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New Continuous-flow Total Artificial Heart for Use in Smaller Sized Adults and Pediatric Patients

Thursday, May 23, 2019

11:30 AM-1:30 PM

BIOMED PhD Thesis Defense

New Continuous-flow Total Artificial Heart for Use in Smaller Sized Adults and Pediatric Patients

Carson Solon Fox, PhD Candidate
School of Biomedical Engineering, Science and Health Systems
Drexel University

Amy L. Throckmorton, PhD
Associate Professor
School of Biomedical Engineering, Science and Health Systems
Drexel University

Congestive heart failure (CHF) is a progressive and debilitating disease that affects millions of adults and children worldwide. Hundreds of thousands of new cases of CHF are diagnosed each year in the U.S., and this high volume of patients costs the healthcare industry tens of billions annually. The inadequate number of donor hearts and limited long-term effectiveness of pharmacologic treatment necessitate the development and use of mechanical circulatory support (MCS) therapies. Clinical utilization of MCS devices has demonstrated that patients derive substantial survival and quality of life benefits from short and long-term MCS. Only two total artificial hearts (TAHs) are approved for implantation in the U.S., and the implementation of TAHs in the treatment of patients with CHF has increased more than 3 fold in the last 6 years. To address the limitations of current technology and to provide a new and novel therapeutic alternative, we are developing an innovative, hybrid-design, continuous flow, implantable, magnetically levitated TAH (Dragon Heart).
The Dragon Heart is designed to provide cardiovascular support to pediatric and adult patients. This compact medical device has a target diameter and height of 70 mm by 50 mm, respectively; it is designed to generate the physiologic pressures and flows necessary to support CHF patients. This TAH has only 2 moving parts: an axial flow impeller to drive blood flow through the pulmonary circulation and a centrifugal flow impeller to drive blood flow through the systemic circulation. This device utilizes the latest generation of magnetic bearing technology to levitate the impellers, thus enabling an operational lifespan of 15 years. The design incorporates wider clearances between the rotating impellers and pump housing. Larger clearances lead to lower fluid shear stresses, hence mitigating the risk of thrombosis and hemolysis. This design avoids the use of mechanical or biologic valves and has an antithrombogenic coating applied to blood-contacting surfaces, thus further reducing the risk of thrombosis. It integrates state-of-the-art monitoring with Wifi-based sensors to report operational status and produces both continuous and pulsatile blood flow. A transcutaneous energy transfer system using wireless technology will be incorporated to supply power to the device and to eliminate the percutaneous driveline that protrudes from the abdomen, which is a major source of infection for patients who are supported by current MCS technology. This dissertation research concentrated on advancing the development of the axial and centrifugal blood pumps that constitute the core components of the Dragon Heart.
Three substantial design phases were completed. The pump geometries (axial and centrifugal) were established using advanced pump design equations, 3D modeling and pump design software, and available literature on blood pumps. ANSYS computational fluid dynamic software was used to evaluate the pressure flow generation, irregular blood flow velocities and patterns, estimated power consumption, radial and axial fluid forces on the rotor, fluid stress levels, blood cell residence time in the device, and blood damage predictions. The computational models served as the foundation by which prototype manufacturing was completed for hydraulic testing. Three hydraulic test rigs were constructed to test the pressure generation and levels of hemolysis in the prototypes. A blood analog solution of water and glycerin was utilized for the hydraulic experiments, and bovine blood was used for the repeated hemolytic studies.
During the design process, the axial and centrifugal pump designs were improved iteratively to reduce the size of the pumps without compromising pump performance. This process resulted in a small device size of 67 mm by 50 mm, surpassing the target goal. The simulations revealed that both pumps were able to generate adequate pressure and blood flow to support adult and pediatric patients. Computational results followed expected theoretically trends for pumps in general. Radial and axial fluid forces were estimated to be less than 0.4 N and 3 N, respectively. Maximum fluid stress levels remained less than 320 Pascal with maximum exposure times of less than .54 seconds. Blood damage models for several operating conditions indicated low damage levels of less than 2%. Estimated power consumption was determined to be less than 6 Watts.
Physical prototypes of the axial and centrifugal pump designs were manufactured for hydraulic and hemolytic testing. The experiments demonstrated that the Dragon Heart is capable of delivering the target blood flows of 1-5 LPM and pressure rises of greater than 15 mmHg for the pulmonary circulation and greater than 95 mmHg for the systemic circulation for acceptable rotational speeds. The centrifugal prototypes had a general trend of outperforming the computational predictions by 37.5%; while the axial flow prototypes showed a decreased pressure-flow range during testing as compared to the computational studies. The data trends of the hemolytic studies followed expectations with a linear increase in plasma-free hemoglobin levels, slow decrease in hematocrit, and a consistent maintenance of operational conditions of the pump during the experiments. The Normalized Index of Hemolysis levels, however, were higher than anticipated in comparison to clinically used MCS devices. This is likely due to the materials of construction of the prototypes and surface roughness factors, which will be addressed in future work.
This research and development effort is significant progress in the design of the Dragon Heart and represents a strong foundation by which to begin further optimization and development. The long-term goal of this research is to commercialize a novel, less expensive, more compact, low thrombus, and effective therapeutic alternative for adult and pediatric patients with CHF, thereby saving thousands of lives annually.

Contact Information

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