Infrared Rays Law and Read

8/13/2019 Infrared Rays Law and Read

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Infrared Rays


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Infrared radiations gives rise to heating

when absorbed by matter.

Infrared radiations are longer than that of

visible red light extending to the microwave

region, i.e., from 760 nm to 1 mm.


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Subdivided :- A, B, C

- Distinguished by their absorption characteristics.- (A and B ) utilized therapeutically and correspondsroughly to an older classification of near and far

infrared

IRA - 760 nm to 1400 nm IRB - 1400 nm to 3000 nm

IRC - 3000 nm to 1 mm

Former Classification Near or Short IR 760 nm to 1500 nm

Far or Long IR 1500 nm to 15000 nm


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Infrared radiations are produced in all matterby various kinds of molecular vibration. Any hotbody emits infrared rays; the sun, gas fires, coal

fires, electric fires, hot water pipes, etc. Thus any

object emits infrared radiations and materialthat is at temperature above absolute zeroemits infrared. The frequencies at which themaximum intensity of radiation is emitted are

proportional to temperature. Thus the higherthe temperature the higher the frequency andhence the shorter the wavelength.


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At the higher temperatures generated by atungsten filament light bulb the peak emission isabout 960 nm, i.e., in the near infrared, withplenty of emission in the visible region. Thehuman body also emits a whole range of infrared

radiations, mainly type C, and with peak around10,000 nm. Absorption of all these radiationscauses similar kinds of molecular vibrations andthereby produces heating effect.

The shorter, visible radiations not only causemolecular and atomic motion but can also breakchemical bonds when they are absorbed.


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This provokes chemical changes in the retinal

pigments, which are detected via the optic

nerve as sight.


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Production of Infrared Radiations:

Any heated material will produce infraredradiations, the wavelength being determinedby the temperature.

If short infrared is to be produced efficientlythe material must not be oxidized (burnt) bythe higher temperatures used.

The most convenient method is to heat aresistance wire by passing an electric currentthrough it.


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Therapeutic Infrared Lamps:

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).

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 ,gives only infrared and no visible

radiations


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Some infrared lamps for therapy have the wire embedded inthe insulating ceramic so that no visible radiations are givenout.

The heater wire can also be mounted behind a metal plateor inside a metal tube, which does not become red-hot butemits infrared in the same way.

As such a lamp becomes hotter all the protective wire meshand the reflector become heated, giving off a range ofwavelengths from near to far infrared.

The infrared emitter is placed in front of a reflector to forma uniform beam.

Metal stand, which can be adjusted to alter the height andangle of the reflector/emitter.


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When such lamps are switched on they

require some time to reach a stable, peak

level of heat emission as the molecular

oscillation causing heating spreads slowly

through the body of the heater.


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Luminous Generators:

consist of a tungsten filament in a large glass envelope, which containsinert gas at low pressure.

Part of the inside of the glass bulb is often silvered to provide a reflector,the filament is heated to a high temperature (around 3000C) by thecurrent passed through it and so gives off a continuous spectrum in theinfrared 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 long

infrared ,visible rays to the ultraviolet which are absorbed by the glassand are not therefore transmitted by the lamp.

Sometimes the glass is reddened, to give a red visible emission; this isbelieved to make little difference therapeutically.

Luminous generators are sometimes called radiant heat generators,indicating that heating is by both infrared and visible radiations.


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Large lamps are fitted with wire-mesh screens

over the front of the reflector to prevent

accidental contact with the hot emitter. The

screen will also diminish any remote risk of

the hot emitter element falling out.


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Nonluminous:

Mainly 30004000 nm (long IR), with about

10% between 1500 nm and visible (short IR)

Luminous:

Approximately 70% short IR ,5% visible, 24%

long IR, 1% UVR absorbed by glass of bulb


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Absorption of IR

Some radiations striking the surface of the skin will be reflectedand some will penetrate, to be scattered, refracted, and ultimatelyabsorbed in the tissues.

