We receive many inquiries regarding what the modes on the best TENS units do. The BioStim M7, for example, by Biomedical Life Systems, Inc. This device has seven modes of operation, which leaves many people wondering which mode to choose. I want to preface this by saying before utilizing a TENS unit or choosing a mode, it is important to discuss your specific needs with your physician. This is meant to be an overview of how the TENS device functions and should not be mistaken for medical advice.
First of all, every mode on a TENS unit is designed for pain relief. That is what TENS units are designed to do, relieve pain. But not every person is the same, so adjustments can be made to obtain optimal relief over time. There is no limit to how long or how often a TENS unit can be worn, it is at the discretion of the prescribing practitioner.
In a previous post, we discussed that there are three parts to a TENS unit waveform:
1. Pulse Rate
Pulse Rate (P.R.) is also known as any and all of the following: Hertz (Hz), Frequency, or Pulses Per Second (pps).
To simplify this, I like to think of it as “Pulses Per Second.” The Frequency of the T.E.N.S. unit waveform can range from approximately 1-250Hz depending upon the model. Pulse Rate is important because different frequency settings target different nerve groups and the setting will determine if the “Gate Theory” or “Endorphin Theory” of T.E.N.S. will be used.
2. Pulse Width
Pulse Width (P.W.), is also known as any and all of the following: Microseconds (uS), and Pulse Duration.
To simplify this, the pulse width is how wide each pulse is. It’s measured in extremely small intervals called microseconds. The Pulse Width on T.E.N.S. devices usually range from 1-250uS. Generally speaking, the higher the pulse width, the more “aggressive” the stimulation feels. If the pulse width is set high enough, it will elicit a muscle contraction, which is typically not the desired result with a T.E.N.S. unit. However, if the pulse width is too low, the patient may not perceive the stimulation.
Amplitude is also known as any and all of the following: Intensity or Milliamps (mA).
To simplify this, the amplitude is what you feel when you “turn the unit up”. This is what causes the “buzzing” sensation of the T.E.N.S. unit to go higher or lower. Portable T.E.N.S. units can range from approximately 0-100 mA. This is often set to patient comfort levels.
I like to compare adjusting the sensation of the TENS unit to adjusting a stereo. Increasing Pulse Width (uS) would be like adjusting the bass, adjusting the Amplitude (mA) would be like adjusting the volume and adjusting the Pulse Rate (Hz) could be compared to adjusting the speed of the music.
There are two theories behind how TENS units work.
1. Gate Theory: It is theorized that the “Gate Theory” of TENS is attained when “High Frequency” (also known as Pulse Rate) is used (approximately 80 Hz- 150 Hz.). This works on the premise that the asymmetrical biphasic square wave output at high frequencies will “block” the pain signal from the end of the nerve to the brain, so when it reaches the brain it is not perceived as pain. This works very quickly (15 minutes, for example) but when the unit is removed from the body, the signals are no longer being blocked. The pain returns quicker than with the Endorphin Theory (discussed below). However, this works for a greater percentage of the population (approximately 80% of those who respond positively to TENS units) especially if the patient is taking pain medication. If the patient is already taking pain medication, the release of endorphins needed for the Endorphin Theory (discussed below) will be hindered because the medications are often already chemically releasing endorphins throughout the body vs. the localization that is achieved with TENS unit endorphin release.
2. Endorphin Theory: It is theorized that the “Endorphin Theory” is attained when “Low Frequency” (also know as Pulse Rate) is used (approximately 1-10 Hz) or if a Burst Mode is used. Endorphins are the body’s natural pain fighting mechanism. For example, when you stub your toe, your immediate reaction is to rub it. This “rubbing” or “pulsing” sensation is what triggers localized endorphin release. Endorphins can take up to 45 minutes to reach the area when a TENS unit is applied, but once they are there, the pain relief can last up to six hours after the patient takes the TENS unit off. This works for about 20% of the population that respond positively to the TENS unit. It takes more patience, because it takes longer for the pain relief to begin than with the Gate Theory. If the patient is already on pain medication, the endorphins are already being released chemically in the body and the localized effect is hindered. If the patient is on pain medication, typically the Gate Theory will be the delivery method of choice.
We will now discuss the seven modes for the BioStim M7 by Biomedical Life Systems, Inc. as an example of how the parts of the waveform can be adjusted to achieve pain relief results.
1.CONST: also known as Constant or Continuous Mode.
This mode functions exactly how it sounds. It constantly outputs the set Pulse Rate, Pulse Width and Amplitude. The Pulse Rate determines which theory of TENS will be administered (Gate or Endorphin). A Pulse Rate set from 80-150 Hz will be the Gate Theory and a Pulse Rate of 1-10Hz will be the Endorphin Theory. The Pulse Width and Amplitude are typically set to patient comfort (enough to feel the pulsing sensation, and just under the threshold of a muscle contraction). The patient should feel the stimulation, but it should not be painful. The Constant Mode is typically used to determine the baseline (or the best settings) for the patient, since there is no shift of the settings while it’s worn and to determine if Gate or Endorphin Theory will work best for the individual. As with most pain relief mechanisms, the patient will acclimate to the perceived sensation of the output over time. It is believed that when using the Constant Mode, the patient will acclimate more quickly because there is no modulation or change of any of the settings. Again, most practitioners will use this mode to determine the optimal comfort settings and choose a modulation mode for the patient to use long term.
