Abstract:
Systems and methods are disclosed to stimulate nerves to treat medical conditions such as pain, and other conditions, such as, CHF, obesity, incontinence, etc., that could be controlled by the stimulation of the vagal nerves. The invention uses electrical stimulation of the nerve, where vibrational energy from a source is received by an implanted device and converted to electrical energy and the converted electrical energy is used by implanted electrodes to stimulate the pre-determined nerve site. The vibrational energy is generated by a controller-transmitter, which could be implanted or located externally. The vibrational energy is received by a receiver-stimulator, which could be located in the various regions on or around the nerve that needs to be stimulated. The implantable receiver-stimulator stimulates different nerves and regions of a nerve to provide therapeutic benefit.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
       [0001]    The present application is a divisional of U.S. patent application Ser. No. 11/764,592 (Attorney Docket No. 021834-001810US), filed Jun. 18, 2007, which claims the benefit of provisional U.S. Application No. 60/805,319 (Attorney Docket No. 021834-001800US), filed Jun. 20, 2006, the full disclosures of which are incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The systems and methods of this invention relate to direct electrical stimulation of nerves, nerve bundles, nerve tissue, and regions in proximity to nerves of the body to treat a variety of medical conditions. Specifically, the present invention relates to methods and apparatus for applying such stimulation to selected nerves without the use of conventional lead/electrode systems. 
         [0004]    2. Description of the Background Art 
         [0005]    Electrical stimulation of nerves, nerve roots, and/or other nerve bundles for the purpose of treating patients has been known and actively practiced for several decades. Application of an electrical field between electrodes to stimulate nerve tissues is known to effectively modify signal pathways both with unidirectional and bidirectional stimulation along the nervous system to signal the brain or to signal organs to alleviate symptoms or control function. These applications are currently practiced with, both, externally applied devices and implanted devices. For example, applying specific electrical pulses to nerve tissue or to peripheral nerve fibers that corresponds to regions of the body afflicted with chronic pain can induce paresthesia, or a subjective sensation of numbness or tingling, or can in effect block pain transmission to the brain from the pain-afflicted regions. Many other examples include electrical stimulation of various branches of the vagus nerve bundle for control of heart rate, mediating hypertension, treating congestive heart failure, controlling movement disorders, treating obesity, treating migraine headache, and effecting the urinary, gastrointestinal, and/or other pelvic structure in order to treat urgency frequency, urinary incontinence, and/or fecal incontinence. Still other branches of the vagus nerve have been used to treat neuropsychiatric disorders. Additionally, applications are also known for electrical stimulation of nerves and nerve bundles in many other specific, selected nerve regions: for example, the pudendal or sacral nerves for controlling the lower urinary tract. 
         [0006]    Depending on the individual patient, direct nerve stimulation can effectively modify signal pathways along the nerve, to and from the brain, and to and from organs in the body and thus provide relief of symptoms or control of bodily function. Treatment regimens and targeted nerve locations are known in related art through use of current, common stimulation devices and methods. Commonly implanted devices for nerve stimulation are made by such companies as Cyberonics, Medtronic, Advanced Bionics, and others. 
         [0007]    The nervous system is a complex anatomical network that is organized to connect the brain to all areas of the body. The brain uses the nervous system to control bodily processes and adjust the body to its environment. The nervous system is conceptualized by two parts; the central nervous system (CNS), and the peripheral nervous system (PNS). The CNS generally consists of the brain and the spinal cord. The PNS consists of a series of nerves and nerve bundles branching out to all organs and tissue areas of the body. The PNS is connected to the CNS and thus together provides the network of control between the brain and all specific bodily functions. As illustrated in  FIG. 1 , the central nervous system is pervasive throughout the body with individual nerves and nerve bundles reaching to all bodily functions. The PNS consists of the cervical, thoracic, lumbar, and sacral nerve trunks leading away from the spine to all regions of the body. The peripheral nervous system also includes cranial nerves. Sensory and control signals travel between the brain and other regions of the body using this network of nerves that all travel along the spinal cord. 
         [0008]    Transcutaneous electrical nerve stimulation (TENS) is a well known medical treatment used primarily for symptomatic relief and management of chronic intractable pain and as an adjunctive treatment in the management of post surgical and post traumatic acute pain. TENS involves the application of electrical pulses to the skin of a patient, which pulses are generally of a low frequency and are intended to affect the nervous system in such a way as to suppress the sensation of pain, in the area that the electrodes are applied. This typically would be indicated for use in acute or chronic injury or otherwise used as a protective mechanism against pain. Typically, two electrodes are secured to the skin at appropriately selected locations. Mild electrical impulses are then passed into the skin through the electrodes to interact with the nerves lying thereunder. As a symptomatic treatment, TENS has proven to effectively reduce both chronic and acute pain of patients. 
