Patent Publication Number: US-2023149150-A1

Title: Stent Graft

Description:
REFERENCE TO RELATED APPLICATIONS 
     This application is a Continuation Application of International Application No. PCT/JP2021/025628, filed Jul. 7, 2021, which claims priority from Japanese Patent Application No. 2020-116957, filed on Jul. 7, 2020. This disclosure of the foregoing application is hereby incorporated by reference in its entirety. 
    
    
     BACKGROUND ART 
     Stent-graft insertion is known as a medical treatment for an aortic aneurysm. With stent-graft insertion, a catheter fit with a deflated stent graft is inserted into the aorta and moved to the affected area, after which the stent graft is placed in position. The stent graft that has been placed at the affected area then expands from the restoring force of the stent, and sticks to the inner wall of the blood vessel. As a result, the stent graft inhibits the flow of blood into the aortic aneurysm. Because stent-graft insertion does not require surgery where a large incision would be made in the body, it is a minimally invasive medical treatment. 
     A stent graft to be placed in an aortic arch is known. The stent graft has, as a structure for accommodating the sharp bend of the aortic arch, a graded structure. The graded structure is formed by changing, in the circumferential direction, the length in the longitudinal direction between the mountains and valleys of linear struts that form the tubular unit of the stent graft. 
     DESCRIPTION 
     With the known stent graft, there are cases in which the stent graft is unable to follow the sharp curve of the aortic arch and the closeness of contact with respect to the inner wall of the blood vessel therefore decreases. 
     The object of the present disclosure is to provide a stent graft able to suitably closely contact the inner wall of a blood vessel. 
     A stent graft of the present disclosure includes a tubular member and a plurality of stent rings. The tubular member extends between a proximal end that is an end portion on one side in a predetermined axial direction, and a distal end that is an end portion on the other side in the axial direction. The plurality of stent rings are fixed to a side wall of the tubular member and formed of struts extending in a ring shape in a circumferential direction of the tubular member, while alternatingly bending toward the proximal end side and toward the distal end side. The plurality of stent rings include at least a plurality of fluctuating rings and a small fixed ring. The plurality of fluctuating rings include a first region in which an amplitude in the axial direction is a first value, and a second region in which an amplitude is a second value that is smaller than the first value. A maximum value of an amplitude of the small fixed ring is a third value that is smaller than the first value. The plurality of fluctuating rings are arranged in order of a first fluctuating ring, a second fluctuating ring . . . , and an Nth (where N is an integer of 3 or more) fluctuating ring, from the proximal end side toward the distal end side. The first distance that is a maximum value of a distance between a center position in the axial direction of the first fluctuating ring and a center position in the axial direction of the second fluctuating ring is greater than any nth distance that is a maximum value of a distance in the axial direction between a center position in the axial direction of an nth (where n is an integer equal to or greater than 2 and equal to or less than N−1) fluctuating ring and a center position in the axial direction of an n+1th fluctuating ring. 
     The portion of the stent graft between the first fluctuating ring and the second fluctuating ring bends more easily than the portion between the nth fluctuating ring and the n+1th fluctuating ring. Therefore, with the stent graft, the portion between the first fluctuating ring and the second fluctuating ring can be made to follow the sharp curve of an aortic blood vessel, so the tubular member can be made to suitably closely contact the inner wall of the blood vessel at this portion. 
    
    
     
         FIG.  1    is a side view of a stent graft. 
         FIG.  2    is an enlarged side view of the area near a proximal end of the stent graft. 
         FIG.  3    is an developed view of a small fixed ring. 
         FIG.  4    is an enlarged side view of the area near a first fluctuating ring to a third fluctuating ring of the stent graft. 
         FIG.  5    is an developed view of the first fluctuating ring. 
         FIG.  6    is an developed view of an nth fluctuating ring. 
         FIG.  7    is an enlarged side view of the area near a distal end of the stent graft. 
         FIG.  8    is an developed view of an mth large fixed ring. 
         FIG.  9    is a side view of the stent graft. 
         FIG.  10    is an developed view of an uncovered section and the small fixed ring. 
         FIG.  11    is an enlarged side view of the area near the proximal end of the stent graft. 
         FIG.  12    is a view showing the stent graft placed in a thoracic aorta. 
         FIG.  13    is an enlarged view of a portion of  FIG.  12   . 
     
    
    
     A stent graft  1 A of one embodiment of the present disclosure will be described. In the present embodiment, unless otherwise specified, direction and distance and the like will be described assuming that the stent graft  1 A is in a linearly extended state. A left side and a right side in  FIG.  1    define a proximal side and a distal side, respectively, of the stent graft  1 A. A direction extending between the proximal side and the distal side will be defined as an axial direction D. An upper side and a lower side in  FIG.  1    define a greater curvature side and a lesser curvature side, respectively, of the stent graft  1 A. A direction extending between the greater curvature side and the lesser curvature side will be defined as an expansion-contraction direction E. 
     Overview of Stent Graft  1 A 
     The stent graft  1 A is used to treat, by stent-graft insertion, an aortic aneurysm formed near an aortic arch of a thoracic aorta, or an aortic dissection in which a proximal dissection cavity (entry) has formed near the aortic arch. As shown in  FIG.  1   , the stent graft  1 A has, as the main constituent elements, a tubular member  2 A, a plurality of stent rings  2 B, and an uncovered section  7 . 
     The stent graft  1 A is fitted into a delivery system, not shown in the drawings, in a state folded up inside. The delivery system is inserted into the body through an incision opened in a blood vessel at the base of a leg, and guided to the affected area. Then, the stent graft  1 A is placed at the affected area. The tubular member  2 A of the stent graft  1 A is expanded by the elastic force of the plurality of stent rings  2 B to closely contact the inside of the affected area. The tubular member  2 A inhibits blood from flowing into a portion of a blood vessel where there is an aneurysm or dissection cavity, thereby protecting the blood vessel. By optimizing the angle of the proximal end, the uncovered section  7  of the stent graft  1 A inhibits the occurrence of a phenomenon (end leak) where blood leaks from an opening  21 A of the tubular member  2 A placed at the affected area and flows into the aortic aneurysm or dissection cavity. Note that hereinafter, unless otherwise specified, each structure of the stent graft  1 A will be described assuming that the tubular member  2 A is in an expanded state (the state shown in  FIG.  1   , etc.) by the plurality of stent rings  2 B. 
     Tubular Member  2 A 
     The tubular member  2 A is an artificial blood vessel (graft) with low water permeability. The tubular member  2 A is formed by synthetic-resin graft material. The tubular member  2 A has a hollow, long, thin structure, and extends along the axial direction D. Of both end portions in the axial direction D of the tubular member  2 A, the end portion on the proximal side will be referred to as a proximal end  21 , and the end portion on the distal side will be referred to as a distal end  22 . The tubular member  2 A extends between the proximal end  21  and the distal end  22 . The cross-sectional shape when a side wall  20  of the tubular member  2 A is cut by a plane orthogonal to the axial direction D is circular. An inner surface  23  of the side wall  20  has an internal cavity  20 P that passes through in the axial direction D. The diameter r of the internal cavity  20 P is constant between the proximal end  21  and the distal end  22 . The stent graft  1 A fits inside a delivery system and moves inside the blood vessel along a guide wire. A virtual line extending in the axial direction D and passing through the center of the internal cavity  20 P of the tubular member  2 A will be defined as a center line C. The direction following an outer surface  24  of the side wall  20  of the tubular member  2 A and intersecting the axial direction D will be defined as a circumferential direction. 
     A thickness d of the tubular member  2 A, a length  1  in the axial direction D from the proximal end  21  to the distal end  22  of the tubular member  2 A, and the diameter r, are not particularly limited. As an example, the thickness d is equal to or less than 0.1 mm, the length  1  is 100 to 200 mm, and the diameter r is 20 to 45 mm. The diameter r need not be uniform from the proximal end  21  to the distal end  22  of the tubular member  2 A. The cross-sectional shape when the side wall  20  of the tubular member  2 A is cut by a plane orthogonal to the axial direction D need not be circular, and may be polygonal or ellipse, or the like. 
     Plurality of Stent Rings  2 B 
     The plurality of stent rings  2 B are stent struts, each of which extends in a ring shape along the circumferential direction of the tubular member  2 A. More specifically, each of the plurality of stent rings  2 B is a wire having a cross-sectional shape that is circular or square with curved corners. Each of the plurality of stent rings  2 B extends in a ring shape while alternatingly bending in the axial direction D toward the proximal side and toward the distal side. In other words, the plurality of stent rings  2 B extend in a ring shape along the outer surface  24  of the side wall  20  of the tubular member  2 A while alternatingly bending toward the proximal end  21  side and toward the distal end  22  side of the tubular member  2 A. The plurality of stent rings  2 B are fixed by being sewn on with sutures to the outer surface  24  of the side wall  20  of the tubular member  2 A. Note that the method by which the plurality of stent rings  2 B are fixed to the tubular member  2 A may be another method. For example, the plurality of stent rings  2 B may be fixed to the tubular member  2 A by an adhesive or tape. Also, for example, the plurality of stent rings  2 B may be disposed between a member equivalent to the tubular member  2 A and the tubular member  2 A, and fixed to the tubular member  2 A by adhering the member equivalent to the tubular member  2 A to the tubular member  2 A with heat or the like. 
     The plurality of stent rings  2 B include a small fixed ring  3 , a plurality of fluctuating rings  5 , and a plurality of large fixed rings  6 , which will be described later. The thickness of the struts forming the small fixed ring  3 , the plurality of fluctuating rings  5 , and the plurality of large fixed rings  6  need not be the same. The small fixed ring  3 , the plurality of fluctuating rings  5 , and the plurality of large fixed rings  6  will be described in detail later. 
     Each of a plurality of poles where each of the plurality of stent rings  2 B bends back from the proximal end  21  side to the distal end  22  will be referred to as a proximal pole P. In other words, the proximal pole P corresponds to a pole on the proximal end  21  side, of each of the plurality of stent rings  2 B. The proximal pole P curves in a protruding shape toward the proximal end  21  side. A ring-shaped virtual line formed by connecting a plurality of line segments extending between two adjacent proximal poles P will be referred to as a proximal envelope curve S. Each of a plurality of poles where each of the plurality of stent rings  2 B bends back from the distal end  22  side to the proximal end  21  side will be referred to as a distal pole Q. In other words, the distal pole Q corresponds to a pole on the distal end  22  side, of each of the plurality of stent rings  2 B. The distal pole Q curves in a protruding shape toward the distal end  22  side. A ring-shaped virtual line formed by connecting a plurality of line segments extending between two adjacent distal poles Q will be referred to as a distal envelope curve T. The distance in the axial direction D between the proximal envelope curve S and the distal envelope curve T will be defined as an amplitude G. 
     The center position in the axial direction D between the proximal envelope curve S and the distal envelope curve T will be defined as a center position H. The center position H is disposed between the proximal envelope curve S and the distal envelope curve T in the axial direction D, and extends in a ring shape. The reciprocal of the number of the proximal poles P and the distal poles Q will be referred to as a bend cycle W. 
     Small Fixed Ring  3   
     As shown in  FIG.  2   , the small fixed ring  3  is disposed such that the positions of the proximal end  21  of the tubular member  2 A and a plurality of proximal poles P 3  of the small fixed ring  3  are the same position in the axial direction D. That is, the plurality of proximal poles P 3  of the small fixed ring  3  are disposed along the proximal end  21  of the tubular member  2 A.  FIG.  3    shows a state in which the small fixed ring  3  is cut at a portion corresponding to the end portion on the lesser curvature side in the expansion-contraction direction E, and laid out in a plane. The number of each of the plurality of proximal poles P 3  and a plurality of distal poles Q 3  of the small fixed ring  3  is, for example, 18, and a bend cycle W 3  is, for example, 1/18. 
     As shown in  FIG.  2    and  FIG.  3   , the small fixed ring  3  has curved portions  31  and  32 , and a linear portion  33 . The curved portion  31  is a portion near the each of the plurality of proximal poles P 3  of the small fixed ring  3 . The curved portion  32  is a portion near each of the plurality of distal poles Q 3  of the small fixed ring  3 . The linear portion  33  is a portion extending linearly between the curved portions  31  and  32  of the small fixed ring  3 . A curvature R 3  of the curved portions  31  and  32  is the same, and is 0.6 mm, for example. The linear portion  33  extending inclined on the lesser curvature side with respect to the axial direction D from the curved portion  32  toward the proximal side will be referred to as a linear portion  33 A. The linear portion  33  extending inclined on the greater curvature side with respect to the axial direction D from the curved portion  32  toward the proximal side will be referred to as a linear portion  33 B. The linear portions  33 A and  33 B are disposed symmetrically about a reference axis extending in the axial direction D through the curved portion  32  to which they each connect. An angle θ 3  formed between the linear portion  33  and the axial direction D is, for example, 14.5°. 
     A proximal envelope curve S 3  that connects the plurality of proximal poles P 3 , and a distal envelope curve T 3  that connects the plurality of distal poles Q 3  are each orthogonal to the axial direction D. The directions in which the proximal envelope curve S 3  and the distal envelope curve T 3  extend are parallel to each other. A center position H 3  in the axial direction D of the proximal envelope curve S 3  and the distal envelope curve T 3  is orthogonal to the axial direction D. A third amplitude G 3  which is the distance between the proximal envelope curve S 3  and the distal envelope curve T 3  is constant along the entire ring-shaped area of the small fixed ring  3 , and is, for example, 6.5 mm. 
     Plurality of Fluctuating Rings  5   
     As shown in  FIG.  1   , the plurality of fluctuating rings  5  include a first fluctuating ring  51 , a second fluctuating ring  52 , a third fluctuating ring  53 , a fourth fluctuating ring  54 , and a fifth fluctuating ring  55 . The first fluctuating ring  51  to the fifth fluctuating ring  55  are arranged in the order of the first fluctuating ring  51 , the second fluctuating ring  52 , the third fluctuating ring  53 , the fourth fluctuating ring  54 , and the fifth fluctuating ring  55 , from the proximal end  21  side to the distal end  22  side of the tubular member  2 A. As shown in  FIG.  1    and  FIG.  4   , the shapes of the second fluctuating ring  52  to the fifth fluctuating ring  55  are the same. The shape of the first fluctuating ring  51  is different from the shape of the second fluctuating ring  52  to fifth fluctuating ring  55 . This will be described in more detail later. 
       FIG.  5    shows a state in which the first fluctuating ring  51  is cut at a portion corresponding to the end portion on the lesser curvature side in the expansion-contraction direction E, and laid out in a plane.  FIG.  6    shows a state in which each of the second fluctuating ring  52  to the fifth fluctuating ring  55  is cut at a portion corresponding to the end portion on the lesser curvature side in the expansion-contraction direction E, and laid out in a plane. 
     As shown in  FIG.  2   ,  FIG.  4   ,  FIG.  5   , and  FIG.  6   , the number of each of a plurality of proximal poles P 5  (refer to  FIG.  2    and  FIG.  4   ) and a plurality of distal poles Q 5  (refer to  FIG.  2    and  FIG.  4   ) of each of the plurality of fluctuating rings  5  is the same with the first fluctuating ring  51  to the fifth fluctuating ring  55 , and is, for example, 7. A bend cycle W 5  is, for example, 1/7. Each of the plurality of fluctuating rings  5  has curved portions  501  and  502  and a linear portion  503 . The curved portion  501  is a portion near each of the plurality of proximal poles P 5 . The curved portion  502  is a portion near each of the plurality of distal poles Q 5 . The linear portion  503  is a portion extending linearly between the curved portions  501  and  502 . The linear portion  503  extending inclined on the lesser curvature side with respect to the axial direction D from the curved portion  502  toward the proximal side will be referred to as a linear portion  503 A. The linear portion  503  extending inclined on the greater curvature side with respect to the axial direction D from the curved portion  502  toward the proximal side will be referred to as a linear portion  503 B. The linear portions  503 A and  503 B are disposed symmetrically about a reference axis extending in the axial direction D through the curved portion  502  to which they each connect. 
     Hereinafter, each of the first fluctuating ring  51  to the fifth fluctuating ring  55  may be written as the Nth (with N being any integer from 1 to 5) fluctuating ring  5 N. Each of the second fluctuating ring  52  to the fifth fluctuating ring  55  may be written as the nth (with n being any integer from 2 to 5) fluctuating ring  5   n.    
     First Fluctuating Ring  51   
     As shown in  FIG.  2   , the first fluctuating ring  51  is disposed adjacent on the distal end  22  (refer to  FIG.  1   ) side with respect to the small fixed ring  3 . A proximal envelope curve S 51  that connects a plurality of proximal poles P 51  of the first fluctuating ring  51  extends in the circumferential direction and is orthogonal to the axial direction D. In other words, the plurality of proximal poles P 51  of the first fluctuating ring  51  are lined up on a virtual line (proximal envelope curve S 51 ) extending in the circumferential direction along the outer surface  24  of the tubular member  2 A and orthogonal to the axial direction D. The positions in the axial direction D of the plurality of proximal poles P 51  of the first fluctuating ring  51  are the same. 
     The distal envelope curve T 3  of the small fixed ring  3  and the proximal envelope curve S 51  of the first fluctuating ring  51  are parallel to each other. A distance L 12  in the axial direction D between the distal envelope curve T 3  and the proximal envelope curve S 51  corresponds to the distance in the axial direction D between the distal poles Q 3  of the small fixed ring  3  and the proximal poles P 51  of the first fluctuating ring  51 . The distance L 12  is the same along the circumferential direction, and is, for example, 0.5 mm. 
     As shown in  FIG.  5   , the proximal poles P 51  of the first fluctuating ring  51  are written as proximal poles P 51  [ 1 ], P 51  [ 2 ] . . . P 51  [ 7 ], and distal poles Q 51  of the first fluctuating ring  51  are written as distal poles Q 51  [ 1 ], Q 51  [ 2 ] . . . Q 51  [ 7 ]. A distal envelope curve T 51  that connects the plurality of distal poles Q 51  of the first fluctuating ring  51  has orthogonal portions T 511  and T 521  that are orthogonal to the axial direction D, and inclined portions T 531  and T 541  that are inclined with respect to the axial direction D. The orthogonal portion T 511  extends between the distal poles Q 51  [ 4 ] and Q 51  [ 5 ]. The orthogonal portion T 521  extends between the distal poles Q 51  [ 6 ], Q 51  [ 7 ], Q 51  [ 1 ], Q 51  [ 2 ], and Q 51  [ 3 ]. The inclined portion T 531  extends between the distal poles Q 51  [ 3 ] and Q 51  [ 4 ]. The inclined portion T 541  extends between the distal poles Q 51  [ 5 ] and Q 51  [ 6 ]. The orthogonal portion T 511  extends along the portion of the tubular member  2 A near the end portion on the greater curvature side of the tubular member  2 A in the expansion-contraction direction E. The orthogonal portion T 521  extends along the portion of the tubular member  2 A from the portion on the greater curvature side of the center of the tubular member  2 A in the expansion-contraction direction E to the end portion on the lesser curvature side. 
     The maximum value of the distance in the axial direction D between the proximal envelope curve S 51  and the distal envelope curve T 51  will be referred to as a first amplitude G 511 . The first amplitude G 511  corresponds to the distance in the axial direction D between the proximal envelope curve S 51  and the orthogonal portion T 511  of the distal envelope curve T 51 . The first amplitude G 511  is, for example, 15 mm. The minimum value of the distance in the axial direction D between the proximal envelope curve S 51  and the distal envelope curve T 51  will be referred to as a second amplitude G 521 . The second amplitude G 521  corresponds to the distance in the axial direction D between the proximal envelope curve S 51  and the orthogonal portion T 521  of the distal envelope curve T 51 . The second amplitude G 521  is, for example, 10 mm. The first amplitude G 511  is larger than the second amplitude G 521 . The first amplitude G 511  and the second amplitude G 521  are both larger than the third amplitude G 3  (refer to  FIG.  2   ) of the small fixed ring  3 . 
     As shown in  FIG.  5   , a portion of the first fluctuating ring  51  where the distance between the proximal envelope curve S 51  and the distal envelope curve T 51  is the first amplitude G 511  will be referred to as a first region A 511 . In particular, the first region A 511  includes the proximal pole P 51  [ 4 ] and the distal poles Q 51  [ 4 ] and Q 51  [ 5 ] of the first fluctuating ring  51 . A portion of the first fluctuating ring  51  where the distance between the proximal envelope curve S 51  and the distal envelope curve T 51  is the second amplitude G 521  will be referred to as a second region A 521 . In particular, the second region A 521  includes the proximal poles P 51  [ 1 ], P 51  [ 2 ], P 51  [ 6 ], and P 51  [ 7 ], and the distal poles Q 51  [ 1 ] to Q 51  [ 3 ], Q 51  [ 6 ], and Q 51  [ 7 ] of the first fluctuating ring  51 . 
     A center position H 51  in the axial direction D between the proximal envelope curve S 51  and the distal envelope curve T 51  of the first fluctuating ring  51  extends along the circumferential direction while curving with respect to a direction orthogonal to the axial direction D, in accordance with the curving of the distal envelope curve T 51  with respect to a direction orthogonal to the axial direction D. As shown in  FIG.  2   , a minimum distance L 30  in the axial direction D between the center position H 3  of the small fixed ring  3  and the center position H 51  of the first fluctuating ring  51  corresponds to the distance between the positions of the end portions on the lesser curvature side in the expansion-contraction direction E of the center positions H 3  and H 51 . The distance L 30  is, for example, 8.75 mm. 
     nth fluctuating ring  5   n  (second fluctuating ring  52  to fifth fluctuating ring  55 ) 
     As shown in  FIG.  4   , the second fluctuating ring  52  is disposed on the distal end  22  (refer to  FIG.  1   ) side with respect to the first fluctuating ring  51 . The nth fluctuating ring  5   n  (except where n=2) is disposed on the distal end  22  side with respect to the n−1th fluctuating ring  5  (n−1) (expect where n=2). 
     As shown in  FIG.  6   , a proximal envelope curve S 5   n  that connects a plurality of proximal poles P 5   n  of the nth fluctuating ring  5   n  differs from the first fluctuating ring  51 , and curves in the axial direction D. The plurality of proximal poles P 5   n  of the nth fluctuating ring  5   n  will be written as proximal pole P 5   n  [ 1 ], P 5   n  [ 2 ] . . . P 5   n  [ 7 ], and distal poles Q 5   n  of the nth fluctuating ring  5   n  will be written as distal poles Q 5   n  [ 1 ], Q 5   n  [ 2 ] . . . Q 5   n  [ 7 ]. The proximal envelope curve S 5   n  that connects the plurality of proximal poles P 5   n  of the nth fluctuating ring  5   n  has an orthogonal portion S 51   n  that is orthogonal to the axial direction D, and inclined portions T 53   n  and T 54   n  that are inclined with respect to the axial direction D. The orthogonal portion S 51   n  extends between the proximal poles P 5   n  [ 5 ], P 5   n  [ 6 ], P 5   n  [ 7 ], P 5   n  [ 1 ], P 5   n  [ 2 ], and P 5   n  [ 3 ]. An inclined portion S 53   n  extends between the proximal poles P 5   n  [ 3 ] and P 5   n  [ 4 ]. An inclined portion S 54   n  extends between the proximal poles P 5   n  [ 4 ] and P 5   n  [ 5 ]. A distal envelope curve T 5   n  that connects the plurality of distal poles Q 5   n  of the nth fluctuating ring  5   n  has orthogonal portions T 51   n  and T 52   n  that are orthogonal to the axial direction D, and inclined portions T 53   n  and T 54   n  that are inclined with respect to the axial direction D. The orthogonal portion T 5  In extends between the distal poles Q 5   n  [ 4 ] and Q 5   n  [ 5 ]. The orthogonal portion T 52   n  extends between the distal poles Q 5   n  [ 6 ], Q 5   n  [ 7 ], Q 5   n  [ 1 ], Q 5   n  [ 2 ], and Q 5   n  [ 3 ]. The inclined portion T 53   n  extends between distal poles Q 5   n  [ 3 ] and Q 5   n  [ 4 ]. The inclined portion T 54   n  extends between the distal poles Q 5   n  [ 5 ] and Q 5   n  [ 6 ]. 
     As shown in  FIG.  4   , the orthogonal portion S 5  In (S 512  and S 513 ) extends along a portion of the tubular member  2 A from the portion on the greater curvature side of the center in the expansion-contraction direction E to the end portion on the lesser curvature side. The inclined portions S 53   n  (S 532  and S 533 ) and S 54   n  (refer to  FIG.  6   ) extend along a portion of the tubular member  2 A near the end portion on the greater curvature side in the expansion-contraction direction E. The orthogonal portion T 52   n  (T 522  and T 523 ) extends along a portion of the tubular member  2 A from the greater curvature side of the center of the tubular member  2 A in the expansion-contraction direction E to the end portion on the lesser curvature side. 
     As shown in  FIG.  6   , a maximum value of the distance in the axial direction D between the proximal envelope curve S 5   n  and the distal envelope curve T 5   n  will be referred to as a first amplitude G 51   n . The first amplitude G 51   n  corresponds to the distance in the axial direction D between the point of intersection of the inclined portions S 53   n  and S 54   n  of the proximal envelope curve S 5   n , i.e., the proximal pole P 5   n  [ 4 ], and the orthogonal portion T 51   n  of the distal envelope curve T 5   n . The first amplitude G 51   n  is, for example, 15 mm. A minimum value of the distance in the axial direction D between the proximal envelope curve S 51  and the distal envelope curve T 51  will be referred to as a second amplitude G 52   n . The second amplitude G 52   n  corresponds to the distance in the axial direction D between the orthogonal portion S 51   n  of the proximal envelope curve S 5   n  and the orthogonal portion T 52   n  of the distal envelope curve T 5   n . The second amplitude G 52   n  is, for example, 10 mm. The first amplitude G 51   n  is larger than the second amplitude G 52   n . The first amplitude G 51   n  and the second amplitude G 52   n  are larger than the third amplitude G 3  (refer to  FIG.  2   ) of the small fixed ring  3 . The first amplitude G 51   n  is the same as the first amplitude G 511  of the first fluctuating ring  51 . The second amplitude G 52   n  is the same as the second amplitude G 521  of the first fluctuating ring  51 . Hereinafter, the first amplitudes G 511  and G 51   n  will collectively be referred to as the first amplitudes G 51 . The second amplitudes G 521  and G 52   n  will collectively be referred to as the second amplitudes G 52 . The second amplitudes G 52  are larger than the third amplitude G 3 . 
     As shown in  FIG.  6   , a portion of the nth fluctuating ring  5   n  where the distance between the proximal envelope curve S 51  and the distal envelope curve T 51  become the first amplitude G 51   n  will be referred to as a first region A 51   n . In particular, the first region A 51   n  includes the proximal pole P 5   n  [ 4 ] and the distal poles Q 5   n  [ 4 ] and Q 5   n  [ 5 ] of the nth fluctuating ring  5   n . A portion of the nth fluctuating ring  5   n  where the distance between the proximal envelope curve S 5   n  and the distal envelope curve T 5   n  is the second amplitude G 52   n  will be referred to as a second region A 52   n . In particular, the second region A 52   n  includes the proximal poles P 5   n  [ 1 ], P 5   n  [ 2 ], P 5   n  [ 6 ], and P 5   n  [ 7 ], and the distal poles Q 5   n  [ 1 ] to Q 5   n  [ 3 ], Q 5   n  [ 6 ], and Q 5   n  [ 7 ] of the nth fluctuating ring  5   n.    
     The center position H 5   n  in the axial direction D between the proximal envelope curve S 5   n  and the distal envelope curve T 5   n  of the nth fluctuating ring  5   n  extends in a direction orthogonal to the axial direction D along the circumferential direction. As shown in  FIG.  9   , a first distance L 31 , which is the maximum distance in the axial direction D between the center position H 51  of the first fluctuating ring  51  and a center position H 52  of the second fluctuating ring  52 , corresponds to the distance between the positions of the end portions on the lesser curvature side in the expansion-contraction direction E of the center positions H 51  and H 52 . The first distance L 31  is, for example, 21.5 mm. An nth distance L 3   n , which is the maximum distance in the axial direction D between the center position H 5   n  of the nth fluctuating ring  5   n  and the center position H 5  (n+1) of an n+1th fluctuating ring  5  (n+1), corresponds to the distance between the positions of the end portions on the lesser curvature side in the expansion-contraction direction E of the center positions H 5   n  and H 5  (n+1). The nth distance L 3   n  (second distance L 32 , third distance L 33 , and fourth distance L 34 ) is the same regardless of the value of n, and is, for example, 19 mm. The first distance L 31  is equal to or greater than the nth distance L 3   n.    
     As shown in  FIG.  4   , a maximum distance L 41  in the axial direction D between the distal envelope curve T 51  of the first fluctuating ring  51  and a proximal envelope curve S 52  of the second fluctuating ring  52  corresponds to the distance between the positions of the end portions on the lesser curvature side in the expansion-contraction direction E of the distal envelope curve T 51  and the proximal envelope curve S 52 . The distance L 41  is, for example, 11.5 mm. A minimum distance L 61  in the axial direction D between the distal envelope curve T 51  of the first fluctuating ring  51  and the proximal envelope curve S 52  of the second fluctuating ring  52  corresponds to the distance between the positions of the end portions on the greater curvature side in the expansion-contraction direction E of the distal envelope curve T 51  and the proximal envelope curve S 52 . The distance L 61  is, for example, 4 mm. 
     As shown in  FIG.  9   , a maximum distance L 4   n  (distances L 42 , L 43 , and L 44 ) in the axial direction D between the distal envelope curve T 5   n  of the nth fluctuating ring  5   n  and the proximal envelope curve S 5  (n+1) of the n+1th fluctuating ring  5  (n+1) corresponds to the distance between the positions of the end portions on the lesser curvature side in the expansion-contraction direction E of the distal envelope curve T 5   n  and the proximal envelope curve S 5  (n+1). The distance L 4   n  is the same regardless of the value of n, and is, for example, 9 mm. The distance L 41  is equal to or greater than the distance L 4   n . A minimum distance L 6   n  (distances L 62 , L 63 , and L 64 ) in the axial direction D between the distal envelope curve T 5   n  of the nth fluctuating ring  5   n  and the proximal envelope curve S 5  (n+1) of the n+1th fluctuating ring  5  (n+1) corresponds to the distance between the positions of the end portions on the greater curvature side in the expansion-contraction direction E of the distal envelope curve T 5   n  and the proximal envelope curve S 5  (n+1). The distance L 6   n  is the same regardless of the value of n, and is, for example, 4 mm. 
     The parameters (first distance L 31 , nth distance L 3   n , distances L 41 , L 4   n , L 61 , and L 6   n , first amplitude G 51   n , and second amplitude G 52   n ) of the nth fluctuating ring  5   n  are not limited to the aforementioned embodiment, and may be other values. For example, the distance L 61  may be any value greater than 0 mm. The distance L 6   n  may be any value greater than 0 mm. The ratio of the first amplitude G 51   n  to the second amplitude G 52   n  (first amplitude G 51   n /second amplitude G 52   n ) may be within a range of 1.5 to 2. 
     Plurality of Large Fixed Rings  6   
     As shown in  FIG.  1    and  FIG.  7   , the plurality of large fixed rings  6  include a first large fixed ring  61 , a second large fixed ring  62 , and a third large fixed ring  63 . The first large fixed ring  61  to the third large fixed ring  63  are arranged in the order of the first large fixed ring  61 , the second large fixed ring  62 , and the third large fixed ring  63 , from the proximal end  21  side toward the distal end  22  side of the tubular member  2 A. The shapes of the first large fixed ring  61  to the third large fixed ring  63  are the same. The first large fixed ring  61  is disposed adjacent, on the distal end  22  side, to the fifth fluctuating ring  55 . The third large fixed ring  63  is disposed in a position where the positions of the distal end  22  of the tubular member  2 A and a plurality of distal poles Q 6  of the third large fixed ring  63  are the same in the axial direction D. That is, the plurality of distal poles Q 6  of the third large fixed ring  63  are disposed along the distal end  22  of the tubular member  2 A. 
       FIG.  8    shows a state in which the first large fixed ring  61  is cut at a portion corresponding to the end portion on the lesser curvature side in the expansion-contraction direction E, and laid out in a plane. As shown in  FIG.  7    and  FIG.  8   , the number of each of a plurality of proximal poles P 6  and the plurality of distal poles Q 6  of the plurality of large fixed rings  6  is the same for the first large fixed ring  61  to the third large fixed ring  63 , and is, for example, 6. A bend cycle W 6  is, for example, ⅙. Each of the plurality of large fixed rings  6  has a curved portion  601  near each of the proximal poles P 6 , a curved portion  602  near each of the plurality of distal poles Q 6 , and a linear portion  603  extending linearly between the curved portions  601  and  602 . A curvature R 6  of the curved portions  601  and  602  is the same for the first large fixed ring  61  to the third large fixed ring  63 , and is, for example, 0.8. The linear portion  603  extending inclined on the lesser curvature side with respect to the axial direction D from the curved portion  602  toward the proximal side will be referred to as a linear portion  603 A. The linear portion  603  extending inclined on the greater curvature side with respect to the axial direction D from the curved portion  602  toward the proximal side will be referred to as a linear portion  603 B. The linear portions  603 A and  603 B are disposed symmetrically about a reference axis extending in the axial direction D through the curved portion  602  to which they each connect. An angle θ 6  formed between the linear portion  603  and the axial direction D is the same for the first large fixed ring  61  to the third large fixed ring  63 , and is, for example, 26°. 
     A proximal envelope curve S 6  connecting the plurality of proximal poles P 6 , and a distal envelope curve T 6  connecting a plurality of distal poles Q 6  each extend in a direction orthogonal to the axial direction D. The directions in which both the proximal envelope curve S 6  and the distal envelope curve T 6  extend are parallel to each other. The center position H 6  in the axial direction D of the proximal envelope curve S 6  and the distal envelope curve T 6  is orthogonal to the axial direction D. A fourth amplitude G 6 , which is the distance between the proximal envelope curve S 6  and the distal envelope curve T 6 , is constant along the entire ring-shaped area of each of the plurality of large fixed rings  6 , and is, for example, 15 mm. The fourth amplitude G 6  is larger than the third amplitude G 3  of the small fixed ring  3 , and is the same as the first amplitudes G 51  of the plurality of fluctuating rings  5 . 
     A distance L 51  in the axial direction D between a distal envelope curve T 61  of the first large fixed ring  61  and a proximal envelope curve S 62  of the second large fixed ring  62  is the same as a distance L 52  in the axial direction D between a distal envelope curve T 62  of the second large fixed ring  62  and a proximal envelope curve S 63  of the third large fixed ring  63 . The distances L 51  and L 52  are, for example, 4 mm. 
     As shown in  FIG.  9   , a maximum distance L 40  in the axial direction D between a center position H 55  of the fifth fluctuating ring  55  and the center position H 61  of the first large fixed ring  61  corresponds to the distance between the positions of the end portions on the lesser curvature side in the expansion-contraction direction E of the center positions H 55  and H 61 . The distance L 40  is, for example, 19 mm. As shown in  FIG.  7   , the distance L 41  in the axial direction D between the center position H 61  of the first large fixed ring  61  and the center position H 62  of the second large fixed ring  62  is the same as a distance L 42  in the axial direction D between the center position H 62  of the second large fixed ring  62  and the center position H 63  of the third large fixed ring  63 . The distances L 41  and L 42  are, for example, 19 mm. The distal end  22  of the tubular member  2 A and the distal pole Q 63  of the third large fixed ring  63  are disposed in the same position in the axial direction D. 
     The parameters (bend cycle W 6 , curvature R 6 , angle θ 6 , fourth amplitude G 6 , and distances L 30 , L 41 , L 42 , L 51 , and L 52 ) of the plurality of large fixed rings  6  are not limited to the aforementioned embodiment, and may be other values. For example, the bend cycle W 6  may be any value within a range of ¼ to 1/12. The distance L 51  may be any value greater than 0 mm. The distance L 52  may be any value greater than 0 mm. 
     Uncovered Section  7   
     As shown in  FIG.  1   , the uncovered section  7  is disposed on the proximal end  21  side of the tubular member  2 A with respect to the small fixed ring  3 . The uncovered section  7  is a strut that extends in a ring shape, and more particularly, is a wire with a rectangular cross-section. The uncovered section  7  extends in a ring shape while alternatingly bending toward the proximal side and toward the distal side in the axial direction D. 
     As shown in  FIG.  2   , an end portion on the proximal side in the axial direction D of the uncovered section  7  will be referred to as a tip end  71 , and an end portion on the distal side in the axial direction D will be referred to as a base end  72 . That is, the uncovered section  7  extends in a ring shape while bending alternatingly toward the tip end  71  side and toward the base end  72  side. The base end  72  is an end portion of the uncovered section  7  on the distal end  22  side of the tubular member  2 A, and corresponds to each of a plurality of poles (hereinafter, referred to as a plurality of distal poles Q 7 ) curving in a protruding fashion toward the distal end  22  side. The tip end  71  is an end portion of the uncovered section  7  on the side opposite the distal end  22  with respect to the proximal end  21  of the tubular member  2 A, and corresponds to each of a plurality of poles (hereinafter, referred to as a plurality of proximal poles P 7 ) curving in a protruding fashion toward the proximal side in the axial direction D. A proximal envelope curve S 7  connecting the plurality of proximal poles P 7  and a distal envelope curve T 7  connecting the plurality of distal poles Q 7  are both orthogonal to the axial direction D. An uncovered section amplitude G 7 , which is the distance between the proximal envelope curve S 7  and the distal envelope curve T 7 , is constant across the entire ring-shaped area of the uncovered section  7 , and is, for example, 12 mm. 
       FIG.  10    shows a state in which the uncovered section  7  and the small fixed ring  3  are cut at a portion corresponding to the end portion on the lesser curvature side in the expansion-contraction direction E, and laid out in a plane. The number of each of the plurality of proximal poles P 7  and the plurality of distal poles Q 7  of the uncovered section  7  is, for example, 8, and a bend cycle W 7  is, for example, ⅛. The uncovered section  7  has a curved portion  701  near each proximal pole P 7 , a curved portion  702  near each distal pole Q 7 , and a linear portion  703  extending between the curved portions  701  and  702 . The linear portion  703  extending inclined on the lesser curvature side with respect to the axial direction D from the curved portion  702  toward the proximal side will be referred to as a linear portion  703 A. The linear portion  703  extending inclined on the greater curvature side with respect to the axial direction D from the curved portion  702  toward the proximal side will be referred to as a linear portion  703 B. The linear portions  703 A and  703 B are disposed symmetrically about a reference axis extending in the axial direction D through the curved portion  702  to which they each connect. An angle θ 7  formed between the linear portion  703  and the axial direction D is, for example, 12.5°. 
     As shown in  FIG.  2   , the uncovered section  7  is such that a portion including the base end  72  is fixed to the inner surface  23  of the proximal end  21  of the tubular member  2 A. A portion (including the base end  72 ) of the uncovered section  7  that is fixed to the tubular member  2 A is disposed on the distal end  22  side with respect to the proximal end  21  of the tubular member  2 A. A distance L 21  in the axial direction D between the proximal end  21  of the tubular member  2 A and the base end  72  of the uncovered section  7  is, for example, 4 mm. Therefore, a distance L 11  in the axial direction D between the base end  72  of the uncovered section  7  and the plurality of proximal poles P 3  of the small fixed ring  3  is also 4 mm. 
     The positions in the circumferential direction of the distal poles Q 7  of the uncovered section  7  and the plurality of proximal poles P 3  of the small fixed ring  3  are different. More specifically, as shown in  FIG.  10   , a virtual straight line Di extending in the axial direction D through the distal poles Q 7  of the uncovered section  7 , and a virtual straight line Dj extending in the axial direction D through the plurality of proximal poles P 3  of the small fixed ring  3  are not disposed on a straight line. 
     As shown in  FIG.  2   , a portion excluding a portion (including the base end  72 ) of the uncovered section  7  that is fixed to the base end  72  is disposed on the proximal end side in the axial direction D with respect to the proximal end  21  of the tubular member  2 A, in other words, on the side opposite the distal end  22  with respect to the proximal end  21  of the tubular member  2 A. Hereinafter, this portion will be referred to as a protruding portion  70 . A distance L 20  in the axial direction D of the protruding portion  70  corresponds to the distance in the axial direction D between the tip end  71  of the uncovered section  7  and the proximal end  21  of the tubular member  2 A. The distance L 20  is, for example, 8 mm. 
     In the protruding portion  70 , a direction from the base end  72  toward the tip end  71  will be referred to as the extending direction F. The extending direction is inclined with respect to the axial direction D. More specifically, the extending direction F extends inclined in a direction away from the center line C. Therefore, the diameter of the proximal envelope curve S 7  connecting the plurality of proximal poles P 7  of the tip end  71  becomes larger than the diameter of the distal envelope curve T 7  connecting the plurality of distal poles Q 7  of the base end  72 . 
     Further details are as follows. As shown in  FIG.  11   , the uncovered section  7  is curved. The uncovered section  7  has a base end portion  76 , a first portion  77 , and a second portion  78 . The base end portion  76  is a portion fixed to the tubular member  2 A. The first portion  77  is connected to the tip end of the base end portion  76  and extends along an extending direction F 77  toward the proximal side. The second portion  78  is connected to the tip end of the first portion  77  and extends along an extending direction F 78  toward the proximal side. The tip end of the second portion  78  corresponds to the tip end  71  of the uncovered section  7 . The angles formed between each of the extending directions F 77  and F 78  and a reference direction B parallel to the center line C are written as a first angle θ 77  and a second angle θ 78 . The first angle θ 77  is, for example, 12°. The second angle θ 78  is, for example, 0°. The second angle θ 78  is smaller than the first angle θ 77 . 
     The parameters (the uncovered section amplitude G 7 , the bend cycle W 7 , the curvature R 7 , the angle θ 7 , the distances L 11 , L 20 , and L 21 , the first angle θ 77 , and the second angle θ 78 ) of the uncovered section  7  are not limited to the aforementioned embodiment, and may be other values. For example, the bend cycle W 7  may be any value within a range of ¼ to 1/12. The distance L 11  may be any value within a range of 0 mm to 4 mm. The distance L 21  may be any value within a range of 0 mm to 4 mm. 
     Method of Use 
     The stent graft  1 A is fitted folded up in a delivery system. The delivery system is inserted into a body through an incision in a blood vessel in the base of a leg. At this time, the proximal side of the stent graft  1 A, in other words, the side where the uncovered section  7  is provided in the axial direction D, faces the direction of travel of the delivery system. After the stent graft  1 A is guided to the affected area, it is then pushed out of the delivery system and placed inside the blood vessel. The tubular member  2 A of the stent graft  1 A then expands due to the elastic force of the plurality of stent rings  2 B. 
     As shown in  FIG.  12   , the stent graft  1 A closely contacts the inside of the thoracic aorta  8  and curves along an aortic arch  8 B. The uncovered section  7  of the stent graft  1 A closely contacts the position of the thoracic aorta that is closer to the heart, in the aortic arch  8 B. The lesser curvature side in the expansion-contraction direction E of the tubular member  2 A of the stent graft  1 A is disposed on a lesser curvature portion  81  side of the aortic arch  8 B. An end portion on the lesser curvature side of each of the plurality of fluctuating rings  5  closely contacts the lesser curvature portion  81  that becomes the sharply curved portion of the aortic arch  8 B. The greater curvature side in the expansion-contraction direction E of the tubular member  2 A is disposed on a greater curvature portion  82  side of the aortic arch  8 B. An end portion on the greater curvature side of each of the plurality of fluctuating rings  5  closely contacts the greater curvature portion  82  of the aortic arch  8 B. The plurality of large fixed rings  6  closely contact the position of a descending aorta  8 C closer to the abdominal aorta, of the thoracic aorta  8 . 
     As shown in  FIG.  13   , the tubular member  2 A curves at the lesser curvature portion  81  that becomes the sharply curved portion of the aortic arch  8 B, by contracting the portions between the plurality of fluctuating rings  5 , of the portions on the lesser curvature side in the expansion-contraction direction E. Here, as shown in  FIG.  9   , the distance L 41  on the lesser curvature side between the first fluctuating ring  51  and the second fluctuating ring  52  is greater than the distance L 61  on the greater curvature side. The distance L 42  on the lesser curvature side between the second fluctuating ring  52  and the third fluctuating ring  53  is greater than the distance L 62  on the greater curvature side. The distance L 43  on the lesser curvature side between the third fluctuating ring  53  and the fourth fluctuating ring  54  is greater than the distance L 63  on the greater curvature side. The distance L 44  on the lesser curvature side between the fourth fluctuating ring  54  and the fifth fluctuating ring  55  is greater than the distance L 64  on the greater curvature side. Therefore, the tubular member  2 A contracts easier and curves easier on the lesser curvature side than on the greater curvature side at the position where the plurality of fluctuating rings  5  are fixed. Therefore, with the stent graft  1 A, the tubular member  2 A can be made to closely contact the lesser curvature portion  81  that becomes the sharply curved portion of the aortic arch  8 B. 
     As shown in  FIG.  12   , the stent graft  1 A protects the thoracic aorta  8  by inhibiting, with the tubular member  2 A, the flow of blood to the portion of an aortic aneurysm  80  formed in the aortic arch  8 B. By combining the uncovered section  7  of the stent graft  1 A with a plurality of stents, the opening  21 A formed in the proximal end  21  of the tubular member  2 A can be made to more suitably closely contact the inner wall of the blood vessel. Therefore, the stent graft  1 A can inhibit the occurrence of a phenomenon in which blood leaks out of the opening of the proximal end  21  of the tubular member  2 A and flows into the aortic aneurysm  80 , i.e., an end leak. 
     Operations and Effects of the Present Embodiment 
     The first distance L 31  that is the maximum value of the distance between the center position H 51  in the axial direction D of the first fluctuating ring  51  and the center position H 52  in the axial direction D of the second fluctuating ring  52  is greater than any nth distance L 3   n  that is the maximum value of the distance in the axial direction D between the center position H 5   n  in the axial direction D of the nth fluctuating ring  5   n  and the center position H 5  (n+1) in the axial direction D of the n+1th fluctuating ring  5  (n+1). In this case, the portion of the tubular member  2 A between the first fluctuating ring  51  and the second fluctuating ring  52  bends more easily than the portion between the nth fluctuating ring  5  ( n ) and the n+1th fluctuating ring  5  (n+1). Therefore, with the stent graft  1 A, the portion between the first fluctuating ring  51  and the second fluctuating ring  52  can be made to follow the sharp curve of the aortic arch  8 B, so the tubular member  2 A can be made to suitably closely contact the inner wall of the blood vessel at this portion. 
     The small fixed ring  3  is disposed on the proximal end  21  of the tubular member  2 A. The plurality of fluctuating rings  5  are adjacent on the distal end  22  side of the tubular member  2 A with respect to the small fixed ring  3 . That is, the small fixed ring  3  is disposed on the proximal end  21  side of the tubular member  2 A with respect to the plurality of fluctuating rings  5  provided to enable the tubular member  2 A to bend well. The third amplitude G 3  of the small fixed ring  3  is smaller than the first amplitudes G 511  and G 51   n  of the plurality of fluctuating rings  5 . Also, the bend cycle W 3  of the small fixed ring  3  is larger than the bend cycle W 5  of the plurality of fluctuating rings  5 . Therefore, the small fixed ring  3  can bring the opening of the proximal end  21  of the tubular member  2 A into close contact with the blood vessel with greater elastic force. Therefore, with the stent graft  1 A, the opening  21 A formed in the proximal end  21  of the tubular member  2 A can be made to more closely contact the inner wall of the blood vessel by the small fixed ring  3 . 
     The proximal envelope curve S 51  connecting the plurality of proximal poles P 51  of the first fluctuating ring  51  extends in a circumferential direction and is orthogonal to the axial direction D. That is, the plurality of proximal poles P 51  of the first fluctuating ring  51  is arranged on a virtual line (proximal envelope curve S 51 ) that extends in the circumferential direction along the outer surface  24  of the tubular member  2 A and is orthogonal to the axial direction D. In this case, the small fixed ring  3  and the first fluctuating ring  51  are arranged maintaining a constant distance from each other, so the force that expands the tubular member  2 A outward is particularly strong at the proximal end  21  of the tubular member  2 A. Therefore, the stent graft  1 A can further increase the force that brings the opening  21 A of the proximal end  21  of the tubular member  2 A into close contact with the inner wall of the blood vessel. 
     The plurality of fluctuating rings  5  include the five fluctuating rings  5  (the first fluctuating ring  51  to the fifth fluctuating ring  55 ). The nth distance L 3   n  between the center position H 5   n  in the axial direction D of the nth fluctuating ring  5   n  (except where n=1) and the center position H 5  (n+1) in the axial direction D of the n+1th fluctuating ring  5  (n+1) is the same regardless of the value of n. In this case, the curvature at the portion of the tubular member  2 A to which the nth fluctuating ring  5   n  is fixed, when that portion bends in response to external force, is constant. Therefore, with the stent graft  1 A, the portion of the tubular member  2 A to which the nth fluctuating ring  5   n  is fixed can be made to bend with a uniform curvature. 
     The stent graft  1 A is provided with the plurality of large fixed rings  6  having the fourth amplitude G 6 . The plurality of large fixed rings  6  are disposed on the distal end  22  side with respect to the plurality of fluctuating rings  5  and the small fixed ring  3 . In this case, the stent graft  1 A causes the plurality of large fixed rings  6  to closely contact a portion (for example, the descending aorta  8 C) extending linearly from the sharply curved portion of the blood vessel. The fourth amplitude G 6  of the plurality of large fixed rings  6  is larger than the third amplitude G 3  of the small fixed ring  3 . Therefore, the plurality of large fixed rings  6  can press the tubular member  2 A with an appropriate amount of force so that it closely contacts the linearly extending descending aorta  8 C that is closer to the abdominal aorta, of the thoracic aorta  8 . 
     The third amplitude G 3  of the small fixed ring  3  is smaller than the second amplitudes G 521  and  52   n  of the plurality of fluctuating rings  5 . Also, the bend cycle W 3  of the small fixed ring  3  is larger than the bend cycle W 5  of the plurality of fluctuating rings  5 . In this case, the force that expands the tubular member  2 A outward can be increased by the elastic force of the small fixed ring  3 . Therefore, the stent graft  1 A can further increase the force that brings the opening of the proximal end  21  of the tubular member  2 A into suitably close contact with the inner wall of the blood vessel. 
     The stent graft  1 A is further provided with the uncovered section  7 . The uncovered section  7  can bring the opening  21 A of the proximal end  21  of the tubular member  2 A into suitably close contact with the inner wall of the blood vessel. Also, the uncovered section  7  is such that the base end  72  of the tubular member  2 A is fixed with sutures or the like to the inner surface  23  of the proximal end  21 . In this case, elastic force of the uncovered section  7  expands the opening  21 A of the proximal end  21  of the tubular member  2 A outward. Therefore, the stent graft  1 A can suitably bring the proximal end  21  of the tubular member  2 A into close contact with the inner wall of the blood vessel. Also, the plurality of stent rings  2 B are fixed to the outer surface  24  of the tubular member  2 A. Therefore, the stent graft  1 A can reduce the possibility that various devices that pass through the inside of the tubular member  2 A will catch on the plurality of stent rings  2 B. 
     Note that each amplitude G of the plurality of stent rings  2 B is defined as the distance in the axial direction D between the proximal envelope curve S connecting the plurality of proximal poles P on the proximal end  21  side, and the distal envelope curve T connecting the plurality of distal poles Q on the distal end  22  side. As a result, the shapes of the plurality of stent rings  2 B that enable close contact with the inner wall of the blood vessel can easily be defined on the basis of the amplitudes G. 
     While the invention has been described in conjunction with various example structures outlined above and illustrated in the figures, various alternatives, modifications, variations, improvements, and/or substantial equivalents, whether known or that may be presently unforeseen, may become apparent to those having at least ordinary skill in the art. Accordingly, the example embodiments of the disclosure, as set forth above, are intended to be illustrative of the invention, and not limiting the invention. Various changes may be made without departing from the spirit and scope of the disclosure. Therefore, the disclosure is intended to embrace all known or later developed alternatives, modifications, variations, improvements, and/or substantial equivalents. Some specific examples of potential alternatives, modifications, or variations in the described invention are provided below: 
     Modified Examples 
     The present disclosure is not limited to the aforementioned embodiment; various modifications are possible. The stent graft  1 A is not limited to being used placed in the aortic arch, and may be used placed in another portion of a blood vessel. 
     The amplitudes of the plurality of fluctuating rings  5  may gradually become smaller from the largest first amplitude G 51  toward the smallest second amplitude G 52 . In this case, the proximal envelope curve G 5  and the distal envelope curve T 5  may extend linearly in a direction toward one another. 
     The number and sequence of the uncovered section  7 , the small fixed ring  3 , the plurality of fluctuating rings  5 , and the plurality of large fixed rings  6  are not limited to those in the aforementioned embodiment. For example, they may be arranged in the order of the uncovered section  7 , the first fluctuating ring  51 , the small fixed ring  3 , the nth fluctuating ring  5   n , and the plurality of large fixed rings  6 . The small fixed ring  3  may be provided between the plurality of fluctuating rings  5  and the plurality of large fixed rings  6 . The small fixed ring  3  may be provided on the distal end  22  side of the tubular member  2 A with respect to the third large fixed ring  63 . The small fixed ring  3  may be provided in plurality. An uncovered section may also be provided on the distal end  22  of the tubular member  2 A. 
     The positions in the axial direction D of the plurality of proximal poles P 51  of the first fluctuating ring  51  need not be the same. More specifically, having at least a portion of the proximal envelope curve S 51  that connects the plurality of proximal poles P 51  of the first fluctuating ring  51  be inclined with respect to a direction orthogonal to the axial direction D is sufficient. For example, the first fluctuating ring  51  may have the same shape as the nth fluctuating ring  5   n.    
     The plurality of fluctuating rings  5  may include only the first fluctuating ring  51 , the second fluctuating ring  52 , and the third fluctuating ring  53 . The center positions H 52  and H 53  in the axial direction D of the second fluctuating ring  52  and the third fluctuating ring  53  may extend along the circumferential direction. The first distance L 31 , which is the maximum value of the distance between the center position H 51  in the axial direction D of the first fluctuating ring  51  and the center position H 52  in the axial direction D of the second fluctuating ring  52 , may be greater than the second distance L 32 , which is the maximum value of the distance between the center position H 52  in the axial direction D of the second fluctuating ring  52  and the center position H 53  in the axial direction D of the third fluctuating ring  53 . In this case, the stent graft  1 A will bend more easily between the first fluctuating ring  51  and the second fluctuating ring  52 . Therefore, with the stent graft  1 A, the portion between the first fluctuating ring  51  and the second fluctuating ring  52  can be made to suitably follow the bend in the aortic arch  8 B. 
     The plurality of stent rings  2 B may include only the small fixed ring  3  and the plurality of fluctuating rings  5 , and need not necessarily include the plurality of large fixed rings  6 . In this case, the plurality of fluctuating rings  5  may be disposed up to near the distal end  22  of the tubular member  2 A. 
     The first amplitudes G 511  and G 51   n  of the plurality of fluctuating rings  5  may be different from the fourth amplitude G 6  of the plurality of large fixed rings  6 . The third amplitude G 3  of the small fixed ring  3  may be larger than the second amplitudes G 521  and  52   n  of the plurality of fluctuating rings  5 , or the third amplitude G 3  and the second amplitudes G 521  and  52   n  may be the same. 
     The stent graft  1 A may be a structure without the uncovered section  7 . In this case, the opening of the proximal end  21  of the tubular member  2 A is expanded outward so as to closely contact the blood vessel by the small fixed ring  3 . 
     The uncovered section  7  may be such that the base end  72  is fixed to the outer surface  24  of the proximal end  21  of the tubular member  2 A. In this case, the uncovered section  7  can easily be attached to the tubular member  2 A. The plurality of stent rings  2 B may be fixed to the inner surface  23  of the tubular member  2 A. In this case, with the stent graft  1 A, the proximal end of the tubular member can be made to closely contact the blood vessel. 
     The plurality of proximal poles P 3  of the small fixed ring  3  may be disposed on the distal side with respect to the proximal end  21  of the tubular member  2 A. That is, the plurality of proximal poles P 3  of the small fixed ring  3  and the proximal end  21  of the tubular member  2 A may be disposed in different positions in the axial direction D. The plurality of distal poles Q 6  of the third large fixed ring  63  disposed on the distal-most end may be disposed on the proximal side with respect to the distal end  22  of the tubular member  2 A. That is, the plurality of distal poles Q 6  of the third large fixed ring  63  and the distal end  22  of the tubular member  2 A may be disposed at different positions in the axial direction D. 
     The curvature of the curved portion  701  and the curvature of the curved portion  702  of the uncovered section  7  may be the same or they may be different. The curvature of the curved portion  701  may be the same for all of the plurality of proximal poles P 7 , or it may be different for each of the plurality of proximal poles P 7 . 
     The plurality of proximal poles P 3  of the small fixed ring  3  need not be disposed in the same position in the axial direction D. Having at least a portion of the proximal envelope curve S 3  that connects the plurality of proximal poles P 3  be inclined with respect to the axial direction D is sufficient. Similarly, the plurality of distal poles Q 3  of the small fixed ring  3  need not be disposed at the same position in the axial direction D. Having at least a portion of the distal envelope curve T 3  that connects the plurality of distal poles Q 3  be inclined with respect to the axial direction D is sufficient. The third amplitude G 3  that is the distance between the proximal envelope curve S 3  and the distal envelope curve T 3  may fluctuate in accordance with the position in the circumferential direction of the small fixed ring  3 .