Infrared Radiation 6u5n5h

Infrared Radiations Infrared radiations lie within that part of the electromagnetic spectrum which gives rise to heating when absorbed by matter. Infrared radiations are those, whose wavelengths are longer than that of visible red light extending to the microwave region, i.e., from 760 nm to 1 mm. These infrared radiations can be subdivided into three regions or bands, A, B, and C, approximately distinguished by their absorption characteristics. A and B are utilized therapeutically and corresponds roughly to an older classification of ‘near’ and ‘far’ infrared. Type IRA IRB IRC

Wavelength 760 nm to 1400 nm 1400 nm to 3000 nm 3000 nm to 1 mm (not used in therapy) Former Classification Near or Short IR 760 nm to 1500 nm Far or Long IR 1500 nm to 15000 nm Infrared radiations are produced in all matter by various kinds of molecular vibration. Any hot body emits infrared rays; the sun, gas fires, coal fires, electric fires, hot water pipes, etc. Thus any object emits infrared radiations and material that is at temperature above absolute zero emits infrared. The frequencies at which the maximum intensity of radiation is emitted are proportional to temperature. Thus the higher the temperature the higher the frequency and hence the shorter the wavelength. At the higher temperatures generated by a tungsten filament light bulb the peak emission is about 960 nm, i.e., in the near infrared, with plenty of emission in the visible region. The human body also emits a whole range of infrared radiations, mainly type C, and with peak around 10,000 nm. Absorption of all these radiations causes similar kinds of molecular vibrations and thereby produces heating effect. The shorter, visible radiations not only cause molecular and atomic motion but can also break chemical bonds when they are absorbed. This provokes chemical changes in the retinal pigments, which are detected via the optic nerve as sight.

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Ö Production of Infrared Radiations: Any heated material will produce infrared radiations, the wavelength being determined by the temperature. If short infrared is to be produced efficiently the material must not be oxidized (burnt) by the higher temperatures used. The most convenient method is to heat a resistance wire by ing an electric current through it. D Therapeutic Infrared Lamps: Various kinds of infrared lamps are used for therapy. Infrared sources can be either natural (sun) or artificial (luminous or non-luminous lamps). 1) Non – Luminous Generators: One type is made in a similar way to an electric fire (it is made up of a coil of suitable resistance wire, such as nickel-chrome alloy, wound on a ceramic insulator). In these heaters the wire glows red thus giving some radiations in the visible region but peak emission in the short infrared. The ceramic material, being heated to a lower temperature than the wire, gives only infrared and no visible radiations. Some infrared lamps for therapy have the wire embedded in the insulating ceramic (or porcelain or fireclay) so that no visible radiations are given out. The heater wire can also be mounted behind a metal plate or inside a metal tube, which does not become red-hot but emits infrared in the same way. As such a lamp becomes hotter all the protective wire mesh and the reflector – become heated, giving off a range of wavelengths from near to far infrared. The infrared emitter is placed at the focus of a hemispherical or parabolic reflector to reflect the radiations into an approximately uniform beam. However, the beam does diverge somewhat due to the relatively large size of the emitter compared to the reflector, and this serves to reduce the risk of ‘hot spots’. The reflector and emitter are mounted on a strong, firmly ed metal stand, which can be adjusted to alter the height and angle of the reflector/emitter. When such lamps are switched on they require some time to warm up because of the thermal inertia of the considerable mass of the metal and insulating material that has to be heated. Non – luminous lamps take longer than luminous lamps to reach a stable, peak level of heat emission as the molecular oscillation causing heating spreads through the body of the heater. 2

