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Claims  |
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I claim:
1. In a cannula having a proximal end portion adapted to be connected to a
hub, a distal end portion and a longitudinal duct therethrough from the
distal end portion to the proximal end portion, the cannula being of a
material selected such that an inner cross-section of the duct increases
to form an enlarged duct cross-section when at least a part of the distal
end portion is inserted through the skin and into a blood vessel of a
living subject and maintained therein and/or when the duct is contacted by
an aqueous liquid for a period of time sufficient for the enlarged duct
cross-section to form, an improvement comprising:
where in the cannula has a larger outer cross-section and the duct has a
larger inner cross-section starting from the proximal end portion and
continuing to a position along the cannula than have the cannula and the
duct starting at the distal end portion and continuing to the position,
the position being located such that when the distal end portion is
inserted in the blood vessel the position is located beneath the skin
short of the blood vessel; and further including:
a reinforcing tube having an outer surface matingly held within the duct
and having an inner passageway, the tube extending from the proximal end
portion to adjacent the position.
2. A cannula as set forth in claim 1, wherein the inner passageway has an
inside cross-section substantially equal to or greater than the enlarged
duct cross-section at the distal end portion.
3. A cannula as set forth in claim 1, wherein the reinforcing tube is of a
polymeric material.
4. A cannula as set forth in claim 1, wherein the reinforcing tube is of a
plastic material.
5. A cannula as set forth in claim 1, wherein the cannula is of a material
having a 2.5% Secant modulus which reduces more than about 3:1 upon
formation of the enlarged duct cross-section.
6. A cannula as set forth in claim 1, wherein the cannula is of a material
through which medicaments can diffuse and wherein the reinforcing tube is
of a material substantially impervious to medicaments.
7. A cannula as set forth in claim 1, wherein the cannula includes a
tapered section extending from said position towards said proximal end
portion to an end of taper location adjacent said position and wherein the
reinforcing tube terminates at the end of taper location.
8. A cannula as set forth in claim 7, wherein the tapered section is
tapered at an angle of less than about 45.degree..
9. A cannula as set forth in claim 7, wherein said reinforcing tube is of a
polymeric material.
10. A cannula as set forth in claim 7, wherein said reinforcing tube is of
a plastic material.
11. A cannula as set forth in claim 7, wherein said cannula is of a
material through which medicaments can diffuse and wherein said
reinforcing tube is of a material substantially impervious to medicaments.
12. A cannula as set forth in claim 7, wherein the tapered section is
tapered at an angle of less than about 15.degree..
13. A cannula as set forth in claim 7, wherein the tapered section is
tapered at an angle of less than about 5.degree..
14. A cannula as set forth in claim 1, wherein the cannula is an
over-the-needle type cannula.
15. A cannula as set forth in claim 1, wherein the inner passageway has an
inside cross-section substantially equal to said enlarged duct
cross-section.
16. In a cannula having a proximal end portion adapted to be connected to a
hub, a distal end portion and a longitudinal duct therethrough from the
distal end portion to the proximal end portion, the cannula being of a
material selected such that an inner cross-section of the duct increases
to form an enlarged duct cross-section when at least a part of the distal
end portion is inserted through the skin and into a blood vessel of a
living subject and maintained therein and/or when the duct is contacted by
an aqueous liquid for a period of time sufficient for the enlarged duct
cross-section to form, an improvement comprising:
wherein the cannula has a larger outer cross-section and the duct has a
larger inner cross-section starting from the proximal end portion and
continuing to a position along the cannula than have the cannula and the
duct starting at the distal end portion and continuing to the position,
the position being located such that when the distal end portion is
inserted in the blood vessel the position is located beneath the skin
short of the blood vessel; and further including:
a reinforcing tube having an outer surface matingly held within the duct
and having an inner passageway, the tube extending from the proximal end
portion to adjacent the position; and
wherein the cannula includes a tapered section extending from said position
towards said proximal end portion to an end of taper location adjacent
said position and wherein the
17. In a cannula having a proximal end portion adapted to be connected to a
hub, a distal end portion and a longitudinal duct there through from the
distal end portion to the proximal end portion, the cannula being of a
material selected such that an inner cross-section of the duct increases
to form an enlarged duct cross-section when at least a part of the distal
end portion is inserted through the skin and in to a blood vessel of a
living subject and maintained there in and/or when the duct is contacted
by an aqueous liquid for a period of time sufficient for the enlarged duct
cross-section to form, an improvement comprising:
wherein the cannula has a larger outer cross-section and the duct has a
larger inner cross-section starting from the proximal end portion and
continuing to a position along the cannula than have the cannula and the
duct starting at the distal end portion and continuing to the position,
the position being located such that when the distal end portion is
inserted in the blood vessel the position is located beneath the skin
short of the blood vessel; and further including:
a reinforcing tube having an outer surface matingly held within the duct
and having an inner passageway, the tube extending from the proximal end
portion to adjacent the position; and
wherein the cannula includes a tapered section extending from said position
towards said proximal end portion to an end of taper location adjacent
said position and wherein the reinforcing tube terminates at the end of
taper location; and
wherein said cannula is of a material having a 2.5% Secant modulus which
reduces more than about 3:1 upon formation of said enlarged duct
cross-section.
