Experimental investigation into the effect of compliance of a mock aorta on cardiac performance

Abstract

Demand for heart transplants far exceeds supply of donated organs. This is attributed to the high percentage of donor hearts that are discarded and to the narrow six-hour time window currently available for transplantation. Ex-vivo heart perfusion (EVHP) provides the opportunity for resuscitation of damaged organs and extended transplantation time window by enabling functional assessment of the hearts in a near-physiologic state. Present work investigates the fluid mechanics of the ex-vivo flow loop and corresponding impact on cardiac performance. A mechanical flow loop is developed that is analogous to the region of the EVHP system that mimics in-vivo systemic circulation, including the body's largest and most compliant artery, the aorta. This investigation is focused on determining the effect of mock aortic tubing compliance on pump performance. A custom-made silicone mock aorta was developed to simulate a range of in-vivo conditions and a physiological flow was generated using a commercial ventricular assist device (VAD). Monitored parameters, including pressure, tube distension and downstream velocity, acquired using time-resolved particle imaging velocimetry (PIV), were applied to an unsteady Bernoulli analysis of the flow in a novel way to evaluate pump performance as a proxy for cardiac workload. When compared to the rigid case, the compliant mock aorta case demonstrated healthier physiologic pressure waveforms, steadier downstream flow and reduced energetic demands on the pump. These results provide experimental verification of Windkessel theory and support the need for a compliant mock aorta in the EVHP system.

Experimental Investigation Of The Effect Of Compliance Properties On The Flow In An Analogous Ex-Vivo Heart Perfusion System

“…However, such aorta compliance feature is not currently involved in the EVHP system because its hydraulic circuit is essentially composed of rigid tubes. In a previous work, it was shown that the use of a compliant tube, mimicking the aorta, instead of a rigid tubing in the EVHP system's flow loop could alter the flow-pressure relationship of the pulsatile flow, making it more similar to the physiological profile and also reducing the workload of the heart [19]. However, this study was conducted with only a single compliant tube.…”