INTERFERENTIAL THERAPY – A
MEDIUM FREQUENCY CURRENT
Dr/ Amal Mohamed Abd El Baky
Mr. Chandrasekar.L
353 RHPT - 1st SEM - 1435-1436H / Electrotherapy - 2
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Lecture outlines

Definition & Physics of interferential current

Physiological effects, therapeutic effects of
interferential current

Indication, Contraindication, of interferential
current

Technique of application of interferential
current
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Learning Objective
• Define & outline about the different types & basic physics
of interferential current
• Describe the operation of apparatus, parameters & types of
electrode placements, physiological & therapeutic effects,
indication , contraindication, of interferential current.
• Demonstrate safely the application of interferential current
in certain conditions or disorders
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INTRODUCTION – KEY POINTS
The medium frequency current range from 1000 – •
10000Hz.
I.F.T was developed by – Dr. Hans Nemec •
It is used to treat deep pain, idiopathic pain, relieve edema, •
stress incontinence.
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Definition
I.F.T current is the transcutaneous application of
2 alternating medium frequency currents, which
are slightly out of phase, causing AMPLITUDE
modulation at LOW FREQUENCY, used for
therapeutic purpose.
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Advantages of using Medium
Frequency current
• Reduce skin resistance – e.g. 50Hz (low frequency) –
4000 Ω (ohms), at 4000Hz (medium frequency) – 40 Ω (ohms)
• Producing low frequency effects within the tissues
• Produce deeper effects – amplitude modulation.
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Physical principles & Production of IFT
current.
• The current is produced by mixing two medium frequency
currents
One current (Channel – 1) is normally of the fixed frequency,
4000Hz & the other current is adjustable between (4000 &
4100Hz – channel - 2). The electrodes are placed on the skin
so that the 2 Ac currents intersect.
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Physical principles & Production of IFT
current.
When the currents intersect, they interfere producing a higher
amplitude, when both currents are in same phase & a lower
amplitude when both currents are in the opposite phase.
Interference pattern
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Beat Frequency (BF) /
Amplitude Modulated Frequency (AMF)
This produces envelops of pulses known as BEATS. The beat
frequency called as (amplitude modulated frequency - AMF)
which is equal to the difference between the frequencies of the
2 original AC currents.
For example, if current A is 4000Hz and current B is 4100 Hz,
the resultant frequency is 100Hz.
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(a) Interference of two medium-frequency currents. (b) Partial beating.
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Parameter setting & type of electrode
placement in IFT
Amplitude
modulated
frequency
(AMF)
Frequency
modulation,
swing or sweep
Quadripolar/
bipolar
application
Vector/scanning
mode
Suction versus
plate electrodes
Current intensity
Duration
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Amplitude modulated frequency
• It is also called beat frequency which is effective
and similar to low frequency current and produce
stimulation of nerve and tissues(muscles, tendons,
periosteum).
• It is more comfortable because of low skin
resistance to the flow of current & allow a high
amplitude of current to stimulate deeper tissues.
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Low AMF (5Hz) produce beating or tapping sensation,
while higher AMF (50-100 Hz) produce buzzing and
tingling sensation.
Most interferential machines allow a constant beat
frequency to be selected, e.g. 10,50 or 100 Hz — in fact any
frequency from I to 250 Hz — called the constant or static
mode.
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Frequency modulation, swing or sweep
It an arrangement that allows the beat frequency to
change automatically and regularly between some pre-set
pair of frequencies over a specified time period.
Thus the machine could be set to sweep, for example,
between 20 and 80 Hz over a period of 6s and back over
the next 6s.
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• The time and the pattern of this modulation is usually adjusted and called as the
spectrum
• Advantages of Spectrum:
1.
Reduce nerve adaptation
2.
Allow stimulation of greater range of excitable tissues
Variable beat frequency – example;
- 0 to 5 Hz stimulates sympathetic nerves
- 5 to 10 Hz stimulates parasympathetic nerves
- 10 to 50 Hz stimulates motor nerves
- 50 to 90 Hz produces sedative and spasmolytic effect
- 90 to 100 Hz produce analgesic or pain relief effect
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Areas of maximum stimulation - The clover-leaf shape of maximum current modulation
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Vector/scanning mode
The clover-leaf shape of maximum current modulation is a static pattern
but, by varying the current intensity in the 2 circuits with respect to each
other, it is possible to move the clover-leaf pattern of maximum modulation
to and fro through 45°, thus giving a more uniform total distribution of the
interferential current in the tissues.
