Patent Publication Number: US-2022211432-A1

Title: Medical device

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application is a continuation of International Patent Application No. PCT/JP2020/036815 filed on Sep. 29, 2020, which claims priority to Japanese Patent Application No. 2019-179477 filed on Sep. 30, 2019, the entire content of both of which is incorporated herein by reference. 
    
    
     TECHNOLOGICAL FIELD 
     The present invention generally relates to a medical device that expands and maintains a hole in biological tissue, and a treatment method involving expanding and maintaining a hole in biological tissue. 
     BACKGROUND DISCUSSION 
     Chronic heart failure is one of several known heart diseases. Chronic heart failure is broadly classified into a systolic heart failure and a diastolic heart failure, based on a cardiac function index. In a patient suffering from the diastolic heart failure, a myocardium is hypertrophied and increases in stiffness (hardness), so that the blood pressure in a left atrium increases and the pumping function of a heart is decreased. Accordingly, the patient shows a heart failure symptom such as a pulmonary edema. There is also a heart disease in which the blood pressure on a right atrium side increases due to pulmonary hypertension or the like, and the pumping function of a heart is decreased, thereby showing heart failure symptoms. 
     In recent years, for patients suffering from a heart failure, attention has been paid to a shunt treatment in which a shunt (through-hole) serving as an escape route for increased atrial pressure is formed in an atrial septum, thereby being able to reduce heart failure symptoms. In the shunt treatment, the atrial septum is accessed using a transvenous approach method, and a through-hole is formed. Then, a method has been known in which a through-hole is widened to a desired size and the through-hole is subjected to energy and cauterized, to form a shunt hole. 
     In addition, a method for widening a formed hole in a biological lumen is performed in cases other than the case of forming a shunt hole in the atrial septum. For example, Japanese Patent Application Publication No. 2018-23840 discloses a device that cuts and widens a blood vessel that is narrowed by arterioscleosis. In the device, an outer shaft is fixed to proximal portions of a plurality of expandable portions extending in an axial direction at a distal portion of the device, and an inner shaft penetrating through the outer shaft is fixed to distal portions of the plurality of expandable portions. Therefore, when the inner shaft is pulled to a proximal side with respect to the outer shaft, a compression force acts on the expandable portions, and the expandable portions are expanded to bend outward in a radial direction. 
     SUMMARY 
     In the device disclosed in Japanese Patent Application Publication No. 2018-23840, when the inner shaft is pulled to expand the expandable portions, the inner shaft may be bent, and a central axis of the expandable portions and a pulling axis of the inner shaft may be displaced from each other. In this case, the plurality of expandable portions arranged in a circumferential direction are not uniform, and an expansion force of the expandable portions is not uniform. Accordingly, the expansion force may be decreased, or a hole in a living body may be not expandable to a desired shape. 
     On the other hand, when a tube side shaft to be pulled so as to expand the expandable portions is made rigid, since the device is difficult to bend, the passability of the device in a delivery sheath that allows the device to reach a target site, or in a biological lumen such as a blood vessel is decreased. 
     The medical device disclosed here exhibits improved passability in a tubular member or in a biological lumen, and suppressing a decrease in expansion force to widen a biological tissue. 
     According to one aspect, there is provided a medical device including: a shaft portion that is elongate; and an expansion body provided at a distal portion of the shaft portion to be expandable and contractable in a radial direction. The shaft portion includes an outer tube, and an inner tube that is slidable in an axial direction inside the outer tube. The expansion body includes a first connecting portion connected to the outer tube, and a second connecting portion connected to the inner tube. The outer tube includes an opening end at which an opening portion is formed, the inner tube entering and exiting from the opening portion. The expansion body is settable to a reference form where the expansion body is widened in the radial direction in a natural state, and is settable to a contracted form where the expansion body is contracted in the radial direction, when the first connecting portion and the second connecting portion are more separated from each other than in the reference form. In the reference form, the opening end is located between the first connecting portion and the second connecting portion, and when the expansion body is deformed from the reference form into the contracted form, a part of the inner tube is extracted from the opening portion. 
     In the medical device configured as described above, in the contracted form where the inner tube is extracted from the outer tube, a range where the outer tube and the inner tube overlap each other between the first connecting portion and the second connecting portion is shortened. For this reason, in the contracted form where the expansion body is contracted, the flexibility of the medical device between the first connecting portion and the second connecting portion is improved, and the passability of the medical device in a tubular member such as a sheath or in a biological lumen is improved. In addition, in the medical device, in the reference form where the expansion body is expanded, the range where the outer tube and the inner tube overlap each other between the first connecting portion and the second connecting portion is lengthened. For this reason, in the medical device, the shaft portion is difficult to bend between the first connecting portion and the second connecting portion. For this reason, the medical device can maintain the expansion body in a proper shape in the reference form, so that a decrease in expansion force can be suppressed. 
     The expansion body may be settable to an expanded form where the expansion body is expanded in the radial direction, when the first connecting portion and the second connecting portion approach each other from the reference form, and when the expansion body is deformed from the reference form into the expanded form, a part of the inner tube may be stored inside the outer tube from the opening portion. Accordingly, even when a compression force is acted on the expansion body in the axial direction to set the expansion body to the expanded form where the expansion body is more expanded in the radial direction than in the reference form, the shaft portion is difficult to bend between the first connecting portion and the second connecting portion, so that buckling can be suppressed. For this reason, in the medical device, the expansion body is settable to the expanded form of a desired shape that is uniform in a circumferential direction, so that a decrease in expansion force can be suppressed and a biological tissue can be uniformly widened in the radial direction. 
     The outer tube and/or the inner tube may include a flexible portion having lower flexural rigidity than a portion adjacent to the flexible portion in the axial direction. In the reference form, the flexible portion may be located in a range where the outer tube and the inner tube overlap each other. In the contracted form, the flexible portion may be located in a range different from the range where the outer tube and the inner tube overlap each other. Accordingly, in the contracted form, the flexible portion is located outside the range where the outer tube and the inner tube overlap each other, so that the flexible portion can be flexibly bent. For this reason, in the contracted form, the flexibility of the medical device between the first connecting portion and the second connecting portion is improved, and the passability of the medical device in a tubular member such as a sheath or in a biological lumen is improved. In addition, in the reference form, since the flexible portion is located in the range where the outer tube and the inner tube overlap each other, the medical device is difficult to bend between the first connecting portion and the second connecting portion. Therefore, the medical device can maintain the expansion body in a proper shape in the reference form, so that a decrease in expansion force can be suppressed and a biological tissue can be uniformly widened in the radial direction. 
