Abstract:
A method and system for neuromodulating vagus nerve(s) to provide therapy for neurological and neuropsychiatric disorders comprises implantable and external components. The pulsed electrical stimulation to vagus nerve(s) is used for disorders such as epilepsy, depression, anxiety disorders, neurogenic pain, compulsive eating disorders, obesity, dementia including Alzheimer&#39;s disease, and migraines. The pulsed electrical stimulation to vagus nerve(s) may be provided using one of the following stimulation systems, such as: a) an implanted stimulus-receiver with an external stimulator; b) an implanted stimulus-receiver comprising a high value capacitor for storing charge, used in conjunction with an external stimulator; c) a programmer-less implantable pulse generator (IPG) which is operable with a magnet; d) a programmable implantable pulse generator; e) a combination implantable device comprising both a stimulus-receiver and a programmable IPG; and f) an IPG comprising a rechargeable battery.

Description:
This Application is a continuation-in-part of application Ser. No. 10/196,533 filed Jul. 16, 2002, which is a continuation-in-part of Ser. No. 10/142,298 filed on May 9, 2002, entitled “METHOD AND SYSTEM FOR MODULATING THE VAGUS NERVE (10 th  CRANIAL NERVE) USING MODULATED ELECTRICAL PULSES WITH AN INDUCTIVELY COUPLED STIMULATION SYSTEM”. The invention claimed herein was made on the behalf of the parties to a joint research agreement between Birinder R. Boveja and Angela Widhany, dated May 10, 2001 and was a result of activities undertaken within the scope of the joint research agreement. 

   FIELD OF INVENTION 
   The present invention relates to neuromodulation, more specifically neuromodulation of vagus nerve with pulsed electrical stimulation, to provide therapy for neurological and neuropsychiatric disorders. 
   BACKGROUND 
   The 10 th  cranial nerve or the vagus nerve plays a role in mediating afferent information from visceral organs to the brain. The vagus nerve arises directly from the brain, but unlike the other cranial nerves extends well beyond the head. At its farthest extension it reaches the lower parts of the intestines. The vagus nerve provides an easily accessible, peripheral route to modulate central nervous system (CNS) function. Observations on the profound effect of electrical stimulation of the vagus nerve on central nervous system (CNS) activity extends back to the 1930&#39;s. 
   The present invention is primarily directed to a method and system for selective electrical stimulation or neuromodulation of vagus nerve, for providing adjunct therapy for neurological and neuropsychiatric disorders such as epilepsy, depression, involuntary movement disorders including Parkinson&#39;s disease, anxiety disorders, neurogenic/psycogenic pain, obsessive compulsive disorders, migraines, obesity, dementia including Alzheimer&#39;s disease, and the like. 
   In the human body there are two vagal nerves (VN), the right VN and the left VN. Each vagus nerve is encased in the carotid sheath along with the carotid artery and jugular vein. The innervation of the right and left vagus nerves is different. The innervation of the right vagus nerve is such that stimulating it results in profound bradycardia (slowing of the heart rate). The left vagus nerve has some innervation to the heart, but mostly innervates the visceral organs such as the gastrointestinal tract. It is known that stimulation of the left vagus nerve does not cause substantial slowing of the heart rate or cause any other significant deleterious side effects. 
   Background of Neuromodulation 
   One of the fundamental features of the nervous system is its ability to generate and conduct electrical impulses. Most nerves in the human body are composed of thousands of fibers of different sizes. This is shown schematically in  FIG. 1 . The different sizes of nerve fibers, which carry signals to and from the brain, are designated by groups A, B, and C. The vagus nerve, for example, may have approximately 100,000 fibers of the three different types, each carrying signals. Each axon or fiber of that nerve conducts only in one direction, in normal circumstances. In the vagus nerve sensory fibers outnumber parasympathetic fibers four to one. 
   In a cross section of peripheral nerve it is seen that the diameter of individual fibers vary substantially, as is also shown schematically in  FIG. 2 . The largest nerve fibers are approximately 20 μm in diameter and are heavily myelinated (i.e., have a myelin sheath, constituting a substance largely composed of fat), whereas the smallest nerve fibers are less than 1 μm in diameter and are unmyelinated. 
   The diameters of group A and group B fibers include the thickness of the myelin sheaths. Group A is further subdivided into alpha, beta, gamma, and delta fibers in decreasing order of size. There is some overlapping of the diameters of the A, B, and C groups because physiological properties, especially in the form of the action potential, are taken into consideration when defining the groups. The smallest fibers (group C) are unmyelinated and have the slowest conduction rate, whereas the myelinated fibers of group B and group A exhibit rates of conduction that progressively increase with diameter. 
   Nerve cells have membranes that are composed of lipids and proteins (shown schematically in  FIGS. 3A and 3B ), and have unique properties of excitability such that an adequate disturbance of the cell&#39;s resting potential can trigger a sudden change in the membrane conductance. Under resting conditions, the inside of the nerve cell is approximately −90 mV relative to the outside. The electrical signaling capabilities of neurons are based on ionic concentration gradients between the intracellular and extracellular compartments. The cell membrane is a complex of a bilayer of lipid molecules with an assortment of protein molecules embedded in it ( FIG. 3A ), separating these two compartments. Electrical balance is provided by concentration gradients which are maintained by a combination of selective permeability characteristics and active pumping mechanism. 
   The lipid component of the membrane is a double sheet of phospholipids, elongated molecules with polar groups at one end and the fatty acid chains at the other. The ions that carry the currents used for neuronal signaling are among these water-soluble substances, so the lipid bilayer is also an insulator, across which membrane potentials develop. In biophysical terms, the lipid bilayer is not permeable to ions. In electrical terms, it functions as a capacitor, able to store charges of opposite sign that are attracted to each other but unable to cross the membrane. Embedded in the lipid bilayer is a large assortment of proteins. These are proteins that regulate the passage of ions into or out of the cell. Certain membrane-spanning proteins allow selected ions to flow down electrical or concentration gradients or by pumping them across. 
   These membrane-spanning proteins consist of several subunits surrounding a central aqueous pore (shown in  FIG. 3B ). Ions whose size and charge “fit” the pore can diffuse through it, allowing these proteins to serve as ion channels. Hence, unlike the lipid bilayer, ion channels have an appreciable permeability (or conductance) to at least some ions. In electrical terms, they function as resistors, allowing a predicable amount of current flow in response to a voltage across them. 
   A nerve cell can be excited by increasing the electrical charge within the neuron, thus increasing the membrane potential inside the nerve with respect to the surrounding extracellular fluid. As shown in  FIG. 4 , stimuli  4  and  5  are subthreshold, and do not induce a response. Stimulus  6  exceeds a threshold value and induces an action potential (AP) which will be propagated. The threshold stimulus intensity is defined as that value at which the net inward current (which is largely determined by Sodium ions) is just greater than the net outward current (which is largely carried by Potassium ions), and is typically around −55 mV inside the nerve cell relative to the outside (critical firing threshold). If however, the threshold is not reached, the graded depolarization will not generate an action potential and the signal will not be propagated along the axon. This fundamental feature of the nervous system i.e., its ability to generate and conduct electrical impulses, can take the form of action potentials, which are defined as a single electrical impulse passing down an axon. This action potential (nerve impulse or spike) is an “all or nothing” phenomenon, that is to say once the threshold stimulus intensity is reached, an action potential will be generated. 
     FIG. 5A  illustrates a segment of the surface of the membrane of an excitable cell. Metabolic activity maintains ionic gradients across the membrane, resulting in a high concentration of potassium (K + ) ions inside the cell and a high concentration of sodium (Na + ) ions in the extracellular environment. The net result of the ionic gradient is a transmembrane potential that is largely dependent on the K +  gradient. 
   Typically in nerve cells, the resting membrane potential (RMP) is slightly less than 90 mV, with the outside being positive with respect to inside. 
   To stimulate an excitable cell, it is only necessary to reduce the transmembrane potential by a critical amount. When the membrane potential is reduced by an amount ΔV, reaching the critical or threshold potential (TP); Which is shown in  FIG. 5B . When the threshold potential (TP) is reached, a regenerative process takes place: sodium ions enter the cell, potassium ions exit the cell, and the transmembrane potential falls to zero (depolarizes), reverses slightly, and then recovers or repolarizes to the resting membrane potential (RMP). 
   For a stimulus to be effective in producing an excitation, it must have an abrupt onset, be intense enough, and last long enough. These facts can be drawn together by considering the delivery of a suddenly rising cathodal constant-current stimulus of duration d to the cell membrane as shown in  FIG. 5B . 
   Cell membranes can be reasonably well represented by a capacitance C, shunted by a resistance R as shown by a simplified electrical model in diagram  5 C, and shown in a more realistic electrical model in  FIG. 6 , where neuronal process is divided into unit lengths, which is represented in an electrical equivalent circuit. Each unit length of the process is a circuit with its own membrane resistance (r m ), membrane capacitance (c m ), and axonal resistance (r a ). 
   When the stimulation pulse is strong enough, an action potential will be generated and propagated. As shown in  FIG. 7 , the action potential is traveling from right to left. Immediately after the spike of the action potential there is a refractory period when the neuron is either unexcitable (absolute refractory period) or only activated to sub-maximal responses by supra-threshold stimuli (relative refractory period). The absolute refractory period occurs at the time of maximal Sodium channel inactivation while the relative refractory period occurs at a later time when most of the Na +  channels have returned to their resting state by the voltage activated K +  current. The refractory period has two important implications for action potential generation and conduction. First, action potentials can be conducted only in one direction, away from the site of its generation, and secondly, they can be generated only up to certain limiting frequencies. 
   A single electrical impulse passing down an axon is shown schematically in  FIG. 8 . The top portion of the figure (A) shows conduction over mylinated axon (fiber) and the bottom portion (B) shows conduction over nonmylinated axon (fiber). These electrical signals will travel along the nerve fibers. 
   The information in the nervous system is coded by frequency of firing rather than the size of the action potential. This is shown schematically in  FIG. 9 . The bottom portion of the figure shows a train of action potentials. 
   In terms of electrical conduction, myelinated fibers conduct faster, are typically larger, have very low stimulation thresholds, and exhibit a particular strength-duration curve or respond to a specific pulse width versus amplitude for stimulation, compared to unmyelinated fibers. The A and B fibers can be stimulated with relatively narrow pulse widths, from 50 to 200 microseconds (μs), for example. The A fiber conducts slightly faster than the B fiber and has a slightly lower threshold. The C fibers are very small, conduct electrical signals very slowly, and have high stimulation thresholds typically requiring a wider pulse width (300–1,000 μs) and a higher amplitude for activation. Because of their very slow conduction, C fibers would not be highly responsive to rapid stimulation. Selective stimulation of only A and B fibers is readily accomplished. The requirement of a larger and wider pulse to stimulate the C fibers, however, makes selective stimulation of only C fibers, to the exclusion of the A and B fibers, virtually unachievable inasmuch as the large signal will tend to activate the A and B fibers to some extent as well. 
   As shown in  FIG. 10A , when the distal part of a nerve is electrically stimulated, a compound action potential is recorded by an electrode located more proximally. A compound action potential contains several peaks or waves of activity that represent the summated response of multiple fibers having similar conduction velocities. The waves in a compound action potential represent different types of nerve fibers that are classified into corresponding functional categories as shown in the Table one below, 
   
     
       
             
             
             
             
             
           
         
             
                 
               TABLE 1 
             
             
                 
                 
             
             
                 
                 
               Conduction 
               Fiber 
                 
             
             
                 
               Fiber 
               Velocity 
               Diameter 
             
             
                 
               Type 
               (m/sec) 
               (μm) 
               Myelination 
             
             
                 
                 
             
           
           
             
                 
               A Fibers 
                 
                 
                 
             
             
                 
               Alpha 
                70–120 
               12–20 
               Yes 
             
             
                 
               Beta 
               40–70 
                5–12 
               Yes 
             
             
                 
               Gamma 
               10–50 
               3–6 
               Yes 
             
             
                 
               Delta 
                6–30 
               2–5 
               Yes 
             
             
                 
               B Fibers 
                5–15 
               &lt;3 
               Yes 
             
             
                 
               C Fibers 
               0.5–2.0 
               0.4–1.2 
               No 
             
             
                 
                 
             
           
        
       
     
   
     FIG. 10B  further clarifies the differences in action potential conduction velocities between the Aδ-fibers and the C-fibers. For many of the application of current patent application, it is the slow conduction C-fibers that are stimulated by the pulse generator. 
   The modulation of nerve in the periphery, as done by the body, in response to different types of pain is illustrated schematically in  FIGS. 11 and 12 . As shown schematically in  FIG. 11 , the electrical impulses in response to acute pain sensations are transmitted to brain through peripheral nerve and the spinal cord. The first-order peripheral neurons at the point of injury transmit a signal along A-type nerve fibers to the dorsal horns of the spinal cord. Here the second-order neurons take over, transfer the signal to the other side of the spinal cord, and pass it through the spinothalamic tracts to thalamus of the brain. As shown in  FIG. 12 , duller and more persistent pain travel by another-slower route using unmyelinated C-fibers. This route made up from a chain of interconnected neurons, which run up the spinal cord to connect with the brainstem, the thalamus and finally the cerebral cortex. The autonomic nervous system also senses pain and transmits signals to the brain using a similar route to that for dull pain. 
   Vagus nerve stimulation, as performed by the system and method of the current patent application, is a means of directly affecting central function.  FIG. 13  shows cranial nerves have both afferent pathway  19  (inward conducting nerve fibers which convey impulses toward the brain) and efferent pathway  21  (outward conducting nerve fibers which convey impulses to an effector). Vagus nerve is composed of 80% afferent sensory fibers carrying information to the brain from the head, neck, thorax, and abdomen. The sensory afferent cell bodies of the vagus reside in the nodose ganglion and relay information to the nucleus tractus solitarius (NTS). 
   The vagus nerve is composed of somatic and visceral afferents and efferents. Usually, nerve stimulation activates signals in both directions (bi-directionally). It is possible however, through the use of special electrodes and waveforms, to selectively stimulate a nerve in one direction only (unidirectionally). The vast majority of vagus nerve fibers are C fibers, and a majority are visceral afferents having cell bodies lying in masses or ganglia in the skull. 
   In considering the anatomy, the vagus nerve spans from the brain stem all the way to the splenic flexure of the colon. Not only is the vagus the parasympathetic nerve to the thoracic and abdominal viscera, it also the largest visceral sensory (afferent) nerve. Sensory fibers outnumber parasympathetic fibers four to one. In the medulla, the vagal fibers are connected to the nucleus of the tractus solitarius (viceral sensory), and three other nuclei. The central projections terminate largely in the nucleus of the solitary tract, which sends fibers to various regions of the brain (e.g., the thalamus, hypothalamus and amygdala). 
   As shown in  FIG. 14 , the vagus nerve emerges from the medulla of the brain stem dorsal to the olive as eight to ten rootlets. These rootlets converge into a flat cord that exits the skull through the jugular foramen. Exiting the Jugular foramen, the vagus nerve enlarges into a second swelling, the inferior ganglion. 
   In the neck, the vagus lies in a groove between the internal jugular vein and the internal carotid artery. It descends vertically within the carotid sheath, giving off branches to the pharynx, larynx, and constrictor muscles. From the root of the neck downward, the vagus nerve takes a different path on each side of the body to reach the cardiac, pulmonary, and esophageal plexus (consisting of both sympathetic and parasympathetic axons). From the esophageal plexus, right and left gastric nerves arise to supply the abdominal viscera as far caudal as the splenic flexure. 
   In the body, the vagus nerve regulates viscera, swallowing, speech, and taste. It has sensory, motor, and parasympathetic components. Table two below outlines the innervation and function of these components. 
   
     
       
             
           
             
             
             
           
         
             
               TABLE 2 
             
           
           
             
                 
             
             
               Vagus Nerve Components 
             
           
        
         
             
               Component fibers 
               Structures innervated 
               Functions 
             
             
                 
             
             
               SENSORY 
               Pharynx. larynx, 
               General sensation 
             
             
                 
               esophagus, external ear 
             
             
                 
               Aortic bodies, aortic arch 
               Chemo- and baroreception 
             
             
                 
               Thoracic and abdominal 
             
             
                 
               viscera 
             
             
               MOTOR 
               Soft palate, pharynx, 
               Speech, swallowing 
             
             
                 
               larynx, upper esophagus 
             
             
               PARA- 
               Thoracic and abdominal 
               Control of cardiovascular 
             
             
               SYMPATHETIC 
               viscera 
               system, respiratory and 
             
             
                 
                 
               gastrointestinal tracts 
             
             
                 
             
           
        
       
     
   
   On the Afferent side, visceral sensation is carried in the visceral sensory component of the vagus nerve. As shown in  FIGS. 15A and 15B , visceral sensory fibers from plexus around the abdominal viscera converge and join with the right and left gastric nerves of the vagus. These nerves pass upward through the esophageal hiatus (opening) of the diaphragm to merge with the plexus of nerves around the esophagus. Sensory fibers from plexus around the heart and lungs also converge with the esophageal plexus and continue up through the thorax in the right and left vagus nerves. As shown in  FIG. 15B , the central process of the nerve cell bodies in the inferior vagal ganglion enter the medulla and descend in the tractus solitarius to enter the caudal part of the nucleus of the tractus solitarius. From the nucleus, bilateral connections important in the reflex control of cardiovascular, respiratory, and gastrointestinal functions are made with several areas of the reticular formation and the hypothalamus. 
   The afferent fibers project primarily to the nucleus of the solitary tract (shown schematically in  FIGS. 16 and 17 ) which extends throughout the length of the medulla oblongata. A small number of fibers pass directly to the spinal trigeminal nucleus and the reticular formation. As shown in  FIG. 16 , the nucleus of the solitary tract has widespread projections to cerebral cortex, basal forebrain, thalamus, hypothalamus, amygdala, hippocampus, dorsal raphe, and cerebellum. Because of the widespread projections of the Nucleus of the Solitary Tract, neuromodulation of the vagal afferent nerve fibers produce alleviation of symptoms of the neurological and neuropsychiatric disorders covered in this patent application, such as epilepsy, depression, involuntary movement disorders including Parkinson&#39;s disease, anxiety disorders, neurogenic pain, psycogenic pain, obsessive compulsive disorders, migraines, obesity, dementia including Alzheimer&#39;s disease, and the like. 
   PRIOR ART 
   U.S. Pat. Nos. 4,702,254, 4,867,164 and 5,025,807 (Zabara) generally disclose animal research and experimentation related to epilepsy and the like. Applicant&#39;s method of neuromodulation is significantly different than that disclosed in Zabara &#39;254, ‘164’ and &#39;807 patents. 
   U.S. Pat. No. 3,796,221 (Hagfors) is directed to controlling the amplitude, duration and frequency of electrical stimulation applied from an externally located transmitter to an implanted receiver by inductively coupling. Electrical circuitry is schematically illustrated for compensating for the variability in the amplitude of the electrical signal available to the receiver because of the shifting of the relative positions of the transmitter-receiver pair. By highlighting the difficulty of delivering consistent pulses, this patent points away from applications such as the current application, where consistent therapy needs to be continuously sustained over a prolonged period of time. The methodology disclosed is focused on circuitry within the receiver, which would not be sufficient when the transmitting coil and receiving coil assume significantly different orientation, which is likely in the current application. 
   U.S. Pat. No. 5,299,569 (Wernicke et al.) is directed to the use of implantable pulse generator technology for treating and controlling neuropsychiatric disorders including schizophrenia, depression, and borderline personality disorder. 
   U.S. Pat. No. 6,205,359 B1 (Boveja) and U.S. Pat. No. 6,356,788 B2 (Boveja) are directed to adjunct therapy for neurological and neuropsychiatric disorders using an implanted lead-receiver and an external stimulator. 
   U.S. Pat. No. 5,807,397 (Barreras) is directed to an implantable stimulator with replenishable, high value capacitive power source. 
   U.S. Pat. No. 5,193,539 (Schulman, et al) is generally directed to an addressable, implantable microstimulator that is of size and shape which is capable of being implanted by expulsion through a hypodermic needle. In the Schulman patent, up to 256 microstimulators may be implanted within a muscle and they can be used to stimulate in any order as each one is addressable, thereby providing therapy for muscle paralysis. 
   U.S. Pat. No. 5,405,367 (Schulman, et al) is generally directed to the structure and method of manufacture of an implantable microstimulator. 
   U.S. Pat. No. 6,622,041 B2 (Terry, Jr. et al.) is directed to treatment of congestive heart failure and autonomic cardiovascular drive disorders using implantable neurostimulator. 
   SUMMARY OF THE INVENTION 
   The method and system of the current invention provides afferent neuromodulation therapy using pulsed electrical stimulation to a cranial nerve such as a vagus nerve(s). The selective stimulation is to provide therapy for at least one of epilepsy, depression, anxiety disorders, neurogenic pain, compulsive eating disorders, obesity, dementia including Alzheimer&#39;s disease, and migraines. The method and system comprises both implantable and external components. The power source may also be external or implanted in the body. The system to provide selective stimulation may be selected from a group consisting of: 
   a) an implanted stimulus-receiver with an external stimulator; 
   b) an implanted stimulus-receiver comprising a high value capacitor for storing charge, used in conjunction with an external stimulator; 
   c) a programmer-less implantable pulse generator (IPG) which is operable with a magnet; 
   d) a programmable implantable pulse generator (IPG); 
   e) a combination implantable device comprising both a stimulus-receiver and a programmable IPG; and 
   f) an IPG comprising a rechargeable battery. 
   In one aspect of the invention, the selective stimulation to a vagus nerve(s) may be anywhere along the length of the nerve, such as at the cervical level or at a level near the diaphram. 
   In another aspect of the invention, the stimulation may be unilateral or bilateral. 
   In another aspect of the invention, the external components such as the external stimulator or programmer comprise telemetry means adapted to be networked, for remote interrogation or remote programming of the device. 
   In another aspect of the invention, the pulse generator may be implanted in the body. 
   In another aspect of the invention, the implanted pulse generator is adapted to be re-chargable via an external power source. 
   In another aspect of the invention, the implanted lead body may be made of a material selected from the group consisting of polyurethane, silicone, and silicone with polytetrafluoroethylene. 
   In another aspect of the invention, the implanted lead comprises at least one electrode selected from the group consisting of platinum, platinum/iridium alloy, platinum/iridium alloy coated with titanium nitride, and carbon. 
   In yet another aspect of the invention, the implanted lead comprises at least one electrode selected from the group consisting of spiral electrodes, cuff electrodes, steroid eluting electrodes, wrap-around electrodes, and hydrogel electrodes. 
   Various other features, objects and advantages of the invention will be made apparent from the following description taken together with the drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For the purpose of illustrating the invention, there are shown in accompanying drawing forms which are presently preferred, it being understood that the invention is not intended to be limited to the precise arrangement and instrumentalities shown. 
       FIG. 1  is a diagram of the structure of a nerve. 
       FIG. 2  is a diagram showing different types of nerve fibers. 
       FIGS. 3A and 3B  are schematic illustrations of the biochemical makeup of nerve cell membrane. 
       FIG. 4  is a figure demonstrating subthreshold and suprathreshold stimuli. 
       FIGS. 5A ,  5 B,  5 C are schematic illustrations of the electrical properties of nerve cell membrane. 
       FIG. 6  is a schematic illustration of electrical circuit model of nerve cell membrane. 
       FIG. 7  is an illustration of propagation of action potential in nerve cell membrane. 
       FIG. 8  is an illustration showing propagation of action potential along a myelinated axon and non-myelinated axon. 
       FIG. 9  is an illustration showing a train of action potentials. 
       FIG. 10A  is a diagram showing recordings of compound action potentials. 
       FIG. 10B  is a schematic diagram showing conduction of first pain and second pain. 
       FIG. 11  is a schematic illustration showing mild stimulation being carried over the large diameter A-fibers. 
       FIG. 12  is a schematic illustration showing painful stimulation being carried over small diameter C-fibers 
       FIG. 13  is a schematic diagram of brain showing afferent and efferent pathways. 
       FIG. 14  is a schematic diagram showing the vagus nerve at the level of the nucleus of the solitary tract. 
       FIG. 15A  is a schematic diagram showing the thoracic and visceral innervations of the vagal nerves. 
       FIG. 15B  is a schematic diagram of the medullary section of the brain. 
       FIG. 16  is a simplified block diagram illustrating the connections of solitary tract nucleus to other centers of the brain. 
       FIG. 17  is a schematic diagram of brain showing the relationship of the solitary tract nucleus to other centers of the brain. 
       FIG. 18  is a simplified block diagram depicting supplying amplitude and pulse width modulated electromagnetic pulses to an implanted coil. 
       FIG. 19  depicts a customized garment for placing an external coil to be in close proximity to an implanted coil. 
       FIG. 20  is a diagram showing the implanted lead-receiver in contact with the vagus nerve at the distal end. 
       FIG. 21  is a schematic of the passive circuitry in the implanted lead-receiver. 
       FIG. 22A  is a schematic of an alternative embodiment of the implanted lead-receiver. 
       FIG. 22B  is another alternative embodiment of the implanted lead-receiver. 
       FIG. 23  shows coupling of the external stimulator and the implanted stimulus-receiver. 
       FIG. 24  is a top-level block diagram of the external stimulator and proximity sensing mechanism. 
       FIG. 25  is a diagram showing the proximity sensor circuitry. 
       FIG. 26A  shows the pulse train to be transmitted to the vagus nerve. 
       FIG. 26B  shows the ramp-up and ramp-down characteristic of the pulse train. 
       FIG. 27  is a schematic diagram of the implantable lead. 
       FIG. 28A  is diagram depicting stimulating electrode-tissue interface. 
       FIG. 28B  is diagram depicting an electrical model of the electrode-tissue interface. 
       FIG. 29  is a schematic diagram showing the implantable lead and one form of stimulus-receiver. 
       FIG. 30  is a schematic block diagram showing a system for neuromodulation of the vagus nerve, with an implanted component which is both RF coupled and contains a capacitor power source. 
       FIG. 31  is a simplified block diagram showing control of the implantable neurostimulator with a magnet. 
       FIG. 32  is a schematic diagram showing implementation of a multi-state converter. 
       FIG. 33  is a schematic diagram depicting digital circuitry for state machine. 
       FIG. 34  is a simplified block diagram of the implantable pulse generator. 
       FIG. 35  is a functional block diagram of a microprocessor-based implantable pulse generator. 
       FIG. 36  shows details of implanted pulse generator. 
       FIGS. 37A and 37B  shows details of digital components of the implantable circuitry. 
       FIG. 38A  shows a schematic diagram of the register file, timers and ROM/RAM. 
       FIG. 38B  shows datapath and control of custom-designed microprocessor based pulse generator. 
       FIG. 39  is a block diagram for generation of a pre-determined stimulation pulse. 
       FIG. 40  is a simplified schematic for delivering stimulation pulses. 
       FIG. 41  is a circuit diagram of a voltage doubler. 
       FIG. 42  is a diagram depicting ramping-up of a pulse train. 
       FIG. 43A  depicts an implantable system with tripolar lead for selective unidirectional blocking of vagus nerve stimulation 
       FIG. 43B  depicts selective efferent blocking in the large diameter A and B fibers. 
       FIG. 44A  depicts unilateral stimulation of vagus nerve at near the diaphram level. 
       FIG. 44B  depicts bilateral stimulation of vagus nerves with one stimulator, near the diaphramatic level. 
       FIG. 44C  depicts bilateral stimulation with two stimulators, near the diaphramatic level. 
       FIGS. 45A and 45B  are diagrams showing communication of programmer with the implanted stimulator. 
       FIGS. 46A and 46B  show diagrammatically encoding and decoding of programming pulses. 
       FIG. 47  is a simplified overall block diagram of implanted pulse generator (IPG) programmer. 
       FIG. 48  shows a programmer head positioning circuit. 
       FIG. 49  depicts typical encoding and modulation of programming messages. 
       FIG. 50  shows decoding one bit of the signal from  FIG. 48 . 
       FIG. 51  shows a diagram of receiving and decoding circuitry for programming data. 
       FIG. 52  shows a diagram of receiving and decoding circuitry for telemetry data. 
       FIG. 53  is a block diagram of a battery status test circuit. 
       FIG. 54  is a diagram showing the two modules of the implanted pulse generator (IPG). 
       FIG. 55  is a schematic and functional block diagram showing the components and their relationships to the implantable pulse generator/stimulus-receiver. 
       FIGS. 56A ,  56 B and  56 C show output pulses from a comparator when input exceeds a reference voltage. 
       FIGS. 57A and 57B  are simplified block diagrams showing the switching relationships between the inductively coupled and battery powered assemblies of the pulse generator. 
       FIG. 58  shows a picture of the combination implantable stimulator. 
       FIG. 59  shows assembly features of the implantable portion of the system. 
       FIG. 60  depicts an embodiment where the implantable system is used as an implantable, rechargeable system. 
       FIG. 61  depicts remote monitoring of stimulation devices. 
       FIG. 62  is an overall schematic diagram of the external stimulator, showing wireless communication. 
       FIG. 63  is a schematic diagram showing application of Wireless Application Protocol (WAP). 
       FIG. 64  is a simplified block diagram of the networking interface board. 
       FIGS. 65A and 65B  is a simplified diagram showing communication of modified PDA/phone with an external stimulator via a cellular tower/base station. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Co-pending patent application Ser. No. 10/195,961 and Ser. No. 10/142,298 are directed to method and system for modulating a vagus nerve (10 th  Cranial Nerve in the body) using modulated electrical pulses with an inductively coupled stimulation system. In the disclosure of this patent application, the electrical stimulation system comprises both implanted and external components. 
   In the method and system of this Application, selective pulsed electrical stimulation is applied to a vagus nerve(s) for afferent neuromodulation. An implantalbe lead is surgically implanted in the patient. The vagus nerve(s) is/are surgically exposed and isolated. The electrodes on the distal end of the lead are wrapped around the vagus nerve(s), and the lead is tunneled subcutaneously. A pulse generator means is connected to the proximal end of the lead. The power source may be external, implantable, or a combination device. 
   Also, in the method of this invention, a cheaper and simpler pulse generator may be used to test a patient&#39;s response to neuromodulation therapy. As one example only, an implanted stimulus-receiver in conjunction with an external stimulator may be used initially to test patient&#39;s response. At a later time, the pulse generator may be exchanged for a more elaborate implanted pulse generator (IPG) model, keeping the same lead. Some examples of stimulation and power sources that may be used for the practice of this invention, and disclosed in this Application, include: 
   a) an implanted stimulus-receiver with an external stimulator; 
   b) an implanted stimulus-receiver comprising a high value capacitor for storing charge, used in conjunction with an external stimulator; 
   c) a programmer-less implantable pulse generator (IPG) which is operable with a magnet; 
   d) a programmable implantable pulse generator (IPG); 
   e) a combination implantable device comprising both a stimulus-receiver and a programmable IPG; and 
   f) an IPG comprising a rechargeable battery. 
   Implanted Stimulus-Receiver with an External Stimulator 
   For an external power source, a passive implanted stimulus-receiver may be used. Such a system is disclosed in the parent application Ser. No. 10/142,298 and mentioned here for convenience. 
   The selective stimulation of various nerve fibers of a cranial nerve such as the vagus nerve (or neuromodulation of the vagus nerve), as performed by one embodiment of the method and system of this invention is shown schematically in  FIG. 18 , as a block diagram. A modulator  246  receives analog (sine wave) high frequency “carrier” signal and modulating signal. The modulating signal can be multilevel digital, binary, or even an analog signal. In this embodiment, mostly multilevel digital type modulating signals are used. The modulated signal is amplified  250 , 252 , conditioned  254 , and transmitted via a primary coil  46  which is external to the body. A secondary coil  48  of an implanted stimulus receiver, receives, demodulates, and delivers these pulses to the vagus nerve  54  via electrodes  61  and  62 . The receiver circuitry  256  is described later. 
   The carrier frequency is optimized. One preferred embodiment utilizes electrical signals of around 1 Mega-Hertz, even though other frequencies can be used. Low frequencies are generally not suitable because of energy requirements for longer wavelengths, whereas higher frequencies are absorbed by the tissues and are converted to heat, which again results in power losses. 
   Shown in conjunction with  FIG. 19 , the coil for the external transmitter (primary coil  46 ) may be placed in the pocket  301  of a customized garment  302 , for patient convenience. 
   Shown in conjunction with  FIG. 20 , the primary (external) coil  46  of the external stimulator  42  is inductively coupled to the secondary (implanted) coil  48  of the implanted stimulus-receiver  34 . The implantable stimulus-receiver  34  has circuitry at the proximal end  49 , and has two stimulating electrodes at the distal end  61 , 62 . The negative electrode (cathode)  61  is positioned towards the brain and the positive electrode (anode)  62  is positioned away from the brain. 
   The circuitry contained in the proximal end of the implantable stimulus-receiver  34  is shown schematically in  FIG. 21 , for one embodiment. In this embodiment, the circuit uses all passive components. Approximately 25 turn copper wire of 30 gauge, or comparable thickness, is used for the primary coil  46  and secondary coil  48 . This wire is concentrically wound with the windings all in one plane. The frequency of the pulse-waveform delivered to the implanted coil  48  can vary, and so a variable capacitor  152  provides ability to tune secondary implanted circuit  167  to the signal from the primary coil  46 . The pulse signal from secondary (implanted) coil  48  is rectified by the diode bridge  154  and frequency reduction obtained by capacitor  158  and resistor  164 . The last component in line is capacitor  166 , used for isolating the output signal from the electrode wire. The return path of signal from cathode  61  will be through anode  62  placed in proximity to the cathode  61  for “Bipolar” stimulation. In this embodiment bipolar mode of stimulation is used, however, the return path can be connected to the remote ground connection (case) of implantable circuit  167 , providing for much larger intermediate tissue for “Unipolar” stimulation. The “Bipolar” stimulation offers localized stimulation of tissue compared to “Unipolar” stimulation and is therefore, preferred in this embodiment. Unipolar stimulation is more likely to stimulate skeletal muscle in addition to nerve stimulation. The implanted circuit  167  in this embodiment is passive, so a battery does not have to be implanted. 
   The circuitry shown in  FIGS. 22A and 22B  can be used as an alternative, for the implanted stimulus-receiver. The circuitry of  FIG. 22A  is a slightly simpler version, and circuitry of  FIG. 22B  contains a conventional NPN transistor  168  connected in an emitter-follower configuration. 
   For therapy to commence, the primary (external) coil  46  is placed on the skin  60  on top of the surgically implanted (secondary) coil  48 . An adhesive tape is then placed on the skin  60  and external coil  46  such that the external coil  46 , is taped to the skin  60 . For efficient energy transfer to occur, it is important that the primary (external) and secondary (internal) coils  46 , 48  be positioned along the same axis and be optimally positioned relative to each other. In this embodiment, the external coil  46  may be connected to proximity sensing circuitry  50 . The correct positioning of the external coil  46  with respect to the internal coil  48  is indicated by turning “on” of a light emitting diode (LED) on the external stimulator  42 . 
   Optimal placement of the external (primary) coil  46  is done with the aid of proximity sensing circuitry incorporated in the system, in this embodiment. Proximity sensing occurs utilizing a combination of external and implantable components. The implanted components contains a relatively small magnet composed of materials that exhibit Giant Magneto-Resistor (GMR) characteristics such as Samarium-cobalt, a coil, and passive circuitry. Shown in conjunction with  FIG. 23 , the external coil  46  and proximity sensor circuitry  50  are rigidly connected in a convenient enclosure which is attached externally on the skin. The sensors measure the direction of the field applied from the magnet to sensors within a specific range of field strength magnitude. The dual sensors exhibit accurate sensing under relatively large separation between the sensor and the target magnet. As the external coil  46  placement is “fine tuned”, the condition where the external (primary) coil  46  comes in optimal position, i.e. is located adjacent and parallel to the subcutaneous (secondary) coil  48 , along its axis, is recorded and indicated by a light emitting diode (LED) on the external stimulator  42 . 
     FIG. 24  shows an overall block diagram of the components of the external stimulator and the proximity sensing mechanism. The proximity sensing components are the primary (external) coil  46 , supercutaneous (external) proximity sensors  648 ,  652  ( FIG. 25 ) in the proximity sensor circuit unit  50 , and a subcutaneous secondary coil  48  with a Giant Magneto Resister (GMR) magnet  53  associated with the proximity sensor unit. The proximity sensor circuit  50  provides a measure of the position of the secondary implanted coil  48 . The signal output from proximity sensor circuit  50  is derived from the relative location of the primary and secondary coils  46 ,  48 . The sub-assemblies consist of the coil and the associated electronic components, that are rigidly connected to the coil. 
   The proximity sensors (external) contained in the proximity sensor circuit  50  detect the presence of a GMR magnet  53 , composed of Samarium Cobalt, that is rigidly attached to the implanted secondary coil  48 . The proximity sensors, are mounted externally as a rigid assembly and sense the actual separation between the coils, also known as the proximity distance. In the event that the distance exceeds the system limit, the signal drops off and an alarm sounds to indicate failure of the production of adequate signal in the secondary implanted circuit  167 , as applied in this embodiment of the device. This signal is provided to the location indicator LED  280 . 
     FIG. 25  shows the circuit used to drive the proximity sensors  648 ,  652  of the proximity sensor circuit  50 . The two proximity sensors  648 ,  652  obtain a proximity signal based on their position with respect to the implanted GMR magnet  53 . This circuit also provides temperature compensation. The sensors  648 ,  652  are ‘Giant Magneto Resistor’ (GMR) type sensors packaged as proximity sensor unit  50 . There are two components of the complete proximity sensor circuit. One component is mounted supercutaneously  50 , and the other component, the proximity sensor signal control unit  57  is within the external stimulator  42 . The resistance effect depends on the combination of the soft magnetic layer of magnet  53 , where the change of direction of magnetization from external source can be large, and the hard magnetic layer, where the direction of magnetization remains unchanged. The resistance of this sensor  50  varies along a straight motion through the curvature of the magnetic field. A bridge differential voltage is suitably amplified and used as the proximity signal. 
   The Siemens GMR B6 (Siemens Corp., Special Components Inc., New Jersey) is used for this function in one embodiment. The maximum value of the peak-to-peak signal is observed as the external magnetic field becomes strong enough, at which point the resistance increases, resulting in the increase of the field-angle between the soft magnetic and hard magnetic material. The bridge voltage also increases. In this application, the two sensors  648 ,  652  are oriented orthogonal to each other. 
   The distance between the magnet  53  and sensor  50  is not relevant as long as the magnetic field is between 5 and 15 KA/m, and provides a range of distances between the sensors  648 ,  652  and the magnetic material  53 . The GMR sensor registers the direction of the external magnetic field. A typical magnet to induce permanent magnetic field is approximately 15 by 8 by 5 mm 3 , for this application and these components. The sensors  648 ,  652  are sensitive to temperature, such that the corresponding resistance drops as temperature increases. This effect is quite minimal until about 100° C. A full bridge circuit is used for temperature compensation, as shown in temperature compensation circuit  50  of  FIG. 25 . The sensors  648 ,  652  and a pair of resistors  650 ,  654  are shown as part of the bridge network for temperature compensation. It is also possible to use a full bridge network of two additional sensors in place of the resistors  650 ,  654 . 
   The signal from either proximity sensor  648 ,  652  is rectangular if the surface of the magnetic material is normal to the sensor and is radial to the axis of a circular GMR device. This indicates a shearing motion between the sensor and the magnetic device. When the sensor is parallel to the vertical axis of this device, there is a fall off of the relatively constant signal at about 25 mm. separation. The GMR sensor combination varies its resistance according to the direction of the external magnetic field, thereby providing an absolute angle sensor. The position of the GMR magnet can be registered at any angle from 0 to 360 degrees. 
   In the external stimulator  42  shown in  FIG. 24 , an indicator unit  280  which is provided to indicate proximity distance or coil proximity failure (for situations where the patch containing the external coil  46 , has been removed, or is twisted abnormally etc.). Indication is also provided to assist in the placement of the patch. In case of general failure, a red light with audible signal is provided when the signal is not reaching the subcutaneous circuit. The indicator unit  280  also displays low battery status. The information on the low battery, normal and out of power conditions forewarns the user of the requirements of any corrective actions. 
   Also shown in  FIG. 24 , the programmable parameters are stored in a programmable logic  264 . The predetermined programs stored in the external stimulator are capable of being modified through the use of a separate programming station  77 . The Programmable Array Logic Unit  264  and interface unit  270  are interfaced to the programming station  77 . The programming station  77  can be used to load new programs, change the existing predetermined programs or the program parameters for various stimulation programs. The programming station is connected to the programmable array unit  75  (comprising programmable array logic  304  and interface unit  270 ) with an RS232-C serial connection. The main purpose of the serial line interface is to provide an RS232-C standard interface. 
   This method enables any portable computer with a serial interface to communicate and program the parameters for storing the various programs. The serial communication interface receives the serial data, buffers this data and converts it to a 16 bit parallel data. The programmable array logic  264  component of programmable array unit receives the parallel data bus and stores or modifies the data into a random access matrix. This array of data also contains special logic and instructions along with the actual data. These special instructions also provide an algorithm for storing, updating and retrieving the parameters from long-term memory. The programmable logic array unit  264 , interfaces with long term memory to store the predetermined programs. All the previously modified programs can be stored here for access at any time, as well as, additional programs can be locked out for the patient. The programs consist of specific parameters and each unique program will be stored sequentially in long-term memory. A battery unit is present to provide power to all the components. The logic for the storage and decoding is stored in a random addressable storage matrix (RASM). 
   Conventional microprocessor and integrated circuits are used for the logic, control and timing circuits. Conventional bipolar transistors are used in radio-frequency oscillator, pulse amplitude ramp control and power amplifier. A standard voltage regulator is used in low-voltage detector. The hardware and software to deliver the pre-determined programs is well known to those skilled in the art. 
   The pulses delivered to the nerve tissue for stimulation therapy are shown graphically in  FIG. 26A . As shown in  FIG. 26B , for patient comfort when the electrical stimulation is turned on, the electrical stimulation is ramped up and ramped down, instead of abrupt delivery of electrical pulses. 
   The selective stimulation to the vagus nerve can be performed in one of two ways. One method is to activate one of several “pre-determined” programs. A second method is to “custom” program the electrical parameters which can be selectively programmed, for specific therapy to the individual patient. The electrical parameters which can be individually programmed, include variables such as pulse amplitude, pulse width, frequency of stimulation, stimulation on-time, and stimulation off-time. Table two below defines the approximate range of parameters, 
   
     
       
             
           
             
             
             
           
         
             
               TABLE 2 
             
           
           
             
                 
             
             
               Electrical parameter range delivered to the nerve 
             
           
        
         
             
                 
               PARAMER 
               RANGE 
             
             
                 
                 
             
             
                 
               Pulse Amplitude 
               0.1 Volt–10 Volts 
             
             
                 
               Pulse width 
               20 μS–5 mSec. 
             
             
                 
               Frequency 
                5 Hz–200 Hz 
             
             
                 
               On-time 
               10 Secs–24 hours 
             
             
                 
               Off-time 
               10 Secs–24 hours 
             
             
                 
                 
             
           
        
       
     
   
   The parameters in Table 2 are the electrical signals delivered to the nerve via the two electrodes  61 , 62  (distal and proximal) around the nerve, as shown in  FIG. 20 . It being understood that the signals generated by the external pulse generator  42  and transmitted via the primary coil  46  are larger, because the attenuation factor between the primary coil and secondary coil is approximately 10–20 times, depending upon the distance, and orientation between the two coils. Accordingly, the range of transmitted signals of the external pulse generator are approximately 10–20 times larger than shown in Table 2. 
   Referring now to  FIG. 27 , the implanted lead component of the system is similar to cardiac pacemaker leads, except for distal portion (or electrode end) of the lead. The lead terminal preferably is linear bipolar, even though it can be bifurcated, and plug(s) into the cavity of the pulse generator means. The lead body  59  insulation may be constructed of medical grade silicone, silicone reinforced with polytetrafluoro-ethylene (PTFE), or polyurethane. The electrodes  61 , 62  for stimulating the vagus nerve  54  may either wrap around the nerve once or may be spiral shaped. These stimulating electrodes may be made of pure platinum, platinum/Iridium alloy or platinum/iridium coated with titanium nitride. The conductor connecting the terminal to the electrodes  61 , 62  is made of an alloy of nickel-cobalt. The implanted lead design variables are also summarized in table three below. 
   
     
       
             
           
             
             
           
             
             
             
             
             
             
           
         
             
               TABLE 3 
             
           
           
             
                 
             
             
               Lead design variables 
             
           
        
         
             
               Proximal 
               Distal 
             
             
               End 
               End 
             
           
        
         
             
                 
                 
                 
               Conductor 
                 
                 
             
             
                 
                 
                 
               (connecting 
             
             
                 
               Lead body- 
                 
               proximal 
             
             
               Lead 
               Insulation 
                 
               and distal 
               Electrode - 
               Electrode - 
             
             
               Terminal 
               Materials 
               Lead-Coating 
               ends) 
               Material 
               Type 
             
             
                 
             
             
               Linear 
               Polyurethane 
               Antimicrobial 
               Alloy of 
               Pure 
               Spiral 
             
             
               bipolar 
                 
               coating 
               Nickel- 
               Platinum 
               electrode 
             
             
                 
                 
                 
               Cobalt 
             
             
               Bifurcated 
               Silicone 
               Anti- 
                 
               Platinum- 
               Wrap-around 
             
             
                 
                 
               Inflammatory 
                 
               Iridium 
               electrode 
             
             
                 
                 
               coating 
                 
               (Pt/Ir) Alloy 
             
             
                 
               Silicone with 
               Lubricious 
                 
               Pt/Ir coated 
               Steroid 
             
             
                 
               Polytetrafluoro- 
               coating 
                 
               with Titanium 
               eluting 
             
             
                 
               ethylene 
                 
                 
               Nitride 
             
             
                 
               (PTFE) 
             
             
                 
                 
                 
                 
               Carbon 
               Hydrogel 
             
             
                 
                 
                 
                 
                 
               electrodes 
             
             
                 
                 
                 
                 
                 
               Cuff 
             
             
                 
                 
                 
                 
                 
               electrodes 
             
             
                 
             
           
        
       
     
   