D Luminous Generators: Luminous generators (incandescent lamps) consist of a tungsten filament in a large glass envelope, which contains inert gas at low pressure. Part of the inside of the glass bulb is often silvered to provide a reflector. These lamps work on the same principle as a simple electric light bulb; the filament is heated to a high temperature (around 3000°C) by the current ed through it and so gives off a continuous spectrum in the infrared and visible regions. Oxidation of the filament does not occur because there is no oxygen present, only a trace of some inert gas. The peak emission occurs at near 1000 nm but radiation extends from the long infrared throughout the visible to the ultraviolet. These later radiations are absorbed by the glass and are not therefore transmitted by the lamp. Sometimes the glass is reddened, absorbing some of the green and blue rays to give a red visible emission; this is believed to make little difference therapeutically. Luminous generators are sometimes called ‘radiant heat’ generators, indicating that heating is by both infrared and visible radiations. D Power: The power of infrared sources can broadly be described as: y Smaller lamps (luminous & non – luminous), usually 250 – 500 W y Large, non – luminous, 750 – 1000 W y Large, luminous, 600 – 1500 W Generally, the larger lamps are used to treat extensive areas but the same effect can be achieved by mounting three smaller luminous bulbs, which can be separately controlled in one holder. In this way a large area can be covered with all the bulbs in use and a small area using only one or two. Large lamps are fitted with wire-mesh screens over the front of the reflector to prevent accidental with the hot emitter. The screen will also diminish any remote risk of the hot emitter element falling out. D Emission: Non – luminous: y Mainly 3000 – 4000 nm (long IR), with about 10% between 1500 nm and visible (short IR) Luminous: y Approximately 70% short IR 5% visible 24% long IR 1% UVR absorbed by glass of bulb 3

Ö Absorption & Penetration of Infrared & Visible Radiations: Some radiations striking the surface of the skin will be reflected and some will penetrate, to be scattered, refracted, and ultimately absorbed in the tissues. The amount of reflection of visible radiation varies with skin colour but, for therapeutic infrared, is negligible. Close to 95% of the radiation applied perpendicular to the skin is absorbed. Small amounts of radiations in some circumstances may actually be transmitted, not only through the skin, but also through the underlying tissues and even through a part of the body. Skin (epidermis & dermis) is not, of course, a single homogeneous tissue but a complicated multilayered structure full of irregular forms, such as hair follicles and sweat glands. In general, water and proteins are strong absorbers of infrared. Therefore, any radiation entering into skin is highly complex and depends on y Structure y Vascularity y Pigmentation of the skin y Wavelength of the radiation Therefore, it is difficult to determine pattern of penetration and absorption of infrared radiation in the skin. D Penetration: The penetration depth is the depth at which approximately 63% of the radiation energy has been absorbed and 37% remains. It is neither the depth to which all radiations penetrate nor the depth beyond which none penetrate. Very long wavelength infrared (around 40,000 nm) behaves like microwave and penetrates several centimeters. However, the long infrared used therapeutically is absorbed at the surface, much of it by the water on the skin surface. Penetration of energy into a medium is dependent upon y Intensity of the source of infrared y Wavelength and consequent frequency y Angle at which the radiation hits the surface y Coefficient of absorption of the material Short wavelengths are scattered more than long wavelengths but that the differences are minimized as the thickness of the skin increases. Penetration therefore depends both on the absorptive properties of the constituents of the skin and on the degree of scattering brought about by the skin microstructure. 4

Because the energy penetration decreases exponentially with depth, most heating due to infrared will occur superficially. At around 3000 nm, penetrating depth is about 0.1 mm. From here there is increasing penetration with decreasing wavelength in the short infrared region, to maximum penetration depth of about 3 mm around the 1000 nm wavelength region. The very short infrared and red visible radiations have penetration depths of about 1 to 2 mm, while those of the rest of the visible spectrum penetrate much less. So, effect is marked heating of the skin. Some of this heat will be conducted more deeply into the subcutaneous tissues, both due to simple conduction and to increased local circulation of heated blood.

