Near-Wall Fluid Mechanics Of A Pulsatile Flow Through A Compliant Tube

Abstract

The demand for heart transplantation far exceeds the supply. This shortage is mainly due to the high percentage of discarded hearts and the narrow time window of only six hours that the current standard preservation method, static cold storage (SCS), allows for completing the entire procedure from donor to recipient patient. An alternative method called ex-vivo heart perfusion (EVHP) maintains a human donor heart beating outside the body for the time preceding transplantation surgery. By keeping the donor heart beating in a quasi-physiological mode of operation and assessing its functions, the organ's health can be monitored so that, ultimately, the transplant time window can be extended to increase the geographic availability of donors. In order to improve and optimize the EVHP system, fundamental understanding of the system physics is needed. To achieve this, the present work aims to investigate the relationship between pulsatile flow and compliance, evaluating the near wall region of a compliant tube with a particular focus on the formation of the viscous boundary layer. Thus, an experimental setup was designed to replicate the flow loop of the EVHP system and an optical transparent compliant tube that mimics the functioning of the body's largest and most compliant artery, the aorta, was custom-made to allow optical access to the flow field matching the refractive index of the working fluid. A pulsatile waveform is generated using a computer-controlled mechanical diaphragm pump, also equipped with a tri-leaf exit valve to simulate the physiological working condition of the heart. In the present work, the flow field is assessed by first performing stereo particle image velocimetry (PIV) on the bulk flow to investigate the large-scale phenomena within a compliant tube and the results of these experiments will be further used as a guide to interrogate smaller near-wall regions of interest in the flow. The preliminary results show, in addition to the general characteristics of a pulsatile flow through a compliant tube, a potential complex fluid-structure relationship between the pulsatile flow and the moving wall of the tube has been observed. The presentation of this work will discuss the experimental setup and review the preliminary results presented here in addition to others findings that are still being analyzed, data processing is underway to do so.