The Experts below are selected from a list of 237 Experts worldwide ranked by ideXlab platform
Daniel Timms - One of the best experts on this subject based on the ideXlab platform.
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physiological control of dual Rotary Pumps as a biventricular assist device using a master slave approach
Artificial Organs, 2014Co-Authors: Michael C. Stevens, Andrew P. Bradley, Stephen Wilson, John F Fraser, Daniel TimmsAbstract:Dual Rotary left ventricular assist devices (LVADs) can provide biventricular mechanical support during heart failure. Coordination of left and right pump speeds is critical not only to avoid ventricular suction and to match cardiac output with demand, but also to ensure balanced systemic and pulmonary circulatory volumes. Physiological control systems for dual LVADs must meet these objectives across a variety of clinical scenarios by automatically adjusting left and right pump speeds to avoid catastrophic physiological consequences. In this study we evaluate a novel master/slave physiological control system for dual LVADs. The master controller is a Starling-like controller, which sets flow rate as a function of end-diastolic ventricular pressure (EDP). The slave controller then maintains a linear relationship between right and left EDPs. Both left/right and right/left master/slave combinations were evaluated by subjecting them to four clinical scenarios (rest, postural change, Valsalva maneuver, and exercise) simulated in a mock circulation loop. The controller's performance was compared to constant-rotational-speed control and two other dual LVAD control systems: dual constant inlet pressure and dual Frank-Starling control. The results showed that the master/slave physiological control system produced fewer suction events than constant-speed control (6 vs. 62 over a 7-min period). Left/right master/slave control had lower risk of pulmonary congestion than the other control systems, as indicated by lower maximum EDPs (15.1 vs. 25.2-28.4mmHg). During exercise, master/slave control increased total flow from 5.2 to 10.1L/min, primarily due to an increase of left and right pump speed. Use of the left pump as the master resulted in fewer suction events and lower EDPs than when the right pump was master. Based on these results, master/slave control using the left pump as the master automatically adjusts pump speed to avoid suction and increases pump flow during exercise without causing pulmonary venous congestion.
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physiological control of dual Rotary Pumps as a biventricular assist device using a master slave approach
Artificial Organs, 2014Co-Authors: Michael C. Stevens, Andrew P. Bradley, Stephen Wilson, John F Fraser, Daniel TimmsAbstract:Dual Rotary left ventricular assist devices (LVADs) can provide biventricular mechanical support during heart failure. Coordination of left and right pump speeds is critical not only to avoid ventricular suction and to match cardiac output with demand, but also to ensure balanced systemic and pulmonary circulatory volumes. Physiological control systems for dual LVADs must meet these objectives across a variety of clinical scenarios by automatically adjusting left and right pump speeds to avoid catastrophic physiological consequences. In this study we evaluate a novel master/slave physiological control system for dual LVADs. The master controller is a Starling-like controller, which sets flow rate as a function of end-diastolic ventricular pressure (EDP). The slave controller then maintains a linear relationship between right and left EDPs. Both left/right and right/left master/slave combinations were evaluated by subjecting them to four clinical scenarios (rest, postural change, Valsalva maneuver, and exercise) simulated in a mock circulation loop. The controller's performance was compared to constant-rotational-speed control and two other dual LVAD control systems: dual constant inlet pressure and dual Frank-Starling control. The results showed that the master/slave physiological control system produced fewer suction events than constant-speed control (6 vs. 62 over a 7-min period). Left/right master/slave control had lower risk of pulmonary congestion than the other control systems, as indicated by lower maximum EDPs (15.1 vs. 25.2-28.4mmHg). During exercise, master/slave control increased total flow from 5.2 to 10.1L/min, primarily due to an increase of left and right pump speed. Use of the left pump as the master resulted in fewer suction events and lower EDPs than when the right pump was master. Based on these results, master/slave control using the left pump as the master automatically adjusts pump speed to avoid suction and increases pump flow during exercise without causing pulmonary venous congestion. © 2014 International Center for Artificial Organs and Transplantation and Wiley Periodicals, Inc.
