LEAD LOCKING DEVICE

TECHNICAL FIELD

[0001] The technical field generally relates to endovascular procedures and more particularly relates to systems and apparatuses for enabling lead extraction using current lead locking devices (LLD) that can be un-deployed and use a dielectric elastomer (DE) configured in a tubular shape to allow for the deployment of a locking mechanism inside a lead to apply traction providing locking/unlocking functionality.

BACKGROUND

[0002] With increased numbers of cardiac implantable electronic devices (CIEDs) such as pacemakers, defibrillators (ICD), and cardiac resynchronization therapy (CRT) devices in patients, and consistent with the higher numbers of CIED implanted, there is also more complications, infections, and malfunctions by the greater number of CIEDs in use that necessitate more lead extraction procedures. A rationale for lead removal is given for both infectious and non-infectious conditions: the non-infectious condition can include malfunctioning leads or leads which can cause harm to the patient while the presence of an infection is for infection-based lead removal.

[0003] Currently lead locking devices (LLDs) are not able to be un-deploy ed if the user (i.e., medical provider) desires to abort a lead extraction procedure (i.e. after the insertion and engaging of the locking mechanism in the endoscopic lead extraction procedure).

[0004] Hence, it is desirable to implement a lead locking device that can be both be able to be deployed and un-deployed as desired.

[0005] It is desirable to utilize a dielectric elastomer (DE) with the lead locking mechanism which is the tubular shape to allow the deployment of a locking mechanism inside the lead that also enables un deployment of the locking mechanism inside the lead and to extract the lead locking device.

[0006] It is desirable to implement an electrostatic charge with the tubular DE to cause the DE to have geometric changes in shape and to be either smaller or larger to engage and disengage locking and unlocking functionalities of the lead locking device in an endoscopic procedure. [0007] Accordingly, technologically improved systems and methods for valve resection and reshaping using a catheter with a resection tool to perform the is desirable. The following disclosure provides these technological enhancements, in addition to addressing related issues.

BRIEF SUMMARY

[0008] This summary is provided to describe select concepts in a simplified form that are further described in the Detailed Description. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.

[0009] In one exemplary embodiment, an apparatus including a current lead locking mechanism for a lead extraction procedure is provided. The apparatus includes a lead locking device (LLD) including an elastomer tube is configured to deploy from a proximate end of a lead in an interior cavity of a lead lumen to near an approximate location of a lead tip at a distal end of the lead in the lead lumen; in response to the deployment of the elastomer tube near the approximate location of the lead tip in the interior cavity at the lead’s distal end, a set of electrodes coupled to the elastomer tube to create a charge field that causes electrostatic pressure to deform a cylindrical shape of the elastomer tube; and a locking mechanism created by the expansion of diameter by deformation of the cylindrical shape of the elastomer tube to hold the inner lumen of the lead.

[0010] In at least one exemplary embodiment, an apparatus includes the LLD with an elastomer tube includes a dielectric elastomer (DE) that deforms in response to the charge field placed across the DE; and a radiopaque marker that is located on the distal end of the LLD to visualize at least the LLD location in the lead extraction procedure.

[0011] In at least one exemplary embodiment, an apparatus includes the LLD with an external section that included a voltage source coupled to the set of electrodes to cause to apply a voltage across a first positive electrode and a second negative electrode of the electrode set that causes traction exhibited by elastomer to the lead to enable the LLD for lead extraction.

[0012] In at least one exemplary embodiment, an apparatus includes the LLD with the first positive electrode is configured at an exterior location of the elastomer tube and the second negative electrode is configured at an interior location of the elastomer tube wherein the LLD with the second negative electrode is coupled to a central wire.

[0013] In at least one exemplary embodiment, an apparatus includes a loop handle located on the proximal end of LLD for use to pull after locking of the LLD to lead, and to retract the LLD after unlocking.

[0014] In at least one exemplary embodiment, an apparatus includes the LLD with the first positive electrode is configured to enable an exciting state of the elastomer tube by applying a voltage to cause an opposing force to expand the elastomer tube in the interior cavity to press against an inner lumen of the lead.

[0015] Furthermore, other desirable features and characteristics of the system and method will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the preceding background.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The present application will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and:

[0017] FIG. 1A illustrates an exemplary diagram of the construction of the elements that form the lead locking device, in accordance with an exemplary embodiment;

[0018] FIG. IB illustrates an exemplary diagram of geometric changes that occur when an electric field is placed across an elastomer tube of the lead locking device, in accordance with an exemplary embodiment;

[0019] FIG. 2 A illustrates an exemplary diagram of the lead locking and unlocking system mechanism in accordance with an embodiment;

[0020] FIG. 2B illustrates an exemplary diagram of the lead locking and unlocking system mechanism in accordance with an embodiment;

[0021] FIG. 3 A illustrates an exemplary diagram of an alternative configuration using reverse polarities of the electrode pairs where the elastomer in the lead locking device (LLD) is inserted into the lead in an excited state for the lead locking device mechanism in accordance with an embodiment;

[0022] FIG. 3B illustrates an exemplary diagram of an alternative configuration using reverse polarities of the electrode pairs where the elastomer in the lead locking device (LLD) is inserted into the lead in an excited state for the lead locking device mechanism in accordance with an embodiment;

[0023] FIGS. 4A illustrates an exemplary diagram of an elastomer configuration subdivided into tubular sections to apply a longitudinal electrostatic force on the cylinder of the dialectic elastomer to compress under electrostatic pressure, and to increase the outer diameters of the elastomer tubular cylinder to press against the lead lumen for the lead locking device in accordance with an embodiment;

[0024] FIGS. 4B illustrates an exemplary diagram of an elastomer configuration subdivided into tubular sections to apply a longitudinal electrostatic force on the cylinder of the dialectic elastomer to compress under electrostatic pressure, and to increase the outer diameters of the elastomer tubular cylinder to press against the lead lumen for the lead locking device in accordance with an embodiment;

[0025] FIG. 5 illustrates an exemplary lead locking device handle for use with the lead locking device mechanism of the lead locking device in accordance with an exemplary embodiment; and

[0026] FIG. 6 illustrates an exemplary flowchart for a method system, in accordance with an exemplary embodiment.

DETAILED DESCRIPTION

[0027] The following detailed description is merely illustrative in nature and is not intended to limit the embodiments of the subject matter or the application and uses of such embodiments. As used herein, the word “exemplary” means “serving as an example, instance, or illustration.” Thus, any embodiment described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments. The embodiments described herein are exemplary embodiments provided to enable persons skilled in the art to make or use the invention and not to limit the scope of the invention that is defined by the claims. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding technical field, background, summary, or the following detailed description.

[0028] Lead locking devices (LLDs) in use are not able to be un-deployed if the physician desires to abort a lead extraction procedure. As an example, in a current LLD mechanism that may include a stainless-steel braid on a stainless-steel mandrel. The braid is initially tight against the mandrel and inserted into the lead central lumen. Then the braid is expanded inside the lumen, and the mandrel is pulled on. This creates a reverse Chinese finger trap effect, but also deforms the braid such that the LLD cannot be un-deployed from the lead. If for example, the medical personnel needs to stop a lead extraction procedure, there is no ability to abort the procedure. As a result of this obstacle, medical personnel often do not extract leads because their ability to redo a failed attempt removal is limited. Instead, medical personnel in the instance are left to cap leads and leave the unremovable sections in the vessel. The result is that a patient is more susceptible to infections as a result of the implant left therein. It is estimated that approximately sixty percent of all leads are capped and left in the body because of the obstacle posed of not being able to redeploy the LLD mechanism in the lead extraction procedure.

[0029] Exemplary embodiments provide a technical solution to this problem in the form of a lead extraction deployment mechanism that enables deploying the LLD and if desired un deploying the LLD.

