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Thread: Electrical currents?

  1. #1

    Electrical currents?

    Typical stimulation units and machines operate on DC current (direct current). A few others work on AC current (alternating current) From what research states, there is a difference between the two. Findings show that amperes is the part that causes pain when dealing with electricity. One(AC units) has low milliamps/amperes with high voltage but the other (DC units) has high milliamps with low voltage. It's understood that polarization can be switched to offset but the question that remains is: Do DC current stimulation units have enough volts to recruit or activate inactive muscle fibers? If so, what is the amount of time alloted for use without receiving possible nerve or skin damge?

  2. #2
    Quote Originally Posted by zechari View Post
    Typical stimulation units and machines operate on DC current (direct current). A few others work on AC current (alternating current) From what research states, there is a difference between the two. Findings show that amperes is the part that causes pain when dealing with electricity. One(AC units) has low milliamps/amperes with high voltage but the other (DC units) has high milliamps with low voltage. It's understood that polarization can be switched to offset but the question that remains is: Do DC current stimulation units have enough volts to recruit or activate inactive muscle fibers? If so, what is the amount of time alloted for use without receiving possible nerve or skin damge?
    zechari,

    What you call DC (direct current) stimulation is really not DC, in the sense that they are not just application of voltage. All stimulation of muscles require changes in current polarity, whether it is a square wave pulse, more complicating ramped pulses, or AC (alternating current) sinusoidal waves. The reason is because long duration constant current usually produces high impedance in the electrodes and will not stimulate muscle. So, really, what you call DC stimulation is really pulsed current.

    Two factors in biological tissues determine passage of current: resistance (R) and capacitance (C). The product of the two, i.e. R•C, is a complex factor that predicts impedance which is frequency dependent resistance of the tissue. Capacitance is the capacity of the tissue to take up electrons before releasing them. High capacitance slows down increases in voltage associated with any given current pulse. High resistance causes larger voltage changes per current, as described by Ohm's law V = IR where V is the voltage, I is current, and R is resistance.

    When you attach an electrode to the skin, the electrical current that the electrode passes into the skin depends on the resistance and capacitance of the skin. The higher the impedance of the skin, the more energy the skin takes up for a given current. In other words, a small amount of current creates a large amount of voltage which in turn can heat and damage the skin.

    To reduce damage, one needs to reduce the resistance of the skin. You can do this by applying conductive cream that reduces the impedance of the contact surface between the electrode and the skin. You should also use larger electrodes so that the current passage per square mm of skin is less. Finally, you have to pulse the current.

    While there are many devices that make all sorts of claims that different pulse shapes are better than others, the evidence that this actually increases muscle activation is, in my opinion, poorly documented. A "constant current unit" is usually better than a "constant voltage unit" because the amount of current that passes across the skin is what stimulates the muscle.

    A constant current unit may also be more likely to damage skin because it is more likely to produce very high voltages if the electrode is not in good contact with the skin or the surface area of contact is small. In any case, careful application of the electrode is essential for making sure that high currents pass across the skin.

    Most commercial stimulation devices are limited to 20-30 milliamperes (mA) of current pulses. If applied to the skin of a person who has intact sensation in that part of the skin, even 20 mA can be quite painful. The pain increases with duration of the pulses, up to several milliseconds (msec).

    It is also useful to have bipolar pulses, i.e. pulses that is initially in one direction and then go in the opposite direction. This will prevent polarization of the electrode which may increase impedance of the electrodes. On the other hand, this is not a big problem when one is not stimulating for long periods of time.

    Regarding skin damage at the electrode contact point, the first and most frequently observed skin change is redness, almost like a burn. Indeed, heat may be one of the major causes of skin damage at eletrode contact surfaces. The larger the contact surface, the less current per surface area and hence the less the injury.

    Wise.

  3. #3
    Wise,

    You are truly wise! Better explanation than I got in Electrical Engineering 101!

    Thank you for all you do for us. I personnally have found your responses extremely helpful and informative, we a blessed to have you.

    God Bless,

    Bill

  4. #4

    In so many words...

    I noticed you did answer a portion of my question, thanks. You stated,"Most commercial stimulation devices are limited to 20-30 milliamperes (mA) of current pulses. If applied to the skin of a person who has intact sensation in that part of the skin, even 20 mA can be quite painful. The pain increases with duration of the pulses, up to several milliseconds (msec)."

    So in fact you are stating I'm correct, milliamps is the portion that causes pain and most commercial devices fit in the "painful category."

