Patent Publication Number: US-8532787-B2

Title: Implantable therapy system having multiple operating modes

Description:
CROSS REFERENCE 
     This application claims priority to U.S. Provisional Application Ser. No. 60/941,118, filed May 31, 2007, and entitled “IMPLANTABLE DEVICE,” the disclosure of which is hereby incorporated by reference herein. 
    
    
     This application discloses and claims subject matter disclosed in commonly assigned U.S. application Ser. Nos. 11/943,069, now U.S. Pat. No. 8,140,167, and 11/943,093, now abandoned, filed concurrently herewith and titled “Implantable Therapy System” and “Therapy System,” respectively. 
     I. BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention pertains to systems for applying electrical signals to an anatomical feature of a patient. While many of the disclosed concepts are applicable to a wide variety of therapies (e.g., cardiac pacing with electrodes applied to heart tissue), the invention is described in a preferred embodiment where the invention pertains to the treatment of gastro-intestinal disorders such as obesity, pancreatitis, irritable bowel syndrome and inflammatory disorders. In a most preferred embodiment, this invention pertains to the treatment of a gastrointestinal disorder by the application of a high frequency signal to a vagus nerve of a patient. 
     2. Description of the Prior Art 
     A blocking therapy can be used alone or in combination with traditional electrical nerve stimulation in which impulses are created for propagation along a nerve. The disorders to be treated include, without limitation, functional gastrointestinal disorders (FGIDs) (such as functional dyspepsia (dysmotility-like) and irritable bowel syndrome (IBS)), gastroparesis, gastroesophageal reflux disease (GERD), inflammation, discomfort and other disorders. 
     In a blocking therapy, an electrode (or multiple electrodes) is placed on or near a vagus nerve or nerves of a patient. By “near”, it is meant close enough that a field created by the electrode captures the nerve. As disclosed in the foregoing patent and applications, the electrode can be placed directly on a nerve, overlying tissue surrounding a nerve or on or in an organ near a nerve. 
     Higher frequencies (e.g., 2,500 Hz-20,000 Hz) are believed to result in more consistent neural conduction block. Particularly, the nerve conduction block is applied with an electrical signal selected to block the entire cross-section of the nerve (e.g., both afferent and efferent signals on both myelinated and non-myelinated fibers) at the site of application of the blocking signal. 
     In one embodiment of the electrodes a signal amplitude of 0.5 mA to 8 mA at the electrode-nerve interface has been found to be adequate for blocking. However, depending on electrode design, other amplitudes may suffice. Other signal parameters, as non-limiting examples, include an adjustable pulse width (e.g., 50 μsec to 500 μsec), and a frequency range of (by non-limiting example) 1000 Hz to 10,000 Hz. It must be recognized that the frequency sets certain limitations on the available pulse width; for example, the pulse width cannot exceed 50% of the cycle time for a symmetrical biphasic pulse. 
     A typical duty cycle of therapy could consist of 5 minutes on and 10 minutes off. These are representative only. For example, a duty cycle could be 2 minutes on and 5 minutes off or be 30 minutes on per day. These examples are given to illustrate the wide latitude available in selecting particular signal parameters for a particular patient. 
     A complete system for applying a signal to a nerve may include systems for addressing the potential for charge build-up, assuring good communication between implanted and external components, recharging implantable batteries, physician and patient controls and programming and communication with the system. These issues and selected prior art systems for addressing these issues will now be discussed. 
     II. SUMMARY OF THE INVENTION 
     According to a preferred embodiment of the present invention, a therapy system is disclosed for applying therapy to an internal anatomical feature of a patient. The system includes at least one electrode for implantation within the patient and placement at the anatomical feature (e.g., a nerve) for applying the therapy signal to the feature upon application of a treatment signal to the electrode. An implantable component is placed in the patient&#39;s body beneath a skin layer and coupled to the electrode. The implantable component includes an implanted antenna. An external component has an external antenna for placement above the skin and adapted to be electrically coupled to the implanted antenna across the skin through radiofrequency transmission. 
     According to aspects, the external component is adapted to be configured into multiple selectable operating modes including an operating room mode, a programming mode, and a charging mode. 
     For example, communicatively coupling the external component to peripheral devices can automatically configure the external component into one of the operating modes. 
     According to other aspects, the implantable component is adapted to be configured into multiple selectable operating modes including a training mode for simulating a therapy, and a therapy mode for providing therapy. 
     According to other aspects, the implantable component may be configured to increment therapy settings automatically by a predetermined amount after a predetermined period of time. 
    
    
     
       III. BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic representation of a therapy system having features that are examples of inventive aspects of the principles of the present invention, the therapy system including a neuroregulator and an external charger; 
         FIG. 2A  is a plan view of an implantable neuroregulator for use in the therapy system of  FIG. 1  according to aspects of the present disclosure; 
         FIG. 2B  is a plan view of another implantable neuroregulator for use in the therapy system of  FIG. 1  according to aspects of the present disclosure. 
         FIG. 3A  is a block diagram of a representative circuit module for the neuroregulator of  FIG. 2A  and  FIG. 2B  according to aspects of the present disclosure; 
         FIG. 3B  is a block diagram of another representative circuit module for the neuroregulator of  FIG. 2A  and  FIG. 2B  according to aspects of the present disclosure; 
         FIG. 4  is a block diagram of a circuit module for an external charger for use in the therapy system of  FIG. 1  according to aspects of the present disclosure; 
         FIG. 5  is a plan schematic view of an example external charger for use in the therapy system of  FIG. 1  according to aspects of the present disclosure; 
         FIG. 6  is a plan, schematic view of an external charger and schematic views of a patient transmit coil and a physician transmit coil configured to couple to the external charger according to aspects of the present disclosure; 
         FIG. 7  is a side elevation, schematic view of an external coil in a desired alignment over an implanted coil according to aspects of the present disclosure; 
         FIG. 8  illustrates the external coil and implanted coil of  FIG. 7  arranged in a misaligned position according to aspects of the present disclosure; 
         FIG. 9  is a perspective view of a distal portion of a bipolar therapy lead according to aspects of the present disclosure; 
         FIG. 10  is a schematic representation of an electrode placement for a blocking therapy according to aspects of the present disclosure; 
         FIG. 11  is a schematic representation of a first electrode configuration according to aspects of the present disclosure; 
         FIG. 12  is a schematic representation of a typical waveform according to aspects of the present disclosure; 
         FIG. 13  is a schematic representation of a second electrode configuration according to aspects of the present disclosure; 
         FIG. 14  is a schematic representation of a typical waveform according to aspects of the present disclosure; 
         FIG. 15  is a schematic representation of a third electrode configuration according to aspects of the present disclosure; 
         FIG. 16  is a schematic representation of a typical waveform according to aspects of the present disclosure; 
         FIG. 17  is a schematic representation of a fourth electrode configuration according to aspects of the present disclosure; 
         FIG. 18  is a schematic representation of a typical waveform according to aspects of the present disclosure; 
         FIG. 19  is a graphical illustration of a treatment schedule according to aspects of the present disclosure; 
         FIG. 20  is a schematic representation of a signal pulse illustrating charge balancing according to aspects of the present disclosure; 
         FIG. 21  is a schematic representation of an alternative means of charge balancing according to aspects of the present disclosure; 
         FIG. 22  is a schematic illustration of a charge balancing system shown in a shorting state according to aspects of the present disclosure; 
         FIG. 23  is the view of  FIG. 22  in a non-shorting state according to aspects of the present disclosure; and 
         FIG. 24  is a graphical illustration comparing waveforms in shorting and non-shorting states according to aspects of the present disclosure. 
     
    
    
     IV. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     With reference now to the various drawing figures in which identical elements are numbered identically throughout, a description of the preferred embodiments of the present invention will now be described. While the invention is applicable to treating a wide variety of gastro-intestinal disorders, the invention will be described in preferred embodiments for the treatment of obesity. 
       FIG. 1  schematically illustrates a therapy system  100  for treating obesity or other gastro-intestinal disorders. The therapy system  100  includes a neuroregulator  104 , an electrical lead arrangement  108 , and an external charger  101 . The neuroregulator  104  is adapted for implantation within a patient to be treated for obesity. As will be more fully described herein, the neuroregulator  104  typically is implanted just beneath a skin layer  103 . 
     The neuroregulator  104  is configured to connect electrically to the lead arrangement  108 . In general, the lead arrangement  108  includes two or more electrical lead assemblies  106 ,  106   a . In the example shown, the lead arrangement  108  includes two identical (bipolar) electrical lead assemblies  106 ,  106   a . The neuroregulator  104  generates therapy signals and transmits the therapy signals to the lead assemblies  106 ,  106   a.    
     The lead assemblies  106 ,  106   a  up-regulate and/or down-regulate nerves of a patient based on the therapy signals provided by the neuroregulator  104 . In an embodiment, the lead assemblies  106 ,  106   a  include distal electrodes  212 ,  212   a , which are placed on one or more nerves of a patient. For example, the electrodes  212 ,  212   a  may be individually placed on the anterior vagal nerve AVN and posterior vagal nerve PVN, respectively, of a patient. For example, the distal electrodes  212 ,  212   a  can be placed just below the patient&#39;s diaphragm. In other embodiments, however, fewer or more electrodes can be placed on or near fewer or more nerves. 
     The external charger  101  includes circuitry for communicating with the implanted neuroregulator  104 . In general, the communication is transmitted across the skin  103  along a two-way signal path as indicated by arrows A. Example communication signals transmitted between the external charger  101  and the neuroregulator  104  include treatment instructions, patient data, and other signals as will be described herein. Energy also can be transmitted from the external charger  101  to the neuroregulator  104  as will be described herein. 
     In the example shown, the external charger  101  can communicate with the implanted neuroregulator  104  via bidirectional telemetry (e.g. via radiofrequency (RF) signals). The external charger  101  shown in  FIG. 1  includes a coil  102 , which can send and receive RF signals. A similar coil  105  can be implanted within the patient and coupled to the neuroregulator  104 . In an embodiment, the coil  105  is integral with the neuroregulator  104 . The coil  105  serves to receive and transmit signals from and to the coil  102  of the external charger  101 . 
     For example, the external charger  101  can encode the information as a bit stream by amplitude modulating or frequency modulating an RF carrier wave. The signals transmitted between the coils  102 ,  105  preferably have a carrier frequency of about 6.78 MHz. For example, during an information communication phase, the value of a parameter can be transmitted by toggling a rectification level between half-wave rectification and no rectification. In other embodiments, however, higher or lower carrier wave frequencies may be used. 
     In an embodiment, the neuroregulator  104  communicates with the external charger  101  using load shifting (e.g., modification of the load induced on the external charger  101 ). This change in the load can be sensed by the inductively coupled external charger  101 . In other embodiments, however, the neuroregulator  104  and external charger  101  can communicate using other types of signals. 
     In an embodiment, the neuroregulator  104  receives power to generate the therapy signals from an implantable power source  151  (see  FIG. 3A ), such as a battery. In a preferred embodiment, the power source  151  is a rechargeable battery. In some embodiments, the power source  151  can provide power to the implanted neuroregulator  104  when the external charger  101  is not connected. In other embodiments, the external charger  101  also can be configured to provide for periodic recharging of the internal power source  151  of the neuroregulator  104 . In an alternative embodiment, however, the neuroregulator  104  can entirely depend upon power received from an external source (see  FIG. 3B ). For example, the external charger  101  can transmit power to the neuroregulator  104  via the RF link (e.g., between coils  102 ,  105 ). 
     In some embodiments, the neuroregulator  104  initiates the generation and transmission of therapy signals to the lead assemblies  106 ,  106   a . In an embodiment, the neuroregulator  104  initiates therapy when powered by the internal battery  151 . In other embodiments, however, the external charger  101  triggers the neuroregulator  104  to begin generating therapy signals. After receiving initiation signals from the external charger  101 , the neuroregulator  104  generates the therapy signals (e.g., pacing signals) and transmits the therapy signals to the lead assemblies  106 ,  106   a.    
     In other embodiments, the external charger  101  also can provide the instructions according to which the therapy signals are generated (e.g., pulse-width, amplitude, and other such parameters). In a preferred embodiment, the external charger  101  includes memory in which several predetermined programs/therapy schedules can be stored for transmission to the neuroregulator  104 . The external charger  101  also can enable a user to select a program/therapy schedule stored in memory for transmission to the neuroregulator  104 . In another embodiment, the external charger  101  can provide treatment instructions with each initiation signal. 
     Typically, each of the programs/therapy schedules stored on the external charger  101  can be adjusted by a physician to suit the individual needs of the patient. For example, a computing device (e.g., a notebook computer, a personal computer, etc.)  107  can be communicatively connected to the external charger  101 . With such a connection established, a physician can use the computing device  107  to program therapies into the external charger  101  for either storage or transmission to the neuroregulator  104 . 
