U.S. patent application number 15/473116 was filed with the patent office on 2017-07-13 for devices and methods for control of blood pressure.
The applicant listed for this patent is Vascular Dynamics, Inc.. Invention is credited to Yaron Assaf, Itzik Avneri, Moshe Elazar, Moshe Eshkol, Tanhum Feld, Yossi Gross, Tal Oren, Ori Weisberg.
Application Number | 20170196713 15/473116 |
Document ID | / |
Family ID | 48695503 |
Filed Date | 2017-07-13 |
United States Patent
Application |
20170196713 |
Kind Code |
A1 |
Gross; Yossi ; et
al. |
July 13, 2017 |
DEVICES AND METHODS FOR CONTROL OF BLOOD PRESSURE
Abstract
Apparatus and methods are described including an implantable
device having first and second longitudinal ends, the device having
a length of less than 80 mm when the device is unconstrained. The
device includes struts arranged such that, when the device is
unconstrained, along a continuous portion of the device having a
length that is at least 5 mm, a maximum inter-strut distance
defined by any set of two adjacent struts is more than 1.5 times as
great as a maximum inter-strut distance defined by any set of two
adjacent struts within longitudinal portions of the device within 3
mm of the longitudinal ends of the device. Other applications are
also described.
Inventors: |
Gross; Yossi; (Moshav Mazor,
IL) ; Avneri; Itzik; (Tel Aviv, IL) ;
Weisberg; Ori; (Shdema, IL) ; Eshkol; Moshe;
(Harutzim, IL) ; Oren; Tal; (Ra'anana, IL)
; Assaf; Yaron; (Maagan-Michael, IL) ; Feld;
Tanhum; (Moshav Merhavya, IL) ; Elazar; Moshe;
(Azor, IL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Vascular Dynamics, Inc. |
Mountain View |
CA |
US |
|
|
Family ID: |
48695503 |
Appl. No.: |
15/473116 |
Filed: |
March 29, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13455005 |
Apr 24, 2012 |
9642726 |
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15473116 |
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13030384 |
Feb 18, 2011 |
9125732 |
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13455005 |
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12774254 |
May 5, 2010 |
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13030384 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61F 2230/0021 20130101;
A61F 2/90 20130101; A61B 5/0053 20130101; A61F 2/915 20130101; A61F
2/06 20130101; A61F 2250/0059 20130101; A61F 2/856 20130101; A61B
5/0215 20130101; A61F 2/82 20130101; A61F 2230/0069 20130101 |
International
Class: |
A61F 2/82 20060101
A61F002/82; A61B 5/00 20060101 A61B005/00; A61F 2/90 20060101
A61F002/90; A61B 5/0215 20060101 A61B005/0215; A61F 2/856 20060101
A61F002/856 |
Claims
1. Apparatus comprising: an implantable device having first and
second longitudinal ends, the device having a length of less than
80 mm when the device is unconstrained; the device comprising
struts, arranged such that, when the device is unconstrained, along
a continuous portion of the device having a length that is at least
5 mm, a maximum inter-strut distance defined by any set of two
adjacent struts is more than 1.5 times as great as a maximum
inter-strut distance defined by any set of two adjacent struts
within longitudinal portions of the device within 3 mm of the
longitudinal ends of the device.
2. The apparatus according to claim 1, wherein the device is
configured to lower blood pressure of a patient, by being implanted
proximate to a baroreceptor within an artery of the subject.
3. The apparatus according to claim 2, wherein the continuous
portion of the device comprises a portion of a region of the device
that defines no struts, the region having a non-circular shape.
4. The apparatus according to claim 2, wherein the continuous
portion of the device comprises a portion of a region of the device
that defines no struts, a center of the region being disposed
asymmetrically with respect to a length of the device.
5. The apparatus according to claim 2, wherein along the continuous
portion of the device, the maximum inter-strut distance defined by
any set of two adjacent struts is more than 3 times as great as the
maximum inter-strut distance defined by any set of two adjacent
struts within longitudinal portions of the device within 3 mm of
the longitudinal ends of the device.
6. The apparatus according to claim 2, wherein the device has a
length of less than 50 mm.
7. The apparatus according to claim 1, wherein the device has a
spring constant of less than 2 N/mm.
8. The apparatus according to claim 7, wherein the device has a
spring constant of less than 1.5 N/mm.
9. The apparatus according to claim 1, wherein along the continuous
portion of the device, the maximum inter-strut distance defines an
arc of more than 30 degrees around a longitudinal axis of the
device.
10. The apparatus according to claim 9, wherein along the
continuous portion of the device, the maximum inter-strut distance
defines an arc of more than 60 degrees around the longitudinal axis
of the device.
11. The apparatus according to claim 1, wherein within the
longitudinal portions of the device within 3 mm of the longitudinal
ends of the device the struts define angles therebetween, wherein
within the continuous portion the struts define angles
therebetween, and wherein a minimum angle defined by the struts
within the longitudinal portions of the device within 3 mm of the
longitudinal ends of the device is greater than a minimum angle
defined by the struts within the continuous portion.
12. The apparatus according to claim 11, wherein a ratio of the
minimum angle defined by the struts within the longitudinal
portions of the device within 3 mm of the longitudinal ends of the
device to the minimum angle defined by the struts within the
continuous portion is greater than 1.25.
13. The apparatus according to claim 12, wherein the ratio of the
minimum angle defined by the struts within the longitudinal
portions of the device within 3 mm of the longitudinal ends of the
device to the minimum angle defined by the struts within the
continuous portion is greater than 2.
14. Apparatus comprising: an implantable device that is shaped to
define struts arranged such that, when the device is unconstrained,
along a continuous portion of the device having a length that is at
least 5 mm, a maximum inter-strut distance defined by any set of
two adjacent struts is more than 5 mm, the implantable device
having a length of less than 80 mm when the device is
unconstrained, the implantable device, at any location along the
length of the device, defining a ratio of a perimeter of a
cross-section of the device at the location to the cross-sectional
area defined by the struts of the device at the longitudinal
location, and the implantable device defining a maximum value of
said ratio, the ratio being more than 80 percent of the maximum
value of the ratio along more than 80 percent of a length of the
device.
15. The apparatus according to claim 14, wherein the device is
configured to lower blood pressure of a patient, by being implanted
proximate to a baroreceptor within an artery of the subject.
16. The apparatus according to claim 15, wherein the continuous
portion of the device comprises a portion of a region of the device
that defines no struts, the region having a non-circular shape.
17. The apparatus according to claim 15, wherein the continuous
portion of the device comprises a portion of a region of the device
that defines no struts, a center of the region being disposed
asymmetrically with respect to a length of the device.
18. The apparatus according to claim 15, wherein the device has a
length of less than 50 mm.
19. The apparatus according to claim 14, wherein the device has a
spring constant of less than 2 N/mm.
20. The apparatus according to claim 19, wherein the device has a
spring constant of less than 1.5 N/mm.
21. The apparatus according to claim 14, wherein along the
continuous portion of the device, the maximum inter-strut distance
defines an arc of more than 30 degrees around a longitudinal axis
of the device.
22. The apparatus according to claim 21, wherein along the
continuous portion of the device, the maximum inter-strut distance
defines an arc of more than 60 degrees around the longitudinal axis
of the device.
23. The apparatus according to claim 14, wherein along the
continuous portion of the device, the maximum inter-strut distance
defined by any set of two adjacent struts is more than 1.5 times as
great as a maximum inter-strut distance defined by any set of two
adjacent struts within longitudinal portions of the device within 3
mm of longitudinal ends of the device.
24. The apparatus according to claim 23, wherein along the
continuous portion of the device, the maximum inter-strut distance
defined by any set of two adjacent struts is more than 3 times as
great as the maximum inter-strut distance defined by any set of two
adjacent struts within the longitudinal portions of the device
within 3 mm of longitudinal ends of the device.
25. Apparatus comprising: an implantable device that is shaped to
define struts, the device being shaped such that over a continuous
portion of the device having a length that is at least 5 mm, the
device defines at least one circumferential region in which no
struts are disposed, the region defining an arc of at least 30
degrees around a longitudinal axis of the device, a cross-sectional
shape of the device at the region being shaped to define a major
axis and a minor axis, at least when the device is in a
non-constrained state thereof, a major axis of the cross-sectional
shape being parallel to a plane defined by the region in which no
struts are disposed, and a minor axis of the cross-sectional shape
being perpendicular to the plane.
26. The apparatus according to claim 25, wherein the device is
configured to lower blood pressure of a patient, by being implanted
proximate to a baroreceptor within an artery of the subject.
27. The apparatus according to claim 26, wherein the region defines
an arc of at least 60 degrees around the longitudinal axis of the
device.
Description
CROSS-REFERENCES TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. patent application
Ser. No. 13/455,005, filed Apr. 24, 2012, which is a
continuation-in-part of U.S. patent application Ser. No.
12/774,254, filed May 5, 2010, and a continuation-in-part of U.S.
patent application Ser. No. 13/030,384, filed Feb. 18, 2011, now
U.S. Pat. No. 9,125,732, which is a continuation-in-part of U.S.
patent application Ser. No. 12/774,254, filed May 5, 2010, the
entire contents of which are incorporated herein by reference.
[0002] The present application is related to U.S. patent
application Ser. No. 11/881,256 (US 2008/0033501), filed Jul. 25,
2007, entitled "Elliptical element for blood pressure reduction,"
which is a continuation-in-part of PCT Application No.
PCT/IL2006/000856 to Gross (WO 07/013065), filed Jul. 25, 2006,
entitled, "Electrical stimulation of blood vessels," which claims
the benefit of (a) U.S. Provisional Application 60/702,491, filed
Jul. 25, 2005, entitled, "Electrical stimulation of blood vessels,"
and (b) U.S. Provisional Application 60/721,728, filed Sep. 28,
2005, entitled, "Electrical stimulation of blood vessels." The
present application is related to U.S. patent application Ser. No.
12/602,787 (published as US 2011/0213408), which is the U.S.
national phase of PCT Application No. PCT/IL2009/000932 to Gross et
al. (WO 10/035271), filed Sep. 29, 2009, which claims priority from
U.S. Provisional Patent Application 61/194,339, filed Sep. 26,
2008, entitled "Devices and methods for control of blood pressure."
All of the above applications are incorporated herein by
reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
[0003] Some applications of the present invention generally relate
to implanted medical apparatus. Specifically, some applications of
the present invention relate to apparatus and methods for reducing
blood pressure.
[0004] Hypertension is a condition from which many people suffer.
It is a constant state of elevated blood pressure which can be
caused by a number of factors, for example, genetics, obesity or
diet. Baroreceptors located in the walls of blood vessels act to
regulate blood pressure. They do so by sending information to the
central nervous system (CNS) regarding the extent to which the
blood vessel walls are stretched by the pressure of the blood
flowing therethrough. In response to these signals, the CNS adjusts
certain parameters so as to maintain a stable blood pressure.
BRIEF SUMMARY OF THE INVENTION
[0005] For some applications, a subject's hypertension is treated
by modulating the subject's baroreceptor activity. Mechanical and
other forces are applied directly or indirectly to one or more of
the subject's arteries in order to modulate the baroreceptor
response to the blood pressure. The forces are typically applied to
arteries that are rich in baroreceptors, for example, the carotid
arteries, the aorta, the subclavian arteries and/or arteries of the
brain. For some applications, the forces are applied to other
regions of the body that contain baroreceptors, such as the atria,
the renal arteries, or veins.
[0006] Baroreceptors measure strain, which, in the case of a
circular vessel, depends on the pressure and the radius of the
vessel. As pressure increases, the stress exerted on the wall
increases, thereby increasing the strain in the vessel wall.
Equation 1 relates the wall stress a in a thin walled tube, to
internal pressure p, internal radius r, and wall thickness t.
.sigma.=pr/2t [Equation 1]
[0007] In a hypertensive patient, the pressure-strain relationship
is typically shifted to higher pressures, such that the artery is
subject to a given strain at a higher blood pressure than the blood
pressure in a healthy vessel that would give rise to the given
strain. Thus, the baroreceptors are activated at a higher blood
pressure in a hypertensive patient than they are in a healthy
patient. The devices described herein typically cause the
pressure-strain curve to shift back to lower pressures.
[0008] The inventors hypothesize that, at constant pressure, by
increasing the radius of curvature of a region of an arterial wall,
the strain in the region of the wall may be increased. Thus, the
baroreceptor nerve endings in the region (which are typically
disposed between the medial and adventitial layers of the artery,
as described in further detail hereinbelow) experience greater
strain, ceteris paribus. The intravascular devices described herein
typically increase the radius of curvature of regions of the
arterial wall, but do not cause a substantial decrease in the
cross-section of the artery (and, typically, cause an increase in
the cross-section of the artery), thereby maintaining blood flow
through the artery. For some applications, the devices change the
shape of the artery such that the artery is less circular than in
the absence of the device, thereby increasing the radius of
curvature of sections of the arterial wall.
[0009] Typically, the devices described herein change the shape of
the artery by being placed inside or outside the artery, but by
maintaining less than 360 degrees of contact with the surface of
the artery at any given site along the length of the artery.
Further typically, contact between the device and the artery is
limited to several (e.g., two to six, or three to six) contact
regions around the circumference of the artery, and is generally
minimized. Still further typically, the device is placed inside the
artery such that there are several regions at which the device does
not contact the artery, each of the non-contact regions being
contiguous, and defining an angle that is greater than 10 degrees
around the longitudinal axis of the artery, as described in further
detail hereinbelow. This may be beneficial for the following
reasons:
[0010] (1) A greater area of the artery pulsates in response to
pressure changes than if the device were to maintain a greater
degree of contact with the vessel wall. It is generally desirable
to allow at least a portion of the vessel to pulsate freely. This
is because pulsation of the vessel over the course of the cardiac
cycle typically activates and maintains normal functioning of the
baroreceptors. For some applications, baroreceptor activity in the
portions of the vessel that are in contact with the device may be
reduced, since the movement of those portions in response to
changes in blood pressure is reduced. Therefore, for some
applications, contact between the device and the artery is
minimized.
[0011] (2) A smaller metal to lumen ratio typically causes less
reactive growth of endothelial and smooth muscle cells. Typically,
reducing this reactive growth reduces the chances of stenosis being
caused by the device. Further typically, reducing this reactive
growth facilitates explantation, and/or movement of the device,
when desired.
[0012] For some applications the devices described herein are
implanted temporarily, and are subsequently removed. For example,
one of the devices described herein may be implanted for a period
of less than one month, e.g., less than one week. Temporary
implantation of the devices is typically used to treat an acute
condition of the subject. For some applications, the shape of the
artery in which the device is implanted is permanently altered by
temporarily implanting the device.
[0013] Typically, the devices described herein are implanted inside
or outside of the subject's carotid artery, e.g., in the vicinity
of the carotid bifurcation. In accordance with respective
embodiments, the devices are implanted bilaterally, or inside or
outside of only one of the subject's carotid arteries.
Alternatively or additionally, the devices are placed inside or
outside of a different artery, e.g., the aorta or the pulmonary
artery.
[0014] The devices are typically self-anchoring and structurally
stable. Further typically, the devices are passive devices, i.e.,
subsequent to the devices being implanted inside or outside of the
artery, the devices act to increase baroreceptor sensitivity
without requiring electrical or real-time mechanical
activation.
