Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to angioplasty catheters for use
in the treatment of stenosed blood vessels. The invention also
relates to a method of manufacturing the catheter.
Angioplasty catheters have been successfully used for a
number of years in the treatment of blood vessels obstructed or
stenosed with plaque. An angioplasty catheter includes, near
its distal end, a balloon which can be inflated by means of
pressurized fluid supplied through a lumen in the catheter. The
treatment involves the location of the balloon in the stenosed
section of the blood vessel, followed by inflation and
deflation. During inflation, the balloon compresses the plaque
and stretches the blood vessel such that the cross-sectional
area of the stenosis is increased until it is comparable to that
of the unobstructed blood vessel. When the treatment has been
completed the balloon is deflated and the catheter removed. The
treated blood vessel maintains substantially its enlarged
cross-section to permit the free flow of blood through this
portion.
To perform satisfactorily a suitable angioplasty
catheter must possess a number of properties. For ease of
insertion it is preferable that the catheter is flexible, has a
relatively small cross-sectional area, and has a smooth outer
surface. The catheter preferably has a tapered end and a main
lumen to receive a Seldinger guide wire. The catheter ends at
an aperture in the tapered end. A ballon is attached to the
catheter near the distal end for inflation by entering a
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pressurized fluid into a secondary lumen running in parallel
with the main lumen through the body of the catheter.
The balloon must display a small profile during
insertion in the collapsed condition, it must inflate evenly to
compress the plaque, and then after deflation, the balloon
profile should return to the original shape for removal of the
catheter without damaging veins.
Examples of typical structures for use in angioplasty
are found in U.S. Patent Nos. 4,338,942 to Fogarty, 4,646,719 to
Neuman et al, and 4,402,307 to Hanson et al.
A series of unexpected problems have arisen in using
balloons in angioplasty. The balloons are usually of a filmic
Nylon (trade mark) made to have a cylindrical appearance when
infiated and made with a molecular orientation along the length
of the balloon. The catheter body extends through the balloon
which is attached at its ends to the body. On inflation, the
balloon is subject to very high hoop stresses which tend to
cause some radial stretching and this causes sympathetic tensile
forces longitudinally which place a compressive loading on the
body inside the balloon. It is not uncommon that these
compressive forces exceed the buckling load of the body and the
body takes on a curve or buckle (see Fig. 1) thereby allowing
the hoop stresses to exceed the elastic limit of the balloon
resulting in some distortion. As a result the balloon is
sometimes shorter when it is subsequently deflated and the body
then remains in the buckled state (see Fig. 2). This resulting
shape is most undesirable for withdrawing the catheter.
It would seem that the problem could be overcome by
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using a balloon which is longer than the spacing between the
connections to the catheter body. Extra material will be
available and it was thought that this would allow the balloon
to inflate without stressing the catheter. However, this leads
to a different problem because the balloon will simply stretch
until it induces compression in the body, and also an enlarged
balloon tends to lose the desirable cylindrical shape and become
spherical. The result is that the loading on the plaque is less
than optimal and can cause large localized stresses in the
stenosed vein.
It is therefore an object of the present invention to
provide a catheter for angioplasty which controls undesirable
changes of shape in the balloon and catheter body resulting from
balloon inflation.
In one of its aspects the invention provides an
angioplasty catheter comprising a main body having proximal and
distal ends and defining a first lumen extending to the distal
end and a second lumen terminating at an opening spaced from the
distal end, and a collapsible connection piece in the main body
between said opening and the distal end. A balloon is attached
at the ends of the balloon to the main body and contains the
opening and the connection piece, and the connection piece
collapses axially when the balloon is inflated to minimise
energy stored in the main body. This accommodates changes in
length of the balloon so that the body will remain straight both
during and after inflation of the balloon.
In another of its aspects, a method of making an
angioplasty catheter is provided.
This and other aspects of the invention will be better
understood with reference to the drawings, in which:
Figs. 1 and 2 are diagrammatic illustrations
demonstrating the problem with prior art angioplasty catheters;
Fig. 3 is an isometric view of an angioplasty catheter
in accordance with a preferred embodiment of the present
invention;
Fig. 4 is an enlarged isometric view of balloon forming
part of the catheter;
Fig. 5 is an enlarged sectional view on line 5-5 of
Fig. 4;
Fig. 6 is a enlarged sectional view on line 6-6 of Fig.
4; and
Fig. 7 is an enlarged sectional view on line 7-7 of
Fig. 4.
As previously discussed, prior art balloon structures
caused deformation of the catheter body as seen in Figs. 1 and
2. The preferred embodiment of the invention is seen in Fig. 3
which shows an angioplasty catheter, designated generally by the
numeral 20, including a flexible main body 22 having a distal
end 24 defining a tapered tip 25 to facilitate insertion into a
vein of a patient, and a proximal end 26 for connection, by
means of junction piece 28, to the respective distal ends of a
25 guide wire tube 30 and a fluid supply tube 32. The tubes 30, 32
are in communication with respective circular guide wire and
fluid supply lumens 34, 36 defined within the main body 22
(Fig.3) and are provided with luer fittings 35, 37 at the
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respective proximal ends.
The body 22 extends from the connection piece 28 to the
tip 24 and passes through a transparent Nylon (trade mark)
balloon 40, details of which are provlded below. A tubular
shipping protector (not shown) for location over the distal end
24 and balloon 40 would normally be provided to protect the
balloon and to retain it in a collapsed condition ready for
insertion.
As seen in Fig. 4, the transparent balloon 40 is shown
inflated and this is achieved by applying fluid pressure to the
lumen 32 (Fig. 1) which is available through an opening 42
adjacent the end of this lumen as will be described. The
opening 42 is inside the balloon which is attached at its ends
46, 48 to the main body 22. Also within the balloon is an
axially collapsable connection piece 47 forming part of the main
body and attached to a distal end of a first part 49 of the body
and to a proximal end of a second or tip portion 46 as will be
more fully described with reference to Fig. 7. Radiopaque bands
50. 53 are applied to the main body as is conventional in the
angioplasty art.
The main body 22 has a constant cross-section over the
majority of its length as shown in Fig. 5 which also shows the
position of opening 42. The main body 22 defines lumens 52, 54
with the lumen 52 being the lumen carrying fluid pressure for
inflating the balloon and the main lumen 54 being available for
Seldinger insertion and extending all the way to the tip 25.
Immediately adjacent to the opening 42 and towards the tip 25,
the portions of the main body 49 and 51 are deformed using heat
and a mandril which is placed in the main lumen 54. The purpose
of this is to seal off the lumen 52 so that it is closed
immediately adjacent the opening 42. Consequently, from the
opening 42 forwardly to the tip 25 there is but the main lumen
54 which extends also through the connection piece 47. The
resulting circular cross-section shown in Fig. 6 receives the
connecion piece as shown in Fig. 7.
Referring now to Fig. 7, the connection piece 47 is
tubular, flexible and thin-walled and bonded at its ends to ends
of the portions 49, 51 which are slightly tapered to assist in
engagement of the piece 47. The body 22 is made initially in
one piece without the connection piece 47 and then cut to form
the two distinct portions 49 and 51 so that the piece 47 can be
engaged. The materials must, of course, be compatable and it is
found that a Nylon (trade mark) material sold under the trade
mark Pebax is suitable for the purpose.
In use, the assembly is of course entered with the
balloon in the collapsed condition and once it has reached the
stenosed portion of the vein, and located by conventional use of
the opaque bands 50, 53, fluid pressure is applied to the lumen
52 (Fig. 5) and, because of the opening 42, this pressure is
applied inside the balloon to inflate it. As mentioned with
reference to the prior art, there is a tendency for the balloon
to expand radially bringing the ends 46, 48 (Fig. 4) of the
balloon towards one another. This can be accommodated by the
connection piece 47 which because of its inherent flexibility
will simply deform so that there is no reaction to this load
created by the balloon. The balloon will then stiffen and
remain in the cylindrical shape shown in Fig. 4. After use, and
if the balloon has stretched, the balloon will nevertheless
collapse back to its essentially original condition, because if
it has shrunk longitudinally, this shrinkage is accommodated in
the piece 47. Consequently the problems demonstrated with
reference to Figs. 1 and 2 are obviated.
The catheter is manufactured by first providing an
extrusion for the body 22 and then, after cutting the body to
form the portions 49, 51 shown in Fig. 4, the connection piece
47 is assembled and bonded in place. The tip 25 is formed
conventionally using a cylindrical internal mandrel and a
tapered external mandrel and the body is attached to the
junction piece 28 shown in Fig. 3 where the tubes 30, 32 are
assembled at the same time. After this is done the hole 42 is
formed into the lumen 52 and the balloon is engaged. Preferably
the integrity of the main body is ensured by using a mandrel in
the lumen 54 while this assembly takes place and then the ends
46, 48 of the balloon are bonded to the main body.
It will be evident that the principles behind the
invention can be reduced to a number of different forms, all
within the scope of the claims.
