Other Therapeutic Effects of Infrared Therapy
The following information has been summarized from Chapter 9 of Therapeutic Heat and Cold, Fourth Edition, Editors Justus F. Lehmann, MD, Williams, and Wilkin, or concluded from data gathered there.Generally it is accepted that heat produces the following desirable therapeutic effects:
1. Infrared heat increases the extensibility of collagen tissues. Tissues heated to 45 degrees Celsius and then stretched exhibit a nonelastic residual elongation of about 0.5 to 0.9 percent that persists after the stretch is removed. This does not occur in these same tissues when stretched at normal tissue temperature.
Stretching of tissue in the presence of heat would be especially valuable in working with ligaments, joint capsules, tendons, fasciae, and synoviurn that have become scarred, thickened, or contracted. Experiments cited clearly showed low-force stretching could produce significant residual elongation when heat is applied together with stretching or range of motion exercises.
2. Infrared heat decreases joint stiffness. There was a 20% decrease in rheumatoid finger joint stiffness at 45 degrees Celsius (112°F) as compared with 33 degrees Celsius (92°F) which correlated perfectly to both subjective and objective observation of stiffness. Speculation has it that any stiffened joint and thickened connective tissues may respond in a similar fashion.
3. Infrared heat relieves muscle spasms. Muscle spasms have long been observed to be reduced through the use of heat, be they secondary to underlying skeletal, joint, or neuropathological conditions. This result is possibly produced by the combined effect of heat on both primary and secondary afferent nerves from spindle cells and from its effect on Golgi tendon organs.
4. Infrared heat treatment leads to pain relief. Pain may be relieved via the reduction of attendant or secondary spasms. Pain is also at times related to ischemia due to tension or spasm that can be improved by hyperthermia that heat-induced vasodialation produces, thus breaking the feedback loop in which ischemia leads to further spasm and then more pain. Heat has been shown to reduce pain sensation by direct action on both free-nerve endings in tissues and on peripheral nerves. In one dental study, repeated heat applications led finally to abolishment of the whole nerve response responsible for pain arising from dental pulp. Heat may lead to increased endorphin production and a shutting down of the so-called "spinal gate" of Melzack and Wall, each of which can reduce pain.
Localized infrared therapy using lamps tuned to the 2 to 25 micron wave band is used for the treatment and relief of pain by over 40 reputable Chinese medical institutes.
5. Infrared heat increases blood flow. Heating one area of the body produces reflex-modulated vasodilators in distant-body areas, even in the absence of a change in core temperature. Heat one extremity and the contralateral extremity also dilates; heat a forearm and both lower extremities dilate.
Heating muscles produces an increased blood flow level similar to that seen during exercise. Temperature elevation also produces increased blood flow and dilation directly in capillaries, arterioles, and venules, probably through direct action on their smooth muscles. The release of bradykinin, released as a conseqence of sweat gland activity, also produces increased blood flow and vasodilation.