RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 11/707,053, now U.S. Pat. No. 7,725,195, filed on Feb. 16, 2007 which claims priority to U.S. Provisional Applications 60/774,039, 60/774,040, and 60/774,041 filed on Feb. 16, 2006, all of which are expressly incorporated herein by reference in their entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to an apparatus, system, and method for implantable therapeutic treatment of obstructive sleep apnea. 
     BACKGROUND OF THE INVENTION 
     Sleep apnea is a physiological condition affecting millions of people worldwide. It is described as an iterated failure to respire properly during sleep. Those affected by sleep apnea stop breathing during sleep numerous times during the night. There are two types of sleep apnea, generally described in medical literature as central sleep apnea and obstructive sleep apnea. Central sleep apnea is a failure of the nervous system to produce proper signals for excitation of the muscles involved with respiration. Obstructive sleep apnea (OSA) is cause by physical obstruction of the upper airway channel (UAW). 
     Obstruction of the upper airway is associated with a depression of the respiratory system caused by a loss of tone of the oropharyngeal muscles involved in maintaining UAW patency. As those muscles lose tone, the tongue and soft tissue of the upper airway collapse, blocking the upper airway channel. Blockage of the upper airway prevents air from flowing into the lungs. This creates a decrease in blood oxygen level, which in turn increases blood pressure and heart dilation. This causes a reflexive forced opening of the UAW until the patient regains normal patency, followed by normal respiration until the next apneic event. These reflexes briefly arouse the patient from sleep (microarousals). 
     Current treatment options range from non-invasive approaches such as continuous positive applied pressure (CPAP) to more invasive surgical procedures such as uvulopalatopharyngoplasty (UPPP) and tracheostomy. In both cases patient acceptance and therapy compliance is well below desired levels, rendering the current solutions ineffective as a long term solution-for therapeutic treatment of OSA. 
     Implants are a promising alternative to these forms of treatment. Pharyngeal dilation via hypoglossal nerve (XII) stimulation has been shown to be an effective treatment method for OSA. The nerves are stimulated using an implanted electrode. In particular, the medial XII nerve branch (i.e., in. genioglossus), has demonstrated significant reductions in UAW airflow resistance (i.e., increased pharyngeal caliber). 
     Reduced UAW airflow resistance, however, does not address the issue of UAW compliance (i.e., decreased UAW stiffness), another critical factor involved with maintaining patency. To this end, co-activation of both the lateral XII nerve branches (which innervate the hyoglossus (HG) and styloglossus (SG) muscles) and the medial nerve branch has shown that the added effects of the HG (tongue retraction and depression) and the SG (retraction and elevation of lateral aspect of tongue) result in an increased maximum rate of airflow and mechanical stability of the UAW. 
     While coarse (non-selective) stimulation has shown improvement to the AHI (Apnea+Hypopnea Index) the therapeutic effects of coarse stimulation are inconclusive. Selective stimulation of the functional branches is more effective, since each branch-controlled muscle affects different functions and locations of the upper airway. For example, activation of the GH muscle moves the hyoid bone in the anterosuperior direction (towards the tip of the chin). This causes dilation of the pharynx, but at a point along the upper airway that is more caudal (below) to the base of the tongue. In contrast, activation of the HG dilates the oropharynx (the most commonly identified point of collapse, where the tongue and soft palate meet) by causing tongue protrusion. Finally, the tongue retractor muscles (HG and SG) do not themselves generate therapeutic effects, but they have been shown to improve upper airway stability when co-activated with the HG muscle. 
     While electrical stimulation of the hypoglossal nerve (HGN) has been experimentally shown to remove obstructions in the UAW, current implementation methods require accurate detection of an obstruction, selective stimulation of the correct tongue muscles, and a coupling of the detection and stimulation components. Additionally, attempts at selective stimulation have to date required multiple implants with multiple power sources, and the scope of therapeutic efficacy has been limited. A need therefore exists for an apparatus and method for programmable and/or selective neural stimulation of multiple implants or contact excitation combinations using a single controller power source. 
     SUMMARY OF THE INVENTION 
     The present invention relates to an apparatus, system, and method for selective and programmable implants for the therapeutic treatment of obstructive sleep apnea. 
     In one embodiment, an implantable RFID-enabled micro-electronic neurostimulator system for treating obstructive sleep apnea includes an external subsystem and an internal subsystem. In this embodiment, the internal subsystem includes an implant having a top and a bottom layer, the bottom layer serving as an attachment mechanism such that the bottom layer of the implant encompasses the HGN and attaches to the top layer of the implant. A printed circuit board (PCB) is attached to the top layer of the implant, with the PCB having first and second opposing sides. A neural interface attaches to the second side of the PCB. A core subsystem (CSS) attaches to the first side of the PCB and electrically connects to the neural interface. An internal radio frequency (RF) interface attaches to the first side of the PCB and is electrically connected to the CSS. The power may be supplied by RF energy emitted from the external subsystem. 
