Abstract:
An epicardial stabilizer foot comprises a frame configured to reside adjacent to a target portion of a beating heart and a number of self-retaining flexible suction cups attached to the frame for adhering the frame to the surface of the beating heart adjacent the target portion. The frame may be configured to partially surround the target portion with the associated suction cups surrounding the target portion as well. A method for stabilizing a target portion of a beating heart comprises pressing the suction cups of the suction cup stabilizer foot adjacent the target portion of a beating heart to form a partial vacuum attachment therebetween and fixing the position of the frame to prevent motion of the frame relative to the beating heart.

Description:
TECHNICAL FIELD 
       [0001]    The present invention is directed toward surgical tools including surgical tools for cardiac surgery, and more particularly toward an epicardial stabilizer foot for cardiac surgery. 
       BACKGROUND ART 
       [0002]    Off-Pump Coronary Artery Bypass (OPCAB) is coronary surgery that is carried out on the beating heart. Prior to the advent of OPCAB surgery the patient was placed on cardiopulmonary bypass, using a heart lung machine including a cardiotomy reservoir, oxygenator associated connecting tubing and more. Following the commencement of total cardiopulmonary bypass the heart was arrested. The surgeon was then able to operate on a still, and flaccid heart. The OPCAB technique has evolved over the past decade, and started to find increasing acceptance from around 1997 and onwards. Currently, it is estimated that approximately 20%-25% of all coronary bypass surgeries are using OPCAB techniques. 
         [0003]    While a minority of surgeons use OPCAB exclusively, or nearly so, the majority of surgeons using OPCAB use the technique as an adjunct to conventional coronary artery bypass with cardio-pulmonary bypass support. The driving force that brought this operative change includes a reduction in post-operative complications due to embolism or micro-embolism; and the potential to shorten hospital and recovery time and hence reduce overall costs of the treatment procedure. 
         [0004]    To more easily and accurately bypass a coronary artery on the beating heart, the immediate surface of the heart surrounding the anastomotic site must be rendered relatively akinetic. Stabilization of this local area may be achieved by placing a stabilizing foot, attached to a suitably rigid fixture (usually to a sternal retractor), on the surface of the heart partially surrounding the anastomotic site. An arm (articulated or otherwise) is firmly attached between the stabilization foot and the sternal retractor, thus fixing and immobilizing the stabilization foot relative to the general position of the heart. A more detailed description of a representative support arm and a procedure for stabilization can be found in Nguyen, U.S. Patent Application Publication No. US 2003-0158542 A1, the contents of which are expressly incorporated by reference herein. 
         [0005]    Currently available stabilization feet include: 
         [0006]    a) Rigid “U” shaped mechanical foot (Guidant ACROBAT™ mechanical off-pump system, Genesee BioMedical ANASTOSURE™ stabilizer, and similar mechanical friction feet from Estech, US Surgical and Genzyme). A foot having a high friction face is pushed onto the surface of the heart, and the friction forces generated between the foot and the surface of the heart renders the area of the heart within the area of the foot relatively akinetic. 
         [0007]    b) Active vacuum, multi-port foot connected via a flexible tube to a controlled vacuum source (Medtronic Octopus® 4.3 Tissue Stabilizer, Guidant ACROBAT™ SUV Vacuum Off-Pump System). The foot is place onto the heart, the vacuum is turned on and the partial vacuum in the space between the surface of the heart and the vacuum port of the epicardial stabilizer causes the stabilizer to cling to the surface of the heart, generating the stabilization force. These devices have the disadvantage that they require an external vacuum source and vacuum regulator, vacuum tubing and blood trap, all which add to the complexity and cost of the procedure. 
         [0008]    The majority of the devices currently marketed for myocardial stabilization are single patient use. Usually, the arm and the foot are disposable. One exception is the Genesee BioMedical LocNess® Tissue stabilizer system that utilizes a reusable arm and disposable Anastosure™ mechanical epicardial stabilizer feet, described in U.S. Publication No. US 2003-0158542 A1. 
         [0009]    The stabilizer feet currently available rely solely upon friction forces or require connection to a vacuum source to secure the epicardial surface of a beating heart. Those dependent on friction require considerable downward force on the heart that can be difficult to maintain. Those requiring a vacuum source implicate tubes and equipment that can crowd an operating theater. 
