Patent Publication Number: US-2010114236-A1

Title: Hybrid battery system with bioelectric cell for implantable cardiac therapy device

Description:
RELATED APPLICATIONS 
     This application is related to co-pending and commonly-owned U.S. patent application Ser. No. 11/737,307, entitled “Bioelectric Battery for Implantable Device Applications”, filed Apr. 19, 2007; co-pending and commonly-owned U.S. patent application Ser. No. ______, entitled “Hybrid Battery System For Implantable Cardiac Therapy Device”, filed on even date herewith (attorney docket number A06E3099); and co-pending and commonly-owned U.S. patent application Ser. No. 11/940,552, entitled “Blood Oxygen Saturation Measurement Utilizing A Bioelectric Battery”, filed Nov. 15, 2007; each of which is incorporated by reference herein as if reproduced in full below. 
    
    
     BACKGROUND 
     1. Field of the Invention 
     The present invention relates generally to implantable cardiac therapy devices, and to power sources for the same. More particularly, the invention relates to a hybrid battery system which includes a bioelectric cell coupled to a rechargeable cell. 
     2. Background Art 
     Implantable cardiac therapy devices (ICTDs) enjoy widespread use for providing convenient, portable, sustained therapy for cardiac patients with a variety of cardiac arrhythmias. An ICTD may be a pacemaker, or may combine a pacemaker and defibrillator in a single implantable device. Such devices may be configured to provide ongoing cardiac pacing in order to maintain an appropriate cardiac rhythm. In addition, should the ICTD detect that the patient is experiencing an episode of ventricular fibrillation (or an episode of ventricular tachycardia), an ICTD may be configured to deliver appropriate defibrillation therapy. 
     An ICTD requires a portable power supply in the form of a battery. The battery has several inherent requirements including safety and also the ability to provide power to the ICTD for an extended period of time, thereby minimizing the frequency of invasive procedures to replace the battery. 
     ICTDs have additional, specialized power requirements due to the specific nature of their function. Long-term cardiac pacing can be supported by a low voltage, low current power source. Defibrillation therapy, however, requires rapid, high voltage, high current delivery to the heart. 
     A standard battery for many ICTD applications has been the Lithium Silver Vanadium Oxide (LiSVO) cell, which provides sufficient voltage for cardiac pacing and background operations such as sensing and communications. The LiSVO cell also can provide an adequate, if not entirely ideal, voltage and current flow for cardiac shocking (that is, defibrillation therapy). 
     However, the LiSVO battery suffers from disadvantages as well. Its internal resistances from both the anode and cathode tend to increase in the discharging process, particularly during midlife. As a result, over time, the loaded voltage will be lower and the time for discharging (that is, the time for charging the shocking capacitors of the ICTD) increases. In some cases, the discharge time could be doubled, which may render the battery unacceptable for defibrillation. This may result in a medical decision to replace the device, which in turn means the patient may have to accept a premature surgery. In the past, the increased battery discharge time has been a major issue for ICTDs. 
     Another possible power source for an ICTD is a bioelectric battery, which generates energy from a replenishable substance of the patient. Typically, a body fluid is an electrolyte, providing the replenishable substance. In one embodiment the replenishable substance may be the blood oxygen of the patient. Embodiments of such a bioelectric battery are described, for example, in co-pending and commonly-owned U.S. patent application Ser. No. 11/737,307, entitled “Bioelectric Battery for Implantable Device Applications”, filed Apr. 19, 2007, which is incorporated by reference herein in its entirety. 
     An implantable bioelectric battery configured to generate power from a replenishable substance of the patient may present significant advantages as a power source, as compared to standard power cells (such as the LiSVO power cells currently employed in many ICTDs). For example, a bioelectric cell may have a more consistent current and/or voltage delivery over the lifetime of the cell. In addition, the bioelectric cell may also have a longer lifetime than the LiSVO cell, and therefore require less frequent replacement. This spares the patient unnecessary surgery. 
     However, a bioelectric power cell may not offer all the features or power capabilities desired for an ICTD. For example, the relatively low current available from a bioelectric cell (e.g., on the order of 100 μAmps) may not be sufficient to power high voltage shocking. Also, the current available from a bioelectric cell may not be sufficient for certain kinds of data telemetry, or for certain high speed telemetry data rates. Further, because the bioelectric cell requires a replenishable substance of a patient to generate power, the cell cannot provide any power when the device is not implanted in a patient. However, power may be required, even during non-implantation, for device testing, final programming, and during the pre-implant shelf life of the ICTD. 
     In short, there does not exist a single power cell which is optimized to effectively provide optimized electrical sourcing for an ICTD. 
     A recent improvement has been the use of a hybrid battery source. A hybrid battery system combines two different physical batteries, with different but complementary electrical properties, into a single functional package. The single functional package effectively serves as the battery for the ICTD. A first physical battery (which may also be referred to as a cell) of the hybrid battery typically has a high energy density for long battery life, but may have a relatively low voltage and low current output. A second physical battery (or cell) has higher voltage output, higher current delivery (typically a result of lower internal resistance), and superior recharging time and recharging properties. However, the second cell typically has lower energy density that the first battery. The two cells are coupled in the hybrid battery, with the first cell providing charging to the second cell. 
     In many applications, a hybrid battery may be an improvement over the standard batteries (such as the Li/SVO cells) currently employed in many ICTD applications. However, the lifetime of a hybrid battery is still limited by the energy storage of the primary cell. 
     What is needed, then, is a battery designed for use in an ICTD which takes advantage of the optimized electrical properties of a hybrid battery design, and which further takes advantage of long life and other benefits of a bioelectric cell. 
     BRIEF SUMMARY 
     The present system and method employs a hybrid battery comprised of at least two types of cells to power an implantable cardiac therapy device (ICTD). A first type of cell is a bioelectric cell which generates electrical power from a replenishable organic substance. In one example embodiment, the bioelectric cell provides low voltage but high energy density. 
     The bioelectric cell is coupled to a secondary cell which is not a bioelectric cell. The bioelectric cell is coupled to the secondary cell via charging means, which may for example be a simple DC-to-DC converter. The secondary cell is maintained at full or nearly full charge by the energy provided by the bioelectric cell. In one example embodiment, the secondary cell has low internal resistance and high voltage, making it suitable to rapidly charge ICTD capacitors for cardiac shocking (e.g., for defibrillation). The secondary cell may also provide power for other ICTD operations which may require relatively high voltage or high current. For example, the secondary cell may power high speed data telemetry. 
     In an embodiment, the bioelectric cell directly provides power to the ICTD for purposes of routine cardiac monitoring, pacing, and other low voltage, low current operations. In an alternative embodiment, the secondary cell provides power to the ICTD for purposes of routine cardiac monitoring, pacing, and other low voltage, low current operations. In another alternative embodiment, some low current operations (cardiac monitoring, pacing, etc.) are powered via power from the bioelectric cell, while other low current operations are powered via power from the secondary cell. 
     An optimized energy density distribution may be implemented between the bioelectric cell and the secondary cell. In one embodiment, the first type of cell is the bioelectric cell, while the secondary cell is a Li ion polymer cell. Each type of cell may be implemented as a single physical cell, or alternatively as two or more physical cells of the same type. 
     Further embodiments, features, and advantages of the present system and method, as well as the structure and operation of various exemplary embodiments of the present system and method, are described in detail below with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES 
       The accompanying drawings, which are incorporated herein and form part of the specification, illustrate the methods and systems presented herein for a hybrid bioelectric battery optimized for an implantable cardiac therapy device. Together with the detailed description, the drawings further serve to explain the principles of and to enable a person skilled in the relevant art(s) to make and use the methods and systems presented herein. 
       In the drawings, like reference numbers indicate identical or functionally similar elements. Further, the drawing in which an element first appears is typically indicated by the leftmost digit(s) in the corresponding reference number (e.g., an element numbered  302  first appears in  FIG. 3 ). (There are some exceptions. For example, element  404  first appears in  FIG. 2B  of this document, but is discussed in detail in conjunction with  FIG. 4 .) 
       Additionally, some elements may be labeled with only a number to indicate a generic form of the element, while other elements labeled with the same number followed by another number or a letter (or a letter/number combination) may indicate a species of the element. A period or underscore may be introduced in the label for clarity of reading, and has no other significance. 
         FIG. 1  is a simplified diagram illustrating an exemplary implantable cardiac therapy device (ICTD) having a bioelectric cell and being in electrical communication with a patient&#39;s heart by means of leads suitable for delivering multi-chamber stimulation and pacing therapy, and for detecting cardiac electrical activity. 
         FIG. 2A  is a functional block diagram of an exemplary ICTD that can detect cardiac electrical activity and analyze cardiac electrical activity, as well as provide cardioversion, defibrillation, and pacing stimulation in four chambers of a heart. 
         FIG. 2B  is a functional block diagram of another exemplary ICTD with an exemplary hybrid battery which includes a bioelectric cell. 
         FIG. 2C  is a functional block diagram of another embodiment of an exemplary ICTD with an exemplary hybrid battery which includes a bioelectric cell. 
         FIG. 3  is a functional block diagram of the internal architecture and principle external connections of an exemplary external programming device which may be used by to monitor or program an ICTD. 
         FIG. 4A-4D  show functional block diagrams of exemplary bioelectric hybrid battery systems employing a bioelectric cell, along with interconnections to some elements of an exemplary ICTD, according to embodiments of the present system and method. 
         FIG. 5  shows a set of experimentally measured plots of the time required for various Li ion polymer cells to charge shocking capacitors in a representative ICTD. 
         FIG. 6  shows a set of experimentally measured plots of the time required for various Li ion polymer cells to charge shocking capacitors in another representative ICTD. 
         FIG. 7  shows a set of experimentally measured plots of the time required for a representative Li ion polymer cell to charge the shocking capacitors of a representative ICTD at different current levels. 
     
    
    
     DETAILED DESCRIPTION 
     1. Overview 
     2. Exemplary Environment—Overview 
     3. Exemplary ICTD in Electrical Communication with a Patient&#39;s Heart 
     4. Exemplary Bioelectric Cell 
     5. Functional Elements of an Exemplary ICTD 
     6. ICTD Programmer 
     7. Hybrid Battery with Bioelectric Cell
 
8. Further Elements of Hybrid Battery with Bioelectric Cell
 
     9. Choice of Secondary Power Cell 
     10. Lithium Ion Polymer Cell vs. Standard Lithium Ion Cell 
     11. Storage Capacities and Power Delivery for Cells for Different ICTD Applications 
     12. Alternative Embodiments 
     13. Conclusion 
     1. Overview 
     The following detailed description of systems and methods for a hybrid battery system with a bioelectric cell for implantable cardiac therapy devices refers to the accompanying drawings that illustrate exemplary embodiments consistent with these systems and methods. Other embodiments are possible, and modifications may be made to the embodiments within the spirit and scope of the methods and systems presented herein. Therefore, the following detailed description is not meant to limit the methods and systems described herein. Rather, the scope of these methods and systems is defined by the appended claims. 
     It would be apparent to one of skill in the art that the systems and methods for a hybrid battery system with a bioelectric cell for implantable cardiac therapy devices, as described below, may be implemented in many different embodiments of hardware, software, firmware, and/or the entities illustrated in the figures. Any actual hardware and/or software described herein is not limiting of these methods and systems. In addition, more than one embodiment of the present system and method may be presented below, and it will be understood that not all embodiments necessarily exhibit all elements, that some elements may be combined or connected in a manner different than that specifically described herein, and that some differing elements from the different embodiments presented herein may be functionally and structurally combined to achieve still further embodiments of the present system and method. 
     Thus, the operation and behavior of the methods and systems will be described with the understanding that modifications and variations of the embodiments are possible, given the level of detail presented herein. 
     2. Exemplary Environment—Overview 
     Before describing in detail the methods and systems for a hybrid battery system with a bioelectric cell for implantable cardiac therapy devices, it is helpful to describe an example environment in which these methods and systems may be implemented. The methods and systems described herein may be particularly useful in the environment of an implantable cardiac therapy device (ICTD). 
     An ICTD may also be referred to synonymously herein as a “stimulation device”, emphasizing the role of the ICTD in providing pacing and shocking to a human heart. However, an ICTD may provide operations or services in addition to stimulation, including but not limited to cardiac monitoring. Also, some ICTDs may provide cardiac pacing and monitoring, but may not provide cardiac shocking (that is, may not provide defibrillation). 
     The bioelectric hybrid battery described herein, as well as the ICTD described herein, are typically implanted in a living organism which is typically a mammal, and is typically a human being, though these devices may be implanted in other mammals as well. The human being is typically referred to as a patient. The terms “organism”, “mammal”, “person”, and “patient” may be used interchangeably in this document to refer to the organism in which an ICTD may be implanted, and in which a bioelectric hybrid battery may be implanted. 
