Abstract:
A system for enabling the insertion and removal of an embolic protection device, for capturing and retaining embolic debris which may be created during the performance of a therapeutic interventional procedure in a stenosed or occluded region of a blood vessel. The system, in an embodiment thereof, enables the device to be snap-fitted so as to engage the distal end of a guide wire, to provide a reference for positioning the device at a location distal to the interventional procedure site, and to enable an end of the device to be in tension to assist in the tracking and deploying of the system.

Description:
[0001]    This application is a continuation of application Ser. No. 09/919,503 filed Jul. 31, 2001 which is a continuation-in-part of application Ser. No. 09/896,142 filed on Jun. 29, 2001. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    The present invention relates generally to improvements in embolic protection systems and methods. In particular, it relates to an improved system and method for enabling an embolic protection device to be efficiently and conveniently engaged with the distal end of a guide wire. The system also enables the device to effectively expand against the inner surface of a blood vessel wall, and to seal off the inner surface thereof upon deployment thereof at a location distal to an interventional procedure site. Such deployment enables the efficient capture of embolic material, which may be created and released into the bloodstream during the performance of the interventional procedure in a stenosed or occluded region of a blood vessel, and prevents embolic material from bypassing the embolic protection device. The system further enables the embolic protection device to provide a reference for the effective positioning thereof at the location distal to the interventional procedure site. It also is formed of expandable material for enabling efficient expansion thereof, and includes an end thereof formed so as to be in tension, to effectively assist in the tracking and deploying of the system.  
           [0003]    The systems and methods of the present invention are particularly useful when performing balloon angioplasty, stenting procedures, laser angioplasty or atherectomy in critical vessels, such as the carotid, renal, and saphenous vein graft arteries, where the release of embolic debris into the bloodstream could possibly occlude the flow of oxygenated blood to the brain or other vital organs which can cause devastating consequences to the patient.  
           [0004]    A variety of non-surgical interventional procedures have been developed over the years for opening stenosed or occluded blood vessels in a patient caused by the build up of plaque or other substances on the walls of the blood vessel. Such procedures usually involve the percutaneous introduction of the interventional device into the lumen of the artery, usually through a catheter. One widely known and medically accepted procedure is balloon angioplasty in which an inflatable balloon is introduced within the stenosed region of the blood vessel to dilate the occluded vessel. The balloon catheter is initially inserted into the patient&#39;s arterial system and is advanced and manipulated into the area of stenosis in the artery. The balloon is inflated to compress the plaque and press the vessel wall radially outward to increase the diameter of the blood vessel.  
           [0005]    Another procedure is laser angioplasty which utilizes a laser to ablate the stenosis by super heating and vaporizing the deposited plaque. Atherectomy is yet another method of treating a stenosed blood vessel in which a cutting blade is rotated to shave the deposited plaque from the arterial wall. A vacuum catheter may be used to capture the shaved plaque or thrombus from the blood stream during this procedure.  
           [0006]    In another widely practiced procedure, the stenosis can be treated by placing a device known as a stent into the stenosed region to hold open and sometimes expand the segment of the blood vessel or other arterial lumen. Stents are particularly useful in the treatment or repair of blood vessels after a stenosis has been compressed by percutaneous transluminal coronary angioplasty (PTCA), percutaneous transluminal angioplasty (PTA) or removal by atherectomy or other means. Stents are usually delivered in a compressed condition to the target site, and then are deployed at the target location into an expanded condition to support the vessel and help maintain it in an open position.  
           [0007]    In the past, stents typically have fallen into two general categories of construction. The first type of stent is expandable upon application of a controlled force, often through the inflation of the balloon portion of a dilatation catheter which, upon inflation of the balloon or other expansion means, expands the compressed stent to a larger diameter to be left in place within the artery at the target site. The second type of stent is a self-expanding stent formed from, for example, shape memory metals or super-elastic nickel-titanum (NiTi) alloys, which will automatically expand from a compressed state when the stent is advanced out of the distal end of the delivery catheter into the body lumen. Such stents manufactured from self-expandable materials allow for phase transformations of the material to occur, contributing to the expansion and contraction of the stent.  
