Superficial heat treatments are very commonly used for aches and pains by the public although rather less so by physiotherapists nowadays. These types of treatment do not heat deep into the body so cannot affect muscles directly as the subcutaneous fat layer below the skin functions as a heat insulator. Superficial heating also causes increased blood flow through the skin of the heated area, which carries off some of the heat being applied. The methods of heating are varied and are generally described as heat conduction, heat convection and heat conversion.
Conductive heating is accomplished by the transfer of heat from one object to another without any movement involved, with direct contact between the source of heat and the tissues to be heated. Hot packs, hot water baths, electric heat pads, paraffin or wax baths and hot compresses all fall into this category. Convective heating is less commonly used and works by movement of the heat medium which is a fluid or the air. Whirlpool baths and hot air devices come into this category. Conversion heating involves the conversion of one type of energy to another such as light energy from a heat lamp being converted into heat at the skin surface.
The body's tissues respond biologically to heat depending on various measures: the length of time the increased temperature is applied, how fast the temperature increase occurs, the applied area size and the overall time the heat is applied. Hydrocollator packs, a form of hot packs more used in the past, employ conductive heating but can be risky as it is possible to heat the tissues too greatly and cause burns. As they do not mould well to body parts such as the ankle or foot it is difficult to be sure of consistent heating. The local heating response can be greater than expected if the weight of the pack or of the limb on the pack diminishes the local blood supply.
after, for example, persistent ankle swelling after fracture or repeated ankle sprains. Hot and cold water baths are used with a differential of 25 degrees centigrade between them. The cycle bringing on the greatest changes in blood supply involves ten minutes in the hot bath followed by one in the cold bath, continuing with four minutes hot and one minute cold. This cycle can be repeated until thirty minutes have elapsed and be performed several times a day. This technique uses convective heating which is also employed in pool or hydrotherapy.
Hydrotherapy involves immersion of the body in a large pool of warm water and the heat and support from the water helps pain and weakness and allows increased joint ranges particularly in arthritic conditions. A temperature above 34 degrees centigrade is used and this heat can have side effects such as changes in blood pressure as the heat and water pressure affects the body.
The most common method of conversion heating is to employ infra-red radiation from a heat lamp by light particles, with their high energy levels, being converted into heat in the tissues. Infra-red lamps, with the red part of the light spectrum added to indicate when they are working as infra-red is invisible, are widespread domestic items used for self treatment. Arthritic joints, low back pain and muscle discomfort and spasms are typical treatment targets for this type of therapy.
The tissues do not undergo deep heating with this method and the superficial heating gives some sensory nerve sedation and heat input to the spinal cord processing areas. Physiotherapists are very careful with the distances between skin and heat source to prevent burns, as a quadrupling of heat intensity is achieved by merely halving the distance between the two.
Heat therapy should not be routinely applied and physiotherapists make careful clinical judgments as to whether superficial heating is indicated in the light of the effects being small, short lived and not deep. Skin sensibility should be normal for this method as a deficiency in this could risk a burn as the patient cannot tell when their skin is being overheated. Heating should be avoided in areas of infection and its use in inflammation should be clinically reasoned for appropriateness.
