Patent Publication Number: US-2011066226-A1

Title: Implantable Venous Valve for Treatment of Erectile Dysfunction

Description:
FIELD OF THE INVENTION 
     The present invention relates to an intravascular device for treatment of erectile dysfunction. More particularly, the intravascular device is a venous valve that may be implanted in a penile vein to selectively restrict blood outflow through the penile vein in order to achieve and/or maintain an erection. 
     BACKGROUND OF THE INVENTION 
     The National Institutes of Health estimates that 30 million American men suffer from mild, moderate or complete erectile dysfunction. Erectile dysfunction is the chronic, i.e., greater than three months duration, inability to maintain a penile erection for satisfactory sexual intercourse. 
     There are both psychological and physical causes of erectile dysfunction. Most causes of erectile dysfunction have an adverse effect on nerves and/or blood vessels to, from, and within the penis. Vascular disease is considered a leading physical cause of erectile dysfunction with atherosclerosis of the penile arteries alone accounting for about 40% of patients over 40 years of age with erectile dysfunction. Other possible vascular-related causes include diabetes, hypertension, high cholesterol, renal disease, and smoking. 
     Essentially, penile erection occurs when the two corpora cavernosa fill with blood and maintain pressure adequate for penetration. Each corpus cavernosum is fed by a deep artery of the penis located in the center of each cavernosum. Each deep artery has many smaller coil-shaped arteries, called helicine arteries extending downstream therefrom that open directly into the corpora cavernosa. Erection of the penis is a parasympathetic nervous system process that effects the release of neurotransmitters, which allows the relaxation of smooth muscle fibers surrounding the helicine arteries resulting in an increase in arterial inflow in the corpora cavernosa. Blood then fills these erectile compartments, and in the process compresses the penile veins that drain these tissues. The obstruction of venous flow is as important in obtaining and maintaining an erection as is an adequate arterial blood supply. The net effect of this increased inflow and decreased blood outflow is to raise the pressure of the corpora cavernosa to approximately the mean arterial pressure of the cavernosal artery, which in a normal patient is approximately 100 mm Hg. Subsequent activation of the sympathetic nervous system returns the penis to a flaccid state. With reference to  FIG. 1  that depicts a sectional view of a portion of a penis, major venous drainage of the penis occurs through the deep dorsal vein  100  that returns blood from the shaft or pendulous portion of the cavernosa as well as from the glans penis. In addition to a few other penile veins, such as the cavernosal veins, blood also exits the penis via the superficial dorsal vein  102 . 
     In cases where erectile dysfunction occurs due to, or is complicated by venous leakage there are various bands, rings and ligatures that have been suggested to restrict blood flow leaving the penis and thereby enable a patient to achieve an erection. Some such restrictive devices are externally secured around the base of the penis and are worn only during sexual activity, whereas others are surgically or laparoscopically implanted and are externally activated to temporarily contract around penile tissue or exit veins of the penis to enable the erection. A binary duct valve has also been suggested for use in penile veins to selectively induce tumescence. The binary duct valve is implanted surgically or via a needle puncture into the vein and includes a ball valve of a magnetic material that is operated extracorporeally by a user manipulating a magnet. Each of the afore-mentioned apparatuses for treating erectile dysfunction that is caused or aggravated by venous leakage suffers from disadvantages, some of which are addressed by a venous valve according to the present invention. 
     BRIEF SUMMARY OF THE INVENTION 
     Embodiments hereof are directed to an implantable venous valve for selectively restricting the outflow of blood from a penile vein to aid a user in achieving and/or maintaining an erection. The venous valve includes a self-expanding stent framework defining a blood flow lumen therethrough. The self-expanding stent framework is constructed to recoil from a radially compressed configuration in which the blood flow lumen is narrowed to restrict blood flow through the venous valve to a radially expanded configuration in which the blood flow lumen is fully open to permit unrestricted blood flow through the venous valve. A recoil delay component is attached to the self-expanding stent framework for slowing the recoil of the self-expanding stent framework and thereby provides an extended time period during which the blood flow lumen is narrowed such that blood flow through the venous valve is restricted. 