     The outer tube may include a first engagement portion. The inner tube may include a second engagement portion. At least in the reference form, the first engagement portion and the second engagement portion may be slidable in the axial direction, and come into contact with each other in a circumferential direction to limit relative rotation between the outer tube and the inner tube. Accordingly, at least in the reference form, relative rotation between the outer tube and the inner tube is limited. For this reason, at least in the reference form, the twisting of the expansion body can be suppressed. Therefore, in the medical device, the expansion body is settable to the reference form of a desired shape, and a decrease in expansion force can be suppressed. 
     A flexible portion may be formed of a slit portion having a spiral shape or a groove provided in the outer tube and/or in the inner tube. Accordingly, the flexible portion of the outer tube and/or the inner tube can be flexibly bent and easily processed. 
     A flexible portion may be formed of a plurality of wires. Accordingly, the flexible portion of the outer tube and/or the inner tube can be flexibly bent. 
     A flexible portion may be formed in a coil shape. Accordingly, the flexible portion of the outer tube and/or the inner tube can be flexibly bent. 
     A flexible portion may be made of a material softer than a material of a portion adjacent to the flexible portion in the axial direction. Accordingly, the flexible portion of the outer tube and/or the inner tube can be flexibly bent. 
     In addition, according to another aspect, there is provided a medical device including: a shaft portion that is elongate. The shaft portion may include an outer tube, and an inner tube that is slidable in an axial direction inside the outer tube. The outer tube may include an opening end at which an opening portion is formed, the inner tube entering and exiting from the opening portion. The shaft portion may be settable to an accommodated form where at least a part of the inner tube is accommodated in the outer tube, and may be settable to an extended form where the inner tube is extracted from the opening portion from the accommodated form. The outer tube and/or the inner tube may include a flexible portion having lower flexural rigidity than a portion adjacent to the flexible portion in the axial direction. In the accommodated form, the flexible portion may be located in a range where the outer tube and the inner tube overlap each other. In the extended form, the flexible portion may be located in a range different from the range where the outer tube and the inner tube overlap each other. 
     Accordingly, in the extended form, the flexible portion is located outside the range where the outer tube and the inner tube overlap each other, so that the flexible portion can be flexibly bent. For this reason, in the extended form, the flexibility of the medical device is improved, and the passability of the medical device in a tubular member such as a sheath or in a biological lumen is improved. In addition, in the accommodated form, the flexible portion is located in the range where the outer tube and the inner tube overlap each other. For this reason, in the accommodated form, it is possible to make the medical device difficult to bend. 
     According to another aspect, a treatment method to widen a through-hole in biological tissue comprises introducing an expansion body into the through-hole in the biological tissue so that the expansion body is positioned in the through hole. The expansion body includes a first connecting portion connected to an outer tube and a second connecting portion connected to an inner tube, with the inner tube being axially movable relative to the outer tube, and the outer tube includes an extending portion that extends from the first connecting portion and is located inwardly of the expansion body, with the extending portion of the outer tube having a distal open end. The introducing of the expansion body into the through-hole in the biological tissue occurs while the expansion body is in a contracted form and while a proximal portion of the inner tube extends from the distal open end of the extending portion of the outer tube. The treatment method may further involve radially outwardly widening the through-hole in the biological tissue by radially outwardly expanding the expansion body, wherein the radially outward expanding of the expansion body includes moving the first connecting portion and the second connecting portion towards one another while moving the proximal portion of the inner tube into the extending portion of the outer tube so that an axial distance between the first connecting portion and the second connecting portion when the expansion body is in the contracted state and is introduced into the through-hole in the biological tissue is greater than the axial distance between the first connecting portion and the second connecting portion when the expansion body is radially outwardly expanded during the radially outward widening of the through-hole in the biological tissue. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a front view illustrating an overall configuration of a medical device according to the present embodiment. 
         FIG. 2  is an enlarged perspective view of the vicinity of an expansion body. 
         FIGS. 3(A)-3(C)  illustrate front views of the vicinity of an outer tube and an inner tube through a storage sheath and through the expansion body,  FIG. 3(A)  illustrates a contracted form where the expansion body is contracted,  FIG. 3(B)  illustrates a reference form where the expansion body is in an original shape, and  FIG. 3(C)  illustrates an expanded form where the expansion body is expanded. 
         FIG. 4  is a view for describing a treatment method using the medical device according to the present embodiment, and is a view for schematically describing a state where the expansion body is disposed in a through-hole of an atrial septum, in which the medical device and a biological tissue are illustrated in a front view and in a cross-sectional view, respectively. 
         FIG. 5  is a front view illustrating the medical device that is bent in a delivery sheath, through the storage sheath and through the expansion body. 
         FIG. 6  is a view for schematically describing a state where the expansion body is disposed in the atrial septum, in which the medical device and the biological tissue are illustrated in a front view and in a cross-sectional view, respectively. 
         FIG. 7  is a view for schematically describing a state where the expansion body is expanded in diameter in the atrial septum, in which the medical device and the biological tissue are illustrated in a front view and in a cross-sectional view, respectively. 
         FIGS. 8(A) and 8(B)  illustrate plan views of the vicinity of an outer tube and an inner tube of a medical device according to a first modification example through a storage sheath and through an expansion body,  FIG. 8(A)  illustrates a contracted form, and  FIG. 8(B)  illustrates a reference form. 
         FIGS. 9(A) and 9(B)  illustrate plan views of the vicinity of an outer tube and an inner tube of a medical device according to a second modification example through a storage sheath and through an expansion body,  FIG. 9(A)  illustrates a contracted form, and  FIG. 9(B)  illustrates a reference form. 
         FIGS. 10(A) and 10(B)  illustrate plan views of the vicinity of an outer tube and an inner tube of a medical device according to a third modification example,  FIG. 10(A)  illustrates an extended form, and  FIG. 10(B)  illustrates an accommodated form. 
         FIGS. 11(A)-11(E)  illustrate plan views of the vicinities of flexible portions of modification examples in a medical device,  FIG. 11(A)  illustrates a fourth modification example,  FIG. 11(B)  illustrates a fifth modification example,  FIG. 11(C)  illustrates a sixth modification example,  FIG. 11(D)  illustrates a seventh modification example, and  FIG. 11(E)  illustrates an eighth modification example. 
         FIG. 12  is a front view of an expanded form illustrating the vicinity of the outer tube and the inner tube through the storage sheath and through the expansion body. 
     
    
    
     DETAILED DESCRIPTION 
     Set forth below with reference to the accompanying drawings is a detailed description of embodiments of a medical device representing examples of the medical device disclosed here. The dimensions or scales on the drawings may be exaggerated or different from actuality/reality for convenience of description and illustration. Dimensional ratios in the drawings may be exaggerated and different from actual ratios for convenience of description. In addition, in the specification, a side on which a medical device  10  is inserted into a biological lumen is referred to as a “distal side”, and a side on which operation is performed is referred to as a “proximal side”. 
     As illustrated in  FIG. 4 , the medical device  10  according to the present embodiment is configured to be able to expand a through-hole Hh formed in an atrial septum HA of a heart H of a patient and to perform maintenance treatment to maintain the size of the expanded through-hole Hh. 
     As illustrated in  FIGS. 1 and 2 , the medical device  10  of the present embodiment includes a shaft portion  20  that is elongate (elongated), an expansion body  21  provided at a distal portion of the shaft portion  20 , a pulling shaft  33  that expands the expansion body  21 , and an operation unit  23  provided at a proximal portion of the shaft portion  20 . The expansion body  21  is provided with an energy transmission element  22  for performing the aforementioned maintenance treatment. 
     The shaft portion  20  includes a main shaft  31  that holds the expansion body  21  at a distal portion of the main shaft  31 , a storage sheath  30  that stores the main shaft  31 , an outer tube  70  connected to the distal portion of the main shaft  31 , and an inner tube  60  that can be stored in the outer tube  70 . The storage sheath  30  is movable forward and backward with respect to the main shaft  31  in an axial direction. In a state where the storage sheath  30  is moved to a distal side or in the distal (forward) direction of the shaft portion  20 , the storage sheath  30  can store the expansion body  21  thereinside. The storage sheath  30  is moved to the proximal side or in the proximal direction from a state where the expansion body  21  is stored, and thus the expansion body  21  can be exposed. 
     A proximal portion of the main shaft  31  is connected to the operation unit  23 . The distal portion of the main shaft  31  is connected to a proximal portion of the expansion body  21  and to a proximal portion of the outer tube  70 . The outer tube  70  extends to the distal side from the distal portion of the main shaft  31 . That is, the outer tube  70  extends distally beyond the distal portion of the main shaft  31 . 
     The pulling shaft  33  is stored inside the main shaft  31 , the outer tube  70 , and the inner tube  60 . The pulling shaft  33  is a shaft for pulling to apply a compression force on the expansion body  21 . An axially orthogonal cross section of an outer peripheral surface of the pulling shaft  33  is a substantially circular shape. The pulling shaft  33  protrudes from a distal end of the inner tube  60  to the distal side, and a distal portion of the pulling shaft  33  is connected to a distal member  35 . A proximal portion of the pulling shaft  33  extends out to the proximal side or in the proximal direction from the operation unit  23  as shown in  FIG. 1 . The distal member  35  to which the distal portion of the pulling shaft  33  is fixed may not be fixed to the expansion body  21 . Accordingly, the distal member  35  can pull the expansion body  21  in a compression direction. In addition, when the expansion body  21  is stored in the storage sheath  30 , the distal member  35  is separated to the distal side from the expansion body  21 , so that the expansion body  21  can be easily moved in a stretching direction and storability can be improved. 
     The operation unit  23  includes a housing  40  to be gripped by an operator, an operation dial  41  to be rotationally operable by the operator, and a conversion mechanism  42  that operates in conjunction with rotation of the operation dial  41 . The pulling shaft  33  is held by the conversion mechanism  42  inside the operation unit  23 . The conversion mechanism  42  can move the held pulling shaft  33  forward and backward along the axial direction with rotation of the operation dial  41 . For example, a rack and pinion mechanism can be used as the conversion mechanism  42 . 
     As illustrated in  FIG. 2 , the expansion body  21  includes a plurality of wire portions  50  arranged or spaced apart from one another in a circumferential direction. In the present embodiment, four wire portions  50  are provided in the circumferential direction. The number of the wire portions  50  is not particularly limited. Each of the wire portions  50  is expandable and contractable in a radial direction of the expansion body  21 . A proximal portion of the wire portion  50  is connected to a first connecting portion  58  provided at the distal portion of the main shaft  31 . The first connecting portion  58  located at the proximal portion of the wire portion  50  is connected to the proximal portion of the inner tube  60  and to the distal portion of the main shaft  31 . A second connecting portion  59  located at a distal portion of the wire portion  50  is connected to a distal portion of the inner tube  60 . The distal portion of the wire portion  50  extends from the distal portion of the inner tube  60  to the proximal side or in the proximal direction. The wire portion  50  is inclined such that the size in the radial direction increases from both end portions toward a central portion in the axial direction. In addition, the wire portion  50  includes a holding portion  51  having a valley shape in the radial direction of the expansion body  21 , at the central portion of the wire portion  50  in the axial direction. 
     The holding portion  51  includes a proximal side holding portion  52 , and a distal side holding portion  53  located closer to the distal side than the proximal side holding portion  52 . That is, the distal side holding portion  53  is distal of the proximal side holding portion  52 . The holding portion  51  further includes a proximal side outward projection portion  55 , an inward projection portion  56 , and a distal side outward projection portion  57 . It is preferable that an interval between the proximal side holding portion  52  and the distal side holding portion  53  in the axial direction is slightly wider on a radially outward side than on a radially inward side, in a natural state where no external force acts thereon. Accordingly, a biological tissue is easily disposed between the proximal side holding portion  52  and the distal side holding portion  53  from the radially outward side. 
     The proximal side holding portion  52  includes a projection portion  54  protruding toward the distal side. The energy transmission element  22  is disposed on the projection portion  54 . The proximal side holding portion  52  may not include the projection portion  54 . Namely, the energy transmission element  22  may not protrude to the distal side. 
     The proximal side outward projection portion  55  is located on a proximal side of the proximal side holding portion  52 , and is formed in a shape projecting outward in the radial direction. The distal side outward projection portion  57  is located on a distal side of the distal side holding portion  53 , and is formed in a shape projecting outward in the radial direction. The inward projection portion  56  is located between the proximal side holding portion  52  and the distal side holding portion  53 , and is formed in a shape projecting inward in the radial direction. The proximal side outward projection portion  55 , the inward projection portion  56 , and the distal side outward projection portion  57  are stored in the storage sheath  30 , thus being deformable from a projection shape into a shape close to being flat. 
     In the present embodiment, the energy transmission element  22  is provided at the proximal side holding portion  52 , but the energy transmission element  22  may be provided at the distal side holding portion  53 . 
     Each of the wire portions  50  forming the expansion body  21  has, for example, a flat plate shape obtained by cutting a cylinder. A wire forming the expansion body  21  can have a thickness of 50 to 500 μm and a width of 0.3 to 2.0 mm. However, a wire forming the expansion body  21  may have dimensions outside these ranges. In addition, the shape of the wire portion  50  is not limited, and may have, for example, a circular cross-sectional shape or other cross-sectional shapes. 
     Since the energy transmission element  22  is provided at the projection portion  54  of the proximal side holding portion  52 , when the holding portion  51  holds the atrial septum HA, energy from the energy transmission element  22  is transmitted from a right atrium side to the atrial septum HA. When the energy transmission element  22  is provided at the distal side holding portion  53 , energy from the energy transmission element  22  is transmitted from a left atrium side to the atrial septum HA. 
     The energy transmission element  22  is configured as, for example, a bipolar electrode that receives electric energy from an energy supply device (not illustrated) that is an external device. In this case, energization is performed between the energy transmission elements  22  disposed on the wire portions  50 . The energy transmission element  22  and the energy supply device are connected to each other by a conducting wire (not illustrated) coated with an insulating coating material. The conducting wire is led out to the outside via the shaft portion  20  and via the operation unit  23 , and is connected to the energy supply device. 
     Alternatively, the energy transmission element  22  may be configured as a monopolar electrode. In this case, energization is performed between the energy transmission element  22  and a counter electrode plate prepared outside a body. In addition, the energy transmission element  22  may be a heating element (electrode chip) that receives high-frequency electric energy from the energy supply device to generate heat. In this case, energization is performed between the energy transmission elements  22  disposed on the wire portions  50 . Further, the energy transmission element  22  can be configured as an element capable of applying energy to the through-hole Hh, such as an element that exerts a heating or cooling action using microwave energy, ultrasound energy, coherent light such as laser, a heated fluid, a cooled fluid, or a chemical medium, an element that generates frictional heat, or a heater including an electric wire or the like, and a specific form of the energy transmission element  22  is not particularly limited. 
     The wire portion  50  can be made of a metallic material. As the metallic material, for example, a titanium-based (Ti—Ni, Ti—Pd, Ti—Nb—Sn, or the like) alloy, a copper-based alloy, stainless steel, β-titanium steel, or a Co—Cr alloy can be used. It is better to use an alloy or the like having a spring property such as a nickel-titanium alloy. However, the material for the wire portion  50  is not limited to these materials, and the wire portion  50  may be made of other materials. 
     The pulling shaft  33  is stored inside the shaft portion  20 . A guide wire lumen is formed in the pulling shaft  33  and in the distal member  35  along the axial direction, and a guide wire  11  can be inserted into the guide wire lumen. 
     Next, the outer tube  70  and the inner tube  60  will be described. As illustrated in  FIGS. 2 and 3 (B), the outer tube  70  extends to the distal side from the first connecting portion  58  at the proximal portion of the expansion body  21 . The outer tube  70  includes an opening end (open end)  72  at which an opening portion  71  is formed, on the distal side. In addition, a first engagement portion  73  having a slit shape and extending from the opening end  72  to the proximal side along the axial direction is formed in the outer tube  70 . The first engagement portion  73  has such a width in the circumferential direction that a second engagement portion  61  formed in the inner tube  60  can enter the first engagement portion  73 . It is preferable that the width of the first engagement portion  73  in the circumferential direction is widened at a distal portion of the first engagement portion  73 . Accordingly, the first engagement portion  73  easily receives the second engagement portion  61  from the distal side. The outer tube  70  includes one first engagement portion  73 , but may include two or more first engagement portions  73  at different locations in the circumferential direction. In a natural state where no external force acts on the expansion body  21 , the expansion body  21  is in a reference form where the expansion body  21  is deployed in the radial direction. In the reference form, the opening end  72  is located closer to the distal side than the first connecting portion  58 , and is closer to the proximal side than the second connecting portion  59 . 
     In the reference form where the expansion body  21  is widened with no external force acting on the expansion body  21 , a distance L 1  from the first connecting portion  58  to the opening end  72  is more than 0% of a distance L 2  from the first connecting portion  58  to the second connecting portion  59 , preferably 30% to 80%, more preferably 40% to 70%, and further preferably 50% to 60%. When the distance L 1  is too short, the range where the outer tube  70  and the inner tube  60  overlap each other between the first connecting portion  58  and the second connecting portion  59  is shortened, so that the effect of making the shaft portion difficult to bend in the reference form is decreased. When the distance L 1  is too long, the range where the outer tube  70  and the inner tube  60  overlap each other between the first connecting portion  58  and the second connecting portion  59  is lengthened, so that the effect of making the shaft portion  20  easy to bend in a contracted form where the expansion body  21  is contracted (refer to  FIG. 3(A) ) is decreased. 
     The inner tube  60  is slidable in the axial direction inside the outer tube  70 . The inner tube  60  extends to the proximal side or in the proximal direction from the second connecting portion  59  at the distal portion of the expansion body  21 . A proximal-most end  64  of the inner tube  60  is located closer to the proximal side than the opening end  72  of the outer tube  70 . That is, the proximal-most end  64  of the inner tube  60  is proximal of the opening end  72  of the outer tube  70 . The inner tube  60  includes a flexible portion  62  that has lower flexural rigidity and is easier to bend than a portion of the inner tube  60  adjacent to the flexible portion  62  in the axial direction. The flexible portion  62  can be disposed inside the outer tube  70  as illustrated in  FIGS. 3(B) and 3(C) , and can be extracted from the outer tube  70  to the distal side and disposed closer to the distal side than the outer tube  70  as illustrated in  FIG. 3(A) . The flexible portion  62  is formed in a spiral shape by forming a slit portion  63  having a spiral shape and penetrating through the flexible portion  62  from an outer peripheral surface to an inner peripheral surface. The slit portion  63  can be easily formed by, for example, laser processing. Protruding portions  66  to be fitted to a recessed portion  65  and to a recessed portion  65  are formed in surfaces that face each other while interposing the slit portion  63  therebetween. The protruding portions  66  are widened on a protruding direction side. For this reason, the protruding portion  66  has a structure where the protruding portion  66  does not come off from the recessed portion  65 . Therefore, the flexible portion  62  has a structure where the flexible portion  62  is easy to bend but is strong against a tensile force. In addition, the second engagement portion  61  protruding outward in the radial direction is formed on an outer peripheral surface of the inner tube  60 . As illustrated in  FIGS. 3(B) and 3(C) , the second engagement portion  61  can slidably enter the first engagement portion  73  of the outer tube  70 . The second engagement portion  61  is formed closer to the distal side than the flexible portion  62  (i.e., the second engagement portion  61  is distal of the flexible portion  62 ), but the position of the second engagement portion  61  is not particularly limited. Therefore, the second engagement portion  61  may be formed closer to the proximal side than the flexible portion  62 , or may be formed to overlap the flexible portion  62 . 
     It is preferable that the storage sheath  30  and the main shaft  31  of the shaft portion  20  are made of a material having a certain degree of flexibility. Examples of such a material include polyolefins such as polyethylene, polypropylene, polybutene, ethylene-propylene copolymer, ethylene-vinyl acetate copolymer, ionomer, and a mixture of two or more thereof, fluororesins such as soft polyvinyl chloride resin, polyamide, polyamide elastomer, polyether blockamide, polyester, polyester elastomer, polyurethane, and polytetrafluoroethylene, polyimide, PEEK, silicone rubber, and latex rubber. 
     The pulling shaft  33  can be made of, for example, an elongate wire such as a metallic material such as stainless steel or a super-elastic alloy such as a nickel-titanium alloy or a copper-zinc alloy, or a resin material having relatively high rigidity. In addition, the pulling shaft  33  may be formed by coating the above material with a resin material such as polyvinyl chloride, polyethylene, polypropylene, ethylene-propylene copolymer, or fluororesin. 
     The distal member  35 , the inner tube  60 , and the outer tube  70  can be made of, for example, a metallic material such as stainless steel or a super-elastic alloy such as a nickel-titanium alloy or a copper-zinc alloy, or a resin material having relatively high rigidity. 
     Next, a treatment method using the medical device  10  according to the present embodiment will be described. The treatment method is performed on a patient suffering from a heart failure (left heart failure). More specifically, as illustrated in  FIG. 4 , the treatment method is performed on a patient suffering from a chronic heart failure in which a myocardium of a left ventricle of the heart H is hypertrophied and increases in stiffness (hardness) to cause an increase in blood pressure in a left atrium HLa. 
     When the operator forms the through-hole Hh, the operator delivers an introducer in which a guiding sheath and a dilator are combined together, to the vicinity of the atrial septum HA. The introducer can be delivered to, for example, a right atrium HRa via an inferior vena cava Iv. In addition, the introducer can be delivered using the guide wire  11 . The operator can insert the guide wire  11  into the dilator, and deliver the introducer along the guide wire  11 . The insertion of the introducer into or the insertion of the guide wire  11  into a living body can be performed using a known method such as using an introducer for blood vessel introduction. 
     Next, the operator causes a puncture device and the dilator to penetrate through the atrial septum HA from a right atrium HRa side toward a left atrium HLa side to form the through-hole Hh. For example, a device such as a wire having a sharp distal end can be used as the puncture device. The puncture device is inserted into the dilator, and is delivered to the atrial septum HA. After the guide wire  11  is removed from the dilator, instead of the guide wire  11 , the puncture device can be delivered to the atrial septum HA. 
     Next, the operator delivers the medical device  10  to the vicinity of the atrial septum HA along the guide wire  11  inserted into the left atrium HLa from the right atrium HRa via the through-hole Hh in advance. At this time, a part of a distal portion of the medical device  10  passes through the through-hole Hh opened in the atrial septum HA, and reaches the left atrium HLa. In addition, when the medical device  10  is inserted, as illustrated in  FIG. 3(A) , the expansion body  21  is in the contracted form where the expansion body  21  is stored in the storage sheath  30 . In the contracted form, the proximal side outward projection portion  55 , the inward projection portion  56 , and the distal side outward projection portion  57  that have a projection shape in the reference form are elastically deformed into a shape close to being flat, so that the expansion body  21  is contracted in the radial direction. In the contracted form, the flexible portion  62  of the inner tube  60  is located closer to the distal side than the outer tube  70  (i.e., the flexible portion  62  is distal of the outer tube  70 ). For this reason, the flexible portion  62  is not covered with the outer tube  70 . Accordingly, the flexible portion  62  can be flexibly bent. Therefore, as illustrated in  FIG. 5 , when the flexible portion  62  is moved in a delivery sheath  80  for transporting the distal portion of the medical device  10  to a target position in the living body, or in a blood vessel, the flexible portion  62  can be easily bent according to the bending of the delivery sheath  80  or of the blood vessel. For this reason, the passability of the medical device  10  in the delivery sheath  80  or in the blood vessel is improved. 
     Next, the storage sheath  30  is moved to the proximal side or in the proximal direction to expose a distal side portion of the expansion body  21  into the left atrium HLa. Accordingly, the distal side portion of the expansion body  21  is deployed in the radial direction inside the left atrium HLa by its own restoring force. Next, as illustrated in  FIGS. 3(B)  and  6 , the storage sheath  30  is moved to the proximal side to expose the entirety of the expansion body  21 . Accordingly, a proximal side portion of the expansion body  21  is deployed in the radial direction inside the right atrium HRa by its own restoring force. At this time, the inward projection portion  56  is disposed inside the through-hole Hh. Accordingly, the entirety of the expansion body  21  is deployed by its own elastic force, and restores to the original reference form or to a form close to the reference form. At this time, the atrial septum HA is disposed between the proximal side holding portion  52  and the distal side holding portion  53 . The expansion body  21  may come into contact with the through-hole Hh, thereby returning to a shape close to the reference form instead of completely returning to the reference form. In this state, the expansion body  21  is not covered with the storage sheath  30  and does not receive a force from the pulling shaft  33 . This form of the expansion body  21  can be defined as being included in the reference form. 
     When the expansion body  21  is deformed from the contracted state into the reference form, the first connecting portion  58  and the second connecting portion  59  approach each other. Accordingly, the inner tube  60  connected to the second connecting portion  59  moves to the proximal side or in the proximal direction. For this reason, the flexible portion  62  of the inner tube  60  enters the inside of the outer tube  70  from the opening portion  71 . For this reason, the flexible portion  62  is surrounded by the outer tube  70 , and overlaps the outer tube  70 . As a result, the flexible portion  62  is difficult to bend. In addition, the range in the axial direction where the outer tube  70  and the inner tube  60  overlap each other is longer in the reference form (refer to  FIG. 3(B) ) and in an expanded form (refer to  FIG. 3(C) ) than in the contracted form (refer to  FIG. 3(A) ). For this reason, the outer tube  70  and the inner tube  60  between the first connecting portion  58  and the second connecting portion  59  are more difficult to bend in the reference form and in the expanded form than in the contracted form. For this reason, the expansion body  21  can be uniformly widened to cause an expansion force to uniformly act on the through-hole Hh of the atrial septum HA. 
     In addition, when the expansion body  21  is in the reference form, the second engagement portion  61  protruding from the outer peripheral surface of the inner tube  60  is accommodated in the first engagement portion  73  having a slit shape which is formed in the outer tube  70 . Accordingly, the first engagement portion  73  and the second engagement portion  61  engage with each other, and the inner tube  60  is not rotatable with respect to the outer tube  70 . For this reason, it is possible to suppress the twisting of the expansion body  21 . For this reason, the expansion body  21  can be uniformly widened with a uniform expansion force to cause an expansion force to uniformly act on the through-hole Hh of the atrial septum HA. 