           [0008]    The above non-surgical interventional procedures, when successful, avoid the necessity of major surgical operations. However, there is one common problem associated with all of these non-surgical procedures, namely, the potential release of embolic debris into the bloodstream which can occlude distal vasculature and cause significant health problems to the patient. For example, during deployment of a stent, it is possible that the metal struts of the stent can cut into the stenosis and shear off pieces of plaque which become embolic debris that can travel downstream and lodge somewhere in the patient&#39;s vascular system. Pieces of plaque material can sometimes dislodge from the stenosis during a balloon angioplasty procedure and become released into the bloodstream. Additionally, while complete vaporization of plaque is the intended goal during a laser angioplasty procedure, particles are not always fully vaporized and may enter the bloodstream.  
           [0009]    When any of the above-described procedures are performed for example in the carotid arteries, the release of emboli into the circulatory system can be extremely dangerous to the patient. Debris that is carried by the bloodstream to distal vessels of the brain may cause these cerebral vessels to occlude, resulting in a stroke, and in some cases, death. Therefore, although carotid percutaneous transluminal angioplasty has been performed in the past, the number of procedures performed has been limited due to the justifiable fear of causing an embolic stroke should embolic debris enter the bloodstream and block vital downstream blood passages.  
           [0010]    Medical devices have been developed to attempt to deal with the problem created when debris or fragments enter the circulatory system following treatment utilizing any one of the above-identified procedures. One approach which has been attempted is the cutting of any debris into minute sizes which pose little chance of becoming occluded in major vessels within the patient&#39;s vasculature. However, it is often difficult to control the size of the fragments which are formed, and the potential risk of vessel occlusion still exists, making such procedures in the carotid arteries a high-risk proposition.  
           [0011]    Other techniques which have been developed to address the problem of removing embolic debris include the use of catheters with a vacuum source which provides temporary suction to remove embolic debris from the bloodstream. However, as mentioned above, there have been complications with such systems since the vacuum catheter may not always remove all of the embolic material from the bloodstream, and a powerful suction could cause problems to the patient&#39;s vasculature.  
           [0012]    Further techniques which have had some limited success include the placement of an embolic protection device such as a filter or trap downstream from the treatment site to capture embolic debris before it reaches the smaller blood vessels downstream. Such embolic protection devices enable the filtering of embolic debris which may be released into the bloodstream during the treatment to the vessel, and yet allow a sufficient amount of oxygenated blood to flow past the device to supply vital organs downstream from the treatment site.  
           [0013]    However, there have been problems associated with embolic protection devices, particularly during the assembly, insertion, and deployment thereof. The device may be mounted on the guide wire in an inconvenient manner so as to be fixedly secured thereto. Also, the mounting of the device on the guide wire, such that the device is affixed to and rotatable with the guide wire, may result in the entangling of the device in a delivery sheath, upon the device being directed in the delivery sheath through the patient&#39;s anatomy to the position distal to the interventional procedure site. Further, the expansion and deployment of the embolic protection device may not result in full and complete expansion thereof, and consequently may not seal off the inner wall of the blood vessel about the entire circumference thereof, which can result in embolic material bypassing the device. The guiding, tracking, positioning and deployment of the embolic protection device in the patient&#39;s vasculature and at the location distal to the interventional procedure site for embolic protection can be difficult and formidable.  
           [0014]    Therefore, the present invention provides improved systems and methods for treating stenosis in blood vessels which enable an embolic protection device to be efficiently assembled and to effectively navigate through a patient&#39;s vasculature for deployment at a location distal to an interventional procedure site. It also enables the device to expand so as to effectively seal off the inner surface of the blood vessel wall, to capture embolic material, and to prevent embolic material from bypassing the embolic protection device. The improved systems and methods of the present invention further enable the efficient positioning of the embolic protection device at the location distal to the interventional procedure site, to enable the effective capture of embolic material. Also, the invention is formed of expandable material in such a manner as to accommodate the effective tracking and deploying thereof. Moreover, the systems and methods are relatively easy for a physician to use, while enabling the effective delivery and recovery of a filtering system capable of removing embolic debris released into the bloodstream. The inventions disclosed herein satisfy these and other needs.  