   Once the lead is fabricated, coating such as anti-microbial, anti-inflammatory, or lubricious coating may be applied to the body of the lead. 
     FIG. 28A  summarizes electrode-tissue interface between the nerve tissue and electrodes  61 ,  62 . There is a thin layer of fibrotic tissue between the stimulating electrode  61  and the excitable nerve fibers of the vagus nerve  54 .  FIG. 28B  summarizes the most important properties of the metal/tissue phase boundary in an equivalent circuit diagram. Both the membrane of the nerve fibers and the electrode surface are represented by parallel capacitance and resistance. Application of a constant battery voltage Vbat from the pulse generator, produces voltage changes and current flow, the time course of which is crucially determined by the capacitive components in the equivalent circuit diagram. During the pulse, the capacitors Co, Ch and Cm are charged through the ohmic resistances, and when the voltage Vbat is turned off, the capacitors discharge with current flow on the opposite direction. 
   Implanted Stimulus-Receiver Comprising a High Value Capacitor for Storing Charge, Used in Conjunction with An External Stimulator 
   In one embodiment, the implanted stimulus-receiver may be a system which is RF coupled combined with a power source. In this embodiment, the implanted stimulus-receiver contains high value, small sized capacitor(s) for storing charge and delivering electric stimulation pulses for up to several hours by itself, once the capacitors are charged. The packaging is shown in  FIG. 29 . Using mostly hybrid components and appropriate packaging, the implanted portion of the system described below is conducive to miniaturization. As shown in  FIG. 29 , a solenoid coil  382  wrapped around a ferrite core  380  is used as the secondary of an air-gap transformer for receiving power and data to the implanted device. The primary coil is external to the body. Since the coupling between the external transmitter coil and receiver coil  382  may be weak, a high-efficiency transmitter/amplifier is used in order to supply enough power to the receiver coil  382 . Class-D or Class-E power amplifiers may be used for this purpose. The coil for the external transmitter (primary coil) may be placed in the pocket of a customized garment. 
   As shown in conjunction with  FIG. 30  of the implanted stimulus-receiver  490  and the system, the receiving inductor  48 A and tuning capacitor  403  are tuned to the frequency of the transmitter. The diode  408  rectifies the AC signals, and a small sized capacitor  406  is utilized for smoothing the input voltage V I  fed into the voltage regulator  402 . The output voltage V D  of regulator  402  is applied to capacitive energy power supply and source  400  which establishes source power V DD . Capacitor  400  is a big value, small sized capacative energy source which is classified as low internal impedance, low power loss and high charge rate capacitor, such as Panasonic Model No. 641. 
   The refresh-recharge transmitter unit  460  includes a primary battery  426 , an ON/Off switch  427 , a transmitter electronic module  442 , an RF inductor power coil  46 A, a modulator/demodulator  420  and an antenna  422 . 
   When the ON/OFF switch is on, the primary coil  46 A is placed in close proximity to skin  60  and secondary coil  48 A of the implanted stimulator  490 . The inductor coil  46 A emits RF waves establishing EMF wave fronts which are received by secondary inductor  48 A. Further, transmitter electronic module  442  sends out command signals which are converted by modulator/demodulator decoder  420  and sent via antenna  422  to antenna  418  in the implanted stimulator  490 . These received command signals are demodulated by decoder  416  and replied and responded to, based on a program in memory  414  (matched against a “command table” in the memory). Memory  414  then activates the proper controls and the inductor receiver coil  48 A accepts the RF coupled power from inductor  46 A. 
   The RF coupled power, which is alternating or AC in nature, is converted by the rectifier  408  into a high DC voltage. Small value capacitor  406  operates to filter and level this high DC voltage at a certain level. Voltage regulator  402  converts the high DC voltage to a lower precise DC voltage while capacitive power source  400  refreshes and replenishes. 
   When the voltage in capacative source  400  reaches a predetermined level (that is V DD  reaches a certain predetermined high level), the high threshold comparator  430  fires and stimulating electronic module  412  sends an appropriate command signal to modulator/decoder  416 . Modulator/decoder  416  then sends an appropriate “fully charged” signal indicating that capacitive power source  400  is fully charged, is received by antenna  422  in the refresh-recharge transmitter unit  460 . 
   In one mode of operation, the patient may start or stop stimulation by waving the magnet  442  once near the implant. The magnet emits a magnetic force L m  which pulls reed switch  410  closed. Upon closure of reed switch  410 , stimulating electronic module  412  in conjunction with memory  414  begins the delivery (or cessation as the case may be) of controlled electronic stimulation pulses to the vagus nerve  54  via electrodes  61 ,  62 . In another mode (AUTO), the stimulation is automatically delivered to the implanted lead based upon programmed ON/OFF times. 
   The programmer unit  450  includes keyboard  432 , programming circuit  438 , rechargeable battery  436 , and display  434 . The physician or medical technician programs programming unit  450  via keyboard  432 . This program regarding the frequency, pulse width, modulation program, ON time etc. is stored in programming circuit  438 . The programming unit  450  must be placed relatively close to the implanted stimulator  490  in order to transfer the commands and programming information from antenna  440  to antenna  418 . Upon receipt of this programming data, modulator/demodulator and decoder  416  decodes and conditions these signals, and the digital programming information is captured by memory  414 . This digital programming information is further processed by stimulating electronic module  412 . In the DEMAND operating mode, after programming the implanted stimulator, the patient turns ON and OFF the implanted stimulator via hand held magnet  442  and the reed switch  410 . In the automatic mode (AUTO), the implanted stimulator turns ON and OFF automatically according to the programmed values for the ON and OFF times. 
   Other simplified versions of such a system may also be used. For example, a system such as this, where a separate programmer is eliminated, and simplified programming is performed with a magnet and reed switch, can also be used. 
   Programmer-less Implantable Pulse Generator (IPG) 
   In one embodiment, a programmer-less implantable pulse generator (IPG) may be used. In this embodiment, shown in conjunction with  FIG. 31 , the implantable pulse generator  171  is provided with a reed switch  92  and memory circuitry  102 . The reed switch  92  being remotely actuable by means of a magnet  90  brought into proximity of the pulse generator  171 , in accordance with common practice in the art. In this embodiment, the reed switch  92  is coupled to a multi-state converter/timer circuit  96 , such that a single short closure of the reed switch can be used as a means for non-invasive encoding and programming of the pulse generator  171  parameters. 
   In one embodiment, shown in conjunction with  FIG. 32 , the closing of the reed switch  92  triggers a counter. The magnet  90  and timer are ANDed together. The system is configured such that during the time that the magnet  82  is held over the pulse generator  171 , the output level goes from LOW stimulation state to the next higher stimulation state every 5 seconds. Once the magnet  82  is removed, regardless of the state of stimulation, an application of the magnet, without holding it over the pulse generator  171 , triggers the OFF state, which also resets the counter. 
   Once the prepackaged/predetermined logic state is activated by the logic and control circuit  102 , as shown in  FIG. 31 , the pulse generation and amplification circuit  106  deliver the appropriate electrical pulses to the vagus nerve  54  of the patient via an output buffer  108 . The delivery of output pulses is configured such that the distal electrode  61  (electrode closer to the brain) is the cathode and the proximal electrode  62  is the anode. Timing signals for the logic and control circuit  102  of the pulse generator  171  are provided by a crystal oscillator  104 . The battery  86  of the pulse generator  171  has terminals connected to the input of a voltage regulator  94 . The regulator  94  smoothes the battery output and supplies power to the internal components of the pulse generator  171 . A microprocessor  100  controls the program parameters of the device, such as the voltage, pulse width, frequency of pulses, on-time and off-time. The microprocessor may be a commercially-available, general purpose microprocessor or microcontroller, or may be a custom integrated circuit device augmented by standard RAM/ROM components. 
   In one embodiment, there are four stimulation states. A larger (or lower) number of states can be achieved using the same methodology, and such is considered within the scope of the invention. These four states are, LOW stimulation state, LOW-MED stimulation state, MED stimulation state, and HIGH stimulation state. Examples of stimulation parameters (delivered to the vagus nerve) for each state are as follows, 
   LOW stimulation state example is, 
   
     
       
             
             
             
           
         
             
                 
                 
             
           
           
             
                 
               Current output: 
               0.75 milliAmps. 
             
             
                 
               Pulse width: 
               0.20 msec. 
             
             
                 
               Pulse frequency: 
               20 Hz 
             
             
                 
               Cycles: 
               20 sec. on-time and 2.0 min. 
             
             
                 
                 
               off-time in repeating cycles. 
             
             
                 
                 
             
           
        
       
     
   
   LOW-MED stimulation state example is, 
   
     
       
             
             
             
           
         
             
                 
                 
             
           
           
             
                 
               Current output: 
               1.5 milliAmps, 
             
             
                 
               Pulse width: 
               0.30 msec. 
             
             
                 
               Pulse frequency: 
               25 Hz 
             
             
                 
               Cycles: 
               1.5 min. on-time and 20.0 min. 
             
             
                 
                 
               off-time in repeating cycles. 
             
             
                 
                 
             
           
        
       
     
   
   MED stimulation state example is, 
   
     
       
             
             
             
           
         
             
                 
                 
             
           
           
             
                 
               Current output: 
               2.0 milliAmps. 
             
             
                 
               Pulse width: 
               0.30 msec. 
             
             
                 
               Pulse frequency: 
               30 Hz 
             
             
                 
               Cycles: 
               1.5 min. on-time and 20.0 min. 
             
             
                 
                 
               off-time in repeating cycles. 
             
             
                 
                 
             
           
        
       
     
   
   HIGH stimulation state example is, 
   
     
       
             
             
             
           
         
             
                 
                 
             
           
           
             
                 
               Current output: 
               3.0 milliAmps, 
             
             
                 
               Pulse width: 
               0.40 msec. 
             
             
                 
               Pulse frequency: 
               30 Hz 
             
             
                 
               Cycles: 
               2.0 min. on-time and 20.0 min. 
             
             
                 
                 
               off-time in repeating cycles. 
             
             
                 
                 
             
           
        
       
     
   
   These prepackaged/predetermined programs are mearly examples, and the actual stimulation parameters will deviate from these depending on the treatment application. 
   It will be readily apparent to one skilled in the art, that other schemes can be used for the same purpose. For example, instead of placing the magnet  90  on the pulse generator  171  for a prolonged period of time, different stimulation states can be encoded by the sequence of magnet applications. Accordingly, in an alternative embodiment there can be three logic states, OFF, LOW stimulation (LS) state, and HIGH stimulation (HS) state. Each logic state again corresponds to a prepackaged/predetermined program such as presented above. In such an embodiment, the system could be configured such that one application of the magnet triggers the generator into LS State. If the generator is already in the LS state then one application triggers the device into OFF State. Two successive magnet applications triggers the generator into MED stimulation state, and three successive magnet applications triggers the pulse generator in the HIGH Stimulation State. Subsequently, one application of the magnet while the device is in any stimulation state, triggers the device OFF. 
     FIG. 33  shows a representative digital circuitry used for the basic state machine circuit. The circuit consists of a PROM  462  that has part of its data fed back as a state address. Other address lines  469  are used as circuit inputs, and the state machine changes its state address on the basis of these inputs. The clock  104  is used to pass the new address to the PROM  462  and then pass the output from the PROM  462  to the outputs and input state circuits. The two latches  464 ,  465  are operated 180° out of phase to prevent glitches from unexpectedly affecting any output circuits when the ROM changes state. Each state responds differently according to the inputs it receives. 
   The advantage of this embodiment is that it is cheaper to manufacture than a fully programmable implantable pulse generator (IPG). 
   Programmable Implantable Pulse Generator (IPG) 
   In one embodiment, a fully programmable implantable pulse generator (IPG) may be used. Shown in conjunction with  FIG. 34 , the implantable pulse generator unit  391  is preferably a microprocessor based device, where the entire circuitry is encased in a hermetically sealed titanium can. As shown in the overall block diagram, the logic &amp; control unit  398  provides the proper timing for the output circuitry  385  to generate electrical pulses that are delivered to electrodes  61 ,  62  via a lead  40 . Programming of the implantable pulse generator (IPG) is done via an external programmer  85 , as described later. Once programmed via an external programmer  85 , the implanted pulse generator  391  provides appropriate electrical stimulation pulses to the vagus nerve(s)  54  via electrodes  61 , 62 . 
   This embodiment may also comprise fixed pre-determined/pre-packaged programs. Examples of LOW, LOW-MED, MED, and HIGH stimulation states were given in the previous section, under “Programmer-less Implantable Pulse Generator (IPG)”. These pre-packaged/pre-determined programs comprise unique combinations of pulse amplitude, pulse width, pulse frequency, ON-time and OFF-time. 
   In addition, each parameter may be individually programmed and stored in memory. The range of programmable electrical stimulation parameters are shown in table 4 below. 
   
