Dilator

Abstract

The purpose of the present invention is to provide a dilator capable of preventing a helical projection from separating from a hollow shaft.A dilator 1 comprises a hollow shaft 11 having a conical portion 111 whose outer diameter at the distal end is smaller than the outer diameter at the base end, a distal end tip 21 whose base end is located at the distal end of the conical portion 111 and extends into the distal end direction, and a helical projection 31 disposed at least on the outer circumferential surface 11s of the conical portion 111, wherein: the helical projection 31 is formed by winding a wire 31w and has gaps 31g in adjacent portions in the longitudinal direction of the hollow shaft 11; and the inner circumference radius CIDmin of the portion of the helical projection 31 where the inner circumference radius is smaller is less than the outer circumference radius TODmax of the portion of the distal end tip 21 where the outer circumference radius is larger.

Description

Dilator Technical field The revealed achievements refer to a dilator. Precedent technique A dilator is understood to be, for example, an instrument for expanding a hole made in a body surface or organ, etc., or expanding a constricted portion formed in a bile duct or pancreatic duct, etc. Such a dilator requires a strong propulsive force for expansion, and thus, an example disclosed (see, for example, patent literature 1) is a dilator provided with a coil body on the outer peripheral surface of the conical portion of a shaft for expansion, in order to supplement the propulsive force by using the screwing action resulting from rotation. Document WO 2019 / 225025 A1 discloses a dilator with which it is possible to reliably and safely expand a hole in an object. The dilator comprises a hollow shaft and a screw-shaped protrusion.The shaft has a conical portion, a point portion, and a main body, or it does not have a point portion, but it has a conical portion and a main body. The coil body as described above is configured, for example, by winding a wire around the outer peripheral surface of the conical portion above, so that the coil body can be easily formed. List of appointments Patent literature Patent Literature 1: Document WO 2013 / 038720 A1 Patent Literature 2: Document WO 2019 / 225025 A1 Summary of the invention Technical problem However, a conventional dilator as described above is configured in such a way that a wire forming a coil body is simply wound around the outer peripheral surface of a shaft, and therefore may cause a risk of the coil body detaching from the shaft due to a tissue drag force when expanding a hole or a pulling force when withdrawing. The disclosed embodiments have been made in view of the above circumstances, and one object of the disclosed embodiments is to provide a dilator capable of preventing a spirally arranged protruding portion from detaching from the hollow shaft. Solution to the problem The problem is solved by a dilator according to claim 1. Note that, in memory, the "distal end direction" is a direction along the longitudinal direction of a dilator and refers to the direction in which the dilator advances toward a portion, whose diameter it expands. The "proximal end direction" is a direction along the longitudinal direction of the dilator and refers to a direction opposite to the distal end direction. Furthermore, the "distal end" refers to an end in the direction of the distal end of an arbitrary limb or portion, and the "proximal end" refers to an end in the direction of the proximal end of an arbitrary limb or portion. The "inner peripheral radius" refers to the distance between the long axis of a dilator and the innermost peripheral portion of a relevant portion, and the "outer peripheral radius" refers to the distance between the long axis of the dilator and the outermost peripheral portion of the relevant portion. Advantageous effects of the invention The revealed realizations can provide a dilator capable of preventing a spirally arranged protruding portion from detaching from a hollow shaft. Brief description of the drawings FIG.1 is a schematic side view illustrating a first embodiment. FIG.2 is a schematic side view illustrating a portion of FIG.1 in an enlarged manner. FIG.3 is a schematic side view illustrating a second embodiment. FIG.4 is a schematic side view illustrating a third embodiment. FIG. 5 is a schematic side view illustrating a fourth embodiment. Description of the forms of implementation A dilator of the unveiled includes: a hollow shaft having a conical portion whose outer diameter at the distal end is smaller than the outer diameter at the proximal end; a