Variable durometer dilator for intravascular access devices

Abstract

Disclosed herein is a medical device including an introducer sheath (100) including a stiffness transition portion (110) and a dilator (300) including a stiffness transition portion (312). When the dilator (300) occupies the lumen of the introducer sheath (100), the stiffness transition portion (110) of the introducer sheath is longitudinally offset from the stiffness transition portion (312) of the dilator. The medical device can navigate significantly more bends in the vasculature compared to a medical device without a longitudinally offset stiffness transition portion.

Description

[Technical Field]

[0001] Related Applications This application claims the benefit of U.S. Provisional Patent Application No. 63 / 412,946, filed October 4, 2022, which is incorporated herein by reference in its entirety.

[0002] FIELD OF THE DISCLOSURE The present disclosure relates to medical devices, and more particularly to an introducer sheath and dilator having an offset stiffness transition. [Background technology]

[0003] The statements in this section merely provide background information related to the present disclosure and may constitute prior art.

[0004] In today's medical field, many medical procedures, such as angioplasty and stent placement, require access to a blood vessel to access a desired site. To access the desired site, a sheath is typically advanced through the blood vessel. Once in place within the patient's blood vessel, various types of medical devices can be delivered through the sheath and positioned at the desired site so that the procedure can be performed.

[0005] To initially access a particular site within a patient's body, a needle is used to puncture the patient's skin and enter the desired blood vessel. A guidewire is then inserted into the lumen of the needle and advanced into the blood vessel. The needle is then removed, leaving the guidewire in place.

[0006] A dilator / sheath assembly is then placed over the guidewire and advanced to a location within the blood vessel. The distal end of the dilator is tapered to a relatively small diameter and may extend beyond the distal end of the sheath. The tapered distal end of the dilator allows the dilator / sheath assembly to be introduced into the patient's blood vessel in a manner that gradually increases the size of the opening within the vessel, thereby ultimately allowing the vessel to accommodate the larger sized sheath without causing trauma, injury, or other problems to the patient. Once the guidewire and dilator / sheath assembly have been advanced within the blood vessel to the desired location, the dilator is removed. Summary of the Invention [Means for solving the problem]

[0007] In one example, the present disclosure provides a medical device. The medical device includes an introducer sheath. The introducer sheath includes a tubular structure. The tubular structure includes a wall defining a sheath lumen extending longitudinally throughout the tubular structure. The tubular structure defines a longitudinal axis through the tubular structure. The tubular structure further includes a first longitudinal sheath section having a first sheath stiffness, a second longitudinal sheath section distal to the first longitudinal sheath section, the second longitudinal sheath section having a second sheath stiffness less than the first sheath stiffness, and a sheath transition from the first longitudinal sheath section to the second longitudinal sheath section. The medical device further includes a dilator configured to occupy the sheath lumen. The dilator includes a shaft having a wall defining a dilator lumen extending longitudinally therethrough, the shaft defining a second longitudinal axis coaxial with the longitudinal axis when the dilator occupies the sheath lumen. The shaft further includes a first longitudinal dilator section having a first dilator stiffness, a second longitudinal dilator section distal to the first longitudinal dilator section, the second longitudinal dilator section having a second dilator stiffness less than the first dilator stiffness, and a dilator transition section from the first longitudinal dilator section to the second longitudinal dilator section. When the dilator occupies the sheath lumen, the sheath transition section is longitudinally offset from the dilator transition section. In some examples, the first sheath stiffness can be less than the first dilator stiffness. In other examples, the sheath transition section can be distal to the dilator transition section. In yet another example, the second dilator stiffness can be less than the first sheath stiffness and greater than the second sheath stiffness. In yet another example, the dilator transition can be distal to the sheath transition. In yet another example, the second dilator stiffness can be less than the second sheath stiffness. In yet another example, the second longitudinal sheath section can include a distal sheath tip at a distal end of the second longitudinal sheath section, and the second longitudinal dilator section can be configured to extend at least one centimeter distally through the distal sheath tip when the dilator occupies the sheath lumen.In yet other examples, the shaft can further include a third longitudinal dilator section distal to the second longitudinal dilator section, the third longitudinal dilator section having a third dilator stiffness different from the second dilator stiffness. In yet other examples, the third dilator stiffness can be less than the second dilator stiffness. In yet other examples, the third dilator stiffness can be greater than the second dilator stiffness and / or equal to the first dilator stiffness. In yet other examples, the longitudinal dilator length can be greater than the longitudinal sheath length.

[0008] In another example, the present disclosure provides an introducer sheath including a wall defining a sheath lumen extending longitudinally throughout a tubular structure defining a longitudinal axis therethrough. The tubular structure includes a first longitudinal sheath section having a first sheath stiffness, a second longitudinal sheath section distal to the first longitudinal sheath section, the second longitudinal sheath section having a second sheath stiffness less than the first sheath stiffness, and a sheath transition from the first longitudinal sheath section to the second longitudinal sheath section. A dilator is configured to occupy the sheath lumen, such that the sheath transition is longitudinally offset from the dilator transition from the first longitudinal dilator section to the second longitudinal dilator section. The dilator includes a shaft having a wall defining a dilator lumen extending longitudinally through the shaft, a first longitudinal dilator section having a first dilator stiffness, and a second longitudinal dilator section distal to the first longitudinal dilator section having a second dilator stiffness less than the first dilator stiffness. In some examples, the first sheath stiffness may be less than the first dilator stiffness. In other examples, a sheath transition may be configured distal to the dilator transition. In yet other examples, the second dilator stiffness may be less than the first sheath stiffness and greater than the second sheath stiffness. In yet other examples, the dilator transition may be configured distal to the sheath transition.

[0009] In yet another example, the present disclosure provides a dilator including a shaft having a wall defining a dilator lumen extending longitudinally throughout the shaft, a first longitudinal dilator section having a first dilator stiffness, a second longitudinal dilator section distal to the first longitudinal dilator section, the second longitudinal dilator section having a second dilator stiffness less than the first dilator stiffness, and a dilator transition from the first longitudinal dilator section to the second longitudinal dilator section. The dilator is configured to occupy a sheath lumen of an introducer sheath such that the sheath transition from the first longitudinal sheath section to the second longitudinal sheath section is longitudinally offset from the dilator transition. The introducer sheath includes a tubular structure including a wall defining a sheath lumen extending longitudinally therethrough, the tubular structure defining a longitudinal axis therethrough, the tubular structure including a first longitudinal sheath section having a first sheath stiffness and a second longitudinal sheath section distal to the first longitudinal sheath section, the second sheath stiffness being less than the first sheath stiffness. In some examples, the first sheath stiffness may be less than the first dilator stiffness. In other examples, the sheath transition may be configured distal to the dilator transition. In other examples, the second dilator stiffness may be less than the first sheath stiffness and greater than the second sheath stiffness.

[0010] Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.

[0011] In order that the present disclosure may be fully understood, various aspects of the disclosure will now be described, by way of example, with reference to the accompanying drawings, in which components are not necessarily to scale. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the various views. [Brief explanation of the drawings]

[0012] [Figure 1] 1 illustrates a side view of an example introducer sheath according to the principles of the present disclosure; [Figure 2] 2 shows a cross-sectional view of the distal tip of the example introducer sheath of FIG. 1. [Figure 3] 1 illustrates a side view of an example of a dilator according to the principles of the present disclosure. [Figure 4] 10 shows a side view of another example of a dilator according to the principles of the present disclosure. [Figure 5] 5 shows a distal end view of the example dilator of FIG. 4. [Figure 6] 1 shows a model tracking path used to analyze various medical devices for their ability to complete bends within the vasculature without device failure. [Figure 7] FIG. 7 is an exploded view of the model tracking path of FIG. 6, showing the number of bends in the vasculature at each point along the model tracking path. [Figure 8] 1 illustrates a side view of an example introducer sheath and an example dilator, shown separately, in accordance with the principles of the present disclosure. [Figure 9] 1 illustrates a side view of an example introducer sheath and an example dilator, with the dilator occupying the sheath lumen, in accordance with the principles of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0013] The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way.

[0014] The following description provides examples and is not intended to limit the present disclosure, application, or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features.

[0015] When adding reference symbols to elements in each drawing, it should be noted that the same elements have the same symbols even though they are displayed in different drawings. In addition, when describing certain aspects of the present disclosure, if it is determined that a detailed description of related known structures or functions would obscure the gist of certain aspects of the present disclosure, the description will be omitted.

[0016] In the following discussion, the terms "proximal" and "distal" are used to describe the axial ends of various components, as well as the opposing axial ends of a device. The term "proximal" is used in its conventional sense to refer to the end of a device (or component) that is closest to a medical professional during use of the assembly. The term "distal" is used in its conventional sense to refer to the end of a device (or component) that is first inserted into a patient's body or that is closest to the patient during use. The term "longitudinal" is used to refer to an axis aligned with the proximal-distal axis of a device (or component). The terms "radially" and "radially" are used to refer to elements, surfaces, or assemblies relative to one another that may extend perpendicularly from the longitudinal axis. The terms "peripheral," "circumferentially," and "circumferential" are used to refer to elements, surfaces, or assemblies relative to one another that radially surround the longitudinal axis.

[0017] In the context of describing this disclosure (particularly in the context of the claims which follow), the use of "a," "an," and "the" and similar referents should be construed to encompass both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The use of the term "plurality" has been given its broadest definition by the applicant and supersedes any other implied definition or limitation, either prior or subsequent, unless expressly asserted to the contrary by the applicant, to mean a quantity of two or more. The recitation of ranges of values ​​herein, unless otherwise indicated herein, is intended merely to serve as a shorthand method of individually referencing each separate value falling within the range, and each separate value is incorporated herein as if set forth individually herein. All methods described herein can be performed in any suitable order, unless otherwise indicated herein or clearly contradicted by context.

[0018] As used herein, the terms "comprise," "include," "having," "has," "can," and "contain," and variations thereof, are intended to be open-ended transitional phrases, terms, or words that do not exclude the possibility of additional acts or structures. The present application description also contemplates other examples of "comprising," "consisting of," and "consisting essentially of" the examples or elements presented herein, whether explicitly stated or not.

[0019] In describing elements of the present disclosure, the present specification refers to st , 2 nd Terms such as, first, second, A, B, (a), (b), etc. may be used. These terms are used only to distinguish one element from another and do not limit the corresponding elements without regard to the nature or order of the corresponding elements.

[0020] Unless otherwise specified, all terms used herein, including technical and scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure pertains. Terms as defined in commonly used dictionaries should be interpreted as having the same meaning as given in context in the relevant art.

[0021] As used herein, the term "about," when used in reference to a stated numerical value or range, refers to a variation of no more than ±15% of that numerical value. For example, values ​​that vary by ±15%, ±14%, ±10%, or ±5%, among others, meet the definition of "about," unless a more narrow definition is given in a specific instance.

[0022] The term "stiffness," as used herein, refers to a measure of the hardness of a material, such as a polymer, elastomer, or rubber. While the term is relative and unitless, a higher stiffness indicates a harder material that is more resistant to indentation and therefore less flexible and pliable, while a lower relative stiffness indicates a softer material that is less resistant to indentation and therefore more flexible and pliable. Methods for measuring or otherwise determining the relative stiffness of a material are generally known to those skilled in the art. In a specific example, stiffness can be measured by a Shore durometer, which measures the depth of indentation of a material produced by a given force against a standardized presser foot. This depth can depend on the hardness of the material, the viscoelastic properties of the material, the shape of the pressure surface, and the duration of the test. There are several durometer scales that can be used for materials with different properties, but the two most common scales are the ASTM D2240 Type A scale, in which the pressure foot presses into the material with a force of approximately 10 N for 15 seconds, and the Type D scale, in which the pressure foot penetrates the surface of the material with a force of approximately 50 N for 15 seconds. Each durometer scale yields a value from 0 to 100, with higher values ​​indicating harder materials.

[0023] Referring to FIG. 1 , a side view of an example introducer sheath 100 is shown. The introducer sheath 100 includes a tubular structure 104 having a wall 118 defining a sheath lumen 120 extending longitudinally through the entire tubular structure 104 from a proximal end 114 to a distal tip 112. The tubular structure 104 defines a first longitudinal axis 122 extending therethrough. The proximal end 114 of the tubular structure 104 is secured to the valve body 102. The tubular structure 104 includes a first longitudinal sheath section 106 and a second longitudinal sheath section 108. The second longitudinal sheath section 108 is distal to the first longitudinal sheath section 106. The first longitudinal sheath section 106 has a first sheath stiffness. The second longitudinal sheath section 106 has a second sheath stiffness that is less than the first sheath stiffness. The first longitudinal sheath section 106 and the second longitudinal sheath section 108 are connected at a sheath transition 110, and the tubular structure 104 can be fabricated by butt-joining the first longitudinal sheath section 106 to the second longitudinal sheath section 108. Alternatively, the second longitudinal sheath section 108 can be integral with the first longitudinal sheath section 106, and the tubular structure 104 can be formed by a process such as total intermittent extrusion, in which the tubular structure 104 is fabricated so that the first longitudinal sheath section 106 has the first sheath stiffness and the second longitudinal sheath section 108 has the second sheath stiffness. The tubular structure 104 has a length L from a proximal end 114 to a distal tip 112. S The second longitudinal sheath section 108 has a length L A , i.e., the length of the intermediate longitudinal segment 116, and L B , i.e., the longitudinal length of the distal tip 112. The first longitudinal sheath section 106 has a length L S From L A +L B The length minus the sum of the S -(L A +L B )

