Patent Publication Number: US-2006020242-A1

Title: Artificial blood vessel system, connecting assist tool and blood pump system

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to an artificial blood vessel system, a connecting assist tool and a blood pump system.  
      2. Related Art  
      As one of methods for curing a serious heart disease, a medical treatment using a blood pump has been performed. To perform such a medical treatment, it is necessary to connect the blood pump and a heart as well as the blood pump and an aorta respectively using artificial blood vessels. Accordingly, various artificial blood vessel connecting structures are used at portions where these parts and organs are connected (see, for example, German Laid-open Patent Publication 10108813A1 ( FIG. 1  to  FIG. 3 )).  
       FIG. 9  is a cross-sectional view showing the artificial blood vessel connecting structure which is described in the above-mentioned patent publication. This artificial blood vessel connecting structure  901  is, as shown in  FIG. 9 , an artificial blood vessel connecting structure which is served for connecting a blood pump  940  and an artificial blood vessel  920 . The artificial blood vessel connecting structure  901  includes a tubular connecting member  910  which is connected with the blood pump  940  by way of a bend  942  and has a male threaded portion  910   a , the artificial blood vessel  920  which is connected with an opening end portion on a side opposite to the blood pump  940  out of both opening end portions of the tubular connecting member  910 , and a connecting assist tool  930  which is served for strengthening the connection between the artificial blood vessel  920  and the tubular connecting member  910 .  
      The connecting assist tool  930  is constituted of a nut  932  and a pressure ring  934 . The nut  932  includes a female threaded portion  932   a  and a flange  932   b  and the female threaded portion  932   a  of the nut  932  is threadedly engaged with the male threaded portion  910   a  of the tubular connecting member  910 . The pressure ring  934  includes a flange  934   a  which is interposed between an outer peripheral surface of the artificial blood vessel  920  and the nut  932 .  
      In such an artificial blood vessel connecting structure  901 , in connecting the artificial blood vessel  920  with the tubular connecting member  910 , first of all, the connecting assist tool  930  is mounted on a periphery of the artificial blood vessel  920 . Then, the artificial blood vessel  920  in this state is fitted on and connected with the tubular connecting member  910  such that the artificial blood vessel  920  covers a distal end portion of the tubular connecting member  910 . Thereafter, the female threaded portion  932   a  of the nut  932  of the connecting assist tool  930  is threadedly engaged with the male threaded portion  910   a  of the tubular connecting member  910 . Here, in advancing the nut  932  in the L 1  direction in  FIG. 9  by performing the rotational manipulation of the nut  932 , the flange  932   b  of the nut  932  is brought into contact with pressure contact with the flange  934   a  of the pressure ring  934  in the L 1  direction in  FIG. 9 . In such an artificial blood vessel connecting structure  901 , a profile of the tubular connecting member  910  is gradually increased in the L 1  direction in  FIG. 9  and hence, the artificial blood vessel  920  is brought into pressure contact with the tubular connecting member  910  due to this pressure contact force. Accordingly, the artificial blood vessel  920  and the tubular connecting member  910  are firmly connected with each other.  
     SUMMARY OF THE INVENTION  
      However, in such an artificial blood vessel connecting structure  901 , the artificial blood vessel  920  and the tubular connecting member  910  are connected with each other by making use of a so-called wedge effect. Accordingly, a contact pressure force component along the radial direction of the tubular connecting member  910  out of a contact pressure force applied to the artificial blood vessel  920  from the pressure ring  934  is gradually decreased from the blood-pump-side end portion (connection terminal end portion) to the artificial-blood-vessel-side end portion (connection start end portion) (along the L 2  direction in  FIG. 9 ).  
      Accordingly, at the artificial-blood-vessel-side distal end (indicated by symbol M in  FIG. 9 ) of the tubular connecting member  910 , the pressure contact of the artificial blood vessel  920  with the tubular connecting member  910  is not guaranteed. As a result, there arises a possibility that a minute gap is formed between the tubular connecting member  910  and the artificial blood vessel  920  at the artificial-blood-vessel-side distal end (M) of the tubular connecting member  910 . When the artificial blood vessel is flexible, the possibility that such a gap is formed is particularly increased. Once such a gap is formed, due to the presence of the gap, a blood flow is stagnated thus giving rise to a drawback that there exists a possibility of the occurrence of the thrombus.  
      Further, in the artificial blood vessel connecting structure  901 , since the nut  932  and the pressure ring  934  are brought into contact with each other only in the axial direction at both flanges  932   b ,  934   a  portions and are not brought into contact with each other in the radial direction and hence, there exists a play in the radial direction between the nut  932  and the pressure ring  934 .  
      Accordingly, when the artificial blood vessel  920  is bent in the vicinity of the artificial-blood-vessel-side distal end (M) of the tubular connecting member  910 , the pressure ring  934  assumes an eccentric position with respect to the tubular connecting member  910  and hence, there arises a possibility that a minute gap is formed between the artificial blood vessel  920  and the tubular connecting member  910 . When the gap is formed, in the same manner as the above-mentioned case, the blood flow is stagnated due to the presence of the gap thus giving rise to a drawback that there exists a possibility of the occurrence of the thrombus.  
      Further, in this artificial blood vessel connecting structure  901 , the artificial blood vessel  920  and the tubular connecting member  910  are connected with each other while turning around the pressure ring  934  and hence, an undesired stress attributed to twisting or the like is applied to the artificial blood vessel  920 . Accordingly, the connection of the artificial blood vessel is liable to easily become non-uniform thus lowering the reliability of the connection between the artificial blood vessel  920  and the tubular connecting member  910  in the artificial blood vessel connecting structure  901 . Further, there has been also a drawback that the artificial blood vessel  920  is easily damaged and hence, the lifetime of the artificial blood vessel connecting structure  901  is shortened. Still further, this undesired stress attributed to twisting or the like is transmitted to a portion where the artificial blood vessel is connected with a living tissue anastomosis portion, the blood pump and the like and imparts an adverse effect on the portion.  
      The present invention has been made to overcome such drawbacks and it is an object of the present invention to provide an artificial blood vessel system and a blood pump system which include the artificial blood vessel connecting structure which can suppress the stagnation of a blood flow and, eventually, the occurrence of the thrombus and can prolong the lifetime of the artificial blood vessel connecting structure without lowering the reliability of the connection.  
      It is another object of the present invention to provide a connecting assist tool which can be suitably used in such an artificial blood vessel system.  
      (1) An artificial blood vessel system according to the present invention includes an artificial blood vessel, a tubular connecting member which is connected with the artificial blood vessel, and connecting assist means for strengthening the connection between the artificial blood vessel and the tubular connecting member, wherein the connecting assist means is configured to be capable of bringing the artificial blood vessel into pressure contact with the tubular connecting member not only along the radial direction of the tubular connecting member but also at an artificial-blood-vessel-side distal end of the tubular connecting member.  
      Due to such a constitution, according to the artificial blood vessel system of the present invention, the connecting assist means can bring the artificial blood vessel into pressure contact with the tubular connecting member along the radial direction of the tubular connecting member and hence, an undesired stress attributed to twisting or the like is not applied to the artificial blood vessel. As a result, the connection of the artificial blood vessel can be performed more uniformly and hence, the reliability of connection between the artificial blood vessel and the tubular connecting member in the artificial blood vessel system can be enhanced. Further, damage to the artificial blood vessel can be effectively prevented and hence, the lifetime of the artificial blood vessel system can be prolonged. Further, it is possible to suppress any adverse influence to a part such as a living tissue anastomosis portion, a blood pump or the like to which the artificial blood vessel system is connected.  
