referring now to fig1 the sheath is designated therein in its entirety by the numeral 10 . the sheath is elongate and proportioned to expand , when relaxed , to an outside diameter approximately equal to the inside diameter of the body passage within which the sheath is to be used . as shown in the example of fig1 the body passage comprises an artery 11 . in a typical embodiment for vascular use , the sheath has an expanded &# 34 ; relaxed &# 34 ; diameter of from 6 to 7 mm , a contracted reduced diameter of 2 to 3 mm and a length of from 15 to 30 cm . the distal end of the sheath , designated 12 , extends obliquely to the longitudinal axis of the sheath . the proximal end of the sheath is open and sealingly secured to the interior of a y - shaped hemostasis hub 14 . the hub 14 is tubular and has a primary leg 16 secured in sealed fluid communication to the interior of the sheath 10 and secondary legs 18 and 20 merging into communication with the primary leg . the free end of the secondary leg 18 carries an externally threaded coupling 22 for receipt of a hemostasis valve 24 . the free end of the secondary leg 20 carries an externally threaded coupling 26 for receipt of a hemostasis valve 28 . in the embodiment illustrated , the valve 24 is of the type shown in copending application ser . no . 429 , 854 , filed oct . 31 , 1989 . this type of valve may be selectively sealed , or opened to permit elongate objects to be slid therethrough and into the sheath . it may also be provided with a sideport tube 30 secured in sealed fluid communication with the interior of the valve , which sideport tube is provided with a conventional stopcock 32 . levers 34 forming part of the valve 24 cooperate with a seal within the valve to normally close the valve and , when compressed toward one another , open the valve for the passage of elongate elements therethrough . the valve 28 carries a seal 35 ( see fig4 ) for sealed slidable engagement with a flexible tubular stylet 36 extended therethrough . the internal construction of the preferred embodiment of the sheath 10 comprises a tubular braid 38 encapsulated within a coating 40 of high - elongation silicone polymer to provide an impermeable body 41 . the braid is a woven structure of flexible generally inelastic polyester monofilaments 42 , such as dacron . while the proportions of the sheath may vary , depending upon the size and type of body passage within which it is intended to be used , the following is a typical example for arterial use : ______________________________________tubular sheath body 41 : 30 cm long and 6 mm od in relaxed condition ; 37 cm long and 3 mm od in axially distended contracted conditionwall thickness of 0 . 50 mmtubular sheath body 41 : braid 38 : 6 mil . polyester monofilament manufactured by atkins pearce manufacturing of covington , kentucky under no . gp - 4819425coating 34 : high elongation silicone elastomer manufactured by dow corning of midland , michigan under no . q7 - 2213______________________________________ in this example , the filaments 42 extend at an angle α of approximately 35 °- 50 ° relative to the longitudinal axis , designated 46 , of the sheath when the sheath is in the relaxed expanded condition . in the distended contracted condition ( see fig1 ) the filaments extend at an angle β of approximately 20 ° relative to the longitudinal axis 46 of the sheath . the filaments 42 and their angular relationship relative to the longitudinal axis 46 both reinforce the elastomeric coating 40 and facilitate contraction and expansion of the sheath . the filaments also serve to control expansion , contraction and the elongation of the sheath . the distal end 12 extends at an oblique angle relative to the axis 46 . this angle is chosen so as to increase the area of the open distal end and to provide a gentler taper to facilitate introduction , as compared to what would occur if the angle were 90 °. in the preferred embodiment , the angle is chosen so as to be approximately equal to the angle α so that the distal most filaments run generally parallel to the distal edge . the edge of the distal end 12 is bounded by an extension 48 of highly pliable elastomeric material corresponding to that of the coating 40 . this extension facilitates guiding of the sheath into place and minimizes the possibility that the end of the sheath will serve to abrade the interior of a body passage within which the sheath is received . elongation of the sheath to contract its tubular body is provided by extending the stylet 36 through the sheath to a compression - imparting connection adjacent the distal end 12 . in the preferred embodiment , the stylet 36 is tubular and secured adjacent the distal end 12 by a wire 52 which loops through the side wall of the sheath and around a filament therein and is folded upon itself and received within a fine flexible tube 54 . the wire 52 is ideally a corrosion resistant material of