what is the history of the development of IFC
- Dr Hans Nemec mid 1950s
- developed to help overcome the body’s resistance to low frequency current
- increasing frequency of IFC decreases capacitative skin resistance
IFC devices
multifunction unit with IFC
dedicated IFC unit
portable IFC unit
what is IFC?
modality used to treat pain
- transcutaneous (through the skin) application of two alternating medium frequency sinusiodal currents at slightly different frequencies
low frequency current: range and example
0-100 Hz - TENS, NMES
medium frequency current: range and example
1000-10000 Hz - IFC
high frequency current: range and example
> 10000 Hz - shortwave diathermy (not used anymore)
what does it mean that IFC uses 2 currents at slightly different frequencies?
two alternating medium frequency sinusoidal currents at slightly different frequencies
- current 1 = 4000 Hz
- current 2 = 4100 Hz
(not in the same phase most of the time)
what happens when the currents are out of phase?
the current alternates over time
- amplitude modulated current
- the net effect is the sum of the two currents
- because the highs and lows do not coincide, the net current is an alternating current which varies in amplitude
what is another name for the amplitude modulated frequency current?
beat frequency current (sometimes displayed on machines)
what is the difference between TENS and IFC?
TENS 5 Hz
IFC AMF 5 Hz
- tens is pulsed whereas IFC is continuous
- IFC delivers a much higher charge to the tissue and pulse durations are much shorter (goes much deeper into the tissues)
what is the AMF? (amplitude modulated frequency)
the difference between the 2 currents (subtract them)
what does current attenuation depend on with IFC?
depends on conductivity of tissues and conductivity varies through the electrical field
what do experimental observations suggest about the realistic view of the interference field?
- 50-100% occurs in 70% of area between electrodes
- interference also occurs under elecrodes
- 100% interference is not in a fixed orientation to the electrodes
IFC adjustable parameters of IFC?
- intensity of current
- amplitude modulated frequency (fixed or sweep - adjust the frequency)
- suction / no suction
what is frequency sweep?
- occurs when frequency of AMF current is altered over time
- one channel is fixed and the other channel changes its frequency
- frequency of the second channel can be changed to slowly increased over a period of 6 seconds and then decrease over a period of 6 seconds
benefits of frequency sweep?
prevents habituation
vector option?
- refers to small changes in amplitude (intensity) in one of the channels
- also referred to as “phase scan” or “field rotation”
- PT can set up by what percentage the amplitude on the second channel can vary (e.g., up and down by 10%)
- helps prevent habituation
IFC waveforms?
sinusoidal
Premodulated IFC
- delivered using one channel
- two currents can be “mixed” in the unit prior to application, requiring only one pair of electrodes
- this type of arrangement is also called “bipolar”, “2-pole” IFC
what is the issue with premodulated IFC?
- only one circuit
- currents do not interfere with one another as in quadripolar
- it’s jjust a single channel medium frequency current which is premodulated but not interferential
advantage of using IFC?
- with increased frequency of stimulation, capacitive reactance of the skin is decreased
- therefore the current can reach deeper structures
advantages of using IFC over TENS
- reduces discomfort incurred by the low frequency current of TENS (IFC has less resistance encountered by the skin)
- due to amplitude modulation at low frequency, will get the low frequency effects (prevent habituation)
- brusts of sinusoidal current deliver greater total change than single pulses thereby activating more sensory nerve endings in skin and deep tissue than TENS
- enables treatment of deep tissue
advantages of IFC
- zero net charge on skin (no chemical burn)
- intensity within the field is up to twice that on the skin
- beat frequency can be varied to decrease patient habituation
- few contraindications, therefore wide application
how is IFC applied?
- using carbon electrodes with a damp sponge
- may be applied with or without suction
- with suction enables better contact for irregular surfaces
- some clinicians use carbon electrodes with gel or self-adhesive (not preferred)