     An ICTD is a physiologic measuring device and therapeutic device that is implanted in a patient to monitor cardiac function and to deliver appropriate electrical therapy, for example, pacing pulses, cardioverting and defibrillator pulses, and drug therapy, as required. ICTDs include, for example and without limitation, pacemakers, cardioverters, defibrillators, implantable cardioverter defibrillators, implantable cardiac rhythm management devices, and the like. Such devices may also be used in particular to monitor cardiac electrical activity and to analyze cardiac electrical activity. The term “implantable cardiac therapy device” or simply “ICTD” is used herein to refer to any such implantable cardiac therapy device. 
     Persons skilled in the relevant arts will recognize that the term “battery” is sometimes employed in place of the word “cell” so that, for example, a “lithium ion polymer cell” may also be described, equivalently, as a “lithium ion polymer battery”. Similarly, the terms “bioelectric cell” and “bioelectric battery” may be used interchangeably within the art. 
     Within this document, individual batteries (a bioelectric battery, a standard lithium ion battery, a lithium ion polymer battery, a lithium/silver vanadium oxide battery, a lithium magnesium oxide battery, etc.) are generally referred to as “cells” rather than batteries. So, for example, the usage is “a bioelectric cell”, “a lithium ion polymer cell”, etc. This usage is strictly to help distinguish these cells from the overall hybrid battery system of the present system and method. The hybrid battery system of the present system and method is comprised of multiple cells. The usage employed herein (“cell” for individual batteries vs. “battery” for the hybrid battery system) has no further significance. 
     3. Exemplary ICTD in Electrical Communication with a Patient&#39;s Heart 
     The techniques described below are intended to be implemented in connection with any ICTD or any similar stimulation device that is configured or configurable to stimulate nerves and/or stimulate and/or shock a patient&#39;s heart. 
       FIG. 1  shows an exemplary stimulation device or ICTD  100  in electrical communication with a patient&#39;s heart  102  by way of three leads  104 ,  106 ,  108 , suitable for delivering multi-chamber stimulation and shock therapy. The leads  104 ,  106 ,  108  are optionally configurable for delivery of stimulation pulses suitable for stimulation of autonomic nerves. In addition, the device  100  includes a fourth lead  110  having, in this implementation, three electrodes  144 ,  144 ′,  144 ″ suitable for stimulation of autonomic nerves. This lead may be positioned in and/or near a patient&#39;s heart or near an autonomic nerve within a patient&#39;s body and remote from the heart. Of course, such a lead may be positioned epicardially or at some other location to stimulate other tissue. 
     The right atrial lead  104 , as the name implies, is positioned in and/or passes through a patient&#39;s right atrium. The right atrial lead  104  optionally senses atrial cardiac signals and/or provide right atrial chamber stimulation therapy. As shown in  FIG. 1 , the stimulation device  100  is coupled to an implantable right atrial lead  104  having, for example, an atrial tip electrode  120 , which typically is implanted in the patient&#39;s right atrial appendage. The lead  104 , as shown in  FIG. 1 , also includes an atrial ring electrode  121 . Of course, the lead  104  may have other electrodes as well. For example, the right atrial lead optionally includes a distal bifurcation having electrodes suitable for stimulation of autonomic nerves. 
     To sense atrial cardiac signals, ventricular cardiac signals and/or to provide chamber pacing therapy, particularly on the left side of a patient&#39;s heart, the stimulation device  100  is coupled to a coronary sinus lead  106  designed for placement in the coronary sinus and/or tributary veins of the coronary sinus. Thus, the coronary sinus lead  106  is optionally suitable for positioning at least one distal electrode adjacent to the left ventricle and/or additional electrode(s) adjacent to the left atrium. In a normal heart, tributary veins of the coronary sinus include, but may not be limited to, the great cardiac vein, the left marginal vein, the left posterior ventricular vein, the middle cardiac vein, and the small cardiac vein. 
     Accordingly, an exemplary coronary sinus lead  106  is optionally designed to receive atrial and ventricular cardiac signals and to deliver left ventricular pacing therapy using, for example, at least a left ventricular tip electrode  122 , left atrial pacing therapy using at least a left atrial ring electrode  124 , and shocking therapy using at least a left atrial coil electrode  126 . For a complete description of a coronary sinus lead, the reader is directed to U.S. Pat. No. 5,466,254, “Coronary Sinus Lead with Atrial Sensing Capability” (Helland), which is incorporated herein by reference. The coronary sinus lead  106  further optionally includes electrodes for stimulation of autonomic nerves. Such a lead may include pacing and autonomic nerve stimulation functionality and may further include bifurcations or legs. For example, an exemplary coronary sinus lead includes pacing electrodes capable of delivering pacing pulses to a patient&#39;s left ventricle and at least one electrode capable of stimulating an autonomic nerve. An exemplary coronary sinus lead (or left ventricular lead or left atrial lead) may also include at least one electrode capable of stimulating an autonomic nerve, such an electrode may be positioned on the lead or a bifurcation or leg of the lead. 
     Stimulation device  100  is also shown in electrical communication with the patient&#39;s heart  102  by way of an implantable right ventricular lead  108  having, in this exemplary implementation, a right ventricular tip electrode  128 , a right ventricular ring electrode  130 , a right ventricular (RV) coil electrode  132 , and an SVC coil electrode  134 . Typically, the right ventricular lead  108  is transvenously inserted into the heart  102  to place the right ventricular tip electrode  128  in the right ventricular apex so that the RV coil electrode  132  will be positioned in the right ventricle and the SVC coil electrode  134  will be positioned in the superior vena cava. Accordingly, the right ventricular lead  108  is capable of sensing or receiving cardiac signals, and delivering stimulation in the form of pacing and shock therapy to the right ventricle. An exemplary right ventricular lead may also include at least one electrode capable of stimulating an autonomic nerve, such an electrode may be positioned on the lead or a bifurcation or leg of the lead. 
     4. Exemplary Bioelectric Cell 
     The present system and method for a hybrid battery system includes a bioelectric cell  176  implanted in the patient&#39;s body. In an embodiment, and as illustrated in  FIG. 1 , bioelectric cell  176  may be external to the case  200  (see  FIG. 2 ) of ICTD  100  but is electrically coupled to ICTD  100 . In particular, bioelectric cell  176  is coupled to a secondary, rechargeable cell  404  (see  FIG. 4 ) which may be internal to ICTD  100 . In an alternative embodiment, both bioelectric cell  176  and rechargeable cell  404  are external to ICTD  100 , and together are coupled to ICTD  100 . 
     In an alternative embodiment (not illustrated in  FIG. 1 ), bioelectric cell  176  may be embedded or partially embedded within ICTD  100 , provided both an anode material  182  and a cathode material  180  of bioelectric cell  176  are configured to receive a bodily fluid of the patient. For example, an anode  182  and cathode  180  (both discussed further below) of bioelectric cell  176  may be attached to, embedded within, project from, be contiguous with, or otherwise be part of external case  200  of ICTD  100 . 
     A detailed discussion of exemplary bioelectric cells is presented in co-pending and commonly-owned U.S. patent application Ser. No. 11/737,307, entitled “Bioelectric Battery for Implantable Device Applications”, filed Apr. 19, 2007, which is incorporated by reference herein in its entirety. A partial discussion of some embodiments of a bioelectric cell  176  is included here to provide context and background, it being understood that many other embodiments are possible as well. 
     Bioelectric cells, also known as bioelectric batteries or biogalvanic cells, are implanted in the body and may rely on oxygen in internal body fluids for creating a voltage between an anode electrode  182  and a cathode electrode  180 . Oxygen in the body fluids reacts with the anode  182  and consumes the anode  182 , thereby creating an electric potential between the anode  182  and cathode  180  electrodes. Oxygen is present in the body in plentiful supply so the lifetime of the battery is limited only by the amount of anode material  182 . 
     A first embodiment of a bioelectric cell will be described with reference to  FIG. 1 . A first embodiment of a bioelectric cell is generally shown at  176  in  FIG. 1 . Bioelectric cell  176  has a cathode electrode  180  and an anode electrode  182 , which in an embodiment are built into a single unit. Cathode  180  and anode  182  are separated by an insulating member  184 . Insulating member  184  may be a dielectric material including, for example and without limitation, silicone, polytetrafluoroethylene, or other dielectric polymer and may be formed in the shape of a cylindrical tube. Anode  182  may also be cylindrical in shape and inserted into a first end of insulating member  184 . Cathode  180  may be in the form of a wire and may be coiled around insulating member  184 . 
     Materials are chosen for anode  182  and cathode  180  that do not exhibit toxicity to the body of the organism in which they are implanted. Anode  182  is a reactive consumable metal that is consumed during the operation of the bioelectric cell and released into the body. Therefore it should be a material that is normally present in the body and of a size that when released into the body does not increase the levels of the material beyond a normally recommended level. 
     Anode material  182  should generate a high voltage when in reaction with oxygen. The material for anode  182  may include, but is not limited to, magnesium alloys. Magnesium alloys include magnesium along with aluminum, zinc, manganese, silver, copper, nickel, zirconium and/or rare earth elements, such as neodymium, gadolinium, and yttrium. Such magnesium alloys include, for example and without limitation, AZ61A supplied by Metal Mart International (5828 Smithway Street, Commerce, Calif. 90040) or AZ91E, EL21, or WE43 supplied by Magnesium Elektron (1001 College Street, Madison, Ill. 62060 USA). 
     The material for cathode  180  is a non-consumable metal including, for example and without limitation, platinum or titanium. Cathode  180  may be in the form of, for example and without limitation, a metal foil or wire. Cathode  180  may also have a coating that acts as a catalyst for the reaction at cathode  180 . A coating increases the surface area of cathode  180 , thereby resulting in a faster reaction and increased voltage generation. The coating may include, for example and without limitation, platinum black, iridium oxide (IrO2), ruthenium oxide (RuO2) or an IrO2/RuO2 mixture. For example, cathode  180  may be a platinum black coated platinum wire or an iridium oxide coated titanium wire. The coating may be applied using conventional methods including, without limitation, electrochemical deposition, thermal decomposition or sputtering. 
     The electrolyte for the bioelectric cell  176  may be a body fluid including, for example and without limitation, blood or other fluids extant in body cavities. When the electrolyte is a body fluid, the body fluid directly contacts cathode  180  and anode  182 , such that oxygen dissolved in the body fluid is absorbed onto a surface of cathode  180  and reacts with anode  182 . 
     A first end of a lead  190 , such as a pacing lead with an IS-1 connection, extends from a second end of insulating member  184  and provides a current flow between anode  182  and cathode  180 . Lead  190  further provides power to a load, including, for example and without limitation, an implantable medical device  100  or a secondary power cell  404  (not illustrated in  FIG. 1 , see  FIG. 4 ), connected to a second end of lead  190 . Exemplary implantable medical devices include, for example and without limitation, pacemakers, monitors or implantable cardioverter defibrillators (ICDs), and more generally any form of implantable cardiac therapy devices (ICTDs). Exemplary implantable medical devices further include implantable pumps and drug infusions devices. 
     Bioelectric cell  176  may be sufficient to power an implantable monitor; intrapericardial pacemaker, intraventricular pacemaker or standard pacemaker; or the background operations of ICTD  100 . Bioelectric cell  176  may also be coupled to a rechargeable secondary cell  404  (not illustrated in  FIG. 1 , see  FIG. 4 ) which may be internal to ICTD  100  or which may external to ICTD  100 . When coupled to secondary cell  404 , bioelectric cell  176  and secondary cell  404  together, possibly along with other associated electronics, may comprise a hybrid battery system. Such a hybrid battery system is discussed in more detail below. 
     In one embodiment of bioelectric cell  176 , a magnesium alloy cylinder  182  is inserted into silicone tubing  184  and a platinum wire  180  is coiled around the silicone tubing. The magnesium alloy cylinder  182  and platinum wire  180  are connected to lead  190  to act as the anode electrode  182  and cathode electrode  180 , respectively, of bioelectric cell  176 . Magnesium from anode  182  and oxygen in the body fluids are slowly consumed as a current is generated. The platinum wire may be coated, such as with a platinum black coating. Alternatively, a titanium wire may be used as the cathode electrode  180 . The titanium wire may be coated, such as with a platinum black, iridium oxide or ruthenium oxide coating. 
     The lifetime of anode electrode  182  may be five years, ten years, or in some embodiments even as long as twenty years. The exceptionally long lifetime of bioelectric cell  176  makes a bioelectric hybrid battery system  276 B (not shown in  FIG. 1 , but discussed in conjunctions with  FIGS. 2B ,  2 C,  4 A- 4 D, and other figures below) an excellent choice for a power supply for ICTD  100 . The long lifetime minimizes the need for surgical interventions to replace the ICTD power source. 
