Artificial Heart Pump Research Articles

MINIMUM POWER/MAXIMUM LOAD CONTROL STRATEGIES FOR ACTIVE MAGNETIC BEARINGS IN ARTIFICIAL HEARTS

Ventricular assist device impellers using active magnetic bearings are now in the development stages. These pumps must be very compact yet have two important control strategies for operation: minimum power consumption and high static and dynamic load capacity. It is very important that the power consumption be minimized to avoid heating the blood yet provide large load capacity to keep the pump impeller magnetically suspended under high forces due to fluid pressures. The magnetic suspension must operate over large ranges of clearance, from one side of the pump housing clearance to the other, and over large ranges of force relative to the magnetic bearing maximum load capacity. Normal control strategies for magnetic bearings assuming small variation about a nominal operating point will generally not be applicable for artificial heart pumps. Two specific control active magnetic bearing strategies are considered: 1) constant flux sum (CFS) and 2) constant flux product (CFP). In CFS, the sum of two magnetic actuator fluxes, one on each side of the impeller, is kept fixed but the bias flux is adjusted to minimimize the power while keeping a specified value of static and dynamic load capacity. In CFP, the product of the two magnetic actuator fluxes is kept constant while adjusting the bias flux to minimize power yet obtain maximim load capacity. It is shown that under certain conditions, the CFS is better yet under different conditions, the CFP has advantages. The implications for control of artificial heart pumps are discussed.

Electronmicroscopic changes in selected vital organs after long-term total artificial heart pumping in animal experiments.

Electronmicroscopic (EM) evaluation of selected vital organs (liver, kidney, lung) informs us about otherwise hardly detectable changes during total artificial heart (TAH) pumping. In our experiments, we compared 2 groups of long-surviving animals in which the TAH TNS-BRNO pneumatic device was implanted (TNS-BRNO-II and VII in 45 experiments, TNS-BRNO-III in 1 experiment, and TNS-BRNO-VIII in 1 experiment). In 4 experiments, the Rostock TAH (NABEL, TAH Research Center, Rostock, Germany) was implanted. One group of 22 animals with an average survival of 162 days (the longest, 293 days) was submitted to an antihypertensive treatment; another 1 of 29 calves with an average survival of 98 days (the longest, 173 days) was untreated. The evaluation was performed using a scale (0 to 3) based on very precisely fixed criteria. EM pathologic changes documented various stages of ischemic damage. Except for the liver, no significant difference was found between both groups, despite the substantially prolonged survival in the treated group. Very important was the general state of mitochondria, endoplasmic reticulum, and nucleus. Further, the state of glomerular podocytes in the kidney and the state of interalveolar septa and of pneumocytes constituting the air-blood barrier for gas exchange in the lungs are especially important. In some animals of both groups, the EM findings were completely normal, especially in the lung.

Numerical analysis of blood flow in the clearance regions of a continuous flow artificial heart pump.

The CFVAD3 is the third prototype of a continuous flow ventricular assist device being developed for implantation in humans. The pump consists of a fully shrouded 4-blade impeller supported by magnetic bearings. On either side of this suspended rotating impeller is a small clearance region through which the blood flows. The spacing and geometry of these clearance regions are very important to the successful operation of this blood pump. Computational fluid dynamics (CFD) solutions for this flow were obtained using TascFlow, a software package available from AEA Technology, U.K. Flow in these clearance regions was studied parametrically by varying the size of the clearance, the blood flow rate into the pump, and the rotational speed of the pump. The numerical solutions yield the direction and magnitude of the flow and the dynamic pressure. Experimentally measured pump flow rates are compared to the numerical study. The results of the study provide guidance for improving pump efficiency. It is determined that current clearances can be significantly reduced to improve pump efficiency without negative impacts.

