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PTHY 7403 Phys Agents; Electrotherapeutics unit; outline 2
Electrotherapeutics –Interferential Current
Reading: Cameron pgs 224-225; 259-260
Interferential Current (IFC)
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A unique use of kilohertz AC waveform; theoretically, it produces the IFC endogenously
Emphasis on use for pain control (pretty good evidence) & some limited NMES applications
(minimal evidence)
Anecdotal support w/ a smattering of evidence - - tissue healing & increase circulation via autonomic
stimulation
Hx - Dr. Hans Nemec 1950’s in Austria; popularized in US in late 70s / early 80s; remains popular
IFC Waveform Precursors
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2 electrical circuits (channels) of AC
– Medium Frequency kilohertz AC ( btwn 1,000 - 10,000 Hz is “medium frequency” in
electrophysics); typically 4000 or 5000Hz on most IFC units
– One channel is the Carrier (fixed) frequency AC
– One channel is the Variable frequency AC
– Example: 5000 Hz (carrier) / 5100 Hz (variable)
The difference is called the Beat Frequency
( beat freq = 100bps in the example above)
Why Medium Frequency (kilohertz) AC [ie. MFAC]?
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Comfortable, penetrates tissues easily, With AC: higher frequency = shorter phase duration =
lower skin impedance
Possibility of neural block – electrically induced paresthesia produced by MFAC; nerve fibers kept in
a state of depolarization.
Production of the endogenous IFC (theory);
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Interference of 2 MFACs within the tissues (at 90 degree angle to each other) results in the
endogenously created IFC with a Beat Frequency; Variable freq minus Carrier freq = Beat
frequency.
Theoretically, in a uniform 3D medium like water or metal: IFC results from constructive and
destructive interference of the 2 MFACs when they interact at 90° to each other.
Waveform interaction (in 2D);
(as viewed on an oscilloscope)
Theoretical Benefit of endogenous production of IFC: the IFC can be much stronger in amplitude
than either of the MFACs but the IFC doesn’t have to penetrate the skin, since it is created in the
tissue.
PTHY 7403 Phys Agents; Electrotherapeutics unit; outline 2
IFC production - in a uniform 3-D medium (like water or metal)
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Clover-leaf Pattern of IFC is produced (3D)
Known to occur in a uniform medium with each MFAC circuit at equal amplitude and at a 90 degree
angle to each other. Works like adding vectors
that have the same magnitude but different direction;
adding the vectors together to create a new vector
with a new direction - - this creates the IFC clover-leaf
Parameters to be used
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Choose and set a Beat Freq, and Amplitude.
Options with the Beat Freq:
– Can use Fixed vs Scanning Beat Freq. (WHY?; scanning to help delay neural accommodation
and for pt comfort/preference)
“Vectoring” /aka “Sweeping” of IFC: theoretically results in “oscillation of the
cloverleaf”
– Purpose: Increase stim area; can help with neural accommodation also.
– Physics: Amplitude of each circuit fluctuates up and down . . . . like vectors
of different magnitude interacting; the resultant IFC 3D cloverleaf will
oscillate/turn, NOT spin
IFC in human tissues: Reality ??
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Interference between the MFAC electrical fields hopefully occurs BUT the pure 3D Clover-Leaf IFC
pattern is not realistic b/c of variations in impedance of tissue (different layers, hydration,
location/orientation of nerve fibers, etc);
IFC technology seems complex but from a pain control standpoint, the mechanisms of
effectiveness are likely same as TENS.
IFC offers potentially better pain control due to increased depth of current and comfort with
stimulation. Typically an in-the-clinic Rx only. Though portable IFC units do exist, they are often
quite a bit more expensive than TENS AND most use biphasic pulsed current in the kilohertz range as
the waveform, not pure MFAC; does this make a difference?? We don’t know.
Application and Treatment Guideline
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Treatment of an area of pain (joint OR soft tissue) with IFC. Requires quadpolar application (2
channels, surrounding the pain; “X marks the spot”; channel 1 & 2 oriented at 90 degree angles to
each other as best you can on a 3D area of tissue or joint)
o Acute Pain: use High Beat Freq (> 50Hz) , do Sensory to Low Motor Amplitude
o Chronic Pain: use Low Beat Freq (< 10 Hz), do Motor to Noxious Amplitude
scanning the beat frequency is optional, but may be preferred for delaying accommodation or if
scanning “feels better”;
use of vector is optional but may be preferred if treating a large area or if vector “feels better”
Premodulated IFC (Bipolar)
o IFC produced in the unit & delivered thru 1 channel, not as comfortable but can put
directly on & over pain; offers convenience but is not pure IFC. Potentially more useful
for targeting motors points (NMES).