Impact of red cell distribution in sheared blood flow upon quantification of hemolysis rate in artificial organs

  • Einfluß der Verteilung der roten Blutkörperchen in einer Scherströmung auf die Hämolyse in künstlichen Organen

Poorkhalil, Ali; Büchs, Jochen (Thesis advisor); Mottaghy, Khosrow (Thesis advisor)

1. Auflage. - Aachen : Verlagshaus Mainz GmbH (2016)
Dissertation / PhD Thesis

Dissertation, RWTH Aachen University, 2016

Abstract

Blood contacting artificial organs, whether used as a bridge to transplantation, or even as a permanent organ replacement, find ever increasing application in contemporary medicine. Hemocompatibility and blood trauma minimization (e.g. hemolysis) are the two key factors in artificial organ development and design optimization. These issues become rather imperative for blood contacting devices, designed for long term application. Hemolysis is considered to be a function of shear stress and shear exposure time. Each device, based on its function, it may perform under a very broad range of operational conditions; high shear stress and short exposure time, e.g. ventricle assist devices (VADs) or low shear stress and long exposure time (e.g. dialyzers). Where VADs are concerned, high shear regions might be unavoidable on the ground of pumping performance maximization, but on the other hand, the existence of these regions tends to be avoided, due to design modifications for improved hemocompatibility. However, the performance and design characteristics have contradictory effects on each other, concerning their optimization. In spite of their low shear stress, conventional dialyzers exhibit relatively long exposure and contact time with foreign surfaces, which highlights the necessity of design optimization for good hemocompatibility. In an effort to address the above stated challenges, the first part of this study describes the theoretical and physiological background (chapter 1-4) and further the experimental studies (Chapters 5-6), as a manifestation of shear field induced erythrocyte distribution and local hematocrit, on the resulting hemolysis, through an innovative hypothesis that treats blood as a multiphase fluid. Two modified Taylor – Couette devices mimicking the VADs blood flow pattern, are designed and manufactured to investigate the outcomes of shear field variation on the resulting hemolysis. In addition, a semi-empirical hemolysis model that considers the dominant phenomena involved in the process, is presented, to provide a better understanding and prediction of the resulting hemolysis mechanism. The proposed hypothesis as well as the semi-empirical hemolysis model are then validated by in-vitro investigations, using fresh human and animal (porcine) blood. The effect of filtration and backfiltration processes on local hematocrit in dialyzers, and the subsequent generation of hemolysis, is studied in the second part (Chapters 7-9) as a counter case to VADs. Semi-empirical models predicting the courses of hematocrit, flow rate and pressure, are introduced, and mathematical equations governing the mass transfer phenomena are established, in order to further the understanding of dialysis hemodynamics. In-vitro investigations are carried out for different validation purposes, using porcine blood, in pursuance of the aforementioned mathematical models. The findings of this study emphasize the importance of the consideration of shear induced cell migration and distribution, has a significant impact on the resulting hemolysis, and is a key factor for the design and performance optimization of artificial organs with various flow characteristics.

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