Magnetic field coils - mechanism of tissue action

[Guest guest]

Hello rifers,

There is now plenty literature available describing the primary action of magetic fields on tissues. At the Rife forum, a member posted a link to an article about guidelines for transcranial magnetic stimulation (hat-tip to ): http://www.aipass.org/files/TMS_Safe...guidelines.pdfThis article had an interesting passage that caught my attention. It concerns the primary phenomenon of how magnetic fields work in tissues: they induce e-fields and then low-level current. I wondered how I had missed this in the past! When I checked it out at other sources to see if this concept was verified in them - well, it certainly was.Here's the relevant passage from p. 5 of the article, the writing from which is unusually lucid. By way of background information, the reader will want to know that an electric field will tend to move free charges on the outside of cell membranes, which polarizes the cell into having + and - ends (the charge tends to "bunch up); additionally molecules with charged ends or sidechains will tend to orient (polarize) in the field to some degree, depending on how free they are to move in response to the field.

Quote:

In TMS [transcranial magnetic stimulation], electric charge stored in a capacitor is discharged through a stimulation coil, producing a current pulse in the circuit that generates a magnetic field pulse in the vicinity of the coil. According to Faraday’s law of electromagnetic induction, this time-varying magnetic field induces an electric field whose magnitude is proportional to the time rate of change of the magnetic field, which in the case of TMS is determined by the rate of change of the current in the coil. If the coil is held over a subject’s head, the magnetic field penetrates scalp and skull, and induces an electric field in the brain. The induced electric field causes ions to flow in the brain, without the need for current to flow across the skull and without charged particles being injected into the scalp. In contrast, in transcranial electric stimulation (TES) charge is injected into the scalp at the electrodes and current must flow through the skull. Due to the low conductivity of the skull, in TES a large potential difference must be applied between the electrodes in order to achieve a current density in the brain high enough to stimulate neurons, and this leads to a much higher current density in the scalp. Thus, the ratio of the maximum current density in the scalp to the maximum current density in the brain is much lower in TMS than for TES, allowing TMS to stimulate cortical neurons without the pain associated with TES. The flow of ions brought about by the electric field induced in the brain alters the electric charge stored on both sides of cell membranes, depolarizing or hyperpolarizing neurons. The existence of passive ion channels renders the membrane permeable to these ions: an increased membrane conductance decreases the amplitude of the change in membrane potential due to the induced electric field and decreases the time constant that characterizes the leakage of the induced charge. So we note several steps:1. The external magnetic field induces an electric field in the tissues. It is well known that because air and tissues have nearly exactly the same type of magnetic characteristics, the m-field does not weaken at the air-tissue boundary. However, magnetic fields do weaken with distance from the coil (see below).2. The induced electric field in turn induces current (movement of the charged free ions that are already in the tissues).3. Because cells have what are called "passive ion channels", current (including alternating current) will to some extent pass through membranes even at very low frequencies. Some ion channels respond in a different way: to the voltage difference across the membrane - these are called voltage gated channels. So if an electric field causes ions to "bunch" at the polar ends of cells, that can cause these types of membrane channels to open (or close) at specific regions on the cells' membranes. Note this can happen even at low frequency ranges, because the m-field and/or e-field factors are the initial major triggering influences. And there is evidence that Rife was able to induce an e-field into his lab samples (a subject for another post).If the cells tend to be innately unstable, such as cancer cells are (they have already a low membrane potential difference), or if the cell cannot escape the prolonged influence of the field(s), it can eventually destroy it through various mechanisms, or even make it unable to reproduce.I checked some other sources to verify this inducing action of a magnetic field. In the CRC Handbook of Biological Effects of Electromagnetic Fields (1986), Polk writes on p. 9 (H fields are magnetic fields):

Quote:

Time-varying H fields...may interact with living organisms through the same mechanisms that can be triggered by static H fields, provided the variation with time is slow enough to allow particles of finite size and mass, located in a viscous medium, to change orientation or position where required...and provided the field intensity is sufficient to produce the particular effect. However, time-varying H fields, including ELF H fields, can also induce electric currents into stationary conducting objects... In view of Faraday's law, a time-varying magnetic flux will induce e-fields with resulting electrical potential differences and "eddy" currents through available conducting paths. Polk also gives some real numbers: the induced electric field magnitude is the product of frequency times 2 pi, times the m-field strength, times the closed coil radius, all divided by 2. And that the resultant current density is then the strength of the internal e-field times the conductivity of whatever tissue is being affected (conductivity does vary from one type of tissue to another). He gives an example using a frequency of 60 Hz, a coil radius of 0.1 m, a conductivity of 0.1 siemens/meter. He states that the magnetic flux density required to obtain a potentially physiologically significant current density of 1 mA/meter-sq is 0.53 milli-Tesla or about 5 Gauss." And that "the e-field induced by that flux density along the circular path is 10 mV/meter."So here we not only have verification from a major biophysics text of e-field and current induction by m-field, but an actual mathematical example with real numbers.There's a related article (free full text) at http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2836366/. It has a nice picture at figure 1 showing the m-field, the induced e-field, and the induced current on a person's head. The caption reads:

Quote:

The current flowing in the coil generated a sinusoidally alternating magnetic field, which in turn induced an electric current in the tissue, in the opposite direction. One of the coil device manufacturers was very good to put on his website a diagram of how m-fields attentuate with distance, at http://www.coilmachines.com/rifeimag...neticfield.jpg. For instance, if the strength right at the center of the coil is 200 gauss, it will be approximately 40 gauss at about 5 inches away from the coil surface, and approximately 10 gauss at about 10 inches away.There are a few more interesting details available in some articles - actually quite relevant as frequency range is discussed, but the material cited above shows the major concept of e-field and current induction by an m-field.Char