The term "pain relief machine" is a very confusing phrase and it's understandable how people can not differentiate a "muscle stimulator" from a "tens unit" to an "interferential unit" or "pulsed galvanic stimulator" or a "micro amperage stimulator".

  
    Four of the 5 listed units are actually intended to be used for the treatment of chronic and acute pain.

   On the internet the following terms are searched on and the patient often gets some reference to a "pain machine" as a solution and then the confusion really begins.

* neck traction
* sciatic nerve pain
* sciatic nerve pain relief
* back pain relief machine
* pain relief machine
* sciatic nerve treatment
* painreliefmachine.com
* sore neck stretches
* stretches for sore neck

  Of the 5 machines listed the only one that is not intended for pain relief is a "muscle stimulator" which should be correctly called a "functional electrical stimulator" - FES.  The purpose of a muscle stimulator is to help a patient restore function or prevent atrophy to muscles. All of the listed "pain machines" can literally be adjusted to the point that a muscle contraction can be elicited but that is not the purpose of a "pain machine".

  There are basically three methods of controlling pain that each of the pain machines relies upon.

1. Melzack/Wall Gate Control Theory:
 
  This is simply the process of stopping the transmission of the pain impulse to the spinal cord for transmission to the brain where the pain is perceived.  The method of operation is to stimulate non-pain fibers so the actual pain message is not transmitted and the pain impulse is not transmitted. When that happens the brain does not receive the message therefore there is no pain. In reality though for the chronic pain patient the actual results are less transmissions rather than 100% total cessation meaning pain reduction, not total pain elimination.

2. Sjolund Opioid Peptide Production ( Pain Killers)

  In this application, which rarely ever works, the actual pain fibers, c fibers, are stimulated for 20 - 30 minutes and that stimulation by the pain machine results in the brain increasing the production of pain killers, aka endorphins and enkaphlins are the general terms used. As long as there is an increased amount of the peptides in the blood stream then the pain is not felt. As the peptides wear off and decrease in total volume then the pain reappears. This is not theory but has been proved however as stated earlier this application rarely is effective for the vast preponderance of chronic pain patients.

3. Glial Dysregulation of Pain and Opioid Actions

  This is very recent, appearing in research being done by Linda Watkins, PhD. - Univ. of Colorado - Boulder. Her work involves the blocking of pathological pain by inhibiting glial activation in the spinal column where the glial cells exist. The glial cells actually release many neuroexcitatory substances which can lead to pain amplification.

  The latter explanation helps to clarify what is now occurring with the use of interferential pain machines, unlike the other tens, micro, PGS machines where there is no carryover or residual pain relief once the pain machine is turned off.  With interferential therapy using the Infrex Plus there is residual or carryover pain relief during and following the treatment for hours or in some situations days/weeks. Glial cell inhibition may explain the effects of portable interferential units as well as replicate the clinical interferential treatments.