U.S. patent application number 12/072471 was filed with the patent office on 2009-04-30 for intravascular ventricular assist device.
Invention is credited to Jeffrey A. LaRose, Richard A. Marquis, Charles R. Shambaugh, JR., Kartikeyan Trichi, Daniel G. White, Steven A. White.
Application Number | 20090112312 12/072471 |
Document ID | / |
Family ID | 39721795 |
Filed Date | 2009-04-30 |
United States Patent
Application |
20090112312 |
Kind Code |
A1 |
LaRose; Jeffrey A. ; et
al. |
April 30, 2009 |
Intravascular ventricular assist device
Abstract
One aspect of an intravascular ventricular assist device is an
implantable blood pump where the pump includes a housing defining a
bore having an axis, one or more rotors disposed within the bore,
each rotor including a plurality of magnetic poles, and one or more
stators surrounding the bore for providing a magnetic field within
the bore to induce rotation of each of the one or more rotors.
Another aspect of the invention includes methods of providing
cardiac assistance to a mammalian subject as, for example, a human.
Further aspects of the invention include rotor bodies having
helical channels formed longitudinally along the length of the body
of the rotor where each helical channel is formed between
peripheral support surface areas facing radially outwardly and
extending generally in circumferential directions around the
rotational axis of the rotor.
Inventors: |
LaRose; Jeffrey A.;
(Parkland, FL) ; Shambaugh, JR.; Charles R.;
(Coral Gables, FL) ; White; Daniel G.; (Pembroke
Pines, FL) ; Marquis; Richard A.; (Miami, FL)
; White; Steven A.; (Wellington, FL) ; Trichi;
Kartikeyan; (Miami Lakes, FL) |
Correspondence
Address: |
COOPER & DUNHAM, LLP
30 Rockefeller Plaza, 20th Floor
NEW YORK
NY
10112
US
|
Family ID: |
39721795 |
Appl. No.: |
12/072471 |
Filed: |
February 26, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60903781 |
Feb 26, 2007 |
|
|
|
Current U.S.
Class: |
623/3.13 ;
417/423.1; 600/16 |
Current CPC
Class: |
A61M 60/205 20210101;
A61M 2205/0211 20130101; A61M 60/135 20210101; A61M 60/422
20210101; A61M 60/148 20210101; A61M 2205/8206 20130101; A61M
60/824 20210101; A61M 2210/127 20130101; A61M 60/419 20210101; A61M
2205/0272 20130101; A61M 60/857 20210101 |
Class at
Publication: |
623/3.13 ;
600/16; 417/423.1 |
International
Class: |
A61M 1/12 20060101
A61M001/12 |
Claims
1. An implantable blood pump comprising: (a) a housing defining a
bore having an axis; (b) one or more rotors disposed within the
bore, each rotor including a permanent magnet; and (c) one or more
stators disposed outside of the bore for providing a rotating
magnetic field within the bore each of the one or more rotors, the
one or more rotors being constructed and arranged so that during
operation of the pump the one or more rotors are suspended within
the bore of the housing and out of contact with the housing solely
by forces selected from the group consisting of magnetic and
hydrodynamic forces on the one or more rotors, the pump having a
maximum lateral dimension in any direction perpendicular to the
axis of the bore of 20 mm or less and being operable to impel at
least one liter per minute of blood through the bore against at a
pressure difference of at least about 70 mm Hg between the inlet
and outlet.
2. A pump as claimed in claim 1 wherein said maximum lateral
dimension is 14 mm or less.
3. A pump as claimed in claim 2 wherein the pump is operable to
impel about 1-3 liters per minute of blood through the bore against
a pressure difference of about 70-90 mm Hg.
4. A pump as claimed in claim 1 wherein the pump has no moving
parts which contact one another during operation.
5. A pump as claimed in claim 1 wherein the pump has no seals
between parts which move during operation.
6. A pump as claimed in claim 1 further comprising a gripper
adapted to engage an inner surface of an artery, the gripper being
mechanically coupled to the housing and the one or more
stators.
7. A pump as claimed in claim 6 further comprising an intake tube
coupled to the housing, the intake tube having a bore communicating
with the bore of the housing at the inlet of the housing.
8. A method of providing cardiac assistance to a mammalian subject
comprising the steps of: (a) advancing a pump including a housing
having a bore, one or more rotors disposed within the bore and one
or more stators disposed outside of the housing, through the
vascular system of the subject until the pump is disposed at an
operative position at least partially within an artery of the
subject; (b) securing the pump at the operative position; (c)
actuating the pump to spin the one or more rotors and pump blood
distally within the artery solely by applying electrical currents
to the one or more stators and to suspend the one or more stators
within the bore solely by forces selected from the group consisting
of magnetic and hydrodynamic forces applied to the one or more
rotors.
9. A method as claimed in claim 8 wherein the advancing step
includes advancing one or more grippers mechanically connected to
the pump along with the pump and the securing step includes
actuating the one or more grippers to engage a wall of the
artery.
10. A method as claimed in claim 8 wherein the artery is the aorta
of the subject.
11. A method as claimed in claim 10 wherein the housing has an
inlet and an outlet and the advancing step is performed so as to
place the inlet in fluid communication with the left ventricle of
the subject's heart and place the outlet within the subject's
aorta.
12. A method as claimed in claim 11 wherein the pump includes an
intake tube and the advancing and securing steps are preformed so
as to place the intake tube through the aortic valve of the subject
and position the pump entirely within the aorta with the inlet of
the housing communicating with the left ventricle through the
intake tube.
13. An implantable blood pump comprising: (a) a housing defining a
bore having an inlet, an outlet and an axis extending between the
ends; (b) one or more rotors disposed within the bore substantially
coaxial with the bore, each rotor including a permanent magnet; (c)
one or more stators disposed outside of the bore each substantially
opposite a rotor for providing a rotating magnetic field within the
bore; and (d) a gripper mechanically connected to the housing and
to the one or more stators, the gripper being adapted to engage a
wall of an artery and hold the housing and stators in an operative
position at least partially within the artery, the one or more
rotors being constructed and arranged so that during operation of
the pump the one or more rotors are suspended within the bore of
the housing and out of contact with the housing solely by forces
selected from the group consisting of magnetic and hydrodynamic
forces on the rotors.
14. A pump as claimed in claim 13 wherein the one or more rotors
the only elements of the pump which move during operation.
15. A pump as claimed in claim 16 wherein the housing is elongated
and has an inlet end and an outlet end, and wherein the gripper
includes an expansible element connected to the housing adjacent
the outlet end.
16. A pump as claimed in claim 15 wherein the expansible element
includes a tubular stent.
17. A pump as claimed in claim 15 wherein the housing has an axis
and the expansible element includes a plurality of fingers spaced
circumferentially around the axis.
18. A pump as claimed in claim 15 wherein the housing has an axis
and the expansible element includes a first and second spiral
spring having an inner ends secured to the housing and extending in
opposite circumferential directions around the axis of the
housing.
19. A rotor for a blood circulating pump, the rotor comprising a
body having an upstream end, a downstream end and a rotational
axis, the rotor body including a plurality of lobes, each of said
lobes having a circumferential extent which increases in a radially
outward direction away from the axis, each of said lobes having a
support surface facing generally radially outwardly, the rotor
being adapted to pump blood downstream upon rotation in a forward
circumferential direction, each said support surface including a
hydrodynamic bearing region sloping radially outwardly away from
the axis in a reverse circumferential direction opposite to the
forward circumferential direction.
