Note: Descriptions are shown in the official language in which they were submitted.
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BEARING AND SEAL-FREE BLOOD PUMP
BACKGROUND OF THE INVENTION
The present invention relates generally to an
improved pump for transferring fragile or aggressive
S fluids. Examples of fragile fluids include human or
animal blood, neither of which can tolerate exposure to
unusual impact and/or sheer forces. Aggressive fluids
include corrosive or poisonous fluids, as well as fluids
which cannot tolerate contamination, or which otherwise
may destroy seals and/or bearings to reduce the lifetime
and/or longevity of the pump structure. Poisonous
fluids, for example, are extremely dangerous if a leak
develops. More particularly, the present invention
relates to a pump which is bearing and seal-free and
wherein the rotor is dynamically balanced by a
combination of hydrodynamic and buoyant forces. The pump
of the present invention is particularly adapted for
transferring human blood and is capable of creating a
flow of such liquids without damaging and/or otherwise
adversely affecting the quality of the material being
pumped. The rotor employed in the pump of the present
invention is rotated electromagnetically by means of an
electromagnetic drive system operating in conjunction
with an array of permanent magnets disposed on the rotor
in a brushless motor configuration. Alternatively, a
permanent magnet-to-permanent magnet coupling may be
employed. As such, the arrangement of the present
invention is capable of achieving relative rotation while
at the same time being bearing and seal-free.
In the past, pumps and pumping systems have been
designed which have been characterized as being bearing
and seal-free. Such systems typically employ magnetic
levitation means which is in effect an actual form of
bearing, much the same as sleeve bearings, ball bearings)
or other friction-inducing bearings. Such arrangements
using magnetic bearings, while being operational and
functional, may be rendered complex and accordingly
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require significant number of additional components
including magnetic devices, position sensors, and rapid-
response magnetic drive means. A number of such patents
have been granted in the past, including those to Olsen
et al. 4,688,998 and 5,195,877. The apparatus of the
present invention, by contrast, is fully bearing and
seal-free, with dynamic balance being achieved through a
combination of hydrodynamic and buoyant forces.
Among the disadvantages inherent in pumps utilizing
friction-reducing bearings include local heat generation
such as may occur from the use of ball bearings, friction
bearings, sleeve bearings, and the like. Low flow and
high pressure may result in local areas due to the use of
such structures. In addition, with all such bearing-
equipped pumps, a high spring constant is provided
wherein a small displacement of the rotor (or impeller)
introduces very high forces which can damage or
effectively destroy bearings. In addition, different
forces are introduced in the structure whenever
variations in axial positions occur.
In the present structure, the pump is bearing and
seal-free, with the effective low compliance of the rotor
allowing for relatively high displacement without the
creation of large forces otherwise required to hold the
rotor in its predetermined position. In addition, the
rotor seeks and finds an equilibrium position which in
certain situations can be off-set from the housing axis
(in either the rotational or transverse axes) which
typically occurs when the rotational axis of the pump is
altered. Rotational movement of the pump housing will be
manifested in displacement of the rotational or vertical
axis of the rotor. The present arrangement has been
found to eliminate the need for a highly precise axis in
design, fabrication and operation. The lack of a
positionally fixed rotational axis reduces the
introduction of large forces which otherwise would be
created when the axis of the rotor is shifted away from
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its normal centrally disposed position.
In the arrangement of the present invention, the
' pump includes a pumping chamber with a central axis, and
with a rotor body being disposed within the chamber for
' S bearing and seal-free rotation therewithin. The rotor
has a double or dual-conical configuration which
converges toward opposed polar regions, and with the axis
of rotation extending between these polar regions. Fluid
inlet ports are arranged in the pumping chamber in
oppositely disposed relationship within the chamber, with
the fluid being transported or transferred to the inlet
port area either externally or internally of the chamber.
Except for those occasions when the rotor is displaced,
it is normally arranged in coaxial relationship with both
the pumping chamber and the fluid inlet ports. The
outlet port or ports are arranged generally medially of
the chamber, midway between the inlet ports and typically
are positioned tangentially of the medial portion of the
pumping chamber. In those situations where the axis of
rotation of the rotor is arranged vertically, the dual-
conical configuration is such that flow on the outside
portion of the rotor proceeds downwardly on the upper
portion, and upwardly on the lower portion of the dual-
cone.
An example of an external transfer of fluids between
the oppositely disposed fluid inlet ports is a fluid
transfer line which introduces the fluids at opposite
ends of the housing. As an example of an internal
transfer, a bore may be provided which extends between
opposite ends of the rotor, thereby permitting transfer
of fluids internally of the structure.
The term "oppositely disposed inlet ports" is
. intended to reflect the utilization of fluid introduction
at opposite ends of the rotor, and is intended to include
those arrangements wherein all of the fluid being pumped
is initially introduced into one polar region of the
housing, the fluid nevertheless is transferred either
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internally or externally to the oppositely disposed polar
region.
Levitation of the rotor, as indicated, is achieved
by a combination of hydrodynamic and buoyant forces.
Briefly, the buoyant component is achieved as a result of
careful selection of the rotor density, with the
preferred relative density being between about 0.1 and
0.9 of the relative density of the fluid being pumped.
In a dynamic and operational mode, the buoyant forces
merely become a component of lesser or secondary
importance to the more significant and more highly
effective hydrodynamic force.
The hydrodynamic force component is achieved as a
result of the motion of the fluid as it is being moved
through the pumping chamber. As the velocity of the
fluid increases, the hydrodynamic forces increase
substantially, and with the proper selection of rotor
density, the hydrodynamic forces which are created during
normal operation result in achieving a precise, steady
and controllably repeatable centering of the rotor within
the pumping chamber.
The pump structure of the present invention has
particular application for transferring fragile and/or
aggressive liquids, in particular, for transferring human
blood. Since certain components in blood are extremely
fragile and are damaged upon exposure to external forces,
conventional pumps are simply unsuited for the
application. Additionally, conventional seals and/or
bearings typically found within conventional pump
structures pose substantial and significant threats to
cell damage. A further feature of the pump of the
present invention rendering the pump well suited for
transfer of blood is its essentially friction-free
operation. Any frictional force creates the risk of
generation of thermal energy, and thus may contribute to
heat build-up. Since blood is extremely sensitive to
temperature change, particularly any increase in
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temperature above conventional body temperature,
reduction and/or virtual elimination of friction provides
significant and substantial advantages.
Since the structure of the present invention does
' 5 not require bearings, energy consumption is reduced
through the elimination of energy losses otherwise
occurring in the bearings, including energy lost in
contact bearings as well as electrical losses in magnetic
bearings. The driving forces for the impeller are
located generally in the plane of the center of gravity
or center of mass of the impeller, or at least closely
adjacent thereto. This feature results in the creation
of a gyroscopic effect of a free-body gyroscope, and the
configuration of the present invention is such as to
stabilize the impeller when the axis of the housing is
rotated relative to the spin axis of the rotor. In other
words, the spin axis of the rotor may be altered because
of a change-of-position of the housing, and thus the spin
axis may not always be about the vertical axis, but can
be about the horizontal axis as well.
In addition to blood pump applications, the device
of the present invention finds utility in connection with
other fluids as well. Certainly non-delicate fluids may
be appropriately treated and/or moved with pump devices
of the present invention including the aggressive fluids
as discussed hereinabove.
SUMMARY OF THE INVENTION
Therefore, it is a primary object of the present
invention to provide an improved pump for transferring
fragile liquids such as human blood, and wherein the pump
is bearing and seal-free, with the rotor being
dynamically balanced by a combination of hydrodynamic and
buoyant forces.
It is yet a further object of the present invention
to provide an improved pump for application with human
blood which is capable of creating a uniform and
consistent flow of such liquids without damaging or
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otherwise adversely affecting the quality of the material
being pumped.
It is yet a further object of the present invention
to provide a pump structure utilizing a pumping chamber
housing a rotor wherein rotation of the rotor is achieved
by an electromagnetic drive system operating in
conjunction with an array of permanent magnets disposed
on the rotor in a brushless configuration.
Other and further objects of the present invention
will become apparent to those skilled in the art upon a
study of the following specification, appended claims,
and accompanying drawings.
IN THE DRAWINGS
Figure 1 is a perspective view of a pump assembly
prepared in accordance with the present invention;
Figure 2 is a vertical sectional view taken through
the axis of the structure as illustrated in Figure 1, and
illustrating the flow pattern created by the pump when in
actual operation;
Figure 3 is a horizontal sectional view of the pump
structure illustrated in Figure 1, and showing the detail
of the flow pattern of the pump in operation;
Figure 4 is a fragmentary sectional view taken on a
slightly enlarged scale and illustrating the tapering of
the clearance between the rotor and housing, and
illustrating the manner in which the rate of fluid flow
may be held substantially constant;
Figure 5 is a perspective view of a pump prepared in
accordance with the present invention and illustrating
one application of the pump functioning as a portion of
the natural heart of a patient; and
Figure 6 is a schematic diagram illustrating a
typical system in which the device of the present
invention may function.
