Abstract:
To provide an artificial annulus sizing tool capable of determining a suitable size for an artificial annulus to be implanted in a patient. 
     [Solution] An artificial annulus sizing tool comprising an annular core material and a cover material covering the core material to a predetermined thickness, the cover material portion being attached to the annulus using suturing thread for implanting artificial annuli, and the part of the cover material engaged with the suturing thread being broken after a suitable artificial annulus size is determined for the annulus, allowing for removal from the suturing thread.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to an artificial annulus sizing tool used to determine the size of an artificial annulus when implanting an artificial-annulus-forming member as treatment for insufficiency of the mitral valve situated between the left atrium and the left ventriculum. 
       BACKGROUND OF THE INVENTION 
       [0002]    A backflow-preventing valve referred to as the mitral valve is located between the left atrium and the left ventriculum of the heart. The mitral valve opens simultaneously with the contraction of the left atrium, sending blood into the left ventriculum, and closes simultaneously with the contraction of the left ventriculum, serving to prevent the flow of blood back to the left atrium. 
         [0003]      FIG. 1  depicts the mitral valve. The mitral valve comprises a roughly ellipsoid annulus  1  situated between the left atrium and the left ventriculum, and two leaflets, an anterior leaflet  2  and a posterior leaflet  3 , that extend from the annulus  1  toward the left ventriculum. During diastole, negative pressure forms in the interior of the left ventriculum, causing the anterior leaflet  2  and posterior leaflet  3  to open so that blood flows from the left atrium to the left ventriculum; during systole, positive pressure forms in the interior of the left ventriculum, causing the anterior leaflet  2  and the posterior leaflet  3  to coapt and preventing the flow of blood from the left ventriculum back to the left atrium. 
         [0004]    However, the annulus  1  of the mitral valve can, through various causes, expand or become enlarged, with the result that the anterior leaflet  2  and posterior leaflet  3  do not coapt, allowing slight amounts of blood to flow back even during systole. This condition is known as mitral valve insufficiency, and is typically treated via mitral valve annuloplasty. 
         [0005]    In mitral valve annuloplasty, an artificial annulus is sutured to the annulus in order to correct the expanded annulus  1  back to its original size.  FIG. 2  is a schematic illustration of a process of fitting an artificial annulus  4  to the expanded annulus  1  and suturing the former to the latter. Because the diameter of the annulus  1  varies between patients, it is vital to select an artificial annulus of a suitable size for the artificial annulus  4 . Therefore, a special measure (annulus sizing tool)  5  known as a “sizer” is conventionally placed against the afflicted area to measure the diameter of the annulus, as shown in  FIG. 3 . The surface area of the anterior leaflet  2  and the commissural distance H between the anterior leaflet  2  and the posterior leaflet  3 , as shown in  FIG. 1 , is used as the standard for selecting the size of the artificial annulus  4  during this process. 
         [0006]    In order to measure these two items (surface area and commissural distance), a conventional sizer  5  comprises two notches  6 ,  7 , as shown in  FIG. 3 , that are matched with the commissural distance. A flat plate section corresponds to the surface area of the anterior leaflet, and the sizer  5  exhibiting the nearest dimensions and area yields the size of the optimal artificial annulus  4  for the patient. 
         [0007]    However, selection standards may vary depending upon the condition suffered by the patient; for example, a downsizing approach is effective in selecting a suitable artificial annulus size for patients suffering functional mitral valve insufficiency. Meanwhile, it is recommended to select the larger size when selecting from two sizes for patients exhibiting dystrophic valve disease. As can be seen, then, there is no unified standard for selection. 
         [0008]    In addition, mitral valve annuloplasty is a procedure performed under extracorporeal circulation using a cardiopulmonary bypass; thus, during the procedure, there is no blood in the heart, and the mitral valve maintains a shape not seen in natural physiological conditions. Therefore, it is difficult to reliably determine a suitable size for an artificial annulus when using a sizer such as described above during the procedure. 
         [0009]    If, by chance, an artificial annulus not matching the diameter of the mitral valve of the patient is selected, there is a risk of blood flowing back through the mitral valve after the procedure, leading to complications. Moreover, if a flaw in the repair of the mitral valve is discovered following the procedure, the artificial annulus must be swapped out or replaced with an artificial valve; however, as the insurance costs of artificial annuli can run into the hundreds of thousands of yen, replacing annuli during surgery presents an extremely weighty economic burden, which creates another difficulty. 
         [0010]    One strategy for solving these problems is the invention disclosed in patent document 1. 
         [0011]    The invention disclosed in patent document 1 is a pseudo-artificial annulus that has a size different from that of an ordinary sizer and a shape corresponding to that of an artificial annulus, with engaging projections for engaging artificial annulus suturing thread being provided on the surface thereof, and annulus suturing thread being wrapped around the engaging projections in order to engage there with and anchor the sizer to the annulus. In accordance with this invention, this pseudo-artificial annulus can be used to perform a valve function evaluation test using physiological saline before the artificial annulus is attached, allowing for reliable evaluation of the size of the artificial annulus to be attached. In addition, the document indicates that, when removing the pseudo-annulus from the annulus, the artificial annulus suturing thread need only be removed from the engaging projections, simplifying the process. 
         [0012]    However, in the invention disclosed in patent document 1, it is necessary to wrap suturing thread around the projections on the pseudo-annulus; this wrapping action is not present in ordinary clinical techniques. For example, the thread tends to slacken during wrapping, and it is difficult to sense the state of the thread when adjusting pressure following wrapping. Therefore, this pseudo-annulus cannot be considered as being sutured in a manner similar to that actually used in clinical practice in a state similar to an actual artificial annulus. Therefore, using a pseudo-annulus of this sort cannot be considered to yield reliable valve function evaluation. 
         [0013]    In addition, because the projections have outer diameters of only a few millimeters, the suturing thread exhibits a high level of curvature (bending) when being wrapped. The projections are rigid, and present the risk of damage to the thread. In addition, the positions of the projections are fixed. Therefore, it is impossible to alter the suturing position or number of sutures to fit the situation. 
         [0000]    Patent document 1: Unexamined Japanese Patent Application Publication 2008-104472 
       SUMMARY OF THE INVENTION 
       [0014]    The present convention was conceived in view of these circumstances, and has an object of providing a sizer that is capable of evaluating post-operative mitral valve leakage and valve behavior even when the mitral valve is in a non-physiological state. In particular, an object of the present invention is to provide a sizer that allows the evaluation described above to be performed swiftly and without placing burdens upon patients undergoing extracorporeal circulation, and allows mitral valve behavior to be evaluated via a method that is inexpensive and can easily be adopted at hospitals. 
         [0015]    In order to attain the objects described above, a main aspect of the present invention is an artificial annulus sizing tool comprising an annular core material and a cover material covering the core material to a predetermined thickness, the cover material portion being attached to the annulus using suturing thread for implanting artificial annuli, and the part of the cover material engaged with the suturing thread being broken after a suitable artificial annulus size is determined for the annulus, allowing for removal from the suturing thread, the cover material being formed so that the break strength thereof with respect to the suturing thread is such that a physician can perform said breakage by applying force of a level that will not damage the annular tissue and so that the material will not break when a force is applied that is less than the force of a level that will not damage the annular tissue applied by the physician during said breakage. 
         [0016]    In the embodiments of the present invention, the following aspects are essential. 
         [0017]    1) Having a Suitable Break Strength 
         [0018]    The artificial annulus sizing tool of the present invention will not function if the break strength thereof is too high or too low. 
         [0019]    A suitable range for break strength is a level of strength such that failure will not occur when the cover material is sutured with the suturing thread and the physician performs sizing, and also a level allowing for easy breakage when the artificial annulus sizing tool of the present invention is held in one hand and the suturing threads are pulled with the other hand. 
         [0020]    A level of strength allowing for easy breakage is a level that will not burden the annular tissue of the patient during the act of breaking, or that will not cause a physician to be concerned about the risk of such. 
         [0021]    2) No Off-Gassing 
         [0022]    The artificial annulus sizing tool of the present invention is used within the human body, especially the interior cavities of the heart. When breaking the cover material following sizing, it is imperative that no fragments of the cover material separate from the base material and remain within the interior cavities of the patient&#39;s heart. Therefore, the cover material of the present invention must be of a material and structure that permits only the suturing threads to release and produces no other fragments or gas. 
         [0023]    For example, in an embodiment of the present invention, break strength can be adjusted so as to satisfy the conditions described above by adding oil to a silicone resin constituting a main component of the cover material during manufacture. 
         [0024]    In accordance with one embodiment of the present invention, the break strength is set so as to be in a range of 0.2 N to 4.5 N when breaking using #20 suture thread. 
         [0025]    In accordance with another embodiment, the artificial annulus sizing tool configured as described above is modeled after the external shape and size of the artificial annulus being sized, and several types of tools are prepared according to various shapes and sizes. 
         [0026]    In accordance with yet another embodiment, the core material has a letter-C shape. Alternatively, the core material may have an endless ring shape. 
         [0027]    In accordance with yet another embodiment, the core material is formed by injection molding a resin material. 
         [0028]    In accordance with yet another embodiment, the cover material comprises a reinforcing material and a cushioning material that envelops the cover material and covers the core material, and the suturing thread is passed through the cover material so as to penetrate the resin material and the reinforcing material. 
         [0029]    In accordance with yet another embodiment, the cushioning material is silicone resin. 
         [0030]    In accordance with yet another embodiment of the artificial annulus sizing tool, the cover material has a specific level of viscoelasticity so as only to be broken by the suturing thread without shedding any material. 
         [0031]    In accordance with the present invention, the following effects can be obtained. 
         [0000]    (1) Because the artificial annulus sizing tool of the present invention is directly sewn in place using thread used to suture the artificial annulus in place, and can be immediately removed, no special preparations are necessary, and the tool can easily be incorporated into the surgical theater.
 
