Currently two types of TENS are being researched for pain and symptom relief treatment of cancer patients. Conventional TENS is the more basic and well-known of the two stimulation types whereas acupuncture-like TENS known as ALTENS aims to produce similar effects despite using different parameters and electrode placements.
TENS Parameters:
The aim of conventional TENS is to selectively stimulate large-diameter
A-beta nerve fibres without stimulating other A or C nerve fibres and motor
efferents. This means that the electrical impulses generated from the TENS
machine are stimulating nerve fibres that are specific to touch and sensation.
By stimulating these nerve fibre types, it disrupts the sensation of pain
arising in the surrounding tissues and reduces the amount of information
regarding the pain being projected to the brain. In theory, high frequency and
low intensity pulsed currents would be most effective in achieving this type of
stimulation. Large diameter nerve fibres, known as A-beta fibres, have short
refractory periods and can generate nerve impulses at high frequencies. The
usual frequencies used are 80-120Hz. The intensity (measured in milliamps) of
this treatment is highly dependent on the patient, what they can tolerate and
what feels good for them. The intensity is therefore adjusted to suit the
patient. A standard TENS device delivers biphasic pulsed currents in a
repetitive manner using pulse durations of 50–150ms and pulse frequencies of
1–200pulses/s. Effects usually do not last as long as those produced by ALTENS
and often do not outlast the duration of the treatment.
 |
| Figure 1. A schematic showing TENS affecting the mechanoreceptors of the skin, which then inhibit nocioceptors transmitting signals of pain to the brain, thereby reducing pain perception. Image retrieved from: Jones, I. & M, Johnson. (2009). Transcutaneous electrical nerve stimulation. Continuing Education in Anaesthesia, Critical Care & Plan, 9(4), 130-135. |
ALTENS parameters:
ALTENS is similar to conventional TENS however, the electrodes are
placed in areas of the body that would normally represent acupuncture sites. As
a result this allows for TENS stimulation as well as acupuncture-like
treatments. However, unlike TENS, ALTENS stimulates small diameter A-delta
fibres which leads to an opioid release resulting in a decrease in C fibre
activity, this effectively decreases pain perception. Another difference
between the two types of TENS is the frequency and the intensity that ALTENS
offers. ALTENS offers low frequency and high intensity electrical stimulation
to the areas applied. In general, ALTENS offers a frequency of 1-10Hz and a pulse
duration of 150-300ms. Low frequency/high intensity TENS appears to cause a
release of endogenous opioids in the spinal cord and higher brain centres in
the brain in the same manner as acupuncture, without being invasive. The
effects of this stimulation outlast the treatment by hours or even days. Also,
unlike TENS which has a fairly short treatment duration, ALTENS may be
administered for as long as 30 minutes of a given treatment.
Table 1. TENS techniques
Physiological intention
|
Clinical technique
| |
Conventional TENS
|
Selective activation of A-beta nerve fibres eliciting segmental pain relief
|
Low-intensity/high-frequency
Apply at site of pain "Strong but comfortable TENS paraesthesiae" Use when in pain |
Acupuncture-like TENS
|
Activation of A-delta nerve fibres leading to inhibition of C nerve fibres resulting in extra-segmental pain relief
|
High-intensity/low-frequency Apply to muscles, acupuncture point or trigger point
"Strong but comfortable muscle contractions" Long duration; 15-30mins |
Types of cancer pains & effectiveness of TENS:
Following
on from our last post, you may be curious to know exactly what type of pain is
experienced by palliative cancer patients and how effectively TENS reducing
this pain. Simon (2008) listed
the following as types of pain experienced by those in palliative care: bone
pain, abdominal pain, neuropathic pain, rectal pain, muscle pain, bladder
pain/spasm and pain of short duration. Of these types of pain, Simon (2008)
only states TENS as a treatment option to relieve neuropathic pain. However, it
was also noted that physiotherapy might be useful for muscle pain relief. Searle et. al
(2009) conducted a case study and concluded from the findings
that TENS may also be helpful in the relief of bone pain in cancer patients.
The researchers also indicated ALTENS to be used as
an alternate option to conventional TENS should it prove ineffective.
However, ALTENS delivers a higher intensity dose than conventional TENS and as
a result not all patients will be able to tolerate this treatment. In
conclusion it is evident from these two research articles that TENS can be
useful to cancer patients experiencing the described types of pain. Whilst it
is not apparent from the evidence, that TENS relieves pain under all
conditions, we are of the opinion that it should always be a viable option for
palliative cancer sufferers as any pain relief is better than none.
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