Subcutaneously implanted cannula and methods for vascular access

A catheter with valve for implantation in a vascular structure of a living being. The catheter is in the general shape of a "T" with the top of the "T" implanted within the lumen of or anastomotically attached to a vascular structure. The lumen of the implanted portion of the catheter completely occupies or may be aligned with the lumen of the vascular structure, causing all blood flow through the vascular structure to be directed through the implanted portion of the catheter. A valve is placed in the wall of the implanted portion of the catheter which opens into the lumen of the leg of the "T" of the catheter upon application of sufficient differential pressure between the lumens of the two portions of the catheter. The leg of the "T" may be connected to the side wall of the implant portion of the catheter at an angle, such that the axis of the lumen of the leg of the "T" intersects the axis of the lumen of the implanted portion of the catheter at approximately a 45.degree. angle.

BACKGROUND OF THE INVENTION 
1. The Field of Invention 
The present invention relates to subcutaneously implanted cannulas used to 
access the body's circulation. More particularly, this invention provides 
a cannula and method for establishing intermittent vascular access using 
an implanted cannula in the general shape of a "T". 
The advent of hemodialysis for the treatment of end-stage renal disease has 
prompted the development of many vascular access devices for the purpose 
of acquiring and returning large quantities of blood for passage through 
an extracorporeal circuit during hemodialysis procedure. Available devices 
have generally relied on the use of either indwelling venous catheters or 
flow through shunt devices which create an artificial fistula between an 
artery and vein. 
Venous catheters are limited by relatively poor draw flows and by their 
tendency to be irritative resulting in vessel stenosis, thrombosis, and 
occasionally vessel perforation. They frequently fail because of 
infection, weakness in the vessel wall, poor catheter position, and/or 
thrombus formation in the catheter lumen. Shunt devices which create a 
fistulous blood flow between an artery and a vein have been the mainstay 
of modern vascular access for dialysis but are similarly problematic. 
Installation of these "shunts" is an extensive surgical procedure 
resulting in significant tissue trauma and pain. Once in place, the shunts 
result in additional cardiac output needs with as much as one-fifth of the 
cardiac output (approximately 1000 ml per minute) required for adequate 
function. In addition, the transfer of the arterial pressure wave results 
in damage to the vein at the point of anastomosis with the shunt and can 
result in intimal hyperplasia and subsequent thrombosis and shunt 
occlusion. When such occlusion occurs, another vein segment must be used 
for shunt revision, and exhaustion of available sites is distressingly 
common and can be fatal. Repeated punctures of the wall of the shunt often 
result in eventual failure and require additional surgery to repair or 
replace the shunt. The expense in terms of both health care dollars and 
human misery is enormous. 
Each of the available access technologies mentioned thus far are also 
complicated by the possibility of recirculation of blood already passed 
through the extra-corporeal circuit resulting in the loss of treatment 
efficiency. The harm done to patients by the "recirculation syndrome" is 
insidious and at times undetected until great harm has been done. 
Indwelling catheters which occupy only a portion of the vessel lumen are 
subject to movement within the vessel, which can cause irritation or even 
vessel perforation. Further, catheters which occupy only a portion of the 
vessel lumen, and which are inserted or threaded through the lumen for 
substantial distances tend to disrupt the normal flow of blood through the 
vascular structure, altering the hemodynamics of the blood flow in a 
manner which can damage the vessel, the components of the blood, and which 
can encourage thrombosis. Such catheters are generally unsuitable for long 
term implantation in arteries. 
What is needed is a cannula which can be implanted within or otherwise 
attached to a blood vessel, which causes minimal disruption of blood flow 
through the lumen of the blood vessel during use and nonuse of the 
cannula, which does not cause vessel stenosis, thrombosis, or vessel 
perforation, which is capable of handling large quantities of blood, and 
which will retain its usefulness for a long period of time after 
implantation. 