     Embodiments hereof are also directed to methods of using a venous valve for selectively restricting the outflow of blood from a penile vein to aid in achieving and/or maintaining an erection. The methods include implanting a venous valve into a penile vein at a target location that is susceptible to a compressive radial force exerted on the penis. A venous valve for use in methods hereof includes a self-expanding stent framework defining a blood flow lumen there through and a recoil delay component attached to the self-expanding stent framework that delays the recoil of the self-expanding stent framework from a radial compressed configuration to a radially expanded configuration. The methods further include firmly pressing on the penis to impart a compressive radial force on the venous valve implanted at the target location thereby radially compressing the self-expanding stent framework and initiating an extended time period during which the blood flow lumen is narrowed to restrict blood outflow from the penile vein. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The foregoing and other features and advantages of the invention will be apparent from the following description of embodiments thereof as illustrated in the accompanying drawings. The accompanying drawings, which are incorporated herein and form a part of the specification, further serve to explain the principles of the invention and to enable a person skilled in the pertinent art to make and use the invention. The drawings are not to scale. 
         FIG. 1  is a partial sectional view of a portion of a penis. 
         FIG. 2  is a perspective view of a venous valve in accordance with an embodiment hereof 
         FIG. 2A  is a transverse cross-sectional view of the venous valve of  FIG. 2  taken along line A-A shown in a radially expanded or open configuration. 
         FIG. 2B  is the venous valve cross-section of  FIG. 2A  shown in a radially compressed or closed configuration. 
         FIG. 3  is a perspective view of a venous valve in accordance with another embodiment hereof. 
         FIG. 3A  is a transverse cross-sectional view of the venous valve of  FIG. 3  taken along line A-A shown in a radially expanded or open configuration. 
         FIG. 4  is a perspective view of a venous valve in accordance with another embodiment hereof. 
         FIG. 4A  is a transverse cross-sectional view of the venous valve of  FIG. 4  taken along line A-A shown in a radially expanded or open configuration. 
         FIG. 5  is a longitudinal sectional view of an alternate embodiment of the venous valve shown in  FIG. 2  deployed within a penile vein. 
         FIG. 6  is a longitudinal sectional view of the venous valve of  FIG. 5  radially compressed within the penile vein to restrict blood flow there through. 
         FIG. 7  is a perspective view of a catheter-based delivery system having a distal portion shown in partial section to expose a venous valve in accordance with an embodiment hereof loaded therein. 
         FIG. 8  is a longitudinal sectional view of the venous valve shown in  FIG. 5  being deployed in a penile vein by the catheter-based delivery system shown in  FIG. 7 . 
         FIG. 9  is a longitudinal sectional view of the venous valve shown in  FIG. 5  being expanded by a balloon upon initial deployment within the penile vein. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Specific embodiments of the present invention are now described with reference to the figures, wherein like reference numbers indicate identical or functionally similar elements. The terms “distal” and “proximal” are used in the following description with respect to a position or direction relative to the treating clinician. “Distal” or “distally” are a position distant from or in a direction away from the clinician. “Proximal” and “proximally” are a position near or in a direction toward the clinician. 
     The following detailed description is merely exemplary in nature and is not intended to limit the invention or the clinical application and uses of the invention. Although the description of the invention is in the context of placement within a blood vessel such as the superficial and deep dorsal veins, the invention may also be used in any other body passageways where it is deemed useful. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding technical field, background, brief summary or the following 
     DETAILED DESCRIPTION 
       FIG. 2  is a perspective view of an implantable venous valve  204  according to an embodiment hereof with  FIG. 2A  being a cross-sectional view taken along line A-A. Venous valve  204  includes a self-expanding stent framework  206  that defines a blood flow lumen  208  between a first end  210  and a second end  212  thereof. A recoil delay component  214 , which will be further described below, is attached to an inner surface  205  of stent framework  206  and covers interstitial spaces or openings  207  of stent framework  206 , such that an interior surface  213  of recoil delay component  214  outlines blood flow lumen  208 . Recoil delay component  214  is a tubular construction that is attached to the stent framework by either thermal or adhesive bonding. 
