Infrared Radiation

History•Late 19th century- Edison light lamps as a source of heat for medical purposes.

•1800 – William Herschel» Who discovered a type of visible radiation in the light

spectrum beyond red light, by means of its effect upon a thermometer.

•1891- radiant heat tunnel or baker» First medical luminous heat source

Infrared Radiation•Infrared radiations are a small segment of the electromagnetic spectrum adjacent to the long-wavelength, low-frequency(red)end of the visible spectrum .

• emitted from any substance with a temperature above absolute zero.

•Infrared produces heating by inducing molecular vibriation.

• IR has a frequency of 7x10 14 to 400x10 14 Hz• Wavelengths from 700 to 15000 nm

Short infrared rays 700nm to 4000 nm

Long infrared rays 4000nm to 15000nm

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Determinants• Distance and angle of delivery.• The inverse square law states that the

intensity of radiation varies inversely with the square of the distance of the source.

» this means that doubling the distance from a heat lamp reduces the heating intensity of four.

• typical distances are 30 to 60 cm from the patient's body depending on heat lamp wattage

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• Maximal radiation is applied when the source of radiation is perpendicular to the source.

• As the angle away from perpendicular increases, the intensity of the radiation decreases in proportion to the cosine of the angle.

Two types of generators

•Luminous generator•Non luminous generator

Non luminous generator provides infrared rays only while luminous generator emits visible and a few ultraviolet rays as luminous generator is often called radiant heat. The term infrared is generally being applied to the radiations from non luminous source.

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• Luminous infrared heat lamps emit radiation in the near-infrared spectrum.

– wavelength 770 to 1500 nm

• Non-Luminous infrared heat lamps emit radiation in the far-infrared spectrum.

– wavelength 1500 to 12,500 nm

• Heat lamps often use 175 or 250-watt bulbs and are usually placed about 40 to 50 cm from the patient.

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Absorption and penetration of IR

» Frequency or wavelength of the rays» Thermal conductivity of the tissues» Density of each tissue» Specific heat of each tissue» Angle of incidence of the rays» Distance from the source of infrared » Patency of the circulation» Source of the infrared

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• Indications– Pain and muscle spasm– Oedema– Healing of wounds and

chronic suppurative areas

• Contra-indications– Impaired sensation– Dermatological conditions– Eyes– Analgesic and narcotic drugs– Skin tumors– Acute infection

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Technique for Infrared Therapy

• Equipment required» luminous or non-luminous infrared

generator» test tubes» pillows» sheets» towels

• Position the patient with pillows and towel under the area to be treated. Make sure that the limb, trunk and head is supported in a pain-free position with the area to be treated adequately exposed.

• Remove all metal objects• Ensure that there is ample room around the patient to

position the lamp.

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• Inform the patient regarding:– the choice of modality– rationale for treatment– sensation to be experienced– frequency and duration of treatment

• Check for any contra-indications to heat.• Check the patency of the circulation in the underlying areas.• NEVER position the lamp directly over the patient.• Make sure that the lamp is steady and not likely to fall.• The patient must not MOVE,TOUCH the lamp or LOOK at the

generator.• Advice the patient not to sleep or read during the treatment.• Give patient an adequate method of calling your atention.• Switch on the lamp and stay with the patient.

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• as the lamp warms up, put your hand between the lamp and the patient to check that it is producing heat.

• Ask thepatient to tell you when heat is felt and to describe the intensity.

• At the end of the treatment time, switch the lamp off and remove it before assessing the are for any excessive erythema and for relief of symptoms.

• Advantages: – Infrared can be used to treat large areas– patients may be taught to apply infrared for home use.

• Disadvantage:– Heating is only very superficial– Equipment is often rather unstable

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References

• DeLisa's Physical Medicine & Rehabilitation• Physical Medicine & Rehabilitation• Electrophysical Agents in Physiotherapy• http://www.newexamtable.com/

luminousheatlamps.aspx• http://electrotherapyforphysio.blogspot.com/

2012/11/infrared-radiations.html