[0015] There is therefore provided, in accordance with some
applications of the present invention, apparatus including:
[0016] an implantable device having first and second longitudinal
ends, the device having a length of less than 80 mm when the device
is unconstrained,
the device including struts, arranged such that, when the device is
unconstrained, along a continuous portion of the device having a
length that is at least 5 mm, a maximum inter-strut distance
defined by any set of two adjacent struts is more than 1.5 times as
great as a maximum inter-strut distance defined by any set of two
adjacent struts within longitudinal portions of the device within 3
mm of the longitudinal ends of the device.
[0017] For some applications, the device is configured to lower
blood pressure of a patient, by being implanted proximate to a
baroreceptor within an artery of the subject.
[0018] For some applications, the continuous portion of the device
includes a portion of a region of the device that defines no
struts, the region having a non-circular shape.
[0019] For some applications, the continuous portion of the device
includes a portion of a region of the device that defines no
struts, a center of the region being disposed asymmetrically with
respect to a length of the device.
[0020] For some applications, along the continuous portion of the
device, the maximum inter-strut distance defined by any set of two
adjacent struts is more than 3 times as great as the maximum
inter-strut distance defined by any set of two adjacent struts
within longitudinal portions of the device within 3 mm of the
longitudinal ends of the device.
[0021] For some applications, the device has a length of less than
50 mm.
[0022] For some applications, the device has a spring constant of
less than 2 N/mm.
[0023] For some applications, the device has a spring constant of
less than 1.5 N/mm.
[0024] For some applications, along the continuous portion of the
device, the maximum inter-strut distance defines an arc of more
than 30 degrees around a longitudinal axis of the device.
[0025] For some applications, along the continuous portion of the
device, the maximum inter-strut distance defines an arc of more
than 60 degrees around the longitudinal axis of the device.
[0026] For some applications, within the longitudinal portions of
the device within 3 mm of the longitudinal ends of the device the
struts define angles therebetween, within the continuous portion
the struts define angles therebetween, and a minimum angle defined
by the struts within the longitudinal portions of the device within
3 mm of the longitudinal ends of the device is greater than a
minimum angle defined by the struts within the continuous
portion.
[0027] For some applications, a ratio of the minimum angle defined
by the struts within the longitudinal portions of the device within
3 mm of the longitudinal ends of the device to the minimum angle
defined by the struts within the continuous portion is greater than
1.25.
[0028] For some applications, the ratio of the minimum angle
defined by the struts within the longitudinal portions of the
device within 3 mm of the longitudinal ends of the device to the
minimum angle defined by the struts within the continuous portion
is greater than 2.
[0029] There is further provided, in accordance with some
applications of the present invention, apparatus including:
[0030] an implantable device that is shaped to define struts
arranged such that, when the device is unconstrained, along a
continuous portion of the device having a length that is at least 5
mm, a maximum inter-strut distance defined by any set of two
adjacent struts is more than 5 mm,
[0031] the implantable device having a length of less than 80 mm
when the device is unconstrained,
[0032] the implantable device, at any location along the length of
the device, defining a ratio of a perimeter of a cross-section of
the device at the location to the cross-sectional area defined by
the struts of the device at the longitudinal location, and
[0033] the implantable device defining a maximum value of said
ratio, [0034] the ratio being more than 80 percent of the maximum
value of the ratio along more than 80 percent of a length of the
device.
[0035] For some applications, the device is configured to lower
blood pressure of a patient, by being implanted proximate to a
baroreceptor within an artery of the subject.
[0036] For some applications, the continuous portion of the device
includes a portion of a region of the device that defines no
struts, the region having a non-circular shape.
[0037] For some applications, the continuous portion of the device
includes a portion of a region of the device that defines no
struts, a center of the region being disposed asymmetrically with
respect to a length of the device.
[0038] For some applications, the device has a length of less than
50 mm.
[0039] For some applications, the device has a spring constant of
less than 2 N/mm.
[0040] For some applications, the device has a spring constant of
less than 1.5 N/mm.
[0041] For some applications, along the continuous portion of the
device, the maximum inter-strut distance defines an arc of more
than 30 degrees around a longitudinal axis of the device.
[0042] For some applications, along the continuous portion of the
device, the maximum inter-strut distance defines an arc of more
than 60 degrees around the longitudinal axis of the device.
[0043] For some applications, along the continuous portion of the
device, the maximum inter-strut distance defined by any set of two
adjacent struts is more than 1.5 times as great as a maximum
inter-strut distance defined by any set of two adjacent struts
within longitudinal portions of the device within 3 mm of
longitudinal ends of the device.
[0044] For some applications, along the continuous portion of the
device, the maximum inter-strut distance defined by any set of two
adjacent struts is more than 3 times as great as the maximum
inter-strut distance defined by any set of two adjacent struts
within the longitudinal portions of the device within 3 mm of
longitudinal ends of the device.
[0045] There is additionally provided, in accordance with some
applications of the present invention, apparatus including:
[0046] an implantable device that is shaped to define struts, the
device being shaped such that over a continuous portion of the
device having a length that is at least 5 mm, the device defines at
least one circumferential region in which no struts are disposed,
the region defining an arc of at least 30 degrees around a
longitudinal axis of the device,
[0047] a cross-sectional shape of the device at the region being
shaped to define a major axis and a minor axis, at least when the
device is in a non-constrained state thereof,
[0048] a major axis of the cross-sectional shape being parallel to
a plane defined by the region in which no struts are disposed, and
a minor axis of the cross-sectional shape being perpendicular to
the plane.
[0049] For some applications, the device is configured to lower
blood pressure of a patient, by being implanted proximate to a
baroreceptor within an artery of the subject.
[0050] For some applications, the region defines an arc of at least
60 degrees around the longitudinal axis of the device.
[0051] There is additionally provided, in accordance with some
applications of the present invention, a method including:
[0052] providing an implantable device having first and second
longitudinal ends, the device including struts, arranged such that,
when the device is unconstrained, along a continuous portion of the
device having a length that is at least 5 mm, a maximum inter-strut
distance defined by any set of two adjacent struts is more than 1.5
times as great as a maximum inter-strut distance defined by any set
of two adjacent struts within longitudinal portions of the device
within 3 mm of the longitudinal ends of the device; and
[0053] implanting the device in a carotid artery of a subject.
[0054] For some applications, the method further includes
identifying the subject as suffering from hypertension, and
implanting the device in the subject's carotid artery includes
lowering blood pressure of the subject.
[0055] There is additionally provided, in accordance with some
applications of the present invention, a method, including:
[0056] providing an implantable device,
[0057] the device being shaped to define struts arranged such that,
when the device is unconstrained, over a continuous portion of the
device having a length that is at least 5 mm, a maximum inter-strut
distance defined by any set of two adjacent struts is more than 5
mm,
[0058] a ratio of a perimeter of a cross-section of the device at
any at any location along the length of the device, being more than
80 percent of the maximum value of the ratio along more than 50
percent of a length of the device; and
[0059] implanting the device in a carotid artery of a subject.
[0060] For some applications, the method further includes
identifying the subject as suffering from hypertension, and
implanting the device in the subject's carotid artery includes
lowering blood pressure of the subject.
[0061] There is further provided, in accordance with some
applications of the present invention, a method, including:
[0062] providing an implantable device that is shaped to define
struts,
[0063] the device being shaped such that over a continuous portion
of the device having a length that is at least 5 mm, the device
defines at least one circumferential region in which no struts are
disposed, the region defining an arc of at least 30 degrees around
a longitudinal axis of the device,
[0064] a cross-sectional shape of the device at the region being
shaped to define a major axis and a minor axis, at least when the
device is in a non-constrained state thereof,
[0065] the major axis of the cross-sectional shape being parallel
to a plane defined by the region in which no struts are disposed,
and the minor axis of the cross-sectional shape being perpendicular
to the plane; and
[0066] implanting the device in a carotid artery of a subject.
[0067] For some applications, the method further includes
identifying the subject as suffering from hypertension, and
implanting the device in the subject's carotid artery includes
lowering blood pressure of the subject.
[0068] The present invention will be more fully understood from the
following detailed description of embodiments thereof, taken
together with the drawings, in which:
BRIEF DESCRIPTION OF THE DRAWINGS
[0069] FIG. 1 is a cross-sectional illustration of an artery;
[0070] FIGS. 2A-B are contour plots of the strain in the wall of an
artery, respectively, when the artery does have and does not have
inserted therein an intravascular device, in accordance with some
applications of the present invention;
[0071] FIG. 3 is a contour plot of the strain in the wall of an
artery, an extravascular device having been implanted outside the
wall, in accordance with some applications of the present
invention;
[0072] FIG. 4 is a schematic illustration of an intravascular
device for placing inside an artery of a subject suffering from
hypertension, in accordance with some applications of the present
invention;
[0073] FIGS. 5A-B are schematic illustrations of an artery, showing
the radius of curvature of the artery, respectively, before and
after placement of the device shown in FIG. 4, in accordance with
some applications of the present invention;
[0074] FIG. 5C is a schematic illustration of the device of FIG. 4
disposed inside the artery, without stretching the artery, for
illustrative purposes;
[0075] FIGS. 6A-B are schematic illustrations of, respectively, a
device, and the device implanted inside an artery, in accordance
with some applications of the present invention;
[0076] FIGS. 7A-B are schematic illustrations of, respectively,
another device, and the device implanted inside an artery, in
accordance with some applications of the present invention;
[0077] FIGS. 8A-B are schematic illustrations of, respectively, a
further device, and the device implanted inside an artery, in
accordance with some applications of the present invention;
[0078] FIGS. 9A-D are schematic illustrations of extravascular
devices placed around an artery, in accordance with some
applications of the present invention;
[0079] FIG. 10 is a graph that indicates the portion of an arterial
wall having a strain that is greater than a threshold value, as a
function of the reduction in the cross-sectional area of the
artery, for respective extravascular devices, in accordance with
some applications of the present invention;
[0080] FIG. 11 is a graph showing the maximum percentage increase
in the strain of the arterial wall as a function of the reduction
in the cross-sectional area of the artery, for respective
extravascular devices, in accordance with some applications of the
present invention;
[0081] FIG. 12 is a schematic illustration of a device for
measuring the baroreceptor response of a subject to pressure that
is exerted on the inner wall of an artery of the subject, in
accordance with some applications of the present invention;
[0082] FIG. 13 is a graph showing the blood pressure measured in a
dog before and after the insertion of intravascular devices into
the dog's carotid sinuses, in accordance with some applications of
the present invention;
[0083] FIG. 14 is a graph showing the pressure-strain curve of the
artery of a healthy subject, a hypertensive subject, and a
hypertensive subject that uses a device as described herein, in
accordance with some applications of the present invention;
[0084] FIGS. 15A-B, and 15E are schematic illustrations of a device
for placing in a subject's artery, in accordance with some
applications of the present invention;
[0085] FIGS. 15C-D are schematic illustrations of an arterial wall
exerting a force on struts of a device, in accordance with some
applications of the present invention;
[0086] FIGS. 16A-D are schematic illustrations of another device
for placing in a subject's artery, in accordance with some
applications of the present invention;
[0087] FIGS. 17A-D are schematic illustrations of yet another
device for placing in a subject's artery, in accordance with some
applications of the present invention;
[0088] FIGS. 18A-D are schematic illustrations of further devices
for placing in a subject's artery, in accordance with some
applications of the present invention;
[0089] FIG. 19 is a schematic illustration of a device having a
D-shaped cross-section for placing in a subject's artery, in
accordance with some applications of the present invention;
[0090] FIG. 20 is a schematic illustration of an intra-arterial
device that includes a mesh between artery contact regions of the
device, in accordance with some applications of the present
invention;
[0091] FIG. 21 is a graph showing the derivative of strain versus
pressure as a function of rotational position around the artery, in
accordance with respective models of an artery, in accordance with
some applications of the present invention;
[0092] FIGS. 22A-C are schematic illustrations of a delivery device
for placing an intra-arterial device at a subject's carotid
bifurcation, in accordance with some applications of the present
invention;
[0093] FIGS. 23A-B, 24A-B, 25A-B, 26A-B, 27A-D, and 28A-C are
schematic illustration of stent-based intra-arterial devices, in
accordance with some applications of the present invention;
[0094] FIG. 29 is a schematic illustration of a further
intra-arterial device, in accordance with some applications of the
present invention;
[0095] FIG. 30 is a schematic illustration of an extra-arterial
device configured to be placed around the outside of an artery, in
accordance with some applications of the present invention;
[0096] FIGS. 31A-B are graphs showing the Herring's nerve firing
rate at respective blood pressures recorded in dogs that had been
implanted with medical devices, in accordance with some
applications of the present invention; and
[0097] FIGS. 31C-D are graphs showing the Herring's nerve
integrated nerve activity at respective blood pressures recorded in
dogs that been implanted with medical devices, in accordance with
some applications of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0098] Reference is now made to FIG. 1, which is a cross-sectional
illustration of an artery 20. The arterial wall includes three
layers 22, 24, and 26, which are called, respectively, the intima,
the media, and the adventitia. For some applications of the present
invention, an intravascular device is placed inside an artery,
baroreceptors being disposed at the interface between adventitia 26
and media 24 of the artery. The device causes the curvature of the
arterial wall to flatten in some regions of the circumference of
the arterial wall, thereby causing the baroreceptors to become
stretched, while allowing the regions to pulsate over the course of
the subject's cardiac cycle.
[0099] Reference is now made to FIGS. 2A and 2B, which are contour
plots of the strain in the top right quarter of an arterial wall,
in the absence of an intravascular device (FIG. 2A) and in the
presence of an intravascular device (FIG. 2B), analyzed and/or
provided in accordance with some applications of the present
invention. The contour plot in FIG. 2B was generated for a device
(e.g., as shown hereinbelow in FIGS. 7A-B) having four elements,
each of which contacts the arterial wall at a contact region 42.
The contour plots shown in FIGS. 2A-B are computer simulations of
the strain in the wall of an artery, at a blood pressure of 100
mmHg, the artery having a radius of 3 mm, and a wall thickness of
0.6 mm. The scope of the present application includes intravascular
devices having different structures from that used to generate FIG.
2B, as would be obvious to one skilled in the art.
[0100] As seen in FIGS. 2A-B, relative to the strain in the
arterial wall in the absence of an intravascular device, the
intravascular device causes there to be increased strain in the
arterial wall both (a) in the vicinity of contact regions 42, at
which the arterial wall becomes more curved than in the absence of
the device, and (b) in flattened regions 44 of the wall, in which
regions the arterial wall is flatter than it is in the absence of
the device. Thus, the intravascular device increases the strain in
the arterial wall even in regions of the arterial wall which are
able to pulsate, i.e., flattened regions 44. The increased strain
in the flattened regions relative to the strain in the wall in the
absence of the intravascular device is due to the increased radius
of curvature of the flattened regions of the wall.
[0101] Reference is now made to FIG. 3, which is a contour plot of
the strain in the top right quarter of an arterial wall, in the
presence of an extravascular device, in accordance with some
applications of the present invention. The contour plot in FIG. 3
was generated for a device having four elements that contact the
artery at four contact regions 52. However, the scope of the
present invention includes extravascular devices having different
structures, as described hereinbelow. For example, an extravascular
device may provide three to six contact regions. The contour plot
shown in FIG. 3 is a computer simulation of the strain in the wall
of an artery, at a blood pressure of 100 mmHg, the artery having a
radius of 3 mm, and a wall thickness of 0.6 mm.
[0102] As may be observed by comparing FIG. 3 to FIG. 2A, the
extravascular device causes there to be strain in the arterial wall
in the vicinity of contact regions 52, at which the arterial wall
becomes more curved than in the absence of the device. Furthermore,
it may be observed that the strain at non-contact regions 54 of the
wall is lower than in the absence of the device. The extravascular
device typically breaks the circumferential symmetry of the
arterial strain by applying force at discrete points or surfaces
around the sinus. For some applications, the extravascular device
increases the strain in certain regions of the arterial wall, and
decreases the strain in other regions of the arterial wall, while
maintaining the average strain almost unchanged or even slightly
reduced with respect to the strain in the wall in the absence of
the device. For some applications, the extravascular device
increases the strain in the arterial wall even at non-contact
regions 54, by causing the non-contact regions to become more
curved than in the absence of the device.
[0103] Reference is now made to FIG. 4, which is a schematic
illustration of an intravascular device 60 for placing inside
artery 20 of a subject suffering from hypertension, in accordance
with some applications of the present invention. As shown, device
60 contacts the arterial wall at two contact regions 62. At the
contact regions, device 60 pushes the arterial wall outward,
thereby flattening non-contact regions 64 of the arterial wall
between the contact regions. Typically, non-contact regions 64 are
flattened, or partially flattened during diastole of the subject,
but expand during systole such that they become more curved than
during diastole. Therefore, strain in the flattened regions of the
arterial wall is increased. However, the flattened regions still
pulsate over the course of the subject's cardiac cycle in the
presence of device 60.
[0104] As shown, device 60 is shaped such that the device
substantially does not reduce blood flow. Typically, device 60 is
shaped such that no portion of the device intersects the
longitudinal axis of the artery. For example, as shown, contact
surfaces of the device (which contact the arterial wall at contact
regions 60) are coupled to each other by a joint 66 that does not
intersect the longitudinal axis of the artery. The joint is
disposed asymmetrically with respect to centers of the contact
surfaces of the device.
[0105] Reference is now made to FIGS. 5A-B, which are schematic
illustrations of an artery, showing the radius R of artery 20,
respectively, before and after placement of the device 60 shown in
FIG. 4, in accordance with some applications of the present
invention. It may be observed that, for some applications,
insertion of device 60 increases the systolic radius of curvature
of the artery at non-contact regions 64, for example, such that the
radius of curvature at non-contact regions 64 is more than 1.1
times (e.g., twice, or more than twenty times) the systolic radius
of curvature of regions 64 in the absence of device 60, ceteris
paribus. For some applications, device 60 causes the radius of
curvature of at least a portion of a non-contact region to become
infinite, by flattening the non-contact regions. For example, the
center of non-contact region 64 in FIG. 5B has an infinite radius
of curvature.
[0106] For some applications, device 60 increases the systolic
radius of curvature of the artery at non-contact regions 64 in the
aforementioned manner, and increases the systolic cross-sectional
area of the artery by more than five percent (e.g., ten percent),
relative to the systolic cross-sectional area of the artery in the
absence of device 60.
[0107] In accordance with the description hereinabove, by
flattening non-contact regions 64 of the wall of artery 20, device
60 causes increased strain in regions 64, thereby causing an
increase in baroreceptor firing at regions 64. Alternatively or
additionally, device 60 causes increased baroreceptor firing at
contact regions 62, by deforming the arterial wall at the contact
regions.
[0108] Typically, device 60 exerts a force on artery 20, such that,
during systole when the artery is in the stretched configuration
shown in FIG. 5B, non-contact regions 64 comprise more than ten
percent, e.g., more than 20 percent, of the circumference of the
arterial wall at longitudinal sites at which device 60 stretches
the artery. For some applications, during systole, non-contact
regions 64 comprise more than 60 percent, e.g., more than 80
percent, of the circumference of the arterial wall at longitudinal
sites at which device 60 stretches the artery.
[0109] Reference is now made to FIG. 5C, which shows device 60
disposed inside artery 20, but without the device stretching artery
20. FIG. 5C is for illustrative purposes, since typically once
device 60 is inserted into the artery, the device will stretch the
artery, as shown in FIG. 5B. FIG. 5C demonstrates that the device
contacts the walls of the artery at contact regions 62 at less than
360 degrees of the circumference of the artery at any longitudinal
point along artery 20 (e.g., at the cross-section shown in FIGS.
5A-C). As shown in FIG. 5C, each of the contact regions 62
encompasses an angle alpha of the circumference of the artery, such
that the contact that device 60 makes with the walls of the artery
encompasses two times alpha degrees. For devices that contact the
artery at more than two contact regions, the contact that the
device makes with the walls of the artery encompasses an angle that
is a correspondingly greater multiple of alpha degrees. Typically,
device 60 (and the other intravascular devices described herein)
contacts the walls of the artery at less than 180 degrees (e.g.,
less than 90 degrees) of the circumference of the artery at any
longitudinal site along the artery. Typically, device 60 contacts
the walls of the artery at more than 5 degrees (e.g., more than 10
degrees) of the circumference of the artery at any longitudinal
site along the artery. For example, device 60 may contact the walls
of the artery at 5-180 degrees, e.g., 10-90 degrees, at a given
longitudinal site.
[0110] Reference is now made to FIGS. 6A-B, which are schematic
illustrations of, respectively, a device 70, and device 70
implanted inside artery 20, in accordance with some applications of
the present invention. Device 70 contacts the wall of the artery at
three contact regions 72, thereby increasing the radius of
curvature (i.e., flattening) of non-contact regions 74 of the
artery that are between the contact regions. The flattened
non-contact regions and the contact regions alternate with each
other. The flattened non-contact regions are typically able to
pulsate over the course of the subject's cardiac cycle, as
described hereinabove. As shown in FIG. 6B, each contiguous
non-contact region at a given longitudinal site of the artery,
encompasses an angle beta around a longitudinal axis 76 of the
artery. For some devices (e.g., device 70, and device 90 described
hereinbelow with reference to FIGS. 8A-B), the angle beta is also
defined by the angle that edges of adjacent contact regions of the
device define around longitudinal axis 78 of the device. When the
device is placed in the artery longitudinal axis 78 of the device
is typically aligned with longitudinal axis 76 of the artery.
Typically, angle beta is greater than 10 degree, e.g., greater than
20 degree, or greater than 50 degrees. Further typically, angle
beta is less than 180 degrees, e.g., less than 90 degrees. For some
applications angle beta is 10-180 degree, e.g., 20-90 degrees.
Typically, each of the contiguous non-contact regions is able to
pulsate.
[0111] Reference is now made to FIGS. 7A-B, which are schematic
illustrations of, respectively, a device 80, and device 80
implanted inside artery 20, in accordance with some applications of
the present invention. Device 80 contacts the wall of the artery at
four contact regions, thereby flattening the non-contact regions of
the artery that are between the contact regions. Each contiguous
non-contact region at a given longitudinal site of the artery,
encompasses an angle beta around the longitudinal axis of the
artery, angle beta being as described hereinabove.
[0112] Reference is now made to FIGS. 8A-B, which are schematic
illustrations of, respectively, a device 90, and device 90
implanted inside artery 20, in accordance with some applications of
the present invention. Device 90 contacts the wall of the artery at
five contact regions, thereby flattening the non-contact regions of
the artery that are between the contact regions. Each contiguous
non-contact region at a given longitudinal site of the artery,
encompasses an angle beta around the longitudinal axis of, angle
beta being as described hereinabove.
[0113] Apart from the fact that devices 70, 80, and 90 contact the
artery at, respectively three, four, and five contact regions,
devices 70, 80, and 90 function in a generally similar manner to
each other, and to device 60, described with reference to FIGS. 4
and 5A-C. For example, devices 70, 80, and 90 typically contact the
arterial wall around substantially less than 360 degrees of the
circumference of the artery, for example, around 10-90 degrees, or
around an angle as described hereinabove with reference to FIGS.
5A-C. Furthermore, devices 70, 80, and 90 typically increase the
cross-sectional area of the artery relative to the cross-sectional
area of the artery in the absence of the device.
[0114] For some applications, a device having three or more contact
regions with the arterial wall, for example, as shown in FIGS.
6A-8B, is used. It is noted that since device 60 (shown in FIG. 4)
contacts the artery at two contact points, as the device applies
increasing pressure to the artery, it will, at a given stage,
decrease the cross-section of the artery, as the artery becomes
increasingly elliptical. By contrast, devices 70, 80, and 90, which
contact the artery at three or more contact points, increase the
cross-section of the artery, as they apply increasing pressure to
the wall of the artery. Thus, for some applications, a device with
three or more contact regions is used in order that the
cross-sectional area of the artery is increased as the force which
the device exerts on the wall increases, as compared with a device
with only two contact regions.
[0115] Although devices that contact artery 20 at two, three, four
and five contact regions have been described, the scope of the
present invention includes devices that contact the artery at a
different number of contact regions, and/or that have different
structures from those shown, mutatis mutandis.
[0116] The intravascular devices described herein are generally
shaped such that the devices contact the intravascular wall at
relatively small contact regions, and provide relatively large
contiguous non-contact regions, which are able to pulsate due to
the subject's cardiac cycle.
[0117] The devices are typically shaped such that the total contact
region that the device makes with the arterial wall at any
longitudinal point along the artery is less than 2 mm, e.g., less
than 0.5 mm. The contact region is usually larger than 0.05 mm,
e.g., greater than 0.2 mm. For example, the contact region may be
0.05-2 mm, e.g., 0.1-0.4 mm, or 0.2-0.5 mm. The devices are
typically inserted into an artery that has an internal
circumference during systole of 6-8 mm. Thus, the intravascular
devices described herein are typically configured to contact less
than 35 percent of the circumference of the artery at any
longitudinal point along the artery, and at any point in the
subject's cardiac cycle (or, for at least a portion of the cardiac
cycle). Further typically, the intravascular devices described
herein are configured to contact more than 0.5 percent of the
circumference of the artery at any longitudinal point along the
artery, and at any point in the subject's cardiac cycle (or, for at
least a portion of the cardiac cycle). For some applications, the
contact region may be 0.5-35 percent of the circumference of the
artery (or, for at least a portion of the cardiac cycle).
[0118] For some applications, the intravascular devices described
herein have a total cross-sectional area of less than 5 sq mm,
e.g., less than 0.8 sq mm, or less than 0.5 sq mm. (The total
cross-sectional area should be understood to refer to the
cross-sectional area of the solid portions of the devices, and not
the space in between the solid portions.) The devices typically
have this cross-sectional area over a length of the device of more
than 4 mm, e.g., more than 6 mm, and/or less than 12 mm, e.g. less
than 10 mm. For example, the devices may have the aforementioned
cross sectional area over a length of 4 mm-12 mm, e.g., 6 mm-10 mm.
The devices are typically manufactured from nitinol, cobalt chrome,
and/or passivated stainless steel 316L.
[0119] Reference is now made to FIGS. 9A-D, which are schematic
illustrations of extravascular devices 100 that are implanted
around the outside of artery 20, in accordance with some
applications of the present invention. For some applications, an
extravascular device having three contact elements 102 (as shown in
FIGS. 9A and 9C) is placed around the artery. Alternatively, the
extravascular device has a different number of contact elements
102, e.g., four to six contact elements. The contact elements
increase the strain in the arterial wall at the regions at which
the contact elements contact the arterial wall, relative to the
strain in the arterial wall in the absence of device 100. For some
applications, the device increases the strain in the arterial wall
even at regions of the arterial wall between the contact regions,
relative to the strain of the arterial wall in the absence of the
device.
[0120] As with the intravascular devices described hereinabove,
typically contact between extravascular device 100 and the artery
at a given longitudinal location is limited to several (e.g., three
to six) contact regions around the circumference of the artery, and
is generally minimized. Thus, when the device is placed around the
artery there is at least one, and typically a plurality of,
non-contact regions 104 around the circumference of the artery, at
which the device does not contact the arterial wall. As shown in
FIG. 9A, each contiguous non-contact region at a given longitudinal
site of the artery, encompasses an angle theta around a
longitudinal axis 76 of the artery. For some devices, as shown, the
angle theta is also defined by the edges of adjacent contact
elements 102 of the device and longitudinal axis 108 of the device.
When the device is placed in the artery longitudinal axis 108 of
the device is typically aligned with longitudinal axis 76 of the
artery.
[0121] Typically, angle theta is greater than 10 degrees, e.g.,
greater than 20 degrees, or greater than 50 degrees. Further
typically, angle theta is less than 180 degrees, e.g., less than 90
degrees. For some applications angle theta is 10-180 degrees, e.g.,
20-90 degrees. This may be beneficial, since providing contiguous
non-contact regions around the artery, as described, allows a
greater area of the artery to pulsate in response to pressure
changes than if the device were to provide smaller contiguous
non-contact regions.
[0122] FIG. 9B shows a cross-section of one of contact elements 102
on a wall of artery 20, in accordance with some applications of the
present invention. For some applications, some or all of contact
elements 102 are shaped to define grooves. Each of the grooves has
a length L. Typically, length L is more than 0.5 mm (e.g., more
than 2 mm), and/or less than 8 mm (e.g., less than 6 mm). For
example, length L may be 0.5-8 mm, e.g., 2-6 mm. The contact
element typically facilitates pulsation of the arterial wall into
the groove.
[0123] Typically (as shown for example in FIGS. 9A and 9C),
extravascular device 100 does not encompass the full circumference
of the artery. For example, the extravascular device may encompass
less than 90 percent, e.g., less than 70 percent of the
circumference of the artery. For some applications, using a device
that does not encompass the whole circumference of the artery
facilitates placement of the device on the artery. For example, it
may be possible to place such a device on the artery (a) without
dissecting the artery free from its surrounding tissues, and/or (b)
without fully mobilizing the artery.
[0124] For some applications, using a device that does not
encompass the whole circumference of the artery reduces damage to
the artery, and/or damage to baroreceptors, during placement of the
device on the artery. Alternatively or additionally, using a device
that does not encompass the whole circumference of the artery makes
placement of the device on the artery a less complex procedure than
placement on the artery of a device that fully encompasses the
artery.
[0125] For some applications, device 100 does not encompass the
whole circumference of the artery, and contact elements 102 curve
around the artery, as shown in FIG. 9C. Typically, the curvature of
the contact elements facilitates coupling of device 100 to the
artery.
[0126] Typically, extravascular device 100 encompasses more than 50
percent of the circumference of the artery, for example, in order
to prevent the device from slipping from the artery. However, the
scope of the present invention includes devices that encompass less
than 50 percent of the artery.
[0127] For some applications, extravascular device 100 encompasses
the whole circumference of artery 20. For example, an extravascular
device may be used that comprises two pieces that are coupled to
each other such that the device encompasses the whole artery.
[0128] Typically, the device causes an increase in the strain in at
least a portion of the arterial wall, relative to the strain in the
arterial wall in the absence of the device, without substantially
reducing the cross-sectional area of the artery. For example, the
cross-sectional area of the artery in the presence of device 100
may be more than 50 percent, e.g., more than 80 percent of the
cross-sectional area of the artery in the absence of the device, at
a given stage in the subject's cardiac cycle. The device does not
cause a substantial reduction in the cross-sectional area of the
artery because the device only contacts the artery at discrete
points around the circumference of the artery. Therefore the device
does not substantially constrict the artery, but rather reshapes
the artery relative to the shape of the artery in the absence of
the device.
[0129] Further typically, the device causes an increase in the
strain in at least a portion of the arterial wall, relative to the
strain in the arterial wall in the absence of the device, without
substantially affecting blood flow through the artery. For example,
the rate of blood flow through the artery in the presence of device
100 may be more than 70 percent, e.g., more than 90 percent of the
blood flow in the absence of the device.
[0130] For some applications, an insubstantial effect on flow is
achieved by maintaining an internal diameter of the artery, in the
presence of the device, that is at least 30 percent of the diameter
of the artery, in the absence of the device, throughout the cardiac
cycle. Alternatively or additionally, an insubstantial effect on
flow is achieved by maintaining the cross sectional area of the
artery, in the presence of the device, to be at least 20 percent of
the sectional area, in the absence of the device, at a given stage
in the subject's cardiac cycle.
[0131] For some applications, the flow through the artery to which
the device is coupled is monitored during the implantation of the
device, and the device is configured to not reduce the flow by more
than 15 percent. For some applications, the degree of force applied
to the artery, and/or a physical distance between parts of the
device, is modulated until the measured flow is not reduced by more
than 15 percent. For some applications the absolute minimal
distance across the artery is limited to no less than 1.5 mm.
[0132] For some applications, the extravascular devices contact the
artery around which they are placed along a length of 5 mm.
[0133] For some applications, an extravascular device is used that
is in accordance with one or more of the devices described in U.S.
patent application Ser. No. 12/602,787 to Gross, which is
incorporated herein by reference.
[0134] For some applications, a plurality of extravascular devices
100 are placed around the artery, as shown in FIG. 9D. For some
applications, the plurality of extravascular devices are coupled to
each other by a coupling element 105. The extravascular devices are
typically spaced from each other such that there are non-contact
regions 103 between each of the extravascular devices. Each of the
non-contact regions is contiguous and, typically, has a length L1
of more than 0.5 mm (e.g., more than 2 mm), and/or less than 8 mm
(e.g., less than 6 mm). For example, length L1 may be 0.5-8 mm,
e.g., 2-6 mm. The arterial wall is typically able to pulsate at the
non-contact regions.
[0135] Reference is now made to FIG. 10, which is a graph generated
by computer simulation, which indicates the circumferential portion
of an arterial wall having a strain that is greater than a
threshold value, as a function of the reduction in the
cross-sectional area of the artery, for respective extravascular
devices. For some applications of the present invention, an
extravascular device is placed around an artery, as described
hereinabove. Typically, the extravascular device increases strain
in at least regions of the arterial wall without substantially
reducing the cross-sectional area of the artery, as described
hereinabove. Further typically, the extravascular device increases
strain in at least regions of the arterial wall without
substantially affecting blood flow through the artery, as described
hereinabove.
[0136] The graph shows several lines, the lines corresponding to
extravascular devices that are similar to the extravascular device
described hereinabove with reference to FIGS. 3 and 9A. The lines
correspond to extravascular devices that have, respectively, three,
four, five, six, and seven contact regions with the arterial wall
around the circumference of the artery. In addition, one of the
lines corresponds to two flat plates that are placed against the
outer surface of the artery.
[0137] The simulation was generated for an artery at 100 mmHg of
pressure. When the extravascular devices herein are placed on the
arterial wall, the strain in at least some portions of the arterial
wall is increased. Placing the extravascular devices on the
arterial wall typically reduces the cross-sectional area of the
artery. For a given device, the more the device compresses the
artery, the greater the increase in the strain in the arterial
walls, and the greater the reduction in the cross-sectional area of
the artery.
[0138] The x-axis of the graph of FIG. 10 indicates the reduction
in the cross-sectional area of the artery generated by the devices.
The y-axis measures the percentage of the circumference of the
arterial wall having a strain that is at least equivalent to what
the strain of the arterial wall would be, if the pressure in the
artery were 120 mmHg. Typically, the baroreceptor firing rate in
such areas when the pressure is 100 mmHg, during use of the devices
described hereinabove, will be generally equivalent to, or greater
than the baroreceptor firing rate at 120 mmHg pressure in the
absence of use of the devices. Thus, each of the lines in the graph
is a measure of the percentage of the circumference of the arterial
wall having the increased strain as a function of the reduction in
the arterial cross-sectional area that is necessary to induce the
increase in strain.
[0139] It may be observed that the devices having a smaller number
of contact regions with the artery are typically more effective at
increasing the strain in the arterial wall by applying a
compression force that does not substantially reduce the
cross-sectional area of the artery. For example, devices having
three and four contact regions with the artery increase the strain
of, respectively, 13 percent and 14 percent of the arterial wall to
the equivalent of 120 mmHg of pressure while only reducing the
cross-sectional area of the artery by 10 percent. Typically, a 10
percent reduction in the cross-sectional area of the artery does
not substantially reduce blood flow through the artery in a manner
that has significant adverse physiological effects.
[0140] The inventors hypothesize that the devices having a larger
number of contact regions with the artery are less effective at
increasing the strain in the arterial wall than those with a
smaller number of contact regions, because the device acts to
support the arterial wall at the contact regions, thereby reducing
pulsation of the arterial wall over the course of the cardiac
cycle. For this reason, the inventors hypothesize that, at low
pressures, the two plates are relatively effective at increasing
the strain in the arterial wall, since there is a small amount of
contact between the plates and the wall. However, at higher
compressive forces, the plates provide more support to the wall
since there is a greater contact area between the plates and the
wall. Therefore, the plates limit the pulsation of the wall by an
increasing amount. At higher compressive forces, the decrease in
baroreceptor stimulation due to the reduced pulsation of the artery
overrides the increase in baroreceptor stimulation due to the
plates exerting pressure on the arterial wall. Thus, at higher
compressive forces, the plates are not as effective as the other
extravascular devices at increasing the strain in regions of the
arterial wall. Nevertheless, the scope of the present invention
includes the use of such plates, e.g., when strain increase is not
the only parameter of importance in selecting an implant.
[0141] It is additionally noted that for a broad range of allowed
reductions in cross-section, e.g., about 17-30 percent, 3-6 contact
regions all function generally well. Thus, at higher compression
forces (i.e., by reducing the cross-sectional area of the artery by
a greater amount), the devices having a greater number of contact
regions with the artery become more effective at increasing the
strain in the arterial wall. For example, by reducing the
cross-sectional area of the artery by 30 percent, each of the
devices having three to six contact regions with the artery
increases the strain of between 22 percent and 26 percent of the
arterial wall to the equivalent of 120 mmHg of pressure.
[0142] Reference is now made to FIG. 11, which is a graph showing
the maximum percentage increase in the strain of the arterial wall
as a function of the reduction in the cross-sectional area of the
artery, for respective extravascular devices.
[0143] The graph shows several lines, the lines corresponding to
extravascular devices that are similar to the extravascular device
described hereinabove with reference to FIGS. 3 and 9A. The lines
correspond to extravascular devices that have, respectively, three,
four, five, six, and seven contact regions with the arterial wall
around the circumference of the artery. In addition, one of the
lines corresponds to two plates that are placed against the outside
surface of the artery.
[0144] The simulation was generated for an artery at 100 mmHg of
pressure. The bottom, middle, and top horizontal lines correspond,
respectively, to the maximum strain in the vessel wall at 120 mmHg,
140 mmHg, and 160 mmHg pressure, when no device is placed on the
artery. When the devices herein are placed on the arterial wall,
the maximum strain of the arterial wall is increased. Placing the
devices on the arterial wall typically reduces the cross-sectional
area of the artery. For a given device, the more the device
compresses the artery, the greater the maximum strain in the
arterial walls, and the greater the reduction in the
cross-sectional area of the artery.
[0145] The x-axis of the graph of FIG. 11 measures the reduction in
the cross-sectional area of the artery generated by the devices.
The y-axis measures the maximum strain in the arterial wall.
[0146] It may be observed that for the devices for which the data
shown in the graph was generated, the fewer the number of contact
regions that the device made with the arterial wall, the more
effective the device is at increasing the maximum strain in the
arterial wall for a given reduction in the cross-sectional area of
the artery that is caused by the device. For example, by
compressing the artery such that it has a 20 percent reduction in
its cross-sectional area:
[0147] the device having three contact regions generates a maximum
increase of 75 percent in the arterial wall strain,
[0148] the device having four contact regions generates a maximum
increase of 62 percent in the arterial wall strain,
[0149] the device having five contact regions generates a maximum
increase of 50 percent in the arterial wall strain,
[0150] the device having six contact regions generates a maximum
increase of 23 percent in the arterial wall strain, and
[0151] the device having seven contact regions generates a maximum
increase of less than 5 percent in the arterial wall strain.
[0152] Thus, in accordance with some applications of the present
invention, extravascular devices having three or more contact
regions (e.g., three to six) with the artery are placed around the
outside of the artery. The devices typically provide contact
regions and non-contact regions of the arterial wall, as described
hereinabove. The devices typically increase the strain in the
arterial wall, thereby generating increased baroreceptor firing in
the artery.
[0153] Reference is now made to FIG. 12, which is a schematic
illustration of a device 110 that is used to test the baroreceptor
response of a subject to a range of intravascular pressures, in
accordance with some applications of the present invention. For
some applications, before an intravascular device is inserted into
a subject's artery, the baroreceptor response of the subject is
tested using measuring device 110. Cather 112 is inserted into
artery 20, in which the intravascular device will be implanted.
Extendable arms 114 are extendable from the distal end of the
catheter, and are configured such that the pressure that the arms
exert on the arterial wall increases, as the portion of the arms
that extends from the catheter increases.
[0154] Extendable arms 114 are extended incrementally from the
distal end of the catheter. At each of the increments, the
subject's blood pressure is measured in order to determine the
baroreceptor response to the pressure that the arms are exerting on
the arterial wall. On the basis of the blood pressure measurements,
it is determined which intravascular device should be inserted into
the subject's artery, and/or what dimensions the intravascular
device should have.
[0155] For some applications, a measuring device including arms 114
or a similar measuring device is left in place in the artery, but
catheter 112 is removed before the blood pressure measurements are
taken. For example, the catheter may be removed in order to
increase blood flow through the artery, relative to when the
catheter is in place. Once it has been determined, using the
measuring device, which intravascular device should be placed
inside the artery, and/or what dimensions the intravascular device
should have, the measuring device is removed from the artery and
the intravascular device is placed inside the artery.
[0156] For some applications, a toroid balloon is placed inside the
artery and is used as a measuring device. The balloon is inflated
incrementally such that the balloon applies varying amounts of
pressure to the arterial wall, and the subject's blood pressure is
measured in order to measure the response to the pressure being
applied to the wall. In this manner, it is determined which
intravascular device should be used, and/or what dimensions the
intravascular device should have. During the aforementioned
measuring procedure, blood continues to flow through the artery,
via a central hole in the toroid balloon.
[0157] For some applications, the intravascular devices described
herein are inserted to an implantation site inside or (using a
non-transvascular route) outside of the subject's artery, while the
device is in a first configuration thereof. When the device has
been placed at the implantation site, the configuration of the
device is changed to a second configuration, in which the device is
effective to increase baroreceptor stimulation, in accordance with
the techniques described herein. For example, the device may be
made of nitinol, or another shape memory material, and the
configuration of the device may be changed by applying an RF
signal, and/or another form of energy, to the device. For some
applications, the device is implanted at an implantation site that
is close to the subject's skin, and the RF signal is applied to the
device via the subject's skin.
[0158] For some applications, devices are applied to the carotid
artery of a subject who suffers from carotid sinus
hypersensitivity, in order to reduce baroreceptor sensitivity of
the carotid sinus, by reducing pulsation of the artery. For
example, a device may be placed inside or outside the artery such
that the device makes contact with the artery at more than six
contact points, and/or over more than 180 degrees of the
circumference of the artery. For some applications, a device (e.g.,
a stent) is placed inside or outside of the artery such that the
device makes 270-360 degrees of contact with the artery.
[0159] Reference is now made to FIG. 13, which is a graph showing
blood pressure measured in a dog, before, during and after the
bilateral placement of intravascular devices into the dog's carotid
sinuses, in accordance with some applications of the present
invention. Intravascular devices which made contact with the
carotid sinus at four contact regions (the devices being generally
as shown in FIGS. 7A-B) were placed in the dog's left and right
carotid sinuses. The beginning and end of the implantation period
is indicated in FIG. 13 by, respectively, the left and right
vertical dashed lines at about five minutes and 153 minutes.
[0160] It may be observed that the implantation of the devices in
both sinuses resulted in the dog's systolic blood pressure dropping
from above 120 mmHg to below 80 mmHg, and in the dog's diastolic
blood pressure dropping from about 60 mmHg to about 40 mmHg. During
the implantation procedure the dog's blood pressure rose. The
inventors hypothesize that the rise in blood pressure is due to
catheters blocking the flow of blood to the carotid arteries during
the implantation, resulting in reduced baroreceptor stimulation
during the implantation procedure. It is noted that the placement
of the device in the dog's sinuses did not have a substantial
effect in the dog's heart rate.
[0161] Reference is now made to FIG. 14, which is a graph showing
the pressure-strain curve of an artery of a normal subject, a
hypertensive subject, and a hypertensive subject who uses one of
the devices described herein. One of the causes of hypertension is
that the arterial wall of the subject does not experience as much
strain at any given pressure, as the arterial wall of a normal
subject. Thus, the pressure-strain curve of the hypertensive
subject is flattened with respect to that of a healthy subject and
the strain response is shifted to higher pressures.
[0162] The devices described herein increase the strain in the
arterial wall at all pressure levels within the artery. For some
applications, as shown, at increasing arterial pressures, the
absolute increase in the strain in the arterial wall caused by the
device increases, relative to the strain experienced by the
hypertensive subject before implantation of the device. Thus, the
devices described herein both shift the pressure-strain curve of a
hypertensive subject upwards and increase the gradient of the
curve. A device is typically selected such that the subject's
pressure-strain curve, subsequent to implantation of the device,
will intersect the normal pressure-strain curve at a pressure of
between 80 mmHg and 240 mmHg.
[0163] Reference is now made to FIGS. 15A-B, which are schematic
illustrations of a device 120 for placing in artery 20, in
accordance with some applications of the present invention. Device
120 is generally similar to the intra-arterial devices described
hereinabove, except for the differences described hereinbelow. FIG.
15A shows a three-dimensional view of device 120, as the device is
shaped when the device is inside the artery, and FIG. 15B shows a
flattened, opened, profile of device 120. Device 120 is generally
similar to device 80 described hereinabove with reference to FIGS.
7A-B. Device 120 contacts the wall of the artery at four contact
regions 122 (which comprise strut portions), thereby flattening the
non-contact regions of the artery that are between the contact
regions. For some applications, device 120 includes radiopaque
markers 126 at proximal and distal ends of the device (as shown) or
at other portions of the device.
[0164] As shown in FIG. 15B, each of the strut portions is
generally spaced from its two adjacent strut portions by respective
distances D1 and D2, D1 being smaller than D2. Thus, the device
defines a first set of two sides 124A, having widths D1, and a
second set of two sides 124B, having widths D2. Placement of device
120 inside artery 20 typically results in the artery having a
cross-sectional shape that is more rectangular than in the absence
of the device, the cross-sectional shape having sides with lengths
D1 and D2. Each of the sides of the cross-sectional shape is
supported by a respective side 124A or 124B of device 120.
Typically, the ratio of distance D2 to distance D1 is greater than
1:1, e.g., greater than 2:1, and/or less than 5:1, e.g., between
1.1:1 and 5:1 (e.g., between 1.5:1 and 3:1).
