Pressure measuring guide wire

Abstract: The pressure measuring guide wire comprises an elongated flexible shaft 1 with a lumen 4 extending therethrough. The lumen is surrounded by a wall 5 forming the shaft and the distal portion (6) of which is provided with slots 10 for pressure medium entry. The distal portion 6 has a thickness 8, greater than the thickness 9 of the proximal area of the shaft. A coil 13 surrounds the proximal area of the shaft to compensate the difference in kinking resistance between the proximal and distal areas of the shaft.

Description: This invention relates to a pressure measuring guide wire comprising an elongated flexible shaft with a proximal area, a distal area, a lumen extending through the shaft, wall means surrounding said lumen, and aperture means for entry of a pressure medium into the lumen. The value of intracoronary pressure recordings gives a valuable information to the cardiologist to assess both coronary and myocardial flow reserve and collateral blood flow. The problem of pressure measuring guide wires is to provide an uninterrupted lumen throughout the shaft which has to be highly flexible to conform with the tortuous pathways of the blood vessels; simultaneously, the shaft must have a reasonably high stiffness to assure pushability and torque transmission thereto; and furthermore, the shaft must have a very good kink resistance to avoid the risk of constrictions resulting in modification of the advance of pressure waves through the lumen. Current pressure measuring guide wires are made of a plastic tube and a stiffening wire. This is, however, very costly and leads to constrictions in the lumen which obstruct the advance of pressure waves in the lumen. Another approach is shown in the document EP-A1-0419277 which describes a guide wire for use in measuring a characteristic of liquid flow in a vessel comprising a flexible elongate element in the form of a tube with a core wire provided therein the distal extremity of which is tapered and extends beyond the distal end of the tube. The tapered extremity of the core wire extends into a coil spring which is soldered to the tube.. The coil spring is formed of two parts which are screwed together and the spring is bonded to the core wire by solder at the region where the two portions of the coil spring are screwed together. A safety wire extends from the joint of the two coils to the distal extremity of the coil spring where it is secured to a transducer carried by the distal end of the coil spring. Front and rear contacts are provided on the transducer and are connected to a two conductor wire which extends rearwardly and interiorly of the coil spring and further extends into the tube between the core wire and the interior of the tube to get out of the tube for connection to a male connector. According to a variant, an insulating sleeve may form a tight fit with the exterior surface of the core wire and it may also fit within the tube to insulate the core from the tube so that the core and the tube and core may serve as separate and independent electrical conductors. Document EP 0 397 173 shows a pressure monitoring guidewire with a flexible distal portion. This guidewire comprises an elongated flexible shaft with proximal and distal area, wall means surrounding a lumen and aperture means for entry of a pressure medium. The wall means have a first portion of length with a first resistance to kinking, a second portion of length with a second resistance to kinking smaller than said first resistance and coils means for supporting said second portion of length. It is an object of this invention to improve over the cited art by means of a pressure measuring guide wire which is easy and cheap to manufacture, which is highly versatile while having excellent qualities of pushability and resistance to kinking, and which allows a smooth advance of pressure waves through the lumen. Towards fulfilling of these and other objects, the invention provides for a pressure measuring guide wire comprising an elongated flexible shaft with a proximal area, a distal area, a lumen extending through the shaft, wall means surrounding said lumen, and aperture means for entry of a pressure medium into the lumen, wherein said wall means have a first portion of length having a first resistance to kinking, a second portion of length having a second resistance to kinking, said second resistance to kinking being smaller than said first resistance to kinking, and wherein coil means are supporting said second portion of length. Accordingly, it becomes possible to modulate the resistance to kinking as a function of the structural organization for the pressure medium entry into the lumen. The wall thickness may be selected at will, whereby the shaft can be made flexible and stiff enough to be pushed. The resistance to kinking can be practically constant and the risk of constrictions due to kinking is eliminated. A stiffening wire is no more needed, and there is a better frequency behaviour for the fluid medium. The first portion of length is in the distal area of the shaft, making it possible to select at will the configuration of the supporting coil means. Where the first portion of length has a first thickness and the second portion of length a second thickness smaller than the first one, with the first portion of length having a plurality of slots formed therein for entry of the pressure medium, the mere choice of thickness allows mastering the difference in resistance to kinking due to the presence of the slots. Within this frame, the first portion of length may have a first outer diameter and the second portion of length may have a second outer diameter smaller than the first outer diameter, whereby the coil means may surround the second portion of length. In this configuration, the coil means and diameters may be easily chosen to have the coil means in flush alignment with the first outer diameter, for having an overall outer diameter constant and reduced friction upon travelling through the blood vessels. And to assure simple positioning of the coil means on the second portion of length, this second portion of length may be preceded proximally by a third portion of length having a third outer diameter larger than said second outer diameter, with the coil means surrounding the second portion of length between said first and third outer diameters. In that configuration the coil means may also be in flush alignment with the first outer diameter for the same reason of diameter constancy and friction reduction. Still within this frame, the first portion of length may have a first inner diameter and the second portion of length may have a second inner diameter larger than the first inner diameter, whereby the coil means may be located within the second portion of length. In this configuration, the coil means and diameters may also be easily chosen to have the coil means in flush alignment with the first inner diameter for having an overall outer shaft surface which is homogeneous while the inner diameter of the shaft remains constant. In any of the arrangements with the first portion of length in the distal area of the shaft and with slots formed in the first portion of length, some of the slots may be proximal of the first portion of length with some other slots being distal of the first portion of length, thereby avoiding too many holes on the same diameter in order to minimize the risk of kinking resistance reduction in that area. Where the second portion of length has a plurality of elongated slots formed therein for entry of the pressure medium and the coil means are located inside the shaft and extend at least under the slots, a very small thickness of the wall may be achieved all along the shaft, including the weakened area of slot location which is supported by the coil means which avoids the risk of kinking in that delicate area. And as the slots are fully supported by the coil means, they can be located at the same level along the second portion of length. To facilitate entry of the pressure medium, the coil means may have adjacent windings which are spaced apart from one another extending at least under the slots. In order to stiffen the coil means without interfering with the shaft, core means may extend through the coil means. Where such core means have a proximal portion for longitudinal abutment against a proximal end of the coil means and a distal portion for longitudinal abutment with a distal end of the coil means, a stress free assembly is achieved which stiffens the turns of the coil means and which leaves the shaft lumen free of any obstruction proximally of the coil means. The core means may also have their proximal portion integral with a wire which extends proximally along and out of the lumen of the shaft. In that case, the supporting coil may be placed under the slots only for insertion of the guide wire to assure the required resistance to kinking. During insertion, the wire extending the core also has some stiffening effect for the shaft and improves its pushability. When the guide wire is properly located, the wire and supporting coil are removed from the guide wire to have the shaft lumen fully free of obstruction for pressure measurements. These and other objects, features and advantages of the invention will become readily apparent from the following detailed description with reference to the accompanying drawings which show, diagrammatically and by way of example only, one embodiment of the invention. Figure 1 is a cross sectional view of the first embodiment. The guide wire shown in Figure 1 comprises an elongated flexible shaft 1 having a distal area 2 and a proximal area 3. A lumen 4 extends through the shaft 1, and the proximal area 3 of the shaft is intended to be connected to a pressure measuring and monitoring equipment (not shown) common in the art. Preferably, the shaft 1 is made of an elastic Nickel Titanium alloy such as for instance Nitinol (Trade Name) or Tinel Alloy (Trade Name). Other materials are also possible, for instance plastic materials. The lumen 4 is surrounded by a wall 5 forming the shaft 1 and having a first portion of length 6 and a second portion of length 7. The first portion of length 6 is located in the distal area 2 of the shaft 1 and it has a first thickness 8; the second portion of length 7 is located in the proximal area 3 of shaft 1 and it has a second thickness 9, smaller than the first thickness 8, thereby achieving a resistance to kinking which is smaller than that of the first portion of length 6. The difference in thickness results from the fact that the first portion of length 6 has an outer diameter 11 longer than the diameter 12 of the second portion of length 7. The first portion of length 6 has a plurality of slots 10 formed therein for entry of the pressure medium; some of these slots 10 are proximal of the first portion of length 6 and some other