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optimizing the response from a passively controlled biventricular assist device
Artificial Organs, 2010Co-Authors: Nicholas Gaddum, Daniel Timms, Mark J PearcyAbstract:Recent studies into Rotary biventricular support have indicated that inadequate left/right flow balancing may lead to vascular congestion and/or ventricular suckdown. The implementation of a passive controller that automatically adjusts left/right flow during total and partial cardiac support would improve physiological interaction. This has encouraged the development of a biventricular assist device (BiVAD) prototype that achieves passive control of the two Rotary Pumps' hydraulic output by way of a nonrotating double pressure plate configuration, the hub, suspended between the ventricular assist device (VAD) impellers. Fluctuations in either the VAD's inlet or outlet pressure will cause the hub to translate, and in doing so, affect each pump's hydraulic outputs. In order to achieve partial support, the floating assembly needed to respond to pathologic blood pressure signals while being insensitive to residual ventricular function. An incorporated mechanical spring–mass–damper assembly affects the passive response to optimize the dynamic interaction between the prototype and the supported cardiovascular system. It was found that increasing the damping from a medium to a high level was effective in filtering out the higher frequency ventricular pressure signals, reducing a modified amplitude ratio by up to 72%. A spring response was also identified as being inherent in the passive response and was characterized as being highly nonlinear at the extremes of the floating assembly's translation range. The results from this study introduce a new means of BiVAD control as well as the characterization of a fully passive mechanical physiological controller.
Francis D. Pagani - One of the best experts on this subject based on the ideXlab platform.
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Understanding the Principles of Continuous-Flow Rotary Left Ventricular Assist Devices
2019Co-Authors: Francis D. PaganiAbstract:Abstract Mechanical circulatory support with durable, left ventricular assist devices has become a mainstay therapy for treatment of advanced heart failure refractory to optimal medical management and has now surpassed cardiac transplantation as the most frequently utilized surgical therapy for the treatment of end-stage heart failure. Important progress in the field has occurred with the introduction of continuous-flow Rotary pump technology that has supplanted older pulsatile displacement Pumps. Continuous-flow Rotary pump technology has afforded patients improved survival and reduced occurrence of major adverse events owing to the smaller size of these Pumps, quieter operation, improved power efficiency, and greater reliability and durability. Continuous-flow Rotary Pumps have significantly different flow characteristics compared to pulsatile Pumps, and continuous-flow Rotary Pumps in clinical use have differing device designs that influence the flow properties of the pump and its interaction with the native heart. There are several important features of the continuous-flow Rotary pump technology that permit characterization of the Pumps based on axial versus centrifugal design, bearing design, hydrodynamic properties, and mode of pump speed operation. Despite the marked advantages of this technology, this technology raises numerous challenges in the management of patients related, in part, on limitations in the ability of continuous-flow Rotary Pumps to adapt to marked changes in preload and afterload conditions, reduced pulsatility, and lack of algorithms that provide physiologic input into pump speed control. A thorough understanding of the theory of operation and design features of the Pumps is necessary to provide care for patients supported with this technology.
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second intermacs annual report more than 1 000 primary left ventricular assist device implants
Journal of Heart and Lung Transplantation, 2010Co-Authors: James K. Kirklin, Francis D. Pagani, David C Naftel, Robert L Kormos, Lynne W Stevenson, Marissa A Miller, Karen L Ulisney, Timothy J Baldwin, James B YoungAbstract:The Interagency Registry For Mechanical Circulatory Support (INTERMACS)1 an NHLBI-sponsored collaboration between the National Heart, Lung, and Blood Institute (NHLBI), the Food and Drug Administration (FDA), the Center for Medicaid and Medicare Services (CMS), and the advanced heart failure/mechanical circulatory support professional community, began prospective patient enrollment and data collection on June 23, 2006. On 3/27/09, CMS mandated that all United States hospitals approved for mechanical circulatory support as Destination Therapy (DT) must enter mechanical circulatory support patient data into a national database, INTERMACS. The power of INTERMACS data stems from the mandatory data submission on all durable mechanical circulatory devices, a formal process for adverse event adjudication, dedicated innovative electronic data submission, data element design to create a template for comparison with medical therapy, rigorous data monitoring, hospital auditing through the United Network of Organ Sharing, and a formal process for data access and publications. Since the inception of INTERMACS, an ongoing evolution of both strategies for device application and the types of available devices has continued to refine the