Buffer system artificial blood vessel

Abstract

To provide a buffer-system artificial blood vessel capable of preventing intima hyperplasia by supplying blood, which flows through the lumen of the artificial blood vessel, to a downstream vein while buffering and decreasing the blood (performing low-pressure buffer of hemodynamics) to a range, which can be permitted by a healthy venous wall, from arterial hemodynamics.SOLUTION: A buffer-system artificial blood vessel of the present invention comprises the function of buffering a dynamic state of blood flowing into a vein from an artery. The function of buffering the blood flow is the function of making the blood flow out to the side of the vein by reducing pressure of blood flowing in from the side of the artery and the pulsatile change of the pressure and / or a flow velocity and the magnitude of the change of the flow velocity.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a buffer system artificial blood vessel, and more particularly to a buffer system artificial blood vessel that can be suitably used as a short circuit (shunt) constructed between an artery and a vein. [Background technology]

[0002] The majority of the arterial system branching off from the aorta consists of muscular arteries. With the exception of a few arteries, these muscular arteries begin at the aorta, pass through small and medium-sized arteries, and then flow into small arterioles just before they flow into arterioles. These muscular arteries are responsible for delivering pulsatile blood pressure and blood flow to the arterioles (inner diameters of 100 to several hundred microns) at the extremities without damping. For example, from the abdominal aorta, which has an inner diameter of approximately 25 mm, to the 1-mm-diameter arteries in the limbs, the vascular lumen becomes smaller and the vascular walls become thinner. However, the blood pressure, pulse amplitude, and mean flow velocity remain almost unchanged from the aorta, remaining at 120 / 80 mmHg (see Non-Patent Document 1). If blood pressure, pulse pressure, and blood flow were damped or damped at any point between the aorta and the 1-mm-diameter arteries in the limbs, the supply of oxygen and nutrients to the limbs would be reduced, leading to necrosis. In other words, natural arteries function to never dampen or dampen the pulsatile arterial blood flow, which flows at high pressure and high speed. Since conventional artificial blood vessels are used to replace this function of natural muscular arteries, they have the function of delivering sufficient blood flow downstream to the natural artery connected downstream while maintaining blood pressure and pulsation so as not to attenuate the blood pressure and pulsation of the blood flow. In other words, they are designed and manufactured so that the blood flow flowing inside the artificial blood vessel does not buffer the blood pressure or pulsation when delivering blood. Thus, conventional artificial blood vessels do not have a shock-absorbing function, and in fact, eliminate the shock-absorbing function.

[0003] The walls of arteries are thick and strong, and even when pulsatile high pressure is applied to the internal blood flow, there is little change in the pulsation of the walls (due to the viscosity of the smooth muscle layer), and there is little generation of turbulence due to wall pulsation or severe fluctuations in friction stress. On the other hand, thin and soft venous walls have such weak resistance to increased intravenous pressure that even exposure to a state of increased venous pressure that is very weak compared to arterial pressure, such as venous congestion in the lower limbs, can easily lead to serious pathological conditions such as varicose veins, venous thrombosis, and even tissue necrosis due to venous congestion. Therefore, when arterial blood flows directly from the artery to the vein without passing through the capillaries due to an arteriovenous shunt, and the venous wall is directly exposed to high-speed blood flow with highly pulsatile blood pressure, the intense pulsatile movement of the wall causes blood turbulence and severe fluctuations in stress on the vascular wall. These severe fluctuations are particularly pronounced at the anastomosis between the artery (or artificial blood vessel) and the vein, where there is a significant difference in stiffness between the arterial and venous sides (compliance mismatch). Therefore, when conventional artificial blood vessels are used as a shunt between an artery and a vein, there is a risk of causing local or systemic pathology, as described in detail below.

[0004] For patients with serious kidney disease, hemodialysis is regularly performed, in which blood is extracted from the patient's body, waste products, excess water, minerals, etc. are removed using a dialysis machine, and the blood is then returned to the patient's body. When performing hemodialysis, a special needle is usually inserted into a vein, but because normal venous blood flow is insufficient for dialysis, it is necessary to divert some of the blood flow from an artery, which has a rich blood flow, into the vein to create a venous blood vessel that can be used for dialysis. Such a blood vessel is called blood access. Blood access usually involves making an incision in the skin of the limb to expose the artery and vein, making a small incision in the artery and anastomosing the vein to it, and creating a shunt through which some of the arterial blood flow is diverted to the vein. Sometimes, one end of an artificial blood vessel is anastomosed to the small incision in the artery, and the other end of the artificial vessel is anastomosed to the vein, creating an artificial vessel between the artery and vein, allowing some of the arterial blood flow to be diverted to the vein via this artificial vessel.

[0005] The dynamics of blood flow on the arterial side are characterized by high blood pressure, large pulsations with large pressure differences (large pulse pressure), very fast flow velocity, and large changes in flow velocity (hemodynamics characteristic of arterial blood as described above will be referred to as "arterial hemodynamics" in the following text). In contrast, the dynamics of blood on the venous side are characterized by low pressure, small pulsatile pressure changes, slow average blood flow velocity, and small changes in flow velocity (hemodynamics characteristic of venous blood as described above will be referred to as "venous hemodynamics" in the following text). At the shunt site, the venous wall has very low rigidity compared to the arterial wall or the wall of the artificial blood vessel anastomosed to the artery, and the difference in rigidity between the two is significant. Therefore, when arterial blood, which has arterial hemodynamics and does not act on the venous wall under normal conditions, flows from the exit of the artificial blood vessel into a vein with a thin wall and low rigidity, blood flow will occur under normal conditions. This causes blood turbulence and pulsation changes in the venous wall. In other words, it is a state in which stresses that do not occur under normal conditions are applied. As a response to this abnormal state, the body's intimal thickening occurs in the veins, which can easily lead to abnormal changes, i.e., pathological changes, such as stenosis, occlusion, varicose veins, and internal thrombosis. Furthermore, if the shunt blood flow state cannot be adjusted while still placing a heavy burden on the body, it can lead to more widespread local (such as aneurysm formation and stenosis in downstream veins) or systemic (such as steal syndrome due to excessive shunt blood flow or heart failure due to overcirculation) pathologies. If the conditions on the living body side are favorable, appropriate remodeling occurs as a defensive adaptive response by changes in the stiffness of the venous wall, avoiding stenosis or occlusion due to intimal thickening, and the shunt blood flow state may be self-regulated to a state that does not burden the living body. However, if local conditions such as shunt blood flow rate or anastomotic shape or systemic conditions (diabetes, hypertension, arteriosclerosis, blood properties, etc.) are poor, the range of appropriate defensive adaptive responses may be exceeded, resulting in a pathological biological response and causing local and systemic pathologies. In particular, artificial blood vessels are more stiff than natural arteries, so the difference in stiffness between them and veins is significant, preventing the appropriate defensive adaptive responses described above, often resulting in the local or systemic pathologies described above.

[0006] To prevent such pathological conditions, vascular banding is performed (Non-Patent Document 2). Patent Document 1 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 pile-less knitted fabric. Patent Documents 2 and 3 disclose that an arteriovenous graft (AVG) wrapped with a restrictive fiber matrix of a biodegradable polymer exhibited pulsatile radial deviation similar to that of the carotid artery. However, the above-mentioned vascular banding has not been able to sufficiently prevent lesions such as intimal hyperplasia (Non-Patent Document 2). [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Special Publication No. 2004-535896 [Patent Document 2] Special Publication No. 2010-516437 [Patent Document 3] Special Publication No. 2013-509258 [Non-patent literature]

[0008] [Non-Patent Document 1] Shinji Maeda: Educational Lecture: Blood Rheology and Physiological Functions, Part 1: Fundamentals of Hemodynamics and Blood Viscosity, Nissei Shigashi 234-244, 66, 7-8, 2004 [Non-patent document 2] Hiroaki Haruguchi, "I. Problems Associated with Blood Access Blood Flow Insufficiency," Journal of the Japanese Society of Dialysis Therapy, Vol. 15, No. 1, 68-70, 2000 Summary of the Invention [Problem to be solved by the invention]

[0009] In conventional vascular banding, the reinforced venous wall is modified (arterialized) to resemble the natural arterial wall structure. However, as mentioned above, natural arteries function to never dampen or buffer pulsatile arterial blood flow at high speeds and high blood pressures. Therefore, when blood passes through the reinforced area and flows into an unreinforced vein, the blood pressure and pulsation are not dampened and it is delivered downstream. This simply postpones the problem to be solved downstream and does not fundamentally resolve the cause of intimal thickening. To resolve this, it is necessary to gradually dampen and reduce arterial hemodynamics (hemodynamics with high pressure, large pulsatile pressure changes, fast flow velocity, and large flow velocity changes) from the anastomosis downstream, so that at the most downstream vein, only venous hemodynamics (mean flow velocity is sufficiently reduced, flow velocity changes are flat, and blood pressure is sufficiently low and pressure changes are small) acts on the venous wall. The present invention has been made in consideration of the above circumstances, and aims to provide a buffer-type artificial blood vessel that can prevent intimal thickening by buffering and lowering the blood flowing through the lumen of the artificial blood vessel from arterial hemodynamics to a range that can be tolerated by a healthy venous wall (low-pressure buffering of hemodynamics) while delivering it to the downstream vein. [Means for solving the problem]

[0010] As a result of extensive research, the present inventors have found that the above-mentioned problems can be solved by adopting the following configuration.

[0011] In other words, the buffer system artificial blood vessel of the present invention is a buffer system artificial blood vessel that has the function of buffering the dynamics of blood flowing from an artery to a vein, and is characterized in that the function of buffering the blood flow is a low-pressure buffering function that reduces the pressure and pulsatile pressure changes, and / or the flow velocity and magnitude of the flow velocity changes, of the blood flowing in from the arterial side and allows it to flow out to the venous side. A typical example of a buffer system artificial blood vessel of the present invention is a shunt constructed between an artery and a vein, but it also includes cases where the shunt is constructed between an artery and a vein at a location where the vein downstream of the construction site has undergone pathological changes such as stenosis due to arterial blood flow, or at a location where there is a risk of such pathological changes occurring. [Effects of the Invention]

[0012] The buffer cylinder of the buffer-system artificial blood vessel of the present invention differs from the conventional flow path section upstream of it in that it exhibits a gradient change in shear stress due to blood flowing through the lumen of the buffer cylinder, pressure perpendicular to the artificial blood vessel wall, and blood flow rate, flow velocity, and pulsation-related changes. In other words, it has the function of delivering blood to the downstream vein while buffering and reducing the arterial hemodynamics of the blood flowing through the lumen of the buffer cylinder. This function suppresses elastic incompatibility of the venous wall anastomosed downstream, as well as blood turbulence and high flow velocity, and prevents stenosis and occlusion of the vascular lumen due to intimal hyperplasia and thrombus formation.

[0013] The buffer system artificial blood vessel of the present invention exhibits the above-mentioned performance through the following two mechanisms. The first is the buffering effect of the physical structure of the buffer artificial blood vessel at the time of its creation, which acts to buffer arterial hemodynamics, and can be called a "physical buffering effect." The second is the biological effect of the elasticity of the buffer artificial blood vessel on the shunt vein, which induces the vein itself to remodel (remodel) its own structure and function into a buffer system vessel, which can be called a "biological buffering effect." Although buffering blood vessels can be effective with just one of the above-mentioned "physical buffering" and "biological buffering" functions, it is thought that in actual applications to living organisms, both functions often work together to achieve a buffering effect. In this document, for the sake of clarity, we will explain both separately.

[0014] The former, "physical buffering action," will be explained first below, and the latter, "biological buffering action," will be discussed later. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is an overall view showing a buffer system artificial blood vessel according to a first embodiment of the present invention. [Figure 2] FIG. 1 is a side view showing a buffer-type artificial blood vessel according to a first embodiment of the present invention. [Figure 3]FIG. 10 is a side view showing a buffer system artificial blood vessel according to a second embodiment of the present invention. [Figure 4] FIG. 10 is a side view showing a buffer system artificial blood vessel according to a third embodiment of the present invention. [Figure 5] FIG. 10 is a side view showing a buffer system artificial blood vessel according to a fourth embodiment of the present invention. [Figure 6] FIG. 10 is a side view showing a buffer system artificial blood vessel according to a fifth embodiment of the present invention. [Figure 7] FIG. 10 is a side view showing a buffer system artificial blood vessel according to a sixth embodiment of the present invention. [Figure 8] FIG. 10 is a cross-sectional view of a buffer cylinder of a buffer system artificial blood vessel according to a sixth embodiment of the present invention. [Figure 9] FIG. 10 is a side view showing a buffer system artificial blood vessel according to a seventh embodiment of the present invention. [Figure 10] FIG. 11 is a cross-sectional view of a buffer cylinder of a buffer system artificial blood vessel according to a seventh embodiment of the present invention. [Figure 11] FIG. 1 is a perspective view showing a sample for measuring an elasticity index. [Figure 12] FIG. 2 is a plan view of a sample for measuring an elasticity index, viewed from above. [Figure 13] FIG. 1 is a side view showing the shape of an artificial blood vessel produced in an example. [Figure 14] FIG. 1 is a side view showing the shape of an artificial blood vessel produced in an example. [Figure 15] FIG. 1 is a side view showing the shape of an artificial blood vessel produced in an example. [Figure 16] FIG. 1 is a side view showing the shape of an artificial blood vessel produced in an example. [Figure 17] FIG. 1 is a side view showing the shape of an artificial blood vessel produced in an example. [Figure 18] FIG. 1 is a side view showing the shape of an artificial blood vessel produced in an example. [Figure 19] FIG. 1 is a side view showing the shape of an artificial blood vessel produced in an example. [Figure 20] FIG. 1 is a side view showing the shape of an artificial blood vessel produced in an example. [Figure 21] FIG. 1 is a side view showing the shape of an artificial blood vessel produced in an example. [Figure 22] FIG. 1 is a side view showing the shape of an artificial blood vessel produced in an example. [Figure 23] FIG. 1 is a side view showing the shape of an artificial blood vessel produced in an example. [Figure 24] FIG. 1 is a side view showing the shape of an artificial blood vessel produced in an example. [Figure 25] FIG. 1 is a side view showing the shape of an artificial blood vessel produced in an example. [Figure 26] FIG. 1 is an explanatory diagram of an AV shunt for animal experiments prepared in an animal experiment according to an embodiment. [Figure 27] FIG. 1 is a side view showing the basic shape of a trumpet-shaped buffer cylinder. [Figure 28] FIG. 10 is an explanatory diagram of the relative lengths of the buffer cylinder in a trumpet-shaped buffer cylinder. [Figure 29] 1 shows a photograph of EvG staining in the evaluation test of Example 27. DETAILED DESCRIPTION OF THE INVENTION

[0016] Preferred embodiments of the buffer-type artificial blood vessel according to the present invention will be described in detail below, with reference to the drawings as appropriate. However, the scope of the present invention is not limited to these descriptions, and modifications other than those exemplified below may be made as appropriate within the scope of the present invention.

[0017] [First embodiment] 1 and 2 show a buffer system artificial blood vessel 1 according to a first embodiment of the present invention. The buffer system artificial blood vessel 1 is tubular overall, with both ends open. One end of the buffer system artificial blood vessel 1 is anastomosed to a small incision in the artery A, and the other end is anastomosed to the vein V, thereby constructing the buffer system artificial blood vessel 1 between the artery A and the vein V. The white arrows in Figure 1 indicate the flow of blood. Part of the blood flows from artery A into buffer system artificial blood vessel 1, passes through buffer system artificial blood vessel 1, and is buffered and reduced from arterial hemodynamics to a range that can be tolerated by healthy venous walls, and then flows out into vein V. Blood can be removed and returned from artificial dialyzer D.

