U.S. patent application number 09/774725 was filed with the patent office on 2001-07-19 for stent installation method using balloon catheter having stepped compliance curve.
Invention is credited to Wang, Lixiao.
Application Number | 20010008976 09/774725 |
Document ID | / |
Family ID | 23571933 |
Filed Date | 2001-07-19 |
United States Patent
Application |
20010008976 |
Kind Code |
A1 |
Wang, Lixiao |
July 19, 2001 |
Stent installation method using balloon catheter having stepped
compliance curve
Abstract
A method for installing a stent in a vessel utilizes a single
balloon catheter for both low pressure predilation at a relatively
small diameter to open the lesion sufficiently to allow insertion
and deployment of the stent across the lesion and for subsequent
high pressure embedding of the stent in the vessel wall. The same
balloon catheter may also be employed to insert and deploy the
stent. The balloons utilized in the method have a stepped
compliance curve which allows for predilation at a low pressure and
predetermined diameter and for high pressure embedding at a
substantially larger diameter. The balloons may be provided with a
configuration in which only a portion of the balloon has a stepped
compliance curve while a further portion has a generally linear
compliance profile. With such balloons high pressure treatment of
the vessel wall areas not reinforced by the stent can be avoided
despite the occurence of longitudinal shrinkage of the stent during
expansion thereof.
Inventors: |
Wang, Lixiao; (Maple Grove,
MN) |
Correspondence
Address: |
VIDAS, ARRETT & STEINKRAUS, P.A.
6109 BLUE CIRCLE DRIVE
SUITE 2000
MINNETONKA
MN
55343-9185
US
|
Family ID: |
23571933 |
Appl. No.: |
09/774725 |
Filed: |
January 31, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09774725 |
Jan 31, 2001 |
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09396841 |
Sep 15, 1999 |
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09396841 |
Sep 15, 1999 |
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08931190 |
Sep 16, 1997 |
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5980532 |
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08931190 |
Sep 16, 1997 |
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08397615 |
Mar 2, 1995 |
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5749851 |
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Current U.S.
Class: |
623/1.11 ;
604/103.11; 604/96.01; 606/108; 606/192; 606/194 |
Current CPC
Class: |
A61F 2250/0039 20130101;
A61M 25/1029 20130101; A61M 2025/1075 20130101; A61M 25/104
20130101; A61M 25/10 20130101; A61M 25/1002 20130101; A61M
2025/1059 20130101; A61F 2/958 20130101 |
Class at
Publication: |
623/1.11 ;
606/108; 606/194; 604/103.11; 604/96.01; 606/192 |
International
Class: |
A61F 002/06; A61M
029/00; A61F 011/00 |
Claims
We claim:
1. A balloon for a dilation procedure, the balloon having first and
second adjacent body longitudinal portions the first body portion
having a generally linear compliance curve to burst pressure and
the second body portion having a stepped compliance curve
characterized by a low pressure segment generally collinear with
the corresponding segment of the first body portion, a transition
segment during which the balloon expands rapidly relative to the
first body portion and a high pressure segment during which the
compliance curve of the second portion expands slowly relative to
the transition region.
2. A balloon as in claim 1 wherein the balloon has a burst pressure
of at least 16 atm.
3. A balloon as in claim 1 wherein when the balloon is inflated to
a pressure of 6 atm the second body portion is on the low pressure
segment of its compliance curve and when the balloon is inflated to
15 atm the second body portion is on the high pressure segment of
its compliance curve.
4. A balloon as in claim 3 wherein the diameter of the second body
portion at 6 atm is in the range of 2.35-2.65 mm and the diameter
of the second body portion at 15 atm is in the range of 2.75 to
4.75 mm.
5. A balloon as in claim 1 wherein the balloon further comprises a
third body portion adjacent the second body portion so that the
second body portion lies between the first and third body portions,
the third body portion having a compliance curve which is generally
linear to burst and generally collinear with the compliance curve
of the first body portion to burst.
6. A balloon as in claim 5 wherein the lengths of the first and
third body portions are substantially equal and the length of the
second body portion is approximately twice the length of the first
body portion.
7. A balloon as in claim 1 made of a thermoplastic polymer selected
from the group consisting of high strength polyesters, nylons,
thermoplastic polyimides and high strength engineering
thermoplastic polyurethanes.
8. A balloon as in claim 7 made of a polyester selected from
poly(ethylene terephthalate) and poly(ethylene
napthalenedicarboxylate).
9. A balloon as in claim 1 wherein the high pressure segment has a
compliance curve according to which the balloon expands at a rate
of no more than 0.1 mm/atm from 15 atm to burst.
10. A balloon as in claim 9 wherein according to said high pressure
compliance curve the balloon expands at a rate no more than is no
more than 0.06 mm/atm from 15 atm to burst.
11. A balloon as in claim 1 having a wall strength of at least
18,000 psi.
12. A balloon as in claim 11 wherein said wall strength is greater
than 20,000 psi.
13. A method for preparing a balloon as in claim 1 wherein the
balloon is blown in a mold having a configuration providing the
first and second body portions of the balloon with different
diameters, the second body portion diameter being greater than the
first body portion, and then shrinking the second body portion to a
diameter approximately equal to the diameter of the first body
portion by annealing the second body portion at a temperature and
pressure which will cause the balloon material to shrink.
14. A method as in claim 13 wherein the annealing of said second
body portion is accomplished by dipping the second body portion in
a heated fluid while the first body portion is kept out of said
fluid.
15. A method as in claim 13 wherein the mold configuration further
provides the balloon with a third body portion adjacent the second
body portion so that the second body portion is between said first
and said third body portions.
16. A method as in claim 15 wherein the annealing of said second
body portion is accomplished by dipping the second and third body
portions in a heated fluid while the first body portion is kept out
of said fluid, and then after the second body portion has shrunk to
the diameter of the first body portion, the third body portion is
heated and reblown to restore it to the diameter of the first and
second body portions.
17. A method for introducing a stent into a vessel at a lesion
site, the method comprising the steps of: first, introducing into
the vessel a catheter carrying a balloon on a distal end thereof so
that the balloon crosses the lesion and pre-dilating the lesion by
inflating the balloon to a predetermined first diameter, and then
withdrawing the catheter, second, introducing into the vessel a
catheter carrying a stent and on a distal end thereof so that the
stent crosses the lesion and then deploying the stent and further
dilating the lesion to a second diameter greater than said first
diameter; third, introducing into the vessel a catheter carrying a
low-compliance balloon on a distal end thereof so that the balloon
is positioned within the deployed stent and post-dilating with the
low-compliance balloon to a third diameter greater than or equal to
said second diameter at a pressure substantially higher than the
pressure of said further dilation, so that the stent is embedded in
the vessel wall at the lesion site, wherein: the catheter used in
said first and third steps are the same, at least a portion of the
balloon carried thereon has a compliance curve which has a stepped
profile characterized by a first generally linear low pressure
segment of the compliance curve and a second generally linear
higher pressure segment of the curve, the two regions being
non-collinear so that linear extensions of each segment into the
pressure range of the other would diverge by at least 0.25 mm, the
predetermined first diameter is on the first segment of the stepped
profile compliance curve and the third diameter is on the second
segment of the stepped profile compliance curve.
18. The method of claim 17 wherein said stepped compliance curve is
provided on only a portion of the balloon, the remainder of the
balloon having a generally linear compliance curve.
19. The method of claim 17 wherein the balloon portion having said
stepped compliance curve is a central portion located between two
side portions, each said side portion having a generally linear
compliance curve.
20. The method as set forth in claim 17 wherein the balloon having
said stepped compliance curve is made of a thermoplastic polymer
selected from the group consisting of high strength polyesters,
nylons, thermoplastic polyimides and high strength engineering
thermoplastic polyurethanes.
21. A method as set forth in claim 20 wherein the balloon having
said stepped compliance curve is made of a polyester selected from
poly(ethylene terephthalate) and poly(ethylene
napthalenedicarboxylate).
22. A method as in claim 17 wherein the high pressure segment of
said stepped compliance curve provides an expansion rate of no more
than 0.1 mm/atm from 15 atm to burst.
23. A method as in claim 22 wherein the high pressure segment of
said stepped compliance curve provides an expansion rate of no more
than 0.06 mm/atm from 15 atm to burst.
24. A method as set forth in claim 17 wherein the balloon having
said stepped compliance curve has a wall strength of at least
18,000 psi.
25. A method as in claim 24 wherein said wall strength is greater
than 20,000 psi.
26. A method as in claim 17 wherein said balloon is a single
tubular element mounted on said catheter.
27. A method as in claim 17 wherein said balloon comprises two
coextensive tubular elements of different nominal diameter mounted
coaxially on said catheter.
28. A method for introducing a stent into a vessel at a lesion
site, the method comprising the steps of: first, introducing into
the vessel a catheter carrying a balloon on a distal end thereof so
that the balloon crosses the lesion and pre-dilating the lesion by
inflating the balloon to a predetermined first diameter, and then
withdrawing the catheter, second, mounting a stent on said catheter
over said balloon and reintroducing the catheter into said vessel
and on a distal end thereof so that the stent crosses the lesion
and then deploying the stent and further dilating the lesion by
inflating said balloon to a second diameter greater than said first
diameter and pressurizing the balloon to a pressure sufficient to
embed the stent in the vessel wall at the lesion site, the method
further characterized in that at least a portion of said balloon
has a compliance curve which has a stepped profile characterized by
a first generally linear low pressure segment of the compliance
curve and a second generally linear higher pressure segment of the
curve, the two regions being non-collinear so that linear
extensions of each segment into the pressure range of the other
would diverge by at least 0.25 mm, the predetermined first diameter
is on the first segment of the stepped profile compliance curve and
the second diameter is on the second segment of the stepped profile
compliance curve.
29. The method of claim 28 wherein said stepped compliance curve is
provided on only a portion of the balloon, the remainder of the
balloon having a generally linear compliance curve.
30. The method of claim 28 wherein the balloon portion having said
stepped compliance curve is a central portion located between two
side portions, each said side portion having a generally linear
compliance curve.
31. The method as set forth in claim 28 wherein the balloon having
said stepped compliance curve is made of a thermoplastic polymer
selected from the group consisting of high strength polyesters,
nylons, thermoplastic polyimides and high strength engineering
thermoplastic polyurethanes.
32. A method as set forth in claim 31 wherein the balloon having
said stepped compliance curve is made of a polyester selected from
poly(ethylene terephthalate) and poly(ethylene
napthalenedicarboxylate).
33. A method as in claim 28 wherein the high pressure segment of
said stepped compliance curve provides an expansion rate of no more
than 0.1 mm/atm from 15 atm to burst.
34. A method as in claim 33 wherein the high pressure segment of
said stepped compliance curve provides an expansion rate of no more
than 0.06 mm/atm from 15 atm to burst.
35. A method as set forth in claim 28 wherein the balloon having
said stepped compliance curve has a wall strength of at least
18,000 psi.
36. A method as in claim 35 wherein said wall strength is greater
than 20,000 psi.
37. A method as in claim 28 wherein said balloon is a single
tubular element mounted on said catheter.
38. A method as in claim 28 wherein said balloon comprises two
coextensive tubular elements of different nominal diameter mounted
coaxially on said catheter.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates generally to a method of
installing a stent utilizing a balloon catheter to perform an
initial angioplasty and to seat the stent after it has been located
in the vessel. The invention also relates to novel balloon
structures which have particular use in the method of the
invention.
[0002] Angioplasty, an accepted and well known medical practice
involves inserting a balloon catheter into the blood vessel of a
patient, maneuvering and steering the catheter through the
patient's vessels to the site of the lesion with the balloon in an
uninflated form. The uninflated balloon portion of the catheter is
located within the blood vessel such that it crosses the lesion or
reduced area. Pressurized inflation fluid is metered to the
inflatable balloon through a lumen formed in the catheter to thus
dilate the restricted area. The inflation fluid is generally a
liquid and is applied at relatively high pressures, usually in the
area of six to twenty atmospheres. As the balloon is inflated it
expands and forces open the previously closed area of the blood
vessel. Balloons used in angioplasty procedures such as this are
generally fabricated by molding and have predetermined design
dimensions such as length, wall thickness and nominal diameter.
Balloon catheters are also used in other systems of the body for
example the prostate and the urethra. Balloon catheters come in a
large range of sizes and must be suitably dimensioned for their
intended use.
[0003] Recently the use of a catheter delivered stent to prevent an
opened lesion from reclosing or to reinforce a weakened vessel
segment, such as an aneurism, has become a common procedure. A
typical procedure for stent installation involves performing an
initial angioplasty to open the vessel to a predetermined diameter
sufficent to permit passage of a stent delivery catheter across the
lesion, removal of the angioplasty balloon catheter, insertion of a
delivery catheter carrying the stent and a stent deploying
mechanism, deploying the stent across the opened lesion so as to
seperate the stent from the catheter and bring it into contact with
the vessel wall, usually with dilation to a larger diameter using a
balloon larger than the balloon of the predilation catheter, and
then removing the delivery catheter (after deflating the balloon if
used). In many cases it has become the practice to then "retouch"
the dilation by deploying a third catheter carrying a balloon
capable of dilating at a substantially higher pressure to drive the
stent into the vessel wall, thereby to assure that there is no risk
of the stent later shifting its position and to reduce occurance of
restenosis or thrombus formation. This third "retouch" dilation is
often considered necessary when the balloon used to seat the stent
is made of a compliant material because such balloons generally
cannot be safely pressurized above 9-12 atm., and higher pressures
are generally considered necessary to assure full uniform lesion
dilation and seating of the stent.
[0004] A wide variety of stent configurations and deployment
methods are known. For instance, stent configurations include
various forms of bent wire devices, self-expanding stents; stents
which unroll from a wrapped configuration on the catheter; and
stents which are made of a deformable material so that the device
may be deformed on deployment from a small diameter to a larger
diameter configuration. References disclosing stent devices and
deployment catheters include:
1 US 4733665 Palmaz US 4681110 Wiktor US 4776337 Palmaz US 4800882
Gianturco US 5195984 Schatz US 4830003 Wolff et al US 5234457
Andersen US 4856516 Hillstead US 5116360 Pinchuck et al US 4922905
Strecker US 5116318 Hillstead US 4886062 Wiktor US 4649922 Wiktor
US 4907336 Gianturco US 4655771 Wallsten US 4913141 Hillstead US
5089006 Stiles US 5092877 Pinchuk US 5007926 Derbyshire US 5123917
Lee US 4705517 DiPisa, Jr. US 5116309 Coll US 4740207 Kreamer US
5122154 Rhodes US 4877030 Beck et al US 5133732 Wiktor US 5108417
Sawyer US 5135536 Hillstead US 4923464 DiPisa, Jr. US 5282824
Gianturco US 5078726 Kreamer US 5292331 Boneau US 5171262 MacGregor
US 5035706 Gianturco et al US 5059211 Stack et al US 5041126
Gianturco US 5104399 Lazarus US 5061275 Wallsten et al US 5104404
Wolff US 5064435 Porter US 5019090 Pinchuk US 5092841 Spears US
4954126 Wallsten US 5108416 Ryan et al US 4994071 MacGregor US
4990151 Wallsten US 4580568 Gianturco US 4990155 Wilkoff US 4969890
Sugita et al US 5147385 Beck et al US 4795458 Regan US 5163952
Froix US 4760849 Kropf US 5192297 Hull
[0005] In U.S. Pat. No. 5,348,538, incorporated herein by
reference, there is described a single layer balloon which follows
a stepped compliance curve. The stepped compliance curves of these
balloons has a lower pressure segment following a first generally
linear profile, a transition region, typically in the 8-14 atm
range, during which the balloon rapidly expands yielding
inelastically, and a higher pressure region in which the balloon
expands along a generally linear, low compliance curve. The stepped
compliance curve allows a physician to dilate different sized
lesions without using multiple balloon catheters.
[0006] Stepped compliance curve catheter balloon devices using two
different coextensively mounted balloon portions of different
initial inflated diameter, are also described in co-pending U.S.
application Ser. No. 08/243,473, filed May 16, 1994 as a
continuation of now abandoned U.S. application Ser. No. 07/927,062,
filed Aug. 8, 1992, and in U.S. Pat. No. 5,358,487 to Miller. These
dual layer balloons are designed with the outer balloon portion
larger than the inner portion so that the compliance curve follows
the inner balloon portion until it reaches burst diameter and then,
after the inner balloon bursts, the outer balloon becomes inflated
and can be expanded to a larger diameter than the burst diameter of
the inner balloon.
[0007] A polyethylene ionomer balloon with a stepped compliance
curve is disclosed in EP 540 858. The reference suggests that the
balloon can be used on stent delivery catheters. The disclosed
balloon material of this reference, however, yields a compliant
balloon and therefore a stent delivered with such a balloon would
typically require "retouch."
SUMMARY OF THE INVENTION
[0008] The invention in one aspect is directed to a method for
method for installing a stent in a vessel utilizes a single balloon
catheter for both low pressure predilation at a relatively small
diameter to open the lesion sufficiently to allow insertion and
deployment of the stent across the lesion and for subsequent high
pressure embedding of the stent in the vessel wall. The same
balloon catheter may also be employed to insert and deploy the
stent. Thus at least one catheter may be eliminated from what has
heretofore been a two or three catheter installation process. The
balloons utilized in the method have a stepped compliance curve
which allows for predilation at a low pressure and predetermined
diameter and for high pressure embedding at a substantially larger
diameter.
[0009] In a further aspect of the invention novel balloon
structures having high wall strengths, high burst pressures and low
compliance are provided in which a first portion of the balloon
body has a generally linear compliance curve and a second portion
of the balloon body has a stepped compliance curve. Both portions
of the balloon are configured to have essentially the same diameter
at low pressure so that the entire balloon may be used to predilate
a lesion. However at higher pressure the configuration of the
balloon changes due to rapid expansion of the second balloon
portion. At still higher pressures the compliance curve of the
second portion levels off to a low compliance profile so that this
portion of the balloon can be used for high pressure embedment of
the stent without substantially increasing the stent size. With
such balloons, exposure of the vessel wall areas which are not
reinforced by the stent to high pressure can be avoided, despite
the typically shorter length of conventional stents than the
typical length of predilation balloons.
[0010] The novel balloons of the invention are made by molding a
balloon into a configuration in which the second portion has a
larger diameter than the first portion and then shrinking the
second portion to the diameter of the first portion. The method of
making such balloons comprises yet another aspect of the
invention.
[0011] These and other aspects and advantages of the present
invention will no doubt become apparent to those skilled in the art
after having read the following detailed description of the
invention as illustrated by the various drawing figures.
BRIEF DESCRIPTION OF DRAWINGS
[0012] FIG. 1 is a longitudinal sectional view of a vessel showing
an angioplasty catheter, not in section and having a stepped
compliance curve balloon on the distal end thereof, inserted in the
vessel and predilating a lesion in the vessel.
[0013] FIG. 2 is a view of a vessel as in FIG. 1 after installation
of a stent but before a "retouch" procedure.
[0014] FIG. 3 is a view as in FIG. 1 in which after predilation and
with the same catheter, now carrying a stent mounted over the
balloon, reinserted to deliver the stent to the lesion.
[0015] FIG. 4 is a view as in FIG. 3 with the balloon expanded to
install the stent and further dilate the lesion.
[0016] FIG. 5 is a view as in FIG. 3 after completion of the
procedure of FIG. 3.
[0017] FIG. 6 is a side view the distal end of a catheter having an
alternate balloon of the invention, shown in hyper-extended
form.
[0018] FIG. 7 is a schematic illustration depicting the process
stages for preparing a balloon as in FIG. 6.
[0019] FIG. 8 is a view of a catheter as in FIG. 6 except that a
second alternate balloon of the invention is depicted.
[0020] FIG. 9 is a schematic illustration depicting the process
stages for preparing a balloon as in FIG. 8.
[0021] FIG. 10 is a graph showing the compliance curves of several
balloons of the type shown in FIGS. 1, 3 and 4 compared to a
conventional 3.5 mm angioplasty balloon of the same material.
[0022] FIG. 11 is a graph of the compliance curves of a balloon of
the type shown in FIG. 6.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0023] The catheters employed in the practice of the present
invention are most conveniently constructed as over-the-wire
balloon catheters of conventional form for use in angioplasty,
except that the balloon has a stepped compliance curve. However it
should be understood that the present invention can be applied, in
addition to over-the-wire catheters, to fixed-wire catheters, to
shortened guide wire lumens or single operator exchange catheters,
and to non over-the-wire balloon catheters. Furthermore this
invention can be used with balloon catheters intended for use in
any and all vascular systems or cavities of the body.
[0024] Referring to FIGS. 1-5, the process of the invention is
illustrated by these Figures. In FIG. 1, a catheter 10 carrying a
balloon 12 on the distal end thereof has been inserted over guide
wire 13 into a vessel 14 and fed to a lesion 16 where it is used to
predilate the lesion to a predetermined diameter, typically about
2.5 mm. In the process of the invention, balloon 12 is made of a
high strength polymer, such as PET and has a stepped compliance
curve, the predilation diameter is below the transition region on
that curve and the desired final dilated diameter, typically
2.75-4.0 mm, lies on the portion of the curve above the transition
region. After the predilation the balloon is deflated and the
catheter 10 is removed from the vessel 14.
[0025] The next step is to deliver the stent to the lesion. In a
first embodiment of the process, a separate stent delivery catheter
of any conventional type is used to deliver the stent to the
lesion, install the stent in place across the lesion, and further
dilate the lesion to a larger diameter, typically 2.75-4.0 mm. The
delivery catheter is then withdrawn to leave the stent 17 in place
across the dilated lesion, as shown in FIG. 2. Occasionally as
indicated in FIG. 2 the stent is not fully seated or can move
somewhat after installation if the installation process is
discontinued at this point.
[0026] To assure that the stent is firmly seated in the lesion so
that it cannot move and to additionally reduce occurances of
restenosis and thrombus formation, in this embodiment of the
inventive process, after the delivery catheter has been removed,
catheter 10 is reinserted and expanded to a retouch pressure,
typically above 9 atm and preferably in the range of 12-20 atm.
[0027] Alternatively, catheter 10 may be employed as a delivery
catheter. In the specific embodiment illustrated in FIGS. 3-4, an
unexpanded stent 18 has been mounted on the catheter 10 over
balloon 12 after catheter 10 has been used to predilate the lesion
and has been removed from the lesion. Catheter 10 is then
reinserted into the vessel 14 and located across the lesion (FIG.
3). Balloon 12 is then reinflated as shown in FIG. 4 to expand and
install the stent 18 and to dilate the lesion. The pressure
employed is one which inflates the balloon to a diameter above the
transition region and therefore the same balloon as used in
predilation can be used to deliver the catheter and dilate the
lesion. Further, because the balloon 12 follows a low compliance
curve above the transition region, the pressure can safely be
increased above 12 atm so as to firmly seat stent 18 without having
to undergo "retouch." Typically the balloon 12 will be capable of
inflation to at least as high as 20 atm.
[0028] FIG. 5 depicts the stent 18 in place after high pressure
dilation. A similar result is obtained if the catheter 10 is used
for predilation and for "retouch" but not for stent installation.
It should be noted that the specific configuration of the stents 17
and 18 is not critical and two different configurations have been
depicted merely to indicate that different configurations may be
employed in either embodiment of the inventive installation
process. The particular configurations employed may be reversed or
another stent configuration, including balloon expandable stents
and self-expandable stents, may be substituted without departing
from the invention hereof.
[0029] Thus unlike the prior art methods for accomplishing the same
sequences of predilation, stent delivery/dilation and high pressure
seating or "retouch," a separate catheter is not required to be
used in the final high pressure seating step from the catheter used
in the predilation step. This significantly reduces the cost of the
procedure, since the catheter costs are a significant part of the
overall cost of the procedure.
[0030] The stepped compliance curve balloons should be made of a
thermoplastic polymer material which has a high strength, and gives
a low compliance balloon at pressures above about 15 atmospheres.
For purposes of this application "low compliance" is considered to
correspond to a diameter increase of no more than 0.1 mm per
increased atmosphere of pressure, preferably less than 0.06 mm/atm.
Suitably the balloon polymer is poly(ethylene terephthalate) (PET)
of initial intrinsic viscosity of at least 0.5, more preferably
0.7-0.9. Other high strength polyester materials, such as
poly(ethylene napthalenedicarboxylate) (PEN), nylons such as nylon
11 or nylon 12, thermoplastic polyimides and high strength
engineering thermoplastic polyurethanes such as Isoplast 301 sold
by Dow Chemical Co., are considered suitable alternative materials.
Desirably the balloon is blown in a way which will give a wall
strength of at least 18,000 psi, preferably greater than 20,000
psi. Techniques for manufacturing balloons with such wall strengths
are well known.
[0031] After being blown, the balloon is provided with a stepped
compliance curve by annealing the balloon for a short time after
blowing at a pressure at or only slightly above ambient and at a
temperature which causes the blown balloon to shrink. The process
is described in U.S. Pat. No. 5,348,538.However, the balloons of
the invention are desirably constructed with a greater difference
between the low pressure and high pressure linear regions of the
compliance curve so that the transition between the two regions
results in a step-up of diameter of the balloon of at least 0.4 mm.
This is accomplished by blowing the balloon to the larger diameter
and then shrinking to a greater extent than was done in the
specific illustrative examples of U.S. Pat. No. 5,348,538. The
amount of shrinkage is controlled by the pressure maintained in the
balloon during annealing and the temperature and time of the
annealing. For a balloon made from 0.74 intrinsic viscosity PET,
the blowing pressure is suitably in the range 200-400 psi, and
temperature is suitably in the range of 90-100.degree.C., and the
annealing pressure is in the range of 0-20, preferably 5-10 psi at
90-100.degree.C. for 3-10 seconds.
[0032] In a further aspect of the invention, the balloons employed
in the inventive process are configured so that a first portion of
the body of the balloon has a stepped compliance curve and the
remainder of the balloon has an unstopped compliance curve, the low
pressure regions of the compliance curves of both the first portion
and the remainder portion(s) being generally collinear. By this
means the length of the balloon which will expand and seat the
stent will be smaller than the length which is used to accomplish
predilation. Since many stents are in the 7-10 mm length range
whereas predilation balloons are desirably 15-20 mm or even longer,
this shorter configuration for the portion which will step-up to a
larger diameter ("hyper-extend") is desirable so that the
hyper-extension will not overlap tissue which is unreinforced by
the stent. Two balloons of this preferred configuration are shown,
mounted on catheters, in FIGS. 6 and 8.
[0033] In FIG. 6, the balloon 30 is shown in its fully expanded
high pressure configuration, mounted on a catheter 28. As shown
schematically in FIG. 7, this balloon is blown in a mold of the
general shape of the balloon in FIG. 6 and then the annealing step
is performed on the enlarged portion 32 by dipping the balloon in
the direction indicated by arrows 36 to level A in a bath of heated
water or other suitable heated fluid while the balloon is
pressurized at low pressure, for instance 0-10 psi, so that only
portion 32 is annealed. After annealing portion 32 will be shrunken
so that, the configuration of the balloon will be substantially
linear and will expand generally linearly until pressurized above
about 8-12 atm. At higher pressures, the portion 34 of balloon 30
will continue to expand along the same generally linear curve but
portion 32 will rapidly expand until the balloon configuration is
restored to shape shown in FIG. 6, after which the expansion
profile of portion 32 will level out again to a non-compliant curve
but at a substantial increase in absolute diameter relative to the
diameter of portion 34. Balloons of this configuration, have been
used to produce compliance curves as shown in FIG. 11.
[0034] It should be understood that while FIG. 6 shows portion 32
of balloon 30 mounted distally on catheter 28, balloon 30 may
instead be mounted with portion 34 mounted distally without
departing from the invention hereof.
[0035] If the balloon of FIG. 6 is used to deliver and install the
stent, the catheter 28 will have to be backed up a short distance
to center portion 32 under the stent after expansion of balloon 30
sufficiently to bring it into contact with the lesion but before
the balloon portion 32 is fully expanded to fully dilate the lesion
and set the stent. This can be accomplished by providing marker
bands (not shown) on the portion of the catheter shaft under the
balloon to indicate the proximal and distal boundries of portion
32.
[0036] In the alternate embodiment of FIG. 8, the balloon 40,
mounted on catheter 38, has a hyper-extensible portion 42 located
centrally on the balloon body. Therefore, after installation of the
stent, the high pressure stent setting step can be performed
immediately without repositioning the catheter and without risking
damage to tissue unreinforced by the stent. This balloon is blown
in a mold having a configuration which is substantially the shape
shown in FIG. 8. To anneal and shrink portion 42 to the diameter of
portions 44, 46, heating during annealing may be confined to the
central portion 42, suitably by heating with a hot air stream,
using baffles to protect the end regions 44, 46 from the air
stream. Alternatively, as shown schematically in FIG. 9, the
balloon 40 is dipped in the direction of arrows 47 to level A in a
heated bath to fully immerse portions 42 and 46, until portion 42
has reached the diameter of portion 44. At this point portion 46
will be shrunk to a diameter less than portion 44. Balloon 40 is
then dipped into a heated bath in the direction of arrows 49 to
level B so that only portion 46 is immersed and then portion 46 is
reblown to the diameters of portion 44 and shrunken portion 42.
This reblowing step may be accomplished either with the aid of a
mold or by free-blowing.
[0037] Referring now to the graph shown in FIG. 10, in which
pressure in atmospheres is plotted on the x-axis and balloon
diameter in millimeters is plotted on the y-axis. The compliance
curves of several balloons have been manufactured in accordance
with U.S. Pat. No. 5,348,538 and useful in the practice of this
invention have been plotted on this graph and compared to a
conventional 3.5 mm angioplasty balloon Q of the same PET material.
The stepped compliance curve balloons, X, Y and Z, plotted on this
graph had nominal diameters prior to being shrunk of 3.0, 3.5 and
4.0 millimeters, respectively.
[0038] FIG. 11 is a graph of the compliance curves of a balloon of
the type shown as balloon 30 in FIG. 6. Curve 11a is the compliance
curve of portion 32 of balloon 30 and curve 11b is the compliance
curve of the portion 34 of balloon 30. The balloon was made from
PET of 0.74 intrinsic viscosity and, after blowing had a body wall
thickness of 0.0013 inches. Portion 32 thereof was annealed by
dipping in a 95.degree.C. water bath for 5 seconds, while
pressurized at 10 atm pressure, to shrink portion 32 to the
diameter of portion 34. The balloon was then mounted on a catheter
and the compliance curve obtained by incrementally inflating the
balloon until burst, measuring the diameter of both portions 32 and
34 at each incremental pressure.
[0039] With regard to definitions, FIG. 11 can be referred to for
illustration of what is meant by "generally linear" with reference
to the portions of curve 11a between 3 and 10 atm and again between
about 13 and 26 atm. Curve 11b is considered generally linear
through out its entire length. "Generally collinear" is considered
to encompass divergences between two curves of no more than about
0.2 atm, preferably less than 0.15 mm divergence between the two
curves. Curves 11a and 11b are "generally collinear" in the range
from 3 atm to about 10 atm.
[0040] The invention may also be practiced by use of dual layer
balloons such as described in co-pending U.S. application Ser. No.
08/243,473, filed May 16, 1994 as a continuation of now abandoned
U.S. application Ser. No. 07/927,062, filed Aug. 8, 1992,
incorporated herein by reference, and in U.S. Pat. No. 5,358,487,
incorporated herein by reference. Suitably both balloons of the
dual layer balloons are low compliance balloons designed with the
outer balloon portion larger by at least 0.25 mm than the inner
portion and the inner balloon designed to burst at a pressure below
about 15 atm so that the compliance curve follows the inner balloon
portion until it reaches burst diameter and then, after the inner
balloon bursts, the outer balloon becomes inflated and can be
expanded to a larger diameter than the burst diameter of the inner
balloon.
[0041] Although the present invention has been described in terms
of specific embodiments, it is anticipated that alterations and
modifications thereof will no doubt be come apparent to those
skilled in the art. It is therefore intended that the following
claims be interpreted as covering all such alterations and
modifications as fall within the true spirit and scope of the
invention.
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