GB2397231A

GB2397231A - Feeding tube or catheter having internal conductors connected to external moulded annular electrodes

Info

Publication number: GB2397231A
Application number: GB0301180A
Authority: GB
Inventors: Paul Ellsmore
Original assignee: EP ADVANCE Ltd
Current assignee: EP ADVANCE Ltd
Priority date: 2003-01-18
Filing date: 2003-01-18
Publication date: 2004-07-21
Also published as: AU2003282240A1; GB0301180D0; WO2004065098A1

Abstract

An electrode is formed on the external surface of a elongate member 3 having a lumen 2 and an internal electrical conductor 4, the member preferably being a catheter or a feeding tube (see fig. 1). Preferably the conductor 4 is arranged longitudinally within the wall 3,4' of member. The construction method comprises a first step of exposing the conductor within the member, preferably by laser ablation of the material 6 adjacent the conductor (see figs 3a-f, 4a-b) and a second step of forming an electrode on to the external surface of the member in electrical contact with the exposed conductor. Preferably the electrode is annular and formed by moulding (see figs 5,6) of conducting material, such as a conducting plastic, onto the member. The moulding may comprise a step of either stretching the member during the moulding process or pressurising the internal lumen of the member during the moulding process.

Description

An elongate member having an internal electrical conductor, and a method

of manufacture thereof The present invention relates to an elongate member having an internal electrical conductor such as, for example, a catheter that can be used as a neo-natal feeding tube.

It also relates to a moulding process suitable for, but not limited to, use in the manufacture of such an elongate member.

Newborn babies who are unwell, or who were born prematurely, are normally fed by means of a feeding tube that is passed directly into the oesophagus of the baby, for example through the baby's nose. A feeding tube for a neo-natal baby, or "neo-natal feeding tube", typically consists of a piece of plastic tubing having an outside diameter of around 1.7mm and a length of about 30cm. The tube has a hole, or lumen, having a diameter of around 0.6mm running its full length. Liquid containing nutrients and/or medicine is fed into the end of the feeding tube that is outside the baby, for example by using a syringe. The liquid passes through the lumen of the feeding tube, and passes directly into the oesophagus of the baby by means of one or more holes at the internal end of the feeding tube.

Premature or unwell babies may also require to have their heart rate and breathing monitored. This has been done by placing external electrodes on, for example, the baby's chest - but this has been found to be undesirable. A newly born baby has a fragile skin, and the skin may well break when an electrode is applied. This is uncomfortable for the baby, and also introduces the risk of infection.

It has been proposed to provide a neo-natal feeding tube with one or more electrical conductors running along its length. The end of the feeding tube that is to be inserted into the baby is provided with one or more electrodes that are connected to the, or to a respective, electrical conductor disposed within the feeding tube. At the external end of the feeding tube, the or each electrical conductor forms, or is electrically connected to, a lead which can be connected to instruments such as an electrocardiograph. r

Neo-natal feeding tubes that are provided with an electrical conductor running along their length are disclosed in, for example, GB-A-2 254 253 and EP-A-0 582 400.

A conventional feeding tube with electrodes is manufactured in the following way.

Initially, plastic tubing is formed by an extrusion process. The tubing is extruded with one lumen for passing food and medicine into the baby, and with at least one additional lumen for carrying an electrical wire. The tubing is extruded in long lengths, and this is then cut into sections of the correct length for a neo-natal feeding tube.

A wire is then inserted into the additional lumen in the feeding tube. This is normally done by making an opening in the wall of the tube at the position where it is desired to form an electrode, such that the opening connects with the additional lumen. One end of a piece of wire is then inserted into this hole, and the wire is pushed into and along the lumen until the free end protrudes from the lumen at the other end of the tube (which will become the instrumentation end of the feeding tube). A metallic electrode is then placed over the external surface of the feeding tube in such a way that it makes contact with, and so is electrically connected to, the wire. For example, a cylindrical metallic hoop may be swayed in place over the feeding tube and the wire - the swaying process makes electrical contact between the wire and the hoop, and the hoop acts as the electrode.

The wire that protrudes from the feeding tube at the instrumentation end is normally turned into a "flying lead". A suitable electrical connector, such as a spring-loaded clip or a plug, is attached to the wire, to enable connection to instrumentation. Since the wire itself is very fine and has little physical strength, the connector is attached to the tube by means of a stress-relief member so that the connector does not exert any force on the wire.