[0165] An experiment was conducted by the inventors of the present
application in which a spring constant of a device having generally
similar characteristics to device 120 was measured. For the
purposes of the experiment, the spring constant of the device was
measured by measuring the change in force applied by the device
versus the change in the diameter of the device during cycles of
crimping and expansion of the device. A plot of the force versus
the diameter of the device during such a cycle forms a hysteresis
curve. It is noted that, subsequent to implantation of the device
in a subject's artery, the variation in force versus diameter that
the device undergoes during a characteristic cardiac cycle also
forms a hysteresis curve. When the device is implanted, the maximum
force that the device exerts on the arterial wall, which generates
the loading branch of the hysteresis curve, is exerted during
diastole. The minimum force that the device exerts on the artery,
which generates the unloading branch of the hysteresis curve, is
exerted during systole. In the experiment that was conducted by the
inventors, the spring constant of the device was determined based
upon measurements that were performed using an M250-3 CT Materials
Testing Machine manufactured by The Testometric Company Ltd.
(Lancashire, UK). The device had a spring constant of 1.14 N/mm. In
accordance with the aforementioned experimental result, in
accordance with some applications of the invention, a device is
inserted into a subject's artery in accordance with the techniques
described herein, the device having a spring constant of less than
2 N/mm, e.g., less than 1.5 N/mm, or less than 1.3 N/mm.
[0166] Typically, at the distal and proximal ends of device 120,
the device is shaped to define crimping arches 125. During
transcatheteral insertion of the device into the subject's artery,
the device is crimped about the crimping arches, such that the span
of the device is reduced relative to the span of the device in its
expanded state. Upon emerging from the distal end of the catheter,
the device expands against the arterial wall.
[0167] For some applications, each crimping arch 125 has a radius
of curvature r that is less than 6 mm (e.g., less than 1 mm), in
order to facilitate crimping of device 120 about the crimping arch.
For some applications, each crimping arch has a radius of curvature
r that is greater than 0.3 mm, since a crimping arch having a
smaller radius of curvature may damage the arterial wall.
Furthermore, when the expanded device exerts pressure on the
arterial wall, much of the pressure that is exerted on the device
by the arterial wall is resisted by the crimping arches. Therefore,
for some applications, each crimping arch has a radius of curvature
that is greater than 0.3 mm, in order to facilitate resistance to
the pressure that is exerted on the device at the crimping arches.
Therefore, for some applications, each crimping arch has a radius
of curvature that is 0.3-0.6 mm.
[0168] For some applications, the thickness of the struts of device
120 at the crimping arches is greater than the thickness of the
struts at other portions of the device, in order to facilitate
resistance to the pressure that is exerted on the device at the
crimping arches. For some applications, there are additional
regions of the struts that are susceptible to absorbing much of the
pressure that is exerted on the device by the arterial wall, and
the thickness of the struts at the additional regions is greater
than the thickness of the struts at other portions of the
device.
[0169] Typically, when device 120 is in a non-constrained state
thereof, the strut portions of device 120 project outwardly from
crimping arch 125 at an angle theta, angle theta being greater than
30 degrees, e.g., greater than 60 degrees, or greater than 75
degrees. Typically, the outward projection of the struts from the
crimping arch at such an angle reduces the moment that the arterial
wall exerts about the crimping arch, relative to if the struts
projected outwardly from the crimping arch at a smaller angle. This
is demonstrated with reference to FIGS. 15C-D, which show a force F
of the arterial wall being exerted on struts that project
outwardly, respectively, at angles of alpha and beta, alpha being
greater than beta. In FIG. 15C, the force is exerted on the strut
at a distance d1 from the crimping arch, and in FIG. 15D, the force
is exerted on the strut at a distance d2 from the crimping arch, d1
being less than d2. Therefore, the moment that is exerted about
crimping point 125 for the strut shown in FIG. 15C is less than
that of FIG. 15D.
[0170] Typically, as a result of angle theta being greater than 30
degrees, e.g., greater than 60 degrees, or greater than 75 degrees,
when in the non-constrained state, the perimeter of the
cross-section of device 120 at any location along the length of the
device is more than 80% (e.g., more than 90%) of the maximum
perimeter of the cross-section of the device along more than 80%
(e.g., more than 90%) of the length of the device. Conversely, if
angle theta were smaller, the perimeter of the cross-section of
device 120 would be more than 80% of the maximum perimeter of the
cross-section of the device along less than 80% of the length of
the device. It is noted that the perimeter of the cross-section of
the device at any location along the length of the device is
defined as the line that bounds the solid components (e.g., the
struts) of device 120 at the location. This is demonstrated with
reference to FIG. 15E, which shows a dotted line indicating the
perimeter of the cross-section of the device. Further typically, as
a result of angle theta being greater than 30 degrees, e.g.,
greater than 60 degrees, or greater than 75 degrees, the ratio of
the perimeter of the cross-section of device 120 to the
cross-sectional area of the solid components of the device is more
than is more than 80% (e.g., more than 90%) of the maximum value of
this ratio along more than 80% (e.g., more than 90%) of the length
of the device.
[0171] Reference is now made to FIGS. 16A-D, which are schematic
illustrations of another device 130 for placing in artery 20, in
accordance with some applications of the present invention. Device
130 is generally similar to the intra-arterial devices described
hereinabove, except for the differences described hereinbelow.
FIGS. 16B-D show device 130 during the shaping of the device, the
device typically being placed on a shaping mandrel 132 during the
shaping process. As shown, the cross-sectional shape of
intra-arterial device 130 varies along the longitudinal axis of the
device. Typically, the device defines strut portions 134, all of
which diverge from each other, from a first end of the device to
the second end of the device. For some applications, each strut
portion includes two or more parallel struts, as described
hereinbelow.
[0172] As shown in FIGS. 16C-D, device 130 is shaped such that at
the second end of the device, the device has a greater span S2,
than the span of the device S1 at the first end of the device.
Typically, the ratio of S2 to S1 is greater than 1:1, e.g., greater
than 1.1:1, and/or less than 2:1, e.g., between 1.1:1 and 2:1
(e.g., between 1.1:1 and 1.4:1).
[0173] For some applications, devices are inserted into a subject's
artery that are shaped differently from device 130, but which are
also shaped such that at the second end of the device, the device
has a greater span S2, than the span of the device S1 at the first
end of the device, for example, as described with reference to
FIGS. 18A-D.
[0174] Due to the ratio of S2 to S1, upon placement of device 130
inside the artery, the shape of the artery typically becomes
increasingly non-circular (e.g., elliptical or rectangular), along
the length of the artery, from the first end of the device (having
span S1) to the second end of the device (having span S2).
Furthermore, due to the ratio of S2 to S1, upon placement of device
130 inside the artery, the cross-sectional area of the artery
typically increases along the length of the artery, from the first
end of the device (having span S1) to the second end of the device
(having span S2). Typically, the device is placed such that the
first end of the device (which has the smaller span) is disposed
within the internal carotid artery, and the second end of the
device (which has the greater span) is disposed in the vicinity of
the carotid bifurcation. In this configuration, the device thus
stretches the internal carotid artery in the vicinity of the
bifurcation, due to the span of the device at the second end of the
device, but does not substantially stretch the internal carotid
artery downstream of the bifurcation.
[0175] Typically, the device is shaped such that the device can be
viewed as defining three zones along the length of the device. The
second end may be viewed as the maximum-span zone, which is
configured to be placed in the common carotid artery and/or within
the internal carotid artery in the vicinity of the carotid
bifurcation. The first end may be viewed as the minimum-span zone,
which is configured to be placed at a location within the internal
carotid artery that is downstream of the bifurcation and to reduce
strain on the internal carotid artery at the downstream location
relative to if the minimum-span zone had a greater span. The
portion of the device between the first and second zones may be
viewed as the pulsation zone, at which the device exerts strain on
the artery, while facilitating pulsation of the artery by having
non-contact regions at which the device does not contact the
artery. It is noted that, for some applications, the second end
(i.e., the maximum-span zone) is configured to be placed downstream
of the carotid bifurcation, but to cause stretching of the carotid
artery in the vicinity of the carotid bifurcation, due to the span
of the device at the second end.
[0176] As shown in FIGS. 16C-D, device 130 is shaped such that in
the vicinity of the second end of the device, the device has a
greater span S2 in a first direction than a span S3 of the device
in a second direction. For some applications, the ratio of S2 to S3
is greater than 1:1, e.g., greater than 2:1, and/or less than 5:1,
e.g., between 1.1:1 and 5:1 (e.g., between 1.5:1 and 3:1).
Typically, the ratio of S2 to S3 enhances flattening of the artery
in which device 130 is placed in the direction of span S2.
[0177] Typically, device 130 includes three or more diverging strut
portions 134, e.g., four diverging strut portions, as shown. For
some applications, device 130 includes crimping arches 125 at the
ends of the device, the crimping arches being generally similar to
crimping arches 125, as described hereinabove with reference to
device 120. For some applications, the strut portions of device 130
project outwardly from crimping arches 125 at an angle theta, angle
theta being greater than 30 degrees, e.g., greater than 60 degrees,
or greater than 75 degrees, in a generally similar manner to that
described with reference to device 120. For some applications, each
of the strut portions comprises two struts that are translated
longitudinally with respect to one another (i.e., the struts are
doubled), in order to provide mechanical strength to the struts.
Alternatively, each strut portion includes a single strut, or more
than two struts that are translated longitudinally with respect to
each other.
[0178] Reference is now made to FIGS. 17A-D, which are schematic
illustrations of yet another device 140 for placing in artery 20,
in accordance with some applications of the present invention.
Device 140 is generally similar to the intra-arterial devices
described hereinabove, except for the differences described
hereinbelow. FIG. 17A shows device 140 during the shaping of the
device, the device typically being placed on shaping mandrel 132
during the shaping process. As shown, the cross-sectional shape of
intra-arterial device 140 varies along the longitudinal axis of the
device.
[0179] As shown in FIG. 17B, device 140 is shaped such that at the
second end of the device, the device has a greater span S2, than
the span of the device S1 at the first end of the device.
Typically, the ratio of S2 to S1 is greater than 1:1, e.g., e.g.,
greater than 1.1:1, and/or less than 2:1, e.g., between 1.1:1 and
2:1 (e.g., between 1.1:1 and 1.4:1).
[0180] Due to the ratio of S2 to S1, upon placement of device 140
inside the artery, the shape of the artery typically becomes
increasingly non-circular (e.g., elliptical or rectangular), along
the length of the artery, from the first end of the device (having
span S1) to the second end of the device (having span S2).
Furthermore, due to the ratio of S2 to S1, upon placement of device
130 inside the artery, the cross-sectional area of the artery
typically increases along the length of the artery, from the first
end of the device (having span S1) to the second end of the device
(having span S2). Typically, the device is placed such that the
second end of the device (which has the greater span) is disposed
in the common carotid artery and/or within the internal carotid
artery in the vicinity of the carotid bifurcation and the first end
of the device (which has the smaller span) is disposed within the
internal carotid artery downstream of the bifurcation. In this
configuration, the device thus stretches the internal carotid
artery in the vicinity of the bifurcation, due to the span of the
device at the second end of the device, but does not substantially
stretch the internal carotid artery downstream of the
bifurcation.
[0181] Device 140 is shaped to define four sides. Two of the sides,
which are opposite to one another, are configured to act as artery
contact regions 142 (shown in FIG. 17C), and apply pressure to the
walls of the artery by contacting the artery. The other two sides
of device 140, which are also opposite to one another, are
configured to act as crimping regions 144 (shown in FIG. 17D).
During transcatheteral implantation of the device into the artery,
the crimping regions facilitate crimping of the device.
[0182] It is noted that the sides of device 140 that act as artery
contact regions 142 are typically also somewhat crimpable.
Typically, as shown, the sides of device 140 that act as artery
contact regions 142 include crimping arches 125 (as described
hereinabove), which facilitate crimping of the device.
[0183] An artery contacting region 142 of device 140 is shown in
FIG. 17C. Upon implantation inside an artery, artery contact
regions 142 exert pressure on the artery wall, thereby flattening
regions of the arterial wall between the artery contact regions,
and increasing the strain in the arterial wall at the flattened
regions, as described hereinabove. For some applications, the
artery contact regions comprise two or more struts 146 that are
translated longitudinally with respect to one another. Typically,
the struts of a given artery contact region are coupled to one
another by a reinforcing element 148. For some applications, the
reinforcing element is disposed such that when the artery contact
region is crimped, the longitudinal translation of the struts with
respect to one another is maintained. For some applications, struts
146 of device 140 project outwardly from crimping arches 125 at an
angle theta, angle theta being greater than 30 degrees, e.g.,
greater than 60 degrees, or greater than 75 degrees, in a generally
similar manner to that described with reference to device 120.
[0184] A crimping region 144 of device 140 is shown in FIG. 17D.
For some applications, crimping region 144 comprises a locking
mechanism 149. During crimping of the device, the locking mechanism
is unlocked, to facilitate crimping of the device. When the device
is implanted into artery 20, the locking mechanism is locked, so as
to prevent the crimping regions from becoming crimped due to
pressure that is exerted on the device by the artery. For example,
the locking mechanism may comprise two struts 150 that are shaped
so as to become locked in placed with respect to one another at a
locking interface 152. In order to crimp the device, one of the
struts is forced above or below the plane of the locking interface.
The struts are pre-shaped, such that when the struts are not locked
with respect to one another, the struts move toward one another,
such that the struts at least partially overlap with one another.
Alternatively or additionally, other locking mechanisms are used.
For example, a hinged-based mechanism may be used.
[0185] For some applications, device 140 is configured to be at
least partially crimpable about the crimping regions even when the
device is placed inside the artery. The crimping regions thus
facilitate flexing of device 140 when the device is placed inside
the artery. For example, the crimping regions may facilitate
passive flexing of the device in coordination with the subject's
cardiac cycle, due to variations in the pressure that is exerted on
the device by the arterial walls, over the course of the cardiac
cycle.
[0186] Reference is now made to FIGS. 18A-B, which are schematic
illustrations of respective sides 124A and 124B of device 120 for
placing in artery 20, in accordance with some applications of the
present invention. Device 120 is generally as described hereinabove
with reference to FIGS. 15A-B, except that device 120 as shown in
FIGS. 18A-B is shaped such that at the second end of the device,
the device has a greater span S2, than the span of the device S1 at
the first end of the device. Typically, the ratio of S2 to S1 is
greater than 1:1, e.g., e.g., greater than 1.1:1, and/or less than
2:1, e.g., between 1.1:1 and 2:1 (e.g., between 1.1:1 and
1.4:1).
[0187] Reference is now made to FIGS. 18C-D, which are schematic
illustrations of respective sides 124A and 124B of device 120 for
placing in artery 20, in accordance with some applications of the
present invention. Device 120 is generally as described hereinabove
with reference to FIGS. 15A-B and FIGS. 18A-B, except that device
120 as shown in FIGS. 18C-D is shaped such that (a) sides 124A and
124B are of equal widths, and (b) at the second end of the device,
the device has a greater span S2, than the span of the device S1 at
the first end of the device. For some applications, a device is
used that defines four parallel artery contact regions 122, all of
which are separated from adjacent artery contact regions by an
equal distance, as shown in FIGS. 18C-D.
[0188] Typically, the ratio of S2 to S1 of device 120 as shown in
FIGS. 18C-D is as described hereinabove. Thus, the ratio of S2 to
S1 is typically greater than 1:1, e.g., e.g., greater than 1.1:1,
and/or less than 2:1, e.g., between 1.1:1 and 2:1 (e.g., between
1.1:1 and 1.4:1).
[0189] Reference is now made to FIG. 19, which is a schematic
illustration of a D-shaped device 150 for placing inside artery 20,
in accordance with some applications of the present invention. For
some applications, a device having a D-shaped cross-section, as
shown, is placed inside the artery. A straight portion 152 of the
cross-sectional shape flattens a portion of the arterial wall that
is adjacent to the straight portion, thereby increasing the strain
in the portion of the arterial wall relative to the strain in the
portion of the arterial wall in the absence of the device.
[0190] It is noted that device 120 and other intra-arterial devices
described herein (such as devices 70, 80, and 90) define contact
regions that contact the intra-arterial wall, the contact regions
comprising a plurality of generally parallel strut portions.
Typically, for each of the devices, the minimum distance between a
first strut portion of the device and an adjacent strut portion to
the first strut portion is 2 mm. It is further noted that the
intra-arterial devices described herein (such as devices 60, 70,
80, 90, 120, 130 140, 150, 170, 174, 176, 190, and/or 200) cause
the artery to assume a non-circular cross-sectional shape, such as
a triangular, a rectangular, or an oval shape.
[0191] For some applications, the intra-arterial devices described
herein (such as devices 60, 70, 80, 90, 120, 130, 140, 150, 170,
174, 176, and/or 190) are configured, upon implantation of the
device inside the artery, to cause one or more contiguous portions
of the arterial wall to become flattened, each of the contiguous
portions having an area of more than 10% of the total surface area
of the artery in the region in which the device is placed.
Typically, the aforementioned devices contact less than 20 percent
(e.g., less than 10 percent) of the wall of the artery along more
than 80% of the length of the region of the artery along which the
device is placed. As described hereinabove, for some applications,
the intravascular devices described herein (such as devices 60, 70,
80, 90, 120, 130, 140, and 150) have a total cross-sectional area
of less than 5 sq mm, e.g., less than 0.8 sq mm, or less than 0.5
sq mm. (The total cross-sectional area should be understood to
refer to the cross-sectional area of the solid portions of the
devices, and not the space in between the solid portions.) The
devices typically have this cross-sectional area over a length of
the device of more than 4 mm, e.g., more than 6 mm, and/or less
than 12 mm, e.g. less than 10 mm. For example, the devices may have
the aforementioned cross sectional area over a length of 4 mm-12
mm, e.g., 6 mm-10 mm, or over a length of 10 mm-30 mm.
[0192] For some applications, the dimensions of the intra-arterial
devices described herein (such as devices 60, 70, 80, 90, 120, 130,
140, 150, 170, 174, 176, 190, and/or 200) are chosen based upon
patient-specific parameters.
[0193] For some applications, the intra-arterial devices described
herein (such as devices 60, 70, 80, 90, 120, 130, 140, 150, 170,
174, 176, 190, and/or 200) are made of a shape-memory alloy, such
as nitinol. The nitinol is configured to assume an open, deployed
configuration at body temperature, and to assume a crimped
configuration in response to being heated or cooled to a
temperature that differs from body temperature by a given amount,
such as by 5 C. In order to insert the device, the device is heated
or cooled, so that the device assumes its crimped configuration.
The device is placed inside the artery, and upon assuming body
temperature (or a temperature that is similar to body temperature),
the device assumes its deployed, open configuration. Subsequently,
the device is retrieved from the artery by locally heating or
cooling the region of the artery in which the device is disposed.
The device assumes its crimped configuration and is retrieved from
the artery using a retrieval device. For some applications, a
device is inserted into the artery temporarily in order to cause
the artery to undergo a permanent shape change. Subsequent to
changing the shape of the artery, the device is retrieved from the
artery, for example, in accordance with the techniques described
above.
[0194] For some applications, the intra-arterial devices described
herein (such as devices 60, 70, 80, 90, 120, 130, 140, 150, 170,
174, 176, 190, and/or 200) are configured to expand both radially
and longitudinally upon implantation of the device inside the
subject's artery.
[0195] For some applications, the intra-arterial devices described
herein (such as devices 60, 70, 80, 90, 120, 130, 140, 150, 170,
174, 176, 190, and/or 200) are configured such that, upon
implantation of the device inside artery 20, the shape of the
device remains substantially the same for the duration of a cardiac
cycle of the subject. Alternatively, the device is configured to
flex in response to the subject's cardiac cycle. For some
applications the device flexes passively, in response to blood
pressure changes in the artery. Alternatively or additionally, the
device is actively flexed. For example, the device may include a
piezoelectric element, and an inductive charged coil (inside or
outside of the subject's body), drives the piezoelectric element to
flex.
[0196] For some applications, baroreceptors of the subject are
activated by driving an electrical current toward the baroreceptors
via an intra-arterial device described herein (such as device 60,
70, 80, 90, 120, 130, 140, 150, 170, 174, 176, 190, and/or 200).
Thus, the baroreceptors are stimulated both by mechanical shape
changes to the artery as a result of the device being placed inside
the artery, and via the electrical stimulation of the
baroreceptors. For some applications, baroreceptors at least
partially adapt to the shape change of the artery due to the
placement of intra-arterial device inside the artery, and the
baroreceptors fire with a lower firing rate at a given blood
pressure, relative to when the device was first implanted. For some
applications, in response to the lowered firing rate of the
baroreceptors, due to the adaptation of the baroreceptors to the
implanted device, electrical stimulation of the baroreceptors is
increased.
[0197] Reference is now made to FIG. 20, which is a schematic
illustration of intra-arterial device 120, the device including a
mesh 160 between artery contact regions 122 of the device, in
accordance with some applications of the present invention. For
some applications, any one of the intra-arterial devices described
herein (such as devices 60, 70, 80, 90, 120, 130, 140, 150, 170,
174, 176, 190, and/or 200) is shaped to define struts, or other
artery contact regions, that are configured to change a shape of
the arterial wall, by exerting a force on the arterial wall. The
device additionally includes a mesh in between the regions that are
configured to change the shape of the arterial wall. The mesh is
configured not to change the mechanical behavior of the artery
(e.g., by changing the shape of the arterial wall), but is
configured to prevent strokes caused by embolization of arterial
plaque, by stabilizing the arterial plaque, in a generally similar
manner to a regular stent. In general, for some applications, the
intra-arterial devices described herein are used to treat
hypertension, and are additionally used to treat arterial disease.
For some applications, the intra-arterial devices described herein
are placed in a subject's carotid artery subsequent to, or during,
a carotid endarterectomy procedure.
[0198] Reference is made to FIG. 21, which is a graph showing the
derivative of strain versus pressure as a function of rotational
position around the artery, in accordance with respective models of
an artery, in accordance with some applications of the present
invention. The graph shows the derivative of strain versus pressure
as a function of rotational position around a quadrant of an
artery, for the following four models of the artery:
[0199] 1) A circular elastic artery having no device placed
therein, at 150 mmHg.
[0200] 2) An artery having device 120 placed therein, the device
causing the artery to assume a rectangular shape. The artery is
modeled at a pressure of 150 mmHg. One of the contact points of the
device with the artery wall is between 40 and 80 arbitrary units
along the x-axis.
[0201] 3) A rectangular artery without a device placed therein, at
80 mmHg. One of the corners of the rectangle is at 40 and 80
arbitrary units along the x-axis. This model of the artery was
generated in order to separate the effect of changing the shape of
the artery to a rectangular shape from the effect of having a
device (such as device 120) placed inside the artery.
[0202] 4) The rectangular artery without a device placed therein,
at 150 mmHg.
[0203] The shapes of the curves indicate the following:
[0204] 1) As expected, the derivative of the strain with respect to
pressure of the circular, elastic artery is constant due to the
elasticity of the artery.
[0205] 2) At the contact point of the intra-arterial device with
the artery, the strain-pressure derivative is reduced relative to
the rounded artery. At the non-contact regions of the artery, the
strain-pressure derivative is also reduced relative to the rounded
artery. However, at the non-contact regions, the pressure-strain
derivative is still approximately half that of the rounded artery.
This indicates that at the non-contact regions, the pulsatility of
the artery is reduced, relative to a rounded artery, but that the
artery is still substantially pulsatile. Therefore, for some
applications, devices are inserted into an artery which re-shape
the arterial wall, such that at any longitudinal point along the
artery there are non-contact regions at which regions there is no
contact between the device and the arterial wall, such that the
artery is able to pulsate.
[0206] 3) Based on the two rectangular models of the artery (at 80
mmHg and 150 mmHg), it may be observed that at the straightened
regions of the artery (i.e., not at the corner of the rectangle),
the strain-pressure derivative of the artery increases at
low-pressures (e.g., 80 mmHg), relative to a rounded, elastic
artery. At higher pressures (e.g., 150 mmHg), the strain-pressure
derivative of the straightened regions of the artery is roughly
equal to that of the rounded, elastic artery. This indicates that
straightening the wall of the artery, by causing the artery to
assume a rectangular or an elliptical shape, may increase the
pulsatility of the artery. Therefore, for some applications,
devices are inserted into the artery that straighten regions of the
arterial wall.
[0207] Reference is now made to FIGS. 22A-C, which are schematic
illustrations of a delivery device 160 for placing an
intra-arterial device in the vicinity of a subject's carotid
bifurcation, in accordance with some applications of the present
invention. For some applications, the intra-arterial devices
described herein (such as devices 60, 70, 80, 90, 120, 130, 140,
150, 170, 174, 176, 190, and/or 200) are implanted in the vicinity
of a subject's carotid bifurcation, via a delivery device, e.g.,
delivery device 160. During the implantation of the device, the
proximal end of the device is released from the delivery device
such that the proximal end of the device is positioned at the start
of the bifurcation. Subsequent to the proximal end of the device
having been positioned, the distal end of the intravascular device
is released from the delivery device. For some applications, prior
to releasing the distal end of the device, the effect of the device
on baroreceptor firing and/or blood pressure is measured, and the
position of the device is adjusted, in response thereto.
[0208] For some applications, delivery device 160 is used to
facilitate the above-described implantation procedure. (FIGS. 22A-C
show device 120 being implanted inside the artery, by way of
illustration and not limitation.) Delivery device 160 includes a
retractable sheath 162 at a distal end thereof. During the
insertion of the intra-arterial device, the retractable sheath
covers the intra-arterial device, as shown in FIG. 22A. The
retractable sheath is configured such that, by pulling the sheath
proximally, the proximal end of the intra-arterial device is
released. Typically, the intra-arterial device is self-expandable.
Thus, by releasing the proximal end of the device, the proximal end
expands and becomes coupled to the surrounding arterial walls.
During the implantation of the device, the proximal end of the
device is released from the delivery device, by retracting the
retractable sheath, such that the proximal end of the device is
positioned at the start of the bifurcation, as shown in FIG. 22B.
Subsequent to the proximal end of the device having been
positioned, the distal end of the intravascular device is released
from the delivery device, by further retracting retractable sheath
162, as shown in FIG. 22C. For some applications, prior to
releasing the distal end of the device, the effect of the device on
baroreceptor firing is measured, and the position of the device is
adjusted, in response thereto.
[0209] Although delivery device 160 has been described as being
used to facilitate delivery of an intra-arterial device as
described herein, the scope of the present invention includes using
delivery device 160 to facilitate the delivery of any
intra-arterial device, in a manner that facilitates the release of
the proximal end of the intra-arterial device, before the distal
end of the intra-arterial device is released. For example, delivery
device 160 could be used with a prosthetic valve and/or a stent,
such as a bifurcation stent.
[0210] Reference is now made to FIGS. 23A-B, which are schematic
illustrations of respective views of a stent-based intra-arterial
device 170, in accordance with some applications of the present
invention. The views shown in FIGS. 23A and 23B are rotated through
90 degrees about the longitudinal axis of the device, with respect
to one another. Device 170 is generally similar to a stent. For
example, device 170 is typically cut from nitinol cobalt chrome,
and/or stainless steel, such that the device is shaped to define
crimpable cells that are defined by struts. However, device 170
typically defines at least one (e.g., two, as shown, or more)
non-contact regions 172, at which the device, when placed inside an
artery, does not contact the arterial wall.
[0211] Typically, each non-contact region 172 defines a contiguous
region in which no struts are disposed. Length L of the device is
typically greater than 10 mm (e.g., greater than 40 mm), and/or
less than 80 mm (e.g., less than 40 mm). At least one of the
non-contact regions has a maximum length l, which is typically
greater than 5 mm and/or less than 20 mm. Each of the non-contact
regions has a maximum width that defines an arc A that defines an
angle of more than 30 degrees, e.g., more than 60 degrees. At
locations along the length of the device at which a non-contact
region is defined, over a continuous portion of the device having a
length that is at least 5 mm, a maximum inter-strut distance d4
defined by any set of two adjacent struts is typically at least 1.5
times (e.g., three times) a maximum inter-strut distance d3 defined
by any set of two adjacent struts at locations within 3 mm of the
longitudinal ends of the device. Thus, by way of illustration and
not limitation, if a maximum inter-strut distance defined by any
set of two adjacent struts at locations within 3 mm of the
longitudinal ends of the device is 3 mm, then, at locations along
the length of the device at which a non-contact region is defined,
over a continuous portion of the device having a length that is at
least 5 mm, a maximum inter-strut distance defined by any set of
two adjacent struts is typically at least 4.5 mm.
[0212] Although non-contact region 172 is shown having a diamond
shape, for some applications, non-contact regions of the devices
described herein have different shapes, e.g., a square shape, or a
rectangular shape. Typically, non-contact region 172 has a
non-circular shape. Although non-contact region 172 is shown as
being disposed mid-way along the length of device 170, for some
applications, non-contact regions of the devices described herein
are disposed such that a center of the non-contact region is closer
to a proximal end of the device than to a distal end of the device,
or vice versa.
[0213] FIGS. 23A-B show device 170 during the shaping of the
device, the device typically being placed on a shaping mandrel 172,
during the shaping process. For some applications, device 170 is
shaped such that at the second end of the device, the device has a
span S2 that is greater than span S1 of the device at the first end
of the device. Typically, the ratio of S2 to S1 is greater than
1:1, e.g., greater than 1.1:1, and/or less than 2:1, e.g., between
1.1:1 and 2:1 (e.g., between 1.1:1 and 1.4:1).
[0214] Due to the ratio of S2 to S1, upon placement of device 170
inside the artery, the shape of the artery typically becomes
increasingly non-circular (e.g., elliptical or rectangular), along
the length of the artery, from the first end of the device (having
span S1) to the second end of the device (having span S2).
Furthermore, due to the ratio of S2 to S1, upon placement of device
170 inside the artery, the cross-sectional area of the artery
typically increases along the length of the artery, from the first
end of the device (having span S1) to the second end of the device
(having span S2). Typically, the device is placed such that the
second end of the device (which has the greater span) is disposed
in the common carotid artery and/or within the internal carotid
artery in the vicinity of the carotid bifurcation, and the first
end of the device (which has the smaller span) is disposed within
the internal carotid artery, downstream of the bifurcation. In this
configuration, the device thus stretches the internal carotid
artery in the vicinity of the bifurcation, due to the span of the
device at the second end of the device, but does not substantially
stretch the internal carotid artery downstream of the
bifurcation.
[0215] Typically, device 170 is shaped such that the device can be
viewed as defining three zones along the length of the device. The
second end may be viewed as the maximum-span zone, which is
configured to be placed in the vicinity of the carotid bifurcation
(or downstream of the carotid bifurcation, as described
hereinabove) and to stretch the internal carotid artery in the
vicinity of the bifurcation. The first end may be viewed as the
minimum-span zone, which is configured to be placed at a location
within the internal carotid artery downstream of the bifurcation
and to reduce strain on the internal carotid artery at the
downstream location relative to if the minimum-span zone had a
greater span. The portion of the device between the first and
second zones may be viewed as the pulsation zone, at which the
device exerts strain on the artery, while facilitating pulsation of
the artery by defining non-contact regions at which the device does
not contact the artery.
[0216] Reference is now made to FIGS. 24A-B, which are schematic
illustrations of respective views of stent-based intra-arterial
device 170, in accordance with some applications of the present
invention. The views shown in FIGS. 24A and 24B are rotated through
90 degrees about the longitudinal axis of the device, with respect
to one another. Device 170, as shown in FIGS. 24A-B is generally
similar to device 170 as shown in FIGS. 23A-B. For example, device
170 typically defines at least two non-contact regions 172, at
which the device, when placed inside an artery, does not contact
the arterial wall, which are as described hereinabove. However,
whereas device 170 as shown in FIGS. 23A-B is shaped such that span
S2, at the second end of the device, is greater than span S1, at
the first end of the device, device 170 as shown in FIGS. 24A-B is
shaped such that spans S1 and S2 are approximately equal.
[0217] Reference is now made to FIGS. 25A-B, which are schematic
illustrations of respective views of stent-based intra-arterial
device 174, in accordance with some applications of the present
invention. The views shown in FIGS. 25A and 25B are rotated through
90 degrees about the longitudinal axis of the device, with respect
to one another. Device 174, shown in FIGS. 25A-B is generally
similar to device 170, shown in FIGS. 23A-B. For example, device
174 typically defines at least two non-contact regions 172, at
which the device, when placed inside an artery, does not contact
the arterial wall, which are as described hereinabove. However, the
cells of device 174 are typically larger than those of device 170.
For some applications, due to larger cells of device 174 relative
to those of device 170, device 174 has a smaller area of metal in
contact with the intra-arterial wall when device 174 is placed in
the artery than does device 170, when device 170 is placed inside
the artery.
[0218] An experiment was conducted by the inventors of the present
application in which a spring constant of a device having generally
similar characteristics to device 174 was measured. As described
hereinabove with reference to FIGS. 15A-B, for the purposes of the
experiment, the spring constant of the device was measured by
measuring the change in force applied by the device to the artery
versus the change in the diameter of the device during cycles of
crimping and expansion of the device. The spring constant of the
device was determined based upon measurements that were performed
using M250-3 CT Materials Testing Machine manufactured by The
Testometric Company Ltd. (Lancashire, UK). The device had a spring
constant of 1.5 N/mm. In accordance with the aforementioned
experimental result, in accordance with some applications of the
invention, a device is inserted into a subject's artery in
accordance with the techniques described herein, the device having
a spring constant of less than 3 N/mm, e.g., less than 2 N/mm, or
less than 1.8 N/mm.
[0219] Reference is now made to FIGS. 26A-B, which are schematic
illustrations of respective views of stent-based intra-arterial
device 176, in accordance with some applications of the present
invention. The views shown in FIGS. 26A and 26B are rotated through
90 degrees about the longitudinal axis of the device, with respect
to one another. Device 176 typically defines end portions 177, at
which struts are typically disposed evenly around the circumference
of the device. Device 176 further defines a central portion 178,
which defines one or more (e.g., four, as shown) non-contact
regions 172. Non-contact regions 172 are typically generally as
described hereinabove. The central portion of the device also
defines three or more (e.g., four as shown) struts 179, the struts
typically being parallel to each other.
[0220] As described with reference to device 170, shown in FIGS.
23A-B, the length of device 176 is typically greater than 10 mm
(e.g., greater than 40 mm), and/or less than 80 mm (e.g., less than
40 mm). At least one of the non-contact regions has a maximum
length, which is typically greater than 5 mm and/or less than 20
mm. Each of the non-contact regions has a maximum width that
defines an arc A (FIG. 26B) that defines an angle of more than 30
degrees, e.g., more than 60 degrees. At locations along the length
of the device at which a non-contact region is defined, over a
continuous portion of the device having a length that is at least 5
mm, a maximum inter-strut distance d4 (FIG. 26A) defined by any set
of two adjacent struts is typically at least 1.5 times (e.g., three
times) a maximum inter-strut distance d3 defined by any set of two
adjacent struts at locations within 3 mm of the longitudinal ends
of the device. Thus, by way of illustration and not limitation, if
a maximum inter-strut distance defined by any set of two adjacent
struts at locations within 3 mm of the longitudinal ends of the
device is 3 mm, then, at locations along the length of the device
at which a non-contact region is defined, over a continuous portion
of the device having a length that is at least 5 mm, a maximum
inter-strut distance defined by any set of two adjacent struts is
typically at least 4.5 mm.
[0221] Reference is now made to FIGS. 27A-C, which are schematic
illustrations of a stent-based intra-arterial device 190, in
accordance with some applications of the present invention. FIG.
27A shows device 190 disposed inside a subject's internal carotid
artery 192. Device 190 is generally similar to a stent. For
example, device 190 is typically cut from nitinol, cobalt chrome,
and/or stainless steel such that the device is shaped to define
crimpable cells that are defined by struts. However, device 190
typically defines a non-contact region 191 at which the device does
not define any struts. Region 191 is generally similar to
non-contact region 172 described hereinabove, except for the
differences described hereinbelow.
[0222] As described hereinabove, typically, the intra-arterial
devices described herein are implanted in a vicinity of the carotid
bifurcation, so as to increase the radius of curvature of the
internal carotid artery in the vicinity of the bifurcation, thereby
causing increased baroreceptor firing. For some applications, the
devices described herein, when placed in the vicinity of the
bifurcation, are placed such that a proximal end of the device is
placed within internal carotid artery 192 immediately distal (i.e.,
downstream) to the carotid bifurcation, and such that the distal
end of the device is placed further downstream from the
bifurcation. The device is typically placed such that a non-contact
region of the device is placed over a region of the internal
carotid artery on a side 195 of the internal carotid artery that
defines the carotid bifurcation (i.e., the side of the internal
carotid artery that is closer to external carotid artery 194).
Thus, the device stretches the region of the internal carotid
artery, while facilitating pulsation of the region of the internal
carotid artery, in accordance with the techniques described
hereinabove.
[0223] For some applications, device 190 is placed in the subject's
common carotid artery such that a proximal end of the device is
placed proximal to (i.e., upstream of) the carotid bifurcation, and
such that the distal end of the device is placed within the
internal carotid artery downstream of the bifurcation. For such
applications, device 190 is typically placed in the common carotid
artery such that region 191 is disposed (a) adjacent to the
bifurcation of external carotid artery 194 from the common carotid
artery, and (b) adjacent to a region of the internal carotid artery
on the side of the internal carotid artery that defines the carotid
bifurcation (i.e., the side that is closer to the external carotid
artery). That is, the device is placed in the carotid artery such
that region 191 extends from a location within the common carotid
artery that is proximal to the carotid bifurcation until a location
within the internal carotid artery that is downstream of the
carotid bifurcation. Typically, a maximum length l3 of region 191
is greater than 15 mm and/or less than 45 mm. Further typically,
region 191 defines a maximum width thereof that defines an arc A2
that defines an angle of more than 30 degrees, e.g., more than 40
degrees.
[0224] Typically, the placement of region 191 adjacent to the
bifurcation of the external carotid artery from the common carotid
artery facilitates blood flow into the external carotid artery from
the common carotid artery, relative to if a portion of a device
that defined struts were placed adjacent to the bifurcation (e.g.,
if a regular stent were placed along the common carotid artery
adjacent to the bifurcation of the common carotid artery with the
external carotid artery). This is because, since device 190 does
not define any struts in region 191, struts of device 190 do not
interfere with blood flow through region 191. Furthermore, since
device 190 does not define any struts in region 191, there is no
build up of matter (e.g., fibrosis) at region 191.
[0225] Typically, the placement of region 191 adjacent to the
region of the internal carotid artery on the side of the internal
carotid artery that defines the carotid bifurcation (i.e., the side
of the internal carotid artery that is closer to the external
carotid artery), is such that the device stretches the region of
the internal carotid artery, while facilitating pulsation of the
region of the internal carotid artery, in accordance with the
techniques described hereinabove.
[0226] For some applications, device 190 is shaped to conform with
the shape of the common and internal carotid arteries. Thus, for
some applications, a first side of device 190 that is configured to
be placed in contact with side 195 of the internal carotid artery
is shorter than a second side of the device that is opposite the
first side. For some applications, all of the cells of the second
side of the device are closed, and at least some of the cells on
the first side are open cells, so as to facilitate shortening of
the cells of the first side of the device, upon placement of the
device inside the artery. Alternatively some of the cells of the
second side are also open, but more of the cells of the first side
are open than those of the second side. Typically, a maximum length
l2 of device 190 is greater than 20 mm, and/or less than 80 mm.
[0227] It is noted that the devices shown in FIGS. 23A-27C may be
defined as having (a) stent-like proximal and distal end portions,
and (b) a central portion in between the end portion that defines
one or more non-contact regions in which the device does not define
any struts, the non-contact region(s) being contiguous regions,
having dimensions as described hereinabove. For example, the end
portions may be stent-like in that, within the end portions, a
maximum distance between any strut and an adjacent strut thereto is
less than 5 mm. For some applications, using devices that have
stent-like end portions reduces thickening of the arterial wall
adjacent to the end portions relative to if devices were used
having end portions that define struts that are adjacent to one
another and that are at a distance from one another of more than 3
mm. Typically, the stent-based devices described herein are cut
from nitinol, and/or a different metal or alloy (such as cobalt
chrome, and/or stainless steel). Alternatively, one or more of the
stent-based devices described herein are made of braided mesh.
[0228] In general, the devices described herein are typically
configured such that the devices define (a) first and second end
portions at the proximal and distal end of the device, configured
to couple the device to the artery, and (b) a central portion,
between the first and second end portions, that defines one or more
non-contact regions, configured to increase the radius of a
curvature of a portion of the artery adjacent to the non-contact
regions while facilitating pulsation of the portion of the artery.
The non-contact regions are typically contiguous regions that
define no struts having dimensions as described hereinabove. At
locations along the length of the device at which a non-contact
region is defined, over a continuous portion of the device having a
length that is at least 5 mm, a maximum inter-strut distance
defined by any set of two adjacent struts is typically at least 1.5
times (e.g., three times) a maximum inter-strut distance d3 defined
by any set of two adjacent struts at locations within 3 mm of the
longitudinal ends of the device.
[0229] Further typically, the cross-section of the device within 3
mm of the longitudinal ends of the device defines a plurality of
dots, corresponding to the struts at the end portions. Similarly,
the cross-section of the device at any longitudinal location along
the length of the device at which a non-contact region is defined,
over a continuous portion of the device having a length that is at
least 5 mm, typically defines a plurality of dots, corresponding to
the struts at the longitudinal location, the number of dots defined
by the cross-section at the longitudinal location typically being
less than that of the cross-section of the device within 3 mm of
the longitudinal ends of the device. Typically, the minimum angle
defined by any set of three of adjacent dots of the cross-section
within 3 mm of the longitudinal ends of the device is greater than
150 degrees, and the minimum angle defined by any set of three of
adjacent dots of the cross-section at any longitudinal location
along the length of the device at which a non-contact region is
defined, over a continuous portion of the device having a length
that is at least 5 mm, is less than 150 degrees. For example, a
ratio of the minimum angle defined by the cross-section within 3 mm
of the longitudinal ends of the device to the minimum angle defined
by the cross-section at any longitudinal location along the length
of the device at which a non-contact region is defined, over a
continuous portion of the device having a length that is at least 5
mm, may be greater than 1.25 (e.g., 2).
[0230] Reference is now made to FIG. 27D, which is a schematic
illustration of a stent-based intra-arterial device 200 that
defines a C-shaped cross-section, the device defining a non-contact
region 202 that runs along the full length of the device, around a
given portion of the circumference of the device, in accordance
with some applications of the present invention. For some
applications, the non-contact region may define an arc about the
longitudinal axis of the device that is greater than 30 degrees
(e.g., greater than 60 degrees). For some applications, device 200
is placed in the subject's carotid artery (FIG. 27A) such that a
proximal end of the device is placed proximal to the carotid
bifurcation, and such that the distal end of the device is placed
within the internal carotid artery downstream of the carotid
bifurcation. For such applications, device 200 is typically placed
in the carotid artery such that region 202 is disposed (a) adjacent
to the bifurcation of the external carotid artery with the common
carotid artery, and (b) adjacent to a region of the internal
carotid artery on side 195 of the internal carotid artery that
defines the carotid bifurcation (i.e., the side that is closer to
the external carotid artery).
[0231] As described hereinabove with reference to device 190,
typically, the placement of region 202 adjacent to the bifurcation
facilitates blood flow into the external carotid artery from the
common carotid artery, relative to if a portion of a device that
defined struts were placed adjacent to the bifurcation (e.g., if a
regular stent were placed along the common carotid artery adjacent
to the bifurcation of the common carotid artery with the external
carotid artery). This is because, since device 200 does not define
any struts in region 202, struts of device 200 do not interfere
with blood flow through region 202. Furthermore, since device 200
does not define any struts in region 202, there is no build up of
matter (e.g., fibrosis) at region 202.
[0232] Typically, the placement of region 202 adjacent to the
region of the internal carotid artery on the side of the internal
carotid artery that defines the carotid bifurcation, is such that
the device stretches the region of the internal carotid artery,
while facilitating pulsation of the region of the internal carotid
artery, in accordance with the techniques described
hereinabove.
[0233] Reference is now made to FIGS. 28A-C, which are schematic
illustrations of cross-sectional views of device 170, in accordance
with some applications of the present invention. Typically, the
devices described herein are configured to increase the radius of
curvature of the internal carotid artery on side 195 of internal
carotid artery 192, i.e., the side defining the carotid
bifurcation. Therefore, devices described herein as defining
non-contact regions are typically placed in the carotid artery such
that at least one non-contact region (e.g., region 172 of device
170) is placed adjacent to side 195. (For some applications, the
devices described herein define one or more additional non-contact
regions, which are placed adjacent to other regions of the internal
carotid artery.) As described hereinabove, for example with
reference to FIGS. 15A-B, for some applications, placement of a
device inside the artery results in the artery having a
cross-sectional shape that is more rectangular and/or less circular
than in the absence of the device. For such applications, the
devices are typically placed in the internal carotid artery, such
that radius of curvature of side 195 of the internal carotid artery
is increased by more than that of the opposite side of the internal
carotid artery.
[0234] Some of the stent-like devices described herein (e.g.,
device 190, and device 200) define a single contiguous region that
defines no struts and that is configured to be placed adjacent to
side 195 of the internal carotid artery. Others of the stent-like
devices (such as device 170, and device 174) define two regions 172
that are disposed on opposite sides of the device from one another,
each of which is contiguous and defines no struts. For some
applications, one or more of devices 170, 174, and/or 190, shown in
FIGS. 23A-27C, and/or others of the devices described herein, are
configured such that, at least when the device is in a
non-constrained state, the device has a cross-sectional shape, such
as a rectangular, an elliptical, or a racetrack-shaped
cross-sectional shape, that defines a major axis (i.e., a longest
axis defined by the cross-sectional shape) and a minor axis (i.e.,
a shortest axis defined by the cross-sectional shape). The major
axis of the cross-section is parallel to the one or two regions of
the device that define no struts, and the minor axis of the
cross-section is disposed perpendicularly to the one or more
regions that define no struts. For example, FIG. 28A shows device
170 in a non-constrained state thereof. Device 170 defines a
racetrack-shaped cross-section, the major axis of the cross-section
being parallel to non-contact region 172, and the minor axis of the
cross-section being perpendicular to region 172. The major axis of
the cross-section has a length l4, and the minor axis has a length
l5. Typically the ratio of l4 to l5 is greater than 1.1:1.
[0235] For some applications, the devices are configured such that,
when the device is in a constrained state inside the internal
carotid artery, the device assumes a cross-section, such as a
square or circular cross-section, in which the major and minor axes
become approximately equal, as shown in FIG. 28B. For example, this
may be because the device is more compliant in the direction that
is parallel to the non-contact regions than in the direction that
is perpendicular to the non-contact regions. Therefore, the device
becomes more radially compressed in the direction that is parallel
to the non-contact regions than in the direction that is
perpendicular to the non-contact regions.
[0236] Alternatively, the devices are configured such that the
device maintains a cross-sectional shape that defines major and
minor axes, when the device is in the constrained state inside the
internal carotid artery, as shown in FIG. 28C. Thus, the radius of
curvature of side 195 of the internal carotid artery is increased
by more than the radius of curvature would be increased by a device
having a similar cross-section but that is circularly shaped. For
some applications, by maintaining the cross-sectional shape that
defines major and minor axes inside the artery, the device reduces
damage caused to the arterial wall due to discontinuities in the
curvature of the wall at edges of the non-contact regions. This is
because, the change in the radius of curvature of the artery at the
edges of the non-contact region(s) is typically more gradual for a
device having a cross-sectional shape that defines major and minor
axes (e.g., an elliptical shape or a racetrack-shape), as
described, than for that of a device shaped to define a
cross-section, such as a square or circular cross-section, in which
the major and minor axes are approximately equal.
[0237] For some applications, compression of the device in the
direction that is parallel to the non-contact regions is reduced by
forming thickened struts for the struts that are adjacent to the
non-contact regions. The thickened struts are configured to provide
resistance to the constraining force of the artery on the device
that causes the device to become compressed.
[0238] Reference is now made FIG. 29, which is a schematic
illustration of a further intra-arterial device 180, in accordance
with some applications of the present invention. For some
applications, intra-arterial device comprises ribs 182 that are
disposed on a spine 184, the ribs being configured to expand into
contact with the wall of artery 20. Typically, ribs 182 are
configured to apply a sufficient mechanical force to the wall of
the artery to change a shape of the wall. Further typically, the
ribs are placed in a vicinity of a baroreceptor (e.g., within the
internal carotid artery in the vicinity of the carotid
bifurcation), and are configured to change the shape of the wall in
the vicinity of the baroreceptor. Typically, device 180 is
configured to accommodate pulsation of regions of the walls between
the ribs. For some applications, the springiness of the ribs is
adjustable, such as by mechanical, electrical, or thermal means
(e.g., at least a portion of the rib may comprises nitinol). The
springiness may be mechanically adjusted by sliding a portion of
the ribs into a chamber such that such the portion is no longer
springy. For some applications, the ribs are configured as
electrodes, and an electrical signal is applied to the arterial
wall via the ribs. For some applications, device 180 is generally
similar to electrode device 20 as described with reference to FIG.
3 of WO 07/013065 to Gross, which is incorporated herein by
reference.
[0239] Although device 180 is shown in FIG. 29 as having two ribs
at each longitudinal location along the device at which the ribs
are disposed, for some application, device 180 has more than two,
e.g., more than 2, and/or less than 6 ribs at each longitudinal
location along the device at which the ribs are disposed.
[0240] Reference is now made to FIG. 30, which is a schematic
illustration of an extra-arterial device 210 configured to be
placed around the outside of an artery, in accordance with some
applications of the present invention. For some applications, the
intra-arterial devices described herein (such as devices 60, 70,
80, 90, 120, 130, 140, 150, 170, 174, 180, 190, and/or 200) are
implanted inside artery 20, and expand at least a portion of the
artery, by applying a force to the arterial wall that is directed
radially-outwardly. (FIG. 25 shows device 120 implanted inside the
artery, by way of illustration and not limitation.) For some
applications, extra-arterial device 210 is placed outside the
artery and acts to limit the extent to which the intra-arterial
device expands the artery. For example, extra-arterial device 210
may comprise sutures as shown, or a ring that is placed on the
outside of the artery.
Experimental Data
[0241] A number of experiments were conducted by the inventors in
accordance with the techniques described herein.
[0242] In one experiment, acute unilateral carotid stimulation was
applied to a first set of dogs, either the left or right carotid
sinus of the dogs of the first set being squeezed between two
smooth metal plates for a period of two to five minutes. Acute
bilateral carotid stimulation was applied to a second set of dogs,
both carotid sinuses of the dogs of the second set being squeezed
between two smooth metal plates for a period of 10 to 30 minutes.
The mean effect of the unilateral carotid sinus stimulation was to
decrease systolic blood pressure by 11 mmHg, and the mean effect of
the bilateral stimulation was to decrease systolic blood pressure
by 29 mmHg. The results of the bilateral stimulation had a p-value
of less than 0.001. These results indicate that using the devices
described herein for either unilateral or for bilateral carotid
sinus stimulation may be effective at reducing a subject's blood
pressure.
[0243] In another experiment, two dogs were chronically implanted
(for periods of more than two months) with plates that squeezed the
carotid sinus, in accordance with the techniques described herein.
The dogs had the plates implanted around both carotid sinuses. On a
first one of the dogs, the plates became dislodged from one of the
sinuses within two days of implantation. The plates remained
implanted around both carotid sinuses of the second dog, until the
plates were removed. The blood pressure of the dogs was measured,
via an implanted telemeter, for two to four weeks before the device
implantation. In the first dog, the dog's blood pressure was
measured after the implantation of the device for two weeks, and
was subsequently terminated, due to a malfunction in the
transmission of the telemeter. In the second dog, the dog's blood
pressure was measured for six weeks after the implantation of the
device.
[0244] For the dog that had the plates chronically implanted around
only one carotid sinus, the average diastolic blood pressure
measured in the dog over two weeks post-implantation was 6 mmHg
less than the average diastolic blood pressure measured in the dog
over two weeks pre-implantation. The average systolic blood
pressure measured in the dog over two weeks post-implantation was 8
mmHg less than the average systolic blood pressure measured in the
dog over two weeks pre-implantation.
[0245] For the dog that had the plates chronically implanted
bilaterally, the average diastolic blood pressure measured in the
dog over six weeks post-implantation was 10 mmHg less than the
average diastolic blood pressure measured in the dog over two weeks
pre-implantation. The average systolic blood pressure measured in
the dog over six weeks post-implantation was 18 mmHg less than the
average systolic blood pressure measured in the dog over two weeks
pre-implantation.
[0246] These results indicate that chronic implantation of the
devices described herein for either unilateral or for bilateral
carotid sinus stimulation may be effective at chronically reducing
a subject's blood pressure.
[0247] In addition to measuring the blood pressure of the dog that
had plates chronically implanted bilaterally around its carotid
sinuses, the inventors measured the baroreceptor sensitivity of the
dog, for several weeks, both pre-implantation and post-implantation
of the device using generally similar techniques to those described
in "The effect of baroreceptor activity on cardiovascular
regulation," by Davos (Hellenic J Cardiol 43: 145-155, 2002), which
is incorporated herein by reference. Pre-implantation of the
device, the mean baroreceptor sensitivity was 14.+-.5 sec/mmHg.
Post-implantation of the device, the mean baroreceptor sensitivity
was 20.+-.8 sec/mmHg. These results indicate that chronic
implantation of the devices described herein may be effective at
increasing baroreceptor sensitivity.
[0248] In a further experiment that was conducted in accordance
with the techniques described herein, five human patients had a
device placed around either the left or right carotid sinus,
subsequent to undergoing endarterectomy procedures. The device was
configured to flatten regions of the wall of the carotid sinus, in
accordance with techniques described herein. Of the five patients,
two were excluded from the study, since these patients were
administered atropine, which may have interfered with the results.
Of the three patients who were included in the study, the placement
of the device in all of the patients resulted in a decrease in both
the systolic and diastolic blood pressure of the patient. For the
three patients who were included in the study, the placement of the
device resulted in a mean decrease in diastolic blood pressure of 8
mmHg (standard deviation 5) and a mean decrease in systolic blood
pressure of 22 mmHg (standard deviation 14), relative to the blood
pressures before placement of the device. These results indicate
that using the devices described herein for carotid sinus
stimulation may be effective at reducing a human subject's blood
pressure.
[0249] Reference is now made to FIGS. 31A-B, which are graphs
showing the herring's nerve firing rate at respective blood
pressures recorded in dogs that had been implanted with medical
devices, in accordance with some applications of the present
invention. Reference is also made to FIGS. 32A-B, which are graphs
showing the herring's nerve integrated nerve activity at respective
blood pressures recorded in dogs that been implanted with medical
devices, in accordance with some applications of the present
invention
[0250] Four dogs were used in the experiments. In each of the dogs,
one femoral artery was accessed with a 6 Fr sheath for the purposes
of catheterization, and the contralateral femoral artery was
accessed with a 4 Fr sheath, via which invasive blood pressure
monitoring was performed. In three out of the four dogs, bilateral
vagotomy was performed before the carotid artery was exposed, by
complete cutting of the vagus nerve approximately 6 cm caudal to
the level of the neck dissection. Unilateral exploration of the
neck was directed to the hypogloseal nerve and lingual artery. The
hypogloseal nerve and lingual artery were cut such as to expose the
plane at which the herring's nerve crosses to join the
carnio-cervical ganglion. Following identification of herring's
nerve, the nerve was desheathed and divided to micro bundles under
a surgical microscope. The nerve bundle was isolated and placed on
an electrode.
[0251] The nerve biopotentials at respective blood pressures was
recorded (a) on the native, untreated carotid sinus (i.e., baseline
recordings), and (b) following implantation in the carotid sinus of
either a device that is similar to device 140 (FIGS. 17A-D), or a
control stent. Each event recording was initiated at a low blood
pressure (e.g., systolic blood pressure of approximately 60 mmHg).
The blood pressure was lowered via continuous intravenous infusion
of nitroglycerine 1.2 mcg/kg/min. During the event recording, the
blood pressure of the dog was gradually raised by continuous
intravenous infusion of phenylephrine 150 mcg/kg/min, the dosage of
which was gradually increased. When the event recording was
completed for the native carotid sinus, a device similar to device
140, or a control stent, was endovascularly implanted in the
carotid sinus. An event recording was performed subsequent to the
device implantation, the event recording being as described above.
In two of the dogs, subsequent to performing the event recording
after the implantation of the first device in the carotid sinus,
the other type of device was implanted within the contralateral
carotid sinus, and the event recording as described hereinabove was
then repeated. All of the dogs were euthanized at the end of the
procedures.
[0252] FIG. 31A shows (a) a line that plots the average firing rate
of the dogs' herring's nerves during the baseline recordings, in
addition to (b) two sets of raw nerve firing rate recordings that
were recorded subsequent to the implantation of a device that is
similar to device 140 into two of the dogs, and (c) two sets of raw
nerve firing rate recordings that were recorded subsequent to the
implantation of control stents into two of the dogs. Each of the
raw data points in FIG. 31A is based on data averaged over a 1
second running interval. FIG. 31B shows a linear fit of the region
of interest of the raw data for each of the experiments. The linear
fit assumes that overall shape of the curve is sigmoid, and that
the region of interest is in the sloped region of the sigmoid. The
flat portions at pressures above and below the region of interest
were assumed to be saturation regions, the effect of the implanted
devices being limited within these regions. In all cases, the
transition from the flat portion of the sigmoid to the linear slope
was assumed to be at approximately 100 mmHg. For the device
indicated as device 140-2 in FIGS. 31A-D, it was assumed that at
pressures above 140 mmHg, the effect of the device was saturated,
and the data corresponding to this region were not used in the
generation of the linear fit line for this device. For all other
event recordings, it was assumed that the upper saturation region
was not reached within the blood pressure range that was generated
during the experiment. It is noted that the size of the device
indicated as device 140-2 in FIGS. 31A-D was too small for the
carotid sinus in which the device was implanted. This may be the
reason why the response curve for this device appears to have an
upper saturation region from a pressure of approximately 140
mmHg.
[0253] It is noted that there was a discontinuity in the data
recorded during the event recording for the device indicted by
control stent-2 in FIGS. 31A-D. The experiment that was conducted
with control stent-2 was prolonged due to technical issues, which
caused increased bleeding of the animal. This gave rise to
electronic noise that was captured by the electrodes and which
caused a discontinuity in the data. The discontinuity was corrected
for in the data plotted in FIGS. 31A-D.
[0254] It is noted that experimental data for one of the dogs are
not shown. This is because one of the dogs did not undergo a
vagotomy. Therefore, the administration of nitroglycerine and
phenylephrine to the dog (which was performed in order to induce
changes in the dog's blood pressure, as described above) did not
substantially affect the dog's blood pressure. The experimental
results from this dog are not included in the data shown in FIGS.
31A-D.
[0255] In addition, in a second one of the four dogs, only the
control stent deployed correctly, and in a third one of the dogs,
only the device that was similar to device 140 was deployed due to
difficulties in locating the nerve innervating the carotid sinus on
the dog. Therefore, for the second dog, experimental results for
the device that was similar to device 140 are not included in the
data shown in FIGS. 31A-D, and, for the third dog, experimental
results for the control stent are not included in the data shown in
FIGS. 31A-D.
[0256] FIGS. 31C-D are generally similar to FIGS. 31A-B
respectively but show the integrated nerve activity recorded in the
dogs' herring's nerves during the events, rather than the nerve
firing rates.
[0257] As indicated in FIGS. 31A-D, the effect of the implantation
of both device 140 and the control stent in the dogs' carotid
sinuses resulted in a shift of the response curve of the herring's
nerve to lower pressures. This is because, at all blood pressures,
the implanted devices increase nerve activity by deforming the
carotid sinus, thereby increasing baroreceptor stimulation. The
shift in the response curve resulting from the implantation of
device 140 is greater than that resulting from the implantation of
the control stents. In addition, the shapes of the response curves
indicate that implantation of device 140 resulted in a steeper
nerve response curve than the response curve that resulted from the
implantation of the control stents. The shape of the response curve
resulting from the implantation of device 140 is similar in shape
to the shape of the baseline curve.
[0258] The results shown in FIGS. 31A-D indicate that the devices
described herein are effective at (a) shifting the baroreceptor
response curve of a subject toward lower blood pressures, without
(b) substantially impairing (and possibly improving) the
responsiveness of the baroreceptors to changes in blood pressure.
The inventors hypothesize that the implantation of the devices
described herein do not substantially impair, and may even improve,
the responsiveness of the baroreceptors to changes in blood
pressure, since the devices are shaped such as to maintain
pulsatility of the carotid artery, subsequent to implantation of
the devices inside the carotid artery. The inventors hypothesize
that by maintaining the natural arterial baroreceptor response
curve, the devices described herein may prevent long-term resetting
of the responsiveness of the baroreceptors subsequent to device
implantation. Alternatively, it is possible that in the experiments
described with reference to FIGS. 31A-D, the devices activated the
high pressure c-fibers which are not normally activated and do not
reset.
[0259] The scope of the present invention includes combining the
apparatus and methods described herein with those described in US
2008/0033501 to Gross, WO 10/035271 to Gross, US 2011/0213408 to
Gross, US 2011/0077729 to Gross, and/or US 2011/0178416 to Gross,
all of which applications are incorporated herein by reference.
[0260] It will be appreciated by persons skilled in the art that
the present invention is not limited to what has been particularly
shown and described hereinabove. Rather, the scope of the present
invention includes both combinations and subcombinations of the
various features described hereinabove, as well as variations and
modifications thereof that are not in the prior art, which would
occur to persons skilled in the art upon reading the foregoing
description.
* * * * *