     In some embodiments, the external subsystem includes a controller. The controller may include a port for interfacing with a computer. A computer may interface with the controller through the port to program patient-specific nerve physiology and stimulation parameters into the controller. The controller may be shaped for placement around a patient&#39;s ear. The controller may identify an implant having a unique ID tag, communicate with an implant having the unique ID tag, and send a signal to a transponder located in the implant. In some embodiments, the transponder is a passive RFID transponder. In other embodiments, the transponder is an active transponder. In still further embodiments, the controller provides an RF signal to the implant, senses and records data, and interfaces with a programming device. The controller may also communicate with the implant at preprogrammed intervals. In other embodiments, the controller initiates a stimulation cycle by making a request to the CSS, the request being in the form of an encoded RF waveform including control data. The request may be encrypted. 
     In some embodiments, the implant provides continuous open loop electrical stimulation to the HGN. In other embodiments, the implant provides closed loop stimulation. The stimulation may be constant, or it may be at preprogrammed conditions. Stimulation may be applied during sleep hours, or it may be applied while the patient is awake. The stimulation may be bi-phasic stimulation of the HGN, with a stimulation pulse width of about 200 microseconds and a stimulation frequency of about 10-40 Hertz. The implant may be hermetically sealed. In other embodiments, the implant delivers multiple modes of stimulation. The stimulation can be in multiple dimensions. 
     Stimulation may be provided by a neural interface. This stimulation may be applied to the HGN. In certain embodiments, the neural interface includes a plurality of individual electrodes. In further embodiments, the neural interface electrodes include an array of anodes and cathodes, which in some embodiments are a plurality of exposed electrode pairs serving as anode and cathode complementary elements. In certain other embodiments, the electrodes are spot welded to the PCB and include material selected from the group consisting of platinum and iridium. In certain embodiments, the neural interface includes no external wires or leads. In still further embodiments, the neural interface includes a matrix of platinum electrodes coupled to the fascicles of the hypoglossal nerve (HGN). In some embodiments, the neural interface senses neural activity of the nerve it interfaces with, and transmits that sensed neural activity to the core subsystem. 
     In some embodiments, the core subsystem (CSS) of the implant is included in a silicon chip placed on the top of the printed circuit board PCB, with the chip connected to the neural interface via traced wires printed on the PCB. The chip may be powered by and receive a customized electrode stimulation program protocol from the controller. Upon receiving a request to enter into a stimulation state the CSS selects a trained waveform from memory and starts stimulation by providing an electrical signal to the neural interface. In some embodiments, the core subsystem reports completion of a stimulation state to the controller via an RF communication and optionally goes to an idle state. 
     Methods for treating obstructive sleep apnea are also disclosed. In one method, a hypoglossal nerve (HGN) is selectively stimulated. A neural interface is implanted in a fascicle of the HGN. The neural interface senses and records neural activity, and feeds the sensed neural activity information into a parameterized control algorithm. In certain embodiments, an external subsystem inductively coupled to an RFID senses and records the neural activity. The algorithm compares the sensed information to a reference data set in real time, transmits in real time an output of the parameterized control algorithm from an external RF interface to an internal RF interface, and from the internal RF interface to a microprocessor. Stimulus information may be calculated and communicated between the external RF interface and the internal RF interface in real time. In another method, bi-phasic electrical stimulation is applied to individual fascicles of the hypoglossal nerve using selectively excitable individual electrodes arranged in a planar field. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention, and together with the description serve to explain the principles of the invention. In the drawings: 
         FIG. 1  shows an embodiment of an internal subsystem. 
         FIG. 2  shows an embodiment of an internal subsystem with the core subsystem and internal RF interface in a silicon package. 
         FIG. 3  shows a hypoglossal nerve an implant. 
         FIG. 4  shows multiple embodiments of neural interface electrode arrays. 
         FIG. 5  shows an embodiment of an internal subsystem mplant. 
         FIG. 5A  is a breakout view of  FIG. 1 . 
         FIG. 6A  shows an embodiment of an internal subsystem with the neural interface electrodes on the bottom layer of the implant. 
         FIG. 6B  shows an embodiment of an internal subsystem with the neural interface electrodes on the top and bottom layers of the implant. 
         FIG. 7  shows an embodiment of an external subsystem with a controller. 
         FIG. 8  shows two embodiments of the external controller. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. 
     One embodiment the present invention includes an external subsystem and an internal subsystem. In certain embodiments, the external subsystem includes one or more of (1) a controller, (2) an external RF interface, and (3) an optional power source. The internal subsystem may include an implant. In certain embodiments, the implant includes one or more of (1) a neural interface which can include an array of electrodes where at least one electrode contacts a nerve, (2) a core subsystem, and (3) an internal RF interface. In some embodiments, the neural interface may further include a digital to analog signal converter and a multiplexer. 
     In some embodiments the core subsystem may include a microprocessor. The microprocessor may have a micrologic CPU and memory to store protocols selective to a patient. The microprocessor may be part of an integrated silicon package. In still further embodiments, the internal RF interface may include one or more of a transponder, internal antenna, modulator, demodulator, clock, and rectifier. The transponder can be passive or active. In some embodiments, one or more of a controller, external RF interface, and optional power source are positioned on the skin of a user/patient, typically directly over or in close proximity to, an implant. 
     In certain embodiments, the external subsystem controller can be in the form of an earpiece or patch including any one or more of the controller, external RF interface, and optional power source, e.g., a battery, AC to DC converter, or other power sources known to those skilled in the art. In certain embodiments, the external subsystem can send and receive control logic and power using an external RF interface. In such embodiments, the external subsystem can further include one or more of a crypto block, data storage, memory, recording unit, microprocessor, and data port. In some embodiments the microprocessor may have a micrologic CPU and memory to store protocols selective to a patient. The microprocessor may be part of an integrated silicon package. 
     Each of the components of various embodiments of the claimed invention is described hereafter. In certain embodiments, the present invention is an open loop system. In other embodiments the present invention is a closed loop system. The components of the embodiments can be rearranged or combined with other embodiments without departing from the scope of the present invention. 
     The Internal Subsystem 
     In certain embodiments, the internal subsystem includes an implant, which includes one or more of (1) a core subsystem, (2) a neural interface, and (3) an internal RF interface. Certain embodiments of the implant components and component arrangements are described below. 
     Implant Components 
     The following paragraphs describe embodiments of the implant of the present invention, which includes one or more of a core subsystem, neural interface, and internal RF interface components. 
     The Core Subsystem 
       FIG. 1  shows an embodiment of the internal subsystem  100 . In certain embodiments the internal subsystem  100  includes an implant  105  (non-limiting representative embodiments of implant  105  are shown in  FIGS. 3 ,  5 ,  5 A,  6 A,  6 B, and  8 ) which may have a core subsystem  140 . The middle portion of  FIG. 1  shows a detailed view of an embodiment of the core subsystem  140 . The core subsystem  140  may include one or more of a power module  144 , microprocessor  141 , crypto block  142 , and input output buffer  143 . In certain embodiments, the microprocessor  141  may have a micrologic CPU, and may have memory to store protocols selective to a patient. In the embodiment shown, the core subsystem includes a power module  144 , a core subsystem microprocessor  141  for managing communication with an external RF interface  203 , at least one I/O buffer  143  for storing inbound and outbound signal data, and a core subsystem crypto block  142 . In some embodiments, the core subsystem microprocessor  141  communicates with the external RF interface  203  in full duplex. The core subsystem microprocessor  141  may generate signals for controlling stimulation delivered by the neural interface  160 , and it may processes signals received from the neural interface  160 . In certain embodiments, the core subsystem microprocessor logic includes an anti-collision protocol for managing in-range multiple transponders and readers, a management protocol for reset, initialization, and tuning of the implant  105 , and a protocol to facilitate the exchange of data with the neural interface  160 . The core subsystem microprocessor  141  is programmable and may further include an attached non-volatile memory. The microprocessor  141  may be a single chip  145  or part of an integrated silicon package  170 . 
       FIG. 2  shows an embodiment of an internal subsystem  100  with the core subsystem  140  and internal RF interface  150  in a silicon package  170 . For size comparison,  FIG. 2  shows the core subsystem  140 , internal RF interface  150 , and core subsystem microprocessor  141  next to the silicon package  170 . 
     The Neural Interface 
     The right portion of  FIG. 1  shows an embodiment of a neural interface  160 . The neural interface  160  can include an array of electrodes  161  where at least one electrode  161  contacts a nerve. In one embodiment, the neural interface  160  includes an array of 10 to 16 electrodes  161 . This arrangement is exemplary only however, and not limited to the quantity or arrangement shown. The core subsystem  140  connects to the neural interface  160 , and controls neural interface stimulation. In the embodiment shown, the neural interface  160  is attached to the printed circuit board  130 . In some embodiments, the neural interface  160  may further include a digital to analog signal converter  164  and a multiplexer  166 . In certain embodiments the multiplexer  166  is included on the printed circuit board  130 . In other embodiments, the multiplexer  166  is included on a thin layer film or flexible membrane around the surface of the chip. 
     In the embodiment shown, the neural interface  160  receives power from RF waves received by the implant  105 . In one embodiment, the D/A converter  164  uses the RF waves to power one or more capacitors  165 , which may be located in the converter  164 . In certain embodiments, the capacitors  165  are arranged in an array on a microfilm. These capacitors  165  store charges, which are used to generate analog burst pulses for delivery by the neural interface  160 . In embodiments including a multiplexer  166 , the multiplexer  166  may be used to deliver power to multiple capacitors  165 , and can be used to deliver power to multiple electrodes  161  in the neural interface  160 . In still further embodiments, the multiplexer  166  is programmable. 
     In certain embodiments, the neural interface  160  is physically located on the opposite side of the printed circuit board  130  to which the core subsystem  140  is attached. In other embodiments, the one or more electrodes  161  are physically separated from the core subsystem  140  by the printed circuit board  130 . Each electrode  161  connects to the core subsystem  140  through wires  133  (e.g., traced wires) on the printed circuit board  130 . This layered approach to separating the core subsystem  140  from the electrodes  161  has significant benefits in the bio-compatible coating and manufacturing of the implant. By minimizing the area exposed to the HGN, the bio-compatible coating is only required in the area surrounding the exposed parts of the electrodes  161 . 
     The electrodes  161  may be manufactured with biocompatible material coating. In certain embodiments, the electrodes may include embedded platinum contacts spot-welded to a printed circuit board  130  on the implant  105 . The electrodes  161  may be arrayed in a matrix, with the bottoms of the electrodes  161  exposed for contact to the HGN. Since the electrodes  161  attach to the top portion of the core subsystem  140  through leads on the printed circuit board, there is no need for wire-based leads attached to the contact points, allowing for miniaturization of the electrodes  161 . 
       FIG. 3  shows a hypoglossal nerve implanted with a neural interface  160 . In one embodiment, exposed portions of the neural interface  160  deliver selective stimulation to fascicles of the HGN. Selective stimulation allows co-activation of both the lateral HGN branches, which innervate the hypoglossus (HG) and styloglossus (SG), and the medial branch. This selective stimulation of HG (tongue retraction and depression) and the SG (retraction and elevation of lateral aspect of tongue) results in an increased maximum rate of airflow and mechanical stability of the upper airway (UAW). Selective stimulation is a unique approach to nerve stimulation when implanted on the hypoglossal nerve (HGN). The neural interface  160  may also sense the neural activity of the nerve it interfaces with and may transmit that sensed activity to the core subsystem microprocessor  141 . 
       FIG. 4  shows embodiments of neural interface electrode arrays. These embodiments are exemplary only, and the arrays are not limited to the quantity or arrangement of the electrodes shown in the figure. In one embodiment, at least one electrode  161  is in contact with a nerve. In certain embodiments, the electrodes  161  may be in the shape of a linear, regular, or irregular array. In certain embodiments, the electrode  161  array may be in a form suitable for wrapping around a nerve (e.g., a helical shape or spring-like shape as shown in  FIG. 3 ). The electrodes  161  may also be arranged in a planar form to help reshape the nerve and move the axons closer to the electrodes  161 . This facilitates access to multiple nerve axons, which enables multiple modes of stimulation for enhanced UAW dilation and stability. With a planar form factor, stimulation can also be delivered in two dimensions, enabling optimal excitation of the functional branches of the nerve. Excitation happens through bi-phasic electrical stimulation of individual electrodes  161 . 
     The Internal RF Interface 
     The left portion of  FIG. 1  shows a detailed view of an embodiment of the internal RF interface  150 . The internal RF interface  150  may include one or more of a transponder  156 , internal antenna  151 , modulator  157 , demodulator  158 , clock  159 , and rectifier. The transponder  156  can be passive or active. In certain embodiments, the internal RF interface  150  can send and/or receive one or more of (1) control logic, and (2) power. In still further embodiments, the internal RF interface  150  delivers one or more of power, clock, and data to the implant core subsystem  140 . In certain embodiments the data is delivered via a full duplex data connection. In some embodiments, the internal RF interface  150  sends data (e.g., function status) of one or more electrodes  161  to a controller  205 , described below, for review by a technician or physician. 
     The internal RF interface  150  operates according to the principle of inductive coupling. In an embodiment, the present invention exploits the near-field characteristics of short wave carrier frequencies of approximately 13.56 MHz. This carrier frequency is further divided into at least one sub-carrier frequency. In certain embodiments, the present invention can use between 10 and 15 MHz. The internal RF interface  150  uses a sub carrier for communication with an external RF interface  203 , which may be located in the controller  205 . The sub-carrier frequency is obtained by the binary division of the external RF interface  203  carrier frequency. In the embodiment shown, the internal RF interface  150  is realized as part of a single silicon package  170 . The package  170  may further include a chip  145  which is a programmable receive/transmit RF chip. 
     In certain embodiments, the internal RF interface  150  also includes a passive RFID transponder  156  with a demodulator  158  and a modulator  157 . The transponder  156  uses the sub carrier to modulate a signal back to the external RF interface  203 . In certain embodiments, the transponder  156  may further have two channels, Channel A and Channel B. Channel A is for power delivery and Channel B is for data and control. The transponder  156  may employ a secure full-duplex data protocol. 
     The internal RF interface  150  further includes an inductive coupler  152 , an RF to DC converter  155 , and an internal antenna  151 . In certain embodiments, the internal antenna  151  includes a magnetic component. In such embodiments, silicon traces may be used as magnetic antennas. In other embodiments, the antenna may be a high Q coil electroplated onto a silicon substrate. A parallel resonant circuit  153  may be attached to the internal antenna  151  to improve the efficiency of the inductive coupling. The internal antenna  151  may be realized as a set of PCB traces  133  on the implant  105 . Size of the antenna traces is chosen on the basis of power requirements, operating frequency, and distance to the controller  205 . Both the internal RF interface  150  and the core subsystem microprocessor  141  are powered from an RF signal received by the internal antenna  151 . A shunt regulator  154  in the resonant circuit  153  keeps the derived voltage at a proper level. 
     Implant Component Arrangement 
     The implant  105  may be located on any suitable substrate and may be a single layer or multi-layer form.  FIG. 5  shows an implant  105  constructed as a single integrated unit, with a top layer  110  and a bottom layer  110  which may be implanted in proximity to, in contact with, or circumferentially around a nerve, e.g., the hypoglossal nerve.  FIG. 5A  is a breakout view of  FIG. 5 . 
     In certain embodiments, implant components are layered on a nerve. This alleviates the need for complex wiring and leads. In  FIGS. 5 and 5A , the top layer  110  includes a core subsystem  140 , an internal RF interface  150 , and a neural interface  160 . The top layer  110  serves as the attachment mechanism, with the implant components on the bottom layer  110 . The neural interface  160  may be surface bonded to contacts on a printed circuit board  130 . The bottom layer  110  is complementary to the top layer  110 , and serves as an attachment mechanism so that the implant  105  encompasses the HGN. Although conductive parts in contact with the HGN may be located at any suitable position on the implant  105 , in the embodiment shown in  FIGS. 5 and 5A , the bottom layer  110  has no conductive parts. 
     In the embodiment shown in  FIGS. 5 and 5A , and as described above, the core subsystem  140  is included in a silicon package  170  ( FIG. 2 ) attached to a printed circuit board (PCB)  130  on the top layer  110 . The PCB  130  has a first side  131  and a second side  132 . The silicon package  170  is placed on a first side  131  of the printed circuit board  130 . In certain embodiments the PCB  130  may be replaced with a flexible membrane substrate. In the embodiment shown, the silicon package  170  further includes the internal RF interface  150 . The neural interface  160  attaches to the second side  132  of the PCB  130 . In this embodiment, the neural interface  160  ( FIG. 6B ) further includes a plurality of neural interface electrodes  161  ( FIG. 4 ) arranged into anode and cathode pairs  162 / 163 , shown in this embodiment as an array of 10 to 16 elements. The number and arrangement of anode and cathode pairs  162 / 163  is exemplary only, and not limited to the embodiment shown. The silicon package  170  ( FIG. 2 ) connects to the anode and cathode pairs  162 / 163  via traced wires  133  printed on the PCB  130 . 
     In other embodiments, such as the one shown in  FIG. 6A , the neural interface electrode anode and cathode pairs  162 / 163  are located on the bottom layer  110  of the implant  105 . In still other embodiments, such as the one shown in  FIG. 6B , the neural interface electrode anode and cathode pairs  162 / 163  are located on both the top and the bottom layers  110 / 120 . The matrix arrangement of electrodes  161  provides multiple nerve stimulating points, and has several advantages. The matrix arrangement allows a web of nerve fascicles of the hypoglossal nerve to be accessed, enabling selective stimulation of particular areas of the nerve. In some embodiments, power is delivered to the matrix of electrodes  161  from the D/A converter  164  to capacitors  165  via a multiplexer  166 . 
     The implant  105  may further include an isolation layer  112  ( FIG. 6A ). In certain embodiments a protective coating  114  ( FIGS. 6A and 6B ) may be applied to the top and bottom layers  110 / 120  of the implant  105 . The implant  105  may further be coated with a protective coating  114  for biological implantation. Further, in certain embodiments all or a portion of the device may be encased in a biocompatible casing. In such embodiments, the casing may be a material selected from the group consisting of one or more titanium alloys, ceramic, and polyetheretherketone (PEEK). 
     The External Subsystem 
     In certain embodiments, the external subsystem  200  may include one or more of (1) a controller, (2) an external RF interface and (3) an optional power source. An embodiment of an external subsystem  200  including these elements is shown in  FIG. 7 . Typically the external subsystem  200  is located externally on or near the skin of a patient. 
     The Controller 
       FIG. 7  shows an embodiment of an external subsystem  200  with a controller  205 . The controller  205  controls and initiates implant functions. In other embodiments, the controller  205  may be part of the internal subsystem  100  instead of external subsystem  200 , and in still further embodiments, portions of the controller  205  may be in both the external and internal subsystems  200 / 100 . In certain embodiments, the controller  205  may further have one or more of a controller crypto block  201 , data storage  206 , a recording unit  207 , and a controller microprocessor  204 . In some embodiments the controller microprocessor  204  may have a micrologic CPU and memory to store protocols selective to a patient. The controller microprocessor  204  is programmable and may further include an attached non-volatile memory. The microprocessor  204  may be a single chip or part of an integrated silicon package. 
     In certain embodiments, the controller may further include includes one or more of an external RF interface having RF transmit and receive logic, a data storage that may be used to store patient protocols, an interface (e.g., a USB port), a microprocessor, an external antenna, a functionality to permit the controller to interface with a particular implant, and an optional power source. In certain embodiments, the controller electronics can be either physically or electromagnetically coupled to an antenna. The distance between the external RF interface antenna (not shown) and the implant  105  may vary with indication. In certain embodiments, distance is minimized to reduce the possibility of interference from other RF waves or frequencies. Minimizing the distance between the external antenna and the implant  105  provides a better RF coupling between the external and internal subsystems  200 / 100 , further reducing the possibility of implant activation by a foreign RF source. An encrypted link between the external and internal subsystems  200 / 100  further reduces the possibility of implant activation by foreign RF. In other embodiments, one or more of the internal antenna  151  and external antennas  209  are maintained in a fixed position. Potential design complexity associated with internal RF interface antenna  151  orientation is minimized through the ability to position the external RF interface antenna in a specific location (e.g., near the patient&#39;s ear). Even if the patient moves, the internal RF interface antenna  151  and controller  205  remain coupled. 
     In certain other embodiments, the controller  205  can also serve as (1) a data gathering and/or (2) programming interface to the implant  105 . The controller  205  has full control over the operation of the implant  105 . It can turn the implant  105  on/off, and may be paired to the implant  105  via a device specific ID, as described herein below with respect to use of the implant  105  and controller  205  of the present invention. In still further embodiments, the controller microprocessor  204  calculates stimulus information. The stimulus information is then communicated to the implant  105 . The implant  105  then provides a calculated stimulus to a nerve. In another embodiment, the controller  205  preloads the implant  105  with an algorithmic protocol for neural stimulation and then provides power to the implant  105 . 
     External RF Interface 
     In the embodiment shown in  FIG. 7 , the external subsystem  200  includes an external RF interface  203  that provides an RF signal for powering and controlling the implant  105 . The external RF interface  203  can be realized as a single chip, a plurality of chips, a printed circuit board, or even a plurality of printed circuit boards. In other embodiments, the printed circuit board can be replaced with a flexible membrane. The external RF interface  203  may include one or more of a transponder  208  (not shown), external antenna (not shown), modulator  210  (not shown), and demodulator  211  (not shown), clock  212  (not shown), and rectifier  213  (not shown) (not shown). The external RF interface transponder  208  can be passive or active. In certain embodiments, the external RF interface  203  can send and/or receive one or more of (1) control logic, and (2) power. In still further embodiments, the external RF interface  203  delivers one or more of power, clock, and data to one or more of the external subsystem controller  205  and the internal subsystem  100  via the internal RF interface  150 . In certain embodiments the data is delivered via a full duplex data connection. 
     In an embodiment, the external RF interface  203  operates at a carrier frequency of approximately 13.56 MHz. In certain embodiments, the external RF interface  203  can operate between 10 and 15 MHz. This carrier frequency is further divided into at least one sub-carrier frequency. The sub-carrier frequency is obtained by binary division of the external RF interface  203  carrier frequency. The external RF interface  203  uses the sub carrier for communication with the internal RF interface  150 . The external RF interface transponder  208  (not shown) uses the sub carrier to modulate a signal to the internal RF interface  150 . The transponder  208  (not shown) may further have two channels, Channel A and Channel B. Channel A is for power delivery and Channel B is for data and control. The transponder  208  (not shown) may employ a secure full-duplex data protocol. 
     In certain embodiments, the external RF interface  203  may further include a demodulator  211  (not shown) and a modulator  210  (not shown). In still further embodiments, the external RF interface  203  further includes an external antenna. In certain embodiments, the external antenna includes a magnetic component. In such embodiments, silicon traces may be used as magnetic antennas. The antenna may be realized as a set of PCB traces. Size of the antenna traces is chosen on the basis of power requirements, operating frequency, and distance to the internal subsystem  100 . In certain embodiments, the external antenna may transmit the power received by internal subsystem  100 . In certain other embodiments, the external antenna may be larger, and have a higher power handling capacity than the internal antenna  151 , and can be realized using other antenna embodiments known by those skilled in the art. 
     In certain embodiments, the external subsystem  200  is loosely coupled to an optional power source  215 . In one embodiment, the controller power source  215  is not co-located with the external RF interface antenna. The external power source  215  may be in one location, and the external RF interface  203  and optionally the controller  205  are in a second location and/or third location. For example, each of the power source  215 , controller  205  and external RF interface  203  can be located in difference areas. In one embodiment, the power source  215  and the controller  205  and the external RF interface  203  are each connected by one or more conductive members, e.g. a flexible cable or wire. Additionally, in certain embodiments, the controller  205  and optional power source  215  may be co-located, and the external RF interface  203  may be located elsewhere (i.e., loosely coupled to the controller  205 ). In such embodiments, the external RF interface  203  is connected to the controller  205  by a flexible cable or wire. 
     Since the power source  215  may be separately located from the controller  205  and/or external RF interface antenna, a larger power source  215  can be externally located but positioned away from the nerve that requires stimulation. Further, to reduce wasted power, a larger external RF interface antenna can be used. This provides the advantage of less discomfort to a user and therefore enhances patient compliance. 
