CENTRIFUGAL BLOOD PUMP FOR CARDIOPULMONARY
BYPASS AND CIRCULATION SUPPORT WITH LOW PRIMING
AND CERAMIC BEARING
Juliana Leme1,2, Cibele da Silva1,3, Jeison Fonseca1, Bruno Utiyama1,3, Beatriz
Uebelhart 1,3, Pedro Antunes1, Jarbas Dinkhuysen1, José Biscegli1,2, Aron Andrade1,2
1
Bioengineering Division, Adib Jatene Foundation, São Paulo (SP), Brazil
Medicine/Technology and Intervention in Cardiology, University of São Paulo, São Paulo (SP), Brazil
3
Mechanical Engineering, University of Campinas, Campinas (SP), Brazil
E-mail: [email protected]
2
Abstract: A new model of centrifugal blood pump for temporary ventricle assist device has been
developed and evaluated. This pump can be used as cardiopulmonary bypass (CPB) and circulation
support application. Device design is based on centrifugal pumping principle associated to the usage of
ceramic bearing, resulting in a pump with reduced priming (35 ± 5 ml) and application up to 30 days.
Computational fluid dynamic (CFD) analysis is an efficient tool to optimize flow path geometry,
maximize hydraulic performance and minimize shear stress, consequently, decreasing hemolysis. Initial
studies were conducted with three different impellers, analyzing flow behavior in pump inlet port. Flow
analysis in different impellers can determine the best impeller design. After CFD studies, rapid
prototyping was made for production of pump prototypes with three different impellers. “In vitro”
experiments were performed with those three prototypes with small differences in their impeller designs,
using a mock loop system composed by Tygon® tubes, oxygenator, digital flow meter, pressure monitor,
electronic driver and adjustable clamp for flow control. Each prototype was tested, where flow versus
pressure curves were obtained for rotational speed of 1000, 1500, 2000, 2500 and 3000 rpm. In the next
future, the results of CFD analysis and hydrodynamic performance will be compared to flow visualization
studies and hemolysis tests.
Keywords: blood pump, centrifugal pump, cardiopulmonary bypass
1.
INTRODUTION
The use of centrifugal blood pumps in various applications has increased
rapidly. This fact became understandable because of some advantages when compared
to other devices as roller pumps, axial pumps or pulsatile pumps (Nosé, 1997).
Centrifugal pumps are safer and less traumatic for cardiopulmonary bypass
(CPB), because they cannot pump large amounts of air and cannot create considerable
low pressure at inlet port or high pressure at outlet port (Lynch, 1978).
The Department of Bioengineering from Institute Dante Pazzanese of
Cardiology has developed and evaluated a new model of centrifugal blood pump for
temporary ventricle assist device (TVAD). This pump can be used as cardiopulmonary
bypass (CPB) and circulatory support application with or without membrane
oxygenator. Device design is based on centrifugal pumping principle associated to the
usage of ceramic bearing, eliminating the use of conventional bearings and sealing to
increase durability and anti-thrombogenic features, resulting in a pump with reduced
priming (35 ± 2 ml) and application up to 30 days, the Fig. 1 shows the external shape
of this new centrifugal blood pump.
Figure 1. This image shows the external shape of this new centrifugal blood pump.
The main objective of using computational fluid dynamic (CFD) analysis is to
get some relevant information of the device performance, before making a prototype.
This can help to achieve an efficient hydrodynamic performance by changing the
geometry of some pump.
2.
MATERIALS AND METHODS
Computational Fluid Dynamics (CFD)
CFD analysis is an efficient tool to optimize flow path geometry, maximize
hydraulic performance and minimize shear stress, consequently, decreasing hemolysis.
Initial studies were conducted with two different rotors, without impellers for
analysis of flow direction and with impellers for analysis of flow behavior in pump inlet
port as, shown in Fig. 2.
Figure 2. (a) This image shows the rotor without impeller and (b) the rotor with
impeller for analysis of inlet flow behavior and direction.
CFD analysis was performed with based commercial CFD package (ANSYS,
Canonsburg, Pennsylvania, USA).
In this study, fluid (blood) was assumed as being incompressible homogeneous
Newtonian fluid. The pump was operating at constant fluid velocity, flow rate of 5
L/min and total pressure head of 350 mmHg.