distal tip whose proximal end is located at the distal end of the conical portion and is provided to extend in the direction of the distal end; and a spirally arranged protruding portion provided at least on the outer peripheral surface of the conical portion. The spirally arranged protruding portion is formed by coiling a wire and has spaces between adjacent portions along the longitudinal direction of the hollow shaft. The inner peripheral radius of a portion, which is the minimum inner peripheral radius of the spirally arranged protruding portion, is smaller than the outer peripheral radius of a portion, which is the maximum outer peripheral radius of the distal tip. Note that in the memory, "longitudinal direction" refers to the longitudinal direction of a dilator, unless otherwise specified. Hereafter, the first four of the revealed realizations are described with reference to the accompanying drawings. However, the revealed realizations are not limited to those illustrated in the drawings. Furthermore, the size of the dilator in each drawing is an illustrative size to facilitate understanding of the realizations and does not correspond to the actual size. [First realization] FIG. 1 is a schematic side view illustrating the first embodiment. The dilator 1 is configured approximately from a hollow shaft 11, a distal tip 21, a spirally arranged projecting portion 31, and a base portion 41, as shown in FIG. 1. The hollow shaft 11 is a hollow-shaped shaft. The hollow shaft 11 has a tapered portion 111, a main body portion 112, and an inner cavity 11h, for example. A conical portion 111 is a portion whose outer diameter at the distal end is smaller than the outer diameter at the proximal end. Specifically, a conical portion 111 can be exemplified as having an outer diameter that increases linearly from the distal end to the proximal end (see FIG. 1), an outer diameter that increases from the distal end to the proximal end (not shown) while the surface is curved in a convex or concave shape, or similar. The main portion of body 112, whose distal end is located at the proximal end of the conical portion 111, is proportioned to extend toward the proximal side of the end. The main portion of body 112 can be configured such that it has a given outside diameter from its distal end to its proximal end. The internal cavity 11h is a through hole for the insertion of a guide wire (not shown), etc. The internal cavity 11h can be configured to have a continuous space (e.g., a portion within the common inscribed lines indicated by broken lines in FIG. 1) penetrating from the distal end to the proximal end of the hollow shaft 11 along the longitudinal direction, e.g. The tapered portion 111 and the main portion 112 of the body may be integrally formed or formed as separate bodies. The hollow shaft 11 of the embodiment is configured from a coil body 11C (hereafter also referred to as the "first coil body 11C"), wherein the tapered portion 111 and the main portion 112 of the body are integrally formed, and a wire 11w made of solid wire is continuously wound spirally around the long Z-axis of the dilator to form the coil body 11C. Since the hollow shaft 11 is formed by winding the wire 11w, the torque (the certainty of transmitting the rotational force applied to the proximal portion of the dilator end 1 to the distal end portion) can be increased. The materials forming the hollow shaft 11 are preferably antithrombotic, flexible, and biocompatible because the dilator 1 must be inserted into a body cavity. Examples of the above materials that can be used here include resin materials such as a polyamide resin, a polyolefin resin, a polyester resin, a polyurethane resin, a silicone resin, and a fluorocarbon resin, and metallic materials such as stainless steel and superelastic alloys (a nickel-titanium alloy). The materials forming the tapered portion 111 and the main body portion 112 can be the same or different materials. The tapered portion 111 and the main body portion 112 of the first coil body 11C can be formed integrally or separately. Furthermore, the tapered portion 111 and the main body portion 112 can be formed from the same or different materials.Furthermore, the wire diameters of the coil body, composed of the tapered portion 111 and the main body portion 112, may be the same or different. The tapered portion 111 and the main body portion 112 of the first coil body 11C in the embodiment are formed by spirally winding solid wire 11w, which is made of the same material and has the same wire diameter. Note that the hollow shaft 11 may have various coatings (not shown) on its outer peripheral surface 11s. Examples of coatings