Artificial Heart Pumps and Driving Systems

Artificial Heart Pumps and Driving Systems

Development of Total Artificial Heart with Economical and Durability Advantages

To develop a total artificial heart (TAH) pump system, we created a design paying particular attention to durability and cost. We adopted a pneumatically driven sac type artificial heart, where the configuration of the sac was decided according to the methodology of flow visualization. Its configuration is almost round to achieve as little stagnation as possible and a low turbulent flow. The main body of the sac was made using polyvinyl chloride (PVC) paste. The paste was poured into an external mold, and heated in a hot air drying oven. Coating was performed using polyurethane. The basic performance of this pump system was tested using a model circulation circuit, and a fitting study through acute animal experiment, using a healthy adult goat, was carried out. As for the TAH produced experimentally, a pump output exceeding 5.0 l/min in the model circulation circuit was provided. Implantation in the internal pleural cavity of a healthy adult goat, 55 kg in weight, proved possible and quite easy in comparison. It is thought that a more refined design in the connector part is desirable. Furthermore, a chronic experiment with the TAH will be carried out, and examination will need to be repeated in the future.

A remotely controlled and powered artificial heart pump.

An intrathoracic pulsatile artificial heart pump has been developed. Transcutaneous energy transfer and biotelemetry systems provide continuous power and remote monitoring and control, with no percutaneous connections required. The electrohydraulic system can be used either as a ventricular assist device or with modifications as a total artificial heart. The device uses a unidirectional axial flow pump coupled with a pressure activated one-way valve to allow hydraulic fluid to passively return to the volume displacement chamber during diastole. The transcutaneous energy transfer system provides power to the device and recharges the implantable battery pack. A wearable external controller and external battery pack provide the patient enhanced mobility and thus an improved quality of life. The biotelemetry system allows control and monitoring of the device after implantation, as well as an added capability to monitor and control the device remotely over public communication lines. Early prototypes have functioned failure free for up to 3 years in vitro. The device has sustained circulation in vivo for up to 4 days. Design optimization is continuing, and chronic in vivo evaluation is planned.

The artificial heart: history and current status.

Twenty-years ago groups from California to Massachusetts were actively involved in the development of an artificial heart. From biomaterials development to biomedical power sources, the supporting industry and spin-off benefit was broad indeed. Young people were seeking careers in biomedical engineering and science. The National Institutes of Health was supporting artificial heart research at $10 to $12 million dollar levels. Groups at Andros, Inc. (now Baxter Novacor) and Stanford, Thoratec, Penn State and the Hershey Medical Center, Cleveland Clinic and the Division of Artificial Organs, the University of Utah, the Texas Heart Institute and the Baylor College of Medicine, Thermal Electron Corporation, and many more were the source of research and breakthrough development of pumps and systems for artificial hearts. We reported on performance criteria for an artificial heart pump at the First Biomechanics Symposium in 1973 [1]. By the beginning of the decade of the 90's, thousands of presentations had been made and manuscripts written reporting significant progress in the development of artificial heart pumps and systems. The Heart, Lung and Blood Institute of the National Institutes of Health was supporting an artificial heart contract research and development program at a level of $6 million dollars in 1991 [2]. Broad basic research grant activity also continues. The National Institutes of Health's artificial heart program received renewed support from the Institute of Medicine's special review in 1991 [3]. In December of 1992, the 16th Annual Cardiovascular Science and Technology Conference attracted over 500 attendees. This annual conference has provided a continuing forum for an update on progress in artificial heart development.

Development of Artificial Heart and Intra Aortic Balloon Pump Using Linear Pulse Motor

This paper deals with an Intra-Aortic Balloon Pump (IABP) and Artificial Heart (AH) using linear pulse motors (LPMs). The device characteristics may be summarized as follows. The maximum static thrusts of the LPM for the IABP and the LPM for the AH were 530 N and 107 N respectively. The kinetic thrusts of the LPMs for the IABP and for the AH were 350 N and 67 N respectively. The target thrust values were obtained in experiments. In mock tests, the expansion time of the balloon in the LPM-driven IABP was found to be 100 ms. In future, existing IABPs will be miniaturized by the adoption of LPMs. The instantaneous flow rate of the LPM-driven AH can be controlled by employing an acceleration drive pattern with the LPM. In mock circulatory tests, an LPM-driven AH delivered a flow rate of 5.3 L/min at a pulse rate of 100 beats/min, sufficient to sustain an adult's life. The temperature of the AH rose 11C during operation; suppression of increases in temperature is recognized as an important problem.

