LVAD Research Project – The Full Story

Team Members: Alara Blofield, Jorge Cortes

In its early beginnings (February 2020), the LVAD Team initially looked into a broad range of Cardiovascular Device topics before finally taking interest in the subject of Left Ventricular Assist Devices (LVAD). Upon doing so, the Team dove into problems such current LVAD complications, contraindications, and limitations. It was then discovered that research is being conducted worldwide to design a simple LVAD pump that would be situated within the ascending aorta itself, rather than within an external pump housing that bypasses the heart (as current LVADs do).

An internal, or “series,” LVAD device, such as the aforementioned, would theoretically reduce certain risks and potential complications associated with current external, or “bypass” LVADs (Zhang et al., 2016). However, research on this type of LVAD design did not appear to include published models and/or Computational Fluid Dynamics (CFD) simulation results for a complete pump structure including bearings and fixtures. Thus, the LVAD Team’s research aim was born: to develop a functionally suitable design, with schematics for deployment in the ascending aorta (AA), of a complete series LVAD with associated suspensions and bearings.

Current Findings

During 2021, the Team focused on developing a pump model that would demonstrate physiologically optimal Computational Fluid Dynamics (CFD) simulation results while (1) simplifying LVAD design to reduce areas of risk for thrombosis and mechanical failure, and (2) retaining the integrity of the AV to reduce the risk of AV disease.

Methods involved the use of ANSYS SpaceClaim and DesignModeler to develop pump design, which included a rotor to produce flow and stator for flow stabilization. Transient-state ANSYS Fluent CFD simulations were then conducted using generalized aorta boundary conditions based on literature values. Analysis was done by finding rpm-dependent axial flow rates, shear stress levels, and inlet-outlet pressure changes.

Results show successful rotor-speed dependent flow rates of at least 4 L/min for each set rpm value. Optimized shear stress levels (<200 Pa) around the rotor were seen in 2000rpm and 6000rpm simulations. Ideal changes in inlet-outlet pressure, comparable to current bypass LVAD devices, were seen at 6000rpm (18-22 mmHg), while 2000rpm CFD only showed a change of 3-6 mmHg. Results reveal a functional, reduced-risk LVAD pump with bearings and a suspension mechanism for AA placement in HF patients.

Pictures of current findings are as follows:

Future Work

Since the Team successfully developed a working model of a series LVAD along with bearings and suspensions, future work (Fall 2021) consists of developing a mechanism for deployment for the device, especially the rotor and stator blades. The plan is to make the device deployable through a less invasive procedure than required by current LVADs, ideally a transapical approach, which would mean confining the device into a smaller space and folding the blades until it can be expanded and fixed into its final form.

After achieving the deployment-dependent design alterations and plan, the Team hopes to shift focus onto electrical implications and solutions, including powering without use of a percutaneous driveline that connects to an external battery.

References

Zhang, Q., Gao, B., & Chang, Y. (2016). The study on hemodynamic effect of series type LVAD on aortic blood flow pattern: a primary numerical study. Biomedical engineering online, 15(2), 293-307.