• Shortwave means the application of high frequency electrical energy to the body tissues in order to bring physiological and therapeutic effects

•SHORTWAVE DIATHERMY is a means of producing therapeutic heat in the tissue by the use of radio waves of high frequency.

Electromagnetic Phenomena• Electric field:

• An electric field Exists between and around charged particles, e.g. protons/electrons.

• moving electrical charges = electric current

• Magnetic field:• Magnetic force generated at 90 to the current

• Area where this force acts = magnetic field

Electromagnetic Phenomena

• Electromagnetic phenomena can beconsidered from two different aspects:

• 1- Electrostatic field .

Electromagnetic Phenomena

2- Electromagnetic field

• Diathermy is the application ofhigh-frequency electromagneticenergy that is primarily used togenerate heat in body tissues.

•• Heat is produced by resistance of

the tissue to the passage of theenergy.

• Diathermy may also be used toproduce nonthermal effects

• The depth of penetration is greater than with any of the infrared modalities

• Pulsed shortwave diathermy produces the same magnitude and depth of muscle heating as 1 MHz ultrasound

• The SWD machines used by physical therapist utilize the frequency of 27.12MHz and wavelength greater than 11meter

• Or • 13.56 MHz at 22 M• 40.68 MHz at 7.5 M

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• Generates Both an Electrical and a Magnetic Field

• Ratio Depends on Characteristics of Both The Generator and the Electrodes• SWD Units at 13.56 MHz= Stronger Magnetic Field

• SWD Units at 27.12 MHz = Stronger Electrical Field

Uses

Thermal Effects(Contenous)

• Deep heat• Increased blood flow• Increased cellmetabolism

• Increased tissueextensibility

• Muscular relaxation• Possible changes in• enzyme reactions

Non-thermal Effects(Pulsed)

• Edema reduction• Lymphedema reduction• Superficial woundhealing

• Treatment of venousstasis ulcers

Electromagnetic Radiation

CSWD PSWD

Electromag. Energy absorption

Incr. molecular KE cell ion-binding properties, protein synthesis, ATP production

Thermal Effect Athermal Effect

Increased cell metabolism and function

Enhanced soft-tissue healing

• Implanted pacemakers• Metal in tissues or external fixators• Lack of thermal sensitivity• Pregnancy• Haemorrhaging areas (may be temporary increase in bleeding during menstruation if pelvis irradiated)

• Ischaemic tissue• Malignant tumors• Active tuberculosis• Recent venous thrombosis• Pyrexia• Devitalised skin (e.g. after Radiotherapy)• Growing epiphysis

other electrical equipment is kept at least 3m from the machine during operation

• The component parts of a shortwave diathermy unit. To apply SWD we have two main circuits,

the machine circuit which produce high frequency current coupled with the

patient circuit through inductors to transfer the electrical energy to the

patient.

• Control panel of a shortwavediathermy unit: A, Powerswitch;

• B, timer;• C, output power meter (monitorscurrent drawn from power supplyonly and not in patientcircuit);

• D, output intensity (controlsthe percentage of maximum powertransferred to the patient);and

• E, tuning control (tunes theoutput circuit for maximumenergy transfer fromradiofrequency oscillator)

• Living tissue consists of 3 molecule /particle types:

1. Charged molecules (ions, Na+, some proteins)

2. Dipolar Molecules (water, some proteins)

3. Non polar molecules (fat)

HEAT PRODUCTION

• Dependent on:SPECIFIC ABSORPTION RATE (rate of energy absorbed /unit area of tissue mass)

Tissue conductivity

charged molecules

dipolar molecules

non-polar molecules

Charged Molecules

Ions and certain proteins

Molecules are accelerated along lines of electric force

• Attraction/repulsion forces between charged molecules compel them to accelerate along the lines of electrical force

• Causes collisions & loss of kinetic energy

Most efficient way of heat production

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Dipolar Molecules

Water and some proteinsPositive pole of the molecule aligns itself to the negative pole of the electric field (vice versa)

• Alternating field -produces rotation

Moderately efficient heat production

Non-Polar Molecules• Fat• Electron cloud is distorted butnegligible heat is produced

• Alternating field causeselectron clouds to move back &forth

• Temperature ↑ due to bloodelectrolytes - fat theninsulates heat

• 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 InductionField 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

• Create Stronger Electrical Field Than Magnetic Field

• Ions Will Be Attracted Or Repelled Depending on the Charge of the Pole

• Can be applied in 3 ways: contraplanar, coplanar, or longitudinal

• The Tissue That Offers The Greatest Resistance To Current Flow Develops The Most Heat

• Fat Tissue Resists Current Flow• Thus Fat Is Heated In An Electrical Field • Typical With Capacitor Electrodes• Muscle is heated via conduction from the adipose

• Also referred to as “condenser field diathermy”

• Air space plates• Pad electrodes

• This type of electrode consists of two metal plates with a diameter of 7.5-17.5 cm surrounded by a glass or plastic plate guard. The metal plates may be adjusted approximately 3 cm within the plate guard, thus changing the distance from the skin

Ways of ApplicationContraplanar- 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

Cross-fireHalf the treatment is given with electrodes in one contra planar position & for 2nd half the electrodes repositioned at right angles; for deeply placed organs & air-filled cavities e.g. Chronic Synovitisof Knee Joint

! GUIDELINES !

Electrodes should be:Equal in sizeSlightly larger than the area treated

Equidistant and at right angles to the skin surface

• Sensation Of Heat In Direct Proportion To Distance Of Electrode From Skin

• Closer Plate Generates More Surface Heat• Parts Of Body Low In Subcutaneous Fat Best Treated(e.g., hands, feet, wrists, and ankles)

• This technique is also very effective for treating the spine and the ribs.

Flexible pads: consist of metal electrode encased in rubber and produce an electrostatic field • They are true capacitor electrodes, and they must have uniform contact pressure on the body part if they are to be effective in producing deep heat, as well as in avoiding skin burns

Pad electrodes showing correct placement and spacingcloser the spacing of the

pads, the higher the current density in the superficial tissues. Increasing the space between the pads will increase the depth of penetration in the tissues

• Pad electrodes should be separated by at least the diameter of the electrodes.

• A.Electrodes placed close together produce more superficial heating.

• B. As spacing increases, the current density increases in the deeper tissues

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

Induction Field Diathermy• creates a stronger magnetic field than an electrical field

• Selectively heats muscle • Also referred to as:

• Condenser field diathermy • Magnetic field diathermy

• A coil is housed within a drum • Current flowing within the coil produces a rotating magnetic field

• Magnetic field produces eddy currents in the tissues

• Eddy currents cause friction that produce heat • Although rare, cables are sometimes used in place of drums

• Cable electrodes• Drum Electrodes

• The cable electrode is an induction electrode, which produces a magnetic field

• provide more even heating because they are able to follow the contours of the skin

• There are two basic types of arrangements: • the pancake coil • the wraparound coil

• In either arrangement, there should be at least 1 cm of toweling between the cable and the skin.

• Stiff spacers should be used to keep the coils or the turns of the pancake or the wraparound coil between 5 and 10 cm between turns of the cable, thus providing spacing consistency

• It is important that the cables not touch each other because they will short out and cause excessive heat buildup

• Diathermy units that operate on a frequency of 13.56 MHz are probably best suited to cable electrode-type applications. This is primarily because the lower frequency provides better production of a magnetic field

pancake coil wraparound coil

• also produces a magnetic field• The drum electrode is made up of one or more monoplanar coils that are rigidly fixed inside some kind of housing

• One Or More Monopolar Coils Rigidly Fixed In A Housing Unit

• May Use More Than One Drum Depending On Area Treated • Penetration

• Deeper Soft Tissues

• Toweling Important

• The maximum penetration of shortwave diathermy with a drum electrode is 3 cm, provided there is no more than 2 cm of fat beneath the skin

• For best absorption of energy, the housing of the drum should be in contact with the towel that is covering the skin

Arrangement of Inductive CoilMonode: 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

Fat muscle bone

Inductive coil Minimum maximum None

Capacitive plate Maximum Moderate Low

1- Spacing: allows the lines of force in the electrostatic fieldto diverge before entering the tissues. This preventsconcentration of heat in the super-facial tissues andensures more heating through the part.

• Spacing provided by: 1- wrapping flexible pads intowel.

2-flat felt spacing padsbetween pad electrodeand skin.

3-air when using spaceplates.

1- Spacing: allows the lines of force in the electrostatic field to diverge before entering the tissues. This prevents concentration of heat in the super-facial tissues and ensures more heating through the part.

• Spacing provided by: 1- Wrapping flexible pads in towel.2- Flat felt spacing pads between pad electrode and skin.

3- Air when using space plates.

• a- Normal spacing even field distribution.

• b- Increased spacingdeep field concentration.

• c- Decreased spacingsuperficial concentration.

• It has been suggested that for most short wave sources at maximum output spacing of about 4 cm to the maximum that will give the greatest absolute heating of the deep tissues.

• Conversely the minimum skin electrode distance is about 2 cm.

• Note: the spacing refers to the distance of the metal electrode, not the plastic cover, from the skin.

2- Air in cavities: as sinuses or uterus, the lines of force deviate to avoid air as it offers a high resistance. As a result only the sides of air cavity will be heated.

3- 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 slight larger than the area treated.

4- Metal: metal causes the lines of force to concentrate on the metal