Miniaturized pressure sensor.

The numbers in parentheses indicate the international identification code. INID code Letter in parentheses indicates international document code.

460 396

The present invention relates to a miniaturized pressure sensor intended for in vivo measurements of physical pressures, for example blood measurement of the pressure in the coronary arteries of the heart by inserting the pressure sensor into the great hemisphere.

Pressure sensors of the above-mentioned type are known from our WO 88 / 00023- Such a known pressure sensor is shown in Fig. 1 and comprises an inner tube 1 in which a pressure sensor element in the form of a silicon wafer 2 and an optical fiber 3 is inserted. The lumen 4 of the tube is in communicating connection with atmospheric pressure. The distal portion of the inner tube 1 is completely surrounded by a membrane 5. The inner tube has an opening 6 which the membrane covers. The membrane is mechanically affected by the physical pressure to be measured and its movements are transmitted to the light guide 3- The amount of light that the light guide then reflects in the flat surface 7 of the silicon wafer 2 is proportional to the physical pressure to be measured.

A disadvantage of the known construction is that the membrane is unprotected and that it risks being exposed to damage. Such damage could mean that membrane material is torn off from the tip of the pressure sensor.

The risk of membrane damage arises in particular if the pressure sensor, the outer circumference of which is of the order of 0.5 mm, is inserted into a catheter which perforates the tissue in which the pressure is to be measured.

The present invention aims to provide a solution to the above-mentioned problem.

The membrane must meet certain mechanical requirements. It must be tight, flexible and not temperature dependent. The more flexible the membrane material, the better the resolution

460 > 96 pressure signals. In the known pressure sensor, however, a balance must be struck between the mechanical flexibility and the mechanical tear strength of the membrane material.

The pressure sensor itself is subject to certain requirements regarding its external dimensions. The outer diameter of the pressure sensor should therefore not exceed approx. 0.46 mm and its axial length should be short, hardly longer than approx. 4 mm.

The above-mentioned problem is solved according to the invention in that the membrane is mechanically protected by an outer tube which is threaded over the inner tube and which has a wall opening located in the middle of the opening of the inner tube. The diaphragm, the size of which is then considerably reduced, is fixed between the outer and inner tubes and only the part of the diaphragm which is exposed by the opening of the outer tube can be exposed to damage. This exposed membrane surface is considerably smaller than the exposed membrane surface in the exemplary embodiment in FIG.

1.

The provision of an outer tube whose outer diameter is not larger than 0.46 mm has been made possible by an additional miniaturization of the silicon wafer 2 and a reduction of the diameter of the optical fiber 3 compared to the pressure sensor described in the WO 88/00023.

As the exposed merabran surface is considerably reduced, the requirement for the tear strength of the membrane material is also reduced, which in turn means that significantly more types of membrane material than before can be considered. This makes it possible to use membrane materials that are soft and give rise to high-resolution signals. Various embodiments of the invention will be described in more detail below in connection with the accompanying drawings, in which Figs. 1 is a longitudinal sectional view of a known miniaturized pressure sensor,

460 Fig. 2 is a longitudinal sectional view of a first embodiment of the pressure sensor according to the invention, and Fig. 3 is a longitudinal sectional view of a second embodiment of the pressure sensor according to the invention, Fig. 4 is a longitudinal sectional view of a third embodiment of the invention, and Fig. 5 is an end view of the tip in the embodiment of Fig. 4.

The pressure sensor in Fig. 2 comprises an inner tube 1, a silicon wafer 2, an optical fiber 3 which together with the silicon wafer runs in the lumen 4 of the inner tube. The membrane, which here is much smaller than that in Fig. 1, covers the opening 6 in the inner tube. An outer tube 8 with a wall opening 9 is arranged on the outside of the inner tube coaxially therewith. The openings 6 and 9 are radially opposite each other and the membrane is firmly anchored between the outer and inner tubes in the area around the openings. The outer tube 8 is arranged in the distal portion 10 of the pressure sensor. A distal end closure 11 tightly closes the distal ends of the inner and outer tubes. A spiral 12 is anchored in the end closure 11 and extends forward in the longitudinal direction of the tubes. A safety wire 13 extends between, on the one hand, the front end of the spiral 12 and the end closure 11. The purpose of the safety wire is that if the spiral detaches from the end closure 11, it should accompany the pressure sensor when it is pulled out of the body and that the spiral turns should not be pulled out unauthorized much when the pressure sensor is pulled back. A core wire 14 is anchored in the end closure 11 and is preferably conical. The coil 12 surrounds the core wire. The coil 12 can be bent back over itself and the task of the core wire 14 is to increase the bending resistance of the coil with increasing degree of such backbending460 3 * 9 6

C '? · *

The inner tube 1 is joined at its spirit opposite the distal end to a thin tube 15 which communicates with atmospheric pressure. The joint between the thin tube 15 and the inner tube 1 lies inside the end of the outer tube 8 which is opposite the distal end. In order not to bend the tube when the pressure sensor is passed through veins and arteries, it is wrapped with a dimensionally stabilizing spiral band 17. The outer tube 8 has an annular joint 16 against the thin tube

15. This joining seal is provided in the end of the outer tube which is opposite the distal end and may be a weld, solder or glue joint.

The assembly formed by the optical fiber 3 and the silicon wafer 2 is glued to the inner wall of the inner tube 1 as shown at the glue joint 18. The inner tube 1 is in turn glued to the inner wall of the outer tube 8 as shown at the glue joint 19. An additional, not shown, wall opening for glue may be present in the inner tube for gluing the said assembly of the optical fiber 3 and the silicon wafer.

The inner tube 1 and the thin tube 15 can be joined together using welding techniques. According to an alternative embodiment, the tube 1, which is wider than the tube 15, can be made in a continuous part with the narrower tube 15 in that the units 1, 15 are made of a single material blank by using etching techniques.

According to a second embodiment of the invention shown in Fig. 3, the tubes 1 and 15 are made in a continuous piece and have the same inner and outer diameters. Again, the length of the distal portion 10 is only 4 mm and the outer diameter D 0.46 mm.

In the embodiment according to Figs. 4 and 5, the flexible tip formed by the details 12-14 in the embodiments according to Figs.

1-3, replaced with a rigid, faceted tip 20 for penetration

460 396 of tissue in which pressure is to be measured. The tip is formed by facet grinding of the end closure 11 and the outer tube 8. An example of the edges 21 arising from the grinding of the tip is shown in Fig. 5., the embodiments described above, the diameter of the optical fiber 3 is 0.125 mm or less. The wall opening 9 is essentially rectangular - seen in a plan view from above. The dimensions of the wall opening are in the order of approx. 0.5 x 0.2 mm.

The outer tube 8 is preferably a Teflonized steel tube, i.e. a steel tube in the surface of which Teflon has been applied. The inner tube 1 is preferably also made of steel. The inner diameter of the outer tube 8 is approx. 0.35 mm and the outer diameter of the inner tube 1 is approx. 0.3 mm, thus the thickness of the membrane 5 is in the order of 0.05 mm. Many different membrane materials are conceivable, including silicone rubber and latex. The membrane is held between the outer and inner tubes either by squeezing and / or in combination with it being glued between the tubes. The end closure 11 and the joint 16 are glue or solder. Silver or pewter is used as solder.

The embodiments described above can be modified within the scope of the basic idea of ​​the invention.