Thermal Agent: Superficial Cold and Heat

Physical Therapy Thermal Agent: Superficial Cold and Heat

1. THERMAL AGENT; SUPERFICIAL COLD AND HEAT Introduction to USMAN, SANTOS, ABUBAKAR

2. Lesson Outline SPECIFIC HEAT DISCUSS MODES OF HEAT TRANSFER CRYOTHERAPY CONTRAINDICATIONS AND PRECAUTIONS FOR CRYOTHERAPY/THERMOTHERAPY APPLICATION TECHNIQUES THERMOTHERAPY USES OF SUPERFICIAL HEAT

3. Introduction of thermal agents: are those that primarilychange the temperature of the skin and of superficialsubcutaneous tissue. increase the temperature of deepertissue including large muscles and periarticularstructures and generally reach to a depth of about 5cm. The therapeutic application of thermal agents results inthe transfer of heat to or from a patient’s body and between tissues and fluid of the body. Thermoregulation by the body uses to maintaincore body temperature and to maintainequilibrium between internal metabolic heat production and heat loss or gain at the skinsurface. Superficial thermal agents: Deep heating agents:

4. The specific heat of different materials and body tissues differs. For example: ➤ Skin has higher specific heat than fat or bone. ➤ Water has higher specific heat than air. Materials with high specific heat require more energy to heat up and hold more energy at a given temperature than materials with low specific heat Specific heat is the amount of energy required toraise the temperature of a given weight of amaterial by a given number of degrees. SPECIFIC HEAT The specific heat of a material is generally expressed in Joules per gram per degree Celsius (J/g/°C)

5. MODES OF HEAT TRANSFER Heat can be transferred to, from, or within the body by con- duction, convection, conversion, radiation, or evaporation. 1-CONDUCTION: > Heating by conduction is the result of energy exchange by direct collision between the molecules of two materials at different temperatures > Heat is conducted from the material at the higher temperature to the material at the lower temperature as faster moving molecules in the warmer material collide.With molecules in the cooler material causing them to accelerate. > Heat transfer continues until the temperature and the speed of molecular movement of both materials become equal. > Heat transfer by conduction occurs only between materials of different temperatures that are in direct contact with each other. e.g. hot pack and paraffin transfer heat by conduction

6. Rate of Heat Transfer by Conduction Rate of Heat Transfer by Conduction The rate at which heat is transferred by conduction between two materials depends on the temperature difference between the materials, their thermal conductivity, and their area of contact. The relationship among these variables is expressed by the following formula: The thermal conductivity of a material describes the rate at which it transfers heat by conduction and is generally expressed in (cal/second)/(cm2 3 °C/cm).

7. GUIDELINES FOR HEAT TRANSFER BY CONDUCTION: The greater the temperature difference between a heating and cooling agent and the body part it is applied to the faster the rate of heat transfer for e.g the higher the temperature of a hot pack the more rapidly the temperature of the area of the patient's skin in contact with the hot pack will increase. Material with high thermal conductivity transfer heat faster than those with low thermal conductivity water has moderate thermal conductivity and air has low thermal conductivity. Heating and cooling agents generally are composed of materials with moderate thermal conductivity to provide a safe and effective rate of heat transfer. Material with low thermal conductivity can be used as insulators to limit the rate of heat transfer.

8. GUIDELINES FOR HEAT TRANSFER BY CONDUCTION: If the pack is applied directly to a patients skin, the patient probably will soon feel uncomfortably hot and could easily be burned. Therefore towel or terry cloth hot pack covers that trap air which has low thermal conductivity are placed between the pack and the patient to limit the rate of heat transfer usually 6 to 8 layer of toweling are placed between hot pack and patient Metal has high thermal conductivity, metal jewelry should be removed from any area that will be in contact with a conductive thermal agent. The larger the area of contact between a thermal agent and patient the greater the heat transfer. The rate of temperature rise decreases in proportion to tissue thickness,skin temperature increases the most and deeper tissue are progressively less effective. Conductive thermal agents are used for heating and cooling superficial tissue.

9. 2-CONVECTION: Heat transfer by convection occur as the result of direct contact between a circulating medium and another material of different temperature. As a result heat transfer by convection transfer more heat in the same period of time than heat transfer by conduction. Circulating blood helps to keep local body temperature at base line. The risk of thermal injury is increased when circulation is impaired. 3-CONVERSION: Heat transfer by conversion involves a non thermal form of energy such as mechanical, electrical or chemical energy in to heat. In Ultrasound a mechanical form of energy is converted in to heat. When using diathermy an electromagnetic energy is converted in to heat.

10. 4-RADIATION: Heating by radiation involves the direct transfer of energy from a material with a higher temperature to one with a lower temperature without the need for an intervening medium or contact. The rate of temperature increase caused by radiation depends on the intensity of the radiation the relative size of the radiation source and the area being treated, the distance of the Source from the treatment area and the angle of the radiation to the tissue. e.g infra red lamp transfer heat by radiation. 5-EVAPORATION: A material must absorb energy to evaporate and thus change form from a liquid to a gas or vapor. This energy is absorbed in the form of heat derived from the material itself or from an adjoining material resulting in a decrease in temperature. For e.g. when a vapo-coolant spray is heated by the warm skin of the body it changes from its liquid form to a vapor at its specific evaporation temperature. During this process the spray absorbs heat and thus cools the skin.

11. Cyrotherapy

12. Cyrotherapy Cryotherapy, the therapeutic use of cold, has clinical applications in rehabilitation and in other areas of medicine. Cryotherapy is used primarily outside of rehabilitation for the destruction of malignant and nonmalignant tissue growths In rehabilitation, mild cooling is used to control inflammation, pain, and edema; to reduce spasticity; to control symptoms of multiple sclerosis; and to facilitate movement .

13. EFFECTS OF COLD HEMODYNAMIC EFFECTS Initial Decrease in Blood Flow Generally, cold applied to the skin causes immediate constriction of the cutaneous vessels and reduction in blood flow. Initial decrease in blood flow Later increase in blood flow In rehabilitation, mild cooling is used to control inflammation, pain, and edema; to reduce spasticity; to control symptoms of multiple sclerosis; and to facilitate movement Neuromuscular effects Decrease nerve conduction velocity Increased pain threshold Altered muscle strength Decrease spasticity Facilitation of muscle contration metabolic effects Decreased metabolic rate

14. Heating by radiation involves the direct transfer of energy from a material with a higher temperature to one with a lower temperature without the need for an intervening medium or contact. The rate of temperature increase caused by radiation depends on the intensity of the radiation the relative size of the radiation source and the area being treated, the distance of the Source from the treatment area and the angle of the radiation to the tissue. e.g infra red lamp transfer heat by radiation.

15. Aftermath based by Lewis Hunting The immediate vasoconstriction response to cold is a consistent and well-documented phenomenon; however, when cold is applied for longer periods of time, or when the tissue temperature reaches less than 10° C (50° F), vasodilation may occur. This phenomenon, known as cold-induced vasodilation (CIVD), was first reported by Lewis in 1930.(Lewis hunting reaction) Lewis reported that when an individual’s fingers were immersed in an ice bath, his or her temperature initially decreased; however, after 15 minutes, his or her temperature cyclically increased and decreased.

16. NEUROMUSCULAR EFFECTS Cold has a variety of effects on neuromuscular function, including decreasing nerve conduction velocity, elevating the pain threshold, altering muscle force generation, decreasing spasticity, and facilitating muscle contraction. Decreased Nerve Conduction Velocity -When nerve temperature is decreased, nerve conduction velocity decreases in proportion to the degree and duration of the temperature change. Increased Pain Threshold -Applying cryotherapy can increase the pain threshold and decrease the sensation of pain. Proposed mechanisms for these effects include counterirritation via the gate control mechanism and reduction of muscle spasm, sensory nerve conduction velocity, or postinjury edema. Altered Muscle Strength -Depending on the duration of the intervention and the timing of measurement, cryotherapy has been associated with both increases and decreases in muscle strength. Decreased Spasticity -When applied appropriately, cryotherapy can temporarily decrease spasticity.

17. Two mechanisms A decrease in gamma motor neuron activity, and later, a decrease in afferent spindle and Golgi tendon organ (GTO) activity A decrease in the amplitude of the Achilles tendon reflex and integrated electromyography (EMG) activity have been observed within a few seconds of application of cold to the skin Facilitation of Muscle Contraction -Brief application of cryotherapy is thought to facilitate alpha motor neuron activity to produce a contraction in a muscle that is flaccid because of upper motor neuron dysfunction.

18. Metabolic effects Decreased Metabolic Rate Cold decreases the rate of all metabolic reactions, including those involved in inflammation and healing. -A 2010 study found that cryotherapy significantly reduced the levels of histamine, an inflammatory mediator, in the blood of patients with rheumatoid arthritis.

