U.S. patent application number 09/157846 was filed with the patent office on 2001-06-21 for ventricular assist device with valved blood conduit and method of making.
Invention is credited to CHEN, HERBERT, GREENBERG, SHELDON I., NESS, RONALD A., NGUYEN, THAN, ROMLEY, RICHARD M., WOODARD, JOHN C..
Application Number | 20010004675 09/157846 |
Document ID | / |
Family ID | 22711458 |
Filed Date | 2001-06-21 |
United States Patent
Application |
20010004675 |
Kind Code |
A1 |
WOODARD, JOHN C. ; et
al. |
June 21, 2001 |
VENTRICULAR ASSIST DEVICE WITH VALVED BLOOD CONDUIT AND METHOD OF
MAKING
Abstract
A ventricular assist device includes a pair of valved conduits
and a pumping portion connected by these conduits into the
circulatory system of a host patient. The pumping portion and
valved conduits are constructed and configured to minimize the
number of material-surface transitions which blood must cross in
flowing through the device. Also, the valved conduits include
porcine xenograft valves, which are externally supported by
stenting structure located outside of the blood-contacting flow
path of the device. A flexible shape-retaining inner wall member of
the valved conduits is impervious to blood, but defines a porous
inner surface on which a stable biological interface may form.
Also, this inner wall member is shaped with sinuses which do not
replicate either the porcine sinuses from which the xenograft
valves were taken, or human aortic sinuses. However, the sinuses of
the inner wall member are configured to provide effective valve
action by the formation of vigorous vortices in the blood flow
downstream of these valves, and to avoid the formation of clots on
the blood-contacting surfaces of the valved conduits.
Inventors: |
WOODARD, JOHN C.; (WALNUT
CREEK, CA) ; GREENBERG, SHELDON I.; (OAKLAND, CA)
; NESS, RONALD A.; (CASTROL VALLEY, CA) ; ROMLEY,
RICHARD M.; (ALAMEDA, CA) ; NGUYEN, THAN;
(HUNTINGTON BEACH, CA) ; CHEN, HERBERT;
(KENSINGTON, CA) |
Correspondence
Address: |
BAXTER HEALTHCARE CORPORATION
17221 RED HILL AVENUE
IRVINE
CA
92614
US
|
Family ID: |
22711458 |
Appl. No.: |
09/157846 |
Filed: |
September 21, 1998 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09157846 |
Sep 21, 1998 |
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08471438 |
Jun 6, 1995 |
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5810708 |
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08471438 |
Jun 6, 1995 |
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08192894 |
Feb 7, 1994 |
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6102845 |
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Current U.S.
Class: |
600/16 |
Current CPC
Class: |
A61M 60/896 20210101;
A61M 60/268 20210101; A61F 2/2412 20130101; A61M 60/148 20210101;
A61M 60/178 20210101; A61M 60/857 20210101; Y10S 623/90 20130101;
A61M 1/3659 20140204; A61M 60/427 20210101; A61M 60/89
20210101 |
Class at
Publication: |
600/16 |
International
Class: |
A61M 001/12 |
Claims
We claim:
1. A ventricular assist device comprising: a pumping portion
including a unitary flexible wall member having a singular
blood-contacting inner surface entirely defining a variable-volume
chamber for receiving and discharging-blood, said unitary flexible
wall member also defining one of an inflow port and an outflow port
for respective flow of blood to and from said variable-volume
chamber; and a flexible conduit member having a side wall defining
a second blood-contacting inner surface, said flexible conduit
member communicating blood between the variable-volume chamber and
the circulatory system of a host organism, said side wall of said
flexible conduit member sealingly engaging said unitary flexible
wall member at a respective one of said inflow and outflow ports;
whereby flowing blood of said host organism, in passing through
said flexible conduit and said variable-volume chamber of said
pumping portion, contacts only the first and the second
blood-contacting inner surfaces.
2. The ventricular assist device of claim 1 further including a
prosthetic valve disposed within said flexible conduit member for
limiting blood flow therein to a single direction, and a stenting
structure for said prosthetic valve disposed outside of said
flexible conduit member.
3. The ventricular assist device of claim 2 further including
sutures attaching said prosthetic valve to said stenting structure
through said side wall of said flexible conduit member, whereby
blood flowing through said flexible conduit member contacts only
said second blood-contacting inner surface, said prosthetic valve,
and said sutures.
4. The ventricular assist device of claim 2 wherein said prosthetic
valve is a natural tissue xenograft valve.
5. The ventricular assist device of claim 4 wherein said natural
tissue xenograft valve is a porcine xenograft.
6. The ventricular assist device of claim 2 wherein said prosthetic
valve includes at least a pair of valve leaflets, said flexible
conduit member further defining a like number of sinuses downstream
of and axially aligning with said prosthetic valve leaflets.
7. The ventricular assist device of claim 6 wherein said sinuses of
said flexible conduit are smaller than human natural aortic valve
sinuses.
8. The ventricular assist device of claim 6 wherein said sinuses of
said flexible conduit define a portion of said second
blood-contacting surface, and downstream of said prosthetic valve
said sinus-portion of said second surface rejoins at an acute
glancing angle a substantially-cylindrical remainder portion of
said second surface.
9. The ventricular assist device of claim 6 wherein said sinuses of
said flexible conduit have an aspect ratio of at least 1.3.
10. The ventricular assist device of claim 9 wherein said sinuses
of said flexible conduit have an aspect ratio in the range from
about 1.3 to about 1.6 or more.
11. The ventricular assist device of claim 6 wherein said sinuses
of said flexible conduit have an aspect ratio of substantially
1.45.
12. The ventricular assist device of claim 1 additionally including
an elongate conduit member connecting with said flexible conduit
member, said elongate conduit member at one end thereof fluidly
communicating with said host organism's circulatory system and at
an opposite end fluidly communicating with said flexible conduit
member to communicate blood from said host's circulatory system to
or from said variable-volume chamber, said inner wall of said
flexible conduit member directly sealingly engaging said elongate
conduit member at an end of the latter.
13. The ventricular assist device of claim 1 further including a
tubular housing supportingly receiving said flexible conduit
member, said housing defining at least one perforation therethrough
outwardly exposing said flexible conduit member to body fluids of
said host organism.
14. The ventricular assist device of claim 13 additionally
including means for resiliently retaining said flexible conduit
member in sealing engagement with said flexible wall member at said
respective one of said inflow or outflow ports.
15. The ventricular assist device of claim 14 wherein said means
for resiliently retaining sealing engagement of said flexible
conduit member with said flexible wall member includes said pumping
portion having a respective housing defining a recess into which
said flexible conduit and tubular housing thereof is received to
sealingly engage said flexible wall member, said tubular housing
carrying means for engaging and securing axially with said pump
portion housing and urging said flexible conduit into sealing
engagement with said flexible wall member, and resilient means
interposing axially between said means for engaging and said
tubular housing for allowing a limited amount of axial relative
movement therebetween.
16. The ventricular assist device of claim 15 wherein said means
for resiliently retaining sealing engagement of said flexible
conduit member with said flexible wall includes said tubular
housing rotationally carrying a collar which threadably engages
into said recess of said pump portion housing to urge a flange
portion of said tubular housing into engagement with said pump
portion housing, and a circumferentially extending
axially-resilient washer member interposed axially between said
collar and said flange of said tubular housing.
17. The ventricular assist device of claim 16 wherein said
axially-resilient washer member includes a metallic wave
washer.
18. The ventricular assist device of claim 12 further including
said elongate conduit member including on an inner blood-contacting
surface thereof a bio-degradable organic coating for rendering said
elongate conduit initially more leak resistant post-implantation
with respect to blood loss from said organism's circulatory
system.
19. The ventricular assist device of claim 18 wherein said tubular
housing further includes means for sealingly connecting with said
elongate conduit member while sealingly accommodating change of
dimension thereof as said biodegradable coating is absorbed by said
host organism.
20. The ventricular assist device of claim 19 wherein said means
for sealingly connecting includes said tubular housing defining a
tapered seating feature to which an end of said elongate conduit
sealingly connects, a shoulder on said elongate conduit, and a
threaded ring engaging both said shoulder and said tubular housing
to threadingly urge said elongate conduit into sealing engagement
with said seating feature, and an axially-resilient washer member
interposing axially between said shoulder and said ring to take up
axial dimension lost by said elongate conduit in response to
absorption of said bio-degradable coating.
21. The ventricular assist device of claim 20 wherein said
axially-resilient washer member includes a metallic wave
washer.
22. A shape-retaining flexible conduit for carrying blood in a
living organism, said conduit comprising: fabric sheet material
defining a tubular body having an inner surface bounding a flow
path for said blood and an outer surface, at said outer surface
said tubular body carrying an impermeable coating of
biologically-compatible polymeric material penetrating into said
fabric toward but short of said inner surface, said impermeable
polymeric coating being continuous axially and circumferentially to
render said tubular body impervious to blood, and said inner fabric
surface remaining porous to provide for attachment of a stable
biological interface thereon.
23. The flexible conduit of claim 22 further including valve means
disposed in said conduit flow path for limiting blood flow therein
to a single direction.
24. The flexible conduit of claim 23 wherein said valve means
includes a prosthetic valve.
25. The flexible conduit of claim 24 wherein said prosthetic valve
is a porcine xenograft.
26. The flexible conduit of claim 23 further including a stenting
structure for supporting said valve means, said stenting structure
being disposed outside of said polymeric coating and being isolated
thereby from contact with said blood.
27. The flexible conduit of claim 24 wherein said prosthetic valve
includes at least a pair of valve leaflets, said flexible conduit
member further defining a like number of sinuses downstream of and
axially aligning with said prosthetic valve leaflets.
28. The flexible conduit of claim 27 wherein said sinuses of said
flexible conduit are smaller than human natural aortic valve
sinuses.
29. The flexible conduit of claim 28 wherein said sinuses of said
flexible conduit define a portion of said inner surface, and
downstream of said prosthetic valve said sinus-portion of said
inner surface rejoining at an acute glancing angle a
substantially-cylindrical remainder portion of said inner
surface.
30. The flexible conduit of claim 28 wherein said sinuses have an
aspect ratio of at least 1.3.
31. The flexible conduit of claim 30 wherein said sinuses have an
aspect ratio in the range from about 1.3 to about 1.6 or more.
32. The flexible conduit of claim 31 wherein said sinuses have an
aspect ratio of substantially 1.45.
33. A valved prosthetic conduit for carrying a unidirectional blood
flow in a living organism, said valved conduit comprising: a
natural-tissue xenograft valve defining a first blood-contacting
surface; a fabric conduit in which said valve is secured and
defining a second blood-contacting surface; and sutures securing
said xenograft-tissue valve into said fabric conduit and defining a
third blood-contacting surface; whereby the valved conduit has only
the first, the second, and the third blood-contacting surfaces
contacted by blood flowing through said conduit.
34. The valved conduit of claim 33 further including a stenting
structure for said xenograft valve, said stenting structure being
disposed outside of said fabric conduit.
35. The valved conduit of claim 34 wherein said fabric conduit is
impervious to blood, and said fabric conduit isolates said stenting
structure from blood contact.
36. The valved conduit of claim 33 wherein said fabric conduit is
flexible and shape-retaining, said fabric conduit defining plural
sinuses downstream of said xenograft valve, and said plural sinuses
being the same in number and aligning axially with the natural
valve leaflets of said xenograft valve.
37. The valved conduit of claim 36 wherein said plural sinuses
differ from both the natural sinuses from which said xenograft
valve was removed, and from natural human sinuses.
38. The valved conduit of claim 37 wherein said sinuses of said
flexible conduit are smaller than human natural aortic valve
sinuses.
39. The valved conduit of claim 38 wherein said sinuses have an
aspect ratio of at least 1.3.
40. The valved conduit of claim 39 wherein said sinuses have an
aspect ratio in the range from about 1.3 to about 1.6 or more.
41. The valved conduit of claim 40 wherein said sinuses have an
aspect ratio of substantially 1.45.
42. A method of making a flexible shape-retaining blood-impermeable
fabric conduit member with a porous inner surface for use in
carrying blood within a living organism and providing for formation
of a stable biological interface on said porous inner surface, said
method comprising the steps of: forming a tubular porous fabric
body having an inner surface and an outer surface; on said outer
surface applying a continuous coating of biologically-compatible
blood-impervious polymeric material into said fabric toward but
short of said inner surface while maintaining porosity of said
inner surface; employing said coating of polymeric material to
render said tubular fabric body impermeable to blood flow; and
forming said fabric conduit member from said fabric body coated
with said polymeric material.
43. The method of claim 42 including the steps of using a thermoset
material as said blood-impervious polymeric material, and curing
said thermoset material sufficiently to prevent further mobility of
said polymeric material in said fabric before forming said conduit
member therefrom.
44. The method of claim 43 further including the steps of using a
rotational cylindrical mandrel to support said tubular porous
fabric body, pressing a movable support surface against said
tubular porous fabric body on said mandrel, and feeding a sheet of
raw polymeric material between said fabric and said movable support
surface as the latter and said mandrel are moved in unison.
45. The method of claim 43 additionally including the steps of:
further forming said fabric body coated with said polymeric
material into a selected shape subsequent to curing of said
thermoset material by; providing a mold having a cavity of said
selected shape; placing said fabric body into said cavity;
inserting a balloon into said fabric body; forcefully inflating
said balloon while heating said cavity to require said fabric body
to take the shape of said cavity; and cooling said shaped fabric
body to cause the latter to retain said selected shape.
46. A method of providing for assistance to a selected heart
chamber of a living organism having a blood circulatory system,
said method comprising the steps of: providing an artificial flow
path for a flow of blood leading from said circulatory system and
returning to said circulatory system downstream of said selected
heart chamber; providing a variable-volume chamber in said
artificial flow path; providing a pair of like-disposed one-way
valves bracketing said variable-volume chamber in said artificial
flow path; providing means securing said pair of one-way valves in
respective ones of a pair of portions of said artificial flow path;
expanding and contracting said variable-volume chamber to withdraw
blood from said circulatory system, and to return said blood to
said circulatory system downstream of said selected heart chamber
to assist or replace the function of the heart chamber in
circulating said blood in said circulatory system; using a singular
flexible wall member to define said variable-volume chamber; using
a pair of respective artificial conduit members to define said pair
of portions of said artificial flow path and to receive said
one-way valves; and sealingly contacting said pair of respective
artificial conduit members directly with said singular flexible
wall member; whereby blood from said circulatory system in flowing
past said pair of one-way valves and through said variable-volume
chamber contacts only said singular flexible wall member, said pair
of artificial conduit members, said pair of one-way valves, and
said means securing said pair of one-way valves into said pair of
artificial conduit members.
47. A conduit for carrying blood comprising: a tubular body having
an inner surface bounding a flow path for said blood; prosthetic
valve means sealingly disposed in said flow path for limiting blood
flow therein to a single direction, and including at least one
valve leaflet; said flexible conduit member further defining the
same number of sinuses as the number of valve leaflets of said
prosthetic valve, each said sinus being downstream of and axially
aligning respectively with a respective one leaflet of said
prosthetic valve; wherein each said sinus of said flexible conduit
is shallower and longer than a human natural aortic valve
sinus.
48. The conduit of claim 47 wherein said sinus has an aspect ratio
of at least 1.3.
49. The conduit of claim 48 wherein said sinus has an aspect ratio
in the range from about 1.3 to about 1.6 or more.
50. The conduit of claim 49 wherein said sinus has an aspect ratio
of substantially 1.45.
51. The conduit of claim 47 wherein said prosthetic valve is a
porcine xenograft.
52. The conduit of claim 47 further including a stenting structure
for supporting said prosthetic valve means, said stenting structure
being disposed outside of said tubular body and being isolated
thereby from contact with blood flowing in said conduit.
53. The conduit of claim 47 wherein each said sinus at a downstream
termination thereof rejoins a cylindrical projection of said
tubular body at an acute glancing angle.
54. A valved prosthetic conduit for carrying a unidirectional blood
flow in a living organism, said valved conduit comprising: a
prosthetic valve; a prosthetic conduit in which said valve is
secured; a stenting structure for said prosthetic valve, said
stenting structure being disposed outside of said conduit; whereby
the stenting structure is isolated from contact with flowing blood
by said conduit.
55. The valved conduit of claim 54 wherein said conduit is
impervious to blood and defines a porous inner surface providing
for a stable biological interface within said conduit.
56. The valved conduit of claim 54 wherein said conduit is formed
of flexible and shape-retaining fabric defining plural sinuses
downstream of said prosthetic valve, said prosthetic valve
including plural valve leaflets and said plural sinuses being the
same in number and aligning axially with the valve leaflets of said
prosthetic valve.
57. A blood-carrying conduit apparatus,comprising: a first flexible
conduit member defining a flow path for communicating a flow of
blood therethrough, and having a flexible side wall defining a
blood-contacting inner surface bounding said flow path; a second
blood-carrying member defining a flow path for communicating blood
therein; said side wall including a reentrant portion defining an
end surface for said first flexible conduit member; and means
urging said end surface of said conduit member sealingly into
engagement with said second blood-carrying member.
58. The conduit apparatus of claim 57 wherein said means for urging
further including means for resiliently accommodating relative
axial movement of said conduit member relative to said second
member while maintaining sealing contact therebetween.
59. The conduit apparatus of claim 58 wherein said means urging
said end surface of said conduit into sealing engagement with said
second member includes a collar member circumscribing said conduit
member and engaging said second member and a radially extending
portion of said conduit member to urge the latter into sealing
engagement at said end surface with said second member.
60. The conduit apparatus of claim 59 wherein said means for
resiliently accommodating relative axial movement of said conduit
member relative to said second member includes an axially-resilient
element interposing between said collar member and said radially
extending portion of said conduit member.
61. The conduit apparatus of claim 60 wherein said
axially-resilient element includes a circumferentially extending
wave washer interposing between said collar and said radially
extending portion of said conduit.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention is in the field of ventricular assist
devices, and of artificial prosthetic conduits used for
transporting blood in the circulatory system of a living organism.
More particularly, the present invention relates to a ventricular
assist device which includes a continuous unitary blood-contacting
membrane defining a variable-volume cavity, expansion and
contraction of which is effective to pump blood; and to a valved
blood conduit for communicating blood to or from the
variable-volume chamber, and having liquid-impermeable membrane or
inner wall defining a blood-contacting surface within the conduit.
The inner wall of the conduit sealingly engages the unitary
blood-contacting membrane of the variable-volume chamber without a
blood-contacting gasket or sealing member, so that only a single
material-surface transition is experienced by the flowing blood
upon entry into or outflow from the ventricular assist device.
[0003] Also, the present invention relates to an artificial conduit
having therein a prosthetic bio-material valve structure, and
associated conduit structure for ensuring a substantially laminar
central jet of blood flow through the conduit and valve structure,
while also ensuring that flow disruption is minimized, and that no
blood stagnation or stasis volumes are formed downstream of or
behind the valve structure. Still more particularly, the present
invention relates to such a valved blood conduit having woven
and/or knitted filamentary fabric walls which are impregnated
outwardly with a biologically-compatible impermeable material so
that the conduit walls are impermeable to blood, while the inner
surface of the conduit wall remains textured or porous to promote
the growth of a stable biological interface. Provision is made for
sealingly connecting the valved blood conduit to other
blood-carrying components without disruption of smooth and
stasis-free blood flow. The connecting provisions also minimize the
number of blood-contacting material-surface transitions, and
provide for accommodation without loss of sealing integrity of
dimensional changes which will occur at the connections after
implantation of the valved conduit and assist device. These
dimensional changes will occur as a transitional collagen or other
biodegradable coating of the conduit is absorbed, as components of
the valved conduit and adjacent structure take a set with the
passage of time after surgical implantation, and as a biological
interface is formed on the blood-contacting surfaces by the host's
circulatory system.
[0004] 2. Related Technology
[0005] Ventricular assist devices have become increasingly
recognized as potentially able to allow patient's whose natural
heart is diseased or has been injured by trauma or heart attack, to
recover and continue life, either while their natural heart heals,
while awaiting a heart transplant, or even on a long-term basis
with the extended aid of the ventricular assist device.
[0006] Particularly, left-ventricular assist devices (LVAD) are
recognized as potentially very valuable for assisting patients who
suffer from congestive heart failure. More than two and one-half
million Americans suffer from congestive heart failure. Recently, a
National Institutes of Health study estimated that as many as
thirty-five thousand people could be candidates for use of a
left-ventricular assist device. At present, the conventional
ventricular assist devices are used for patients who are waiting
for a heart transplant (a so-called, "bridge to transplant"), for
patients whose natural heart is of such poor condition that the
patient cannot be removed from a heart-lung machine without
providing some assistance to the patient's heart following
otherwise successful open-heart surgery, and for patients suffering
from massive heart attacks that lead to circulatory collapse. The
conventional left-ventricular assist devices are not generally
considered to be viable candidates for long-term utilization
outside of the clinical environment for a plurality of reasons.
[0007] Most heart disease involves the left ventricle of the heart.
This pumping chamber is generally known as the workhorse of the
heart. A patient with a non-functioning right ventricle can survive
quite successfully provided that their pulmonary blood flow
resistance is low enough to allow circulation through the lungs and
the rest of the body entirely as a result of the efforts of the
left ventricle. However, collapse of the left ventricle is most
often fatal. An LVAD is able to fully take over the function of
this ventricle, thus perfusing the body with oxygen-rich blood. The
LVAD attaches to the patient's natural heart, and to a natural
artery, and can be removed if the natural heart recovers.
[0008] Blood flow in the LVAD is effected by expansion and
contraction of a variable-volume chamber. One-way valves associated
with the inflow and outflow ports of the LVAD provide for blood
flow into the variable-volume chamber during expansion, and for
blood flow out of this chamber, usually to the ascending thoracic
aorta. These one-way flow valves may be constructed as part of the
LVAD itself, or may be disposed in the blood-flow conduits which
connect the LVAD to the heart and aorta. A pair of conduits
respectively connect the inlet port of the assist device to the
left ventricle and the outlet port to the major artery which is to
receive the blood flow from the device.
[0009] As described above, artificial blood conduits have become a
valuable tool of modern medicine. One use of such artificial blood
conduits is as a temporary or permanent prosthetic artery. Another
use is in the connection of temporary blood pumps, or ventricular
assist devices, between the left ventricle of the heart and a major
artery. In such a use, the demands on the artificial blood conduit
are great. The artificial conduit must deal with the pulsatile
blood flow created by the host's own heart, as well as with the
flow, pressure, and pulsations created by the assist device. The
artificial conduit must function within or outside of the host
patient's body, and not introduce or allow the entry of bacterial
or other contamination into the host's body or circulatory system.
Also, the artificial conduit must be connected to both the heart,
or to a major artery of the host's circulatory system in order to
allow connection of both the artificial conduit, and also of the
ventricular assist device or pump.
[0010] A persistent problem with artificial blood conduits has been
the provision of a valving device of the one-way type in these
conduits so that a ventricular assist device can achieve pulsatile
blood flow in response to the expansion and contractions of a
variable-volume chamber of the assist device.
[0011] A conventional artificial blood conduit is know in accord
with U.S. Pat. No. 4,086,665, issued May 2, 1978, to Poirier. The
blood conduit of the Poirier patent is believed to include an
internal convoluted fabric tube of essentially circular cylindrical
configuration throughout its length. This inner fabric tube is
carried within an outer tube, which is also convoluted over part of
its length. The inner tube is porous while the outer tube is liquid
impervious. A tri-foliate valving structure is provided in the
conduit to ensure unidirectional blood flow in the conduit. This
tri-foliate valving structure is taught by the Poirier patent to be
a porcine xenograft, sutured into the fabric of the inner tube. A
circular support ring may be disposed outside of the inner tube
wall to assist in support of the xenograft. Provision is made for
connection of the artificial blood conduit of Poirier to other
blood-carrying structure, and to the vascular tissue or heart
tissue of the host via suture rings. Essentially, Poirier teaches
that the valved conduit may be connected to other blood-carrying
structure by means of flanged connections using gasket-sealed
interfaces and threaded collars which engage onto threaded portions
of the adjacent conduit or other blood-carrying structure.
[0012] With the artificial blood conduit taught by the Poirier
patent, the conduit structure itself is quite bulky, being composed
of several concentric structures or elements, some of which are
spaced apart radially from one another. As a result, the Poirier
conduit has a considerable wall thickness built up by all of these
individual wall elements. Additionally, the inner lumen or
passageway of this artificial conduit does not provide for
elimination of blood flow stagnation or stasis downstream of the
tri-foliate valve structure. Accordingly, the stagnant blood may
clot or may adhere to the walls of the conduit, to be shed
eventually as emboli in the circulatory system of the host. Also,
the annular space between the inner porous conduit and the outer
impervious conduit may harbor bacterial contamination, and provide
a site for bacterial growth and infection which is hidden from the
patient's immune system.
[0013] A conventional bio-material xenograft valve is known in
accord with U.S. Pat. No. 4,247,292, issued Jan. 27, 1981, to W. W.
Angell. The Angell patent is believed to disclose an
externally-stented natural tissue valve for heart implantation in
which the natural xenograft tissue is sutured to a fabric covered
plastic stent. The valve is secured into a patient's heart by
sutures between the suture ring and the heart tissue. There is no
artificial conduit which is valved by the device of Angell.
[0014] Another conventional artificial conduit is disclosed by U.S.
Pat. No. 5,139,515, issued Aug. 18, 1992 to F. Robicsek. The
Robicsek patent is believed to disclose an artificial aortic root
portion which includes a convoluted wall formed with sinuses
generally aligned with the leaflets of the natural tri-foliate
valve of the patient's heart. As so configured, it is asserted that
the blood flow "recoil" downstream of the valve leaflets will
assist in their closing, resulting in a more natural valve
function, with reduced regurgitation. However, the artificial
aortic root portion taught by Robicsek includes out-pouchings, or
sinuses, which are themselves formed with corrugations or
convolutions like the rest of the artificial conduit. These
convolutions at the sinuses themselves may contribute to the
formation of small localized turbulent zones, or to the formation
of stasis or stagnation volumes where blood flow is slowed or
stopped. In either case, the fluid flow dynamics of the artificial
conduit suggested by the Robicsek patent is highly questionable
because it may cause the formation of clots which are eventually
shed as emboli in the circulatory system.
[0015] Yet another artificial valve is known in accord with British
patent specification No. 1315845, of B. J. Bellhouse, the complete
specification for which was published on May 2, 1973. The Bellhouse
specification is believed to disclose an artificial valve for
implantation within the natural aortic root, with a ring part
formed of silicone-coated uncut polyethylene terephthalate fabric.
The cusps of this valve are formed of woven and/or knitted material
of the same type of polyethylene terephthalate fabric, which is
also coated with silicone rubber. However, the valve of Bellhouse
is implanted into the natural aortic root, with the natural sinuses
present, and does not include a prosthetic conduit for blood
flow.
[0016] A persistent problem with all of the above-identified
conventional devices, and with others which are known also in the
art, is the rather high number of material-surface transitions, or
changes in the material across which the patient's blood must flow
in passing through the devices. For example, in the artificial
blood conduit of Poirier, disclosed in the '665 patent, the flowing
blood is exposed to at least nine different surfaces in flowing
through this device. These different surfaces include the tissue
surfaces of the porcine xenograft, the sutures which secure this
graft, the fabric inner conduit, the gasket surfaces at the ends of
the valved conduit, and the end connectors to which the fabric
inner conduit connects. When the entire ventricular assist device
of Poirier is considered, several additional blood-contacting
surfaces of different materials, or material-surface transitions,
must also be added to this list. Each of these blood-contacting
material-surface transitions represents a potential source of
turbulence in the flowing blood if the adjacent surfaces do not
align perfectly with one another.
[0017] Additionally, the flowing blood may not have the same
affinity for creating a stable biological interface with each of
the various materials. That is, the material surfaces may have a
differing degrees of surface porosity, of surface roughness, of
surface energy, or of bio-compatibility with the host, for example.
Consequently, with the passage of time, the biological interface
between the flowing blood and the artificial, "not self" surfaces
will be laid down with discontinuities, or with changes in tenacity
of attachment to the underlying artificial surfaces, for example,
at these material-surface transitions in the device. Each of these
discontinuities or changes in tenacity of attachment of the
biological interface with the underlying artificial structure
represents an opportunity for a portion of the interface to slough
off to become an emboli in the circulating blood. Also, blood may
clot at these unstable interfaces, also representing a risk of
forming emboli in the blood.
SUMMARY OF THE INVENTION
[0018] In view of the deficiencies of the conventional related
technology outlined above, it is an object for this invention to
provide a ventricular assist device having a variable-volume
chamber, and a pair of valved conduits connecting the
variable-volume chamber to the circulatory system of a patient, and
in which the number of blood-contacting material-surface
transitions is minimized.
[0019] More particularly, the present invention has as an object
the provision of a ventricular assist device in which the
variable-volume pumping chamber is formed of a single unitary
blood-contacting flexible wall member, and this wall member is
sealingly contacted by the material defining the blood-contacting
wall of the valved conduit itself, without the use of gaskets or
other sealing devices which are exposed to the flowing blood.
[0020] Still further to the above, the present invention has as an
object the provision of a valved conduit in which the flowing blood
is exposed only to the surfaces of a prosthetic valve, such as a
porcine xenograft valve, to the sutures which secure this valve,
and to the inner porous surface of a fabric conduit communicating
the patient's circulatory system with the variable-volume chamber
of the assist device.
[0021] Additionally, a further object of the present invention is
to provide such a ventricular assist device, and valved conduit for
such a device in which the fabric which defines the inner
blood-contacting surface of the valved conduit is internally
porous, but is impermeable to blood. Consequently, the fabric of
this conduit presents a very favorable surface upon which a stable
biological interface may be laid down by the flowing blood. On the
other hand, this impervious fabric does not require an outer
impervious conduit or tube like that used in the Poirier '665
patent in order to prevent blood from seeping through the fabric.
This impervious fabric conduit can then be disposed in a perforate
cage or support structure which is outwardly exposed to body
fluids. Because the cage and fabric conduit are outwardly exposed
to body fluids they do not provide a cavity or void in which a
bacterial infection may be hidden from the immune system, as may
occur with the device taught by the Poirier '665 patent.
[0022] Still further, an object of the present invention is to
provide such a valved conduit in which the conduit is formed with
sinuses downstream of the tri-foliate prosthetic valve, such as a
natural tissue porcine xenograft valve, and which sinuses do not
replicate either the natural porcine sinuses of the aortic root
from which the valve is removed, for example, or the natural human
aortic sinuses. However, these sinuses are especially shaped and
sized to cooperate with the prosthetic valve to ensure the
formation of vigorous blood-flow vortices behind each valve leaf.
These vortices in the flowing blood contribute to an improved valve
action, and to prompt closing of the valve leaflets upon the
systole ending, as is recognized in the art. However, the vigorous
vortices provided by the present inventive sinus configuration of
the valved conduit also ensures that the blood-exposed surfaces of
the conduit are scrubbed by the flowing blood. Consequently, blood
stagnation or stasis is avoided, and clots do not form on the
conduit walls to be later sloughed off as emboli in the circulatory
system.
[0023] Yet another object for the present invention is to provide
such a valved conduit in which the prosthetic valve, such as a
porcine xenograft valve, is externally stented with the fabric of
the conduit interposing between the material of the prosthetic
valve and the stent structure. Consequently, the prosthetic valve
is supported effectively for its operation to control the blood
flow in the valved conduit to a unidirectional flow. The prosthetic
valve is supported with superior strength to successfully resist
the large pressure variations and rapid changes in fluid flow
involved with the ventricular assist device. Further, the flowing
blood is not exposed to the surfaces of the stenting structure, the
formation of clots in the blood on additional blood-exposed
surfaces is thus avoided and is reduced. That is, the stent
structure is entirely removed from and is isolated from the flowing
blood.
[0024] Accordingly, the present invention provides a ventricular
assist device including a unitary flexible wall member having a
singular blood-contacting inner surface entirely defining a
variable-volume chamber for receiving and discharging blood, the
unitary flexible wall member also defining one of an inlet port and
an outflow port for respective flow of blood, and a flexible
conduit member having a side wall defining a second
blood-contacting inner surface and communicating blood between the
variable-volume chamber and the circulatory system of a host
organism, the side wall of the flexible conduit member sealingly
engaging the unitary flexible wall member at the respective one of
said inlet and outflow ports so that flowing blood in passing
through said flexible conduit and said variable-volume chamber
contacts only the first and the second blood-contacting inner
surfaces.
[0025] According to a further aspect of the present invention, a
valved conduit is formed of fabric sheet material having an outer
surface thereof coated with impermeable polymeric material
partially impregnating into the intersticial spaces of the fabric
between fibers thereof toward but short of the inner surface of the
fabric conduit.
[0026] Still another aspect of the present invention provides a
valved conduit for a ventricular assist device including a
prosthetic valve, such as a natural tissue porcine xenograft valve,
defining a first blood-contacting surface, a fabric conduit in
which the prosthetic valve is secured and defining a second
blood-contacting surface, and sutures securing the prosthetic valve
into the fabric conduit and defining a third blood-contacting
surface, the valved conduit having only the first, the second, and
the third blood-contacting surfaces which contact blood flowing
through said conduit.
[0027] The present invention provides according to another aspect a
valved conduit including a porcine xenograft valve and defining
sinuses downstream of the valve which sinuses do not replicate
either the porcine sinuses or human sinuses, and which by their
configuration ensure that blood flow past the leaflets of the valve
forms vigorous vortices behind these leaflets without blood
stagnation.
[0028] Still further, the present invention provides a valved
conduit in which a resilient connection is provided between the
valved conduit and adjacent blood-carrying structures. This
resilient connection provides for all of post-implantation
absorption of a collagen or other biodegradable transitional
coating from the inner surfaces of the valved conduit with
attendant dimensional changes, for the subsequent formation of a
stable biological interface on these surfaces also possibly with
attendant change of dimensions, and for components of the valved
conduit and adjacent structure taking a set with the passage of
time after surgical implantation, all without loss of sealing
integrity between the connected structures. Such a loss of sealing
integrity could create a leakage path at the interface of the
valved conduit and an adjacent structure.
[0029] Additionally, the present invention provides such a valved
conduit which is interfaced with adjacent blood-carrying structure
by a polarized connection both preventing incorrect assembly of the
valved conduit to the adjacent structure, and preventing damage to
the conduit or adjacent structure from the application of excessive
tightening force, while also accommodating changing dimensions as
components of the valved conduit and adjacent structure take a set
with the passage of time after surgical implantation.
[0030] Additional objects and advantages of the present invention
will be apparent from a reading of the following detailed
description of a single preferred embodiment of the present
invention, taken in conjunction with the appended drawing Figures,
in which the same reference numeral refers to the same feature in
each of the various views, or to features which are analogous in
structure or function.
BRIEF DESCRIPTION OF THE DRAWING FIGURES
[0031] FIG. 1 is a fragmentary frontal elevational view
diagrammatically depicting a ventricular assist device according to
the present invention implanted in a human host patient;
[0032] FIG. 2 provides a fragmentary cross sectional view of a
portion of the ventricular assist device seen in FIG. 1, with a
portion of the external housing of the device removed for clarity
of illustration;
[0033] FIG. 3 provides a fragmentary exploded perspective view of
the ventricular assist device with valved conduits thereof
separated from a pump portion of the device in order to more
clearly show a polarized connection structure for each of the
valved conduits;
[0034] FIGS. 4 and 5 show respective longitudinal cross sectional
views taken through the inflow and outflow valved conduits of the
ventricular assist device of the present invention;
[0035] FIG. 6 provides a greatly enlarged fragmentary cross
sectional view taken through the inflow conduit connection with the
pump portion of the present assist device;
[0036] FIG. 7 provides an enlarged transverse sectional view taken
at line 7-7 of FIG. 4;
[0037] FIG. 8 provides an enlarged fragmentary longitudinal cross
sectional view taken along line 8-8 of FIG. 7;
[0038] FIG. 9 is a somewhat diagrammatic presentation of a step in
the process of manufacturing a valved conduit according to the
present invention;
[0039] FIG. 10 is a somewhat diagrammatic and cross sectional view
of a step of the manufacturing process for making a valved conduit
according to the present invention, and is subsequent to the step
seen in FIG. 9;
[0040] FIG. 11 is a greatly enlarged and somewhat schematic
representation of an inwardly porous, but blood-impermeable, fabric
resulting from the manufacturing steps seen in FIGS. 9 and 10, and
which forms a wall of the valved conduit of the present
invention.
DESCRIPTION OF AN EXEMPLARY EMBODIMENT OF THE INVENTION
[0041] With reference first to FIG. 1, a living human host patient
10 is shown in fragmentary front elevational view, and with parts
of the patient's anatomy shown in phantom or removed solely for
better illustration of the salient features of the present
invention. It will be understood that the human host patient 10
preferably has a complete anatomy, and that the use of the present
invention does not generally require that any part of the patient's
normal anatomy be removed, as might be suggested by FIG. 1.
[0042] Surgically implanted into the patient's abdominal cavity 12
is the pumping portion 14 of a ventricular assist device, generally
referenced with the numeral 16. The ventricular assist device 16
includes an inflow conduit 18 communicating blood from the
patient's left ventricle into the pumping portion 14, and an
outflow conduit 20 communicating blood from the pumping portion 14
to the patients ascending thoracic aorta. At the end of the inflow
conduit 18 which is connected to the patient's heart, and at the
end of the outflow conduit 20 which is connected to the ascending
thoracic aorta, these conduits are attached to the natural tissues
by suture rings so that blood flow communication is established and
maintained. From the pumping portion 14 a power cable 22 extends
outwardly of the patient's body via an incision 24 to a compact
controller 26. A power source, such as a battery pack worn on a
belt about the patient's waist, and generally referenced with the
numeral 27, is connected with the controller 26.
[0043] Viewing FIG. 2, it is seen that the pumping portion 14
includes a housing 28 within which is received a flexible unitary
liner or bag member 30. This bag member 30 defines a singular
blood-contacting inner surface 32, bounding a variable-volume
chamber 34. The bag member 30 includes a diaphragm portion (not
shown) which is reciprocally movable in response to reciprocating
movements of a power member (referenced generally with the numeral
14') of the pumping portion 14 to expand and contract the
variable-volume chamber 34. As FIG. 2 illustrates, the bag member
30 also defines tubular leg portions 36, 38, extending to and
through respective inlet and outlet fitting features 40, 42 of the
housing 28. At each of the inlet and outlet fitting features 40,
42, of the housing 28, the tubular legs 36, 38 form reentrant
portions 44, each of which is generally J-shaped in cross section.
At the inlet and outlet fitting features 40, and 42, the housing 28
includes structural provisions allowing connection and
disconnection of the respective inflow and outflow conduits 18, 20,
as will be further described.
[0044] Importantly, as FIG. 2 shows, each of the inflow and outflow
conduits 18, 20, respectively includes a tubular flexible, but
shape-retaining fabric-composite inner wall member 46, having an
inner blood-contacting surface 48. As will be further explained,
the inner blood-contacting surfaces 48 of the conduits 18 and 20
each also defines a respective reentrant end portion 50. The
reentrant end portions 50 are also J-shaped in cross section. As is
seen in FIG. 2, the reentrant end portions 50 of the conduits 18
and 20 sealingly contact the reentrant portions 44 of the bag
member 30. These sealingly contacting reentrant portions 44 and 50
cooperatively define a sealing line 51. Consequently, the flowing
blood in moving from the inflow conduit 18 to the bag 30, and from
this bag to the outflow conduit 20, crosses only two
material-surface transitions. The first of these material-surface
transitions is from the surface 48 of the inner wall member 46 at
the inflow conduit 18 to the surface 32 of the bag 30, the second
of these material-surface transitions is from the surface 32 to the
surface 48 of the conduit 46 at the outflow conduit 20. As will be
further described and explained, this minimizing of
material-surface transitions which are exposed to flowing blood in
the ventricular assist device 16 is a consistent feature throughout
the device.
[0045] FIG. 3 provides a fragmentary exploded perspective view of
the pumping portion 14, and of the two blood flow conduits 18, and
20, as they may appear, for example, during surgical implantation
of the assist device 16. FIG. 3 illustrates that as part of the
fitting features 40 and 42, the housing 28 defines a respective
inflow port 52 and a respective outflow port 54, each with a
respective female threaded recess 56 leading to the corresponding
one of the exposed reentrant portions 44 of the bag 30. These
threaded recesses 56 are in most respects identical with one
another. That is, they define the same diameter, and have the same
type and pitch of screw thread. However, the fluid flow
configuration of the pumping chamber 34, and of the transitions of
the legs 36 and 38 into and from this chamber, is different for the
inflow port than for the outflow port because of the differing
pressure and momentum conditions for the flowing blood passing
through these leg portions of the bag 30. Accordingly, the
physician must properly connect the inflow conduit 18 to the inflow
port 52, and the outflow conduit 20 to the outflow port 54.
[0046] In order to insure that the implantation physician does not
mistakenly connect the conduits, each conduit includes a respective
exclusive-fitting key feature 58, 60. The inflow conduit key
feature 58 includes four axially extending and circumferentially
evenly spaced key elements 62. At the inflow port 52, the recess 56
of housing 28 defines four matching slots 64. The outflow conduit
key feature 60 includes five axially extending and
circumferentially evenly spaced key elements 66. At the outflow
port 54, the recess 56 of housing 28 defines five matching slots
68. Each of the conduits 18, 20 includes a knurled and
male-threaded connector collar 70, which is freely rotatable on the
end of the conduit to be connected to the pump housing 28. This
collar 70 is threadably receivable into the recesses 56.
Consequently, the physician can connect the valved conduits 18, 20
to the housing 28 of the pumping portion 14 of the assist device by
feel alone if necessary.
[0047] That is, in the environment of the surgical implantation,
the physicians need not rely on color coding or some other visual
device to assure themselves that the conduit connections are being
effected correctly. The conduits 18, 20 will mate with the housing
28 only in the proper location, and this proper mating of the
conduits with the housing can be determined by the tactile feel of
the keys 62 and 66 dropping into the slots 64 and 68 when the
connections are made properly. When these proper connections are
made, then the threaded collars 70 will threadably engage the
threads of the corresponding recess 56 to retain the conduit
connections.
[0048] FIGS. 4 and 5 provide respective axial cross sectional views
through the respective inflow and outflow conduits 18 and 20.
Because many of the features of these two conduits are the same,
they are described together, and the same reference numeral is used
with respect to features of each which are the same or which are
analogous in structure or function to one another. Each of the
conduits 18, 20 includes a tubular metallic housing 72. This
housing is flanged at 74, and defines an outward cylindrical
portion 76 upon which the collar 70 is rotationally carried,
viewing also FIG. 6. Interposed between the collar 70 and the
flange 74 is a circumferentially extending wave washer 78, the
purpose of which will be described below. However, viewing FIGS. 4
and 5, and recalling the description above, it is apparent that
when the collars 70 are threaded into the recesses 56 of the
housing 28 they confront the flanges 74 to retain the conduits 18,
20, with the reentrant end portions 50 in sealing engagement with
the reentrant portions 44 of bag 30 to define the singular sealing
lines 51. The housings 72 define plural perforations 73, in the
form of slots, to allow body fluid to access the internal surfaces
of these housings and avoid the formation of cavities or voids
which are hidden from the immune system.
[0049] At the end of each housing 72 of conduits 18, 20 distally
from the pumping portion 14, a male-threaded portion 80
circumscribes a tapered seating feature 82. On the tapered seating
feature 82 with an interposed radially extending annular portion 84
of the inner wall 46 is sealingly connected the adjacent end 86 of
an elongate flexible polyethylene terephthalate fabric blood
conduit 88. The conduits 88 lead to the pumping portion 14 from the
patient's left ventricle, and from this pumping portion to the
patient's ascending aorta. The ends of these conduits 88 remote
from the pumping portion 14 are sutured to the heart and aorta at
appropriate incisions in each to achieve communication of the
conduits 18, 20, and of the pumping portion 14 with the patient's
circulatory system. The end 86 of the conduit 88, and the portion
84 of inner wall 46 sealingly engage one another to cooperatively
define the sealing line 89.
[0050] Around the polyethylene terephthalate fabric blood conduit
88 is a flexible plastic sheath 90. This plastic sheath 90 defines
an end shoulder 92, and rotationally carries an internally-threaded
collar 94. Collar 94 threadably engages the thread portion 80 of
the housing 72 to maintain sealing engagement of the conduit 88
with the portion 84 of the inner wall 46 at the tapered seating
feature 82. Interposed between the collar 94 and the end shoulder
92 is a circumferentially extending wave washer 96. On the inner
surface of each polyethylene terephthalate fabric blood conduit is
a thin bio-compatible collagen coating, indicated with arrowed lead
line 98. This collagen coating serves to make the polyethylene
terephthalate fabric conduit 88 more leak resistant at the time of
implantation, and also more compatible with the patient's
blood.
[0051] However, this collagen coating 98 is biodegradable, and is
eventually absorbed by the patient's body. At the same time that
the collagen coating 98 is being absorbed by the patient's body, a
biological interface is deposited on the inner surfaces of the
conduits 88. As the collagen coating 98 is absorbed from the area
of conduit 88 at the end 86 seating on wall portion 84 and seating
feature 82, the dimensions of the conduit 88 may decrease slightly.
This slight change of dimension could lead to a blood seepage at
the connection of the polyethylene terephthalate fabric conduits 88
to the metallic housings 72 perhaps weeks or months after the
surgical implantation of the assist device 16. To avoid this
possibility, the wave washer is provided so that the connection
between the conduits 88 and the housings 72 has an axial resilience
accommodating changes in thickness dimensions of the conduits.
Also, this axial resilience provides for maintenance of sealing
engagement between the conduits 88 and the housings 72 as these
parts take a set over time following implantation.
[0052] With attention now more particularly to the fabric-composite
tubular inner wall member 46, it will be noted that this inner wall
member defines the inner surface 48, which extends continuously
between and is integral with the reentrant end portion 50 at the
housing 28 (which is sealingly engaged by bag member 30 at sealing
line 51) and the radially extending portion 84 (which is sealingly
engaged by the fabric conduit 88 at sealing line 89). This inner
surface 48 defines the blood-contacting boundary for the conduits
18, 20. Within this inner surface 48, and secured to the fabric of
the fabric-composite inner wall member 46, and to an external stent
structure 100, is a porcine xenograft tri-foliate valve 102. It
will be understood that other types of prosthetic valve may be used
in the conduits 18 and 20. For example, one type of prosthetic
valve now available is fashioned from a sheet of either animal or
human tissue, or from artificial material. This and other types of
prosthetic valves may be used in the present invention. This
xenograft valve defines tissue surfaces 104. In the inflow conduit
18, the valve 102, and supporting stent structure 100, are disposed
for unidirectional blood flow toward the chamber 34. In the outflow
conduit, the valve 102 and supporting stent structure 100 are
oppositely disposed. The porcine xenograft valve 102 is secured to
the inner wall 46 and to stent structure 100 by sutures 106.
Accordingly, it is seen that blood flow through the conduits 18,
20, contacts only the inner surface 48 of conduit 46, the tissue
surface 104 of the xenograft valve 102, and the sutures 106.
[0053] Returning to a consideration of FIG. 6, it is seen that
within the recess 56, the housing 28 also defines an additional
annular recess 108. Disposed in this recess 108 is an annular
elastomeric sealing member 110. When the conduit 18 or 20 is
received into the respective one of the recesses 56, the reentrant
portion 50 of the inner wall member 46 sealingly engages with the
reentrant portion 44 of the pumping bag member 30. This sealing
interface is inwardly exposed to flowing blood. However, radially
outwardly of the sealing interface of surfaces 44 and 50, the
sealing member 110 is sealingly engaged by an end edge surface 112
of the housing 72 in order to provide a redundant secondary sealing
interface between the conduits 18, 20 and the housing 28. This
secondary sealing feature (member 110 and metallic end edge surface
112) is not exposed to flowing blood. Also, as is seen in FIG. 6,
the housing 28 at recess 56 defines a slot 64 for receiving a
respective one of the exclusive-fitting keys 62. This same feature
is found at the recess 56 for the conduit 20, recalling that the
number of keys, and slots for these keys, differs between the
recess 56 for inflow conduit 18 and the recess 56 for outflow
conduit 20.
[0054] Returning to consideration of FIGS. 4 and 5, immediately
downstream of the xenograft valve 102, the tubular inner wall
member 46 defines three out-bulgings, or sinuses 114. These sinuses
114 are aligned axially with each one of the three valve leaflets
of the valve 102, viewing also FIGS. 7 and 8. As is understood in
the art, a sinus at this location having a downstream termination
which is located somewhat downstream of the leaflets in their open
positions (viewing FIG. 8), promotes the entry into the sinuses of
a flow vortex 116 formed at the downstream end of the valve
leaflets. This vortex flow contributes to a prompt closing of the
valve at the end of the systole with little regurgitation.
[0055] However, the natural porcine or human sinuses are
considerably larger than the Applicants have determined to be
optimum for use with the prosthetic valve 102. In fact, the natural
human sinuses at the aortic valve form a circular boundary with the
valve leaflet if viewed in an oblique plane extending
perpendicularly to the axis of the leaflet surface. Also, in a
transverse plane the natural human sinuses are pouch-like and at
their maximum dimension define a diameter almost twice the diameter
of the aorta. The sinuses 114 of the conduits 18 and 20 are smaller
than natural sinuses, and rejoin the generally cylindrical tubular
inner wall member 46 at an acute or glancing angle, indicated with
the arrowed lead line 118. Further, the sinuses 114 are longer and
shallower than natural sinuses, as is explained below.
[0056] More particularly, if the inner valve leaflet radius at the
base of the tri-foliate valve 102 is referred to as R.sub.b, and
the radius at maximum dimension of the sinuses 114 is referred to
as d.sub.s, with the length of the sinuses 114 from the attachment
of the valve leaflets to the rejoining of the sinus wall with the
projected cylindrical shape of the remainder of the inner wall 46
(i.e., at the arrow 112) being referred to as h.sub.s (viewing
FIGS. 7 and 8), then for natural sinuses of several mammalian
species, including rabbits, canine, Ox, sheep, calf, pig, and human
an aspect ratio of h.sub.s divided by d.sub.s can be calculated.
The dimensions of usual aortic valves for these species is found in
the literature. It is seen that the ratio value naturally ranges
from 0.71 to 1.2. For the conduits 18 and 20, the aspect ratio of
the sinuses 114 is in the range from at least about 1.3 to about
1.6 or more. More preferably, the aspect ratio for the sinuses 114
is about 1.45.
[0057] The Applicants have determined that the above-described
range of sinus aspect ratios is preferable for achieving vigorous
vortex blood flow downstream of the valve 102 in the inflow conduit
18, with resulting elimination of blood stasis or stagnation. Blood
flow into the pumping portion 14 via this conduit 18 results merely
from the natural blood pressure prevailing in the circulatory
system of the host patient 10. The variable-volume pumping chamber
34 does not effectively aspirate blood into this chamber by
expansion. Instead, blood flows by its own pressure through the
conduit 18 and into this chamber, expanding the chamber 34.
Accordingly, the inflow of blood via conduit 18 is comparatively
slow. The increased aspect ratio of the conduit 18 in comparison
with the natural sinuses is important to the prevention of clot
formations in the conduit 18.
[0058] On the other hand, the blood flow out of pumping chamber 34
is forceful and vigorous. A sinus configuration at conduit 20 which
replicated the natural sinuses might be acceptable. However, as
pointed out above, the natural sinuses are more bulged out and take
up more room. The sinus shape of the present invention with an
aspect ratio of at least 1.3 or higher, when used also at the
outflow conduit 20, results in an outflow conduit of smaller
diameter, reduces the size of the apparatus implanted into the host
patient 10, and serves very well to promote vigorous blood vortex
flow downstream of the valve 102 without the formation of clots in
the conduit 20.
[0059] As will be further explained, the tubular fabric-composite
inner wall member 46 is formed with the sinuses 114, and with
adjacent arcuate transition portions 120, transitioning between a
downstream edge 122 of the xenograft valve 102 and the sinuses 114,
viewing FIGS. 4 and 5. These transition portions 120 allow the
xenograft valve 102 to be externally stented with the stent
structure 100 being located outside of the flexible fabric tubular
inner wall member 46, while still providing a smooth surface for
blood flow transition from the xenograft valve 102, to the surface
48 of the wall member 46 downstream of the valve 102. The stent
structure 100 includes a metallic wire-form 124 having three
axially-extending commissure support parts, which are not visible
in the drawing Figures, but which align with and follow the shape
of the natural commissures 126 of the porcine xenograft valve 102.
Received in the wire-form 124 is a polyester support member 128.
Around the wire-form 124, and the support member 128, is formed a
fitted polyethylene terephthalate fabric drape 130. The
polyethylene terephthalate fabric drape 130 is formed closely to
the wire-form 124 and support member 128. However, sutures 106
engage this drape 130 and the underlying wire-form 124, pass
through the corresponding inner wall member 46, and secure the
tissue xenograft valves 102 in the conduits 18, 20, respectively.
The fabric composite inner wall member 46 is also formed with very
slight recesses between the sinuses 114, which recesses accommodate
the radial thickness of the commissures of the wire-form 124.
[0060] Considering now FIGS. 9, 10, and 11, the first two of these
Figures show steps in the process of making a flexibly
shape-retaining fabric-composite tubular inner wall member 46 for a
valved conduit, such as conduit 18 or 20. FIG. 11 shows a greatly
enlarged cross sectional view through the fabric-composite tubular
inner wall member 46. As FIG. 11 shows, this inner wall member 46
includes a single ply of tubular-woven and/or knitted polyethylene
terephthalate fabric 132. Even though this woven and/or knitted
fabric 132 is of made of fine-dimension fibers, and is closely
woven or knitted, it nevertheless is liquid permeable.
Consequently, the fabric 132 is porous, and must be considered to
be substantially blood permeable. However, in order to render the
inner fabric composite wall 46 substantially blood impermeable
while still providing a porous inner surface 48 to which a stable
biological interface may attach, the tubular fabric 132 is
transfer-coated externally with sheet silicone rubber material
134.
[0061] As FIG. 11 shows, this silicone rubber 134 is permeated
inwardly into and partially through the woven or knitted fabric
132, toward but short of the inner surface 48 of this fabric. The
silicone rubber 134 is axially and circumferentially continuous, so
that it forms a liquid-impermeable barrier or membrane integral
with the fabric 132, and an integral part of the inner wall member
46. Inwardly of this silicone rubber 134, the woven and/or knitted
fabric 132 through a part of its thickness still forms a
filamentary permeable structure providing a porous inner surface
(i.e., the inner surface 48 of the conduit 46), into which a stable
biological interface may implant. This surface 48 is still porous
like conventional woven and/or knitted polyethylene terephthalate
fabric vascular grafts, but the porosity of the fabric no longer
extends completely through the thickness of the fabric 132.
[0062] Viewing FIG. 9 it is seen that the tubular woven and/or
knitted fabric 132 in a limp cylindrical configuration without the
silicone rubber 134, sinuses 114 or other features, is placed on a
cylindrical mandrel 136. Adjacent to this mandrel 136 is disposed a
cylindrical roller 138 with a smooth hard surface. On the roller
138 is disposed a sheet 140 of raw silicone rubber material. The
mandrel 136 and roller 138 are pressed together (indicated by
arrows 142) while being rotated in unison (indicated by arrows 144)
to transfer the silicone rubber sheet material 140 onto and into
the woven and/or knitted fabric 132. By control of the state of the
silicone rubber material of sheet 140 (i.e., its degree of partial
curing), and the amount of pressure applied, the degree or depth of
penetration of the silicone rubber material into the woven or
knitted fabric 132 is controlled. The woven or knitted fabric
material 132 and silicone sheet material 140 are then removed
together from the mandrel 136. Subsequently, the silicone material
140, which is a thermoset material, is completely, or substantially
completely cured to produce as a manufacturing intermediate article
or work piece, a cylindrical sleeve of woven or knitted fabric
outwardly coated and partially impregnated with silicone
rubber.
[0063] Next, the work piece including the cylindrical woven or
knitted fabric sleeve 132 and silicone rubber 140, referred to in
FIG. 10 with the composite reference numeral 132/140, is placed
into a heated female-cavity mold 146. This mold 146 defines a
cavity 148 generally matching to the cylindrical shape of the work
piece 132/140, but also having radially outwardly extending
recesses 150 corresponding to the sinuses 114, slight indentations
between the recesses 150 for accommodation of the commissures of
the wire-form 124, and one or more circumferential grooves or
diametral steps 152, which will form the reentrant surface 50 or
annular portion 84 of the fabric-composite inner wall member 46,
recalling FIGS. 4 and 5. Into the cavity 148 and within the tubular
work piece 132/140 is placed a thin-walled high-pressure expansible
balloon 154. This balloon is made of an elastomeric material, such
as a vulcanized natural or synthetic rubber, which is able to
withstand both an elevated temperature and internal pressure. The
balloon 154 is inflated by applying an internal pressure (indicated
with arrow 156) to force the work piece 132/140 against the inner
surfaces of the cavity 148.
[0064] Even though the silicone rubber 140 of the work piece
132/140 is a thermoset material, and is at least substantially
cured, the polyethylene terephthalate fabric 132 is a thermoplastic
material. Consequently, the work piece 132 takes on and retains a
shape replicating the internal shape of the cavity 148. The cavity
148 is cooled, the balloon 154 is deflated to return it to its
original size for removal from the cavity 148, and the work piece
is removed from this cavity. Although the polyethylene
terephthalate fabric material 132 is a thermoplastic material and
is changed in shape by the above-described process, at least in the
area of the sinuses and at the features 50 and 84 of the inner
fabric composite wall member 46, the penetration or impregnation of
the silicone rubber 140 partially through this fabric is
substantially not changed. The silicone rubber was cured fully or
substantially enough before this shaping step so that the silicone
rubber is no longer mobile in the fabric 132 of the work piece
132/140. This work piece 132/140, having woven and/or knitted
fabric 132 with silicone rubber liquid barrier 134, is
substantially ready for use in making the fabric composite inner
wall member 46. Subsequently, the work piece 132/140 is trimmed to
fit into the conduit 18 or 20, the xenograft valve 102, and stent
100 is added, and the combination is placed into the housing 72 and
completed at the ends for sealing cooperation with the pump portion
14 and conduits 88, as described above.
[0065] While the present invention has been depicted, described,
and is defined by reference to a particularly preferred embodiment
of the invention, such reference does not imply a limitation on the
invention, and no such limitation is to be inferred. The invention
is capable of considerable modification, alteration, and
equivalents in form and function, as will occur to those ordinarily
skilled in the pertinent arts. The depicted and described preferred
embodiment of the invention is exemplary only, and is not
exhaustive of the scope of the invention. Consequently, the
invention is intended to be limited only by the spirit and scope of
the appended claims, giving full cognizance to equivalents in all
respects.
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