(2) Following suturing to the mitral valve, the area can be flushed using physiological saline to visually evaluate leakage and changes in the shape of the mitral valve, allowing for more reliable selection of an artificial annulus of optimal size.
 
(3) Only a very short time, on the order of a few minutes, is necessary from suturing until evaluation, and there is little effect upon operating time, thus also reducing the burden placed upon the patient.
 
         [0032]    Other features and noteworthy effects of the present invention will be apparent to a person skilled in the art from the embodiment described in the “Best mode for embodying the invention” section and from the drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0033]      FIG. 1  is a schematic illustration of the mitral valve. 
           [0034]      FIG. 2  is a schematic illustration of an artificial annulus being attached. 
           [0035]      FIG. 3  is a schematic illustration of a method of using a conventional example of a sizer. 
           [0036]      FIG. 4  is a plan view of a sizer according to an embodiment of the present invention. 
           [0037]      FIG. 5  is a longitudinal cross-sectional view of the embodiment along line A-A in  FIG. 4 . 
           [0038]      FIG. 6  is a longitudinal cross-sectional view of the embodiment along line B-B in  FIG. 4 . 
           [0039]      FIG. 7  is a magnified schematic illustration of the cross-sectional surface of the embodiment. 
           [0040]      FIG. 8  is a schematic illustration of a good example of suturing thread insertion in the embodiment. 
           [0041]      FIG. 9  is a schematic illustration of a poor example of suturing thread insertion in the embodiment. 
           [0042]      FIG. 10  is a flow chart for a method of manufacturing a sizer according to the embodiment. 
           [0043]      FIG. 11  is a schematic illustration of a fiber material being cut according to the embodiment. 
           [0044]      FIG. 12  is a schematic illustration of a core material being bent according to the embodiment. 
           [0045]      FIG. 13  is a schematic illustration of molding using a mold according to the embodiment. 
           [0046]      FIG. 14  is a schematic illustration of a molded article being bent and shaped according to the embodiment. 
           [0047]      FIG. 15  is a schematic illustration of a process of attaching and removing a sizer in the embodiment. 
           [0048]      FIG. 16  is a schematic illustration of a process of attaching and removing a sizer in the embodiment. 
           [0049]      FIG. 17  is a schematic illustration of a process of attaching and removing a sizer in the embodiment. 
           [0050]      FIG. 18  is a schematic illustration of a process of attaching and removing a sizer in the embodiment. 
           [0051]      FIG. 19  is a plan view of a sizer according to another embodiment of the present invention. 
           [0052]      FIG. 20  is a plan view of a sizer according to another embodiment of the present invention. 
           [0053]      FIG. 21  is a graph of testing results. 
           [0054]      FIG. 22  is a graph of testing results. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0055]    An embodiment of the present invention will now be described with reference to the attached drawings. In the following description, the artificial annulus sizing tool of the present invention will be referred to as a “sizer”. 
         [0056]    (Configuration of Sizer) 
         [0057]      FIG. 4  is a plan view of a sizer  10  according to the present embodiment,  FIG. 5  is a cross-sectional view along line A-A (major axis) thereof, and  FIG. 6  is a longitudinal cross-sectional view along line B-B (minor axis) thereof.  FIG. 7  shows a magnified view of the longitudinal cross section of the sizer  10 . 
         [0058]    As shown in  FIGS. 5 to 7 , the sizer  10  comprises a core material  11  and a cover material  12  covering the core material  11 . As shown in magnified view in  FIG. 7 , the cover material  12  is constituted by a fiber material  13  disposed around the core material  11 , and a section of silicone rubber  14  that envelops the fiber material  13  and seals the core material  11 . The sizer  10  has an endless ring shape (roughly identical to that of the artificial annulus  4 ; see  FIG. 2 ), as shown in  FIG. 4 , and is formed in an overall curved shape having a concave central section, as shown in the longitudinal cross-sectional views of  FIGS. 5 and 6 . 
         [0059]    The core material  11  is, for example, a stainless steel wire having a diameter of 1.2 mm, and has a specific level of rigidity, with the result that the core serves to maintain the shape of the sizer  10  during the procedure. As shown in  FIG. 7 , the core material  11  is disposed within the cover material  10  so as to be offset toward the center of the sizer  10 . This arrangement prevents the needle from entangling the core material  11  when the sizer  10  is being sutured to the annulus. Specifically, when using a needle  16  to pass thread  17  through the cover material  12  of the sizer  10 , the core material  11  will rarely be entangled if disposed in an offset position as shown in  FIG. 8 , whereas there is a possibility of the needle  16  passing to the inside of the core material  11  if the core material  11  is disposed at a central position as shown in  FIG. 9 . Such entanglement of the core material  10  by the needle  16  must be avoided, as this will make it impossible to remove the sizer  10  from the thread  17  later. 