18. In a cannula having a proximal end portion adapted to be connected to a
hub, a distal end portion and a longitudinal duct therethrough from the
distal end portion to the proximal end portion, an improvement comprising:
wherein the cannula has a larger outer cross-section and the duct has a
larger inner cross-section starting from the proximal end portion and
continuing to a position a long the cannula than have the cannula and the
duct starting at the distal end portion and continuing to the position,
the position being located such that when the distal end portion is
inserted in the blood vessel the position is located beneath the skin
short of the blood vessel and where in the cannula is of a material which
softens on being inserted into a living subject; and further including:
a reinforcing tube having an outer surface matingly held within the duct
and having an inner passageway, the tube extending from the proximal end
portion to adjacent the position.
19. A cannula as set forth in claim 18, wherein the inner passageway has an
inside cross-section substantially equal to or greater than the duct
cross-section at the distal end portion.
20. A cannula as set forth in claim 18, wherein the reinforcing tube is of
a polymeric material.
21. A cannula as set forth in claim 18, wherein the reinforcing tube is of
a plastic material.
22. A cannula having a proximal end portion adapted to be connected to a
hub, a distal end portion and a longitudinal duct therethrough from the
distal end portion to the proximal end portion, an improvement comprising:
wherein the cannula has a larger outer cross-section and the duct has a
larger inner cross-section starting from the proximal end portion and
continuing to a position along the cannula than have the cannula and the
duct starting at the distal end portion and continuing to the position,
the position being located such that when the distal end portion is
inserted in the blood vessel the position is located beneath the skin
short of the blood vessel; and further including:
a reinforcing tube having an outer surface matingly held within the duct
and having an inner passageway, the tube extending from the proximal end
portion to adjacent the position; and
wherein the cannula is of a material through which medicaments can diffuse
and wherein the reinforcing tube is of a material substantially impervious
to medicaments.
23. A cannula as set forth in claim 18, wherein the cannula includes a
tapered section extending from said position towards said proximal end
portion to an end of taper location adjacent said position and wherein the
reinforcing tube terminates at the end of taper location.
24. A cannula as set forth in claim 23, further including:
means for easing the transition from the unreinforced cannula distal of the
reinforcing tube to the reinforced cannula proximal the reinforcing tube.
25. A cannula as set forth in claim 24, wherein said means comprises a
distal end of said reinforcing tube being thinned to a reduced thickness.
26. A cannula as set forth in claim 23, wherein the tapered section is
tapered at an angle of less than about 45.degree..
27. A cannula as set forth in claim 26, wherein said angle is less than
about 15.degree..
28. A cannula as set forth in claim 27, wherein said angle is less than
about 5.degree..
29. A cannula as set forth in claim 23, wherein the tapered section is
tapered at an angle at less than about 15.degree..
30. A cannula as set forth in claim 23, wherein the tapered section is
tapered at an angle of less than about 5.degree..
31. In a cannula having a proximal end portion adapted to be connected to a
hub, a distal end portion and a longitudinal duct therethrough from the
distal end portion to the proximal end portion, and improvement
comprising:
wherein the cannula has a larger outer cross-section and the duct has a
larger inner cross-section starting from the proximal end portion and
continuing to a position along the cannula than have the cannula and the
duct starting at the distal end portion and continuing to the position,
the position being located such that when the distal end portion is
inserted in the blood vessel the position is located beneath the skin
short of the blood vessel; and further including:
a reinforcing tube having an outer surface matingly held within the duct
and having an inner passageway, the tube extending from the proximal end
portion to adjacent the position, said reinforcing tube having a 2.5%
Secant modulus between about 3450 and about 48,000 N/cm.sup.2.
32. A cannula as set forth in claim 18, wherein the cannula is an
over-the-needle type cannula.