[0018] The material of the buffer-type artificial blood vessel 1 may be the same as that of a general artificial blood vessel. Specifically, the material of the buffer system artificial blood vessel 1 may be any of synthetic polymers, natural polymers, and hybrids thereof, and may also be woven, knitted, nonwoven fabric, or porous such as sponge. Examples of synthetic polymers include fluorine-based polymers such as expanded polytetrafluoroethylene (ePTFE) and polytetrafluoroethylene (PTFE), polyolefins such as polyethylene and polypropylene, polyesters, polyamides, acrylic polymers, aromatic polyether ketone resins such as PEEK, polyester elastomers such as polyether polyamide resins and polyester polyols, polyimide resins, acrylic polymers, polyurethanes, silicones, and copolymers thereof. Biodegradable materials, such as bioabsorbable polymers including aliphatic polyesters such as polylactic acid, polyglycolic acid, caprolactam, polybutylene succinate, and polyhydroxyalkanoic acid; aliphatic polyethers such as polyethylene glycol; and polyvinyl alcohol, as well as copolymers thereof, may also be used. Examples of natural polymers include silk, cotton, konjac components, spider silk components, as well as bioabsorbable elastin, alginic acid, chitosan, collagen, gelatin, and the like. Elastic fibers include natural elastomers, as well as synthetic fibers such as urethane and silicone-based fibers, polytrimethylene terephthalate fibers and polybutylene terephthalate fibers, and even side-by-side fibers that combine two different types of polymers, as well as woolly processed fibers (yarns). Furthermore, bioabsorbable materials and metals may also be used. When woolly processed fibers are used, those made of polyamide (nylon), polyester (tetron), or bioabsorbable polylactic acid are preferably used.

[0019] The buffer system artificial blood vessel 1 is provided with a buffer cylinder 10 having a buffering function. The buffer system artificial blood vessel may be composed of only this buffer cylinder 10, or may be composed of both this buffer cylinder 10 and a normal flow path section 20, as in this embodiment. The normal flow path section 20 has the basic shape of the buffer system artificial blood vessel 1, and by reducing the thickness of the tube wall, changing the diameter size or cross-sectional shape of the diameter, or changing the material of this normal flow path section 20, a buffer cylinder 10 is formed continuously on the vein V side, in principle.

[0020] The dimensions of the flow path section 20, such as the inner diameter, outer diameter, and thickness, may be similar to those of a typical artificial blood vessel, and may vary depending on the site of use in the body and the material, but may be, for example, about 2 to 8 mm inner diameter, 3.5 to 11 mm outer diameter, and 0.5 to 2 mm thick. When used for dialysis, which is generally performed three times a week, the strength and thickness must be such that they will not deteriorate even when punctured with a thick needle in two places three times a week.

[0021] The buffer cylinder 10 on the vein V side is preferably formed as close to the vein V as possible, but this is not necessarily required. The reason why it is preferable to form it as close to the vein V as possible is that, for blood removal, the normal flow path section 20 before passing through the buffer cylinder 10 is usually used, and the farther the buffer cylinder 10 on the vein V side is from the vein V, the shorter the area used for blood removal often becomes. The reason why this is not necessarily required is that the opposite may sometimes be desirable depending on the systemic pathology or local pathology. The buffer cylinder 10 on the vein V side has an expanded diameter portion 11 on the vein V side, the diameter of which expands from the artery A side to the vein V side. Due to the enlarged diameter at the enlarged diameter portion 11, the blood flowing in from the artery A side is buffered in arterial hemodynamics and flows out from the vein V side.

[0022] The degree of diameter change of the expanded diameter section 11 is not particularly limited, but for example, the maximum diameter on the vein V side can be approximately 1.01 to 5 times the minimum diameter on the artery A side, more preferably 1.2 to 2.5 times. The diameter expansion angle can be approximately 1 to 90°, more preferably 10 to 70°, and even more preferably 15 to 60°. Although depending on factors such as the elasticity of the wall, if the diameter change is too large, problems such as turbulence may occur. Although depending on factors such as the elasticity of the wall, if the diameter change is too small, the buffering effect may be insufficient. Furthermore, it is desirable for the angle at which the diameter changes to be a smoothly changing curve, as this provides an excellent effect in preventing turbulence.

[0023] The buffer cylinder 10 also has an elastic portion 12 that is more elastic (easily stretchable) than the normal path portion 20. This is also effective in buffering and reducing arterial hemodynamics. One method for increasing elasticity is to make the thickness of the buffer cylinder 10 thinner than that of the normal path section 20. Specific methods include, for example, making the buffer cylinder 10 thinner than the surrounding area when molding the buffer system artificial blood vessel 1, or making the buffer system artificial blood vessel 1 partially laminated (for example, molding a highly elastic resin material such as polyurethane thin to create the overall base shape, and then laminating a resin material such as a fluorine-based polymer on areas other than the buffer cylinder 10 to make the wall thicker). Although the innovation in this embodiment is implemented in the enlarged diameter portion, this innovation may also be implemented in the straight lumen portion other than the enlarged diameter portion.

[0024] Second Embodiment FIG. 3 shows a buffer system artificial blood vessel 2 according to a second embodiment of the present invention. The buffer cylinder 10 of the buffer system artificial blood vessel 2 has a narrowed portion 13 with a reduced diameter upstream of the enlarged diameter portion 11. The other configurations are the same as those of the buffer-type artificial blood vessel 1, and therefore the explanation will be omitted.

[0025] Here, arterial blood pressure is expressed as cardiac output (Q) × peripheral resistance (R), and according to Poiseuille's law, peripheral resistance (R) is proportional to blood viscosity (η) and inversely proportional to the fourth power of the blood vessel radius (r) (Educational Lecture: Blood Rheology and Physiological Function, Part 1: Fundamentals of Hemodynamics and Blood Viscosity, by Shinji Maeda, Journal of the Physiological Society of Japan, Vol. 66, No. 7-8, 234-244, 2004). In other words, in natural arteries or artificial blood vessels with higher rigidity, a 10% reduction in vessel diameter increases resistance by (1 / 0.9)^4 ≒ 1.5 times, and a 10% increase in vessel diameter decreases resistance by (1.0 / 1.1)^4 ≒ 0.68 times = 68%.

[0026] A very schematic and simplified explanation follows. As a first example, consider an arteriovenous shunt constructed by side-to-end anastomosing a conventional artificial blood vessel to a natural artery. The inner diameter of a conventional artificial blood vessel is typically 6 mm, and a vein is anastomosed end-to-end to the downstream end of the sufficiently long conventional artificial blood vessel. The vein is free of surrounding tissue, leaving only the venous wall tissue. Under normal arterial pressure, it expands to more than 6 mm. Because conventional artificial blood vessels are designed without any buffering function for blood pressure or blood flow, the arterial hemodynamics act on the venous wall without any buffering at the downstream end of the artificial blood vessel (i.e., the point where blood flows out of the artificial blood vessel into the vein). The venous wall expands and contracts repeatedly due to the arterial hemodynamic pressure pulsation, causing the venous diameter to change. Generally, the flow velocity and resistance of venous blood under physiological conditions (normal, healthy conditions are medically referred to as physiological conditions; abnormal conditions are referred to as pathological conditions) are significantly lower than those under arterial hemodynamic conditions. Therefore, the stress and changes acting on the venous wall under arterial hemodynamics acting on the anastomotic vein are much greater than those under physiological conditions. A venous wall placed in this abnormal, or pathological, state can be a major cause of pathological changes such as intimal hyperplasia and stenosis as a result of pathological reactions.

[0027] As a second example, we consider a buffer-type artificial blood vessel with a sufficiently long conventional artificial blood vessel, but with a short, expanded diameter section (buffer section) at the most downstream end of the vessel. In this case, the expanded diameter section is located downstream of the conventional artificial blood vessel, and a vein similar to that of the conventional artificial blood vessel described above is anastomosed end-to-end to the downstream end of the expanded diameter section. Since the diameter of the conventional blood vessel, which accounts for most of the area upstream of the expanded diameter section, determines the actual resistance of this artificial blood vessel, we can assume that the hemodynamics of the conventional artificial blood vessel portion immediately before the inflow to the expanded diameter section will be virtually unchanged with or without the expanded diameter section, and will be virtually identical to the most downstream section of the conventional artificial blood vessel in the first example. Compared to the section immediately before the inflow to the expanded diameter section, the resistance in the expanded diameter section (i.e., the buffer section with a 10% expanded diameter) will be reduced by 68%. However, the resistance in this area is greater than that of the vein anastomosed to the downstream end of the enlarged section, and blood flow is largely determined by the resistance of the sufficiently long conventional vascular artificial blood vessel upstream of the enlarged section and systemic blood pressure. Therefore, in the enlarged section, blood pressure and blood flow are directed halfway between the upstream conventional vascular artificial blood vessel and the vein. This is the buffering effect of the blood flow conditions at the enlarged section. If a very rough estimate is allowed, a buffering effect is expected that will reduce changes in blood pressure and blood flow, as indicated by a decrease in resistance, by approximately 68%.

[0028] As a third example, consider a buffer-type artificial blood vessel with a sufficiently long conventional artificial blood vessel, a sufficiently short narrowed section (10% smaller in diameter) placed downstream, and an expanded section (10% larger in diameter) just downstream of that narrowed section. The overall blood flow through the artificial blood vessel is reduced by the increased resistance caused by the narrowed section (a very rough estimate is to 1 / 1.5, or 67%, of that of the conventional artificial blood vessel). However, because blood pressure is largely determined by systemic blood pressure, the change in blood pressure is small; the dominant changes are the increased resistance and the decrease in average flow velocity through the conventional artificial blood vessel section (i.e., the flow rate of the entire artificial blood vessel). Then, due to the effect of the expanded section (1.1 times larger than the conventional artificial blood vessel section and 1.1 x 1.1 times larger than the narrowed section), the blood pressure and flow velocity in the expanded section are guided to somewhere between those of the conventional artificial blood vessel section and the venous section. In terms of blood flow dynamics, this expanded area is a "buffer pond" of the same size as in the second example, but because the blood flow flowing in from the narrowed area is a "smaller river," the buffering effect of the expanded area is relatively greater, showing a greater buffering effect than in the second example, and it is expected that the arterial blood flow dynamics will be buffered by roughly 45%.

[0029] As a fourth example, consider a buffer-type artificial blood vessel with an expanded section downstream of a conventional artificial blood vessel, which is 10% larger in diameter than the conventional artificial blood vessel, and a relatively narrow section just downstream of that, which is smaller in diameter than the expanded section. The expanded section, which is 10% larger in diameter, acts as a "buffer basin" that buffers the inflow of arterial blood, while the relatively narrow section downstream of that acts as an "exit gate," further enhancing the buffering effect of the buffer basin. In this case, the buffering effect is maximized when the expanded section acting as a buffer basin and the relatively narrow section downstream of it, acting as the "exit gate," have appropriate elasticity.

[0030] As described above, by appropriately combining an expanded diameter section and a narrow section, such as by providing a narrow section and an expanded diameter section downstream thereof, or conversely by providing a narrow section downstream of an expanded diameter section, the buffering effect can be further enhanced. Therefore, by providing the narrowed portion 13 in addition to the diameter expansion and elasticity change, the effect of buffering and reducing arterial hemodynamics can be further enhanced. Furthermore, by combining multiple buffer means in this way, a high buffer effect can be obtained while reducing the risk of turbulence, etc., compared to when relying on a single buffer means. By efficiently obtaining a buffer effect, the length of the buffer cylinder 10 can be shortened, and the normal flow path section 20 used for puncturing can be made longer. The diameter change of the narrowed portion 13 is not particularly limited, but for example, the minimum diameter at the center of the narrowed portion 13 can be about 99% to 5% of the inner diameter of the normal path portion 20, more preferably about 90% to 30%, and even more preferably about 80% to 40%. If the diameter change is too sudden, problems such as turbulence may occur. If the degree of diameter change is too small, the buffering effect may be insufficient.

[0031] Third Embodiment FIG. 4 shows a buffer system artificial blood vessel 3 according to a third embodiment of the present invention. The buffer system artificial blood vessel 3 has a buffer cylinder 10 formed not only on the vein V side but also on the artery A side, and the buffer cylinder 10 on the artery A side has a narrowed section 13 whose diameter decreases from the vein V side to the artery A side. The end of the narrowed section 13 on the artery A side is open and is anastomosed to the small incision in the artery A. In this way, a narrowed portion may be provided on the arterial side.

[0032] [Fourth embodiment] FIG. 5 shows a buffer system artificial blood vessel 4 according to a fourth embodiment of the present invention. In the buffer system artificial blood vessel 4, the lumen of the enlarged diameter portion 11 is spiral. The other configurations are the same as those of the buffer-type artificial blood vessel 1, and therefore the explanation will be omitted. In the buffer system artificial blood vessel 4, the lumen of the expanded diameter portion 11 is spiral, and therefore in addition to the buffering effect due to the expanded diameter and change in elasticity, the buffering and reducing effect on arterial hemodynamics can be further enhanced. As described above, by combining multiple buffering means, it is possible to obtain a high buffering effect while reducing the risk of turbulence and the like compared to relying on a single buffering means, and thereby it is possible to shorten the length of the buffer cylinder 10 and ensure a long normal flow path section 20 that can be used for puncturing. Although the innovation in this embodiment is implemented in the enlarged diameter portion, this innovation may also be implemented in the straight lumen portion other than the enlarged diameter portion.

[0033] Fifth Embodiment FIG. 6 shows a buffer system artificial blood vessel 5 according to a fifth embodiment of the present invention. The buffer system artificial blood vessel 5 has a buffer cylinder 10 in which sections with different elasticity are combined in a patch-like manner. It differs from the buffer system artificial blood vessel 1 in that it has multiple elastic sections 12, 12... that are highly elastic (easily stretchable). That is, while the entire buffer cylinder 10 of the buffer system artificial blood vessel 1 is highly elastic, the buffer system artificial blood vessel 5 has multiple elastic sections 12, 12... arranged in parts of the buffer cylinder 10, with the elastic sections 12, 12... and other sections coexisting in a patch-like manner. As with the buffer system artificial blood vessel 1, the elastic sections 12, 12... can be formed by making the thickness of the elastic section 11 thinner than the surrounding area or by using a different material. In the buffer-system artificial blood vessel 5, the elastic portions 12, 12... are diamond-shaped, but may be other shapes. However, from the viewpoint of achieving a balanced buffer effect and preventing turbulence, it is preferable that the shape and arrangement have a certain degree of regularity. Although the innovation in this embodiment is implemented in the enlarged diameter portion, this innovation may also be implemented in the straight lumen portion other than the enlarged diameter portion.

[0034] Sixth Embodiment 7 and 8 show a buffer-type artificial blood vessel 6 according to a sixth embodiment of the present invention. Figures 8(a) to 8(c) are cross sections taken along lines aa, bb, and cc in Figure 7, respectively. The buffer system artificial blood vessel 6 is a buffer system artificial blood vessel 1 to which a different kind of innovation has been applied. As shown in Figures 8(b) and 8(c), the expanded diameter section 11 of the buffer system artificial blood vessel 6 has an elliptical cross section, with the tube wall on the major axis side being thicker and the tube wall on the minor axis side being thinner. It is intended to exert a buffering effect with a thin tube wall on the short diameter side, while preventing a series of risks such as compression, stenosis, and occlusion of blood vessels with a thick tube wall on the long diameter side. The reason for thickening the tube wall on the long diameter side instead of the short diameter side is that in the normal method of installing an artificial blood vessel, if the tube wall on the long diameter side is thin, the buffered blood tends to have a slow flow rate, and if that part is compressed and stenosed, it is likely to form a thrombus, and in the worst case, the risk of permanent occlusion increases. However, the reverse (thick tube wall on the long diameter side and thin tube wall on the short diameter side) is also acceptable. The reason is that sometimes, due to the positional relationship between the skin and the fascia, the installation may be reversed from the normal situation. The improvement in this embodiment is made in the expanded diameter portion, but this improvement may also be made in the straight lumen portion that is not the expanded diameter portion.

[0035] 〔The 7th Embodiment〕 Figs. 9 and 10 show a buffer-type artificial blood vessel 7 which is the 7th embodiment of the present invention. Figs. 10(a) to (c) are respectively the a-a cross section, b-b cross section, c-c cross section, and d-d cross section in Fig. 9. The buffer-type artificial blood vessel 7 has a configuration similar to that of the buffer-type artificial blood vessel 6, but is different in that the thickness of the tube wall on the long diameter side is gradually changed. As shown in Figs. 10(c) and (d), among the tube walls on the long diameter side, the tube wall located on the upper side as viewed in the figure is thin in the c-c cross section, gradually changes in thickness, and becomes thick in the d-d cross section. The tube wall located on the lower side as viewed in the figure is opposite to the tube wall located on the upper side, is thick in the c-c cross section, gradually changes in thickness, and becomes thin in the d-d cross section, and is balanced as a whole.

[0036] 〔Preferred Conditions for Buffer-Type Artificial Blood Vessels〕 <X% Elastic Index> In the description of each of the above embodiments, the elasticity of the buffer cylinder 10 was mentioned. Regarding this elasticity, the following "X% Elastic Index" can be used as an index. In the present invention, the "X% Elastic Index" refers to the value defined below.