[0024] In some examples, the first sheath stiffness and the second sheath stiffness may differ by a value of at least 5D, or at least 10D, or at least 15D, or at least 20D, or at least 25D, or at least 30D, or at least 35D, or at least 40D, or at least 45D, or at least 50D, or at least 55D, or at least 60D, or at least 65D, or at least 70D, or at least 75D, or at least 80D, or at least 85D, or at least 90D, or at least 95D on the ASTM D2240 Type D scale for measurement by Shore Durometer. In particular examples, the first sheath stiffness may be greater than 50D, or greater than 55D, or greater than 60D, or greater than 65D, or greater than 70D, or greater than 75D, and the second sheath stiffness may be less than 50D, or less than 45D, or less than 40D, or less than 35D, or less than 30D, or less than 25D. In other specific examples, the first sheath stiffness can be about 52D, or about 54D, or about 56D, or about 58D, or about 60D, or about 62D, or about 64D, or about 66D, or about 68D, or about 70D, or about 72D, or about 74D, or about 76D, or about 78D, or about 80D, and the second sheath stiffness can be about 48D, or about 46D, or about 44D, or about 42D, or about 40D, or about 38D, or about 36D, or about 34D, or about 32D, or about 30D, or about 28D, or about 26D, or about 24D, or about 22D, or about 20D.

[0025] In some examples, the length L of the tubular structure 104 Smay be at least about 20 cm, or at least about 22 cm, or at least about 24 cm, or at least about 26 cm, or at least about 28 cm, or at least about 30 cm, or at least about 32 cm, or at least about 34 cm, or at least about 36 cm, or at least about 38 cm, or at least about 40 cm, or at least about 42 cm, or at least about 44 cm, or at least about 46 cm, or at least about 48 cm, or at least about 50 cm, or at least about 52 cm, or at least about 54 cm, or at least about 56 cm, or at least about 58 cm, or at least about 60 cm. B may be at least about 0.2 cm, or at least about 0.3 cm, or at least about 0.4 cm, or at least about 0.5 cm, or at least about 0.6 cm, or at least about 0.7 cm, or at least about 0.8 cm, or at least about 0.9 cm, or at least about 1.0 cm, or at least about 1.1 cm, or at least about 1.2 cm, or at least about 1.3 cm, or at least about 1.4 cm, or at least about 1.5 cm.

[0026] In one example, the tubular structure 104 may have a longitudinal cross-sectional size ranging from 4 French ("Fr") to 24 Fr. As will be understood by those skilled in the art, the French scale or French gauge system, commonly used to measure the size of medical devices such as catheters, refers to three times the length, measured in millimeters ("mm"), of the outer diameter of the medical device. In the case of the tubular structure 104, the French gauge system refers to three times the length, measured in millimeters, from wall 118 to wall 118 of the tubular structure 104. For example, a 1 French circular tubular structure 104 has an outer diameter of 1 / 3 of a millimeter, and a 3 French circular catheter has an outer diameter of 1 millimeter. In some examples, the tubular structure 104 is from 5 French, or from 6 French, or from 7 French, or from 8 French, or from 9 French, or from 10 French, or from 11 French, or from 12 French, or from 13 French, or from 14 French, or from 15 French, or from 16 French, or from 17 French, or from 18 French, or from 19 French, or from 20 French, or from 21 French, or from 22 French, or from 23 French to 24 French; or from 4 French to 5 French, or from 6 French, or from 7 French. The french may have a size from 4 French to 24 French, including up to, or up to 8 French, or up to 9 French, or up to 10 French, or up to 11 French, or up to 12 French, or up to 13 French, or up to 14 French, or up to 15 French, or up to 16 French, or up to 17 French, or up to 18 French, or up to 19 French, or up to 20 French, or up to 21 French, or up to 22 French, or up to 23 French, or up to 24 French, or any other range of sizes from one of the minimum values ​​recited above to one of the maximum values ​​recited above.

[0027] In one example, the first longitudinal sheath section 106 and the second longitudinal sheath section 108 can each comprise a blend of 0-95% polypropylene ("PP") impact copolymer and 5-100% high performance elastomer. Examples of high performance elastomers include thermoplastic elastomers such as thermoplastic olefins ("TPO"), thermoplastic polyurethanes ("TPU"), thermoplastic vulcanizates ("TPV"), polyester elastomers, polyamide elastomers such as polyester block amides ("PEBA"), nylon, polyethylene, and fluoropolymers such as fluorinated ethylene propylene ("FEP"), perfluoroalkoxyalkanes ("PFA"), and ethylene tetrafluoroethylene ("ETFE").

[0028] Referring to Figure 2, a cross-sectional view of the distal tip 112 of an example introducer sheath 100 is shown. As shown in Figure 2, the wall 118 may be slightly tapered toward the distal end of the tubular structure 104. The sheath lumen 120 of the tubular structure 104 has a diameter L T The diameter L T can be sized to allow the dilator to reversibly occupy the sheath lumen 120.

[0029] Referring to FIG. 3 , a side view of an example dilator 300 is illustrated. The dilator 300 includes a shaft 302 having a wall defining a dilator lumen extending longitudinally therethrough. The shaft 302 defines a second longitudinal axis 316. The second longitudinal axis 316 is coaxial with the first longitudinal axis 122 of the introducer sheath 100 when the dilator 300 occupies the sheath lumen 120 of the introducer sheath 100. The shaft 302 extends from a proximal end 304 to a distal tip 306. The shaft 302 includes a first longitudinal dilator section 308 and a second longitudinal dilator section 310. The second longitudinal dilator section 310 is distal to the first longitudinal dilator section 308. The first longitudinal dilator section 308 has a first dilator stiffness. The second longitudinal dilator section 310 has a second dilator stiffness that is less than the first dilator stiffness. The first and second longitudinal dilator sections 308, 310 are connected at a dilator transition 312, and the shaft 302 can be fabricated by butt-joining the first longitudinal dilator section 308 to the second longitudinal dilator section 310. Alternatively, the second longitudinal dilator section 310 can be integral with the first longitudinal dilator section 308, and the shaft 302 can be formed by a process such as full intermittent extrusion, in which the shaft 302 is fabricated so that the first longitudinal dilator section 308 has a first dilator stiffness and the second longitudinal dilator section 310 has a second dilator stiffness. The proximal end 304 is attached to a dilator hub 314. The shaft 302 has a length L from the proximal end 304 to the distal tip 306. D The second longitudinal dilator section 310 has a length L C It has a length L C L A +L B Alternatively, the length L C L A +L B The first longitudinal dilator section 310 may be smaller than the sum of the length L of the shaft 302. Dto the length L of the second longitudinal section 310 C When the dilator 300 occupies the sheath lumen 120 of the introducer sheath 100, the sheath transition 110 is longitudinally offset from the dilator transition 312, with the sheath transition 110 being either proximal or distal to the dilator transition 312.

[0030] In one example, when the dilator 300 occupies the sheath lumen 120 of the introducer sheath 100, the sheath transition 110 is longitudinally spaced from the dilator transition 312 by at least about 0.1 cm, or at least about 0.2 cm, or at least about 0.3 cm, or at least about 0.4 cm, or at least about 0.5 cm, or at least about 0.6 cm, or at least about 0.7 cm, or at least about 0.8 cm, or at least about 0.9 cm, or at least about 1.0 cm, or at least about 1.1 cm, or at least about 1.2 cm, or at least about 1.3 cm, or at least about 1.4 cm, or at least about 1.5 cm, or at least about 1.6 cm, or at least about 1.7 cm, or at least about 1.8 cm, or at least about 1.9 cm, or at least about 2.0 cm, or at least about 2.1 cm, or at least about 2.2 cm, or at least about 2.3 cm, or at least about 2.4 cm, or at least about 2.5 cm, or at least about 2.6 cm, or at least about 2.7 cm, or at least about 2.8 cm, or at least about 2.9 cm, or at least about 3.0 cm, or at least about 3.1 cm m, or at least about 3.2 cm, or at least about 3.3 cm, or at least about 3.4 cm, or at least about 3.5 cm, or at least about 3.6 cm, or at least about 3.7 cm, or at least about 3.8 cm, or at least about 3.9 cm, or at least about 4.0 cm, or at least about 4.1 cm, or at least about 4.2 cm, or at least about 4.3 cm, or at least about 4.4 cm, or at least about 4.5 cm, or at least about 4.6 cm, or at least about 4.7 cm, or at least about 4.8 cm, or at least about 4. 9cm, or at least about 5.0cm, or at least about 5.1cm, or at least about 5.2cm, or at least about 5.3cm, or at least about 5.4cm, or at least about 5.5cm, or at least about 5.6cm, or at least about 5.7cm, or at least about 5.8cm, or at least about 5.9cm, or at least about 6.0cm, at least about 6.1cm, or at least about 6.2cm, or at least about 6.3cm, or at least about 6.4cm, or at least about 6.5cm, or at least about 6.6cm, or at least about 6.7 cm, or at least about 6.8 cm, or at least about 6.9 cm, or at least about 7.0 cm, or at least about 7.1 cm, or at least about 7.2 cm, or at least about 7.3 cm, or at least about 7.4 cm, or at least about 7.5 cm, or at least about 7.6 cm, or at least about 7.7 cm, or at least about 7.8 cm, or at least about 7.9 cm, or at least about 8.0 cm, or at least about 8.1 cm, or at least about 8.2 cm, or at least about 8.3 cm, or at least about 8. 4 cm, or at least about 8.5 cm, or at least about 8.6 cm, or at least about 8.7 cm, or at least about 8.8 cm, or at least about 8.9 cm, or at least about 9.0 cm, or at least about 9.1 cm, or at least about 9.2 cm, or at least about 9.3 cm, or at least about 9.4 cm, or at least about 9.5 cm, or at least about 9.6 cm, or at least about 9.7 cm, or at least about 9.8 cm, or at least about 9.9 cm, or at least about 10.0 cm.

[0031] In some examples, the first dilator stiffness and the second dilator stiffness can differ by a value of at least 5D, or at least 10D, or at least 15D, or at least 20D, or at least 25D, or at least 30D, or at least 35D, or at least 40D, or at least 45D, or at least 50D, or at least 55D, or at least 60D, or at least 65D, or at least 70D, or at least 75D, or at least 80D, or at least 85D, or at least 90D, or at least 95D on the ASTM D2240 Type D scale for measurement by Shore Durometer. In certain examples, the first dilator stiffness can be greater than the first sheath stiffness, such as greater than 55D, or greater than 60D, or greater than 65D, or greater than 70D, or greater than 75D. In other specific examples, when the shaft 302 of the dilator 300 occupies the sheath lumen 120 of the introducer sheath 100 and the dilator transition 312 is proximal to the sheath transition 110, the second dilator stiffness can be greater than the second sheath stiffness but less than the first sheath stiffness. In yet other specific examples, when the shaft 302 of the dilator 300 occupies the sheath lumen 120 of the introducer sheath 100 and the dilator transition 312 is distal to the sheath transition 110, the second dilator stiffness can be less than the second sheath stiffness, and can be less than 45D, or less than 40D, or less than 35D, or less than 30D, or less than 25D. In yet other specific examples, the first dilator stiffness can be about 56D, or about 58D, or about 60D, or about 62D, or about 64D, or about 66D, or about 68D, or about 70D, or about 72D, or about 74D, or about 76D, or about 78D, or about 80D, and the second dilator stiffness can be about 55D, or about 54D, or about 52D, or about 50D, or about 48D, or about 46D, or about 44D, or about 42D, or about 40D, or about 38D, or about 36D, or about 34D, or about 32D, or about 30D, or about 28D, or about 26D, or about 24D, or about 22D, or about 20D.

[0032] By including a single stiffness transition in the dilator 300 and a single stiffness transition in the introducer sheath 100, and offsetting the longitudinal dilator transition 312 from the sheath transition 110, the offset stiffness transition advantageously provides the compound effect of a series of stiffness transitions. The combined series of stiffness transitions ranges from highest stiffness at the first longitudinal dilator section 308, to lower stiffness at the first longitudinal sheath section 106, to lower stiffness at the second longitudinal dilator section 310 (or second longitudinal sheath section 108), and finally to lowest stiffness at the second longitudinal sheath section 108 (or second longitudinal dilator section 310). The offset stiffness transitions minimize stiffness transitions in each of the introducer sheath 100 and dilator 300, while advantageously providing a unique feel transition for the operator of the introducer sheath 100 and dilator 300.

[0033] In some examples, the length L of the shaft 302 D is the length L of the tubular structure 104 S At least about 0.5 cm longer than the length L SIt may be at least about 1.0 cm longer, or at least about 1.5 cm longer, or at least about 2.0 cm longer, or at least about 2.5 cm longer, or at least about 3.0 cm longer, or at least about 3.5 cm longer, or at least about 4.0 cm longer, or at least about 4.5 cm longer, or at least about 5.0 cm longer, or at least about 5.5 cm longer, or at least about 6.0 cm longer, or at least about 6.5 cm longer, or at least about 7.0 cm longer, or at least about 7.5 cm longer, or at least about 8.0 cm longer, or at least about 8.5 cm longer, or at least about 9.0 cm longer, or at least about 9.5 cm longer, or at least about 10.0 cm longer. In other examples, when the shaft 302 of the dilator 300 occupies the sheath lumen 120 of the introducer sheath 100, the distal end of the distal tip 306 of the dilator 300 may extend beyond the distal end of the distal tip 112 of the introducer sheath 100 by at least about 0.5 cm, or by at least about 1.0 cm, or by at least about 1.5 cm, or by at least about 2.0 cm, or by at least about 2.5 cm, or by at least about 3.0 cm, or by at least about 3.5 cm, or by at least about 4.0 cm, or by at least about 4.5 cm, or by at least about 5.0 cm.

[0034] In some examples, the shaft 302 of the dilator 300 can have a longitudinal cross-sectional size that allows the shaft 302 to reversibly occupy the sheath lumen 120 of the introducer sheath 100.

[0035] In one example, the first longitudinal dilator section 308 and the second longitudinal dilator section 310 can each comprise a blend of 0-95% polypropylene (PP) impact copolymer and 5-100% high performance elastomer, such as thermoplastic elastomers such as thermoplastic olefin (TPO), thermoplastic polyurethane (TPU), thermoplastic vulcanizate (TPV), polyester elastomers, polyamide elastomers such as polyester block amide (PEBA), nylon, polyethylene, and fluoropolymers such as fluorinated ethylene propylene (FEP), perfluoroalkoxyalkane (PFA), and ethylene tetrafluoroethylene (ETFE).

[0036] Referring to FIG. 4 , a side view of another example of a dilator 400 is illustrated. The dilator 400 includes a shaft 402 having a wall defining a dilator lumen extending longitudinally therethrough. The shaft 402 defines a second longitudinal axis 422. The second longitudinal axis 422 is coaxial with the first longitudinal axis 122 of the introducer sheath 100 when the dilator 400 occupies the sheath lumen 120 of the introducer sheath 100. The shaft 402 extends from a proximal end 404 to a distal tip 406. The shaft 402 includes a first longitudinal dilator section 410, a second longitudinal dilator section 412, and a third longitudinal dilator section 416. The second longitudinal dilator section 412 is distal to the first longitudinal dilator section 410. The third longitudinal dilator section 416 is distal to the second longitudinal dilator section 412. The first longitudinal dilator section 410 has a first dilator stiffness. The second longitudinal dilator section 412 has a second dilator stiffness that is less than the first dilator stiffness. The third longitudinal dilator section 416 has a third dilator stiffness that is different from the second dilator stiffness. The first longitudinal dilator section 410 and the second longitudinal dilator section 412 are connected at a first dilator transition 414. The second longitudinal dilator section 412 and the third longitudinal dilator section 416 are connected at a second dilator transition 418. The shaft 402 can be fabricated by butt-joining the first longitudinal dilator section 410 to the second longitudinal dilator section 412 and the second longitudinal dilator section 412 to the third longitudinal dilator section 416. Alternatively, the second longitudinal dilator section 412 may be integral with the first longitudinal dilator section 410, the third longitudinal dilator section 416 may be integral with the second longitudinal dilator section 412, and the shaft 402 may be formed by a process such as full intermittent extrusion in which the shaft 402 is processed so that the first longitudinal dilator section 410 has a first dilator stiffness, the second longitudinal dilator section 412 has a second dilator stiffness, and the third longitudinal dilator section 416 has a third dilator stiffness.The proximal end 404 is attached to a dilator hub 408. The shaft 402 has a length L from the proximal end 404 to the distal tip 406. E It has a length L E may be at least about 0.5 cm, or at least about 1.0 cm, or at least about 1.5 cm, or at least about 2.0 cm, or at least about 2.5 cm, or at least about 3.0 cm, or at least about 3.5 cm, or at least about 4.0 cm, or at least about 4.5 cm, or at least about 5.0 cm, or at least about 5.5 cm, or at least about 6.0 cm, or at least about 6.5 cm, or at least about 7.0 cm, or at least about 7.5 cm, or at least about 8.0 cm, or at least about 8.5 cm, or at least about 9.0 cm, or at least about 9.5 cm, or at least about 10.0 cm longer than the length of the tubular structure 104 of the introducer sheath 100.

[0037] The third longitudinal dilator section 416 has a longitudinal length L G When the dilator 400 occupies the sheath lumen 120 of the introducer sheath 100, the distal tip 406 of the dilator 400 extends beyond the distal tip of the introducer sheath by approximately a length L G is larger than the length L G Smaller than or approximately the length L G and the longitudinal distance that the distal tip 406 of the dilator 400 extends beyond the distal tip of the introducer sheath may correspond to at least about 0.5 cm, or at least about 1.0 cm, or at least about 1.5 cm, or at least about 2.0 cm, or at least about 2.5 cm, or at least about 3.0 cm, or at least about 3.5 cm, or at least about 4.0 cm, or at least about 4.5 cm, or at least about 5.0 cm.

[0038] The second longitudinal dilator section 412 and the third longitudinal dilator section 416 have a combined longitudinal length L F The second longitudinal dilator section 412 has a length L F-L G The longitudinal length L of the second longitudinal dilator section 412 corresponds to F -L Gcan be of a length such that the sheath transition 110 is longitudinally offset from each of the first dilator transition 414 and the second dilator transition 418 when the dilator 400 occupies the sheath lumen 120 of the introducer sheath 100. The sheath transition 110 can be longitudinally offset from the first dilator transition 414, and additionally or alternatively, the sheath transition 110 can be longitudinally offset from the second dilator transition 418 by at least about 0.1 cm, or at least about 0.2 cm, or at least about 0.3 cm, or at least about 0.4 cm, or at least about 0.5 cm, or at least about 0.6 cm, or at least about 0.7 cm, or at least about 0.8 cm, or at least about 0.9 cm, or at least about 1.0 cm, or at least or at least about 1.1 cm, or at least about 1.2 cm, or at least about 1.3 cm, or at least about 1.4 cm, or at least about 1.5 cm, or at least about 1.6 cm, or at least about 1.7 cm, or at least about 1.8 cm, or at least about 1.9 cm, or at least about 2.0 cm, or at least about 2.1 cm, or at least about 2.2 cm, or at least about 2.3 cm, or at least about 2.4 cm, or at least about 2.5 cm, or at least about 2.6 cm, or at least about 2.7 cm, or at least about 2.8 cm, or at least about 2.9 cm, or at least about 3.0 cm, or at least about 3.1 cm, or at least about 3.2 cm, or at least about 3.3 cm, or at least about 3.4 cm, or at least about 3.5 cm, or at least about 3.6 cm, or at least about 3.7 cm, or at least about 3.8 cm, or at least about 3.9 cm, or at least about 4.0 cm, or at least about 4.1 cm, or at least about 4.2 cm , or at least about 4.3 cm, or at least about 4.4 cm, or at least about 4.5 cm, or at least about 4.6 cm, or at least about 4.7 cm, or at least about 4.8 cm, or at least about 4.9 cm, or at least about 5.0 cm, or at least about 5.1 cm, or at least about 5.2 cm, or at least about 5.3 cm, or at least about 5.4 cm, or at least about 5.5 cm, or at least about 5.6 cm, or at least about 5.7 cm, or at least about 5.8cm, or at least about 5.9cm, or at least about 6.0cm, or at least about 6.1cm, or at least about 6.2cm, or at least about 6.3cm, or at least about 6.4cm, or at least about 6.5cm, or at least about 6.6cm, or at least about 6.7cm, or at least about 6.8cm, or at least about 6.9cm, or at least about 7.0cm, or at least about 7.1cm, or at least about 7.2cm, or at least about 7.3cm, or at least about 7.4cm, or at least about 7.5cm, or at least about 7.6cm, or at least about 7.7cm, or at least about 7.8cm, or at least about 7.9cm, or at least The offset may be at least about 8.0 cm, or at least about 8.1 cm, or at least about 8.2 cm, or at least about 8.3 cm, or at least about 8.4 cm, or at least about 8.5 cm, or at least about 8.6 cm, or at least about 8.7 cm, or at least about 8.8 cm, or at least about 8.9 cm, or at least about 9.0 cm, or at least about 9.1 cm, or at least about 9.2 cm, or at least about 9.3 cm, or at least about 9.4 cm, or at least about 9.5 cm, or at least about 9.6 cm, or at least about 9.7 cm, or at least about 9.8 cm, or at least about 9.9 cm, or at least about 1.0 cm.

[0039] The first longitudinal dilator section 410 is L E -L F , and can be such that when the dilator 400 occupies the sheath lumen 120 of the introducer sheath 100, the distal surface 502 of the dilator hub 408 abuts or approaches the proximal end 122 of the valve body 102 of the introducer sheath 100.

[0040] In some examples, the first dilator stiffness can differ from the second dilator stiffness by at least 5D, or at least 10D, or at least 15D, or at least 20D, or at least 25D, or at least 30D, or at least 35D, or at least 40D, or at least 45D, or at least 50D, or at least 55D, or at least 60D, or at least 65D, or at least 70D, or at least 75D, or at least 80D, or at least 85D, or at least 90D, or at least 95D on the ASTM D2240 Type D scale for measurement by Shore Durometer. In certain examples, the first dilator stiffness can be greater than the first sheath stiffness, such as by more than 55D, or more than 60D, or more than 65D, or more than 70D, or more than 75D. In other specific examples, when the shaft 402 of the dilator 400 occupies the sheath lumen 120 of the introducer sheath 100 and the first dilator transition 414 is proximal to the sheath transition 110, the second dilator stiffness can be greater than the second sheath stiffness but less than the first sheath stiffness. In yet other specific examples, when the shaft 402 of the dilator 400 occupies the sheath lumen 120 of the introducer sheath 100 and the first dilator transition 414 is distal to the sheath transition 110, the second dilator stiffness can be less than the second sheath stiffness, and can be less than 45D, or less than 40D, or less than 35D, or less than 30D, or less than 25D. In yet other specific examples, the first dilator stiffness can be about 56D, or about 58D, or about 60D, or about 62D, or about 64D, or about 66D, or about 68D, or about 70D, or about 72D, or about 74D, or about 76D, or about 78D, or about 80D, and the second dilator stiffness can be about 55D, or about 54D, or about 52D, or about 50D, or about 48D, or about 46D, or about 44D, or about 42D, or about 40D, or about 38D, or about 36D, or about 34D, or about 32D, or about 30D, or about 28D, or about 26D, or about 24D, or about 22D, or about 20D. In yet other specific examples, the third dilator stiffness can be less than the second dilator stiffness.In yet other particular instances, the stiffness of the third dilator is greater than the stiffness of the second dilator and / or equal to the stiffness of the first dilator.

[0041] By limiting the stiffness transitions of the dilator 400 when the dilator 400 occupies the sheath lumen 120 of the introducer sheath 100, regardless of whether the first dilator transition 414 is distal or proximal to the sheath transition 110, and by including only a single stiffness transition in the introducer sheath 100 and longitudinally offsetting the first dilator transition 414, the sheath transition 110, and the second dilator transition 418 from one another, advantageously, offset stiffness transitions can be achieved. creates a combined effect of a series of stiffness transitions from highest stiffness in the first longitudinal dilator section 410, to lower stiffness in the first longitudinal sheath section 106, to lower stiffness in the second longitudinal dilator section 412 (or second longitudinal sheath section 108), and finally to lowest stiffness in the second longitudinal sheath section 108 (or second longitudinal dilator section 412, or third longitudinal dilator section 416). The offset stiffness transitions minimize stiffness transitions in each of the introducer sheath 100 and dilator 400, while advantageously providing a unique feel transition for the operator of the introducer sheath 100 and dilator 400.

[0042] In some examples, the shaft 402 of the dilator 400 can have a longitudinal cross-sectional size that allows the shaft 402 to reversibly occupy the sheath lumen 120 of the introducer sheath 100.

[0043] In one example, the first longitudinal dilator section 410, the second longitudinal dilator section 412, and the third longitudinal dilator section 416 can each comprise a blend of 0-95% polypropylene (PP) impact copolymer and 5-100% high performance elastomer, such as thermoplastic elastomers such as thermoplastic olefin (TPO), thermoplastic polyurethane (TPU), thermoplastic vulcanizate (TPV), polyester elastomers, polyamide elastomers such as polyester block amide (PEBA), nylon, polyethylene, and fluoropolymers such as fluorinated ethylene propylene (FEP), perfluoroalkoxyalkane (PFA), and ethylene tetrafluoroethylene (ETFE).