of these slots are distal of the first portion of length 6. A coil 13, preferably of a high density metal such as for instance Tungsten, is mounted on the second portion of length 7 for supporting purposes. This high density metal coil also provides a radiopaque reference for the first portion of length 6. This coil 13 is in flush alignment with the outer diameter 11 of the first portion of length 6. The second portion of length 7 is preceded proximally by a third portion of length 14 of wall 5 having an outer diameter 15 greater than the second diameter 12, in the example shown, equal to the first outer diameter 11. The coil 13 is thus comprised between the first diameter 11 and the third diameter 15. The distal area 2 of shaft 1 terminates in a flexible assembly 16 comprising a coil 17, preferably made of a high density metal such as Tungsten, which also provides a radiopaque reference for the first portion of length 6 which is thus easily locatable between the two radiopaque references provided for by coils 13 and 17. The coil 17 abuts proximally on the distal end 18 of shaft 1 and its distal extremity terminates into a tip 19. A cylindrical core 20, for example of stainless steel, has its proximal portion 21 affixed, for instance welded, into the distal end 18 of shaft 1; core 19 tapers into a flattened straight .and narrow distal portion 22 which terminates by welding into the tip 19. Variants are available without departing from the scope of the invention. For instance, the flexible assembly 16 of the first embodiment of Figure 1 may be replaced by the flexible assembly 44 of the embodiment of Figure 2 and vice versa. The second portion of length 7 of the embodiment of Figure 1 may have an inner diameter which is larger than the inner diameter of the first portion of length 6, whereby the coil 13 may be located inside the second portion of length 7, preferably in flush alignment with the inner diameter of the first portion of length.

Claims: A pressure measuring guide wire comprising an elongated flexible shaft (1, 31) with a proximal area (3, 33), a distal area (2, 32), a lumen (4, 34) extending through the shaft, wall means (5, 35) surrounding said lumen, and lateral aperture means (10, 38) for entry of a pressure medium into the lumen, wherein said wall means (5, 35) have a first portion of length (6, 36) having a first resistance to kinking, a second portion of length (7, 37) having a second resistance to kinking, said second resistance to kinking being smaller than said first resistance to kinking, and wherein coil means (13, 39) are supporting said second portion of length (7, 37), characterized in that said first portion of length (6) is in the distal area (2) of the shaft (1). A pressure measuring guide wire according to claim 1, wherein said first portion of length (6) has a first thickness (8) and said second portion of length (7) has a second thickness (9) smaller than said first thickness (7), and wherein said first portion of length (6) has a plurality of slots (10) formed therein as aperture means. A pressure measuring guide wire according to claim 2, wherein said first portion of length (6) has a first outer diameter (11) and said second portion of length (7) has a second outer diameter (12) smaller than said first outer diameter (11), and wherein said coil means (13) surround said second portion of length (7). A pressure measuring guide wire according to claim 3, wherein said second portion of length (7) is preceded proximally by a third portion of length (14) having a third outer diameter (15) larger than said second outer diameter (12), and wherein the coil means (13) surround the second portion of length (7) between said first (11) and third (15) outer diameters. A pressure measuring guide wire according to any of claims 3 or 4, wherein the coil means (13) are in flush alignment with said first outer diameter (11). A pressure measuring guide wire according to claim 2, wherein said first portion of length (6) has a first inner diameter and said second portion of length (7) has a second inner diameter larger than said first inner diameter, and wherein said coil means (13) are located within said second portion of length. A pressure measuring guide wire according to claim 6, wherein the coil means (13) are in flush alignment with said first inner diameter. A pressure measuring guide wire according to any of claims 2, 3, 4, 5, 6 or 7, wherein some of said slots (10) are proximal of said first portion of length (6) and some other slots (10) are distal of the first portion of length (6). A pressure measuring guide wire according to any preceding claim, wherein the shaft (1) is made of an elastic Nickel Titanium alloy. A pressure measuring guide wire according to any preceding claim, wherein said coil means (13) are made of high density metal. A pressure measuring guide wire according to claim 10, wherein the coil means (13 ) are made of tungsten. A pressure measuring guide wire according to any preceding claim, wherein the distal area of the shaft (1) terminates in helical coil means (17) defining a flexible assembly (16) having a distal portion terminating into a tip (19). A pressure measuring guide wire according to claim 12, wherein said helical coil means (17) are made of high density metal.

Inventors: SCHWAGER MICHAEL, SCHWAGER, MICHAEL
Applicants: SCHNEIDER EUROP GMBH, SCHNEIDER (EUROPE) GMBH
Application year: 1995
Main classification: A61B5
IPC codes: A61B5, A61M25