The conventional process described above is very labour intensive, and the cost of manufacturing a feeding tube is therefore high. The cost is particularly important, since the feeding tubes must be disposed of after use, for reasons of hygiene, and cannot be re-used. Normally the electrical connectors and stress relief members are disposed of with the feeding tube, since it would require time and effort to remove these and the parts would be rendered unusable by the removal process.

A first aspect of the present invention provides a method of providing an elongate member having an internal electrical conductor extending longitudinally therein with an electrode, the method comprising: exposing a first portion of the internal electrical conductor; and forming a first electrode on an external surface of the member so as to be in electrical contact with the exposed first portion of the electrical conductor.

Where the method of the present invention is applied to a catheter, one or more electrical conductors are disposed within the wall of a length of catheter tubing before it is cut to length. This may be done by coextruding the electrical conductor(s) with the catheter tubing. The electrical conductor is exposed at a site where it is desired to provide an electrode. An electrode may then be formed on the external surface of the catheter tubing so as to be in electrical contact with the exposed portion of the conductor. The extruded tubing is cut into a suitable length for a catheter, either before or after formation of the electrode.

It has conventionally been believed that the material of the catheter tubing - normally a polymer material - would adhere so well to fine electrical wires that it would be impossible to expose a wire embedded in the catheter wall to enable connection to an electrode without damaging and breaking a wire. It has, however, been found that the catheter material may be removed, without damage to the wire, by means of a thermally-induced ablation process, such as a laser ablation process.

The method may further comprise the steps of: exposing a second portion of the electrical conductor, the second portion being spatially separated from the first exposed portion along the length of the elongate member; and forming a second electrode on the external surface of the elongate member so as to be in electrical contact with the exposed second portion of the electrical conductor. When applied to a catheter, this embodiment provides a catheter having two electrodes - one electrode disposed at or near the instrumentation end of the catheter, and another electrode disposed at or near the other end of the catheter. The two electrodes are electrically connected to one another by means of the conductor disposed in the wall of the catheter. The electrode at the instrumentation end is used for connection to instrumentation. This avoids the need; to provide the "flying leads" and the associated stress-relief members. Furthermore, leads and connectors used to connect the electrode at the instrumentation end of the catheter to instrumentation can be re-used - whereas, in a conventional catheter feeding tube the flying leads and stress relief members must be disposed of together with the catheter.

The invention also provides a method of moulding comprising the steps of: stretching a former substantially along a longitudinal axis thereby to reduce its dimension along a transverse axis; and disposing a mould around the former. Because the dimension of the former, in the transverse direction, has been reduced the risk of the mould pinching the former and thereby damaging it is reduced. This method is particularly advantageous where the mould comprises two or more portions that are closed around the former. It may be applied with any former that is elastic and so will shrink in one I dimension if stretched in another, non-parallel, direction.

The invention also provides a method of moulding comprising the step of: pressurizing I the interior of a hollow former to a pressure above atmospheric pressure during the step of moulding material onto an exterior surface of the former. This prevents the interior of the former from collapsing during the moulding process.

Further aspects and preferred features of the present invention are defined in the appended claims.

Preferred embodiments of the present invention will now be described by way of illustrative example with reference to accompanying figures in which: Figure l(a) is a side view of catheter according to the present invention; Figure l(b) is a schematic sectional view of a catheter according to the present invention; Figure 2(a) is a cross-section through a catheter according to the present invention; Figure 2(b) is a cross-section view through an alternative catheter according to the present invention; Figure 3(a) is a partial sectional view of a catheter according to the present invention; Figures 3(b) and 3(c) are crosssectional views through the catheter of figure 3(a); Figure 3(d) is a partial sectional view of a catheter according to another embodiment of the invention; Figures 3(e) and 3(f) are cross-sectional views of the catheter of figure 3d; Figure 4(a) shows the catheter of figure 2(a) after removal of material; Figure 4(b) shows the catheter of figure 2(b) after removal of material; Figure 5(a) is a schematic view of a moulding tool for use in manufacture of a catheter of the present invention; Figure S(b) is a schematic cross-section though the moulding tool of figure 5(a); Figure 5(c) is a longitudinal section of the moulding tool of figure 5(a); Figure 6(a) is a schematic sectional view of another moulding tool for use in the manufacture of a catheter of the present invention; and Figure 6(b) is a cross-sectional view through the moulding tool of figure 6(a).