[0037] (Measurement Method of X% Elastic Index) The X% elasticity index is the elasticity index obtained when the inner diameter of a sample of a buffer cylinder having an axial length of 5 mm is expanded by X% from its natural state. The method for measuring the elasticity index will be explained with reference to Figures 11 and 12. Figure 11 shows a perspective view of a measurement sample 100 for the elasticity index, and Figure 12 shows a plan view of the measurement sample 100 shown in Figure 11 when viewed from above. [Measurement method] The buffer cylinder is cut out in the axial direction up to a portion extending 5 mm to prepare a cylindrical sample 100 having an axial length of 5 mm. The cylindrical sample 100 is cut out along a cut surface perpendicular to the axial direction, i.e., along a cutting line in the circumferential direction, so as to obtain a cylindrical sample 100 having an axial length of 5 mm and continuous all around. However, in a buffer-type artificial blood vessel in which cuts are formed in the buffer cylinder and the wall can be separated along the cuts, the wall is discontinuous at the cuts, making it impossible to prepare a "cylindrical sample that is continuous all around." Therefore, a cylindrical sample that is continuous all around except for the cuts in the wall is cut out. 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 in parallel with 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 with a force F. When the distance between the first pin 101 and the second pin 102 is L, the force F when πd+2L is (1+0.01X) times the circumferential length of the cylindrical sample 100 in its natural state is calculated. 1+0.01X The value obtained by dividing by the strain [((1+0.01X)-1.0) / 1.0] is the X% elasticity index. 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. 12. 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. For example, 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 1.3Dividing by the strain [(1.3-1.0) / 1.0] gives the 30% elasticity index.

[0038] If it is difficult to measure using the above-mentioned measurement method using a cylindrical sample, the X% elasticity index can be measured using a strip-shaped sample developed from the cylindrical sample instead. Specifically, a cylindrical sample is unfolded to prepare a strip-shaped sample, and both ends of the sample in the longitudinal direction are gripped with two jigs and pulled outward. The distance (L) between the gripping positions of the jigs is recorded when no force is applied to the jigs (natural state), and then the distance (L+S) between the gripping positions of the jigs when a force is applied and pulling is determined. The value S obtained by subtracting L from L+S is divided by L (S÷L×100=X), i.e., the strain (X) is calculated. In addition, the force F when both ends of the strip-shaped sample are pulled and the distance between the gripping positions of the jigs becomes (1+0.01X) times the distance between the jigs in the natural state is calculated. 1+0.01X The value obtained by dividing by the strain [((1+0.01X)-1.0) / 1.0] is obtained. The value obtained by doubling this value corresponds to the X% elasticity index obtained by the above measurement method using a cylindrical sample. For example, in Example 30 described later, the above measurement method using a cylindrical sample was not possible, so the elasticity index was measured using the following method. Specifically, a single zigzag iron wire was held at both ends with two jigs while still in its heat-treated, tubular shape, and the jigs were pulled in a direction to straighten the zigzag iron wire. First, the distance (L) between the gripping positions of the jigs was recorded when no force was applied to the jigs (natural state). Next, the distance (L + S) between the gripping positions of the jigs when a force was applied and the wire was pulled was calculated. The value S obtained by subtracting L from L + S was divided by L (S ÷ L × 100 = X), i.e., the strain (X). Furthermore, the force F when the zigzag iron wire was pulled and the distance between the gripping positions of the jigs became (1 + 0.01X) times the distance between the jigs in the natural state was calculated. 1+0.01X The value obtained by dividing by the strain [((1+0.01X)-1.0) / 1.0] and doubling it was taken as the X% elasticity index.

[0039] When cutting samples from the buffer cylinder, if the values ​​vary depending on the cut-out portion, the value of the lowest sample shall be the X% elasticity index of the buffer cylinder. Furthermore, if the buffer cylinder to be measured is, for example, trumpet-shaped and it is not possible to cut out a uniform cylindrical sample with an axial length of 5 mm, a straight cylindrical buffer cylinder made in the same manner as the part to be measured can be prepared, and the elastic index of the sample with an axial length of 5 mm of this buffer cylinder can be measured using the method described above. Furthermore, when the buffer cylinder used for measurement is an artificial blood vessel reinforced with, for example, a spiral reinforcement material called a reinforcement material or support, or an artificial blood vessel made of knitted or woven fabric, cutting out a cylindrical sample 5 mm in axial length and pulling it often results in the fraying of the support or fabric. In this case, therefore, a cylindrical sample with an appropriate axial length of Y mm (for example, 25 mm) is cut out, the elasticity index is measured using the above method, and the value is divided by Y / 5 (for example, if Y=25, then 25 mm ÷ 5 mm = 5) to determine the elasticity index per 5 mm.

[0040] Among the X% elasticity indices defined above, the 30% elasticity index, the 60% elasticity index, and the 100% elasticity index are particularly useful as indicators. The reasons are as follows.

[0041] First, the reasons for setting the 30% elasticity index are explained below. As a preliminary study, the inventors created an arteriovenous shunt between the carotid artery and jugular vein of a dog as an experimental model similar to that of a human arteriovenous shunt, and conducted an experiment on the expansion of the venous side when arterial blood flow flows from the arterial side to the venous side through this arteriovenous shunt. To create an arteriovenous shunt, a 60 mm long aluminum tube with a circular lumen and a fixed diameter was placed over the vein. The aluminum tube had a spiral or helical layered wall, allowing the inner diameter to be freely adjusted within a small range. The aluminum tube was then moved to the most upstream shunt vein connected to the artery, covering the entire vein over a 60 mm length. A vascular clamp was then placed on the upstream artery to block arterial blood flow. The vein's outer diameter was measured in the state where a small amount of blood remained inside the vein (hereinafter referred to as the "natural state"). The vascular clamp was then removed, allowing arterial pressure to flow from the upstream artery into the vein. The vein's outer diameter was then immediately measured at the point just downstream of the tubing. Next, we used an ultrasonic blood flowmeter to assess whether the arterial blood flow dynamics at the vein diameter measurement site were buffered. When the inner diameter of the coated aluminum tube was set to 1.3 times or more the natural vein diameter, 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 blood flow dynamics immediately downstream of the coated portion of the tube were buffered. On the other hand, when the inner diameter of the coated tube was set to 1.15 times or less the natural vein diameter, i.e., when the play between the inner diameter of the tube and the vein wall was set to 2 / 3 times 30% (=20%) or less of the natural vein diameter, the buffering effect was sometimes not observed. Although these experimental results are only for reference, when considering the buffering of arterial blood flow, it is believed that when the natural vein expands to 1.3 times or more its original diameter, the buffering effect due to the elasticity of the vascular wall is more likely to be observed than when the expansion is less than 1.3 times. Using this data as a guideline, the inventors determined that the elasticity index of the buffer system blood vessels when the inner diameter is expanded by 30% (30% elasticity index) is useful as an indicator of the vascular wall elasticity involved in the buffer function when the expansion of the artificial blood vessel is relatively small. Although venous 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.

[0042] Next, we will explain the reason for setting the 100% elasticity index. Similar to the experiment for establishing a 30% elasticity index, an arteriovenous shunt was created in a dog, and the outer diameter of the vein in its natural state was measured. Next, without covering the vein with any aluminum tube, the vascular clamp that had been attached to the upstream artery to block arterial blood flow was removed. Arterial blood flow was then allowed to flow from the artery upstream of the shunt through the arteriovenous shunt into the vein, and the vein immediately downstream of the shunt was observed to dilate due to the inflow of blood. The vein diameter immediately downstream of the shunt was then immediately measured. As a result, we observed that the vein diameter, upon receiving arterial blood flow, always dilated to more than twice its natural diameter (100% increase in dilation from the natural state). However, less than half of the vein diameters dilated to more than three times its natural diameter (200% increase in dilation from the natural state). Therefore, we determined that the 100% elasticity index, which is the elasticity index when the vein is dilated to twice its natural diameter, is useful as an elasticity index of the vascular wall involved in the buffering effect when the vein is strongly dilated.

[0043] Next, we will explain the reason for setting the 60% elasticity index. Arterial blood pressure acts as a pulsating wave, shifting alternately from very high pressure (systolic pressure) to relatively low pressure (diastolic pressure). As mentioned above, the 30% elasticity index (30% elasticity index) is used as the elasticity index of the buffer system vessels. It is useful as an index of vascular wall elasticity, which contributes to the buffering function when the artificial blood vessel is relatively small in dilation, i.e., when blood pressure is relatively low. Furthermore, the 100% elasticity index, which is the elasticity index when the vein is dilated twice its natural diameter, is useful as an elasticity index of the vascular wall, which contributes to the buffering effect when the vein is highly dilated, i.e., when high blood pressure is applied. The buffering of arterial blood flow in the buffer system is actually the combined result of the buffering effect under all blood pressure conditions between these two conditions, i.e., all dilation conditions between 30% and 100%. Therefore, we have determined that a 60% elasticity index, which is roughly halfway between 30% and 100%, is useful as an index of vascular elasticity involved in buffering function from another perspective, that is, as an elasticity index of the vascular wall involved in the buffering effect in the overall average dilation state, or, if we may say, the overall average blood pressure state.

[0044] In order to obtain a cushioning effect through the elastic force (ease of stretching) of the buffer cylinder 10, it is preferable that the 30% elastic index of the buffer cylinder 10 defined above is 11 N or less, and more preferably, it is 1.6 N or less in order to provide a cushioning effect through uniform wall elasticity alone, even in the case of a buffer cylinder with unfavorable conditions such as a straight buffer cylinder with no change in inner diameter or wall elasticity. The lower the 30% elasticity index of the buffer cylinder 10, the more advantageous it is for the buffer effect to be exhibited. In addition, a lower 100% elasticity index of the buffer cylinder 10 is advantageous for exhibiting a cushioning effect; for example, 7.5 N or less is desirable, and more desirably, even for a buffer cylinder with unfavorable conditions such as no change in the inner diameter or wall elasticity and being straight, a buffering effect can be exhibited solely through uniform wall elasticity, with a value of 6.5 N or less, and even more desirably, 2.5 or less. Furthermore, a lower 60% elasticity index of the buffer cylinder 10 is advantageous for exhibiting a cushioning effect, and a value of 4.6 N or less is desirable, and even in the case of a buffer cylinder with unfavorable conditions such as a straight shape where the inner diameter and wall elasticity do not change at all, a value of 3.2 N or less is desirable in order to exhibit a cushioning effect with uniform wall elasticity alone, and even more desirable is a value of 1.6 N or less. However, in some cases where the cushioning function is provided in combination with other means, such as by providing an enlarged diameter portion, the desired cushioning function may be achieved even when the above-mentioned preferred ranges are exceeded.

[0045] In order to exert a cushioning function, the lower limit of the 30% elasticity index may be as close to 0 as possible. It is also possible to use values ​​other than the 30% elasticity index, 60% elasticity index, and 100% elasticity index as guidelines. For example, in the case of a buffer cylinder 10 that is a straight cylindrical tube of exactly the same inner diameter and has uniform wall elasticity, a lower 150% elasticity index is advantageous for exhibiting a buffer effect. For a buffer cylinder in the unfavorable condition of exhibiting a buffer effect solely through uniform wall elasticity, a value of 9.8 N or less is desirable, more preferably 8.4 N or less, and even more preferably 4.6 N or less.

[0046] <Buffer cylinder length> It is desirable for the buffer cylinder to have a certain length. In the present invention, the ratio R (=X / Φ) of the axial length X mm of the buffer cylinder to the inner diameter Φ of the blood inlet section can be used as a guide. As can be seen from Figure 23 (described later) regarding a trumpet-shaped buffer cylinder, the axial length X of the buffer cylinder can be determined by considering cylindrical cut surfaces perpendicular to the axial direction at one end and the other end of the buffer cylinder and measuring the distance between these two planes. With a shape such as a trumpet-shaped buffer cylinder, X may be 0 mm. R is preferably 1 or more, more preferably 1.2 or more, and even more preferably 1.5 or more. However, in cases where the buffer cylinder 10 is highly elastic (easily stretchable) or has an enlarged diameter section, or in other cases where it is combined with other means for imparting a buffer function, the desired buffer function may be achieved even if R is less than 1. The buffer cylinder does not necessarily have to be an exact cylinder. For example, if only a certain portion of the wall constituting the tubular blood flow path of the artificial blood vessel has a protruding, bulging shape toward the outside of the lumen, the entire tubular blood flow path including this protruding portion is considered to be a buffer cylinder. Furthermore, if there are multiple short buffer cylinders, the total length of the short buffer cylinders is considered to be the length of the buffer cylinder.

[0047] Other Embodiments The present invention is not limited to the above-described first to seventh embodiments, nor is it limited to the examples described below. For example, although each of the buffer system artificial blood vessels in the first to seventh embodiments above includes the buffer cylinder 10 and the normal flow path section 20, it may not include the normal flow path section 20. That is, the entire buffer system artificial blood vessel (the entire section from the anastomosis with the artery to the anastomosis with the vein) may be formed of the buffer cylinder 10. In this case as well, the pressure and pulsatile pressure changes, as well as the magnitude of the flow velocity and flow velocity changes, of blood flowing in from the artery side can be reduced and then flowed out to the venous side. The buffering artificial blood vessels, which have the "physical buffering effect" described above, also have the effect of remodeling the wall of the natural vein anastomosed downstream as a "biological buffering effect." In particular, microscopic findings (discussed below) are often clearly observed in a range of about 15 mm of the anastomosed natural vein wall closest to the artificial blood vessel. However, the "biological buffering effect" can be more typically achieved by placing a buffer cylinder on the outside or inner lumen of the shunt vein wall, overlapping it with the vein wall, as described below. Therefore, the following explanation of the "biological buffering effect" will use an example of such an installation, overlapping with the vein wall. By installing this buffer system blood vessel in this manner, its physical properties, such as elasticity, allow it to function as a buffer cylinder for the buffer system artificial blood vessel (physical buffering effect). At the same time, its physical properties, such as elasticity, induce the biological response of the overlying natural vein wall, remodeling the vein wall into a buffer system blood vessel (biological buffering effect). The combined effects of these two actions are expected to result in an even better buffer cylinder for the buffer system artificial blood vessel.

[0048] [Biological buffering effect] So far, the action of the buffer system artificial blood vessel of the present invention has been described from the viewpoint of "physical buffer action." Next, the buffer action of the present invention will be described from the viewpoint of "biological buffer action." The buffer system artificial blood vessel of the present invention, by its biological buffering effect, induces the formation of a gradient two-layer structure in the wall of the natural vein at the site of shunt creation: a smooth muscle layer that is richer in elastic fibers than the smooth muscle layer of a normal vein and thinner than the smooth muscle layer of a normal artery, and an outer collagen fiber layer that is rich in elastic fibers and thicker than the smooth muscle layer described above, thereby remodeling the vein at the site of shunt creation into a natural buffer system vessel (the "biological buffering effect of the buffer system artificial blood vessel"). In this way, the artificial blood vessel induces the remodeling of the natural vein at the site of shunt creation into a natural buffer system vessel with two layers: a smooth muscle layer rich in elastic fibers and a collagen fiber layer that is thicker than the smooth muscle layer and rich in elastic fibers. This induced natural buffer system vessel gradually buffers the highly pulsatile, high-speed arterial hemodynamics at the arteriovenous anastomosis and the artificial blood vessel-venous anastomosis downstream, ultimately transitioning to venous hemodynamics, thereby enabling a low-pressure buffering effect. As a result, blood turbulence and pulsation changes in the venous wall are suppressed, and pathological changes such as intimal hyperplasia and thrombus formation can be prevented.

[0049] In connection with the above, the differences between buffer system vessels and normal arteries are explained in more detail below. The walls of arteries and veins are composed of three layers: the tunica intima, tunica media, and tunica adventitia. Of these, the tunica intima contributes greatly to anticoagulation but has very little mechanical contribution. The arteries of the limbs used for hemodialysis shunt construction are typical muscular arteries, with two main mechanical components: the tunica media, which contains some elastic fibers and abundant smooth muscle, and the outer tunica adventitia, which is made up of elastic fibers, collagen fibers, etc. Among these, the relatively small number of elastic fibers have a buffering function like a rubber tube, resisting and mitigating the high pulsatile blood pressure of the arteries due to their elasticity. On the other hand, the smooth muscle layer, especially in normal muscular arteries, is particularly thick to minimize pulsatile changes in the vascular wall and prevent turbulence and frictional stress fluctuations in response to pulsating, high-pressure arterial hemodynamics. Because this abundant smooth muscle is muscular, it has an active mechanical function, constricting the blood vessels while resisting arterial blood pressure. On the other hand, it also has the active and proactive function of delivering high, pulsatile arterial blood pressure to the periphery without attenuating it. Due to the pressure-transmitting function of this abundant smooth muscle in arteries, blood pressure remains almost constant in muscular arteries, from large aortas with internal diameters measured in centimeters to small arteries with internal diameters measured in fractions of a millimeter. In other words, normal arteries (composed of "smooth muscle > elastic fiber") do not have the function of buffering high, pulsatile arterial pressure due to the action of their abundant smooth muscle. As described above, normal muscular arteries are composed of a very large amount of smooth muscle and relatively few elastic fibers (i.e., "smooth muscle > elastic fibers"), and are highly rigid against arterial hemodynamics.