         [0060]    The cover material  12  (fiber material  13  and silicone rubber  14 ) serves as a body through for passing the thread  17  (needle  16 ) through the sizer  10 . Of the various elements constituting the cover material  12 , the fiber material  13  is constituted by a polyurethane elastomer. The polyurethane elastomer is soft and stretchable, but is durable against being broken by the thread  17 , allowing the elastomer to serve as a reinforcing material that improves the ability of the thread  17  to hold the sizer  10  in place while maintaining the flexibility of the sizer  10 . Meanwhile, the silicone rubber  14  serves as a shock-absorbing material that, along with the fiber material, yields a specific level of break strength, as will be discussed hereafter. 
         [0061]    Multiple sizers  10  of different sizes having the shape described above are provided, and sizers of different sizes can be exchanged, as appropriate, to identify a single optimal size for the annulus of the patient. 
         [0062]    In the present embodiment, for example, nine sizers are provided in which the average of the outer diameter and the inner diameter along the major axis varies in 2 mm intervals from 24 mm to 38 mm. The diameter of the cross section of the sizers varies from 3.5 to 5 mm as the sizers increase in size. 
         [0063]    (Method of Manufacturing Sizer) 
         [0064]    Next, the configuration of the sizer  10  according to the present embodiment will be described in further detail by describing a method of manufacturing the sizer  10 . 
         [0065]      FIG. 10  is a flow chart for a method of manufacturing a sizer. The labels S 1  to S 7  in the drawing correspond to steps S 1  to S 7  described hereafter. 
       (1) Step S 1 : Cutting the Reinforcing Fiber Material 
       [0066]    In step S 1 , the polyurethane elastomer fiber material  13  is cut out using a laser cutter into the same shape as the sizer  10  for implantation into the sizer as a reinforcing material.  FIG. 11  shows the fiber material  13  having been cut from a polyurethane elastomer fiber material sheet  18 . 
       (2) Preparation of Silicone Rubber 
       [0067]    In step S 2 , a specific proportion of silicone rubber  14  constituting the greater part of the cover material  12  is prepared. It is important to bear the following points in mind and select optimal materials when deciding upon the materials and composition for the cover material  12  (including the fiber material  13  and silicone rubber  14 ) 
         [0068]    Specifically, the artificial annulus sizing tool of the present invention is used within the human body, especially the interior cavities of the heart. When breaking the cover material  12  following sizing, it is imperative that no fragments of the cover material  12  separate from the base material and remain within the interior cavities of the patient&#39;s heart. Therefore, the cover material of the present invention must be of a material that permits only the suturing threads to release and produces no other fragments or gas. 
         [0069]    Therefore, in the present embodiment, viscoelasticity is imparted and break strength is adjusted to a level satisfying the conditions described above by adding oil to the silicone rubber  14  constituting a main component of the cover material  12  during manufacture. 
       (3) Bending of Core Material 
       [0070]    In step S 3 , a stainless steel wire  19  such as shown in  FIG. 12( a )  is bent using a wire bender into the same shape as the sizer, as shown in  FIG. 12( b ) . 
         [0000]    (4) Insertion of Core Material and Fiber Material into Mold 
         [0071]    In step S 4 , the core material  11  and fiber material  13  prepared in steps S 1  and S 3  are disposed in a lower mold  20   a  of a mold  20  in the order fiber material  13 , core material  11 , fiber material  13 , as shown in  FIG. 13 . 
       (5) Injection of Silicone Rubber 
       [0072]    In step S 5 , upper and lower molds  20   a ,  20   b  of the mold  20  are closed together, and silicone rubber  14  is injected through a resin injection inlet  21  in the upper mold  20   b . Subsequently, the mold is heated for one hour at a predetermined curing temperature to cure the silicone rubber  14 . 
         [0073]    The silicone rubber  14  is a thermoset resin that cures when heated, affecting manufacturing efficiency. However, the rubber has the property of exhibiting increased physical properties values for elasticity and brittleness following curing if the heating temperature is higher than a certain level. 
         [0074]    For this reason, manufacturing at optimum efficiency at the desired physical properties is possible by heating the rubber at a suitable temperature. 
         [0075]    It is also possible to sterilize the surface of the sizer  10  through this heating. Specifically, the present invention is used within the human body, especially the endocardial spaces, albeit for short periods of time; thus, the surface of the article must be sterilized. 
         [0000]    (6) Demolding from Mold 
         [0076]    In step S 6 , the mold  20  is cooled once heating is complete, and the molded article is removed. 
       (7) Bending of Molded Article 
       [0077]    In step S 7 , the molded article is bent using a specific jig to deform the article into a saddle-like shape as shown in  FIG. 14 . This completes the sizer  10  of the present embodiment. 
