Variable diameter balloon dilatation catheter

A dilatation catheter includes an inflation balloon having a variable diameter inflation profile. The balloon has a first inflation profile, in which it exhibits a substantially cylindrical central working profile. The first inflation profile of the balloon is achieved by inflating the balloon to a first inflation pressure. The balloon has a second inflation profile which is achieved by increasing the inflation pressure to a second, higher pressure. In the second inflation profile, a proximal segment and a distal segment of the balloon have a first inflated diameter and a central focal segment, separating the proximal and distal segments, has a second inflated diameter, such that the second inflated diameter is greater than the first inflated diameter.

BACKGROUND OF THE INVENTION 
The present invention relates to catheters for insertion into a body lumen. 
More particularly, the present invention relates to a "focal" balloon 
dilatation catheter for use in the vascular system. 
Prior art vascular dilatation balloons on typical dilatation catheters tend 
to fall into one of two broad classes. Most are considered noncompliant 
balloons, formed from a generally nondistensible material such as 
polyethylene. The perceived advantage of the noncompliant balloons is that 
they exhibit a substantially uniform exterior inflated profile which 
remains substantially unchanged upon incremental increases in inflation 
pressure. In theory, noncompliant balloons are advantageous because they 
allow the introduction of increased inflation pressure to break 
particularly calcified lesions, yet retain a predictable inflated profile 
so that damage to the surrounding native lumen is minimized. 
Certain compliant balloons are also known in the art. A compliant balloon 
is one which is able to grow in diameter in response to increased 
inflation pressure. One difficulty with compliant balloons, however, is 
that inflation within a difficult lesion can cause the balloon to inflate 
around the plaque to produce a generally hourglass-shaped inflated 
profile. This can result in damage to the native vessel adjacent the 
obstruction, while at the same time failing to sufficiently alleviate the 
stenosis. 
Therefore, there exists a need in the art for a vascular dilatation 
catheter with a balloon which is able to grow in diameter in response to 
increased inflation pressure, and which expands in a predictable inflation 
profile while minimizing any damage to the native vessel. 
SUMMARY OF THE INVENTION 
There is provided in accordance with one aspect of the present invention a 
balloon catheter, such as for performing balloon dilatation procedures in 
a body lumen. The catheter comprises an elongate flexible tubular body, 
and an inflatable balloon on the tubular body. The balloon is inflatable 
to a first diameter, and at least one portion of the balloon is inflatable 
to a second, larger diameter. In one embodiment, a proximal end and a 
distal end of the balloon are inflatable to a first diameter and a central 
segment of the balloon is inflatable to both the first diameter and also 
to a second greater diameter. Preferably, inflation to the first diameter 
is achieved by inflation to a first pressure, and inflation to the second 
diameter is achieved by inflation to a second, higher pressure. In one 
embodiment, the catheter comprises proximal and distal expansion limiting 
bands positioned on the proximal end and distal end of the inflation 
balloon to limit expansion of the proximal end and the distal end of the 
inflation balloon at the first diameter. 
In accordance with a further aspect of the present invention, there is 
provided a method of treating a site in a body lumen. The method comprises 
the steps of providing a catheter of the type having an elongate, 
flexible, tubular body and a dilatation balloon on the body. Preferably, a 
proximal segment and a distal segment of the balloon are inflatable to a 
first diameter and a central segment of the balloon is inflatable to a 
second greater diameter. The catheter is positioned within a body lumen so 
that the balloon is adjacent a treatment site. The balloon is inflated to 
a first inflation profile, wherein the proximal segment, the distal 
segment and the central segment are inflated to the first inflation 
diameter, to treat the site. The balloon is thereafter inflated to a 
second inflation profile, wherein the proximal segment and the distal 
segment are inflated to the first inflation diameter and the central 
segment is inflated to the second inflation diameter, to further treat the 
site. 
Further features and advantages of the present invention will become 
apparent to one of skill in the art in view of the Detailed Description of 
Preferred Embodiments which follows, when considered together with the 
attached drawings and claims.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to FIG. 1, there is disclosed a variable diameter inflation 
catheter 10 in accordance with of one aspect of the present invention. 
Catheters embodying additional features known in the vascular dilatation 
art, such as implantable stents, drug delivery, perfusion and dilatation 
features, or any combination of these features, can be used in combination 
with the focal balloon of the present invention as will be readily 
apparent to one of skill in the art in view of the disclosure herein. 
The catheter 10 generally comprises an elongate tubular body 12 extending 
between a proximal control end 14 and a distal functional end 16. The 
length of the tubular body 12 depends upon the desired application. For 
example, lengths in the area of about 120 cm to about 140 cm are typical 
for use in percutaneous transluminal coronary angioplasty applications. 
The tubular body 12 may be produced in accordance with any of a variety of 
known techniques for manufacturing balloon-tipped catheter bodies, such as 
by extrusion of appropriate biocompatible plastic materials. 
Alternatively, at least a portion or all of the length of tubular body 12 
may comprise a spring coil, solid walled hypodermic needle tubing, or 
braided reinforced wall, as is understood in the catheter and guide wire 
arts. 
In general, tubular body 12, in accordance with the present invention, is 
provided with a generally circular cross-sectional configuration having an 
external diameter within the range of from about 0.03 inches to about 
0.065 inches. In accordance with one preferred embodiment of the 
invention, the tubular body 12 has an external diameter of about 0.042 
inches (3.2 f) throughout most of its length. Alternatively, generally 
triangular or oval cross-sectional configurations can also be used, as 
well as other noncircular configurations, depending upon the number of 
lumen extending through the catheter, the method of manufacture and the 
intended use. 
In a catheter intended for peripheral vascular applications, the tubular 
body 12 will typically have an outside diameter within the range of from 
about 0.039 inches to about 0.065 inches. In coronary vascular 
applications, the tubular body 12 will typically have an outside diameter 
within the range of from about 0.026 inches to about 0.045 inches. 
Diameters outside of the preferred ranges may also be used, provided that 
the functional consequences of the diameter are acceptable for the 
intended purpose of the catheter. For example, the lower limit of the 
diameter for tubular body 12 in a given application will be a function of 
the number of fluid or other functional lumen, support structures and the 
like contained in the catheter, and the desired structural integrity. 
Tubular body 12 must have sufficient structural integrity (e.g., 
"pushability") to permit the catheter to be advanced to distal arterial 
locations without buckling or undesirable bending of the tubular body 12. 
The ability of the body 12 to transmit torque may also be desirable, such 
as in embodiments having a drug delivery capability on less than the 
entire circumference of the delivery balloon. Larger diameters generally 
have sufficient internal flow properties and structural integrity, but 
reduce perfusion in the artery in which the catheter is placed. Increased 
diameter catheter bodies also tend to exhibit reduced flexibility, which 
can be disadvantageous in applications requiring placement of the distal 
end of the catheter in a remote vascular location. In addition, lesions 
requiring treatment are sometimes located in particularly small diameter 
arteries, necessitating the lowest possible profile. 
As illustrated schematically in FIG. 1, the distal end 16 of catheter 10 is 
provided with at least one inflation balloon 18 having a variable 
diameter. The proximal end 14 of catheter 10 is provided with a manifold 
20 having a plurality of access ports, as is known in the art. Generally, 
manifold 20 is provided with a guide wire port 22 in an over the wire 
embodiment and a balloon inflation port 24. Additional access ports are 
provided as needed, depending upon the functional capabilities of the 
catheter 10. The balloon 18 can also be mounted on a rapid exchange type 
catheter, in which the proximal guidewire port 22 would be unnecessary as 
is understood in the art. In a rapid exchange embodiment, the proximal 
guidewire access port is positioned along the length of the tubular body 
12, such as between about 4 and about 20 cm from the distal end of the 
catheter. 
Referring to FIGS. 2 and 3, the two-step inflation profile of the inflation 
balloon 18 is illustrated. In FIG. 2, the balloon 18 is illustrated at a 
first inflation profile, in which it exhibits a substantially cylindrical 
central working profile. The dimensions in FIG. 2 are exaggerated to 
illustrate a proximal segment 26 and a distal segment 28 which are axially 
separated by a central focal segment 30. However, as will be understood by 
one of ordinary skill in the art, when the balloon 18 is inflated to the 
first inflation profile, the exterior of the balloon 18 preferably 
exhibits a substantially smooth cylindrical working profile. 
In FIG. 3, the inflation balloon 18 is illustrated at a second inflation 
profile. The proximal segment 26 and the distal segment 28 of the balloon 
are separated by the central focal segment 30 having a greater diameter. 
The configuration of FIG. 2 is achieved by inflating the balloon 18 to a 
first inflation pressure, while the configuration of FIG. 3 is achieved by 
increasing the inflation pressure to a second, higher pressure as will be 
discussed below. 
The details of one preferred embodiment of the variable diameter inflation 
catheter 10 are discussed with reference to FIGS. 2 and 3. Preferably, the 
tubular body 12 is provided with at least a guidewire lumen 32 extending 
all the way through the balloon 18, and an inflation lumen 34 extending 
into the proximal end of the balloon 18. 
In the illustrated embodiment, an inner balloon 36 is disposed coaxially 
within an outer balloon 38. A substantially nondistensible expansion 
limiting band 40 is disposed in between the balloons 36 and 38 adjacent a 
proximal annular shoulder 42, to limit the radial expansion of the balloon 
18. Similarly, a distal expansion limiting band 44 is disposed between the 
inner balloon 36 and outer balloon 38 adjacent a distal annular shoulder 
46. 
Expansion limiting bands 40 and 44 or other inflation limiting structures 
can be provided in any of a variety of ways which will be well-understood 
by one of skill in the art in view of the disclosure herein. For example, 
in one embodiment, the bands 40 and 44 each comprise a tubular section of 
polyester, each having an axial length of about 5 mm, a diameter of about 
2.5 mm and a wall thickness of about 0.0003 inches. Other generally 
nondistensible materials such as nylon, polyimide, Kevlar fiber, 
cross-linked polyethylene, polyethylene terephthalate and others, may be 
utilized to accomplish the expansion-limiting effect. 
The expansion limiting characteristics can be achieved by the addition of a 
structure that is discrete from the balloon, or by modifying the expansion 
properties of the balloon material itself. For example, the balloon can be 
provided with zones of differing wall thickness, or zones having different 
levels of cross linking as will be discussed. 
In general, the bands 40 and 44 must be of a sufficient thickness or 
structural integrity for the particular material used to substantially 
withstand inflation under the pressures normally utilized in the context 
of dilatation catheters. However, the bands 40 and 44 are preferably thin 
enough to provide a substantially smooth exterior surface of the balloon 
18. 
Preferably, as illustrated in FIGS. 2 and 3, the expansion-limiting bands 
40 and 44 are sandwiched between the inner balloon 36 and the outer 
balloon 38. In alternative embodiments, the expansion-limiting bands 40 
and 44 or other inflation limiting structures may be coated or mounted on 
the exterior surface of the balloon 18, the interior surface of the 
balloon 18 or within the wall of the balloon 18. Balloon 18 can be 
provided with two or more layers as illustrated, or with only a single 
layer as will be discussed. 
The axial length of the bands 40 and 44 can be varied widely depending upon 
the dimensions and the objectives of the catheter 10 as will be apparent 
to one of ordinary skill in the art. Further, the proximal band 40 and 
distal band 44 need not be of similar lengths. In general, however, some 
examples of dimensions which are useful in the coronary angioplasty 
dilatation environment are reproduced in Table 1 below, in which A 
represents the axial length of the balloon 18 between proximal shoulder 42 
and distal shoulder 46, B represents the axial distance between distal 
shoulder 46 and transition point 48, and C represents the axial length of 
the central focal segment 30. The dimensions of Table 1 are exemplary 
only, and the present invention can be accomplished using a wide variety 
of other dimensions as will be apparent to one of skill in the art. 
TABLE 1 
______________________________________ 
A B C 
______________________________________ 
20 mm 5 mm 10 mm 
30 mm 5 mm 20 mm 
40 mm 5-10 mm 20-30 mm 
______________________________________ 
The catheter 10 illustrated in FIGS. 2 and 3 can be manufactured in 
accordance with any of a variety of techniques which will be appreciated 
by one of ordinary skill in the art in view of the disclosure herein. In 
the following disclosure, particular materials and dimensions will be used 
as an example only, and other dimensions and materials can be selected 
depending upon the desired characteristics of the finished product. 
In one particular method of manufacturing, a low density polyethylene 
extrusion stock tube having an inside diameter of about 0.018 inches and 
an outside diameter of about 0.043 inches is used for the inner and outer 
balloons 36, 38. 
The polyethylene stock tubing is cross-linked by exposure to an electron 
beam in accordance with techniques well known in the art. A test segment 
of the cross-linked stock tubing is free blown up to 3.0 mm in diameter. 
If the cross-linked stock tubing can be free blown to a diameter greater 
then 3.0 mm, the stock tubing is cross-linked again and retested until the 
desired free blow diameter is achieved. 
The appropriately cross-linked stock tubing is then blown to a diameter of 
2.5 mm within a teflon capture tube (not shown) which acts to mold the 
balloon to its desired first inflation diameter. The teflon capture tube 
is a generally tubular body which has approximately the same inside 
diameter as the desired inflation diameter of the balloon. The teflon 
capture tube is heated by any of a number of heating means such as 
electric coils or a furnace to a temperature which is sufficient to mold 
the balloon to the desired inflation diameter. In this case, the 
cross-linked polyethylene balloon is preferably heated to a temperature of 
about 300.degree. F. The teflon chamber is then cooled to a temperature 
below the softening temperature of the balloon. Once cooled, the balloon 
is deflated and removed from the capture tube. 
A section of inflation balloon material is thereafter stretched with 
application of heat to neck down the proximal and distal ends 37, 39 to a 
thickness of about 0.001 inches and a diameter which relatively closely 
fits the portion of the tubular catheter body 12 to which it is to be 
sealed. 
The balloon is then attached to the tubular body 12 by any of a variety of 
bonding techniques known to one of skill in the art such as solvent 
bonding, thermal adhesive bonding or by heat shrinking/sealing. The choice 
of bonding techniques is dependent on the type of balloon material and 
tubular body material used to form the catheter 10. 
In one particular method of manufacture, inner balloon 36 and outer balloon 
38 are attached to the catheter body 10. The proximal necked end 37 of the 
inner balloon 36 is heat sealed around the catheter body 12. The distal 
necked end 39 of the inner balloon 36 is thereafter heat sealed around the 
distal end 16 of the catheter body 12. In general, the length of the 
proximal end 37 and the distal end 39 of the inner balloon 36 which is 
secured to the catheter body 12 is within the range of from about 3 mm to 
about 10 mm, however the proximal and distal balloon necked ends 37, 39 
are as long as necessary to accomplish their functions as a proximal and 
distal seal. 
Expansion limiting bands 40 and 44 are respectively positioned at the 
proximal segment 26 and the distal segment 28 of the inner balloon 236 and 
may be bonded or otherwise secured to the inner balloon 36. The outer 
balloon 38 is thereafter be mounted to the catheter body 12 in a similar 
manner as the inner balloon 36, following "necking down" of the proximal 
and distal axial ends of the outer balloon 38 by axial stretching under 
the application of heat. The outer balloon 38 is advanced axially over the 
inner balloon 36 and the expansion limiting bands 40 and 44. The outer 
balloon 38 may thereafter be bonded to the inner balloon 36, and to the 
expansion limiting bands 40 and 44 by any of a variety of bonding 
techniques such as solvent bonding, thermal adhesive bonding or by heat 
sealing also depending on the type of balloon material used. 
Alternatively, the expansion limiting bands are simply entrapped between 
the balloons without any bonding or adhesion. 
In a preferred embodiment, the inner balloon and the outer balloon 36, 38 
are both cross-linked polyethylene balloons which are difficult to bond 
together using conventional solvents. If sealing is desired, the inner 
balloon 38 and the outer balloon 38 are heat sealed together as described 
below. In another embodiment, the inner balloon 36 and outer balloon 38 
are secured together through the use of a UV-curable adhesive. 
The inner balloon 36 and the outer balloon 38, once mounted to the catheter 
body 12, can be heat sealed together in a heating chamber (not shown) such 
as a Teflon capture tube. Inner balloon 36 and outer balloon 38 are 
inflated in the chamber until the inner balloon and the outer balloon 
inflate to the first inflation diameter. The heating chamber is heated by 
any of a number of heating means such as electric coils or a furnace to 
heat air to a temperature which is sufficient to bond the two balloons 36, 
38 together. In this case, the cross-linked polyethylene balloons are 
preferably heated to a temperature of about 300.degree. F. within the 
chamber which causes both balloons 36, 38 to seal together to form a 
double walled variable diameter inflation balloon 18. The chamber is then 
cooled to a temperature below the softening temperature of the inner and 
outer balloons 36 and 38. Once cooled, the variable diameter balloon 18 is 
deflated and the catheter 10 is removed from the chamber. 
It will be apparent to one of skill in the art, that it is possible to 
attach the inner balloon 36 and the outer balloon 38 to the catheter body 
12 without adhesively bonding or otherwise securing the two balloons 
together. In this case, the two balloons will respond to the applied 
inflation pressure with the inner balloon 36 forcing the outer balloon 38 
to simultaneously inflate both balloons 36, 38. The expansion limiting 
bands 40 and 44 can be merely sandwiched between the inner balloon 36 and 
the outer balloon 38 and do not in this embodiment need to be bonded to 
either balloon. 
The variable diameter balloon design of the present invention can also be 
accomplished with a single layer balloon or a double layer balloon without 
the inclusion of additional expansion limiting bands. This is accomplished 
by decreasing the relative compliance of the zones of the balloon that are 
intended to remain at the first inflated diameter. For example, 
polyethylene extrusion stock is cross-linked to 3.0 mm and blown into a 
mold of a diameter of about 2.5 mm as described above to form a balloon. 
The balloon is attached to the catheter as described above. The balloon is 
inflated and the central focal segment 30 of the balloon on the catheter 
10 is masked such as with a steel clamp or other mask known in the art to 
block electron beam penetration, leaving the proximal segment 26 and the 
distal segment 28 of the balloon exposed. The inflated proximal segment 26 
and distal segment 28 of the balloon 18 are exposed again to an electron 
beam source to further cross-link the segments 26, 28 at the 2.5 mm 
diameter. Balloons manufactured in this manner have been found to exhibit 
a relatively highly compliant central zone and relatively less complaint 
axial end zones in a manner that achieves the two-step dilatation as 
illustrated in FIGS. 2 and 3. 
Preferably, however, a dual balloon structure is used, which incorporates 
the expansion limiting bands as illustrated in FIGS. 2 and 3. Balloons 18 
made in accordance with the design illustrated in FIGS. 2 and 3 have been 
found to exhibit the inflation pressure profile illustrated in Table 2. 
TABLE 2 
______________________________________ 
CENTRAL 
SEGMENT PROXIMAL AND DISTAL 
PRESSURE DIAMETER SEGMENT DIAMETER 
______________________________________ 
6 atm 2.5 mm 2.5 mm 
7 atm 2.6 mm 2.5 mm 
8 atm 2.7 mm 2.5 mm 
9 atm 2.8 mm 2.5 mm 
10 atm 2.9 mm 2.5 mm 
11 atm 3.0 mm 2.5 mm 
12 atm 3.1 mm 2.5 mm 
13 atm 3.2 mm 2.5 mm 
14 atm 3.3 mm 2.6 mm 
______________________________________ 
The inflation pressure profile of the variable diameter inflation balloon 
18 illustrated in Table 2 provides an example of the manner in which a 
balloon 18 made in accordance with the foregoing method is inflated with 
the application of increased pressure. Initially, the central segment 30 
and the proximal and distal segments 26, 28 of the balloon 18 inflate 
together as the pressure increases. When the pressure reaches 6 atm, for 
example, the diameter of the proximal and distal segments 26, 28 and the 
central segment 30 of the balloon all remain at about 2.5 mm. At 11 atm, 
the diameter of the central segment 30 of the balloon 18 has grown to 
about 3 mm while the proximal and distal segments 26, 28 remained inflated 
to the first diameter of 2.5 mm. The diameter of the central section 30 of 
the balloon 18 will continue to increase until the burst pressure of the 
balloon 18 is reached. In one prototype, the burst pressure was 
approximately 16 atm at normal body temperature. 
Both the first inflation diameter and the second inflation diameter can 
also be varied depending upon the desired catheter characteristics as will 
be understood by one of ordinary skill in the art. In a preferred 
embodiment, a first inflated diameter of the catheter for coronary 
angioplasty applications is approximately 2.5 mm. Upon an increase of 
pressure, this diameter grows to a second inflated diameter of 
approximately 3 mm in the central focal segment 30. In general, balloons 
can be readily constructed having a difference between the first inflation 
diameter and second inflation diameter anywhere within the range of from 
about 0.1 mm up to 1.0 mm or more, depending upon the elastic limits of 
the material from which the balloon was constructed. Typically, coronary 
angioplasty dilatation balloons will have a first diameter within the 
range of from about 1.5 mm to about 4.0 mm. Typical balloons for use in 
peripheral vascular applications will have a first inflation diameter 
within the range of from about 2 mm to about 10 mm. 
Dilatation balloons can readily be constructed in accordance with the 
present invention in which entire length of the balloon from, for example, 
proximal shoulder 42 to distal shoulder 46 (FIG. 2) is variable from a 
first inflated diameter to a second larger inflated diameter in response 
to increasing pressure. Alternatively, balloons in accordance with the 
present invention can readily be constructed in which a proximal portion 
of the balloon is compliant so that it can grow in response to increased 
pressure, while a distal portion of the balloon has a fixed inflated 
diameter. This configuration may be desirable, for example, when the 
native vessel diameter is decreasing in the distal catheter direction. 
Positioning the catheter so that the compliant portion is on the proximal 
(larger diameter) portion of the vessel may minimize damage to the vessel 
wall in certain applications. Alternatively, the compliant segment can 
readily be positioned on the distal end of the balloon with a 
substantially fixed inflated diameter segment on the proximal end of the 
balloon. 
A variable diameter balloon 18 made in accordance with the foregoing 
designs has been found to benefit certain conventional percutaneous 
transluminal coronary angioplasty (PTCA) procedures. In accordance with 
the method of the present invention, the variable diameter balloon 18 is 
percutaneously advanced and positioned such that the central segment 30 of 
the balloon 18 is adjacent a vascular treatment site. Generally, the 
treatment site is a stenosis such as due to a plaque or thrombus. The 
variable diameter balloon 18 is inflated to a first inflation profile to 
begin dilation of the stenosis. Preferably, the first inflation profile is 
achieved by applying up to about 6 atm of pressure to the balloon 18. At 
the first inflation profile, the entire balloon is inflated to the inner 
diameter of the vessel, thus restoring patency to the vascular lumen. In 
one embodiment, the variable diameter balloon 18 is inflated to a first 
inflation diameter, of about 2.5 mm, at an inflation pressure of 6 atm. 
The first inflation diameter is preferably about the native diameter of 
the vessel. 
As additional pressure is applied to the variable diameter balloon 18, a 
second inflation profile is achieved wherein the central segment 30 of the 
balloon 18 expands beyond the diameter of the first inflation profile to a 
second inflation diameter, while the proximal segment 26 and the distal 
segment 28 remain at the first inflation diameter. As the pressure applied 
to the variable diameter balloon 18 increases, the diameter of the central 
segment 30 of the balloon 18 extends past the native diameter of the 
vessel to the second inflation diameter. Utilizing this method, and 
depending upon the balloon size selected, the stenosis is compressed to a 
point which is beyond the native diameter of the vessel. In a preferred 
embodiment, at an applied pressure of 11 atm the diameter of the central 
segment 30 of the balloon 18 at the second inflation diameter is 3 mm and 
the diameter of the proximal end 26 and the distal end 28 at the first 
inflation diameter is 2.5 mm. Second inflation diameters in between the 
first inflation diameter and the maximum inflation diameter can be readily 
achieved by controlling inflation pressure, as illustrated for one 
embodiment in Table 2, above. 
After the stenosis is compressed to or beyond the native diameter of the 
vessel, the balloon is evacuated and the catheter withdrawn. 
Alternatively, if desired, the pressure is reduced until the balloon 18 
resumes the first inflation profile. At this point, the balloon 18 may be 
held at the first inflation diameter for short periods to continue to 
maintain patency of the lumen if short term rebound is a concern. This 
post dilatation step is preferably accomplished using a catheter having 
perfusion capabilities. Finally, the remaining pressure applied to the 
balloon 18 is reduced causing the variable diameter balloon 18 to deflate. 
The catheter is then extracted from the vessel utilizing conventional PTCA 
procedures. 
In accordance with a further aspect of the present invention, there is 
provided a method of implanting a tubular stent within a body lumen. 
Tubular stents of the type adapted to be carried to a vascular site on a 
balloon catheter, and for expansion from a first insertion diameter to a 
second implanted diameter are well-known in the art. 
In accordance with the method of implanting a tubular stent, an expandable 
stent is positioned about the deflated balloon of a variable diameter 
balloon catheter in accordance with the present invention. The balloon is 
thereafter percutaneously inserted into the vascular system and 
transluminally advanced to position the stent at the treatment site. The 
balloon is thereafter inflated to at least a first inflation 
configuration, wherein the balloon exhibits a substantially cylindrical 
profile throughout its axial length. Thereafter, the balloon is optionally 
inflated to a second inflation profile, thereby inflating at least a 
portion of the stent to a second, greater diameter. Depending upon the 
etiology of the underlying condition, the central region of the stent may 
preferably be inflated to a larger diameter than either of the axial ends 
of the stent. 
Alternatively, the axial length of the stent is selected to approximately 
equal the axial length of the focal zone on the inflation balloon. In this 
manner, the inflation balloon within the stent is expandable to a diameter 
slightly larger than the native diameter of the adjacent vessel. This 
permits subsequent overgrowth of endothelium along the interior wall of 
the stent while still leaving a lumen having an interior diameter within 
the stent approximately equal to the native diameter of the lumen adjacent 
the stent. 
In accordance with a further aspect of the present invention, the variable 
diameter balloon is utilized to "tack down" a previously positioned 
tubular stent. In accordance with this aspect of the present invention, a 
tubular stent is identified within a body lumen. The focal balloon is 
positioned within the stent in accordance with conventional PTCA 
procedures, and the balloon is inflated so that the central, focal section 
enlarges the diameter of at least a first portion of the stent. The 
balloon is thereafter reduced in diameter, and, preferably, repositioned 
within a second region within the stent and then reinflated to expand at 
least the second region of the stent. Expansions of this type can be 
repeated until the stent has been expanded as desired. The balloon is 
thereafter evacuated and removed from the patient. 
In accordance with a further aspect of the present invention, there is 
provided a method of percutaneous transluminal angioplasty in which 
multiple lesions of differing sizes are dilated without removing the 
catheter from the body. In accordance with this aspect of the present 
invention, the variable diameter balloon is positioned within a first 
stenosis in accordance with conventional PTCA techniques. The balloon is 
dilated to a sufficient diameter to restore patency to the vascular lumen. 
The balloon is thereafter deflated, and repositioned within a second 
stenosis in the vascular system. The balloon is inflated to restore 
patency of the vessel in the region of the second stenosis. Optionally, 
the balloon may be deflated, and repositioned within a third stenosis in 
the body lumen. The balloon is then inflated to a sufficient diameter to 
restore patency in the body lumen in the region of the third stenosis. 
Four or more lesions can be treated seriatim in this manner. 
Preferably, the balloon is inflated to a first diameter in the first 
stenosis, and to a second, different diameter, in the second stenosis. In 
this manner, multiple dilatations at different diameters can be 
accomplished utilizing the balloon of the present invention. This method 
is accomplished by supplying a first inflation pressure to the balloon 
while the balloon is positioned in a first position in the vascular 
system, and thereafter supplying a second pressure to the balloon when the 
balloon is in a second position in the vascular system. In accordance with 
the previous disclosure herein, each of the first and second inflation 
pressures is selected to achieve a preselected inflation diameter of the 
balloon. 
The present invention may be embodied in other specific forms without 
departing from its spirit or essential characteristics. The described 
embodiments are to be considered in all respects only as illustrative and 
not restrictive. The scope of the invention is, therefore, indicated by 
the appended claims rather than the foregoing description. All changes 
which come within the meaning and range of equivalency of the claims are 
to be embraced within their scope.