[0050] On the other hand, veins have thin walls and lack the thick smooth muscle and elastic fiber layers found in arteries, resulting in low rigidity. Therefore, if an unusual blood flow condition occurs in which arterial blood flows directly from an artery to a vein via an arteriovenous shunt, the vein often has difficulty adapting to this condition, resulting in pathological biological reactions such as intimal thickening. To prevent this from happening, the vein itself must remodel itself into a low-pressure buffer system, capable of withstanding 100% pulsatile arterial pressure at the anastomosis site (i.e., the most upstream part of the vein), gradually attenuating and reducing blood pressure, pulsatility, and maximum flow velocity downstream, ultimately shifting to low-pressure venous hemodynamics with almost no pulsatility at the most downstream vein.

[0051] As mentioned above, normal arteries, such as the limb arteries used in shunts, are muscular arteries, composed of a very large amount of smooth muscle and relatively few elastic fibers (i.e., "smooth muscle > elastic fiber"), and are highly rigid against arterial hemodynamics. On the other hand, when the native veins in the shunt area are remodeled into buffer vessels, the ratio of elastic fibers to smooth muscle is completely reversed from that of normal arteries, with a very abundant elastic fiber and a relatively thin smooth muscle layer ("elastic fiber > smooth muscle"). Therefore, in buffer vessels, the pressure transmission function of the smooth muscle layer is greatly reduced, while the pressure buffering function of the elastic fiber is extremely dominant. While maintaining the above-mentioned "elastic fiber > smooth muscle" configuration, i.e., maintaining the buffering function, buffer vessels have a characteristic morphology in which the entire native vascular wall gradually thins and transitions into a vein, i.e., gradually transitioning to a normal vein as the buffered pressure decreases (low-pressure buffer vessels).

[0052] On the other hand, conventional vascular banding techniques, such as those using coatings to reinforce natural veins as surgical implants, result in arterialization (remodeling into an artery), not remodeling into a low-pressure buffer system. With conventional vascular banding, even if the vein gradually weakens in arterialization and naturally transitions downstream into a completely normal vein, the "smooth muscle > elastic fiber" structure is retained, resulting in the gradual thinning and transition into a vein. This "arterialized" vein lacks buffering function. Therefore, the high pulsatile blood pressure and high blood flow caused by arterial hemodynamics affect the venous wall downstream of the shunt, resulting in pathological changes in the downstream vein. This is the clear functional difference between the gradual thinning and transition into a buffer system and the gradual thinning and transition into a normal vein.

[0053] It is also worth noting that the morphological change of "elastic fiber > smooth muscle" described above is a necessary but not sufficient condition for the definition of a low-pressure buffering vessel. In order to be able to define a vessel as a buffering vessel, in addition to this morphological characteristic, it is necessary to demonstrate the low-pressure buffering of hemodynamics through actual observation using blood flow measurements.

[0054] The inventors have found that this "biological buffering effect," i.e., the effect of remodeling the vein itself into a buffer system vessel, is more pronounced when a buffer system artificial vessel with appropriate blood flow buffering function is placed over the vein wall. Furthermore, as an application of this technique, the buffer system artificial vessel of the present invention, which has the aforementioned "physical buffering effect" and has the appropriate elasticity and shape to buffer hemodynamics, is placed over the vein wall and juxtaposed to the venous wall as an external stent, or to the lumen as an internal stent, or both. By placing this juxtaposed buffer system artificial vessel, the vein wall remodels into a low-pressure buffer system vessel within 1 to 4 weeks due to the action of the buffer system artificial vessel placed over the vein wall. As a result, the buffering function of the venous wall remodeled into a buffer system vessel, in addition to the buffering function of the juxtaposed buffer system artificial vessel, is also functioning, resulting in a more appropriate overall buffering function. If this layered, juxtaposed buffer system artificial blood vessel is made of a bioabsorbable material, the buffering function of the veins being remodeled into buffer system blood vessels will be enhanced as the juxtaposed buffer system artificial blood vessel made of a bioabsorbable material is gradually decomposed and absorbed, and after the juxtaposed buffer system artificial blood vessel is absorbed and disappears, the remaining natural veins will be able to independently exert a buffering effect as buffer system blood vessels.

[0055] As described above, the buffer system artificial blood vessel of the present invention may not only exhibit a buffer function by itself, but may also exhibit a buffer function in cooperation with other members or living tissues. A simple method of making a cut in a shape such as a spiral is effective as a configuration advantageous for the above-mentioned "biological buffering effect." On the other hand, a linear cut is not so desirable because the vein wall in that area may change linearly, such as expanding or hardening. The buffer system vascular prosthesis of the present invention includes a buffer system vascular prosthesis having such cuts.

[0056] Specifically, the buffer system artificial blood vessel of the present invention includes an artificial blood vessel having a buffer cylinder that functions to buffer the dynamics of blood flowing from an artery to a vein, and has slits formed in the buffer cylinder to allow the artificial blood vessel wall to separate. The shape of the slits can be, for example, a spiral shape, but is not limited to this.

[0057] The buffer system artificial blood vessel with the above-mentioned cuts can have its wall separated along the cuts, so it can be wrapped around the outside of the shunt vein wall and installed. This installation forms an artificial outer wall of the blood vessel as an external stent-like elastic body acting as an artificial blood vessel. As this outer wall overlaps with the inner vein, the natural vein wall itself is remodeled into a buffer system blood vessel (biological buffering action). As a result, the wrapped outer wall and the inner vein wall as a whole can be made into a buffer cylinder of a buffer system artificial blood vessel.

[0058] The buffer system artificial blood vessel can also be placed inside the blood vessel lumen at the shunt site and its drainage basin. This placement forms the innermost wall of the artificial blood vessel as an internal stent-like elastic body. This innermost wall overlaps with the outer blood vessel wall, remodeling the natural vein wall itself into a buffer system blood vessel (biological buffering action). As a result, the entire buffer system artificial blood vessel with the outer wall and inner slits on the blood vessel wall can function as a buffer cylinder for the buffer system artificial blood vessel. While buffer system artificial blood vessels placed inside the lumen can be either slit or not, buffer system artificial blood vessels with slits can be deformed into an elongated shape due to the slits, making them easy to insert into the blood vessel lumen and easily restore to an appropriate outer diameter in the lumen.

[0059] In the above, it is preferable that the buffer cylinder having the cuts formed therein in the buffer system artificial blood vessel satisfies at least one of the following conditions at least in part: 30% elasticity index of 3.1 N or less, 60% elasticity index of 4.2 N or less, 100% elasticity index of 6.2 N or less, and 150% elasticity index of 8.9 N or less.

[0060] The scored buffer cylinder, like the other buffer cylinders, may be made entirely or partially from, for example, a bioabsorbable material or a metal, without any particular limitation. [Example]

[0061] Examples and comparative examples of the buffer-type artificial blood vessel according to the present invention are given below, but the present invention is not limited to these examples. 13 to 28 are shown as reference figures for the following examples and comparative examples, but these are conceptual diagrams of the shapes and are not necessarily the actual measured shapes. In each figure, the symbols T and K represent the normal path portion and the buffer cylinder, respectively. In the following, the 30% elasticity index, 60% elasticity index, 100% elasticity index and 150% elasticity index are values ​​measured by the above-mentioned measurement method, and the load measurements were carried out using the following measuring instruments. Load measuring equipment: Desktop load measuring instrument MODEL-1356R (AIKOH ENGINEERING) Force gauge: MODEL-RX-10 (AIKOH ENGINEERING) Hardware: Powerlab2 / 26 (AD Instrument) Software: Labchart (AD Instrument) Furthermore, Examples 1 to 24 are presented mainly from the viewpoint of "physical buffering action," while Examples 25 and onward are presented mainly from the viewpoint of "biological buffering action."

[0062] Example 1 A buffer-type artificial blood vessel having the shape shown in FIG. 13 was fabricated by the following procedure. Monofilament polyurethane fiber was wound cylindrically around a rotating iron core with an outer diameter of 6 mm. During this process, the traverse of the iron core was adjusted so that more fiber was wound on one side and gradually less fiber was wound on the other side. A heat-welding process was then performed to produce a polyurethane tube with an inner diameter of 6 mm. A 60 mm long section of this tube was cut out to serve as a buffer cylinder, with the thicker end facing upstream. A 14 cm long section with an inner diameter of 6 mm was cut from the center of a conventional, commercially available artificial blood vessel (Distaflo®, manufactured by CRBard, Inc., with support), and the upstream end of the buffer cylinder was anastomosed to this section with adhesive. This was used in the experiment as a buffer-type artificial blood vessel with a buffer cylinder.

[0063] Example 2 A buffer-type artificial blood vessel having the shape shown in FIG. 14 was fabricated by the following procedure. A PTFE tube in a trumpet shape (Fig. 14) was produced by the hot coining method. After annealing, the tube was 60 mm long and had a circular inner diameter, with an inner diameter of 6 mm at one end and an inner diameter of 8 to 10 mm at the other end. Of these, the tube with an inner diameter of 8 mm at the other end was used in Example 2. This tube was used as a buffer cylinder with the end with an inner diameter of 6 mm as the upstream end, and a buffer-system artificial blood vessel with a buffer cylinder was obtained in the same manner as in Example 1.

[0064] Example 3 A buffer-type artificial blood vessel having the shape shown in FIG. 15 was fabricated by the following procedure. A 6 mm outer diameter aluminum tube was deformed to create a core mold. One end of the core mold remained circular, but the cross-sectional shape gradually changed from a 6 mm diameter circular shape to a rectangular shape with a rounded ellipse toward the other end. A mesh woven with polyurethane and nylon support threads was wrapped around the core mold, and silicone rubber was applied over the mesh. The silicone rubber wall thickness was uniform around the entire circumference at the circular cross-section end, but varied around the entire circumference at the other end, with the thickness being thinner at the short axis end of the elliptical cross-section. A 60 mm length of this tube was cut into a buffer cylinder, with the circular end serving as the upstream end. A buffer-system artificial blood vessel with a buffer cylinder was obtained, as in Example 1. The cross-sectional shape of this buffer cylinder changed from an ellipse (lower right in Figure 15 ) to a circle (upper right in Figure 15 ) due to changes in the internal pressure of arterial blood. The combination of two fibers with different elastic properties that make up this support thread is as follows: polyurethane monofilament is soft and highly extensible, while the nylon thread wrapped around it has poor elasticity. Therefore, even if the polyurethane monofilament stretches due to blood pressure, if the stretch is small, there is slack in the area where the nylon thread is wrapped, allowing the polyurethane thread to stretch freely and expand the artificial blood vessel. However, if higher blood pressure is applied, the polyurethane stretches even more, causing the lumen of the artificial blood vessel to attempt further expansion, and the slack in the area where the nylon thread is wrapped reaches its limit, applying tension to the nylon thread and restricting the elongation of the polyurethane thread. In this way, by supporting the extensible thread with a non-extensible thread, the limit of elongation can be adjusted. This effect allows the buffer cylinder to expand easily up to a certain blood pressure, providing a significant buffering effect, but above that blood pressure, the expansion of the buffer cylinder is restricted, regulating excessive expansion of the buffer cylinder and ultimately providing an appropriate buffering effect.

[0065] Example 4 A buffer-type artificial blood vessel having the shape shown in FIG. 16 was fabricated by the following procedure. A 60 mm long PTFE tube, as shown in Figure 16, was produced using the hot coining method. After annealing, the cut end on one end was circular with an inner diameter of 6 mm (circumference approximately 18.8 mm), and the cross-sectional shape of the other end was a rectangle with a rounded shape close to an oval, with a circumference of 25 to 40 mm. Of these, the tube with a circumference of 25 mm on the other end was used in Example 4. The PTFE wall had a uniform thickness around the entire circumference of the circular cross section. This tube was used as a buffer cylinder, with the circular side with an inner diameter of 6 mm serving as the upstream side, and a buffer-type artificial blood vessel with a buffer cylinder was obtained in the same manner as in Example 1.

[0066] Example 5 A buffer-type artificial blood vessel having the shape shown in FIG. 17 was fabricated by the following procedure. A 6 mm inner diameter silicone rubber tube was placed over a 6 mm outer diameter iron core, and a 0.8 mm thick polypropylene monofilament thread was wound spirally from the outside at a pitch of 6 mm and adhesively fixed to reinforce the tube. A 60 mm long piece of the tube was cut out as a buffer cylinder, and a buffer-type artificial blood vessel with a buffer cylinder was obtained in the same manner as in Example 1. This buffer cylinder moves spirally in response to changes in the internal arterial pressure.

[0067] Example 6 A buffer-type artificial blood vessel having the shape shown in FIG. 18 was fabricated by the following procedure. A 60 mm long PTFE tube, as shown in Figure 18, was fabricated using the hot coining method. After annealing, one end was circular with an inner diameter of 6 mm (circumference approximately 18.8 mm), and the other end had a rectangular cross-sectional shape with a rounded shape close to an oval, with circumferences ranging from 25 mm to 40 mm. Various tubes were fabricated. Example 6 used one of these tubes with a circumference of 25 mm. The PTFE wall thickness gradually decreased from the circular cross-sectional end toward the other end. In addition, in the cross-section perpendicular to the axial direction, the wall thickness varied along the circumference, with the minor axis end of the oval being thinner. The end with the circular cross-sectional shape of this tube was used as the upstream side, and a buffer-system artificial blood vessel with a buffer cylinder was obtained, as in Example 1. The cross-sectional shape of this buffer cylinder changed from oval to circular due to changes in the internal pressure of the arterial blood.

[0068] Example 7 A buffer-type artificial blood vessel having the shape shown in FIG. 19 was fabricated by the following procedure. A monofilament polyurethane thread was wound cylindrically around a rotating iron core with an outer diameter of 6 mm while sprinkling salt granule spacers on the surface. During this process, the traverse of the iron core was adjusted so that more fibers were wound around both ends of the core and fewer fibers were wound around the center. A larger amount of salt granules was sprinkled in the center, creating a highly porous, highly porous central region. The spacers were washed and removed under running water, followed by a fusion process to produce a polyurethane tube with an inner diameter of 6 mm. A 60 mm-long section was cut from the center of this tube, and the thick-walled end was used as the upstream end to form a buffer cylinder. A buffer-type artificial blood vessel with a buffer cylinder was obtained, as in Example 1. The cross-sectional shape of the thin-walled central region of this buffer cylinder expands and changes with changes in the internal pressure of arterial blood. The function of the thick-walled downstream portion of the buffer cylinder in this embodiment will be briefly explained below. The wall of the buffer cylinder's central portion is thinner, so it acts as a "buffer basin" that expands with the inflow of arterial blood flow and provides a buffering function. The downstream portion is also elastic because it is made of polyurethane, a highly elastic material, but its wall is thicker than the central portion of the buffer cylinder, so it is less elastic than the central portion. Therefore, this thick-walled downstream portion acts as a relatively flexible "exit gate" of the buffer basin, further enhancing the buffering effect of the buffer basin.

[0069] Example 8 A buffer-type artificial blood vessel having the shape shown in FIG. 20 was fabricated by the following procedure. An 8 mm outer diameter aluminum rod was machined to create two 2 mm deep grooves with a 16 mm pitch, carved into opposing 180-degree spirals in the same direction. While rotating the aluminum rod with the two unidirectional spiral grooves, a monofilament polyester thread was wound around it in a cylindrical shape. During this process, an anticoagulant-containing glue was sprayed onto the polyester tube to bond the threads together, and a 1 mm thick aluminum wire was then wrapped around the grooves to compress them. This process was repeated twice to form helical pleats in the tube. The tube was then cut into 60 mm lengths to form a buffer cylinder. Similar to Example 1, a buffer-type artificial blood vessel with a buffer cylinder was obtained. The inner diameter of this buffer cylinder fluctuates in a spiral pattern due to changes in internal arterial pressure.