         [0009]    In the context of this application, Specific Nerve Stimulation (SNS) refers to treatments for a variety of medical conditions that apply electrical stimulation directly to nerves, nerve roots, nerve bundles, tissue or regions in proximity to nerves that are in the PNS. Currently available stimulator systems for SNS are fully implanted electronic devices placed subcutaneously under the skin and connected via insulated metal lead(s) to electrodes which are invasively inserted into, around, or onto a nerve or proximate the nerve. A common implanted SNS system contains a battery to power the system. Some implanted SNS systems use an RF wireless connection instead of a battery to power the implanted device. In these RF systems, a receiver device is implanted subcutaneously and a transmitter is worn on the outside of the body. The antenna are tuned to each other and aligned such that control information and power is transmitted to the receiver and then directs the electrical impulses to the electrodes through the leads. The external transmitter contains batteries to power the transmission. All systems have the capability to externally adjust settings of the implanted system through a programming device. 
         [0010]    In SNS and TENS systems, electrical energy is delivered through lead wires to the electrodes. For SNS, implanted electrodes are positioned on, around, or in close proximity of the nerve to be stimulated. SNS uses the implanted electrodes to deliver a variety of stimulation modalities including unidirectional and bidirectional propagation along the nerve with the electric pulse waveform defined by a plurality of variables, including, pulse width, pulse frequency (Hz) or duty cycle, amplitude (V), and waveform shape (e.g., mono-phasic or bi-phasic). 
         [0011]    SNS is used for treatment of headache, migraine headache, or facial pain by selection of branches in the peripheral nervous system in the cranium or along the vagus nerve bundle. SNS is used for the treatment of chronic pelvic pain due to such conditions as lumbosacral radiculitis, lumbosacral radiculopathy, lumbosacral plexitis, lumbosacral plexopathy, vulvadynia, coccygodynia, peripheral neuritis, and peripheral neuropathy, by applying stimulation to the peripheral nervous system in the sacrum. 
         [0012]    SNS is also applied to branches of the vagus nerve in a wide variety of applications, but not limited to the treatment of heart failure; hypertension; obesity; migraine; neuropsychiatric disorders; urinary, gastrointestinal, and/or other pelvic area structures in order to treat urinary urgency, urinary incontinence, and/or fecal incontinence. SNS is also used for severe chronic pain. Stimulation of specific nerves is known to reduce symptoms and enhance the quality of life in patients with chronic pain. 
         [0013]    As described above, TENS and SNS devices are battery-powered electronic devices either used transcutaneously (TENS) or implanted (SNS) and connected via insulated metal lead(s) to electrodes which are either placed on the skin (TENS) over the spine or implanted onto, around, or in close proximity to the nerve or nerve bundle selected for stimulation. The implanted electrodes for SNS are positioned on leads that are placed percutaneously, through needle punctures, or through minimally invasive surgical procedures such as laminectomy, or through direct surgical access to position the electrodes on, around, or in proximity to the targeted nerve. On some leads, between 2 and 16 electrodes are available and are positioned in the region that is targeted for electrical stimulation. The implanted leads are then subcutaneously tunneled to the pulse generator (also referred to as a controller) that is implanted in a subcutaneous pocket. The use of these lead wires is associated with significant problems such as complications due to infection, lead failure, lead migration, and electrode/lead dislodgement. Application of electrodes to the nerves can be difficult because of the need to precisely locate electrodes for effective therapy. 
         [0014]    Other prior art has attempted to deal with the complications and limitations imposed by the use of electrical leads. For example, self-contained implantable microstimulators and remotely powered microstimulators have been described; however each approach suffers from some significant limitation. A self-contained microstimulator must incorporate a battery or some other power supply; this imposes constraints on size, device lifetime, available stimulation energy, or all three. Due to high use or high energy requirements of the therapeutic stimulation some SNS devices contain recharageable batteries or are powered remotely with an RF coupling to the controller. 
         [0015]    For leadless solutions in other similar stimulation applications, remotely powered devices have previously utilized either radiofrequency (RF) or electromagnetic transformer power transmission. RF energy transmission, unless the transmitting and receiving antennae are placed in close proximity, suffers from inefficiency and limited safe power transfer capabilities, limiting its usefulness in applications where recharging or stimulation must be accomplished at any significant depth (&gt;1-2 cm) within the body, in particular where it is desired to permanently implant both the transmitter and receiver-stimulator. Electromagnetic coupling can more efficiently transfer electrical power, and can safely transfer higher levels of power (devices with capacity in excess of 20 Watts have been produced), but again relies on close proximity between transmitting and receiving coils, or the utilization of relatively large devices for deeper (5-8 cm maximum) implantation. 
         [0016]    The methods and apparatus of the current invention utilize vibrational energy, particularly at ultrasonic frequencies, to overcome many of the limitations of currently known solutions for selected nerve stimulation, by achieving a nerve stimulation capability without the use of leads connected to a stimulation controller/pulse generator. It is not the intent to limit the scope of this invention to the nerves and nerve bundles in the description but rather to provide a broad solution for stimulation of any selected nerve in the body without the use of leads. 
         [0017]    The following patents, all of which are incorporated in this disclosure in their entirety, describe various aspects of using electrical stimulation for achieving various beneficial effects by selected nerve stimulation. U.S. Pat. No. 3,835,833 titled “Method for Obtaining Neurophysiological Effects” by Limoge describes delivery and parameters for electrical stimulation in a TENS stimulation system. U.S. Pat. No. 4,690,144 titled “Wireless Transcutaneous Electrical Tissue Stimulator” by Rise et al. also describes delivery, systems, and application parameters for a TENS stimulation system. U.S. Pat. No. 6,735,475 titled “Fully implantable miniature neurostimulator for stimulation as a therapy for headache and/or facial pain” by Whitehurst et al. describes an implantable microstimulator used for treatment of pain in peripheral nerves generally in the skull or the cervical regions of the spine. U.S. Pat. No. 3,522,811 titled “Implantable Nerve Stimulator and Method of Use” by Schwartz et al. describes an implantable application for stimulation of the carotid sinus nerve as a treatment for hypertension. U.S. Pat. No. 6,615,081 titled “Apparatus and method for adjunct (add-on) treatment of diabetes by neuromodulation with an external stimulator” by Boveja describes an implantable application for stimulation of the vagus nerve as a treatment for diabetes. U.S. Pat. No. 6,684,105 titled “Treatment of disorders by unidirectional nerve stimulation” by Cohen et al. describes an application of electrical stimulation of nerves in unidirectional and bidirectional propagation of the electrical treatment along the nerve. U.S. Pat. No. 5,282,468 titled “Implantable neural electrode” by Klepinski describes an implantable neural electrode for stimulation in contact with nerve tissue. U.S. Pat. No. 5,330,515 titled “Treatment of pain by vagal afferent stimulation” by Rutecki et al. describes an implantable application for stimulation of the vagus nerve as a treatment for pain. U.S. Pat. No. 6,622,038 titled “Treatment of movement disorders by near-diaphragmatic nerve stimulation” by Barrett et al. describes an implantable application for stimulation of branches of the vagus nerve near the diaphragm as a treatment for movement disorders such as epileptic seizure, essential tremor, etc. U.S. Pat. No. 6,622,041 titled “Treatment of congestive heart failure and autonomic cardiovascular drive disorders” by Terry et al. describes an implantable application for stimulation of the cardiac branch of the vagus nerve as a treatment for congestive heart failure. U.S. Pat. No. 5,188,104 titled “Treatment of eating disorders by nerve stimulation” by Wernicke et al. describes an implantable application for stimulation of the vagus nerve as a treatment for eating disorders. U.S. Pat. No. 6,879,859 titled “External pulse generator for adjunct (add-on) treatment of obesity, eating disorders, neurological, neuropsychiatric, and urological disorders” by Boveja describes an external application for stimulation of the vagus nerve as a treatment for a variety of conditions for example, obesity, urological disorders, etc. where the application of the stimulation can be turned off and on by the patient or caregiver. U.S. Pat. No. 6,505,074 titled “Method and apparatus for electrical stimulation adjunct (add-on) treatment of urinary incontinence and urological disorders using an external stimulator” by Boveja describes an external application for stimulation of the sacral nerves and its branches as a treatment for a variety of urological conditions. U.S. Pat. No. 5,215,086 titled “Therapeutic treatment of migraine symptoms by stimulation” by Terry et al. describes an implantable application for stimulation of the vagus nerve as a treatment for migraine headache. U.S. Pat. No. 5,531,778 titled “Circumneural electrode assembly” by Maschino et al. describes an electrode design for attachment to a nerve. U.S. Pat. No. 5,251,634 titled “Helical nerve electrode” by Weinberg describes an electrode design for attachment to a nerve. U.S. Pat. No. 6,622,047 titled “Treatment of neuropsychiatric disorders by near-diaphragmatic nerve stimulation” by Barrett et al. describes an implantable application for stimulation of the vagus nerve as a treatment for neuropsychiatric disorders. U.S. Pat. No. 7,047,078 titled “Methods for stimulating components in, on, or near the pudendal nerve or its branches to achieve selective physiologic responses” by Boggs et al. describes an implantable application for stimulation of the pudenal nerve to control physiologic responses, for example for control of the urinary tract. U.S. Pat. No. 6,002,965 titled “Epidural nerve root stimulation” by Feler et al. describes treating pelvic pain by application of stimulation of nerves in the sacral and lumbar