US20070167984A1 - Method and apparatus for stimulation of baroreceptors - Google Patents

Abstract

Devices and methods for controlling the baroreflex system for the treatment and/or management of cardiovascular, renal, and neurological disorders.

Description

CROSS-REFERENCES TO RELATED APPLICATIONS
• This application is a continuation of U.S. patent application Ser. No. 10/284,063, (Attorney Docket No. 021433-000150US), filed on Oct. 29, 2002, which is a continuation-in-part of U.S. patent application Ser. No. 09/671,850 (Attorney Docket No. 021433-000100US), filed on Sep. 27, 2000, which is now issued as U.S. Pat. No. 6,522,926, the full disclosures of which are incorporated herein by reference. The parent application for this application has incorporated by reference the disclosures of the following U.S. Patent Applications: U.S. patent application Ser. No. 09/964,079 (Attorney Docket No. 021433-000110US), filed on Sep. 26, 2001, now issued as U.S. Pat. No. 6,985,774, U.S. patent application Ser. No. 09/963,777 (Attorney Docket No. 021433-000120US), filed Sept. 26, 2001, and U.S. patent application Ser. No. 09/963,991, filed on Sept. 26, 2001, now issued as U.S. Pat. No. 6,850,801, (Attorney Docket No. 021433-000130US), the disclosures of which are also effectively incorporated by reference herein.
BACKGROUND OF THE INVENTION
• 1. Field of the Invention
• 1. Field of the Invention. The present invention generally relates to medical devices and methods of use for the treatment and/or management of cardiovascular, renal, and neurological disorders. Specifically, the present invention relates to devices and methods for controlling the baroreflex system for the treatment and/or management of cardiovascular, renal, and neurological disorders.
• 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. Hypertension occurs when the body'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.
• 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'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. Heart failure results in the activation of a number of body systems to compensate for the heart'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.
• 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's neurohormonal responses, and other medicaments. 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. No one drug, surgical procedure, or assist system, however, has provided a complete solution to the problems of hypertension and heart failure.
• For these reasons, it would be desirable to provide alternative and improved methods for treating hypertension, heart failure, and other cardiovascular, neurological, and renal disorders. Such methods and systems should allow for treatment of patients where other therapies have failed or are unavailable, such as heart transplantation. It would be further desirable if the methods could lessen or eliminate the need for chronic drug use in at least some patients. Additionally, it would be desirable if the methods and systems were mechanically simple and inherently reliable, in contrast to complex mechanical systems such as VAD's, IABP's, and the like.
• One particularly promising approach for improving the treatment of hypertension, heart failure, and other cardiovascular and renal disorders is described in published PCT Application No. WO 02/026314, which claims the benefit of U.S. patent application Ser. No. 09/671,850, which is the parent of the present application. The full disclosures of both WO 02/026314 and U.S. Ser. No. 09/671,850, are incorporated herein by reference. WO 02/026314 describes the direct activation of baroreceptors for inducing changes in a patient's baroreflex system to control blood pressure and other patient functions. The prior applications are particularly directed at the activation of the baroreceptors present in the carotid sinus and the aortic arch. Both the carotid sinus and aortic arch are on the high-pressure or arterial side of the patient's vasculature. They are referred to as high-pressure since pressures in the systemic arterial circulation are higher than those in the veins and pulmonary circulation. Activation of the high-pressure baroreceptors can send signals to the brain that cause reflex alterations in nervous system function which result in changes in activity of target organs, including the heart, vasculature, kidneys, and the like, typically to maintain homeostasis.
• While highly promising, the need to implant electrodes or other effectors on the arterial or high-pressure side of the vasculature may be disadvantageous in some respects. Arteries and other vessels on the high-pressure side of the vasculature are at risk of damage, and implantation of an electrode on or in the carotid sinus or aortic arch requires more care, and improper device implantation on the arterial side presents a small risk of arterial thromboembolism which in turn can cause stroke and other organ damage. Some arterial locations can also cause unwanted tissue or nerve stimulation due to current leakage.
• Thus, it would be desirable to provide improved methods and systems for artificial and selective activation of a patient's baroreflex system in order to achieve a variety of therapeutic objectives, including the control of hypertension, renal function, heart failure, and the treatment of other cardiovascular and neurological disorders. It would be particularly desirable if such methods and systems did not require intervention on the arterial or high-pressure side of a patient's vasculature, thus lessening the risk to the patient of arterial damage and damage resulting from thromboembolism or hemorrhage. At least some of these objectives will be met by the inventions described hereinafter.
• 2. Description of the Background Art
• U.S. Pat. Nos. 6,073,048 and 6,178,349, each having a common invention with the present application, describe the stimulation of nerves to regulate the heart, vasculature, and other body systems. Nerve stimulation for other purposes is described in, for example, U.S. Pat. Nos. 6,292,695 B1 and 5,700,282. Publications describing baropacing of the carotid arteries for controlling hypertension include Neufeld et al. (1965)Israel J. Med. Sci1:630-632; Bilgutay et al., Proc. Baroreceptors and Hypertension, Dayton, Ohio, Nov. 16-17, 1965, pp 425-437; Bilgutary and Lillehei (1966)Am. J. Cariol.17:663-667; and Itoh (1972)Jap. Heart J.13: 136-149. Publications which describe the existence of baroreceptors and/or related receptors in the venous vasculature and atria include Goldberger et al. (1999)J. Neuro. Meth.91:109-114; Kostreva and Pontus (1993)Am. J. Physiol.265:G15-G20; Coleridge et al. (1973)Circ. Res.23:87-97; Mifflin and Kunze (1982)Circ. Res.51:241-249; and Schaurte et al. (2000)J. Cardiovasc Electrophysiol.11:64-69.
BRIEF SUMMARY OF THE INVENTION
• To address hypertension, heart failure, cardia arrhythmias, and associated cardiovascular, renal, 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.
• In an exemplary embodiment, the present invention provides a system and method 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 venous or low-pressure side of a patient's vasculature. As used hereinafter, the phrase “low-pressure side of the vasculature” will mean the venous and cardiopulmonary vasculature, including particularly the chambers in the heart, veins near the entrances to the atria, the pulmonary artery, the portal vein of the liver, the superior vena cava (SVC), the inferior vena cava (IVC), the jugular vein, the subclavian veins, the iliac veins, the femoral veins, and other peripheral areas of the vasculature where baroreceptor and baroreceptor-like receptors are found. Particular target mechanoreceptors are described in Kostreva and Pontus (1993), cited above, the full disclosure of which is incorporated herein by reference.
• The baroreceptors and baroreceptor-like receptors on the low-pressure side of the vasculature will function similarly to, but not necessarily identically to, baroreceptors on the high-pressure side of the vasculature. In general, cardiovascular receptors may be sensitive to pressure and/or mechanical deformation and are referred to as baroreceptors, mechanoreceptors, pressoreceptors, stretch receptors, and the like. For cardiovascular and renal therapies, the present invention is intended to activate or otherwise interact with any or all of these types of receptors so long as such activation or interaction results in modulation of the reflex control of the patient's circulation. While there may be small structural or anatomical differences among various receptors in the vasculature, for the purposes of the present invention, activation may be directed at any of these receptors so long as they provide the desired effects. In particular, such receptors will provide afferent signals, i.e., signals to the brain, which provide the blood pressure and/or volume information to the brain which allow the brain to cause “reflex” changes in the autonomic nervous system which in turn modulate organ activity to maintain desired hemodynamics and organ perfusion. Such activation of afferent pathways may also affect brain functions in such a way that could aid in the treatment of neurologic disease.
• The ability to control the baroreflex response and cardiovascular, renal, and neurological function, by intervention on the low-pressure side of the vasculature is advantageous in several respects. Intervention on the venous and cardiopulmonary side of the vasculature reduces the risk of organ damage, including stroke, from systemic arterial thromboembolism. Moreover, the devices and structures used for intervening on the venous and cardiopulmonary side of the vasculature may be less complicated since the risk they pose to venous circulation is much less than to arterial circulation. Additionally, the availability of venous and cardiopulmonary baroreceptors allows placement of electrodes and other devices which reduce the risk of unwanted tissue stimulation resulting from current leakage to closely adjacent nerves, muscles, and other tissues.
• Generally speaking, the baroreceptor activation device 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 mechanical, electrical, thermal, chemical, biological, or other means 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 inside the vascular lumen (i.e., intravascularly), outside the vascular wall (i.e., extravascularly) or within the vascular wall (i.e., intramurally). The particular activation patterns may be selected to mimic those which naturally occur in the venous and cardiopulmonary vasculature, which conditions might vary from those characteristic of the arterial vasculature. In other cases, the activation patterns may be different from the natural patterns and selected to achieve an optimized barosystem response.
• A control system may be used to generate a control signal which activates, deactivates or otherwise modulates the baroreceptor activation device. The control system may operate in an open-loop or a closed-loop mode. For example, in the open-loop mode, the patient and/or physician may directly or remotely interface with the control system to prescribe the control signal. In the closed-loop mode, the control signal may be responsive to feedback from a sensor, wherein the response is dictated by a preset or programmable algorithm.
• To address low blood pressure and other conditions requiring blood pressure augmentation, the present invention provides a number of devices, systems and methods by which the blood pressure may be selectively and controllably regulated by inhibiting or dampening baroreceptor signals. By selectively and controllably inhibiting or dampening baroreceptor signals, the present invention reduces conditions associated with low blood pressure.
• To address hypertension, heart failure, cardiac arrhythmias, 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, baroreceptor-like mechanoreceptors or pressoreceptors, or the like. 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.
• In an exemplary embodiment, the present invention provides a system and method 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 a vein, the pulmonary vasculature, in a heart chamber, at a veno-atrial junction, or the like.
• Generally speaking, the baroreceptor activation device 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 mechanical, electrical, thermal, chemical, biological, or other means 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 inside the vascular lumen (i.e., intravascularly), outside the vascular wall (i.e., extravascularly) or within the vascular wall (i.e., intramurally).
• A control system may be used to generate a control signal which activates, deactivates or otherwise modulates the baroreceptor activation device. The control system may operate in an open-loop or a closed-loop mode. For example, in the open-loop mode, the patient and/or physician may directly or remotely interface with the control system to prescribe the control signal. In the closed-loop mode, the control signal may be responsive to feedback from a sensor, wherein the response is dictated by a preset or programmable algorithm.
• To address low blood pressure and other conditions requiring blood pressure augmentation, the present invention provides a number of devices, systems and methods by which the blood pressure may be selectively and controllably regulated by inhibiting or dampening baroreceptor signals. By selectively and controllably inhibiting or dampening baroreceptor signals, the present invention reduces conditions associated with low blood pressure.
BRIEF DESCRIPTION OF THE DRAWINGS
• FIG. 1 is a schematic illustration of the upper torso of a human body showing the major arteries and veins and associated anatomy.
• FIG. 1A is a schematic illustration of the lower abdominal vasculature including the abdominal aorta and the inferior vena cava.
• FIG. 2 is a cross-sectional schematic illustration of baroreceptors within a vascular wall.
• FIG. 3 is a schematic illustration of a baroreceptor activation system in accordance with the present invention.
• FIG. 4 is a schematic illustration of a baroreceptor activation device in the form of an internal inflatable balloon which mechanically induces a baroreceptor signal in accordance with an embodiment of the present invention.
• FIG. 5 is a schematic illustration of a baroreceptor activation device in the form of an external pressure cuff which mechanically induces a baroreceptor signal in accordance with an embodiment of the present invention.
• FIG. 6A is a schematic illustration of a baroreceptor activation device in the form of an internal deformable coil structure which mechanically induces a baroreceptor signal in accordance with an embodiment of the present invention.
• FIGS. 6B and 6C are cross-sectional views of alternative embodiments of the coil member illustrated inFIG. 6.