     Disclosed immediately above are exemplary embodiments of a bioelectric cell. Many other embodiments are possible consistent with the present system and method for a hybrid battery system which includes a bioelectric cell. Additional exemplary embodiments of a bioelectric cell are presented in above referenced U.S. patent application Ser. No. 11/737,307 
     Bioelectric cell  176  may be implanted anywhere in the body of an organism including, for example and without limitation, subcutaneously in the neck, the pectoral cavity, the superior vena cava, the intrapericardial space or the peritoneal cavity. Bioelectric cell  176  is implanted in tissue or blood vessels such that cathode  180  and anode  182  are in direct contact with body fluids. Therefore, the body fluids may act as the electrolyte for bioelectric cell  176 . 
     In an alternative embodiment, bioelectric cell  176  may have an internal electrolyte (not illustrated in  FIG. 1 ) in contact with anode  182  and cathode  180 , where the internal electrolyte is not a bodily fluid of the patient. The internal electrolyte may be surrounded by a semipermeable membrane (not illustrated in  FIG. 1 ) or other semipermeable material which permits diffusion or transfer of a replenishable organic material of the patient. For example, blood oxygen may diffuse from the patient&#39;s blood, across the membrane, through the internal electrolyte, and thereby reach anode  182  and cathode  180 . 
     5. Functional Elements of an Exemplary ICTD 
     An implantable cardiac therapy device  100  may be referred to variously, and equivalently, throughout this document as an “implantable cardiac therapy device” (“ICTD”), an “implantable device”, a “stimulation device”, a “pacemaker”, a “monitor”, or an “implantable cardioverter defibrillator” (“ICD”), and the respective plurals thereof. 
       FIG. 2A  shows an exemplary, simplified block diagram depicting various components of stimulation device  100 . The stimulation device  100  can be capable of treating both fast and slow arrhythmias with stimulation therapy, including cardioversion, defibrillation, and pacing stimulation. The stimulation device can be solely or further capable of delivering stimuli to autonomic nerves. In addition to cardioversion, defibrillation, and pacing stimulation, stimulation device  100  is generally enabled to perform various supporting tasks, also referred to as “background tasks” or “background operations”. Background operations may include, for example and without limitation, sensing cardiac activity, sensing related physiological activity, analyzing cardiac activity or other physiological data, data storage and retrieval, and transmission of physiological data via radio frequency signals. 
     While a particular multi-chamber device is shown, it is to be appreciated and understood that this is done for illustration purposes only. For example, various methods may be implemented on a pacing device suited for single ventricular stimulation and not bi-ventricular stimulation. Thus, the techniques and methods described below can be implemented in connection with any suitably configured or configurable stimulation device. Accordingly, one of skill in the art could readily duplicate, eliminate, or disable the appropriate circuitry in any desired combination to provide a device capable of treating the appropriate chamber(s) or regions of a patient&#39;s heart with cardioversion, defibrillation, pacing stimulation, and/or autonomic nerve stimulation. 
     Housing  200  for stimulation device  100  is often referred to as the “can”, “case” or “case electrode”, and may be programmably selected to act as the return electrode for all “unipolar” modes. Housing  200  may further be used as a return electrode alone or in combination with one or more of the coil electrodes  126 ,  132  and  134  (see  FIG. 1 ) for shocking purposes. Housing  200  further includes a connector (not shown) having a plurality of terminals  201 ,  202 ,  204 ,  206 ,  208 ,  212 ,  214 ,  216 ,  218 ,  221  (shown schematically and, for convenience, the names of the electrodes to which they are connected are shown next to the terminals). 
     To achieve right atrial sensing, pacing and/or autonomic stimulation, the connector includes at least a right atrial tip terminal (AR TIP)  202  adapted for connection to the atrial tip electrode  120 . A right atrial ring terminal (AR RING)  201  is also shown, which is adapted for connection to the atrial ring electrode  121 . To achieve left chamber sensing, pacing, shocking, and/or autonomic stimulation, the connector includes at least a left ventricular tip terminal (VL TIP)  204 , a left atrial ring terminal (AL RING)  206 , and a left atrial shocking terminal (AL COIL)  208 , which are adapted for connection to the left ventricular tip electrode  122 , the left atrial ring electrode  124 , and the left atrial coil electrode  126 , respectively. Connection to suitable autonomic nerve stimulation electrodes is also possible via these and/or other terminals (e.g., via a nerve stimulation terminal S ELEC  221 ). 
     To support right chamber sensing, pacing, shocking, and/or autonomic nerve stimulation, the connector further includes a right ventricular tip terminal (VR TIP)  212 , a right ventricular ring terminal (VR RING)  214 , a right ventricular shocking terminal (RV COIL)  216 , and a superior vena cava shocking terminal (SVC COIL)  218 , which are adapted for connection to the right ventricular tip electrode  128 , right ventricular ring electrode  130 , the RV coil electrode  132 , and the SVC coil electrode  134 , respectively. Connection to suitable autonomic nerve stimulation electrodes is also possible via these and/or other terminals (e.g., via the nerve stimulation terminal S ELEC  221 ). 
     At the core of the stimulation device  100  is a programmable microcontroller  220  that controls the various modes of stimulation therapy. As is well known in the art, microcontroller  220  typically includes a processor or microprocessor  231 , or equivalent control circuitry, designed specifically for controlling the delivery of stimulation therapy, and may further include onboard memory  232  (which may be, for example and without limitation, RAM, ROM, PROM, one or more internal registers, etc.), logic and timing circuitry, state machine circuitry, and I/O circuitry. 
     Typically, microcontroller  220  includes the ability to process or monitor input signals (data or information) as controlled by a program code stored in a designated block of memory. The type of microcontroller is not critical to the described implementations. Rather, any suitable microcontroller  220  may be used that carries out the functions described herein. The use of microprocessor-based control circuits for performing timing and data analysis functions are well known in the art. 
     Representative types of control circuitry that may be used in connection with the described embodiments can include the microprocessor-based control system of U.S. Pat. No. 4,940,052 (Mann et al.), the state-machine of U.S. Pat. Nos. 4,712,555 (Thornander) and 4,944,298 (Sholder), all of which are incorporated by reference herein. For a more detailed description of the various timing intervals used within the stimulation device and their inter-relationship, see U.S. Pat. No. 4,788,980 (Mann et al.), also incorporated herein by reference. 
       FIG. 2A  also shows an atrial pulse generator  222  and a ventricular pulse generator  224  that generate pacing stimulation pulses for delivery by the right atrial lead  104 , the coronary sinus lead  106 , and/or the right ventricular lead  108  via an electrode configuration switch  226 . It is understood that in order to provide stimulation therapy in each of the four chambers of the heart (or to autonomic nerves or other tissue) the atrial and ventricular pulse generators,  222  and  224 , may include dedicated, independent pulse generators, multiplexed pulse generators, or shared pulse generators. The pulse generators  222  and  224  are controlled by the microcontroller  220  via appropriate control signals  228  and  230 , respectively, to trigger or inhibit the stimulation pulses. 
     Microcontroller  220  further includes timing control circuitry  233  to control the timing of the stimulation pulses (e.g., pacing rate, atrio-ventricular (e.g., AV) delay, atrial interconduction (AA) delay, or ventricular interconduction (VV) delay, etc.) as well as to keep track of the timing of refractory periods, blanking intervals, noise detection windows, evoked response windows, alert intervals, marker channel timing, etc., which is well known in the art. 
     Microcontroller  220  further includes an arrhythmia detector  234 , a morphology detector  236 , and optionally an orthostatic compensator and a minute ventilation (MV) response module (the latter two are not shown in  FIG. 2A ). These components can be utilized by the stimulation device  100  for determining desirable times to administer various therapies, including those to reduce the effects of orthostatic hypotension. The aforementioned components may be implemented in hardware as part of the microcontroller  220 , or as software/firmware instructions programmed into the device and executed on the microcontroller  220  during certain modes of operation. 
     Microcontroller  220  further includes an AA delay, AV delay and/or W delay module  238  for performing a variety of tasks related to AA delay, AV delay and/or VV delay. This component can be utilized by the stimulation device  100  for determining desirable times to administer various therapies, including, but not limited to, ventricular stimulation therapy, bi-ventricular stimulation therapy, resynchronization therapy, atrial stimulation therapy, etc. The AA/AV/VV module  238  may be implemented in hardware as part of the microcontroller  220 , or as software/firmware instructions programmed into the device and executed on the microcontroller  220  during certain modes of operation. Of course, such a module may be limited to one or more of the particular functions of AA delay, AV delay and/or W delay. Such a module may include other capabilities related to other functions that may be germane to the delays. Such a module may help make determinations as to fusion. 
     The microcontroller  220  of  FIG. 2A  also includes an activity module  239 . This module may include control logic for one or more activity related features. For example, the module  239  may include an algorithm for determining patient activity level, calling for an activity test, calling for a change in one or more pacing parameters, etc. The module  239  may be implemented in hardware as part of the microcontroller  220 , or as software/firmware instructions programmed into the device and executed on the microcontroller  220  during certain modes of operation. The module  239  may act cooperatively with the AA/AV/VV module  238 . 
     Microcontroller  220  may also include a battery control module  286 . Battery control module  286  may be used, for example, to control a battery  276  (which may be a hybrid battery  276 H, and in particular a bioelectric hybrid battery  276 B, illustrated in  FIGS. 2B ,  2 C, and  4 A- 4 D) as discussed in further detail below. Battery control  286  may be hardwired circuitry, or may be implemented as software or firmware running on microcontroller  220 . Battery control  286  may be coupled to battery  276  via battery signal line  290  and battery control line  292 . Battery signal line  290  may deliver to battery control  286  status or operational information regarding battery  276 . Battery control line  292  may be used to change an operational state of battery  276 . For example, battery control line  292  may deliver control signals from battery control  286  to battery  276 . For example, in an embodiment where battery  276  is a hybrid battery, battery control  286  may send control signals to determine if a second cell is connected to a first cell for recharging of the second cell. 
     In an alternative embodiment, battery control  286  may be a separate module from microcontroller  220 , but may be coupled to microcontroller  220 . For example, separate module battery control  286  may obtain required ICTD operational status information from microcontroller  220 . Or, for example, separate module battery control  286  may report battery status or battery operational information to microcontroller  220 . In addition, separate module battery control  286  may also be coupled to battery  276 . 
     In an alternative embodiment, battery control  286  may be implemented as an internal physical module of battery  276  (for example, battery control  286  may be implemented as a microchip which is situated internally to the exterior housing of battery  276 ). However, battery control  286  may still be coupled to microcontroller  220  via battery signal line  290  and battery control line  292 . In an alternative embodiment, battery control functions of battery control  286  may be distributed across a first module which is part of battery  276 , and one or more additional modules which are external to battery  276 . The battery control module(s) external to battery  276  may for example be part of microcontroller  220 . 
     Battery  276  is discussed in more detail below. 
     The electrode configuration switch  226  includes a plurality of switches for connecting the desired electrodes to the appropriate I/O circuits, thereby providing complete electrode programmability. Accordingly, switch  226 , in response to a control signal  242  from the microcontroller  220 , determines the polarity of the stimulation pulses (e.g., unipolar, bipolar, combipolar, etc.) by selectively closing the appropriate combination of switches (not shown) as is known in the art. 
     Atrial sensing circuits  244  and ventricular sensing circuits  246  may also be selectively coupled to the right atrial lead  104 , coronary sinus lead  106 , and the right ventricular lead  108 , through the switch  226  for detecting the presence of cardiac activity in each of the four chambers of the heart. Accordingly, the atrial (ATR. SENSE) and ventricular (VTR. SENSE) sensing circuits,  244  and  246 , may include dedicated sense amplifiers, multiplexed amplifiers, or shared amplifiers. Switch  226  determines the “sensing polarity” of the cardiac signal by selectively closing the appropriate switches, as is also known in the art. In this way, the clinician may program the sensing polarity independent of the stimulation polarity. The sensing circuits (e.g.,  244  and  246 ) are optionally capable of obtaining information indicative of tissue capture. 
     Each sensing circuit  244  and  246  preferably employs one or more low power, precision amplifiers with programmable gain and/or automatic gain control, bandpass filtering, and a threshold detection circuit, as known in the art, to selectively sense the cardiac signal of interest. The automatic gain control enables the device  100  to deal effectively with the difficult problem of sensing the low amplitude signal characteristics of atrial or ventricular fibrillation. 
     The outputs of the atrial and ventricular sensing circuits  244  and  246  are connected to the microcontroller  220 , which, in turn, is able to trigger or inhibit the atrial and ventricular pulse generators  222  and  224 , respectively, in a demand fashion in response to the absence or presence of cardiac activity in the appropriate chambers of the heart. Furthermore, as described herein, the microcontroller  220  is also capable of analyzing information output from the sensing circuits  244  and  246  and/or the analog-to-digital (A/D) data acquisition system  252  to determine or detect whether and to what degree tissue capture has occurred and to program a pulse, or pulses, in response to such determinations. The sensing circuits  244  and  246 , in turn, receive control signals over signal lines  248  and  250  from the microcontroller  220  for purposes of controlling the gain, threshold, polarization charge removal circuitry (not shown), and the timing of any blocking circuitry (not shown) coupled to the inputs of the sensing circuits  244 ,  246 , as is known in the art. 