         [0010]    The present invention is intended to overcome one or more of the problems associated with the stabilizer feet discussed above. 
       SUMMARY OF THE INVENTION 
       [0011]    A first aspect of the invention is an suction stabilizer foot comprising a frame configured to reside adjacent to a target portion of a beating heart and a number of self retaining flexible suction cups attached to the frame for adhering the frame to the surface of the beating heart adjacent the target portion. In one embodiment, the frame partially surrounds the target portion and the associated suction cups partially surround the target portion as well. In such an embodiment the frame may comprise two arms extending substantially in parallel joined at their proximal ends to a bridge extending therebetween. The suction cups are spaced lengthwise of each of the extending arms. The arms may be canted relative to each other along a lengthwise axis to define a substantially concave configuration therebetween or the arms may be coplanar. The frame may be malleable to allow a surgeon to conform the frame to the surface of the heart adjacent a target portion. 
         [0012]    A second aspect of the invention is a method for stabilizing a target portion of a beating heart. A frame having at least two suction cups attached thereto is provided. The suction cups are pressed onto tissue adjacent the target portion of the beating heart to form a partial vacuum attachment therebetween. The position of the frame is fixed to prevent motion of the frame. The method may further include providing suture stays spaced along the frame and pressing the suction cups to partially surround a lengthwise portion of the target artery. Sutures are inserted around axially spaced lengthwise portions of the target artery to form a loop around each axially spaced lengthwise portion of the target artery. The sutures are tensioned to occlude the lengthwise portions of the target artery and attached to the suture stays. The frame may comprise two elongate arms extending substantially in parallel joined at proximal ends to a bridge extending therebetween, at least two of the plurality of suture stays and at least two suction cups being spaced along the length of each lengthwise arm. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0013]      FIG. 1  is a perspective view of a sternal retractor having a support arm clamped thereto with a suction cup stabilizer foot in accordance with the present invention attached to a distal end of the support arm; 
           [0014]      FIG. 2  is a perspective view of the suction cup stabilizer foot of  FIG. 1 ; 
           [0015]      FIG. 3  is a plan view of the suction cup stabilizer foot of  FIG. 2 ; 
           [0016]      FIG. 4  is a cross-section of the suction cup stabilizer foot taken along line A-A of  FIG. 3 ; 
           [0017]      FIG. 5  is a perspective view of a second embodiment of a suction cup stabilizer foot in accordance with the present invention; 
           [0018]      FIG. 6  is a plan view of the second embodiment of the suction cup stabilizer foot of  FIG. 5 ; 
           [0019]      FIG. 7  is a cross-section of the second embodiment of the suction cup stabilizer foot taken along line B-B of  FIG. 6 ; 
           [0020]      FIG. 8  is a cross-section of a suction cup stabilizer leg taken along line A-A of  FIG. 3  showing an alternate embodiment of an attachment button allowing for gimbaled movement of the suction cup relative to a frame; 
           [0021]      FIG. 9 . is a perspective view of a third embodiment of a suction cup stabilizer foot; 
           [0022]      FIG. 10  is a fourth embodiment of a suction cup stabilizer foot; 
           [0023]      FIG. 11  is a fifth embodiment of a suction cup stabilizer foot; 
           [0024]      FIG. 12  is a cross-section of the suction cup stabilizer as shown in  FIG. 4  attached to an epicardial surface of a heart. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0025]      FIG. 1  is a perspective view of a support arm  10  for assisting in the performance of cardiac surgery attached to a blade arm of a sternal retractor  12 . Attached at a distal end  14  of the support arm  10  is a suction cup stabilizer foot  16 . 
         [0026]    The support arm  10  is described in detail in U.S. Patent Application Publication No. US 2003-0158542 A1. The support arm  10  is intended for connection to a sternal retractor  12  as illustrated in  FIG. 1  and the support arm  10  facilitates stationary or fixed placement of suction cup stabilizer foot  16  relative to a patient&#39;s heart to immobilize or stabilize a target portion of a beating heart through a procedure described in Publication No. US 2003-0158542 A1. While this application speaks to the suction cup stabilizer foot for use in association with the stabilization of a target portion of a beating heart, it should be appreciated by those of skill in the art that the suction cup stabilizer foot could be used for stabilization of other tissue in a human or other animal in conjunction with a support arm and sternal retractor or any other support fixture that allows the suction cup stabilizer foot  16  to be stationary or fixed relative to the target tissue. 
