Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Quantitative PEMF therapy data please

  1. Jan 20, 2013 #1
    I discovered Physics Forums when I searched for PEMF on Google.

    I became interested in PEMF when I was asked if I could repair two PEMF machines.
    (I have acquired a reputation as a "Mr Fix-it" in our small community here in Spain!)

    The first was a small portable device with a hand "paddle".
    The "paddle" had been dropped from a great height onto a tiled floor. (There are a lot of tiled floors in Spain!)

    The drop had exposed the innards of the paddle which consisted of a tightly wound coil of approx 1mm diam magnet wire.
    The overall diameter of the coil was about 60mm and the depth 20mm.(Somewhat distorted by the fall!)
    This coil was connected to the control box by a length of 3 core mains cable in which two cores were used.

    I measured the inductance of the coil and was convinced there were shorted turns.
    This prompted an e-mail to the Canadian Manufacturer requesting specs for the device.
    They suggested I should stick the plastic sheath for the paddle back together and give it back to the owner !
    She wasn't happy with that (it wasn't very pretty) and we ordered a new paddle.
    The cost of shipping from Canada was nearly as much as the cost of the paddle.

    Measuring the inductance of the new paddle proved that the damage to the old paddle was definitely more than cosmetic.
    The control unit was a simple circuit in which a large electrolytic capacitor was charged to about 150 volts.
    This was discharged through the coil by triggering a silicon controlled rectifier.
    A series of green Leds were arranged prettily on the front panel and lit sequentially as the capacitor charged.
    A couple of pre-set pots on the board adjusted the peak voltage and the charge time.

    I asked the manufacturer for some guidance on how these should be adjusted.
    I was told that if the top green led illuminated just before the magnetic pulse occurred "it would be right".

    The second machine was a bit more exotic.
    It consisted of a large coil of about 0.5 metre diameter very nicely packaged in white and charcoal grey plastic.
    This was connected by heavy duty mains cable to the control unit.(Mains cable seems to be a popular choice)

    The control circuit was essentially a class D audio amp driven by a waveform function generator.
    Various waveforms and amplitudes could be selected on the front panel.
    These were indicated by a series of LEDs arranged in the shape of the different waveforms..

    Selectable waveforms were Sine,Half Sine,Square and Half Square.
    The frequencies were adjustable from 1Hz to 100Hz and the amplitude from 0 to 150 ???? (Units not defined!)
    A digital timer controlled the duration of the treatment.

    With this machine I also received a set of schematics and a user manual.
    The schematics were a reasonable representation of the actual hardware but some component values were different.
    There were no voltages, currents or waveforms shown.

    Having diagnosed and corrected three faults, I requested data from the manufacturer on how to adjust the pre-sets in the circuit.
    The response was a little vague.
    It seemed that intensity readouts of 0 to 150 and frequency readouts of 0 to 100 were satisfactory.
    However these were derived from the output of the function generator and had little to do with how the power stage handled the signals.

    Supplied with the machine was a small ferrite magnet.
    The instruction in the user manual was to hold this it in the centre of the coil in the palm of the hand.
    This should jiggle (vibrate) more violently as the field intensity increased.

    Class D amplifiers generally require a low pass filter in series with the output to the load.
    This had an LC filter using 10Amp power inductors and a bipolar electrolytic capacitor.
    The low pass characteristic of this filter meant that at all but the lowest frequencies there was little difference between the wave shapes applied to the coil.
    There was a higher frequency ring on all waveforms. This was a little less pronounced when Sine was selected.
    The difference between full and half waveforms was a DC shift which made the magnetic field unipolar.

    (Unfounded anecdote removed)

    The Physics Forun PEMF thread was created in 2009 and was a mix of enthusiasm and scepticism for the technology.
    I'm intrigued to know if more serious research has been done on this technology with available published peer reviews.
    Quantitative rather than qualitative work would be preferred!
    Last edited by a moderator: Jan 20, 2013
  2. jcsd
  3. Jan 20, 2013 #2
    Pulsed electromagnetic fields have been used since the 1840's and remain controversial. The mechanism of action is not well understood. This 2012 paper presents its application in cases of delayed union or non-union of tibial bone fractures. Note this is a prospective study without controls and the result is suggestive but not statistically significant (p=0.08) It's not clear how this value was calculated. Thirty-four patients out of 44 had a successful outcome according to the authors.

    "It seems that the introduction of electromagnetic fields at the fracture site can stimulate the bone in a way similar to mechanical loading [1]. However, there is still ongoing debate regarding the mechanism of action of PEMF at cellular and molecular level. PEMF have been advocated to stimulate the synthesis of extracellular matrix proteins and exert a direct effect on the production of proteins that regulate gene transcription [9]. Electromagnetic fields may also affect several membrane receptors including PTH, insulin, IGF-2, LDL and calcitonin receptors [10]. Moreover, when osteoblasts are stimulated by PEMF, they secrete several growth factors such as bone morphogenic proteins 2 and 4 and TGF-beta [6,11].

    The principle underlying the application of PEMF is that of inductive coupling [6,11]. The electric current is produced by a coil, driven by an external field generator. The outcome is a secondary electrical field produced in the bone [1]. The secondary field is dependent on the characteristics of the applied magnetic field and tissue properties. Magnetic fields varying from 0.1 to 20 G are usually applied in order to produce electrical fields in bone, ranging from 1 to 100 mV/cm [11]. Contra-indications to the use of PEMF include segmental bone loss, infected nonunions, synovial pseudarthrosis and poor stability of fracture site [11]."

    Last edited: Jan 20, 2013
  4. Jan 21, 2013 #3
    Thanks SW VandeCarr for the post.
    I guess I need to learn some of the biological language before understanding what I'm reading.
    My experience with medical equipment revolved around radiation therapy in the Christie Hospital in Manchester UK.
    The major concern was developing systems which controlled the dosage delivered to different parts of the patient. This involved 3D geometry, servo control of position, real time beam intensity control and time control. The idea being to deliver the appropriate dose to the target volume, but minimise exposure in surrounding tissue.
    If PEMF shows promise as a non-invasive treatment, has anyone examined the effects of field orientation on its effectiveness?
  5. Jan 21, 2013 #4
    I don't know but I would think the most effective orientations would be those that maximize the desired characteristics of the induced secondary EM field in the target tissue. The US FDA has approved PEMF therapy for bone fractures utilizing quasi-triangular and quasi-rectangular wave forms.


    http://en.wikipedia.org/wiki/Pulsed_electromagnetic_field_therapy (see History)
    Last edited: Jan 22, 2013
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook