# Patent

## Title
Electrically conductive coaxial guide wire

## Abstract

The present invention relates to A device for measurements, insertable into a living body, comprising an elongated flexible member (2, 30) with a proximal end and a distal end and a central lumen with an inner wall. The lumen is filled with a core (22) and an insulating material (21) is provided between the core and the inner wall; the core (22) is made of an electrically conductive material and has an essentially constant diameter over its entire length. An electrical sensor (44) is attached to the distal end of the elongated flexible member and is electrically connected (52) to the core (22).

## Background
BACKGROUND
1. Field of the Invention
The present invention relates generally to guide wire/sensor assemblies, wherein there are at least two electrical leads or conductors required for energizing the sensor and for signal transmission, said leads extending along the length of the guide wire between a proximal end and a distal end. In particular it relates to a coaxial, electrically conductive guide wire provided with an electrical sensor.
2. Description of the Related Art
For medical purposes many devices and applications have been disclosed and patented, wherein a miniaturized sensor is positioned in the distal region of a guide wire or a catheter. Such sensors can have various purposes, such as the measurement of pressure, temperature, flow, or for the detection of some property in vivo in a living body, e.g., pH, O2, CO2, etc.
For most applications it is required that the sensors be energized electrically, and the response be transmitted back to the exterior of the patient via electrical signals. Some applications use optical sensor devices having fiber optic signal transmission, but these fall outside the scope of the present invention.
Thus, some means of signal and energy transmission is required, and most commonly extremely thin electrical leads are provided inside the guide wire, which itself is provided in the form of a tube (of the order of 0.35 mm in outer diameter), oftentimes made of steel. In order to increase the bending strength of the tubular guide wire, a core wire is positioned inside the tube. The mentioned electrical leads are positioned in the space between the inner lumen wall and the core wire.
This design has certain drawbacks. First, it renders the assembly non-rotationally symmetric, since it is virtually impossible to distribute the electrical leads uniformly over the circumference of the core wire inside the space between the inner lumen wall and the core wire. An asymmetric configuration of leads gives rise to different bending properties in different directions of bending.
Second, there is a risk that the extremely thin leads (although coated with an insulating layer) will become damaged due to friction forces appearing in the lumen, in particular at junctions in the proximal and distal regions, where the core wire changes dimension, and where manipulations during manufacture (e.g. soldering) can cause damage to the coating and possibly cause a short-circuit.
Third, it is relatively complicated to assemble the device because of the extremely small dimensions of tubes, leads and sensors. And, fourth, electrical contacts at the proximal end of the guide wire are made using discrete components, thereby complicating the assembly.
A guide wire disclosed in EP 0 925 803, assigned to the same assignee as the present invention, attempts to solve the symmetry problem by providing electrical leads in the form of concentric layers of conducting material with insulation provide between layers. Although representing an improvement, this device also has certain drawbacks. For example, there is a risk that the concentric layers may break and cause a short-circuit. Another possible problem could be “pinholes” in the very thin insulating layers, representing a potential risk for short-circuiting.
SUMMARY
Thus, in view of the problems with the prior art devices, it is the object of the present invention to provide a guide wire design that overcomes the drawbacks of the prior art sensor/guide wire assembly designs.
Therefore, a measuring device, insertable into a living body, is provided which comprises an elongated flexible member having a proximal end and a distal end and a central lumen with an inner wall, a core filling said lumen, an insulating material provided between said core and said inner wall, said core being made of an electrically conductive material and having an essentially constant diameter over its entire length, an electrical sensor attached to the distal end of said elongated flexible member, said electrical sensor being electrically coupled to said core.
By making the guide wire from a coaxial wire, in particular having a central core of essentially constant diameter, the cost of manufacturing is lowered and the complexity by which the guide wire is manufactured is reduced.
The manufacturing process can be implemented as a continuous process, wherein long lengths of wire can be made, as opposed to the prior art device, where the wire must be made piece by piece.
Also, the guide wire becomes rotationally symmetric, which is a significant advantage in terms of ease of manipulation of the device by a physician when using the device.
Furthermore, the structure is much less prone to develop “pin holes” that could lead to short circuiting problems.



BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be described in greater detail with reference to the attached drawings, in which
FIG. 1 is a longitudinal cross-sectional view through a prior art guide wire according to EP 0 925 803;
FIG. 2 is a cross-sectional view through a first embodiment of a coaxial guide wire suitable for use in the invention;
FIG. 3 is a schematic cross-section in the longitudinal direction of a guide wire suitable for use according to the invention;
FIG. 4A shows, in greater detail, the distal end portion with a sensor mount, and a sensor mounted therein, in a top view;
FIG. 4B shows a cross sectional view in longitudinal direction of the device shown in FIG. 4A;
FIG. 5A shows a cross sectional view taken along line 5A—5A in FIG. 4B;
FIG. 5B shows a cross sectional view taken along line 5B—5B in FIG. 4B;
FIG. 5C shows a cross sectional view taken along line 5C—5C in FIG. 4B;
FIG. 6A shows a cross sectional view of a second embodiment of a coaxial guide wire suitable for use in the invention;
FIG. 6B is a longitudinal cross sectional view through a sensor and guide wire assembly according to a second embodiment, namely the distal end portion with a sensor mount, and a sensor mounted therein;
FIG. 7A shows a proximal contact;
FIG. 7B shows a second embodiment of a proximal contact; and
FIG. 8 illustrates a further embodiment of a sensor and guide wire assembly according to the invention.