DESCRIPTION OF THE PREFERRED EMBODIMENT
In accordance with the preferred embodiment of the
present invention, and with particular attention being
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directed to Figures 1, 2 and 3 of the drawings, the pump
generally designated 10 comprises a housing 11, the
interior of which defines pumping chamber 12. In other
words, the inner periphery 13 of housing 11 is the outer
" 5 periphery of the chamber 12. As is clear from the views
of Figures 2 and 3, housing 11 and chamber 12 share a
central axis which extends along axis 14 as set forth in
Figure 2. Housing 11, and accordingly chamber 12, is
provided with a pair of inlet ports as at 16 and 17,
along with outlet ports as at 18 and 19. Inlet ports 16
and 17, collectively, define the inlets to the chamber,
while outlet ports 18 and 19 collectively define the
outlets. The inlet ports 16 and 17 are arranged
coaxially with the chamber, that is, along axis 14, with
the inlet ports being arranged in oppositely disposed
relationship to chamber 12. Outlet ports 18 and 19 are
arranged medially of the inlet ports, and are, as
indicated, disposed generally transversely of axis 14.
With continued attention being directed to Figures 2
and 3 of the drawings, rotor 20 is disposed within
chamber 12 and has a symmetrical dual conical
configuration. This configuration provides dual cones
converging toward opposed polar regions such as 21 and
22, and the rotor is provided with an axis of rotation
which extends between the polar regions 21 and 22. The
base of each of the two cones forming the dual cone
configuration are coupled together and form a common
center plane. This common center is further utilized as
a mounting base for a plurality of permanent magnets such
as magnets 24-24. These magnets are arranged at radially
spaced locations generally medially along the axis of
rotation of rotor 20, with the permanent magnets being
provided at equally radially and arcuately spaced
locations. Electromagnetic drive means are provided as
at 26-26 and 27-27, with the electromagnetic drive means
being, in turn, coupled to a source of electrical energy
and arranged to deliver rotational driving energy to the
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rotor through the permanent magnets 24-24. The drive
arrangement is, of course, commonly referred to as a
brushless motor configuration and brushless motor drives
are, of course, well known in the art. The rate of
rotation of rotor 20 is conveniently controlled by means
of the frequency of the field applied to electromagnetic
members 26-26 and 27-27, with the rate of rotation being
controlled by the frequency of the applied
electromagnetic field, or by selective energization of
the electromagnetic means 26-26 and 27-27. Such drives
are, of course, commonly utilized and well known in the
art.
Rotor 20 is further defined by walls 29 and 30, with
the material of construction being either similar or
identical to that employed in housing 11. A suitable
biocompatible material such as polycarbonate, acrylic, or
copolymers of polystyrene may be employed, or
alternatively a coating may be applied to a suitable
substrate in order to enhance the biocompatibility of the
structure. In those instances where the device is not
being employed for implantation, then, of course, other
materials.may be employed, provided that the blood-
contacting surfaces be formed and/or coated with a non-
thrombogenic material.
Rotor 20 is provided with a hollow core or void area
as at 32, with this area providing a means for
controlling the relative density of the rotor body.
Preferably, the relative density is selected by the ratio
of the relative density of the rotor to that of the fluid
being pumped, and in most applications, the relative
density of the rotor to the fluid being pumped is between
about 0.3 and 0.6, with it being understood that relative
densities of between about 0.1 and 0.9 may be found
useful. Also, the dual conical configuration of rotor 20
provides the finished structure with an axial length
along the axis of rotation as being generally equal to
the axial length of the pumping chamber between the inlet
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ports 16 and 17. The transverse diameter of the rotor 20
is defined along a medial plane, as along medial line 33
and with the configuration of the dual converging cones
providing a clearance between the surface of the rotor
' S and the inner surface of the pumping chamber as
illustrated in greater detail in Figure 4. Generally
speaking, the clearance as indicated at A-A and B-B is
such that the clearance increases from the inlet port
area to the outlet port area. The rate of increase is
preferably proportional to the increase of the
circumference of the rotor from the polar tip to the
medial plane, with this increase in clearance providing a
generally consistent rate of motion for the fluid being
pumped as it moves along its translational and rotational
motions and/or vectors. With these considerations in
mind, the clearance between the inner surface of the
pumping chamber and the periphery of the rotor preferably
ranges from between about 1 millimeter up to about 7
millimeters, with a narrower range of between about 1
millimeter and 3 millimeters being generally preferred.
Generally, a clearance of about 1.5 millimeters is
preferred.
With respect to the areas of the inlet and outlet
ports, it is generally preferred that the combined area
of the inlet ports be generally equal to the combined
areas of the outlet ports, thereby providing more
consistency in flow and pressures, and also providing for
an appropriate hydrodynamic balancing of the rotor 20
within the chamber 12.
As has been indicated, the drive means for the
electromagnetic drive elements 26-26 and 27-27 is
preferably in the form of conductor windings, and for
purposes of achieving appropriate hydrodynamic balance,
the windings are carefully controlled and selectively
made so as to preserve the hydrodynamic balance of the
rotating rotor while eliminating the need for any form of
bearing.
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As has been indicated, the moment of inertia of the
impeller is effectively minimized by virtue of the
positioning of the mass of the impeller closer to the
center of gravity (or center of mass). This may be
obtained by moving the mass of the impeller needed for
structural integrity closer to the center, and generally
as closely as possible to the rotational axis. The
moment of inertia may be controlably adjusted in
connection with the structure of the present invention by
arranging and mounting the permanent magnets within a
circular or annular zone which is at the maximum radius
of the rotor inner impeller, as required, while
increasing the strength of the structure along its axis
of rotation.
With respect to the fluid being pumped, it should be
noted that the human blood has a viscosity of about 4
centipoises at 25° C., and this viscosity is sufficient
to provide for sufficient friction between a relatively
smooth rotor surface and blood so as to achieve a
sufficient rotational component of motion for
hydrodynamic balancing. As the rotational velocity of
the fluid being pumped increases, its hydrodynamic
balance effect will, of course, increase correspondingly
and proportionately. With a rotational velocity of
approximately 1000 rpm, the hydrodynamic balancing effect
substantially overwhelms the buoyant effect afforded by
the relative density of the rotor within the chamber.
For start-up purposes, saline is normally preferred
as the functional material, with the saline being
employed for a period of time until the desired
rotational velocity is achieved, and thereafter blood may
be introduced as the working solution being pumped and/or
transferred.
While the rotor structure illustrated is described
as being relatively smooth, vanes may be employed on the
structure with the vanes forming arcuately spaced
passages within the rotor. In other words, the vanes may
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be formed as individual arcuately spaced paddles to form
spaced-apart fluid passages and/or channels.
The inlet and outlet diameters are preferably 7
millimeters and the relative density is preferably
between 0.1 to 0.9, with a relative density of 0.5 being
preferred.
For most operational purposes, an inlet pressure
ranging from between about 5 millimeters of Hg (mercury)
up to about 40 millimeters Hg (mercury? is considered
normal and appropriate for fluid dynamics dealing with
human blood. Outlet pressures of between about 40
millimeters Hg (mercury) up to about 150 or 200
millimeters Hg (mercury) may be employed. When the
device of the present invention is functioning as an
implantable unit, the outlet pressure will, of course,
depend upon the patient's activity and circulatory
requirements being indicated.
Attention is now directed to Figure 5 of the
drawings wherein a system is illustrated for utilization
of the pump device of the present invention as a patient-
assist unit. In the drawing of Figure 5, the pump 40 may
be employed as a device with the outlets coupled to the
aorta. In an alternative construction, the outlet may be
coupled to the pulmonary artery. As indicated, the
device of the present invention has application as a
transfer pump as well, and may be employed, therefore, in
surgical procedures which involve temporarily removing
and/or temporarily disabling the heart function.
Attention is now directed to Figure 6 of the
drawings wherein the pump 10 is coupled in a system which
functions as a ventricular or heart-assist device. Pump
10 is powered by power supply 50 and sensors, including
pickup ratio sensor 51 and ratio control 52 are employed.
The patient pressure level monitor provides an input to
ratio control 52 with the level monitor receiving
information including patient pressure level input as at
54 and pressure level signal 55. These systems are known
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in the art and may be employed effectively in connection
with the device of the present invention.
While double cones have been discussed, it is
possible that multiple cones may be employed in lieu of
vanes, wherein the rotor is provided with surfaces of
revolution disposed axially outwardly of the rotor, and
with the surfaces of revolution being arranged coaxially
with the axis of rotation of the rotor.
While the term "double conical configuration" has
been employed throughout, it will be understood that
other surfaces of revolution may be employed, such as
those surfaces of revolution generated by a curved line
such as parabola, or a straight line so as to form a
cone. Thus, the term "cone" is understood to be broadly
defined herein.
It will be appreciated, of course, that various
modifications may be made in the preferred embodiment
illustrated above, and these modifications may be made
without actually departing from the spirit and scope of
the present invention.
What is claimed is:
