U.S. patent application number 15/900116 was filed with the patent office on 2019-08-22 for catheter with tapered compliant balloon and tapered stent.
This patent application is currently assigned to Abbott Cardiovascular Systems Inc.. The applicant listed for this patent is Abbott Cardiovascular Systems Inc.. Invention is credited to Erik Eli, Senthil Eswaran, Stephen Craig Olson, JR..
Application Number | 20190254849 15/900116 |
Document ID | / |
Family ID | 67616543 |
Filed Date | 2019-08-22 |
United States Patent
Application |
20190254849 |
Kind Code |
A1 |
Olson, JR.; Stephen Craig ;
et al. |
August 22, 2019 |
CATHETER WITH TAPERED COMPLIANT BALLOON AND TAPERED STENT
Abstract
A balloon comprising: a center portion having a proximal end, a
distal end opposite the proximal end, and a length between the
proximal end and the distal end. The center portion comprises: a
first nominal diameter and a first radial modulus at the proximal
end; a second nominal diameter and a second radial modulus at the
distal end; further wherein, the first nominal diameter is equal to
the second nominal diameter, such that, when the balloon is
inflated to a nominal pressure, the center portion has a constant
diameter over the length; and further wherein, the first radial
modulus is smaller than the second radial modulus, such that, when
the balloon is inflated above a nominal pressure, the center
portion adopts a tapered shape in which the proximal end has a
first stretched diameter and the distal end has a second stretched
diameter, the first stretched diameter being larger than the second
stretched diameter.
Inventors: |
Olson, JR.; Stephen Craig;
(Temecula, CA) ; Eswaran; Senthil; (Sunnyvale,
CA) ; Eli; Erik; (Redwood City, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Abbott Cardiovascular Systems Inc. |
Sant Clara |
CA |
US |
|
|
Assignee: |
Abbott Cardiovascular Systems
Inc.
Santa Clara
CA
|
Family ID: |
67616543 |
Appl. No.: |
15/900116 |
Filed: |
February 20, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61M 25/1002 20130101;
A61F 2002/91533 20130101; A61F 2002/91575 20130101; A61F 2250/0039
20130101; A61F 2210/0076 20130101; A61M 2025/1059 20130101; A61F
2/915 20130101; A61F 2/89 20130101; A61M 2205/0216 20130101; A61M
2025/1088 20130101; A61F 2/958 20130101; A61M 2025/1084
20130101 |
International
Class: |
A61F 2/958 20060101
A61F002/958; A61M 25/10 20060101 A61M025/10; A61F 2/89 20060101
A61F002/89 |
Claims
1. A balloon for attachment to a distal portion of a medical
catheter, the balloon comprising: a center portion having a
proximal end, a distal end opposite the proximal end, and a length
between the proximal end and the distal end, wherein the center
portion further comprises: a first nominal diameter and a first
radial modulus at the proximal end; a second nominal diameter and a
second radial modulus at the distal end; wherein, the first nominal
diameter is equal to the second nominal diameter, such that, when
the balloon is inflated to a nominal pressure, the center portion
has a constant diameter over the length; and further wherein, the
first radial modulus is smaller than the second radial modulus,
such that, when the balloon is inflated above a nominal pressure,
the center portion adopts a tapered shape in which the proximal end
has a first stretched diameter and the distal end has a second
stretched diameter, the first stretched diameter being larger than
the second stretched diameter.
2. The balloon of claim 1, wherein the center portion comprises a
compliant polymer membrane which has a first thickness at the
proximal end and a second thickness at the distal end, wherein the
first thickness is less than the second thickness.
3. The balloon of claim 1, wherein the center portion comprises a
compliant polymer membrane and wherein a plurality of successive
threads are wrapped circumferentially around the center portion to
reinforce the center portion, the threads being spaced along the
center portion at a constant pitch and being adhesively attached to
the center portion; further wherein an initial successive thread is
located at the proximal end and has a first cross sectional area, a
final successive thread is located at the distal end and has a
second cross sectional area, and a medial successive thread is
located between the initial successive thread wherein the final
successive thread has a third cross sectional area, and further
wherein the first cross sectional area is smaller than the second
cross sectional area and the third cross sectional area is larger
than the first cross sectional area but smaller than the second
cross sectional area.
4. The balloon of claim 1, wherein the center portion comprises a
compliant polymer membrane and wherein an initial two consecutive
threads are located at the proximal end and have a first pitch
between them, a final two consecutive threads are located at the
distal end and have a second pitch between them, and a medial
consecutive two threads are located between the initial two
consecutive threads and the final two consecutive threads and have
a third pitch between them, wherein the first pitch is larger than
the second pitch and the third pitch is smaller than the first
pitch but smaller than the third pitch.
5. The balloon of claim 1, wherein the center portion comprises a
compliant polymer membrane and wherein a first thread is wound in a
helix along the center portion and a first two successive windings
are located at the proximal end and have a first pitch, a final two
successive windings are located at the distal end and have a second
pitch, and a medial two successive windings are located between the
first two successive windings and the final two successive windings
and have a third pitch, wherein the first pitch is larger than the
second pitch and the third pitch is smaller than the first pitch
but larger than the third pitch.
6. The balloon of claim 1, wherein the center portion comprises a
compliant polymer membrane and wherein an initial successive thread
is located at the proximal end and is formed from a material having
a first elastic modulus, a final successive thread is located at
the distal end and is formed from a material having a second
elastic modulus, and a medial successive thread is located between
the initial successive thread and final successive thread, and is
formed from a material having a third elastic modulus; wherein the
first elastic modulus is smaller than the second elastic modulus
and the third elastic modulus is larger than the first elastic
modulus but smaller than the second elastic modulus.
7. A stent for insertion into a vessel of a patient comprising: a
plurality of rings that are successively connected to each other by
a plurality of links, the plurality of rings extending in an axial
direction from a first ring at a proximal end followed by a
plurality of succeeding rings to a final ring at a distal end,
wherein, each succeeding ring is preceded by a preceding ring; each
of the plurality of rings includes a plurality of adjacent peaks
and valleys, wherein each valley is connected to an adjacent peak
by a strut to provide an undulating pattern within each ring; and
each of the plurality of rings has a compressed condition for
delivery into the patient and an expanded condition after
deployment in the patient, wherein, in the compressed condition
each preceding ring has a preceding ring length measured in the
axial direction and each succeeding ring has a succeeding ring
length measured in the axial direction, wherein a ratio of each
succeeding ring length divided by each preceding ring length is a
constant number that is smaller than unity.
8. The stent of claim 7, wherein the first ring has a first ring
length and is connected to a second ring by a first link having a
first link length, the first link length being equal to the first
ring length.
9. The stent of claim 7, wherein the ratio is in a range of 0.90 to
0.95.
10. A method of expanding a stent within a vasculature of a patient
comprising: disposing a stent upon a balloon that is deflated, the
balloon comprising a center portion having a proximal end, a distal
end opposite the proximal end, and a length between the proximal
end and the distal end; inserting the balloon inside the
vasculature of the patient; inflating the balloon to a nominal
pressure and, simultaneously, imparting a cylindrical shape to the
center portion of the balloon; and further inflating the balloon to
a pressure beyond nominal pressure and, simultaneously, imparting a
tapered shape to the center portion of the balloon.
11. The method of claim 10, wherein imparting a cylindrical shape
to the center portion of the balloon includes imparting a
cylindrical shape to the stent.
12. The method of claim 10, wherein imparting a tapered shape to
the center portion of the balloon includes imparting a tapered
shape to the stent.
Description
BACKGROUND
[0001] This application relates to balloon catheters for medical
purposes such as angioplasty and stent delivery, and to stents
suitable for delivery with such catheters.
[0002] Balloon catheters are well known in the art. Balloon
catheters have been developed for various purposes including
angioplasty, stent delivery, and many other applications in which
medical devices must be expanded within a body cavity of a patient.
The balloon is inserted inside the medical device on the tip of a
catheter, and when the device has been successfully introduced into
a body cavity via the vasculature of the patient, the balloon is
expanded by a fluid medium transmitted via a lumen in the catheter.
The expanding balloon expands the device by an amount that can be
adjusted by the operating physician through visualization means
such as fluoroscopy. FIG. 1 shows a known catheter system 10, which
is tipped by a balloon 16 at its distal end upon which a stent 12
is mounted for delivery. A sheath 18 may cover the stent/balloon
combination during delivery, and may be withdrawn prior to
deployment of the stent 12.
[0003] Balloons on catheters have been provided with various
properties. Some balloons have been configured to be compliant,
which is to say, elastic. Under such structure, the greater the
internal pressure, the greater the diameter of the expanded
balloon. Some balloons have been configured to be non-compliant,
which is to say inelastic. Such inelastic balloons have
substantially only one expanded diameter, so that the operating
physician can be assured that when the device is implanted, it will
assume only one final diameter under a range of pressures.
[0004] However, in some procedures, it is desired by a physician
for a balloon to assume a non-uniform diameter. Such a situation
may arise where a stent having a substantial length is to be
implanted in a vessel. While most vessels show no appreciable taper
over a short length such as over 20 mm-30 mm, it is common for a
vessel to taper appreciably over a substantial length, such as for
example from 40 mm-80 mm. Specifically, the coronary artery lumen
has unique character. It is well-known that the left anterior
descending (LAD) artery diameter is typically not constant, and
that it typically tapers narrower in its distal course. This is in
comparison with the right coronary artery (RCA) which is more
cylindrical over its course. It is estimated that the LAD loses 15%
of its diameter for every 30 mm in its length.
[0005] FIGS. 1A-1C show a catheter with a balloon/stent mounted at
a distal tip, in a body lumen 14 of a patient that tapers narrower
along its distal course. In cases where a physician wishes to
implant a stent having substantial length, the physician may be
confronted by one or both of two problems. First, the physician may
initially conclude that he/she is confronted with an artery that is
substantially tubular with a constant diameter over the length.
Therefore, he/she may select a balloon/stent capable of achieving a
substantially tubular shape over the length. However, as she
proceeds to deploy the stent, it may become apparent that the
artery does in fact possess a taper along its length. Where, as in
the case of a left anterior descending artery, the taper is 15% it
will be appreciated that the cone angle of taper is 8 degrees. It
is therefore quite possible that the surgeon discovers during
deployment that the artery is in fact substantially tapered.
[0006] The problem that then may arise is that, having chosen a
balloon/stent combination having a constant diameter, it may
transpire that it is sized correctly at the proximal end in an
expanded condition, but is too large at the distal end.
Alternatively, he/she may be left with a constant diameter
balloon/stent that is correctly sized at the distal end but is too
small at the proximal end. This latter condition is exemplified in
FIGS. 2 and 3. Thus, the physician, hoping to implant a
substantially long stent that is uniformly shaped along its length
and placed on a balloon having a uniform expanded shape along its
length, may be compelled to compromise, and size the final expanded
diameter to fit the vessel in the middle of the stent, and have a
proximal end that is too small and a distal end that is too large
for the vessel.
[0007] It is known how to impart an actual taper to a balloon.
Typically, such is accomplished by imparting an initially tapered
shape at the molding stage, and then upon inflation by expansion
medium, the balloon adopts a tapered shape at nominal pressure, and
continues to possess a tapered shape throughout the inflation
process. This type of balloon however does not give the physician a
choice of inflating the balloon to a uniform diameter at nominal
pressure in the event that a uniform vessel is encountered, and
then, in the event that it turns out that the vessel is tapered, to
continue to inflate the balloon beyond nominal pressure to increase
the diameter of the balloon only at the proximal end, while leaving
the diameter of the balloon substantially unchanged at the distal
end--thereby producing a suitable tapered balloon.
[0008] Thus there is a need in the art for a balloon that expands
to a constant diameter at nominal pressure, but which expands to a
tapered diameter in excess of nominal pressure. The present
invention addresses these and other needs.
[0009] A corollary need in the art is for a stent that is suitable
for use in conjunction with any of the balloons described
herein.
[0010] The present invention addresses these, and other needs.
SUMMARY OF THE INVENTION
[0011] In one embodiment, the invention is a balloon for attachment
to a distal portion of a medical catheter. The balloon comprises a
center portion having a proximal end, a distal end opposite the
proximal end, and a length between the proximal end and the distal
end. The center portion further comprises a first nominal diameter
and a first radial modulus at the proximal end; and a second
nominal diameter and a second radial modulus at the distal end. The
first nominal diameter is equal to the second nominal diameter,
such that, when the balloon is inflated to a nominal pressure, the
center portion has a constant diameter over the length.
Furthermore, the first radial modulus is smaller than the second
radial modulus, such that, when the balloon is inflated above a
nominal pressure, the center portion adopts a tapered shape in
which the proximal end has a first stretched diameter and the
distal end has a second stretched diameter, the first stretched
diameter being larger than the second stretched diameter.
[0012] In some embodiments, the center portion comprises a
compliant polymer membrane which has a first thickness at the
proximal end and a second thickness at the distal end, wherein the
first thickness is less than the second thickness.
[0013] In other embodiments, the center portion comprises a
compliant polymer membrane.
[0014] A plurality of successive threads are wrapped
circumferentially around the center portion to reinforce the center
portion, the threads being spaced along the center portion at a
constant pitch and being adhesively attached to the center portion.
Further, an initial successive thread is located at the proximal
end and has a first cross sectional area. A final successive thread
is located at the distal end and has a second cross sectional area.
A medial successive thread is located between the initial
successive thread wherein the final successive thread has a third
cross sectional area. Further, the first cross sectional area is
smaller than the second cross sectional area and the third cross
sectional area is larger than the first cross sectional area but
smaller than the second cross sectional area. In further
embodiments, the center portion comprises a compliant polymer
membrane. An initial two consecutive threads are located at the
proximal end and have a first pitch between them; a final two
consecutive threads are located at the distal end and have a second
pitch between them; and a medial consecutive two threads are
located between the initial two consecutive threads and the final
two consecutive threads and have a third pitch between them,
wherein the first pitch is larger than the second pitch and the
third pitch is smaller than the first pitch but smaller than the
third pitch. In yet further embodiments, the center portion
comprises a compliant polymer membrane. A first thread is wound in
a helix along the center portion and a first two successive
windings are located at the proximal end and have a first pitch. A
final two successive windings are located at the distal end and
have a second pitch, and a medial two successive windings are
located between the first two successive windings and the final two
successive windings and have a third pitch. The first pitch is
larger than the second pitch and the third pitch is smaller than
the first pitch but larger than the third pitch.
[0015] In yet a further embodiment, the center portion comprises a
compliant polymer membrane. An initial successive thread is located
at the proximal end and is formed from a material having a first
elastic modulus. A final successive thread is located at the distal
end and is formed from a material having a second elastic modulus.
A medial successive thread is located between the initial
successive thread and final successive thread, and is formed from a
material having a third elastic modulus. The first elastic modulus
is smaller than the second elastic modulus and the third elastic
modulus is larger than the first elastic modulus but smaller than
the second elastic modulus.
[0016] In another embodiment, the invention is a stent for
insertion into a vessel of a patient. The stent comprises a
plurality of rings that are successively connected to each other by
a plurality of links, the plurality of rings extending in an axial
direction from a first ring at a proximal end followed by a
plurality of succeeding rings to a final ring at a distal end. Each
succeeding ring is preceded by a preceding ring. Each of the
plurality of rings includes a plurality of adjacent peaks and
valleys, wherein each valley is connected to an adjacent peak by a
strut to provide an undulating pattern within each ring. Each of
the plurality of rings has a compressed condition for delivery into
the patient and an expanded condition after deployment in the
patient, wherein, in the compressed condition each preceding ring
has a preceding ring length measured in the axial direction and
each succeeding ring has a succeeding ring length measured in the
axial direction, wherein a ratio of each succeeding ring length
divided by each preceding ring length is a constant number that is
smaller than unity.
[0017] In some embodiments, the first ring has a first ring length
and is connected to a second ring by a first link having a first
link length, the first link length being equal to the first ring
length. In further embodiment, the ratio is in a range of 0.90 to
0.95.
[0018] In yet a further embodiment, the invention is a method of
expanding a stent within a vasculature of a patient. The method
comprises disposing a stent upon a balloon that is deflated, the
balloon comprising a center portion having a proximal end, a distal
end opposite the proximal end, and a length between the proximal
end and the distal end; inserting the balloon inside the
vasculature of the patient; inflating the balloon to a nominal
pressure and, simultaneously, imparting a cylindrical shape to the
center portion of the balloon; and further inflating the balloon to
a pressure beyond nominal pressure and, simultaneously, imparting a
tapered shape to the center portion of the balloon. In some
embodiments, imparting a cylindrical shape to the center portion of
the balloon includes imparting a cylindrical shape to the stent. In
further embodiments, imparting a tapered shape to the center
portion of the balloon includes imparting a tapered shape to the
stent.
[0019] These and other advantages of the invention will appear when
read in conjunction with the description of the drawings and
detailed description of some embodiments.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIG. 1A is a schematic view of a delivery catheter that is
known in the art, tipped by a balloon at a distal end, upon which
is mounted a stent.
[0021] FIG. 1B is a schematic view of a distal tip of the catheter
of FIG. 1A, in the process of expanding the balloon for deployment
in a vessel that tapers down in the distal direction.
[0022] FIG. 1C is a schematic view of a stent having a constant
diameter known in the art that has been deployed in a vessel of a
patient.
[0023] FIG. 2 is a schematic side elevational view of a first
embodiment of a balloon having features of the invention.
[0024] FIG. 3 is a sectional view of the embodiment of FIG. 2.
[0025] FIG. 4 is a schematic side elevational view of a second
embodiment of a balloon having features of the invention.
[0026] FIG. 5 is a sectional view of the embodiment of FIG. 4.
[0027] FIG. 6 is a schematic side elevational view of a third
embodiment of a balloon having features of the invention.
[0028] FIG. 7 is a sectional view of the embodiment of FIG. 6.
[0029] FIG. 8 is a schematic side elevational view of a fourth
embodiment of a balloon having features of the invention.
[0030] FIG. 9 is a sectional view of the embodiment of FIG. 8.
[0031] FIG. 10 is a schematic side elevational view of a fifth
embodiment of a balloon having features of the invention.
[0032] FIG. 11 is a sectional view of the embodiment of FIG.
10.
[0033] FIG. 12 is a "rollout" view of a stent, in unexpanded
condition, suitable for use with any embodiment of the balloons in
FIGS. 2-11.
[0034] FIG. 13 is a "rollout" view of the stent shown in FIG. 12,
in expanded condition.
DETAILED DESCRIPTION OF SOME EMBODIMENTS
[0035] Referring now to the drawings, wherein like reference
numbers are used herein to designate like elements throughout, the
various views and embodiments of a balloon configured for
delivering a tapered stent are illustrated and described, and other
possible embodiments are described. The figures are not necessarily
drawn to scale, and in some instances the drawings have been
exaggerated and/or simplified in places for illustrative purposes
only. One of ordinary skill in the art will appreciate the many
possible applications and variations based on the following
examples of possible embodiments.
[0036] FIGS. 2-3 exemplify a first embodiment of the invention.
FIG. 2 is a side sectional view of a balloon 50 configured for
being fixed to the distal tip of a known catheter such as shown in
FIG. 1A. The balloon 50 may be formed of a compliant membrane 51
formed of a suitable polymer material. A proximal section 52 of the
balloon is configured to have an outwardly extending conical shape
extending from the center towards the outer diameter of the balloon
in the distal direction, and a distal section 54 configured to have
an inwardly extending conical shape extending from the outer
diameter of the balloon towards the center of the balloon in the
distal direction. A central section 56, having a proximal end 60
and a distal end 62, joins the proximal section 52 to the distal
section 54. The thickness of the membrane 51 is structured to have
a thickness T1 at a first point where the proximal section 52 joins
the central section 56, and a thickness T2 at a second point where
the central section 56 joins the distal section 54. Importantly in
this embodiment, T1 is thinner than T2. The thickness between the
first point and the second point varies linearly between T1 and T2.
(The membrane may be given this linearly varying thickness during
the molding of the balloon by using an outer shaping mandrel with
cylindrical internal bore surface, and an inner shaping mandrel
with conical shaped exterior surface.) It will be understood that
this configuration gives the balloon a higher radial modulus at the
distal end, and a lower radial modulus at the proximal end. The
term "radial modulus" means herein the amount of force that is
needed to stretch the balloon membrane a certain amount in a radial
direction. Because the pressure inside the balloon is the same at
every point inside the balloon, the force applied inside the
balloon, per unit length of the balloon, is the same at every point
along the length of the balloon. Therefore, at a constant pressure
when the balloon membrane is being stretched, the portion of the
balloon having a higher radial modulus will stretch less than the
portion of the balloon having the lower radial modulus.
Accordingly, the higher radial modulus at the distant end of the
balloon will cause the balloon at the distal end to stretch,
radially, less than the balloon will stretch at the proximal end
where the radial modulus is lower relative to the distal end.
[0037] The native balloon in this embodiment is initially formed to
possess a constant uniform outer diameter over the central section
56 (as shown in FIG. 2) over its length at nominal pressure.
("Nominal pressure" is used herein to mean a pressure in the
balloon that is sufficient to expand the balloon to remove all
folds and wrinkles in the membrane 51 of the balloon, but not
sufficient to place the membrane of the balloon under a tensile
stress which is to say, it will not "stretch" the balloon membrane.
The term "nominal diameter" of a balloon is used herein to mean a
diameter that is achieved under nominal pressure.)
[0038] The result of this structural arrangement of the varying
thickness of the balloon 50 may be understood with reference to
FIGS. 2-3. Upon delivery of the balloon to the desired location
within the vascular anatomy, the deflated balloon may be inflated
to nominal pressure, which will cause the central section 56 of the
balloon to achieve its constant diameter cylindrical shape along
the length of the central section 56, as shown in FIG. 2, under
which pressure the balloon membrane merely unfolds but does not
begin to stretch. At this stage, the physician may assess, using
known visualization techniques such as fluoroscopy, whether a
satisfactory degree of apposition between the stent (not shown in
FIG. 2) mounted on the balloon 50 and the vessel wall has been
achieved in circumstances where the vessel may taper downward
substantially towards the distal end. If the visualization shows
that the taper of the vessel has left insufficient apposition at
the proximal end, the physician may elect to continue to inflate
the balloon to a higher pressure than nominal--under which
circumstances the balloon membrane will begin to stretch. The
result of such further inflation may be visualized by reference to
FIG. 3, which shows the balloon 50 expanded to a larger diameter on
the proximal end 60 than on the distal end 62, thereby imparting a
distinct taper to the balloon over its length.
[0039] By relying on the emergence of this taper after nominal
pressure has been reached and further inflation of the balloon is
applied, the physician may elect to continue to inflate the balloon
higher than nominal pressure, thereby improving the apposition of
the stent over its length because it has been given a tapered
profile to match the taper of the vessel.
[0040] FIGS. 4-5 exemplify a second embodiment of the invention.
FIG. 4 is a side elevational view, in partial cutaway section, of a
balloon 100 configured for being fixed to the distal tip of a known
catheter such as shown in FIG. 1. The balloon 100 may be formed of
a compliant or semi-compliant membrane 101 formed of a suitable
polymer material. A proximal section 102 of the balloon is
configured to have an outwardly extending conical shape extending
from the center towards the outer diameter of the balloon in the
distal direction, and a distal section 104 configured to have a
inwardly extending conical shape extending from the outer diameter
of the balloon towards the center of the balloon in the distal
direction. A central section 106, having a proximal end 111 and a
distal end 112, joins the proximal section 102 to the distal
section 104. The native balloon in this embodiment is initially
formed to possess a constant uniform diameter over the central
section 106 (as shown in FIG. 4) over its length at nominal
pressure, and also a constant thickness of the membrane 101.
[0041] Further shown schematically are circumferential threads 108
that run circumferentially around the outside of the balloon to
reinforce the balloon and add a controllable response to internal
balloon pressure as will be described herein. These threads may
either be annular in shape, and slipped over the balloon at a
constant pitch P1 when the balloon is nominally inflated, or it may
be wound around the balloon in a helical spiral having a constant
pitch, when the balloon is nominally inflated. In either case,
threads 108 may be attached to the surface of the balloon using a
liquid adhesive, in known manner. In some embodiments, axial
threads 110 may be applied and adhered to the outside of the
balloon to extend horizontally, in order to reinforce and limit the
expansion of the balloon along its longitudinal axis under
inflation.
[0042] In the embodiment being described in FIGS. 4-5, the
circumferential threads 108 may be selected to be compliant or semi
compliant. To accomplish this objective, the threads may be made
from a suitable polymer. In this embodiment, the circumferential
threads are configured to have a diameter that increases as the
threads move from the proximal end of the balloon (here, the left
end of the balloon) to the distal end of the balloon (here, the
right end). This effect may be envisaged by reference to FIGS. 4-5
where a schematic representation of gradually thickening threads
108 is shown. Where the threads are annuli affixed to the external
surface of the balloon, each annulus may be formed to possess a
slightly larger diameter than those adjacent, in an incrementally
increasing fashion. Where the threads 108 comprise a single thread
helically wound about the balloon, the diameter of the single
thread increases from the proximal end to the distal end giving
rise to the same effect, namely that the balloon is more rigidly
constrained against radial expansion at the distal end, and less
rigidly constrained against expansion at the proximal end. It will
be understood that this configuration gives the balloon a higher
radial modulus on average at the distal end, and a lower radial
modulus on average at the proximal end.
[0043] The result of this structural arrangement of the threads 108
around the balloon may be understood with reference to FIGS. 4-5.
Upon delivery of the balloon to the desired location within the
vascular anatomy, the deflated balloon may be inflated to nominal
pressure, which will cause the balloon to achieve its constant
diameter cylindrical shape along its length, as shown in FIG. 4. At
this stage, the physician may assess, using known visualization
techniques such as fluoroscopy, whether a satisfactory degree of
apposition between the stent (not shown in FIG. 4) and the vessel
wall has been achieved in circumstances where the vessel tapers
downward substantially towards the distal end. If the visualization
shows that the taper of the vessel has left insufficient apposition
at the proximal end, the physician may elect to continue to inflate
the balloon to a higher pressure. The result of such further
inflation may be visualized by reference to FIG. 5, which shows the
balloon 100 expanded to a larger diameter on the proximal end 102
than on the distal end 104, thereby imparting a distinct taper to
the balloon over its length. By relying on the emergence of this
taper after nominal pressure has been reached and further inflation
of the balloon is applied, the physician may elect to continue to
inflate the balloon higher than nominal pressure, thereby improving
the apposition of the stent over its length.
[0044] FIGS. 6-7 exemplify yet another embodiment of the invention,
a balloon 200. The balloon 200 may be formed of a compliant
membrane 201. A proximal section 202 of the balloon is configured
to have an outwardly extending conical shape extending from the
center towards the outer diameter of the balloon in the distal
direction, and a distal section 204 configured to have an inwardly
extending conical shape extending from the outer diameter of the
balloon towards the center of the balloon in the distal direction.
A central section 206, having a proximal end 211 and a distal end
212, joins the proximal section 202 to the distal section 204.
[0045] The underlying balloon membrane 201 here is the same as the
membrane 101 in the previous embodiment. However, in this
embodiment, the threads 208 around the balloon membrane have a
constant diameter throughout the length of the balloon. Further,
the threads 208 are in the form of annuli that are slipped onto and
adhered to the external surface of the membrane at nominal
pressure. In this embodiment, however, the pitch of the annuli does
not remain constant. Rather, the pitch of the annuli start at a set
pitch P2 on the proximal end of the balloon, the pitch gradually
decreasing to a smaller pitch P4 at the distal end of the balloon
via an intermediate size pitch P3 in the middle. This gives rise to
the effect that the balloon is more rigidly constrained against
radial expansion at the distal end, and less rigidly constrained
against expansion at the proximal end. In other words, this
configuration gives the balloon a higher radial modulus on average
at the distal end, and a lower radial modulus on average at the
proximal end. The advantage of this arrangement has been described
and explained above with respect to the embodiment in FIGS. 4-5,
and is no less advantageous.
[0046] FIGS. 8-9 exemplify yet another embodiment of the invention,
balloon 300. The balloon 300 may also be formed of a compliant
membrane 301. A proximal section 302 of the balloon is configured
to have an outwardly extending conical shape extending from the
center towards the outer diameter of the balloon in the distal
direction, and a distal section 304 configured to have an inwardly
extending conical shape extending from the outer diameter of the
balloon towards the center of the balloon in the distal direction.
A central section 306, having a proximal end 311 and a distal end
312, joins the proximal section 302 to the distal section 304.
[0047] The underlying balloon membrane 301 here is the same as the
membrane 101 above. However, in this embodiment, the threads 308
around the balloon membrane have a constant diameter throughout the
length of the balloon. Further, the threads 308 are in the form of
a single thread wound around the exterior of the membrane 301 at
nominal pressure. In this embodiment, however, the pitch of the
single wound threads 308 has a helical pitch that starts at a set
pitch P5 on the proximal end of the balloon, the pitch gradually
decreasing to a smaller pitch P7 at the distal end of the balloon
with an intermediate pitch P6 in the middle. It will be appreciated
that, as the pitch moves to a smaller amount, the angle of each
thread changes from a shallow angle A to a steep angle B. This
gives rise to the effect that the balloon is more rigidly
constrained against radial expansion at the distal end, and less
rigidly constrained against expansion at the proximal end. In other
words, this configuration gives the balloon a higher radial modulus
on average at the distal end, and a lower radial modulus on average
at the proximal end.
[0048] The advantage of this arrangement has been described and
explained above with respect to the embodiment in FIGS. 4-5, and is
no less advantageous.
[0049] FIGS. 10-11 exemplify yet another embodiment of the
invention, balloon 400. The underlying balloon membrane 401 here is
the same as the membrane 101 above. The balloon 400 may also be
formed of a compliant membrane 401. A proximal section 402 of the
balloon is configured to have an outwardly extending conical shape
extending from the center towards the outer diameter of the balloon
in the distal direction, and a distal section 404 configured to
have an inwardly extending conical shape extending from the outer
diameter of the balloon towards the center of the balloon in the
distal direction. A central section 406, having a proximal end 411
and a distal end 412, joins the proximal section 402 to the distal
section 404.
[0050] However, in this embodiment, the threads 408 around the
balloon membrane have been selected to possess a constantly
changing elastic modulus. In this embodiment, the pitch of the
annuli may remain constant at a pitch of P8. Under this embodiment,
the center portion 406 of the balloon is divided into sub zones,
for example proximal zone 406a, center zone 406b, and distal zone
406c. It will be appreciated that three zones are exemplary, and
that more than, or fewer than, three zones may be used. In the
proximal zone 406a, the threads 408 are selected for having a
highly compliant modulus of elasticity, and may be made from a
suitable polymer. In the center zone 406b, the threads are selected
for having a semi-compliant modulus of elasticity, and may be made
from a suitable polymer. In the distal zone 406c, the threads are
selected for having a non-compliant modulus of elasticity, and may
be made from a suitable polymer. It will be appreciated that, if
the designer wishes to achieve a smoother transition of
elasticities along the length of the balloon, then the threads may
be made a mixture of the identified materials, with a stronger
admixture of non-compliant material being added as the threads are
added towards the distal end. This structural arrangement gives
rise to the effect that the balloon 403 is more rigidly constrained
against radial expansion at the distal end, and less rigidly
constrained against expansion at the proximal end. In other words,
this configuration gives the balloon a higher radial modulus on
average at the distal end, and a lower radial modulus on average at
the proximal end.
[0051] The advantage of this arrangement has been described and
explained above with respect to the embodiment in FIGS. 4-5, and is
no less advantageous.
[0052] Thus, a number of balloon embodiments are described that
produce a balloon that adopts a constant cylindrical diameter at
nominal pressure, but that adopts a tapering form at pressures
above nominal.
[0053] Turning now to a stent configuration that is highly
appropriate for use in combination with the balloon embodiments
that have been described, the stent configuration is described with
reference to FIGS. 12 and 13.
[0054] FIG. 12 is a "rollout view" of a stent 500 having features
of an embodiment of the invention in a condition before it is
deployed (compressed or crimped condition) and FIG. 13 shows the
same stent in a rollout condition after it is deployed (expanded
condition). The form of the stent is one of a "ring and link"
structure, in which short cylindrical rings 502 are connected to
each other by links 504 extending parallel with the elongate axis
of the stent. Each ring 502 is formed by a series of peaks 508 and
valleys 510 that are connected to each other by arms 506 to provide
a ring that extends the circumference of a cylinder while adopting
an oscillating or wave-like shape. Peaks 508 on one ring are
connected to valleys 510 of an adjacent ring to make up the stent,
which has a great amount of flexibility in the longitudinal
direction.
[0055] Of significance in the present invention, however, is that
the axial length of each ring 502 in the compressed condition
decreases from the proximal end towards the distal end. This is
understood with reference to FIG. 12, where there is shown a stent
having "n" rings along its length. The first ring on the proximal
end has a length L1, the second ring has a length L2, and on . . .
to the nth ring at the distal end which has a length Ln. As shown
in FIG. 12, the length of L1 is longer than L2, which is longer
than L3, . . . all the way to Ln which has the shortest length. In
a preferred embodiment, the rate at which the rings shorten in
length is constant, by which it is meant that the ratio of the
length of any ring to the length of the preceding ring is a
constant number. Thus, for example, if there are "n" rings, the
length of the first ring is L1, and the ratio of L2/L1 is 0.95,
then the length of the "nth" ring Ln will be L1*(0.95%).sup.n-1
and, in a practical example, if n=10, then the "nth" ring will have
length L1*0.63, or stated otherwise, 63% of L1, with the length of
the intermediate rings being evenly distributed between L1 and
L1*0.63 in length.
[0056] The structure shown in FIG. 12 may be cut from a cylinder
having a constant diameter over its length and a constant
thickness, according to known means by laser energy. The number of
peaks and valleys are preferably the same in each ring 502, and the
number of links 504 are the same between each ring. The only aspect
that varies from ring to ring is the length of each ring.
Preferably, the length of each link may also vary, in order to
allow the spacing between the rings to remain constant.
[0057] The advantage provided by the structure described above is
that the stent 500 will, upon expansion by a balloon, be capable of
adopting a configuration such as is shown in FIG. 13, in which each
ring is expanded to a similar degree, yet the stent will have a
gradual taper from the proximal end narrowing to the distal end.
The term "similar degree" to describe expansion of a ring indicates
that when two rings are expanded to a "similar degree," then each
arm 506 of each ring will be angled at substantially the same angle
to the elongate axis of the stent. For example, the angles shown as
E, F, G in FIG. 13 are all substantially equal to each other, and
reflect the fact that the rings identified are expanded to a
similar degree to each other. This geometric consequence follows
necessarily from the fact that, according to the geometry of the
rings, the proximal rings have a longer length than the distal
rings. It will be appreciated by one of ordinary skill that a stent
in which all the rings are expanded to a "similar degree" will
possess expanded rings that possess similar radial strength to each
other. This is a desirable outcome, and has an advantage over a
stent with identical rings that is deformed into a tapered shape,
because in such a stent the rings will be expanded to different
degrees, and will possess different radial strength from each
other.
[0058] It will be appreciated that the stent described in reference
to FIGS. 12-13 will benefit from the balloon embodiments that have
been described. The balloon embodiments are capable of providing a
balloon that can be shaped with a relatively precise taper after
the balloon passes beyond nominal pressure. Further, the stent may
be cut so that it also will expand with a relatively precise taper,
while at the same time possessing a uniform and constant radial
strength along its length.
[0059] Thus, the balloons and stent of the present invention
provide an advantageous structure and method for improving the
apposition of stents within tapered vessels. The present invention
may, of course, be carried out in other specific ways than those
herein set forth without departing from the essential
characteristics of the invention. The present embodiments are,
therefore, to be considered in all respects as illustrative and not
restrictive, while the scope of the invention is set forth in the
claims that follow.
* * * * *