DETAILED DESCRIPTION
FIG. 1 illustrates a prior art guide wire according to EP 0 925 803 in cross section in the longitudinal direction. It comprises a core wire 2, on which a plurality of concentric layers 4, 6 of conductive material have been provided. Between the conductive layers there are insulating layers 10, 12, and another insulating layer 14 is provided on top of layer 6. In addition to the drawbacks mentioned in the discussion of the background of the invention, the manufacturing process is rather complex, either by a complex extrusion process or by a process involving a consecutive deposition of the various layers.
FIG. 2 illustrates the key feature of the present invention. It shows a cross section through a guide wire 20 having a central core 22 of a conductive material (e.g. stainless steel or superelastic metal (e.g. Nitinol®)) disposed within the lumen of a thick-walled tube 24 also of a conductive material (e.g. stainless steel or superelastic metal (e.g. Nitinol®)). There is an insulating layer 21 between the core 22 and the tube 24.
This structure of the core/insulator/tube can suitably be manufactured by an extrusion process, or by shrinking a tube onto a core. Thus, the core is located inside the tube in a tight fit. The outer surface of the tube 24 is preferably covered by an insulating layer 23, in order to protect the wire from blood and other fluids, which could otherwise cause short circuiting. The insulating material usable with the invention for the outer surface layer 23, can e.g. be selected among a number of polymer materials, Teflon®, poly-imide or ParyleneTM, just to mention a few. Also ceramic type materials, e.g. alumina or silicon nitride, in its various possible forms can be used. For the intermediate layer 21, however, the ceramic materials are not suitable, and therefor polymer materials of the same type as mentioned above are usable.
The diameter of the core over its entire length is constant, and is suitably less than 50% of the outer diameter of the elongated flexible member (and is preferably less than 25% thereof), except in the distal end, where the outer layer is reduced in order to provide the necessary constructive details, as later described.
The constant diameter of the core is a significant advantage over the prior art structure according to EP 0 925 803, in that it makes possible a continuous manufacturing process whereas the '803 structure must be made piece by piece. Thus, by using a coaxial wire according to the teachings herein, the manufacturing time will be considerably reduced and simplified, and therefore, much more economical.
Other great benefits of this structure include: (a) that it is rotationally symmetric; (b) that the torque can be controlled by controlling the relative dimensions of core and tube; and (c) that the mounting of a sensor element on the guide wire becomes very simple, as will later be described in further detail.
FIG. 3 is a schematic view of an embodiment of an elongated flexible member forming a guide wire, generally designated with reference numeral 30, having the basic construction of FIG. 2, however shown without certain details at the distal end (protective coil, sensor etc). The various segments of the wire are not shown to scale, and the total length of the wire is typically about 1.80 meters, although other lengths are possible, even up to about 3 meters.
As can be seen in FIG. 3 the diameter of the elongated flexible member varies, and in the distal end has segments of reduced diameter to increase the flexibility of the wire in the distal region. However, the very distal end portion 32, which comprises a thicker portion forming a mounting structure for the sensor, has a thickness corresponding to the diameter of the wire in its proximal region (e.g. approximately 0.35 mm).
This thicker portion 32 comprises a mount (shown in FIGS. 4a and 4b) for a sensor element. This mounting structure comprises a recess, having a bottom surface in a first portion of which the core is exposed so as to form a first contact surface for the sensor (i.e., the mounting structure forms an arrangement which is in accordance with the teachings of our U.S. Pat. No. 6,142,958 (incorporated herein by reference)).
FIGS. 4A and 4B illustrate the distal end portion 32 of one embodiment in greater detail. FIG. 4A shows the sensor mount in a top view and FIG. 4B shows a side view with parts in cross section. FIGS. 5A–5C are cross sections taken along lines 5A—5A, 5B—5B, and 5C—5C, respectively.
Thus, the thicker distal sensor mount portion 32 has a recess 40 formed therein (which is formed by suitable machining, e.g., EDM cutting or laser cutting) which constitutes said sensor mount for a miniaturized sensor 44. Thereby, the bottom surface of the recess will exhibit two regions of conductive material. Namely, the central core 22 (indicated with broken lines in the part not shown in cross section) will be exposed to form a first contact surface 46, separated from the bulk material of the tube by the insulation material 21. The bulk material of the tube will form a second contact surface 48.
A sensor chip 44 having two contact terminals 50, 52 (located on the bottom side of the sensor chip, indicated by circles in broken lines), can thus be attached by suitable bonding or soldering to these surfaces, as can be seen in FIG. 4B. In this way, electrical energy can be supplied for energizing purposes in the two leads formed by the core and the tube, respectively. By suitable techniques for modulation of the energizing current, the same leads can be used for signal transmission.
