U.S. patent number 3,668,708 [Application Number 04/887,566] was granted by the patent office on 1972-06-13 for artificial heart.
This patent grant is currently assigned to North American Rockwell Corporation. Invention is credited to James A. Tindal.
United States Patent |
3,668,708 |
Tindal |
June 13, 1972 |
ARTIFICIAL HEART
Abstract
An artificial heart has a number of flat structural members
arranged circumferentially about a central support. An inner layer
of material confines blood to chambers of the artificial heart and
an outer layer of material, which fully encloses the flat
structural members, defines cavities between the inner layer of
material and the outer layer. Fluid is pumped into the cavities for
expanding the structural members to cause heart pumping action in
response to measured values of preselected blood chemistry
parameters. The structural members contact to their original
positions to complete the pumping action.
Inventors: |
Tindal; James A. (Gardena,
CA) |
Assignee: |
North American Rockwell
Corporation (N/A)
|
Family
ID: |
25391410 |
Appl.
No.: |
04/887,566 |
Filed: |
December 23, 1969 |
Current U.S.
Class: |
623/3.21;
417/389; 417/394 |
Current CPC
Class: |
A61M
1/361 (20140204); A61M 60/268 (20210101); A61M
60/435 (20210101); A61M 60/148 (20210101); A61M
2205/33 (20130101); A61M 60/896 (20210101); A61M
60/50 (20210101); A61M 60/40 (20210101); A61M
60/122 (20210101); A61M 2205/3303 (20130101) |
Current International
Class: |
A61M
1/10 (20060101); A61M 1/36 (20060101); A61M
1/12 (20060101); A61f 001/24 () |
Field of
Search: |
;3/1,DIG.2 ;128/1,214
;417/389,394 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
"Air-Driven Artificial Hearts Inside the Chest," by W. Seidel et
al., Transactions of the Amer. Society of Artificial Internal
Organs, Vol. 7, 1961, pages 378-385. .
"Development of an Artificial Intrathoracic Heart" by C. K. Kirby
et al., Surgery, Vol. 56, No. 4, Oct. 1964, pages 719-729.
|
Primary Examiner: Truluck; Dalton L.
Assistant Examiner: Frinks; Ronald L.
Claims
What is claimed is:
1. An artificial heart comprising a central support,
resiliently flexible flat structural members disposed around said
central support, an inner layer of flexible elastic material
supported between said flexible flat structural members and said
central support, said inner layer forming a first cavity for said
artificial heart, said cavity being divided into a plurality of
heart chambers,
inlet and outlet valve means communicating with the chambers of
said heart cavity,
outer layer of flexible elastic material encapsulating the flexible
flat structural members, connecting means between said inner and
outer layers,
a plurality of second cavities formed between said inner and outer
layers for selectively receiving and discharging a pressure
imparting fluid for flexing said flat structural members outwardly
and inwardly whereby blood is enabled to flow through said
artificial heart via said valve means and heart cavity in response
to outward and inward flexing of said outer layer
2. The artificial heart according to claim 1 wherein said flexible
flat structural members comprise leaf springs arranged
circumferentially about said central support.
3. The artificial heart of claim 1 wherein said outer layer is
composed of strips of flexible, elastic material cross-laced
perpendicularly and obliquely to each other and bonded to form a
laminate.
4. The artificial heart recited in claim 1 including a plurality of
first cavity partitioning means forming said chambers inside said
heart cavity, and
drive means for forcing fluid into a selected second cavity for
applying pressure to said flexible flat structural members whereby
aid chamber is expanded.
5. The artificial heart recited in claim 1 wherein said connecting
means comprises a layer of material interconnecting said inner and
outer layers of material for maintaining a spaced relationship
between said inner and outer layers of material when fluid is
received by said cavities between said inner and outer layers.
6. The artificial heart recited in claim 5 wherein said partition
means form four chambers inside said first cavity and further
comprising:
first valve means for permitting the flow of blood into two of said
four chambers;
second valve means for permitting the flow of blood from said two
of said four chambers into the remaining two of said four chambers,
and
third valve means for permitting the flow of blood from said
remaining two of said four chambers.
7. A device for simulating a natural heart comprising:
inner and outer flexible elastic coverings substantially closed on
themselves, said coverings defining a cavity therebetween,
connecting means between said inner and outer coverings;
at least two strips of resiliently flexible material attached to
one of said coverings;
prime mover means for causing a fluid to flow into said cavity
between said inner and outer covering;
partition means internal to and integral with said inner coverings,
said partition means defining at least two cavities internal to
said inner covering inlet and outlet valve means communicating with
said internal cavities whereby blood can flow through said internal
cavities; and
sensing and control means for driving said prime mover means in a
manner substantially similar to the rate of a natural heart.
8. The device according to claim 7 and further comprising power
system means, said power system providing driving power to said
sensing and control means.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention pertains to an artificial heart and more
specifically to an artificial heart having enclosed structural
members circumferentially disposed around heart blood chambers for
simulating natural heart pumping action when expanded by a
fluid.
2. BACKGROUND OF THE INVENTION
Much effort has been recently devoted in the medical fields to
implantation devices. Particular interest has developed concerning
implantation of portions of a natural heart or implantation of a
complete natural heart. It is well known that several implantation
operations have been performed using human hearts, and that several
transplantations have been performed using artificial heart valves
or other portions of an artificial heart.
Transplantations of hearts and heart devices can be broadly
categorized into two types. One type concerns transplantation of
hearts from other humans or animals into a living being. In this
particular field of medical practice there have been transplants
with full hearts of deceased humans into the chest of living
persons as well as transplanation of, for instance, the valves from
a heart of a pig into a living person.
Another broad categorization can be made with respect to use of
natural or artificial heart valves and devices. Into this category
falls implantations of artificially manufactured heart valves;
certain types of pacemakers, and devices that simulate arteries,
veins and heart wall structures.
A broad form of categorization for heart implantation devices can
also be made with respect to whether or not the implanted device is
designed to accurately mimic the performance of a natural device or
whether the device is to merely perform the same heart function
without necessarily mimicking a natural device. For instance, a
pacemaker may be simply a fixed pulsation device operating with
response to body demands. A fixed period pacemaker is not designed
to accurately mimic a natural heart since a natural heart responds
to various parameters of the body. Similarly, a heart device that
merely functions as a blood pump without regard to blood volume and
pressure demands could be classified as a non-mimicking device.
Many of the artificially designed heart valves do, however, strive
to accurately mimic the performance of a natural heart valve. Such
valves are designed to close and open at prespecified pressures and
to allow predetermined amounts of flow through a given channel.
Optimum success with any implanted device when considered from a
functional point of view (that is, without regard to rejection and
other nonfunctional problems) is when such device accurately mimics
the operation of the natural device. The best practical
manufactured device could be classified, as noted above, as an
artificial mimicking device. It is within this category that the
instant invention can be placed. The instant device will serve as a
completely responsive self-sufficient implantable heart that
contains all necessary functional elements to duplicate the
physiological functions of a natural heart process in addition to
merely serving as a heart pump.
SUMMARY OF THE INVENTION
The major structure of the present invention comprises a number of
resiliently flexible flat structural members disposed around a
central support. The flexible flat structural members are attached
to the central support and define the basic form of the artificial
heart. An inner layer of flexible, elastic material is supported
between the flexible structural member and the central support. The
inner laver forms the basic cavity of the artificial heart and may
be divided into a number of chambers, such as two or four.
An outer laver of flexible elastic material encapsulates the
flexible structural members. The outer layer is comprised of strips
of elastic material that are cross-laced to simulate the muscle
structure that surrounds a natural heart. Various ones of the outer
layers are crisscrossed in the horizontal, vertical and oblique
directions to form a single laminate laver of interlacing flexible
strips.
The outer layer and the inner layer define a number of cavities
between them. The number of cavities is the same as the number of
chambers of the heart. The cavities are outside the chambers and
conform to the external surface of the heart chambers. As fluid
flows to and from the cavities the heart chambers sequentially
expand and contract.
The central support tube houses a pump, working fluid, control
equipment and fluid flow ports. The pump causes the working fluid
to flow in the cavity between the inner and outer layers of the
artificial heart.
Flow of working fluid in a preselected manner to various cavities
of the artificial heart causes pumping action similar to that of a
natural heart. The fluid causes expansion of the heart chambers and
the natural contraction of the flexible outer layer and flexible
structural members causes contraction of the chambers. Sequentially
causing the expansion and contraction to the various heart chambers
results in heart pumping action.
Physiological sensors located in the blood flow stream returning
from the body and from the lungs sense body chemistry parameters.
The sensor through appropriate circuitry drive the pump that
regulates the pumping rate of the artificial heart.
It is therefore an object of this invention to provide an
artificial heart.
It is another object of this invention to provide an artificial
heart that fully simulates the physiological functions of a natural
heart.
It is yet another object of this invention to provide an artificial
heart that requires power only in the expansion stroke of the
artificial heart.
It is still another object of this invention to provide an
artificial heart that responds to sensed parameter changes of
measured values in the blood.
Another object of this invention is to provide an artificial heart
comprising a number of flexible structural members arranged around
a central support member.
Additional object of this invention is to provide an artificial
heart with an outer layer that closely approximates muscle action
of a natural heart.
These and other objects of the invention will become more apparent
from the description of the drawings, a brief description of which
follows:
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a cutaway view showing the basic components of the
artificial heart of the present invention.
FIG. 2 is a cutaway drawing showing one embodiment of the
orientation of the longitudinal, horizontal and oblique outer
"muscle" fiber layers.
FIG. 3a and 3b is a cross-sectional view of the inner and outer
wall structure of the artificial heart in expanded and contracted
positions respectively.
FIG. 4a and 4b show the internal wall structure of the artificial
heart that divides the heart into four chambers in expanded and
contracted positions respectively.
FIG. 5 shows the central support structure housing a hydraulic pump
for moving the working fluid to and from cavities around the inner
layer of the artificial heart.
FIG. 6 is a cross-sectional view of one embodiment of a heart
expansion pump.
FIG. 7 is one embodiment of a valve that would be suitable for use
between an atrium and a ventricle chamber.
FIG. 8a shows one embodiment in cross-section of a valve that is
suitable for permitting one way passage of blood between the
artificial heart and the systemic circulation system.
FIG. 8b is a cross-sectional view cut in the plane of the diameter
of the valve of FIG. 8a.
FIGS. 9a through 9h depicts a four chamber artificial heart of the
instant invention during a normal cycle of operation.
FIG. 10 shows an embodiment of an artificial heart having two
chambers.
FIG. 11a through 11d diagrammatically represents the two chamber
heart of the instant invention during a complete pumping
sequence.
