Shortwave and Microwave Diathermy

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Shortwave and Microwave Diathermy

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Diathermy

• Application of High-Frequency Electromagnetic
  Energy
• Used To Generate Heat In Body Tissues
• Heat Produced By Resistance of Tissues
• Also Used For Non-Thermal Effects

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Physiologic Responses To Diathermy

• Not Capable of Producing Depolarization and
  Contraction of Muscles
• Wavelengths Too Short

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Physiologic Responses To Diathermy

• Physiologic Effects Are Those of Heat In General
• Tissue Temperature Increase
• Increased Blood Flow (Vasodilation)
• Increased Venous and Lymphatic Flow
• Increased Metabolism
• Changes In Physical Properties of Tissues
• Muscle Relaxation
• Analgesia

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Diathermy Heating

• Doses Are Not Precisely Controlled Thus The
  Amount of Heating Cannot Be Accurately Measured
• Basically means amount of heating patient
  receives cannot be directly measured
• Heating Current2 X Resistance

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Non-Thermal Effects

• Pulsed SWD Used To Treat Soft Tissue Injuries and
  Wounds
• Related To Depolarization of Damaged Cells
• Loss of Cell Division
• Loss of Proliferation
• Loss of Regenerative capabilities
• Repolarization Corrects Cell Dysfunction
• Generates A Magnetic Field To Increase Na Pump
  Activity

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SWD Physiological Events Summary
Electromagnetic Radiation
PSWD
CSWD
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
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Shortwave Diathermy

• Radio Transmitter With FCC Assigned Frequencies
• 27.12 MHz at 11 M
• 13.56 MHz at 22 M
• 40.68 MHz at 7.5 M

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Shortwave Diathermy Unit

• Power Supply Powers Radio Frequency Oscillator
  (RFO)
• RFO Provides Stable Drift-Free Oscillations at
  Given Frequency
• Power Amplifier Generate Power To Drive
  Electrodes
• Output Resonant Tank Tunes In The Patient for
  Maximum Power Transfer

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Possible Shortwave Diathermy Unit

• APower Switch
• BTimer
• CPower Meter(monitors current from power supply
  not current entering patient-volume control)
• DOutput Intensity(max power to patient)
• ETuning Control(tunes output from RFO)

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Shortwave Diathermy Unit

• Power Output Should Provide Energy To Raise
  Tissue Temp To Therapeutic Range (40-45 deg C)
  (80-120 watts)
• Should Exceed SAR-Specific Absorption Rate (rate
  of energy absorbed /unit area of tissue mass)

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Adjusting Resonance of SWD Unit (Tuning)

• Manual vs Automatic Tuning
• When patients circuit (biologic tissue)
  oscillates at same frequency as device frequency
• Only when tuned will is the electromagnetic
  energy fully delivered
• Most automatic
• Can lose tuning due to movement at skin/electrode
  interface
• Manual Tuning (adjusts patient circuit)
• Set Output Intensity at 30-40
• Adjust Tuning Control Until Power Output Meter
  Reaches Max
• Then Adjust Down to Patient Tolerance Which Is
  About 50
• If More Than 50 Patient Is Out of Resonance

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Shortwave Diathermy Unit

• 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

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SWD Electrodes

• Capacitor Electrodes
• Inductor Electrodes
• Selection of Appropriate Electrodes Can Influence
  The Treatment

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Capacitor (Condenser) Electrodes

• Create Stronger Electrical Field Than Magnetic
  Field
• Ions Will Be Attracted Or Repelled Depending on
  the Charge of the Pole

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Capacitor Electrodes

• Electrical Field Is The Lines of Force Exerted on
  Charged Ions That Cause Movement From One Pole To
  Another
• Center Has Higher Current Density Than Periphery

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Capacitor Electrodes

• Patient Is Between Electrodes and Becomes Part of
  Circuit
• Tissue Is Between Electrodes in a Series Circuit
  Arrangement

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Electrical Field

• 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
• Precaution electrical field may overheat area
  with large fat content

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Capacitor Electrodes(Air Space Plates)

• Two Metal Plates Surrounded By Plastic Guard
• Can Be Moved 3cm Within Guard
• Produce High-Frequency Oscillating Current

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Air Space Plate Electrodes

• Area To Be Treated Is Placed Between Electrodes
  Becoming Part of Circuit

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Air Space Place Electrodes

• 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

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Capacitor Electrodes(Pad Electrodes)

• Greater Electrical Field
• Patient Part of Circuit
• Must Have Uniform Contact (toweling)
• Spacing Equal To Cross-sectional Diameter of Pads
• Part To Be Treated Should Be Centered

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Pad Electrodes

• Increasing The Spacing Will Increase The Depth Of
  Penetration But Will Decrease The Current Density
• Capacitive Method Good for Treating Superficial
  Soft Tissues

