Thermal Modalities: The content for this lecture corresponds to Chapter 5 in the Therapeutic Modalities text by Chad Starkey and Chapter 10 and 11 in the Therapeutic Modality: The Art and Science by Kenneth Knight and David Draper. At the end of this lecture, you will be able to: define thermotherapy and its principles, define cryotherapy and its principles, and finally know when to transition from cold to heat during the patient's treatment as indicated by the inflammatory process. Temperature and their effects are all relative: heat is the term that's used to describe a type of energy transfer. Everything essentially possesses energy and therefore heat; up to -460° Fahrenheit, so the concept of cold really does not exist; it is really the lack of heat that makes cold modalities. The effect of temperature and the classification of heat and cold are relative based on the physiological response elicited by temperature.
Temperature is defined as the measurement of the speed of the molecular motion that describes the amount of kinetic energy or heat within an object. Thermal modalities are therefore the transfer of heat across a temperature gradient. For example, one object is hotter than another. Heat is lost from the warmer object and moved into the cooler object. The greater the temperature gradient, the more quickly the energy is transferred.
An example of this temperature exchange occurs frequently in modalities, for example, when a moist hot pack is placed on a patient, the energy is transferred away from the hot pack and absorbed by the patient's tissues. When an ice pack is applied, heat is drawn away from the patient's tissue and absorbed by the ice pack, thus melting the ice. On the slide, there are two cylinders with different temperatures: 60° Fahrenheit and 40° Fahrenheit.
According to the transfer of heat, energy will be processed from the area of high temperature (the 60° cylinder) to the 40° cylinder. Now, if we had a third cylinder at 80° Fahrenheit, we would see the same type of energy transfer. Energy is going to flow from the 80° Fahrenheit cylinder to the 60° Fahrenheit cylinder.
During the course of this lecture, we will focus on the superficial thermotherapies. Later in the semester, we will also get into the deeper thermotherapies. Superficial thermotherapy treats tissue approximately one to two centimeters deep. These treatments include: moist hot packs, paraffin baths, warm whirlpools, cold whirlpools, cold packs, ice bags, and ice massage. Deep thermotherapy treats tissues approximately three to four centimeters deep. These treatments include diathermy and ultrasound. Superficial thermotherapies only treat one to two centimeters deep.
As we can see, one to two centimeters is really relatively shallow when we consider the skin and the underlying tissue layers. The skin contains receptors that are sensitive to temperature also known as thermoreceptors. The majority of these receptors are responsive to cold with a decreased number of receptors that respond to heat. Thermoreceptors have a dynamic range of neurons that trigger response, usually pain, when the temperature becomes too cold or too hot.
The sensation of cold or heat, while noticeable, is an external stimulation. The cellular changes associated with temperature are often the greatest benefit seen in thermal modalities. For example, with the use of ice to decrease the metabolic activity following an acute injury.
The rate of the body's chemical or metabolic processes is affected by changes in temperature. For every 1.8° Fahrenheit, or 1° Celsius change in tissue temperature, it results in a 13% increase for heat or decrease in cold of the tissues metabolic rate. There are five modes of therapeutic heat transfer that will be discussed within this lecture and throughout the semester. The five modes of therapeutic heat transfer include conduction, convection, conversion, radiation, and evaporation. As we discuss the use of therapeutic modalities, it is worth mentioning that some modalities work via more than one of these heat transfer theories.
Conduction occurs with the direct contact of two objects at differing temperatures. This occurs at a cellular level until the two objects reach equilibrium. This is the most commonly used mode of heat transfer. Examples of conduction include moist hot packs, ice packs, ice massage, among other modalities.
Some materials are better conductors of heat than are others. For example, a wooden and metal picnic table that have been in direct sunlight. If you touch each table top, the metal one would feel hotter more rapidly than the wooden top, even though you are touching two objects with equal temperatures, the greater ability of metal to conduct heat warms your hand more rapidly. Each type of tissue conducts heat at a different rate. In table 5-1 Page 109 in the Starkey text, skin has a thermal conductivity of 0.96 watts per meter. Adipose tissue has a thermal conductivity of 0.19 watts per meter and the muscle has a thermal conductivity of 0.64 watts per meter. The higher the volume for the thermal conductivity indicates more energy must be transmitted to the tissue to have an effect just like the wooden picnic table.
