Investigation into the effect of compliant response on fluid flow in an ex vivo heart perfusion test system

• Author / Creator

  Cameron, Katie G.

• Demand for heart transplants far exceeds supply. This is often attributed to the high percentage of donor hearts that are discarded due to cell injury and to the narrow six-hour time window currently available for transplantation. A method called ex vivo heart perfusion (EVHP) enables the use of damaged donor hearts and extends the available time window by preserving the heart’s beating function outside the body from the time of donation until transplantation. To-date, research efforts have focused on controlling the metabolic environment required to maintain cardiac tissue health. However, the effect of the fluid mechanics of the system on cardiac performance has yet to be investigated. The region of the system where the fluid mechanics are most complex and the potential for adverse organ-machine interaction is highest is the region following the left ventricle where, in vivo, blood is ejected into the body’s largest and most compliant artery, the aorta. The well-understood expansion-recoil function of the aorta plays the crucial roles in vivo of ensuring forward blood flow in the peripheral vasculature and reducing cardiac workload. These functions help mitigate the fatigue and remodeling of cardiac muscle that occur in response to elevated cardiac workload. It is likely that the introduction of compliant aortic response into the EVHP system would have a similarly positive effect on cardiac performance, but this idea has not been explored prior to this investigation. This work has been undertaken to study of aortic compliant response in a mechanical flow loop analogous to the left side of the EVHP system in order to determine the impact of compliance on system performance. To this end, two experiments were performed; one established a fundamental case and the other explored a physiological case. The first experiment studied the pulsatile flow from a peristaltic pump in the analog system to establish a fundamental case of compliant response in a pulsatile flow regime. This experiment also compared the response of a Newtonian fluid to that of non-Newtonian fluid to ascertain whether or not non-Newtonian effects in the system warrant further investigation. The second experiment generated a simulated cardiac flow through the system using a commercial ventricular assist device (VAD). This experiment addressed the effect of compliance in a physiological pulsatile flow regime. For both experiments, three parameters were used to assess the impact of compliance on system performance: pressure, tube response and downstream velocity fields. Pressure was monitored at the inlet and outlet of the compliant section, as well as downstream where the velocity fields were obtained. Tube response was monitored with a camera and the downstream flow fields were captured using time-resolved particle imaging velocimetry (PIV). These parameters were used to assess the performance of the pump by applying unsteady Bernoulli analysis to the system and comparing these values to those obtained with a rigid test section. In the case of the peristaltic pump experiment, it was found that the introduction of compliance into the system smoothed out the pressure and velocity responses and increased the energy applied by the pump for both fluids. The relationship between pulse frequency and pump energy was different for each fluid; the Newtonian case reached a peak at a pulse frequency of 1.67 Hz, while the non-Newtonian case maintained a positive linear relationship across the range of tested frequencies. For the VAD experiment, the introduction of compliant response into the system was found to improve all evaluated system performance parameters. The compliant mock aorta case demonstrated healthier pressure waveform profiles, less downstream reverse flow and lower pump energy requirements. This is an important finding, as is suggests that the introduction of aortic response into the EVHP system is likely to have a positive impact on cardiac performance. Further, this work on pump energy requirements may serve as a useful proxy for quantifying cardiac performance in future work.

• Subjects / Keywords

  • Particle imaging velocimetry (PIV)
  • Ex vivo heart perfusion
  • Compliance
  • Pulsatile flow
  • Aorta

• Graduation date

  Spring 2017

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/R35T3GB9F

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.