1. Physiological effects of heat
Ass.Prof.Dr. Gehan Mosad

2. At the end of the lecture the student should be able to:
1- Know classification of the heating agents.
2- Discuss the local effects of heat exposure.
3- Know systemic effect of heat exposure.
4- Identify general indications and contraindications of thermal agents

3. Classification of heating agents
Superficial heat
Infrared
Heat packs
Hydrotherapy
Deep heat
Shortwave diathermy
Microwave diathermy
Ultrasound

4. Physiological effect of heat
The application of heat to the body is called thermotherapy.
There are two types of heat effects:
Local effect
Systemic or general effect

5. Local effects of heat Increase metabolic rate
Increase blood flow ( hyperemia)
Improve fluid dynamics
Pain control
Decrease muscle spasm
Increase tissue elasticity

6. 1- Increase metabolic rate
Increase tissue temperature leads to increase rate of cell metabolism as a result of increase enzymatic activities and biological reactions.
Increase in the cell metabolic rate leads to the followings:
1- Increase demand for oxygen and nutrients.
2- Increase amount of wastes excreted from the cell.

7. Increase metabolic rate(cont.)
For each increase of 10 oC in skin temperature, the cell metabolic rate increase by a factor of two to three.
Enzymatic activities increase with increase temperature up to 45 oC. Above this level, increase temperature leads to de-naturation of enzymes and proteins and destruction process begins.

8. 2- Increase blood flow Increase temperature causes
Vasodilatation of local blood vessels that leads to increase in blood flow to the heated area to dissipate heat
Increase blood flow will lead to
1- Increase supply of oxygen and nutrients to the heated area.
2- Increase antibodies to the heated area.

9. Increase blood flow (cont.)
Vasodilatation of local blood vessels occurs due to
1- Stimulation of cutaneous thermoreceptors by heat leads to reflex vasodilatation of blood vessels
2- Increase local release of chemical mediators of inflammation as histamine like substance, bradykinins.

10. 3- Increase fluid dynamics
Heat leads to
- Increase capillary permeability which aids in re-absorption of edema.
- Increase blood flow that increases capillary pressure which forces edema and metabolites from the area.
These wastes then can be drained into the venous and lymphatic systems
SO, heat leads to increase venous and lymphatic drainage which aids removal of wastes and re-absorption of edema.

11. 4- Pain control
Heat leads to decrease pain by the following mechanisms
1- Direct mechanism:
Stimulation of free nerve ending (A-beta) leads to blocking the transmission of pain at level of spinal cord.
2- Indirect mechanism:
- Removal of irritant waste products
- Re-absorption of edema
- Decrease muscle spasm
- Improving tissue healing

12. 5- Decrease muscle spasm
Increase temperature decrease muscle spasm due to the following:
Decrease primary and secondary muscle spindle sensitivity to stretch
Increase blood flow

13. 6- Increase tissue elasticity
Increase temperature leads to increase extensibility of collagen and soft tissue.
So, heating is indicated before stretching or range of motion exercises.

14. Systemic effects of heat exposure
The following systemic effects occurs when large area of the body or entire body is exposed to heat
Generalized skin vasodilatation
Generalized sweating
Increase pulse rate
Increase respiratory rate
Decrease blood pressure

15. General indications of thermal agents
Subacute and chronic pain
Subacute and chronic inflammation
Subacute and chronic infection
Tissue healing
Muscle spasm
Reduction of edema
Prior to range of motion exercises

16. General contraindications of thermal agents
Acute injuries ( sprain & strain)
Acute inflammation
Impaired circulation
Impaired sensation
Neoplasm

17. Thank you