[0044] 5, a distal end view of the dilator 400 is shown. The distal surface 502 of the dilator hub 408 is shown in the background, and the distal surface 504 of the distal tip 406 is shown in the foreground. The shaft 402 includes a wall that defines a dilator lumen 506.

[0045] Referring to FIG. 6 , a model tracked path 602 is shown in a test fixture 600 used to analyze various medical devices for their ability to complete bends within the vasculature. In FIG. 7 , lines numbered in half-integer increments that intersect the model tracked path 602 indicate the number of bends through the vasculature within the model tracked path 602 that the medical device completes at each line, i.e., 0.5 to 5.0 full bends. Table 1 below provides the average number of bends through the model tracked path 602 that each tested introducer sheath and dilator assembly was able to complete before the introducer sheath and dilator assembly could no longer advance. As shown in Table 1, the example introducer sheath and dilator of the present disclosure completed an average of 4.7 full bends, while the use of a standard introducer sheath and / or standard dilator only completed an average of 1 to 2.2 full bends. Thus, the introducer sheath and dilator of the present disclosure demonstrates approximately 187.8% greater performance than the commercially available sheath and dilator.

[0046] [Table 1]

[0047] Referring to Figure 8, there is shown a side view of the introducer sheath 100 and dilator 400, shown separately. Figure 9, a side view of the introducer sheath 100 and dilator 400, shows the dilator 400 occupying the sheath lumen 120. When the distal surface 502 of the distal end 420 of the dilator hub 408 of the dilator 400 abuts or approaches the proximal end 122 of the valve body 102 of the introducer sheath 100, each of the first dilator transition 414, sheath transition 110, and second dilator transition 418 are longitudinally offset from one another, with the distal tip 406 extending beyond the distal tip 112.

[0048] While the present disclosure has been described with reference to examples and accompanying drawings, the present disclosure is not limited thereto and various changes and modifications can be made by those skilled in the art to which the present disclosure pertains without departing from the spirit and scope of the present disclosure.

[0049] The subject matter of the present disclosure may also relate to the following aspects, among others:

[0050] A first aspect is an introducer sheath comprising a tubular structure including a wall defining a sheath lumen extending longitudinally throughout the tubular structure, the tubular structure defining a longitudinal axis therethrough, the tubular structure further comprising a first longitudinal sheath section having a first sheath stiffness, a second longitudinal sheath section distal to the first longitudinal sheath section, the second longitudinal sheath section having a second sheath stiffness less than the first sheath stiffness, and a sheath transition from the first longitudinal sheath section to the second longitudinal sheath section; and a dilator configured to occupy the sheath lumen, the dilator being a shaft. and a dilator comprising a shaft, the shaft including a wall defining a dilator lumen extending longitudinally through the shaft, the shaft defining a second longitudinal axis that is coaxial with the longitudinal axis when the dilator occupies the sheath lumen, the shaft further including a first longitudinal dilator section having a first dilator stiffness, a second longitudinal dilator section distal to the first longitudinal dilator section, the second longitudinal dilator section having a second dilator stiffness that is less than the first dilator stiffness, and a dilator transition from the first longitudinal dilator section to the second longitudinal dilator section, wherein the sheath transition is longitudinally offset from the dilator transition when the dilator occupies the sheath lumen.

[0051] A second aspect relates to the medical device of aspect 1, wherein the first sheath stiffness is less than the first dilator stiffness.

[0052] A third aspect relates to the medical device of any preceding aspect, wherein the sheath transition is distal to the dilator transition.

[0053] A fourth aspect relates to the medical device of any preceding aspect, wherein the second dilator stiffness is less than the first sheath stiffness and greater than the second sheath stiffness.

[0054] A fifth aspect relates to the medical device of aspect 1 or 2, wherein the dilator transition is distal to the sheath transition.

[0055] A sixth aspect relates to the medical device of aspect 5, wherein the second dilator stiffness is less than the second sheath stiffness.

[0056] A seventh aspect relates to the medical device of any preceding aspect, wherein the second longitudinal sheath section comprises a distal sheath tip at a distal end of the second longitudinal sheath section, and wherein the second longitudinal dilator section is configured to extend at least one centimeter distally through the distal sheath tip when the dilator occupies the sheath lumen.

[0057] An eighth aspect relates to the medical device of any preceding aspect, wherein the shaft further includes a third longitudinal dilator section distal to the second longitudinal dilator section, the third longitudinal dilator section having a third dilator stiffness different from the second dilator stiffness.

[0058] A ninth aspect relates to the medical device of aspect 8, wherein the third dilator stiffness is less than the second dilator stiffness.

[0059] A tenth aspect relates to the medical device of aspect 8, wherein the third dilator stiffness is greater than the second dilator stiffness and / or equal to the first dilator stiffness.

[0060] An eleventh aspect relates to the medical device of any preceding aspect, wherein the longitudinal dilator length is greater than the longitudinal sheath length.

[0061] A twelfth aspect is an introducer sheath comprising a tubular structure, the tubular structure including a wall defining a sheath lumen extending longitudinally throughout the tubular structure, the tubular structure defining a longitudinal axis through the tubular structure, the tubular structure including a first longitudinal sheath section having a first sheath stiffness, a second longitudinal sheath section distal to the first longitudinal sheath section, the second longitudinal sheath section having a second sheath stiffness less than the first sheath stiffness, and a sheath transition from the first longitudinal sheath section to the second longitudinal sheath section. a dilator configured to occupy a sheath lumen, the sheath transition being longitudinally offset from the dilator transition from the first longitudinal dilator section to the second longitudinal dilator section, the dilator having a shaft including a wall defining a dilator lumen extending longitudinally throughout the shaft, the first longitudinal dilator section having a first dilator stiffness, and a second longitudinal dilator section distal to the first longitudinal dilator section and having a second dilator stiffness less than the first dilator stiffness.

[0062] A thirteenth aspect relates to the introducer sheath of aspect 12, wherein the first sheath stiffness is less than the first dilator stiffness.

[0063] A fourteenth aspect relates to the introducer sheath of aspects 12 or 13, wherein the sheath transition is configured distal to the dilator transition.

[0064] A fifteenth aspect relates to the introducer sheath of any of aspects 12-14, wherein the second dilator stiffness is less than the first sheath stiffness and greater than the second sheath stiffness.

[0065] A sixteenth aspect relates to the introducer sheath of aspects 12 or 13, wherein the dilator transition is configured distal to the sheath transition.