リニアモータ駆動型両心人工心臓の性能試験

In order to actualize an implantable use, a linear pulse motor-driven artificial heart, LAH-S91, with left and right blood pumps was studied continuously by the authors. Small size and high thrust actuators are required in the development of the LAH, and the evaluation method of a trial actuator is a problem one should not ignore. This paper deals with the results of performance test on LAH-S91 as follows: 1) Driving characteristics of the LAH-S91 are calculated using cardiovascular simulation. The thrust of LAH-S91 is insufficient for the life of a human being; it must be increased more than 10%. 2) The calculated value of the cardiovascular simulation approximately agrees with the experimental value of a mock circulatory system. 3) The maximum permissible loss of the LAH is defined by considering the cooling effect of the blood flow. The loss is 42 Watts, when the temperature rise is 1°C. The temperature rise is the subject for a future study.

Biomechanics of valvular plane displacement of the heart

There has been no consensus concerning the particular movement of the valvular plane of the heart (VPM). As shown in this study involving a mathematical model based upon the momentum equation and experiments on a specially designed artificial heart pump, the VPM not only results from the shortening of the heart, but also from blood flow within the heart and large blood vessels, from the forces caused by the muscle movements, and from the elastic properties of the heart's suspension. The results of the calculations and the experiments confirm the effect of the so-called valve mechanism and its influence on the economic beating action of the heart.

A Permanent Magnet Linear Oscillatory Motor for the Total Artificial Heart

ABSTRACT This paper discusses the analysis, construction and initial tests of a permanent magnet linear oscillatory motor suitable for application in an artificial heart pump. Description of the motor design and power conditioning drive are presented. A hardware realization of a microprocessor based controller is also described. Test results indicate the nature of attraction and repulsion forces, and thus lead to the feasibility of the motor to drive the pump of an artificial heart.

A tubular self-synchronous motor for artificial heart pump drive.

Buildup and test of a permanent magnet, tubular, self-synchronous motor and the associated microprocessor-based power conditioning link are discussed. The motor is controlled for variable frequency axial oscillation demonstrating suitability to function as an energy conversion intermediary between a battery pack and an artificial heart pumping element. Strengths and weaknesses of the test bed system are discussed along with future plans directed toward development of an implantable pump drive for an artificial heart.

Mechanical Circulatory Assistance: Established (IABP) and Evolving (LVAD). A Narrative Summary

Comparisons of the physiologic bases of intraaortic balloon and extracorporeal or implantable left ventricular assist device or partial artificial heart pumping in experimental and clinical setting are made. The concepts and first principles common and unique to both of these forms of mechanical circulatory support are presented with emphasis on the similarities and important differences. Intraaortic balloon counterpulsation is examined as an intravascular, volume displacement device in series with the systemic circulations. Left ventricular assist devices are analyzed as extravascular in-series or parallel volume-capturing/ejecting devices and as true blood pumps which can be implanted. The interrelated mechanisms of synchronous, diversion/counterpulsation/diastolic augmentation are discussed in relation to quantitative indices of myocardial ischemia, myocardial oxygen supply/demand ratios, the Sarnoff theorem and the Laplace relationship, vis à vis ventricular unloading/impedance reductions. Some of the many clinical settings of IABP are mentioned, along with hydraulic considerations which allow non-invasive determination of stroke volume during clinical IABP mechanical circulatory support. Cardiogenic shock/left ventricular failure/low cardiac output are defined in terms of failure to generate pressure and displace volume and deficits of ejection fraction and stroke volume. Vasodilator therapy (nitroprusside), IABP, and LVAD are then viewed as escalating methods of reversing these deficits. Finally, pressure volume loops of the human left ventricle are compared with those of LVADs, experimentally and clinically, to indicate that LVADs can function and support the circulation during all low output states including ventricular fibrillation and standstill. Representative hemodynamic traces (Fig. 5 and 6) obtained during clinical LVAD trials in man are included to illustrate these theoretical and practical considerations. The use of LVADs in any instance of IABP inadequacy is implicit and inferred.

Modeling technique of prosthetic heart valves.

This paper demonstrates a modeling technique of prosthetic heart valves. In the modeling, a pumping cycle is divided into four phases, in which the state of the valve and flow is different. The pressure-flow relation across the valve is formulated separately in each phase. This technique is developed to build a mathematical model used in the real time estimation of the hemodynamic state under artificial heart pumping. The model built by this technique is simple enough for saving the computational time in the real time estimation. The model is described by the first-order ordinary differential equation with 12 parameters. These parameters can be uniquely determined beforehand from in-vitro experimental data. It is shown that the model can adapt, with sufficient accuracy, to a change in the practical pumping condition and the viscosity of the fluid in their practical range, and is also demonstrated that the estimated backflow volume by model agrees closely with the actual one.