     
       
             
           
             
             
             
           
         
             
               TABLE 4 
             
           
           
             
                 
             
             
               Programmable electrical parameter range 
             
           
        
         
             
                 
               PARAMER 
               RANGE 
             
             
                 
                 
             
             
                 
               Pulse Amplitude 
               0.1 Volt–10 Volts 
             
             
                 
               Pulse width 
               20 μS–5 mSec. 
             
             
                 
               Frequency 
               3 Hz–300 Hz 
             
             
                 
               On-time 
               5 Secs–24 hours 
             
             
                 
               Off-time 
               5 Secs–24 hours 
             
             
                 
               Ramp 
               ON/OFF 
             
             
                 
                 
             
           
        
       
     
   
   Shown in conjunction with  FIGS. 35 and 36 , the electronic stimulation module comprises both digital  350  and analog  352  circuits. A main timing generator  330  (shown in  FIG. 35 ), controls the timing of the analog output circuitry for delivering neuromodulating pulses to the vagus nerve  54 , via output amplifier  334 . Limiter  183  prevents excessive stimulation energy from getting into the vagus nerve  54 . The main timing generator  330  receiving clock pulses from crystal oscillator  393 . Main timing generator  330  also receiving input from programmer  85  via coil  399 .  FIG. 36  highlights other portions of the digital system such as CPU  338 , ROM  337 , RAM  339 , program interface  346 , interrogation interface  348 , timers  340 , and digital O/I  342 . 
   Most of the digital functional circuitry  350  is on a single chip (IC). This monolithic chip along with other IC&#39;s and components such as capacitors and the input protection diodes are assembled together on a hybrid circuit. As well known in the art, hybrid technology is used to establish the connections between the circuit and the other passive components. The integrated circuit is hermetically encapsulated in a chip carrier. A coil  399  situated under the hybrid substrate is used for bidirectional telemetry. The hybrid and battery  397  are encased in a titanium can  65 . This housing is a two-part titanium capsule that is hermetically sealed by laser welding. Alternatively, electron-beam welding can also be used. The header  79  is a cast epoxy-resin with hermetically sealed feed-through, and form the lead  40  connection block. 
   For further details,  FIG. 37A  highlights the general components of an 8-bit microprocessor as an example. It will be obvious to one skilled in the art that higher level microprocessor, such as a 16-bit or 32-bit may be utilized, and is considered within the scope of this invention. It comprises a ROM  337  to store the instructions of the program to be executed and various programmable parameters, a RAM  339  to store the various intermediate parameters, timers  340  to track the elapsed intervals, a register file  321  to hold intermediate values, an ALU  320  to perform the arithmetic calculation, and other auxiliary units that enhance the performance of a microprocessor-based IPG system. 
   The size of ROM  337  and RAM  339  units are selected based on the requirements of the algorithms and the parameters to be stored. The number of registers in the register file  321  are decided based upon the complexity of computation and the required number of intermediate values. Timers  340  of different precision are used to measure the elapsed intervals. Even though this embodiment does not have external sensors to control timing, future embodiments may have sensors  322  to effect the timing as shown in conjunction with  FIG. 37B . 
   In this embodiment, the two main components of microprocessor are the datapath and control. The datapath performs the arithmetic operation and the control directs the datapath, memory, and I/O devices to execute the instruction of the program. The hardware components of the microprocessor are designed to execute a set of simple instructions. In general the complexity of the instruction set determines the complexity of datapth elements and controls of the microprocessor. 
   In this embodiment, the microprocessor is provided with a fixed operating routine. Future embodiments may be provided with the capability of actually introducing program changes in the implanted pulse generator. The instruction set of the microprocessor, the size of the register files, RAM and ROM are selected based on the performance needed and the type of the algorithms used. In this application of pulse generator, in which several algorithms can be loaded and modified, Reduced Instruction Set Computer (RISC) architecture is useful. RISC architecture offers advantages because it can be optimized to reduce the instruction cycle which in turn reduces the run time of the program and hence the current drain. The simple instruction set architecture of RISC and its simple hardware can be used to implement any algorithm without much difficulty. Since size is also a major consideration, an 8-bit microprocessor is used for the purpose. As most of the arithmetic calculation are based on a few parameters and are rather simple, an accumulator architecture is used to save bits from specifying registers. Each instruction is executed in multiple clock cycles, and the clock cycles are broadly classified into five stages: an instruction fetch, instruction decode, execution, memory reference, and write back stages. Depending on the type of the instruction, all or some of these stages are executed for proper completion. 
   Initially, an optimal instruction set architecture is selected based on the algorithm to be implemented and also taking into consideration the special needs of a microprocessor based implanted pulse generator (IPG). The instructions are broadly classified into Load/store instructions, Arithmetic and logic instructions (ALU), control instructions and special purpose instructions. 
   The instruction format is decided based upon the total number of instructions in the instruction set. The instructions fetched from memory are 8 bits long in this example. Each instruction has an opcode field (2 bits), a register specifier field (3-bits), and a 3-bit immediate field. The opcode field indicates the type of the instruction that was fetched. The register specifier indicates the address of the register in the register file on which the operations are performed. The immediate field is shifted and sign extended to obtain the address of the memory location in load/store instruction. Similarly, in branch and jump instruction, the offset field is used to calculate the address of the memory location the control needs to be transferred to. 
   Shown in conjunction with  FIG. 38A , the register file  321 , which is a collection of registers in which any register can be read from or written to specifying the number of the register in the file. Based on the requirements of the design, the size of the register file is decided. For the purposes of implementation of stimulation pulses algorithms, a register file of eight registers is sufficient, with three special purpose register ( 0 – 2 ) and five general purpose registers ( 3 – 7 ), as shown in  FIG. 38A . Register “ 0 ” always holds the value “zero”. Register “ 1 ” is dedicated to the pulse flags. Register “ 2 ” is an accumulator in which all the arithmetic calculations are performed. The read/write address port provides a 3-bit address to identify the register being read or written into. The write data port provides 8-bit data to be written into the registers either from ROM/RAM or timers. Read enable control, when asserted enables the register file to provide data at the read data port. Write enable control enables writing of data being provided at the write data port into a register specified by the read/write address. 
   Generally, two or more timers are required to implement the algorithm for the IPG. The timers are read and written into just as any other memory location. The timers are provided with read and write enable controls. 
   The arithmetic logic unit is an important component of the microprocessor. It performs the arithmetic operation such as addition, subtraction and logical operations such as AND and OR. The instruction format of ALU instructions consists of an opcode field (2 bits), a function field (2 bits) to indicate the function that needs to be performed, and a register specifier (3 bits) or an immediate field (4 bits) to provide an operand. 
   The hardware components discussed above constitute the important components of a datapath. Shown in conjunction with  FIG. 38B , there are some special purpose registers such a program counter (PC) to hold the address of the instruction being fetched from ROM  337  and instruction register (IR)  323 , to hold the instruction that is fetched for further decoding and execution. The program counter is incremented in each instruction fetch stage to fetch sequential instruction from memory. In the case of a branch or jump instruction, the PC multiplexer allows to choose from the incremented PC value or the branch or jump address calculated. The opcode of the instruction fetched (IR) is provided to the control unit to generate the appropriate sequence of control signals, enabling data flow through the datapath. The register specification field of the instruction is given as read/write address to the register file, which provides data from the specified field on the read data port. One port of the ALU is always provided with the contents of the accumulator and the other with the read data port. This design is therefore referred to as accumulator-based architecture. The sign-extended offset is used for address calculation in branch and jump instructions. The timers are used to measure the elapsed interval and are enabled to count down on a low-frequency clock. The timers are read and written into, just as any other memory location ( FIG. 38B ). 
   In a multicycle implementation, each stage of instruction execution takes one clock cycle. Since the datapath takes multiple clock cycles per instruction, the control must specify the signals to be asserted in each stage and also the next step in the sequence. This can be easily implemented as a finite state machine. 
   A finite state machine consists of a set of states and directions on how to change states. The directions are defined by a next-state function, which maps the current state and the inputs to a new state. Each stage also indicates the control signals that need to be asserted. Every state in the finite state machine takes one clock cycle. Since the instruction fetch and decode stages are common to all the instruction, the initial two states are common to all the instruction. After the execution of the last step, the finite state machine returns to the fetch state. 
   A finite state machine can be implemented with a register that holds the current stage and a block of combinational logic such as a PLA. It determines the datapath signals that need to be asserted as well as the next state. A PLA is described as an array of AND gates followed by an array of OR gates. Since any function can be computed in two levels of logic, the two-level logic of PLA is used for generating control signals. 
   The occurrence of a wakeup event initiates a stored operating routine corresponding to the event. In the time interval between a completed operating routine and a next wake up event, the internal logic components of the processor are deactivated and no energy is being expended in performing an operating routine. 
   A further reduction in the average operating current is obtained by providing a plurality of counting rates to minimize the number of state changes during counting cycles. Thus intervals which do not require great precision, may be timed using relatively low counting rates, and intervals requiring relatively high precision, such as stimulating pulse width, may be timed using relatively high counting rates. 
   The logic and control unit  398  of the IPG controls the output amplifiers. The pulses have predetermined energy (pulse amplitude and pulse width) and are delivered at a time determined by the therapy stimulus controller. The circuitry in the output amplifier, shown in conjunction with ( FIG. 39 ) generates an analog voltage or current that represents the pulse amplitude. The stimulation controller module initiates a stimulus pulse by closing a switch  208  that transmits the analog voltage or current pulse to the nerve tissue through the tip electrode  61  of the lead  40 . The output circuit receiving instructions from the stimulus therapy controller  398  that regulates the timing of stimulus pulses and the amplitude and duration (pulse width) of the stimulus. The pulse amplitude generator  206  determines the configuration of charging and output capacitors necessary to generate the programmed stimulus amplitude. The output switch  208  is closed for a period of time that is controlled by the pulse width generator  204 . When the output switch  208  is closed, a stimulus is delivered to the tip electrode  61  of the lead  40 . 
   The constant-voltage output amplifier applies a voltage pulse to the distal electrode (cathode)  61  of the lead  40 . A typical circuit diagram of a voltage output circuit is shown in  FIG. 40 . This configuration contains a stimulus amplitude generator  206  for generating an analog voltage. The analog voltage represents the stimulus amplitude and is stored on a holding capacitor C h    225 . Two switches are used to deliver the stimulus pulses to the lead  40 , a stimulating delivery switch  220 , and a recharge switch  222 , that reestablishes the charge equilibrium after the stimulating pulse has been delivered to the nerve tissue. Since these switches have leakage currents that can cause direct current (DC) to flow into the lead system  40 , a DC blocking capacitor C b    229 , is included. This is to prevent any possible corrosion that may result from the leakage of current in the lead  40 . When the stimulus delivery switch  220  is closed, the pulse amplitude analog voltage stored in the (C h    225 ) holding capacitor is transferred to the cathode electrode  61  of the lead  40  through the coupling capacitor, C b    229 . At the end of the stimulus pulse, the stimulus delivery switch  220  opens. The pulse duration being the interval from the closing of the switch  220  to its reopening. During the stimulus delivery, some of the charge stored on C h    225  has been transferred to C b    229 , and some has been delivered to the lead system  40  to stimulate the nerve tissue. 
   To re-establish equilibrium, the recharge switch  222  is closed, and a rapid recharge pulse is delivered. This is intended to remove any residual charge remaining on the coupling capacitor C b    229 , and the stimulus electrodes on the lead (polarization). Thus, the stimulus is delivered as the result of closing and opening of the stimulus delivery  220  switch and the closing and opening of the RCHG switch  222 . At this point, the charge on the holding C h    225  must be replenished by the stimulus amplitude generator  206  before another stimulus pulse can be delivered. 
   The pulse generating unit charges up a capacitor and the capacitor is discharged when the control (timing) circuitry requires the delivery of a pulse. This embodiment utilizes a constant voltage pulse generator, even though a constant current pulse generator can also be utilized. Pump-up capacitors are used to deliver pulses of larger magnitude than the potential of the batteries. The pump up capacitors are charged in parallel and discharged into the output capacitor in series. Shown in conjunction with  FIG. 41  is a circuit diagram of a voltage doubler which is shown here as an example. For higher multiples of battery voltage, this doubling circuit can be cascaded with other doubling circuits. As shown in  FIG. 41 , during phase I (top of  FIG. 41 ), the pump capacitor C p  is charged to V bat  and the output capacitor C o  supplies charge to the load. During phase II, the pump capacitor charges the output capacitor, which is still supplying the load current. In this case, the voltage drop across the output capacitor is twice the battery voltage. 
     FIG. 42  shows an example of the pulse trains that are delivered with this embodiment. The microcontroller is configured to deliver the pulse train as shown in the figure, i.e. there is “ramping up” of the pulse train. The purpose of the ramping-up is to avoid sudden changes in stimulation, when the pulse train begins. 
   Since a key concept of this invention is to deliver afferent stimulation, in one aspect efferent stimulation of selected types of fibers may be substantially blocked, utilizing the “greenwave” effect. In such a case, as shown in conjunction with  FIGS. 43A and 43B , a tripolar lead is utilized. As depicted on the top right portion of  FIG. 43A , a depolarization peak  10  on the vagus nerve bundle corresponding to electrode  61  (cathode) and the two hyper-polarization peaks  8 ,  12  corresponding to electrodes  62 ,  63  (anodes). With the microcontroller controlling the tripolar device, the size and timing of the hyper-polarizations  8 ,  12  can be controlled. As was shown previously in  FIGS. 2 and 10A , since the speed of conduction is different between the larger diameter A and B fibers and the smaller diameter c-fibers, by appropriately timing the pulses, collision blocks can be created for conduction via the large diameter A and B fibers in the efferent direction. This is depicted schematically in  FIG. 43B . A number of blocking techniques are known in the art, such as collision blocking, high frequency blocking, and anodal blocking. Any of these well known blocking techniques may be used with the practice of this invention, and are considered within the scope of this invention. 
   In one aspect of the invention, the pulsed electrical stimulation to the vagus nerve(s) may be provided anywhere along the length of the vagus nerve(s). As was shown earlier in conjunction with  FIG. 20 , the pulsed electrical stimulation may be at the cervical level. Alternatively, shown in conjunction with  FIGS. 44A ,  44 B, and  44 C, the stimulation to the vagus nerve(s) may be around the diaphramatic level. Either above the diaphragm or below the diaphragm. Further, the stimulation may be unilateral or bilateral, i.e. stimulation is to one or both vagus nerves.  FIG. 44A  depicts unilateral vagal stimulation at around the level of the diaphragm.  FIGS. 44B and 44C  depict bilateral vagal nerve stimulation at around the level of the diaphragm. Any combination of vagal nerve(s) stimulation, either unilateral or bilateral, anywhere along the length of the vagal nerve(s) is considered within the scope of this invention. 
   The programming of the implanted pulse generator (IPG)  391  is shown in conjunction with  FIGS. 45A and 45B . With the magnetic Reed Switch  389  ( FIG. 34 ) in the closed position, a coil in the head of the programmer  85 , communicates with a telemetry coil  399  of the implanted pulse generator  391 . Bi-directional inductive telemetry is used to exchange data with the implanted unit  391  by means of the external programming unit  85 . 
   The transmission of programming information involves manipulation of the carrier signal in a manner that is recognizable by the pulse generator  391  as a valid set of instructions. The process of modulation serves as a means of encoding the programming instruction in a language that is interpretable by the implanted pulse generator  391 . Modulation of signal amplitude, pulse width, and time between pulses are all used in the programming system, as will be appreciated by those skilled in the art.  FIG. 46A  shows an example of pulse count modulation, and  FIG. 46B  shows an example of pulse width modulation, that can be used for encoding. 
     FIG. 47  shows a simplified overall block diagram of the implanted pulse generator (IPG)  391  programming and telemetry interface. The left half of  FIG. 47  is programmer  85  which communicates programming and telemetry information with the IPG  391 . The sections of the IPG  391  associated with programming and telemetry are shown on the right half of  FIG. 47 . In this case, the programming sequence is initiated by bringing a permanent magnet in the proximity of the IPG  391  which closes a reed switch  389  in the IPG  391 . Information is then encoded into a special error-correcting pulse sequence and transmitted electromagnetically through a set of coils. The received message is decoded, checked for errors, and passed on to the unit&#39;s logic circuitry. The IPG  391  of this embodiment includes the capability of bi-directional communication. 
   The reed switch  389  is a magnetically-sensitive mechanical switch, which consists of two thin strips of metal (the “reed”) which are ferromagnetic. The reeds normally spring apart when no magnetic field is present. When a field is applied, the reeds come together to form a closed circuit because doing so creates a path of least reluctance. The programming head of the programmer contains a high-field-strength ceramic magnet. 
   When the switch closes, it activates the programming hardware, and initiates an interrupt of the IPG central processor. Closing the reed switch  389  also presents the logic used to encode and decode programming and telemetry signals. A nonmaskable interrupt (NMI) is sent to the IPG processor, which then executes special programming software. Since the NMI is an edge-triggered signal and the reed switch is vulnerable to mechanical bounce, a debouncing circuit is used to avoid multiple interrupts. The overall current consumption of the IPG increases during programming because of the debouncing circuit and other communication circuits. 
   A coil  399  is used as an antenna for both reception and transmission. Another set of coils  383  is placed in the programming head, a relatively small sized unit connected to the programmer  85 . All coils are tuned to the same resonant frequency. The interface is half-duplex with one unit transmitting at a time. 