In the shown embodiment, the recess 40 has a deeper portion 54 in the region where the sensitive part of the sensor chip 44 is positioned, such that the sensitive part of the chip extends out over the deeper recess part 54, which is seen in FIG. 4B. This is in accordance with the teachings in our U.S. Pat. No. 6,112,598 (incorporated herein by reference), and reduces or even eliminates bending artifacts.
The recess in this embodiment reaches through the core 22.
In an alternative design, the deeper recess portion can extend all the way through the thicker portion, as indicated by broken lines 56 in FIG. 4B. Such a design would yield a cross section of the type shown in FIG. 5C which is taken along line 5C—5C in FIG. 4B.
In this embodiment the diameter of the enlarged sensor mount portion 32 has the same diameter as the diameter of the guide wire. Therefore, it is not possible to attach the coil 59 by sliding it over the wire. Instead it must be wound onto the wire at the correct position, i.e., proximally of the sensor mount.
FIG. 5A shows a cross section taken along line 5A—5A in FIG. 4B. Here it can be clearly seen how the sensor chip 44 is attached to the two contact surfaces 46 and 48, respectively, by the contact terminals 50, 52 respectively.
An alternative way of connecting the sensor chip to the outer tube is by bonding an electrical lead 53 thereto. Thereby eliminating the contact terminal 52.
FIG. 5B shows the cross section taken along line 5B—5B in FIG. 4B, which clearly illustrates the “cantilevering” end of the sensor chip.
In order not to short circuit the core 22 and the outer tube material 32, when the recess is exposed to body fluids, the inner surface of the recess must be covered with some protective material 58 (not shown in FIGS. 5A–5C). This can be easily achieved by providing silicone or some similar material to cover at least those areas where fluids could cause a short circuit.
In the embodiment described above with reference to FIGS. 4–5, the core has a relatively small diameter compared to the surrounding tube. However, it is also possible to make a coaxial guide wire 60 with a thicker core 62, and a thinner outer tube 66 with an insulating layer 64 provided between the core and the tube, as shown in FIG. 6A. In addition, preferably an insulating layer 63 is applied to the outer surface of the tube 66.
In this embodiment, the recess 68 forming the sensor mount will not reach all the way through the core 62, as can be seen in FIG. 6B. This requires that the entire bottom surface and parts of the walls of the recess 68 be covered with insulating material 67. It also necessitates protection of the distal end surface 69 of the core with insulating material 67b so that the very distal tip 65 that is to be attached thereto will not be in electrical contact with the inner core 62. For the purpose of securing the tip 65, it is convenient to provide a piece of tubing 61 over the enlarged portion forming the sensor mount.
This piece of tubing extends slightly beyond the distal end 69, so as to form a cylindrical recess in which the proximal end of the tip 65 can be inserted, and secured by soldering, gluing, or shrinking. Thus, in this case the sensor mount has a diameter that is smaller than the diameter of the wire 60. Therefore, in this case the coil 59 can be slid over the mount and secured by soldering or gluing, before the piece of tubing 61 is positioned on the mount.
In a further advantageous aspect of the invention, the novel guide wire design provides for a very simple way to construct a proximal male connector, for connecting the guide wire assembly to external equipment.
In FIG. 7A the proximal end 70 of a guide wire 80 is shown in cross section. It comprises an outer tube member 72, an inner core 74 with an insulating layer 75 disposed between said core and said tube.
In order to make a connector having two contact elements or surfaces, a circumferential recess 71 is made in the outer tube 72, down to the insulating layer 75 (this embodiment is shown in FIG. 7A), or through the insulating layer 75 down to a depth at which the inner core 74 is exposed (FIG. 7B). It is of course essential that there be no electrical connection between the distal and the proximal end of the outer tube. The recess is filled with an insulating material 76, e.g. some polymer (Teflon®, poly-imide or Parylene or the like) or an inorganic material such as ceramic type materials, e.g. alumina or silicon nitride, in its various possible forms.
Finally, the very end surface of the coaxial wire 80 is “capped” with a layer 78 of conductive material so as to short circuit the core 74 with the proximal end portion of the tube, now electrically insulated from the remainder of the tube on the distal side of the recess 71 filled with insulating material 76.
FIG. 8 illustrates an alternative way of providing the sensor mount at the distal end of the wire.
It encompasses providing a tube segment 82 having an inner diameter corresponding to the outer diameter of the coaxial wire 84, and positioning said tube segment 82 over the distal end of the wire 84. Thereby a portion of the tube segment 82 should extend around the wire 84 so as to form a cylindrical recess 86 at the distal end. This recess will be used for attaching a tip 88 by press fitting and/or soldering.
When the tube 82 is mounted on the wire 84, a recess 90 is formed by any suitable technique, e.g., EDM cutting or laser cutting, down to a depth such that the inner core 92 is exposed. The exposed bottom surface 94 can be used as a first contact surface for a sensor element (not shown). The walls 96 of the recess 90 can be used as a second contact surface for said sensor.