There are various names for such a mechanism, including vector sweep’,
‘scanning’, ‘rotating vector system’ or ‘dynamic interference field system’.
It serves to increase the area of effective treatment. When the accuracy of
the lesion can not be localized or is doubtful, this mode is selected.
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Types of vector mode
Vector field with Classical
Interferential
Dipole vector field
Isoplanar vector field
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Quadripolar application - Method of electrode
application:
In this method four electrodes are used, and two unmodulated currents leave the
equipment. Interference occurs where the two currents intersect within the tissue. The
modulation depth depends on the direction of the currents, and can vary from 0 to
100%. 100% modulation depth only occurs at the diagonals (and hence at the
intersection) of the two currents.(clover-leaf pattern)
In the four-pole method, the modulation depth is only 100% at the diagonals.
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Bipolar application - Method of electrode application:
In this method two electrodes are used and superimposition of the two
alternating currents takes place within the equipment. The current leaving
the equipment is a fully modulated alternating current.
In the two-pole method the modulation depth is always 100%
Bipolar interferential therapy
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• AMC was set up in both in the central area between the
electrodes and also beneath it
• Quadripolar produce deeper effects within tissues, while
bipolar application produces a current flow in the manner
of electrical stimulation with maximum intensity under the
electrodes.
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Suction versus plate electrodes
• Suction electrode
1.
It can be used for large flat area or for patient who are
relatively immobile.
2.
it also can be used for the anatomical areas that are less
accessible
3.
It stimulate cutaneous nerves and cause vasodilatation.
• Flat carbon rubber electrodes
1.
It can be easily applied for peripheral limbs, it can be held in
position by bandage or Velcro strap.
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Current intensity
• Factors affecting sensation produced intensity:
1. The treated area
2. Size of electrode
3. Electrode placement
• Intensity should be slowly turned up until the required
sensation has been reached
• Periodic adjustment of intensity is recommended to
compensate any adaptation.
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Duration
• 10- 15 min not exceeding 20 min to one area.
• 10 min for most painful area is suggested
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summary, controls on the interferential
machine are:
1. Settings for constant beat frequency, e.g. 80 Hz.
2. Settings for variable beat frequencies, e.g. 20—80 Hz.
3. Control for time of variable beat frequencies cycle, e.g. 6s.
4. Intensity control.
5. Control for using rotating vector mechanisms, e.g. on or off.
6. Control for total treatment time, e.g. 10 mm.
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Physiological effects of IFT
Relief of pain – Pain gate mechanisms
Motor stimulation – Muscle contraction
Absorption of exudate
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Factors affects the physiological effects
1. Magnitude of the current
2. Current mode (constant, sweep)
3. Frequency range
4. The accuracy of electrode placements
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1. Relief of pain - Mechanisms
1. Pain Gait Mechanism - Stimulation of large- diameter, lowthreshold nerve fibers with high-beat frequencies — around 100 Hz.
2. Descending pain suppression - A delta and C fibers causing
encephalin and endorphin release, probably activated by low
frequency (10—25 Hz).
3. Physiological block of nerve conduction - high-frequency (above
50Hz) stimulation of finely myelinated and non-myelinated
nociceptive fibers.
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1. Relief pain - Mechanisms
4. The local increased fluid flow and fluid exchange consequent on
mild muscle contraction and possibly stimulation of autonomic nerves
may help to remove chemical irritants affecting pain nerve endings
and reduce local tissue pressure.
Frequencies of 10—150 Hz stimulate the parasympathetic nerves
increasing blood flow through the area, and 0—5 Hz the sympathetic
nerves.(Savage – 1984).
5. A placebo effect
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2. Motor stimulation
Due to the higher frequency of the medium-frequency current,
not every (alternating current) pulse will result in depolarization
of the nerve fibre. Depolarization of the nerve fibre is the result
of the summation principle (Gildemeister effect).
A. With a medium-frequency current an action potential only arises after a certain
number of periods (summation principle).
B. With a direct-current pulse of the same duration an action potential arises at a
significantly lower amplitude.