The present invention will be described with particular reference to a catheter intended for use as a feeding tube, such as a neo-natal feeding tube. The invention is not, however, limited to this, and may be applied to any catheter. Indeed, the invention is not limited to catheters, and may be applied to an elongate member that does not have an internal lumen.

Like reference numerals denote like components throughout the drawings.

Figure l(a) shows a catheter 21 according to the present invention, Figure l(b) is a schematic sectional view of the catheter 21 of Figure l(a), and Figure 2(a) is a cross- sectional view through the catheter 21 of Figure l(a). As can be seen, the catheter 16 consists essentially of a tube I having a feeding lumen 2 surrounded by a wall 3. One or more electrical wires extend for substantially the entire length of the tube 1. The tube l of figure 1 contains two wires 4, 5 but the invention is not limited to this and, in principle, only one wire or more than two wires could be provided.

The catheter 1 further comprises two sets of electrodes. One set of electrodes Al, B1 are disposed at or near the end of the catheter that is intended to be inserted, in use, into the oesophagus of a baby when the catheter is used as a feeding tube. The other set of electrodes, in this embodiment formed by the electrodes A2 and B2, is placed at or near the end of the catheter that will, when the catheter is in use as a feeding tube, be outside the baby (this end will be referred to as the "instrumentation end" since it will in general be connected to monitoring instruments).

One electrode Al of the first set and one electrode A2 of the second set are each connected to the wire 4. Thus, any electrical signals received in the baby's oesophagus by the electrode Al are transmitted along the wire 4 to the electrode A2. Similarly, the other electrode B1 of the first set and the other electrode B2 of the second set are connected to the other wire 5 in the wall 3 of the catheter 16, so that electrical signals received at the electrode Bl are transmitted along the wire B5 to the electrode B2. In use, monitoring equipment may be connected to the electrodes A2, B2 by means of suitable leads and connectors, and this allows electrical signals received at the electrodes Al, B1 within the baby's oesophagus to be transmitted to monitoring equipment. For example, a lead may be connected to one of the electrodes A2, B2 using a springloaded clip.

As indicated in figure 1, the wires 4, 5 extend over substantially the entire length of the catheter 1. This allows the catheter tubing to be produced by a reel-to-reel process in which a large length of tubing having integral electrical wires is produced, the tubing is then cut into individual lengths each suitable for a catheter, and electrodes are added at desired locations. Alternatively, electrodes may be added before the catheter tubing is cut into lengths suitable for individual catheters.

A method of manufacturing the catheter 16 shown in figures l(a) and l(b) will now be described.

Initially, catheter tubing having integral electrical wires is manufactured. This can be carried out in any convenient manner. In one preferred embodiment, a co-extrusion process is used, and this introduces the wires 4, 5 into the molten material that will form the wall 3 of the catheter tubing as it passes through the extrusion die. The material for the wall 3 may in principle be any flexible, non-toxic material, and is conveniently a plastics material or a polymer material. The result of such a co-extrusion process is that the wires 4, 5 are firmly embedded in the wall 3 of the tubing, and are completely enclosed by the material of the wall. This is shown in figure 2(a).

An alternative method of manufacturing the tubing is to extrude the tubing with more than one lumen. In addition to the feeding lumen 2, the tubing would have at least one additional lumen for carrying an electrical wire. This is illustrated in figure 2(b), which shows tubing having a feeding lumen 2 and two additional lumen 4', 5' for carrying a wire. In this embodiment, it is necessary that the internal diameter of each wirecarrying lumen 4', 5' is greater than the external diameter of the wire 4, 5 that it is desired to introduce into the lumen, since it will otherwise be very difficult to insert the wire into the lumen. As a result, the wires 4, 5 make incomplete contact with the material of the tubing wall 3, as indicated schematically in figure 2(b). The degree of contact between the wires and the tubing wall can be modified and controlled by introducing air pressure into the wire-carrying lumen 4, 5 through the extrusion die.