## Claims

1. A measuring device adapted to be inserted into a living body, the device comprising:
an elongated flexible member having a proximal end and a distal end and a central lumen formed in a thick-walled tube with an inner wall;
a core provided in said lumen, said core being made of an electrically conductive material and having an essentially constant diameter over its entire length;
an insulating material provided between said core and said inner wall; and
an electrical sensor attached to the distal end of said elongated flexible member, said electrical sensor being electrically coupled to said core;
wherein said core is provided inside said lumen, substantially along the entire length of the elongated flexible member, in a tight fit, and wherein a diameter of the core, substantially along the entire length of the elongated flexible member, is less than about 50% of an outer diameter of the elongated flexible member.

2. The device as claimed in claim 1, wherein said elongated flexible member is rotationally symmetric.

3. A measuring device adapted to be inserted into a living body, the device comprising:
an elongated flexible member having a proximal end and a distal end and a central lumen with an inner wall;
a core provided in said lumen, said core being made of an electrically conductive material and having an essentially constant diameter over its entire length;
an insulating material provided between said core and said inner wall; and
an electrical sensor attached to the distal end of said elongated flexible member, said electrical sensor being electrically coupled to said core;
wherein the diameter of the core, except in the distal region, is less than about 25% of the outer diameter of the elongated flexible member; and
wherein a diameter of the elongated flexible member comprises segments in the distal region having varying diameters.

4. The device as claimed in claim 3, wherein the lumen is formed in a thick-walled tube.

5. A measuring device adapted to be inserted into a living body, the device comprising:
an elongated flexible member having a proximal end and a distal end and a central lumen with an inner wall;
a core provided in said lumen, said core being made of an electrically conductive material and having an essentially constant diameter over its entire length;
an insulating material provided between said core and said inner wall; and
an electrical sensor attached to the distal end of said elongated flexible member, said electrical sensor being electrically coupled to said core;
wherein said core is provided inside said lumen, substantially along the entire length of the elongated flexible member, in a tight fit, and wherein a diameter of the core, substantially along the entire length of the elongated flexible member, is less than about 50% of an outer diameter of the elongated flexible member; and
wherein said elongated flexible member, at its distal end, comprises a thicker portion forming a mounting structure for said sensor, and wherein said mounting structure comprises a recess having a bottom surface in a first portion of which the core is exposed so as to form a first contact surface for said sensor.

6. A measuring device adapted to be inserted into a living body, the device comprising:
an elongated flexible member having a proximal end and a distal end and a central lumen with an inner wall;
a core provided in said lumen, said core being made of an electrically conductive material and having an essentially constant diameter over its entire length;
an insulating material provided between said core and said inner wall; and
an electrical sensor attached to the distal end of said elongated flexible member, said electrical sensor being electrically coupled to said core;
wherein said elongated flexible member, at its distal end, comprises a thicker portion forming a mounting structure for said sensor, and wherein said mounting structure comprises a recess having a bottom surface in a first portion of which the core is exposed so as to form a first contact surface for said sensor; and
wherein said elongated flexible member is made of a conductive material, and wherein the conductive material of said elongated flexible member in a second portion of said bottom surface forms a second contact surface for said sensor.

7. A measuring device adapted to be inserted into a living body, the device comprising:
an elongated flexible member having a proximal end and a distal end and a central lumen with an inner wall;
a core provided in said lumen, said core being made of an electrically conductive material and having an essentially constant diameter over its entire length;
an insulating material provided between said core and said inner wall; and
an electrical sensor attached to the distal end of said elongated flexible member, said electrical sensor being electrically coupled to said core;
wherein said core is provided inside said lumen, substantially along the entire length of the elongated flexible member, in a tight fit, and wherein a diameter of the core, substantially along the entire length of the elongated flexible member, is less than about 50% of an outer diameter of the elongated flexible member; and
wherein said elongated flexible member, at its distal end, comprises a mounting structure for said sensor, wherein said mounting structure comprises a recess, wherein the recess has a bottom surface in a first portion of which the core is exposed so as to form a first contact surface for said sensor, and wherein said mounting structure has a diameter that is smaller than a diameter of the flexible member.

