Estimation and control of the pump pressure rise and flow from intrinsic parameters for a magnetically-levitated axial blood pump

An increase in the number of cardiac patients and a decrease in number of heart donors has triggered the development of artificial heart pump to support the proper functioning of the heart. There is also an increase in demand for smaller sized pumps with long term application. All these factors have stimulated the use of a magnetically-levitated rotary blood pump as Left Ventricular Assistant Devices. The demand of volume and pressure of blood varies from person to person. Moreover, the prevention of cannular ventricle collapse at suction, dependence of pump performance on its inlet, and outlet conditions has necessitated control of the pump. Also, the available invasive pressure and flow transducers limit the use, due to their low reliability, periodic calibration, and assembling problem. In this work, three independent and quantitative non-invasive measurement methods for the estimation of pump parameters from intrinsic parameters were developed, substantiated, and compared. The first method used DC motor current and the motor speed as the inputs to the system. In this method, behavior of brushless DC motor was studied using its working model. Pump speed and bearing current were the inputs for the second estimation technique. In this method, pump performance and impeller behavior were continuously monitored in three axes (X,Y, ). The third method is conceptualized on the output of the Hall Effect sensors, which were used for sensing the position of impeller, and the pump speed. The behavior of the sensor output with the impeller position in four axes (X,Y,Z, ) was developed using a real impeller in model housing. The data were analyzed in Microsoft Excel 2007 and MATLAB using least square estimation techniques and Fourier series expansion. An algorithm for each technique was developed. In addition, the propagation of errors and uncertainties at each step of estimation method were accounted and calculated, with the results for each method compared

The Effects of Ambulatory Accelerations on the Stability of a Magnetically Suspended Impeller for an Implantable Blood Pump

National Institute for Health Research. Grant Number: II-LB-1111-2000

A Heart Artificial: Building the Foundation for the Development and Maintenance of In Vitro Tissue Mimetic Cardiovascular Models

Given the prevalence of cardiovascular disorders and the distinct lack of significant repair mechanisms within cardiovascular systems, effective therapy for long-term treatment of cardiovascular degeneration remains a significant challenge. Further, the fundamental importance of such systems to all mammalian life begs the development of realistic component structures for in vitro assessment. Significant effort was expended to create in vitro models which mimicked a subset of structure and function of coordinate native components within cardiovascular systems. Towards this end, we developed a 3D-Artificial Heart Muscle (AHM) model utilizing fibrin gel and neonatal cardiac myocytes. We extracted functional metrics in order to probe the optimal protocol for generation of the tissue model. Building on the outcome of this experiment, we applied the optimal 3D-AHM model to a decellularized adult rat heart in order to re-append function to a complex acellular scaffold. The resultant bioartifical heart (BAH) model was assessed to identify the efficacy of 3D-AHM as a functional delivery mechanism and to lay a framework for heart model development. An alternative strategy for the generation of 3D heart muscle was explored through magnetic levitation of cardiovascular cells. Magnetic sensitivity was appended to cells through incubation with ferromagnetic nanoparticles. The cells were then levitated and cultured within a magnetic field to form 3D multicellular aggregates. (MCAs) We utilized a magnetized fibrin gel scaffold in order to apply non-contact, magnetic stretch conditioning to our AHM model through a novel bioreactor system. We were able to develop a highly functional 3D-AHM and extracted 4M cells as the optimal concentration for the generation of our artificial heart muscle. Application of a layer of 3D-AHM to an acellular rat heart proved the 3D-AHM an effective mechanism for delivery of a subset of function to a structure. Magnetic levitation generated hundreds of cell-dense, functional and phenotypically relevant heart muscle analogs. We have developed a completely novel system for the application of mechanical stretch conditioning to artificial heart muscle models and are working to implement more complex conditioning systems. The work presented herein surveys the generation of 3 unique cardiovascular model systems and a novel method for model conditioning.Biomedical Engineering, Department o

Development and characterization of the arterial windkessel and its role during left ventricular assist device assistance

