Apparatus and method for retaining a catheter in a blood vessel in a fixed position

A method and apparatus for retaining a catheter tip in a fixed position within a blood flow and preventing it from contacting a blood vessel wall. The apparatus includes a tip retainer at the distal end of the catheter that anchors the tip of the catheter within the blood vessel. The catheter tip is retained within the blood vessel spaced from the wall to ensure that it does not contact the wall of the blood vessel. This reduces damage to the blood vessel caused by chronic movement and contact between the catheter tip and the wall of the blood vessel. In one embodiment, the tip retainer includes a prong that penetrates the wall of the blood vessel, thus preventing the catheter tip from moving longitudinally within the blood vessel. In alternative embodiments, the tip retainer contacts the wall but does not penetrate the wall.

TECHNICAL FIELD 
This invention relates to intravascular catheters that have means for 
reducing stenosis and thrombosis at the tip of the catheter. 
BACKGROUND OF THE INVENTION 
The treatment of a number of medical conditions requires the placement of 
catheters within a patient's blood vessel for an extended period of time. 
These long-term applications include blood access for hemodialysis, 
chemotherapy, parental nutrition, blood transfusions and blood sampling. 
Vascular access with catheters was first introduced more than 20 years ago. 
With the advent of soft, flexible silicone double lumen catheters, both 
acute and chronic hemodialysis became a routine procedure. Although 
subclavian dialysis catheters are easily inserted and well tolerated, 
catheter lifespan averages about three months. This is of great concern to 
patients on maintenance dialysis. 
It is well known in the medical field that chronic placement of a catheter 
in a patient's blood vessel often results in catheter failure due to 
aspiration of the blood vessel wall into the tip of the catheter, clot or 
thrombus formation at the tip of the catheter, or stenosis around the tip 
of the catheter. A catheter failure resulting from one or more of these 
mechanisms is evidenced by an inability to aspirate and/or infuse fluid 
through the catheter, generally referred to as catheter occlusion. 
Typically, catheter occlusions caused by aspiration of the blood vessel 
wall or clot formation at the catheter tip may be resolved by 
repositioning the catheter tip or infusing antithrombotic agents. 
Stenosis is a narrowing of the blood vessel lumen as seen in a venogram 
and, in general, can be due to either the formation of a thrombus within 
the blood vessel or a thickening of the blood vessel wall. The generally 
accepted view is that stenosis around the tip of a catheter implanted 
within a blood vessel is due to the formation of a thrombus resulting from 
a biochemical reaction to the introduction of a foreign material into the 
blood vessel. Previous attempts to prevent catheter occlusion have 
centered around thromboresistant coatings on the catheter surface in order 
to prevent the biochemical reaction of the patient's blood to the material 
of which the catheter is formed. 
Prior art related to the present invention deals with the placement of 
stents within a diseased blood vessel to treat the problems associated 
with stenosis. Stents range from simple wire meshes used in U.S. Pat. No. 
4,800,882, to a canister made of hydrophilic plastic which expands upon 
placement in a blood vessel as in U.S. Pat. No. 4,434,797. Stents are 
typically secured to a deployment catheter for insertion into the 
patient's blood vessel via a percutaneous procedure. Surgical placement of 
these stents is achieved by feeding the catheter from a distant site, 
e.g., a percutaneous puncture into the femoral artery, to the stenosis 
target. The deployment catheter is then removed, leaving the stent within 
the blood vessel lumen. 
Prior publications on the subject of mounting devices in the blood stream 
include "Registration of Phoric Changes of Blood Flow by Means of a 
Catheter-Type Flowmeter," by Heinz Pieper printed in The Review of 
Scientific Instrument 29(11):965-967, November 1958, and U.S. Pat. Nos. 
4,425,908; 4,936,823; 4,813,930; 5,135,517; and 4,654,028. However, none 
of these address and solve the problems presented in the field of the 
present invention. 
SUMMARY OF THE INVENTION 
The present invention is directed to an intravascular catheter that has 
means to retain the tip of the catheter within a blood vessel lumen such 
that the tip of the catheter is prevented from contacting the wall of the 
blood vessel. This prevents repeated impact between the catheter tip and 
blood vessel wall. This reduces denudation and damage to the endothelial 
and smooth muscle cells that line the blood vessel wall. By reducing 
damage to these cells, the invention allows for the cells to continue to 
release the bioactive molecules that normally prevent and reverse the 
thrombotic and coagulation processes in blood. 
Most vascular injury research is in the area of arterial injury; however, 
the mechanism that regulates cellular growth in injured veins is not 
known. It is a reasonable assumption that the "response to injury 
hypotheses" proposed in Ross, R., Glomset, J. A., "The Pathogenesis of 
Atherosclerosis," N. Engl. J. Med. 295:369-77, 1976, can also be applied 
to injuries in the venous system. This hypothesis is based on the 
following observations after injury to the lumen of the blood vessel: (1) 
platelet adherence and degranulation precedes smooth muscle cell 
proliferation; (2) intimal thickening in injured arteries of 
thrombocytopenic animals is reduced; (3) platelet granules contain potent 
mitogens for cultured smooth muscle cells. Based upon these observations, 
Ross and Glomset suggested that a high local concentration of growth 
factors, particularly platelet-derived growth factors released from 
degranulating platelets could stimulate smooth muscle cell proliferation. 
Their hypothesis is based on a relationship between the thrombosis that 
occurs within an injured vessel and the subsequent cell growth associated 
with repair of the injured vessel wall. 
Normally, hemostasis results from a delicate balance between 
clot-stimulating and clot-inhibiting processes. Endothelial cells and 
smooth muscle cells in a normal blood vessel are probably the main source 
of clot regulating factors such as heparin or heparan sulfate. These 
heparin and heparin-like molecules prevent the adherence of blood proteins 
and platelets to the surface of a normal blood vessel. Since the 
endothelium is a critical component of hemostasis control, localized 
injury and denudation of the endothelium by repeated impact with a 
catheter tip results in a shift of this delicate balance toward clot and 
thrombus formation within a denuded region. This clot formation may occur 
even if the catheter is composed of a material that normally would not 
create a reaction in the body. 
Physical damage to the wall of the blood vessel affects the release and 
production of a number of growth-stimulating factors such as basic 
fibroblast growth factor and platelet-derived growth factor. These growth 
factors help to overcome the antiproliferative activities of the heparan 
sulfates, thus helping to initiate cellular proliferation and the 
migration of smooth muscle cells that ultimately leads to stenosis. 
Therefore, preventing physical damage to the endothelial cell lining of 
the blood vessel wall reduced stenosis, as well as thrombosis, at the tip 
of the catheter. 
Prior art catheters allow chronic and repeated contact between the catheter 
tip and the wall of the blood vessel, resulting in damage to the blood 
vessel as discussed previously. The tip of the catheter may repeatedly 
bump into different locations inside the blood vessel, or the same 
location a number of different times, causing a reaction, or worse, damage 
to the vessel wall. Further damage is caused by the aspiration of the 
blood vessel wall into the catheter lumen. This occurs when blood is 
withdrawn through the catheter, such as in the performance of dialysis. 
The present invention solves the problems by approaching them from an 
entirely different view than the prior art attempts; namely, by preventing 
repeated impact between the catheter tip and the blood vessel wall. The 
inventor has found that repeated impact with the vessel wall and a 
catheter tip, even if it is a soft tip, causes a physical reaction in the 
blood vessel wall. This reaction occurs because of repeated contact 
between the catheter tip and the wall of the blood vessel even if the 
catheter tip is soft, and even if the tip is properly coated with 
antithrombotic agents. This catheter-induced reaction in the blood vessel 
wall may lead to the formation of a mural thrombus and/or abnormal 
cellular proliferation within the blood vessel wall, thus resulting in 
stenosis and catheter occlusion. Prior art efforts to prevent catheter 
occlusion through the use of thromboresistant coatings do not alleviate 
the physical reaction that the catheter tip may cause to the blood vessel 
wall by repeated impact. Therefore, chronic placement of a catheter in a 
patient still results in catheter occlusion in the majority of cases. 
In accordance with aspects of the present invention, chronic contact 
between and aspiration of the blood vessel wall by the catheter tip is 
prevented. This reduces damage to the endothelial cells lining the blood 
vessel, thus reducing catheter occlusion due to stenosis and thrombosis. 
In addition, the occurrence of catheter occlusion resulting from 
aspiration of the vessel wall will be reduced. 
The present invention includes, in one embodiment, an antistenotic 
intravascular catheter for insertion into a blood vessel. The catheter 
includes a tip retainer, located at the distal end of the catheter, for 
retaining the tip of the catheter within the blood vessel and preventing 
the catheter from contacting the wall of the blood vessel. The tip 
retainer positions the tip of the catheter within the blood vessel without 
substantially obstructing fluid flow through the blood vessel. The 
catheter also includes an internal passageway for permitting fluids to 
pass through the catheter. Preferably, the catheter is a double lumen 
catheter of the type used generally in kidney dialysis. 
In all embodiments, the tip of the catheter is retained in the blood vessel 
by anchoring the tip with respect to the wall of the blood vessel. 
Advantageously, the tip retainer permits some movement of the catheter tip 
with respect to the vessel wall, such as slight movement forward and back 
or side to side with the pulsation of the blood flow. However, movement is 
restricted to minimize repeated contact (or all contact) of the tip with 
the blood vessel wall. Just as the anchor of a ship anchors a ship to the 
bottom but permits some movement of the ship as the water rises and falls 
or flows, similarly the tip retainer can be said to anchor the tip to the 
vessel wall but still permit some movement of the tip based on changes of 
the flow in which it is anchored. 
Numerous alternative embodiments are disclosed for the tip retainer. In 
some embodiments, the tip retainer does not penetrate the wall of the 
blood vessel. In one embodiment, the tip retainer includes a penetrating 
member that does penetrate the blood vessel wall. In all embodiments, the 
tip of the catheter is retained in the blood vessel by anchoring the tip 
with respect to the wall of the blood vessel. 
In one preferred embodiment, the tip retainer is two or more loops of wire 
that flex outward and contact the wall. The loops do not penetrate the 
wall tissue, but do anchor the tip in a fixed position in the blood 
vessel, retaining it in the blood flow and preventing contact of the tip 
with the vessel walls. 
In another preferred embodiment, a single loop extends from the tip portion 
of a double lumen catheter. The single loop is composed of a flexible wire 
coated with silicone, silicone tubing or, alternatively, is composed of 
silicone tubing alone. The diameter of the loop is selected to be 
sufficiently large that the loop bridges any branches in the blood vessel 
which are likely to be encountered when the catheter is positioned within 
the blood vessel. 
As a further alternative, the silicone tubing which forms the loop may be 
in fluid communication with the lumen of the catheter separate from the 
lumen used for the kidney dialysis. Medication can be delivered through 
the lumen for delivery to the walls of the blood vessel at the point of 
contact by the loop. This provides the distinct advantage that 
anticoagulant medication can be delivered specifically to walls of the 
blood vessel near the catheter tip. 
In a further embodiment the tip retainer includes fletching to anchor the 
catheter tip in the blood vessel. Alternatively, the tip retainer is a 
plurality of single straight wires that are prestressed to flex outward or 
straight wires with loops on the end. 
In accordance with one embodiment of the invention, the tip retainer 
includes penetration means for penetrating the wall of the blood vessel 
and preventing the tip of the catheter from moving longitudinally within 
the blood vessel. In this embodiment, the tip includes a loop for limiting 
the depth of penetration. 
In one embodiment of the invention, a plurality of members run from the 
proximal end of the catheter to the distal end where they extend radially 
outward until they contact the wall of the blood vessel. In this 
embodiment, the catheter includes withdrawal means for withdrawing the 
positioning means into the catheter such that the positioning means is 
prevented from damaging the wall of the blood vessel when the catheter is 
withdrawn from the blood vessel. The withdrawal means includes a guideway 
that runs from the proximal end of the catheter to the distal end of the 
catheter. The positioning means extends from the proximal end to the 
distal end of the catheter within the guideway. 
According to one aspect of the present invention, a method for reducing 
catheter failure due to stenosis or thrombosis at a catheter tip is 
provided. Positioning means is attached to the catheter tip, and the 
catheter tip and attached positioning means are placed within the blood 
vessel without substantially obstructing fluid flow through the blood 
vessel and such that the catheter tip is prevented from contacting the 
blood vessel wall.

DETAILED DESCRIPTION OF THE INVENTION 
FIG. 1 is a perspective view of a first preferred embodiment of an 
antistenotic intravascular catheter 2 of the present invention. Catheter 2 
includes a tube 4 formed from a material suitable for placement in a blood 
vessel, such as silicone rubber. The catheter includes a Dacron anchor 
cuff 14 for anchoring the catheter subcutaneously. An in-line clamp 16, 
for preventing fluid flow, is placed on tube 4 adjacent the proximal end 
6. The proximal end 6 of the catheter is attached to a luer-lock adapter 
18 which is sealed by threading an injection sealing cap 20 onto the 
adapter in a manner known in the art. 
According to one aspect of one embodiment of the present invention, the 
intravascular catheter 2 includes a tip retainer 9 for retaining the 
distal end 8 in the bloodstream and preventing the tip of the catheter 
from contacting the wall of a blood vessel 30 as shown in FIG. 2A. 
In a first embodiment, the tip retainer 9 includes four wires 12 positioned 
within the catheter wall and extending along the length of the catheter, 
from the distal end of the catheter towards the proximal end 6 of the 
catheter. This ensures that the proximal ends 34 of the wires 12 will be 
accessible outside the patient's body after the catheter has been 
implanted in a blood vessel 30. The proximal ends 34 of the wires 12 are 
secured to the catheter by an appropriate method such as heat shrink 
Teflon.TM. tubing 32 that is placed over the wires and shrunk in place. 
The proximal end of the wires could also be secured through the use of a 
band integrally formed in the tube 4 or other structures which prevent 
movement of the proximal end 34 of the wires 12 until they are controlled 
by a physician. 
The wires 12 are preferably made of or coated with a material which does 
not cause an adverse reaction when placed in the patient's body. Suitable 
materials include stainless steel, titanium, some plastics such as nylon, 
some composite materials, and Teflon.TM.-coated wires, including 
Teflon.TM.-coated stainless steel. Depending upon the application, the 
wires 12 have a diameter ranging from 0.0025 to 0.076 cm. In some 
applications, it may be desirable to treat the wires 12 with an 
antithrombotic coating, for example, dipping or plating the wires in a 
coating or applying a coating through plasma polymerization in order to 
reduce blood clotting on the wires. Plasma polymerization is explained in 
detail in Yeh et al., "Blood compatibility of surfaces modified by plasma 
polymerization," Journal of Biomedical Materials Research 22:795-818, 
1988. 
As shown in FIG. 2A, in one embodiment, the wires 12 extend along the 
length of the catheter through guideways 38 and exit the guideways at 
openings 40. The guideways 38 protect the wires 12 while also maintaining 
proper positioning between the individual wires. Guideways 38 and wires 12 
are preferably extruded as an integral part of tube 4, or alternatively 
are extruded individually and are later attached onto the outside of the 
tube 4 or inserted into tube 4. In the embodiment shown, four wires 12 are 
used, however, a different number of wires, such as three or five, could 
be used, depending upon the application. 
Preferably, the four wires 12 are equally spaced circumferentially around 
the distal end 8 such that they serve as a tip retainer 9 and positioning 
means for positioning the tip of the catheter within the blood vessel 30. 
The tip retainer ensures that the tip of the catheter does not contact the 
inner wall 27 of the blood vessel 30. The thin wires 12 restrict movement 
of the tip of the catheter to prevent it from hitting the inner wall 27 
while not substantially obstructing the fluid flow through the blood 
vessel and not causing clots. 
In the embodiment illustrated in FIG. 2A, a loop 25 is formed near the end 
of each wire 12, and a short penetration prong 26 is formed that extends 
outwardly from each loop. The prongs 26 penetrate the wall of the blood 
vessel 30. Each prong 26 is sized and extends from loop 25 such that the 
prong penetrates the wall of the blood vessel to a depth in the range of 
0.1 to 3 mm after placement within the blood vessel. The loops 25 serve as 
limiting means for limiting the depth to which the prongs 26 penetrate. 
This prevents the tip 8 of the catheter from moving longitudinally within 
the blood vessel 30. 
Other structures could also be used to perform the penetration and depth 
limiting functions. As an example, instead of forming a loop near the end 
of each wire, an enlarged section such as thickening of the wire band 
welded or bonded to the wire or a bend near the tip of the wire could be 
used. 
The distal end of the catheter is retained within the blood vessel and 
prevented from contacting the endothelial cells lining the blood vessel by 
rubbing or aspirating the wall of the blood vessel by the tip retainer 9. 
Additionally, noncontact damage to the endothelial cells of the blood 
vessel, such as through fluid dynamics wherein the force of the flow of 
fluid around the openings of the catheter may cause cellular damage, is 
believed to be reduced by the present invention. Although penetration of 
the wall 27 by prongs 26 causes some damage to the blood vessel, the 
damage caused is not significant in comparison to the damage that would be 
caused by repeated impact or chronic rubbing of the tip 8 or by aspiration 
of the inner wall 27, which may occur with prior art catheter designs. By 
reducing the contact with and damage to the endothelial cells, the present 
invention allows for the continued release of anticoagulant molecules by 
the endothelial cells in the vicinity of the distal end of the catheter as 
explained previously. Correspondingly, there is a reduction in thrombosis 
and/or stenosis of the blood vessel lumen at the distal end of the 
catheter and thus reduced catheter occlusion. 
The antistenotic intravascular catheter 2 (FIG. 1) may be placed within the 
blood vessel 30 using a sheath introducer of the type shown in more detail 
in FIGS. 22-24, an embodiment of which is explained with respect to those 
Figures. In one embodiment, a tubular introducer sheath is inserted within 
a patient's blood vessel, with the sheath terminating at the point within 
the blood vessel where the distal end 8 of the catheter is to be placed. 
The catheter 2 is then placed within the introducer sheath with the wires 
temporarily constrained along the catheter's longitudinal axis by the 
sheath. The catheter is then pushed down the sheath until the distal end 8 
of the catheter exits the introducer sheath. As the distal end of the 
catheter exits the introducer sheath, the wires 12 spread radially to 
contact and penetrate the blood vessel wall as shown in FIG. 2A. After 
placement of the catheter into the blood vessel, the introducer sheath is 
removed from the blood vessel. 
Another technique for placing the inventive catheter tip retainer within 
the blood vessel wall is with an inflatable balloon. Small balloons for 
insertion into the blood stream and methods to inflate them are known in 
the field of medical treatment devices. According to one aspect of 
installing this invention, the wires 12 are positioned circumferentially 
around such a deflated balloon. The balloon is then introduced into the 
blood vessel by any acceptable technique. When the tip of the catheter is 
at the proper location, the balloon is inflated and the wires 12 contact 
the wall 30. In the embodiment in which prongs 26 are present on the ends 
of wires 12, the prongs are solidly pressed and embedded into the vessel 
wall 30 under the force of the balloon. The balloon is then deflated and 
removed. If this installation technique is used, the wires 12 do not need 
to be spring-biased outward; the force of the balloon will press them 
outward into contact with the wall 30. 
The catheter 2 is removed from the blood vessel by first removing the heat 
shrink Teflon.TM. tubing 32 or other structure which secures the proximal 
ends 34 of the wires. Each wire 12 is then withdrawn from contact with the 
blood vessel wall 27 into its respective guide tube 38. FIG. 2B shows the 
wires in this partially withdrawn position. Each wire 12 is withdrawn 
until the loops 25 and prongs 26 are retracted into the soft silicon 
rubber that forms tube 4 and guideways 38. After withdrawing each wire 12 
into its respective guide tube, the catheter is withdrawn from the blood 
vessel using standard catheter withdrawal procedures. The ability to 
withdraw the prongs 26 and loops 25 into the guideways 38 reduces damage 
to the blood vessel upon removal of the catheter. 
FIG. 3 shows the distal end of a second embodiment of the present 
invention. The second embodiment comprises a tube 41 with an elliptical 
cross section and two lumens 42 and 44 that run the length of the 
catheter. The second embodiment is intended to be used for hemodialysis 
applications in which one of the lumens is used to aspirate blood and the 
other lumen is used to infuse blood after dialysis. As in the first 
embodiment, four positioning wires 50 extend the length of the catheter 
within guideways 52. In the second embodiment, two of the wires 50 are 
located along the major axis of the elliptical tube 41 while the other 
wires are located along the minor axis. In this embodiment, the two wires 
50 located along the major axis may extend from the tube 41 at a different 
angle than the two positioning wires which are located along the minor 
axis. Each wire 50 has a loop 54 and tip 56 near its end. The tips 56 
serve as penetration means for penetrating the wall of the blood vessel, 
while the loops 54 serve as limiting means for limiting the depth to which 
the tips 56 penetrate. 
FIG. 4 shows the distal end of a third embodiment of the present invention. 
The third embodiment has four positioning wires 60 attached to the distal 
end 62 through the use of securing hoops 64 and heat shrink Teflon.TM. 
tubing 66, which is placed over the hoops and shrunk into place. The 
combination of the securing hoops 64 and Teflon.TM. tubing 66 helps ensure 
that the hoops 64 and wires 60 are securely attached to the distal end 62 
of the catheter. In an alternate embodiment, not shown, the wires 60 could 
be integrally formed into the catheter, thus eliminating the need for 
securing hoops 64 and tubing 66. 
The positioning wires 60 extend radially outward from the securing hoops 
64. The wires 60 may be attached to securing hoops 64 by welding, brazing 
or other appropriate means. In some applications, it may be desirable to 
treat the wires 60 with an antithrombotic coating to reduce blood clotting 
on the wires, as explained for the first embodiment. Each wire 60 has a 
loop 68 formed near the end of the wire, such that a short penetration tip 
70 extends outwardly from each loop. The prongs 70 serve as penetration 
means for penetrating the wall of the blood vessel, while the loops 68 
serve as limiting means for limiting the depth of penetration. 
This third embodiment of the antistenotic intravascular catheter is 
inserted into a patient's blood vessel using the same process as described 
for the first embodiment. Although the third embodiment is structurally 
simpler than the first embodiment, it requires a more complex procedure in 
order to remove the catheter from the patient's blood vessel. The third 
embodiment may be removed using a procedure similar to the catheter 
insertion procedure described in the first embodiment. A tubular 
introduction sheath of the type shown in FIGS. 22-24 is placed over the 
catheter at the location where the catheter enters the blood vessel, and 
is subsequently slid down the catheter until it reaches the distal end of 
the catheter. The tubular introduction sheath slides over the positioning 
wires 60, withdrawing the loops 68 and prongs 70 from contact with the 
wall of the blood vessel. After withdrawing the loops and tips into the 
introduction sheath, the catheter is slid within the introduction sheath 
and withdrawn from the blood vessel. The introduction sheath could be 
removed during or subsequent to removal of the catheter from the patient's 
blood vessel. 
FIG. 5 illustrates a tip retainer 9 at the distal end 8 of the catheter 
constructed according to an alternative embodiment for retaining the 
catheter tip within the blood flow stream and preventing the tip from 
contacting the inner wall 27 of the blood vessel 30. According to this 
alternative embodiment of FIG. 5, the tip retainer 9 includes wires 72 
having a blunt terminating end 74 for contacting the inner wall 27 of the 
blood vessel 30. The blunt end 74 does not include a sharp tip of the type 
previously described with respect to tips 26, 56 and 70. Instead, the 
blunt end 74 contacts the inner wall 27 but does not penetrate the wall of 
the blood vessel 30. The four wires 72 act to anchor the tip of the 
catheter with respect to the blood vessel wall and retain the tip within 
the flow in the blood vessel while preventing the tip 8 from contacting 
the blood vessel wall with the advantages as previously described. The 
wires 72 are prestressed to be resiliently spring biased outward with an 
equal pressure from each of the wires 72 such that the tip 8 is generally 
centered within the blood vessel 30. 
An indexing mark 76 is also included on the catheter tube 4, extending 
along the length of the catheter tube 4. The indexing mark 76 visually 
indicates to a user the rotational orientation of the tip 8 within the 
blood vessel and thus indicates the rotational orientation of the tip 
retainer assembly. The position of the indexing mark 76 may indicate, for 
example, that the rotational orientation of the tip 8 is such that one of 
the wires 72 is positioned where two of the blood vessels join together 
and is not contacting any wall of the blood vessel or providing 
stabilization. The user may then elect to change the rotational 
orientation of the tip 8 such that each of the wires 72 is firmly in 
contact with the blood vessel wall. This visualization could also be done, 
for example, with the catheter positioned within the introducer sheath. 
However, one reason for providing at least three and more preferably four 
wires 72 is because contact with three wires is generally deemed 
sufficient to stabilize and retain the tip 8 such that it does not contact 
the wall 27. For example, the catheter 4 having the inventive tip retainer 
at the distal end 8 may be positioned at or near the brachial cephalic 
junction and there is a likelihood that one or more of the wires 12 may 
fall into the junction. One advantage of having multiple wires is that the 
tip 8 can be stably anchored even if one of the wires is not anchored to 
the wall because the other wires will hold it in position. Thus, even if 
one of the wires 72 is not contacting the blood vessel wall because it is 
positioned in or along the junction, the other wires 72 will be contacting 
the wall and will retain the tip 8 in a position to prevent it from 
repeatedly bumping against the inner wall 27 of the blood vessel 30. 
FIG. 6 illustrates an alternative embodiment for the tip retainer 9 having 
wires 78. The wires 78 include enlarged loops 80 at their distal end. The 
enlarged loops 80 do not penetrate the blood vessel wall 30. Instead, they 
rest firmly against the inner wall 27, as an anchor to firmly retain the 
tip 8 in a fixed position within the blood vessel. The loops 80 have an 
enlarged surface area to ensure that the blood vessel wall 30 is not 
penetrated while providing a firm support for the tip retainer 9. The loop 
80 abuts firmly against the inner wall 27 without penetrating it in a 
manner similar to the anchor of a ship resting on the sea bottom but not 
penetrating through the sea floor. The tip retainer 9 in this way anchors 
the tip 8 without penetrating the wall of the blood vessel 30. 
FIG. 7 illustrates an alternative embodiment of the tip retainer 9 having 
wires 82 formed in an enlarged loop 84. The loops 84 are formed from a 
single piece of wire that is bent at the end and terminates by being 
contacted to itself at the end 87, a single wire being within the 
guideway. Alternatively, the loop 84 is formed from the wire 82 being bent 
in half and having two sections of the wire 82 extend within the guideway 
86. The two ends of the wire 82 extend out of the proximal end of the tube 
4 at position 34 as shown with respect to FIG. 1. The wires 82 can 
therefore be extended or retracted, according to the user's preference, to 
provide loops 84 of a desired size and shape. The wires of the loops 84 
are prestressed or bent to be resiliently spring biased outward so they 
extend with equal force and equal distance from the tip 8 so as to retain 
the tip 8 in approximately the center of the blood vessel 30. Use of loops 
84 provides the advantage of broad contact area 85 with the inner wall 27 
while ensuring there is no penetration of the wall. The broad contact area 
at a distal region of each of the loops 84 is a further aid for centering 
the tip 8 and ensuring that it is firmly retained within the blood flow 
and the blood vessel and does not contact the inner wall 27. 
FIG. 8 is an alternative embodiment generally along the lines of FIG. 7 
with the loops 84 formed in a cloverleaf arrangement. The cloverleaf shape 
of the wires 84 serve to further increase the contact area and provides 
strength in anchoring the tip 8 of the catheter 4 within the blood vessel 
but without penetrating the wall of the blood vessel. In one embodiment, 
the loops exit from the tip region 8 a selected distance 95 back from the 
end of the tip. Having the wires exit spaced apart from the tip end 120 
decreases the risk of creating blood clots at the end 120 or forcing the 
lumen shut at the face 120 under a heavy spring force by the wire loops 
84. The end region 8, particularly the face 120, may be constructed of a 
somewhat stiffer material to keep the lumen opening from being partially 
closed when the wire loops 84 are deployed. 
In the cloverleaf arrangement of FIG. 8, each end of one wire extends down 
its own guideway 86, or alternatively multiple wires may extend down the 
same guideway 86, permitting user manipulation of individual wires. The 
wires may exit from the face 120 of tip 8, or, as shown, exit from a 
location along the sidewall and extend forward, toward the tip. 
FIG. 9 illustrates an alternative embodiment for the tip retainer 9 of a 
three-leaf clover configuration. Three loops 89, 91, and 93 are provided 
that extend out of the surface of tip end 120 if desired. The three loops 
89, 91, and 93 are positioned equidistant around the catheter tube 4. 
Using three wires provide the advantage of fewer wires in the blood flow, 
but still produces sufficient force for anchoring. For example, as 
previously discussed with respect to FIG. 5, the catheter may be installed 
such that the tip is at or near the brachial cephalic junction. Even if 
one of the loops 89 falls into the junction itself, the other two loops 91 
and 93 will contact the wall and provide a stable contact to anchor the 
tip 8 within the vessel. The term anchor is used in this embodiment and 
all others herein in the broad sense of providing a general positioning of 
the catheter in the blood vessel. Some slight movement from side to side 
or back and forth is permitted by the various tip retainers as they anchor 
the tip 8 to the wall, just as a ship's anchor permits some ship movement 
but holds it generally in position. 
The wires 82 of loops of FIGS. 8 and 9 are formed with a preselected 
resilient bias outwards as determined by their shape and construction. In 
some embodiments, a very light spring action is provided by having a 
light, resilient bias outward so that the device may be used in a wide 
range of size of blood vessels, from very small to very large, with 
assurances that the blood vessel wall will not be penetrated. In the 
embodiment of FIGS. 8 and 9, the spring bias force outward is easily 
adjusted by varying the angle of connection between the straight portion 
within the guideway and the loop portion 84. For example, the angle at 
which the straight portion 83 extends from the tip 8 can be selected at a 
desired angle. 
One distinct advantage of the present invention over the prior art is that 
the catheter end 8 is retained within the flow of the blood and prevented 
from contacting the wall of the blood vessel without holding the catheter 
end 8 absolutely rigid. According to some prior art techniques, such as 
that described in the article of Pieper, as discussed in the background of 
the invention, the concept is to hold the tip as rigid as absolutely 
possible. While this may have some benefit in some embodiments, one 
distinct advantage of the present invention is that the invention will 
still operate properly even if the tip is permitted to move to different 
locations within the blood vessel. For example, the tip 8 may move to one 
side or the other within the blood vessel, based on movement of the 
patient, or of a rubbing of the blood vessel. Additionally, the tip 8 may 
move longitudinally, along the direction of the blood flow as the blood 
pulses. This is desirable in many embodiments and may actually act to 
relieve some of the stress created by the presence of the catheter. The 
tip retainer 9 includes members having a light spring force which permits 
some relative movement between the catheter tip 8 and the wall 27 of the 
blood vessel. However, the springs have sufficient force that the catheter 
tip rarely actually contacts the blood vessel wall, thus preventing damage 
to the blood vessel wall. In some of the embodiments described herein, the 
spring force becomes stronger as the catheter tip approaches the wall, 
thus serving to maintain the catheter tip in a spaced relationship from 
the vessel wall, even if some force is acting on the catheter tip 8 to 
push it toward the wall. The light spring force at an extended location of 
the spring permits some catheter tip movement, but as the catheter tip 
becomes closer to the wall, the spring force gradually increases, making 
it more difficult for the catheter tip to actually contact the wall. In 
some embodiments disclosed herein, the spring force is sufficiently strong 
that as the catheter gets extremely close to the wall, it is forced back 
with significant pressure to prevent an actual impact with the wall. 
As will be appreciated, the tip retainer assembly 9 of each of the 
embodiments described herein may be made of or coated with an appropriate 
antithrombotic material that does not cause an adverse reaction when 
placed within a patient's body, as previously described. 
The physician extends or withdraws the wires in the embodiments of FIGS. 
1-9 to contact the blood vessel wall with the desired force. If the vessel 
wall has a large diameter, the wires are extended further. Similarly, if a 
high retaining force is desired, the wires can be extended slightly 
farther. On one hand, if the physician encounters a small vessel, or one 
in which a weak retaining force is sufficient to anchor the tip 8, he may 
withdraw the wires as necessary. 
The physician also selects a catheter tip having a properly sized and 
spring biased tip retainer assembly 9 for his intended uses. If the spring 
force is found to be too weak, or alternatively, too strong, he may select 
another tip that is manufactured having a tip assembly 9 of a slightly 
different spring force, as necessary. (This may be done for each of the 
embodiments described herein, as desired.) Similarly, a range of loop 
sizes and shapes is provided to permit the physician to select the one 
that best suits the needs of a particular use. 
The physician may observe the placement and operation of the catheter tip 
inside the blood vessel to ensure that it is properly anchored as the 
procedure progresses. This observation can be carried out with known 
ultrasonic imaging equipment, for example. Alternatively, the tip 8 may 
have a radioactive isotope or other marker placed therein to permit the 
physician to ensure that the tip is immobilized and not contacting the 
vessel wall. A fluoroscope or X-ray device may also be used to image the 
tip. 
Often the tip must be in position in the blood vessel for an extended 
period. Solid placement of the tip in a position which is spaced from the 
wall and securely anchored with respect to the wall followed by confirmed 
observation of this by a physician is thus helpful to permit long-term 
placement of the catheter without injury to the blood vessel. 
FIGS. 10A and 10B illustrate a further alternative embodiment of the 
invention. According to this alternative embodiment, an intravascular 
stent 154 is provided at the distal tip 8 of the catheter 4 for the 
prevention of stenosis and subsequent catheter occlusion. The stent 154 is 
an intraluminal vascular prosthesis constructed of braided stainless 
steel, or other materials. They are, of course, coated with the 
appropriate materials to prevent interaction with the blood. Current 
applications of a standard stent include placement in the urinary system, 
and more recently, within arteries for arterial and coronary disease as an 
intra-arterial wall support usually following balloon angioplasty. 
To deploy the stent according to the invention, an expandable balloon 162 
is positioned near the tip region 8 along the outer wall of the catheter 
4, or alternatively, a rolling membrane is provided around the stent 154 
and constructed near the catheter tip. The balloon 162 is covered with the 
self-anchoring stent 154, the entire assembly being attached along the 
sidewall of the catheter tube 4 when it is inserted into the blood vessel. 
After the catheter 4 has been inserted into the blood vessel with a tip 8 
at the desired location, the balloon 162 is inflated to deploy the stent 
154. The stent 154 includes prongs 163 that penetrate the wall of the 
blood vessel to solidly affix the stent 154 and the catheter end 8 to the 
wall of the blood vessel. The balloon 162 is then deflated. The stent 154 
is connected to the catheter tip 8 by one or more anchoring wires 156, 
158, and 160. If desired, to facilitate catheter removal, the prongs 163 
may be connected to the stent 154 with prestressed breakaway points so 
that they may be easily broken off and the stent 154 removed. The prongs 
163 may be composed of a material which is absorbed by the body over time. 
Alternatively, the wires 156, 158, and 160 which connect the tip 8 to the 
stent 154 may have prestressed breakaway points at the surface of the 
stent, interfacing between the catheter and the stent 154. The catheter 4 
may be removed by withdrawing it, applying pressure to sever the 
prestressed breakaway points near the surface of the stent 154. In this 
embodiment, the stent 154 remains within the body and, is preferably 
constructed of a material which can be absorbed by the body over time 
rather than being constructed of stainless steel. Materials which can be 
absorbed by the body are well known in the art and any of those which is 
commonly known is acceptable for use to construct stent 154 or prongs 163. 
According to the embodiment of FIGS. 10A and 10B, the stent 154 is 
preferably a braided mesh, or an alternative embodiment, includes a slit 
extending longitudinally along its entire length. Having a slit in the 
stent 154, or alternatively constructing it of a braided material permits 
the stent to be completely collapsed, in a tight position around the 
catheter 4 and then expanded by balloon 162 to have enlarged diameter 
along the inside surface of the blood vessel. 
By using the techniques according to the concept of this invention, as 
disclosed in FIGS. 10A and 10B, as well as all other figures of this 
invention, the catheter tip 8 is anchored, preventing damage to the blood 
vessel wall and thus preventing cellular proliferation and stenosis. 
FIG. 11 illustrates a further alternative embodiment of the catheter having 
a tip retainer 9 at a distal end thereof composed of fletching 100. The 
fletching 100 is positioned adjacent to the tip 8 or, in one embodiment, 
recessed back from the tip portion 8 a slight distance as shown in FIGS. 
15 and 16 and explained in more detail herein. 
An advantage of the use of fletching 100 is that the tip retainer 9 is 
constructed in which the fletching 100 is a plastic or polymer which is 
injection molded. In one preferred embodiment, the fletching 100 is 
injection molded or extruded simultaneously with the injection molding or 
extruding on the tube 4 so that the manufacturing cost is minimized and 
the entire assembly is provided as a single, unitary member. 
FIGS. 12-14 illustrate alternative embodiments for the shape of the 
fletching 100 which provides the tip retainer assembly 9. According to the 
embodiment of FIG. 12, three fletchings are provided, 102, 104 and 106. 
The fletching 100 is composed of the same material as the tube 4, being 
constructed from a unitary member in a preferred embodiment. In the 
embodiment of FIG. 12, the fletching 102 contains a flat surface region 
108. The flat surface region 108 extends circumferentially along the same 
radius of the catheter 4. That is, the flat surface 108 faces upward, 
presenting a planar surface generally at a tangent to the circular 
catheter 4. The fletching 102 then extends upward, away from the tip 
portion 8, narrowing to terminate in a tip region 110. The fletching 102 
has a preselected resilient spring bias outward as it extends upward from 
a base region 112 towards the tip region 110. The tip region 110 contacts 
the wall of the blood vessel but does not penetrate the wall. The contact 
at the tip 110 performs the function of anchoring the tip 8 with respect 
to the blood vessel wall so that the tip 8 is retained in a fixed position 
with respect to the blood vessel wall, without contacting the wall and 
remaining within the blood flow. In a preferred embodiment, three 
fletchings are provided, 102, 104 and 106, each constructed similarly to 
that which has been described in detail with respect to fletching 102 and 
each providing a similar spring biased force outward to center the tip 
portion 8 within the blood vessel. 
According to the embodiment as shown in FIG. 12, the tip portion 110 of 
each of the fletchings 102, 104 and 106 is positioned beyond the end of 
the tip region 8, so that the anchoring position is beyond the distal end 
of the tip portion 8. Providing fletchings 102, 104 and 106 that extend 
beyond the tip 8 is easily provided during the manufacturing process 
during the molding or extruding of the tubing 4, or alternatively by 
cutting the tip short after the extruding process so that the tip 110 
extends beyond the end of the tip 8. 
In an alternative embodiment the fletchings 100 are positioned such that 
the tip portion 110 of the fletching 102 that contacts the blood vessel 
wall is approximately at the end of the tip portion 8 as explained with 
respect to other alternative embodiments herein. 
FIG. 13 shows an embodiment in which a fletching 114 has a flat planar 
portion 116 in generally the same orientation as the planar portion 108 of 
fletching 102. That is, the fletching extends flat with respect to the 
tubing 4, generally in the same circumferentially extending radius as the 
tubing 4. However, the fletching 114 has a rounded tip portion 118 
providing a broader contact surface for anchoring the tip region 8 with 
respect to the blood vessel wall. The broad surface area 118 provides a 
large contact surface area to ensure that the tip portion 8 is firmly 
retained in the desired position, spaced from the wall a selected distance 
at all times. Three fletchings are provided similar to fletching 114, 
spaced equidistant around the tubing 4. 
FIG. 13 also illustrates an embodiment in which the contacting portion 118 
terminates prior to the end 120 of the tip portion 8 of the catheter 
tubing 4. In some embodiments, having the contact location to the blood 
vessel wall approximately aligned with or slightly behind the actual tip 
120 of the tip portion 8 provides advantages in the operation and 
structure of the device. 
FIG. 14 illustrates an alternative embodiment for fletchings 100 
illustrating individual fletchings 122, 124 and 126. According to the 
embodiment of FIG. 14, the fletching 122 extends perpendicular to the 
catheter tubing 4. That is, the fletching 122 is vertical with respect to 
the catheter tube 4, like feathers on an arrow. As best shown in FIG. 14, 
in this embodiment the fletching is formed in a shape which curves quickly 
upward, and extends in a generally straight, long tapered edge 127 for an 
extended distance. The thin edge 127 contacts the inter wall 27 of the 
blood vessel, to anchor the tip portion 8 at a selected position with 
respect to the blood vessel wall. The fletching has an extended contact 
edge along the blood vessel wall, to more firmly retain the tubing 4 in a 
desired angular orientation and prevent rotation of the tubing 4. (This 
same advantage is provided by selected shapes of the wires of FIGS. 1-9 as 
well.) 
In one embodiment, the fletching 100 is relatively stiff, so as to slightly 
stretch the blood vessel and at the particular point of contact create a 
slight depressed channel in which the fletching rests to anchor the 
catheter. Preferably, the fletching is not so stiff as to penetrate the 
wall of the blood vessel but, is sufficiently stiff to prevent excessive 
undesirable rotation of the tip 8. The upper edge 127 may also be tapered 
to be thinner in cross section than the lower edge 130 if desired, as 
explained in more detail with respect to FIGS. 18 and 19 herein. 
FIGS. 15 and 16 illustrate an alternative embodiment in which the tip 
retainer 9 is composed of fletchings 132, 134 and 136 very much like the 
fletchings on an arrow. That is, as explained specifically with respect to 
fletching 132, the fletching has a long, tapered region 138, a rounded 
upper region 140 and a rounded end or tip region 142. Just like the 
fletching on an arrow, the fletching 132 extends vertically away from the 
tube 4, perpendicular to the catheter tubing 4, similar to the direction 
of orientation of fletching 122 of FIG. 14. 
In the embodiment of FIG. 15, the fletchings 132, 134, and 136 are spaced a 
selected distance 137 from the end 120 of the tip portion 8. The rounded 
upper portion 140 contacts the blood vessel wall spaced a selected 
distance from the tip portion 8, as illustrated in FIG. 15. In the 
embodiment of FIG. 16, the fletchings 132, 134 and 136 are positioned such 
that the rounded upper portion 140 is positioned approximately aligned at 
the end 120. 
An advantage of the embodiment of FIG. 15 is that the flow at the catheter 
end 120 is not obstructed, interfered or altered by the fletchings 132, 
134 and 136. Rather, the blood flow is affected only by the presence of 
the tip portion 8 which can be configured along conventional lines as 
known in the art to achieve a desired purpose. The contact to the blood 
vessel walls by the rounded portion 140 is sufficiently close to the tip 
portion 8 that the tip portion is retained within the blood flow and is 
prevented from contacting the blood vessel wall. 
On the other hand, in the alternative embodiment of FIG. 16, having the 
rounded portion 140 approximately aligned with the end 120 provides a firm 
control exactly at the tip 120 to ensure the maintaining of the tip 
portion 8 at a fixed location within the blood vessel at all times. The 
end 120 is exactly anchored in position and undergoes little or no 
movement because the anchor locations around the blood vessel wall are 
directly aligned with the tip end 120. This provides a firm positioning 
system for the tip portion 8 to ensure that the end 120 does not contact 
the blood vessel wall, even under agitated conditions. 
It is contemplated, for example, that in one embodiment a thin wire 139, 
such as the type shown in FIG. 17A, could be positioned along the tapered 
edge 138 and along the rounded edge 140 if desired for ensuring that the 
rounded tip portion 140 always has sufficient spring bias to perform the 
anchoring function, even in a large blood vessel, and yet have the 
fletching sufficiently thin for an extended length that it can roll over, 
providing the improved characteristics of an increased surface contact 
area if desired. 
FIG. 17B illustrates a further alternative embodiment for the fletching in 
which an aperture 143 extends through the fletching. The fletching is thus 
a ridge of material having a top edge 140. The aperture 143 provides an 
additional opening for blood flow while the ridges firmly retain the tube 
4 within the vessel. The size and shape of the aperture can be varied to 
alter the spring strength, as desired. 
FIGS. 18 and 19 illustrate a particular advantage of the fletching 
according to the present invention. The fletching is tapered as it extends 
outward. That is, the fletching is relatively thick at the base 144 where 
it extends from the tubing 4 and tapers to a very thin edge at the outside 
regions, particularly at region 140. Having the fletching tapered provides 
the advantage that one size fletching will fit all blood vessel sizes 
within a selected range. 
For example, as best shown in FIG. 18, the catheter 4 is in a relatively 
large blood vessel the fletchings 132, 134 and 136 extend straight, and 
into contact with the blood vessel wall 27. The tip of the fletching 140 
may roll over slightly, depending upon the size of the blood vessel. The 
size of the fletching 132 is selected to ensure that it will at least 
contact the inner wall 27 of any blood vessel into which it is to be used 
so that it may perform the tip retaining function as has previously been 
described. However, in a large blood vessel, such as the type shown in 
FIG. 18, the tip 140 may slightly contact the edge, thus providing an 
adequate anchor surface area to retain the catheter tubing 4 in a fixed 
position as has been described. 
FIG. 19 illustrates a smaller blood vessel and the same tip retainer as 
used in FIG. 18 herein; the fletching is rolled over at the edges, in a 
broad circumferential contact with the blood vessel wall 27'. The edge 140 
can easily roll over and be positioned along the surface of the wall 27' 
without taking up significant blood vessel area while providing a 
relatively large contact surface within a small blood vessel. The tapering 
of the fletching and providing it with thin edges at 140 provides the 
advantage that even in a small blood vessel, the same fletching may be 
used except that a larger surface area of the edge portion of the 
fletching 140 will be in abutting contact with the surface of the wall. 
This provides the additional advantage of increasing the cross-sectional 
area of contact between the fletching and the blood vessel, to more 
securely retain the tip portion 8 within the central region of the blood 
vessel and prevent contact with the wall 27'. 
The tapered fletching provides the additional advantage that a preformed 
tip assembly 9 can be used in many sizes of blood vessels. A single blood 
vessel may have a large inner diameter lumen at one region and a small 
inner diameter lumen in a different region. The difference in diameter may 
be caused by localized thickening of the walls, injury, fatty build up, or 
other causes. When the catheter is placed in the vessel, the physician may 
not be aware of the exact diameter of the blood vessel at the desired 
location (even though it might be measured ultrasonically, for example). 
The physician is assured that the catheter tip will be properly retained 
in the blood flow and spaced from the wall even if the exact dimensions 
are not as was expected at the installation site. (This advantage is 
provided in other embodiments also, such as the embodiments of FIGS. 1-9 
by the selective withdrawal or extension of the wires, as previously 
explained.) 
Having tapered edges provides another distinct advantage: the relative 
flexibility and spring bias within the fletching may be easily altered 
along the fletching as it extends outward. That is, at the very edge of 
the fletching near rounded portion 140, the resilient bias can be very 
light because the fletching is very thin at the edges. Closer to the base, 
the fletching gradually becomes thicker, naturally increasing the spring 
strength and resilient bias within the fletching. This has the advantage 
of increasing the centering ability of the tubing 4 because if the tubing 
begins to be pressed out of position, towards one wall the fletching on 
that side of the tubing will have the base region pressed closer to the 
wall; however, the base region being thicker and having a stronger spring 
action will tend to increase the resilient bias away from the wall to push 
with more force away from the wall and tend to center the tubing 4 within 
the blood vessel. Each of the fletchings are constructed with uniform 
spring bias to act together in generally centering the tubing 4 within the 
blood vessel and prevent the tubing from becoming too close to the blood 
vessel wall on any side. 
In one embodiment, the spring strength of the fletching varies proportional 
to the thickness of the fletching. In an alternative embodiment, the 
fletching is constructed such that the spring bias is not uniform with 
respect to the thickness of the fletching. For example, a relatively 
strong spring bias can be placed adjacent the base, even more than would 
otherwise be present, to ensure that the tubing 4 is always spaced at 
least a minimum distance from the wall 27. Alternatively, a slightly 
stronger spring bias may be placed right at the tip 140 than would 
otherwise be present based on the edges being extremely thin because the 
edges may be so thin as to have little or no spring bias based on their 
own thickness. In such an embodiment, the properties of the material or 
the type of material used may be slightly altered at the very tip region 
140 to provide sufficient spring strength to anchor the end even though 
the tip portions are extremely thin. 
FIGS. 18-21 also illustrate alternative embodiments for the orientation of 
the fletching on the tubing 4. According to one alternative embodiment as 
shown in FIGS. 18 and 19, the fletching is straight, directly in line with 
the tubing 4. This is the same style for mounting the fletching on some 
arrows, as is known in the prior art. Alternatively, the fletching may be 
mounted at a cant to provide a spiraled fletching as best shown in FIGS. 
20 and 21. When the fletching is mounted at a cant, so as to slightly 
spiral around the tubing 4 this provides the advantageous effect of 
smoother blood flow through the blood vessel while aiding to maintain the 
tip 4 in a straight-line orientation with respect to the blood vessel. 
The fletching as illustrated in FIGS. 12-21 has the advantage of being 
easily constructed. In one embodiment, the molding 4 and fletching is 
constructed as an integral piece by injection molding methods known the 
art. The material can be constructed from a polymer, silicone, or any 
other well-known nonthrombogenic material. Alternatively, the tubing 4 can 
be extruded with the fletching being provided in an extrusion mold 
process. Another advantage of the fletching is that it permits easy sheath 
removal and insertion, as will be explained later in more detail. The 
fletching also is easily constructed with graduated stiffness along the 
length of the fletching as it extends away from the tubing 4 providing the 
advantages previously described. 
The insertion and removal of the catheter tubing 4 having the tip retainer 
on the end thereof will now be explained in particular detail with respect 
to FIGS. 22-24. The description of FIGS. 22-24 is particularly directed 
towards an embodiment having loops generally of the type previously 
described with respect to FIG. 9; however, this is for illustration 
purposes only and the same or similar method of insertion and removal is 
uniformly applicable to each of the embodiments described herein. 
Referring now to FIG. 22, the catheter 4 having the tip retainer 9 at the 
end thereof is prepared for introduction into the blood vessel by placing 
it within an introducer sheath 148. The introducer sheath 148 is 
preferably made of polyurethane, plastic or some other relatively pliable 
material that is sufficiently stiff to overcome the spring bias of the 
retainer member so that the entire assembly has a diameter approximately 
equal to that of the catheter tubing 4. The introducer sheath 148 includes 
a handle portion 150 which the physician may use to manipulate the 
introducer sheath 148 and guide it into the proper position within the 
blood vessel. In a preferred embodiment, the introducer sheath 148 has a 
slight taper 152 at the distal end to make the introduction into the blood 
vessel more simple. 
As shown in FIG. 23, the introducer sheath is advanced into the blood 
vessel 30 until the catheter tube is at the desired location within the 
blood vessel. At this position, the tip retainer 9 is held within the 
introducer sheath and does not contact the wall of the blood vessel 30. 
As shown in FIG. 24, the introducer sheath 148 is then removed from the 
catheter tubing 4. According to a preferred embodiment, the introducer 
sheath 148 is constructed of a relatively thin layer of polyurethane which 
is easily ripped or torn by the physician. In order to remove the 
introducer sheath, the physician firmly grabs the handles 150 on either 
side and begins to tear apart the introducer sheath. The introducer sheath 
will separate into two pieces, tearing apart outside of the blood vessel 
and withdrawing the introducer sheath from the catheter tubing 4. As the 
introducer sheath is withdrawn from the catheter tubing 4, the tip 
retainer is released and automatically extends outward according to the 
preset spring bias to contact the blood vessel wall and retain the tip 
portion 8 at the selected location as has been previously described. 
In an alternative embodiment, the sheath is simply removed by sliding it 
backwards, rather than tearing the sheath into two pieces. As will be 
appreciated, tearing the sheath into two separate pieces provides the 
distinct advantage of permitting the introducer sheath to be easily 
separated from a portion of the tubing without having to completely slide 
off the end of the tubing outside the body. It also provides the advantage 
that the physician may easily and uniformly withdraw the introducer sheath 
while leaving the tubing 4 in the preset position, to permit the tip 
retainer to be deployed to retain the tip portion 8 in the desired 
position within the blood vessel. 
Removal of the catheter 4 having the tip retainer 9 on the end thereof is 
easily accomplished with each of the alternative embodiments. In the 
alternative embodiments of FIGS. 5-21, it will be appreciated that the tip 
retainer does not penetrate the blood vessel wall 27. Further, in many of 
these embodiments the tip retainer is constructed to permit easy 
withdrawal or removal from the blood vessel. According to one method of 
removal, the catheter 4 is simply withdrawn from the blood vessel, and 
simultaneously withdraws the tip retainer while in the deployed position. 
Even though the tip retainer is deployed, such is shown in FIGS. 8 and 9 
and others, the orientation is such that the withdrawal may be easily 
accomplished because the spring bias permits the tip retainer 9 to be 
pressed inward slightly as necessary. To advance the tip retainer would be 
difficult, or impossible, because this would serve to increase the spring 
bias and press the tip retainer 9 more firmly into position against the 
blood vessel wall, increasing the anchor strength. On the other hand, the 
withdrawal of the catheter tube 4 tends to pull the tip retainer 9 away 
from the wall and permit easy removal without excessive stress on the 
blood vessel wall. 
According to an alternative embodiment, the tip retainer is withdrawn from 
the deployed position so as to not contact the wall by sliding an 
introducer sheath once more over the tip portion 8 to withdraw the tip 
retainer 9 from the blood vessel wall. The sheath and catheter tube 4 may 
then be withdrawn from the blood vessel. 
FIGS. 25 and 26 illustrate another preferred embodiment of the tip retainer 
9 composed of a loop 168 according to principles of the invention. In the 
embodiment shown in FIGS. 25 and 26 the tip retainer 9 is comprised of a 
single loop 168 of wire 166 and silicone tubing 160 having one end 162 and 
the other end 164 connected to the distal end. Inside the silicone tubing 
160 is the stainless steel wire 166. The silicone tubing 160 with the 
steel wire 166 on the inside thereof form the loop 168, which functions as 
the tip retainer 9. 
The size of the loop 168 is selected based on the size of the blood vessel 
and position placement of the catheter 4 in that blood vessel. In one 
embodiment, the loop 168 has a diameter of 20 millimeters and the ends 162 
and 164 are connected to the tip portion 8 spaced from the tip portion 8 
approximately 7 millimeters. In other alternative embodiments, the 
diameter of the loop 168 is considerably smaller, in order to be properly 
sized for placement in the selected vessel of the human body during a 
kidney dialysis or other procedure, as explained herein. 
The ends of the loop 168 are fixed to the catheter 4 by any suitable 
technique including silicone adhesive, forming an incision in the tubing 4 
and insertion into this incision followed by sealing with silicone 
adhesion, or the like. 
The diameter and spring strength of the steel wire 166 is selected to 
provide the desired spring force to urge the loop 168 to return to the 
round position as shown in FIG. 25. Generally, a relatively light spring 
force is acceptable as would be provided small diameter wire 166. Other 
materials besides stainless steel, such as various alloys of steel, spring 
steel, teflon coated steel, and the like are also acceptable. The silicone 
tubing 160 is provided as antithrombogenic coating which is easily 
manufactured attached to the catheter 4. Any other acceptable 
antithrombogenic coating besides the silicone tubing 160 could also be 
used, such as the antithrombogenic coatings described with respect to the 
other embodiments herein. 
In one embodiment, the wire 166 is not present. Instead, only the silicone 
tubing at 160 is used to form the loop 168 because the proper spring 
constant is provided from the natural spring within the silicone tubing 
itself. 
FIG. 27 illustrates the tip retainer of FIG. 25 positioned at one possible 
location within the blood vessel 30 (the tip region 8 must be positioned 
at a desired location according to the medical procedure being carried 
out). Preferably, the tip portion 8 is not adjacent a junction 170 between 
two blood vessels 30 and 30' as shown in FIG. 27. To carry out many 
medical procedures the tip region 8 must be positioned at a desired 
location according to the medical procedure being carried out. In some 
situations, either accidentally or by medical design, the tip region 8 may 
be adjacent a branch 170 between one blood vessel 30 and another blood 
vessel 30'. to guard against falling into the junction 170, the diameter 
of the loop 160 is selected to ensure that the tip retainer 9 bridges the 
junction 170 so that the catheter 4 is anchored within the blood vessel 30 
and does not contact the walls of the blood vessels 30 or 30'. Preferably, 
the diameter of the loop 168 is selected such that when the catheter 4 is 
compressed within the blood vessel that the longitudinal length of the 
loop 168 denoted by the distance x in FIG. 27 is longer than the diameter 
d of a blood vessel which may form a junction with the blood vessel 30'. 
By selecting a loop sized 168 such that the distance x larger than the 
diameter of any blood vessel 30' for which a junction 170 is expected to 
be encountered, the loop can be assured of adequately bridging the blood 
vessel at the branch 170 and still have sufficient support from the main 
blood vessel 30 on either side of the walls 27 of the main blood vessel 
30. For example, the distance x can be in the range of 1.5 to 3 times the 
distance d sufficient support along the blood vessel wall 27 from the tip 
retainer 9 that the tip portion is maintained in a central region of the 
vessel 30. Of course, the distance x can be significantly longer than 
three times the diameter d, if desired and depending upon the diameter d 
which is encountered at various locations within the blood vessel 30. The 
distance x may be somewhat larger than the diameter of the loop 168 in the 
round position because as the loop 168 is compressed, the distance x 
increases to provide an elongated contact position along the length of the 
wall 27. 
The loop 168 is preferably constructed of a small diameter material, such 
as a silicone tubing having an outside diameter of 1 millimeter or less or 
a wire having an outside diameter of 0.5 millimeters or less. Using a 
small diameter material to construct the loop 168 provides the advantage 
that blood flow through the main blood vessel 30 is not impeded by the tip 
retaining member 9. If the tip portion 8 happens to be positioned adjacent 
a junction 170, the additional advantage is that blood flow into or out of 
the blood vessel 30' that junctions with the blood vessel 30 is not 
impeded by the loop 168 bridging the junction 170 between the blood 
vessels. Even if the loop 168 is positioned directly over the opening of 
30' at the junction itself, the loop diameter is sufficiently small that 
blood may easily flow through the blood vessel 30' as needed. 
The operation of the device of embodiments 25-27 is as follows. The 
catheter 4 is positioned in the blood vessel using any acceptable delivery 
system. The delivery system of the type shown and described with respect 
to FIGS. 22-24 is acceptable. Upon being positioned within the blood 
vessel 30, the loop 168 becomes elongated by compression from the walls 27 
of the blood vessel 30. The spring constant of the wire 166 is selected to 
be sufficiently light that the loop 168 is easily compressed by the wall 
30 and exerts only a light force upon the inner surface. However, the 
spring force is sufficiently strong to engage the blood vessel wall 27 and 
prevent repeated contact between the tip portion 8 and the blood vessel 
wall 27. 
At the conclusion of the medical procedure, the catheter 4 is simply 
withdrawn by being retracted it while leaving the loop 168 in the deployed 
position. Alternatively, a retraction sheath may be placed around the 
catheter 4 which slides along the outer diameter of catheter 4 and 
compresses the loop 160 to move it away from the wall of the blood vessel 
similar to that shown in the introduction position of FIG. 23. The 
catheter 4 is then removed. 
FIGS. 28A-28C illustrate alternative embodiments which have been found 
useful for performing kidney dialysis. Preferably, for kidney dialysis 
catheter 4 is a double lumen catheter having an inflow lumen 42 and an 
outflow lumen 44. The tip portions 8 of the lumens are slightly staggered 
to provide improved inflow and outflow characteristics for kidney 
dialysis. The attachment locations for ends 162 and 164 (not shown) are 
selected proximal to the outflow region 42 of one lumen with the loop 
extending forward, beyond the tip of the in flow lumen 44. FIG. 28A 
illustrates the embodiment in which the loop 168 is composed only of the 
silicone 160 and does not include an internal wire 166. 
FIGS. 3, 28B and 28C illustrate alternative embodiments for the catheter 4 
double lumen!. FIG. 3 illustrates a double lumen catheter with the lumens 
side by side. As shown in FIG. 28B, the catheter 4 can be a double "D" 
lumen catheter having staggered tip portions for each of the lumens 42 and 
44. The walls of the catheter 4 are solid walls formed of any suitable 
material known in the art. The loop 168 is attached by any acceptable 
technique, such as silicone adhesive, insertion into the wall of the 
catheter 4 or the like. FIG. 28C illustrates the embodiment in which the 
catheter 4 includes additional guideway lumens within the wall of the 
catheter 4. Specifically, lumens 172 and 174 are provided in a 
circumferential region of the catheter 4. The lumens extend along the 
length of the catheter. The loop 168 extends from the lumens 172 and 174, 
the lumens acting as guideways for the loop 168. The ends of the material 
that form the loop 168 may extend along the length off the catheter 4 so 
that the loop 168 may be retracted and extended as necessary. An 
additional lumen 176 is also provided in the central wall between the two 
lumens 42 and 44 for additional uses, if desired. 
FIG. 29 illustrates a still further alternative embodiment instructed 
according to principles of the present invention. The loop 168 is formed 
by being rigidly attached at one end 162 to the tip portion 8 and having 
the other end 164 inserted into a lumen 178 of the catheter 4. In this 
embodiment, the loop 168 includes a hollow silicone tubing 160 of the type 
previously described. The wire 166 is within the tubing 160, or 
alternatively is not used, as desired. The other end of the loop 168 
extends into a lumen 178 within the catheter 4. The lumen 178 may be a 
lumen of the type formed within a wall of the catheter or, alternatively, 
may be an extension of the silicone tubing 160 connected along the outside 
of the wall of the catheter 4 or embedded within the wall. In each 
structure, the lumen 178 provides an open passage way from the tip portion 
8 to a proximal portion of the catheter 4, which is external to the 
patient. 
The tubing 160 contains a plurality of apertures 180 spaced from each other 
around the loop 168. In one embodiment, the apertures 180 are equally 
spaced from each other around the entire loop. Alternatively, the 
apertures 180 are positioned only along the side portions of the loop 168, 
which are anticipated to contact the wall 27 of the blood vessel as shown 
in FIG. 27. The very tip region 182 of the loop does not contain any 
apertures in this alternative embodiment. 
Medication can then be delivered through the lumen 178, into the loop 168 
constructed from the hollow tubing 160 and exit the apertures 180 for 
administration to the patient. The silicone tube 160 thus becomes a 
medication delivery system. When the catheter is positioned for an 
extended time within the human body, as may occur with kidney dialysis, it 
is known in the art that smooth muscle cell growth, platelet aggregation, 
and the like to deliver medication may occur. The use of a tip retainer to 
deliver medication constructed according to principles of the present 
invention minimizes occlusion of the blood vessel, and reduces destruction 
of the blood vessel by delivering specific anti-clotting agents to the tip 
region 8 via the apertures 180 in the loop 168. It is known in the art 
that the smooth muscle walls surrounding the blood vessel are inhibited 
from excessive growth by certain medications. One of the problems 
identified according to principles of the present invention and which the 
invention seeks to prevent is excessive growth of the smooth muscles 
around the blood vessel wall which may overgrow into and cause occlusion 
of the blood vessel 30. The medication delivery system as illustrated in 
FIG. 29 and described herein advantageously delivers medication precisely 
to the location desired for inhibiting excessive growth of the muscle 
cells around the blood vessel wall and for inhibiting platelet aggregation 
along the wall of the blood vessel or other clotting along the walls of 
the blood vessel. The medications which may delivered include TPA, an 
anticlotting agent; strepokinase, heparin, hirudin, or the like. In some 
instances, clotting beings to occur along the walls 27 of the blood vessel 
30. The loop 168 is in actual contact with the blood vessel wall 27. The 
medication can therefore be delivered directly to the wall of the blood 
vessel with benefits obtained in addition to those which may be obtained 
by delivering the same medication exiting from the main lumen 28 of the 
catheter. 
The position, size and relative location of the apertures 180 are selected 
to provide the desired delivery medication. In some embodiments, having 
the apertures 180 spaced equidistance from each other and opening to both 
the inside and outside of the loop 168 is desirable to provide medication 
equally around the loop 168. In an alternative embodiment, the apertures 
180 are spaced only on an outside surface of the loop 168 to deliver the 
medication outward from the loop. In a further alternative embodiment, the 
apertures 180 are positioned only at or near locations which are 
anticipated to come in contact with the wall 27 of the blood vessel 30. 
The apertures 180 may be oriented to discharge the medication along the 
surface of the blood vessel wall 27 and thus are radially offset from the 
outside position to deliver the medication adjacent the wall 27 so that 
the wall 27 does not block outflow of the medication. 
Having the tubing 160 or, alternatively, a wire 166 within the tubing 160 
extend to the proximal end of the catheter 4 provides the additional 
advantage that the loop 168 may be retracted or extended as necessary. 
When the catheter 4 is inserted into the patient, the loop 168 can be in a 
retracted, small diameter position held tightly against the tip portion 8. 
Once the catheter is at the proper location, the wire 166, if present, or 
alternatively the tubing 160, may be pushed along the lumen 178 to enlarge 
the loop 168 to a size and shape as described with respect to FIG. 27. The 
loop 168 thereafter remains in the extended position during the medical 
procedure. At the conclusion of the medical procedure, the wire 166, or 
alternatively the tube 160, are retracted down the lumen 178 to again 
reduce the diameter of the loop 168. The loop 168 may also be retracted or 
extended using the lumens 172 and 174 of the catheter of FIG. 28C. The 
catheter 4 is then withdrawn from the patient. Alternatively, a delivery 
system of the type described with respect to FIGS. 22-24 may be used and 
the loop 168 starting in the deployed position and only being retracted 
for removal of the catheter 4. 
FIG. 30 illustrates a further alternative embodiment of the tip retainer 9. 
According to the embodiment of FIG. 30, two triangular silicone strips 182 
and 184 are positioned adjacent the tip portion 8. The length x of the 
silicone strips 182 for combination with the angle .theta. with respect to 
the wall of the catheter 4 are selected to cause the respective tip 
regions 186 and 188 to contact the walls of the blood vessel 30 with light 
spring force to anchor the tip portion 8 to the blood vessel 30. The angle 
.theta. is also selected to be sufficiently small that if the tip portion 
8 happens to be positioned adjacent a junction 170 that the sides of the 
triangular member contact the walls 27 at either edge of the junction 170 
and prevent the tip portion 8 from becoming sufficiently close to the wall 
adjacent the junction that it contacts the junction itself or the wall 
adjacent junction. In the event one of the triangular members 184 enters 
the blood vessel 301 at junction 170, two contact points are 
advantageously provided instead of the single previous point 188, thus 
further increasing the stability of the anchoring of the tip portion 8. 
The number of triangular members 182, 184 used depends on the particular 
application, and preferably 2, 3 or 4 such triangular members are used. 
The triangular members 182 and 184 include respective apertures 185. The 
apertures 185 advantageously permit the spring constant of the triangular 
members 182 to be selected by making the aperture small or large to 
provide a correspondingly large or small spring constant as desired. 
Further, the apertures may also provide the benefit of the triangular 
members 182 and 184 minimizing interference with the flow of blood. 
Constructing the triangular members 182, 184 from a strip of silicone 
provides the advantage previously described with respect to the loop 168 
that blood flow through the blood vessels 30 or 30' is not impeded with 
the catheter 4 in position. Flow to or from the branch at the junction is 
not restricted. 
FIG. 31 illustrates an alternative embodiment for the tip retaining member 
9 comprised of triangular members 190 constructed from sheets of silicone. 
Preferably, the sheets are solid sheets of silicone which are relatively 
thin, less than 1 millimeter, so as to not impede the blood flow and yet 
be sufficiently strong to retain the catheter 4 anchored in a space 
position from the blood vessel wall 27. 
FIGS. 33A, 33B and 34 illustrate an alternative embodiment for a tip 
retainer in the form of longitudinal strips 192 of silicone sheeting. In 
the embodiment of FIG. 33A, the tips 194 are rounded to reduce the trauma 
in the blood vessel and spread the spring force over a greater area in the 
blood vessel. In the alternative embodiment of FIG. 33B, the tip portions 
196 are pointed to concentrate the spring forces at a single location and 
slightly deflect the wall 27 of the blood vessel at the point of contact 
196. Having a more pointed tip 196 increases the force with which the tip 
member 9 is embedded into the wall 27 of the blood vessel and may be 
desired in some embodiments. In the embodiments shown in FIGS. 33A, 33B 
and 34 two strips 192 of silicone sheeting are shown. However, it is 
contemplated that three or four strips may also be used spaced 
equidistance around the catheter 4 similar to that shown in FIGS. 12-21, 
if desired. 
FIGS. 35 and 36 illustrate an alternative embodiment for the tip retainer 9 
composed of two loops 198 and 200. The embodiment of FIGS. 35 and 36 is 
particularly adapted to use on a catheter for having a double lumen with 
the opening staggered as illustrated in FIGS. 36 and 28A. According to 
this embodiment, a first end 162 of each loop originates near the upper 
region 202 of the most forward tip of the catheter 4, extends outward, in 
a loop of the desired shape, and terminates at the base region 204 of the 
opening of the other lumen where the other end 164 is attached. The loops 
198 and 200 are constructed from silicone tubing, silicone sheeting or 
alternatively, from a tubing having a spring wire therein of the type 
previously described with respect to FIGS. 25-27. The use of loops or loop 
having their terminated ends 162 and 164 spaced longitudinally along the 
catheter may be used in the other embodiments of FIGS. 25-29 and is 
desired in some medical procedures to provide increased stability at 
different points along the tip portion 8 of the catheter 4. 
FIG. 37 illustrates an alternative embodiment in which the catheter itself 
is modified to provide the tip retaining member 9. In this embodiment, the 
tip portion of the catheter 4 is severed by an incision along the tip for 
a selected distance creating two halves, 206 and 208. A string, wire or 
other attachment device is connected to the ends 210 and 212 respectively 
of the halves 206 and 208. The strings 207 and 209 are then retracted a 
desired amount to form two loops 214 and 216 in the end of the catheter 4 
similar to that shown in the embodiment of FIGS. 35 and 36. The attaching 
members 207 and 209 are retracted the desired amount to form the loops 214 
and 216 of a selected size and shape. A slight retraction of the 
attachment means 207 and 209 will cause the loops 214 and 216 to be 
relatively large and extend into solid abutting contact with the walls of 
the blood vessel. If the loop catheter 4 is positioned in a smaller 
portion of the blood vessel, the attachment members 207 and 209 can be 
further withdrawn, decreasing the size of the loops 214 and 216 to provide 
the desired spring bias force for retaining the tip portion 8 within the 
blood vessel 30. The embodiment of FIG. 37 provides the advantage of ease 
of manufacture because the catheter itself is modified to form the tip 
retaining member 9. Alternative to using wires 207 and 209, if the size of 
the loops 214 and 216 is previously known, the tip portions 210 and 212 
may be attached to the side wall of the lumen 4 by the appropriate 
adhesive to easily form the loops 214 and 216 having a desired size and 
spring constant. For this embodiment, the attachment wires 207 and 209 are 
not necessary and loops similar to that shown in FIG. 35 can easily be 
formed by sacrificing a portion of the tip region of the catheter itself 
and using a catheter material to form the loops 214 and 216. 
FIGS. 38A and 38B illustrate an alternative embodiment for the tip retainer 
9. A loop 219 constructed from any acceptable material having the desired 
spring constant is attached to the tip region 8 of the catheter for using 
any one of the acceptable techniques described herein. In addition, a 
retraction wire 220 is attached adjacent a tip region 222 of the loop 219. 
The retraction wire 220 extends along the catheter 4, either along the 
outside surface or through a lumen in its position near the proximal end 
for manipulation by a physician. The loop 219 is formed with the shape 
such that the spring memory forces if into an extended, elongated position 
while relaxed, such as shown in FIG. 38A. Preferably, the loop 219 in the 
relaxed position will have a height h approximately equal to that of the 
catheter for itself. After the catheter 4 is advanced to the desired 
position of the blood vessel 30, the retraction wire 220 is retracted by 
the physician causing the loop 219 to go outward and engage in abutting 
contact with the walls 27 of the blood vessel 30. The retraction line 220 
is then secured at a proximal end in the catheter 4, outside the patient, 
and acts as a tip retainer deployment device to maintain the tip portion 8 
of the catheter 4 within the blood vessel. At the conclusion of the 
medical procedure, retraction line 220 is released which permits the wire 
219 to return to its relaxed position as shown in FIG. 38A. The catheter 4 
is then removed from the blood vessel. The loop 219 may be composed of a 
single loop of material of the type shown in FIGS. 25-27, or 
alternatively, may be composed of two or more loops in the form of an egg 
beater type pattern to provide multiple abutting contact points with the 
wall of the blood vessel when the retraction wire 220 is retracted. 
FIG. 39 illustrates a further alternative embodiment at the tip retainer 9 
in which a circle 224 of silicone sheeting is affixed near the distal end 
8 of the catheter 4 to form the tip retainer 9. The loop 224 provides 
extended contact points with the blood vessel wall along its entire length 
similar to that shown for the loop of FIG. 27. In the embodiment of FIG. 
39, the loop 224 is positioned with its most forward end adjacent the tip 
portion 8 and extending backwards, while in the embodiment of FIG. 27, the 
loop 168 extends forward from the tip portion 8. Similar to the embodiment 
shown and described with respect to FIGS. 25-27, the loop 224 may be 
composed of flat silicone sheeting, hollow silicone tubing having a spring 
wire therein, or alternatively a spring wire by itself coated with an 
antithrombogenic material. 
FIG. 40 illustrates a further alternative embodiment at the tip retainer 
member 9 according to the present invention which includes vanes 226 
having a generally triangular shape. The shape of the vanes 226 are 
slightly different from the shape of the vanes 192 because they extend in 
a triangular shape from the catheter wall 4. The broader, triangular base 
of the vanes 226 advantageously permits the strength of the vein 226, and 
thus the spring constant to gradually increase towards the body of the 
catheter 4 while maintaining the same thickness for the vein 226 as shown 
in FIG. 34. The particular shape of the triangle 226 is selected depending 
upon the desired location within the blood vessel to provide the spring 
constant which maintains the catheter 4 at a spaced position from the 
blood vessel wall at all times, even as may occur from repeated movement 
of the patient. 
While the preferred embodiment of the invention has been illustrated and 
described, it will be appreciated that various changes can be made therein 
without departing from the spirit and scope of the invention.