Abstract:
Method, controller and system for an implantable medical device having a plurality of electrodes, the implantable medical device capable of delivering therapeutic stimulation to a patient, comprising a control module, a user interface operatively coupled to the control module, the user interface providing control of the control module by a medical professional or other user, and an electrode interface operatively coupled between the plurality of electrodes and the control module. The control module uses the electrode interface to obtain a plurality of measurements of integrity metrics for a plurality of selected pairs of individual ones of the plurality of electrodes. The control module determines a prescriptive analysis using the plurality of measurements of integrity metrics of the selected pairs of individual ones of the plurality of electrodes comparative to a range, and the user interface displays the prescriptive analysis.

Description:
FIELD 
       [0001]    The present invention relates generally to controllers, systems and methods for implantable medical devices and, more particularly, to such controllers, systems and methods for implantable medical devices having therapeutic electrodes. 
       BACKGROUND 
       [0002]    The medical device industry produces a wide variety of electronic devices for treating patient medical conditions. Depending upon medical condition, medical devices can be surgically implanted or connected externally to the patient receiving treatment. Medical professionals or other clinicians use medical devices alone or in combination with drug therapies and surgery to treat patient medical conditions. For some medical conditions, medical devices provide the best, and sometimes the only, therapy to restore an individual to a more healthful condition and a fuller life. Examples of implantable medical devices designed to deliver therapeutic electrical stimulation include neurological stimulators, pacemakers and defibrillators. 
         [0003]    Implantable medical devices configured to deliver therapeutic electrical stimulation commonly deliver therapy via electrodes positioned on one or more leads operatively connected to the implantable medical device. In some instances, the housing of the implantable medical device may also serve as an electrode or an electrode may be positioned on the housing of the implantable medical device. The electrode or electrodes are commonly positioned in the patient&#39;s body during the same surgical procedure in which the implantable medical device is implanted. Sometimes the electrode or electrodes are placed in a follow-up procedure. 
         [0004]    The medical device industry produces a wide variety of electronic devices for treating patient medical conditions. Depending upon the medical condition, medical devices can be surgically implanted or connected externally to the patient receiving treatment. Medical professionals or other clinicians use medical devices alone or in combination with drug therapies and surgery to treat patient medical conditions. For some medical conditions, medical devices provide the best and sometimes the only therapy to restore an individual to a more healthful condition and a fuller life. Examples of implantable medical devices designed to deliver therapeutic electrical stimulation include neurological stimulators, pacemakers and defibrillators. 
         [0005]    Implantable medical devices configured to deliver therapeutic electrical stimulation commonly deliver therapy via electrodes positioned on one or more leads operatively connected to the implantable medical device. In some instances, the housing of the implantable medical device may also serve as an electrode or an electrode may be positioned on the housing. The electrode or electrodes are commonly positioned in the patient&#39;s body during the same surgical procedure in which the implantable medical device is implanted. 
         [0006]    The positioning of electrodes, and associated leads, is often an inexact procedure and may commonly be dependent on the particular physiologic characteristics of the patient. 
         [0007]    In addition, electrodes may commonly be positioned within the patient without the medical professional or user conducting the procedure being capable of actually seeing where the electrodes are positioned. Instead, external aides such as fluoroscopes and/or endoscopes may commonly be employed to inform the medical professional or other user as to an approximate location of the electrodes during implantation. Electrodes may also be placed by stereotactic head frame which allows placement of the lead without direct visualization. Further, the ideal target is often not known a priori and time constraints may not allow for perfect targeting in the operating room. 
         [0008]    Due to the inherent uncertainty involved in the placement of electrodes for an implantable medical device, implantable medical devices and the external controllers that interface with the devices are commonly operable to perform a test on the leads and electrodes to verify that the leads and electrodes are functioning properly and are positioned correctly. A common test is to check the impedance between pairs of electrodes. During testing, an electrode can be driven with a signal having known electrical characteristics. The signal may be measured, e.g., on another electrode or electrodes, and the impedance computed between electrodes using known fundamental relationships. The measured impedance value can give a medical professional or other user information relating to whether the electrodes involved in the test are positioned correctly and operating properly. 
