1. HEAT – THERMAL ENERGY
PHT 221 – SECTION

2. Lecture Outline
This lecture deals about the topic of heat in following sub-categories;
1. Basics of heat & Modes of heat transfer
2. Physiological effects of heat
3. Therapeutic effects of heat
PHT 221 – SECTION
9/20/2018

3. Lecture Objective
At the end of this lecture, the students will be able to;
1. Differentiate between the modes of thermal transfer.
2. List down the different physiological changes which occurs as a result of application of heating agent to the patient.
3. Explain the different therapeutic effects of thermal application.
PHT 221 – SECTION
9/20/2018

4. HEAT - INTRODUCTION Every living organism produces heat.
In man’s natural environment the predominant form of radiation is THERMAL.
Heat is continually produced in the body as a by- product of METABOLISM.
PHT 221 – SECTION
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5. BALANCE OF HEAT 1. Basal metabolism Muscular activity Food intake
HEAT PRODUCTION
HEAT LOSS
1. Basal metabolism
Muscular activity
Food intake
Temperature effect on cells
1. Radiation
2. Conduction
3. Evaporation of sweat, Respiration
4. Urination & Defecation
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6. Physical Effects of Heat
1. EXPANSION: It is the result of increased kinetic energy producing a greater vibration of molecules, which thus move further apart.
2. CHANGE OF STATE: One form of state (Solid) to the other form of state (Liquid)
3. ACCELERATION OF CHEMICAL ACTION: Van’t Hoff’s Law states that “Any chemical action capable of being accelerated is accelerated by a rise in temperature”.
PHT 221 – SECTION
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7. Physical Effects of Heat
4. THERMOCOUPLE PRINCIPLE: If the junction of two dissimilar metals is heated, a potential difference is produced between their free ends.
5. PRODUCTION OF ELECTROMAGNETIC WAVES: If energy is added to an atom by heat, this can cause electron to move out to a HIGHER-ENERGY electron shell. It is then said to be in a EXCITED STATE. When the electron returns to its normal level, energy is released as a PULSE of electromagnetic energy (A PHOTON).
PHT 221 – SECTION
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8. Physical Effects of Heat
6. THERMIONIC EMISSION: The heating of molecules of some materials (e.g.) TUNGSTEN may cause such molecular AGITATION that some electrons leave their atoms.
7. REDUCED VISCOSITY OF FLUIDS: The molecules in viscous fluids are fairly strongly attracted to one another. Heating increases the KINETIC MOVEMENT of these molecules & reduces their COHESIVE MUTUAL ATTRACTION; this makes the fluid less viscous.
PHT 221 – SECTION
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9. THERAPEUTIC HEAT -
In physical therapy, Several THERMAL AGENTS are available for heat application to tissues.
Types of therapeutic heating agents are classified as follows;
SUPERFICIAL HEATING DEEP HEATING AGENT AGENTS
PHT 221 – SECTION
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10. 1. SUPERFICIAL HEATING AGENTS:
Heat from outside or external source transferred to skin by conduction, convection or radiation – DOES NOT PASS THROUGH the THERMAL BARRIER.
Note:-
Adipose tissue acts as insulation (THERMAL BARRIER) to the underlying tissues, thus limiting the degree of temperature change.
PHT 221 – SECTION
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11. EXAMPLES OF SUPERFICIAL HEATING AGENTS/ MODALITIES PRODUCING HEAT
Hot water bottle
Hot packs
Hydro collator unit
Hot water bath
Hot mud's
Wax Bath
Electric heat pad
Fluido therapy
Hydrotherapy
I.R.R.
PHT 221 – SECTION
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12. 2. DEEP HEATING AGENTS
One form of energy is converted to heat in the tissues – can PASS THE THERMAL BARRIER.
EXAMPLES OF DEEP HEATING AGENTS ARE:
Ultrasound therapy (U.S.T)
Shortwave Diathermy (S.W.D)
Microwave Diathermy (M.W.D)
PHT 221 – SECTION
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13. MECHANISM/MODES OF HEAT EXCHANGE
The means by which therapeutic heat is delivered to the target tissues is attributed to the following physical mechanisms;
1. CONDUCTION
2. CONVECTION
3. RADIATION
4. CONVERSION
5. EVAPORATION
PHT 221 – SECTION
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14. 1. CONDUCTION
Heat gain or loss through DIRECT CONTACT between materials with DIFFERENT TEMPERATURE is called conduction.
E.g. Heat is absorbed by the body tissues when using a HEATING PAD – heat exchange by conduction.
PHT 221 – SECTION
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15. 2. CONVECTION:-
It is defined as the transference of heat to a body by the MOVEMENT OF AIR, MATTER OR LIQUID around or past the body.
The heat is carried by the particles themselves moving Convection currents
e.g. Warm or cool whirlpool in which movement of the water around a body part results in a temperature change.
