Expansion devices
The expansion device addresses blood flow obstruction and size limitations of balloon catheters by using a rotatable inner shaft to adjustably expand an expansion member, ensuring versatility and maintaining blood flow.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- ASAHI INTECC CO LTD
- Filing Date
- 2024-10-23
- Publication Date
- 2026-05-11
AI Technical Summary
Balloon catheters can temporarily block blood flow and require multiple sizes to accommodate varying expansion sites, posing risks of ischemia and necessitating extensive preparation.
An expansion device with a hollow outer shaft, a rotatable inner shaft, and an expansion member that expands radially by rotating the inner shaft relative to the outer shaft, allowing adjustable expansion without complete vessel blockage.
The device ensures blood flow is maintained and provides versatility by eliminating the need for specific balloon catheter sizes, enabling adjustable expansion and contraction.
Smart Images
Figure 2026075726000001_ABST
Abstract
Description
Technical Field
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[0001] The present disclosure relates to an expansion device.
Background Art
[0002] A balloon catheter is known as one of medical devices. The balloon catheter is used, for example, when widening a stenosis in a blood vessel or removing a thrombus.
[0003] As a balloon catheter, for example, a device has been proposed in which a balloon is provided in the middle of a shaft and the balloon is expanded by injecting an expansion liquid (see, for example, Patent Document 1).
Prior Art Documents
Patent Documents
[0004]
Patent Document 1
Summary of the Invention
Problems to be Solved by the Invention
[0005] When using a balloon catheter, the blood flow in the blood vessel may be temporarily blocked by the expanded balloon. Therefore, there is a risk of temporary ischemia. In addition, depending on the state of the site to be expanded, it is necessary to use a balloon of a specific size. Therefore, it is also necessary to prepare balloon catheters of various sizes in advance.
[0006] The present disclosure provides an expansion device that secures blood flow and has excellent versatility.
Means for Solving the Problems
[0007] The expansion device of this disclosure comprises a hollow outer shaft having a slot that penetrates radially and extends along the longitudinal axis; an inner shaft disposed within the lumen of the outer shaft and rotatable relative to the outer shaft; and an expansion member disposed to pass through the slot, with one end joined to the outer shaft and the other end opposite to the one end joined to the inner shaft, wherein the expansion member is pushed out of the slot by rotating the inner shaft relative to the outer shaft so that the expansion member expands radially outward. [Brief explanation of the drawing]
[0008] [Figure 1] This is a schematic longitudinal cross-sectional view showing the first embodiment. [Figure 2] This is a schematic perspective view showing an enlarged portion of Figure 1. [Figure 3] This is a schematic cross-sectional view taken along line III-III in Figure 1, showing the expansion member in its unexpanded state. [Figure 4] Figure 3 is a schematic cross-sectional view showing the expanded member in its expanded state. [Figure 5] This is a schematic perspective view showing an enlarged portion of the second embodiment. [Figure 6] This is a schematic perspective view showing an enlarged portion of the third embodiment. [Figure 7] This is a schematic perspective view showing an enlarged portion of another embodiment. [Modes for carrying out the invention]
[0009] (1) The expansion device of the present disclosure comprises a hollow outer shaft having a slot that penetrates radially and extends along the longitudinal axis; an inner shaft disposed within the lumen of the outer shaft and rotatable relative to the outer shaft; and an expansion member disposed to pass through the slot, with one end joined to the outer shaft and the other end opposite to the one end joined to the inner shaft, wherein the expansion member is pushed out of the slot by rotating the inner shaft relative to the outer shaft so that the expansion member expands radially outward. This configuration allows for adjustment of the degree to which the expansion member expands. As a result, it eliminates the need to prepare balloon catheters of specific sizes, thus improving versatility. In addition, it helps to suppress blood flow obstruction even when the expansion member is expanding.
[0010] (2) In the expansion device described in (1) above, the expansion member may expand radially outward by rotating the inner shaft relative to the outer shaft in a first direction, and the expansion member may contract radially inward by rotating the inner shaft relative to the outer shaft in a second direction opposite to the first direction. With this configuration, the expansion member can be easily and repeatedly expanded and contracted.
[0011] (3) In the expansion devices of (1) and (2) above, when the expansion member is expanded, the inner circumference of the expansion member and the outer circumference of the outer shaft may be partially separated. This configuration allows the expansion member to be extended radially outward.
[0012] (4) In the extension devices described in (1) to (3) above, the maximum distance between the long axis and the extension member may vary depending on the circumferential position of the outer shaft. This configuration allows the extension member to be extended asymmetrically with respect to its long axis.
[0013] (5) In the expansion device according to (1) to (4) above, the expansion member may be formed of a wire. According to this configuration, a large local pressure can be applied to the lesion part, and for example, an incision can be made in the lesion.
[0014] (6) In the expansion device according to (1) to (4) above, the expansion member may be formed of a sheet. According to this configuration, the lesion part can be expanded without applying a large local pressure to the lesion part.
[0015] (7) In the expansion device according to (1) to (6) above, the outer shaft may be formed of an outer coil body in which strands are spirally wound, and the inner shaft may be formed of an inner coil body in which strands are spirally wound. According to this configuration, the flexibility and the body cavity followability of the expansion device can be enhanced, and the torque transmission property can be improved.
[0016] In this specification, the "tip side" refers to the direction along the long axis of the expansion device (long axis direction), which is the direction in which the expansion device advances toward a predetermined site in the body cavity (distal side). The "base end side" refers to the direction along the long axis of the expansion device (long axis direction), which is the direction opposite to the tip side (proximal side). The "tip" refers to the end portion on the tip side of any member. The "base end" refers to the end portion on the base end side of any member. The "radial direction" refers to the radial direction orthogonal to the long axis direction of the expansion device.
[0017] The first to third embodiments of the present disclosure will be described with reference to the drawings. The present disclosure is not limited only to the embodiments described in the drawings. The dimensions of each part shown in the drawings are the dimensions shown for facilitating the understanding of the implementation content, and do not necessarily correspond to the actual dimensions.
[0018] In FIGS. 1, 2, 5 to 7, the left side shown in the figure is the tip side (distal side) inserted deeper into the body, and the right side is the proximal side (near side, hand side) operated by a technician such as a doctor. FIGS. 2, 5 to 7 show only the tip of the expansion device.
[0019] [First Embodiment] FIGS. 1 to 4 are schematic views showing the first embodiment. As shown in FIGS. 1 to 3, the expansion device 1 includes, for example, an outer shaft 11, an inner shaft 21, an expansion member 31, and a gripping member 41.
[0020] The outer shaft 11 is a hollow member having a slot 11a. Specifically, the outer shaft 11 can be formed of, for example, a cylindrical member (tube) having a lumen 11h penetrating from the tip to the base.
[0021] The slot 11a is formed to penetrate in the radial direction and extend along the long axis direction. The shape of the slot 11a is not particularly limited as long as it is an elongated through-hole through which the expansion member 31 can pass. Examples of the opening shape of the slot 11a on the outer peripheral surface of the outer shaft 11 include a rectangle, an ellipse, a notch, etc. In the expansion device 1, a rectangular slot 11a extending along the long axis direction is illustrated. The slot 11a may be provided at any position in the long axis direction of the expansion device 1. In the expansion device 1, the slot 11a is provided at the tip of the outer shaft 11. The expansion member 31 is inserted into the slot 11a. The length and width of the slot 11a can be appropriately determined according to the size of the expansion member 31.
[0022] The inner shaft 21 is disposed in the lumen 11h of the outer shaft 11 and is a member rotatable with respect to the outer shaft 11. Specifically, the inner shaft 21 can be formed of, for example, a cylindrical member (tube) having an opening 21a located at the tip and a lumen 21h penetrating from the tip to the base. The inner shaft 21 is disposed coaxially with the outer shaft 11 along the long axis Z of the expansion device 1.
[0023] The materials forming the outer shaft 11 and the inner shaft 21 may have antithrombotic, flexible, and biocompatible properties, since the expansion device 1 is inserted into a body cavity such as a blood vessel. Examples of such materials include resin materials such as polyamide resin, polyolefin resin, polyester resin, polyurethane resin, silicone resin, and fluororesin; and metallic materials such as stainless steel and superelastic alloys (nickel-titanium alloy).
[0024] The expansion member 31 is a member whose outer circumferential surface expands radially outward. The expansion member 31 is positioned to pass through the slot 11a. The shape of the expansion member 31 is not particularly limited as long as it can expand radially outward.
[0025] In the expansion device 1, an expansion member 31 (hereinafter also referred to as the "wire structure 31") formed of wires is exemplified. The configuration of the wire structure 31 is not particularly limited. As shown in Figure 2, the wire structure 31 may be formed, for example, by two wires a1 and a2 extending along the circumferential direction of the outer shaft 11, and wires b1 to b4 located between wires a1 and a2.
[0026] Wires a1 and a2 are arranged parallel to each other, with wire a2 located on the base end side of wire a1. One end of wire a1 is joined to the inner shaft 21 at joint X1, and the other end is joined to the outer shaft 11 at connection Y1. One end of wire a2 is joined to the inner shaft 21 at joint X2, and the other end is joined to the outer shaft 11 at connection Y2.
[0027] Wires b1, b2, and b3 are arranged substantially parallel to each other in the direction of their long axes. Wire b1 is joined to wire a1 at connection X1 at one end and to wire a2 at connection X2 at the other end. Wire b1 may also be directly joined to the inner shaft 21 (connection N1). Wire b2 is joined to wire a1 at connection Y1 at one end and to wire a2 at connection Y2 at the other end. Wire b2 may also be directly joined to the outer shaft 11 (connection M1). Wire b3 is positioned between wires b1 and b2 in the circumferential direction of the outer shaft 11. Wire b3 is joined to wire a1 at one end and to wire a2 at the other end.
[0028] Wire b4 extends at an angle with respect to its long axis. Wire b4 can be joined, for example, by connecting the diagonals of a roughly quadrilateral formed by wires a1, a2, b1, b2, and b3.
[0029] The curvature of wires a1 and a2 increases as the expansion member 31 expands. By rotating the inner shaft 21 in a first direction relative to the outer shaft 11, a portion of the expansion member 31 housed between the outer shaft 11 and the inner shaft 21 is pushed out to the outside of the outer shaft 11 through the slot 11a, causing the expansion member 31 to expand radially outward. As wire b1 approaches the slot 11a, the proportion of the expansion member 31 located outside the outer shaft 11 increases. As a result, the curvature of wires a1 and a2 increases, and the maximum value Lmax of the distance between the major axis Z and the expansion member 31 (hereinafter also referred to as "maximum expansion radius Lmax") increases. As the maximum expansion radius Lmax increases, the expansion force (the force that causes the expansion member 31 to expand radially outward) increases.
[0030] When the expansion member 31 is expanded, the inner circumference of the expansion member 31 and the outer circumference of the outer shaft 11 are partially separated. When the expansion member 31 is expanded, the maximum value Lmax of the distance between the major axis Z and the expansion member 31 varies depending on the circumferential position of the outer shaft 11 (see Figure 4).
[0031] By rotating the inner shaft 21 in a second direction opposite to the first direction relative to the outer shaft 11, a portion of the expansion member 31 located outside the outer shaft 11 is accommodated between the outer shaft 11 and the inner shaft 21, causing the expansion member 31 to contract radially inward (maximum expansion radius Lmax becomes smaller). As wire b1 moves further away from slot 11a, the proportion of the expansion member 31 accommodated between the outer shaft 11 and the inner shaft 21 increases. As a result, the maximum expansion radius Lmax decreases while the curvature of wires a1 and a2 decreases. The maximum expansion radius Lmax can decrease until the entire expansion member 31 contacts the outer circumferential surface of the outer shaft 11.
[0032] In this way, by forming the expansion member 31 with a wire w, tissues such as thrombi and stenoses can be partially compressed with high pressure.
[0033] The material forming the wire w preferably has high strength because it presses the expansion member 31 against the tissue. Examples of such materials include metal materials such as stainless steel (SUS304, etc.), superelastic alloys (Ni-Ti alloy, etc.), and resin materials such as reinforced plastics.
[0034] One end of the expansion member 31 is joined to the outer shaft 11, and the other end opposite to the one end is joined to the inner shaft 21. In this embodiment, as described above, the wire b2 of the wire structure 31 is joined to the outer circumferential surface 11g of the outer shaft 11 at a joint M1, and the wire b1 of the wire structure 1 is joined to the outer circumferential surface 21g of the inner shaft 21 at a joint N1.
[0035] The method for joining the wire structure 31 to the outer shaft 11 and the inner shaft 21 is not particularly limited. Examples of joining methods include welding by heating, bonding using an adhesive, and brazing using a soldering material.
[0036] The gripping member 41 is a member used by the operator to operate the extension device 1. The gripping member 41 is attached to the base ends of the outer shaft 11 and the inner shaft 21 and is configured to allow the inner shaft 21 to rotate relative to the outer shaft 11. The gripping member 41 has, for example, an opening 41a located at the base end and a lumen 41h that communicates with the inner lumen 21h. The shape of the gripping member 41 is not particularly limited. The gripping member 41 can be formed, for example, in a shape that is easy for the operator to operate.
[0037] In this embodiment, a lumen L is formed by the lumen 21h of the inner shaft 21 and the lumen 41h of the gripping member 41. A medical device, such as a guidewire, is inserted through the lumen L.
[0038] The usage of the dilation device 1 will be explained. Here, the procedure for widening a narrowed area in a blood vessel using the dilation device 1 will be described.
[0039] The proximal end of a guidewire, whose tip has been pre-inserted into the blood vessel, is inserted into the opening 21a of the dilation device 1, and the un-expanded dilation device 1 (see Figure 3) is pushed along the guidewire to the stenosis. At this time, the tip of the dilation device 1 (the part where the dilation member 31 is located) is positioned so that the un-expanded dilation member 31 is located inside the stenosis.
[0040] Next, the expansion member 31 is expanded. Specifically, the gripping member 41 is operated to push the expansion member 31 out of the slot 11a while rotating the inner shaft 21 relative to the outer shaft 11. As a result, the expansion member 31 expands radially outward, as shown in Figure 4. The degree to which the expansion member 31 expands (maximum expansion radius Lmax, expansion force, etc.) can be appropriately determined by the amount of rotation of the inner shaft 21. When the expansion member 31 expands, it does not completely block the blood vessel like a balloon catheter, so blood flow is maintained. In addition, the wire w can make an incision in the lesion by applying localized pressure to it, making it easier to expand the narrowed area.
[0041] As described above, the expansion device 1 has the above configuration, allowing the degree to which the expansion member 31 expands to be adjusted. As a result, there is no need to prepare a balloon catheter of a specific size, thus improving versatility. In addition, even when the expansion member 31 is expanded, it is possible to suppress the obstruction of blood flow.
[0042] [Second Embodiment] Figure 5 is a schematic diagram showing a second embodiment. The expansion device 2 of this embodiment includes, for example, an outer shaft 11, an inner shaft 21, an expansion member 32, and a gripping member 41 (not shown). The expansion device 2 differs from the expansion device 1 in that it includes an expansion member 32. The configurations of the outer shaft 11, the inner shaft 21, and the gripping member 41 are the same as in the first embodiment, so the same parts are denoted by the same reference numerals and their detailed descriptions are omitted. The configurations of the expansion members, other than the configuration of the expansion member 32 shown below, are the same as in the first embodiment.
[0043] The expansion member 32 is positioned to pass through the slot 11a, with one end joined to the outer shaft 11 and the other end opposite to that joined to the inner shaft 21. By rotating the inner shaft 21 relative to the outer shaft 11, the expansion member 32 is pushed out of the slot 11a. As a result, the substantially cylindrical outer surface formed by the expansion member 32 expands radially outward.
[0044] The expansion member 32 of the expansion device 2 is formed of a sheet. In this embodiment, a sheet that is rectangular in shape when unfolded (hereinafter also referred to as "sheet 32") is shown as an example. By forming the expansion member 32 of a sheet, the entire surface of the sheet 32 can be used to press against the tissue. For this reason, for example, the constricted area can be expanded by pressing the sheet 32 against the inner circumference of the constricted area.
[0045] The material forming the sheet 32 preferably has high strength because it presses the expanded member 32 against the tissue. Examples of such materials include metal materials such as stainless steel (SUS304, etc.), superelastic alloys (Ni-Ti alloy, etc.), and resin materials such as reinforced plastics.
[0046] One side of the sheet 32 is joined to the outer surface 11g of the outer shaft 11 by a joint M2. The other side of the sheet (the side opposite to the above-mentioned side) is joined to the outer surface 21g of the inner shaft 21 by a joint N2. The method of joining the sheet 32 is not particularly limited. Examples of joining methods include welding by heating, bonding with an adhesive, and brazing with a soldering material.
[0047] The usage of the expansion device 2 will be explained. Here, the procedure for using the expansion device 2 to dilate a stenotic area will be described.
[0048] The proximal end of a guidewire, whose tip has been pre-inserted into the blood vessel, is inserted into the opening 21a of the dilation device 2, and the un-expanded dilation device 2 is pushed along the guidewire to the stenosis. At this time, the tip of the dilation device 2 (the part where the dilation member 32 is located) is positioned so that the un-expanded dilation member 32 is located inside the stenosis.
[0049] Next, the expansion member 32 is expanded. Specifically, the gripping member 41 is operated to push the expansion member 32 out of the slot 11a while rotating the inner shaft 21 relative to the outer shaft 11. This causes the expansion member 32 to expand radially outward, and the sheet 32 presses against and expands the constricted area. The degree to which the expansion member 32 expands (maximum expansion radius Lmax, expansion force, etc.) can be appropriately determined by the amount of rotation of the inner shaft 21. When the expansion member 32 expands, it does not completely block the blood vessel like a balloon catheter, so blood flow is maintained.
[0050] A stent is then placed in the widened area, for example, using a known stent placement device. This maintains the blood vessel in an expanded state, restoring sustained blood flow. After widening the stenosis, the procedure is completed by removing the dilation device, guidewire, etc. from the body.
[0051] As described above, the expansion device 2 has the above configuration, allowing the degree to which the expansion member 32 expands to be adjusted. As a result, there is no need to prepare a balloon catheter of a specific size, thus improving versatility. In addition, even when the expansion member 32 is expanded, it is possible to suppress the obstruction of blood flow.
[0052] [Third Embodiment] Figure 6 is a schematic diagram showing a third embodiment. The expansion device 3 of this embodiment includes, for example, an outer shaft 13, an inner shaft 23, an expansion member 31, and a gripping member 41 (not shown). The expansion device 3 differs from the expansion device 1 in that it includes an outer shaft 13 and an inner shaft 23. The configuration of the expansion member 31 and the gripping member 41 is the same as in the first embodiment, so the same parts are denoted by the same reference numerals and their detailed description is omitted. The configuration of the outer shaft and inner shaft, other than the configuration of the outer shaft 13 and inner shaft 23 shown below, is the same as in the first embodiment. The usage mode of the expansion device 3 can also be illustrated in the same way as in the first embodiment.
[0053] The outer shaft 13 is a hollow member having a slot 13a that penetrates radially and extends along the longitudinal axis. The outer shaft 13 has an internal lumen 13h. The outer shaft 13 of the expansion device 3 is formed from an outer coil body (hereinafter also referred to as "outer coil body 13") in which strands w1 are wound spirally. The outer coil body 13 is formed so that adjacent strands w1 along the longitudinal axis are in contact with each other (tightly wound).
[0054] The inner shaft 23 is positioned in the lumen 13h of the outer shaft 13 and is a rotatable member relative to the outer shaft 13. The inner shaft 23 of the expansion device 3 is formed from an inner coil body (hereinafter also referred to as "inner coil body 23") in which strands w2 are wound in a spiral shape. Specifically, the inner shaft 23 has, for example, an opening 23a located at the tip and a lumen 23h that penetrates from the tip to the base. The inner coil body 23 is formed so that adjacent strands w2 along the long axis are in contact with each other (tightly wound).
[0055] The strands w1 and w2 forming the outer coil body 13 and the inner coil body 23 may be single wires. The strands w1 and w2 may be stranded wires. The strands w1 and w2 may be a combination of single wires and stranded wires. A single wire refers to one single wire. A stranded wire refers to a bundle of wires formed by twisting multiple single wires together in advance.
[0056] The wires w1 and w2 forming the outer coil 13 and inner coil 23 may have antithrombotic, flexible, and biocompatible properties, as the expansion device 3 is inserted into blood vessels, etc. Examples of materials for the wires w1 and w2 include resin materials such as polyamide resin, polyolefin resin, polyester resin, polyurethane resin, silicone resin, and fluororesin; and metal materials such as stainless steel and superelastic alloy (nickel-titanium alloy). The wires w1 of the outer coil 13 and w2 of the inner coil 23 may be the same or different.
[0057] As described above, the expansion device 3 has the above configuration, making it highly versatile and capable of suppressing blood flow obstruction even when the expansion member is expanded.
[0058] The outer shaft 13 and the inner shaft 23 are each formed from coil bodies. This increases the flexibility of the expansion device 3. As a result, the ability to follow the body cavity can be improved. In addition, torque transmission can be improved. As a result, the inner shaft 23 can rotate smoothly relative to the outer shaft 13.
[0059] This disclosure is not limited to the configurations of the embodiments described above, but is intended to include all modifications within the meaning and scope of the claims as indicated by the claims. Some of the configurations of the embodiments described above may be deleted or replaced with other configurations, or other configurations may be added to the configurations of the embodiments described above.
[0060] In the first and second embodiments described above, expansion devices 1 and 2 were described in which both the outer shaft 11 and the inner shaft 21 were formed from cylindrical members (tubes). In the third embodiment, an expansion device 3 was described in which both the outer shaft 13 and the inner shaft 23 were formed from coil bodies. However, the outer shaft and the inner shaft can be used in any combination of cylindrical members and coil bodies. For example, the outer shaft may be formed from a cylindrical member and the inner shaft from a coil body. Or, the outer shaft may be formed from a coil body and the inner shaft from a cylindrical member.
[0061] In the first and third embodiments described above, expansion devices 1 and 3 were described in which the expansion member was formed of a wire structure 31. In the second embodiment, expansion device 2 was described in which the expansion member was formed of a sheet 32. However, the expansion member is not limited to the above configurations. As shown in Figure 7, the expansion member 34 may be, for example, a wire structure (braided body) in which wires w are braided into a mesh. The expansion member may also be a wire structure with a sheet attached to it so as to reinforce the sheet. Any of the above-described forms of expansion members can be arbitrarily adopted in the expansion device, regardless of the form of the outer shaft and inner shaft.
[0062] In the third embodiment described above, an expansion device 3 was described in which both the outer coil 13 and the inner coil 23 are tightly wound. The outer coil 13 and the inner coil 23 may each be tightly wound independently, or they may be loosely wound with gaps between adjacent strands along the long axis. Both tightly wound and loosely wound coils may be included in a single coil.
Claims
1. A hollow outer shaft (11, 13) having slots (11a, 13a) that penetrate radially and extend along the longitudinal axis, An inner shaft (21, 23) is positioned in the lumen (11h, 13h) of the outer shaft (11, 13) and is rotatable relative to the outer shaft (11, 13), The system includes expansion members (31, 32, 34) arranged to pass through the slots (11a, 13a), with one end joined to the outer shafts (11, 13) and the other end opposite to the one end joined to the inner shafts (21, 23), Expansion devices (1, 2, 3) in which the expansion members (31, 32, 34) are pushed out of the slots (11a, 13a) by rotating the inner shafts (21, 23) relative to the outer shafts (11, 13) so that the expansion members (31, 32, 34) expand radially outward.
2. By rotating the inner shafts (21, 23) relative to the outer shafts (11, 13) in a first direction, the expansion members (31, 32, 34) expand radially outward. The expansion device (1, 2, 3) according to claim 1, wherein the expansion members (31, 32, 34) contract radially inward by rotating the inner shafts (21, 23) relative to the outer shafts (11, 13) in a second direction opposite to the first direction.
3. The expansion device (1, 2, 3) according to claim 1 or 2, wherein when the expansion members (31, 32, 34) are expanded, the inner circumference of the expansion members (31, 32, 34) and the outer circumference of the outer shafts (11, 13) are partially separated.
4. The expansion device (1, 2, 3) according to any one of claims 1 to 3, wherein the maximum distance (Lmax) between the long axis (Z) and the expansion members (31, 32, 34) varies depending on the circumferential position of the outer shafts (11, 13).
5. The expansion device (1, 3) according to any one of claims 1 to 4, wherein the expansion members (31, 34) are formed of wire.
6. The expansion device (2) according to any one of claims 1 to 4, wherein the expansion member (32) is formed of a sheet.
7. The outer shaft (13) is formed from an outer coil body (13) in which strands (w1) are wound in a spiral shape. The expansion device (3) according to any one of claims 1 to 6, wherein the inner shaft (23) is formed of an inner coil body (23) in which strands (w2) are wound in a spiral shape.