US20130238044A1 - Acoustically powered implantable stimulating device - Google Patents

Abstract

An implantable stimulation system comprises an implantable stimulator and a control device. The control device is configured to transmit acoustic waves to the implantable stimulator, and the implantable stimulator is configured to transform the acoustic waves into electrical current, and generate stimulation energy based on the electrical current. For example, the electrical current can be transformed into electrical energy that can be used to generate the stimulation energy. Or the electrical current can contain signals used to directly or indirectly control the generation of the stimulation energy.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS
• This application is a continuation of co-pending U.S. application Ser. No. 13/046,083, filed Mar. 11, 2011, which is a continuation of U.S. application Ser. No. 11/871,017, filed Oct. 11, 2007 (now U.S. Pat. No. 7,930,031), which is a continuation of U.S. application Ser. No. 10/632,265, filed Jul. 31, 2003 (now U.S. Pat. No. 7,283,874), which is a (1) a continuation-in-part of U.S. application Ser. No. 09/989,912, filed Nov. 19, 2001 (now U.S. Pat. No. 7,024,248), which is a continuation-in-part of U.S. application Ser. No. 09/690,615, filed Oct. 16, 2000 (now U.S. Pat. No. 6,628,989); (2) a continuation-in-part of U.S. application Ser. No. 09/888,272, filed Jun. 21, 2001 (now U.S. Pat. No. 6,764,446), which is a continuation-in-part of U.S. application Ser. No. 09/690,615, filed Oct. 16, 2000 (now U.S. Pat. No. 6,628,989); and (3) a continuation-in-part of U.S. patent application Ser. No. 10/413,428, filed Apr. 14, 2003 (now U.S. Pat. No. 7,198,603). All of these applications are expressly incorporated herein by reference in their entirety for all purposes.
TECHNICAL FIELD
• The present invention relates generally to medical devices for implantation within a patient's body.
BACKGROUND
• Since the introduction of the heart rhythm control system—first as an implantable pacemaker in the 1960's, and then as an implantable defibrillator in 1980, implantable electrical stimulating devices have been developed to treat various medical diseases and physiological ailments, such as chronic pain disorders (e.g., nerve injury, failed back syndrome, intractable facial pain, failed neck syndrome, reflex sympathetic dystrophy, thoracic outlet syndrome, and cancer), neurological disorders (e.g., intractable epilepsy and Parkinson's disease), motor disorders (e.g., spasticity, dystonia, spasmodic torticollis, athetosis, head injury, spinal cord injury, stroke, multiple sclerosis, and cerebral palsy), cardiac rhythm disorders (e.g., tachycardia and bradycardia), and psychosomatic disorders (e.g. depression and eating disorders).
• Some of these implantable devices are currently being marketed. For example, implantable spinal cord stimulators are currently being used in patients to relieve pain in various parts of the body, e.g., chronic back and leg pain, cancer pain, postoperative spinal cord injury pain, and reflex sympathetic dystrophy pain. The implantation process involves placing leads in the epidural space of the spinal canal in a location that corresponds to the patient's zone of pain. A pulse generator is then implanted in the lower anterior abdominal wall and then connected to electrodes on the leads via an extension that is percutaneously routed from the pulse generator to the leads. Once the system is fully implanted, the pulse generator can then be operated to provide low-voltage electrical stimulation of the spinal cord via the leads.
• Another means for managing pain involves implanting micro-current electrical neuromuscular stimulators (MENS) within a patient in the area of the perceived pain. These devices use a very low current (typically 1-100 μA) and operate on a cellular level to speed the healing process, thereby reducing pain. These devices have been specifically used to treat arthritic conditions, sports injuries, low back pain, carpal tunnel, tennis elbow, migraines and other disorders.
• A stimulation system similar to the spinal cord stimulator described above is currently being used to treat Parkinson's Disease. In this application, a lead is surgically implanted into the patient's brain adjacent the subthalamic nucleus (STN) or globus pallidus internal (GPi), which control the involuntary movement symptomatic of Parkinson's Disease. A pulse generator is implanted in the patient's chest near the collarbone, and then connected to electrodes on the lead via an extension that percutaneously runs from the pulse generator to the lead. The pulse generator can then be operated to electrically stimulate the effected regions of the brain in order to block the signals that cause the disabling motor symptoms.
• Pacemakers are used to alter the heart rate of a patient. A pacemaker, like the previously described devices, includes a pulse generator and leads. The pulse generator is implanted in a sub-dermal pocket in the patient chest, while the leads are inserted into a vein underneath the collar bone and threaded into the heart. Depending on the specific medical problem, a pacemaker can replace the S-A node signals that are delayed or get lost in the electrical pathway between the upper and lower heart. A pacemaker can also maintain a normal timing sequence between the upper and lower heart, and make sure that the critical lower chambers of the heart contract at an adequate rate. A pacemaker can pace a single chamber or two chambers of the right side of the heart, or even synchronize the two ventricles for optimizing the heart pumping capability.
• Other electrical stimulating devices might include peripheral nerve stimulators, medical delivery or activation systems, pumps for supporting a failing heart, controlling incontinence, or controlling the opening of a body passage, such as in a shunt for treating hydrocephalus.
• All of the above-described devices provide power to the pulse generator in one of two ways: installing a battery within the pulse generator or transmitting wireless energy to the generator, e.g., by wirelessly transmitting power from an external transmitter via radio frequency (RF) telemetry to an internal sub-dermal receiver hard-wired to the pulse generator. In some cases, the pulse generators may be wirelessly controlled by an external command, for example, to obtain data, and/or to activate or otherwise control the pulse generator. For those devices that use a battery, the size of the battery required to support the operational life of the device prevents the pulse generator from being located adjacent the stimulated region. As a result, the pulse generator is usually located in the body remote from electrodes, and a lead must be used to connect the generator and electrodes. For those devices that wirelessly supply power or data to the generator, RF energy may only penetrate a few millimeters into a body, because of the body's dielectric nature. Thus, RF energy may not be able to provide power to, or otherwise communicate with, an implant that is located deep within the body.
• Regardless of the means used to supply power to the pulse generator, it is sometimes possible to feel the pulse generator under the skin and visually notice a slight deformity of the skin region that covers the generator. In addition, the requirement of a lead adds complexity to the medical procedure and increases the risk of infection, and in the case of pacemakers and spinal cord stimulators, increases the risk of damaging heart valves that are crossed by the lead or the spinal cord over which the lead is routed. In some cases, the electrodes may become destabilized due to the forces applied on them by the lead. In addition, the leads are typically composed of metal formed as a coil in which electrical current may be adversely induced in the presence of a strong magnetic field, such as that created during Magnetic Resonance Imaging (MRI). As a result, those patients in which these leads are implanted cannot undergo an MRI.
SUMMARY
• In accordance with a first aspect of the present invention, an implantable stimulator is provided. The implantable stimulator comprises one or more acoustic transducers that are configured to transform acoustic waves into electrical current. The acoustic transducers can comprise any material capable of transforming acoustic energy into electrical energy, but in the preferred embodiment, a piezoelectric material is used. In the preferred embodiment, an array of acoustic transducers are used to maximize the received energy. The implantable stimulator further comprises a stimulating electrode configured to output stimulation energy to adjacent tissue. For example, the tissue can be heart tissue, in which case, the implantable stimulator may be a pacemaker or other cardiac therapeutic device, or the tissue can be nerve tissue, in which case, the implantable stimulator may be a neurostimulator. Other therapeutic devices are also contemplated by the present invention. The stimulation energy is based on the electrical current resulting from the transformation in the acoustic transducers. For example, the energy of the electrical current can be used to generate the stimulation energy and/or signals within the electrical current can be used to define the characteristics of the stimulation energy.
• Although the present invention should not be so limited in its broadest aspects, the use of low-frequency acoustic energy (e.g., around 40 KHz) to energize and communicate with the implantable stimulator allows the stimulator to be implanted deep within the tissue of a patient.
• In one preferred embodiment, the implantable stimulator comprises an energy storage device configured for storing the electrical current as electrical energy. In this case, the stored electrical energy can be subsequently used to generate stimulation energy under control of the implantable stimulator or another control device. The implantable stimulator may also comprise a switch configured for selectively outputting the electrical energy from the energy storage device to alternately activate and deactivate the implantable stimulator. In this manner, the implantable stimulator can be placed in a “dormant mode” when not in operation in order to conserve energy, and placed in an “active mode” when operated.
• In one preferred embodiment, the implantable stimulator comprises control circuitry configured to control the stimulation energy output from the stimulation electrode. For example, the control circuitry can generate and output the stimulation energy or alternately open and close a switch to generate the stimulation energy. Memory can be provided for storing stimulation parameters, which can be used by the control circuitry to control the stimulation energy output from the stimulation electrode.
• In another preferred embodiment, the implantable stimulator can be a “dumb device” in that it lacks control circuitry. In this case, the stimulation energy can be generated in response to the electrical current. For example, the electrical current can contain communication signals that alternately open and close a switch in order to generate the stimulation energy. Or the electrical current can be directly transformed into the stimulation energy.
• In accordance with a second aspect of the present invention, a self-contained implantable stimulator is provided. The implantable stimulator comprises a casing that integrates the previously described acoustic transducers, stimulator electrode, and control circuitry. In this manner, external leads are not required, since all components necessary to generate the stimulation energy are provided in the casing.
• In accordance with a third aspect of the present invention, a stimulation system is provided. The stimulation system comprises a control device configured for transmitting acoustic waves through tissue. The control device can be an external device that can be applied to the skin of the patient or worn by the patient. Or the control device can be an implantable device. In the latter case, the implantable control device may be advantageously charged by an external device using acoustic or radio frequency (RF) energy.
• The stimulation system further comprises at least one implantable stimulator configured for transforming the acoustic waves into electrical current, and outputting stimulation energy to adjacent tissue, e.g., heart or nerve tissue. The implantable stimulator(s) can be configured to control the stimulation energy output from the implantable stimulator, in which case, stimulation parameters used to control the stimulation energy can be stored in the implantable stimulator. The controller can alternatively be configured to directly control the stimulation energy output from the implantable stimulator.
• In one preferred embodiment, the implantable stimulator(s) is configured for storing the electrical current as electrical energy. The control device may be configured for transmitting other acoustic waves through the tissue to alternately activate and deactivate the implantable stimulator(s). If a plurality of implantable stimulators is provided, each stimulator can be assigned a unique identification code, so that the control device can specifically address the implantable stimulators. For example, the use of unique identification codes may be particularly useful when the timing of the stimulation amongst the implantable stimulators must be coordinated.
• In another preferred embodiment, the implantable stimulator(s) is configured for transmitting diagnostic information to the control device, and the control device is configured for controlling the stimulation energy output from the implantable stimulator(s) based on these acoustic waves. For example, if the implantable stimulator(s) is configured for stimulating heart tissue (e.g., in the case of a pacemaker or implantable cardioverter defibrillator (ICD)), the diagnostic information can be pressure information indicative of blood flow, in which case the heart tissue can be stimulated based on this pressure information.
• Other objects and features of the present invention will become apparent from consideration of the following description taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
• The drawings illustrate the design and utility of preferred embodiment(s) of the present invention, in which similar elements are referred to by common reference numerals. In order to better appreciate the advantages and objects of the present invention, reference should be made to the accompanying drawings that illustrate the preferred embodiment(s). The drawings depict only an embodiment(s) of the invention, and should not be taken as limiting its scope. With this caveat, the preferred embodiment(s) will be described and explained with additional specificity and detail through the use of the accompanying drawings in which:
• FIG. 1 is a plan view of an acoustic stimulation system constructed in accordance with a preferred embodiment of the present invention, particularly showing its use within a patient;
• FIG. 2 is a partially cut-away side view of an implantable stimulator used in the acoustic stimulation system ofFIG. 1;
• FIG. 3 is a top view of the implantable stimulator ofFIG. 2;
• FIG. 4 is a block diagram of a preferred power/communication unit that can be used in the implantable stimulator ofFIG. 2;
• FIG. 5 is a block diagram of an alternative power/communication unit that can be used in the implantable stimulator ofFIG. 2;
• FIG. 6 is a block diagram of another alternative power/communication unit that can be used in the implantable stimulator ofFIG. 2;
• FIG. 7 is a block diagram of still another alternative power/communication unit that can be used in the implantable stimulator ofFIG. 2;
• FIG. 8 is a block diagram of yet another alternative power/communication unit that can be used in the implantable stimulator ofFIG. 2;
• FIG. 9 is a side view of an alternative implantable stimulator that can be used in the acoustic stimulation system ofFIG. 1;
• FIG. 10 is a side view of an external control device used in the acoustic stimulation system ofFIG. 1;
• FIG. 11 is a block diagram illustrating the components of the external control device ofFIG. 10; and
• FIG. 12 is a side view showing the use of an alternative implantable control device used to control implantable stimulators within a patient.
DETAILED DESCRIPTION
• Referring toFIG. 1, an acoustic stimulatingsystem10 constructed in accordance with one preferred embodiment of the present invention is described. The stimulatingsystem10 generally comprises a plurality ofimplantable stimulators12, which in this embodiment, take the form of pacemakers implanted within theheart18 of apatient16. Theimplantable stimulators12 are implanted within theheart18 using minimally invasive means, e.g., a catheter. The stimulatingsystem10 further comprises acontrol device14 configured for being placed on the skin of the patient16 in order to acoustically transmitacoustic waves20 through the tissue of the patient16 to theimplantable stimulators12. In the illustrated embodiment, theacoustic waves20 can either be acoustic energizing waves or acoustic communication waves, as will be discussed in further detail below. Although, in the illustrated embodiment, thecontrol device14 is disclosed as an external device, an implantable control device can also be used to transmitacoustic waves20 to theimplantable stimulators12, as will be described in further detail below.