     The neuroregulator  104  also may include memory  152  (see  FIGS. 3A and 3B ) in which treatment instructions and/or patient data can be stored. For example, the neuroregulator  104  can store therapy programs indicating what therapy should be delivered to the patient. The neuroregulator  104  also can store patient data indicating how the patient utilized the therapy system  100  and/or reacted to the delivered therapy. 
     In what follows, the focus of the detailed description is the preferred embodiment in which the neuroregulator  104  contains a rechargeable battery  151  from which the neuroregulator  104  may draw power ( FIG. 3A ). 
     1. System Hardware Components 
     a. Neuroregulator 
     Different embodiments of the neuroregulator  104 ,  104 ′ are illustrated schematically in  FIGS. 2A and 2B , respectively. The neuroregulator  104 ,  104 ′ is configured to be implanted subcutaneously within the body of a patient. Preferably, the neuroregulator  104 ,  104 ′ is implanted subcutaneously on the thoracic sidewall in the area slightly anterior to the axial line and caudal to the arm pit. In other embodiments, alternative implantation locations may be determined by the implanting surgeon. 
     The neuroregulator  104 ,  104 ′ is generally sized for such implantation in the human body. By way of non-limiting example, an outer diameter D, D′ of the neuroregulator  104 ,  104 ′ is typically less than or equal to about sixty mm and a thickness of the neuroregulator  104 ,  104 ′ is less than or equal to about fifteen mm. In a preferred embodiment, the neuroregulator  104 ,  104 ′ has a maximum outer diameter D, D′ of about fifty-five mm and a maximum thickness of about nine mm. In one embodiment, the neuroregulator  104 ,  104 ′ weighs less than about one hundred twenty grams. 
     Typically, the neuroregulator  104 ,  104 ′ is implanted parallel to the skin surface to maximize RF coupling efficiency with the external charger  101 . In an embodiment, to facilitate optimal information and power transfer between the internal coil  105 ,  105 ′ of the neuroregulator  104 ,  104 ′ and the external coil  102  of the external charger  101 , the patient can ascertain the position of the neuroregulator  104 ,  104 ′ (e.g., through palpation or with the help of a fixed marking on the skin). In an embodiment, the external charger  101  can facilitate coil positioning as discussed herein with reference to  FIGS. 7 and 8 . 
     As shown in  FIGS. 2A and 2B , the neuroregulator  104 ,  104 ′ generally includes a housing  109 ,  109 ′ overmolded with the internal coil  105 ,  105 ′, respectively. The overmold  110 ,  110 ′ of the neuroregulator  104 ,  104 ′ is formed from a bio-compatible material that is transmissive to RF signals (i.e., or other such communication signals). Some such bio-compatible materials are well known in the art. For example, the overmold  110 ,  110 ′ of the neuroregulator  104 ,  104 ′ may be formed from silicone rubber or other suitable materials. The overmold  110 ,  110 ′ also can include suture tabs or holes  119 ,  119 ′ to facilitate placement within the patient&#39;s body. 
     The housing  109 ,  109 ′ of the neuroregulator  104 ,  104 ′ also may contain a circuit module, such as circuit  112  (see  FIGS. 1 ,  3 A, and  3 B), to which the coil  105 ,  105 ′ may be electrically connected along a path  105   a ,  105   a ′. The circuit module within the housing  109  may be electrically connected to the lead assemblies  106 ,  106   a  ( FIG. 1 ) through conductors  114 ,  114   a . In the example shown in  FIG. 2A , the conductors  114 ,  114   a  extend out of the housing  109  through strain reliefs  118 ,  118   a . Such conductors  114 ,  114   a  are well known in the art. 
     The conductors  114 ,  114   a  terminate at connectors  122 ,  122   a , which are configured to receive or otherwise connect the lead assemblies  106 ,  106   a  ( FIG. 1 ) to the conductors  114 ,  114   a . By providing connectors  122 ,  122   a  between the neuroregulator  104  and the lead assemblies  106 ,  106   a , the lead assemblies  106 ,  106   a  may be implanted separately from the neuroregulator  104 . Also, following implantation, the lead assemblies  106 ,  106   a  may be left in place while the originally implanted neuroregulator  104  is replaced by a different neuroregulator. 
     As shown in  FIG. 2A , the neuroregulator connectors  122 ,  122   a  can be configured to receive connectors  126  of the lead assemblies  106 ,  106   a . For example, the connectors  122 ,  122   a  of the neuroregulator  104  may be configured to receive pin connectors (not shown) of the lead assemblies  106 ,  106   a . In another embodiment, the connectors  122 ,  122   a  may be configured to secure to the lead assemblies  106 ,  106   a  using set-screws  123 ,  123   a , respectively, or other such fasteners. In a preferred embodiment, the connectors  122 ,  122   a  are well-known IS-1 connectors. As used herein, the term “IS-1” refers to a connector standard used by the cardiac pacing industry, and is governed by the international standard ISO 5841-3. 
     In the example shown in  FIG. 2B , female connectors  122 ′,  122   a ′ configured to receive the leads  106 ,  106   a  are molded into a portion of the overmold  110 ′ of the neuroregulator  104 ′. The leads connectors  126  are inserted into these molded connectors  122 ′,  122   a ′ and secured via setscrews  123 ′,  123   a ′, seals (e.g., Bal Seals®), and/or another fastener. 
     The circuit module  112  (see  FIGS. 1 ,  3 A, and  3 B) is generally configured to generate therapy signals and to transmit the therapy signals to the lead assemblies  106 ,  106   a . The circuit module  112  also may be configured to receive power and/or data transmissions from the external charger  101  via the internal coil  105 . The internal coil  105  may be configured to send the power received from the external charger to the circuit module  112  for use or to the internal power source (e.g., battery)  151  of the neuroregulator  104  to recharge the power source  151 . 
     Block diagrams of example circuit modules  112 ,  112 ″ are shown in  FIGS. 3A ,  3 B, respectively. Either circuit module  112 ,  112 ″ can be utilized with any neuroregulator, such as neuroregulators  104 ,  104 ′ described above. The circuit modules  112 ,  112 ″ differ in that the circuit module  112  includes an internal power source  151  and a charge control module  153  and the circuit module  112 ″ does not. Accordingly, power for operation of the circuit module  112 ″ is provided entirely by the external charger  101  via the internal coil  105 . Power operation for circuit module  112  may be provided by the external charger  101  or by the internal power source  151 . Either circuit module  112 ,  112 ″ may be used with either neuroregulator  104 ,  104 ′ shown in  FIGS. 2A ,  2 B. For ease in understanding, the following description will focus on the circuit module  112  shown in  FIG. 3A . 
     The circuit module  112  includes an RF input  157  including a rectifier  164 . The rectifier  164  converts the RF power received from the internal coil  105  into DC electric current. For example, the RF input  157  may receive the RF power from the internal coil  105 , rectify the RF power to a DC power, and transmit the DC current to the internal power source  151  for storage. In one embodiment, the RF input  157  and the coil  105  may be tuned such that the natural frequency maximizes the power transferred from the external charger  101 . 
     In an embodiment, the RF input  157  can first transmit the received power to a charge control module  153 . The charge control module  153  receives power from the RF input  157  and delivers the power where needed through a power regulator  156 . For example, the RF input  157  may forward the power to the battery  151  for charging or to circuitry for use in creating therapy signals as will be described below. When no power is received from the coil  105 , the charge control  153  may draw power from the battery  151  and transmit the power through the power regulator  160  for use. For example, a central processing unit (CPU)  154  of the neuroregulator  104  may manage the charge control module  153  to determine whether power obtained from the coil  105  should be used to recharge the power source  151  or whether the power should be used to produce therapy signals. The CPU  154  also may determine when the power stored in the power source  151  should be used to produce therapy signals. 
     The transmission of energy and data via RF/inductive coupling is well known in the art. Further details describing recharging a battery via an RF/inductive coupling and controlling the proportion of energy obtained from the battery with energy obtained via inductive coupling can be found in the following references, all of which are hereby incorporated by reference herein: U.S. Pat. No. 3,727,616, issued Apr. 17, 1973, U.S. Pat. No. 4,612,934, issued Sep. 23, 1986, U.S. Pat. No. 4,793,353, issued Dec. 27, 1988, U.S. Pat. No. 5,279,292, issued Jan. 18, 1994, and U.S. Pat. No. 5,733,313, issued Mar. 31, 1998. 
     In general, the internal coil  105  may be configured to pass data transmissions between the external charger  101  and a telemetry module  155  of the neuroregulator  104 . The telemetry module  155  generally converts the modulated signals received from the external charger  101  into data signals understandable to the CPU  154  of the neuroregulator  104 . For example, the telemetry module  155  may demodulate an amplitude modulated carrier wave to obtain a data signal. In one embodiment, the signals received from the internal coil  105  are programming instructions from a physician (e.g., provided at the time of implant or on subsequent follow-up visits). The telemetry module  155  also may receive signals (e.g., patient data signals) from the CPU  154  and may send the data signals to the internal coil  105  for transmission to the external charger  101 . 
     The CPU  154  may store operating parameters and data signals received at the neuroregulator  104  in an optional memory  152  of the neuroregulator  104 . Typically, the memory  152  includes non-volatile memory. In other embodiments, the memory  152  also can store serial numbers and/or model numbers of the leads  106 ; serial number, model number, and/or firmware revision number of the external charger  101 ; and/or a serial number, model number, and/or firmware revision number of the neuroregulator  104 . 
     The CPU  154  of the neuroregulator  104  also may receive input signals and produce output signals to control a signal generation module  159  of the neuroregulator  104 . Signal generation timing may be communicated to the CPU  154  from the external charger  101  via the coil  105  and the telemetry module  155 . In other embodiments, the signal generation timing may be provided to the CPU  154  from an oscillator module (not shown). The CPU  154  also may receive scheduling signals from a clock, such as 32 KHz real time clock (not shown). 
     The CPU  154  forwards the timing signals to the signal generation module  159  when therapy signals are to be produced. The CPU  154  also may forward information about the configuration of the electrode arrangement  108  to the signal generation module  159 . For example, the CPU  154  can forward information obtained from the external charger  101  via the coil  105  and the telemetry module  155 . 
     The signal generation module  159  provides control signals to an output module  161  to produce therapy signals. In an embodiment, the control signals are based at least in part on the timing signals received from the CPU  154 . The control signals also can be based on the electrode configuration information received from the CPU  154 . 
     The output module  161  produces the therapy signals based on the control signals received from the signal generation module  159 . In an embodiment, the output module  161  produces the therapy signals by amplifying the control signals. The output module  161  then forwards the therapy signals to the lead arrangement  108 . 
     In an embodiment, the signal generation module  159  receives power via a first power regulator  156 . The power regulator  156  regulates the voltage of the power to a predetermined voltage appropriate for driving the signal generation module  159 . For example, the power regulator  156  can regulate the voltage to about 2.5 volts. 
     In an embodiment, the output module  161  receives power via a second power regulator  160 . The second power regulator  160  may regulate the voltage of the power in response to instructions from the CPU  154  to achieve specified constant current levels. The second power regulator  160  also may provide the voltage necessary to deliver constant current to the output module  161 . 
     The output module  161  can measures the voltage of the therapy signals being outputted to the lead arrangement  108  and reports the measured voltage to the CPU  154 . A capacitive divider  162  may be provided to scale the voltage measurement to a level compatible with the CPU  154 . In another embodiment, the output module  161  can measure the impedance of the lead arrangement  108  to determine whether the leads  106 ,  106   a  are in contact with tissue. This impedance measurement also may be reported to the CPU  154 . 
     b. External Charger 
     A block diagram view of an example external charger  101  is shown in  FIG. 4 . The example external charger  101  may cooperate with any of the neuroregulators  104 ,  104 ′ discussed above to provide therapy to a patient. The external charger  101  is configured to transmit to the neuroregulator  104  (e.g., via an RF link) desired therapy parameters and treatment schedules and to receive data (e.g., patient data) from the neuroregulator  104 . The external charger  101  also is configured to transmit energy to the neuroregulator  104  to power the generation of therapy signals and/or to recharge an internal battery  151  of the neuroregulator  104 . The external charger  101  also can communicate with an external computer  107 . 
     In general, the external charger  101  includes power and communications circuitry  170 . The power and communications circuitry  170  is configured to accept input from multiple sources, to process the input at a central processing unit (CPU)  200 , and to output data and/or energy (e.g., via coil  102 , socket  174 , or display  172 ). It will be appreciated that it is well within the skill of one of ordinary skill in the art (having the benefit of the teachings of the present invention) to create such circuit components with such function. 