20. A rotor for a blood circulating pump, the rotor comprising a
body having an upstream end, a downstream end and a rotational
axis, the rotor body including a helix region and a support region
axially offset from the helix region, the helix region defining a
plurality of generally helical channels, the support region
defining one or more support surfaces facing substantially radially
outwardly and extending generally in circumferential directions
around the axis, the support region defining one or more passages
connected to said helical channels so that the one or more passages
and said helical channels cooperatively define one or more
continuous flow paths extending between the upstream and downstream
ends, the channels having greater aggregate cross-sectional area
than the one or more passages.
21. A rotor for a blood circulating pump, the rotor comprising a
body having an upstream end, a downstream end and a rotational
axis, the rotor body including a helix region and a support region
axially offset from the helix region, the helix region of the body
defining a plurality of generally helical channels, the support
region defining one or more support surfaces facing substantially
radially outwardly and extending generally in circumferential
directions around the axis, the support region defining one or more
passages connected to the channels so that the one or more passages
and the channels cooperatively define one or more continuous flow
paths extending between the upstream and downstream ends, the
support region having greater solidity than the helix region.
22. A rotor for a blood circulating pump, the rotor comprising a
body having an upstream end, a downstream end and a rotational
axis, the rotor body including a helix region and a support region
axially offset from the helix region, the helix region defining a
plurality of generally helical channels and having peripheral
surfaces facing outwardly away from said axis, the support region
including a plurality of lobes projecting outwardly away from said
axis and passages between the lobes, the passages being continuous
with the channels, the lobes defining one or more support surfaces
facing outwardly away from the axis, the support surfaces having an
aggregate extent in a circumferential direction around the axis
greater than an aggregate extent of said peripheral surfaces in the
circumferential direction.
23. A rotor as claimed in claim 22 wherein the helix region is
disposed upstream of the support region, the channels of the helix
region being open at the upstream end of the body and the grooves
of the support region being open at the downstream end of the
body.
24. A rotor as claimed in claim 23 wherein, over at least a portion
of the axial extent of the support region, each said lobe has a
circumferential extent which increases in a radially outward
direction away from the axis toward said support surfaces.
25. A rotor as claimed in claim 23 wherein the walls of said
helical channels have a pitch in a forward circumferential
direction toward the upstream end of said body and the support
surfaces include hydrodynamic bearing regions sloping outwardly
away from the axis in a reverse circumferential direction opposite
to the forward circumferential direction.
26. A rotor as claimed in claim 25 wherein each of the lobes
includes a first hydrodynamic bearing region, a second hydrodynamic
bearing region disposed downstream of the first hydrodynamic
bearing region, and a land between the first and second
hydrodynamic bearing regions, the land extending radially outwardly
from the hydrodynamic bearing regions over at least a portion of
the circumferential extent of the hydrodynamic bearing regions.
27. A rotor as claimed in claim 24 wherein said support region
includes a ferromagnetic material.
28. A rotor as claimed in claim 27 wherein said support region is a
unitary mass of a ferromagnetic material.
29. A rotor as claimed in claim 28 wherein the entire rotor body is
a unitary mass of a ferromagnetic material.
30. A rotor as claimed in claim 27 wherein said ferromagnetic
material has permanent magnetization and said support surfaces
constitute poles of a permanent magnet.
31. An implantable blood pump comprising a housing defining a bore
having an axis, a first rotor as claimed in claim 30 disposed
within the bore substantially coaxial with the bore, and a first
stator disposed outside of the bore for providing a rotating
magnetic field within the bore at the first rotor.
32. A pump as claimed in claim 31 wherein the stator has a maximum
dimension transverse to the axis of the bore of 13 mm or less.
33. A pump as claimed in claim 31 wherein the plurality of lobes
consists of two lobes.
34. A pump as claimed in claim 31 wherein the housing includes a
ceramic material at the surface defining the bore.
35. A pump as claimed in claim 31 wherein the bore includes an
inflow section upstream from the upstream end of the rotor, the
inflow section being substantially free of obstructions to
rotational flow of blood about the axis of the bore.
36. A pump as claimed in claim 31 further comprising a second rotor
disposed in the bore, the second rotor comprising a body having an
upstream end, a downstream end and an axis extending between said
ends, the second rotor being coaxial with the first rotor, the body
of the second rotor including a permanent magnet and defining a
plurality of generally helical channels and one or more support
surfaces facing substantially radially outwardly and extending
generally in circumferential directions around the axis, the pump
further comprising a second stator axially offset from the first
stator for providing a rotating magnetic field at the second
rotor.
37. A pump as claimed in claim 37 wherein the channels of the first
rotor have a pitch in a first direction and the channels of the
second rotor have a pitch in a second direction opposite to the
first direction.
38. A pump as claimed in claim 37 wherein the first rotor is
disposed upstream of the second rotor.
39. A pump as claimed in claim 38 wherein the channels of the
second rotor have a pitch angle greater than the channels of the
first rotor.
40. A pump as claimed in claim 39 wherein a portion of the bore
between the first and second rotors is substantially in the form of
a surface of revolution about the axis of the bore and
substantially free of obstructions to rotational flow of blood
about the axis of the bore.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to pumps usable as implantable
ventricular assist devices, to components useful in such pumps, and
to methods of using the same.
[0002] In certain disease states, the heart lacks sufficient
pumping capacity to meet the needs of the body. This inadequacy can
be alleviated by providing a mechanical pump referred to as a
ventricular assist device to supplement the pumping action of the
heart. It would be desirable to provide a ventricular assist device
which can be implanted and which can remain in operation for months
or years to keep the patient alive while the heart heals, or which
can remain in operation permanently during the patient's lifetime
if the heart does not heal, or which can keep the patient alive
until a suitable donor heart becomes available.
[0003] Design of a ventricular assist device presents a daunting
engineering challenge. The device must function reliably for the
desired period of implantation. Moreover, blood is not a simple
fluid, but instead is a complex system containing cells. Severe
mechanical action can lead to hemolysis, or rupture of the red
blood cells, with serious consequences to the patient. Also, blood
in contact with an artificial surface, such as the surfaces of a
pump, tends to clot. While this tendency can be suppressed to some
extent by proper choice of materials, surface finishes and by
administration of anticoagulants, it is still important to design
the pump so that there are no regions within the device where blood
can be trapped or flow is interrupted for relatively prolonged
periods. To provide clinically useful assistance to the heart, the
device must be capable of delivering a substantial blood flow at a
pressure corresponding to normal blood pressure. For example, a
ventricular assist device for an adult human patient of normal size
should deliver about 1-10 liters per minute of blood at a pressure
of about 70-110 mm Hg depending on the needs of the patient.
[0004] One type of ventricular assist device or pump uses a
balloon. The balloon is placed within the aorta. The balloon is
connected to an external pump adapted to repeatedly inflate and
deflate the balloon in synchronism with the contractions of the
heart muscle to assist the pumping action. Balloon assist devices
of this nature have numerous limitations including limited
durability and limited capacity.