The greater the temperature gradient, the quicker the rate of the movement of energy. As the gradient decreases, the rate of transfer slows. Several other factors affect the perception of heat. Number One: the temperature differential or the gradient between the body and the modality. Number Two: the dissipation of the tissue heat and/or the modality heating.
Number Three: the heat storage capacity of the modality. Number Four: the size of the modality Number Five: the amount of tissue in contact with the modality. Convection is the transfer of heat by movement of a medium, usually water, or air, or particles. Of the three states of matter, gases are poor conductors of heat, liquids are better, and solids are the best conductors.
Circulating air or water increases the ability to transport heat. The actual transfer of energy from a medium to the body still occurs via conduction. Factors that affect convection include the rate of flow of the medium and the temperature gradient of the two objects. Examples of modalities which utilize convection include whirlpools, both cold and heat, and fluidotherapy. For many of you, fluidotherapy is a relatively new modality in something you have not been exposed to. This modality uses convection by moving particles called Selex around the body as the treatment is being processed.
Some forms of energy must be changed to other forms to be effective treatment for the body. This process of changing energy from one form to another is termed conversion. Examples of modalities which utilize conversion include ultrasound, friction, and shortwave diathermy among others.
Therapeutic ultrasound occurs when acoustical energy is converted into heat. Friction or shivering occur so that the mechanical energy can be converted into heat. Radiation is the transfer of energy in the form of rays or waves without the use of a medium. The heat gained or lost through radiation is termed radiant energy.
Radiant energy diverges as it travels resulting in a reduction of energy perceived at different distances along its path. All thermal modalities provide radiant energy. Some examples of therapeutic modalities which use radiation include laser, sunlight, shortwave diathermy, among others. Heat loss can also occur through evaporation. The change from a liquid state to the gaseous state requires that thermal energy be removed from the body. The heat absorbed by the liquid cools the tissue as liquid changes its state into gas via conversion. Vapocoolant spray is an example of a modality the operates via evaporation. This is also important to the body's ability to cool itself during exercise.
Once the heat, especially the humidity outside reaches a certain level, it can be difficult for the body to cool itself during exercise as the sweat on the skin can no longer evaporate because of so much water in the air. This picture includes an example of the five types of heat transfer. At the top left is convection, or the transfer of heat by the movement of a medium, or the heat moving off the top of the fire via the air, which also keeps the fire going. At the bottom left is evaporation or the heat loss from the exchange from a liquid state to a gaseous state, which occurs when the fire changing the state of the wood as it burns. At the middle top is conduction, in which the metal poker becomes hot from the direct contact of two objects at different temperatures. The metal poker conducts the heat from being in the fire.
At the bottom middle is radiation which is the transfer of energy without the use of a medium or feeling the heat off of the fire. At the bottom right is conversion, which is when the form of energy changes from one form to another. Shivering from being away from the fire for too long results in a mechanical energy to help keep the body warm. In physics, an inverse square law is any physical law stating that is specified physical quantity or intensity is inversely proportional to the square of the distance from the source of that physical quantity.
The fundamental cause for this can be understood as a geometric dilution corresponding to point source radiation into three-dimensional space. The mathematical formula is intensity equals divided by the distance squared. We see examples of the inverse square law applied two modalities such as low-level laser light therapy and UV lamp therapy. This is a pictorial example of the inverse square law. S represents the light source while the r’s represent the measured points away from the light source. The lines represent the flux emanating from the source. The total number of flux lines depends on the strength of the source and it's constant with increasing distance.
A greater density of flux lines, or lines per unit of area, means a stronger field. The density of flux lines is inversely proportional to the square of the distance from the source because the surface of the area of a sphere increases with the square of the radius, thus the strength of any field is inversely proportional to the square of the distance from the source. The Grotthus-Draper Law, also called the principle of photochemical activation, states that there is an inverse relationship between the amount of penetration and absorption: the more energy that is absorbent superficial tissues, the less that remains to be transmitted to underlying tissues. Energy that is absorbed by one tissue layer cannot be transmitted to deeper layers. This is a law of Grotthus-Draper. This means that the applied energy must be able to affect the target tissue to be effective as a treatment modality. Using a superficial heating or cooling agent for a deep injury affects only the superficial sensory nerves and blood vessels, but does not produce the needed metabolic change for the traumatized tissue if it's deep. Protons possess inertia, so they exert pressure on any object or substance they strike.
