U.S. patent application number 12/566141 was filed with the patent office on 2010-03-18 for variable characteristic venous access catheter shaft.
This patent application is currently assigned to AngioDynamics, Inc.. Invention is credited to William M. Appling.
Application Number | 20100069883 12/566141 |
Document ID | / |
Family ID | 32469584 |
Filed Date | 2010-03-18 |
United States Patent
Application |
20100069883 |
Kind Code |
A1 |
Appling; William M. |
March 18, 2010 |
VARIABLE CHARACTERISTIC VENOUS ACCESS CATHETER SHAFT
Abstract
A central venous catheter is provided having a proximal tube
segment, a distal tube segment and a transition tube segment
interposed between the proximal and distal tube segments which are
preferably formed as a single integrated tube containing polymer
material of different durometer and varying amounts of radiopaque
filler material. The polymer durometer of the proximal segment is
higher than the polymer durometer of the distal segment. By
contrast, the percentage by weight of the filler material contained
in the distal segment is higher than that of the proximal segment.
The variation in the polymer durometer and the filler amount along
the length of the tube provide the desired tensile strength,
hardness, chemical resistance and fatigue resistance at the
proximal segment and at the same time provide the desired
flexibility and radiopacity at the distal segment.
Inventors: |
Appling; William M.;
(Granville, NY) |
Correspondence
Address: |
ANGIODYNAMICS, INC.
603 QUEENSBURY AVENUE
QUEENSBURY
NY
12804
US
|
Assignee: |
AngioDynamics, Inc.
Queensbury
NY
|
Family ID: |
32469584 |
Appl. No.: |
12/566141 |
Filed: |
September 24, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10728267 |
Dec 4, 2003 |
7618411 |
|
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12566141 |
|
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60430998 |
Dec 4, 2002 |
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Current U.S.
Class: |
604/525 ;
604/529 |
Current CPC
Class: |
A61L 29/18 20130101;
A61M 25/0054 20130101; A61M 25/0108 20130101; A61M 1/3659
20140204 |
Class at
Publication: |
604/525 ;
604/529 |
International
Class: |
A61M 25/00 20060101
A61M025/00; A61M 25/098 20060101 A61M025/098 |
Claims
1. A catheter shaft, comprising: a monolithic tube comprising: a
proximal tube segment comprising a polymer material of a first
durometer and a first amount of a radiopaque filler; a distal tube
segment comprising a polymer material of a second durometer and a
second amount of the radiopaque filler, wherein the first durometer
is higher than the second durometer and the percentage by weight of
the first amount of the radiopaque filler is lower than that of the
second amount of the radiopaque filler; and a transition tube
segment seamlessly interposed between the proximal tube segment and
the distal tube segment.
2. The catheter shaft of claim 1, wherein the transition tube
segment comprises a mixture of a first polymer material and a
second polymer material having a different durometer than the first
polymer material.
3. The catheter shaft of claim 1, wherein the transition tube
segment comprises a mixture of the polymer material of the first
durometer and the polymer material of the second durometer.
4. The catheter shaft of claim 1 or 3, wherein the durometer of the
polymer material comprised therein the transition tube segment
varies over the length of the transition tube segment.
5. The catheter shaft of claim 4, wherein the durometer of the
polymer material comprised therein the transition tube segment
continuously decreases from a proximal end of the transition tube
segment to a distal end of the transition tube segment.
6. The catheter shaft of claim 4, wherein a proximal end of the
transition tube segment is seamlessly connected to the proximal
tube segment and a distal end of the transition tube segment is
seamlessly connected to the distal tube segment, and wherein the
durometer of the polymer material comprised therein the transition
tube segment decreases from the first durometer at the proximal end
of the transition tube segment to the second durometer at the
distal end of the transition tube segment.
7. The catheter shaft of claim 6, wherein the durometer of the
polymer material comprised therein the transition tube segment
continuously decreases from the first durometer at the proximal end
of the transition tube segment to the second durometer at the
distal end of the transition tube segment with no abrupt durometer
shift.
8. The catheter shaft of claim 1, wherein the transition tube
segment comprises a radiopaque filler, and wherein the percentage
by weight of the radiopaque filler comprised therein continuously
varies over the length of the transition tube segment.
9. The catheter shaft of claim 8, wherein a proximal end of the
transition tube segment is seamlessly connected to the proximal
tube segment and a distal end of the transition tube segment is
seamlessly connected to the distal tube segment, and wherein the
percentage by weight of the radiopaque filler comprised therein the
transition tube segment increases from the proximal end of the
transition tube segment to the distal end of the transition tube
segment.
10. The catheter shaft of claim 1, wherein the monolithic tube
defines one or more lumens.
11. The catheter shaft of claim 1, further comprising a hub
component attached to the proximal tube segment and configured to
remain outside of a patient body.
12. The catheter shaft of claim 1, wherein the transition tube
segment has greater flexibility than the proximal tube segment.
13. The catheter shaft of claim 12, wherein the flexibility of the
transition tube segment varies along the length of the transition
tube segment.
14. The catheter shaft of claim 13, wherein a proximal end of the
transition tube segment is seamlessly connected to the proximal
tube segment and a distal end of the transition tube segment is
seamlessly connected to the distal tube segment, and wherein the
proximal end of the transition tube segment is less flexible than
the distal end of the transition tube segment.
15. The catheter shaft of claim 1, wherein the transition tube
segment is more flexible than the proximal tube segment, and
wherein the distal tube segment is more flexible than the
transition tube segment.
16. The catheter shaft of claim 1, wherein the flexibility of the
proximal tube segment is substantially equal to the flexibility at
a proximal end of the transition tube segment and the flexibility
of the distal tube segment is substantially equal to the
flexibility of a distal end of the transition tube segment.
17. The catheter shaft of claim 1, wherein the proximal tube
segment comprises about 0 to about 30% radiopaque filler by weight,
and wherein the distal tube segment comprises about 30 to about 50%
radiopaque filler by weight.
18. The catheter shaft of claim 1, wherein the monolithic tube is
configured to have a high burst strength.
19. The catheter shaft of claim 18, wherein the monolithic tube is
configured to withstand injection pressures of up to about 300 psi
without bursting.
20. The catheter shaft of claim 1, wherein the proximal tube
segment is configured to withstand higher pressures than the distal
tube segment.
21. A catheter shaft, comprising: a proximal tube segment
comprising a polymer material of a first durometer and a first
amount of a radiopaque filler; a distal tube segment comprising a
polymer material of a second durometer and a second amount of a
radiopaque filler, wherein the first durometer is higher than the
second durometer and the percentage by weight of the first amount
is lower than that of the second amount; a transition tube segment;
and a means for seamlessly interposing the transition tube segment
between the proximal tube segment and the distal tube segment such
that the proximal, distal and transition tube segments together
form a monolithic tube.
22. The catheter shaft of claim 21, wherein the transition tube
segment comprises a mixture of a first polymer material and a
second polymer material having a different durometer than the first
polymer material.
23. The catheter shaft of claim 21, wherein the transition tube
segment comprises a mixture of the polymer material of the first
durometer and the polymer material of the second durometer.
24. The catheter shaft of claim 22 or 24, wherein the durometer of
the polymer material comprised therein the transition tube segment
continuously decreases from the first durometer at a proximal end
of the transition tube segment to the second durometer at a distal
end of the transition tube segment with no abrupt durometer
shift.
25. The catheter shaft of claim 24, wherein the percentage by
weight of the radiopaque filler comprised therein the transition
tube segment continuously increases from the proximal end to the
distal end of the transition tube segment.
26. The catheter shaft of claim 21, wherein the monolithic tube
defines one or more lumens.
27. The catheter shaft of claim 21, further comprising a hub
component attached to the proximal tube segment and configured to
remain outside of a patient body.
28. A catheter shaft, comprising: a monolithic tube comprising: a
proximal tube segment of a first durometer; a distal tube segment
of a second durometer, wherein the second durometer is lower than
the first durometer; and a transition tube segment seamlessly
interposed between the proximal tube segment and the distal tube
segment, wherein the durometer of the transition tube segment
varies over the length of the transition tube segment.
29. The catheter shaft of claim 28, wherein the durometer of the
transition tube segment varies continuously over the length of the
transition tube segment
30. The catheter shaft of claim 28, wherein each of the respective
proximal and distal tube segments comprise a radiopaque filler, and
wherein the percentage by weight of radiopaque filler contained in
the proximal tube segment is lower than the percentage by weight of
radiopaque filler contained in the distal tube segment.
31. The catheter shaft of claim 28, wherein the transition tube
segment comprises a mixture of a first polymer material and a
second polymer material having a different durometer than the first
polymer material.
32. The catheter shaft of claim 28, wherein the transition tube
segment comprises a mixture of a polymer material of the first
durometer and a polymer material of the second durometer.
33. The catheter shaft of claim 32, wherein the durometer of the
polymer material contained in the transition tube segment
continuously decreases from the first durometer at a proximal end
of the transition tube segment to the second durometer at a distal
end of the transition tube segment with no abrupt durometer
shift.
34. The catheter shaft of claim 33, wherein the transition tube
segment comprises a radiopaque filler, and wherein the percentage
by weight of the radiopaque filler contained in the transition tube
segment continuously increases from the proximal end of the
transition tube segment to the distal end of the transition tube
segment.
35. The catheter shaft of claim 28, wherein the monolithic tube
defines one or more lumens.
36. The catheter shaft of claim 28, further comprising a hub
component attached to the proximal tube segment and configured to
remain outside of a patient body.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation application of U.S.
application Ser. No. 10/728,267, filed Dec. 4, 2003, which
application claims priority to U.S. Provisional Application Ser.
No. 60/430,998, filed Dec. 4, 2002, which applications are
incorporated herein by reference.
FIELD OF THE INVENTION
[0002] The present invention relates to a medical device apparatus
and method for the delivery and withdrawal of fluids and
medications. More particularly, the present invention relates to a
venous access catheter device with variable shaft characteristics
and method of manufacture.
BACKGROUND
[0003] Venous access catheters provide venous access to the central
circulatory system. Venous access catheters include central venous
catheters, dialysis catheters and peripherally inserted central
catheters, also known as PICC lines. The access line is used for
the delivery of intravenous fluids, medications such as
chemotherapy drugs and antibiotics, and blood products. Venous
access catheters may also be used as access mechanisms for blood
sampling and the administration of contrast agents during
diagnostic Computer Tomography (CT) procedures.
[0004] One type of venous access catheters, PICC lines, provide
venous access to the central circulatory system through a
peripheral vein. PICC lines have been in use for many years with a
variety of configurations. These include single lumen, dual lumen
and other multi-lumen configurations. They come in various lengths
to accommodate different anatomy and catheter insertion sites.
Generally, a PICC line is inserted through a peripheral location
such as the arm, with the tip placed in the central circulation,
such as the superior vena cava. The PICC line is designed to remain
within the patient for a period of one week to a year and can be
accessed in an inpatient, outpatient or home setting.
[0005] The majority of the PICC lines presently on the market are
made from single material such as silicone rubber or polyurethane.
While these catheters are biocompatible and designed to minimize
indwelling side effects and optimize patient comfort, they do have
several drawbacks. The soft material characteristics of the
catheter provide patient comfort but increase insertion
difficulties and reduce the long-term durability of the catheter.
The material characteristics of the catheter shaft also restrict
use to only low pressure injections, typically less than 100
psi.
[0006] The PICC line should be sufficiently flexible so that it
minimizes patient discomfort and does not cause trauma to the vein
wall during insertion or over prolonged periods. On the other hand,
it should be rigid enough to facilitate insertion over a guidewire.
Pushability and resistance to kinking during and after insertion
require a stiffer shaft material. These opposing technical
requirements have been partially addressed by some manufacturers by
incorporating a softer tip welded to the catheter shaft. While this
design provides a soft, atraumatic distal end allowing a stiffer,
more rigid shaft body, the catheter is uncomfortable to the patient
because the majority of the shaft is stiff. In addition, the
physician cannot customize the length of these catheters by cutting
at the tip, as is commonly done in the practice.
