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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.
"TRUE INTERFERENTIAL" VS. "PRE-MODULATE INTERFERENTIAL"
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 in phase 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 frequency difference
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 pre-modulate 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 "pre-modulated
interferential" Units capable of pre-modulation are not necessarily
pre-modulated interferential and may only provide pre-modulation 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 occur beneath the
This will create
numbness and what will be perceived 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
CONTACT AND SAFETY
interferential clinical 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 disbursement of the current over the entire
surface area of the electrode. If water only is used as a conductive agent,
pooling may occur 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 over stimulation of tissue under the water pools and even possible
tissue burns as depolarized tissue will not be able to sense the over
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
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
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.
The best selection
for this device is re-usable Silver Connector Electrodes.
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 release
of beta-endorphins. Nerve block techniques, 4000Hz, normally require 10 minutes
or more depending upon the size of the area being treated.
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 over
stimulation of the tissue and even minor burns, particularly when treating with
a unit that produces "true interferential" due to the Widensky inhibition
This procedure is
utilized for muscle strength and rehabilitation and is an added feature of
interferential units. Space does not permit adequate explanation of this
technique at this time; however, Russian Stimulation may be the topic of a
CONTRAINDICATIONS AND PRECAUTIONS
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
recommended that the clinician review each manufacturer’s warnings prior to
treatment with any device.
devices are non-addictive.
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