     Next, the operator operates the operation unit  23  in a state where the atrial septum HA is held by the holding portion  51 , to move the pulling shaft  33  to the proximal side. Accordingly, as illustrated in  FIGS. 3(C)  and  7 , the expansion body  21  receiving a compression force in the axial direction is deformed into the expanded form where the expansion body  21  is more expanded in the radial direction than in the reference form. In the expanded form of the expansion body  21 , the proximal side holding portion  52  and the distal side holding portion  53  approach each other, and the atrial septum HA is held between the proximal side holding portion  52  and the distal side holding portion  53 . The holding portion  51  additionally expands in a state where the holding portion  51  holds the atrial septum HA, to widen the through-hole Hh in the radial direction. 
     In the expanded form, similarly to the reference form, the flexible portion  62  is surrounded by the outer tube  70 , and axially overlaps the outer tube  70 . For this reason, the flexible portion  62  is difficult to bend. In addition, since the range in the axial direction where the outer tube  70  and the inner tube  60  axially overlap each other is longer in the expanded form than in the contracted form, the outer tube  70  and the inner tube  60  between the first connecting portion  58  and the second connecting portion  59  are difficult to bend in the expanded form. For this reason, even when the outer tube  70  and the inner tube  60  between the first connecting portion  58  and the second connecting portion  59  receives a compression force due to pulling of the pulling shaft  33 , the outer tube  70  and the inner tube  60  are difficult to buckle. Therefore, the expansion body  21  can be uniformly widened with a uniform expansion force to uniformly widen the through-hole Hh in the radial direction. 
     In addition, in the expanded form, similarly to the reference form, the first engagement portion  73  and the second engagement portion  61  engage with each other, and the inner tube  60  is not rotatable with respect to the outer tube  70 . For this reason, it is possible to suppress the twisting of the expansion body  21 . For this reason, the expansion body  21  can be uniformly widened with a uniform expansion force to uniformly widen the through-hole Hh in the radial direction. 
     In the expanded form, when the operator moves the pulling shaft  33  further to the proximal side than in the state illustrated in  FIGS. 3(C)  and  7 , as illustrated in  FIG. 12 , the opening end  72  that is a distal side end portion of the outer tube  70  abuts against the second connecting portion  59 . Accordingly, a relative axial movement between the outer tube  70  and the inner tube  60  is limited, and excessive expansion of the expansion body  21  is limited. As a result, excessive expansion of the through-hole Hh can be limited, and safety can be improved. The proximal-most end  64  of the inner tube  60  may abut against, for example, a structure protruding from an inner peripheral surface of the outer tube  70  before the opening end  72  of the outer tube  70  abuts against the second connecting portion  59  when the operator moves the pulling shaft  33  to the proximal side. Even with such a configuration, a relative movement between the outer tube  70  and the inner tube  60  can be limited, and excessive expansion of the expansion body  21  can be limited. As a result, excessive expansion of the through-hole Hh can be limited, and safety can be improved. 
     After the through-hole Hh is expanded, hemodynamics is confirmed. As illustrated in  FIG. 4 , the operator delivers a hemodynamics confirmation device  100  to the right atrium HRa via the inferior vena cava Iv. For example, a known echo catheter can be used as the hemodynamics confirmation device  100 . The operator can cause a display device such as a display to display an echo image acquired by the hemodynamics confirmation device  100 , and confirm the amount of blood passing through the through-hole Hh, based on a display result. 
     Next, the operator performs a maintenance treatment to maintain the size of the through-hole Hh. In the maintenance treatment, energy is applied to an edge portion of the through-hole Hh through the energy transmission element  22 , so that the edge portion of the through-hole Hh is cauterized (heated and cauterized) by the energy. When a biological tissue in the vicinity of the edge portion of the through-hole Hh is cauterized through the energy transmission element  22 , a degenerated portion in which the biological tissue is degenerated is formed in the vicinity of the edge portion. Since the biological tissue in the degenerated portion is in a state where elasticity is lost, the through-hole Hh can maintain a shape when the through-hole Hh is widened by the expansion body  21 . 
     In the expanded form, as described above, since the expansion body  21  is uniformly widened with a uniform expansion force, the energy transmission element  22  provided in each of the wire portions  50  is properly pressed against the atrial septum HA. In addition, the energy transmission element  22  is disposed on the projection portion  54  of the proximal side holding portion  52 . For this reason, the maintenance treatment is performed in a state where the energy transmission element  22  is buried in the biological tissue by pressing the projection portion  54  against the atrial septum HA. Accordingly, the energy transmission element  22  does not come into contact with the blood during the maintenance treatment, so that it is possible to suppress the generation of blood clots or the like caused by the leakage of a current to the blood. 
     After the maintenance treatment, hemodynamics is confirmed again, and when the amount of the blood passing through the through-hole Hh reaches a desired amount, the operator reduces the expansion body  21  in diameter. The operator moves the storage sheath  30  with respect to the expansion body  21  in a distal end direction. Accordingly, the expansion body  21  is stored in the storage sheath  30  from the proximal side, and is in the contracted form. Further, the operator removes the entirety of the medical device  10  out of the living body to end the treatment. 
     As described above, the medical device  10  according to the aforementioned embodiment is a medical device including: the shaft portion  20  that is elongate; and the expansion body  21  provided at the distal portion of the shaft portion  20  to be expandable and contractable in a radial direction. The shaft portion  20  includes the outer tube  70 , and the inner tube  60  that is slidable in the axial direction inside the outer tube  70 . The expansion body  21  includes the first connecting portion  58  connected to the outer tube  70 , and the second connecting portion  59  connected to the inner tube  60 . The outer tube  70  includes the opening end  72  at which the opening portion  71  is formed, the inner tube  60  entering and exiting from the opening portion  71 . The expansion body  21  is settable to or positionable in the reference form where the expansion body  21  is widened in the radial direction in a natural state, and is settable to or positionable in the contracted form where the expansion body  21  is contracted in the radial direction, when the first connecting portion  58  and the second connecting portion  59  are more separated from each other compared to the reference form. In the reference form, the opening end  72  is located between the first connecting portion  58  and the second connecting portion  59 , and when the expansion body  21  is deformed from the reference form into the contracted form, a part of the inner tube  60  is extracted from the opening portion  71 . Accordingly, in the medical device  10 , in the contracted form where the inner tube  60  is extracted from the outer tube  70 , the range where the outer tube  70  and the inner tube  60  overlap (axially overlap) each other between the first connecting portion  58  and the second connecting portion  59  is shortened. For this reason, in the contracted form where the expansion body  21  is contracted, the flexibility of the medical device  10  between the first connecting portion  58  and the second connecting portion  59  is improved, and the passability of the medical device  10  in a tubular member such as the delivery sheath  80  or in a biological lumen is improved. In addition, in the medical device  10 , in the reference form where the expansion body  21  is expanded, the range where the outer tube  70  and the inner tube  60  overlap each other between the first connecting portion  58  and the second connecting portion  59  is lengthened. For this reason, in the medical device  10 , the shaft portion  20  is difficult to bend between the first connecting portion  58  and the second connecting portion  59 . For this reason, the medical device  10  can maintain the expansion body  21  in a proper shape in the reference form, so that a decrease in expansion force can be suppressed and a biological tissue can be uniformly widened in the radial direction. The first connecting portion  58  of the expansion body  21  may be directly connected to the outer tube  70  or may be indirectly connected to the outer tube  70  via another member. In addition, the second connecting portion  59  of the expansion body  21  may be directly connected to the inner tube  60  or may be indirectly connected to the inner tube  60  via another member. 