high tensile strength , such as stainless steel . the tube 54 is made of a highly flexible material capable of being fabricated into a thin wall and having a low coefficient of friction , such as polyimide . the stylet 36 is fabricated of a highly flexible generally incompressible material , such as polyurethane . it is formed with a bore 56 proportioned for slidable extension over the tube 54 . the tube 54 , with the folded wire 52 therein , extends through the full length of the sheath 10 and from the proximal end thereof through the leg 20 of the hub 14 . in the extended condition shown in fig4 the stylet 36 is slidably received on the tube 54 and also extends through the full length of the sheath 10 and from the leg 20 of the hub 14 . the proximal end of the stylet 36 has a handle 58 fixedly secured thereto ( see fig4 ) which rotatably carries an internally threaded nut 60 engagable with an externally threaded extension 62 on the valve 28 . when threadably engaged ( see fig4 ) the nut 60 and extension 62 serve to secure the stylet in the condition extending the sheath to the contracted condition and also serve as stop means to limit the extent of such extension . when disengaged , the nut and extension permit the stylet to be retracted from the sheath , thus relaxing the sheath for expansion . in the latter condition , the stylet may be fully withdrawn from the sheath ( see fig5 ), thus leaving the sheath in a condition of maximum flexibility with the passage therein substantially unobstructed , except for the presence of the tube 54 . in use , the hub 14 serves as a grip to restrain the proximal portion of the sheath against movement as the distal end is longitudinally extended by the stylet 36 . fig1 shows the sheath 10 in the process of being introduced into the artery 11 through a percutaneous puncture 66 providing a point of ingress into the artery . although percutaneous insertion is shown in the illustration , it should be understood that insertion might also be provided surgically through an incision made in the artery . fig1 and 2 also show a stenosis 68 within the artery 11 at a location remote from the point of ingress 66 . from fig1 it will be seen that the sheath 10 is of a length sufficient to extend from the point of ingress 66 to the stenosis 68 , thereby enabling the sheath to be used to direct instruments , such as dilatation catheters , through the sheath and into treating relationship to the stenosis . in the condition shown in fig1 the stylet 36 has been distended by engagement of the nut 60 with the extension 62 , thus fully contracting the external diameter of the stylet for insertion into the artery . once fully in place within the artery , as shown in fig2 the nut 60 is disengaged from the extension 62 and the stylet is withdrawn , thus permitting the sheath to fully expand within the artery and removing the stylet from the interior of the sheath . in the latter condition , the interior of the sheath is unobstructed , except for the presence of the tube 54 . with the sheath fully in place as shown in fig2 a dilatation catheter , or other desired instrument , may be extended through the hemostasis valve 24 and the full length of the sheath 10 . the valve 24 may be selectively opened to accommodate such extension . the phantom lines shown in fig2 illustrate a dilatation catheter 70 extended fully through the sheath and out of the distal end thereof into treating relationship to the stenosis 68 . it should be appreciated that the sheath may be left in place within the artery and that instruments may be traversed back and forth through the sheath without abrading the internal surfaces of the artery . when the desired treatment is complete , the instrument , such as the dilatation catheter 70 , is removed from the sheath and the sheath is once again distended to the contracted condition , as shown in fig1 . then , the sheath may be withdrawn from the artery in the reduced diameter condition , with a minimum of abrasion or disturbance to the wall of the artery . in addition to providing for the introduction of instruments into the artery , the sheath may also be used for purposes of taking pressure measurements , or making injections . the sideport tube 30 may be used for such purposes . while a preferred embodiment of the invention has been illustrated and described , it should be understood that the invention is not intended to be limited to this embodiment , but rather is defined by the accompanying claims .
a tubular sheath capable of assuming a reduced diameter state for insertion into a body passage and of expanding once in place within the passage . the sheath is fabricated of a composite elastomeric material and axially stretched to assume the reduced diameter state . selective axial stretching is achieved by an elongate stylet which extends slidably through the sheath for compression imparting engagement with a distal portion thereof .