In contrast to deep heating modalities, superficial heating modalities usually do not heat deep tissues, including muscles, because the subcutaneous layer of fat beneath the skin surface acts as a thermal insulator and inhibits heat transfer. Additionally, increased cutaneous blood flow from superficial heating causes a cooling reaction as it removes the heat that is applied externally. In general, the transfer of heat (whether the purpose is heating or cooling) often is classified into 3 general types of heat transfer: conduction, convection, and conversion.[1, 2] They are characterized as follows:
conductive heating - This is defined as heat transfer from one point to another without noticeable movement in the conducting medium.Typically, direct contact takes place between the heat source and the target tissues. Superficial heat is usually conductive heat (eg, hot water baths, hot packs, electric heating pads, warm compresses).
convective heating - This form of heating is produced by themovement of the transferring heating medium, usually air or a fluid. Methods for providing convective superficial heat include Fluidotherapy, whirlpool, moist air baths, and hot air baths.
conversion heating - This involves the conversion of one energy form (eg, light, sound) into another (heat). Superficial heat is produced by heat lamps or radiant light bakers, with heat being transferred when the conveying medium (light energy) is converted to heat energy at the skin surface.
Superficial heat modalities categorized by primary heat transfer mode are summarized as follows:
Several factors determine the extent of the physiologic response to heat, including the following:
level of the tissue temperature (usually 40-45ºC)
Duration of the tissue temperature increase
Rate of increase in the tissue temperature
Size of the area being treated
Cryotherapy has the primary effect of cooling tissue. Depending upon the application method and duration of this therapy, the basic physiologic effects include the following :
Decreased local metabolism
Reduced muscle efficiency
Analgesia secondary to impaired neuromuscular transmission
Pain reduction associated with the application of cold relaxes muscle spasm and minimizes upper motor neuron spasticity.
Conductive heatingIndications for the application of hot packs may include painful muscle spasms, abdominal muscle cramping,menstrual cramps, and superficial thrombophlebitis.
Fluidotherapy: Uses of fluidotherapy may include pain relief in arthritic conditions of small joints, joint mobilization following trauma/mobility, and analgesia/sedation in young patients undergoing exercise programs with painful and contracted joints due to sickle cell anemia.
Hydrotherapy: Uses of hydrotherapy may include the treatment of infected draining wounds; contrast baths can be used as therapeutic hyperemia for management of rheumatoid arthritis or sympathetically mediated pain.
Moist air: This modality is used to treat back muscle spasms and polyarticular arthritic conditions.
The most common indications for radiant heat therapy include muscle spasms from underlying joint/skeletal conditions, rheumatic joints in which direct heating of the joint is contraindicated, and the treatment of superficial skin breakdown in the intertriginous areas.
The most common indications and uses for the local application of therapeutic cold modalities include the following: