Amy L Throckmorton's research while affiliated with Drexel University and other places

The majority of bearingless permanent magnet slice motors (BPMSMs) used in commercially available rotary blood pumps use a two-phase configuration, but it is unclear as to whether or not a comparable three-phase configuration would offer a better performance. This study compares the performance of two-phase and three-phase BPMSM configurations. Initially, two nominal designs were manufactured and empirically tested for their performance characteristics, namely, the axial stiffness, radial stiffness, and current force. Subsequently, finite element analysis (FEA) models were developed based on these nominal devices and validated against the empirical results. Simulations were then employed to assess the sensitivity of performance characteristics to variations in seven different geometric features of the models for both configurations. Our findings indicate that the nominal three-phase design had a higher axial stiffness and radial stiffness, but resulted in a lower axial-to-radial-stiffness ratio when compared to the nominal two-phase design. Additionally, while the nominal two-phase design shows a higher current force, the nominal three-phase design proves to be slightly superior when the force generated is considered relative to the power usage. Notably, the three-phase configuration demonstrates a greater sensitivity to dimensional changes in the geometric features. We observed that alterations in the air gap and rotor length lead to the most significant variations in performance characteristics. Although most changes in specific geometric features entail equal tradeoffs, increasing the head protrusion positively influences the overall performance. Moreover, we illustrated the interdependent nature of the head height and rotor height on the performance characteristics. Overall, this study delineates the strengths and weaknesses of each configuration, while also providing general insights into the relationship between specific geometric features and performance characteristics of BPMSMs.

To address the unmet clinical need for pediatric circulatory support, we are developing an operationally versatile, hybrid, continuous-flow, total artificial heart (“Dragon Heart”). This device integrates a magnetically levitated axial and centrifugal blood pump. Here, we utilized a validated axial flow pump, and we focused on the development of the centrifugal pump. A motor was integrated to drive the centrifugal pump, achieving 50% size reduction. The motor design was simulated by finite element analysis, and pump design improvement was attained by computational fluid dynamics. A prototype centrifugal pump was constructed from biocompatible 3D printed parts for the housing and machined metal parts for the drive system. Centrifugal prototype testing was conducted using water and then bovine blood. The fully combined device ( i.e. , axial pump nested inside of the centrifugal pump) was tested to ensure proper operation. We demonstrated the hydraulic performance of the two pumps operating in tandem, and we found that the centrifugal blood pump performance was not adversely impacted by the simultaneous operation of the axial blood pump. The current iteration of this design achieved a range of operation overlapping our target range. Future design iterations will further reduce size and incorporate complete and active magnetic levitation.

Background: Mechanical circulatory support (MCS), including ventricular assist devices (VADs), have emerged as promising therapeutic alternatives for end-stage congestive heart failure (CHF). The latest generation of these devices are continuous flow (CF) blood pumps. While there have been demonstrated benefits to patient outcomes due to CF-MCS, there continue to be significant clinical challenges. Research to-date has concentrated on mitigating thromboembolic risk (stroke), while the downstream impact of CF-MCS on the cerebrospinal fluid (CSF) flow has not been well investigated. Disturbances in the CSF pressure and flow patterns are known to be associated with neurologic impairment and diseased states. Thus, here we seek to develop an understanding of the pathophysiologic consequences of CF-MCS on CSF dynamics. Methods: We built and validated a computational framework using lumped parameter modeling of cardiovascular, cerebrovascular physics, CSF dynamics, and autoregulation. A sensitivity analysis was performed to confirm robustness of the modeling framework. Then, we characterized the impact of CF-MCS on the CSF and investigated cardiovascular conditions of healthy and end-stage heart failure. Results: Modeling results demonstrated appropriate hemodynamics and indicated that CSF pressure depends on blood flow pulsatility more than CSF flow. An acute equilibrium between CSF production and absorption was observed in the CF-MCS case, characterized by CSF pressure remaining elevated, and CSF flow rates remaining below healthy, but higher than CHF states. Conclusion: This research has advanced our understanding of the impact of CF-MCS on CSF dynamics and cerebral hemodynamics.

Background: The purpose of this research is to address ongoing device shortfalls for pediatric patients by developing a novel pediatric hybrid total artificial heart (TAH). The valveless magnetically-levitated MCS device (Dragon Heart) has only two moving parts, integrates an axial and centrifugal blood pump into a single device, and will occupy a compact footprint within the chest for the pediatric patient population. Methods: Prior work on the Dragon Heart focused on development of the pump designs to achieve hemodynamic requirements. The impeller of these pumps were shaft-driven and could not be integrated for testing. The presented research leverages an existing magnetically levitated axial flow pump and focuses on the centrifugal pump development. Using axial pump diameter as a geometric constraint, a shaftless, magnetically supported centrifugal pump was designed for placement circumferentially around the axial pump domain. The new design process included the computational analysis of more than 50 potential centrifugal impeller geometries. The resulting centrifugal pump designs were prototyped and tested for levitation and no-load rotation, followed by in vitro testing using a blood analog. To meet physiologic demands, target performance goals were pressure rises exceeding 90mmHg for flow rates of 1-5 L/min with operating speeds of less than 5000 RPM. Results: Three puck-shaped, channel impellers for the centrifugal blood pump were selected based on achieving performance and space requirements for magnetic integration. A quasi-steady flow analysis revealed that the impeller rotational position led to a pulsatile component in the pressure generation. After prototyping, the centrifugal prototypes (3, 4, and 5 channel designs) demonstrated levitation and no-load rotation. Hydraulic experiments established pressure generation capabilities beyond target requirements. The pressure-flow performance of the prototypes followed expected trends with dependence on rotational speed. Pulsatile flow was observed without pump-speed modulation due to rotating channel passage frequency. Conclusion: The results are promising in the advancement of the design and development of a pediatric TAH. The channeled impeller design creates pressure-flow curves that are decoupled from flow rate, a benefit that could reduce the required controller inputs and a limitation in hypertensive patients.

