U.S. patent number 3,896,501 [Application Number 05/412,397] was granted by the patent office on 1975-07-29 for mechanical drive for blood pump.
This patent grant is currently assigned to The United States of America as represented by the United States Energy. Invention is credited to Natale J. Bifano, Walter David Pouchot.
United States Patent |
3,896,501 |
Bifano , et al. |
July 29, 1975 |
Mechanical drive for blood pump
Abstract
The invention presents a highly efficient blood pump to be used
as a replacement for a ventricle of the human heart to restore
people disabled by heart disease. The mechanical drive of the
present invention is designed to operate in conjunction with a
thermoelectric converter power source. The mechanical drive system
essentially converts the output of a rotary motor into pulsatile
motion so that the power demand from the thermoelectric converter
remains essentially constant while the blood pump output is
pulsed.
Inventors: |
Bifano; Natale J. (Pittsburgh,
PA), Pouchot; Walter David (Monroeville, PA) |
Assignee: |
The United States of America as
represented by the United States Energy (Washington,
DC)
|
Family
ID: |
23632801 |
Appl.
No.: |
05/412,397 |
Filed: |
November 2, 1973 |
Current U.S.
Class: |
623/3.18;
417/472; 74/52 |
Current CPC
Class: |
A61M
60/40 (20210101); A61M 60/869 (20210101); A61M
60/148 (20210101); A61M 60/268 (20210101); A61M
60/871 (20210101); A61M 60/122 (20210101); Y10T
74/18272 (20150115) |
Current International
Class: |
A61M
1/10 (20060101); A61M 1/12 (20060101); A61F
001/24 () |
Field of
Search: |
;74/52,423 ;417/472
;128/1D ;3/1.7 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Scott; Samuel
Assistant Examiner: Ratliff, Jr.; Wesley S.
Attorney, Agent or Firm: Carlson; Dean E. Marchick; Robert
J.
Claims
We claim:
1. A blood pump of an artificial heart comprising:
a substantially hemispherical pump housing;
a drive shaft extending into said housing;
a rotatable flywheel disposed in said housing and having a diameter
slightly less than the maximum inner diameter of said housing;
meshing bevel gears disposed on said shaft and said flywheel for
rotating said flywheel;
a compound planetary gear set disposed within housing comprising a
sun gear integral with said flywheel, a stationary ring gear
affixed to said housing, compound planetary gears meshing with said
sun gear and the ring gear, and a spider carrying said planetary
gears and rotatable within said housing by said planetary gears at
a speed less than the rotational speed of said flywheel;
a single bevel gear secured to and rotatable by said spider;
a pair of bevel gears meshing with said single bevel gear having
their axis of rotation parallel to one another and rotatable by
said single bevel gear;
a rotatable crank arm attached to each of said pair of bevel
gears;
a pair of scotch yokes disposed within said housing with each of
said yokes in contact with each of said cranks and vertically
displaceable in response to the rotation of said cranks;
a diaphragm disposed within said housing above said scotch yokes
and defining with said housing a blood receiving chamber; and
a pusher cup disposed intermediate said diaphragm and said scotch
yokes and alternately displaceable by said scotch yokes upon the
vertical displacement thereof by said crank for moving the
diaphragm into said chamber and expelling blood therefrom and by
the blood entering the chamber when said scotch yokes are not
vertically displaced by said cranks.
Description
BACKGROUND OF THE INVENTION
At the present time, there is a need for artificial blood pumps to
take over all or part of the blood pumping function of the natural
heart in some heart patients on a permanent basis. Attempts to use
currently available equipment have resulted in extension of the
patients life by at most weeks and more often days or hours. One of
the important requirements for successful partial or total longterm
heart replacement is that the replacement system, including the
blood pump, be totally implantable. Totally implantable means that
there are no penetrations through the body's protective converings,
such as to external power supplies or controls, to provide a
conduit for infection.
Another important requirement for such a blood pump is that it
provide a pulsatile flow of pressure level and pulse rate
acceptable to the rest of the body. In addition, such a pump must
be sufficiently small, light, and vibration-free to be installed
within the body without undue stress on other body components. It
should also cause minimal damage to the blood pumped.
