Blood vessel cover

Abstract

Provided is a blood vessel cover capable of preventing intimal thickening by remodeling a vein into a low-pressure buffer vessel.　A blood vessel cover (10) is disposed on the outer peripheral side of a vein (4) anastomosed to an artificial blood vessel (5) anastomosed to an artery, the blood vessel cover (10) including, in the axial direction (x): one end portion (11) extending up to a point of 5 mm from one end (10a) of the blood vessel cover (10) toward the other end (10b); and the other end portion (12) extending up to a point of 5 mm from the other end (10b) toward the one end (10a). The 30% elastic index of the one end portion (11) is 0.6 N or more, and the 30% elastic index of the other end portion (12) is 0.4 N or less.

Description

Blood vessel cover

[0001] The present invention relates to a vascular cover for use at an anastomosis site where blood vessels are anastomosed, such as an anastomosis between an artery and a vein at a shunt creation site, or an anastomosis between an artificial blood vessel anastomosed to an artery and a vein, and relates to a vascular cover that can be placed on the outer periphery of the vein at the anastomosis site.

[0002] Patients with severe kidney disease, including renal failure, regularly undergo hemodialysis treatment, in which blood is withdrawn from the patient's body, removed from the body using a dialyzer to remove waste products, excess water, minerals, and other substances, and then returned to the patient's body. Hemodialysis typically involves inserting a specialized needle into a vein. Because normal venous blood flow is insufficient for dialysis, an artery is anastomosed to a vein. This type of blood vessel is called a shunt, and is typically created by exposing the artery and vein through an incision in the skin of the arm, making a small incision in the artery, anastomosing the vein thereto, and diverting a portion of the arterial blood flow to the vein. A shunt can be created by anastomosing the vein directly to the artery, or by anastomosing one end of an artificial blood vessel to the small incision in the artery and the other end of the artificial blood vessel to the vein, creating a shunt between the artery and vein.

[0003] If this abnormal blood flow state is within the range that the body can tolerate, appropriate remodeling due to changes in the elasticity of the venous wall may occur as a defensive and adaptive response, avoiding stenosis or occlusion due to intimal thickening, or the shunt blood flow state may be self-regulated to a state that does not burden the body. However, if this abnormal blood flow state exceeds the local conditions at the shunt or systemic conditions (diabetes, hypertension, arteriosclerosis, blood condition, etc.), appropriate defensive and adaptive responses will not occur, resulting in a pathological biological reaction and causing local or systemic pathology.

[0004] To address these issues, for example, Non-Patent Document 1 discloses that venous wall reinforcement using vascular banding or a vascular cover is used to suppress the initial rapid increase in blood flow immediately after surgery by reinforcing the venous wall from the outside, thereby preventing excessive blood pressure in the inner vein and the resulting overstretching and blood turbulence. Patent Document 1 also discloses a covering for reinforcing natural veins used as surgical implants, which is a knitted fabric net covering made by forming a seamless, tubular, and substantially pileless knitted fabric. Furthermore, Patent Documents 2 and 3 disclose that arteriovenous grafts (AVGs) wrapped with a restrictive fiber matrix of a biodegradable polymer exhibited pulsatile radial deviation similar to that of the carotid artery.

[0005] Special table 2004-535896 Publication Special table 2010-516437 Publication Special table 2013-509258

[0006] Hiroaki Haruguchi, "I. Blood Access: Problems Associated with Blood Flow Insufficiency," Journal of the Japanese Society of Dialysis Therapy, Vol. 15, No. 1, 68-70, 2000

[0007] However, the above-mentioned reinforcement methods, such as vascular banding, have not been able to sufficiently prevent lesions such as intimal hyperplasia. In conventional vascular banding, the reinforcing material has a "hard" elasticity that is close to the mechanical compliance of an artery. A vein wall reinforced with such a "hard" reinforcing material is modified (arterialized) into a structure similar to that of an arterial wall only under certain conditions.

[0008] Here, we will explain "arterialization." Except for a few special arteries, such as those upstream of the human thoracic aorta, most normal arteries in the body, including all arteries in the limbs, are called muscular arteries. These normal arteries, or muscular arteries, comprise, for example, the most central arteries in the limbs, through the smaller arteries further downstream, and down to the small arterioles just before they flow into the arterioles. These muscular arteries have a unique structure and a unique function achieved by that structure. This unique structure, as described below, is a structure with a "smooth muscle > elastic fiber" structure. Another unique function is that, due to the unique structure described above, arteries maintain the sufficiently rigid wall rigidity characteristic of arteries, which allows them to deliver pulsatile blood pressure and blood flow to the arterioles (inner diameters of 100 to several hundred microns) at the extremities without damping or buffering. As the diameter of these muscular arteries decreases from a few millimeters to less than 1 mm, the vascular lumen becomes smaller and the vascular wall becomes thinner, but the blood pressure, pulse amplitude, and mean flow velocity remain constant at approximately 120 / 80 mmHg, almost unchanged from the aorta. If blood pressure, pulse pressure, and blood flow were to be dampened or reduced anywhere between the aorta and arteries in the limbs with an inner diameter of less than 1 mm, the supply of oxygen and nutrients to the limbs would be reduced, leading to necrosis. In other words, normal arteries in the limbs have a uniquely high wall rigidity, functioning to never dampen or dampen the pulsatile arterial blood flow that flows through their lumen at high blood pressure and high speeds. In other words, normal arteries do not possess a buffering function; rather, they are specialized in maintaining and delivering pulsatile arterial blood flow at high speeds, eliminating the buffering function for high-speed pulsatile arterial blood flow under high blood pressure. Therefore, even in veins that have been arterialized, i.e., remodeled to have a structure similar to that of a normal artery, they do not have the function of buffering the pulsatile arterial blood flow that flows through their lumen at high speeds and high blood pressures, and therefore cannot be expected to have this buffering function.

[0009] As described above, the "arterialized" vein has a stiff wall stiffness similar to that of a normal artery and only very low buffering function. Therefore, when blood flows from the "arterialized" reinforced vein to the unreinforced downstream vein, the blood pressure and pulsation are delivered directly to the downstream vein with little or no buffering. As described above, conventional reinforcement methods such as vascular banding create a stiff vein wall, reinforced with a "hard" cover, or an arterialized vein, whose mechanical compliance is similar to that of a conventional artery. This creates a significant compliance mismatch between the stiff vein wall at this location and the soft, unreinforced vein wall immediately downstream. Insufficiently buffered arterial blood flow flows into this compliance mismatch, causing the soft vein wall to overstretch due to the pulsatile, high-pressure arterial blood flow, resulting in intimal thickening and stenosis as a pathological response. Thus, conventional reinforcement methods have not fundamentally resolved the causes of intimal thickening. To resolve this, the upstream end of the anastomosis needs to have a "hard" elasticity that is relatively similar to that of an artery or artificial blood vessel, while the downstream end of the anastomosis needs to have a "soft" elasticity that is relatively similar to that of a vein. This prevents the formation of a compliance mismatch area at these two ends. Furthermore, by reinforcing the wall between the upstream and downstream ends with a reinforcing material that provides sufficient buffering functionality, the blood pressure and pulsatility can be gradually reduced from the anastomosis to the downstream end, and the downstream vein side can be remodeled to a vascular state with poor pulsatility and low pressure, i.e., a low-pressure buffering vessel state.

[0010] The present invention has been made in consideration of the above circumstances, and aims to provide a vascular cover that can prevent intimal thickening by remodeling a vein into a low-pressure buffering vessel that does not cause compliance mismatch at both ends as described above and can deliver blood to a downstream vein while gradually reducing the blood pressure, pulse pressure, excessive blood flow rate, and flow velocity of the blood flowing through the lumen.

[0011] A vascular cover according to one embodiment of the present invention that solves the above problems is as follows: [1] A vascular cover to be placed on the outer periphery of a vein anastomosed to an artificial blood vessel anastomosed to an artery, the vascular cover having one end extending 5 mm from one end of the vascular cover toward the other end in the axial direction, and another end extending 5 mm from the other end toward the one end, and when the elasticity index (hereinafter referred to as the 30% elasticity index) when the inner diameter of the vascular cover is radially expanded 30% from its natural state (hereinafter referred to as the 30% elasticity index) is measured using the following method, the 30% elasticity index of the one end is 0.6 N or more, and the 30% elasticity index of the other end is 0.4 N or less. [Measurement Method] The vascular cover is cut along a circumferential cut line perpendicular to the axial direction to prepare a sample with an axial length of 5 mm. A first pin and a second pin with a diameter d of 0.75 mm are inserted into the lumen of the sample parallel to the axial direction of the sample. The first pin is fixed, and the second pin is pulled outward in the radial direction of the sample. When the distance between the first pin and the second pin is L, the force F when πd+2L becomes 1.3 times the circumferential length of the sample in its natural state is １．３ Measure and F １．３ The value obtained by dividing by the strain [(1.3-1.0) / 1.0] is defined as the 30% elasticity index. The reason why the 30% elasticity index is useful as an index will be explained later.

[0012] The vascular cover of the above [1] is preferably the following [2] or [3]: [2] The vascular cover of [1], wherein the 30% elasticity index of the one end is 15 N or less. [3] The vascular cover of [1] or [2], wherein the 30% elasticity index of the other end is 0.1 mN or more.

[0013] Another embodiment of the present invention that solves the above problem is as follows: [4] A vascular cover placed on the outer periphery of a vein anastomosed to an artery, the vascular cover having one end extending 5 mm from one end of the vascular cover toward the other end in the axial direction and another end extending 5 mm from the other end toward the one end, and when the elasticity index (hereinafter referred to as the 30% elasticity index) when the inner diameter of the vascular cover is radially expanded 30% from its natural state is measured using the following method, the 30% elasticity index of the one end is 0.4 N or more and the 30% elasticity index of the other end is 0.3 N or less. [Measurement Method] The vascular cover is cut along a circumferential cut line perpendicular to the axial direction to prepare a sample with an axial length of 5 mm. A first pin and a second pin with a diameter d of 0.75 mm are inserted into the lumen of the sample parallel to the axial direction of the sample. The first pin is fixed, and the second pin is pulled outward in the radial direction of the sample. When the distance between the first pin and the second pin is L, the force F when πd+2L becomes 1.3 times the circumferential length of the sample in its natural state is １．３ Measure and F １．３ The value obtained by dividing by the strain [(1.3-1.0) / 1.0] is the 30% elasticity index.

[0014] The vascular cover of the above [4] is preferably the following [5] or [6]. [5] The vascular cover of [4], wherein the 30% elasticity index of the one end is 3N or less. [6] The vascular cover of [4] or [5], wherein the 30% elasticity index of the other end is 0.1 mN or more.

[0015] The vascular cover has a 30% elasticity index of 0.6 N or more at one end and a 30% elasticity index of 0.4 N or less at the other end in the case of artificial vascular venous anastomosis (AVG), and a 30% elasticity index of 0.4 N or more at one end and a 30% elasticity index of 0.3 N or less at the other end in the case of arteriovenous anastomosis (AVF). With this configuration, by placing one end on the outer periphery of the vein upstream of the shunt creation site and the other end on the outer periphery of the vein downstream, the downstream side of the vein can be covered more loosely. As a result, pulsatile blood flow with high arterial pressure that flows into the vein at the shunt creation site is gradually buffered in the portion covered by the vascular cover and ultimately transitions to venous blood flow, allowing the vein at the shunt creation site to gradually remodel into a low-pressure buffering vessel from upstream to downstream. Furthermore, while veins may grow outward during the process of remodeling into low-pressure buffer vessels, the vascular cover having the above-described configuration does not impede this growth because the 30% elasticity index of the other end is 0.4 N or less or 0.3 N or less, thereby maintaining a wide lumen of the covered blood vessel and ensuring sufficient blood flow. Thus, the vascular cover of the present invention enables shunt construction that ensures sufficient blood flow while suppressing lesions such as intimal hyperplasia by remodeling veins into low-pressure buffer vessels. Furthermore, as already mentioned, the formation of compliance mismatch areas can be avoided at both ends.

