Afterload system design for functional donor heart assessment

Abstract: Heart transplantation is a life-saving procedure for patients with end-stage heart failure. However, conservative acceptance criteria result in most donated hearts being discarded. Enabling clinicians to assess heart function after organ procurement can pave the way for the safe use of hearts that are currently rejected. This thesis focuses on improving techniques for the direct, controlled assessment of a recovered heart's hemodynamic performance. The first paper reviews ex situ working heart models and cardiac afterload devices, discussing challenges in emulating cardiac afterload and detailing an experimental method for a working porcine heart model. Paper II analyzes Windkessel models, which are the standard cardiac afterload model. It assesses their applicability and limitations, and presents a method for identifying model parameters from sampled data. The analysis concludes that complex models like the 4-element Windkessel model are not identifiable from relevant experimental data. The third paper reformulates traditional Windkessel models for a more accurate representation of hemodynamic responses. Using power as model input, the paper offers a more physiological representation of the hemodynamic response to various afterloads, aiding in afterload device design. In Paper IV, the efficacy of a pneumatic afterload device creating a range of physiological loading conditions is investigated in six porcine hearts. The experiments show the concept's utility in testing hearts under multiple conditions. Paper V introduces an actively controlled variable flow resistance, demonstrating its ability to reproduce a wide range of afterload dynamics while enforcing safe pressure limits for heart assessment. The afterload concept, outlined in Paper I, is investigated in silico using the methods from Paper III. A physical prototype and pilot experiments led to a patent submission for the design. These papers advance functional heart assessment by both refining Windkessel-model-based simulation tools (Papers II and III) and exploring novel afterload device concepts (Papers I, IV, and V). Together, they constitute a step towards clinical implementation of technology that can safely enable more transplantations by providing an improved basis for decision-making.