U.S. patent application number 10/892656 was filed with the patent office on 2005-01-06 for blood pump device and method of producing.
Invention is credited to Clark, Richard E., Goldstein, Andrew H., Magovern, George J., Moeller, Fred W., Pacella, John J., Trumble, Dennis R..
Application Number | 20050004421 10/892656 |
Document ID | / |
Family ID | 33162895 |
Filed Date | 2005-01-06 |
United States Patent
Application |
20050004421 |
Kind Code |
A1 |
Pacella, John J. ; et
al. |
January 6, 2005 |
Blood pump device and method of producing
Abstract
The present invention pertains to a blood pump device which
comprises a blood pump having blood transport ports and cannulae
connected to the ports. The blood pump device also comprises a
coating material covering the junction between the inner surfaces
of the ports and cannulae. This forms a smooth transition so blood
can flow unimpeded therefrom and collection cavities for the blood
are eliminated. The invention is also related to a method of
producing a smooth coating. The present invention is a blood pump
device comprising a second portion having a stator mechanism and a
rotor mechanism disposed adjacent to and driven by the stator
mechanism. The second portion has a journal disposed about the
rotor mechanism to provide support therewith. The second portion
has an impeller disposed in the chamber and a one-piece seal member
for sealing about a shaft of the impeller. The seal member is
fixedly attached to the journal so that the seal member is
supported by the journal. The present invention is also related to
means for providing power to the blood pump so that blood can be
pumped through a cannulae. The providing means includes a
controller having means for sensing pump failure and an output
terminal for actuating a safety occluder in an event of pump
failure. Preferably, there is a safety occluder device disposed
about the cannulae and in communication with the output terminal.
Preferably, the blood pump comprises a motor having stator
mechanism and a rotor mechanism driven by the stator mechanism. The
sensing means comprises means for determining back electromagnetic
force within the stator mechanism. Preferably, the controlling
means has means for providing signals indicate of stator current
and rotor speed, respectively. The providing means is in
communication with the means for determining back electromagnetic
force in the stator mechanism.
Inventors: |
Pacella, John J.;
(Pittsburgh, PA) ; Goldstein, Andrew H.;
(Branford, CT) ; Trumble, Dennis R.; (Pittsburgh,
PA) ; Clark, Richard E.; (Sewickley, PA) ;
Moeller, Fred W.; (McKeesport, PA) ; Magovern, George
J.; (Pittsburgh, PA) |
Correspondence
Address: |
Ansel M. Schwartz
Suite 304
201 N. Craig Street
Pittsburgh
PA
15213
US
|
Family ID: |
33162895 |
Appl. No.: |
10/892656 |
Filed: |
July 16, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10892656 |
Jul 16, 2004 |
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09668090 |
Sep 22, 2000 |
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6808482 |
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09668090 |
Sep 22, 2000 |
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08898584 |
Jul 21, 1997 |
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6162167 |
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08898584 |
Jul 21, 1997 |
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08618084 |
Mar 18, 1996 |
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5711753 |
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08618084 |
Mar 18, 1996 |
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08228433 |
Apr 15, 1994 |
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Current U.S.
Class: |
600/16 |
Current CPC
Class: |
A61M 60/829 20210101;
A61M 60/205 20210101; A61M 60/857 20210101; A61M 60/50 20210101;
A61M 2205/3334 20130101; A61M 60/148 20210101; A61M 60/422
20210101 |
Class at
Publication: |
600/016 |
International
Class: |
A61N 001/362 |
Claims
What is claimed is:
1. A blood pump device comprising: a blood pump having a blood
transport port; a cannulae connected to the port; and a coating
material covering a junction between inner surfaces of the port and
cannulae so that a smooth transition surface is formed so blood can
flow smoothly therefrom and collection areas for the blood are
eliminated.
2. A device as described in claim 1 wherein the coating material is
comprised of polyurethane.
3. A method of producing a smooth transition junction coating
between a blood pump and a cannulae comprising the steps of:
connecting a cannulae to a port of a blood pump; and applying a
coating material to cover a junction between inner surface of the
port and cannulae so that a smooth transition surface is formed so
blood can flow smoothly therefrom and collection areas for the
blood are eliminated.
4. A method as described in claim 3 wherein the applying step
includes the steps of injecting coating material through the
cannulae about the junction and rotating the port and cannulae to
evenly distribute the coating about the junction.
5. A method as described in claim 4 wherein during the rotating
step, there is the step of circulating a fluid through the cannulae
past the junction to carry away solvent gases formed during curing
of the coating material.
6. A method as described in claim 5 wherein the rotating step
includes the step of spinning the port and cannulae with a motor
device during curing of the coating material.
7. A blood pump device comprising: a first portion having a chamber
and an inlet and outlet port in fluidic communication with the
chamber; and a second portion having a stator mechanism and a rotor
mechanism disposed adjacent to and driven by the stator mechanism,
said second portion having a journal disposed about the rotor
mechanism to provide support therewith, said second portion having
an impeller disposed in the chamber and a one-piece seal member for
sealing about a shaft of the impeller, said seal member fixedly
attached to said journal so that the seal member is supported by
the journal.
8. A blood pump as described in claim 7 wherein said rotor having a
rotor post connected to the impeller shaft and having an end
adjacent to the seal member, said end having rounded edges to
prevent abutment against any adhesive material disposed between the
seal member and the journal.
9. A device as described in claim 8 wherein the journal has a
surface adjacent to the rotor which has been polished to a surface
finish of less than 2.54 .mu.m for enhanced durability.
10. A device as described in claim 9 wherein the rotor has an outer
surface which has been polished to a surface finish of 2.54
.mu.m.
11. A device as described in claim 10 wherein the seal member
comprises a coating surrounding and sealing its outer surface.
12. A device as described in claim 11 wherein the rotor comprises a
rust-proof coating disposed on its outer surface.
13. A blood pump device comprising: a first portion having a
chamber and an inlet and outlet port in fluidic communication with
the chamber; and a second portion having a stator mechanism and a
rotor mechanism disposed adjacent to and driven by the stator
mechanism, said second portion having a journal disposed about the
rotor mechanism to provide support therewith, said second portion
having an impeller disposed in the chamber, said second portion
having an infusion port for providing lubricant material about the
rotor, said infusion port having an inner diameter greater than
0.05 inches for minimizing pressure needed to introduce lubricant
material into the blood pump.
14. A device as described in claim 13 wherein said second portion
having a barbed tubing connector attached directly into a housing
member of the second portion in direct fluid communication with the
infusion port.
15. A device as described in claim 14 wherein the infusion port is
polished to a surface finish of less than 2.54 .mu.m.
16. An improved blood pump device comprising: a first portion
having a chamber and an inlet and outlet port in fluidic
communication with the chamber; and a second portion having a
stator mechanism and a rotor mechanism disposed adjacent to and
driven by the stator mechanism, said second portion having a
journal disposed about the rotor mechanism to provide support
therewith, said second portion having an impeller disposed in the
chamber, said stator comprised of a thermally conductive epoxy
material to efficiently transmit heat to surrounding tissues about
the blood pump.
17. A device as described in claim 16 wherein the second portion
comprises an environmentally sealed connector for attaching a power
wire to the stator mechanism.
18. A device as described in claim 17 wherein the stator has a
coating sealing its outer surface.
