Abstract:
The present invention is a method for stimulating living tissue with an electrical neurostimulator, by maintaining a plurality of stimulation sets of stimulation parameters with each set of stimulation parameters defining at least a pulse characteristic and an electrode configuration in memory of the neurostimulator. Further, a repetition parameter for at least one of the plurality of stimulation sets in memory of the neurostimulator is maintained, wherein the repetition parameter identifies a number of times that a pulse is to be repeated in a consecutive manner for the at least one stimulation set. Also, living tissue is stimulated using a substantially continuous set of pulses wherein the stimulating includes selecting a stimulation set, generating a pulse according to the pulse characteristic of the selected stimulation set, and delivering the generated pulse to living tissue through electrodes according to the electrode configuration of the selected stimulation set.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. patent application Ser. No. 10/402,393, filed on Mar. 27, 2003 which is: (i) a continuation-in-part of U.S. patent application Ser. No. 09/964,079, filed on Sep. 26, 2001, now issued as U.S. Pat. No. 6,985,774, which is a continuation-in-part of U.S. patent application Ser. No. 09/671,850, filed on Sep. 27, 2000, now issued as U.S. Pat. No. 6,522,926; and (ii) claims the benefit of U.S. Provisional Patent Application No. 60/368,222, filed on Mar. 27, 2002, the disclosures of each of the above being hereby incorporated by reference in their entirety. 
     
    
     BACKGROUND OF THE INVENTION 
     FIELD OF THE INVENTION 
       [0002]    The present invention generally relates to medical devices and methods of use for the treatment and/or management of cardiovascular and renal disorders. Specifically, the present invention relates to devices and methods for controlling the baroreflex system for the treatment and/or management of cardiovascular and renal disorders and their underlying causes and conditions. 
         [0003]    Cardiovascular disease is a major contributor to patient illness and mortality. It also is a primary driver of health care expenditure, costing more than $326 billion each year in the United States. Hypertension, or high blood pressure, is a major cardiovascular disorder that is estimated to affect over 50 million people in the United Sates alone. Of those with hypertension, it is reported that fewer than 30% have their blood pressure under control. Hypertension is a leading cause of heart failure and stroke. It is the primary cause of death in over 42,000 patients per year and is listed as a primary or contributing cause of death in over 200,000 patients per year in the U.S. Accordingly, hypertension is a serious health problem demanding significant research and development for the treatment thereof. 
         [0004]    Hypertension occurs when the body&#39;s smaller blood vessels (arterioles) constrict, causing an increase in blood pressure. Because the blood vessels constrict, the heart must work harder to maintain blood flow at the higher pressures. Although the body may tolerate short periods of increased blood pressure, sustained hypertension may eventually result in damage to multiple body organs, including the kidneys, brain, eyes and other tissues, causing a variety of maladies associated therewith. The elevated blood pressure may also damage the lining of the blood vessels, accelerating the process of atherosclerosis and increasing the likelihood that a blood clot may develop. This could lead to a heart attack and/or stroke. Sustained high blood pressure may eventually result in an enlarged and damaged heart (hypertrophy), which may lead to heart failure. 
         [0005]    Heart failure is the final common expression of a variety of cardiovascular disorders, including ischemic heart disease. It is characterized by an inability of the heart to pump enough blood to meet the body&#39;s needs and results in fatigue, reduced exercise capacity and poor survival. It is estimated that approximately 5,000,000 people in the United States suffer from heart failure, directly leading to 39,000 deaths per year and contributing to another 225,000 deaths per year. It is also estimated that greater than 400,000 new cases of heart failure are diagnosed each year. Heart failure accounts for over 900,000 hospital admissions annually, and is the most common discharge diagnosis in patients over the age of 65 years. It has been reported that the cost of treating heart failure in the United States exceeds $20 billion annually. Accordingly, heart failure is also a serious health problem demanding significant research and development for the treatment and/or management thereof. 
         [0006]    Heart failure results in the activation of a number of body systems to compensate for the heart&#39;s inability to pump sufficient blood. Many of these responses are mediated by an increase in the level of activation of the sympathetic nervous system, as well as by activation of multiple other neurohormonal responses. Generally speaking, this sympathetic nervous system activation signals the heart to increase heart rate and force of contraction to increase the cardiac output; it signals the kidneys to expand the blood volume by retaining sodium and water; and it signals the arterioles to constrict to elevate the blood pressure. The cardiac, renal and vascular responses increase the workload of the heart, further accelerating myocardial damage and exacerbating the heart failure state. Accordingly, it is desirable to reduce the level of sympathetic nervous system activation in order to stop or at least minimize this vicious cycle and thereby treat or manage the heart failure. 
         [0007]    A number of drug treatments have been proposed for the management of hypertension, heart failure and other cardiovascular disorders. These include vasodilators to reduce the blood pressure and ease the workload of the heart, diuretics to reduce fluid overload, inhibitors and blocking agents of the body&#39;s neurohormonal responses, and other medicaments. 
         [0008]    Various surgical procedures have also been proposed for these maladies. For example, heart transplantation has been proposed for patients who suffer from severe, refractory heart failure. Alternatively, an implantable medical device such as a ventricular assist device (VAD) may be implanted in the chest to increase the pumping action of the heart. Alternatively, an intra-aortic balloon pump (IABP) may be used for maintaining heart function for short periods of time, but typically no longer than one month. Other surgical procedures are available as well. 
         [0009]    It has been known for decades that the wall of the carotid sinus, a structure at the bifurcation of the common carotid arteries, contains stretch receptors (baroreceptors) that are sensitive to the blood pressure. These receptors send signals via the carotid sinus nerve to the brain, which in turn regulates the cardiovascular system to maintain normal blood pressure (the baroreflex), in part through activation of the sympathetic nervous system. Electrical stimulation of the carotid sinus nerve (baropacing) has previously been proposed to reduce blood pressure and the workload of the heart in the treatment of high blood pressure and angina. For example, U.S. Pat. No. 6,073,048 to Kieval et al. discloses a baroreflex modulation system and method for activating the baroreflex arc based on various cardiovascular and pulmonary parameters. 
         [0010]    Although each of these alternative approaches is beneficial in some ways, each of the therapies has its own disadvantages. For example, drug therapy is often incompletely effective. Some patients may be unresponsive (refractory) to medical therapy. Drugs often have unwanted side effects and may need to be given in complex regimens. These and other factors contribute to poor patient compliance with medical therapy. Drug therapy may also be expensive, adding to the health care costs associated with these disorders. Likewise, surgical approaches are very costly, may be associated with significant patient morbidity and mortality and may not alter the natural history of the disease. Baropacing also has not gained acceptance. Several problems with electrical carotid sinus nerve stimulation have been reported in the medical literature. These include the invasiveness of the surgical procedure to implant the nerve electrodes, and postoperative pain in the jaw, throat, face and head during stimulation. In addition, it has been noted that high voltages sometimes required for nerve stimulation may damage the carotid sinus nerves. Accordingly, there continues to be a substantial and long felt need for new devices and methods for treating and/or managing high blood pressure, heart failure and their associated cardiovascular and nervous system disorders. 
         [0011]    A particularly promising approach for activating baroreceptors and other blood vessel receptors would be to implant an electrode structure or other activating device in an artery or vein adjacent to the receptor. The electrode structure could be similar to an inner arterial stent or graft and could be modified to have the needed electrical contact components for electrically activating the receptor. Energizing the implanted electrode structure, however, presents a number of difficulties. In particular, it is undesirable to run leads to the electrode structure through the arterial lumen and/or through an arterial or to a lesser extent venous wall. Such connection is particularly challenging if the target baroreceptors or other receptors are at or near the carotid sinus. 
         [0012]    For these reasons, it would be desirable to provide non-traumatic systems and methods for electrically activating electrode structures implanted in the vasculature, particularly the arterial vasculature, such as those implanted adjacent baroreceptors or other receptors. Such systems and methods should preferably provide for “wireless” connection of the implanted electrode structure with a control system or other driver located remotely from the electrode structure, typically being implanted at a location in the body away from the site where the electrode structure is implanted. In particular, it is desirable to reduce or eliminate the need to run cable, wires, or other conductors within a lumen to connect the electrode structure to a power source. It is still further desirable if such wireless connections could provide for efficient and reliable energy transfer. This is a particular problem with fully implanted systems which have a limited battery or other power source. The sum of these objectives will be met by the inventions described hereinafter. 
