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1. WO1999000158 - DISPOSITIF POUR INDUIRE UNE ANESTHESIE

Note: Texte fondé sur des processus automatiques de reconnaissance optique de caractères. Seule la version PDF a une valeur juridique

[ EN ]

A device for inducing
anaesthesia
The present invention relates to a device for inducing anaesthesia in the limbs or spinal cord of a patient. More particularly, but not exclusively, the present invention relates to a device for inducing anaesthesia comprising a magnetic field generating means adapted to generate a
rotating magnetic field, the rotating magnetic field being adapted to urge negative charges located within the field towards the axis of rotation of said field.

Several types of anaesthetic are known. Such anaesthetics are almost invariably either injected into, or inhaled by, the patient, and are therefore necessarily intrusive. General anaesthetics depress brain function, suppress protective reflexes such as the gag and cough reflexes and take time to recover from. They are particularly dangerous if the patient has a full stomach or is intoxicated or taking other
medication. They are particularly hazardous to children, the elderly and patients with concurrent illness. There is a small but important risk of death with general anaesthesia.

Local anaesthetics require injections which makes them particularly unsuitable for children. The injection itself is unpleasant, the duration of the effect is limited and the dose that can be given before the onset of toxic side effects is limited. There is a risk of allergic reaction, fits, cardiovascular effects and deaths have occurred from the administration of local anaesthetics.

Accordingly, the present invention provides a device for inducing local anaesthesia in a patient by inhibiting the passage of a nerve impulse through a nerve containing portion of the patient, said device comprising a magnetic field generating means for producing a moving " magnetic field which is rotatable about an axis; and,

a support means arranged to support said nerve containing portion of the patient in such relationship to said axis of rotation so as to co-operate with said magnetic field generating means such that rotation of the magnetic field is able to induce a flow of negatively charged particles within the nerve containing portion towards the axis of rotation of the rotating magnetic field.

The device of the invention inhibits the passage of nerve impulses through the nerve containing portion of the patient located within the rotating magnetic field. Once the device is activated the patient will lose all feeling in any portion of his/her body separated from his/her brain by the rotating magnetic field.

The device of the invention has the advantage that it can be used with patients who have head injuries, are intoxicated or have a full stomach.

The device of the invention also has the advantage that it is safer to use than known anaesthetics.

The device of the invention is also relatively easy to use and so could be used by unskilled staff. There is no
requirement for a skilled anaesthetist to be present. This reduces the cost of surgery and decreases the time preparing the patient before surgery. Surgery can start as soon as the surgeon is ready.

The device of the invention also has the advantage that it can provide instant pain relief. There is often a delay •between administering a known anaesthetic and achieving pain relief.

Preferably, the particles include at least one of ions and molecules .

Preferably, the rate of change of flux linkage between the rotating magnetic field and the nerve containing portion is sufficient to hyperpolarise a portion of a nerve cell membrane of the nerve containing portion so blocking the conduction of nerve impulses by said nerve cell membrane.

Preferably the magnetic field generating means is adapted to produce a rotating magnetic field having a rate of change of flux linkage in a vacuum of at least 10 Webers .πf2. s"1, preferably 50 Webers .m-2. s"1 . A magnetic field generation means producing such a rate of change of flux will
hyperpolarise a nerve cell membrane located within the rotating magnetic field.

Preferably, the magnetic field generating means comprises at least one of an electromagnetic coil or a permanent magnet. The electromagnetic coil can be a superconducting coil. Such coils or magnets provide a simple and inexpensive magnetic field generating means. The magnetic field generating means may further comprise rotation means for rotating the magnet to produce a rotating magnetic field.

Preferably, the magnetic field generating means comprises first and second magnets adapted to generate a substantially uniform magnetic field therebetween, the axis of rotation of said magnetic field being parallel to the field direction of the magnetic field.

Preferably, the device further comprises a charged elongate member which extends along the axis of rotation of the magnetic field, wherein a first end of the elongate member is adapted such that in use it is located proximate to the nerve containing portion of the patient. Such a charged elongate member has the advantage that it attracts charge located in the extracellular fluid surrounding the nerve cell membrane towards the skin of the patient, so increasing the
hyperpolarisation of depolarisation of the nerve cell
membrane .

The elongate member of the device can be an insulator or an insulated conducting rod. Preferably the rod is adapted to abut against the patient when in use.

