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