8. A measuring device adapted to be inserted into a living body, the device comprising:
an elongated flexible member having a proximal end and a distal end and a central lumen with an inner wall;
a core provided in said lumen, said core being made of an electrically conductive material and having an essentially constant diameter over its entire length;
an insulating material provided between said core and said inner wall; and
an electrical sensor attached to the distal end of said elongated flexible member, said electrical sensor being electrically coupled to said core;
wherein said elongated flexible member, at its distal end, comprises a mounting structure for said sensor, wherein said mounting structure comprises a recess, wherein the recess has a bottom surface in a first portion of which the core is exposed so as to form a first contact surface for said sensor, and wherein said mounting structure has a diameter that is smaller than a diameter of the flexible member;
wherein said elongated flexible member is made of a conductive material; and
wherein the conductive material of said elongated flexible member in a second portion of said bottom surface forms a second contact surface for said sensor.

9. A measuring device adapted to be inserted into a living body, the device comprising:
an elongated flexible member having a proximal end and a distal end and a central lumen with an inner wall;
a core provided in said lumen, said core being made of an electrically conductive material and having an essentially constant diameter over its entire length;
an insulating material provided between said core and said inner wall; and
an electrical sensor attached to the distal end of said elongated flexible member, said electrical sensor being electrically coupled to said core;
wherein said elongated flexible member, at its distal end, comprises a mounting structure for said sensor, wherein said mounting structure comprises a recess, wherein the recess has a bottom surface in a first portion of which the core is exposed so as to form a first contact surface for said sensor, and wherein said mounting structure has a diameter that is smaller than a diameter of the flexible member;
wherein said elongated flexible member is made of a conductive material; and
wherein a protective material is provided in said recess which is adapted to prevent a short circuit between the core and the conductive material of the elongated flexible member.

10. A measuring device adapted to be inserted into a living body, the device comprising:
an elongated flexible member having a proximal end and a distal end and a central lumen with an inner wall;
a core provided in said lumen, said core being made of an electrically conductive material and having an essentially constant diameter over its entire length;
an insulating material provided between said core and said inner wall; and
an electrical sensor attached to the distal end of said elongated flexible member, said electrical sensor being electrically coupled to said core; and
a connector at the proximal end, comprising:
a circumferential recess in the elongated flexible member extending at least down to the insulating material, the recess being filled with an insulation so as to ensure that there is no electrical connection between the proximal part and the distal part of the elongated flexible member, and

a proximal end cap, short circuiting the core and the proximal part of the elongated flexible member.

11. A guide wire and sensor assembly comprising:
an elongated flexible member comprising:
a thick-walled tube having an inner lumen;
a core provided in said lumen in a tight fit, wherein said core has an essentially constant diameter over the entire length of said elongated flexible member, the constant diameter being less than about 50% of an outer diameter of the tube, and wherein said tube and said core are made of an electrically conductive material; and
an insulating layer provided between said core and said tube; and

a sensor located at the distal end of the assembly and in electrical contact with the core and the tube.

12. A guide wire and sensor assembly comprising:
an elongated flexible member comprising:
a thick-walled tube having an inner lumen; and
a core provided in said lumen in a tight fit, wherein said core has an essentially constant diameter and is provided in the tight fit over the entire length of said elongated flexible member, wherein said core is made of an electrically conductive material, and wherein said tube is made of an insulating non-conductive material; and
a sensor located at the distal end of the assembly and in electrical contact with the core.

13. A guide wire and sensor assembly comprising:
an elongated flexible member comprising:
a tube having an inner lumen;
a core provided in said lumen in a tight fit, wherein said core has an essentially constant diameter over the entire length of said elongated flexible member, and wherein said tube and said core are made of an electrically conductive material; and an insulating layer provided between said core and said tube; and

a sensor located at the distal end of the assembly and in electrical contact with at least the core;
wherein a diameter of the elongated flexible member comprises segments in the distal region having varying diameters, and wherein the diameter of the core, except in the distal region, is less than about 25% of the outer diameter of the elongated flexible member.

