Tarcísio Leão

Implantable centrifugal blood pump with dual impeller and double pivot bearing system: electromechanical actuator, prototyping, and anatomical studies.

An implantable centrifugal blood pump has been developed with original features for a left ventricular assist device. This pump is part of a multicenter and international study with the objective to offer simple, affordable, and reliable devices to developing countries. Previous computational fluid dynamics investigations and wear evaluation in bearing system were performed followed by prototyping and in vitro tests. In addition, previous blood tests for assessment of normalized index of hemolysis show results of 0.0054±2.46 × 10⁻³ mg/100 L. An electromechanical actuator was tested in order to define the best motor topology and controller configuration. Three different topologies of brushless direct current motor (BLDCM) were analyzed. An electronic driver was tested in different situations, and the BLDCM had its mechanical properties tested in a dynamometer. Prior to evaluation of performance during in vivo animal studies, anatomical studies were necessary to achieve the best configuration and cannulation for left ventricular assistance. The results were considered satisfactory, and the next step is to test the performance of the device in vivo.

Speed control of the Implantable Centrifugal Blood Pump to avoid aortic valve stenosis: Simulation and implementation

This paper presents a computational simulation and implementation of electromechanical actuator performance of the Implantable Centrifugal Blood Pump (ICBP) as part of a speed controller study to avoid aortic valve stenosis. The ICBP as Left Ventricular Assist Device (LVAD) is an electromechanical device designed for long-term assist left heart in performing its functions. The centrifugal pumps are controlled by varying the rotor (impeller) speed. ICBP successful operation depends on an appropriate rotational speed control system, ensuring: 1) no reverse flow through the pump during left ventricle diastolic phase, and 2) aortic valve correct opening, avoiding later valve stenosis. A computational model of the actuator done in Matlab / Simulink (R2010b, Mathworks, Massachusetts, USA) was used in the simulations. Control and signal processing was used Labview (National Instruments, Austin, USA). Signals equivalent to intraventricular pressure and a variable rotational reference were used to evaluate motor and speed controller performance. Speed values were chosen so that pressure pump exceeds intraventricular pressure only after the opening of aortic valve. The proposed controller is Proportional-Integral (PI) type. The simulation results were satisfactory, no steady error in response speed. Practical tests showed satisfactory results to follow speed reference signal, as simulated. Future studies will evaluate the bands control.

Modeling study of an Implantable Centrifugal Blood Pump actuator with redundant sensorless control

The permanent magnet brushless direct current motor (BLDC), have been the main component in most of the Ventricular Assist Devices (VAD) development. An Implantable Centrifugal Blood Pump is being developed at the Institute Dante Pazzanese of Cardiology (IDPC) as VAD to assist patients with cardiovascular diseases. To develop a high performance controller is necessary to have a reliable virtual model of the BLDC. Toolbox SimPowerSystems software package was used to study the dynamic system. Permant Magnet Synchronous Machine (PMSM)block implements the differential equations for the motor through a state-space model, this is main contribution of this work. Sensorless control was used as redundant position rotor control. The model showed satisfactory results when compared with data given by the manufacturer in its catalog. In future works, the results presented in this work will be used to improve the motor model. Thus, it will allow reliable simulations of new proposed controllers.

Introductory tests to in vivo evaluation: magnetic coupling influence in motor controller.

An implantable centrifugal blood pump has been developed with original features for a ventricle assist device (VAD). This pump is part of a multicenter and international study with objective to offer simple, affordable, and reliable devices to developing countries. Previous computational fluid dynamics investigations were performed followed by prototyping and in vitro tests. Also, previous blood tests for assessment of hemolysis showed mean normalized index of hemolysis (NIH) results of 0.0054 ± 2.46 × 10−3 mg/100 L (at 5 L/min and 100 mm Hg). To precede in vivo evaluation, measurements of magnetic coupling interference and enhancements of actuator control were necessary. Methodology was based on the study of two different work situations (1 and 2) studied with two different types of motors (A and B). Situation 1 is when the rotor of pump is closest to the motor and situation 2 its opposite. Torque and mechanical power were collected with a dynamometer (80 g/cm) and then plotted and compared for two situations and both motors. The results showed that motor A has better mechanical behavior and less influence of coupling. Results for situation 1 showed that it is more often under magnetic coupling influence than situation 2. The studies lead to the conclusion that motor A is the best option for in vivo studies as it has less influence of magnetic coupling in both situations.

Study of a Centrifugal Blood Pump in a Mock Loop System

An implantable centrifugal blood pump (ICBP) is being developed to be used as a ventricular assist device (VAD) in patients with severe cardiovascular diseases. The ICBP system is composed of a centrifugal pump, a motor, a controller, and a power supply. The electricity source provides power to the controller and to a motor that moves the pumps rotor through magnetic coupling. The centrifugal pump is composed of four parts: external conical house, external base, impeller, and impeller base. The rotor is supported by a pivot bearing system, and its impeller base is responsible for sheltering four permanent magnets. A hybrid cardiovascular simulator (HCS) was used to evaluate the ICBPs performance. A heart failure (HF) (when the heart increases beat frequency to compensate for decrease in blood flow) was simulated in the HCS. The main objective of this work is to analyze changes in physiological parameters such as cardiac output, blood pressure, and heart rate in three situations: healthy heart, HF, and HF with left circulatory assistance by ICBP. The results showed that parameters such as aortic pressure and cardiac output affected by the HF situation returned to normal values when the ICBP was connected to the HCS. In conclusion, the test results showed satisfactory performance for the ICBP as a VAD.