landscape of mechanical circulatory support. Throughout this experience, the only device approved in the United States for permanent “destination” therapy was the HeartMate XVE2, a pulsatile ventricular assist device which is now known to frequently develop bearing wear and require device replacement within 2 years of implantation. Yet, in many countries outside the United States, newer axial flow and centrifugal flow Rotary Pumps provide chronic circulatory support. INTERMACS only collects data on devices which are FDA-approved for clinical use, and no adult Rotary pump was approved in the United States for the first several years of the INTERMACS experience. The spectrum of devices entered into INTERMACS must also be viewed in the context of multiple concurrent U.S. clinical trials of continuous flow Pumps implanted as bridge-to-transplant therapy as well as permanent support. Thus, for the first 2 years, despite the rigorous requirements for data completeness and accuracy, INTERMACS suffered from its inability to collect data on newer, more promising Rotary Pumps which were not yet FDA approved. The INTERMACS playing field changed dramatically in April of 2008, when the HeartMate II axial flow pump received FDA approval for clinical use as bridge-to-transplant therapy in the United States. A portion of this report will examine the changing practice patterns in the application of device type (continuous flow vs. pulsatile) and device strategies over the past three years. In fact, the genesis of INTERMACS, partly by chance and partly by design, uniquely positioned this database to observe, record, and analyze this historical transition (at least for the immediate future) from larger, powerful pulsatile Pumps to the world of continuous flow technology, with the unproven promise of greater durability while retaining long-term patient functionality. This report begins the process of long-term evaluation of continuous flow technology against the background of a large registry of detailed patient and device data based on pulsatile pump technology.
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hemodynamic and exercise performance with pulsatile and continuous flow left ventricular assist devices
Circulation, 2007Co-Authors: Jonathan W Haft, William F Armstrong, D B Dyke, Keith D Aaronson, Todd M Koelling, David J Farrar, Francis D. PaganiAbstract:Background— Continuous-flow Rotary Pumps with axial design are increasingly used for left ventricular assist support. The efficacy of this design compared with pulsatile, volume displacement Pumps, with respect to characteristics of left ventricular unloading, and exercise performance remains largely unstudied. Methods and Results— Thirty-four patients undergoing implantation with a pulsatile, volume displacement pump operating in a full-to-empty cycle (HeartMate XVE; Thoratec Inc, Pleasanton, Calif; n=16) or continuous-flow Rotary pump with an axial design operating at a fixed rotor speed (HeartMate II; Thoratec Inc; n=18) were evaluated with right heart catheterization and echocardiography preoperatively and at 3 months postoperatively and cardiopulmonary exercise testing 3 months postoperatively. Support with either the XVE or II resulted in significant ( P 2 −XVE: 46.8±10.2 versus II: 49.1±13.6). Echocardiography at 3 months demonstrated a significantly ( P Conclusions— The HeartMate XVE or II provided equivalent degrees of hemodynamic support and exercise capacity. The XVE was associated with greater left ventricular volume unloading. Characteristics of left ventricular pressure and volume unloading between these pump designs and mode of operation do not influence early exercise performance.
Andreas Goetzenich - One of the best experts on this subject based on the ideXlab platform.
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Fluid Dynamics in Rotary Piston Blood Pumps
Annals of Biomedical Engineering, 2017Co-Authors: Johannes Wappenschmidt, R Autschbach, Simon J. Sonntag, Martin Buesen, Sascha Gross-hardt, Tim Kaufmann, Thomas Schmitz-rode, Andreas GoetzenichAbstract:Mechanical circulatory support can maintain a sufficient blood circulation if the native heart is failing. The first implantable devices were displacement Pumps with membranes. They were able to provide a sufficient blood flow, yet, were limited because of size and low durability. Rotary Pumps have resolved these technical drawbacks, enabled a growing number of mechanical circulatory support therapy and a safer application. However, clinical complications like gastrointestinal bleeding, aortic insufficiency, thromboembolic complications, and impaired renal function are observed with their application. This is traced back to their working principle with attenuated or non-pulsatile flow and high shear stress. Rotary piston Pumps potentially merge the benefits of available pump types and seem to avoid their complications. However, a profound assessment and their development requires the knowledge of the flow characteristics. This study aimed at their investigation. A functional model was manufactured and investigated with particle image velocimetry. Furthermore, a fluid–structure interaction computational simulation was established to extend the laboratory capabilities. The numerical results precisely converged with the laboratory measurements. Thus, the in silico model enabled the investigation of relevant areas like gap flows that were hardly feasible with laboratory means. Moreover, an economic method for the investigation of design variations was established.