The amount of reflection of visible radiation varies with skin colorbut, for therapeutic infrared, is negligible.

Close to 95% of the radiation applied perpendicular to the skin isabsorbed.

Small amounts of radiations in some circumstances may actually betransmitted, not only through the skin, but also through theunderlying tissues and even through a part of the body.

Skin (epidermis & dermis) is not, of course, a single homogeneoustissue but a complicated multilayered structure full of irregularforms, such as hair follicles and sweat glands.


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In general, water and proteins are strong absorbers ofinfrared.

Therefore, any radiation entering into skin is highlycomplex and depends on

1.Structure2.Vascularity

3.Pigmentation of the skin

4.Wavelength of the radiation

Therefore, it is difficult to determine pattern ofpenetration and absorption of infrared radiation inthe skin.


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Penetration:

The penetration depth is the depth at whichapproximately 63% of the radiation energyhas been absorbed and 37% remains.

It is neither the depth to which all radiationspenetrate nor the depth beyond which nonepenetrate.

Very long wavelength infrared (around40,000 nm) behaves like microwave andpenetrates several centimeters.


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However, the long infrared used therapeuticallyis absorbed at the surface, much of it by thewater on the skin surface.

Penetration of energy into a medium isdependent upon

-Intensity of the source of infrared

-Wavelength and consequent frequency

-Angle at which the radiation hits the surface

-Coefficient of absorption of the material


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Short wavelengths are scattered more than long wavelengths but that thedifferences are minimized as the thickness of the skin increases.

Penetration therefore depends both on the absorptive properties of theconstituents of the skin and on the degree of scattering brought about by theskin microstructure.

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 wavelengthin theshort infrared region, to maximum penetration depth of about 3 mm around the1000 nm wavelength region.

The very short infrared and red visible radiations have penetration depths ofabout 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 toincreased local circulation of heated blood.


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Physiological effects of Infrared

Radiations:

Cutaneous Vasodilatation:

As a consequence of heating with infrared radiationslocal cutaneous vasodilatation will occur.

This is due to the liberation of chemical vasodilators,

histamine and similar substances, as well as a possibledirect effect on the blood vessels by the axon reflexmechanism.

The vasodilatation starts after a short latent period of 12 minutes and appears to be largely due to arteriolarvasodilatation.

The erythema which develops due to vasodilatation isof irregular patchy appearance and is quite differentthan that caused by ultraviolet radiations


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The irregular margin of the erythema shows where somearterioles have dilated, engorging the capillaries theysupply while adjacent one are unaffected.

The rate at which the erythema develops and its intensityare related to the rate and degree of heating.

Reflex dilatation of other cutaneous vessels will also occurin order to maintain a normal body heat balance.

The local erythema lasts for about 30 minutes afterirradiation has stopped.

For normal individuals heating the skin to about coretemperature (37C) over some 20 minutes lead to very milderythema; heating to around 42C will lead to markederythema.


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Sweating:

With prolonged or intense heating, sweating will start to occur.

This will absorb some of the applied infrared irradiation and leads to surfacecooling as it evaporates.

This does not necessarily lead to inefficiency since cooling the surface may allowbetter penetration.

Sensation: Thermal heat receptors will be stimulated in the skin so that the patient is aware

of the heating.

Increase in Metabolism:

Due to increase in temperature there will be an increase in the rate ofmetabolism.

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 fromprolonged exposure of the legs to domestic fires.


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Therapeutic Uses of Infrared

Radiations:Relief of Pain:

When the heating is mild, the relief of pain is probably due to thesedative effect on the superficial sensory nerve endings. Strongerheating irritates the superficial sensory nerve endings, and sorelieves pain by counter-irritation.

It has been suggested that pain may be due to the accumulation inthe tissues of waste products of metabolism, and an increased flowof blood through the part removes these substances and sorelieves pain.