       BRIEF SUMMARY OF THE INVENTION 
       [0013]    To address hypertension, heart failure and their associated cardiovascular and nervous system disorders, the present invention provides a number of devices, systems and methods by which the blood pressure, nervous system activity, and neurohormonal activity may be selectively and controllably regulated by activating baroreceptors. By selectively and controllably activating baroreceptors, the present invention reduces excessive blood pressure, sympathetic nervous system activation and neurohormonal activation, thereby minimizing their deleterious effects on the heart, vasculature and other organs and tissues. 
         [0014]    The present invention provides systems and methods for treating a patient by inducing a baroreceptor signal to effect a change in the baroreflex system (e.g., reduced heart rate, reduced blood pressure, etc.). The baroreceptor signal is activated or otherwise modified by selectively activating baroreceptors. To accomplish this, the system and method of the present invention utilize a baroreceptor activation device positioned near a baroreceptor in the carotid sinus, aortic arch, heart, common carotid arteries, subclavian arteries, brachiocephalic artery and/or other arterial and venous locations. Preferably, the baroreceptor activation device is located in the right and/or left carotid sinus (near the bifurcation of the common carotid artery) and/or the aortic arch. By way of example, not limitation, the present invention is described with reference to the carotid sinus location. 
         [0015]    Generally speaking, the baroreceptor activation devices may be activated, deactivated or otherwise modulated to activate one or more baroreceptors and induce a baroreceptor signal or a change in the baroreceptor signal to thereby effect a change in the baroreflex system. The baroreceptor activation device may be activated, deactivated, or otherwise modulated continuously, periodically, or episodically. The baroreceptor activation device may comprise a wide variety of devices which utilize electrical (or in some instances electrically induced thermal or mechanical) to activate the baroreceptor. The baroreceptor may be activated directly, or activated indirectly via the adjacent vascular tissue. The baroreceptor activation device may be positioned at least in part inside the vascular lumen (i.e., intravascularly), outside the vascular wall (i.e., extravascularly) or within the vascular wall (i.e., intramurally). 
         [0016]    In a particular aspect of the present invention, systems for inducing a baroreceptor signal to effect a change in the baroreflex system of a patient comprise a baroreceptor activation device and a control system. The baroreceptor activation device is positionable in, or in come cases on, a blood vessel, e.g., in a vascular lumen or over an outer surface of the blood vessel proximate a baroreceptor so that activation of the device can induce a baroreceptor signal in the baroreceptor. The control system is coupled to the baroreceptor activation device and includes a processor and a memory. The memory includes software defining a stimulus or activation regimen which can generate a control signal as a function of the regimen. The coupling between the baroreceptor activation device and the control system includes at least one wireless link between the device and the control system, the link usually but not necessarily being provided across a vascular wall. Alternately, direct wireless linkage between an implanted controller and an implanted activation device is sometimes preferred to reduce the need for tunneling to implant cables. The activation device typically comprises an antenna, coil, or the like, implanted in a blood vessel, adjacent a baroreceptor, and the control system typically comprises an antenna, coil, or the like, implantable at a site in the patient&#39;s body remote from the activation device, typically being located in a venous lumen adjacent to the arterial or venous implantation site of the activation device. Venous sites for coil or antenna implantation will usually be preferred. 
         [0017]    In another aspect of the present invention, systems for activating vascular receptors comprise an extravascular transmitter and an electrode structure implantable in or over a blood vessel. The electrode structure is adapted to receive a signal transmitted from the extravascular transmitter and to produce electrical current in response thereto which activates the vascular receptor. The extravascular transmitter can have a variety of forms, such as an inductive coil, a radiofrequency transmitter, a microwave transmitter, or the like. The extravascular transmitter is usually adapted to be implanted in the patient&#39;s body, typically in a vein adjacent to a target receptor in an artery. In the case of venous implantation, the transmitter may comprise an antenna to be located adjacent the arterial site and a cable adapted to pass through the venous lumen to a remote penetration. The cable is useful for connecting the transmitter to a control system. The control system typically includes a driver which generates a control signal to be coupled to the extravascular transmitter. The control system will usually, although not necessarily, also be implantable, typically at a remote location or it may be connected to the transmitter via the cable. 
         [0018]    The electrode structure may comprise a wide variety of forms, typically being a stent-like structure which may be intravascularly deployed, typically being delivered in a collapsed state and expanded or otherwise deployed at the implantation site near the target receptor. The electrode structure will usually comprise a conductive metal which can be energized by radiofrequency (RF) or other electromagnetic (EM) transmission from the transmitter, and the conductive metal is preferably insulated over at least some surfaces. In particular, the electrode structure may comprise a (metal) receiving coil and may further comprise electrode pads connected to the receiving coil, where the electrode pads directly contact the internal vascular wall to activate the baroreceptors. Alternatively, extravascular electrode structures may find use as described in copending application Ser. No. 10/402,911 (Attorney Docket No. 21433-000410), filed on Mar. 27, 2003, the full disclosure of which is incorporated herein by reference. 
         [0019]    In a still further aspect of the present invention, a system for activating a baroreceptor in a carotid artery comprises an electrode structure and a transmitter. The electrode is deployable, usually implantable, or otherwise deployable in the carotid artery, typically near the carotid sinus in any of the common carotid artery, internal carotid artery, external carotid artery, or regions spanning therebetween. The electrode structure typically comprises a receiving coil, and the transmitter typically comprises a transmitting coil. The transmitting coil or antenna delivers EM energy to the receiving coil or structure and a responsive current is generated to activate the baroreceptor. Preferably, the system further comprises a control system which produces the EM control signal. The control system is connected to the transmitter implanted in the jugular vein by leads which pass through the lumen of the jugular vein and are connected to the control system via remote entry site. The control system is also preferably implantable at or near the remote entry site. 
         [0020]    In a still further aspect of the present invention, methods for activating a vascular receptor comprise transmitting a control signal from an extravascular location, where the control signal is received by an electrode structure implanted in or on a blood vessel. The site of implantation of the electrode structure is adjacent to the vascular receptor, and the control signal induces electrical current in the electrode structure which can activate the receptor. The control signal is preferably transmitted from a vein adjacent to the vascular receptor. The control signal is preferably generated by a control system implanted remotely from the vascular receptor, where the control system is wired through a venous (or in some cases arterial) lumen to a transmitter in a vein (or artery) adjacent to the target vascular receptor. 
         [0021]    In yet another aspect of the present invention, methods for implanting an electrode structure in an artery comprise intravascularly positioning the electrode structure at the target location in the artery, typically using intravascular implantation procedures of the type employed with the implantation of arterial stents and grafts. At least one electrical lead is advanced through a lumen of a vein adjacent to the arterial location of the electrode structure. The at least one lead may then be connected to the electrode structure in the artery by passing the lead through the arterial and venous walls. Such connections are preferably formed using an intravenous catheter having one or more stylets for penetrating the vascular walls and for threading and connecting the leads to the implanted electrode structure. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0022]      FIG. 1  is a schematic illustration of the upper torso of a human body showing the major arteries and veins and associated anatomy. 
           [0023]      FIG. 2A  is a cross-sectional schematic illustration of the carotid sinus and baroreceptors within the vascular wall. 
           [0024]      FIG. 2B  is a schematic illustration of baroreceptors within the vascular wall and the baroreflex system. 
           [0025]      FIG. 3  is a schematic illustration of a baroreceptor activation system in accordance with the present invention. 
           [0026]      FIGS. 4A and 4B  are schematic illustrations of a baroreceptor activation device which electro-mechanically induces a baroreceptor signal in accordance with an embodiment of the present invention. 
           [0027]      FIGS. 5A-5C  are schematic illustrations of baroreceptor activation devices in the form of an internal conductive structure, activated by an adjacent inductor, which electrically or thermally induces a baroreceptor signal in accordance with embodiments of the present invention. In  FIGS. 5A and 5B , a transmitting coil is located remotely from an implanted control system, while in  FIG. 5C , the transmitting coil or other antenna is located in the implanted control system itself. 
           [0028]      FIGS. 6A and 6B  are schematic illustrations of a baroreceptor activation device in the form of an internal conductive structure, activated by an internal inductor located in an adjacent vessel, which electrically or thermally induces a baroreceptor signal in accordance with an embodiment of the present invention. 
           [0029]      FIGS. 7A and 7B  are schematic illustrations of a baroreceptor activation device in the form of an internal conductive structure, activated by an external (skin mounted) inductor, which electrically or thermally induces a baroreceptor signal in accordance with an embodiment of the present invention. 
           [0030]      FIGS. 8A and 8B  are schematic illustrations of an electromagnetic baroreceptor activation device which directly induces a baroreceptor signal via a thermal or electrical mechanism in accordance with an embodiment of the present invention. 
           [0031]      FIGS. 9A-9C  are schematic illustrations of a preferred embodiment of an inductively activated electrically conductive structure. 
           [0032]      FIG. 10  illustrates an electrical intravascular baroreceptor activation device comprising a stent-like structure. 
           [0033]      FIGS. 11 and 12  illustrate an electrical intravascular baroreceptor activation device including an electrode and receiving assembly wrapped or upon the outside surface of an intravascular stent. 
           [0034]      FIGS. 13A-13D  illustrate alternative examples of electrode pad assemblies useful in the activation devices of the present invention. 
           [0035]      FIG. 14  illustrates an electrical intravascular baroreceptor activation device comprising a tubular braided stent-like structure. 
           [0036]      FIG. 15  is a detailed view of a portion of the stent structure of  FIG. 14 , showing a bipolar design. 
           [0037]      FIGS. 16A and 16B  show electrical activation circuits useful in the apparatus of the present invention. 
           [0038]      FIG. 17  shows an electrical baroreceptor activation device according to the present invention which incorporates an electronics module. 
           [0039]      FIG. 18  shows the embodiment of  FIG. 17  with the electronic module disposed on an electrode/receiver coil assembly. 
           [0040]      FIG. 19  is a schematic illustration of a wireless transmission arrangement where a coil activation device is implanted in an artery and a transmitting coil is implanted in an adjacent vein. The coils are aligned along a common axle. 
           [0041]      FIGS. 19A and 19C , illustrate alternative wireless transmission arrangements. 
           [0042]      FIG. 20  shows an implanted baroreceptor activation device which hard wired to a control system in the lumen of an adjacent vein. 
           [0043]      FIGS. 21-24  illustrate a catheter system including a stylet which may be used to implant and electrically connect a baroreceptor activation device in accordance with the principles of the present invention. 
           [0044]      FIGS. 25A-25C  illustrate a method of using the delivery catheter of  FIGS. 21-24  for electrically connecting a braided stent-like activation structure in accordance with the principles of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0045]    The following detailed description should be read with reference to the drawings in which similar elements in different drawings are numbered the same. The drawings, which are not necessarily to scale, depict illustrative embodiments and are not intended to limit the scope of the invention. 
         [0046]    To better understand the present invention, it may be useful to explain some of the basic vascular anatomy associated with the cardiovascular system. Refer to  FIG. 1  which is a schematic illustration of the upper torso of a human body  10  showing some of the major arteries and veins of the cardiovascular system. The left ventricle of the heart  11  pumps oxygenated blood up into the aortic arch  12 . The right subclavian artery  13 , the right common carotid artery  14 , the left common carotid artery  15  and the left subclavian artery  16  branch off the aortic arch  12  proximal of the descending thoracic aorta  17 . Although relatively short, a distinct vascular segment referred to as the brachiocephalic artery  22  connects the right subclavian artery  13  and the right common carotid artery  14  to the aortic arch  12 . The right carotid artery  14  bifurcates into the right external carotid artery  18  and the right internal carotid artery  19  at the right carotid sinus  20 . Although not shown for purposes of clarity only, the left carotid artery  15  similarly bifurcates into the left external carotid artery and the left internal carotid artery at the left carotid sinus. 
         [0047]    From the aortic arch  12 , oxygenated blood flows into the carotid arteries  18 / 19  and the subclavian arteries  13 / 16 . From the carotid arteries  18 / 19 , oxygenated blood circulates through the head and cerebral vasculature and oxygen depleted blood returns to the heart  11  by way of the jugular veins, of which only the right internal jugular vein  21  is shown for sake of clarity. From the subclavian arteries  13 / 16 , oxygenated blood circulates through the upper peripheral vasculature and oxygen depleted blood returns to the heart by way of the subclavian veins, of which only the right subclavian vein  23  is shown, also for sake of clarity. The heart  11  pumps the oxygen depleted blood through the pulmonary system where it is re-oxygenated. The re-oxygenated blood returns to the heart  11  which pumps the re-oxygenated blood into the aortic arch as described above, and the cycle repeats. 
         [0048]    Within the arterial walls of the aortic arch  12 , common carotid arteries  14 / 15  (near the right carotid sinus  20  and left carotid sinus), subclavian arteries  13 / 16  and brachiocephalic artery  22  there are baroreceptors  30 . For example, as best seen in  FIG. 2A , baroreceptors  30  reside within the vascular walls of the carotid sinus  20 . Baroreceptors  30  are a type of stretch receptor used by the body to sense blood pressure. An increase in blood pressure causes the arterial wall to stretch, and a decrease in blood pressure causes the arterial wall to return to its original size. Such a cycle is repeated with each beat of the heart. Because baroreceptors  30  are located within the arterial wall, they are able to sense deformation of the adjacent tissue, which is indicative of a change in blood pressure. The baroreceptors  30  located in the right carotid sinus  20 , the left carotid sinus and the aortic arch  12  play the most significant role in sensing blood pressure that affects the baroreflex system  50 , which is described in more detail with reference to  FIG. 2B . 
         [0049]    Refer now to  FIG. 2B , which shows a schematic illustration of baroreceptors  30  disposed in a generic vascular wall  40  and a schematic flow chart of the baroreflex system  50 . Baroreceptors  30  are profusely distributed within the arterial walls  40  of the major arteries discussed previously, and generally form an arbor  32 . The baroreceptor arbor  32  comprises a plurality of baroreceptors  30 , each of which transmits baroreceptor signals to the brain  52  via nerve  38 . The baroreceptors  30  are so profusely distributed and arborized within the vascular wall  40  that discrete baroreceptor arbors  32  are not readily discernable. To this end, those skilled in the art will appreciate that the baroreceptors  30  shown in  FIG. 2B  are primarily schematic for purposes of illustration and discussion. 
         [0050]    Baroreceptor signals are used to activate a number of body systems which collectively may be referred to as the baroreflex system  50 . Baroreceptors  30  are connected to the brain  52  via the nervous system  51 . Thus, the brain  52  is able to detect changes in blood pressure, which is indicative of cardiac output. If cardiac output is insufficient to meet demand (i.e., the heart  11  is unable to pump sufficient blood), the baroreflex system  50  activates a number of body systems, including the heart  11 , kidneys  53 , vessels  54 , and other organs/tissues. Such activation of the baroreflex system  50  generally corresponds to an increase in neurohormonal activity. Specifically, the baroreflex system  50  initiates a neurohormonal sequence that signals the heart  11  to increase heart rate and increase contraction force in order to increase cardiac output, signals the kidneys  53  to increase blood volume by retaining sodium and water, and signals the vessels  54  to constrict to elevate blood pressure. The cardiac, renal and vascular responses increase blood pressure and cardiac output  55 , and thus increase the workload of the heart  11 . In a patient with heart failure, this further accelerates myocardial damage and exacerbates the heart failure state. 
         [0051]    To address the problems of hypertension, heart failure, other cardiovascular disorders and renal disorders, the present invention basically provides a number of devices, systems and methods by which the baroreflex system  50  is activated to reduce excessive blood pressure, autonomic nervous system activity and neurohormonal activation. In particular, the present invention provides a number of devices, systems and methods by which baroreceptors  30  may be activated, thereby indicating an increase in blood pressure and signaling the brain  52  to reduce the body&#39;s blood pressure and level of sympathetic nervous system and neurohormonal activation, and increase parasypathetic nervous system activation, thus having a beneficial effect on the cardiovascular system and other body systems. 
         [0052]    With reference to  FIG. 3 , the present invention generally provides a system including a control system  60 , a baroreceptor activation device  70 , and a sensor  80  (optional), which generally operate in the following manner. The sensor  80  optionally senses and/or monitors a parameter (e.g., cardiovascular function) indicative of the need to modify the baroreflex system and generates a signal indicative of the parameter. In some embodiments (not shown), the sensor  80  may be incorporated into the structure of the activation device  70 . The control system  60  generates a control signal as a function of the received sensor signal. The control signal activates, deactivates or otherwise modulates the baroreceptor activation device  70 . Typically, activation of the device  70  results in activation of the baroreceptors  30 . Alternatively, deactivation or modulation of the baroreceptor activation device  70  may cause or modify activation of the baroreceptors  30 . The baroreceptor activation device  70  may comprise a wide variety of devices which utilize mechanical, electrical, thermal, chemical, biological, or other means to activate baroreceptors  30 . Thus, when the sensor  80  detects a parameter indicative of the need to modify the baroreflex system activity (e.g., excessive blood pressure), the control system  60  generates a control signal to modulate (e.g. activate) the baroreceptor activation device  70  thereby inducing a baroreceptor  30  signal that is perceived by the brain  52  to be apparent excessive blood pressure. When the sensor  80  detects a parameter indicative of normal body function (e.g., normal blood pressure), the control system  60  generates a control signal to modulate (e.g., deactivate) the baroreceptor activation device  70 . 
         [0053]    The baroreceptor activation device  70  may directly activate one or more baroreceptors  30  by changing the electrical potential across the baroreceptors  30 . It is also possible that changing the electrical potential might indirectly change the thermal or chemical potential across the tissue surrounding the baroreceptors  30  and/or otherwise may cause the surrounding tissue to stretch or otherwise deform, thus mechanically activating the baroreceptors  30 . 
         [0054]    The baroreceptor activation device  70  are suitable for implantation, and are preferably implanted using a minimally invasive percutaneous transluminal approach and/or a minimally invasive surgical approach. The baroreceptor activation device  70  may be positioned anywhere baroreceptors  30  effecting the baroreflex system  50  are numerous, such as in the heart  11 , in the aortic arch  12 , in the common carotid arteries  18 / 19  near the carotid sinus  20 , in the subclavian arteries  13 / 16 , or in the brachiocephalic artery  22 . The baroreceptor activation device  70  may be implanted such that the device  70  is positioned immediately adjacent the baroreceptors  30 . Alternatively, the baroreceptor activation device  70  may be outside the body such that the device  70  is positioned a short distance from but proximate to the baroreceptors  30 . Preferably, the baroreceptor activation device  70  is implanted near the right carotid sinus  20  and/or the left carotid sinus (near the bifurcation of the common carotid artery) and/or the aortic arch  12 , where baroreceptors  30  have a significant impact on the baroreflex system  50 . For purposes of illustration only, the present invention is described with reference to baroreceptor activation device  70  positioned near the carotid sinus  20 . 
         [0055]    The optional sensor  80  is operably coupled to the control system  60  by electric sensor cable or lead  82 . Optionally, the sensor could be coupled “wirelessly” and/or could be located on the activation device  70 . The sensor  80  may comprise any suitable device that measures or monitors a parameter indicative of the need to modify the activity of the baroreflex system. For example, the sensor  80  may comprise a physiologic transducer or gauge that measures ECG, blood pressure (systolic, diastolic, average or pulse pressure), blood volumetric flow rate, blood flow velocity, blood pH, O2 or CO2 content, mixed venous oxygen saturation (SVO2), vasoactivity, nerve activity, tissue activity or composition. Examples of suitable transducers or gauges for the sensor  80  include ECG electrodes, a piezoelectric pressure transducer, an ultrasonic flow velocity transducer, an ultrasonic volumetric flow rate transducer, a thermodilution flow velocity transducer, a capacitive pressure transducer, a membrane pH electrode, an optical detector (SVO2) or a strain gage. Although only one sensor  80  is shown, multiple sensors  80  of the same or different type at the same or different locations may be utilized. 
         [0056]    An example of an implantable blood pressure measurement device that may be disposed about a blood vessel is disclosed in U.S. Pat. No. 6,106,477 to Miesel et al., the entire disclosure of which is incorporated herein by reference. An example of a subcutaneous ECG monitor is available from Medtronic under the trade name REVEAL ILR and is disclosed in PCT Publication No. WO 98/02209, the entire disclosure of which is incorporated herein by reference. Other examples are disclosed in U.S. Pat. Nos. 5,987,352 and 5,331,966, the entire disclosures of which are incorporated herein by reference. Examples of devices and methods for measuring absolute blood pressure utilizing an ambient pressure reference are disclosed in U.S. Pat. No. 5,810,735 to Halperin et al., U.S. Patent No. 5,904,708 to Goedeke, and PCT Publication No. WO 00/16686 to Brockway et al., the entire disclosures of which are incorporated herein by reference. The sensor  80  described herein may take the form of any of these devices or other devices that generally serve the same purpose. 
         [0057]    The sensor  80  is preferably positioned in a chamber of the heart  11 , or in/on a major artery such as the aortic arch  12 , a common carotid artery  14 / 15 , a subclavian artery  13 / 16  or the brachiocephalic artery  22 , such that the parameter of interest may be readily ascertained. The sensor  80  may be disposed inside the body such as in or on an artery, a vein or a nerve (e.g. vagus nerve), or disposed outside the body, depending on the type of transducer or gauge utilized. The sensor  80  may be separate from the baroreceptor activation device  70  or combined therewith. For purposes of illustration only, the sensor  80  is shown positioned on the right subclavian artery  13 . 
         [0058]    By way of example, the control system  60  includes a control block  61  comprising a processor  63  and a memory  62 . Control system  60  is connected to the sensor  80  by way of sensor cable  82 . Control system  60  is also connected to the baroreceptor activation device  70  by way of electric control cable  72 . Thus, the control system  60  receives a sensor signal from the sensor  80  by way of sensor cable  82 , and transmits a control signal to the baroreceptor activation device  70  by way of control cable  72 . 
         [0059]    The system components  60 / 70 / 80  may be directly linked via cables  72 / 82  or by indirect means such as RF signal transceivers, ultrasonic transceivers or galvanic couplings. Examples of such indirect interconnection devices are disclosed in U.S. Pat. No. 4,987,897 to Funke and U.S. Pat. No. 5,113,859 to Funke, the entire disclosures of which are incorporated herein by reference. 
         [0060]    The memory  62  may contain data related to the sensor signal, the control signal, and/or values and commands provided by the input device  64 . The memory  62  may also include software containing one or more algorithms defining one or more functions or relationships between the control signal and the sensor signal. The algorithm may dictate activation or deactivation control signals depending on the sensor signal or a mathematical derivative thereof. The algorithm may dictate an activation or deactivation control signal when the sensor signal falls below a lower predetermined threshold value, rises above an upper predetermined threshold value or when the sensor signal indicates a specific physiologic event. The algorithm may dynamically alter the threshold value as determined by the sensor input values. 
         [0061]    As mentioned previously, the baroreceptor activation device  70  activates baroreceptors  30  electrically, optionally in combination with mechanical, thermal, chemical, biological or other co-activation. In some instances, the control system  60  includes a driver  66  to provide the desired power mode for the baroreceptor activation device  70 . For example, the driver  66  may comprise a power amplifier or the like and the cable  72  may comprise electrical lead(s). In other instances, the driver  66  may not be necessary, particularly if the processor  63  generates a sufficiently strong electrical signal for low level electrical actuation of the baroreceptor activation device  70 . 
         [0062]    The control system  60  may operate as a closed loop utilizing feedback from the sensor  80 , or other sensors, such as heart rate sensors which may be incorporated on the electrode assembly, or as an open loop utilizing reprogramming commands received by input device  64 . The closed loop operation of the control system  60  preferably utilizes some feedback from the transducer  80 , but may also operate in an open loop mode without feedback. Programming commands received by the input device  64  may directly influence the control signal, the output activation parameters, or may alter the software and related algorithms contained in memory  62 . The treating physician and/or patient may provide commands to input device  64 . Display  65  may be used to view the sensor signal, control signal and/or the software/data contained in memory  62 . 
         [0063]    The control signal generated by the control system  60  may be continuous, periodic, alternating, episodic or a combination thereof, as dictated by an algorithm contained in memory  62 . Continuous control signals include a constant pulse, a constant train of pulses, a triggered pulse and a triggered train of pulses. Examples of periodic control signals include each of the continuous control signals described above which have a designated start time (e.g., beginning of each period as designated by minutes, hours, or days in combinations of) and a designated duration (e.g., seconds, minutes, hours, or days in combinations of). Examples of alternating control signals include each of the continuous control signals as described above which alternate between the right and left output channels. Examples of episodic control signals include each of the continuous control signals described above which are triggered by an episode (e.g., activation by the physician/patient, an increase/decrease in blood pressure above a certain threshold, heart rate above/below certain levels, etc.). 
         [0064]    The stimulus regimen governed by the control system  60  may be selected to promote long term efficacy. It is theorized that uninterrupted or otherwise unchanging activation of the baroreceptors  30  may result in the baroreceptors and/or the baroreflex system becoming less responsive over time, thereby diminishing the long term effectiveness of the therapy. Therefore, the stimulus regimen maybe selected to activate, deactivate or otherwise modulate the baroreceptor activation device  70  in such a way that therapeutic efficacy is maintained for months, preferably for years. 
         [0065]    In addition to maintaining therapeutic efficacy over time, the stimulus regimens of the present invention may be selected reduce power requirement/consumption of the system  60 . As will be described in more detail hereinafter, the stimulus regimen may dictate that the baroreceptor activation device  70  be initially activated at a relatively higher energy and/or power level, and subsequently activated at a relatively lower energy and/or power level. The first level attains the desired initial therapeutic affect, and the second (lower) level sustains the desired therapeutic affect long term. By reducing the energy and/or power levels after the desired therapeutic affect is initially attained, the energy required or consumed by the activation device  70  is also reduced long term. This may correlate into systems having greater longevity and/or reduced size (due to reductions in the size of the power supply and associated components). 
         [0066]    A first general approach for a stimulus regimen which promotes long term efficacy and reduces power requirements/consumption involves generating a control signal to cause the baroreceptor activation device  70  to have a first output level of relatively higher energy and/or power, and subsequently changing the control signal to cause the baroreceptor activation device  70  to have a second output level of relatively lower energy and/or power. The first output level may be selected and maintained for sufficient time to attain the desired initial affect (e.g., reduced heart rate and/or blood pressure), after which the output level may be reduced to the second level for sufficient time to sustain the desired affect for the desired period of time. 
         [0067]    For example, if the first output level has a power and/or energy value of X1, the second output level may have a power and/or energy value of X2, wherein X2 is less than X1. In some instances, X2 may be equal to zero, such that the first level is “on” and the second level is “off”. It is recognized that power and energy refer to two different parameters, and in some cases, a change in one of the parameters (power or energy) may not correlate to the same or similar change in the other parameter. In the present invention, it is contemplated that a change in one or both of the parameters may be suitable to obtain the desired result of promoting long term efficacy. 
         [0068]    It is also contemplated that more than two levels may be used. Each further level may increase the output energy or power to attain the desired affect, or decrease the output energy or power to retain the desired affect. For example, in some instances, it may be desirable to have further reductions in the output level if the desired affect may be sustained at lower power or energy levels. In other instances, particularly when the desired affect is diminishing or is otherwise not sustained, it may be desirable to increase the output level until the desired affect is reestablished, and subsequently decrease the output level to sustain the affect. 
         [0069]    The transition from each level may be a step function (e.g., a single step or a series of steps), a gradual transition over a period of time, or a combination thereof. In addition, the signal levels may be continuous, periodic, alternating, or episodic as discussed previously. 
         [0070]    In electrical activation using a non-modulated signal, the output (power or energy) level of the baroreceptor activation device  70  may be changed by adjusting the output signal voltage level, current level and/or signal duration. The output signal of the baroreceptor activation device  70  may be, for example, constant current or constant voltage. In electrical activation embodiments using a modulated signal, wherein the output signal comprises, for example, a series of pulses, several pulse characteristics may be changed individually or in combination to change the power or energy level of the output signal. Such pulse characteristics include, but are not limited to: pulse amplitude (PA), pulse frequency (PF), pulse width or duration (PW), pulse waveform (square, triangular, sinusoidal, etc.), pulse polarity and pulse phase (monophasic, biphasic), and sequential. 
         [0071]    In electrical activation wherein the output signal comprises a pulse train, several other signal characteristics may be changed in addition to the pulse characteristics described above, as described in copending application Ser. No. 09/964,079, the full disclosure of which is incorporated herein by reference. 
         [0072]    The control system  60  may be implanted in whole or in part. For example, the entire control system  60  may be carried externally by the patient utilizing transdermal connections to the sensor lead  82  and the control lead  72 . Alternatively, the control block  61  and driver  66  may be implanted with the input device  64  and display  65  carried externally by the patient utilizing transdermal connections therebetween. As a further alternative, the transdermal connections may be replaced by cooperating transmitters/receivers to remotely communicate between components of the control system  60  and/or the sensor  80  and baroreceptor activation device  70 . 
         [0073]    With general reference to  FIGS. 4-9 , schematic illustrations of specific embodiments of the baroreceptor activation device  70  are shown. The design, function and use of these specific embodiments, in addition to the control system  60  and sensor  80  (not shown), are the same as described with reference to  FIG. 3 , unless otherwise noted or apparent from the description. In addition, the anatomical features illustrated in  FIGS. 4-8  are the same as discussed with reference to  FIGS. 1 ,  2 A and  2 B, unless otherwise noted. In each embodiment, the connections between the components  60 / 70 / 80  may be physical (e.g., wires, tubes, cables, etc.) or remote (e.g., transmitter/receiver, inductive, magnetic, etc.). For physical connections, the connection may travel intra-arterially, intravenously, subcutaneously, or through other natural tissue paths. 
         [0074]    Refer now to  FIGS. 4A and 4B  which show schematic illustrations of a baroreceptor activation device  220  in the form of magnetic particles  222  disposed in the vascular wall  40 . The magnetic particles  222  may comprise magnetically responsive materials (i.e., ferrous based materials) and may be magnetically neutral or magnetically active. Preferably, the magnetic particles  222  comprise permanent magnets having an elongate cylinder shape with north and south poles to strongly respond to magnetic fields. The magnetic particles  222  are actuated by an electromagnetic coil  224  which is operably coupled to the driver  66  of the control system  60  by way of an electrical cable  226 . The electromagnetic coil  224  may be implanted as shown, or located outside the body, in which case the driver  66  and the remainder of the control system  60  would also be located outside the body. By selectively activating the electromagnetic coil  224  to create a magnetic field, the magnetic particles  222  may be repelled, attracted or rotated. Alternatively, the magnetic field created by the electromagnetic coil  224  may be alternated such that the magnetic particles  222  vibrate within the vascular wall  40 . When the magnetic particles are repelled, attracted, rotated, vibrated or otherwise moved by the magnetic field created by the electromagnetic coil  224 , the baroreceptors  30  are mechanically activated. 
         [0075]    The electromagnetic coil  224  is preferably placed as close as possible to the magnetic particles  222  in the vascular wall  40 , and may be placed intravascularly, extravascularly, or in any of the alternative locations discussed with reference to inductor shown in  FIGS. 5-7 . The magnetic particles  222  may be implanted in the vascular wall  40  by injecting a ferro-fluid or a ferro-particle suspension into the vascular wall adjacent to the baroreceptors  30 . To increase biocompatibility, the particles  222  may be coated with a ceramic, polymeric or other inert material. Injection of the fluid carrying the magnetic particles  222  is preferably performed percutaneously. 
         [0076]    Electrical activation signals may be indirectly delivered utilizing an inductor as illustrated in  FIGS. 5-9 . The embodiments of  FIGS. 5-7  utilize an inductor  286  which is operably connected to the driver  66  of the control system  60  by way of electrical lead  284 . The inductor  286  comprises an electrical winding which creates a magnetic field  287  (as seen in  FIG. 9 ) around the electrode structure  282 . The magnetic field  287  may be alternated by alternating the direction of current flow through the inductor  286 . Accordingly, the inductor  286  may be utilized to create current flow in the electrode structure  282  to thereby deliver electrical signals to the vascular wall  40  to directly or indirectly activate the baroreceptors  30 . In all embodiments, the inductor  286  may be covered with an electrically insulating material to eliminate direct electrical stimulation of tissues surrounding the inductor  286 . A preferred embodiment of an inductively activated electrode structure  282  is described in more detail with reference to  FIGS. 9A-9C . 
         [0077]    The embodiments of  FIGS. 5-7  may be modified to form a cathode/anode arrangement. Specifically, the electrical inductor  286  would be connected to the driver  66  as shown in  FIGS. 5-7  and the electrode structure  282  would be connected to the driver  66 . With this arrangement, the electrode structure  282  and the inductor  286  may be any suitable geometry and need not be coiled for purposes of induction. The electrode structure  282  and the inductor  286  would comprise a cathode/anode or anode/cathode pair. For example, when activated, the cathode  282  may generate a primary stream of electrons which travel through the inter-electrode space (i.e., vascular tissue and baroreceptors  30 ) to the anode  286 . The cathode is preferably cold, as opposed to thermionic, during electron emission. The electrons may be used to electrically or thermally activate the baroreceptors  30  as discussed previously. 