         [0078]    (Method of Using Sizer) 
         [0079]    Next, a method of using the sizer  10  of the present embodiment will be described. 
         [0080]    In a mitral valve annuloplasty using an artificial annulus, the periphery is first sutured in place using thread  17 , as shown in  FIG. 15 , thereby exposing the mitral valve and establishing a field of view. 
         [0081]    In conventional procedures, a sizer  5  of the same shape as the artificial annulus is then placed against the mitral valve as shown in  FIG. 3  to determine an optimal size; in the present embodiment, however, the sizer  10  described above is used to size the artificial annulus instead of the sizer shown in  FIG. 3 . 
         [0082]    About four stitches of thread  17  for suturing the artificial annulus in place are used to actually attach the sizer  10  of the present invention to the annulus of the mitral valve, as shown in  FIG. 16 . During this process, the thread  17  is passed through the cover material  12  so that the needle  16  passes to the outside of the core material  10 , as shown in  FIG. 8 . During this process, it is vital that the needle  16  not passed to the inside of the core material  11 , as shown in  FIG. 9 ; the eccentric disposition of the core material  11  in the present embodiment allows the chances of this happening to be reduced. 
         [0083]    Next, physiological saline is injected using a syringe  22 , as shown in  FIG. 17 , and valve behavior and water leakage are evaluated. Once evaluation is complete, the threads  17  are grasped with the fingers and used to break the cover material  12  of the size of 10, as shown in  FIG. 18 , and the sizer  10  is removed from the threads  17 . If it is determined, as the result of the evaluation, that the size is unsuitable, the process returns to the procedure shown in  FIG. 16 , and a sizer  10  of a different size is reattached and the behavior of the valve is re-evaluated. 
         [0084]    Once a sizer  10  of an optimal size has been identified, an artificial annulus of the same size as the sizer  10  is selected and attached according to a procedure similar to that used in ordinary operations. 
         [0085]    Therefore, the size of 10 of the present invention is preferably prepared so as to match commercially available artificial annuli of various shapes actually used in clinical practice. In other words, the sizer of the present invention is not limited to the shapes shown in  FIGS. 4 to 7 , and may have other shapes. For example, the sizer may have shapes such as those shown in  FIGS. 19 and 20  (letter-C shape, deformed ring-shape). 
         [0086]    (Cover Material Break Strength Test Examples) 
         [0087]    Next, testing performed in order to identify optimal specifications for the cover material used in the sizer of the present embodiment will be described. 
         [0088]    1. Purpose of Testing 
         [0089]    Because the sizer of the present invention is used for immediate manual evaluation during a mitral valve annuloplasty, the sizer must simultaneously be strong enough to withstand the process of being attached to the mitral valve and brittle enough to be manually broken and removed by the physician once sizing is complete. Defining “strength” as break strength, the following test was performed in order to quantify a range for break strength that is applicable for the sizer. 
         [0090]    Specifically, the sizer of the present invention will not function if the break strength thereof is too high or too low. 
         [0091]    A suitable range for break strength is a level of strength such that failure will not occur when the cover material is sutured with the suturing thread and the physician performs sizing, and also a level allowing for easy breakage when the sizer of the present invention is held in one hand and the suturing threads are pulled with the other hand. 
         [0092]    A level of strength allowing for easy breakage is a level that will not burden the annular tissue of the patient during the act of breaking, or that will not cause a physician to be concerned about the risk of such. 
         [0093]    2. Testing Method 
         [0094]    Two types of testing were performed: a qualitative evaluation test performed by physicians, and a quantitative breaking test. First, physicians sutured test strips formed from various materials capable of constituting the cover material of the sizer, and qualitatively evaluated whether or not the materials exhibited a level of strength suitable for a sizer material. Next, a breaking test was performed to quantify the strength of the test strips and attain an applicable range of strengths for the sizer. 
         [0095]    3. Qualitative Testing Performed by Physicians 
       (1) Purpose of Testing 
       [0096]    To select a material strength allowing for application as a sizer cover material via qualitative evaluation performed by physicians. 
       (2) Test Sample Specifications 
       [0097]    Square-cut strips were prepared for the test strips of the test. A commercially available rubber sheet that was comparatively hard and believed to have a high level of strength was used for the test strip used to determine an upper limit. Softened silicone rubber obtained by adding oil to a base material of molding silicone rubber was used for the test strip used to obtain a lower limit. Specific specifications for the test strips are shown in tables 1 and 2. 
         [0000]    
       
