Abstract:
A hand-held transmyocardial revascularization gun for ablatively creating channels in tissue, such as heart muscle. The gun is configured with a barrel having a chamber therein for enclosing a probing mechanism and a coring mechanism. The barrel has an opening to permit the surgeon to utilize a finger to slidably move the probing mechanism into the tissue to verify the position is suitable for channel formation. A trigger attached to the gun is used to extend the coring mechanism into the tissue to core out a section thereof for the channel. The opening allows the surgeon to finely control the movement of the probe mechanism to provide tactile feed back, while advancing the probe through the tissue, thus avoiding damage to the internal tissue structures. Stents with or without angiogenic agents thereon can be inserted into the channels to promote vascular or heart cell growth.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application claims the benefit of U.S. Provisional Application No. 60/311,627 filed Aug. 13, 2001. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    A. Field of the Invention  
           [0003]    The field of the present invention relates generally to apparatuses and methods for creating vascular channels in the heart and other tissue to enhance blood flow in, and hence healing of, the tissue. More particularly, the present invention relates to such apparatuses and methods that create vascular channels without damaging the tissue along the interior wall of the channel.  
           [0004]    B. Background  
           [0005]    Heart disease is a major medical concern in the United States and the rest of the world. Many deaths and debilitating injuries result from heart attacks and strokes each year. One of the major heart problems is coronary artery disease that results from the blockage of the blood vessels (coronary arteries) that feed oxygen and blood to the muscle tissue that makes up the heart. The coronary arteries become blocked from a build-up of fats and plaques in the arteries. When the coronary arteries are severely narrowed or completely blocked, as shown in FIG. 1, the heart muscle cells in the part of the heart that was receiving the blood flow dies. This can lead to a heart attack. Often warning signs exist prior to the heart attack that can indicate there is a problem. One such warning sign is known as angina, which is a transient pain or discomfort primarily in the chest area due to a temporary imbalance between the demand for oxygen by the heart muscle and the ability of the coronary arteries to supply enough blood to meet that demand.  
           [0006]    The typical medical procedure for treating someone with severe or complete blockage has been to utilize bypass surgery or angioplasty. Bypass surgery involves the removal of a healthy blood vessel (i.e., either an artery or a vein) from one part of the body and attachment of the blood vessel to the heart so as to detour or bypass around the blocked portion of the coronary artery. Blood then flows in the coronary artery, through the bypass section, to nourish the heart with oxygen. Often, a person needing bypass surgery will undergo more than one bypass at the same time. Angioplasty utilizes a balloon like device to push the fatty plaque back against the artery wall to make more room for blood to flow through the artery so as to increase blood flow to the heart. Typically, the balloon is attached on the end of a catheter that is inserted into the femoral artery in the upper thigh or groin area and then snaked up through the artery to the heart. Once at the location of the blockage, the balloon is inflated to clear the artery. Often, a stent formed from a wire meshed tube is then inserted into the artery to hold it open.  
           [0007]    For various reasons, such as too much of the coronary artery is blocked or the patient cannot handle the stress of major surgery, neither the bypass surgery nor angioplasty procedures are appropriate for a number of people. If medication does not help, the only recourse has been to have a heart transplant. In recent years, doctors have developed new procedures, such as transmyocardial revascularization (hereinafter referred to as “TMR”), to alleviate the problems associated with blocked coronary arteries and new technologies to stimulate the patient&#39;s own body to grow new blood vessels so as to improve blood flow to the heart (interventional angiogenesis). In the typical prior art TMR procedure, the surgeon makes a small opening into the patient&#39;s chest and places a specially manufactured laser against the exposed heart. As illustrated in FIG. 2, the surgeon utilizes the laser to “drill” a series of very small holes through the heart muscle, the myocardium, into the pumping chamber inside the heart. Typically, the surgeon will drill between twenty and forty 1 mm holes with the laser apparatus. These holes, commonly referred to as channels, open a pathway from the heart chamber to the muscle around the heart to allow oxygen-filled blood to flow into the heart muscle, a process which is similar to the way certain reptiles (including snakes and alligators) deliver blood/oxygen to their heart. In addition, it is believed that the creation of the channels promotes the body&#39;s release of angiogenic agents that encourages the growth of small blood vessels (i.e., angiogenic capillary formation). After the surgery, the exterior entrance is blocked to form a clot and/or stitched to close the opening.  
           [0008]    Although the laser TMR procedure has had some substantial success, it does have some significant limitations. One of these is the fact that the laser, while cutting the channel, also damages the heart muscle around the channel (i.e., vaporization creating a zone of necrosis), thereby limiting the amount of blood that can flow into the heart muscle through the channel wall. Often, this may altogether prevent blood flow through the channel. Another limitation with laser TMR is that the laser must be very carefully utilized to prevent damaging the heart wall. Because of the risk of damage, the laser is only fired during the second phase (the systole phase) of the heartbeat cycle when the heart wall is the thickest, as measured by an electrocardiogram connected to the patient. Another limitation is the cost of the laser equipment itself, which can be as much as $300,000 or more, and the special facilities and safety measures that must be employed. The cost and required facilities makes it very difficult for most small hospitals to provide the laser TMR procedure.  
           [0009]    As an alternative to the laser TMR device, U.S. Pat. No. 6,306,125 to Parker, et al. describes an angiogenic implant delivery system and method that is used to non-ablatively (i.e., by not removing any portion of the subject tissue) create a channel in the heart muscle and introduce a biodegradable implant into the channel to stimulate production of angiogenic agents by the heart. A method of enhancing blood flow in tissue, which can utilize the above TMR device is described in 6,263,880 to Parker, et al. Theses patents, the full disclosures of which are incorporated herein by reference, describe an implant delivery device for use with the patented method of enhancing blood flow that has an actuator-driven section of hypodermic tubing which is configured to pierce the heart tissue while carrying and then placing the implant into the channel created by the tubing (i.e., by pushing tissue aside). The actuator, such as a double acting pneumatic cylinder, rapidly drives the tubing into the heart tissue while the heart is at rest. The TMR device can include a depth gauge for controlling the distance in which the tubing is driven into the heart tissue. The preferred stint enters the channel in a relatively stiff state that softens to form a compliant hydrodynamic polymer gel that can absorb the angiogenic agents produced by the tissue and, over time, reintroduce those agents into the tissue to prolong and enhance the angiogenic response and revascularization of the tissue. In an alternative embodiment, the splint itself is configured to pierce the heart tissue.  
           [0010]    A disadvantage of the actuator-driven implant delivery system of the Parker, et al. patents is that the device rapidly drives the hypodermic tubing into the heart tissue independent of any tactile feedback for or direct control by the surgeon. As is known in the art, any resistence against entry of the tubing into the tissue could indicate the presence of an obstruction that may not be desirable to pass through or to place an implant into the channel created through the obstruction. As with the laser TMR, the use of an actuator, such as the double acting pneumatic cylinder of the preferred embodiment, removes the control away from the surgeon once the actuator is activated, thereby preventing the surgeon from stopping the penetration and insertion if he or she encounters an obstruction. In addition, the device non-ablatively introduces the implant into the heart by merely moving the heart tissue aside, as opposed to actually removing the tissue, as with the laser TMR (which vaporizes the tissue away).  
           [0011]    Therefore, what is needed is an TMR apparatus to more efficiently and effectively open channels into the heart while eliminating the risks associated with the use of laser surgery and actuator-driven systems. The preferred apparatus should be easy to use, adaptable to current surgery techniques and significantly less expensive than lasers. To be effective, such an apparatus should be suitable for opening one or more channels into the heart muscle without damaging the walls of the channels so as to allow blood to flow into the heart muscle and allow the surgeon direct control over the channel creation process.  
         SUMMARY OF THE INVENTION  
         [0012]    The TMR gun of the present invention solves the problems identified above. That is to say, the present invention discloses a new and useful mechanical apparatus for TMR procedures which is relatively inexpensive to manufacture, easy to use and effective at opening channels into the heart muscle. The TMR gun of the present invention simplifies the process of creating such channels and significantly reduces the cost of performing TMR procedures (relative to the cost of the laser machines for laser TMR).  
           [0013]    In the preferred embodiment of the present invention, the TMR gun for ablatively forming a channel in a tissue has a barrel with a proximal end and an opposing distal end (relative to the position of the surgeon holding the gun). The distal end of the barrel is shaped to abut the tissue and inside the barrel is a chamber, which can be configured as a longitudinal channel. A probing mechanism for initially penetrating the tissue is slidably disposed in the chamber. The first end of the probing mechanism is shaped and configured to penetrate the tissue and the opposing second end of the probing mechanism is, in the preferred embodiment, configured to wrap or coil around a rotatable shaft at or near the proximal end of the barrel. Also located inside the chamber and disposed at or near the distal end of the barrel is a coring mechanism, such as a core biopsy device, that is configured for coring out a section of the tissue, such as the heart muscle, to form the channel. The preferred embodiment also has a trigger operatively connected to the coring mechanism to move it from a retracted position inside the barrel to an extended position outside the distal end of the barrel so as to core out the channel and a handle for holding the TMR gun.  
           [0014]    In the preferred embodiment of the TMR gun of the present invention, the gun further comprises a probe control mechanism to allow the surgeon to receive tactile feedback from the probe so as to selectively control the movement of the probing mechanism while moving the first end of the probing mechanism from a first position in the chamber to a second position extending beyond the distal end of the barrel. The control mechanism can be an opening in the barrel that allows the surgeon to contact the probing mechanism in the chamber and cause the probe mechanism to move in and out of the distal end of the barrel. Preferably, the opening is sized and configured to allow the surgeon to place a finger into the opening to move the probing mechanism from the first position to the second position and back. In another embodiment, the control mechanism can be a wheel member disposed in the barrel, with the wheel member being in operative engagement with the probing mechanism to move the probing mechanism from the first position to the second position.  
           [0015]    The probing mechanism of the preferred embodiment is a wire or wire-type component that is slidably disposed inside the chamber. The probe wire is pushed into the tissue by the surgeon&#39;s finger movement of the probe wire in the opening. The probe wire moves inside the coring mechanism, such that the coring mechanism cores out and removes a portion of the tissue around the probe wire to form the channel. After the probe wire enters the tissue, indicating that there are no obstructions that could be a problem with formation of the channel, the trigger is operated to cause the coring mechanism to core out the channel. Release of the trigger results in the coring mechanism moving back into the distal end of the barrel. The probe wire is then slid back into the chamber by movement of the probe wire in the opening or in conjunction with the coring mechanism.  
           [0016]    Accordingly, the primary objective of the present invention is to provide a TMR gun that overcomes the disadvantages associated with laser TMR and with non-ablative TMR devices that are used to form a channel in a tissue, such as heart muscle.  
           [0017]    It is also an important objective of the present invention to provide a TMR gun that creates channels into the heart without damaging the channel walls to allow blood to flow from the interior chamber of the heart into the heart muscle.  
           [0018]    It is also an important objective of the present invention to provide a TMR gun that is an easily operated, hand-held device that does not require source of electrical or pneumatic power.  
           [0019]    It is also an important objective of the present invention to provide a TMR gun comprising a probing mechanism and a coring mechanism in a housing having a chamber or channel inside for slidable movement of the probing mechanism to facilitate safe and effective coring of a tissue.  
           [0020]    The above and other objectives of the present invention will be explained in greater detail by reference to the attached figures and the description of the preferred embodiment which follows. As set forth herein, the present invention resides in the novel features of form, construction, mode of operation and combination of processes presently described and understood by the claims. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]    In the drawings which illustrate the best modes presently contemplated for carrying out the present invention:  
         [0022]    [0022]FIG. 1 illustrates a heart having both a partial and complete coronary artery blockage;  
         [0023]    [0023]FIG. 2 illustrates the prior art method and device of utilizing lasers to perform the TMR procedure;  
         [0024]    [0024]FIG. 3 is a perspective view of the TMR gun of the present invention showing the various components thereof in a non-use condition (i.e., retracted into the barrel);  
         [0025]    [0025]FIG. 4 is a cut-away side view of the TMR gun of the present invention showing the probe wire extended beyond the distal end of the gun;  
         [0026]    [0026]FIG. 5 is a cut-away side view of the TMR gun of the present invention showing the probe wire and the coring mechanism extended beyond the distal end of the gun;  
         [0027]    [0027]FIG. 6 is a top view of the TMR gun of the present invention with the coring apparatus shown partially deployed;  
         [0028]    [0028]FIG. 7 is an end view of the distal end of the TMR gun of the present invention;  
         [0029]    [0029]FIG. 8 is a cut-away section of the heart muscle showing a channel formed therein by the TMR gun of the present invention and a stent to be placed in the channel;  
         [0030]    [0030]FIG. 9 is a cut-away section of the heart muscle showing a stent positioned in the channel formed by the TMR gun of the present invention;  
         [0031]    [0031]FIG. 10 is a photomicrograph of a myocardial channel created with a laser TMR device;  
         [0032]    [0032]FIG. 11 is a photomicrograph of a myocardial channel created with a prototype TMR gun of the present invention;  
         [0033]    [0033]FIG. 12 is a top view of an alternative embodiment of the present invention showing use of a wheel member to control movement of the probe wire. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0034]    With reference to the figures where like elements have been given like numerical designations to facilitate the reader&#39;s understanding of the present invention, and particularly with reference to the embodiment of the present invention illustrated in FIGS. 3 through 7, the preferred embodiments of the present invention are set forth below. In the preferred embodiment of the present invention, the TMR gun of the present invention, identified generally as  10 , is a small hand-held gun type of instrument having a barrel  12 , handle  14  and a trigger  16 . As set forth below and in the figures, handle  14  and trigger  16  project generally outwardly from the barrel and trigger  16  can be of the type that is operated by pulling or squeezing trigger  16  towards handle  14  with pressure supplied by one or more of the surgeon&#39;s fingers as the palm of the surgeon&#39;s hand is held against handle  14 .  
         [0035]    Barrel  12  should be made out of plastic or other lightweight, strong and chemical resistant material that is configured to provide a surgical tool which is easy to hold for extended periods (i.e., during a length surgery) and which is easy to clean and sterilize. Many other materials may also be suitable for gun  10 , including various metals or composite materials, including stainless steel and carbon fiber materials. The TMR gun can be made to be disposable or it can be made to be cleanable by presently available cleaning methods. In the embodiment of the present invention shown in the figures, barrel  12  is shown to comprise a generally cylindrical shape having opposing ends, proximal end  18  and distal end  20  (designated as such relative to the position of the surgeon when performing the TMR procedures described herein). In one embodiment, the barrel has an outer diameter of one-half inches and a length of six inches. However, barrel  12  of the TMR gun  10  of the present invention can be configured into a variety of sizes and shapes, as may be suitable for comfortably holding the gun  10  and for desirable aesthetic purposes. Distal end  20  should be configured to abut or be engagable with the tissue that is to be treated. While a generally planar distal end  20  is typically suitable for most TMR procedures, distal end  20  can be contoured or otherwise configured to more preferentially abut the tissue that is to be treated.  
         [0036]    The interior of barrel  12  comprises a chamber  22 , which can be in the form of an elongated channel for all or part of the length of barrel  12 , in which is located and through which travels a probing mechanism, such as thin, stiff probe wire  24  having a first end  26  and second end  28 . The first end  26  of probe wire  24  should be appropriately configured, such as by being cut at an angle, to allow probe wire  24  to efficiently penetrate the tissue. As explained more fully below and shown in FIGS. 3 and 4, probe wire  24  should be sufficiently stiff to allow the surgeon to slide the probe wire  24  inside chamber  22  so as to cause probe wire  24  to move from a first position  30  where first end  26  is inside barrel  12  to a second position  32  where first end  26  extends beyond the distal end  20  of barrel  12 . In one embodiment, probe wire  24  has a diameter of one mm and has a length approximately equal to the full length of barrel  12 , although it would not be necessary for it to be that long. In a preferred embodiment, the second end  28  of probing mechanism wraps or coils around a rotatable shaft  34  positioned at or near the proximal end  18  of barrel  12  as the first end  26  of probe wire  24  moves back from the second position  32  to the first position  30 . In an alternative embodiment, the probing mechanism can be a stiff wire or needle that merely moves, in a generally longitudinal direction, inside chamber  22  but does not coil around any shaft, such that shaft  34  is not needed. In this embodiment, the probe wire  24  or other wire-like member could frictionally engage the walls of chamber  22  to allow the surgeon to maintain sufficient control over the movement of probe wire  24 . In the preferred embodiment, when wire probe  24  is not being used for a TMR procedure it is preferred that probe wire  24  be fully contained inside barrel  12  to protect first end  26  from damage. The probing mechanism should be made out of a material suitable for use to pierce human tissue, including the heart. Such materials include stainless steel, carbon fiber and like materials.  
         [0037]    The TMR gun  10  of the present invention also includes a mechanism for controlling or allowing control of the movement of the probing mechanism (i.e., probe wire  24 ). In the preferred embodiment, as best shown in FIG. 6, the barrel includes an opening  36  in a side  38  of barrel  12  that is in communication with chamber  22  to expose a section of probe wire  24 . Also in the preferred embodiment, opening  36  is sized and configured to allow the surgeon to place his or her finger inside opening  36  to push against and slide probe wire  24  so as to cause first end  26  of probe wire  24  to move from first position  30  to second position  32  to penetrate the tissue or to move from second position  32  to first position to retract probe wire  24  after piercing the tissue. When the surgeon places his or her finger inside opening  36  and pushes against probe wire  24  to cause it to penetrate the tissue, any resistance against probe wire  24  will be felt by the surgeon, providing the surgeon with nearly instant tactile feedback on his or her progress. Depending on the nature of the resistance, the surgeon can decide to cease any further penetration into the tissue and either further evaluate that area of the tissue or move to a different penetration point. For instance, the heart is made up of internal cardiac structures that could be damaged by further penetration. Use of opening  36 , such as a generally square or rectangular opening that is approximately three inches long, allows the surgeon substantially more feel of what is happening and control over the penetration than is possible with presently available mechanical or electro-mechanical devices.  
         [0038]    Operatively connected to trigger  16  is a coring mechanism  40 , such as those used for performing biopsy cores, suitable for coring a 1 mm section (or other desirable size of core) from the tissue (i.e., the heart muscle). As is well known, core biopsy devices generally comprise two sharp metal projections, one orientated adjacent to the other. A typical size for coring mechanism  40  is an outside diameter of approximately 1.3 mm and a length of 30 mm. As with probe wire  24 , coring mechanism  40  should be made out of a material suitable for penetrating and coring out a section of human tissue. As shown in the figures, coring mechanism  40  is located at or near the distal end  20  of barrel  12  and configured for probe wire  24  to travel through coring mechanism  40  (as best shown in FIG. 7). In use, the coring instrument is advanced to abut the tissue to be cored and then fired, causing one of the metal projections to advance relative to the other, thus cutting out a core of tissue. In its non-use condition, coring mechanism  40  is retracted into barrel  12  such that the distal end  20  of gun  10  is generally planar. Coring mechanism  40  is operatively connected to trigger  16  such that when trigger  16  is activated, coring mechanism  40  rapidly extends beyond distal end  20  of barrel  12  to core out a section of the heart muscle (similar to the way a biopsy is performed). Upon release of trigger  16 , coring mechanism  40  retracts back into barrel  12 .  
         [0039]    In use, the surgeon exposes the patient&#39;s heart or other tissue and, with both the probe wire  24  and coring mechanism  40  in their retracted positions, as shown in FIG. 3, places the distal end of barrel  12  against the portion of the heart muscle or other tissue that is to receive the TMR procedure. Once in position, the surgeon places his or her finger in opening  36  to push or slide the probe wire  24  forward using his or her finger in the opening  36 , as shown in FIG. 4. Pushing on probe wire  24  by the surgeon causes probe wire  24  to extend beyond distal end  20  of barrel  12 , causing the probe wire  24  to enter into the heart muscle and penetrate it to the chamber inside. By utilizing a finger to control the forward movement of the probe wire  24 , the surgeon can receive tactile feedback so as to finely control the speed of the probe wire  24  and the amount which it penetrates the heart muscle. Once probe wire  24  is in its proper place and has penetrated the heart muscle without damage, the surgeon activates coring mechanism  40  by pulling trigger  16  towards handle  14 . When activated, coring mechanism  40  extends beyond the distal end  20  of barrel  12 , as shown in FIG. 5, to core out a section (i.e., a 1 mm diameter core) of the heart tissue and form channel  42 . Upon release of trigger  16 , the coring mechanism  40  retracts. The surgeon then backs probe wire  24  out by using his or her finger in the opening  36  to slide probe wire  24  backward into barrel  12 , causing it to wrap or coil around shaft  34  (if it is used). When the surgeon removes gun  10  from the heart, a channel  42  (shown in FIGS. 8 and 11) is left in the heart, the outside end of which is typically closed utilizing currently available procedures (i.e., holding a finger against the hole and/or using sutures).  
         [0040]    Use of TMR gun  10  having a coring mechanism  40  instead of the laser to ablatively create channel  42  has certain significant advantages, including leaving a channel  42  that is much less likely to have any traumatized tissue along the channel wall  44  or any vaporization that results in a zone of necrosis. FIGS. 10 and 11 are photomicrographs of myocardial channels created with a prior art laser TMR device (FIG. 10) and a prototype of the TMR gun  10  of the present invention. As shown in these figures, the channel  42  in FIG. 11 is cleaner and much more open. Because the channels  42  in the heart formed with the TMR gun  10  of the present invention are much more open, the procedure will improve the flow of blood and oxygen to the heart muscle, which is more likely to encourage growth of small blood vessels and improve the patient&#39;s health. In addition, the cleaner channel  42  will better facilitate the use of a biodegradable, porous stent  46  (shown in FIGS. 8 and 9) that can be inserted into the channel  42  created by the TMR gun  10  of the present invention. Stent  46  can be coated or otherwise contain cell cultures or other substances that may promote heart cell or vascular growth or repair to further improve the health of the heart. Another advantage of gun  10  is that the surgeon controls the entry of probe wire  24  with his or her finger, therefore, the surgeon can feel any obstruction or other problems with the entry of probe wire  24  before it fully enters the heart muscle, something which cannot be done with use of the laser to create channel  42  or with the non-ablative device of Parker, et al. Yet another advantage of the TMR gun  10  is that is relatively inexpensive to make, particularly relative to the laser, which should allow many more facilities and doctors to offer the TMR procedure.  
         [0041]    Various modifications can be made to the TMR gun  10  of the present invention. One such modification, shown in FIG. 10, is to utilize a wheel member  48  placed in opening  36  and operatively engaged with probe wire  24  so the surgeon can push or roll his or her finger against the wheel member  48  to move the probe wire  24  forward (out of the barrel  12 ) or backward (back into barrel  12 ). The use of wheel member  48  may make it easer for the surgeon to move probe wire  24  in and out of gun  10  and still provide the surgeon with the feel and control of probe wire  24  necessary to prevent damaging the heart muscle. Other types of control devices, as are known in the industry, can be used to control the forward and backward movement of probe wire  24 , including various mechanical and electronic devices. Another modification to gun  10  is the use of a different trigger mechanism to activate the coring mechanism  40 , rather than squeezing trigger  16  as described above. Trigger  16  can be a variety of mechanical and/or electrical devices that allow the surgeon to selectively cause coring mechanism  40  to penetrate and core the heart tissue to form channel  42 . For instance, trigger  16  can be an electronic device that the surgeon merely pushes to cause the coring device to rapidly extend from the distal end  20  of gun  10  into the heart tissue. Trigger  16  and coring mechanism  40  can be jointly configured such that the coring mechanism  40  automatically retracts upon coring the heart tissue. In addition, the retraction of the coring mechanism  40  can be configured so that it also retracts probe wire  24  when the core is done, such that the retraction of probe wire  24  and coring mechanism  40  can occur with one motion, either simultaneously or sequentially, thereby avoiding the need of having to manually retract probe wire  24 .  
         [0042]    The TMR gun  20  of the present invention can also be configured to be able to insert any desired stents or implants  46 , with or without any angionic agents thereon to promote vascular growth and/or heart cell growth. Such agents include myocyte cell culture and/or vascular endothelialgrowth factor (VEGF), as well as other known agents. The Parker, et al. patents referenced herein, describe the operation and configuration of implants and the use of agents and growth factors on or in the implant.  
         [0043]    While there are shown and described herein certain specific alternative forms of the invention, it will be readily apparent to those skilled in the art that the invention is not so limited, but is susceptible to various modifications and rearrangements in design and materials without departing from the spirit and scope of the invention. In particular, it should be noted that the present invention is subject to modification with regard to the dimensional relationships set forth herein and modifications in assembly, materials, size, shape and use.