     Stent framework  206  is an exemplary stent framework in accordance with an embodiment of the present invention that is made self-expanding by virtue of the internal restoring forces of the spring-type or superelastic material selected for its construction. In an embodiment hereof, stent framework  206  is formed of a pseudoelastic or stress induced martensitic (SIM) alloy of nickel-titanium (nitinol). Stent framework  206  is a patterned tubular device that includes a plurality of radially expandable cylindrical rings  216 . Cylindrical rings  216  are formed from struts  218  having a generally sinusoidal pattern that includes peaks  220 , valleys  222 , and generally straight segments  224  connecting peaks  220  and valleys  222 . Connecting links  226  connect adjacent cylindrical rings  216  together. In  FIG. 2 , connecting links  226  are shown as generally straight links connecting a peak  220  of one ring  216  to a valley  222  of an adjacent ring  216 . However, connecting links  226  may connect a peak of one ring to a peak of an adjacent ring, or a valley to a valley, or a straight segment to a straight segment. Further, connecting links  226  may be curved. Connecting links  226  may also be excluded, with a peak or valley of one ring being directly attached to a valley or a peak of an adjacent ring, such as by welding soldering, or the manner in which stent framework  206  is formed, for e.g., by etching the pattern from a flat sheet or a tube. It will be appreciated by those of ordinary skill in the art that stent framework  206  of  FIG. 2  is merely an exemplary stent framework and that self-expanding stent frameworks of various forms and methods of fabrication can be used in accordance with various embodiments of the present invention. Stent framework  206  may have any stent configuration or design known in the art. Some examples of stent configurations that are suitable for use in embodiments of the present invention are shown in U.S. Pat. No. 4,733,665 to Palmaz, U.S. Pat. No. 4,800,882 to Gianturco, U.S. Pat. No. 4,886,062 to Wiktor, U.S. Pat. No. 5,133,732 to Wiktor, U.S. Pat. No. 5,292,331 to Boneau, U.S. Pat. No. 5,421,955 to Lau, U.S. Pat. No. 5,776,161 to Globerman, U.S. Pat. No. 5,935,162 to Dang, U.S. Pat. No. 6,090,127 to Globerman, U.S. Pat. No. 6,113,627 to Jang, U.S. Pat. No. 6,663,661 to Boneau, and U.S. Pat. No. 6,730,116 to Wolinsky et al., each of which is incorporated by reference herein in its entirety. 
     The superelastic or pseudoelastic material selected for forming self-expanding stent framework  206  permits venous valve  204  to recoil or recover from a radially compressed configuration in which blood flow lumen  208  is narrowed, as shown in  FIG. 2B , and return to a radially expanded configuration in which blood flow lumen  208  is fully open, as shown in  FIG. 2A . As used herein, the radially compressed configuration of a venous valve in accordance herewith does not mean the radial compression of the venous valve is uniform or uniformly applied about a circumference of the venous valve but instead means that the venous valve has been flattened or otherwise distorted by lateral or transverse compression that may be applied by a user pressing on one side of the venous valve thereby radially compressing the venous valve as discussed further below. As such radial compression of a venous valve in accordance herewith may result in the venous valve having an asymmetrical cross-section in the radially compressed configuration and/or may occur along only a portion of the length of the venous valve. 
