Publications by authors named "Amy L Throckmorton"

53 Publications

Technology landscape of pediatric mechanical circulatory support devices: A systematic review 2010-2021.

Artif Organs 2022 Mar 31. Epub 2022 Mar 31.

BioCirc Research Laboratory, School of Biomedical Engineering, Science, and Health Systems, Drexel University, Philadelphia, Pennsylvania, USA.

Background: Mechanical circulatory support (MCS) devices, such as ventricular assist devices (VADs) and total artificial hearts (TAHs), have become a vital therapeutic option in the treatment of end-stage heart failure for adult patients. Such therapeutic options continue to be limited for pediatric patients. Clinicians initially adapted or scaled existing adult devices for pediatric patients; however, these adult devices are not designed to support the anatomical structure and varying flow capacities required for this population and are generally operated "off-design," which risks complications such as hemolysis and thrombosis. Devices designed specifically for the pediatric population which seek to address these shortcomings are now emerging and gaining FDA approval.

Methods: To analyze the competitive landscape of pediatric MCS devices, we conducted a systematic literature review. Approximately 27 devices were studied in detail: 8 were established or previously approved designs, and 19 were under development (11 VADs, 5 Fontan assist devices, and 3 TAHs).

Results: Despite significant progress, there is still no pediatric pump technology that satisfies the unique and distinct design constraints and requirements to support pediatric patients, including the wide range of patient sizes, increased cardiovascular demand with growth, and anatomic and physiologic heterogeneity of congenital heart disease.

Conclusions: Forward-thinking design solutions are required to overcome these challenges and to ensure the translation of new therapeutic MCS devices for pediatric patients.
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http://dx.doi.org/10.1111/aor.14242DOI Listing
March 2022

Tunable Blood Shunt for Neonates With Complex Congenital Heart Defects.

Front Bioeng Biotechnol 2021 13;9:734310. Epub 2022 Jan 13.

BioCirc Research Laboratory, School of Biomedical Engineering, Science, and Health Systems, Drexel University, Philadelphia, PA, United States.

Despite advancements in procedures and patient care, mortality rates for neonatal recipients of the Norwood procedure, a palliation for single ventricle congenital malformations, remain high due to the use of a fixed-diameter blood shunt. In this study, a new geometrically tunable blood shunt was investigated to address limitations of the current treatment paradigm (e.g., Modified Blalock-Taussig Shunt) by allowing for controlled modulation of blood flow through the shunt to accommodate physiological changes due to the patient's growth. First, mathematical and computational cardiovascular models were established to investigate the hemodynamic requirements of growing neonatal patients with shunts and to inform design criteria for shunt diameter changes. Then, two stages of prototyping were performed to design, build and test responsive hydrogel systems that facilitate tuning of the shunt diameter by adjusting the hydrogel's degree of crosslinking. We examined two mechanisms to drive crosslinking: infusion of chemical crosslinking agents and near-UV photoinitiation. The growth model showed that 15-18% increases in shunt diameter were required to accommodate growing patients' increasing blood flow; similarly, the computational models demonstrated that blood flow magnitudes were in agreement with previous reports. These target levels of diameter increases were achieved experimentally with model hydrogel systems. We also verified that the photocrosslinkable hydrogel, composed of methacrylated dextran, was contact-nonhemolytic. These results demonstrate proof-of-concept feasibility and reflect the first steps in the development of this novel blood shunt. A tunable shunt design offers a new methodology to rebalance blood flow in this vulnerable patient population during growth and development.
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http://dx.doi.org/10.3389/fbioe.2021.734310DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8794538PMC
January 2022

Microscale impeller pump for recirculating flow in organs-on-chip and microreactors.

Lab Chip 2022 02 1;22(3):605-620. Epub 2022 Feb 1.

Departments of Chemistry and Biomedical Engineering, University of Virginia, 248 McCormick Rd, Charlottesville, VA 22904, USA.

Fluid flow is an integral part of microfluidic and organ-on-chip technology, ideally providing biomimetic fluid, cell, and nutrient exchange as well as physiological or pathological shear stress. Currently, many of the pumps that actively perfuse fluid at biomimetic flow rates are incompatible with use inside cell culture incubators, require many tubing connections, or are too large to run many devices in a confined space. To address these issues, we developed a user-friendly impeller pump that uses a 3D-printed device and impeller to recirculate fluid and cells on-chip. Impeller rotation was driven by a rotating magnetic field generated by magnets mounted on a computer fan; this pump platform required no tubing connections and could accommodate up to 36 devices at once in a standard cell culture incubator. A computational model was used to predict shear stress, velocity, and changes in pressure throughout the device. The impeller pump generated biomimetic fluid velocities (50-6400 μm s) controllable by tuning channel and inlet dimensions and the rotational speed of the impeller, which were comparable to the order of magnitude of the velocities predicted by the computational model. Predicted shear stress was in the physiological range throughout the microchannel and over the majority of the impeller. The impeller pump successfully recirculated primary murine splenocytes for 1 h and Jurkat T cells for 24 h with no impact on cell viability, showing the impeller pump's feasibility for white blood cell recirculation on-chip. In the future, we envision that this pump will be integrated into single- or multi-tissue platforms to study communication between organs.
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http://dx.doi.org/10.1039/d1lc01081fDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8892988PMC
February 2022

The newly emerging field of pediatric engineering: Innovation for our next generation.

Artif Organs 2021 Jun 17;45(6):537-541. Epub 2021 May 17.

School of Biomedical Engineering, Science, and Health Systems, Drexel University, Philadelphia, PA, USA.

Neonates, infants, and children have unique physiology and body surface areas that dramatically change during growth and development, and the substantial diversity of complicated pediatric illnesses and rare childhood diseases are distinct from the adult sphere. Unfortunately, medical innovation is generally constrained to retrofitting adult treatment strategies for this heterogeneous population. This conventional, but limited, approach ignores the dynamic biopsychosocial, growth, and developmental complexities that abound, as one progresses through this life cycle from newborn onward toward early adulthood. Forward-thinking solutions are essential to advance the state-of-the-art to address the challenges and unmet clinical needs that are uniquely presented by the pediatric population, and it has become obvious that newly trained engineers are essential for success. These unmet clinical needs and the necessity of new technical skills and expertise give rise to the emergence of an entirely new field of engineering and applied science: Pediatric Engineering. The field of Pediatric Engineering flips conventional wisdom that adult therapies can simply be scaled or successfully modified for children. It commandeers design to suit the specific needs of the child, while anticipating the dynamic growth and development into adulthood. We are growing a new pipeline of educated scientists and engineers who will have developed a unique toolbox of skills that they can use to tackle unmet clinical needs in global pediatric healthcare for years to come.
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http://dx.doi.org/10.1111/aor.13973DOI Listing
June 2021

A Cross University-Led COVID-19 Rapid-Response Effort: Design, Build, and Distribute Drexel AJFlex Face Shields.

Ann Biomed Eng 2021 Mar 26;49(3):950-958. Epub 2021 Feb 26.

Drexel University, Philadelphia, PA, USA.

The purpose of this article is to demonstrate how a new cross-community leadership team came together, collaborated, coordinated across academic units with external community partners, and executed a joint mission to address the unmet clinical need for medical face shields during these unprecedented times. Key aspects of this success include the ability to forge and leverage new opportunities, overcome challenges, adapt to changing constraints, and serve the significant need across the Philadelphia region and healthcare systems. We teamed to design-build durable face shields (AJFlex Shields). This was accomplished by high-volume manufacturing via injection molding and by 3-D printing the key headband component that supports the protective shield. Partnering with industry collaborators and civic-minded community allies proved to be essential to bolster production and deliver approximately 33,000 face shields to more than 100 organizations in the region. Our interdisciplinary team of engineers, clinicians, product designers, manufacturers, distributors, and dedicated volunteers is committed to continuing the design-build effort and providing Drexel AJFlex Shields to our communities.
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http://dx.doi.org/10.1007/s10439-021-02743-wDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7908945PMC
March 2021

On the path to permanent artificial heart technology: Greater energy independence is paramount.

Artif Organs 2021 Apr 12;45(4):332-335. Epub 2021 Feb 12.

Division of Cardiac Surgery, Department of Surgery, Thomas Jefferson University Hospital, Philadelphia, PA, USA.

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http://dx.doi.org/10.1111/aor.13907DOI Listing
April 2021

Fluid-structure interaction analysis of a collapsible axial flow blood pump impeller and protective cage for Fontan patients.

Artif Organs 2020 Aug 14;44(8):E337-E347. Epub 2020 Apr 14.

BioCirc Research Laboratory, School of Biomedical Engineering, Science, and Health Systems, Drexel University, Philadelphia, PA, USA.

Limited donor organs and alternative therapies have led to a growing interest in the use of blood pumps as a treatment strategy for patients with single functional ventricle. The present study examines the use of collapsible and flexible impeller, cage, and diffuser designs of an axial blood pump for Fontan patients. Using one-way fluid-structure interaction (FSI) studies, the impact of blade deformation on blood damage and pump performance was investigated for flexible impellers. We evaluated biocompatible materials, including Nitinol, Bionate 80A polyurethane, and silicone for flow rates between 2.0-4.0 L/min and rotational speeds of 3000-9000 rpm. The level of deformation experienced by a cage and diffuser made of surgical stainless steel (control), Nitinol, and Bionate 80A polyurethane was also predicted using one-way FSI. The fluid pressure on the surface of the impeller, cage, and diffuser was determined using computational fluid dynamics (CFD), and then, the surface pressure was exported and used to investigate the impeller, cage, and diffuser deformation using finite element analysis. Finally, deformed impeller geometries were imported into the CFD software to determine the implication of deformation on pressure generation, blood damage index, and fluid streamlines. It was found that rotational speed, and not flow rate, is the largest determinant of impeller deformation, occurring at the blade trailing edges. The models predicted the maximum impeller deformation for Nitinol to be 40 nm, Bionate 80A polyurethane to be 106 μm, and silicone to be 2.8 mm, all occurring at 9000 rpm. The effects of silicone deformation on performance were significant, particularly at speeds above 5000 rpm where a decrease in pressure generation of more than 10% was observed. Despite this loss, the pressure generation at 5000 rpm exceeded the level required to alleviate Fontan complications. A blood damage estimation was performed and levels remained low. The effect of significant impeller deformation on blood damage was inconsistent and requires additional investigation. Cage and diffuser geometries made of steel and Nitinol deformed minimally but Bionate 80A experienced unacceptable levels of deformation, particularly in the free-flow case without a spinning impeller. These results support the continued evaluation of a flexible, pitch-adjusting, axial-flow, mechanical assist device as a clinical therapeutic option for patients with dysfunctional Fontan physiology.
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http://dx.doi.org/10.1111/aor.13685DOI Listing
August 2020

Clinical implications of LDH isoenzymes in hemolysis and continuous-flow left ventricular assist device-induced thrombosis.

Artif Organs 2020 Mar 6;44(3):231-238. Epub 2019 Oct 6.

Division of Cardiac Surgery, Thomas Jefferson University Hospital, Philadelphia, Pennsylvania.

Pump-induced thrombosis continues to be a major complication of continuous-flow left ventricular assist devices (CF-LVADs), which increases the risks of thromboembolic stroke, peripheral thromboembolism, reduced pump flow, pump failure, cardiogenic shock, and death. This is confounded by the fact that there is currently no direct measure for a proper diagnosis during pump support. Given the severity of this complication and its required treatment, the ability to accurately differentiate CF-LVAD pump thrombosis from other complications is vital. Hemolysis measured by elevated lactate dehydrogenase (LDH) enzyme levels, when there is clinical suspicion of pump-induced thrombosis, is currently accepted as an important metric used by clinicians for diagnosis; however, LDH is a relatively nonspecific finding. LDH exists as five isoenzymes in the body, each with a unique tissue distribution. CF-LVAD pump thrombosis has been associated with elevated serum LDH-1 and LDH-2, as well as decreased LDH-4 and LDH-5. Herein, we review the various isoenzymes of LDH and their utility in differentiating hemolysis seen in CF-LVAD pump thrombosis from other physiologic and pathologic conditions as reported in the literature.
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http://dx.doi.org/10.1111/aor.13565DOI Listing
March 2020

Mechanical Circulatory Support of the Right Ventricle for Adult and Pediatric Patients With Heart Failure.

ASAIO J 2019 02;65(2):106-116

From the BioCirc Research Laboratory, School of Biomedical Engineering, Science, and Health Systems, Drexel University, Philadelphia, Pennsylvania.

The clinical implementation of mechanical circulatory assistance for a significantly dysfunctional or failing left ventricle as a bridge-to-transplant or bridge-to-recovery is on the rise. Thousands of patients with left-sided heart failure are readily benefitting from these life-saving technologies, and left ventricular failure often leads to severe right ventricular dysfunction or failure. Right ventricular failure (RVF) has a high rate of mortality caused by the risk of multisystem organ failure and prolonged hospitalization for patients after treatment. The use of a blood pump to support the left ventricle also typically results in an increase in right ventricular preload and may impair right ventricular contractility during left ventricular unloading. Patients with RVF might also suffer from severe pulmonary dysfunction, cardiac defects, congenital heart disease states, or a heterogeneity of cardiophysiologic challenges because of symptomatic congestive heart failure. Thus, the uniqueness and complexity of RVF is emerging as a new domain of significant clinical interest that motivates the development of right ventricular assist devices. In this review, we present the current state-of-the-art for clinically used blood pumps to support adults and pediatric patients with right ventricular dysfunction or failure concomitant with left ventricular failure. New innovative devices specifically for RVF are also highlighted. There continues to be a compelling need for novel treatment options to support patients with significant right heart dysfunction or failure.
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http://dx.doi.org/10.1097/MAT.0000000000000815DOI Listing
February 2019

Externally applied compression therapy for Fontan patients.

Transl Pediatr 2018 Jan;7(1):14-22

BioCirc Research Laboratory, School of Biomedical Engineering, Science and Health Systems, Drexel University, Philadelphia, PA, USA.

Background: Limited therapeutic options are available for Fontan patients with dysfunctional or failing single ventricle physiology. This study describes the evaluation of an alternative, non-invasive, at-home therapeutic compression treatment for Fontan patients. Our hypothesis is that routinely administered, externally applied compression treatments to the lower extremities will augment systemic venous return, improve ventricular preload, and thus enhance cardiac output in Fontan patients.

Methods: To initially evaluate this hypothesis, we employed the NormaTec pneumatic compression device (PCD) in a pilot clinical study (n=2). This device is composed of inflatable trouser compartments that facilitate circumferentially and uniformly applied pressure to a patient's lower extremities. Following an initial health screening, test subjects were pre-evaluated with a modified-Bruce treadmill exercise stress test, and baseline data on cardiorespiratory health was collected. After training, test subjects conducted 6 days of external compression therapy at-home. Subjects were then re-evaluated with a final treadmill stress test and data acquisition of new cardiorespiratory parameters.

Results: Both subjects demonstrated improvement in exercise duration time, peak oxygen volume, and ventilator threshold, as compared to the baseline evaluation.

Conclusions: These findings are promising and provide the foundation for future studies that will focus on increasing study participation (sample size) to better assess the clinical benefit of compression therapy for Fontan patients.
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http://dx.doi.org/10.21037/tp.2017.08.01DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5803019PMC
January 2018

Mechanical Circulatory Support Devices for Pediatric Patients With Congenital Heart Disease.

Artif Organs 2017 Jan 8;41(1):E1-E14. Epub 2016 Nov 8.

BioCirc Research Laboratory, School of Biomedical Engineering, Science and Health Systems, Drexel University, Philadelphia, PA.

The use of mechanical circulatory support (MCS) devices is a viable therapeutic treatment option for patients with congestive heart failure. Ventricular assist devices, cavopulmonary assist devices, and total artificial heart pumps continue to gain acceptance as viable treatment strategies for both adults and pediatric patients as bridge-to-transplant, bridge-to-recovery, and longer-term circulatory support alternatives. We present a review of the current and future MCS devices for patients having congenital heart disease (CHD) with biventricular or univentricular circulations. Several devices that are specifically designed for patients with complex CHD are in the development pipeline undergoing rigorous animal testing as readiness experiments in preparation for future clinical trials. These advances in the development of new blood pumps for patients with CHD will address a significant unmet clinical need, as well as generally improve innovation of the current state of the art in MCS technology.
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http://dx.doi.org/10.1111/aor.12760DOI Listing
January 2017

Physics-driven impeller designs for a novel intravascular blood pump for patients with congenital heart disease.

Med Eng Phys 2016 07 26;38(7):622-632. Epub 2016 Apr 26.

BioCirc Research Laboratory, School of Biomedical Engineering, Science and Health Systems, Drexel University, Philadelphia, PA, United States . Electronic address:

Mechanical circulatory support offers an alternative therapeutic treatment for patients with dysfunctional single ventricle physiology. An intravascular axial flow pump is being developed as a cavopulmonary assist device for these patients. This study details the development of a new rotating impeller geometry. We examined the performance of 8 impeller geometries with blade stagger or twist angles varying from 100° to 800° using computational methods. A refined range of blade twist angles between 300° and 400° was then identified, and 4 additional geometries were evaluated. Generally, the impeller designs produced 4-26mmHg for flow rates of 1-4L/min for 6000-8000 RPM. A data regression analysis was completed and found the impeller with 400° of blade twist to be the superior performer. A hydraulic test was conducted on a prototype of the 400° impeller, which generated measurable pressure rises of 7-28mmHg for flow rates of 1-4L/min at 6000-8000 RPM. The findings of the numerical model and experiment were in reasonable agreement within approximately 20%. These results support the continued development of an axial-flow, mechanical cavopulmonary assist device as a new clinical therapeutic option for Fontan patients.
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http://dx.doi.org/10.1016/j.medengphy.2016.03.010DOI Listing
July 2016

Vortical flow characteristics of mechanical cavopulmonary assistance: Pre- and post-swirl dynamics.

Technol Health Care 2016 Sep;24(5):627-38

Departments of Cardiothoracic Surgery and Medicine, College of Medicine, Drexel University, Philadelphia, PA, USA.

Surgical optimization of the cavopulmonary connection and pharmacological therapy for dysfunctional Fontan physiology continue to advance, but these treatment approaches only slow the progression of decline to end-stage heart failure. The development of a mechanical cavopulmonary assist device will provide a viable therapeutic option in the bridging of patients to transplant or to stabilization. We hypothesize that rotational blood flow, delivered by an implantable axial flow blood pump, could effectively assist the venous circulation in Fontan patients by mimicking vortical blood flow patterns in the cardiovascular system. This study investigated seven new models of mechanical cavopulmonary assistance (single and dual-pump assist), created combinations of pump designs that deliver counter rotating vortical flow conditions, and analyzed pump performance, velocity streamlines, swirling strength, and energy augmentation in the cavopulmonary circuit for each support scenario. The model having an axial clockwise-oriented impeller in the inferior vena cava and an axial counterclockwise-oriented impeller rotating in the superior vena cava outperformed all of the support scenarios by enhancing the energy of the cavopulmonary circulation an average of 10.3% over the entire flow range and a maximum of 27.4% at %the higher flow rates. This research will guide the development of axial flow blood pumps for Fontan patients and demonstrated the high probability of %a cardiovascular benefit using counter rotating pumps in a dual support scenario, but found that this is dependent upon the patient-specific cavopulmonary anatomy.
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http://dx.doi.org/10.3233/THC-161154DOI Listing
September 2016

Beyond the VAD: Human Factors Engineering for Mechanically Assisted Circulation in the 21st Century.

Artif Organs 2016 Jun 29;40(6):539-48. Epub 2015 Oct 29.

Department of Information Science, College of Computing and Informatics, Drexel University, Philadelphia, PA, USA.

Thousands of ventricular assist devices (VADs) currently provide circulatory support to patients worldwide, and dozens of heart pump designs for adults and pediatric patients are under various stages of development in preparation for translation to clinical use. The successful bench-to-bedside development of a VAD involves a structured evaluation of possible system states, including human interaction with the device and auxiliary component usage in the hospital or home environment. In this study, we review the literature and present the current landscape of preclinical design and assessment, decision support tools and procedures, and patient-centered therapy. Gaps of knowledge are identified. The study findings support the need for more attention to user-centered design approaches for medical devices, such as mechanical circulatory assist systems, that specifically involve detailed qualitative and quantitative assessments of human-device interaction to mitigate risk and failure.
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http://dx.doi.org/10.1111/aor.12600DOI Listing
June 2016

Total Artificial Hearts-Past, Current, and Future.

J Card Surg 2015 Nov 24;30(11):856-64. Epub 2015 Sep 24.

From the BioCirc Research Laboratory, School of Biomedical Engineering, Science and Health Systems, Drexel University, Philadelphia, Pennsylvania.

We present a review of the evolution of total artificial hearts (TAHs) and new directions in development, including the coupling of VADs as biventricular TAH support.
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http://dx.doi.org/10.1111/jocs.12644DOI Listing
November 2015

Pressure-Flow Experimental Performance of New Intravascular Blood Pump Designs for Fontan Patients.

Artif Organs 2016 Mar 2;40(3):233-42. Epub 2015 Sep 2.

BioCirc Research Laboratory, School of Biomedical Engineering, Science, and Health Systems, Drexel University, Philadelphia, PA, USA.

An intravascular axial flow pump is being developed as a mechanical cavopulmonary assist device for adolescent and adult patients with dysfunctional Fontan physiology. Coupling computational modeling with experimental evaluation of prototypic designs, this study examined the hydraulic performance of 11 impeller prototypes with blade stagger or twist angles varying from 100 to 600 degrees. A refined range of twisted blade angles between 300 and 400 degrees with 20-degree increments was then selected, and four additional geometries were constructed and hydraulically evaluated. The prototypes met performance expectations and produced 3-31 mm Hg for flow rates of 1-5 L/min for 6000-8000 rpm. A regression analysis was completed with all characteristic coefficients contributing significantly (P < 0.0001). This analysis revealed that the impeller with 400 degrees of blade twist outperformed the other designs. The findings of the numerical model for 300-degree twisted case and the experimental results deviated within approximately 20%. In an effort to simplify the impeller geometry, this work advanced the design of this intravascular cavopulmonary assist device closer to preclinical animal testing.
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http://dx.doi.org/10.1111/aor.12549DOI Listing
March 2016

Three-dimensional laser flow measurements of a patient-specific fontan physiology with mechanical circulatory assistance.