         [0009]    An external controller, or physician programmer, is commonly utilized in lead impedance tests. Physician programmers can be similar in size and composition to a large laptop computer. The physician programmer provides a user interface via a display screen, and is manipulated by a medical professional via a variety of inputs, such as buttons and touchscreens. The physician programmer commonly communicates with the implantable medical device via inductive telemetry. In order to accomplish this, a coil, operatively coupled to the controller, is placed in proximity of a coil operatively coupled to the electronics in the implantable medical device, thereby establishing an inductive link over which data may be passed in either direction. Because physician programmers are typically not sterilized, the physician programmer itself may be placed outside of the sterile field, and only the coil and its housing is taken inside the sterile field, e.g., using a sterile bag. 
         [0010]    For example, United States Patent Application Publication No. 2006/0036186, Goetz et al, Automatic Impedance Measurement of an Implantable Medical Device; U.S. Pat. No. 5,891,179, Er et al, Method and Apparatus for Monitoring and Displaying Lead Impedance in Real-Time for an Implantable Medical Device; United States Patent Application Publication No. 2003/0114899, Samuelsson et al, Programming System for Medical Devices; United States Patent Application Publication No. 2005/0033385, Peterson et al, Implantable Medical Device Programming Apparatus Having a Graphical User Interface; and U.S. Pat. No. 6,721,600, Jorgenson et al, Implantable Lead Functional Status Monitor and Method, all disclose devices that measure electrode impedance or otherwise test electrodes of an implantable medical device. 
       SUMMARY 
       [0011]    As the number of electrodes associated with an implantable medical device has increased from one or two, to just a few and then to many electrodes, the time and hardware and software resources necessary to perform proper measurements for all of the electrodes associated with an implantable medical device has, in many cases, become burdensome. 
         [0012]    In an embodiment, a controller or system containing such a controller or a method therefore, can be pre-configured by a user to test only a subset of the total number of electrodes and electrode pair combinations available in an implantable medical device. 
         [0013]    None of the above documents show, disclose or suggest allowing a medical professional to pre-configure electrode functionality tests in order to improve efficiency of the test by testing only such leads and electrodes as the medical professional considers necessary. The controller may provide a range of integrity metrics, e.g., impedance values, considered normal, bounded on either end by values fixed for the test. In addition, a medical professional may specify which electrodes are to be tested, and the range of integrity metrics considered normal for those particular electrodes. Inter-electrode impedance tests may also be conducted at voltage and current levels that are used by the device to deliver therapy in order to determine functionality at operation voltage levels. 
         [0014]    In an embodiment, the present invention provides a controller for an implantable medical device having a plurality of electrodes, the implantable medical device being capable of delivering therapeutic stimulation to a patient via the plurality of electrodes. A control module is operatively coupled to the plurality of electrodes. A user interface is operatively coupled to the control module, the user interface providing at least partial control of the control module by a user. The control module obtains a plurality of measurements of integrity metrics for a group of individual ones of the plurality of the electrodes, the group of individual ones of the plurality of electrodes being based upon a selection made via the user interface. 
         [0015]    In an embodiment, the control module obtains a plurality of measurements of integrity metrics of the individual ones of the plurality of electrodes included in a selected group of individual ones of the plurality of the electrodes selected via the user interface. 
         [0016]    In an embodiment, the control module obtains a plurality of measurements of integrity metrics of the individual ones of the plurality of electrodes not included in a selected group of individual ones of the plurality of the electrodes selected via the user interface. 
         [0017]    In an embodiment, the control module uses a plurality of parameters selected via the user interface to obtain the plurality of measurements of integrity metrics. 
         [0018]    In an embodiment, the plurality of parameters are selected from the group consisting of voltage, amplitude, pulse width, frequency, current, power and electrode polarity. 
         [0019]    In an embodiment, the user interface presents for possible measurement of impedance value only ones of the plurality of electrodes having previously received a measurement of impedance value comparative to a predetermined range. 
         [0020]    In an embodiment, the user interface presents for possible measurement of impedance value only ones of the plurality of electrodes currently in use by the implantable medical device. 
         [0021]    In an embodiment, the user interface presents for possible measurement of impedance value only ones of said plurality of electrodes that have previously been selected by the user. 
         [0022]    In an embodiment, the user interface presents for possible measurement of impedance value only ones of the plurality of electrodes having previously received a measurement of impedance value comparative to a predetermined range. 