     In addition, the expansion body  21  is settable to or positionable in the expanded form where the expansion body  21  is expanded in the radial direction, when the first connecting portion  58  and the second connecting portion  59  approach each other from the reference form, and when the expansion body  21  is deformed from the reference form into the expanded form, a part of the inner tube  60  is stored inside or positioned in the outer tube  70  from the opening portion  71 . Accordingly, even when a compression force is acted on the expansion body  21  in the axial direction to set the expansion body  21  to the expanded form where the expansion body  21  is more expanded in the radial direction than in the reference form, the shaft portion  20  is difficult to bend between the first connecting portion  58  and the second connecting portion  59 , so that buckling can be suppressed. For this reason, in the medical device  10 , the expansion body  21  is settable to the expanded form of a desired shape that is uniform in the circumferential direction, so that a decrease in expansion force can be suppressed and a biological tissue can be uniformly widened in the radial direction. 
     In addition, the inner tube  60  includes the flexible portion  62  having lower flexural rigidity than a portion adjacent to the flexible portion  62  in the axial direction. In the reference form, the flexible portion  62  is located in a range where the outer tube  70  and the inner tube  60  overlap (axially overlap) each other. In the contracted form, the flexible portion  62  is located in a range different from the range where the outer tube  70  and the inner tube  60  axially overlap each other. Accordingly, in the contracted form, the flexible portion  62  is located outside the range where the outer tube  70  and the inner tube  60  overlap each other, so that the flexible portion  62  can be flexibly bent. For this reason, in the contracted form, the flexibility of the medical device  10  between the first connecting portion  58  and the second connecting portion  59  is improved, and the passability of the medical device  10  in a tubular member such as the delivery sheath  80  or in a biological lumen is improved. In addition, in the reference form, since the flexible portion  62  is located in the range where the outer tube  70  and the inner tube  60  overlap each other, the medical device  10  is difficult to bend between the first connecting portion  58  and the second connecting portion  59 . Therefore, the medical device  10  can maintain the expansion body  21  in a proper shape in the reference form, so that a decrease in expansion force can be suppressed and a biological tissue can be uniformly widened in the radial direction. 
     In addition, the outer tube  70  includes the first engagement portion  73 . The inner tube  60  includes the second engagement portion  61 . At least in the reference form, the first engagement portion  73  and the second engagement portion  61  are slidable in the axial direction, and come into contact with each other in the circumferential direction to limit relative rotation between the outer tube  70  and the inner tube  60 . Accordingly, at least in the reference form, relative rotation between the outer tube  70  and the inner tube  60  is limited. For this reason, at least in the reference form, the twisting of the expansion body  21  can be suppressed. Therefore, in the medical device  10 , the expansion body  21  is settable to the reference form of a desired shape, and a decrease in expansion force can be suppressed. 
     In addition, the flexible portion  62  is formed of the slit portion  63  having a spiral shape provided in the inner tube  60 . Accordingly, the flexible portion  62  can be flexibly bent and easily processed. 
     Another aspect of the disclosure here involves the treatment method. The treatment method is a treatment method in which the through-hole Hh that is opened in a biological tissue is widened using the medical device  10 , in which the medical device  10  includes the shaft portion  20  that is elongate, and the expansion body  21  provided at the distal portion of the shaft portion  20  to be expandable and contractable in the radial direction, the shaft portion  20  includes the outer tube  70 , and the inner tube  60  that is slidable in the axial direction inside the outer tube  70 , the expansion body  21  includes the first connecting portion  58  connected to the outer tube  70 , and the second connecting portion  59  connected to the inner tube  60 , the outer tube  70  includes the opening end  72  at which the opening portion  71  is formed, the inner tube  60  entering and exiting from the opening portion  71 , and the expansion body  21  is settable to the reference form where the expansion body  21  is widened in the radial direction, and is settable to the contracted form where the expansion body  21  is contracted in the radial direction, when the first connecting portion  58  and the second connecting portion  59  are more separated from each other than in the reference form, the method including: transporting the expansion body  21  in a living body and inserting the expansion body  21  into the through-hole Hh that is opened in the biological tissue, with the expansion body  21  set to the contracted form; and widening the through-hole Hh using the expansion body  21  with the expansion body  21  set to the reference form inside the through-hole Hh. 
     In the treatment method configured as described above, in the contracted form where the inner tube  60  is extracted from the outer tube  70 , the range where the outer tube  70  and the inner tube  60  overlap each other between the first connecting portion  58  and the second connecting portion  59  is shortened. For this reason, according to the treatment method, in the contracted form where the expansion body  21  is contracted, flexibility between the first connecting portion  58  and the second connecting portion  59  is improved, and passability in a tubular member such as the delivery sheath  80  or in a biological lumen is improved. In addition, in the reference form where the expansion body  21  is expanded, the range where the outer tube  70  and the inner tube  60  overlap each other between the first connecting portion  58  and the second connecting portion  59  is lengthened. For this reason, in the medical device  10 , the shaft portion  20  is difficult to bend between the first connecting portion  58  and the second connecting portion  59 . For this reason, according to the treatment method, the expansion body  21  can be maintained in a proper shape in the reference form, so that a decrease in expansion force can be suppressed and a biological tissue can be uniformly widened in the radial direction. 
     The invention is not limited only to the aforementioned embodiment and various modifications can be made by those skilled in the art without departing from the technical concept of the invention. For example, the biological lumen to which the medical device  10  is applied is not limited to blood vessels, and may be, for example, a vessel, a ureter, a bile duct, an ovarian duct, a hepatic duct, a lymph duct, or the like. 
