Traditionally, an empirical power-law model relating hemolysis to shear stress and exposure time has been used to estimate hemolysis related to flow--however, this basis alone has been insufficient in attempts to predict hemolysis through computational fluid dynamics. Because of this deficiency, we sought to re-examine flow features related to hemolysis in a shearing flow by computationally modeling a set of classic experiments performed in a capillary tube. Simulating 21 different flows of varying entrance contraction ratio, flowrate and viscosity, we identified hemolysis threshold streamlines and analyzed the stresses present. Constant damage thresholds for radial and axial extensional stresses of approximately 3000 Pa for exposure times on the order of microseconds were observed, while no such threshold was found for the maximum shear stress or gradient of the shear stress. The extensional flow seen at the entrance of the capillary appears to be most consistently related to hemolysis. An account of how extensional stresses can lead to lysis of a red cell undergoing tank-tread motion in a shearing flow is provided. This work shows that extensional components of the stress tensor are integral in causing hemolysis for some flows, and should be considered when attempting to predict hemolysis computationally.

A patient supported by a left ventricular assist device (LVAD) presented with an abdominal tumor requiring consolidative radiation therapy. To assess the effects of radiation therapy on the operation of the ventricular assist device (VAD) system and assure that the treatment would be safe for the patient with regard to the operation of the VAD system, sample equipment was irradiated and then tested for functionality. Changes in the mechanical properties of components of the percutaneous lead were measured. After testing, it was concluded that radiation therapy would not impede the operation of the pump or produce deleterious alterations of mechanical properties of the various system components. The patient underwent radiation therapy with a total dose of 2,000 cGy without evident complications. There were no observed effects on the LVAD operation nor any indication of alarms or malfunctions. Subsequently, the patient recovered adequate cardiac function for explant of the LVAD and the recovered components were also analyzed confirming the absence of alterations in material properties that would endanger patient safety.

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Superior fillet radii for both renal arteries are similar to the optimal value to reduce energy losses while the inferior radii are not. Ostial asymmetry may have been induced by higher levels of shear stress present on the superior portion of a developing symmetric ostium of small r/D.