19. A blood pump device comprising: a blood pump; and means for
providing power to the blood pump so that blood can be pumped
through a cannulae, said providing means comprising a controller
having means for sensing pump failure and an output terminal for
actuating a safety occluder in an event of pump failure.
20. A device as described in claim 19 including a safety occluder
device disposed about the cannulae and in communication with the
output terminal.
21. A device as described in claim 20 wherein the blood pump
comprises a motor having stator mechanism and a rotor mechanism
driven by the stator mechanism, said sensing means comprises means
for determining back electromagnetic force within the stator
mechanism.
22. A device as described in claim 21 wherein said controlling
means having means for providing signals indicate of stator current
and rotor speed, respectively, said providing means in
communication with the means for determining back electromagnetic
force in the stator mechanism.
23. A device as described in claim 22 including means for supplying
lubricant to the motor, said supplying means in fluidic
communication with the blood pump, said controlling means having
means for measuring lubricant pressure.
24. A device as described in claim 23 wherein the power providing
means comprises a modular driver unit remote from said pump and in
communication therewith.
25. A device as described in claim 24 wherein the controlling means
comprises means for adjusting speed of the motor mechanism with a
greater than 5% accuracy.
26. A device as described in claim 25 wherein the controlling means
comprises a display mechanism for providing values of stator
current, rotor speed and lubricant pressure.
27. A pumping system for fluid comprising: a sensorless pump for
moving the fluid; and a controller connected to the pump for
controlling the pump so a desired flow rate of fluid can be
maintained by the pump.
Description
FIELD OF THE INVENTION
[0001] The present invention is related in general to medical
devices. More specifically, the present invention is related to a
blood pump device for cardiac assist.
BACKGROUND OF THE INVENTION
[0002] Ventricular assist devices are receiving ever-increasing
attention in our society where 400,000 Americans are diagnosed with
congestive heart failure each year (Rutan, P. M., Galvin, E. A.:
Adult and pediatric ventricular heart failure, in Quall, S. H.
(ed), Cardiac Mechanical Assistance Beyond Balloon Pumping, St.
Louis, Mosby, 1993, pp. 3-24). As a result, collaborative efforts
among health care professionals have focussed on the development of
various systems to assist the failing heart. These comprise both
extracorporeal and implantable pulsatile ventricular assist devices
(VAD), as well as non-pulsatile assist pumps.
[0003] Extracorporeal systems include the Pierce-Donachy VAD and
the Abiomed BVS-5000 VAD. The Pierce-Donachy VAD is positioned on
the patient's abdomen and propels blood by means of a pneumatically
actuated diaphragm. Its use as a bridge to transplant is
well-documented (Pae, W. E., Rosenberg, G., Donachy, J. H., et al.:
Mechanical circulatory assistance for postoperative cardiogenic
shock: A three-year experience. ASAIO Trans 26:256-260, 1980;
Pennington, D. G., Kanter, K. R., McBride, L. R., et al.: Seven
years' experience with the Pierce-Donachy ventricular assist
device. J Thorac Cardiovasc Surg 96:901-911, 1988). The Abiomed
BVS-5000, also an extracorporeal device, is fixed vertically at the
patient's bedside and is attached to the heart with percutaneous
cannulae that exit the patient's chest below the costal margin
(Champsaur, G., Ninet, J., Vigneron, M., et al.: Use of the Abiomed
BVS System 5000 as a bridge to cardiac transplantation. J Thorac
Cardiovasc Surg 100:122-128, 1990).
[0004] The most frequently used implantable systems for clinical
application include the Novacor VAD (Novacor Division, Baxter
Health Care Corp.) and the Heartmate (Thermocardiosystems) (Rowles,
J. R., Mortimer, B. J., Olsen, D. B.: Ventricular Assist and Total
Artificial Heart Devices for Clinical Use in 1993. ASAIO J
39:840-855, 1993). The Novacor uses a solenoid-driven spring to
actuate a dual pusher plate. The pusher plate compresses a
polyurethane-lined chamber which causes ejection of blood (Portner,
P. M., Jassawalla, J. S., Chen, H., et al: A new dual pusher-plate
left heart assist blood pump. Artif Organs (Suppl) 3:361-365,
1979). Likewise, the Heartmate consists of a polyurethane lined
chamber surrounded by a pusher plate assembly, but a pneumatic
system is used to actuate the pusher plate (Dasse, K. A., Chipman,
S. D., Sherman, C. N., et al.: Clinical experience with textured
blood contacting surfaces in ventricular assist devices. ASAIO
Trans 33:418-425, 1987).
[0005] Efficacy of both the extracorporeal and implantable
pulsatile systems has been shown (Rowles, J. R., Mortimer, B. J.,
Olsen, D. B.: Ventricular Assist and Total Artificial Heart Devices
for Clinical Use in 1993. ASAIO J 39:840-855, 1993). However,
certain complications are associated with the use of extracorporeal
systems, including relatively lengthy surgical implantation
procedures and limited patient mobility. The use of totally
implantable systems raises concerns such as high cost of the
device, complex device design, and again, relatively difficult
insertion techniques.
[0006] Centrifugal pump VADs offer several advantages over their
pulsatile counterparts. They are much less costly; they rely on
less complicated operating principles; and, in general, they
require less involved surgical implantation procedures since, in
some applications, cardiopulmonary bypass (CPB) is not required.
Thus, an implantable centrifugal pump may be a better alternative
to currently available extracorporeal VADs for short- or
medium-term assist (1-6 months). In addition, the use of
centrifugal pumps in medium-term applications (1-6 months) may
allow the more complex, expensive VADs, namely the Novacor and the
Heartmate, to be used in longer term applications where higher
cost, increased device complexity, and involved surgical procedures
may be justified.
[0007] Prior art relating to centrifugal blood pumps is Canadian
Patent No. 1078255 to Reich; U.S. Pat. No. 4,927,407 to Dorman;
U.S. Pat. No. 3,608,088 to Dorman; U.S. Pat. No. 4,135,253 to
Reich; Development of the Baylor-Nikkiso centrifugal pump with a
purging system for circulatory support, Naifo, K., Miyazoe, Y.,
Aizawa, T., Mizuguchi, K., Tasai, K., Ohara, Y., Orime, Y., Glueck,
J., Takatani, S., Noon, G. P., and Nose', Y., Artif. Organs, 1993;
17:614-618; A compact centrifugal pump for cardiopulmonary bypass,
Sasaki, T., Jikuya, T., Aizawa, T., Shiono, M., Sakuma, I.,
Takatani, S., Glueck, J., Noon, G. P., Nose', Y., and Debakey, M.
E., Artif. Organs 1992;16:592-598; Development of a Compact
Centrifugal Pump with Purging System for Circulatory Support; Four
Month Survival with an Implanted Centrifugal Ventricular Assist
Device, A. H. Goldstein, MD; U.S. patent application titled "Radial
Drive for Implantable Centrifugal Cardiac Assist Pump", University
of Minnesota; Baylor Multipurpose Circulatory Support System for
Short-to-Long Term Use, Shiono et al., ASAIO Journal 1992,
M301.
[0008] Currently, centrifugal pumps are not implantable and are
used clinically only for CPB. Examples include the Biomedicus and
the Sarns centrifugal pumps. The Biomedicus pump consists of an
impeller comprised of stacked parallel cones. A constrained vortex
is created upon rotation of the impeller with an output blood flow
proportional to pump rotational speed (Lynch, M. F., Paterson, D.,
Baxter, V.: Centrifugal blood pumping for open-heart surgery. Minn
Med 61:536, 1978). The Sarns pump consists of a vaned impeller.
Rotation of the impeller causes flow to be drawn through the inlet
port of the pump and discharged via the pump outlet port (Joyce, L.
D., Kiser, J. C., Eales, F., et al.: Experience with the Sarns
centrifugal pump as a ventricular assist device. ASAIO Trans
36:M619-M623, 1990). Because of the interface between the spinning
impeller shaft and the blood seal, several problems exist with both
these pumps, including excessive wear at this interface, thrombus
formation, and blood seepage into the motor causing eventual pump
failure (Sharp, M. K.: An orbiting scroll blood pump without valves
or rotating seals. ASAIO J 40:41-48, 1994; Ohara, Y., Makihiko, K.,
Orime, Y., et al.: An ultimate, compact, seal-less centrifugal
ventricular assist device: baylor C-Gyro pump. Artif Organs
18:17-24, 1994).
[0009] The AB-180 is another type of centrifugal blood pump that is
designed to assist blood circulation in patients who suffer heart
failure. As illustrated in FIG. 1, the pump consists of seven
primary components: a lower housing 1, a stator 2, a rotor 3, a
journal 4, a seal 5, an impeller 6, and an upper housing 7. The
components are manufactured by various vendors. The fabrication is
performed at Allegheny-Singer Research Institute in Pittsburgh,
Pa.
[0010] The rotor 3 is in the lower housing 1 and its post protrudes
through a hole in the journal 4. The impeller 6 pumps blood in the
upper housing 7 and is threaded into and rotates with the rotor 3.
The impeller shaft passes through a rubber seal 5 disposed between
the upper housing 7 and the journal 4, rotor and stator assembly.
The upper housing 7 is threaded into the lower housing 1 and it
compresses the outer edge of a rubber seal 5 to create a blood
contacting chamber. In this manner, blood does not contact the
rotor 3, journal 4, or lower housing 1. The upper housing 7 is
connected to an inlet and outlet flow tubes 8, 9, called cannulae,
that are connected to the patient's circulatory system, such as
between the left atrium, LA, and the descending. thoracic aorta,
DTA, respectively. Through this connection, blood can be drawn from
the left atrium, LA, through the pump, and out to the aorta,
DTA.
[0011] The impeller 6 spins by means of the rotor 3 and stator 2
which make up a DC brushless motor. The base of the rotor 3 has
four magnets that make up two north-south pole pairs which are
positioned 90 degrees apart. The stator 2 is positioned around the
rotor 3 on the lower housing 1. The stator 2 comprises three
phases. When it is energized, it creates a magnetic force that
counteracts the magnets in the rotor 3 causing the rotor 3 and
impeller 6 to spin, as is well known with brushless DC motors.
[0012] A peristaltic pump infuses lubricating fluid into a port of
the lower housing to lubricate the spinning rotor. The fluid
prevents contact between any solid internal pump components during
pump activation. It forms a layer of approximately 0.001 inches
around the rotor and the impeller shaft. This fluid bearing
essentially allows wear-free operation of the pump. The fluid
passes around the rotor and flows up along the rotor post.
Eventually, it passes out through the rubber seal 5 and into the
upper housing 7 at the impeller shaft/seal interface. Fluid does
not escape through the outer periphery of the housing seal because
the upper housing is tightened down and sealed with a rubber O-ring
to prevent leakage.
[0013] The spinning impeller 6 within the top housing 7 causes
fluid to be drawn from the inlet flow tube 8 toward the eye of the
impeller. The impeller 6 then thrusts the fluid out to the
periphery of the upper housing 7. At this point, the fluid is
pushed through the outlet tube 9 by centrifugal force. The pump
typically consumes 3-5 Watts of input power to perform the
hydraulic work necessary to attain significant physiologic
benefits.
[0014] The prior art AB-180 pump has certain drawbacks which limit
its efficacy as a cardiac assist device. The present invention
describes several discoveries and novel constructions and methods
which vastly improve such a pump's operation.
SUMMARY OF THE INVENTION
[0015] The present invention pertains to a blood pump device. The
blood pump device comprises a blood pump having blood transport
ports and cannulae connected to the ports. The blood pump device
also comprises a coating material covering the junction between the
inner surfaces of the ports and cannulae. This forms a smooth
transition so blood can flow unimpeded therefrom and collection
cavities for the blood are eliminated. The invention is also
related to a method of producing a smooth coating.
[0016] The present invention is a blood pump device comprising a
second portion having a stator mechanism and a rotor mechanism
disposed adjacent to and driven by the stator mechanism. The second
portion has a journal disposed about the rotor mechanism to provide
support therewith. The second portion has an impeller disposed in
the chamber and a one-piece seal member for sealing about a shaft
of the impeller. The seal member is fixedly attached to the journal
so that the seal member is supported by the journal.
[0017] Preferably, the rotor has a rotor post connected to the
impeller shaft and an end adjacent to the seal member. The end has
rounded edges to prevent abutment against any adhesive material
disposed between the seal member and the journal.
[0018] The present invention is also a blood pump device which has
an infusion port for providing lubricant material about the rotor,
the infusion port has an inner diameter greater than 0.05 inches
for minimizing pressure needed to introduce lubricant material into
the blood pump.
[0019] The present invention is also related to means for providing
power to the blood pump so that blood can be pumped through a
cannulae. The providing means includes a controller having means
for sensing pump failure and an output terminal for actuating a
safety occluder in an event of pump failure. Preferably, there is a
safety occluder device disposed about the cannulae and in
communication with the output terminal. Preferably, the blood pump
comprises a motor having stator mechanism and a rotor mechanism
driven by the stator mechanism. The sensing means comprises means
for determining back electromagnetic force within the stator
mechanism. Preferably, the controlling means has means for
providing signals indicate of stator current and rotor speed,
respectively. The providing means is in communication with the
means for determining back electromagnetic force in the stator
mechanism.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] In the accompanying drawings, the preferred embodiment of
the invention and preferred methods of practicing the invention are
illustrated in which:
[0021] FIG. 1 is a schematic representation showing a centrifugal
blood pump device of the prior art.
[0022] FIG. 2 is a schematic representation showing the blood pump
device of the present invention and an associated system.
[0023] FIGS. 3a and 3b are schematic representations showing a
blood collection cavity at the junction between port and cannulae
and coating material over the junction between port and cannulae,
respectively.
[0024] FIGS. 4a and 4b are schematic representations showing a
prior art seal construction and the present inventions seal
construction, respectively.
[0025] FIGS. 5a and 5b are schematic representations showing a
prior art rotor post and the rotor post of the present invention,
respectively.
[0026] FIGS. 6a and 6b are schematic representations showing a
prior art infusion port and the infusion port of the present
invention, respectively.
[0027] FIGS. 7a and 7b are schematic representations showing a mold
for casting the stator of thermally conductive epoxy.
[0028] FIG. 8 is a schematic representation showing the housing jig
of the cannulae coating apparatus.
[0029] FIG. 9 is a schematic representation showing the cannulae
coating apparatus.
[0030] FIG. 10a is a photograph showing a massive clot on the
impeller and at shaft/seal interface from the 14-day study.
