Surgery – Magnetic field applied to body for therapy – Electromagnetic coil
Patent
1995-12-14
1998-02-17
Lacyk, John P.
Surgery
Magnetic field applied to body for therapy
Electromagnetic coil
128897, A61N 100
Patent
active
057186626
DESCRIPTION:
BRIEF SUMMARY
This invention relates to apparatus for magnetically stimulating neurones and in particular neuro-muscular tissue by inducing therein electric current using time varying magnetic fields, and for similar purposes such as the stimulation of cells in cell cultures. Broadly, the invention concerns a magnetic stimulator which is capable of producing pulse trains of which both frequency and amplitude are controllably variable and particularly concerns a stimulator comprising a multiplicity of capacitor discharge units of which the outputs can be coupled in parallel.
In a preferred form of the invention, a multiplicity of discharge units, each of which is capable of independent operation and is disposed to provide an output in parallel with the output of one or more other units so as to provide various outputs such as pulses of greater power or pulse strains of different frequency. Each unit may be coupled to a charging circuit and may include at least one pulse forming capacitor and a controllable discharge circuit.
The various units may be supervised by an electronic control circuit which may itself be controllable by means of a remote controller.
In a preferred form of the invention, the outputs from the discharge units maybe combined and fed to an output so that, for example, two of the units may provide outputs which can be coupled to a first output terminal and two or more further units may provide an output which can be coupled to a second output terminal. This arrangement enables the use of either one or two stimulating coils with independent pulsing control. It also provides for a certain fault tolerance, so that if one or two units failed it would still be possible to utilize one of the outputs of the circuit.
The stimulating power of each unit can be controlled by varying the energy initially installed in the unit by variation of the stored capacitor voltage. Thus a multiplicity of different amplitudes can be selected, one for each of the plurality of magnetic stimulator units for each pulse train thereby to provide amplitude variation or modulation of the pulse train. Random variation could also be employed.
The use of a multiplicity of units in parallel enables the spacing between successive stimulating pulses to be very short, even zero. Frequency modulation can be provided by variation of the interpulse spacing.
The combined outputs from a multiplicity of units may also be such as to increase output power by simultaneous or nearly simultaneous multi-channel discharge.
Each unit may typically recharge in a cycle which lasts approximately two to four seconds depending on the power level, stored energy and charging rate. It is feasible to increase the discharge repetition rate by at least a factor of N where N is the number of capacitors, by discharging all the capacitors in a time sequence. Thus at lower power levels and for a two second recharge time, a 4 Hz discharge repetition rate is possible for an eight capacitor system. More versatile systems containing additional capacitors enabling a wider range of amplitude and frequency variation can be envisaged.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic representation of a magnetic stimulator according to the invention; and
FIG. 2 is a more detailed schematic diagram of part of a stimulator according to the invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
FIG. 1 illustrates an apparatus for providing magnetic stimulation of neuro-muscular tissues by the application of time varying magnetic fields produced by the application of a multiplicity of capacitor discharge pulses to a stimulating coil, which may be, for example, specially shaped to fit the cranium of a patient. For example, the coil maybe in the form described in our published British Patent Application GB-A-2261820.
In the illustrated system, the apparatus comprises two sets of capacitors 3 each having a respective, independently controllable discharge control, connected in parallel to provide one common output for each set of capacitors. The two outputs maybe used to
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