[0016] The vascular cover is preferably any one of the following [7] to

[11] . [7] The vascular cover according to any one of [1] to [6], wherein the value obtained by dividing the difference between the 30% elastic index of one end and the 30% elastic index of the other end by the axial length of the vascular cover (hereinafter, the value obtained by dividing the difference between the elastic index of the one end and the other end by the axial length of the vascular cover may be referred to as the "elastic change rate") is less than 0.6 N / cm. [8] The vascular cover according to any one of [1] to [7], wherein, when the elastic index when the inner diameter of the vascular cover is expanded 60% in the radial direction from the natural state (hereinafter, referred to as the 60% elastic index), is measured by the following method, the value obtained by dividing the difference between the 60% elastic index of one end and the 60% elastic index of the other end by the axial length of the vascular cover, i.e., the elastic change rate of the 60% elastic index, is less than 1.5 N / cm. [Measurement Method] The vascular cover is cut perpendicular to the axial direction along a circumferential cut line of the vascular cover to prepare a sample with an axial length of 5 mm. A first pin and a second pin with a diameter d of 0.75 mm are inserted into the lumen of the sample parallel to the axial direction of the sample. The first pin is fixed, and the second pin is pulled radially outward of the sample. When the distance between the first pin and the second pin is L, the force F when πd + 2L is 1.6 times the circumferential length of the sample in its natural state is measured. １．６ Measure and F １．６ The value obtained by dividing by the strain [(1.6-1.0) / 1.0] is defined as the 60% elasticity index. [9] A vascular cover according to any one of [1] to [8], wherein the inner diameter of the vascular cover is expandable from its natural state to at least 100% in the radial direction throughout the entire axial direction.

[10] A vascular cover according to any one of [1] to [9], wherein the length in the axial direction is 5 mm or more and 150 mm or less.

[11] A vascular cover according to any one of [1] to

[10] , wherein the vascular cover has at least one of a knitted fabric, a woven fabric, and a nonwoven fabric as a partial or entire component.

[0017] A vascular cover according to still another embodiment of the present invention that solves the above-mentioned problems is as follows:

[12] A vascular cover to be placed on the outer periphery of a vein anastomosed to an artificial blood vessel anastomosed to an artery, the vascular cover having one end extending 5 mm from one end of the vascular cover toward the other end in the axial direction, and another end extending 5 mm from the other end toward the one end, and when the elastic index (hereinafter referred to as the 60% elastic index) when the inner diameter of the vascular cover is radially expanded 60% from its natural state is measured by the following method, the 60% elastic index of the one end is 0.65 N or more and the 60% elastic index of the other end is 1.15 N or less, and the 60% elastic index of the other end is smaller than the 60% elastic index of the one end. [Measurement method] The vascular cover is cut perpendicular to the axial direction along a circumferential cut line of the vascular cover to prepare a sample having an axial length of 5 mm. A first pin and a second pin with a diameter d of 0.75 mm are inserted into the inner cavity of the sample parallel to the axial direction of the sample. The first pin is fixed, and the second pin is pulled outward in the radial direction of the sample. When the distance between the first pin and the second pin is L, the force F when πd+2L is 1.6 times the circumference of the sample in its natural state is calculated. １．６ Measure and F １．６ The value obtained by dividing by the strain [(1.6-1.0) / 1.0] is defined as the 60% elasticity index. The reason why the 60% elasticity index is useful as an index will be explained later.

[0018] The blood vessel cover of the above item

[12] is preferably the following item

[13] :

[13] The blood vessel cover according to item

[12] , wherein the 60% elasticity index of the one end is 25 N or less.

[0019] A vascular cover according to still another embodiment of the present invention that solves the above-mentioned problems is as follows:

[14] A vascular cover to be placed on the outer periphery of a vein anastomosed to an artery, the vascular cover having one end extending 5 mm from one end of the vascular cover toward the other end in the axial direction, and another end extending 5 mm from the other end toward the one end, and when the elastic index (hereinafter referred to as the 60% elastic index) when the inner diameter of the vascular cover is radially expanded 60% from its natural state is measured by the following measurement method, the 60% elastic index of the one end is 0.42 N or more and the 60% elastic index of the other end is 1.15 N or less, and the 60% elastic index of the other end is smaller than the 60% elastic index of the one end. [Measurement method] The vascular cover is cut perpendicular to the axial direction along a circumferential cut line of the vascular cover to prepare a sample having an axial length of 5 mm. A first pin and a second pin with a diameter d of 0.75 mm are inserted into the inner cavity of the sample parallel to the axial direction of the sample. The first pin is fixed, and the second pin is pulled outward in the radial direction of the sample. When the distance between the first pin and the second pin is L, the force F when πd+2L is 1.6 times the circumference of the sample in its natural state is calculated. １．６ Measure and F １．６ The value obtained by dividing by the strain [(1.6-1.0) / 1.0] is the 60% elasticity index.

[0020] The blood vessel cover of the above item

[14] is preferably the following item

[15] :

[15] The blood vessel cover according to item

[14] , wherein the 60% elasticity index of the one end is 5N or less.

[0021] The vascular cover is preferably the following

[16] :

[16] The vascular cover according to any one of

[12] to

[15] , wherein the difference between the 60% elastic index of the one end and the 60% elastic index of the other end is divided by the length of the vascular cover in the axial direction, i.e., the elastic change rate of the 60% elastic index is less than 1.5 N / cm.

[0022] The vascular cover of the present invention, having the above-described configuration, can prevent the formation of compliance mismatch areas at both ends, and further, by covering the vein at the shunt creation site, it gradually changes the vein wall structure from the anastomosis site downstream, and within the covered vein, it is possible to gradually change the shear stress, pressure perpendicular to the vascular wall, blood flow rate, blood flow velocity, and the amplitude of change associated with pulsation, thereby suppressing vascular wall elasticity mismatch, blood turbulence, and excessively high blood flow rates, preventing intimal thickening, and ultimately enabling successful remodeling into a low-pressure buffered blood vessel. The following are thought to be the reasons why the vascular cover of the present invention has such effects.

[0023] Both arteries and veins consist of a tunica intima, a tunica media, and a tunica adventitia. In arteries, the tunica media is composed of a smooth muscle cell-rich smooth muscle layer and an elastic fiber layer. Arteries possess thick smooth muscle and elastic fiber layers to minimize pulsatile changes in the vascular wall and minimize turbulence and frictional stress fluctuations even under the pressure of pulsatile intraluminal blood flow. On the other hand, veins have thin vascular walls and lack the thick smooth muscle and elastic fiber layers found in arteries. When arterial blood flows directly into such veins via an arteriovenous shunt, the compliance mismatch between the artery and the vein, as described above, can lead to lesions such as intimal thickening. To prevent this, the anastomosis site, i.e., the most upstream part of the vein, experiences 100% pulsatile arterial pressure, but the blood pressure, pulsatility, blood flow rate, and maximum flow velocity gradually decrease downstream. The most downstream vein requires remodeling to create a low-pressure buffer vessel, i.e., a vessel with attenuated pulsatility and capable of lowering blood pressure.

[0024] The vascular cover of the present invention, having the above-described configuration, can remodel the vein at the shunt creation site so that the high-pressure pulsatile blood flow that flows into the vein at the arteriovenous anastomosis of the shunt creation site or the venous anastomosis of the artificial blood vessel is gradually buffered downstream and finally converted into venous blood flow, thereby forming a low-pressure buffering vessel. As a result, blood turbulence and pulsatile expansion and stress changes in the venous wall are suppressed, and lesions such as intimal hyperplasia can be prevented.

[0025] Furthermore, the vascular cover of the present invention having the above-mentioned configuration does not interfere with the gradual outward growth that may occur during the process of remodeling of the vein into a low-pressure buffering vessel, and as a result, it is possible to maintain a wide vascular lumen and ensure sufficient blood flow, thereby enabling the creation of a shunt that ensures sufficient blood flow while suppressing lesions such as intimal hyperplasia.

[0026] FIG. 5 shows a schematic diagram of an example of a shunt creation portion in an artificial vascular venous anastomosis (AVG). FIG. 6 shows a schematic diagram of an example of a shunt creation portion in an arteriovenous anastomosis (AVF). FIG. 7 shows a perspective view of a vascular cover according to one embodiment of the present invention when placed on the outer peripheral side of a vein at a shunt creation portion in an artificial vascular venous anastomosis (AVG). FIG. 8 shows a perspective view of a vascular cover according to one embodiment of the present invention when placed on the outer peripheral side of a vein at a shunt creation portion in an arteriovenous anastomosis (AVF). FIG. 9 shows a perspective view illustrating a method for measuring an elasticity index. FIG. 10 shows a plan view of FIG. 5 as viewed from above.

[0027] The present invention will be described below based on the embodiments, but the present invention is not limited to the following embodiments and can be implemented with appropriate modifications within the scope of the above and below-described purposes, and all such modifications are included within the technical scope of the present invention. In addition, hatching and component symbols may be omitted in each drawing for convenience. In such cases, please refer to the specification or other drawings. Furthermore, the dimensions of various components in the drawings may differ from the actual dimensions, as priority is given to helping understand the features of the present invention.

[0028] A vascular cover according to an embodiment of the present invention will be described with reference to the drawings. It should be noted that the present invention is not limited to the embodiments shown in the drawings. Fig. 1 is a schematic diagram of a shunt construction site in an artificial vascular venous anastomosis (AVG), i.e., a shunt construction site in which one end of an artificial blood vessel is anastomosed to a small incision in an artery and a vein is anastomosed to the other end of the artificial blood vessel. Fig. 2 is a schematic diagram of a shunt construction site in an arteriovenous anastomosis (AVF), i.e., a shunt construction site in which an autologous vein is anastomosed to a small incision in an artery. Fig. 3 is a perspective view of a vascular cover according to an embodiment of the present invention placed on the outer periphery of a vein at a shunt construction site in an artificial vascular venous anastomosis (AVG). Fig. 4 is a perspective view of a vascular cover according to an embodiment of the present invention placed on the outer periphery of a vein at a shunt construction site in an arteriovenous anastomosis (AVF). Fig. 5 is a perspective view showing a method for measuring the elasticity index, and Fig. 6 is a plan view of Fig. 5 viewed from above.

[0029] The shunt 1 can be formed by performing an artificial vascular venous anastomosis (AVG) as shown in FIG. 1 or an arteriovenous anastomosis (AVF) as shown in FIG.

[0030] As shown in Figure 1, a shunt 1 can be formed by anastomosing one end of an artificial blood vessel 5 to a small incision in an artery 3 in an arm 2, and anastomosing a vein 4 to the other end of the artificial blood vessel 5. In this case, blood flows from the artery 3 through the artificial blood vessel 5 and further through the anastomosis 6 to the vein 4 in the direction shown by arrow B. This type of anastomosis is generally called an artificial venous anastomosis (AVG).

[0031] As shown in Figure 2, a shunt 1 can also be created by anastomosing a vein 4 to a small incision in an artery 3 in an arm 2, allowing blood flow from the artery 3 to flow into the vein 4. In this case, blood flows from the artery 3 through the anastomosis 6 and into the vein 4 in the direction indicated by arrow B. This type of anastomosis is generally called an arteriovenous anastomosis (AVF).

[0032] The vascular cover 10 according to an embodiment of the present invention can be placed on the outer periphery of the vein 4 downstream from the anastomosis 6 in either the artificial blood vessel venous anastomosis shown in FIG. 1 or the arteriovenous anastomosis shown in FIG. 2, and can remodel the vein 4 into a low-pressure buffering vessel.

[0033] In either case, as shown in Figures 3 and 4, the vascular cover 10 is preferably placed from the most upstream part of the vein 4 on the anastomosis 6 side. The vascular cover 10 has one end 10a and the other end 10b, and it is preferable that the one end 10a is placed on the outer periphery of the vein 4 on the most upstream part of the vein 4 on the anastomosis 6 side, and the other end 10b is placed on the outer periphery of the vein 4 on the downstream side away from the anastomosis 6.

[0034] Although not shown, regardless of whether the vascular cover 10 is anastomosed to the artery 3 or the artificial blood vessel 5, the vascular cover 10 may be positioned to cover not only the vein 4 but also a portion of the artery 3 and the artificial blood vessel 5 on the anastomosis site 6 side.

[0035] The vascular cover 10 may have an accessory further upstream than the one end 10a located on the outer periphery of the vein 4, and this accessory may be located so as to cover a portion of the artery 3 and artificial blood vessel 5 on the anastomosis 6 side. Specifically, the accessory covering the artery 3 or a portion of the artificial blood vessel 5 on the anastomosis 6 side (i.e., the portion attached to the vascular cover 10 further upstream than the one end 10a located on the outer periphery of the vein 4) may be an accessory continuous with the vascular cover 10 and processed into a shape suitable for covering a portion of the artery 3 or artificial blood vessel 5, or a separate member dedicated to covering a portion of the artery 3 or artificial blood vessel 5 may be added further upstream of the one end 10a. Incidentally, these accessory portions of the vascular cover 10 are described in this specification as separate from the description regarding the elasticity of the vascular cover 10 unless otherwise specified.