         [0027]    A first embodiment of the suction cup stabilizer foot  16  is shown in perspective view in  FIG. 2 . The suction cup stabilizer foot  16  includes a frame  18  having first and second arms  20 ,  22  extending in parallel from a bridge  24  joining proximal ends of first and second arms  20 ,  22 . An attachment ball  26  extends from the frame  18 , and more particularly from the bridge  24 , to allow for gimbaled attachment of the suction cup stabilizer foot  16  to the distal end  14  of a support arm  10  as described in Publication No. US 2003-0158542 A1. The frame  18 , including the arms  20 ,  22 , the bridge  24  and the attachment ball  26  are made of a rigid material, for example, stainless steel. As illustrated in  FIG. 2 , the bridge  24  has an arch shape extending between the first and second arms  20 ,  22 . It is also within the scope of the present invention that the bridge  24  resides within a single plane between the first and second arms  20 ,  22  in the manner depicted in FIG. 11A of Publication No. US 2003-0158542 A1. The arched bridge allows the device to be used for anastomosis without occluding a target blood vessel (i.e., vein or artery). The arched bridge may not be necessary because suction cups  32  space the bridge above the target blood vessel to prevent occlusion. 
         [0028]    Spaced lengthwise along the first and second arms  20 ,  22  are a number of holes  28  (see  FIG. 4 ) receiving attachment buttons  30  of suction cups  32 . Referring to  FIG. 4 , the suction cups  32  each consist of a cup  34  with the button  30  extending opposite the cup  34  and an annular groove  36  between the button  30  and the back surface of the cup  34 . As depicted in  FIG. 4 , this configuration of the cup allows the button to be snap fit into the hole  28  with the annular groove  36  receiving an edge of the hole  28  to secure the suction cup  32  to the first and second legs  20 ,  22 . The suction cups  32  may be integrally formed of a biocompatible rubber such as silicone rubber. Forming the suction cups of a material having a durometer of about 50 Shore A has proven effective. 
         [0029]    As illustrated in  FIG. 4 , the first and second legs  20 ,  22  are canted relative to each other about a lengthwise axis in a concave manner facilitating attachment to convex surfaces. 
         [0030]      FIG. 5  is a second embodiment of the suction cup stabilizer foot  60  in accordance with the present invention. The second embodiment  60  is substantially identical to the suction cup stabilizer foot  16  illustrated in  FIGS. 2-4  and like reference numbers are used to describe like elements. Referring to  FIG. 7 , the difference between the first embodiment  16  and second embodiment  60  of the suction cup stabilizer foot is in the second embodiment  60  the first and second legs  20 ,  22  are not canted relative to each other and reside within substantially the same plane. The second embodiment of the suction cup stabilizer foot  60  would therefore be of advantage for stabilizing substantially planar tissue surfaces. 
         [0031]    In another alternate embodiment, the suction cups  32  have a gimbaled attachment to the first and second legs of the frame  18 . The gimbaled attachment facilitates stabilization of non-uniform epicardial and other tissue surfaces. Such a gimbaled attachment can also obviate the need for canted first and second legs  20 ,  22  as illustrated with respect to the first embodiment in  FIGS. 2-4 . The gimbaling could be provided through a relatively simple structure illustrated in  FIG. 8  where an underside of the button  30  has an arcuate surface  38  to enable gimbaled movement of the suction cup  32  relative to the frame  18 , such as a ball and socket connection. As appreciated by those of skill in the art, any number of substitute attachment structures between the suction cup  32  and the frame  18  could be provided to enable gimbaled movement of the suction cup  32  relative to the frame  18 . 
         [0032]    Also shown in  FIG. 8  is a mushroom-shaped cavity  39  in the wall of the cup  34 . This cavity will receive blood or other fluid in use while inhibiting removal of fluid from the cavity. In this manner, the cavity  39  renders the suction cup incapable of adequate sanitization. This feature will encourage disposal of the suction cups and minimize any practice of reusing the suction cups which could present a disease vector and a health hazard. The cavity  39  may be used in any embodiment of the suction cup stabilizer disclosed herein or within the scope of the claims. 