Artif Organs 2015 Jun 10;39(6):E67-78. Epub 2015 Apr 10.

Department of Mechanical and Nuclear Engineering, School of Engineering, Virginia Commonwealth University, Richmond, VA, USA.

Mechanical assistance of the Fontan circulation is hypothesized to enhance ventricular preload and improve cardiac output; however, little is known about the fluid dynamics. This study is the first to investigate the three-dimensional flow conditions of a blood pump in an anatomic Fontan. Laser measurements were conducted having an axial flow impeller in the inferior vena cava. Experiments were performed for a physiologic cardiac output, pulmonary arterial flows, and pump speeds of 1000-4000 rpm. The impeller had a modest effect on the flow conditions entering the total cavopulmonary connection at low pump speeds, but a substantial impact on the velocity at higher speeds. The higher speeds of the pump disrupted the recirculation region in the center of the anastomosis, which could be advantageous for washout purposes. No retrograde velocities in the superior vena cava were measured. These findings indicate that mechanical assistance is a viable therapeutic option for patients having dysfunctional single ventricle physiology.
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http://dx.doi.org/10.1111/aor.12426DOI Listing
June 2015

Design of axial blood pumps for patients with dysfunctional fontan physiology: computational studies and performance testing.

Artif Organs 2015 Jan;39(1):34-42

Department of Mechanical and Nuclear Engineering, School of Engineering, Virginia Commonwealth University, Richmond, VA, USA.

Limited treatment options for patients having dysfunctional single ventricle physiology motivate the necessity for alternative therapeutic options. To address this unmet need, we are developing a collapsible axial flow blood pump. This study investigated the impact of geometric simplicity to facilitate percutaneous placement and maintain optimal performance. Three new pump designs were numerically evaluated. A transient simulation explored the impact of respiration on blood flow conditions over the entire respiratory cycle. Prototype testing of the top performing pump design was completed. The top performing Rec design generated the highest pressure rise range of 2-38 mm Hg for flow rates of 1-4 L/min at 4000-7000 RPM, exceeding the performance of the other two configurations by more than 26%. The blood damage indices for the new pump designs were determined to be below 0.5% and predicted hemolysis levels remained low at less than 7 × 10(-5)  g/100 L. Prototype testing of the Rec design confirmed numerical predictions to within an average of approximately 22%. These findings demonstrate that the pumps are reasonably versatile in operational ability, meet pressure-flow requirements to support Fontan patients, and are expected to have low levels of blood trauma.
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http://dx.doi.org/10.1111/aor.12443DOI Listing
January 2015

Stereo-particle image velocimetry measurements of a patient-specific Fontan physiology utilizing novel pressure augmentation stents.

Artif Organs 2015 Mar 16;39(3):228-36. Epub 2015 Jan 16.

Department of Mechanical and Nuclear Engineering, School of Engineering, Virginia Commonwealth University, Richmond, VA.

Single ventricle anomalies are a challenging set of congenital heart defects that require lifelong clinical management due to progressive decline of cardiovascular function. Few therapeutic devices are available for these patients, and conventional blood pumps are not designed for the unique anatomy of the single ventricle physiology. To address this unmet need, we are developing an axial flow blood pump with a protective cage or stent for Fontan patients. This study investigates the 3-D particle image velocimetry measurements of two cage designs being deployed in a patient-specific Fontan anatomy. We considered a control case without a pump, impeller placed in the inferior vena cava, and two cases where the impeller has two protective stents with unique geometric characteristics. The experiments were evaluated at a cardiac output of 3 L/min, a fixed vena caval flow split of 40%/60%, a fixed pulmonary arterial flow split of 50%/50%, and for operating speeds of 1000-4000 rpm. The introduction of the cardiovascular stents had a substantial impact on the flow conditions leaving the pump and entering the cavopulmonary circulation. The findings indicated that rotational speeds above 4000 rpm for this pump could result in irregular flows in this specific circulatory condition. Although retrograde flow into the superior vena cava was not measured, the risk of this occurrence increases with higher pump speeds. The against-with stent geometry outperformed the other configurations by generating higher pressures and more energetic flows. These results provide further support for the viability of mechanical cavopulmonary assistance as a therapeutic treatment strategy for Fontan patients.
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http://dx.doi.org/10.1111/aor.12364DOI Listing
March 2015

Experimental measurements of energy augmentation for mechanical circulatory assistance in a patient-specific Fontan model.

Artif Organs 2014 Sep 10;38(9):791-9. Epub 2014 Jan 10.

BioCirc Research Laboratory, Department of Mechanical and Nuclear Engineering, School of Engineering, Virginia Commonwealth University, Richmond, VA, USA.

A mechanical blood pump specifically designed to increase pressure in the great veins would improve hemodynamic stability in adolescent and adult Fontan patients having dysfunctional cavopulmonary circulation. This study investigates the impact of axial-flow blood pumps on pressure, flow rate, and energy augmentation in the total cavopulmonary circulation (TCPC) using a patient-specific Fontan model. The experiments were conducted for three mechanical support configurations, which included an axial-flow impeller alone in the inferior vena cava (IVC) and an impeller with one of two different protective stent designs. All of the pump configurations led to an increase in pressure generation and flow in the Fontan circuit. The increase in IVC flow was found to augment pulmonary arterial flow, having only a small impact on the pressure and flow in the superior vena cava (SVC). Retrograde flow was neither observed nor measured from the TCPC junction into the SVC. All of the pump configurations enhanced the rate of power gain of the cavopulmonary circulation by adding energy and rotational force to the fluid flow. We measured an enhancement of forward flow into the TCPC junction, reduction in IVC pressure, and only minimally increased pulmonary arterial pressure under conditions of pump support.
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http://dx.doi.org/10.1111/aor.12255DOI Listing
September 2014

Steady and transient flow analysis of a magnetically levitated pediatric VAD: time varying boundary conditions.