2. Description of the Background Art 
Vascular access employing indwelling catheters is described in a number of 
patents and publications including U.S. Pat. Nos. 3,888,249; 4,543,088; 
4,634,422; 4,673,394; 4,685,905; 4,692,146; 4,695,273; 4,704,103; 
4,705,501; 4,772,270; 4,846,806; 5,063,013; 5,057,084; 5,100,392; 
5,167,638; 5,108,365; 5,226,879; 5,263,930; 5,281,199; 5,306,255; 
5,318,545; 5,324,518; 5,336,194; 5,350,360; 5,360,407; 5,399,168; 
5,417,656; 5,476;451; 5,503,630; 5,520,643; 5,527,277; and 5,527,278; and 
EP 228 532; and Wigness et al. (1982) paper entitled "Biodirectional 
Implantable Vascular Access Modality" presented at the Meeting of the 
American Society for Artificial Internal Organs, Apr. 14-16, 1982, 
Chicago, Ill. 
Catheters having distal valves are described in a number of patents 
including U.S. Pat. Nos. 274,447; 3,331,371; 3,888,249; 4,549,879; 
4,657,536; 4,671,796; 4,701,166; 4,705,501; 4,759,752; 4,846,806; 
4,973,319; 5,030,210; 5,112,301; 5,156,600; and 5,224,938. 
T-shaped catheters and cannulas for a variety of purposes, some having 
isolation valves, are described in U.S. Pat. Nos. 5,512,043; 5,443,497; 
5,169,385; 5,041,101; 4,822,341; 4,639,247; 3,826,257; 4,421,507; and 
3,516,408. 
Implantable dialysis connection parts are described in a number of patents 
including U.S. Pat. Nos. 4,692,146; 4,892,518; 5,041,098; 5,180,365; and 
5,350,360. 
SUMMARY OF THE INVENTION 
The present invention provides improved vascular cannulas which are 
particularly useful for providing long-term access to a patient's 
vasculature, including native arteries, native veins, and artificial 
arterial lumens such as an arteriovenous (AV) shunt or an arterial graft. 
The vascular cannulas may also be used for establishing AV shunts in 
between an artery and a vein. The cannulas of the present invention 
comprise a tubular body which is implantable within or anastomotically 
attachable to a blood vessel and an access leg having one end attached to 
a side wall of the tubular body. Both the tubular body and the access leg 
have lumens therethrough, with the lumen of the tubular body being 
configured to receive at least a portion of the blood flow of a vascular 
lumen in which it is implanted or to which it is anastomotically attached. 
The access leg, which is attached to the tubular body in a generally 
T-shaped configuration, thus provides for access into the lumen of the 
tubular body for either withdrawing or returning blood (e.g. for 
hemodialysis or other extracorporeal treatment) or for introducing drugs 
or other media into the arterial or venous blood flow. 
The vascular access cannula may be implanted either subcutaneously or 
transcutaneously. By transcutaneous, it is meant that a portion of the 
access leg will pass outwardly through the patient's skin to permit direct 
vascular access using external pumps, syringes, or other equipment. It 
will be appreciated, of course, that a hemostasis valve must be provided 
on the access leg to prevent uncontrolled blood loss. Often, any 
transcutaneous use of the cannula of the present invention will be only 
for a short time. 
More usually, the cannula of the present invention will be intended for 
subcutaneous use. In that case, an access port is connected to the open 
end of the access leg and is also subcutaneously implanted beneath the 
patient's skin. The access port will be suitable for attachment to 
needles, tubes, catheters, and other devices which may be percutaneously 
introduced into the access port to provide a desired external connection. 
An example of an access port comprises a chamber having a penetrable 
membrane on one side thereof. Temporary access to the chamber is formed by 
penetrating the needle, tube, or catheter through the penetrable membrane. 
A preferred subcutaneous port having an internal valve is described below. 
In all cases, the T-configured cannula of the present invention is an 
improvement over prior indwelling catheters in a number of respects. The 
tubular body is firmly anchored within or to the blood vessel and not 
subject to being moved or dislodged by blood flow. Thus, trauma to an 
arterial wall from movement of the cannula is significantly lessened. 
Moreover, by assuring that the lumen of the tubular body has a 
cross-sectional shape and dimensions which closely match those of the 
arterial lumen, smooth blood flow through the cannula can be enhanced 
while the risk of thrombus formation is substantially reduced. 