     The recoil or recovery of stent framework  206  alone, i.e., without recoil delay component  214  attached thereto, from a radially compressed configuration to a radially expanded configuration conventionally occurs immediately upon removal of the external force causing the compression, which means that stent framework  206  conventionally will quickly or over a short time period such as 0.1-1.0 seconds, return to its radially expanded configuration. In order to slow or delay the recoil of self-expanding stent framework  206  after release of an external force in accordance with an embodiment hereof, recoil delay component  214  is coupled to self-expanding stent framework  206  to increase or extend a time period after release of an external force during which venous valve  204  is in a radially compressed configuration and blood flow lumen  208  is narrowed or flattened. Recoil delay component  214  is formed of a viscoelastic polymeric material having a thickness of 0.1-1.0 mm that exhibits slow elastic recovery in order to impart a damping effect on self-expanding stent framework  206  and that is biostable such that recoil delay component  214  will not biodegrade or bioabsorb during prolonged implantation in vivo. In another embodiment, recoil delay component  214  may be formed of a biostable elastomeric material, such as biostable polyurethane elastomers or silicone foams. The damping effect of recoil delay component  214  is expected to inhibit or delay the internal restoring forces of stent framework  206  from quickly returning venous valve  204  to a radially expanded configuration upon release of an external force. The viscoelastic polymeric material selected for recoil delay component  214  undergoes time dependent strain and therefore takes a longer period of time to elastically recover from an applied external force than does self-expanding stent framework  206  formed from a superelastic material. 
     In an embodiment, recoil delay component  214  should sufficiently slow the recovery of stent framework  206  from the radially compressed configuration such that blood flow lumen  208  of venous valve  204  will be narrowed or closed for a time period of between 20 to 60 minutes. When venous valve  204  is positioned in vivo within a penile vein, such as the deep dorsal vein or the superficial dorsal vein as further discussed below, blood flow through venous valve  204  may be restricted for 20 to 60 minutes so that outflow of blood from the penile vein is diminished for this time period thereby aiding the user in achieving and/or maintaining an erection. The end of the restricted time period may be defined as the time at which venous valve  204  has completely reverted to the radially expanded configuration shown in  FIG. 2A . Recoil delay component  214  is expected to provide a gradual damping effect that takes place over the restricted time period such that venous valve  204  is substantially closed at the beginning of the restricted time period, completely open at the end of the restricted time period, and partially closed during the restricted time period. 
     Viscoelastic polymeric materials that may be adapted for use in forming recoil delay components in accordance with embodiments hereof include but are not limited to foam rubber such as foam polyurethane sold under the trademark PPT and available from Langer Biomechanics, Deer Park, N.Y., and thermoset polyether-based polyurethane material sold under the trademark SORBOTHANE, available from Sorbothane, Inc. of Kent, Ohio, and acrylate polymer sold under the trademark 3M Viscoelastic Damping Polymer 242NR02 available from 3M Corporation of St. Paul, Minn. As well, viscoelastic polymeric gels, thermoset polyurethane gels, cohesive polymeric silicone gels sold under trademarks MEMORY GEL and COHESIL available from Mentor Corporation, Santa Barbara, Calif., and slow elastic recovery hydrogels, such as hydrogels disclosed in U.S. Pat. No. 4,452,776 to Refojo which is incorporated by reference herein in its entirety, may be adapted for use in embodiments hereof. 
     In the embodiment of venous valve  204  shown in  FIG. 2 , recoil delay component  214  is shown extending within stent framework  206  over its entire length from first end  210  to second end  212 . In another embodiment shown in  FIG. 3 , venous valve  304  includes recoil delay component  314  that extends along only a middle or intermediate section  330  of self-expanding stent framework  306 . Self-expanding stent framework  306  is formed of a superelastic material and has the construction described above with reference to the embodiment of  FIG. 2 . However in the embodiment of  FIG. 3 , a first end section  310  and a second end section  312  of stent framework  306  remain bare or uncovered by recoil delay component  330  and therefore sections  310 ,  312  are not encumbered or delayed by recoil delay component  314  when recovering from a radially compressive external force. Accordingly, first and second end sections  310 ,  312  of stent framework  306  immediately recoil from a radially compressed configuration to a radially expanded configuration upon removal of the external force whereas intermediate section  330  of self-expanding stent framework  306  that includes recoil delay component  314  recoils over an extended period of time, such as between 20 and 60 minutes as described above with reference to the embodiment of  FIG. 2 . In addition, when venous valve  304  is delivered to a delivery site within a penile vein, first and second end sections  310 ,  312  should readily deploy into contact with a wall of the vessel upon delivery and allow intimal growth around bare struts  318  in end sections  310 ,  312  after implantation. 