A further method of producing the tubing having integral electrical wires is a "braiding process", in which the wires are introduced to the outer surface of the tubing in a spiral fashion and embed themselves into the material of the wall. The braiding process requires that the tubing has solidified after the extrusion process, and may be carried out immediately the tubing has left the extrusion tool or at any subsequent point. The tubing may optionally be "polished" to cause the surface of the tubing to re-melt and completely cover the wires. This achieves a similar result to the co-extrusion process of figure 2(a) since the wires are fully embedded in the wall 3 of the tubing.

The electrical wires 4, 5 may each be a single strand of wire, or they may be a multi- stranded wire. Multi-stranded wire has the advantage that adhesion between the electrode material and the wire may be greater, since the additional surface area of the additional surface area of multi-stranded wire helps to "key" the electrode material in place.

Once the tubing with integral wires has been manufactured, it is then necessary to expose the wires 4, 5 at locations where it is desired to provide an electrode. The wires 4, 5 are very fine, typically with a diameter of less than 0.3mm. It has conventionally been believed that removing the overlying wall material without damaging or breaking the wires 4, 5 would be very difficult, if not impossible. It has, however, been found that a laser ablation process, or other thermally-induced ablation process, may be used to remove wall material overlying a wire 4, 5 without damaging the wire. All that is necessary is to remove the wall material over a small, accurately defined area so that the electrical material, when it is applied, may make electrical contact to the appropriate wire 4, 5.

Figures 3(a) to 3(c) illustrate a laser ablation process for removing wall material to expose a wire 4. Figure 3(a) is a partial sectional view through a catheter tubing, at a point where it is desired to provide an electrode. Laser radiation, indicated schematically by "hv', in Figure 3(a) is directed at the catheter tubing so that material is removed from a region 6 of the wall 3 until the wire 4 is exposed. Use of a laser ablation process allows the material of the wall to be removed over a small, accurately defined region.

As an example, an Excimer laser operating at 193nm, with a pulse repetition frequency of lkHz and pulse energy of 20mJ will successfully remove polyurethane at a rate of about one micron depth per shot, over an area of a few square millimetres or less. This pulse energy is not sufficient to damage the conductor with a single shot, and the conductivity of the wire is high enough to avoid cumulative heating problems. Other laser types, such as an Nd:YAG can also be used.

The laser ablation process may conveniently be controlled by monitoring the amount of laser radiation reflected by the catheter. The reflectivity of the conductor is much higher than the reflectivity of the plastic wall of the catheter, and the amount of reflected light will therefore increase when the wall has been ablated to a depth sufficient to expose the conductor.

Figure 3(b) is a cross-section through the section indicated as C-C in figure 3(a), and again shows the region 6 where wall material has been removed by the laser ablation process so as to expose the wire 4. Figure 3(c) is included for comparison, and shows a cross-section through the catheter of figure 3(a) in a region A-A where the laser ablation process has not been carried out.

In addition to removing wall material in order to expose a wire, the laser ablation process may be used for further processing of the catheter tubing. As shown in figure 3(d), it may be used to form an annular recess 7 extending around the outer circumference of the catheter tubing, which will receive the electrode when this is applied. The annular recess may be formed before or after material is removed from the region 6. The laser ablation process may also be used to etch a pattern into the exposed surface of the tubing wall, in order to improve adhesion between the electrode material and the tubing.

Figure 3(e) is a cross-section through the catheter of figure 3(d) along the line D-D showing the region 6 of material removed to expose the wire 4 and the annular recess 7.

Figure 3(f) shows, for comparison purposes, a cross-section through the catheter of figure 3(d) along the section B-B where no material has been removed.

In principle, a mechanical process could be used to remove wall material to expose the wire 4, but it extremely difficult to do this successfully using a mechanical process. A mechanical process may, in principle, be used to form the annular recess 7 in the embodiment of figure 3(d), although in practice it is likely to be more convenient to form the annular recess using laser ablation if laser ablation has been, or will be, used to expose the wire 4.

A further advantage of the laser ablation process, over a mechanical process, is that laser ablation is able to "undercut" the wire 4, by removing material from underneath the wire. This is illustrated in figure 4(a), in which the region 6 of removed material extends underneath the wire 4. The advantage of undercutting the wire 4 is that, when the electrode is applied, there is a greater contact area between the electrode and the wire, and this makes a more solid attachment and also provides improved electrical contact. Furthermore, when the electrode is deposited by moulding, as will be described below, the molten electrode material can flow around the wire 4 thereby "keying" the electrode material in place.

