VASCULAR PROSTHESIS

Abstract: A vascular prosthesis for replacing a portion of a blood vessel in a human or animal body comprises a tube (1) of textile material formed with corrugations in the form of a primary helix (2) and secondary corrugations in the form of a secondary helix (3) of pitch opposite and greater than the pitch of the primary helix superposed on the corrugations of the primary helix.

Description: YA§CULAR_P_ROSTHESIS At The subject of this invention is a vascular prosthesis and particularly a prosthesis in the form of a tube of textile material to be used for. replacing a portion of a blood vessel in a human or animal body. 5 Vascular prostheses are well known and are customarily constructed of knitted tubes formed with circumferential corrugations. The corrugations are provided for two reasons, one to allow the prosthesis to be extended in length during fitting and the other 10 to provide rigidity against collapsing or buckling while maintaining adequate flexibility. For that reason it has heretofore been necessary to provide for any given diameter of graft corrugations of a certain minimum amplitude. The corrugations always present some 15 impedence to the flow of blood through the implanted .graft and for that reason it is desirable to have the amplitude of the corrugations as low as possible while providing the desired degree of stiffness and resistance to buckling and collapse. 20 It would obviously be of great advantage in the use of vascular grafts if there could be provided a corrugated tube having the same characteristics of stiffness and resistance to buckling and collapse but with a much lower amplitude of corrugations in 25 proportion to its diameter, or a greater degree of stuffness and resistance to buckling and collapse for a given proportion of amplitude of corrugations to internal diameter and it is an object of the present invention to provide such a vascular prosthesis. 30 A vascular prosthesis according to the invention comprises a tube of textile material formed with corrugations in the form of a primary helix and is characterized in that secondary corrugations in the form of a secondary helix of opposite and greater pitch than the primary helix are superposed on the corrugations of the primary helix. For removal of doubt it is explained that one helix is of left hand or S pitch and the other helix is of right hand or Z pitch. The tube of textile material may be formed by warp knitting, by weaving or by braiding and is preferably seamless. A prosthesis according to the invention may be formed by winding a thread in one direction around the tube while it is held on a rigid former to delineate the primary helix then winding another thread around the tube in the opposite direction and with a greater pitch to delineate the secondary helix then applying axial pressure in opposite directions from the two ends whereby to reduce the length of the tube and cause the portions of the tube between the thread convolutions to bulge outwardly and form the corrugations and while the tube is held in this position heat-treating the material to set the tube material and cause the corrugations to be permanent. A practical embodiment of a vascular prosthesis according to the invention is illustrated in the accompanying drawing in which 1 denotes a tube of textile material,2 denotes a primary helix and 3 denotes a secondary helix superposed on the primary helix 2. The dimensions of a typical prosthesis according to the invention are: minimum internal diameter - 10 mm, pitch of primary helix - 10 turns/cm, pitch of secondary helix — 2 turns/cm, depth of corrugations - O.δ mm. The corrugation depth given provides the required degree of stiffness and resistance to buckling and collapse in a prosthesis of the minimum diameter. A known prosthesis of the same minimum diameter having a single set of corrugations would have required corrugations of at least 1.2 mm depth with a pitch of about 7 turns/cm. t . It has been found by practical experiment that a vascular prosthesis as described according to 5 the invention having two sets of contra-pitch corrugations of low amplitude presents much less impedence to blood flow through the tube and also a greater evenness in build up of fibrous tissue than a known vascular prosthesis of the same degree of 10 stiffness and resistance to buckling and collapse obtained from a single set of higher amplitude corrugations since the graft formed by a prosthesis of the invention provides a closer approach to a constant diameter blood vessel than do the previously known 15 grafts having a"single set of corrugations of high amplitude. Conversely a prosthesis according to the invention formed with corrugations of the same amplitude as a known vascular prosthesis has a greater degree of stiffness and resistance to buckling and 20 collapse . y^ξ EJ ' ' OMPI

Claims: CLAIMS 1. A vascular prosthesis which comprises a tube (1) of textile material formed with corrugations in the form of a primary helix (2) is characterized in tha secondary corrugations in the form of a secondary helix (3) of a pitch opposite to and greater than the pitch of the primary helix (2) are superposed on the corrugations of the primary helix (2) . 2. A method of forming a prosthesis by winding a thread in one direction in the form of a helix (2) around a plain tube (1) of textile material which is subsequently compressed axially and heat set is characterized by additionally winding another thread around the tube in the opposite direction to form a secondary helix (3) having a pitch greater than the pitch of the first helix before axial pressure is applied to the tube. SUBSTITUTE SHEET f OI.ΓPI

Inventors: HOOD ROBERT GORDON, HOOD, ROBERT, GORDON
Applicants: COATS LTD J & P, J. & P. COATS, LIMITED
Application year: 1983
Main classification: A61F1
IPC codes: A61F2, F16L11