Sensor Guide Construction and Use Thereof

The present invention relates to guide construction and the use thereof.

A sensor mounted on a guide to be used for pressure measuring in stenotic vessels belonging to atherosclerotic patients is described in patent application WO 90/01294. Briefly, the known sensor guide construction comprises a cannula tube for establishing an air channel from the sensor to atmospheric pressure. The drawback of the cannula tube is that it easily takes form when it passes strong bends. Furthermore, the known sensor guide construction requires the mounting of several tubes, having different dimensions, over each other to obtain different flexibility and that security threads are attached in the ends of the tubes. This kind of tube assembly is also described in EP A2 313 836 and involves a complex production process.

In WO 89/10088 there is described a guide wire for catheters, but since this does not comprise a sensor it does not solve the problems with establishing an air channel as described above.

An object of the invention is to provide a sensor guide construction which is less sensitive to mechanical stress and which is easier to produce from a production technical point of view.

The above object is met by providing a sensor guide having a sensor element, an electronic unit, a signal transmitting cable connecting the sensor element to the electronic unit, a flexible tube having the cable and the sensor element disposed therein, a solid metal wire having a plurality of sections of differing thicknesses such that each of the sections has a different flexibility, and a coil which is attached to a distal end of the wire. An inside portion of the flexible tube acts as an air channel to establish communication between the sensor element and atmospheric pressure. In addition, the wire is rigidly disposed in the sensor guide and extends along the entire sensor guide inside of the tube. Moreover, one of the plurality of sections is an enlarged portion having a slot therein and the sensor element is disposed in the slot between the coil and the proximal end of the wire.

The invention will now be described more closely below in connection to the accompanying drawings in which

FIG. 1 is a longitudinal section view of a sensor guide construction according to the present invention;

FIG. 2 is a section view similar to FIG. 1 of an alternative embodiment;

FIG. 3 is a section along line A--A in FIG. 1;

FIG. 4 is a section along line B--B in FIG. 1;

FIG. 5 is a section view of yet another alternative embodiment;

FIG. 6 is a schematic view showing the mounting of the embodiment shown in FIG. 5; and

FIG. 7 is a schematic top plan view of a solid metal wire having a continuous slot from the position of the sensor element to the proximal end of the wire.

In FIG. 1 a sensor guide construction according to the present invention is shown. The sensor guide construction 1 has, in the drawing, been divided into five sections, 2-6, for illustrative purposes. The section 2 is the most distal portion, i.e. that portion which is going to be inserted fartherst into the vessel, and section 6 is the most proximal portion, i.e. that portion being situated closest to a not shown electronic unit. Section 2 is about 10-50 mm, section 3 about 1-5 mm, section 4 about 200-400 mm, section 5 about 1000-2000 mm and section 6 about 10-100 mm.

Section 2 comprises a radiopaque coil 8, being made of e.g. platinum, provided with an arced tip 7 being or alternatively welded thereon. In the platinum coil 8 and respectively in tip 7, there is also attached a stainless, solid metal wire 9 which in section 2 is formed like a thin conical tip and functions as a security thread for the platinum coil 8. The successive tapering of the metal wire 9 in section 2 towards the arced tip 7 results in that the front portion of the sensor guide construction becomes succesively softer. The tapering is obtained by cylindrical grinding of the metal wire 9.

At the transition between the sections 2 and 3 the lower end of the coil 8 is attached to the wire 9 with glue or alternatively, solder, thereby forming a joint 10. At the joint 10 a thin outer tube 11 commences which is made of a biocompatible material, e.g. polyimid, and extends downwards in the FIGURE all the way to section 6. The tube 11 has been treated to give the sensor guide construction a smooth outer surface with low friction. The metal wire 9 is heavily expanded in section 3 and is in this expansion provided with a slot 12 in which a sensor element 14 is arranged, e.g. a pressure gauge. The expansion of the metal wire 9 in which the sensor element 14 is attached decreases the stress, exerted on the sensor element 14 in sharp vessel bends. Preferably a recess 13 is arranged in the slot 12, providing an extra deep area under the site of the pressure sensitive part of the sensor element 14 so that the sensor element will not experience any mechanical stress if the wire 9 is bent, i.e. the recess forms a clearance for the sensor element 14.

