Guidewire with internal pressure sensor

Abstract

There is described a pressure guidewire. It comprises a sensor housing and a sensor assembly embedded in the sensor housing and comprising a pressure sensor. There is a band to support the pressure sensor assembly, the band being embedded inside the sensor housing and fixed to the pressure sensor assembly for holding the pressure sensor inside the sensor housing.

Claims

1. A pressure guidewire comprising: a sensor housing; a sensor assembly embedded in the sensor housing and comprising a pressure sensor; and a band to support the pressure sensor assembly, the band being embedded inside the sensor housing and fixed to the pressure sensor assembly for holding the pressure sensor inside the sensor housing.

2. The pressure guidewire of claim 1, wherein the pressure guidewire has a longitudinal axis, the pressure sensor adapted to measure a pressure of a fluid which is substantially applied in an axis collinear with the longitudinal axis of the guidewire.

3. The pressure guidewire of claim 1, wherein the sensor housing has a distal end, further comprising a tip portion extending distally relative to the sensor housing, the tip portion having a proximal end attached to the distal end of the sensor housing, the tip portion being the most distal portion of the pressure guidewire.

4. The pressure guidewire of claim 1, wherein the pressure guidewire comprises a shaft tube comprising the sensor housing, the shaft tube comprising a proximal section, the proximal section and the sensor housing being the continuity of the same shaft tube.

5. The pressure guidewire of claim 4, wherein the shaft tube further comprises: a proximal section to provide pushability to the pressure guidewire; and a middle section extending distally relative to the proximal section, the middle section comprising a cut pattern to provide greater flexibility in the middle section than the proximal section, wherein the sensor housing extends distally relative to the middle section.

6. The pressure guidewire of claim 5, further comprising an inner hypotube comprising a proximal end portion and a distal end portion, the inner hypotube positioned entirely radially inward of the shaft tube and within at least the middle section, the proximal end portion and the distal end portion of the inner hypotube being joined to the shaft tube.

7. The pressure guidewire of claim 6, further comprising a window giving access to the inner hypotube for welding, soldering or bonding the inner hypotube within the middle section of the pressure guidewire.

8. The pressure guidewire of claim 7, further comprising a small piece of material in contact with a wall of the inner hypotube and protruding within the window, the small piece of material being welded to the inner hypotube.

9. The pressure guidewire of claim 1, wherein the band is a radio opaque marker band.

10. The pressure guidewire of claim 1, wherein the band is spaced apart from the pressure sensor.

11. The pressure guidewire of claim 1, wherein the band is disposed immediately proximal to the pressure sensor.

12. The pressure guidewire of claim 1, wherein the band is bonded to the sensor housing.

13. The pressure guidewire of claim 12, wherein the band is bonded by an adhesive.

14. The pressure guidewire of claim 13, wherein the band is bonded by an adhesive to the pressure sensor assembly.

15. The pressure guidewire of claim 1, wherein the band is secured to the sensor housing by a weld.

16. The pressure guidewire of claim 1, wherein the band is secured within the sensor housing by soldering.

17. The pressure guidewire of claim 1, wherein the sensor housing defines a cavity, inside the sensor housing, which is distal relative to the pressure sensor and delimited at a proximal end thereof by the pressure sensor, the pressure sensor comprises a diaphragm sensitive to a pressure of a fluid within the cavity.

18. A sensor housing of a pressure guidewire having a distal end to be inserted in a patient's vessels, comprising: a fiber optic pressure sensor assembly embedded in a sensor housing and comprising a pressure sensor and an optical fiber extending within the sensor housing; and a band maintaining the fiber optic pressure sensor assembly in the sensor housing.

19. The sensor housing of claim 18, wherein the band is spaced apart from the pressure sensor.

20. The sensor housing of claim 18, wherein the band is disposed immediately proximal to the pressure sensor.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further features and advantages of the present disclosure will become apparent from the following detailed description, taken in combination with the appended drawings, in which:

(2) FIG. 1 is a schematic diagram which illustrates partial side view of an embodiment of the pressure guidewire;

(3) FIG. 2 is a partial perspective view showing the interfacing portion between the proximal and middle sections of pressure guidewire of FIG. 1;

(4) FIG. 3 is a partial perspective view showing the interfacing portion between the middle and sensor housing sections of the pressure guidewire of FIG. 1;

(5) FIG. 4 is a schematic showing the profiling, in part, of the distal end of inner tube of the pressure guidewire of FIG. 1;

(6) FIG. 5. is a perspective view showing the tip section of pressure guidewire of FIG. 1,

(7) FIGS. 6A and 6B are perspective views showing the small piece fitted to join or interlock nitinol inner tube to shaft tube; and

(8) FIG. 7 is a schematic diagram showing blood vessels with a cut-out portion in which a pressure guidewire is inserted.

