Series multi-blood pump with dual activation for pediatric patients with heart failure

Thomas C. Palazzolo

doi:10.17918/00011077

Pediatric heart failure (HF), arising from both congenital and acquired disorders, is a serious pathology that affects thousands of children each year. Severe cases of pediatric HF are life-threatening and often require immediate surgical intervention. Initial treatments are administered through pharmacological interventions, but these treatments fail to address the root causes of HF, and thus do not arrest disease progression to end-stage HF. Patients in end-stage HF require a donor heart transplant, but there are difficulties related to donor heart procurement in the pediatric population; a limited number of donor organs are available, and there are significant challenges with donor-patient size matching due to significant patient heterogeneity. Due to these factors, it is not uncommon for children to wait months, even years, before a donor heart becomes available. To support HF patients as they await a donor heart, mechanical circulatory support (MCS) solutions have been developed to provide sufficient blood pressure and flow for end-stage organ perfusion. This new technology has greatly improved clinical outcomes in the adult population, and has seen increasing adoption in pediatrics. However, MCS technology for pediatric patients lags far behind the adult treatment paradigm. Only two ventricular assist devices (VADs) are clinically approved-- the paracorporeal valve-based BerlinHeart EXCOR has a limited operating range and is associated with a high rate of serious clinical complications, while the implantable HeartMate 3, an adult device adapted for pediatric applications, is too large to implant in a large contingent of the pediatric population. The limited device pool contributes to the off-design use of adult devices in children, but adult devices, which are not designed to support the unique needs of pediatric patients, are correlated with worse clinical outcomes. No single VAD technology can adapt to the considerable heterogeneity present in the pediatric population, and there remains a significant unmet clinical need for a single-device solution able to provide robust long-term support from infancy through adolescence. We are developing a novel double-blood pump pediatric VAD, the Drexel Double DragonVAD, to address this gap in the standard of care. This design uniquely incorporates both an axial pump and a centrifugal pump into a single VAD device. The axial pump operates independently to sustain younger patients at lower flows. As cardiac demands increase due to patient growth, a novel activation mechanism is used to activate the secondary centrifugal pump flow path, and the axial pump runs with the centrifugal pump in tandem to boost pressure-flow support at higher flow rates. This versatile VAD technology is designed to provide up to 120 mmHg of pressure rise over a wide range of flows, from 1-5 L/min. It also incorporates magnetic suspension to limit the number of moving parts and increase clearances between stationary and moving components, considerably improving the blood damage profile. The compact device will be able to provide implantable support in children as young as 4, and can provide paracorporeal support in even younger patients. Previous work resulted in the development of axial and centrifugal pump designs, as well as proposals for the device housing and overall design configuration. In this thesis, I leveraged prior research to develop a novel design concept which satisfied anatomical fit constraints, computationally evaluated and improved flow path geometry through CFD analysis, validated the flow path geometry through in vitro testing, demonstrated the function and hemolytic profile of the novel activation mechanism, and evaluated the flow path geometry and activation mechanism function in vitro. Design requirements were developed from previous work and a systematic literature review, and were used to iterate through multiple generations of design concepts. The final design concept satisfied anatomical fit requirements and produced a single-piece activation mechanism design which saved space and minimized the number of moving parts. The device flow path geometry was then evaluated through CFD, and improved using an independently developed prioritized design improvement process. The resultant improved flow path geometry satisfied design requirements according to k-epsilon simulations. Further computational analyses were conducted: an additional (SST) turbulence model was investigated, blood stress and blood damage potential were evaluated through the SSG model, and transient analyses were performed to characterize the impact of time-dependent phenomena such as blade passage and a non-uniform inflow profile on overall pump performance. This was the first steady-state and transient evaluation of a double-blood pump VAD. The VAD design was then validated on the benchtop through in vitro testing, which was performed in three stages. First, the hydraulic performance of the flow paths was validated through a shaft-drive test rig using a water-glycerol blood analog solution. The resultant data demonstrated a strong correlation with simulation predictions from the SST turbulence model. Nondimensionalized analysis supported this correlation, with the combined flow path averaging less than 5% deviation. In addition, the activation mechanism design proposal was functionally examined through multiple rounds of prototype development, producing an actuated prototype which could provide long-term leak-free support at pressures and flows exceeding design limits. Blood studies with this mechanism prototype demonstrated a hemolytic profile in line with current clinically approved blood pump technologies. Finally, the activation mechanism and flow path geometry were examined in tandem through integrated testing. The scaled integrated prototype, despite a minor leak, demonstrated effective actuator function and hydraulic performance, and the resultant data showed qualitative alignment with previous flow path studies. Significant translational progress has been made in the development of the Drexel Double DragonVAD. We have created a device configuration which satisfies anatomical fit constraints. The flow path geometry achieved design targets in the k-epsilon simulation domain. In vitro flow path studies validated computational pump performance predictions, and also produced a functional actuated activation mechanism prototype with an acceptable hemolytic profile. The final integrated prototype satisfied functional and actuation requirements. These successes provide a strong foundation for future design improvements, including magnetic suspension development, integrated hemolytic studies, in vivo animal trials, and eventual clinical implementation.

Series multi-blood pump with dual activation for pediatric patients with heart failure

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Series multi-blood pump with dual activation for pediatric patients with heart failure

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