Patent number 8771338 is assigned to
The following quote was obtained by the news editors from the background information supplied by the inventors: "Intralumenally implantable frames can be implanted to treat a variety of medical conditions. Implantable frames can maintain patency of body vessels or provide support for a valve or valve leaflets for regulating fluid flow within a body lumen. For example, flexible leaflet material can be attached to an implantable frame to form a valve prosthesis useful in providing an artificial valve for treating venous valve insufficiency. In addition, a variety of other implantable prostheses, such as stents, stent grafts and the like, comprise a radially expandable support frame placed within the body to improve the function of a body lumen. Support frames may be implanted in vessels, ducts or channels of the human body and can form part of a valve to regulate fluid flow within a body lumen or as scaffolding to maintain the patency of a body vessel, duct or channel to treat various conditions.
"Endolumenal prostheses comprising support frames can be placed in a body lumen from a delivery system which includes a catheter. Implantable frames can be intralumenally delivered inside the body by a catheter that supports the stent in a radially compressed form as it is transported to a desired site in a body vessel. Upon reaching the site, the implantable frame can be radially expanded and securably positioned within the lumen of the body vessel, for example by engaging the walls of the body vessel with a portion of the implantable frame. The expansion mechanism may involve expanding the implantable frame radially outward, for example by inflation of a balloon carried by the catheter. Alternatively, when the implantable frame is formed of a self-expanding material, the implantable frame may be delivered in a radially restrained configuration and deployed by removing the restraint at a point of treatment to allow the implantable frame to self-expand by its own internal elastic restoring force at a point of treatment. After expansion of the implantable frame, the catheter delivery system is subsequently withdrawn from the body vessel. Endolumenally implantable support frames preferably possess sufficient hoop strength to resist collapse of the body vessel, while maintaining a desired degree of radial or longitudinal flexibility to prevent damage to the body vessel.
"Implantable frames are subjected to various mechanical forces before, during and after deployment within a body lumen. Before deployment, implantable frames can be compressed and maintained in a compacted form, which can include subjecting the implantable frame to a prolonged inward radial restraining force. During deployment, implantable frames can be subjected to an outward radial expanding force, for example from a balloon expansion or self-expansion process. The implantable frames can also be subjected to an inward radial compressive force upon contact with the body vessel wall during deployment expansion. After deployment, implanted frames can be subject to continued inward radial force from the body vessel wall, in addition to a variety of shearing or tortional forces imparted by movement of the body vessel wall or fluid flow within the body vessel. Uneven mechanical load bearing within an implantable frame can result in uneven wear and distortion of the implantable frame shape, or even failure of structural integrity. In typical sinusoidal and near sinusoidal designs, the bends or radial arcs experience areas of high strain and stress, which can lead to areas of frame fatigue or fracture. However, the stress and/or strain experienced along the length of the radial arc may not be uniform, and there are areas of relatively high stress and/or strain. Therefore, it is desirable to provide implantable frames that more evenly distribute mechanical loads.
"Dynamic fluctuations in the shape of the lumen of a body vessel, such as a vein, pose challenges to the design of support frames for implantation within the body vessel. For instance, the flow velocity and diameter of veins do not remain essentially constant at a given systemic vascular resistance. Instead, the shape of vein lumens can fluctuate dynamically in response to the respiration, body position, central venous pressure, arterial inflow and calf muscle pump action of a mammalian subject. The veins also provide the principal volume capacitance organ. For example, an increase of almost 100% in the diameter of the common femoral vein has been observed in human patients simply by rotation of the patient by about 40 degrees, corresponding to a four-fold increase in blood flow volume.
"Preferably, implantable frames are also configured to minimize undesirable irritation of the lining of a body vessel upon implantation, for example by minimizing the surface area of the frame in contact with the body vessel. However, reducing the surface area of the frame may increase the mechanical stress and strain on particular portions of the frame, particularly bends or arcuate sections. What is needed are endolumenally implantable medical device frames configured to withstand radial compression upon implantation by desirably distributing the associated mechanical strain on the implanted frame, while also minimizing potential irritation of a body vessel that may result from contact between the body vessel and the external surface of the implanted frame."
In addition to the background information obtained for this patent, VerticalNews journalists also obtained the inventors' summary information for this patent: "Intralumenally implantable frame configurations adapted for placement within a body passage are provided herein. The present disclosure provides implantable frames configured to balance often competing concerns of minimizing potentially irritating external surface area, minimizing foreshortening during radial expansion, and providing a desirable distribution of mechanical loading within the frame during movement of the frame within a dynamic body vessel such as a vein. These implantable frames are particularly useful, for example, as a support for a valve for correcting fluid flow within a body passage, or for opening, dilating and maintaining body vessels and other biological ducts which are at risk of closure or constriction. For example, the implantable frames may be configured as stents for maintaining the patency of a body vessel or as support frames for valves or stent grafts.
