U.S. patent application number 11/482505 was filed with the patent office on 2007-07-19 for method and apparatus for stimulation of baroreceptors.
This patent application is currently assigned to CVRx, Inc.. Invention is credited to Matthew M. Burns, Peter T. Keith, Robert S. Kieval, Martin A. Rossing, David J. Serdar.
Application Number | 20070167984 11/482505 |
Document ID | / |
Family ID | 37743521 |
Filed Date | 2007-07-19 |
United States Patent
Application |
20070167984 |
Kind Code |
A1 |
Kieval; Robert S. ; et
al. |
July 19, 2007 |
Method and apparatus for stimulation of baroreceptors
Abstract
Devices and methods for controlling the baroreflex system for
the treatment and/or management of cardiovascular, renal, and
neurological disorders.
Inventors: |
Kieval; Robert S.; (Medina,
MN) ; Burns; Matthew M.; (Orono, MN) ; Keith;
Peter T.; (St. Paul, MN) ; Serdar; David J.;
(Shorewood, MN) ; Rossing; Martin A.; (Coon
Rapids, MN) |
Correspondence
Address: |
TOWNSEND AND TOWNSEND AND CREW, LLP
TWO EMBARCADERO CENTER
EIGHTH FLOOR
SAN FRANCISCO
CA
94111-3834
US
|
Assignee: |
CVRx, Inc.
Maple Grove
MN
|
Family ID: |
37743521 |
Appl. No.: |
11/482505 |
Filed: |
July 7, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10284063 |
Oct 29, 2002 |
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11482505 |
Jul 7, 2006 |
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09671850 |
Sep 27, 2000 |
6522926 |
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10284063 |
Oct 29, 2002 |
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Current U.S.
Class: |
607/2 |
Current CPC
Class: |
A61N 1/36114 20130101;
A61N 1/36117 20130101 |
Class at
Publication: |
607/002 |
International
Class: |
A61N 1/32 20060101
A61N001/32 |
Claims
1. A baroreflex stimulator, comprising: a pulse generator to
provide a baroreflex stimulation signal through an electrode; and a
modulator to modulate the baroreflex stimulation signal based on a
circadian rhythm template.
2. The stimulator of claim 1, further comprising a waveform
generator to produce baroreceptor signals of a desired morphology,
wherein the modulator includes a modulator to change the morphology
of the baroreflex stimulation signal based on the circadian rhythm
template.
3. The stimulator of claim 1, wherein the circadian rhythm template
includes a template selected from the group consisting of a
pre-programmed circadian rhythm template, a patient-specific
circadian rhythm template, a mean arterial pressure template, a
heart rate template, a stroke volume template, a cardiac output
template, and a total peripheral resistance template.
4. The stimulator of claim 1, wherein the electrode includes an
electrode adapted to stimulate baroreceptors in a vessel wall.
5. A baroreflex stimulator, comprising: a pulse generator to
provide a baroreflex stimulation signal through an electrode; and
means for modulating the baroreflex stimulation signal based on a
circadian rhythm template.
6. The stimulator of claim 5, wherein the circadian rhythm template
includes a template selected from the group consisting of a
pre-programmed circadian rhythm template, a patient-specific
circadian rhythm template, a mean arterial pressure template, a
heart rate template, a stroke volume template, a cardiac output
template, and a total peripheral resistance template.
7. A method for operating an implantable medical device,
comprising: applying a baroreflex stimulation therapy using a
baroreflex stimulator in the implantable medical device; and
modulating the baroreflex stimulation therapy based on a circadian
rhythm template.
8. The method of claim 7, wherein modulating the baroreflex
stimulation therapy based on the circadian rhythm template is
accomplished using a pre-programmed circadian rhythm template.
9. The method of claim 7, further comprising: sensing and recording
parameters related to hypertension; and generating a
patient-specific circadian rhythm template based on the recorded
parameters, wherein the baroreflex stimulation therapy is modulated
based on the patient-specific circadian rhythm template.
10. The method of claim 7, wherein modulating the baroreflex
stimulation therapy based on the circadian rhythm template is
accomplished with a template selected from the set of a mean
arterial pressure template, a heart rate template, a stroke volume
template, a cardiac output template, and a total peripheral
resistance template.
11. The method of claim 7, wherein applying baroreflex therapy
includes stimulating a baroreceptor in a vessel wall.
12. A baroreflex stimulator, comprising: a driver adapted to
provide a control signal through a baroreceptor activation device;
and a controller to periodically modulate the control signal based
on an algorithm.
13. A baroreflex stimulator, comprising: a driver adapted to
provide a control signal through a baroreceptor activation device;
and means for periodically modulating the control signal based on
an algorithm.
14. A method for operating an implantable medical device,
comprising: applying a baroreflex stimulation therapy using a
baroreceptor activation device in the implantable medical device;
and periodically modulating the baroreflex stimulation therapy
based on an algorithm.
15. An implantable medical system, comprising: a baroreflex
stimulator to apply a baroreflex stimulation signal through an
electrode; a myocardial infarction detector to detect an event
indicative of myocardial infarction; and a controller connected to
the baroreflex stimulator and to the myocardial infarction
detector, the controller adapted to apply a baroreflex therapy in
response to a detected event indicative of myocardial
infarction.
16. The device of claim 15, wherein the controller includes a
controller adapted to initiate a baroreflex therapy in response to
a detected event indicative of myocardial infarction.
17. The device of claim 15, wherein the controller includes a
controller adapted to increase an existing baroreflex therapy in
response to a detected event indicative of myocardial
infarction.
18. An implantable medical system, comprising: means for detecting
a myocardial infarction; and means for applying baroreflex therapy
to a pressoreceptive region to decrease coronary vascular
resistance and increase blood flow in response to detecting the
myocardial infarction.
19. The system of claim 18, wherein the means for applying
baroreflex therapy includes means for increasing baroreflex
stimulation in response to the myocardial infarction.
20. The system of claim 18, further comprising means for monitoring
systemic blood pressure, and means for modulating the baroreflex
therapy based on the systemic blood pressure.
21. The system of claim 18, further comprising means for sensing
the blood pressure.
22. The system of claim 18, further comprising means for sensing
respiration as a surrogate parameter for blood pressure.
23. A method, comprising: detecting an event corresponding to a
myocardial infarction; and in response to a detected event
corresponding to a myocardial infarction, applying a baroreflex
therapy using an electrode positioned proximate to a baroreflex
neural target.
24. The method of claim 23, further comprising monitoring systemic
blood pressure and modulating the baroreflex therapy based on the
blood pressure.
25. The method of claim 23, further comprising monitoring a
surrogate parameter of systemic blood pressure and modulating the
baroreflex therapy based on the surrogate parameter.
26. The method of claim 23, wherein monitoring the surrogate
parameter includes monitoring a respiration parameter.
27. An implantable medical system, comprising: a baroreflex
stimulator to apply a baroreflex stimulation signal to an
electrode; a sensor to detect a parameter indicative of heart
failure; and a control system connected to the baroreflex
stimulator and to the sensor, the control system adapted to apply a
baroreflex therapy in response to a detected parameter indicative
of heart failure.
28. An implantable medical system, comprising: means for detecting
a heart failure; and means for applying baroreflex therapy to a
baroreceptor region to regulate blood pressure and sympathetic
nervous system activity.
29. A method, comprising: detecting a parameter corresponding to
heart failure; and applying a baroreflex therapy using a
baroreceptor activation device positioned adjacent a baroreceptor
in response to detecting a parameter corresponding to heart
failure.
30. A system for providing baroreflex stimulation, comprising: an
adverse event detector to sense an adverse event and provide a
signal indicative of the adverse event; and a baroreflex
stimulator, including: a pulse generator to provide a baroreflex
stimulation signal adapted to provide a baroreflex therapy; and a
modulator to receive the signal indicative of the adverse event and
modulate the baroreflex stimulation signal based on the signal
indicative of the adverse event to change the baroreflex therapy
from a first baroreflex therapy to a second baroreflex therapy.
31. The system of claim 30, further comprising a waveform generator
to produce baroreflex signals of a desired morphology, wherein the
modulator includes a modulator to change the morphology of the
barobreflex stimulation signal based on the signal indicative of
the adverse event.
32. The system of claim 30, further comprising an implantable
medical device, wherein the implantable medical device includes the
adverse event detector and the baroreflex stimulator.
33. The system of claim 30, wherein the adverse event includes an
adverse cardiac event.
34. The system of claim 30, wherein the adverse cardiac event
includes an arrhythmia.
35. The system of claim 30, wherein the adverse cardiac event
includes a non-arrhythmic cardiac event.
36. A baroreflex stimulator, comprising: an implantable pulse
generator to provide a baroreflex stimulation signal adapted to
provide a baroreflex therapy; and means for modulating the
baroreflex stimulation signal based on a signal indicative of an
adverse event to change the baroreflex therapy from a first
baroreflex therapy to a second baroreflex therapy.
37. The baroreflex stimulator of claim 36, wherein the means for
modulating the baroreflex stimulation signal based on a signal
indicative of an adverse event includes means for modulating the
baroreflex stimulation signal based on a signal indicative of an
adverse cardiac event.
38. The baroreflex stimulator of claim 37, wherein the means for
modulating the baroreflex stimulation signal based on a signal
indicative of an adverse cardiac event includes means for
modulating the baroreflex stimulation signal based on a signal
indicative of an arrhythmia.
39. The baroreflex stimulator of claim 37, wherein the means for
modulating the baroreflex stimulation signal based on a signal
indicative of an adverse cardiac event includes means for
modulating the baroreflex stimulation signal based on a signal
indicative of a non-arrhythmic cardiac event.
40. The baroreflex stimulator of claim 36, wherein the baroreflex
stimulation signal has a morphology, and the means for modulating
the baroreflex stimulation signal includes means for adjusting the
morphology of the baroreflex stimulation signal.
41. A method for operating an implantable medical device,
comprising: receiving a signal regarding a detected adverse event
at a baroreceptor stimulator; performing a first baropacing therapy
using the baroreceptor stimulator when the adverse event is not
detected; and automatically performing a second baropacing therapy
using the baroreceptor stimulator when the adverse event is
detected.
42. The method of claim 41, wherein performing the first baropacing
therapy includes withholding baropacing therapy and performing the
second baropacing therapy includes providing baropacing
stimulation.
43. The method of claim 41, wherein performing the first baropacing
therapy includes providing baropacing stimulation and performing
the second baropacing therapy includes withholding baropacing
therapy.
44. The method of claim 41, wherein performing baropacing therapy
includes identifying the adverse event, and applying a baropacing
therapy for the adverse event.
45. The method of claim 41, further comprising detecting the
adverse event using an adverse event detector in the implantable
medical device, and sending the signal regarding the adverse event
to a baroreflex stimulator in the implantable medical device.
46. A system for providing baroreflex stimulation, comprising: a
sensor to detect a parameter and provide a signal indicative of the
parameter; and a baroreflex stimulator, including: a driver to
provide a control signal adapted to deliver a baroreflex therapy;
controller to receive the signal indicative of the parameter and
modulate the control signal based on the signal indicative of the
parameter to change the baroreflex therapy from a first baroreflex
therapy to a second baroreflex therapy.
47. A baroreflex stimulator, comprising: an implantable driver to
provide a control signal adapted to provide a baroreflex therapy;
and a controller to receive the signal indicative of the parameter
and modulate the control signal based on the signal indicative of
the parameter to change the baroreflex therapy from a first
baroreflex therapy to a second baroreflex therapy.
48. A method for operating an implantable medical device,
comprising: receiving a signal indicative of a parameter at a
baroreceptor stimulator; performing a first baropacing therapy
using the baroreceptor stimulator when the parameter is not
detected; and performing a second baropacing therapy using the
baroreceptor stimulator when the parameter is detected.
49. A system for providing baroreflex stimulation, comprising: a
heart rate monitor to sense a heart rate and provide a signal
indicative of the heart rate; and a baroreflex stimulator,
including: a pulse generator to intermittently generate a
stimulation signal to provide baroreflex stimulation for a
baroreflex therapy; and a modulator to adjust the stimulation
signal based on the signal indicative of the heart rate such that
the stimulation signal provides a desired baroreflex stimulation
corresponding to a desired heart rate.
50. The system of claim 49, wherein the desired heart rate includes
a programmable value.
51. The system of claim 49, wherein the desired heart rate includes
a percent change based on a heart rate during a time without
baroreflex stimulation and a heart rate during a time with
baroreflex stimulation.
52. The system of claim 49, wherein the desired heart rate includes
a change in a number of heart beats for a heart rate during a time
without baroreflex stimulation and a heart rate during a time with
baroreflex stimulation.
53. The system of claim 49, wherein the modulator is adapted to
adjust signal characteristic of the stimulation signal, wherein the
signal characteristic is selected from a group consisting of: an
amplitude, a frequency, a burst frequency, a pulse width, and a
duty cycle.
54. The system of claim 49, wherein the modulator is adapted to
adjust any combination of at least two stimulation signal
attributes from a group of stimulation signal attributes consisting
of: an amplitude, a frequency, a burst frequency, a pulse width,
and a duty cycle.
55. A system for providing baroreflex stimulation, comprising: a
baroreflex stimulator, including: a pulse generator to generate a
stimulation signal to provide intermittent baroreflex stimulation
for a baroreflex therapy; and a modulator to adjust the stimulation
signal; a cardiovascular parameter monitor to monitor at least one
cardiovascular parameter and provide a first signal indicative of
the cardiovascular parameter during the baroreflex stimulation and
a second signal indicative of the cardiovascular parameter without
the baroreflex stimulation; and a comparator to provide a detected
change for the cardiovascular parameter based on the first and
second signals, and to provide a therapy control signal based on a
desired change for the cardiovascular parameter and the detected
change.
56. The system of claim 55, wherein the modulator is adapted to
adjust at least one stimulation signal attribute from a group of
stimulation signal attributes consisting of: an amplitude, a
frequency, a burst frequency, a pulse width, and a duty cycle.
57. The system of claim 55, wherein the cardiovascular parameter
monitor is adapted to monitor a parameter selected from the group
consisting of: heart rate, blood pressure, respiration rate, a
surrogate parameter for heart rate that increases and decreases
with the heart rate, a percent change for the cardiovascular
parameter when influenced by the baroreflex stimulation and a
quantitative change associated with the cardiovascular parameter
when influenced by the baroreflex stimulation.
58. The system of claim 55, wherein the desired change for the
cardiovascular parameter includes a percent change for the
cardiovascular parameter when influenced by the baroreflex
stimulation.
59. The system of claim 55, wherein the desired change for the
cardiovascular parameter includes a quantitative change associated
with the cardiovascular parameter when influenced by the baroreflex
stimulation.
60. A baroreflex stimulator, comprising: means for intermittently
providing baroreflex stimulation for a baroreflex therapy over a
period of time; means for comparing values for at least one
cardiovascular feedback parameter when the baroreflex stimulation
is applied and when then baroreflex stimulation is not applied to
provide a detected feedback change; means for comparing the
detected feedback change to a desired feedback change to provide a
comparison result; and means for adjusting the baroreflex
stimulation based on the comparison result to control the
baroreflex therapy over the period of time.
61. The baroreflex stimulator of claim 60, wherein the means for
comparing values for at least one cardiovascular feedback parameter
includes means for comparing heart rate when the baroreflex
stimulation is applied and when then baroreflex stimulation is not
applied.
62. The baroreflex stimulator of claim 60, further comprising means
for programming the desired feedback change.
63. A method, comprising: intermittently providing baroreflex
stimulation for a baroreflex therapy over a period of time;
comparing values for at least one cardiovascular feedback parameter
when the baroreflex stimulation is applied and when then baroreflex
stimulation is not applied to provide a detected feedback change;
comparing the detected feedback change to a desired feedback change
to provide a comparison result; and adjusting the baroreflex
stimulation based on the comparison result to control the
baroreflex therapy over the period of time.
64. The method of claim 63, further comprising programming the
desired feedback change for use in comparing the detected feedback
change to the desired feedback change.
65. The method of claim 64, wherein programming the desired
feedback change includes programming a percent change for the at
least one cardiovascular feedback parameter when the baroreflex
stimulation is applied and when then baroreflex stimulation is not
applied.
66. The method of claim 64, wherein programming the desired
feedback change includes programming a quantitative value change
for the at least one cardiovascular feedback parameter when the
baroreflex stimulation is applied and when then baroreflex
stimulation is not applied.
67. A system for providing baroreceptor stimulation comprising: a
sensor to sense a physiologic parameter and provide a signal
indicative of the physiologic parameter; and a baroreceptor
activation device, including a pulse generator to intermittently
generate a stimulation signal to provide baroreceptor stimulation
for a baroreflex therapy; and a control system to adjust the
stimulation signal based on the signal indicative of the
physiologic parameter such that the stimulation signal provides a
desired baroreceptor stimulation corresponding to a desired
physiologic parameter.
68. A system for providing baroreceptor stimulation, comprising: a
baroreceptor activation device including: a pulse generator to
generate a stimulation signal to provide intermittent baroreceptor
stimulation for a baroreflex therapy; and a sensor to monitor at
least one physiologic parameter and provide a first a signal
indicative of the physiologic parameter during the baroreceptor
stimulation and a second signal indicative of a threshold value of
a physiologic parameter; a comparator to provide a detected change
for the physiologic parameter based on the first and second
signals, and to provide a therapy control signal based on the
desired change for the physiologic parameter and the desired
change.
69. A baroreceptor stimulator, comprising means for intermittently
providing baroreceptor stimulation for a baroreflex for a
baroreflex therapy over a period of time; means for comparing
values for at least one physiologic parameter when the baroreceptor
stimulation is applied and values indicative of a threshold value
to provide a detected change in the physiologic parameter; means
for comparing the detected physiologic parameter change to a
desired physiologic parameter change to provide a comparison
result; and means for adjusting the baroreceptor stimulation based
on the comparison result to control the baroreflex therapy over a
period of time.
70. A method, comprising: intermittently providing baroreceptor
stimulation for a baroreflex therapy over a period of time;
comparing values for at least one physiologic parameter when the
baroreceptor stimulation is applied and values indicative of a
threshold parameter to provide a detected physiologic parameter
change; comparing the detected physiologic parameter change to a
desired physiologic parameter change to provide a comparison
result; and adjusting the baroreceptor stimulation based on the
comparison result to control the baroreflex therapy over a period
of time.
71. An implantable medical device, comprising: a pulse generator to
generate baroreflex stimulation pulses; a sensor circuitry; a lead
adapted to be electrically connected to the pulse generator and to
the sensor circuitry, the lead including an electrode to distribute
the baroreflex stimulation pulses to a baroreflex site and a
pressure sensor to provide a signal indicative of blood pressure to
the sensor circuitry; and a controller connected to the pulse
generator and the sensor circuitry, the controller adapted to
adjust the baroreflex stimulation pulses based on the blood
pressure.
72. The device of claim 71, wherein the controller is adapted to
modulate two or more characteristics selected from a group of
characteristics consisting of an amplitude, a frequency, and a
pulse frequency.
73. The device of claim 71, wherein the pressure sensor includes a
micro-electrical mechanical system (MEMS) device to detect blood
pressure.
74. An implantable medical device, comprising: means for delivering
baroreflex therapy to a baroreflex neural target site using an
intravascular lead and an electrode on the lead; means for
monitoring blood pressure near the baroreflex neural target site
using a pressure sensor on the lead; and means for adjusting the
baroreflex therapy based on the blood pressure.
75. An implantable medical device, comprising: a pulse generator to
generate baroreflex stimulation pulses; a sensor circuitry; a lead
adapted to be electrically connected to the pulse generator and to
the sensor circuitry, the lead including an electrode to distribute
the baroreflex stimulation pulses to a baroreflex site and a sensor
to provide a signal to the sensor circuitry that corresponds to a
pre-ejection period measured between a sensed electrical event in a
ventricle and onset of ventricular ejection derived from a
pulmonary arterial blood pressure sensor; and a controller
connected to the pulse generator and the sensor circuitry, the
controller adapted to adjust the baroreflex stimulation pulses
based on the blood pressure.
76. The device of claim 75, wherein the sensed electrical event in
a ventricle includes a sensed electrical event in a right
ventricle.
77. The device of claim 75, wherein the sensed electrical event in
a ventricle includes a sensed electrical event in a left
ventricle.
78. The device of claim 75, wherein the controller is adapted to
modulate a characteristic of the baroreflex stimulation pulses
based on the pre-ejection period selected from the group consisting
of: an amplitude, a frequency, a pulse frequency and a
morphology.
79. The device of claim 75, wherein the controller is adapted to
modulate two or more characteristics selected from a group of
characteristics consisting of an amplitude, a frequency, and a
pulse frequency.
80. A method, comprising: delivering baroreflex therapy to a
baroreflex neural target site using an intravascular lead and an
electrode on the lead; monitoring blood pressure near the
baroreflex neural target site using a pressure sensor on the lead;
and adjusting the baroreflex therapy based on the blood
pressure.
81. An implantable medical device, comprising: a pulse generator to
generate baroreceptor stimulation pulses; a sensor circuitry; a
lead adapted to be electrically connected to the pulse generator
and to the sensor circuitry, the lead including an electrode to
distribute the baroreceptor stimulation pulses to a baroreceptor
site and a pressure sensor to provide a signal indicative of blood
pressure to the sensor circuitry; and a controller connected to the
pulse generator and the sensor circuitry, the controller adapted to
adjust the baroreceptor stimulation pulses based on the blood
pressure.
82. An implantable medical device, comprising: means for delivering
baroreflex therapy to a barorecetor neural target site using an
intravascular lead and an electrode on the lead; means for
monitoring blood pressure near the baroreceptor neural target site
using a pressure sensor on the lead; and means for adjusting the
baroreflex therapy based on the blood pressure.
83. An implantable medical device, comprising: a pulse generator to
generate baroreceptor stimulation pulses; a sensor circuitry; a
lead adapted to be electrically connected to the pulse generator
and to the sensor circuitry, the lead including an electrode to
distribute the baroreceptor stimulation pulses to a baroreceptor
site and a sensor to provide a signal to the sensor circuitry that
includes a measure of blood pressure and corresponds to a specific
physiologic event; and a controller connected to the pulse
generator and the sensor circuitry, the controller adapted to
adjust the baroreceptor stimulation pulses based on the blood
pressure.
84. A method, comprising: delivering baroreflex therapy to a
baroreceptor neural target site using an intravascular lead and an
electrode on the lead; monitoring blood pressure near the
baroreceptor neural target site using a pressure sensor on the
lead; and adjusting the baroreflex therapy based on the blood
pressure.
85. An implantable medical device, comprising: a pulse generator to
generate a baroreflex stimulation signal as part of a baroreflex
therapy; a lead to be electrically connected to the pulse generator
and to be intravascularly fed into a heart, the lead including an
electrode to be positioned in or proximate to the heart to deliver
the baroreflex signal to a baroreceptor region in or proximate to
the heart; a sensor to sense a physiological parameter regarding an
efficacy of the baroreflex therapy and to provide a signal
indicative of the efficacy of the baroreflex therapy; and a
controller connected to the pulse generator to control the
baroreflex stimulation signal and to the sensor to receive the
signal indicative of the efficacy of the baroreflex therapy.
86. The device of claim 85, further comprising a telemetry circuit
to communicate with the controller and to wirelessly communicate
with an external programmer, wherein the implantable medical device
is adapted to communicate therapy data to the programmer for
processing and display by the programmer, and is adapted to receive
programming commands from the programmer.
87. The device of claim 85, wherein the lead is adapted to position
the electrode near an endocardial baroreceptor site within the
heart.
88. The device of claim 85, wherein the pulse generator is further
adapted to generate a cardiac pacing signal, the lead further
including a second electrode to be positioned to deliver the
cardiac pacing signal to capture the heart.
89. The device of claim 88, further comprising sensing circuitry to
sense intrinsic signals indicative of refractories, the sensing
circuitry being connected to the controller.
90. An implantable baroreflex stimulator, comprising: means for
delivering baroreflex therapy through a lead intravascularly fed
through at least a portion of the heart to a baroreceptor region
proximate to a heart to inhibit sympathetic activity; and means for
providing feedback regarding an efficacy of the baroreflex therapy
for use to control delivery of the baroreflex therapy.
91. The stimulator of claim 90, wherein the means for delivering
baroreflex therapy includes means for delivering the baroreflex
therapy to endocardial baroreceptor tissues.
92. The stimulator of claim 90, further comprising means for
determining an appropriate time to deliver the stimulation
signal.
93. The stimulator of claim 90, further comprising means for
communicating with a programmer for data display and patient
management.
94. The stimulator of claim 90, wherein the means for providing
feedback includes means for sensing systemic blood pressure.
95. The stimulator of claim 90, wherein the means for providing
feedback includes means for sensing respiration.
96. The stimulator of claim 90, further comprising means for pacing
the heart.
97. A method, comprising: applying baroreflex therapy, including
electrically stimulating a baroreceptor region in or near a heart
using a lead intravascularly fed into at least a portion of the
heart; sensing a physiologic parameter indicative of an efficacy of
the baroreflex therapy; and modifying the baroreflex therapy based
on the physiological parameter.
98. The method of claim 97, wherein the lead emerges from an
implantable device, the method further comprising pacing the heart
using the lead.
99. An implantable medical device, comprising: a pulse generator to
generate a baroreflex stimulation signal as part of a baroreflex
therapy; a lead to be electrically connected to the pulse
generator, the lead including an electrode to deliver the
baroreflex signal to a baroreflex neural target; a sensor to sense
a physiological parameter regarding an efficacy of the baroreflex
therapy and to provide a signal indicative of the efficacy of the
baroreflex therapy; and a controller connected to the pulse
generator to control the baroreflex stimulation signal and to the
sensor to receive the signal indicative of the efficacy of the
baroreflex therapy.
100. A method, comprising: applying baroreflex therapy, including
electrically stimulating a baroreceptor region using a lead with an
electrode; sensing a physiologic parameter indicative of an
efficacy of the baroreflex therapy; and modifying the baroreflex
therapy based on the physiological parameter.
101. An implantable medical device, comprising: a pulse generator
to generate a baroreceptor stimulation signal as part of a
baroreflex therapy; a lead to be electrically connected to the
pulse generator and to be intravascularly fed into a heart, the
lead including an electrode to be positioned in or proximate to the
heart to deliver the baroreceptor signal to a baroreceptor region
in or proximate to the heart; a sensor to sense a physiological
parameter regarding the need to modify the baroreflex system and to
provide a signal indicative of the need to modify the baroreflex
system; and a controller connected to the pulse generator to
control the baroreceptor stimulation signal and to the sensor to
receive the signal indicative of the need to modify the baroreflex
system.
102. An implantable baroreflex stimulator, comprising: means for
delivering baroreflex therapy through a lead intravascularly fed
through at least a portion of the heart to a baroreceptor region
proximate to a heart to inhibit sympathetic activity; and means for
providing feedback regarding an efficacy of the baroreflex therapy
for use to control delivery of the baroreflex therapy.
103. A method, comprising: applying baroreflex therapy, including
electrically stimulating a baroreceptor region in or near a heart
using a lead intravascularly fed into at least a portion of the
heart; sensing a physiologic parameter indicative of the need to
modify the baroreflex system; and modifying the baroreflex therapy
based on the physiological parameter.
104. An implantable medical device, comprising: a pulse generator
to generate a baroreceptor stimulation signal as part of a
baroreflex therapy; a lead to be electrically connected to the
pulse generator, the lead including an electrode to deliver the
baroreceptor signal to a baroreceptor neural target; a sensor to
sense a physiological parameter and to provide a signal indicative
of the need to modify the baroreflex system; and a controller
connected to the pulse generator to control the baroreceptor
stimulation signal and to the sensor to receive the signal
indicative of the need to modify the baroreflex system.
105. A system for providing baroreflex stimulation, comprising: a
cardiac activity monitor to sense cardiac activity and provide a
signal indicative of the cardiac activity; and a baroreflex
stimulator, including: a pulse generator to provide a baroreflex
stimulation signal adapted to provide a baroreflex therapy; and a
modulator to receive the signal indicative of the cardiac activity
and modulate the baroreflex stimulation signal based on the signal
indicative of the cardiac activity to change the baroreflex therapy
from a first baroreflex therapy to a second baroreflex therapy.
106. The system of claim 105, further comprising a waveform
generator to produce baroreflex stimulation signals of a desired
morphology, wherein the modulator includes a modulator to change
the morphology of the baroreflex stimulation signal based on the
signal indicative of the cardiac activity.
107. The system of claim 105, wherein the cardiac activity monitor
includes a respiration monitor, and the signal indicative of the
cardiac activity includes a respiration signal.
108. The system of claim 107, wherein the respiration monitor
includes a tidal volume monitor.
109. The system of claim 107, wherein the respiration monitor
includes a minute ventilation monitor.
110. The system of claim 105, wherein the cardiac activity monitor
includes an acceleration sensor, and the signal indicative of the
cardiac activity includes an acceleration signal.
111. The system of claim 105, wherein: the cardiac activity monitor
includes a combination of two or more of the following sensors: a
heart rate sensor; a minute ventilation sensor; and an acceleration
sensor; and the signal indicative of the cardiac activity includes
a composite of two or more of the following signals: a heart rate
signal; a minute ventilation signal; and an acceleration
signal.
112. The system of claim 105, wherein the cardiac activity monitor
includes a sensor to sense at least one pressure parameter, and the
signal indicative of the cardiac activity includes a signal
indicative of the at least one pressure parameter.
113. The system of claim 112, wherein the at least one pressure
parameter is selected from the group consisting of: mean arterial
pressure, pulse pressure, end systolic pressure and end diastolic
pressure.
114. The system of claim 105, wherein the cardiac activity monitor
includes a stroke volume monitor, and the signal indicative of the
cardiac activity includes a signal indicative of the stroke
volume.
115. The system of claim 105, wherein the cardiac activity monitor
includes a monitor to measure at least one electrogram measurement,
and the signal indicative of the cardiac activity includes a signal
indicative of the at least one electrogram measurement.
116. The system of claim 105, wherein the cardiac activity monitor
includes a monitor to measure at least one electrocardiogram (ECG)
measurement, and the signal indicative of the cardiac activity
includes a signal indicative of the at least one ECG
measurement.
117. The system of claim 105, further comprising an implantable
medical device, wherein the implantable medical device includes the
cardiac activity monitor and the baroreflex stimulator.
118. A baroreflex stimulator, comprising: an implantable pulse
generator to provide a baroreflex stimulation signal adapted to
provide a baroreflex therapy; and means for modulating the
baroreflex stimulation signal based on a signal indicative of
cardiac activity to change the baroreflex therapy from a first
baroreflex therapy to a second baroreflex therapy.
119. The baroreflex stimulator of claim 118, wherein the means for
modulating the baroreflex stimulation signal includes means for
modulating the baroreflex stimulation signal based on a parameter
selected from the group consisting of: heart rate, respiration,
tidal volume, acceleration.
120. The baroreflex stimulator of claim 119, wherein the means for
modulating the baroreflex stimulation signal based on respiration
includes means for modulating the baroreflex stimulation based on
minute ventilation.
121. The baroreflex stimulator of claim 118, wherein the baroreflex
stimulation signal has a morphology, and the means for modulating
the baroreflex stimulation signal includes means for adjusting the
morphology of the baroreflex stimulation signal.
122. A method for operating an implantable medical device,
comprising: receiving a signal regarding an activity level; and
setting a baroreflex stimulation level for a baroreflex stimulator
of the device based on the signal regarding the activity level.
123. The method of claim 122, further comprising determining
whether the activity level is rest or exercise, wherein setting a
baroreflex stimulation level includes applying baroreflex
stimulation during rest and withdrawing baroreflex stimulation
during exercise.
124. The method of claim 122, further comprising determining
whether the activity level is a first activity level or a second
activity level where the first activity level is higher than the
second activity, wherein setting a baroreflex stimulation level
includes setting a first baroreflex stimulation level when the
activity level is determined to be the second activity level and
setting a second baroreflex stimulation level when the activity
level is determined to be the first activity level, wherein the
first baroreflex stimulation level is higher than the second
baroreflex stimulation level.
125. The method of claim 122, wherein the activity level is one of
a plurality of activity levels and the baroreflex stimulation level
is one of a plurality of baroreflex stimulation levels; and the
baroreflex stimulation levels have an inverse relationship with the
activity levels such that an incremental increase in the activity
level corresponds with an incremental decrease in the baroreflex
stimulation level.
126. The method of claim 122, further comprising comparing the
activity parameter to a target activity parameter, wherein setting
a baroreflex stimulation level includes increasing the baroreflex
stimulation level when the acquired activity parameter is lower
than the target parameter and decreasing the baroreflex stimulation
level when the acquired activity parameter is higher than the
target parameter.
127. The method of claim 122, wherein receiving a signal regarding
an activity level includes sensing a heart rate using a sensor of
the implantable medical device; and setting a baroreflex
stimulation level includes setting the baroreflex stimulation level
based on the heart rate.
128. The method of claim 122, wherein receiving a signal regarding
an activity level includes sensing respiration using a sensor of
the implantable medical device; and setting a baroreflex
stimulation level includes setting the baroreflex stimulation level
based on the respiration.
129. The method of claim 128, wherein sensing respiration includes
sensing tidal volume, and setting the baroreflex stimulation level
based on the respiration includes setting the baroreflex
stimulation level based on the tidal volume.
130. The method of claim 128, wherein sensing respiration includes
sensing minute ventilation, and setting the baroreflex stimulation
level based on the respiration includes setting the baroreflex
stimulation level based on the minute ventilation.
131. The method of claim 122, wherein receiving a signal regarding
an activity level includes sensing acceleration using a sensor of
the implantable medical device; and setting a baroreflex
stimulation level includes setting the baroreflex stimulation level
based on the acceleration.
132. A method, comprising: determining an activity level; setting a
baroreflex stimulation level based on the activity level; and
applying baroreflex stimulation at the baroreflex stimulation
level.
133. The method of claim 132, wherein determining the activity
level includes determining whether the activity level is rest or
exercise; and setting a baroreflex stimulation level based on the
activity level includes providing a signal to apply baroreflex
stimulation during rest and withdraw baroreflex stimulation during
exercise.
134. The method of claim 132, wherein determining the activity
level includes determining whether the activity level is a first
activity level or a second activity level, wherein the first
activity level is higher than the second activity level; and
setting a baroreflex stimulation level based on the activity level
includes setting a first baroreflex stimulation level when the
activity level is determined to be the second activity level, and
setting a second baroreflex stimulation level when the activity
level is determined to be the first activity level, wherein the
first baroreflex stimulation level is higher than the second
baroreflex stimulation level.
135. The method of claim 132, wherein the activity level is one of
a plurality of activity levels and the baroreflex stimulation level
is one of a plurality of baroreflex stimulation levels; and the
baroreflex stimulation levels have an inverse relationship with the
activity levels such that an incremental increase in the activity
level corresponds with an incremental decrease in the baroreflex
stimulation level.
136. The method of claim 132, further comprising comparing the
activity parameter to a cardiac activity parameter, wherein setting
a baroreflex stimulation level based on the activity level includes
increasing the baroreflex stimulation level when the acquired
activity parameter is lower than the target parameter and
decreasing the baroreflex stimulation level when the acquired
activity parameter is higher than the target parameter.
137. A system for providing baroreceptor stimulation, comprising: a
sensor to sense a physiologic parameter and provide a signal
indicative of the physiologic parameter; and a baroreceptor
stimulator, including: a pulse generator to provide a baroreceptor
stimulation signal adapted to provide a baroreflex therapy; and a
control system to receive the signal indicative of the physiologic
parameter and modify the baroreceptor stimulation signal based on
the signal indicative of the physiologic parameter.
138. A baroreceptor stimulator, comprising: an implantable pulse
generator to provide a baroreceptor stimulation signal adapted to
provide a baroreflex therapy; and means for modulating the
baroreceptor stimulation signal based on a signal indicative of a
physiologic parameter to modify the baroreflex therapy.
Description
CROSS-REFERENCES TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 10/284,063, (Attorney Docket No.
021433-000150US), filed on Oct. 29, 2002, which is a
continuation-in-part of U.S. patent application Ser. No. 09/671,850
(Attorney Docket No. 021433-000100US), filed on Sep. 27, 2000,
which is now issued as U.S. Pat. No. 6,522,926, the full
disclosures of which are incorporated herein by reference. The
parent application for this application has incorporated by
reference the disclosures of the following U.S. Patent
Applications: U.S. patent application Ser. No. 09/964,079 (Attorney
Docket No. 021433-000110US), filed on Sep. 26, 2001, now issued as
U.S. Pat. No. 6,985,774, U.S. patent application Ser. No.
09/963,777 (Attorney Docket No. 021433-000120US), filed Sept. 26,
2001, and U.S. patent application Ser. No. 09/963,991, filed on
Sept. 26, 2001, now issued as U.S. Pat. No. 6,850,801, (Attorney
Docket No. 021433-000130US), the disclosures of which are also
effectively incorporated by reference herein.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] 1. Field of the Invention. The present invention generally
relates to medical devices and methods of use for the treatment
and/or management of cardiovascular, renal, and neurological
disorders. Specifically, the present invention relates to devices
and methods for controlling the baroreflex system for the treatment
and/or management of cardiovascular, renal, and neurological
disorders.
[0004] Cardiovascular disease is a major contributor to patient
illness and mortality. It also is a primary driver of health care
expenditure, costing more than $326 billion each year in the United
States. Hypertension, or high blood pressure, is a major
cardiovascular disorder that is estimated to affect over 50 million
people in the United Sates alone. Hypertension occurs when the
body's smaller blood vessels (arterioles) constrict, causing an
increase in blood pressure. Because the blood vessels constrict,
the heart must work harder to maintain blood flow at the higher
pressures. Although the body may tolerate short periods of
increased blood pressure, sustained hypertension may eventually
result in damage to multiple body organs, including the kidneys,
brain, eyes and other tissues, causing a variety of maladies
associated therewith.
[0005] Heart failure is the final common expression of a variety of
cardiovascular disorders, including ischemic heart disease. It is
characterized by an inability of the heart to pump enough blood to
meet the body's needs and results in fatigue, reduced exercise
capacity and poor survival. It is estimated that approximately
5,000,000 people in the United States suffer from heart failure,
directly leading to 39,000 deaths per year and contributing to
another 225,000 deaths per year. Heart failure results in the
activation of a number of body systems to compensate for the
heart's inability to pump sufficient blood. Many of these responses
are mediated by an increase in the level of activation of the
sympathetic nervous system, as well as by activation of multiple
other neurohormonal responses. Generally speaking, this sympathetic
nervous system activation signals the heart to increase heart rate
and force of contraction to increase the cardiac output; it signals
the kidneys to expand the blood volume by retaining sodium and
water; and it signals the arterioles to constrict to elevate the
blood pressure. The cardiac, renal and vascular responses increase
the workload of the heart, further accelerating myocardial damage
and exacerbating the heart failure state. Accordingly, it is
desirable to reduce the level of sympathetic nervous system
activation in order to stop or at least minimize this vicious cycle
and thereby treat or manage the heart failure.
[0006] A number of drug treatments have been proposed for the
management of hypertension, heart failure and other cardiovascular
disorders. These include vasodilators to reduce the blood pressure
and ease the workload of the heart, diuretics to reduce fluid
overload, inhibitors and blocking agents of the body's
neurohormonal responses, and other medicaments. Various surgical
procedures have also been proposed for these maladies. For example,
heart transplantation has been proposed for patients who suffer
from severe, refractory heart failure. Alternatively, an
implantable medical device such as a ventricular assist device
(VAD) may be implanted in the chest to increase the pumping action
of the heart. Alternatively, an intra-aortic balloon pump (IABP)
may be used for maintaining heart function for short periods of
time, but typically no longer than one month. Other surgical
procedures are available as well. No one drug, surgical procedure,
or assist system, however, has provided a complete solution to the
problems of hypertension and heart failure.
[0007] For these reasons, it would be desirable to provide
alternative and improved methods for treating hypertension, heart
failure, and other cardiovascular, neurological, and renal
disorders. Such methods and systems should allow for treatment of
patients where other therapies have failed or are unavailable, such
as heart transplantation. It would be further desirable if the
methods could lessen or eliminate the need for chronic drug use in
at least some patients. Additionally, it would be desirable if the
methods and systems were mechanically simple and inherently
reliable, in contrast to complex mechanical systems such as VAD's,
IABP's, and the like.
[0008] One particularly promising approach for improving the
treatment of hypertension, heart failure, and other cardiovascular
and renal disorders is described in published PCT Application No.
WO 02/026314, which claims the benefit of U.S. patent application
Ser. No. 09/671,850, which is the parent of the present
application. The full disclosures of both WO 02/026314 and U.S.
Ser. No. 09/671,850, are incorporated herein by reference. WO
02/026314 describes the direct activation of baroreceptors for
inducing changes in a patient's baroreflex system to control blood
pressure and other patient functions. The prior applications are
particularly directed at the activation of the baroreceptors
present in the carotid sinus and the aortic arch. Both the carotid
sinus and aortic arch are on the high-pressure or arterial side of
the patient's vasculature. They are referred to as high-pressure
since pressures in the systemic arterial circulation are higher
than those in the veins and pulmonary circulation. Activation of
the high-pressure baroreceptors can send signals to the brain that
cause reflex alterations in nervous system function which result in
changes in activity of target organs, including the heart,
vasculature, kidneys, and the like, typically to maintain
homeostasis.
[0009] While highly promising, the need to implant electrodes or
other effectors on the arterial or high-pressure side of the
vasculature may be disadvantageous in some respects. Arteries and
other vessels on the high-pressure side of the vasculature are at
risk of damage, and implantation of an electrode on or in the
carotid sinus or aortic arch requires more care, and improper
device implantation on the arterial side presents a small risk of
arterial thromboembolism which in turn can cause stroke and other
organ damage. Some arterial locations can also cause unwanted
tissue or nerve stimulation due to current leakage.
[0010] Thus, it would be desirable to provide improved methods and
systems for artificial and selective activation of a patient's
baroreflex system in order to achieve a variety of therapeutic
objectives, including the control of hypertension, renal function,
heart failure, and the treatment of other cardiovascular and
neurological disorders. It would be particularly desirable if such
methods and systems did not require intervention on the arterial or
high-pressure side of a patient's vasculature, thus lessening the
risk to the patient of arterial damage and damage resulting from
thromboembolism or hemorrhage. At least some of these objectives
will be met by the inventions described hereinafter.
[0011] 2. Description of the Background Art
[0012] U.S. Pat. Nos. 6,073,048 and 6,178,349, each having a common
invention with the present application, describe the stimulation of
nerves to regulate the heart, vasculature, and other body systems.
Nerve stimulation for other purposes is described in, for example,
U.S. Pat. Nos. 6,292,695 B1 and 5,700,282. Publications describing
baropacing of the carotid arteries for controlling hypertension
include Neufeld et al. (1965) Israel J. Med. Sci 1:630-632;
Bilgutay et al., Proc. Baroreceptors and Hypertension, Dayton,
Ohio, Nov. 16-17, 1965, pp 425-437; Bilgutary and Lillehei (1966)
Am. J. Cariol. 17:663-667; and Itoh (1972) Jap. Heart J. 13:
136-149. Publications which describe the existence of baroreceptors
and/or related receptors in the venous vasculature and atria
include Goldberger et al. (1999) J. Neuro. Meth. 91:109-114;
Kostreva and Pontus (1993) Am. J. Physiol. 265:G15-G20; Coleridge
et al. (1973) Circ. Res. 23:87-97; Mifflin and Kunze (1982) Circ.
Res. 51:241-249; and Schaurte et al. (2000) J. Cardiovasc
Electrophysiol. 11:64-69.
BRIEF SUMMARY OF THE INVENTION
[0013] To address hypertension, heart failure, cardia arrhythmias,
and associated cardiovascular, renal, and nervous system disorders,
the present invention provides a number of devices, systems and
methods by which the blood pressure, nervous system activity, and
neurohormonal activity may be selectively and controllably
regulated by activating baroreceptors. By selectively and
controllably activating baroreceptors, the present invention
reduces excessive blood pressure, sympathetic nervous system
activation and neurohormonal activation, thereby minimizing their
deleterious effects on the heart, vasculature and other organs and
tissues.
[0014] In an exemplary embodiment, the present invention provides a
system and method for treating a patient by inducing a baroreceptor
signal to effect a change in the baroreflex system (e.g., reduced
heart rate, reduced blood pressure, etc.). The baroreceptor signal
is activated or otherwise modified by selectively activating
baroreceptors. To accomplish this, the system and method of the
present invention utilize a baroreceptor activation device
positioned near a baroreceptor in the venous or low-pressure side
of a patient's vasculature. As used hereinafter, the phrase
"low-pressure side of the vasculature" will mean the venous and
cardiopulmonary vasculature, including particularly the chambers in
the heart, veins near the entrances to the atria, the pulmonary
artery, the portal vein of the liver, the superior vena cava (SVC),
the inferior vena cava (IVC), the jugular vein, the subclavian
veins, the iliac veins, the femoral veins, and other peripheral
areas of the vasculature where baroreceptor and baroreceptor-like
receptors are found. Particular target mechanoreceptors are
described in Kostreva and Pontus (1993), cited above, the full
disclosure of which is incorporated herein by reference.
[0015] The baroreceptors and baroreceptor-like receptors on the
low-pressure side of the vasculature will function similarly to,
but not necessarily identically to, baroreceptors on the
high-pressure side of the vasculature. In general, cardiovascular
receptors may be sensitive to pressure and/or mechanical
deformation and are referred to as baroreceptors, mechanoreceptors,
pressoreceptors, stretch receptors, and the like. For
cardiovascular and renal therapies, the present invention is
intended to activate or otherwise interact with any or all of these
types of receptors so long as such activation or interaction
results in modulation of the reflex control of the patient's
circulation. While there may be small structural or anatomical
differences among various receptors in the vasculature, for the
purposes of the present invention, activation may be directed at
any of these receptors so long as they provide the desired effects.
In particular, such receptors will provide afferent signals, i.e.,
signals to the brain, which provide the blood pressure and/or
volume information to the brain which allow the brain to cause
"reflex" changes in the autonomic nervous system which in turn
modulate organ activity to maintain desired hemodynamics and organ
perfusion. Such activation of afferent pathways may also affect
brain functions in such a way that could aid in the treatment of
neurologic disease.
[0016] The ability to control the baroreflex response and
cardiovascular, renal, and neurological function, by intervention
on the low-pressure side of the vasculature is advantageous in
several respects. Intervention on the venous and cardiopulmonary
side of the vasculature reduces the risk of organ damage, including
stroke, from systemic arterial thromboembolism. Moreover, the
devices and structures used for intervening on the venous and
cardiopulmonary side of the vasculature may be less complicated
since the risk they pose to venous circulation is much less than to
arterial circulation. Additionally, the availability of venous and
cardiopulmonary baroreceptors allows placement of electrodes and
other devices which reduce the risk of unwanted tissue stimulation
resulting from current leakage to closely adjacent nerves, muscles,
and other tissues.
[0017] Generally speaking, the baroreceptor activation device may
be activated, deactivated or otherwise modulated to activate one or
more baroreceptors and induce a baroreceptor signal or a change in
the baroreceptor signal to thereby effect a change in the
baroreflex system. The baroreceptor activation device may be
activated, deactivated, or otherwise modulated continuously,
periodically, or episodically. The baroreceptor activation device
may comprise a wide variety of devices which utilize mechanical,
electrical, thermal, chemical, biological, or other means to
activate the baroreceptor. The baroreceptor may be activated
directly, or activated indirectly via the adjacent vascular tissue.
The baroreceptor activation device may be positioned inside the
vascular lumen (i.e., intravascularly), outside the vascular wall
(i.e., extravascularly) or within the vascular wall (i.e.,
intramurally). The particular activation patterns may be selected
to mimic those which naturally occur in the venous and
cardiopulmonary vasculature, which conditions might vary from those
characteristic of the arterial vasculature. In other cases, the
activation patterns may be different from the natural patterns and
selected to achieve an optimized barosystem response.
[0018] A control system may be used to generate a control signal
which activates, deactivates or otherwise modulates the
baroreceptor activation device. The control system may operate in
an open-loop or a closed-loop mode. For example, in the open-loop
mode, the patient and/or physician may directly or remotely
interface with the control system to prescribe the control signal.
In the closed-loop mode, the control signal may be responsive to
feedback from a sensor, wherein the response is dictated by a
preset or programmable algorithm.
[0019] To address low blood pressure and other conditions requiring
blood pressure augmentation, the present invention provides a
number of devices, systems and methods by which the blood pressure
may be selectively and controllably regulated by inhibiting or
dampening baroreceptor signals. By selectively and controllably
inhibiting or dampening baroreceptor signals, the present invention
reduces conditions associated with low blood pressure.
[0020] To address hypertension, heart failure, cardiac arrhythmias,
and their associated cardiovascular and nervous system disorders,
the present invention provides a number of devices, systems and
methods by which the blood pressure, nervous system activity, and
neurohormonal activity may be selectively and controllably
regulated by activating baroreceptors, baroreceptor-like
mechanoreceptors or pressoreceptors, or the like. By selectively
and controllably activating baroreceptors, the present invention
reduces excessive blood pressure, sympathetic nervous system
activation and neurohormonal activation, thereby minimizing their
deleterious effects on the heart, vasculature and other organs and
tissues.
[0021] In an exemplary embodiment, the present invention provides a
system and method for treating a patient by inducing a baroreceptor
signal to effect a change in the baroreflex system (e.g., reduced
heart rate, reduced blood pressure, etc.). The baroreceptor signal
is activated or otherwise modified by selectively activating
baroreceptors. To accomplish this, the system and method of the
present invention utilize a baroreceptor activation device
positioned near a baroreceptor in a vein, the pulmonary
vasculature, in a heart chamber, at a veno-atrial junction, or the
like.
[0022] Generally speaking, the baroreceptor activation device may
be activated, deactivated or otherwise modulated to activate one or
more baroreceptors and induce a baroreceptor signal or a change in
the baroreceptor signal to thereby effect a change in the
baroreflex system. The baroreceptor activation device may be
activated, deactivated, or otherwise modulated continuously,
periodically, or episodically. The baroreceptor activation device
may comprise a wide variety of devices which utilize mechanical,
electrical, thermal, chemical, biological, or other means to
activate the baroreceptor. The baroreceptor may be activated
directly, or activated indirectly via the adjacent vascular tissue.
The baroreceptor activation device may be positioned inside the
vascular lumen (i.e., intravascularly), outside the vascular wall
(i.e., extravascularly) or within the vascular wall (i.e.,
intramurally).
[0023] A control system may be used to generate a control signal
which activates, deactivates or otherwise modulates the
baroreceptor activation device. The control system may operate in
an open-loop or a closed-loop mode. For example, in the open-loop
mode, the patient and/or physician may directly or remotely
interface with the control system to prescribe the control signal.
In the closed-loop mode, the control signal may be responsive to
feedback from a sensor, wherein the response is dictated by a
preset or programmable algorithm.
[0024] To address low blood pressure and other conditions requiring
blood pressure augmentation, the present invention provides a
number of devices, systems and methods by which the blood pressure
may be selectively and controllably regulated by inhibiting or
dampening baroreceptor signals. By selectively and controllably
inhibiting or dampening baroreceptor signals, the present invention
reduces conditions associated with low blood pressure.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] FIG. 1 is a schematic illustration of the upper torso of a
human body showing the major arteries and veins and associated
anatomy.
[0026] FIG. 1A is a schematic illustration of the lower abdominal
vasculature including the abdominal aorta and the inferior vena
cava.
[0027] FIG. 2 is a cross-sectional schematic illustration of
baroreceptors within a vascular wall.
[0028] FIG. 3 is a schematic illustration of a baroreceptor
activation system in accordance with the present invention.
[0029] FIG. 4 is a schematic illustration of a baroreceptor
activation device in the form of an internal inflatable balloon
which mechanically induces a baroreceptor signal in accordance with
an embodiment of the present invention.
[0030] FIG. 5 is a schematic illustration of a baroreceptor
activation device in the form of an external pressure cuff which
mechanically induces a baroreceptor signal in accordance with an
embodiment of the present invention.
[0031] FIG. 6A is a schematic illustration of a baroreceptor
activation device in the form of an internal deformable coil
structure which mechanically induces a baroreceptor signal in
accordance with an embodiment of the present invention.
[0032] FIGS. 6B and 6C are cross-sectional views of alternative
embodiments of the coil member illustrated in FIG. 6.
[0033] FIG. 7 is a schematic illustration of a baroreceptor
activation device in the form of an external deformable coil
structure which mechanically induces a baroreceptor signal in
accordance with an embodiment of the present invention.
[0034] FIG. 8 is a schematic illustration of a baroreceptor
activation device in the form of an external flow regulator which
artificially creates back pressure to induce a baroreceptor signal
in accordance with an embodiment of the present invention.
[0035] FIG. 9 is a schematic illustration of a baroreceptor
activation device in the form of an internal flow regulator which
artificially creates back pressure to induce a baroreceptor signal
in accordance with an embodiment of the present invention.
[0036] FIG. 10 is a schematic illustration of a baroreceptor
activation device in the form of a magnetic device which
mechanically induces a baroreceptor signal in accordance with an
embodiment of the present invention.
[0037] FIG. 11 is a schematic illustration of a baroreceptor
activation device in the form of a transducer which mechanically
induces a baroreceptor signal in accordance with an embodiment of
the present invention.
[0038] FIG. 12 is a schematic illustration of a baroreceptor
activation device in the form of a fluid delivery device which may
be used to deliver an agent which chemically or biologically
induces a baroreceptor signal in accordance with an embodiment of
the present invention.
[0039] FIG. 13 is a schematic illustration of a baroreceptor
activation device in the form of an internal conductive structure
which electrically or thermally induces a baroreceptor signal in
accordance with an embodiment of the present invention.
[0040] FIG. 14 is a schematic illustration of a baroreceptor
activation device in the form of an internal conductive structure,
activated by an internal inductor, which electrically or thermally
induces a baroreceptor signal in accordance with an embodiment of
the present invention.
[0041] FIG. 15 is a schematic illustration of a baroreceptor
activation device in the form of an internal conductive structure,
activated by an internal inductor located in an adjacent vessel,
which electrically or thermally induces a baroreceptor signal in
accordance with an embodiment of the present invention.
[0042] FIG. 16 is a schematic illustration of a baroreceptor
activation device in the form of an internal conductive structure,
activated by an external inductor, which electrically or thermally
induces a baroreceptor signal in accordance with an embodiment of
the present invention.
[0043] FIG. 17 is a schematic illustration of a baroreceptor
activation device in the form of an external conductive structure
which electrically or thermally induces a baroreceptor signal in
accordance with an embodiment of the present invention.
[0044] FIG. 18 is a schematic illustration of a baroreceptor
activation device in the form of an internal bipolar conductive
structure which electrically or thermally induces a baroreceptor
signal in accordance with an embodiment of the present
invention.
[0045] FIG. 19 is a schematic illustration of a baroreceptor
activation device in the form of an electromagnetic field
responsive device which electrically or thermally induces a
baroreceptor signal in accordance with an embodiment of the present
invention.
[0046] FIG. 20 is a schematic illustration of a baroreceptor
activation device in the form of an external Peltier device which
thermally induces a baroreceptor signal in accordance with an
embodiment of the present invention.
[0047] FIGS. 21A-21C are schematic illustrations of a preferred
embodiment of an inductively activated electrically conductive
structure.
[0048] FIGS. 22A-22C are ECG charts of a dog undergoing stimulation
of the abdominal IVC.
DETAILED DESCRIPTION OF THE INVENTION
[0049] The following detailed description should be read with
reference to the drawings in which similar elements in different
drawings are numbered the same. The drawings, which are not
necessarily to scale, depict illustrative embodiments and are not
intended to limit the scope of the invention.
[0050] To better understand the present invention, it may be useful
to explain some of the basic vascular anatomy associated with the
cardiovascular system. Refer to FIG. 1 which is a schematic
illustration of the upper torso of a human body 10 showing some of
the major arteries and veins of the cardiovascular system. The left
ventricle of the heart 11 pumps oxygenated blood up into the aortic
arch 12. The right subclavian artery 13, the right common carotid
artery 14, the left common carotid artery 15 and the left
subclavian artery 16 branch off the aortic arch 12 proximal of the
descending thoracic aorta 17. Although relatively short, a distinct
vascular segment referred to as the brachiocephalic artery 22
connects the right subclavian artery 13 and the right common
carotid artery 14 to the aortic arch 12. The right carotid artery
14 bifurcates into the right external carotid artery 18 and the
right internal carotid artery 19 at the right carotid sinus 20.
Although not shown for purposes of clarity only, the left carotid
artery 15 similarly bifurcates into the left external carotid
artery and the left internal carotid artery at the left carotid
sinus.
[0051] From the aortic arch 12, oxygenated blood flows into the
carotid arteries 18/19 and the subclavian arteries 13/16. From the
carotid arteries 18/19, oxygenated blood circulates through the
head and cerebral vasculature and oxygen depleted blood returns to
the heart 11 by way of the jugular veins, of which only the right
internal jugular vein 21 is shown for sake of clarity. From the
subclavian arteries 13/16, oxygenated blood circulates through the
upper peripheral vasculature and oxygen depleted blood returns to
the heart by way of the subclavian veins, of which only the right
subclavian vein 23 is shown, also for sake of clarity. Deoxygenated
blood from the upper torso and head eventually return to the heart
11 through the superior vena cava 23.1, shown diagrammatically
only. The heart 11 pumps the oxygen-depleted blood through the
pulmonary system where it is re-oxygenated. The re-oxygenated blood
returns to the heart 11 which pumps the re-oxygenated blood into
the aortic arch as described above, and the cycle repeats. In the
abdomen and lower extremities, oxygenated blood is delivered to the
organs and lower limbs through the abdominal aorta 23.2.
Deoxygenated blood returns to the heart through the inferior vena
cava 23.3.
[0052] Within the walls of many veins, the pulmonary vasculature
and the chambers of the heart, as in the walls of the carotid
sinus, aorta and other arterial structures, there are
baroreceptors. Baroreceptors are a type of stretch receptor used by
the body to sense blood pressure and blood volume. An increase in
blood pressure or volume causes the vascular wall to stretch, and a
decrease in blood pressure or volume causes the vascular wall to
return to its original size. In many vessels, such a cycle is
repeated with each beat of the heart. In others, in particular some
of the body's veins, the pressure and volume change more slowly.
Because baroreceptors are located within the vascular wall, they
are able to sense deformation of the adjacent tissue, which is
indicative of a change in blood pressure or volume.
[0053] Refer now to FIG. 2, which shows a schematic illustration of
baroreceptors 30 disposed in a generic vascular wall 40 and a
schematic flow chart of the baroreflex system 50. Baroreceptors 30
are profusely distributed within the arterial walls 40 of the blood
vessels major arteries discussed previously, and are presently
believed by the inventors to form an arbor 32 as is characteristic
of the analogous receptors in the arterial system as described in
parent application Ser. No. 09/672,850, previously incorporated
herein by reference. A baroreceptor arbor 32 would comprise a
plurality of baroreceptors 30, each of which transmits baroreceptor
signals to the brain 52 via nerve 38. The baroreceptors 30 may be
so profusely distributed and arborized within the vascular wall 40
that discrete baroreceptor arbors 32 are not readily discemable. To
this end, those skilled in the art will appreciate that the
baroreceptors 30 shown in FIG. 2 are primarily schematic for
purposes of illustration and discussion. In other regions, the
baroreceptors may be so sparsely distributed that activation over a
relatively greater length of the vein would be required than would
be with an artery where the receptors might be more
concentrated.
[0054] Baroreceptor signals in the arterial vasculature are used to
activate a number of body systems which collectively may be
referred to as the baroreflex system 50. For the purposes of the
present invention, it will be assumed that the "receptors" in the
venous and cardiopulmonary vasculature and heart chambers function
analogously to the baroreceptors in the arterial vasculature, but
such assumption is not intended to limit the present invention in
any way. In particular, the methods described herein will function
and achieve at least some of the stated therapeutic objectives
regardless of the precise and actual mechanism responsible for the
result. Moreover, the present invention may activate baroreceptors,
mechanoreceptors, pressoreceptors, or any other venous heart, or
cardiopulmonary receptors which affect the blood pressure, nervous
system activity, and neurohormonal activity in a manner analogous
to baroreceptors in the arterial vasculation. For convenience, all
such venous receptors will be referred to collectively herein as
"baroreceptors." Thus for discussion purposes, it will be assumed
that baroreceptors 30 are connected to the brain 52 via the nervous
system 51. Thus, the brain 52 is able to detect changes in blood
pressure which are indicative of cardiac output and/or blood
volume. If cardiac output and/or blood volume are insufficient to
meet demand (i.e., the heart 11 is unable to pump sufficient
blood), the baroreflex system 50 activates a number of body
systems, including the heart 11, kidneys 53, vessels 54, and other
organs/tissues. Such activation of the baroreflex system 50
generally corresponds to an increase in neurohormonal activity.
Specifically, the baroreflex system 50 initiates a neurohormonal
sequence that signals the heart 11 to increase heart rate and
increase contraction force in order to increase cardiac output,
signals the kidneys 53 to increase blood volume by retaining sodium
and water, and signals the vessels 54 to constrict to elevate blood
pressure. The cardiac, renal and vascular responses increase blood
pressure and cardiac output 55, and thus increase the workload of
the heart 11. In a patient with heart failure, this further
accelerates myocardial damage and exacerbates the heart failure
state.
[0055] To address the problems of hypertension, heart failure,
cardiac arrhythmias, renal dysfunction, and nervous system other
cardiovascular disorders, the present invention basically provides
a number of devices, systems and methods by which the baroreflex
system 50 is activated to reduce excessive blood pressure,
autonomic nervous system activity and neurohormonal activation. In
particular, the present invention provides a number of devices,
systems and methods by which baroreceptors 30 may be activated,
thereby indicating an increase in blood pressure and signaling the
brain 52 to reduce the body's blood pressure and level of
sympathetic nervous system and neurohormonal activation, and
increase parasypathetic nervous system activation, thus having a
beneficial effect on the cardiovascular system and other body
systems.
[0056] With reference to FIG. 3, the present invention generally
provides a system including a control system 60, a baroreceptor
activation device 70, and a sensor 80 (optional). For purposes of
illustration, the baroreceptor activation device 70 is shown to be
located on, in or near the inferior vena cava 23.3, but it could
also be located at the other baroreceptor target locations
discussed elsewhere in this application. The exemplary control
system 60, generally operates in the following manner. The sensor
80 senses and/or monitors a parameter (e.g., cardiovascular
function) indicative of the need to modify the baroreflex system
and generates a signal indicative of the parameter. The control
system 60 generates a control signal as a function of the received
sensor signal. The control signal activates, deactivates or
otherwise modulates the baroreceptor activation device 70.
Typically, activation of the device 70 results in activation of the
baroreceptors 30 (FIG. 2). Alternatively, deactivation or
modulation of the baroreceptor activation device 70 may cause or
modify activation of the baroreceptors 30. The baroreceptor
activation device 70 may comprise a wide variety of devices which
utilize mechanical, electrical, thermal, chemical, biological, or
other means to activate baroreceptors 30. Thus, when the sensor 80
detects a parameter indicative of the need to modify the baroreflex
system activity (e.g., excessive blood pressure), the control
system 60 generates a control signal to modulate (e.g. activate)
the baroreceptor activation device 70 thereby inducing a
baroreceptor 30 signal that is perceived by the brain 52 to be
apparent excessive blood pressure. When the sensor 80 detects a
parameter indicative of normal body function (e.g., normal blood
pressure), the control system 60 generates a control signal to
modulate (e.g., deactivate) the baroreceptor activation device
70.
[0057] As mentioned previously, the baroreceptor activation device
70 may comprise a wide variety of devices which utilize mechanical,
electrical, thermal, chemical, biological or other means to
activate the baroreceptors 30. Specific embodiments of the generic
baroreceptor activation device 70 are discussed with reference to
FIGS. 4-21. In most instances, particularly the mechanical
activation embodiments, the baroreceptor activation device 70
indirectly activates one or more baroreceptors 30 by stretching or
otherwise deforming the vascular wall 40 surrounding the
baroreceptors 30. In some other instances, particularly the
non-mechanical activation embodiments, the baroreceptor activation
device 70 may directly activate one or more baroreceptors 30 by
changing the electrical, thermal or chemical environment or
potential across the baroreceptors 30. It is also possible that
changing the electrical, thermal or chemical potential across the
tissue surrounding the baroreceptors 30 may cause the surrounding
tissue to stretch or otherwise deform, thus mechanically activating
the baroreceptors 30. In other instances, particularly the
biological activation embodiments, a change in the function or
sensitivity of the baroreceptors 30 may be induced by changing the
biological activity in the baroreceptors 30 and altering their
intracellular makeup and function.
[0058] All of the specific embodiments of the baroreceptor
activation device 70 are suitable for implantation, and are
preferably implanted using a minimally invasive percutaneous
transluminal approach and/or a minimally invasive surgical
approach, depending on whether the device 70 is disposed
intravascularly, extravascularly or within the vascular wall 40.
The baroreceptor activation device 70 may be positioned anywhere in
or proximate the venous or cardiopulmonary vasculature, and/or the
heart chambers, where baroreceptors capable of modulating the
baroreflex system 50 are present. The baroreceptor activation
device 70 will usually be implanted such that the device 70 is
positioned immediately adjacent the baroreceptors 30.
Alternatively, the baroreceptor activation device 70 may be outside
the body such that the device 70 is positioned a short distance
from but proximate to the baroreceptors 30. Preferably, the
baroreceptor activation device 70 is implanted at a location which
permits selective activation of the target baroreceptor, typically
being in, around, or near the target baroreceptor. For purposes of
illustration only, the present invention is described with
reference to baroreceptor activation device 70 positioned near the
inferior vena cava 23.3.
[0059] The optional sensor 80 is operably coupled to the control
system 60 by electric sensor cable or lead 82. The sensor 80 may
comprise any suitable device that measures or monitors a parameter
indicative of the need to modify the activity of the baroreflex
system. For example, the sensor 80 may comprise a physiologic
transducer or gauge that measures ECG, blood pressure (systolic,
diastolic, average or pulse pressure), blood volumetric flow rate,
blood flow velocity, blood pH, O2 or CO2 content, mixed venous
oxygen saturation (SVO2), vasoactivity, nerve activity, tissue
activity or composition. Examples of suitable transducers or gauges
for the sensor 80 include ECG electrodes, a piezoelectric pressure
transducer, an ultrasonic flow velocity transducer, an ultrasonic
volumetric flow rate transducer, a thermodilution flow velocity
transducer, a capacitive pressure transducer, a membrane pH
electrode, an optical detector (SVO2) or a strain gage. Although
only one sensor 80 is shown, multiple sensors 80 of the same or
different type at the same or different locations may be
utilized.
[0060] The sensor 80 is preferably positioned in a chamber of the
heart 11, or in/on a major artery such as the aortic arch 12, a
common carotid artery 14/15, a subclavian artery 13/16 or the
brachiocephalic artery 22, or in any of the low-pressure venous or
cardiopulmonary sites, such that the parameter of interest may be
readily ascertained. The sensor 80 may be disposed inside the body
such as in or on an artery, a vein or a nerve (e.g. vagus nerve),
or disposed outside the body, depending on the type of transducer
or gauge utilized. The sensor 80 may be separate from the
baroreceptor activation device 70 or combined therewith. For
purposes of illustration only, the sensor 80 is shown positioned on
the right subclavian artery 13.
[0061] By way of example, the control system 60 includes a control
block 61 comprising a processor 63 and a memory 62. Control system
60 is connected to the sensor 80 by way of sensor cable 82. Control
system 60 is also connected to the baroreceptor activation device
70 by way of electric control cable 72. Thus, the control system 60
receives a sensor signal from the sensor 80 by way of sensor cable
82, and transmits a control signal to the baroreceptor activation
device 70 by way of control cable 72.
[0062] The memory 62 may contain data related to the sensor signal,
the control signal, and/or values and commands provided by the
input device 64. The memory 62 may also include software containing
one or more algorithms defining one or more functions or
relationships between the control signal and the sensor signal. The
algorithm may dictate activation or deactivation control signals
depending on the sensor signal or a mathematical derivative
thereof. The algorithm may dictate an activation or deactivation
control signal when the sensor signal falls below a lower
predetermined threshold value, rises above an upper predetermined
threshold value or when the sensor signal indicates a specific
physiologic event.
[0063] As mentioned previously, the baroreceptor activation device
70 may activate baroreceptors 30 mechanically, electrically,
thermally, chemically, biologically or otherwise. In some
instances, the control system 60 includes a driver 66 to provide
the desired power mode for the baroreceptor activation device 70.
For example if the baroreceptor activation device 70 utilizes
pneumatic or hydraulic actuation, the driver 66 may comprise a
pressure/vacuum source and the cable 72 may comprise fluid line(s).
If the baroreceptor activation device 70 utilizes electrical or
thermal actuation, the driver 66 may comprise a power amplifier or
the like and the cable 72 may comprise electrical lead(s). If the
baroreceptor activation device 70 utilizes chemical or biological
actuation, the driver 66 may comprise a fluid reservoir and a
pressure/vacuum source, and the cable 72 may comprise fluid
line(s). In other instances, the driver 66 may not be necessary,
particularly if the processor 63 generates a sufficiently strong
electrical signal for low level electrical or thermal actuation of
the baroreceptor activation device 70.
[0064] The control system 60 may operate as a closed loop utilizing
feedback from the sensor 80, or as an open loop utilizing commands
received by input device 64. The open loop operation of the control
system 60 preferably utilizes some feedback from the transducer 80,
but may also operate without feedback. Commands received by the
input device 64 may directly influence the control signal or may
alter the software and related algorithms contained in memory 62.
The patient and/or treating physician may provide commands to input
device 64. Display 65 may be used to view the sensor signal,
control signal and/or the software/data contained in memory 62.
[0065] The control signal generated by the control system 60 may be
continuous, periodic, episodic or a combination thereof, as
dictated by an algorithm contained in memory 62. Continuous control
signals include a constant pulse, a constant train of pulses, a
triggered pulse and a triggered train of pulses. Examples of
periodic control signals include each of the continuous control
signals described above which have a designated start time (e.g.,
beginning of each minute, hour or day) and a designated duration
(e.g., 1 second, 1 minute, 1 hour). Examples of episodic control
signals include each of the continuous control signals described
above which are triggered by an episode (e.g., activation by the
patient/physician, an increase in blood pressure above a certain
threshold, etc.).
[0066] The control system 60 may be implanted in whole or in part.
For example, the entire control system 60 may be carried externally
by the patient utilizing transdermal connections to the sensor lead
82 and the control lead 72. Alternatively, the control block 61 and
driver 66 may be implanted with the input device 64 and display 65
carried externally by the patient utilizing transdermal connections
therebetween. As a further alternative, the transdermal connections
may be replaced by cooperating transmitters/receivers to remotely
communicate between components of the control system 60 and/or the
sensor 80 and baroreceptor activation device 70.
[0067] With general reference to FIGS. 4-21, schematic
illustrations of specific embodiments of the baroreceptor
activation device 70 are shown. The design, function and use of
these specific embodiments, in addition to the control system 60
and sensor 80 (not shown), are the same as described with reference
to FIG. 3, unless otherwise noted or apparent from the description.
In addition, the anatomical features illustrated in FIGS. 4-20 are
the same as discussed with reference to FIGS. 1, 1A, and 2 , unless
otherwise noted. In each embodiment, the connections between the
components 60/70/80 may be physical (e.g., wires, tubes, cables,
etc.) or remote (e.g., transmitter/receiver, inductive, magnetic,
etc.). For physical connections, the connection may travel
intraarterially, intravenously, subcutaneously, or through other
natural tissue paths.
[0068] Refer now to FIG. 4 which shows schematic illustrations of a
baroreceptor activation device 100 in the form of an intravascular
inflatable balloon 100. The inflatable balloon device 100 includes
a helical balloon 102 which is connected to a fluid line 104. An
example of a similar helical balloon is disclosed in U.S. Pat. No.
5,181,911 to Shturman, the entire disclosure of which is hereby
incorporated by reference. The balloon 102 preferably has a helical
geometry or any other geometry which allows blood perfusion
therethrough. The fluid line 104 is connected to the driver 66 of
the control system 60 (FIG. 3). In this embodiment, the driver 66
comprises a pressure/vacuum source (i.e., an inflation device)
which selectively inflates and deflates the helical balloon 102.
Upon inflation, the helical balloon 102 expands, preferably
increasing in outside diameter only, to mechanically activate
baroreceptors 30 by stretching or otherwise deforming them and/or
the vascular wall 40. Upon deflation, the helical balloon 102
returns to its relaxed geometry such that the vascular wall 40
returns to its nominal state. Thus, by selectively inflating the
helical balloon 102, the baroreceptors 30 adjacent thereto may be
selectively activated.
[0069] As an alternative to pneumatic or hydraulic expansion
utilizing a balloon, a mechanical expansion device (not shown) may
be used to expand or dilate the vascular wall 40 and thereby
mechanically activate the baroreceptors 30. For example, the
mechanical expansion device may comprise a tubular wire braid
structure that diametrically expands when longitudinally compressed
as disclosed in U.S. Pat. No. 5,222,971 to Willard et al., the
entire disclosure of which is hereby incorporated by reference. The
tubular braid may be disposed intravascularly and permits blood
perfusion through the wire mesh. In this embodiment, the driver 66
may comprise a linear actuator connected by actuation cables to
opposite ends of the braid. When the opposite ends of the tubular
braid are brought closer together by actuation of the cables, the
diameter of the braid increases to expand the vascular wall 40 and
activate the baroreceptors 30.
[0070] Refer now to FIG. 5 which shows a baroreceptor activation
device 120 in the form of an extravascular pressure cuff 120. The
pressure cuff device 120 includes an inflatable cuff 122 which is
connected to a fluid line 124. Examples of a similar cuffs 122 are
disclosed in U.S. Pat. No. 4,256,094 to Kapp et al. and U.S. Pat.
No. 4,881,939 to Newman, the entire disclosures of which are hereby
incorporated by reference. The fluid line 124 is connected to the
driver 66 (FIG. 3) of the control system 60. In this embodiment,
the driver 66 comprises a pressure/vacuum source (i.e., an
inflation device) which selectively inflates and deflates the cuff
122. Upon inflation, the cuff 122 expands, preferably increasing in
inside diameter only, to mechanically activate baroreceptors 30 by
stretching or otherwise deforming them and/or the vascular wall 40.
Upon deflation, the cuff 122 returns to its relaxed geometry such
that the vascular wall 40 returns to its nominal state. Thus, by
selectively inflating the inflatable cuff 122, the baroreceptors 30
adjacent thereto may be selectively activated.
[0071] The driver 66 may be automatically actuated by the control
system 60 as discussed above, or may be manually actuated. An
example of an externally manually actuated pressure/vacuum source
is disclosed in U.S. Pat. No. 4,709,690 to Haber, the entire
disclosure of which is hereby incorporated by reference. Examples
of transdermally manually actuated pressure/vacuum sources are
disclosed in U.S. Pat. No. 4,586,501 to Claracq, U.S. Pat. No.
4,828,544 to Lane et al., and U.S. Pat. No. 5,634,878 to Grundei et
al., the entire disclosures of which are hereby incorporated by
reference.
[0072] Those skilled in the art will recognize that other external
compression devices may be used in place of the inflatable cuff
device 120. For example, a piston actuated by a solenoid may apply
compression to the vascular wall. An example of a solenoid actuated
piston device is disclosed in U.S. Pat. No. 4,014,318 to Dokum et
al, and an example of a hydraulically or pneumatically actuated
piston device is disclosed in U.S. Pat. No. 4,586,501 to Claracq,
the entire disclosures of which are hereby incorporated by
reference. Other examples include a rotary ring compression device
as disclosed in U.S. Pat. No. 4,551,862 to Haber, and an
electromagnetically actuated compression ring device as disclosed
in U.S. Pat. No. 5,509,888 to Miller, the entire disclosures of
which are hereby incorporated by reference.
[0073] Refer now to FIG. 6 which shows a baroreceptor activation
device 140 in the form of an intravascular deformable structure.
The deformable structure device 140 includes a coil, braid or other
stent-like structure 142 disposed in the vascular lumen. The
deformable structure 142 includes one or more individual structural
members connected to an electrical lead 144. Each of the structural
members forming deformable structure 142 may comprise a shape
memory material 146 (e.g., nickel titanium alloy) as illustrated in
FIG. 6B, or a bimetallic material 148 as illustrated in FIG. 6C.
The electrical lead 144 is connected to the driver 66 of the
control system 60. In this embodiment, the driver 66 comprises an
electric power generator or amplifier which selectively delivers
electric current to the structure 142 which resistively heats the
structural members 146/148. The structure 142 may be unipolar as
shown using the surrounding tissue as ground, or bipolar or
multipolar using leads connected to either end of the structure
142. Electrical power may also be delivered to the structure 142
inductively as described hereinafter with reference to FIGS.
14-16.
[0074] Upon application of electrical current to the shape memory
material 146, it is resistively heated causing a phase change and a
corresponding change in shape. Upon application of electrical
current to the bimetallic material 148, it is resistively heated
causing a differential in thermal expansion and a corresponding
change in shape. In either case, the material 146/148 is designed
such that the change in shape causes expansion of the structure 142
to mechanically activate baroreceptors 30 by stretching or
otherwise deforming them and/or the vascular wall 40. Upon removal
of the electrical current, the material 146/148 cools and the
structure 142 returns to its relaxed geometry such that the
baroreceptors 30 and/or the vascular wall 40 return to their
nominal state. Thus, by selectively expanding the structure 142,
the baroreceptors 30 adjacent thereto may be selectively
activated.
[0075] Refer now to FIG. 7 which shows a baroreceptor activation
device 160 in the form of an extravascular deformable structure.
The extravascular deformable structure device 160 is substantially
the same as the intravascular deformable structure device 140
described with reference to FIGS. 6A and 6B, except that the
extravascular device 160 is disposed about the vascular wall, and
therefore compresses, rather than expands, the vascular wall 40.
The deformable structure device 160 includes a coil, braid or other
stent-like structure 162 comprising one or more individual
structural members connected to an electrical lead 164. Each of the
structural members may comprise a shape memory material 166 (e.g.,
nickel titanium alloy) as illustrated in FIG. 7C, or a bimetallic
material 168. The structure 162 may be unipolar as shown using the
surrounding tissue as ground, or bipolar or multipolar using leads
connected to either end of the structure 162. Electrical power may
also be delivered to the structure 162 inductively as described
hereinafter with reference to FIGS. 14-16.
[0076] Upon application of electrical current to the shape memory
material 166, it is resistively heated causing a phase change and a
corresponding change in shape. Upon application of electrical
current to the bimetallic material 168, it is resistively heated
causing a differential in thermal expansion and a corresponding
change in shape. In either case, the material 166/168 is designed
such that the change in shape causes constriction of the structure
162 to mechanically activate baroreceptors 30 by compressing or
otherwise deforming the baroreceptors 30 and/or the vascular wall
40. Upon removal of the electrical current, the material 166/168
cools and the structure 162 returns to its relaxed geometry such
that the baroreceptors 30 and/or the vascular wall 40 return to
their nominal state. Thus, by selectively compressing the structure
162, the baroreceptors 30 adjacent thereto may be selectively
activated.
[0077] Refer now to FIG. 8 which shows a baroreceptor activation
device 180 in the form of an extravascular flow regulator which
artificially creates back pressure adjacent the baroreceptors 30.
The flow regulator device 180 includes an external compression
device 182, which may comprise any of the external compression
devices described with reference to FIG. 5. The external
compression device 182 is operably connected to the driver 66 of
the control system 60 by way of cable 184, which may comprise a
fluid line or electrical lead, depending on the type of external
compression device 182 utilized. The external compression device
182 is disposed about the vascular wall distal of the baroreceptors
30. For example, the external compression device 182 may be located
in the distal portions of the inferior vena cava 23.3 to create
back pressure adjacent the baroreceptors 30 upstream in the
inferior vena cava.
[0078] Upon actuation of the external compression device 182, the
vascular wall is constricted thereby reducing the size of the
vascular lumen therein. By reducing the size of the vascular lumen,
pressure proximal of the external compression device 182 is
increased thereby expanding the vascular wall. Thus, by selectively
activating the external compression device 182 to constrict the
vascular lumen and create back pressure, the baroreceptors 30 may
be selectively activated.
[0079] Refer now to FIG. 9 which shows a baroreceptor activation
device 200 in the form of an intravascular flow regular which
artificially creates back pressure adjacent the baroreceptors 30.
The intravascular flow regulator device 200 is substantially
similar in function and use as extravascular flow regulator 180
described with reference to FIG. 8, except that the intravascular
flow regulator device 200 is disposed in the vascular lumen.
[0080] Intravascular flow regulator 200 includes an internal valve
202 to at least partially close the vascular lumen distal of the
baroreceptors 30. By at least partially closing the vascular lumen
distal of the baroreceptors 30, back pressure is created proximal
of the internal valve 202 such that the vascular wall expands to
activate the baroreceptors 30. The internal valve 202 may be
positioned at any of the locations described with reference to the
external compression device 182, except that the internal valve 202
is placed within the vascular lumen. Specifically, the internal
compression device 202 may be located in the distal portions of the
vasculature to create back pressure adjacent to the baroreceptors
30 in the veins or cardiopulmonary system.
[0081] The internal valve 202 is operably coupled to the driver 66
of the control system 60 by way of electrical lead 204. The control
system 60 may selectively open, close or change the flow resistance
of the valve 202 as described in more detail hereinafter. The
internal valve 202 may include valve leaflets 206 (bi-leaflet or
tri-leaflet) which rotate inside housing 208 about an axis between
an open position and a closed position. The closed position may be
completely closed or partially closed, depending on the desired
amount of back pressure to be created. The opening and closing of
the internal valve 202 may be selectively controlled by altering
the resistance of leaflet 206 rotation or by altering the opening
force of the leaflets 206. The resistance of rotation of the
leaflets 206 may be altered utilizing electromagnetically actuated
metallic bearings carried by the housing 208. The opening force of
the leaflets 206 may be altered by utilizing electromagnetic coils
in each of the leaflets to selectively magnetize the leaflets such
that they either repel or attract each other, thereby facilitating
valve opening and closing, respectively.
[0082] A wide variety of intravascular flow regulators may be used
in place of internal valve 202. For example, internal inflatable
balloon devices as disclosed in U.S. Pat. No. 4,682,583 to Burton
et al. and U.S. Pat. No. 5,634,878 to Grundei et al., the entire
disclosures of which is hereby incorporated by reference, may be
adapted for use in place of valve 202. Such inflatable balloon
devices may be operated in a similar manner as the inflatable cuff
122 described with reference to FIG. 5. Specifically, in this
embodiment, the driver 66 would comprises a pressure/vacuum source
(i.e., an inflation device) which selectively inflates and deflates
the internal balloon. Upon inflation, the balloon expands to
partially occlude blood flow and create back pressure to
mechanically activate baroreceptors 30 by stretching or otherwise
deforming them and/or the vascular wall 40. Upon deflation, the
internal balloon returns to its normal profile such that flow is
not hindered and back pressure is eliminated. Thus, by selectively
inflating the internal balloon, the baroreceptors 30 proximal
thereof may be selectively activated by creating back pressure.
[0083] Refer now to FIG. 10 which shows a baroreceptor activation
device 220 in the form of magnetic particles 222 disposed in the
vascular wall 40. The magnetic particles 222 may comprise
magnetically responsive materials (i.e., ferrous based materials)
and may be magnetically neutral or magnetically active. Preferably,
the magnetic particles 222 comprise permanent magnets having an
elongate cylinder shape with north and south poles to strongly
respond to magnetic fields. The magnetic particles 222 are actuated
by an electromagnetic coil 224 which is operably coupled to the
driver 66 of the control system 60 by way of an electrical cable
226. The electromagnetic coil 224 may be implanted as shown, or
located outside the body, in which case the driver 66 and the
remainder of the control system 60 would also be located outside
the body. By selectively activating the electromagnetic coil 224 to
create a magnetic field, the magnetic particles 222 may be
repelled, attracted or rotated. Alternatively, the magnetic field
created by the electromagnetic coil 224 may be alternated such that
the magnetic particles 222 vibrate within the vascular wall 40.
When the magnetic particles are repelled, attracted, rotated,
vibrated or otherwise moved by the magnetic field created by the
electromagnetic coil 224, the baroreceptors 30 are mechanically
activated.
[0084] The electromagnetic coil 224 is preferably placed as close
as possible to the magnetic particles 222 in the vascular wall 40,
and may be placed intravascularly, extravascularly, or in any of
the alternative locations discussed with reference to inductor
shown in FIGS. 14-16. The magnetic particles 222 may be implanted
in the vascular wall 40 by injecting a ferro-fluid or a
ferro-particle suspension into the vascular wall adjacent to the
baroreceptors 30. To increase biocompatibility, the particles 222
may be coated with a ceramic, polymeric or other inert material.
Injection of the fluid carrying the magnetic particles 222 is
preferably performed percutaneously.
[0085] Refer now to FIG. 11 which shows a baroreceptor activation
device 240 in the form of one or more transducers 242. Preferably,
the transducers 242 comprise an array surrounding the vascular
wall. The transducers 242 may be intravascularly or extravascularly
positioned adjacent to the baroreceptors 30. In this embodiment,
the transducers 242 comprise devices which convert electrical
signals into some physical phenomena, such as mechanical vibration
or acoustic waves. The electrical signals are provided to the
transducers 242 by way of electrical cables 244 which are connected
to the driver 66 of the control system 60. By selectively
activating the transducers 242 to create a physical phenomena, the
baroreceptors 30 may be mechanically activated.
[0086] The transducers 242 may comprise an acoustic transmitter
which transmits sonic or ultrasonic sound waves into the vascular
wall 40 to activate the baroreceptors 30. Alternatively, the
transducers 242 may comprise a piezoelectric material which
vibrates the vascular wall to activate the baroreceptors 30. As a
further alternative, the transducers 242 may comprise an artificial
muscle which deflects upon application of an electrical signal. An
example of an artificial muscle transducer comprises plastic
impregnated with a lithium-perchlorate electrolyte disposed between
sheets of polypyrrole, a conductive polymer. Such plastic muscles
may be electrically activated to cause deflection in different
directions depending on the polarity of the applied current.
[0087] Refer now to FIG. 12 which shows a baroreceptor activation
device 260 in the form of a local fluid delivery device 262
suitable for delivering a chemical or biological fluid agent to the
vascular wall adjacent the baroreceptors 30. The local fluid
delivery device 262 may be located intravascularly,
extravascularly, or intramurally. For purposes of illustration
only, the local fluid delivery device 262 is positioned
extravascularly.
[0088] The local fluid delivery device 262 may include proximal and
distal seals 266 which retain the fluid agent disposed in the lumen
or cavity 268 adjacent to vascular wall. Preferably, the local
fluid delivery device 262 completely surrounds the vascular wall 40
to maintain an effective seal. Those skilled in the art will
recognize that the local fluid delivery device 262 may comprise a
wide variety of implantable drug delivery devices or pumps known in
the art.
[0089] The local fluid delivery device 260 is connected to a fluid
line 264 which is connected to the driver 66 of the control system
60. In this embodiment, the driver 66 comprises a pressure/vacuum
source and fluid reservoir containing the desired chemical or
biological fluid agent. The chemical or biological fluid agent may
comprise a wide variety of stimulatory substances. Examples include
veratridine, bradykinin, prostaglandins, and related substances.
Such stimulatory substances activate the baroreceptors 30 directly
or enhance their sensitivity to other stimuli and therefore may be
used in combination with the other baroreceptor activation devices
described herein. Other examples include growth factors and other
agents that modify the function of the baroreceptors 30 or the
cells of the vascular tissue surrounding the baroreceptors 30
causing the baroreceptors 30 to be activated or causing alteration
of their responsiveness or activation pattern to other stimuli. It
is also contemplated that injectable stimulators that are induced
remotely, as described in U.S. Pat. No. 6,061,596 which is
incorporated herein by reference, may be used with the present
invention.
[0090] As an alternative, the fluid delivery device 260 may be used
to deliver a photochemical that is essentially inert until
activated by light to have a stimulatory effect as described above.
In this embodiment, the fluid delivery device 260 would include a
light source such as a light emitting diode (LED), and the driver
66 of the control system 60 would include a pulse generator for the
LED combined with a pressure/vacuum source and fluid reservoir
described previously. The photochemical would be delivered with the
fluid delivery device 260 as described above, and the photochemical
would be activated, deactivated or modulated by activating,
deactivating or modulating the LED.
[0091] As a further alternative, the fluid delivery device 260 may
be used to deliver a warm or hot fluid (e.g. saline) to thermally
activate the baroreceptors 30. In this embodiment, the driver 66 of
the control system 60 would include a heat generator for heating
the fluid, combined with a pressure/vacuum source and fluid
reservoir described previously. The hot or warm fluid would be
delivered and preferably circulated with the fluid delivery device
260 as described above, and the temperature of the fluid would be
controlled by the driver 66.
[0092] Refer now to FIG. 13 which shows a baroreceptor activation
device 280 in the form of an intravascular electrically conductive
structure or electrode 282. The electrode structure 282 may
comprise a self-expanding or balloon expandable coil, braid or
other stent-like structure disposed in the vascular lumen. The
electrode structure 282 may serve the dual purpose of maintaining
lumen patency while also delivering electrical stimuli. To this
end, the electrode structure 282 may be implanted utilizing
conventional intravascular stent and filter delivery techniques.
Preferably, the electrode structure 282 comprises a geometry which
allows blood perfusion therethrough. The electrode structure 282
comprises electrically conductive material which may be selectively
insulated to establish contact with the inside surface of the
vascular wall 40 at desired locations, and limit extraneous
electrical contact with blood flowing through the vessel and other
tissues.
[0093] The electrode structure 282 is connected to electric lead
284 which is connected to the driver 66 of the control system 60.
The driver 66, in this embodiment, may comprise a power amplifier,
pulse generator or the like to selectively deliver electrical
control signals to structure 282. As mentioned previously, the
electrical control signal generated by the driver 66 may be
continuous, periodic, episodic or a combination thereof, as
dictated by an algorithm contained in memory 62 of the control
system 60. Continuous control signals include a constant pulse, a
constant train of pulses, a triggered pulse and a triggered train
of pulses. Periodic control signals include each of the continuous
control signals described above which have a designated start time
and a designated duration. Episodic control signals include each of
the continuous control signals described above which are triggered
by an episode.
[0094] By selectively activating, deactivating or otherwise
modulating the electrical control signal transmitted to the
electrode structure 282, electrical energy may be delivered to the
vascular wall to activate the baroreceptors 30. As discussed
previously, activation of the baroreceptors 30 may occur directly
or indirectly. In particular, the electrical signal delivered to
the vascular wall 40 by the electrode structure 282 may cause the
vascular wall to stretch or otherwise deform thereby indirectly
activating the baroreceptors 30 disposed therein. Alternatively,
the electrical signals delivered to the vascular wall by the
electrode structure 282 may directly activate the baroreceptors 30
by changing the electrical potential across the baroreceptors 30.
In either case, the electrical signal is delivered to the vascular
wall 40 immediately adjacent to the baroreceptors 30. It is also
contemplated that the electrode structure 282 may delivery thermal
energy by utilizing a semi-conductive material having a higher
resistance such that the electrode structure 282 resistively
generates heat upon application of electrical energy.
[0095] Various alternative embodiments are contemplated for the
electrode structure 282, including its design, implanted location,
and method of electrical activation. For example, the electrode
structure 282 may be unipolar as shown in FIG. 13 using the
surrounding tissue as ground, or bipolar using leads connected to
either end of the structure 282 as shown in Figure. In the
embodiment of FIGS. 18A and 18B, the electrode structure 282
includes two or more individual electrically conductive members
283/285 which are electrically isolated at their respective
cross-over points utilizing insulative materials. Each of the
members 283/285 is connected to a separate conductor contained
within the electrical lead 284. Alternatively, an array of bipoles
may be used as described in more detail with reference to FIG. 21.
As a further alternative, a multipolar arrangement may be used
wherein three or more electrically conductive members are included
in the structure 282. For example, a tripolar arrangement may be
provided by one electrically conductive member having a polarity
disposed between two electrically conductive members having the
opposite polarity.
[0096] In terms of electrical activation, the electrical signals
may be directly delivered to the electrode structure 282 as
described with reference to FIG. 13, or indirectly delivered
utilizing an inductor 286 as illustrated in FIGS. 14-16 and 21. The
embodiments of FIGS. 14-16 and 21 utilize an inductor 286 which is
operably connected to the driver 66 of the control system 60 by way
of electrical lead 284. The inductor 286 comprises an electrical
winding which creates a magnetic field 287 (as seen in FIG. 21)
around the electrode structure 282. The magnetic field 287 may be
alternated by alternating the direction of current flow through the
inductor 286. Accordingly, the inductor 286 may be utilized to
create current flow in the electrode structure 282 to thereby
deliver electrical signals to the vascular wall 40 to directly or
indirectly activate the baroreceptors 30. In all embodiments, the
inductor 286 may be covered with an electrically insulative
material to eliminate direct electrical stimulation of tissues
surrounding the inductor 286. A preferred embodiment of an
inductively activated electrode structure 282 is described in more
detail with reference to FIGS. 21A-21C.
[0097] The embodiments of FIGS. 13-16 may be modified to form a
cathode/anode arrangement. Specifically, the electrical inductor
286 would be connected to the driver 66 as shown in FIGS. 14-16 and
the electrode structure 282 would be connected to the driver 66 as
shown in FIG. 13. With this arrangement, the electrode structure
282 and the inductor 286 may be any suitable geometry and need not
be coiled for purposes of induction. The electrode structure 282
and the inductor 286 would comprise a cathode/anode or
anode/cathode pair. For example, when activated, the cathode 282
may generate a primary stream of electrons which travel through the
inter-electrode space (i.e., vascular tissue and baroreceptors 30)
to the anode 286. The cathode is preferably cold, as opposed to
thermionic, during electron emission. The electrons may be used to
electrically or thermally activate the baroreceptors 30 as
discussed previously.
[0098] The electrical inductor 286 is preferably disposed as close
as possible to the electrode structure 282. For example, the
electrical inductor 286 may be disposed adjacent the vascular wall
as illustrated in FIG. 14. Alternatively, the inductor 286 may be
disposed in an adjacent vessel 289 as illustrated in FIG. 15. If
the electrode structure 282 is disposed in the carotid sinus 20,
for example, the inductor 286 may be disposed in the internal
jugular vein 21 as illustrated in FIG. 15. In the embodiment of
FIG. 15, the electrical inductor 286 may comprise a similar
structure as the electrode structure 282. As a further alternative,
the electrical inductor 286 may be disposed outside the patient's
body, but as close as possible to the electrode structure 282. If
the electrode structure 282 is disposed in the carotid sinus 20,
for example, the electrical inductor 286 may be disposed on the
right or left side of the neck of the patient as illustrated in
FIG. 16. In the embodiment of FIG. 16, wherein the electrical
inductor 286 is disposed outside the patient's body, the control
system 60 may also be disposed outside the patient's body.
[0099] In terms of implant location, the electrode structure 282
may be intravascularly disposed as described with reference to FIG.
13, or extravascularly disposed as described with reference to FIG.
17, which show schematic illustrations of a baroreceptor activation
device 300 in the form of an extravascular electrically conductive
structure or electrode 302. Except as described herein, the
extravascular electrode structure 302 is the same in design,
function, and use as the intravascular electrode structure 282. The
electrode structure 302 may comprise a coil, braid or other
structure capable of surrounding the vascular wall. Alternatively,
the electrode structure 302 may comprise one or more electrode
patches distributed around the outside surface of the vascular
wall. Because the electrode structure 302 is disposed on the
outside surface of the vascular wall, intravascular delivery
techniques may not be practical, but minimally invasive surgical
techniques will suffice. The extravascular electrode structure 302
may receive electrical signals directly from the driver 66 of the
control system 60 by way of electrical lead 304, or indirectly by
utilizing an inductor (not shown) as described with reference to
FIGS. 14-16.
[0100] Refer now to FIG. 19 which shows a baroreceptor activation
device 320 in the form of electrically conductive particles 322
disposed in the vascular wall. This embodiment is substantially the
same as the embodiments described with reference to FIGS. 13-18,
except that the electrically conductive particles 322 are disposed
within the vascular wall, as opposed to the electrically conductive
structures 282/302 which are disposed on either side of the
vascular wall. In addition, this embodiment is similar to the
embodiment described with reference to FIG. 10, except that the
electrically conductive particles 322 are not necessarily magnetic
as with magnetic particles 222, and the electrically conductive
particles 322 are driven by an electromagnetic filed rather than by
a magnetic field.
[0101] In this embodiment, the driver 66 of the control system 60
comprises an electromagnetic transmitter such as an radiofrequency
or microwave transmitter. Electromagnetic radiation is created by
the transmitter 66 which is operably coupled to an antenna 324 by
way of electrical lead 326. Electromagnetic waves are emitted by
the antenna 324 and received by the electrically conductive
particles 322 disposed in the vascular wall 40. Electromagnetic
energy creates oscillating current flow within the electrically
conductive particles 322, and depending on the intensity of the
electromagnetic radiation and the resistivity of the conductive
particles 322, may cause the electrical particles 322 to generate
heat. The electrical or thermal energy generated by the
electrically conductive particles 322 may directly activate the
baroreceptors 30, or indirectly activate the baroreceptors 30 by
way of the surrounding vascular wall tissue.
[0102] The electromagnetic radiation transmitter 66 and antenna 324
may be disposed in the patient's body, with the antenna 324
disposed adjacent to the conductive particles in the vascular wall
40 as illustrated in FIG. 19. Alternatively, the antenna 324 may be
disposed in any of the positions described with reference to the
electrical inductor shown in FIGS. 14-16. It is also contemplated
that the electromagnetic radiation transmitter 66 and antenna 324
may be utilized in combination with the intravascular and
extravascular electrically conductive structures 282/302 described
with reference to FIGS. 13-18 to generate thermal energy on either
side of the vascular wall.
[0103] As an alternative, the electromagnetic radiation transmitter
66 and antenna 324 may be used without the electrically conductive
particles 322. Specifically, the electromagnetic radiation
transmitter 66 and antenna 324 may be used to deliver
electromagnetic radiation (e.g., RF, microwave) directly to the
baroreceptors 30 or the tissue adjacent thereto to cause localized
heating, thereby thermally inducing a baroreceptor 30 signal.
[0104] Refer now to FIG. 20 which shows a baroreceptor activation
device 340 in the form of a Peltier effect device 342. The Peltier
effect device 342 may be extravascularly positioned as illustrated,
or may be intravascularly positioned similar to an intravascular
stent or filter. The Peltier effect device 342 is operably
connected to the driver 66 of the control system 60 by way of
electrical lead 344. The Peltier effect device 342 includes two
dissimilar metals or semiconductors 343/345 separated by a thermal
transfer junction 347. In this particular embodiment, the driver 66
comprises a power source which delivers electrical energy to the
dissimilar metals or semiconductors 343/345 to create current flow
across the thermal junction 347.
[0105] When current is delivered in an appropriate direction, a
cooling effect is created at the thermal junction 347. There is
also a heating effect created at the junction between the
individual leads 344 connected to the dissimilar metals or
semiconductors 343/345. This heating effect, which is proportional
to the cooling effect, may be utilized to activate the
baroreceptors 30 by positioning the junction between the electrical
leads 344 and the dissimilar metals or semiconductors 343/345
adjacent to the vascular wall 40.
[0106] Refer now to FIGS. 21A-21C which show schematic
illustrations of a preferred embodiment of an inductively activated
electrode structure 282 for use with the embodiments described with
reference to FIGS. 14-16. In this embodiment, current flow in the
electrode structure 282 is induced by a magnetic field 287 created
by an inductor 286 which is operably coupled to the driver 66 of
the control system 60 by way of electrical cable 284. The electrode
structure 282 preferably comprises a multi-filar self-expanding
braid structure including a plurality of individual members 282a,
282b, 282c and 282d. However, the electrode structure 282 may
simply comprise a single coil for purposes of this embodiment.
[0107] Each of the individual coil members 282a-282d comprising the
electrode structure 282 consists of a plurality of individual coil
turns 281 connected end to end as illustrated in FIGS. 21B and 21C.
FIG. 21C is a detailed view of the connection between adjacent coil
turns 281 as shown in FIG. 21B. Each coil turn 281 comprises
electrically isolated wires or receivers in which a current flow is
established when a changing magnetic field 287 is created by the
inductor 286. The inductor 286 is preferably covered with an
electrically insulative material to eliminate direct electrical
stimulation of tissues surrounding the inductor 286. Current flow
through each coil turn 281 results in a potential drop 288 between
each end of the coil turn 281. With a potential drop defined at
each junction between adjacent coil turns 281, a localized current
flow cell is created in the vessel wall adjacent each junction.
Thus an array or plurality of bipoles are created by the electrode
structure 282 and uniformly distributed around the vessel wall.
Each coil turn 281 comprises an electrically conductive wire
material 290 surrounded by an electrically insulative material 292.
The ends of each coil turn 281 are connected by an electrically
insulated material 294 such that each coil turn 281 remains
electrically isolated. The insulative material 294 mechanically
joins but electrically isolates adjacent coil turns 281 such that
each turn 281 responds with a similar potential drop 288 when
current flow is induced by the changing magnetic field 287 of the
inductor 286. An exposed portion 296 is provided at each end of
each coil turn 281 to facilitate contact with the vascular wall
tissue. Each exposed portion 296 comprises an isolated electrode in
contact with the vessel wall. The changing magnetic field 287 of
the inductor 286 causes a potential drop in each coil turn 281
thereby creating small current flow cells in the vessel wall
corresponding to adjacent exposed regions 296. The creation of
multiple small current cells along the inner wall of the blood
vessel serves to create a cylindrical zone of relatively high
current density such that the baroreceptors 30 are activated.
However, the cylindrical current density field quickly reduces to a
negligible current density near the outer wall of the vascular
wall, which serves to limit extraneous current leakage to minimize
or eliminate unwanted activation of extravascular tissues and
structures such as nerves or muscles.
[0108] To address low blood pressure and other conditions requiring
blood pressure augmentation, some of the baroreceptor activation
devices described previously may be used to selectively and
controllably regulate blood pressure by inhibiting or dampening
baroreceptor signals. By selectively and controllably inhibiting or
dampening baroreceptor signals, the present invention reduces
conditions associated with low blood pressure as described
previously. Specifically, the present invention would function to
increase the blood pressure and level of sympathetic nervous system
activation by inhibiting or dampening the activation of
baroreceptors.
[0109] This may be accomplished by utilizing mechanical, thermal,
electrical and chemical or biological means. Mechanical means may
be triggered off the pressure pulse of the heart to mechanically
limit deformation of the arterial wall. For example, either of the
external compression devices 120/160 described previously may be
used to limit deformation of the arterial wall. Alternatively, the
external compression device may simply limit diametrical expansion
of the vascular wall adjacent the baroreceptors without the need
for a trigger or control signal.
[0110] Thermal means may be used to cool the baroreceptors 30 and
adjacent tissue to reduce the responsiveness of the baroreceptors
30 and thereby dampen baroreceptor signals. Specifically, the
baroreceptor 30 signals may be dampened by either directly cooling
the baroreceptors 30, to reduce their sensitivity, metabolic
activity and function, or by cooling the surrounding vascular wall
tissue thereby causing the wall to become less responsive to
increases in blood pressure. An example of this approach is to use
the cooling effect of the Peltier device 340. Specifically, the
thermal transfer junction 347 may be positioned adjacent the
vascular wall to provide a cooling effect. The cooling effect may
be used to dampen signals generated by the baroreceptors 30.
Another example of this approach is to use the fluid delivery
device 260 to deliver a cool or cold fluid (e.g. saline). In this
embodiment, the driver 66 would include a heat exchanger to cool
the fluid and the control system 60 may be used to regulate the
temperature of the fluid, thereby regulating the degree of
baroreceptor 30 signal dampening.
[0111] Electrical means may be used to inhibit baroreceptor 30
activation by, for example, hyperpolarizing cells in or adjacent to
the baroreceptors 30. Examples of devices and method of
hyperpolarizing cells are disclosed in U.S. Pat. No. 5,814,079 to
Kieval, and U.S. Pat. No. 5,800,464 to Kieval, the entire
disclosures of which are hereby incorporated by reference. Such
electrical means may be implemented using any of the embodiments
discussed with reference to FIGS. 13-18 and 21.
[0112] Chemical or biological means may be used to reduce the
sensitivity of the baroreceptors 30. For example, a substance that
reduces baroreceptor sensitivity may be delivered using the fluid
delivery device 260 described previously. The desensitizing agent
may comprise, for example, tetrodotoxin or other inhibitor of
excitable tissues. From the foregoing, it should be apparent to
those skilled in the art that the present invention provides a
number of devices, systems and methods by which the blood pressure,
nervous system activity, and neurohormonal activity may be
selectively and controllably regulated by activating baroreceptors
or by inhibiting/dampening baroreceptor signals. Thus, the present
invention may be used to increase or decrease blood pressure,
sympathetic nervous system activity and neurohormonal activity, as
needed to minimize deleterious effects on the heart, vasculature
and other organs and tissues.
[0113] The baroreceptor activation devices described previously may
also be used to provide antiarrhythmic effects. It is well known
that the susceptibility of the myocardium to the development of
conduction disturbances and malignant cardiac arrhythmias is
influenced by the balance between sympathetic and parasympathetic
nervous system stimulation to the heart. That is, heightened
sympathetic nervous system activation, coupled with decreased
parasympathetic stimulation, increases the irritability of the
myocardium and likelihood of an arrhythmia. Thus, by decreasing the
level of sympathetic nervous system activation and enhancing the
level of parasympathetic activation, the devices, systems and
methods of the current invention may be used to provide a
protective effect against the development of cardiac conduction
disturbances.
Experimental
[0114] An electrode system was introduced into the inferior vena
cava of an anesthetized dog. The electrode system was an eight
lead, 64-electrode 8F Constellation.RTM. catheter from Boston
Scientific EP Technologies, Sunnyvale, Calif. The electrode system
was placed endovascularly in the abdominal vena cava. The electrode
system was activated using trains of electrical impulses of 0-6
volts, a frequency of 100 hz, and a pulse width of 0.5 ms. During
various activation experiments, arterial pressure, mean arterial
pressure and heart rate were monitored. The results of three
experiments are shown in FIGS. 22A-C. These figures demonstrate a
change in blood pressure as energy is applied to the vessel wall,
with recovery to pre-activation levels when the energy is
discontinued.
[0115] Those skilled in the art will recognize that the present
invention may be manifested in a variety of forms other than the
specific embodiments described and contemplated herein.
Accordingly, departures in form and detail may be made without
departing from the scope and spirit of the present invention as
described in the appended claims.
* * * * *