Cardiovascular simulator improvement: pressure versus volume loop assessment.

This article presents improvement on a physical cardiovascular simulator (PCS) system. Intraventricular pressure versus intraventricular volume (PxV) loop was obtained to evaluate performance of a pulsatile chamber mimicking the human left ventricle. PxV loop shows heart contractility and is normally used to evaluate heart performance. In many heart diseases, the stroke volume decreases because of low heart contractility. This pathological situation must be simulated by the PCS in order to evaluate the assistance provided by a ventricular assist device (VAD). The PCS system is automatically controlled by a computer and is an auxiliary tool for VAD control strategies development. This PCS system is according to a Windkessel model where lumped parameters are used for cardiovascular system analysis. Peripheral resistance, arteries compliance, and fluid inertance are simulated. The simulator has an actuator with a roller screw and brushless direct current motor, and the stroke volume is regulated by the actuator displacement. Internal pressure and volume measurements are monitored to obtain the PxV loop. Left chamber internal pressure is directly obtained by pressure transducer; however, internal volume has been obtained indirectly by using a linear variable differential transformer, which senses the diaphragm displacement. Correlations between the internal volume and diaphragm position are made. LabVIEW integrates these signals and shows the pressure versus internal volume loop. The results that have been obtained from the PCS system show PxV loops at different ventricle elastances, making possible the simulation of pathological situations. A preliminary test with a pulsatile VAD attached to PCS system was made.

An electro-fluid-dynamic simulator for the cardiovascular system.

This work presents the initial studies and the proposal for a cardiovascular system electro-fluid-dynamic simulator to be applied in the development of left ventricular assist devices (LVADs). The simulator, which is being developed at University Sao Judas Tadeu and at Institute Dante Pazzanese of Cardiology, is composed of three modules: (i) an electrical analog model of the cardiovascular system operating in the PSpice electrical simulator environment; (ii) an electronic controller, based on laboratory virtual instrumentation engineering workbench (LabVIEW) acquisition and control tool, which will act over the physical simulator; and (iii) the physical simulator: a fluid-dynamic equipment composed of pneumatic actuators and compliance tubes for the simulation of active cardiac chambers and big vessels. The physical simulator (iii) is based on results obtained from the electrical analog model (i) and physiological parameters.

A new technique to control brushless motor for blood pump application.

This article presents a back-electromotive force (BEMF)-based technique of detection for sensorless brushless direct current motor (BLDCM) drivers. The BLDCM has been chosen as the energy converter in rotary or pulsatile blood pumps that use electrical motors for pumping. However, in order to operate properly, the BLDCM driver needs to know the shaft position. Usually, that information is obtained through a set of Hall sensors assembled close to the rotor and connected to the electronic controller by wires. Sometimes, a large distance between the motor and controller makes the system susceptible to interference on the sensor signal because of winding current switching. Thus, the goal of the sensorless technique presented in this study is to avoid this problem. First, the operation of BLDCM was evaluated on the electronic simulator PSpice. Then, a BEMF detector circuitry was assembled in our laboratories. For the tests, a sensor-dependent system was assembled where the direct comparison between the Hall sensors signals and the detected signals was performed. The obtained results showed that the output sensorless detector signals are very similar to the Hall signals at speeds of more than 2500 rpm. Therefore, the sensorless technique is recommended as a responsible or redundant system to be used in rotary blood pumps.

Mock circulatory system for the evaluation of left ventricular assist devices, endoluminal prostheses, and vascular diseases.

A new digital computer mock circulatory system has been developed in order to replicate the physiologic and pathophysiologic characteristics of the human cardiovascular system. The computer performs the acquisition of pressure, flow, and temperature in an open loop system. A computer program has been developed in Labview programming environment to evaluate all these physical parameters. The acquisition system was composed of pressure, flow, and temperature sensors and also signal conditioning modules. In this study, some results of flow, cardiac frequencies, pressures, and temperature were evaluated according to physiologic ventricular states. The results were compared with literature data. In further works, performance investigations will be conducted on a ventricular assist device and endoprosthesis. Also, this device should allow for evaluation of several kinds of vascular diseases.

Avaliação de desempenho em um medidor eletromagnético de baixo custo desenvolvido para aplicações em simulação cardiovascular / Performance evaluation on low cost electromagnetic flow meter for cardiovascular simulation system application

Técnicas cirúrgicas, próteses e dispositivos implantáveis utilizados pela cardiologia estão em constante desenvolvimento. Alguns institutos de pesquisas e universidades desenvolvem simuladores hidrodinâmicos com capacidade de reproduzir os níveis de pressão e vazão do sistema cardiovascular humano, com pistões, válvulas, câmaras de complacência, dispositivos para ajustes e medição de pressão e vazão. Este artigo apresenta o desenvolvimento e a avaliação de um fluxômetro eletromagnético (FE). O custo elevado de um fluxômetro por ultrassom (FUS) pode inviabilizar algumas pesquisas com simuladores; desta forma, uma alternativa com menor custo é apresentada neste trabalho. Baseado na indução eletromagnética para medição de vazão em um fluido iônico, o FE desenvolvido mostrou ser uma solução de baixo custo. O transdutor foi montado em um tubo de plástico com diâmetro interno de 9,5 mm, excitado por um campo magnético de 0,35 T, possui 4 eletrodos que, ligados a um circuito eletrônico, fornecem tensão elétrica proporcional à velocidade do fluido. A equação da tensão induzida, técnicas para calibração, ensaios e resultados são apresentados. Para a realização dos ensaios, foram utilizados um simulador cardiovascular e um FUS como referência. Os dados foram obtidos por hardware e software da National Instruments. Dentre os resultados, destaca-se o baixo desvio padrão de 0,043 L/min do FE para uma vazão de 3,56 L/min. O maior erro porcentual relativo foi de 1,49 ± 1,25%. Em um dos gráficos de vazão do FE observou-se um comportamento não monotônico, confirmado por uma análise da resposta em freqüência, observando-se maior amplitude na segunda, terceira e quarta harmônicas. Os resultados indicaram que o FE pode substituir o FUS em aplicações com simuladores hidrodinâmicos.

Implantable devices, prosthesis and their associated surgical techniques in cardiology are constantly under development. Many research groups have been using hydrodynamic simulators as a tool to assist the development in cardiovascular area, capable to mimic pressure and flow found in human cardiovascular system. They are made with plastic tubes, compliances chambers, valves, moving diaphragms and clamps for pressure and flow adjustments. The high cost of ultrasonic flow meters (UF) may difficult, for some research groups, the development of their own mock systems. This paper presents a simple and low cost electromagnetic flow meter (EF) useful for those cardiovascular simulation systems. EF measures flow of ionic fluids based on electromagnetic induction. A special transducer was assembled directly on a plastic tube with 9.5 mm of inner diameter. The transducer has 4 electrodes and, when excited by a magnetic field of 0.35 tesla, detects electric tension that is proportional to the fluid velocity. In this paper, induced electric potential equation, calibration techniques, performance tests and results are presented. A cardiovascular simulation system was used as test setup with an UF (Transonic Systems Inc.) as comparative flow meter. The signals were acquired by a PCI-6036E card and processed with LabView® 7.1 (National Instruments). The results from EF showed a standard deviation (SD) of 0.043 L/min for a flow of 3.56 L/min. The largest relative error was of 1.49 ± 1.25%. In one flow signal from the EF, the non monotonic behavior suggests a rich harmonic signal, which was confirmed by an analysis in the frequency domain. In vitro performance tests indicated that our EF can substitute the commercial available UF for hydrodynamic simulator application.