Note: Descriptions are shown in the official language in which they were submitted.
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S P E C I F I C A T I o N
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This invention relates to flexible tubing which is
particularly suitable for medical use, such as in catheters
and the lika.
, . . . .
In surgical and other hospital practice of medicine,
the use of flexible tubing is necessary and commonplace.
Tubes are used for catheters, for nasogastric suction,
for administration of intravenous fluids and blood, to
mention but a few uses. Occasionally tubing is implanted
in the body permanently, as for the drainage of spinal
fluid into the venous system or peritoneal cavity for hydro-
cephalus; or as for drainage of ascitic fluid in a periteneo-
; venous shunt. At other times, tubing is temporarily inserted,
as for taking venous pressure, or for infusing concentrated
glucose solution into the vena cava.
Generally, thexe are two problems whi~h are encaun~tered in the medical use of tubing. ~he first of these is
the problem caused by unnoticed, inadvertent kinking. The
second problem arises from the need, particularly where the
tubing is inserted or implanted within the body, to ascer-
tain the location of the center of the tubing, for example :
by radiography.
Generally, tubing which is sufficiently fle~ible formedical use, as described above, must be constructed of
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material which is relatively flexible and must be con-
structed with relatively thin walls, not only to permit
the necessary flexibility but also to accommodate flow
through the tubing. Such tubing is subject, upon bending,
to kinking and consequently collapse and blockage of
flow. When kinking inadvertantly occurs and is unnoticed,
the tubing ceases to function as desired.
If the tubing is part of a urinary collecting system
with drainage of the bladder by a catheter, the flow of
urine is interrputed by kinking of the tubing and accumu-
lates in the bladder. While this may not be catastrophic,
in other circumstances the kinking of a drainage tube
could cause fatal consequences. Consequently, non-kinkable
tubing is achieved by utili~ing thicker wall sections by
using stiffer materialsl or by both. These corrective fac-
tors result in lowering the flexibility of the tubing to
the point where it no longer is useful. Alternatively,
steel or other resilient metal springs can be incorporated
into the wall of plastic tubing by a complicated helical
; laminating process which not only is expensive but creates
problems in terminating the tubing to avoid corrosion and
the like. An additional problem encountered when metal
wire is ~ncorporated into the flexible tubing is that the
tubing must often be transected in order to shorten it.
This is accomplished with some difficulty since the spring
wire is difficult to cut and cutting the tubing will ex-
pose the wire to the corrosive action of the ~issues. In
addition, the exposed wire may pierce the lumen of the wall
of the body structure in which the tube was placed. There
are, therefore, good medical reasons why wire is less
satisfactory as an anti-kinking means in flexible
tubing, which, as well as the problems encountered in
the manufacture of wire containing tubing, make such
tubing undesirable.
It is heretobefore been proposed in utilizing
tubing, either introduced into or implanted within the
body, that the tubing be made radiopaque. This results
in tubing which is not optically translucent, and there-
fore presents problems in determinins the presenc~ and
position of foreign matter and the like when the tubing
is cleaned and sterilized. One solution to the latter
problem is the coextrusion of a radiopaque stripe in the
wall of the otherwise translucent tubing tU. S. Patent
2,857,915) but such stripes do not give an indication of
the aize of the lumen, and hence of it:s center, and
also are a poor indication that a sect:ion of tubing has
kinked.
It is accordingly a principal object to the present
invention to provide a flexible tubing suitable for medi-
cal use which is highly resistent to kinking. It is a -
further object of this invention to provide such tubing
in which the size of the tubing and the presence of a
kink are immediately apparent on radiography, but in
which the tubing is optically translucent to facilitate
cleaning.
These and other objects of the present invention,
which will become more apparent hereinafter, are basically
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achieved by forming tubing, for example by extrusion tech-
niques, having a generally homogeneous tubular wall sec-
tion composed of a relatively flexible material, in
which there is embedded a helical strand of relatively
stiff, resilient material, extending leng~hwise of the
wall portion along a helical path about the wall portion.
Radiopa~ue materials are incorporated either in the wall
portion o~ in the strand portion, and the other portion
is formed of optically translucent material. Preferably
the radiopaque materials are incorporated in the strand
portion.
Generally the combination of a relatively flexible
wall portion reinforced with a resilient, stiff helical
strand is substantially unkinkable, maintains its lumen
even on acute flexion and yet is sufficiently flexible
for most medical uses, enabling relatively thin wall
constructions to maximize flow through the tubing. Such
a construction is readily manufactured by coextrusion,
preferably of two melt-extrudable, compatible ~hermo-
plastic materials, one, when set, being relatively flex-
ibl~ and the other, the helical portion, when set, being
stiff and resilient. Such coextrusion is readily
achieved utilizing apparatus, for example as described in
Meneidis, U. S. Patent 3,642,396. As noted above, either
the wall portion or the strand portion should be of
radiopaque material to permit visual location of the out-
side dimensions of the tubing by radiography. Since those
materials which impart radiopaque character to plastic
materials are, for the most part, pigments which also
cause the material to become optically opaque~ the other
of the wall portion or strand portion sho~d be optically
translucent to permit visual inspection of the tubing
for cleaning puxposes: preferably the radiopaque mate-
rial is utilized in the helical strand portion of the
construction to ~btain the most efficiènt inspection of
the tubing for cleaning purposes.
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For a more complete understanding of the practical
application of this invention, reference is made to the
appended drawings in which:
FIG~ 1 is a partially sectioned plan view of a
length of flexible tubing constructed with accordance
of the present invention; and
FIG. 2 is a view similar to FIG. 1 illustrating
flexing of the tubing.
In the drawings, the reference numeral 10 generally
designates a section of flexible tubing in accordance
with the present invention. Tubing 10 basically includes
a tubular wall portion 11 formed by extrusion, preferably
of a melt-extrudable material, such as a silicone rubber,
which after cooling, sets to a relatively flexible homo-
geneous structure. Embedded in wall portion 11 is a
helical strand 12 which i9 formed by coextrusion with
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wall portion 11 utilizing a rotating injection port,
such that, while the wall portion 11 is extruded as a
cylinder, the rotating injection port introduces the
material from which strand 12 is formed describ~ng a
helical path in the cylindrical portion 11. Strand
portion 12 is formed, for example, of a diffe~nt sili-
cone rubber, which when set is highly stiff and resi- -
lient and in which is incorporated a radiopaque pigment,
such as calcium carbonate, barium sulfate, bismuth
oxychloride or the like.
While combinations of melt-extrudable, compatible
materials such as flexible and stiff, resilient silicone
rubbers can be utilized to form wall portion 11 and strand
portion 12, respectively, other materials and combinations
can be employed; for example in place of the stiff resi-
lient silicone rubber, strand 12 can be formed by a coex- -
truded thinner helical band of polysulfone. Polysulfone
is particularly useful in combination with the fle*ihle
silicone rubber wall portion 11 since the polysulfone is
exceedingly stiff and has an extremely high heat deflection
temperature which is important in permitting heat sterili-
zation. Other "engineering-type" plastics can be substi-
tuted for helical strand 12, by coextrusion with ethylene
vinyl acetate copolymer, ~orming wall portion 11. Poly-
butylene, polypropylene and ultra high molecular weight
polyethylene have sufficient rigidity to prevent kinking
of the soft, more flexible ethylene vinyl acetate copolymer.
In addition, many different grades of ethylene vinyl acetate
copolymer are available some o~ which are extremely soft and
flexible and can be combined with grades that are quite
stiff and hard. Still other examples of combinations
of melt-extrudable compatible materials include a
rigid vinyl strand 12 with a highly plasticized flexible
vinyl thermoplastic wall portion 11. Thermoplastic
urethane plastics are specially suitable for this appli-
cation because urethanes adhere well to other plastics
and have a wide range of flectural modulus. In addi- -
tion, glass fibers and other materials can be incorpo-
rated into plastics to stiffen them for the purpose of
forming strand portion 12. This technique is especially
useful with flexible urethane plastic.
Generally, in accordance with this invention, the
stiff and less resilient, i.e., rigid, engineering
plastic~type material is utilized to form the helical
strand which acts as the backbone of the structure and
maintains the radius of the relatively flexible plastic
of wall portion 11 during flexion of the tube, as illu-
strated with reference to FIG. 2. At the same time, theflexible plastic wall portion 11 can be kept clear, or
at least optically translucent, to permit i~spection to
insure against the accidental inclusion of foreign
material and to permit the observation of liquid flow.
The radiopaque materials are added to the backbone, that
is strand 12. In some circumstances, it may be more
desirable to make tubing of wall portion 11 radiopaque
and retain the spiral rigid material 12 as an optically
translucent strip, as for example to increase the
radiopacity of the tubing for some applications.
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