[0070] Example 9 A buffer-type artificial blood vessel having the shape shown in FIG. 21 was fabricated by the following procedure. Silicone rubber was applied in layers around an iron core with an outer diameter of 6 mm to obtain a cylindrical multilayer structure consisting of approximately four layers, each layer offset from the others. During this process, the rubber layers were adjusted to form uniform thicknesses throughout the axial direction of the cylinder. A 60 mm long tube was cut from this silicone rubber tube with an inner diameter of 6 mm and a uniform wall thickness to form a buffer cylinder. Similar to Example 1, a buffer-type artificial blood vessel with a buffer cylinder offset from the layers was obtained. In this buffer artificial blood vessel, the layers are displaced relative to one another, and the layers are displaced by pulse pressure, providing a buffer effect.

[0071] Example 10 A buffer-type artificial blood vessel having the shape shown in FIG. 22 was fabricated by the following procedure. A cylinder with an inner diameter of 5 mm was obtained by knitting woolly nylon fibers using the whole garment method. This cylinder was cut into 50 mm lengths and placed twice on an iron core with an outer diameter of 6 mm. One end of this double layer was then covered with another 20 mm length of the cylinder, so that the 20 mm section from the end was triple-layered and the remaining 30 mm was double-layered. The mesh of the resulting 50 mm cylindrical mesh fabric, which had one end triple-layered and the other double-layered, was treated with an anticoagulant-containing glue to smooth out the stitches, yielding a layered structure. This was used as a buffer cylinder, with the triple-layered end of the wall as the upstream end, to obtain a buffer-type artificial blood vessel with a buffer cylinder, as in Example 1. The layered layers can shift due to pulse pressure, enhancing the buffering effect. Furthermore, after the inner diameter of the buffer cylinder expanded to 130% in 100 seconds, it returned to 125% or less within 200 seconds after the external force was removed. Furthermore, the buffer cylinder is knitted using the Whole Garment method, a weft knitting technique that can seamlessly knit even complex shapes based on a small diameter cylinder of millimeters, so it is required to have the mobility to expand and contract in the radial direction, and the shape of the inner diameter and wall can change. For comparison, a comparative buffer cylinder was prepared in the same manner except that non-woolly processed nylon fibers were used. After the inner diameter of the comparative buffer cylinder expanded to 130% in 100 seconds, the inner diameter did not return to 125% or less within 200 seconds after the external force was removed.

[0072] Example 11 A buffer-type artificial blood vessel having the shape shown in FIG. 17 was fabricated by the following procedure. A 6mm inner diameter polyurethane tube was placed over a 6mm outer diameter iron core, and a 1.1mm thick silicone rubber monofilament thread was wound spirally from the outside at a pitch of 6mm and adhesively fixed to reinforce the tube. A 60mm long piece of the tube was cut out as a buffer cylinder, and a buffer-type artificial blood vessel with a buffer cylinder was obtained in the same manner as in Example 1. The expansion section of this tube fluctuates spirally in response to changes in the internal arterial pressure.

[0073] Example 12 A buffer-type artificial blood vessel having the shape shown in FIG. 24 was fabricated by the following procedure. Using the hot coining method, a PTFE trumpet-shaped tube was fabricated. The inner diameter was 6 mm at one end after annealing, and the wall thickness gradually decreased toward the other end as shown in Figure 23. This trumpet-shaped tube did not exhibit the wall thickness change in the lateral direction of the cross section perpendicular to the axial direction (in Example 6, the wall thickness along the minor axis of the oval cross section) becoming thinner than the wall thickness along the major axis, as in Example 6. This trumpet-shaped tube was cut as shown in Figure 24, and a buffer-type artificial blood vessel with a buffer cylinder was obtained, similar to Example 1, with the smaller-diameter end serving as the upstream buffer cylinder. In Example 12, the distance X was set to 1.6, i.e., X÷Φ=R=9.6 mm.

[0074] Example 13 A trumpet-shaped tube prepared in the same manner as in Example 12 was cut as shown in Figure 24, and the end with the smaller diameter was used as a buffer cylinder with the upstream end, to obtain a buffer-type artificial blood vessel with a buffer cylinder in the same manner as in Example 1. In Example 13, the distance X was set to X÷Φ=R=1.5, i.e., X=9 mm.

[0075] Example 14 A trumpet-shaped tube similar to that shown in Figure 23 was prepared by applying silicone rubber to the periphery of a trumpet-shaped core mold having the same shape as the lumen in Figure 23. In this case, the thickness of the silicone rubber toward the opening side of the trumpet was gradually reduced as shown in Figure 23. This trumpet-shaped tube was cut as shown in Figure 24, and the end with the smaller diameter was used as the upstream buffer cylinder, to obtain a buffer-type artificial blood vessel with a buffer cylinder as in Example 1. In the case of Example 14, the distance X was set to X÷Φ=R=1, i.e., X=6 mm.

[0076] Example 15 A trumpet-shaped tube was prepared by winding polyurethane monofilament around a trumpet-shaped core mold similar to the lumen in Figure 23. The thickness of the polyurethane monofilament wound on the open side of the trumpet was gradually reduced as shown in Figure 23. After the welding process, this trumpet-shaped tube was cut as shown in Figure 25, and the end with the smaller diameter of the stump was used as the upstream buffer cylinder, to obtain a buffer-type artificial blood vessel with a buffer cylinder in the same manner as in Example 1. In Example 15, the distance X was set so that X÷Φ=R was 0, i.e., X=0 mm.

[0077] Example 16 Using the hot coining method, a PTFE trumpet-shaped cylinder was produced, with an inner diameter of 6 mm at one end after annealing, and the inner diameter widening toward the other end as shown in Figure 18, with the wall thickness of the oval minor axis of the trumpet-shaped tube gradually becoming thinner than that of the major axis of the oval. This trumpet-shaped tube was cut as shown in Figure 24, and a buffer-type artificial blood vessel with a buffer cylinder was obtained, as in Example 1, with the end with the smaller diameter serving as the upstream buffer cylinder. In Example 16, the distance X was set to X÷Φ=R=1.2, i.e., X=7.2 mm.

[0078] Example 17 A PTFE trumpet-shaped tube was prepared in the same manner as in Example 16. This trumpet-shaped tube was cut as shown in Figure 24 to form a buffer cylinder with the end with the smaller diameter on the upstream side, and a buffer-type artificial blood vessel with a buffer cylinder was obtained in the same manner as in Example 1. In Example 17, the distance X was set to X÷Φ=R=1, i.e., X=6 mm.

[0079] Example 18 A PTFE trumpet-shaped tube was prepared in the same manner as in Example 16. This trumpet-shaped tube was cut as shown in Figure 25, and the end with the smaller diameter of the stump was used as the upstream buffer cylinder, to obtain a buffer-type artificial blood vessel with a buffer cylinder in the same manner as in Example 1. In Example 18, the distance X was set to 0, i.e., X÷Φ=R, i.e., X=0 mm.

[0080] Example 19 A 60 mm long mesh knitted using support threads made of polyurethane monofilament wrapped with ultra-fine Tetron thread was wrapped around an aluminum tube with an outer diameter of 6 mm. Next, a 30 mm long mesh was wrapped around one end of the mesh wrapped around the aluminum tube, and then a 15 mm long mesh was wrapped twice around one end of the double-layered mesh section, creating a single-layered 30 mm downstream section, a double-layered 15 mm central mesh section, and a quadruple-layered 15 mm upstream section. The stumps of the mesh were heat-fixed. Alginic acid was sprayed onto the 6 mm inner diameter tube with the multilayered structure thus created and cross-linked with calcium to create a buffer cylinder with the quadruple-layered end as the upstream end. A buffer-system artificial blood vessel with this buffer cylinder was fabricated in the same manner as in Example 1, designated Example 19. The multilayered structure has layers that shift relative to each other due to pulse pressure, enhancing its buffering effect.

[0081] Example 20 A mesh knitted using support threads made of polyurethane monofilaments wrapped with ultrafine Tetron yarn was wrapped around an aluminum tube with an outer diameter of 6 mm. Unlike Example 19, the mesh was wrapped evenly in two layers over its entire length. The stumps of the mesh were heat-fixed. Alginic acid was sprayed onto the tube with an inner diameter of 6 mm thus prepared, followed by cross-linking and fixation with calcium, and then cut into a length of 60 mm to prepare a buffer cylinder. A buffer-system artificial blood vessel with this buffer cylinder was prepared in the same manner as in Example 1, and designated Example 20.

[0082] Example 21 A cylindrical body with an inner diameter of 8 mm made of woolly processed polyester yarn was placed on an aluminum tube with an outer diameter of 6 mm, and then contracted in the axial direction of the aluminum tube to form a bellows-shaped cylindrical body. This bellows-shaped cylinder was placed over an aluminum tube and then treated with alginic acid and cross-linked with calcium. The bellows-shaped cylinder, which had been cross-linked and maintained in its bellows shape, was cut into a length of 60 mm to obtain a buffer cylinder. A buffer-type artificial blood vessel having this buffer cylinder was then fabricated in the same manner as in Example 1, and designated Example 21. Because this buffer cylinder has a bellows shape, it expands and contracts in response to pulse pressure, thereby enhancing its buffering effect.

[0083] Example 22 Polyurethane thread was uniformly wrapped around the surface of an aluminum tube with an outer diameter of 6 mm and fixed by heating. This tube was cut into a length of 60 mm to form a buffer cylinder. A buffer-type artificial blood vessel having this buffer cylinder was fabricated in the same manner as in Example 1, and this was designated Example 22.

[0084] Example 23 Silicone rubber (KE-4896, Shin-Etsu Chemical Co., Ltd.) was evenly applied to a core of an aluminum tube with an outer diameter of 6 mm. This tube was cut into a length of 60 mm to form a buffer cylinder. A buffer-type artificial blood vessel having this buffer cylinder was fabricated in the same manner as in Example 1, and this was designated Example 23.

[0085] Example 24 Resin clay was applied to the entire periphery of the center of an aluminum tube with an outer diameter of 6 mm, creating a 50 mm long section with an outer diameter of 8 mm. Liquid molding urethane resin (Gummy Cast Zero, Nissin Resin Co., Ltd.) was then evenly applied to the entire aluminum tube. Immediately afterwards, while the urethane was still liquid, polypropylene monofilament reinforcement was wrapped around the entire length at a pitch of 20 mm per wrap. Further molding urethane resin was applied evenly on top of this, embedding the previously wrapped polypropylene monofilament. After the urethane resin hardened into a gummy state, the aluminum tube and resin clay were removed, resulting in a tube reinforced with polypropylene monofilament. A 60 mm long section was cut from this tube, consisting of a 50 mm long central section with an inner diameter of 8 mm and two end sections with an inner diameter of 6 mm, each of which was 5 mm long and connected to the central section. This resulted in a 60 mm long reinforced tube. This tube was used as a buffer cylinder, and a buffer-type artificial blood vessel having a buffer cylinder was obtained in the same manner as in Example 1. The wrapped polypropylene monofilament is a relatively inelastic material, gradually thickening from 0.2 mm to 1.0 mm and then gradually tapering back to 0.2 mm over a 20 mm interval. As a result, the extremely soft and stretchable polyurethane wall expands outward in response to arterial hemodynamics, expanding the lumen. Meanwhile, the polypropylene spiral reinforcement, or spiral valve-like portion, resists lumen expansion. The interaction between these two components causes the vessel wall to expand into a spiral lumen, enhancing the buffering effect. Because the height of the spiral valves varies depending on the thickness of the polypropylene, the valve-like spiral structure protruding into the lumen forms a series of crescent-shaped valves, with smaller protrusions in the thinner reinforcement sections and larger protrusions in the thicker reinforcement sections. At the same time, the polypropylene reinforcement prevents the soft urethane wall of the buffer cylinder from becoming constricted or blocked by twisting or external pressure.

[0086] Example 25 Four layers of No. 1 bioabsorbable suture thread (Lacron®, purchased from Kono Seisakusho, Ichikawa City, Japan) made from a copolymer of 75% lactic acid and 25% caprolactam (hereinafter sometimes referred to as LA / CL) were prepared and wound around an aluminum tube with an outer diameter of 6 mm and a length of 60 mm, forming a counter-helix structure with overlapping strands. The threads were wound closely together at one end of the tube, with adjacent strands touching each other, and gradually spaced apart until the spacing was adjusted to 2.5 mm at the opposite end. The helical morphology of the LA / CL suture was stabilized by heat treatment, and this 60 mm long, counter-helix-shaped section with an inner diameter of 6 mm was fabricated as a buffer artificial blood vessel for placement in a vein. In animal experiments, a 14-cm section with a 6 mm inner diameter was cut from the center of a conventional artificial blood vessel, the same as in other examples. This artificial blood vessel was used to create an arteriovenous shunt between the external jugular vein and the common carotid artery. The shunt artificial blood vessel was wrapped around the outside of the vein wall anastomosed to the artificial blood vessel, 60 mm downstream from the anastomosis, overlapping the vein wall. The dense end of the spiral LA / CL suture was placed on the artificial blood vessel side, i.e., upstream of the blood flow, and the sparse end of the spiral LA / CL suture was placed on the opposite side, i.e., downstream of the blood flow, creating a 60 mm reverse-direction double-spiral buffer artificial blood vessel. A glue (hereinafter sometimes referred to as LA / CL glue) prepared by dissolving LA / CL at a concentration of 100 mg / ml in 1,3-dioxolane was used to glue and fix the intersection of the two reverse-direction spiral LA / CL sutures. This buffer artificial blood vessel functions as a cylindrical buffer blood vessel hybridized with the vein wall.

[0087] Example 26 A bioabsorbable medical nonwoven fabric (Neoveil®, R015G type, purchased from Gunze Co., Ltd., Osaka City) coated with calcium phosphate slurry was cut into a 20 mm wide spiral tape. This tape was then spirally wrapped around an aluminum tube with an outer diameter of 6 mm and a length of 60 mm. The tape was then completely overlapped at one end of the aluminum tube, gradually reducing the overlap until it was doubled at the other end. The upstream portion of the tape was heat-treated more intensely to stabilize the spiral shape. This 60 mm long, 6 mm inner diameter spiral was fabricated as a buffer artificial blood vessel for placement alongside a vein. In animal experiments, a 14-cm section with an inner diameter of 6 mm was cut from the center of a conventional artificial blood vessel, the same as in the other examples. This artificial blood vessel was used to create an arteriovenous shunt between the external jugular vein and the common carotid artery. A spiral tape-shaped buffer artificial blood vessel was wrapped around the venous wall, overlapping it, at a location 60 mm downstream from the anastomosis, on the outside of the venous wall anastomosed to the artificial blood vessel of the shunt. The four-fold overlapping end of the spiral tape was positioned on the artificial blood vessel side, i.e., upstream of the blood flow, and the single-fold overlapping end was positioned on the opposite side, i.e., downstream of the blood flow, to create a 60-mm spiral buffer artificial blood vessel. Finally, the spiral tape was adjusted to ensure the desired shunt blood flow was achieved using an ultrasonic hemometer, and a 20 mg / ml aqueous solution of sodium alginate (Snow Algin L, purchased from Fuji Chemical Industry Co., Ltd., Wakayama City) was sprayed evenly to maintain this state. The reason for spraying evenly was to adjust the cross-linking of alginate so that it would be stronger in the upstream area due to the abundant calcium phosphate, and weaker in the downstream area due to the lack of calcium phosphate. This buffer cylinder functions as a cylindrical buffer vessel hybrid with the venous wall.

[0088] Example 27 Two types of sodium alginate aqueous solutions were prepared as materials for the buffer cylinder. Namely, Snow Algin M as high-viscosity sodium alginate and Snow Algin SL as low-viscosity sodium alginate (both manufactured by Fuji Chemical Industry Co., Ltd.) were prepared as aqueous solutions at a concentration of 20 mg / ml. Furthermore, a 20-fold diluted solution of calcium gluconate (Calcicol, manufactured by Nichi-Iko Pharmaceutical Co., Ltd.) was prepared as a cross-linking agent. In animal experiments, a 14-cm section with an inner diameter of 6 mm was cut from the center of a conventional artificial blood vessel, the same as in the other examples. This artificial blood vessel was used to create an arteriovenous shunt between the external jugular vein and the common carotid artery. The sodium alginate and calcium gluconate solutions were simultaneously sprayed in three or more separate doses around the venous wall at a distance of 60 mm downstream from the anastomosis of the shunt with the conventional artificial blood vessel. The high-viscosity sodium alginate solution was sprayed in large amounts on the side closest to the conventional artificial blood vessel (upstream side), and the low-viscosity sodium alginate solution was sprayed in large amounts on the opposite side (downstream side). During the separate sprayings, the desired blood flow was monitored using an ultrasonic blood flowmeter, and the administration of alginic acid and calcium gluconate was adjusted to maintain the desired blood flow. This buffer cylinder functions as a cylindrical buffer vessel hybrid with the venous wall.

