Note: Descriptions are shown in the official language in which they were submitted.
1222901
PUMP ACTUATOR
~ACKGROUND AND_~U~I~AR~
The present invention relates to an actuator
mechanism for a pump, and in particular, to an improved
actuator mechanism and fluid chamber structure for use
in an internally implantable blood pump or the like.
In any type of blood pump, the device must be
constructed in size, shape and design to be readily
implanted in a body cavity and to be comfortable over
extended periods. The construction of the device must
allow for efficient connections between the pump and
the vascular system near the heart. The pump must be
highly reliable for long periods of continuous use.
Specifically, the actuator mechanism in the pump must
be efficient, long-lasting, and relatively smooth
working. The chambered part of the pump - which in
the case of a deformable-sac pump, includes the
deformable sac itself -- must be constructed to operate
over long periods of continuous use with minimum
stress-related fatigue and creasing. The sac design
and operating characteristics must minimize thrombus
formation in the fluid-containing portions of the pump.
Additionally, the sac itself should be easy and
relatively inexpensive to manufacture and incorporate
into a rigid housing portion of the pump.
U. S. Patent No. 4,167,046 discloses a
deformable sac blood pump which solves or minimizes a
number of problems associated with previously developed
deformable sac blood pumps. The pump of that invention
is composed of a disc-like deformable sac having an
annular side wall and a pair of opposed circular walls
which are adapted to be recurrently and sychronously
moved toward one another, through the action of a pair
of opposed pusher plates ~o produce pumping action.
Inlet and outlet conduits in the sac are arranged to
122XC~Ol
direct inlet and outlet flow substantially tangentially
with respect to the annulus Eormed by the inner surface
of the sac's annular side wall~ The inlet and outlet
conduits are disposed on either side of the pump region
occupied by the pump actuator, producing a
space~conserving arrangement of pump components The
sac itself is formed as a unitary seamless article from
flexible resiliant material, providing a smooth
interior sac surface which acts to prevent thrombus
formation in the pump.
The actuator which is used in a deformable~sac
pump of the type just described operates to move the
opposed pusher plates recurrently from their more
displaced to their less displaced positions, preferably
in a manner which produces controlled-rate, synchronous
plate movement. At the same time, the actuator must be
efficient, relatively smooth working, and reliable over
long periods of continued use. One type of actuator
which provides a number of advantages in a
deformable-blood sac has been described in U. S. Patent
No. 4,384,829.
The actuator disclosed in the just-mentioned
patent includes a solenoid device which operates
between open and closed positions to produce increased
bending in opposed prestressed beam springs which
operatively connect opposed armatures in the actuator
to associated pusher plates The increased bending in
the springs is released by movement of the two pusher
plates inwardly toward their less displaced
end-of-stroke positions. An important feature of the
actuator is that the beam springs, in acting between
less stressed and more stressed conditions, produce a
relatively flat output force profile in acting against
the associated pusher plates. As a result, peak loads
on the pump components are minimized. The actuator,
having few moving parts, is also simple in construction
,,
~2~X90~
and operation, and is therefore quite reliable over long periods
of continued use.
The novel chamber structure of the invention includes
a deformable sac which has an annular rigidified side wall
and a movable wall joined to the side wall through an outwardly
convex flexible wall portion. A pusher means acts against the
movable wall and is adapted for movement from an initial deflec-
tion position, at which the flexible wall portion takes the
form of a circumferentially uniform roll having a bulge cross-
sectional curvature, toward inwardly moved positions, at which
the roll maintains its circumferentially uniform, bulge like
character.
In a speciflc embodiment of the invention, the
annular side wall is held in a rigid condition by attachment
to curved inner wall portions of a rigid housing ring. The
sac includes a pair of opposed, substantially parallel circular
movable walls disposed on opposite sides of the housing ring,
each wall being joined to the side wall by an outwardly convex
flexible wall portion. A pair of pusher plates acting against
associated circular walls are coordinately movable from such
initial deflection positions to inwardly displaced positions
under the control of an actuator in the pump.
Accordingly, it is an object of the present invention
to provide in a deformable sac blood pump, a chamber structure
which incorporates many of the advantageous features known in
the prior art, including those of the pump described in U.S.
Patent No. 4,167,046, and which provides a number of unique
and hitherto unknown features which enhance pump reliability
and operational characteristics.
A more specific object of the invention is to provide
in such a structure a deformable sac having flexing zones which
are circumferentially uniform, preferably being entirely defined
by machined elements.
mab/ ~
lX.~Z~
A related object of the invention is to provide
such a structure in which flexing oE the sac during pump
operations occurs primarily by a smooth rolling action in
the flexing por-tions of the sac.
Yet another object of the invention is to provide
such structure in which creasing and stress-related fatigue
in the deformable sac are minimized.
Another object of the invention is to provide
such structure designed to produce, during pumping operation
a circular flow action which substantially reduces the degree
of thrombus formation on inner sac surfaces.
It is still another object of the invention
to provide such a chamber strucutre ha~ing a reduced thickness.
According to another aspect of the present invention
there is provided an improved actuator and sac which incorporate
many of the advantageous features of the actuator and sac
just described, and further include a number of unique
and hitherto unknown features which enhance pump reliability
and operational characteristics and contribute to compactness
in the pump design.
Accordingly, one object of the present invention
is to provide an actuator for use in a deformable-sac type
implantable blood pump, where the actuator is quite compact.
Another object of the invention is to provide
such an actuator having highly reliable and predictable
performance characteristics.
It is yet another ob~ect of the invention to
provide such an actuator whose operation can be accurately
monitored and controlled.
More specifically, the actuator of the invention
includes an armature which is mounted for movement between
~ mab/ t i ~
~2~;~9~
open and closed posi~ions, and which includes a solenoid
core defining an internal front-to-back slot. An elongate
main spring in the actuator is attached at one spring end
to the back region of the armature, extends through the
core slot, and is attached at its other end -to a pusher
element adapted to act against a deformable sac. An elongate
preload spring connected at one of its ends to the armature
and operatively connected at its other end to the main spring
functions to support the main spring in a relatively less
stressed condition when the armature is in its open position.
In a specific embodiment of the invention, the
main spring includes a plate-like spring which is curved
in the direction of its action on the pusher element, and
is in a more planar configuration when in its relatively
more stressed condition.
Also in a specific embodiment of the invention,
the actuator includes a symmetrical arrangement of components
acting on opposed pusher elements to compress the sac symmetri-
cally from opposite sides. The actuator may further include
position sensors for monitoring solenoid armature and/or
main spring positions, to provide data used in controlling
the operation of the actuator.
These and other objects and features of the
present invention will become more fully apparent when the
following detailed description of a preferred embodiment
of the invention is read in con~unction with the accompanying
drawings.
Brief Description of the Drawinqs
FIGURE 1 is a side, partially cross-sectional
schematic view of a pump employing an actuator constructed
in accordance with the invention;
FIGURE 2 is a view like FIGURE 1, with additional
parts cut away, illustrating a second
mab/Y)I~
~2;~Z90~
condition of the pump;
FIGURE 3 is a view similar to FIGURE l, with
other actuator parts added, illustrating a third
condi~ion of the pump;
FIGURE ~ is a top view of the pump shown in
FIGURES 1-3;
FIGUP~E 5 is a sectional view taken generally
along line 5-5 in FIGUR~ 4;
FIGURE 6 is a graph illustrating the force
exerted on a pusher plate in the pump by an associated
spring beam in the actuator, as a function of the
position of the pusher plate between start-of-stroke
and end-of-stroke positions;
FIGURE 7 is a schematized plan view, partially
cutawayJ of a blood pump constructed in accordance with
the invention;
FIGURE 8 is a sectional view taken generally
along line 8-8 in FIGURE l;
FIGURE 9 shows in perspective view, a chamber
structure in the pump;
FIGURE 10 is a perspective view like that of
FIGURE 9, with housing ring and pusher plate parts
removed to show the condition of a deformable sac in
the structure in a relaxed state (upper part of the
figure) and in a start-of-stroke stroke condition
(lower part of the figure); and
FIGURE ll is a view like FIGURE lO, but
showing the sac in an end-of-stroke condition in the
lower part of the figure.
Detailed Description of a Preferred Embodiment
of the Invention
FIGURES 1-4 illustrate an implantable blood
pump lO which is driven by an actuator, or actuator
mechanism, 12 constructed according to the present
invention. The pump generally includes a deformable
sac 14 having an annular side wall 16 (FIGURES 2 and 3)
1~2290~
and a pair of opposed circular movable walls 18, 20
each of which i5 joined to the side wall through an
annular flexible wall portion, such as wall portion 22
adjoining wall 18 to wall 16. The sac, which is also
referred to as a flexible enclosure, defines an
internal variable-volume pump chamber 24. In pump
operation, fluid such as blood is supplied to the pump
chamber through a valved inlet conduit 26, shown
fragmentarily in FIGURE 4, and is expelled under
pressure, through a valved outlet conduit, shown
fragmentarily at 28 in FIGURE 4.
The pump includes opposed pusher elements, or
pusher plates 30, 32 which are attached to, and
substantially cover, sac walls 18, 20, respectively.
The`two pusher plates are movable, under the control of
actuator 12, from initial, start-of-stroke posi~ions
shown in FIGURE 1 inwardly and synchronously, to
end-of-stroke positions shown in FIGURE 3. Such plate
movemenk causes fluid in chamber 24 to be expelled from
the pump, through outlet conduit 28~
The central portions of the sac, including
side wall 16 and the inlet and o~ltlet conduits formed
therewith, are encased in a rigid housing 34. As can
be appreciated in FIGURES 2 and 3, the housing
functions to support the sac side wall in a stationary
position as walls 18, 20 are moved toward and away from
one another during pumping action. The rigid housing
is also used in attaching actuator 12 rigidly to the
pump chamber.
Considering now details of the actuator 12, a
frame 36 in the actuator includes a generally U-shaped
frame member 38, a side 38~ of which is seen in FIGURE
3, and the three sides 38~, 38~, and 38c of which are
~een in top view in FIGURE 4. Opposed parallel sides
38~, 38~ in the frame member are provided with pairs of
aligned bores, such as the pair including bore 40, and
~222901
the pair including bore 42, both in side 38a, (FIGURE
3).
A front frame plate 44 seen sectionally in
FIGURES 1 and 2, and in top view in FIGURE 4 extends
between the open sides of the frame member and is
secured thereto as by bolting. The upper and lower
surfaces of plate 44 are provided with energy absorbing
pads, such as pad 46, which serve a purpose to be
described. The pads are preferably formed of rubber,
polyurethane, or other resilient pad material. Also
attached to the frame plate is a stop member 48 having
opposed, rearwardly projecting stops 48~, 48b seen in
FIGURES 1 and 2.
The actuator includes pair of solenoid
armatures 50, 52 mounted on the frame for pivoting
between open and closed positions which are shown in
FIGURES 1 and 2, respectively. Armature 50, which is
representative, comprises an armature support 54 whose
front and back end regions are indicated at 54~, 54b,
respectively, in FIGURB 1. The armature support is
pivotally mounted on frame 36 by a pin 58 which extends
through the pair of aligned frame bores which includes
bore 40, and is received in bearings, such as bearings
56 held in the armature support. The pivot axis,
indicated by dashed-dot line 60 in FIGURE 4, is normal
to the direction of movement of the two pusher plates
and is also normal to the plane of FIGURES 1-3.
Also included in armature 50 is a C-shaped
solenoid core 62 having the general shape seen in side
view in FIGURES 1 and 2 and front-on in FIGURE 5. It
can be seen in FIGURE 5 that the core is received
within a central cavity 64 formed in the support
member, with a pair of opposed side projections in the
core, such a projection 66, being received against side
shoulder portions in the cavity. According to an
important feature of the invention, core 62 is provided
",
2901
with an elongate slot 68 extending in a front-to-back
direction as seen in FIGURES 1 and 2. The slot serves
a purpose which will be described below. Core 62,
which is conventionally bonded to the support member,
is formed of a suitable ferromagnetic material such as
an iron-colbalt-vanadium al loy ~
Each of the two inwardly extending poles in
the core, such as pole 70, is wrapped with a
conductive-wire winding, or coil, such as coil 72 seen
cross sectionally in FIGURE 5. The lead wires of the
two coils in the core are connected to an actuator
control device (not shown) which controls the operation
of the actuator in a manner which will be detailed
below.
Likewise armature 52 comprises an armature
support 74 which is mounted on frame 36 for pivoting
about an axis 75 defined by the aligned pair of frame
bores which includes bore 42 in FIGURE 3. Axis 75 is
parallel to axis 60, and the two axes are equidistant
from a mirror image plane which bisects the pump sac
axially, and which is indicated by dashed-dot line 76
in FIGURES 1 and 2. Armature 52 also includes a
solenoid core 78 having a pair of windings, such as
winding 80 seen in FIGURES 1-3, whose lead wires are
connected to the above-mentioned control unit. The
core windings in the two armatures are energized from a
storage capacitor, or by other suitable means in the
control unit to set up magnetic fields in the two cores
which draw the two armatures together, from their open
positions shown in FIGURE 1 toward their closed
positions shown in FIGURE 2.
As the armatures approach their closed
positions, the armature supports make initial,
cushioned contact with associated pads, such as pad 46,
on plate 44 as seen in FIGURE 2~ These pads cushion
solenoid closure at the closed positions of the two
122290~
--10--
armatures, and define a residual solenoid gap between
the confronting poles in cores 62, 78. Specifically,
the pads are constructed and dimensioned to prevent
actual contact between the two cores with solenoid
closure. The open, unenergi~ed positions of the
armatures are determined by the positions of the
associated pump pusher plates.
The actuator also includes a mechanical
linkage between the two armatures for constraining the
armatures to move toward and away from one another
symmetrically with respect to the mirror-image plane
represented by line 76. This linkage includes a
linkage arm 82 formed on the back end of armature
support 54, and a more forwardly disposed linkage arm
84 formed on support 74. A connecting link 86
pivotally joins the two arms through pivot pins which
are seen cross sectionally in FIGURES 1 and 2. It can
be appreciated with reference to the latter figures,
that as one of the armatures, for example armature 50,
pivots toward its closed positions, movement of arm 82
acts on arm 84 through link 86 to move the other
armature substantially the same amount toward its
closed position. Similarly, the two armatures move in
a symmetrical, coordinated manner when moving from
their closed toward their open positions
The actuator is also provided with a pair of
armature position detectors, such as the detector shown
schematically in dashed outlines at 88 in FIGURE 4.
Preferably each detector is a conventional eddy current
type detector which operates to measure the spacing
between a current-signaling surface and a target
surface, according to current changes produced by
magnetic induction in the target surface. In the
particular construction herein, each detector is
suitably mounted on the rear part of frame 36 to
interact with a target surface formed on the associated
122Z9o~
armature support. The two detectors are operable to
provide accurate instantaneous data as to the positions
of the associated armatures, as these move between
their open and closed positions. The detector position
data is supplied to the above-mentioned control device,
to provide control feedback information to the control
unit during solenoid actuation.
Armatures 50, 52 are operatively connected to
associated pusher plates 30, 32 by main springs 90, 9~,
respectively. Spring 90, which is representative,
includes an elongate plate or ribbon-like spring which
is seen in side view in FIGURE 1-3 and in plan view in
FIGURE 4. The back end of the spring is attached as by
bolting to the back end of armature support 54,
According to an important feature of the present
invention the spring extends through slot 68 formed in
armature core 62, as seen in FIGURES 1 and 2~ As seen
in FIGURE 5, the width of the spring extends along a
major portion of the length of the slot. The right end
of the main spring in FIGURES 1-4 terminates at an
enlargement 94 having a bore formed axially (normal to
the long axis of the spring) therein. A pillow block
98 is attached as by bolting to pusher plate 30, as
seen best in FIGURE 4. The main spring is pivotally
attached to the pillow block by a pivot pin 100
extending through the spring enlargement bore and
through bores formed in a pair of mounts, such as mount
102 in the pillow block.
A preload stop member 104 associated with
mainspring 90 includes a central slotted portion 106
through which the main spring is received and at which
the stop member is secured to the main spring as by
bolting. The central portion is seen cross sectionally
in FIGURES 1 and 2. Member 104 has a pair of axially
opposed preload stops, such as stop 108, each having
the general rectangular shape in cross section seen in
:
122~90~
-12-
FIGURE 3.
The main spring is formed of a suitable spring
material such as titanium, steel, a fiber composite or
the like and is curved, in a relaxed, or unstressed
condition in the direction of its action on pusher
plate 30, i.e., inwardly on progressing away from the
spring's attachment to the armature. As will be seen
below with reference to the described operation of the
actuator, the curvature of spring 90 seen in FIGURE 1
(and the substantially mirror-image curvature of spring
92) represent the curvature in the spring with such in
a relatively less-stressed condition. This curvature
is somewhat less than that of the main spring in a
totally unstressed or relaxed condition.
The spacing between an inner surface portion
of spring 90 and frame 36 is monitored by a position
detector 109 similar to the eddy current armature
position detectors described above.
The construction of spring 92 and its
attachment at one end to armature 52 and at its other
end to an associated pusher plate 32 through a pillow
block is similar to what has already been described
with reference to main spring 90. Also a stop member
110 in the actuator is like stop member 104 in its
2'; construction and attachment to the associated main
spring.
Completing the description of the actuator,
there is associated with each main spring, such as main
spring 90, a pair of preload springs/ such as springs
112, 114, disposed on either side of the associated
main spring as seen in FIGURE 4. The preload springs
are attached, as by bolting, to the front end region of
support 54 and are dimensioned to contact associated
stops, such as stop 10~, in the stop member as can be
appreciated particularly in FIGURE 3. According to an
12;~290~
-13-
important feature of the present invention, the preload
springs have a selected curvature and spring constant
which, with the pump in the condition shown in FIGURE
1, that is, with the solenoid armatures in their open
positions, and the pusher plates in their relatively
more displaced positions, act to bend spring 90 from
its more curved, relaxed position to a less curved
condition seen in FIGURES 1 and 3. The action of the
preload springs against the main spring, of course,
bends the preload springs inwardly somewhat from their
relaxed, unstressed positions.
Similar preload springs, such as spring 116
seen in FIGURES 1-3, function to hold main spring 92 in
a relatively less stressed position, with the pump in
L5 the figuration shown in FIGURE 1, which is a mirror
image of the less stressed condition main spring 90
The pair of preload springs associated with each main
spring is also referred to herein as preload meansO
Such means may also include relatively rigid elongate
members.
In this condition, each main spring in the
actuator is held in its relatively less stressed
position by the action of the associated preload
springs acting against the stop member on that main
spring. Specifically, the preload springs act in an
outwardly direction to move the associated main spring
from a maximally curved configuration outwardly (away
from the mirror image plane in the pump) to the
position shown in solid lines in FIGURE 1.
The operation of the pump and particularly the
operation of the actuator therein may be observed
sequentially in FIGURES 1-3. FIGURE 1 illustrates the
pump in a start-of-stroke condition in which pump sac
14 is filled and ~olenoid armatures 50, 52 are in their
open, unenergized positions. The pump ejection stroke
is initiated by the control unit, typically with the
~122ZgOl
supply of current to the windings in the armatures from
a storage capacitor in the control unit. When
energized, the armatures are drawn toward one another,
symmetrically with respect to the mirror image plane in
the pump, and at a rate which may be controlled by
varying the instantaneous current supplied to the
windings~
FIGURE 2 shows the condition of the pump
immediately after solenoid closure. At this point, the
inertia of the filled pump chamber retains the ends of
the main springs essentially in the same axially spaced
positions as in FIGURE 1. At the same time, the
preload springs are moved inwardly with the armatures,
out of contact with the stops on the main springs, and
the main springs are placed in relatively more
stressed, more planar configurations illustrated in
solid lines in FIGVRE 2~ Thus, t~he energy used in
solenoid closure is used initially to produce a greater
loading in the main springs, whereby they contain
greater stored energy.
After initial solenoid closure, the armatures
therein may be held in their closed positions by a
relatively small latching current supplied by the
control unit. If additional holding force is needed, a
small permanent magnet may be used. The force of the
latter may be overcome, in returning the armatures to
their open positions, by a small reverse current in the
solenoid windings.
If the energizing means used to hold the
armatures in their closed positions inadvertently
fails, with the pusher plates still in their relatively
more spaced positions, the relatively greater stress in
the main springs may act to open the armatures rapidly
beyond their usual open positions. when this occurs,
contact between the armatures and associated stops 48~,
48k acts to limit armature "overshoot" to positions
1222~0~
-15
only slightly beyond such open positions, and to dampen
oscillattory motion in the armatures.
From the condition shown in FIGURE 2, the
tendency of the two main springs to relieve the
stressed condition therein results in plates 30, 32
being moved toward each other, thus expelling contents
of the pump chamber and producing the desired pumping
action in the pump. It can be appreciated that as the
pusher plates approach their end-of-stroke positions
shown in FIGURE 3, the main springs are again
positioned to make contact with the associated preload
springs through the stops on the main springs.
Immediately after contact of the main spring preload
stops with the associated preload springs through the
stops on the main springs Immediately after contact
of the main spring preload stops with the associated
preload springs, a portion of the stored loading energy
in the main springs is imparted to the preload springs,
bending the latter inwardly until the force and
counterforce exerted by the main spring and the preload
springs, respectively, are equalized. At this point,
the main springs are again in the relatively less
stressed, more curved conditions described with respect
to FIGURE 1. Once this has occurred, the solenoid
coils are deenergized or unlatched.
The apparatus is returned to the condition
described with respect to FIGURE 1 as a result of
filling of the sac, as by cardiac systole. This
filling may take place passively, wherein movement of
the pusher plates outwardly to their relatively more
spaced positions is accommodated by pivoting of the
armatures toward their open positions.
The positions of the pusher plates during the
just-described pumping operation may be monitored by
position detector 109 which inputs the control unit.
Specifically, at the point where the two pusher plates
~2~29(~L
-~6-
rea~h their most inwardly moved position, the control
unit in the pump may respond to a minimum threshold
spacing signal or to a minimum threshold rate of change
signal fro~ the detectoL to release the latching
curren~ in the pump to allow pump filling to occur.
During pump filling, as the pump returns from its
FIGURE 3 condition ~o its FIGURE I condition, either
the detector 105 or the armature position detectors, or
both, may signal the control unit, as to a threshold
spacing or threshold rate of movement condition which
occurs when the pump chamber is filled, and the pump is
ready to resume its pumping function.
FIGURE 6 is a graph of the force curve which
characterizes the force of a pusher plate, such as
plate ~0, acting against the associated sac wall during
pumping action. The left-hand edge oE the curve
represents the start of the eject stroke, represented
by the FIGURE 2 condition of the pump just after
solenoid closure. The nearly horizontal portion of the
curve between the start of the eject stroke and the
point at which the spring makes contact with the
preload stop is the normal characteristic of stress
relief in a beam spring between relatively more and
relatively less stressed conditions. Each main spring
is selected to have a relatively low spring constant so
that this portion of the curve is as horizontal as
possible. After the main spring makes contact with the
preload springs, the force of the pusher plate acting
against the sac falls relatively quickly to a zero
level as stored energy in the spring is given up to the
preload springs and the main spring comes to rest in
its relatively less stressed condition.
The construction and operation of the
invention has been described above with reference to an
actuator having a pair of opposed main springs which
are under the control of a pair of coordinately movable
l~X2~
-17-
armatures. The invention also contemplates an actuator
adapted for driving an asymetric deformable pum~ sac in
which the pumping action is achieved by recurrently
moving a single pusher plate against a deformable sac
surfacei Such actuator includes a single armature,
like armature 50, connected to the pusher plate
operatively by a main spring, such as rnain spring gO,
this being held in a relatively less stressed position
during nonpumping phases of the pump operation by one
or more preload springs which act on the main spring in
the manner described above.
FIGURE 7 shows a view of a pump 110 similar to
the pump 10 of FIGURES 1-6. The pump includes the
chamber structure which is shown generally at 112 and
whose components are shown removed from other parts of
the pump. Structure 112, whose construction and unique
features will be described in greater detail below,
includes the deformable sac 114 having the annular side
wall 116, and the pair of opposed circular, movable
walls 118, 120 (seen in FIGURE 8) joined to the side
wall through flexible curved wall portions 122, 124,
respectively. These parts define a variable-volume
annular sac chamber, or annulus, 126. Fluid is
supplied to the annulus through an inlet conduit 128
and is expelled under pressure, through an outlet
conduit 130.
The inlet and outlet conduits are provided
with suitable valves, such as inlet valve 132 (FIGURE
8), to produce the requisite one direction flow valving
in the pump. Several clinical valves which are
commercially available are suitable for use in the
pump. In the particular embodiment illustrated herein,
29 mm and 27 mm porcine issue valves are used in the
inlet and outlet conduits, respectively.
A pair of opposed pusher plates 134, 136
(FIGURE 8) attached to associated walls 118, 120,
12i~9~
-18--
respectively, are movable inwardly, under the control
of an actuator 138, to produce expulsion of fluid from
the sac annulus. The actuator is mechanically
connected to each pusher plate through connecting arms,
such as arms l40 connecting the actuator to plate 134.
Actuator 138, whose design forms no part of the present
invention, is preferably an electrically powered
solenoid-type actuator which functions to "close"
opposed connecting arms coordinately and at a
predetermined rate, to produce the desired pumping
action in the pump.
Completing the description of what is shown
generally in FIGURE 7, pump 110 has a housing 142 which
includes a rigid housing ring 144, to be described in
detail below, and rigid shell 146 encasing the central
region of structure 12, including ring 144. ~lore
particularly, the shell encases ring 144, the adjacent
side wall region of sac 114, and is formed with
passages which accomadate the inlet and outlet conduits
in the sac.
The two valves in the pump are held in
suitable fittings cast in the housing shell to anchor
the valves in place in the deformable sac. The
actuator is secured to the housing by suitable means to
provide a rigid connection between the actuator and the
nondeformable (side wall) portions of the pump sac.
The entire pump structure just described may
additionally be encased in a fluid tight outer housing
(not shown) which is coated with a suitable
biocompatible material.
Details of structure 112 will now be
considered with particular reference to FIGURES 8-11.
Referring first to FIG~RES 8 and 9, ring 144 takes the
form of an annular band having a substantially
3'~ straight-walled central portion 148 and a pair of
circumferentially continuous annular lip portions 150,
12~X9C~l.
--19--
152 haviny the inwardly curved cross sectional shape
seen in FIGURE 8. A pair of slots 154, 156 (FI~URE 9)
fsrmed in the ring accommodate inlet and outlet
conduits in the sac, respectively. Each slot extends
about an approximately 90 arc, with the width of each
slot corresponding approximately to ~he width of the
central wall portion in ~he ring. That is, each slot
extends in width substantially between the two opposed
annular lip portions in the housing ring. The ring is
preferably formed from a lightweight
corrosion-resistant material, such as titanium, or a
strong rigid polymeric material or the like. The inner
surfaces of the curved lip portions in the ring are
preferably machined or molded surfaces, for a purpose
to be described.
With continued reference to FIGURES 8 and 9,
plate 134, which is representative, includes a
circular, substantially planar portion 158, and a
curved annular lip portion 160 having the
cross-sectional curvature seen in FIGURE 8. Plate 136
likewise has a circular planar portion 162 bordered by
an annular curved lip portion 164. The pusher plates
are preferably formed of a lightweight
corrosion-resistant material such as titanium, or of a
strong, rigid fiber composite. The inner surfaces of
the lip portions in the two pusher plates, like the
inner surfaces of the lip portions in the housing ring,
are preferably machined or molded, also for a purpose
to be described.
While not shown in FIGURES 8 and 9, the pusher
plates include mounting structure through which the
associated connecting arms such as arms 140, are
attached to the associated plates, as can be
appreciated with reference to FIGURE 7. According to
an important feature of the present invention, the two
plates are movable, under the control of actuator 138,
:12~:~90~.
-20-
acting through the connecting arms, from axially
symmetric initial deflection positions, shown in solid
lines in FIGURE 8, toward inwardly moved positions.
The positions of the inner surfaces of the sac at the
5 end-of-stroke pusher plate positions are shown in
dashed lines at 166 in FIGURE 8,
Considering details of sac 14, inlet and
outlet conduits 128, ~30, respectively, communicate
with the sac annulus through elongate ports, such as
inlet port 168 (FIGURE 8), formed in the sac. As seen
in FIGURE 8, port 168, which is representative, is
defined cross-sectionally by a pair of confronting,
inwardly convex rolling surfaces which join the annulus
and conduit sides of the sac, defining a minimum flow
area of width denoted dt W in FIGURE 8. Each port,
such as port 168, is substantially coextensive, in an
arcuate directions, with the corresponding housing ring
slot, such as slot 154, through which that part of the
sac extends. An advantage of this construction is that
a port having a relatively large fluid passage area is
formed in an anchored, stationary side wall portion of
the sac, whereby the shape of the port is substantially
constant during pump operation
Sac 14 is formed as a unitary seamless article
from flexible resiliant, blood compatible material.
This material may be oE any type suitable for pumping
blood, such as certain types of polyurethanes. The
material of which the sac is comprised should have
long-term retention of physical strength under combined
dynamic stressing and hydrolysis. The material should
be of low toxicity and long-term stability for
compatibility with blood. The material should also be
of high strength, be capable of being repeatedly
flexed, be capable of being sterilized and be easily
fabricated.- Suitable materials are linear segmented
polyurethanes, for example BIOMER from Ethicon>
12;~:~9~.
-21-
One preferred ~lethod of making the sac
comprises successively coating an accurately machines
and polished aluminum mandrel whose outer surfaces
define the inner surEaces of the sac. Since both of
the opposed annular flexible portions in the sac are
circumferentially uniform, the surfaces of ~he mandrel
forming such flexible surfaces can be accurately
machined, polished, and coated to produce extremely
regular and smooth surfaces. To form the sac, the
coated mandrel is repeatedly dipped in the selected
polymer solution and dried with rotation under infrared
lamps. The dipping and drying steps are preferably
performed under low humidity conditions. After
dipping, the sac is annealed in a vacuum oven. The sac
is washed thoroughly in distilled water r solvent
extracted and dried in a vacuum oven.
Referring to FIGURE 8, the sac is fitted
within ring 144, and flexible sac portions are
attached, as with adhesives, to confronting ring lip
portions in the region of the ring slots 154, 15~. The
opposed circular walls in the sac are attached, by a
suitable adhesive or the like, to the circular plate
portion in the associated pusher plate. The flexing
zones of the sac which are not bonded to either the
pusher plate or the housing ring are coated with a
release agent.
Sac 114 in a relaxed, "as cast" condition, has
the general shape seen at the top in FIGURES 10 and 11.
In this condition, the circular walls and associated
sac flexible portions have the cross-sectional
curvature seen in dash-dot lines in FIGURE 8.
According to an important feature of the invention, the
pusher plates in the pump are placed at symmetrical,
initial deflection positions, seen in solid lines in
FIGURE 8, at which the circular walls have been moved
inwardly toward one another a distance indicated at
l;~Z~
~22-
Dl in the figure. ~n the particular pump embodiment
being described, Dl is preferably about 5.1 mm.
With plates 134, 136 in their initial
deflection positionsr the associated flexible wall
portions in the sac assume the form of
circumferentially uniform, outwardly convex rolls, each
having the bulged cross~sectional curvature seen in
solid lines in FIGURE 8. The rolls formed in wall
portions 122, 124 are denoted at 122', 12~',
respectively in FIGURE 8. It can be appreciated in
this figure that the radius of curvature of each roll
is substantially less than that of the flexible wall
when the sac is in its relaxed condition.
In operation, the two pusher plates are moved,
under the control of actuator 138, coordinately and at
desired displacement rates, inwardly toward one another
from their initial deflection positions ~oward
end-of-stroke positions which place the inner surfaces
of the interior of the sac at the positions indicated
by the two dashed lines 166 in FIGURE 8. The total
working stroke, or distance that each plate is moved,
is denoted D2 in FIGURES 8 and 11. In the particular
embodiment herein, D2 is about 6.4 mm.
Movement of the pusher plates from their
initial deflection positions inwardly is accommodated
by a smooth rolling action of the inner and outer
annular regions of each roll ayainst the lip portions
in the associated pusher plate and housing ring. The
sac-to-housing bond lines in the slot regions of the
housing ring, indicated at B in FIGURE 8, are located
at the point where the sac roll is tangential to the
associated housing ring lip portion at the
end-of-stroke position. According to an important
feature of the invention, and as can be appreciated
with reference to FIGURES 8, 10 and 11, each roll in
the sac remains circumferentially uniform and bulged in
-23 ~2~2901
cross-sectional curvature as the pusher plates are
moved inwardly from their initial deflection positions.
As noted above, the ports communicating the inlet and
outlet conduits with the sac annulus are formed
entirely within the portion of the sac attached to ring
144. Consequently, the flexing action in the sac
occurs substantially independently of, and without
effect on, the shape of the ports.
The pusher plates are moved back to their
initial deflection position either under the control of
the actuator, or passively by inflow of fluid, such as
from heart pumping. Sac expansion is accommodated by a
smooth, circumferentially uniform rolling action in the
sac rolls which characterizes movement of the two rolls
during sac contraction.
In flow visualiza~ion studies conducted with a
pump having clear pusher plates, it was observed that
during pump expansion, a circular flow pattern was
established which acted to evenly wash the interior
surfaces of the sac In particular,a portion of the
flow in the sac is directed back into the inflow
conduit to wash the inflow valve. The circular,
diastolic flow pattern was very well established and
existed until early systole. The improved washing in
the valve regions of the pump is due in part to the
fact that the inflow conduit is relatively short. The
fact that both conduits communicate with the sac
annulus through elongate ports whose widths and lengths
are substantially fixed during sac contraction and
expansion also promotes washing and tangential flow
between the conduit regions and the sac annulus.
Analysis of the stress characteristic in the
operating pump indicate that the pump design provides a
number of improved stress characteristics. Sac
stresses were found to be comparable to those in
earlier-developed pumps, particularly that described in
12X~90~
-24-
U. S. Patent No. 4,167,046. However, the stresses in
the instant pump are more repeatable and predictable
due to the fact that flexing occurs in a region of the
deformable sac defined by machined or molded
components, this region being itself formed on machined
surfaces in the mandrel.
Reduced tendency of the flexing zones to
crease is another important feature of the invention~
Generally, for a given sac thickness and pusher-plate
diameter, the factors which lead to crease formation
are long working strokes, and a large housing-to-pusher
plate separation. One advantage of the present
invention is that due to the predeflection of the
pusher plates, the total working stroke in the pump is
only about 60% of the total allowed deflection in the
sac. Studies on crease formation indicate that, at the
pusher plate-housing ring clearance selected, the
working stroke in the pump is at least about 10~ less
than that which can lead to creasing.
From the above, it can be seen how the present
invention provides improved operation and reliability
in a deformable sac type blood pump. The two annular
flexing zones in the pump are each circumferentially
uniform and defined by annular machined or molded
components to increase stability and circular flow
characteristics. The predeflection feature in the pump
functions to create a bulged annular roll in each of
the flexing zones, which can accommodate recurrent sac
wall movement by a smooth rolling action that minimizes
localized stressed and the tendency to crease over
extended operation.
The predeflection feature in the pump produces
two other significant advantages. First, the thickness
of the pump chamber structure, with such in a filled,
3'j start-of-stroke condition, is considerably reduced over
the tickness the structure would have with the sac in a
~25- 122Z90~
~ully expanded condition. The reduced thickness is two
time Dl, or about 10 mm in the particular pump
described herein. The advantage of the reduced pump
thickness in an implantable pump can be appreciated.
Secondly, a relatively small internal volume in the
pump chamber, at the end of stroke, can be achieved
with a relatively small total stroke. The small
internal volume promotes "flushing" of fluid from the
pump, thereby reducing the potential for thrombus
formation.
The problem of thrombus formation in the sac
is reduced both by the improved flow characteristics
which are observed during pump operation, and by the
features of the sac construction which promote washing
in the conduit regions of the sac. In this regard, the
elongate ports communicating ~he conduits with the
annulus in the sac and the relatively short inflow
valve are important.
While a preferred embodiment of the invention
has been described herein, it will be evident to those
skilled in the art that various changes and
modifications may be made without departing from the
spirit of the invention. In particular, the invention
also contemplates an asymetric chamber structure in
which pumping occurs through movement of a single wall,
where such movement is accommodated by the rolling
action of a circumferentially uniform bulged roll, as
described.
The invention also contemplates a sac which is
formed to have, in a relaxed, or unstressed, condition,
the general cross-sectional shape seen in solid lines
in FIGURE 8. That is, the sac, as cast, is formed to
have a pair of opposed recessed circular walls bordered
by a circumferentially uniform roll having a bulged
cross-sectional curvature. The sac may also be
constructed to have an annular side wall which is, by
1;~2~901
-26-
its construction, inherently rigid and therefore does
not re~uire external rigidifying structure, such as the
housing ring described.
From the foregoing, it can also be seen how
the advantageous features of the pump actuator
mechanism described in the above-mentioned U. S.
patents are improved upon. These advantages include
mechanical simplicity, and greater efficiency and
reliability inherent in the operation of a beam spring
acting between relatively less stressed and relatively
more stressed conditions and directly coupled to a
solenoid armature and a pusher plate acting on a
deformable sac.
The present invention provides additional
advantages which are not present in pump actuators
disclosed in the prior art. One important advantage is
that the unique armature construction, and in
particular, the slotted armature core in the actuator,
allows the armature to be operatively coupled to the
associated pusher plate by a single, relatively wide
main spring extending from the back of the armature
through the solenoid core slot to its point of
attachment on the pusher plate. A significant
advantage in the use of the single main spring is that
problems of matching the spring constant
characteristics of two or more springs working in
parallel are avoided, as are problems of nonuniform
changes in spring performance characteristics over
extended periods of pump use.
The actuator construction also allows for
greater compactness. In this regard, it is noted that
the placement of a portion of the main spring within
the solenoid core in the armature permits the main
spring to be disposed relatively close to the mirror
image plane in the actuator~ Further, the inward
curvature of the main spring and the preload springs in
12i~
-27-
the actuator act to reduce overall pump thickness.
Symmetry of pump design and operation largely
eliminates loads between the actuator and the pump
housing. The linkage mechanism insures that movement
of the armatures is symmetrical, particularly during
pump filling. Because the armatures operate in a
symmetrical manner, information about the position of
one armature can be used to provide accurate position
information as to both armatures.
While preferred embodiments of the invention
has been described herein, it will be appreciated by
those skilled in the art that various changes and
modifications can be made without departing from the
spirit of the invention.