Ö Physiological effects of Infrared Radiations: D Cutaneous Vasodilatation: As a consequence of heating with infrared radiations local cutaneous vasodilatation will occur. This is due to the liberation of chemical vasodilators, histamine and similar substances, as well as a possible direct effect on the blood vessels by the axon reflex mechanism. The vasodilatation starts after a short latent period of 1–2 minutes and appears to be largely due to arteriolar vasodilatation. The erythema which develops due to vasodilatation is of irregular patchy appearance and is quite different than that caused by ultraviolet radiations. The irregular margin of the erythema shows where some arterioles have dilated, engorging the capillaries they supply while adjacent one are unaffected. The rate at which the erythema develops and its intensity are related to the rate and degree of heating. Reflex dilatation of other cutaneous vessels will also occur in order to maintain a normal body heat balance. The local erythema lasts for about 30 minutes after irradiation has stopped. For normal individuals heating the skin to about core temperature (37°C) over some 20 minutes lead to very mild erythema; heating to around 42°C will lead to marked erythema. D Sweating: With prolonged or intense heating, sweating will start to occur. This will absorb some of the applied infrared irradiation and leads to surface cooling as it evaporates. 5

This does not necessarily lead to inefficiency since cooling the surface may allow better penetration. D Sensation: Thermal heat receptors will be stimulated in the skin so that the patient is aware of the heating. D Increase in Metabolism: Due to increase in temperature there will be an increase in the rate of metabolism. D Chronic Changes: Excessive and prolonged infrared application can cause the destruction of erythrocytes, releasing pigments and causing brown discoloration of the skin. This rarely occurs as a sequel to normal treatment; it usually results from prolonged exposure of the legs to domestic fires.

Ö Therapeutic Uses of Infrared Radiations: D Relief of Pain: Infrared radiation is frequently an effective means of relieving pain. When the heating is mild, the relief of pain is probably due to the sedative effect on the superficial sensory nerve endings. Stronger heating irritates the superficial sensory nerve endings, and so relieves pain by counter-irritation. It has been suggested that pain may be due to the accumulation in the tissues of waste products of metabolism, and an increased flow of blood through the part removes these substances and so relieves pain. Mild heating relieves pain due to acute inflammation or recent injury most effectively. When pain is due to lesions of a more chronic type, stronger heating is required. The irradiation should cause comfortable warmth and the treatment last for at least thirty minutes. D Muscle Relaxation: Muscles relax most readily when the tissues are warm, and the relief of pain also facilitates relaxation. Infrared radiation is thus of value in helping to achieve muscular relaxation and for the relief of muscle spasm associated with injury or inflammation. After irradiation movements can frequently be made through a greater range than before, and the relief of pain makes it possible to perform exercises more efficiently. 6

D Increased Blood Supply: This effect is most marked in the superficial tissues, and may be used in the treatment of superficial wounds and infections. Good blood supplies is essential for healing to take place, and if there is infection the increased number of white blood cells and the increased exudation of fluid are of assistance in destroying the bacteria. Infrared treatment is frequently used for arthritic ts and other inflammatory lesions, and for the after-effects of injuries. In these cases the relief of pain and muscle spasm is undoubtedly of value, but the effect of irradiation on the flow of blood through the site of the lesion is uncertain. When superficial structures are affected, e.g., small ts of the hands and feet, there may be some heating and consequent vasodilatation. This will increase the supply of oxygen and foodstuffs available to the tissues accelerate the removal of waste products and help to bring about the resolution of inflammation. On other hand, irradiation of the skin over deeply placed structures is more likely to cause vasoconstriction in the deep tissues, but this may be of value in relieving congestion. D Pressure Sores: Infrared has also been suggested for the prophylaxis of pressure sores, to promote a greater blood flow in the skin. D Oedema: Infrared is sometimes used for surface heating of a part in elevation in order to hasten reabsorption of oedema. This effect is limited because infrared heats the superficial tissues and because it is usually only applied to one aspect at a time. Combining infrared radiation from several aspects with conduction heating, placing the elevated hand in a hot-air cabinet for example, is likely to be a more effective treatment. Heating the whole hand exploits the large surface area to volume ratio of the hand. D Prior to other Treatments: Infrared is sometimes chosen as a form of heat prior to stretching, mobilization, traction, massage and exercise therapy. It may also be used prior to electrical stimulation, testing or bio to warm the skin, making it more vascular and hence a better conductor. This is done before wetting the skin to lower its electrical resistance further. A warm soak would seem preferable for circumstances in which it is practical and possible. 7

