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
1Bioengineering Division, Adib Jatene Foundation, São Paulo (SP), Brazil
2Medicine/Technology and Intervention in Cardiology, University of São Paulo, São Paulo (SP), Brazil
3Mechanical Engineering, University of Campinas, Campinas (SP), Brazil
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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
- 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.
- 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 5L/min and total pressure head of 350 mmHg.
In Vitro Tests
In Vitro test was performed withone 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).
Figure 3. Thisimage shows the closed loop circuitry for hydrodynamic performance tests.
- 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.
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.
- 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.
Bock, E., Ribeiro, A., Silva, M., Antunes, P., Fonseca, J., Legendre, D., Leme, J., Arruda, C., Biscegli, J., 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.