         [0023]    In an embodiment, the user interface presents for possible measurement of impedance value only ones of said plurality of electrodes that are associated as being at least one of free of side effects or free of side effects above a predetermined threshold. 
         [0024]    In an embodiment, the present invention provides a controller for an implantable medical device having a plurality of electrodes. The implantable medical device being capable of delivering therapeutic stimulation to a patient via the plurality of electrodes. A control module is operatively coupled to the plurality of electrodes. A user interface is operatively coupled to the control module. The user interface provides at least partial control of the control module by a user. The control module obtains a plurality of measurements of integrity metrics for one of a plurality of groups of individual ones of plurality of electrodes with the one of a plurality of groups being based upon a selection made via the user interface. 
         [0025]    In an embodiment, at least one of the plurality of groups are determined, at least in part, on a modality of measurement. 
         [0026]    In an embodiment, the modality of measurement is at least one of current based impedance measurement, voltage based impedance measurement, real impedance, complex impedance, number of measurement pulses, timing of measurement pulses, sampling of measurement data and oversampling of measurement data. 
         [0027]    In an embodiment, the present invention provides a system for delivering therapeutic stimulation to a patient. The system includes an implantable medical device having a plurality of electrodes, and a controller. The controller includes a control module operatively coupled to the plurality of electrodes, and a user interface operatively coupled to the control module, the user interface providing control of the control module by a user. The control module obtains a plurality of measurements of integrity metrics for a group of individual ones of the plurality of the electrodes, the group of individual ones of the plurality of electrodes being based upon a selection made via the user interface. 
         [0028]    In an embodiment, the present invention provides a system for delivering therapeutic stimulation to a patient. The system includes an implantable medical device having a plurality of electrodes, and a controller. The controller includes a control module operatively coupled to the plurality of electrodes, and a user interface operatively coupled to the control module, the user interface providing control of the control module by a user. The control module obtains a plurality of measurements of integrity metrics for one of a plurality of groups of individual ones of plurality of electrodes with the one of a plurality of groups being based upon a selection made via the user interface. 
         [0029]    In an embodiment, the present invention provides a method for delivering therapeutic stimulation to a patient using an implantable medical device having a plurality of electrodes, comprising the steps of creating a selected group of individual ones of the plurality of electrodes via a user interface, and obtaining a plurality of measurements of integrity metrics for a group of individual ones of the plurality of the electrodes, the group of individual ones of the plurality of electrodes being based upon a selection made via the user interface. 
         [0030]    In an embodiment, the obtaining step utilizes individual ones of the plurality of electrodes included in a selected group of individual ones of the plurality of the electrodes selected via the user interface. 
         [0031]    In an embodiment, the obtaining step utilizes individual ones of the plurality of electrodes not included in a selected group of individual ones of the plurality of the electrodes selected via the user interface. 
         [0032]    In an embodiment, the obtaining step uses a plurality of parameters selected via the user interface. 
         [0033]    In an embodiment, the plurality of parameters are selected from the group consisting of voltage, amplitude, pulse width, frequency, current, power and electrode polarity. 
         [0034]    In an embodiment, there is a further comprising the step of presenting via the user interface for possible measurement of impedance value only ones of the plurality of electrodes having previously received a measurement of impedance value comparative to a predetermined range. 
         [0035]    In an embodiment, the presenting step presents for possible measurement of impedance value only ones of the plurality of electrodes currently in use by the implantable medical device. 
         [0036]    In an embodiment, the presenting step presents for possible measurement of impedance value only ones of the plurality of electrodes having previously received a measurement of impedance value comparative to a predetermined range. 
         [0037]    In an embodiment, the present invention provides a method for delivering therapeutic stimulation to a patient using an implantable medical device having a plurality of electrodes, comprising the steps of creating a plurality of groups of individual ones of said plurality of electrodes, and obtaining a plurality of measurements of integrity metrics for one of a plurality of groups of individual ones of the plurality of electrodes, the one of a plurality of groups being based upon a selection made via a user interface. 