[0031] FIG. 10b is a photograph showing a clot-free pump seal in
the 10-day study.
[0032] FIG. 10c is a photograph showing a 2 mm clot at the
shaft/seal interface in the 28-day study.
[0033] FIG. 10d is a photograph showing a clot-free pump seal in
the 154-day study.
[0034] FIGS. 11a and 11b are photographs showing rust on the rotor
in the 14-day study and no rust present in the 154-day study,
respectively.
[0035] FIGS. 12a and 12b are photographs showing the prior art
stator and the stator of the present invention, respectively.
[0036] FIG. 13 is a block diagram of one embodiment of the
sensorless blood pump controller in accordance with the present
invention showing the external connections to the personal computer
BLDC motor (blood pump device), occluder, extended battery supply,
power supply, and infusion pressure input.
[0037] FIG. 14 is a block diagram of one embodiment of the
sensorless blood pump controller in accordance with the present
invention showing the components that control and regulate and
monitor the operation of the sensorless blood pump controller.
[0038] FIG. 15 is a block diagram of one embodiment of the
sensorless blood pump controller in accordance with the present
invention showing the internal power supply, external power supply,
battery back-up, and battery charger circuits.
[0039] FIG. 16 is a block diagram of one embodiment of the
sensorless blood pump controller in accordance with the present
invention showing the power distribution.
[0040] FIG. 17 is a block diagram of one embodiment of the
sensorless blood pump controller in accordance with the present
invention showing the Control Entry Device as used with the control
entry microcomputer and the control computer.
[0041] FIG. 18 is a flowchart showing the start-up sequence for the
motor, the measurement of the pump parameters, display of pump
parameters, and downloading of pump parameters to an IBM personal
computer.
[0042] FIG. 19 is a block diagram of one embodiment of the
sensorless blood pump controller in accordance with the present
invention showing the signal conditioner inputs to the control
microcomputer, the output that compensates for a retrograde flow,
the alarm that is activated for low infusion pressure, the low
battery indicator, the occluder output, the alphanumeric LCD
display, and the connection to an external IBM computer.
[0043] FIG. 20 is a flowchart of the error checks including blood
pump malfunction, retrograde flow and low infusion pressure that
results in a corrective action or alarm.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0044] Referring now to the drawings wherein like reference
numerals refer to similar or identical parts throughout the several
views, and more specifically to FIG. 2 thereof, there is shown a
blood pump device 10. The blood pump 10 comprises a blood pump 12
having a blood transport port 14 and a cannulae 16 connected to the
port 14. As best shown in FIG. 3b, the blood pump device 10 also
comprises a coating material 18 covering the junction between the
inner surfaces of the port 14 and cannulae 16 so that a smooth
transition surface 20 is formed and blood can flow smoothly
therefrom and collection cavities for the blood are eliminated.
[0045] The inlet cannulae 16 can be inserted into the left atrium
of the patient 22 and fixed with a double purse string suture. The
outlet cannulae 15 can be sewn to the aorta of the patient 22. The
inner junctions of the cannulae 15, 16 are coated with a
polyurethane coating material 18 such as Biomer, manufactured by
Ethicon, Inc. The coating material 18 provides a smooth transition
surface 20 for the blood to flow on. This uniform transition is
essential for reduction of clot formation.
[0046] The technique used to apply this coating material 18 is
novel. It involves applying the polyurethane material 18 to the
collection cavity 93 at the cannulae/port internal interface with a
needle and syringe. After the polyurethane 18 is deposited, it is
distributed evenly by hand rotation of the housing.
[0047] Next, as shown in FIGS. 9 and 10, the upper housing 26 is
spun axially for each cannula 15, 16 in a motor driven coating
chamber 92 for 24 hours. This promotes more uniform distribution of
the polyurethane 18 and allows full curing. It also assures that
the polyurethane coating 18 fills the step-off between the housing
ports and the cannulae. The coating chamber 92 consists of a motor
shaft 94 enclosed by a plexiglass box 96. The shaft 94 is connected
to a variable speed motor 95 protruding through the rear of the
box. Nitrogen is passed through a jig 97 which fastens to the motor
95 and holds the pump housing 26 and cannulae 15, 16. The jig 97
directs nitrogen from container 98 to pass over the junction being
coated. The nitrogen carries away the solvent gases from the
polyurethane 18 that would otherwise attack and degrade other areas
of the pump housing 26. The custom jig 97 functions to hold the top
housing 26 in both configurations, one for coating the inlet flow
cannulae 15 and the other for coating the outlet flow cannulae 17.
Once the polyurethane 18 is cured and evenly distributed, the
housing 26 is removed and the process is repeated for the other
cannula.
[0048] As shown in FIG. 3a, a prior art pump without the coating
technique forms a collection cavity 93. The prior art blood pump
was implanted in 14 sheep in an experiment from December 1988 to
October 1990. (Modified Fabrication Techniques Lead to Improved
Centrifugal Blood Pump Performance, John J. Pacella et al.,
presented at the 40th Anniversary Meeting of the American Society
for Artificial Internal Organs, San Francisco, Calif., April 1994,
incorporated by reference herein). The pump was arranged
extracorporeally in a left atrial to descending aortic cannulation
scheme and the animals survived up to 13 days with the implanted
prior art device. These experiments revealed that a major problem
of the prior art pump was thrombus formation within the collection
cavity 93 at the cannulae/housing interfaces.
[0049] In contrast, using the described antithrombogenic coating
technique with coating material 18, 44 sheep were implanted with
the blood pump device from 1992-1993 for periods of 1 day to 154
days and no thrombus was found at the interface. This represents a
100% success rate to date.
[0050] As shown in FIG. 2, the blood pump device 10 comprises a
first portion 28 having a chamber 30 and an inlet and outlet port
13, 14 in fluidic communication with the chamber 30. The blood pump
device 10 also comprises a second portion 32 having a stator
mechanism 34 and a rotor mechanism 36 disposed adjacent to and
driven by the stator mechanism 34. Together, the stator mechanism
34 and the rotor mechanism 36 form the motor 888. Preferably, the
motor 888 is a brushless DC motor (BLDC) 888. The second portion 32
has a journal 38 disposed about the rotor mechanism 36 to provide
support therewith. The second portion 32 also has an impeller 40
disposed in the chamber 30 and a one-piece seal member 42 for
sealing about a shaft of the impeller 40. The seal member 42 is
fixedly attached to the journal 38, such as with adhesive, so that
the seal member 42 is supported by the journal 38. Preferably, the
seal member 42 comprises a coating surrounding and sealing its
outer surface. Further, the rotor 36 preferably has a surface 44
which has been polished to a surface finish of less than 2.54 .mu.m
for enhanced low friction operation. The amount of material removed
from the rotor 36 during the polishing process is less than 0.0001
inches (2.54 um).
[0051] As shown in FIGS. 4a and 4b, the hard plastic journal 38 and
seal member 42 is fastened together, such as with Loctite 401
adhesive, to achieve seal stiffness, which was previously provided
by the metal insert 45 molded into the prior seal 43. Also, the
seal member 42 can be coated with Biomer (Ethicon, Inc.)
polyurethane for enhanced antithrombogenicity.
[0052] Two improvements in pump characteristics have been made
through this new seal 42. First, the cost of production of the seal
member 42 has been decreased significantly. The prior seal 43 had a
metal insert 45 that was required to maintain seal stiffness, since
the seal 43 is made of soft, flexible rubber. The disclosed
construction of the present invention eliminates the need for an
insert and simplifies the molding process. The seal member 42 is
glued directly to the journal 38, which is made of hard plastic, to
achieve overall seal stiffness. The process of gluing these two
components is simple and relies on an inexpensive adhesive. Second,
this insert 45 had to be machined separately placed in the rubber
seal 43. As a result, the fabrication process of the seal left
metallic sections of the insert 45 exposed to fluid contamination
and therefore prone to rust. Since the seal member 42 of the
present invention eliminates the insert, no steel is present for
potential iron oxidation.
[0053] Further, the overall height, E, of the journal/seal assembly
has been increased from approximately 0.928 inches to 0.944 inches.
This has resulted in a tighter seal at the junction between the
outer rim 49 of the seal member 42 and the top housing 26,
decreasing the chance for blood stasis and clot formation. As the
top housing 26 is tightened down upon the lower housing 24 through
their threaded connection, it compresses the outer rim 49 of the
seal 42. The increased journal/seal height allows this compression
to occur closer to the beginning of the threads. In other words,
the upper housing does not need to be rotated as far through the
threads to achieve the same tightness as it would if the
journal/seal height, E, was not increased. Because of this, there
is more room to achieve a tighter seal.
[0054] The following are preferred dimensions of the seal
constructions shown in FIGS. 4a and 4b:
[0055] A=0.273 in.
[0056] B=0.208 in.
[0057] C=0.06 in.
[0058] D=0.192 in.
[0059] E=0.944 in.
[0060] The journal/seal design, as shown in FIG. 4b, has been used
in the disclosed sheep implantation studies and has functioned
superbly. Results of the studies have shown inconsequential
quantities of thrombus around the periphery of the top housing 26
in a few cases and none in the majority of the studies.
[0061] As best shown in FIG. 5b, the top edge 50 of the rotor post
46 is preferably rounded to allow a better fit under the seal
member 42. The rotor post 46 is inserted into the journal 38 and
fits just beneath the seal member 42. The junction between the
journal 38 and the seal member 46 occurs at this point and the two
components are affixed with adhesive (i.e. Loctite 401). The
rounding of the edge 50 on the rotor post 46 prevents the rotor 36
from rubbing against any excess glue that may be present after the
seal member 42 and journal 38 are fastened together.
[0062] The surfaces of the rotor 36 are preferably polished to 2.54
.mu.m and given a rust-proof coating 58. Results from the sheep
studies have revealed little evidence of rust and polished surfaces
have been shown to greatly increase durability between the rotor 36
and journal 38 and between the rotor 56 and the lower housing
60.
[0063] As best shown in FIGS. 6a and 6b, the infusion port 62 is
preferably enlarged from 0.03 inches to 0.062 inches. The housing
24 and port 62 can also be cryogenically deburred. Further, a 1/4
28 UNF male luer lock 66 is used instead of the prior 1/4 28 UNF
threaded hex barb 68 to eliminate the male-female junction 64 at
this point.
[0064] The port 62 serves as a passageway for pump lubricant, such
as water or saline, which is delivered to the pump and exits
through the rubber seal member 42 into the blood stream. The port
62 is enlarged because it assists in attaining lower pump lubricant
pressures, which diminishes the stress on all lubricant system
components. Also, a small port is more likely to become occluded
with debris (e.g. salt deposit from lubricant saline solution) and
cause increases in lubricant pressures.
[0065] The male-female junction 64 in the previous design (FIG. 6a)
was eliminated to decrease the chance of foreign debris in the
chest cavity from infiltrating into the lubricant system. The use
of a threaded barb 66 helps to solve this problem because there is
one less junction. The threaded end is screwed into the lower
housing 60 and chemically sealed and the barbed end is inserted
directly into the lubricant tubing 69 creating a mechanical
seal.
[0066] The deburring of the housing 60 results in increased
durability and improved pump performance and lower internal
lubricant temperatures. The internal lubricant temperature was
measured by inserting an Omega, Inc 33 Gauge hypodermic needle
thermocouple directly through the pump baffle seal, just below the
lip of the seal where the lubricant passes out. We found that rough
(undeburred) component surfaces of the prior pump resulted in
internal lubricant temperatures of 50.degree. C. The lubricant
temperatures of a pump device 10 with polished, deburred components
was found to be 42-43.degree. C., which is significantly less.
Since heat is thought to be a possible contributor to thrombus
formation, this may have increased the antithrombogenicity of the
pump as well as increasing its durability.
[0067] As shown in FIGS. 7a and 7b, a new mold 70 was designed for
stator fabrication. New, thermally conductive epoxy material is
used for fabricating the stator 34. The new mold 70 has two halves
72, 74, a removable center stem 76 and handles 78 for quick
releasing of the halves 72, 74. Fastening bolts 80 hold the halves
72, 74 and center stem 76 together. The mold 70 has significantly
increased the quality of the stator 34 as indicated by the
progressive increases in the survival times of sheep in the
disclosed blood pump implantation studies. In chronological order,
the five studies of durations greater than ten days were 14, 10,
28, 35, and 154 day durations. The new mold 70 was used in the 35
and 154 day studies.
[0068] Thermally conductive epoxy material was used for stator
fabrication to help carry heat away from the stator 34 and allow it
to conduct readily to the surrounding tissues. As a result, the
present stator 34 with thermally conductive epoxy has surface
temperatures rarely exceeding 2.5.degree. C. above ambient
temperature versus 5-7 C. in the 14 and 10 day studies. Referring
to FIG. 2, environmentally sealed connectors 72 replace older style
connectors used for controller/stator electrical connections.
Further, the stator 34 can be dip coated in polyurethane before
potting.
[0069] A commercially available environmentally sealed connector 72
(LEMO USA, Inc.) is preferably used to prevent the electrical
connections from failing in the event of exposure to fluid. The
prior art connector was not waterproof. To hermetically seal the
stator 34, it can be dipped in polyurethane several times during
the fabrication process. FIGS. 12a and 12b show the prior art
stator and the stator 34 of the present pump device 10.
[0070] The control means 80 of the present invention preferably has
an output 82 for actuation of a safety occluder device 83 in the
event of motor failure. Also, there are standardized outputs for
current 84, speed 86, and lubricant system pressure 88 (0-1 Volt).
The controller 80 uses isolated circuitry to cut down on noise by
stator commutation. Three meters 90 of a display means 81, with
both digital and bar graph output show the outputs.
[0071] The automated occluder initiation output 82 greatly enhances
safety for in vivo use of the blood pump. In the event of motor
failure, detected by back the EMF sensor means 92, the controller
80 will activate the safety occluder device 83 to prevent
retrograde pump flow through the cannulae 16. If pump current
becomes zero, the controller 80 will attempt to restart the pump
five times and if it is unsuccessful, it will send a signal to
actuate the occluder device 83 through output 82. The increased
reliability allows more time for intervention and troubleshooting.
The standardized analog outputs for current 84, speed 86, and
perfusion pressure 88 (0-1 volt) provides enhanced and
comprehensive data collection. The outputs 84, 86, 88 can be used
for trend recording on a strip chart recorder 94, as opposed to
direct measurements once a day. Furthermore, isolated circuitry and
display means 89 with three meters 90 with both digital and bar
graph output with .+-.1% accuracy on all readings prevent noise
caused by stator commutation and provides reliable data
collection.
