JP2001309984A - Stent for maintaining openability of stenosis portion in lumen - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a stent for maintaining the openability of a stenosis portion in lumen by which the restenosis due to excess cell growth in tunica intima can be suppressed. SOLUTION: A coil stent is provided, with which the openability of the stenosis portion of lumen is maintained. The coil pitch PA at the center O of the stent 11A is smaller than the coil pitch PB at the end of the stent 11A.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a stent for securing the patency of a stenosis site in a body lumen.

[0002]

2. Description of the Related Art PTCA (Percutaneous Transluminal Coro) which expands a coronary artery constricted by arteriosclerosis using a balloon or the like.
Although nary angioplasty is an effective treatment, the occurrence of restenosis after treatment is problematic. As a countermeasure, it is known that a coiled or cylindrical intravascular support called a stent is placed in a blood vessel to secure the patency of the blood vessel. Tube stents and coil stents are known as stents. Each stent is for preventing restenosis of a blood vessel by a function of mechanically supporting the inside of the blood vessel. For the stent, for example, "INNERV
ISION "(9-1) 1994, pp. 40-43 (clinical application of wall stents) and" Modern Medicine "Vol.
27, no. 9. 1995, pages 177-182, "Advances in Angioplasty and Expansion of Indications".

[0003] Coil stents are generally structurally flexible and are suitable for placement in tortuous blood vessels. On the other hand, there is a problem that it is relatively weak against stress in the radial direction and is easily deformed. Products include “Cord
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[0004]

However, even when a conventional stent is placed at a stenosis site in a blood vessel, the stenosis may again occur at this site. This is mainly due to the proliferation of cells in the intima. However, in the conventional stent, no measures have been taken against restenosis caused by hyperproliferation of cells in the intima of the blood vessel.

[0005] It is an object of the present invention to provide a stent for securing the patency of a stenosis site in a body lumen so as to suppress restenosis caused by hyperproliferation of cells in a vascular intima. .

[0006]

SUMMARY OF THE INVENTION The present invention relates to a stent for securing the patency of a stenosis site in a body lumen. The stent comprises a constant width portion having a constant diameter, and a constant width portion. And a pair of reduced diameter portions each having a diameter smaller than the diameter of the constant width portion.

Further, the present invention relates to a coil stent for securing the patency of a stenosis site in a body lumen, wherein the coil pitch at the center of the coil stent is greater than the coil pitch at the end of the coil stent. The present invention relates to a coil stent characterized by being small.

The present inventor has identified one of the causes of hyperproliferation of the intima of the blood vessel.
One of the reasons is that the stent is in compression and hyperextension of the blood vessel wall. It was conceived that this would suppress the hyperproliferation of cells in the vascular intima. As a result, restenosis due to hyperproliferation of cells in the vascular intima can be suppressed. Conventional stents all have a constant overall length or wide ends.

Particularly preferably, from the boundary between the reduced diameter portion and the constant width portion, toward the end of the reduced diameter portion (the end of the stent)
The diameter of the stent gradually decreases. If the diameter of the reduced diameter portion is reduced stepwise (stepwise), a relatively large stress may be applied to the blood vessel wall at the step where the diameter changes, or cell growth may be promoted. This problem can be eliminated by gradually reducing the diameter of the reduced diameter portion. In particular, by providing the reduced diameter portion on the rotational cosine curved surface, the average tension applied from the stent to the blood vessel wall can be reduced by 15-.
It was confirmed that it could be reduced by about 30%.

FIG. 1A is a perspective view schematically showing a coil stent 1 according to an embodiment of the present invention.
(B) is a graph showing a cosine curve before rotation. FIG.
FIG. 2 is a cross-sectional view of the coil stent 1 of FIG.

The coil stent 1 is wound in the direction of the central axis x-axis. A constant width portion 2 having a constant diameter is provided at the center of the coil stent 1, and reduced diameter portions 3A and 3B are provided on both sides of the constant width portion 2, respectively. The diameter of the constant width part 2 is a + μa, and the diameter of the end of the reduced diameter part is a. A is the outer diameter of the stent before expansion. On the x-axis, -xa to xa is the constant width portion 2;
xa to -xb and xa to xb are reduced diameter portions 3A and 3B
It is. In FIG. 1B, the area corresponding to the reduced diameter portion is x
It is a cosine curve centered on the axis. By rotating this cosine curve around the x-axis, a rotation cosine curve is obtained. A coil stent is formed along a rotation cosine curve.

The metal wires 4 constituting the coil stent 1 are:
Preferably, besides medical stainless steel, tanta
Can be made from lum or nitinol. Further, a shape memory alloy, a medical synthetic resin, or the like can be used.