     For example, the circuit power and communications circuit  170  can be electrically connected to the external coil  102  for inductive electrical coupling to the coil  105  of the neuroregulator  104 . The power and communications circuit  170  also can be coupled to interface components enabling input from the patient or an external computing device (e.g., a personal computer, a laptop, a personal digital assistant, etc.)  107 . For example, the external charger  101  can communicate with the computing device  107  via an electrically isolated Serial port. 
     The external charger  101  also includes a memory or data storage module  181  in which data received from the neuroregulator  104  (e.g., via coil  102  and socket input  176 ), the external computer  107  (e.g., via socket input  174 ), and/or the patient (e.g. via select input  178 ) can be stored. For example, the memory  181  can store one or more predetermined therapy programs and/or therapy schedules provided from the external computer  107 . The memory  181  also can store software to operate the external charger  101  (e.g., to connect to the external computer  107 , to program external operating parameters, to transmit data/energy to the neuroregulator  104 , and/or to upgrades the operations of the CPU  200 ). Alternatively, the external charger  101  can include firmware to provide these functions. The memory  181  also can store diagnostic information, e.g., software and hardware error conditions. 
     An external computer or programmer  107  may connect to the communications circuit  170  through the first input  174 . In an embodiment, the first input  174  is a port or socket into which a cable coupled to the external computer  107  can be plugged. In other embodiments, however, the first input  174  may include any connection mechanism capable of connecting the external computer  107  to the external charger  101 . The external computer  107  provides an interface between the external charger  101  and a physician (e.g., or other medical professional) to enable the physician to program therapies into the external charger  101 , to run diagnostic and system tests, and to retrieve data from the external charger  101 . 
     The second input  176  permits the external charger  101  to couple selectively to one of either an external power source  180  or the external coil  102  (see  FIG. 1 ). For example, the second input  176  can define a socket or port into which the power source  180  or external coil  102  can plug. In other embodiments, however, the second input  176  can be configured to couple to a cable or other coupling device via any desired connection mechanism. In one embodiment, the external charger  101  does not simultaneously connect to both the coil  102  and the external power source  180 . Accordingly, in such an embodiment, the external power source  180  does not connect directly to the implanted neuroregulator  104 . 
     The external power source  180  can provide power to the external charger  101  via the second input  176  when the external charger  101  is not coupled to the coil  102 . In an embodiment, the external power source  180  enables the external charger  101  to process therapy programs and schedules. In another embodiment, the external power source  180  supplies power to enable the external charger  101  to communicate with the external computer  107  (see  FIG. 1 ). 
     The external charger  101  optionally may include a battery, capacitor, or other storage device  182  ( FIG. 4 ) enclosed within the external charger  101  that can supply power to the CPU  200  (e.g., when the external charger  101  is disconnected from the external power source  180 ). The power and communications circuit  170  can include a power regulator  192  configured to receive power from the battery  182 , to regulate the voltage, and to direct the voltage to the CPU  200 . In a preferred embodiment, the power regulator  192  sends a 2.5 volt signal to the CPU  200 . 
     The battery  182  also can supply power to operate the external coil  102  when the coil  102  is coupled to the external charger  101 . The battery  182  also can supply power to enable the external charger  101  to communicate with the external computer  107  when the external power source  180  is disconnected from the external charger  101 . An indicator  190  may provide a visual or auditory indication of the remaining power in the battery  182  to the user. 
     In an embodiment, the battery  182  of the external charger  101  is rechargeable. For example, the external power source  180  may couple to the external charger  101  to supply a voltage to the battery  182 . In such an embodiment, the external charger  101  then can be disconnected from the external power source  180  and connected to the external coil  102  to transmit power and/or data to the neuroregulator  104 . Further details regarding example rechargeable systems include U.S. Pat. No. 6,516,227 to Meadows, issued Feb. 4, 2003; U.S. Pat. No. 6,895,280 to Meadows, issued May 17, 2005; and U.S. patent application Publication No. US 2005/0107841 to Meadows May 19, 2005, the disclosures of which are hereby incorporated herein by reference. 
     In an alternative embodiment, the battery  180  is a replaceable, rechargeable battery, which is recharged external to the external charger  101  in its own recharging stand. In yet another embodiment, the battery  182  in the external charger  101  can be a replaceable, non-rechargeable battery. 
     In use, energy from the external power source  180  flows through the second input  176  to an energy transfer module  199  of the power and communications circuit  170 . The energy transfer module  199  directs the energy either to the CPU  200  to power the internal processing of the external charger  101  or to the battery  182 . In an embodiment, the energy transfer module  199  first directs the energy to a power regulator  194 , which can regulate the voltage of the energy signal before sending the energy to the battery  182 . 
     In some embodiments, the external coil  102  of the external charger  101  can supply energy from the battery  182  to the internal coil  105  of the neuroregulator  104  (e.g., to recharge the internal power source  151  ( FIG. 3 ) of the neuroregulator  104 ). In such embodiments, the energy transfer module  199  receives power from the battery  182  via the power regulator  194 . For example, the power regulator  194  can provide a sufficient voltage to activate the energy transfer module  199 . The energy transfer module  199  also can receive instructions from the CPU  200  regarding when to obtain power from the battery  182  and/or when to forward power to the external coil  102 . The energy transfer module  199  delivers the energy received from the battery  182  to the coil  102  of the external charger  101  in accordance with the instructions provided by the CPU  200 . The energy is sent from the external coil  102  to the internal coil  105  of the neuroregulator  104  via RF signals or any other desired power transfer signal. In an embodiment, therapy delivery at the neuroregulator  104  is suspended and power is delivered from the external charger  101  during recharging of the internal power source  151 . 
     In some embodiments, the external charger  101  controls when the internal battery  151  of the implanted neuroregulator  104  is recharged. For example, the external charger  101  can determine when to recharge the battery  151  using the processes described in U.S. Pat. No. 6,895,280 to Meadows issued May 17, the disclosure of which is hereby incorporated herein by reference. In other embodiments, however, the implanted neuroregulator  104  controls when the battery  151  is recharged. Details pertaining to controlling the battery recharging process can be found in U.S. Pat. No. 3,942,535 to Schulman, issued Mar. 9, 1976; U.S. Pat. No. 4,082,097 to Mann, issued Apr. 4, 1978; U.S. Pat. No. 5,279,292 to Baumann, issued Apr. 4, 1978; and U.S. Pat. No. 6,516,227 to Meadows, issued Feb. 4, 2003, the disclosures of which are hereby incorporated herein by reference. These details typically parallel the battery manufacturer&#39;s recommendations regarding how to charge the battery. 
     As noted above, in addition to power transmissions, the external coil  102  also can be configured to receive data from and to transmit programming instructions to the neuroregulator  104  (e.g., via an RF link). A data transfer module  196  may receive and transmit data and instructions between the CPU  200  and the internal coil  105 . In an embodiment, the programming instructions include therapy schedules and parameter settings. Further examples of instructions and data transmitted between the external coil  102  and the implanted coil  105  are discussed in greater detail herein. 
       FIG. 5  shows a front view of an example external charger  101 . The external charger  101  includes a housing  171  defining a first input (e.g., socket input)  174 , a second input (e.g., socket input)  176 , and a third input (e.g., select input)  178  coupled to the communications circuit  170 . In an embodiment, the housing  171  also may enclose a battery  182  configured to supply power to the external charger  101  via the power and communications circuit  170 . Alternatively, the external charger  101  can receive power from an external source  180  ( FIG. 1 ). 
     As shown in  FIG. 5 , visual display  172  also is provided on the housing  171  for presenting human readable information processed by the communications circuit  170 . In an embodiment, the visual display  172  is a liquid crystal display (LCD) screen. In other embodiments, however, the visual display  172  can include any display mechanism (e.g., a light-emitting diode (LED) screen, vacuum fluorescent display (VFD) screen, etc.). Non-limiting examples of information that can be shown on the visual display  172  include the status of the battery  182  of the external charger  101 , the status of the battery  151  in the implanted neuroregulator  104 , coil position (as will be described), impedances between the electrodes  212 ,  212   a  and attached tissue, and error conditions. 
     As shown in  FIG. 5 , the third input  178  of the external charger  101  includes a selection input  178  with which the user can interact with the external charger  101 . In an embodiment, the selection input  178  can include a button, which sequentially selects menu options for various operations performed by the external charger  101  when pressed successively. In other embodiments, however, the third input  178  includes another type of selection input (e.g., a touch screen, a toggle-switch, a microphone for accepting voice-activated commands, etc.). 
     Example functions capable of selection by the user include device reset, interrogation of battery status, interrogation of coil position, and/or interrogation of lead/tissue impedance. In other embodiments, a user also can select measurement of tissue/lead impedance and/or initiation of a stomach contraction test. Typically, the measurement and testing operations are performed when the patient is located in an operating room, doctor&#39;s office, or is otherwise surrounded by medical personnel. 
     In another embodiment, the user can select one or more programs and/or therapy schedules to submit to the memory  152  of the neuroregulator  104 . For example, the user can cycle through available programs by repeatedly pressing the selection button  178  on the external charger  101 . The user can indicate the user&#39;s choice by, e.g., depressing the selector button  178  for a predetermined period of time or pressing the selector button  178  in quick succession within a predetermined period of time. 
     In use, in some embodiments, the external charger  101  may be configured into one of multiple modes of operation. Each mode of operation can enable the external charger  101  to perform different functions with different limitations. In an embodiment, the external charger  101  can be configured into five modes of operation: an Operating Room mode; a Programming mode; a Therapy Delivery mode; a Charging mode; and a Diagnostic mode. 
     When configured in the Operating Room mode, the external charger  101  can be used to determine whether the implanted neuroregulator  104  and/or the implanted lead arrangement  108  are functioning appropriately. If any component of the therapy system  100  is not functioning as desired, then the medical personnel can trouble-shoot the problem while still in the operation room or can abandon the procedure, if necessary. 
     For example, the external charger  101  can be used to determine whether the impedance at the electrodes  212 ,  212   a  of the lead arrangement  108  ( FIG. 1 ) is within a prescribed range. When the impedance is within the prescribed range, a gastric contraction test can be initiated to demonstrate that the electrodes  212 ,  212   a  are appropriately positioned and can become active. If the impedance is outside an acceptable range, the system integrity can be checked (e.g. connections to the leads can be verified). Additionally, the therapy electrodes  212 ,  212   a  may be repositioned to provide better electrode-tissue contact. 
     In another embodiment, the external charger  101  can be used to initiate a stomach contraction test in the operating room. The stomach contraction test enables medical personnel to confirm the electrodes  212 ,  212   a  of the lead arrangement  108  ( FIG. 1 ) are in contact with the appropriate nerves and not with some other tissue. For example, the external charger  101  can instruct the neuroregulator  104  to generate a signal tailored to cause the stomach to contract if the signal reaches the appropriate nerves. 
     Typically, the external charger  101  is not connected to an external computer  107  when configured in the Operating Room mode. In a preferred embodiment, the external charger is connected (e.g., via socket input  176 ) to a physician coil  102 ′ (shown schematically in  FIG. 6 ) instead of a patient coil  102  (described above). The physician coil  102 ′ can differ from the patient coil  102  in one or more respects. 
     For example, as shown in  FIG. 6 , a length L′ of the connection cable  102   a ′ on the physician coil  102 ′ can be longer than a length L of the cable  102   a  of the patient coil  102 . In one example embodiment, the length L′ of the connection cable  102   a ′ of the physician coil  102 ′ can be about 300 cm and the length L of the connection cable  102   a  of the patient coil  102  can be about 60 cm. The longer length L′ allows the external charger  101  to be located outside the sterile field in the operating room when the physician coil  102 ′ is connected. 
     In another embodiment, the physician coil  102 ′ can include an indicator circuit to identify the coil  102 ′ as a physician coil to the external charger  101 . For example, the physician coil  102 ′ can contain a small resistor  102   b ′, which can be recognized by the external charger  101  when the physician coil  102 ′ is plugged into the socket  176 . When the external charger  101  detects the presence of the indicator circuit, the external charger  101  automatically configures itself into an Operating Room mode. This mode allows the physician to conduct various system and patient response tests, such as those described above, without the need for connection to a clinician computer  107 . 
     When configured in the Programming mode, the external charger  101  is connected with the external computer  107  ( FIG. 1 ) via which the physician manages the components of the therapy system  100 . In general, the physician may select a therapy program and a therapy schedule stored on the external computer  107  to transfer to the external charger  101 . In certain embodiments, the external charger  101  forwards the programs and schedule to the neuroregulator  104 . In an embodiment, the external charger  101  can be coupled to the physician coil  102 ′ during programming. In another embodiment, the external charger  101  can be coupled to the patient coil  102 . In addition, in different embodiments, the external computer  107  also can assess the impedance of the electrodes  212 ,  212   a , initiate system and/or diagnostic tests, and take corrective action when the external charger  101  is configured into the Programming mode. 
     After the neuroregulator  104  has been implanted and the external charger  101  and/or neuroregulator  104  have been programmed, the external charger  101  can be configured into the Therapy Delivery mode. When configured in the Therapy Delivery mode, the external charger  101  communicates with and/or powers the neuroregulator  104  as described above. Typically, the external charger  101  is coupled to the patient coil  102  and not to the external computer  107  when configured in the Therapy Delivery mode. 
     The external charger  101  also can interact with the user via the third input (e.g., the selector button)  178  and the display  172  to select the therapy to be provided. In an embodiment, the external charger  101  can send instructions indicating which program the neuroregulator  104  should follow while administering therapy. In another embodiment, the external charger  101  sends instructions in accordance with a selected program stored on the external charger  101 . 
     If the neuroregulator  104  includes an internal power source  151 , then the external charger  101  can enter a Charging mode in which the external charger  101  recharges the internal power source  151  of the neuroregulator  104  when the neuroregulator  104  is not delivering therapy. Typically, the external charger  101  enters the Charging mode at the request of the neuroregulator  104 . In a preferred embodiment, the neuroregulator  104  controls how much power is sent by the external charger  101 . 
     During follow-up visits between the patient and the physician, the external charger  101  may be configured into a Diagnostic mode. In this mode, the external charger  101  is coupled to the external computer  107  to provide an interface for the physician to obtain data stored on the external charger  101  and to download therapy and/or software updates. In an embodiment, the display  172  on the external charger  101  is disabled and all information is conveyed to the physician via the external computer  107  only. The external charger  101  may be coupled to either coil  102 ,  102 ′ when configured in the Diagnostic mode. 
     In an embodiment, the external charger  101  also can be configured into a Shipping mode, in which the battery  182  is disconnected from the rest of the circuitry. The Shipping mode avoids draining the battery  182  and enhances safety. In one such embodiment, pressing the selector button  172  causes the external charger  101  to change from this Shipping mode into another mode, such as the Therapy Delivery mode. 
     c. Alignment of External and Implanted Coils 
     The external charger  101  enables alignment of the relative positions of the external and implanted coils  102 ,  105  and optimization of the signal strength. Optimizing the alignment of the coils  102 ,  105  and the power of the transmission signal facilitates continuous, transcutaneous transmission of power and/or information. 
     i. Positioning of External Coil 
     In general, the external coil  102  is adapted to be placed on the patient&#39;s skin (e.g., by adhesives) overlying the implanted internal coil  105 . The position and orientation of the coils  102 ,  105  can affect signal reliability. In addition, the strength of the transmission signals between the external coil  102  and the implanted coil  105  also is affected by the distance between the coils  102 ,  105 . Implanting the neuroregulator  104  very close to the surface of the skin  103  typically results in a large and expanded range of signal strengths. Conversely, implanting the neuroregulator  104  at a large distance beneath the skin  103  yields a generally weak transmission link and a compressed range of signal strengths. 
       FIG. 7  illustrates an external coil  102  appropriately aligned with an implanted coil  105 . The coil  105  is implanted beneath the skin  103  at a preferred depth D 1  (e.g., about two centimeters to about three centimeters beneath the skin  103 ). Preferably, a plane of the coil  105  extends parallel to the surface of the skin  103 . In an embodiment, each coil  102 ,  105  is a circular coil surrounding a central axis X-X, Y-Y, respectively. As shown in  FIG. 7 , in a preferred alignment configuration, the axes X-X, Y-Y are collinear so that there is no lateral offset of the axes X-X, Y-Y and the planes of the coils  102 ,  105  are parallel to one another. Such an alignment configuration may be attained, e.g., when the external coil  102  is applied to a patient&#39;s skin  103  when the patient is lying flat (e.g., on the patient&#39;s back). 
       FIG. 8  illustrates misalignment between the coils  102 ,  105  resulting from movement of the patient (e.g., a change in posture). For example, when the patient sits, excess fat may cause the skin  103  to roll. This rolling may cause the spacing between the coils  102 ,  105  to increase to a distance D 2 . Also, the orientation of the external coil  102  may change so that the axes X-X and Y-Y of the coils  102 ,  105 , respectively, have a lateral offset T and an angular offset A. Such changes in spacing and orientation may be occurring constantly throughout the day. 
     The relative position of the coils  102 ,  105  may be optimized (e.g., for each use) when the external charger  101  senses the transmission link is weakened (e.g., on initial power up or when the energy transfer to the implantable neuroregulator  104  has degraded). For example, the external charger  101  can sound an alarm and invite the user to configure the external charger  101  into a Locate mode. Alternatively, the user can decide independently to enter the Locate mode (e.g., through a menu selection). 
     When configured in the Locate mode, the external charger  101  prompts the user to adjust the orientation of the external coil  102  to achieve an alignment (e.g., coaxial alignment) facilitating better coil interaction. The external charger  101  also provides feedback to the user indicating the current degree of alignment of the coils  102 ,  105 . Examples of such feedback include audio signals, lit LED&#39;s, bar graphs or other textual, graphical, and/or auditory signals provided to the user. 
     In general, when the external charger  101  is configured in the Locate mode, the user sweeps the external coil  102  back and forth across the general location of the implanted neuroregulator  104 . During the sweep, the external charger  101  sends a locator signal S 1  to the implanted coil  105  (see  FIG. 7 ). The implanted coil  105  responds with a feedback signal S 2  ( FIG. 7 ). The external charger  101  analyzes the feedback signal S 2  to determine the strength of the transmission link between the coils  102 ,  105 . 
     In an embodiment, the external charger  101  keeps track of the strongest and weakest signals found during the sweep. The maximum signal strength and the minimum signal strength can be indicated to the user, e.g., via the visual display  172 . These maximum and minimum values provide the user with context for judging the relative strength of a given signal at each location during the sweep. In an embodiment, the relative strength of the signal at a given position also can be displayed to the user as the user passes the external coil  102  over the position. 
     For example, in one embodiment, the first signal may be indicated initially as the maximum and minimum signal strength on the visual display  172 . As the external coil  102  is moved about, any subsequent signals having greater signal strength replace the maximum signal shown. The strength of any subsequent, weaker signal also can be tracked by the external charger  101 . The strength of the weakest signal can be indicated to the user as the minimum signal strength found. In one embodiment, if the strength of a subsequent signal falls between the currently established values for minimum and maximum, then an interpolated value representing the relative strength of the signal at the respective coil position can be displayed. 
     Thus the external charger  101  learns the maximum and minimum values for signal strength pertaining to external coil positions relative to the location of the implanted coil  105 . By identifying the context of the signal strength measurements (i.e., the maximum and minimum signal strength found during a sweep), the external charger  101  can provide consistent and context-sensitive measurements of signal strength to the user regardless of the distance of the coil  102  from the implanted coil  105 . Such measurements facilitate identification of an optimum coil position. 
     After the initial placement, the external coil  102  may need to be repositioned with respect to the implanted coil  105  to maintain the signal integrity. The external charger  101  can monitor whether the neuroregulator  104  is receiving signals having sufficient signal strength. If the external charger  101  determines the neuroregulator  104  is not receiving a sufficient signal, then the external charger  101  may sound an alarm (e.g., auditory and/or visual) to alert the user that coil transmission effectiveness has been lost. 
     In an embodiment, after indicating the loss of transmission effectiveness, the external charger  101  may invite the user to configure the external charger  101  into the Locate mode to reposition the external coil  102 . Alternatively, the external charger  101  may invite the user to modify the position of the external coil  102  without entering the Locate mode. In an embodiment, when the coil transmission effectiveness is re-established, the system automatically self-corrects and resumes therapy delivery. 
     ii. Dynamic Signal Power Adjustment 
     The amount of power received at the neuroregulator  104  can vary due to relative movement of the coils  102 ,  105  after the initial placement of the external coil  102 . For example, the signal strength may vary based on the distance between coils  102 ,  105 , the lateral alignment of the coils  102 ,  105 , and/or the parallel alignment of the coils  102 ,  105 . In general, the greater the distance between the coils  102 ,  105 , the weaker the transmission signal will be. In extreme cases, the strength of the transmission signal may decrease sufficiently to inhibit the ability of the neuroregulator  104  to provide therapy. 
     The coils  102 ,  105  may move relative to one another when the patient moves (e.g., walks, stretches, etc.) to perform everyday activities. Furthermore, even when the patient is inactive, the external coil  102  may be placed on tissue with substantial underlying fat layers. The surface contour of such tissue can vary in response to changes in patient posture (e.g., sitting, standing, or lying down). In the treatment of obesity, the distance from the top layer of skin  103  to the implanted coil  105  can vary from patient to patient. Moreover, the distance can be expected to vary with time as the patient progresses with anti-obesity therapy. 
     In addition, the power consumption needs of the neuroregulator  104  can change over time due to differences in activity. For example, the neuroregulator  104  will require less power to transmit data to the external charger  101  or to generate therapy signals than it will need to recharge the internal battery  151 . 
     To overcome these and other difficulties, an embodiment of the external charger  101  can change the amplification level of the transmission signal (e.g., of power and/or data) to facilitate effective transmission at different distances between, and for different relative orientations of, the coils  102 ,  105 . If the level of power received from the external charger  101  varies, or if the power needs of the neuroregulator  104  change, then the external charger  101  can adjust the power level of the transmitted signal dynamically to meet the desired target level for the implanted neuroregulator  104 . 
     Adjustments to the power amplification level can be made either manually or automatically. In an embodiment, the external charger  101  may determine a target strength of the transmission signal (e.g., a predetermined strength selected to provide sufficient power to the neuroregulator  104 ), assess the effectiveness of the transmission signals currently being sent to the implanted coil  105 , and automatically adjust the amplification levels of the transmitted signals to enhance the effectiveness of the transmissions between the external coil  102  and the implanted coil  105 . 
     For example, if the neuroregulator  104  indicates it is recharging its battery  151 , then the external charger  101  may establish a transmission link having a first power level appropriate for the task. At the conclusion of recharging, and when the neuroregulator  104  subsequently indicates it will begin therapy delivery, then the external charger  101  may change the power of the transmission link to a second power level sufficient to initiate therapy generation and delivery. 
     The external charger  101  also may increase the power level of the signal if the signal is lost due to separation and/or misalignment of the coils. If the external charger  101  is unable to sufficiently increase the power level of the transmitted signal, however, then the external charger  101  may issue an alarm and/or an invitation to the user to reposition the external coil  102  as described above. 
     The external charger  101  also may decrease the strength of the signal (i.e., the amount of power) being sent to the neuroregulator  104 . For example, due to safety concerns, the amount of power that can be transmitted across skin via RF signals is limited. Receiving excessive amounts of power could cause the neuroregulator  104  to heat up and potentially burn the patient. 
     In an embodiment, the neuroregulator  104  includes a temperature sensor (not shown) configured to monitor the temperature of the neuroregulator  104 . The neuroregulator  104  can communicate the temperature to the external charger  101 . Alternatively, the neuroregulator  104  can issue a warning to the external charger  101  if the neuroregulator  104  becomes too warm. When the temperature of the neuroregulator  104  is too high, the external charger  101  may lower the power transmitted to the implanted coil  105  of the neuroregulator  104  to bring the temperature down to an acceptable level. Alternatively, the neuroregulator  104  may detune its receiving RF input circuit  157  to reduce power and temperature. 
     In a preferred embodiment, the temperature of the neuroregulator  104  should not exceed the surface temperature of the surrounding skin by greater than about 2° C. (assuming a normal body temperature of 37° C.). Operational parameters, such as current, frequency, surface area, and duty cycle, also can be limited to ensure safe operation within the temperature limit. Further details regarding safety concerns pertaining to transdermal power transmission can be found, e.g., in  The Cenelec European Standard , EN 45502-1 (August 1997), page 18, paragraph 17.1, the disclosure of which is hereby incorporated by reference herein. 
     In an embodiment, the external charger  101  also can decrease the target power level based on a “split threshold” power delivery concept. In such an embodiment, the external charger  101  initially provides a stronger signal than necessary to the neuroregulator  104  to ensure sufficient power is available. The external charger  101  then reduces the strength of the transmissions to a level just above the necessary signal strength when the actual requirements have been established. This subsequent reduction in power saves drain on the external battery  182  or power source  180 . 
     For example, the external charger  101  can provide a low level of power capable of sustaining basic operation of the neuroregulator  104  when the neuroregulator  104  indicates it is not actively providing therapy or recharging its battery  151 . When the neuroregulator  104  indicates it is about to initiate therapy, however, the external charger  101  can increase the power level of the transmission signal to a first threshold level, which is comfortably in excess of the power required to provide basic operation of the neuroregulator  104  as well as provide therapy. When the actual power requirements for therapy delivery become apparent, the external charger  101  may decreases the power level of the signal to a second threshold level, which is closer to the minimum power level required to provide basic functionality and maintain therapy delivery. 
     To perform this dynamic adjustment of signal strength, the external charger  101  analyzes a feedback signal (e.g., signal S 2  of  FIG. 7 ) received from the implanted neuroregulator  104  indicating the amount of power required by the neuroregulator  104 . The signal S 2  also may provide information to the external charger  101  indicating the power level of the signal S 1  being received by the implanted coil  105  of the neuroregulator  104 . Such signal analysis would be within the skill of one of ordinary skill in the art (having the benefit of the teachings of the present invention). 
     In an embodiment, the external charger  101  sets the signal power level based on a predetermined target power level for the transmission signal S 1 . In response to the feedback signal S 2 , the external charger  101  modifies the power level of the transmission signal S 1  to be within a tolerance range of the target power level. In an embodiment, the external charger  101  iteratively modifies the power level of the transmission signal S 1  until the feedback signal S 2  indicates the power level is within the tolerance range. 
     In addition to the dynamic adjustment of transmitted signal power described above, the neuroregulator  104  can be configured to optimize the power received from the external charger  101  when the neuroregulator  104  is recharging its battery  151 . For example, the neuroregulator  104  may tune (e.g., using a combination of hardware and software) the natural resonant frequency of a recharging circuit (not shown) to maximize the power delivered to a load resistance for a given set of input parameters such as voltage, current and impedance at the implanted coil  105 . 
     Transmission of power and/or information between the external charger  101  and the implanted neuroregulator  104  is typically performed using a carrier frequency of 6.78 MHz. Emission requirements of industrial, scientific and medical equipment are governed by Federal Communications Commission requirements described in FCC Title 47, Parts 15 and 18, and in EN 55011. The FCC requirements in the vicinity of this frequency are more restrictive than those of EN 55011. 
     A preferred method for managing the temperature and carrier frequency of the neuroregulator  104  during the recharging process includes passing a high power unmodulated transmission between the external charger  101  and the implantable neuroregulator  104  for a finite time (e.g., from about half of a minute to about five minutes), during which time no informational communication takes place between the external charger  101  and the implantable neuroregulator  104  (i.e., no information is passed between the charger  101  and the neuroregulator  104 ). At the conclusion of this finite time period, the unmodulated transmission ceases. 
     An informational, modulated communicational transmission then is passed at low power (e.g., within the requirements of FCC Title 47 Part 15) during which the temperature of the implantable neuroregulator  104  is communicated periodically to the external charger  101 . If the temperature rises within certain restrictions (e.g., within the restrictions of  The Cenelec European Standard, EN  45502-1 (August 1997), page 18, paragraph 17.1), then the communications transmission may be terminated, and the whole cycle may be repeated beginning with the initiation of the high power, unmodulated, recharging transmission. 
     In an additional preferred embodiment, when the informational, modulated communicational transmission is performed, the requisite signal power is reduced by using only externally transmitted power for the telemetered communications, and by simultaneously using internal battery power to operate the rest of the implanted circuitry  112  ( FIGS. 3A and 3B ), such as a microcontroller and/or peripherals. In such embodiments, the transmitted power may be less than if implant components (microcontroller and/or peripherals) also were receiving power from the RF transmission. Accordingly, the transmitted power may be limited to the power required for communications at short distances of six centimeters or less. Advantageously, such a power reduction reduces the total power required to below FCC Part 15 limits for telemetry communications. 
     During the phase in which the battery  151  of the implantable neuromodulator  104  is being recharged by a high powered, unmodulated transmission (e.g., under the requirements of FCC Title 47 Part 18), the temperature of the implanted neuroregulator  104  may be monitored and, if necessary, steps taken to inhibit the temperature from exceeding certain requirements (e.g., the requirements of  The Cenelec European Standard , EN 45502-1 (August 1997), page 18, paragraph 17.1). For example, the temperature may be reduced by terminating the high powered, unmodulated transmission. In an alternative embodiment, the power level of the high powered, unmodulated transmission may be reduced in later cycles to limit the increase in temperature. In another embodiment, a control loop is established between the temperature rise and the power level of the unmodulated transmission to ensure the increase in temperature always remains within the identified requirements. 
     d. Implanted Leads 
       FIG. 9  shows an example distal end of a bipolar lead, such as lead  106  (see  FIG. 1 ). The lead  106  includes a lead body  210  curved to receive a nerve (e.g., a vagus nerve). The lead body  210  contains an exposed tip electrode  212  configured to contact with the nerve received within the lead body  210 . The tip electrode  212  is capable of delivering an electrical charge to nerves having a diameter ranging from about one millimeter to about four millimeters. 
     The lead body  210  also can have a suture tab  214  to attach the lead body  210  to the patient&#39;s anatomy to stabilize the position of the lead body  210 . A first end of a flexible lead extension  216 , which encloses a conductor from the electrode  212 , couples with the lead body  210 . A second, opposite end of the lead extension  216  terminates at a pin connector (not shown) for attachment to a connector (e.g., an IS-1 connector)  122  (shown in  FIG. 1 ). 
     The lead  106  shown in  FIG. 9  also includes a ring electrode  218  surrounding the lead extension  216  at a position spaced from the tip electrode  212 . In an embodiment, the surface area of each electrode  212 ,  218  is greater than or equal to about thirteen square millimeters. A suture tab  220  may be provided for placement of the ring electrode  218  on the patient&#39;s anatomy in general proximity to the placement of the tip electrode  212  on the nerve. 
     In an alternative embodiment, a monopolar lead (not shown) may be implanted instead of the bipolar lead  106 . Typically, the monopolar lead is the same as the bipolar lead  106 , except the monopolar lead lacks a ring electrode  218 . Such a monopolar lead is described in commonly assigned and co-pending U.S. patent application Ser. No. 11/205,962, to Foster et al, filed Aug. 17, 2005, the disclosure of which is hereby incorporated by reference. 
     Further details pertaining to example electrode placement and application of treatment can be found, e.g., in U.S. Pat. No. 4,979,511 to Terry, Jr., issued Dec. 25, 1990; U.S. Pat. No. 5,215,089 to Baker, Jr., issued Jun. 1, 1993; U.S. Pat. No. 5,251,634 to Weinberg, issued Oct. 12, 1993; U.S. Pat. No. 5,531,778 to Maschino et al., issued Jul. 2, 1996; and U.S. Pat. No. 6,600,956 to Maschino et al., issued Jul. 29, 2003, the disclosures of which are hereby incorporated by reference herein. 
     2. Placement of Electrodes and Electrode Configuration Options 
       FIG. 10  shows a posterior vagus nerve PVN and an anterior vagus nerve AVN extending along a length of a patient&#39;s esophagus E. The posterior nerve PVN and the anterior AVN are generally on diametrically opposite sides of the esophagus E just below the patient&#39;s diaphragm (not shown). A first tip electrode  212  of a lead arrangement  108  ( FIG. 1 ) is placed on the anterior vagus nerve AVN. A second electrode  212   a  of the lead arrangement  108  is placed on the posterior vagus nerve PVN. The electrodes  212 ,  212   a  are connected by leads  106 ,  106   a  to a neuroregulator  104  ( FIG. 1 ). 
     At the time of placement of the leads  106 ,  106   a , it may be advantageous for the tip electrodes  212 ,  212   a  to be individually energized with a stimulation signal selected to impart a neural impulse to cause a detectable physiological response (e.g., the generation of antropyloric waves). The absence of a physiological response may indicate the absence of an overlying relation of the tested electrode  212 ,  212   a  to a vagus nerve PVN, AVN. Conversely, the presence of a physiological response may indicate an overlying relation (e.g., correct placement) of the tested electrode  212 ,  212   a  to a vagus nerve. After determining the leads  106 ,  106   a  create a physiologic response, the electrodes  212 ,  212   a  can be attached to the nerves PVN, AVN. 
     A preferred embodiment of the leads  106 ,  106   a  for treating obesity is shown in  FIG. 10 . The lead arrangement  108  includes bipolar leads  106 ,  106   a . The bipolar leads  106 ,  106   a  each include one tip (i.e., or cathode) electrode  212 ,  212   a  that can be placed directly on the nerve PVN, AVN and one ring (i.e., or anode) electrode  218 ,  218   a  that is not placed on the nerve PVN, AVN, but rather may be attached to another structure (e.g., the stomach). In other embodiments, however, the lead arrangement  108  may include monopolar leads (i.e., each lead  106 ,  106   a  having only a tip electrode  212 ,  212   a ). 
     Electrical connection between the neuroregulator  104  and the therapy leads  106 ,  106   a  is made through bipolar IS-1 compatible lead adapters  122 ,  122   a  attached to the neuroregulator  104 . If the bipolar lead design is used, two bipolar electrode pairs—one for the anterior vagus and one for the posterior vagus—are provided. One bipolar lead feeds a bipolar electrode pair. If the monopolar lead design is used, only the conductor connected to the distal tip electrode of each bipolar IS-1 connector is used. 
     The therapies as previously described could be employed by using blocking electrodes or stimulation electrodes or both in order to down-regulate and/or up-regulate the vagus nerve. A blocking signal down-regulates a level of vagal activity and simulates, at least partially, a reversible vagotomy. 
     Referring to  FIGS. 11-18 , the pacing signals to the electrodes  212 ,  212   a  can be selected to create different types of signals and signal paths (referred to herein as “configurations”).  FIGS. 11-18  illustrate four different electrode configurations. 
     a. Blocking Electrode Configuration (1) 
     A first blocking electrode configuration is shown in  FIG. 11 . This configuration creates a current path (see arrow  1  in  FIG. 11 ) with current flowing between the anterior and posterior nerves AVN, PVN. The tip electrodes  212 ,  212   a , which are located directly on the anterior and posterior vagal nerves AVN, PVN, respectively, are electrically active. The anodic ring electrodes  218 ,  218   a  are not energized. 
     A continuous waveform (e.g., the square waveform W 10  shown in  FIG. 12 ) propagates along the current path (see arrow  1 ) extending across the esophagus E. Such an electrode configuration is generally monopolar (i.e., only one location on each nerve PVN, AVN is subject to the treatment) and could be accomplished with monopolar leads (i.e., leads without ring electrodes  218 ,  218   a ). 
     b. Blocking Electrode Configuration (2) 
       FIG. 13  illustrates a second blocking electrode configuration in which each of the tip electrodes  212 ,  212   a  is associated with an anode electrode  218 ,  218   a , respectively. Therapy signals are applied only to the anterior vagus nerve AVN between the distal electrode  212  and the anode electrode  218 . Advantageously, current (see arrow  2  in  FIG. 13 ) does not flow through the esophagus E, thereby decreasing the likelihood of the patient sensing the treatment (e.g., feeling discomfort or pain). 
     In general, the anode electrodes  218 ,  218   a  can be positioned on any anatomical structure. In a preferred embodiment, the anode electrodes  218 ,  218   a  are placed on structures in generally close proximity (e.g., within about five centimeters) of the tip electrodes  212 ,  212   a . For example, the anode electrodes  218 ,  218   a  can be placed on the same vagal nerve PVN, AVN as the anode electrode&#39;s associated electrode  212 ,  212   a.    
     In other embodiments, however, the anode electrodes  218 ,  218   a  can be placed on the stomach, the esophagus, or other anatomical structure in the general vicinity of the electrodes  212 ,  212   a . In an embodiment, the anode electrodes  218 ,  218   a  can be placed on the stomach to permit monitoring of stomach contractions (e.g., by strain receptors associated with the anode electrodes  218 ,  218   a ). The arrangement of  FIG. 13  results in a pacing waveform W 11  ( FIG. 14 ). 
     c. Blocking Electrode Configuration (3) 
       FIG. 15  illustrates the same electrode configuration shown in  FIG. 13 , except the signals are applied only to the posterior vagus nerve PVN between the tip electrode  212   a  and the anode electrode  218   a . The corresponding current path is shown by arrow  3  in  FIG. 15 . In an embodiment, the example signal waveform W 12  (see  FIG. 16 ) propagating across the current path is the same as the waveform W 11  in  FIG. 14 . In other embodiments, however, any desired waveform can be utilized. 
     d. Blocking Electrode Configuration (4) 
     The electrode configuration of  FIG. 17  is generally the same as the electrode configurations of  FIGS. 11 ,  13  and  15 . In  FIG. 17 , however, an electrically active anode (e.g., ring electrode  218 ,  218   a ) and cathode (e.g., tip electrode  212 ,  212   a ) are associated with each nerve PVN, AVN to provide a dual channel system. Such an electrode arrangement routes current flow through both nerves PVN, AVN as indicated by arrows  4 . 
     In an embodiment, a first electrode (e.g., the tip electrode  212 ,  212   a ) is placed directly on each of the nerve trunks and a second electrode (e.g., ring electrode  218 ,  218   a ) is located in proximity to the first electrode. Two waveforms (e.g., an anterior nerve waveform W 12A  and a posterior nerve waveform W 12P  shown in  FIG. 18 ) are generated. In the example shown, the pulses of one of the waveforms occur during no-pulse periods of the other waveform. In such a configuration, a complete charging and rebalancing cycle can occur on one channel before the second channel is charged and rebalanced. Accordingly, only one channel is electrically paced at a time. Typically, the electrodes on the nerve are energized cathodically first. 
     3. Post-Operative Testing of Electrodes 
     After completing implantation, assembly, and positioning of the neuroregulator  104  and the electrode arrangement  108 , a physician can determine the lead integrity by measuring the lead impedance and assessing whether the lead impedance is within an acceptable range. If the lead impedance is within range, the physician can connect an external computer  107  (e.g., a clinician computer) to the external charger  101  (see  FIG. 1 ). 
     The clinician computer  107  can transmit treatment therapy settings and treatment data to the neuroregulator  104  via the external charger  101 . The clinician computer  107  also can retrieve data from the external charger  101  or neuroregulator  104 . For example, in one embodiment, the clinician computer  107  detects serial numbers of the external charger  101  and neuroregulator  104  automatically. After adjustment of blocking parameters and retrieval of data, the clinician computer  107  may be disconnected from the external charger  101 . 
     After the patient has adequately recovered from the surgery (e.g., approximately fourteen days after the implantation surgery), the physician may program initial treatment parameters into the external charger  101 . For example, the physician can couple the clinician computer  107  to the external charger  101  and follow menu commands on the computer  107  to upload select therapy programs to the external charger  101 . In certain embodiments, the uploaded programs can then be transferred to the implanted neuroregulator  104 . 
     Additionally, the physician can use the clinician computer  107  to select treatment start times for the patient. In an embodiment, treatment start times are selected based on the individual patient&#39;s anticipated waking and initial meal times. The start times can be set differently for each day of the week. Further details regarding scheduling treatment will be discussed herein with respect to  FIG. 19 . 
     4. System Software 
     The external charger  101  and the neuroregulator  104  contain software to permit use of the therapy system  100  in a variety of treatment schedules, operational modes, system monitoring and interfaces as will be described herein. 
     a. Treatment Schedule 
     To initiate the treatment regimen, the clinician downloads a treatment specification and a therapy schedule from an external computer  107  to the external charger  101 . In general, the treatment specification indicates configuration values for the neuroregulator  104 . For example, in the case of vagal nerve treatment for obesity, the treatment specification may define the amplitude, frequency, and pulse width for the electrical signals emitted by the implanted neuroregulator  104 . In another embodiment, “ramp up” time (i.e., the time period during which the electrical signals builds up to a target amplitude) and “ramp down” time (i.e., the time period during which the signals decrease from the target amplitude to about zero) can be specified. 
     In general, the therapy schedule indicates an episode start time and an episode duration for at least one day of the week. An episode refers to the administration of therapy over a discrete period of time. Preferably, the clinician programs an episode start time and duration for each day of the week. In an embodiment, multiple episodes can be scheduled within a single day. Therapy also can be withheld for one or more days at the determination of the clinician. 
     During a therapy episode, the neuroregulator  104  completes one or more treatment cycles in which the neuroregulator  104  sequences between an “on” state and an “off” state. For the purposes of this disclosure, a treatment cycle includes a time period during which the neuroregulator  104  continuously emits treatment (i.e., the “on” state) and a time period during which the neuroregulator  104  does not emit treatment (i.e., the “off” state). Typically, each therapy episode includes multiple treatment cycles. The clinician can program the duration of each treatment cycle (e.g., via the clinician computer  107 ). 
     When configured in the “on” state, the neuroregulator  104  continuously applies treatment (e.g., emits an electrical signal). The neuroregulator  104  is cycled to an “off” state, in which no signal is emitted by the neuroregulator  104 , at intermittent periods to mitigate the chances of triggering a compensatory mechanism by the body. For example, if a continuous signal is applied to a patient&#39;s nerve for a sufficient duration, the patient&#39;s digestive system eventually can learn to operate autonomously. 
     An example daily treatment schedule  1900  is schematically shown in  FIG. 19 . The daily schedule  1900  includes a timeline indicating the times during the day when the treatment is scheduled to be applied to a patient. Duty cycle lines (dashed lines) extend along the time periods during which treatment is scheduled. For example, a first episode is scheduled between 8 AM and 9 AM. In certain embodiments, the treatment schedules  1900  address other details as well. For example, the daily schedule  1900  of  FIG. 19  indicates details of the waveform (e.g., ramp-up/ramp-down characteristics) and details of the treatment cycles. 
     b. System Operational Modes 
     The therapy system  100  can be configured into two basic operational modes—a training mode and a treatment mode—as will be described herein. In an embodiment, the therapy system  100  also can be configured into a placebo mode for use in clinical trials. 
     i. Training Mode 
     The training mode is used post-operatively to train the patient on using the therapy system  100 . In this mode, electrical signals are not delivered to the nerves for the purpose of creating blocking action potentials. In a preferred embodiment, the neuroregulator  104  does not generate any electrical signals. In some embodiments, the training therapy setting can be preset by the therapy system manufacturer and are unavailable to the treating physician. 
     The training mode allows the physician to familiarize the patient with the positioning of the external charger  101  relative to the implanted neuroregulator  104 . The physician also instructs the patient in how to respond to the feedback parameters within the therapy system  100 . Training also can cover information and menus which can be displayed on the external charger  101 , for example: the status of the battery  182  of the external charger  101 , the status of the battery  151  of the implanted neuroregulator  104 , coil position, lead/tissue impedances, and error conditions. 
     The physician also can train the patient in how to interact with the external charger  101 . In an embodiment, the patient interacts with the external charger  101  using the selection input button  174 . For example, by successively pressing the button  174 , the patient can select one of multiple device operations, such as: device reset, selective interrogation of battery status, and coil position status. 
     ii. Treatment Mode 
     The treatment mode is the normal operating mode of the neuroregulator  104  in which the neuroregulator  104  applies a blocking signal to the nerves using blocking therapy settings. In general, the therapy settings are specified by the physician based on the specific needs of the patient and timing of the patient&#39;s meals. In some embodiments, the neuroregulator  104  controls the therapy being provided according to therapy programs and schedules stored on the neuroregulator  104 . In other embodiments, the neuroregulator  104  follows the instructions of the external charger  101  to deliver therapy. 
     iii. Placebo Mode 
     This mode may be used for patients randomized to a placebo treatment in a randomized, double-blind clinical trial. In this mode, the neuroregulator  104  does not apply therapy signals to the lead arrangement  108 . Rather, in different embodiments, therapy signals can be supplied to a dummy resistor to drain the internal power source  151  ( FIG. 3 ) of the neuroregulator  104 . 
     The external charger  101  interacts with the patient and the physician as if therapy was being applied. For example, the patient and/or physician can view system status messages and a battery drain rate of the external charger  101  and neuroregulator  104 . Because the external charger  101  functions as normal, the physician and the patient are blind to the fact that no significant therapy is being applied. 
     To give the patient the sensation that therapy is being applied, current pulses may be applied to the vagal nerve trunks during impedance measurements at the start of therapy. However, no therapy is delivered during the remainder of the blocking cycle. These sensations are felt by the patient and provide a misleading indication of activity. These sensations, therefore, help in maintaining the double blindness of the study. 
     c. Treatment Therapy Settings 
     The neuroregulator  104  is configured to provide therapy signals to the electrode arrangement  108 . In general, the therapy signals can induce stimulation of the nerves, blocking of nerve impulses, or some combination of the two. 
     i. Blocking Treatment 
     During treatment, the neuroregulator  104  provides blocking signals to the nerves of a patient. Blocking signals include high frequency waveforms that inhibit the transmission of signals along the nerves. In general, the physician selects and sets therapy settings (e.g., waveform characteristics and treatment schedule) based on meal times and a patient&#39;s eating pattern. In an embodiment, the therapy system  100  can provide a choice of at least three unique blocking therapy settings which can be applied as part of a daily treatment schedule. 
     ii. Low Frequency Mode 
     The low frequency mode provides low frequency stimulating signals along the patient&#39;s nerves to create a brief, potentially observable, physiological response as an intra-operative screen. Such a physiologic response could be, for example, the twitching of a muscle or organ, such as the stomach. 
     This therapy setting may be used by the physician to confirm correct electrode placement. The system operates in this mode for short time periods and, typically, only when the patient is under physician care. This mode may be accessed through the programmer interface. In an embodiment, this mode can be enabled/disabled (e.g., by the manufacturer) through the programming interface. 
     iii. Temporary Test Therapy Setting Mode 
     The therapy system  100  has the ability to program special treatment/testing therapy settings to support “one-time” physiological evaluations. Special testing therapy parameters can be preset (e.g., by the manufacturer) to be made available for use by the physician. 
     d. System Monitoring 
     The therapy system  100  facilitates monitoring the operation of the therapy system  100  and its components. By monitoring the operation of the therapy system  100 , faults and malfunctions can be caught early and dealt with before becoming problematic. The therapy system  100  can record the operation and/or the fault conditions for later analysis. The therapy system  100  also can notify the patient and/or physician of the system operating status and non-compliant conditions. For example, an error message can be displayed on screen  172  (see  FIG. 5 ) of the external charger  101  or on a display screen (not shown) of the external computing device  107  (see  FIG. 1 ). 
     Embodiments of the therapy system  100  can confirm proper functioning of and communication between the components of the therapy system  100 . For example, the therapy system  100  can monitor the link strength between the external charger  101  and the neuroregulator  104 . In an embodiment, immediate feedback indicating the link strength can be provided to the patient (e.g., through the display  172  of the external charger  101 ) and/or to the physician (e.g., through the external computing device  107 ). 
     The therapy system  100  also can determine one or both of the coils  102 ,  105  are broken, shorted, or disconnected. In an embodiment, the therapy system  100  determines whether the coils  102 ,  105  are operational by measuring the impedance between the coils and determining whether the measured impedance falls within an acceptable range. 
     The therapy system  100  also can measure the impedance between the electrodes  212 ,  212   a  of the lead arrangement  108  and determine whether the impedance is out of range (e.g., due to inadequate electrode-nerve contact, or shorted electrodes). Details regarding the measurement of lead impedance are discussed later herein. Impedance measurements also can be used to verify proper lead placement, verify nerve capture, and monitor stomach contraction during the implant procedure. 
     The therapy system  100  also can communicate other types of system errors, component failures, and software malfunctions to the patient and/or physician. For example, the therapy system  100  can monitor the battery status (e.g., low battery, no charge, battery disconnected, etc.) of the neuroregulator  104  and/or the external charger  101  and warn the patient and/or physician when the battery should be recharged and/or replaced. 
     The therapy system  100  can indicate an inability to deliver a signal having the specified current (e.g., due to the impedance being out of range or due to internal component failure) to the lead arrangement  108  during treatment delivery. The therapy system  100  also can indicate whether the external charger  101  and/or the neuroregulator  104  have sufficient power to transmit and/or receive signals (e.g., based on antenna alignment, battery power, etc.). 
     i. Lead Impedance Measurement 
     Embodiments of the therapy system  100  have the ability to independently measure and record lead impedance values. Lead impedance values outside a predefined range may indicate problems or malfunctions within the therapy system  100 . High impedance, for example, could mean that the electrodes  212 ,  212   a  are not properly coupled to the nerves of the patient. Low impedance could mean inappropriate shorting of the electrodes  212 ,  212   a.    
     These embodiments of the therapy system  100  allow the physician to measure lead impedance on-demand. The therapy system  100  also can enables the physician to periodically measure impedance (e.g., during the Training Mode) without initiating a blocking therapy setting. Generally, impedance is measured and stored separately for each channel of each electrode configuration. These measurements may be used to establish a nominal impedance value for each patient by calculating a moving average. The nominal impedance and impedance tolerance range can be used for system non-compliance monitoring, as will be described below. 
     e. External Computer Interface 
     Programmer software, with which the physician can program treatment configurations and schedules, resides on and is compatible with an external computing device  107  ( FIG. 1 ) that communicates with the external charger  101 . In general, application software for the computing device  107  is capable of generating treatment programs stored in a commonly accepted data file format upon demand. 
