The following is summarized from Therapeutic Heat and Cold, 4th Edition, ED. Justus F. Lehmann, M.D., Williams and Wilkins, Chapter 9 or concluded from the data therein.
Generally it is accepted that heat produces the following desirable therapeutic effects: |
| 1. It increases the extensibility of collagen tissues |
- Tissues heated to 45 C and then stretched exhibit a non-elastic residual elongation of about 0.5 – 0.9% that persists after the stretch is removed which does not occur in these same tissues when stretched at normal tissue temperatures. Thus 20 stretching sessions can produce a 10 – 18% increase in length in tissues heated and stretched.
- This effect would be especially valuable in working with ligaments, joint capsules, tendons, fasciae, and synovium that have become scarred, thickened or contracted.
- Such stretching at 45 C caused much less weakening in stretched tissues for a given elongation than a similar elongation produces at normal tissue temperatures.
- The experiments cited clearly showed that low-force stretching can produce significant residual elongation when heat is applied together with stretching or range-of-motion exercises, which is also safer than stretching tissues at normal tissue temperatures.
- This safer stretching effect is crucial in properly training competitive athletes so as to minimize their "down" time from injuries.
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| 2. It decreases joint stiffness directly |
- There was a 20% decrease in stiffness at 45 C as compared with 33 C in rheumatoid finger joints, which correlated perfectly to both subjective and objective observation of stiffness.
- Any stiffened joint and thickened connective tissues should respond in a similar fashion.
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| 3. It 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 afferents from spindle cells and from its effects on Golgi tendon organs. The effects produced by each of these mechanisms demonstrated their peak effect within the therapeutic temperature range obtainable with radiant heat.
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| 4. It produces pain relief |
- Pain may be relieved via the reduction of attendant or secondary muscle spasms.
- Pain is also at times related to ischemia due to tension or spasm which can be improved by the hyperemia that heat-induced vasodilation produces, thus breaking the feedback loop, in which the 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 both 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.
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| 5. It increases blood flow |
- Heating of one area of the body produces reflex-modulated vasodilations in distant-body area, even in the absence of a change in core body temperature; ie. heat one extremity and the contralateral extremity also dilates: heat a forearm and both lower extremities dilate; heat the front of the trunk and the hand dilates.
- Heating of muscles produces an increased blood flow level similar to that seen during exercise.
- Temperature elevation produces an increase in blood flow and dilation directly in capillaries, arterioles and venuies, probably through direct action on the smooth muscles. The release of bradykinin, released as a consequence of sweat-gland activity, also produces increased blood flow and vasodilation.
- Whole-body hyperthermia, with a consequent core temperature elevation, further induces vasodilation via a hypothalamic-induced decrease in sympathetic tone on the arteriovenous anastomoses. Vasodilation is also produced by axonal reflexes and by flexes that change vasomotor balance.
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| 6. It assists in resolution of inflammatory infiltrates, edema and exudates |
- The increased peripheral circulation provides the transport needed to help evacuate edema which can help end inflammation, decrease pain and help speed healing.
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| 7. More recently, it has been used in cancer therapy |
- This is a new and experimental procedure.
- It shows great promise in some cases when used properly.
- American researchers favor careful monitoring of the tumor temperature; whereas, the successes reported in Japan make no mention of such precaution.
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Infrared healing is now becoming the leading edge in the care of soft tissue injuries to promote both relief in chronic and intractable "permanent" cases, and accelerated healing in newer injuries.
Localized infrared therapy using lamps tuned to the 2 – 25 micron waveband is used for the treatment and relief of pain by over 40 reputable Chinese Medical Institutes.
Researchers reported over 90% success in a summary of Chinese studies that assessed the effect of infrared therapy on:
Soft tissue injury
Lumbar strain
Periarthritis of the shoulder
Sciatica
Pain during menstruation
Neurodermatitis
Eczema with infection
Post-surgical infections |
Facial Paralysis (Bells’ Palsey)
Diarrhea
Cholecystitis
Neurasthenia
Pelvic infection
Pediatric pneumonia
Tineas
Frostbite with inflammation |
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