Preferably, the device further comprises an electrode
connected to the skin of the patient and a conducting wire extending from the electrode along the axis of rotation of the magnetic field to earth. Such an electrode can be used to drain away any excess charge in the extracellular fluid which collects along the axis of rotation of the magnetic field.

In a further aspect the invention provides a method of inducing local anaesthesia in a patient by use of an
anaesthesia device, the anaesthesia device comprising

a magnetic field generating means for producing a moving magnetic field which is rotatable about an axis; and,

a support means arranged to support said nerve containing portion of the patient in such relationship to said axis of rotation so as to co-operate with said magnetic field
generating means such that rotation of the magnetic field is able to induce a flow of negatively charged particles within the nerve containing portion towards the axis of rotation of the nerve containing portion towards the axis of rotation- of the rotating magnetic field; the method comprising the steps of

supporting said nerve containing portion of the patient on said support means and,

generating said rotating magnetic field.

The present invention will now be described by way of example only and not in any limitative sense with reference to the figures in which

figure 1 shows a schematic view of a nerve cell membrane;

figure 2 shows a schematic view of the propagation of a nerve pulse along a nerve cell membrane;

figure 3 shows a perspective view of a device according to the invention;

figure 4 shows a schematic view of the forces on charges within the nerve and in the surrounding extracellular fluid during use of the device according to the invention;

figure 5 shows a further embodiment of the invention in cross section;

figure 6 shows a further embodiment of the invention in cross section; and,

figure 7 shows a schematic diagram of the control circuitry of a device according to a second aspect of the invention.

Shown in figure 1 is a schematic view of a human nerve
membrane 1. Located on the outside of the membrane 1 is an extra-cellular 2 fluid comprising a high concentration of Na ions. Located on the inside of the membrane 1 is an
intracellular fluid 3 comprising a high concentration of K+ ions. In equilibrium the potential difference between the intra- and extra-cellular fluids 2,3 (the membrane potential) is approximately -90mV. The potential of the extra cellular fluid 2 is higher than the potential of the intracellular fluid 3.

Located within the nerve cell membrane 1 are a number of voltage gated sodium channels 4. Each sodium channel 4 comprises two gates, an activation gate 5 and an inactivation gate 6. When the membrane potential is approximately -90mV the activation gate 5 is closed (as shown) so preventing entry of the sodium ions to the interior of the nerve cell membrane 1. The inactivation gate 6 is open and so does not prevent movement of the sodium ions.

As the membrane potential is raised to a potential usually between -70 to -50 mV the activation gate 5 suddenly flips to an open configuration. Sodium ions rush into the
intracellular fluid 3 so raising the membrane potential still further. A few 10, OOOths of a second after the activation gate 5 opens the inactivation gate 6 closes so preventing the further entry of sodium ions. The inactivation gate 6 will remain closed until the membrane potential drops back to approximately -90mV.

Also located within the nerve cell membrane 1 are a number of potassium channels 7. Each potassium channel 7 comprises only one gate, the potassium gate 8. When the membrane potential is approximately -90mV the potassium gate 8 is closed so preventing the diffusion of potassium ions from the intracellular fluid 3 to the extracellular fluid 2. As the membrane potential rises from -90mV towards zero the"
potassium gate 8 opens slowly, becoming fully open just as the sodium inactivation gate 6 is closing. As potassium ions diffuse from the intracellular fluid 3 through the open potassium channel 7 to the extra cellular fluid 2 the
membrane potential drops and the potassium gate 8 slowly closes again.

Impulses travel along a nerve fibre as a localised change in nerve cell membrane potential. At rest the membrane potential along the entire length of a nerve fibre is approximately -90mV. If an external stimulus raises the membrane potential at a point on the membrane 1 above a threshold voltage of -70mV the activation gate 5 of the sodium channel at that point on the membrane 1 opens allowing an influx of sodium ions into the intracellular fluid 3. Shortly afterwards the inactivation gate 6 will close so preventing the further influx of sodium ions. The sodium ions which enter the intracellular fluid 3 through the sodium channel 4 diffuse along the intracellular fluid 3 for typically 3mm so raising the potential at secondary sodium channels 9,10 proximate to the original sodium channel 4. If the potential at the secondary sodium channels 9, 10 exceeds approximately -70mV the activation gates 11 of these secondary channels 9,10 will open. Sodium ions will diffuse from the extracellular fluid 2 through these newly opened sodium channels 9,10 and along the nerve so repeating the process. Hence, once a first sodium channel 4 has opened other channels will open in a wave along the length of the nerve, so transmitting the excitation signal along the length of the nerve. This process is shown schematically in figures 2 (a) -2(c).