• Theacoustic waves20 transmitted by thecontrol device14 have a low frequency (e.g., 40 KHz). As such, theimplantable stimulators12 can be implanted within the deep tissue (such as the heart in this case) of thepatient16 without the need to route and implant leads within the body, thereby avoiding, or at least minimizing, the previously described complications. That is, all of the components necessary to stimulate tissue over the lifetime of theimplantable stimulators12 are contained within theimplantable stimulators12.
• Thecontrol device14 is configured to energize theimplantable stimulators12, so that theimplantable stimulators12 may subsequently or immediately output stimulation energy into the heart tissue. Besides energizing theimplantable stimulators12, thecontrol device14 is also configured to control the operation and configuration of theimplantable stimulators12. For example, thecontrol device14 may activate and deactivate implantable stimulators12 (i.e., alternately placing them in an “active mode” and “dormant mode”). Thecontrol device14 may also control the parameters of the stimulation energy (e.g., stimulation intensity, pulse duration, and frequency) output from any of theimplantable stimulators12. Significantly, many cardiac applications require that different regions of the heart be stimulated in a particular sequence and delay between stimulations. For example, the two ventricles of the heart may need to be synchronized to optimize the heart pumping capability. As such, thecontrol device14 may also control the stimulation sequence and timing of theimplantable stimulators12 to achieve this goal.
• Thecontrol device14 can selectively communicate with theimplantable stimulators12 by assigning a unique identification code to eachimplantable stimulator12. Thus, thecontrol device14 can selectively energize or communicate with a specificimplantable stimulator12 by incorporating a corresponding unique identification code into the signal transmitted from thecontrol device14, or alternatively, by transmitting a predetermined pulse sequence representing the identification code prior to energizing or communicating with the specifiedimplantable stimulator12. By the same token, a specificimplantable stimulator12 can identify itself to thecontrol device14 by incorporating its unique identification code into the signal transmitting from thecontrol device14 or by transmitting a pulse sequence representing the unique identification code.
• The stimulatingsystem10 can be designed in a number of manners. For example, in the preferred embodiment, thecontrol device14 transmits acoustic energizing waves to animplantable stimulator14, which transforms the acoustic waves into electrical current that are then stored as electrical energy. Theimplantable stimulator12 is designed with control logic, in which case, thecontrol device14 need only transmit stimulation parameters in the form of acoustic communication waves to program the control logic within theimplantable stimulator12, or alternatively, theimplantable stimulator12 can be preprogrammed with the stimulation parameters. The control logic will then control the stimulation energy output from theimplantable stimulator12 in accordance with these programmed stimulation parameters. For example, the control logic can, itself, generate and output the stimulation energy, or the control logic can alternately open and close a switch that selectively outputs the stored electrical energy as stimulation energy.
• As another example, thecontrol device14 may transmit acoustic energizing waves to theimplantable stimulator12, which are then transformed into electrical energy that is immediately used to generate the stimulation energy. In this case, the control logic transforms the electrical energy into stimulation energy in accordance with stimulation parameters stored in theimplantable stimulator12. As still another example, thecontrol device14 may transmit acoustic energizing waves in accordance with stimulation parameters stored in thecontrol device14, in which case, the resulting electrical current in theimplantable stimulator12 are immediately output from theimplantable stimulator12 as stimulation energy. In the later case, the electrical current may be further processed in order to generate stimulation energy that is suitable for the intended therapy. The key here is that no energy storage device is required, since the stimulation energy is immediately output in response to the electrical current.
• As still another example, thecontrol device14 may transmit a series of acoustic communication waves in accordance with stimulation parameters stored in thecontrol device14. Theimplantable stimulator12 transforms the acoustic waves into electrical current that alternately open and close a switch that generates the stimulation energy.
• Although theimplantable stimulators12 have been described as pacemakers, it should be appreciated that theimplantable stimulators12 may take the form of any device used to therapeutically stimulate body tissue using electrical energy, e.g., an implantable cardioverter defibrillator (ICD), deep brain stimulator (DBS), pain relief nerve stimulator, vagus nerve stimulator, or bladder control stimulator. It should also be appreciated that, although fourimplantable stimulators12 are shown, any suitable number ofimplantable stimulators12 can be used, including a singleimplantable stimulator12.
• Referring toFIGS. 2 and 3, theimplantable stimulator10 will now be described in greater detail. Theimplantable stimulator10 generally includes acasing22 that is composed of a biocompatible material, e.g., titanium, gold, platinum, tantalum, stainless steel, or other metal. Alternatively, other biocompatible materials may be used, e.g., a polymer, such as a fluorocarbon, polyamide, or poly ether ether ketone (PEEK), preferably covered with a metallization layer to improve the polymer's performance and/or to enhance its moisture resistance. Thecasing22 is shaped such that theimplantable stimulator10 can be embedded within the tissue to be stimulated. In the illustrated embodiment, thecasing22 is bullet-shaped, i.e., it has aflat end24 that tapers down to a pointedregion26, which can penetrate into tissue. In order to secure and stabilize theimplantable stimulator10 within the tissue, several fixation hooks28 are mounted to the exterior of thecasing22 near the pointedregion26.
• Thecasing22 is substantially sealed, and preferably hermetically sealed, to isolate the components of theimplantable stimulator12 from the environment in which theimplantable stimulator10 is to be placed. Thecasing22 may include one or more regions that facilitate the passage of acoustic energy through thecasing22. For example, an acousticallytransparent panel30 is suitably mounted over the exposedflat side24 of thecasing22. Preferably, thepanel30 is a relatively thin wall of titanium or other material, e.g., having a thickness of about one half millimeter (0.5 mm) or less, that may allow theacoustic waves20 to pass substantially therethrough.
• Theimplantable stimulator10 further includes anacoustic transducer array32, astimulation electrode34, areference electrode36, and a power/communication unit38. Thestimulation electrode34 is mounted on the pointedregion26 of thecasing22, and thereference electrode36 is mounted on theflat side24 of thecasing22. Thestimulation electrode34 is used to electrically stimulate adjacent tissue, and thereference electrode36 is used as a reference. In the illustrated embodiment, thetransducer array32 comprises four acoustic transducer cells40 (shown in phantom inFIG. 3). It should be appreciated, however, that the number oftransducer cells40 will ultimately depend on the amount of power needed to energize theimplantable stimulator10, as will be described in further detail below.
• The power/communication unit38 is coupled to theacoustic transducer array32 andreference electrode36 via lead42 and coupled to thestimulation electrode34 via lead44 (shown partially in phantom). The power/communication unit38 is configured for providing electrical stimulation energy to thestimulation electrode34 in accordance with stimulation parameters stored within theimplantable stimulator12.
• Theimplantable stimulator12 may optionally include additional secondary stimulation electrodes (not shown), which may be coupled to the power/communication unit38 via either separate leads, so that the power/communication unit38 can independently transmit stimulation energy to the electrodes, or usinglead44, so that the power/communication unit38 can transmit stimulation energy to the electrodes as a group. Theimplantable stimulator12 may optionally include one or more sensors (not shown) capable of measuring physiological parameters, such as temperature, electrical impedance, pressure, position, strain, pH, fluid flow, and the like. As will be described in further detail below, this diagnostic information can be used to control the transmission of stimulation energy. Further details regarding the use of sensors and corresponding componentry is disclosed in U.S. patent application Ser. No. 09/989,912, which is expressly incorporated herein by reference.
• Referring still toFIG. 2, theacoustic transducer array32 comprises asubstrate46, fourcavities48 formed completely or partially through thesubstrate46, and a flexiblepiezoelectric layer50 disposed over thesubstrate46 across thecavities48. The fourcavities48 are filled with a gas, such as air, and thus, thepiezoelectric layer50 will vibrate over thecavities48, preferably at a frequency equal to the natural frequency of thepiezoelectric layer50. In the illustrated embodiment, eachcavity48 is circular, but can also have other shapes, such as elliptical or rectangular.
• The previously describedreference electrode36 is mounted to the outer surface of thepiezoelectric layer50 between thecavities48. Thus, it can be appreciated that thereference transducer36 serves as both a common electrode that couples thetransducer cells40 together to provide energizing electrical energy, and a reference point during electrical stimulation of thestimulation electrode34. Alternatively, a separate common electrode or multiple electrodes (one for each transducer cell40) can be used to provide the energizing electrical energy to the power/communication unit38. Theacoustic transducer array32 further comprises four counter electrodes52 (only two shown inFIG. 2) that are mounted to the inner surface of thepiezoelectric layer50 within therespective cavities48. In the illustrated embodiment, thetransducer cells40 are connected in parallel by thecommon electrode36 in order to increase the generated current. Alternatively, thetransducer cells40 can be connected in series in order to increase the generated voltage.
• Thus, it can be appreciated that acoustic waves transmitted to theacoustic transducer array32 from an external source will cause thepiezoelectric layer50 to vibrate above thecavities48. As a result, the periodic mechanical strain exerted on thepiezoelectric layer50 generates electrical current at thecommon electrode36. Similarly, as electrical current are transmitted to theacoustic transducer array32 from the power/communication unit38, an electrical charge will be induced in thepiezoelectric layer50, thereby causing thepiezoelectric layer50 above thecavities48 to periodically vibrate, resulting in the transmission of acoustic waves.
• As best illustrated inFIG. 2, a plurality of depressions are formed in thepiezoelectric layer50, thereby enhancing the efficiency and/or sensitivity of theacoustic transducer array32. The depressions may also be used to tune the natural resonant frequency of thepiezoelectric layer50. The depressions can be formed by providing thecavities48 with an internal pressure that is less than the atmospheric pressure, such that thepiezoelectric layer50 partially enters thecavities48.
• In the illustrated embodiment, the diameter of eachcavity48 is approximately 1.2 mm, which results in a maximum acoustic to electrical energy exchange at a frequency of about 40 KHz-translating to a wavelength of 4 cm in water. Since eachtransducer cell40 is much smaller than this wavelength, the performance of theimplantable stimulator12 is not affected by the orientation of thetransducer array32 with respect to theacoustic waves20 transmitted by thecontrol device14. Further details regarding the structure and manufacture of acoustic transducer arrays are described in U.S. Pat. No. 6,140,740, which is expressly incorporated herein by reference.
• Referring now toFIG. 4, the power/communication unit38 comprises arectifier54 and anenergy storage device56. Therectifier54 is coupled to thetransducer array32 for converting the electrical current generated by thetransducer array32 into a form suitable for powering components of theimplantable stimulator12. Specifically, therectifier54 is configured for converting incoming alternating current (AC) voltage from thetransducer array32 into direct current (DC) voltage for storage by theenergy storage device56. The rectification may be performed by diodes arranged in a configuration suitable for the requirements of the mode of operation, preferably resulting in a passive circuit that draws substantially no current. For example, a half-bridge and full-bridge configuration can be used. Alternatively, other rectification circuits (not shown) may be used, including Schottky diodes, voltage triplers or other multiplier circuits, and the like. In addition, therectifier54 may include an overvoltage protector (not shown), which may prevent theenergy storage device56 from overcharging to unsafe levels. For example, the overvoltage protector may include a Zener diode, or a transistor that opens at a predetermined threshold voltage.
• Theenergy storage device56 is capable of being charged from an external source (such as the control device14) using acoustic energy received by theacoustic transducer array32. Theenergy storage device56 may include any of a variety of devices, such as an energy exchanger, a battery, and/or a capacitor. Preferably, theenergy storage device56 is a battery capable of storing electrical energy substantially indefinitely unless actively discharged. In another embodiment, theenergy storage device56 may include both a capacitor and a primary, non-rechargeable battery, although, alternatively, theenergy storage device56 may include a secondary, rechargeable battery and/or capacitor that may be energized before activation or use of theimplantable stimulator12. For example, theenergy storage device56 may include a Lithium thin film battery, such as those available from Oak Ridge Micro-energy Inc. of Salt Lake City, Utah, Infinite Power Supply of Denver, Colo., or Cymber Corporation of Elk River, Minn. Alternatively, theenergy storage device56 may include a standard coin type manganese lithium rechargeable battery, such as those available from Matsushita Battery Industrial Co., Ltd. (MBI) of Osaka, Japan.
• The power/communication unit38 further comprises acontroller58 coupled between theelectrodes34 and36 for providing electrical stimulation energy to theelectrode34. Thecontroller58 may include one or more controllers for controlling components of theimplantable stimulator12, timer circuitry (e.g., a clock or counter), reset and threshold circuitry, and/or a processor for generating electrical signals being transmitted by and/or analyzing electrical signals received by thetransducer array32. Thecontroller58 can be configured using digital signal processors (DSPs), Field Programmable Gate Arrays (FPGAs), Application Specific Integrated Circuit (ASIC)-compatible microprocessors, such as a CoolRISC processor available from Xemics, or other programmable devices, and/or any other hardware components or software modules that may be required for processing, analyzing, storing data, and controlling operation of theimplantable stimulator12.
• The power/communication unit38 further comprises signal detectcircuitry60 coupled to thetransducer array32 for providing a communication channel into theimplantable stimulator12, and specifically, to pass commands and/or information in the acoustic communication waves received by thetransducer array32 for use by thecontroller58. For example, the signal detectcircuitry60 may pass commands or other signals to thecontroller58, e.g., that acoustic energizing waves have been discontinued, that theimplantable stimulator12 should become operative and/or stimulation parameters. The signal detectcircuitry60 may be a passive FET circuit, thereby drawing substantially no current. The signal detectcircuitry60 may also include a smoothing capacitor (not shown) and/or logic for reducing the sensitivity of the signal detectcircuitry60 to spurious transient signals.