include a protective film (coating film and the like) to protect the surface of the hollow shaft 11, a base film, etc., to improve adhesion between the hollow shaft 11 and the spirally arranged protruding portion 31 (described later). A distal tip 21, whose proximal end is located at the distal end of the conical portion 111, is a member provided to extend in the direction of the distal tip. The distal tip 21 can be specifically formed, for example, tapering towards the distal side of the tip, so that the dilator 1 can be more easily advanced into a body cavity. The distal tip 21 may have an internal cavity 21h. The internal cavity 21h may be configured so that it penetrates from the distal end to the proximal end of the distal tip 21, to communicate with the internal cavity 11h of the hollow shaft 11. The material forming the distal tip 21 is preferably flexible to allow the dilator 1 to be advanced into a body cavity. Examples of this material forming the distal tip 21 include resin materials such as polyurethane and polyurethane elastomer. The spirally arranged protruding portion 31 is a portion provided at least on the outer peripheral surface of the tapered portion 111. The spirally arranged protruding portion 31 is configured from a coil body 31C (hereinafter also referred to as the "second coil body 31C") formed by winding a wire and has 31g spacings in adjacent portions along the longitudinal direction of the hollow shaft. Specifically, the spirally arranged protruding portion 31 can be formed, for example, by spiraling a continuous or intermittent single- or multi-threaded wire(s) 31w along the longitudinal direction of the hollow shaft 11 such that the wire(s) 31w are in contact with the outer peripheral surface 11s. In the embodiment, the spirally arranged protruding portion 31 is provided on the outer peripheral surface 11s of the tapered portion 111 and the main portion of the body 112. The wire(s) 31w forming the spirally arranged protruding portion 31 may be a solid wire, stranded wires, or a combination of solid and stranded wires. Note that "solid wire" refers to a single wire and "stranded wires" refers to a bundle (group) of wires formed by pre-twisting a plurality of individual wires together. For example, the materials that form the spirally arranged protruding portion 31 can be the same or similar materials exemplified as the materials that form the hollow shaft 11. Here, the spirally arranged protruding portion 31 and the distal tip 21 of dilator 1 are formed as shown in FIG. 2, such that the internal peripheral radius (CIDmin) of a portion, which is the minimum internal peripheral radius of the spirally arranged protruding portion 31, is less than the external peripheral radius (TODmax) of a portion, which is the maximum external peripheral radius of the distal tip 21 (CIDmin). <TODmax) . Furthermore, the spirally arranged protruding portion 31 and the distal tip 21 can be formed such that the distance (CMD, hereafter also referred to as "center of minimum distance") between the long axis of the hollow shaft 11 and the center of a wire in a portion having the minimum inner peripheral radius of the spirally arranged protruding portion 31 is less than the outer peripheral radius (TODmax) of a portion, which is the maximum outer peripheral radius of the distal tip 21 (see FIG. 1 and FIG. 2). Specifically, for example, the appropriate selection of the wire diameter of the second coil body 31C, the outer peripheral radius (TODmax) of the distal tip 21, and an outer peripheral radius of the tapered portion 111 can make the center of minimum distance (CMD) of the spirally arranged protruding portion 31 smaller than the outer peripheral radius (TODmax) of the distal tip 21.This can ensure the prevention of detachment of the spirally arranged protruding portion 31 from the hollow shaft 11. Such a portion having the minimum inner peripheral radius (the portion of the spirally arranged protruding portion having the minimum inner peripheral radius (CIDmin)) of the spirally arranged portion 31 may be located anywhere on the spirally arranged protruding portion 31, unless the portion impairs the effects of the disclosed embodiments. The portion of the spirally arranged protruding portion 31 having the minimum inner peripheral radius (CIDmin) may be located at the distal end of the spirally arranged protruding portion 31 in the longitudinal direction (see FIG. 1 and FIG. 2) or located in the center of the spirally arranged protruding portion 31 in the longitudinal direction (not shown). In this embodiment, the portion of the spirally arranged protruding portion 31 that has the inner peripheral radius (CIDmin) is