      Further, according to the artificial blood vessel system of the present invention, the connecting assist means can bring the artificial blood vessel into pressure contact with the tubular connecting member also at the artificial-blood-vessel-side distal end of the tubular connecting member and hence, it is possible to effectively prevent the formation of a minute gap between the artificial blood vessel and the tubular connecting member whereby it is possible to effectively prevent the occurrence of the stagnation of the blood flow and, eventually, the occurrence of the thrombus.  
      In this case, it is considered that, when the artificial blood vessel is bent in the vicinity of the artificial-blood-vessel-side distal end of the tubular connecting member, a minute gap is formed between the artificial blood vessel and the tubular connecting member and eventually the blood flow is stagnated thus considerably increasing the possibility of the occurrence of the thrombus. However, even in such a case, according to the artificial blood vessel system of the present invention, the artificial blood vessel is brought into pressure contact with the tubular connecting member also at the artificial-blood-vessel-side distal end of the tubular connecting member and hence, the formation of the minute gap between the artificial blood vessel and the tubular connecting member can be effectively suppressed. As a result, it is possible to effectively prevent the occurrence of the stagnation of the blood flow and, eventually, the occurrence of the thrombus.  
      Here, in the artificial blood vessel system of the present invention, by using the connecting assist means which brings the artificial blood vessel into pressure contact with the tubular connecting member in the radial direction of the tubular connecting member at the artificial-blood-vessel-side distal end of the tubular connecting member as the connecting assist means, it is possible to obtain the substantially equal advantageous effects.  
      (2) In the artificial blood vessel system having the above-mentioned constitution (1), it is preferable that the connecting assist means has the property of narrowing an inner diameter thereof.  
      Due to such a constitution, it is possible to bring the artificial blood vessel into pressure contact with the tubular connecting member more uniformly and hence, it is possible to further effectively prevent the applying of the undesired stress attributed to twisting or the like to the artificial blood vessel.  
      In this case, as the connecting assist means which has the property of narrowing the inner diameter thereof, a winding member which applies a fastening force in the direction to make an inner diameter thereof small, a heat-shrinkable tube which is liable to shrink in the direction to make an inner diameter thereof small, a shape memory alloy which is liable to shrink in the direction to make an inner diameter thereof small, a resilient member such as a tube or a ring made of silicone rubber, a tube or a ring made of fluoric rubber can be exemplified. Further, connecting assist means which may be wound around with a tie band, strings or wires may be also used as the connecting assist means.  
      (3) In the artificial blood vessel system having the above-mentioned constitution (1) or (2), it is preferable that the connecting assist means is constituted of a connecting assist tool which satisfies a following relationship (a): 
          (a) the relationship “Za&lt;Zc and Zb−Zc≧−2×t”, wherein assuming an imaginary axis which sets the direction heading for the artificial blood vessel from the tubular connecting member as the normal direction as a z axis, Za are coordinates of the z axis at a tubular-connecting-member-side end of the connecting assist tool, Zb are coordinates of the z axis at an artificial-blood-vessel-side end of the connecting assist tool, Zc are coordinates of the z axis at an artificial-blood-vessel-side distal end of the tubular connecting member, and “t” is a wall thickness of an unconnected portion of the artificial blood vessel.        

      In the artificial blood vessel system of the present invention, to surely bring the artificial blood vessel into pressure contact with the tubular connecting member even at the artificial-blood-vessel-side distal end of the tubular connecting member, it is preferable that the position of the artificial-blood-vessel-side end of the connecting assist means is arranged closer to the artificial-blood-vessel side than the artificial-blood-vessel-side distal end of the tubular connecting member.  
      However, according to a result of an experiment carried out by inventors of the present invention, it has been found that even when the position of the artificial-blood-vessel-side end of the connecting assist means is arranged closer to the tubular-connecting-member side than the artificial-blood-vessel-side distal end of the tubular connecting member, with the use of the connecting assist tool which satisfies the relationship “Za&lt;Zc and Zb−Zc≧−2×t”, the connecting assist tool can bring the artificial blood vessel into pressure contact with the tubular connecting member with a sufficient force even at the artificial-blood-vessel-side distal end of the tubular connecting member and hence, the occurrence of the minute gap between the artificial blood vessel and the tubular connecting member can be suppressed whereby it is possible to effectively suppress the occurrence of the stagnation of the blood flow and, eventually, the occurrence of the thrombus. It is estimated that the artificial blood vessel is brought into pressure contact with the tubular connecting member with a greater force due to the resiliency of the artificial blood vessel.  
      Here, as the artificial blood vessel, it is preferable to use an artificial blood vessel having a wall thickness “t” of 0.1 mm to 2.5 mm.  
      However, to allow the connecting assist tool to bring the artificial blood vessel into pressure contact with the tubular connecting member with a sufficient force even at the artificial-blood-vessel-side distal end of the tubular connecting member thus further effectively suppressing the occurrence of the stagnation of the blood flow and, eventually, the occurrence of the thrombus, it is desirable that a relationship “Zb−Zc≧−t” is satisfied. It is further desirable that a relationship “Zb−Zc≧−0.5×t” is satisfied. It is still further desirable that a relationship “Zb−Zc≧−0 mm” is satisfied.  
      On the other hand, when the value of “Zb−Zc” is excessively large, a range within which the artificial blood vessel is not bent is increased and hence, the degree of freedom at the time of embedding the artificial blood vessel into a living body becomes low. From this point of view, it is preferable that a relationship “Zb−Zc≦20×t” is satisfied. It is more preferable that a relationship “Zb−Zc≦10×t” is satisfied. It is still more preferable that a relationship “Zb−Zc≦5×t” is satisfied.  
      (4) In the artificial blood vessel system having the above-mentioned constitution (3), it is preferable that a member which prevents the artificial blood vessel from being sharply bent is mounted on an outer periphery of the artificial blood vessel.  
      As an artificial blood vessel, there has been known an artificial blood vessel which winds a resilient member called “auxiliary helix” on an outer periphery thereof as a member which prevents the artificial blood vessel from being sharply bent. When the artificial blood vessel which winds the auxiliary helix thereon is used in the artificial blood vessel system, it is possible to easily maintain an open state of the artificial blood vessel due to the resiliency of the auxiliary helix and hence, it is possible to suppress the sharp bending of the artificial blood vessel.  
      Here, as the member which prevents the sharp bending of the artificial blood vessel, besides the auxiliary helix, the structure which arranges ring-like members on an outer periphery of the artificial blood vessel at a given interval or the structure which arranges a mesh-like member on an outer periphery of the artificial blood vessel can be exemplified.  
      Here, it is preferable that the member which is provided for preventing the sharp bending of the artificial blood vessel is brought into contact with the connecting assist tool. Due to such a constitution, it is possible to suppress the concentration of a stress on the artificial blood vessel at the artificial-blood-vessel-side distal end of the tubular connecting member and hence, buckling and wrinkles are hardly generated whereby the flow of the blood is hardly impeded and the thrombus hardly occurs.  
      (5) In the artificial blood vessel system having the above-mentioned constitution (1) or (2), it is preferable that a member for preventing the artificial blood vessel from being sharply bent is mounted on an outer periphery of the artificial blood vessel, and the connecting assist means is constituted of a connecting assist tool which satisfies a following relationship (b) and the member for preventing the artificial blood vessel from being sharply bent, and the tubular-connecting-member-side end of the member for preventing the artificial blood vessel from being sharply bent is brought into contact with the artificial-blood-vessel-side end of the connecting assist tool:  
      (b) the relationship “Zb&lt;Zc”, wherein assuming an imaginary axis which sets the direction heading for the artificial blood vessel from the tubular connecting member as the normal direction as a z axis, Zb are coordinates of the z axis at an artificial-blood-vessel-side end of the connecting assist tool, and Zc are coordinates of the z axis at an artificial-blood-vessel-side distal end of the tubular connecting member.  
      As mentioned above, as an artificial blood vessel, there has been known an artificial blood vessel which winds a resilient member called “auxiliary helix” on an outer periphery thereof as a member for preventing the artificial blood vessel from being sharply bent. When the artificial blood vessel which winds the auxiliary helix thereon is used in the artificial blood vessel system, by bringing the tubular-connecting-member-side end of the auxiliary helix into contact with the artificial-blood-vessel-side end of the connecting assist tool, the auxiliary helix brings the artificial blood vessel into pressure contact with the tubular connecting member even at the artificial-blood-vessel-side distal end of the tubular connecting member and hence, the formation of a minute gap between the artificial blood vessel and the tubular connecting member can be suppressed whereby it is possible to effectively suppress the occurrence of the stagnation of the blood flow and, eventually, the occurrence of the thrombus. The same goes for the case in which a member other than the auxiliary helix is used as a member for preventing the sharp bending of the artificial blood vessel.  
      (6) In the artificial blood vessel system having any one of the above-mentioned constitutions (1) to (5), it is preferable that a relationship “ID 1 ≧ID 0 ” is satisfied wherein ID 0  is an inner diameter of an unconnected portion of the artificial blood vessel and ID 1  is an inner diameter of the artificial blood vessel at an artificial-blood-vessel-side distal end of the tubular connecting member.  
      Due to such a constitution, at the artificial-blood-vessel-side distal end of the tubular connecting member, the artificial blood vessel is brought into pressure contact with the tubular connecting member even with a resilient force of the artificial blood vessel per se and hence, it is possible to further effectively suppress the occurrence of the stagnation of the blood flow and, eventually, the occurrence of the thrombus.  
      In this case, It is more preferable that the relationship “ID 1 &gt;ID 0 ” is satisfied. This is because that the artificial blood vessel is brought into pressure contact with the tubular connecting member with a greater force due to the resilient force of the artificial blood vessel per se.  
      (7) In the artificial blood vessel system having the above-mentioned constitution (6), it is preferable that a relationship “ID 1 /ID 0 &lt;1+0.11×t −1/2 ” is satisfied wherein t(mm) is a wall thickness of an unconnected portion of the artificial blood vessel.  
      When the artificial blood vessel system satisfies such a relationship, the bending of the artificial blood vessel in the vicinity of the artificial-blood-vessel-side distal end of the tubular connecting member can be made gentle and hence, it is possible to suppress the occurrence of the stagnation of the blood flow and, eventually, the occurrence of the thrombus. Here, this relationship is an empirical relationship which is introduced by an experiment carried out by inventors of the present invention and does not always have the physical implication.  
      (8) In the artificial blood vessel system having any one of the above-mentioned constitutions (1) to (7), it is preferable that relationships “OD 1 &gt;OD 0 ” and “OD 1 &gt;OD 2 ” are satisfied wherein OD 0  is an outer diameter of an unconnected portion of the artificial blood vessel, OD 1  is an outer diameter of a portion which is not subjected to a contact pressure force attributed to the connecting assist means out of portions of the artificial blood vessel which is applied to an outer periphery of the tubular connecting member, and OD 2  is an outer diameter of a portion which is subjected to the contact pressure force attributed to the connecting assist means out of the portions of the artificial blood vessel which is applied to the outer periphery of the tubular connecting member.  
      Due to such a constitution, it is guaranteed that the pressure contact force exerted by the connecting assist means is surely applied to the artificial blood vessel. Accordingly, even at the artificial-blood-vessel-side distal end of the tubular connecting member, the artificial blood vessel is surely brought into pressure contact with the tubular connecting member and hence, the formation of a minute gap between the artificial blood vessel and the tubular connecting member can be further effectively suppressed whereby the occurrence of the stagnation of the blood flow and, eventually, the occurrence of the thrombus can be further effectively suppressed.  
      (9) In the artificial blood vessel system having any one of the above-mentioned constitutions (1) to (8), it is preferable that, on the artificial-blood-vessel-side end portion of the tubular connecting member, a sharpened end portion whose wall thickness is gradually decreased from the tubular-connecting-member side to the artificial-blood-vessel side is formed.  
      Due to such a constitution, the flow of the blood at a portion where the artificial blood vessel and the tubular connecting member are connected with each other can be made further smoother and hence, it is possible to further effectively suppress the occurrence of the stagnation of the blood flow and, eventually, the occurrence of the thrombus. Further, it is also possible to obtain an advantageous effect that the assembling operation at the time of connecting the artificial blood vessel to the tubular connecting member is facilitated.  
      (10) In the artificial blood vessel system having the above-mentioned constitution (9), it is preferable that the rounding treatment is applied to the sharpened end portion of the tubular connecting member.  
      Due to such a constitution, a load applied to the artificial blood vessel from the sharpened end portion of the tubular connecting member can be alleviated and hence, an undesired biting of the sharpened end portion of the tubular connecting member into the artificial blood vessel can be obviated. Accordingly, damage to the artificial blood vessel can be effectively suppressed and hence, the lifetime of the artificial blood vessel system can be further prolonged. Further, it is possible to further effectively suppress the occurrence of the stagnation of the blood flow and, eventually, the occurrence of the thrombus at the artificial-blood-vessel-side distal end of the tubular connecting member.  
      (11) In the artificial blood vessel system having any one of the above-mentioned constitutions (1) to (10), it is preferable that an uneven portion is formed on an outer peripheral surface of the tubular connecting member.  
      Due to such a constitution, the artificial blood vessel and the tubular connecting member are connected with each other by way of the uneven portion. Accordingly, it is possible to realize the firm connection between the artificial blood vessel and the tubular connecting member whereby the occurrence of slipping of the artificial blood vessel from the tubular connecting member can be effectively prevented.  
      (12) In the artificial blood vessel system having any one of the above-mentioned constitutions (3) to (5), it is preferable that the connecting assist tool is a connecting assist tool which includes a fastening member arranged on an outer peripheral surface of the artificial blood vessel by way of a receiving member, and the connecting assist tool is arranged on an outer peripheral surface of the artificial blood vessel in a state that a fastening force of the fastening member is applied to the connecting assist tool.  
      Due to such a constitution, the fastening force of the fastening member is transmitted along the radial direction of the tubular connecting member by way of the receiving member. Accordingly, the connecting assist tool brings the artificial blood vessel into pressure contact with the tubular connecting member along the radial direction of the tubular connecting member and hence, an undesired stress attributed to twisting or the like is not applied to the artificial blood vessel. As a result, the connection of the artificial blood vessel can be made more uniform and hence, the reliability of the connection between the artificial blood vessel and the tubular connecting member can be further enhanced. Further, damage to the artificial blood vessel can be effectively suppressed and hence, it is possible to further prolong the lifetime of the artificial blood vessel system. Still further, it is possible to suppress any adverse influence to a part such as a living tissue anastomosis portion, a blood pump or the like to which the artificial blood vessel system is connected.  
      In this case, as the fastening member, a winding member which applies a fastening force in the direction which makes an inner diameter thereof small, a heat-shrinkable tube which is liable to shrink in the direction to make an inner diameter thereof small, a shape memory alloy which is liable to shrink in the direction to make an inner diameter thereof small, a resilient member such as a tube or a ring made of silicone rubber, a tube or a ring made of fluoric rubber can be exemplified. Further, a fastening member which may be wound around with a tie band, strings or wires may be also used as the fastening member.  
      (13) In the artificial blood vessel system having any one the above-mentioned constitutions (1) to (12), it is preferable that the artificial blood vessel is made of a material which exhibits a favorable blood compatibility.  
      Due to such a constitution, it is possible to suppress the occurrence of the thrombus in the inside of the artificial blood vessel. As the material having the favorable blood compatibility, fluoric resin, polyurethane resin, polyester resin or the like can be used. However, from a viewpoint of the blood compatibility, the resiliency and the like, it is particularly preferable to use expanded polytetrafluoroethylene.  
      (14) In the artificial blood vessel system having any one of the above-mentioned constitutions (1) to (13), it is preferable that the tubular connecting member is made of a material which exhibits a favorable blood compatibility.  
      Due to such a constitution, it is possible to suppress the occurrence of the thrombus in the inside of the tubular connecting member. As the material which exhibits the favorable blood compatibility, it is preferable to use pure titanium or titanium alloy. As the titanium alloy, it is preferable to use Ti-6AI-4V alloy (particularly, alloy of ELI (Extra Low Interstitial) grade) which is obtained by adding 6% of aluminum and 4% of vanadium to titanium.  
      (15) In the artificial blood vessel system having any one of the above-mentioned constitutions (1) to (14), it is preferable that, on a blood contact surface of the artificial blood vessel system, a coating film made of a material having blood compatibility and antithrombogenicity is formed.  
      Due to such a constitution, it is possible to suppress the occurrence of the thrombus on the blood contact surface of the artificial blood vessel system.  
      Here, as the material which possesses the blood compatibility and the antithrombogenicity, phospholipid polymer can be preferably used.  
      (16) In the artificial blood vessel system having any one of the above-mentioned constitutions (1) to (15), it is preferable that the artificial blood vessel system further includes a connecting ring for connecting the artificial blood vessel to the blood pump.  
      Due to such a constitution, it is possible to easily connect the excellent artificial blood vessel system which has the prolonged lifetime, exhibits the high reliability in connection and can effectively suppress the occurrence of the thrombus with the blood pump.  
      (17) In the artificial blood vessel system having any one of the above-mentioned constitutions (1) to (16), it is preferable that the artificial blood vessel system further includes a cannula for connecting the artificial blood vessel to the heart.  
      Due to such a constitution, it is possible to connect the excellent artificial blood vessel system which has the prolonged lifetime, exhibits the high reliability in connection and can effectively suppress the occurrence of the thrombus with the heart.  
      (18) A connecting assist tool of the present invention is a connecting assist tool for strengthening the connection between a tubular connecting member and an artificial blood vessel, wherein the connecting assist tool is served for the artificial blood vessel system having the above-mentioned constitution (3), (4), (5) or (12).  
      Accordingly, by connecting the artificial blood vessel to the tubular connecting member using the connecting assist tool of the present invention, the connecting assist tool can bring the artificial blood vessel into pressure contact with the tubular connecting member along the radial direction of the tubular connecting member and hence, an undesired stress attributed to twisting or the like is not applied to the artificial blood vessel. As a result, the connection of the artificial blood vessel can be made more uniform and hence, the reliability of connection between the artificial blood vessel and the tubular connecting member can be enhanced. Further, damage to the artificial blood vessel can be effectively suppressed and hence, the lifetime of the artificial blood vessel system can be prolonged.  
      Further, by connecting the artificial blood vessel to the tubular connecting member using the connecting assist tool of the present invention, the connecting assist tool can bring the artificial blood vessel into pressure contact with the tubular connecting member even at the artificial-blood-vessel-side distal end of the tubular connecting member and hence, the formation of a minute gap between the artificial blood vessel and the tubular connecting member can be effectively suppressed. As a result, it is possible to effectively suppress the occurrence of the stagnation of the blood flow and, eventually, the occurrence of the thrombus.  
      In this case, it is considered that, when the artificial blood vessel is bent in the vicinity of the artificial-blood-vessel-side distal end of the tubular connecting member, a minute gap is formed between the artificial blood vessel and the tubular connecting member and eventually the blood flow is stagnated thus considerably increasing the possibility of the occurrence of the thrombus. However, even in such a case, with use of the connecting assist tool of the present invention, the connecting assist tool can bring the artificial blood vessel into pressure contact with the tubular connecting member also at the artificial-blood-vessel-side distal end of the tubular connecting member and hence, the formation of the minute gap between the artificial blood vessel and the tubular connecting member can be effectively suppressed. As a result, it is possible to effectively prevent the occurrence of the stagnation of the blood flow and, eventually, the occurrence of the thrombus.  
      (19) A blood pump system of the present invention is a blood pump system which includes a blood pump and an artificial blood vessel system which is connected to at least one side out of a suction side and a discharge side of the blood pump, wherein the artificial blood vessel system is the artificial blood vessel system having the above-mentioned constitution (16).  
      Accordingly, the blood pump system of the present invention is provided with the artificial blood vessel system which exhibits the prolonged lifetime, has high reliability in connection and can effectively suppress the occurrence of the thrombus and, at the same time, can be easily connected with the blood pump and hence, it is possible to provide the highly reliable and excellent blood pump system which can reduce a burden imposed on an operator at the time of embedding the blood pump into a living body and can suppress the occurrence of the thrombus after embedding the blood pump into the living body.  
      (20) A blood pump system of the present invention is a blood pump system which comprises a blood pump which includes a tubular connecting member having at least one side out of a suction side and a discharge side thereof, an artificial blood vessel which is connected with the tubular connecting member, and connecting assist means which is served for strengthening the connection between the artificial blood vessel and the tubular connecting member, wherein the connecting assist means is configured to be capable of bringing the artificial blood vessel into pressure contact with the tubular connecting member not only in the radial direction of the tubular connecting member but also at an artificial-blood-vessel-side distal end of the tubular connecting member.  
      Accordingly, the blood pump system of the present invention is provided with the artificial blood vessel system which exhibits the prolonged lifetime, has high reliability in connection and can effectively suppress the occurrence of the thrombus and hence, it is possible to provide the highly reliable and excellent blood pump system which can suppress the occurrence of the thrombus. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a view for explaining a blood pump system including an artificial blood vessel system according to an embodiment of the present invention;  
       FIG. 2  is a cross-sectional view showing a blood pump used in the blood pump system shown in  FIG. 1 ;  
       FIG. 3  is a view for explaining the artificial blood vessel system according to the embodiment 1 of the present invention;  
       FIG. 4A  and  FIG. 4B  are views for explaining the artificial blood vessel connecting structure  100 A shown in  FIG. 3 ;  
       FIG. 5A  and  FIG. 5B  are views for explaining the artificial blood vessel connecting structure  100 B shown in  FIG. 3 ;  
       FIG. 6  is a view for explaining an artificial blood vessel system according to an embodiment 2 of the present invention;  
       FIG. 7  is a view for explaining an artificial blood vessel system according to an embodiment 3 of the present invention;  
       FIG. 8  is a view showing the artificial blood vessel connecting structure which is used in the blood pump system according to an embodiment 4 of the present invention; and  
       FIG. 9  is a cross-sectional view showing the conventional artificial blood vessel connecting structure. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      An artificial blood vessel system, a connecting assist tool and a blood pump system to which the present invention is applied are explained hereinafter in conjunction with drawings.  
      First of all, the blood pump system and the blood pump are explained in conjunction with  FIG. 1  and  FIG. 2 .  
       FIG. 1  is a view for explaining the blood pump system including the artificial blood vessel system according to an embodiment of the present invention.  FIG. 2  is a cross-sectional view showing the blood pump used in the blood pump system shown in  FIG. 1 .  
      The blood pump system  10  includes, as shown in  FIG. 1 , a blood pump  20 , artificial blood vessels  120 ,  121 , a cannula  40 , an external controller  50  for performing a drive control of the blood pump  20 , and a cable  60  which is served for connecting the external controller  50  and the blood pump  20 . The blood pump  20  is connected with a left ventricle A of a heart by way of the artificial blood vessel  120  and the cannula  40  and, at the same time, is connected with an aorta B by way of the artificial blood vessel  121 .  
      Here, the detail of the cannula  40  is explained later.  
      The cable  60  which is connected with the blood pump  20  penetrates a skin of a living body at a portion of a cable fixing tool  70  which is adhered to a belly part of the living body and is led out from the living body and, thereafter, the cable  60  is wrapped around the living body by a half turn or more along a belly belt  80  for cable which is wrapped around the belly part of the living body and, then, the cable  60  is connected with the external controller  50 .  
      The blood pump  20  includes, as shown in  FIG. 2 , a pump base portion  21  which has a cylindrical motor and a pump portion  22  which is connected with the pump base portion  21 . The pump portion  22  includes pump vanes  23  which are driven by way of a rotary shaft of the motor and a pump casing  24  which is connected with the pump base portion  21  such that the pump casing  24  covers the pump vanes  23 . That is, the blood pump  20  is configured as follows. Blood in the inside of the left ventricle A of a heart in a human body H flows into the inside of the pump casing  24  through the artificial blood vessel  120  and an inlet opening  25 . After being given a flow energy from the pump vanes  23 , the blood flows out from the blood pump  20  and flows into the aorta B through an outlet opening  26  formed in a side surface of the pump casing  24  and the artificial blood vessel  121 .  
      Here, although a centrifugal pump is used as the blood pump  20  in the blood pump system  10  according to the embodiment of the present invention, an axial flow pump, a mixed flow pump or a pulsatile pump can be used in place of the centrifugal pump.  
      Next, the artificial blood vessel system including the artificial blood vessel  120  which connects the blood pump  20  and the left ventricle A of the heart is explained in conjunction with the embodiments of the present invention.  
     Embodiment 1  
      First of all, the artificial blood vessel system according to the embodiment 1 of the present invention is explained in conjunction with  FIG. 3  to  FIG. 5B .  
       FIG. 3  is a view for explaining the artificial blood vessel system according to the embodiment 1 of the present invention.  FIG. 4A  and  FIG. 4B  are views for explaining the artificial blood vessel connecting structure  100 A shown in  FIG. 3 , wherein  FIG. 4A  is a partial cross-sectional view and  FIG. 4B  is an enlarged cross-sectional view of an essential part.  FIG. 5A  and  FIG. 5B  are views for explaining the artificial blood vessel connecting structure  100 B shown in  FIG. 3 , wherein  FIG. 5A  is a partial cross-sectional view and  FIG. 5B  is an enlarged cross-sectional view of an essential part. Here, in  FIG. 4A  and  FIG. 5A , an auxiliary helix is omitted for simplifying the drawings.  
      The artificial blood vessel system  30  is, as shown in  FIG. 3 , configured to include the artificial blood vessel  120 , the artificial blood vessel connecting structure  100 A at the blood pump side, the artificial blood vessel connecting structure  100 B at the cannula side, and a connecting ring  140  which is connected with the artificial blood vessel connecting structure  100 A and is served for connecting the artificial blood vessel system  30  with the blood pump  20 . In the artificial blood vessel system  30 , the artificial blood vessel  120  and two tubular connecting members  110 A,  110 B are connected with each other at these two artificial blood vessel connecting structures  100 A,  100 B. Since the artificial blood vessel system  30  can obtain the excellent advantageous effects due to the operation of these two artificial blood vessel connecting structures, the artificial blood vessel system  30  is explained in detail by reference with these two artificial blood vessel connecting structures  100 A,  100 B.  
      First of all, the artificial blood vessel connecting structure  100 A is explained.  
      The artificial blood vessel connecting structure  100 A includes, as shown in  FIG. 3  and  FIG. 4A , a tubular connecting member  110 A, the artificial blood vessel  120 , and a connecting assist tool  130 A which is served for further strengthening the connection between the tubular connecting member  110 A and the artificial blood vessel  120 .  
      Here, the connecting assist tool  130 A is configured to bring the artificial blood vessel  120  into pressure contact with the tubular connecting member  110 A along the radial direction of the tubular connecting member  110 A and, at the same time, brings the artificial blood vessel  120  into pressure contact with the tubular connecting member  110 A at the artificial-blood-vessel-side distal end EA (see  FIG. 4B ) of the tubular connecting member  110 A.  
      Accordingly, in the artificial blood vessel connecting structure  100 A, since the connecting assist tool  130 A brings the artificial blood vessel  120  into pressure contact with the tubular connecting member  110 A along the radial direction of the tubular connecting member  110 A, an undesired stress attributed to twisting or the like is not applied to the artificial blood vessel  120 . As a result, the connection of the artificial blood vessel  120  becomes more uniform and hence, the reliability of the connection of the artificial blood vessel connecting structure  100 A can be enhanced. Further, damage to the artificial blood vessel  120  can be effectively suppressed whereby the lifetime of the artificial blood vessel connecting structure  100 A can be prolonged. Further, it is also possible to suppress the adverse influence to the blood pump.  
      Further, according to the artificial blood vessel connecting structure  100 A, since the connecting assist tool  130 A also brings the artificial blood vessel  120  into pressure contact with the tubular connecting member  110 A at the artificial-blood-vessel-side distal end EA of the tubular connecting member  110 A, it is possible to effectively suppress the formation of the minute gap between the artificial blood vessel  120  and the tubular connecting member  110 A. As a result, it is possible to effectively suppress the occurrence of the stagnation of the blood flow and, eventually, the occurrence of the thrombus.  
      In this case, it is considered that, when the artificial blood vessel  120  is bent in the vicinity of the artificial-blood-vessel-side distal end of the tubular connecting member  110 A, a minute gap is formed between the artificial blood vessel  120  and the tubular connecting member  110 A and eventually the blood flow is stagnated thus considerably increasing the possibility of the occurrence of the thrombus. However, even in such a case, the connecting assist tool  130 A brings the artificial blood vessel  120  into pressure contact with the tubular connecting member  110 A also at the artificial-blood-vessel-side distal end EA of the tubular connecting member  110 A and hence, the formation of the minute gap between the artificial blood vessel  120  and the tubular connecting member  110 A can be effectively suppressed. As a result, it is possible to effectively suppress the occurrence of the stagnation of the blood flow and, eventually, the occurrence of the thrombus.  
      In the artificial blood vessel connecting structure  100 A, the connecting assist tool  130 A has the property of narrowing an inner diameter thereof. Due to such a constitution, it is possible to bring the artificial blood vessel  120  into pressure contact with the tubular connecting member  110 A more uniformly and hence, it is possible to further effectively suppress the applying of the undesired stress attributed to twisting or the like to the artificial blood vessel  120 .  
      In the artificial blood vessel connecting structure  100 A, as shown in  FIG. 4A , the connecting assist tool  130 A satisfies the relationship “Za&lt;Zc and Zb−Zc≧−2×t”, wherein assuming an imaginary axis which sets the direction heading for the artificial blood vessel  120  from the tubular connecting member  110 A as the normal direction as a z axis, Za are coordinates of the z axis at a tubular-connecting-member-side end of the connecting assist tool  130 A, Zb are coordinates of the z axis at an artificial-blood-vessel-side end of the connecting assist tool  130 A, Zc are coordinates of the z axis at an artificial-blood-vessel-side distal end EA of the tubular connecting member  110 A, and “t” is a wall thickness of an unconnected portion of the artificial blood vessel  120 .  
      To enable the connecting assist tool  130 A to surely bring the artificial blood vessel  120  into pressure contact with the tubular connecting member  110 A even at the artificial-blood-vessel-side distal end of the tubular connecting member  110 A, it is preferable that the position of the artificial-blood-vessel-side end of the connecting assist tool  130 A is arranged closer to the artificial-blood-vessel-side than the artificial-blood-vessel-side distal end of the tubular connecting member  110 A. However, even when the position of the artificial-blood-vessel-side end of the connecting assist tool  130 A is arranged closer to the tubular-connecting-member side than the artificial-blood-vessel-side distal end of the tubular connecting member  110 A, with the use of the connecting assist tool  130 A which satisfies the relationship “Zb−Zc≧−2×t”, the connecting assist tool  130 A can bring the artificial blood vessel  120  into pressure contact with the tubular connecting member  110 A with a sufficient force even at the artificial-blood-vessel-side distal end of the tubular connecting member  110 A and hence, the occurrence of the minute gap between the artificial blood vessel  120  and the tubular connecting member  110 A can be suppressed whereby it is possible to effectively suppress the occurrence of the stagnation of the blood flow and, eventually, the occurrence of the thrombus.  
      In the artificial blood vessel connecting structure  100 A, as shown in  FIG. 3 , an auxiliary helix  122  is wrapped around an outer periphery of the artificial blood vessel  120 . Due to such a constitution, it is possible to easily maintain an open state of the artificial blood vessel  120  by making use of the resiliency of the auxiliary helix  122  whereby it is possible to effectively suppress the sharp bending of the artificial blood vessel  120 .  
      The artificial blood vessel connecting structure  100 A is also configured such that a relationship “ID 1 &gt;ID 0 ” is satisfied wherein ID 0  is an inner diameter of an unconnected portion of the artificial blood vessel  120 , and ID 1  is an inner diameter of the artificial blood vessel  120  at an artificial-blood-vessel-side distal end of the tubular connecting member  110 A. Due to such a constitution, at the artificial-blood-vessel-side distal end of the tubular connecting member  110 A, the artificial blood vessel  120  is brought into pressure contact with the tubular connecting member  110 A even with a resilient force of the artificial blood vessel  120  per se and hence, the formation of the minute gap between the artificial blood vessel  120  and the tubular connecting member  110 A can be suppressed whereby it is possible to further effectively suppress the occurrence of the stagnation of the blood flow and, eventually, the occurrence of the thrombus.  
      The artificial blood vessel connecting structure  100 A is preferable that a relationship “ID 1 /ID 0 &lt;1+0.11×t 1/2 ” is satisfied wherein t(mm) is a wall thickness of an unconnected portion of the artificial blood vessel  120 . Due to such a constitution, the bending of the artificial blood vessel  120  in the vicinity of the artificial-blood-vessel-side distal end of the tubular connecting member  110 A can be made gentle and hence, it is possible to suppress the occurrence of the stagnation of the blood flow and, eventually, the occurrence of the thrombus. Here, this relationship is an empirical relationship which is introduced by an experiment carried out by inventors of the present invention and does not always have the physical implication.  
      The artificial blood vessel connecting structure  100 A is configured such that relationships “OD 1 &gt;OD 0 ” and “OD 1 &gt;OD 2 ” are satisfied wherein OD 0  is an outer diameter of an unconnected portion of the artificial blood vessel  120 , OD 1  is an outer diameter of a portion which is not subjected to a contact pressure force attributed to the connecting assist tool  130 A out of portions of the artificial blood vessel  120  which is applied to an outer periphery of the tubular connecting member  110 A, and OD 2  is an outer diameter of a portion which is subjected to the contact pressure force attributed to the connecting assist tool  130 A out of the portions of the artificial blood vessel  120  which is applied to the outer periphery of the tubular connecting member  110 A. Due to such a constitution, it is guaranteed that the pressure contact force exerted by the connecting assist tool  130 A is surely applied to the artificial blood vessel  120 . Accordingly, even at the artificial-blood-vessel-side distal end EA of the tubular connecting member  110 A, the artificial blood vessel  120  is surely brought into pressure contact with the tubular connecting member  110 A and hence, the formation of a minute gap between the artificial blood vessel  120  and the tubular connecting member  110 A can be further effectively suppressed whereby the occurrence of the stagnation of the blood flow and, eventually, the occurrence of the thrombus can be further effectively suppressed.  
      In the artificial blood vessel connecting structure  100 A, on the artificial-blood-vessel-side end portion of the tubular connecting member  110 A, a sharpened end portion  112 A whose wall thickness is gradually decreased from the tubular-connecting-member side to the artificial-blood-vessel side is formed. Due to such a constitution, the flow of the blood at a portion where the artificial blood vessel  120  and the tubular connecting member  110 A are connected with each other can be made further smoother and hence, it is possible to further effectively suppress the occurrence of the stagnation of the blood flow and, eventually, the occurrence of the thrombus.  
      Further, the rounding treatment is applied to the sharpened end portion  112 A of the tubular connecting member  110 A (see  FIG. 4B ). Due to such a constitution, a load applied to the artificial blood vessel  120  from the sharpened end portion  112 A of the tubular connecting member  110 A can be alleviated and hence, an undesired biting of the sharpened end portion  112 A of the tubular connecting member  110 A into the artificial blood vessel  120  can be obviated. Accordingly, damage to the artificial blood vessel  120  can be effectively suppressed and hence, the lifetime of the artificial blood vessel connecting structure  100 A can be further prolonged. Further, it is possible to further effectively suppress the occurrence of the stagnation of the blood flow and, eventually, the occurrence of the thrombus at the artificial-blood-vessel-side distal end of the tubular connecting member  110 A. Still further, the assembling operation at the time of connecting the artificial blood vessel  120  with the tubular connecting member  110 A can be facilitated.  
      In the artificial blood vessel connecting structure  100 A, an uneven portion  114 A is formed on an outer peripheral surface of the tubular connecting member  110 A. Due to such a constitution, the artificial blood vessel  120  and the tubular connecting member  110 A are connected with each other by way of the uneven portion  114 A. Accordingly, it is possible to realize the firm connection between the artificial blood vessel  120  and the tubular connecting member  110 A whereby the occurrence of slipping of the artificial blood vessel  120  from the tubular connecting member  110 A can be effectively prevented.  
      The connecting assist tool  130 A of the artificial blood vessel connecting structure  100 A is, as shown in  FIG. 3A , a connecting assist tool which includes two fastening members  134 A 1 ,  134 A 2  which are arranged on an outer peripheral surface of the artificial blood vessel  120  by way of a receiving member  132 A, wherein the connecting assist tool  130 A is arranged on the outer peripheral surface of the artificial blood vessel  120  in a state that a fastening force of the fastening members  134 A 1 ,  134 A 2  is applied to the connecting assist tool  130 A. Due to such a constitution, the fastening force of the fastening members  134 A 1 ,  134 A 2  is transmitted along the radial direction of the tubular connecting member  110 A by way of the receiving member  132 A. Accordingly, the connecting assist tool  130 A brings the artificial blood vessel  120  into pressure contact with the tubular connecting member  110 A along the radial direction of the tubular connecting member  110 A and hence, an undesired stress attributed to twisting or the like is not applied to the artificial blood vessel  120 . As a result, the connection of the artificial blood vessel  120  can be made more uniform and hence, the reliability of the connection between the artificial blood vessel  120  and the tubular connecting member  110 A can be further enhanced. Further, damage to the artificial blood vessel  120  can be effectively suppressed and hence, it is possible to further prolong the lifetime of the artificial blood vessel connecting structure  100 A.  
      In the artificial blood vessel connecting structure  100 A, as the fastening members  134 A 1 ,  134 A 2 , a winding member which applies a fastening force in the direction which makes an inner diameter thereof small is used. However, the present invention is not limited to such a winding member and the fastening members  134 A 1 ,  134 A 2  made of a heat-shrinkable tube which is liable to shrink in the direction to make an inner diameter thereof small, a shape memory alloy which is liable to shrink in the direction to make an inner diameter thereof small, a tube or a ring made of silicone rubber, a tube or a ring made of fluoric rubber can be also preferably used. Further, fastening members which may be wound around with a tie band, strings or wires may be also used as the fastening members  134 A 1 ,  134 A 2 .  
      In the artificial blood vessel connecting structure  100 A, as the artificial blood vessel  120 , an artificial blood vessel made of expanded polytetrafluoroethylene (ePTFE) which exhibits the favorable blood compatibility and the sufficient resiliency is used. Due to such a constitution, it is possible to suppress the occurrence of the thrombus in the inside of the artificial blood vessel  120 . Further, it is possible to obtain the favorable connection performance between the artificial blood vessel  120  and the tubular connecting member  110 A.  
      In the artificial blood vessel connecting structure  100 A, the tubular connecting member  110 A is made of pure titanium which is a material exhibiting a favorable blood compatibility. Due to such a constitution, it is possible to suppress the occurrence of the thrombus in the inside of the tubular connecting member  110 A. In place of pure titanium, it is possible to use the titanium alloy (Ti-6AI-4V alloy being particularly favorable).  
      On a blood contact surface of the artificial blood vessel connecting structure  100 A, a coating film made of phospholipid polymer is formed. Due to such a constitution, it is possible to suppress the occurrence of the thrombus on the blood contact surface of the artificial blood vessel connecting structure  100 A.  
      Then, the artificial blood vessel connecting structure  100 B is explained hereinafter.  
      The artificial blood vessel connecting structure  100 B includes, as shown in  FIG. 3  and  FIG. 5A , a tubular connecting member  110 B, an artificial blood vessel  120 , and a connecting assist tool  130 B which is served for firmly connecting the tubular connecting member  110 B and the artificial blood vessel  120 .  
      The tubular connecting member  110 B is integrally formed with the cannula  40  shown in  FIG. 1 .  
      The cannula  40  is, as shown in  FIG. 1 , a member which allows a portion thereof to face the inside of the left ventricle A and is interposed between the artificial blood vessel  120  which constitutes a portion of the artificial blood vessel system  30  (see  FIG. 3 ) and the heart. The cannula  40  is formed of a cylindrical member which is wholly made of pure titanium or titanium alloy. Due to such a constitution, the cannula  40  can obtain the favorable blood compatibility and hence, the occurrence of the thrombus inside and outside the cannula  40  can be suppressed. Further, as shown in  FIG. 3 , in the inside of a heart-side opening portion of the cannula  40 , a taper portion  116 B which has an inner diameter thereof gradually increased from the artificial-blood-vessel side to the heart side is formed. On a middle portion of the cannula  40 , a cannula mounting cuff  44  made of felt is mounted using an annular screw  42 . The cannula mounting cuff  44  is stitched to the heart.  
      In the artificial blood vessel connecting structure  100 B, the connecting assist tool  130 B brings the artificial blood vessel  120  into pressure contact with the tubular connecting member  110 B along the radial direction of the tubular connecting member  110 B and, at the same time, brings the artificial blood vessel  120  into pressure contact with the tubular connecting member  110 B at the artificial-blood-vessel-side distal end EB (see  FIG. 5B ) of the tubular connecting member  110 B.  
      Accordingly, in the artificial blood vessel connecting structure  100 B, in the same manner as the case of the artificial blood vessel connecting structure  100 A, since the connecting assist tool  130 B brings the artificial blood vessel  120  into pressure contact with the tubular connecting member  110 B along the radial direction of the tubular connecting member  110 A, an undesired stress attributed to twisting or the like is not applied to the artificial blood vessel  120 . As a result, the connection of the artificial blood vessel  120  becomes more uniform and hence, the reliability of the connection of the artificial blood vessel connecting structure  100 B can be enhanced. Further, damage to the artificial blood vessel  120  can be effectively suppressed whereby the lifetime of the artificial blood vessel connecting structure  100 B can be prolonged.  
      Further, according to the artificial blood vessel connecting structure  100 B, in the same manner as the artificial blood vessel connecting structure  100 A, since the connecting assist tool  130 B also brings the artificial blood vessel  120  into pressure contact with the tubular connecting member  110 B at the artificial-blood-vessel-side distal end EB of the tubular connecting member  110 B, it is possible to effectively suppress the formation of the minute gap between the artificial blood vessel  120  and the tubular connecting member  110 B. As a result, it is possible to effectively suppress the occurrence of the stagnation of the blood flow and, eventually, the occurrence of the thrombus.  
      In this case, it is considered that, when the artificial blood vessel  120  is bent in the vicinity of the artificial-blood-vessel-side distal end of the tubular connecting member  110 B, a minute gap is formed between the artificial blood vessel  120  and the tubular connecting member  110 B and eventually the blood flow is stagnated thus considerably increasing the possibility of the occurrence of the thrombus. However, even in such a case, according to the artificial blood vessel connecting structure  100 B, the connecting assist tool  130 B brings the artificial blood vessel  120  into pressure contact with the tubular connecting member  110 B also at the artificial-blood-vessel-side distal end EB of the tubular connecting member  110 B and hence, the formation of the minute gap between the artificial blood vessel  120  and the tubular connecting member  110 B can be effectively suppressed. As a result, it is possible to effectively prevent the occurrence of the stagnation of the blood flow and, eventually, the occurrence of the thrombus.  
      In the artificial blood vessel connecting structure  100 B, the connecting assist tool  130 B has the property of narrowing an inner diameter thereof. Due to such a constitution, it is possible to bring the artificial blood vessel  120  into pressure contact with the tubular connecting member  110 B more uniformly and hence, it is possible to further effectively prevent the applying of the undesired stress attributed to twisting or the like to the artificial blood vessel  120 .  
      Here, in the artificial blood vessel connecting structure  100 B, the tubular connecting member  110 B and the cannula  40  are integrally formed. However, the present invention is not limited to such a constitution, and the tubular connecting member  110 B and the cannula  40  may be formed separately.  
      As described above, the artificial blood vessel system  30  according to the embodiment 1 is the artificial blood vessel system which exhibits the prolonged lifetime, has high reliability in connection and can effectively suppress the occurrence of the thrombus and, at the same time, can be easily connected with the blood pump. Accordingly, by incorporating such an excellent artificial blood vessel system  30  into the blood pump, at the time of embedding the blood pump into the living body, it is possible to obtain the excellent blood pump system which can reduce a burden imposed on an operator at the time of embedding the blood pump into a living body and can suppress the occurrence of the thrombus after embedding the blood pump into the living body.  
     Embodiment 2  
      The embodiment 2 according to the present invention is explained in conjunction with  FIG. 6 .  
       FIG. 6  is a view for explaining an artificial blood vessel system according to the embodiment 2 of the present invention. In  FIG. 6 , parts which are identical with the parts shown in  FIG. 3  are given the same symbols and their detailed explanation is omitted.  
      The artificial blood vessel system  32  according to the embodiment 2 differs from the artificial blood vessel system  30  according to the embodiment 1 in the configuration and the number of the connecting assist tools. That is, in the artificial blood vessel system  30  according to the embodiment 1, one connecting assist tool  130 A having one receiving member  132 A which is relatively long in the z direction and two fastening members  134 A 1 ,  134 A 2  is used (in case of the artificial blood vessel connecting structure  100 A). The same goes for the artificial blood vessel connecting structure  100 B.  
      On the other hand, in the artificial blood vessel system  32  according to the embodiment 2, two connecting assist tools  230 A 1 ,  230 A 2  including two receiving members  232 A 1 ,  232 A 2  which are relatively short in the z direction and two fastening members  234 A 1 ,  234 A 2  which are arranged corresponding to these two receiving members  232 A 1 ,  232 A 2  respectively are used (in case of the artificial blood vessel connecting structure  200 A). The same goes for the artificial blood vessel connecting structure  200 B.  