     The programming interface of the computing device  107  is designed to enable the physician to interact with the components of the therapy system  100 . For example, the programming interface can enable the physician to modify the operational modes (e.g., training mode, treatment mode) of the external charger  101 . The programming interface also can facilitate downloading treatment parameters to the external charger  101 . The programming interface enables the physician to alter the treatment parameters of the neuroregulator  104 , and to schedule treatment episodes via the external charger  101 . 
     The programming interface also enables the physician to conduct intra-operative testing amongst the components of the therapy system  100 . For example, the physician can initiate a lead impedance test via the programming interface. The physician also can program temporary treatment settings for special physiologic testing. The programming interface also can facilitate conducting diagnostic stimulation at follow-up visits between the patient and the physician. 
     The programming interface of the computing device  107  also enables the physician to access patient data (e.g., treatments delivered and noted physiological effects of the treatment). For example, the programming interface can enable the physician to access and analyze patient data recorded by the therapy system  100  (e.g., stored in the memory  152  of the neuroregulator  104  and/or the memory  181  of the external charger  101 ). The physician also can upload the patient data to the external computing device  107  for storage and analysis. 
     The programming interface also can enable the physician to view system operation information such as non-compliant conditions, system faults, and other operational information (e.g., lead impedance) of the therapy system  100 . This operational data also can be uploaded to the external computing device  107  for storage and analysis. 
     i. Programming Access Level 
     In certain embodiments, the programming interface defines at least two levels of access, one for the physician and one for the system manufacturer. The programming interface can provide different types of information to a requestor depending on what level of access the requestor has. For example, the programming interface may enable the system manufacturer to program system settings (e.g., default values for treatment parameters, acceptable ranges for treatment parameters and/or system settings, system tolerances, etc.) that cannot be adjusted by the physician. 
     In an embodiment, a user with a high level of access can select, for each system setting, the level of access required before the programming interface will enable a user to modify the system setting. For example, the system manufacturer may wish to prevent treating physicians from modifying default treatment settings. It will be appreciated that generating software implementing the above-described features of the programming interface is within the skill of one of ordinary skill in the art having the benefits of the teachings of the present application. 
     5. Charge Balancing 
     Nerves may be damaged when exposed to direct current (e.g., net current from electrical stimulation) over extended periods of time. Such damage may result from very small net currents acting over a long time, e.g. microamperes of current over minutes. For example, direct current can be caused by a voltage buildup at the electrodes  212 ,  212   a  ( FIG. 1 ) due to inherent differences in electrode component values. 
     Charge-balancing advantageously mitigates (and may eliminate) damage to the nerve due to charge build-up during treatment. However, conventional processes for achieving a current/charge balance to within (for example) 1 μA in a current of about 6 mA place inordinate requirements on the implantable device of providing consistent power at a consistent frequency. Below are descriptions of two processes for balancing charge, a timing process and a shorting process, that do not require such inordinate consistency. 
     a. Timing Correction 
     Referring to  FIGS. 20-24 , charge or current on the patient&#39;s nerves can be balanced by applying a correction to a pulse-width PW of a treatment signal pulse  2000  over a number of cycles (see  FIG. 20 ). A cycle refers to a single iteration of the pulse. The correction includes adding or subtracting a “timer tick” to the pulse-width PW of at least one phase of the treatment signal pulse  2000  to increase or decrease the pulse-width for a period of time. In an embodiment, an example timer tick can equate to the minimum resolution of the applied clock frequency (e.g., about 560 nanoseconds). 
     Typically, the treatment signal pulse  2000  is a bi-phasic (e.g., having a negative phase and a positive phase) pulse signal having a pulse-width PW. In general, the negative charge provided by the first phase of the signal pulse  2000  is balanced by the positive charge provided by the second phase of the signal pulse  2000 . One or more timer ticks can be added to one or both phases of the pulse  2000  to correct a charge imbalance. 
     In the example shown in  FIG. 20 , the first phase of the signal pulse  2000  has a first pulse-width PW 1  and the second phase of the signal pulse  2000  has a second pulse-width PW 2 . One or more timer ticks can be added to the pulse-width PW 1 , PW 2  of one or both phases of the signal pulse  2000 . For example, the pulse-width PW 1  of the first phase can be increased by two timer ticks to a pulse-width of PW 1 ′. Alternatively, the pulse-width PW 2  of the second phase can be decreased by two timer tick to a pulse-width of PW 2 ′. 
     To determine the number of timer ticks to add or subtract from each pulse-width, the neuroregulator  104  periodically can measure the voltage of the signal applied to each lead electrode  212 ,  212   a  of lead arrangement  108 . The combination of charge buildup sensing and pulse width control creates a feedback loop to minimize the resulting voltage offset. Advantageously, this sense and control process is effective in the presence of physiologic variations, circuit tolerances, differences in electrode size, and temperature changes. 
     For example, as shown in  FIGS. 3A and 3B , the electrodes of each lead (e.g., the tip electrodes  212 ,  212   a  in contact with the anterior and posterior vagal nerves AVN, PVN, respectively) are coupled to the CPU  154  of the neuroregulator  104  via a capacitive divider  162 . The CPU  154  provides timed instructions to the output module  161  for controlling the voltage measurements VA, VB of the signals applied by the electrodes  212 ,  212   a  ( FIG. 1 ). 
     Between pulses, the microprocessor CPU  154  can zero the capacitive divider  162 , release the capacitive divider  162  at a predetermined time relative to the signal cycle, and measure the voltages VA, VB of the electrodes  212 ,  212   a . For example, the CPU  154  can zero the capacitive divider  162 , release the capacitive divider  162  approximately ten microseconds into a negative phase of the pulse, and measure the voltages VA, VB (see  FIG. 20 ). The CPU  154  can subsequently measure the voltages VA, VB at approximately 10 microseconds into a positive phase of the pulse. If the voltage measurement VA of the electrode  212  is greater than the voltage measurement VB of the second electrode  212   a , then the CPU  154  delivers instructions to decrease the pulse width (e.g., by about 560 nanoseconds) of the negative phase of the pulse of the next/subsequent cycle. 
     The above process may be repeated at a sampling frequency (e.g., typically about 40 Hz). Gradually, the number of pulse width corrective increments (“timer ticks”) applied to the signal can be adjusted. For example, the pulse width PW 1  of the positive phase of the pulse can be increased or decreased every sample period until the voltage measurement VA of the first electrode  212  is less than the voltage measurement VB of the second electrode  212   a . In such a case, the pulse width PW 2  of the negative pulse then can be increased to achieve balance. When the maximum pulse width PW 2  of the negative phase of the pulse is reached, then the pulse width PW 1  of the positive phase of the biphasic pulse may be decreased to maintain balance. In a preferred embodiment, the corrective increment is applied to a series of signals until the net offset current is well below a target current (e.g., about 1 μA). 
     In an embodiment, the amplitudes of the positive and negative phases of the pulse are compared very early in the cycle, and a relatively large correction is initially applied to the pulse width of the signal. Subsequently, the balancing correction is refined by changing the pulse width by only the one or two ticks as described above. 
     Advantageously, the charge-balancing goal can be achieved over a number of these cycles using the above described processes without requiring a high clock frequency. Because the charge buildup tends to be a slow process, correcting the charge buildup can be done less frequently than delivering therapy signals. For example, in an embodiment, therapy signals can be delivered at about 5 kHz and correction pulses can be delivered at about 40 Hertz. 
       FIG. 21  illustrates an example application of charge balancing through timing corrections.  FIG. 21  illustrates a blocking waveform  222  (e.g., a biphasic, symmetric current waveform), which results in a voltage waveform  224  at the electrode-tissue interface. The voltage waveform  224  includes an exponential voltage component  226  which reflects the fact that the electrode-tissue interface has capacitive elements, resulting in charging and discharging of this capacitance. 
     In one cycle of the current waveform  222 , the charge applied to the electrode-tissue interface is balanced when the voltages V C  and V D  are equal. Accordingly, in such a case, the net potential of the electrode-tissue interface is zero. As described above, however, there are a number of reasons why, in practice, voltages V C  and V D  may not be equal, resulting in a charge imbalance. 
     Typically, in practical operation, the voltage values of V C  and V D  are measured periodically (e.g., about every 25 milliseconds). If the voltage V C  is greater than the voltage V D , then the pulse width  228  of the first phase of the current waveform  222  is reduced by one “timer tick,” and applied for about 1 millisecond. At the end of subsequent measurement periods (e.g., about every 25 milliseconds), the values of voltages V C  and V D  are measured again. When the voltage V C  is greater than the voltage V D , the pulse width  228  of the first phase is reduced by an additional timer tick. The current waveform  222  having the phase with the reduced pulse-width  228  is applied for an additional 1 millisecond. 
     When the value of the voltage V C  is eventually less than the value of the voltage V D , then the pulse width  228  of the first phase can be increased by one timer tick for 1 millisecond for each measurement period. In this situation, it may be that the maximum pulse width (as determined by the applied frequency of the therapy)  228 , is reached while the voltage V C  is still less than the voltage V D . If this occurs, then the pulse width  230  of the second phase of the current pulse  222  is decreased one timer tick at a time, as described above, until equilibrium is established (i.e., V C =V D ). 
     Additionally, in the methods represented by  FIGS. 20 and 21 , the microprocessor CPU  154  can short out the electrodes  212 ,  212   a  at the beginning, midpoint and/or end of the biphasic, square-wave, current pulse, as described in more detail herein. Over a series of such sampling cycles, it has been demonstrated that the net offset current is well below the design goal of 1 μA. 
     During a feedback cycle, software stored in the microprocessor CPU  154  can initiate a therapy shut down if the sensed voltage offset exceeds safe values. This is an advantageous feature in actual use, where electrode configurations and other parameters could vary. 
     By using a combination of both hardware (i.e., electrode shorting) and closed-loop software techniques, the average charge imbalance may be lower than with either method individually. 
     At the end of therapy delivery, it is useful to have the hardware briefly drain any residual charge. Subsequently, the circuitry may be made safe until the next therapy delivery and the software loop turned off. 
     b. Shorting Correction 
     Some processing for achieving charge balance have involved the use of biphasic pulses in which, for example, the negative charge provided by the first part of the waveform is balanced by the positive charge provided by the second part of the waveform. Further details describing the use of electrode shorting to achieve charge balancing can be found in U.S. Pat. No. 4,498,478 to Bourgeois, issued Feb. 12, 1985; U.S. Pat. No. 4,592,359 to Galbraith, issued Jun. 3, 1986; and U.S. Pat. No. 5,755,747 to Daly et al, issued May 26, 1998, the disclosures of which are hereby incorporated by reference herein. 
       FIGS. 22-24  illustrate a preferred charge balancing process.  FIGS. 22 and 23  schematically illustrate an implanted circuit  112  of a neuroregulator  104  connected to nerve electrodes  212 ,  212   a . The circuit  112  has components schematically illustrated as a switch  150  for selectively creating an electrical short between the electrodes  212 ,  212   a . In  FIG. 22 , the switch  150  is arranged in a short state to create an electrical short between electrodes  212 ,  212   a . In  FIG. 23 , the switch  150  is arranged in a non-short state with no short being created between the electrodes  212 ,  212   a.    
       FIG. 24  schematically illustrates signal waveforms W 1 , W 2 , W 1A , W 2A  produced at the electrodes  212 ,  212   a  under various conditions of operation of the switch  150 . The waveforms W 1  and W 2  show the signals produced at electrodes  212 ,  212   a , respectively, when the switch  150  is arranged in the non-short state. Each waveform W 1  and W 2  has a negative pulse and a positive pulse of equal pulse width PW. The waveforms W 1 , W 2  are out of phase so that the negative pulses of the waveform W 1  occur during the positive pulses of the waveform W 2 . 
     It will be appreciated, these waveforms are illustrative only. Any other waveform (e.g., the time offset waveform W 12A  of  FIG. 18  could be used). In addition, while the short is shown between electrodes  212 ,  212   a , the short alternatively or additionally could be created between cathode and anode pairs  212 ,  218  and  212   a ,  218   a , previously described. 
     In the example shown, the switch  150  is operated to create a short between electrodes  212 ,  212   a  at the start of each pulse and for a duration Ds. The waveforms at electrodes  212 ,  212   a  resulting from such shorting are shown in  FIG. 24  as W 1A , W 2A . As a result of the short, any charge build-up at an electrode (e.g., electrode  212 ) is distributed to the oppositely charged electrode (e.g., electrode  212   a ). The pulse width PW of each pulse is reduced to a pulse width PW A . Advantageously, repeating this process throughout the therapy maintains any net charge build-up below tolerable levels. 
     The example given shows the short state occurring at the beginning of each signal pulse. This is illustrative only. The short state can occur at the beginning, end or any intermediate time of a signal pulse. Furthermore, the short state need not be applied to every pulse, but rather can occur intermittently throughout the pulse cycles or even during time delays between pulses. When applied during a pulse cycle, the duration Ds of the short is preferable not greater than about 10% of the pulse width PW. For example, the duration Ds can range from about 10 μs to about 20 μs. 
     6. Therapy Calibration and Safety Limits 
     The design of the neuroregulator  104  ( FIG. 3 ) includes a capacitive divider  162  and an output module  161  to measure the voltage present at the lead arrangement  108  (e.g., the tip electrodes  212 ,  212   a  and/or ring electrodes  218  and  218   a  of both anterior and posterior leads  106 ,  106   a ). The output module  161  can measure the current flow through the electrodes arranged in any of the four electrode configurations (see  FIGS. 11 ,  13 ,  15 , and  17 ). A programmable current source (not shown) can enable a physician to select how current is delivered through the electrodes  212 ,  212   a ,  218 , and  218   a  to the nerve. 
     Before therapy is delivered, the physician can calibrate the neuroregulator  104  to ensure the desired current can be delivered to the nerves. For example, this calibration can be accomplished by connecting the programmable current source from a power source to ground and adjusting the current to the desired level. Current does not flow through the leads  106  during this calibration procedure. If the desired current cannot be delivered, or if the DC voltage offset is greater than a programmed limit, then the therapy can be terminated (e.g., such conditions trigger a flag or error alert). 
     Advantageously, calibrating the therapy system  100  significantly reduces the effect of component tolerance, drift, and aging on the amount of current delivered. Temperature effects are not likely to be significant since the neuroregulator  104  is at body temperature when implanted. In addition, the capacitive divider  162  can be calibrated before therapy is delivered. Advantageously, calibrating the divider  162  can enhance the accuracy of the safety checks from a 20% worst case value to approximately 2%. 
     During therapy, the current between the active electrodes is measured during each signal pulse to ensure that the delivered current is within the programmed tolerance (e.g., +/−about 5%). 
     Additionally, in order to determine the state of charge balance, the therapy system  100  can determine a peak-to-peak voltage quantity for each signal pulse. The peak-to-peak voltage quantity is divided by two and compared to the peak voltage measurement of each phase of the waveform. If the deviation exceeds a predetermined value, the therapy can be shut down. 
     The normal shutdown of the output module  161  shorts the electrodes together and connects them to ground through one of the current sources. Normally, this is a desirable and safe condition. However, certain failures could cause current to flow after shutdown, resulting in damage to the nerve. To eliminate this problem, an additional check can be made after normal shutdown has been completed. If current flow is detected, the leads are disconnected from each other (allowed to float) and the current sources are programmed to zero current. 
     7. Auto-Increment Therapy Delivery 
     For blocking therapy to be effective, energy delivery may need to be increased beyond the level that a patient perceives as acceptable at the initiation of therapy. The power of the therapy signals can be increased in small increments to enable the patient to acclimate to the more powerful therapy signals. 
     For example, the current of the therapy signal can be increased in steps of about 1 mA at weekly follow-up visits. Over time, patients may willingly accept multiple increments of 1 mA/week through periodic follow-up visits and programming sessions. For example, an initial setting of 3 mA may rise to at least 6 mA as a result of such follow-up sessions. 
     In certain embodiments of the therapy system  100 , energy (i.e., power) delivery can be incrementally increased or decreased automatically over a pre-determined period of time. Advantageously, this automatic incremental increase can mitigate the need for frequent doctor office visits. This flexibility is especially convenient for patients who are located remote from the implanting bariatric center. 
     In an embodiment, the therapy system  100  automatically increases the current of the therapy signal by, for example, 0.25 mA every other day, cumulatively achieving the 1 mA/week incremental increase. In another embodiment, the therapy system  100  increases the current by about 0.125 mA per day. Initial studies have demonstrated such increment levels as acceptable. 
     The patient can retain the ability to turn therapy off at any time and return to the physician for re-evaluation. Alternatively, the patient can revert to previously acceptable therapy delivery levels (e.g., the therapy level of the previous day). For example, the patient can interact with the external charger  101  to issue such an instruction. 
     The physician can choose whether to activate the auto-increment therapy capability. The physician also can specify the date and/or time of therapy initiation and therapy parameters (e.g., including the starting and ending therapy parameters). The physician also may specify safety limits or tolerances for the therapy parameters. Additionally, the physician can specify the rate at which the therapy parameters are incremented over various time periods (e.g., about 0.5 mA/day for the first 7 days, then 0.125 mA/day over the following 24 days). 
     8. Predetermined Programs 
     One or more therapy programs can be stored in the memory of the external computer  107 . The therapy programs include predetermined parameters and therapy delivery schedules. For example, each therapy program can specify an output voltage, a frequency, a pulse width, ramp-up rates, ramp-down rates, and an on-off cycle period. In an embodiment, the ramp-up rates and ramp-down rates can be individually and separately programmed. 
     In use, the physician may select any one of these therapy programs and transmit the selected therapy program to the implanted neuroregulator  104  (e.g., via the external charger  101 ) for storage in the memory of the neuroregulator  104 . The stored therapy program then can control the parameters of the therapy signal delivered to the patient via the neuroregulator  104 . 
     Typically, the parameter settings of the predetermined programs are set at the factory, prior to shipment. However, each of these parameters can be adjusted over a certain range, by the physician, using the computer  100  to produce selectable, customized, predetermined therapy programs. Using these selectable, customized therapy programs, the physician can manage the patient&#39;s care in an appropriate manner. 
     For example, when patients require more varied therapies, the neuroregulator  104  can store a therapy program including one or more combinations of multiple therapy modes sequenced throughout the day. 
     For example, referring to electrode configuration shown in  FIG. 10 , a single therapy program can include instructions to apply a blocking signal between electrode tips  212  (anterior vagal nerve) and  212   a  (posterior vagal nerve) from 8 a.m. to noon at 6 mA and kHz; alternating between applying a blocking signal to posterior tip  212   a  to ring  218   a  and applying a blocking signal to anterior tip  212  to ring  218  from noon to 2 p.m. at 3 mA and 2.5 kHz; and applying a blocking signal from electrode tip  212  to electrode tip  212   a  from 2 p.m. from 2 p.m. to midnight at 6 mA and 5 kHz. 
     9. Operation Logs 
     In general, the neuroregulator  104  can have a time base to facilitate the delivery of therapy according to the treatment schedule. To determine this time base, the neuroregulator  104  can maintain one or more operating logs indicating the operations of the therapy system  100 . 
     For example, the neuroregulator  104  maintains a time-and-date-stamped delivery log of the actual delivery of therapy. For example, the delivery log can include the time and date of initiation of each therapy episode, the time and date of completion of the therapy episode, the therapy parameters associated with the therapy episode. Both scheduled therapy and automatically-initiated therapy can be logged. The delivery log also can include a parameter to indicate whether the therapy episode was scheduled or automatically initiated. 
     Additionally, the neuroregulator  104  can maintain a time-and-date-stamped error log of all conditions that interfered with the delivery of therapy. For example, the error log can record all impedances measured, temperatures measured by the on-board temperature sensor, each instance in which the battery was charged by the external charger  101 , each instance in which the battery reached its low-charge threshold, and each instance in which the battery reached its depleted threshold. 
     The delivery log and the error log are readable by the external computer  107  (e.g., a clinician programmer). In an embodiment, the delivery log and the error log each can accommodate up to about 3 months of data. 
     10. Detection of Food Passage Through the Esophagus 
     Neural blocking therapy can affect the rate at which the stomach empties and the level of intestinal motility. When applying neural blocking therapy for obesity control, it is desirable to determine the approximate times at which the patient ingests food (i.e., mealtimes) and the approximate quantity of food being consumed at each meal. Advantageously, with this information, the duty cycle of the therapy system  100  can be synchronized with the mealtimes. Additionally, the nature of the therapy can be adjusted in accordance with the quantity of food being consumed. For example, food detection is described in U.S. Pat. No. 5,263,480 to Wernicke et al, issued Nov. 23, 1993, the disclosure of which is hereby incorporated herein by reference. 
     In certain embodiments of the therapy system  100 , the anterior and posterior vagal nerve electrodes  212 ,  212   a  can be positioned on the esophagus E adjacent to the junction between the esophagus E and the stomach. An impedance measurement between the anterior and posterior vagal nerve electrodes  212 ,  212   a  provides a measure of the presence of food in the esophagus E between the electrodes  212 ,  212   a  (e.g., see  FIG. 11 ). The time integration of this impedance value provides a measure of the quantity of food consumed. 
     The impedance value between the electrodes  212 ,  212   a  can be measured by passing a low amplitude, sinusoidal signal (e.g., having a frequency of about 500-1000 Hz) between the electrodes  212 ,  212   a . In an alternative embodiment, the impedance can be measured by passing the signal between the ring electrodes  218 ,  218   a . In other embodiments, the dual bipolar lead/electrode configuration can operate as a quadripolar array. 
     In a quadripolar electrode array, two pairs of electrodes are typically secured in generally the same plane and normal to the length of the esophagus E. In such a configuration, a small signal applied across one pair of the electrodes (e.g., tip electrode  212 , ring electrode  218 ) can be detected across the other pair (e.g., tip electrode  212   a , ring electrode  218   a ). In general, changes in relative amplitude of the detected signal are proportional to changes in resistance of the signal path. 
     The impedance of the signal changes when food progresses down the esophagus E. This impedance change causes the amplitude of the detected signal to change, thereby providing an indication of the fact that food has passed, and giving an indication of the quantity of food. While a bipolar electrode pair may be used for both signal application and sensing across the esophagus E, it has the disadvantage of some interference as a result of polarization potentials. 
     More generally, this technology can be used to detect changes in the nature of the fluid within a vessel or lumen of the body. Such technology can be utilized in multiple applications. For example, this impedance measurement technology can be used to detect the presence of liquid/food in the distal esophagus to ascertain the presence of esophageal reflux. 
     In another embodiment, this impedance measurement technology can be used in diagnosing eating abnormalities, such as bulimia. 
     In one embodiment, the time history of the transesophageal impedance measurement is recorded in the memory of the implanted module (e.g., in an operating log), for later telemetry to the external module, for review and analysis by the physician. With this information, the physician can preferentially choose the operating parameters of the system to best suit the eating habits of an individual patient. 
     In an alternative embodiment, the output of the transesophageal impedance measurement becomes a control input into CPU  154  of circuit  112  in neuroregulator  104  ( FIG. 3 ). The therapy signal output of the neuroregulator  104  can be timed automatically to correspond to the timing and quantity of food consumed via a suitable algorithm. 
     11. Activity Monitoring System 
     The weight reduction resulting from the application of therapy described in this patent application is expected to produce an increased feeling of well-being in the patient, and possibly an increase in the amount of activity in which the patient is comfortable becoming involved. 
     In certain embodiments, the therapy system  100  monitors the activity of the patient. Generally, the therapy system  100  records the change in activity over the course of treatment. The therapy is applied to accomplish a goal (e.g., obesity reduction), and the activity level as a consequence of achieving the goal (e.g., weight loss) is then measured. 
     In an embodiment, this change in activity then can be mapped to the affects of the treatment. This mapping of the change in activity to the results of treatment can be personally advantageous to patients as well as advantageous to the medical community. For example, knowledge of the likely change, both in weight and in activity level, could be useful information for patients who are contemplating the implant and associated therapy. 
     In addition, such mapping would advantageously provide documented evidence of the positive effect of the weight control system to reimbursement groups. Additionally, from a medical/scientific perspective, it is known that weight loss is generally related to caloric intake, activity level, and metabolic rate. Increased quantification in the area of activity level would aid in developing a robust relationship among these factors. 
     There are a variety of methods which can be used for measuring activity level. Some of these models have been used as the basis for determining the preferred rate of implantable pacemakers and defibrillators. For example, a sensor of movement or acceleration (e.g., a gyroscope-based sensor), can provide an instantaneous measurement of activity level. Suitable hardware, software, and/or algorithm systems can then derive from these measurements the activity level averaged over a period of time (e.g., a 24 hr period). 
     An accelerometer also can be used to track patient activity. Other examples of activity sensing options include tracking the respiratory rate of the patient, by monitoring bio-impedance measurements (e.g., intrathoracic impedance), measuring a minute volume of, e.g., a compendium of respiratory rate and tidal volume, and monitoring blood pH, blood oxygen level, and blood pressure. In each case, the instantaneous value of the measurement can be integrated over a suitable time period. 
     With the foregoing detailed description of the present invention, it has been shown how the objects of the invention have been attained in a preferred manner. Modifications and equivalents of disclosed concepts such as those which might readily occur to one skilled in the art are intended to be included in the scope of the claims which are appended hereto.