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Description  |
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BACKGROUND OF INVENTION
I. Field of the Invention
This invention relates generally catheter structures adapted to be
introduced into a living body, and more specifically to the design of a
catheter which may be introduced and routed through the vascular system of
a patient with a minimum of damage or trauma to endothelial tissue.
II. Discussion of the Prior Art
Present day surgical procedures permit the introduction of tubular
catheters into the vascular system of a body. For example, angiographic
catheters are commonly introduced into the femoral artery and routed
through the arterial system and to the coronary ostium so that radiopaque
contrast or medicaments may be injected as part of a diagnostic or
treatment procedure. Typically, such catheters comprise elongated,
flexible plastic tubes of a predetermined small diameter significantly
less than the cross section of the vessels through which the catheter must
pass. Other forms of catheters which the present invention may find use
are those associated with cardiac pacemakers. Here, the catheter takes the
form of a pacing lead which is typically made to pass through the
subclavian vein and through the superior vena cava into the right
ventrical of the heart. Here, the catheter takes the form of a flexible
sheath surrounding elongated conductors which terminate at the distal end
in one or more surface electrodes adapted to contact endocardial heart
tissue.
Prior art, angiographic and other diagnostic catheters as well as cardiac
pacing leads are generally formed from polyethylene, polyurethane,
polypropylene or silicone rubber or other non-thrombogenic material. So
that they may be passed through the vascular system without folding or
buckling, they must possess a wall thickness and a hardness which is
capable of damaging vascular tissue, especially where the distal tip of
the catheter is blunt or possessed of a sharp edge. While perhaps rare,
there have been instances where small diameter catheters having sharp
edged tips have been advanced through the wall of the aorta, resulting in
the death of the patient.
SUMMARY OF THE INVENTION
The present invention obviates the above-described problems inherent in
certain prior art catheters through the inclusion of a soft, deformable
member attached to the distal tip of the catheter. In one embodiment, the
deformable tip member comprises an annular inflatable flexible,
non-distensible "balloon" element attached to the distal end of the
otherwise relatively rigid tip of the catheter. In this arrangement, the
catheter itself is provided with a lumen extending substantially the
entire length of the catheter and communicating with the deformable tip
member whereby a fluid may be introduced to control the size, shape and
firmness of the tip portion of the catheter. By selectively inflating the
balloon tip, the effective area of the tip can be increased to reduce the
overall force per unit area at the point of contact between the tip of the
catheter and a blood vessel.
In a second embodiment, the soft deformable tip member comprises an annular
plastic or rubber sleeve surrounding the otherwise rigid tip of the
catheter and normally extending therebeyond by a predetermined distance.
The thickness or composition of the sleeve is altered about a
circumferential line so as to provide a preferred location for the folding
and collapse of the sleeve as the terminal end of the sleeve is forced
against body tissues. When the sleeve is made to collapse, the effective
area of contact between the deformable tip and the body tissue increases
to again reduce the pressure or force per unit area applied to the tissue.
OBJECTS
It is accordingly a principal object of the present invention to provide a
new and improved catheter arrangement for medical applications.
Another object of the invention is to provide a catheter with a soft,
deformable tip to thereby reduce the likelihood of damage to vascular
tissue as the catheter is introduced and routed through the vascular
system.
A still further object of the invention is to provide a catheter with an
inflatable tip member whereby the shape and firmness of the distal end of
the catheter can be controlled through the introduction of a fluid at the
proximal end of the catheter.
Yet another object of the invention is to provide a catheter with a soft,
deformable tip in the form of a sleeve member of a predetermined wall
thickness profile such that the deformable tip member will collapse in a
predictable manner to effectively increase the overall area of contact
between the distal tip and body tissue which it contacts.
These and other objects and advantages of the invention will become
apparent to those skilled in the art from the following detailed
description of the preferred embodiments, especially when considered in
conjunction with the accompanying drawings in which like numerals in the
several views referred to corresponding parts.
DESCRIPTION OF THE DRAWINGS
FIG. 1 shows the distal tip portion of a conventional, prior art
angiographic or diagnostic catheter;
FIG. 2 is a cross sectional view of a catheter having an inflatable tip
secured thereto;
FIG. 3 is a cross sectional view of a catheter having an inflatable,
non-distensible tip and an elastomeric band or sleeve in fluid
communication therewith;
FIG. 4 is a cross sectional view of an angiographic catheter having a
collapsable sleeve as its distal tip, the sleeve being illustrated in its
uncompressed state;
FIG. 5 is a partial cross sectional view of FIG. 4 illustrating the sleeve
in its collapsed state; and
FIG. 6 is a partial cross sectional view of an alternative arrangement of a
deformable tip on a catheter.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring first to FIG. 1, there is illustrated a longitudinal cross
section of the distal end portion of a typical, prior art angiographic
catheter. It is seen as comprising a predetermined length of flexible
plastic tubing 10 having a central lumen 11 extending the length of the
catheter thereof from its proximal end (not shown) to its distal end 12.
The lumen 11 is provided so that angiographic dyes or other medicaments
may be introduced into the catheter at its promixal end located outside
the body and made to flow through the lumen to a predetermined site within
the body at which the distal end 12 of the catheter is positioned.
It is to be especially noted that the distal tip 12 of the prior art
catheter of FIG. 1 terminates in an abrupt edge 13 which is relatively
sharp and, depending upon the type of material used for the body of the
catheter 10 may possess sufficient rigidity to cause damage to vascular
tissue, especially the endotheliel layer (tunica intima) lining the blood
vessels as the catheter is routed through the vascular system.
To obviate this problem, in accordance with a first embodiment of the
invention illustrated in FIG. 2, the catheter body 10 is provided with a
double lumen, namely the lumen 11 for allowing the flow of angiographic
dyes or other fluids and a further lumen 14 which also runs the entire
length of the catheter. Secured to the distal tip of the catheter body is
a flexible, non-distensible inflatable "balloon" member 15 which, in its
expanded form, has the general shape of a toroid. The lumen 14 is arranged
to communicate with the interior of the torus comprising the tip 15 while
the lumen 11 communicates with the central opening 17 of that toroid.
While fluid introduced into the lumen 11 at the proximal end of the
catheter may ultimately be made to flow outwardly through the opening 17
of the soft, flexible tip 15, fluid introduced into the lumen 14 flows
into the annular chamber 16 causing the tip member to become inflated. The
tip member 15 is preferably formed from a bioaxially oriented or
cross-linked polyolefin film and may have a thickness in the range of from
0.001 to 0.0025 inches. As such, when unflated or evacuated, it lacks
rigidity and wraps about and conforms approximately to the shape of the
end portion of the catheter body 10. However, once properly pressurized,
it expands so as to increase the desired effective area of contact between
the end of the catheter and and body tissue which it may abut as it is
being routed or positioned within the body. The degree of inflation, of
course, determines the degree of softness or deformability of the tip.
Thus, the physician has considerable control over the tip properties of
the catheter so that tissue damage will be minimized.
The toroidal balloon member 15 is preferably molded separate and apart from
the catheter body 10 and then affixed thereto by thermal or chemical
bonding but may be a cavity formed in the walls of the distal end of the
catheter which, when filled with a fluid under pressure, causes the wall
of the catheter itself to bulge.
FIG. 3 illustrates an alternative form of the embodiment of FIG. 2 which
has been modified to incorporate a distensible elastomeric sleeve 18 for
controlling the internal pressure of the non-extensible tip member 15. The
distensible elastomeric sleeve 18 may be positioned at any point along the
length of the catheter body 10 and, in fact, may be disposed at the
extreme proximal end of the catheter at a location which remain outside of
the body following its insertion in routing. The elastomeric sleeve is
preferably disposed within a ring-like recess formed in the outside
surface of the catheter body 10 and is suitably bonded in a fluid-tight
fashion to the catheter body at its end edges thereof as indicated by
numerals 19 and 20, respectively. A radial bore 21 extends from the recess
surface of the catheter body to the secondary lumen 14. The radial bore
21, as well as the portion of the lumen 14 distally thereof, and the
chamber 16 of the deformable tip 15 are filled with an incompressible
fluid, and a suitable plug 22 is disposed within the lumen 14 at a point
proximal of the radial bore 21.
When a force is applied to the tip member 15 in FIG. 3, the internal
pressure of this tip member is increased causing bulging (inflation) of
the elastomeric sleeve member 18 and a corresponding deflation of the tip
member 15. The degree of deflation is, of course, proportional to the
force exerted on it which, in turn, is a function of the "stiffness" of
the elastomeric sleeve 18. A decrease in the volume in the tip member
results in an increase in the area of contact between it and any mating
surface against which it is forced.
When the sleeve 18 is located at a point external to the body, it may be
suitably coupled to a transducer which will directly indicate the fluid
pressure within the system causing it to expand.
With continued attention being directed to the tip member 15 in FIG. 3, it
has been found expedient to incorporate a heavier toroidal ring as at 23
to define the annular opening 17. This ring has an outside diameter which
is no greater than the internal diameter of any introducer through which
the catheter must be passed during implantation. Using this construction,
the tip member 15 will conform to a lumen smaller than the fully extended
diameter of the tip member 15 because, as the force bearing on the wall
increases, the internal pressure in the tip member will decrease due to
the expansion of the elastomeric sleeve 18.
In practice, the lumen 14 may have a diameter in the range of from 0.002
inches to 0.004 inches extending from the tip member 15 through and
including the radial side port 21. The lumen 14 may be continued to the
proximal end of the catheter where the elastomeric sleeve 18 and its
included side port 21 may be disposed.
As with the embodiment of FIG. 2, the tip member 15 is preferably formed
from a non-extensible polyolefin film and may have a thickness range from
0.001 inch to 0.0025 inch. These dimensions and materials are set forth
herein for illustrative purposes only and should not be considered as
necessarily limiting the scope of the invention.
Referring next to FIG. 4, there is shown an alternative preferred
embodiment of a catheter having a soft, deformable distal tip member
affixed thereto. As viewed in FIG. 4, this tip member comprises a tubular
sleeve 24 which surrounds and fits by means of a lap joint at the distal
end of the catheter body 10 and the sleeve 24 extends beyond the distal
end thereof by a predetermined length. Rather than being of a constant
thickness, the walls of the flexible plastic sleeve 24 are shaped so that
when the extreme tip or end 25 thereof is pushed against a stationary
object with a predetermined low force, the tip will collapse to yield the
configuration shown in FIG. 5. More specifically, the wall thickness of
the portion of the tip member 24 extending beyond the end of the catheter
10 is generally constant but at the location identified by numeral 27 is
relieved about an annular line, i.e., made to be of a lesser thickness, so
as to fold about that circumferential line as a hinge. Likewise, the soft,
compressible tip member 24 folds along the outside periphery of the end of
the catheter as at 28 like a hinge. Instead of reducing the sleeve wall
thickness to create a preferential hinge or fold line, it is also possible
to achieve the desired folding pattern by having a discontinuity in the
sleeve material so as to have a different (lower) stiffness than the
adjacent material.
By properly choosing the durometer of the plastic material comprising the
soft collapsible tip 24, it will posses a "memory" property so that when
the tip is no longer compressed against a stationary object, it will again
snap back to the shape illustrated in FIG. 4. It has also been found
expedient to increase the amount of material surrounding the central
opening 29 in the tip as at 30. This increase in material defines a ring
which stablizes and strengthens the opening preventing it from sagging.
With reference to FIG. 5, it can be seen that when the tip member
collapses, the effective area of contact between it and the object against
which it is pressed is increased to thereby decrease the effective
pressure exerted by the catheter structure against that tissue.
With no limitation intended and for illustrative purposes only, the lumen
of the catheter may have a diameter of 0.045 inches and a wall thickness
of 0.0085 inches at its distal end. The soft tip member 24 in FIGS. 4 and
5 is preferably about 0.005 inches thick but reducing to about 0.004
inches thick about the circular hinge line 27. When in its undeformed
state, the distal end may exhibit a cross-sectional area of about 0.0012
square inches and, when collapsed as in FIG. 5, an area of 0.0041 square
inches, representing a 3.41 times increase in area.
FIG. 6 illustrates a still further embodiment in which the catheter is
fitted at its distal end with a tubular cylindrical tip member 31
fabricated from silastic or some other soft, deformable plastic material.
When forces against an obstacle, the soft plastic tip will deform by
spreading and bending to present an increased area of contact with respect
to this obstacle.
The invention has been described herein in considerable detail, in order to
comply with the Patent Statutes and to provide those skilled in the art
with information needed to apply the novel principles, and to construct
and use such specialized components as are required. However, it is to be
understood that the invention can be carried out by specifically different
equipment and devices, and at various modifications, both as to equipment
details and operating procedures can be effected without departing from
the scope of the invention itself.
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