(9) It will be noted that throughout the appended drawings, like features are identified by like reference numerals.

DETAILED DESCRIPTION

(10) Referring now to the drawings, and more particularly to FIGS. 1 to 6, there is shown an embodiment of a pressure guidewire 10.

(11) The general design for the pressure guidewire shown in FIG. 1 herein, although it is made of fewer parts than prior art pressure guidewires, it is also made of same four sections, namely, the proximal section 12, the middle section 14, the sensor housing section 15 and the tip section 16. Although, as it will become clear hereinafter, the first three sections 12, 14 and 15 are to some extent made of the continuity of the same shaft tube 18, the above sections of shaft tube 18 may also be called herein after as proximal section 12, middle section 14 and sensor housing section 15.

(12) According to an embodiment, the proximal section 12 is made of a stainless steel hypotube, with an OD of about 0.014″ and by way of non limiting example with an ID of about 0.009″. The proximal section is used to push other more distal sections of the pressure guidewire within the vasculature. The proximal section resides within the guiding catheter at one end, with the other end exiting the patient through the introducer (not shown), therefore allowing the physician to remotely control the pressure guidewire within the blood vessel, such as pushing and torquing the wire. According to an embodiment, the length of the sensor housing 15 is in a range between 1 mm to 3.5 mm. According to an embodiment, the length of the sensor housing 15 is 2.5 mm.

(13) The middle section is the one that faces the most challenging trade-offs. The middle section 14 must not damage the vessel and hence it must be fairly flexible. It must however transmit the torque for better navigability, be stiff enough to deliver a good pushability and provide a good support for an angioplasty balloon. The middle section can be made by extending the proximal section 12 further, but it would be too stiff to navigate within the vessels. On the other hand, the middle section 14 can be softened by cutting the tube as a spiral or other cutting patterns as known by those skilled in the art. Those skilled in the art also know that such cut patterns are achieved using laser, etching and other processes. Spiral cutting the tube would result in a very soft section whether the pitch is high or low, and would not deliver any of the required tensile force and torque response. Other non continuous cut patterns can provide adequate tensile force, but the stiffness is controlled by adjusting the pitch and cut pattern. It is however difficult to provide a smooth and continuous variation of stiffness. There is also a critical safety challenges when torquing such a cut patterned guidewire as the torque induced stresses are concentrated in narrow cut regions of the guidewire, hence potentially provoking guidewire failure.

(14) Using the device described hereinafter it is possible to control safely the mechanical performance of the middle section 14 by way of a) extending the proximal section 12 further; b) cut this extended section to soften it; and c) combining this cut section with an additional inner hypotube 20 overlapping the whole cut region of middle section 14, the inner hypotube geometry being chosen such that the desired mechanical characteristics are achieved. The middle section 14 is the continuity of the proximal section 12, where the portion corresponding to the 27 cm middle section 14 of the shaft tube 18 is cut, such as a spiral cut shaft tubing 22 according to one embodiment. The spiral cut section of the shaft tubing 22 does not provide any significant tensile strength nor does it provide significant bending or torque strength.

(15) The inner hypotube 20 is inserted within the shaft tube 18 such that it overlaps the middle section 14, where the tubing is cut. The outside diameter (OD) of the inner hypotube 20 fits the inside diameter (ID) of shaft tube 18 and can be of 0.009″ in an embodiment. The ID of the inner hypotube 20 must accommodates the sensor lead wire, or communication means (not shown in FIG. 1), as is the case of the ID of the shaft tube 18. Sensor communication means can be made fairly small, especially if optical fiber is used, so the inner hypotube 20 can provide the desired mechanical properties. By way of another non-limiting example, inner hypotube ID can be of 0.005″.

(16) One problem if such an inner hypotube 20 was used alone is that it may not provide adequate resistance against kinking. In the absence of the spiral cut shaft tubing overlay, or other cut pattern, a more conventional design would involve the addition of an elastomer coating to bring the outer diameter of the inner tube to a similar diameter as that of the shaft tube 18 (i.e., the stainless steel hypotube). However, this would not improve the resistance against kinking, which is a safety consideration.

