Controlled vortex inducing vascular prosthesis

Details Controlled vortex inducing vascular prosthesis Controlled vortex inducing vascular prosthesis

1998-10-30

2001-04-24

Milano, Michael J. (Department: 3738)

Prosthesis (i.e., artificial body members), parts thereof, or ai

Arterial prosthesis

Having variable diameter

C623S001100

Reexamination Certificate

active

06221101

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to aiding vascular surgery, including improving nature and use of prosthetic grafts, particularly for by-passes to relatively small arteries.
2. Description of Related Art
By-passes required to save limbs can be long even stretching from a groin to below a knee. The arteries to which by-passes are connected may be as small as one to five millimeter across. Where patients have no suitable veins to use as by-passes, which is often the case for patients with relevant serious conditions, the only positive alternative is use of prosthetic grafts made of synthetic materials, for such as flexible tube of PTFE (polytetrafluoroethylene). Justification would become questionable without reasonable success rates and/or improvement prospects. Making simple direct end connections or anastomoses of prosthetic graft tubes (usually run at an acute angle or more or less parallel with the artery and end cut at an angle) to side apertures in arteries, perhaps particulary arteries substantially less than five millimeters across, has been followed by such liability to fibrous intimal hyperplasia as later to lead to serious blood flow reduction, even stoppage. Such problems have led to various theoretical considerations and assumptions, including as backing to more complex practical proposals.
We are particularly familiar with one such practical proposal, namely use of a small piece of natural vein to make a short cuff that is joined by surgical stitching to and between the artery opening and the end of the prosthetic graft tube. Improved success rates for indirect prosthesis-to-vein-to-artery connection, compared with direct prosthesis-to-artery, have involved reduced adverse effect from intimal hyperplasia. Contributory factors, for cuff-type and other prosthesis types, have been considered and postulated as including reducing tendencies to turbulence of blood flow, and/or optimising approximation to laminar blood flow, and/or for suppleness of the natural vein parts to aid absorption or cushioning blood pulsing. These factors have further been seen particulary as contributing to avoiding or minimising occurrence of artery wall shear stress.
This invention has arisen from questioning such theorising and assumption, particulary after reflecting on the fact that success of autologous natural vein cuffs has included using cuff sizes so large as to make us doubt that either of laminar flow or pulse absorption would be likely to occur. Close observation of careful simulations has not only supported that view, but has further led us to develop successful proposals based on contradicting both of the prior objectives for maximising laminar flow and minimising artery wall shear stress.
BRIEF SUMMARY OF THE INVENTION
According to one aspect of this invention, there is provided a vascular prosthesis comprising a tube of material other than autologous vascular tissue but considered/approved as safe and supple enough for use instead of such tissue; the tube of material having an end formation for surgical connection directly to an opening formed in an artery, said end formation serving to promote, at that end and/or within said direct connection, and in response to normally pulsed blood flow, localised movement of blood having a non-laminar nature with a shear stress inducing relationship to receiving arterial wall.
The term “non-laminar” as used herein is intended to define blood flow other than parallel to arterial walls and, in particular, includes localised laminar movement of blood having significant secondary components.
Separation of flowing blood from the inner wall of the tube near its said end, and associated with non-laminar flow, is preferable such as to produce a swirling action that may include locally circulatory or re-circulatory movement of blood, further preferably in the nature of or including a vortex action. Such blood flow separation will usually be at and adjacent to the end of the prosthesis tube which is acutely angled for connection to the artery. The blood flow separation is also preferably at least partially within an enlarging formation of the prostheses associated with said angled end of the prosthesis tube.
A preferred end formation of the prosthesis tube of the invention is an enlargement which produces a sudden expansion of the blood volume therein and hence an increase in the blood flow rate.
Desired non-laminar blood flow promotion is preferably effective only in phases of cycles of blood-flow pulsing, which phases preferably alternate with other phases of more laminar flow sufficient to assist flow of all blood into the artery away and from that end of the prosthesis. The pulsed nature of normal blood flow involves successive time-spaced rises in pressure. Each pressure rise preferably causes both an initial relatively smooth or laminar blood flow in and out of the prosthesis-to-artery connection and a later transition into desired non-laminar blood movement. The preferred non-laminar vortex type movement preferably collapses before the next pressure rise.
In our simulation of cuff-type of prior prosthesis graft connections to arteries, and modelling/prototyping for the specific embodiment of this invention to be described with reference to the accompanying drawings, we discovered and sought to develop and/or improve pronounced single vortex action as will become clear. In looking at other prior prostheses actually in use, such as the so-called Taylor Patch and/or St. Mary's Boot, we also observed definite though somewhat different non-laminar flows in and through the arterial connections involved, including two lesser relatively fore and aft vortex actions and a quite large turbulence that seems not to develop fully into clear vortex action. It now appears to us that the cuff-connections are effective mainly by reason of their geometry, leaving space for beneficial non-laminar blood movement, particulary clear vortex action as in the specific description to follow. It is further the case that the different non-laminar blood flows through other types of prosthesis graft tube ends in to arteries can also be reproduced by tube ends appropriately replicating significant features of arterial connection geometry described herein. It is a further aspect of this invention that any successful prior prostheses using autologous vein material or other compound structure be made with similar end-connection formations, but be of homogeneous wholly synthetic material for direct arterial connection.
According to another aspect of this invention, there is provided a vascular prothesis comprising a tube of material other than autologous vascular tissue but considered/approved as safe and supple enough for use in substitution for such tissue, the tube of material having a relatively enlarged end for actual connection directly to an opening formed in an artery. Suitable said end enlargement can assure that pulsed blood flow from the prosthesis into the artery periodically separates from said material before and on its way out of the prosthesis. The resulting non-laminar blood flow appears to be generally beneficial, particularly, if not exclusively, if with a strong vortex action component or otherwise inducing shear stress in arterial walls.
Evolution and exemplary specific implementation will now be specifically described with reference to the accompanying diagrammatic drawings.


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patent: 5443497 (1995-08-01), Venbrux
patent: 5456714 (1995-10-01), Owen
patent: 5472404 (1995-12-01), Volgushev
patent: 5500014 (1996-03-01), Quijano et al.

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