     For arrhythmia detection, the device  100  utilizes the atrial and ventricular sensing circuits,  244  and  246 , to sense cardiac signals to determine whether a rhythm is physiologic or pathologic. In reference to arrhythmias, as used herein, “sensing” is reserved for the noting of an electrical signal or obtaining data (information), and “detection” is the processing (analysis) of these sensed signals and noting the presence of an arrhythmia. In some instances, detection or detecting includes sensing and in some instances sensing of a particular signal alone is sufficient for detection (e.g., presence/absence, etc.). 
     The timing intervals between sensed events (e.g., P-waves, R-waves, and depolarization signals associated with fibrillation which are sometimes referred to as “F-waves” or “Fib-waves”) are then classified by the arrhythmia detector  234  of the microcontroller  220  by comparing them to a predefined rate zone limit (i.e., bradycardia, normal, low rate VT, high rate VT, and fibrillation rate zones) and various other characteristics (e.g., sudden onset, stability, physiological sensors, and morphology, etc.) in order to determine the type of remedial therapy that is needed (e.g., bradycardia pacing, anti-tachycardia pacing, cardioversion shocks or defibrillation shocks, collectively referred to as “tiered therapy”). 
     Cardiac signals are also applied to inputs of an analog-to-digital (A/D) data acquisition system  252 . The data acquisition system  252  is configured to acquire intracardiac electrogram (EGM) signals, convert the raw analog data into a digital signal, and store the digital signals for later processing and/or telemetric transmission to an external device  254 . Data acquisition system  252  may be configured by microcontroller  220  via control signals  256 . The data acquisition system  252  is coupled to the right atrial lead  104 , the coronary sinus lead  106 , the right ventricular lead  108  and/or the nerve stimulation lead  110  through the switch  226  to sample cardiac signals across any pair of desired electrodes. 
     The microcontroller  220  is further coupled to a memory  260  by a suitable data/address bus  262 , wherein the programmable operating parameters used by the microcontroller  220  are stored and modified, as required, in order to customize the operation of the stimulation device  100  to suit the needs of a particular patient. Such operating parameters define, for example, pacing pulse amplitude, pulse duration, electrode polarity, rate, sensitivity, automatic features, arrhythmia detection criteria, and the amplitude, waveshape, number of pulses, and vector of each shocking pulse to be delivered to the patient&#39;s heart  102  within each respective tier of therapy. One feature may be the ability to sense and store a relatively large amount of data (e.g., from the data acquisition system  252 ), which data may then be used for subsequent analysis to guide the programming of the device. 
     Essentially, the operation of the ICTD control circuitry, including but not limited to pulse generators, timing control circuitry, delay modules, the activity module, battery utilization and related voltage and current control, and sensing and detection circuits, may be controlled, partly controlled, or fine-tuned by a variety of parameters, such as those indicated above which may be stored and modified, and may be set via an external ICTD programming device  254 . 
     Advantageously, the operating parameters of the implantable device  100  may be non-invasively programmed into the memory  260  through a telemetry circuit  264  in telemetric communication via communication link  266  with the external device  254 , which may be a general purpose computer, a dedicated ICTD programmer, a transtelephonic transceiver, or a diagnostic system analyzer. The microcontroller  220  activates the telemetry circuit  264  with a control signal  268 . The telemetry circuit  264  advantageously allows intracardiac electrograms and status information relating to the operation of the device  100  (as contained in the microcontroller  220  or memory  260 ) to be sent to the external device  254  through an established communication link  266 . The ICTD  100  may also receive human programmer instructions via the external device  254 . 
     The stimulation device  100  can further include a physiological sensor  270 , commonly referred to as a “rate-responsive” sensor because it is typically used to adjust pacing stimulation rate according to the exercise state of the patient. However, physiological sensor  270  may further be used to detect changes in cardiac output (see, e.g., U.S. Pat. No. 6,314,323, entitled “Heart stimulator determining cardiac output, by measuring the systolic pressure, for controlling the stimulation”, to Ekwall, issued Nov. 6, 2001, which discusses a pressure sensor adapted to sense pressure in a right ventricle and to generate an electrical pressure signal corresponding to the sensed pressure, an integrator supplied with the pressure signal which integrates the pressure signal between a start time and a stop time to produce an integration result that corresponds to cardiac output), changes in the physiological condition of the heart, or diurnal changes in activity (e.g., detecting sleep and wake states). Accordingly, the microcontroller  220  may respond by adjusting the various pacing parameters (such as rate, AA delay, AV delay, VV delay, etc.) at which the atrial and ventricular pulse generators,  222  and  224 , generate stimulation pulses. 
     While shown as being included within the stimulation device  100 , it is to be understood that the physiological sensor  270  may also be external to the stimulation device  100 , yet still be implanted within or carried by the patient. Examples of physiological sensors that may be implemented in device  100  include known sensors that, for example, sense respiration rate, pH of blood, ventricular gradient, cardiac output, preload, afterload, contractility, hemodynamics, pressure, and so forth. Another sensor that may be used is one that detects activity variance, wherein an activity sensor is monitored diurnally to detect the low variance in the measurement corresponding to the sleep state. For a complete description of an example activity variance sensor, the reader is directed to U.S. Pat. No. 5,476,483 (Bornzin et al.), issued Dec. 19, 1995, which patent is hereby incorporated by reference. 
     More specifically, physiological sensors  270  optionally include sensors for detecting movement and minute ventilation in the patient. Physiological sensors  270  may include a position sensor and/or a minute ventilation (MV) sensor to sense minute ventilation, which is defined as the total volume of air that moves in and out of a patient&#39;s lungs in a minute. Signals generated by the position sensor and MV sensor are passed to the microcontroller  220  for analysis in determining whether to adjust the pacing rate, etc. The microcontroller  220  monitors the signals for indications of the patient&#39;s position and activity status, such as whether the patient is climbing upstairs or descending downstairs or whether the patient is sitting up after lying down. 
     Stimulation device  100  additionally includes battery  276  that provides operating power to all of the circuits shown in  FIG. 2A , as well as to any additional circuits which may be present in alternative embodiments. Operating power in the form of electrical current and/or voltage may be provided via a power bus or power buses  294 , depicted in  FIG. 2A  as a first power bus  294 . 1  and a second power bus  294 . 2 . In  FIG. 2A , the connection(s) of power bus(es)  294  to other elements of ICTD  100  for purposes of powering those elements is not illustrated, but is implied by the dotted end-lines of bus(es)  294 . 
     For stimulation device  100 , which employs shocking therapy, the battery  276  is capable of operating at low current drains for long periods of time (e.g., preferably less than 10 μAmps), and is capable of providing high-current pulses (for capacitor charging) when the patient requires a shock pulse (e.g., preferably, in excess of 2 Amps, at voltages above 2 volts, for periods of 10 seconds or more). In an embodiment, discussed in detail below, battery  276  may be configured to provide a current as high as 3 to 4.5 Amps and/or unloaded voltages in excess of 4 volts, for rapid charging of shocking circuitry. Battery  276  also desirably has a predictable discharge characteristic so that elective replacement time can be determined. 
     In an embodiment, battery  276  may be a hybrid battery system comprised of dual types of cells, as described further below. Such a hybrid battery system may provide power via a plurality of power buses, such as buses  249 . 1  and  294 . 2  of  FIG. 2A . In an embodiment, each power bus may be configured to deliver different voltages, different currents, and/or different power levels. Battery  276  may be monitored and/or controlled via battery control  286 , as discussed in part above, and as also discussed further below. 
     Further embodiments of a hybrid battery  276  employing a bioelectric cell  176  are discussed below. 
     The stimulation device  100  can further include magnet detection circuitry (not shown), coupled to the microcontroller  220 , to detect when a magnet is placed over the stimulation device  100 . A magnet may be used by a clinician to perform various test functions of the stimulation device  100  and/or to signal the microcontroller  220  that the external programmer  254  is in place to receive or transmit data to the microcontroller  220  through the telemetry circuit  264 . 
     The stimulation device  100  further includes an impedance measuring circuit  278  that is enabled by the microcontroller  220  via a control signal  280 . The known uses for an impedance measuring circuit  278  include, but are not limited to, lead impedance surveillance during the acute and chronic phases for proper lead positioning or dislodgement; detecting operable electrodes and automatically switching to an operable pair if dislodgement occurs; measuring respiration or minute ventilation; measuring thoracic impedance for determining shock thresholds; detecting when the device has been implanted; measuring stroke volume; and detecting the opening of heart valves, etc. The impedance measuring circuit  278  is advantageously coupled to the switch  226  via circuit line(s)  291  so that any desired electrode may be used. 
     In the case where the stimulation device  100  is intended to operate as an implantable cardioverter/defibrillator (ICTD) device, it detects the occurrence of an arrhythmia, and automatically applies an appropriate therapy to the heart aimed at terminating the detected arrhythmia. To this end, the microcontroller  220  further controls a shocking circuit  282  by way of a control signal  284 . The shocking circuit  282  generates shocking pulses of low (e.g., up to approximately 0.5 J), moderate (e.g., approximately 0.5 J to approximately 10 J), or high energy (e.g., approximately 11 J to approximately 40 J), as controlled by the microcontroller  220 . Such shocking pulses are applied to the patient&#39;s heart  102  through at least two shocking electrodes, and as shown in this embodiment, selected from the left atrial coil electrode  126 , the RV coil electrode  132 , and/or the SVC coil electrode  134 . As noted above, the housing  200  may act as an active electrode in combination with the RV coil electrode  132 , or as part of a split electrical vector using the SVC coil electrode  134  or the left atrial coil electrode  126  (i.e., using the RV electrode as a common electrode). Other exemplary devices may include one or more other coil electrodes or suitable shock electrodes (e.g., a LV coil, etc.). Shocking circuit  282  either has within it, or is coupled to, one or more shocking capacitors. The shocking capacitor(s) may be used to store up energy, and then release that energy, during the generation of shocking pulses. 
     Cardioversion level shocks are generally considered to be of low to moderate energy level (where possible, so as to minimize pain felt by the patient), and/or synchronized with an R-wave and/or pertaining to the treatment of tachycardia. Defibrillation shocks are generally of moderate to high energy level (i.e., corresponding to thresholds in the range of approximately 5 J to approximately 40 J), delivered asynchronously (since R-waves may be too disorganized), and pertaining exclusively to the treatment of fibrillation. Accordingly, microcontroller  220  is capable of controlling the synchronous or asynchronous delivery of the shocking pulses. 
     6. ICTD Programmer 
     As indicated above, the operating parameters of the implantable device  100  may be non-invasively programmed into the memory  260  through a telemetry circuit  264  in telemetric communication via communication link  266  with the external device  254 . The external device  254  may be a general purpose computer running custom software for programming the ICTD  100 , a dedicated external programmer device of ICTD  100 , a transtelephonic transceiver, or a diagnostic system analyzer. Generically, all such devices may be understood as embodying computers, computational devices, or computational systems with supporting hardware or software which enable interaction with, data reception from, and programming of ICTD  100 . 
     Throughout this document, where a person is intended to program or monitor ICTD  100  (where such person is typically a physician or other medical professional or clinician), the person is always referred to as a “human programmer” or as a “user”. The term “human programmer” may be viewed as synonymous with “a person who is a user of an ICTD programming device”, or simply with a “user”. Any other reference to “programmer” or similar terms, such as “ICTD programmer”, “external programmer”, “programming device”, etc., refers specifically to the hardware, firmware, software, and/or physical communications links used to interface with and program ICTD  100 . 
     The terms “computer program”, “computer code”, and “computer control logic” are generally used synonymously and interchangeably in this document to refer to the instructions or code which control the behavior of a computational system. The term “software” may be employed as well, it being understood however that the associated code may in some embodiments be implemented via firmware or hardware, rather than as software in the strict sense of the term (e.g., as computer code stored on a removable medium, or transferred via a network connection, etc.). 
     A “computer program product” or “computational system program product” is a medium (for example, a magnetic disk drive, magnetic tape, optical disk (e.g., CD, DVD), firmware, ROM, PROM, flash memory, a network connection to a server from which software may be downloaded, etc) which is suitable for use in a computer or computation system, or suitable for input into a computer or computational system, where the medium has control logic stored therein for causing a processor of the computational system to execute computer code or a computer program. Such medium, also referred to as “computer program medium”, “computer usable medium”, and “computational system usable medium”, are discussed further below. 