In any body implantable system, a miniaturized power source is
necessary. Most, if not all, miniature power sources, whether
electromechanical or thermo-mechanical, provide power through
shafts rotating at speeds considerably above heart rate. Such power
sources are effectively high speed, constant power output devices,
in contrast to the relatively low frequency, pulsatile output
required of a satisfactory blood pump. Therefore, another
requirement of the pump drive is that it accept a relatively high
speed, constant power input and efficiently convert that in order
to provide a low frequency pulsatile blood output.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a
mechanical drive for a blood pump which translates input rotary
motion to reduced speed pulsatile motion compatible with bodily
needs.
While the blood pump of this invention is capable of attachment to
an external power source, it has features which make it
particularly suited to be a part of the totally implanted system.
This is accomplished by incorporating the desirable principles of
control and hemodynamics of the Kwan-Gett blood pump, a
pneumatically driven blood pump, in a mechanically driven pump. For
a reference describing the Kwan-Gett principle see Kwan-Gett, C.
S., et al., "Total Replacement Artificial Heart and Driving System
with Inherent Regulation of Cardiac Output," Trans. Amer. Soc.
Artif. Int. Organs, 15:245, 1969. The Kwan-Gett pump is unsuited
for full implantation because the expanded gas volume at the end of
the pneumatic stroke is too large to conveniently retain within the
body. In addition, gas leakage will be a problem for relatively
long implantation periods. Further, pneumatic drives are less
efficient than mechanical drives and will therefore require larger
power supplies for equivalent blood pumping capability.
Incorporation of the Kwan-Gett control principle is important to
the total implantability of the mechanical blood pump drive
proposed. The Kwan-Gett principle includes driving the blood pump
at a constant beat rate. The bladder which expells the blood is
driven only during the expelling period (systole). During the
filling period, (diastole), the extent of filling of the bladder is
set by the body through its control over venous pressure and flow
rate. That is, the blood pump expels whatever blood is returned to
it up to the maximum capacity of the expulsion bladder. The blood
pump maintains system balance using a speed sensor and control as
the sole artificial control components.
The bladder configuration of the Kwan-Gett pump is also retained in
the blood pump of the present invention since it has demonstrated
good hemodynamics in animal experiments.
The purpose of the blood pump and drive embodiment of the present
invention is to replace, functionally, a ventricle of the natural
heart. This may be accomplished by connecting the blood pump into
the blood system in parallel with the natural ventricle. The pump
is to be implanted in the chest cavity and will circulate blood at
rates required at, for instance, the left side of the heart to
support body activities. It maintains sufficient pressure in the
aorta (main left side artery) at all times so that the left
ventricle discharge valve of the natural heart never opens. Thus,
the left ventricle, which does 87 percent of all the heart's work,
is relieved of all effort. The device of the present invention can
be used as a total right ventricle replacement as well. In this
capacity, the pump will be installed in parallel with the right
ventricle. Total heart replacement can be effected by using two
such ventricles in by-passing modes.
DESCRIPTION OF THE DRAWINGS
FIG. 1 presents a view of the blood pump and its mechanical
drive.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The blood pump and its driving mechanism are shown in FIG. 1. The
flexible shaft 11 from a power source converter enters the pump
assembly and drives a flywheel 12 through a set of right angle
bevel gears 13. The flywheel which has a diameter slightly less
than the maximum inner diameter of the pump as shown is a key
element in this concept. It is the means by which the relatively
constant power output of the power source is stored efficiently to
meet the wide variation of power necessary to produce pulsatile
blood flow. From the flywheel the power is transmitted through a
compound planetary gear speed reducer generally shown at 14 to
reduce the rotational speed of the system as required to achieve
the desired pump beat rate. The sun gear 15 of the speed reducer is
integral with the flywheel, the ring gear 16 is held stationary in
the substantially hemispherical pump housing 18 and the compound
planetary gears 28 and 29 are mounted on a spider 17 attached to a
sleeve 30 which rotates on ball bearings carried by a vertically
extending boss 31 centrally disposed in the pump housing. As shown,
the sun gear 15 is driven by the flywheel and, in turn, rotates the
larger planet gear 28 and the smaller planet gear 29 attached
thereto. The rotation of gear 29 in mesh with the stationary ring
gear 16 causes the planet gears and the spider to revolve about the
boss 31 at a speed less than the rotational speed of the sun gear
15. Attached to the spider sleeve 30 is a right angle bevel gear 19
which drives two bevel gears 20 and 21 that rotate in opposite
directions on a common axis. Each of the driven gears 20 and 21 are
connected to a crank arm 22 with a ballbearing roller 23 that bears
against two flat bearing surface 32 and 33 on partial Scotch yokes
24 and 24'. As depicted, the flat bearing surfaces 32 and 33 of the
Scotch yokes will provide a sinusodial blood pulse. If animal
experiments indicate that a different blood pulse form is
desirable, the Scotch yoke bearing surfaces can be contoured to
produce other pulse forms. As the bevel gears and crank arms are
rotated the rollers on the crank arms bear against the bearing
surfaces 32 and 33 to cause a vertical displacement of the yokes.
The yokes are tied together with beams and the beams are connected
through pivots 34 to a pusher cup 35 which in turn displaces the
blood pump diaphragm 25 to expel the blood in systole from a blood
receiving chamber 26 defined within the pump housing by the latter
and the diaphragm 25. Because the crank rollers can only push the
yokes outward and cannot pull them back, the pump diaphragm is
displaced inward by the blood returning to the pump. The volume
displaced during diastole will depend on the amount of blood
received from the pulmonary vein before the crank rollers re-engage
in the systole portion of the pump cycle. The pusher cup 35 and the
yoke assembly are supported in the transverse plane by means of a
guide pin 37 which moves vertically in a ball bushing that is
supported by the pump housing. The small yoke torque due to the
friction of the crank roller is resisted by the bellows 26 that
surrounds the driving mechanism. The drive system is fully balanced
except for the small friction component. It is therefore
essentially vibration-free.
In addition, because the two crank arms rotate in opposite
directions, the crank rollers translate on the yoke assembly
bearing surface in opposite directions and apply vertical loads
which are balanced about the axis of the diaphragm pusher cup guide
pin. This feature avoids side loads on the guide pin ball bushing.
The yoke assembly is connected to the diaphragm pusher cup through
pivots to insure that both crank rollers transmit power to the yoke
assembly at all times. If, due to dimensional variations, only one
crank pin attempts to drive the yoke assembly, the yoke connecting
beam tilts and permits the other crank roller to also bear against
the yoke assembly. Rolling element bearings are used throughout the
pump driving mechanism to minimize the frictional power losses and
the possibility of seizures which would render the mechanism
inoperative.
The entire actuation space below the pump diaphragm is gas and
vapor filled. Sealing of this space is accomplished by the pump
diaphragm on one side and the compliance bladder 27 on the other.
Since both of these sealing components will be made of reinforced
silastic or other polymeric material, diffusions of water vapor and
body absorbed gases (mostly air) to and from the space to reach an
equilibrium condition can be expected.
Table I provides a listing of the materials to be used in a
preferred embodiment of the present invention. Table 2 presents
approximate weight of the various components used in the preferred
embodiment.
TABLE I ______________________________________ MECHANICAL BLOOD
PUMP MATERIALS Component Material
______________________________________ Pump Housing Titanium
Diaphragm Silastic (Dacron rein- forced) Compliance Bag Silastic
(Dacron rein- forced) Flexible Drive Shaft Shaft Stainless Steel
Wire Guide Tube Teflon Bellows Titanium Ball Bearings Balls and
Races A1S1 440 C Stainless Steel Retainer Rings Plastic (filled
with lubricant) Flywheel Kennertium (95% Tungsten) Internal Bellows
Titanium Diaphragm Pusher Cup Titanium Guide Pin Beam Titanium Yoke
Assembly A1S1 440 C Stainless Steel Diaphragm Pusher Cup Guide Pin
A1S1 440 C Stainless Steel Ball Bushing Balls and Outer Race Sleeve
A1S1 440 C Stainless Steel Ball Retainer Plastic or Porous Metal
Gears High Strength Plastic Crank Arm Titanium Drive Shafts and
Planetary Spider Titanium
______________________________________
TABLE 2 ______________________________________ Component Weight
(gm) ______________________________________ Housing 203 Flywheel
and attached gears 88 Planetary gears and spider 29 Scotch yoke and
bevel gears 19 Blood pump diaphragm assembly 32 Compliance bladder
25 Torsion bellows 44 Bearings and ball bushing 15
______________________________________
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