• FIG. 7 is a schematic illustration of a baroreceptor activation device in the form of an external deformable coil structure which mechanically induces a baroreceptor signal in accordance with an embodiment of the present invention.
• FIG. 8 is a schematic illustration of a baroreceptor activation device in the form of an external flow regulator which artificially creates back pressure to induce a baroreceptor signal in accordance with an embodiment of the present invention.
• FIG. 9 is a schematic illustration of a baroreceptor activation device in the form of an internal flow regulator which artificially creates back pressure to induce a baroreceptor signal in accordance with an embodiment of the present invention.
• FIG. 10 is a schematic illustration of a baroreceptor activation device in the form of a magnetic device which mechanically induces a baroreceptor signal in accordance with an embodiment of the present invention.
• FIG. 11 is a schematic illustration of a baroreceptor activation device in the form of a transducer which mechanically induces a baroreceptor signal in accordance with an embodiment of the present invention.
• FIG. 12 is a schematic illustration of a baroreceptor activation device in the form of a fluid delivery device which may be used to deliver an agent which chemically or biologically induces a baroreceptor signal in accordance with an embodiment of the present invention.
• FIG. 13 is a schematic illustration of a baroreceptor activation device in the form of an internal conductive structure which electrically or thermally induces a baroreceptor signal in accordance with an embodiment of the present invention.
• FIG. 14 is a schematic illustration of a baroreceptor activation device in the form of an internal conductive structure, activated by an internal inductor, which electrically or thermally induces a baroreceptor signal in accordance with an embodiment of the present invention.
• FIG. 15 is a schematic illustration 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.
• FIG. 16 is a schematic illustration of a baroreceptor activation device in the form of an internal conductive structure, activated by an external inductor, which electrically or thermally induces a baroreceptor signal in accordance with an embodiment of the present invention.
• FIG. 17 is a schematic illustration of a baroreceptor activation device in the form of an external conductive structure which electrically or thermally induces a baroreceptor signal in accordance with an embodiment of the present invention.
• FIG. 18 is a schematic illustration of a baroreceptor activation device in the form of an internal bipolar conductive structure which electrically or thermally induces a baroreceptor signal in accordance with an embodiment of the present invention.
• FIG. 19 is a schematic illustration of a baroreceptor activation device in the form of an electromagnetic field responsive device which electrically or thermally induces a baroreceptor signal in accordance with an embodiment of the present invention.
• FIG. 20 is a schematic illustration of a baroreceptor activation device in the form of an external Peltier device which thermally induces a baroreceptor signal in accordance with an embodiment of the present invention.
• FIGS. 21A-21C are schematic illustrations of a preferred embodiment of an inductively activated electrically conductive structure.
• FIGS. 22A-22C are ECG charts of a dog undergoing stimulation of the abdominal IVC.
DETAILED DESCRIPTION OF THE INVENTION
• 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.
• To better understand the present invention, it may be useful to explain some of the basic vascular anatomy associated with the cardiovascular system. Refer toFIG. 1 which is a schematic illustration of the upper torso of ahuman body10 showing some of the major arteries and veins of the cardiovascular system. The left ventricle of theheart11 pumps oxygenated blood up into theaortic arch12. The rightsubclavian artery13, the right commoncarotid artery14, the left commoncarotid artery15 and the leftsubclavian artery16 branch off theaortic arch12 proximal of the descendingthoracic aorta17. Although relatively short, a distinct vascular segment referred to as thebrachiocephalic artery22 connects the rightsubclavian artery13 and the right commoncarotid artery14 to theaortic arch12. The rightcarotid artery14 bifurcates into the right externalcarotid artery18 and the right internalcarotid artery19 at the rightcarotid sinus20. Although not shown for purposes of clarity only, the leftcarotid artery15 similarly bifurcates into the left external carotid artery and the left internal carotid artery at the left carotid sinus.
• From theaortic arch12, oxygenated blood flows into thecarotid arteries18/19 and thesubclavian arteries13/16. From thecarotid arteries18/19, oxygenated blood circulates through the head and cerebral vasculature and oxygen depleted blood returns to theheart11 by way of the jugular veins, of which only the right internaljugular vein21 is shown for sake of clarity. From thesubclavian arteries13/16, 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 rightsubclavian vein23 is shown, also for sake of clarity. Deoxygenated blood from the upper torso and head eventually return to theheart11 through the superior vena cava23.1, shown diagrammatically only. Theheart11 pumps the oxygen-depleted blood through the pulmonary system where it is re-oxygenated. The re-oxygenated blood returns to theheart11 which pumps the re-oxygenated blood into the aortic arch as described above, and the cycle repeats. In the abdomen and lower extremities, oxygenated blood is delivered to the organs and lower limbs through the abdominal aorta23.2. Deoxygenated blood returns to the heart through the inferior vena cava23.3.
• Within the walls of many veins, the pulmonary vasculature and the chambers of the heart, as in the walls of the carotid sinus, aorta and other arterial structures, there are baroreceptors. Baroreceptors are a type of stretch receptor used by the body to sense blood pressure and blood volume. An increase in blood pressure or volume causes the vascular wall to stretch, and a decrease in blood pressure or volume causes the vascular wall to return to its original size. In many vessels, such a cycle is repeated with each beat of the heart. In others, in particular some of the body's veins, the pressure and volume change more slowly. Because baroreceptors are located within the vascular wall, they are able to sense deformation of the adjacent tissue, which is indicative of a change in blood pressure or volume.
• Refer now toFIG. 2, which shows a schematic illustration ofbaroreceptors30 disposed in a genericvascular wall40 and a schematic flow chart of thebaroreflex system50.Baroreceptors30 are profusely distributed within thearterial walls40 of the blood vessels major arteries discussed previously, and are presently believed by the inventors to form anarbor32 as is characteristic of the analogous receptors in the arterial system as described in parent application Ser. No. 09/672,850, previously incorporated herein by reference. Abaroreceptor arbor32 would comprise a plurality ofbaroreceptors30, each of which transmits baroreceptor signals to thebrain52 vianerve38. Thebaroreceptors30 may be so profusely distributed and arborized within thevascular wall40 thatdiscrete baroreceptor arbors32 are not readily discemable. To this end, those skilled in the art will appreciate that thebaroreceptors30 shown inFIG. 2 are primarily schematic for purposes of illustration and discussion. In other regions, the baroreceptors may be so sparsely distributed that activation over a relatively greater length of the vein would be required than would be with an artery where the receptors might be more concentrated.
• Baroreceptor signals in the arterial vasculature are used to activate a number of body systems which collectively may be referred to as thebaroreflex system50. For the purposes of the present invention, it will be assumed that the “receptors” in the venous and cardiopulmonary vasculature and heart chambers function analogously to the baroreceptors in the arterial vasculature, but such assumption is not intended to limit the present invention in any way. In particular, the methods described herein will function and achieve at least some of the stated therapeutic objectives regardless of the precise and actual mechanism responsible for the result. Moreover, the present invention may activate baroreceptors, mechanoreceptors, pressoreceptors, or any other venous heart, or cardiopulmonary receptors which affect the blood pressure, nervous system activity, and neurohormonal activity in a manner analogous to baroreceptors in the arterial vasculation. For convenience, all such venous receptors will be referred to collectively herein as “baroreceptors.” Thus for discussion purposes, it will be assumed thatbaroreceptors30 are connected to thebrain52 via thenervous system51. Thus, thebrain52 is able to detect changes in blood pressure which are indicative of cardiac output and/or blood volume. If cardiac output and/or blood volume are insufficient to meet demand (i.e., theheart11 is unable to pump sufficient blood), thebaroreflex system50 activates a number of body systems, including theheart11,kidneys53,vessels54, and other organs/tissues. Such activation of thebaroreflex system50 generally corresponds to an increase in neurohormonal activity. Specifically, thebaroreflex system50 initiates a neurohormonal sequence that signals theheart11 to increase heart rate and increase contraction force in order to increase cardiac output, signals thekidneys53 to increase blood volume by retaining sodium and water, and signals thevessels54 to constrict to elevate blood pressure. The cardiac, renal and vascular responses increase blood pressure andcardiac output55, and thus increase the workload of theheart11. In a patient with heart failure, this further accelerates myocardial damage and exacerbates the heart failure state.
• To address the problems of hypertension, heart failure, cardiac arrhythmias, renal dysfunction, and nervous system other cardiovascular disorders, the present invention basically provides a number of devices, systems and methods by which thebaroreflex system50 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 whichbaroreceptors30 may be activated, thereby indicating an increase in blood pressure and signaling thebrain52 to reduce the body'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.
• With reference toFIG. 3, the present invention generally provides a system including acontrol system60, abaroreceptor activation device70, and a sensor80 (optional). For purposes of illustration, thebaroreceptor activation device70 is shown to be located on, in or near the inferior vena cava23.3, but it could also be located at the other baroreceptor target locations discussed elsewhere in this application. Theexemplary control system60, generally operates in the following manner. Thesensor80 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. Thecontrol system60 generates a control signal as a function of the received sensor signal. The control signal activates, deactivates or otherwise modulates thebaroreceptor activation device70. Typically, activation of thedevice70 results in activation of the baroreceptors30 (FIG. 2). Alternatively, deactivation or modulation of thebaroreceptor activation device70 may cause or modify activation of thebaroreceptors30. Thebaroreceptor activation device70 may comprise a wide variety of devices which utilize mechanical, electrical, thermal, chemical, biological, or other means to activatebaroreceptors30. Thus, when thesensor80 detects a parameter indicative of the need to modify the baroreflex system activity (e.g., excessive blood pressure), thecontrol system60 generates a control signal to modulate (e.g. activate) thebaroreceptor activation device70 thereby inducing abaroreceptor30 signal that is perceived by thebrain52 to be apparent excessive blood pressure. When thesensor80 detects a parameter indicative of normal body function (e.g., normal blood pressure), thecontrol system60 generates a control signal to modulate (e.g., deactivate) thebaroreceptor activation device70.
• As mentioned previously, thebaroreceptor activation device70 may comprise a wide variety of devices which utilize mechanical, electrical, thermal, chemical, biological or other means to activate thebaroreceptors30. Specific embodiments of the genericbaroreceptor activation device70 are discussed with reference toFIGS. 4-21. In most instances, particularly the mechanical activation embodiments, thebaroreceptor activation device70 indirectly activates one ormore baroreceptors30 by stretching or otherwise deforming thevascular wall40 surrounding thebaroreceptors30. In some other instances, particularly the non-mechanical activation embodiments, thebaroreceptor activation device70 may directly activate one ormore baroreceptors30 by changing the electrical, thermal or chemical environment or potential across thebaroreceptors30. It is also possible that changing the electrical, thermal or chemical potential across the tissue surrounding thebaroreceptors30 may cause the surrounding tissue to stretch or otherwise deform, thus mechanically activating thebaroreceptors30. In other instances, particularly the biological activation embodiments, a change in the function or sensitivity of thebaroreceptors30 may be induced by changing the biological activity in thebaroreceptors30 and altering their intracellular makeup and function.
• All of the specific embodiments of thebaroreceptor activation device70 are suitable for implantation, and are preferably implanted using a minimally invasive percutaneous transluminal approach and/or a minimally invasive surgical approach, depending on whether thedevice70 is disposed intravascularly, extravascularly or within thevascular wall40. Thebaroreceptor activation device70 may be positioned anywhere in or proximate the venous or cardiopulmonary vasculature, and/or the heart chambers, where baroreceptors capable of modulating thebaroreflex system50 are present. Thebaroreceptor activation device70 will usually be implanted such that thedevice70 is positioned immediately adjacent thebaroreceptors30. Alternatively, thebaroreceptor activation device70 may be outside the body such that thedevice70 is positioned a short distance from but proximate to thebaroreceptors30. Preferably, thebaroreceptor activation device70 is implanted at a location which permits selective activation of the target baroreceptor, typically being in, around, or near the target baroreceptor. For purposes of illustration only, the present invention is described with reference tobaroreceptor activation device70 positioned near the inferior vena cava23.3.
• Theoptional sensor80 is operably coupled to thecontrol system60 by electric sensor cable or lead82. Thesensor80 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, thesensor80 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 thesensor80 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 onesensor80 is shown,multiple sensors80 of the same or different type at the same or different locations may be utilized.
• Thesensor80 is preferably positioned in a chamber of theheart11, or in/on a major artery such as theaortic arch12, a commoncarotid artery14/15, asubclavian artery13/16 or thebrachiocephalic artery22, or in any of the low-pressure venous or cardiopulmonary sites, such that the parameter of interest may be readily ascertained. Thesensor80 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. Thesensor80 may be separate from thebaroreceptor activation device70 or combined therewith. For purposes of illustration only, thesensor80 is shown positioned on the rightsubclavian artery13.
• By way of example, thecontrol system60 includes acontrol block61 comprising aprocessor63 and amemory62.Control system60 is connected to thesensor80 by way ofsensor cable82.Control system60 is also connected to thebaroreceptor activation device70 by way ofelectric control cable72. Thus, thecontrol system60 receives a sensor signal from thesensor80 by way ofsensor cable82, and transmits a control signal to thebaroreceptor activation device70 by way ofcontrol cable72.
• Thememory62 may contain data related to the sensor signal, the control signal, and/or values and commands provided by theinput device64. Thememory62 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.
• As mentioned previously, thebaroreceptor activation device70 may activatebaroreceptors30 mechanically, electrically, thermally, chemically, biologically or otherwise. In some instances, thecontrol system60 includes adriver66 to provide the desired power mode for thebaroreceptor activation device70. For example if thebaroreceptor activation device70 utilizes pneumatic or hydraulic actuation, thedriver66 may comprise a pressure/vacuum source and thecable72 may comprise fluid line(s). If thebaroreceptor activation device70 utilizes electrical or thermal actuation, thedriver66 may comprise a power amplifier or the like and thecable72 may comprise electrical lead(s). If thebaroreceptor activation device70 utilizes chemical or biological actuation, thedriver66 may comprise a fluid reservoir and a pressure/vacuum source, and thecable72 may comprise fluid line(s). In other instances, thedriver66 may not be necessary, particularly if theprocessor63 generates a sufficiently strong electrical signal for low level electrical or thermal actuation of thebaroreceptor activation device70.
• Thecontrol system60 may operate as a closed loop utilizing feedback from thesensor80, or as an open loop utilizing commands received byinput device64. The open loop operation of thecontrol system60 preferably utilizes some feedback from thetransducer80, but may also operate without feedback. Commands received by theinput device64 may directly influence the control signal or may alter the software and related algorithms contained inmemory62. The patient and/or treating physician may provide commands to inputdevice64.Display65 may be used to view the sensor signal, control signal and/or the software/data contained inmemory62.
• The control signal generated by thecontrol system60 may be continuous, periodic, episodic or a combination thereof, as dictated by an algorithm contained inmemory62. 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 minute, hour or day) and a designated duration (e.g., 1 second, 1 minute, 1 hour). 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 patient/physician, an increase in blood pressure above a certain threshold, etc.).
• Thecontrol system60 may be implanted in whole or in part. For example, theentire control system60 may be carried externally by the patient utilizing transdermal connections to thesensor lead82 and thecontrol lead72. Alternatively, thecontrol block61 anddriver66 may be implanted with theinput device64 anddisplay65 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 thecontrol system60 and/or thesensor80 andbaroreceptor activation device70.
• With general reference toFIGS. 4-21, schematic illustrations of specific embodiments of thebaroreceptor activation device70 are shown. The design, function and use of these specific embodiments, in addition to thecontrol system60 and sensor80 (not shown), are the same as described with reference toFIG. 3, unless otherwise noted or apparent from the description. In addition, the anatomical features illustrated inFIGS. 4-20 are the same as discussed with reference toFIGS. 1, 1A, and2 , unless otherwise noted. In each embodiment, the connections between thecomponents60/70/80 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 intraarterially, intravenously, subcutaneously, or through other natural tissue paths.
• Refer now toFIG. 4 which shows schematic illustrations of abaroreceptor activation device100 in the form of an intravascularinflatable balloon100. Theinflatable balloon device100 includes a helical balloon102 which is connected to afluid line104. An example of a similar helical balloon is disclosed in U.S. Pat. No. 5,181,911 to Shturman, the entire disclosure of which is hereby incorporated by reference. The balloon102 preferably has a helical geometry or any other geometry which allows blood perfusion therethrough. Thefluid line104 is connected to thedriver66 of the control system60 (FIG. 3). In this embodiment, thedriver66 comprises a pressure/vacuum source (i.e., an inflation device) which selectively inflates and deflates the helical balloon102. Upon inflation, the helical balloon102 expands, preferably increasing in outside diameter only, to mechanically activatebaroreceptors30 by stretching or otherwise deforming them and/or thevascular wall40. Upon deflation, the helical balloon102 returns to its relaxed geometry such that thevascular wall40 returns to its nominal state. Thus, by selectively inflating the helical balloon102, thebaroreceptors30 adjacent thereto may be selectively activated.
• As an alternative to pneumatic or hydraulic expansion utilizing a balloon, a mechanical expansion device (not shown) may be used to expand or dilate thevascular wall40 and thereby mechanically activate thebaroreceptors30. For example, the mechanical expansion device may comprise a tubular wire braid structure that diametrically expands when longitudinally compressed as disclosed in U.S. Pat. No. 5,222,971 to Willard et al., the entire disclosure of which is hereby incorporated by reference. The tubular braid may be disposed intravascularly and permits blood perfusion through the wire mesh. In this embodiment, thedriver66 may comprise a linear actuator connected by actuation cables to opposite ends of the braid. When the opposite ends of the tubular braid are brought closer together by actuation of the cables, the diameter of the braid increases to expand thevascular wall40 and activate thebaroreceptors30.
• Refer now toFIG. 5 which shows abaroreceptor activation device120 in the form of anextravascular pressure cuff120. Thepressure cuff device120 includes aninflatable cuff122 which is connected to afluid line124. Examples of asimilar cuffs122 are disclosed in U.S. Pat. No. 4,256,094 to Kapp et al. and U.S. Pat. No. 4,881,939 to Newman, the entire disclosures of which are hereby incorporated by reference. Thefluid line124 is connected to the driver66 (FIG. 3) of thecontrol system60. In this embodiment, thedriver66 comprises a pressure/vacuum source (i.e., an inflation device) which selectively inflates and deflates thecuff122. Upon inflation, thecuff122 expands, preferably increasing in inside diameter only, to mechanically activatebaroreceptors30 by stretching or otherwise deforming them and/or thevascular wall40. Upon deflation, thecuff122 returns to its relaxed geometry such that thevascular wall40 returns to its nominal state. Thus, by selectively inflating theinflatable cuff122, thebaroreceptors30 adjacent thereto may be selectively activated.
• Thedriver66 may be automatically actuated by thecontrol system60 as discussed above, or may be manually actuated. An example of an externally manually actuated pressure/vacuum source is disclosed in U.S. Pat. No. 4,709,690 to Haber, the entire disclosure of which is hereby incorporated by reference. Examples of transdermally manually actuated pressure/vacuum sources are disclosed in U.S. Pat. No. 4,586,501 to Claracq, U.S. Pat. No. 4,828,544 to Lane et al., and U.S. Pat. No. 5,634,878 to Grundei et al., the entire disclosures of which are hereby incorporated by reference.
• Those skilled in the art will recognize that other external compression devices may be used in place of theinflatable cuff device120. For example, a piston actuated by a solenoid may apply compression to the vascular wall. An example of a solenoid actuated piston device is disclosed in U.S. Pat. No. 4,014,318 to Dokum et al, and an example of a hydraulically or pneumatically actuated piston device is disclosed in U.S. Pat. No. 4,586,501 to Claracq, the entire disclosures of which are hereby incorporated by reference. Other examples include a rotary ring compression device as disclosed in U.S. Pat. No. 4,551,862 to Haber, and an electromagnetically actuated compression ring device as disclosed in U.S. Pat. No. 5,509,888 to Miller, the entire disclosures of which are hereby incorporated by reference.
• Refer now toFIG. 6 which shows abaroreceptor activation device140 in the form of an intravascular deformable structure. Thedeformable structure device140 includes a coil, braid or other stent-like structure142 disposed in the vascular lumen. Thedeformable structure142 includes one or more individual structural members connected to anelectrical lead144. Each of the structural members formingdeformable structure142 may comprise a shape memory material146 (e.g., nickel titanium alloy) as illustrated inFIG. 6B, or abimetallic material148 as illustrated inFIG. 6C. Theelectrical lead144 is connected to thedriver66 of thecontrol system60. In this embodiment, thedriver66 comprises an electric power generator or amplifier which selectively delivers electric current to thestructure142 which resistively heats thestructural members146/148. Thestructure142 may be unipolar as shown using the surrounding tissue as ground, or bipolar or multipolar using leads connected to either end of thestructure142. Electrical power may also be delivered to thestructure142 inductively as described hereinafter with reference toFIGS. 14-16.
• Upon application of electrical current to theshape memory material146, it is resistively heated causing a phase change and a corresponding change in shape. Upon application of electrical current to thebimetallic material148, it is resistively heated causing a differential in thermal expansion and a corresponding change in shape. In either case, thematerial146/148 is designed such that the change in shape causes expansion of thestructure142 to mechanically activatebaroreceptors30 by stretching or otherwise deforming them and/or thevascular wall40. Upon removal of the electrical current, thematerial146/148 cools and thestructure142 returns to its relaxed geometry such that thebaroreceptors30 and/or thevascular wall40 return to their nominal state. Thus, by selectively expanding thestructure142, thebaroreceptors30 adjacent thereto may be selectively activated.
• Refer now toFIG. 7 which shows abaroreceptor activation device160 in the form of an extravascular deformable structure. The extravasculardeformable structure device160 is substantially the same as the intravasculardeformable structure device140 described with reference toFIGS. 6A and 6B, except that theextravascular device160 is disposed about the vascular wall, and therefore compresses, rather than expands, thevascular wall40. Thedeformable structure device160 includes a coil, braid or other stent-like structure162 comprising one or more individual structural members connected to anelectrical lead164. Each of the structural members may comprise a shape memory material166 (e.g., nickel titanium alloy) as illustrated inFIG. 7C, or a bimetallic material168. Thestructure162 may be unipolar as shown using the surrounding tissue as ground, or bipolar or multipolar using leads connected to either end of thestructure162. Electrical power may also be delivered to thestructure162 inductively as described hereinafter with reference toFIGS. 14-16.
• Upon application of electrical current to the shape memory material166, it is resistively heated causing a phase change and a corresponding change in shape. Upon application of electrical current to the bimetallic material168, it is resistively heated causing a differential in thermal expansion and a corresponding change in shape. In either case, the material166/168 is designed such that the change in shape causes constriction of thestructure162 to mechanically activatebaroreceptors30 by compressing or otherwise deforming thebaroreceptors30 and/or thevascular wall40. Upon removal of the electrical current, the material166/168 cools and thestructure162 returns to its relaxed geometry such that thebaroreceptors30 and/or thevascular wall40 return to their nominal state. Thus, by selectively compressing thestructure162, thebaroreceptors30 adjacent thereto may be selectively activated.
• Refer now toFIG. 8 which shows abaroreceptor activation device180 in the form of an extravascular flow regulator which artificially creates back pressure adjacent thebaroreceptors30. Theflow regulator device180 includes anexternal compression device182, which may comprise any of the external compression devices described with reference toFIG. 5. Theexternal compression device182 is operably connected to thedriver66 of thecontrol system60 by way ofcable184, which may comprise a fluid line or electrical lead, depending on the type ofexternal compression device182 utilized. Theexternal compression device182 is disposed about the vascular wall distal of thebaroreceptors30. For example, theexternal compression device182 may be located in the distal portions of the inferior vena cava23.3 to create back pressure adjacent thebaroreceptors30 upstream in the inferior vena cava.
• Upon actuation of theexternal compression device182, the vascular wall is constricted thereby reducing the size of the vascular lumen therein. By reducing the size of the vascular lumen, pressure proximal of theexternal compression device182 is increased thereby expanding the vascular wall. Thus, by selectively activating theexternal compression device182 to constrict the vascular lumen and create back pressure, thebaroreceptors30 may be selectively activated.
• Refer now toFIG. 9 which shows abaroreceptor activation device200 in the form of an intravascular flow regular which artificially creates back pressure adjacent thebaroreceptors30. The intravascularflow regulator device200 is substantially similar in function and use asextravascular flow regulator180 described with reference toFIG. 8, except that the intravascularflow regulator device200 is disposed in the vascular lumen.
• Intravascular flow regulator200 includes aninternal valve202 to at least partially close the vascular lumen distal of thebaroreceptors30. By at least partially closing the vascular lumen distal of thebaroreceptors30, back pressure is created proximal of theinternal valve202 such that the vascular wall expands to activate thebaroreceptors30. Theinternal valve202 may be positioned at any of the locations described with reference to theexternal compression device182, except that theinternal valve202 is placed within the vascular lumen. Specifically, theinternal compression device202 may be located in the distal portions of the vasculature to create back pressure adjacent to thebaroreceptors30 in the veins or cardiopulmonary system.
• Theinternal valve202 is operably coupled to thedriver66 of thecontrol system60 by way ofelectrical lead204. Thecontrol system60 may selectively open, close or change the flow resistance of thevalve202 as described in more detail hereinafter. Theinternal valve202 may include valve leaflets206 (bi-leaflet or tri-leaflet) which rotate inside housing208 about an axis between an open position and a closed position. The closed position may be completely closed or partially closed, depending on the desired amount of back pressure to be created. The opening and closing of theinternal valve202 may be selectively controlled by altering the resistance of leaflet206 rotation or by altering the opening force of the leaflets206. The resistance of rotation of the leaflets206 may be altered utilizing electromagnetically actuated metallic bearings carried by the housing208. The opening force of the leaflets206 may be altered by utilizing electromagnetic coils in each of the leaflets to selectively magnetize the leaflets such that they either repel or attract each other, thereby facilitating valve opening and closing, respectively.
• A wide variety of intravascular flow regulators may be used in place ofinternal valve202. For example, internal inflatable balloon devices as disclosed in U.S. Pat. No. 4,682,583 to Burton et al. and U.S. Pat. No. 5,634,878 to Grundei et al., the entire disclosures of which is hereby incorporated by reference, may be adapted for use in place ofvalve202. Such inflatable balloon devices may be operated in a similar manner as theinflatable cuff122 described with reference toFIG. 5. Specifically, in this embodiment, thedriver66 would comprises a pressure/vacuum source (i.e., an inflation device) which selectively inflates and deflates the internal balloon. Upon inflation, the balloon expands to partially occlude blood flow and create back pressure to mechanically activatebaroreceptors30 by stretching or otherwise deforming them and/or thevascular wall40. Upon deflation, the internal balloon returns to its normal profile such that flow is not hindered and back pressure is eliminated. Thus, by selectively inflating the internal balloon, thebaroreceptors30 proximal thereof may be selectively activated by creating back pressure.
• Refer now toFIG. 10 which shows abaroreceptor activation device220 in the form ofmagnetic particles222 disposed in thevascular wall40. Themagnetic particles222 may comprise magnetically responsive materials (i.e., ferrous based materials) and may be magnetically neutral or magnetically active. Preferably, themagnetic particles222 comprise permanent magnets having an elongate cylinder shape with north and south poles to strongly respond to magnetic fields. Themagnetic particles222 are actuated by anelectromagnetic coil224 which is operably coupled to thedriver66 of thecontrol system60 by way of anelectrical cable226. Theelectromagnetic coil224 may be implanted as shown, or located outside the body, in which case thedriver66 and the remainder of thecontrol system60 would also be located outside the body. By selectively activating theelectromagnetic coil224 to create a magnetic field, themagnetic particles222 may be repelled, attracted or rotated. Alternatively, the magnetic field created by theelectromagnetic coil224 may be alternated such that themagnetic particles222 vibrate within thevascular wall40. When the magnetic particles are repelled, attracted, rotated, vibrated or otherwise moved by the magnetic field created by theelectromagnetic coil224, thebaroreceptors30 are mechanically activated.
• Theelectromagnetic coil224 is preferably placed as close as possible to themagnetic particles222 in thevascular wall40, and may be placed intravascularly, extravascularly, or in any of the alternative locations discussed with reference to inductor shown inFIGS. 14-16. Themagnetic particles222 may be implanted in thevascular wall40 by injecting a ferro-fluid or a ferro-particle suspension into the vascular wall adjacent to thebaroreceptors30. To increase biocompatibility, theparticles222 may be coated with a ceramic, polymeric or other inert material. Injection of the fluid carrying themagnetic particles222 is preferably performed percutaneously.
• Refer now toFIG. 11 which shows abaroreceptor activation device240 in the form of one ormore transducers242. Preferably, thetransducers242 comprise an array surrounding the vascular wall. Thetransducers242 may be intravascularly or extravascularly positioned adjacent to thebaroreceptors30. In this embodiment, thetransducers242 comprise devices which convert electrical signals into some physical phenomena, such as mechanical vibration or acoustic waves. The electrical signals are provided to thetransducers242 by way ofelectrical cables244 which are connected to thedriver66 of thecontrol system60. By selectively activating thetransducers242 to create a physical phenomena, thebaroreceptors30 may be mechanically activated.
• Thetransducers242 may comprise an acoustic transmitter which transmits sonic or ultrasonic sound waves into thevascular wall40 to activate thebaroreceptors30. Alternatively, thetransducers242 may comprise a piezoelectric material which vibrates the vascular wall to activate thebaroreceptors30. As a further alternative, thetransducers242 may comprise an artificial muscle which deflects upon application of an electrical signal. An example of an artificial muscle transducer comprises plastic impregnated with a lithium-perchlorate electrolyte disposed between sheets of polypyrrole, a conductive polymer. Such plastic muscles may be electrically activated to cause deflection in different directions depending on the polarity of the applied current.
• Refer now toFIG. 12 which shows abaroreceptor activation device260 in the form of a local fluid delivery device262 suitable for delivering a chemical or biological fluid agent to the vascular wall adjacent thebaroreceptors30. The local fluid delivery device262 may be located intravascularly, extravascularly, or intramurally. For purposes of illustration only, the local fluid delivery device262 is positioned extravascularly.
• The local fluid delivery device262 may include proximal anddistal seals266 which retain the fluid agent disposed in the lumen orcavity268 adjacent to vascular wall. Preferably, the local fluid delivery device262 completely surrounds thevascular wall40 to maintain an effective seal. Those skilled in the art will recognize that the local fluid delivery device262 may comprise a wide variety of implantable drug delivery devices or pumps known in the art.
• The localfluid delivery device260 is connected to afluid line264 which is connected to thedriver66 of thecontrol system60. In this embodiment, thedriver66 comprises a pressure/vacuum source and fluid reservoir containing the desired chemical or biological fluid agent. The chemical or biological fluid agent may comprise a wide variety of stimulatory substances. Examples include veratridine, bradykinin, prostaglandins, and related substances. Such stimulatory substances activate thebaroreceptors30 directly or enhance their sensitivity to other stimuli and therefore may be used in combination with the other baroreceptor activation devices described herein. Other examples include growth factors and other agents that modify the function of thebaroreceptors30 or the cells of the vascular tissue surrounding thebaroreceptors30 causing thebaroreceptors30 to be activated or causing alteration of their responsiveness or activation pattern to other stimuli. It is also contemplated that injectable stimulators that are induced remotely, as described in U.S. Pat. No. 6,061,596 which is incorporated herein by reference, may be used with the present invention.
• As an alternative, thefluid delivery device260 may be used to deliver a photochemical that is essentially inert until activated by light to have a stimulatory effect as described above. In this embodiment, thefluid delivery device260 would include a light source such as a light emitting diode (LED), and thedriver66 of thecontrol system60 would include a pulse generator for the LED combined with a pressure/vacuum source and fluid reservoir described previously. The photochemical would be delivered with thefluid delivery device260 as described above, and the photochemical would be activated, deactivated or modulated by activating, deactivating or modulating the LED.
• As a further alternative, thefluid delivery device260 may be used to deliver a warm or hot fluid (e.g. saline) to thermally activate thebaroreceptors30. In this embodiment, thedriver66 of thecontrol system60 would include a heat generator for heating the fluid, combined with a pressure/vacuum source and fluid reservoir described previously. The hot or warm fluid would be delivered and preferably circulated with thefluid delivery device260 as described above, and the temperature of the fluid would be controlled by thedriver66.
• Refer now toFIG. 13 which shows abaroreceptor activation device280 in the form of an intravascular electrically conductive structure orelectrode282. Theelectrode structure282 may comprise a self-expanding or balloon expandable coil, braid or other stent-like structure disposed in the vascular lumen. Theelectrode structure282 may serve the dual purpose of maintaining lumen patency while also delivering electrical stimuli. To this end, theelectrode structure282 may be implanted utilizing conventional intravascular stent and filter delivery techniques. Preferably, theelectrode structure282 comprises a geometry which allows blood perfusion therethrough. Theelectrode structure282 comprises electrically conductive material which may be selectively insulated to establish contact with the inside surface of thevascular wall40 at desired locations, and limit extraneous electrical contact with blood flowing through the vessel and other tissues.
• Theelectrode structure282 is connected toelectric lead284 which is connected to thedriver66 of thecontrol system60. Thedriver66, in this embodiment, may comprise a power amplifier, pulse generator or the like to selectively deliver electrical control signals to structure282. As mentioned previously, the electrical control signal generated by thedriver66 may be continuous, periodic, episodic or a combination thereof, as dictated by an algorithm contained inmemory62 of thecontrol system60. Continuous control signals include a constant pulse, a constant train of pulses, a triggered pulse and a triggered train of pulses. Periodic control signals include each of the continuous control signals described above which have a designated start time and a designated duration. Episodic control signals include each of the continuous control signals described above which are triggered by an episode.
• By selectively activating, deactivating or otherwise modulating the electrical control signal transmitted to theelectrode structure282, electrical energy may be delivered to the vascular wall to activate thebaroreceptors30. As discussed previously, activation of thebaroreceptors30 may occur directly or indirectly. In particular, the electrical signal delivered to thevascular wall40 by theelectrode structure282 may cause the vascular wall to stretch or otherwise deform thereby indirectly activating thebaroreceptors30 disposed therein. Alternatively, the electrical signals delivered to the vascular wall by theelectrode structure282 may directly activate thebaroreceptors30 by changing the electrical potential across thebaroreceptors30. In either case, the electrical signal is delivered to thevascular wall40 immediately adjacent to thebaroreceptors30. It is also contemplated that theelectrode structure282 may delivery thermal energy by utilizing a semi-conductive material having a higher resistance such that theelectrode structure282 resistively generates heat upon application of electrical energy.
• Various alternative embodiments are contemplated for theelectrode structure282, including its design, implanted location, and method of electrical activation. For example, theelectrode structure282 may be unipolar as shown inFIG. 13 using the surrounding tissue as ground, or bipolar using leads connected to either end of thestructure282 as shown in Figure. In the embodiment ofFIGS. 18A and 18B, theelectrode structure282 includes two or more individual electrically conductive members283/285 which are electrically isolated at their respective cross-over points utilizing insulative materials. Each of the members283/285 is connected to a separate conductor contained within theelectrical lead284. Alternatively, an array of bipoles may be used as described in more detail with reference toFIG. 21. As a further alternative, a multipolar arrangement may be used wherein three or more electrically conductive members are included in thestructure282. For example, a tripolar arrangement may be provided by one electrically conductive member having a polarity disposed between two electrically conductive members having the opposite polarity.
• In terms of electrical activation, the electrical signals may be directly delivered to theelectrode structure282 as described with reference toFIG. 13, or indirectly delivered utilizing aninductor286 as illustrated inFIGS. 14-16 and21. The embodiments ofFIGS. 14-16 and21 utilize aninductor286 which is operably connected to thedriver66 of thecontrol system60 by way ofelectrical lead284. Theinductor286 comprises an electrical winding which creates a magnetic field287 (as seen inFIG. 21) around theelectrode structure282. Themagnetic field287 may be alternated by alternating the direction of current flow through theinductor286. Accordingly, theinductor286 may be utilized to create current flow in theelectrode structure282 to thereby deliver electrical signals to thevascular wall40 to directly or indirectly activate thebaroreceptors30. In all embodiments, theinductor286 may be covered with an electrically insulative material to eliminate direct electrical stimulation of tissues surrounding theinductor286. A preferred embodiment of an inductively activatedelectrode structure282 is described in more detail with reference toFIGS. 21A-21C.