       FIG. 3  presents a system diagram representing an exemplary computer, computational system, or other programming device, which will be referred to for convenience as ICTD programmer  254 . It will be understood that while the device is referred to an “ICTD programmer”, indicating that the device may send programming data, programming instructions, programming code, and/or programming parameters to ICTD  100 , the ICTD programmer  254  may receive data from ICTD  100  as well, and may display the received data in a variety of formats, analyze the received data, store the received data in a variety of formats, transmit the received data to other computer systems or technologies, and perform other tasks related to operational and/or physiologic data received from ICTD  100 . 
     ICTD programmer  254  includes one or more processors, such as processor  304 . Processor  304  is used for standard computational tasks well known in the art, such as retrieving instructions from a memory, processing the instructions, receiving data from memory, performing calculations and analyses on the data in accordance with the previously indicated instructions, storing the results of calculations back to memory, programming other internal devices within ICTD programmer  254 , and transmitting data to and receiving data from various external devices such as ICTD  100 . 
     Processor  304  is connected to a communication infrastructure  306  which is typically an internal communications bus of ICTD programmer  254 ; however, if ICTD programmer  254  is implemented in whole or in part as a distributed system, communication infrastructure  306  may further include or may be a network connection. 
     ICTD programmer  254  may include a display interface  302  that forwards graphics, text, and other data from the communication infrastructure  306  (or from a frame buffer not shown) for display on a display unit  330 . The display unit may be, for example, a CRT, an LCD, or some other display device. Display unit  330  may also be more generally understood as any device which may convey data to a human programmer. 
     Display unit  330  may also be used to present a user interface which displays internal features of, operating modes or parameters of, or data from ICTD  100 . The user interface presented via display unit  330  of ICTD programmer  254  may include various options that may be selected, deselected, or otherwise changed or modified by a human programmer of ICTD  100 . The options for programming the ICTD  100  may be presented to the human programmer via the user interface in the form of buttons, check boxes, menu options, dialog boxes, text entry fields, or other icons or means of visual display well known in the art. 
     ICTD programmer  254  may include a data entry interface  342  that accepts data entry from a human programmer via data entry devices  340 . Such data entry devices  340  may include, for example and without limitation, a keyboard, a mouse, a touchpad, a touch-sensitive screen, a microphone for voice input, or other means of data entry, which the human programmer uses in conjunction with display unit  330  in a manner well known in the art. For example, either a mouse or keystrokes entered on a keyboard may be used to select check boxes, option buttons, menu items, or other display elements indicating human programmer choices for programming ICTD  100 . Direct text entry may be employed as well. Data entry device  340  may also take other forms, such as a dedicated control panel with specialized buttons and/or other mechanical elements or tactile sensitive elements for programming ICTD  100 . 
     In the context of the present system and method, display interface  302  may present on display unit  330  a variety of data related to patient cardiac function and performance, and also data related to the present operating mode, operational state, or operating parameters of ICTD  100 . Modifications to ICTD  100  operational state(s) may be accepted via data entry interface  342  and data entry device  340 . In general, any interface means which enables a human programmer to interact with and program ICTD  100  may be employed. In one embodiment, for example, a visual data display may be combined with tactile data entry via a touch-screen display. 
     In another embodiment, a system of auditory output (such as a speaker or headset and suitable output port for same, not shown) may be employed to output data relayed from ICTD  100 , and a system of verbal input (such as a microphone and suitable microphone port, not shown) may be employed to program ICTD  100 . Other modes of input and output means may be employed as well including, for example and without limitation, a remote interaction with ICTD  100 , viewing printed data which has been downloaded from ICTD  100 , or the programming of ICTD  100  via a previously coded program script. 
     All such means of receiving data from ICTD  100  and/or programming ICTD  100  constitute an interface  302 ,  330 ,  342 ,  340  between ICTD  100  and a human programmer of ICTD  100 , where the interface is enabled via both the input/output hardware (e.g., display screen, mouse, keyboard, touchscreen, speakers, microphone, input/output ports, etc.) and the hardware, firmware, and/or software of ICTD programmer  254 . 
     ICTD programmer  254  also includes a main memory  308 , preferably random access memory (RAM), and may also include a secondary memory  310 . The secondary memory  310  may include, for example, a hard disk drive  312  and/or a removable storage drive  314 , representing a floppy disk drive, a magnetic tape drive, an optical disk drive, etc. The removable storage drive  314  reads from and/or writes to a removable storage unit  318  in a well known manner. Removable storage unit  318  represents a magnetic disk, magnetic tape, optical disk, etc. which is read by and written to by removable storage drive  314 . As will be appreciated, the removable storage unit  318  includes a computer usable storage medium having stored therein computer software and/or data. 
     In alternative embodiments, secondary memory  310  may include other similar devices for allowing computer programs or other instructions to be loaded into ICTD programmer  254 . Such devices may include, for example, a removable storage unit  322  and an interface  320 . Examples of such may include a program cartridge and cartridge interface (such as that found in video game devices), a removable memory chip (such as an erasable programmable read only memory (EPROM), programmable read only memory (PROM), or flash memory) and associated socket, and other removable storage units  322  and interfaces  320 , which allow software and data to be transferred from the removable storage unit  322  to ICTD programmer  254 . 
     ICTD programmer  254  also contains a communications link  266  to ICTD  100 , which may be comprised in part of a dedicated port of ICTD programmer  254 . From the perspective of ICTD programmer  254 , communications link  266  may also be viewed as an ICTD interface. Communications link  266  enables two-way communications of data between ICTD programmer  254  and ICTD  100 . Communications link  266  has been discussed above (see the discussion of  FIG. 2A ). 
     ICTD programmer  254  may also include a communications interface  324 . Communications interface  324  allows software and data to be transferred between ICTD programmer  254  and other external devices (apart from ICTD  100 ). Examples of communications interface  324  may include a modem, a network interface (such as an Ethernet card), a communications port, a Personal Computer Memory Card International Association (PCMCIA) slot and card, a USB port, an IEEE 1394 (FireWire) port, etc. Software and data transferred via communications interface  324  are in the form of signals  328  which may be electronic, electromagnetic, optical (e.g., infrared) or other signals capable of being received by communications interface  324 . These signals  328  are provided to communications interface  324  via a communications path (e.g., channel)  326 . This channel  326  carries signals  328  and may be implemented using wire or cable, fiber optics, a telephone line, a cellular link, an radio frequency (RF) link, in infrared link, and other communications channels. 
     The terms “computer program medium”, “computer usable medium”, and “computational system usable medium” are used, synonymously, to generally refer to media such as removable storage drive  314  and removable storage unit  381 , a hard disk installed in hard disk drive  312 , a secondary memory interface (such as a flash memory port, USB port, FireWire port, etc.) and removable storage unit  322  (such as flash memory), and removable storage units  318  and  322 . These computer program products or computational system program products provide software to ICTD programmer  254 . 
     It should be noted, however, that it is not necessarily the case that the necessary software, computer code, or computer program (any of which may also referred to as computer control logic) be loaded into ICTD programmer  254  via a removable storage medium. Such computer program may be loaded into ICTD programmer  254  via communications link  328 , or may be stored in memory  308  of ICTD programmer  254 . Computer programs are stored in main memory  308  and/or secondary memory  310 . Computer programs may also be received via communications interface  324 . 
     Accordingly, such computer programs represent controllers of ICTD programmer  254 , and thereby controllers of ICTD  100 . Software may be stored in a computer program product and loaded into ICTD programmer  254  using removable storage drive  314 , hard drive  312 , secondary memory interface  320 , or communications interface  324 . 
     In an embodiment of the present system and method, ICTD programmer  254  may be used to modify ICTD operating parameters of battery control  286 . In this way, ICTD programmer  254  may be used to modify the operations of a battery  276 , such as a bioelectric hybrid battery  276 B discussed in further detail below. 
     7. Hybrid Battery with Bioelectric Cell 
     A hybrid battery system which includes a bioelectric cell may be referred to synonymously as a “bioelectric hybrid battery system”, or simply as a “bioelectric hybrid battery”. 
     In an embodiment illustrated in  FIGS. 2B and 2C , battery  276  of ICTD  100  may be an exemplary bioelectric hybrid battery system  276 B, also referred to simply as bioelectric hybrid battery  276 B. Bioelectric hybrid battery  276 B may be comprised of a bioelectric cell  176  (already described above in conjunction with  FIG. 1 ) and a secondary cell  404  (discussed in further detail in conjunction with  FIGS. 4A-4D  below). 
     As discussed in conjunction with  FIG. 1  above, bioelectric cell  176  of bioelectric hybrid battery  276 B may be external to can  200  of ICTD  100 . In an embodiment, secondary cell  404  may be located internally to can  200  of ICTD  100 . 
     Bioelectric cell  176  may be electrically coupled to ICTD  100  partly via lead  190 , such as a pacing lead with an IS-1 connection. Lead  190  may connect to battery terminal  298  of ICTD  100 . In turn, an electrical connection between bioelectric cell  176  and secondary cell  404  may be completed by internal power line  296  of ICTD  100 . Internal power line  296  couples battery terminal  298  to secondary cell  404 . 
     In the embodiment illustrated in  FIG. 2B , internal buses  294 . 1  and  294 . 2  functional in a manner substantially the same or similar to that already discussed above in conjunction with  FIG. 2A . If a single bus  294  is employed, bus  294  may deliver a voltage from secondary cell  404  of bioelectric hybrid battery  276 B. If two or more buses are employed, such as buses  294 . 1  and  294 . 2 , then each bus may deliver a voltage from a different source and at a different level. For example, first bus  294 . 1  may deliver voltage and current which is delivered from bioelectric cell  176 , while second bus  294 . 2  may deliver voltage and current which is delivered from secondary cell  404 . 
     Similarly, battery signal line  290  and battery control line  292  may function in a manner substantially the same or similar to that already discussed above, providing suitable monitoring and control connection(s) between bioelectric hybrid battery  276 B and battery control  286 . 
     Bioelectric hybrid battery system  276 B may include other elements and components in addition to bioelectric cell  176 , secondary cell  404 , and associated power lines, control lines, and signaling lines. Exemplary additional elements are discussed further below in conjunction with  FIGS. 4A-4D . 
     An alternative exemplary embodiment of bioelectric hybrid battery system  276 B is illustrated in  FIG. 2C . In this exemplary embodiment, both bioelectric cell  176  and secondary cell  404  are external to ICTD  100 , and are housed within a shared external casing  428  (discussed in more detail in conjunction with  FIGS. 4A-4D , below). Bioelectric cell  176  and secondary cell  404  are illustrated in  FIG. 2C  as being electrically coupled via a simple coupling  299 , however, this is representational only. Typically, additional elements may be required to couple bioelectric cell  176  and secondary cell  404 , including for example and without limitation a voltage converter such as a DC-to-DC converter. These elements are discussed in more detail below in conjunction with  FIGS. 4A-4D . 
     Bioelectric hybrid battery system  276 B may be coupled to ICTD  100  partly via lead  190 . Additional leads may be used as well (not illustrated in  FIG. 2C ), possibly along with signaling and control lines (also not illustrated in  FIG. 2C ). Lead  190  may connect to battery terminal  298  of ICTD  100 . In turn, an electrical coupling may be completed by internal power line  296  between bioelectric hybrid battery  276 B and an internal power coupling  223  of ICTD  100 . Internal power coupling  223  may be used to route electrical power supplied by external bioelectric hybrid battery  276 B to various elements within ICTD  100 . Power coupling  223  may be, for example, a digitally controlled switch that receives inputs from cell  176  and cell  404  and connects a selected cell to provide power to selected elements of ICTD  100  including operations circuitry and/or shocking circuitry. 
     In the exemplary embodiment illustrated in  FIG. 2C , internal buses  294 . 1  and  294 . 2  function in a manner substantially the same or similar to that already discussed above in conjunction with  FIG. 2A , routing power, including possibly power at different voltages or different currents, from power coupling  223  to elements of ICTD  100 . 
     Similarly, battery signal line  290  and battery control line  292  may function in a manner substantially the same or similar to that already discussed above. That is, battery signal line  290  and battery control line  292  may provide suitable monitoring and control connection(s) between bioelectric hybrid battery  276 B and battery control  286 . In an embodiment, monitoring and control connections may be routed via power coupling  223 . In an alternative embodiment, other monitoring and control connections may be used to route monitoring and control signals to and from bioelectric hybrid battery  276 B, without routing through power coupling  223 . 
     In an alternative embodiment of the present system and method, bioelectric hybrid battery system  276 B may be substantially contained within ICTD  100 . In such an embodiment, secondary cell  404  will typically be contained substantially or completely within case  200  of ICTD  100 . Similarly, coupling elements  299  (discussed in further detail below in conjunction with  FIGS. 4A-4D ) will typically be contained substantially or completely within case  200  of ICTD  100 . 
     In such an embodiment (that is, an embodiment where bioelectric hybrid battery  276 B is substantially contained within ICTD  100 ), several elements or all elements of bioelectric cell  176  may be completely or substantially contained within case  200  or ICTD  100 . However, bioelectric cell  176  is configured so that a replenishable bodily substance of the patient can reach anode  182  and cathode  180  of bioelectric cell  176 . Typically, this may be achieved by configuring anode  182  and cathode  180  to receive a bodily fluid of the patient, such as the patient&#39;s blood. 
     In an embodiment, anode  182  and/or cathode  180  of bioelectric cell  176  may be attached to, embedded within, project from, be contiguous with, or otherwise be part of external case  200  of ICTD  100 , thereby allowing access to bodily fluids which may surround case  200 . In an alternative embodiment, anode  182  and/or cathode  180  may be configured to be interior to external case  200  of ICTD  100 . Channels, pipes, or other fluid conveying elements may run through ICTD  100 , and permit bodily fluids to reach anode  182  and/or cathode  180  of bioelectric cell  176 . 
     8. Further Elements of Hybrid Battery with Bioelectric Cell 
       FIGS. 4A-4D  present schematic diagrams of exemplary bioelectric hybrid battery systems  276 B according to the present system and method.  FIGS. 4A-4D  also includes some elements of exemplary connections between exemplary hybrid battery systems  276 B and other elements of ICTD  100 . 
       FIG. 4A  is a block diagram of an exemplary bioelectric hybrid battery system  276 B. 1  according to an embodiment of the present system and method. Bioelectric hybrid battery system  276 B. 1  may be comprised of an bioelectric cell  176  and a secondary cell  404 . In an alternative embodiment, two or more bioelectric cells  176  may be employed in place of just a single bioelectric cell  176 . In an alternative embodiment, two or more secondary cells  404  may be employed in place of just a single secondary cell  404 . 
     Exemplary embodiments of bioelectric cell  176  have already been described above. Other embodiments are possible as well. In an embodiment, secondary cell  404  may be a lithium ion polymer cell. The present system and method may enjoy several advantages due to the specific selection secondary cells. These advantages are discussed in detail below in the section entitled “Choice of Secondary Power Cell”. 
     In an embodiment, and as illustrated in  FIG. 4A , bioelectric cell  176  may be external to the can  200  of ICTD  100 , while secondary cell  404  may be internal to the can  200  of ICTD  100 . Bioelectric cell  176  may be coupled to ICTD  100  via lead  190 , which may connected to battery terminal  298 . Bioelectric cell  176  may be further coupled to secondary cell  404  via ICTD internal power line  296 , which may also be coupled to battery terminal  298 . 
     Bioelectric cell  176  and secondary cell  404  may be further coupled by charging means  406 . Further coupled between charging means  406  and secondary cell  404  may be an variable resistor  412 . In an embodiment, and as shown in  FIG. 4A , bioelectric cell  176  and secondary cell  404  may be coupled in parallel. Hybrid bioelectric battery system  276 B. 1  may include an internal power bus  420  configured to deliver power from hybrid bioelectric battery system  276 B. 1  to elements of ICTD  100 . 
     In  FIG. 4A , the dashed box contains those elements which may comprise exemplary bioelectric hybrid battery system  276 B. 1 . Bioelectric hybrid battery system  276 B. 1  is comprised of bioelectric cell  176 , secondary cell  404 , and charging means  406 . Bioelectric hybrid battery system  276 B. 1  may therefore be comprised of elements which are both internal to and external to ICTD  100 . Bioelectric hybrid battery system  176 B may be further comprised of other elements including, for example and without limitation, variable resistor  412 , internal power bus  420 , and a case  428 . Case  428  may enclose some elements of bioelectric hybrid battery system  276 B. 1 , as illustrated with exemplary embodiments throughout this document. 
     Bioelectric hybrid battery system  276 B. 1  may be coupled to an ICTD power bus  294 . In turn, power bus  294  may be connected to numerous elements of ICTD  100  already discussed above. These elements may include, for example and without limitation, memory  260 , telemetry circuit  264 , physiological sensor  270 , impedance measuring circuit  278 , microcontroller  220 , atrial pulse generator  222 , atrial sensing circuits  244 , ventricular sensing circuits  246 , analog-to-digital converter  252 , electrode configuration switch  226 , and shocking circuit  282 . Collectively, these elements and similar elements of ICTD  100  may be referred to as ICTD operations circuitry  430 . ICTD operations circuitry  430  is thereby powered by bioelectric hybrid battery system  276 B. 1 . 
     Additional elements of hybrid battery system  276 B. 1  may include connections or leads to grounding elements  426 . Grounding elements  426  may, for example, be the exterior housing or “can”  200  of ICTD  100 . 
     Variable resistor  412  may also be coupled between charging means  416  and secondary cell  404 . As discussed further below, secondary cell  404  may be charged from bioelectric cell  176  via an unregulated charging process, meaning that secondary cell  404  can received current at a steady rate without risk of damage to secondary cell  404 , and without risk of harm to the patient in whom ICTD  100  is implanted. However, bioelectric cell(s)  176  may only be able to discharge current provided the current flow from bioelectric cell(s)  176  is below a certain rate, for example, typically on the order of 100 μAmps. Variable resistor  412  may therefore serve the purpose of limiting a rate at which current is drawn from bioelectric cell  176 . The exact resistance of variable resistor  412  may be slowly varied over an extended period of time (such as over periods of several months) via control circuitry. 
     As used herein, an “unregulated charging process” is a charging process where there is no requirement for circuitry or for a method to monitor and adjust the charging process on account of the possibility of overcharge of secondary cell  404 . The term “unregulated charging process” is not intended to refer to the operation of charging means  406  (discussed further below), but only to the regulation of the charging of secondary cell  404  to prevent an overcharging condition. For example, a person skilled in the art will recognize that charging means  406  may be implemented as a regulated DC-to-DC converter which will use feedback to regulate the output voltage at a desired voltage level. Such regulation is separate and apart from overcharge regulation. 
     Further, even with an unregulated charging process, it may be desirable to control the rate of current flow, for example, to set a maximum limit to the current drawn from bioelectric cell  176  to secondary cell  404 . This limit may be set, for example, via variable resistor  412 . The phrase “unregulated charging process” may be further understood to mean that such a maximum limit to the current flow, once set, does not need to be further regulated or controlled over time in order to prevent overcharge or damage to secondary cell  404 . The maximum permitted current flow from bioelectric cell  176  to secondary cell  404  may be set, for example, as part of a fixed design element of hybrid battery system  276 .H, or may be set on a per unit basis during an initial configuration or set up of hybrid battery system  276 .H. 
     As discussed further below, the ability to charge secondary cell  404  via an unregulated charging process may be enabled by a choice of a specific type of secondary cell  404 , such as for example a lithium ion polymer cell. 
     Bioelectric cell  176  may also be coupled via charging means  406  to secondary cell  404 . Bioelectric cell  176  and secondary cell  404  are configured so that secondary cell  404  may be continuously charged via charging means  406 . 
     It is an advantage of the present system and method that because secondary cell  404  may be a lithium ion polymer cell, it is possible to continually charge secondary cell  404 . Other possible types of secondary cells, such as, for example, a standard lithium ion cell (which is not a lithium ion polymer cell), may require careful regulation of the charging process. For example, regulation may be required to ensure that the other types of secondary cells do not charge too rapidly. Charging too rapidly may damage these other types of secondary cells and may even result in rupture or burning of the secondary cell. 
     However, when a secondary cell  404  is a lithium ion polymer cell, it is possible to charge secondary cell  404  from bioelectric cell  176  according to an unregulated charging process, as that term is defined above. Put another way, bioelectric cell  176  may transfer power to secondary cell  404  as rapidly as secondary cell  404  is capable of absorbing the power. As a result, there is no requirement for complex regulation circuitry to regulate, control, or limit the charging process. Secondary cell  404  may be continuously charged from bioelectric cell  176 , or put another way, secondary cell  404  may be charged from bioelectric cell  176  via an unregulated charging process. 
     Charging means  406  may be, for example, a DC-to-DC converter. In an embodiment, no other charging circuitry is required to charge secondary cell  404  from bioelectric cell  176 . In an alternative embodiment, variable resistor  412  may limit the rate of current flow to secondary cell  404 . 
     In an embodiment of the present system and method, bioelectric cell  176  may put out a voltage anywhere in a range of approximately 0.5 volts up to 2 volts, depending on the exact configuration of bioelectric cell  176 . DC-to-DC converter  406  steps up this voltage to a voltage above four volts. In this way secondary cell  404  is maintained at a voltage, such as, for example, approximately 4.1 to 4.2 volts, which is substantially above the voltage of bioelectric cell  176 . The output voltage of charging means  406  may therefore be set at approximately 4.1 to 4.2 volts, so that secondary cell  404  can be maintained at a voltage level higher than 4.0 volts. In an embodiment of the present system and method, DC-to-DC converter  406  is configured for high-efficiency voltage conversion, resulting in minimal energy loss. 
       FIG. 4B  presents a block diagram of another exemplary bioelectric hybrid battery system  276 B. 2  according to an embodiment of the present system and method. Many elements of exemplary bioelectric hybrid battery system  276 B. 2  are substantially the same or similar to those presented in conjunction with exemplary bioelectric hybrid battery system  276 B. 1  discussed above (see  FIG. 4A ), and a detailed discussion of those elements will not be repeated here. 
     In  FIG. 4B , the dashed box (labeled  276 B. 2 ) contains those elements which may comprise exemplary bioelectric hybrid battery system  276 B. 2 . Exemplary bioelectric hybrid battery system  276 B. 2  is entirely external to case  200  of ICTD  100 . Therefore, in an embodiment, all elements of bioelectric hybrid battery system  276 B. 2  may be packaged together, for example, either within or on the surface of exterior case  428 . These elements may include bioelectric cell  176 , charging means  406 , secondary cell  404 , variable resistor  412 , and various internal connectors and leads, and possibly other electrical and control elements (not illustrated in  FIG. 4B ). In an alternative embodiment, some elements may be on a surface of or external to exterior case  428 . For example, either or both of cathode  180  and/or anode  182  of bioelectric cell  176  may be on a surface of case  428 . Or, for example, either or both of cathode  180  and/or anode  182  of bioelectric cell  176  may be external to case  428 , and coupled to bioelectric hybrid battery system  276 B. 2  via an electrical lead (not shown). 
     Exemplary bioelectric hybrid battery system  276 B. 2  may be coupled to ICTD  100  via lead  190 , thereby providing electrical power to ICTD  100 . Lead  190  may connect to battery terminal  298  of ICTD  100 . From there, internal power line  296  delivers power to power coupling  223 . Power coupling  223  may deliver power via power bus  294  to ICTD operations circuitry  430 . 
       FIG. 4C  presents a block diagram of another exemplary bioelectric hybrid battery system  276 B. 3  according to an embodiment of the present system and method. Many elements of exemplary bioelectric hybrid battery system  276 B. 3  are substantially the same or similar to those presented in conjunction with exemplary bioelectric hybrid battery systems  276 B. 1 ,  276 B. 2  discussed above (see  FIGS. 4A and 4B ), and a detailed discussion of those elements will not be repeated here. 
     In  FIG. 4C , the outer dashed box (labeled  276 B. 3 ) contains those elements which may comprise exemplary bioelectric hybrid battery system  276 B. 3 . The inner dashed box (labeled  176 ) contains those elements which may comprise bioelectric cell  176  of bioelectric hybrid battery system  276 B. 3 . 
     Anode  182  of bioelectric hybrid battery system  276 B. 3  is external to case  428  which contains some elements of bioelectric hybrid battery system  276 B. 3 . Anode  182  is further external to case  200  of ICTD  100 , and in an embodiment may be connected to ICTD  100  by lead  190 . In an alternative embodiment, anode  182  may be placed on, mechanically coupled to, or otherwise situated on an external surface of ICTD case  200 . Anode  182  may be a lead-like structure including, for example and without limitation, a wire, a coiled wire, a flattened metallic element, or similar structure. Anode  182 , which is coupled to cathode  180 , may be configured to be in close proximity to cathode  180 , or may be configured to be at some distance from cathode  180 . 
     Over the lifetime of bioelectric cell  176  and bioelectric hybrid battery system  276 B. 3 , anode  182  is slowly consumed (that is, absorbed into the patient&#39;s body) as part of the power generation process. By placing anode  182  external to case  428  and case  200 , it is possible to restore the power-generating capability of bioelectric hybrid battery system  276 B. 3  by replacing only anode  182 . For example, anode  182  may be situated in a body cavity close to a skin surface of a patient. As a result, any surgery necessary to replace anode  182  may be minimally invasive for the patient. 