[0072] The controller in more detail is shown in FIG. 13.
[0073] The sensorless blood pump controller 80 is preferably used
to control the motor 888. It is called sensorless because no
sensors are disposed in the pump 12 itself. Referring to FIG. 14, a
block diagram is provided of the preferred embodiment of many
possible embodiments of the sensorless blood pump controller
80.
[0074] A highly integrated control I.C. 170, such as ML4411
available from Microlinear, San Jose, Calif., is comprised of the
VCO 130 connected to a Back-Emf sampler 230 and to a logic and
control 140. The control I.C. 170 also includes gate drivers 240
for connection to power driver 260, linear control 901 connected to
power driver 260 and I limit 110 and integrator 101 and R sense
270. The control I.C. 170 additionally includes power fail detect
160. The ML4411 I.C. 170 provides commutation for the BLDC motor
888 utilizing a sensorless technology to determine the proper phase
angle for the phase locked loop. The function and operation of the
specific features and elements of the control I.C. 170 itself is
well known in the art. Motor commutation is detected by the
Back-EMF sampler 230.
[0075] For closed loop control, loop filter 900, connected to VCO
130 and amplifier 290, charges on late commutation, discharges on
early commutation and is buffered by a non-inverting amplifier 290,
model LM324 available from National Semiconductor, Santa Clara,
Calif. The buffered output provides feedback to the integrator 101
that includes an inverting amplifier, model LM324. Preferably,
non-inverting amplifier 290 and integrator 101 with an inverting
amplifier are disposed on one chip. The speed control 120 uses a
20K ohm dailpot, model 3600S-001-203 available from BOURNS,
Riverside, Calif. The speed control 120 in conjunction with summer
700 provides the set point for integrator 101. The output from the
integrator 101 is used in conjunction with the input from R Sense
270, 0.05 ohms, part number MP821-0.05, available from Caddock
Electronics, Riverside, Calif., to the linear control 901 to
modulate gate drivers 240. The power drivers 260 consists of six
N-channel field effect transistors, part number RFP70N03, available
from Harris Semiconductor, Melbourne, Fla. The power drivers 260,
connected to the gate drivers 240, drive the BLDC motor 888.
[0076] The integrator 101 receives the desired speed control from
the speed control 120 and also receives a feedback signal from the
control I.C. 170 through its Back-EMF sampler 23 which passes the
speed of the rotor 36 in the BLDC motor 888. The output signal from
the integrator 101, which essentially is an error correction signal
corresponding to the difference between the speed control set point
signal and the sensed velocity of the rotor mechanism 36 of the
BLDC motor 888, is provided to the linear control 901. The linear
control 901, with the error correction voltage signal from the
integrator 101 and the voltage signal from the R sense 270, which
corresponds to the stator mechanism 34 current, modulates the gate
drivers 240 to ultimately control the current to the stator
mechanism 34 of the DC motor 888. The R sense 270 is in series with
the power drivers 260 to detect the current flowing through the
power drivers 260 to the stator mechanism 34 windings of the BLDC
motor 888.
[0077] Power fail detect 160, an open collector output from the
ML4411 control I.C. 170, is active when the +12VDC or the +5VDC
from the power supply 180 is under-voltage. The power fail detect
160, alerts the microcomputer 880 that a fault condition
exists.
[0078] Referring to FIG. 15, external power supply 144 provides 12
VDC for the sensorless controller 80. Switching the external power
supply 144 on or off is accomplished by the on/off control entry
microcomputer 800. A logic `1` gates the external power supply 1
off and vice-versa. Battery back-Up is accomplished by solid state
relay 777, P.N. AQV210, available from AROMAT, New Providence, N.J.
When external power is lost, the internal power supply 180, P.N
V1-J01-CY, available from Vicor, Andover, Mass. is enabled. The
internal power supply 180 which derives power from the battery 490
P.N. V1-J01-CY, available from Vicor, Andover, Mass. is enabled.
The internal power supply 180 derives power from the battery 490
P.N. 642-78002-003, available from GATES, Gainsville, Fla. Charge
relay 333, P.N. 81H5D312-12, available from Potter and Brumfield,
Princeton, Ind. switches out the external battery charger 214 when
the control entry microcomputer 800 is `ON`. Schottky diode 134,
P.N. MBR1545, available from International Rectifier, Segundo,
Calif., performs a logic `OR` on the External Power 144 or Internal
power supply 180 to the 12V Buss 250.
[0079] Referring to FIG. 16, power is derived from the 12V Buss 250
and feeds DC to DC converter 410, P.N. NME1212S, available from
International Power Sources, Ashland, Mass. and provides +12, -12V
for the Analog circuitry. The DC/DC converter 820, P.N. 78SR105
available from Power Trends, Batavia, Ill. provides +5 VDC power
for the DVM's and the control I.C. 170. The DC/DC converter 122,
P.N. 11450, available from Toko America, Prospect, Ill. provides
+5VDC to the microcomputer 880.
[0080] Referring to FIG. 17, depression of the "ON" switch, p/o of
switch assembly of the control entry device 190, P.N. 15.502,
available from Solico/MEC, Hartford, Conn., discharges capacitor
(RC) p/o external reset circuit 660 initiating a reset signal to
the Control Entry microcomputer 800, P.N. PIC16C54, available from
Microchip, San Jose, Calif. The control entry computer 800 toggles
an I/O line to signal the External Power Supply 144 to power up and
to turn status indicator 222 on. The START, RESET, and MUTE lines
from 190 are connected to resistor pack 480 P.N. R-9103-10K,
available from Panasonic, Secacus, N.J. The control entry
microcomputer 800, sends control lines including START, RESET, and
MUTE to the control microcomputer 880, P.N. PIC16C71, available
from Microchip, San Jose, Calif. and to the Status Indicators 222,
P.N. 16.921-08, available from Solic/MEC, Hartford, Conn.
Depressing the START on control entry device 190 causes the Control
Entry microcomputer 800, to assert the START signal to Control
microcomputer 880. The Control microcomputer 880 initiates the
sequence to start the motor 888. Refer to FIG. 18. Upon successful
completion of the START routine, referring to FIG. 19, the control
microcomputer 880, digitizes three analog inputs including current
conditioner 460 connected to the motor 888, Infusion Pressure
conditioner 280 and the internal battery voltage 490. The Control
I.C. 170 is connected to the RPM conditioner 380. The control
microcomputer 880 is connected to the RPM conditioner 380.
Referring to FIG. 18, the control microcomputer 880 measures the
period of the RPM input and calculates the RPM. Referring to FIG.
19, the control microcomputer 880 updates the LCD Display 603, P.N.
97-20947-0, available from EPSON, Terrance, Calif. and downloads
the data including RPM, current, infusion pressure, and battery
voltage to the external connection connecting the SBPC to the IBM
printer port 604. The control microcomputer 880 is connected to the
alarm 602, P.N. P9923, available from Panasonic, Secaucus, N.J. and
is activated when the infusion pressure is low. See FIG. 20. Upon
an error detected with the retrograde flow, the control
microprocessor 880 of FIG. 19, outputs ramped voltage to the
digital to analog converter 500, P.N. MAX531, available from Maxim,
Sunnyvale, Calif. The D/A converter 500 is connected to an analog
summer 700. The speed control 120 is connected to the analog summer
700, which is part of four amplifiers in a package. P.N. LM324,
available from national semiconductor, Santa Clara, Calif. The
summer 700 is connected to the integrator 101. The integrator 101
is connected to the control I.C. 170.
[0081] Referring to FIG. 20, the control microcontroller 880, upon
detecting an error that RPM is less than 2000 or zero motor current
tries to restart the motor 888 five times. After five times, if the
motor 888 does not start, then the SBPC activates an external
occluder. See U.S. patent application Ser. No. ______, titled
"Occluder Device and Method of Making", by John J. Pacella and
Richard E. Clark, having attorney docket number AHS-3, incorporated
by reference herein, filed contemporaneously with this application
for a description of the occluder.
[0082] An implantable centrifugal blood pump for short and
medium-term (1-6 months), left ventricular assist is disclosed in
"Modified Fabrication Techniques Lead to Improved Centrifugal Blood
Pump Performance", John J. Pacella et al., presented at the 40th
Anniversary Meeting of the American Society for Artificial Internal
Organs, San Francisco, Calif., April 1994. Pump operation such as
durability and resistance to clot formation was studied. The
antithrombogenic character of the pump 10 is superior to prior art
pumps due to the coating 18 at the cannula-housing interfaces and
at the baffle seal. Also, the impeller blade material has been
changed from polysulfone to pyrolytic carbon. The electronic
components of the pump have been sealed for implantable use through
specialized processes of dipping, potting, and ultraviolet-assisted
sealing. The surfaces of the internal pump components have been
treated in order to minimize friction. These treatments include
polishing, ion deposition, and cryogenic deburring. The pump device
10 has demonstrated efficacy in five chronic sheep implantation
studies of 10, 14, 28, 35 and 113+ day durations. Post-mortem
findings of the 14-day experiment revealed stable fibrin entangled
around the impeller shaft and blades. Following pump modification
with refined coating techniques and advanced impeller materials,
autopsy findings of the ten-day study showed no evidence of clot.
Additionally, the results of the 28-day experiment showed only a
small (2.0 mm) ring of fibrin at the shaft-seal interface. In this
study, however, the pump failed on day 28 due to erosion of the
stator epoxy.
[0083] In the experiments of 35 and 113+ day durations, the stators
were re-designed, and the results of both experiments have shown no
evidence of motor failure. Furthermore, the 35-day study revealed a
small deposit of fibrin 0.5 mm wide at the lip of the seal. Based
on these studies, it can be ascertained that these new pump
constructions have significantly contributed to the improvements in
durability and resistance to clot formation. In this study, the
pump device 10 was implanted in five sheep for a minimum of 10
days. Prior to surgery, the sheep were fasted for 24 hours, but
were allowed unlimited access to water. The pump device 10 was
implanted through a left thoracotomy and arranged in a left
atrial-to-descending aortic cannulation scheme. Two percutaneous
tubes were required for pump operation: one was used to jacket the
conductors that supply power to the stator 34 and the other
provided a conduit for pump lubricant infusion. The animals were
infused at a constant rate with either 0.9% saline or sterile water
as the pump lubricant. Daily measurements of pump speed, current,
voltage, flow, animal body temperature, and stator surface
temperature were obtained. The animals were free to ambulate within
a 4-foot by 6-foot pen and were tethered to a custom-made swivel
tether device as disclosed in U.S. Pat. No. 5,305,712. Weekly blood
draws consisted of blood counts, electrolytes, coagulation
profiles, hepatic and renal function, and hemolysis. Blood cultures
were obtained as needed. The autopsy included complete
histopathologic studies and a microscopic analysis of the pump
10.
[0084] Various modifications in the pump configuration throughout
the course of the five studies were made to improve the
antithrombogenicity, corrosion resistance, and durability of the
pump. Antithrombogenicity was addressed by applying polyurethane
coatings to the cannulae housing interface and the seal and
substituting pyrolytic carbon for polysulfone as the impeller blade
material. In addition, alterations in the lubricant infusion rate
and the anticoagulation scheme were incorporated. The rotor
surfaces 46 were conditioned through polishing and passivating
procedures with the goal of increasing pump durability, and the
lower housing rotor bearing surface was cryogenically deburred for
the same purpose. Finally, the pump stator 34 was dip-coated in
polyurethane and potted in a larger sized mold to provide more
material coverage of the stator to increase the resistance of the
pump to fluid corrosion.
[0085] Pump modifications were made continuously throughout the
five studies, depending on the results of each preceding study, as
shown below in Table I:
1TABLE I Result Dependent Modifications Experiment Duration (Days)
Modification 14 10 28 35 154 Lower Housing X X Conditioning Rotor
Conditioning X X Re-designed Stator X X Seal Coating X X X X
Cannula/Housing X X X X X Coating Impeller P C C.sup.1 C.sup.1
C.sup.1 Material Perfusion Flow 2 4 10 10 10 Rate (ml/hr)
Anticoagulation N H, S A, H, C, S A, H, C, S A, H, C, S, U N =
none; A = aspirin; H = heparin; C = coumadin; S = streptokinase; U
= urokinase; P = polysulfone; C.sup.1 = pyroltic carbon
[0086] The 14-day study incorporated a prior art rotor and lower
housing, a polysulfone impeller, and a polyurethane coating applied
to the cannulae/housing interfaces. The lubricant flow rate was 2
ml/hr and no anticoagulants were used. Autopsy findings revealed a
massive clot entangled within the impeller blades and fixed to the
impeller shaft at the shaft/seal junction, as shown in FIG. 10a.
The cannulae/housing interfaces were free to clot due to the
sealing material 18. Rust was present on the rotor, as shown in
FIG. 11a.
[0087] The second study of 10 days duration included pump
alterations consisting of a polyurethane coating (Biomer, Ethicon,
Inc.) applied to the seal 42, a pyrolytic carbon impeller 40, a
0.9% saline lubricant flow rate of 4 ml/hr, and the use of heparin
in the saline lubricant. Streptokinase was administered every third
day with the lubricant. The explanted pump was found completely
devoid of thrombus, as shown in FIG. 10b.
[0088] In a third study of 28 days duration, the pump was arranged
similarly to the 10-day study. However, the lubricant flow rate was
increased to 10 ml/hr and 325 mg aspirin and 5-20 mg coumadin were
given daily by mouth to broaden the anticoagulant regimen. A 2 mm
ring thrombus was found at the impeller shaft/seal interface, as
shown in FIG. 10c, and the motor was found to be contaminated by
chest cavity fluid as indicated by chemical corrosion of select
stator windings.
[0089] The fourth study of 35 days used several of the new pump
components. These comprised a stator 34 with several polyurethane
coatings and an increased epoxy potting thickness to prevent fluid
corrosion, as shown in FIG. 12b. Also, a thin layer of titanium
ion-coating was used to passivate the rotor surfaces 46 and reduce
the opportunity for rust formation. Furthermore, the lower housing
bearing surface was deburred to decrease wear on the rotor 36. The
perfusion flow rate and anticoagulation scheme remained unaltered
in this study. The explanted pump had a small irregular ring clot
of 0.5 mm at its widest point surrounding the impeller shaft/seal
junction. The pump lubricant system became completely occluded due
to precipitation of salt from the saline solution. As a result,
significant seepage of blood products below the seal caused
increased friction between the rotor 36 and its bearing surfaces
and eventually caused pump stoppage. However, there were no emboli
at autopsy.
[0090] The last study of 154 days duration included variations from
the previous study. For instance, thin layer chromium ion-coating
was used in place of titanium coating to passivate the rotor 36
because it was available and cheaper. The lubricant was changed
from 0.9% saline to sterile water on post-operative day (POD) 86 in
order to reduce the chance of lubricant system occlusion due to
salt precipitation. Next, based on published reports and
preliminary studies of various antithrombotic drugs in sheep,
urokinase was used as an alternative to streptokinase beginning on
POD 130 because of its suspected superior thrombolytic effect. This
study revealed a pump devoid of thrombus and free of measurable
wear based on light microscopic and dimensional analysis, as shown
in FIG. 10d. Furthermore, no evidence of rust was found on the
rotor surface, as shown in FIG. 11b. However, the pump stator 34
completely failed due to fluid corrosion.
[0091] The lubricant rate was increased from 2 to 10 ml/hr over the
course of the five studies. The intention was to increase fluid
washing of the seal/impeller shaft interface to prevent blood
stasis and thrombus formation. Precipitated salt was identified as
a potential source of lubricant blockage in the 35-day study. As a
result, the 154-day study underwent a change in lubricant from 0.9%
saline to sterile water. The hematocrit and serum free hemoglobin
measures were unaffected by this change.
[0092] Efficiency was calculated for each study by applying
interpolation techniques to bench data of hydraulic performance and
using pump input power as the product of pump voltage and current.
Table II, shown below, shows stator temperature, animal body
temperature, and their difference for each experiment. The average
difference between the stator surface temperature and the animal
core temperature decreased from 5.5-7.degree. C. in the 14 and 10
day studies to approximately 1-3.degree. C. in the 28, 35, and
154-day studies:
2TABLE II Average Values of Pump Efficiency, Stator Temperature,
Animal Temperature, and Temperature Difference for Each Study Study
Duration (days) 14 10 28 35 154 Pump Efficiency (%) 13.6 .+-. 2.1
16.3 .+-. 4.7 20.5 .+-. 2.6 15.0 .+-. 1.6 13.2 .+-. 2.2 Stator
Temperature (.degree. C.) 45.4 .+-. 1.4 44.8 .+-. 1.4 41.8 .+-. 0.7
41.5 .+-. 0.7 41.6 .+-. 1.0 Animal Temperature (.degree. C.) 39.2
.+-. 0.3 39.0.sup.1 40.6 .+-. 0.7 39.0 .+-. 0.7 39.1 .+-. 0.6
Temperature Difference.sup.2 (.degree. C.) 6.8 .+-. 1.5 5.8 .+-.
1.4 1.3 .+-. 0.7 2.4 .+-. 0.5 2.6 .+-. 0.6 Note: All values are
averages over the course of each study .sup.1Measurement taken on
first post-operative day only. .sup.2Temperature Difference =
Stator Temperature-Animal Temperature
[0093] The novel construction of the pump device 10 contributed to
overall improved pump performance as compared to previous pump
devices. Conditioning of both the rotor 36 and lower housing
surfaces has included polishing and passivating and cryogenic
deburring, respectively. These techniques provide even distribution
of lubricant over the moving components, smoother surfaces for
direct contact in the event of lubricant system failure, and
resistance to the oxidation of iron. These studies show that
passivation of the rotor surfaces caused elimination of rotor rust,
as evidenced by a comparison of the prior art rotor used in the
14-day study (FIG. 11a) with the chromium-coated rotor used in the
154-day study (FIG. 11b). The decreases in temperature difference
between the stator and ambient can be related to increases in
lubricant flow rate from 2 to 10 ml/hr (Table II). Based on these
five studies, the implications are that the temperature difference
between the stator surface and ambient decreased by means of
increased convective heat loss through higher lubricant infusion
rates.
[0094] Also, since this pump relies on a fluid bearing between the
rotor and its adjacent surfaces, no correlation between efficiency
and pump surface modification should necessarily be expected. That
is, regardless of the coefficient of static and dynamic friction
between the rotor and journal or rotor and lower housing, the
no-slip condition for the lubricant holds at the solid surfaces,
and the frictional losses are viscous in nature.
[0095] The polyurethane coatings have contributed significantly to
the antithrombogenicity of the pump. Specifically, the application
of polyurethane material 18 to the cannulae/housing interface has
had striking results: no clots have been found in any of the five
studies at this juncture, nor have they been found in 39 other
accumulated implantation studies. This has been a major improvement
of the present pump device 10 based on prior studies (Goldstein, A.
H., Pacella, J. J., Trumble, D. R., et al.: Development of an
implantable centrifugal blood pump. ASAIO Trans 38:M362-M365,
1992). In addition, the polyurethane coating of the seal and the
use of pyrolytic carbon impeller blades have been associated with
decreased thrombus formation, as shown in comparisons of the first
study of 14 days duration and all four subsequent studies (10, 28,
35, and 154-day lengths).
[0096] The prevention of thoracic cavity fluid leakage into the
electronic components of the pump stator 34 through various
environmental sealing techniques has been of utmost importance.
Developed methods involve coating the stator windings in
polyurethane and increasing the size of the stator mold to allow
thicker epoxy coverage. As a result, the occurrence of fluid-based
corrosion has been significantly reduced. No evidence of motor
failure was found in the 35-day study; however, the 154-day study
was ended due to corrosion of the stator by chest fluid. In this
study, the time to catastrophic motor failure secondary to
corrosion was increased significantly from the 28-day study.
[0097] The use of anticoagulation administered in all experiments
following the first 14-day study appears to have contributed to a
significant reduction in pump thrombosis. However, the role of
specific anticoagulant drugs as antithrombotic agents in sheep will
be addressed separately.
[0098] The change from 0.9% saline lubricant to sterile water in
the 154-day study on POD 86 was made based on the findings from the
35-day experiment. This change appears to have reduced the
occurrence of salt deposition within the occlusion system as
indicated by decreased variation in the perfusion system pressures
and flows and more reliable delivery of lubricant to the pump.
[0099] Thus, with the present pump device, modifications in blood
surface materials, blood surface coatings, and electronic component
fabrication and environmental sealing have had a positive impact on
pump performance as indicated by increased survival times,
decreased pump clot formation, less pump component wear, lower pump
stator surface temperatures, and increased in fluid corrosion
resistance. Moreover, both the expense and the learning curve
associated with these long-term implantation studies have prompted
changes from one study to the next. For example, in the 35-day
study, salt thought to be was precipitating from saline solution
due to low lubricant flow rates, blocking the lubricant conduit,
and preventing lubricant from reaching the pump. Eventually, pump
failure occurred. This knowledge was applied in an ongoing study of
154 days by substituting sterile water for saline. The result was
increased reliability of pump lubricant delivery and elimination of
episodes of flow blockage.
[0100] The myriad of device-centered modifications in these studies
were made with the goals of achieving longer survival times,
increasing pump reliability, and proving feasibility of the device
as a VAD. As a result, the centrifugal pump has evolved through
multiple intermediate forms, with increasing improvements in its
performance.
[0101] Although the invention has been described in detail in the
foregoing embodiments for the purpose of illustration, it is to be
understood that such detail is solely for that purpose and that
variations can be made therein by those skilled in the art without
departing from the spirit and scope of the invention except as it
may be described by the following claims.
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