[0030] Provided embodiments in the present disclosure describe systems and apparatuses of an LLD that include a dielectric elastomer (DE) in a tubular shape to allow deployment and retraction of the deployment of a locking mechanism inside the lead. When an electric charge is applied from a switched DC source, the electrostatic charge is received by the tubular DE of the LLD and it causes the geometry of the DE to deform or change (i.e., either to contract or expand). This change in shape in the DE can cause a perpendicular force that provides traction to an inner lumen of the lead to enable the LLD to hold the lead. Once, traction is applied, a medical provider can via manual manipulation extract the lead. Alternately, the medical provider can cause the DE to contract to abort the procedure and extract the LLD after it has been deployed. [0031] In an exemplary embodiment, the present disclosure describes systems and apparatuses that enable a locking mechanism consisting of a set of elements of a soft elastomer tube with flexible electrodes oriented in a manner that creates an electric field between each element or sections that deforms the elastomer tube diameter.

[0032] In an exemplary embodiment, the present disclosure describes systems and apparatuses that enable an external section configured with a voltage source connected to a set of flexible electrodes via a set of small wires connected (i.e., coupled directly or indirectly) transversally across the LLD, a switch and/or trigger to activate/deactivate a voltage source. The LLD is also configured with a convenient design for the medical provider (i.e., a physician performing the endoscopic procedure) to hold and to apply with manual traction, and subsequent lead extraction.

[0033] The figures and descriptions below provide more detail.

[0034] Turning now to FIGS. 1A and IB, in an embodiment, FIG. 1A illustrates a structure of the locking and unlocking system mechanism 100 that enables the deforming of dielectric elastomers (DE). When two electrodes of an outer electrode 105 and an inner electrode 120 are placed on flexible (soft) elastomer 120 with opposite charges on each, the electric field 115 (shown in FIG. IB) causes the elastomer center to compressive under attractive electric force. The same mechanism can be applied across the length of a cylindrical elastomeric tube, in which electrodes on inside lumen (inner electrode 120) and outside lumen (outer electrode 105) to the elastomer 110 which is located in between.

[0035] When an electric field 115 (shown in FIG. IB) is passed across the electrodes, the attractive electric force (dependent on the direction of the electric field) causes the elastomer tube 110 geometry to change. In an exemplary embodiment, when the electric field 115 is directed in a direction towards the inner electrode 120 (in this case the inner electrode is configured with negative polarity and the outer electrode is 105 is configured with positive polarity) the diameter 140 decreases because of the electrostatic force exerting pressure toward the inner lumen area of the elastomer 110. While the diameter 140 decreases (i.e., restricted), the longitudinal length (not shown) of the elastomer 110 increases because of the flexible properties exhibited by the material that makes up the elastomer 110. [0036] In an alternative exemplary embodiment, when opposing charges (that is the polarity is reversed of the pair of electrodes) are introduced to the electrodes, and the opposing electric force can cause the diameters to expand, which enables the unlockable lead locking functionality.

[0037] Turning to FIGS. 2A and 2B that illustrate exemplary diagrams of embodiments of the lead locking and unlocking system mechanism in accordance with an embodiment. In FIG. 2A, the lead locking device 200 system mechanism includes a soft/flexible cylindrical elastomer tube 210 with an opposing pair of electrodes of an inner electrode 270 and an outer electrode 265 of opposite polarity. The inner electrode 270 is located in the inner lumen of the elastomer tube 210 and the outer electrode 270 is located at the other lumen about the elastomer tube 210. In FIG. 2B, the inner electrode 270 and the outer electrode 265 are configured to create an electric field 275 across a cross-section (i.e., the diameter) of the elastomer 210, where electrostatic pressure will deform the cylinder such that the diameter will increase (expanded elastomer 260) and hold the inner lumen 220 of the lead 235. The pair of electrodes can be configured in a few different ways to create the diameter change. In an exemplary embodiment, FIG. 2A illustrates the deployment of a relaxed DE LLD into lead 235 lumen, and with the subsequent deployment of the lead locking device 200 mechanisms by application of a voltage 290 by manual actuation of the switch 295, an electrostatic field 255 (i.e., the electric field caused by opposite polarities of the electrode pair) is created across the electrodes.

[0038] In an exemplary embodiment, when the LLD 200 is deployed with the elastomer 210 is a relaxed state, the positive electrode is located on the outside (outer electrode 265), and on the inside of the elastomer 210-cylinder tube, the negative electrode (inner electrode 270) is located on a central wire 285. The excited positive electrodes create an opposing force expanding the elastomer tube (expanded tube 260), pressing up against the inner lumen 220 of the lead 235.

[0039] In an exemplary embodiment, in FIG 2A, the LLD 200 is inserted into the lead 235 lumen (cavity 225) in its “relaxed” state, then electrically excited in FIG. 2B to create the locking mechanism against the inner lumen 220 of the lead 235 and also against the lead coils 215 of the lead 235. A simple amount of traction is all that is necessary for the lead removal by manual operation of the medical provider. [0040] If it is desired, to retract the LLD 200 after deployment, switch 295 is switched to an off position, to deactivate the electric field 255 across the expanded elastomer 260, to return the LLD 200 from an excited state to a relaxed state. Further, to change the expanded elastomer 260 to a similar state to the prior or relaxed state with a lesser diameter so that there is no longer any traction between the inner lumen 220 of the lead 235. In this case, a medical provider can manually un deploy or retract the LLD 200 from the cavity 235 as desired without or with lesser traction applied to the lead 235 to enable the un-deployment.

[0041] FIGS. 3 A and 3B illustrate an alternative configuration using reverse polarities of the electrode pairs where the elastomer in the lead locking device (LLD) is inserted into the lead in an excited state for the lead locking device mechanism in accordance with an embodiment.

[0042] In FIG. 3A, the elastomer (i.e., the contracted elastomer 310) is inserted with a decreased diameter into the cavity 325 of the lead 325. In this case, the electric field 355 is applied and because the polarities of the inner electrode 270 and the outer electrode 365 are reversed, an electrostatic force is exerted towards the inner lumen of the elastomer to cause the elastomer to contract in diameter to be easily inserted into the lead 335 inner lumen 320 in the cavity 325. As the exited is relaxed, and the electric field 355 applied across the elastomer is lessened, the elastomer (i.e., the dielectric elastomer) deforms to change in shape and expands. In FIG. 3B, the expanded elastomer 360 is shown with a diameter that is greater than in the relaxed state. The expanded diameter causes the elastomer in the expanded state to exert a force sufficient to cause a hold or traction to the inner lumen 320 of the lead 335 or the lead coils 315. In the excited state, the dielectric elastomer diameter decreases while in the relaxed state it increases. The change in diameter and expansion of the elastomer is caused by configuring the outer electrode 365 with an opposite charge to in the inner electrode 270 so that the electrostatic force between the electrodes causes an attraction in the excited state to shrink the diameter. While when switched off by switch 395 and the electric field 355 no longer applied the attraction fades between the electrodes releasing the elastomer for expansion.

[0043] FIGS. 4A and 4B illustrate an elastomer configuration subdivided into tubular sections to apply a longitudinal electrostatic force on the cylinder of the dialectic elastomer to compress under electrostatic pressure and to increase the outer diameters of the elastomer tubular cylinder to press against the lead lumen for the lead locking device in accordance with an embodiment.

[0044] In FIG. 4A the dielectric elastomer 410 is partitioned or divided into sections 407 along its entirety from the proximate to the distal end of the tubular cylinder. In the relaxed state, the dielectric elastomer 410 can be inserted into the inner lumen 420 of the lead 455 with space in between the outer lumen 422 of the dielectric elastomer 410 and the inner lumen 420 of the lead 455. Multiple pairs of electrodes 427 are configured in a manner (i.e., a changed electrode configuration longitudinally across each tubular section 407) that causes the electrostatic force to act or to be applied longitudinally across the long axis of the dielectric elastomer 410 cylindrical tubes. The intensity of the electric field (i.e., electrostatic force 413 exhibited across each tubular cylinder section) decreases in intensity with a square of the distance; hence, the pairs of electrodes cannot be spaced too far apart to maintain a sufficient electric field. Therefore, to maintain a nearness in distance, the electrodes are configured in an alternating pattern of positive and negative electrodes throughout the locking portion of the dielectric elastomer LLD. This results in multiple alternate configurations of opposite or alternating sets of positive and negative electrodes in multiple tubular segments in FIG. 4A and also in FIG. 4B.

[0045] In FIG, 4B, once the alternating sets of electrode pairs are excited, the LLD is in an excited state, the tubular segments 407 would compress or push against each other in the longitudinal direction via the longitudinal electrostatic forces 413. Since each of the tubular sections are next to each other, there is no space for expansion in the longitudinal direction across the X-axis. Therefore, the only available area for expansion is the perpendicular direction (Y-axis). As a result, as shown in FIG. 4B, the elastomer expands in diameter (the expanded elastomer 460) to push against the inner lumen 420 of the lead 455 to cause the traction and initiate the locking mechanism of the LLD 400. Once excited, the tubular segments compress under electrostatic pressure and increase the outer diameters to press against the lead lumen, locking the LLD 400. The inner electrode 457 of the LLD 400 could be a flexible electrode separate from the center mandrel 459 or could be incorporated into or integrated with the center mandrel 459.

[0046] In an exemplary embodiment, the outer electrode 427 can be configured with a textured surface to promote locking against the inner coil surface of the lead, laser-cut pattern, knurled, sandblasted, etc. The outer electrode 427 can also be configured with wire through the LLD 400, or the inner coil 415 of the lead 415 can be used as a conductor to the outer electrode 427.

[0047] The voltage source 490 is configured to excite the electrodes and to activate the dielectric elastomer (DE) as required. It as is configured as a DC source and can be either a battery or power via an AC/DC converter from a standard 110V outlet.

[0048] FIG. 5 illustrates an exemplary lead locking device handle for use with the lead locking device mechanism of the lead locking device in accordance with an exemplary embodiment. In FIG. 5 there is illustrated a lead locking device (FED) 518 with a loop handle 516, radiopaque marker 524, mandrel 514, proximal end 540 and distal end 522. The loop handle 516 on the proximal end of FED 518 is for use by medical provider to pull after locking of the FED to lead, and retracting of the FED 518 after unlocking. The radiopaque marker 524 on the distal end 522 is to visualize the FED 518 location and related characteristics under fluoroscopy in the lead extraction procedure.

[0049] FIG. 6 is an exemplary flowchart illustrating the steps to implement by a medical provider or the like, the lead locking device in a lead extraction procedure in accordance with an embodiment. At task 605, a medical provider deploys an elastomer tube is configured to deploy from a proximate end of a lead in an interior cavity of a lead lumen to near an approximate location of a lead tip at a distal end of the lead in the lead lumen. At task 615, once the elastomer tube is near the approximate location of the lead tip in the interior cavity at the lead’s distal end by manual insertion in the lumen of the lead by the medical provider, then the medical provider can actuate via a switch, a set of electrodes coupled to the elastomer tube to create a charge field that causes electrostatic pressure to deform a cylindrical shape of the elastomer tube.

[0050] At task 620, the locking mechanism created by the expansion of diameter by deformation of the cylindrical shape of the elastomer tube pressing against the inner lumen of the lead and causes traction or holding to the inner lumen of the lead or coil located at the inner lumen of the lead. At task 625, in response to the charge field placed across the DE, the elastomer tube deforms. Also, an external section is configured with a voltage source coupled to the set of electrodes to cause to apply a voltage across a first positive electrode and a second negative electrode of the electrode set that causes traction exhibited by elastomer to the lead to enable the FED for lead extraction. The first positive electrode is configured at an exterior location of the elastomer tube and the second negative electrode is configured at an interior location of the elastomer tube. Also, the second negative electrode is coupled to a central wire. At task 630, the first positive electrode is configured to enable an excited state of the elastomer tube by applying a voltage to cause an opposing force to expand the elastomer tube in the interior cavity to press against an inner lumen of the lead. At task 635, an elastomer cylindrical tube partitioned in a continuous set of tubular segments that are configured for deployment between a proximate end of a lead in an interior cavity in a lead lumen to near an approximate location of a lead tip at a distal end of the lead in the lead lumen. At task 640, in response to the deployment of the elastomer tube near the approximate location of the lead tip in the interior cavity at the lead’s distal end, a set of electrodes coupled to each of the tubular segments to apply an electrostatic charge across a longitudinal axis of each of an elastomer cylindrical tubular segment for placement in an excited state. At task 645, in response to placement of the elastomer tubular segment in the excited state, the elastomer tubular segment is compressed under electrostatic pressure when deployed to increase the outer diameter of each tubular segment resulting in an outer end of each tubular segment expanded to press against and hold the inner lumen of the lead.

