U.S. patent application number 10/746846 was filed with the patent office on 2005-07-07 for automatic baroreflex modulation based on cardiac activity.
Invention is credited to Libbus, Imad.
Application Number | 20050149132 10/746846 |
Document ID | / |
Family ID | 34700678 |
Filed Date | 2005-07-07 |
United States Patent
Application |
20050149132 |
Kind Code |
A1 |
Libbus, Imad |
July 7, 2005 |
Automatic baroreflex modulation based on cardiac activity
Abstract
An aspect of the present subject matter relates to a system for
providing baroreflex stimulation. An embodiment of the system
comprises a cardiac activity monitor to sense cardiac activity and
provide a signal indicative of the cardiac activity, and a
baroreflex stimulator. The stimulator includes a pulse generator
and a modulator. The pulse generator provides a baroreflex
stimulation signal adapted to provide a baroreflex therapy. The
modulator receives the signal indicative of the cardiac activity
and modulates 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.
Other aspects are provided herein.
Inventors: |
Libbus, Imad; (St. Paul,
MN) |
Correspondence
Address: |
SCHWEGMAN, LUNDBERG, WOESSNER & KLUTH, P.A.
P.O. BOX 2938
MINNEAPOLIS
MN
55402-0938
US
|
Family ID: |
34700678 |
Appl. No.: |
10/746846 |
Filed: |
December 24, 2003 |
Current U.S.
Class: |
607/9 |
Current CPC
Class: |
A61B 5/1118 20130101;
A61B 5/4035 20130101; A61N 1/36117 20130101; A61B 5/4047 20130101;
A61N 1/36139 20130101; A61B 5/349 20210101; A61N 1/3611 20130101;
A61B 5/0215 20130101 |
Class at
Publication: |
607/009 |
International
Class: |
A61N 001/362 |
Claims
1. 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.
2. The system of claim 1, wherein the baroreflex stimulation signal
has an amplitude, and the modulator includes a modulator to
modulate the amplitude based on the signal indicative of the
cardiac activity.
3. The system of claim 1, wherein the baroreflex stimulation signal
has a frequency, and the modulator includes a modulator to modulate
the frequency based on the signal indicative of the cardiac
activity.
4. The system of claim 1, wherein the baroreflex stimulation signal
has a burst frequency, and the modulator includes a modulator to
modulate the burst frequency based on the signal indicative of the
cardiac activity.
5. The system of claim 1, 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.
6. The system of claim 1, wherein the cardiac activity monitor
includes a heart rate sensor, and the signal indicative of the
cardiac activity includes a heart rate signal.
7. The system of claim 1, wherein the cardiac activity monitor
includes a respiration monitor, and the signal indicative of the
cardiac activity includes a respiration signal.
8. The system of claim 7, wherein the respiration monitor includes
a tidal volume monitor.
9. The system of claim 7, wherein the respiration monitor includes
a minute ventilation monitor.
10. The system of claim 1, wherein the cardiac activity monitor
includes an acceleration sensor, and the signal indicative of the
cardiac activity includes an acceleration signal.
11. The system of claim 1, 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.
12. The system of claim 1, 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.
13. The system of claim 12, wherein the at least one pressure
parameter includes mean arterial pressure.
14. The system of claim 12, wherein the at least one pressure
parameter includes a pulse pressure.
15. The system of claim 12, wherein the at least one pressure
parameter includes an end systolic pressure.
16. The system of claim 12, wherein the at least one pressure
parameter includes an end diastolic pressure.
17. The system of claim 1, 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.
18. The system of claim 1, 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.
19. The system of claim 1, 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.
20. The system of claim 1, further comprising an implantable
medical device, wherein the implantable medical device includes the
cardiac activity monitor and the baroreflex stimulator.
21. The system of claim 1, further comprising an implantable neural
stimulator (NS) device and an implantable cardiac stimulator,
wherein the implantable NS device includes the baroreflex
stimulator and the implantable cardiac stimulator includes the
cardiac activity monitor, and both the implantable cardiac
stimulator and the implantable NS device include transceivers to
wirelessly communicate with each other.
22. The system of claim 21, wherein the transceivers include a
telemetry coil.
23. The system of claim 1, wherein the stimulator is implantable,
the stimulator further comprising a lead adapted to be electrically
connected to the pulse generator and to be fed through a right
ventricle and into a pulmonary artery, the lead including the
electrode, the electrode to be positioned in the pulmonary artery
and to deliver the baroreflex stimulation signal to a baroreceptor
site in the pulmonary artery.
24. 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.
25. The baroreflex stimulator of claim 24, wherein the means for
modulating the baroreflex stimulation signal includes means for
modulating the baroreflex stimulation signal based on heart
rate.
26. The baroreflex stimulator of claim 24, wherein the means for
modulating the baroreflex stimulation signal includes means for
modulating the baroreflex stimulation signal based on
respiration.
27. The baroreflex stimulator of claim 26, wherein the means for
modulating the baroreflex stimulation signal based on respiration
includes means for modulating the baroreflex stimulation based on
tidal volume.
28. The baroreflex stimulator of claim 26, wherein the means for
modulating the baroreflex stimulation signal based on respiration
includes means for modulating the baroreflex stimulation based on
minute ventilation.
29. The baroreflex stimulator of claim 24, wherein the means for
modulating the baroreflex stimulation signal includes means for
modulating the baroreflex stimulation signal based on
acceleration.
30. The baroreflex stimulator of claim 24, wherein the stimulator
is implantable, the stimulator further comprising a lead adapted to
be electrically connected to the pulse generator, to be fed through
a right ventricle and into a pulmonary artery, and to deliver the
baroreflex stimulation signal to a baroreceptor site in the
pulmonary artery.
31. The baroreflex stimulator of claim 24, wherein the baroreflex
stimulation signal has an amplitude, and the means for modulating
the baroreflex stimulation signal includes means for adjusting the
amplitude of the baroreflex stimulation signal.
32. The baroreflex stimulator of claim 24, wherein the baroreflex
stimulation signal has a frequency, and the means for modulating
the baroreflex stimulation signal includes means for adjusting the
frequency of the baroreflex stimulation signal.
33. The baroreflex stimulator of claim 24, wherein the baroreflex
stimulation signal has a duty cycle, and the means for modulating
the baroreflex stimulation signal includes means for adjusting the
duty cycle of the baroreflex stimulation signal.
34. The baroreflex stimulator of claim 24, 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.
35. 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.
36. The method of claim 35, 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.
37. The method of claim 35, 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.
38. The method of claim 35, 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.
39. The method of claim 35, 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.
40. The method of claim 35, 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.
41. The method of claim 35, wherein: receiving a signal regarding
an activity level includes communicating with an implantable
cardiac stimulator to receive heart rate data acquired by the
implantable cardiac stimulator; and setting a baroreflex
stimulation level includes setting the baroreflex stimulation level
based on the heart rate data.
42. The method of claim 35, 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.
43. The method of claim 42, 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.
44. The method of claim 42, 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.
45. The method of claim 35, wherein: receiving a signal regarding
an activity level includes communicating with an implantable
cardiac stimulator to receive respiration data acquired by the
implantable cardiac stimulator; and setting a baroreflex
stimulation level includes setting the baroreflex stimulation level
based on the respiration data.
46. The method of claim 35, 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.
47. The method of claim 35, wherein: receiving a signal regarding
an activity level includes communicating with an implantable
cardiac stimulator to receive acceleration data acquired by the
implantable cardiac stimulator; and setting a baroreflex
stimulation level includes setting the baroreflex stimulation level
based on the acceleration data.
48. The method of claim 35, further comprising delivering
baroreflex stimulation through a lead adapted to be fed through a
right ventricle and pulmonary valve into a pulmonary artery.
49. 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.
50. The method of claim 49, wherein: determining an 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.
51. The method of claim 49, wherein: determining an 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.
52. The method of claim 49, 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.
53. The method of claim 49, 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.
54. The method of claim 49, wherein applying baroreflex stimulation
includes stimulating an afferent nerve using a cuff electrode.
55. The method of claim 49, wherein applying baroreflex stimulation
includes transvascularly stimulating an afferent nerve using an
intravascularly-fed electrode.
56. The method of claim 49, wherein applying baroreflex stimulation
includes stimulating a cardiac fat pad using an electrode in the
cardiac fat pad.
57. The method of claim 49, wherein applying baroreflex stimulation
includes transvascularly stimulating a cardiac fat pad using an
intravascularly-fed electrode.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] The following commonly assigned U.S. patent applications are
related, are all filed on the same date as the present application
and are all herein incorporated by reference in their entirety:
"Baroreflex Stimulation System to Reduce Hypertension," Ser.
No.______, filed on______ (Attorney Docket No. 279.675US1);
"Sensing With Compensation for Neural Stimulator," Ser. No.______,
filed on______ (Attorney Docket No. 279.677US1); "Implantable
Baroreflex Stimulator with Integrated Pressure Sensor," Ser.
No.______, filed on______ (Attorney Docket No. 279.678US1);
"Automatic Baroreflex Modulation Based on Cardiac Activity," Ser.
No.______, filed on______ (Attorney Docket No. 279.679US1);
"Automatic Baroreflex Modulation Responsive to Adverse Event," Ser.
No.______, filed on______ (Attorney Docket No. 279.680US1);
"Baroreflex Modulation to Gradually Increase Blood Pressure," Ser.
No.______, filed on______ (Attorney Docket No. 279.703US1);
"Baroreflex Stimulation to Treat Acute Myocardial Infarction," Ser.
No.______, filed on______ (Attorney Docket No. 279.705US1);
"Baropacing and Cardiac Pacing to Control Output," Ser. No.______,
filed on______ (Attorney Docket No. 279.706US1); "Baroreflex
Stimulation Synchronized to Circadian Rhythm," Ser. No.______,
filed on______ (Attorney Docket No. 279.707US1); "A Lead for
Stimulating the Baroreflex in the Pulmonary Artery," Ser.
No.______, filed on______ (Attorney Docket No. 279.694US1); and "A
Stimulation Lead for Stimulating the Baroreceptors in the Pulmonary
Artery," Ser. No.______, filed on______ (Attorney Docket No.
279.695US1).
TECHNICAL FIELD
[0002] This application relates generally to implantable medical
devices and, more particularly, to automatically modulating
baroreflex stimulation based on cardiac activity.
BACKGROUND
[0003] Implanting a chronic electrical stimulator, such as a
cardiac stimulator, to deliver medical therapy(ies) is known.
Examples of cardiac stimulators include implantable cardiac rhythm
management (CRM) device such as pacemakers, implantable cardiac
defibrillators (ICDs), and implantable devices capable of
performing pacing and defibrillating functions.
[0004] CRM devices are implantable devices that provide electrical
stimulation to selected chambers of the heart in order to treat
disorders of cardiac rhythm. An implantable pacemaker, for example,
is a CRM device that paces the heart with timed pacing pulses. If
functioning properly, the pacemaker makes up for the heart's
inability to pace itself at an appropriate rhythm in order to meet
metabolic demand by enforcing a minimum heart rate. Some CRM
devices synchronize pacing pulses delivered to different areas of
the heart in order to coordinate the contractions. Coordinated
contractions allow the heart to pump efficiently while providing
sufficient cardiac output.
[0005] Heart failure refers to a clinical syndrome in which cardiac
function causes a below normal cardiac output that can fall below a
level adequate to meet the metabolic demand of peripheral tissues.
Heart failure may present itself as congestive heart failure (CHF)
due to the accompanying venous and pulmonary congestion. Heart
failure can be due to a variety of etiologies such as ischemic
heart disease.
[0006] Hypertension is a cause of heart disease and other related
cardiac co-morbidities. Hypertension occurs when blood vessels
constrict. As a result, the heart works harder to maintain flow at
a higher blood pressure, which can contribute to heart failure. A
large segment of the general population, as well as a large segment
of patients implanted with pacemakers or defibrillators, suffer
from hypertension. The long term mortality as well as the quality
of life can be improved for this population if blood pressure and
hypertension can be reduced. Many patients who suffer from
hypertension do not respond to treatment, such as treatments
related to lifestyle changes and hypertension drugs.
[0007] A pressoreceptive region or field is capable of sensing
changes in pressure, such as changes in blood pressure.
Pressoreceptor regions are referred to herein as baroreceptors,
which generally include any sensors of pressure changes. For
example, baroreceptors include afferent nerves and further include
sensory nerve endings that are sensitive to the stretching of the
wall that results from increased blood pressure from within, and
function as the receptor of a central reflex mechanism that tends
to reduce the pressure. Baroreflex functions as a negative feedback
system, and relates to a reflex mechanism triggered by stimulation
of a baroreceptor. Increased pressure stretches blood vessels,
which in turn activates baroreceptors in the vessel walls.
Activation of baroreceptors naturally occurs through internal
pressure and stretching of the arterial wall, causing baroreflex
inhibition of sympathetic nerve activity (SNA) and a reduction in
systemic arterial pressure. An increase in baroreceptor activity
induces a reduction of SNA, which reduces blood pressure by
decreasing peripheral vascular resistance.
[0008] The general concept of stimulating afferent nerve trunks
leading from baroreceptors is known. For example, direct electrical
stimulation has been applied to the vagal nerve and carotid sinus.
Research has indicated that electrical stimulation of the carotid
sinus nerve can result in reduction of experimental hypertension,
and that direct electrical stimulation to the pressoreceptive
regions of the carotid sinus itself brings about reflex reduction
in experimental hypertension.
[0009] Electrical systems have been proposed to treat hypertension
in patients who do not otherwise respond to therapy involving
lifestyle changes and hypertension drugs, and possibly to reduce
drug dependency for other patients.
SUMMARY
[0010] Various aspects and embodiments of the present subject
matter use a parameter related to cardiac activity to automatically
modulate baroreceptor stimulation. The use of indices of cardiac
activity allows an implantable neural stimulator to respond to
changes in metabolic demand.
[0011] An aspect of the present subject matter relates to a system
for providing baroreflex stimulation. An embodiment of the system
comprises a cardiac activity monitor to sense cardiac activity and
provide a signal indicative of the cardiac activity, and a
baroreflex stimulator. The stimulator includes a pulse generator
and a modulator. The pulse generator provides a baroreflex
stimulation signal adapted to provide a baroreflex therapy. The
modulator receives the signal indicative of the cardiac activity
and modulates 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.
[0012] An aspect of the present subject matter relates to a
baroreflex stimulator. An embodiment of the stimulator comprises 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.
[0013] An aspect of the present subject matter relates to a method
for operating an implantable medical device. In an embodiment of
the method, a signal regarding an activity level is received, a
baroreflex stimulation level for a baroreflex stimulator of the
device is set based on the signal regarding the activity level.
[0014] According to one method embodiment, an activity level is
determined, a baroreflex stimulation level is set based on the
activity level, and baroreflex stimulation is applied at the
baroreflex stimulation level.
[0015] This Summary is an overview of some of the teachings of the
present application and not intended to be an exclusive or
exhaustive treatment of the present subject matter. Further details
about the present subject matter are found in the detailed
description and appended claims. Other aspects will be apparent to
persons skilled in the art upon reading and understanding the
following detailed description and viewing the drawings that form a
part thereof, each of which are not to be taken in a limiting
sense. The scope of the present invention is defined by the
appended claims and their equivalents.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIGS. 1A and 1B illustrate neural mechanisms for peripheral
vascular control.
[0017] FIGS. 2A-2C illustrate a heart.
[0018] FIG. 3 illustrates baroreceptors and afferent nerves in the
area of the carotid sinuses and aortic arch.
[0019] FIG. 4 illustrates baroreceptors in and around the pulmonary
artery.
[0020] FIG. 5 illustrates baroreceptor fields in the aortic arch,
the ligamentum arteriosum and the trunk of the pulmonary
artery.
[0021] FIG. 6 illustrates a known relationship between respiration
and blood pressure when the baroreflex is stimulated.
[0022] FIG. 7 illustrates a blood pressure response to carotid
nerve stimulation in a hypertensive dog during 6 months of
intermittent carotid nerve stimulation.
[0023] FIG. 8 illustrates a system including an implantable medical
device (IMD) and a programmer, according to various embodiments of
the present subject matter.
[0024] FIG. 9 illustrates an implantable medical device (IMD) such
as shown in the system of FIG. 8, according to various embodiments
of the present subject matter.
[0025] FIGS. 10A-10C illustrate a baroreceptor stimulation lead
with an integrated pressure sensor (IPS), according to various
embodiments of the present subject matter.
[0026] FIG. 11 illustrates an implantable medical device (IMD) such
as shown in FIG. 8 having a neural stimulator (NS) component and
cardiac rhythm management (CRM) component, according to various
embodiments of the present subject matter.
[0027] FIG. 12 illustrates a system including a programmer, an
implantable neural stimulator (NS) device and an implantable
cardiac rhythm management (CRM) device, according to various
embodiments of the present subject matter.
[0028] FIG. 13 illustrates an implantable neural stimulator (NS)
device such as shown in the system of FIG. 12, according to various
embodiments of the present subject matter.
[0029] FIG. 14 illustrates an implantable cardiac rhythm management
(CRM) device such as shown in the system of FIG. 12, according to
various embodiments of the present subject matter.
[0030] FIG. 15 illustrates a programmer such as illustrated in the
systems of FIGS. 8 and 12 or other external device to communicate
with the implantable medical device(s), according to various
embodiments of the present subject matter.
[0031] FIGS. 16A-16D illustrate a system and methods to prevent
interference between electrical stimulation from a neural
stimulator (NS) device and sensing by a cardiac rhythm management
(CRM) device, according to various embodiments of the present
subject matter.
[0032] FIG. 17 illustrates a system to modulate baroreflex
stimulation, according to various embodiments of the present
subject matter.
[0033] FIGS. 18A-18C illustrate methods for modulating baroreceptor
stimulation based on a cardiac activity parameter, according to
various embodiments of the present subject matter.
[0034] FIGS. 19A-19B illustrate methods for modulating baroreceptor
stimulation based on a respiration parameter, according to various
embodiments of the present subject matter.
[0035] FIGS. 20A-20B illustrate methods for modulating baroreceptor
stimulation based on detection of an adverse event, according to
various embodiments of the present subject matter.
[0036] FIGS. 21A-21E illustrate circadian rhythm.
[0037] FIG. 22 illustrates a method for modulating baroreceptor
stimulation based on circadian rhythm, according to various
embodiments of the present subject matter.
[0038] FIG. 23A-B illustrate methods for modulating baroreceptor
stimulation based on a cardiac output parameter, according to
various embodiments of the present subject matter.
[0039] FIG. 24 illustrates a method for modulating baroreceptor
stimulation to reverse remodel stiffening, according to various
embodiments of the present subject matter.
[0040] FIGS. 25A-25B illustrate a system and method to detect
myocardial infarction and perform baropacing in response to the
detected myocardial infarction, according to various embodiments of
the present subject matter.
DETAILED DESCRIPTION
[0041] The following detailed description of the present subject
matter refers to the accompanying drawings which show, by way of
illustration, specific aspects and embodiments in which the present
subject matter may be practiced. These embodiments are described in
sufficient detail to enable those skilled in the art to practice
the present subject matter. Other embodiments may be utilized and
structural, logical, and electrical changes may be made without
departing from the scope of the present subject matter. References
to "an", "one", or "various" embodiments in this disclosure are not
necessarily to the same embodiment, and such references contemplate
more than one embodiment. The following detailed description is,
therefore, not to be taken in a limiting sense, and the scope is
defined only by the appended claims, along with the full scope of
legal equivalents to which such claims are entitled.
Hypertension and Baroreflex Physiology
[0042] A brief discussion of hypertension and the physiology
related to baroreceptors is provided to assist the reader with
understanding this disclosure. This brief discussion introduces
hypertension, the autonomic nervous system, and baroreflex.
[0043] Hypertension is a cause of heart disease and other related
cardiac co-morbidities. Hypertension generally relates to high
blood pressure, such as a transitory or sustained elevation of
systemic arterial blood pressure to a level that is likely to
induce cardiovascular damage or other adverse consequences.
Hypertension has been arbitrarily defined as a systolic blood
pressure above 140 mm Hg or a diastolic blood pressure above 90 mm
Hg. Hypertension occurs when blood vessels constrict. As a result,
the heart works harder to maintain flow at a higher blood pressure.
Consequences of uncontrolled hypertension include, but are not
limited to, retinal vascular disease and stroke, left ventricular
hypertrophy and failure, myocardial infarction, dissecting
aneurysm, and renovascular disease.
[0044] The automatic nervous system (ANS) regulates "involuntary"
organs, while the contraction of voluntary (skeletal) muscles is
controlled by somatic motor nerves. Examples of involuntary organs
include respiratory and digestive organs, and also include blood
vessels and the heart. Often, the ANS functions in an involuntary,
reflexive manner to regulate glands, to regulate muscles in the
skin, eye, stomach, intestines and bladder, and to regulate cardiac
muscle and the muscle around blood vessels, for example.
[0045] The ANS includes, but is not limited to, the sympathetic
nervous system and the parasympathetic nervous system. The
sympathetic nervous system is affiliated with stress and the "fight
or flight response" to emergencies. Among other effects, the "fight
or flight response" increases blood pressure and heart rate to
increase skeletal muscle blood flow, and decreases digestion to
provide the energy for "fighting or fleeing." The parasympathetic
nervous system is affiliated with relaxation and the "rest and
digest response" which, among other effects, decreases blood
pressure and heart rate, and increases digestion to conserve
energy. The ANS maintains normal internal function and works with
the somatic nervous system.
[0046] The subject matter of this disclosure generally refers to
the effects that the ANS has on the heart rate and blood pressure,
including vasodilation and vasoconstriction. The heart rate and
force is increased when the sympathetic nervous system is
stimulated, and is decreased when the sympathetic nervous system is
inhibited (the parasympathetic nervous system is stimulated). FIGS.
1A and 1B illustrate neural mechanisms for peripheral vascular
control. FIG. 1A generally illustrates afferent nerves to vasomotor
centers. An afferent nerve conveys impulses toward a nerve center.
A vasomotor center relates to nerves that dilate and constrict
blood vessels to control the size of the blood vessels. FIG. 1B
generally illustrates efferent nerves from vasomotor centers. An
efferent nerve conveys impulses away from a nerve center.
[0047] Stimulating the systematic and parasympathetic nervous
systems can have effects other than heart rate and blood pressure.
For example, stimulating the sympathetic nervous system dilates the
pupil, reduces saliva and mucus production, relaxes the bronchial
muscle, reduces the successive waves of involuntary contraction
(peristalsis) of the stomach and the motility of the stomach,
increases the conversion of glycogen to glucose by the liver,
decreases urine secretion by the kidneys, and relaxes the wall and
closes the sphincter of the bladder. Stimulating the
parasympathetic nervous system (inhibiting the sympathetic nervous
system) constricts the pupil, increases saliva and mucus
production, contracts the bronchial muscle, increases secretions
and motility in the stomach and large intestine, and increases
digestion in the small intention, increases urine secretion, and
contracts the wall and relaxes the sphincter of the bladder. The
functions associated with the sympathetic and parasympathetic
nervous systems are many and can be complexly integrated with each
other. Thus, an indiscriminate stimulation of the sympathetic
and/or parasympathetic nervous systems to achieve a desired
response, such as vasodilation, in one physiological system may
also result in an undesired response in other physiological
systems.
[0048] Baroreflex is a reflex triggered by stimulation of a
baroreceptor. A baroreceptor includes any sensor of pressure
changes, such as sensory nerve endings in the wall of the auricles
of the heart, cardiac fat pads, vena cava, aortic arch and carotid
sinus, that is sensitive to stretching of the wall resulting from
increased pressure from within, and that functions as the receptor
of the central reflex mechanism that tends to reduce that pressure.
Additionally, a baroreceptor includes afferent nerve trunks, such
as the vagus, aortic and carotid nerves, leading from the sensory
nerve endings. Stimulating baroreceptors inhibits sympathetic nerve
activity (stimulates the parasympathetic nervous system) and
reduces systemic arterial pressure by decreasing peripheral
vascular resistance and cardiac contractility. Baroreceptors are
naturally stimulated by internal pressure and the stretching of the
arterial wall.
[0049] Some aspects of the present subject matter locally stimulate
specific nerve endings in arterial walls rather than stimulate
afferent nerve trunks in an effort to stimulate a desire response
(e.g. reduced hypertension) while reducing the undesired effects of
indiscriminate stimulation of the nervous system. For example, some
embodiments stimulate baroreceptor sites in the pulmonary artery.
Some embodiments of the present subject matter involve stimulating
either baroreceptor sites or nerve endings in the aorta, the
chambers of the heart, the fat pads of the heart, and some
embodiments of the present subject matter involve stimulating an
afferent nerve trunk, such as the vagus, carotid and aortic nerves.
Some embodiments stimulate afferent nerve trunks using a cuff
electrode, and some embodiments stimulate afferent nerve trunks
using an intravascular lead positioned in a blood vessel proximate
to the nerve, such that the electrical stimulation passes through
the vessel wall to stimulate the afferent nerve trunk.
[0050] FIGS. 2A-2C illustrate a heart. As illustrated in FIG. 2A,
the heart 201 includes a superior vena cava 202, an aortic arch
203, and a pulmonary artery 204, and is useful to provide a
contextual relationship with the illustrations in FIGS. 3-5. As is
discussed in more detail below, the pulmonary artery 204 includes
baroreceptors. A lead is capable of being intravascularly inserted
through a peripheral vein and through the tricuspid valve into the
right ventricle of the heart (not expressly shown in the figure)
similar to a cardiac pacemaker lead, and continue from the right
ventricle through the pulmonary valve into the pulmonary artery. A
portion of the pulmonary artery and aorta are proximate to each
other. Various embodiments stimulate baroreceptors in the aorta
using a lead intravascularly positioned in the pulmonary artery.
Thus, according to various aspects of the present subject matter,
the baroreflex is stimulated in or around the pulmonary artery by
at least one electrode intravascularly inserted into the pulmonary
artery. Alternatively, a wireless stimulating device, with or
without pressure sensing capability, may be positioned via catheter
into the pulmonary artery. Control of stimulation and/or energy for
stimulation may be supplied by another implantable or external
device via ultrasonic, electromagnetic or a combination thereof.
Aspects of the present subject matter provide a relatively
noninvasive surgical technique to implant a baroreceptor stimulator
intravascularly into the pulmonary artery.
[0051] FIGS. 2B-2C illustrate the right side and left side of the
heart, respectively, and further illustrate cardiac fat pads which
have nerve endings that function as baroreceptor sites. FIG. 2B
illustrates the right atrium 267, right ventricle 268, sinoatrial
node 269, superior vena cava 202, inferior vena cava 270, aorta
271, right pulmonary veins 272, and right pulmonary artery 273.
FIG. 2B also illustrates a cardiac fat pad 274 between the superior
vena cava and aorta. Baroreceptor nerve endings in the cardiac fat
pad 274 are stimulated in some embodiments using an electrode
screwed into the fat pad, and are stimulated in some embodiments
using an intravenously-fed lead proximately positioned to the fat
pad in a vessel such as the right pulmonary artery or superior vena
cava, for example. FIG. 2C illustrates the left atrium 275, left
ventricle 276, right atrium 267, right ventricle 268, superior vena
cava 202, inferior vena cava 270, aorta 271, right pulmonary veins
272, left pulmonary vein 277, right pulmonary artery 273, and
coronary sinus 278. FIG. 2C also illustrates a cardiac fat pad 279
located proximate to the right cardiac veins and a cardiac fat pad
280 located proximate to the inferior vena cava and left atrium.
Baroreceptor nerve endings in the fat pad 279 are stimulated in
some embodiments using an electrode screwed into the fat pad 279,
and are stimulated in some embodiments using an intravenously-fed
lead proximately positioned to the fat pad in a vessel such as the
right pulmonary artery 273 or right pulmonary vein 272, for
example. Baroreceptors in the 280 are stimulated in some
embodiments using an electrode screwed into the fat pad, and are
stimulated in some embodiments using an intravenously-fed lead
proximately positioned to the fat pad in a vessel such as the
inferior vena cava 270 or coronary sinus or a lead in the left
atrium 275, for example.
[0052] FIG. 3 illustrates baroreceptors in the area of the carotid
sinuses 305, aortic arch 303 and pulmonary artery 304. The aortic
arch 303 and pulmonary artery 304 were previously illustrated with
respect to the heart in FIG. 2A. As illustrated in FIG. 3, the
vagus nerve 306 extends and provides sensory nerve endings 307 that
function as baroreceptors in the aortic arch 303, in the carotid
sinus 305 and in the common carotid artery 310. The
glossopharyngeal nerve 308 provides nerve endings 309 that function
as baroreceptors in the carotid sinus 305. These nerve endings 307
and 309, for example, are sensitive to stretching of the wall
resulting from increased pressure from within. Activation of these
nerve endings reduce pressure. Although not illustrated in the
figures, the fat pads and the atrial and ventricular chambers of
the heart also include baroreceptors. Cuffs have been placed around
afferent nerve trunks, such as the vagal nerve, leading from
baroreceptors to vasomotor centers to stimulate the baroreflex.
According to various embodiments of the present subject matter,
afferent nerve trunks can be stimulated using a cuff or
intravascularly-fed lead positioned in a blood vessel proximate to
the afferent nerves.
[0053] FIG. 4 illustrates baroreceptors in and around a pulmonary
artery 404. The superior vena cava 402 and the aortic arch 403 are
also illustrated. As illustrated, the pulmonary artery 404 includes
a number of baroreceptors 411, as generally indicated by the dark
area. Furthermore, a cluster of closely spaced baroreceptors is
situated near the attachment of the ligamentum arteriosum 412. FIG.
4 also illustrates the right ventricle 413 of the heart, and the
pulmonary valve 414 separating the right ventricle 413 from the
pulmonary artery 404. According to various embodiments of the
present subject matter, a lead is inserted through a peripheral
vein and threaded through the tricuspid valve into the right
ventricle, and from the right ventricle 413 through the pulmonary
valve 414 and into the pulmonary artery 404 to stimulate
baroreceptors in and/or around the pulmonary artery. In various
embodiments, for example, the lead is positioned to stimulate the
cluster of baroreceptors near the ligamentum arteriosum 412. FIG. 5
illustrates baroreceptor fields 511 in the aortic arch 503, near
the ligamentum arteriosum 512 and the trunk of the pulmonary artery
504. Some embodiments position the lead in the pulmonary artery to
stimulate baroreceptor sites in the aorta and/or fat pads, such as
are illustrated in FIGS. 2B-2C.
[0054] FIG. 6 illustrates a known relationship between respiration
615 and blood pressure 616 when the left aortic nerve is
stimulated. When the nerve is stimulated at 617, the blood pressure
616 drops, and the respiration 615 becomes faster and deeper, as
illustrated by the higher frequency and amplitude of the
respiration waveform. The respiration and blood pressure appear to
return to the pre-stimulated state in approximately one to two
minutes after the stimulation is removed. Various embodiments of
the present subject matter use this relationship between
respiration and blood pressure by using respiration as a surrogate
parameter for blood pressure.
[0055] FIG. 7 illustrates a known blood pressure response to
carotid nerve stimulation in a hypertensive dog during 6 months of
intermittent carotid nerve stimulation. The figure illustrates that
the blood pressure of a stimulated dog 718 is significantly less
than the blood pressure of a control dog 719 that also has high
blood pressure. Thus, intermittent stimulation is capable of
triggering the baroreflex to reduce high blood pressure.
Baroreflex Stimulator Systems
[0056] Various embodiments of the present subject matter relate to
baroreflex stimulator systems. Such baroreflex stimulation systems
are also referred to herein as neural stimulator (NS) devices or
components. Examples of neural stimulators include
anti-hypertension (AHT) devices or AHT components that are used to
treat hypertension. Various embodiments of the present subject
matter include stand-alone implantable baroreceptor stimulator
systems, include implantable devices that have integrated NS and
cardiac rhythm management (CRM) components, and include systems
with at least one implantable NS device and an implantable CRM
device capable of communicating with each other either wirelessly
or through a wire lead connecting the implantable devices.
Integrating NS and CRM functions that are either performed in the
same or separate devices improves aspects of the NS therapy and
cardiac therapy by allowing these therapies to work together
intelligently.
[0057] FIG. 8 illustrates a system 820 including an implantable
medical device (IMD) 821 and a programmer 822, according to various
embodiments of the present subject matter. Various embodiments of
the IMD 821 include neural stimulator functions only, and various
embodiments include a combination of NS and CRM functions. Some
embodiments of the neural stimulator provide AHT functions. The
programmer 822 and the IMD 821 are capable of wirelessly
communicating data and instructions. In various embodiments, for
example, the programmer 822 and IMD 821 use telemetry coils to
wirelessly communicate data and instructions. Thus, the programmer
can be used to adjust the programmed therapy provided by the IMD
821, and the IMD can report device data (such as battery and lead
resistance) and therapy data (such as sense and stimulation data)
to the programmer using radio telemetry, for example. According to
various embodiments, the IMD 821 stimulates baroreceptors to
provide NS therapy such as AHT therapy. Various embodiments of the
IMD 821 stimulate baroreceptors in the pulmonary artery using a
lead fed through the right ventricle similar to a cardiac pacemaker
lead, and further fed into the pulmonary artery. According to
various embodiments, the IMD 821 includes a sensor to sense ANS
activity. Such a sensor can be used to perform feedback in a closed
loop control system. For example, various embodiments sense
surrogate parameters, such as respiration and blood pressure,
indicative of ANS activity. According to various embodiments, the
IMD further includes cardiac stimulation capabilities, such as
pacing and defibrillating capabilities in addition to the
capabilities to stimulate baroreceptors and/or sense ANS
activity.
[0058] FIG. 9 illustrates an implantable medical device (IMD) 921
such as the IMD 821 shown in the system 820 of FIG. 8, according to
various embodiments of the present subject matter. The illustrated
IMD 921 performs NS functions. Some embodiments of the illustrated
IMD 921 performs an AHT function, and thus illustrates an
implantable AHT device. The illustrated device 921 includes
controller circuitry 923 and a memory 924. The controller circuitry
923 is capable of being implemented using hardware, software, and
combinations of hardware and software. For example, according to
various embodiments, the controller circuitry 923 includes a
processor to perform instructions embedded in the memory 924 to
perform functions associated with NS therapy such as AHT therapy.
For example, the illustrated device 921 further includes a
transceiver 925 and associated circuitry for use to communicate
with a programmer or another external or internal device. Various
embodiments have wireless communication capabilities. For example,
some transceiver embodiments use a telemetry coil to wirelessly
communicate with a programmer or another external or internal
device.
[0059] The illustrated device 921 further includes baroreceptor
stimulation circuitry 926. Various embodiments of the device 921
also includes sensor circuitry 927. One or more leads are able to
be connected to the sensor circuitry 927 and baroreceptor
stimulation circuitry 926. The baroreceptor stimulation circuitry
926 is used to apply electrical stimulation pulses to desired
baroreceptors sites, such as baroreceptor sites in the pulmonary
artery, through one or more stimulation electrodes. The sensor
circuitry 927 is used to detect and process ANS nerve activity
and/or surrogate parameters such as blood pressure, respiration and
the like, to determine the ANS activity.
[0060] According to various embodiments, the stimulator circuitry
926 includes modules to set any one or any combination of two or
more of the following pulse features: the amplitude 928 of the
stimulation pulse, the frequency 929 of the stimulation pulse, the
burst frequency 930 or duty cycle of the pulse, and the wave
morphology 931 of the pulse. Examples of wave morphology include a
square wave, triangle wave, sinusoidal wave, and waves with desired
harmonic components to mimic white noise such as is indicative of
naturally-occurring baroreflex stimulation.
[0061] FIGS. 10A-10C illustrate a baroreceptor stimulation lead
with an integrated pressure sensor (IPS), according to various
embodiments of the present subject matter. Although not drawn to
scale, these illustrated leads 1032A, 1032B and 1032C include an
IPS 1033 with a baroreceptor stimulator electrode 1034 to monitor
changes in blood pressure, and thus the effect of the baroreceptor
stimulation. These lead illustrations should not be read as
limiting other aspects and embodiments of the present subject
matter. In various embodiments, for example, micro-electrical
mechanical systems (MEMS) technology is used to sense the blood
pressure. Some sensor embodiments determine blood pressure based on
a displacement of a membrane.
[0062] FIGS. 10A-10C illustrate an IPS on a lead. Some embodiments
implant an IPS in an IMD or NS device. The stimulator and sensor
functions can be integrated, even if the stimulator and sensors are
located in separate leads or positions.
[0063] The lead 1032A illustrated in FIG. 10A includes a
distally-positioned baroreceptor stimulator electrode 1034 and an
IPS 1033. This lead, for example, is capable of being
intravascularly introduced to stimulate a baroreceptor site, such
as the baroreceptor sites in the pulmonary artery, aortic arch,
ligamentum arteriosum, the coronary sinus, in the atrial and
ventricular chambers, and/or in cardiac fat pads.
[0064] The lead 1032B illustrated in FIG. 10B includes a tip
electrode 1035, a first ring electrode 1036, second ring electrode
1034, and an IPS 1033. This lead may be intravascularly inserted
into or proximate to chambers of the heart and further positioned
proximate to baroreceptor sites such that at least some of the
electrodes 1035, 1036 and 1034 are capable of being used to pace or
otherwise stimulate the heart, and at least some of the electrodes
are capable of stimulating at least one baroreceptor site. The IPS
1033 is used to sense the blood pressure. In various embodiments,
the IPS is used to sense the blood pressure in the vessel proximate
to the baroreceptor site selected for stimulation.
[0065] The lead 1032C illustrated in FIG. 10C includes a
distally-positioned baroreceptor stimulator electrode 1034, an IPS
1033 and a ring electrode 1036. This lead 1032C may, for example,
be intravascularly inserted into the right atrium and ventricle,
and then through the pulmonary valve into the pulmonary artery.
Depending on programming in the device, the electrode 1036 can be
used to pace and/or sense cardiac activity, such as that which may
occur within the right ventricle, and the electrode 1034 and IPS
1033 are located near baroreceptors in or near the pulmonary artery
to stimulate and sense, either directly or indirectly through
surrogate parameters, baroreflex activity.
[0066] Thus, various embodiments of the present subject matter
provide an implantable NS device that automatically modulates
baroreceptor stimulation using an IPS. Integrating the pressure
sensor into the lead provides localized feedback for the
stimulation. This localized sensing improves feedback control. For
example, the integrated sensor can be used to compensate for
inertia of the baroreflex such that the target is not continuously
overshot. According to various embodiments, the device monitors
pressure parameters such as mean arterial pressure, systolic
pressure, diastolic pressure and the like. As mean arterial
pressure increases or remains above a programmable target pressure,
for example, the device stimulates baroreceptors at an increased
rate to reduce blood pressure and control hypertension. As mean
arterial pressure decreases towards the target pressure, the device
responds by reducing baroreceptor stimulation. In various
embodiments, the algorithm takes into account the current metabolic
state (cardiac demand) and adjusts neural stimulation accordingly.
A NS device having an IPS is able to automatically modulate
baroreceptor stimulation, which allows an implantable NS device to
determine the level of hypertension in the patient and respond by
delivering the appropriate level of therapy. However, it is noted
that other sensors, including sensors that do not reside in an NS
or neural stimulator device, can be used to provide close loop
feedback control.
[0067] FIG. 11 illustrates an implantable medical device (IMD) 1121
such as shown at 821 in FIG. 8 having an anti-hypertension (AHT)
component 1137 and cardiac rhythm management (CRM) component 1138,
according to various embodiments of the present subject matter. The
illustrated device 1121 includes a controller 1123 and a memory
1124. According to various embodiments, the controller 1123
includes hardware, software, or a combination of hardware and
software to perform the baroreceptor stimulation and CRM functions.
For example, the programmed therapy applications discussed in this
disclosure are capable of being stored as computer-readable
instructions embodied in memory and executed by a processor.
According to various embodiments, the controller 1123 includes a
processor to execute instructions embedded in memory to perform the
baroreceptor stimulation and CRM functions. The illustrated device
1121 further includes a transceiver and associated circuitry for
use to communicate with a programmer or another external or
internal device. Various embodiments include a telemetry coil.
[0068] The CRM therapy section 1138 includes components, under the
control of the controller, to stimulate a heart and/or sense
cardiac signals using one or more electrodes. The CRM therapy
section includes a pulse generator 1139 for use to provide an
electrical signal through an electrode to stimulate a heart, and
further includes sense circuitry 1140 to detect and process sensed
cardiac signals. An interface 1141 is generally illustrated for use
to communicate between the controller 1123 and the pulse generator
1139 and sense circuitry 1140. Three electrodes are illustrated as
an example for use to provide CRM therapy. However, the present
subject matter is not limited to a particular number of electrode
sites. Each electrode may include its own pulse generator and sense
circuitry. However, the present subject matter is not so limited.
The pulse generating and sensing functions can be multiplexed to
function with multiple electrodes.
[0069] The NS therapy section 1137 includes components, under the
control of the controller, to stimulate a baroreceptor and/or sense
ANS parameters associated with nerve activity or surrogates of ANS
parameters such as blood pressure and respiration. Three interfaces
1142 are illustrated for use to provide ANS therapy. However, the
present subject matter is not limited to a particular number
interfaces, or to any particular stimulating or sensing functions.
Pulse generators 1143 are used to provide electrical pulses to an
electrode for use to stimulate a baroreceptor site. According to
various embodiments, the pulse generator includes circuitry to set,
and in some embodiments change, the amplitude of the stimulation
pulse, the frequency of the stimulation pulse, the burst frequency
of the pulse, and the morphology of the pulse such as a square
wave, triangle wave, sinusoidal wave, and waves with desired
harmonic components to mimic white noise or other signals. Sense
circuits 1144 are used to detect and process signals from a sensor,
such as a sensor of nerve activity, blood pressure, respiration,
and the like. The interfaces 1142 are generally illustrated for use
to communicate between the controller 1123 and the pulse generator
1143 and sense circuitry 1144. Each interface, for example, may be
used to control a separate lead. Various embodiments of the NS
therapy section only include a pulse generator to stimulate
baroreceptors. For example, the NS therapy section provides AHT
therapy.
[0070] An aspect of the present subject matter relates to a
chronically-implanted stimulation system specially designed to
treat hypertension by monitoring blood pressure and stimulating
baroreceptors to activate the baroreceptor reflex and inhibit
sympathetic discharge from the vasomotor center. Baroreceptors are
located in various anatomical locations such as the carotid sinus
and the aortic arch. Other baroreceptor locations include the
pulmonary artery, including the ligamentum arteriosum, and sites in
the atrial and ventricular chambers. In various embodiments, the
system is integrated into a pacemaker/defibrillator or other
electrical stimulator system. Components of the system include a
high-frequency pulse generator, sensors to monitor blood pressure
or other pertinent physiological parameters, leads to apply
electrical stimulation to baroreceptors, algorithms to determine
the appropriate time to administer stimulation, and algorithms to
manipulate data for display and patient management.
[0071] Various embodiments relate to a system that seeks to deliver
electrically mediated NS therapy, such as AHT therapy, to patients.
Various embodiments combine a "stand-alone" pulse generator with a
minimally invasive, unipolar lead that directly stimulates
baroreceptors in the vicinity of the heart, such as in the
pulmonary artery. This embodiment is such that general medical
practitioners lacking the skills of specialist can implant it.
Various embodiments incorporate a simple implanted system that can
sense parameters indicative of blood pressure. This system adjusts
the therapeutic output (waveform amplitude, frequency, etc.) so as
to maintain a desired quality of life. In various embodiments, an
implanted system includes a pulse generating device and lead
system, the stimulating electrode of which is positioned near
endocardial baroreceptor tissues using transvenous implant
technique(s). Another embodiment includes a system that combines NS
therapy with traditional bradyarrhythmia, tachyarrhythmia, and/or
congestive heart failure (CHF) therapies. Some embodiments use an
additional "baroreceptor lead" that emerges from the device header
and is paced from a modified traditional pulse generating system.
In another embodiment, a traditional CRM lead is modified to
incorporate proximal electrodes that are naturally positioned near
baroreceptor sites. With these leads, distal electrodes provide CRM
therapy and proximate electrodes stimulate baroreceptors.
[0072] A system according to these embodiments can be used to
augment partially successful treatment strategies. As an example,
undesired side effects may limit the use of some pharmaceutical
agents. The combination of a system according to these embodiments
with reduced drug doses may be particularly beneficial.
[0073] According to various embodiments, the lead(s) and the
electrode(s) on the leads are physically arranged with respect to
the heart in a fashion that enables the electrodes to properly
transmit pulses and sense signals from the heart, and with respect
to baroreceptors to stimulate the baroreflex. As there may be a
number of leads and a number of electrodes per lead, the
configuration can be programmed to use a particular electrode or
electrodes. According to various embodiments, the baroreflex is
stimulated by stimulating afferent nerve trunks.
[0074] FIG. 12 illustrates a system 1220 including a programmer
1222, an implantable neural stimulator (NS) device 1237 and an
implantable cardiac rhythm management (CRM) device 1238, according
to various embodiments of the present subject matter. Various
aspects involve a method for communicating between an NS device
1237, such as an AHT device, and a CRM device 1238 or other cardiac
stimulator. In various embodiments, this communication allows one
of the devices 1237 or 1238 to deliver more appropriate therapy
(i.e. more appropriate NS therapy or CRM therapy) based on data
received from the other device. Some embodiments provide on-demand
communications. In various embodiments, this communication allows
each of the devices 1237 and 1238 to deliver more appropriate
therapy (i.e. more appropriate NS therapy and CRM therapy) based on
data received from the other device. The illustrated NS device 1237
and the CRM device 1238 are capable of wirelessly communicating
with each other, and the programmer is capable of wirelessly
communicating with at least one of the NS and the CRM devices 1237
and 1238. For example, various embodiments use telemetry coils to
wirelessly communicate data and instructions to each other. In
other embodiments, communication of data and/or energy is by
ultrasonic means.
[0075] In some embodiments, the NS device 1237 stimulates the
baroreflex to provide NS therapy, and senses ANS activity directly
or using surrogate parameters, such as respiration and blood
pressure, indicative of ANS activity. The CRM device 1238 includes
cardiac stimulation capabilities, such as pacing and defibrillating
capabilities. Rather than providing wireless communication between
the NS and CRM devices 1237 and 1238, various embodiments provide a
communication cable or wire, such as an intravenously-fed lead, for
use to communicate between the NS device 1237 and the CRM device
1238.
[0076] FIG. 13 illustrates an implantable neural stimulator (NS)
device 1337 such as shown at 1237 in the system of FIG. 12,
according to various embodiments of the present subject matter.
FIG. 14 illustrates an implantable cardiac rhythm management (CRM)
device 1438 such as shown at 1238 in the system of FIG. 12,
according to various embodiments of the present subject matter.
Functions of the components for the NS device 1337 were previously
discussed with respect to FIGS. 9 and 11 (the NS component 1137),
and functions of the components for the CRM device 1238 were
previously discussed with respect to FIG. 11 (the CRM component
1138). In the interest of brevity, these discussions with respect
to the NS and CRM functions are not repeated here. Various
embodiments of the NS and CRM devices include wireless transceivers
1325 and 1425, respectively, to wirelessly communicate with each
other. Various embodiments of the NS and CRM devices include a
telemetry coil or ultrasonic transducer to wirelessly communicate
with each other.
[0077] According to various embodiments, for example, the NS device
is equipped with a telemetry coil, allowing data to be exchanged
between it and the CRM device, allowing the NS device to modify
therapy based on electrophysiological parameters such as heart
rate, minute ventilation, atrial activation, ventricular
activation, and cardiac events. In addition, the CRM device
modifies therapy based on data received from the NS device, such as
mean arterial pressure, systolic and diastolic pressure, and
baroreceptors stimulation rate.
[0078] Some NS device embodiments are able to be implanted in
patients with existing CRM devices, such that the functionality of
the NS device is enhanced by receiving physiological data that is
acquired by the CRM device. The functionality of two or more
implanted devices is enhanced by providing communication
capabilities between or among the implanted devices. In various
embodiments, the functionality is further enhanced by designing the
devices to wirelessly communicate with each other.
[0079] FIG. 15 illustrates a programmer 1522, such as the
programmer 822 and 1222 illustrated in the systems of FIGS. 8 and
12, or other external device to communicate with the implantable
medical device(s) 1237 and/or 1238, according to various
embodiments of the present subject matter. An example of another
external device includes Personal Digital Assistants (PDAs) or
personal laptop and desktop computers in an Advanced Patient
Management (APM) system. The illustrated device 1522 includes
controller circuitry 1545 and a memory 1546. The controller
circuitry 1545 is capable of being implemented using hardware,
software, and combinations of hardware and software. For example,
according to various embodiments, the controller circuitry 1545
includes a processor to perform instructions embedded in the memory
1546 to perform a number of functions, including communicating data
and/or programming instructions to the implantable devices. The
illustrated device 1522 further includes a transceiver 1547 and
associated circuitry for use to communicate with an implantable
device. Various embodiments have wireless communication
capabilities. For example, various embodiments of the transceiver
1547 and associated circuitry include a telemetry coil for use to
wirelessly communicate with an implantable device. The illustrated
device 1522 further includes a display 1548, input/output (I/O)
devices 1549 such as a keyboard or mouse/pointer, and a
communications interface 1550 for use to communicate with other
devices, such as over a communication network.
Programmed Therapy Applications
[0080] NS and/or CRM functions of a system, whether implemented in
two separate and distinct implantable devices or integrated as
components into one implantable device, includes processes for
performing NS and/or CRM therapy or portions of the therapy. In
some embodiments, the NS therapy provides AHT therapy. These
processes can be performed by a processor executing
computer-readable instructions embedded in memory, for example.
These therapies include a number of applications, which have
various processes and functions, some of which are identified and
discussed below. The processes and functions of these therapies are
not necessarily mutually exclusive, as some embodiments of the
present subject matter include combinations of two or more of the
below-identified processes and functions.
[0081] Accounting For Neural Stimulation To Accurately Sense
Signals
[0082] FIGS. 16A-16D illustrate a system and methods to prevent
interference between electrical stimulation from an neural
stimulator (NS) device and sensing by a cardiac rhythm management
(CRM) device, according to various embodiments of the present
subject matter. Neural stimulation is accounted for to improve the
ability to sense signals, and thus reduce or eliminate false
positives associated with detecting a cardiac event. The NS device
includes an AHT device in some embodiments. For example, the NS
device communicates with and prevents or otherwise compensates for
baroreflex stimulation such that the CRM device does not
unintentionally react to the baroreflex stimulation, according to
some embodiments. Some embodiments automatically synchronize the
baroreflex stimulation with an appropriate refraction in the heart.
For example, some systems automatically synchronize stimulation of
baroreceptors in or around the pulmonary artery with atrial
activation. Thus, the functions of the CRM device are not adversely
affected by detecting far-field noise generated by the baroreflex
stimulation, even when the baroreflex stimulations are generated
near the heart and the CRM sensors that detect the cardiac
electrical activation.
[0083] FIG. 16A generally illustrates a system 1654 that includes
NS functions 1651 (such as may be performed by a NS device or a NS
component in an integrated NS/CRM device), CRM functions 1652 (such
as may be performed by a CRM device or a CRM component in an
integrated NS/CRM device) and capabilities to communicate 1653
between the NS and CRM functions. The illustrated communication is
bidirectional wireless communication. However, the present subject
matter also contemplates unidirectional communication, and further
contemplates wired communication. Additionally, the present subject
matter contemplates that the NS and CRM functions 1651 and 1652 can
be integrated into a single implantable device such that the
communication signal is sent and received in the device, or in
separate implantable devices. Although baroreflex stimulation as
part of neural stimulation is specifically discussed, this aspect
of the present subject matter is also applicable to prevent, or
account or other wise compensate for, unintentional interference
detectable by a sensor and generated from other electrical
stimulators.
[0084] FIG. 16B illustrates a process where CRM functions do not
unintentionally react to baroreflex stimulation, according to
various embodiments. FIG. 16B illustrates a process where the NS
device or component 1651 sends an alert or otherwise informs the
CRM device or component when baroreceptors are being electrically
stimulated. In the illustrated embodiment, the NS device/component
determines at 1655 if electrical stimulation, such as baroreflex
stimulation, is to be applied. When electrical stimulation is to be
applied, the NS device or component 1651 sends at 1656 an alert
1657 or otherwise informs the CRM device or component 1652 of the
electrical stimulation. At 1658, the electrical stimulation is
applied by the NS device/component. At 1659 CRM therapy, including
sensing, is performed. At 1660, the CRM device/component determines
whether an alert 1657 has been received from the NS
device/component. If an alert has been received, an event detection
algorithm is modified at 1661 to raise a detection threshold,
provide a blackout or blanking window, or otherwise prevent the
electrical stimulation in the NS device or component from being
misinterpreted as an event by the CRM device/component.
[0085] FIG. 16C illustrates a process where CRM functions do not
unintentionally react to baroreflex stimulation, according to
various embodiments. The CRM device/component 1652 determines a
refractory period for the heart at 1662. At 1663, if a refractory
period is occurring or is expected to occur in a predictable amount
of time, an enable 1664 corresponding to the refractory is provided
to the NS device/component 1651. The AHT device/component 1651
determines if electrical stimulation is desired at 1665. When
desired, the AHT device/component applies electrical stimulation
during a refractory period at 1666, as controlled by the enable
signal 1664. FIG. 16D illustrates a refractory period at 1667 in a
heart and a baroreflex stimulation 1668, and further illustrates
that baroreflex stimulation is applied during the refractory
period.
[0086] A refractory period includes both absolute and relative
refractory periods. Cardiac tissue is not capable of being
stimulated during the absolute refractory period. The required
stimulation threshold during an absolute refractory period is
basically infinite. The relative refractory period occurs after the
absolute refractory period. During the relative refractory period,
as the cardiac tissue begins to repolarize, the stimulation
threshold is initially very high and drops to a normal stimulation
threshold by the end of the relative refractory period. Thus,
according to various embodiments, a neural stimulator applies
neural stimulation during either the absolute refractory period or
during a portion of the relative refractory period corresponding a
sufficiently high stimulation threshold to prevent the neural
stimulation from capturing cardiac tissue.
[0087] Various embodiments of the present subject matter relate to
a method of sensing atrial activation and confining pulmonary
artery stimulation to the atrial refractory period, preventing
unintentional stimulation of nearby atrial tissue. An implantable
baroreceptor stimulation device monitors atrial activation with an
atrial sensing lead. A lead in the pulmonary artery stimulates
baroreceptors in the vessel wall. However, instead of stimulating
these baroreceptors continuously, the stimulation of baroreceptors
in the pulmonary artery occurs during the atrial refractory period
to avoid capturing nearby atrial myocardium, maintaining the
intrinsic atrial rate and activation. Various embodiments of the
present subject matter combine an implantable device for
stimulating baroreceptors in the wall of the pulmonary artery with
the capability for atrial sensing. Various embodiments stimulate
baroreceptors in the cardiac fat pads, in the heart chambers,
and/or afferent nerves.
[0088] FIG. 17 illustrates a system 1769 to modulate baroreflex
stimulation, according to various embodiments of the present
subject matter. The illustrated system 1769 includes a baroreflex
stimulator 1751, such as stimulator to stimulate baroreceptors in
and around the pulmonary artery. The baroreflex stimulator can be
included in a stand-alone NS device or as a NS component in an
integrated NS/CRM device, for example. The illustrated stimulator
1751 includes a modulator 1769 for use to selectively increase and
decrease the applied baroreflex stimulation. According to various
embodiments, the modulator 1769 includes any one of the following
modules: a module 1770 to change the amplitude of the stimulation
pulse; a module 1771 to change the frequency of the stimulation
pulse; and a module 1772 to change the burst frequency of the
stimulation pulse. The burst frequency can also be referred to as a
duty cycle. According to various embodiments, the modulator 1769
includes functions for the various combinations of two or more of
the modules 1770, 1771 and 1772. Additionally, a stimulator can
include a waveform generator capable of providing different
waveforms in response to a control signal.
[0089] Various embodiments of the system include any one or any
combination of a cardiac activity monitor 1773, an adverse event
detector 1774, a respiration monitor 1775, and a circadian rhythm
template 1776 which are capable of controlling the modulator 1769
of the stimulator 1759 to appropriately apply a desired level of
baroreflex stimulation. Each of these 1773, 1774, 1775, and 1776
are associated with a method to modulate a baroreflex signal.
According to various embodiments, the system includes means to
modulate a baroreflex signal based on the following parameters or
parameter combinations: cardiac activity (1773); an adverse event
(1774); respiration (1775); circadian rhythm (1776); cardiac
activity (1773) and an adverse event (1774); cardiac activity
(1773) and respiration (1775); cardiac activity (1773) and
circadian rhythm (1776); an adverse event (1774) and respiration
(1775); an adverse event (1774) and circadian rhythm (1776);
respiration (1775) and circadian rhythm (1776); cardiac activity
(1773), an adverse event (1774), and respiration (1775); cardiac
activity (1773), an adverse event (1774), and circadian rhythm
(1776); cardiac activity (1773), respiration (1775), and circadian
rhythm (1776); an adverse event (1774), respiration (1775) and
circadian rhythm (1776); and cardiac activity (1773), an adverse
event (1774), respiration (1775) and circadian rhythm (1776).
[0090] The stimulation can be applied to an afferent nerve trunk
such as the vagal nerve using a cuff electrode or an
intravascularly-fed lead positioned proximate to the nerve trunk.
The stimulation can be applied to baroreceptor sites such are
located in the pulmonary artery, aortic arch, and carotid sinus,
for example, using intravenously-fed leads. The stimulation can be
applied to baroreceptor sites located in cardiac fat pads using
intravenously-fed leads or by screwing electrodes into the fat
pads. Embodiments of the cardiac activity detector 1774, for
example, include any one or any combination of a heart rate monitor
1777, a minute ventilation monitor 1778, and an acceleration
monitor 1779. The respiration monitor 1775 functions as a surrogate
for monitoring blood pressure. Embodiments of the respiration
monitor 1775 include any one or any combination of a tidal volume
monitor 1780 and a minute ventilation module 1781. Embodiments of
the circadian rhythm template 1776 include any one or combination
of a custom generated template 1782 and a preprogrammed template
1783. These embodiments are discussed in more detail below with
respect to FIGS. 18A-18C, 19A-19B, 20A-20B, 21A-21E, 22 and
23A-23C.
[0091] Various embodiments use the circadian rhythm template to
provide AHT therapy. Various embodiments use the circadian rhythm
template to provide apnea therapy.
[0092] Modulation of Baroreflex Stimulation Based on Systolic
Intervals
[0093] Activation of the sympathetic or parasympathetic nervous
systems is known to alter certain systolic intervals, primarily the
pre-ejection period (PEP), the time interval between sensed
electrical activity within the ventricle (e.g. sensing of the "R"
wave) and the onset of ventricular ejection of blood. The PEP may
be measured from the sensed electrical event to the beginning of
pressure increase in the pulmonary artery, using a pulmonary
arterial pressure sensor, or may be measured to the beginning of an
increase in intracardiac impedance, accompanying a decrease in
ventricular volume during ejection, using electrodes positioned in
the right or spanning the left ventricle. At rest, as determined by
heart rate or body activity measured with an accelerometer for
example, neural stimulation is modulated to maintain PEP in a
pre-programmed range. A sudden decrease in PEP indicates an
increase in sympathetic tone associated with exercise or emotional
stress. This condition may be used to decrease neural stimulation
permitting increases in heart rate and contractility necessary to
meet metabolic demand. In like manner, a subsequent dramatic
lengthening of PEP marks the end of increased metabolic demand. At
this time control of blood pressure with neural stimulation could
recommence.
[0094] Modulation of Baroreflex Stimulation Based on Cardiac
Activity
[0095] The present subject matter describes a method of
automatically modulating baroreceptor stimulation based on cardiac
activity, such as can be determined by the heart rate, minute
ventilation, acceleration and combinations thereof. The
functionality of a device for electrically stimulating
baroreceptors is enhanced by applying at least a relatively high
baropacing rate during rest when metabolic demand is relatively
low, and progressively less baropacing during physical exertion as
metabolic demand increases. Indices of cardiac activity are used to
automatically modulate the electrical stimulation of baroreceptors,
allowing an implantable anti-hypertension device to respond to
changes in metabolic demand. According to various embodiments, a
CRM device, such as a pacemaker, AICD or CRT devices, also has a
baroreceptor stimulation lead. The device monitors cardiac activity
through existing methods using, for example, a blended sensor. A
blended sensor includes two sensors to measure parameters such as
acceleration and minute ventilation. The output of the blended
sensor represents a composite parameter. Various NS and AHT
therapies use composite parameters derived from two or more sensed
parameters as discussed within this disclosure. At rest (lower
cardiac activity) the device stimulates baroreceptors at a higher
rate, reducing blood pressure and controlling hypertension. As
cardiac activity increases, the device responds by temporarily
reducing baroreceptor stimulation. This results in a temporary
increase in blood pressure and cardiac output, allowing the body to
respond to increased metabolic demand. For example, some
embodiments provide baroreflex stimulation during rest and withdraw
baroreflex stimulation during exercise to match normal blood
pressure response to exercise. A pressure transducer can be used to
determine activity. Furthermore, activity can be sensed using
sensors that are or have been used to drive rate adaptive pacing.
Examples of such sensors include sensor to detect body movement,
heart rate, QT interval, respiration rate, transthoracic impedance,
tidal volume, minute ventilation, body posture,
electroencephalogram (EEG), electrocardiogram (ECG),
electrooculogram (EOG), electromyogram (EMG), muscle tone, body
temperature, pulse oximetry, time of day and pre-ejection interval
from intracardiac impedance.
[0096] Various embodiments of the cardiac activity monitor includes
a sensor to detect at least one pressure parameter such as a mean
arterial parameter, a pulse pressure determined by the difference
between the systolic and diastolic pressures, end systolic pressure
(pressure at the end of the systole), and end diastolic pressure
(pressure at the end of the diastole). Various embodiments of the
cardiac activity monitor include a stroke volume monitor. Heart
rate and pressure can be used to derive stroke volume. Various
embodiments of the cardiac activity monitor use at least one
electrogram measurement to determine cardiac activity. Examples of
such electrogram measurements include the R-R interval, the P-R
interval, and the QT interval. Various embodiments of the cardiac
activity monitor use at least one electrocardiogram (ECG)
measurement to determine cardiac activity.
[0097] FIGS. 18A-18C illustrate methods for modulating baroreceptor
stimulation based on a cardiac activity parameter, according to
various embodiments of the present subject matter. The cardiac
activity can be determined by a CRM device, an NS device, or an
implantable device with NS/CRM capabilities. A first process 1884A
for modulating baroreceptor stimulation based on cardiac activity
is illustrated in FIG. 18A. At 1885A the activity level is
determined. According to various embodiments, the determination of
activity level is based on heart rate, minute ventilation,
acceleration or any combination of heart rate, minute ventilation,
acceleration. In the illustrated process, the activity level has
two defined binary levels (e.g. HI and LO). In some embodiments,
the LO level includes no stimulation. It is determined whether the
activity level is HI or LO. At 1886A, the baroreceptor stimulation
level is set based on the determined activity level. A LO
stimulation level is set if the activity level is determined to be
HI, and a HI stimulation level is set if the activity level is
determined to be LO.
[0098] A second process 1884B for modulating baroreceptor
stimulation based on cardiac activity is illustrated in FIG. 18B.
At 1885B the activity level is determined. According to various
embodiments, the determination of activity level is based on heart
rate, minute ventilation, acceleration or any combination of heart
rate, minute ventilation, acceleration. In the illustrated process,
the activity level has more than two defined levels or n defined
levels. It is determined whether the activity level is level 1,
level 2 . . . or level n. The activity level labels correspond to
an increasing activity. At 1886B, the baroreceptor stimulation
level is set based on the determined activity level. Available
stimulation levels include level n . . . level 2 and level 1, where
the stimulation level labels correspond to increasing stimulation.
According to various embodiments, the selected baroreceptor
stimulation level is inversely related to the determined activity
level. For example, if it is determined that the cardiac activity
level is at the highest level n, then the stimulation level is set
to the lowest level n. If it determined that the stimulation level
is at the first or second to the lowest level, level 1 or level 2
respectively, then the stimulation level is set to the first or
second to the highest level, level 1 or level 2 respectively.
[0099] Another process 1884C for modulating baroreceptor
stimulation based on cardiac activity is illustrated in FIG. 18C.
At 1887, an acquired cardiac activity parameter is compared to a
target activity parameter. If the acquired cardiac activity is
lower than the target activity parameter, baroreceptor stimulation
is increased at 1888. If the acquired cardiac activity is higher
than the target activity parameter, baroreceptor stimulation is
decreased at 1889.
[0100] An aspect of the present subject matter relates to a method
of automatically modulating the intensity of baroreceptor
stimulation based on respiration, as determined by tidal volume or
minute ventilation. Instead of applying continuous baroreceptor
stimulation, the NS device monitors the level of hypertension and
delivers an appropriate level of therapy, using respiration as a
surrogate for blood pressure, allowing the device to modulate the
level of therapy. The present subject matter uses indices of
respiration, such as impedance, to determined tidal volume and
minute ventilation and to automatically modulate baroreceptor
stimulation. Thus, an implantable NS device is capable of
determining the level of hypertension in the patient and respond by
delivering an appropriate level of therapy. In various embodiments,
an implantable NS device contains a sensor to measure tidal volume
or minute ventilation. For example, various embodiments measure
transthoracic impedance to obtain a rate of respiration. The device
receives this data from a CRM device in some embodiments. The NS
device periodically monitors these respiration parameters. As
respiration decreases or remains below a programmable target, the
device stimulates baroreceptors at an increased rate, reducing
blood pressure and controlling hypertension. As mean arterial
pressure increases towards the target, the device responds by
reducing baroreceptor stimulation. In this way, the AHT device
continuously delivers an appropriate level of therapy.
[0101] FIGS. 19A-19B illustrate methods for modulating baroreceptor
stimulation based on a respiration parameter, according to various
embodiments of the present subject matter. The respiration
parameter can be determined by a CRM device, an NS device, or an
implantable device with NS/CRM capabilities. One embodiment of a
method for modulating baroreceptor stimulation based on a
respiration parameter is illustrated at 1910A in FIG. 19A. The
respiration level is determined at 1911, and the baroreceptor
stimulation level is set at 1912 based on the determined
respiration level. According to various embodiments, the desired
baropacing level is tuned at 1913. For example, one embodiment
compares an acquired parameter to a target parameter at 1914. The
baropacing can be increased at 1915 or decreased at 1916 based on
the comparison of the acquired parameter to the target
parameter.
[0102] One embodiment of a method for modulating baroreceptor
stimulation based on a respiration parameter is illustrated at
1910B in FIG. 19B. At 1916, a baroreflex event trigger occurs,
which triggers an algorithm for a baroreflex stimulation process.
At 1917, respiration is compared to a target parameter. Baroreflex
stimulation is increased at 1918 if respiration is below the target
and is decreased at 1919 if respiration is above the target.
According to various embodiments, the stimulation is not changed if
the respiration falls within a blanking window. Various embodiments
use memory to provide a hysteresis effect to stabilize the applied
stimulation and the baroreflex response. Additionally, in various
embodiments, the respiration target is modified during the therapy
based on various factors such as the time of day or activity level.
At 1920, it is determined whether to continue with the baroreflex
therapy algorithm based on, for example, sensed parameters or the
receipt of an event interrupt. If the baroreflex algorithm is to
continue, then the process returns to 1917 where respiration is
again compared to a target parameter; else the baroreflex algorithm
is discontinued at 1921.
[0103] Modulation of Baroreflex Stimulation Based on Adverse
Event
[0104] Aspects of the present subject matter include a method of
automatically increasing baroreceptor stimulation upon detection of
an adverse cardiac event to increase vasodilatory response and
potentially prevent or reduce myocardial ischemic damage. Various
embodiments include a feedback mechanism in a cardiac rhythm
management device (such as a pacemaker, AICD or CRT device), which
also has a stimulation lead for electrically stimulating
baroreceptors. The device monitors cardiac electrical activity
through existing methods. In the event of an adverse cardiac event
such as ventricular fibrillation (VF) and atrial fibrillation (AF),
ventricular tachycardia (VT) and atrial tachycardia (AT) above a
predefined rate, and dyspnea as detected by a minute ventilation
sensor, angina, decompensation and ischemia, the device responds by
increasing baroreceptors stimulation to the maximally allowable
level. As a result, blood pressure is temporarily lowered,
potentially preventing or reducing myocardial damage due to
ischemia. The functionality of a device to treat hypertension can
be expanded if it can respond to adverse cardiac events by
temporarily modulating the extent of baroreceptors stimulation.
Event detection algorithms automatically modulate baroreceptors
stimulation, allowing an implantable AHT device to respond to an
adverse event by increasing baroreceptors stimulation, potentially
preventing or reducing myocardial ischemic damage.
[0105] FIGS. 20A-20B illustrate methods for modulating baroreceptor
stimulation based on detection of an adverse event, according to
various embodiments of the present subject matter. The adverse
event can be determined by a CRM device, an NS device, or an
implantable device with NS/CRM capabilities. FIG. 20A illustrates
one embodiment for modulating baroreceptor stimulation based on
detection of an adverse event. At 2090A, it is determined whether
an adverse event has been detected. If an adverse event has not
been detected, normal baropacing (baropacing according to a normal
routine) is performed at 2091A. If an adverse event has been
detected, enhanced baropacing is performed at 2092. In various
embodiments, the maximum allowable baropacing is performed when an
adverse event is detected. Other baropacing procedures can be
implemented. For example, various embodiments normally apply
baropacing stimulation and withholds baropacing therapy when an
adverse event is detected, and various embodiments normally
withhold baropacing therapy and apply baropacing stimulation when
an adverse event is detected. FIG. 20B illustrate on embodiment for
modulating baroreceptor stimulation based on detection of an
adverse event. At 2090B, it is determined whether an adverse event
has been detected. If an adverse event has not been detected,
normal baropacing (baropacing according to a normal routine) is
performed at 2091B. If an adverse event has been detected, the
event is identified at 2093, and the appropriate baropacing for the
identified adverse event is applied at 2094. For example, proper
blood pressure treatment may be different for ventricular
fibrillation than for ischemia. According to various embodiments,
the desired baropacing is tuned for the identified event at 2095.
For example, one embodiment compares an acquired parameter to a
target parameter at 2096. The baropacing can be increased at 2097
or decreased at 2098 based on the comparison of the acquired
parameter to the target parameter.
[0106] According to various embodiments, an adverse event includes
detectable precursors, such that therapy can be applied to prevent
cardiac arrhythmia. In some embodiments, an adverse event includes
both cardiac events and non-cardiac events such as a stroke.
Furthermore, some embodiments identify both arrhythmic and
non-arrhythmic events as adverse events.
[0107] Modulation of Baroreflex Stimulation Based on Circadian
Rhythm
[0108] An aspect of the present subject matter relates to a method
for stimulating the baroreflex in hypertension patients so as to
mimic the natural fluctuation in blood pressure that occurs over a
24-hour period. Reflex reduction in hypertension is achieved during
long-term baroreceptor stimulation without altering the intrinsic
fluctuation in arterial pressure. According to various embodiments,
an implantable device is designed to stimulate baroreceptors in the
carotid sinus, pulmonary artery, or aortic arch using short,
high-frequency bursts (such as a square wave with a frequency
within a range from approximately 20-150 Hz), for example. Some
embodiments directly stimulate the carotid sinus nerve, aortic
nerve or vagus nerve with a cuff electrode. However, the bursts do
not occur at a constant rate. Rather the stimulation frequency,
amplitude, and/or burst frequency rises and falls during the day
mimicking the natural circadian rhythm.
[0109] Thus, various embodiments of a NS device accounts for
natural fluctuations in arterial pressure that occur in both normal
and hypertensive individuals. Aside from activity-related changes
in mean arterial pressure, subjects also exhibit a consistent
fluctuation in pressure on a 24-hour cycle. A device which provides
periodic baroreceptor stimulation mimics the intrinsic circadian
rhythm, allowing for reflex inhibition of the systematic nervous
system and reduced systemic blood pressure without disturbing this
rhythm. The present subject matter provides a pacing protocol which
varies the baroreceptor stimulation frequency/amplitude in order to
reduce mean arterial pressure without disturbing the intrinsic
circadian rhythm.
[0110] FIGS. 21A-21E illustrate circadian rhythm. FIG. 21A
illustrates the circadian rhythm associated with mean arterial
pressure for 24 hours from noon to noon; FIG. 21B illustrates the
circadian rhythm associated with heart rate for 24 hours from noon
to noon; FIG. 21C illustrates the circadian rhythm associated with
percent change of stroke volume (SV %) for 24 hours from noon to
noon; FIG. 21D illustrates the circadian rhythm associated with the
percent change of cardiac output (CO) for 24 hours from noon to
noon; and FIG. 21E illustrates the circadian rhythm associated with
percent change of total peripheral resistance (TPR %), an index of
vasodilation, for 24 hours from noon to noon. Various embodiments
graph absolute values, and various embodiments graph percent
values. In these figures, the shaded portion represents night hours
from about 10 PM to 7 AM, and thus represents rest or sleep times.
Referring to FIGS. 21A and 21B, for example, it is evident that
both the mean arterial pressure and the heart rate are lowered
during periods of rest. A higher blood pressure and heart rate can
adversely affect rest. Additionally, a lower blood pressure and
heart rate during the day can adversely affect a person's level of
energy.
[0111] Various embodiments of the present subject matter modulate
baroreflex stimulation using a pre-programmed template intended to
match the circadian rhythm for a number of subjects. Various
embodiments of the present subject matter generate a template
customized to match a subject.
[0112] FIG. 22 illustrates a method for modulating baroreceptor
stimulation based on circadian rhythm, according to various
embodiments of the present subject matter, using a customized
circadian rhythm template. The illustrated method 2222 senses and
records parameters related to hypertension at 2223. Examples of
such parameters include heart rate and mean arterial pressure. At
2224, a circadian rhythm template is generated based on these
recorded parameters. At 2225, the baroreflex stimulation is
modulated using the circadian rhythm template generated in
2224.
[0113] Modulation of Baroreflex Stimulation To Provide Desired
Cardiac Output
[0114] An aspect of the present subject matter relates to an
implantable medical device that provides NS therapy to lower
systemic blood pressure by stimulating the baroreflex, and further
provides cardiac pacing therapy using a cardiac pacing lead for
rate control. Baroreflex stimulation and cardiac pacing occurs in
tandem, allowing blood pressure to be lowered without sacrificing
cardiac output.
[0115] According to various embodiments, a baroreflex stimulator
communicates with a separate implantable CRM device, and uses the
existing pacing lead. In various embodiments, baroreflex
stimulation occurs through baroreceptors in the pulmonary artery,
carotid sinus, or aortic arch with an electrode placed in or
adjacent to the vessel wall. In various embodiments, afferent
nerves such as the aortic nerve, carotid sinus nerve, or vagus
nerve are stimulated directly with a cuff electrode.
[0116] Baroreflex stimulation quickly results in vasodilation, and
decreases systemic blood pressure. To compensate for the concurrent
decrease in cardiac output, the pacing rate is increased during
baroreflex stimulation. The present subject matter allows blood
pressure to be gradually lowered through baroreflex stimulation
while avoiding the drop in cardiac output that otherwise
accompanies such stimulation by combining baroreflex stimulation
with cardiac pacing, allowing an implantable device to maintain
cardiac output during blood pressure control.
[0117] FIG. 23A-B illustrate methods for modulating baroreceptor
stimulation based on a cardiac output parameter, according to
various embodiments of the present subject matter. FIG. 23A
illustrates one embodiment for modulating baroreceptor stimulation
based on a cardiac output parameter. In the illustrated process
2326A, it is determined whether baroreflex stimulation is being
applied at 2327. If baroreflex stimulation is not being applied,
the present subject matter implements the appropriate pacing
therapy, if any, at 2328 with the appropriate pacing rate. If
baroreflex stimulation is not being applied, the present subject
matter implements a pacing therapy at 2329 with a higher pacing
rate to maintain cardiac output.
[0118] FIG. 23B illustrates one embodiment for modulating
baroreceptor stimulation based on a cardiac output parameter. In
the illustrated process 2326B, baroreflex stimulation is applied at
2330, and it is determined whether the cardiac output is adequate
at 2331. Upon determining that the cardiac output is not adequate,
the pacing rate is increased at 2332 to maintain adequate cardiac
output.
[0119] According to various embodiments, an existing pacing rate is
increased by a predetermined factor during baroreflex stimulation
to maintain cardiac output. In various embodiments, a pacing rate
is initiated during baroreflex stimulation to maintain cardiac
output. Modulating baroreflex stimulation to provide desired
cardiac output can be implemented with atrial and ventricular rate
control, AV delay control, resynchronization, and multisite
stimulation. Alternatively, the stroke volume may be monitored by
right ventricular impedance using electrodes within the right
ventricular cavity or by left ventricular impedance using
electrodes within or spanning the left ventricular cavity, and the
pacing rate may be increased using application of neural
stimulation to maintain a fixed cardiac output.
[0120] Modulation of Baroreflex Stimulation To Remodel Stiffening
Process
[0121] Aspects of the present subject matter involve a method for
baroreflex stimulation, used by an implantable NS device, to lower
systemic blood pressure in patients with refractory hypertension. A
baroreflex stimulation algorithm gradually increases baroreflex
stimulation to slowly adjust blood pressure towards a programmable
target. This algorithm prevents the central nervous system from
adapting to a constant increased level of baroreflex stimulation,
which ordinarily attenuates the pressure-lowering effect. In
addition, the gradual nature of the blood pressure change allows
the patient to better tolerate the therapy, without abrupt changes
in systemic blood pressure and cardiac output.
[0122] The present subject matter provides a specific algorithm or
process designed to prevent central nervous system adaptation to
increased baroreflex stimulation, to slowly decrease blood pressure
levels with time to enable for the reversion of the arterial
stiffening process triggered by the previous hypertensive state
present in the patient, and to prevent cardiac output decreases
during baroreceptor stimulation. It is expected that, with time,
the arterial system reverse remodels the stiffening process that
was started by the previously present hypertension. The slow and
progressive lowering of the mean/median blood pressure enables the
slow reversion of this stiffening process through the reverse
remodeling. Blood pressure is reduced without compromising cardiac
output in the process, thus avoiding undesired patient
symptoms.
[0123] In various embodiments, the device stimulates baroreceptors
in the pulmonary artery, carotid sinus, or aortic arch with an
electrode placed in or adjacent to the vessel wall. In various
embodiments afferent nerves such as the aortic nerve, carotid sinus
nerve, or vagus nerve are stimulated directly with a cuff
electrode. The stimulated baroreflex quickly results in
vasodilation, and a decrease in systemic blood pressure. However,
rather than stimulating the baroreflex at a constant, elevated
level, the device of the present subject matter initially
stimulates at a slightly increased level, and then gradually
increases the stimulation over a period of weeks or months, for
example. The rate of change is determined by the device based on
current and target arterial pressure. In various embodiments, the
system determines the rate of change based on direct or indirect
measurements of cardiac output, to ensure that the decrease in
pressure is not occurring at the expense of a decreased cardiac
output. In various embodiments, the rate of baroreflex stimulation
is not constant but has a white noise type distribution to more
closely mimic the nerve traffic distribution. By mimicking the
nerve traffic distribution, it is expected that the baroreflex is
more responsive to the stimulation, thus lowering the threshold for
stimulating the baroreflex.
[0124] FIG. 24 illustrates a method for modulating baroreceptor
stimulation to reverse remodel stiffening, according to various
embodiments of the present subject matter. A baroreflex event
trigger occurs at 2433. This trigger includes any event which
initiates baroreflex stimulation, including the activation of an
AHT device. At 2434, an algorithm is implemented to increase
baroreflex stimulation by a predetermined rate of change to
gradually lower the blood pressure to a target pressure in order to
reverse remodel the stiffening process. At 2435, it is determined
whether to continue with the baroreflex stimulation algorithm. The
algorithm may be discontinued at 2436 based on an event interrupt,
sensed parameters, and/or reaching the target blood pressure, for
example. At 2437, it is determined whether the cardiac output is
acceptable. If the cardiac output in not acceptable, at 2438 the
rate of change for the baroreflex stimulate is modified based on
the cardiac output.
[0125] Baroreflex Stimulation To Treat Myocardial Infarction
[0126] Following a myocardial infarction, myocytes in the infarcted
region die and are replaced by scar tissue, which has different
mechanical and elastic properties from functional myocardium. Over
time, this infarcted area can thin and expand, causing a
redistribution of myocardial stresses over the entire heart.
Eventually, this process leads to impaired mechanical function in
the highly stressed regions and heart failure. The highly stressed
regions are referred to as being heavily "loaded" and a reduction
in stress is termed "unloading." A device to treat acute myocardial
infarction to prevent or reduce myocardial damage is desirable.
[0127] An aspect of the present subject matter relates to an
implantable device that monitors cardiac electrical activity. Upon
detection of a myocardial infarction, the device electrically
stimulates the baroreflex, by stimulating baroreceptors in or
adjacent to the vessel walls and/or by directly stimulating
pressure-sensitive nerves. Increased baroreflex stimulation
compensates for reduced baroreflex sensitivity, and improves the
clinical outcome in patients following a myocardial infarction. An
implantable device (for example, a CRM device) monitors cardiac
electrical activity. Upon detection of a myocardial infarction, the
device stimulates the baroreflex. Some embodiments of the device
stimulate baroreceptors in the pulmonary artery, carotid sinus, or
aortic arch with an electrode placed in or adjacent to the vessel
wall. In various embodiments, afferent nerves such as the aortic
nerve are stimulated directly with a cuff electrode, or with a lead
intravenously placed near the afferent nerve. Afferent nerves such
as the carotid sinus nerve or vagus nerve are stimulated directly
with a cuff electrode, or with a lead intravenously placed near the
afferent nerve. In various embodiments, a cardiac fat pad is
stimulated using an electrode screwed into the fat pad, or a lead
intravenously fed into a vessel or chamber proximate to the fat
pad.
[0128] Baroreflex stimulation quickly results in vasodilation, and
a decrease in systemic blood pressure. This compensates for reduced
baroreflex sensitivity and reduces myocardial infarction. According
to various embodiments, systemic blood pressure, or a surrogate
parameter, are monitored during baroreflex stimulation to insure
that an appropriate level of stimulation is delivered. Some aspects
and embodiments of the present subject matter provides baroreflex
stimulation to prevent ischemic damage following myocardial
infarction.
[0129] FIGS. 25A-25B illustrate a system and method to detect
myocardial infarction and perform baropacing in response to the
detected myocardial infarction, according to various embodiments of
the present subject matter. FIG. 25A illustrates a system that
includes a myocardial infarction detector 2539 and a baroreflex or
baroreceptor stimulator 2540. A myocardial infarction can be
detected using an electrocardiogram, for example. For example, a
template can be compared to the electrocardiogram to determine a
myocardial infarction. Another example detects changes in the ST
segment elevation to detect myocardial infarction. In various
embodiments, the detector 2539 and stimulator 2540 are integrated
into a single implantable device such as in an AHT device or a CRM
device, for example. In various embodiments, the detector 2539 and
stimulator 2540 are implemented in separate implantable devices
that are adapted to communicate with each other.
[0130] FIG. 25B illustrates a method to detect myocardial
infarction and perform baropacing in response to the detected
myocardial infarction, according to various embodiments of the
present subject matter. At 2541, it is determined whether a
myocardial infarction has occurred. Upon determining that a
myocardial infarction has occurred, the baroreflex is stimulated at
2542. For example, in various embodiments, the baroreceptors in and
around the pulmonary artery are stimulated using a lead fed through
the right atrium and the pulmonary valve and into the pulmonary
artery. Other embodiments stimulate other baroreceptor sites and
pressure sensitive nerves. Some embodiments monitor the systemic
blood pressure or a surrogate parameter at 2543, and determines at
2544 if the stimulation should be adjusted based on this
monitoring. If the stimulation is to be adjusted, the baroreflex
stimulation is modulated at 2545. Examples of modulation include
changing the amplitude, frequency, burst frequency and/or waveform
of the stimulation.
[0131] Neural stimulation, such as baroreflex stimulation, can be
used to unload after a myocardial infarction. Various embodiments
use an acute myocardial infraction detection sensor, such as an
ischemia sensor, within a feedback control system of an NS device.
However, a myocardial infraction detection sensor is not required.
For example, a stimulation lead can be implanted after a myocardial
infarction. In various embodiments, the stimulation lead is
implanted through the right atrium and into the pulmonary artery to
stimulate baroreceptors in and around the pulmonary artery. Various
embodiments implant stimulation cuffs or leads to stimulate
afferent nerves, electrode screws or leads to stimulate cardiac fat
pads, and leads to stimulate other baroreceptors as provided
elsewhere in this disclosure.
[0132] Electrical pre-excitation of a heavily loaded region will
reduce loading on this region. This pre-excitation may
significantly reduce cardiac output resulting in sympathetic
activation and an increase in global stress, ultimately leading to
deleterious remodeling of the heart. This process may be
circumvented by increased neural stimulation to reduce the impact
of this reflex. Thus, activation of the parasympathetic nervous
system during pre-excitation may prevent the undesirable
side-effects of unloading by electrical pre-excitation.
[0133] One of ordinary skill in the art will understand that, the
modules and other circuitry shown and described herein can be
implemented using software, hardware, and combinations of software
and hardware. As such, the term module is intended to encompass
software implementations, hardware implementations, and software
and hardware implementations.
[0134] The methods illustrated in this disclosure are not intended
to be exclusive of other methods within the scope of the present
subject matter. Those of ordinary skill in the art will understand,
upon reading and comprehending this disclosure, other methods
within the scope of the present subject matter. The
above-identified embodiments, and portions of the illustrated
embodiments, are not necessarily mutually exclusive. These
embodiments, or portions thereof, can be combined. For example,
various embodiments combine two or more of the illustrated
processes. Two or more sensed parameters can be combined into a
composite parameter used to provide a desired neural stimulation
(NS) or anti-hypertension (AHT) therapy. In various embodiments,
the methods provided above are implemented as a computer data
signal embodied in a carrier wave or propagated signal, that
represents a sequence of instructions which, when executed by a
processor cause the processor to perform the respective method. In
various embodiments, methods provided above are implemented as a
set of instructions contained on a computer-accessible medium
capable of directing a processor to perform the respective method.
In various embodiments, the medium is a magnetic medium, an
electronic medium, or an optical medium.
[0135] Although specific embodiments have been illustrated and
described herein, it will be appreciated by those of ordinary skill
in the art that any arrangement which is calculated to achieve the
same purpose may be substituted for the specific embodiment shown.
This application is intended to cover adaptations or variations of
the present subject matter. It is to be understood that the above
description is intended to be illustrative, and not restrictive.
Combinations of the above embodiments as well as combinations of
portions of the above embodiments in other embodiments will be
apparent to those of skill in the art upon reviewing the above
description. The scope of the present subject matter should be
determined with reference to the appended claims, along with the
full scope of equivalents to which such claims are entitled.
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