regions of the spine. U.S. Pat. No. 5,405,367 titled “Structure and Method of Manufacture of an Implantable Microstimulator” by Schulman et al. describes an implantable microstimulator used generally for stimulation of tissue. U.S. Pat. No. 6,037,704 titled “Ultrasonic Power Communication System” by Welle describes the use of ultrasound energy transfer from a transmitter to a receiver for purposes of powering a sensor or actuator without being connected by a lead/wire. U.S. Pat. No. 6,366,816 titled “Electronic Stimulation Equipment with Wireless Satellite Units” by Marchesi describes a tissue stimulation system based on a wireless radio transmission requiring the charging of a battery at the receiver and separate command signals used to control the delivery of stimulation. German patent application DE4330680A1 titled “Device for Electrical Stimulation of Cells within a Living Human or Animal” by Zwicker describes a general approach to power transfer using acoustic energy for tissue stimulation. 
       BRIEF SUMMARY OF THE INVENTION 
       [0018]    This invention relates to methods and devices for using electrical stimulation of nerves as a treatment for effectively modulating signal pathways along the nerve, to and from the brain, and to and from organs in the body and thus provide relief of symptoms or control of bodily function. This invention uses vibrational energy as a means to transmit energy and signal information from a first device, to a second device containing means to receive such vibrational energy and converting it into electrical energy and then apply that electrical energy to stimulating electrodes. The first device is intended to be either implanted or to be used externally. The second device is intended to be either permanently or temporarily implanted with stimulating electrodes in contact with or in close proximity to the specific nerve, nerve bundle, nerve branch or nerve root to be stimulated. 
         [0019]    This application of leadless electrical stimulation is for specific nerve stimulation applications where the stimulation acts unidirectionally or bidirectionally between the peripheral nerve and the brain. The invention is a system comprising a controller-transmitter, an implanted receiver-stimulator, a programmer to adjust therapy parameters, and stimulation electrodes, such that the stimulation electrodes would be in contact with nerves, in close proximity to the nerve or nerve tissue region to be stimulated to facilitate treatment. Systems incorporating the concepts presented herein have significant advantages over currently available devices, particularly by eliminating the requirement for electrical leads, and by providing the capability for simultaneous or sequenced stimulation of multiple sites. 
         [0020]    In one embodiment, the controller-transmitter is implanted. The controller-transmitter is implanted subcutaneously beneath the skin. In another embodiment, the controller-transmitter is applied on the patient&#39;s body surface or skin. The transmitted vibrational energy is directed to the receiver-stimulator to cause electrical stimulation at the electrodes of the receiver-stimulator. 
         [0021]    In one use of the external embodiment of the controller-transmitter, the device is for treating urge incontinence; in another use of the external embodiment, it is for recurring but non-continuous pain, for example, headache. In the external embodiment, miniaturized receiver-stimulator devices are implanted, but the controller-transmitter unit is external to the body, possibly hand-held or worn attached to a belt or harness. The acoustic energy from the external controller-transmitter is coupled through the skin as well as any underlying tissues, to the implanted device. The external controller-transmitter is under control of the patient. Thus, when the patient begins to feel discomfort, the controller-transmitter unit is applied and/or switched on, and certain characteristics, for example the level of stimulating energy and possibly the frequency or pulse duration of the stimulating waveform, is modified by the user, enabling the user to tailor the stimulation as needed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]      FIG. 1  is a schematic showing the basics of the nervous system anatomy. 
           [0023]      FIG. 2  is a schematic showing the leadless stimulation system in application with an implantable controller-transmitter for stimulation of a peripheral branch of the vagus nerve. 
           [0024]      FIG. 3  is a schematic showing the leadless stimulation system in application with an externally applied controller-transmitter for stimulation of a peripheral branch of the vagus nerve. 
           [0025]      FIGS. 4   a  and  4   b  are block diagrams showing the components of the acoustic controller-transmitter and acoustic receiver-stimulators of the present invention. 
           [0026]      FIG. 5  illustrates representative acoustic and electrical signals useful in the systems and methods of the present invention. 
           [0027]      FIGS. 6   a ,  6   b , and  6   c  are schematic illustrations showing components of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0028]    The systems and devices describe here comprise a controller-transmitter device that will deliver vibrational energy and signal information to one or more implanted receiver-stimulator device(s) that will convert the vibrational energy to electrical energy of a form that can be used to electrically stimulate nerve tissue. The vibrational energy can be applied with ultrasound as a single burst or as multiple bursts or as a continuous wave with appropriate selection of the following parameters: 
         [0000]    
       
         
               
               
               
             
           
               
                   
                   
               
               
                   
                 Parameter 
                 Value Range 
               
               
                   
                   
               
             
             
               
                   
                 Ultrasound frequency 
                 20 kHz-10 MHz 
               
               
                   
                 Burst Length (#cycles) 
                 3-Continuous 
               
               
                   
                 Stimulation Pulse Duration 
                 0.1 μsec-Continuous 
               
               
                   
                 Duty Cycle 
                 0-100% 
               
               
                   
                 Mechanical Index 
                 ≦1.9 
               
               
                   
                   
               
             
          
         
       
     
         [0029]    The controller-transmitter device would contain one or more ultrasound transducers of appropriate size(s) and aperture(s) to generate sufficient acoustic power to achieve the desired stimulation at the location of an implanted receiver-stimulator device. Additionally, multiple implanted receiver-stimulator devices may be placed within the region insonified by the controller-transmitter device. Multiple receiver-stimulator implants may function simultaneously; it is also possible for multiple devices to function independently, either by responding only to a specific transmitted frequency, or through the use of a selective modulation technique such as pulse width modulation, or through encoding techniques such as time-division multiplexing. 
         [0030]    A leadless pulse stimulator would be applied percutaneously or surgically. Utilizing a percutaneous needle delivery technique to access the nerve, a miniaturized receiver-stimulator device disposed within the delivery needle is implanted into tissue or attached to the desired location on the nerve. Various techniques and tools for surgical access and probing of nerve tissue are commonly known. These could be adapted to facilitate delivery of the receiver-stimulator to these locations; the receiver-transmitter may incorporate means to provide permanent attachment to the implant site including possibly helical coils, barbs, tines, or the like or could be adapted in form to surround the nerve as a wrap or along the longitudinal length of the nerve. 
         [0031]    Functionally, the receiver-stimulator device comprises an ultrasound transducer to receive acoustic energy and transform it into electrical energy, an electrical circuit to transform the alternating electrical energy into a direct current or a pre-determined waveform, and electrodes to transfer the electrical field energy between an electrode pair to the nerve. 
         [0032]    Additionally, a controller-transmitter device is adapted for directional, vibrational energy transmission emitted by the device to intersect the implanted receiver-stimulator. In an implanted version, the controller-transmitter device containing the transmitting transducer is implanted typically just beneath the skin in a subcutaneous space. If not implanted, the transducer portion of the transmitter would be placed over the skin directionally angled to the target region containing the receiver-stimulator with acoustic gel, or other means, used for coupling the acoustic energy to the skin. 
         [0033]    In an alternative embodiment, the controller-transmitter device is incorporated into a device also providing conventional lead-based electrical stimulation, in a nerve stimulation system wherein a conventional lead/electrode system would provide stimulus to directly connected regions of the nerve using leads and transmitting vibrational energy to provide stimulation to regions of the nerve where receiver-stimulators are implanted. 
         [0034]    The controller-transmitter device would contain similar elements of most currently available stimulator systems including a power source, stimulation control and timing circuitry, physiologic sensing systems, and in the implanted embodiment, a system to communicate with an outside console for data transmission, diagnostic, and programming functions typically through a radiofrequency (RF) link is provided. Additionally, the controller-transmitter device would contain an ultrasound amplifier and one or more ultrasound transducers to generate acoustic energy, and transmit such energy in the general direction of the receiver-stimulator implanted in the body. The duration, timing, and power of the acoustic energy transmission would be controlled as required, per tested parameters that are constructed for specific treatments. 