[0089] Example 28 A commercially available, conventional polyester artificial blood vessel (Dacron® artificial blood vessel (Japan Lifeline Co., Ltd., J-Graft, Shield Neo S) with an inner diameter of 7 mm was cut to a length of 60 mm and a helical slit was made using a hot scalpel to create a first spiral tape. The helical pitch was 5 mm. Next, a similar spiral tape was made with the spiral direction reversed (the second spiral tape). The edges of the helical slits were curved outward, and the cut ends were rounded with silicone rubber (KE-4896, Shin-Etsu Chemical Co., Ltd.). These spiral tapes were tightly wrapped around aluminum tubes with an inner diameter of 6 mm and heat-treated to stabilize the shape. In animal experiments, a 14-cm length of a 6 mm inner diameter section was cut from the center of a conventional artificial blood vessel, the same as in other examples. This artificial blood vessel was used to create an arteriovenous shunt between the external jugular vein and the common carotid artery. A first spiral tape was wrapped around the venous wall, 60 mm downstream from the anastomosis, on the outside of the shunt artificial blood vessel. The downstream end of the conventional artificial blood vessel overlapped the upstream end of the spiral tape by 5 mm. A second spiral tape, wound in the opposite direction, was wrapped around the first spiral tape in the same way. Finally, the two spiral tapes were stacked to form a 60 mm buffer cylinder. The overlap between the upstream end of the spiral tape and the downstream end of the conventional artificial blood vessel was secured with a hook-and-loop fastener. Finally, the desired blood flow was confirmed using an ultrasonic blood flowmeter, and the tightness of the two spiral tapes and the hook-and-loop fastener were adjusted to maintain the desired flow. This buffer cylinder functions as a cylindrical buffer vessel hybrid with the venous wall.

[0090] Example 29 A commercially available artificial blood vessel graft (Distaflo®, manufactured by CR Bard, Inc., with support), a conventional artificial blood vessel made of ePTFE, was used. A straight central section with an inner diameter of 6 mm was cut out to a length of 65 mm to create a spiral tape similar to that of Example 28. However, the pitch of the spiral shape gradually decreased from 5 mm at the long end to 2.5 mm at the short end. To stabilize the shape and protect the surrounding tissue, the cut end was rounded with silicone rubber (KE-4896). In animal experiments, a 14-cm section with an inner diameter of 6 mm was cut from the center of a conventional artificial blood vessel, the same as in the other examples. This artificial blood vessel was used to create an arteriovenous shunt between the external jugular vein and the common carotid artery. A spiral tape was wrapped around the venous wall 60 mm downstream from the anastomosis on the outside of the shunt artificial blood vessel. The end of the spiral tape with the shorter pitch was positioned on the conventional artificial blood vessel side, i.e., upstream of the blood flow, and the end with the longer pitch was positioned on the opposite side, i.e., downstream of the blood flow. The downstream end of the conventional artificial blood vessel and the upstream end of the spiral tape overlapped by 5 mm. Finally, the desired blood flow state was confirmed using an ultrasonic blood flowmeter, and the wrapping of the spiral tape was adjusted so that the desired state could be maintained.To maintain this wrapping state, the walls of the spiral tape were glued and fixed with 100 mg / ml LA / CL glue at four locations, 20 mm apart from the most upstream part, in the order of 12 o'clock, 4 o'clock, 8 o'clock, and 12 o'clock on the circumference of the pitch.In addition, the overlapping part between the downstream end of the conventional artificial blood vessel and the upstream end of the spiral tape was glued and fixed with LA / CL glue around the entire circumference. This buffer artificial blood vessel functions as a cylindrical buffer blood vessel by hybridizing with the vein wall. Furthermore, by using a biodegradable material such as LA / CL glue, the LA / CL glue prevents the spiral tape from gradually loosening due to blood pressure, and during this time the LA / CL glue gradually decomposes while the biological buffering action matures. As a result, the physical buffering action is gradually replaced by the biological buffering action, and it is expected that the self-regulating function of the overall buffering action will become more advanced.

[0091] Example 30 A 0.098 mm diameter stainless steel spring wire (SUS304, NAS304-0.1, purchased from Seiwa Steel Wire Co., Ltd., Osaka) was bent into a shape with 11 180-degree zigzag bends in opposite directions every 35 mm. The bends were alternating between 180-degree U-shaped bends, 180-degree V-shaped bends, and 180-degree U-shaped bends, resulting in six U-shaped bends sandwiched between V-shaped bends. This zigzag wire was wrapped around a 5 mm outer diameter iron core, with the U-shaped bends aligned in one direction and the V-shaped bends aligned in the opposite direction. The shape was stabilized by heat treatment, and the wire surface was coated with silicone rubber (KE-4896). A 35 mm long, 6 mm inner diameter tube was formed from the zigzag spring wire. The tube, made of spring-shaped iron wire coated with silicone rubber, was covered with a porous membrane of ethylene-vinyl alcohol copolymer, and was created as a buffer cylinder to be placed in layers alongside the lumen of the vein. In animal experiments, a 14-cm section with a 6 mm inner diameter was cut from the center of a conventional artificial blood vessel, the same as in other examples. This conventional artificial blood vessel was used to create an arteriovenous shunt between the external jugular vein and the common carotid artery. Specifically, the shunt was placed 35 mm downstream from the downstream end of the conventional artificial blood vessel, on the lumen side of the vein wall, as a buffer cylinder. A 5 mm section of the tubing near the V-shaped bend was placed on the lumen side of the wall at the downstream end of the conventional artificial blood vessel and secured to the downstream end of the conventional artificial blood vessel by the elasticity of a spring. The opposite end of the tubing, a 30 mm section near the U-shaped bend, was placed on the downstream side of the vein wall, allowing the elasticity of the spring to gently expand the vein wall. After placement, patients were treated with Bayer aspirin-based anticoagulation therapy. This buffer cylinder hybridizes with the vein wall and functions as a cylindrical buffer vessel.

[0092] Example 31 A coil spring was fabricated by winding a 0.02 mm diameter stainless steel spring wire (SUS304, 751107), thinner than that used in Example 30, around a 60 mm long core, transitioning from an oval with an average outer diameter of 6 mm (minor diameter 4 mm × major diameter 8 mm) to a perfect circle with an outer diameter of 7 mm. The wire was wound in an oval shape on the 6 mm diameter side, with the end of the first winding touching the beginning of the winding, forming an oval. The spiral was then wound in a circular shape with a gradually increasing pitch until the opposite end, the 7 mm diameter, reached a pitch of 10 mm. To prevent the tip of the 10 mm pitch from contacting the vein wall, the end of the wire was curled into a 2 mm diameter spiral. The shape was stabilized by heat treatment, and the wire surface was coated with silicone rubber (KE-4896), to fabricate a 60 mm long spiral tube. In the animal experiment, unlike Example 30, a buffer artificial blood vessel was placed on the lumen side of the venous wall at a location 60 mm downstream from the upstream end of the venous anastomosis of the autologous blood vessel of an arteriovenous shunt that did not use a conventional artificial blood vessel, with the 6 mm diameter side facing upstream. After placement, anticoagulant therapy using mainly Bayer aspirin was administered. This buffer cylinder hybridizes with the vein wall and functions as a cylindrical buffer vessel.

[0093] Comparative Example 1 A commercially available conventional artificial blood vessel (Venaflo (registered trademark), manufactured by CRBard, Inc., inner diameter 6 mm, unsupported) was used, and a central portion with an inner diameter of 6 mm was cut out to a length of 20 cm and used as the artificial blood vessel of Comparative Example 1. The shape is a right cylinder as shown in FIG.

[0094] Comparative Example 2 A 20 cm length of a 6 mm inner diameter central portion of a conventional commercially available artificial blood vessel (Distaflo (registered trademark), manufactured by CR Bard, Inc., with support) was cut out and used as the artificial blood vessel of Comparative Example 2. The shape is a reinforced right cylinder as shown in Figure 17.

[0095] Comparative Example 3 As in Example 12, a PTFE trumpet-shaped tube was fabricated by the hot coining method, with the trumpet-shaped wall gradually thinning as shown in Figure 23. This trumpet-shaped tube was cut as shown in Figure 24 to fabricate a buffer cylinder with the smaller diameter end on the upstream side of the buffer cylinder. For Comparative Example 3, the distance X was set to 1.2, i.e., X÷Φ=R, i.e., X=7.2 mm. The upstream end of this buffer cylinder was adhesively fixed to a 6 mm inner diameter central portion of a commercially available conventional artificial blood vessel (Distaflo®, manufactured by CRBard, Inc., with support). The conventional artificial blood vessel was then cut at a point within the buffer cylinder where the total length of the circumferential cylindrical portion and the conventional artificial blood vessel was 20 cm. This 20 cm portion was used as the artificial blood vessel of Comparative Example 3.

[0096] Comparative Example 4 As in Comparative Example 3, a PTFE trumpet-shaped tube was fabricated by the hot coining method, with the trumpet-shaped wall gradually thinning as shown in Figure 23. This trumpet-shaped tube was cut as shown in Figure 24 to fabricate a buffer cylinder with the smaller-diameter end on the upstream side of the buffer cylinder. In Comparative Example 4, the distance X was set to 1 (X÷Φ=R), i.e., X=6 mm. The upstream end of this buffer cylinder was adhesively fixed to a 6 mm inner diameter central portion of a commercially available conventional artificial blood vessel (Distaflo®, manufactured by CRBard, Inc., with support). The conventional artificial blood vessel was then cut at a point within the buffer cylinder where the total length of the circumferential cylindrical portion and the conventional artificial blood vessel was 20 cm. This 20 cm portion was used as the artificial blood vessel of Comparative Example 4.

[0097] Comparative Example 5 As in Comparative Example 3, a PTFE trumpet-shaped tube was fabricated by the hot coining method, with the trumpet-shaped wall gradually thinning as shown in Figure 23. This trumpet-shaped tube was cut as shown in Figure 25 to fabricate a buffer cylinder with the smaller circumferential diameter of the stump on the upstream side of the buffer cylinder. In Comparative Example 5, the distance X was set to 0 (X÷Φ=R), i.e., X=0 mm. The upstream end of this buffer cylinder was adhesively fixed to a 6 mm inner diameter central portion of a commercially available conventional artificial blood vessel (Distaflo®, manufactured by CRBard, Inc., with support). The conventional artificial blood vessel was then cut at a point within the buffer cylinder where the total length of the circumferential cylindrical portion and the conventional artificial blood vessel was 20 cm. This 20 cm portion was used as the artificial blood vessel of Comparative Example 5.

[0098] Comparative Example 6 A conventional, commercially available artificial blood vessel (Distaflo (registered trademark), manufactured by CRBard, Inc., with support) was cut at a location where the length of the circumferential cylindrical portion, including the cuffed portion, was 20 cm, and this 20 cm portion was used as the artificial blood vessel of Comparative Example 6, which had an inner diameter of 6 mm (Distaflo (registered trademark) has a 1 mm taper in the inner diameter from 25 cm upstream of the cuff, so the inner diameter of the 20 cm upstream of the cuff in an artificial blood vessel with a "7 mm inner diameter standard" is 6 mm). In the case of Comparative Example 6, the distance X was set to X÷Φ=R, which was 1.2.

[0099] Comparative Example 7 A portion of the cuff end of a conventional, commercially available artificial blood vessel (Distaflo (registered trademark), manufactured by CRBard, Inc., with support) was removed, and the conventional artificial blood vessel was cut at a location where the length of the circumferential cylindrical portion, including the remaining cuff portion, was 20 cm. This 20 cm portion was used as the artificial blood vessel of Comparative Example 7, which had an inner diameter of 6 mm (Distaflo (registered trademark) has a 1 mm taper in the inner diameter from 25 cm upstream of the cuff, so the inner diameter of the 20 cm upstream of the cuff in an artificial blood vessel with a "7 mm inner diameter standard" is 6 mm). In the case of Comparative Example 7, the distance X was set to X÷Φ=R, which was 1.0.

[0100] Comparative Example 8 A portion of the cuff of a conventional commercially available artificial blood vessel (Distaflo (registered trademark), manufactured by CRBard, Inc., with support) was resected and shortened as shown in Figure 25, to form a buffer cylinder with the opposite end of the trumpet-shaped stump on the upstream side. In Comparative Example 8, the distance X was set to 0 (X÷Φ=R), i.e., X=0 mm. A portion of the circumferential cylindrical portion with a length of 20 cm and an inner diameter of 6 mm was used (Distaflo (registered trademark) has a 1 mm taper in the inner diameter from 25 cm upstream of the cuff, so the inner diameter of the "7 mm inner diameter standard" artificial blood vessel 20 cm upstream of the cuff is 6 mm).

[0101] Comparative Example 9 A 20 cm long circumferential cylindrical portion including the cuffed portion of a conventional commercially available artificial blood vessel (Venaflo (registered trademark), manufactured by CRBard, Inc., unsupported) was used as the artificial blood vessel of Comparative Example 9.

[0102] Comparative Example 10 For the comparative example, both ends of a commercially available artificial blood vessel (Soratec artificial blood vessel, code number 38435, model number 10002-6020-002, sold by Goodman Co., Ltd., Nagoya City) made of a reinforcing material added to a polyurethane tube with an inner diameter of 6 mm and a length of 20 cm was cut out to a length of 60 mm and connected to the downstream side of the same artificial blood vessel as Comparative Example 1, which was 140 mm long, to create the artificial blood vessel of Comparative Example 10, with a total length of 200 mm.

[0103] Comparative Example 11 A commercially available conventional artificial blood vessel (Dacron (registered trademark) artificial blood vessel (J-Graft, Shield Neo S, manufactured by Japan Lifeline Co., Ltd.) with an inner diameter of 7 mm was cut to a length of 60 mm and used as a buffer cylinder for the "external layered juxtaposition type" of Comparative Example 11. That is, a section with an inner diameter of 6 mm was cut from the center of the conventional artificial blood vessel, the same as in the other Examples, to a length of 14 cm, and this artificial blood vessel was used to construct an arteriovenous shunt using a conventional artificial blood vessel between the external jugular vein and the common carotid artery. Next, a buffer cylinder was placed on the outer periphery of the venous wall at a position 60 mm downstream from the downstream end of the conventional artificial blood vessel of this shunt, layered on the natural venous wall, to form a buffer system cylinder in juxtaposition.

[0104] [Animal experiments] Using the artificial blood vessels of the above Examples and Comparative Examples, animal experiments were carried out as follows. Male or female beagle dogs weighing 12-16 kg and approximately one year old were used as experimental animals (hereafter referred to as dogs). During the experiment, the dogs were housed individually and kept under standard conditions for at least one week before the experiment, with free access to standard dog chow and water.

[0105] <Experimental Method> All surgical procedures were performed under aseptic conditions by a single surgical team. The dogs were given basal anesthesia with 35 mg / kg of intravenous pentobarbital, a breathing tube was intubated into the trachea, and general anesthesia was administered with 40% oxygen and inhalation anesthesia using sevoflurane or isoflurane. Under general anesthesia, the dogs were fixed in an extended neck position and the abdominal hair was shaved. The skin was cleaned with 80% ethanol containing 5% chlorhexidine and disinfected with 10% povidone-iodine solution. A 15-cm vertical skin incision was made in the right or left side of the neck, the fascia and muscle were separated, and the external jugular vein and common carotid artery were exposed. An anastomotic shunt was created between the external jugular vein and the common carotid artery, as shown in Figure 26. After the shunt was created, the fascia and skin were sutured according to the natural anatomical structure, and the surgical incision was closed. However, Examples 25 to 31 and Comparative Example 11 shown in Table 6 were installed using the installation method described in the respective production method paragraphs. During surgery and periodically after surgery (basically every 4 weeks), observations were made with an ultrasound tomography device at the following sites before and after shunt creation: the cardiac and cranial sides of the common carotid artery anastomosis, the arterial anastomosis end of the vascular graft, the midpoint of the vascular graft, the venous anastomosis end with the vascular graft, and the downstream side of the venous anastomosis with the vascular graft (i.e., the cardiac side). Observations included the vessel internal diameter, abnormal findings in the vessel wall (including abnormal wall thickening and wall irregularities), the presence or absence of luminal stenosis / occlusion or thrombus formation, and the pulsation of the vessel wall due to blood flow. Blood flow velocity and its waveform changes were also measured and recorded at the same sites using an ultrasound Doppler flowmeter. The time-dependent blood flow rate was calculated from the vessel internal diameter and flow velocity waveform using built-in software. After 12 weeks to 18 months of surgery, the dogs were euthanized with an intravenous injection of 100 mg / kg pentobarbital and autopsied. The shunt site was incised, and the vascular system and surrounding tissues in the implanted graft were surgically removed en bloc, preparing a resected specimen for macroscopic and microscopic examination. The resected specimens were evaluated macroscopically and under a stereomicroscope. The evaluation criteria were essentially the same as those evaluated using ultrasound imaging, but other pathological evaluation criteria were also added when necessary. After this evaluation, the specimens were fixed in 10% neutral formalin and cut into 4 μm-thick microscopic sections using standard techniques. They were stained with hematoxylin and eosin (HE stain) and Elastica-van Gieson (EvG) stain and observed under a light microscope.