[0036] The vascular cover 10 has an axial direction x, a radial direction y, and a circumferential direction z. The axial direction x of the vascular cover 10 is the direction in which the central axis of the vascular cover 10 extends, the radial direction y of the vascular cover 10 is the direction connecting the central axis of the vascular cover 10 and a point on the outer edge of the vascular cover 10 in a cross section perpendicular to the axial direction x, and the circumferential direction z is the direction along the outer edge of the vascular cover 10 in a cross section perpendicular to the axial direction x. The vascular cover 10 may have a cylindrical shape that is continuous around its entire circumference, or may have a discontinuous portion in the circumferential direction z in at least a portion in the axial direction x. The vascular cover 10 is made of knitted fabric, woven fabric, net, etc., and may have discontinuous portions due to the shape of the material.

[0037] As shown in FIG. 4, the vascular cover 10 is preferably flexible and can be bent in the axial direction x of the vascular cover 10 so as to follow the extension direction of the vein 4 to be covered.

[0038] The vascular cover 10 preferably has an inner lumen that is circular or elliptical in cross section in the radial direction y. Depending on the material constituting the vascular cover 10 and the structure of the vascular cover 10, the inner periphery or outer periphery of the cross section in the radial direction y may have fine irregularities.

[0039] The vascular cover 10 may have a lumen collapsed under its own weight in its natural state. Even in such a case, the shape of the cross section in the axial direction x, radial direction y, circumferential direction z, and radial direction y can be defined in the same manner as described above by expanding the lumen. One method for expanding a lumen collapsed under its own weight is to insert into the lumen of the vascular cover 10 a tube whose lumen will not collapse under its own weight, whose central axis is parallel to the central axis of the vascular cover 10, and which is inscribed in the inner wall of the vascular cover 10.

[0040] The vascular cover 10 may be cylindrical. Alternatively, the vascular cover 10 may have a joint formed by rolling a flat member into a cylindrical shape and joining it by a method such as suturing. In this case, the joint such as the suture is preferably formed on the outer surface of the vascular cover 10. This prevents the joint from affecting the vein 4. Alternatively, a seamless tubular member without a joint may be formed by using a molded member or knitted fabric.

[0041] The inner diameter of the vascular cover 10 is the diameter of the lumen in the cross section in the radial direction y, and if the shape of the lumen in the cross section in the radial direction y is circular, it is the diameter of the circle. The inner diameter of the vascular cover 10 can also be defined as the value obtained by dividing the perimeter of the inner wall of the vascular cover 10 in the cross section in the radial direction y by pi. This makes it possible to obtain the inner diameter of the vascular cover 10 even if the cross section in the radial direction y of the vascular cover 10 is not circular or if the lumen of the vascular cover 10 is collapsed due to its own weight.

[0042] 1 and 3, the vascular cover 10 is disposed on the outer periphery of the vein 4 anastomosed to the artificial blood vessel 5 anastomosed to the artery 3, and has one end 11 extending 5 mm in the axial direction x from one end 10a of the vascular cover 10 toward the other end 10b, and the other end 12 extending 5 mm in the axial direction x from the other end 10b. When the elastic index (hereinafter referred to as the 30% elastic index) when the inner diameter of the vascular cover 10 is expanded 30% in the radial direction y from its natural state is measured by the following measurement method, the 30% elastic index of the one end 11 is 0.6 N or more, and the elastic index of the other end 12 is 0.4 N or less. [Measurement Method] The vascular cover 10 is cut out perpendicular to the axial direction x along a tangent line in the circumferential direction z of the vascular cover 10, to prepare a cylindrical sample 100 having a length in the axial direction x of 5 mm. A first pin 101 and a second pin 102 with a diameter d of 0.75 mm are inserted into the inner cavity of the cylindrical sample 100 parallel to the axial direction of the cylindrical sample 100. The first pin 101 is fixed, and the second pin 102 is pulled outward in the radial direction of the cylindrical sample 100. When the distance between the first pin 101 and the second pin 102 is L, the force F when πd+2L is 1.3 times the circumferential length of the cylindrical sample 100 in its natural state is calculated. １．３ Measure the force F １．３The value obtained by dividing by the strain [(1.3-1.0) / 1.0] is the 30% elasticity index.

[0043] In such an artificial vascular venous anastomosis (AVG), the vascular cover 10 has a 30% elastic index of 0.6 N or more at one end 11 and a 30% elastic index of 0.4 or less at the other end 12. By positioning the one end 11 upstream of the vein 4 at the shunt 1 and the other end 12 downstream, compliance mismatch between the two ends is avoided, and the stiffness gradually decays between the two ends, allowing for looser coverage of the downstream side of the vein 4. This allows pulsatile blood flow with high arterial pressure that flows into the vein 4 at the shunt 1 to be gradually buffered in the area covered by the vascular cover 10 and ultimately transition to venous blood flow, further enabling the vein 4 at the shunt 1 to be remodeled into a low-pressure buffering vessel. As a result, blood flow turbulence and pulsatile expansion and stress changes in the venous wall are suppressed, preventing lesions such as intimal thickening. The present inventors have found that in the case of an artificial vascular venous anastomosis (AVG) as shown in FIG. 1, the above-mentioned effects can be achieved when the 30% elasticity index of one end 11 and the other end 12 is within the above-mentioned range.

[0044] The preventive effect (effectiveness) of the vascular cover 10 against intimal thickening and occlusion is primarily due to the buffering effect on arterial blood flow caused by the elasticity of the cover wall. This buffering effect can be expressed by three independent elasticity indices: a 30% elasticity index, a 60% elasticity index, and, preferably, the difference between the elasticity indices at one end 10a and the other end 10b divided by the axial length (elasticity change rate). The reason for selecting the 30% elasticity index is explained below. As a preliminary study, the inventors created an arteriovenous shunt between the carotid artery and jugular vein in a dog as an experimental model similar to a human arteriovenous shunt. They then conducted an experiment to examine the expansion of the venous side when arterial blood flow flows from the arterial side to the venous side through the shunt. The reason for selecting the 30% elasticity index was derived from the following experimental findings. To create the arteriovenous shunt, a 60 mm long aluminum tube with a circular lumen and a constant diameter, i.e., a rigid tube with no wall elasticity, was placed over the vein. The aluminum tube has a spirally layered wall, allowing its inner diameter to be freely adjusted and set within a narrow range. The aluminum tube was then moved to the outer periphery of the shunt vein at the most upstream side of the vein anastomosed to the arteriovenous anastomosis, covering the entire circumference of the vein over a length of 60 mm. A vascular clamp was then attached to the upstream artery to block arterial blood flow, and the outer diameter of the vein was measured in a state where a small amount of blood remained inside the vein (hereinafter referred to as the "natural state"). This state is considered to be roughly equivalent to the natural state in vivo, where venous blood is contained within the lumen. The vascular clamp was then removed, and arterial pressure was allowed to flow into the vein from the artery upstream of the shunt. The outer diameter of the vein was then immediately measured at a location just downstream of the covered portion. Next, an ultrasonic blood flowmeter was used to evaluate whether the hemodynamics of the flow through this location were buffered compared to the arterial hemodynamics of the arteriovenous anastomosis.The results showed that when the inner diameter of the coated aluminum tube was set to 1.3 times or more the outer diameter of the natural vein, i.e., when the play between the inner diameter of the tube and the natural vein wall was set to 30% or more of the natural vein diameter, the hemodynamics immediately downstream of the coated portion of the tube was not completely buffered, but was clearly buffered compared to the hemodynamics at the arteriovenous anastomosis. On the other hand, when the inner diameter of the coated tube was set to 1.2 times or less the outer diameter of the natural vein, i.e., when the play between the inner diameter of the tube and the vein wall was set to 2 / 3 times (=20%) or less of 30% of the natural vein diameter, no buffering effect was observed in some cases. These experimental results suggest that when the natural vein dilated to 1.3 times or more its original diameter, a buffering effect due to the elasticity of the vascular wall was observed in all experimental cases, unlike when the vein dilated to 1.2 times or less. Therefore, when considering the buffering of arterial blood flow due to venous dilation, it is more appropriate to use the elasticity at dilation of 1.3 times or more as an indicator rather than the elasticity at dilation of 1.2 times or less. Using this data as a guideline, the inventors used the elasticity index (30% elasticity index) of the low-pressure buffering vessel when the inner diameter was expanded by 1.3 times (i.e., 30%). Furthermore, considering 1.3-fold expansion, although the vein was forcibly expanded from its natural state by internal pressure, this degree of expansion was the minimum expansion state at which a buffering effect was observed in all experimental cases. Therefore, since the expansion stimulus at 1.3 times is gentle, the risk of pathological biological reactions such as intimal hyperplasia is low. Therefore, this is an index of elasticity at gentle expansion stimulus that leads to remodeling into a low-pressure buffering vessel, which is a healthy adaptive response, and is considered useful as a basic elasticity index showing the preventive effect of pathological reactions such as intimal hyperplasia. Of course, in actual arteriovenous shunts, venous expansion does not remain at 30% in clinical practice, and it goes without saying that even greater forced expansion would occur if a reinforcing material were not in place. Although vein expansion was measured by the expansion of the outer diameter, measuring the inner diameter does not change the degree (%) to which the vascular wall has expanded from its original size. Therefore, when measuring the elasticity index, the expansion of the inner diameter was used as an indicator.

[0045] 2 and 4, the vascular cover 10 is disposed on the outer periphery of the vein 4 anastomosed to the artery 3, and has one end 11 extending from one end 10a of the vascular cover 10 toward the other end 10b in the axial direction x, and the other end 12 extending from the other end 10b toward the one end 10a in the axial direction x, and when the elastic index (hereinafter referred to as the 30% elastic index) when the inner diameter of the vascular cover 10 is expanded 30% in the radial direction y from its natural state is measured by the following measurement method, the 30% elastic index of the one end 11 is 0.4 N or more, and the elastic index of the other end 12 is 0.3 N or less. [Measurement Method] The vascular cover 10 is cut out perpendicular to the axial direction x along a tangent line in the circumferential direction z of the vascular cover 10, to prepare a cylindrical sample 100 having a length in the axial direction x of 5 mm. A first pin 101 and a second pin 102 with a diameter d of 0.75 mm are inserted into the inner cavity of the cylindrical sample 100 parallel to the axial direction of the cylindrical sample 100. The first pin 101 is fixed, and the second pin 102 is pulled outward in the radial direction of the cylindrical sample 100. When the distance between the first pin 101 and the second pin 102 is L, the force F when πd+2L is 1.3 times the circumferential length of the cylindrical sample 100 in its natural state is calculated. １．３ Measure the force F １．３ The value obtained by dividing by the strain [(1.3-1.0) / 1.0] is the 30% elasticity index.

[0046] In this type of arteriovenous anastomosis (AVF), the vascular cover 10 has a 30% elasticity index of 0.4 N or greater at one end 11 and a 30% elasticity index of 0.3 N or less at the other end 12. Therefore, by positioning the one end 11 on the outer periphery of the vein 4 upstream of the shunt 1 and the other end 12 on the outer periphery of the vein downstream of the shunt 1, compliance mismatch between the two ends is avoided, and the stiffness gradually decays between the two ends, allowing for looser coverage of the downstream side of the vein 4. This allows the high-pressure pulsatile blood flow that flows into the vein 4 at the shunt 1 to be gradually buffered in the area covered by the vascular cover 10, ultimately transitioning the flow to a state similar to normal venous blood flow, and further enabling the vein 4 at the shunt 1 to be remodeled into a low-pressure buffered vessel. This suppresses blood flow turbulence and pulsatile expansion and stress changes in the venous wall, preventing lesions such as intimal thickening. The present inventors have found that in the case of arteriovenous anastomosis (AVF) as shown in FIG. 2, the above effect can be achieved when the 30% elasticity index of one end 11 and the other end 12 is within the above range.

[0047] Here, the cylindrical sample 100 may have a length of 5 mm in the axial direction x and a continuous configuration over the entire axial region x, or may be a knitted fabric, woven fabric, net, or the like that is continuously configured over the entire periphery. Also, the cylindrical sample 100 may have a discontinuous portion at least in a part thereof.

[0048] By having the other end 12 have a 30% elastic index within the above-mentioned predetermined range, the vascular cover 10 can have a mechanical compliance different from that of the artery 3. The configuration of the vascular cover 10, in which the 30% elastic index of the one end 11 is relatively large and the 30% elastic index of the other end 12 is relatively small, differs from blood vessels such as arteries and veins in a living body, and this configuration allows the vascular cover 10 to achieve the above-mentioned effects.

[0049] More specifically, due to the effect of the above-mentioned vascular cover 10, a two-layer structure is formed in the wall of the vein 4 at the shunt construction site 1 in an inclined manner, consisting of a smooth muscle layer containing an elastic fiber layer that is thicker than the smooth muscle layer of a normal vein, and an elastic fiber layer on the outside of that that contains collagen fibers that are even thicker than the smooth muscle layer, thereby remodeling the vein 4 at the shunt construction site 1 into a low-pressure buffering blood vessel.

[0050] The following explains the differences between the low-pressure buffering vessels and normal arteries. Blood vessels are morphologically composed of three layers: the tunica intima, tunica media, and tunica adventitia. The tunica intima contributes significantly to anticoagulation but has minimal mechanical contribution. The arteries of the extremities, which are typically used for hemodialysis, are muscular arteries. The morphological structure of the mechanical elements of muscular arteries is composed of the tunica media, which contains a small amount of elastic fibers and abundant smooth muscle, and the tunica adventitia, which is composed of collagen fibers and other components, making up a large proportion. In other words, these arteries contain a very large amount of smooth muscle and relatively few elastic fibers (a "smooth muscle > elastic fiber" structure). Elastic fibers, due to their elasticity, function as a buffer, like a rubber tube, by resisting and absorbing the high pulsatile arterial pressure. On the other hand, smooth muscle, being a muscle, also has a more active mechanical function, resisting arterial pressure while actively delivering high pulsatile arterial pressure to the periphery without attenuating it (the blood transport function of muscular arteries). Due to the pressure delivery function of the abundant smooth muscle in arteries, blood pressure remains almost constant from large arteries with internal diameters of several millimeters to small arteries with internal diameters of a fraction of a millimeter. In other words, normal arteries are called muscular arteries, and their "smooth muscle > elastic fiber" structure does not function to buffer pulsatile, high arterial pressure due to the abundant smooth muscle. Thus, the histological structure of arteries and the resulting mechanical compliance are very distinctive. On the other hand, when the vein at the shunt site is remodeled into a low-pressure buffering vessel by this device, the ratio of elastic fiber to smooth muscle is the opposite of that of normal arteries, with abundant elastic fiber and relatively thin smooth muscle ("elastic fiber > smooth muscle" structure). Therefore, in low-pressure buffering vessels, the pressure buffering function is significantly more important than the pressure maintenance and delivery function. While maintaining the "elastic fiber > smooth muscle" structure, i.e., maintaining the buffering function, the low-pressure buffering vessel gradually thins out and transitions to a venous form, i.e., gradually transitions to a normal venous form as the buffered pressure decreases. If the venous wall changes to resemble a normal artery, it is arterialization (remodeling into an artery) and not remodeling into a low-pressure buffering vessel.If the arterialization gradually weakens and the veins naturally transition downstream into completely normal veins, this means that the veins will gradually become thinner while retaining their "smooth muscle > elastic fiber" structure, and in this case, a function similar to the mechanical compliance of arteries will prevail, with almost no buffering function, so high pulsatile blood pressure will be postponed downstream, and as a result, insufficiently buffered pulsatile, high-pressure blood flow will act on the downstream venous wall, potentially causing pathological changes in the veins downstream. This is the clear functional difference between when low-pressure buffering vessels gradually thin and transition into normal veins, and when vessels that have changed to resemble normal arteries gradually thin and transition into normal veins.

[0051] Furthermore, the vein 4 may gradually grow outward and expand during the process of remodeling into a low-pressure buffering vessel, but the vascular cover 10 according to an embodiment of the present invention has a small portion with a 30% elasticity index of 0.4 N or less (in the case of artificial vascular venous anastomosis (AVG)) or 0.3 N or less (in the case of arteriovenous anastomosis (AVF)), thereby reducing the inhibition of the growth of the vein 4 by the vascular cover 10, and maintaining a wide lumen of the vein 4 to ensure sufficient blood flow.

[0052] As a result, the vascular cover 10 according to the embodiment of the present invention makes it possible to form a shunt creation site 1 that can ensure sufficient blood flow while suppressing lesions such as intimal thickening.

[0053] When the vascular cover 10 is placed on the outer periphery of a vein 4 anastomosed to an artificial blood vessel 5 anastomosed to an artery 3 (in the case of artificial vascular venous anastomosis (AVG)), the 30% elastic index of one end 11 is 0.60 N or more, preferably 0.8 N or more, and more preferably 1.2 N or more, and the 30% elastic index of the other end 12 is 0.40 N or less, preferably 0.3 N or less, and more preferably 0.1 N or less.

[0054] When the vascular cover 10 is placed on the outer periphery of the vein 4 anastomosed to the artificial blood vessel 5 anastomosed to the artery 3 (in the case of artificial blood vessel venous anastomosis (AVG)), the 30% elasticity index of the one end 11 is preferably 15 N or less, more preferably 7 N or less, even more preferably 5 N or less, and may be 4.5 N or less, or 4 N or less. When the upper limit of the 30% elasticity index of the one end 11 is within the above range, it is possible to prevent the upstream side of the vein 4 from being covered too strongly, and remodeling of the vein 4 becomes easier.

[0055] When the vascular cover 10 is placed on the outer periphery of a vein 4 anastomosed to an artificial blood vessel 5 anastomosed to an artery 3 (in the case of artificial vascular venous anastomosis (AVG)), the 30% elastic index of the other end 12 is preferably 0.1 mN or more, more preferably 0.5 mN or more, and even more preferably 1 mN or more. When the 30% elastic index of the other end 12 is a predetermined value or more, the blood vessel can be covered with a force greater than a predetermined value.

[0056] When the vascular cover 10 is placed on the outer periphery of the vein 4 anastomosed to the artery 3 (in the case of arteriovenous anastomosis (AVF)), the 30% elasticity index of one end 11 is 0.40 N or more, preferably 0.6 N or more, more preferably 0.8 N or more, and even more preferably 1.0 N or more, and the 30% elasticity index of the other end 12 is 0.30 N or less, preferably 0.2 N or less, and more preferably 0.1 N or less.

[0057] When the vascular cover 10 is placed on the outer periphery of the vein 4 anastomosed to the artery 3 (in the case of arteriovenous anastomosis (AVF)), the 30% elasticity index of the one end 11 is preferably 3 N or less, more preferably 2.5 N or less, and even more preferably 2 N or less. When the upper limit of the 30% elasticity index of the one end 11 is within the above range, it is possible to prevent the upstream side of the vein 4 from being covered too strongly, and remodeling of the vein 4 becomes easier.

[0058] When the vascular cover 10 is placed on the outer periphery of the vein 4 anastomosed to the artery 3 (in the case of arteriovenous anastomosis (AVF)), the 30% elastic index of the other end 12 is preferably 0.1 mN or more, more preferably 0.5 mN or more, and even more preferably 1 mN or more. When the 30% elastic index of the other end 12 is a predetermined value or more, the blood vessel can be covered with a force greater than a predetermined value.

[0059] The method for measuring the 30% elasticity index will be described with reference to Figures 5 and 6. The cylindrical sample 100 is prepared by cutting the vascular cover 10 perpendicular to the axial direction x along a tangent line in the circumferential direction z of the vascular cover 10. It is preferable to cut the vascular cover 10 along a cut surface perpendicular to the axial direction x, i.e., along the tangent line in the circumferential direction z, so that a cylindrical sample 100 with a length of 5 mm in the axial direction x and a continuous cylindrical shape with no discontinuities in the wall is obtained throughout the entire axial direction x. Alternatively, at least a portion of the cylindrical sample 100 may have a discontinuous portion. Next, as shown in Figure 5, a first pin 101 and a second pin 102, each with a diameter d of 0.75 mm, are inserted into the lumen of the cylindrical sample 100 parallel to the axial direction of the cylindrical sample 100. The lengths of the first pin 101 and the second pin 102 are not particularly limited, but are preferably longer than the axial length of the cylindrical sample 100. The first pin 101 is fixed, and the second pin 102 is pulled outward in the radial direction of the cylindrical sample 100. When the distance between the first pin 101 and the second pin 102 is L, the force F is calculated when πd+2L is 1.3 times the circumferential length of the cylindrical sample 100 in its natural state. １．３ Measure the force F １．３ The value obtained by dividing by the strain [(1.3-1.0) / 1.0] is the 30% elasticity index.

[0060] The case where there is a discontinuity in at least a part of the cylindrical sample 100 includes, for example, a case where the vascular cover 10 is made of a mesh material or a porous material, and there are voids in the side wall of the vascular cover 10, so that when the cylindrical sample 100 is cut out from the vascular cover 10, there are voids in the side wall of the cylindrical sample 100. However, the configuration where there is a discontinuity in at least a part of the cylindrical sample 100 is not limited to the above, as long as the elasticity index can be measured by the above method.

[0061] Here, the distance L between the first pin 101 and the second pin 102 is the distance from the center of the first pin 101 and the second pin 102, as shown in Fig. 6. The inner diameter of the cylindrical sample 100 is equal to the sum of 1 / 2 the circumference πd of the first pin 101, 1 / 2 the circumference πd of the second pin 102, and twice the distance L between the first pin 101 and the second pin 102, i.e., πd + 2L. Therefore, when the inner diameter of the cylindrical sample 100 expands by 30% from its natural state, i.e., when πd + 2L becomes 1.3 times the circumferential length of the cylindrical sample 100 in its natural state, the pulling force F on the second pin 102 is １．３ The 30% elasticity number can be obtained by dividing by the strain [(1.3-1.0) / 1.0].

[0062] The inner diameter of the vascular cover 10 can be adjusted to an appropriate value depending on the diameter of the blood vessel to be used. In this case, a size appropriate for the actual size of each case is selected. Since the outer diameter of a blood vessel typically ranges widely, from 1 mm to 20 mm, the inner diameter of the vascular cover 10 must also match this. Specifically, some vascular covers 10 have a trumpet-shaped or tapered inner diameter, or other configurations in which the inner diameter changes depending on the axial position. Therefore, when the required inner diameter of the vascular cover 10 is expressed at its narrowest point, the inner diameter ranges from 1 mm to 20 mm, with most ranging from 2 mm to 14 mm, and the more central range being 3 mm to 10 mm. Furthermore, within the 3 mm to 10 mm range, the majority ranges from 4 mm to 8 mm, with the majority ranging from 4 mm to 6 mm. However, since there are patients with sizes other than these, the above sizes are not necessarily limited. The vascular cover 10 may have an inner diameter that varies depending on the axial direction x. The vascular cover 10 may have a straight shape with a constant inner diameter from one end 10a to the other end 10b, or may have a tapered shape with the inner diameter gradually increasing from one end 10a to the other end 10b. The vascular cover 10 may also have a bellows-shaped or spiral lumen with an inner diameter that changes periodically in the axial direction x.

[0063] In the axial direction x, the section from the midpoint 10c between one end 10a and the other end 10b of the vascular cover 10 to the one end 10a is defined as the first section 10A, and the section from the midpoint 10c to the other end 10b is defined as the second section 10B. The 30% elasticity index of the second section 10B is preferably smaller than the 30% elasticity index of the first section 10A. This allows the first section 10A of the vascular cover 10 to be positioned upstream of the vein 4 of the shunt 1, providing looser coverage of the downstream side of the vein 4. This allows the vein 4 to gradually remodel from upstream to downstream, buffering transmural pressure, shear stress, pulsatile pulse pressure, blood flow velocity, and excessive blood flow, resulting in changes from upstream to downstream. This makes it easier to remodel the vein into a low-pressure buffering vessel and ensure sufficient blood flow.

[0064] In the vascular cover 10, the difference between the 30% elastic index of one end 11 and the 30% elastic index of the other end 12 is divided by the length X of the vascular cover 10 in the axial direction x. ３０ , that is, the rate of change in elasticity of the 30% elastic index is preferably less than 0.6 N / cm. If the rate of change in the 30% elastic index between the 30% elastic index of one end 11 and the 30% elastic index of the other end 12 is too large, the elasticity of the vein wall in the flow path between the one end 11 and the other end 12 will not be able to keep up with the change in elasticity of the vascular cover 10, which will have an adverse effect on the remodeling of the vein 4, and the buffering action within this flow path will be insufficient, which may result in adverse effects such as pathological reactions in the vein both in the covered portion by the vascular cover 10 and further downstream. ３０ By having a value D of less than 0.6 N / cm, the vascular cover 10 can cover the vein 4 at the shunt creation site 1 with an appropriate force while the stiffness gradually decreases from upstream to downstream, and as a result, the pulsatile blood flow with high pressure that has flowed into the vein 4 at the shunt creation site 1 is gradually buffered in the area covered by the vascular cover 10, and ultimately can more easily transition to a blood flow state closer to normal venous blood flow. As a result, remodeling of the vein 4 into a low-pressure buffered blood vessel is facilitated, and the buffering effect within the flow path is sufficient, making it less likely that adverse effects such as pathological reactions will occur in the vein, both in the flow path within the vascular cover 10 and further downstream. ３０is preferably less than 0.60 N / cm, more preferably 0.4 N / cm or less, even more preferably 0.3 N / cm or less, particularly preferably 0.1 N / cm or less, and is preferably 0.01 N / cm or more.

