Thermal Agents: Heat Flashcards by Dessie Alvarado

Mechanisms of Heat Transfer: Conduction

Transfer of heat between 2 objects that
are in contact with each other
Ex: Hot packs/cold packs, movement of heat through tissue layers

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Mechanisms of Heat Transfer: Convection

Transfer of heat by the movement of a
medium
Ex: Whirlpool or Air

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Mechanisms of Heat Transfer: Radiation

Transfer of Energy w/out contact or the
use of a medium
Energy moves through space
Ex: Laser or UV Light

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Mechanisms of Heat Transfer: Conversion

One form of energy changed to heat
energy
Ex: Diathermy (electromagnetic energy
changed to heat energy) or Ultrasound
(acoustical energy changed to heat)

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Mechanisms of Heat Transfer: Evaporation

Loss of heat by changing a liquid to a gas
(endothermic reaction)
Ex: Vapo-coolant spray

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What is Thermotherapy?

The application of therapeutic heat to the
body, which increases tissue temperature
to between 104 - 115 degrees
Heat is removed from the modality and
absorbed by the body
~ Requires a heat gradient

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What are the Effects of Heat Application?

Increased Cell Metabolism
Increased Circulation
Increased Permeability
Decreased Tissue Stiffness
Decreased Pain
Decreased Muscle Tone and Spasm

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Effects of Heat Application: Increased Cell Metabolism

Cell metabolism increases 2-3 times for
each increase of 18 degrees
Results of increased metabolism
~ Increased O2 consumption (Bad)
> Can increase secondary damage/
hypoxia
~ Increased Cellular wastes (Bad)
~ Increased tissue temperature (Good)
~ Increased tissue activity (Depends)
> Good during repair and
maturation phases
• Speeds up fibroblasts
> Bad during acute phase
• Inhibits WBC

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Effects of Heat Application: Increased Circulation

Doubles
Due to local vasodilation
Results of increased Circulation
~ Increased cellular waste removal
~ Increased supply of O2, Leukocytes,
Nutrients, and Enzymes

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Effects of Heat Application: Increased Permeability

Increased Potential for Venous and
Lymphatic drainage

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Effects of Heat Application: Decreased Tissue Stiffness

Increased Elasticity of Collagen
Decreased fluid viscosity
~ Ground Substance

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Effects of Heat Application: Decreased Pain

Increased blood flow = Increased O2 =
Decreased Pain (chemical mediators get
flushed out)
Counter-irritant
Removal of pain stimulating chemicals
~ Pain - spasm - stasis; removal of one,
removes all

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Effects of Heat Application: Decreased muscle tone and spasm

Reduction in pain
Decreased muscle spindle sensitivity
Reduction of cellular metabolites

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Heating Factors: Rate of Heating

Rate of Heating
~ Depends on difference between
temperature of modality and tissues
treated
> The greater the difference, the
more rapid the rate of heat
transfer
> If tissue temperature is high, it will
decrease the magnitude of the
gradient
Adipose can be a limiting factor for
heating because it insulates
~ Can be a benefit in terms of
decreasing heat loss after treatment
Pt. needs to be at a resting state or
normal temperature to apply heat

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Special Considerations for Heat Application

During the first 5-6 minutes of treatment,
the body absorbs heat faster than it can
dissipate it
After 7-9 minutes the body is able to
counteract the heat by moving blood to
the area to cool it
~ Vasodilation
After 20 minutes, when the intensity of
the treatment stays constant superficial
blood vessels constrict (rebound
vasoconstriction: the body’s attempt to
save underlying tissues)
If intensity is too strong during
vasoconstriction, burns will occur
~ Mottling

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Thermotherapy Indications

Decreased ROM (usually due to scar
tissue)
Subacute Inflammatory Conditions
(repair/maturation)
Pain (increased blood flow)
Hematoma Resolution
Edema Removal
~ Increased permeability and
vasodilation = drainage through
venous and lymphatic systems
~ Heat opens the door for osmosis:
moving water into tissues

Thermotherapy Contraindications

Acute Conditions
~ Increases Secondary Damage
~ Increases Edema Accumulation
Compromised Circulation
~ Body unable to cool area
Infection/Open Wounds
Compromised Sensation
~ Body may not sense overheating and
will be less able to protect area

