Omentum diffusion catheter

An implantable catheter for use in delivering insulin or other therapeutic fluids is disclosed which uses a novel terminator design to prevent the growth of fibrotic tissue from obstruction the catheter. The catheter takes advantage of fibrotic encapsulation by utilizing a depression in the surface of the terminator which will effectively keep fibrotic tissue spaced sufficiently away therefrom to allow fluid to be infused. In addition to being capable of long term implant, the catheter is implantable in the omentum, enabling the body's natural absorption of insulin to be successfully mimicked.

BACKGROUND OF THE INVENTION 
Field of the Invention 
The present invention relates generally to an implantable catheter for use 
in the infusion of a therapeutic fluid into a living patient over a 
substantial period of time, and more particularly to an implantable 
catheter which both exhibits substantial resistance to flow diminution or 
elimination due to the growth of fibrotic tissue around the catheter and 
exhibits enhanced absorption kinetics. 
Metabolism of glucose in the body is a particularly important chemical 
reaction which allows the utilization of the energy contained in food. The 
physiological system of the body has a sophisticated regulatory system 
which, when operating properly, maintains the level of blood glucose at an 
optimum level, thereby assuring the availability of adequate amounts of 
glucose when needed by the body. 
This glucose regulatory system utilizes insulin to regulate blood glucose 
in two ways. First, the rate of glucose transport through the cell 
membrane of many body cell types is increased by insulin. In the absence 
of insulin, the rate of glucose transport through such cells is 
dramatically reduced to less than one-fourth the normal rate of glucose 
transport. However excessively high insulin levels can greatly increase 
the rate of glucose transport to five times the normal rate. It is thereby 
apparent that insulin level has at least the capacity to adjust the rate 
of glucose absorption in the body by a factor of twenty. 
Secondly, insulin acts as a regulatory hormone which is supplied to the 
liver. The secretion of insulin by the pancreas is stimulated by digestion 
and the accompanying higher glucose levels in the body, resulting in an 
increase in the amount of insulin secreted into the portal vein. While 
approximately half of the insulin secreted into the portal vein is 
distributed throughout the body by the cardiovascular system, the rest of 
the insulin is immediately absorbed by the liver. In response to the surge 
of insulin, the liver produces large quantities of glucokinase, an enzyme 
enabling conversion of glucose into glycogen, which may be stored by the 
body. Much of the excess glucose entering the cardiovascular system as a 
result of digestion is thereby quickly removed to maintain relatively 
normal levels of glucose concentration in the blood. 
When the level of glucose concentration in the blood later begins to drop 
below normal, the level of insulin secretion by the pancreas is reduced, 
and production of the hormone glucagon is begun. Glucagon enables the 
conversion of glycogen in the liver back into glucose by activating liver 
phosphorylase, an enzyme, and the result is the release of glucose into 
the cardiovascular system for distribution throughout the body. Once 
again, the body acts to maintain the concentration of glucose in the blood 
at a normal level. 
The system which maintains a normal level of blood glucose is finely 
balanced, and the relationship between the pancreas and the liver can be 
easily upset. The most common problem is the situation when the pancreas 
no longer secretes adequate levels of insulin, a condition known as 
"diabetes mellitus." In some instances, the pancreas may completely cease 
the production of insulin. 
In any event, the diminution or reduction in insulin production results in 
a rise in the concentration of glucose in the blood, which causes the 
osmotic pressure in extracellular fluids to rise above normal pressure. 
The result of this increase in osmotic pressure is typically significant 
cellular dehydration. The increase in the blood glucose concentration also 
affects the kidneys, thereby causing them to act to remove excess glucose 
from the blood, in which process fluids are further removed from the body. 
The diminution of insulin production is also accompanied by a substantial 
reduction in the transportation of glucose into most tissues of the body. 
In addition, an insulin shortage also prevents glucose from being stored 
in the liver as glycogen, thereby resulting in a lack of available glucose 
in the times of glucose need. In conditions in which there is an absence 
of sufficient levels of glucose, body cell metabolism becomes fat based 
instead of carbohydrate based Heavy dependence on fat metabolism due to 
insufficient blood glucose concentration results in a substantial rise in 
the concentration of acetoacetic acid and other keto acids to as much as 
thirty times normal levels, thereby causing a significant reduction in the 
pH of blood below its normal pH level of 7.4. 
When the kidneys attempt to alleviate the concentration of the various keto 
acids in the blood, substantial amounts of sodium are also removed, 
thereby further lowering the blood pH. Should the blood pH fall below 7.0, 
a coma state will typically be experienced, with the results frequently 
being fatal. 
Diabetic treatment has centered on restoring proper carbohydrate metabolism 
by the administration of insulin. For years insulin has been administered 
by multiple daily injections into the peripheral circulation, either by 
intramuscular or subcutaneous injection. More recently, insulin infusion 
pumps have been used to deliver insulin from a small, portable insulin 
infusion pump to a subcutaneous injection location on a more or less 
continuous basis. Both of these techniques have certain disadvantages, 
particularly the multiple daily injection technique. 
Peripheral insulin administration results in only about ten percent of the 
insulin administered reaching the liver, as compared to the fifty percent 
or so in normal individuals. Therefore, rather than hepatic glucose 
production being lowered first, blood glucose level is reduced due to the 
presence of higher than normal levels of insulin in the peripheral 
circulation by an increased utilization of glucose by body tissues. It is 
more difficult to maintain a normal level of blood glucose by using 
insulin injection, since, unlike the natural feedback system of the body, 
hepatic glucose production is not substantially decreased by insulin which 
is injected peripherally. 
It is therefore apparent that it would be desirable to administer insulin 
to a patient in a manner whereby a greater percentage of the insulin 
reaches the liver than in peripheral administration of insulin A catheter 
which would deliver insulin internally rather than peripherally would 
accomplish this objective, but since it would be internally implanted it 
would have to be capable of continuing to function effectively over an 
extended period of time. 
The problem with implantable catheters is that they rapidly tend to become 
overgrown with fibrotic tissue which will close off the catheter in short 
order. This is particularly true in those cases where only a small flow of 
medication is being delivered through the catheter. Several types of 
catheters have been used, with the most common being a simple tube having 
an aperture therethrough. At the end of the tube, the aperture allows 
medication to exit the tube and enter the body. It will be appreciated 
that such an arrangement is susceptible to being covered with fibrotic 
tissue relatively rapidly, since the fibrotic tissue will grow around the 
end of the tube. 
Variations include the addition of a disk which is mounted at the end of 
the catheter with the tube leading orthogonally to the disk with 
medication exiting the aperture of the tube at the center of the disk. 
While this design is somewhat less susceptible to clogging by the rapid 
growth of fibrotic tissue, in time the entire disk will be covered and the 
opening will be closed by the fibrotic tissue. The other approach that has 
been used is to make the opening of a small diameter to cause the fluid to 
exit the catheter with a relatively high velocity. 
It will be appreciated that these approaches leave something to be desired 
in an implantable catheter Since the implantation of a catheter generally 
involves major surgery, it is desirable that an implantable catheter be 
capable of operating over an extended period of time without requiring 
repair or replacement. Since catheters known in the art do not meet this 
need, the use of implantable catheters has been minimized to prevent the 
adverse effect of requiring frequent catheter repair or replacement 
SUMMARY OF THE INVENTION 
The disadvantages and imitations of the background art discussed above are 
overcome by the present invention. With this invention, an implantable 
catheter having a novel delivery end configuration is implanted in the 
tissue of the omentum. The distal or delivery end is placed into a fold in 
the omentum tissue, which is then sutured around the delivery end of the 
catheter. 
The present invention utilizes a novel configuration for the distal or 
delivery end of the catheter which greatly inhibits the ability of 
fibrotic tissue to choke off fluid delivered through the catheter. The 
configuration may be loosely called a "spoon," since it superficially 
resembles a spoon, but will be referred to herein as a catheter 
terminator. The terminator includes an area having well defined walls 
around the area, thereby creating a recessed area. Insulin (or another 
therapeutic fluid) is supplied through the catheter to the terminator, 
where it is supplied to a location on said recessed area relatively near 
one or more of the walls through a passageway in the terminator which 
leads to an aperture in the recessed area. 
The location of the terminator of the catheter in the omentum tissue is an 
ideal location The insulin will be absorbed effectively in a manner 
mimicking to the greatest extent possible the body's utilization of 
insulin The terminator of the catheter will be held in a secure location, 
with predictable absorption of the insulin. In addition, fibrotic tissue 
growth may happen at a somewhat reduced pace from other locations in the 
body. 
In a first embodiment, the distal or delivery end is a plastic terminator 
which includes at least one recessed surface or depression therein A 
segment of tubing connects the proximal end of the catheter, usually a 
pump connector, to the terminator of the catheter. The tubing may be 
connected to the terminator in a variety of ways, such as by insertion of 
the tubing into a cylindrical recess in the terminator, or by extending 
the tubing over one or more tapered frictional ridges on the terminator. 
A passageway in the terminator communicating with the tubing provides a 
supply of insulin from the tubing to the interior of the terminator The 
passageway communicates with the recessed surface through an aperture 
located near the edge of the recessed surface, and therefore near a wall 
defining the edge of the recessed surface. 
The aperture could also be located right at the edge between the recessed 
surface and the wall. Also, the terminator may have a recessed surface in 
the opposite side of the terminator from the first recessed surface, with 
a second aperture leading from the passageway to the second recessed 
surface. 
In a second embodiment, a plastic terminator is shaped more like the blade 
of a shovel than a spoon. The recessed area is formed by a longitudinal 
segment of a cylinder, typically of approximately 120-220 degrees, with 
one end closed. A passageway delivers insulin to an aperture located in 
the closed end, near to the cylindrical segment. The same type of 
connecting means described above may be used to connect the terminator to 
the tubing. 
While fibrotic tissue will grow around the catheter, occlusion of the 
aperture is prevented in both embodiments by the fact that the recessed 
surface is spaced away from the place where fibrotic tissue will grow. In 
the first embodiment, the walls surrounding the recessed surface support 
the fibrotic tissue away from the recessed surface, particularly the 
portion of the recessed surface near the walls where the aperture is 
located. In the second embodiment, the cylindrical segment performs the 
same function, supporting fibrotic tissue away from the area inside the 
cylindrical segment and the aperture. 
The effect of supporting the fibrotic tissue away from the recessed surface 
is to provide a pool area for the insulin as it exits the terminator 
through the aperture, thereby also aiding in absorption of the insulin. It 
will be realized that the design of the catheter of the present invention 
provides a more viable alternative for long term use than previously 
available catheters. It is capable of long term use without succumbing to 
catheter blockage due to the growth of fibrotic tissue around the 
terminator. It is of inexpensive construction, and affords substantially 
no relative disadvantages over other catheter designs. Its location in the 
omentum successfully mimics the body's absorption of insulin. It may 
therefore be perceived that the present invention affords substantial 
advantage over the art and is a highly desirable approach.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
The first embodiment in its preferred construction is illustrated in FIGS. 
1-3. A pump connector 20 of conventional construction for the infusion 
pump (not shown) is to be used as the proximal end of the catheter, and is 
connected to a length of tubing 22. The other end of the tubing 22 is 
connected to a catheter terminator 24 at the proximal end 26 of the 
catheter terminator 24. 
The catheter terminator 24 has a longitudinally extending cylindrical 
recess 28 in the proximal end 26 of the catheter terminator 24 for 
receiving the end of the tubing 22 which is not connected to the pump 
connector 20. The tubing 22 may be made of any medical grade material such 
as silastic, but is preferably constructed using multiwall tubing having 
as an annular inner layer polyethylene and as an annular outer layer 
silicone rubber or another suitable implantable medical grade material In 
order to utilize the catheter of the present invention with insulin, a 
coextruded or two layer tubing is necessary. Multiwall tubing is generally 
manufactured by extruding the inner or innermost tubing first, and 
successively extruding an outer annular layer around the previously 
extruded inner layer. 
The tubing 22 may be bonded to the cylindrical recess 28 to form a strong, 
durable seal with excellent shelf life characteristics in an economical, 
highly repeatable operation. Alternatively, the catheter terminator 24 may 
be made of polyethylene, and have a number of small apertures 34 on the 
top, bottom, and sides of the proximal end 26 of the catheter terminator 
24, which small apertures 34 lead into the cylindrical recess 28. In this 
case, as illustrated in the figures, the tubing 22 may be inserted into 
the cylindrical recess 28, and medical adhesive adhering only to the 
tubing 22 may be applied through the small apertures 34. In this case, the 
mechanical bond between the cured adhesive in the small apertures 34 and 
the outer layer 32 of the tubing 22 provides the force retaining the 
tubing 22 in the cylindrical recess 28. 
The configuration of the catheter terminator 24 is specifically designed to 
facilitate long term implantation without catheter blockage due to the 
growth of fibrotic tissue. Since it is recognized that some degree of 
encapsulation of the catheter terminator 24 by fibrotic tissue is 
inevitable, the design of the catheter terminator 24 takes advantage of 
the encapsulation by choosing the form and configuration of the 
encapsulation. It will be noted that the overall configuration of the 
catheter terminator 24 is accomplished to eliminate sharp edges, thereby 
minimizing encapsulation due to irritation or rejection. 
Specifically, the distal end 36 of the catheter terminator 24 is rounded, 
and the thickness of the catheter terminator 24 is tapered from the 
proximal end 26 to the distal end 36, as best shown in FIG. 2. The width 
of the catheter terminator 24 is of diminishing taper on both the proximal 
end 26 and the distal end 36 as shown in FIG. 1, with the maximum width 
being approximately one-third of the way from the proximal end 26 toward 
the distal end 36. The diminishing taper on the proximal end 26 of the 
catheter terminator 24 is necessary to facilitate removal of the catheter, 
if it should become necessary to do so. 
On the top surface of the catheter terminator 24 is a depression 38 
extending from the widest part of the catheter terminator 24 to the distal 
end 36 of the catheter terminator 24. The depression 38 is close to the 
sides of the catheter terminator 24, and the wall 40 on the edges of the 
depression 38 rises sharply from the depression 38. It will at once be 
appreciated by those skilled in the art that as the catheter terminator 24 
becomes encapsulated in fibrotic tissue, the fibrotic tissue will not as 
easily conform to the depression 38, particularly to those portions of the 
depression 38 near the wall 40. 
Within the catheter terminator 24 is a passageway 42 leading from the 
interior of the tubing 22 to an aperture 44 in the depression 38. The 
passageway 42 may have a right angle bend in it, as shown in FIG. 3, or it 
may have a gentler bend or a curve in it as shown in FIG. 4. The important 
consideration is that the aperture 44 in the depression 38 be located 
relatively near the wall 40, as opposed to being located centrally in the 
depression 38. The aperture 44 in the depression 38 may be located a short 
distance away from the wall 40 as shown in FIG. 3, or it may be located in 
the edge between the depression 38 and the wall 40, as shown in FIG. 4. It 
is also within the scope of the invention to locate the aperture 44 on the 
wall 44 rather than in the depression 38. 
A variation of this construction is shown in FIG. 5, which is like the 
catheter terminator 24 shown in FIGS. 1-3, with the exception that a 
second depression 46 is added to the bottom of the catheter terminator 24. 
In addition, the passageway 42 also leads to a second aperture 48 in the 
second depression 46. 
A second variation is shown in FIG. 6, with the catheter terminator 24 not 
having a diminishing taper on the distal end 36. 
The typical size of the terminator 24 may be, for example, approximately 
one and one-half inches long, seven-sixteenths of an inch wide, and from 
one-tenth to three twentieths of an inch in thickness, although it will be 
recognized by those skilled in the art that the size may vary 
significantly without departing from the spirit of the invention. 
In FIGS. 7-10, a second embodiment of the catheter of the present invention 
is shown. A catheter terminator 50 has at the proximal end 52 two tapered 
frictional ridges 54 used to sealingly retain the tubing 22 thereon. 
Inside the two tapered frictional ridges 54 to a cylindrical portion 56 of 
the catheter terminator 50 is a passageway 58 leading to an aperture 60 in 
the end of the cylindrical portion 56 of the catheter terminator 50 facing 
the distal end 62 of the catheter terminator 50. 
Extending from the end of the cylindrical portion 56 of the catheter 
terminator 50 facing the distal end 62 of the catheter terminator 50 is a 
curved surface 64 which is a longitudinal segment of a cylinder the same 
diameter and colinear with the cylindrical portion 56 of the catheter 
terminator 50. The curved surface 64 is typically from a 120 to 220 
degrees segment of a cylinder, and may also be U-shaped rather than 
arcuate in cross-section. 
The aperture 60 is located near to the inner surface of the curved surface 
64; alternatively, if the curved surface 64 is of sufficient curvature, 
the aperture 60 may be located centrally in the cylindrical portion 56 of 
the catheter terminator 50. It will again be appreciated by those skilled 
in the art that the catheter terminator 50 will also be highly resistant 
to occlusion caused by the growth of fibrotic tissue 
The typical size of the terminator 50 may be, for example, approximately 
one and one-fourth inches long and one-eighth of an inch in diameter, 
although again it will be recognized by those skilled in the art that the 
size may vary significantly without departing from the spirit of the 
invention. It will also be recognized that the diameter is critical, since 
the inner curvature must be small enough to inhibit fibrotic tissue from 
conforming thereto. 
The catheters using the terminators 24 or 50 may be implanted in the tissue 
of the omentum (not shown), with a fold of omentum tissue being sutured 
around the terminators 24 or 50. The location of the terminator of the 
catheter in the omentum tissue is an ideal location, since the insulin 
will be absorbed effectively in a manner mimicking to the greatest extent 
possible the body's utilization of insulin and the terminator 24 or 50 
will be held in a secure location 
The effect of supporting the fibrotic tissue away from the depression 38 
(and 46) or the inside of the curved surface 64 is to provide a pool are 
for the insulin as it exits the terminator 24 or 50 through the aperture 
44 (and 48) or 60, thereby also aiding in absorption of the insulin. The 
design of the catheter of the present invention provides a more viable 
alternative for long term use than previously available catheters, since 
it is capable of long term use without succumbing to catheter blockage due 
to the growth of fibrotic tissue. It is of inexpensive construction, and 
affords substantially no relative disadvantages over other catheter 
designs while attaining the advantages enumerated herein. The present 
invention therefore affords a substantial number of advantages over the 
art and is a highly desirable device. 
Although an exemplary embodiment of the present invention has been shown 
and described, it will be apparent to those having ordinary skill in the 
art that a number of changes, modifications, or alterations to the 
invention as described herein may be made, none of which depart from the 
spirit of the present invention. All such changes, modifications, and 
alterations should therefore be seen as within the scope of the present 
invention.