Further, the present inventor has discovered that in a coil stent, the blood flow rate can be controlled by adjusting the coil pitch. Factors involved in the proliferation of cells in the intima of the blood vessel include wall shear stress applied to the blood vessel wall by blood flow. Therefore, the present inventor conducted a perfusion model experiment and confirmed that when the coil stent was inserted into the circular tube, the flow velocity near the inner wall of the circular tube also increased or decreased as the coil pitch increased or decreased. In particular, it has been found that the flow velocity near the inner wall of the pipe becomes smaller by decreasing the coil pitch, and the flow velocity becomes larger near the inner wall of the pipe by increasing the coil pitch when the flow velocity exceeds a certain level. Moreover, the flow velocity near the bottom wall of the circular pipe was substantially linearly proportional to the coil pitch. Therefore, by controlling the coil pitch,
When the coil stent is inserted into a blood vessel, the flow rate of blood near the inner wall of the blood vessel can be controlled. Based on this finding, the present inventor has conceived to make the coil pitch at the center of the coil stent smaller than at least the coil pitch at the end.

When such a coil stent is placed at a stenosis site, the flow velocity near the inner wall of the blood vessel is optimized at the stenosis site, whereby the proliferation of cells in the intima of the blood vessel can be suppressed. This is because the center of the coil stent is located near the center of the stenosis site. In the vicinity of the center of the stenosis site, the proliferation of cells naturally tends to be most active, and the degree of cell proliferation generally decreases as the distance from the center increases. Therefore, it is necessary to minimize the cell proliferation near the center of the stenosis site, particularly by reducing the blood flow velocity near the inner wall of the blood vessel. According to the coil stent of the present invention,
Since the center of the coil stent is located near the center of the stenosis site and the coil pitch at the center of the coil stent is small, it is possible to reduce the flow velocity near the inner wall of the blood vessel near the center of the stenosis site.

In the coil stent of the present invention, the coil pitch on the terminal side is relatively increased at the same time, thereby improving the blood circulation state on the terminal side. On the other hand, if the coil pitch on the distal side is also reduced, the blood flow velocity near the inner wall of the blood vessel certainly decreases. However, if the coil pitch of the coil stent is reduced over its entire length,
Resistance to blood flow inside the coil stent is increased (flow velocity near the central axis is increased). In the present invention, such an increase in the resistance to blood flow is suppressed, and in particular, by reducing the coil pitch in the vicinity of the center of the stenosis site, the flow velocity in the vicinity of the inner wall of the blood vessel is reduced, and the proliferation of intimal cells is suppressed. It is.

Generally, disadvantages of the coil stent include:
It is stated that resistance to radial stress is weak. If the resistance in the radial direction is weak, the coil stent is likely to be crushed when the cells in the intima of the blood vessel proliferate, so that restenosis is likely to occur. However, when the coil stent of the present invention is placed in a stenosis site, the proliferation of cells in the intima of the blood vessel itself can be suppressed as described above, and thus the weakness against radial stress can be covered. In addition, flexibility, which is an advantage of the coil stent, can be enjoyed.

(Coil pitch at the end of the coil stent) / (coil pitch at the center of the coil stent) is preferably 1.5 times or more, more preferably 2 times or more. Further, the coil pitch is preferably in the range of 1-2 mm as a whole.

The center of the coil stent means a position corresponding to the center of the coil stent when viewed in the direction of the central axis of the coil stent.

In a preferred embodiment of the present invention, the coil stent comprises a central portion having a constant coil pitch,
A pair of ends provided on both sides of the central portion and having a constant coil pitch larger than the coil pitch of the central portion. In this case, the coil pitch changes stepwise between the center and the end. Such coil stents are relatively easy to manufacture.

FIG. 3 is a sectional view showing a coil stent 11A according to this embodiment. Coil stent 11A
Includes a central portion 12 having a coil pitch of PA and a pair of end portions 13A and 13B having a coil pitch of PB. As mentioned above, PA is smaller than PB.
O is the center of the coil stent 11A.

In another embodiment of the present invention, the coil pitch gradually decreases from the distal end to the center of the coil stent. FIG. 4 is a sectional view showing a coil stent 11B according to this embodiment. Coil stent 1
The coil pitch at the center O of 1B is P1, but the coil pitch becomes P2, P3, P
Increase toward four.

As shown in FIG. 5, a constant width portion having a constant diameter, and a constant width portion are provided on both sides of the constant width portion, respectively.
A pair of reduced diameter portions having a diameter smaller than the diameter of the constant width portion can be provided. For example, the coil stent 1 shown in FIG.
1C has a central portion 12B and a pair of end portions 13C and 13D. The coil pitch in the central portion 12B is PA, and the diameter is constant. The coil pitch at the ends 13C and 13D is PB, which also serves as a reduced diameter portion.
PA is smaller than PB. The center portion is a constant width portion having a constant diameter, and the end portions 13C and 13D have coils formed on the above-described curved cosine curved surface.