positioned at the distal end of the spirally arranged protruding portion 31. This prevents the spirally arranged protruding portion 31 from extending from the distal tip 21 in the distal end direction. For example, this can inhibit the second coil body 31C from damaging tissues. The spirally arranged protruding portion 31 and the conical portion 111 may or may not join together (the two portions are in a state where they are simply in contact with each other) at least a portion of the portion where the two portions are in contact with each other. In the present invention, the spirally arranged protruding portion 31 and the conical portion 111 are not joined together, and the second coil body 31C is wound around the peripheral surface 11s of the hollow shaft 11 in a state of being merely in contact with the outer peripheral surface 11s. This can suppress a decrease in the flexibility of the dilator portion 1 corresponding to the conical portion 111. The base portion 41 is a site where a technician operates the dilator 1. The base portion 41 has, for example, an internal cavity 41h that communicates with an internal cavity 11h of the hollow shaft 11 and extends from the distal end to the proximal end. The base portion 41 can be configured so that the distal end is connected to the proximal end of the hollow shaft 11. During operation, a guide wire or similar device is inserted into the internal cavity 41h, for example. Furthermore, when the base portion 41 is rotated, the hollow shaft 11, the distal tip 21, and the spirally arranged protruding portion 31 are rotated together. The following describes one method of using dilator 1. This involves using dilator 1 to expand a portion of a blood vessel, such as a chronic total occlusion (CTO). First, use an introducer needle (not shown) to create a hole while puncturing the portion to be expanded. Next, after inserting a guide wire (not shown) into the inner cavity of the introducer needle, pull the introducer needle out. Then, insert the proximal end of the guide wire into the inner cavity 21h from the distal end of the distal tip 21, and push the hollow shaft 11 until it reaches the portion to be expanded. At this point, advance the distal end portion of the dilator 1 while following the shape of the curved portion to be inserted (e.g., blood vessel, esophagus, stomach, bile duct, etc.). Next, after inserting the distal end portion of dilator 1 with its distal tip 21 into the dilator head 1 in the hole made in the portion to be expanded, operate the base portion 41 to expand the hole by the conical portion 111 while rotating and advancing the hollow shaft 11. At this time, dilator 1 is formed in such a way that the inner peripheral radius (CIDmin) is smaller than the outer peripheral radius (TODmax), and therefore the portion to be expanded expands smoothly without causing the detachment of the second coil body 31C from the hollow shaft 11. The dilator 1 is configured as described above, in order to prevent the spirally arranged protruding portion 31 from detaching from the hollow shaft 11 and to allow smooth operation. [Second realization] Figure 3 is a schematic side view illustrating the second embodiment. The dilator 2 is configured approximately with a hollow shaft 12, a distal tip 21, a spirally arranged protruding portion 31, and a base portion 42, as shown in Figure 3. The dilator 2 differs from that of the first embodiment in that it includes the hollow shaft 12 and the base portion 42. Since the configurations of the distal tip 21 and the spirally arranged protruding portion 31 are the same as those of the first embodiment, the same portions / positions are represented by the same reference symbols, and detailed descriptions of these are omitted. Furthermore, since the configurations of the hollow shaft 12 and the base portion 42 described below and the mode of use of the dilator 2 are the same as those of the first embodiment, detailed descriptions of these are omitted. The hollow shaft 12 is a hollow-shaped shaft. The hollow shaft 12 has a tapered portion 121, a main body portion 122, and an internal cavity 12h, for example. The tapered portion 121 is a portion where the outer diameter of the distal end is smaller than the outer diameter of the proximal end. The main body portion 122, whose distal end lies at the proximal end of the tapered portion 121, is a portion proportioned to extend toward the proximal side of the end. The internal cavity 12h is a through-hole for the insertion of a guide wire (not shown) or similar. The conical portion 121 and the main portion 122 of the body may be formed integrally or separately. Note that the conical portion 121 and the