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physiology of heat and cold

  1. Physiology of Heat and Cold
  2. CONTENTS Objectives Introduction Principles of heat and cold Energy transfer Physical effects of heat Latent heat Thermoregulatory mechanism and thermo receptors Thermoregulation Physiological effects of heat and cold Therapeutic effects of heat and cold conclusion
  3. Objectives 1. To know about the principles of heat and cold 2. To know about the energy transfer mechanism related to therapeutic modalities 3. To know about thermoregulatory mechanism 4. To know about physiological and therapeutic effects of heat and cold
  4. INTRODUCTION Using a sunbath to relax acing muscle or splashing cool water when overheated.  At present, both heat and cold are widely used physical therapy modalities.  Often thermal modalities are used as adjunct to other physical therapy treatments.
  5. PRINCIPLES Heat Closely packed atoms or molecules move vibrate about their equilibrium position and it is these movement kinetic energy which are recognized as heat. As the temperature of a substance increases the motion of the molecules increases. Thus increased molecular motion produces heat.
  6. Cold When ice is applied to the skin, heat is conducted from the skin to the ice in order to melt it. to change its state, ice requires considerable energy (latent heat of fusion ) to raise the temperature of 1 g of ice at 0 0 to 1gm of water at 37 0 C requires 491 J, whereas to raise 1g of water at 0 0 C to 37 0 C requires only 155 J.
  7. Physical Effects of Heat Expansion •increased kinetic energy A change of state •cohesive force •kinetic force An increased state of chemical reaction • Van’t Hoff’s law
  8. Production of electromagnetic radiation By movement of electrons within the atom. If energy is added to an atom, e.g. by heat this can cause an electron to move out to a higher energy electron shell. (Excited stage) when the electron returns to its normal level energy is released as a pulse of electro magnetic energy
  9. A potential difference between dissimilar metals •If the junction of two dissimilar metals is heated a potential difference is produced between their free ends. Thermionic emission •The heating of molecules of some materials e.g. tungsten. Reduced viscosity in fluids •. Heating increases the kinetic movement of these molecules and reduces their cohesive mutual attraction. This made the fluid less viscous
  10. Energy transfer Conduction Conduction is a method of heat transfer from one place to another by successive molecular collision. Heat transfer by conduction is a slow process. When two objects of different temperature come in contact
  11. Convection Convection is a method of heat transfer in which heated molecules move from one place to another. This method heat transfer is more rapid than conduction and occurs in liquids and gases.
  12. Radiation All objects can give off or take on thermal energy through the process of radiation
  13. Latent heat A specific amount of energy is required to change the solid form of a particular substance into liquid, or the liquid into gas. This energy is called latent heat The freezing point of water is 0 0 C The boiling point of water is 100 0 C
  14. Thermoregulatory mechanism Major heat is from metabolism which is vastly increased during vigorous exercise. When the body is exposed to cold the loss of heat can be much reduced by vasoconstriction The temperature gradient between the core and surface can be expressed by the isothermal lines
  15. Cutaneous receptors Pain nerve endings discharge at the extremes of temperature range where the temperature stimulus becomes merged with pain beyond 45 0 c for heating and 15 0 c for cooling.
  16. • These endings are sometimes described as warm pain and cold pain endings respectively. The more numerous cold receptors discharge over a wide range, different neurons have different ranges and different peak discharges, many around 25 0 C. the warm receptors also vary greatly many with peaks around 40 0 c
  17. Thermal regulation Metabolic control Vasomotor control Hidrotic control Behavioural control
  18. Physiological effects Metabolic activity Viscosity Collagenous tissue changes Nerve stimulation Blood vessel changes Blood and the tissue fluid
  19. Therapeutic effects Heat ►Healing. ► Control of infection ►Relief of pains ►Muscle spasm ►Sedative effect ►ROM ►Pressure sores ►Oedema ►skin diseases
  20. Cold Recent injuries Pain and ms spasm Spasticity Ms strength
  21. References Clayton’s Electrotherapy – Angela forster, Nigel Palastanga Electrotherapy Explained – John low & Ann Reed Physical Agents – Bernadette Hecox, Tsega Andemicael Mehreteab, Joseph Weisberg E – Medicine Superficial Heat and Cold by Milton J Klien 2006 Feb 13.