Project Summary Millions of Americans are affected by heart and lung diseases. Mechanically assisted circulation (MAC), including mechanical circulatory support (MCS) with ventricular assist devices (VADs), extracorporeal membrane oxygenation (ECMO) and cardiopulmonary bypass (CPB), is routinely implemented to treat patients with advanced heart failure (HF) or respiratory failure or cardiac surgery. Recent data shows that approximately 85% and 75% of patients supported with continuous flow VADs (CF-VADs) are expected to survive 12 and 24 months, respectively, which are close to the survival rates of heart transplant patients. ECMO use expanded rapidly over the last decade. While these device-based therapies save many patients' lives and improve their quality of life, infections are a common postoperative complication in these patients and are associated with increased morbidity and mortality. It is critical to understand the risk of infections in patients receiving CF-VAD or ECMO support and its underlying mechanisms. Both contemporary CF-VADs and ECMO systems are based on the rotary blood pump technology. The high-speed rotation of the impeller in a rotary blood pump inevitably introduces a high mechanical shear stress (HMSS) on the blood cells flowing through the pump. We believe that HMSS generated by the action of pumping in CF-VAD and ECMO therapies can cause damage/injury to leukocytes, leading to their dysfunction which affects patients’ immune defense to infection. Given the potential of CF-VAD and ECMO therapies for patients and the need to reduce the significant complications associated with the devices, we propose to conduct a series of bioengineering experiments to gain a better understanding of HMMS-induced neutrophil dysfunction. Three specific aims of the proposed project are: (1) to characterize HMSS-induced structural, rolling/adhesion and phenotypical alterations of neutrophils, and to establish the quantitative relationships between structural alterations of neutrophils and HMSS over the range relevant to CF-VAD or ECMO therapies; (2) To assess phenotypical profiles and dysfunction of leukocytes using an in vivo ovine model under low and high HMSS settings of CF- VAD support; (3) To explore potential mechanisms of HMSS-induced neutrophil structural alterations relevant to CF-VAD and ECMO therapies. Successful completion of this project will create new knowledge of HMSS- induced leukocyte dysfunction associated with CF-VADs or ECMO systems. The new knowledge can be used by engineers to develop less traumatic, next-generation biocompatible VADs and ECMO systems and by clinicians to provide better postoperative management.