     
    
     
       DRAWINGS 
         [0038]      FIG. 1  shows an example of an implantable neurological stimulator implanted in the side of a patient, with electrodes positioned along the patient&#39;s sacral nerves; 
           [0039]      FIG. 2  shows an implantable neurological stimulator with a lead and lead extender and electrodes; 
           [0040]      FIG. 3  shows a cutaway diagram of a lead with electrodes, and a lead extender, for an implantable medical device; 
           [0041]      FIG. 4  shows a screen shot of a window for controlling an electrode impedance test of an implantable neurological stimulator; 
           [0042]      FIG. 5  shows a screen shot of a window for displaying out-of-range results of an electrode impedance test of an implantable neurological stimulator; 
           [0043]      FIG. 6  shows a screen shot of a window for displaying results of an electrode impedance test of an implantable neurological stimulator; 
           [0044]      FIG. 7  shows a block diagram of a controller for an implantable medical device; 
           [0045]      FIG. 8  is a flow chart for conducting an electrode impedance test for an implantable medical device. 
       
    
    
     DESCRIPTION 
       [0046]    While electrode tests are illustrated and described herein generally as being electrode impedance tests, it is to be recognized and understood that other forms of electrode integrity testing is also contemplated. In general, an integrity metric, which may be an impedance measurement, may be measured for a plurality of electrodes and the efficacy of each of the plurality of electrodes determined, at least in part. While electrode impedance is one such integrity metric, others are contemplated such as admittance, real or complex. Other integrity metrics could be the current flowing into or out of a particular electrode or group of electrodes, voltage potential measured at an electrode due to stimulus on another electrode or electrodes, capacitance of an electrode with respect to another electrode or electrodes, inductance of an electrode with respect to another electrode or electrodes, frequency response of an electrode with respect to stimulus on another electrode or electrodes, measured reflection of a stimulus signal driven into an electrode (as in an electromagnetic transmission line). 
         [0047]      FIG. 1  shows the general environment of one rechargeable implantable medical device  20  embodiment. Implantable neurological stimulator  22  is shown, but other embodiments such as pacemakers and defibrillators and the like are also applicable. Implantable neurological stimulator  22  is implanted subcutaneously in side  28  of patient  30 . Lead  24  is operatively coupled to implantable neurological stimulator  22  at header  26 . Lead  24  is positioned along spinal chord  31  of patient  30 . Controller  32 , which may be a physician programmer or patient programmer, may become transcutaneously coupled to implantable neurological stimulator  22  via an inductive communication link through the tissue of patient  30  when controller  32  is placed in proximity to implantable neurological stimulator  22 . 
         [0048]      FIGS. 2 and 3  show a closer view of implantable neurological stimulator  22  and lead  24 , operatively coupled by extender  36 . Electrodes  38  are mounted on distal end  37  of lead  24 . Electrodes  38  are comprised of a conductive material, in an embodiment, metal, that come into direct contact with tissue of patient  30 . Electrodes  38  are operatively coupled with implantable neurological stimulator  22  via header  26  through wires  39  comprised of conductive material that pass through the interior  41  of lead  24  and are operatively coupled with conductive wires  39  in the interior  40  of extender  36 . 
         [0049]      FIG. 4  shows electrode impedance panel  140  for neurological stimulator  22 , in this case a deep brain stimulator. Pick menus  142  allow selection of different leads  24  to test. Pick boxes  44  allow the medical professional or other user to select which electrodes  38  will be tested and whether those electrodes  38  will be tested in unipolar or bipolar configuration. Scroll menu  46  allows the medical professional or other user to set the voltage amplitude, and optionally, pulse width and frequency, at which point the test will be conducted. Pressing button  48  begins the test according to the parameters that have been chosen on panel  140 . Alternatively, the test may begin without the necessity of a button press. After the test has completed a summary of the results is displayed in window  50 , while buttons  52  give the medical professional or other user access to panel  60  ( FIG. 5 ) that displays all results that were out of the predetermined range and to panel  80  ( FIG. 6 ) that displays all results. 
         [0050]    In a typical electrode impedance test, each electrode  38  will be tested both in unipolar mode and bipolar mode. Each electrode  38  in unipolar mode is paired up with neurological stimulator case  23  and the impedance between each electrode  38  and implantable neurological stimulator case  23  is measured and stored. In addition, each electrode  38  in bipolar mode is paired up with every other electrode  38  and the impedance between each electrode  38  and every other electrode  38  is measured and stored. An exception may be that electrodes  38  that are located in different physiologic regions of the body, e.g., the head, the chest, are never paired and tested. 
         [0051]      FIG. 5  shows out of range results panel  60  for displaying the results of testing initiated from electrode impedance panel  140 . Text  62  at top of out of range results panel  60  informs the medical professional or other user what test the current results pertain to by displaying which electrodes  38  were tested, in which mode electrodes  38  were tested and at which voltage amplitude electrodes  38  were tested. Possible open circuits window  64  lists possible locations, e.g., all possible locations, of open circuits that cause faults of tested electrodes  38 . Possible short circuits window  66  lists possible locations, e.g., all possible locations, of short circuits that cause faults. 
         [0052]    Open circuits are typically detectable when all measured impedance values for one electrode  38  are higher than the allowable maximum value. For instance, if all impedance values involving electrode ( 38 ) number two exceed the maximum value and all impedance values not involving electrode  38  number two are within the allowable value, the controller could conclude that an open circuit existed on the path along which electrode ( 38 ) number two was operatively coupled with implantable neurological stimulator  22 . Similarly, if all measured impedance values pertaining to electrodes ( 38 ) number two and six exceeded the maximum value and all impedance values not involving electrodes ( 38 ) number two and six are within the allowable a values, the controller could conclude that both electrodes ( 38 ) number two and six were open. 
         [0053]    By contrast, short circuits are typically detectable when all measured impedance values involving those two electrodes ( 38 ) are lower than average and the measured impedance value between the two electrodes  38  is below the minimum allowable value. For instance, if the average impedance between electrodes ( 38 ) is five hundred ohms, but between electrodes ( 38 ) four and five, and four and six, in bipolar mode, and electrodes ( 38 ) five and case  23  and six and case  23  were all four hundred ohms, and the impedance between electrodes  38  five and six was below the allowable minimum value, controller  120  ( FIG. 7 ) could conclude that there is a short circuit between electrodes ( 38 ) five and six. Such short circuits can occur, among other reasons, because the electrodes  38  in question are physically touching, or insulation  42  between wires  39  operatively coupling electrodes  38  with implantable neurological stimulator  22  have frayed. Other examples of possible electrodes shorts are crushing of the lead body causing conductive wires to contact each other or adjoining wires and fluid ingress to a connector, e.g., lead to lead extension, lead extension to implantable medical device, lead to implantable medical device, causing one or more of the electrodes to short. 
         [0054]    Occasionally, the results of testing may provide ambiguous results. For instance, if the impedance between electrodes ( 38 ) zero and two, three and two and between electrode ( 38 ) two and case  23  are all greater than the maximum allowable value, but the impedance between electrodes ( 38 ) one and two is within the allowable range, then it might not be clear what is the underlying cause of the issue. 
         [0055]      FIG. 6  shows all results panel  80 , for displaying all results of testing initiated from electrode impedance panel  140 , regardless of whether testing resulted in an indication of failure or failures or not. Text  82  at the top of all results panel  80  informs the medical professional or other user to what test the current results pertain by displaying which electrodes  38  were tested, in which mode electrodes  38  were tested and at which voltage amplitude electrodes  38  were tested. Results are displayed in one of two windows  84 ,  86  depending on if the test mode was unipolar  84  or bipolar  86 . Buttons  88  provide access to electrode impedance panel  140  and a print command. 
         [0056]      FIG. 7  shows a block diagram of the functional blocks of controller  120 , which may be employed as, and be similar to, controller  32  of  FIG. 1 . Control module  122  comprises a variety of off the shelf electronic components commonly found in a variety of commercial applications, such as personal computers. These electronic components include: a microprocessor, RAM, ROM and hard disks. These off the shelf components are integrated into control module  122  and additional operational features are added via custom electronics. These custom electronics are comprised of off the shelf integrated circuits and discrete components, and programmable components, such as FPGAs and DSPs, and custom integrated circuits and PCBs. 
         [0057]      FIG. 8  is a flow chart for pre-configuring an electrode impedance test. A user may select ( 160 ) electrodes  38  to be tested using electrode impedance panel  140  on controller  32 . The user may then select ( 162 ) the test parameters at which the impedance test is conducted, again using electrode impedance panel  140  on controller  32 . Once electrodes  38  and the test parameters have been selected, the user may commence ( 164 ) the electrode impedance test by selecting the Take Measurements button  48  on electrode impedance panel  140 . Once the electrode impedance test has been conducted, results may be indicated ( 166 ) in results window  50  of electrode impedance panel  140 , on out-of-range results panel  60 , or all results panel  80  of controller  32 . The user may then continue programming ( 168 ) implantable medical device  20 . 