14. The guide wire and sensor assembly as claimed in claim 13, wherein the tube is a thin-walled tube.

15. A guide wire and sensor assembly comprising:
an elongated flexible member comprising:
a tube having an inner lumen;
a core provided in said lumen in a tight fit, wherein said core has an essentially constant diameter over the entire length of said elongated flexible member, and wherein said tube and said core are made of an electrically conductive material; and
an insulating layer provided between said core and said tube; and

a sensor, located at the distal end of the assembly and in electrical contact with at least the core;
wherein a diameter of the elongated flexible member comprises segments in the distal region having varying diameters; and
wherein the diameter of the core, except in the distal region, is less than about 25% of the outer diameter of the elongated flexible member.

16. The guide wire and sensor assembly as claimed in claim 15, wherein the tube is a thin-walled tube.

17. A guide wire and sensor assembly comprising:
an elongated flexible member comprising:
a tube having an inner lumen;
a core provided in said lumen in a tight fit, wherein said core has an essentially constant diameter over the entire length of said elongated flexible member; and wherein said tube and said core are made of an electrically conductive material;
an insulating layer provided between said core and said tube; and
a sensor located at the distal end of the assembly and in electrical contact with at least the core;
wherein a diameter of the elongated flexible member comprises segments in the distal region having varying diameters, wherein the diameter of the core, except in the distal region, is less than about 50% of the outer diameter of the elongated flexible member, wherein said elongated flexible member is rotationally symmetric, wherein said elongated flexible member is made of a conductive material, wherein said elongated flexible member at its distal end comprises a mounting structure for said sensor, wherein said mounting structure comprises a recess, wherein the recess has a bottom surface in a first portion of which the core is exposed so as to form a first contact surface for said sensor, and wherein the conductive material of said elongated flexible member in a second portion of said bottom surface forms a second contact surface for said sensor.

18. The guide wire and sensor assembly as claimed in claim 17, wherein the diameter of the core, except in the distal region, is less than about 25% of the outer diameter of the elongated flexible member.

19. A measuring device adapted to be inserted into a living body, the device comprising:
an elongated flexible member having a proximal end and a distal end and a central lumen formed in a thick-walled tube with an inner wall;
a core provided in said lumen, said core being made of an electrically conductive material and having an essentially constant diameter over its entire length;
an insulating material provided between said core and said inner wall; and
an electrical sensor attached to the distal end of said elongated flexible member, said electrical sensor being electrically coupled to said core;
wherein the diameter of the core, except in the distal region, is less than about 25% of the outer diameter of the elongated flexible member.

20. The device as claimed in claim 19, wherein said core is provided inside said lumen in a tight fit.

21. A measuring device adapted to be inserted into a living body, the device comprising:
an elongated flexible member having a proximal end and a distal end and a central lumen formed in a thick-walled tube with an inner wall;
a core provided in said lumen, said core being made of an electrically conductive material and having an essentially constant diameter over its entire length;
an insulating material provided between said core and said inner wall; and
an electrical sensor attached to the distal end of said elongated flexible member, said electrical sensor being electrically coupled to said core;
wherein said core is provided inside said tube in a tight fit; and
wherein a diameter of the core, except in the distal region, is less than about 25% of an outer diameter of the elongated flexible member.

22. A measuring device adapted to be inserted into a living body, the device comprising:
an elongated flexible member having a proximal end and a distal end and a central lumen formed in a thick-walled tube with an inner wall;
a core provided in said lumen, said core being made of an electrically conductive material and having an essentially constant diameter over its entire length;
an insulating material provided between said core and said inner wall; and
an electrical sensor attached to the distal end of said elongated flexible member, said electrical sensor being electrically coupled to said core;
wherein the measuring device, substantially along the entire length of the elongated flexible member, is rotationally symmetric.

23. A guide wire and sensor assembly comprising:
an elongated flexible member comprising:
a tube having an inner lumen;
a core provided in said lumen, wherein said core has an essentially constant diameter over a substantial portion of the length of the tube, wherein the constant diameter of the core, substantially along the entire length of the tube, is about the same as a wall thickness of the tube substantially along the entire length of the tube, and wherein said tube and said core are made of an electrically conductive material;
an insulating layer provided between said core and said tube; and
a sensor located at the distal end of the assembly and in electrical contact with the core and the tube.