The recess 13 and the slot 12 are made by spark machining in the metal wire 9. The slot 12 has the approximate dimensions 100 .mu.m width.times.100 .mu.m depth. The length of the slot can be varied as desired. The sensor element 14 is sealed against surrounding blood pressure with a hose 15 covering the expansion of the wire 9 The hose 15 functions as a soft membrane and is made of a flexible material. On the outside of the sensor element 14 and the hose 15, and lying thereover, is an opening arranged in the tube 11, so that the sensor element comes in contact with the environment in order to perform, for example, pressure measuring.

From the sensor element 14 there is arranged a signal transmitting cable 16 which can be an optic fiber or electric cables 16. The signal transmitting cable 16 extends from the sensor element 14 to a not shown electronic unit being situated below the section 6. The metal wire 9 is substantially thinner in the beginning of section 4 to obtain good flexibility of the front portion of the sensor guide construction. Between the tube 11 and the metal wire 9 there is also an air channel 17 giving the sensor guide construction an atmosheric pressure in the slot 12 in which the sensor 14 is arranged. The air channel 17 begins in section 6 at the proximal end of the tube 11 and extends thereafter inside of the tube 11 to the sensor element 14 in the slot 12. The function of the tube 11 is to create the air channel 17 and enclose the cable 16. Furthermore the same tube 11 protects the hose 15, which according to prior art has been protected by a separate short steel tube. In the end of section 4 and in the whole of section 5, the metal wire 9 is thicker in order to make it easier to push the sensor guide construction 1 forward in the vessel. In section 6 the metal wire 9 is as coarse as possible to be easy to handle and is here provided with a slot 20 in which the cable 16 is attached with e.g. glue. The signal transmitting cable 16 is centrated in this second slot 20 which is especially important if the cable 16 is an optic fiber intended to be connected to another optic fiber by a conncection, as is described in our pending patent application with the title "Fiber optic connection and use thereof" to which is referred. In section 6 the air channel 17 communicates with atmospheric pressure via the slot 20 arranged here since the tube 11 is not covering the whole of this section.

In the alternative embodiment shown in FIG. 2, the front portion of the metal wire 9 is not fastened in the tip 7 but in security thread 18 is arranged inside the tube 11 and at its distal end is attached in section 6 and at its prymid end is attached in the tip 7. Alternatively the front end of the metal wire can be attached in section 5.

FIG. 3 is a cross section along line A--A in FIG. 1, showing the tube 11, the hose 15, the sensor element 14 in the slot 12 of the metal wire 9 and the opening in the tube 11 in front of the sensor element 14 to enable e.g. pressure measuring.

FIG. 4 shows the cross section along line B--B in FIG. 1 showing the fiber or cables 16 attached with an inner glueing in the front of the slot 20 of the metal wire 9. It is possible, as shown in FIG. 17, to have a single slot 21 which extends to entire length from the expansion in which the sensor element is attached down to the profined end of wire 9. The cable 16 and the air channel 17 are enclosed in this slot. Alternatively, the air channel can be arranged between the wire 9 and the tube 11 are included the two slots 12 and 20, situated in sections 3 and 6, respectively, as described above.

In FIG. 5, an alternative embodiment of the sensor guide construction according to the present invention is shown in mainly the same scale as the FIG. 1-4. The section 3 is substantially thinner in this embodiment than in the former. This means that section 3 of the sensor guide construction can be made smaller, which is advantageous with regard to production and use.

The production of section 3 of the sensor guide construction according to FIG. 5 is shown in FIG. 6. In a round solid wire 9 a recess 13 is spark machined. Over this, there is glued or soldered a previously obtained part 19 provided with the slot 12. The part 19 is obtained in that the slot having the same dimensions as the slot 12 is sparked out in a tube having the same inner diameter as the outer diameter of the metal wire 9. Thereafter the portion of the tube in which the slot is situated, is cut out, whereby the portion 19 according to FIG. 6 is obtained. It also appears where the sensor element 14 is going to be situated in the ready mounted construction according to Fig 5.

The sensor guide construction according to the present invention does not take form after it has been bent. Different flexibility is obtained without complex production since only the coarseness of the metal wire 9 has to be varied. Furthermore the need of several security threads is avoided. The metal wire 9 consists preferably of memory metal or stainless steel.

The sensor element can be fiber optic or electric depending on whether the signal transmitting cable 16 is fiber optic fiber or electric cables.