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2. Motor stimulation
• If IFT with frequency between 1-100 Hz is used this will
stimulate the normal innervated muscle
• At 5-20 Hz a partial tetanic is produced and from 30- 100
Hz tetanic contraction is produced
• Muscle contraction is produce with little sensory
stimulation
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3. Absorption of the exudate
1. 1-10 Hz is effective to produce rhythmic muscle
contraction
2. Improvement of circulation
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Indications
Pain relief
Edema relief
Stress incontinence
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1. Pain relief
• For acute pain : Frequency should be high
70-150 Hz
• For chronic and sub acute pain : Frequency should be less
Below 50 Hz
2.Edema relief:
AMF of 1-10 Hz
3. Stress incontinence:
• Quadripolar technique where electrodes are placed over the lower
abdomen and inner thigh.
• In female one electrode under both ischial tuberosity and one over
anterior perineum immediately under the symphysis pubis
• In male two electrodes are placed either side of the gluteal cleft
under the ischial tuberosity anterior the anus.
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Contraindications
Hemorrhage
Deep vein
thrombosis
Skin infection
Malignancy
Pacemaker
Chest wall in
patient with
heart problem
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Dangers
• Burn : it is not uncommon due to alternated current occur with
contact of the electrode with skin , or the two electrode are
near to each other.
• Increased pain: if the intensity is too high, if the bare electrode
touch skin, or they are near to each other
• General malaise
• Nausea
• Dizziness/ faintness
• Migraine/ headache
• Neurological effects.
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Combination therapy
• IFT can be used in combination with other treatment
methods as ultrasound when there are musculoskeletal
condition with pain.
• One electrode is used for bipolar technique placed in
adjoining region of injury and the circuit is completed by
the ultrasound
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Practical application
• Machine check - plugs, cable, electrodes etc.
• Test machine
• Position patient comfortably
• Explain nature of the treatment, what they will feel
and the benefits
• Prepare and wash the skin
• Inspect skin for any lesions - cover with petroleum
jelly
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Preparation of the skin
• Skin has a high electrical resistance as the outer
surface is dry and contains few conducting ions
• Skin is normally washed to remove excess oils
and to moisten it
• Any lesions can cause a concentration of current
which will result in pain
• Small lesions can be insulated with petroleum
jelly
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Practical application.
• Give the patient a warning - will feel a tingling
sensation which should not be uncomfortable or
burn
• Select the frequency required
• Increase the intensity - may need to adjust due to
accommodation
• Turn the machine off after treatment completed
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General guidelines on Parameter selection
1. (Laycock and Green, 1988) have found that 2 kHz is
preferable for muscle strengthening.
2. A high AMF (70—150 Hz) for acute problems and pain.
3. Frequencies below 50Hz for chronic and sub acute
conditions and where muscle contraction is required.
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General guidelines on Parameter selection
4. The dynamic vector techniques should be used when the
region to be treated is relatively large.
5. If localized treatment is required, the bi-pole method is
preferable.
6. For a optimum stimulation effect - modulation depth of 100%
is chosen.
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The application methods are as follows:
The selected application method will depend on the
application points;
• pain-point or trigger-point application,
• nerve application;
• (para) vertebral application;
• transregional application;
• muscular application
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Malleable electrode application
Malleable carbon rubber electrodes in
moistened sponge pockets
Interferential machine
set up with malleable carbon rubber
electrodes
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Suction electrode application
Suction electrodes
with moistened
sponges
Suction machine
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Appropriate positioning of the knee
for placement of electrodes for
treatment with IFC. The knee is
supported and in an open joint
position.
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Knee with IFC applied using two
channels of electrodes that have
been crossed.
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Electrode placement
Electrodes placed so that the
two circuits produce an interference
current and the patient experiences
the tingling sensation on and around
the site of their problem
Left knee
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Hypertonia of trapezius muscle
Objective : tonus regulation
Patient position : prone
Electrode positions : on course of muscle
Current type : two-channel two-pole
interference, 4000 Hz
Output characteristic : CC
Frequency : AMF 50 Hz
Phase time : Burst : Frequency modulation : 80 Hz
Sweep mode : 1/1
Amplitude : sensory – motor level
Treatment time : 10 minutes
Frequency of treatment : three times weekly
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Lateral epicondylitis
Objective : improving circulation
Patient position : sitting
Electrode positions : segmental and local
Current type : two-pole interferential,
4000 Hz
Output characteristic : CC
Frequency : AMF 80 Hz
Phase time : Burst : Frequency modulation : 100 Hz
Sweep mode : 1/30/1/30
Amplitude : sensory level
Treatment time : 15 minutes
Frequency of treatment : four times weekly
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Termination of treatment
• Remove electrodes
• Inspect the skin
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