     Such embodiments can also provide power to 2, 3, 4, 5 or more loosely coupled external RF interfaces  203 . Thus, each external RF interface  203  can be positioned at or near the site of an implant  105  without the need for a co-located power source  215 . In certain embodiments, each external RF interface  203  draws power from a single power source  215 , and thus a single power source  215  powers a plurality of implants  105 . Of course, the amount of power provided to each implant  105  will vary by indication and distance between the external RF interface  203  and the implant  105 . The greater the distance between the external RF interface  203  and the implant  105 , the greater the power level required. For example, a lower power is generally required to stimulate peripheral nerves, which are closer to the surface of the skin. As apparent to one of skill in the art, the power received at the implant  105  must be high enough to produce the desired nerve stimulus, but low enough to avoid damaging the nerve or surrounding tissue. 
     The external RF interface  203  may further include a programmable receive/transmit RF chip, and may interface with the controller crypto unit  201  for secure and one-to-one communication with its associated implant  105 . The external RF interface  203  includes a parameterized control algorithm, wherein the parameterized control algorithm compares the sensed information to a reference data set in real time. The algorithm may be included in the controller microprocessor  204 . Depending upon the patient&#39;s size and severity of disease state, the algorithm will vary a number of parameters which include frequency, amplitude of the signal, number of electrodes involved, etc. 
     Interaction With Outside Information Sources 
     The external subsystem controller  205  may also interface with a computer. In some embodiments, the controller interface  202  is a built-in data port (e.g., a USB port). Via the controller interface  202  a computer may tune (and re-tune) the implant system, and transfer historical data recorded by the implant  105 . The controller  205  may obtain and update its software from the computer, and may upload and download neural interface data to and from the computer. The software may be included in the controller microprocessor  204  and associated memory. The software allows a user to interface with the controller  205 , and stores the patient&#39;s protocol program. 
     External Subsystem Design 
     The external subsystem  200  can be of regular or irregular shape.  FIG. 8  shows two embodiments of an external subsystem controller  205 , one with the controller  205  included with an earpiece much like a Bluetooth earpiece, and one with the controller  205  included with a patch. In the embodiments shown, potential design complexity associated with internal RF antenna  151  orientation is minimized through the single and fixed position of the controller  205 . The patient may move and turn without disrupting the coupling between the controller  205  and the internal antenna  151 . In the embodiment with the controller  205  in an earpiece, a flexible receive/transmit tip in the earpiece aligns the controller external RF interface antenna with the implant  105 . In the embodiment with the controller  205  in a patch, the patch is aligned with the implant  105  and placed skin. The patch may include one or more of the controller  205 , a replaceable adhesive layer, power and RFID coupling indication LED, and a thin layer rechargeable battery. Still further embodiments include incorporation of the external subsystem  200  into a watch-like device for, e.g., the treatment of arthritic pain, or in a belt. Yet another range of variations are flexible antennas and the controller RF chip woven into clothing or an elastic cuff, attached to controller electronics and remotely powered. Controller  205  designs may be indication specific, and can vary widely. The controller  205  embodiments in  FIG. 8  are exemplary only, and not limited to those shown. 
     Communication with the Implant as a Function of Design 
     The distance between this contact area and the actual implant  100  on a nerve is 1 to 10 cm, typically 3 cm, through human flesh. This distance, along with the controller crypto unit  201  and the core subsystem crypto unit  142  in the implant  100 , reduces potential interference from other RF signals. 
     Implant and Controller Positioning 
     Prior to implantation of the present invention for the treatment of sleep apnea, patients are diagnosed in a sleep lab, and an implant  105  is prescribed for their specifically diagnosed condition. Once diagnosis is complete, the implant  105  is surgically implanted in the patient&#39;s body, typically on or in the vicinity of a nerve. In certain embodiments, the implant  105  is implanted on the HGN. In such embodiments, the implant  105  may be implanted below the ear unilaterally at the sub-mandibular triangle, encasing the hypoglossal nerve. 
     Stimulation of the HGN can act to maintain nerve activity. Hence in certain embodiments, the present invention can maintain muscular tone (e.g., in the tongue, thereby preventing apnea). Therefore, in certain embodiments, controller  205 , described in more detail above, activates implant  105  to stimulate HGN activity to ameliorate the negative physiological impact associated with insufficient tone muscles caused by, e.g., insufficient HGN activity. 
     Once implanted, the implant  105  is used to stimulate the nerve. In embodiments where the device is implanted in a manner to stimulate the HGN, the implant  105  delivers tone to the tongue. Maintaining tongue muscle tone stops the tongue from falling back and obstructing the upper airway. The stimulation may be provided continuously during sleep hours, or upon preprogrammed patient-specific intervals. The implant  105  may also sense and record neural activity. 
     Implant and Controller Security 
     In certain embodiments, the controller  205  identifies the patient&#39;s unique ID tag, communicates with and sends signals to the implant  105 . In certain embodiments, a controller crypto unit  201  may be installed to ensure that communication between the controller  205  and the implant  105  is secure and one-to-one. The controller crypto unit  201  may include the implant&#39;s unique ID tag. 
     In particular, the implant  105  may have a unique ID tag, which the controller  205  can be programmed to recognize. A controller microprocessor  204  confirms the identity of the implant  105  associated with the controller  205 , thereby allowing setting of the patient&#39;s specific protocol. The setting may be accomplished using a computer interfaced with the controller  205  through an interface  202  on the controller  205 . 
     More particularly, once the controller crypto unit  201  establishes a link with the core subsystem crypto unit  142 , the controller  205  communicates a stimulation scenario to the core subsystem microprocessor  141 . The controller  205  initiates a stimulation cycle by making a request to the core subsystem  140  by sending an encoded RF waveform including control data via the external RF interface  203 . The core subsystem  140  selects a trained waveform from memory and transmits the stimulation waveform to the core subsystem microprocessor  141 . Once the core subsystem microprocessor  141  receives the waveform, the core subsystem  140  generates a stimulating signal for distribution to the neural interface  160 . 
     Interaction with the Implant In certain embodiments, the controller  205  prevents self-activation or autonomous operation by the implant  105  by handshaking. Handshaking occurs during each communications cycle and ensures that security is maintained. This prevents other devices operating in the same frequency range from compromising operation of the implant  105 . Implant stimulus will not commence unless an encrypted connection is established between the external RF interface  203  and the implant  105 . This serves as an anti-tampering mechanism by providing the implant  105  with a unique ID tag. The external controller  205  is matched, either at the point manufacture or by a physician, to a particular ID tag of the implant  105 , typically located in an EPROM of the implant  105 . In certain embodiments, the EPROM may be included in the core subsystem microprocessor  141 . In other embodiments, the EPROM may be included in the controller microprocessor  204 . This prevents alien RF interference from ‘triggering’ activation of the implant  105 . While arbitrary RF sources may provide power to the implant  105 , the uniquely matched controller  205  establishes an encrypted connection before directing the implant  105  to commence stimulus, thereby serving as a security mechanism. 
     System Programming 
     Desired system programming is determined by measuring a patient&#39;s tongue activity against predetermined stimulation protocols. The effectiveness of the neural interface  160  stimulation protocols are measured until a desired tongue stimulation level is achieved. Once a desired tongue stimulation level is achieved, those protocols are programmed into the controller  205 . Stimulation may be programmed for delivery in an open loop or closed loop at a suitable frequency. In certain embodiments, a stimulation frequency of about 10-40 Hz is used. Stimulation may also be delivered in pulses, with pulse widths about 100 to 300 microseconds, more typically 200 microseconds. Although any suitable pulse width can be used, preferred pulses are at a width that simultaneously prevent nerve damage and reduce or eliminate corrosion of neural interface electrodes. After the controller  205  is programmed, the patient activates the controller  205  at bed time or at desired intervals. 
     In certain embodiments, controller  205  can also determine when the patient is asleep, and stimulate the HGN based on that determination. In order to determine when the patient is asleep, controller  205  can include one or more sensors that generate signals as a function of the activity and/or posture of the patient. In such embodiments, controller  205  determines when the patient is asleep based on the signal. Controller  205  can also have an acoustic sensor, to indicate when snoring starts, and can determine whether the patient is asleep based on the presence of snoring. In other embodiments the patient may enter an input into the controller  205  telling it to commence treatment. However, as noted above, controller  205  can be activated by a user and then function in a manner such that the implant is continuously active until the patient awakens and manually deactivates the controller by pressing a button on the controller  205  or by moving the controller  205  out of range of the implant. 
     This electrical stimulation provides a signal to the HGN and starts the treatment of the airway obstruction. Upon completion of one cycle, the duration of which is determined in the tuning phase of the implantation procedure, described above, the core subsystem  140  can report completion back to the controller  205  via RF communication, and optionally goes to an idle state until receiving another set of instructions. 
     As described above, in certain embodiments, the implant  105  is externally powered by near field RF waves, the RF waves are inductively converted to DC power, which powers the implant  105  and delivers electrical signals to selected elements of the neural interface  160 . The implant uses between 0.1 to about 1 milliamps, preferably averaging about 0.5 milliamps of current and about 10 to 30 microwatts of power. 
     In some embodiments, the near field RF waves are emitted from the controller  205 . In certain embodiments, controller  205  can be powered by an optional power source  215 , e.g., a battery, AC to DC converter, or other power source known to those skilled in the art. 
     Other embodiments of the apparatus and methods described can be used in the present invention. Various alternatives, substitutions and modifications for each of the embodiments and methods of the invention may be made without departing from the scope thereof, which is defined by the following claims. All references, patents and patent applications cited in this application are herein incorporated by reference in their entirety.
An implantable neurostimulator for treating obstructive sleep apnea comprises an implant configured to at least partially surround a Hypoglossal nerve (HGN) and a plurality of electrodes each attached to the implant. Each electrode configured to contact the HGN and electrically stimulate one or more regions or groups of the HGN.