D t stiffness: t stiffness encomes a number of parameters such as the behavior of ligaments, t capsule and periarticular structures, and alterations in fluid pressure. t stiffness can also be treated by application of infrared radiation to the t to some extent. D Skin Lesions: Some skin lesions may benefit from a drying heat. Fungal infections, such as paronychia, and psoriasis may be managed with infrared treatment. Infrared radiation has been used in the treatment of psoriasis, on the grounds that moderate hyperthermia can affect cell replication and therefore could benefit a hyperproliferative disease like psoriasis. [Paronychia: An infection of the nail fold especially of the lateral, and it becomes red, swollen, tender and very painful is known as paronychia. It involves a single nail at a time. Psoriasis: A chronic disorder characterized by well-defined, scaly, erthematous plaques in the extensor surfaces of the extremities like elbows ands knees, trunk, back and scalp is known as psoriasis. It is an autoimmune disease.]

Ö Dangers of Infrared Radiations: D Burns: The most obvious danger is of a heat burn, which occurs if the patient is unaware of the heat by reason of defective sensation or reduced consciousness. Rarely, a mentally abnormal or perhaps masochistic patient may stoically tolerate painful and damaging levels of heat. Occasionally patients accidentally touch the hot element if there is no protective guard. These dangers can be avoided by: y Careful application y Adequate warnings to the patient y Checking the effects on the skin several times during the application Metal on the surface could cause a burn in the underlying skin. This will only be a danger if the metal itself becomes heated to the point at which with it is injurious. Metal will reflect radiations and for that reason could lead to irregular application of infrared, so is often removed from the irradiated area.

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D Skin Irritation: Most acute inflammatory skin conditions are made worse by heating. Some chemical irritants on the skin have their effects increased by heating, sometimes to the point of irritation or inflammation. For this reason liniments, which cause mild erythema, should be removed prior to treatment. D Lowered Blood Pressure: As infrared treatment causes marked cutaneous vasodilatation it may lead to temporary lowering of blood pressure, particularly in elderly people who have less effective vasomotor control. This may lead to faintness especially on standing up immediately after treatment. It may also cause headache. D Areas of Defective Arterial Blood Flow: Areas in which the arteries and arterioles cannot respond by adequate vasodilatation to the demands of additional heating should not be treated. Such areas would be those affected by arterial disease such as altherosclerosis, arterial injury or after skin grafting. The possible result of heating such tissue would be tissue necrosis (gangrene). D Eye Damage: Prolonged and extensive exposure to infrared, such as occurs in furnacemen, has been associated with eye damage. Long-term irradiation can cause corneal burns from far infrared, and retinal and lenticular damage from near infrared. This is not a significant danger for the usual lengths of treatment time. However, infrared applied to the eyes causes surface drying, hence irritation, and should be avoided. D Dehydration: Prolonged and intensive treatment to large body areas could cause sweating, sufficient to provoke dehydration if the water is not replaced. Local dehydration of open wounds is also thought to be deleterious.

Ö Contraindications of Infrared Radiations: Impaired cutaneous thermal sensation Defective arterial cutaneous circulation Patients whose level of consciousness is markedly lowered by drugs or disease Acute skin disease, e.g., dermatitis or eczema [Dermatitis: Inflammation of the skin characterized by itching, redness and various skin lesions is known as dermatitis. 9

Eczema: A superficial inflammation affecting the epidermis, which manifests in redness, itching, weeping, oozing and crusting is known as eczema.] Skin damage due to deep X-ray therapy or other ionizing radiation Defective blood pressure regulation Acute febrile illness – additional heating is not helpful and possibly dangerous to patients whose heat regulation system is under stress. Tumours of the skin may be stimulated to increase growth Testes Subjects with advanced cardiovascular disease

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