33. In a cannula having a proximal end portion adapted to be connected to a
hub, a distal end portion and a longitudinal duct therethrough from the
distal end portion to the proximal end portion, an improvement comprising:
wherein the cannula has a larger outer cross-section and the duct has a
larger inner cross-section starting from the proximal end portion and
continuing to a position along the cannula than have the cannula and the
duct starting at the distal end portion and continuing to the position,
the position being located such that when the distal end portion is
inserted in the blood vessel the position is located beneath the skin
short of the blood vessel; and further including:
a reinforcing tube having an outer surface matingly held within the duct
and having an inner passageway, the tube extending from the proximal end
portion to adjacent the position; and
wherein the inner passageway has an inside cross-section substantially
equal to said enlarged duct cross-section.
34. In a cannula having a proximal end portion adapted to be connected to a
hub, a distal end portion and a longitudinal duct therethrough from the
distal end portion to the proximal end portion, an improvement comprising:
wherein the cannula has a larger outer cross-section and the duct has a
larger inner cross-section starting from the proximal end portion and
continuing to a position along the cannula than have the cannula and the
duct starting at the distal end portion and continuing to the position,
the position being located such that when the distal end portion is
inserted in the blood vessel the position is located beneath the skin
short of the blood vessel; and further including:
a reinforcing tube having an outer surface matingly held within the duct
and having an inner passageway, the tube extending from the proximal end
portion to adjacent the position;
wherein the cannula includes a tapered section extending from said position
towards said proximal end portion to an end of taper location adjacent
said position and where in the reinforcing tube terminates at the end of
tapered location; and
means for easing the transition from the unreinforced cannula distal of the
reinforcing tube to the reinforced cannula proximal the reinforcing tube,
wherein said means comprises a cut away portion in said reinforcing tube
beginning and extending proximally from where said reinforcing tube
terminates.
35. In a cannula having a proximal end portion adapted to be connected to a
hub, a distal end portion and a longitudinal duct therethrough from the
distal end portion to the proximal end portion, an improvement comprising:
wherein the cannula has a larger outer cross-section and the duct has a
larger inner cross-section starting from the proximal end portion and
continuing to a position along the cannula than have the cannula and the
duct starting at the distal end portion and continuing to the position,
the position being located such that when the distal end portion is
inserted in the blood vessel the position is located beneath the skin
short of the blood vessel; and further including:
a reinforcing tube having an outer surface matingly held within the duct
and having an inner passageway, the tube extending from the proximal end
portion to adjacent the position;
wherein the cannula includes a tapered section extending from said position
toward said proximal end portion to an end of taper location adjacent said
position and wherein the reinforcing tube terminates at the end of taper
location;
means for easing the transition from the unreinforced cannula distal of the
reinforcing tube to the reinforced cannula proximal the reinforcing tube,
said means comprising one or more fingers extending from where said
reinforcing tube terminates towards said position.
36. In a cannula having a proximal end portion adapted to be connected to a
hub, a distal end portion and a longitudinal duct therethrough from the
distal end portion to the proximal end portion, an improvement comprising:
wherein the cannula has a larger outer cross-section and the duct has a
larger inner cross-section starting from the proximal end portion and
continuing to a position along the cannula than have the cannula and the
duct starting at the distal end portion and continuing to the position,
the position being located distally from the hub, the cannula including a
tapered section extending from said position toward said proximal end
portion to an end of taper location adjacent said position, said tapered
section being tapered at an angle of less than about 15.degree., the
cannula being of a material which softens on being inserted into a living
subject; and further including:
a reinforcing tube having an outer surface matingly held within the duct
and having an inner passageway, the tube extending from the proximal end
portion distally beyond the hub towards the position, said reinforcing
tube terminating at said end of taper location; and
means for easing the transition from the unreinforced cannula distal of the
reinforcing tube to the reinforced cannula proximal of the reinforced
tube.
37. A cannula as set forth in claim 36, wherein the inner passageway has an
inside cross-section substantially equal to or greater than the duct
cross-section at the distal end portion.
38. A cannula as set forth in claim 36, wherein the reinforcing tube is of
a polymeric material.
39. A cannula as set forth in claim 36, wherein the reinforcing tube is of
a plastic material.