All electromagnetic waves move in a straight line until they come into contact with some other substance. As energy hit the human body it can be reflected. Reflection is when there is a return of waves from an object. As the wave hits the tissue, they bounce back, which means there's no penetration of the modality.
The angle of the reflection is determined by the angle of the strike. Things can also be transmitted; transmission is when the wave is transmitted through the deep tissues. Transmission can be completed such as with x-rays through an arm. The depth of the penetration is a function of the energy of the waves. Refraction can also occur. Refraction is the bending of a wave as it passes through an object.
The waves bend as they pass through the substance; an example is light passing through a prism. The amount of bending depends on the frequency of the waves. Energy can also be absorbed.
Absorption is the process of a medium collecting thermal energy and changing it to kinetic energy. Partially transmitted waves are absorbed by the tissues and are turned into heat. The law of Grotthus-Draper states that electromagnetic waves or energy must be absorbed to benefit target tissue. The effects of the modality are seen at the point of absorption. Energy absorbed superficially does not have a chance to affect deeper tissues; therefore we must choose a modality that effectively reaches the target tissue.
For example, applying a cold pack will mostly affect superficial skin tissue. The heat exchange will occur at the target tissue for the skin and the fat level. If we want to target muscle tissue than flying ultrasound will allow us to treat much deeper tissues. The key to all treatment parameters is to determine a level and the depth of the target tissue and then choosing the appropriate modality and its parameters to treat said tissue. This section of the lecture will focus on cryotherapy, most commonly referred to as cold modality treatments.
Cold modality treatments have a lot of benefit; they're very versatile and can be safely utilized throughout the healing process. Most commonly, cold modalities operate in temperature of 32° Fahrenheit to 65° Fahrenheit. This translates to 0° Celsius to 18° Celsius. The term cold describes a relative temperature state characterized by a decreased molecular motion and the relative absence of heat. Cold applied to the skin will result in a heat transfer from the body or the skin tissue to the cold modality, usually resulting in melting. Cold cannot be transferred because the thermal energy always moves from a high energy concentration to a lower energy concentration. This transfer of heat will occur until the temperatures between the two objects have reached an equilibrium.
The effects of cryotherapy are related to the slowing of cellular metabolism among the injured tissues. The body responds to the loss of heat with a series of local responses including vasoconstriction, decreased metabolic rate, and decreased inflammation and decreased pain. The decreased cellular metabolism results in a decrease need for oxygen of the damaged tissues.
Limiting secondary injury and neural inhibition are extremely important to the injury healing. During a 20-minute icepack treatment, cellular metabolism is decreased by approximately 19%. Secondary injury is relatively slow developing.
As has been described by several researchers, the maximum benefit of cold application in reducing secondary injury occurs when the cold treatment is initiated within the first 30 minutes following the trauma. Some of the physiological effects of cryotherapy; this is the decreased blood flow theory. The traditional theory for immediate care is the cold limits swelling by decreasing blood flow. The logic of this theory is as follows: cold causes vasoconstriction, which decreases blood flow, and therefore decreases hemorrhaging, and therefore there is less swelling. Cold does decrease blood flow by vasoconstriction and decreased vascular permeability. Compression helps decrease underlying blood flow and elevation reduces blood pressure; however, there are some pitfalls to this research. Cold is rarely applied sooner than five to thirty minutes post-injury. It takes time to remove the injured person, evaluate them, and come up with a treatment plan.
Once cold has been applied, it takes an additional five to thirty minutes, depending on the depth of the injured tissue, to reach significant target tissue cooling. For most injuries, clotting occurs within a few minutes of the injury, thus hemorrhage ceases long before the blood vessels at the site of the injury are affected by vasoconstriction, therefore, the benefits of cold on swelling cannot be attributed to decrease circulation. Despite the errors in the theory application, many individuals still buy into this theory of cryotherapy. More frequently among researchers their theory is being replaced by the secondary injury theory. A second physiological effect of cryotherapy is decreased inflammation. The decrease secondary injury theory is an alternative theory that cryotherapy has little effect on hemorrhaging; rather current research suggests that cryotherapy limits the amount of secondary injury and edema.