(17) Another safety issue is the risk of leaving parts inside the patient as a result of joint failure between inner tube and proximal tube or sensor housing. In case of a joint failure in more conventional designs, such as the one proposed in U.S. Pat. No. 5,085,223 and Patent appl. No. US2010/0318000, the risk of leaving the distal parts of the guidewire within the blood vessel in case of joint failure is quite important. The proposed design mitigates this risk by providing a spiral cut pattern external tube that covers an inner hypotube, the inner tube providing most of the mechanical characteristics of the middle section. In case of joint failure resulting from applying a pulling force too strongly, the spiral cut tube will collapse over and grip the inner hypotube 20, thereby bringing along the distal portion of the guidewire.

(18) The spiral cut shaft tubing 22, when provided with an inner hypotube 20, delivers the desired mechanical characteristics. Stiffness (flexibility), torque transfer, pushability and support are provided by the inner hypotube 20. Inner hypotube 20 dimensions are easily adapted to provide optimal mechanical performance. On the other hand, kink resistance, distal parts safety retainer, and guidewire outside diameter continuity are provided by the spiral cut shaft tubing 22. It is worth mentioning that kink resistance provided by the spiral cut section is useful mostly in cases where the inner hypotube is not nitinol, e.g., it is useful when inner hypotube is stainless steel.

(19) As shown by FIG. 4, it is also desirable to shape the outside diameter of the inner tube, especially over the last 1 to 3 cm, in order to further improve trackability. In this case, the external diameter of the distal portion of the inner hypotube 20 can be slightly grinded to taper its outer diameter 40 and hence, optimizing mechanical response.

(20) The very end 41 of the inner hypotube 20, the portion that fits within the sensor housing section, should be enlarged, e.g., to the same diameter as its proximal section, so as to assure a good joint with the internal wall of the sensor housing section 15 (see FIGS. 1, 5 and 6). The very end 41 of the inner hypotube being enlarged assures a better joint for at least two reasons. One is that the gap between the inner hypotube and the internal surface of the sensor housing is minimized, which in turns optimizes the shear strength of the adhesive or soldering in between the sensor housing internal diameter and outside diameter of the very end 41 of inner hypotube. Another important reason is that an enlarged portion will have a much lower internal stress. When using nitinol, the risk of reaching a stress level corresponding to the first plateau of nitinol stress to strain curve as known by those skilled in the art, is much lower. When such first plateau is reached, the strain induced within a nitinol tubing is increasing dramatically, which may provoke a delamination of the adhesive or soldering, which in turn may cause the failure of the joint.

(21) One method of joining the inner hypotube 20 to the ends of middle section 14 of shaft tube 18 is shown in FIG. 2. A window 32 is provided through the wall of the shaft tube 18, where the inner hypotube 20 is to be welded. The inner hypotube 20 is slid past the window and welded to the middle section 14 using a laser beam or other suitable welding or joining means. The laser beam melts and joins together the edges of the window 32 to the inner hypotube 20 and therefore, secures the two parts together. It is also possible to use the same window 32 to apply adhesive at the joint between the inner and outer tubes. It is also possible to weld the tubes together without such window by heating the outer surface of the outer tube such that it welds to inner tube. Such heat can be generated using a laser, an electron beam or another heat source.

(22) Similar methods apply for joining the inner hypotube 20 to the other end of middle section 14, where another window 26 (FIG. 3) is provided at the distal end of middle section 14 of shaft tube 18. According to an embodiment, the length of windows 32 and 26 is in a range between 0.2 mm to 0.5 mm. According to an embodiment, the length of windows 32 and 26 is 0.3 mm. Both ends of inner hypotube 20 extend a little further past the position of windows 26 and 32.

(23) Without the presence of an inner hypotube 20 within the cut middle section 14, blood may leak inside the shaft tube 18, which constitutes a fairly large volume, which in turn may cause biocompatibility issues. The presence of the inner hypotube 20 seals off the inside of the shaft tube 18 where it is cut.

(24) The sensor housing section 15 is made of the very last 2 to 3 mm of the shaft tube 18. The spiral cut, or other cut patterns, stops some 2 to 3 mm before the end of the shaft tube 18, where the sensor 34 (see FIG. 3) is to be fitted. A sensor joining window 28 is provided to bond or to fix the sensor 34 within the sensor housing section 15. Blood pressure is applied to sensor 34 via opening 30. In the present description, sensor 34 comprises a pressure sensor. According to an embodiment, the length of the opening 30 is in a range between 0.2 mm to 0.5 mm. According to an embodiment, the length of the opening 30 is 0.3 mm. According to an embodiment, the diameter of the sensor joining window 28 is in a range between 0.1 mm to 0.3 mm. According to an embodiment, the diameter of the sensor joining window 28 is 0.2 mm. According to an embodiment, the pressure sensor comprises an optical pressure sensor.

