Interferential Therapy:
by
Jim Lane
Interferential therapy, during the past
ten years, has increased in popularity to the
point that it is now perhaps the most widely used
form of electrotherapy in the United States.
First developed in Europe, where this unique form
of stimulation has been utilized for numerous
indications, interferential units have been
marketed since the early 1950's. It seems,
however, that a great deal of confusion, mystery
and perhaps even misinformation still exists
concerning this therapy. The purpose of this
article is to shed some light on areas that may
be confusing to the clinician, share information
on proper treatment protocols and offer a few
insights into treating patients with
interferential therapy effectively and safely.
The original concept of interferential therapy
was developed by Austrian physician, Dr. Hans
Nemec, approximately forty years ago. Dr. Nemec
proposed that by crossing two slightly different
medium frequency alternating currents within the
tissue, a third frequency current of greater
intensity is created in the deeper tissue. As an
example, a frequency of 4000Hz interfering with
another frequency of 4080Hz creates a third
current of 80Hz. This is caused by the inphase
and out of phase relationship of the two original
currents as they alternate from positive to
negative polarity. The third current, referred to
as the "beat frequency" becomes the
actual therapeutic frequency. One output of the
unit is a constant 4000Hz while the second output
frequency is adjustable from perhaps 4001Hz to as
much as 4250Hz. This form of interferential
therapy has become known as "true
interferential" oe "frequency
difference interferential".
A second method of creating the interference
effect has been developed in recent years and has
become known as "pre-modulated
interferential". With this method, both
outputs of the unit provide a carrier frequency
of 4000Hz, however, each output has the ability
to premodulate or burst the frequency within the
unit. It is important that this unit has the
capability of perfectly synchronizing these
bursts in the same polarity, at the same time in
order to create "premodulated
interferential" . Units capable of
premodulation are not necessarily premodulated
interferential and may only provide premodulation
for the purpose of bi-polar (two electrodes)
stimulation.
When considering the relative merits of these two
methods, many clinicians have noted that while
both create the interference effect, there may be
a distinct advantage to the pre-modulated
technique. Since the "true
interferential" provides an uninterrupted,
constant 4000Hz frequency to the tissue, a
condition known as Widensky inhibition
(depolarization of the nerve fibers) will occure
beneath the electrodes. This will create a
numbness and what will be percieved by the
patient as a reduction in the intensity of
current. With pre-modulated interferential,
however, since the current is being burst inside
the unit itself, Widensky inhibition will not
occur and a larger treatment area is established
with the actual therapeutic frequency.
Virtually all interferential units are supplied
with carbon rubber electrodes. The clinician
should be aware that either water soaked sponges
or a conducting gel should always be used between
the electrode and the tissue. This will insure a
uniform contact and provide for even dibursement
of the current over the entire surface area of
the electrode. If water only is used as a
conductive agent, pooling may occure with
resulting dry spots under the electrode. The
current will then become intensified at the site
of best conduction, the water pools, with little
or no current flow elsewhere. With "true
interferential" units this could result in
overstimulation of tissue under the water pools
and even possible tissue burns as depolarized
tissue will not be able to sense the over
stimulation.
While some interferential units still offer the
vacuum electrode system, many clinicians have
discontinued their use. Extra maintenance, tissue
bruising and uneven current flow have been cited
as reasons for a reduction in the popularity of
vacuum systems.
Self adhesive electrodes are rapidly becoming the
favorite of clinicians due to the ease of use,
patient acceptance and elimination of possible
cross-contamination. Difficult to apply areas
such as shoulders, hips and the cervical spine
are easily treated with the self-adhesive
electrodes. Also, recent improvements in adhesive
agents have made longer use possible and prices
have been reduced substantially.
If carbon rubber electrodes are used, care should
be taken to insure proper current flow. When
conductive gels are used, the gel will create a
glaze over the surface of the electrodes with
long-term use. The glaze may prevent the flow of
current over the entire electrode surface.
Cleaning the electrode periodically with a mild
soap and water and soft brush is recommended. It
is not a good practice to use conducting mist
sprays in lieu of other conducting agents. This
is due to the saline content of the sprays which
has been shown to destroy the carbon content of
the electrode, thus rendering the electrode
useless.
While frequency ranges vary from manufacturer to
manufacturer, basic therapy ranges are fairly
consistent. Frequencies which vary from
approximately 80Hz to 120Hz are considered most
effective for acute pain while lower frequencies
of perhaps 3Hz to 5Hz or 2Hz to 10Hz are
preferred for the treatment of chronic pain. Some
units feature a nerve block setting where both
channels produce an output of 4000Hz to create an
interferential nerve block to quickly block out
acute pain. Most clinicians prefer a setting of 1
Hz to 15Hz for treating acute edema.
When treating acute pain with the 80Hz to 120Hz
setting, interferential therapy will provide a
release of enkephalin with a treatment time of 10
to 12 minutes. Chronic pain, however, requires 15
to 20 minutes of the 3Hz to 15Hz setting to
provide relase of beta-endorphins. Nerve block
techniques, 4000Hz, normally requires 10 minutes
or more depending upon the size of the area being
treated.
Interferential therapy provides a comfortable,
soothing stimulation and should never be strong
enough to cause any discomfort to the patient.
Higher intensities should not be considered
"better" as far as obtaining results.
It is important to note that once the patients
comfort level is established at the onset of
therapy, the intensity should not be increased
during the treatment. This could cause
overstimulation of the tissue and even minor
burns, particularly when treating with a unit
that produces "true interferential" due
to the Widensky inhibition effect.
This procedure is utilized for muscle strengthing
and rehabilitation and is an added feature of
interferential units. Space does not permit
adequate explanation of this technique at this
time, howver, Russian Stimulation may be the
topic of a future article.
Interferential therapy is considered a very safe
modality when used properly for appropriate
conditions. Most manufacturers list similar
contraindications and precautions, most of which
are the same as other electrotherapy devices. It
is always recommened that the clinician review
each manufacturers warnings prior to treatment
with any device.
Jim Lane
lectures regularly at colleges throughout the
United States and is the CEO of LSI, Inc. he can
be reached @ 800-832-0053
Reprinted from The
Professional, April 1991
|
Download Adobe PDF Reader