There continues to be an unmet therapeutic need for an alternative treatment strategy for respiratory distress and lung disease. We are developing a portable cardiopulmonary support system that integrates an implantable oxygenator with a hybrid, dual‐support, continuous‐flow total artificial heart (TAH). The TAH has a centrifugal flow pump that is rotating about an axial flow pump. By attaching the hollow fiber bundle of the oxygenator to the base of the TAH, we establish a new cardiopulmonary support technology that permits a patient to be ambulatory during usage. In this study, we investigated the design and improvement of the blood flow pathway from the inflow‐to‐outflow of four oxygenators using a mathematical model and computational fluid dynamics (CFD). Pressure loss and gas transport through diffusion were examined to assess oxygenator design. The oxygenator designs led to a resistance‐driven pressure loss range of less than 35 mmHg for flow rates of 1–7 L/min. All of the designs met requirements. The configuration having an outside‐to‐inside blood flow direction was found to have higher oxygen transport. Based on this advantageous flow direction, two designs (Model 1 and 3) were then integrated with the axial‐flow impeller of the TAH for simulation. Flow rates of 1–7 L/min and speeds of 10,000–16,000 RPM were analyzed. Blood damage studies were performed, and Model 1 demonstrated the lowest potential for hemolysis. Future work will focus on developing and testing a physical prototype for integration into the new cardiopulmonary assist system.

Clinically-available blood pumps and total artificial hearts for pediatric patients continue to lag well behind those developed for adults. We are developing a hybrid, continuous-flow, magnetically levitated, pediatric total artificial heart (TAH). The hybrid TAH design integrates both an axial and centrifugal blood pump within a single, compact housing. The centrifugal pump rotates around the separate axial pump domain, and both impellers rotate around a common central axis. Here, we concentrate our development effort on the centrifugal blood pump by performing computational fluid dynamics (CFD) analysis of the blood flow through the pump. We also conducted transient CFD analyses (quasi-steady and transient rotational sliding interfaces) to assess the pump's dynamic performance conditions. Through modeling, we estimated the pressure generation, scalar stress levels, and fluid forces exerted on the magnetically levitated impellers. To further the development of the centrifugal pump, we also built magnetically-supported prototypes and tested these in an in vitro hydraulic flow loop and via 4-h blood bag hemolytic studies (n = 6) using bovine blood. The magnetically levitated centrifugal prototype delivered 0–6.75 L/min at 0–182 mmHg for 2,750–4,250 RPM. Computations predicted lower pressure-flow performance results than measured by testing; axial and radial fluid forces were found to be <3 N, and mechanical power usage was predicted to be <5 Watts. Blood damage indices (power law weighted exposure time and scalar stress) were <2%. All data trends followed expectations for the centrifugal pump design. Six peaks in the pressure rise were observed in the quasi-steady and transient simulations, correlating to the blade passage frequency of the 6-bladed impeller. The average N.I.H value (n = 6) was determined to be 0.09 ± 0.02 g/100 L, which is higher than desired and must be addressed through design improvement. These data serve as a strong foundation to build upon in the next development phase, whereby we will integrate the axial flow pump component.

Cervantes‐Salazar and colleagues report the long‐term surgical outcomes of 414 patients with total anomalous pulmonary venous connection (TAPVC) from January 2003 to June 2019. With an overall survival rate of 87.2% from 2003 to 2019, the authors found that an increased mortality risk was associated with infracardiac TAPVC, pulmonary venous obstruction, and postoperative mechanical ventilation. Their comprehensive study with a large sample size of varying age groups, and patients with late referrals for surgery, provide valuable insight into TAPVC surgical outcomes. Improved survival for these patients continues to be a major goal of clinical teams striving to transform treatment paradigms. The promising result of the study reported by Cervantes‐Salazar and colleagues gives our field hope for a better future for these patients.

Cervantes-Salazar and colleagues report the long-term surgical outcomes of 414 patients with total anomalous pulmonary venous connection (TAPVC) from January 2003 to June 2019. With an overall survival rate of 87.2% from 2003 to 2019, the authors found that an increased mortality risk was associated with infra-cardiac TAPVC, pulmonary venous obstruction (PVO), and postoperative mechanical ventilation. Their comprehensive study with a large sample size of varying age groups, and patients with late referrals for surgery, provide valuable insight into TAPVC surgical outcomes. Improved survival for these patients continues to be a major goal of clinical teams striving to transform treatment paradigms. The comprehensive and promising results of the study reported by Cervantes-Salazar and colleagues gives our field hope for a better future for these patients.