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Heat Therapy

​Specific heat-amount of energy required to raise the temperature of 1 calorit of H20 by 1 degree Celsius. 

Why does this matter? The higher the specific heat of an object, the more energy is needed to heat it and hold energy. The average specific heat of the human body is 3.56 J/g C

 

Heat transfer occurs through conduction, convection, conversion, radiation, and evaporation.  With thermal modalities, we can utilize each of these principles of heat transfer in order to facilitate superficial tissue heating. 



​Conduction: through direct contact (Hot pack, paraffin wax)

​Convection: circulation of molecules with different temperatures cause transfer (whirlpool)

​Conversion: nonthermal energy is changed into thermal energy (therapeutic ultrasound, diathermy)

​Radiation: direct transfer of energy from higher temperatures to lower temperatures (infrared lamps)
Evaporation: absorbs energy to change form, causes cooling (vapocoolant spray, sweat)

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Thermal therapy heats approximately 3cm into bodily tissues.  So, these modalities are great for heating superficial tissues, but if you want to get down into the muscle and below, you need to utilize other heating modalities (e.g. therapeutic ultrasound with the deeper sound head). 



​​Effects of heat:

Vasodilation- increases rate of blood flow through direct reflex action of smooth muscle (by cutaneous thermoreceptors, causing the blood vessels to dilate), through indirect activation of spinal reflexes, and/or by increasing the local release of chemical mediators of inflammation. 



Changes in nerve conduction velocity- increased temperature increases the velocity of nerve conduction and decreases the latency of sensory & motor nerves. NCV increases 2m/s for every 1 deg C increase in temp. Decreased firing rate of type II muscle spindle efferents & gamma efferents, plus increased firing in type Ib fibers from GTO, causing relaxation of muscle contraction



Increased pain threshold- possibly may occur due to the spinothalamic tract. Both pain and temperature sensations are conveyed through this tract, so the brain may recognize the temperature stimulus instead of the pain signals. 



Changes in muscle strength- muscle strength and endurance decrease during the initial 30 min of application, then gradually recovers and increases pretreatment levels of strength (due to the increase in pain threshold). *Always test muscle strength and endurance prior to applying heat



Increased metabolic rate- heat increases the rate of enzymatic biological reactions (up to 113 deg F). This includes ALL biological reactions, hence the problem with heat at acute injury (since it would increase the inflammatory response)



Increased collagen extensibility- So, heat before stretching in order to get a greater increase in length of a stretch and maintain that elongation (max increase when temperature is at 40-45 deg C for 5-10min)

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​Indications:

Pain control, accelerate healing, increase range of motion & decrease joint stiffness

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​Contraindications:

Recent or potential hemorrhage (within past 24-72hrs)

Thrombophlebitis

Impaired sensation

Impaired mentation

Malignant tumor

No infrared radiation to the eyes

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Precautions:

Acute injury of inflammation (no heat within 48 hrs), pregnancy (don't bake the baby), impaired circulation (you'd recognize this through decreased skin temp, thin skin, poor nail bed health, and tissue swelling), edema, cardiac insufficiency, metal in area (metal conducts heat more quickly than skin or tissues), over an open wound, over topical counterirritants recently applied, and not over demyelinated nerves (because heat can cause conduction block)



Careful of adverse effects!! Burns, fainting (due to peripheral vasodilation and lack of blood flow to the brain), or increased bleeding in areas of acute trauma or in persons with hemophilia. 



Parameters for various heating elements

Hot pack- store in water approximately 70-75 degrees Celsius. Use 6-8 towels between hot pack and the skin in order to minimize burns (if towels are wet, heat transfer will occur more rapidly).

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Paraffin wax- good for distal extremities (e.g. hand). Layer 5-10 times 



Infrared lamps- emit radiation that gives rise to heat when absorbed by matter. Wavelength 750-1300nm (increases superficial tissue temp)



 

​TREATMENT RATIONALES

REFERENCES

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