A laser ablation technique may also be used when a wire is carried in separate lumen, as shown in figure 2(b). In this case, material has to be removed until the region of removed material 6 breaks through into the lumen 4' in which the wire 4 is disposed.

Where the electrode is applied by a moulding process, the electrode material is able to flow into the lumen 4' carrying the wire, and can also flow along the lumen 4' to some extent. This ensure that there is good mechanical and electrical contact between the electrode and the wire 4.

Where the tubing contains braided electrical wires, a laser ablation process may again be used to remove wall material in order to expose the wires. It is again possible to "undercut" the wires in order to improve the mechanical and electrical contact between the electrode and the wires.

If the wires 4, S are insulated, it is of course necessary to remove the insulation from the wires in order to ensure good electrical contact between the wires and the electrode. A laser ablation process is again effective at removing insulation and, unlike a mechanical process, is able to remove the insulation with a low risk of causing damage to the conductive core of the wire.

In principle, once the wire 4 has been exposed, it is possible to form an electrode in any convenient manner. One preferred method of forming an electrode, however, is to mould the electrode in-situ on the catheter tubing. The electrode may be moulded using any suitable material such as, for example, a conductive plastics material; this may be a thermoplastics material that contains a conductive material. The material for the electrode may alternatively consist of a non-conductive polymer or adhesive host material that contains a conductive guest material. For example, an adhesive material that is loaded with silver or graphite to provide the desired electrical conductivity may be used as the material to form an electrode. The moulding process may be an injection moulding process, in which the electrode material is moulded under pressure to form the electrode. Alternatively, the moulding process may use a solventdiluted conductive material, which is put in place and is then allowed to harden through evaporation of the solvent. As further alternatives, a Wcuring conductive material or a heat-curing conductive material may be used.

Figures 5(a) to 5(c) are schematic illustrations of a mould that is suitable for moulding an electrode of a catheter of the present invention using an injection moulding process.

Figure 5(a) is a side view of the mould 16. Figure 5(b) is a crosssection along the line E-E, and figure 5(c) is a longitudinal section through the mould. The mould 16 consists of two mould tools 8, 9, and these will be referred to as "upper" and "lower" mould tools respectively for convenience of description, although the mould is not limited to use in the orientation shown in figure 5(a) to 5(c).

Figure 5(a) shows the two mould tools 8,9 separated from one another. The upper mould tool 8 has a recess, having a cross-section that corresponds to the external cross- section of the catheter, in one face 11. The lower mould tool 9 has a recess 12, again having a cross-section that corresponds to the external cross-section of the catheter, in a face 13. When the mould is closed, the face 11 of the upper mould tool abuts against the face 13 of the lower mould tool 9, and the two recesses 10, 12 co-operate to form a recess having a cross-section that is substantially the same, in shape and size, as the external cross-section of the catheter tubing that is to be provided with an electrode.

The mould 16 shown in Figure 5(a) is intended for use with a catheter having an approximately circular external cross section, and each recess 10,12 therefore has a cross-section that is approximately semi-circular with a radius that is substantially equal to the external radius of the catheter tubing that is to be provided with an electrode. The invention is not however limited to use with a catheter having a circular external cross section.

The face 11 of the upper mould tool 8 comprises a further recess 1 4 which is continuous with the first semi-circular recess 10. The second recess 14 again has a cross-section that is substantially a semi-circle, but it has a greater radius than the first recess 10. A similar recess 15 is provided in the face 13 of the lower mould tool 9. When the two mould tools are brought together, the recess 14 in the upper mould tool and the second recess 15 in the lower mould tool 9 co-operate to form an annular recess with a diameter equal to the desired diameter of one of the electrodes At, B1, A2, B2.

In operation, a length of catheter tubing which has previously been processed to expose one of the wires is inserted into the moulding tool 16, such that the region 6 where the wall of the tubing has been removed to expose a wire 4 is adjacent the larger-diameter recess 14,15 in one mould tool. The two mould tools 8,9 are then brought together such that the face 11 of the upper mould tool abuts against the face 13 of the lower mould tool 9. Molten electrode material is then injected into the recess 14,15 via a hole (not shown) in one of the moulding tools, thereby to form the electrode around the catheter tube. The molten electrode material also flows into the region 6 of the tube where the wall material has been removed, so that there is good mechanical and electrical contact between the electrode material and the wire.