Int J Artif Organs 2013 Oct 26;36(10):693-9. Epub 2013 Sep 26.

BioCirc Research Laboratory, Department of Mechanical & Nuclear Engineering, School of Engineering, Virginia ?Commonwealth University, Richmond, VA - USA.

A magnetically levitated impeller within a pediatric ventricular assist device operates under highly transient flow conditions. In this study, computational analyses were performed to investigate the hydraulic performance and fluid forces on the impeller under the steady and dynamic flow conditions, including: 1) time-varying boundary conditions (TVBC) considering a pulsed pump flow rate and pulsed left ventricular pressure; 2) transient rotational sliding interfaces (TRSI) to capture virtual blade rotation. Under steady flow conditions, the pressure generation for 0.5-6 l/min over 6000-10000 rpm was 20-140 mmHg; experimental validation agreed to within 6-27%. Under transient flow conditions, the outflow pressure of the pump increased with higher inlet pressure during the TVBC simulation. During TVBC, the pressure rise across the pump decreased as a function of higher flow rates and increased as a function of lower flow rates. The radial fluid forces varied directly with the flow rate by demonstrating larger forces at higher flow rates. For TRSI simulations, pressure fluctuations due the blade passage frequency were found to have 12 peaks per revolution, having magnitude ranges of 
0.7 and 1.0 mmHg for 8 000 and 10 000 rpm, respectively. At 8 000 rpm, the fluid forces ranged from 1.15-1.17 N (axial) and 0.02-0.11 N (radial). Transient simulations model implant scenarios more realistically and provide critical information about the fluid conditions in the pump.
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http://dx.doi.org/10.5301/ijao.5000240DOI Listing
October 2013

Pneumatically-driven external pressure applicator to augment Fontan hemodynamics: preliminary findings.

Transl Pediatr 2013 Oct;2(4):148-53

Division of Pediatric Cardiology, Children's Hospital of Richmond and School of Medicine, Virginia Commonwealth University, Richmond, VA, USA.

Background: This study investigated the application of circumferentially applied, external pressure to the lower extremities as a preventative measure and long-term clinical treatment strategy for Fontan patients.

Objective: We hypothesized that the application of circumferential pressure to the lower limbs will augment venous return and thus cardiac output.

Methods: Two patients (an extra-cardiac and intra-atrial Fontan) were evaluated. Both trials were conducted during a routine cardiac catheterization. The aortic and inferior vena cava (IVC) pressures were recorded. We applied three different external pressures to the lower limbs based on the patient's diastolic pressure. Each pressure was applied with a one-minute rapid inflate/deflate period for a total of five cycles and a rest period between pressure intervals.

Results: Patient 1 (age 37, female) demonstrated pressure rises of 10-15 mmHg in both the aortic and IVC pressures. Patient 2 (age 24, male) had undetectable pressure rise during the first pressure cycles and notable pressures rise of approximately 8-12 mmHg during the third cycle.

Conclusions: External pressure application redistributes blood volume or cardiac output as a result of impedance in the lower extremities, enhancing venous pressure and return. Our findings strongly suggest an acute benefit from the implementation of external mechanical compression of the lower vasculature to increase cardiac output in Fontan patients.
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http://dx.doi.org/10.3978/j.issn.2224-4336.2013.10.02DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4729077PMC
October 2013

Dual-pump support in the inferior and superior vena cavae of a patient-specific fontan physiology.

Artif Organs 2013 Jun 20;37(6):513-22. Epub 2013 May 20.

BioCirc Research Laboratory, Department of Mechanical and Nuclear Engineering, School of Engineering, Virginia Commonwealth University, Richmond, VA 23284, USA.

The implementation of simultaneous mechanical cavopulmonary assistance having blood pumps located in both of the vena cavae is investigated as an approach to treating patients with an ailing Fontan physiology. Identical intravascular blood pumps are employed to model the hemodynamic support of a patient-specific Fontan. Pressure flow characteristics, energy gain calculations, and blood damage analyses are assessed for each model. The performance of the dual-support scenario is compared to conditions of mechanical support in the inferior vena cava only and to a nonsupported cavopulmonary circuit. The blood pump in the superior vena cava generates pressures ranging from 1 to 22 mm Hg for flow rates of 1-4 L/min at operating speeds of 1250-2500 rpm. The blood pump in the inferior vena cava produces pressures at levels approximately 20% lower. The blood pumps positively augment the hydraulic energy in the total cavopulmonary connection circuit as a function of flow rate and rotational speed. Scalar stress levels and fluid residence times are at acceptable levels. Damage indices for the dual-support case, however, are elevated slightly above 3.5%. These results suggest that concurrent, mechanical assistance of the inferior vena cava and superior vena cava in Fontan patients has the potential to be beneficial, but additional studies are needed to further explore this approach.
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http://dx.doi.org/10.1111/aor.12039DOI Listing
June 2013

A viable therapeutic option: mechanical circulatory support of the failing Fontan physiology.

Pediatr Cardiol 2013 Aug 15;34(6):1357-65. Epub 2013 Feb 15.

BioCirc Research Laboratory, Department of Mechanical and Nuclear Engineering, Virginia Commonwealth University, 401 West Main Street, Rm. E3221, Richmond, VA 23284, USA.

