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

Katie Cameron,Darren H Freed,Mouhammad El Hassan,Reza Sabbagh,David S Nobes,Iman Borazjani

doi:10.1371/journal.pone.0239604

Katie Cameron, Darren H Freed + Show 4 more

Open Access

https://doi.org/10.1371/journal.pone.0239604

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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.

Highlights

Heart transplantation is the gold standard treatment for end-stage heart failure patients but demand for viable donor hearts far outweighs supply [1,2]. This critical shortage is most often attributed to three factors: high discard rate amongst available donor hearts [1,3], the limited time window of six hours available for transplantation using the current standard of care [4]
Mean arterial pressure
The results outlined in this paper include the presentation of pressure, tube distension and downstream velocity results obtained from one set of operating conditions, where pressure chamber (Pch) = 103 mmHg and ωAl pump = 1235 RPM

Summary

Introduction

Heart transplantation is the gold standard treatment for end-stage heart failure patients but demand for viable donor hearts far outweighs supply [1,2]. Information about the cardiac cycle, as well as assessment of cardiac performance, is most commonly understood through interpretation of the pressure waveforms in the peripheral arteries, those that are far from the heart [24] While this is common clinical practice due to the non-invasive nature of such a measurement, more important information can be obtained from central aortic pressure waveforms that are obtained directly from the aorta [25]. Systolic pressure (Ps) is defined as the peak pressure achieved during this ejection phase Once this peak pressure is reached toward the end of the contraction of the left ventricle, there is a gradual decrease in pressure in the aorta.

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