[0106] <Experimental Results> The experimental results are shown below. The results of the overall evaluation were determined as a success (◯ in the table) when all of the evaluation items (A) to (D) were satisfied, and as a failure (× in the table) when all other cases were satisfied, as explained in the evaluation criteria below. However, for Examples 25 to 31 and Comparative Example 11 listed in Table 6, when all of the evaluation items (A) to (D) as well as (E) were satisfied, the results were determined as a success (◯ in the table), and as a failure (× in the table) when all other cases were satisfied.

[0107] (Experimental result 1: Evaluation of shape and buffering effect) The buffering function of artificial blood vessels was evaluated using the shape of the buffer cylinder as an index. The results are shown in Table 1 below.

[0108] [Table 1]

[0109] From the results in Table 1 above, a cushioning effect was observed in the various shapes shown in Examples 1 to 11. The cushioning effect can be achieved by installing multiple identical pieces of each shape of Examples 1 to 11, or by appropriately combining the other shapes of Examples 1 to 11. On the other hand, no cushioning effect was observed in the straight cylindrical shape made of ePTFE with a high elastic index, such as conventional artificial blood vessels (Comparative Examples 1 and 2).

[0110] (Experimental result 2: Evaluation of buffering effect using 30% elasticity index) The buffer function of a straight cylindrical buffer cylinder with an inner diameter of 6 mm and a length of 60 mm was examined using the 30% elasticity index as an index. Note that in Example 8, the height of the spiral projections is not included in the bore diameter. The results are shown in Table 2 below.

[0111] [Table 2]

[0112] The cushioning effect was observed over a wide range of 30% elasticity index from 0.08 to 10.1 N shown in Examples 1, 5, and 7 to 11. On the other hand, no cushioning effect was observed in the conventional artificial blood vessels (Comparative Examples 1 and 2) where the 30% elasticity index was 13.6 N or more.

[0113] Examples 1, 5, and 7 to 11 all have a straight shape and are constructed with walls that are softer than conventional artificial blood vessels, and the softness of the walls contributes to the cushioning effect.In addition to this, it is believed that the factors described below also contribute to the cushioning effect.

[0114] Example 7 Generally, in arteries, areas of high internal pressure move and are transmitted from upstream to downstream as blood flows pulsatilely. This causes areas of the blood vessel wall to expand downstream, resulting in a wave-like expansion of the lumen. The artificial blood vessel of Example 7 has a section with a low elasticity value (the softest section, with a 30% elasticity index of 0.08 N) in the middle of the tube. When internal pressure is applied, this section expands more than other sections, providing the effect of a decompression chamber (buffer basin) that repeatedly expands in a pulsatile manner in response to the wave-like increase in internal pressure. The section downstream of this buffer basin, with a relatively high 30% elasticity index of 0.9 N, acts as a sluice gate at the outlet of the buffer basin, enhancing its effectiveness. These effects enhance the buffering effect.

[0115] Example 1 As mentioned above, pulsatile blood flow in the artery causes areas of high internal pressure to move from the upstream side to the downstream side, and as a result, areas of dilation in the vascular wall move and are transmitted downstream, resulting in wave-like lumen expansion. In the artificial blood vessel of Example 1, the wall thickness gradually decreases toward the downstream side, gradually changing to a softer state. In the artificial blood vessel of Example 1, the 30% elasticity index of the most upstream portion (closest to the artery) is 4.5 N, and the 30% elasticity index of the most downstream portion (closest to the vein) is 3.9 N. Therefore, the wave-like lumen expansion caused by this change in softness increases the further downstream. In this way, the wave-like lumen expansion increases downstream, enhancing the cushioning effect. Furthermore, if there is a large step in the change in softness, this step will cause a large discontinuous change in the wave-like lumen expansion, which is likely to cause large turbulent blood flow and lead to thrombus formation. Conversely, if the softness is changed gradually, the wave-like expansion will move and be transmitted smoothly, and large discontinuous changes will not occur, resulting in small blood turbulence and, as a result, there is the advantage that the risk of thrombus formation and other problems will be reduced.

[0116] Example 9 As described above, the artificial blood vessel of Example 9 was produced by applying a layer of silicone rubber around the iron core. The buffer cylinder had a right cylindrical shape and the elasticity of the wall was uniform.

[0117] Example 10 The artificial blood vessel of Example 10 has a wall that is thinner in two stages going downstream. This produces the same effect as Example 1. In addition, the weave is very loose, and the openings of the windows in the loose mesh are sealed with soft glucomannan glue (containing an anticoagulant). The glucomannan windows that seal the loose mesh protrude outward under internal pressure (a structure similar to that shown in Figure 6. The lumen itself does not expand, but only the windows expand and protrude outward under pressure), thereby enhancing the buffering effect.

[0118] Example 8 By creating a spiral groove in the lumen, the blood flows in a spiral pattern, enhancing the buffering effect. This is the same effect as in Figure 5.

[0119] Example 11, Example 5 This example is similar to Example 8, but features a spiral compression / reinforcement material made of a non-stretchable fiber attached to the outside. As previously mentioned, pulsatile blood flow in arteries creates areas of high internal pressure, which leads to vascular wall lumen expansion. When a spiral compression / reinforcement material is attached to a vessel wall with a certain degree of flexibility from the outside, this lumen expansion due to internal pressure creates a spiral expansion-suppressing area. As a result, in addition to the pulsatile lumen expansion effect to the outside, blood flow becomes spiral, enhancing the cushioning effect as shown in Figure 5. The 30% elasticity index listed in Table 2 is largely due to the elasticity of the spiral reinforcement material, which is less stretchable than the wall material (in Example 5, the wall material is silicone rubber and the reinforcement material is polypropylene monofilament fiber; in Example 11, the wall material is polyurethane and the reinforcement material is silicone rubber). Therefore, the 30% elasticity index of the wall material is significantly smaller than the elasticity index listed in Table 2.

[0120] Although Comparative Example 2 also has spiral reinforcement (support), the wall material is hard and does not expand due to arterial pressure, so it does not exhibit the cushioning effect seen in Examples 11 and 5. Incidentally, Example 2 is installed with the aim of preventing the risk of blood clot formation or blood circulation interruption due to the blood vessel wall "collapsed" when the artificial blood vessel is twisted or compressed from the outside, causing the lumen to narrow or close.

[0121] It goes without saying that the compression / reinforcement materials of Examples 11, 24, and 5 also have the effect of preventing the risk of thrombus formation and blood circulation interruption caused by twisting or compression of the artificial blood vessel. (This effect is extremely useful because buffer system blood vessels with soft blood vessel walls must be considered, as the risk of thrombus formation and blood circulation interruption caused by twisting or compression of the artificial blood vessel must be taken into consideration.)

[0122] (Experimental result 3: Buffering effect of the trumpet-shaped buffer cylinder using the relative length R and 30% elasticity index as indicators) The buffering effect of the trumpet-shaped buffer cylinder was investigated using the relative length R of the buffer cylinder and the 30% elasticity index as indicators. The results are shown in Table 3 below.

[0123] [Table 3]

[0124] (1) The relationship between the relative length of the buffer cylinder and its buffer effect was examined for a trumpet-shaped buffer cylinder with a configuration such as that shown in Figure 27. The ratio R (=X÷Φ) of the axial length X of the buffer cylinder to the inner diameter Φ of the blood inlet portion, as shown in Figure 28, was used as an indicator of the buffer cylinder's relative length. Even for trumpet-shaped buffer cylinders made of the same PTFE material and with the same 30% elastic index of 11.8 N, a buffer effect was observed when the buffer cylinder's relative length R = X÷Φ ≥ 1.5 (Examples 12 and 13), but not when R = X÷Φ ≤ 1.2 (Comparative Examples 3 to 5). Furthermore, when R = X÷Φ ≤ 1.2, no buffer effect was observed in Comparative Examples 6 to 9, which were made of ePTFE and had a higher 30% elastic index of 12.0 N or higher. This indicates that when the trumpet-shaped configuration and 30% elastic index are 11.8 N or higher, a buffer effect can be achieved if the condition of the buffer cylinder's relative length R ≥ 1.5 is met. (2) The relationship between the 30% elasticity index and the cushioning effect of the trumpet-shaped buffer cylinder was examined. A cushioning effect was observed even when R<1.5, as in Example 14 (R=1) where the 30% elasticity was low at 7 N, and Example 15 (R=0) where it was 3.9 N. On the other hand, even when the relative length R of the buffer cylinder was the same (R<1.5) and the 30% elasticity index of the buffer cylinder was high at 11.8 N or higher (Comparative Examples 3 to 9), no cushioning effect was observed. In other words, a lower 30% elasticity index is required for a buffer cylinder with a relative length R<1.5 to exhibit a cushioning effect. This indicates that a cushioning effect is observed when the 30% elasticity index is 7 N or lower when R=1, and when R=0, a 30% elasticity index of 3.9 or lower.

[0125] (Experimental result 4: Changes in wall thickness of the trumpet-shaped buffer cylinder and buffering effect) The change in wall thickness and the buffering effect of the trumpet-shaped buffer cylinder were investigated. The results are shown in Table 4 below.

[0126] [Table 4]

[0127] The relationship between the change in wall thickness of the horn-shaped buffer cylinder and the buffer effect was examined when the relative length R of the buffer cylinder was 1.2 or less. When the same PTFE horn-shaped buffer cylinder was used and the relative length R of the buffer cylinder was 1.2 or less, a buffer effect was observed when the wall thickness was reduced in the lateral direction within the same cross section perpendicular to the axial direction (Examples 16 to 18), regardless of the value of the relative length. However, when the wall thickness of the lateral side of the same cross section did not change as described above, no buffer effect was observed when the relative length R of the buffer cylinder was 1.2 or less, regardless of the value of the relative length (Comparative Examples 3 to 5).

[0128] (Experimental Result 5: Evaluation of buffering effect using 60%, 100% and 150% elasticity index) Examples and comparative examples for 60%, 100% and 150% elasticity index are shown in the table below. The evaluation method is the same as that for 30% elasticity index.

[0129] [Table 5]

[0130] Example 24 in Table 5 has a straight shape, an inner diameter of 6 mm, and a length of 60 mm, but includes a buffer cylinder whose wall elasticity changes spirally. This spiral change is thought to enhance the buffering effect, and considering this, in order to have a buffering effect, it is necessary for the buffer cylinder wall to satisfy at least one of the following conditions: a 60% elasticity index of 4.6 N or less, a 100% elasticity index of 7.5 N or less, or a 150% elasticity index of 9.8 N or less (Example 23). Examples 20, 21, 22, and 23 in Table 5 are the experimental results for cases where the cylinder is straight and has no changes in shape or elasticity, i.e., where the cushioning effect is achieved solely through uniform wall elasticity. Based on these results, the indicators for a cushioning cylinder with an inner diameter of 6 mm and a length of 60 mm that demonstrate cushioning effect solely through uniform wall elasticity should desirably satisfy at least one of the following conditions: 60% elasticity index of 3.2 N or less, 100% elasticity index of 6.5 N or less, and 150% elasticity index of 9.8 N or less; more desirably, 60% elasticity index of 1.6 N or less, 100% elasticity index of 2.5 N or less, and 150% elasticity index of 8.4 N or less; and even more desirably, 60% elasticity index of 0.8 N or less, 100% elasticity index of 1.5 N or less, and 150% elasticity index of 4.6 N or less. In Comparative Examples 10, 1 and 2, which used conventional artificial blood vessels, the elasticity indexes did not satisfy the above conditions, and no cushioning effect was observed.

[0131] (Experimental result 6: Evaluation of the buffering effect of layered, parallel-arranged buffer cylinders) The buffering effect of layered, parallel-placed buffer cylinders is shown in the table below.

[0132] [Table 6]

[0133] The examples in Table 6 are all buffer-type artificial blood vessels with overlapping, juxtaposed buffer cylinders that are placed side by side on top of the vein wall. These are hybrid buffer-type artificial blood vessels that not only have the "physical buffering effect" of the installed buffer cylinders but also a pronounced "biological buffering effect" of remodeling the natural vein. Among these, Examples 25 to 29 are what might be called "external overlapping apposition type" or "external stent type," which are placed on the outer periphery of the venous wall in overlapping relation to the venous wall. After placement, the buffer cylinder has a cross-section of the desired cylindrical shape, such as a circle or ellipse. However, before placement, the shape has a discontinuity in the wall of the cylindrical portion, i.e., a slit that starts at one end of the cylinder and continues to the other end. The advantage of this slit is that it allows for re-placement and adjustment of the placement state. Without the "gap," reinstallation would require disrupting the continuity between the conventional vascular graft and the vein, reinstalling a new buffer cylinder around the vein, and then re-anastomosing the vascular graft to the vein after installation. However, with the "gap," the cylinder can be opened, for example, into a single coiled tape, and the tape can be simply "covered" or "wrapped" around the vein wall. This eliminates the need to disrupt the continuity between the vascular graft and the vein, and eliminates the need for re-anastomosing. Furthermore, as mentioned above, the placement can be adjusted by utilizing the "gap" while evaluating the blood flow status using an ultrasound blood flow system, allowing for optimal placement to achieve the desired blood flow status. Furthermore, if the installed "seamless" buffer cylinder is not expected to achieve the desired blood flow condition due to an improper installation condition, such as being "too loose," it is possible to correct the "too loose" installation condition and adjust it to an appropriate installation condition that achieves the desired blood flow condition by layering part or all of a "slit" buffer cylinder on top of the previously installed "seamless" buffer cylinder. The remaining Examples 30 and 31 listed in Table 6 are what should be called "internal overlapping apposition type" or "internal stent type," which are overlapped and apposed to the venous wall on the lumen side of the venous wall. This type can also be deformed into an elongated shape by stretching it in the longitudinal direction without necessarily creating a "slit," and can be deformed into an elongated shape even without a slit by puncturing the vascular wall to create a small hole, allowing it to be re-installed in the venous lumen or the installation state to be readjusted, but Examples 30 and 31 have a "slit." The results of the animal experiment evaluation showed that all of Examples 25 to 31 met not only the individual evaluation results (A) to (D) but also (E), confirming the buffering effect of the buffer-system artificial blood vessels, confirming their effectiveness, and confirming their biological buffering action. In particular, in Example 26, at the time of evaluation after 12 months, the PGA nonwoven fabric and alginic acid had been almost completely decomposed and absorbed, indicating that the natural veins that had been remodeled into buffering blood vessels were independently exerting their buffering function. From the above experimental results, the minimum conditions for a buffer cylinder that is placed in juxtaposition with the venous wall to exhibit a buffering effect are that the buffer cylinder wall has a 30% elastic index of 3.1 N or less, a 60% elastic index of 4.2 N or less, a 100% elastic index of 6.2 N or less, or a 150% elastic index of 8.9 N or less; more preferably, it has a minimum of 30% elastic index of 1.5 N or less, a 60% elastic index of 1.6 N or less, a 100% elastic index of 3.3 N or less, or a 150% elastic index of 8.2 N or less; and even more preferably, it has a minimum of 30% elastic index of 0.53 N or less, a 60% elastic index of 1.4 N or less, a 100% elastic index of 2.7 N or less, or a 150% elastic index of 3.9 N or less. In Comparative Example 11, which used a conventional commercially available artificial blood vessel, the elasticity indexes did not satisfy the above conditions, and no cushioning effect was observed.

