Abstract:
A bi-directional steerable catheter that, for a given tip deflection angle, generates a first articulation radius in a first lateral direction and a second articulation radius in a second lateral direction, the second articulation radius being different than the first articulation radius. The catheter includes two pull wire portions that can be individually and selectively put under tension to cause deflection of the tip in a corresponding lateral direction. Actuation of a first of the pull wire portions causes a shift in the neutral axis of the catheter over a portion of the steering section, resulting in articulation over a shorter length of the steering section and thus a smaller bend radius. Actuation of a second of the pull wire portions does not result in a neutral axis shift, so that articulation is over substantially the entire length of the steering section, resulting in a larger bend radius.

Description:
RELATED APPLICATION 
       [0001]    This application claims the benefit of U.S. Provisional Patent Application No. 61/819,216, filed May 3, 2013, the disclosure of which is hereby incorporated by reference in its entirety. 
     
    
     FIELD OF THE DISCLOSURE 
       [0002]    The present disclosure is directed generally to catheter assemblies, and more specifically to catheter assemblies having deflectable distal tips for manipulation and steering. 
       BACKGROUND 
       [0003]    Many steering catheter designs exist which are capable of deflecting the distal end of a catheter in various ways using a control handle. In one form of steering catheters, a control handle is coupled with a pull wire or wires in an arrangement that applies or releases tension in the pull wire(s) as the plunger or steering mechanism is manipulated, thereby causing a controlled deflection of the distal tip of the catheter. Controlled deflection is in a single direction in some steering catheters, and is bi-directional in other applications. 
         [0004]    For bi-directional applications, one design challenge is to allow for sufficient range and control of movements with controls which are not unduly complicated. In many devices, rather elaborate designs have been attempted which are not sufficiently simple, effective, and easy to use. 
         [0005]    A steering catheter that provides a desirable and diverse range of deflection movement with a simple and easy to operate internal structure would be welcome. 
       SUMMARY 
       [0006]    Various embodiments of the disclosure include a bidirectional steering catheter that provides lateral deflection control of the distal end of a catheter system in two directions where each direction of bending deflection is associated with a different bend radius. In various embodiments, such dual bending is made possible through use of a single compression coil disposed only in a segment of the steering section of the catheter. The design can enable easier assembly and with fewer components than conventional bidirectional steering catheters, and can also provide a reduced profile than conventional bidirectional steering catheters. 
         [0007]    Structurally, a catheter assembly in accordance with the present disclosure includes a shaft portion and a steering portion. The shaft portion has a proximal end and a distal end and including a shaft section sidewall that defines a central lumen. The steering portion having a proximal end and a distal end, the proximal end of the steering portion being operatively coupled with the distal end of the shaft portion. The steering portion includes a steering section sidewall having a first steering section sidewall lumen and a second steering section sidewall lumen formed therein. The catheter assembly defines a central axis that passes through the proximal end of the shaft portion and the distal end of the steering portion, the shaft portion and the steering portion being substantially concentric about the central axis. A uni-directional stiffening member can be operatively coupled to the steering section sidewall proximate the first steering section sidewall lumen and over a standoff length of the steering section, the uni-directional stiffening member defining a uni-directional bending portion of the steering section and an offset axis that is radially offset from and substantially parallel to the central axis. 
         [0008]    A first pull wire portion extends through the central lumen and the first steering section sidewall lumen such that actuation of the first pull wire portion causes deflection of the steering portion in a first lateral direction, the first pull wire portion being routed proximate the uni-directional stiffening member. During actuation of the first pull wire portion, a neutral axis of the catheter assembly along the uni-directional bending portion is proximate the offset axis such that a first bend radius of the steering section is defined for a steering angle α. 
         [0000]    A second pull wire portion extends through the central lumen and the second steering section sidewall lumen such that actuation of the second pull wire portion causes deflection of the steering portion in a second lateral direction. In one embodiment, the second lateral direction is different than the first lateral direction. During actuation of the second pull wire portion, a neutral axis of the catheter assembly along the uni-directional bending portion is proximate the central axis such that a second bend radius of the steering section is defined for the same steering angle α, the second steering radius being greater than the first steering radius. 