         SUMMARY OF THE INVENTION  
         [0015]    The present invention, in general, provides a system and method for enabling the insertion and removal of a filtering system for capturing and retaining embolic debris from a blood vessel. The embolic debris may be created during the performance of a therapeutic interventional procedure, such as a balloon angioplasty or stenting procedure. The filtering system prevents the embolic debris from lodging and blocking blood vessels downstream from the interventional site. The present invention is particularly useful for enabling an interventional procedure to be performed in vital arteries, such as the carotid arteries, in which critical downstream blood vessels can become blocked with embolic debris, including the main blood vessels leading to the brain or other vital organs. As a result, the present invention provides the physician with a higher degree of confidence in the efficient operation of a filtering system for the collection and removal of embolic debris from the blood vessel when performing high-risk interventional procedures.  
           [0016]    The present invention enables a filtering system to be deployed in the blood vessel at a location distal to the area of treatment in the interventional procedure site. It also enables the blood to pass therethrough to enable blood to flow past the filter. It further enables the blood to be filtered to capture and retain any embolic debris which may be created during the interventional procedure.  
           [0017]    More particularly, for example, in an embodiment of the present invention, a system is provided for enabling the effective assembly thereof for engagement with a guide wire. The present invention also enables the system to expand against the inner surface of a wall of a blood vessel so as to efficiently seal off the inner surface thereof, for enabling the capture of embolic material which may be released into the blood vessel during the therapeutic interventional procedure. Further, the system enables navigation thereof through a patient&#39;s blood vessel, including tortuous vasculature, to a position distal to an interventional procedure site, for deployment of the embolic protection device.  
           [0018]    The system includes a guide wire, including a distal end, which is positionable within the blood vessel so as to extend to a position distal to an interventional procedure site. The system also includes a filter device, which is snap-fittable so as to engage the distal end of the guide wire, for effective and convenient engagement therewith. Elements of the filter device which enable the filter device to be snap-fitted to the guide wire are comprised of radiopaque material, for providing a reference for positioning the filter device in the patient&#39;s vasculature. The filter device is comprised of expandable material, and is formed so that an end thereof is in tension, to assist in tracking and deploying thereof in tortuous vasculature.  
           [0019]    The above objects and advantages of the present invention, as well as others, are described in greater detail in the following description, when taken in conjunction with the accompanying drawings of illustrative embodiments. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]    [0020]FIG. 1 is an elevational fragmentary partly-sectional view of an embodiment of the present invention, disposed within the internal carotid artery of a patient, including a delivery sheath and an unexpanded filter device.  
         [0021]    [0021]FIG. 2 is a similar view of the embodiment shown in FIG. 1, wherein the delivery sheath has been removed and the filter device has expanded.  
         [0022]    [0022]FIG. 3 is a partly cross-sectional view taken along the line  3 - 3  of FIG. 1.  
         [0023]    [0023]FIG. 4 is a plan view of a flattened rolled out form of a tube of material for forming the filter device, in the embodiment of the invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0024]    The present invention is directed to an improved system and method for enabling the capture of embolic material which may be released into the blood vessel during the therapeutic interventional procedure, in an efficient and effective manner. The invention enables a filter device to be snap-fitted to a guide wire for effective and convenient engagement therewith, enables rotational movement of the filter device independent of rotational movement of the guide wire, and inhibits translational movement of the filter device. The present invention is further directed to efficiently providing a reference for positioning the filter device in the patient&#39;s anatomy. The filter device is also formed of expandable material, and includes an end thereof which is formed so as to be in tension, to aid in tracking and deploying the filter device.  
         [0025]    The embodiments of the improved system and method are illustrated and described herein by way of example only and not by way of limitation. While the present invention is described as applied to the carotid arteries of the patient, those skilled in the art will appreciate that it can also be used in other body lumens as well, such as the coronary arteries, renal arteries, saphenous vein grafts and other peripheral arteries. Additionally, the present invention can be utilized when performing any one of a number of interventional procedures, such as stenting, balloon angioplasty, laser angioplasty or atherectomy.  