    "Other EMS units achieve the 125 volts at 90 milliamps of current. Neurocare 1000™ achieves the 440 volts at 4 milliamps of current. Patients can normally tolerate a maximum of about 10 milliamps of current, therefore normal EMS units very seldom reach the potential of 90 milliamps and 125 volts, thus they cannot “saturate” the “active” muscle fibers to reach the “inactive” muscle fibers. Ten milliamps on normal muscle stimulators is 30 volts. Four milliamps on the Neurocare 1000™ is 440 volts."
    As read on the Neuro Care website,

    "The Neuro Care™ uses a biphasic pyramidal wave with a frequency of 47 Hz. Duty cycles are fixed at 1.5 seconds on and 1.8 seconds off. There is no ramp time. These settings are preset with the intensity being the only variable.
    Thus allowing an accurate treatment to be administered by the patient or care giver in the patient's home. In medicine there is always a standard, but until the Neuro Care™ 1000 it has been impossible to standardize electro-therapy treatments. All other EMS units have variable settings, so there is no standardization of treatment between patients, even within the clinic setting. Neuro Care's (TM) standardization has allowed practitioners to treat more accurately and consistently when using electro-therapy.

    The Neuro Care (TM) has combined high voltage, ultra low amperage, built-in parameters for ease and simplicity of use to achieve its remarkable effectiveness.

    The Neuro Care™ 1000 is not unique due to its packaging, number of outputs, or portability. These are all very desirable features - but are NOT unique. What separates the Neuro Care™ as being unique, is the aforementioned extreme specificity of its electrical output and its preset parameters. As 104.5 and 105.1 on the radio dial are unique and specifically different and very far apart practically, so is the Neuro Care™ 1000 from other modalities.

    Any deviation from these, tends to be less effacious. Accordingly, these parameters are not adjustable by the operator, thus the operator does not run the risk of producing a sub optimal result. The placement of the electrodes is not critical, which is a tremendous boost to the real world use of these modalities. It is possible to overlap the electrodes and short out, they must not be used face to face. This allows the operator a greatly enhanced degree of flexibility for an individual's determination for best pad placement."

    Thanks for stating my original idea as correct, in as many words.

  5. #5
    I think you're still missing something. As Wise said, it's the current that that stimulates the cells (and also that causes pain, also due to stimulation of cells). Actually, it's the current density, or current per unit area that's important. I suspect that what the "Neuro Care" people are doing is quoting a root-mean-square current; that way by playing with the waveform and duty cycle they can claim a relatively low rms current along with a high peak voltage. Nevertheless, to first order, the higher the voltage the higher the current, and vice-versa; it's hard to get away from that.
    I must also say that I don't find the "Neuro Care" site very informative. For example, they say here, in a page rather strangely entitled as a case study:
    These were so dramatic that our medical department began looking at specific pad placements and protocols for the different symptoms the paralyzed patients were having. The more the symptoms were worked, the more feeling returned. They then turned their attention to protocols directed at opening the neurological pathway at the site of injury to the extremities. Results were seen in every case of paralysis in which the spinal cord was intact. … Although each patient has an individual recovery schedule, there is a pattern of recovery developing as the pathway reopens/repairs.
    and they claim that "This Publication is to assist physicians, practitioners and other medical personnel in developing a treatment program." Frankly, that looks pretty nebulous to me, with vague promises and few or no facts; not something on which I would want my medical practitioner to be basing treatment. But apparently they received FDA clearance to market their product; if their device manages muscle stimulation with less pain, more power to them.
    - Richard

  6. #6

    Re-read it all carefully...

    You misread what Wise stated because nowhere does he mention cells or what you state causes pain. Besides, the topic at hand should be about axons and its sheaths, not cells.

    You also misread/misinterpreted the portion of a treatment program, the protocols and pad placements needed (of which a practicioner not knowledgable about the device would be capable of doing). If you know of a device of AC current and FDA approved for 7 different uses, feel free to fill us in, the SCI community. Until then, it'd be nice for the misquoting or inferring of Wise would be appreciated, thanks.

    You apparently did not read through the site and its referrences etc. It seems that some of Dr. Stephen G. Waxman's work is mentioned along with other material on the site(of whom has various creditations). Neither did I see any "vague promises." What kind of facts should be found other than info of the device, references, and uses?

    When using any device it is common sense for the ultimate factor involved regarding results is "user error." In other words, if a can opener is used incorrectly then it wouldn't open the can.

    The topic at hand is about electrical currents used in devices and I have yet to find another with AC current/FDA approved uses. This wouldn't make this a "typical FES," but more a true NMES able to recruit inactive muscle fibers.

    Think,
    -In a class size 1-30 if one is #30 "he" would still be considered a "doctor," yet he is still given the title (although would be considered in last place).
    Last edited by zechari; 08-25-2009 at 04:08 PM.

  7. #7
    I did omit to mention that contribution to pain caused by destruction of cells due to heating where the current density is highest (near the electrodes); that is different from the direct electrical stimulation of nerve cells that register pain (that I did mention).
    But it's not clear to me that someone isn't playing fast and loose with the complex form of Ohm's law, E=IZ (where Z is impedance).
    - Richard

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