         [0009]    In one embodiment, the first sidewall lumen is rotationally offset from the second sidewall lumen. The first steering section sidewall lumen can be diametrically opposed to the second steering section sidewall lumen. A transition piece can optionally extend partially into the shaft portion and partially into the steering portion. Also, the first pull wire portion and the second pull wire portion can be e two separate pull wires, or can be portions of the same wire that is looped through the catheter assembly. 
         [0010]    In one embodiment, the uni-directional stiffening member is a compression coil. In one non-limiting example, the compression coil has an outer diameter of about 0.42 mm and an inner diameter of about 0.26 mm. In another non-limiting example, the compression coil is formed of a 0.003 inch by 0.010 inch rectangular section wire. The compression coil can be configured so as not to delaminate from the first steering section sidewall lumen. In one embodiment, a compressibility ratio of the compression coil relative to the steering section sidewall is at least 1:5. 
         [0011]    In some embodiments, the shaft section sidewall defines a first shaft sidewall passageway and a second shaft sidewall passageway formed therein, the first shaft sidewall passageway and the second shaft sidewall passageway extending parallel to the central axis over at least a portion of the shaft portion and passing through the distal end of the shaft portion. In one embodiment, the first shaft sidewall passageway is axially aligned with the first steering section sidewall lumen, and the second shaft sidewall passageway is axially aligned with the second steering section sidewall lumen. In this embodiment, the first pull wire portion and the second pull wire portion can pass through the first shaft sidewall passageway and the second shaft sidewall passageway, respectively. 
         [0012]    The first sidewall passageway and the second sidewall passageway can define lumens in the shaft section sidewall. Alternatively, the first sidewall passageway and the second sidewall passageway are channels formed in the shaft sidewall. A transition piece can extend partially into the shaft portion and partially into the steering portion. In one embodiment, the transition piece defines spaced-apart, longitudinally extending slots on diametrically opposed sides of the transition piece. 
         [0013]    In another embodiment of the disclosure, a method of deflecting a distal tip of a catheter is described. The method comprises:
       providing a catheter assembly including a shaft portion and a steering portion that define a central axis, the catheter assembly including a first pull wire portion and a second pull wire portion;   within the shaft portion, routing the first pull wire portion and the second pull wire portion proximate the central axis;   within the steering portion, routing the first pull wire portion and the second pull wire portion parallel to and radially offset from the central axis, the first pull wire portion being rotationally offset from the second pull wire portion within the steering portion,   causing a neutral axis of the catheter assembly to align substantially with the central axis throughout the shaft portion and the steering portion during actuation of the second pull wire portion; and   causing the neutral axis of the catheter assembly to substantially coincide with the first pull wire portion along a proximal portion of the steering section when the first pull wire portion is actuated, the neutral axis being substantially aligned with the central axis at locations proximal to and distal to the proximal portion of the steering section.       
 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    The disclosure may be more completely understood in consideration of the following detailed description of various embodiments in connection with the accompanying drawings, in which: 
           [0020]      FIG. 1  is a schematic of a catheter system in an embodiment of the disclosure; 
           [0021]      FIGS. 2A through 2C  are an enlarged partial sectional views of the catheter system of  FIG. 1 , according to an embodiment of the disclosure; 
           [0022]      FIG. 3A  is an enlarged sectional schematic of a tip deflection with a compression coil in compression in an embodiment of the disclosure; 
           [0023]      FIG. 3B  is an enlarged sectional schematic of a tip deflection with the compression coil in expansion in an embodiment of the disclosure; 
           [0024]      FIG. 4  is a schematic of a catheter system with the compression coil in compression in an embodiment of the disclosure; 
           [0025]      FIG. 5  is a schematic of a catheter system with the compression coil in expansion in an embodiment of the disclosure; 
           [0026]      FIG. 6A  is an alternate embodiment of the enlarged partial sectional views depicted in  FIG. 2B  of the catheter system of  FIG. 1 , according to an embodiment of the disclosure; 
           [0027]      FIG. 6B  is an enlarged partial sectional view of the alternate embodiment of the catheter system depicted in  FIG. 6A , according to an embodiment of the disclosure; 
           [0028]      FIG. 7  is a perspective view of the transition piece, pull wire portions and steering portion of the catheter system of  FIGS. 6A and 6B  with the proximal shaft portion removed according to an embodiment of the disclosure; and 
           [0029]      FIG. 8  is a perspective view of the distal end of the steerable distal portion of the catheter system and end effector according to an embodiment of the disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0030]    Referring to  FIG. 1 , a catheter system  20  is depicted in a disclosed embodiment. The catheter system  20  comprises an elongated catheter assembly  22  having a shaft portion  24  and a steerable distal portion  26 . The shaft portion  24  includes a proximal end  28  and a distal end  32 . The steerable distal portion  26  includes a proximal end  34  and a distal end  36 , with the proximal end  34  coupled with the distal end  32  of the shaft portion  24 . The catheter assembly  22  can also include an end effector  38 . 
         [0031]    The catheter assembly  22  further comprises at least one pull wire  42  (depicted in the various figures), providing two pull wire portions  42   a  and  42   b  operatively coupled to the steerable distal portion  26 . Applying a pulling force to one of the at least one pull wires  42  causes steerable distal portion  26  to deflect laterally. 
         [0032]    The shaft portion  24  can be operatively connected to a control handle  44  for manipulating the pull wire portions  42   a  and  42   b . The control handle  44  can be operatively coupled with a controller  46  containing various appurtenances that augment the operation of the catheter system  20 . Handles for the manipulation of the pull wire portions are disclosed, for example, at U.S. Patent Application Publication No. 2011/0251554 to Romoscanu, at U.S. patent application Ser. No. 13/842,349 to Romoscanu et al., filed Mar. 15, 2013, and at U.S. Patent Application No. 61/817,661 to Romoscanu, filed on Apr. 30, 2013, the disclosures of which are owned by the owner of the instant application and which are incorporated by reference herein in their entirety except for express definitions contained therein. It is understood that any control handle suitable for actuation of the two pull wire portions  42   a  and  42   b  can be implemented in the catheter system  20 . 
         [0033]    In another example, end effector  38  can be fitted with an ablation head coupled to an energy source (not depicted). The energy source can be located within the controller  46 . In some embodiments, controller  46  can include analog electronic components to execute the control logic required to monitor operational parameters. 
         [0034]    Referring to  FIGS. 2A through 2C , views of the catheter assembly  22  are depicted in a disclosed embodiment. In one embodiment, the shaft portion  24  includes a shaft section sidewall  62  and the steering portion  26  includes a steering section sidewall  64  that together define a central lumen  66  and a central axis  68  extending through shaft portion  24  and the steering portion  26 . The shaft portion  24  can include first and second shaft sidewall lumens  72  and  74  formed in the shaft section sidewall  62  that extend parallel to the central axis  68  over at least a portion of the length of the shaft portion  24  and passing through the distal end  32  of the shaft portion  24 . 
         [0035]    In one embodiment, the steering portion  26  can include first and second steering section sidewall lumens  76  and  78  formed in the steering section sidewall  64  that extend parallel to the central axis  68  over the entire length of the shaft portion  24  and passing through the distal end  36  of the steering portion  26 . 
         [0036]    The first shaft sidewall lumen  72  is rotationally offset from the second shaft sidewall lumen  74  relative to the central axis  68 . In the depicted embodiment, the rotational offset is 180°, i.e., the first and second shaft sidewall lumens  72  and  74  are diametrically opposed to each other. Likewise, the first steering section sidewall lumen  76  is rotationally offset from the second steering section sidewall lumen  78  in the same manner, such that the first shaft sidewall lumen  72  is in axial alignment with the first steering section sidewall lumen  76  and the second shaft sidewall lumen  74  is in axial alignment with the second steering section sidewall lumen  78 . 
         [0037]    A compression coil  82  having a proximal end  84  and a distal end  86  can disposed in the first steering section sidewall lumen  76 . The compression coil  82  can be disposed within the first steering section sidewall lumen  76  to define a uni-directional bending portion  89 . The uni-directional bending portion  89  is characterized as having a standoff length  88  defined between the proximal end  34  of the steering section  26  and the distal end  86  of the compression coil  82 . The compression coil  82  defines an offset axis  87  that, within the uni-directional bending portion  89 , is substantially parallel to and radially offset from the central axis  68  of the catheter assembly  22 . In one embodiment, the compression coil  82  also extends into the first shaft sidewall lumen  72 . 