         [0026]    In the drawings, wherein like reference numerals denote like or corresponding parts throughout the drawing figures, and particularly in the embodiments in accordance with the invention as shown in FIGS.  1 - 4 , for example, a system  10  is provided for enabling an interventional procedure to be performed in a blood vessel  12  at an area of treatment  14 . The system  10  is atraumatic, to inhibit injury to the patient. It includes a guide wire  16  which enables the system  10  to be positioned distal to the area of treatment  14 . The system  10  is placed within the carotid artery  18  or other blood vessel of the patient, and is guided into position by the guide wire  16 . The guide wire  16  includes a tip coil  20  at a distal end  22  thereof. The tip coil includes a proximal end  24 . The carotid artery  18  has the area of treatment  14  therein, which comprises the interventional procedure site, wherein atherosclerotic plaque  26  has built up against the inside wall  28 , which decreases the diameter of the carotid artery  18 . As a result, blood flow is diminished through this area.  
         [0027]    The therapeutic interventional procedure comprises implanting an expandable interventional instrument at the interventional procedure site  14 , to press the build-up of plaque  26  of the stenosis against the inside wall  28 , to increase the diameter of the occluded area  14  of the artery  18 , and to help restore sufficient flow of blood to the downstream vessels leading to the brain. The expandable interventional instrument not only helps increase the diameter of the occluded area, but helps prevent restenosis in the area of treatment  14 . The interventional instrument is expandable upon deployment thereof at the interventional procedure site  14 .  
         [0028]    The system  10  of the present invention enables the delivery of a filter device  30  to a location distal to the area of treatment  14 , to enable deployment of the filter device  30  at the location distal to the area of treatment  14 , and to enable the removal of the filter device  30  from the delivered and deployed position thereof. The filter device  30  filters the blood in the blood vessel  12 , so as to pass blood therethrough and capture embolic material  32  which may be released in the blood vessel  12  during the interventional procedure. It engages the distal end  22  of the guide wire  16 , so as to enable the filter device  30  to be placed within the carotid artery  18  or other blood vessel of the patient and guided into position distal to the area of treatment  14 . The filter device  30  includes a proximal portion  34  and a distal portion  36 .  
         [0029]    Referring to FIGS.  1 - 4 , in an embodiment pursuant to the present invention, for example, the system  10  enables movement thereof through the patient&#39;s blood vessel  12  to a position distal to the area of treatment  14  for deployment of the filter device  30 . The system  10  further enables expansion of the filter device  30  against the inside wall  28  of the blood vessel  12  and the sealing off of the inside wall  28 , to enable the capture of embolic material  32  which may be released into the blood vessel  12  during the therapeutic interventional procedure.  
         [0030]    As illustrated in FIGS.  1 - 3 , the system  10  in accordance with the embodiment of the invention includes the guide wire  16 , positionable within the blood vessel  12 , and extendable to a position distal to the interventional procedure site  14 . The system  10  further includes the filter device  30 , which is snap-fitted for engagement with the distal end  22  of the guide wire  16 . The filter device  30  extends within a delivery sheath  38  for delivery to the interventional procedure site  14 . The delivery sheath  38  includes a distal portion  40 . The system  10  further includes an obturator  42 , which includes a proximal end  44  and a distal end  46 . The obturator  42  extends between the delivery sheath  38  and the tip coil  20 , such that the distal end  46  of the obturator  42  extends along the proximal end  24  of the tip coil  20 , and the proximal end  44  of the obturator  42  is substantially abutted by the distal portion  40  of the delivery sheath  38  when the delivery sheath  38  is extended over the filter device  30 . The obturator  42  provides a smooth transition between the delivery sheath  38  and the tip coil  20 , so as to slide smoothly around tortuous anatomy in the blood vessel  12 , and to inhibit digging into the inside wall  28  of the blood vessel  12  thereby.  
         [0031]    The filter device  30  is deployed at the location in the patient&#39;s blood vessel  12  distal to the area of treatment  14 , upon withdrawal of the delivery sheath  38 . It captures embolic material  32  which may be released into the blood in the blood vessel  12  during the interventional procedure. Upon being snap-fitted onto the distal end  22  of the guide wire  16 , the filter device  30  engages the guide wire  16 , and enables rotation of the filter device  30  independent of rotation of the guide wire  16 , while inhibiting translation thereof along the guide wire  16 .  
         [0032]    A cage  48  is included in the filter device  30 . The cage  48  is snap-fitted onto the distal end  22  of the guide wire  16  for engagement therewith, and filter material  50 , for filtering embolic material  32 , is secured to the cage  48 . The cage  48  includes a proximal portion  52  and a distal portion  54 , and the filter material  50  includes a proximal end  52 , a distal end  54 , and a plurality of holes  60  therein for filtering embolic material  32 . The proximal end  56  of the filter material  50  is secured to the cage  48 , and the proximal end  44  of the obturator  42  extends over the distal portion  58  of the filter material  50 .  