         [0078]    Alternative means of indirect or wireless transmission of electrical energy are described in U.S. Pat. No. 6,231,516 to Keilman et al., the entire disclosure of which is hereby incorporated by reference. The therapeutic transducer disclosed by Keilman et al. may be replaced by electrode structure  282 , electrodes  302  or electrodes  520 , to which power may be delivered by the RF coupling coil system described by Keilman et al. 
         [0079]    The electrical inductor  286  is preferably disposed as close as possible to the electrode structure  282 . For example, the electrical inductor  286  may be disposed adjacent the vascular wall as illustrated in  FIGS. 5A and 5B . Alternatively, the inductor  286  may be disposed in an adjacent vessel as illustrated in  FIGS. 6A and 6B . If the electrode structure  282  is disposed in the carotid sinus  20 , for example, the inductor  286  may be disposed in the internal jugular vein  21  as illustrated in  FIGS. 6A and 6B . In the embodiment of  FIGS. 6A and 6B , the electrical inductor  286  may comprise a similar structure as the electrode structure  282 . As a further alternative, the electrical inductor  286  may be disposed outside the patient&#39;s body, but as close as possible to the electrode structure  282 . If the electrode structure  282  is disposed in the carotid sinus  20 , for example, the electrical inductor  286  may be disposed on the right or left side of the neck of the patient as illustrated in  FIGS. 7A and 7B . In the embodiment of  FIGS. 7A and 7B , wherein the electrical inductor  286  is disposed outside the patient&#39;s body, the control system  60  may also be disposed outside the patient&#39;s body. 
         [0080]    In terms of implant location, the electrode structure  282  may be intravascularly disposed as described with reference to  FIGS. 6A and 6B , or extravascularly disposed. Except as described herein, the extravascular electrode structure is the same in design, function, and use as the intravascular electrode structure  282 . The electrode structure may comprise a coil, braid or other structure capable of surrounding the vascular wall. Alternatively, the electrode structure may comprise one or more electrode patches distributed around the outside surface of the vascular wall. Because the electrode structure is disposed on the outside surface of the vascular wall, intravascular delivery techniques may not be practical, but minimally invasive surgical techniques will suffice. 
         [0081]    Refer now to  FIGS. 8A and 8B  which show schematic illustrations of a baroreceptor activation device  320  in the form of electrically conductive particles  322  disposed in the vascular wall. This embodiment is substantially the same as the embodiments described with reference to  FIGS. 5-7 , except that the electrically conductive particles  322  are disposed within the vascular wall, as opposed to the electrically conductive structures  288  which are disposed on either side of the vascular wall. 
         [0082]    In this embodiment, the driver  66  of the control system  60  comprises an electromagnetic transmitter such as a radiofrequency or microwave transmitter. Electromagnetic radiation is created by the transmitter  66  which is operably coupled to an antenna  324  by way of electrical lead  326 . Electromagnetic waves are emitted by the antenna  324  and received by the electrically conductive particles  322  disposed in the vascular wall  40 . Electromagnetic energy creates oscillating current flow within the electrically conductive particles  322 , and depending on the intensity of the electromagnetic radiation and the resistivity of the conductive particles  322 , may cause the electrical particles  322  to generate heat. The electrical or thermal energy generated by the electrically conductive particles  322  may directly activate the baroreceptors  30 , or indirectly activate the baroreceptors  30  by way of the surrounding vascular wall tissue. 
         [0083]    The electromagnetic radiation transmitter  66  and antenna  324  may be disposed in the patient&#39;s body, with the antenna  324  disposed adjacent to the conductive particles in the vascular wall  40  as illustrated in  FIGS. 8A and 8B . Alternatively, the antenna  324  may be disposed in any of the positions described with reference to the electrical inductor shown in  FIGS. 5-7 . It is also contemplated that the electromagnetic radiation transmitter  66  and antenna  324  may be utilized in combination with the intravascular and extravascular electrically conductive structures  282  (acting like heater coils) described with reference to  FIGS. 5-7  to generate thermal energy on either side of the vascular wall. 
         [0084]    As an alternative, the electromagnetic radiation transmitter  66  and antenna  324  may be used without the electrically conductive particles  322 . Specifically, the electromagnetic radiation transmitter  66  and antenna  324  may be used to deliver electromagnetic radiation (e.g., RF, microwave) directly to the baroreceptors  30  or the tissue adjacent thereto to cause localized heating, thereby thermally inducing a baroreceptor  30  signal. 
         [0085]    Refer now to  FIGS. 9A-9C  which show schematic illustrations of a specific embodiment of an inductively activated electrode structure  282  for use with the embodiments described with reference to  FIGS. 5 -7 . In this embodiment, current flow in the electrode structure  282  is induced by a magnetic field  287  created by an inductor  286  which is operably coupled to the driver  66  of the control system  60  by way of electrical cable  284 . The electrode structure  282  preferably comprises a multi-filar self-expanding braid structure including a plurality of individual members  282   a ,  282   b ,  282   c  and  282   d . However, the electrode structure  282  may simply comprise a single coil for purposes of this embodiment. 
         [0086]    Each of the individual coil members  282   a - 282   d  comprising the electrode structure  282  consists of a plurality of individual coil turns  281  connected end to end as illustrated in  FIGS. 9B and 9C .  FIG. 9C  is a detailed view of the connection between adjacent coil turns  281  as shown in  FIG. 9B . Each coil turn  281  comprises electrically isolated wires or receivers in which a current flow is established when a changing magnetic field  287  is created by the inductor  286 . The inductor  286  is preferably covered with an electrically insulating material to eliminate direct electrical stimulation of tissues surrounding the inductor  286 . Current flow through each coil turn  281  results in a potential drop  288  between each end of the coil turn  281 . With a potential drop defined at each junction between adjacent coil turns  281 , a localized current flow cell is created in the vessel wall adjacent each junction. Thus an array or plurality of bipoles are created by the electrode structure  282  and uniformly distributed around the vessel wall. Each coil turn  281  comprises an electrically conductive wire material  290  surrounded by an electrically insulating material  292 . The ends of each coil turn  281  are connected by an electrically insulated material  294  such that each coil turn  281  remains electrically isolated. The insulating material  294  mechanically joins but electrically isolates adjacent coil turns  281  such that each turn  281  responds with a similar potential drop  288  when current flow is induced by the changing magnetic field  287  of the inductor  286 . An exposed portion  296  is provided at each end of each coil turn  281  to facilitate contact with the vascular wall tissue. Each exposed portion  296  comprises an isolated electrode in contact with the vessel wall. The changing magnetic field  287  of the inductor  286  causes a potential drop in each coil turn  281  thereby creating small current flow cells in the vessel wall corresponding to adjacent exposed regions  296 . The creation of multiple small current cells along the inner wall of the blood vessel serves to create a cylindrical zone of relatively high current density such that the baroreceptors  30  are activated. However, the cylindrical current density field quickly reduces to a negligible current density near the outer wall of the vascular wall, which serves to limit extraneous current leakage to minimize or eliminate unwanted activation of extravascular tissues and structures such as nerves or muscles. 
         [0087]    Refer now to  FIGS. 10-15  which illustrate variations on the intravascular baroreceptor activation device  280  and electrode structure  282  described previously. In the embodiments illustrated in  FIGS. 10-15 , the electrical baroreceptor activation devices comprise stent like structures that may be directly or wirelessly coupled to the control system  60  as described previously. In particular, wireless transmission of electrical energy may be employed as described in U.S. Pat. No. 6,231,516 to Keilman et al., the entire disclosure of which is hereby incorporated by reference. The stent like structures may comprise conventional intravascular stents that carry one or more electrodes and/or receiving coils, or a portion of the stent like structure may serve as one or more electrodes and/or receiving coils. The stent like structures may be intravascularly delivered in a collapsed state, and deployed to an expanded state in much the same way that intravascular stents are implanted in coronary and peripheral applications. 
         [0088]    For example, in the embodiment illustrated in  FIG. 10 , the electrical intravascular baroreceptor activation device  610  comprises a stent like structure having a coil mid portion  612  and two ratcheting end portions  614 . The coil mid portion  612  unwinds as the device  610  is deployed in the vessel lumen, and the ratcheting ends portions  614  selectively expand (self expanded or balloon expanded) to the desired diameter, with tabs  615  engaging openings  616  to lock the device  610  in the expanded state. Those skilled in the art will recognize that other stent like structures may be employed as well, such as self expanding stent structures. 
         [0089]    In the embodiment of  FIG. 10 , the coil mid portion  612  may comprise an insulated conductive metal such as MP 35, SST, or a NiTi alloy, and may serve as an RF receiving coil which receives RF transmissions from an antenna or coupling coil (not shown) connected to the control system  60 . In this embodiment, the winding axis of the coil  612  is common with the longitudinal center axis of the tubular device  610 . The ratcheting end portions  614  may comprise a conductive material such as MP 35, SST, or a NiTi alloy, with the inside surface of the end portions  614  insulated and the outside surface of the end portions  614  at least partially uninsulated to serve as electrodes which contact the inside surface of the vessel wall. Alternatively, the end portions  614  may incorporate conductive barbs to serve as electrodes which extend into the vascular wall upon expansion of the device  610 . One end  611  of the coil  612  is connected to one end portion  614 , and the other end  613  of the coil  612  is connected to the other end portion  614 . With this arrangement, a signal transmitted by control system  60  is received by the coil  612  and travels to inside surface of the vascular wall adjacent baroreceptors via the outside surface of the end portions  614 . Optionally, an electronics module  670  may be electrically connected between the end portions  614  and mounted to the mid portion  612 , for example. The electronics module  670  may comprise a tuning capacitor, for example, as will be described in more detail hereinafter. 
         [0090]    Refer now to  FIGS. 11 and 12  which illustrate an electrical intravascular baroreceptor activation device  620 , including an electrode and receiving coil assembly  630  wrapped about the outside surface of an intravascular stent  640 . The electrode and receiving coil assembly  630  may be movably attached to the intravascular stent  640  to permit free expansion of the stent  640 , and/or may be made expandable to permit expansion of the assembly  630  with expansion of the stent  640 . Stent  640  may comprise a self expanding stent, a balloon expandable stent, or any of a wide variety of other types of intravascular stents known to those skilled in the art. In the embodiment illustrated, the stent  640  is shown in the form of a tubular metal stent having a plurality of slots. 
         [0091]    The assembly  630  shown in  FIG. 11  may be in the shape of a semi cylinder (shown) or tubular sleeve (not shown) and may include a receiving coil  632  and one or more electrode pads  634 . The coil  632  and the pads  634  may comprise a conductive metal such as Pt or a Pt alloy disposed on a flex circuit substrate material  636  such as polyimide. The metal may be laminated on the flex circuit substrate  636  and may be chemically etched to define the pattern of the coil  632  and pads  634 . One end  631  of the coil  632  is connected to one of the electrode pads  634 , and the other end  633  of the coil  632  is connected via a backside tracer to the other electrode pad  634 . With this arrangement, a signal transmitted by control system  60  is received by the coil  632  and travels to inside surface of the vascular wall adjacent baroreceptors via the electrode pads  634 . An electronics module  670  may be electrically connected via backside tracers between the pads  634  and mounted to the substrate  636 , for example. The electronics module  670  may comprise a tuning capacitor, for example, as will be described in more detail hereinafter. 
         [0092]    The assembly  630  may include both the receiving coil  632  and the electrode pads  634 , or simply the electrode pads  634  without the coil  632  as when the device  620  is hard wired to the control system  60 . In this latter instance, the electrode pads  634  may be shaped and arranged in a wide variety of manners, a few examples of which are shown in  FIGS. 13A-13D . In  FIG. 13A , the pads  634  are disposed about the ends of the substrate  636  substantially parallel to the circumference. In  FIG. 13B , the pads are disposed about the mid portion of the substrate  636  substantially parallel to the longitudinal axis. In  FIG. 13C , the electrode pads  634  comprise circles or concentric rings distributed about the substrate  636 . In  FIG. 13D , the pads  634  are disposed along the entire substrate  636  substantially parallel to the circumference. 
         [0093]    Refer now to  FIG. 14  which illustrates an electrical intravascular baroreceptor activation device  650  comprising a tubular braided stent like structure, for example. The intravascular electrical baroreceptor activation device  650  may comprise a wide variety of stent like structures including, without limitation, self expanding multi-filar braid, self expanding interconnected zig-zag bands, self expanding coil bands, etc. Generally speaking, for the intravascular stent like baroreceptor activation devices disclosed herein, elastic self expanding stent like structures may be preferred to avoid accidental collapse if the device is to be implanted in the carotid sinus which is relatively unprotected from external forces. 
         [0094]    In addition, for electrical activation devices disclosed herein, it is generally desirable to limit unwanted collateral stimulation of adjacent tissues (i.e., to limit the electrical field beyond to vascular wall wherein the baroreceptors reside) by creating localized cells or electrical fields. Localized cells may be created, for example, by spacing the electrodes or poles very close together (e.g., &lt;1 mm), placing the anode in a carotid artery and placing the cathode in an adjacent jugular vein (or vice versa), biasing the electrical filed with conductors and/or magnetic fields (e.g., an electrical field generator in the jugular vein with a conductive device in the carotid sinus to attract the e field), etc. 
         [0095]    Alternatively, if it is desired to stimulate the carotid sinus nerve (CSN), the electrical field may be directed from one or more intravascular and/or extravascular electrical activation devices disposed near the CSN. For example, one electrode may be placed in the external carotid artery and another electrode may be placed in the internal carotid artery, or one electrode may be placed in the external carotid artery and another electrode may be placed in the jugular vein, etc. With this arrangement, the electrical field created between the electrodes may be used to stimulate the CSN for baropacing applications. 
         [0096]    In the specific embodiment shown in  FIG. 14 , the braided tube structure  650  includes a plurality of interwoven members  652 / 654 , one set  652  (e.g., half) of which are helically wound in one direction (e.g., CW) and another set  654  (e.g., the other half) of which are helically wound in the other direction (e.g., CCW). In  FIG. 14 , one set of members is shown in black thick lines and the other set is shown in gray thick lines (the thin lines represent members running along the back side of the tubular device  650 ). For example, in a 16 wire braid, 8 members run CW, and 8 members run CCW. One set of members  652  comprises electrically conductive wires, and the other set of members comprises electrically insulating members  654 . The electrically conductive wires  652  may comprise a conductive metal such as MP 35N, SST, Elgiloy, or a NiTi alloy, and the electrically insulating members  654  may comprise a non-conductive material such as a polymer or a metal wire covered by a non-conductive insulating material, for example. Because the electrically conductive wires  652  run in the same helical direction, each wire remains electrically isolated from adjacent wires. In addition, the electrically insulating members  654  aid in maintaining the electrical isolation of each conductive wire  652  by maintaining the spacing between adjacent wires  652 . To this end, each conductive wire  652  acts like a helically extending electrode. 
         [0097]    Of the conductive members  652 , adjacent members may have a dissimilar polarity so as to create current flow  658  between adjacent wires as shown in  FIG. 15 . For example, every other wire  652  may have a positive polarity, with every other remaining wire having a negative polarity (bipolar or anode/cathode arrangement). As such, the electrical field may be in the form of a series of helices having a width substantially equal to the spacing between adjacent wires  652 . The wires  652  may have a bipolar, tripolar, or any other multipolar arrangement, depending on how each wire  652  is connected to and activated by the control system  60 . The control system  60  (not shown) may be coupled to the conductive wires  652  by cable  656 . Cable  656  may be hardwired to the control system  60  or wirelessly coupled to the control system by incorporating a receiver coil in or near the device  650 . As with the prior embodiments, an electronics module  670  (not shown) may be electrically connected to adjacent wires  652 . 
         [0098]    When implanted, the electrical activation embodiments may create an L C circuit as shown in the schematic  660  shown in  FIG. 16A . In particular, an L C circuit may be created between electrode contacts when using a receiving coil (L) due to the parasitic capacitance (CP) of tissue (e.g., vascular wall tissue), and thus the device would potentially have a resonating frequency. Alternatively, an electronics module  670  such as a tuning circuit or a simple capacitor (C) may be employed to create an L C tuned circuit as shown in  FIG. 16B . The EM or RF signal generated by the control system may be located within the body (e.g., neck) or outside the body. 
         [0099]    The activation devices described herein may be passive with the intelligence carried by the control system  60 . Alternatively, the activation devices may incorporate intelligence in the form of an electronics module  670  which cooperates with the control system  60  to actively control power transmission, activation energy, activation regimen, electrode activation sequencing, etc. For example, as seen in the schematic illustration of  FIG. 17 , (where reference to RF is intended to include all EM sources) the activation device may incorporate an electronics module  670 . The electronics module  670  may be disposed on the electrode/receiver coil assembly  630  (to be deployed for example on a stent-like electrode assembly) as shown in  FIG. 18 . The electronics module  670  may include a power supply circuit  672  which receives power from the EM energy transmitted by the control system  60  to a receiver coil  671  of the activation device. The electronics module  670  may include a signal decoding circuit  674  to decode an encoded signal transmitted by the control system  60 . The electronics module may also include an activation control circuit  676  that delivers the desired electrical signals to specific electrodes as a function of an internal algorithm and the decoded information received from circuit  674 . Optionally, the module  670  may be configured to both receive and transmit back encoded information. Data to be sent backing include pressure, pulse, or other information obtained from sensors on the activation device or elsewhere. 
         [0100]    Refer now to  FIG. 19  which schematically illustrates a wireless transmission arrangement for use with any of the intravascular and extravascular electrical baroreceptor activation devices described herein. For sake of illustration and discussion only, intravascular electrical baroreceptor activation device  620  is shown in  FIG. 19 , including the flexible receiver coil and electrode circuit assembly  630  deployed on the outer surface of a stent-like or other electrode structure  640 . The activation device  620  may be disposed in the artery containing the baroreceptors, such as internal carotid artery  19  or common carotid artery  14 . A transmitting device  680  may be disposed in an adjacent vein such as jugular vein  21  which lies in close proximity to the internal carotid artery  19  and the common carotid artery  14 . 
         [0101]    In this embodiment, ( FIG. 19 ) the transmitting device includes a coil assembly  682  disposed on a stent like tubular structure  684 , similar to the construction and arrangement of assembly  630  disposed on stent like structure  640  as described previously. The coil assembly  682  emits an RF or other EM signal picked up by coil assembly  630  on the activation device  620 . The coil assembly  682  on the transmitting device  680  acts as an antenna and is operably coupled to the control system  60  (not shown) via leads  686  which travel down the vein  21  to a remote entry site. The presence of leads  686  in the venous side of the vascular system is less concerning due to the reduced risk of thromboembolism and stroke. 
         [0102]      FIG. 19  illustrates coupling between two generally “planar” coils which are arranged face-to-face in adjacent blood vessels.  FIGS. 19A-19C  illustrate alternative embodiments. In  FIG. 19A , a helical transmitting coil  691  is positioned in a first blood vessel and a helical receiving coil  693  is positioned in a second blood vessel immediately adjacent the transmitting coil. The coil axes are aligned, and transmissions may be made as described previously. The coils  691  and  693  may also be arranged with parallel axes, but longitudinally separated, as shown in  FIG. 19B , and a specific implantation in the common carotid artery CC is shown if  FIG. 19C . 
         [0103]    As an alternative to wireless transmission, the activation device  620  may be hard wired to the control system  60  as shown in  FIG. 20 . In this embodiment, the activation device  620  may be disposed in the artery containing the baroreceptors, such as internal carotid artery  19  or common carotid artery  14 . The activation device includes two or more laterally facing extensions or barbs  638  which extend through the arterial wall and into an adjacent vein such as jugular vein  21 , which lies in close proximity to the internal carotid artery  19  and the common carotid artery  14 . The electrode pads  634  are electrically connected to the extensions  638  which are coupled to the control system  60  (not shown) via leads  639  which travel down the vein  21  to a remote entry site. The presence of leads  639  in the venous side of the vascular system is less concerning due to the reduced risk of thromboembolism and stroke. 
         [0104]    Refer now to  FIGS. 21-25  which schematically illustrate tools and methods for making a connection between an electrical activation device disposed in or on a vessel containing baroreceptors (e.g., carotid artery  14 / 19 ) and leads disposed in an adjacent vessel (e.g., jugular vein  21 ). The tools and methods described with reference to  FIG. 21-25  facilitate minimally invasive transluminal techniques, and presume the activation device  650  has been previously implanted by minimally invasive transluminal techniques, for example. These tools and methods may be applied to many of the intravascular electrical activation devices described herein, and are described with reference to braided stent like structure  650  for sake of illustration, not limitation. 
         [0105]      FIG. 24  illustrates a top view of a distal portion of a delivery catheter  710 . Catheter  710  is sized and adapted for intravascular insertion and navigation from a remove vascular access point leading to the jugular vein  21  adjacent the carotid sinus  20 .  FIG. 22  is a longitudinal sectional view taken along line  22 - 22  in  FIG. 21 , and  FIG. 23  is a cross sectional view taken along line  23 - 23  in  FIG. 21 . As may be seen in  FIGS. 21-23 , catheter  710  includes an elongate shaft  712  with a first pair of lumens  714  leading to proximal ports  715 , and a second pair of lumens  716  leading to distal ports  717 . A plane of separability  718  such as a peelable seam may be provided along the centerline of the shaft  712  to permit subsequent removal over the leads as will be described in more detail hereinafter. 
         [0106]      FIG. 25  illustrates a distal portion of a curved stylet  720  formed of a flexible metal such as NiTi, for example. The stylet  720  includes an elongate shaft  722  that is sized and adapted to be inserted and advanced through the lumens  714 / 716  of the delivery catheter  710 . The distal end of the stylet  720  includes a sharpened tip  724  to facilitate tissue penetration. A distal portion of the stylet  720  includes a primary curve  726  having a resting nominal diameter roughly equal to the distance between the center points of the ports  715 / 717  of the delivery catheter  710 . The distal portion of the stylet  720  may also include a secondary curve  728  to facilitate orientation of the primary curve  726  relative to the catheter  710  as the stylet is advanced out of the ports  715 / 717 . 
         [0107]    Refer now to  FIGS. 25A-25C  which illustrate a method of using the delivery catheter  710  and two stylets  720  to make an electrical connection to the braided stent like structure  650 . To facilitate connection to the two different sets of conductive members  652  as described previously, two separate and relatively short tail leads  656  are provided corresponding to each set of conductive members  652 . The short tail leads  656  may be uninsulated to ensure good electrical connection. Optionally, a biasing member  711  such as a deflection wire or eccentric balloon may be incorporated into the delivery catheter  710  to urge the ports  715 / 717  into contact with the inside surface of the vein  19 . 
         [0108]    The delivery catheter  710  is navigated to the jugular vein  21  until the distal portion thereof is adjacent the activation device  650  previously deployed in the artery  14 / 19  as seen in  FIG. 25A . Stylets  720  are then advanced through one lumen in each pair of lumens  714 / 716  until the distal ends of the stylets  720  exit the ports  715 / 717 . The distal ends  724  exit the ports  715 / 717 , penetrate through the wall of the vein  21 , penetrate through the wall of the artery  14 / 19 , and wrap around the tail leads  656  due to the curved portion  726 . Further advancement of the stylets  720  cause the tips  724  to reenter the ports  715 / 717  as shown with the proximal stylet  720  shown in  FIG. 25A . The stylets  720  may be fully advanced along a return path through another of the pair of lumens  714 / 716  until the proximal and distal ends of the stylets  720  extend out the proximal end of the delivery catheter  710 , after which the catheter  710  may be removed from the stylets  720  along the plane of separability  718  as seen in  FIG. 25B . 
         [0109]    Flexible leads  730  are then attached to the stylets  720  by connection one end of each lead  730  to one end of each stylet  720 , respectively. The other ends of the stylets  720  may then be pulled proximally to thread the leads through the lumen of the vein  21  and around the lead tails  656  as shown in  FIG. 25C . The lead wires  730  may comprise a conductive metal such as MP35N twisted cable or braid. After the leads  730  are in place, friction clamps  732  may be advanced thereover with a push catheter (not shown) to snug the leads  730  around the lead tails  656 . Insulating tubular jackets (not shown) may then be placed over the lead wires  730 , and the leads  730  may then be attached to the control system  60  and operated as described elsewhere herein. 
         [0110]    Those skilled in the art will recognize that the present invention may be manifested in a variety of forms other than the specific embodiments described and contemplated herein. Accordingly, departures in form and detail may be made without departing from the scope and spirit of the present invention as described in the appended claims.