         [0038]    In the depicted embodiment, the first and second pull wire portions  42   a  and  42   b  are routed from the handle  44  into the central lumen of the shaft portion  24 . Near the distal end  32  of the shaft portion  24 , the first and second pull wire portions  42   a  and  42   b  are routed into the first and second shaft sidewall lumens  72  and  74 , respectively, where they pass through the first and second steering section sidewall lumens  76  and  78 , respectively. The first pull wire portion  42   a  also passes through the compression coil  82 . 
         [0039]    Referring to  FIGS. 3A and 3B , a formulation of the bending at the distal end  36  of the steering portion  26  of the catheter assembly  22  is depicted in a disclosed embodiment. The  FIG. 3A  depiction illustrates an actuation of the first pull wire portion  42   a  by an axial displacement ΔL, whereas  FIG. 3B  illustrates an actuation of the second pull wire portion  42   b  by the same axial displacement ΔL. The equations for quantifying the various parameters for the flexing operation are as follows: 
         [0000]        LCi=RCi·α   Eq. (1)
 
         [0000]        LIi=RIi·α   Eq. (2)
 
         [0000]        d=RCi·RIi   Eq. (3)
 
         [0000]      Δ Li=LCi·LIi=RCi ·α−( RCi−d )·α= d·α=&gt;α=ΔLi/d   Eq. (4)
 
         [0000]        RCi=LCi /α=( LCi/ΔLi )· d   Eq. (5)
 
         [0000]    where: 
         [0040]    LC=length of the arc bow along the central axis 
         [0041]    RC=bend radius of the arc bow along the central axis 
         [0042]    LI=Length of the arc bow of the actuated pull wire portion along the sidewall lumen 
         [0043]    RI=Radius of the arc bow of the actuated pull wire portion along the sidewall lumen 
         [0044]    ΔL=axial displacement of the actuated pull wire portion 
         [0045]    α=steering angle 
         [0046]    d=radial distance between neutral axis and sidewall lumen 
         [0047]    i=1 or 2 (suffix indicating bend direction 1 or bend direction 2) 
         [0048]    From Eq. 4, the steering angle α depends on the axial displacement ΔLi of the actuated pull wire and the radial distance d. However, from Eq. (5), the bend radius RCi depends on the steering arc length LCi and the angle α, or the axial displacement ΔLi and the radial distance d. Thus, for a given axial displacement ΔLi, the same steering angle αi is provided, independent of the steering arc length LCi, but the bend radius RCi is influenced by the steering arc length LCi. 
         [0049]    In the depicted embodiment, actuation of the pull wire portion  42   a  or  42   b  does not impart an appreciable bend radius on the shaft portion  24  because of the passage of the pull wire portions  42   a ,  42   b  through the central lumen  66 . That is, because the pull wire portions  42   a  and  42   b  are close to the central axis  68  in the shaft portion  24 , which is also the neutral axis of the shaft portion  24 , the actuation axis of the pull wire portions  42   a  and  42   b  and the (neutral) central axis  68  are closely aligned over essentially all of the length of the shaft portion  24  (i.e., small “d” value), so that the shaft portion  24  does not undergo a significant deflection. 
         [0050]    Referring to  FIGS. 4 and 5 , operation of the catheter assembly is depicted in a disclosed embodiment. Functionally, the compression coil  82  introduces an asymmetry that effectively reduces the steering arc length LC1 of  FIG. 3A  by the standoff length  88  of the compression coil into the steering portion  26 . During actuation of the first pull wire portion  42   a  (i.e., on the side of the catheter assembly  22  having the compression coil  82 ), a neutral axis  90  becomes coaxial with the first pull wire portion  42   a  over the length of the compression coil  82  ( FIG. 3A ). Thus, when pull wire portion  42   a  is actuated, the neutral axis  90  lies proximate the central axis  68  at axial locations proximal to and distal to the compression coil  82 ; however, the neutral axis  90  shifts to be substantially coincident with the offset axis  87  over the length of the compression coil  82  ( FIG. 3A ). 
         [0051]    This shifting of the neutral axis  90  effectively eliminates the standoff length  88  from LC1, which, in accordance with the mathematical descriptions of Eqs. (1) through (4), causes a smaller bend radius RC1 than would be realized absent the shift of the neutral axis  90 . Also from Eqs. (1) through (4), while the bend radius RC1 is reduced by the reduction in LC1, the steering angle α remains the same as if there were no shift in the neutral axis. Accordingly, the presence of the compression coil  82  causes a reduction in the bend radius RC1 while not affecting the steering angle α. 
