Superficial Heat, Thermotherapy, Thermal agents, physiotherapy,

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PHYSICAL PRINCIPLES
THERMAL AGENTS

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Specific Heat
….is the amount of energy required to raise the
temperature of a given weight of a material by
a given number of degrees
Latent Heat
…. is the heat energy required to change a
substance from one state to another.

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Mode of Heat Transfer
Conduction
Convection
Conversion/Radiation
Evaporation

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Conduction
Heat loss or gain through
direct contact between
materials with different
temperatures
Guidelines for heat transfer by
conduction
Greater the temperature
difference faster the heat
transfer
Materials with high thermal
conductivity
Larger area of contact
Rate of temperature rise
decreases in proportion to tissue
thickness

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Convection
Transference of heat to a
body by the movement of air,
matter, or liquid around or
past the body
During heating or cooling by
convection the thermal
agent is in motion, so new
parts of the agent at the
initial treatment temperature
keep coming into

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Radiation
This is conversion of
non thermal form of
energy into Heat
Transfer of energy
from a material with
high temperature to
one with lower
temperature without
the need for an
intervening medium or
contact

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Evaporation
Evaporation is a
cooling process.

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Temperature has an effect on:
Viscosity
Nerve conduction—heat increases nerve
conduction velocity; cold decreases it
Blood flow—heat increases arterial and capillary
blood flow; cold decreases blood flow
Collagen extensibility—heat increases tendon
extensibility, collagenase activity is increased; cold
decreases enzyme activity
Temperatures > 45–50°C or < 0°C can injure tissue

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THERMOTHERAPY

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Therapeutic Heat
Superficial Heat
Convective agents Conductive agents Conversive agents
Fluidotherapy Hydrotherapy
Hot packs Heating pads Paraffin wax bath
IR
Deep heat
Ultrasound SWD MWD
Contrast Bath

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Physiological Effects of heat
• Hemodynamic effect
• Neuromuscular effect
• Metabolic effect
• Tissue extensibility

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Physiological Effects of heat
↑ Temperature
Inflammation
↑ Vasodilator
(Histamine &
Prostaglandin)
release
Vasodilatiation
Cutaneous
thermoreceptors
Spinal cord dorsal
root ganglion
Smooth muscle
relaxation
Hemodynamic effect

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Physiological Effects of heat
Neuromuscular effect
•Increased NCV
•Increased pain threshold
•Changes in muscle strength
Metabolic effect
•Increased metabolic rate
Tissue extensibility
•Increased tissue extensibility

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Applications for heat therapy
Generally used for chronic process
• Decrease muscle spasms
• Decrease pain
• Reduction in joint stiffness,
contractures

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Contraindications
• Ischemia. e.g., arterial insufficiency
• Haemorrhage. there is an increased arterial
and capillary blood flow with heat
• Impaired sensation. e.g., spinal cord injury
(SCI) may predispose to burns
• Inability to communicate or respond to
pain. e.g., dementia
• Malignancy. May increase tumour growth

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Contraindications
• Acute trauma or inflammation. Diffusion
across membranes is increased
• Scar tissue. Elevation of temperature
increases the metabolic demand of the
tissue. Scar tissue has inadequate vascular
supply, and is not able to provide an
adequate vascular response when heated,
which can lead to ischemic necrosis.
• Poor thermal regulation