Aron Andrade

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.

Characteristics of a Blood Pump Combining the Centrifugal and Axial Pumping Principles: The Spiral Pump

Two well-known centrifugal and axial pumping principles are used simultaneously in a new blood pump design. Inside the pump housing is a spiral impeller, a conically shaped structure with threads on the surface. The worm gears provide an axial motion of the blood column through the threads of the central cone. The rotational motion of the conical shape generates the centrifugal pumping effect and improves the efficiency of the pump without increasing hemolysis. The hydrodynamic performance of the pump was examined with a 40% glycerin-water solution at several rotation speeds. The gap between the housing and the top of the thread is a very important factor: when the gap increases, the hydrodynamic performance decreases. To determine the optimum gap, several in vitro hemolysis tests were performed with different gaps using bovine blood in a closed circuit loop under two conditions. The first simulated condition was a left ventricular assist device (LVAD) with a flow rate of 5 L/min against a pressure head of 100 mm Hg, and the second was a cardiopulmonary bypass (CPB) simulation with a flow rate of 5 L/min against 350 mm Hg of pressure. The best hemolysis results were seen at a gap of 1.5 mm with the normalized index of hemolysis (NIH) of 0.0063 ± 0.0020 g/100 L and 0.0251 ± 0.0124 g/100 L (mean ± SD; n = 4) for LVAD and CPB conditions, respectively.

Computational Fluid Dynamics Investigation of a Centrifugal Blood Pump

In the development of a ventricular assist device, computational fluid dynamics (CFD) analysis is an efficient tool to obtain the best design before making the final prototype. In this study, different designs of a centrifugal blood pump were developed to investigate flow characteristics and performance. This study assumed the blood flow as being an incompressible homogeneous Newtonian fluid. A constant velocity was applied at the inlet; no slip boundary conditions were applied at device wall; and pressure boundary conditions were applied at the outlet. The CFD code used in this work was based on the finite volume method. In the future, the results of CFD analysis can be compared with flow visualization and hemolysis tests.

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.

Magnetic suspension of the rotor of a ventricular assist device of mixed flow type.

This work presents results of preliminary studies concerning application of magnetic bearing in a ventricular assist device (VAD) being developed by Dante Pazzanese Institute of Cardiology-IDPC (São Paulo, Brazil). The VAD-IDPC has a novel architecture that distinguishes from other known VADs. In this, the rotor has a conical geometry with spiral impellers, showing characteristics that are intermediate between a centrifugal VAD and an axial VAD. The effectiveness of this new type of blood pumping principle was showed by tests and by using it in heart surgery for external blood circulation. However, the developed VAD uses a combination of ball bearings and mechanical seals, limiting the life for some 10 h, making impossible its long-term use or its use as an implantable VAD. As a part of development of an implantable VAD, this work aims at the replacement of ball bearings by a magnetic bearing. The most important magnetic bearing principles are studied and the magnetic bearing developed by Escola Politécnica of São Paulo University (EPUSP-MB) is elected because of its very simple architecture. Besides presenting the principle of the EPUSP-MB, this work presents one possible alternative for applying the EPUSP-MB in the IDPC-VAD.

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.

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.

A New Model of Centrifugal Blood Pump for Cardiopulmonary Bypass: Design Improvement, Performance, and Hemolysis Tests

A new model of blood pump for cardiopulmonary bypass (CPB) application has been developed and evaluated in our laboratories. Inside the pump housing is a spiral impeller that is conically shaped and has threads on its surface. Worm gears provide an axial motion of the blood column. Rotational motion of the conical shape generates a centrifugal pumping effect and improves pumping performance. One annular magnet with six poles is inside the impeller, providing magnetic coupling to a brushless direct current motor. In order to study the pumping performance, a mock loop system was assembled. Mock loop was composed of Tygon tubes (Saint-Gobain Corporation, Courbevoie, France), oxygenator, digital flowmeter, pressure monitor, electronic driver, and adjustable clamp for flow control. Experiments were performed on six prototypes with small differences in their design. Each prototype was tested and flow and pressure data were obtained for rotational speed of 1000, 1500, 2000, 2500, and 3000 rpm. Hemolysis was studied using pumps with different internal gap sizes (1.35, 1.45, 1.55, and 1.7 mm). Hemolysis tests simulated CPB application with flow rate of 5 L/min against total pressure head of 350 mm Hg. The results from six prototypes were satisfactory, compared to the results from the literature. However, prototype #6 showed the best results. Best hemolysis results were observed with a gap of 1.45 mm, and showed a normalized index of hemolysis of 0.013 g/100 L. When combined, axial and centrifugal pumping principles produce better hydrodynamic performance without increasing hemolysis.