PHT 221 – SECTION
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16. 3. RADIATION:-
Transfer of heat directly form the source to the object by a wave, travelling as rays. It transfers heat (usually through air) from a warmer source to a cooler source.
Heat radiation is also known as INFRARED RADIATION.
All objects that are hotter than their surroundings give out heat as infra- red radiation
e.g. Infra red radiation lamp (I.R.R.)
PHT 221 – SECTION
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17. 4. CONVERSION:-
It refers to the temperature change that results when energy is transformed from one form to another such as the conversion from
MECHANICAL or ELECTRICAL ENERGY to THERMAL ENERGY.
e.g. Ultrasound Therapy (U.S.T.)
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18. 5. EVAPORATION:-
It is defined as the transformation from a liquid state to a gas state.
Heat is given off when liquids transform to gases.
e.g. Sweating results from heat production within the body. Cooling occurs as the perspiration evaporates from the surface of the skin.
PHT 221 – SECTION
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19. Physiological effects of heat
Physiological effect of heat
Blood vessels effects
Metabolic effect
Neuromuscular effects
Tissue effects
PHT 221 – SECTION
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20. PHYSIOLOGICAL EFFECTS OF HEAT
local body tissue heating
complicated set of physiological changes
complex responses.
Heating is MILD when less than 40˚C.
VIGOROUS heating occurs when tissue temperature reaches 40˚ - 45˚C
PHT 221 – SECTION
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21. Vascular effects on Heat Application
At these temperatures HYPEREMIA or READNESS is noted which indicates an INCREASE BLOOD FLOW. Vasodilatation occurs not only to distribute the additional heat around the body – compensatory heat loss, but also to protect the heated skin.
Temperature increase greater than 45˚C may potentially result in THERMAL(HEAT) PAIN & IRREVESIBLE TISSUE DAMAGE – BURNS.
1. HYPEREMIA or READNESS indicates
INCREASE BLOOD FLOW.
2. Temperature increase > 45˚C
THERMAL(HEAT) PAIN &
IRREVESIBLE TISSUE DAMAGE – BURNS.
PHT 221 – SECTION
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22. METABOLIC ACTIVITY:-
1. Metabolism series of chemical reactions, will INCREASE with a RISE of temperature & DECREASE with a FALL of temperature.
(Van’t Hoff’s Law)
2. Increase in temperature
LIVING TISSUES
DENATURE PROTEINS
PHT 221 – SECTION
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23. METABOLIC ACTIVITY CONT….
3. Temperatures > 45˚C
protein damage occurs
destruction of cells & tissues.
4. With appropriate rise in temperature
all CELL ACTIVITY INCREASE, INCLUDING CELL MOTILITY &
the synthesis & release of CHEMICAL MEDIATORS.
The rate of cellular interactions such as PHAGOCYTOSIS or GROWTH is ACCELERATED.
PHT 221 – SECTION
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24. VISCOSITY:-
The resistance to flow in a blood vessel depends directly on the viscosity of the fluid & inversely on the 4th power of the radius of the vessels.
It is temperature dependent, so raising the temperature in the liquids lowers the viscosity.
Viscosity changes affect not only the fluids in narrow vessels (Blood & Lymph), but also fluid movement with in & throughout the tissue spaces.
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25. COLLAGENOUS TISSUE:-
1. It is the most abundant protein in mammals making up about 25% to 35% of the whole-body protein content.
Collagen constitutes 1% to 2% of muscle tissue, and accounts for 6% of the weight of strong, tendinous muscles.
3. At normal tissue temperatures, collagen primarily exhibits elastic properties & only minimal viscous flow. E.g. Cooking of meat.
4. At temperatures within the range (40 – 45˚C), the extensibility of collagen tissue INCREASE.
5. Collagen melts at temperature above 50˚C.
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26. NERVE STIMULATION:- Heat stimulate the sensory receptor of the skin
heat regulating centers
control of body temperatures
ANALGESIC EFFECT
GATE CONTROL MECHANISM.
PHT 221 – SECTION
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27. NERVE STIMULATION CONT….
Heating the SECONDARY afferent NERVES
i.e. MUSCLE SPINDLE NERVE ENDINGS & GOLGI TENDON ENDINGS
MUSCLE SPASM DECREASE.
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28. PHYSIOLOGICAL GENERALISED - EFFECTS OF HEAT
Increasing sweating - owing to the stimulation of ANTERIOR HYPOTHALAMUS.
Increased PULSE RATE.
Lowering of BLOOD PRESSURE due to decrease in sodium concentration, loss of urea & other nitrogenous substance.
Increased rate of BREATHING.
Increased elimination through KIDNEYS.
PHT 221 – SECTION
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29. THERAPEUTIC EFFECTS OF HEAT
1.ENCOURAGEMENT OF HEALING:-
It is evident that any condition in which increased metabolic rate, cell activity & local blood flow were beneficial could be appropriately treated by MILD HEATING.
Note:-
The application of heat to INFLAMMATORY injuries on the EARLY STAGES is NOT BENEFICIAL.