[0005] As described, for example, in U.S. Pat. No. 6,688,861, a
miniature electrically-powered rotary pump can be implanted
surgically within the patient. Such a pump has a housing with an
inlet and an outlet, and a rotor which is suspended within the
housing and driven by a rotating magnetic field provided by a
stator or winding disposed outside of the housing. During
operation, the rotor is suspended within the housing by
hydrodynamic and magnetic forces. In such a pump, the rotor may be
the only moving part. Because the rotor does not contact the
housing during operation, such a pump can operate without wear.
Pumps according to the preferred embodiments taught in the '861
patent and related patents have sufficient pumping capacity to
provide clinically useful assistance to the heart and can be small
enough that they may be implanted within the heart and extend
within the patient's thoracic cavity. Pumps of this nature provide
numerous advantages including reliability and substantial freedom
from hemolysis and thrombogenesis. However, implantation of such a
pump involves a majorly invasive surgical procedure.
[0006] As described, for example, in Nash, U.S. Pat. No. 4,919,647;
Siess, U.S. Pat. No. 7,011,620; and Siess et al., U.S. Pat. No.
7,027,875; as well as in International Patent Publication No. WO
2006/051023, it has been proposed to provide a ventricular assist
device in the form of a rotary pump which can be implanted within
the vascular system, such as within the aorta during use.
Aboul-hosn et al., U.S. Pat. No. 7,022,100, proposes a rotary pump
which can be placed within the aorta so that the inlet end of the
pump extends through the aortic valve into the left ventricle of
the heart.
[0007] A ventricular assist device implanted into the vascular
system must be extraordinarily compact. For example, such a device
typically should have an elongated housing or other element with a
diameter or maximum dimension transverse to the direction of
elongation less than about 13 mm, and most preferably about 12 mm
or less. To meet this constraint, the vascularly-placed ventricular
assist devices proposed heretofore resort to mechanically complex
arrangements. For example, the device described in U.S. Pat. No.
7,011,620 incorporates an electric motor in an elongated housing.
The motor drive shaft extends out of the housing and a seal
surrounds the shaft. An impeller is mounted at the distal end of
the drive shaft outside of the motor housing and within a separate
tubular housing. The pump taught in U.S. Pat. No. 7,022,100
consists of a separate motor using a flexible drive shaft extending
through the patient's vascular system to the impeller, with an
extraordinarily complex arrangement of seals, bearings, and a
circulating pressurized fluid to prevent entry of blood into the
flexible shaft. The arrangement taught in WO 2006/051023 and in
U.S. Pat. No. 4,919,647 also utilizes flexible shaft drives and
external drive motors. These complex systems are susceptible to
failure.
[0008] Thus, despite very considerable effort devoted in the art
heretofore to development of ventricular assist devices, further
improvement would be desirable.
SUMMARY OF THE INVENTION
[0009] One aspect of the invention is an implantable blood pump.
The pump according to this aspect of the invention includes a
housing defining a bore having an axis, one or more rotors disposed
within the bore, each rotor including a plurality of magnet poles,
and one or more stators surrounding the bore for providing a
rotating magnetic field within the bore to induce rotation of each
of the one or more rotors. The one or more rotors may be
constructed and arranged so that during operation of the pump the
one or more rotors are suspended within the bore of the housing and
out of contact with the housing solely by forces selected from the
group consisting of magnetic and hydrodynamic forces. In this
embodiment the pump has a maximum lateral dimension in any
direction perpendicular to the axis of the bore, or a diameter of
up to about 20 mm. In one embodiment the diameter of the bore is
about 14 mm. In another embodiment the diameter of the bore is
between 9 and 11 mm. The pump of the present invention can impel
from about 1-3 liters of blood per minute. In one embodiment the
pump is adapted to impel about 2 liters of blood per minute. Blood
pressure can be maintained within the range of from 70-120 mm Hg
between the inlet and outlet. The pump is adapted for positioning
within an artery, and may include a gripper adapted to engage the
wall of an artery.
[0010] Another aspect of the invention includes methods of
providing cardiac assistance to a mammalian subject as, for
example, a human. Methods according to this aspect of the invention
include advancing a pump including a housing having a bore, one or
more rotors disposed within the bore and one or more motor stators
disposed outside of the housing through the vascular system of the
subject until the pump is disposed at an operative position at
least partially within an artery of the subject, and securing the
pump at the operative position. The method includes the step of
actuating the pump to spin the one or more rotors and pump blood
distally within the artery solely by applying electrical currents
to the one or more motor stators and to suspend the one or more
rotors within the bore solely by forces selected from the group
consisting of magnetic and hydrodynamic forces applied to the one
or more rotors.
[0011] Still further aspects of the present invention include rotor
bodies having helical channels formed longitudinally along the
length of the body of the rotor. Each helical channel is formed
between peripheral support surface areas facing substantially
radially outwardly and extending generally in circumferential
directions around the rotational axis of the rotor. Each channel
has a generally axial downstream portion. The helical and axial
portions of each of the channels cooperatively define one or more
continuous flow paths extending between the upstream and downstream
ends of the rotor. In one embodiment, the axial regions of the
channels have greater aggregate cross-sectional area than the one
or more passages. The support surfaces of the rotor body are formed
on a plurality of lobes. Each lobe has a circumferential extent
which increases in a radially outward direction away from the
rotational axis of the rotor. The support surfaces face generally
radially outwardly away from the rotor axis and define hydrodynamic
bearing surfaces. The circumferential extent of the support
surfaces is greater than the circumferential extent of peripheral
surface areas.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a diagrammatic perspective view of a pump in
accordance with one embodiment of the present invention, with
components omitted for clarity of illustration.
[0013] FIG. 2 is a diagrammatic view of components used in the pump
of FIG. 1, with certain components depicted as transparent for
clarity of illustration.
[0014] FIG. 3 is a partial cut-away view of the pump depicted in
FIGS. 1 and 2.
[0015] FIG. 4 is a fragmentary sectional view depicting a portion
of the pump shown in FIGS. 1-3.
[0016] FIG. 5 is a further fragmentary sectional view depicting
another portion of the pump shown in FIGS. 1-3.
[0017] FIGS. 6 and 7 are perspective views depicting a rotor used
in the pump of FIGS. 1-5.
[0018] FIGS. 8 and 9 are elevational views of the rotor shown in
FIGS. 6 and 7.
[0019] FIGS. 10-14 are sectional views taken along frames 10-14
respectively in FIG. 9.
[0020] FIG. 15 is a fragmentary, diagrammatic sectional view
depicting a portion of the rotor depicted in FIGS. 6-14 in
conjunction with another component of the pump.
[0021] FIG. 16 is a diagrammatic perspective view depicting another
rotor utilized in the pump of FIG. 1.
[0022] FIG. 17 is a diagrammatic elevational view of the rotor
shown in FIG. 16.
[0023] FIG. 18 is a diagrammatic perspective view of the pump
depicted in FIGS. 1-17 in conjunction with a further component.
[0024] FIG. 19 is a partially blocked diagrammatic view depicting
the pump of FIGS. 1-17 in operating position in the cardiovascular
system of a subject.
[0025] FIGS. 20 and 21 are diagrammatic perspective views depicting
components used in further embodiments of the invention.
[0026] FIG. 22 is a diagrammatic perspective view of a rotor
according to a further embodiment of the invention.
[0027] FIG. 23 is a diagrammatic sectional view taking along line
23-23 in FIG. 22.
[0028] FIG. 24 is a diagrammatic elevational view depicting a rotor
according to yet another embodiment of the invention.
[0029] FIG. 25 is a diagrammatic elevational view depicting a
component of a stator used in a pump of FIGS. 1-17.
[0030] FIG. 26 is an electrical schematic diagram of the stator
used in the pump of FIGS. 1-17.
DETAILED DESCRIPTION
[0031] A pump 10 in accordance with one embodiment of the invention
includes a housing 12 (FIGS. 1, 2 and 3). Housing 12 is a ceramic
tube defining a central bore 14 having an axis 16. Bore 14 is
cylindrical and has a constant diameter over the major portion of
its length. The interior surface 13 of the housing defining bore 14
is smooth, and desirably has a surface roughness on the order of 4
micro inches rms or less. Merely by way of example, the inside
diameter of bore 14 in this constant diameter region may be about
0.178 inches ("in"), and the wall thickness of the housing may be
about 0.010 in. Housing 12 defines an inlet 18 at an end 20 of the
housing, referred to herein as the inlet or upstream end, and an
outlet 22 communicating with bore 14 at an output or downstream end
24 of the housing. The inside diameter of inlet 18 is slightly less
than the inside diameter of bore 14. The housing includes an inlet
transition section 26 having an inside diameter which increases
progressively in the downstream direction at the juncture between
inlet 18 and bore 14. The inside diameter of the housing increases
progressively at an outlet transition section 23 immediately
upstream from outlet 22.
[0032] As best seen in FIG. 4, a thin-walled metallic tube 28 is
fitted over the inlet or upstream end of the housing so that the
interior of tube 28 communicates with inlet opening 18. Tube 28 may
be formed from a metal such as titanium, titanium alloy, or
platinum, and may be brazed to the ceramic housing. An upstream end
fitting 30 surrounds tube 28, and also surrounds the upstream end
20 of the ceramic housing 12. A flexible intake tube 32 surrounds
the upstream end of fitting 30 and tube 28, and is held in place by
a crimp metal band 34. As best seen in FIG. 1, intake tube 32
extends upstream from fitting 30 and from housing 12, and
terminates at a castellated opening 36 at its upstream end. As best
seen in FIG. 4, the interior of tube 32 communicates with inlet 18
of housing 12, and thus with the bore 14 of the housing, through
tube 28. In one embodiment, intake tube 32 is formed from a
non-thrombogenic flexible polymer such as, for example, a
fluoropolymer, polydimethylsiloxane, silicone polycarbonate
urethanes, thermoplastic polyurethanes, polycarbonate urethanes,
segmented polyurethanes, poly(styrene-b-isobutylene-b-styrene, or
sulfonated styrene containing copolymers.
[0033] A metallic outflow tube 40 (FIG. 5) surrounds the downstream
end 24 of housing 12 and communicates with the bore 14 of the
housing. Outflow tube 40 may be formed from materials as discussed
above with respect to tube 28. The downstream end of outflow tube
40 defines the outlet 41 of the pump 10.
[0034] A downstream end fitting 42 surrounds outflow tube 40 and
the downstream end 24 of housing 12. An elongated electrical cable
44, of which only a portion is shown in FIGS. 1 and 5, is secured
to downstream end fitting 42. As best seen in FIG. 1, the
downstream end fitting 42 carries several miniature electrical
feedthroughs 46, which are electrically isolated from one another
and which are connected to the individual conductors of cable
44.
[0035] A first stator 48 surrounds housing 12 adjacent the upstream
end thereof, shown in FIG. 25. The stator 48 includes a
magnetically permeable frame 700. The frame is configured as a
cylindrical, tubular ring 702 having a plurality of poles 704
projecting inwardly from the ring 702 to the exterior of housing
12; six poles are used in this particular embodiment depicted. Ring
portion 702 is concentric with housing 12 and bore axis 16. Each
pole includes a widened portion at the tip of the pole, where the
pole confronts the exterior surface of housing 12. The poles define
six slots, 706-1 through 706-6, between them. The dimensions of the
stator are substantially uniform along the axial length of the
stator. In this embodiment the stator is formed from numerous
uniform laminations stacked on one another. The laminations are
formed from a magnetically permeable material selected to minimize
power losses due to magnetic hysteresis. For example, the
laminations may be formed from 29-gauge silicon steel of the type
sold under the designation M15 electrical steel.
[0036] In the particular embodiment depicted, the exterior diameter
OD of ring portion 702 is about 0.395 inches, and the interior
diameter ID of the ring portion is about 0.304 inches. The width or
circumferential extent PW of each pole is about 0.035 inches at its
juncture with the ring portion 702. The interior diameter PD
between opposed pole tips may be about 0.221 inches. The axial
length of the frame is selected according to desired output power,
and may be, for example, about 0.35 inches for about 1 watt output
to about 0.85 inches for about 3 watts output.
[0037] Stator 48 further includes coils 710, 712, and 714 shown in
electrical schematic in FIG. 26. In the particular embodiment
depicted, each coil includes about 11 to about 14 turns of 33- or
34-gauge insulated wire, and may be impregnated with a material
such as a varnish after winding. The coils are connected in a WYE
configuration to a common neutral 718. Coils 710, 712, and 714 are
disposed respectively in slots 706-1 through 706-6 of frame 700
(FIG. 25). Coil 710 is wound through slots 706-1 and 706-4, whereas
coil 712 is wound through slots 706-3 and 706-6, and coil 714 is
wound through slots 706-5 and 706-2. This arrangement is commonly
referred to as a balanced three-phase integral slot winding. The
ends of the coils remote from the neutral point 718 are connected
to inputs P1, P2, and P3. When these inputs are energized with
three sinusoidal voltages offset from one another in phase by
60.degree., the coils provide a magnetic field within the bore
which is directed transverse to the bore axis 16 and which rotates
around the axis, within a first region 50 (FIGS. 1 and 2) of the
bore. A second stator 52 is disposed downstream from first stator
48, and is arranged to apply a rotating magnetic field within a
second region 54 of bore 14 downstream from the first region. The
second stator may be similar to the first stator. Pump 10 further
includes a casing 47, depicted in broken lines in FIG. 1, extending
between the outflow fitting 42 and the inflow fitting 30, and
covering the stators 48 and 52. A potting material (not shown)
fills space within casing 47 around the stators.
[0038] A first or upstream rotor 56 is disposed within bore 14
adjacent the upstream end of bore, within region the first region
50. A second rotor 58 is disposed within the bore downstream from
first rotor 56, within region 54.
[0039] The first rotor 56, shown in FIGS. 2 and 6-15, is formed as
a solid, unitary body of a ferromagnetic, biocompatible material,
such as an alloy including platinum and cobalt, as, for example, an
alloy consisting essentially of platinum and cobalt such as 77.3%
Pt and 22.7% Co. The rotor has an upstream or inlet end 60, a
downstream or outlet end 62, and a rotational axis 64 depicted in
dotted line in FIG. 6. The rotor includes a unitary central shaft
portion 66 immediately surrounding the axis and coaxial therewith,
extending throughout the length of the rotor. The central shaft
portion has a generally spherical dome 67 at its upstream end and a
conical, tapered region 65 at the downstream end 62.
[0040] The body of rotor 56 is described herein with reference to
axis 64. As used herein with reference to a structure such as rotor
having upstream and downstream ends and an axis, the upstream
direction is the direction parallel to the axis toward the upstream
end, whereas the downstream direction is the opposite direction. A
"radial" direction is a direction outwardly, away from the axis. A
"circumferential" direction is a direction around an arc in a plane
perpendicular to axis 64. The "forward" circumferential direction
indicated by one end F of the arrow FR in FIG. 6 corresponds to the
direction of rotation of rotor 56 about axis 64 in service. The
opposite circumferential direction indicated by one end R of the
arrow FR (FIG. 7) is referred to herein as the reverse
circumferential direction.
[0041] A region 68 of the rotor adjacent the upstream end 60,
referred to herein as the "helix" region, rotor 56 has helical
channels 74 and 76 defining a pair of raised peripheral surface
areas 70 and 72 radially outwardly from the central shaft 66. The
channel 74 defines a surface area 78 facing in the forward
circumferential direction, referred to herein as the pressure
surface or, alternatively referred to as the leading surface.
Pressure surface 78 is a helical surface of variable pitch along
the axial length. The pressure surface has a pitch angle A (FIG. 8)
of about 60.degree.. As used in this disclosure with reference to a
helical surface, the term "pitch angle" refers to the angle between
the axis of revolution, axis 64, and a line tangent to the surface.
The channel 76 defines a surface area 80, facing in the rearward
circumferential direction, referred to herein as the suction
surface or alternatively referred to as the trailing surface.
Suction surface 80 is also helical, but has a slightly larger pitch
angle than pressure surface 78, so that the thickness or
circumferential extent of raised surface area 70 increases
progressively in the downstream direction (to the right as seen in
FIG. 9). The suction surface 80 is truncated by a small flat
surface 83 in a plane perpendicular to the axis 64 at the upstream
end of the helix region, thereby defining a sharp,
radially-extensive edge 85, having a radius of about 0.003 inches,
at the upstream end of the helix region. The raised peripheral
surface area 70 is arcuate and of constant radius about axis 64.
The surface area 70 extends through about 130.degree. of arc about
axis 64 from its upstream edge to its downstream edge.
[0042] The surface area 72 is identical to surface area 70, and is
offset from surface area 70 by 180.degree. about axis 64. As best
appreciated with reference to the cross-sectional view of FIG. 10,
the surface areas 70 and 72 are thin. The circumferential extent of
surface area 70 is about 15.degree. of arc around axis 64, and thus
the aggregate circumferential extent of surface areas 70 and 72
amounts to about 30.degree. of arc.
[0043] As used in this disclosure, the term "major diameter" of a
body having an axis refers to the dimension which is twice the
greatest radius from the axis to any point on the body in a
particular plane perpendicular to the axis. For rotor 56, the major
diameter is simply the length of a line extending between the
peripheral surfaces 70 and 72 through axis 64. As used in this
disclosure, the term "solidity" refers to the ratio between the
cross-sectional area of the solid features of the body to the area
of a circle having a diameter equal to the major diameter of the
body. The solidity of the helix portion 68 is in the range of about
10-20% at the upstream or inlet end of the body. In one embodiment
the solidity is in the range of about 10-15%, and about 14%, and
increases progressively to about 15-25% at the downstream end of
the helix region, to about 18-23%. In one embodiment the solidity
is about 20%. Stated another way, the helix region is largely open
for entry of blood at its upstream end.
[0044] The rotor 56 further includes a support region 88 (FIG. 6)
disposed downstream from the helix region 68. The rotor has a first
lobe 90 and second lobe 92 projecting outwardly from central shaft
66 in the support region. First lobe 90 has a pressure surface 94
(FIG. 9), also referred to as a leading surface, facing in the
forward circumferential direction. Pressure surface 94 is
continuous with the pressure surface 78. First lobe 90 also has a
suction surface 96 (FIG. 6), also referred to as a trailing
surface. Suction surface 96 is continuous with the suction surface
80. Thus, the periphery of the first lobe 90 constitutes a
continuation of the peripheral surface area 70 in the downstream
direction. The first lobe also has a surface 98 (FIG. 13) facing
generally radially outwardly away from axis 64, this surface being
referred to herein as a "support" surface. The opposite lobe 92 has
a similar pressure surface 99 continuous with the pressure surface
at area 72, and suction surface 100 (FIG. 9) continuous with the
suction surface at area 72. Lobes 90 and 92 are diametrically
opposite to one another and define passages 106 and 108 between
them. Passage 106 is continuous with channel 74, whereas passage
108 is continuous with channel 76. The passages extend to the
downstream end of the body and are open at the downstream end, so
that the channels of the helix region and the passages of the
support region cooperatively define continuous flow paths extending
between the upstream and downstream ends of the body. The pressure
and suction surfaces of the lobes have substantially constant pitch
angle, and the pitch angles of the pressure and suction surfaces
are substantially equal to one another, so that the circumferential
extent of each lobe remains substantially constant throughout the
support region 88. The pitch angle of the pressure and suction
surfaces of the lobes are substantially smaller than the pitch
angle of the pressure and suction surfaces in the helix regions.
For example, the pitch angles of the lobe pressure and suction
surfaces may be on the order of about 10.degree..
[0045] The major diameter of the support section defined by the
lobes is equal to the major diameter of helix section. However, as
best appreciated by comparison of FIG. 13 with FIG. 10, the
circumferential extent of support surfaces 98 and 104 of the lobes
is much greater than the circumferential extent of the peripheral
edge surfaces 82 and 84 of the helix regions. For example, each
support surface may have a circumferential extent of about
90-110.degree. of arc about axis 64, so that the aggregate
circumferential extent of the support surfaces is about
180-220.degree.. Moreover, the solidity of the support region
including the lobes is substantially greater than the solidity of
the helix region. The solidity of the support region may be about
30-40%.
[0046] As also apparent from FIGS. 13 and 14, the pressure surface
94 and suction surface 96 of lobe 90 diverge from one another in
the radially outward direction, away from axis 64. Similarly, the
pressure surface 99 and suction surface 100 of lobe 92 diverge from
one another in the radially outward direction. Stated another way,
the circumferential extent of each lobe increases progressively in
the radially outward direction, so that the mass of each lobe is
concentrated in the region of the lobe remote from axis 64.
[0047] Support surface 104 of lobe 92 has a trailing land area 110
(FIGS. 8 and 9) disposed at the same radius from axis 64 as the
peripheral surfaces of the helix regions. The trailing land area
110 extends along the trailing or suction edge of support surface
104, i.e., the edge of the support surface at its juncture with the
suction surface 100 of lobe 92. Land area 110 merges into the
peripheral surface 84 of helix area 72, as best seen in FIG. 8. The
support surface 104 further includes a first or upstream
hydrodynamic-bearing surface 112 and a separating land 114
extending in the forward circumferential direction from trailing
edge land 110 to the forward edge of the support surface, at its
juncture with pressure surface 99. Land 114 lies at the same radius
from axis 64 as the trailing edge land 110. Thus, bearing surface
112 is bounded on its trailing and upstream sides by trailing edge
land surface 110 and peripheral surface 84, and on its downstream
side by separating land 114. As best seen in FIG. 15, bearing
surface 112 is disposed radially inwardly from the land surfaces
and slopes radially outwardly towards its trailing edge, i.e., in
the reverse circumferential direction toward trailing land surface
110. Stated another way, the land surfaces define a generally
cylindrical surface at the major diameter, and bearing surface 112
defines a depression in this generally cylindrical surface which
tapers to a decreasing depth in the reverse circumferential
direction. As also shown in FIG. 15, the major diameter of the
rotor defined by land surfaces 110 is just slightly less than the
internal diameter of bore 14 in the housing. For example, the
internal diameter of the bore may be about 0.002 inches larger than
the major diameter of the rotor.