Bomba sangüínea espiral: concepção, desenvolvimento e aplicação clínica de projeto original

Introduction: This paper addresses an original project that encompasses the concept, development, and clinical application of a helical bypass pump using the association of the centrifuge and axial propulsion forces based on the Archimedes principle, referred to as Spiral Pump. This project has obtained Brazilian Patent and a Preliminary International Report defining it as an invention. Methods: We seek to evaluate the homodynamic capacity and the impact of its application to the blood cells by means of experimental “in vitro” tests, such as Hydrodynamic Efficiency, Normalized Hemolytic, and Flow Visualization. The “in vivo” experimental tests were carried-out in lambs submitted to bypass for 6 hours and in 43 patients undergoing bypass heart surgery using the Spiral Pump. Results: When the rotor – plastic carcass gap was 1.5 mm, the generated flow was nearly 9 L/min; pressure above 400 mmHg at 1500 rpm, normalized hemolytic indexes not superior to 0.0375 g/1001 under high-flow and pressure conditions, and by the flow visualization at the entrance and exit of the pump, as well as the extremity of the spindles. At the “in vivo” tests in the lambs, the pump was capable of maintaining adequate pressure and the Free Hemoglobin ranged between 16.36 mg% and 44.90 mg%. Evaluating the results of the 43 patients using this pump in bypass heart operations we observed that the Free Hemoglobin ranged from 9.34 mg% to 44.16 mg% before and after surgery, respectively; the Serum Fibrinogen from 236.65 mg% to 547.26 mg%; Platelet Blood Count from 152.465 to 98.139; and the Lactic Dehydrogenase from 238.12 mg% to 547.26

Testes in vitro e in vivo com o Coração Artificial Auxiliar (CAA): um novo modelo de coração artificial totalmente implantável e heterotópico

A miniaturized artificial heart is being developed in the authors laboratories, the Auxiliary Total Artificial Heart (ATAH). This device is an electromechanically driven ATAH using a brushless direct current (DC) motor fixed in a center aluminum piece. This pusher plate type ATAH is controlled based on Frank-Starlings law. The beating frequency is regulated through the change of the left preload, assisting the natural heart in obtaining adequate blood flow. With the miniaturization of this pump, the average sized patient can have the surgical procedure of implantation in the right thoracic cavity performed without removal of the natural heart. The left and right stroke volumes are 35 ml and 32 ml, respectively. In vitro tests were made and the performance curves demonstrated that the ATAH produces 5L/min of cardiac output at 180 bpm (10 mmHg of left inlet mean pressure and 100 mmHg of left outlet mean pressure). Preliminary acute In vivo tests were performed in two sheeps with 50 ± 5 kg, during 5 hours. The ATAH performance is satisfactory for helping the natural heart to obtain the required blood flow and arterial pressure. With the ATAH and the natural heart working simultaneously the ATAH control system is simpler, also the risks of a fatal misoperation is minor compared to a total artificial heart, for patients that still present some cardiac function.A miniaturized artificial heart is being developed in the authors laboratories, the Auxiliary Total Artificial Heart (ATAH). This device is an electromechanically driven ATAH using a brushless direct current (DC) motor fixed in a center aluminum piece. This pusher plate type ATAH is controlled based on Frank-Starlings law. The beating frequency is regulated through the change of the left preload, assisting the natural heart in obtaining adequate blood flow. With the miniaturization of this pump, the average sized patient can have the surgical procedure of implantation in the right thoracic cavity performed without removal of the natural heart. The left and right stroke volumes are 35 ml and 32 ml, respectively. In vitro tests were made and the performance curves demonstrated that the ATAH produces 5L/min of cardiac output at 180 bpm (10 mmHg of left inlet mean pressure and 100 mmHg of left outlet mean pressure). Preliminary acute In vivo tests were performed in two sheeps with 50 ± 5 kg, during 5 hours. The ATAH performance is satisfactory for helping the natural heart to obtain the required blood flow and arterial pressure. With the ATAH and the natural heart working simultaneously the ATAH control system is simpler, also the risks of a fatal misoperation is minor compared to a total artificial heart, for patients that still present some cardiac function.