Method for filtering blood in a blood vessel of a patient

A method of filtering blood in a blood vessel of a patient wherein a catheter is initially introduced into the blood vessel and then advanced to a desired location within the blood vessel. Subsequently, a portion of a positioning assembly having a filter distally attached thereto is guided through the catheter. The filter is then positioned at a location beyond the distal end of the catheter within the blood vessel with the positioning assembly. The positioning assembly is then locked to the catheter. The catheter is then anchored to an object located outside of the blood vessel. Thereafter, an amount of blood is filtered within the blood vessel with the filter. The filter can be readily repositioned by unlocking the positioning assembly from the catheter, repositioning the filter within the blood vessel with the positioning assembly and then relocking the positioning assembly to the catheter.

BACKGROUND OF THE INVENTION 
This invention relates generally to a method and apparatus for filtering 
blood in a blood vessel of a patient. 
Blood clot filtering devices have heretofore been provided to filter blood 
for clots such as emboli and thrombi in a patient's blood vessel. Certain 
of these devices were designed. to be permanently remotely placed in a 
blood vessel and included an anchoring means to prevent the migration of 
the filter from one point to another within the blood vessel. Once the 
filtering device was remotely placed within the vessel, the device was 
left indefinitely. An example of such a blood clot filtering device is 
disclosed in U.S. Pat. No. 4,619,246 issued to Molgaard-Nielsen et al. 
This reference shows the use of a collapsible filter basket adapted to be 
introduced into a blood vessel for the purpose of entrapping thrombi and 
emboli in the blood flowing through the vessel. The Molgaard-Nielsen 
device is designed to be placed remotely within a blood vessel. A 
plurality of anchoring legs are secured to a filter basket. The free end 
of each leg is bent outwardly to form a hook. When the filter basket is 
positioned in a blood vessel, each hook penetrates slightly into the wall 
of the vessel so as to hold the filter basket in position. 
A device described by Driller et al. in a 1976 technical article is another 
example of a permanently placed vena cava filter. Such device consists of 
an open cone formed by straight strands of thin stainless steel wire. Each 
wire strand has three barbs at the tip to hold the filter basket at one 
location within the vessel. The strands are joined together at a central 
hub. In order to place the filter, a plug-ended wire guide is inserted 
into a length of polyethylene tubing. The collapsed filter is placed in 
the distal end of a length of polyethylene tubing with the filter hub in 
the proximal position. The plug-end of the wire guide is then brought into 
contact with hub of the filter. A Touhy clamp is attached to the proximal 
end of the tubing. The Touhy clamp permits the plug-ended guide to be 
securely held a few centimeters proximal the filter while the catheter is 
advanced. In this way the filter will not be inadvertently ejected. The 
loaded tubing is then introduced into the jugular vein and advanced under 
fluoroscopy into the subrenal inferior vena cava. The Touhy clamp is 
loosened and the plug-end of the wire guide is then advanced to contact 
the filter. The filter is ejected by withdrawing the tube sleeve while the 
filter is kept stationary during ejection by the plug-ended wire guide. 
The strands spring out as the tubing is withdrawn from about the filter. 
The guide wire and tubing are then withdrawn. 
Another device which is designed to filter blood for clots in a blood 
vessel of a patient is described by Major et al. in a 1974 technical 
article. This device consists of a multiple ribbed catheter which is 
introduced through the saphenous vein. After passage into the vena cava, 
the ribs of tile catheter are extended to contact the cava wall. This 
produces a sieve through which blood will flow but which will entrap 
emboli. After the filtering portion is positioned in the vena cava, the 
tubing which extends proximally from the patient's body is severed and the 
device is left in place indefinitely until the patient's risk of pulmonary 
embolism had passed. 
The above and other similar prior art devices have the disadvantage that 
the filter remains in contact with the interior wall of the vena cava for 
a substantial period of time at the same location with the result that the 
filter becomes endothelialized and hence attached to tile interior wall of 
vena cava. This condition tends to block flow of blood in the vena cava 
and often results in trauma to the interior wall of the vein when tile 
filter is torn free from its attachment with the wall. 
SUMMARY OF THE INVENTION 
One embodiment of the present invention involves a method for filtering 
blood in a blood vessel of a patient wherein a catheter is initially 
introduced into the blood vessel and then advanced to a desired location 
within the blood vessel. Subsequently, a portion of a positioning means 
having a filter distally attached thereto is guided through the catheter. 
The filter is then positioned at a location beyond the distal end of the 
catheter within the blood vessel with the positioning means. The 
positioning means is then locked to the catheter. The catheter is then 
anchored to the patient and blood is filtered. Before the filter has 
become endothelialized to the blood vessel, the positioning means is 
unlocked and the filter is repositioned within the blood vessel with the 
positioning means. 
Another embodiment of the present invention involves an apparatus for 
filtering blood in a blood vessel of a patient which comprises a filter 
and a positioning means connected to the filter for positioning the filter 
at a location within the blood vessel. In addition, the apparatus 
comprises means for guiding a portion of the positioning means within the 
blood vessel and means for anchoring the guiding means to an object 
outside of the blood vessel. The apparatus further includes a means for 
releasably locking the positioning means to the guiding means thereby 
allowing the filter to be readily repositioned from a certain location to 
another location within the blood vessel with the positioning means. 
One object of the present invention is to provide an improved method and 
apparatus for filtering blood. 
Still another object of the present invention is to provide a method of 
apparatus for filtering blood in which the filter does not become 
endothelialized and hence attached to the vena cava wall. 
Other objects and benefits of the present invention can be discerned from 
the following written description and accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
For the purposes of promoting an understanding of the principles of the 
invention, reference will now be made to the embodiments illustrated in 
the drawings and specific language will be used to describe the same. It 
will nevertheless be understood that no limitation of the scope of the 
invention is thereby intended, such alterations and further modifications 
in the illustrated devices and methods, and such further applications of 
the principles of the invention as illustrated therein being contemplated 
as would normally occur to one skilled in the art to which the invention 
relates. 
Referring now to FIG. 1, there is illustrated an apparatus for filtering 
blood in a blood vessel of a patient which is generally designated by the 
numeral 10. Apparatus 10 includes a collapsible filter basket 11, a 
positioning assembly 12, a catheter 30, an anchoring device 35, a 
connecting tube 40 and a Touhy-Borst fitting 45. 
As shown in FIGS. 2 and 3, filter basket 11 is comprised of a plurality of 
thin resilient wires 13 composed of a stainless steel alloy. Wires 13 are 
interconnected at each end of filter basket 11 by means of a pair of 
ferrules 17 and 18 which are respectively secured to the wires by any 
appropriate means, such as brazing. Ferrule 17 extends 3.0 millimeters in 
length while ferrule 18 extends 5.0 millimeters in length. FIGS. 1, 3 and 
4 show filter basket 11 in its expanded and relaxed state while FIG. 2 
shows filter basket 11 in its collapsed and unrelaxed state. Filter 11 is 
3.3 centimeters in length in its expanded state and 6.0 centimeters in its 
collapsed state. Connected to filter basket 11 is positioning assembly 12 
as shown in FIGS. 2 and 3. Positioning assembly 12 comprises a central 
wire 15, a short segment of wire guide coil 16, a sliding lock assembly 
23, a filter expander assembly 19, a short segment of cannula 25 and 
ferrule 17. 
As can be seen in FIG. 5A, filter basket 11 is symmetrical about a 
hypothetical plane 101 that perpendicularly bisects cannula segment 25, 
which is disposed within basket 11. Filter basket 11 can be thought of as 
having two substantially identical halves which are disposed in 
symmetrical relationship on either side of plane 101. Because of this 
symmetry, the filtering apparatus of the present invention works equally 
well when the filter is located either upstream or downstream with respect 
to the distal end of catheter 30. FIGS. 4 and 6 illustrate this feature of 
the invention. While the filter basket 11 of both FIGS. 4 and 6 is 
positioned in the inferior vena cava 63, FIG. 4 shows the blood filter 
apparatus entering the patient's venous system through the femural vein, 
and FIG. 6 shows the filter apparatus entering the patient's venous system 
through the jugular vein 102 and passing through the right atrium of heart 
103 to arrive at the inferior vena cava 63. This ability of the present 
invention is referred to hereinafter as a blood filter apparatus having a 
reversible filter. Thus, the physician utilizing the present invention has 
the freedom to choose the best entry point on a particular patient to 
arrive at the desired filter location from either an upstream or 
downstream entry point into the body. 
Central wire 15 extends 1130 centimeters in length and is connected at one 
of its ends to ferrule 17 and at its other end to coil segment 16. Coil 
segment 16 is 1.0 centimeter in length and has an outer diameter of 0.052 
inch. Central wire 15 extends through but is not fixedly attached to 
sliding lock assembly 23, expander assembly 19, filter basket 11 and 
cannula segment 25. 
Expander assembly 19 is comprised of a ferrule 21, a segment of wire guide 
coil 20 and ferrule 18. Ferrule 21 is 1.0 centimeters in length. Coil 
segment 20 is 99 centimeters in length and has an outer diameter of 0.052 
inch. Coil segment 20 is composed of a stainless steel alloy and has a 
passageway therethrough as alluded to above. Coil segment 20 is secured at 
one end to ferrule 18 and at the other end to ferrule 21 by any appropriate 
means, such as brazing. Ferrules 18 and 21 also have passageways 
therethrough. Coil segment 20 includes a section 27 in which the coil is 
stretched as shown in FIGS. 2 and 3. Stretched section 27 extends 20.0 
centimeters in length and is located intermediate the ends of coil segment 
20. The proximal end of stretched section 27 is 29.0 centimeters in 
distance from the distal end of ferrule 21. 
Cannula segment 25 is positioned concentrically with central wire 15 and 
within the interior of filter basket 11. The length of cannula segment 25 
is 3.0 centimeters. Cannula segment 25 limits the axial displacement of 
expander assembly 19 toward ferrule 17 along central wire 15. The purpose 
of this limitation is to allow filter basket 11 to be easily deployed to a 
desired optimal shape and size without the need for visual aid. 
Once filter basket 11 is deployed to its desired optimal shape and size, 
sliding lock assembly 23 can be used to maintain filter basket 11 in that 
state. In other words, sliding lock assembly 23 provides a means for 
maintaining the filter in a desired shape that is independent of both 
catheter 30 and the inner wall of the blood vessel. Thus, the filter of 
the present invention can be fully deployed in the blood vessel without 
the filter applying unwanted pressure to the interior wall of the blood 
vessel and without any interaction between the filter and the distal end 
of catheter 30. Sliding lock assembly 23 is comprised of a short segment 
of wire guide coil 14 and a slightly larger segment of cannula 22. The 
length of coil segment 14 is 3.5 centimeters and the length of cannula 
segment 22 is 4.0 centimeters. The outer diameter of coil segment 14 is 
0.052 inch. Coil segment 14 and cannula segment 22 each has a passageway 
therethrough and is concentrically positioned relative to central wire 15. 
Cannula segment 22 is positioned adjacent and affixed to the interior of 
coil segment 14. A small portion 24 of cannula segment 22 extends beyond 
the distal end of coil segment 14. The length of small cannula portion 24 
is 0.25 centimeters. Cannula segment 22 has an outer diameter slightly 
larger than the inner diameter of ferrule 21. The outer diameter of 
cannula segment 22 is 0.02 inch and tile inner diameter of ferrule 21 is 
0.033 inch. As a result, when it is desired to maintain filter basket 11 
at its optimal shape and size, sliding lock assembly 23 can be slid over 
central wire 15 towards ferrule 21 to ultimately wedge small cannula 
portion 24 of cannula 22 into the interior of the proximal end portion of 
ferrule 21 thus forcing the interior of small cannula portion 24 to grasp 
central wire 15 in a friction fit and consequently prevent expander 
assembly 19 from being proximally axially displaced relative to central 
wire 15. As a result, since the proximal end of filter basket 11 is 
secured to the distal end of expander assembly 19, filter basket 11 is 
thus made highly resistant to collapse. This feature is important because 
filter baskets encounter various stresses during normal use due to a 
variety of different loads such as thrombi and emboli. The filter basket 
11 is shown locked in its expanded state by sliding lock assembly 23 in 
FIG. 3. 
When it is desired to collapse filter basket 11 such as for insertion into 
or removal from the blood vessel, sliding lock assembly 23 is pulled 
axially over central wire 15 toward coil segment 16 thus unlocking 
expander assembly 19. Expander assembly 19 is then slid axially over 
central wire 15 toward coil segment 16 causing the proximal ends of wires 
13 to advance axially over central wire 15 toward coil segment 16. The 
axial movement of the proximal ends of wires 13 toward coil segment 16 
correspondingly causes filter basket 11 to collapse and to become longer 
and thinner. Sliding lock assembly 23 is shown in FIG. 2 in an unlocked 
position thus allowing filter basket 11 to assume a collapsed state. 
Catheter 30 is nontapered and open-ended and has a proximal fitting 31 
fixed thereon as shown in FIGS. 1 and 4. Catheter 30 is 60.0 centimeters 
in length and has an outer diameter of 0.092 inch. Fixedly secured to the 
outer surface and intermediate the ends of catheter 30 is a silicone 
rubber winged anchoring device 35. The purpose of anchoring device 35 is 
to anchor apparatus 10 via sutures 36 to the skin 37 of time patient as 
shown in FIGS. 4 and 5B. 
The proximal fitting 31 is releasably attachable to a Touhy-Borst type 
fitting 45. Such a fitting is a commercially available device, for 
example, from Cook Inc. of Bloomington, Indiana, Model No. UCC-1 and 
includes a rubber O-ring that may be squeezed by the operation of the 
device to grip a wire or other member inside of the rubber O-ring. The 
fitting 45 is provided to releasably lock positioning assembly 12 to 
catheter 30 at one of a plurality of positions on the outer surface of 
stretched section 27 of positioning assembly 12. Stretched section 27 
possesses an irregular surface onto which fitting 45 can lock. Since 
positioning assembly 12 can be locked to catheter 30 at one of a plurality 
positions, filter 11 can be readily repositioned from a one position to 
another position within tile blood vessel via positioning assembly 12. 
A connecting tube 40 is provided to cover the portion of positioning 
assembly 12 which extends beyond catheter 30 and fitting 45 in order to 
maintain the sterility of positioning assembly 12. Connecting tube 40 is 
64.0 centimeters in length and has an outer diameter of 0.125 inch. 
Connecting tube 40 has a proximal fitting 42 and a distal fitting 41 
thereon. The distal fitting 41 is provided to releasably attach connecting 
tube 40 to catheter 30 via Touhy-Borst fitting 45. 
A fragmentary, median section through a human body from the left and right 
thighs upward is shown in FIG. 4 to aid in illustrating a medical 
procedure performed in accordance with the preferred embodiment of the 
present invention. In addition, FIGS. 5A and 5B show an enlarged view of 
the distal and proximal end portions respectively of the blood filtering 
apparatus 10 as it is used in accordance with the aforementioned medical 
procedure shown in FIG. 4. 
A portion of a nontapered open-ended catheter 30 is introduced into and 
guided through the femoral vein 60 and advanced through the external iliac 
vein 61 and the common iliac vein 62 and then into the inferior vena cava 
63. The distal end of catheter 30 is advanced to the location CD1 as 
represented on position indicator D. The catheter can be assisted in 
initial placement into the femoral vein by a sheath, wire guide and 
dilator combination. The filter basket 11 and attached positioning 
assembly 12 (described above and shown in FIGS. 2 and 3) are inserted into 
the proximal end of catheter 30 with tile filter basket end inserted first. 
This can be done by collapsing filter basket 11 before insertion with the 
aid of a short piece of tubing that has the same inner and outer diameters 
as catheter 30. This short piece of tubing is then removed over the 
proximal end of positioning assembly 12 and discarded after filter 11 is 
inside catheter 30. 
Filter basket 11 is then advanced through the catheter, and upon exiting 
the distal end thereof, it changes from a collapsed to an expanded state. 
Once filter basket 11 is deployed to its expanded state, sliding lock 
assembly 23 carl be used to maintain filter basket 11 in that state, as 
described above. The distal end of expanded filter basket 11 is then 
advanced to the location D1 as represented on position indicator D. When 
the distal end of filter basket 11 is positioned as above, the proximal 
end of positioning assembly 12 will correspondingly be at location P1 as 
represented on position indicator P. In FIGS. 4, 5A and 5B positioning 
assembly 12 is shown, in phantom, extending through connecting tube 40, 
fitting 45 and catheter 30. Once filter basket 11 and positioning assembly 
12 are positioned at this desired location, the Touhy-Borst fitting 45 is 
used to lock together catheter 30 and positioning assembly 12. Connecting 
tube 40 is then slid over the portion of positioning assembly 12 which 
extends beyond fitting 45 in order to maintain the sterility of the 
positioning assembly 12. The connecting tube 40 is then secured to fitting 
45. Catheter 30 is then anchored to the skin 37 of the patient with sutures 
36 via the anchoring device 35. This has the effect of anchoring the entire 
apparatus 10 at a fixed location. 
After the filter has been in place for a period of time, it may be 
desirable to reposition filter basket 11 within the vena cava to prevent 
filter basket 11 from becoming endothelialized and hence attached to the 
interior wall of the vena cava. The design of the present invention allows 
an operator to readily reposition the filter basket within the vena cava. 
This is accomplished by removing connector tube 40 from the proximal end 
portion of positioning assembly 12, loosening fitting 45 to unlock 
positioning assembly 12 from catheter 30, repositioning positioning 
assembly 12 and the attached filter basket 11, tightening fitting 45 to 
relock positioning assembly 12 to catheter 30 and then recovering the 
proximal end portion of positioning assembly 12 with connecting tube 40. 
Referring to FIGS. 4, 5A and 5B, filter basket 11F and a distal end portion 
12F of positioning assembly 12 are shown, phantom, at a repositioned 
location. In this repositioned location, the distal end of filter basket 
11F is at location D2 as represented on position indicator D and the 
proximal end of positioning assembly 12 (not shown) is correspondingly at 
location P2 as represented on position indicator P. As is shown in FIGS. 4 
and 5A tile filter basket contacts the interior wall of the vena cava at 
different locations after each act of repositioning in accordance with the 
present invention. Since the filter basket does not become endothelialized 
to the interior wall of the vena cava with tile above procedure, it can be 
left in the vena cava for several weeks without damage thereto. It should 
be noted that before and after the repositioning of the filter basket 11 
and attached positioning assembly 12, the location of the distal end of 
catheter 30 as represented on position indicator D is maintained at CD1. 
Further, before and after the repositioning of the filter basket 11 and 
attached positioning assembly 12, the location of the proximal end of 
connecting tube 40 as represented on position indicator D is maintained at 
CP1. 
While the invention has been illustrated and described in detail in the 
drawings and foregoing description, the same is to be considered as 
illustrative and not restrictive in character, it being understood that 
only the preferred embodiments have been shown and described and that all 
changes and modifications that come within the spirit of the invention are 
desired to be protected.