19. Uses Cyrotherapy

20. Cryotherapy can be used to control acute inflammation, thereby accelerating recovery from injury or trauma. Decreasing tissue temperature slows the rate of chemical reactions that occur during the acute inflammatory response and also reduces the heat, redness, edema, pain, and loss of function associated with this phase of tissue healing. Cryotherapy directly reduces the heat associated with inflammation by decreasing the temperature of the area to which it is applied. INFLAMMATION CONTROL

21. During acute inflammation, edema is caused by extravasation of fluid into the interstitium as a result of increased intravascular fluid pressure and increased vascular permeability. Cryotherapy reduces intravascular fluid pressure by reducing blood flow into the area via vasoconstriction and increased blood viscosity. This immediate analgesic effect of cold is exploited when vapocoolant sprays or ice massage is used to cool the skin before stretching of the muscles below. The reduced sensation of pain allows the stretch to be more forceful and thus potentially more effective. Applying cryotherapy for 10 to 15 minutes or longer can control pain for 1 hour or longer. PAIN CONTROL EDEMA CONTROL

22. MODIFICATION OF SPASTICITY FACILITATION SYMPTOM MANAGEMENT IN MULTIPLE SCLEROSIS Cryotherapy can be used to temporarily reduce spasticity in patients with upper motor neuron dysfunction. Rapid application of ice as a stimulus to elicit desired motor patterns, known as quick icing, is a technique developed by Rood. Although this technique may be used effectively in the rehabilitation of patients with flaccidity resulting from upper motor neuron dysfunction, it tends to have unreliable results and therefore is not commonly used. The symptoms of some patients with multiple sclerosis are aggravated by generalized heating such as occurs in warm environments or with activity

23. CONTRAINDICATIONS AND PRECAUTIONS FOR CRYOTHERAPY Cryotherapy may be applied by a qualified clinician or by a properly instructed patient. Rehabilitation clinicians may use all forms of cryotherapy that are noninvasive and do not destroy tissue. Patients may use cold packs or ice packs, ice massage, or contrast baths to treat themselves. Cold hypersensitivity (cold-induced urticaria) Cold intolerance Cryoglobulinemia Paroxysmal cold hemoglobinuria Raynaud’s disease or phenomenon Over-regenerating peripheral nerves Over an area with circulatory compromise or peripheral vascular disease

24. PRECAUTIONS FOR THE USE OF CRYOTHERAPY Over the superficial main branch of a nerve Over an open wound Hypertension Poor sensation or mentation Very young and very old patients

25. PRECAUTIONS FOR THE UAPPLICATION TECHNIQUES SE OF CRYOTHERAPY

26. Thermotherapy

27. The therapeutic application of heat is called thermotherapy. Outside of the rehabilitation setting, thermotherapy is used primarily to destroy malignant tissue or to treat cold-related injuries. Within rehabilitation, thermotherapy is used primarily to control pain, increase soft tissue extensibility and circulation, and accelerate healing. Heat has these therapeutic effects because of its influence on hemodynamic, neuromuscular, and metabolic processes, the mechanisms of which are explained in detail in the following section.

28. EFFECTS OF HEAT

29. HEMODYNAMIC EFFECTS Vasodilation Heat causes vasodilation and thus an increase in the rate of blood flow.92 When heat is applied to one area of the body, there is vasodilation where the heat is applied and to a lesser degree, systemically, in areas distant from the site of heat application. Superficial heating agents produce more pronounced vasodilation in local cutaneous blood vessels, where they cause the greatest change in temperature, and less pronounced dilation in the deeper vessels that run through muscles, where they cause little if any change in temperature. Thermotherapy applied to the whole body can cause generalized vasodilation and may improve vascular endothelial function in the setting of cardiac risk factors and in chronic heart failure. Thermotherapy may cause vasodilation by a variety of mechanisms, including direct reflex activation of the smooth muscles of the blood vessels by cutaneous thermos-receptors, indirect activation of local spinal cord reflexes by cutaneous thermos-receptors, or local release of chemical mediators of inflammation (Fig. 8-19). One study demonstrated that at least two independent mechanisms contribute to the rise in skin blood flow during local heating: a fast-responding vasodilator system mediated by axon reflexes, and a more slowly responding vasodilator system that relies on local production of nitrous oxide.

30. PRECAUTIONS FOR THE USE OF CRYOTHERAPY Superficial heating agents stimulate the activity of cutaneous thermos-receptors. It is proposed that transmission from these cutaneous thermos-receptors via their axons directly to nearby cutaneous blood vessels causes the release of bradykinin and nitrous oxide, and that bradykinin and nitrous oxide then stimulate relaxation of the smooth muscles of the vessel walls to cause vasodilation in the area where the heat is applied.98-100 However, the role of bradykinin in heat-mediated vasodilation was recently called into question when it was found that blocking bradykinin receptors during whole-body heating did not alter the amount of cutaneous vasodilation.101 This finding suggests that nitrous oxide is the primary chemical mediator of heat-induced vasodilation. Superficial heating agents stimulate the activity of cutaneous thermos-receptors. It is proposed that transmission from these cutaneous thermos-receptors via their axons directly to nearby cutaneous blood vessels causes the release of bradykinin and nitrous oxide, and that bradykinin and nitrous oxide then stimulate relaxation of the smooth muscles of the vessel walls to cause vasodilation in the area where the heat is applied.98-100 However, the role of bradykinin in heat-mediated vasodilation was recently called into question when it was found that blocking bradykinin receptors during whole-body heating did not alter the amount of cutaneous vasodilation.101 This finding suggests that nitrous oxide is the primary chemical mediator of heat-induced vasodilation.