The logic of this theory is twofold: first without cryotherapy, cells within the injured tissue that are not damaged during the primary injury suffer secondary metabolic injury because of inadequate blood flow and oxygen. Cryotherapy decreases the metabolic needs of these cells so they require less oxygen to function, effectively putting these cells into a state of temporary hibernation. Cells are therefore more resistant to an ischemic state caused by the compromise circulation as seen by the primary injury. The result is decreased secondary metabolic injury, so there is less total injury. This also means that there are less free proteins that are generated by phagocytosis unless edema develops.
Secondary: damage cells release chemical mediators, which attack the tissues surrounding the uninjured cells, causing secondary anosmatic injury. Cold applications suppresses the inflammatory response by: reducing the release of inflammatory mediators, decreasing the prostaglandin synthesis, decreasing capillary permeability, decreasing leukocyte in endothelial interaction, and decreasing creating kinase activity. This decrease secondary metabolic injury means that there are fewer damaged cells to release these chemicals. Cryotherapy has no effect on the primary traumatic injury. As has been said before, this cannot be prevented.
Cryotherapy also has no effect on hemorrhaging that occurs prior to clotting. We can only limit the amount of secondary injury; however, we cannot totally eliminate secondary injury with the use of Cryotherapy. Suppressing the release of inflammatory mediators decreases the amount of hemorrhage and swelling decreasing the mechanical pressure on nerves decreases pain.
As muscle spasm and edema are reduced, the area is less congested, thus limiting the amount of secondary hypoxic cell death. Cold application decreases the rate that nerve impulses are transmitted and increases the depolarization threshold required to initiate the impulse. Changes in nerve depolarization and nerve conduction do not occur simultaneously because tissues cool at different rates. Superficial nerves are affected before deeper nerves. Decreasing nerve conduction velocity reduces the rate of synaptic transmission and increases the time required for the nerve to depolarize and repolarize. Cold application is useful in both primary and secondary pain control approaches.
Pain is controlled via cryotherapy by: removing chemical and mechanical pain triggers, reducing inflammation, and limiting swelling. Cryotherapy interrupts the nerve transmission and decreases nerve conduction velocity. Cold can inhibit pain transmission by acting as a counterirritant, which triggers the descending pain control mechanism, resulting in enkephalin release. Cold also decreases lymphatic vessel diameter, but not as quickly as blood vessels; this is beneficial in that you can apply cold, perform some active exercises, and have a pain-free way of decreasing large proteins. Cryotherapy also decreases muscle spasm by suppressing the stretch reflex, by reducing the threshold of afferent nerve endings, and decreasing the sensitivity of the muscle spindles. The use of cryotherapy decreases the nerve conduction velocity, thus breaking the paint spasm cycle, which decreases the speed of the reflex response and slows the spasm, and therefore the sympathetic nervous system stimulation decreases muscle tone through the reduced muscle spindle activity and gamma motor neuron potentials.
The use of cryotherapy will result in a decreased ability to perform rapid movements and decreased overall strength in the muscles. Muscle tissues need adequate rewarming prior to intensive work or athletic type activities; this requires approximately 30 minutes for tissue rewarming to occur. The sensations of cold are experienced in phases. The acronym CBAN can be used to describe the sensations: it starts with the sensation of cold, followed by burning, then aching, and finally numbness. It takes approximately 20 minutes to achieve the final phase of numbness. For the thermal effects to be applied, numbness is sensation that's required for treatment parameters. If an individual applies ice, determines it’s too cold and removes the ice, and then reapplies the modality, the sensations of cold start over.
Therefore, those individuals who were sensitive to the cold treatment should be educated about the sensations in which they should be experiencing. For every modality, we need to understand the indications, precautions, and contraindications. An indication is a sign or symptom that indicates a certain intervention may be used. It could also be signs or symptoms this specifies a positive relationship for the use of that particular treatment. Indications for the use of cryotherapy include acute injury or inflammation, acute, subacute, or chronic pain, prevention of edema formation, prior to or with rehabilitation exercises, muscle spasm or spasticity, and neuralgia. A precaution is a measure taken in advance to prevent something dangerous or damaging. We need to be aware that there might be a reaction depending on the individual, and if an individual exhibits certain signs or symptoms, there may be a higher risk than someone who does not have those signs or symptoms. The precaution for the use of cryotherapy are: avoiding large treatment areas if the patient has cardiac or respiratory issues, cold allergies or hyper sensitivity to cold, previous experience with frostbite, or cold-induced neuropathy.