[0048] Support surface 104 further includes a second or downstream
bearing surface 116 immediately downstream from separating land
114, and a downstream end land surface 118 immediately downstream
of the bearing surface 116. Bearing surface 116 is configured in
the same way as bearing surface 112, and forms a similar depression
in the cylindrical outer surface tapering to a progressively
decreasing depth in the reverse circumferential direction, toward
the trailing edge land surface 110.
[0049] All of the surfaces of rotor 56 are smooth, desirably to a
surface roughness of about 4 micro inches or less. Rotor 56 may be
formed, for example, by machining from a solid rod and polishing
using techniques such as electropolishing and drag polishing. Rotor
56 has a permanent magnetization with a flux direction transverse
to axis 64, so that lobe 92 forms one pole of a permanent magnet,
where lobe 90 forms the opposite pole.
[0050] Rotor 56 may have an axial length, from the upstream edges
of the helix areas to the downstream end of the lobes of about
0.5-0.95 inches, preferably 0.6 inches long. The helix region may
be about 0.15-0.25 inches long, preferably about 0.2 inches long
whereas the support region may be about 0.35-0.45 inches long in
the axial direction, preferably about 0.4 inches long. The ratio
between the length of support region and the length of the helix
region is about 1:1 to 3:1, preferably about 2:1.
[0051] The second rotor 58 (FIGS. 16 and 17) is similar to the
first rotor 56 discussed above. Thus, the second rotor includes a
helix region defined by channels 174 and 176 adjacent the upstream
or inlet end 160 of the rotor. The second rotor has lobes 190 and
192 defining passages between them, the passages between the lobes
being continuous with the channels in the helix region. Lobes 190
and 192 are configured in substantially the same way as the lobes
of the first rotor discussed above with reference to FIG. 13. Thus,
in this rotor as well, each lobe has a circumferential extent which
increases in the radially outward direction so as to provide a
support surface having a substantial circumferential extent. Here
again, the solidity of the rotor in the support region occupied by
the lobes is substantially greater than the solidity of the rotor
in the helix region.
[0052] Second rotor 58 has a pitch opposite to the pitch of the
first rotor. The forward circumferential direction F' of second
rotor 58 is the clockwise direction of rotation about axis 164 as
seen from the upstream end 160 of the rotor, whereas the forward
circumferential direction of the first rotor 56 (FIG. 6) is the
counterclockwise direction as seen from the upstream end 60 of the
rotor. Also, the second rotor 58 is substantially shorter in the
axial direction than the first rotor. The axial length of the
second rotor may be about 0.3-0.5 inches. In one embodiment the
axial length is 0.4 inches. Of this length, approximately 0.15
inches is occupied by the helix region, and approximately 0.25 is
occupied by the support section consisting of the lobes 190, 192.
The pitch angle A' (FIG. 17) of the channel surfaces defining the
helix region is substantially greater than the pitch angle A (FIG.
8) of the corresponding surfaces in the first rotor. Here again,
each channel surface extends helically around axis 64 by about
130.degree. from the upstream end to its juncture with the
associated lobe.
[0053] As best seen in FIG. 18, pump 10 desirably is provided with
an expansible gripper adapted to engage the interior surface of an
artery. Unless otherwise stated, dimensions of the pump referred to
herein exclude the gripper. The gripper depicted is a stent 200
which includes a thin-walled cylindrical shell 204 having numerous
perforations extending through it. Stent 200 also includes a
central collar 206 and three legs 208 which extend from the collar
to the downstream edge of shell 204, i.e., the edge of the shell
facing upwardly in FIG. 18. Collar 206 is mounted on the outflow
end fitting 42 of pump 10 at the downstream or outlet end of the
pump. Power cable 44 projects downstream through the interior of
shell 204.
[0054] In the expanded condition depicted in FIG. 18, stent 204 is
spaced radially outwardly from the pump. Stent 204 has a collapsed
condition (not shown) in which the stent is disposed downstream
from the outlet fitting 42, with legs 208 extending generally
parallel to the axis of the pump and downstream from the pump. In
this collapsed condition, stent 204 has an exterior diameter
approximately equal to or smaller than the exterior diameter of
pump 10, i.e., about 13 mm or less. In one embodiment the stent
diameter is about 12 mm.
[0055] In one embodiment stent 200 is formed from a shape-memory
alloy such as the alloy sold under the registered trademark
Nitinol.TM.. The stent is initially provided in the collapsed
condition, and is arranged to return spontaneously to the expanded
condition when the stent is left unconstrained and heated to body
temperature.
[0056] In operation, pump 10 and stent 200 are inserted into the
patient's vascular system as, for example, into the femoral artery
or another artery having good access to the desired placement site,
and advanced through the vascular system, with the intake tube 32
leading, until the pump is in the desired location. As shown in
FIG. 19, the pump may be placed within the patient's aorta, with
intake tube 32 extending through the aortic valve 220 of the
subject's heart, and with the upstream end 36 of the inflow tube
protruding into the left ventricle. In this position, power cable
44 extends through the aorta.
[0057] The step of advancing the pump through the vascular system
may be performed using generally conventional techniques for
placement of intra-arterial devices. For example, an introducer
catheter may be placed using a guidewire; the guidewire may be
removed, and then the pump may be advanced through the introducer
catheter, whereupon the introducer catheter is removed.
Alternatively, the pump may be provided with fittings suitable for
engaging the guidewire. For example, the stent itself may serve as
one such fitting at the downstream or output end of the pump,
whereas the inflow tube 32 may be provided with a hole (not shown)
extending through its wall adjacent its upstream end 36, so that
the guidewire is threaded through the interior of the stent and
through the hole in the intake tube. In this case, the pump is
advanced over the guidewire without using an introducer
catheter.
[0058] Before or after placement of the pump, the end of power
cable 44 remote from the pump is connected to a control unit 222.
The control unit 222, in turn, is connected to a storage battery
224. The control unit and battery may be provided as a unitary
device in a common implantable housing. Control unit 222 is
electrically connected through cable 44 to the stators 48 and 52 of
pump 10 (FIGS. 1 and 3), and is arranged to apply appropriate
excitation currents to these stators to provide rotating magnetic
fields as discussed below. The control unit senses the voltage on
the stators and thus detect back EMF generated by rotation of the
rotors. The control unit controls the excitations of the stators so
as to maintain the rotors at a predetermined speed of rotation.
Battery 224 is a rechargeable battery, and is connected to a
transdermal power connection 226 Control unit 222. The battery 224
may be implanted in a location within the subject's body outside of
the vascular system. The transdermal power connection may include a
coil adapted to draw energy from a magnetic field applied through
the skin, or may include a fitting extending through the patient's
skin and carrying connectors adapted for conductive connection to a
power source.
[0059] With the pump in place and secured, controller 222 actuates
the first or upstream stator to apply magnetic flux within region
50 of housing bore 14 (FIG. 2). The flux direction is transverse to
the axis 16 of the housing, and hence transverse to the axis of the
first or upstream stator 48. The controller varies the direction of
the flux progressively, so that the magnetic field direction
rotates about axis 16 in the forward direction of first rotor 56.
Because of its permanent magnetization, first rotor 56 aligns
itself with the flux direction, and thus spins about its axis at
the same rate as the flux. The lobes 90 and 92 provide a strong
permanent magnet. Moreover, the magnetic material of the lobes is
concentrated near the outside of the stator, in close proximity to
the wall of bore 14, and thus in close proximity to stator 48. This
provides a strong magnetic interaction between the stator and the
rotor. In one embodiment the field and rotor rotate within the
range of about 20,000-60,000 revolutions per minute (rpm), most
typically about 50,000 rpm.
[0060] As the rotor spins about its axis, the bearing surfaces on
the lobes advance with the rotor in the forward circumferential
direction. As best appreciated with reference to FIG. 15, there is
a relatively large clearance (about 0.004 inches) between the
interior surface of tube 14 and bearing surface 112 at the forward
edge, where the surface intersects forward surface 99 of the lobe.
There is a smaller clearance at the rearward edge of the bearing
surface, near land 110, where the bearing surface transitions
smoothly into the land 110. There is an even smaller clearance
between the land 110 and the wall of the housing. Thus, as the
bearing surface advances in the forward direction, a high
hydrodynamic pressure is created at the rearward portion of the
bearing surface. The same is true for the downstream bearing
surface 116 (FIGS. 8 and 9), and for the bearing surfaces of the
opposite lobe 90. The hydrodynamic pressures keep the rotor
centered in the bore and out of contact with the wall of the bore.
The land portion 114 between bearing surfaces forms a barrier to
axial flow of blood between the upstream bearing surface 112 and
the downstream bearing surface 116. The same is true for the
bearing surfaces of the opposite lobe. This helps to assure that
the bearing surfaces provide independent separating forces at
axially spaced locations along the support region of the rotor, so
that the rotor resists pitch or yaw of the rotor axis relative to
the central axis of the bore.
[0061] The magnetic field applied by stator 48 maintains the rotor
in axial alignment with the stator, and prevents the rotor from
moving axially within the bore. Thus, during operation, the rotor
is suspended within the bore by the hydrodynamic and magnetic
forces applied to it, and is entirely out of contact with any solid
element of the pump. The rotor thus operates with no wear on the
rotor or the housing.
[0062] As the first rotor spins, the leading and suction surfaces
of the channels 74 and 76 (FIG. 6) of the first rotor impinge on
blood present within the bore 14 of the housing, and impel the
blood downstream. The relatively low solidity provided by the helix
region promotes inflow of blood into the flow channels and thus
helps to provide effective pumping action. The lobes 90 and 92
provide relatively little pumping action. However, the passages 106
and 108 between the lobes provide a relatively low-resistance flow
path from the channels in the helix region 68 (FIG. 6) to the
downstream end of the first rotor. As discussed above, the support
region 88 and lobes 90 and 92 serve to provide support for the
rotor within the bore and to provide an effective drive action.
Surprisingly, it has been found that varying the configuration and
solidity of the rotors along their axial extent, so that the
helical region exhibits relatively low solidity and relatively
small peripheral surfaces and the lobes have relatively high
solidity and substantial circumferential surfaces, provides a
particularly good combination of pumping action with adequate
support and adequate magnetic linkage to the rotating flux of the
stator.
[0063] As the upstream rotor 56 spins about its axis, viscous drag
exerted by the rotor and the blood entrained therewith on the blood
immediately upstream of the rotor within bore 14 tends to impart a
swirling or rotational motion to the blood upstream from the rotor,
so that the blood approaching the rotor is already spinning in the
forward direction of the rotor. In theory, this effect tends to
reduce the pumping action imparted by the rotor. This effect could
be mitigated by providing fixed axial vanes inside the bore just
upstream from the rotor. However, it is believed that a significant
advantage is obtained by omitting such vanes, so that the bore
immediately upstream from the rotor is an unobstructed surface of
revolution about the central axis 16, with no obstruction to
swirling flow. In one embodiment, the unobstructed bore extends
upstream from the rotor for at least about 2 times the bore
diameter. Leaving the bore unobstructed in this manner provides a
gentler action at the upstream end of the rotor and thus tends to
reduce hemolysis. Stated another way, limitations on rotor speed
which may be imposed by hemolysis considerations are relaxed by
providing such an unobstructed bore upstream from the rotor.
[0064] All of the surfaces of the rotor and the interior surface of
the housing in the vicinity of the rotor are continually washed by
flowing blood, so that there is no stasis or pooling of blood. This
substantially mitigates the risk of thrombus formation. Moreover,
because the rotor operates without wear on the rotor or the
housing, the surfaces of the rotor and housing remain smooth, which
further reduces thrombogenesis. The rotors constitute the only
parts of the pump which move during operation. As the rotors are
maintained out of contact with other parts of the pump, the pump
has no moving parts which contact one another during operation. In
particular, the pump has no seals which contact moving parts during
operation. A pump without such seals can be referred to as a
"seal-less" pump.
[0065] Because rotor 56 is a simple, two-pole magnet, the stator
need provide only two flux reversals per revolution. Each flux
reversal requires that the control unit and battery overcome the
inductive impedance of the stator, and each flux reversal consumes
power in hysteresis of the ferromagnetic material in the stator.
Accordingly, the frequency of motor commutation required for a
given rotational speed is lower for a two-pole rotor than for
rotors with a greater number of poles.
[0066] The second or downstream rotor 58 operates in substantially
the same manner as the first rotor 56, and is suspended within bore
14 of housing 12 by a similar combination of magnetic and
hydrodynamic forces. The second rotor spins in the opposite
direction from the first rotor. The blood passing downstream from
the upstream rotor 56 has a swirling motion in the forward or
rotational direction of the first rotor, i.e., in the direction
opposite to the direction of rotation of the second rotor. In the
particular embodiment illustrated, the downstream or second rotor
provides approximately a third of the pumping work performed on the
blood passing through the pump, whereas the upstream rotor provides
approximately two-thirds of the pumping work. As the magnetic
fields associated with each stator apply torque to the rotors to
turn the rotors about their axes, an equal but opposite torque is
applied to the stators. Because the rotors turn in opposite
directions, these reaction torques applied to the two stators tend
to counteract one another, and thus reduce the torque load applied
to stent 200 (FIG. 19).
[0067] Pump 10 in the embodiment described can pump approximately 3
liters per minute against a pressure differential of approximately
100 mm Hg, a typical physiological blood pressure. The pump thus
provides substantial assistance to the pumping action applied by
the left ventricle of the heart. Moreover, the pump provides this
effective pumping assistance in a device that is small enough to be
implanted in the aorta using a minimally invasive procedure, and
which can operate for extended periods without wear or mechanical
failure.
[0068] The leaflets of the patient's aortic valve 220 (FIG. 19)
seal against the exterior surface of inflow tube 32, and thus
prevent backflow of blood into the left ventricle during diastole.
When the ventricle contracts, during systole, blood pumped by the
heart flows through the aortic valve around the inflow tube and the
pump. The pump and the stent do not occlude the aorta, and do not
prevent the heart from exerting its normal pumping action. Thus, in
the unlikely event of a pump failure, the patient's heart can
continue to provide some blood circulation. Depending upon the
patient's condition, this circulation may be adequate to sustain
life until corrective action can be taken.
[0069] Numerous variations and combinations of the features
described above can be utilized without departing from the present
invention. For example, the second or downstream rotor and the
corresponding stator may be omitted to provide a smaller pump with
somewhat lesser pumping capacity. Conversely, three or more rotors
may be utilized. The dimensions and proportions discussed above can
be varied. For example, the housing, rotors and stators can be made
with a substantially larger diameter to provide more pumping
capacity in a pump which is to be implanted surgically, as for
example, by connection through the apex of the heart.
[0070] The pump can be positioned in other locations. In one such
variant, the intake tube is omitted and the pump is positioned
proximally from the position illustrated in FIG. 19, with the inlet
end of the pump housing itself protruding through the aortic valve.
In yet another variant, the pump may be positioned in the
descending aorta, in the femoral artery or in another artery, so as
to provide localized circulatory assistance. The pump also may be
implanted into a pulmonary artery to provide assistance to the
right ventricle.
[0071] A pump 310 in accordance with a further embodiment (FIG. 20)
includes a gripper 300 having a collar 302 attached to the outflow
fitting or shroud of the pump adjacent the downstream or outlet end
of the pump, and a set of fingers 304 attached to collar 302 at
locations spaced apart from one another circumferentially around
the axis of the pump. Each finger has a tip 306 remote from the
collar and a crown section having a relatively large
circumferential extent disposed near the tip. Each finger also
includes a beam section 311 between the crown section 308 and
collar 302. In the expanded condition illustrated in FIG. 20, the
beam sections 311 project outwardly from the collar 302, and the
crown sections have a curvature so that the tips 306 point inwardly
toward the axis of the pump. The crown sections 308 bear on the
interior wall of an artery (not shown), whereas the tips 306 are
maintained out of contact with the artery wall. The beam sections
311 have relatively low resistance to flow of blood in the axial
direction. Fingers 304 may be formed from a shape memory alloy as
discussed above, and have a collapsed condition in which they
project axially and thus lie flat against the exterior surfaces of
pump 310. In a variant, the tips 306 may project inwardly toward
one another at the upstream or inlet end of the pump to facilitate
movement of the pump along the artery during placement.
[0072] Referring to FIG. 21, a pump 410 according to yet another
embodiment of the invention includes a gripper in the form of two
strips 402 and 406. In the collapsed condition, strip 406 is wound
in a helix, closely overlying the exterior surface of the pump. The
downstream end of the strip 406, closest to the downstream end 412
of the pump, is affixed to the pump body. The upstream end 414 is
free, and is secured to the pump only by the other turns of the
helix. The second strip 402 has its upstream end 409 affixed to the
pump body, and its downstream end 408 free to move relative to the
pump body, constrained only by the remaining turns of the helix.
When the pump is implanted, strip 402 assumes the expanded position
shown at 402'. In this condition, strip 402 is generally in the
form of a spiral extending clockwise about the axis of pump 410, as
seen from the downstream end 412 of the pump. Strip 406 assumes the
shape shown at 406' and approximates a spiral with the opposite
direction from spiral 402', i.e., extending counter-clockwise from
its juncture with the pump body to its free end 414, again as seen
from the downstream end 412 of the pump.
[0073] Grippers described herein can be configured at intervals
along a driveline that extends from the pump to a battery or a
controller. Such driveline is downstream of the pump and a
configuration of grippers along its length can be used to maintain
driveline position in a main path of blood flow and away from
arterial walls. The combination of gripper support of the pump and
gripper support of the driveline eases the removability of the pump
if, for example, repair is needed or the pump is no longer needed
by the patient. Driveline gripper supports may be attached to the
driveline in intervals of roughly 0.23-0.46 inches along the length
of the driveline.
[0074] As discussed above, the proportions of the rotors can be
varied. More than two lobes and helix sections may be employed. In
one embodiment, the number of lobes is equal to the number of helix
sections. However, other configurations can be employed. Also, the
rotors discussed above have the same major diameter over the length
of the pump body so that, considering the major diameter only, the
rotor is generally cylindrical. This also is not essential. For
example, a rotor may have a helix section with a greater major
diameter than the support section. Such a rotor may be used with a
tapered housing. The stator may surround only the region of the
housing which receives the support region, so that the pump as a
whole has a small diameter.
[0075] Merely by way of example, a rotor according to a further
embodiment of the invention (FIGS. 22 and 23) includes a helix
section 568 as discussed above, but includes a support section 588
in the form of a hollow tubular shell having a single interior bore
502, best seen in FIG. 23, which depicts a cross section view
looking from the downstream end of the rotor. The shell also
defines a support surface in the form of a cylinder with a full
360.degree. extent around the axis 564 of the rotor. The channels
574 and 576 of the helix section communicate with passage 502 of
the support section through ports 506 at the juncture between the
support section and the helix section. The particular configuration
of the ports 506 in FIGS. 22 and 23 is schematic. Desirably, the
ports would have surfaces merging smoothly with the channels
defining the helix section. The cylindrical support surface can act
as a hydrodynamic bearing surface. To assure continuous washing of
the support surface 504 and the interior bore of the housing, holes
508 may be provided through the wall of the tubular support
section.
[0076] Referring to FIG. 24, a rotor 600 according to a further
embodiment of the invention includes a helix region 602 with
peripheral surface areas 606 and channels 608 similar to those
discussed above. The rotor also includes a support region 604. In
this embodiment, the support region includes an upstream portion
610, a downstream portion 620 spaced-apart from the upstream
portion in the axial direction and a shaft 630 extending between
these portions. Upstream portion 610 has lobes 614 and channels 616
between the lobes. Here again, lobes 614 have radially outwardly
facing support surfaces which incorporate hydrodynamic bearing
surfaces 618. The downstream portion 620 has lobes 624 and passages
626 between the lobes. Lobes 624 define further hydrodynamic
bearing surfaces 628. Shaft 630 has a relatively small
cross-sectional area. Passages 616 and 626 communicate with the
space surrounding the shaft. The small cross-sectional area of the
shaft provides a relatively low resistance to axial fluid flow. The
axial spacing of the upstream and downstream portions from one
another provides a greater axial distance between the hydrodynamic
bearing surfaces, and thus provides greater resistance to yaw or
tilting of the rotor in directions transverse to the central axis
of the housing.
[0077] In the embodiments discussed above, each rotor is formed
entirely as a unitary body of a single ferromagnetic material.
However, this is not essential. For example, the rotor could be
formed from a ferromagnetic material such as iron or an iron-nickel
alloy, which has desirable ferromagnetic properties, but which is
far less compatible with the blood. The rotor may be plated with a
metal having desirable blood compatibility of properties such as
platinum, with or without one or more intermediate plating layers.
In yet another variant, the helix section of each rotor may be
formed from a non-ferromagnetic material which is bonded to a
support section incorporating a ferromagnetic material.
[0078] As these and other variations and combinations of the
features discussed above can be utilized, the foregoing description
of the preferred embodiments should be taken by way of illustration
rather than by way of limitation of the invention as defined by the
claims.
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