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CROSS REFERENCE TO RELATED APPLICATIONS
This is a division and a continuation-in-part of application Ser. No.
098,097, filed Sept. 17, 1987, now U.S. Pat. No. 4,784,638.
TECHNICAL FIELD
The present invention relates to an apparatus for making a ventricular
catheter having specifically angled apertures which facilitate access to
or drainage of cerebral spinal fluid.
BACKGROUND OF THE INVENTION
The four ventricles of the human brain are interconnected cavities that
produce and circulate cerebral spinal fluid (CSF). Procedures involving
ventriculostomy, i.e., placement of a catheter into the ventricular system
of the brain, form a major part of a neurosurgeon's clinical practice.
General areas of application of ventricular catheter placement include
intracranial pressure monitoring (ICP), draining or shunting of CSF and
the installation of pharmacological therapeutic agents.
CSF drainage is essential for patients with congenital or acquired
hydrocephalus. CSF drainage, which can only be performed with an
intraventricular catheter, is a life-preserving procedure, because it can
immediately reduce intracranial pressure. The ventricular catheter, used
to drain CSF, is connected to a peripheral subcutaneous drainage system,
i.e., to the peritoneal cavity or systemic circulation via the heart or in
the case of ICP to an external drainage collection system. Standard
procedures for ventricular catheterization are disclosed in the textbook
literature. See, for example, Neurosurgery, edited by Robert H. Wilkins
and Setti S. Rengachary, Section A, Chapter 13, Techniques of Ventricular
Puncture (McGraw Hill 1984).
The most frequently chosen site for ventricular catheterization is coronal.
In most cases, a catheter is inserted in the anterior horn of the lateral
ventricle through an orifice or burr hole drilled just anterior to the
coronal suture in the midpupillary line of the cranium, i.e., in the
frontal bone over the ventricle. The burr hole, only slightly larger than
the diameter of the selected catheter to insure a snug fit and provide a
seal against CSF leakage, is placed approximately 1 cm anterior to the
coronal suture, approximately 10 to 12 cm above the nasion, and
approximately 2 to 3 cm from the midline over the nondominant hemisphere.
After the burr hole is made, the dura and underlying piaarachnoid are
opened and coagulated, for example, with a fine-tipped blade after
cauterizing the dural surface.
The lateral ventricles of the human brain form an arc parallel to the arc
of the cranium, i.e., the contour of the lateral ventricles parallels the
arc of the surface of the skull. Thus, a catheter guided perpendicular to
the cranial surface at the point of entry into the cranium will enter the
ventricular system. Specifically, any line penetrating a burr hole in the
surface of the skull at a 90.degree. angle also bisects the lateral
ventricle.
A more recently developed procedure to ensure correct catheter placement is
disclosed in U.S. Pat. No. 4,613,324. The apparatus comprises a guide
assembly which, when positioned over an orifice drilled in the cranium
above the anterior horn of the lateral ventricle, guides a catheter and
obturator through the orifice and into the lateral ventricle at an angle
normal to an imaginary plane formed by a tangent to the cranium at the
orifice, while the corresponding method comprises providing an orifice in
the cranium just anterior to a coronal suture in a midpupillary line of
the cranium and inserting a ventricular catheter containing an obturator
through the orifice towards a lateral ventricle, wherein the catheter
containing the obturator is guided through the orifice, by means of a
novel guide assembly, at an angle normal to an imaginary plane formed by a
tangent to the cranium at the orifice.
A wide variety of catheters are known in the prior art for the purpose of
penetrating the ventricular cavity. Such catheters are typically in the
form of a hollow tube which is provided with a plurality of apertures at
the ventricular or inflow end to permit the passage of CSF from the brain
into the catheter and thence to the bloodstream or peritoneal cavity of
the patient or to an external drainage system. However, malfunctions
frequently occur with such a catheter due to the blockage of the apertures
in the inflow end of the catheter. Such blockage is usually caused by the
growth of choroid plexus or ependymal tissue within the ventricle into the
apertures in the inflow end of the catheter. This tissue may block the
apertures in the inflow end of the catheter in a relatively short period
of time after the catheter has been inserted into the ventricle thereby
rendering the catheter inoperative in relieving excess pressure due to the
build-up of CSF within the ventricle. Furthermore, prior art catheter
apertures are cut perpendicular to the length of the catheter, thus
causing abrasion of brain tissue when the catheter is inserted.