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Induction Method

• Creates A Stronger Magnetic Field Than Electrical
  Field
• A Cable Or Coil Is Wrapped Circumferentially
  Around An Extremity Or Coiled Within n Electrode

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Induction Electrodes

• Passing Current Through A Coiled Cable Creates A
  Magnetic Field By Inducing Eddy Currents (small
  circular electrical fields) That Generate Heat

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Induction Electrodes

• Patient In A Magnetic Field Not Part Of A Circuit
• Greatest Current Flow Through Tissue With Least
  Resistance
• Tissues react like a parallel circuit
• Fat does not provide as much resistance to
  electromagnetic energy
• Tissue High In Electrolytic Content Respond Best
  To A Magnetic Field
• Muscle and blood
• Precaution Not as much superficial sensation of
  heat with electromagnetic

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Induction Electrodes(Cable Electrode)

• Two Arrangements
• Pancake Coils
• Wraparound Coils
• Toweling Is Essential
• Pancake Coil Must Have 6 in Center Then 5-10cm
  Spacing Between Turns
• Best Frequency

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Induction Electrodes(Drum Electrode)

• 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

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Heating With Continuous SWD

• Patient Sensation Provides Basis For
  Recommendations Of Continuous SWD
• Dose I (Lowest) (lt38 W) - No Sensation of Heat
• Dose II (Low) (80 W)- Mild Heating Sensation
• Dose III (Medium) (80-300 W) - Moderate or
  Pleasant Heating Sensation
• Dose IV (Heavy) (gt300 W) -Vigorous Heating Within
  Pain Threshold

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Pulsed SWD

• Referred To By Different Names
• Pulsed Electromagnetic Energy (PEME)
• Pulsed Electromagnetic Field (PEMF)
• Pulsed Electromagnetic Energy Treatment (PEMET)

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Pulsed SWD
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PSWD Mean Power Calculations

• Pulse Period (Pulse on off time)
• Peak Pulse Power (W) / Pulse Rep Freq (Hz)
• Percentage On Time
• Pulse Duration (msec) / Pulse Period (msec)
• Mean Power
• Peak Pulse Power (W) / Percentage on Time

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Example

• Peak Pulse Power 800 W
• Pulse Duration .4 ms
• Pulse Frequency 200 Hz
• Pulse Period 800 W / 200 Hz 4 ms
• on time .4 / 4 .10 or 10
• Mean Power 10 of 800 80 W
• End Result thermal effect
• lt 38 W no heating

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Pulsed SWD

• Interrupted Output Delivered In Series Of
  High-Frequency Bursts (40-400 usec)
• Pulse Rate Selected With Pulse Frequency Control
  (11000 Hz)
• Off-Time Longer Than On-Time
• Low Mean Power Output
• Uses Drum Electrode

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Shortwave Diathermy vs.Ultrasound

• Pulsed SWD Produces The Same Magnitude And Depth
  Of Muscle Heating as 1MHz Ultrasound (Draper, JAT
  1997)

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Treatment Time

• Most Typically SWD Treatments Last For 20-30
  Minutes
• Remember As Skin Temperature Rises Resistance
  Falls

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When Should Diathermy Be Used?

• If The Skin Or Some Underlying Soft Tissue Is
  Tender And Will Not Tolerate Pressure
• In Areas Where Subcutaneous Fat Is Thick And Deep
  Heating Is Required
• Induction method
• When The Treatment Goal Is To Increase Tissue
  Temperatures Over A Large Area

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SWD Guidelines

• Indications
• Continuous and Pulsed
• Precautions
• Contraindications

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Microwave Diathermy

• Two FCC Assigned Frequencies-2456 MHz and 915 MHz
• MWD Has Higher Frequency and Shorter Wavelength
  Than SWD
• Generates Strong Electrical Field and Relatively
  Little Magnetic Field
• Advantage better focus wave on body, thereby
  more local heating affects
• Disadvantage Depth Of Penetration Is Minimal In
  Areas With Subcutaneous Fat gt 1 cm

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Microwave Diathermy Unit

• A Power Switch
• BTimer
• COutput Meter (indicates relative output in
  watts
• D Power Output Level Knob
• E Amber Light-Warming up / Red Light- Ready

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MWD Applicators (Electrodes)

• Circular Shaped Applicators
• 4 or 6
• Maximum Temperature At Periphery
• Rectangular Shaped Applicators
• 4.5 x 5 or 5 x 21
• Maximum Temperature At Center

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Microwave Applicator Set-Up

• Microwave Applicator Beams Energy To Patient
• Must Pay Attention To Cosine Law
• In 915 MHz Units Applicators Placed 1 cm From
  Skin
• 2456 MHz Units Have Manufacturer Recommended
  Distances and Power Outputs (Uses Antenna)

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Best Treated areas for Microwave

• Tendons of foot, hand and wrist
• AC and SC joints
• Patellar tendon
• Distal tendons of hamstrings
• Achilles tendon
• Other areas of low subcutaneous fat