         [0033]    A third embodiment of a suction cup stabilizer  100  in accordance with the present invention is shown in perspective view in  FIG. 9 . The third embodiment  100  is similar in structure to the suction cup stabilizer foot  16  illustrated in  FIGS. 2-4  and like reference numbers are used to describe like elements. The third embodiment differs by providing a number of sutures stays  102  spaced lengthwise of the arms  20 ,  22 . The third embodiment  100  also includes a pinch cleat  104  at a proximal end of the arm  20 . The pinch cleat  104  consists of a number of tines  106  having V-shaped slots  108  between adjacent tines  106 . The V-shaped slots  108  are configured to pinch a suture  110  therein to retain it in place as illustrated in  FIG. 10 . 
         [0034]    In use, the third embodiment of the suction cup stabilizer foot  100  is oriented with the arms  20 ,  22  extending lengthwise of a portion of a target artery. One or more vascular loops  110  are formed into loops  112  around axially spaced lengthwise portions of the target artery. The frame  18  is pressed onto the heart to create a partial vacuum between the epicardial tissue and the suction cups, attaching the suction cups to the heart. The vascular loop  110  is then tensioned to occlude the lengthwise portions of the target artery. Ends of the suture are secured within the pinch cleat  104  to maintain the tension in the vascular loop. The act of looping the vascular loop around the target artery not only occludes the target artery, it also serves to elevate the target artery relatively to the epicardium to improve access and to further secure the suction cup stabilizer foot to the surface of the heart. 
         [0035]      FIG. 10  is a fourth embodiment of the suction cup stabilizer foot  200  that is substantially identical to the third embodiment  100  of  FIG. 10 , only the attachment ball  26  is replaced by an attachment post  202 . The attachment post  202  has an annular slot  204  which can receive a pin at a distal end of a support arm assembly such as the snout 332 illustrated in FIG. 4C of U.S. Patent Publication No. US 2003-0158542 A1. The attachment post  202  allows the stabilizer foot  200  pivot about the axis of the post  202  but does not permit fully gimbaled movement of the suction cup stabilizer foot  200 . The attachment post  202  may be substituted for the attachment ball in any embodiment discussed herein or within the scope of the claims. 
         [0036]      FIG. 11  illustrates a fifth embodiment  300  which is substantially identical to the fourth embodiment  200  of  FIG. 11 . The only difference is that a cog  302  is disposed about the base of the post  202 . The cog  302  may be engaged by a structure similar to the snout described above with respect to  FIG. 11  to more rigidly secure the fifth embodiment of the suction cup stabilizer  300  against pivoting about the axis of the attachment post  202 . Again, this form of the attachment post could be used with any embodiment of the invention. 
         [0037]      FIG. 12  illustrates the suction cup stabilizer applied to the epicardium  40  of a heart bridging and parallel to a target coronary artery  43 . More particularly, the first embodiment  16  with the first and second feet  20 ,  22  defining an essentially concave relation therebetween is shown adhered to a convex target portion  42  of the epicardium bridging and parallel to a target coronary artery  43 . With the suction cup stabilizer foot  16  adhered as illustrated in  FIG. 8  and the attachment ball  26  attached to a distal end  14  of a support arm  10  which is in turn attached to a sternal retractor  12  deployed in open heart surgery, the target portion  42  of the epicardium is thereby stabilized notwithstanding continued beating of the heart. 
         [0038]    The frame, including the arms, may be made of a malleable material to enable a surgeon to bend and conform the frame to approximate the profile of a target portion of the heart. Such a frame material may be included in all embodiments disclosed herein and within the scope of the claims. One sample material is 304 stainless steel having a thickness of 0.034 inch. 
         [0039]    In use, the suction cups are adhered to a tissue surface by placing the mouth of each cup  34  into contact with the tissue surface and exerting a normal force on the frame that causes the cups  34  to distort as illustrated in  FIG. 9  and displace air within the cups  34 , thereby creating a partial vacuum with the tissue surface. It may be necessary or desired to first wet the perimeter of the cup  34  mouth with a suitable liquid such as saline, glycerol or water to ensure a seal enabling the partial vacuum to secure the tissue. 
         [0040]    The first, second, third, fourth and fifth embodiments  16 ,  60 ,  100 ,  200 ,  300  as described herein have parallel arms  20 ,  22  (and  20 ′,  22 ′) which, as illustrated in  FIG. 12 , partially surround a target portion  42  of an epicardium. The suction cup stabilizer foot  16  may be suitable for use in stabilizing a target portion of an epicardium if it consists of only a single arm having more than one suction cup attached to and partially surrounding a target portion of an epicardium surface. Other configurations of the suction cup epicardial stabilizer are also considered to be within the scope of the invention, including an annular frame with suction cups deployed therein, an arcuate frame, an L-shaped frame, the generally U-shaped frame of the first and second embodiments  16 ,  60  (which could also include a suction cup on the bridge  24 ) as well as any other structure deploying the suction cups performing a stabilizing function on a target portion of the epicardium or other bodily tissue upon which the suction cup stabilizer foot is deployed. 
       EXAMPLE 
       [0041]    Performance of a suction cup stabilizer substantially as illustrated in  FIGS. 2-4  was compared to a Genesee Biomedical ANASTOSURE™ stabilizer, model Number MSS-SRN and a suction cup stabilizer with the suction cups compromised to prevent formation of the partial vacuum. The suction cup stabilizers included six suction cups, each 0.5 inch in diameter and made of a silicon elastomer having a hardness of about Shore 50 A. 
         [0042]    Tests were conducted on fresh pig hearts (weighing approximately 380 gm). Perfused pig hearts had a perfusion catheter placed in the left coronary ostia and retained in place by an external suture. The left coronary tree was perfused with room temperature tap water at a pressure of about 75-80 mm Hg, which inflated the left ventricle of the heart. The surface of the heart was moistened. 
         [0043]    In those tests using the suction cup stabilizer, the suction cup stabilizer was firmly pressed down onto the left ventricular epicardium causing it to attach and the downward pressure was released. 
         [0044]    In those tests using the compromised suction cup stabilizer the procedure was the same, only the suction cups did not attach. 
         [0045]    In those tests using the ANASTOSURE™ stabilizer, the method was similar only no weight or the indicated weights were applied vertically to the stabilizer. 
         [0046]    Table 1 sets forth a vertical adhesion force produced by the suction cup stabilizer on a perfused pig heart. Table 2 sets forth a vertical adhesion force produced by the suction cup stabilizer on a flaccid pig heart. 
         [0047]    Table 3 sets forth a shear force produced by the suction cub stabilizer on a perfused pig heart. The shear force was applied substantially parallel to the legs of the stabilizer in all tests. Table 4 sets forth the shear force produced by a compromised suction cup stabilizer on a perfused pig heart. Table 5 shows a shear force produced by the ANASTOSURE™ stabilizer under a zero and a four ounce applied vertical load. 
         [0048]    Tables 3-5 demonstrate significantly improved shear force of the suction cup stabilizer when employed on a perfused pig heart over the compromised suction cup stabilizer and the ANASTOSURE™ stabilizer even under an applied load of 4 ounces. 
         [0049]    Table 6 sets forth a shear force of the suction cup stabilizer on a flaccid pig heart under loads of zero and four ounces. Table 7 sets forth a shear force of the compromised suction cup stabilizer on the flaccid pig heart under no load. Table 8 sets forth a shear force of an ANASTOSURE™ stabilizer under vertical loads of zero, four and eight ounces. 
         [0050]    While under an applied vertical load of eight ounces, the ANASTOSURE™ stabilizer produced the highest shear force on a flaccid heart, the suction cup stabilizer produced superior shear forces under zero or four ounce loads. Data for shear force of the suction cup stabilizer under a vertical load of eight ounces was not collected. 
         [0051]    The suction cup stabilizer of the present invention provides an inexpensive means for stabilizing an epicardial surface without requiring connection to a vacuum source as contemplated in prior art vacuum stabilizers. The suction cup stabilizer provides a suction grip providing a higher degree of stabilization than is possible from friction based devices under minimal vertical loads, such as those devices described and illustrated in Publication No. US 2003-0158542 A1, the Guidant Acrobat Mechanical Off Pump System and comparable systems of U.S. Surgical, Genzyme, Genesee Biomedical and Estech. The suction cup stabilizer can be inexpensively manufactured, thus facilitating its use and the many inherent advantages. 
         [0000]    
       
         
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Applied Vertical Load oz 
                 Vertical Pull (lbs) 
               
               
                   
                   
               
             
             
               
                   
                 0 
                 0.70 
               
               
                   
                 0 
                 0.72 
               
               
                   
                 0 
                 0.84 
               
               
                   
                 0 
                 0.78 
               
               
                   
                 0 
                 0.94 
               
               
                   
                 0 
                 0.84 
               
               
                   
                 0 
                 1.28 
               
               
                   
                 0 
                 1.00 
               
               
                   
                 0 
                 0.84 
               
               
                   
                 0 
                 1.02 
               
               
                   
                   
                 Mean 0.896, SD 0.17 
               
               
                   
                   
               
             
          
         
       
     
         [0000]    
       
         
               
               
               
             
           
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                 Applied Vertical Load oz 
                 Vertical Pull (lbs) 
               
               
                   
                   
               
             
             
               
                   
                 0 
                 0.22 
               
               
                   
                 0 
                 0.44 
               
               
                   
                 0 
                 0.18 
               
               
                   
                 0 
                 0.36 
               
               
                   
                 0 
                 0.38 
               
               
                   
                 0 
                 0.16 
               
               
                   
                 0 
                 0.40 
               
               
                   
                 0 
                 0.38 
               
               
                   
                 0 
                 0.38 
               
               
                   
                 0 
                 0.28 
               
               
                   
                   
                 Mean 0.32, SD 0.01 
               
               
                   
                   
               
             
          
         
       
     
         [0000]    
       
         
               
               
               
             
           
               
                   
                 TABLE 3 
               
               
                   
                   
               
               
                   
                 Applied Vertical Load oz 
                 Shear Pull (lbs) 
               
               
                   
                   
               
             
             
               
                   
                 0 
                 0.30 
               
               
                   
                 0 
                 0.18 
               
               
                   
                 0 
                 0.26 
               
               
                   
                 0 
                 0.28 
               
               
                   
                 0 
                 0.42 
               
               
                   
                 0 
                 0.34 
               
               
                   
                 0 
                 0.34 
               
               
                   
                 0 
                 0.38 
               
               
                   
                   
                 Mean 0.31, SD 0.08 
               
               
                   
                   
               
             
          
         
       
     
         [0000]    
       
         
               
