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Fluid dynamics of a pediatric ventricular assist device
C Bachmann1, G Hugo, G Rosenberg
1Bioengineering Department, the Pennsylvania State University, University Park, PA 16802, USA.
Insights
Scaling down ventricular assist devices for pediatric use is challenging. Reduced pump size alters fluid dynamics, increasing clot formation risk and impacting patient outcomes.
Area of Science:
- Biomedical Engineering
- Cardiovascular Research
- Pediatric Medical Devices
Background:
- Mechanical circulatory support is increasingly vital for pediatric patients undergoing cardiac procedures and transplantation.
- Current salvage rates for pediatric patients requiring circulatory support remain low, highlighting a critical unmet need.
- Existing adult-sized pneumatic ventricular assist devices demonstrate high success rates, but pediatric versions face significant challenges.
Purpose of the Study:
- To investigate the fluid dynamic factors contributing to thrombus formation in a scaled-down (15 cc) pediatric ventricular assist device.
- To understand why a smaller version of a successful adult device failed in animal experiments.
- To identify design modifications for improved pediatric mechanical circulatory support.
Main Methods:
- Dimensional analysis to compare key dimensionless parameters (Reynolds and Strouhal numbers) between successful and unsuccessful pumps.
- Two-component laser Doppler velocimetry to quantitatively characterize internal flow fields.
- Comparative analysis of flow field data with established data from a successful 70 cc device.
Main Results:
- Significant differences in Reynolds (Re) and Strouhal (St) numbers were identified between the 70 cc and 15 cc pumps.
- The 15 cc pump exhibited reduced wall shear stress and lower turbulence levels compared to the 70 cc pump.
- These altered fluid dynamic conditions in the smaller pump create an environment conducive to thrombus deposition.
Conclusions:
- The failure of the 15 cc pediatric ventricular assist device is attributed to altered fluid dynamics resulting from size reduction, not material or operational principles.
- Reduced pump size leads to suboptimal flow conditions that promote clot formation, compromising device efficacy.
- Further research into pediatric ventricular assist device design must prioritize fluid dynamics to mitigate thrombus risk and improve patient outcomes.
Abstract:
The number of pediatric patients requiring some form of mechanical circulatory assistance is growing throughout the world because of new surgical procedures and the success of pediatric cardiac transplantation. However, the salvage rate for those patients requiring circulatory support may be as low as 25%. Despite the fact that Penn State's 70 cc pneumatic ventricular assist device has been used with a success rate of over 90% in more than 250 patients worldwide, efforts to scale down the pump have encountered difficulties. Animal experiments with a 15 cc version were unsuccessful, with explanted pumps showing extensive thrombus deposition within the pumping chamber. The materials used to fabricate the smaller pump as well as the basic operating principles are identical to the successful adult-sized version. It is therefore believed that reducing the size of the pump altered the internal flow field, and that fluid dynamic factors were responsible for the high degree of thrombus observed with the implanted devices. A dimensional analysis was conducted that revealed significant differences in both Reynolds (Re) and Strouhal (St) numbers between the successful and unsuccessful pumps. Two component laser Doppler velocimetry was then used to characterize the internal flow field quantitatively. Comparison with data from the 70 cc pump showed a reduction in wall shear stress and turbulence levels in the 15 cc pump that would yield an environment conducive to clot formation.
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