In a preferred construction, the vascular cannula will include an isolation 
valve, at or near the junction between the access leg and the tubular 
body. The isolation valve can be any type of pressure-responsive valve 
that closes or inhibits flow between the tubular body lumen and the access 
leg lumen in the absence of a pressure drop therebetween. Thus, when blood 
is not being withdrawn or returned and/or when drugs or other media are 
not being introduced, the isolation valve will close and isolate the lumen 
of the access leg from arterial blood flow. Such isolation is a 
significant advantage since it reduces the risk of thrombus formation 
within the access leg and thrombus release into the arterial lumen. 
Often, it will be desirable to flush the lumen of the access leg with an 
anti-coagulant fluid after each use. The removal of static blood and the 
placement of the anti-coagulant fluid further decreases the risk of 
thrombus formation and release. The isolation valve may be in a variety of 
forms, including slit valves, flap valves, ball valves, and may further be 
configured to provide for one-way or bi-direction flow. For example, in 
the case of arterial cannulas used for withdrawing blood, it may be 
advantageous to have a one-way isolation valve which permits blood flow 
from the tubular body into the access leg, but inhibits reverse flow of 
any materials from the access leg into the lumen. In the case of drug and 
other infusions into an artery or vein, it may be desirable to provide a 
one-way isolation valve which permits such introduction, but prevents 
reflux of blood into the access leg. A particularly preferred valve is a 
slit valve formed adjacent to or integrally within the wall of the tubular 
body, as illustrated in detail hereinafter. When such a slit valve is 
closed, the inner profile of the tubular body lumen will be generally 
smooth and free from discontinuities caused by the valve. 
The vascular cannula may be formed from any one or a combination of a 
variety of biocompatible materials. By biocompatible, it is meant that the 
material(s) will be suitable for a long term implantation within patient 
vasculature and tissue and will be free from immunogenicity and 
inflammatory response. Usually, the cannula will be formed in whole or in 
part from an organic polymer, such as silicone rubber, polyethylenes, 
polyurethanes, polyvinylchloride, polytetrafluoroethylene (PTFE), 
polysulfone, or the like. Portions of the cannula may be reinforced, for 
example the access leg may include circumferential reinforcement to 
enhance its hoop strength without significantly diminishing flexibility. 
Such reinforcement may take the form of a helical wire or ribbon, axially 
spaced-apart hoops, or the like. Preferably, the reinforcement may be 
achieved by molding the access leg to incorporate circumferential 
corrugation, i.e. a plurality of axially spaced-apart circumferential ribs 
along all or a portion of its lengths. In all cases, it is desirable that 
the internal lumen of the access leg and the tubular body remain as smooth 
as possible to avoid disturbances to blood flow. 
In a first embodiment, the tubular body of the vascular cannula will have 
dimensions compatible with implantation within a variety of the lumens of 
arteries and veins, including both native (natural) arteries and native 
(natural) veins, and implanted synthetic arteries. The most common native 
arteries in which the cannulas may be implanted include the proximal 
ulnar, proximal radial, brachial artery, axillary artery, and subclavian 
artery. The most common veins include the subclavian, the brachiocephalic, 
and the saphenous. Implanted synthetic arteries include bypasses, shunts 
(e.g. AV shunts), arterial grafts, and the like. Both native arteries and 
implanted synthetic arteries have lumens, and reference to "arterial 
lumens" herein is intended to refer to both such lumens. 
In a second embodiment, the tubular body of the vascular cannula will be 
configured for anastomotic attachment to a blood vessel. In particular, 
each end of the tubular body will be configured to permit conventional 
end-to-end or end-to-side anastomotic attachment to a blood vessel by 
conventional techniques, including suturing, stapling, clamping, use of 
adhesives, and the like. When the vascular cannula is to be implanted in a 
blood vessel to receive the entire flow of that blood vessel therethrough, 
a gap will be surgically created in the blood vessel to produce opposed 
ends thereof. Each end of the tubular body of the cannula may then be 
attached to an opposed end of the blood vessel by end-to-end anastomosis. 