         
               
               
               
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Test 
                   
                 Silicone rubber/oil weight ratio 
                   
               
             
          
           
               
                 No. 
                 Test strip name 
                 KE1310ST 
                 KF-96-50CS 
                 Oil content 
               
               
                   
               
             
          
           
               
                 1 
                 ST20 
                 10 
                 20 
                 47.6% 
               
               
                 2 
                 ST30 
                 10 
                 30 
                 64.5% 
               
               
                 3 
                 ST32.5 
                 10 
                 32.5 
                 73.2% 
               
               
                 4 
                 ST35 
                 10 
                 35 
                 76.1% 
               
               
                 5 
                 ST37.5 
                 10 
                 37.5 
                 77.3% 
               
               
                 6 
                 ST40 
                 10 
                 40 
                 78.4% 
               
               
                 7 
                 ST42.5 
                 10 
                 42.5 
                 79.4% 
               
               
                 8 
                 ST45 
                 10 
                 45 
                 80.4% 
               
               
                 9 
                 ST47.5 
                 10 
                 47.5 
                 81.2% 
               
               
                 10 
                 ST50 
                 10 
                 50 
                 82.0% 
               
               
                 11 
                 ST52.5 
                 10 
                 52.5 
                 82.7% 
               
               
                 12 
                 ST55 
                 10 
                 55 
                 83.3% 
               
               
                   
               
             
          
         
       
     
         [0000]    
       
         
               
               
               
             
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                 Test No. 
                 Name 
                 Thickness (mm) 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 1 
                 Black cell sponge 
                 3 
               
               
                 2 
                 Plain rubber 
                 3 
               
               
                 3 
                 Neocell rubber 
                 1.5 
               
               
                 4 
                 EVA sheet 
                 2 
               
               
                 5 
                 Black rubber sheet 
                 0.5 
               
               
                 6 
                 Black rubber sheet 
                 1 
               
               
                 7 
                 Black rubber sheet 
                 2 
               
               
                 8 
                 Black rubber sheet 
                 3 
               
               
                   
               
             
          
         
       
     
         [0098]    Grid lines were drawn at 1 mm intervals to a distance of 3 mm from the ends of the testing strips in order to serve as stitching guides for the needle during the test. 
       (3) Testing Method 
       [0099]    In the test, the suture thread was passed through the test strip in order to place the same load thereupon as placed upon the sizer, and the durability of the test strip with respect to the load was qualitatively evaluated. The test was performed according to the following procedure. 
         [0000]    3-1. The test strip was clamped in place using chucks.
 
3-2. Suturing thread used in mitral valve annuloplasties was passed through the test strip from the rear. The guideline for the distance from the ends of the test strip to the stitching position was 2 mm, a value obtained from previous extermination.
 
3-3. After a certain length of thread had passed through the test strip, the thread was used to break the test strip.
 
       (4) Evaluation Method 
       [0100]    The test strips were evaluated by soliciting comments from the physicians regarding the following two points. 
         [0000]    4-1. Whether or not the material could be used as material for a sizer
 
4-2. Additional comments regarding strength and behavior
 
       (5) Results 
       [0101]    Evaluation results for the rubber sheets and silicone sheets are shown in tables 3 and 4. The physician comments indicated that, of the rubber sheets used to obtain an upper limit, the black cell sponge and the Neocell rubber were of usable strength. Regarding the silicone sheets used to obtain a lower limit, comments indicated that silicone rubber up to S 400  was usable, but that oiled rubber test strips of S 425  or higher broke during testing, making them too brittle for application to sizers. 
         [0000]    
       
         
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 3 
               
               
                   
               
               
                   
                   
                 Stitching 
                   
                   
               
               
                   
                   
                 distance 
                   
                   
               
               
                 No. 
                 Type 
                 (mm) 
                 Evaluation 
                 Physician comments 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 1 
                 S200 
                 3.0 
                 OK 
                 Usable line. 
               
               
                 2 
                 S300 
                 3.0 
                 OK 
                 Durability not bad. Usable line. 
               
               
                 3 
                 S325 
                 3.0 
                 Fail 
                 Strength slightly low 
               
               
                 4 
                 S350 
                 4.0 
                 OK 
                 Usable line. 
               
               
                 5 
                 S375 
                 3.0 
                 OK 
                 Slightly weak, but not bad. Usable 
               
               
                   
                   
                   
                   
                 line. 
               
               
                 6 
                 S400 
                 3.0 
                 OK 
                 Usable line. 
               
               
                 7 
                 S425 
                 3.0 
                 Fail 
                 The needle holes expanded when 
               
               
                   
                   
                   
                   
                 the threads were moved. 
               
               
                 8 
                 S450 
                 4.0 
                 Fail 
                 Poor strength; could not withstand 
               
               
                   
                   
                   
                   
                 four stitches. 
               
               
                 9 
                 S475 
                 2.0 
                 Fail 
                 Soft, weak. 
               
               
                 10 
                 S500 
                 3.0 
                 Fail 
                 The needle holes expanded when 
               
               
                   
                   
                   
                   
                 the threads were moved. 
               
               
                 11 
                 S525 
                 3.0 
                 Fail 
                 Too weak to use. 
               
               
                 12 
                 S550 
                 3.5 
                 Fail 
                 So soft it shed fragments. 
               
               
                   
               
             
          
         
       
     
         [0000]    
       
         
               
               
               
               
               
               
             
           
               
                 TABLE 4 
               
               
                   
               
               
                   
                   
                   
                 Stitching 
                   
                   
               
               
                   
                   
                 Thickness 
                 distance 
                   
                   
               
               
                 No. 
                 Name 
                 (mm) 
                 (mm) 
                 Evaluation 
                 Physician comments 
               
               
                   
               
             
             
               
                 1 
                 Black cell 
                 3.0 
                 3.0 
                 OK 
                 Just barely OK 
               
               
                   
                 sponge 
                   
                   
                   
                   
               
               
                 2 
                 Plain rubber 
                 3.0 
                 3.0 
                 Fail 
                 Too sticky; would pull on 
               
               
                   
                   
                   
                   
                   
                 tissue when removed. 
               