         [0035]    A single receiver-stimulator device is implanted with the electrodes in contact or close proximity to the nerve, as described above, for single-region stimulation; alternatively, it would be possible to implant a plurality of receiver-stimulator devices to stimulate either simultaneously by receiving the same transmitted acoustic energy or independently by responding only to acoustic energy of a specific character (i.e., of a certain frequency, amplitude, or by other modulation or encoding of the acoustic waveform) intended to energize only that specific device. This enables a much more robust utilization of site and region specific stimulation not currently practical with current lead-based implementations whose electrode spacing is fixed on the lead set selected for use and may not adapt itself to the structure of the nerve. Selecting multiple sites and regions for treatments would be greatly enhanced by eliminating the need to connect multiple electrode sites to the stimulation energy source by the use of multiple leads/wires connected to the electrodes or by attempting to anticipate the required spacing between electrodes. 
         [0036]    These examples are representative and in no way limiting the applications in which an electro-acoustic stimulator may be utilized to stimulate specific nerves in the body to treat symptoms or control bodily functions. 
         [0037]    The delivery of ultrasound energy and, therefore, electrical stimulation could either be automatically triggered based on information received from an internal or external physiological sensor, or be based upon programmed settings, or be manually activated by the patient or other individuals. More specifically, the timing of the initiation of the delivery and/or the duration of the delivery and/or the energy content of the delivery and/or the information content of the delivery could be based upon sensor information or based upon programmed settings or be manually controlled. 
         [0038]    Examples of such an electro-acoustic stimulation system as a nerve stimulator are illustrated in  FIGS. 2 and 3 . 
         [0039]    In  FIG. 2 , a controller-transmitter device  1  containing circuitry to provide stimulation control and ultrasound transmission, plus means to communicate with an outside programmer  3  is implanted subcutaneously. It is situated such that the directional angle of the transmitted ultrasound beam would intersect the receiver-stimulator  2 . An ultrasound signal is transmitted by this device through intervening tissue to the receiver-stimulator device  2  containing means to receive this acoustic energy and convert it into an electrical waveform which may then be applied to the attached electrodes. In  FIG. 2 , this receiver-stimulator device  2  is shown embedded, in this one example, in the neck region and attached to a peripheral branch of the vagus nerve bundle. The receiver-stimulator device  2  is shown here as a small cylindrical or button-shaped device placed on the nerve in similar ways that current stimulator systems apply electrodes to nerves. Optionally, the receiver-stimulator  2  could be deployed onto the nerve or in proximity to the nerve affixed with an attaching coil or other method. Also optionally (not shown), the receiver-stimulator device  2  could be incorporated into a expandable or self-expanding mechanical mesh that would stay located in the tissue by means of spring tension similar to a stent placement in a vascular application but rather held in place between tissue sections near the nerve. 
         [0040]    In  FIG. 3 , an externally applied controller-transmitter device  41  containing circuitry to provide stimulation therapy control and ultrasound transmission, plus control means  42  to allow the patient or operator to directly adjust ultrasound output based on desired therapy parameters including, at least, amplitude, pulse duration, and pulse repetition frequency, to produce an effective control of the nerve. The external transmitter  41  may be handheld, or worn on the body, attached by a belt, harness, or the like. The external controller-transmitter  41  is similar to the implantable controller-transmitter device described previously, containing, at the minimum, an adjustable pulse/frequency generator, ultrasound amplifier, ultrasound transmitter, and battery. Optionally, the battery may be a rechargeable type. It is situated such that the directional angle of the transmitted ultrasound beam would intersect the receiver-stimulator  2 . An ultrasound signal is transmitted by this device through intervening tissue to the receiver-stimulator device  2  containing means to receive this acoustic energy and convert it into an electrical waveform which may then be applied to the attached electrodes. In  FIG. 3 , this receiver-stimulator device  2  is shown embedded, in this one example, in a branch of the vagus nerve in the region of the stomach as a treatment for obesity. 