2. PR MODUL: is also known as Pulse Rate Modulation: 50% decrease/increase of set value over a 5 second cycle.
As previously discussed, the Pulse Rate will determine whether the Gate or Endorphin Theory is used. However, using just one set Pulse Rate, as is done in the Constant Mode, lends itself to quick acclimation by the patient. The Pulse Rate Modulation Mode (varying Frequency) shifts the Hz setting 50% of the set value over 5 seconds. For example, if the Pulse Rate (Hz) is set at 100 Hz, the device will shift down to 50 Hz and up to 150 Hz over 5 seconds. This is still considered “High Frequency” TENS and will still work on the premise of Gate Theory when set this way. If the Pulse Rate is set at 5Hz, then the Hz will shift from 3-8 Hz over 5 seconds utilizing the Endorphin Theory. The difference between Constant Mode and Pulse Rate Modulation is the shift in the Pulse Rate over time so the patient will not acclimate to the sensation as quickly. Each TENS unit will have slightly different mode settings, but by using your knowledge of the Gate and Endorphin Theories you can see which theory of TENS is being administered and adjust Pulse Width and Amplitude settings to patient comfort.
3. PW MODUL: Pulse Width Modulation: 50% decrease/increase of set value over a 5 second cycle.
In the Pulse Width Modulation mode, the feeling of the TENS unit output is varied utilizing a Pulse Width shift. The Pulse Rate setting (Hz) in this mode will remain constant and still determines what theory of TENS is being used, but the varying Pulse Width will, in theory, keep the patient from acclimating to the output over time. When Pulse Width is increased, the sensation typically feels stronger. What is really happening is each individual pulse is lasting longer (duration) when the Pulse Width setting is increased. When choosing a Pulse Width setting, it is important to find the optimal comfort zone for the patient. Typically the Pulse Width is set as high as possible without generating a visible muscle contraction or discomfort.
4. PR & PW MODUL:also known as Pulse Rate & Pulse Width Modulation: 50% decrease in set value over a five second period.
As the Pulse Rate (Hz) increases, the Pulse Width (uS) decreases and vice versa. The Pulse Rate (Hz) setting will still determine whether the Gate or Endorphin Theory will be applied. The Pulse Width will determine how long each pulse is delivered, but both shift over time to prevent acclimation. It is typical when Pulse Rate swings to higher levels, a lower Pulse Width is needed to maintain optimal comfort and vice versa, which is why the two shift in the manner described.
5. Cycled Burst Mode: 2.5 seconds on. 2.5 seconds off. Adjustable Pulse Rate and Pulse Width.
In the Cycled Burst Mode, the Pulse Rate and Pulse Width settings remain constant, but the TENS unit drops the amplitude to “0″ for 2.5 seconds, then turns back on to the original amplitude setting for 2.5 seconds and repeats. Instead of utilizing low frequencies (Hz) to create the “tapping” or “rubbing” sensation to release endorphins as we discussed in the previous settings, the Cycled Burst Mode creates a “tapping” or “rubbing” sensation by pausing the amplitude output (mA) then applying output in rounds of 2.5 seconds, providing an alternative way to apply the Endorphin Theory. In this mode, the Pulse Rate setting (frequency) can be in the 80-120Hz range, but because of the way it is delivered, the pulsing or bursting sensation releases endorphins.
6. SD1: Strength Duration 1 Mode: Increase of set Pulse Width 40%, decrease of set Pulse Rate 45% and decrease of set Amplitude 10% over a 3 second period. Values return to original settings over the next 3 seconds.
Strength Duration 1 Mode is specifically designed to modulate all of the waveform settings to achieve maximum comfort. When the Pulse Width shifts to higher settings (more aggressive sensation) the Amplitude (power level) drops 10% to allow the increase in the Pulse Width setting to be more comfortable to the patient. The Pulse Rate (Hz) still determines whether the Gate or Endorphin Theory will be utilized, but the shift in Frequency (Hz) shifts 40% to prevent acclimation.
7. SD2: Strength Duration 2 Mode: Increase of set pulse width 60%, decrease of set pulse rate 90% and decrease of amplitude 13% over a 6 second period. Values return to original settings over the next 6 seconds.
This mode is very sophisticated because it enables all of the waveform settings to adjust in a proven pattern for maximum patient comfort. In addition, the 90% shift in the Pulse Rate (Hz) setting allows for both the Gate and Endorphin Theories to be utilized in the same mode. Let’s say, for example, the original Pulse Rate (Hz) is set at 80Hz, the 90% shift will allow the Pulse Rate to swing from 80Hz (Gate Theory) down to 9Hz (Endorphin Theory). The shift in Pulse Width and Amplitude allow for maximum comfort. The variance of all the components together will prevent acclimation. Since the SD2 mode encompasses both theories of TENS in the most comfortable way, it is very effective for most patients. The SD2 mode is optimal for those with pain conditions pertaining not only to the parasympathetic nerve group but also to the sympathetic nerve group like Complex Regional Pain Syndrome, for example.
Different models of TENS units will have different modes and the ones that I have discussed here may not be exactly the same. It is important to discuss with your prescribing practitioner or health care professional which model and mode is right for you. In short, if you’re obtaining pain relief you’re doing it right.
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