Why are tens pain machines generally not as effective as portable interferential pain machines?
Much of the difference boils down to the number of times per second the two different machines go off and on.
Tens machines are small devices that can be worn constantly by a pain patient to control the pain impulses being sent to the brain. The tens device goes off and on, emits small electrical charges, in the range of 1 - 150 times per second. The term for going "off and on" is called "frequency" or "rate" or "PPS". Those terms simply mean how many times per second the small tens units is going off and on. A standard 9 volt battery has enough energy to support that frequency for days before it loses its power. 1 - 150 PPS is not a very large drain on the energy source, the battery.
The individual pulses of electricity are intended to stimulate non pain nerves which then are allowed to be transmitted up the spinal cord to the brain. The theory being by stimulating non pain nerves then one "blocks" the pain message and if blocked then it never gets to the brain and therefore there is no pain. This is referred to as the "Melzack/Wall Gate Control Pain Theory". It is the prevailing theory of how a tens unit works.
The issue for a pain patient is, if the patient is not wearing the tens machine then there is no interference, and therefore, absence interference, one has the pain return or never stop. That is the drawback of tens therapy.
An interferential machine actually has a pulse frequency in the ranges of 8,000 to 10,000 times per second. That means the interferential machine goes off and on that many times per second. That frequency is substantially greater than a tens machine has. With a frequency in the higher 000's range it becomes necessary to have a reliable power source such as plugging in the interferential machine to a wall outlet. A 9 volt battery last approximately 1-3 minutes with such a high frequency.
Considering a typical clinical interferential session lasts approximately 12 - 20 minutes then it becomes unrealistic to do an interferential treatment with a machine that can only use batteries, not an AC adaptor plugged into the wall.
The benefit of interferential therapy is it changes the underlying chemistry of our body by stimulating body tissues deeper in the body itself. These more frequent pulses of electricity overcome the resistance of the skin and allow greater depth of penetration to change the chemistry and to stimulate nerves, including the pain nerves - C fibers. That physical and chemical change allows the brain to learn to chemically alter the pain area and by doing so the changes create "carryover pain relief". Carryover simply means that after the interferential treatment the chemistry has changed and the patient may go for hours, days, or a week or so without needing another interferential treatment.
The theory of how interferential provides carryover relief is called the "DeDomenico Descending Pain Theory", named after Dr. Giovanni DeDomenico. The alteration of transmission of non essential pain messages is controlled by the brain creating chemicals to retard the creation of pain chemically through descending messages from the brain to the area, or, by a descending pathway, thusly the "descending pain control theory". Tens operates on an "ascending", upward limitation of pain messages, and is not permanent, only temporary.
The combination of higher frequency and pulse polarities, alternating positive and negative charges, allow for true elimination of pain. It is the ability to use a portable interferential pain machine that allows one to teach the brain, prior to onset of pain, that the chronic pain message is not to occur.
The new advances in chronic pain control have occurred due to the newer technologies allowing a patient to self treat with a portable interferential machine, Infrex Plus and prevent pain. The theories of pain are not new, only the advancement of the electrical technologies now allow patients to treat and prevent pain.