The likelihood of ventricular catheter malfunction by aperture plugging
with brain tissue can be lessened by angling the aperture holes in the
wall of the catheter such that there is "no see through" flow from the
outside to the inside of the lumen. Also, by positioning the rows of
apertures 120.degree. apart there is essentially no chance for direct
ingrowth of ventricular tissue therethrough. In addition, the apertures
are angled away from the direction of the insertion of the catheter into
the brain thus lessening the chance of brain abrasion. Further, by
slightly stretching the catheter by means of the stylet (which is integral
to the catheter and used for placement of it into the brain) the holes
will close so that no opening will be visible during the placement
thereof, with the holes reopening after the tension on the catheter is
relieved by removal of the stylet.
As such, it would be desirable to provide a catheter which overcomes the
problems of previously devised ventricular catheters which are emplaceable
within a ventricle of a human brain to control the flow of excess fluids
to or from the brain. The present invention provides a simple solution
which resolves the problems of prior art catheters in a novel and
unexpected manner.
SUMMARY OF THE INVENTION
The present invention relates to an apparatus for making catheters having a
plurality of angled holes in a flexible, elongated body. Generally, such
catheters are hollow elongated members having a plurality of apertures
near one end. One embodiment of this apparatus comprises an insert and a
molding assembly. The insert includes rod means for forming the plurality
of apertures of a predetermined size and shape and means for forming and
supporting the bore of the elongated member: the rod means being
positioned at a predetermined orientation with respect to the bore forming
means so that the hollow elongated member receives a plurality of
apertures at a predetermined position, orientation and dimension.
The molding assembly includes means for forming and supporting the hollow
elongated member, a plurality of guide holes in the forming means for at
least partially receiving the rod means to properly orient the insert
therein, and means for allowing a polymerizable liquid to be introduced
into the space between the insert and the molding assembly to form the
catheter by polymerization therein. Preferably, the rod means and bore
forming means of the insert are integral and made of a material which is
capable of withstanding temperatures caused by polymerization of the
polymerizable liquid.
Generally, the forming and supporting means is constructed in the form of a
hollow elongated cylinder having an open end and a closed end wherein the
insert is introduced into the open end in a manner such that the rod means
extends into a respective guide hole in the cylinder. These rod means and
corresponding cylinder holes can be oriented in a spiral configuration
around the circumference of the bore forming means or at predetermined
stepped intervals along the length of the bore forming means.
The invention also contemplates an apparatus for making a hollow elongated
member having a plurality of apertures therein which comprises a cutting
assembly having means for cutting a plurality of apertures of a
predetermined size, and a holding assembly. The holding assembly includes
means for supporting and substantially completely surrounding a portion of
a hollow elongated member in the vicinity where apertures are to be made;
means adjacent the supporting means for guidably directing the cutting
assembly through the supporting means for cutting contact with the hollow
elongated member at a predetermined angle thereto; and means operatively
associated with the directing and supporting means for positioning the
portion of the hollow elongated member at a predetermined orientation with
respect to the cutting assembly so that the hollow elongated member can be
placed into the holding assembly in a manner to receive a plurality of
apertures therein at a predetermined position, orientation and dimension.
The holding assembly preferably comprises a holding block containing an
elongated aperture of a size and dimension slightly larger than that of
the hollow elongated member so that the member can be easily and removably
inserted into the elongated aperture, while the cutting assembly comprises
a plurality of elongated rods. The directing means correspondingly
comprises a plurality of elongated guide apertures corresponding to the
rods of the cutting apparatus but being of slightly greater size and
dimension so as to allow the rods to easily and removably pass
therethrough for cutting the apertures in the hollow elongated member.