main portion 122 of the body may be formed from the same or different materials. Furthermore, the conical portion 121 and the main portion 122 of the body may have the same or different wall thicknesses. The conical portion 121 and the main portion 122 of the body in this embodiment are formed using the same materials integrally by casting or similar materials to have different wall thicknesses (the internal cavity 12h has a given inside diameter from the distal end to the proximal end of the hollow shaft 12). The base portion 42 is a site where a technician operates the dilator 2. The base portion 42 of this embodiment has an internal cavity 42h that has the same inner diameter as that of the internal cavity 12h, wherein the internal cavity 42h communicates with the internal cavity 12h of the hollow shaft 12h and penetrates from the distal end to the proximal end. The dilator 2 is configured as described above, in order to prevent the spirally arranged protruding portion 31 from detaching from the hollow shaft 12 and to allow smooth operation. [Third realization] Figure 4 is a schematic side view illustrating the third embodiment. The dilator 3 is configured approximately with a hollow shaft 13, a distal tip 21, a spirally arranged protruding portion 33, and a base portion 41 (not shown), as shown in Figure 4. The dilator 3 differs from that of the first embodiment in that it includes the hollow shaft 13 and the spirally arranged protruding portion 33. Since the configurations of the distal tip 21 and the base portion 41 are the same as those of the first embodiment, the same portions / positions are represented by the same reference symbols, and detailed descriptions of these are omitted. Furthermore, since the configurations other than those of the hollow shaft 13 and the spirally arranged protruding portion 33, and the mode of use of the dilator 3 shown below, are the same as those of the first embodiment, detailed descriptions of these are omitted. The hollow shaft 13 is a hollow-shaped shaft. The hollow shaft 13 has a tapered portion 131, a main body portion 132, and an internal cavity 13h, for example. The tapered portion 131 is a portion where the outside diameter of the distal end is smaller than the outside diameter of the proximal end. The main body portion 132, whose distal end is located at the proximal end of the tapered portion 131, is a portion proportioned to extend toward the proximal side of the end. The main body portion 132 has the same outside diameter as the proximal end of the tapered portion 131. The internal cavity 13h is a through-hole for the insertion of a guide wire (not shown) or similar. The spirally arranged protruding portion 33 is a proportionate portion at least on the outer peripheral surface of the conical portion. The spirally arranged protruding portion 33 is configured from a coil body 33C ("second coil body 33C") formed by winding a wire 33w and has 33g spacings in adjacent portions along the longitudinal direction of the hollow shaft 13. Furthermore, in this embodiment, the dilator 3 is formed such that the outer peripheral radius (CODmax) of one portion, which is the maximum outer peripheral radius of the spirally arranged protruding portion 33, is greater than the outer peripheral radius (TODmax) of one portion, which is the maximum outer peripheral radius of the distal tip 21. Specifically, for example, the dilator 3 can be formed such that the outer diameter of the proximal end of the tapered portion 131 of the anterior hollow shaft 13 is greater than that of the tapered portion 111 of the first embodiment (see FIG. 4). Through appropriate adjustment of the wire diameter of the second coil body 33C, the outer peripheral radius (CODmax) of the second coil body 33C can be larger than the outer peripheral radius (TODmax) of the distal tip 21 (not shown).Such a portion of the spirally arranged protruding portion 33 having the outer peripheral radius (CODmax) may be a portion in the conical portion 131 (not shown) or a portion in the main body portion 132 (see FIG.4). Furthermore, another configuration is possible, such that the outer peripheral radius (CODmax) of a portion, which is the maximum outer peripheral radius between the portions provided on the outer peripheral surface 13s of the conical portion 131 of the spirally arranged protruding portion 33, is greater than the outer peripheral radius (TODmax) of a portion, which is the maximum outer peripheral radius of the distal tip 21. This can further increase the propulsive force of the dilator 3 resulting from the screwing action during tissue expansion (while the conical portion 131 passes through the portion to be