• The power/communication unit38 comprisesoptional transmission circuitry62 coupled to thetransducer array32 for providing a communication channel from theimplantable stimulator12, e.g., to pass status information or optional sensor data to thecontrol device14 as acoustic communication waves. The signals are preferably digital electrical signals, which may be generated, for example, by grounding the counter electrodes52 (shown inFIG. 2) of thetransducer array32 and alternately connecting the common electrode36 (shown inFIG. 2) between ground and a predetermined voltage. Alternatively, the signals may be generated by alternately grounding thecommon electrode36 and connecting thecounter electrodes52 to the predetermined voltage, and then grounding thecounter electrodes52 and connecting thecommon electrode36 to the predetermined voltage. In a further alternative, the signal may be processed or modulated, e.g., using spread spectrum, direct sequence mixing, code division multiple access (CDMA), or other technologies, as will be appreciated by those skilled in the art.
• The power/communication unit38 comprisesmemory64, e.g., volatile or non-volatile memory, including flash memory or ferroelectric memory. Thememory64 may store information, e.g., data received from the optional sensors of theimplantable stimulator12, commands and stimulation parameters for use by thecontroller58 to provide stimulation energy to theelectrode34.
• The power/communication unit38 comprises aswitch66 coupled between theenergy storage device56 and thecontroller58, such that all or part of thecontroller58 may be selectively activated and deactivated under control of thecontrol device14. Optionally, use of theswitch66 may be foregone, in which case thecontroller58 can be directly connected to theenergy storage device56, such that at least some component(s) of thecontroller58 may remain active at all times.
• Theswitch66 can be operated to alternately place theimplantable stimulator12 in an “active mode” or a “dormant mode.” Specifically, to place theimplantable stimulator12 in the active mode, theswitch66 may be closed upon acoustic excitation by an external acoustic energy source, e.g., from thecontrol device14, to allow current flow from theenergy storage device56 to thecontroller58, thereby activating theimplantable stimulator12. To place theimplantable stimulator12 in a “dormant mode,” theswitch66 can may be opened upon acoustic excitation by thecontrol device14, to prevent current from flowing from theenergy storage device56 to thecontroller58. Basically, an acoustic transmission from thecontrol device14 may vibrate thetransducer array32, forming a voltage pulse that is conveyed to theswitch66. When the voltage exceeds a predetermined threshold, e.g., about a half volt (0.5 V), theswitch66 may close if previously in an open state, or open if previously in a closed state.
• Further details regarding the structure and function of the power/communication unit38 are disclosed in U.S. patent application Ser. No. 09/989,912, which has previously been incorporated herein by reference.
• Referring toFIG. 5, an alternative embodiment of a power/communication unit138 that can be used in theacoustic stimulator12 is described. The power/communication unit138 is similar to the power/communication unit38 described above, with the exception that thecontroller58 immediately uses the electrical current to generate the stimulation energy. Specifically, thecontroller58 receives the electrical energy directly from therectifier54 and generates the stimulation energy in response thereto. Any excess electrical energy not used by thecontroller58 to generate the stimulation energy is output to theenergy storage device56 for subsequent use by thecontroller58 or other components.
• The following description illustrates exemplary energy consumption parameters needed for the power/communication unit138 to generate the proper amount of stimulation energy, and, consequently, exemplary power requirements for theacoustic transducer array32. A singleacoustic transducer cell40 will typically generate 15 Pq/KPa at a frequency of approximately 40 KHz and a voltage of 10 V. The theoretical induced current at an acoustic pressure of 50 KPa will be 15 Pq/KPa×50 KPa×40 KHz=30 μA. Assuming a 50% AC to DC rectification efficiency, the practical induced current will be 15 μA. The resulting power will be 15 μA×10 V=0.15 mW. Assuming that twentyacoustic transducer cells40 are connected in parallel, the total power generated by thetransducer array32 will be 20×0.15 mW=3 mW. A typical pacemaker has the following operational characteristics: amplitude of 2.5 V, frequency of 80 Hz, pulse width of 0.4 msec, and impedance of 1000 ohms. Thus, the power required by theacoustic stimulator12 will be (2.5 V)^2× 1/1000 ohms×80 Hz×4×10⁻⁴sec=0.2 mW. As such, the implantable stimulator12 (assuming 20 transducer cells40) will generate 15 times the energy required for pacing theheart18. The excess energy can be used to charge theenergy storage device56 to allow operation of theimplantable stimulator12 without acoustic excitation from thecontrol device14.
• Referring toFIG. 6, another alternative embodiment of a power/communication unit238 that can be used in theacoustic stimulator12 will now be described. The power/communication unit238 is similar to the previously described power/communication unit38, with the exception that thecontroller58 does not output the stimulation energy. Rather, thecontroller58 alternately opens and closes theswitch66 in order to discharge theenergy storage device56 through theswitch66 to produce the stimulation energy. In this case, the frequency that theswitch66 is opened and closed defines the frequency of the stimulation energy, and the duration that theswitch66 is opened in each cycle defines the pulse width of the stimulation energy.
• Referring toFIG. 7, still another alternative embodiment of a power/communication unit338 that can be used in theacoustic stimulator12 will now be described. The power/communication unit338 is similar to the previously described power/communication unit238, with the exception that acontroller58 is not used to alternately open and close theswitch66. Instead, thecontrol device14 alternately opens and closes theswitch66 by transmitting acoustic communication waves20 to theimplantable stimulator12. Because output of the stimulation energy is completely controlled by thecontrol device14, the power/communication unit338 need not include acontroller58, thereby rendering the implantable stimulator12 a “dumb device.” Of course, the power/communication unit338 can alternatively use acontroller58 if control of other functions within theimplantable stimulator12, such as sensing, is needed.
• Referring toFIG. 8, yet another alternative embodiment of a power/communication unit438 that can be used in theacoustic stimulator12 will now be described. Like the power/communication unit338, the power/communication unit438 is a “dumb device.” Unlike the power/communication unit338, the output of the stimulation energy is not controlled by alternately opening and closing aswitch66. Rather, thecontrol device14 transmits acoustic energizingwaves20 in accordance with stimulation parameters stored in thecontrol device14. For example, thecontrol device14 can generate pulsed acoustic energizingwaves20 that is transformed into pulsed electrical energizing waves in theimplantable stimulator12. The power/communication unit338 comprises arectifier54 that then transforms the AC components of the pulsed electrical current into DC components, thereby resulting in a digital electrical signal, which is then output from theimplantable stimulator12 as stimulation energy.
• Although the previously describedimplantable stimulator12 is self-contained, thereby eliminating the need to implant and route external leads, other types of implantable stimulators can be used in thestimulation system10 instead of theimplantable stimulator12. For example,FIG. 9 illustrates an alternative embodiment of animplantable stimulator72 that uses an external lead. Specifically, theimplantable stimulator72 comprises a stimulatingelectrode74 and acontrol unit76 that are coupled together through anexternal lead78. Alternatively, several stimulating electrodes can be provided. For example, the stimulating electrodes may be independent of each other, in which case, the electrodes can be connected to thecontrol unit76 via parallel external leads. Or the stimulating electrodes may be integrated together on a single unit, in which case, the electrode unit can be connected to thecontrol unit76 via a single external lead with one or more wires.
• Thecontrol unit76 comprises acasing80 that is similar to the previously describedcasing22, with the exception that thecasing80 is cylindrically shaped. Thecontrol unit76 further comprises anacoustic transducer array82 that is similar to the previously describedtransducer array32, with the exception thetransducer array82 is circumferentially distributed around thecylindrical casing80. Thecontrol unit76 further comprises the previously described power/communication unit84, which is suitably mounted within thecasing80. Since almost all of the componentry is located within thecontrol unit76, thestimulation electrode74 can be made smaller, thereby facilitating delivery and implantation of thestimulation electrode74 in the target region of theheart18. Thecontrol unit76 may be implanted in the chest region of thepatient16.
• With particular reference toFIGS. 10 and 11, thecontrol device14 will now be described in detail. Thecontrol device14 comprises acontroller86 for controlling its operation, and anenergy storage device88, e.g., a nonrechargeable or a rechargeable battery, coupled to thecontroller86 and/or other components of thecontrol device14, such as a power amplifier or an oscillator (not shown). In addition, thecontrol device14 comprises anacoustic transducer90 configured for converting between electrical current and acoustic waves in a similar manner described above with respect to thetransducer array32. Alternatively, separate and/or multiple acoustic transducers may be provided for transmitting and receiving acoustic waves.
• Thecontrol device14 further comprisesmemory92 coupled to thecontroller86, e.g., for storing commands, stimulation parameters, and/or data provided to thecontrol device14, as explained further below. Thememory92 may be a temporary buffer that holds data before transfer to another device, or non-volatile memory capable of storing the data substantially indefinitely, e.g., until extracted by thecontroller86. For example, thememory92 may be a memory card or an EPROM (not shown) built into thecontrol device14 or otherwise coupled to thecontroller86. In the preferred embodiment, theimplantable stimulator12 may be operated in a “half-duplex” mode. In this mode, theimplantable stimulator12 can only either transmit or receive during any given time. To this end, thecontrol device14 comprises a transmitting/receiving (T/R)switch94, which toggles thetransducer90 to alternately transmit and receive acoustic energy. Lastly, thecontrol device14 comprises acasing96 for housing the previously described components.
• As best illustrated inFIG. 10, thecontrol device14 is preferably carried by apatch15 that may be secured to a patient, e.g., to the patient's skin. For example, thepatch15 may include one or more layers of substantially flexible material to which thecontrol device14 and/or its individual components are attached. Thepatch15 may include a single flexible membrane (not shown) to which thecontrol device14 is bonded or otherwise attached, e.g., using a substantially permanent adhesive, which may facilitate conformance of thepatch15 to the patient's anatomy. Alternatively, thecontrol device14 may be secured between layers of material, e.g., within a pouch or other compartment (not shown) within thepatch15. For example, thepatch15 may include a pair of membranes (not shown) defining the pouch or compartment. The space within which thecontrol device14 is disposed may be filled with material to acoustically couple theacoustic transducer90 of thecontrol device14 to an outer surface of thepatch15. Alternatively, theacoustic transducer90 may be exposed, e.g., in a window formed in a wall of thepatch15.
• Thepatch15 may be formed from a flexible piezoelectric material, such as Polyvinylidene Fluoride (PVDF) or a PVDF copolymer. Such polymers may allow thepatch15 to produce ultrasonic waves, as well as allow thecontrol device14 to be secured to the patient's skin. Thus, the wall of thepatch15 itself may provide an acoustic transducer for thecontrol device14, i.e., for transmitting acoustic energy to and/or receiving acoustic energy from theimplantable stimulator12.
• Thepatch15 may then be secured to the patient's skin using a material, such as a layer of adhesive (not shown), substantially permanently affixed or otherwise provided on a surface of thepatch15. The adhesive may be hydrogel, silicon, polyurethane, polyethylene, polypropylene, fluorocarbon polymer, and the like. Alternatively, a separate adhesive may be applied to thepatch15 and/or to the patient's skin before applying thepatch15 in order to secure thecontrol device14 to the patient's skin. Such an adhesive may enhance acoustic coupling of the acoustic transducer(s) of thecontrol device14 to the patient's skin, and consequently to theimplantable stimulator12. Optionally, additional wetting material, including water, silicone oil, silicone gel, hydrogel, and the like, and/or other acoustically conductive material may be provided between thepatch15 or theacoustic transducer90, and the patient's skin, e.g., to provide substantial continuity and minimize reflection or other losses and/or to secure thepatch15 to thepatient16.
• Thepatch15 may be relatively light and compact, for example, having a maximum surface dimension (e.g., width or height) not more than about ten to two hundred millimeters (10-200 mm), a thickness not more than about five to one hundred millimeters (5-100 mm), and a weight not more than about twenty to four hundred grams (20-400 g), such that thecontrol device14 may be inconspicuously attached to the patient. Thus, thepatient16 may be able to resume normal physical activity, without substantial impairment from thecontrol device14. Yet, theenergy storage device88 may be sufficiently large to communicate with theimplantable stimulator12 for an extended period of time, e.g., for hours or days, without requiring recharging or continuous coupling to a separate energy source.
• Alternatively, thecontrol device14 may be carried by a belt (not shown) that may be secured around the patient, e.g., such that theacoustic transducer90 is secured against the patient's skin. The belt may carry other components, e.g., an external power supply for thecontrol device14. For example, a battery pack (not shown) may be carried by the belt that may be coupled to thecontrol device14 for providing electrical energy for its operation. Alternatively, thecontrol device14 may take the form of a probe that is not worn by thepatient16, but rather can be selectively placed on the chest in order to communicate with theimplantable stimulator16.
• Alternatively, a control device, similar to the previously describedcontrol device14, may be implanted within thepatient16, e.g., the chest near the heart region. For example,FIG. 12 illustrates animplantable control device114 that can be used to communicate with animplantable stimulator16 within theheart18 of thepatient16. In this case, theimplantable control device114 communicates in the same manner as thecontrol device14. The main difference is that theimplantable control device114 is preferably capable of being recharged by an external energizingdevice116 via RF or acoustic energy. In addition, theimplantable control device114 will typically not have the required stored energy for energizing theimplantable stimulators16. Instead, theimplantable stimulators16 may be energized by the external energizingdevice116. In this case, theimplantable control device114 will be used to control the operation of theimplantable stimulators16, e.g., by alternately activating and deactivating selectedimplantable stimulators16, or otherwise controlling the stimulation energy output from theimplantable stimulators16. Further details on this particular arrangement are disclosed in U.S. patent application Ser. No. 10/413,428, which is expressly incorporated herein by reference.
• When used in conjunction with theimplantable stimulator12 having the power/communication unit36 or power/communication unit236 illustrated in respectiveFIGS. 4 and 6, thecontrol device14 can be operated in an “energizing mode” or “activation mode.” When operated in either of these modes, thecontrol device14 transmitsacoustic waves20 from theacoustic transducer90 through the body of thepatient16, with at least a portion of theacoustic waves20 striking thetransducer array32 of theimplantable stimulator12. Thetransducer array32 converts the acoustic waves into electrical current, which are used to either charge theenergy storage device56 or communicate with thecontroller86 in theimplantable stimulator12 depending on the operational mode.
• At the beginning of the energizing mode, thecontrol device14 determines the optimum frequency at which theimplantable stimulator12 should be energized. For example, thecontrol device14 may transmit broadband acoustic waves or scanning waves, i.e., scanning through a range of frequencies, and wait for theimplantable stimulator12 to respond. Theimplantable stimulator12 may transmit acoustic waves at different frequencies in response to the diagnostic signal, and thecontrol device14 may determine the optimal frequency for communicating with theimplantable stimulator12 based upon the responses. For example, thecontrol device14 may repeatedly charge theimplantable stimulator12 using different frequency signals and measure the length of time that theimplantable stimulator12 is capable of transmitting data signals at each frequency to determine the optimal frequency. Alternatively, when theimplantable stimulator12 detects the signal, it may transmit a response at an optimal frequency that should be used to communicate with theimplantable stimulator12.
• Once thecontrol device14 has determined the optimal frequency for communicating with the implantable stimulator12 (or thecontrol device14 may already know the proper frequency to use), thecontrol device14 then transmits acoustic energizingwaves20 to theimplantable stimulator12, which are transformed and stored in theenergy storage device56 as electrical energy. Theenergy storage device56 continues to store electrical energy until a predetermined voltage is achieved, e.g., about eight Volts (8 V), and then thecontroller58 automatically disconnects theenergy storage device56 from thetransducer array32. After a predetermined time, e.g., between about five and sixty seconds (5-60 sec.), thecontrol device14 automatically ceases the energizing transmission. Alternatively, thecontrol device14 may cease energizing theimplantable stimulator12 by transmitting a stop command.
• During the activation mode, thecontrol device14 transmits a command to theimplantable stimulator12 to close theswitch66, thereby placing theimplantable stimulator12 in the active mode. Once activated, theimplantable stimulator12 draws electrical energy from theenergy storage device56, and begins to transmit electrical energy to thestimulation electrode34 in accordance with stimulation parameters, which may be previously stored in thememory92 or may be transmitted from thecontrol device14 immediately after activation of theimplantable stimulator12. Alternatively, if noswitch66 is used, thecontrol device14 may transmit a start command to theimplantable stimulator12, which responds by transmitting electrical energy to thestimulation electrode34.
• Theimplantable stimulator12 continues to stimulate the tissue until thecontrol device14 transmits a command to theimplantable stimulator12 to open theswitch66, thereby deactivating theimplantable stimulator12 and placing it in the dormant mode. Alternatively, if noswitch66 is used, thecontrol device14 may transmit a stop command to theimplantable stimulator12, which responds by ceasing transmission of the electrical energy to thestimulation electrode34. Stimulation may also cease if the voltage of theenergy storage device56 falls below a predetermined threshold, e.g., below a level at which thestimulation electrode34 may not continue to operate effectively, such as 1.5 volts. After the voltage falls below the predetermined threshold, thecontroller58 may automatically discontinue operation of theimplantable stimulator12 by opening theswitch66 and returning to a dormant state until energized and activated by thecontrol device14.
• Prior to, during, or subsequent to the activation mode, thecontrol device14 andimplantable stimulator12 may communicate additional information to each other. For example, theimplantable stimulator12 may transmit diagnostic information, which has been sensed by the optional sensor (not shown), to thecontrol device14. Thecontrol device14 can then use this information to control the operation of theimplantable stimulator12. For example, the optional sensor can be a pressure sensor that can sense the blood flow through the heart chamber in which theimplantable stimulator12 is located. In this case, theimplantable stimulator12 can transmit pressure information to thecontrol device14. Alternatively, the pressure sensor may be even associated with another implantable device that is located in another region of the body, e.g., a pulmonary vein. Thecontrol device14 may then respond to this pressure information by either activating or deactivating theimplantable stimulator12.
• For example, if the pressure information indicates that the blood flow is below normal, thecontrol device14 may activate theimplantable stimulator12 by transmitting commands to close theswitch66, thereby initiating stimulation of the heart tissue. Once the diagnostic information indicates that the blood flow has been normal for a predetermined period of time, thecontrol device14 can then deactivate theimplantable stimulator12 by transmitting commands to open theswitch66, thereby ceasing stimulation of the heart tissue. This technique lends itself well to implantable cardioverter defibrillators (ICDs), which are designed to shock the heart when the blood pressure within the heart falls to a dangerous level. Thecontrol device14 may alternatively or optionally use the diagnostic information to control theimplantable stimulator12 by controlling the parameters of the stimulation energy output by theimplantable stimulator12.
• As another example for communicating information to each other, thecontrol device14 may transmit an identification code when transmitting commands to open or close theswitch66 in theimplantable stimulator12. In this manner, timing and sequence of the stimulation energy output from all of theimplantable stimulators12 can be controlled. Prior to placing theimplantable stimulator12 in the dormant mode, thecontroller58 may transmit status information to thecontrol device14, e.g., an initial confirmation of instructions received from thecontrol device14, an identification code identifying theimplantable stimulator12, and/or a stop notice when stimulation is being discontinued by thecontroller58.
• As a safety measure against false positives (e.g., erroneous activation or deactivation), thecontrol device14 may acoustically transmit an initiation signal followed by a confirmation signal. When theimplantable stimulator12 receives these signals, thecontroller58 may monitor the signals for a proper sequence, thereby ensuring that theswitch66 only closes upon receiving the proper initiation and confirmation signals. For example, thecontroller58 may only acknowledge an activation signal that includes a first pulse followed by a second pulse separated by a predetermined delay. Use of a confirmation signal may be particularly important for certain applications, for example, to prevent unintentional stimulation of theheart18.
• In the case where the power/communication unit138 illustrated inFIG. 5 is used in theimplantable stimulator12, the electrical current transformed by theimplantable stimulator12 is not used to charge theenergy storage device56, but rather to immediately generate stimulation energy. As such, thecontrol device14 is operated in the energizing mode in order to energize theimplantable stimulator12, resulting in immediate output of the stimulation energy to the tissue. Communication between theimplantable stimulator12 andcontrol device14 can be accomplished in the same manner previously discussed above.
• In the case where the power/communication unit238 illustrated inFIG. 7 is used in theimplantable stimulator12, thecontrol device14 can be designed to operate in the previously described “energizing mode” and a “stimulation mode.” In the energizing mode, thecontrol device14 energizes theimplantable stimulator12 in the same manner described above. In the stimulation mode, thecontrol device14 transmits acoustic communication waves to theimplantable stimulator12 in order to alternately open and close theswitch66, so thatenergy storage device56 is periodically discharged to generate and output the stimulation energy,
• In the case where the power/communication unit338 illustrated inFIG. 8 is used in theimplantable stimulator12, thecontrol device14 can be designed to operate in the energizing mode. In this case, thecontrol device14 transmits pulsed acoustic energizing waves in accordance with stimulation parameters stored in thecontrol device14. Theimplantable stimulator12 responds by transforming the AC components of the resulting electrical current into DC components. That is, the pulsed AC electrical current are transformed into pulses DC electrical current, which are then output as the stimulation energy.
• Although particular embodiments of the present invention have been shown and described, it should be understood that the above discussion is not intended to limit the present invention to these embodiments. It will be obvious to those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the present invention. Thus, the present invention is intended to cover alternatives, modifications, and equivalents that may fall within the spirit and scope of the present invention as defined by the claims

Claims (15)

What is claimed is:

1. A cardiac stimulation system, comprising:

an external control device configured for transmitting an acoustic signal through body tissue; and

an implantable cardiac stimulator including a stimulator electrode configured for electrically stimulating adjacent heart tissue, one or more acoustic transducers configured for transforming the signal into an electrical current, and a switch configured for receiving the electrical current and, in response, placing the implantable stimulator in a dormant mode, wherein the implantable stimulator further includes a control unit configured to control delivery of electrical stimulation energy to the stimulator electrode, and wherein in the dormant mode at least a portion of the control unit is deactivated.

2. The system ofclaim 1, further comprising a plurality of stimulator electrodes each configured for electrically stimulating adjacent heart tissue.

3. The system ofclaim 2, wherein the control unit is further configured to control the delivery of electrical stimulation energy to the stimulator electrodes based on one or more stimulation parameters.

4. The system ofclaim 1, wherein in the dormant mode at least a portion of the control unit is activated.

5. An implantable medical device, comprising:

one or more sensing mechanisms configured for sensing a signal and providing an indication of the sensed signal; and

a control unit configured to receive the indication of the sensed signal and, in response, to change a state of the implantable medical device.

6. The device ofclaim 5, the one or more sensing mechanisms comprising one or more acoustic transducers configured for transforming an acoustic signal into an electrical signal.

7. The device ofclaim 5, further comprising a plurality of stimulator electrodes each configured for electrically stimulating nerve tissue within the body.

8. The device ofclaim 7, wherein the control unit is further configured to control the delivery of electrical stimulation energy to the stimulator electrodes based on one or more stimulation parameters.

9. The device ofclaim 5, the one or more sensing mechanisms comprising a sensor configured for sensing one or more parameters within the body.

10. The device ofclaim 5, wherein the state of the implantable medical device comprises one of an at least partially activated state and an at least partially deactivated state.

11. The device ofclaim 5, wherein the control unit is configured to receive the indication of the sensed signal and, in response, to change a state of the control unit.

12. The device ofclaim 5, wherein the control unit is configured to receive the indication of the sensed signal and, in response, to at least partially deactivate the control unit.

13. A stimulation system, comprising:

a control device configured for transmitting a signal through body tissue; and

an implantable stimulator including a stimulator electrode configured for electrically stimulating adjacent body tissue, one or more sensing mechanisms configured for sensing the signal and, in response, providing an electrical signal, and a control unit configured to receive the electrical signal and, in response, to change a state of the implantable stimulator.

14. The system ofclaim 13, wherein the control unit is configured to receive the electrical signal and, in response, at least partially deactivate the implantable stimulator.

15. The system ofclaim 13, wherein control unit is configured to receive the electrical signal and, in response, at least partially deactivate the control unit.

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