         [0033]    The cage  48  further includes an engaging element  62 , located at the proximal portion  52  thereof, as shown in enlarged view in FIG. 3, for enabling the cage  48  to snap-fit so as to engage the distal end  22  of the guide wire  16 . The engaging element  62  enables the cage  48  to be snap-fitted onto the distal end  22  of the guide wire  16 . The cage  48 , upon being snap-fitted onto the distal end  22  of the guide wire  16 , enables rotational movement of the cage  48  independent of rotational movement of the guide wire  16 , and inhibits translational movement of the cage  48  along the guide wire  16 . The cage  48  further includes a plurality of struts  64 .  
         [0034]    In the filter device  30 , as shown in FIG. 4, the plurality of struts  64  of the cage  48  comprise a plurality of proximal ribs  66 , a plurality of distal ribs  68 , and a ring  70 , which extends intermediate the plurality of proximal ribs  66  and the plurality of distal ribs  68 . The ring  70 , for example, includes a plurality of segments  72  and  74 , and each adjacent pair of the plurality of segments  72  and  74  is expandable to form a generally v-shaped section of the ring  70 , to seal off the inside all  28  of the blood vessel  12 , so as to inhibit the formation of a gap between the cage  48  and the blood vessel inside wall  18  through which embolic material  32  may otherwise flow.  
         [0035]    As seen in FIGS.  1 - 3 , the system  10  further includes a proximal stop  76  and a distal stop  78 , to be secured to the distal end  22  of the guide wire  16 , and having a space  80  between the proximal stop  76  and the distal stop  78 . The proximal stop  76  and the distal stop  78  comprise a pair of bushings, which are comprised of radiopaque material, to provide a reference for the operator of the system  10  to position to filter device  30  in the patient&#39;s blood vessel  12 . The engaging element  62  of the cage  48  enables the cage  48  to be snap-fitted to the proximal stop  76  and the distal stop  78  in the space  80  therebetween. The engaging element  62  includes at least one tab  82 , which is bent inwardly, for example, for engaging the proximal stop  76  and the distal stop  78  in the space  80  between the proximal stop  76  and the distal stop  78 . The snap-fitted engaging element  62  also enables rotational movement of the filter device  30  independent of rotational movement of the guide wire  16 , while inhibiting translational movement of the filter device  30  relative to the guide wire  16 .  
         [0036]    The cage  48  of the filter device  30 , as depicted in FIG. 4, may be formed from a hypotube  84  of expandable material. The hypotube  84  includes a pair of ends  86  and  88 . The system  10  further includes a spring  90 , connected to the end  86  of the hypotube  84 , such that a portion of the cage  48  formed by the hypotube  84  is in tension, to aid in tracking and deploying the cage  48  in tortuous vasculature. The tabs  82  are formed at the end  86  of the hypotube  84  to which the spring  90  is connected.  
         [0037]    Referring to FIGS.  1 - 4 , in a method for the use of the embodiment in accordance with the present invention, for example, the system  10  enables movement thereof through the patient&#39;s blood vessel  12  to the location distal to the area of treatment  14  for deployment of the filter device  30 , and seals off the inside wall  28  of the blood vessel  12  to enable the capture of embolic material  32 . The filter device  30  and the obturator  42  are assembled, and the proximal stop  76  and the distal stop  78 , which comprise a pair of bushings, are mounted on the guide wire with the space  80  therebetween. The inner diameter of the filter device  30 , for example, is at least slightly larger than the outer diameter of the tip coil  20 , and the at least one tab  82  is pivotable, so as to enable the filter device  30  to be inserted over the tip coil  20 . The assembly of the filter device  30  and the obturator  42 , for example, is inserted over the tip coil  20  to the position where the tabs  82  snap-fit into the space  80  between the pair of bushings comprising the proximal stop  76  and the distal stop  78  mounted on the guide wire  16 , so as to snap-fit the filter device  30  to the distal end  22  of the guide wire  16 , for efficient engagement therewith. The delivery sheath  38  is extended over the guide wire  16  so as to enclose the filter device  30  therein, and such that the distal portion  40  of the delivery sheath  38  substantially abuts the proximal end  44  of the obturator  42 .  
