physiological properties of thermal modalities (1)
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Physiological Properties of Thermal Modalities (1). Physiological Properties of Thermal Modalities. Heat is a form of energy which is interchangeable with other forms of energy such as electrical or mechanical energy - PowerPoint PPT PresentationTRANSCRIPT
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Physiological Properties of Thermal Modalities (1)
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Heat is a form of energy which is interchangeable with other forms of energy such as electrical or mechanical energy
When the body is heated rise in temperature due to the increased energy of motion of molecules in the body
Physiological Properties of Thermal Modalities
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Heat and Temperature
Various forms of energy converted into heat. There is a constant ratio between the energy
lost and the heat produced
The First Law of Thermodynamics In all processes occurring in an isolated
system, the energy of the system remains constant
Or simply, energy is neither created nor destroyed
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Electrical, chemical and magnetic energy can be converted into heat
One form of energy converted into another form and some energy is always converted into heat
Heat absorbed by small area more than by big area
Temperature is the expression of all status of matter, solid, liquid and gas
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Temperature measured by Celsius (C) and Fahrenheit scales
0°C = 32°F
100°C = 212°F
Heat unit is Joules (J)
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Specific Heat
Specific heat is the amount of heat energy required to raise a unit mass of material by 1°C
S.H. of water = 4.185 J/g/C° S.H. of water = 1.01 J/g/C° S.H. of skin > muscle > fat > bone
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Physical Effects of Heat
When heat added to matter it increases the kinetic energy of its microstructure
1. When rising the temperature, the average kinetic energy of molecules increases
2. Expansion of the material Kinetic energy vibration of molecules
expand the material Gas > liquid > solid
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Physical Effects of Heat
3. Change in physical state: changing substance from one physical state to another requires a specific amount of heat energy
Latent heat: the energy required to convert 1g of water at 100°C to 1g of steam at 100°C
Latent heat of water [2268J]
4. Production of an electrical potential difference
5. Acceleration of chemical reactions
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Physical Effects of Heat
Van Hoff’s Law
Any chemical reaction capable of being accelerated is accelerated by rise of temperature
6. Production of electromagnetic waves
7. Thermionic emission
8. Reduction in viscosity of fluids
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Methods of Heat Transfer
1. Conduction
2. Convection
3. Conversion
4. Radiation
5. Evaporation
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Conduction
Heat transfer by direct contact (e.g. hot pack, cold pack)
Heat conducted from high temperature material to low temperature material
Guidelines of heat transfer by conduction
1. The greater the temperature difference between the heating or cooling agents and the body part it is applied to, the faster the rate of heat transfer
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Guidelines of heat transfer by conduction
2. Materials with high thermal conductivity transfer heat more rapidly than those with low thermal conductivity
Thermal conductivity: is the rate at which a material transfers heat by conduction
Metal > water > air
3. The larger the area of contact between a thermal agent and the patient, the greater the total heat transfer
4. The rate of temperature rise decreases in proportion to tissue thickness
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Convection
Heat transfer by circulation of a medium of a different temperature (e.g. fluidotherapy. Whirlpool)
Due to direct contact between a circulating medium and another material of a different temperature
Heat transfer more than if by conduction
Blood transfers heat to reduce local change in tissue temperature reduce tissue damage
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Conversion
Conversion from one type of energy to another (e.g. ultrasound, diathermy, metabolism)
Conversion of a non thermal form of energy into heat
Not affected by the temperature of thermal agent Rate of heat transfer depends on the power of
energy source Not require direct contact. Require good transmitter
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Radiation
Exchange directly without an intervening medium or contact
Rate of temperature increase depends on intensity of radiation, size of radiation source, treated are, distance and angle of radiation
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Evaporation
Absorption of energy as a result of conversion of a material from a liquid to vapor state (e.g. vapocoolant spray, sweating)
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Body Heat Transfer Heat exchanged by conductive processes between body
surface and the environment
The body core temperature is constant
Equilibrium is maintained between internal heat production and heat loss or gain at skin surface
Heat transfer within tissue is by conduction and convection
Heating modalities are subdivided according to their primary mode of heat
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In Thermotherapy The properties concerned with heat conduction are
thermal conductivity, tissue density and specific heat Convection involves these properties in addition to fluid
viscosity
Thermal homeostasis:
homeothermy is the pattern of temperature in which cyclic variation in deep body teperature (core) is maintained within the limits of -2/+2°C
Hyperthermia +2 °C 39 °C Hypothermia -2 °C 37 °C
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Body Temperature
It consists of two compartments:
1. The core (central compartment)
Controlled by physiological mechanisms at a constant level, it is around 37 °C, more in organs.
2. The shell or superficial layer
In subject to much greater variations in temperature Varies according to the core temperatue and external
environment
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Body Temperature Measurement
It is measured by different types of thermometers
Thermal balance
Core temperature is constant, there is equilibrium between internal heat production and external heat loss
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Metabolic Heat Production (M)
Maximum values of heat production occur during sever physical work
Heat production can increase at rest in cold conditions by involuntary muscle contractions that produce shivering
Control of body temperature
Thermoregulation integrated by a controlling in the CNS respond to heat content of tissues signaled by thermoreceptors
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Good Luck