         [0052]    In contrast, during actuation of the second pull wire portion  42   b , which passes through the second sidewall lumen  78 , the neutral axis  90  remains proximate the central axis  68  over the length of the catheter shaft  24  and steering section  26  ( FIG. 4B ). That is, there is no shift of the neutral axis or attendant reduction in the length of LC2. Furthermore, because the compression coil  82  can be laterally deflected and/or extended, so that the compression coil  82  does not inhibit bending of the steering section during actuation of the second pull wire portion  42   b . In accordance with the mathematical descriptions of Eqs. (1) through (4), the bend radius RC2 will be greater than the bend radius RC1 while the steering angle α remains the same. Accordingly, the absence of a compression coil causes a larger bend radius RC2 while not affecting the steering angle α. 
         [0053]    In various embodiments, the coil  82  is a “compression coil” in which its loops are in contact with neighboring loops such that the coil behaves like a rigid tube when loaded on compression. The compressibility of the coil relative to the steering shaft material has a ratio of at least 1:5 in various embodiments. In such embodiments, at equal compression loads, the coil  82  deforms in compression by at least five times less than the surrounding steering shaft. In general, the coil should be as weak as possible in extension. As for tension loads, in certain embodiments, the coil can extend by five times more than the steering shaft extrusion under equal loads, to provide the desired level of compliance. Coil dimensions can vary. In one embodiment, the coil can have an outer diameter of 0.42 mm, an inner diameter of 0.26 mm, and be formed of a 0.003 inch by 0.010 inch rectangular section wire stainless steel. In one embodiment, the assembly is designed so that the outer diameter of the coil  82  does not delaminate from the inner diameter of the sidewall lumen  76 . 
         [0054]    Although a compression coil is disclosed in this embodiment, other uni-directional stiffening members can be utilized as well. A “uni-directional stiffening member” is a device that is rigid in compression and compliant in bending. A compression coil is considered advantageous as it is also compliant upon extension as well. However, an item which is not compliant in bending only but not in extension could be utilized as well. The neutral axis would be defined by the uni-directional stiffening member when the pull wire in the second lumen is placed under tension. In such a case, a non-infinite, but variable bending radius across the standoff length  88  would be obtained. 
         [0055]    A variety of catheter dimensions may be possible for the catheter system discussed in this disclosure. In certain embodiments, an 8 French catheter can be used, although the principles discussed in this disclosure should generally apply to any dimension catheter. 
         [0056]    Referring to  FIG. 6A  an alternate arrangement of the enlarged partial sectional view depicted in  FIG. 2B  of the catheter system  20  is disclosed, according to an embodiment of the disclosure. Specifically, the embodiment shown in  FIG. 6A  discloses a catheter system including a transition piece  100  proximate the abutment of the distal end  32  of the shaft portion  24  with the proximal end  34  of the steering portion  26 . The transition piece  100  is depicted as a generally tubular structure, having a central bore  102  defining a lumen  104  that is axially aligned with the central axis  68  of the catheter system  20 . The transition piece  100  also contains spaced-apart, longitudinally extending slots  106   a  and  106   b  on diametrically opposed sides of the transition piece  100  that provide passageways from the lumen  104  of the transition piece  100  to the exterior periphery of the transition piece  100 . The transition piece  100  extends partially into the central lumen  66  of the shaft portion  24  and partially into the central lumen  66  of the steering portion  26 . 
         [0057]    Accordingly, embodiments with a transition piece  100 , rather than separating the wires to the first and second shaft sidewall lumens  72  and  74  formed in the sides of the shaft portion  24 , as in shown in  FIG. 2 , the transition piece  100  serves as the mechanism by which centrally located pull wire portions  42   a  and  42   b  are routed from the central lumen  66  of the shaft portion  24  to the first and second steering section sidewall lumens  76  and  78  disposed within the sidewalls of the steering portion  26 . In  FIG. 6A , independent first and second shaft sidewall lumens  72  and  74 , having entirely separate bores from the central lumen, are not found within the shaft portion  24 . Rather, first and second channels  110   a  and  110   b  in diametrically opposed sides of the shaft section sidewall are formed over a short axial length at the distal end  32  of the shaft portion  24  to accommodate the pull wire portions  42   a  and  42   b . The channels  110   a  and  110   b  are open to the bore of the central lumen along an length of their perimeters. Both the first and second shaft sidewall lumens  72  and  74 , as well as the first and second channels  110   a  and  110   b , may be more generally referred to as first and second shaft sidewall “passageways” in this disclosure and claims. 