A contraindication is a sign or symptom or a diagnosis which indicates that certain interventions may not be used. There is a negative association between the condition and the treatment techniques. The contraindications for the use of cryotherapy include: compromised sensation, compromised circulation, uncovered open wounds (especially if we’re reusing the cold pack), Raynaud’s phenomenon, hemoglobinemia, deep vein thrombosis or DVT, and lupus. What about compartment syndrome? It's an acute injury. We can use ice for compartment syndrome, but we wouldn't want to wrap it on. We would not want to increase any pressure associated with the compartment syndrome.
Raynaud’s disease or Raynaud’s phenomenon is an excessively reduced blood flow in response to cold or emotional stress. This causes discoloration of the fingers, toes, and occasionally other areas like the nose and ears. It is also sometimes called idiopathic vasospasm disorder. When the disorders caused is idiopathic, it is referred to as Raynaud’s disease also called Primary Raynaud’s.
If the syndrome is secondary to another disease such as systemic sclerosis, scleroderma, or other connective tissue disorders, it is correctly referred to as Raynaud’s Phenomena or Secondary Raynaud’s. If Raynaud’s Phenomena is suspected to be secondary to systemic sclerosis, one tool which may help aid in the prediction the systemic sclerosis is Thermography. The pathophysiology of Raynaud’s includes hyper activation of the sympathetic nervous system, which causes extreme vasoconstriction of the peripheral blood vessels, which leads to tissue hypoxia.
Chronic recurrent cases of Raynaud’s phenomena can result in atrophy of the skin, subcutaneous tissues, and muscle. In rare cases, it can cause ulcerations and ischemic gangrene. The condition can cause pain within the affected extremities, discoloration or paleness, and the sensation of cold or numbness. This can often be distressing to those who are not diagnosed and sometimes can be obstructive. If someone with Raynaud’s is placed into a cold climate, it could potentially become disastrous.
There are some documented cases of occurrence of Raynaud’s phenomenon in only one extremity or one finger of the hand. When exposed to cold temperatures, the blood supply to the fingers or toes, and in some cases the nose or ear lobes, is markedly reduced. The skin turns pale or white and is called pollar; it becomes cold and numb. When oxygen supply is depleted, the skin turns a blue color or cyanosis. These events are episodic and when the episode subsides, or the area is warmed, the blood flow returns, and the skin color first turns red or ruby, and then back to normal often accompanied by swelling, tingling, and a painful pins and needles sensation. All three color changes are observed in classic Raynaud’s, however, not all patients see the affirmation color changes in all episodes, especially in milder cases of the conditions.
Symptoms are sometimes thought to be due to reactive hyperemia’s of the area's deprived to blood flow. Another condition is frostbite or cold burn, which is on the right. It is a medical condition in which the localized damage is caused to skin and other tissues due to freezing. Frostbite is more likely to happen in body parts furthest from the heart and those with large exposed areas.
The first initial stage of frostbite is sometimes called frostnip. At or below 0° Celsius or 32° Fahrenheit, blood vessels close to the skin start to constrict and blood is shunted away from the extremities via the action of glomus bodies. The same response may also be a result of exposure to high winds. The constriction helps to preserve the core body temperature and extreme cold or when the body is exposed to cold for long periods, this protective strategy can reduce blood flow in some areas of the body to dangerously low levels. This lack of blood flow leads to the eventual freezing and death of skin tissues in the affected areas. Of the four degrees of frostbite, each has varying degrees of pain. First-degree, this is initially called frostnip and only affects the surface of the skin which is frozen, on the onset itching and pain occur, then the skin develops white, red, and yellow patches and becomes numb. The area affected by frostnip usually does not become permanently damaged as it's only the skin’s top layer that becomes affected.
