conductive and convective heating

7/31/2019 Conductive and Convective Heating

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Prepared By: Floriza P. de Leon, PTRP


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Conductive Heating Convective Heating

Specific Heat Thermal Conductivity Hydrocollator Moist Heat Paraffin Wax Bath


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It is the transfer of heat between two objectsin contact, and at different temperatures,

heat being transferred by conduction fromthe warmer object to the cooler one


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It is the transfer of heat energy by means ofconvection currents, which arise due to

temperature and density differences invarious parts of a fluid


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Specific heat of a substance is the heatrequired per unit of mass to change the

temperature one degree celsius. It isexpressed as a ratio of the amounts of heatrequired to raise the temperature of equalmasses of the substance and water by thesame amount. The value for water is taken asone.


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It is the ability of a tissue to absorb heat andconduct it across the tissue


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An automatic heating unit which holds asupply of steam packs heated in water at a

constant temperature ready for use


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The production of heat by a moist source


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Conduction is the diffusion of this energy from one body to another

Speed at which heat will flow and cause a rise in the temperature willdepend upon the thermal greater than that of fat.

Tissues with high water content will conduct faster than tissues with lowwater content.

Specific heat of the tissue will also govern the amount of heat needed to

raise temperature by any particular amount(fat specific heat

0.6)


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Solids mud and peat packs, and electricheating pads

Liquids thermal water baths, and contrastbaths, hot packs, and paraffin wax

Gases

hot air, and hot vapour baths


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Hydrocollator packs

Paraffin wax baths


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Hydrocollator Unit Heater is thermostatically controlled and

maintains water in the unit at a temperaturebetween 76 C and 80 C Hydrocollator Pack Main property of the gel is its capability to

absorb many times its own volume of waterand, when heated, to give off moist heat for30-40 mins.


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Turkish towels, special terry cloth and largepacks may be wrapped in bath blankets

Part selected to be treated must be able totolerate the pressure of the pack (approx 500to 800 gms), and to tolerate and 7-10 C rise intemperature


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Ensure that the circulation can dissipate heat,and that skin sensation responses to thermal

differences are normal (results to burn) Pack retains its heat for 30 mins Care must be taken to have a layer of

towelling Avoid excessive pressure on bony points


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1. Heat production2. Thermal gradient in the tissues

3. Hyperaemia4. Sedative Effects


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Mainly due to the heat generated and issubject to the quantity and depth of

penetration of the long infrared rays emittedfrom the pack IRR penetration is .5-1 mm deep Conduction depth is governed by the

properties of the underlying structures


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Temperature elevation will depend upon thepatency of the circulation and sensation and

the ability of the tissues to dissipate heat Bone and fat will impede heat distribution Temperature rise takes place if the heat

generated exceeds the rate at which thetissues can dissipate the heat


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44 C skin heat tolerance Burns

- 42 C over 2 hours- 44 C over 30 mins- 45 C over 5-10 mins

44 C for 20-30 mins safe and effectiveapplication of heat


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Skin Temperature- Within 7 mins there is a max 7-8 C rise in

temperature and then a drop of about 2 Cover the remainder of the 20-30 minapplication period

- Within 60 mins after tx, the temperaturereturns to normal, a rapid drop occurringduring the 1st 15 mins after treatment


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Subcutaneous tissue and muscle temperature- In areas of tse where there is no obstruction

by fat or bone, the subcutaneous tses show arise of about 3 C maximally in about 20 mins,which then disappears in about 1 hr, the maxdrop being after 15 mins

- In muscle, there is an increase of about 1-2 Cmaximally after 30 mins, and then follows thesame drop in temp pattern as skin andsubcutaneous tissue


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There is an increased vasodilatation of themain venous channels in the skin through the

opening of the AV anastomosis, by passingthe capillaries Some increase in the flow of nutrients,

antibodies, leucocytes, and oxygen in tses Increased skin blood flow (2x at constant

level for about 15 mins


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Increased skin blood flow is due to the releaseof histamine-like substances and bradykinin

producing vasodilatation of the capillaries Local reddening occurs after 20 min

application Increased joint blood flow Blood flow in distal mm may be increased

more than in proximal mm


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Increased vasodilatation of superficial fasciaand mm

Muscle circulation can be increasedeffectively only by exercise The harder and longer the exercise, the

longer-lasting is the muscle hyperaemiaachieved


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Moist heat is a safe analgesic and a musclerelaxant

2 mechanisms- muscle spindle (decrease of gamma fiberactivity decrease muscle spindle activity)- small myelinated C nerve fibers (heatreduces the conduction velocity of the cnerve fibers; counter irritant effect of theheat)


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Increase in tissue metabolism Change in rate of enzymatic activity

Increase in sweating, dehydration anddecrease BP


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Pain and muscle spasm Inflammation

Edema adhesions


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Impaired skin sensation Some dermatological conditions Circulatory dysfunction Analgesic drugs Infections and open wounds Cancer or tuberculosis

Gross edema Lack of comprehension Deep X-ray therapy liniments


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Easy to apply Saves time for personnel Efficient in heat conduction depending on the

area treated Packs are of various sizes which fit most clinicalneeds

Moist heat has a more sedative effect than dryheat

Maximal temp are more uniform than electricpads

Px does not need much handling


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HMP is not easily applied around shouldersand hip

Somewhat heavy Should not be used on extremely sensitive px Some hot packs have a tendency to cause a

skin rash


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Fill in the tank with water without the packsfirst

Thermostat is at 76 C to 80 C Room temperature is 21-23 C Positioning Inspect the are to be treated

