Sonna M. Patel

Pediatric circulatory support systems.

Ventricular assist devices (VADs) are a valid option for long-term circulatory support in pediatric patients with postoperative myocardial failure or debilitating heart defects. Most clinical experience to date has involved the short-term support of patients weighing 6 kg and larger. For cases of VAD implementation in pediatric patients, the assist device showed tremendous promise in reversing cardiac failure and providing adequate support as a bridge to cardiac transplantation. The Medos-HIA system, Berlin Heart, Medtronic Bio-Medicus Pump, Abiomed BVS 5000, Toyobo-Zeon pumps, and Hemopumps have proven successful for short-term circulatory support for the pediatric population. The Jarvik 2000 and Pierce-Donachy pediatric system further demonstrate the potential to be used for pediatric circulatory support. The clinical and experimental success of these support systems provide encouragement to believe that long-term support is possible.

Computational Design and Experimental Testing of a Novel Axial Flow LVAD

Thousands of cardiac failure patients per year in the United States could benefit from long-term mechanical circulatory support as destination therapy. To provide an improvement over currently available devices, we have designed a fully implantable axial-flow ventricular assist device with a magnetically levitated impeller (LEV-VAD). In contrast to currently available devices, the LEV-VAD has an unobstructed blood flow path and no secondary flow regions, generating substantially less retrograde and stagnant flow. The pump design included the extensive use of conventional pump design equations and computational fluid dynamics (CFD) modeling for predicting pressure-flow curves, hydraulic efficiencies, scalar fluid stress levels, exposure times to such stress, and axial fluid forces exerted on the impeller for the suspension design. Flow performance testing was completed on a plastic prototype of the LEV-VAD for comparison with the CFD predictions. Animal fit trials were completed to determine optimum pump location and cannulae configuration for future acute and long-term animal implantations, providing additional insight into the LEV-VAD configuration and implantability. Per the CFD results, the LEV-VAD produces 6 l/min and 100 mm Hg at a rotational speed of approximately 6300 rpm for steady flow conditions. The pressure-flow performance predictions demonstrated the VAD’s ability to deliver adequate flow over physiologic pressures for reasonable rotational speeds with best efficiency points ranging from 25% to 30%. The CFD numerical estimations generally agree within 10% of the experimental measurements over the entire range of rotational speeds tested. Animal fit trials revealed that the LEV-VAD’s size and configuration were adequate, requiring no alterations to cannulae configurations for future animal testing. These acceptable performance results for LEV-VAD design support proceeding with manufacturing of a prototype for extensive mock loop and initial acute animal testing.

The status of failure and reliability testing of artificial blood pumps.

Artificial blood pumps are today’s most promising bridge-to-transplant, bridge-to-recovery, and destination therapy solutions for patients with congestive heart failure. There is a critical need for increased reliability and safety as the next generation of artificial blood pumps approach final development for long-term destination therapy. To date, extensive failure and reliability studies of these devices are considered intellectual property and thus remain unpublished. Presently, the Novacor N100PC, Thoratec VAD, and HeartMate LVAS (IP and XVE) comprise the only four artificial blood pumps commercially available for the treatment of congestive heart failure in the United States. The CardioWest TAH recently received premarket approval from the US Food and Drug Administration. With investigational device exemptions, the AB-180, AbioCor, LionHeart, DeBakey, and Flowmaker are approved for clinical testing. Other blood pumps, such as the American BioMed-Baylor TAH, CorAide, Cleveland Clinic-Nimbus TAH, HeartMate III, Hemadyne, and MagScrew TAH are currently in various stages of mock loop and animal testing, as indicated in published literature. This article extensively reviews in vitro testing, in vivo testing, and the early clinical testing of artificial blood pumps in the United States, as it relates to failure and reliability. This detailed literature review has not been published before and provides a thorough documentation of available data and testing procedures regarding failure and reliability of these various pumps.