   Since the relative positions of the programming head  87  and IPG  391  determine the coupling of the coils, this embodiment utilizes a special circuit which has been devised to aid the positioning of the programming head, and is shown in  FIG. 48 . It operates on similar principles to the linear variable differential transformer. An oscillator tuned to the resonant frequency of the pacemaker coil  399  drives the center coil of a three-coil set in the programmer head. The phase difference between the original oscillator signal and the resulting signal from the two outer coils is measured using a phase shift detector. It is proportional to the distance between the implanted pulse generator and the programmer head. The phase shift, as a voltage, is compared to a reference voltage and is then used to control an indicator such as an LED. An enable signal allows switching the circuit on and off. 
   Actual programming is shown in conjunction with  FIGS. 49 and 50 . Programming and telemetry messages comprise many bits; however, the coil interface can only transmit one bit at a time. In addition, the signal is modulated to the resonant frequency of the coils, and must be transmitted in a relatively short period of time, and must provide detection of erroneous data. 
   A programming message is comprised of five parts  FIG. 49(   a ). The start bit indicates the beginning of the message and is used to synchronize the timing of the rest of the message. The parameter number specifies which parameter (e.g., mode, pulse width, delay) is to be programmed. In the example, in  FIG. 49(   a ) the number 10010000 specifies the pulse rate to be specified. The parameter value represents the value that the parameter should be set to. This value may be an index into a table of possible values; for example, the value 00101100 represents a pulse stimulus rate of 80 pulses/min. The access code is a fixed number based on the stimulus generator model which must be matched exactly for the message to succeed. It acts as a security mechanism against use of the wrong programmer, errors in the message, or spurious programming from environmental noise. It can also potentially allow more than one programmable implant in the patient. Finally, the parity field is the bitwise exclusive-OR of the parameter number and value fields. It is one of several error-detection mechanisms. 
   All of the bits are then encoded as a sequence of pulses of 0.35-ms duration  FIG. 49(   b ). The start bit is a single pulse. The remaining bits are delayed from their previous bit according to their bit value. If the bit is a zero, the delay is short (1.0); if it is a one, the delay is long (2.2 ms). This technique of pulse position coding, makes detection of errors easier. 
   The serial pulse sequence is then amplitude modulated for transmission  FIG. 49(   c ). The carrier frequency is the resonant frequency of the coils. This signal is transmitted from one set of coils to the other and then demodulated back into a pulse sequence  FIG. 49(   d ). 
     FIG. 50  shows how each bit of the pulse sequence is decoded from the demodulated signal. As soon as each bit is received, a timer begins timing the delay to the next pulse. If the pulse occurs within a specific early interval, it is counted as a zero bit ( FIG. 50(   b )). If it otherwise occurs with a later interval, it is considered to be a one bit ( FIG. 50(   d )). Pulses that come too early, too late, or between the two intervals are considered to be errors and the entire message is discarded ( FIG. 50(   a, c, e )). Each bit begins the timing of the bit that follows it. The start bit is used only to time the first bit. 
   Telemetry data may be either analog or digital. Digital signals are first converted into a serial bit stream using an encoding such as shown in  FIG. 50(   b ). The serial stream or the analog data is then frequency modulated for transmission. 
   An advantage of this and other encodings is that they provide multiple forms of error detection. The coils and receiver circuitry are tuned to the modulation frequency, eliminating noise at other frequencies. Pulse-position coding can detect errors by accepting pulses only within narrowly-intervals. The access code acts as a security key to prevent programming by spurious noise or other equipment. Finally, the parity field and other checksums provides a final verification that the message is valid. At any time, if an error is detected, the entire message is discarded. 
   Another more sophisticated type of pulse position modulation may be used to increase the bit transmission rate. In this, the position of a pulse within a frame is encoded into one of a finite number of values, e.g. 16. A special synchronizing bit is transmitted to signal the start of the frame. Typically, the frame contains a code which specifies the type or data contained in the remainder of the frame. 
     FIG. 51  shows a diagram of receiving and decoding circuitry for programming data. The IPG coil, in parallel with capacitor creates a tuned circuit for receiving data. The signal is band-pass filtered  602  and envelope detected  604  to create the pulsed signal in  FIG. 49(   d ). After decoding, the parameter value is placed in a RAM at the location specified by the parameter number. The IPG can have two copies of the RAM—a permanent set and a temporary set—which makes it easy for the physician to set the IPG to a temporary configuration and later reprogram it back to the usual settings. 
     FIG. 52  shows the basic circuit used to receive telemetry data. Again, a coil and capacitor create a resonant circuit tuned to the carrier frequency. The signal is further band-pass filtered  614  and then frequency-demodulated using a phase-locked loop  618 . 
   This embodiment also comprises an optional battery status test circuit. Shown in conjunction with  FIG. 53 , the charge delivered by the battery is estimated by keeping track of the number of pulses delivered by the IPG  391 . An internal charge counter is updated during each test mode to read the total charge delivered. This information about battery status is read from the IPG  391  via telemetry. 
   Combination Implantable Device Comprising Both a Stimulus-receiver and a Programmable Implantable Pulse Generator (IPG) 
   In one embodiment, the implantable device may comprise both a stimulus-receiver and a programmable implantable pulse generator (IPG).  FIG. 54  shows a close up view of the packaging of the implanted stimulator  75  of this embodiment, showing the two subassemblies  120 ,  70 . The two subassemblies are the stimulus-receiver module  120  and the battery operated pulse generator module  70 . The external stimulator  42 , and programmer  85  also being remotely controllable from a distant location via the internet. Controlling circuitry means within the stimulator  75 , makes the inductively coupled stimulator  120  and the IPG  70  operate in harmony with each other. For example, when stimulation is applied via the inductively coupled system, the battery operated portion of the stimulator is triggered to go into the “sleep” mode. Conversely, when programming pulses (which are also inductively coupled) are being applied to the implanted battery operated pulse generator  70 , the inductively coupled stimulation circuitry  120  is disconnected. 
     FIG. 57A  is a simplified diagram of one aspect of control circuitry. In this embodiment, to program the implanted portion of the stimulator  70 , a magnet  144  is placed over the implanted pulse generator  70 , causing a magnetically controlled Reed Switch  182  (which is normally in the open position) to be closed. As is also shown in  FIG. 57A , at the same time a switch  67  going to the stimulator lead  40 , and a switch  69  going to the circuit of the stimulus-receiver module  120  are both opened, disconnecting both subassemblies electrically. Further, protection circuitry  181  is an additional safeguard for inadvertent leakage of electrical energy into the nerve tissue  54  during programming. Alternatively, as shown in  FIG. 57B , instead of a reed switch  182 , a solid state magnet sensor (Hall-effect sensor)  146  may be used for the same purpose. The solid-state magnet sensor  146  is preferred, since there are no moving parts that can get stuck. 
   With reference to  FIG. 55 , for the functioning of the inductively coupled stimulus-receiver  120 , a primary (external) coil  46  is placed in close proximity to secondary (implanted) coil  48 . The primary coil  46  may be taped to skin  60 , or other means may be used for keeping the primary coil  46  in close proximity to the implanted (secondary) coil  48 . Referring to the left portion of  FIG. 55 , the amplitude and pulse width modulated radiofrequency signals from the primary (external) coil  46  are inductively coupled to the secondary (implanted) coil  48  in the implanted unit  75 . The two coils  46  and  48  thus act like an air-gap transformer. The system having means for proximity sensing between the two coils  46 , 48 , and feedback regulation of signals as described earlier. 
   Again with reference to  FIG. 55 , the combination of capacitor  122  and inductor  48  tunes the receiver circuitry to the high frequency of the transmitter with the capacitor  122 . The receiver is made sensitive to frequencies near the resonant frequency of the tuned circuit, and less sensitive to frequencies away from the resonant frequency. A diode bridge  124  rectifies the alternating voltages. Capacitor  128  and resistor  134  filter out the high-frequency component of the receiver signal, and leaves the current pulse of the same duration as the bursts of the high-frequency signal. A zenor diode  139  is used for regulation and capacitor  136  blocks any net direct current. 
   As shown in conjunction with  FIGS. 55 and 56  the pulses generated from the stimulus-receiver circuitry  120  are compared to a reference voltage, which is programmed in the implanted pulse generator  70 . When the voltage of incoming pulses exceeds the reference voltage ( FIG. 56B ), the output of the comparator  178 , 180  sends digital pulse  89  (shown in  FIG. 56C ) to the stimulation electric module  184 . At this predetermined level, the high threshold comparator  178  fires and the controller  184  suspends any stimulation from the implanted pulse generator  70 . The implanted pulse generator  70  goes into “sleep” mode for a predetermined period of time. In one preferred embodiment, the level of voltage needed for the battery operated stimulator to go into “sleep” mode is a programmable parameter. The length of time, the implanted pulse generator  70  remains in “sleep” mode is also a programmable parameter. Therefore, advantageously the external stimulator  42  in conjunction with the inductively coupled part of the stimulator  120  can be used to save the battery life of the implanted stimulator  75 . 
   In one embodiment, the external stimulator  42  is networked using the internet, giving the attending physician full control for activating and de-activating selected programs. Using “trial and error” various programs for electrical pulse therapy can be custom adjusted for the physiology of the individual patent. Also, by using the external stimulator  42 , the battery  188  of the implanted stimulator unit  75  can be greatly extended. Further, even after the battery  188  is depleted, the system can still be used for neuromodulation using the stimulus-receiver module  120 , and the external stimulator  42 . 
     FIG. 58  shows a diagram of the finished implantable stimulator  75 .  FIG. 59  shows the pulse generator with some of the components used in assembly in an exploded view. These components include a coil cover  7 , the secondary coil  48  and associated components, a magnetic shield  9 , and a coil assembly carrier  11 . The coil assembly carrier  11  has at least one positioning detail  13  located between the coil assembly and the feed through for positioning the electrical connection. The positioning detail  13  secures the electrical connection. 
   Implantable Pulse Generator (IPG) Comprising A Rechargable Battery 
   In one embodiment, an implantable pulse generator with rechargeable power source can be used. In such an embodiment (shown in conjunction with  FIG. 60 ), a recharge coil is external to the pulse generator titanium can. The RF pulses transmitted via coil  46  and received via subcutaneous coil  48 A are rectified via diode bridge  154 . These DC pulses are processed and the resulting current applied to recharge the battery  188 A in the implanted pulse generator. 
   In summary, the method of the current invention for neuromodulation of cranial nerve such as the vagus nerve(s), to provide therapy for neurological and neuropsychiatric disorders, can be practiced with any of the several power sources disclosed including, 
   a) an implanted stimulus-receiver with an external stimulator; 
   b) an implanted stimulus-receiver comprising a high value capacitor for storing charge, used in conjunction with an external stimulator; 
   c) a programmer-less implantable pulse generator (IPG) which is operable with a magnet; 
   d) a programmable implantable pulse generator; 
   e) a combination implantable device comprising both a stimulus-receiver and a programmable IPG; and 
   f) an IPG comprising a rechargeable battery. 
   Neuromodulation of vagus nerve(s) with any of these systems is considered within the scope of this invention. 
   In one embodiment, the external stimulator and/or the programmer has a telecommunications module, as described in a co-pending application, and summarized here for reader convenience. The telecommunications module has two-way communications capabilities. 
     FIGS. 61 and 62  depict communication between an external stimulator  42  and a remote hand-held computer  502 . A desktop or laptop computer can be a server  500  which is situated remotely, perhaps at a physician&#39;s office or a hospital. The stimulation parameter data can be viewed at this facility or reviewed remotely by medical personnel on a hand-held personal data assistant (PDA)  502 , such as a “palm-pilot” from PALM corp. (Santa Clara, Calif.), a “Visor” from Handspring Corp. (Mountain view, Calif.) or on a personal computer (PC). The physician or appropriate medical personnel, is able to interrogate the external stimulator  42  device and know what the device is currently programmed to, as well as, get a graphical display of the pulse train. The wireless communication with the remote server  500  and hand-held PDA  502  would be supported in all geographical locations within and outside the United States (US) that provides cell phone voice and data communication service. 
   In one aspect of the invention, the telecommunications component can use Wireless Application Protocol (WAP). The Wireless Application Protocol (WAP), which is a set of communication protocols standardizing Internet access for wireless devices. While previously, manufacturers used different technologies to get Internet on hand-held devices, with WAP devices and services interoperate. WAP also promotes convergence of wireless data and the Internet. The WAP programming model is heavily based on the existing Internet programming model, and is shown schematically in  FIG. 63 . Introducing a gateway function provides a mechanism for optimizing and extending this model to match the characteristics of the wireless environment. Over-the-air traffic is minimized by binary encoding/decoding of Web pages and readapting the Internet Protocol stack to accommodate the unique characteristics of a wireless medium such as call drops. 
   The key components of the WAP technology, as shown in  FIG. 63 , includes 1) Wireless Mark-up Language (WML)  550  which incorporates the concept of cards and decks, where a card is a single unit of interaction with the user. A service constitutes a number of cards collected in a deck. A card can be displayed on a small screen. WML supported Web pages reside on traditional Web servers. 2) WML Script which is a scripting language, enables application modules or applets to be dynamically transmitted to the client device and allows the user interaction with these applets. 3) Microbrowser, which is a lightweight application resident on the wireless terminal that controls the user interface and interprets the WML/WMLScript content. 4) A lightweight protocol stack  520  which minimizes bandwidth requirements, guaranteeing that a broad range of wireless networks can run WAP applications. The protocol stack of WAP can comprise a set of protocols for the transport (WTP), session (WSP), and security (WTLS) layers. WSP is binary encoded and able to support header caching, thereby economizing on bandwidth requirements. WSP also compensates for high latency by allowing requests and responses to be handled asynchronously, sending before receiving the response to an earlier request. For lost data segments, perhaps due to fading or lack of coverage, WTP only retransmits lost segments using selective retransmission, thereby compensating for a less stable connection in wireless. The above mentioned features are industry standards adopted for wireless applications and greater details have been publicized, and well known to those skilled in the art. 
   In this embodiment, two modes of communication are possible. In the first, the server initiates an upload of the actual parameters being applied to the patient, receives these from the stimulator, and stores these in its memory, accessible to the authorized user as a dedicated content driven web page. The physician or authorized user can make alterations to the actual parameters, as available on the server, and then initiate a communication session with the stimulator device to download these parameters. 
   Shown in conjunction with  FIG. 64 , in one embodiment, the external stimulator  42  and/or the programmer  85  may also be networked to a central collaboration computer  286  as well as other devices such as a remote computer  294 , PDA  502 , phone  141 , physician computer  143 . The interface unit  292  in this embodiment communicates with the central collaborative network  290  via land-lines such as cable modem or wirelessly via the internet. A central computer  286  which has sufficient computing power and storage capability to collect and process large amounts of data, contains information regarding device history and serial number, and is in communication with the network  290 . Communication over collaboration network  290  may be effected by way of a TCP/IP connection, particularly one using the internet, as well as a PSTN, DSL, cable modem, LAN, WAN or a direct dial-up connection. 
   The standard components of interface unit shown in block  292  are processor  305 , storage  310 , memory  308 , transmitter/receiver  306 , and a communication device such as network interface card or modem  312 . In the preferred embodiment these components are embedded in the external stimulator  42  and can also be embedded in the programmer  85 . These can be connected to the network  290  through appropriate security measures (Firewall)  293 . 
   Another type of remote unit that may be accessed via central collaborative network  290  is remote computer  294 . This remote computer  294  may be used by an appropriate attending physician to instruct or interact with interface unit  292 , for example, instructing interface unit  292  to send instruction downloaded from central computer  286  to remote implanted unit. 
   Shown in conjunction with  FIGS. 65A and 65B  the physician&#39;s remote communication&#39;s module is a Modified PDA/Phone  502  in this embodiment. The Modified PDA/Phone  502  is a microprocessor based device as shown in a simplified block diagram in  FIGS. 65A and 65B . The PDA/Phone  502  is configured to accept PCM/CIA cards specially configured to fulfill the role of communication module  292  of the present invention. The Modified PDA/Phone  502  may operate under any of the useful software including Microsoft Window&#39;s based, Linux, Palm OS, Java OS, SYMBIAN, or the like. 
   The telemetry module  362  comprises an RF telemetry antenna  142  coupled to a telemetry transceiver and antenna driver circuit board which includes a telemetry transmitter and telemetry receiver. The telemetry transmitter and receiver are coupled to control circuitry and registers, operated under the control of microprocessor  364 . Similarly, within stimulator a telemetry antenna  142  is coupled to a telemetry transceiver comprising RF telemetry transmitter and receiver circuit. This circuit is coupled to control circuitry and registers operated under the control of microcomputer circuit. 
   With reference to the telecommunications aspects of the invention, the communication and data exchange between Modified PDA/Phone  502  and external stimulator  42  operates on commercially available frequency bands. The 2.4-to-2.4853 GHz bands or 5.15 and 5.825 GHz, are the two unlicensed areas of the spectrum, and set aside for industrial, scientific, and medical (ISM) uses. Most of the technology today including this invention, use either the 2.4 or 5 GHz radio bands and spread-spectrum technology. 
   The telecommunications technology, especially the wireless internet technology, which this invention utilizes in one embodiment, is constantly improving and evolving at a rapid pace, due to advances in RF and chip technology as well as software development. Therefore, one of the intents of this invention is to utilize “state of the art” technology available for data communication between Modified PDA/Phone  502  and external stimulator  42 . The intent of this invention is to use 3 G technology for wireless communication and data exchange, even though in some cases 2.5 G is being used currently. 
   For the system of the current invention, the use of any of the “3 G” technologies for communication for the Modified PDA/Phone  502 , is considered within the scope of the invention. Further, it will be evident to one of ordinary skill in the art that as future 4G systems, which will include new technologies such as improved modulation and smart antennas, can be easily incorporated into the system and method of current invention, and are also considered within the scope of the invention.