Evaluation of fluorine-containing segmented polyurethane (FPU) as an artificial heart (AH) pump material

Evaluation of fluorine-containing segmented polyurethane (FPU) as an artificial heart (AH) pump material

Observation of morphological abnormality of erythrocytes during artificial heart (AH) pumping and analysis of its cause

Observation of morphological abnormality of erythrocytes during artificial heart (AH) pumping and analysis of its cause

抗血せん性エラストマとしての含フッ素セグメント化ポリウレタン樹脂

A series of fluorine-containing segmented polyurethanes (FPU) was synthesized from a new fluorinated aliphatic diisocyanate, polyalkylene glycols, and diamines. Electron microscopy showed that FPU have microphase separated structures which may possibly consist of hydrophobic domains of fluorocarbon chains and hydrophilic domains of hydrocarbon chains. FPU-20 E, prepared from polytetramethylene glycol (PTMG) of 1080 in molecular weight and ethylenediamine, exhibited excellent tensile properties as an elastomer and a high degree of in vitro antithrombogenicity. An in vivo evaluation using this material as an artificial heart pump for a goat showed it to have superior blood compatibility and durability, and thus may have possible application as a new biomaterial in cardiovascular devices, such as blood pumps in particular.

Heart Bypass: What Every Patient Must Know

This book is unique in that it provides broad, unbiased data on controversial issues. In this highly informative volume, the author reviews all the options the patient is entitled to know when he decides to undergo heart surgery. Modern cardiology has become a realm of spectacular diagnostic and surgical techniques. Impressive surgical suites, replete with expensive and sophisticated equipment including blinking monitors and artificial heart pumps, have become widely familiar. The patient's expectations for total cure are very high indeed. In separate chapters, this book tries to answer basic questions: What is angina pectoris? What is the bypass operation, and why is it so controversial? Am I a candidate for bypass surgery? What is the operation like, and what are the risks? Can angina be treated without surgery? How is life after surgery? Are there alternatives to surgery? The real advantages and limitations offered by modern cardiology are thus placed

Mean systemic pressure and mean pulmonary pressure: their effects on the total artificial heart.

Mean systemic pressure (MSP) and mean pulmonary pressure (MPF), which are mean driving pressures for venous return in the natural heart, were studied in 11 calves in which the natural heart had been replaced with a total artificial heart (TAH). They were measured simply by stopping the artificial heart pumping. Although blood translocation from the arterial to the venous side was not performed, the eventual right and left atrial pressures reached six to eight seconds after stopping the TAH would represent MSP and MPP with reasonable accuracy. The MSP varied from nine to 3k mmHg (20+/-6 mmHg), whereas the MPP varied from nine to 39 mmHg (22+/-7 mmHg). The MSP varied in close relation to the right atrial pressure prior to cessation of the TAH (r=0.9124). Increases in RAP and MSP were mainly attributed to an increase in circulating blood volume. In the performance of the TAH, MSP (or MPP), proper diastolic duration and vacuum application during diastole was of prime importance in determining the end-diastolic ventricular volume.

Effects of unphysiological factors on cardiac output regulation during artificial heart pumping.

Several Factors affecting artificial heart output were studied employing two mathematical models of prosthetic hearts, i.e., sac and diaphragm heart models. The stroke volume sensitivity to changes in venous pressure was analyzed by numerical computations. Increased inflow valve resistance, increased pump vacuum pressure, decreased elasticity of the ventricular sac or diaphragm and decreased size of the ventricle were shown to depress artificial heart function. In total prosthetic heart replacement experiments in calves, the resistance at the junction of the right heart to the natural atrium was measured by varying the pump vacuum pressure. When the vacuum pressure exceeded ?20 mmHg, the orifice resistance to flow increased approximately 4 times. Optimizing the above factors, a prosthetic heart should be designed that provides sufficient flow with a pump vacuum pressure not greater than ?20 mmHg.