       FIG. 3A  is a cross-sectional view of venous valve  304  of  FIG. 3  taken along line A-A showing a fully open blood flow lumen  308 . In venous valve  304  intermediate section  330  of stent framework  306  is enclosed within recoil delay component  314  such that struts  318  and interstitial spaces  307  of intermediate section  330  are completely covered by the material of recoil delay component  314 . In an embodiment, venous valve  304  may be formed by over-molding recoil delay component  314  onto intermediate section  330  of stent framework  306 . In another embodiment, venous valve  304  may be formed by positioning intermediate section  330  of stent framework  306  between two tubes or layers of the material that forms recoil delay component  314  and then heat bonding the tubes or layers of material together to sandwich stent framework  306  therebetween. Although intermediate section  330  and first and second end sections  310 ,  312  are shown to be of approximately equal lengths in the embodiment of  FIG. 3 , i.e., each extending for approximately a third of the length of venous valve  304 , it should be understood that they may be of unequal lengths with intermediate section  330  being longer than either or both of first and second end sections  310 ,  312 . 
     Recoil delay component  314  of venous valve  304  may be formed of any of the slow elastic recovery materials disclosed above with reference to recoil delay component  214  and may have a thickness of 0.1-1.0 mm in order to impart a damping effect on intermediate section  330  of self-expanding stent framework  306 . The damping effect of recoil delay component  314  inhibits or delays the internal restoring forces of intermediate section  330  of stent framework  306  from quickly returning that portion of venous valve  304  from a radially compressed configuration to a radially expanded configuration upon release of an external force causing the compression. The delayed recoil of intermediate section  330  of venous valve  304  is expected to provide a time period during which blood flow lumen  308  is narrowed or closed and blood flow through venous valve  304  is restricted, such as a time period of between 20 and 60 minutes. 
       FIG. 4  is a perspective view of venous valve  404  in accordance with another embodiment hereof with  FIG. 4A  being a cross-sectional view of venous valve  404  taken along line A-A of  FIG. 4 . Venous valve  404  has a self-expanding stent framework  406  and a recoil delay component  414  that covers only struts  418  of stent framework  406 . The interstitial spaces  407  between struts  418  are open along the length of venous valve  404  to permit intimal growth therein after implantation. As in the previous embodiments, self-expanding stent framework  406  is formed of a superelastic material and has the construction described above with reference to the embodiment of  FIG. 2 . Venous valve  404  may be formed by over-molding recoil delay component  414  only onto struts  418  of stent framework  406  or by dipping struts  418  of stent framework  406  into a solution of a viscoelastic polymeric material to form recoil delay component  414  thereon. As in the embodiment of  FIG. 3 , stent framework  406  of venous valve  404  may have recoil delay component  414  covering only an intermediate section thereof so that first and second end sections thereof are left bare. 
     Recoil delay component  414  of venous valve  404  may be formed of any of the slow elastic recovery materials disclosed above with reference to recoil delay component  214  and may have a thickness of 0.1-1.0 mm in order to impart a damping effect on self-expanding stent framework  406 . The damping effect of recoil delay component  414  inhibits or delays the internal restoring forces of stent framework  406  from quickly returning venous valve  404  from a radially compressed configuration to a radially expanded configuration upon release of an external force causing the compression. The delayed recoil of venous valve  404  is expected to provide a time period during which blood flow lumen  408  is narrowed or closed and blood flow through venous valve  404  is restricted, such as a time period of between 20 and 60 minutes. 
     With reference to  FIG. 7 , deployment of a venous valve  504 , which is described below, may be accomplished by tracking a catheter-based delivery system  750  through the vasculature of the patient until the venous valve is located within a target vessel, such as deep dorsal vein  100  or superficial dorsal vein  102  or other palpable penile vein. An exemplary route for tracking the catheter-based delivery system through the vasculature may include introducing the delivery system into the femoral vein and directing the system through the internal iliac vein and the internal pudendal vein to the delivery site in the target penile vein. 
