Thermal Agents

Question 1

What are the local and systemic physiological reactions to thermal modalities?

Answer 1

Local: sweating, polioerection (goosebumps), changes in blood flow and metabolic rate

Systemic: generalized sweating/shivering, and cardiovascular changes

Question 2

What is superficial heat? How hot can it heat the tissue (depth dependent)?

Answer 2

Heat that capable of raising the temperature of the skin and superficial subcutaneous tissue up to 2cm deep

Can be dry or moist

Skin: up to 18F

1cm: up to 6F
2cm: up to 2F

Question 3

What structures do deep heating agents heat? How deep can they heat the tissue? What are two deep heating PAs?

Answer 3

Heat large muscle groups and periarticular structures

Heat up to 5cm deep

Diathermy and US

Question 4

What are the 5 modes of heat transfer?

Answer 4

Conduction 
Convection 
Conversion 
Radiation 
Evaporation

Question 5

What is specific heat?

Answer 5

The amount of energy required to raise the temperature of a given weight of a material by giving number of degrees

Question 6

Specific heat for skin vs fat/bone

Specific heat for water vs air

Answer 6

Skin has a greater SP than fat or bone

Water has a greater SP than air

Question 7

Material with high SH: (energy)

Answer 7

Require more energy to achieve the same temperature increase as materials with low SH

Hold more energy than materials with low SH at the same temperatures

Question 8

Thermal agents with high specific heat are applied at low or high temperatures? Why?

Answer 8

Thermal agents with high SH (i.e. Water) are applied at lowered temperature than air based thermal agents

Why?: To transfer the same amount of heat to the patient without burning them

***Remember materials with high SH hold more energy

Question 9

What is conduction? Examples?

Answer 9

Heat transfer by conduction occurs between materials of DIFFERENT temperatures that are in DIRECT CONTACT with one another

Hot/Ice packs and paraffin

Question 10

How many layers should be applied between hot packs to decrease heat transfer and prevent burns?

Answer 10

6 to 8 layers

Heat pack cover counts for 2 to 3 layers

Question 11

What is convection? Does it transfer more or less heat than conduction? Examples?

Answer 11

Heat transfer by DIRECT contact between a CIRCULATING medium with another material of a DIFFERENT temperature

Greater heat transfer as compared to conduction

Whirlpool and fluidotherapy

Question 12

What is conversion? Examples?

Answer 12

Converts non thermal energy to heat/cold

Does not require direct contact

Dependent on ENERGY SOURCE not temperature

Ultrasound, diathermy, some cold packs

Question 13

What is the main way in which heat escapes the body?

Answer 13

RADIATION

Question 14

What is radiation? Examples?

Answer 14

Direct transfer of energy from material with higher temp to material with lower temp

no direct contact or medium needed

Infrared lamps

Question 15

What is evaporation? Example?

Answer 15

Liquid changes to gas or vapor

Vapocoolant Spray

Question 16

What are the metabolic, vascular, and systemic responses to heat?

Answer 16

Metabolic: increase in metabolic rate

Vascular: vasodilation

Systemic: increase HR, decrease BP, increased sweating (sudomotor), increase RR (to blow off excess heat), increased urination

Question 17

How should a heat/cold discrimination test be performed?

Answer 17

Test 3-5 skin areas

Position patient in comfortable position

Patient closes eyes

Apply test probe for 10 seconds and ask patient for perception of temperature