While everyone talks about back pain, many doctors often question
whether patients really have it. Clinical and technical examinations
such as X-rays, scans, MRIs and kinesiological evaluations may not
always reveal a clear cause. Classic treatments such as nonsteroidal
anti-inflammatory drugs, epidural infiltration and even surgery do not
always solve the problem.
However, physiotherapists already have a better solution-one that is
pleasant and may competently control the pain without much
interference with daily activities.
In America, the use of a transcutaneous electrical nerve stimulation
(TENS) device is common. On the other hand, microcurrent
electrotherapy (MET), even though it’s not that new, may not be common
enough. In this article, we will compare TENS to MET, using the
eight-parameter law, and see which gets the most credits.
1.
Eight-Parameter Law
Bringing together every possible
influence in electrotherapy leads to a list of eight parameters.
1.1 Waveform Polarity
Biphasic waves are much smoother to the
skin than monophasic. Monophasic waves are known to cause skin burns
in long treatments. This will be no problem for TENS or MET, because
they are both biphasic or can be switched to it. On some occasions,
the polarity is important to get a specific effect such as on wound
healing or on bone. In this matter, we are dealing with back pain so
that these effects are complementary.
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Howson believes that human skin resistance
will deform and decrease the initial wave. Maybe this indicates that
the waveform is not of primal importance as long as it is biphasic.
Keep in mind, however, that these conclusions were made using TENS
devices! They may not apply to the more sophisticated MET
technology. MET stimulators differ through their
waveforms. Though treatment circumstances were comparable,
pain-reducing effects were not always the same with different types of
stimulators. This is an open field for investigation.
1.2 Frequency
There’s no evidence for an overall
efficient frequency. Most studies indicate that TENS frequencies in
the 50-200 Hz range are used often with good effects. MET uses other
frequencies. Empirically extreme low frequencies in the 0.3-3 Hz range
have shown the best results. It seems that 0.5 Hz is especially good
for pain relief. In some cases, 1.5 Hz may give better results.
To release endorphins, one should choose
frequencies less than 8 Hz. At this time it isn’t completely certain
that MET triggers the endorphin release system with electrodes placed
on the trunk. However, MET, being of lower current by
definition, is sometimes used on the head
where the mechanisms are different and where endorphins are more
clearly implicated.
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1.3 Pulse Width
Howson, Li and Bak investigated stimulation
thresholds for afferent nerve fibers. Their findings show how
A and C-fibers can be stimulated with pulse
widths larger than 200 µS. According to many studies on the effect of
electrical stimulation and endogenous opioids, these fibers should be
stimulated to start endorphin release. On the other hand, but still
according to Howson, Li, and Bak, pulse widths in the 60 µS range
should be used only to affect A (-fibers and thus use Melzack and
Walls gate control) to achieve the effect of pain decrease.+
It may be clear that in this latter situation, optimal use of the
gate- control mechanism should not trigger any small, pain
transporting A (-and C-fibers). These two mechanisms of controlling
the pain can be used by adjusting the pulse width of the TENS device.
MET, however, uses much larger pulse widths of 0.1 – 2.0 seconds. Due
to the much lower intensity, it is believed that afferent fibers will
not be affected in the same way. Cheng, etc. reported a significant
increase in ATP at intensity levels below 750 µS. It is probable that
these large pulse widths are also necessary to achieve effects on ATP
production.
1.4 Pulse Train
Interrupting the stimulus is used to avoid adaptation of the central
nervous system. Both TENS and MET pulses use this technique. Some
authors believe that pulsed painful stimuli will trigger the endorphin
release. TENS has an extra possibility to interrupt the current by
switching it into burst-mode causing the patient to report an “on-off
feeling.” A series of pulses alternating with pauses known as the
burst-mode is the real pulse train technique in TENS. |
European perspective: a comparison between TENS and MET.
“MET has a different mechanism than TENS. It works on a cellular
level and has its effects much closer to the cause of the injury.”