Mild heating relieves pain due to acute inflammation or recentinjury most effectively.

When pain is due to lesions of a more chronic type, strongerheating is required.

The irradiation should cause comfortable warmth and thetreatment last for at least thirty minutes.


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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.


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Increased Blood Supply:

This effect is most marked in the superficial tissues, and may be used in thetreatment of superficial wounds and infections.

Good blood supplies is essential for healing to take place, and if there is infectionthe increased number of white blood cells and the increased exudation of fluidare of assistance in destroying the bacteria.

Infrared treatment is frequently used for arthritic joints and other inflammatorylesions, and for the after-effects of injuries.

In these cases the relief of pain and muscle spasm is undoubtedly of value, but theeffect of irradiation on the flow of blood through the site of the lesion is uncertain.

When superficial structures are affected, e.g., small joints 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 tissuesaccelerate the removal of waste products and help to bring about the resolution ofinflammation.

On other hand, irradiation of the skin over deeply placed structures is more likelyto cause vasoconstriction in the deep tissues, but this may be of value in relievingcongestion.


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Pressure Sores:

Infrared has also been suggested for the

prophylaxis of pressure sores, to promote a

greater blood flow in the skin.


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Oedema:

Infrared is sometimes used for surface heating of a part inelevation 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 aspectat a time.

Combining infrared radiation from several aspects withconduction heating, placing the elevated hand in a hot-aircabinet 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.


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Prior to other Treatments:

Infrared is sometimes chosen as a form of heatprior to stretching, mobilization, traction,massage and exercise therapy.

It may also be used prior to electrical stimulation,testing or biofeedback to warm the skin, makingit more vascular and hence a better conductor.This is done before wetting the skin to lower its

electrical resistance further. A warm soak wouldseem preferable for circumstances in which it ispractical and possible.


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Joint stiffness:

Joint stiffness encompasses a number of

parameters such as the behavior of ligaments,

joint capsule and periarticular structures, and

alterations in fluid pressure.

Joint stiffness can also be treated by

application of infrared radiation to the joint

to some extent.


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Skin Lesions:

Some skin lesions may benefit from a drying heat.

Fungal infections, such asparonychia, and

psoriasis may be managed with infraredtreatment.

Infrared radiation has been used in the treatmentof psoriasis, on the grounds that moderate

hyperthermia can affect cell replication andtherefore could benefit a hyperproliferativedisease like psoriasis.


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Dangers of Infrared Radiations:

Burns:

defective sensation or reduced consciousness.

mentally retarded.

Occasionally patients accidentally touch the hotelement if there is no protective guard.

These dangers can be avoided by:

Careful application

Adequate warnings to the patient Checking the effects on the skin several times

during the application


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Skin Irritation:

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.


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Lowered Blood Pressure:

As infrared treatment causes markedcutaneous vasodilatation it may lead to

temporary lowering of blood pressure,particularly in elderly people who have lesseffective vasomotor control.

This may lead tofaintnessespecially onstanding up immediately after treatment. Itmay also cause headache.


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Areas of Defective Arterial Blood Flow:

Areas in which the arteries and arterioles cannotrespond by adequate vasodilatation to the

demands of additional heating should not betreated.

Such areas would be those affected by arterialdisease such as altherosclerosis, arterial injury or

after skin grafting. The possible result of heating such tissue would

be tissue necrosis (gangrene).


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Eye Damage:

Long-term irradiation can cause corneal and

retinal damage leading to cataract.

Protect eyes form irradiation.


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Contraindications of Infrared

Radiations: Impaired cutaneous thermal sensation

Defective arterial cutaneous circulation

Patients whose level of consciousness is markedly lowered bydrugs or disease

Acute skin disease, e.g., dermatitis or 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 andpossibly dangerous to patients whose heat regulation system isunder stress.

Tumours of the skin may be stimulated to increase growth Testes

Subjects with advanced cardiovascular disease

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Infrared Rays Law and Read

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