Long-term insensitivity to both heat and cold can sometimes occur after suffering from frostnip. Second degree; if freezing continues, the skin may freeze in harden, but the deep tissues are not affected and remain soft and normal. Second-degree injuries usually blister 1-2 days after becoming frozen. The blisters may become hard and blackened, but they usually appear worse than they are. Most of the injuries heal within one month, but the area may become permanently insensitive to both heat and cold. Third and fourth degree frostbite; if the area freezes further, deep frostbite occurs.
The muscles, tendons, blood vessels, and nerves all freeze. The skin is hard, feels waxy, and use of the area is temporarily lost, and in severe cases, permanently lost. Deep frostbite results in the areas of purplish blisters, which turn black and are generally blood-filled. Nerve damage in the area can result in a loss of feeling. This extreme frostbite may result in fingers and toes being amputated if the area becomes gangrenous. If the frostbite has gone on untreated, they may actually just fall off.
The extent of the damage done to the area by the freezing process of the frostbite may take several months to assess and this often delays surgery to remove the dead tissue. Cold-induced neuropathy can occur when too much pressure is applied to an elastic rap securing an ice pack over a large superficial nerve, resulting in over cooling of the nerve or neuropathy. Neuropathy causes a loss of sensory function, motor function, or both. Two common areas for cold induced neuropathy are the ulnar nerve the elbow and the common perineal nerve which is demonstrated in this picture. Again, it is ok to apply ice to these areas, you just may want to consider placing a paper towel between the ice in the skin, or reducing the amount of pressure with which the ice is wrapped to the area. This chart is a demonstration of the tissue temperature cooling which occurs over time. After 30 minutes of time, there's a significant decrease in skin tissue temperature, even subcutaneous temperature, and a mild decrease in temperature of the muscle at four centimeters. Over a treatment time of a 120 minutes, which is roughly two hours, we will see a plateau of the skin cooling and a relatively consistent temperature of the subcutaneous tissue while there is still an associated continue decrease in muscle temperature.
Therefore, to reach certain depth of target tissue, increasing the amount of treatment time may be required, although the associated risks, associated with prolonged cryotherapy exposure, increase with the length of the treatment as well. The thickness of the patient’s adipose tissue layer can be calculated by determining the skin fold overlaying the treatment area and then dividing that number two, by which is skin fold divided by two. Thick insulating layers of adipose tissue reduce the rate and depth of inter muscular cooling, and require longer treatment durations to reach therapeutic treatment temperatures. With less than 8 millimeters of subcutaneous adipose tissue, intramuscular cooling occurs at a rate of 1.3° Fahrenheit per minute per 1 centimeter within the muscle.
At 10 millimeters and 18 millimeters of adipose tissue, the rate of cooling decreases to 0.81 ° per minute. As can be seen in the study above, a 25-minute treatment may be adequate for a patient with the skin fold of 20 millimeters of fat or less; however, a 40-minute application is required to produce similar results in a patient with skin folds between21 and 30 millimeters whereas a 60-minute application is required for patients with skin folds of 31 to 40 millimeters. The data from this study suggests that adipose thickness does have indeed a strong influence on cooling. Across all groups, cooling time increased rather dramatically in skinfold thickness increased. Although a 20-minute treatment will produce a typical effect in patients with skin folds of less than 20 millimeters, patients with skin folds between 20 and 30 millimeters will take twice as long: nearly 38 minutes, and patients with the skin folds in the 30 to 40 millimeter range, require three times as long and almost unheard of 59-minute treatment to produce the very same temperature effect. Based on this study's findings, they offer table 1 is a clinical recommendation for cryotherapy duration required to produce a typical cooling effect. Note that the researchers of this article are not implying that this effect is optimal.
Optimal cooling has yet to be adequately identified; therefore, it's apparent that the amount of adipose tissue is highly dependent on the effects of the superficial treatment, especially in those of cryotherapy. Tissue cooling and warming is dependent on several factors. Number One, the temperature gradient: the more difference between the two temperatures, the more rapid and deeper the energy exchange. The duration of the treatment; the longer the treatment the greater the depth of the treatment. Adding compression can also enhance the effects of treatment. The adipose layer acts as an insulator.
Maximum analgesia has been demonstrated to occur at 58° Fahrenheit. Tissue damage may occur below 55° Fahrenheit. You also have to consider whether or not your patient will be sedentary after the ice.