expanded). Dilator 3 is as configured above. Therefore, the outer periphery of the spirally arranged protruding portion 33 extends from the distal tip 21 as in a front view (when dilator 3 is viewed from the distal side of the end in the longitudinal direction to the distal tip 21), in order to increase the propulsive force of dilator 3 resulting from the screwing action. [Fourth realization] Figure 5 is a schematic side view illustrating the fourth embodiment. The dilator 4 is configured approximately with a hollow shaft 14, a distal tip 21, a spirally arranged protruding portion 34, and a base portion 41 (not shown), as shown in Figure 5. The dilator 4 differs from that of the first embodiment in that it includes the hollow shaft 14 and the spirally arranged protruding portion 34. Since the configurations of the distal tip 21 and the base portion 41 are the same as those of the first embodiment, the same portions / positions are represented by the same reference symbols, and detailed descriptions of these are omitted. Furthermore, since the configurations other than those of the hollow shaft 14 and the spirally arranged protruding portion 34 shown below, and the mode of use of the dilator 4, are the same as those of the first embodiment, detailed descriptions of these are omitted. The hollow shaft 14 is a hollow-shaped shaft. The hollow shaft 14 has a tapered portion 141, a main body portion 142, and an internal cavity 14h, for example. The tapered portion 141 is a portion where the outside diameter of the distal end is smaller than the outside diameter of the proximal end. The main body portion 142, whose distal end lies at the proximal end of the tapered portion 141, is a portion proportioned to extend toward the proximal side of the end. The main body portion 142 has the same outside diameter as the proximal end of the tapered portion 141. The internal cavity 14h is a through-hole for the insertion of a guide wire (not shown) or similar. The spirally arranged protruding portion 34 is a proportionate portion at least on the outer peripheral surface of the conical portion 141. The spirally arranged protruding portion 34 is configured from a coil body 34C ("second coil body 34C") formed by winding a wire 34w and has gaps of 34g in adjacent portions along the longitudinal direction of the hollow shaft 14. Furthermore, in this embodiment, the dilator 4 is formed such that the inner peripheral radius (CIDmax) of one portion, which is the maximum inner peripheral radius of the spirally arranged protruding portion 34, is greater than the outer peripheral radius (TODmax) of one portion, which is the maximum outer peripheral radius of the distal tip 21. Specifically, for example, the dilator 4 can be formed such that the outer diameter of the proximal end of the conical portion 141 of the anterior hollow shaft 14 is greater than that of the conical portion 131 of the third embodiment (see FIG. 5). Consequently, the inner peripheral radius (CIDmax) of the second coil body 34C can be larger than the outer peripheral radius (TODmax) of the distal tip 21.Such a portion of the spirally arranged protruding portion 34 having the inner peripheral radius (CIDmax) may be a portion in the conical portion 141 (not shown) or a portion in the main body portion 142 (see FIG.5). Dilator 4 is as previously configured. Therefore, the outer periphery of the spirally arranged protruding portion 34 extends from the distal tip 21 as in a front view, in order to further increase the propulsive force of dilator 4 resulting from the screwing action. Please note that the disclosed embodiments are not limited to the configurations of the embodiments described above, but are defined by the terms of the claims and are intended to include any modifications within the scope and meaning equivalent to the terms of the claims. For example, the first embodiment above describes dilator 1, wherein the portion having the inner peripheral radius (CIDmin) is located at the distal end of the spirally arranged protruding portion 31. However, the portion having the inner peripheral radius (CIDmin) can be any portion of the spirally arranged protruding portion in the longitudinal direction (e.g., a portion located in the middle or at the proximal end of the spirally arranged protruding portion in the longitudinal direction). Furthermore, the hollow shaft 12 formed from casting or similar materials as described above in the second embodiment is also applicable to all other dilators disclosed in this document. Furthermore, the third embodiment above describes the dilator 3 in which, through adjustment of the outer diameter of the hollow shaft 13, the outer peripheral radius (CODmax) of the spirally arranged protruding portion 33 is greater than the outer peripheral radius (TODmax) of the distal tip 21. However, this dilator can be formed in such a way that by adjusting the wire diameter of the second coil body or by adjusting the outer diameter of the hollow shaft and the wire diameter of the second coil body, the outer peripheral radius (CODmax) of the spirally arranged protruding portion is greater than the outer peripheral radius (TODmax) of the distal tip. Furthermore, the above embodiments describe dilators 1 to 4, wherein the portion having the internal peripheral radius (CIDmin) is located in a single position of each of the spirally arranged protruding portions 31 to 34. However, such portion having the internal peripheral radius (CIDmin) may also be provided in two or more positions of the spirally arranged protruding portion, which are separated from each other. Furthermore, the above embodiments describe dilators 1 to 4, wherein the portions having the inner peripheral radius (CIDmin), the outer peripheral radius (CODmax), and the central radius (CMD), respectively, are provided at specific positions on each of the spirally arranged protruding portions 31 to 34. However, each of the above portions may be provided at any position on the spirally arranged protruding portion in the longitudinal direction (any position on the tapered portion and / or on the main portion of the hollow shaft body). List of reference symbols 1, 2, 3, 4 Dilator 11, 12, 13, 14 Hollow shaft 21 Distal tip 31, 33, 34 Spiral-shaped protruding portion 31C, 33C, 34C Coil body (second coil body) 31g, 33g, 34g Space 111, 121, 131, 141 Conical portion

Claims

1. A dilator (1, 2, 3, 4), comprising: a hollow shaft (11, 12, 13, 14) with a conical portion (111, 121, 131, 141) the outer diameter of the distal end being less than the outer diameter of the proximal end; a distal tip (21), the proximal end of which is located at the distal end of the conical portion (111, 121, 131, 141) and which is provided to extend towards the direction of the distal end; and a spirally arranged projecting portion (31, 33, 34) provided at least on the outer peripheral surface of the conical portion (111, 121, 131, 141), wherein: the spirally arranged projecting portion (31, 33, 34) is formed by winding a wire and has spaces (31g, 33g, 34g) between adjacent portions along the longitudinal direction of the hollow shaft (11, 12, 13, 14); and the inner peripheral radius (CIDmin) of a portion, which is the minimum inner peripheral radius (CIDmin) of the spirally arranged projecting portion (31, 33, 34),is less than the outer peripheral radius (TODmax) of a portion, which is the maximum outer peripheral radius (TODmax) of the distal tip (21); characterized in that the spirally arranged protruding portion (31, 33, 34) is not attached to the conical portion (111, 121, 131, 141).

2. The dilator (1, 2, 3, 4) according to claim 1, wherein the outer peripheral radius (TODmax) of the portion, which is the maximum outer peripheral radius (TODmax) of the spirally arranged protruding portion (31, 33, 34), is greater than the outer peripheral radius (TODmax) of the portion, which is the maximum outer peripheral radius (TODmax) of the distal tip (21).

3. The dilator (1, 2, 3, 4) according to claim 2, wherein the outer peripheral radius (TODmax) of the portion, which is the maximum outer peripheral radius (TODmax) between the portions provided on the outer peripheral surface of the conical portion (111, 121, 131, 141) of the spirally arranged projecting portion (31, 33, 34),is larger than the outer peripheral radius (TODmax) of the distal tip (21) 4. The dilator (1, 2, 3, 4) according to claim 2 or 3, wherein the inner peripheral radius (CID min) of the portion, which is the maximum inner peripheral radius (CIDmin) of the spirally arranged protruding portion (31, 33, 34), is larger than the outer peripheral radius (TODmax) of the portion, which is the maximum outer peripheral radius (TODmax) of the distal tip (21).

5. The dilator (1, 2, 3, 4) according to claim 1, wherein the distance between the long axis of the hollow shaft (11, 12, 13, 14) and the center of the wire in the portion having the minimum internal peripheral radius (CIDmin) of the spirally arranged protruding portion (31, 33, 34) is less than the external peripheral radius (TODmax) of the distal tip (21).

6. The dilator (1, 2, 3, 4) according to any one of claims 1 to 5,wherein the portion having the minimum internal peripheral radius (CIDmin) of the spirally arranged protruding portion (31, 33, 34) is located at the distal end of the spirally arranged protruding portion (31, 33, 34).