Moist Heat Packs

1cm of effective depth
Cover pack with a commercial cover and
at least one layer of towel
~ Keeps from burning and clean
Pt. should not be lying or sitting on pack.
This will increase the likelihood of burns

Paraffin

For use of small irregularly shaped areas:
fingers and toes
The body part needs to be cleaned first
in order to limit the spread of infection
Post-treatment, the wax will leave the
skin slippery
Immersion Bath
~ Dip the body part up to 12 times, then
immerse
Pack/Wrap Method
~ Dip body part 6-12 times, then wrap
in plastic wrap and a towel
> The first layer should be the
highest to avoid leakage and burns

Warm Water Immersion/Whirlpool

100 - 108 degrees for whole body
105 - 112 degrees for extremities
~ The extremities are able to keep cool
more than the body because cool
blood can reach them
Containers should be clean and sanitized
~ Iodine can should added to the water
if an open wound is present
This modality is gravity dependent (body
part lower than the heart) which can
cause swelling to go down

Fluidotherapy

Unit contains fine cellulose particles in
which warm air is circulated
The particles will mimic water and form
to the body part simultaneously applying
heat, pressure, and massage

Diathermy

Used mostly to heat tissues, but there’s
some non-thermal effects:
~ Microwave Diathermy
> 300 MHz - 300 GHz
> Not used very much
~ Shortwave Diathermy
> 1.8 - 30 MHz
> Mostly used
~ Main difference between the two is
frequency of electricity

Downside of Microwave Diathermy (MWD)

Main downside is that it’s much more
likely to cause tissue burns
~ Metal can reflect MWD back towards
tissues
~ Does not penetrate deeply so more
energy is absorbed superficially
~ Increased reflection at tissue
interfaces

Production of Diathermy

When electricity flows through a
conductor, a magnetic field is formed
perpendicular to the flow of electricity
SWD generator coverts alternating
current from outlet to SWD frequency
~ Electrical current enters the coil
contained in the drum of the unit and
a magnetic field is produced in the
tissues

Thermal Effects of Diathermy

- The magnetic field in the tissues causes charged ions and molecules within the tissues to oscillate and move ~ The motion causes friction resulting in heat and increased tissue temperature ~ Tissues w/ the highest amounts of water means they have a higher concentration of electrolytes and therefore heat the most > Hamstrings > Quads

Thermal Ultrasound vs. SWD

- Ultrasound ~ Can heat tissues 3-5 cm deep ~ Heats small areas ~ Short stretch/thermal window ~ Can sometimes cause pain if area gets heated too much due to lack of movement of probe - SWD ~ Can heat tissues 3-5 cm deep ~ Heats large areas ~ Long stretch/thermal window ~ Stays warmer longer

Thermal Effects of SWD

- Can increase muscle temperature to 104 degrees in 15 minutes - Decay rate is 2-3 times slower than Ultrasound

Non-Thermal Effects of SWD

- Not well understood, no sound theories - Most theories stem from the relationship between magnetic and electrical fields ~ Thought is that the magnetic field affects the electricity driven functions of the cells > Possibly allows membranes to repolarize so cell function is restored > Fibroblasts, osteoblasts, WBC

Advantages of SWD

- Stationary Drum: no hot spots and even heating - No mess - Can be applied over clothing - Doesn’t require clinician to be present the whole time

SWD Indications

- Pain - Spasm - Decreased ROM - Subacute Inflammation - Edema

Continuous vs. Pulsed SWD

- Continuous SWD ~ Not used very much due to the fact that it tends to heat tissues too fast causing discomfort and possible burning - Pulsed SWD ~ Mostly used ~ Alternates between on and off

Pulsed SWD Parameters

- Pulse width (duration) ~ On time ~ Measured in milliseconds - Pulse Rate ~ Number of pulses per second - Power/Intensity ~ Measured in Watts ~ Function of both pulse width and pulse rate > Higher pulse widths and rates produce more power/intensity = more healing

SWD Contraindications

- Not over the eyes, genitals, and epiphyseal plates in children - Pace maker: effects electrical current - Pregnancy - Cancer - Infection - Metal implants for MWD - Diminished sensation - Circulatory Impairment: won’t be able to cool down area post-treatment

Considering the inflammatory response, when would heat application be most appropriate?

- During the repair and maturation phases because it will speed up the process = speed up healing - Least appropriate acutely because it will increase swelling, bleeding, and secondary damage which will increase WBC and Hypoxia