Tissue Temperature Increase from Infrared:
- It is directly proportional to amount of radiation that penetrates the tissue which relates to power and wavelength of radiation, distance from target tissue to source, the angle of incidence, and absorption coefficient of tissue
- A lamp with power of 50-1500 Watts and wavelength of 780-1500nm, radiation is absorbed by 1-3mm of human tissue.
- Darker tissues will absorb more radiant heat
Distance from the target tissue is extremely important due to the inverse square law.
Which states: the power of the light will be inversely proportional to the square of the distance. So if we take a distance of 2 and square it, we get 4, the inverse of which would be 1/4th or rather a quarter of the original power...not half.
- For example if the lamp is moved from a position of 5cm away from the target tissue, to a position of 10 cm away (2 times away) the intensity of radiation declines to 1/4th of its previous level. Similarly, if you were to move the lamp to a position of 2.5 cm away from target it would be 4 times as intense compared to the original 5cm position.
Amount of Energy reaching Patient:
Maximal energy is absorbed by a surface if the energy strikes at a right angle, this is the cosine law. IR absorption coefficients are affected by skin color.
Control of Heating:
Patient's sensory report is used to gauge skin temperature. Patient should feel a comfortable warmth, if motling occurs, it is too hot. If no hyperemia, it is too cool.
Effects on Tissues:
- Same as superficial heat
- increase metabolism
- sedation, relaxation
- indirect heating
- decreased pain
- decreased muscle spasm
Types of Conditions:
- Chronic inflammatory conditions: Strains, sprains, and bursitis
- Back pain
- Some skin conditions requiring dry heat
When NOT to use:
- Allergy to light or heat
- Scars and other poorly vascularized skin
- Reduced sensation
- Ischemic areas from severe peripheral vascular disease.