       FIG. 4D  presents a block diagram of another exemplary bioelectric hybrid battery system  276 B. 4  according to an embodiment of the present system and method. Many elements of exemplary bioelectric hybrid battery system  276 B. 4  are substantially the same or similar to those presented in conjunction with exemplary bioelectric hybrid battery systems  276 B. 1 ,  276 B. 2 ,  276 B. 3  discussed above (see  FIGS. 4A ,  4 B, and  4 C), and a detailed discussion of those elements will not be repeated here. In  FIG. 4D , the dashed box (labeled  276 B. 4 ) contains those elements which may comprise exemplary bioelectric hybrid battery system  276 B. 4 . 
     In bioelectric hybrid battery system  276 B. 4 , electrical power (that is, current and/or voltage) from bioelectric cell  176  is used to charge secondary cell  404  via charging means  406 , in a manner substantially the same or similar to that already described above in conjunction with other embodiments. In addition, power from bioelectric cell  176  may also be used to directly power some operations of ICTD  100 . 
     In the exemplary embodiment illustrated in  FIG. 4D , power from bioelectric cell  176  is delivered to an internal power coupling  422  of bioelectric hybrid battery system  276 B. 4 . Power from secondary cell  404  is also delivered to internal power coupling  422 . Bioelectric cell  176  may deliver a first power level, while secondary cell  404  may deliver a second power level. For example, bioelectric cell  176  may deliver a voltage of in a range of approximately 0.5 volts to 2 volts, and a current in a range of approximately 100 μAmps to 150 μAmps. Secondary cell  404  may deliver a voltage of approximately 4 volts and a current of approximately 3 to 5 amps. Persons skilled in the relevant arts will recognize that the voltages and currents described here are exemplary only, and other voltage and/or current levels may be delivered as well. 
     Both the first power level and the second power level are delivered to hybrid battery power coupling  422 . The first power level and the second power level are delivered from hybrid battery power coupling  422  to battery terminal  298  of ICTD  100  via lead  190 . The first power level and the second power level are delivered from battery terminal  298  to ICTD power coupling  223  via ICTD internal power line  296 . From ICTD power coupling  223 , either the first power level or the second power level may be delivered to various elements of ICTD  100 . 
     For example, in an embodiment, a first power level from bioelectric cell  176  may be a low voltage, low current power from bioelectric cell  176  (for example, approximately 100 μAmps and approximately 0.5 volts up to approximately 2 volts, depending on the exact configuration of bioelectric cell  176 ). The first power level may be delivered to ICTD operations circuitry  430 ′ via a first internal power bus  294 . 1 . ICTD operations circuitry  430 ′ may be similar to ICTD operations circuitry  430  already discussed above and may include elements of ICTD  100  which can be powered at low voltage and/or low current levels. Low voltage/low current ICTD operations circuitry  430 ′ may include, for example and without limitation, memory  260 , telemetry circuit  264 , physiological sensor  270 , impedance measuring circuit  278 , microcontroller  220 , atrial pulse generator  222 , atrial sensing circuits  244 , ventricular sensing circuits  246 , analog-to-digital converter  252 , and electrode configuration switch  226 . 
     However, ICTD low voltage/low current operations circuitry  230 ′ may explicitly exclude shocking circuit  282  (which was included in ICTD operations circuitry  230 , discussed above). In an embodiment of the present system and method, shocking circuit  282  requires high voltages and currents, and therefore cannot be powered off of a voltage or current provided directly from bioelectric cell  176 . Instead, shocking circuit  282  requires higher voltages and/or currents provided by secondary cell  404 . In an alternative embodiment, some control or switching circuitry associated with or comprising shocking circuit  282  may be powered off of low voltages or low currents, and therefore may be powered via electricity provided by bioelectric cell  176 . However, a shocking capacitor or shocking capacitors  424 , which are used to store up high voltages prior to shocking, may still require high voltages. Therefore, a shocking capacitor or shocking capacitors  424  associated with shocking circuit  282  will still be powered by electricity from secondary cell  404 . 
     Shown in  FIG. 4D  is a second power bus  294 . 2  which provides high voltage and/or high current to shocking circuit  282  via power coupling  223 . For example, the voltage may be an unloaded voltage of approximately 4 to 4.2 volts, or a loaded voltage of approximately 3.5 volts, or a current of approximately 3 amps to 4.5 amps. 
     Persons skilled in the relevant arts will recognize that ICTD  100  may further comprise control circuitry used to determine power routing from power coupling  223  to elements of ICTD  100  via first and second power buses  294 . 1 ,  294 . 2 . Such control circuitry may for example be part of microcontroller  220  (described above in conjunction with  FIG. 1 ), and may in particular be part of battery control element  286 . Such control circuitry may also be an element of bioelectric hybrid battery system  276 B which is apart from microcontroller  220 , but which may be coupled to microcontroller  220 . Persons skilled in the relevant arts will further recognize that more than two power levels may be employed, along with possibly additional power buses  294 . n  (not shown in the  FIGS. 4A-4D ). 
     In the exemplary embodiment shown in  FIG. 4D , a first power level from bioelectric cell  176  and a second power level from a secondary cell  404  are routed to elements of ICTD  100 , where both the bioelectric cell  176  and the secondary cell  404  are elements of a bioelectric hybrid battery system  276 B. 4  which is wholly external to ICTD  100 . The power is routed via various power couplings  422 ,  223  and/or power lines or buses  416 . 1 ,  416 . 2 ,  190 ,  296 ,  294 . 1 ,  294 . 2 , as illustrated in the figure and as described in the exemplary embodiment above. 
     However, in alternative embodiments, a first power level and a second power level from a respective bioelectric cell  176  and a secondary cell  404  may be routed to elements of ICTD  100 , even if one or both of bioelectric cell  176  and/or secondary cell  404  are partly or wholly internal to ICTD  100 . Persons skilled in the relevant arts will recognize that in such alternative embodiments, suitable changes may be made in the linkages, arrangements, connections, or configurations of various power couplings  422 ,  223  and/or power lines or buses  416 . 1 ,  416 . 2 ,  190 ,  296 ,  294 . 1 ,  294 . 2 , in order to achieve the requisite routing of power to elements of ICTD  100 . 
     In an alternative embodiment of the present system and method, when power is routed from secondary cell  404  to shocking circuit  282 , secondary cell  404  may be temporarily decoupled from bioelectric cell  176 . For exemplary embodiments of circuitry which may decouple secondary cell  404  from a primary cell (which may be a bioelectric cell  176 ), see above referenced U.S. patent application Ser. No. ______, Attorney Docket Number A06E3099. 
     Persons skilled in the relevant arts will further appreciate that the exact configurations, connections, and arrangements of electrical components shown in  FIGS. 4A-4D  are exemplary only. Additional components, fewer components, alternative components, and variations in the connections may be employed consistent with the system and method for a hybrid battery system described herein. 
     9. Choice of Secondary Power Cell 
     Several elements distinguish the present system and method with respect to both prior batteries employed for use in ICTDs and to prior hybrid battery systems. Among these elements are the choices of power cells employed with the present system and method. 
     The lithium/silver vanadium oxide (Li/SVO) cell has been used as a power source of ICTDs  100  for many years. While it has some desirable electrical properties, the internal resistance for both the anode and cathode increase as a result of the discharging process, particularly during midlife. This may ultimately result in premature battery replacement. 
     The choice of a bioelectric cell  176  as a primary power source provides a long-term source of power which is safe, reliable, has an extended lifetime (minimizing the frequency of surgery for replacement), and provides for convenient replacement of the power source. In addition, and for as long as anode material  182  is not fully consumed, bioelectric cell  176  does not suffer the degradation in electrical properties associated with the Li/SVO cell, as described above. 
     The inventors have investigated the performance properties of the Li ion polymer cell for use as secondary cell  404 , particularly in the context of charging shocking capacitors  424  within an ICTD. A shocking process (that is, a defibrillation process) may be a single shock, but more typically is a series of shocks closely spaced in time. For example, a series of shocks may be spaced 5 to 10 seconds apart, though shorter or longer intervals are possible. It is therapeutically preferable that the ICTD be capable of delivering multiple shocks within a few seconds of each other, with the option of spacing the shocks at intervals of 5 seconds or less. 
       FIG. 5  shows a set of plots  510  of the measured time required, in seconds, for various Li ion polymer cells (listed in legend  515  at right) to charge the shocking capacitors to approximately 750 to 800 volts in a representative ICTD (the Epic II ICD, manufactured by St. Jude Medical, Inc., of St. Paul, Minn.). The discharge current of the Li ion polymer cells was set at approximately 3 Amperes. As can be seen from plots  510 , charging times were consistently at or below approximately 5 seconds, with only a slight increase in charging times over a series of shocks. 
     As discussed further below in conjunction with  FIG. 5 , charging times of approximately 5 seconds were specifically associated with a discharge current of approximately 3 Amperes. Emerging Li ion polymer cells are capable of significantly higher currents, of approximately 4 to 4.5 Amperes, which may result in charging times of approximately 2.5 to 3 seconds, or even less. 
       FIG. 6  shows a set of plots  610  of the time required, in seconds, for various Li ion polymer cells (listed in legend  615  at right) to charge the shocking capacitors to approximately 750 to 800 volts in another representative ICTD (the Atlas +HF ICD, manufactured by St. Jude Medical, Inc., of St. Paul, Minn.). Again, a current of approximately 3 Amperes from the Li ion polymer cells was employed. As can be seen from plots  610 , charging times were consistently in the neighborhood of 5 seconds, and in many cases below 5 seconds with some of the cells tested. 
       FIG. 7  shows a set of plots  710  of the time required, in seconds, for a representative Li ion polymer cell (the DLG 303448H, manufacturer DLG Battery (Shanghai) Co., Ltd., Fengxian District, Shanghai, China) to charge the shocking capacitors to approximately 750 to 800 volts in a representative ICTD (the Epic II ICD, manufactured by St. Jude Medical, Inc., of St. Paul, Minn.). Different current levels (listed in legend  715 ) were employed, ranging from 3 Amps to 4.5 Amps. As can be seen from plots  710 , charging times of well under 5 seconds could be achieved, in some cases being lower than 2.5 seconds. 
     A charge time of 5 seconds or less represents a significant improvement over charge times available with present systems using Lithium Silver Vanadium Oxide (Li/SVO) batteries. Further, the Li ion polymer cell can provide current levels on the order of several Amps (for example, 3 to 5 Amps), thereby enabling the charge times on the order of 5 seconds or less, in some cases even less than 3.5 seconds, or even less than 3 seconds. Using a standard Li ion cell, current levels of 3 to 5 Amps could only be provided by a standard cell of undesirable size and weight, or a combination of multiple standard Li ion cells of undesirable size and weight, for the present application. Therefore, and as also discussed in further detail below, a Li ion polymer cell is to be preferred over a standard Li ion cell for the present system and method. 
     The Lithium ion polymer (Li ion polymer) cell, already described above as being used as the secondary cell  404  in exemplary embodiments of the present system and method, has both a higher voltage and lower internal resistance compared to the Li/SVO cell, making it desirable for use as the cell which charges shocking capacitor(s)  424  of ICTD  100 . 
     In particular, the Li ion polymer cell has a higher current output than the Li/SVO cell. The discharge current of a typical Li/SVO battery used in an ICTD is approximately 3 Amps. A Li ion polymer cell may be discharged with a higher current, such as 3.5 to 4.5 Amps. Therefore, using the Li ion polymer cell as the power source  404  for the shocking capacitors  424 , the discharge time, or equivalently, the time to charge the shocking capacitors  424 , may be less than with the Li/SVO cell. For example, while it typically requires 10 to 18 seconds for a Li/SVO cell to charge the shocking capacitors  424  to approximately 750 volts to 800 volts, a Li ion polymer cell may charge the shocking capacitors to the same voltage (approximately 750 volts to 800 volts) in approximately 5 seconds, or even less time. 
     A Li ion polymer battery with, for example, LiCoO 2  cathode material, may be recharged up to 4.23V. This is about one volt higher than a new Li/SVO battery. The internal resistance of a Li ion polymer battery may be lower than 0.1Ω. In an embodiment, the output voltage of DC-to-DC converter  406  is set at approximately 4.2 volts. In this way, Li ion polymer cell  404  can be maintained at an unloaded voltage higher than 4.0 volts. A further advantage of the Li ion polymer cell is that, unlike with the Li/SVO cell, there is no significant increase in internal resistance over the life of the Li ion polymer cell. Therefore, in the discharge process the voltage drop will be less, and the loaded voltage remains higher over the life of the Li ion polymer cell as compared with the Li/SVO cell. The unloaded voltage on the Li ion polymer cell can be maintained at approximately 4.1 to 4.2 volts, while the loaded voltage, during charging of shocking capacitor(s)  424 , may be maintained at approximately 3.5 volts. 
     As a result of all these combined advantages of the Li ion polymer cell, the discharge time for high voltage shocking (that is, the time to charge shocking capacitor(s)  424 ) will be significantly less compared to the discharge time using a Li/SVO battery. The time to charge the shocking capacitors is approximately 10 to 20 seconds for the Li/SVO cells presently in use. Charging times of approximately 5 seconds or even less, such as less than 4 seconds, 3.5 seconds, or even less than 3 seconds, may be achieved with the Li ion polymer cell. 
     10. Lithium Ion Polymer Cell vs. Standard Lithium Ion Cell 
     Li ion polymer cells also offer advantages as a secondary cell  404 , as compared with standard Li ion cells that might be considered for use in the same capacity (that is, as a candidate for secondary cell  404 ). 
     Because Li ion polymer cells use gelatinous electrolyte, their self-discharge rate is relatively lower than that of a regular Li ion battery. (The self-discharge rate reflects the rate at which a cell spontaneously loses power, even with no external load or usage, due to internal chemical reactions.) The self-discharge rate of the Li ion polymer cell is in the range from 2% to 5% per month. The self-discharge rate of the standard Li ion cell is in the range of 5% to 10% per month. Because the Li ion polymer cell has a lower self-discharge rate, it will require less electrical charge from bioelectric cell  176  (as compared with the charge that would be required if the standard Li ion cell were employed as secondary cell  404 ). Since less charge is required from bioelectric cell  176 , more power is preserved in bioelectric cell  182  or, equivalently, anode  182  of bioelectric cell  176  is consumed more slowly. This enhances the overall functional lifetime of bioelectric cell  176  and hybrid battery system  276 B. 
     Also, and as noted above, Li ion polymer cells can be manufactured in thin, pliable shapes that offer advantages in device packaging compared with standard Li ion batteries, which have more bulk and are generally of rigid construction. 
     For typical shocking purposes, a desired storage of a secondary cell might be 250 milliAmpHours. This is sufficient to provide power for a series of six shocks during a defibrillation process. A standard lithium ion cell might have a discharge current capacity of 1 C to 2 C, meaning that it can only provide current at a rate equivalent to its storage capacity, or at most twice its storage capacity. For example, a standard Li ion cell with a storage capacity of 250 milliAmpHours and a discharge current of 2 C can provide at most 500 milliAmps of current. At such a current flow, it may take a minute or several minutes to charge the shocking capacitors. This is insufficient for real-world applications, so a larger cell (or additional cells) would be required. 
     By contrast, a Li ion polymer cell may have a discharge current capacity of anywhere from 5 C to 20 C, or even higher. At this discharge current capacity, the Li ion polymer cell may be able to discharge at a rate from 5 times to 20 times its storage capacity. Again assuming a total cell power storage of 250 milliAmpHours, a Li ion polymer cell can deliver a current from 1.25 Amps (for a 5 C cell) to 5 Amps (for a 20 C cell). It may be possible to achieve a shocking capacitor charge time of as short as 5 seconds or even less, such as approximately 3.5 seconds, 3 seconds, or even less. This is a dramatic improvement over the charge times of approximately 10 to 20 seconds achieved with presently used Li/SVO batteries. As shown in  FIG. 7  (already discussed above), with some Li ion polymer cells it may be possible to charge shocking capacitor(s)  424  in times under 3 seconds, and possibly even under 2.5 seconds, which is much less than the charge times available with present devices. 
     11. Storage Capacities and Power Delivery for Cells for Different ICTD Applications 
     In embodiments of the present system and method, the size and capacity of the two different types of cells (bioelectric and secondary) are appropriately selected. The selection may vary depending on the type of ICTD to be powered by the bioelectric hybrid battery system  276 B. 
     An ICTD  100  may be a pacemaker which is not configured to provide shocking (that is, ICTD  100  is not configured to provide defibrillation). Secondary cell  404  is directly connected to pacing circuits (for example, atrial pulse generator  222  and/or ventricular pulse generator  224 ) as pacing power supply. The capacity of the small size secondary cell  404  could be approximately 100 milliAmpHours. A capacity of 100 milliAmpHours for bioelectric hybrid battery system  276 B is more than enough to maintain programming during final testing and shelf life of ICTD  100 . A capacity of 100 milliAmpHours is also sufficient for 64K and RF telemetry (that is, telemetry with transmission frequencies on the order of 100 MHz). In general, higher telemetry speeds are desirable not only for faster data rates and/or increased data density, but also for higher transmission distances (for example, distances on the order of three meters for 100 MHz telemetry, as opposed to distances of only a few inches for kilohertz transmission frequencies). 
     By continuously charging secondary cell  404 , bioelectric cell  176  can compensate for all power consumption and can maintain the secondary cell  404  at full capacity. Therefore, a combination of bioelectric cell  176  and a small size secondary cell  404  can be a power source of pacemakers. 
     For the pacemaker application, the small size secondary cell  404  may be a Li ion button cell such as the LIR2450 cell (capacity 120 milliAmpHours, manufactured by PowerStream Technology, 140 South Mountainway Drive, Orem Utah 84058). However, a Li ion button cell may require more complex charging circuitry to monitor or limit the charging process. In an embodiment, a Li ion polymer cell may instead be used as secondary cell  404 , which may reduced the complexity of the charging circuitry, as already described above. A small Li ion polymer cell, with a capacity of, for example, about 120 to 150 milliAmpHours, can be selected as the secondary cell. For example, possible cells are the model 042025 cell (typical capacity 120 milliAmpHours) or the model 052025 cell (typical capacity 150 milliAmpHours), both manufactured by Gaston Narada International Ltd., Kwai Chung, Hong Kong. 
     For 64K or RF telemetry, secondary cell  404  is occasionally discharged at 1.5 milliAmps for 30 minutes or at 5 milliAmps for 30 minutes, respectively. The power of the above-listed secondary cells  404  is sufficient for these applications. 
     Typically, bioelectric cell  176  and small size secondary cell  404  will be combined with other elements, as described above, to create bioelectric hybrid battery system  276 B. Other elements may include, for example and without limitation, charging means  406  such as a DC-to-DC converter, as already described above. For the pacemaker application, the output voltage of the DC-to-DC converter  406  may be set at for example approximately 3.7 volts. With continuous charging by the bioelectric cell  176 , the voltage of secondary cell  404  can be maintained at this level. 
     An ICTD  100  may be configured to provide shocking (that is defibrillation therapy), as well as cardiac pacing and monitoring. For shocking applications, a larger secondary cell  404  is required. A preferred choice may be a larger size Li ion polymer cell, with the output voltage of DC-to-DC converter  406  set at, for example, approximately 4.1 volts. In an embodiment, bioelectric cell  196  is only used to charge secondary cell  404 , and so compensate for the power consumption from pacing, background operations (such as sensing and communications), shocking, and self-discharge of the Li ion polymer cell  404 . In an alternative embodiment, bioelectric cell  196  may directly provide some of the power for pacing and background operations, as well as recharging the Li ion polymer secondary cell  404 . 
     The Li ion polymer cell  404  is the power source for high voltage charging. The capacity of the Li ion polymer cell  404  should be enough for lifetime high voltage charging usage. Based on statistical data, approximately 25% to 30% of ICD battery capacity is used for high voltage charging, and the other 70% of capacity is used for pacing and background operations. It is appropriate to select a Li ion polymer cell  404  with a capacity greater than 500 milliAmpHours for this application. For example, a possible cell is the DLG 603048H cell (capacity 520 milliAmpHours, manufacturer DLG Battery (Shanghai) Co., Ltd., Fengxian District, Shanghai, China). 
     In general, however, and whether the application is pacing only, or pacing and shocking, it is desirable to avoid a Li ion polymer battery with too small a capacity. If the size is too small, the internal resistance will be higher, and that will negatively impact the discharge rate. In addition, if a patient requires a large number of shocks in a short time, a secondary cell  404  which is too small will be unable to provide the required number of shocks. 
     Cardiac shocking requires more power than cardiac pacing. In addition, a secondary cell  404  used in a shocking device is partially drained during a series of shocks. Therefore, the secondary cell  404  used in a shocking device must have enough reserve capacity to continue powering ICTD  100  operations after a shocking cycle, and before the secondary cell  404  is fully recharged. Therefore, a secondary cell  404  used for cardiac shocking applications will typically be larger (that is, have greater storage capacity, and likely a larger physical volume as well) compared with a secondary cell  404  used only for pacing. 
     In addition, consideration must be given to the size and configuration of a bioelectric cell  176  employed is a bioelectric hybrid battery system  276 B employed for shocking applications as opposed to only pacing applications. Typically, a bioelectric cell  176  puts out a voltage in the range of 0.5 to 2 volts, and a current in a range of approximately 100 microAmps to 150 microAmps. The exact values may vary depending on the specific configuration of bioelectric cell  176 . 
     In an ICTD  100  configured for defibrillation therapy, it is desirable to recharge secondary cell  204  as quickly as possible. A relatively larger bioelectric cell  176  may provide a higher current flow, and therefore be better adapted for faster recharging of secondary cell  204 . In particular, a larger surface area for anode  182  and/or cathode  180  may result in a higher current flow. 
     In addition, cardiac shocking places a significant power drain on a bioelectric hybrid battery system  276 B, typically consuming approximately 25% to 30% of the total power consumed over the lifetime of system  276 B. Therefore, a bioelectric cell  176  configured for greater overall storage capacity is better suited for cardiac shocking purposes. In the case of a bioelectric cell  176 , increased storage capacity may be achieved in whole or in part by use of a larger anode element  182 . 
     12. Alternative Embodiments 
     In an embodiment of the present system and method, each bioelectric cell  176  and/or each secondary cell  404  (for example, each lithium ion polymer cell(s)) is a self-contained battery unit, readily coupled to conventional electrical contacts in a larger system. Secondary cell  404  in particular may be of a kind which may be purchased off-the-shelf. In an alternative embodiment, elements of bioelectric cell  176  and/or secondary cell  404  may be specially tailored for integration into the bioelectric hybrid battery system  276 B of the present system and method, and/or further specially tailored for integration into ICTD  100 . The details of such construction, if any, are beyond the scope of this document. 
     In embodiments described above, the bioelectric hybrid battery system  276 B employs a single bioelectric cell  176  and a single secondary cell  404 . In alternative embodiments, more than one bioelectric cell  176  may be employed. In alternative embodiments, more than one secondary cell  404  may be employed. 
     In embodiments described above, the bioelectric hybrid battery system employs a single type of bioelectric cell  176  and a single type of secondary cell  404 . In an alternative embodiment, different types of bioelectric cells  176  may be employed in combination. In an alternative embodiment, different types of secondary cells  404  may be employed in combination, which may be suitable for different types, patterns, time durations, or required power levels of ICTD activity or ICTD elements. 
     In an alternative embodiment, an additional, non-rechargeable cell or cells may be integrated into the system for any of several reasons. For example, an additional, non-rechargeable cell or cells may provide additional power, or may maintain charge or power in the event of a failure of either of bioelectric cell  176  or secondary cell  404 . In an embodiment, such a non-rechargeable cell or cells may have a higher voltage and/or higher current output than bioelectric cell  176 , but may not have as high a voltage or have as high a current as secondary cell  404 . Such a non-rechargeable cell or cells may be, for example and without limitation, a lithium-silver vanadium oxide (LI/SVO) cell, a lithium-magnesium oxide (Li/MnO 2 ) cell, or a lithium carbon monofluoride (LiCF x ) cell. 
     Suitable switching, logic, and/or coupling circuitry may be employed to select power from and/or to otherwise support the additional power cells or additional type(s) of power cells. as appropriate. 
     13. Conclusion 
     It is to be appreciated that the Detailed Description section, and not the Summary and Abstract sections, is intended to be used to interpret the claims. The Summary and Abstract sections may set forth one or more but not all exemplary embodiments of the present system and method as contemplated by the inventor(s), and thus, are not intended to limit the present method and system and the appended claims in any way. 
     Moreover, while various embodiments of the present system and method have been described above, it should be understood that they have been presented by way of example, and not limitation. It will be apparent to persons skilled in the relevant art(s) that various changes in form and detail can be made therein without departing from the spirit and scope of the present system and method. Thus, the present system and method should not be limited by any of the above described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents. 
     In addition, it should be understood that the figures and screen shots illustrated in the attachments, which highlight the functionality and advantages of the present system and method, are presented for example purposes only. The architecture of the present system and method is sufficiently flexible and configurable, such that it may be utilized (and arranged) in ways other than that shown in the accompanying figures. Moreover, the steps indicated in the exemplary system(s) and method(s) described above may in some cases be performed in a different order than the order described, and some steps may be added, modified, or removed, without departing from the spirit and scope of the present system and method. 
     Further, the purpose of the foregoing Abstract is to enable the U.S. Patent and Trademark Office and the public generally, and especially the scientists, engineers and practitioners in the art who are not familiar with patent or legal terms or phraseology, to determine quickly from a cursory inspection the nature and essence of the technical disclosure of the application. The Abstract is not intended to be limiting as to the scope of the present system and method in any way.