Test for cold and hot sensation Proper draping Explain to the px the degree of warmth to be

expected, the duration and purpose of tx


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Ask the px to inform you if any pain,discomfort, or burning sensation is felt during

the tx Prepare the hot packs Fold towel into 4-6 layers Check that body weight is not occluding

circulation particularly over bony areas


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20-30 mins In cases of severe mm spasm (polyneuritis)

30-45 mins


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Burn- Bright red patch may indicate the possibility

of a burn with blistering to follow- Insufficient towelling- Temp of the pack could be too high- Impaired skin sensation- Impaired circulation- Hypersensitive skin (d/t to liniments)


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Dehydration- Two or more areas or a large area have been

heated- Excessive sweating- Drinking water can help


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Low thermal conductivity It gives off heat slowly Low thermal conductivity of the wax prevents

the px feeling as hot as in water of the sametemperature

Wax is self insulating

Sweat does not evaporate and it alsoinsulates After the removal of the wax, the part cools

quickly


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Heat production Circulatory effects

Analgesic effects Stretching effects


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Pain and mm spasm Edema and inflammation

Adhesion and scars


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Impaired skin sensations Some dermatological conditions

Circulatory dysfunction Analgesic drugs Cancer or tuberculosis Gross edema Lack of comprehension Deep x-ray therapy liniments


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2-3 px can be treated at a time Useful for px with poor heat tolerance

Useful for dry scaly skin (after removal ofPOP) Can be combined with exercises which can be

performed without supervision Useful at home for chronic sufferers (e.g. RA) Can be moulded in bony prominences


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Sedimentation occurs at the bottom of thebath

Bath must be cleaned regularly and emptiedat least 2x year Contamination of the oil by atmospheric dust Water tend to collect at the bottom of the

bath


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There are 6 techniques Tech 5 for edematous, dry scaly skin

Tech 6

limited use, home use Tech 2,3,4 more useful Tech 2,3 temperature rise is maintained

longer


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Therapeutic application of heat is known asthermo-therapy

Used to heat joints with little soft-tissuecovering Heating deeper structures through reflex

mechanisms


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Therapeutic heat 40-45 C More than 45 C painful stimulus (tissue

damage) Less than 40 C mild heating


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Factors affecting magnitude of physiologiceffects

1. Extent of temperature rise2. Temp must be elevated 40-45 C3. Rate at which energy is being added to tissue4. Very slow: heat balanced by cooler blood

5. Very fast: stimulates pain receptors6. Volume of tissue exposed7. Larger tissue area affected: systemic reaction


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Hemodynamic Effect (effect on vascular bed )a) (vasodilatation) leads to hyperemia and

sweating. direct reflex activation of

smooth mm of blood vessels by cutaneousthermo-receptors

b) Indirect activation of spinal cord reflexes by

cutaneous thermo-receptors or byincreasing the local release of chemicalmediators of inflammation (vasodilatorsmediators histamine and prostaglandins)


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Effects on Blood flow- Vasodilatation increase blood flow- Decrease in blood viscosity, increase blood flow

- Response to temp change not always the same- Skin blood flow: maintenance of constant bodycore temp under sympathetic adrenergic nerves

- Has AV anastomosis, impt for heat loss (by passcapillary bed), triggered by heated blood

through anterior hypothalamus- Skeletal-mm blood flow: increase of flow and

metabolic rate


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With maximal vasodilatation there are:- Rise in pulse rate-

Drop in blood pressure- Profuse sweating with chloride loss- Increase fluid transfer across the capillary

wall with increased removal of tissue

metabolites


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On Musclesa) Relaxation- Occurs when the warm blood reaches deeper

and deeper into the mm causing the vessels toexpand- Relaxation relieve of pain by easing any

pinching of nerves or blood vessels and byhelping the mm to remove lactic acids and

other metabolic wastes- Relaxation in ROM allowing for gentle exercises

and stretching


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Heat used to reduce spasm- Elevation of pain threshold-

Increase sensory nerve conduction velocity- Change in mm spindle firing rate (decreasegamma afferent fibers)

- Muscle strength and endurance


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Change in Muscle Strength- Decrease in the initial 30 mins after the

application of superficial and deep agents due

to change in the firing rates of type II mmspindle efferent, gamma efferent and 1bfibers from GTO

-Beyond 30 mins after the application of heatand for the next 2 hrs, muscle strengthgradually recovers and then increase toabove pretreatment levels


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Effects on Connective Tissue- Temperature elevation and stretch: change

viscoelastic properties of connective tissues- Heating decreases joint stiffness and increasetissue extensibility

- Length change with damage: stretch and

heat


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On the whole body and metabolism- Rise body temperature-

Increased pulmonary ventilation- Increased metabolism: 10 C increase in thetemperature will twice or triple the metabolicrate leading to an increase of oxygen uptake,

an increase of nutrients and promotion ofhealing


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Reflex effect of prolonged heat- Prolonged heat to one extremity causes

vasodilatation of the contra-lateral extremity

- Prolonged heat to the abdominal wall causes adecreased in the intestinal blood flow, diminishin the intestinal motility and decrease in thesecretion of acid in the stomach

- Prolonged heat to the pelvis relaxes themusculature of the pelvic organs, dilates theblood vessels and increases menstrual flow


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Hot Packs- Superficial moist heat- Canvas cases filled with hydrophilic silicate- Stored in thermostatically controlled cabinet

in water at temp of 76 C- Wrapped in towelling before application(4-6

layers)- Should feel mild to moderate sensation of

heat- Comes in sizes and shapes


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Paraffin wax- 7:1 ratio of paraffin to oil- 7 techniques


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conductive and convective heating

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