Modeling of the cardiovascular system is challenging, but it has the potential to further advance our understanding of normal and pathological conditions. Morphology and function are closely related. The arterial system provides steady blood flow to each organ and damps out wave fluctuations as a consequence of intermittent ventricular ejection. These actions can be approached separately in terms of mathematical relationships between pressure and flow. Lumped parameter models are helpful for the study of the interactions between the heart and the arterial system. The arterial windkessel model still plays a significant role despite its limitations. This review aims to discuss the model and its modifications and derive the fundamental equations by applying electric circuits theory. In addition, its role during left ventricular assist device assistance is explored and discussed in relation to rotary blood pumps

The potential of a tesla type device as a non pulsatile blood pump

A review of the published work on pumps designed to assist a failing biological heart has been made and discusses the different types of pump presently on the market with the characteristics of each. The materials used to make these pumps are also discussed, together with some of the methods of output control. The application to the patient is described together with the advantages and disadvantages. A Tesla type pump appeared to offer an alternative solution to those problems listed above. This is not a new design but appeared to offer advantages if applied to the application of pumping blood from outside the body. One of these was that at a constant speed, the pump supplied constant fluid pressure irrespective of the delivery. It also appears that the pump can give fluid shear stress levels that are less than the amount that will seriously damage blood components. A prototype pump has been built and tested. The pump achieved the performance target delivery of 10 I/min at a differential pressure of 200 mm Hg. This was considered to be greater than the average performance produced by existing blood pumps but the maximum performance that could be produced by the human heart under extreme conditions. The pump reached a maximum speed of about 4000 rev/min with a maximum power consumption of about 120 Watts. The results indicate that this type of pump is a potential blood pump in terms of the delivery and pressures achieved. The characteristic performance figures are within the envelope of published theoretical results. The pump tested here needs further development to improve the hydraulic performance. Recommendations are made for the direction of future work to improve the pump efficiency and flow patterns, biocompatibility and methods of production. Controls and power supply also need improvement

Drag reducing polymers as simple indicators of hemolytic potential in biomechanical devices

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2009.Cataloged from PDF version of thesis.Includes bibliographical references (p. 23-24).An experimental study was carried out to determine if drag reducing polymers can be simple indicators of hemolytic potential in biomechanical devices. Specifically, three different blood pumps, known as a left ventricle assist devices (LVADs) were operated in a test loop using an aqueous solution of polyethylene glycol (PEO, MW = 5000 kDa), a known drag reducing polymer. The pumps were operated under controlled parameters and the change in viscosity (cP) and drag reduction (%DR) for each pump was monitored over the specified time period. The CentriMag® (CM) was used to confirm the drag reducing behavior of PEO, while HeartMate® II (HM II) and HeartMate® III (HM III) were used to determine if there was a correlation between experimental results and actual hemolysis results. Experimental results showed that the mathematical difference between the average final and initial viscosity of HM II was greater than the difference for HM III. HM II had a difference of 0.21 cP and HM III had a difference of 0.16 cP. Hemolysis results using bovine blood showed that HM II had a higher hemolysis rate of 3.80 +/- 1.11 g/day and a higher milligram normalized index of hemolysis of 0.0393 +/- 0.0155. The average hemolysis rate for HM III was 1.38 +/- 0.63 g/day and the milligram normalized index of hemolysis (mg N.I.H.) was 0.571 +/- 0.333. This positive correlation shows that PEO can be a simple indicator of hemolytic potential for biomechanical devices. More data and experimentation is needed to further understand the behavior of PEO and it's ability to indicate hemolytic potential using a wider range of biomechanical devices.by Sarah Shieh.S.B

The ventricular assist device: a bridge to ventricular recovery, a bridge to heart transplantation or destination therapy?

Despite advances in pharmacological treatments aimed at a neurohormonal blockade for heart failure, there is still a growing number of patients with advanced symptoms who suffer significant morbidity and mortality. At present the most effective cure for end-stage congestive heart failure is cardiac transplantation. This method is severely limited owing to a lack of available organs. This is why ventricular assist devices (VADs) capable of completely supporting the circulation are taking on an increasingly important role in heart failure therapy. VADs are important bridges to cardiac transplantation. The Randomised Evaluation of Mechanical Assistance for the Treatment of Congestive Heart Failure (REMATCH) trial revealed that they could be used as long-term destination therapy for non-transplant candidates. The latest studies show that VAD support may also function as a bridge to ventricular recovery and enable this procedure to take place. Apart from foreign devices, there is the Polish system (PCAS), which is being prepared for introduction into global practice. (Cardiol J 2007; 14: 14–23