• The embodiments ofFIGS. 13-16 may be modified to form a cathode/anode arrangement. Specifically, theelectrical inductor286 would be connected to thedriver66 as shown inFIGS. 14-16 and theelectrode structure282 would be connected to thedriver66 as shown inFIG. 13. With this arrangement, theelectrode structure282 and theinductor286 may be any suitable geometry and need not be coiled for purposes of induction. Theelectrode structure282 and theinductor286 would comprise a cathode/anode or anode/cathode pair. For example, when activated, thecathode282 may generate a primary stream of electrons which travel through the inter-electrode space (i.e., vascular tissue and baroreceptors30) to theanode286. The cathode is preferably cold, as opposed to thermionic, during electron emission. The electrons may be used to electrically or thermally activate thebaroreceptors30 as discussed previously.
• Theelectrical inductor286 is preferably disposed as close as possible to theelectrode structure282. For example, theelectrical inductor286 may be disposed adjacent the vascular wall as illustrated inFIG. 14. Alternatively, theinductor286 may be disposed in anadjacent vessel289 as illustrated inFIG. 15. If theelectrode structure282 is disposed in thecarotid sinus20, for example, theinductor286 may be disposed in the internaljugular vein21 as illustrated inFIG. 15. In the embodiment ofFIG. 15, theelectrical inductor286 may comprise a similar structure as theelectrode structure282. As a further alternative, theelectrical inductor286 may be disposed outside the patient's body, but as close as possible to theelectrode structure282. If theelectrode structure282 is disposed in thecarotid sinus20, for example, theelectrical inductor286 may be disposed on the right or left side of the neck of the patient as illustrated inFIG. 16. In the embodiment ofFIG. 16, wherein theelectrical inductor286 is disposed outside the patient's body, thecontrol system60 may also be disposed outside the patient's body.
• In terms of implant location, theelectrode structure282 may be intravascularly disposed as described with reference toFIG. 13, or extravascularly disposed as described with reference toFIG. 17, which show schematic illustrations of abaroreceptor activation device300 in the form of an extravascular electrically conductive structure orelectrode302. Except as described herein, theextravascular electrode structure302 is the same in design, function, and use as theintravascular electrode structure282. Theelectrode structure302 may comprise a coil, braid or other structure capable of surrounding the vascular wall. Alternatively, theelectrode structure302 may comprise one or more electrode patches distributed around the outside surface of the vascular wall. Because theelectrode structure302 is disposed on the outside surface of the vascular wall, intravascular delivery techniques may not be practical, but minimally invasive surgical techniques will suffice. Theextravascular electrode structure302 may receive electrical signals directly from thedriver66 of thecontrol system60 by way ofelectrical lead304, or indirectly by utilizing an inductor (not shown) as described with reference toFIGS. 14-16.
• Refer now toFIG. 19 which shows abaroreceptor activation device320 in the form of electricallyconductive particles322 disposed in the vascular wall. This embodiment is substantially the same as the embodiments described with reference toFIGS. 13-18, except that the electricallyconductive particles322 are disposed within the vascular wall, as opposed to the electricallyconductive structures282/302 which are disposed on either side of the vascular wall. In addition, this embodiment is similar to the embodiment described with reference toFIG. 10, except that the electricallyconductive particles322 are not necessarily magnetic as withmagnetic particles222, and the electricallyconductive particles322 are driven by an electromagnetic filed rather than by a magnetic field.
• In this embodiment, thedriver66 of thecontrol system60 comprises an electromagnetic transmitter such as an radiofrequency or microwave transmitter. Electromagnetic radiation is created by thetransmitter66 which is operably coupled to anantenna324 by way ofelectrical lead326. Electromagnetic waves are emitted by theantenna324 and received by the electricallyconductive particles322 disposed in thevascular wall40. Electromagnetic energy creates oscillating current flow within the electricallyconductive particles322, and depending on the intensity of the electromagnetic radiation and the resistivity of theconductive particles322, may cause theelectrical particles322 to generate heat. The electrical or thermal energy generated by the electricallyconductive particles322 may directly activate thebaroreceptors30, or indirectly activate thebaroreceptors30 by way of the surrounding vascular wall tissue.
• Theelectromagnetic radiation transmitter66 andantenna324 may be disposed in the patient's body, with theantenna324 disposed adjacent to the conductive particles in thevascular wall40 as illustrated inFIG. 19. Alternatively, theantenna324 may be disposed in any of the positions described with reference to the electrical inductor shown in FIGS.14-16. It is also contemplated that theelectromagnetic radiation transmitter66 andantenna324 may be utilized in combination with the intravascular and extravascular electricallyconductive structures282/302 described with reference toFIGS. 13-18 to generate thermal energy on either side of the vascular wall.
• As an alternative, theelectromagnetic radiation transmitter66 andantenna324 may be used without the electricallyconductive particles322. Specifically, theelectromagnetic radiation transmitter66 andantenna324 may be used to deliver electromagnetic radiation (e.g., RF, microwave) directly to thebaroreceptors30 or the tissue adjacent thereto to cause localized heating, thereby thermally inducing abaroreceptor30 signal.
• Refer now toFIG. 20 which shows abaroreceptor activation device340 in the form of aPeltier effect device342. ThePeltier effect device342 may be extravascularly positioned as illustrated, or may be intravascularly positioned similar to an intravascular stent or filter. ThePeltier effect device342 is operably connected to thedriver66 of thecontrol system60 by way ofelectrical lead344. ThePeltier effect device342 includes two dissimilar metals or semiconductors343/345 separated by athermal transfer junction347. In this particular embodiment, thedriver66 comprises a power source which delivers electrical energy to the dissimilar metals or semiconductors343/345 to create current flow across thethermal junction347.
• When current is delivered in an appropriate direction, a cooling effect is created at thethermal junction347. There is also a heating effect created at the junction between the individual leads344 connected to the dissimilar metals or semiconductors343/345. This heating effect, which is proportional to the cooling effect, may be utilized to activate thebaroreceptors30 by positioning the junction between theelectrical leads344 and the dissimilar metals or semiconductors343/345 adjacent to thevascular wall40.
• Refer now toFIGS. 21A-21C which show schematic illustrations of a preferred embodiment of an inductively activatedelectrode structure282 for use with the embodiments described with reference toFIGS. 14-16. In this embodiment, current flow in theelectrode structure282 is induced by amagnetic field287 created by aninductor286 which is operably coupled to thedriver66 of thecontrol system60 by way ofelectrical cable284. Theelectrode structure282 preferably comprises a multi-filar self-expanding braid structure including a plurality ofindividual members282a,282b,282cand282d. However, theelectrode structure282 may simply comprise a single coil for purposes of this embodiment.
• Each of theindividual coil members282a-282dcomprising theelectrode structure282 consists of a plurality of individual coil turns281 connected end to end as illustrated inFIGS. 21B and 21C.FIG. 21C is a detailed view of the connection between adjacent coil turns281 as shown inFIG. 21B. Eachcoil turn281 comprises electrically isolated wires or receivers in which a current flow is established when a changingmagnetic field287 is created by theinductor286. Theinductor286 is preferably covered with an electrically insulative material to eliminate direct electrical stimulation of tissues surrounding theinductor286. Current flow through eachcoil turn281 results in apotential drop288 between each end of thecoil turn281. With a potential drop defined at each junction between adjacent coil turns281, a localized current flow cell is created in the vessel wall adjacent each junction. Thus an array or plurality of bipoles are created by theelectrode structure282 and uniformly distributed around the vessel wall. Eachcoil turn281 comprises an electricallyconductive wire material290 surrounded by an electricallyinsulative material292. The ends of eachcoil turn281 are connected by an electricallyinsulated material294 such that eachcoil turn281 remains electrically isolated. Theinsulative material294 mechanically joins but electrically isolates adjacent coil turns281 such that eachturn281 responds with a similarpotential drop288 when current flow is induced by the changingmagnetic field287 of theinductor286. An exposedportion296 is provided at each end of eachcoil turn281 to facilitate contact with the vascular wall tissue. Each exposedportion296 comprises an isolated electrode in contact with the vessel wall. The changingmagnetic field287 of theinductor286 causes a potential drop in eachcoil turn281 thereby creating small current flow cells in the vessel wall corresponding to adjacent exposedregions296. 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 thebaroreceptors30 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.
• To address low blood pressure and other conditions requiring blood pressure augmentation, some of the baroreceptor activation devices described previously may be used to selectively and controllably regulate blood pressure by inhibiting or dampening baroreceptor signals. By selectively and controllably inhibiting or dampening baroreceptor signals, the present invention reduces conditions associated with low blood pressure as described previously. Specifically, the present invention would function to increase the blood pressure and level of sympathetic nervous system activation by inhibiting or dampening the activation of baroreceptors.
• This may be accomplished by utilizing mechanical, thermal, electrical and chemical or biological means. Mechanical means may be triggered off the pressure pulse of the heart to mechanically limit deformation of the arterial wall. For example, either of theexternal compression devices120/160 described previously may be used to limit deformation of the arterial wall. Alternatively, the external compression device may simply limit diametrical expansion of the vascular wall adjacent the baroreceptors without the need for a trigger or control signal.
• Thermal means may be used to cool thebaroreceptors30 and adjacent tissue to reduce the responsiveness of thebaroreceptors30 and thereby dampen baroreceptor signals. Specifically, thebaroreceptor30 signals may be dampened by either directly cooling thebaroreceptors30, to reduce their sensitivity, metabolic activity and function, or by cooling the surrounding vascular wall tissue thereby causing the wall to become less responsive to increases in blood pressure. An example of this approach is to use the cooling effect of thePeltier device340. Specifically, thethermal transfer junction347 may be positioned adjacent the vascular wall to provide a cooling effect. The cooling effect may be used to dampen signals generated by thebaroreceptors30. Another example of this approach is to use thefluid delivery device260 to deliver a cool or cold fluid (e.g. saline). In this embodiment, thedriver66 would include a heat exchanger to cool the fluid and thecontrol system60 may be used to regulate the temperature of the fluid, thereby regulating the degree ofbaroreceptor30 signal dampening.
• Electrical means may be used to inhibitbaroreceptor30 activation by, for example, hyperpolarizing cells in or adjacent to thebaroreceptors30. Examples of devices and method of hyperpolarizing cells are disclosed in U.S. Pat. No. 5,814,079 to Kieval, and U.S. Pat. No. 5,800,464 to Kieval, the entire disclosures of which are hereby incorporated by reference. Such electrical means may be implemented using any of the embodiments discussed with reference toFIGS. 13-18 and21.
• Chemical or biological means may be used to reduce the sensitivity of thebaroreceptors30. For example, a substance that reduces baroreceptor sensitivity may be delivered using thefluid delivery device260 described previously. The desensitizing agent may comprise, for example, tetrodotoxin or other inhibitor of excitable tissues. From the foregoing, it should be apparent to those skilled in the art that 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 or by inhibiting/dampening baroreceptor signals. Thus, the present invention may be used to increase or decrease blood pressure, sympathetic nervous system activity and neurohormonal activity, as needed to minimize deleterious effects on the heart, vasculature and other organs and tissues.
• The baroreceptor activation devices described previously may also be used to provide antiarrhythmic effects. It is well known that the susceptibility of the myocardium to the development of conduction disturbances and malignant cardiac arrhythmias is influenced by the balance between sympathetic and parasympathetic nervous system stimulation to the heart. That is, heightened sympathetic nervous system activation, coupled with decreased parasympathetic stimulation, increases the irritability of the myocardium and likelihood of an arrhythmia. Thus, by decreasing the level of sympathetic nervous system activation and enhancing the level of parasympathetic activation, the devices, systems and methods of the current invention may be used to provide a protective effect against the development of cardiac conduction disturbances.
Experimental
• An electrode system was introduced into the inferior vena cava of an anesthetized dog. The electrode system was an eight lead, 64-electrode 8F Constellation® catheter from Boston Scientific EP Technologies, Sunnyvale, Calif. The electrode system was placed endovascularly in the abdominal vena cava. The electrode system was activated using trains of electrical impulses of 0-6 volts, a frequency of 100 hz, and a pulse width of 0.5 ms. During various activation experiments, arterial pressure, mean arterial pressure and heart rate were monitored. The results of three experiments are shown in FIGS.22A-C. These figures demonstrate a change in blood pressure as energy is applied to the vessel wall, with recovery to pre-activation levels when the energy is discontinued.
• 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.

Claims (138)

1. A baroreflex stimulator, comprising:

a pulse generator to provide a baroreflex stimulation signal through an electrode; and

a modulator to modulate the baroreflex stimulation signal based on a circadian rhythm template.

2. The stimulator ofclaim 1, further comprising a waveform generator to produce baroreceptor signals of a desired morphology, wherein the modulator includes a modulator to change the morphology of the baroreflex stimulation signal based on the circadian rhythm template.

3. The stimulator ofclaim 1, wherein the circadian rhythm template includes a template selected from the group consisting of a pre-programmed circadian rhythm template, a patient-specific circadian rhythm template, a mean arterial pressure template, a heart rate template, a stroke volume template, a cardiac output template, and a total peripheral resistance template.

4. The stimulator ofclaim 1, wherein the electrode includes an electrode adapted to stimulate baroreceptors in a vessel wall.

5. A baroreflex stimulator, comprising:

a pulse generator to provide a baroreflex stimulation signal through an electrode; and

means for modulating the baroreflex stimulation signal based on a circadian rhythm template.

6. The stimulator ofclaim 5, wherein the circadian rhythm template includes a template selected from the group consisting of a pre-programmed circadian rhythm template, a patient-specific circadian rhythm template, a mean arterial pressure template, a heart rate template, a stroke volume template, a cardiac output template, and a total peripheral resistance template.

7. A method for operating an implantable medical device, comprising:

applying a baroreflex stimulation therapy using a baroreflex stimulator in the implantable medical device; and

modulating the baroreflex stimulation therapy based on a circadian rhythm template.

8. The method ofclaim 7, wherein modulating the baroreflex stimulation therapy based on the circadian rhythm template is accomplished using a pre-programmed circadian rhythm template.

9. The method ofclaim 7, further comprising:

sensing and recording parameters related to hypertension; and

generating a patient-specific circadian rhythm template based on the recorded parameters, wherein the baroreflex stimulation therapy is modulated based on the patient-specific circadian rhythm template.

10. The method ofclaim 7, wherein modulating the baroreflex stimulation therapy based on the circadian rhythm template is accomplished with a template selected from the set of a mean arterial pressure template, a heart rate template, a stroke volume template, a cardiac output template, and a total peripheral resistance template.

11. The method ofclaim 7, wherein applying baroreflex therapy includes stimulating a baroreceptor in a vessel wall.

12. A baroreflex stimulator, comprising:

a driver adapted to provide a control signal through a baroreceptor activation device; and

a controller to periodically modulate the control signal based on an algorithm.

13. A baroreflex stimulator, comprising:

a driver adapted to provide a control signal through a baroreceptor activation device; and

means for periodically modulating the control signal based on an algorithm.

14. A method for operating an implantable medical device, comprising:

applying a baroreflex stimulation therapy using a baroreceptor activation device in the implantable medical device; and

periodically modulating the baroreflex stimulation therapy based on an algorithm.

15. An implantable medical system, comprising:

a baroreflex stimulator to apply a baroreflex stimulation signal through an electrode;

a myocardial infarction detector to detect an event indicative of myocardial infarction; and

a controller connected to the baroreflex stimulator and to the myocardial infarction detector, the controller adapted to apply a baroreflex therapy in response to a detected event indicative of myocardial infarction.

16. The device ofclaim 15, wherein the controller includes a controller adapted to initiate a baroreflex therapy in response to a detected event indicative of myocardial infarction.

17. The device ofclaim 15, wherein the controller includes a controller adapted to increase an existing baroreflex therapy in response to a detected event indicative of myocardial infarction.

18. An implantable medical system, comprising:

means for detecting a myocardial infarction; and

means for applying baroreflex therapy to a pressoreceptive region to decrease coronary vascular resistance and increase blood flow in response to detecting the myocardial infarction.

19. The system ofclaim 18, wherein the means for applying baroreflex therapy includes means for increasing baroreflex stimulation in response to the myocardial infarction.

20. The system ofclaim 18, further comprising means for monitoring systemic blood pressure, and means for modulating the baroreflex therapy based on the systemic blood pressure.

21. The system ofclaim 18, further comprising means for sensing the blood pressure.

22. The system ofclaim 18, further comprising means for sensing respiration as a surrogate parameter for blood pressure.

23. A method, comprising:

detecting an event corresponding to a myocardial infarction; and

in response to a detected event corresponding to a myocardial infarction, applying a baroreflex therapy using an electrode positioned proximate to a baroreflex neural target.

24. The method ofclaim 23, further comprising monitoring systemic blood pressure and modulating the baroreflex therapy based on the blood pressure.

25. The method ofclaim 23, further comprising monitoring a surrogate parameter of systemic blood pressure and modulating the baroreflex therapy based on the surrogate parameter.

26. The method ofclaim 23, wherein monitoring the surrogate parameter includes monitoring a respiration parameter.

27. An implantable medical system, comprising:

a baroreflex stimulator to apply a baroreflex stimulation signal to an electrode;

a sensor to detect a parameter indicative of heart failure; and

a control system connected to the baroreflex stimulator and to the sensor, the control system adapted to apply a baroreflex therapy in response to a detected parameter indicative of heart failure.

28. An implantable medical system, comprising:

means for detecting a heart failure; and

means for applying baroreflex therapy to a baroreceptor region to regulate blood pressure and sympathetic nervous system activity.

29. A method, comprising:

detecting a parameter corresponding to heart failure; and

applying a baroreflex therapy using a baroreceptor activation device positioned adjacent a baroreceptor in response to detecting a parameter corresponding to heart failure.

30. A system for providing baroreflex stimulation, comprising:

an adverse event detector to sense an adverse event and provide a signal indicative of the adverse event; and

a baroreflex stimulator, including: a pulse generator to provide a baroreflex stimulation signal adapted to provide a baroreflex therapy; and a modulator to receive the signal indicative of the adverse event and modulate the baroreflex stimulation signal based on the signal indicative of the adverse event to change the baroreflex therapy from a first baroreflex therapy to a second baroreflex therapy.

31. The system ofclaim 30, further comprising a waveform generator to produce baroreflex signals of a desired morphology, wherein the modulator includes a modulator to change the morphology of the barobreflex stimulation signal based on the signal indicative of the adverse event.

32. The system ofclaim 30, further comprising an implantable medical device, wherein the implantable medical device includes the adverse event detector and the baroreflex stimulator.

33. The system ofclaim 30, wherein the adverse event includes an adverse cardiac event.

34. The system ofclaim 30, wherein the adverse cardiac event includes an arrhythmia.

35. The system ofclaim 30, wherein the adverse cardiac event includes a non-arrhythmic cardiac event.

36. A baroreflex stimulator, comprising:

an implantable pulse generator to provide a baroreflex stimulation signal adapted to provide a baroreflex therapy; and

means for modulating the baroreflex stimulation signal based on a signal indicative of an adverse event to change the baroreflex therapy from a first baroreflex therapy to a second baroreflex therapy.

37. The baroreflex stimulator ofclaim 36, wherein the means for modulating the baroreflex stimulation signal based on a signal indicative of an adverse event includes means for modulating the baroreflex stimulation signal based on a signal indicative of an adverse cardiac event.

38. The baroreflex stimulator ofclaim 37, wherein the means for modulating the baroreflex stimulation signal based on a signal indicative of an adverse cardiac event includes means for modulating the baroreflex stimulation signal based on a signal indicative of an arrhythmia.

39. The baroreflex stimulator ofclaim 37, wherein the means for modulating the baroreflex stimulation signal based on a signal indicative of an adverse cardiac event includes means for modulating the baroreflex stimulation signal based on a signal indicative of a non-arrhythmic cardiac event.

40. The baroreflex stimulator ofclaim 36, wherein the baroreflex stimulation signal has a morphology, and the means for modulating the baroreflex stimulation signal includes means for adjusting the morphology of the baroreflex stimulation signal.

41. A method for operating an implantable medical device, comprising:

receiving a signal regarding a detected adverse event at a baroreceptor stimulator;

performing a first baropacing therapy using the baroreceptor stimulator when the adverse event is not detected; and

automatically performing a second baropacing therapy using the baroreceptor stimulator when the adverse event is detected.

42. The method ofclaim 41, wherein performing the first baropacing therapy includes withholding baropacing therapy and performing the second baropacing therapy includes providing baropacing stimulation.

43. The method ofclaim 41, wherein performing the first baropacing therapy includes providing baropacing stimulation and performing the second baropacing therapy includes withholding baropacing therapy.

44. The method ofclaim 41, wherein performing baropacing therapy includes identifying the adverse event, and applying a baropacing therapy for the adverse event.

45. The method ofclaim 41, further comprising detecting the adverse event using an adverse event detector in the implantable medical device, and sending the signal regarding the adverse event to a baroreflex stimulator in the implantable medical device.

46. A system for providing baroreflex stimulation, comprising:

a sensor to detect a parameter and provide a signal indicative of the parameter; and

a baroreflex stimulator, including:

a driver to provide a control signal adapted to deliver a baroreflex therapy;

controller to receive the signal indicative of the parameter and modulate the control signal based on the signal indicative of the parameter to change the baroreflex therapy from a first baroreflex therapy to a second baroreflex therapy.

47. A baroreflex stimulator, comprising:

an implantable driver to provide a control signal adapted to provide a baroreflex therapy; and

a controller to receive the signal indicative of the parameter and modulate the control signal based on the signal indicative of the parameter to change the baroreflex therapy from a first baroreflex therapy to a second baroreflex therapy.

48. A method for operating an implantable medical device, comprising:

receiving a signal indicative of a parameter at a baroreceptor stimulator;

performing a first baropacing therapy using the baroreceptor stimulator when the parameter is not detected; and

performing a second baropacing therapy using the baroreceptor stimulator when the parameter is detected.

49. A system for providing baroreflex stimulation, comprising:

a heart rate monitor to sense a heart rate and provide a signal indicative of the heart rate; and a baroreflex stimulator, including: a pulse generator to intermittently generate a stimulation signal to provide baroreflex stimulation for a baroreflex therapy; and

a modulator to adjust the stimulation signal based on the signal indicative of the heart rate such that the stimulation signal provides a desired baroreflex stimulation corresponding to a desired heart rate.

50. The system ofclaim 49, wherein the desired heart rate includes a programmable value.

51. The system ofclaim 49, wherein the desired heart rate includes a percent change based on a heart rate during a time without baroreflex stimulation and a heart rate during a time with baroreflex stimulation.

52. The system ofclaim 49, wherein the desired heart rate includes a change in a number of heart beats for a heart rate during a time without baroreflex stimulation and a heart rate during a time with baroreflex stimulation.

53. The system ofclaim 49, wherein the modulator is adapted to adjust signal characteristic of the stimulation signal, wherein the signal characteristic is selected from a group consisting of: an amplitude, a frequency, a burst frequency, a pulse width, and a duty cycle.

54. The system ofclaim 49, wherein the modulator is adapted to adjust any combination of at least two stimulation signal attributes from a group of stimulation signal attributes consisting of: an amplitude, a frequency, a burst frequency, a pulse width, and a duty cycle.

55. A system for providing baroreflex stimulation, comprising:

a baroreflex stimulator, including: a pulse generator to generate a stimulation signal to provide intermittent baroreflex stimulation for a baroreflex therapy; and

a modulator to adjust the stimulation signal;

a cardiovascular parameter monitor to monitor at least one cardiovascular parameter and provide a first signal indicative of the cardiovascular parameter during the baroreflex stimulation and a second signal indicative of the cardiovascular parameter without the baroreflex stimulation; and

a comparator to provide a detected change for the cardiovascular parameter based on the first and second signals, and to provide a therapy control signal based on a desired change for the cardiovascular parameter and the detected change.

56. The system ofclaim 55, wherein the modulator is adapted to adjust at least one stimulation signal attribute from a group of stimulation signal attributes consisting of: an amplitude, a frequency, a burst frequency, a pulse width, and a duty cycle.

57. The system ofclaim 55, wherein the cardiovascular parameter monitor is adapted to monitor a parameter selected from the group consisting of: heart rate, blood pressure, respiration rate, a surrogate parameter for heart rate that increases and decreases with the heart rate, a percent change for the cardiovascular parameter when influenced by the baroreflex stimulation and a quantitative change associated with the cardiovascular parameter when influenced by the baroreflex stimulation.

58. The system ofclaim 55, wherein the desired change for the cardiovascular parameter includes a percent change for the cardiovascular parameter when influenced by the baroreflex stimulation.

59. The system ofclaim 55, wherein the desired change for the cardiovascular parameter includes a quantitative change associated with the cardiovascular parameter when influenced by the baroreflex stimulation.

60. A baroreflex stimulator, comprising:

means for intermittently providing baroreflex stimulation for a baroreflex therapy over a period of time;

means for comparing values for at least one cardiovascular feedback parameter when the baroreflex stimulation is applied and when then baroreflex stimulation is not applied to provide a detected feedback change;

means for comparing the detected feedback change to a desired feedback change to provide a comparison result; and

means for adjusting the baroreflex stimulation based on the comparison result to control the baroreflex therapy over the period of time.

61. The baroreflex stimulator ofclaim 60, wherein the means for comparing values for at least one cardiovascular feedback parameter includes means for comparing heart rate when the baroreflex stimulation is applied and when then baroreflex stimulation is not applied.

62. The baroreflex stimulator ofclaim 60, further comprising means for programming the desired feedback change.

63. A method, comprising:

intermittently providing baroreflex stimulation for a baroreflex therapy over a period of time;

comparing values for at least one cardiovascular feedback parameter when the baroreflex stimulation is applied and when then baroreflex stimulation is not applied to provide a detected feedback change;

comparing the detected feedback change to a desired feedback change to provide a comparison result; and

adjusting the baroreflex stimulation based on the comparison result to control the baroreflex therapy over the period of time.

64. The method ofclaim 63, further comprising programming the desired feedback change for use in comparing the detected feedback change to the desired feedback change.

65. The method ofclaim 64, wherein programming the desired feedback change includes programming a percent change for the at least one cardiovascular feedback parameter when the baroreflex stimulation is applied and when then baroreflex stimulation is not applied.

66. The method ofclaim 64, wherein programming the desired feedback change includes programming a quantitative value change for the at least one cardiovascular feedback parameter when the baroreflex stimulation is applied and when then baroreflex stimulation is not applied.

67. A system for providing baroreceptor stimulation comprising:

a sensor to sense a physiologic parameter and provide a signal indicative of the physiologic parameter; and

a baroreceptor activation device, including a pulse generator to intermittently generate a stimulation signal to provide baroreceptor stimulation for a baroreflex therapy; and

a control system to adjust the stimulation signal based on the signal indicative of the physiologic parameter such that the stimulation signal provides a desired baroreceptor stimulation corresponding to a desired physiologic parameter.

68. A system for providing baroreceptor stimulation, comprising:

a baroreceptor activation device including:

a pulse generator to generate a stimulation signal to provide intermittent baroreceptor stimulation for a baroreflex therapy; and

a sensor to monitor at least one physiologic parameter and provide a first a signal indicative of the physiologic parameter during the baroreceptor stimulation and a second signal indicative of a threshold value of a physiologic parameter;

a comparator to provide a detected change for the physiologic parameter based on the first and second signals, and to provide a therapy control signal based on the desired change for the physiologic parameter and the desired change.

69. A baroreceptor stimulator, comprising

means for intermittently providing baroreceptor stimulation for a baroreflex for a baroreflex therapy over a period of time;

means for comparing values for at least one physiologic parameter when the baroreceptor stimulation is applied and values indicative of a threshold value to provide a detected change in the physiologic parameter;

means for comparing the detected physiologic parameter change to a desired physiologic parameter change to provide a comparison result; and

means for adjusting the baroreceptor stimulation based on the comparison result to control the baroreflex therapy over a period of time.

70. A method, comprising:

intermittently providing baroreceptor stimulation for a baroreflex therapy over a period of time;

comparing values for at least one physiologic parameter when the baroreceptor stimulation is applied and values indicative of a threshold parameter to provide a detected physiologic parameter change;

comparing the detected physiologic parameter change to a desired physiologic parameter change to provide a comparison result; and

adjusting the baroreceptor stimulation based on the comparison result to control the baroreflex therapy over a period of time.

71. An implantable medical device, comprising:

a pulse generator to generate baroreflex stimulation pulses;

a sensor circuitry;

a lead adapted to be electrically connected to the pulse generator and to the sensor circuitry, the lead including an electrode to distribute the baroreflex stimulation pulses to a baroreflex site and a pressure sensor to provide a signal indicative of blood pressure to the sensor circuitry; and

a controller connected to the pulse generator and the sensor circuitry, the controller adapted to adjust the baroreflex stimulation pulses based on the blood pressure.

72. The device ofclaim 71, wherein the controller is adapted to modulate two or more characteristics selected from a group of characteristics consisting of an amplitude, a frequency, and a pulse frequency.

73. The device ofclaim 71, wherein the pressure sensor includes a micro-electrical mechanical system (MEMS) device to detect blood pressure.

74. An implantable medical device, comprising:

means for delivering baroreflex therapy to a baroreflex neural target site using an intravascular lead and an electrode on the lead;

means for monitoring blood pressure near the baroreflex neural target site using a pressure sensor on the lead; and

means for adjusting the baroreflex therapy based on the blood pressure.

75. An implantable medical device, comprising:

a pulse generator to generate baroreflex stimulation pulses; a sensor circuitry;

a lead adapted to be electrically connected to the pulse generator and to the sensor circuitry, the lead including an electrode to distribute the baroreflex stimulation pulses to a baroreflex site and a sensor to provide a signal to the sensor circuitry that corresponds to a pre-ejection period measured between a sensed electrical event in a ventricle and onset of ventricular ejection derived from a pulmonary arterial blood pressure sensor; and

a controller connected to the pulse generator and the sensor circuitry, the controller adapted to adjust the baroreflex stimulation pulses based on the blood pressure.

76. The device ofclaim 75, wherein the sensed electrical event in a ventricle includes a sensed electrical event in a right ventricle.

77. The device ofclaim 75, wherein the sensed electrical event in a ventricle includes a sensed electrical event in a left ventricle.

78. The device ofclaim 75, wherein the controller is adapted to modulate a characteristic of the baroreflex stimulation pulses based on the pre-ejection period selected from the group consisting of: an amplitude, a frequency, a pulse frequency and a morphology.

79. The device ofclaim 75, wherein the controller is adapted to modulate two or more characteristics selected from a group of characteristics consisting of an amplitude, a frequency, and a pulse frequency.

80. A method, comprising:

delivering baroreflex therapy to a baroreflex neural target site using an intravascular lead and an electrode on the lead;

monitoring blood pressure near the baroreflex neural target site using a pressure sensor on the lead; and

adjusting the baroreflex therapy based on the blood pressure.

81. An implantable medical device, comprising:

a pulse generator to generate baroreceptor stimulation pulses;

a sensor circuitry;

a lead adapted to be electrically connected to the pulse generator and to the sensor circuitry, the lead including an electrode to distribute the baroreceptor stimulation pulses to a baroreceptor site and a pressure sensor to provide a signal indicative of blood pressure to the sensor circuitry; and

a controller connected to the pulse generator and the sensor circuitry, the controller adapted to adjust the baroreceptor stimulation pulses based on the blood pressure.

82. An implantable medical device, comprising:

means for delivering baroreflex therapy to a barorecetor neural target site using an intravascular lead and an electrode on the lead;

means for monitoring blood pressure near the baroreceptor neural target site using a pressure sensor on the lead; and

means for adjusting the baroreflex therapy based on the blood pressure.

83. An implantable medical device, comprising:

a pulse generator to generate baroreceptor stimulation pulses;

a sensor circuitry;

a lead adapted to be electrically connected to the pulse generator and to the sensor circuitry, the lead including an electrode to distribute the baroreceptor stimulation pulses to a baroreceptor site and

a sensor to provide a signal to the sensor circuitry that includes a measure of blood pressure and corresponds to a specific physiologic event; and

a controller connected to the pulse generator and the sensor circuitry, the controller adapted to adjust the baroreceptor stimulation pulses based on the blood pressure.

84. A method, comprising:

delivering baroreflex therapy to a baroreceptor neural target site using an intravascular lead and an electrode on the lead;

monitoring blood pressure near the baroreceptor neural target site using a pressure sensor on the lead; and

adjusting the baroreflex therapy based on the blood pressure.

85. An implantable medical device, comprising:

a pulse generator to generate a baroreflex stimulation signal as part of a baroreflex therapy;

a lead to be electrically connected to the pulse generator and to be intravascularly fed into a heart, the lead including an electrode to be positioned in or proximate to the heart to deliver the baroreflex signal to a baroreceptor region in or proximate to the heart;

a sensor to sense a physiological parameter regarding an efficacy of the baroreflex therapy and to provide a signal indicative of the efficacy of the baroreflex therapy; and

a controller connected to the pulse generator to control the baroreflex stimulation signal and to the sensor to receive the signal indicative of the efficacy of the baroreflex therapy.

86. The device ofclaim 85, further comprising a telemetry circuit to communicate with the controller and to wirelessly communicate with an external programmer, wherein the implantable medical device is adapted to communicate therapy data to the programmer for processing and display by the programmer, and is adapted to receive programming commands from the programmer.

87. The device ofclaim 85, wherein the lead is adapted to position the electrode near an endocardial baroreceptor site within the heart.

88. The device ofclaim 85, wherein the pulse generator is further adapted to generate a cardiac pacing signal, the lead further including a second electrode to be positioned to deliver the cardiac pacing signal to capture the heart.

89. The device ofclaim 88, further comprising sensing circuitry to sense intrinsic signals indicative of refractories, the sensing circuitry being connected to the controller.

90. An implantable baroreflex stimulator, comprising:

means for delivering baroreflex therapy through a lead intravascularly fed through at least a portion of the heart to a baroreceptor region proximate to a heart to inhibit sympathetic activity; and

means for providing feedback regarding an efficacy of the baroreflex therapy for use to control delivery of the baroreflex therapy.

91. The stimulator ofclaim 90, wherein the means for delivering baroreflex therapy includes means for delivering the baroreflex therapy to endocardial baroreceptor tissues.

92. The stimulator ofclaim 90, further comprising means for determining an appropriate time to deliver the stimulation signal.

93. The stimulator ofclaim 90, further comprising means for communicating with a programmer for data display and patient management.

94. The stimulator ofclaim 90, wherein the means for providing feedback includes means for sensing systemic blood pressure.

95. The stimulator ofclaim 90, wherein the means for providing feedback includes means for sensing respiration.

96. The stimulator ofclaim 90, further comprising means for pacing the heart.

97. A method, comprising:

applying baroreflex therapy, including electrically stimulating a baroreceptor region in or near a heart using a lead intravascularly fed into at least a portion of the heart;

sensing a physiologic parameter indicative of an efficacy of the baroreflex therapy; and

modifying the baroreflex therapy based on the physiological parameter.

98. The method ofclaim 97, wherein the lead emerges from an implantable device, the method further comprising pacing the heart using the lead.

99. An implantable medical device, comprising:

a pulse generator to generate a baroreflex stimulation signal as part of a baroreflex therapy;

a lead to be electrically connected to the pulse generator, the lead including an electrode to deliver the baroreflex signal to a baroreflex neural target;

a sensor to sense a physiological parameter regarding an efficacy of the baroreflex therapy and to provide a signal indicative of the efficacy of the baroreflex therapy; and

a controller connected to the pulse generator to control the baroreflex stimulation signal and to the sensor to receive the signal indicative of the efficacy of the baroreflex therapy.

100. A method, comprising:

applying baroreflex therapy, including electrically stimulating a baroreceptor region using a lead with an electrode;

sensing a physiologic parameter indicative of an efficacy of the baroreflex therapy; and

modifying the baroreflex therapy based on the physiological parameter.

101. An implantable medical device, comprising:

a pulse generator to generate a baroreceptor stimulation signal as part of a baroreflex therapy;

a lead to be electrically connected to the pulse generator and to be intravascularly fed into a heart, the lead including an electrode to be positioned in or proximate to the heart to deliver the baroreceptor signal to a baroreceptor region in or proximate to the heart;

a sensor to sense a physiological parameter regarding the need to modify the baroreflex system and to provide a signal indicative of the need to modify the baroreflex system; and

a controller connected to the pulse generator to control the baroreceptor stimulation signal and to the sensor to receive the signal indicative of the need to modify the baroreflex system.

102. An implantable baroreflex stimulator, comprising:

means for delivering baroreflex therapy through a lead intravascularly fed through at least a portion of the heart to a baroreceptor region proximate to a heart to inhibit sympathetic activity; and

means for providing feedback regarding an efficacy of the baroreflex therapy for use to control delivery of the baroreflex therapy.

103. A method, comprising:

applying baroreflex therapy, including electrically stimulating a baroreceptor region in or near a heart using a lead intravascularly fed into at least a portion of the heart;

sensing a physiologic parameter indicative of the need to modify the baroreflex system; and

modifying the baroreflex therapy based on the physiological parameter.

104. An implantable medical device, comprising:

a pulse generator to generate a baroreceptor stimulation signal as part of a baroreflex therapy;

a lead to be electrically connected to the pulse generator, the lead including an electrode to deliver the baroreceptor signal to a baroreceptor neural target;

a sensor to sense a physiological parameter and to provide a signal indicative of the need to modify the baroreflex system; and

a controller connected to the pulse generator to control the baroreceptor stimulation signal and to the sensor to receive the signal indicative of the need to modify the baroreflex system.

105. A system for providing baroreflex stimulation, comprising:

a cardiac activity monitor to sense cardiac activity and provide a signal indicative of the cardiac activity; and

a baroreflex stimulator, including: a pulse generator to provide a baroreflex stimulation signal adapted to provide a baroreflex therapy; and

a modulator to receive the signal indicative of the cardiac activity and modulate the baroreflex stimulation signal based on the signal indicative of the cardiac activity to change the baroreflex therapy from a first baroreflex therapy to a second baroreflex therapy.

106. The system ofclaim 105, further comprising a waveform generator to produce baroreflex stimulation signals of a desired morphology, wherein the modulator includes a modulator to change the morphology of the baroreflex stimulation signal based on the signal indicative of the cardiac activity.

107. The system ofclaim 105, wherein the cardiac activity monitor includes a respiration monitor, and the signal indicative of the cardiac activity includes a respiration signal.

108. The system ofclaim 107, wherein the respiration monitor includes a tidal volume monitor.

109. The system ofclaim 107, wherein the respiration monitor includes a minute ventilation monitor.

110. The system ofclaim 105, wherein the cardiac activity monitor includes an acceleration sensor, and the signal indicative of the cardiac activity includes an acceleration signal.

111. The system ofclaim 105, wherein: the cardiac activity monitor includes a combination of two or more of the following sensors: a heart rate sensor; a minute ventilation sensor; and an acceleration sensor; and the signal indicative of the cardiac activity includes a composite of two or more of the following signals: a heart rate signal; a minute ventilation signal; and an acceleration signal.

112. The system ofclaim 105, wherein the cardiac activity monitor includes a sensor to sense at least one pressure parameter, and the signal indicative of the cardiac activity includes a signal indicative of the at least one pressure parameter.

113. The system ofclaim 112, wherein the at least one pressure parameter is selected from the group consisting of: mean arterial pressure, pulse pressure, end systolic pressure and end diastolic pressure.

114. The system ofclaim 105, wherein the cardiac activity monitor includes a stroke volume monitor, and the signal indicative of the cardiac activity includes a signal indicative of the stroke volume.

115. The system ofclaim 105, wherein the cardiac activity monitor includes a monitor to measure at least one electrogram measurement, and the signal indicative of the cardiac activity includes a signal indicative of the at least one electrogram measurement.

116. The system ofclaim 105, wherein the cardiac activity monitor includes a monitor to measure at least one electrocardiogram (ECG) measurement, and the signal indicative of the cardiac activity includes a signal indicative of the at least one ECG measurement.

117. The system ofclaim 105, further comprising an implantable medical device, wherein the implantable medical device includes the cardiac activity monitor and the baroreflex stimulator.

118. A baroreflex stimulator, comprising: an implantable pulse generator to provide a baroreflex stimulation signal adapted to provide a baroreflex therapy; and means for modulating the baroreflex stimulation signal based on a signal indicative of cardiac activity to change the baroreflex therapy from a first baroreflex therapy to a second baroreflex therapy.

119. The baroreflex stimulator ofclaim 118, wherein the means for modulating the baroreflex stimulation signal includes means for modulating the baroreflex stimulation signal based on a parameter selected from the group consisting of: heart rate, respiration, tidal volume, acceleration.

120. The baroreflex stimulator ofclaim 119, wherein the means for modulating the baroreflex stimulation signal based on respiration includes means for modulating the baroreflex stimulation based on minute ventilation.

121. The baroreflex stimulator ofclaim 118, wherein the baroreflex stimulation signal has a morphology, and the means for modulating the baroreflex stimulation signal includes means for adjusting the morphology of the baroreflex stimulation signal.

122. A method for operating an implantable medical device, comprising:

receiving a signal regarding an activity level; and

setting a baroreflex stimulation level for a baroreflex stimulator of the device based on the signal regarding the activity level.

123. The method ofclaim 122, further comprising determining whether the activity level is rest or exercise, wherein setting a baroreflex stimulation level includes applying baroreflex stimulation during rest and withdrawing baroreflex stimulation during exercise.

124. The method ofclaim 122, further comprising determining whether the activity level is a first activity level or a second activity level where the first activity level is higher than the second activity, wherein setting a baroreflex stimulation level includes setting a first baroreflex stimulation level when the activity level is determined to be the second activity level and setting a second baroreflex stimulation level when the activity level is determined to be the first activity level, wherein the first baroreflex stimulation level is higher than the second baroreflex stimulation level.

125. The method ofclaim 122, wherein the activity level is one of a plurality of activity levels and the baroreflex stimulation level is one of a plurality of baroreflex stimulation levels; and the baroreflex stimulation levels have an inverse relationship with the activity levels such that an incremental increase in the activity level corresponds with an incremental decrease in the baroreflex stimulation level.

126. The method ofclaim 122, further comprising comparing the activity parameter to a target activity parameter, wherein setting a baroreflex stimulation level includes increasing the baroreflex stimulation level when the acquired activity parameter is lower than the target parameter and decreasing the baroreflex stimulation level when the acquired activity parameter is higher than the target parameter.

127. The method ofclaim 122, wherein receiving a signal regarding an activity level includes sensing a heart rate using a sensor of the implantable medical device; and setting a baroreflex stimulation level includes setting the baroreflex stimulation level based on the heart rate.

128. The method ofclaim 122, wherein receiving a signal regarding an activity level includes sensing respiration using a sensor of the implantable medical device; and setting a baroreflex stimulation level includes setting the baroreflex stimulation level based on the respiration.

129. The method ofclaim 128, wherein sensing respiration includes sensing tidal volume, and setting the baroreflex stimulation level based on the respiration includes setting the baroreflex stimulation level based on the tidal volume.

130. The method ofclaim 128, wherein sensing respiration includes sensing minute ventilation, and setting the baroreflex stimulation level based on the respiration includes setting the baroreflex stimulation level based on the minute ventilation.

131. The method ofclaim 122, wherein receiving a signal regarding an activity level includes sensing acceleration using a sensor of the implantable medical device; and setting a baroreflex stimulation level includes setting the baroreflex stimulation level based on the acceleration.

132. A method, comprising:

determining an activity level; setting a baroreflex stimulation level based on the activity level; and

applying baroreflex stimulation at the baroreflex stimulation level.

133. The method ofclaim 132, wherein determining the activity level includes determining whether the activity level is rest or exercise; and setting a baroreflex stimulation level based on the activity level includes providing a signal to apply baroreflex stimulation during rest and withdraw baroreflex stimulation during exercise.

134. The method ofclaim 132, wherein determining the activity level includes determining whether the activity level is a first activity level or a second activity level, wherein the first activity level is higher than the second activity level; and setting a baroreflex stimulation level based on the activity level includes setting a first baroreflex stimulation level when the activity level is determined to be the second activity level, and setting a second baroreflex stimulation level when the activity level is determined to be the first activity level, wherein the first baroreflex stimulation level is higher than the second baroreflex stimulation level.

135. The method ofclaim 132, wherein the activity level is one of a plurality of activity levels and the baroreflex stimulation level is one of a plurality of baroreflex stimulation levels; and the baroreflex stimulation levels have an inverse relationship with the activity levels such that an incremental increase in the activity level corresponds with an incremental decrease in the baroreflex stimulation level.

136. The method ofclaim 132, further comprising comparing the activity parameter to a cardiac activity parameter, wherein setting a baroreflex stimulation level based on the activity level includes increasing the baroreflex stimulation level when the acquired activity parameter is lower than the target parameter and decreasing the baroreflex stimulation level when the acquired activity parameter is higher than the target parameter.

137. A system for providing baroreceptor stimulation, comprising:

a sensor to sense a physiologic parameter and provide a signal indicative of the physiologic parameter; and

a baroreceptor stimulator, including: a pulse generator to provide a baroreceptor stimulation signal adapted to provide a baroreflex therapy; and

a control system to receive the signal indicative of the physiologic parameter and modify the baroreceptor stimulation signal based on the signal indicative of the physiologic parameter.

138. A baroreceptor stimulator, comprising:

an implantable pulse generator to provide a baroreceptor stimulation signal adapted to provide a baroreflex therapy; and

means for modulating the baroreceptor stimulation signal based on a signal indicative of a physiologic parameter to modify the baroreflex therapy.

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