1. © 2004 Thermal Modalities General Principles

2. © 2004 Physical Laws Cosine Law Inverse Square Law Arndth-Schultz Principle Law of Grotthus-Draper

3. © 2004 Cosine Law Angle of incidence: The angle at which radiant energy strikes the body. 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. As the angle of incidence changes from 90º, the less effective the transmission. Based on the cosine of the angle of incidence: Based on the cosine of the angle of incidence: Effective energy = Energy * Cosine (angle) Effective energy = Energy * Cosine (angle) Radiant energy should be ±90º Radiant energy should be ±90º 100% Transmission (cosine of 90º = 1.0) 90º 50% Transmission (cosine of 45º =.50) 45º

4. © 2004 Inverse Square Law Intensity of radiant energy depends on the distance between the source and the target. Intensity of radiant energy depends on the distance between the source and the target. Changing the distance changes the intensity Changing the distance changes the intensity Change is proportional to the square of the distance. Change is proportional to the square of the distance. 100 W 25 W 6.25 W 4” 8” Intensity Distance 0”

5. © 2004 Inverse Square Law Formula: 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. Doubling the distance between the tissues and the target decreases the intensity by a factor of four.

6. © 2004 Arndth-Schultz Principle Energy must be absorbed by the tissues Energy must be absorbed by the tissues Must be sufficient to stimulate a physiological response Must be sufficient to stimulate a physiological response Too little stimulus: no effect Too little stimulus: no effect Too much stimulus: injury Too much stimulus: injury

7. © 2004 Grotthus-Draper Inverse relationship between absorption and penetration of energy. Inverse relationship between absorption and penetration of energy. Energy absorbed by one tissue layer is not passed along to deeper layers. 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. The more energy absorbed in superficial layers, the less available for deeper layers.

8. © 2004 General Physiology

9. © 2004 Metabolic Changes Heat increases metabolism Heat increases metabolism Cold decreases metabolism Cold decreases metabolism A 1.8ºF (1ºC) change in tissue temperature = 13% change in metabolism A 1.8ºF (1ºC) change in tissue temperature = 13% change in metabolism

10. © 2004 Tissue Properties Deeper tissues have higher temperatures Deeper tissues have higher temperatures Different tissues have different conductivity properties: Different tissues have different conductivity properties: TissueThermal Conductivity Skin c 0.96 Adipose Tissue i 0.19 Muscle c 0.64 c – conductor i - insulator

11. © 2004 Thermoreceptors Cold-responsive receptors Cold-responsive receptors Heat-responsive receptors Heat-responsive receptors More cold receptors than heat receptors More cold receptors than heat receptors

12. © 2004 Physics

13. Transfer of Thermal Energy ConductionConvectionRadiationEvaporationConversion

14. © 2004 General Principles Exchange of kinetic energy (heat) Exchange of kinetic energy (heat) Transfer of energy is based on a gradient between two points Transfer of energy is based on a gradient between two points Energy always moves from a high concentration to a low concentration Energy always moves from a high concentration to a low concentration Moist heat pack to the skin Moist heat pack to the skin Skin to an ice pack Skin to an ice pack The greater the gradient, the more energy that is transferred The greater the gradient, the more energy that is transferred 120ºF 80ºF110ºF90ºF100ºF

15. © 2004 Conduction Objects are touching each other Objects are touching each other One object loses heat; the other gains heat One object loses heat; the other gains heat Conductors Conductors Skin Skin Muscle Muscle Insulators Insulators Adipose tissue Adipose tissue Terrycloth towels Terrycloth towels 32.1°F 87°F 32.2°F 83°F 32.4°F 80°F 32.3°F 77°F 32.4°F 74°F 32.4°F 70°F 32.5°F 67°F 32.5°F 64°F 32.6°F 61°F 32.6°F 58°F

16. © 2004 Convection Involves the circulation of air or water Involves the circulation of air or water One object is cooled One object is cooled Another object is heated Another object is heated Example: Example: Whirlpool Whirlpool

17. © 2004 Radiation No medium is required No medium is required Examples: Examples: LASER LASER Infrared light Infrared light Ultraviolet light Ultraviolet light Thermal modalities provide radiant energy Thermal modalities provide radiant energy But is not the primary form of heat exchange But is not the primary form of heat exchange

18. © 2004 Evaporation Change from liquid to gaseous state Change from liquid to gaseous state Draws heat from the body Draws heat from the body Cools superficial tissues Cools superficial tissues Examples: Examples: Sweating Sweating Vapocoolant sprays Vapocoolant sprays

19. © 2004 Conversion Change of one form of energy to another Change of one form of energy to another Electromagnetic energy to heat Electromagnetic energy to heat Acoustical energy to heat Acoustical energy to heat Examples: Examples: Short wave diathermy Short wave diathermy Ultrasound Ultrasound