If they are, then the effects can last for one to two hours. If they're active after the ice, it increases muscular warming; a little less than 15 minutes of exercise will rewarm the tissue. So this begs the question: should we wrap an ace bag on an athlete and send them to class? When this happens, we can't watch them to determine the effects of ice and the amount of exercise required to walk to the next class may negate the effects of cryotherapy at all. The next section of this lecture will include the examination of superficial therapeutic heat. Heat does the increase in molecular vibration and cellular metabolic rate. Heat is produced by four primary methods: the transfer of thermal energy, chemical action associated with cell metabolism, mechanical action such as found with therapeutic ultrasound, and electrical or magnetic currents such as those found in diathermy devices. Superficial heating agents heat a larger area of tissue, but they also have a limited depth of penetration a little less than 2 centimeters. To produce therapeutic effects, superficial heating agents must be capable of increasing the skin temperature to 104° Fahrenheit to 113° Fahrenheit or roughly 40-45° degrees Celsius.
The physiological effects of heat are opposite than those of cryotherapy. The cellular response of thermotherapy results in an increase cellular metabolism, increased demand for oxygen, and may result in an increase in the amount of secondary injury in the case of acute injuries. As far as the inflammatory process, thermotherapy will result in accelerated inflammation by increasing the inflammatory mediators and by increasing the cell permeability.
This also results in a facilitation of soft tissue repair. The effects of heat on the blood and fluid dynamics include immediate vasodilation, decreased blood viscosity, increase blood flow, increased edema with the capability of removing edema; this increase may result in a loosening of the edema. Nerve conduction is also affected by the use of heat in thermal therapy as well.
Heat helps increase nerve conduction rates, decrease mechanical pressure, and reduces ischaemia. There's a picture of ischaemia in the bottom of this slide. Ischaemia is a local in temporary deficiency of blood supply. Heat also helps activate large-diameter neurons via the gate control mechanism, and decreases pain sensations.
Muscle spasms and muscle function are also affected with the use of thermotherapy. Heat helps to alleviate spasms by decreasing the sensitivity of the secondary gamma afferents and increasing blood flow to the muscle. These effects resulting in an increased range of motion by elongation of the collagen-rich tissue; for example, muscle tendon and fascia. It could also possibly increase the strength of the muscle. The indications or why we would use a treatment for thermotherapy include subacute or chronic inflammation, subacute or chronic pain, subacute or chronic muscle spasm, decreased range of motion, joint contractures, which is pictured below on the left, and hematoma resolution.
The contraindications of why we wouldn't use a treatment for thermotherapy include: acute injury that's less than 72 hours old, compromised circulation, compromised sensation, advanced arthritis, fever and pregnancy (we want to avoid systemic heating), thrombophlebitis which is pictured below on the right, and DVT which is pictured below on the left, tumors, and infections. There is a table for the indications and contraindications listed within table 5-7 on page 127 in the Starkey text. The magnitude of heating effects is based on the temperature increase of the target tissue, mild heating is associated with 1° Celsius or 1.8° Fahrenheit, which is utilized for mild inflammation and accelerated metabolic rates. Moderate heating is associated with 2-3° Celsius or 3.6-5.4° Fahrenheit increases, which is utilized for decreasing muscle spasm, decreasing pain, reducing chronic inflammation, and increasing blood flow. Vigorous heating is associated with 3-4° Celsius, most commonly 4° Celsius or 5.4-9° Fahrenheit, which is utilized for tissue elongation, scar tissue reduction, and inhibition of the sympathetic activity. The information on this slide can be found on Page 128 within table 5-8 within the Starkey text. Too much of anything can result in an opposite reaction of what's intended. With cryotherapy by cooling the surface of the skin and underlying tissues, ice causes the narrowing of blood vessels, a process known as vasoconstriction.
This vasoconstriction can lead to a decrease in the amount of blood being delivered to the area, and subsequently lessen the amount of swelling. After a number of minutes, the blood vessels reopen or dilate allowing the blood to return to the area. This phase is followed by another period of vasoconstriction. This process of vasoconstriction followed by dilation is known as the hunting response. Although blood still flows into the area, the amount of swelling is significantly less than if ice is not applied.