     Catheter-based delivery system  750  includes an inner shaft  755  having venous valve  504  mounted around a distal end  760  thereof, and a retractable outer sheath  765  that covers and constrains venous valve  504  in a reduced diameter while delivery system  750  is tracked through a vessel to the delivery site. The operation and structure of catheter-based delivery system  750  is more fully described in U.S. Pat. No. 6,126,685 to Lenker et al., which is incorporated by reference herein in its entirety. In other embodiments, delivery systems that are well known in the art may be used to deliver implantable venous valves in accordance herewith. In embodiments hereof, the delivery site for the venous valve may be within deep dorsal vein  100  or superficial dorsal vein  102  at a location near the base of the penis proximate the point where the penile vein enters the torso. The venous valve is intended to be positioned such that it may be radially compressed within the penile vein by a user pressing firmly on the base of the penis, as discussed further below with reference to the embodiment shown in  FIGS. 5 and 6 . 
     As prophetically illustrated in  FIG. 8 , once venous valve  504  is properly positioned within the penile vein  500 , outer sheath  765  of catheter-based delivery system  750  may be retracted to release venous valve  504  so that venous valve  504  may expand into apposition with the vessel wall of the penile vein. Catheter-based delivery system  750  is then withdrawn from venous valve  504 . In order to accommodate the elastic recovery of venous valve  504  being delayed upon initial deployment from the sheath, means for keeping the venous valve from moving out of the intended location while the venous valve achieves a fully expanded diameter, i.e., its radially expanded configuration, may be implemented. In one means for keeping the venous valve at the target location, venous valve  504  may include barb-like projections (not shown) that engage the vessel wall to hold the venous valve stationary while the venous valve slowly expands to its full radially expanded configuration. 
     Another means for keeping the venous valve  504  at the target location is shown in  FIG. 8 . A compression bandage or external clamp/ring (not shown) may be placed temporarily around the penis to hold the venous valve in place in the penile vein while the venous valve slowly transforms to its full radially expanded configuration. The external clamp/ring may be placed adjacent to and downstream of venous valve  504  to partially pinch off penile vein  500 , as represented by arrow P, to block valve  504  from being displaced from the intended implantation site by the flow of blood, represented by arrows B f . The external clamp/ring may be applied before venous valve  504  is released from catheter-based delivery system  750 . 
     In an embodiment shown prophetically in  FIG. 9 , a post deployment expansion of venous valve  504  may be performed, such as by a balloon catheter  975 , to radially expand venous valve  504  into apposition with a wall of a penile vein  500 . In such an embodiment, delivery system  750  is modified by replacing inner shaft  755  with balloon catheter  975 . Venous valve  504  is mounted in a radially compressed configuration about deflated balloon  980  and outer sheath  765  covers and constrains venous valve  504  in a reduced diameter while delivery system  750  is tracked through a vessel to the delivery site. As described above, once venous valve  504  is properly positioned within the penile vein, outer sheath  765  of catheter-based delivery system  750  may be retracted to uncover venous valve  504 . Then, balloon  980  of catheter  975  is pressurized to hold venous valve  504  at the target location and upon continued inflation of balloon  980  to expand venous valve  504  into its full radially expanded configuration within penile vein  500 . Balloon  980  is a soft elastomeric material to avoid damage to the recoil delay component of venous valve  504  that may be caused by expansion that is too rapid or with too much expansion force. For the embodiment shown in  FIG. 3 , there is no need to use a balloon to expand venous valve  304  because, as described above, first and second end sections  310 ,  312  of stent framework  306  immediately recoil from a radially compressed configuration to a radially expanded configuration that engages the inner wall of the penile vein upon removal of the external force. Besides the soft elastomeric balloon material, catheter  975  may have any catheter configuration or design known in the art, for e.g., dilatation catheters disclosed in U.S. Pat. No. 5,827,225 to Ma Schwab and U.S. Pat. No. 7,297,134 to Krivoruchko, each of which is incorporated by reference herein in its entirety, may be used in embodiments hereof. 