[0065] When the elasticity index (hereinafter referred to as 60% elasticity index) when the inner diameter of the vascular cover 10 is expanded 60% in the radial direction y from the natural state is measured by the following measurement method, the difference between the 60% elasticity index of one end 11 and the 60% elasticity index of the other end 12 is divided by the length X of the vascular cover 10 in the axial direction x. ６０ , that is, the rate of change in elasticity at 60% elasticity is preferably less than 1.5 N / cm. If the rate of change in 60% elasticity between the 60% elasticity index at one end 11 and the 60% elasticity index at the other end 12 is too large, the elasticity of the vein wall in the flow path between the one end 11 and the other end 12 will not be able to keep up with the change in elasticity of the vascular cover 10, adversely affecting the remodeling of the vein 4, and the buffering action within this flow path will be insufficient, which may result in adverse effects such as pathological reactions in the vein both in the flow path within the vascular cover 10 and further downstream. ６０ By having a value D of less than 1.5 N / cm, the vascular cover 10 can cover the vein 4 at the shunt creation site 1 with an appropriate force while the stiffness gradually decreases from upstream to downstream, and as a result, the pulsatile blood flow with high pressure that has flowed into the vein 4 at the shunt creation site 1 is gradually buffered in the area covered by the vascular cover 10, and ultimately can more easily transition to a blood flow state closer to normal venous blood flow. As a result, remodeling of the vein 4 into a low-pressure buffered blood vessel is facilitated, and the buffering effect within the flow path is sufficient, making it less likely that adverse effects such as pathological reactions will occur in the vein, both in the flow path within the vascular cover 10 and further downstream. ６０is preferably less than 1.5 N / cm, more preferably 1.0 N / cm or less, even more preferably 0.6 N / cm or less, particularly preferably 0.3 N / cm or less, and preferably 0.01 N / cm or more. [Measurement Method] The vascular cover 10 is cut out perpendicular to the axial direction x along a tangential line in the circumferential direction z of the vascular cover 10, to prepare a cylindrical sample 100 having a length in the axial direction x of 5 mm. A first pin 101 and a second pin 102 having a diameter d of 0.75 mm are inserted into the lumen of the cylindrical sample 100 parallel to the axial direction of the cylindrical sample 100. The first pin 101 is fixed, and the second pin 102 is pulled radially outward of the cylindrical sample 100. When the distance between the first pin 101 and the second pin 102 is L, the force F is measured when πd + 2L is 1.6 times the circumferential length of the cylindrical sample 100 in its natural state. １．６ Measure the force F １．６ The value obtained by dividing by the strain [(1.6-1.0) / 1.0] is the 60% elasticity index.

[0066] The method for measuring the 60% elasticity index is the same as the method for measuring the 30% elasticity index, and is the force F when πd+2L becomes 1.6 times the circumferential length of the cylindrical sample 100 in its natural state. １．６ The method is the same as that for measuring the 30% elasticity number, except that the 30% elasticity number is measured.

[0067] It is preferable that the inner diameter of the vascular cover 10 be expandable in the radial direction y from its natural state throughout the entire axial direction x. This allows the gradual outward growth of the blood vessel covered by the vascular cover 10 during the remodeling process to be unimpeded, making it easier to maintain a wide vascular lumen and ensure sufficient blood flow. However, the expansion range of the vascular cover 10 is not limited to the above, and it is sufficient that the inner diameter of the vascular cover 10 be expandable in the radial direction y from its natural state throughout the entire axial direction x by at least 60%, and preferred expansion ranges are, for example, at least 70%, 80%, 90%, 100%, 120%, 150%, etc.

[0068] The length X of the vascular cover 10 in the axial direction x is preferably 5 mm or more. The length X of the vascular cover 10 in the axial direction x is more preferably 10 mm or more, even more preferably 20 mm or more, particularly preferably 30 mm or more, and may be 40 mm or more. The length X of the vascular cover 10 in the axial direction x is preferably 150 mm or less, more preferably 120 mm or less, even more preferably 100 mm or less, and may be 90 mm or less. If the length X of the vascular cover 10 in the axial direction x is within the above range, the vein 4 of the shunt creation site 1 can be covered with a vascular cover 10 of a predetermined length or more, making it easier to remodel the vein 4 into a low-pressure buffering vessel.

[0069] It is preferable that the vascular cover 10 contains at least one of knitted fabric, woven fabric, and nonwoven fabric as a partial or entire component, since these materials make it easy to form an elastically deformable vascular cover 10.

[0070] The type of knitted fabric is not particularly limited, and may be warp knitted or weft knitted. Examples of warp knitting structures include half knitting, back half knitting, queen's coat knitting, and satin knitting. Weft knitting includes circular knitting and flat knitting, and examples of weft knitting structures include plain knitting, rib knitting, double knitting, Milano rib knitting, and jacquard knitting. From the viewpoint of excellent stretchability, it is preferable that the knitted fabric be weft knitted. The type of woven fabric is not particularly limited, and may be plain weave, twill weave, satin weave, etc. Alternatively, the vein cover 10 may be made of a nonwoven fabric produced by any method such as meltblowing, needle punching, spunlace, or electrospinning.

[0071] The vascular cover 10 may be made of a combination of two or more different materials, for example, with a portion made of knitted fabric and the remaining portion made of another material, such as nonwoven fabric.

[0072] The wall properties of the vascular cover 10 that are predominantly elastically deformed have better cushioning properties than those that are predominantly plastically deformed. Therefore, it is preferable that the materials constituting the wall, such as the yarns forming the knitted, woven, or nonwoven fabric, and the yarns wound around the wall of the vascular cover 10, be made of resin materials that are predominantly elastically deformed, such as polyurethane and silicone. However, materials that are predominantly plastically deformed, such as polyolefin resins such as polyethylene and polypropylene; polyamide resins such as nylon; polyester resins such as polyethylene terephthalate; polyimide resins; fluorine-based resins such as PTFE, PFA, and ETFE; and synthetic resins such as polyvinyl chloride resins, can also be used. Furthermore, the materials and yarns constituting the wall of the vascular cover 10 may be processed to increase the stretchability, i.e., elasticity, of the wall, or, if processed into yarn, may be subjected to stretching treatment such as wooly processing. The threads forming the knitted or woven fabric may be made from resin materials (e.g., polyester, PTFE) used in artificial blood vessels. Specific examples include ePTFE, which is PTFE that has been stretched, and Dacron (registered trademark), a polyester fiber from DuPont. The vascular cover 10 may also be made from biodegradable materials, such as aliphatic polyesters such as polylactic acid, polyglycolic acid, and polyhydroxyalkanoic acid; aliphatic polyethers, caprolactone, and copolymers thereof. Furthermore, the threads forming the knitted or woven fabric and other wall materials may be made from natural fibers such as silk and cotton, or may be made from a combination of biomaterials such as gelatin and alginate, resin materials, biodegradable materials, and natural fibers.

[0073] Whether the vein 4 has been remodeled into a low-pressure buffering vessel must be confirmed by both the morphological confirmation method described below and the physical confirmation method using buffering effect measurement; confirmation by only one method does not confirm that the vein 4 has been remodeled into a low-pressure buffering vessel. Morphological confirmation can be performed by confirming the formation of a two-layer structure consisting of a smooth muscle layer containing elastic fibers and an outer layer of elastic fibers containing collagen fibers that are thicker than the smooth muscle layer. Specifically, the vein 4 at the shunt site 1 is excised and stained with special stains such as hematoxylin and eosin (HE) and Elastica van Gieson (EvG) staining, and the cross-section of the vein wall is observed under a microscope. For example, EvG staining stains smooth muscle cloudy yellow, elastic fibers deep purple, and collagen fibers dark red. Therefore, the smooth muscle layer containing elastic fibers and the elastic fiber layer containing collagen fibers can be observed, and the thickness of the smooth muscle layer containing elastic fibers and the elastic fiber layer containing collagen fibers can be confirmed to be less than the thickness of the elastic fiber layer containing collagen fibers.

[0074] Furthermore, whether the vein 4 has been remodeled into a low-pressure buffer vessel can be confirmed by measuring the buffering effect through Doppler blood flow measurement and blood flow measurement using a color Doppler ultrasound imaging diagnostic device.

[0075] Hereinafter, vascular covers according to other embodiments of the present invention will be described. In the description of these vascular covers, the drawings describing the vascular cover 10 described above can be referenced, so the same reference numerals will be used and overlapping parts will be omitted.

[0076] 1 and 3, a vascular cover 10 according to another embodiment of the present invention is disposed on the outer periphery of a vein 4 anastomosed to an artificial blood vessel 5 anastomosed to an artery 3, and has one end 11 extending 5 mm in the axial direction x from one end 10a of the vascular cover 10 toward the other end 10b, and the other end 12 extending 5 mm in the axial direction x from the other end 10b. When the elastic index (hereinafter referred to as the 60% elastic index) when the inner diameter of the vascular cover 10 is expanded 60% in the radial direction y from its natural state is measured using the following method, the 60% elastic index of the one end 11 is 0.65 N or more and the 60% elastic index of the other end 12 is 1.15 N or less, and the 60% elastic index of the other end 12 is smaller than that of the one end 11. [Measurement Method] The vascular cover 10 is cut perpendicular to the axial direction x along a tangent line in the circumferential direction z of the vascular cover 10 to prepare a cylindrical sample 100 having a length in the axial direction x of 5 mm. A first pin 101 and a second pin 102 with a diameter d of 0.75 mm are inserted into the inner cavity of the cylindrical sample 100 parallel to the axial direction of the cylindrical sample 100. The first pin 101 is fixed, and the second pin 102 is pulled outward in the radial direction of the cylindrical sample 100. When the distance between the first pin 101 and the second pin 102 is L, the force F when πd+2L is 1.6 times the circumferential length of the cylindrical sample 100 in its natural state is calculated. １．６ Measure and F １．６ The value obtained by dividing by the strain [(1.6-1.0) / 1.0] is the 60% elasticity index.

[0077] In this artificial vascular venous anastomosis (AVG), the vascular cover 10 has a 60% elastic index of 0.65 N or more at one end 11 and a 60% elastic index of 1.15 N or less at the other end 12, and the 60% elastic index of the other end 12 is smaller than the 60% elastic index of the one end 11. Therefore, by positioning the one end 11 upstream of the vein 4 at the shunt 1 and the other end 12 downstream, compliance mismatch between the two ends is eliminated, and the downstream side of the vein 4 can be loosely covered while the stiffness gradually decays between the two ends. This allows the high-pressure pulsatile blood flow that flows into the vein 4 at the shunt 1 to be gradually buffered in the area covered by the vascular cover 10, ultimately transitioning the blood flow to a state similar to normal venous blood flow, and further remodeling the vein 4 at the shunt 1 into a low-pressure buffered vessel. As a result, blood flow turbulence and pulsatile dilation and stress changes in the venous wall are suppressed, preventing lesions such as intimal thickening. The present inventors have found that in the case of an artificial vascular venous anastomosis (AVG) as shown in FIG. 1, the above-mentioned effects can be achieved when the 60% elasticity index of one end 11 and the other end 12 is within the above-mentioned range.