               
                 3 
                 Neocell 
                 1.5 
                 3.0 
                 OK 
                 Hard, but should be usable. 
               
               
                   
                 rubber 
                   
                   
                   
                 Acceptable if no other options 
               
               
                   
                   
                   
                   
                   
                 were available. 
               
               
                 4 
                 EVA sheet 
                 2.0 
                 3.0 
                 Fail 
                 Too hard to use. 
               
               
                 5 
                 Black 
                 0.5 
                 3.0 
                 Fail 
                 Good strength, but unusable 
               
               
                   
                 rubber sheet 
                   
                   
                   
                 due to fragment shedding. 
               
               
                 6 
                 Black 
                 1.0 
                 2.5 
                 Fail 
                 Showed signs of shedding 
               
               
                   
                 rubber sheet 
                   
                   
                   
                 fragments. 
               
               
                   
                   
                   
                   
                   
                 (No comment regarding 
               
               
                   
                   
                   
                   
                   
                 strength) 
               
               
                 7 
                 Black 
                 2.0 
                 2.0 
                 Fail 
                 Would not break at all. 
               
               
                   
                 rubber sheet 
                   
                   
                   
                   
               
               
                 8 
                 Black 
                 3.0 
                 2.5 
                 Fail 
                 Would not break at all. 
               
               
                   
                 rubber sheet 
               
               
                   
               
             
          
         
       
     
       (6) Summary 
       [0102]    An applicable range of break strengths for the sizer was determined via qualitative testing using rubber sheets and silicone sheets. 
         [0103]    S 400  was closest to the minimum applicable specifications for hardness; evaluation showed that rubber having the oil content of S 425  or higher was unusable. 
         [0104]    The evaluation indicated that, of the various rubber sheet test strips, black cell sponge and Neocell rubber were closest to the upper limit for strength. 
       4. Break Testing 
     (1) Purpose of Testing 
       [0105]    This test was a break test performed upon some of the test strips used in the qualitative evaluation. The results obtained from this test were compared with the results of the physician evaluations to set an applicable range of break strength for the sizer. 
       (2) Test Sample Specifications 
       [0106]    The test strips had the same shape as the test strips used in the qualitative testing (see tables 5, 6). 
         [0000]    
       
         
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 5 
               
               
                   
               
               
                   
                   
                   
                 Stitching 
                 Evaluation 
                   
               
               
                 Test 
                   
                   
                 disance 
                 from 
                   
               
               
                 No. 
                 Material 
                 Thickness 
                 (mm) 
                 qualitative 
                 Reason for selection 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 1 
                 Black cell 
                 3 
                 3 
                 OK 
                 Rated as maximum value 
               
               
                   
                 sponge 
                   
                   
                   
                 during qualitative test. 
               
               
                 2 
                 Neocell 
                 1.5 
                 3 
                 OK 
                 Rated as maximum value 
               
               
                   
                 rubber 
                   
                   
                   
                 during qualitative test. 
               
               
                 3 
                 Plain rubber 
                 3 
                 3 
                 Fail 
                 Comments indicated that, of 
               
               
                   
                   
                   
                   
                   
                 the various failed test trips, 
               
               
                   
                   
                   
                   
                   
                 this one had a level of 
               
               
                   
                   
                   
                   
                   
                 strength considerably 
               
               
                   
               
             
          
         
       
     
         [0000]    
       
         
               
               
               
               
               
             
           
               
                 TABLE 6 
               
               
                   
               
               
                   
                   
                   
                 Evaluation 
                   
               
               
                   
                   
                 Stitching 
                 from 
                   
               
               
                 Test 
                   
                 distance 
                 qualitative 
                   
               
               
                 No. 
                 Name 
                 (mm) 
                 test 
                 Reason for selection 
               
               
                   
               
             
             
               
                 4 
                 S350 
                 4 
                 OK 
                 Evaluated as having strength near 
               
               
                   
                   
                   
                   
                 lower limit in qualitative test. 
               
               
                 5 
                 S375 
                 3 
                 OK 
                 Evaluated as having strength near 
               
               
                   
                   
                   
                   
                 lower limit in qualitative test. 
               
               
                 6 
                 S400 
                 3 
                 OK 
                 Evaluated as having strength at 
               
               
                   
                   
                   
                   
                 lower limit in qualitative test. 
               
               
                 7 
                 S425 
                 3 
                 Fail 
                 Evaluated as having strength less 
               
               
                   
                   
                   
                   
                 than lower limit in qualitative test. 
               
               
                   
               
             
          
         
       
     
       (3) Testing Method 
       [0107]    The procedure for the break test is described hereafter, and test conditions are shown in table 7. The position at which the suturing thread (in this embodiment, #20) was inserted was set at 3 mm based on the distance at which the needle was actually inserted into the test strips during qualitative testing. 
         [0108]    1. Suturing thread inserted into test strip. 
         [0109]    2. Test strip and suturing thread chucked on tensile tester. During testing, air chucks were used so that the suturing thread would not slip. 
         [0110]    3. Load upon test strip confirmed as being 0[N]. 
         [0111]    4. Tester operated to determine break strength. 
         [0000]    
       
         
               
               
               
             
           
               
                 TABLE 7 
               
               
                   
               
             
             
               
                   
                 Apparatus used 
                 All-purpose tensile tester 
               
               
                   
                   
                 AG-X 5 kN (Shimadzu) 
               
               
                   
                 Test rate 
                 100 mm/min 
               
               
                   
                 Suturing thread type 
                 2-0 ETHIBOND (ETHICON) 
               
               
                   
                 Stitching distance 
                 3 mm 
               
               
                   
                 Exposed test strip length 
                 10 mm 
               
               
                   
                 No. of samples 
                 6 
               
               
                   
               
             
          
         
       
     
       (4) Evaluation Method 
       [0112]    As shown in  FIG. 21 , the test strips exhibited maximum resistance at the moment at which they broke from the threads. In this test, this maximum value was defined as break strength, and the break strengths of each of the test strips were determined and compared. 
       (5) Results 
       [0113]    Tensile test results are shown in  FIG. 22 . 
       Upper Limit Setting 
       [0114]    Break strengths of 2.5[N] and 4.31[N] were obtained for the black cell rubber and the Neocell rubber, respectively, which were evaluated as having levels of strength just at the upper limit. The average value for plain rubber deemed unusable was 4.29[N], slightly less than that of the Neocell rubber. 
         [0115]    However, whereas the Neocell rubber had a maximum value of 4.48[N], the plain rubber had a maximum value of 4.67[N], a value greater than that of the Neocell rubber. If it is necessary to draw a line between usable and unusable for the plain rubber and the Neocell rubber, 4.5[N], a value exceeding the upper limit for the Neocell rubber that can be demonstrated by the plain rubber, is believed to be the upper limit value for break strength. 
       Lower Limit Setting 
       [0116]    Although no significant difference in break strength could be ascertained between S 400  and S 425 , the minimum value for S 350  was 0.20[N], and the minimum value for S 375 , for which the physician comments indicated uncertainty regarding strength, was 0.19[N]; thus, concerns regarding strength are believed to appear at a lower limit of 0.2[N]. 
         [0117]    S 400  test strips exhibiting a break strength exceeding 0.2[N] and S 425  test strips exhibiting a break strength of less than 0.2[N] were obtained at a probability of 50%; it is believed that, if a model in which S 400  has a strength of 0.2[N] or greater and a model in which S 425  exhibits a strength of less than 0.2[N] is used during qualitative evaluation, the results of the qualitative evaluation and the results of the break test should exhibit the same tendency. 
       (6) Summary 
       [0118]    Break tests were performed on test strips that exhibited values for break strength near the upper and lower limits in qualitative testing. 
         [0119]    The break strengths of the Neocell rubber and the plain rubber were compared, and an upper limit of 4.5[N] was set for the break strength of the sizer. 
         [0120]    The break strengths of the S 350  and S 425  were compared, and a lower limit of 0.2[N] was set for the break strength of the sizer. 
         [0121]    As a result of the testing described above, it was determined that a range having a lower limit of 0.2[N] and an upper limit of 4.5[N] was preferable for the strength of the cover material of the sizer. 
         [0122]    The present invention is not limited to the embodiment described above, and various modifications may be made thereto to the extent that they do not alter the gist of the invention. 
         [0123]    For example, although stainless steel wire is used for the core material  11  in the example described above, a plastic core of identical shape can be manufactured via injection molding. In addition, while the core material  11  is first molded before being covered by the cover material  12  in the embodiment described above, it is also possible to first cover the core material  11 , followed by performing bending so as to mold the overall shape. 
         [0124]    In addition, the cover material  12  is not limited to the configuration of the example described above. While a fiber material was used in the embodiment described above, it is also acceptable to use only the cushioning material constituted by the silicone rubber  14  or the like as long as the desired break strength is exhibited. Moreover, the cushioning material is not limited to being silicone rubber; various materials, including those used in the test examples described above, can be selected. 
         [0125]    The present invention is not limited to the embodiment described above, and various modifications may be made thereto to the extent that they do not alter the gist of the invention. 
       REFERENCE NUMBERS 
       [0000]    
       
           10 : Sizer 
           11 : Core material 
           12 : Cover material 
           13 : Fiber material 
           14 : Silicone rubber