The positioning means includes a stop member for prevention of insertion of
an end of the hollow elongated member beyond a predetermined point in the
elongated aperture of the holding block, which is advantageously in the
shape of a cube with the elongated aperture extending along a diagonal
line passing through the center of the cube.
In the most preferred construction, the directing means comprises three
sets of elongated apertures, each set being spaced from the others so that
the hollow elongated member is provided with rows of apertures spaced
120.degree. apart along its outer periphery. Thus, each of the sets of
elongated apertures of the directing means would extend along a diagonal
line across a face of the holding block cube to achieve this result.
BRIEF DESCRIPTION OF THE DRAWINGS
Preferred embodiments of the invention are described hereinbelow with
reference to the drawing figures wherein:
FIG. 1 is a perspective view of a catheter according to the invention;
FIG. 2 is a cross-sectional view taken along line 2--2 of FIG. 1;
FIG. 3 is a cross-sectional view taken along line 3--3 of FIG. 1;
FIG. 4 is a perspective view of an apparatus for holding the catheter,
during the cutting of apertures therein;
FIG. 5 is a top view of the apparatus of FIG. 4;
FIG. 6 is a section taken along lines 6--6 of FIG. 5 over which is shown,
an apparatus for cutting apertures in the catheter;
FIG. 7 is an enlarged view of the cutting apparatus piercing the catheter
sidewall when the catheter is placed in the holding apparatus of FIG. 4;
FIG. 8 is a perspective view of a symmetric molding insert according to the
invention;
FIG. 9 is a perspective view of a spiral molding insert according to, the
invention;
FIG. 10 is a cross sectional view of a mold housing for use with the insert
of FIG. 8;
FIG. 11 is a cross sectional view of a mold housing for use with the insert
of FIG. 9;
FIG. 12 is a cross sectional view of the mold of FIG. 10 taken along lines
12--12 thereof; and
FIG. 13 is a cross sectional view of the mold of FIG. 11 taken along lines
13--13 thereof.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring initially to FIG. 1 there is illustrated catheter 10 which is
intended for insertion into a ventricle of the human brain for access to
or drainage of CSF such as; for example, would be necessary to drain
excess CSF during treatment of hydrocephalus. Since the present invention
is primarily concerned with the forward or insertion end of the catheter,
a detailed description of the opposite or out flow end of the catheter is
not provided as such details are well known in the relevant surgical art.
This catheter 10 is a flexible, hollow, elongated member having a
sufficient wall thickness for the containment and or transport of fluids
therein and therethrough. The forward end 12 of the catheter includes a
plurality of apertures 14 for access to CSF in the ventricle of the brain.
By "access" what is meant is contact of CSF for removal or drainage from
the brain or, conversely, to enable medicaments or other fluids to be
directed or delivered into the brain from the catheter through the
apertures 14. These apertures 14 are positioned and configured in a
predetermined manner so as to allow for a better and more continuous flow
of fluids in and through the catheter with less chance of plugging the
holes due to ingrowth of a brain tissue when the catheter is placed in the
ventricle. Further, the design of the holes enables the catheter placement
to be made in an improved, easier manner while causing less abrasion
damage to tissue during insertion of the catheter.
As shown in FIGS. 2 and 3, the catheter 10 is designed with 3 sets of holes
set 120.degree. apart. These holes are cut at an angle into the wall of
the catheter such that the angle of the cut is measured along the
longitudinal axis of the catheter in the direction of movement of the
catheter when it is inserted into the ventricle. Further, the diameter of
each hole in the catheter is proportional to the thickness of the catheter
wall so that, as best illustrated in FIG. 3, there is no direct linear
visual access to the interior of the catheter when the holes are viewed
perpendicular to the longitudinal axis of the catheter.
By preparing the holes in this manner, abrasion of brain tissue is
minimized upon insertion of the catheter into the ventricle, so less brain
tissue is destroyed as a direct result of such decreased abrasion.
Further, by stretching the catheter slightly, the holes in the catheter
are closed thus preventing such tissue as may come in contact with the
catheter from entering the lumen upon insertion. The stretching of the
catheter can easily be accomplished when a rigid placement stylet is used:
the body of the catheter being slightly pulled back from the insertion end
while the stylet is held, thus allowing the holes to be somewhat
flattened. This lack of direct access to the inside of the catheter
prevents the growth of brain cells or tissue therein, thus resolving one
of the major causes of plugging and malfunction of prior art catheters
which utilize 90.degree. or perpendicular apertures. The 120.degree.
peripheral offset for each set of holes further minimizes the possibility
that choroid plexus or brain cell growth will extend across the inner
diameter of the catheter even if such growth does penetrate into one or
more of the holes.
Although the holes are advantageously shown as being cut at an angle of
35.degree. with respect to the longitudinal axis of the catheter, it is to
be noted that other angles can also be used in this invention provided
that direct access to the inside of the catheter is prevented. These other
angles would be somewhat dependent upon wall thickness of the catheter,
since heavier wall thicknesses would allow a greater range of angles while
still preventing direct access into the catheter interior. Suitable angles
for any specific catheter construction can be determined from the
relationship d tan .theta.=t, where d is the diameter of the aperture, t
is the wall thickness of the catheter, and .theta. is the angle between
the cut of the aperture and the longitudinal axis of the catheter body. As
shown by the relationship of these variables, the diameter of the aperture
must be less than or equal to the wall thickness of the catheter divided
by the tangent of the angle. To calculate suitable angles for any
particular aperture size and catheter wall thickness, the formula would be
##EQU1##
so that the cosine of the angle, is greater than the quotient of the
diameter divided by the thickness.
To assist in the understanding of the invention, direct access is avoided
when the diameter of the hole on the outside wall of the catheter does not
overlap the diameter of the hole on the inner wall catheter when viewed in
a line perpendicular to the wall of the catheter. Thus, it is possible to
utilize angles other than 35.degree. although 35.degree. has been found to
be particularly advantageous.
By placing the holes to avoid direct access to the inside of the catheter,
it is possible to cut the holes larger in diameter than they would be if
direct access was provided without weakening the structural integrity of
the catheter. These larger holes allow for an increased flow of CSF into
the catheter while also making it more difficult for any possible brain
cell growth to plug the entire hole, compared to the relatively smaller
diameter holes of prior art catheters which provide direct access into the
body of the catheter.
The catheter of the invention can be inserted into the ventricle of the
brain in any manner currently known, including "freehand" or with the use
of a guide. To assist in the proper location and placement of the
catheter, a plurality of markings 16 are provided along the length of the
catheter body. These markings correspond to predetermined insertion
lengths of the catheter and enables the surgeon to know precisely how far
the tip of catheter is inserted into the ventricle. By making these
markings of a radioopaque material such as barium, the depth of placement
of the catheter can easily be monitored by conventional techniques.
Furthermore, if desired, the forward section of the catheter in the area
around the apertures can also be made of a radioopaque material for
viewing on various scanning equipment the precise placement of the forward
end and tip of the catheter.
The improvements provided by the catheter of this invention are significant
in that the physician does not require any guess work to determine the
precise placement of the catheter in the patient's brain. Furthermore,
when so placed, the catheter provides improved fluid delivery and/or
removal with minimal disturbance of the surrounding brain cells while also
discouraging brain tissue growth into the catheter apertures. As mentioned
above, the catheter can be inserted in the brain in any manner commonly
utilized. Rather than a "free hand" technique, it is advantageous to
utilize a guide assembly to insure correct catheter placement.
A preferred guide apparatus and method of insertion of a catheter into the
ventricle is disclosed in U.S. Pat. No. 4,613,324, the disclosure of which
is expressly incorporated herein by reference thereto. As shown in the
patent, a stylet is used to assist in the insertion of the catheter. As
noted above, the stylet can be used to stretch the present catheters so
that the angled apertures can be flattened to minimize the abrasion of
brain tissue during insertion. Also, this flattening operation slightly
reduces the overall diameter of the catheter which further reduces such
abrasion.
It is known for certain applications to utilize a second stylet for guiding
the catheter into the ventricle. In prior art catheters, this second
stylet is inserted into one of the apertures at the forward end of the
catheter. Since those apertures are cut at 90.degree., an unwieldy
assembly is created. Any attempt to align the second stylet parallel to
and adjacent the first stylet and catheter causes the tip to be somewhat
bent, thus causing further difficulties in its insertion and penetration
of the ventricle. The present invention significantly reduces and
minimizes this problem since the angled holes are more receptive to the
introduction of the second stylet in a compact orientation (i.e., in a "V"
shape, rather than an "L" shape) which greatly enhances the manipulation
of the catheter and stylets during placement in the ventricle.
The catheters of the invention can be easily manufactured in a highly
accurate and reproducible manner by utilizing the apparatus of the
invention. In one embodiment, the apparatus includes a holding block with
rod-like cutting elements, while an alternate embodiment relates to an
apparatus for molding these catheters in the desired shape, form and
configuration.
FIGS. 4 and 5 illustrate a holding apparatus 20 in the form of a machined
metal block or cube 22. A longitudinal extending aperture 24 extends
diagonally from one corner of the cube through the center to the opposite
corner. The closed end 26 of the aperture 24 is within the confines of the
cube and serves as a positioning means or stop member for the hollow
elongated member. The diameter of the aperture 24 is only slightly greater
than the diameter of the catheter 10 so that the catheter is fully
supported in the aperture when the angled holes are made in the catheter
wall.
FIG. 6 illustrates a cutting apparatus 30 consisting of a handle 32 and a
plurality of hollow tube cutting elements 34 each of which have a
sharpened tip 36. The tube elements 34 extend through guide apertures 28
on one face of the cube 22 until contact is made with the catheter 10. As
best illustrated in FIG. 7, the cutting tubes 34 penetrate the catheter
wall, thus forming the appropriately sized holes therein at the
predetermined angle, position and configuration.
Prior art catheters, as noted above, have four sets of holes oriented
90.degree. apart along the circumference of the catheter. In addition to
weakening the strength and structural integrity of the catheter in the tip
area, holes on opposite sides of the catheter (i.e., those 180.degree.
apart) are made simultaneously by a punching tool. This results in holes
on one side being larger in diameter than those on the opposite side.
Therefore, two sets of holes are large and two are small. This
non-uniformity affects CSF flow and the smaller holes can easily become
blocked by brain tissue growth, thus causing reduced operation of those
catheters.
The present invention resolves these problems by accurately and precisely
placing three sets of uniform holes cut at the desired angle to the
catheter body and spaced apart exactly by 120.degree.. This results in
increased flow through the holes, higher strength and integrity of the
catheter body, and greater ease of insertion and placement of the catheter
in the ventricle.
FIGS. 4 through 6 illustrate the placement of guide apertures 28 on the
various faces of the cube. In a most preferred arrangement, these guides
are positioned in a diagonal line along the top and two side faces of the
cube 22, so that each set of holes is placed 120.degree. apart around the
periphery or circumference of the catheter body. As noted previously, it
is highly advantageous to make the holes in the catheter 10 at an angle of
35.degree. with respect to the longitudinal axis of the catheter.
This apparatus guarantees the accuracy of the hole cutting at the
appropriate angle as well as the precise spacing of the holes relative to
each other around the periphery or circumference of the catheter. To cut
the holes, the user merely inserts the tubes 34 of cutting apparatus 30
into the guides 28 when a catheter is placed in the holding block 20. The
cutting apparatus 30 after piercing the catheter wall 10 is then removed,
resulting in placement of the holes at the precise orientation and
configuration in a simple manner which allows for repeatable and rapid
production of such angled hole catheters. Further, the precision obtained
in utilizing this apparatus is very high and reproducible to facilitate
mass production.
The preceding apparatus has been found to be suitable for constructing
apertured catheters of a variety of materials for particular applications.
When very small diameter holes in thin-walled silicone catheters are
desired, the quality of side-wall smoothness necessary to prevent cells or
tissue from binding and plugging the catheter holes is difficult to obtain
by the use of the cutting apparatus. Accordingly, applicants have devised
a molding system which achieves all the desired results. This embodiment
illustrated in FIGS. 8 through 13, is discussed below. Generally, a
disposable insert is placed in a molding assembly prior to the injection
of the polymerizable silicone material. This insert is retained in place
until the silicone material cures. Thereafter, the insert and catheter are
removed from the mold and the insert is discarded. This technique enables
the user to produce extremely smooth, very small, angled holes at any
orientation, position or configuration in a relatively simple and highly
reproducible manner.
FIGS. 8 and 9 illustrate two preferred disposable inserts 50, 55. Each of
these inserts has an elongated body portion 52, 57 and a plurality of rod
like extensions 52, 59 extending from the body at a predetermined angle.
As mentioned above, it is highly advantageous to make the holes of the
catheter at an angle of 35 degrees with respect to its longitudinal axis.
Thus, the rod-like extensions 52, 59, of these inserts are positioned at
an angle preferably of 35 degrees with respect to the axis of the body
member 52, 57. FIG. 8 illustrates an insert for forming three rows of
apertures in the catheter, while FIG. 9 illustrates a spiral orientation
of such apertures about the circumference of the catheter body.
FIGS. 10 through 13 illustrate the molding cylinders 60, 80 for use with
the previously described inserts 50, 55. Each mold includes an open end
62, 82 which enables insertion of the corresponding inserts 50, 55, and a
closed end 64, 84 which is used to form the insertion tip of the catheter.
These molds 60, 80 include a plurality of guide apertures 66, 86 for at
least partially receiving the rod like members 52, 59 of the respective
inserts 50, 55. The guide holes 66, 86 extend through the wall 68, 88 of
the molding cylinders 60, 80 at an angle which corresponds to the desired
angle of the catheter holes.
In manufacturing, a plurality of molds 60, 80 and a much greater number of
inserts 50, 55 are prepared. Since the molds 60, 80 are reusable,
basically any material can be used which would provide a useful service
life. This would include, for example, steel, stainless steel, aluminum,
etc. and certain engineering thermoplastics may also be suitable. These
materials must be sufficiently strong to retain the insert and withstand
the temperatures anticipated for the polymerization of the material used
to form the catheter. Such mold material must also be dimensionally stable
over the entire curing temperature range.
The insert 50, 55 should be made of a selflubricating material that does
not bind or stick to the polymerizable liquid used to form the catheter.
Also, the self-lubricating material must be sufficiently flexible so that
it can be easily inserted and drawn out of the mold without damaging the
catheter. At this time, the most preferred material for the insert is an
injection molded polyamide material.
A preferred material for the catheter itself, is a polymerizable silicon
liquid which has a very low injection and curing temperature, i.e., about
100.degree. F. While this requires a relatively long curing time, high
production rates can be achieved through the use of multiple molding
cavities. The inserts are disposable so that each insert can only be used
to make one catheter. As noted above, the mold itself can be reused an
infinite number of times.
During manufacturing, after the insert is placed within the mold, and the
rod member properly positioned within the guide holes of the mold, the
polymerizable liquid is introduced into the space between the insert and
the mold. The liquid is then allowed to polymerize and cure to form the
catheter. The insert and catheter are removed from the mold and the insert
is then destroyed to form the final catheter product.
The preceding molding technique provides numerous advantages, including:
(1) the catheter holes can be configured in any shape or size relative to
the axis of the catheter. For example, spiral, off-set 90 degree or
off-set 120 degree holes can easily be obtained.
(2) the angle of the hole relative to the axis of the catheter can be
easily changed by providing different mold inserts and mold cavities. This
allows optimization of the hole angle compared to the hole diameter as a
function of cell growth. This relationship is governed by the formula
given above.
(3) this apparatus assures that no "flashing" will occur | | |
