GB2261820A - Coils for magnetic nerve stimulators - Google Patents

Abstract

A stimulating coil for use with a magnetic nerve stimulator has two angularly offset windings 4, 5 disposed side by side. The windings are wound 1 in the shape of part of a dome or cone on a former 2, whereby to increase electromagnetic coupling between the coil and a human head. <IMAGE>

Description

The present invention relates to stimulating coils for use with magnetic nerve stimulators. A magnetic nerve stimulator works by inducing eddy currents in the human tissue using a magnetic pulse. The induced eddy currents stimulate nerves as they are sensitive to electric current.

Once stimulated impulses travel through the nerve fibre away from the site of stimulation.

The progress of the impulse can be monitored and recorded by using electrodes placed near the appropriate nerve fibres or near the muscles activated by the nerve endings. Thus, using the magnetic stimulator, a nerve can be stimulated at one location and the result of the stimulus can be recorded at another location. This allows a physician to assess the function of nerves and muscles.

The ability of the magnetic nerve stimulator easily to stimulate the human brain is the instrument's most useful ability.

It is known to provide a single disc or toroidal shaped stimulating coil suitable for general use on the brain, spinal nerve roots and other deep nerves. Although such a coil produces good responses it suffers from the disadvantage of not being very precise in stimulating specific structures. In particular, the area of the human motor cortex which controls movements in the legs is relatively small and positioned more deeply than other areas of the motor cortex and is difficult to find and stimulate using flat circular coils.

It is also known to provide a stimulating coil system comprising two or more windings placed side by side; this allows much more selective stimulation. The induced eddy current is concentrated under the centre where the windings adjoin. These coils, however, suffer from lower stimulating power even though they are more precise. It has accordingly been proposed to make a large angled double coil by placing two windings side by side and bending these to provide better magnetic coupling and also a better fit on the human head.

The present invention is particularly concerned with a double dome or cone or similarly shaped curved coil which uses the concept of an angled double coil and further improves the performance by increasing the coupling between the coil and head. The coil turns in each part of a double dome or cone or similarly shaped curved coil are progressively offset in the direction of the coil axis so that they define part of a dome or cone or a similar shape.

The two cone or dome or similarly shaped windings may be placed side by side such that the flats or the curvatures of the windings are continuous where they meet. Preferably the windings bare their axis of symmetry at an acute angle to each other.

The accompanying Figures 1 to 6 illustrate various stages in the manufacture of a coil according to the invention.

As shown in Figures 1 and 2 of the drawings, a rectangular copper wire 1 is wound on to a cone or dome or a similar shaped curved metal former 2. Hot melt adhesive is used between the turns to hold the winding together. When cool the winding is removed from the former and forms a rigid structure 3 resembling part of a cone or dome or a similar shape with the top removed as shown in Figures 3 and 4. Two such windings are used in each coil. Each winding is individually insulated which also acts as mechanical reinforcement. The two windings 4 and 5 are then placed next to each other and securely held in place using adhesives or potting compound or similar mechanical restraints such that the flats or curvatures of the windings are continuous where they meet (as shown in Figure 5).The coil is then placed inside a plastic cover and provided with a handle 6 that includes one or more manually operable switches 7, as shown in Figure 6.

The use of a coil having two windings each of which has a diameter or span which progressively decreases in the direction along the magnetic axis or axis of symmetry.

produces a much better fit to the human head. All the individual turns of the windings are more proximal to the brain than is the case in other designs. This improves the magnetic coupling and also allowing for easier placement on the head. This results in increased stimulating power and also increased depth of penetration.

A coil as described above may also used to stimulate neuromuscular tissue in the other parts of the body as appropriate. The geometry and curvature of the windings is determined in these cases to fit the outer shape of the area to be stimulated and such that with the two windings placed side by side the flats or the curvatures of the windings are continuous where they meet. This is done to ensure close magnetic coupling with the body especially at the point of peak power where the windings meet.

Claims (2)

CLAIMS:

1. A stimulating coil suitable for use with a magnetic nerve stimulator and comprising two windings disposed side by side, each winding being shaped to conform to part of a dome or cone.

2. A stimulating coil suitable for use with a magnetic nerve stimulator and comprising two angularly offset windings disposed side by side, each winding having a diameter or span which progressively decreases along the axis of the winding.