[0007] The PICC line is inserted percutaneously, either under
fluoroscopic guidance or using a bedside, "blind" approach followed
by x-ray imaging to confirm correct tip placement within the
vessel. With either technique, the medical professional must
confirm that the distal tip of the PICC line is located within the
superior vena cava, rather than in the jugular vein or other
unintended vessel. Typically, a post-placement x-ray is used to
visualize the distal segment of the catheter within the body. Most
venous access catheters do not have sufficient radiopacity to allow
for easy visualization of the distal tip.
[0008] Some venous access catheter designs have attempted to
address this problem by providing a highly radiopaque distal tip
bonded to the shaft. The drawback of this enhanced tip design is
that it prevents the physician from cutting the tip to customize
the length of the PICC line. The design also requires a bond or
weld joint, which decreases the overall strength of the catheter
and increases the risk of fracture at the bond or weld point.
[0009] Other catheter designs have attempted to provide acceptable
distal radiopacity levels by using highly filled polymer throughout
the entire shaft length. Although providing an acceptable level of
visibility, the highly filled shaft material had poor fatigue and
chemical resistance, which resulted in an increased occurrence of
shaft fracture due to external exposure conditions. The shaft is
subject to failure at the proximal end where the catheter exits the
body. At the point at which the catheter shaft exits the patient's
body, the catheter is exposed to extensive bending, manipulation,
and surface contact with site care chemicals such as antibiotics
and antiseptics.
[0010] Some PICC line designs include a separate obturator or other
type stiffener device to provide additional stiffness during
insertion. Once inserted and positioned, the obturator is removed
from the lumen of the PICC line. While this design has the
advantage of ease of insertion, the shaft is soft and not radially
strong enough to handle the internal pressures associated with CT
injections. In addition, for multi-lumen PICC lines, the medical
professional must be cognizant of which lumen to insert the
obturator into as incorrect insertion may damage the catheter.
[0011] Most PICC lines have a capability of withstanding less than
100 pounds per square inch (psi). This is particularly true of
silicone-based PICC lines. Although most PICC line pressure
capabilities are sufficient for the delivery of medications and for
sampling of blood, they are not designed for delivery of contrast
media using a power injector. Power injectors are used in radiology
suites as a method for rapidly delivering diagnostic contrast
media, particularly for CT applications. Contrast media delivered
using a power injector can reach injection pressures of almost 300
psi. Although an in-place PICC line provides an available delivery
path for the contrast media, it often cannot be used because the
PICC line cannot withstand the higher pressures generated when
using a power injector. Instead, the physician must access the
patient's vein in another location using a short IV-type catheter
designed to withstand higher pressures.
[0012] Patients with PICC lines are often very ill and gaining
access to a vein is difficult for the caregiver on the one hand
while it is as painful and traumatic for the patient on the other
hand. Continuous access of the venous system by IV needles or
catheters results in eventual destruction of the available veins.
Accordingly, being able to access the venous system using an
already-in-place PICC line would have significant advantages to
both the patient and the health care providers.
[0013] Therefore, it is desirable to provide a
variable-characteristic venous access catheter that is sufficiently
rigid for ease of placement and yet sufficiently flexible so as not
to damage vessels.
[0014] It is also desirable to provide a venous access catheter
that is comfortable to the patient and also has sufficient
durability including chemical and fatigue resistance to withstand
prolonged indwelling times.
[0015] It is further desirable to provide a venous access catheter
that can withstand higher-pressure injections generated by power
infusion devices without causing catheter damage.
[0016] It is also desirable to provide a venous access catheter
that is designed as a one-piece construction for enhanced
reliability and strength.
[0017] It is further desirable to provide a venous access catheter
with a distal segment having enhanced visibility under X-Ray or
fluoroscopy to aid in placement without compromising overall
catheter strength.
SUMMARY
[0018] According to the principles of the present invention, a
central venous catheter having a proximal tube segment, a distal
tube segment and a transition tube segment interposed between the
proximal and distal tube segments is provided. The three segments
are preferably formed as a single integrated tube containing
polymer material of different durometer and different amounts of
radiopaque filler material. The polymer durometer of the proximal
segment is higher than the polymer durometer of the distal segment.
By contrast, the percentage by weight of the filler material
contained in the distal segment is higher than that of the proximal
segment. The variation in the polymer durometer and the filler
amount along the length of the tube provides the desired tensile
strength, hardness, chemical resistance and fatigue resistance at
the proximal segment and at the same time provides the desired
flexibility and radiopacity at the distal segment.