[0051] In various exemplary embodiments, A system using a lead locking device (LLD) in a lead lumen, including: a lead locking device (LLD) configured with an elastomer tube wherein the elastomer tube is deployed in a lead lumen in an interior cavity to near an approximate location of a lead tip; at least one pair of electrodes coupled to the elastomer tube to create a charge field that causes electrostatic pressure to change a cylindrical shape of the elastomer tube wherein the LLD is placed either in a first state or a second state to deploy a locking mechanism, further including: in response to deployment in the first state, the elastomer tube is configured for placement in a relaxed state in the lead lumen wherein in response to applying a charge field to cause electrostatic pressure to expand a diameter of the elastomer tube to hold the lead; and in response to the deployment in the second state, the elastomer tube is configured for placement in an excited state of a decreased diameter of the elastomer tube in the lead lumen wherein in response to release of a charge field ceasing electrostatic pressure to maintain the decreased diameter of the elastomer tube in the lead lumen and to cause an expansion of the elastomer tube to hold the inner lumen of the lead. The elastomer tube includes a dielectric elastomer (DE) that deforms in response to the charge field placed across the DE. [0052] In various exemplary embodiments, an apparatus including a current lead locking mechanism for a lead extraction procedure is provided. The apparatus includes a lead locking device (LLD) including an elastomer cylindrical tube partitioned in a continuous set of tubular segments that are configured for deployment between a proximate end of a lead in an interior cavity in a lead lumen to near an approximate location of a lead tip at a distal end of the lead in the lead lumen; in response to a deployment of the elastomer tube near the approximate location of the lead tip in the interior cavity at the lead’s distal end, a set of electrodes coupled to each of the tubular segments to apply an electrostatic charge across a longitudinal axis of each of an elastomer cylindrical tubular segments for placement in an excited state; in response to placement of the elastomer tubular segment in the excited state, the elastomer tubular segment is compressed under electrostatic pressure when deployed to increase an outer diameter of each tubular segment resulting in an outer end of each tubular segment expanded to press against and hold the inner lumen of the lead.

[0053] Those of skill in the art will appreciate that the various illustrative logical blocks, modules, circuits, and algorithm steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware, computer software, or combinations of both. Some of the embodiments and implementations are described above in terms of functional and/or logical block components (or modules) and various processing steps.

[0054] However, it should be appreciated that such block components (or modules) may be realized by any number of hardware, software, and/or firmware components configured to perform the specified functions. To clearly illustrate the interchangeability of hardware, various illustrative components, blocks, modules, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the application and design constraints imposed on the overall system.

[0055] Skilled artisans may implement the described functionality in varying ways for each application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present invention. In addition, those skilled in the art will appreciate that the embodiments described herein are merely exemplary implementations.

[0056] In this document, relational terms such as first and second, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Numerical ordinals such as “first," “second," “third,” etc. simply denote different singles of a plurality and do not imply any order or sequence unless specifically defined by the claim language. The sequence of the text in any of the claims does not imply that process steps must be performed in a temporal or logical order according to such sequence unless it is specifically defined by the language of the claim. When “or” is used herein, it is the logical or mathematical or, also called the “inclusive or.” Accordingly, A or B is true for the three cases: A is true, B is true, and A and B are true. In some cases, the exclusive “or” is constructed with “and;” for example, “one from the set A and B” is true for the two cases: A is true, and B is true.

[0057] Furthermore, depending on the context, words such as “connect” or “coupled to” used in describing a relationship between different elements do not imply that a direct physical connection must be made between these elements. For example, two elements may be connected to each other physically, electronically, logically, or in any other manner, through one or more additional elements.

[0058] While at least one exemplary embodiment has been presented in the foregoing detailed description of the invention, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment of the invention. It is understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope of the invention as set forth in the appended claims.