[0078] The reason for setting the 60% elasticity index is explained below. The reason for setting the 60% elasticity index was derived from the following experimental findings. First, the elasticity index when the vein was dilated twice its natural diameter (i.e., the dilation width was 100% of the natural diameter) is described below. As in the experiment for setting the 30% elasticity index, an arteriovenous shunt was created in a dog, and the outer diameter of the vein was measured in its natural state. Next, without any aluminum tube covering the vein, the vascular clamp that had been attached to the upstream artery to block arterial blood flow was removed, and arterial blood flow was allowed to flow from the artery upstream of the shunt through the arteriovenous shunt into the vein. The vein immediately downstream of the shunt was then immediately measured for dilation due to the inflowing blood. As a result, it was observed that the vein diameter, upon receiving arterial blood flow, always dilated to twice its natural diameter (a state in which the dilation width was increased by 100% from the natural state). However, dilation to more than three times its natural diameter (a state in which the dilation width was increased by 200% from the natural state) was observed less than two-thirds of the time. Therefore, an elasticity index of 100% or more, which is the elasticity index when the vein is expanded to more than twice its natural diameter, is considered to be an index of the vascular wall elasticity when the highest blood pressure (i.e., cardiac systolic pressure) in arterial blood pulsation acts directly on the vein, and therefore the vein wall is forced to expand most strongly. In patients who are susceptible to pathological reactions, if the vein is forced to expand to such an extreme state immediately after shunt creation, even if reinforcement materials prevent expansion by more than twice its original size, a pathological reaction will likely occur once the vein has already expanded by two times. Therefore, it is considered that the significance of evaluating the effectiveness of a vascular cover in preventing pathological reactions using the elasticity index when the vein is expanded by more than two times is small. Arterial blood pressure acts as a waveform pressure that alternates and pulsates from the highest pressure (cardiac systolic pressure) to a relatively low pressure (cardiac diastolic pressure). The buffering of arterial blood flow by a low-pressure buffering vessel is actually the combined result of the buffering effect of all pressures of this waveform, i.e., all expansion states between 0% (no blood present in the venous lumen) and 100% or more. Therefore, the 60% elasticity index was established as an index of vascular elasticity related to buffering function from a different perspective than the 30% elasticity index.That is, unlike a gentle expansion stimulus such as a 30% elasticity index, which has a low risk of causing a pathological reaction, a strong forced expansion has a high risk of causing a pathological reaction, but on the other hand, since it is a state lower than an expansion of 100% or more, the elasticity index at 60% expansion was selected as a state in which there is a high possibility that a pathological reaction can be prevented with appropriate reinforcement. In other words, the 60% elasticity index was set as an index of the elasticity of the reinforcement material in an expanded state in which there is a high risk of a pathological reaction if no reinforcement is used, but in which it is highly expected that a pathological reaction can be prevented with appropriate elastic reinforcement. In other words, the 60% elasticity index is a comprehensive elasticity index for a wide range of expansion states, pulsating from low to high blood pressure.

[0079] The 60% elasticity index of the one end 11 is 0.65N or more, preferably 0.70N or more, 0.75N or more, 0.8N or more, or 1N or more.

[0080] The 60% elasticity index of the one end 11 is preferably 25N or less, and may be 20N or less, 15N or less, 10N or less, 12N or less, or 10N or less.

[0081] The 60% elastic index of the other end 12 is 1.15N or less, preferably 1.1N or less, 1.0N or less, or 0.9N or less.

[0082] The lower limit of the 60% elasticity index of the other end 12 is not particularly limited, but can be, for example, 0.1 mN or more, 0.5 mN or more, or 1 mN or more.

[0083] 2 and 4, a vascular cover 10 according to still another embodiment of the present invention is disposed on the outer periphery of a vein 4 anastomosed to an artery 3, and has one end 11 extending from one end 10a of the vascular cover 10 toward the other end 10b in the axial direction x, and the other end 12 extending from the other end 10b toward the one end 10a in the axial direction x. When the elastic index (hereinafter referred to as the 60% elastic index) when the inner diameter of the vascular cover 10 is expanded 60% radially from its natural state is measured by the following measurement method, the 60% elastic index of the one end 11 is 0.42 N or more, and the 60% elastic index of the other end 12 is 1.15 N or less, and the 60% elastic index of the other end 12 is smaller than the 60% elastic index of the one end 11. [Measurement Method] The vascular cover 10 is cut perpendicular to the axial direction x along a tangent line in the circumferential direction z of the vascular cover 10 to prepare a cylindrical sample 100 having a length in the axial direction x of 5 mm. A first pin 101 and a second pin 102 with a diameter d of 0.75 mm are inserted into the inner cavity of the cylindrical sample 100 parallel to the axial direction of the cylindrical sample 100. The first pin 101 is fixed, and the second pin 102 is pulled outward in the radial direction of the cylindrical sample 100. When the distance between the first pin 101 and the second pin 102 is L, the force F when πd+2L is 1.6 times the circumferential length of the cylindrical sample 100 in its natural state is calculated. １．６ Measure and F １．６ The value obtained by dividing by the strain [(1.6-1.0) / 1.0] is the 60% elasticity index.

[0084] In this type of arteriovenous anastomosis (AVF), the 60% elastic index of the vascular cover 10 at one end 11 is 0.42 N or greater, and the 60% elastic index of the other end 12 is 1.15 N or less, and the 60% elastic index of the other end 12 is smaller than the 60% elastic index of the one end 11. Therefore, by positioning the one end 11 upstream of the vein 4 at the shunt 1 and the other end 12 downstream, compliance mismatch between the two ends is avoided, and the stiffness gradually decays between the two ends, allowing for looser coverage of the downstream side of the vein 4. As a result, the pulsatile blood flow with high pressure that flows into the vein 4 at the shunt 1 is gradually buffered in the area covered by the vascular cover 10, ultimately transitioning to a blood flow state similar to normal venous blood flow, and further remodeling the vein 4 at the shunt 1 into a low-pressure buffering vessel. As a result, blood flow turbulence and pulsatile dilation and stress changes in the venous wall are suppressed, preventing lesions such as intimal thickening. The present inventors have found that in the case of arteriovenous anastomosis (AVF) as shown in FIG. 2, the above-mentioned effect can be achieved when the 60% elasticity index of one end 11 and the other end 12 is within the above-mentioned range.

[0085] The 60% elasticity index of the one end 11 is 0.42 N or more, preferably 0.45 N or more, 0.48 N or more, 0.5 N or more, or 0.55 N or more.

[0086] The 60% elasticity index of the one end 11 is preferably 5N or less, and may be 4.5N or less, 4.2 or less, 4N or less, 3.5N or less, or 3N or less.

[0087] The 60% elastic index of the other end 12 is 1.15N or less, preferably 1.1N or less, 1.0N or less, or 0.9N or less.

[0088] The lower limit of the 60% elasticity index of the other end 12 is not particularly limited, but can be, for example, 0.1 mN or more, 0.5 mN or more, or 1 mN or more.

[0089] In the case of the above-mentioned vascular cover 10 in which one end 11 has a predetermined 60% elasticity index in AVG or AVF, the difference between the 60% elasticity index of one end 11 and the 60% elasticity index of the other end 12 is divided by the length of the vascular cover 10 in the axial direction x, and the value d is ６０That is, the rate of change in elasticity of the 60% elastic index is preferably less than 1.5 N / cm. If the rate of change in the 60% elastic index between the 60% elastic index of one end 11 and the 60% elastic index of the other end 12 is too large, the elasticity of the vein wall in the flow path between the one end 11 and the other end 12 will not keep up with the change in elasticity of the vascular cover 10, adversely affecting the remodeling of the vein 4 and also causing insufficient buffering action within this flow path, which may result in adverse effects such as pathological reactions occurring in the flow path within the vascular cover 10 and further downstream. ６０ By having a value d of less than 1.5 N / cm, the vascular cover 10 can cover the vein 4 at the shunt creation site 1 with an appropriate force while the stiffness gradually decreases from upstream to downstream, and as a result, the pulsatile blood flow with high pressure that has flowed into the vein 4 at the shunt creation site 1 is gradually buffered in the area covered by the vascular cover 10, and ultimately transitions to a blood flow state close to normal venous blood flow. As a result, remodeling of the vein 4 into a low-pressure buffering blood vessel is facilitated, and the buffering effect within the flow path is sufficient, making it less likely that adverse effects such as pathological reactions will occur further downstream in the flow path within the vascular cover 10. ６０ is preferably less than 1.5 N / cm, more preferably 1.0 N / cm or less, even more preferably 0.6 N / cm or less, particularly preferably 0.4 N / cm or less, and is preferably 0.01 N / cm or more.

[0090] This application claims the benefit of priority based on Japanese Patent Application No. 2023-181112, filed on October 20, 2023. The entire contents of the specification of Japanese Patent Application No. 2023-181112, filed on October 20, 2023, are incorporated herein by reference.

[0091] The present invention will be described below with reference to examples. The present invention is not limited to the following examples, and can of course be practiced with appropriate modifications within the scope of the above-mentioned and below-mentioned aims, all of which are included in the technical scope of the present invention.

[0092] The measurements and evaluations in the examples were carried out by the following methods.

[0093] (1) 30% Elasticity Index A vascular cover was cut perpendicular to the axial direction along a circumferential cut line of the vascular cover to prepare a cylindrical sample having an axial length of 5 mm and extending over the entire axial length. A first pin and a second pin, each with a diameter of 0.75 mm, were inserted into the lumen of the cylindrical sample parallel to the axial direction of the cylindrical sample. The first pin was fixed, and the second pin was pulled radially outward from the cylindrical sample. The 30% elasticity index was calculated by dividing the force at which the sum of twice the distance between the first and second pins and (π × 0.75 mm) was 1.3 times the circumference of the cylindrical sample in its natural state by the strain [(1.3 - 1.0) / 1.0].

[0094] (2) Animal experiment on covering the shunt site Beagle dogs (male and female, weighing 9-14 kg) were used. A shunt was created between the carotid artery and jugular vein, and a vascular cover was placed over the vein at the shunt site, and the dogs were observed for 16 weeks.

[0095] (3) Observation of the smooth muscle layer and the elastic fiber layer containing collagen fibers After the observation described in (2) above, the beagle dogs were euthanized, and the vein at the site of the shunt construction was excised. The excised vein was stained with Elastica-van Gieson (EvG) staining, and cross sections including a section 5 mm in the direction of blood flow from just below the anastomosis, a section 5 mm in the direction of blood flow near the midpoint of the vascular cover, and a section 5 mm from the other end of the vascular cover were observed under an optical microscope.

[0096] (4) Measurement of the thickness of the smooth muscle layer and the elastic fiber layer containing collagen fibers From the micrographs obtained in (3) above, the thickness of each layer at each distance from the anastomosis of the vein was determined.

[0097] (5) Mechanical evaluation of remodeling into low-pressure buffer vessels After the follow-up observation in (2) above, the blood flow state was measured by Doppler blood flow measurement, and furthermore, diagnosis was performed using a color Doppler ultrasound imaging diagnostic device. Based on these measurements and diagnoses, as well as the results of (3) and (4) above, the remodeling of the vein at the shunt creation site into a low-pressure buffer vessel was evaluated using the following criteria. <Evaluation criteria> If all of the following (a) to (e) were met, the vein at the shunt creation site was evaluated as having remodeled into a low-pressure buffer vessel (○ in each table); otherwise, it was evaluated as not having remodeled (× in each table). (a) Macroscopic findings at autopsy showed that the vascular lumen was patent, the vascular wall was smooth without varicose veins or unnatural irregularities, and there was no intimal thickening, stenosis, or thrombus formation, which are pathological findings that affect blood flow. (a) In the observation in (3) above, a two-layer structure is observed, with an inner smooth muscle layer containing elastic fibers and an outer elastic fiber layer containing collagen fibers that is thicker than the smooth muscle layer, and there is no intimal thickening or thrombus formation. (c) In the measurement in (4) above, the outer elastic fiber layer containing collagen fibers is thicker than the inner smooth muscle layer. (d) In the Doppler blood flow measurement above, blood flow is antegrade, and arterial pulsatile blood flow is buffered, with pulsatility attenuated downstream. (e) In the diagnosis using the color Doppler ultrasound imaging device, the vascular lumen is patent, the vascular wall is smooth, and there is no pathological intimal thickening or thrombus formation that affects blood flow.

[0098] Examples 1-4 and Comparative Examples 1-4: Tubes with an inner diameter freely expandable between 3 mm and 12 mm were prepared using polylactic acid fiber that had been woolly processed to impart excellent elasticity. Separately, an aluminum rod with an outer diameter of 3 mm was prepared, and a silicone sheet was wrapped around the outside of this aluminum rod to arbitrarily adjust the outer diameter between 3 mm at one end and 8 mm at the other end. A shaft manufactured by wrapping a silicone sheet around this aluminum rod was then covered with an expandable tube made from the polylactic acid fiber. The shaft was then rotated in this state, and another woolly processed polylactic acid fiber was wrapped around the entire circumference of the polylactic acid fiber expandable tube. During this operation, the lateral movement of the shaft was adjusted so that more fiber was wrapped around one side and gradually less fiber was wrapped around the other side. During this operation, the tension of the wrapped polylactic acid fiber was also adjusted. These two adjustments allowed the number of turns of polylactic acid fiber wrapped around the tube and the winding strength to be varied depending on the axial location, thereby adjusting the elasticity of any given part of the tube to the desired softness. Finally, a heat treatment was performed to fix the tube shape and elasticity distribution, and the aluminum rod was pulled out to produce tubes with the elasticity distribution adjusted as shown in Table 1. The axial length of each tube was 10 to 60 mm.

