U.S. patent number 3,674,014 [Application Number 05/082,620] was granted by the patent office on 1972-07-04 for magnetically guidable catheter-tip and method.
This patent grant is currently assigned to Astra-Meditec AB. Invention is credited to Hans Tillander.
United States Patent |
3,674,014 |
Tillander |
July 4, 1972 |
MAGNETICALLY GUIDABLE CATHETER-TIP AND METHOD
Abstract
A flexible catheter-tip, guidable by a magnetic field into
selected arteries of the body, includes a plurality of permanent
magnetic tubular sections with ball-shaped ends arranged
end-to-end. Each pair of adjacent ends is encased within a tubular
link formed of non-magnetic material which provides a flexible,
fluid-tight seal between the tubular sections. Each ball-shaped end
has formed thereon a bevel to provide stability between adjacent
sections, and therefore to the whole catheter-tip, at full
bend.
Inventors: |
Tillander; Hans (Goteborg,
SW) |
Assignee: |
Astra-Meditec AB (Goteborg,
SW)
|
Family
ID: |
20299505 |
Appl.
No.: |
05/082,620 |
Filed: |
October 21, 1970 |
Foreign Application Priority Data
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Oct 28, 1969 [SW] |
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14694/69 |
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Current U.S.
Class: |
600/434;
604/95.01; 138/155; 600/11; 138/120; 335/306; 604/264 |
Current CPC
Class: |
A61B
1/0055 (20130101); A61M 25/0127 (20130101); A61M
25/0069 (20130101) |
Current International
Class: |
A61B
1/005 (20060101); A61M 25/01 (20060101); A61M
25/00 (20060101); A61m 025/00 (); A61b
005/02 () |
Field of
Search: |
;128/2M,2.5R,4.6-8,33R,348,349R,35R,1.3,1.4,356 ;138/120,155
;355/302,306 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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1,261,276 |
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Feb 1968 |
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DT |
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635,407 |
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Sep 1936 |
|
DD |
|
Primary Examiner: Truluck; Dalton L.
Claims
I claim:
1. A flexible catheter tip, comprising tubular means having means
therethrough defining an axial bore, said tubular means
including:
a plurality of individual permanent magnetic dipoles disposed along
said tubular means with their magnetic axes codirectional and
parallel to said axial bore; and
means forming a flexible fluid-tight connection between said
magnetic dipoles;
whereby said tubular means may be bent in a curve having a
direction and radius of curvature which is controllable by a
controllable magnetic field.
2. The flexible catheter-tip defined in claim 1, wherein:
said individual magnetic dipoles comprise tubular sections having
ball-shaped ends;
said connection means comprises cylindrical tubular links formed of
non-magnetic material encasing adjacent ball-shaped ends and having
substantially the same interior diameter as the exterior diameter
of the ball-shaped ends encased thereby; and
said connection means and said tubular sections together
constituting said tubular means.
3. The flexible catheter-tip defined in claim 2, wherein:
said ball-shaped ends are bevelled on the outer ends thereof to
form blunt conical ends;
said bevel has a base angle with respect to the axis of its section
substantially the same as the maximum designed angular deflection
of said section from the axis of the link in which said ball-end is
encased.
4. A flexible catheter-tip having a front end and rear end,
comprising:
a plurality of permanent magnets disposed with their respective
magnetic axes mutually co-directional;
means through said magnets defining an axial bore communicating
between said front end and said rear end; and
flexible connecting means for forming a flexible fluid-tight
connection between said magnets whereby said axial bore forms a
fluid-tight conduit from one end of said tip to the other.
5. A flexible catheter-tip, comprising:
a plurality of tubular sections formed of permanent magnetic
material and magnetized such that one axial end thereof is a south
magnetic pole and the other axial end is a north magnetic pole;
said sections arranged axially end-to-end with adjacent ends of
opposite magnetic polarity;
means forming an axial bore through each section; and
means for flexibly connecting the adjacent ends of said sections
together and for establishing fluid-tight communication between
said balls.
6. The flexible catheter-tip defined in claim 5, wherein said
connecting means comprises;
a ball-shaped connector formed on the ends of said sections;
a cylindrical tubular link surrounding each pair of adjacent ball
connectors on adjacent sections;
the interior diameter of said link and the exterior diameter of
said connector being substantially identical;
the outer end of said connector being formed with a blunt conical
face; and
the base angle of said conical face being substantially identical
to the maximum angular deflection of said section from the axis of
said link whereby tangential line contact is established between
abutting conical faces of adjacent connectors at maximum bend of
said tip.
7. The flexible catheter-tip defined in claim 6, further
comprising:
an inwardly directed radial flange formed on each end of each
link;
a reduced diameter neck portion joining said ball connector to said
section and defining, at its junction with said connector, a
shoulder;
said flange having a radial extent sufficient to engage said
shoulder regardless of the angular orientation of said section with
respect to said link.
8. The flexible catheter-tip defined in claim 7, wherein:
each neck and its respective section form at their junction a
second shoulder; and
said neck having an axial extent such that, at full angular
deflection of said section with respect to said link, said flange
engages both of said first and said second shoulders.
Description
BACKGROUND OF THE INVENTION
This invention relates to magnetically guidable catheter-tips and,
more particularly, to a catheter-tip for insertion into the
vascular system of a body and guided therethrough by an external
magnetic field to selected vessels or organs.
Recently developed medical procedures require the placement of a
catheter or fine tube into selected vessels or organs within the
body. For example, in the practice of arteriography of the distal
vessels it is necessary to inject a roentgenographic substance into
the selected area before taking the X-ray. In addition, certain
therapeutic techniques require the injection of certain medicines
by way of the vascular system directly into the selected organ.
The placement of the catheter into the selected region of the body
is accomplished usually by opening an artery in the thigh and
inserting the catheter into the artery whence it is fed up through
the artery system to the aorta. No external guidance is required to
this point since the arteries divide away from the heart and the
catheter will be following a path of converging arteries. To
reverse the direction and feed the catheter into the smaller
arteries branching from the aorta, external guidance is required to
direct the catheter into the desired branch.
Previously, a number of different methods have been suggested for
guiding the catheter to the selected artery. One of the earlier
techniques was the so-called pre-bent tip. The tip of the catheter
was biased in a bent configuration, but was held straight by a
removable means such as a guiding thread. When the catheter reached
the desired branch of the vessel, as observed on an X-ray machine,
the guiding thread extending inside the catheter was extracted and
the catheter-tip would bend into the vessel. This procedure was
extremely difficult because the tip would bend only in one plane
and it was necessary to orient the catheter-tip so that the
direction of bending would coincide with the direction of the
branch of the artery. Moreover, the bending could be accomplished
only once and thereafter the catheter-tip would remain bent. This
device is useful for reaching arteries close to the heart, but not
for reaching the distal vessels.
Another technique uses guiding threads which extend from the
catheter-tip along the bore of the catheter and out the end. By
pulling in selected guiding threads the catheter-tip could be bent
in any desired direction. While this technique appears to eliminate
the single plane bending restriction of the first catheter-tip, it
is still extremely difficult, if not impossible, to bend the
catheter-tip in a new direction once having been bent from the
straight configuration. Moreover, it is an awkward and difficult
device to operate with any precision, especially when the catheter
follows a long and/or tortuous path through the vascular
system.
The inventor has previously described an externally guidable
catheter-tip which includes a number of cylindrical tubular
sections, arranged to each other by means of ball-joints, each of
the sections having a ball at one end and a casing at the other.
The sections, which are identically alike, are made of
non-corroding stainless steel having magnetic properties, that is,
capable of being attracted by a magnet. The catheter-tip is
attracted by a magnetic field generated by equipment outside the
body and swings in that direction, thereby enabling the operator to
cause the tip to swing in any desired direction with no limit to
the number of turns the tip may make. This technique constitutes a
great improvement over the prior art, but itself requires
refinement. This catheter-tip will bend only in an arc with a large
radius of curvature and high intensity magnetic field strengths are
required to effect even this much bending. These high intensity
magnetic field strengths require large, heavy, and expensive
magnetic equipment for their generation and control, and they
interfere with the X-ray observation system.
Thus, a need has arisen in the art for a catheter-tip guidable with
great precision from the exterior of the body using low-intensity
magnetic fields to preclude interference with the X-ray observation
system.
SUMMARY OF THE INVENTION
Accordingly, one object of this invention is to provide a
catheter-tip precisely guidable through the vascular system of a
body from the exterior of the body.
Another object of this invention is to provide an externally
guidable catheter-tip which is precisely guided by small and
low-cost support equipment.
Another object of this invention is to provide a catheter-tip which
may be guided through the body's vascular system without
interference with the observation equipment.
A further object of the invention is to provide a small diameter
catheter-tip bendable under the influence of a weak magnetic field
in an arc of small radius of curvature.
A still further object of this invention is to provide an
externally guidable catheter-tip which may be repeatedly bent and
straightened by means of an externally generated, relatively weak
magnetic field and is of sufficiently fine diameter that it can be
directed into the distal vessels.
These and other objects of the present invention are attained by
providing a catheter-tip having a plurality of short permanent
magnets disposed with their magnetic axes parallel and
co-directional and joined together to form a flexible fluid-tight
conduit which will experience a strong moment in the presence of a
magnetic field.
IN THE DRAWINGS
A more complete appreciation of the invention and its many
attendant advantages will develop as the same becomes better
understood by reference to the following detailed description when
read in connection with the accompanying drawings wherein:
FIG. 1 is an enlarged view of the flexible catheter-tip connected
to a catheter;
FIG. 2 is a greatly enlarged sectional view of the front section
and the rear section of the catheter-tip with the central portion
removed;
FIG. 3 is a sectional view similar to FIG. 2 but showing a single
connection between two tubular sections at partial bend; and
FIG. 4 shows an even more greatly enlarged view of a single end of
a tubular section at full bend.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to the drawings wherein like reference characters
designate similar or identical parts and, more particularly, to
FIG. 1, a catheter 1 is shown having a catheter-tube 2 to which is
connected the flexible catheter-tip 3 of the present invention. Tip
3 is a tube formed of a plurality of individual cylindrical tubular
sections 4 connected end-to-end by cylindrical connecting links 5.
The lengths of sections 4 decrease toward the tip end so that each
section is shorter than its rearwardly adjacent neighbor.
Looking now at FIG. 2, an axial bore 6 extends completely through
each section 4 communicating between both ends, each of which is
formed as a ball connector 7 integrally joined to its tubular
section 4 by means of a reduced diameter neck portion 8. The outer
end of the outermost link 4a is conically tapered towards its front
end and provided with rounded edges to facilitate the introduction
into a vessel. The rear section 4b is intended to be screwed onto
the tapered end of a thermoplastic catheter-tube and for this
purpose is provided at its rear end with an enlarged bore 9
internally threaded at 10. The threads 10 will cut matching threads
into the thermoplastic material of catheter 2 thereby forming a
strong and reliable connection between the catheter-tip and the
catheter and, as shown in FIG. 2, providing an almost stepless
connection between the tip 3 and the tube 2. The inner ends of
sections 4a and 4b are provided with ball connections 7 identical
to the ends of the central sections 4.
Tubular sections 4 are made of a permanent magnetic material that
is inert to blood. One alloy found to give excellent results is a
material sold under the trademark Platinax II which consists of 98%
by weight of cobalt and 2 percent by weight of platinum. The
sections are permanently magnetized and arranged end-to-end with
adjacent ends of opposite polarity so that the magnetic vectors at
each section are aligned and co-directional. The sections are
therefore mutually attractive to yield the combined advantages of
an improved fluid seal between the sections and a
self-straightening feature.
To bend the tip into a selected artery, a magnetic field is applied
in the direction the tip is to bend. Each section, flexibly
connected to its neighbor by a connecting link to be described
below, experiences a pure moment which tends to rotate the section
to align its own magnetic field, and its axis, with the externally
applied magnetic field. The plurality of individual moments
experienced by the plurality of magnetic sections combine to bend
the tip in a tight arc. The pure moment experienced by each section
4 is contrasted with the mechanism by which the prior art flexible
catheter-tip is bent. That bending occurs by mere gross attraction
of the metal tip which causes the free tip end to swing in the
direction of the magnetic field while the other end is restrained
by reason of its attachment to the catheter tube. The "pure moment"
experienced by the section 4 of this invention occurs by reason of
the oppositely directed forces acting on the poles of opposite
polarity.
The flexible connection between adjacent sections will now be
described with reference to FIGS. 3 and 4. The link 5 is made of a
non-magnetic stainless steel to minimize the gross attraction of
the tip in a magnetic field, and is formed as a short length of
cylindrical tubing having each end turned radially inward to form a
full circumferential flange 11 at each end. The interior diameter
of link 5 is substantially identical to the exterior diameter of
ball-end 7 of each tubular section 4. A reliable fluid connection
is thereby achieved between the adjacent tubular sections 4 by
means of the constant close-fitting contact between connecting link
5 and ball-end 7 regardless of the angular orientation of tubular
section 4. It will be noted that connecting link 5 can be made
substantially longer than the combined axial length of the two
ball-ends 7 illustrated in FIG. 3. This greater length of
connecting link 5 is for the purpose of providing maximum strength
and minimum diameter of the flexible catheter-tip 3, as will appear
from the following discussion. Consider a single tubular section 4a
subjected to the influence of a magnetic field, externally applied,
for the purpose of bending the catheter-tip 3. The section 4a,
which is a magnetic dipole, will tend to rotate in the magnetic
field to align its own magnetic field with that of the externally
applied one. The moment that is exerted on section 4a can be
considered a pair of equal, but oppositely directed, forces
respectively exerted on the respective ends of the section and is
equal to the product FT, where F is the force exerted on each end
and T is the length of the section. At the designed maximum angular
bend of the catheter-tip, this moment must be resisted by a
counteracting moment exerted by the catheter-tip itself. This
counteracting moment is supplied by connecting links 5 in the form
of a pair of reaction forces R, one of which is exerted
transversely on the ball-end 7 and the other of which is exerted by
the flange 11 of link 5 on the neck 8. The moment arm between these
forces is the short distance S. Thus, the counteracting moment is
equal to RS, which must be equal to the moment FT. The reason for
the extended length of link 5 now becomes apparent: if the link 5
were shorter, the moment arm S would be shorter. To hold the
counter-acting moment RS equal to moment FT it would then be
necessary to increase the magnitude of reaction force R. To exert
the greater force R, the connecting link 5 would have to be
stronger and therefore thicker. The resulting thick link 5 would
result in a catheter-tip thicker than is achieved with the present
invention and of less utility in the narrow distal vessels wherein
the present invention finds particular utility.
Referring now to FIG. 4, connecting link 5 is held centered on the
junction between tubular sections 4 by choosing the length of neck
8 so that, at the designed maximum bend of the catheter-tip, the
shoulder 13 formed at the junction of the neck 8 and the main
tubular body of each section 4 abuts against the flange 11 of link
5.
The ball-end 7 is bevelled on its outer end to form a blunt conical
end, having a base angle .alpha. of from 10.degree. to 12.degree..
The purpose of the bevel at the end is, first, to shorten the
ball-end by removing portions of the ball not needed to effect the
seal with connecting link 5. This enables the ball-end to extend
farther into connecting link 5, thereby extending the moment arm S
by that amount. The base angle .alpha. is selected to coincide with
the angle of the designed maximum bend between the section axis and
the link axis. Thus, at maximum angular displacement, the outside
face of ball-end 7 will, along one chord, be perpendicular to the
axis of tubular link 5. Since the facing ball-end 7 of the adjacent
tubular section 4 is identically bevelled, the facing surfaces of
the two ball-ends will, along one chord, be in full tangential line
contact. Tangential line contact between ball-ends 7 contributes
significant stability to the flexible catheter-tip at its
configuration of maximum angular deflection. It will be noted that
the angle .beta. subtended by the arc of radius r constituting the
spherical portion of the ball-end is approximately 20.degree. to
24.degree.. This coincides with the full angular swing which the
section will experience from one to the opposite maximum
deflection. It also coincides with the angle between two adjacent
sections at full bend. It may be advisable to increase angle .beta.
a few degrees to provide assurance of fluid integrity since some
tolerance must be designed into the dimensional parameters of the
link 5 and ball-end 7.
The optimum dimensional parameters of the ball connector 7 and
flange 11 to achieve maximum angular displacement with minimum ball
thickness, while assuring a secure fluid seal, are given by the
following conditions: the base angle .alpha. of the ball-end bevel
equals the maximum angular deflection of the tubular section from
the axis of link 5; the diameter D extending from the outside
corner 14 of the ball to the inside corner 15 is, at full bend,
perpendicular to the link axis; the radial dimension of the flange
is such that at full bend one side of the flange touches the neck
portion 8 and the diametrically opposite side touches the inside
corner 16 of the ball 7 diametrically opposite the inside corner
15; and the length n of neck 8 is such that shoulder 13 abuts
against the outside circumferential edge of link 5 at full bend.
Given these conditions, selection of r and .alpha. determines the
magnitude of the dimensional parameters c, d, f, n and s, where c
is the length of the chord of the arc subtending angle .beta., d is
the diameter of neck 8, and f and s are the radial lengths of
flange f and shoulder 17 respectively. The relationships which may
readily be determined by elementary trigonometry, are as
follows:
c = 2r sin.alpha. s = 2f = 4r sin.sup.2 .alpha. d = 2r (cos.alpha.
- 8sin.sup.2 .alpha.) n = 2r sin.alpha. cos.sup.2 .alpha.
This arrangement theoretically, produces the shortest links, the
thinnest ball-ends and the maximum stability and strength for the
flexible tip for a given ball radius and angle .alpha.. In actual
physical embodiments, however, it is necessary to account for the
tolerance that must be built into every manufactured article, as is
well known to those skilled in the art.
The dimensions of the above-described illustrative embodiment of
the invention are as follows: the outside diameter of sections 4 is
about 2.1 mm and their lengths vary from about 6 mm for section 4b
to about 3 mm for section 4a. The inside diameter of the bore 6 is
about 0.6 mm.
The connecting links 5 are all identical, having a diameter of
about 2.1 mm and a length of about 2.2 mm. The links and sections
may be connected by introducing ball-end 7 into the cylindrical
link and then rolling the ends of the links to form the inwardly
turned flange 11.
Naturally, other configurations are possible and expressly
contemplated by this invention. In particular, as noted previously,
the greater the length of link 5, the stronger a resisting moment
may be applied for a given thickness of link material, and the
shorter the flange 11 and the longer the chord c, the greater is
the maximum possible turning angle. With the foregoing description,
it should be within the competence of one skilled in the art to
modify the dimensions of the length and thickness of the link and
its flange, and the parameters of the ball-end 7 and neck 8 to
achieve whatever design specifications are desired. Moreover, it is
possible to design the arc described by the tip by varying the
lengths of sections 4. Thus a circular arc can be achieved by
making all sections 4 of equal length; a parabolic or hyperbolic
arc is achieved by selectively decreasing the length of sections 4
toward the tip end.
Certain alternative connecting means are contemplated for use in
place of the cylindrical stainless steel link 5. For example, it is
contemplated that a short length of flexible plastic-tubing may be
connected between adjacent tubular sections 4 as by heat shrinking
or other technique.
Another embodiment contemplated substitutes for the magnetic
tubular sections and non-magnetic connecting links, a flexible tube
of non-magnetic material such as plastic, and embedded in the walls
of the tube a multiplicity of small magnetic dipoles arranged with
their axes parallel to the tube axis and co-directional, that is,
with like poles all facing the same direction. This arrangement
will permit somewhat greater design flexibility since the shape and
number of the small magnetic magnets can be varied within wide
ranges. For example, it may be desired to use a small number of
thick magnets, slightly narrower than the thickness of the tube
wall, or a multiplicity of fine magnetized wires thinner than a
hair. It is thus possible to select the design for optimum
manufacturing ease and, at the same time, achieve whatever turning
radius and catheter diameter may be desired. It is, therefore, to
be understood that the invention may be practiced otherwise than
specifically described in the foregoing illustrative example while
remaining within the scope of the invention which is claimed as
follows.
* * * * *