A blood pump specifically designed to augment flow from the great veins through the lungs would ameliorate the poor physiology of the failing univentricular circulation and result in a paradigm shift in the treatment strategy for Fontan patients. This study is the first to examine mechanical cavopulmonary assistance with a blood pump in the inferior vena cava (IVC) and hepatic blood flow. Five numerical models of mechanical cavopulmonary assistance were investigated using a three-dimensional, reconstructed, patient-specific Fontan circulation from magnetic resonance imaging data. Pressure flow characteristics of the axial blood pump, energy augmentation calculations for the cavopulmonary circulation with and without pump support, and hemolysis estimations were determined. In all of the pump-supported scenarios, a pressure increase of 7-9.5 mm Hg was achieved. The fluid power of the cavopulmonary circulation was also positive over the range of flow rates. No retrograde flow from the IVC into the hepatic circulation was evident during support cases. Vessel suction risk, however, was found for greater operating rotational speeds. Fluid shear stresses and hemolysis predictions remained at acceptable levels with normalized index of hemolysis estimations at 0.0001 g/100 L. The findings of this study support the continued design and development of this blood pump technology for Fontan patients with progressive cardiovascular insufficiency. Validation of these flow and performance predictions will be completed in the next round of experimental testing with blood bag evaluation.
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http://dx.doi.org/10.1007/s00246-013-0649-9DOI Listing
August 2013

Steady flow analysis of mechanical cavopulmonary assistance in MRI-derived patient-specific fontan configurations.

Artif Organs 2012 Nov 11;36(11):972-80. Epub 2012 Sep 11.

Department of Mechanical and Nuclear Engineering, School of Engineering, Virginia Commonwealth University, Richmond, USA.

This numerical study examined the performance of an intravascular axial flow blood pump for mechanical hemodynamic support of patients in the setting of Fontan failure, which presently has few treatment options. Three anatomically accurate geometries of the total cavopulmonary connection (TCPC) were generated using patients' magnetic resonance imaging data. These patient-specific geometries, as well as an idealized version with cylindrical vessels, were computationally analyzed with and without a pump in the inferior vena cava. Pressure flow characteristics, energy gain calculations, and blood damage analyses were performed for each model. The pump produced pressures of 1-14 mm Hg for 1500-4000 revolutions per minute, flow rates of 1-4 L/min, and pulmonary artery pressures of 8-24 mm Hg. Comparison of pump performance among the four models showed minimal intermodel differences (<5% deviation) in the pressure rise generated by the pump, the IVC pressure, and the energy imparted to the system by the pump. Blood damage analysis showed maximum fluid scalar stress values of 372 Pa or less, and the blood damage index was less than 2% in all of the models. These results suggest that this axial flow blood pump performs consistently in a variety of TCPC vessel geometries with low risk of blood trauma.
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http://dx.doi.org/10.1111/j.1525-1594.2012.01510.xDOI Listing
November 2012

Controlled pitch-adjustment of impeller blades for an intravascular blood pump.

ASAIO J 2012 Jul-Aug;58(4):382-9

Department of Mechanical & Nuclear Engineering, School of Engineering, Virginia Commonwealth University, Richmond, 23284, USA.

Thousands of mechanical blood pumps are currently providing circulatory support, and the incidence of their use continues to increase each year. As the use of blood pumps becomes more pervasive in the treatment of those patients with congestive heart failure, critical advances in design features to address known limitations and the integration of novel technologies become more imperative. To advance the current state-of-the-art in blood pump design, this study investigates the inclusion of pitch-adjusting blade features in intravascular blood pumps as a means to increase energy transfer; an approach not explored to date. A flexible impeller prototype was constructed with a configuration to allow for a variable range of twisted blade geometries of 60-250°. Hydraulic experiments using a blood analog fluid were conducted to characterize the pressure-flow performance for each of these twisted positions. The flexible, twisted impeller was able to produce 1-25 mmHg for 0.5-4 L/min at rotational speeds of 5,000-8,000 RPM. For a given twisted position, the pressure rise was found to decrease as a function of increasing flow rate, as expected. Generally, a steady increase in the pressure rise was observed as a function of higher twisted degrees for a constant rotational speed. Higher rotational speeds for a specific twisted impeller configuration resulted in a more substantial pressure generation. The findings of this study support the continued exploration of this unique design approach in the development of intravascular blood pumps.
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http://dx.doi.org/10.1097/MAT.0b013e31825d018eDOI Listing
November 2012

Twisted cardiovascular cages for intravascular axial flow blood pumps to support the Fontan physiology.

Int J Artif Organs 2012 May;35(5):369-75

BioCirc Research Laboratory, Department of Mechanical and Nuclear Engineering, School of Engineering, Virginia Commonwealth University, Richmond, VA, USA.

Failing single ventricle physiology represents an ongoing challenge in mechanical assist device development, requiring pressure augmentation in the cavopulmonary circuit, reduction of systemic venous pressure, and increased cardiac output to achieve hemodynamic stabilization. To meet these requirements, we are developing a percutaneously-placed, axial flow blood pump to support ailing single ventricle physiology in adolescents and adults. We have modified the outer cage of the device to serve as both a protective and functional design component. This study examined the performance of 3 cage geometries with varying directions of filament twist using numerical simulations and hydraulic experiments. All 3 cage and pump models performed in acceptable ranges to support Fontan patients. The cage design employing filaments that are twisted in the opposite direction to the impeller blades and in the direction of the diffuser blades (against-with) demonstrated superior performance by generating a pressure rise range of 5-38 mmHg of flow rates of 0.5-6 l/min at rotational speeds of 5000-7000 rpm. The blood damage indices for all of the cages were found to be well below 2%, and the scalar stress levels were below 200 Pa. This study represents ongoing progress in the development of the impeller and cage assembly. Validation of the results will continue in experiments with blood bag evaluation as well as by particle image velocimetry measurements.
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http://dx.doi.org/10.5301/ijao.5000105DOI Listing
May 2012

Uniquely shaped cardiovascular stents enhance the pressure generation of intravascular blood pumps.