[0066] A seventeenth aspect is a dilator comprising a shaft, the shaft including a wall defining a dilator lumen extending longitudinally through the shaft, a first longitudinal dilator section having a first dilator stiffness, a second longitudinal dilator section distal to the first longitudinal dilator section, the second longitudinal dilator section having a second dilator stiffness less than the first dilator stiffness, and a dilator transition from the first longitudinal dilator section to the second longitudinal dilator section, wherein the dilator is configured to occupy a sheath lumen of an introducer sheath, and the longitudinal sheath section the introducer sheath comprises a tubular structure including a wall defining a sheath lumen extending longitudinally throughout the tubular structure, the tubular structure defining a longitudinal axis therethrough, the tubular structure including a first longitudinal sheath section having a first sheath stiffness and a second longitudinal sheath section distal to the first longitudinal sheath section, the second longitudinal sheath section having a second sheath stiffness less than the first sheath stiffness.

[0067] An eighteenth aspect relates to the dilator of aspect 17, wherein the first sheath stiffness is less than the first dilator stiffness.

[0068] A nineteenth aspect relates to the dilator of aspects 17 or 18, wherein the sheath transition is configured distal to the dilator transition.

[0069] A twentieth embodiment relates to the dilator of any one of embodiments 17 to 19, wherein the second dilator stiffness is smaller than the first sheath stiffness and larger than the second sheath stiffness.

[0070] In addition to the features described in each of the independent aspects listed above, some examples may exhibit optional features, alone or in combination, described in subordinate aspects and / or as disclosed in the above description and illustrated in the figures.

Claims

1. 1. An introducer sheath, the introducer sheath comprising a tubular structure, the tubular structure including a wall defining a sheath lumen extending longitudinally throughout the tubular structure, the tubular structure defining a longitudinal axis therethrough, the tubular structure comprising: a first longitudinal sheath section having a first sheath stiffness; a second longitudinal sheath section distal to the first longitudinal sheath section, the second longitudinal sheath section having a second sheath stiffness less than the first sheath stiffness; a sheath transition from the first longitudinal sheath section to the second longitudinal sheath section; an introducer sheath, a dilator configured to occupy the sheath lumen, a shaft including a wall defining a dilator lumen extending longitudinally through the shaft, the shaft defining a second longitudinal axis that is coaxial with the longitudinal axis when the dilator occupies the sheath lumen, the shaft comprising: a first longitudinal dilator section having a first dilator stiffness; a second longitudinal dilator section distal to the first longitudinal dilator section, the second longitudinal dilator section having a second dilator stiffness less than the first dilator stiffness; a dilator transition from the first longitudinal dilator section to the second longitudinal dilator section; a shaft an expander comprising: Equipped with A medical device wherein the sheath transition section is longitudinally offset from the dilator transition section when the dilator occupies the sheath lumen.

2. The medical device of claim 1 , wherein the first sheath stiffness is less than the first dilator stiffness.

3. The medical device of claim 1 , wherein the sheath transition is distal to the dilator transition.

4. The medical device of claim 3 , wherein the second dilator stiffness is less than the first sheath stiffness and greater than the second sheath stiffness.

5. The medical device of claim 1 , wherein the dilator transition is distal to the sheath transition.

6. The medical device of claim 5 , wherein the second dilator stiffness is less than the second sheath stiffness.

7. the second longitudinal sheath section comprising a distal sheath tip at a distal end of the second longitudinal sheath section; 10. The medical device of claim 1, wherein the second longitudinal dilator section is configured to extend at least 1 centimeter distally through the distal sheath tip when the dilator occupies the sheath lumen.

8. 2. The medical device of claim 1, wherein the shaft further comprises a third longitudinal dilator section distal to the second longitudinal dilator section, the third longitudinal dilator section having a third dilator stiffness different from the second dilator stiffness.

9. The medical device of claim 8 , wherein the third dilator stiffness is less than the second dilator stiffness.

10. The medical device of claim 8 , wherein the third dilator stiffness is greater than the second dilator stiffness and / or equal to the first dilator stiffness.

11. The medical device of claim 1 , wherein the longitudinal dilator length is greater than the longitudinal sheath length.

12. 1. An introducer sheath comprising a tubular structure, the tubular structure including a wall defining a sheath lumen extending longitudinally throughout the tubular structure, the tubular structure defining a longitudinal axis therethrough, the tubular structure comprising: a first longitudinal sheath section having a first sheath stiffness; a second longitudinal sheath section distal to the first longitudinal sheath section, the second longitudinal sheath section having a second sheath stiffness less than the first sheath stiffness; a sheath transition from the first longitudinal sheath section to the second longitudinal sheath section; Including, a dilator configured to occupy the sheath lumen, such that the sheath transition is longitudinally offset from a dilator transition from the first longitudinal dilator section to the second longitudinal dilator section; an introducer sheath, wherein the dilator comprises a shaft, the shaft including a wall defining a dilator lumen extending longitudinally through the shaft, the first longitudinal dilator section having a first dilator stiffness, and a second longitudinal dilator section distal to the first longitudinal dilator section and having a second dilator stiffness less than the first dilator stiffness.

13. The introducer sheath of claim 12 , wherein the first sheath stiffness is less than the first dilator stiffness.

14. The introducer sheath of claim 12 , wherein the sheath transition is configured distal to the dilator transition.

15. The introducer sheath of claim 14 , wherein the second dilator stiffness is less than the first sheath stiffness and greater than the second sheath stiffness.

16. The introducer sheath of claim 12 , wherein the dilator transition is configured distal to the sheath transition.

17. 1. A dilator comprising a shaft, the shaft comprising: a wall defining a dilator lumen extending longitudinally through the shaft; a first longitudinal dilator section having a first dilator stiffness; a second longitudinal dilator section distal to the first longitudinal dilator section, the second longitudinal dilator section having a second dilator stiffness less than the first dilator stiffness; a dilator transition from the first longitudinal dilator section to the second longitudinal dilator section; Including, the dilator is configured to occupy a sheath lumen of an introducer sheath such that a sheath transition from a first longitudinal sheath section to a second longitudinal sheath section is longitudinally offset from the dilator transition; 1. A dilator comprising: an introducer sheath comprising a tubular structure including a wall defining the sheath lumen extending longitudinally throughout the tubular structure; a tubular structure defining a longitudinal axis through the tubular structure; and a first longitudinal sheath section having a first sheath stiffness and a second longitudinal sheath section distal to the first longitudinal sheath section, the second longitudinal sheath section having a second sheath stiffness less than the first sheath stiffness.

18. 18. The dilator of claim 17, wherein the first sheath stiffness is less than the first dilator stiffness.

19. The dilator of claim 17 , wherein the sheath transition is configured distal to the dilator transition.

20. 20. The dilator of claim 19, wherein the second dilator stiffness is less than the first sheath stiffness and greater than the second sheath stiffness.

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