Design, Manufacturing and Tests of an Implantable Centrifugal Blood Pump

An implantable centrifugal blood pump was developed for long-term ventricular assistance in cardiac patients. In vitro tests were performed, as wear evaluation, performance tests and hemolysis tests in human blood. Numerical computational simulations were performed during design process in order to predict its best geometry. Wear evaluations helped to select the best materials for double pivot bearing system proposed to achieve longer durability. Performance tests pointed the best impeller geometry. The implantable centrifugal blood pump was compared with other blood pumps founded in literature. The proposed implantable centrifugal blood pump showed the best performance. But, its results showed a strong descendant curve in high flow. Other prototype was manufactured with a different inlet port angle to overcome this problem. The normalized index of hemolysis (NIH) measured 0.0054 mg/100L that can be considered excellent since it is close to the minimum found in literature (between 0.004 g/ 100L e 0.02 g/ 100L). The authors’ expectation is that this pump will become a promising Technological Innovation for Sustainability.

ESTUDO DA DINÂMICA DE UM ATUADOR ELETROMECÂNICO DA BOMBA DE SANGUE CENTRÍFUGA IMPLANTÁVEL

O motor de corrente contínua sem escovas (BLDC, do inglês “Brushless Direct Current”), tem sido o principal componente de propulsão no desenvolvimento dos Dispositivos de Assistência Ventricular (DAV). Dentre as características que o faz ser utilizado em bomba implantáveis destaca-se a ausência de escovas, o que permite descartar o desgaste inevitável das escovas observado em outros motores e intolerável neste tipo de dispositivo. A operação em altas velocidades, quando comparado com outras opções de motores, e o tamanho reduzido também são fatores compatíveis com essa utilização [1, 2]. O motor elétrico trifásico de corrente contínua sem escova é um motor síncrono de ímãs permanentes localizados no rotor e bobinas localizadas no estator, geralmente, conectadas em estrela com controle por inversor do tipo ponte H [2, 3]. A operação de um BLDC é realizada através da comutação estratégica das bobinas, assim como ocorre em um motor de passo. A comutação é realizada por um circuito que fornece corrente às bobinas do motor em função da posição do rotor. A corrente de fase de um BLDC, normalmente é retangular e sincronizada com a FCEM (força contra-eletromotriz, ou BEMF do inglês “Back Electromotive Force”) para produzir torque e velocidade constante, apresentando forma trapezoidal, geralmente. Sendo esta a principal característica de controle [4, 5]. A técnica escolhida para o controle da posição do rotor foi a “sensorless”, sem sensores, por dispensar o uso de sensores de posicionamento, que são focos de falhas, o que deve ser evitado em dispositivos implantáveis. A não utilização de sensores também reduz a quantidade de fios para controle do motor, fato que contribui para a prática cirúrgica e reduz complicações pós-operatórias [6 – 8]. Uma bomba centrífuga implantável está sendo estuda no Instituto “Dante Pazzanese” de Cardiologia – IDPC como DAV para auxiliar pacientes com doenças cardiovasculares. Este dispositivo pode ser dividido em: bomba de sangue de fluxo contínuo centrífugo, um motor elétrico BLDC, um controlador para acionar o motor e um sistema de baterias. As bombas centrífugas representam a maioria das pesquisas desenvolvidas atualmente, a qual permite operar em rotações mais baixas que as bombas de fluxo contínuo axiais; obter menores taxas de hemólise, ou seja, menores danos aos elementos do sangue; ter dimensões compatíveis com a implantabilidade total e alcançar vida estimada do conjunto, em assistência, de 2 anos [9 – 11]. Os motores utilizados em bombas sangüíneas centrífugas com acoplamento magnético requerem potência para a movimentação do rotor do motor e para o acoplamento com a bomba, Figura 1 [1, 9, 11, 12]. Nos casos onde o acoplamento é feito diretamente com a bomba é necessário prover potência adicional em função do maior “air gap” (distância entre os magnetos e as bobinas). E quando há um circuito eletromagnético separado do acoplamento, o motor pode assumir maiores dimensões [13]. O objetivo desse trabalho é obter um modelo dinâmico do atuador eletromecânico da bomba centrífuga, com auxílio do programa Matlab / Simulink, onde parâmetros mecânicos e eletromagnéticos foram propostos para as simulações. O programa Matlab/Simulink foi escolhido como ambiente virtual de simulações e modelagem por permitir a integração dos dados de simulações com outros programas, especialmente o programa Comsol Multiphysics, o qual está sendo utilizado para modelar a bomba centrífuga.