MULTI-SCALE ANALYSIS OF COOLING PROTOCOLS FOR HUMAN HEARTS The main current problem of organ transplantation is the relatively short time that organs can survive from the moment of their harvesting to the moment of their surgical transplantation into the recipient's body. In organ preservation, cold preservation is still considered as the best method. Lowering the temperatures of cells, tissues and organs lowers their chemical reaction rates, thus lowering their metabolic decay rate. In currently used standard heart cooling procedures, the extracted human heart is kept submerged in a container with saline solution at a temperature slightly above that of freezing water. The current limit for a heart to remain viable for transplantation using this method of cooling is only 4.5 hours, after which the heart is discarded. Consequently, a large number of viable donated hearts are discarded because the recipient of the heart lives too far away. The ultimate objective of this research is to extend the viability of the extracted human heart to more than 10.5 hours, which was recently computationally demonstrated by the PI as preliminarily feasible. This would provide more than 8 hours for air transport, thus enabling hearts to be transported for transplantation anywhere in the populated North American continent. The results of this project should provide an understanding of the proposed organ cooling protocols that are both viable and widely applicable.The objective of this project is to apply advanced numerical analysis and optimization concepts of rapidly cooling human hearts to explore reducing metabolic decay and extending their use for the purpose of long distance transportation to the transplantation site. The focus will be on performing a multi-scale analysis of the conjugate heat transfer in realistic human hearts including epicardiac and intramural blood vessels. The risk is that adding this geometric and numerical complexity might not increase the cooling rate. As part of achieving this goal, the explanted heart should immediately begin a cooling process utilizing nearly-freezing water in order to cool the heart as uniformly and as fast as possible to minimize permanent damage of the heart muscle due to metabolism. In this preliminary research, coolant flow and the corresponding heat transfer in coronary blood vessels, branching intramural vessels and microcirculation in the heart muscle tissue will be included for the first time. By including these multiple length scale effects into the overall forced convection conjugate heat transfer analysis, it could be expected that the speed and uniformity of cooling of the realistic human hearts can be increased, thus decreasing further the metabolic decay and extending further the viability time limit available for transporting the extracted hearts.