PHT 221 – SECTION
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30. 1.ENCOURAGEMENT OF HEALING CONT…
Chronic inflammatory stages, the stages of repair & regeneration are all appropriately treated with MILD HEATING.
All forms of therapeutic heating are applied to a wide range of CHRONIC & POST-TRAUMATIC CONDITIONS including the ARTHROSES, SOFT TISSUE LESIONS & POST SURGICAL HEATING.
PHT 221 – SECTION
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31. 2. RELIEF OF PAIN:-
Therapeutic heat is widely used for the RELIEF OF PAIN. It was found that heat is the most effective NON-ANALGESIC method of pain control.
Much therapeutic heating is of the skin. It is therefore reasonable to assume that the major pain relieving effects are mainly REFLEX as far as SUBCUTANEOUS structures are concerned.
PHT 221 – SECTION
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32. 2. RELIEF OF PAIN CONT…
Stimulation of SENSORY HEAT RECEPTORS may activate PAIN GATE MECHANISM.
Vascular changes could also decrease LOCAL PAIN.(The increased blood flow that has been observed could WASH OUT some of the pain provoking metabolites resulting from tissue injury.) (PROSTAGLANDINS & BRADYKININ)
PHT 221 – SECTION
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33. 3.REDUCTION OF MUSCLE SPASM:-
It has been suggested that heating the secondary afferent muscle spindle nerve endings & Golgi tendon organs could be a way in which an INHIBITORY INFLUENCE is applied to the MOTOR NEURON POOL to DIMNISH MUSCLE EXCITATION.
The pain & muscle spasm are interdependent – A reduction in one will cause a reduction in the other.
PHT 221 – SECTION
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34. 4. SEDATIVE EFFECT:-
During & after heat treatments patients have been found to sleep more readily.
This might be simply a consequence of pain relief.
This sedative effect of superficial heat could be a REFLEX PHENOMENON.
PHT 221 – SECTION
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35. 5. INCREASE OF RANGE OF JOINT MOTION:
The analgesic effect of heat allows greater tolerance of stretching.
(B)The viscosity of tissues will be decreased which partly account for the REDUCTION OF JOINT STIFFNESS that occurs with heating.
©Increased COLLAGEN EXTENSIBILITY occurs at higher temperatures.
Note:-
Heat is used PRIOR to passive stretching & exercise to increase joint movement or lengthen scars or contractures.
PHT 221 – SECTION
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36. 6. PROPHYLAXIS (PREVENTION) OF PRESSURE SORES:-
Heat applied to areas of skin subjected to prolonged pressure or friction has been suggested in order to promote a greater BLOOD FLOW in the skin & thus decrease the risk of skin breakdown.
PHT 221 – SECTION
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37. 7. OEDEMA OF EXTREMITIES – REDUCTION:
Heat has been recommended for the treatment of CHRONIC OEDEMA of the hand & foot.
This must be given with the part in ELEVATION since the application of superficial heating will tend to increase oedema if the part is dependent.
PHT 221 – SECTION
9/20/2018

38. 7. OEDEMA OF EXTREMITIES – REDUCTION CONT…
Vessel dilatation induced by heating will allow increased rates of fluid exchange & thus may help to increase the reabsorption of exudates.
To be successful, the modality used would need to encompass the whole swollen region. Such heating arrangements coupled with active ex’s are valuable in the treatment of hand injuries in general.
PHT 221 – SECTION
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39. 8. RESOLUTION OF SOME SKIN DISEASES:-
Fungal infections which are difficult to control & thrive in moist conditions are sometimes treated with regular I.R.R. therapy. (PARONYCHIA)
PHT 221 – SECTION
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40. IMPORTANT THINGs TO NOTE
Due to heat there is Increased capillary permeability & Increased capillary dilatation causes – REDNESS + OEDEMA.
2. The skin temperatures over 45˚C causes tissue damage. Further rise in temperature will lead to DENATURATION & DEATH OF CELLS & TISSUES.
3. The dosage of heat treatment can only be guided by the FEELING OF WARMTH on the part of the patient.
PHT 221 – SECTION
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41. Degrees of heat sensation can be categorized AS FOLLOWS;
MINIMAL WARMTH:- Threshold value, Gentle comforting warmth.
MEDIUM WARMTH:- Distinct feeling of agreeable warmth.
MAXIMUM WARMTH:- Intense feeling of heat, maximum heat tolerance is exercised.
DANGER LEVEL:- Intolerable heat, Burning sensation.
PHT 221 – SECTION
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42. TESTING OF THERMAL SENSATION
Apply 2 test tubes of water at 40 – 45˚C & ˚C randomly to the treatment area.
Ask the patient to identify which is hot & cold with the eyes closed.
The patient should actually discriminate between only a few degrees of Celsius.
Temperature over 45˚C or much below 15˚C should not be used. (Because they may test PAIN instead of THERMAL SENSATION)
PHT 221 – SECTION
9/20/2018