         [0058]    In an embodiment, groups of electrodes  38  are selected based upon a task or range of tasks which may be performed. For example, it may be desirable to conduct tests on a select group of electrodes during a regular follow up visit to the medical professional. It may be appropriate to measure a subset of the entire number of plurality of electrodes during such a visit and routine test. However, during a testing procedure to trouble shoot lead or electrodes problems or issues it may be desirable to conduct tests on a greater number of electrodes than would be selected during a routine follow up test in order to gather more information about lead or electrode problems or issues encountered, or to even select all of the electrodes to be testing in such circumstance. Likewise, it may be desirable to group a plurality of electrodes to be tested during a procedure having minimal patient impact. 
         [0059]    For instance, electrodes that are known to have uncomfortable or unpleasant side effects might be excluded from measurement or might be excluded from electrodes presented to a user for possible measurement. In an embodiment, a threshold for any such side effect may be established and electrodes that meet and/or exceed such threshold might be excluded from measurement or from presentation to a user for possible measurement. Similarly, electrodes know or thought to have little or no therapeutic benefit might be excluded from measurement or excluded from presentation for possible measurement. Combinations are also possible, for example, electrodes with some combination of little therapeutic benefit but some side effect might be excluded from measurement or presentation for measurement while an electrode or electrode combination with little therapeutic benefit but no side effect might be included in measurement or presentation for measurement or an electrode with some side effect but substantial therapeutic benefit might be included in measurement or presentation for measurement. A therapeutic benefit to side effect ratio might be established to help make such a determination. 
         [0060]    In this case, a smaller number of electrodes may be selected in order to minimize the time and other impact on the patient. Thus, a plurality of different groups of electrodes may be pre-selected to fall into different categories of tests as may be beneficial. A user may then select a predetermined group of electrodes that may best fit the test being conducted. This may save the user from selecting from the entire list, or long list, of electrodes each time a test is to be conducted. A user may select, for example, the group associated with a routine follow up test and have the electrodes selected for test to be pre-populated in accordance with the predetermined group. In an embodiment, the user could still modify the electrodes to be tested from the starting point of the selected group. 
         [0061]    In an embodiment, after an electrode, electrodes or a group of electrodes that have been selected, for example by modifying the electrode selection, then such modification could be used, at least in part, to determine which electrode, electrodes or groups of electrodes are measured or presented to a user for measurement in the future. For example, only electrodes that were selected by the user for measurement in the previous test would be presented to the user for a current test. The user may be presented with a list of electrodes selected or used during the previous visit or during a visit at a previous visit or a visit at a particular date and/or time. Alternatively, usage of an electrode, electrodes or groups of electrodes could be tracked and either the usage history of an electrode, electrodes or groups of electrodes could be presented to the user or the electrode, electrodes or groups of electrodes presented to the user for measurement could be based, at least in part, on such usage history such as by presenting the electrode, electrodes or groups of electrodes most commonly used, most recently used, least commonly used, etc. 
         [0062]    In an embodiment, a group of electrodes to be tested could be selected or predetermined based upon the modality of the test procedure. As an example, a group could be predetermined that would conduct impedance measurements on selected electrodes that are current based. Another group could be predetermined that would conduct impedance measurements on selected electrodes that are voltage based. Other modalities of testing that are envisioned include, but are not limited to, real impedance, e.g., direct current measurement; complex impedance, e.g., alternating current measurement including capacitance and inductance measures; number of measurement or testing pulses; the timing measurement pulses or the time between measurement pulses; the manipulation of the data obtained from measurement, e.g., averaging of measurement sampling; and oversampling of measurement data. It is envisioned that various groups based upon measurement modality could be configured based upon, for example, which measurement technique would be fastest and which measurement technique would be most accurate or most comprehensive. It is to be recognized and understood that such groups are only exemplary and many other groups based upon measurement modality are envisioned. 
         [0063]    Thus, embodiments of the controller for pre-configuring a test for implantable medical device electrodes, system and method therefore are disclosed. One skilled in the art will appreciate that the present invention can be practiced with embodiments other than those disclosed. The disclosed embodiments are presented for purposes of illustration and not limitation, and the present invention is limited only by the claims that follow.