         [0058]    Accordingly, pull wire portions  42   a  and  42   b  can be understood to extend from the catheter handle  44 , through the central lumen  66  of the shaft portion  24 , into the lumen  104  of the transition piece  100 . Next, one pull wire portion  42   a  extends through the slot  106   a  in one side of the transition piece  100  and the other pull wire portion  42   b  through the slot  106   b  in the diametrically opposed wall. The wire portions  42   a  and  42   b  are routed against the outer perimeter of the transition piece  100  in the respective channels  110   a ,  110   b  in the shaft section sidewalls  62  and into the first and second steering section sidewall lumens  76  and  78  as described above, where one pull wire portion  42   a  also extends through a compression coil  82 . 
         [0059]    Referring to  FIG. 6B , an enlarged partial sectional view of the embodiment of the catheter system of  FIG. 6A  is depicted. The cross section of  FIG. 6B  is taken through the portion of the shaft portion extending over the transition piece  100 . Specifically, the cross section is taken through the portion of the distal end  32  on the shaft portion  24 , containing channels  110   a  and  110   b  in the shaft section sidewall  62 , and through the portion of the transition piece that includes slots  106   a ,  106   b . At this axial location, the pull wire portions  42   a  and  42   b  are outside the perimeter of the transition piece  100  and within the channels  110   a  and  110   b  of the shaft section sidewall  62 . 
         [0060]    Referring to  FIG. 7 , a perspective view of the transition piece  100 , pull wire portions  42   a  and  42   b  and the steering portion  26  of the catheter system  20  is depicted based on the embodiments described in  FIGS. 6A and 6B . The proximal shaft portion  24  has been removed for clarity in  FIG. 7 . The pull wire portions  42   a  and  42   b  can be seen entering the lumen  104  of the transition piece  100  and the pull wire portion  42   a  passing through the longitudinal slot  106   a  of the transition piece  100  and into the first steering section sidewall lumens  76  and  78  of the steering portion  26 . The pull wire portion  42   b  is similarly routed through slot  106   b  and sidewall lumen  78  (hidden from view in  FIG. 7 ). 
         [0061]    Referring to  FIG. 8 , a perspective view of the distal end  36  of the steering portion  26  of the catheter system  20  and end effector  38  is depicted in a disclosed embodiment. The pull wire portion  42  is depicted as forming an end loop  120 . The end loop  120  bridges the distal ends of the pull wire portions  42   a  and  42   b  at substantially right angles, the end loop  120  conforming to the exterior periphery of one of the sides of the end effector  38 . In this way, steering with the single pull portion wire  42  is made possible. 
         [0062]    Alternatively, two separate pull wires (not depicted) can be utilized for the pull wire portions  42   a  and  42   b . In this embodiment, the distal ends of the pull wire portions  42   a  and  42   b  can be anchored to the end effector  38  by conventional methods (e.g., gluing, welding, or by a ball-and-slot arrangement). 
         [0063]    It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with an enabling disclosure for implementing the exemplary embodiment or exemplary embodiments. It should be understood that various changes can be made in the function and arrangement of elements without departing from the scope of the invention as set forth in the appended claims and the legal equivalents thereof. 
         [0064]    The embodiments above are intended to be illustrative and not limiting. Additional embodiments may be defined within the claims. Although the present invention has been described with reference to particular embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention. 
         [0065]    Various modifications to the invention may be apparent to one of skill in the art upon reading this disclosure. For example, persons of ordinary skill in the relevant art will recognize that the various features described for the different embodiments of the invention can be suitably combined, un-combined, and re-combined with other features, alone, or in different combinations, within the spirit of the invention. Likewise, the various features described above should all be regarded as example embodiments, rather than limitations to the scope or spirit of the invention. Therefore, the above is not contemplated to limit the scope of the present invention. 
         [0066]    For purposes of interpreting the claims for the present invention, it is expressly intended that the provisions of Section  112 , sixth paragraph of 35 U.S.C. are not to be invoked unless the specific terms “means for” or “step for” are recited in a claim.