     Another method of delivering a venous valve in accordance with embodiments hereof may include identifying a target penile vein via ultrasound or color Doppler imaging and gaining access to the penile vein by performing a micropuncture procedure on the penis with a cannula. The venous valve may then be deployed within the penile vein through the cannula. 
     After initial deployment within the target penile vein, a venous valve in accordance with embodiments hereof is expected to become attached to or embedded within the penile vein due to endothelialization that occurs as cells grow around the stent framework of the venous valve. Implantable venous valves in accordance with embodiments hereof must be sufficiently endothelialized in order to prevent dislodgment from the penile vein when radially compressed and in order to “pull” the walls of the vein inward upon being radially compressed to stop or restrict the blood flow there through. Full endothelialization of venous valves in accordance herewith may occur as quickly as three weeks or may take up to eight weeks. In order to allow endothelialization of the venous valve, each of the embodiments of  FIGS. 3 and 4  include bare struts and/or interstitial openings through which cell growth may occur. In addition, the recoil delay components used in embodiments hereof may be made porous in order to permit cell growth therein. 
       FIGS. 5 and 6  show venous valve  504  prophetically deployed and endothelialized within a target penile vein  500 . Venous valve  504  is substantially similar to venous valve  204  of  FIG. 2  with the difference being that stent framework  506  is completely enclosed by recoil delay component  514  for the length of venous valve  504  and recoil delay component  514  is porous to permit endothelialization to occur therein. Venous valve  504  is in a radially expanded configuration in  FIG. 5  with blood flow lumen  508  fully open to permit unrestricted blood flow, represented by arrows B f , through venous valve  504 . Although in the expanded configuration venous valve  504  may by its very presence in the penile vein  500  interfere with blood flow, venous valve  504  in the expanded configuration is not expected to interfere with blood outflow from the penis through penile vein  500  in a manner which would be considered clinically relevant. In order to prevent or restrict blood outflow from the penile vein to aid in attaining and/or maintaining a penile erection, the user applies a compressive radial force, represented by arrow C rf , to the penis that is sufficient to radially compress at least a portion of venous valve  504 , as well as the portion of penile vein  500  that has become attached to venous valve  504 . In the radially compressed configuration shown in  FIG. 6 , blood flow lumen  508  is substantially narrowed or closed to restrict blood flow B f  through venous valve  508  and thereby prevent or restrict blood outflow from the penis through penile vein  500 . While venous valve  504  is radially compressed or slowly returning to the radially expanded configuration, blood flow exiting the penis through penile vein  500  will be restricted thus helping to maintain the penile erection. In an embodiment, blood flow may be restricted or prevented from flowing out of the penis via penile vein  500  for a time period of 20 to 60 minutes due to the delayed elastic recovery of venous valve  504 . 
     Penile vein  500  extends within the pendant portion of the penis and is susceptible to finger pressure exerted on the penis by the user, and accordingly may be one of the superficial or deep dorsal veins of the penis. As noted above, venous valve  504  is intended to be positioned at a location along penile vein  500  such that venous valve  504  may be radially compressed within penile vein  500  by a user pressing firmly on or near the base of the penis, i.e., the portion of the penis that is positioned external or outside of the pubic bone and the urogenital diaphragm. In conjunction with the normal parasympathetic nervous system processes associated with arousal, venous valve  504  may be selectively compressed by a user whenever an erection is desired to be attained or maintained. As such, recoil delay component  514  is expected to be capable of repeated/numerous uses over the lifetime of the user in delaying the recoil of stent framework  506  after being subjected to compressions of venous valve  504 . 
     While various embodiments according to the present invention have been described above, it should be understood that they have been presented by way of illustration and example only, and not limitation. It will be apparent to persons skilled in the relevant art that various changes in form and detail can be made therein without departing from the spirit and scope of the invention. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the appended claims and their equivalents. It will also be understood that each feature of each embodiment discussed herein, and of each reference cited herein, can be used in combination with the features of any other embodiment. All patents and publications discussed herein are incorporated by reference herein in their entirety.