The injection moulding process may be carried out by means of positive pressure on the injection side of the tool, by negative pressure on the vented side of the tool, or by a combination of both. As mentioned above, one mould tool is provided with a suitable hole to enable material to be injected into the mould and a suitable vent (also not shown) is provided in the other mould tool.

The injection moulding process illustrated in figures 5(a) to 5(c) is an "over-moulding" process, since the mould 16 closes over the catheter tubing. The tool must close around the catheter tubing with a close tolerance fit, to prevent what is known as "flashing" where molten material injected into the mould is forced out of the area where it is intended to go. In order to ensure that there is a close tolerance fit between the mould tools 8,9 and the catheter tubing (except in the vicinity of the large-diameter recesses 14,15), it is preferable to stretch the catheter tubing longitudinally by applying a suitable stretching force along the catheter tubing. The tubing is, to some extent elastic, so that stretching the tubing longitudinally will reduce the diameter of the tubing. Once the tubing has been stretched, the mould 16 is then closed around the stretched catheter tubing. The tensile force is then released, to allow the catheter tube to relax back to its normal diameter. This enables a close tolerance fit to be obtained between the tubing and the mould tools, without there being risk of the tools accidentally 'pinching" the tubing when they are brought together.

The moulding tool 16 of figure 5(a) to 5(c) is able to form a single electrode. It would alternatively be possible to use a single moulding tool to form two or more electrodes - for example the electrodes Al and Bl or the electrodes A2 and B2 - in one operation.

Some existing products have as many as 10 closely spaced electrodes at or near the end intended to be inserted into a baby's oesophagus and, by use of an appropriate moulding tool, it would be possible for these electrodes to be moulded in a single operation using the method of the invention. In principle, it would even be possible to mould all electrodes on the catheter 21 of figure l(a) in one single operation, by use of an appropriate moulding tool.

Figure 6(a) and 6(b) show another mould 16' that can be used to mould an electrode according to the method of the present invention. This is amodification of the mould 16 of figures S(a) to 5(c), and the features that are common to the previous mould will not be described again. Figure 6(a) shows a longitudinal section through the mould 16', and figure 6(b) shows a cross- section through the mould 16'.

The upper moulding tool 8' of the mould 16' contains portions 17, 19 where the recess has a reduced diameter. One of these reduced diameter portions is disposed on one side of the large-diameter recess 14 for moulding the electrode, and the other reduced diameter portion 19 is disposed on the other side of the large-diameter recess 14 for moulding the electrode. The lower moulding tool 9' similarly has a recess 12 that has regions 18, 20 of reduced diameter. The reduced-diameter regions 18, 20 of the lower mould portion 9 are placed generally opposite the reduced- diameter portions 17, 19 of the upper mould tool.

When the upper and lower mould tools 8', 9' are brought together, the reduced diameter portions 17,18; 19,20 will pinch the catheter tubing and reduce its internal diameter.

This will cause the feeding lumen 2 to close - either partially or completely, depending on the extent to which the diameter of the recess 10 is reduced in the reduced-diameter regions 17,18; 19,20. This closure of the feeding lumen 2 will tend to trap air within the volume of the feeding lumen 2 defined by the two points at which it is partially or completely closed by the reduced-diameter portions. As is clear from figure 6(a), this volume is in the vicinity of, and extends on either side of, the recesses 14, 15 that define the electrode. As a result, the tendency of the injection moulding pressure to collapse the feeding lumen 2 will be resisted, by means of the gas trapped within the feeding lumen.

Additionally, or alternatively, the feeding lumen can be pressurised to above atmospheric pressure when material is injected into the mould, by supplying gas under pressure to the feeding lumen. Pressurising the feeding lumen in this way will again resist the tendency for the injection moulding pressure to collapse the feeding lumen.

The required pressure in the feeding lumen will depend on the viscosity of the material to be injected and on the injection rate.