[0134] <Evaluation of animal experiments> According to the following criteria, it was evaluated whether the artificial blood vessel interposed at the site of shunt construction acted as a low-pressure buffer vessel and prevented pathological changes in the blood vessel at the shunt site. Beagle dogs (weight 12-16 kg) were used. A shunt using an artificial blood vessel with the anastomosis configuration shown in Figure 26 was created between the carotid artery and jugular vein, and the dogs were observed over time. During the observation period, the following assessments were made using a color Doppler blood flowmeter and a color Doppler ultrasound imaging diagnostic device. At the end of the observation period, the dogs were euthanized and evaluated. The vasculature of the shunt site in euthanized dogs was isolated. The vasculature, including the carotid artery, the entire length of the vascular prosthesis, and the vein extending 70 mm from the anastomosis in the direction of blood flow, was examined macroscopically and under a stereomicroscope at up to 10x magnification, both in the isolated and open state. The vascular walls of the isolated vasculature were then prepared as standard 4-μm-thick thin sections, stained with hematoxylin and eosin and Elastica van Gieson (EvG) stains, and examined under a light microscope.

[0135] <Evaluation criteria> If all of the following evaluation items (a) to (d) were met, the artificial blood vessel interposed at the shunt creation site acted as a low-pressure buffer vessel and prevented pathological changes in the blood vessels at the shunt site, and the case was judged as a success (○ in Table 1); otherwise, the case was judged as a failure (× in Table 1). (a) In the measurements using the ultrasonic color Doppler blood flowmeter shown in Figure 26, (1) the blood flow in the carotid artery was an antegrade flow from the heart side to the head side at both the central side of the anastomosis between the carotid artery and the artificial blood vessel, i.e., the heart side of the carotid artery (blood flow measurement site 1 in Figure 26), and the peripheral side, i.e., the head side of the carotid artery (measurement site 2 in Figure 26), and (2) as evidence that the arterial pulsatile blood flow was buffered, both the average velocity of the blood flow and the average change in blood flow pulsation were less than half of the values ​​in the jugular vein (blood flow measurement site 3 in Figure 26) anastomosed to the artificial blood vessel, which is on the downstream side, compared to the blood flow in the carotid artery, which is on the upstream side (blood flow measurement site 1 in Figure 26). (a) In ultrasound tomographic imaging diagnosis, the vascular lumen is patent, the vascular wall is smooth, and there are no pathological findings affecting blood flow from the artificial blood vessel to the jugular vein, such as intimal hyperplasia, thrombus formation, luminal stenosis, or varicose vein formation. (c) Upon macroscopic examination, the vascular lumen is patent, the vascular wall is smooth and free of varicose veins or unnatural irregularities, and there are no pathological findings that affect blood flow, such as intimal hyperplasia, thrombus formation, or luminal narrowing. (d) Observations under a stereomicroscope and a normal optical microscope show that the vascular lumen is patent, the vascular wall is smooth and free of varicose veins or unnatural irregularities, and there is no pathological finding affecting blood flow such as intimal hyperplasia, thrombus formation, or stenosis. However, in cases where a "biological buffering effect" is deemed to have been observed in an experimental case that has been judged to be successful, the microscopic findings described below as (e) must also be observed. (e) The vein at the site of the shunt creation is excised and stained with hematoxylin and eosin and Elastica-van Gieson (EvG) stains and observed microscopically. The observation sites are three: a section extending 10 mm downstream in the direction of blood flow from the upstream end of the buffer cylinder of the buffer system vessel overlying the vein at the site of the shunt creation; a section extending 10 mm upstream in the direction of blood flow from the other end of the buffer cylinder; and a section 10 mm midway between these two. The cross section of the vessel is observed under an optical microscope, and the following two findings (A) and (B) are confirmed at each of the three observation sites: (A) A two-layer structure is confirmed, with a smooth muscle layer containing abundant elastic fibers on the luminal side and an elastic fiber layer containing collagen fibers on the outer side. (B) Furthermore, the outer elastic fiber layer containing collagen fibers is thicker than the inner smooth muscle layer at each observation site.

[0136] <Details of experimental results for representative examples and comparative examples> For reference, detailed experimental results of representative examples and comparative examples are shown below. Example 1 (1) Evaluation results by item (a) Evaluation using an ultrasonic Doppler blood flowmeter [Table 7] (i) Ultrasound imaging diagnosis: No abnormal findings. (c) Macroscopic findings at autopsy: No abnormal findings. (e) Microscopic findings: No abnormal findings. (2) Overall Judgment The buffering effect of the buffer-type artificial blood vessel was confirmed, and its effectiveness was confirmed.

[0137] Example 2 (1) Evaluation results by item (a) Evaluation using an ultrasonic Doppler blood flowmeter [Table 8] (i) Ultrasound imaging diagnosis: No abnormal findings. (c) Macroscopic findings at autopsy: No abnormal findings. (e) Microscopic findings: No abnormal findings. (2) Overall Judgment The buffering effect of the buffer-type artificial blood vessel was confirmed, and its effectiveness was confirmed.

[0138] Example 5 (1) Evaluation results by item (a) Evaluation using an ultrasonic Doppler blood flowmeter [Table 9] (i) Ultrasound imaging diagnosis: No abnormal findings. (c) Macroscopic findings at autopsy: No abnormal findings. (e) Microscopic findings: No abnormal findings. (2) Overall Judgment The buffering effect of the buffer-type artificial blood vessel was confirmed, and its effectiveness was confirmed.

[0139] Example 9 (1) Evaluation results by item (a) Evaluation using an ultrasonic Doppler blood flowmeter [Table 10] (i) Ultrasound imaging diagnosis: No abnormal findings. (c) Macroscopic findings at autopsy: No abnormal findings. (e) Microscopic findings: No abnormal findings. (2) Overall Judgment The buffering effect of the buffer-type artificial blood vessel was confirmed, and its effectiveness was confirmed.

[0140] Example 12 (1) Evaluation results by item (a) Evaluation using an ultrasonic Doppler blood flowmeter [Table 11] (i) Ultrasound imaging diagnosis: No abnormal findings. (c) Macroscopic findings at autopsy: No abnormal findings. (e) Microscopic findings: No abnormal findings. (2) Overall Judgment The buffering effect of the buffer-type artificial blood vessel was confirmed, and its effectiveness was confirmed.

[0141] Example 16 (1) Evaluation results by item (a) Evaluation using an ultrasonic Doppler blood flowmeter [Table 12] (i) Ultrasound imaging diagnosis: No abnormal findings. (c) Macroscopic findings at autopsy: No abnormal findings. (e) Microscopic findings: No abnormal findings. (2) Overall Judgment The buffering effect of the buffer-type artificial blood vessel was confirmed, and its effectiveness was confirmed.

[0142] Example 27 (1) Evaluation results by item (a) Evaluation using an ultrasonic Doppler blood flowmeter [Table 13] (i) Ultrasound imaging diagnosis: No abnormal findings. (c) Macroscopic findings at autopsy: No abnormal findings. (e) Microscopic findings: No abnormal findings. (o) Microscopic findings: Findings (A) and (B) were observed at all three designated observation sites, and it was determined that the vascular system was remodeling to a low-pressure buffering system. (A) An EvG-stained photograph of the center of the buffer cylinder (Figure 29) is shown. A two-layer structure was observed, with a smooth muscle layer containing abundant elastic fibers on the inner side and an elastic fiber layer containing collagen fibers on the outer side. (B) A table (Table 14) of the thickness of the smooth muscle and elastic fiber layer containing collagen at the three observation sites is presented. [Table 14] At all three observation sites, the thickness of the elastic fiber layer was greater than that of the smooth muscle layer. (2) Overall Judgment The buffering effect of the buffer-type artificial blood vessel was confirmed, and its effectiveness was confirmed. It was confirmed that biological buffering action was at work.

[0143] (Comparative Example 1) (1) Evaluation results by item (a) Evaluation using an ultrasonic Doppler blood flowmeter [Table 15] (i) Ultrasound imaging diagnosis: Thickening of the venous wall and prominent varicose veins were observed, with a blood clot inside the vein. (c) Macroscopic findings at autopsy: Significant varicose veins were observed on the venous side, with a blood clot inside. (e) Microscopic findings: Thickening of the venous wall and varicose veins are observed. (2) Overall Judgment No buffering effect of the shunt vessel was observed and it was ineffective.

[0144] (Comparative Example 2) (1) Evaluation results by item (a) Evaluation using an ultrasonic Doppler blood flowmeter [Table 16] (i) Ultrasound imaging diagnosis: The lumen of the artificial blood vessel and the lumen of the vein were completely blocked. (c) Macroscopic findings at autopsy: The lumen from the artificial blood vessel to the vein was completely blocked. (e) Microscopic findings: Pathological intimal hyperplasia and old thrombus were found in the vein, which led to the determination that the lumen had been completely blocked. (2) Overall Judgment The lack of a buffering effect caused intimal hyperplasia, resulting in complete occlusion of the shunt vessel.

[0145] (Comparative Example 3) (1) Evaluation results by item (a) Evaluation using an ultrasonic Doppler blood flowmeter [Table 17] (i) Ultrasound imaging diagnosis: Thickening of the venous wall and prominent varicose veins were observed. (c) Macroscopic findings at autopsy: Thickened and irregular venous walls and prominent varicose veins were observed. (e) Microscopic findings: Pathological intimal thickening of the veins and varicose veins are observed. (2) Overall Judgment No buffering effect of the shunt vessel was observed and it was ineffective. [Explanation of symbols]

[0146] 1~7 Buffer system artificial blood vessel 10 Buffer cylinder 20 Normal route section

Claims

1. A buffer system artificial blood vessel having a function of buffering the dynamics of blood flowing from an artery to a vein, the function of buffering hemodynamics is a function of reducing the pressure and pulsatile changes in pressure, and / or the flow rate and magnitude of the change in flow rate of blood flowing in from the arterial side, and allowing the blood to flow out to the venous side; The device is made of a buffer cylinder having a function of buffering the dynamics of blood flowing from the artery to the vein, or is provided with the buffer cylinder as a part thereof, The buffer cylinder has a portion having a 30% elasticity index of 10.1 N or less. Buffer system artificial blood vessel.

2. A buffer system artificial blood vessel having a function of buffering the dynamics of blood flowing from an artery to a vein, The function of buffering hemodynamics is to reduce the pressure and pulsatile changes in pressure, and the flow rate and magnitude of the change in flow rate of blood flowing in from the arterial side, and to allow the blood to flow out to the venous side. Buffer system artificial blood vessel.

3. A buffer system artificial blood vessel having a function of buffering the dynamics of blood flowing from an artery to a vein, The device is made of a buffer cylinder having a function of buffering the dynamics of blood flowing from the artery to the vein, or is provided with the buffer cylinder as a part thereof, The buffer cylinder has a portion having a 30% elasticity index of 10.1 N or less. The buffer system artificial blood vessel according to claim 2.

4. A buffer system artificial blood vessel having a function of buffering the dynamics of blood flowing from an artery to a vein, The device is made of a buffer cylinder having a function of buffering the dynamics of blood flowing from the artery to the vein, or is provided with the buffer cylinder as a part thereof, The buffer cylinder has a portion having a 100% elasticity index of 7.5 N or less.

4. The buffer system artificial blood vessel according to claim 1.

5. A buffer system artificial blood vessel having a function of buffering the dynamics of blood flowing from an artery to a vein, The device is made of a buffer cylinder having a function of buffering the dynamics of blood flowing from the artery to the vein, or is provided with the buffer cylinder as a part thereof, The buffer cylinder has a portion having a 60% elasticity index of 4.6 N or less.

5. The buffer system artificial blood vessel according to claim 1.

6. A buffer system artificial blood vessel having a function of buffering the dynamics of blood flowing from an artery to a vein, The device is made of a buffer cylinder having a function of buffering the dynamics of blood flowing from the artery to the vein, or is provided with the buffer cylinder as a part thereof, The buffer cylinder has a portion having a 150% elasticity index of 9.8 N or less.

6. The buffer system artificial blood vessel according to claim 1.

7. A buffer system artificial blood vessel having a function of buffering the dynamics of blood flowing from an artery to a vein, The device is made of a buffer cylinder having a function of buffering the dynamics of blood flowing from the artery to the vein, or is provided with the buffer cylinder as a part thereof, The buffer cylinder has an artificial blood vessel wall in which the elastic index of the artificial blood vessel wall on the venous side is smaller than the elastic index of the artificial blood vessel wall on the arterial side.

7. The buffer system artificial blood vessel according to claim 1.

8. A buffer system artificial blood vessel having a function of buffering the dynamics of blood flowing from an artery to a vein, The device is made of a buffer cylinder having a function of buffering the dynamics of blood flowing from the artery to the vein, or is provided with the buffer cylinder as a part thereof, 8. A buffer system artificial blood vessel according to claim 1, wherein the buffer cylinder has an artificial blood vessel wall in which the elastic index of the artificial blood vessel wall on the venous side is greater than the elastic index of the artificial blood vessel wall on the arterial side.

9. A buffer system artificial blood vessel having a function of buffering the dynamics of blood flowing from an artery to a vein, The device is made of a buffer cylinder having a function of buffering the dynamics of blood flowing from the artery to the vein, or is provided with the buffer cylinder as a part thereof, 9. The buffer system artificial blood vessel according to claim 1, wherein the buffer cylinder has a portion whose inner diameter increases from the arterial side to the venous side and / or a narrow portion whose inner diameter decreases from the arterial side to the venous side.

10. A buffer system artificial blood vessel having a function of buffering the dynamics of blood flowing from an artery to a vein, The device is made of a buffer cylinder having a function of buffering the dynamics of blood flowing from the artery to the vein, or is provided with the buffer cylinder as a part thereof, The buffer cylinder has a spiral-shaped inner cavity.

10. The buffered vascular prosthesis according to any one of claims 1 to 9.

11. 11. The buffer system artificial blood vessel according to claim 1, wherein the buffer cylinder has portions with different elasticity combined in a patch-like manner.

12. 12. The buffer system artificial blood vessel according to claim 1, wherein the buffer cylinder has an elliptical cross section, and the elliptical cross section has a wall thickness different between the major axis side and the minor axis side.

13. 13. The buffer system artificial blood vessel according to claim 1, wherein the buffer cylinder has a wall thickness that varies in the axial direction.

14. 14. The buffer system artificial blood vessel according to claim 1, wherein the buffer cylinder has an axial length of X mm and an inner diameter of the blood inlet of Φ mm, and the ratio R (=X / Φ) thereof is 1 or greater.

15. 15. The buffer-type artificial blood vessel according to claim 1, wherein the artificial blood vessel material contains two or more types of fibers with different elastic properties.

16. 16. The buffer-based vascular prosthesis of claim 1, wherein the vascular prosthesis comprises an elastomer as a material.

17. 17. The buffer-type artificial blood vessel according to claim 1, wherein the artificial blood vessel contains a biodegradable material as a material.

18. 18. The buffer-system artificial blood vessel according to claim 1, wherein the artificial blood vessel wall has a continuous or discontinuous spiral or segmental reinforcing structure or a valve-like structure.

19. 19. A buffer-type artificial blood vessel according to any one of claims 1 to 18, wherein a part or all of the wall of the artificial blood vessel has a layered structure consisting of two or more layers, and the layered structure has a structure in which the overlapping layers are displaced from each other.

20. 20. A buffer system artificial blood vessel according to claim 1, wherein a buffer cylinder having a function of buffering the dynamics of blood flowing from an artery to a vein has slits formed therein that allow the artificial blood vessel wall to be separated.

21. 21. The buffer system artificial blood vessel according to claim 20, wherein the buffer cylinder having the cuts formed therein satisfies at least one of the following conditions at least in part: a 30% elastic index of 3.1 N or less, a 60% elastic index of 4.2 N or less, a 100% elastic index of 6.2 N or less, and a 150% elastic index of 8.9 N or less.

22. 22. The buffer system artificial blood vessel of claim 20 or 21, wherein at least a portion of the buffer cylinder in which the cuts are formed is made of a bioabsorbable material or metal.

23. A buffer system artificial blood vessel having a function of buffering the dynamics of blood flowing from an artery to a vein, The device is made of a buffer cylinder having a function of buffering the dynamics of blood flowing from the artery to the vein, or is provided with the buffer cylinder as a part thereof, 23. A buffer system artificial blood vessel according to any one of claims 1 to 22, wherein the buffer cylinder has elasticity such that, when its inner diameter expands to 130% in 100 seconds due to an external force of a certain strength, it returns to an inner diameter smaller than 125% of its inner diameter within 200 seconds after the external force is removed, and / or, when its inner diameter contracts to 80% in 100 seconds due to an external force of a certain strength, it returns to an inner diameter larger than 85% of its inner diameter within 200 seconds after the external force is removed.

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