         [0038]    The system  10  is positioned in the patient&#39;s vasculature  12  utilizing any one of a number of different methods. In one preferred method of positioning the system  10 , the delivery sheath  38 , with the filter device  30  therein, is inserted into and extended through the patient&#39;s vasculature  12 , to cross the stenosis in the blood vessel  12 , so as to extend to a position distal to the interventional procedure site  14 . The radiopaque proximal stop  76  and distal stop  78  of the engaging element  62  provide a reference for enabling the operator to accurately position the filter device  30  in the patient&#39;s vasculature  12 . As seen in FIG. 4, the spring  90 , connected to the end  86  of the hypotube  84  of expandable material at which the tabs  82  are formed, causes such portion of the cage  48  formed by the hypotube  84  to be in tension, aiding in the tracking and deploying of the cage  48  in tortuous vasculature.  
         [0039]    The guide wire  16  is rotatable during insertion thereof through the patient&#39;s vasculature  12 , to enable guiding and directing thereof. The snap-fitted filter device  30  is rotatable on the guide wire  16  independent of rotation of the guide wire  16 , during insertion of the filter device  30  through the patient&#39;s anatomy  12 , to inhibit entanglement thereof, while the filter device  30  is also inhibited from translational movement thereof. The delivery sheath  38  is then withdrawn, enabling the filter device  30  to deploy so as to capture embolic material  32  which may be released in the blood vessel  12  during the interventional procedure.  
         [0040]    After the delivery sheath  38  is withdrawn, the filter device  30 , snap-fitted to the guide wire  16  at the proximal portion  52  of the cage  48  such that the tabs  82  extend between the proximal stop  76  and the distal stop  78 , is released from being enclosed in the delivery sheath  38 . The filter device  30  then expands and bears against the inside wall  28  of the blood vessel  12 . The expansion of the filter device  30  so as to press against the inside wall  28  of the blood vessel  12  seals off the inside wall  28  of the blood vessel  12 , and inhibits the formation of a gap between the filter device  30  and the blood vessel wall  28 , through which embolic material  32  may otherwise flow. The filter material  50  expands with the flow of blood in the blood vessel  12  therethrough, to capture embolic material  32  which may be released during the interventional procedure.  
         [0041]    In accordance with the present invention, the particular embodiments set forth above of the system  10  for filtering embolic material are capable of being positioned in a blood vessel. However, other forms of the system  10  may be utilized with the present invention without departing from the spirit and scope of the invention. For example, the system  10  may be comprised of other forms of material. Additionally, while the system  10  is shown as in various shapes in the embodiments herein, it can be formed in any one of a number of different shapes depending upon the construction desired.  
         [0042]    Further, the various components may be joined by suitable adhesives such as acrylonitrile based adhesives or cyanoacrylate based adhesives. Heat shrinking or heat bonding may also be employed where appropriate. Plastic-to-plastic or plastic-to-metal joints can be effected by a suitable acrylonitrile or cyanoacrylate adhesive. Variations can be made in the composition of the materials to vary properties as needed. Based on the present disclosure, other adhesives and applications are known to one skilled in the art.  
         [0043]    In view of the above, it is apparent that the system and method of the embodiment of the present invention enhances substantially the effectiveness of performing interventional procedures by providing a filter device for filtering embolic material, to be snap-fitted for engagement with a guide wire, and independently rotatable relative to the guide wire, for efficient assembly, insertion and removal thereof. The system and method further enable the filter device to expand against the inner wall of a blood vessel so as to seal off the inner surface thereof, to inhibit gap formation and the passing of embolic material therethrough. The system and method also include a pair of radiopaque bushings for enabling snap-fitting engagement of the filter device with the guide wire, which provide references for the positioning of the filter device in the patient&#39;s vasculature. The filter device of the system and method is formed of expandable material including a portion thereof in tension, for aiding in tracking and deploying the filter device.  
         [0044]    While the present invention has been described in connection with the specific embodiments identified herein, it will be apparent to those skilled in the art that many alternatives, modifications and variations are possible in light of the above description. Accordingly, the invention is intended to embrace all such alternatives, modifications and variations as may fall within the spirit and scope of the invention disclosed herein.