40. In a cannula having a proximal end portion adapted to be connected to a
hub, a distal end portion and a longitudinal duct therethrough from the
distal end portion to the proximal end portion, and improvement
comprising:
wherein the cannula has a larger outer cross-section and the duct has a
larger inner cross-section starting from the proximal end portion and
continuing to a position along the cannula than have the cannula and the
duct starting at the distal end portion and continuing to the position,
the position being located distally from the hub, the cannula including a
tapered section extending from said position toward said proximal end
portion to an end of taper location adjacent said position, said tapered
section being tapered at an angle of less than about 15.degree.;
a reinforcing tube having an outer surface matingly held within the duct
and having an inner passageway, the tube extending from the proximal end
portion distally beyond the hub towards the position, said reinforcing
tube terminating at said end of taper location;
means for easing the transition from the unreinforced cannula distal of the
reinforcing tube to the reinforced cannula proximal of the reinforcing
tube; and
wherein the cannula is of a material through which medicaments can diffuse
and wherein the reinforcing tube is of a material substantially impervious
to medicaments.
41. A cannula as set forth in claim 36, wherein said means comprises a cut
away portion in said reinforcing tube, said cut away portion being cut
away along a plane at a skew angle to said reinforcing tube, said cut away
portion beginning and extending proximally form where said reinforcing
tube terminates.
42. A cannula as set forth in claim 36, wherein said means comprises a
distal end of said reinforcing tube being thinned to a reduced thickness.
43. A cannula as set forth in claim 36, wherein said angle is less than
about 5.degree..
44. A cannula as set forth in claim 36, wherein the position is located
such that when the distal end portion is inserted in the blood vessel the
position is located beneath the skin short of the blood vessel.
45. A cannula as set forth in claim 36, wherein the cannula is an
over-the-needle type cannula.
46. In a cannula having a proximal end portion adapted to be connected to a
hub, a distal end portion and a longitudinal duct therethrough from the
distal end portion to the proximal end portion, an improvement comprising:
wherein the cannula has a larger outer cross-section and the duct has a
larger inner cross-section starting from the proximal end portion and
continuing to a position along the cannula than have the cannula and the
duct starting at the distal end portion and continuing to the position,
the position being located distally from the hub; and further including:
a reinforcing tube having an outer surface matingly held within the duct
and having an inner passageway, the tube extending from the proximal end
portion distally beyond the hub towards the position; and
means for easing the transition from the unreinforced cannula distal of the
reinforced tube to the reinforced cannula proximal of the reinforced tube,
said means comprising one or more fingers extending from where said
reinforcing tube terminates towards said position. |
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Claims |
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Description |
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FIELD OF THE INVENTION
The invention relates to a cannula of the over-the-needle type for
insertion into a blood vessel of a patient.
BACKGROUND OF THE INVENTION
A number of catheter assemblies are known for introduction of a polymeric
cannula into a vein, artery or cavity of a living subject for infusion or
extraction of fluids. A widely used method of inserting such a polymeric
cannula is to position a steel needle (or solid stylet) within the duct of
a cannula with the tip of the needle or stylet extending from the distal
end of the cannula. The needle or stylet is then inserted into a living
subject after which the needle or stylet is removed from the cannula,
leaving the cannula behind with at least its distal end in the subject.
Additional tubing can be attached to the cannula or medicaments or
nutrients can be caused to flow through the cannula into the subject.
The cannulae of the prior art have generally been made of a rigid material
which does not soften and/or exhibit a change in the cross-sectional area
of the duct of the cannula after insertion into a vein. More recently, as
set forth in commonly assigned co-pending U.S. Application Ser. No.
780,543, filed Sept. 26, 1985, now abandoned materials have been developed
which can be formulated into cannulae and which, while they are rigid
enough to retain their shape during insertion, also have the property of
both softening and swelling to form an enlarged duct cross-section on
insertion in a blood vessel due to water pickup. Also, recent publications
discuss cannulae which soften on being raised to a temperature approaching
body temperature.
The cannulae which form enlarged ducts can soften on formation of such
enlarged ducts. This has introduced a problem in that the softened portion
of the cannulae which extends outwardly from the skin of the patient can
kink or be deformed, thereby cutting off flow of nutrients, medicaments
and the like, into the vein. A kinking problem also exists to an extent
with the prior art rigid cannulae which are generally quite thin. To date,
the art has not provided an adequate solution to these problems.
The present invention is directed to overcoming one or more of the problems
as set forth above.
DISCLOSURE OF THE INVENTION
In accordance with an aspect of the present invention an improvement is set
forth in a cannula having a proximal end portion adapted to be connected
to a hub, a distal end portion and a longitudinal duct there through from
the distal end portion to the proximal end portion. The improvement
comprises wherein the cannula has a larger outer cross-section and the
duct has a larger inner cross-section starting from the proximal end
portion and continuing to a position along the cannula than have the
cannula and the duct starting at the distal end portion and continuing to
the position. The position is located distally from the hub. A reinforcing
tube having an outer surface is matingly held within the duct, the
reinforcing tube having an inner passageway. The tube extends from the
proximal end portion distally beyond the hub towards the position.
In accordance with another aspect of the present invention an improvement
is set forth in a cannula having a proximal end portion adapted to be
connected to a hub, a distal end portion and a longitudinal duct
therethrough from the distal end portion to the proximal end portion. The
improvement comprises wherein the cannula has a larger outer cross-section
and the duct has a larger inner cross-section starting from the proximal
end portion and continuing to a position along the cannula than have the
cannula and the duct starting at the distal end portion and continuing to
the position. The position is located such that when the distal end
portion is inserted in the blood vessel the position is located beneath
the skin but short of the blood vessel. A reinforcing tube having an outer
surface is matingly held within the duct, the reinforcing tube having an
inner passageway. The tube extends from the proximal end portion to
adjacent the position.
In accordance with yet another aspect of the present invention an
improvement is set forth in a cannula having a proximal end portion
adapted to be connected to a hub, a distal end portion and a longitudinal
duct therethrough from the distal end portion to the proximal end portion,
the cannula being of a material selected such that an inner cross-section
of the duct increases to form an enlarged duct cross-section when at least
a part of the distal end portion is inserted through the skin and into a
blood vessel of a living subject and maintained therein and/or when the
duct is contacted by an aqueous liquid for a period of time sufficient for
the enlarged duct cross-section to form. The improvement comprises wherein
the cannula has a larger outer cross-section and the duct has a larger
inner cross-section starting from the proximal end portion and continuing
to a position along the cannula than have the cannula and the duct
starting at the distal end portion and continuing to the position. The
position is located such that when the distal end portion is inserted in
the blood vessel the position is located beneath the skin but short of the
blood vessel. A reinforcing tube having an outer surface is matingly held
within the duct, the reinforcing tube having an inner passageway. The tube
extends from the proximal end portion to adjacent the position.
The reinforcing tube greatly reduces the possibility of kinking of at least
a portion of the cannula section which extends from the patients skin to
the hub. Thus the kinking problem is alleviated. One can, if desired, reap
the benefits of utilizing a cannula material which softens whereby
irritation of the vein wall is minimized and/or which enlarges, thereby
also serving to minimize irritation of the vein wall (since the puncturing
needle or stylet can be relatively small for a desired duct size).
BRIEF DESCRIPTION OF THE DRAWING
The invention will be better understood by reference to the figures of the
drawings, wherein:
FIG. 1 illustrates, in side partially sectioned view, a cannula structure
in accordance with an embodiment of the present invention attached to a
hub;
FIG. 2 illustrates, in side view, a reinforcing tube useful with the
embodiment of FIG. 1;
FIG. 3 illustrates, in partial enlarged view in side section, the cannula
structure of FIG. 1 with the cannula not enlarged;
FIG. 4 is a view like FIG. 3 but with the cannula enlarged;
FIG. 5 is a view like FIG. 3 but of an alternative reinforcing tube; FIG. 6
is a view like FIG. 3 but of another alternative reinforcing tube; and
FIG. 7 is a view like FIG. 3 but of still another alternative reinforcing
tube.
BEST MODE FOR CARRYING OUT THE INVENTION
Referring to FIGS. 1, 3 and 4, a cannula 10 in accordance with the present
invention is illustrated. The cannula 10 has a proximal end portion 12
adapted to be connected to a hub 14. A distal end portion 16 of the
cannula 10 is adapted for inserting in a blood vessel 18 of a living
subject. A longitudinal duct 20 (see FIGS. 3 and extends through the
cannula 10 from the distal end portion 16 to the proximal end portion 12.
The cannula 10 can be formulated of a material selected such that it
softens in the area having an inner cross-section 22 (FIG. 3) when at
least a part of the distal portion 16 of the cannula 10 is inserted
through the skin 26 and into the blood vessel 18 of a living subject and
is maintained therein and/or when the duct 20 is contacted by an aqueous
liquid for a period of time sufficient for the enlarged duct cross-section
24 to form. The material can be such that an inner cross-section 22 (FIG.
3) of the duct 20 increases to form an enlarged duct cross-section 24
(FIG. 4) under such circumstances. Alternatively, the cannula can be
formulated of a non-softening and/or non-swelling material such as Teflon
(trademark of Dupont).