FIG. 12 shows the functional relationship of the blood chemistry
sensor system.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to FIG. 1 there is shown a cutaway sectional view of the
artificial heart 10 of the instant invention. The primary structure
consists of a central tube 30 to which is affixed a number of
shaped structural members 11. The structural members 11 are
connected to both ends of a central tube 30. Each structural member
11, usually leaf springs, may be made of machinable metal, plastic,
or other material that exhibits lead spring characteristics. The
strips are shown as flat of substantially rectangular
cross-section, however, a particular cross-sectional configuration
is not mandatory. Articulated joint 12 couples the upper and lower
strip sections to form a continuous strip that extend the full
length of the artificial heart 10. A continuous strip with a
suitable machine junction would also serve well as an articulated
junction. As will be described later for a two chamber artificial
heart, an articulated structural member may be eliminated. The
structural members 11 extend fully around the central tube 30 and
form the principal structure and define the shape of the artificial
heart. The structural members 11 may be quite close together or
somewhat separated. FIG. 1 shows the members somewhat separated so
that the cross-section of the layers is clearer. Furthermore, any
convenient number of structural members may be used.
The flat structural strips or springs are preshaped and connected
to provide the expansion and contraction limits of the heart.
One-half of the lower springs carry one-fifth of the tension or
temper of the other half of the lower springs. The weaker springs
are grouped on one side of the central tube 30 while the stronger
springs are grouped on the opposite side of the device. This
compares to a human heart and approximates the requirements for
simulating the natural functions of the heart. As is well known,
the pressures realized in the left ventricle of a natural heart
exceeds by several times the pressures realized in the right
ventricle (See Cardiac Diagnosis, Noble O. Fowler, M.D., published
by Hoeber Medical Division of Harper and Row Inc., copyright 1968,
at page 16)
The difference in the tension of the two sides of the artificial
heart also insures a necessary pressure differential between the
two halves of the heart when it is in operation.
Besides tension variations in the lower portion of the structural
members 11, the upper structural members of both sides are about
one-tenth as strong as the lower structural members. This also
approximates the relationship between the atriums of the heart and
the respective ventricles of the heart. The upper sections operate
the receiving chamber while the lower sections operate as blood
distribution chambers as will be more fully described in FIGS. 9a
through 9h. Internal structuring of the compartments of the heart
are shown more fully in FIG. 4.
The flexible structural members 11 are surrounded by layers
comprising the outer covEr 20. Outer layer 20 is preferably
comprised of fiberous elastic substance which is laminated to form
a three layer laminate. Many types of material are suitable for
application as "muscle" material, the major requirement being the
elasticity and response of the material. The material must also be
inert and possess properties approximately equivalent to a natural
heart. A material such as crepe latex possesses many of these
properties.
The laminated layers are the equivalent of natural heart muscles
and achieve similar functions. One layer 17 has fibers running
longitudinal to the heart 10, one layer 18 has fibers running
obliquely to the heart 10, and one layer 19 has fibers running
transversely to the heart 10. It is substantially a matter of
choice in what order the transverse, longitudinal and oblique
layers occur in relationship to the outer layer. They form a
laminated layer and perform as an integrated sheet of material.
Thus calling layer 17 the longitudinal layer is merely for
convenience and layer 17 might well be either the transverse or
oblique layer.
The structural members 11 are fully enclosed in the outer layer
comprised by layers 17, 18 and 19. The structural members could
occur between layers 19 and 18 or between layers 17 and 18 with
little matter being dependent on the particular position selected.
The structural members 11 could merely be attached to the innermost
surface of outer layer 20 without even being embedded in layer 20
if so desired.
A final layer 21 completely encloses the entire artificial heart
and is laminated or otherwise bonded to the outermost "muscle"
fiber layer 19. Layer 21 is not required if layer 19 provides
adequate covering for the heart as well as serving as a fibrous
"muscle" layer.
An inner layer 15, also made of fibrous elastic substance exists
interior to the structural members 11 and outer layer 20. The inner
layer 15 is separated from the laminated outer layer and a cavity
22 exists between these layers 15 and 20. The cavity 22 will
increase and decrease during normal operation of the heart as will
be more fully described later.
Connection means 16 exists between the inner layer 15 and the outer
laminated layer 20 so that on expansion of the heart proper
relationship is maintained between these two layers. The connection
means 16 is preferably a thin ribbon or string of inert material
interwoven between the inner and outer layers. This material must
be inert and should occupy small volume compared to the total
volume of the cavity 22. This insures that little resistance to a
flow stream will occur and that flow will be rapid with good
circulation throughout the cavity during operation of the
heart.
FIG. 2 shows one embodiment of the longitudinal, oblique and
transverse layers as comprise that portion of the outer layer of
the artificial heart which simulates the muscle functions of the
natural heart. Longitudinal layer 17, oblique layer 18, and
transverse layer 19 are laminated to form a single structural
member that contains the structural member strips 11 as discussed
in FIG. 1. The order of the longitudinal, oblique and transverse
layers is immaterial so long as the resulting laminated layer
approximates the muscle action of the heart.
The particular embodiment of FIG. 2 shows each layer being
comprised of many strips of elastic material wound around the
heart. This is somewhat different in construction from the single
layer per orientation representation of FIG. 1. In operation,
however, both composite layers perform in the same manner. The
composite outer layer will continue to be represented as in FIG. 1
because of the simplicity achieved in making cross-sections of the
outer layer.
FIG. 3 is a cross-sectional view of the inner wall 15 and the outer
wall 20 of the artificial heart of the instant invention. FIG. 3a
shows the cross-section of the heart wall when the heart is in an
expanded condition with the cavity 22 expanded. FIG. 3b shows the
walls with the heart in a contracted state. The operation
concerning wall expansion and heart action is fully described in
FIG. 9. The purpose of FIG. 3 at this juncture is to clearly
illustrate all the components of the heart.
The layers depicted in FIGS. 3a and 3b are identical to the layers
described for FIG. 1. The outer wall 20 is comprised of outer layer
21, laminated "muscle" layers 17, 18, and 19, wall restraining
material 16 and inner layer 15. Structural members 11 are shown
embedded between laminate layers 18 and 19. As has been noted the
structural members 11 could just as well be between laminate layers
17 and 18 or fully enclosed in either one of the other layers.
The cavity 22 is greatly compressed when the heart is in the
relaxed condition of FIG. 3b and greatly expanded in FIG. 3a where
the contiguous heart chamber is expanded. The cross-sectional
representation of FIG. 3a and 3b is identical for all wall areas of
the artificial heart except where the union of the inner and outer
wall occurs. Each chamber of the heart functions in a similar
manner and is comprised of the same layers of material.
FIGS. 4a and 4b show the internal wall structure that divides the
artificial heart into four chambers. The internal wall structure is
integral with and attached to the inner wall structure 15 described
in FIGS. 1 and 3. Suitable valve means exists between each chamber
and will be more fully discussed in FIGS. 7, 8a and 8b.
FIG. 4a shows the inner chamber walls when the chambers are
expanded while 4b shows the inner chamber walls when the heart is
relaxed. Note how walls 42 and 44 flex to tolerate the expansion
and contraction of the heart. Walls 42 and 44 are more concave in
the relaxed condition than in the expanded condition.
The chamber wall structures surround central support tube 30 and
are attached to the support tube 30. Chamber walls 41, 42, 43, and
44 respectively divide the heart into four chambers, two atrium and
two ventricle chambers by junctioning with the inner surface of the
inner wall 15. Structural support strips 45 and 45b are embedded in
the material that serves to make up the chamber walls. Structural
strips 45a and 45b may be made of any suitable material that will
generally maintain structure rigidity along the major axis of the
structural member.
Structural strips 45a that exist in chamber walls 41 and 43 are
strong enough to prevent deformation to any significant degree of
these chamber walls. The structural strips that are in chamber
walls 42 and 44 are not as rigid as the structural strips 41 and
43.
The structural support strips 45a and 45b may be made of metal,
plastic, or other suitable material. The wall material comprising
the chamber walls might be made of a material similar to the
cross-laced laminate comprising the outer wall 20 of the heart. Of
course such material must be medicinally sterile, must not interact
with blood, must be somewhat elastic, and must be able to be joined
with the inner wall to form a tight seal.
Although the FIG. 4a and 4b show two structural support members in
each of the horizontal and lateral chamber walls, the number of
structural support members for any given design is a matter of
discretion. It is important, however, that the structural support
members 45a in the longitudinal walls provide rigidity to those
walls since, as discussed earlier, there is a five to one pressure
differential between the two sides of the heart. Such a pressure
differential is the same differential that is encountered in a
natural heart. The longitudinal support members 45a are placed in
the manner indicated so as to offer no resistance to the expansion
and contraction strokes of a heart while providing longitudinal
stability.
The structural support members 45b in the lateral walls are
preshaped so that they cause the lateral walls to be slightly
depressed into the ventricles. As can be seen in FIG. 4b the the
lateral walls 42 and 44 are deeply depressed into the ventricles in
the fully compressed condition.
The lateral wall structural members 45b offer resistance to the
expansion of the heart chambers and must be carefully designed to
approximate the actual resistance encountered in a natural heart.
In consideration for overall design of strength members comprising
the artificial heart a force balance must be achieved between the
lateral chamber members 42 and 44, the outer layer 20, and the
structural support members 11. In actual design the total strength
of the structural support members 11 (see FIGS. 1 and 2) in
conjunction with the outer wall structure 20 must be very carefully
balanced mechanically against the prime mover means. As will be
more fully discussed later, fluid is caused to flow in the cavity
22 (shown in FIGS. 3a and 3b) between the inner layer 15 and the
outer layer 20. As hydraulic fluid flows in cavity 22 force
differential is established that causes the structural support
members 11 and the heart walls to become more concave. The
increased concavity causes expansion of the heart chambers. Minimum
power is expanded in causing this expansion stroke if the forced
balance between the combined outer layer 20 and the structural
support members 11 and the lateral structural members 45b is such
that the effort required to move one against the other is small.
Under such a design condition the prime mover output need be
sufficient to merely exceed the force difference to expand the
unit.
Each inner chamber of the artificial heart has a corresponding
cavity outside it. The cavity defined between the inner and outer
layers of the heart is partitioned to correspond to the inner
chambers. No communication of hydraulic fluid is permitted between
the respective cavities.
To keep some sort of consistency in discussing the various cavities
and chambers of the artificial heart, chamber refers to a volume
normally containing blood, i.e. an atrium or ventricle. Cavity is
used to designate the spaces between the inner wall and the outer
wall of the heart. The cavities contain the hydraulic fluid that
actuates the heart chambers.
To summarize briefly then one embodiment of the artificial heart of
the instant invention comprises a four chambered device. The four
chambers approximate the right and left atriums and right and left
ventricles of the natural heart. The primary structure comprises an
inner layer and an outer layer wherein the inner and outer layers
define a cavity between them. The outer layer comprises a laminate
of plastic material that simulates the muscle structure of the
natural heart as well as flat structural members that provide
structural definition and support for the artificial heart. A
hydraulic fluid, preferably other than blood, is caused to flow in
the cavity between the inner and outer layers of the artificial
heart. Blood is undesirable as a hydraulic fluid because of its
poor resistance to damage under varying pressures and flows. This
flow of fluid under pressure causes a change in volume of
respective heart chambers. Releasing pressure of the hydraulic
fluid between the cavities causes the cavity to contract and
thereby forces the fluid from the cavity. The contraction stroke is
a result of natural contraction of the outer "muscle" structure
layer of the artificial heart. The blood pumped by the heart comes
in contact only with the inner layer of the primary heart structure
and the inner chamber walls. No blood comes in contact with the
outer layer of the heart, with the flat structural members, or with
the cavity defined between the inner and outer layers. Thus the
chambers of the heart accommodate blood, while the hydraulic
cavities accommodate only hydraulic fluid.
FIG. 5 represents the devices contained in the central tube 30 (see
FIG. 1) of the artificial heart. Sufficient preliminary structure
has been discussed that consideration may now be given to pump
requirements and actual pumping operation of the heart.
FIG. 5 is a schematic representation of components enclosed within
central tube 30. The components enclosed in central tube 30 provide
control means, power supply, and hydraulic fluid for operation of
the artificial heart.
Heart expansion pump 60 provides fluid under pressure to the
various cavities defined by inner and outer layers of the
artificial heart. Fluid under pressure is provided to the cavity
outside each heart chamber. Four hydraulic fluid cavities exist
between the inner and outer layers of the four chambered artificial
heart, one around each of the four inner chambers. Hydraulic fluid
paths 80, 81, 82, and 83 lead respectively to the left and right
atrium and left and right ventricle of the artificial heart.
Blood chemistry sensor system 100 receives inputs from blood
returning from general body circulation and blood returning from
circulation around the lungs. Preselected parameters of blood are
sampled at the sensor sample points and computer interrogated to
determine proper heart rate based on sensed values of the
parameters. The output from the blood chemistry sensor system 100
is fed to drive control 95. Drive control 95 provides a driving
positional command to rotary valve 90. Rotary valve 90 ports
working fluid under pressure from hydraulic power supply 96 to
opposite sides of a double action piston in heart expansion pump
60. The details concerning the heart expansion pump are described
more fully with reference to FIG. 6.
Drive control 95 provides the positional control for rotary valve
90, the commands of which set the heart rate of the artificial
heart. The logic connected to drive control 95 is contained in
blood chemistry sensor system 100 as shown in FIG. 12.
Drive control 95, in one preferred embodiment, is merely a
flip-flop circuit whose change in electrical sense causes a change
in the position of rotary valve 90. In such an arrangement, rotary
valve 90 would be responsive to electrical signals.
A mechanical actuation of rotary valve 90 could also be provided by
drive control 95. A mechanical linkage between drive control 95 and
rotary valve 90 could be positionally controlled by electrical
signals from blood chemistry sensor system 100. The linkage could
comprise a link pivoted to the periphery of a variable speed,
continuously rotating disc in drive control 95. The other end of
the link could be pivoted to a pin on rotary valve 90. The design
of the linkage could convert the full rotational motion of drive
control 95 to 90.degree. arc motion of a familiar and standard
rotary valve 90.
Naturally many embodiments of drive controls exist and the above
discussions of one embodiment of electrical and one embodiment of
mechanical controls are merely illustrative of two.
Hydraulic power supply 96 provides working fluid under pressures to
the heart expansion pump 60. Hydraulic lines 91 and 92 lead to
rotary valve 90. From rotary valve 90 hydraulic fluid under
pressure travels via path 78 or 79 to the heart expansion pump.
When either of paths 78 or 79 is porting hydraulic fluid under
pressure, the other path is porting return fluid from the heart
expansion pump 60.
FIG. 6 is a cross-sectional view of the detail of one embodiment of
the heart expansion pump 60.
The heart expansion pump 60 is contained in the center support
means 30 of the artificial heart. Casing 61 contains a power piston
that is slidably mounted interior to the casing 61. Structural
member 62 divides the heart expansion pump into two distinct and
fluid isolated sections 63 and 64. The power piston is of the
double acting variety and has two piston flanges 66 and 67 mounted
to a central shaft 65.
The shaft 65 of power piston passes through the structural member
62. Sliding contact is maintained between the shaft 65 and
structural 62. Sliding contacts is also maintained between the
piston surfaces 66 and 67 and the inner surfaces of casing 61.
The upper chamber 63 of heart expansion pump 60 contains 74 and 75
for hydraulic fluid entry and exit to either side of the piston
66.
Hydraulic fluid under pressure is delivered by hydraulic power
supply 96 (see FIG. 5) by lines 91 and 92 to rotary control valve
90. The labeling of line 91 as "from hydraulic power supply" is for
convenience because either of 91 or 92 could serve as a source or
return line. The positioning of rotary control valve 90 will
deliver hydraulic fluid under pressure to either side of power
piston flange 66 in hydraulic cavity 63. Proper positioning of
rotary control valve 90 is provided by drive control 95. Thus as
hydraulic fluid under pressure is ported through orifice 74 to the
upper side of power piston flange 66 the piston is caused to move
down and hydraulic fluid is vented through orifice 75, The porting
of hydraulic fluid under pressure through orifice 75 to the
underside of piston flange 66 causes the piston to rise in cavity
63. Venting of hydraulic fluid would then occur through orifice
74.
The lower cavity 64 of heart expansion pump 60 is the fluid cavity
that contains fluid for heart actuation. The response of piston
flange 67 is naturally a function of the positional relationship of
piston flange 66.
Check valve 68 in piston flange 67 allows heart actuation fluid to
port through the check valve when the piston is returning to a
position adjacent structure 62. Fluid entry and exit ports 70, 71,
72, and 73 provide for passage of fluid from cavity 64 to the
respective heart chambers and return therefrom.
In operation descent of power piston flange 66 forces the lower
piston flange 67 to descend. Hydraulic fluid is forced through
orifices 70, 71, 72 and 73 to the appropriate heart cavities. The
amount of fluid that flows to each cavity is a function of the
positional relationship of the orifices 70, 71, 72, and 73 along
the casing 61 and the resistance of the respective walls of the
heart to deformation. Fluid will naturally start to flow earliest
into chamber cavities that offer the least resistance to
deformation and therefore to flow to the fluid. Thus the balance
previously discussed between the strength of the flat structural
members 11 (see FIG. 1) and the inner 15 and outer layer 21 of the
artificial heart is once more apparent.
As piston flange 67 descends in cavity 64, fluid is ported first
through cavity 70 to the right atrium of the artificial heart.
Lower volumes of flow also starts in each of the other chambers
through ports 71, 72, and 73 but flow through them is quite slight,
again because of structural design. As the piston flange 67 passes
orifice 70 sufficient fluid has ported through left orifice 70 to
fill the cavity around the right atrium and causes the right atrium
chamber to fully expand. As piston flange 67 further descends,
fluid is allowed to return behind piston 67 from orifice 70 while
fluid continues to flow through orifices 71, 72, and 73. The cavity
around the left atrium of the artificial heart is filled with
hydraulic fluid as piston flange 67 approaches orifice 71.
Similarly as piston flange 67 continues to descend towards the
bottom of cavity 64 the cavity around the right ventricle is filled
through orifice 72 and finally the cavity around the left ventricle
is filled through orifice 73. The sequencing of filling and
draining the heart chambers will be more fully described in
discussions concerning FIG. 9.
The porting of hydraulic fluid under pressure to the bottom surface
of piston flange 66 in the chamber 63 caused both piston flange 66
and piston flange 67 to return to the top of their respective
chambers. Check valve 68 allows the passage of hydraulic fluid
through piston flange 67 with minimum resistance so that expansion
of heart chambers does not occur during the return stroke.
FIG. 7 shows one form of valve that would be appropriate for
porting bLood from an atrium chamber to a ventricle chamber in the
artificial heart. Lateral chamber wall 44 is severed to form flap
120. The size of flap 120, and thus the opening through lateral
chamber wall 44, is a function of heart volume blood flow
requirements based on pressure differentials between the atrium and
the ventricle. Naturally the size of the passageway when flap 120
is open could not be large enough to cause substantial strength
loss to lateral chamber wall 44.
A hinge reinforcing member 123 is implanted in lateral chamber wall
44 at a point where flap 120 will hinge to lateral chamber wall 44.
The strength member 123 will allow for proper flexing of flap
120.
Sealing surface exists between flap 120 and the lateral chamber
wall 44 at faces 121 and 122. The design of flap 120 will be such
that when no pressure differential exists across lateral chamber
wall 44 positive sealing of flap 120 will occur. Of course, no
blood flow from the atrium to the ventricle will occur when flap
120 is shut.
FIG. 8a describes a valve that is appropriate for allowing one way
flow of blood into the circulatory system and from a ventricle of
the artificial heart. Tubular channel 130 is fixedly attached to
outer layer 20 of the artificial heart. Mounted to the inner
surface of channel 130 are flaps 131 and 132. Flaps 131 and 132 are
flexibly mounted to channel 130 such that as a pressure
differential exists across the length of flaps 131 and 132, the
flaps open and allow fluid to pass. Once the pressure differential
along the lengths of 131 and 132 subsides, flaps 131 and 132 close
shutting off all flow.
FIG. 8b is a cross-sectional view of the valve of 8a in an open
position. The dashed lines superimpose position of the flap 131 and
132 when closed.
The valves described in FIGS. 7, 8a, and 8b are merely
representative of possible valves for the described application. Of
course there are many types of valves and many new designs of heart
valves that would serve as well as those indicated in FIGS. 7, 8a
and 8b.
FIG. 9 shows the sequential operation of a four chamber artificial
heart of the instant invention through a complete cycle of
operation.
In FIG. 9a all chambers of the heart are devoid of blood. The
cavities defined by the inner and outer layers are also devoid of
any hydraulic fluid. Piston 67 is also at top position and ready to
commence a downward stroke. The hydraulic chamber 64 contains the
hydraulic fluid for actuation of the heart chambers. Chamber 64 is
shown as occupying the entire lower half of central support 30 for
clarity and convenience only. The actual fluid chamber may actually
be much smaller.
As piston 67 starts to descend, hydraulic fluid flows through tube
80 to cavity 26 between the inner and outer layers of the right
atrium. Slight amounts of hydraulic fluid also start to flow in
each of the other chamber cavities 27, 28, and 29. As the hydraulic
fluid enters cavity 26 the right atrium expands causing an intake
of blood through valve 145.
In FIG. 9b the piston 67 has descended further and the right atrium
is approximately half full of blood due to expansion. The piston 67
has not yet cut off hydraulic flow up to cavity 26.
Referring now to FIG. 9c, when piston 67 passes orifice 70 the flow
of hydraulic fluid to the right atrium cavity 26 is secured and
flow to the cavity 27 of the left atrium has caused the left atrium
to fill to approximately one-half full of blood. The flow of fluid
through orifice 71 into the cavity 27 of the left atrium causes the
left atrium to expand and an intake of blood into the left atrium
through valve 146.
It can be seen that in FIG. 9d as piston 67 continues towards the
bottom of the heart expansion pump chamber 64, flow is cut off to
the left atrium cavity 27 and flow increases to the right ventricle
cavity 28. As piston 67 fully passes orifice 70, hydraulic fluid
under pressure from the natural contraction of the outer layer 20
of the right ventricle starts to return through orifice 70 behind
piston 67. This return of the hydraulic fluid and the natural
compression of the right atrium forces blood from the right atrium
to the right ventricle through valve 141. The flow of blood from
the right atrium to the right ventricle is, of course, assisted by
the expansion of the left ventricle under action of hydraulic fluid
from orifice 72 flowing into cavity 28. The left atrium has
continued to expand and fill with blood during this period. In FIG.