31. NEUROMUSCULAR EFFECTS

32. Changes in Nerve Conduction Velocity and Firing Rate Increased temperature increases nerve conduction velocity and decreases the conduction latency of sensory and motor nerves.107-109 Nerve conduction velocity increases by approximately 2 m/second for every 1° C (1.8° F) increase in temperature. Although the clinical implications of these effects are not well understood, they may contribute to the reduced pain perception or improved circulation that occurs in response to increasing tissue temperature.

33. Increased Pain Threshold Several studies demonstrate that the application of local heat can increase the pain threshold. Proposed mechanisms of this effect include a direct and immediate reduction of pain by activation of the spinal gating mechanism and an indirect, later, and more prolonged reduction of pain by reduction of ischemia and muscle spasm or by facilitation of tissue healing. Changes in Muscle Strength Muscle strength and endurance have been found to decrease during the initial 30 minutes after the application of deep or superficial heating agents. It is proposed that this initial decrease in muscle strength is the result of changes in the firing rates of type II muscle spindle efferent, gamma efferent, and type Ib fibers from Golgi tendon organs caused by heating of the motor nerves. In turn, this decreases the firing rate of alpha motor neurons. Beyond 30 minutes after the application of heat and for the next 2 hours, muscle strength gradually recovers and then increases to above pre-treatment levels. This delayed increase in strength is thought to be caused by an increase in pain threshold.

34. METABOLIC EFFECTS Increased Metabolic Rate Heat increases the rate of endothermic chemical reactions, including the rate of enzymatic biological reactions. Increased enzymatic activity has been observed in tissues at 39° C to 43° C (102° F to 109° F), with the reaction rate increasing by approximately 13% for every 1.0°C (1.8°F) increase in temperature and doubling for every 10° C (18° F) increase in temperature.33 Enzymatic and metabolic activity rates continue to increase up to a temperature of 45° C (113° F). Beyond this temperature, the protein constituents of enzymes begin to denature and enzyme activity rates decrease, ceasing completely at about 50° C (122° F).

35. ALTERED TISSUE EXTENSIBILITY Increased Collagen Extensibility Increasing the temperature of soft tissue increases its extensibility. When soft tissue is heated before stretching, it maintains a greater increase in length after the stretching force is applied, less force is required to achieve the increase in length, and the risk of tissue tearing is reduced. If heat is applied to collagenous soft tissue, such as tendon, ligament, scar tissue, or joint capsule, before prolonged stretching, plastic deformation, in which the tissue increases in length and maintains most of the increase after cooling, can be achieved.

36. USES OF SUPERFICIAL HEAT PAIN CONTROL Thermotherapy can be used clinically to control pain. This therapeutic effect may be mediated by gating of pain transmission through activation of cutaneous thermos-receptors, or may indirectly result from improved healing, decreased muscle spasm, or reduced ischemia. INCREASED RANGE OF MOTION AND DECREASED JOINT STIFFNESS Thermotherapy can be used clinically when the goals are to increase joint ROM and decrease joint stiffness. Both of these effects are thought to be the result of the increase in soft tissue extensibility that occurs with increasing soft tissue temperature. Increasing soft tissue extensibility contributes to increasing joint ROM because it results in greater increases in soft tissue length and less injury when a passive stretch is applied.

37. CONTRAINDICATIONS FOR THE USE OF THERMOTHERAPY

38. Recent or Potential Hemorrhage Heat causes vasodilation and an increased rate of blood flow. Because vasodilation may cause reopening of a vascular lesion, increasing the rate of blood flow in an area of recent hemorrhage can restart or worsen the bleeding. In addition, increasing blood flow in an area of potential hemorrhage can cause hemorrhage to start. Therefore, it is recommended that heat not be applied to areas of recent or potential hemorrhage. Thermotherapy should not be applied if the patient reports bruising or bleeding in the previous 48 to 72 hours, or if recently formed red, purple, or blue ecchymosis is present.

39. Infrared Irradiation of the Eyes IR irradiation of the eyes should be avoided because such treatment may cause optical damage. To avoid irradiation of the eyes, IR opaque goggles should be worn by the patient throughout treatment using an IR lamp and by the therapist when near the lamp, as occurs when setting up the treatment.

40. REFERENCE; 1.Michelle H. Cameron, MD, PT, OCS.., 2013Physical Agents in Rehabilitation 4rth edition 2.Darlas Y, Solassol A, Clouard R, et al: Ultrasonothérapie: calcul dela thermogenèse, Ann Readapt Med Phys 32:181-192, 1989.