[0099] A shunt (AVG) was constructed in the neck of a beagle dog by anastomosing a vein to an artificial blood vessel anastomosed to an artery. The vascular cover was then positioned around the vein, with one end of the vascular cover having the 30% elasticity index shown in Table 1 positioned on the anastomosis site. The vascular cover was positioned so that the stiffer end of the vascular cover, i.e., the end with the higher 30% elasticity index, was positioned on the anastomosis site between the artificial blood vessel and the vein, i.e., the upstream vein in the shunt vein. As a result of this positioning, the softer end of the vascular cover, i.e., the end with the lower 30% elasticity index, was positioned on the downstream vein in the shunt vein. The dog was followed for 16 weeks after surgery. The vein was then evaluated using Doppler blood flow measurements and color Doppler ultrasound imaging. The beagle dog was euthanized, and the vein at the shunt site was removed. The smooth muscle layer and elastic fiber layer containing collagen fibers of the excised veins were observed and their thicknesses were measured to evaluate their remodeling into low-pressure buffering blood vessels. The results are shown in Table 1. In Table 1, those that met the requirements for remodeling and gave good results are marked with a circle, and those that did not are marked with an x.

[0100] When evaluating the vascular cover in animal experiments, the most suitable portion was cut out from a vascular cover manufactured to fit the individual vascular size of the experimental animal. Since it is impossible to measure the elasticity index of the vascular cover actually used in the animal experiments before and after the animal experiments, the elasticity index of a vascular cover manufactured exactly the same as the vascular cover used in the animal experiments was measured. The same applies to the other examples and comparative examples below.

[0101]

[0102] In AVG, Examples 1 to 4, in which the 30% elastic index of one end was 0.6 N or more and the 30% elastic index of the other end was 0.4 N or less, were evaluated as ○. In contrast, Comparative Examples 1 and 2, in which the 30% elastic index of one end was 0.6 N or more but the 30% elastic index of the other end exceeded 0.4 N, and Comparative Examples 3 and 4, in which the 30% elastic index of the other end was 0.4 N or less but the 30% elastic index of one end was less than 0.6 N, were evaluated as ×.

[0103] Examples 5-8, Comparative Examples 5-8 Tubes with the elasticity distribution adjusted as shown in Table 2 were prepared using the same method as in Examples 1-4 and Comparative Examples 1-4. A shunt (AVF) was constructed in the neck of a beagle dog by anastomosis of an artery and a vein. A vascular cover was placed on the outer periphery of the vein so that one end of the vascular cover, having a 30% elasticity index as shown in Table 2, was positioned at the anastomosis. The vascular cover was positioned so that the stiffer end of the vascular cover, i.e., the end with the higher 30% elasticity index, was positioned on the outer periphery of the vein on the side of the anastomosis between the artery and the vein, i.e., the upstream side of the blood flow through the shunt vein. As a result of this positioning, the softer end of the vascular cover, i.e., the end with the lower 30% elasticity index, was positioned on the outer periphery of the downstream side of the blood flow through the shunt vein. After this surgery, follow-up observation was performed for 16 weeks. The vein was then evaluated using Doppler blood flow measurement and a color Doppler ultrasound imaging diagnostic device. The beagle dogs were euthanized, and the vein at the site of shunt construction was excised. The smooth muscle layer and the elastic fiber layer containing collagen fibers of the excised vein were observed and their thicknesses were measured, and remodeling into a low-pressure buffering vessel was evaluated. The results are shown in Table 2. In Table 2, cases that met the requirements for remodeling and gave good results are marked with a circle, and cases that did not are marked with an x.

[0104]

[0105] In the AVF, Examples 5 to 8, in which the 30% elastic index of one end was 0.4 N or more and the 30% elastic index of the other end was 0.3 N or less, were evaluated as ○. In contrast, Comparative Examples 5 and 6, in which the 30% elastic index of one end was 0.4 N or more but the 30% elastic index of the other end exceeded 0.3 N, and Comparative Examples 7 and 8, in which the 30% elastic index of the other end was 0.3 N or less but the 30% elastic index of one end was less than 0.4 N, were evaluated as ×.

[0106] Examples 9 to 15 and Comparative Examples 9 to 12: Tubes were prepared in the same manner as described above, with the elasticity distribution and axial length X of the tube adjusted as shown in Table 3. A shunt (AVG) consisting of an artificial blood vessel anastomosed to an artery and a vein, or a shunt (AVF) consisting of an artery anastomosed to a vein, was constructed in the neck of a beagle dog, and a vascular cover was placed on the outer periphery of the vein so that one end of the vascular cover having a 30% elasticity index shown in Table 3 was positioned at the anastomosis. In the case of an AVG, the vascular cover was positioned so that the stiffer end of the vascular cover, i.e., the end with the higher 30% elasticity index, was positioned on the outer periphery of the vein on the upstream side of the blood flow through the shunt vein, i.e., on the side of the anastomosis between the artificial blood vessel and the vein in the case of an AVF. As a result of this arrangement, the softer end of the vascular cover, i.e., the end with the smaller 30% elasticity index, was positioned around the downstream vein in the blood flow through the shunt vein. After this surgery, a 16-week follow-up was performed. The vein was then evaluated using Doppler blood flow measurement and a color Doppler ultrasound imaging diagnostic device. The beagle dog was euthanized, and the vein at the site of the shunt was excised. The smooth muscle layer and the elastic fiber layer containing collagen fibers of the excised vein were observed and their thicknesses were measured, and remodeling into a low-pressure buffering vessel was evaluated. Table 3 shows the difference between the elasticity index of one end and the elasticity index of the other end divided by the axial length X of the vascular cover, resulting in a value D. ３０ The results of the evaluation of remodeling are shown in Table 3. In Table 3, those that met the requirements for remodeling and obtained good results are marked with a circle, and those that did not meet the requirements are marked with an x. ３０In Examples 9 to 15, where the strength was less than 0.6 N / cm, the evaluation was ◯. ３０ In Comparative Examples 9 to 12, where the strength was 0.6 N / cm or more, the evaluation was poor.

[0107]

[0108] For Examples 16-30 and Comparative Examples 13-27, vascular covers were produced using the method described below, with their 60% elasticity index adjusted as shown in Tables 4, 5, and 6. Using a knitting machine and a 3D printer, stretchable cylindrical tubes were produced, each with a knitted structure and a nonwoven structure consisting of a support yarn structure in which polylactic acid yarn or Tetron yarn was wooly-processed to impart excellent stretchability, and a covered yarn structure in which stretchable polyurethane yarn was used as the axial yarn. The tubes had an inner diameter that could be freely stretched from 3 mm to 12 mm or more. Separately, a silicone sheet was wrapped around the outside of an aluminum rod with an outer diameter of 3 mm to create a core shaft whose outer diameter could be freely adjusted between 3 mm at one end and 12 mm at the other end. The core shaft was then covered with the stretchable cylindrical tube. The core shaft was then rotated, and another polyurethane monofilament was wrapped around the entire circumference of the stretchable cylindrical tube. During this winding operation, a relatively large amount of fiber was wound around one end, and a relatively small amount of fiber was wound around the other end, resulting in a relatively less stretchable end and a relatively more stretchable end. The lateral movement of the shaft was adjusted to create varying amounts of winding in the intermediate region between the two ends, such as areas with more, less, or no winding. The tension of the wound thread was also adjusted to a high or low level. The elasticity of any given region of the tube was adjusted to the desired elasticity distribution by adjusting the number of turns and the winding tension of the polyurethane monofilament. Finally, the tube shape and elasticity distribution were fixed by heat treatment. Both ends of these tubes were truncated, and the remaining central tubes were adjusted to the elasticity distributions shown in Tables 4 to 6 and used for the experiments. Tubes of the same specifications were prepared for both the animal experiments and the elasticity index measurement experiments; one was used for the animal experiments and the other for the elasticity index measurement experiments. The axial length of each tube was 10 to 40 mm.

[0109] Examples 16-20 and Comparative Examples 13-17: A shunt (AVG) was constructed in the neck of a beagle dog by anastomosing a vein to an artificial blood vessel anastomosed to an artery. The vascular cover was then placed on the outer periphery of the vein so that one end of the vascular cover, having a 60% elasticity index as shown in Table 4, was positioned at the anastomosis. The harder end of the vascular cover, i.e., the end with the higher 60% elasticity index, was positioned on the anastomosis side between the artificial blood vessel and the vein, i.e., on the outer periphery of the vein upstream of the blood flow through the shunt vein. As a result of this positioning, the softer end of the vascular cover, i.e., the end with the lower 60% elasticity index, was positioned on the outer periphery of the vein downstream of the blood flow through the shunt vein. After this surgery, the dogs were followed up for 16 weeks. The vein was then evaluated using Doppler blood flow measurement and a color Doppler ultrasound imaging diagnostic device. The beagle dogs were euthanized, and the vein at the site of shunt construction was excised. The smooth muscle layer and the elastic fiber layer containing collagen fibers of the excised vein were observed and their thicknesses were measured, and remodeling into a low-pressure buffering vessel was evaluated. The results are shown in Table 4. In Table 4, those that met the requirements for remodeling and obtained good results are marked with a circle, and those that did not are marked with an x.

[0110] In AVG, Examples 16 to 20 in which the 60% elastic index at one end was 0.65 N or more, the 60% elastic index at the other end was 1.15 N or less, and the 60% elastic index at the other end was smaller than the 60% elastic index at one end were rated as ○. In contrast, Comparative Examples 13 to 17 in which the 60% elastic index at one end was less than 0.65 N were rated as ×.

[0111]

[0112] Examples 21-25 and Comparative Examples 18-22: A shunt (AVF) was constructed in the neck of a beagle dog by anastomosis of an artery and a vein. The vascular cover was positioned around the vein so that one end of the vascular cover, having the 60% elasticity index shown in Table 5, was positioned at the anastomosis site. The vascular cover was positioned so that the stiffer end of the vascular cover, i.e., the end with the higher 60% elasticity index, was positioned at the anastomosis site between the artificial blood vessel and the vein, i.e., the upstream side of the blood flow through the shunt vein. As a result of this positioning, the softer end of the vascular cover, i.e., the end with the lower 60% elasticity index, was positioned downstream of the blood flow through the shunt vein. After this surgery, the dogs were followed up for 16 weeks. The vein was then evaluated using Doppler blood flow measurement and a color Doppler ultrasound imaging diagnostic device. The beagle dog was euthanized, and the vein at the shunt site was excised. The smooth muscle layer and the elastic fiber layer containing collagen fibers of the excised veins were observed and their thicknesses were measured to evaluate their remodeling into low-pressure buffering vessels. The results are shown in Table 5. In Table 5, those that met the requirements for remodeling and obtained good results are marked with a circle, and those that did not are marked with an x.

[0113] In the AVF, Examples 21 to 25 in which the 60% elastic index of one end was 0.42 N or more, the 60% elastic index of the other end was 1.15 N or less, and the 60% elastic index of the other end was smaller than the 60% elastic index of the one end were evaluated as ○. In contrast, Comparative Examples 18 to 22 in which the 60% elastic index of one end was less than 0.42 N were evaluated as ×.

[0114]

[0115] Examples 26-30, Comparative Examples 23-27: A shunt (AVG) consisting of an artificial blood vessel anastomosed to an artery and a vein, or a shunt (AVF) consisting of an artery anastomosed to a vein, was constructed in the neck of a beagle dog. A vascular cover was placed around the vein so that one end of the vascular cover, having a 60% elasticity index as shown in Table 6, was positioned at the anastomosis. The vascular cover was positioned so that the stiffer end of the vascular cover, i.e., the end with the higher 60% elasticity index, was positioned on the side of the artificial blood vessel or the anastomosis between the artery and the vein, i.e., the upstream side of the blood flow through the shunt vein. As a result of this positioning, the softer end of the vascular cover, i.e., the end with the lower 60% elasticity index, was positioned downstream of the blood flow through the shunt vein. After this surgery, the dogs were followed up for 16 weeks. The vein was then evaluated using Doppler blood flow measurement and a color Doppler ultrasound imaging diagnostic device. The beagle dogs were euthanized and the vein at the site of shunt construction was excised. The smooth muscle layer and the elastic fiber layer containing collagen fibers of the excised vein were observed and their thicknesses were measured to evaluate the remodeling into a low-pressure buffering vessel. Table 6 shows the 60% elasticity index of one end and the 60% elasticity index of the other end, as well as the value d obtained by dividing the difference between the two by the axial length X of the vascular cover. ６０ The results of the evaluation of the remodeling are shown. Those that met the requirements for remodeling and obtained good results are marked with a circle, and those that did not are marked with an x. Examples 26 to 30 in which the 60% elastic index of the other end was 1.15 N or less were evaluated as ○, while Comparative Examples 23 to 27 in which the 60% elastic index of the other end was more than 1.15 N were evaluated as ×. In addition, in Examples 26 to 30 in which the evaluation was ○, ６０ In Comparative Examples 23 to 27, which were evaluated as "x", the d ６０ was more than 1.5 N / cm.