The potassium channels 7 open shortly after the sodium channels 4 allowing potassium ions to leave the nerve and hence return the membrane potential back to the resting value of -90mV.

Transmittal of a nerve impulse along a nerve membrane 1 will only occur if the number of sodium ions which enter through an open sodium channel 4 before it closes is sufficient to raise the potential at an adjacent sodium channel 9,10 above -70mV so causing it to open. If this is not the case then the membrane potential signal will cease to propagate along the nerve membrane 1. If when the nerve is at rest the membrane potential is approximately -90mV then sufficient sodium ions can enter through an open sodium channel 4 to raise the potential of an adjacent sodium channel 9,10 from -90mV to the opening threshold potential of -70mV. If however the rest membrane potential of the nerve was lower, say -HOmV, then insufficient sodium ions would enter through an open sodium channel 4 to raise the potential of an adjacent sodium channel 9,10 to -70mV. In this case the opening of one sodium channel 4 would not result in the opening of adjacent sodium channels 9,10 and so nerve impulses will not propagate along such a nerve membrane 1. A nerve membrane 1 in this condition is said to be hyperpolarised.

Shown in figure 3 is a perspective view of a device 11 according to the invention. The device 11 comprises a support means 12 for supporting a nerve containing portion 13 of a patient and a magnetic field generating means 14.

The support means 12 comprises a gutter shaped support 15 into which a nerve containing portion 13 of the patient (for example an arm or a leg) can be inserted. The support means 12 is manufactured from an insulating plastics material and is insulated from the ground. Extending from the support means 12 is a body support (not shown) for supporting the remainder of the patient. The body support is also manufactured from an insulating material. When the patient is positioned within the support means 12 and the body support he/she is insulated from the ground.

The magnetic field generating means 14 comprises first and second co-axial cylindrical permanent magnets 15,16 having a gap 17 between them. The North face of the first permanent magnet 15 is parallel and adjacent to the South face of the second permanent magnet 16. A uniform magnetic field extends between the North and South faces as shown.

In use the nerve containing portion of the patient 13
supported by the support means 12 is located within the magnetic field extending between the permanent magnets 15,16. The nerve is arranged to be substantially orthogonal to the flux lines of the magnetic field.

Each of the permanent magnets 15,16 is free to rotate about an axis 18 parallel to its length as shown. This axis 18 is also parallel to the field lines extending between North and South faces of the permanent magnets 15,16. Each of the magnets 15,16 is connected to a motor 19 which can be
adjusted to alter the rotational speed of the magnets 15,16.

Shown schematically in figure 4 is the effect of the rotating magnetic field generated by the rotating permanent magnets 15,16 on the nerve containing portion of the patient 13. The nerve containing portion of the patient 13 comprises an intracellular fluid 3 in the axon of the nerve fibre
surrounded by a nerve membrane 1. Surrounding the nerve membrane 1 is a extracellular fluid 2 which is in turn surrounded by an the skin 20 of the patient. In this figure the nerve membrane 1 extends in a plane parallel to the page whilst the flux lines of the rotating magnetic field extend perpendicular to the page.

As the field is rotated negative ions and molecules in the intracellular and extracellular fluids 2,3 experience a magnetic force which drives them towards the axis of rotation 18 of the field, as shown. On reaching the axis of the field 18 the negative ions in the extracellular fluid 3 travel along the axis of the field 18 (normal to the page) towards the skin 20 of the patient. The negative ions within the intracellular fluid 2 cannot pass through the nerve membrane 1 and along the axis 18 of the rotating field and so build up in the in the intracellular fluid 2 proximate to the axis of rotation 18 of the magnetic field. This build up in negative charge on the inside of the nerve membrane 1 is not balanced by a similar build up in the extracellular fluid proximate to the outside of the membrane. There is therefore a drop in membrane potential proximate to the axis of rotation 18 of the magnetic field.

Once the membrane potential proximate to the axis of rotation 18 of the magnetic field drops to approximately -HOmV to ~140mV or more the nerve cell membrane 1 becomes
hyperpόlarised and will no longer transmit nerve impulses. A surgeon may therefore operate on any point of the patient beyond this region of hyperpolarisation without the patient feeling any pain.

In a further aspect of the invention (not shown) the magnetic field generating means comprises a pair of co-axial
electromagnetic coils. The coils are connected such that the North face of one coil is adjacent to South face of the other coil. The motor rotates the coils about an axis parallel to their length.

Shown in figure 5 is a further embodiment of a device 11 according to the invention. In this embodiment the magnetic field generating means 14 comprises a pair of rotating permanent magnets 21,22. Extending along the axis of rotation 18 of each magnet is a conduit 23,24. Extending along" each of the conduits 23,24 is a conducting rod 25,26 coated in an insulating material. Each of the conducting rods 25,26 is connected to a means 27 for charging or discharging the conducting rods 25,26. In use, the nerve containing portion 13 of the patient is inserted between the magnets 21,22 and the conducing rods 25,26 adjusted until an end portion 28,29 of each rod 25,26 is proximate to or abuts against the patient. The rods 25,26 are then charged. In use, the charge in the rods 25,26 draws the negative charge in the
extracellular fluid towards the skin 20 of the patient so increasing he hyperpolarisation of the nerve cell membrane 1 proximate to the axis of rotation 18 of the magnetic field.

Shown in figure 6 is a further embodiment of a device 11 according to the invention. In this embodiment the magnetic field generating means 14 comprises a pair of rotating permanent magnets 30,31. Extending along the axis of rotation 18 of one of the magnets 30 is conduit 32 through which extends a conducting wire 33. One end 34 of the wire 33 is connected to an electrode 35 which is in turn connected to the skin 20 of the patient on the axis of rotation 18 of the magnetic field. The opposite end 36 of the conducting wire 35 is connected to earth 37. In use the conducting wire 35 tends to draw the negative charge in the extra cellular fluid 2 towards the skin 20 of the patient and away from the nerve membrane 1. This increases the hyperpolarisation of the nerve cell membrane 1 proximate to the axis of rotation 18 of the magnetic field.

In an alternative embodiment (not shown) the conducting wire is connected to a power supply which can be used to
positively charge the wire during use of the device.

In a further embodiment of the invention (not shown) the,, device comprises an insulating rod which extends along the axis of rotation of the permanent magnet or coil. When the device is in use the rod is charged and pressed against the eppidermal layer of the patient to attract negatively charged ions in the extracellular fluid towards this layer.

Shown in figure 7 is a block schematic of control circuitry 38 for a device 11 according to the invention. Attached to the motor 19 is software controlled circuitry 39 which monitors the rotational speed of the magnets 15,16 and, by a feedback mechanism, ensures that the both magnets 15,16 rotate at the correct angular velocities. Also attached to the motor 19 is temperature monitoring and control circuitry 40 to ensure that the motor 19 does not overheat during use. If the electromagnetic coils are superconducting coils this control circuitry 40 will also measure the liquid nitrogen level in the cryostat surrounding the coils to ensure that they do not make a transition to the normal state during an operation.

The motor 19 is typically driven by a mains power supply 41. Attached to the power supply 41 is monitoring circuitry 42 which will automatically switch to a back up supply 43 if the mains supply 41 should fail in order to ensure that there is no reduction in rotation speed or field strength.

The diameter of the magnets 15,16 and hence the rotating magnetic field would usually be greater than the diameter of the limb on which they are to be used. For instance, for the upper limb of an adult 12-14cm diameter magnets 15,16 would typically be used. For the lower limb of an adult 20cm diameter magnets 15,16 would be used.

The separation 17 between the magnets 15,16 is typically, less than the diameter of the magnets 15,16 although this-depends upon the size and shape of the patient.

Typical magnet rotation rates are of the order 10,000
revolutions per second. Typical magnetic field strengths are of the order 0.5 Tesla although this depends greatly on the size of the magnet used.

The rate of change of flux linkage per rrf2 between the
rotating magnets and a plane perpendicular to the axis of rotation of the magnets can be adjusted. In use, this rate of change of flux linkage proximate to the axis of rotation of the magnetic field is at least 10 Webers .rrf2. s"1, preferably at least 50 Webers .irf2. s"1.