The cannula 10 of the present invention is unique in that it has a larger
outer cross-section at 28 and said duct 20 has a larger inner
cross-section at 30 starting from the proximal end portion 12 and
continuing to a position 32 along the cannula than have the cannula 10 and
duct 20 starting at the distal end portion 16 and continuing to the
position 32. In accordance with certain aspects of the present invention
it is desirable that the position 32 be located such that when the distal
end portion 16 is inserted in the blood vessel 18, the position 32 is then
located beneath the skin 26 but short of the proximal wall 34 of the blood
vessel 18.
Further in accordance with the present invention (see FIG. 2) a reinforcing
tube 36, having an outer surface 38 and an inner passageway 39, is
matingly held within the duct 20 and over a metal insert 41 and extends
from the proximal end portion 12 of the cannula 10 and beyond the hub 14.
In this manner the reinforcing tube 36 reinforces at least a portion of
that section of the cannula 10 extending distally beyond the hub 14. In
accordance with certain aspects of the invention the reinforcing tube 36
extends to adjacent the position 32 along the cannula 10. When this is the
case, and when the position 32 is located such that it is beneath the skin
26 when the distal end portion 16 is inserted in the blood vessel 18, the
reinforcing tube 36 is aligned, after insertion of the distal end portion
16 of the cannula 10 in the blood vessel 18, through the skin 26 and
serves to reinforce that portion of the cannula 10 which extends to the
hub 14. This serves to prevent kinking and/or deformation of the cannula
10 outside of the patient's body along its entire length up to the hub 14.
The inner passageway 39 of the reinforcing tube 36 has an inside
cross-section 40 which can suitably be substantially equal to or greater
than the enlarged duct cross-section 24 at the distal end portion 16 of
the cannula 10 when the cannula is of a material which forms such an
enlarged duct cross-section 24 (as in FIG. 4). When the cannula 10 is not
of a material which forms an enlarged duct cross-section 24, the inner
passageway 39 of the reinforcing tube 36 should have its inside
cross-section 40 substantially equal to or greater than the (unchanging)
inner cross-section 22. The reinforcing tube 36 is suitably made of a
polymeric material, most suitably of a plastic material. Suitable
materials include, e.g., polyurethane, polyvinylchloride and polyethylene.
However, the material of the reinforcing tube 36 is not critical.
Accordingly, other materials can also be used. Of course, the material
chosen should not be such as to introduce contaminants or interfere with
analysis should the cannula 10 be used for sampling.
The material of the reinforcing tube 36 preferably exhibits a 2.5% Secant
modulus between about 3450 Newtons/square centimeter (N/cm.sup.2) to about
48,000 N/cm.sup.2, more preferably from about 6900 N/cm.sup.2 to about
34,500 N/cm.sup.2.
The cannula 10 generally includes a tapered section 42 which extends from
the position 32 towards the proximal end portion 12 of the cannula 10 to
an end of taper location 44. The end of taper location 44 is adjacent the
position 32. The taper can be conical, as illustrated, or can be a smooth
curving taper. The reinforcing tube 36 of FIG. 2 terminates at the end of
taper location 44. Suitably the tapered section 42 is tapered at an angle
of less than 45.degree. (from the longitudinal extension of the cannula
10), preferably no more than about 15.degree. and still more preferably no
more than about 5.degree.. This helps to ensure that the cannula 10
advances smoothly through the skin 26.
The reinforcing tube 36 can also serve to attach or hold the proximal end
portion 12 of the cannula 10 in a bore 46 of the hub 14. As illustrated in
FIG. 1, the proximal end portion 12 of the cannula 10 and the reinforcing
tube 36 can be forced over the metal insert 41 and then press fit into the
mating cavity 52 of the hub 14.
Suitably the material of the cannula 10 is selected whereby the tapered
section 42 is strong enough so that it does not crinkle or give
sufficiently to cause problems when the distal end portion 16 of the
cannula 10 is inserted into the blood vessel 18.
FIG. 5 shows an alternative reinforcing tube 536 which extends to adjacent
the position 32, specifically to the end of taper location 44, but which
is cut away along 53 to ease the transition from the unreinforced cannula
10 distal of the reinforcing tube 536 to the proximal end portion 12 of
the cannula 10 as reinforced by the reinforcing tube 536.
FIG. 6 shows another alternative reinforcing tube 636 having one or more
fingers 54 which extend to the position 32. The fingers 54 and the
reinforcing tube 636 are formulated of a material having elastic
properties and, in the case where the cannula 10 forms an enlarged duct
cross-section 24, the fingers 54 are suitably self-impelled to straighten
out so as not to impede fluid flow through the longitudinal duct 20. The
embodiment of FIG. 6, like that of FIG. 5, thus includes means for easing
the transition from the unreinforced cannula 10 distal of the reinforcing
tube 536 or 636 to the reinforced cannula 10 proximal the reinforcing tube
536 or 636. Although not illustrated the alternative reinforcing tubes
536, 636 can extend to between the position 32 and the end of taper
location 44.
FIG. 7 shows still another alternative reinforcing tube 736 which tapers or
thins towards its distal end 56 which extends to adjacent the position 32
and between the position 32 and the end of the taper location 44. The
thinned distal end 56 thus serves as alternative means for easing
transition from the unreinforced cannula 10 distal of the reinforcing tube
736 to the reinforced cannula 10 proximal the reinforcing tube 736.
As has been pointed out above the present invention is useful with any
cannula 10 including when the cannula 10 is formulated of a material that
softens on insertion into the body. The invention is particularly useful
with such softening cannulae 10 when the material is such that the inner
cross-section 22 of the duct 20 increases to form the enlarged duct
cross-sectional area 24, generally enlarged from at least about 25% (to
125% of its initial inner cross-section) to at least about 300%, more
preferably from about 40% to about 300% ; still more preferably from about
35% to about 140% , and most preferably from about 40% to about 100%, when
at least a part of the distal end portion 16 of the cannula 10 is inserted
in to a body, generally into the blood vessel 18, of a living subject and
maintained in contact with that body and/or when the duct 20 is contacted
by, e.g., filled with, an aqueous liquid, for a time sufficient for the
enlarged duct cross-section 24 to form.
In accordance with one embodiment of the present invention the cannula
comprises a multiple phase polymeric composition comprising a first phase
which comprises a substantially non-hydrophilic polymeric component and a
second phase which comprises a hydrophilic polymeric component. The
relative amounts of these components are selected, depending on the
particular polymeric materials employed, to provide a composition having
the desired properties, as discussed more fully below.
Preferably the non-hydrophilic polymeric component forms a continuous
phase. The hydrophilic polymeric component can form a co-continuous phase
with, or a dispersed phase in, the non-hydrophilic polymer phase.
The non-hydrophilic polymeric component comprises a polymer which does not
substantially absorb or attract water. Preferably, the non-hydrophilic
polymer is capable of absorbing an amount of no more than about 30% water,
more preferably no more than about 15%, and most preferably no more than
about 10%, by weight, based on the weight of the non-hydrophilic polymer.
The non-hydrophilic polymer can be for example, a polyurethane such as an
aliphatic polyurethane, a polyether polyurethane, a polyester
polyurethane; an ethylene copolymer such as ethylene-vinyl acetate
copolymer; a polyamide, in particular a polyamide of low crystallinity; an
aliphatic polyester; or the like. A particularly preferred non-hydrophilic
polymer is a polyurethane, especially an aliphatic polyurethane.
The hydrophillic polymer preferably is a polymer that absorbs at least
about 50% water, more preferably about 100%, for example, at least about
150%, by weight based on the weight of the hydrophilic polymer. The
hydrophilic polymer preferably forms a hydrogel on absorption of water.
The hydrophilic polymer is preferably polyvinyl alcohol, poly(ethylene
oxide), polypropylene oxide, poly (ethylene glycol), polypropylene glycol,
polytetramethylene oxide, polyvinyl pyrolidene, polyacrylamide, poly
(hydroxyethyl acrylate), poly (hydroxyethyl methacrylate), or the like.
The multiple phase composition can be prepared by mixing the polymeric
components or by the forming a block or graft copolymer containing the
polymeric components. A mixture of the components can be prepared using,
for example, a two-roll mill, an internal mixer, such as a Brabender or
Banbury mixer, an extruder, e.g., twin-screw extruder, or the like. Block
and graft copolymers can be prepared by appropriate methods depending on
the particular nature of the components used. Typical preparatory methods
can be found, for example, in the "Block and Graft Copolymerization", R.
J. Ceresa (Zd), 1973, Vol. 1 & 2, Wiley-Interscience, New York and "Block
Copolymers", D. C. Allport and W. H. Jane, 1973, Wiley, New York.
Generally, the ratio of non-hydrophilic polymeric component to hydrophilic
polymeric component is 0.65:1 to 9:1. Preferably the ratio of the
polymeric components is 1:1 to 9:1.
The polymeric components are selected to provide a multiple phase system.
Generally, the polymeric components each have a molecular weight of at
least about 3,000 preferably at least about 5,000 and most preferably at
least about 10,000.
As stated above, the relative amounts of non-hydrophilic and hydrophilic
polymeric components are selected, depending on the particular materials
employed, to provide the desired properties. Due to the presence of the
hydrophilic polymeric component, the composition is capable of being
hydrated by the absorption of water. As water is absorbedby the
composition, it may soften with a softening ratio of at least about 2:1,
preferably at least 6:1, more preferably at least about 10:1, most
preferably at least about 20:1, and in particular about 40:1. The term
"softening ratio " is used here into refer to the ratio of the 2.5% Secant
modulus values of the composition in the form of a tubular article, when
substantially non-hydrated, to the 2.5% Secant modulus of the composition
when substantially completely hydrated. The term "substantially completely
hydrated " refers to the state of the composition when it is in
equilibrium with an excess of water at 37.degree. C. and ambient pressure.
The composition may swell on absorption of water with a swelling ratio of
at least about 1.3:1, preferably at least about 1.7:1 and most preferably
at least about 2.0:1. The term "swelling ratio " refers to the ratio of
the volume of a given sample of the composition when substantially
completely hydrated to its volume of a given sample of the composition
when substantially completely non-hydrated.
Preferably the composition both softens and swells when placed in the body.
When substantially completely hydrated the composition has a tensile energy
to break of at least about 700 Newton-centimeters per cubic centimeter
(N-cm/cm.sup.3), preferably at least about 1,400 N-cm/cm.sup.3 and most
preferably about 1,700 N-cm/cm.sup.3. The term "tensile energy to break "
(TEB) is defined in ASTM-D882 as the area under the stress-strain curve or
##EQU1##
where S is the stress at any strain, .epsilon.,; and .EPSILON..sub..tau.
is the strain at rupture. The tensile energy to break provides an
indication of the toughness of the hydrated composition and its ability to
withstand the conditions it will be subjected to in use.
It will be readily appreciated that when a tubular product such as a
cannula is withdrawn from the body it is extremely important that it does
not tear or break leaving pieces remaining inside the body. Neither
tensile strength nor elongation to break are good indicators of toughness.
Brittle materials and notch sensitive materials can have tensile
strengths. Extremely weak materials can have elongation but not the
strength to survive extraction. TEB is a measure of the energy required to
break and is a combination of these two important criteria.
The ultimate elongation of the multiple phase composition should be at
least about 10%, preferably at least about 25% and most preferably at
least about 50%.
The composition when substantially completely hydrated has a 2.5% Secant
modulus of less than about 7,000 Newtons/square centimeter (N/cm.sup.2),
preferably less than about 3,500 N/cm.sup.2 and most preferably less than
about 2,000 N/cm.sup.2. When substantially completely hydrated the 2.5%
Secant modulus can be as low as about 30 N/cm.sup.2 preferably above about
60 N/cm.sup.2 and most preferably above about 120 N/cm.sup.2.
Typically the 2.5% Secant modulus of the composition when substantially
non-hydrated is at least about 15,000 N/cm.sup.2 when used as an over the
needle catheter. Preferably the 2.5% Secant modulus of the composition is
at least about 28,000 N/cm.sup.2. Preferably the 2.5% Secant modules of
the cannula 10 reduces more than about 3:1, more preferably more than
about 10:1 and still more preferably at least about 20:1 upon formation of
the enlarged duct cross-section 24.
The composition may be crosslinked if desired. Cross linking of the
composition gives the polymeric composition strength above the melting or
softening points of the polymeric components permitting sterilization of a
device utilizing the composition at above that temperature. This is
particularly advantageous if the polymeric component of the continuous
phase has a relatively low melting or softening point. Crosslinking of the
composition may also be used to adjust the 2.5% Secant modulus of the
composition to bring it to the desire value for the proposed use of the
composition. When the composition comprises a physical mixture of the
non-hydrophilic and hydrophilic components, crosslinking of the mixture
can control the tendency of the hydrophilic component to leachout of the
composition when it is in extended contact with water or body fluids.
Cross linking may also improve the toughness (TEB) of the composition in
the hydrated state.
Cross linking of the composition can be effected by use of an appropriate
crosslinking agent or by irradiation, preferably in the presence of a
crosslinking promoter, such as triallyl isocyanurate, or the like. In a
preferred embodiment the composition is crosslinked by high energy
radiation from an electron accelerator. The amount of irradiation should
be in the range of about 0.5 to about 30 Megarads (Mrads) preferably about
0.5 to about 15 Mrads and most preferably about 0.5 to about 10 Mrads.
Either or both components of the composition may contain additional
ingredients such as stabilizers, antioxidants, radioopacifiers,
medicaments, fillers or the like. For certain applicati | | |
