Heat and Cold in Medicine

Class 2

Supriya Babu

Topics

• Physical basis of heat and cold• Measurement of temperature:

Thermometry• Mapping of body’s surface

temperature: Thermography• Heat Therapy and uses of cold in

medicine

States of Matter

Solids

Liquids

Gases

http://www.emsb.qc.ca/laurenhill/science/kinetic.html

Vibrations

Kinetic Energy of molecules associated with temperature

Measurement of Temperature

• Indirectly by measuring the change in a physical quantity that changes with temperature

• Different temperature scales

Construction of Thermometer

• Principle: Differential Expansion of materials

• 1cm3 of mercury increases in volume when temperature changes from 0C to 100 C

• Smaller the diameter of capillary greater the sensitivity: 0.1mm

• Visibility is increased by

Cross section of Thermometer

Capillary

Lens Front

White Backing

Temperature Sensitive Devices

• Thermistor • Thermocouple

Variation in body temperature

• External factors• Internal –Metabolic– Circulatory (Major)

• Far Infrared (IR)• Stefan-Boltzmann law–W = e T4

• = 5.7 x 10-12 W/cm2 K4

Thermographic Unit

Diathermy

• diathermy [di´ah-ther″me] means "electrically induced heat" the use of high-frequency electromagnetic currents 

•  Greek words dia and therma, and literally means “heating through.

• short-wave radio frequency (range 1–100 MHz)

• Microwave energy (range 434–915 MHz)

SHORTWAVE DIATHERMYSWD

Description

• High-frequency electrical currents–Radio waves

• Pass through the tissues• Cause molecular vibration• Results in deep heating• Capable of heating large volumes of

tissues• Causes both thermal and non-thermal

effects

Uses

Thermal Effects• Deep heat• Increased blood

flow• Increased cell

metabolism• Increased tissue

extensibility• Muscular relaxation• Possible changes in

enzyme reactions

Non-thermal Effects

• Edema reduction• Lymphedema

reduction• Superficial wound

healing• Treatment of

venous stasis ulcers

Types of Shortwave Diathermy

Induction FieldCapacitive Field

Induction Field Diathermy

• Places the patient in the electromagnetic field

• Selectively heats muscle• Also referred to as:–Condenser field diathermy–Magnetic field diathermy

Induction Field Diathermy (Cont.)

• 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

Capacitive Field Diathermy

• Uses the patient’s tissues as a part of the circuit

• The tissues’ electrical resistance produces heat

• Selectively heats skin–Muscle is heated via conduction from

the adipose

• Also referred to as “condenser field diathermy”

Capacitive Field Diathermy (Cont.)

• Heat is produced by the dipole effect

• Charge particles within membrane align with the field

• The movement produces heat

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Modes of Application

Continuous• Increases tissue temperature• Increased risk of burnsPulsed• May or may not increase

temperature• Pulses allow for increased

treatment intensity and duration• Not the same as “non-thermal”

Ultrasound & SWD Comparison

Diathermy Ultrasound Shortwave

Energy typeAcousticalElectromagneticTissue heated Collage-rich C: Skin,

adipose tissueI: Muscle, vessels

Tissue volume Small (20 cm2) Large (200 cm2)

Temp increase 1 MHz: > 6.3°F C: > 7°F3 MHz: > 14.9°F I: > 18°F

Heat retention 3 min > 9 minC = Capacitive methodI = Induction method

Biophysical Effects

Inflammation• Assists in removal of cellular

debris and toxins• Non-thermal:–Alters diffusion rate across the cell

membrane

• Thermal– Increases intramuscular metabolism

Biophysical Effects

Blood and Fluid Dynamics• Vasodilation increases:–Blood flow–Capillary filtration–Capillary pressure–Oxygen perfusion

• Effects occur deeper than other forms of heat

Biophysical Effects

Tissue Elasticity• SWD can vigorously heat deep tissues • Alters collagen properties, allowing it

to elongate• Requires stretching during and/or

immediately following the treatment• Multiple treatments are required