[0019] In one aspect of the present invention, the transition tube
segment contains a mixture of two polymer materials of different
durometer.
[0020] In another aspect, the durometer of the polymer material
contained in the transition tube segment continuously varies over
the length of the transition tube segment without any abrupt shift
in durometer.
[0021] In another aspect, the durometer of the polymer material
contained in the transition tube segment continuously decreases
from a proximal end of the transition tube segment to a distal end
of the transition tube segment.
[0022] In another aspect, the percentage by weight of the filler
material contained in the transition tube segment continuously
varies over the length of the transition tube segment.
[0023] In another aspect, the percentage by weight of the filler
material contained in the transition tube segment continuously
increases from a proximal end of the transition tube segment to a
distal end of the transition tube segment.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] FIG. 1 is a plan view of a venous access catheter according
to the present invention.
[0025] FIG. 2 is a plan view of the venous access catheter of FIG.
1 which has been inserted into a patient and enlarged partial plan
views of the proximal and distal segments of the catheter.
[0026] FIG. 3A is a graph depicting one method of altering the
filler amount and durometer levels of the polymer material to
achieve the variable characteristics of the venous access catheter
according to the present invention.
[0027] FIG. 3B is a table listing the test results of the filler
and durometer mixture of FIG. 3A.
DETAILED DESCRIPTION OF THE INVENTION
[0028] Referring to FIG. 1, a variable characteristic PICC line of
the present invention is shown from a plan view. The catheter 1 is
comprised of a hub section 2, a tube or shaft 3 with a
substantially rigid proximal segment 4, a transition segment 5 and
a substantially flexible distal segment 6. In the embodiment shown,
a dual-lumen catheter is provided. In this embodiment, the hub 2 is
further comprised of a bifurcated hub component 7 and two extension
legs 8 corresponding to each shaft lumen, as is well known in the
art. The extension legs 8 terminate at the proximal end with a
connector such as a standard luer fitting 9 for connection to
injection or aspiration devices. Leg clamps 10 coaxially arranged
around the extension legs 8 may be used to clamp off or occlude the
leg lumens, preventing the inflow or outflow of fluids through the
catheter 1. The catheter may include measurement markers 11 to
assist in placement within the vessel.
[0029] According to the present invention, a unitary, variable
characteristic catheter shaft for a central venous catheter such as
a PICC line is provided. Characteristics include varying
flexibility along the shaft, increased radiopacity at the distal
segment 6 and enhanced tensile strength and durability at the
proximal segment 4.
[0030] At the proximal segment 4, the shaft is stiff and strong
relative to the distal segment 6. Transition segment 5, interposed
between proximal segment 4 and distal segment 6, is constructed
such that it has more flexibility than proximal segment 4 and less
flexibility than distal segment 6. Within transition segment 5, the
flexibility may vary from less flexible at the proximal end to more
flexible at the distal end. Distal segment 6 is more flexible than
transition segment 5 and substantially more flexible than proximal
segment 4.
[0031] The variable flexibility characteristics of the present
invention provide important advantages over conventional PICC
lines. The proximal segment 4 of the catheter shaft 3, with its
increased rigidity and columnar strength, provides the user with
increased pushability and control during insertion and advancement
through the vessel. The increased stiffness of the proximal segment
4 relative to the distal segment 6 allows for the line to be
inserted and advanced easily with or without the use of a
guidewire.
[0032] The distal segment 6 also provides advantages over
traditional PICC lines. The flexible soft shaft at the distal
segment 6 is similar to the flexibility of silicone catheters. As
such, the shaft minimizes vessel wall trauma caused from contact
with the shaft, particularly along distal segment 6 as shown in
FIG. 2. Vessel trauma has been shown to increase the risk of
thrombus formation, with its resulting complications including
catheter occlusion. Decreasing vessel wall trauma over the extended
implantation time may contribute to a lower risk of thrombus
formation, catheter occlusion and other procedural
complications.
[0033] In addition to the variable flexibility along the shaft
length, the PICC line of the present invention includes enhanced
durability and tensile strength at the proximal segment 4. The
proximal portion 4 also provides increased strength and durability
for that portion of the catheter shaft that is exposed outside of
the patient, as shown in FIG. 2. The risks of damage from patient
movement, stress at the insertion site 12 and decreased shaft
integrity from long-term exposure to chemical substances used
during medical procedures are all minimized by providing a stiffer,
stronger proximal section 4.
[0034] Although implanted PICC lines provide access to the
vasculature for administration of fluids, conventional PICC lines
typically cannot be used for CT power injections because the shaft
cannot withstand the internal pressures generated during the
injection, which may be as high as 300 pounds per square inch
(psi). CT injections are administered as part of a diagnostic
imaging procedure to determine the presence or status of a disease
state. A CT power injector is connected to a high-pressure fluid
line and then to an access needle. The injections are delivered
over a period of time, defined by the flow rate. Typically,
contrast media is delivered through an IV needle or catheter at a
rate of 2-4 cc per second, with a total delivered volume of between
150 and 200 mls. Although venous access is available through the
PICC line, conventional catheters with their relatively low burst
strength cannot withstand the prolonged pressure generated during
the CT injections. Commonly, PICC lines are accompanied by warnings
advising against high-pressure conditions over 100 psi, making them
un-usable for the delivery of contrast media during diagnostic
imaging procedures.
[0035] As a result of the limitations of conventional PICC lines,
the physician needs to gain separate access with an IV-type needle.
Typically, a needle is placed in the forearm area and is used to
inject contrast media during the diagnostic CT procedure. This
separate access site increases the complexity and time of the
diagnostic procedure in addition to increasing the risks associated
with a second access site such as bleeding, hemotomas and
infection.
[0036] With the present invention, however, CT injections through
the PICC line are possible without the risk of catheter failure due
to high pressures created during the procedure. The catheter is
designed to have a higher radial and tensile strength at the
proximal segment 4 than at the distal end 6. Accordingly, the
catheter disclosed herein is capable of withstanding higher
pressures at the proximal section of the shaft than at the distal
segment of the shaft. The peak pressure level during fluid
injection of up to 300 psi occurs at the most proximal point of the
catheter shaft 3, which has the tensile material characteristics to
withstand the higher pressures.
[0037] The pressure created by fluid injections drops as fluid
travels distally down the shaft, approaching systemic pressure as
the fluid enters the target vessel. Because of this decreasing
pressure gradient, the distal segment of the PICC line does not
have to have the same burst pressure properties as the proximal
segment, where the pressure level is higher. Accordingly, the
distal segment of the PICC shaft retains its structural integrity
during injections even though it has reduced tensile and pressure
capabilities.
[0038] In addition to the flexural and tensile characteristics of
the PICC line of the present invention, the design provides for
enhanced visibility of the distal segment 6 under X-ray or
fluoroscopic imaging. The enhanced visibility is achieved by
increasing the radiopaque filler level relative to the polymer at
the distal segment 6 of the catheter. Radiopaque filler materials,
usually in the form of a fine powder are normally added to the
polymer to increase overall density of the mixture. The increased
density serves to block or impede X-ray penetration, thus providing
a visual contrast from surrounding tissue and unfilled polymer
material. Numerous radiopaque filler materials well known in the
art can be used to increase visibility including barium sulfate,
tungsten and bismuth salts. Using these radiopaque fillers,
physicians can easily visualize the distal segment under X-ray to
confirm correct placement within the superior vena cava 13 as shown
in FIG. 2.
[0039] Turning now to the method of manufacturing the PICC line of
the present invention, several different methods can be used to
achieve the varying flexural and strength characteristics described
above. Stiffness and tensile strength characteristics are a
function of the amount of radiopaque filler as well as the selected
durometer of the polymer resin. In one aspect of the invention, the
shaft tubing may be extruded using differing durometer resins and
differing filler ratios within a single extrusion process.
Specifically, the shaft tubing may be extruded using a Total
Intermittent Extruded (TIE) process well known in the art and
described by Daneneau in U.S. Pat. No. 4,888,146, incorporated
herein by reference. In that TIE process, two or more different
durometer polymer resins are mixed with varying levels of
radiopaque filler and then extruded.
[0040] Varying only the levels of filler material does not
adequately achieve the desired characteristics of a venous access
catheter. When only the filler is varied, although the distal end
of the catheter is more radiopaque, it is also less flexible at the
distal segment due to the increased level of filler. When the
durometer by itself is varied, the resulting shaft has the desired
flexibility characteristics but is not sufficiently visible under
X-ray. With the preferred method of the present invention, the
shaft 3 has a first segment 4 of higher durometer resin and less
filler, a second segment 5 of mixed durometer resin with higher
ratio of filler and a final segment 6 of lower durometer resin with
the highest level of filler. With this novel method of varying both
the durometer and level of filler throughout the extrusion process,
a catheter shaft meeting all the requirements of a PICC line can be
produced.
[0041] As an illustrative example, a commonly used medical grade
polymer material such as Thermal Plastic Urethane (TPU) is
available in different durometers with varying percentages of
radiopaque filler. In the embodiment shown in FIGS. 3A and 3B, two
polymer products can be used. A first polymer is a TPU with a base
Shore A hardness of 72 A. After 40% radiopaque filler by weight is
added to the base polymer, the resulting Shore A durometer is 78 A.
A second polymer is a TPU with a base Shore A hardness of 87 A.
After 20% radiopaque filler by weight is added to the base polymer,
the Shore A hardness increases to 90 A.
[0042] Using the TIE process, the first polymer is supplied by a
first extrusion device (not shown) for the distal tube segment 6. A
second polymer is supplied by a second extrusion device (not shown)
for the proximal segment 4. At the transition tube segment 5, the
first polymer flow is shut off while the second polymer flow is
opened, resulting in a transition tube segment 5 containing a mix
of the first and second polymer product. Using the TIE process
described above produces extruded tubing with varying physical
characteristics based on the polymer resin and filler mix.
[0043] FIG. 3A depicts the varying durometer and radiopaque filler
along the length of the catheter shaft after extrusion as described
above. As can be seen in FIGS. 3A and 3B, at the proximal segment 4
of the tubing, the mixture ratio is approximately 20% radiopaque
filler (solid line) and 80% TPU by weight. The filler level
increases along the transition tube segment 5 until it reaches
approximately 40% filler to 60% TPU at the distal segment 6.
Similarly, the TPU durometer, measured in shore A hardness,
decreases from 90 A at the proximal end to 78 A at the distal end.
As shown in FIG. 3A, the transition segment of the extruded tubing
contains a varying degree of both radiopaque filler and TPU
durometer.
[0044] Physical test data on the varying characteristic tubing is
illustrated in FIG. 3B. At the proximal end of the catheter, the
tensile strength of the shaft is high to provide the necessary
strength and durability to the exposed segment of the catheter. The
higher durometer polymer combined with a lesser amount of
radiopaque filler provide the increased strength and durability
characteristics of the proximal segment as evidenced by the
increased tensile strength measurements. Similarly, the chemical
and fatigue resistance levels of the proximal portion of the
catheter shaft are higher than at the distal segment.
[0045] Although the example above utilizes 20% radiopaque filler at
the proximal segment of the catheter, the percentage of radiopaque
filler by weight will depend on the density of the filler as well
as the specific polymer used. Accordingly, the proximal segment may
preferably contain a range of 0% to 30% radiopaque filler by
weight. The distal segment filler ratio preferably may range from
30% to 50%. Similarly, the durometer of the combined polymer and
filler material will depend on the specific polymer as well as the
ratio of filler material to the polymer material. The durometer of
the proximal shaft segment 4 may range from 87-100 Shore A hardness
while the distal segment may range from 70 to 90 Shore A
hardness.
[0046] The flexural modulus is a measurement of the relative
stiffness of an object under applied stress and is measured in
pounds per square inch required to bend the object. The higher the
flexural modulus measurement, the higher the stiffness. As shown in
FIG. 3B, the proximal portion of the catheter shaft measures a
higher flexural modulus psi and is accordingly stiffer than the
distal segment of the shaft. The radiopacity of the distal end,
with its higher level of filler, results in a shaft that is more
visible under X-ray or fluoroscopy at the distal segment. The
increased stiffness created by the higher radiopacity filler load
at the distal end is offset by the lower durometer resin, resulting
in a distal segment that is both highly visible under X-ray and is
flexible and atraumatic to the patient.
[0047] Thus by varying the durometer and the percentage by weight
of the radiopaque filler along the shaft length, optimal
characteristics of a venous access catheter can be achieved. At the
proximal end of the shaft, where the catheter is subject to
increased manipulation and exposure to chemicals, the device is
fatigue and chemical resistant as well as having increased overall
strength as measured by tensile strength. In addition, the
increased strength at the proximal end allows for the safe use of
power injections with their relatively high-pressure levels. At the
distal end, the shaft has enhanced visibility under image guidance
as well as a softer, more flexible atraumatic shaft.
[0048] The single extrusion process also ensures a strong
transition segment which is less subject to failure under high
pressure or tensile force than other welded or bonded transition
segments. Accordingly, the absence of welded or bonded points along
the catheter shaft will increase durability during insertion,
withdrawal and CT injections.
[0049] Other methods of creating a variable characteristic PICC
line are also possible. For example, the TIE extrusion method
previously described can be adjusted to create a transition segment
that is longer or shorter relative to the distal and proximal
segments. Specifically, by controlling the speed at which the two
base polymers are switched during the extrusion process, the length
of the transition segment can be varied. Slowing down the switch
over rate from the first polymer mix to a second polymer mix will
result in a longer transition segment. The rate can be adjusted
such that the majority of the shaft consists of the transition
segment, thus creating a continuously variable characteristic
catheter shaft. Alternatively, increasing the speed at which the
conversion from one polymer mix to the other takes place will
create a shaft with a relatively short transition segment.
[0050] Another method of extrusion, commonly known in the art as
co-extrusion, can also be used to create a variable characteristic
venous access catheter described herein. Two separate extruders can
be utilized to create a single tube with two different material
layers. The cross-sectional wall thickness of each layer is then
varied along the length of the shaft. As an example, the outer
layer may be extruded using the lower durometer polymer, higher
radiopaque filler mixture and the inner layer extruded using the
higher durometer polymer, lower radiopaque filler mixture. The
outer tubing wall thickness transitions from a smaller percentage
of the overall tubing wall cross-section to a larger percentage of
the overall tubing wall as it approaches the distal end.
Conversely, the inner tubing wall thickness transitions from a
larger to smaller percentage of the overall tubing wall as it
approaches the distal end of the shaft. The resulting single tube
would consist of substantially all outer layer material at the
distal end of the catheter transitioning to substantially all inner
layer material at the proximal end of the catheter. Preferably, the
distal segment consists of approximately 90% outer layer with its
high radiopacity and relatively low durometer and 10% inner layer,
although a range of 75% outer to 95% outer layer is possible. At
the proximal segment, the shaft consists of approximately 90% inner
layer with its low radiopacity and higher durometer and 10% outer
layer. A range of between 75% and 95% inner layer for the proximal
segment is acceptable. Although in the example above, the outer
layer consisted of the higher filler, lower durometer material, it
is possible to reverse this approach and use the higher filler,
lower durometer polymer mixture as the inner layer instead. With
either method, varying the thickness of each layer of the tubing
along the length of the shaft will achieve a continually varying
durometer, strength and radiopacity shaft of the optimal venous
access catheter.
[0051] Alternatively, the relative strength and flexibility of the
shaft can also be varied using a cross-linking technique well known
in the art. To achieve the varying flexural characteristics within
a single shaft, the tubing is extruded using a process combining a
cross-linking additive with a polymer. After extrusion, sections of
the tubing are exposed to radiation or another thermal energy
source. Exposure to radiation creates increased cross-linking of
the chemical bonds between the polymer chains. The tubing exposed
to the radiation exhibits a higher tensile strength and is less
flexible than the non-exposed section of tubing.
[0052] Various omissions, modifications, substitutions and changes
in the forms and details of the device illustrated and in its
operation can be made by those skilled in the art without departing
in any way from the spirit of the present invention. Accordingly,
the scope of the invention is not limited to the foregoing
specification, but instead is given by the appended claims along
with their full range of equivalents.
* * * * *