Superficial Heat Treatments
Minor ailments and aches and pains are often treated with superficial heat although this modality is much less commonly used by physiotherapists than it used to be. The heating effect is shallow as the fat layer under the skin acts as an insulator against the heat, preventing transfer of energy to deeper tissues. The heat causes an increase in blood flow to the skin which moves heat away from the area treated and reduces the effect further. Techniques of heating are varied and fall into three main groups: heat convection, heat conversion and heat conduction.
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.
Refractory ankle swelling after fractures or repeated sprains of the ankle and joint inflammatory problems can be treated by contrast bathing where a 25 degree centigrade difference is established between a cold and a hot bath. Moving from one to the other causes great changes in the circulation and typically initial treatment is ten minutes in the hotter container then one in the colder one, then changing to four minutes in the hotter with one following in the colder. Repeated cycles can be performed for up to thirty minutes a few times a day. Pool therapy or hydrotherapy uses this therapeutic technique also, by convective heating.
Hydrotherapy pools involve an expanse of warm water at around 34 degrees centigrade or higher and are used predominantly for rheumatological conditions as the water gives support and the heat is soothing to painful joints. Reductions in pain and increases in joint range of motion are possible with this therapy as long as the side effects on blood pressure and other systems are considered
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.
This technique does not heat the tissues deeply but can soothe the local area due to warmth sedating the local sensory nerves and by allowing heat input to affect central processing. The distance of the light source to the skin is critical to avoid the risk of burns, as halving the distance will increase the intensity of the radiation by four times
Physiotherapists assess their patients for the application of heat therapy and clinically decide whether superficial heating is justified in their treatment plan as the overall effects may be minor and short-lived. One of the contraindications is a lack of normal skin sensibility as this will compromise the patient's ability to tell if they are getting too hot. Infection should not be heated and inflammation should be heated only after careful clinical reasoning.