               
               
             
           
               
                   
                 TABLE 4 
               
               
                   
                   
               
               
                   
                 Applied Vertical Load oz 
                 Shear Pull (lbs) 
               
               
                   
                   
               
             
             
               
                   
                 0 
                 0.00 
               
               
                   
                 0 
                 0.00 
               
               
                   
                 0 
                 0.02 
               
               
                   
                 0 
                 0.00 
               
               
                   
                 0 
                 0.02 
               
               
                   
                 0 
                 0.00 
               
               
                   
                   
                 Mean 0.007, SD 0.01 
               
               
                   
                   
               
             
          
         
       
     
         [0000]    
       
         
               
               
               
             
               
               
               
             
           
               
                   
                 TABLE 5 
               
               
                   
                   
               
               
                   
                 Applied Vertical Load oz 
                 Shear Pull (lbs) 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 0 
                 0 
               
               
                   
                 0 
                 0 
               
               
                   
                 0 
                 Mean 0 
               
               
                   
                 4 
                 0.14 
               
               
                   
                 4 
                 0.20 
               
               
                   
                 4 
                 0.20 
               
               
                   
                 4 
                 0.26 
               
               
                   
                 4 
                 0.20 
               
               
                   
                   
                 Mean 0.20, SD 0.04 
               
               
                   
                   
               
             
          
         
       
     
         [0000]    
       
         
               
               
               
             
           
               
                   
                 TABLE 6 
               
               
                   
                   
               
               
                   
                 Applied Vertical Load oz 
                 Shear Pull (lbs) 
               
               
                   
                   
               
             
             
               
                   
                 0 
                 0.22 
               
               
                   
                 0 
                 0.26 
               
               
                   
                 0 
                 0.22 
               
               
                   
                 0 
                 0.30 
               
               
                   
                 0 
                 0.30 
               
               
                   
                 0 
                 0.36 
               
               
                   
                 0 
                 0.22 
               
               
                   
                 0 
                 Mean 0.29, SD 0.05 
               
               
                   
                 4 
                 0.36 
               
               
                   
                 4 
                 0.32 
               
               
                   
                 4 
                 0.36 
               
               
                   
                 4 
                 0.42 
               
               
                   
                 4 
                 Mean 0.37, SD 0.04 
               
               
                   
                   
               
             
          
         
       
     
         [0000]    
       
         
               
               
               
             
               
               
               
             
           
               
                   
                 TABLE 7 
               
               
                   
                   
               
               
                   
                 Applied Vertical Load oz 
                 Shear Pull (lbs) 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 0 
                 0.02 
               
               
                   
                 0 
                 0 
               
               
                   
                 0 
                 0.02 
               
               
                   
                 0 
                 0 
               
               
                   
                 0 
                 0.06 
               
               
                   
                 0 
                 0 
               
               
                   
                 0 
                 0.04 
               
               
                   
                   
                 Mean 0.02, SD 0.02 
               
               
                   
                   
               
             
          
         
       
     
         [0000]    
       
         
               
               
               
             
               
               
               
             
           
               
                   
                 TABLE 8 
               
               
                   
                   
               
               
                   
                 Applied Vertical Load oz 
                 Shear Pull (lbs) 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 0 
                 0 
               
               
                   
                 0 
                 0 
               
               
                   
                 0 
                 Mean 0 
               
               
                   
                 4 
                 0.30 
               
               
                   
                 4 
                 0.32 
               
               
                   
                 4 
                 0.34 
               
               
                   
                 4 
                 0.28 
               
               
                   
                 4 
                 0.34 
               
               
                   
                 4 
                 Mean 0.32, SD 0.03 
               
               
                   
                 8 
                 0.58 
               
               
                   
                 8 
                 0.56 
               
               
                   
                 8 
                 0.54 
               
               
                   
                 8 
                 0.54 
               
               
                   
                 8 
                 0.58 
               
               
                   
                 8 
                 Mean 0.56, SD 0.02