Download Thermal Modalities

Thermal Modalities
General Principles
© 2004
Physical Laws
Cosine Law
Inverse Square Law
Arndth-Schultz Principle
Law of Grotthus-Draper
© 2004
Cosine Law
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Angle of incidence: The angle
at which radiant energy strikes
the body.
As the angle of incidence
changes from 90º, the less
effective the transmission.
Based on the cosine of the
angle of incidence:
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Effective energy = Energy *
Cosine (angle)
Radiant energy should be
±90º
© 2004
90º
45º
100%
50% Transmission
Transmission
(cosine of 45º
90º = .50)
1.0)
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© 2004
0”
100 W
4”
25 W
8”
6.25 W
Intensity
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Intensity of radiant
energy depends on the
distance between the
source and the target.
Changing the distance
changes the intensity
Change is proportional to
the square of the distance.
Distance
Inverse Square Law
Inverse Square Law
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Formula:
E = Es/D2
E – energy received by the tissue
Es – energy produced by the source
D2 – Square of the distance between the target and
the source
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Doubling the distance between the tissues and
the target decreases the intensity by a factor of
four.
© 2004
Arndth-Schultz Principle
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Energy must be absorbed by the tissues
Must be sufficient to stimulate a physiological
response
Too little stimulus: no effect
 Too much stimulus: injury
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© 2004
Grotthus-Draper
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Inverse relationship between absorption and
penetration of energy.
Energy absorbed by one tissue layer is not
passed along to deeper layers.
The more energy absorbed in superficial layers,
the less available for deeper layers.
© 2004
General Physiology
© 2004
Metabolic Changes
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Heat increases metabolism
Cold decreases metabolism
A 1.8ºF (1ºC) change in tissue temperature =
13% change in metabolism
© 2004
Tissue Properties
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Deeper tissues have higher temperatures
Different tissues have different conductivity
properties:
Tissue
Skinc
Adipose Tissuei
Musclec
c – conductor
i - insulator
© 2004
Thermal Conductivity
0.96
0.19
0.64
Thermoreceptors
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Cold-responsive receptors
Heat-responsive receptors
More cold receptors than heat receptors
© 2004
Physics
© 2004
Transfer of Thermal
Energy
Conduction
Convection
Radiation
Evaporation
Conversion
© 2004
General Principles
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Exchange of kinetic energy
(heat)
Transfer of energy is based on
a gradient between two points
Energy always moves from a
high concentration to a low
concentration
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Moist heat pack to the skin
Skin to an ice pack
The greater the gradient, the
more energy that is transferred
© 2004
100ºF
110ºF
120ºF
100ºF
80ºF
90ºF
Conduction
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Objects are touching each other
One object loses heat; the other gains heat
Conductors
Skin
 Muscle
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Insulators
Adipose tissue
 Terrycloth towels
32.1°F
32.2°F
32.3°F
32.4°F
32.5°F
32.6°F
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87°F
83°F
80°F
77°F
74°F
70°F
67°F
64°F
61°F
58°F
Convection
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Involves the circulation of air or water
One object is cooled
Another object is heated
Example:
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© 2004
Whirlpool
Radiation
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No medium is required
Examples:
LASER
 Infrared light
 Ultraviolet light
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Thermal modalities provide radiant energy
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© 2004
But is not the primary form of heat exchange
Evaporation
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Change from liquid to gaseous state
Draws heat from the body
Cools superficial tissues
Examples:
Sweating
 Vapocoolant sprays
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Conversion
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Change of one form of energy to another
Electromagnetic energy to heat
Acoustical energy to heat
Examples:
Short wave diathermy
 Ultrasound
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© 2004