The technique of pressurising the food lumen can be applied with either the mould of figure 5(a) to 5(c), or the mould of figure 6(a) and 6(b). It is possible to pressurise the feeding lumen of an entire reel of catheter tubing, or the feeding lumen can be pressurised locally by making a side hole through the wall 3 into the feeding lumen to enable the feeding lumen to be pressurised in one or more selected areas.

The reduced-diameter portions 17,18; 19,20 of the mould 16' of figure 6(a) have a further advantage, which relates to the embodiment of the catheter shown in figure 4(b).

Where a wire 4, 5 is extruded into a separate lumen 4', 5', there will be a tendency for the electrode material to migrate along the lumen during the process of moulding the electrode. While this is desirable to some extent, since it ensures good mechanical and electrical contact between the electrode and the wire, it is undesirable for the electrode material to migrate too far through the lumen because this may reduce the flexibility of the catheter. Furthermore, if the catheter is made of transparent material migration of electrode material will be visible to a user and so will diminish the aesthetics of the catheter, particularly if the migration distance varies from one electrode to another. The areas of reduced-diameter in the mould of figure 6(a) will not only constrict the feeding lumen 2, but they will also constrict a wire-carrying lumen 4', 5', and so will confine the migration of the electrical material along a wire-carrying lumen.

Once electrodes have been provided, for example by moulding, at all desired positions on the catheter tubing, the tubing may then be cut to length to form a catheter 21 of the general arrangement shown in figure l(a) or l(b). A conventional syringe fitting (not shown) may then be provided at the instrumentation end of the catheter to enable food and medicine to be introduced into the catheter.

The invention has been described above with reference to a process in which a reel of catheter tubing is prepared, electrodes are fitted, and the tubing is then cut into lengths to form individual catheters. The invention is not, however, limited to this order of carrying out the principal steps, and the tubing could be cut to length before the electrodes are applied.

The present invention makes it possible to easily provide a catheter having electrodes at any desired position. In particular, as shown in figure l(b), it is possible to provide two (or, in principle, more) electrodes that are connected to one wire. It is simply necessary to expose the wire at each position where it is desired to form an electrode connected to that wire, and then provide electrodes at those positions. In particular, this allows a wire to be provided with one electrode at or near the instrumentation end of the catheter 21 as well as with an electrode at or near the end of the catheter intended to be inserted into a baby's oesophagus. Providing an electrode at the instrumentation end of the catheter 21 allows easy contact to be made to instrumentation, and also allows electrical connectors to be re- used. In the conventional manufacturing method, however, it is I very difficult to provide more than one electrode connected to a wire. This is because the conventional process requires that the wire is inserted into a pre-existing lumen, by making a transverse hole in the wall of the catheter, and pushing the wire into the hole and through the lumen. It would, however, be extremely difficult to push a wire into one transverse hole in the side of the catheter, and pull it out through another transverse hole in the side of the catheter. ; The method of stretching the catheter tubing longitudinally by applying a suitable stretching force in order to reduce its diameter before the moulding is closed around the stretched catheter tubing is not limited to use with moulding an electrode onto a catheter tubing. It may in principle be applied to any moulding process that involves over- moulding onto a former that is elastic and so can be caused to shrink in one dimension by stretching it in another, non-parallel direction. ]7

Similarly, the method of pressurising the interior of a hollow former to a pressure above atmospheric pressure during the step of moulding material onto an exterior surface of the former is not limited to manufacture of a catheter. It may be applied in any moulding process that involves over-moulding onto a hollow former, to prevent collapse of the former during the moulding process.

In the embodiments described above, the catheter has been provided with annular electrodes. The invention is not however limited to annular electrodes, and may be applied to provide electrodes having other shapes. Annular electrodes are preferred in a catheter intended for use as a feeding tube, to ensure contact between the electrode and the inner wall of the baby's oesophagus. In other applications the catheter may be immersed in a fluid, such as blood for example, and in such applications the electrode is not required to be a full annulus. A "dot" electrode, for example, may be used - since the electrode is immersed in fluid, good electrical contact will exist between the electrode and the fluid regardless of the shape of the electrode. For some applications, it may be useful if the catheter has a pattern of dot electrodes provided on its surface, with each dot electrode being connected to a different one of the conductors disposed within the catheter wall.

A "dot" electrode would be very hard to produce using conventional techniques. It is however straightforward to produce a dot electrode using the method of the invention.