This decreases swelling or edema, allows more movement in the muscle, and so lessons the functional loss associated with injury. The swelling associated with the inflammatory response also causes a pressure increase in the tissue, which leads the area to become more painful. This pain is intensified by certain chemicals that are released into the blood when the tissue is damaged, hence the vasoconstriction from applying ice to decrease pain. With thermotherapy, when maximum vasodilation has occurred in the intensity of the treatment stays constant or increases, the vessels begin to construct. This is known as rebound vasoconstriction; this occurs approximately 20 minutes after treatment. It causes vasoconstriction after prolonged vasodilation in a way to save the deeper tissues by sacrificing the more superficial tissues.
Modeling of the skin is a warning sign that tissue temperatures are rising to dangerously high levels. In this case, ghostly-white areas and beet-red splotches mark the patient's skin. When modeling occurs, the treatment should be discontinued immediately. As we have previously examined the uses of cryotherapy and thermotherapy, it is also important to discern when a clinician should transition from ice to heat during a treatment of a patient. Many of us automatically will start with ice or cryotherapy in our initial treatments, but many people wonder when it's appropriate to transition a patient to heat. There are some things that you should remember when trying to determine if heat is appropriate. Unfortunately, there isn't any predetermined time frame for the transition, and as some people say: ‘there isn't any cookbook medicine plan for treatment, you need to observe the patient’s signs and symptoms.’ As a clinician, you will need to determine where the patient is at in terms of the healing process.
You also need to think about the desirable physiological responses to determine if heat is appropriate. There's one important role to using thermotherapy: heat should never be applied immediately after an injury. The most important initial goal of the injury process is to limit secondary injury by decreasing cellular metabolism and the release of chemical mediators, and to decrease pain, thus heat is contraindicated for acute injuries. As the injury progresses, we may choose to start employing heat as a modality to help increase joint range of motion, blood flow and cellular metabolism. If motion is restricted due to pain, we will continue to use cryotherapy. For the care of subacute injuries, we may begin to use both heat and cold. The treatment effects of thermotherapy are an increase in tissue compliance, blood flow, and metabolism. Tissue elongation is also desirable to restore range of motion the patient has lost, and our goal as a clinician is to continue to decrease pain and spasm.
The typical protocol is to heat before and then ice after treatment. This is very common in physical therapy, occupational therapy, and athletic training. The following questions can also be helpful in guiding a young clinician to evaluate whether he is appropriate for their patient.
These questions are found on Page 132 in Table 5-10 in the Starkey text. If all the answers to these questions are ‘no’, then heat can safely be used. As the number of yes answers increases, so does the indication to use cold. Number One: does the body area feel warm to the touch? Number Two: is the injured area is still sensitive to light moderate touch? Number Three: does the amount of swelling continue to increase over time Number Four: does swelling increased during activity? Number Five: does pain limit the joints range of motion? Number Six: would you consider the acute inflammation process to still be active? Number Seven: does the patient continue to display improvement with the use of cold modalities? Just as a general review, if motion is limited by pain, then cold should be used.; if the motion is limited by stiffness, then heat should be used; when in doubt, use cold.
As a practical application, here's a scenario for you. You have a 19-year-old patient with an ankle sprain. The injury occurred approximately three days ago and looks something like this. The patient's injury is warm to the touch and he is still complaining of significant pain. You can see from this picture that the patient has a significant edema and ecchymosis; therefore, at this point of the treatment, we should stick to cold treatment since there still appears to be active inflammation. After four visits to the clinic, it has been nearly two weeks since the original injury. The edema has decreased, but there's still a little bit there. The injury is no longer warm to the touch; the patient is now complaining of stiffness and decreasing the range of motion during walking.
At this point in the treatment, we should use heat is the treatment. After six visits to the clinic, it's been nearly three weeks since the original injury. Your patient comes into the clinic and states that he played a pickup game of basketball last night and he tweaked it again. The ankle is warm to the touch and there is visible edema present in the joint. At this point in the treatment, we should research back to cold as a treatment due to the reinitiation of the inflammatory process. It is important to remember that we do not have to eliminate cold treatments at any point during the rehabilitation process; we can always go back to cryotherapy, and remember when in doubt, make sure to use cryotherapy.
Quiz #4 will be over Chapter 5. You will be allowed 10 minutes and it will be worth 10 points; it will be located on blackboard.
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