         [0041]      FIGS. 4   a  and  4   b  show more details of the system described above and shown in  FIG. 2 . In  FIG. 4   a , the controller-transmitter device  1  comprises: a battery  10 , one or more sensors  11 , signal processing circuitry  12 , a communications module  13 , a control and timing module  14 , an ultrasound amplifier  15 , and an ultrasound transducer  16 . The battery  10  which provides power for the controller-transmitter may be of a type commonly used in implanted medical devices such as a lithium iodine cell or lithium silver vanadium oxide cell made by Greatbatch, Inc. or which is optionally a rechargeable battery. One or more sensors  11  are used to detect physiological parameters. Suitable sensors are known for the detection of electrical activity, temperature, motion, pressure, and the like. These sensors are connected to signal processing circuitry  12  and optionally used by the circuitry to adjust delivery of stimulation therapy or to communicate diagnostic information from the sensors. The communications module  13  provides a data path to allow the physician to set device parameters and to acquire diagnostic information about the patient and/or the device. The data path may be by an RF communication link, magnetic coupling, ultrasound pulses, or the like, and would communicate to and from an external unit  3 . Device parameters would be used by the control and timing module  14 . Device parameters would include adjustments to transmissions, such as power amplitude, pulse duration, duty cycle, and the like. The control and timing module  14  uses device parameters in conjunction with the acquired physiological data to generate the required control signals for the ultrasound amplifier  15 , which in turn applies electrical energy to the ultrasound transducer  16 , which in turn produces the desired acoustic beam. The controller-transmitter device  1  is encased in a hermetically sealed case  17  constructed of a biologically compatible material, similar to current SNS devices. 
         [0042]    Referring to  FIG. 4   b , the receiver-stimulator device  2 , implanted in the path of the acoustic beam at the location where electrical stimulation is desired, contains an ultrasound transducer  20 , an electrical circuit  21 , and electrodes  22 . Ultrasound transducer  20 , typically made of a piezoelectric ceramic material, a piezoelectric single crystal, or piezoelectric polymer or copolymer films, intercepts a portion of the transmitted acoustic energy and converts it into an electrical current waveform from the original alternating nature of the applied ultrasound pressure wave. This electrical signal is applied to an electrical circuit  21  which may be one of a type commonly known as an envelope detector, and which may have one of many known circuit configurations; for example, a full-wave rectifier, a half-wave rectifier, a voltage doubler or the like. Electrical circuit  21  produces a voltage pulse with amplitude proportional to the amplitude of the transmitted ultrasound burst and with a pulse length generally equal to the length of the transmitted burst. The circuit  21  may also have different configurations and functions, and provide output signals having characteristics other than a pulse. This signal is applied then to electrodes  22 , which are typically made of platinum, platinum-iridium, gold, or the like. These may be incorporated onto the outer surface of the device, and thus in direct contact within the epidural layer or within close proximity of nerves or nerve fibers which are to be treated by stimulation. Alternatively, the electrodes  22  are connected via wires to a main body that consists of the transducer  20  and electrical circuit  21  and the electrodes  22  are adapted to be shapeable, malleable configurations that conform to the nerve as flexible wraps or the like or that could be placed on the nerve. Electrodes may be adapted that are round, long, segmented, etc. to increase surface area or to control current density at the electrode. Electrodes may be placed on opposing sides of the nerve or in linear alignment with the nerve or in any arrangement suitable for the size and location of the nerve and the targeted nerve stimulation site. The receiver-stimulator device  2  is also enclosed within a sealed case  23  of biologically compatible material 
         [0043]    Referring also to previously described  FIGS. 4   a  and  4   b ,  FIG. 5  provides detail representing exemplary acoustic and electrical signals of the present system.  FIG. 5  first depicts a train of electrical stimulation pulses  31  which have a desired width and are repeated at a desired interval. The controller-transmitter device  1  produces acoustic transmissions  32 , for the desired stimulation pulse width and repeated at the desired stimulation pulse interval, which are emitted from the ultrasound transducer  16 . Below the waveform  32  is shown an enlargement  33  of a single acoustic burst. This burst again has a desired width, a desired oscillation frequency F=1/t, and also a desired acoustic pressure indicated by the peak positive pressure P+ and peak negative pressure P−. The acoustic pressure wave, when striking the receiving transducer  20  of the receiver-stimulator device  2  generates an electrical signal  34  having frequency and burst length matching that of the transmitted waveform  33  and amplitude proportional to the transmitted acoustic pressure (˜+/−P). This electrical waveform is then rectified and filtered by the circuit  21  producing the desired pulse  35  with length equal to the burst length of the transmitted waveform  33  and amplitude (V PULSE ) proportional to the amplitude of the electrical signal  34 . Thus, it can be seen that it is possible in this example to vary the stimulation rate by varying the time between ultrasound bursts, to vary the duration of any one stimulation pulse by varying the duration of the ultrasound burst, and to vary the amplitude of the stimulation pulse by varying the amplitude of the transmitted ultrasound waveform. Circuit  21  could be configured to produce a direct current (DC) output or an alternating current (AC) output, or an output with any arbitrary waveform. Varying the use of signal information within the ultrasound transmission for pulse duration, pulse amplitude, and duty cycle would result in any type of burst sequencing or continuous delivery waveform effective for nerve stimulation. Using signal information in the ultrasound transmission the resultant waveshape may be a square wave, triangle wave, biphasic wave, multi-phase wave, or the like. 