The present inventor conducted an in vitro perfusion test to investigate the relationship between the coil pitch and the flow rate of the fluid near the inner wall of the tube. Specifically, a wire diameter of 0.5 mm, a coil outer diameter of 4 mm, and a glass circular pipe having an inner diameter of 4 mm and an outer diameter of 6 mm are used.
A 45 mm long coil stent was inserted. A fluid (100 ml, hematocrit value of about 0.5%) in which rat erythrocytes were suspended in water as tracer particles was sent into the circular tube. The flow near the coil stent is measured using a microscope and a high-speed video motion analysis system (Kodak EktaP).
ro Modol 1012). The amount of liquid sent was 30, 60, and 90 ml / min. Particles flowing in a region within 1 mm from the inner wall of the circular tube were traced. The movement distance along the trajectory of the particles is measured frame-by-frame (250 frames / second) from the radial direction of the pipe,
The average flow rate was determined.

In the vicinity of the inner wall of the pipe, a complicated spiral flow was observed due to the influence of the flow near the coil stent and the central axis of the pipe. The correlation between the pitch of the coil stent and the flow velocity in the vicinity of the inner wall became higher as the flow rate increased. FIG. 6 (a) shows the relationship between the coil pitch and the flow rate when the flow rate is 60 ml / min, and FIG. 6 (b) shows the relationship between the coil pitch and the flow rate when the flow rate is 90 ml / min. Show. The correlation function r is as follows:
1 / min is 0.07, and the amount of liquid sent is 60 ml / min.
Min. Was 0.11, and when the amount of liquid sent was 90 ml / min, it became remarkably 0.47. As a result, it was found that as the coil pitch decreased, the flow velocity near the inner wall of the circular pipe decreased. Therefore, it can be seen that the flow rate of blood near the inner wall can be reduced by reducing the coil pitch in the central portion of the stenosis site where the proliferation of cells in the vascular intima is active.

[Brief description of the drawings]

FIG. 1 (a) is a perspective view showing a coil stent 1, and FIG. 1 (b) shows a cosine curve before rotation.

FIG. 2 is a cross-sectional view of the coil stent 1 of FIG.

FIG. 3 is a cross-sectional view showing a coil stent 11A including a central portion 12 and a pair of end portions 13A and 13B.

FIG. 4 is a cross-sectional view showing a coil stent 11B in which the coil pitch gradually decreases from the center to the end.

FIG. 5 is a cross-sectional view showing a coil stent 11C having a central portion 12B (also serving as a constant width portion) and a pair of ends 13C and 13D (also serving as a reduced diameter portion).

FIGS. 6A and 6B are graphs showing the relationship between the pitch of a coil stent placed in a circular pipe and the flow velocity of the fluid near the inner wall when the fluid flows in the circular pipe.

[Explanation of symbols]

 1, 11A, 11B, 11C Coil stent 2, 12B Constant width part 3A, 3B, 13C, 13D Reduced diameter part 4 Metal wire 12A, 12B Central part 13A, 13B, 13C, 13D End O Center of coil stent PA, PB , P1, P2, P3, P4 Coil pitch

Claims (8)

[Claims] 1. A stent for securing the patency of a stenosis site in a body lumen, wherein the stent is provided on a constant width portion having a constant diameter and on both sides of the constant width portion. And a pair of reduced diameter portions having a diameter smaller than the diameter of the constant width portion. 2. The method according to claim 1, wherein the diameter of the reduced diameter portion is gradually reduced from a boundary between the reduced diameter portion and the constant width portion toward an end of the reduced diameter portion. The stent according to any of the preceding claims. 3. The stent according to claim 2, wherein the reduced diameter portion is formed on a rotational cosine curved surface obtained by rotating a cosine curve about a central axis of the stent. 4. The stent according to claim 1, wherein the stent comprises a coil stent. 5. A coil stent for securing patency of a stenosis site in a body lumen, wherein a coil pitch at the center of the coil stent is smaller than a coil pitch at an end of the coil stent. Characterized by a coil stent. 6. A central portion having a constant coil pitch, and a pair of end portions provided on both sides of the central portion and having a constant coil pitch larger than the coil pitch of the central portion. The coil stent according to claim 5, comprising: 7. The coil stent according to claim 5, wherein the coil pitch gradually decreases from the end to the center of the coil stent. 8. A constant width portion having a constant diameter, and a pair of reduced diameter portions provided on both sides of the constant width portion and having a diameter smaller than the diameter of the constant width portion. The coil stent according to any one of claims 5 to 7, characterized in that: