Patent Publication Number: US-2022226614-A1

Title: Catheter assembly

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a Divisional of U.S. patent application Ser. No. 16/552,066, filed on Aug. 27, 2019, which is a bypass continuation of PCT Application No. PCT/JP2018/010386, filed on Mar. 16, 2018, which claims priority to Japanese Application No. 2017-051420, filed on Mar. 16, 2017. The contents of these applications are hereby incorporated by reference in their entireties. 
    
    
     BACKGROUND 
     The present disclosure relates to a catheter assembly configured to be punctured and remain indwelled in a blood vessel when performing an infusion or the like to a patient, for example. 
     Conventionally, a catheter assembly used when performing an infusion or the like to a patient has been known. This kind of catheter assembly includes a hollow catheter, a catheter hub fixed to a proximal end of the catheter, a hollow inner needle that is inserted into the catheter and has a sharp needle tip at a distal end, and a needle hub fixed to a proximal end of the inner needle (for example, see JP 2008-43445 A). When using a catheter assembly, skin and a blood vessel of a living body are punctured with each distal end of the inner needle and the catheter, and then, the catheter is advanced with respect to the inner needle so that the catheter is inserted into the blood vessel by a predetermined length. 
     SUMMARY 
     In a conventional catheter assembly having an inner needle and a catheter, a catheter distal end is sometimes caught by a blood vessel back wall (a blood vessel wall opposing a puncture site) when a puncture angle is large. As a result, the catheter may be difficult to insert into a blood vessel, or the blood vessel wall may be damaged by the catheter distal end. 
     Certain embodiments of the present disclosure have been developed in consideration of such problems, and one object thereof is to provide a catheter assembly capable of deterring a catheter distal end from being caught by a blood vessel back wall at the time of advancing a catheter to a blood vessel even when a puncture angle is large. 
     According to one embodiment, a catheter assembly includes: a catheter; and an inner needle inserted into the catheter. The catheter includes: a catheter body; and a flexible portion that is provided at a distal portion of the catheter body, includes a most distal portion of the catheter, and is more flexible than the catheter body. 
     According to the catheter assembly having the above configuration, the flexible portion, which is more flexible than the catheter body, is provided at the distal portion of the catheter body, and thus, it is possible to deter a distal end of the catheter from being caught by a blood vessel back wall even when a puncture angle is large. As a result, it is possible to deter the catheter from being difficult to insert into a blood vessel, or to deter a blood vessel wall from being damaged by the catheter distal end. 
     A flow path for flashback confirmation may be formed between the catheter and the inner needle, the inner needle may be provided with an introduction path that communicates with the flow path to introduce blood into the flow path, and a proximal end of the introduction path may be provided on a proximal side of an axial center position of a portion of the flexible portion present on a distal side of a most distal portion of the catheter body. 
     With this configuration, it is possible to deter the catheter from blocking the introduction path at the time of puncture, and thus, it is possible to easily confirm the flashback of blood. 
     A flow path for flashback confirmation may be formed between the catheter and the inner needle, the inner needle may be provided with an introduction path that communicates with the flow path to introduce blood into the flow path, the catheter may have a close contact portion where at least a part of an inner peripheral surface is in close contact with an outer peripheral surface of the inner needle, and at least a proximal end of the introduction path may be provided on a proximal side of the close contact portion. 
     With this configuration, it is possible to deter the catheter from blocking the introduction path at the time of puncture, and thus, it is possible to easily confirm the flashback of blood. 
     The catheter may have a close contact portion where at least a part of an inner peripheral surface is in close contact with an outer peripheral surface of the inner needle, and both the flexible portion and the catheter body may be in close contact with the inner needle at the close contact portion. 
     With this configuration, an appropriate fitting force between the inner needle and the catheter can be obtained. 
     The catheter may have a mixed region in which the catheter body and the flexible portion overlap each other in a radial direction. 
     With this configuration, a change in rigidity from the catheter body to the flexible portion can be made gradual, and thus, it is possible to more favorably deter the catheter distal end from being caught by the blood vessel back wall at the time of inserting the catheter into the blood vessel. 
     An axial length of the portion of the flexible portion present on the distal side of the most distal portion of the catheter body may be 0.3 to 5.0 mm. 
     With this configuration, it is possible to suppress curling of the distal end (flexible portion) of the catheter at the time of puncture. In addition, it is possible to more preferably suppress the catching by the blood vessel back wall at the time of inserting the catheter. Further, it is possible to suppress crushing of the catheter distal end at the time of blood suction. 
     The catheter may have a mixed region in which the catheter body and the flexible portion overlap each other in a radial direction, and an interface between the catheter body and the flexible portion in the mixed region may be formed in a tapered shape inclined with respect to an axis of the catheter. 
     With this configuration, the change in rigidity from the catheter body to the flexible portion can be made more gradual. 
     A boundary between the catheter body and the flexible portion or a boundary between a first flexible portion and a second flexible portion may be coated. The whole catheter may be coated seamlessly. 
     With this configuration, it is possible to eliminate a step between the catheter body and the flexible portion on an inner peripheral surface and an outer peripheral surface of the catheter. Because the step is eliminated, it is possible to deter thrombus and to reduce a penetration resistance at the time of puncture. 
     A creep strain of the catheter body may be greater than a creep strain of the flexible portion. 
     With this configuration, the catheter body is easily adapted to a shape of the blood vessel after the catheter is inserted into the blood vessel to remain indwelled. Thus, it is possible to reduce a sense of incompatibility given to the patient during indwelling of the catheter. In addition, crushing of the catheter distal end can be reduced. 
     The interface between the catheter body and the flexible portion may be provided with a region having a different acoustic impedance from the catheter body and the flexible portion. 
     With this configuration, the above-described region having the different acoustic impedance functions as an echogenic portion, and thus, it is possible to improve the visibility of the distal portion of the catheter under ultrasound fluoroscopy. 
     At least the flexible portion between the catheter body and the flexible portion may be provided with a deformation suppressing member that suppresses a radial deformation. 
     With this configuration, it is possible to suppress curling of the catheter distal end (flexible portion) at the time of puncture, and to suppress crushing of the catheter distal end at the time of blood suction. 
     The inner needle may be provided with a backcut portion. 
     A cover may be provided on an outer surface of the flexible portion, and a friction coefficient of a surface of the cover may be set to be smaller than a friction coefficient of a surface of the flexible portion. 
     A cover may be provided on an outer surface of the flexible portion and an outer surface of the catheter body, a friction coefficient of a surface of the catheter body may be smaller than a friction coefficient of a surface of the flexible portion, and a friction coefficient of a surface of the cover may be smaller than the friction coefficient of the surface of the catheter body. 
     At least a part of the flexible portion may be in close contact with the inner needle. 
     According to the catheter assembly of the present invention, it is possible to deter the catheter distal end from being caught by the blood vessel back wall at the time of advancing the catheter to the blood vessel even when the puncture angle is large. 
     The flexible portion may have a flexible tapered portion that is inclined with respect to the axis of the catheter such that an outer diameter decreases in a distal direction, the flexible tapered portion may have a first flexible tapered portion including the most distal portion and a second flexible tapered portion provided to be adjacent to a proximal side of the first flexible tapered portion, and an inclination angle of an outer peripheral surface of the first flexible tapered portion with respect to the axis may be larger than that of the second flexible tapered portion. 
     With this configuration, the first flexible tapered portion is relatively thick, and thus, it is possible to suppress the curling of the catheter distal end at the time of puncture. The second flexible tapered portion has the relatively small inclination angle, and thus, the penetration resistance can be reduced. 
     The catheter body may have a body tapered portion that is inclined with respect to the axis of the catheter such that an outer diameter decreases in the distal direction and is arranged on a radially inner side of the flexible tapered portion, the body tapered portion may have a first body tapered portion and a second body tapered portion provided to be adjacent to a proximal side of the first body tapered portion, and an inclination angle of an outer peripheral surface of the first body tapered portion with respect to the axis may be larger than that of the second body tapered portion. 
     With this configuration, the inclination angle of the first body tapered portion is relatively large, and thus, it is possible to support the flexible portion from the inner side at the time of blood suction and to suppress a collapse of the flexible portion. Because the inclination angle of the second body tapered portion is relatively small, the gradual transition from a physical property of the flexible portion to a physical property of the catheter body becomes possible, and a kink of the catheter can be suppressed. 
     The inclination angle of the first body tapered portion may be smaller than the inclination angle of the first flexible tapered portion. 
     An inner peripheral surface of the flexible tapered portion and an inner peripheral surface of the first body tapered portion may be in close contact with the outer peripheral surface of an inner needle. 
     With this configuration, an appropriate fitting force between the inner needle and the catheter can be obtained. 
     A flow path for flashback confirmation may be formed between the catheter and the inner needle, the inner needle may be provided with a side hole that communicates with the flow path and to introduce blood into the flow path, and the side hole may be provided on a proximal side of a most distal portion of the body tapered portion. 
     With this configuration, the side hole is provided at a position opposing the relatively hard catheter body. Therefore, it is possible to deter the catheter from blocking the side hole at the time of puncture, and thus, it is possible to easily confirm the flashback of blood. 
     The distal portion of the catheter may have a close contact portion in close contact with an outer peripheral surface of the inner needle, the outer peripheral surface of the inner needle may be provided with an ultrasound reflection promoting portion having an uneven shape, and a distal portion of the ultrasound reflection promoting portion may be provided on a proximal side of a proximal portion of the close contact portion. 
     With this configuration, the close contact portion and the ultrasound reflection promoting portion do not overlap each other so that the uneven shape of the ultrasound reflection promoting portion does not contribute to a resistance at the time of removing the inner needle, and the removal operation is stabilized. 
     The flexible portion may have a color that is more easily visible than the catheter body, and the catheter body may have transparency that allows an inside of the catheter body to be visible. 
     Because the flexible portion is colored to be easily noticeable while securing the flashback visibility by giving the transparency to the catheter body, it is easy to perform puncture with respect to a target blood vessel. In addition, it is easy to understand that the flexible portion is provided at the distal portion of the catheter, and thus, it is possible to appeal to a user that a function of deterring a blood vessel injury is high. 
     The flexible portion may have a higher X-ray contrast property than the catheter body. 
     It is possible to enhance the contrast property by X-rays at the time of breaking the catheter while securing the flashback visibility by setting the flexible portion to have the higher X-ray contrast property than the catheter body. 
     A deflection suppressing mechanism that is capable of supporting the catheter at the time of puncture and suppresses deflections of the inner needle and the catheter may be provided, and the deflection suppressing mechanism may be arranged on a proximal side of the flexible portion in an initial state of the catheter assembly. 
     With this configuration, it is possible to deter the deflection suppressing mechanism from damaging the flexible portion at the time of advancing the catheter with respect to the inner needle. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective view of a catheter assembly according to an embodiment of the present invention; 
         FIG. 2A  is a cross-sectional view of a distal portion of the catheter assembly;  FIG. 2B  is an explanatory view of a shape of a distal portion of an inner needle; 
         FIG. 3  is a cross-sectional view of a distal portion in another configuration of the catheter assembly; 
         FIG. 4  is a cross-sectional view of a distal portion in yet another configuration of the catheter assembly; 
         FIG. 5  is an explanatory view of a function of the catheter assembly; 
         FIG. 6A  is a cross-sectional view of a catheter having another interface shape,  FIG. 6B  is a cross-sectional view of a catheter having still another interface shape,  FIG. 6C  is a cross-sectional view of a catheter having yet still another interface shape, and  FIG. 6D  is a cross-sectional view of a catheter having even yet still another interface shape; 
         FIG. 7A  is a cross-sectional view of a catheter having a deformation suppressing member, and  FIG. 7B  is a cross-sectional view of a catheter having another deformation suppressing member; 
         FIG. 8  is an explanatory view of a form variation of the deformation suppressing member; 
         FIG. 9A  is a first explanatory view of a method of manufacturing the catheter,  FIG. 9B  is a second explanatory view of the method of manufacturing the catheter, and  FIG. 9C  is a third explanatory view of the method of manufacturing the catheter; 
         FIG. 10A  is a fourth explanatory view of the method of manufacturing the catheter,  FIG. 10B  is a fifth explanatory view of the method of manufacturing the catheter, and  FIG. 10C  is a sixth explanatory view of the method of manufacturing the catheter; 
         FIG. 11A  is a seventh explanatory view of the method of manufacturing the catheter, and  FIG. 11B  is an eighth explanatory view of the method of manufacturing the catheter; 
         FIG. 12A  is an explanatory view of a method of manufacturing a second tube member having a deformation suppressing member,  FIG. 12B  is an explanatory view of a method of manufacturing another second tube member having a deformation suppressing member,  FIG. 12C  is an explanatory view of a method of manufacturing still another second tube member having a deformation suppressing member, and  FIG. 12D  is an explanatory view of a method of manufacturing yet still another second tube member having a deformation suppressing member; 
         FIG. 13  is a cross-sectional view of a catheter having an echogenic portion; 
         FIG. 14A  is a cross-sectional view of a catheter provided with a flexible portion having a plurality of regions different in hardness, and  FIG. 14B  is a cross-sectional view of a catheter provided with another flexible portion having a plurality of regions different in hardness; 
         FIG. 15  is a cross-sectional view of a distal portion of a catheter assembly according to another embodiment of the present invention; 
         FIG. 16  is a cross-sectional view of a distal portion of a catheter assembly according to still another embodiment of the present invention; 
         FIG. 17  is a cross-sectional view of a distal portion of a catheter assembly according to yet still another embodiment of the present invention; 
         FIG. 18  is a table illustrating test results associated with the catheter assembly illustrated in  FIG. 17 ; and 
         FIG. 19  is an overall schematic view of a catheter assembly according to even yet still another embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, preferred embodiments of a catheter assembly according to the present invention will be described with reference to the accompanying drawings. 
     The catheter assembly  10  whose initial state is illustrated in  FIG. 1  is applied when performing an infusion, a blood transfusion, and the like to a patient (living body), and constructs an introduction portion of a medicinal liquid or the like by being tapped into the patient&#39;s body to remain indwelled. The catheter assembly  10  may be configured as a catheter (for example, a central venous catheter, a PICC, a mid-line catheter, and the like) having a longer length than a peripheral venous catheter. Incidentally, the catheter assembly  10  may be configured as the peripheral venous catheter. In addition, the catheter assembly  10  is not limited to the venous catheter, and may be configured as an arterial catheter such as a peripheral arterial catheter. 
     As illustrated in  FIG. 1 , the catheter assembly  10  includes a catheter  12 , a catheter hub  14  fixedly holding the catheter  12 , a hollow inner needle  16  removably inserted into the catheter  12 , a needle hub  18  fixedly holding the inner needle  16 , and a catheter operation member  20  mounted to the catheter hub  14 . The inner needle  16  may be a solid needle. 
     The catheter assembly  10  forms a multi-tube structure (multi-tube portion) in which the catheter  12  and the inner needle  16  are sequentially stacked in an initial state before use. 
     The catheter  12  has flexibility and in which a lumen  13  is formed to penetrate therethrough. The lumen  13  is formed to have a diameter capable of housing the inner needle  16  and capable of causing a medicinal liquid, blood, or the like to flow. A distal end of the catheter  12  is reduced in diameter in order to decrease a puncture resistance, and an inner surface of the catheter  12  is in close contact with an outer surface of the inner needle  16  at such a reduced diameter portion in the initial state of the catheter assembly  10 . A length of the catheter  12  is not particularly limited but can be appropriately designed according to use and various conditions, and is set to, for example, about 14 to 500 mm, about 30 to 400 mm, or about 76 to 200 mm. 
     A proximal portion of the catheter  12  is fixed to a distal portion inside the catheter hub  14 . The catheter  12  and the catheter hub  14  form a catheter member  17 . 
     The catheter hub  14  is exposed on the patient&#39;s skin in a state where the catheter  12  has been inserted into a blood vessel, and indwelled together with the catheter  12  by being pasted with a tape or the like. The catheter hub  14  is formed in a tubular shape tapered in a distal direction. 
     A constituent material of the catheter hub  14  is not particularly limited, but a thermoplastic resin, such as polypropylene, polycarbonate, polyamide, polysulfone, polyarylate, a methacrylate-butylene-styrene copolymer, and polyurethane may be preferably applied. 
     A hollow portion  15  that communicates with the lumen  13  of the catheter  12  and through which an infusion solution can flow is provided inside the catheter hub  14 . A hemostatic valve, a plug, or the like (not illustrated) may be housed inside the hollow portion  15  in order to deter back-flow of blood at the time of puncture with the inner needle  16  and to allow infusion along with insertion of a connector of an infusion tube. 
     The inner needle  16  is configured as a hollow tube having rigidity that enables puncture of a skin of a living body, and is arranged to penetrate through the lumen  13  of the catheter  12  and the hollow portion  15  of the catheter hub  14 . The inner needle  16  is formed to have a total length longer than that of the catheter  12 , and a sharp needle tip  16   a  is provided at a distal end thereof. A lumen penetrating in an axial direction of the inner needle  16  is provided inside the inner needle  16 , and this lumen communicates with a distal opening of the inner needle  16 . 
     Examples of a constituent material of the inner needle  16  include a metal material such as stainless steel, aluminum or an aluminum alloy, and titanium or a titanium alloy, a hard resin, ceramics, and the like. 
     The needle hub  18  has a needle holding member  22  fixed to a proximal portion of the inner needle  16 , and a housing  24  to which the needle holding member  22  is fixed and that extends along the inner needle  16  and the catheter  12 . The catheter assembly  10  houses a part of the multi-tube portion, the catheter hub  14 , and the catheter operation member  20  in the housing  24  in the initial state. Resin materials forming the needle holding member  22  and the housing  24  are not particularly limited, but, for example, the materials exemplified for the catheter hub  14  can be appropriately selected. Incidentally, the needle holding member  22  and the housing  24  may be integrally formed. 
     When the needle hub  18  is moved to a proximal direction with respect to the catheter  12 , the inner needle  16  is also moved in the proximal direction with respect to the catheter  12  along with the movement of the needle hub  18  because the needle hub  18  holds the inner needle  16  at the needle holding member  22 . 
     The catheter operation member  20  is attached to the catheter hub  14 . Thus, when the catheter operation member  20  is advanced relative to the needle hub  18 , the catheter member  17  is advanced relative to the inner needle  16 . The catheter operation member  20  has a hub mounting portion  20   a  detachably mounted on the catheter hub  14 , and an operation plate portion  20   b  extending from the hub mounting portion  20   a  along the catheter  12  in the distal direction. Incidentally, the catheter operation member  20  is not necessarily provided in the catheter assembly  10 . 
     The catheter assembly  10  is provided with a support member  26  on the distal side of the housing  24  in order to support a lower side of the catheter  12  held by the catheter operation member  20 . The support member  26  is rotatably attached to an arrangement recess portion  24   a  provided at a distal portion of the housing  24 . A distal portion of the catheter operation member  20  and the support member  26  constitute a deflection suppressing mechanism  27 . 
     When the skin is punctured with the inner needle  16  and the catheter  12 , the distal portion of the catheter operation member  20  supports the catheter  12  from above and the support member  26  supports the catheter  12  from below, and thus, deflections of the catheter  12  and the inner needle  16  are suppressed. When the catheter operation member  20  is removed out of the housing  24 , the support member  26  is rotated toward an outer side of the housing  24  by being pushed by the hub mounting portion  20   a , and thus, the catheter hub  14  can be withdrawn from the housing  24  in the distal direction. Incidentally, the support member  26  is not necessarily provided. 
     As illustrated to  FIG. 2A , the catheter  12  has a close contact portion  30 , which is in close contact with an outer peripheral surface of the inner needle  16 , in at least a part of an inner peripheral surface. The close contact portion  30  is provided on the inner peripheral surface of a distal portion of the catheter  12 . A flow path for flashback confirmation (hereinafter, referred to as “flashback flow path  32 ”) is formed between the catheter  12  and the inner needle  16  on the proximal side of the close contact portion  30 . The flashback flow path  32  extends up to a proximal opening of the catheter  12 . 
     The catheter  12  has a catheter body  34  that constitutes a main portion of the catheter  12  and a flexible portion  38  provided at a distal portion of the catheter body  34 . Thus, the catheter  12  becomes more flexible toward the most distal portion on the distal side. The flexible portion  38  is exposed from the housing  24  ( FIG. 1 ). 
     The catheter body  34  accounts for most of the whole length of the catheter  12 . Thus, the most distal portion of the catheter body  34  is positioned near the most distal end of the catheter  12 . The catheter  12  and the flexible portion  38  are made of a resin material having flexibility. A creep strain of the catheter body  34  is greater than a creep strain of the flexible portion  38 . 
     The catheter body  34  has: a straight portion  34   a  that has a constant outer diameter along the axial direction; a tapered portion  34   b  that extends from the straight portion  34   a  in the distal direction and has an outer diameter decreasing in the distal direction; and a distal constituting portion  34   c  that extends from the tapered portion  34   b  in the distal direction and constitutes a portion up to the most distal portion of the catheter body  34 . An inner peripheral surface of the distal constituting portion  34   c  and the outer peripheral surface of the inner needle  16  are in close contact with (fitted to) each other in a liquid-tight manner over the entire peripheral. 
     The flashback flow path  32  is formed between an inner peripheral surface of the catheter body  34  (specifically, the straight portion  34   a  and the tapered portion  34   b ) and the outer peripheral surface of the inner needle  16 . At least the catheter body  34  between the catheter body  34  and the flexible portion  38  has transparency such that a flashback can be confirmed. 
     The catheter  12  is supported by the support member  26  ( FIG. 1 ) at a spot of the catheter body  34  (the catheter body  34  is supported by the support member  26 ). As a result, it is possible to reliably support the catheter  12  and to reduce a sliding resistance at the time of advancing the catheter  12 . Moreover, the portion supported by the support member  26  ( FIG. 1 ) is located on the proximal side of an interface  42  between the catheter body  34  and the flexible portion  38 , and thus, it is possible to deter peeling of the interface  42  caused by sliding of the catheter  12  with respect to the support member  26 . 
     It is preferably that the catheter body  34  be less likely to swell as compared to the flexible portion  38 . As a result, it is possible to set an axial distance between a most distal position of the inner needle  16  and a most distal position of the catheter  12  to a desired size and to reduce a variation for each product during steam sterilization (autoclave sterilization) or ethylene oxide gas sterilization in a process of manufacturing the catheter assembly  10 . 
     Examples of a constituent material of the catheter body  34  include a fluorine-based resin such as polytetrafluoroethylene (PTFE), an ethylene-tetrafluoroethylene copolymer (ETFE), and a perfluoroalkoxy fluorine resin (PFA), an olefin-based resin such as polyethylene and polypropylene or a mixture thereof, polyurethane, polyester, polyamide, a polyether nylon resin, a mixture of the olefin-based resin and an ethylene-vinyl acetate copolymer, and the like. The hardness (Shore A) of the catheter body  34  is, for example, less than 70 D. 
     The flexible portion  38  forms the most distal portion of the catheter  12 . The flexible portion  38  is more flexible than the catheter body  34 . That is, an elastic modulus k 1  of the catheter body  34  and an elastic modulus k 2  of the flexible portion  38  have a relationship of k 1 &gt;k 2 . 
     The flexible portion  38  has: a straight portion  38   a  that has a constant outer diameter along the axial direction; and a tapered portion  38   b  that extends from the straight portion  38   a  in the distal direction and has an outer diameter decreasing in the distal direction. An inner peripheral surface of the flexible portion  38  and the outer peripheral surface of the inner needle  16  are in close contact with (fitted to) each other in a liquid-tight manner over the entire periphery of the inner needle  16 . 
     It is preferable that at least the flexible portion  38  between the catheter body  34  and the flexible portion  38  have an X-ray contrast property. As a result, for example, when the catheter  12  is broken in a blood vessel, it is possible to easily confirm a location of the catheter  12 , which has been broken and left in the blood vessel, by X-ray. A contrast layer in the case where the flexible portion  38  has the contrast property may be provided, for example, in any form of a stripe shape, an intermediate layer in the radial direction, or the whole layer. 
     Examples of a constituent material of the flexible portion  38  include various rubber materials such as natural rubber, butyl rubber, isoprene rubber, butadiene rubber, styrene-butadiene rubber, silicone rubber, various thermoplastic elastomers such as polyurethanes, polyesters, polyamides, olefins, and styrenes or a mixture thereof, and the like. 
     In the catheter  12 , a single catheter body region  40 A where only the catheter body  34  between the catheter body  34  and the flexible portion  38  exists, a single flexible portion region  40 B where only the flexible portion  38  between the catheter body  34  and the flexible portion  38  exists, and a mixed region  40 C where the catheter body  34  and the flexible portion  38  exist are arranged in the axial direction. In the catheter  12  illustrated in  FIG. 2A , the interface  42  between the catheter body  34  and the flexible portion  38  is formed in a tapered shape that is inclined at a substantially constant angle with respect to an axis of the catheter  12 . 
     The single catheter body region  40 A is a portion of the catheter body  34  present on the proximal side of a most proximal portion of the flexible portion  38 . 
     The single flexible portion region  40 B is a portion of the flexible portion  38  present on the distal side of the most distal portion of the catheter body  34 . An axial length L 1  of the single flexible portion region  40 B is set to, for example, 0.3 to 5.0 mm, preferably 0.4 to 2.0 mm, and more preferably 0.5 to 0.9 mm. The hardness of the flexible portion  38  (the single flexible portion region  40 B) is, for example, 98 D to 62 D and preferably 46 D to 59 D at 23° C. The flexible portion  38  in the illustrated example is joined to the catheter body  34 . Because the axial length and the hardness of the single flexible portion region  40 B are set within the above ranges, it is possible to deter the distal end (the flexible portion  38 ) of the catheter  12  from being curled at the time of puncture. In addition, it is possible to preferably suppress catching by a blood vessel back wall at the time of inserting the catheter  12 . Further, it is possible to suppress crushing of the distal end of the catheter  12  at the time of blood suction. 
     The mixed region  40 C is a portion in which the catheter body  34  and the flexible portion  38  are stacked in the radial direction. An axial length L 2  of the mixed region  40 C is set to, for example, 1 to 5 mm, and preferably 2 to 3 mm. 
     In the catheter  12  illustrated in  FIG. 2A , the interface  42  between the catheter body  34  and the flexible portion  38  is inclined in the distal direction so as to approach the axis (center) of the catheter  12 . Thus, the flexible portion  38  is present on the outer side of the catheter body  34  in the mixed region  40 C. 
     The catheter assembly  10  may be provided with a needle protection member that covers the needle tip  16   a  when the inner needle  16  is removed from the catheter  12 . In this case, a protrusion (not illustrated) is provided on the outer peripheral surface of the inner needle  16  to deter the needle protection member from being removed from the inner needle  16  in the distal direction, and the protrusion is preferably provided on the proximal side of the single flexible portion region  40 B. As a result, the interface  42  between the catheter body  34  and the flexible portion  38  is not caught by the protrusion at the time of advancing the catheter  12 , and it is possible to deter peeling of the interface  42  caused by the protrusion. 
     The catheter  12  is preferably coated seamlessly with a single coating material on the whole catheter  12  in order to eliminate (or minimize) a step at a boundary between the catheter body  34  and the flexible portion  38  on the inner peripheral surface and an outer peripheral surface of the catheter body  34 . 
     Instead of the above configuration having the interface  42 , the catheter  12  may be formed so as to become soft in the distal direction by changing each compounding amount of materials different in hardness in the axial direction. In this case, extrusion molding may be performed while changing each extrusion speed of different materials. Alternatively, a content of a plasticizer at the distal portion of the catheter may be increased. In this case, the plasticizer may be applied to the distal portion of the catheter. 
     In the inner needle  16 , a backcut portion  16   c , which is continuous with the needle tip  16   a  and is inclined in a reverse direction to the blade face  16   b  with respect to the axis of the inner needle  16 , is provided on the opposite side to a blade face  16   b . In order to suppress piercing of the inner surface of the catheter  12  by the needle tip  16   a  when the catheter  12  is retracted after advancing the catheter  12  once with respect to the inner needle  16 , a radial length Lb from the needle tip  16   a  to the backcut portion  16   c  at a position of 0.05 mm from the needle tip  16   a  in the proximal direction is set to, for example, 0.01 to 0.05 mm, and more preferably, set to 0.02 to 0.04 mm. It is sufficient if the needle tip  16   a  is offset to the radially inner side in order to obtain the same effect, and the needle tip  16   a  may be curved instead of having the backcut portion. 
     As illustrated in  FIG. 2B , among projection lines P forming a contour shape of a projection image when the distal portion of the inner needle  16  is projected from just beside, at least a part of a projection line Pa, which corresponds to a portion (the backcut portion  16   c  in the present embodiment) of the distal portion of the inner needle  16  formed on the opposite side of the blade face  16   b  and continuous with the needle tip  16   a , preferably passes between a straight line C 1  at 10° with respect to a straight line Lp, which passes through the needle tip  16   a  and is perpendicular to a longitudinal direction of the inner needle  16 , and a straight line C 2  at 70° with respect to the straight line Lp. More preferably, at least a part of the projection line Pa passes between a straight line C 3  at 30° with respect to the straight line Lp and a straight line C 4  at 60° with respect to the straight line Lp. In  FIG. 2B , the projection line Pa is a straight line, the whole projection line Pa passes between the straight line C 1  and the straight line C 2 . 
     With this configuration, it is possible to achieve both the deterrence of the piercing of the inner surface of the catheter  12  by the needle tip  16   a  and penetration properties with respect to the skin. When at least a part of the projection line Pa is present in a region closer to the straight line Lp than the straight line C 1 , the above-described piercing is unlikely to occur, but the penetration resistance becomes large. When at least a part of the projection line Pa is present in a region where an angle with the straight line Lp is larger than an angle with the straight line C 4 , the penetration resistance is low, but the above-described piercing is likely to occur. 
     The backcut portion  16   c  may be formed in a curved shape that bulges toward the straight line Lp like a projection line Pa 1 . At least a part of the projection line Pa 1  preferably passes between the straight line C 1  and the straight line C 2 , and more preferably passes between the straight line C 3  and the straight line C 4 . The backcut portion  16   c  may be formed in a shape curved in an S shape like a projection line Pa 2 . At least a part of the projection line Pa 2  preferably passes between the straight line C 1  and the straight line C 2 , and more preferably passes between the straight line C 3  and the straight line C 4 . 
     The inner needle  16  is provided with an introduction path  44  that communicates with the flashback flow path  32  to introduce blood into the flashback flow path  32 . The introduction path  44  illustrated in  FIG. 2A  is a side hole  44 A that penetrates through a wall portion of the inner needle  16  in the radial direction. As illustrated in  FIG. 3 , the introduction path  44  may be a groove portion  44 B extending in the axial direction on the outer peripheral surface of the inner needle  16 . 
     In the initial state of the catheter assembly  10  illustrated in  FIGS. 2A and 3 , a proximal end  44   a  of the introduction path  44  is provided on the proximal side of an axial center position Pc of the single flexible portion region  40 B. More specifically, at least the proximal end  44   a  of the introduction path  44  is provided on the proximal side of a most distal portion of the single catheter body region  40 A. The whole side hole  44 A illustrated in  FIG. 2A  is provided on the proximal side of the most distal portion of the single catheter body region  40 A. Incidentally, a part of the side hole  44 A may be present on the distal side of the most distal portion of the single catheter body region  40 A. 
     In  FIG. 2A , the whole side hole  44 A is provided on the proximal side of the mixed region  40 C. A part of the side hole  44 A may be present on the distal side of a proximal end of the mixed region  40 C. 
     Regarding a position of the introduction path  44  in relation to the close contact portion  30 , at least the proximal end  44   a  of the introduction path  44  (the side hole  44 A or the groove portion  44 B) is provided on the proximal side of the close contact portion  30  in the initial state of the catheter assembly  10  illustrated in  FIGS. 2A and 3 . The whole side hole  44 A illustrated in  FIG. 2A  is provided on the proximal side of the close contact portion  30 . 
     As illustrated in  FIG. 4 , only the inner peripheral surface of the flexible portion  38  between the catheter body  34  and the flexible portion  38  may be in close contact with the outer peripheral surface of the inner needle  16  (the catheter body  34  is not necessarily close contact with the outer peripheral surface of the inner needle  16 ). In addition, in this case, the whole side hole  44 A may be provided on the distal side of the most distal portion (a most distal portion of the interface  42 ) of the single catheter body region  40 A as illustrated in  FIG. 4 . That is, the side hole  44 A may be provided on the inner side of the flexible portion  38 . The side hole  44 A may have a proximal end positioned on the proximal side of the most distal portion of the single catheter body region  40 A and a distal end positioned at the same axial position as the most distal portion or on the distal side of the most distal portion of the single catheter body region  40 A. 
     Next, functions of the catheter assembly  10  configured as described above will be described. 
     In use of the catheter assembly  10  illustrated in  FIG. 1 , a puncturing operation to puncture the patient&#39;s skin with the catheter assembly  10  is performed. In the puncturing operation, a user (a doctor, a nurse, or the like) presses the distal portion of the catheter assembly  10  against the patient while gripping the housing  24 , thereby puncturing the skin toward a puncture target blood vessel. Accordingly, the skin is punctured with the inner needle  16  and each distal portion of the catheter  12 . 
     Next, the user operates the catheter operation member  20  in the distal direction to cause the catheter member  17  (the catheter  12  and the catheter hub  14 ) to advance while fixing the position of the needle hub  18  (the housing  24 ). Accordingly, the catheter  12  is inserted to the target position in the blood vessel. 
     Next, the user pulls the housing  24  in the proximal direction while holding the positions of the catheter operation member  20  and the catheter member  17 . Accordingly, the catheter member  17  and the catheter operation member  20  completely come out of the housing  24 , and the inner needle  16  is removed from the catheter  12  in the proximal direction. 
     Next, the catheter operation member  20  is detached from the catheter hub  14 . Accordingly, the catheter member  17  is indwelled in the patient. Incidentally, the catheter operation member  20  may be kept attached to the catheter hub  14  depending on a preference of the user. 
     Next, the connector of the infusion tube (not illustrated) is connected to the proximal side (the proximal portion of the catheter hub  14 ) of the catheter member  17  from which the inner needle  16  has been removed, and the infusion solution (medicinal liquid) is administered from the infusion tube to the patient. 
     In this case, the catheter assembly  10  according to the present embodiment has the following effects. 
     According to the catheter assembly  10 , the flexible portion  38 , which is more flexible than the catheter body  34 , is provided at the distal portion of the catheter body  34  as illustrated in  FIG. 2A . Thus, it is possible to deter the distal end of the catheter  12  from being caught by a blood vessel back wall  50   a , which is a blood vessel wall of a blood vessel  50  on the opposite side of a puncture spot at the time of advancing the catheter  12  to insert the catheter  12  into the blood vessel  50  after puncturing a skin S with the distal portion of the catheter assembly  10  even when a puncture angle is large as illustrated in  FIG. 5 . 
     That is, the flexible portion  38  is brought into contact with the blood vessel back wall  50   a  and is pressed by the blood vessel back wall  50   a  to be easily deformed at the time of advancing the catheter  12  as illustrated in  FIG. 5 , and thus, it is possible to deter the distal end of catheter  12  from being caught by the blood vessel back wall  50   a . As a result, it is possible to deter the catheter  12  from being difficult to insert into the blood vessel  50  or to deter the blood vessel back wall  50   a  from being damaged by the distal end of the catheter  12 . 
     As illustrated in  FIG. 2A , the flashback flow path  32  is formed between the catheter  12  and the inner needle  16 , and the inner needle  16  is provided with the introduction path  44  that communicates with the flashback flow path  32  to introduce blood into the flashback flow path  32 . The proximal end  44   a  of the introduction path  44  is provided on the proximal side of the axial center position Pc of the portion of the flexible portion  38  present on the distal side of the most distal portion of the catheter body  34 . In addition, the catheter  12  has the close contact portion  30  in which at least a part of the inner peripheral surface is in close contact with the outer peripheral surface of the inner needle  16 , and at least the proximal end of the introduction path  44  is provided on the proximal side of the close contact portion  30 . 
     With the above configuration, it is possible to deter the flexible portion  38  from being deformed to block the introduction path  44  at the time of puncture, and thus, it is possible to easily confirm the flashback of blood. 
     In the close contact portion  30 , both the flexible portion  38  and the catheter body  34  are in close contact with the inner needle  16 . With this configuration, an appropriate fitting force between the inner needle  16  and the catheter  12  can be obtained. With the appropriate fitting force, the flexible portion  38  is deterred from being curled, and the inner needle  16  can be easily removed from the catheter  12  at the time of puncturing the skin. 
     The catheter  12  has the mixed region  40 C in which the catheter body  34  and the flexible portion  38  overlap each other in the radial direction. With this configuration, a change in rigidity from the catheter body  34  to the flexible portion  38  can be made gradual, and thus, it is possible to more favorably deter the distal end of the catheter  12  from being caught by the blood vessel back wall  50   a  at the time of inserting the catheter  12  into the blood vessel  50 . 
     The axial length of the single flexible portion region  40 B (the portion of the flexible portion  38  present on the distal side of the most distal portion of the catheter body  34 ) is 0.3 to 5.0 mm. With this configuration, it is possible to suppress the curling of the distal end (the flexible portion  38 ) of the catheter  12  at the time of puncture. In addition, it is possible to more preferably suppress the catching by the blood vessel back wall  50   a  at the time of inserting the catheter  12 . Further, it is possible to suppress crushing of the distal end of the catheter  12  at the time of blood suction. 
     The interface  42  between the catheter body  34  and the flexible portion  38  in the mixed region  40 C is formed in the tapered shape that is inclined with respect to the axis of the catheter  12 . With this configuration, the change in rigidity from the catheter body  34  to the flexible portion  38  can be made more gradual. 
     The whole catheter  12  is coated seamlessly. With this configuration, it is possible to eliminate the step between the catheter body  34  and the flexible portion  38  on the inner peripheral surface and the outer peripheral surface of the catheter  12 . Because the step is eliminated, it is possible to deter thrombus and to reduce a penetration resistance at the time of puncture. 
     A creep strain of the catheter body  34  is greater than a creep strain of the flexible portion  38 . With this configuration, the catheter body  34  is easily adopted to a shape of the blood vessel after the catheter  12  is inserted into the blood vessel  50  to remain indwelled. Thus, it is possible to reduce a sense of incompatibility given to the patient during indwelling of the catheter  12 . In addition, the flexible portion  38  has the smaller creep strain than the catheter body  34 , and thus, can easily return to the original shape even if being deformed. Thus, it is possible to reduce the crushing of the distal end of the catheter  12  caused by the blood suction. 
     As illustrated in  FIG. 6A , the interface  42  between the catheter body  34  and the flexible portion  38  may be inclined at a substantially constant angle so as to be separated farther from the axis of the catheter  12  in the distal direction. Even with this configuration, the change in rigidity from the catheter body  34  to the flexible portion  38  can be made gradual similarly to the case in which the interface  42  is inclined at the substantially constant angle so as to approach the axis of the catheter  12  in the distal direction ( FIG. 2A ). 
     As illustrated in  FIG. 6B , the interface  42  may have a plurality of regions aligned in the axial direction, and regions adjacent to each other among the plurality of regions may have different angles with respect to the axis of the catheter  12 . With this configuration, it becomes easy to adjust the rigidity in the mixed region  40 C in which the catheter body  34  and the flexible portion  38  overlap each other in the radial direction, and thus, the change in rigidity from the catheter body  34  to the flexible portion  38  can be easily adjusted. 
     In  FIG. 6B , the interface  42  is inclined so as to approach the axis of the catheter  12  in the distal direction. Specifically, the interface  42  has: a first region  42   a ; a second region  42   b  that is adjacent to the distal side of the first region  42   a  and is inclined with respect to the first region  42   a ; and a third region  42   c  that is adjacent to the distal side of the second region  42   b  and is inclined with respect to the second region  42   b . An angle of the second region  42   b  with respect to the axis of the catheter  12  is smaller than angles of the first region  42   a  and the third region  42   c  with respect to the axis of the catheter  12 . The angles of the first region  42   a  and the third region  42   c  with respect to the axis of the catheter  12  may be the same or different from each other. 
     As illustrated in  FIG. 6C , the interface  42  may be inclined so as to be separated farther from the axis of the catheter  12  in the distal direction and may have a plurality of regions aligned in the axial direction. Even with this configuration, it becomes easy to adjust the rigidity in the mixed region  40 C in which the catheter body  34  and the flexible portion  38  overlap each other in the radial direction similarly to the configuration of  FIG. 6B , and thus, the change in rigidity from the catheter body  34  to the flexible portion  38  can be easily adjusted. 
     In  FIG. 6C , the interface  42  has: a first region  42   d ; a second region  42   e  that is adjacent to the distal side of the first region  42   d  and is inclined with respect to the first region  42   d ; and a third region  42   f  that is adjacent to the distal side of the second region  42   e  and is inclined with respect to the second region  42   e . An angle of the second region  42   e  with respect to the axis of the catheter  12  is smaller than angles of the first region  42   d  and the third region  42   f  with respect to the axis of the catheter  12 . The angles of the first region  42   d  and the third region  42   f  with respect to the axis of the catheter  12  may be the same as or different from each other. 
     As in  FIG. 6D , the interface  42  between the catheter body  34  and the flexible portion  38  may be perpendicular to the axis of the catheter  12 . 
     The catheter assembly  10  may employ a catheter  12   a  illustrated in  FIG. 7A  or a catheter  12   b  illustrated in  FIG. 7B . In the catheters  12   a  and  12   b  illustrated in  FIGS. 7A and 7B , deformation suppressing members  54  and  58 , respectively, suppressing a radial deformation are provided in at least the flexible portion  38  between the catheter body  34  and the flexible portion  38 . With this configuration, it is possible to suppress curling of the distal end (the flexible portion  38 ) of the catheter  12   a  or  12   b  at the time of puncture, and to suppress crushing of the distal end of the catheter  12   a  or  12   b  at the time of blood suction. The deformation suppressing member  54  or  58  has a shape that makes at least one turn in a circumferential direction. With this configuration, the radial deformation can be more effectively suppressed. 
     The catheter  12   a  illustrated in  FIG. 7A  is provided with a plurality of the deformation suppressing members  54 . Specifically, the deformation suppressing members  54  are provided on the inner peripheral surface, the outer peripheral surface, the inside, and the distal end of the catheter body  34  in the mixed region  40 C, and on the inner peripheral surface and the outer peripheral surface of the flexible portion  38 , but may be provided at any one spot or a plurality of spots among these sites. The deformation suppressing member  54  provided in the flexible portion  38  is preferably a member harder than the catheter body  34  (a member having a higher elastic modulus). Incidentally, the deformation suppressing member  54  provided in the flexible portion  38  may be a member that has the same hardness as the catheter body  34  or is softer than the catheter body  34 . 
     The deformation suppressing member  54  provided in the flexible portion  38  is preferably a member having a smaller creep strain than the catheter body  34 . Incidentally, the deformation suppressing member  54  provided in the flexible portion  38  is preferably a member having a smaller creep strain than the flexible portion  38 . When the deformation suppressing member  54  having the small creep strain is provided, the distal end of the catheter  12   a  is easily restored to the original shape at the time of stopping suction even if blood is suctioned at an excessive speed so that the distal end of the catheter  12   a  is crushed. 
     In the catheter  12   b  illustrated in  FIG. 7B , the deformation suppressing member  58  continuously extending from the single flexible portion region  40 B over the mixed region  40 C is provided concentrically with the catheter  12   b . Specifically, the deformation suppressing member  58  is provided inside the flexible portion  38 . The deformation suppressing member  58  may be provided on the outer peripheral surface of the flexible portion  38 . The deformation suppressing member  58  is preferably a member harder than the catheter body  34  (a member having a higher elastic modulus). Incidentally, the deformation suppressing member  58  may be a member that has the same hardness as the catheter body  34  or is softer than the catheter body  34 . 
     The deformation suppressing member  54  (or the deformation suppressing member  58 ) can adopt various forms as illustrated in  FIG. 8 . Deformation suppressing members  54   a  to  54   g  in cells A to G have tube-like (ring-like) forms. Specifically, the deformation suppressing member  54   a  in the cell A has a straight shape with a constant outer diameter in the axial direction. The deformation suppressing member  54   b  in the cell B has a tapered shape with an outer diameter changing in the axial direction. The deformation suppressing member  54   c  in the cell C has a straight shape with a constant outer diameter in the axial direction, and has a large number of through-holes  59  penetrating in the radial direction. 
     The deformation suppressing member  54   d  in the cell D has a large number of recess portions  60  on an outer peripheral surface (or an inner peripheral surface). The deformation suppressing member  54   e  in the cell E has a ring-shaped groove  62  on an outer peripheral surface (or an inner peripheral surface). The deformation suppressing member  54   f  in the cell F has a cavity  64  inside a circumferential wall. The deformation suppressing member  54   g  in the cell G is configured using a porous body (for example, a sintered body). 
     Deformation suppressing members  54   h  to  54   j  in cells H to J have coil-like forms. Specifically, the deformation suppressing member  54   h  in the cell H has a straight shape with a constant outer diameter in the axial direction. The deformation suppressing member  54   i  in the cell I has a tapered shape with an outer diameter changing in the axial direction. The deformation suppressing member  54   j  in the cell J is configured in multiple spirals. 
     Deformation suppressing members  54   o  and  54   p  in a cell O and a cell P have tubular net-like forms. Specifically, the deformation suppressing member  54   o  in the cell O has a straight shape with a constant outer diameter in the axial direction. The deformation suppressing member  54   p  in the cell P has a tapered shape with an outer diameter changing in the axial direction. 
     As wires constituting the deformation suppressing members  54   h  to  54   j ,  54   o , and  54   p  in the cell H to the cell J, the cell O, and the cell P, a wire  68  having a circular cross section as in the cell K may be used, wires  68   a  to  68   c  having non-circular cross sections as in cells La to Lc (an elliptical shape in a cell La, a rectangular shape in a cell Lb, and a star shape in a cell Lc) may be used, a hollow wire  70  as in a cell M may be used, or a twisted wire  72  as in a cell N may be used. 
     Next, an example of a method of manufacturing the catheter  12  provided with the deformation suppressing member  54  will be described. As illustrated in  FIG. 9A , the deformation suppressing member  54  is fitted (mounted) to a core member  74 . Next, a first tube member  76 , which is a material of the catheter body  34 , is mounted to the core member  74 , and the other deformation suppressing member  54  is fitted to an outer peripheral surface of a distal portion of the first tube member  76  as illustrated in  FIG. 9B . Next, an object is molded by pressing and heating the first tube member  76  and the deformation suppressing members  54  with a mold (not illustrated). As a result, the catheter body  34  formed in a tapered shape with a tapered distal portion as illustrated in  FIG. 9C  is obtained. 
     Next, the deformation suppressing member  54  is fitted to the core member  74  on the distal side of the catheter body  34  as in  FIG. 10A . Next, a second tube member  78 , which is a material of the flexible portion  38  and has the other deformation suppressing members  54  mounted on an inner peripheral surface and an outer peripheral surface thereof, is mounted to the core member  74  and the distal portion of the catheter body  34  as illustrated in  FIG. 10B . Then, the second tube member  78  and the deformation suppressing member  54  are pressed and heated using a mold (not illustrated) (which may be the same as the mold used at the time of molding the distal portion of the first tube member  76 ). As a result, the flexible portion  38  formed in a tapered shape with a tapered distal portion as illustrated in  FIG. 10C  is obtained. 
     Next, the deformation suppressing member  54  is fitted on the outer peripheral surface of the flexible portion  38  as illustrated in  FIG. 11A . Then, the deformation suppressing member  54  is pressed and heated using a mold (not illustrated) (which may be the same as the mold used at the time of molding the distal portion of the first tube member  76  or the second tube member  78 ) so that the deformation suppressing member  54  is embedded in the outer peripheral surface of the flexible portion  38  as illustrated in  FIG. 11B . As a result, the catheter  12   a  provided with the deformation suppressing members  54  is obtained. 
     Incidentally, installation spots and the number of the deformation suppressing members  54  can be changed as appropriate in the above method of manufacturing the catheter  12 . 
     As illustrated in  FIGS. 12A to 12D , it is also possible to manufacture the second tube member  78  provided with the deformation suppressing member  54  (or the deformation suppressing member  58 ) by performing blade processing or multi-layer molding at the time of manufacturing the second tube member  78 , which is the material of the flexible portion  38 . 
     The second tube member  78  illustrated in  FIG. 12A  is obtained by forming the deformation suppressing member  54  (see deformation suppressing members  54   o  and  54   p  in  FIG. 8 ) having a form of a blade (a tubular net-like member) as an intermediate layer. The second tube member  78  illustrated to  FIG. 12B  is obtained by forming the deformation suppressing member  54  as an inner layer by multi-layer molding. The second tube member  78  illustrated to  FIG. 12C  is obtained by forming the deformation suppressing member  54  as an outer layer by multi-layer molding. The second tube member  78  illustrated to  FIG. 12D  is obtained by forming the deformation suppressing member  54  as an intermediate layer by multi-layer molding. 
     In a catheter  12   c  illustrated in  FIG. 13 , the interface  42  between the catheter body  34  and the flexible portion  38  is provided with a region  80  having a different acoustic impedance from the catheter body  34  and the flexible portion  38 . With this configuration, the above-described region  80  having the different acoustic impedance functions as an echogenic portion, and thus, it is possible to improve the visibility of the distal portion of the catheter  12  under ultrasound fluoroscopy. Hereinafter, the region  80  having the different acoustic impedances is referred to as an “echogenic portion  80   a”.    
     The echogenic portion  80   a  is provided on the proximal side of the portion of the flexible portion  38  present on the distal side of the most distal portion of the catheter body  34 . With this configuration, it is possible to deter peeling at the interface  42  between the catheter body  34  and the flexible portion  38  when the catheter  12   c  is advanced with respect to the inner needle  16 . 
     A shape of the echogenic portion  80   a  may have the same shape as the deformation suppressing member  54 . The shape of the echogenic portion  80   a  may be granular. A material of the echogenic portion  80   a  may be the same as or different from that of the deformation suppressing member  54 . The echogenic portion  80   a  is not necessarily rigid, and thus, may be air, gel, or the like. 
     When a granular body is used as the echogenic portion  80   a , a glass bead is particularly preferable. When a test was performed by providing the glass bead as the echogenic portion  80   a , favorable visibility was obtained with the glass bead having a diameter of 30 to 120 μm. 
     The first tube member  76 , which is the material of the catheter body  34 , or the second tube member  78 , which is the material of the flexible portion  38 , (or both) may be molded by extrusion molding while mixing the granular body that is to form the echogenic portion  80   a  therein. 
     In a catheter  12   d  illustrated in  FIG. 14A , the flexible portion  38  has a first flexible portion  38 A that is more flexible than the catheter body  34 , and a second flexible portion  38 B that is provided to be adjacent to the distal side of the first flexible portion  38 A and is more flexible than the first flexible portion  38 A. That is, an elastic modulus k 2   a  of the first flexible portion  38 A, an elastic modulus k 2   b  of the second flexible portion  38 B, and the elastic modulus k 1  of the catheter body  34  have a relationship of k 1 &gt;k 2   a &gt;k 2   b.    
     With this configuration, the change in rigidity from the catheter body  34  to the flexible portion  38  can be made more gradual. Thus, it is possible to more favorably deter the distal end of the catheter  12   d  from being caught by the blood vessel back wall  50   a  at the time of inserting the catheter  12   d  into the blood vessel  50 , and to deter the peeling of the interface  42  at the joint between the catheter body  34  and the flexible portion  38 . 
     In the catheter  12   e  illustrated in  FIG. 14B , the flexible portion  38  has a first flexible portion  38 C that is more flexible than the catheter body  34 , and a second flexible portion  38 D that is provided on the distal side of the first flexible portion  38 C, includes a most distal portion of the catheter  12   e , and is harder than the first flexible portion  38 C. That is, an elastic modulus k 2   c  of the first flexible portion  38 C, an elastic modulus k 2   d  of the second flexible portion  38 D, and the elastic modulus k 1  of the catheter body  34  have a relationship of k 1 &gt;k 2   d &gt;k 2   c . With this configuration, it is possible to suppress the crushing of the flexible portion  38  at the time of blood suction. 
     In a catheter  12   f  of a catheter assembly  10   a  illustrated in  FIG. 15 , a cover  82  is provided on an outer surface of the flexible portion  38  and an outer surface of the catheter body  34  such that a friction coefficient of an outer surface of the catheter  12   f  decreases. The cover  82  covers the whole outer surface of the catheter  12   f . A friction coefficient T 1  of the surface of the flexible portion  38 , a friction coefficient T 2  of the surface of the catheter body  34 , and a friction coefficient T 3  of the surface of the cover  82  have a relationship of T 3 &lt;T 2 &lt;T 1 . Examples of a material forming the cover  82  include silicone, methoxyethyl (meth) acrylate, and the like. 
     According to the catheter assembly  10   a , the cover  82  is provided on the outer surface of the flexible portion  38 , and the friction coefficient T 3  of the surface of the cover  82  is smaller than the friction coefficient T 1  of the surface of the flexible portion  38 . Because the cover  82  having a small friction coefficient is provided on the outer surface of the flexible portion  38  in this manner, it is possible to suppress the curling of the soft flexible portion  38  at the time of puncturing the skin so that the cover  82  easily passes a skin puncture hole. In addition, at least a part of the flexible portion  38  is in close contact with the inner needle  16 , and thus, the flexible portion  38  is less likely to be displaced from the inner needle  16  at the time of puncturing the skin and can be deterred from being curled. 
     According to the catheter assembly  10   a , the cover  82  is provided on the outer surface of the flexible portion  38  and the outer surface of the catheter body  34 , the friction coefficient T 2  of the surface of the catheter body  34  is smaller than the friction coefficient T 1  of the surface of the flexible portion  38 , and the friction coefficient T 3  of the surface of the cover  82  is smaller than the friction coefficient T 2  of the surface of the catheter body  34 . Thus, it is possible to suppress the curling of the soft flexible portion  38  at the time of puncturing the skin so that the cover  82  easily passes a skin puncture hole. In addition, because the friction coefficient T 2  of the surface of the catheter body  34  is set to be small, it is possible to suppress an increase of a frictional force between the catheter  12   f  and the inner needle  16 , and thus, an advancing operation is easily performed at the time of advancing the catheter  12   f  relative to the inner needle  16 . Further, a difference between the friction coefficient T 2  of the surface of the catheter body  34  and the friction coefficient T 1  of the surface of the flexible portion  38  is not too large, and thus, the flexible portion  38  can be deterred from being curled inward at the time of advancing the catheter  12   f  relative to the inner needle  16 . 
     In an inner needle  16 A of a catheter assembly  10   b  illustrated in  FIG. 16 , a friction-increased shape portion  86  having at least one of a recess portion (groove) and a convex portion (protrusion) that increases a friction coefficient of an outer peripheral surface of the inner needle  16 A is provided on the outer peripheral surface of the inner needle  16 A. With this configuration, the friction coefficient of the outer peripheral surface of the inner needle  16 A is increased, and thus, it is possible to deter the catheter  12  from being curled at the time of puncturing the skin with the catheter  12 . The friction-increased shape portion  86  is provided at a position opposing an inner peripheral surface of the distal portion of the catheter  12 . 
     In  FIG. 16 , the friction-increased shape portion  86  is a groove structure  87 . More specifically, the groove structure  87  is a spiral groove  87   a . Instead of the spiral groove  87   a , a plurality of annular grooves may be provided at intervals in the axial direction. 
     When the friction-increased shape portion  86  is formed using the groove structure  87 , the groove structure  87  is more preferably provided at a position overlapping the flexible portion  38  in the axial direction. When a human body is punctured with the catheter assembly  10   b  and the catheter  12  passes a skin puncture hole, a radial force from the outer surface of the catheter  12  to a central axis of the catheter  12  is applied so that the flexible portion  38  is deformed and the flexible portion  38  bites into the inside (recess portion) of the groove structure  87 . Because a force, which causes the flexible portion  38  biting into the recess portion (the spiral groove  87   a  or the annular groove) of the groove structure  87  and holds the position of the flexible portion  38 , overcomes a force generated as the flexible portion  38  is displaced from the inner needle  16 A and deformed, it is possible to further deter the catheter  12  from being curled at the time of puncture. 
     The friction-increased shape portion  86  is not limited to the groove structure  87  but may be a protrusion structure. The protrusion structure may be a spiral protrusion, or may be a plurality of annular protrusions formed at intervals in the axial direction. The friction-increased shape portion  86  may be a roughened portion that has been subjected to processing to increase surface roughness. In this case, the roughened portion is a structure having a large number of fine recess shapes (grooves) and convex shapes (protrusions) that increase the friction coefficient of the outer peripheral surface of the inner needle  16 A. When the roughened portion is provided, a position of the inner needle  16 A can be confirmed by ultrasound irradiation at the time of puncturing the human body with the catheter assembly  10   b.    
     The above-described groove structure  87  or protrusion structure may be configured to form a gap with respect to the inner peripheral surface of the catheter  12 . As a result, ultrasound reflection of the ultrasound from an ultrasound imaging apparatus at a boundary of the gap is promoted, and a position of the groove structure  87  or the protrusion structure of the inner needle  16 A can be recognized more favorably on a monitor of the ultrasound imaging apparatus. 
     The friction-increased shape portion  86  provided on the outer peripheral surface of the inner needle  16 A is not necessarily provided at the position opposing the most distal portion of the flexible portion  38 . As a result, the distal end of the flexible portion  38  is less likely to be curled at the time of puncture. 
     A catheter  12   g  of a catheter assembly  10   c  illustrated in  FIG. 17  has the catheter body  34  and the flexible portion  38  provided at the distal portion of the catheter body  34 . The inner peripheral surface of the catheter body  34  and the inner peripheral surface of the flexible portion  38  are in close contact with an outer peripheral surface of an inner needle  16 B over the whole circumference. A portion, which is in close contact with the outer peripheral surface of the inner needle  16 B, at the distal portion of the catheter  12   g  constitutes a close contact portion  90 . 
     The catheter body  34  has: a body tapered portion  34   t  that is inclined with respect to an axis of the catheter  12   g  such that an outer diameter decreases in the distal direction; and a flexible tapered portion  38   t  that is inclined with respect to the axis of the catheter  12   g  such that the outer diameter decreases in the distal direction. 
     The body tapered portion  34   t  is arranged on the radially inner side of the flexible tapered portion  38   t . The body tapered portion  34   t  has a first body tapered portion  34   t   1  and a second body tapered portion  34   t   2  provided to be adjacent to the proximal side of the first body tapered portion  34   t   1 . The flexible tapered portion  38   t  has a first flexible tapered portion  38   t   1  including a most distal portion of the catheter  12   g , and a second flexible tapered portion  38   t   2  provided to be adjacent to the proximal side of the first flexible tapered portion  38   t   1 . 
     The first body tapered portion  34   t   1  has an inclination angle at an outer peripheral surface with respect to the axis of the catheter  12   g  larger than that of the second body tapered portion  34   t   2 . According to this configuration, the inclination angle of the first body tapered portion  34   t   1  is relatively large, and thus, it is possible to support the flexible portion  38  from the inner side at the time of blood suction and to suppress a collapse of the flexible portion  38 . Because the inclination angle of the second body tapered portion  34   t   2  is relatively small, the gradual transition from a physical property of the flexible portion  38  to a physical property of the catheter body  34  becomes possible, and a kink of the catheter  12   g  can be suppressed. 
     The first flexible tapered portion  38   t   1  has an inclination angle at an outer peripheral surface with respect to the axis of the catheter  12   g  larger than that of the second flexible tapered portion  38   t   2 . According to this configuration, the first flexible tapered portion  38   t   1  is relatively thick, and thus, it is possible to suppress the curling of the distal end of the catheter  12   g  at the time of puncture. The second flexible tapered portion  38   t   2  has the relatively small inclination angle, and thus, the penetration resistance can be reduced. 
     The inclination angle of the first body tapered portion  34   t   1  is slightly smaller than the inclination angle of the first flexible tapered portion  38   t   1 . The first body tapered portion  34   t   1  is arranged on the radially inner side of the second flexible tapered portion  38   t   2 . A most proximal portion of the second flexible tapered portion  38   t   2  is positioned on the proximal side of a most proximal portion of the first body tapered portion  34   t   1 . The flexible portion  38  has a straight portion  38   s , which is parallel to the axis of the catheter  12   g , on the proximal side of the second flexible tapered portion  38   t   2 . 
     The flow path  32  for flashback confirmation is formed between the catheter  12   g  and the inner needle  16 B. The inner needle  16 B is provided with a side hole  89  that communicates with the flow path  32  to introduce blood into the flow path  32 . The side hole  89  (specifically, a most distal portion of the side hole  89 ) is provided on the proximal side of a most distal portion of the body tapered portion  34   t  (the most distal portion of the catheter body  34 ). With this configuration, the side hole  89  is provided at a position opposing the relatively hard catheter body  34 . Therefore, it is possible to deter the catheter  12   g  from blocking the side hole  89  at the time of puncture, and thus, it is possible to easily confirm the flashback of blood. The side hole  89  is provided on the proximal side of the second body tapered portion  34   t   2 . 
     An inner peripheral surface of the flexible tapered portion  38   t  and an inner peripheral surface of the first body tapered portion  34   t   1  are in close contact with the outer peripheral surface of the inner needle  16 B. That is, the close contact portion  90  is constituted by the inner peripheral surface of the flexible tapered portion  38   t  and the inner peripheral surface of the first body tapered portion  34   t   1 . 
     An ultrasound reflection promoting portion  92  having an uneven shape (step shape) is provided on the outer peripheral surface of the inner needle  16 B. In  FIG. 17 , the ultrasound reflection promoting portion  92  is a spiral groove  93  that is recessed with respect to the outer peripheral surface of the inner needle  16 B. The ultrasound reflection promoting portion  92  may be a spiral protrusion protruding to the radially outer side from the outer peripheral surface of the inner needle  16 B. The ultrasound reflection promoting portion  92  may be configured using a plurality of ring-shaped grooves or a plurality of ring-shaped protrusions arranged at intervals in the axial direction. 
     A most distal portion  92   a  of the ultrasound reflection promoting portion  92  is positioned on the distal side of the side hole  89 . The most distal portion  92   a  of the ultrasound reflection promoting portion  92  is positioned on the distal side of the most proximal portion of the second flexible tapered portion  38   t   2 . The most distal portion  92   a  of the ultrasound reflection promoting portion  92  is positioned on the distal side of a most proximal portion of the second body tapered portion  34   t   2 . 
     The most distal portion  92   a  of the ultrasound reflection promoting portion  92  is provided on the proximal side of a proximal portion of the close contact portion  90 . According to this configuration, the close contact portion  90  and the ultrasound reflection promoting portion  92  do not overlap each other so that the uneven shape of the ultrasound reflection promoting portion  92  does not contribute to a resistance at the time of removing the inner needle  16 B, and the removal operation is stabilized. 
     A most proximal portion  92   b  of the ultrasound reflection promoting portion  92  is positioned on the proximal side of the side hole  89 . The most proximal portion  92   b  of the ultrasound reflection promoting portion  92  is positioned on the proximal side of the most proximal portion of the second flexible tapered portion  38   t   2 . The most proximal portion  92   b  of the ultrasound reflection promoting portion  92  is positioned on the distal side of the most proximal portion of the second body tapered portion  34   t   2 . 
     In the catheter  12   g , the catheter body  34  has transparency that allows the inside of the catheter body  34  to be visible. The flexible portion  38  may have a color that is more easily visible than the catheter body  34 . When configured in this manner, the flexible portion  38  is colored to be easily noticeable while securing the flashback visibility by giving the transparency to the catheter body  34 , it is easy to perform puncture with respect to a target blood vessel. In addition, it is easy to understand that the flexible portion  38  is provided at the distal portion of the catheter  12   g , and thus, it is possible to appeal to the user that a function of deterring a blood vessel injury is high. 
     It is preferable that at least the flexible portion  38  between the catheter body  34  and the flexible portion  38  have an X-ray contrast property. If both the catheter body  34  and the flexible portion  38  have X-ray contrast properties, the flexible portion  38  preferably has a higher X-ray contrast property than the catheter body  34 . A contrast layer in the case where the flexible portion  38  has the contrast property may be provided, for example, in any form of a stripe shape, an intermediate layer in the radial direction, or the whole layer. When the stripe-shaped contrast layer is provided in the flexible portion  38 , the flexible portion  38  can have the higher X-ray contrast property than the catheter body  34  by making the number of stripes thereof larger than that in a stripe-shaped contrast layer provided in the catheter body  34 . 
     A double needle (Sample 1 to 10) consisting of a catheter (1.01 to 1.12 mm) and an inner needle ( 22 G) respectively obtained by applying the configurations of the catheter  12   g  and the inner needle  16 B in the above-described catheter assembly  10  was prepared, and a curling test, a suction test, a penetration resistance test, and a stuck test to be described below were performed. Test results are shown in  FIG. 18 . 
     Samples 1 to 9 had flexible portions (soft tips) at distal portions, respectively, and Sample 10 had no flexible portion at its tip. In Samples 1 to 9, a catheter body was made of relatively hard urethane, and the flexible portion was made of relatively soft urethane. In Sample 10, the catheter was made of only the same hard urethane as the catheter body. 
     In Samples 1 to 9, a “first taper angle” is an inclination angle of a first flexible tapered portion of the flexible portion, and a “second taper angle” is an angle of a second flexible tapered portion of the flexible portion. Sample 10 has no flexible portion, but has a first tapered portion corresponding to the first flexible tapered portion, and a “first taper angle” in a table is an inclination angle of the first tapered portion. Similarly, a “second taper angle” in Sample 10 in the table is an angle of the second tapered portion corresponding to the second flexible tapered portion. Samples 1 to 10 have different second taper angles. Samples 1 to 9 have different distal end tip lengths (distances from most distal portions of the catheter bodies to most distal portions of the flexible portions). 
     1. Curling Test 
     In the curling test, a pig skin and cowhide were used as objects to be punctured, and the object to be punctured was punctured with a sample. The pig skin was used assuming a human skin with standard hardness. The pig skin was punctured at a puncture angle of 20°, and then, its appearance was visually observed. The cowhide was used assuming a stiff human skin. The cowhide was punctured at a puncture angle of 90°, and then, its appearance was visually observed. It was determined as “OK” when the catheter was insertable into the object to be punctured, and it was determined as “NG” when the distal end of the catheter was curled on a surface of the object to be punctured and was not insertable. In the curling test, it is considered that it is disadvantageous if the distal end tip length is long, but the curling does not depend on the second taper angle. 
     2. Suction Test 
     In the suction test, a 5 mL syringe was connected to a catheter hub via an extension tube, and viscosity-adjusted simulated blood at 37° C. was suctioned at a rate of 1 mL/sec to confirm presence or absence of crushing of a catheter. It was determined as “OK” when the crushing did not occur, and it was determined as “NG” when the crushing occurred. In the suction test, it is considered that it is disadvantageous if the distal end tip length is long, and it is disadvantageous if the second taper angle is small. 
     3. Penetration Resistance Test 
     A polyethylene sheet having a thickness of 50 μm was punctured with each sample at 10 mm/min, and a resistance value (N) applied to each sample was measured by an indentation load tester (Autograph AG-1 kNX manufactured by Shimadzu Corporation). It is considered that the penetration resistance depends on an appearance shape (because the resistance is maximized at a most distal end). In addition, it is considered that the penetration resistance also depends on the first taper angle. 
     4. Stuck Test 
     In the stuck test, the following Tests (1) and (2) were performed. 
     Test (1) 
     From a state where a distal end of a double needle was brought close to a silicone sheet having a thickness of 1 mm (obtained assuming a blood vessel back wall) (a distance from a sheet to a needle tip of an inner needle was 2 mm), and only the catheter was advanced to abut on the sheet to confirm whether a distal portion of the catheter could push the catheter forward by changing its direction on a surface of the sheet. It was recognized as a non-insertable state when the catheter abutted on the sheet so that it was not allowed to push the catheter further forward. A puncture angle was increased at 5-degree intervals, and the maximum angle at which the insertion was possible was recorded. 
     Test (2) 
     The puncture angle was fixed at 45°, which is a clinically approximating condition (to actual puncture), a canine blood vessel (inferior vena cava) was punctured with a sample (only Sample 1 and 10) in the same manner as in Test (1) to confirm whether a catheter could be pushed forward to be inserted into the blood vessel. Because one that was insertable in Test (2) (Sample 3) was inserted up to 60° in Test (1), those having the penetration angles of 60° or larger in Test (1) were determined as “OK”. Because one that was non-insertable in Test (2) (Sample 10) was inserted up to 50° in Test (1), those having the penetration angles of 50° or smaller in Test (1) were determined as “NG”. 
     In the stuck test, it is considered that it is advantageous if the distal end tip length is long, and it is advantageous if the second taper angle is small. 
     Based on the test results shown in  FIG. 18 , only Sample 3 showed favorable results in all the tests. A desired range of the distal end tip length is longer than 0.6 mm and shorter than 1.1 mm. In terms of an outer diameter (1.01 to 1.12 mm) of the catheter used for the test, a distal end tip length/catheter outer diameter of the present embodiment is desirably longer than 0.54 and shorter than 1.08. 
     In a catheter assembly  10 d illustrated in  FIG. 19 , a catheter  12   h  has the catheter body  34  and the flexible portion  38  provided at a distal portion of the catheter body  34 . A ratio of a total length Lc of the catheter body  34  to a length Ls of the flexible portion  38  is 2 to 1. Therefore, when the total length Lc of the catheter body  34  is, for example, 50 mm, the length Ls of the flexible portion  38  is 25 mm. 
     As illustrated in  FIG. 19 , the catheter assembly  10   d  includes the deflection suppressing mechanism  27  that is capable of supporting the catheter  12   h  at the time of puncture and suppressing deflections of the inner needle  16  and the catheter  12   h . This deflection suppressing mechanism  27  has the same configuration as the deflection suppressing mechanism  27  in the above-described catheter assembly  10  (see  FIG. 1 ), and is constituted by the support member  26  provided at the distal portion of the housing  24  and the catheter operation member  20  mounted on the catheter hub  14 . 
     The deflection suppressing mechanism  27  is arranged on the proximal side of the flexible portion  38  (the most proximal portion of the flexible portion  38 ) in an initial state (a state before the catheter  12   h  is advanced with respect to the inner needle  16 ) of the catheter assembly  10   d  illustrated in  FIG. 19 . With this configuration, it is possible to deter the deflection suppressing mechanism  27  from damaging the flexible portion  38  at the time of advancing the catheter  12   h  with respect to the inner needle  16 . 
     The deflection suppressing mechanism  27  is preferably arranged on the proximal side of the flexible portion  38  in the vicinity of the flexible portion  38  in the initial state of the catheter assembly  10   d . As a result, the deflection suppressing mechanism  27  can support the catheter  12   h  at a position on the distal side as much as possible within a range not touching the flexible portion  38 , and thus, can appropriately exhibit the function of suppressing the deflections of the inner needle  16  and the catheter  12   h  while deterring the flexible portion  38  from being damaged. 
     The deflection suppressing mechanism  27  may be configured by only any one of the support member  26  and the catheter operation member  20 . The deflection suppressing mechanism  27  may be configured so as to surround the whole circumference of the catheter  12   h.    
     The present invention is not limited to the above-described embodiments, and various modifications can be made within a scope not departing from a gist of the present invention.