         [0044]    In practice, the amount of acoustic energy received by the implanted receiver-stimulator device will vary with ultrasound attenuation caused by loss in the intervening tissue, with spatial location of the receiver-stimulator device with respect to the transmitted ultrasound beam as such a beam is typically non-uniform from edge-to-edge, and possibly with orientation (rotation) of the receiver-stimulator device with respect to the first. Such variation would affect the amplitude of the stimulating pulse for a given ultrasound transmit power (acoustic pressure amplitude). This limitation can be overcome by adjusting the ultrasound transmit power until the resultant stimulation waveform is consistent, a technique similar to that used currently to determine stimulation thresholds at the time of cardiac pacemaker implantation. Another approach would be to automatically adjust using sensing and logic within the first device. The first device would periodically sense the electrical output of the receiver-stimulator device and adjust power transmission accordingly to compensate for any change in the system including relative movement between the transmitting and receiving devices. Yet another embodiment for overcoming this limitation is where the transducer incorporated into the receiver-stimulator device is omni-directional in its reception capability. For example, to improve omni-directional sensitivity, the transducer may be spherical in shape or have specific dimensional characteristics relative to the wavelength of the transmitted ultrasound. Alternatively, multiple transducers are disposed at appropriate angles to reduce or eliminate the directional sensitivity of the device. 
         [0045]      FIGS. 6   a  through  6   c  illustrate two embodiments of a small implantable receiver-stimulator of a cylindrical profile, suitable perhaps for placement by stylet or by injection through a hypodermic needle.  FIG. 6   a  shows in plan view and  6   b  in perspective view such a receiver-stimulator  2  having a hollow, cylindrical ultrasound transducer  71 , a circuit assembly  72  comprising the detector, and two electrodes  73  at either end of the assembly. It can be appreciated that any number of electrodes may be adapted to this embodiment. The transducer  71  would be made of an appropriate piezoelectric ceramic material, having two electrical activity contacts deposited on the outer and inner surfaces of the cylinder, respectively. The transducer and circuit would be encapsulated in an electrically insulating but acoustically transparent medium  74 . The transducer  71  would be of a rigid piezoelectric material, typically a piezo-ceramic with electrodes deposited on the outer and inner surfaces of the cylinder. The circuit assembly  72  may be fabricated using known surface-mount or hybrid assembly techniques, upon either a fiberglass or ceramic substrate. Stimulation electrodes  73  would be fabricated of material commonly used in implanted electrodes, such as platinum, platinum-iridium, or the like. Necessary electrical wiring between the transducer, circuit board, and electrodes is not shown in these drawings. Typical dimensions of such a device would be 1.5 cm in length and 1.5 mm in diameter, and preferably smaller. Multiple electrodes could be adapted as appendages to the embodiment (not shown) or incorporated into fixation elements such as helical screws or barbs (not shown). 
         [0046]    As shown in  FIG. 6   c , by using hybrid circuit techniques it may be possible to further miniaturize the circuit assembly  72  such that it would fit inside the hollow interior of the transducer  71 . This would have the benefit of substantially reducing the length of the finished device. 
         [0047]    While exemplary embodiments have been shown and described in detail for purposes of clarity, it will be clear to those of ordinary skill in the art from a reading of the disclosure that various changes in form or detail, modifications, or other alterations to the invention as described may be made without departing from the true scope of the invention in the appended claims. For example, while specific dimensions and materials for the device have been described, it should be appreciated that changes to the dimensions or the specific materials comprising the device will not detract from the inventive concept. Accordingly, all such changes, modifications, and alterations should be seen as within the scope of the disclosure.