arranged
in one plane
Hinged Diplode: permits
electrode to be
positioned at various
Which is more effective: condenser or induction field?
Some studies argue that inductive diathermy produces greater
increase in temperature of deeper tissues compared to condenser/capacitive technique
Any deep effects following capacitive technique requires
Application of electromagnetic energy to produce heat within tissues.
Can also be used on a pulsed setting, to promote healing
Production of heat differs from US – the electromagnetic energy does not cause a heating effect, the cells within the muscles, nerves, bones and fat oscillate, which produces internal heating (i.e. much safer to use than US)
SWD US
Safer to use (but contra-indications
still apply) Very strict contra-indications apply Covers a large treatment area in a
small amount of time Good for use on localised injuries Very little chance of burning the
patient High chance of burning the patient if therapist does not apply principles Will decrease pain and increase
pain threshold Only decreases pain, locally Safe to use on nerves (central and
peripheral) Not safe for use over central nerves Cannot be combined with
medication Can be combined with medication – healing and antibacterial effect Not for use on extremities Easy to use on extremities
•
Increase tissue temperature (without burning)
•
Increased vasodilation and nerve conduction
•
Elevation of pain threshold
•
Alteration of muscle strength (if appropriate exercise is
given after application)
•
Acceleration of enzyme activity
•
Increased soft tissue extensibility
THERAPEUTIC EFFECTS
(continuous and pulsed)
Increase blood flow
Assist in resolution of inflammation
Increase extensibility of deep collagen tissue
Decrease joint stiffness
•
Increased microvascular perfusion
•
Altered cell membrane function and cell activity (similar
to the effects on 20% duty cycle / pulsed US
Indications for non-thermal SWD:
•
Control of pain and oedema
•
Wound healing
•
Nerve healing
•
Bone healing
Thermal:
• Metal implants
• Pacemakers
• Malignancy
• Pregnancy
• Eyes
• Genitals
• Growth plates (epiphyses)
(Easy way to remember C/I to thermal SWD: MPMPEGG)
Non-Thermal:
• Metal implants
• Pacemakers
• Deep tissues (internal organs)
PrEcAuTiOnS (for Thermal and Non-thermal SWD):
• Obesity
• Copper-bearing intrauterine contraceptive devices
1 ALWAYS ask patient for consent
2 ALWAYS ask patient for contra-indications
3 TEST sensation (for SWD only thermal sensation) 4 APPLY machine
Setting Thermal Non-Thermal
Frequency 200Hz 80-150Hz
Microseconds Acute: 60us
Sub-acute: 150us Chronic: 400us
Acute: 60us
Sub-acute: 150us Chronic: 400us
Intensity 100 W 100W
Duration 10-15 minutes 15-30 minutes