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Rotary piston blood Pumps past developments and future potential of a unique pump type
Expert Review of Medical Devices, 2016Co-Authors: Johannes Wappenschmidt, R Autschbach, Ulrich Steinseifer, Thomas Schmitzrode, R Margreiter, Guenter Klima, Andreas GoetzenichAbstract:ABSTRACTIntroduction: The design of implantable blood Pumps is either based on displacement Pumps with membranes or Rotary Pumps. Both pump types have limitations to meet the clinical requirements. Rotary piston blood Pumps have the potential to overcome these limitations and to merge the benefits. Compared to membrane Pumps, they are smaller and with no need for wear-affected membranes and valves. Compared to Rotary Pumps, the blood flow is pulsatile instead of a non-physiological continuous flow. Furthermore, the risk of flow-induced blood damage and platelet activation may be reduced due to low shear stress to the blood.Areas covered: The past developments of Rotary piston blood Pumps are summarized and the main problem for long-term application is identified: insufficient seals. A new approach with seal-less drives is proposed and current research on a simplified Rotary piston design is presented.Expert commentary: The development of blood Pumps focuses mainly on the improvement of Rotary Pumps. Howev...
Marwan A. Simaan - One of the best experts on this subject based on the ideXlab platform.
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A Dynamical State Space Representation and Performance Analysis of a Feedback-Controlled Rotary Left Ventricular Assist Device
IEEE Transactions on Control Systems Technology, 2009Co-Authors: Marwan A. Simaan, Shaohi Chen, Antonio Ferreira, James F. Antaki, David G. GalatiAbstract:The left ventricular assist device (LVAD) is a mechanical device that can assist an ailing heart in performing its functions. The latest generation of such devices is comprised of Rotary Pumps which are generally much smaller, lighter, and quieter than the conventional pulsatile Pumps. The Rotary Pumps are controlled by varying the rotor (impeller) speed. If the patient is in a health care facility, the pump speed can be adjusted manually by a trained clinician to meet the patient's blood needs. However, an important challenge facing the increased use of these LVADs is the desire to allow the patient to return home. The development of an appropriate feedback controller for the pump speed is therefore crucial to meet this challenge. In addition to being able to adapt to changes in the patient's daily activities by automatically regulating the pump speed, the controller must also be able to prevent the occurrence of excessive pumping (known as suction) which may cause collapse of the ventricle. In this paper we will discuss some theoretical and practical issues associated with the development of such a controller. As a first step, we present and validate a state-space mathematical model, based on a nonlinear equivalent circuit flow model, which represents the interaction of the pump with the left ventricle of the heart. The associated model is a six-dimensional vector of time varying nonlinear differential equations. The time variation occurs over four consecutive intervals representing the contraction, ejection, relaxation, and filling phases of the left ventricle. The pump in the model is represented by a nonlinear differential equation which relates the pump rotational speed and the pump flow to the pressure difference across the pump. Using this model, we discuss a feedback controller which adjusts the pump speed based on the slope of the minimum pump flow signal, which is one of the model state variables that can be measured. The objective of the controller is to increase the speed until the envelope of the minimum pump flow signal reaches an extreme point and maintain it afterwards. Simulation results using the model equipped with this feedback controller are presented for two different scenarios of patient activities. Performance of the controller when measurement noise is added to the pump flow signal is also investigated.
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Physiological control of left ventricular assist devices based on gradient of flow
Proceedings of the 2005 American Control Conference 2005., 2005Co-Authors: Shaohui Chen, Marwan A. Simaan, James F. Antaki, J.r. BostonAbstract:The new generation of left ventricular assist devices (LVADs) is based on Rotary Pumps used to augment the blood flow from the failing heart of a patient. A controller is necessary for these devices to properly control the blood flow, to detect failure modes, and to avoid adverse effects of the pump operation. In particular, it is essential that the pump accommodate changes to preload and afterload of the patient's circulatory system. The pump must increase blood flow in response to additional venous return, and maintain pressure in response to changes in systemic vascular resistance (SVR) of the patient. However, the limited availability of observable variables makes it difficult to explicitly close the feedback loop to generate the control. In this paper, we describe a feedback mechanism which uses the gradients of mean pump flow and minimum (diastolic) pump flow to control the pump speed. The objective of this controller is to optimize flow while avoiding suction. The optimum speed is obtained by minimizing in real time the gradient of blood flow with respect to speed. Simulations were carried out on a state-space model of the cardiovascular system combined with a Rotary pump to demonstrate the responsiveness and robustness of this algorithm. The results show that the gradient methods can continuously track the optimal flow point in response to step perturbations of preload and SVR. Our results also show that a feedback controller based on the gradient method applied on a diastolic pump flow demonstrates better performance than when applied on mean pump flow.