(25) A radiopaque marker band 36 may be located in the sensor housing section 15 to help in localizing the pressure guidewire in the vessels. The marker band, or otherwise similar non radiopaque band, main purpose is however to allow easy assembly of the sensor within the sensor housing. It is indeed preferable to avoid the application of hard adhesive directly on sensor head. The marker band 36 can be bonded to the pressure sensor communication means (e.g., optical fiber) as a pre-assembly in an environment allowing the control of adhesive flow. The sensor 34 is secured within pressure guidewire by bonding the marker band 36, or other non radiopaque band, to the sensor housing section 15 using sensor joining window 28.

(26) A tip section 16 (FIG. 5) is provided at the end of the sensor housing section 15. A conventional atraumatic tip section 16 shown in FIG. 3 can be used as there is no sensor lead wire to be passed therethrough.

(27) Having similar materials for shaft tube 18 and inner hypotube 20, such as stainless steel, makes the above welding process fairly simple and reliable. It may however be desirable to use dissimilar materials that cannot easily be welded together. For example, it is desirable to use shaft tube 18 made of stainless steel for providing a good pushability, while it is also desirable to use nitinol for the inner hypotube 20 for its superior yield strength and lower elastic modulus. It is well known by those skilled in the art that those two materials are not easily welded together, at least not without an intermediate material.

(28) The present description also discloses a method for joining together those dissimilar materials. FIG. 6 shows one method of joining an inner hypotube made of nitinol to a stainless steel middle section 14 hypotube. The inner hypotube 52 is slid within the shaft tube 18 to overlap the cut section, and fed through past the windows 26 and 32 (only window 26 shown in FIGS. 6A and 6B). A small piece 50 of nitinol that fits in the windows is machined, inserted into the window 32 to get in contact with the inner hypotube 52 once in place, and laser welded to the inner hypotube 52, interlocking the two parts together. The small piece 50 then prevents the inner hypotube 52 from sliding within shaft tube 18. A small amount of adhesive can also be added to eliminate any movement of the small piece 50 relative to shaft tube windows 28 and 32.

(29) Another method of joining the above inner hypotube 52 to stainless steel shaft tube 18 is to use an intermediate material, for example nickel, that can be welded to both nitinol and stainless steel. A small piece 50 made of nickel can be laser welded to inner hypotube 52 first. A small hole in the center 51 can be provided to promote heat transfer to inner hypotube 52. The inner hypotube 52 is then interlocked to proximal section 12 as described above. The edges of the small piece 50 of nickel can then be laser welded to shaft tube 18. In this case, no direct welding of nitinol to stainless steel occurs and therefore, no brittle interface is created.

(30) Another method involves the use of adhesive to bond the nitinol inner hypotube 20 to the stainless steel shaft tube 18. The same parts can also be soldered together and by any other methods known by those skilled in the art.

(31) It can be appreciated that the design is made with one single uniform part, from proximal section 12 to the sensor housing section 15, and therefore the guidewire 10 is very smooth with minimum mechanical steps.

(32) The manufacturability of this design is quite easy and very efficient as the number of parts is minimized.

(33) The mechanical properties can be optimized by varying the respective wall thicknesses of inner hypotube 20 and shaft tube 18.

(34) The pitch of the spiral cut or other laser cut pattern can be varied ideally from a larger pitch to a shorter one when approaching the sensor housing section 15. Sharp turns are expected to arise in the region of the sensor housing section 15, near the tip of the guidewire 10 and therefore, it would be best if the pitch of the laser cut pattern was reduced near the sensor housing section 15 to allow a smoother bending of the cut shaft tubing 22.

(35) For improved safety, the spiral cut pattern provides a retainer for distal portions of guidewire. Risks of leaving parts inside patient body are therefore minimized.

(36) There will be an optical connector (not shown) at the very proximal end of the guidewire 10.

(37) As known by those skilled in the art, above described pressure guidewire can be coated with different material such as Teflon or hydrophilic coating so as to reduce friction against wall of vessels and/or guiding catheter.

(38) Now referring to FIG. 7, there is shown blood vessels with a cut-out portion in which a pressure guidewire 10 is inserted.

(39) While preferred embodiments have been described above and illustrated in the accompanying drawings, it will be evident to those skilled in the art that modifications may be made without departing from this disclosure. Such modifications are considered as possible variants comprised in the scope of the disclosure.