9d the right atrium and right ventricle are approximately one-half
full while the left ventricle is full.
Flow to the right ventricle is stopped when continued descent of
piston 67 cuts off orifice 72 as shown by FIG. 9e. By the time this
occurs, the right atrium has fully relaxed and emptied the blood of
the right atrium to the right ventricle through valve 141. The
expansion of the left ventricle is also approximately one-half
completed at this point and blood is flowing from the left atrium
to the left ventricle through valve 142. The flow of blood from the
left atrium to the left ventricle is under the influence of two
factors, the natural compression of the left atrium and the
expansion of the left ventricle.
In FIG. 9f when the piston 67 is at the bottom of the stroke all
fluid has been discharged into the respective cavities 26, 27, 28
and 29. The right ventricle is emptying its hydraulic fluid behind
piston 67 and blood from the right ventricle is flowing through
valve 143 under natural action of compression of the right
ventricle. The left ventricle is full of blood as well as the left
ventricle cavity 29 being full of hydraulic fluid.
Actuation of a rotary valve 90 (see FIG. 6) causes hydraulic fluid
pressure to flow on the lower side of piston flange 66 causing
piston 67 to rise in the casing of heart expansion pump 60. The
check valve in piston 67 allows for passage of the hydraulic fluid
through the piston as it returns to the top of the chamber.
Referring to FIG. 9g, as the piston 67 returns to the top of the
hydraulic chamber 64, the left ventricle compresses under natural
contraction of outer layer 20 forcing blood to flow from the left
ventricle to the body through valve 144.
In FIG. 9h the heart is in its normal condition with all chambers
and cavities devoid of fluid preparatory to starting a new
artificial heart cycle.
It is to be clearly understood that FIGS. 9a through 9h are
schematic only and do not represent proportional area and volumes
between the heart chambers and cavities. Further, no attempt has
been made to scale the relationship of a full chamber to an empty
chamber in the artificial heart.
FIG. 10 shows an artificial heart of the present invention that has
two chambers rather than four. A two chambered heart of the present
invention is completely feasible and operable with the same
efficiencies as a four chambered heart. The difference between the
two chambered heart and the four chambered heart is that the
pressure and flow outputs produced by a two chambered heart
substantially varies from that of a natural heart. However, the two
chambered heart fully performs and meets the physiological
requirements of a human. The four chambered heart, of course, is
designed to produce output characteristics identical to a natural
heart.
The two chambered heart 200 has an outer layer 220 that is
substantially identical to the outer layer of the four chambered
heart previously described (see FIGS. 1, 2, and 3). The outer layer
has an outer covering 206. Elastic material layers in the
longitudinal, transverse and oblique directions comprise layers
203, 204, and 205 as described for the four chambered heart and as
shown in FIG. 2. As was noted in the description of the outer layer
for the four chambered heart the ordering of the laminated layers
is generally not too critical.
Structural support members 208 are shown laminated between layers
205 and 204. The structural support member 208 does not have an
articulated joint as was necessary for the structural support 11 of
the four chambered heart. The structural support members 11 and 208
are otherwise similar in design and function.
Inner layer 202 is connected to the first material layer 203 of the
outer layer by membranes 207. Membranes 207 insure that the
relative position of the inner and outer layers is properly
maintained during expansion and contraction of the cavity. The
cavity defined by inner layer 202 and the inner surface of the
first material layer 203 is for the passage of hydraulic fluid in
much the same manner as was the passages for the four chambered
heart.
The left and right chambers of the two chambered heart are
identical except that strength differences might be incorporated
into each chamber through design of the support members 208 and the
inner and outer layers. That is to say, the volumetric output of
the left chamber under proper pressure would be so as to
approximate the volumetric output at the pressure of the left
ventricle of a natural heart and the right chamber would
approximate the output at the pressure of the right ventricle of a
natural heart.
Valves 209 and 210 provide for one way blood flow input to the
chambers of the artificial heart and valves 210 and 212 provide for
one way blood flow out of the chambers of the artificial heart.
FIGS. 11a through 11d schematically represents a pumping cycle for
a two chambered heart. The heart actuation fluid pump would be
identical to the pump and system described in FIG. 5 and FIG. 6 for
the four chambered heart except that few fluid ports and tubes are
required.
In FIG. 11a, piston 225 (which is double acting as described in
FIG. 6) is at the top of the stroke with both the cavities and the
heart chambers devoid of fluids. As piston 225 descends central
tube 201, hydraulic fluid is ported through tubes 226 and 227 to
heart chamber cavities 240 and 243 respectively. The strength
designs of the respective cavities once again provides for proper
flow of fluid to the respective chambers. Referring to FIG. 11b,
fluid flows substantially at first through line 226 to cavity 240
with slight flow through line 227. The flow of fluid through cavity
240 causes expansion of chamber 241 allowing blood to enter the
chamber through valve 209. In FIG. 11c, there is shown the piston
225 passing line 226 and stopping the flow of hydraulic fluid to
cavity 240. At that point the chamber 241 is full of blood. When
the chamber 241 is full of blood chamber 242 is approximately
one-half full of blood due to partial expansion caused by hydraulic
flow into cavity 243 via line 227.
As piston 225 continues to the bottom of central tube 201 as shown
by FIG. 11d, chamber 242 completely expands and fills with blood.
As the piston 225 passes duct 226 hydraulic fluid commences to flow
behind piston 225 as chamber 241 naturally contracts. During the
natural contraction of chamber 241 blood is forced from chamber 241
through valve 212 to the body. As piston 225 is returned to the top
of the stroke to commence another pumping cycle, natural
contraction of the chamber 242 forces blood from chamber 242
through valve 211 to the body. The piston 225 is then in a position
to commence another pumping stroke.
FIG. 12 shows the functional relationship of the components
comprising the blood chemistry sensor system 100 previously shown
in FIG. 5. Sensor input converter 101 receives eight inputs from
sensors located in the artificial heart. Adrenalin, acetyl colene,
pH and temperature are sensed by sensors located in the chamber
receiving blood from the body, i.e. the left atrium. Sensors
located in the right atrium, i.e. the chamber receiving blood from
the lungs senses 0.sub.2, p.sup.CO.sub.2, and pH. The output
pressure from the left ventricle is also sensed. There are, of
course, many other parameters that may be sensed depending upon the
physiological demands of a particular patient.
The sensor input converter electronically processes the sensed
inputs to provide information that is useful by digital
differential analyzer 102.
Control of the entire artificial heart is accomplished by the
miniturized digital differential analyzer 102. The digital
differential analyzer 102 is programmed to provide 70 equally timed
signals per minute to drive control 95 under normal operating
conditions.
Signals received by the digital differential amplifier 102 from the
sensor input converter 101 are processed with preselected heart
program signals 103. The heart program is a tailored program that
indicates proper heart rate based on the aggregate values of the
sensed parameters. When any of the sensors indicate an out of
tolerance condition the digital differential analyzer 102 performs
a decision of adding to or substracting from the number of normal
output pulses being fed to drive control 95. By comparing the
sensed input signals to a preselected heart program and thereby
regulating the heart functions, the artificial heart can approach
natural heart in operation.
There are at least two ways of varying the output of the artificial
heart. One way, as illustrated by the drawings, is by varying the
rate of heart operation, i.e., the "pulse rate" of the artificial
heart. Increased blood demands would therefore result in an
increased heart rate. An alternate means of changing the flow of
blood from the artificial heart would be to vary the amount of
blood per pump stroke of the heart expansion pump. This type of
variation can be accomplished by changing the rate of flow of
hydraulic fluid to and from the heart expansion pump. A quite
complicated valving arrangement is required to accomplish a change
in heart capacity where the pump stroke remains constant, however.
The orifice size must be regulated to restrict when lower flow
demands are made.
An advantage of an artificial heart of the instant design is that
an artificial heart can be designed to fit the specific need of a
particular patient. The tailoring of the heart can be accomplished
by machining of the flexible support members that comprise the
major structure of the heart. Further tailoring can be accomplished
by suitably programming the preselected heart program for use by
the digital differential analyzer. The machining of the heart
springs can simulate strength and performance outputs of the
individual's natural heart in a normal condition. Similarly, by
knowing normal sensed parameters of the particular patient,
response by the digital differential analyzer can be geared to
those normal responses.
The entire heart pump system and blood chemistry sensor system,
drive control means and hydraulic power supply can be miniturized
to be enclosed in the central support tube 30 of the artificial
heart (see FIGS. 1, 5 and 6). Small power supplies are also
available that would allow the heart to be completely
self-sufficient by having an internally implanted power supply for
driving the hydraulic piston. Of course power supplies other than
those implanted in the body could also be used such as the portable
power packs now in use, and external belly plungers for exerting
pressure on hydraulic fluids.
Power for the artificial heart may also be supplied by implantable
devices that generate their own electric power. These devices could
be remote from the heart but would be connected to it by insulated
conductors.
There are also two methods currently known, where the artificial
heart could generate sufficient power for its own operation. In one
scheme, it is possible to employ a small portion of the oxygenated
blood to supply the necessary power. In this scheme the oxygen is
chemically extracted from the blood to create a gaseous vapor.
A second source of oxygen for use in driving a small turbine could
be obtained by passing hydrogen peroxide through a cadmium-cobalt
screen to free the oxygen from the peroxide. The oxygen could then
be recovered without coming in contact with the patient.
The gaseous vapor is then used to drive a small generator that
provides power to the miniturized circuits of the heart control
system.
A second method could employ a fluid with a vapor point slightly
below normal body temperature. By circulating the fluid through
tubing around the outside of the heart vaporization of the fluid
could be realized through the use of normal body heat. The released
vapor could be conducted through a turbine wheel that drives a
generator. The current from the generator could supply power to the
miniturized circuits.
With the use of a non-blood fluid for providing the vapor the
exhaust of the turbine could not be channeled back into the blood
stream. The exhaust would have to be channeled through a cooling
reservoir where it could be condensed back to its fluid state. The
coating reservoir could, of course, be fully closed. The coolant
itself could be some liquid such as kerosene where a slight
temperature change creates a slight change of viscosity which sets
up a convective cooling current in the liquid itself.
An alternate means of providing motion to the hydraulic prime mover
fluid that flows to an from the cavities around the chamber walls
of the artificial heart is the use of a free floating piston. The
free floating piston, configured much like the double acting piston
of FIG. 6, is composed of highly magnetic material and is slidably
mounted in a cylinder which is either wound to act as a solenoid
body or built-in insulated sections to perform the function of a
solenoid. Windings around the case to affect the solenoid function
are double functioning such that a magnetic pull can be applied to
cause motion of the piston in either direction.
Control of the length of piston stroke in a magnetic piston device
is accomplished through variations in current and the length of
time that current is applied. The application of current to the
cylinder windings or body attracts the piston such that it
progresses from one end of the cylinder to the other. Motion of the
piston would port fluid much as illustrated by FIG. 6
* * * * *