Thermal: heat and cold Flashcards
Sensory appreciation of temperature
0 - 13 = very cold 13 - 18 = cold 18 - 27 = cool 27 - 33 = neutral 33 - 37 = warm 37 - 40 = hot 40 - 44 = very hot > 45 = painful
Heat capacity and conductivity
• Different materials have different heat capacity and conductivity
Heat transfer:
3 modes
- Conduction
- Convection
- Radiation
• Conduction
• The kinetic motion of atoms and molecules being passed from one to the next
• Convection
• By the movement of molecules (liquid or gas) from one place to another e.g. convection ovens
wind
• Radiation
• Conversion of heat energy to electromagnetic radiation
** Physiological effects of heat:
- Increased metabolic activity
- Decreased viscosity
- Blood vessel changes
- Collagen tissue changes
- Pain relief and reduction in muscle spasm
- Tissue healing and resolution of inflammation
- Cutaneous thermoreceptors signal temperature change
Increased metabolic activity
•Metabolic activity inc. with rise in temperature
• Van’t Hoffs Law ‐ 13% increase in metabolism for each 1 degree (eg. 4° rise
– 50% increase in metabolism)
• Increases O2 uptake and healing process
• However, also increase activity of destructive process (enzymes)
• > 45° starts to decrease
• > 50° proteins (enzymes) denature
• For therapy, temperature changes in deep tissues should be no greater than 5‐6 oC above or below core temperature.
Viscosity
- Decrease viscosity of fluid
- Therefore less resistance to flow and more blood into the area
- Affects blood, lymph and fluid movement within tissues, joints
- Clinical significance not clear but may help to flush out inflammatory products
Blood vessel changes
- LOCAL changes thought to be due to several mechanisms:
- Direct effects on local capillaries, arterioles, venules‐ dilate
- vasodilation of local blood vessels is an axon reflex triggered by stimulation of polymodal receptors in the skin
- Increased metabolism leading to more carbon dioxide and lactic acid – greater acidity – provokes dilation of blood vessels
- a mild inflammatory reaction
- GENERAL
- 20 mins ‐ general warming of body • drop in blood pressure
Collagen tissue changes
• Collagen becomes more extensible
• At 40‐45°C – collagen shown to be more extensible
• Only occurs if the tissue is simultaneously stretched
(Robertson et al 2006)
Therefore, heat and stretching should result
• greater increase in length
• less force required
• reduced risk of tissue tearing
Nerve stimulation
- Nerve activity is markedly affected by changes in temperature
- Heat stimulates sensory receptors
- Stimulation of afferent nerves may act on pain gate control mechanism ‐ block pain – local analgesia
- Heat affects muscle spindle nerve endings and Golgi tendon organs and may result in reduced muscle spasm
Increase blood and tissue fluid
- Increased metabolism
- Vasodilation
- Lowered blood viscosity
All Increase in fluid exchange across capillary walls and cell membranes
• Speeding up healing processes
Therapeutic effects
Therapeutic effects
• Tissue healing
• In the sub acute to chronic phases of the inflammatory cycle
• Not well supported by recent literature but general agreement
• Relief of pain
• Most common reason for use
• Some evidence (Barbour et al 1986, Sluka et al 1999, On et al 1997)
• Reduction o fmuscle spasm
• Sedative effect
• Increase joint ROM
• Prophylaxis (prevention)of pressure sores
• Reduction of chronic oedema
•Precursor too their treatment(eg.stretching, joint mobilisation,massage)
Clinical Scenarios for Using Heat
- Generally avoided in acute phase ?potential for increasing bleeding
- Sub‐acute – chronic musculoskeletal conditions e.g. osteoarthritis
- Following immobilisation for extended periods e.g. fractures • Prior to other Rx