      In this manner, although the artificial blood vessel system  32  is provided with the connecting assist tools  230 A 1 ,  230 A 2  having the configuration and the number different from the connecting assist tool in the artificial blood vessel system  30 , in the same manner as the artificial blood vessel system  30 , these connecting assist tools  230 A 1 ,  230 A 2  function so as to bring the artificial blood vessel  120  into pressure contact with the tubular connecting member  110 A along the radial direction of the tubular connecting member  110 A and, at the same time, at the artificial-blood-vessel-side distal end of the tubular connecting member  110 A.  
      This is because that the connecting assist tools  230 A 1 ,  230 A 2  are cooperatively operated so as to bring the artificial blood vessel  120  into pressure contact with the tubular connecting member  110 A along the radial direction of the tubular connecting member  110 A and, at the same time, the connecting assist tool  230 A 2  out of the connecting assist tools  230 A 1 ,  230 A 2  functions so as to bring the artificial blood vessel  120  into pressure contact with the tubular connecting member  110 A at the artificial-blood-vessel-side distal end of the tubular connecting member  110 A.  
      Accordingly, also in the artificial blood vessel system  32 , the substantially same advantageous effects as those of the artificial blood vessel system  30  can be obtained.  
     Embodiment 3  
      The embodiment 3 of the present invention is explained in conjunction with  FIG. 7 .  
       FIG. 7  is a view for explaining an artificial blood vessel system according to the embodiment 3 of the present invention. In  FIG. 7 , parts which are identical with the parts shown in  FIG. 3  are given the same symbols and their detailed explanation is omitted.  
      The artificial blood vessel system  34  according to the embodiment 3 differs from the artificial blood vessel system  32  according to the embodiment 2 in the constitution of the connecting assist means. That is, in the artificial blood vessel system  32  according to the embodiment 2, as the constitution of the connecting assist means, two connecting assist tools  230 A 1 ,  230 A 2  including two receiving members  232 A 1 ,  232 A 2  which are relatively short in the z direction and two fastening members  234 A 1 ,  234 A 2  which are arranged corresponding to these two receiving members  232 A 1 ,  232 A 2  respectively are used (in case of the artificial blood vessel connecting structure  200 A). The same goes for the artificial blood vessel connecting structure  200 B.  
      On the other hand, in the artificial blood vessel system  34  according to the embodiment 3, as the constitution of the connecting assist means, connecting assist means which is constituted of a connecting assist tool  330 A including one receiving member  332 A which is relatively short in the z direction and one fastening member  334 A which is arranged corresponding to this receiving member  332 A and a connecting assist portion  322 A which forms a portion of the auxiliary helix  322  which is arranged close to the contact portion with the connecting assist tool  330 A is used (in case of the artificial blood vessel connecting structure  300 A). The same goes for the artificial blood vessel connecting structure  300 B.  
      In this manner, the artificial blood vessel system  34  is provided with the connecting assist means having the constitution different from the constitution of the artificial blood vessel system  32  (the connecting assist tool  330 A and the connecting assist portion  322 A which is formed of the portion the auxiliary helix). In the same manner as the artificial blood vessel system  32 , these connecting assist means (the connecting assist tool  330 A and the connecting assist portion  322 A which is formed of the portion the auxiliary helix) function so as to bring the artificial blood vessel  120  into pressure contact with the tubular connecting member  110 A along the radial direction of the tubular connecting member  110 A and, at the same time, at the artificial-blood-vessel-side distal end of the tubular connecting member  110 A.  
      This is because that the connecting assist tools  330 A and the connecting assist portion  322 A which is formed of the portion the auxiliary helix are cooperatively operated so as to bring the artificial blood vessel  120  into pressure contact with the tubular connecting member  110 A along the radial direction of the tubular connecting member  110 A and, at the same time, the connecting assist portion  322 A which is formed of the portion the auxiliary helix functions so as to bring the artificial blood vessel  120  into pressure contact with the tubular connecting member  110 A at the artificial-blood-vessel-side distal end of the tubular connecting member  110 A.  
      In this manner, in the artificial blood vessel connecting structure  300 A, the connecting assist tool  330 A is configured to satisfy the relationship “Zb&lt;Zc”, wherein assuming an imaginary axis which sets the direction heading for the artificial blood vessel  120  from the tubular connecting member  110 A as the normal direction as a z axis, Zb are coordinates of the z axis at an artificial-blood-vessel-side end of the connecting assist tool  330 A, and Zc are coordinates of the z axis at an artificial-blood-vessel-side distal end of the tubular connecting member  110 A. Accordingly, although the connecting assist tool  330 A when used in a single form does not perform a function of bringing the artificial blood vessel  120  into pressure contact with the tubular connecting member  110 A at the artificial-blood-vessel-side distal end of the tubular connecting member  110 A, the connecting assist portion  322 A which is formed of the portion the auxiliary helix functions so as to bring the artificial blood vessel  120  into pressure contact with the tubular connecting member  110 A at the artificial-blood-vessel-side distal end of the tubular connecting member  110 A.  
      The same goes for the artificial blood vessel connecting structure  300 B.  
      Accordingly, in the artificial blood vessel system  34  of the embodiment 3 also, the substantially same advantageous effects as the artificial blood vessel system  30  of the embodiment 1 or artificial blood vessel system  32  of the embodiment 2 can be obtained.  
      As has been described heretofore, by using the respective artificial blood vessel systems according to the embodiments 1 to 3, the reliability of connection between the artificial blood vessel and the tubular connecting member in the artificial blood vessel system can be enhanced. Further, the damage to the artificial blood vessel can be effectively suppressed and the lifetime of the artificial blood vessel system can be prolonged. Still further, the occurrence of the stagnation of the blood flow and, eventually, the occurrence of the thrombus can be effectively suppressed. Still further, even when the artificial blood vessel is bent in the vicinity of the artificial-blood-vessel-side distal end of the tubular connecting member, the occurrence of the stagnation of the blood flow and, eventually, the occurrence of the thrombus can be effectively suppressed.  
     Embodiment 4  
       FIG. 8  is a view showing the connection portion (artificial blood vessel connecting structure) between the blood pump and the artificial blood vessel used in the blood pump system according to the embodiment 4. Here, in  FIG. 8 , to simplify the view, the auxiliary helix is omitted.  
      The blood pump system according to the embodiment 4 is, as shown in  FIG. 8 , a blood pump system which includes a blood pump having a tubular connecting member  410  at a suction-side distal end portion of the pump casing  24 , an artificial blood vessel  120  which is connected with the tubular connecting member  410 , and a connecting assist tool  430  for strengthening the connection between the artificial blood vessel  120  and the tubular connecting member  410 . The connecting assist tool  430  is, in the same manner as the embodiment 1, constituted so as to bring the artificial blood vessel  120  into pressure contact with the tubular connecting member  410  along the radial direction of the tubular connecting member  410  and, at the same time, at the artificial blood vessel side distal end of the tubular connecting member  410 .  
      Accordingly, the blood pump system according to the embodiment 4 is provided with the artificial blood vessel connecting structure  400  which can prolong the lifetime and can exhibit the high connection reliability and, further, can effectively suppress the occurrence of the thrombus. Accordingly, this embodiment 4 also can provide the highly reliable excellent blood pump system which can suppress the occurrence of the thrombus.  
      Here, the embodiments 1 to 4 have been explained with respect to the case in which the artificial blood vessel  120  is connected to the suction side of the blood pump as an example. However, the present invention is not limited to such a constitution and the substantially equal advantageous effects can be obtained with respect to a case in which the artificial blood vessel  120  is connected to the discharge side of the blood pump.