For example, removing material from the wall of the catheter to produce a region 6 as shown in Figures 3(a) and 3(b), moulding the electrode, and removing any excess electrode material from the surface of the catheter will produce a dot electrode.

The invention has been described with reference to a catheter but, as noted hereinabove, the invention is not limited to a catheter but may be applied generally to elongate members. For example, it is possible to envisage products having the sole purpose of retrieving electrical signals and that are not required to deliver food or drugs. Such a product could be manufactured according to the methods described above, with the only difference being that member could be formed without the internal feeding lumen 2 since the feeding lumen would not be required.

Claims

CLAIMS: 1. A method of providing an elongate member having an internal

electrical conductor extending longitudinally therein with an electrode, the method comprising: exposing a first portion of the internal electrical conductor; and forming a first electrode on an external surface of the member so as to be in electrical contact with the exposed first portion of the electrical conductor.
2. A method as claimed in claim 1 and comprising forming the member by coextruding an electrical conductor with the member, thereby to form the elongate member having the internal electrical conductor.
3. A method as claimed in claim 1 or 2 wherein the step of exposing the first portion of the electrical conductor comprises thermally-induced ablation of the elongate member overlying the first portion of the conductor.
4. A method as claimed in claim 3 and comprising laser ablation of the elongate member overlying the first portion of the conductor.
5. A method as claimed in any preceding claim wherein the step of forming the electrode comprises disposing a conductive material on the external surface of the elongate member so as to be in electrical contact with the first exposed portion of the electrical conductor.
6. A method as claimed in claim 4 and comprising moulding the conductive material on to the external surface of the elongate member.
7. A method as claimed in any preceding claim wherein the step of forming the electrode comprises forming an annular electrode.
8. A method as claimed in claim 6 wherein the moulding step comprises: stretching the elongate member substantially along its longitudinal axis; disposing a mould around the elongate member; and relaxing the tensile force.
9. A method as claimed in any preceding claim wherein the elongate member is a catheter having a wall and an internal lumen and wherein the internal electrical conductor is disposed within the wall of the catheter.
10. A method as claimed in claim 9 when dependent from claim 6 or 8 and further comprising pressurising the internal lumen of the catheter tubing during the step of moulding the conductive material on to the external surface of the elongate member.
11. A method as claimed in claim 9 when dependent from claim 6 or 8 and further comprising closing or substantially closing a portion of the lumen of the catheter tubing during the step of moulding the conductive material.
12. A method as claimed in any preceding claim and further comprising the steps of: exposing a second portion of the electrical conductor, the second portion being spatially separated from the first exposed portion along the length of the elongate member; and forming a second electrode on the external surface of the elongate member so as to be in electrical contact with the exposed second portion of the electrical conductor.
13. A method of providing an elongate member having an internal electrical conductor extending longitudinally therein with an electrode substantially as described herein with reference to the accompanying drawings.
14. An elongate member produced by a method as defined in any of claims 1 to 12.
15. An elongate member as claimed in claim 14 and comprising a catheter having a wall, an internal lumen, and an electrical conductor disposed within the wall. s 20
16. An elongate member having an internal electrical conductor extending longitudinally therein and further comprising: a first electrode disposed at a first position on the external surface of the elongate member and electrically connected to the electrical conductor; and a second electrode disposed at a second position on the external surface of elongate member and electrically connected to the electrical conductor, the first position being spatially separated from the second position along the length of the elongate member.
17. An elongate member as claimed in claim 15 wherein the first electrode and the second electrode are each an annular electrode.
18. An elongate member as claimed in claim 16 or 17 wherein each electrode is a moulded electrode.
19. An elongate member as claimed in claim 18 wherein each electrode comprises a conductive plastics material, a conductive adhesive material, or a conductive polymer material.
20. An elongate member as claimed in any of claims IS to 19 and comprising a catheter having a wall and an internal lumen, wherein the internal electrical conductor is disposed within the wall.
21. A method of moulding comprising the steps of: stretching a former substantially along a longitudinal axis thereby to reduce its dimension along a transverse axis; and; disposing a mould around the former.
22. A method of moulding comprising the step of: pressurising the interior of a hollow former to a pressure above atmospheric pressure during the step of moulding material onto an exterior surface of the former.