[0116]

[0117] The following explains the usefulness of the three criteria, namely, 30% elasticity index, 60% elasticity index, and preferably elasticity change rate, in that the determination of effectiveness is an independent event, and that the combination of these independent criteria allows the selection of a vascular cover that is clinically optimal for the patient's condition.

[0118] The venous response is a comprehensive response to varying degrees of venous dilation (see the explanation for the 30% and 60% elasticity indices). Furthermore, the low-pressure buffered vascular remodeling of covered veins is influenced by a complex combination of numerous factors, including not only the elasticity index values ​​at both ends of the tube wall, but also the distribution of the elasticity index curve, various shapes of the cover wall and lumen, differences in the diameter and effective anastomotic diameter of the artery and vein used in the shunt, the curvature of the vein (veins are often anastomosed in a J-shape at various angles), and the partial "play" or "excessive compression" between the outer diameter of the vein and the inner diameter of the cover. However, we found that the above three criteria were important determinants among these factors, and we focused our technical efforts on these points to demonstrate the usefulness of this technology.

[0119] The clinical utility of these three criteria is explained below. In actual clinical use, the most effective vascular cover is selected and used based on each patient's vascular size and stiffness, vascular conditions such as the relative position of the artery and vein at the shunt placement site, and patient characteristics such as blood pressure, age, and concomitant diseases such as diabetes. Rather than blindly using one of the three indices (30% elasticity index, 60% elasticity index, or elasticity change rate), it is clinically useful to prepare and supply a vascular cover using one of these three indices that best suits the patient's characteristics. For example, diabetic patients, whose proportion among dialysis patients has increased significantly in recent years, are more likely than other patients to develop shunt vein stenosis and occlusion. This is because even mild vasodilation, which is not likely to cause a pathological reaction in normal patients, is more likely to cause pathological reactions such as intimal hyperplasia due to the poor adaptability of diabetic blood vessels. Furthermore, even a small elastic gap between blood vessels can easily cause pathological reactions at the relevant site. Therefore, when selecting a vascular cover, it is more useful to select a cover based on the numerical value of successful examples of a 30% elasticity index, which represents a mild dilation state unlikely to cause a pathological reaction in normal patients, than a 60% elasticity index. Specifically, it is important that the 30% elasticity index of one upstream end is sufficiently large so that dilation of more than 30% is unlikely to occur at the upstream end. Furthermore, it is important that the 30% elasticity index of the other downstream end of the vascular cover is sufficiently small to reduce the "stiffness" gap between the downstream end of the covered portion and the bare vein immediately downstream. Furthermore, it is important to have a sufficiently large 60% elasticity index of the other end to prevent excessive dilation beyond 30% toward 60%. Furthermore, by selecting a vascular cover with the longest length possible from among vascular covers with appropriate 30% elasticity indices at one end and the other end, as described above, and minimizing the rate of elastic change, it becomes easier to achieve a low-pressure buffering vascularization without strain. By selecting a vascular cover that meets these requirements, the optimal vascular cover can be selected for patients undergoing hemodialysis due to diabetes.

[0120] Next, we will describe an example of a selection for patients with completely different vascular conditions. The primary target population for dialysis is patients undergoing dialysis due to chronic nephritis. These patients are relatively young and have highly adaptable blood vessels. Because such patients are expected to undergo dialysis for a long period of 10 years or more, the implanted vascular cover size is small. Furthermore, leaving a long uncovered vein for vascular puncture during dialysis is a priority, i.e., keeping the vascular cover as short as possible is a priority. Therefore, in contrast to diabetic patients, for patients with highly adaptable blood vessels, it is more useful to select a vascular cover based on the success rate of a 60% elasticity index during strong dilation, which is likely to cause a pathological reaction, rather than a 30% elasticity index during gentle dilation, which is unlikely to cause a pathological reaction. Even a vascular cover with a relatively low 60% elasticity index at one end (upstream) can be expected to provide sufficient protection against pathological reactions in highly adaptable blood vessels. Next, for the downstream end, even if the 60% elasticity index of the other end is relatively large and the "stiffness" gap between the downstream flow channel wall covered by the vascular cover and the bare vein wall immediately downstream is relatively large, the adaptability of the blood vessel can be expected to be sufficient to prevent pathological reactions at the downstream end. Furthermore, regarding the rate of elastic change in wall elasticity between one end and the other end, by determining an appropriate value for the 60% elasticity index between one end and the other end using the method described above, the difference in the 60% elasticity index between one end and the other end can also be set to a relatively small value. Therefore, even if a short vascular cover is selected, the rate of elastic change is small, making it easier to achieve low-pressure buffering vascularization without strain. By selecting a vascular cover in this way, it is possible to select an appropriate vascular cover that is optimal for the conditions of patients who are relatively young and have high vascular adaptability, but who are expected to undergo long-term dialysis.

[0121] As in the selection of clinical vascular covers described above, the three criteria of 30% elasticity index, 60% elasticity index, and preferably elasticity change rate are each independently useful criteria, and appropriate combinations of these enable the selection of clinically beneficial covers.

[0122] 1: Shunt creation site 2: Arm 3: Artery 4: Vein 5: Artificial blood vessel 6: Anastomosis site 10: Vascular cover 10a: One end of vascular cover 10b: Other end of vascular cover 10c: Midpoint of vascular cover 10A: First part 10B: Second part 11: One end 12: Other end 100: Cylindrical sample 101: First pin 102: Second pin x: Axial direction y: Radial direction z: Circumferential direction

Claims

1. A vascular cover to be placed on the outer periphery of a vein anastomosed to an artificial blood vessel anastomosed to an artery, the vascular cover having one end extending 5 mm from one end of the vascular cover to the other end in the axial direction, and the other end extending 5 mm from the other end to the one end, the elasticity index (hereinafter referred to as 30% elasticity index) when the inner diameter of the vascular cover is expanded 30% in the radial direction from the natural state is measured by the following measurement method, the 30% elasticity index of the one end is 0.6 N or more, and the 30% elasticity index of the other end is 0.4 N or less. [Measuring method] The vascular cover is cut perpendicular to the axial direction along the circumferential cut line of the vascular cover to prepare a sample with an axial length of 5 mm. A first pin and a second pin with a diameter d of 0.75 mm are inserted into the lumen of the sample parallel to the axial direction of the sample. The first pin is fixed, and the second pin is pulled outward in the radial direction of the sample. When the distance between the first pin and the second pin is L, πd+2L is 1.3 times the circumference of the sample in its natural state. The force F １．３ Measure and F １．３ The value obtained by dividing by the strain [(1.3-1.0) / 1.0] is the 30% elasticity index.

2. The blood vessel cover according to claim 1, wherein the 30% elasticity index of said one end is 15N or less.

3. The blood vessel cover according to claim 1 or 2, wherein the 30% elasticity index of the other end is 0.1 mN or more.

4. A vascular cover arranged on the outer periphery of a vein anastomosed to an artery, the vascular cover has one end extending 5 mm from one end of the vascular cover to the other end in the axial direction, and the other end extending 5 mm from the other end to the one end, and when the elasticity index (hereinafter referred to as 30% elasticity index) when the inner diameter of the vascular cover is expanded 30% in the radial direction from the natural state is measured by the following measurement method, the 30% elasticity index of the one end is 0.4 N or more, and the 30% elasticity index of the other end is 0.3 N or less. [Measuring method] The vascular cover is cut perpendicular to the axial direction along the circumferential cut line of the vascular cover to prepare a sample with an axial length of 5 mm. A first pin and a second pin with a diameter d of 0.75 mm are inserted into the lumen of the sample parallel to the axial direction of the sample. The first pin is fixed, and the second pin is pulled outward in the radial direction of the sample. When the distance between the first pin and the second pin is L, πd+2L is 1.3 times the circumference of the sample in its natural state. The force F １．３ Measure and F １．３ The value obtained by dividing by the strain [(1.3-1.0) / 1.0] is the 30% elasticity index.

5. The blood vessel cover according to claim 4, wherein the 30% elasticity index of said one end is 3N or less.

6. The blood vessel cover according to claim 4 or 5, wherein the 30% elasticity index of the other end is 0.1 mN or more.

7. A vascular cover as described in claim 1 or 4, wherein the difference between the 30% elasticity index of said one end and the 30% elasticity index of said other end divided by the axial length of said vascular cover is less than 0.6 N / cm.

8. A vascular cover as described in claim 1 or 4, wherein when the elasticity index (hereinafter referred to as 60% elasticity index) when the inner diameter of the vascular cover is expanded radially by 60% from its natural state is measured by the method described below, the difference between the 60% elasticity index of one end and the 60% elasticity index of the other end divided by the axial length of the vascular cover is less than 1.5 N / cm. [Measurement method] The vascular cover is cut perpendicular to the axial direction along the circumferential cut line of the vascular cover to prepare a sample having an axial length of 5 mm. A first pin and a second pin having a diameter d of 0.75 mm are inserted into the inner cavity of the sample in parallel to the axial direction of the sample. The first pin is fixed, and the second pin is pulled outward in the radial direction of the sample. When the distance between the first pin and the second pin is L, πd+2L is 1.6 times the circumference of the sample in its natural state. The force F １．６ Measure and F １．６ The value obtained by dividing by the strain [(1.6-1.0) / 1.0] is the 60% elasticity index.

9. The vascular cover according to claim 1 or 4, wherein the inner diameter of the vascular cover is expandable in the radial direction from its natural state by at least 100% over the entire axial direction.

10. The blood vessel cover according to claim 1 or 4, wherein the axial length is 5 mm or more and 150 mm or less.

11. The blood vessel cover according to claim 1 or 4, which comprises at least one of knitted fabric, woven fabric and nonwoven fabric as a partial or entire component.

12. A vascular cover to be placed on the outer periphery of a vein anastomosed to an artificial blood vessel anastomosed to an artery, the vascular cover having one end extending 5 mm from one end of the vascular cover to the other end and the other end extending 5 mm from the other end to the one end in the axial direction, the elasticity index (hereinafter referred to as 60% elasticity index) when the inner diameter of the vascular cover is expanded 60% in the radial direction from the natural state is measured by the following measurement method, the 60% elasticity index of the one end is 0.65 N or more, the 60% elasticity index of the other end is 1.15 N or less, and the 60% elasticity index of the other end is smaller than the 60% elasticity index of the one end. [Measuring method] The vascular cover is cut perpendicular to the axial direction along the circumferential cut line of the vascular cover to prepare a sample with an axial length of 5 mm. A first pin and a second pin with a diameter d of 0.75 mm are inserted into the inner cavity of the sample parallel to the axial direction of the sample. The first pin is fixed, and the second pin is pulled outward in the radial direction of the sample. When the distance between the first pin and the second pin is L, πd+2L is 1.6 times the circumference of the sample in its natural state. The force F １．６ Measure and F １．６ The value obtained by dividing by the strain [(1.6-1.0) / 1.0] is the 60% elasticity index.

13. The blood vessel cover according to claim 12, wherein the 60% elasticity index of said one end is 25N or less.

14. A vascular cover to be placed on the outer periphery of a vein anastomosed to an artery, the vascular cover having one end extending 5 mm from one end of the vascular cover to the other end and the other end extending 5 mm from the other end to the one end in the axial direction, the elasticity index (hereinafter referred to as 60% elasticity index) when the inner diameter of the vascular cover is expanded 60% in the radial direction from the natural state is measured by the following measurement method, the 60% elasticity index of the one end is 0.42 N or more, the 60% elasticity index of the other end is 1.15 N or less, and the 60% elasticity index of the other end is smaller than the 60% elasticity index of the one end. [Measuring method] The vascular cover is cut perpendicular to the axial direction along the circumferential cut line of the vascular cover to prepare a sample with an axial length of 5 mm. A first pin and a second pin with a diameter d of 0.75 mm are inserted into the lumen of the sample parallel to the axial direction of the sample. The first pin is fixed, and the second pin is pulled outward in the radial direction of the sample. When the distance between the first pin and the second pin is L, πd+2L is 1.6 times the circumference of the sample in its natural state. The force F １．６ Measure and F １．６ The value obtained by dividing by the strain [(1.6-1.0) / 1.0] is the 60% elasticity index.

15. The blood vessel cover according to claim 14, wherein the 60% elasticity index of said one end is 5N or less.

16. A blood vessel cover as described in any one of claims 12 to 15, wherein the difference between the 60% elasticity index of said one end and the 60% elasticity index of said other end divided by the axial length of said blood vessel cover is less than 1.5 N / cm.