J Thorac Cardiovasc Surg 2012 Sep 15;144(3):704-9. Epub 2012 Feb 15.

Department of Mechanical Engineering, Virginia Commonwealth University School of Engineering, Richmond, VA 23284, USA.

Objective: Advances in the geometric design of blood-contacting components are critically important as the use of minimally invasive, intravascular blood pumps becomes more pervasive in the treatment of adult and pediatric patients with congestive heart failure. The present study reports on the evaluation of uniquely shaped filaments and diffuser blades in the development of a protective stent for an intravascular cavopulmonary assist device for patients with a single ventricle.

Methods: We performed numeric modeling, hydraulic testing of 11 stents with an axial flow blood pump, and blood bag experiments (n = 6) of the top-performing stent geometries to measure the levels of hemolysis. A direct comparison using statistical analyses, including regression analysis and analysis of variance, was completed.

Results: The stent geometry with straight filaments and diffuser blades that extended to the vessel wall outperformed all other stent configurations. The pump with this particular stent was able to generate pressures of 2 to 32 mm Hg for flow rates of 0.5 to 4 L/min at 5000 to 7000 RPM. A comparison of the experimental performance data to the numeric predictions demonstrated an excellent agreement within 16%. The addition of diffuser blades to the stent reduced the flow vorticity at the pump outlet. The average and maximum normalized index of hemolysis level was 0.0056 g/100 L and 0.0064 g/100 L, respectively.

Conclusions: The specialized design of the stents, which protect the vessel wall from the rotating components of the pump, proved to be advantageous by further augmenting the pressure generation of the pump, reducing the flow vorticity at the pump outlet, and enhancing flow control.
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http://dx.doi.org/10.1016/j.jtcvs.2011.12.061DOI Listing
September 2012

Laser flow measurements in an idealized total cavopulmonary connection with mechanical circulatory assistance.

Artif Organs 2011 Nov 29;35(11):1052-64. Epub 2011 Sep 29.

Department of Mechanical Engineering, School of Engineering, Virginia Commonwealth University, Richmond, VA, USA.

This study examined the interactive fluid dynamics between a cavopulmonary assist device and univentricular Fontan circulation. We conducted two-dimensional particle image velocimetry measurements on an idealized total cavopulmonary connection (TCPC) with an axial pump prototype intravascularly inserted into the inferior vena cava (IVC) and then in the IVC and the superior vena cava (SVC) for a dual-pump support case. The glass model of the TCPC consisted of rigid vessels having a diameter of 13.4 mm and a one-diameter vessel offset at the TCPC junction. Fluid velocity profiles were examined at a cardiac output of 3 L/min and SVC and IVC flow ratios of 30/70%, 40/60%, and 50/50% and pump rotational speeds from 3000 to 9000 rpm. In addition, cardiac outputs of 5 and 7 L/min were also examined. As compared to the flow profile with the pump present, the measured velocity field demonstrated the presence of rotational (i.e., out of plane) motion, which forced the higher-velocity regions toward the periphery of the vessel. As a result, few flow vortices were captured in the image plane downstream of the pump in the TCPC junction. However, the velocity profiles for all cases demonstrated the expected shunting preference of IVC flow toward the right pulmonary artery. Furthermore, the inclusion of the pump provided a pressure rise of 3 to 9 mm Hg, which would be sufficient to relieve systemic hypertension in Fontan patients with circulatory dysfunction.
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http://dx.doi.org/10.1111/j.1525-1594.2011.01345.xDOI Listing
November 2011

Mechanical cavopulmonary assistance of a patient-specific Fontan physiology: numerical simulations, lumped parameter modeling, and suction experiments.

Artif Organs 2011 Nov 7;35(11):1036-47. Epub 2011 Sep 7.

Department of Mechanical Engineering, School of Engineering, Virginia Commonwealth University, Richmond, VA, USA.

This study investigated the performance of a magnetically levitated, intravascular axial flow blood pump for mechanical circulatory support of the thousands of Fontan patients in desperate need of a therapeutic alternative. Four models of the extracardiac, total cavopulmonary connection (TCPC) Fontan configuration were evaluated to formulate numerical predictions: an idealized TCPC, a patient-specific TCPC per magnetic resonance imaging data, and each of these two models having a blood pump in the inferior vena cava (IVC). A lumped parameter model of the Fontan physiology was used to specify boundary conditions. Pressure-flow characteristics, energy gain calculations, scalar stress levels, and blood damage estimations were executed for each model. Suction limitation experiments using the Sylgard elastomer tubing were also conducted. The pump produced pressures of 1-16 mm Hg for 2000-6000 rpm and flow rates of 0.5-4.5 L/min. The pump inlet or IVC pressure was found to decrease at higher rotational speeds. Maximum scalar stress estimations were 3 Pa for the nonpump models and 290 Pa for the pump-supported cases. The blood residence times for the pump-supported cases were shorter (0.9 s) as compared with the nonsupported configurations (2.5 s). However, the blood damage indices were higher (1.5%) for the anatomic model with pump support. The pump successfully augmented pressure in the TCPC junction and increased the hydraulic energy of the TCPC as a function of flow rate and rotational speed. The suction experiments revealed minimal deformation (<3%) at 9000 rpm. The findings of this study support the continued design and development of this blood pump.
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http://dx.doi.org/10.1111/j.1525-1594.2011.01339.xDOI Listing
November 2011
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