"The implantable frames preferably have a substantially tubular configuration and include two or more hoop members axially aligned around a longitudinal axis and joined by a plurality of longitudinal connecting members. The hoop members and the longitudinal connecting members define a plurality of open spaces in the exterior surface of the tubular frame. The longitudinal connecting members are preferably arranged in a configuration suitable to provide an implantable frame with a desired radial compression upon implantation while favorably distributing the mechanical strain imparted to the implanted frame due to post-implantaiton radial compression of the body vessel at the site of implantation. The implantable frames may be configured to minimize potential irritation of a body vessel that may result from contact between the body vessel and the external surface of the implanted frame, for example by minimizing the surface area and number of hoop members and longitudinal connecting members. The implantable frame is preferably adapted for translumenal percutaneous delivery in a radially compressed state from a delivery system comprising a catheter. The frame is preferably moveable between a radially compressed state and a radially expanded state by any suitable means within a body vessel, including balloon expansion or self-expansion from a delivery catheter positioned within a body vessel.
"Preferably, the implantable frame comprises a plurality of longitudinal connecting members connecting a pair of hoop members to form a tubular frame defining a cylindrical lumen. The plurality of longitudinal connecting members desirably includes one or more pairs of closely-spaced longitudinal connecting members oriented substantially parallel to the longitudinal axis of the tubular implantable frame. Preferably, a tubular implantable frame includes two or more hoop members axially aligned around a longitudinal axis of the frame. The longitudinal connecting members are preferably substantially straight struts aligned substantially parallel to the longitudinal axis of the implantable frame. In one aspect, the longitudinal connecting members are substantially equal in length.
"Longitudinally adjacent hoop members are desirably connected by any suitable number (n) of longitudinal connecting members, where (n) is preferably an integer equal to 2-16, and more preferably 4-8. Preferably, the circumferential distance between longitudinal members varies as a function of the number of longitudinal connecting members, with at least two of the longitudinal connecting members being closely-spaced. Closely-spaced longitudinal connecting members are circumferentially adjacent members that are circumferentially closer to one another than to the next nearest circumferentially adjacent longitudinal connecting member. The circumferential distance between longitudinal connecting members is measured along the outer surface of a transverse cross section of the frame, where the cross section is centered on, and oriented perpendicular to, the longitudinal axis. For example, in a frame having a second longitudinal connecting member circumferentially adjacent to both a first longitudinal connecting member (in a first circumferential direction) and a third longitudinal connecting member (in a circumferential direction opposite the first circumferential direction), the circumferential distance measured between the first longitudinal connecting member and the second longitudinal connecting member that is closely spaced with respect to the first longitudinal connecting member is less than the circumferential distance measured from the first longitudinal connecting member to a third longitudinal connecting member that is not closely-spaced with respect to the first longitudinal connecting member. In one aspect, the angle subtended by a hypothetical arc extending circumferentially along the perimeter of a cross section of a frame from a first longitudinal connecting member to a second longitudinal connecting member that is closely-spaced with respect to the first longitudinal connecting member is less than (2.pi./n) radians, where (n) is an integer equal to the number of longitudinal connecting members between longitudinally adjacent hoop members. In a second aspect, the shortest circumferential distance between the closely paired longitudinal connecting members can be less than about 25%, preferably less than about 15%, of the length of the closely spaced pair of longitudinal connecting members. The frame desirably includes two or more pairs of closely spaced longitudinal connecting members symmetrically positioned across a tubular frame lumen from another pair of closely spaced longitudinal connecting members.
"The hoop members can have any suitable configuration. For example, undulating hoop members typically include a plurality of alternating struts and bends forming a sinusoidal pattern defining a portion of the external surface of a tubular frame. Alternatively, the hoop members can be planar rings formed from a single bent member. Optionally, the frame includes one or more undulating hoop members formed from a plurality of interconnected struts and bends oriented along the longitudinal axis of the frame. For example, a frame can include a first undulating hoop member having a total of (m) struts joined to a total of (2 m) longitudinal connecting members, wherein (m) is preferably an integer equal to 2-16, preferably 2-8. The frame can further comprise a plurality of lateral support arms connecting facing pairs of adjacent struts within the hoop members positioned at the ends of the frame. A lateral support arm preferably comprises a single bend connecting a pair of lateral support struts. The hoop members preferably have substantially similar configurations, although frames may include hoop members with different configurations. The cross section of each hoop member desirably forms a perimeter around a substantially circular or elliptical lumen. Each hoop member can optionally include an undulating pattern of struts and bends extending along the axis of the frame. Preferably, the ratio of bends to struts in an undulating hoop member is 1:1 to 3:1, more preferably 2:1 to 3:1, with the struts having a substantially equal length within each hoop member. Alternatively, one or more hoop members can have a planar geometry, such as a single bent member forming an annular shape. The plurality of hoop members can have the same or different configurations, but are preferably concentrically aligned along the longitudinal axis of the frame. Each of the bends in the hoop members are preferably connected to a longitudinally adjacent hoop member by at least one longitudinal connecting member.
"While the invention is defined by the claims appended hereto, additional understanding of the invention can be gained by reference to the attached drawings and the description of preferred embodiments presented below."
URL and more information on this patent, see: Schaeffer, Darin G.; Flagle, Jacob A.; Garrison,
Keywords for this news article include: Technology.
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