     In addition, as in a first modification example illustrated in  FIGS. 8(A) and 8(B) , a flexible portion  74  may be formed not in the inner tube  60  but in the outer tube  70 . The flexible portion  74  is formed of, for example, a plurality of slit portions  75 . In the contracted form, as illustrated in  FIG. 8(A) , the flexible portion  74  of the outer tube  70  is disposed at a position where the flexible portion  74  does not overlap (axially overlap) the inner tube  60  in the axial direction. For this reason, the flexible portion  74  of the outer tube  70  can be easily bent. In addition, in the reference form and in the expanded form, as illustrated in  FIG. 8(B) , the flexible portion  74  of the outer tube  70  is disposed at a position where the flexible portion  74  overlaps the inner tube  60  in the axial direction. For this reason, the flexible portion  74  of the outer tube  70  is difficult to bend. In addition, the medical device  10  may include both the inner tube  60  including the flexible portion  74  illustrated in  FIG. 3 , and the outer tube  70  including the flexible portion  74  illustrated in  FIGS. 8(A) and 8(B) . 
     In addition, both the inner tube  60  and the outer tube  70  may not include the flexible portion  62 . The range in the axial direction where the outer tube  70  and the inner tube  60  overlap each other is longer in the reference form (refer to  FIG. 3(B) ) and in the expanded form (refer to  FIG. 3(C) ) than in the contracted form (refer to  FIG. 3(A) ). For this reason, even when the outer tube  70  and the inner tube  60  between the first connecting portion  58  and the second connecting portion  59  do not include the flexible portion  62 , bending is more difficult in the reference form and in the expanded form than in the contracted form. 
     In addition, as in a second modification example illustrated in  FIGS. 9(A) and 9(B) , the outer tube  70  may be connected to the second connecting portion  59 , and the inner tube  60  may be connected to the first connecting portion  58 . 
     In addition, as in a third modification example illustrated in  FIGS. 10(A) and 10(B) , the medical device  10  may not include the expansion body  21 . The distal portion of the pulling shaft  33  is connected to the inner tube  60 . When an operator pulls the pulling shaft  33 , as illustrated in  FIG. 10(B) , the medical device  10  is set to the accommodated form where at least a part of the inner tube  60  including the flexible portion  62  is disposed at a position where at least the part overlaps (axially overlaps) the outer tube  70 . In addition, when the operator pushes the pulling shaft  33 , as illustrated in  FIG. 10(A) , the medical device  10  is set to the extended form where the flexible portion  62  of the inner tube  60  is disposed at a position where the flexible portion  62  does not overlap the outer tube  70 . 
     As described above, the medical device  10  according to the third modification example includes the shaft portion  20  that is elongate. The shaft portion  20  includes the outer tube  70 , and the inner tube  60  that is slidable in the axial direction inside the outer tube  70 . The outer tube  70  includes the opening end  72  at which the opening portion  71  is formed, the inner tube  60  entering and exiting from the opening portion  71 . The shaft portion  20  is settable to the accommodated form where at least a part of the inner tube  60  is accommodated in the outer tube  70 , and is settable to the extended form where the inner tube  60  is extracted from the opening portion  71  from the accommodated form. The outer tube  70  and/or the inner tube  60  includes the flexible portion  62  having lower flexural rigidity than a portion adjacent to the flexible portion  62  in the axial direction. In the accommodated form, the flexible portion  62  is located in a range where the outer tube  70  and the inner tube  60  overlap each other, and in the extended form, the flexible portion  62  is located in a range different from the range where the outer tube  70  and the inner tube  60  overlap each other. Accordingly, in the extended form, the flexible portion  62  is located outside the range where the outer tube  70  and the inner tube  60  overlap each other, so that the flexible portion  62  can be flexibly bent. For this reason, in the extended form, the flexibility of the medical device  10  between the first connecting portion  58  and the second connecting portion  59  is improved, and the passability of the medical device  10  in a tubular member such as the delivery sheath  80  or in a biological lumen is improved. In addition, in the accommodated form, the flexible portion  62  is located in the range where the outer tube  70  and the inner tube  60  overlap each other. For this reason, in the accommodated form, it is possible to make the medical device  10  difficult to bend between the first connecting portion  58  and the second connecting portion  59 . The medical device  10  can be, for example, a catheter that bends easily until the catheter reaches a stenosed site and is difficult to bend at the stenosed site to exert a strong pushing force, a catheter that forms a bent or meandering lumen into a linear shape, and the like. 
     In addition, the form of the flexible portion  62  is not particularly limited as long as the flexible portion  62  is more flexible than a portion adjacent to the flexible portion  62  in the axial direction. For example, the flexible portion  62  may be formed as a non-through groove in the inner peripheral surface and/or in the outer peripheral surface of the inner tube  60  or the outer tube  70 . In addition, as illustrated in  FIG. 11(A) , the flexible portion  62  may be a slit portion or a non-through groove that is formed to extend in the circumferential direction instead of having a spiral shape. In addition, as illustrated in  FIG. 11(B) , the flexible portion  62  may be a plurality of through-holes or a plurality of non-through holes. In addition, as illustrated in  FIG. 11(C) , the flexible portion  62  may be formed to be thinner than a portion adjacent to the flexible portion  62  in the axial direction. In addition, as illustrated in  FIG. 11(D) , the flexible portion  62  may be formed in a coil shape. In addition, as illustrated in  FIG. 11(E) , the flexible portion  62  may be formed by twisting or knitting a plurality of wires. In addition, the flexible portion  62  may be made of a material softer than the material of a portion adjacent to the flexible portion  62  in the axial direction. The hardness (softness) of the material can be specified by, for example, Rockwell hardness, Brinnel hardness, Vickers hardness, Shore hardness, durometer hardness, and the like. 
     In addition, the inner tube  60  may be connected to the second connecting portion  59  so as to be slightly movable. In addition, the outer tube  70  may be connected to the first connecting portion  58  so as to be slightly movable. 
     The detailed description above describes embodiments of a medical device and treatment method representing examples of the medical device and treatment method disclosed here. The invention is not limited, however, to the precise embodiments and variations described. Various changes, modifications and equivalents can be effected by one skilled in the art without departing from the spirit and scope of the invention as defined in the accompanying claims. It is expressly intended that all such changes, modifications and equivalents which fall within the scope of the claims are embraced by the claims. 
     REFERENCE SIGNS LIST 
       10 : Medical device 
       11 : Guide wire 
       20 : Shaft portion 
       21 : Expansion body 
       30 : Storage sheath 
       58 : First connecting portion 
       59 : Second connecting portion 
       60 : Inner tube 
       61 : Second engagement portion 
       62 ,  74 : Flexible portion 
       63 ,  75 : Slit portion 
       70 : Outer tube 
       71 : Opening portion 
       72 : Opening end 
       73 : First engagement portion 
       74 : Flexible portion