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Defense Date
2007
Document Type
Thesis
Degree Name
Master of Science
Department
Biomedical Engineering
First Advisor
Dr. Gerald E. Miller
Abstract
Most current designs for Left Ventricular Assist Devices (LVAD) are based on rotary pumps due to their small size and lack of valves. However, the majority of FDA approved LVADs are larger, positive displacement pumps. One reason for this may be because positive displacement pumps produce pulsatile flow, similar to that of the natural heart, while rotary pumps produce continuous flow. Continuous flow has been shown to support the circulation for short periods of time during open-heart surgery, but it has seen limited success with long-term support. It is thought that pulsatile flow provides many metabolic advantages to patients with high total peripheral resistance (TPR) and lower flowrates. This study focused on modifying a continuous flow multiple disk centrifugal pump (MDCP) into a pulsatile pump, to allow for the combined benefits of the pulsatility from positive displacement pumps and the small size and valveless design of rotary pumps. An efficiency study was carried out by evaluating the hydraulic work output and the power requirements of the pump. The pump was evaluated in both pulsatile and continuous flow modes. In continuous mode, the pump was able to maintain a flow of 5.5 L/min against a pressure head of 60mmHg at 1155rpm. Other LVADs have reported rotational speeds around 2400rpm for centrifugal and 10,000rpm for axial pumps to produce flows around 5 L/min. This indicates that the MDCP is capable of producing flowrates at lower rotational speeds than other LVADs, lessening the mechanical wear of the parts, thus potentially increasing the device's lifespan. In pulsatile mode, cardiac outputs of 5 L/min were achieved against a 55/27mmHg outlet pressure. Higher pressures were unattainable with our current testing apparatus, but the results from the pulsatile tests prove that the MDCP can be operated in a pulsatile fashion and produce normal flowrates at low pressures. The pump efficiency was lower than expected, around 0.7-9% in continuous mode and 3-18% in pulsatile mode, consuming 3.5-28W and 0.5-2.3W, respectively. Utilizing a smaller motor may produce higher efficiencies, since the power requirements will be less without decreasing the flowrates, but a further study should be conducted in order to verify this.
Rights
© The Author
Is Part Of
VCU University Archives
Is Part Of
VCU Theses and Dissertations
Date of Submission
June 2008
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Comments
Part of Retrospective ETD Collection, restricted to VCU only.