In Vitro Tests
In Vitro test was performed with one prototype (rotor with impeller) for
hydrodynamic performance analysis. A closed loop circuit filled with solution (1/3
glycerin, 1/3 water and 1/3 alcohol 99%, at 25ºC), simulating the density and viscosity
of blood, was used in these tests (Legendre, 2009).
The circuit consists of a polycarbonate reservoir, normally used for CPB, with
polyvinyl chloride 3/8-inch tubes (Vital, Nipro, Sorocaba, Brazil), see Fig. 3. Pressure
monitor (DX2020, Dixtal, Sao Paulo, Brazil) was used at pump inlet and outlet ports for
total pressure head registration (Bock, 2008). Flowmeter (HT110, Transonic Systems,
Ithaca, NI, USA) was used with flow probe connected at pump outlet tube. Pumping
rotational speed was fixed at 1000, 1500, 2000, 2500 and 3000 rpm, using an electronic
driver (Bio-console 540, Meditronic, Mineapolis, USA). Flow was gradually increased
between 0 L/min and maximum flow for each pumping rotational speed by an
adjustable clamp (Andrade, 1996).
Flowmeter
Electronic
Device
Prototype
Reservoir
Figure 3. This image shows the closed loop circuitry for hydrodynamic
performance tests.
3.
RESULTS
Computational Fluid Dynamics (CFD)
CFD analysis is an efficient tool to get the best design prior to make the final
prototype of a centrifugal blood pump. CFD analysis without impeller, Fig. 4, shows
flow direction vectors homogeneous and high velocity in the outlet port.
Figure 4. This image shows the CFD rotor without impeller. Vectors are homogeneous
in the pump.
CFD analysis with impeller, Fig. 5, shows zones of high velocity, and huge
vortices in the outlet port that could cause more damage to the blood, contributing to
increase hemolysis indexes. Some changes in the outlet port angle or in the impeller
design could minimize those problems.
Figure 5. This image shows the rotor with impeller with high velocity and turbulence at
the outlet port.
In Vitro Tests
The result of pumping rotational speed is shown as the relationship between total
pressure head and flow. Total pressure head (ΔP) were calculated between inlet and
outlet port and flow was adjusted by the clamp.
Figure 6 shows hydrodynamic performance curves for each rotational speed.
Hydrodynamic Performance
300
ΔP (mmHg)
250
200
1000
150
1500
2000
100
2500
50
3000
0
0.00
2.00
4.00
6.00
8.00
10.00
12.00
14.00
16.00
Flow(L/min)
Figure 6. Hydrodynamic performance curves of TVAD prototype.
Hydrodynamic performance was considered satisfactory. However, small
modifications are being studied and new hydrodynamic performance tests are being
prepared conducted.
4.
DISCUSSION
Flow analysis with different impellers can determine the best impeller design.
CFD analysis shows if this pump is efficient. However, some changes are necessary to
reduce turbulence at the outlet port and at the zone of high velocity and will be
performed. In the future, results from CFD analysis will be compared to flow
visualization and hydrodynamic performance studies to determine the best design.
ACKNOWLEDGMENTS
The authors would like to thanks the Adib Jatene Foundation (FAJ), Institute
Dante Pazzanese of Cardiology (IDPC), Heart Hospital (HCor) and FAPESP for
partially supporting this research.
REFERENCES
Andrade, A., et al., 1996, “Characteristics of a Blood Pump Combinig the Centrifugal and Axial Pumping
Principles: The Spiral Pump”, Artificial Organs, 20(6):605-612.
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Nicolosi, D., Andrade, A. New centrifugal blood pump with dual impeller and Double pivot bearing
system: wear evaluation in bearing system, performance tests and preliminary hemolysis. Artificial
Organs, 2008; 32(4), 329-333.
Legendre, D.F., 2009, “Estudo de Comportamento de fluxo através de modelo físico e computacional de
aneurisma de aorta infra-renal obtido por tomografia, Tese de Doutorado, Escola Politécnica da
Universidade de São Paulo.
Lynch, M.F., et al. Centrifugal blood pumping for open heart surgery, Minn Med, 1978; 536-7.
Nosé, Y., Kawahito, K. Hemolysis in different centrifugal pumps. Artificial Organs, 1997; 21(4):323-326.