Controller Design of Left Ventricle Assist Device

A left ventricle assist device (LVAD) is a device composed mainly of a pump and a controller. It is used not only to save lives of patients who suffer from left ventricle failure, but also to help them live like healthy people. Due to the continuing increasing number of left ventricle heart failure cases and limited number of heart donations for heart transplant, the need for LVADs become more and more demanding.Copyright

An initial investigation of insulation fault effects on LVAD motor performance

Thousands of patients suffering from congestive heart failure (CHF) benefit from safe and reliable, temporary left ventricular assist devices (LVAD). Designed to perform in parallel with the left ventricle of the native heart, there are only five devices in the United States approved for use of up to 2 years to support CHF patients until a donor heart becomes available, or the heart recovers some function. With limited donor hearts (~3000), fully implantable LVADs are currently being designed for up to 10 years and are a complex medical device with multiple subsystems. The permanent magnet, brushless DC (BLDC) motor subsystem is evaluated for insulation failures using simulations of the electrical circuit model in MatLab (Mathworks). Variations in the number of turns lost and groundwall insulation have a direct effect on the current available to drive the motor. This preliminary model provides results that support the hypothesis that LVAD insulation failures lead to poor pump performance, and potentially, pump failure

HYDRAULIC PERFORMANCE CHARACTERIZATION OF AN AXIAL FLOW PEDIATRIC VAD PROTOTYPE

FLOW PEDIATRIC VAD PROTOTYPE Amy L Throckmorton, David S Lim, Alexandrina Untaroiu, Sonna M Patel, Houston G Wood, Paul E Allaire, Don B Olsen. Engineering, University of Virginia, Charlottesville, VA; Cardiology, University of Virginia, Charlottesville, VA; Utah Artificial Heart Institute, Salt Lake City, UT. Motivation: Computational fluid dynamics (CFD) was extensively used to predict the hydraulic performance for an axial flow, magnetically levitated, pediatric VAD. Validation of these CFD predictions is critical prior to proceeding with a final magnetic suspension / motor design for the VAD. For design validation, a pump prototype must be built for performance testing. Methods: A modular test rig with a mechanical suspension was employed for preliminary flow measurements of a prototype. Each internal fluid region of the pump was manufactured by stereolithography (SLA) directly from solid modeling drawings of the CFD model and a preliminary magnetic suspension design. The pressure-flow and axial / radial fluid force measurements were determined for a range of operating conditions. The axial fluid forces exerted on the rotor were measured via a load cell. Pressures were measured at locations along the axial length of pump to capture regional hydraulic performances and radial forces exerted on the rotor. Results: The prototype successfully delivered flows of 0.5 to 3 lpm with pressure rises of 50 to 95 mmHg for 6000 to 10,000 RPM. Axial fluid forces reached values of 1N, and radial forces remained small for centered impeller position, as expected, and less than 1N for the off-centered impeller positions. Conclusions: This prototype demonstrated excellent hydraulic performance with a mechanical suspension; the final magnetic suspension and motor design is underway. TRANSIENT FLOW NUMERCIAL SIMULATION OF AN AXIAL FLOW PEDIATRIC VAD FOR INFANTS AND CHILDREN Amy L Throckmorton, Alexandrina Untaroiu, David S Lim, Sonna M Patel, Houston G Wood, Paul E Allaire, Don B Olsen. Engineering, University of Virginia, Charlottesville, VA; Cardiology, University of Virginia, Charlottesville, VA; Utah Artificial Heart Institute, Salt Lake City, UT. Motivation: Thousands of infants and children will benefit from the longer-term bridge-to-transplant capabilities of pediatric VADs (PVADs). Since few mechanical support options are available in the US, we have designed and optimized an axial flow PVAD with an impeller that is fully suspended by magnetic bearings. Computational fluid dynamics (CFD) has been employed during design iterations and multiple optimizations of this VAD. This CFD study explores transient flow phenomena in the pump. Methods: Three types of transient simulations (TS) were completed to mimic physiological flows: 1) pulsed inlet pressure or a timevarying boundary condition (TVBC), 2) rotating-stationary component dynamics to capture the blade passage frequency or transient rotational sliding interfaces (TRSI), and 3) a combination of TVBC and TRSI to simulate the most realistic implant conditions. For each TS, the pressure rise and fluid forces (axial and radial) were estimated for the final magnetic suspension / motor design. Results: The TS demonstrated the dependence of the radial fluid forces on the diffuser region and inflow conditions. Maximum radial fluid forces during TRSI runs were found to be approximately 0.09 N. For TVBC runs, the pressure rise and fluid forces were determined to be sensitive to the tim. Conclusions: These transient simulations illustrated the PVAD’s response to dynamic flow conditions, which are realistic when considering in vivo implant scenarios.