Youngjun Park - One of the best experts on this subject based on the ideXlab platform.
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Development of a Rotary clap mechanism for positive-displacement Rotary Pumps: Experimental verification and optimization
International Journal of Precision Engineering and Manufacturing, 2017Co-Authors: Sung Bo Shim, Youngjun ParkAbstract:We have developed a new positive-displacement type Rotary clap pump. Its structure, working principles and pumping performances have been introduced and analyzed in the previous studies. In this study, the experiment using prototype Rotary clap pump was conducted to verify the analyzed pump performances. The simulated flow rate, differential pressure, driving torque, and efficiencies for the prototype Rotary clap pump were compared with the measurement results. We confirmed the applicability of the analysis model, because the most of simulated values agreed well with the measured values. The parametric study for the prototype Rotary clap pump was conducted using the analysis model. The used parameters were the clearance between the rotor jaws and chambers, the number of jaws, the jaw width, and the jaw height, which are known as the important variables in the pump performance. Base on the parametric study, we found optimized condition that can increase overall efficiency up to 96.3%. The Rotary clap pump generates relatively low pressure pulsation and can increase its displacement with low vibration and power loss compared to the reciprocating pump. This pump could be a better option for high-viscosity fluids at a high flow rate than any other positive-displacement Pumps.
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Development of a Rotary clap mechanism for positive-displacement Rotary Pumps: Pump performance analysis
International Journal of Precision Engineering and Manufacturing, 2017Co-Authors: Sung Bo Shim, Youngjun ParkAbstract:We have introduced a novel positive-displacement Rotary pump named as Rotary clap pump, and analyzed its working principles through a kinematic analysis in the previous study. That study mainly described fundamental design parameters of the Rotary clap pump and their inter-relationships. As a follow-up research, this study presents the pump performance of the Rotary clap pump such as the pressure, driving torque, and efficiency characteristics using related theories and some basic assumptions. In the pressure analysis, the effect of friction, mass acceleration, piping components, and gravity were considered. The forces acting on the pump components and the driving torque are calculated using vector equations based on the results of the previous study. The volumetric, torque, and overall efficiencies are analyzed by calculating the slip flow and frictional forces caused by fluid viscosity. We also present the conditions that minimize the input power and forces acting on the components. The experimental study for the Rotary clap pump including comparison with analysis results is prepared to the follow-up paper.
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development of a Rotary clap mechanism for positive displacement Rotary Pumps kinematic analysis and working principle
Journal of Mechanical Science and Technology, 2015Co-Authors: Sung Bo Shim, Youngjun ParkAbstract:A five-bar spatial mechanism named as a Rotary clap mechanism is developed as a pumping device for positive displacement Rotary Pumps. The mechanism comprises a driving crank, a shaft link with two pins and two gears mounted on the middle and both ends, two rotors with jaws equally spaced along their circumferences, and two fixed internal gears. As the crank rotates, the gear pin-jointed to the crank rotates about the crank pin and at the same time rotates about the center of the fixed internal gears like a hypo-cyclic gear train. The gear-attached shaft link also rotates about the crank pin and about the fixed internal gears at the same time. This motion of the shaft link makes the pins rotate about the center of the fixed internal gears with a periodically varying radius. Therefore, two rotors driven by the pins rotate with different angular velocities. One rotor alternately leads and lags relative to the other rotor. These lead-lag motions between the two jaws of the rotors, which result in suction and discharge required for pumping, resemble hand clapping from which the mechanism was named. Construction and design parameters of the Rotary clap mechanism are introduced, and kinematic analysis of this mechanism is performed. The relationships among design parameters, inherent constraints, and effects of design parameters on the displacement of mechanism are also presented.