When the cannula is being implanted to create a shunt, one end of the 
tubular body will be attached to an artery while the other end is attached 
to a vein. In some instances, the ends of the tubular body will be 
attached to both the artery and the vein by end-to-side anastomoses to 
create a partial bypass flow of blood from the artery to the vein. In 
other instances, both the artery and the vein will be terminated and 
joined together by the tubular body which is attached to each by an 
end-to-end anastomosis. 
Generally, the length of the tubular body will be in the range from 10 mm 
to 50 mm and the outer diameter will be in the range from 3 mm to 10 mm. 
The diameter of the lumen of the tubular body will generally be in the 
range from 1 mm to 8 mm. The access leg will usually have a length in the 
range from 25 mm to 700 mm and an outer diameter in the range from 3 mm to 
10 mm. The lumen diameter of the access leg will generally be in the range 
from 2 mm to 8 mm. 
In a preferred aspect of the present invention, at least a portion of the 
access leg of the arterial cannula will be sufficiently compliant so that 
substantially no forces are transmitted from the access leg back into the 
tubular body. For proper functioning of the arterial cannula, it is 
important that the tubular body remain properly aligned within the 
arterial lumen. This can be achieved by fabricating at least a portion of 
the access leg adjacent to the tubular body to have a low bending 
stiffness. The hoop strength of the access tube, in contrast, should 
remain relatively high, being at least sufficient to maintain patency of 
its lumen at internal pressures below -250 mmHg, preferably below -400 
mmHg. Use of the helical reinforcement designs described above helps 
assure that the access leg can be sufficiently flexible while retaining 
sufficient strength. 
In a first specific aspect of the present invention, a vascular cannula 
comprises a tubular body having a first end, a second end, and a lumen 
therebetween. The ends are adapted for anastomotic attachment to a blood 
vessel, generally as described above. A tubular access leg having a first 
end is connected to the tubular body, and further includes a second end, 
and a lumen between the first and second ends. A pressure-responsive valve 
is disposed at the junction, where the valve inhibits flow between the 
lumen of the tubular body and the lumen of the access leg in the absence 
of a pressure differential therebetween. The tubular body is preferably 
composed of a material of the type generally employed for vascular grafts 
and implants, such as expanded polytetrafluoroethylene (ePTFE), woven 
polyester (e.g. Dacron.RTM., DuPont), expanded polyurethane, and the like. 
In this way, the tubular body of the vascular cannula can be implanted in 
a blood vessel via conventional end-to-end anastomotic techniques. The 
tubular access leg of the vascular cannula is preferably composed of 
silicone rubber, polyurethane, and the like. The valve preferably 
comprises a flange secured to the tubular body and a collar connected to 
the first end of the tubular access leg. Optionally, a rigid tubular 
insert may be placed within the collar of the valve element and joined to 
the first end of the tubular access leg. 
Alternatively, the tubular body of the vascular cannula may comprise a 
rigid middle section and two end sections, where the end sections are 
adapted for anastomotic attachment to a blood vessel, typically being 
composed of a vascular graft material as described above. The rigid middle 
section will typically be composed of a metal or rigid plastic. Such a 
design can facilitate fabrication. 
In a second aspect of the present invention, a method for implanting a 
vascular access cannula comprises providing a cannula having a tubular 
body with two ends, a tubular access leg connected to the tubular body at 
a junction, and a pressure-responsive valve at the junction. An 
implantation site is surgically exposed adjacent a blood vessel, and one 
end of the tubular body is anastomotically attached to the blood vessel. 
The second end of the tubular body is also attached to a blood vessel. In 
a first embodiment, the anastomotic attachment step comprises surgically 
creating a gap in a single blood vessel to produce opposed ends. Each end 
of the tubular body is then attached to an opposed end of the blood vessel 
by end-to-end anastomosis. In this way, the cannula is implanted within a 
single blood vessel to pass the entire blood flow up that vessel 
therethrough. 
In a second embodiment, one end of the tubular body is attached to one 
blood vessel and the other end of the tubular body is attached to another 
blood vessel. The ends of the tubular body may be attached to the 
respective blood vessel by end-to-side anastomoses in order to create a 
partial shunt. Alternatively, the ends of the tubular body may be attached 
to terminal ends of an artery and a vein by end-to-end anastomoses to 
create a complete shunt. 
In all such methods, the tubular access leg may be attached to an implanted 
port to establish a flow between the blood vessel and the port. 
Alternatively, the tubular access leg may be disposed transcutaneously in 
order to establish a transcutaneous flow path to the blood vessel.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to FIG. 1 there is depicted an arterial cannula 10 constructed in 
accordance with the principles of the present invention implanted within 
an arterial lumen 20. The cannula is shaped generally like a "T" and is 
comprised of two primary sections; the tubular body 25 and the access leg 
30. The intravascular tube 25 is an elongated tube having a single lumen 
26, open on both ends. When implanted within the lumen 20, the tubular 
body 25 will have an upstream end 27, and a downstream end 28, determined 
by the direction of blood flow in the vascular structure 20. In FIG. 1 the 
direction of blood flow is indicated by the arrow 21. The cannula however, 
can be implanted in either orientation. 
The access leg 30 is an elongated tube having a single lumen 31. A distal 
end 32 of the access leg 30 is connected to the tubular body 25, generally 
near the mid-point thereof. The access leg 30 may extend from the tubular 
body 25 at any angle, including a 90.degree. angle, but it is preferred 
that the access leg 30 of the cannula 10 extend from the tubular body 25 
in a direction which is inclined toward the upstream end 27 of the tubular 
body 25. The angle formed between the access leg 30 and the upstream end 
27 of the tubular body 25 is an acute angle. The angle formed between the 
access leg 30 and the downstream end 28 of the intravascular tube 25 is an 
obtuse angle. A preferred angle between the access leg 30 and the upstream 
end 27 of the tubular body 25 is between 30.degree. and 60.degree., 
usually being approximately 45.degree.. 
A valve 40 is preferably located at the point of connection between the 
distal end 32 of the access leg 30 and the tubular body 25. The preferred 
valve 40 is a slit valve. Such valves are well known in the art. As best 
shown in FIG. 3, the slit valve is comprised of a membrane 41 which has a 
slit 42 extending partially across the membrane 41 and completely through 
the membrane 41. The membrane 41 acts to prevent fluid flow through the 
lumen 31 of the access leg 30, except when adequate differential pressure 
exists on opposite sides of the membrane 41 to cause the slit 42 to open, 
as is shown in FIG. 4. The membrane 41 is located such that the side of 
the membrane 41 located towards the vascular structure is essentially 
flush with the inner wall of the intravascular tube 25. When the catheter 
10 is not in use, the membrane 41 of the valve 40 and the inner surface of 
the tubular body 25 form a continuous tube that has minimal impact on 
normal blood flow through the arterial lumen. 
In the preferred embodiment, the membrane 41 is comprised of a portion of 
the side wall of the tubular body 25. To create the valve 40, a slit 42 is 
cut in the side wall of the tubular body 25 to correspond to the point of 
connection of the access leg 30. In this manner, when the valve is closed, 
the inner surface of the tubular body 25 is a continuous smooth surface 
which has minimal impact on normal blood flow. When the valve 40 opens, 
fluid flow between the lumen 31 and the access leg 30 and the lumen 26 of 
the intravascular tube 25 occurs. 
The outer circumference of the tubular body 25 is provided with expanded 
barbs 29 to hold cannula 10 in place within the vascular structure 20. One 
each of these expanded barbs 29 may be placed proximate the upstream end 
27 and proximate the downstream end 28 of the tubular body 25. The 
expanded barbs 29 have an enlarged outer circumference which tends to 
slightly distend the wall of the arterial lumen 20, providing a snug fit, 
but not preventing the continued viability of the arterial wall. 
Additional areas of expanded outer diameter (not shown) may be spaced 
along the outer surface of the tubular body 25. The fit between the 
arterial wall and the tubular body 25 must be of sufficient tightness to 
prevent passage of blood between the arterial wall and the outer surface 
of the tubular body 25. Optionally, it may be possible to place ties or 
clamps (not shown) about the outer wall of the artery adjacent to the 
expanded barbs 29 to hold the cannula 10 in place. All blood flowing 
through the arterial lumen should pass through the lumen 26 of the tubular 
member 25. 
In use, the proximal end 33 of the access leg 30 of the cannula 10 may be 
connected to a subcutaneous port, or may extend transcutaneously (i.e. 
through the skin). The cannula 10 is suitable for use with any device 
requiring or facilitating intermittent vascular access. The cannula 10 of 
the present invention is particularly useful for arterial access in 
hemodialysis, since such treatment requires large quantity blood flow, and 
requires relatively frequent vascular access over a long period of time. 
For such use two cannulas 10 may be surgically implanted. One of the 
devices is implanted in an artery. The other device is implanted in a 
vein. Usually, however, a conventional in-dwelling catheter will be used 
for the venous access since vein access is easer to establish. In this 
manner both the venous and arterial circulations are accessed separately, 
without fistulous communication. Current use of shunts, which create a 
fistulous connection between artery and vein, not only involve a more 
extensive surgical procedure, but are fraught with problems including 
increased cardiac output requirements, damage to the vein due to arterial 
pressure waves, and frequent shunt occlusion or thrombosis. 
During hemodialysis, blood is removed from the arterial cannula 10 
implanted in an artery and is subjected to the extracorporeal dialysis 
circuit. Removal occurs by reducing the pressure in the access leg 30 of 
the cannula 10, until the slit valve 40 opens, and blood flows from the 
tubular body 25 into the access leg 30. The treated blood is returned to a 
cannula implanted in a vein. At the completion of the dialysis treatment 
of the access leg 30 of cannula 10 is filled with anti-coagulant fluid, to 
discourage thrombosis and occlusion of the access legs 30. A similar 
process may be used for apheresis or exchange transfusion procedures. 
Additionally, a single arterial cannula 10 may be used for frequent 
administration of medication into artery or vein, or for large volume 
fluid infusions. 
Surgical implantation of the arterial cannula 10 is a straight forward 
procedure. The chosen artery is located and isolated, and a small incision 
is made in the lumenal wall. The tubular body 25 of the cannula 10 is 
inserted into the incision, with the access leg 30 extending out of the 
lumen through the incision. The incision is then sutured to provide a snug 
fit around the access leg 30. The proximal end 33 of access leg 30 of the 
cannula 10 is then attached to a subcutaneous port (described hereinafter) 
or other device requiring intermittent vascular access. 
Materials of construction well known in the art may be used for the 
manufacture of the cannula 10. However, it is important that the tubular 
body 25 be particularly biocompatible with the arterial wall 20, since it 
is intended that the wall in contact with the cannula 10 remain viable. 
Since the cannula 10, unlike most prior art catheters, is not designed to 
be pushed or threaded some distance into a blood vessel, the access tube 
of the cannula may be comprised of relatively flexible material. This may 
be accomplished by including a spring or other reinforcement element (not 
shown) within the walls of the cannula 10 to maintain hoop strength. The 
materials of construction of the tubular body should be of sufficient 
rigidity to maintain the preferred angle between the access leg 30 and the 
tubular body. The dimensions of the catheter 10 depend upon the size of 
the vascular structure 20 to be accessed. Typically the outer diameter of 
the tubular body 25 will be between 3 and 10 mm, with a wall thickness of 
approximately 0.5 to 1 mm, yielding a lumen 26 diameter of between 1 and 8 
mm. A typical length of the tubular body 25 from upstream end 27 to 
downstream end 28 is between 10 and 50 mm. The maximum diameter of the 
outer surface of the expanded barbs 29 is approximately 30 percent greater 
than the diameter of the tubular body 25 where no expanded barb 29 is 
present. The length and flexibility of the access leg can vary depending 
upon the use of the catheter 10. For use with subcutaneous ports an access 
leg 30 length of approximately 25 mm to 700 mm, usually about 100 mm is 
generally sufficient. 
Referring now to FIGS. 5-8, an exemplary implantable port 100 will be 
described. The implantable port 100 may be used with either the arterial 
cannula 10 described above, or with more conventional in-dwelling cannula 
which may be used in systems for venous access, as described in more 
detail hereinafter. The port 100 includes a single hematologic chamber 
125, where the base and sides are formed by a circumferential wall 126. 
The port 100 further includes wall 126 and a cover 120 which holds a 
replaceable diaphragm 127 in place. The cover 120 is removable to allow 
replacement of the diaphragm 127 if needed. A base 129 of the port 100 
comprises a flange having apertures 130 which permit fastening of the port 
to underlying tissue, typically using sutures. A connector 128 open to one 
end of the chamber 125 is connectable to the free end of access leg 30 
which forms part of the arterial cannula 10 described above. 
Referring now to FIGS. 9 and 10, an alternative embodiment of an arterial 
cannula 200 constructed in accordance with the principles of the present 
invention will be described. The cannula 200 includes both a tubular body 
202 and an access leg 204. The access leg 204 comprises a portion adjacent 
to the tubular body 202 including a plurality of circumferential ribs or 
corrugations 206 which provides substantial hoop strength to the leg 
without diminishing the desired flexibility. The remainder of the access 
leg 204 comprises larger sections 208, with the distal end 210 being 
suitable for attachment to the vascular port 100 at connector 128, as 
described previously. 
The tubular body 202 comprises a molded insert 230 including a main body 
portion 32 and a branch portion 234. An isolation valve 36 is formed at 
the end of branch 234, generally as described above with previous 
embodiments. Tubular body 202 is connected to the adjacent end of the 
access leg 206 by over molding an exterior body 238. Usually, a titanium 
tube 240 is placed within the junction between the end of access leg 206 
and the end of branch portion 234. The tube may be titanium or other 
biocompatible metal. The insert 230 is typically formed from a relatively 
soft material, such as 40D to 50D silicone rubber. The outer portion 238 
of the tubular body 202 is formed from a similar material, such as 50 D 
silicone rubber. The access tube may be also formed from silicone having a 
hardness of 40D to 50D. Conventional molding techniques may be used to 
form all these parts. 
Referring now to FIG. 11, the tubular body 202 of the arterial cannula 200 
may be implanted within an artery A by first surgically exposing the 
artery and thereafter forming an incision in the side of the artery. The 
tubular body 202 is the introduced through the incision, and the incision 
sutured to hold the body within the arterial lumen. The access leg 204 is 
then moved to a location where the arterial port 100 is to be implanted. 
Note that the entire assembly of the arterial cannula 200 and arterial 
port 100 may be implanted together within a single incision. 
Alternatively, the arterial cannula 200 and the arterial port 100 may be 
separately implanted, with the access leg 204 being separately positioned 
therebetween. 
Referring now to FIGS. 12-14, a third embodiment of a vascular cannula 300 
constructed in accordance with the principles of the present invention 
will be described. The cannula 300 includes both a tubular body 302 and an 
access leg 304. The access leg 304 is generally as described above with 
respect to access leg 204 in the previous embodiment. The tubular body 
302, however, differs significantly from the tubular bodies described 
previously. In particular, tubular body 302 is intended and adapted for 
anastomotic attachment within a single blood vessel or between two blood 
vessels, typically an artery and a vein. In the embodiment of FIGS. 12-14, 
the tubular body 302 comprises a continuous tube formed from a single 
material or composite structure, where the construction and material(s) 
are both of type generally employed for vascular grafts and implants. The 
construction of vascular grafts and implants is well known and well 
described in patent and medical literature. See, e.g., U.S. Pat. Nos. 
4,728,328; 4,731,073; 4,822,361; 4,842,575; 4,892,539; 4,955,899; and 
4,957,508, the full disclosures of which are incorporated herein by 
reference. Preferred materials for forming the tubular body 302 include 
expanded polytetrafluoroethylene (ePTFE), woven polyester, expanded 
polyurethane, and the like. 
The access leg 304 is joined to the tubular body by a valve assembly 306 
including a flange 308 and a collar 310. The flange is secured to an 
inside surface 312 of the tubular body 302, typically by an adhesive, such 
as a silicone adhesive. The collar 310 extends out through an opening 
formed in the wall 312, preferably at an angle in the range from 
30.degree. to 90.degree., often from 30.degree. to 60.degree., typically 
being 45.degree. as illustrated. The collar 310 is attached to a lower end 
of the access leg 304. Conveniently, such attachment may be effected using 
an inner sleeve 314 which is coaxially received in the collar in the end 
of the access leg 304. These joints may also be formed or reinforced by an 
adhesive, usually a silicone adhesive. The valve assembly 306 further 
comprises a split-membrane valve 320 at its lower end. A split 322 extends 
in the axial direction of the tubular body 302 and opens and closes in 
response to a differential pressure across the valve. 
Referring now to FIG. 16, instead of a flange 308, as illustrated in FIGS. 
13 and 14, the valve assembly 306 of vascular cannula 300 can be formed 
with a full tubular insert 308', as shown in FIG. 16. All other aspects of 
the cannula 300 would remain unchanged. Use of the tubular insert 308' is 
advantageous since it forms a more secure attachment to the tubular body 
302. The flange construction 308, in contrast, is advantageous in that it 
is less restrictive to the flow lumen through tubular body 302. 
Referring now to FIG. 15, a fourth embodiment of a vascular cannula 400 
constructed in accordance with the principles of the present invention 
will be described. The cannula 400 includes a tubular body assembly 402 
and an access leg 404. The access leg 404 will generally be a silicone 
rubber or similar tube, generally of the type described above in 
connection with the previous embodiments. The tubular body assembly 402 
comprises a rigid middle section 406 and two end sections 408 and 410, 
where the end sections are generally formed from tubular material of a 
type employed for fabricating vascular grafts and implants, also as 
described above. The rigid middle section 406 may be a hard plastic, but 
will usually be a biocompatible metal, such as titanium, vanadium, 
stainless steel, or the like. The middle section will have a silicone slit 
valve 412 positioned adjacent its lumen in a boss 414 formed on the side 
of the section. The slit valve is held in place by a male connector 416 
which will usually also be composed of a metal, more usually being 
titanium. An O-ring 418 helps maintain the seal, and the connector 416 may 
be attached to the boss 414 by threading or any other conventional 
attachment. The access leg 404 is attached over a barb 418 formed at the 
upper end of the connector 416. The ends 408 and 410 are attached to barbs 
420 and 422 formed at each end of the middle section 406. The attachment 
may be effected using an elastic ring 430 or a clamp (not shown), or any 
equivalent means. The remote ends 408 and 410 may be connected to a blood 
vessel by conventional anastomotic techniques. 
Referring now to FIGS. 17 and 18, a fifth embodiment of a vascular cannula 
500 constructed in accordance with the principles of the present invention 
will be described. Instead of a tubular body, as described in previous 
embodiments, the cannula 500 includes a patch 502 which is used to secure 
the cannula to a blood vessel, typically a large vein. The patch 502 may 
be formed from any of the materials described above for tubular bodies, 
including ePTFE, woven polyester, expanded polyurethane, preferably being 
formed from ePTFE. An access leg 504 is constructed generally as described 
above for previous embodiments, except that it terminates in a small 
flange 506, typically having a diameter in the range from 4.5 mm to 45 mm, 
usually from 15 mm to 25 mm. The flange 506 comprises slit valve 508 and 
is attached at its periphery to an aperture formed in the patch 502. The 
patch 502 will be secured to the target blood vessel, typically being 
inserted through an incision, secured to the outside of the blood vessel, 
e.g. by suturing, by tissue adhesives, or the like, or sutured or 
otherwise secured into a region of the blood vessel which has been cut 
away. The slit valve 508 will thus be positioned adjacent to the blood 
vessel lumen, as with previous embodiments. 
Although the foregoing invention has been described in some detail by way 
of illustration and example, for purposes of clarity of understanding, it 
will be obvious that certain changes and modifications may be practiced 
within the scope of the appended claims.