Showing papers by "Takashi Yamane published in 2006"

Hemolysis resulting from surface roughness under shear flow conditions using a rotational shear stressor.

Abstract: The degree of hemolysis as a function of surface roughness value and roughened area under shear flow conditions was investigated using a rotational shear stressor. The shearing portion of the stressor is cone shaped in its upper and lower positions, with a cylindrical central section. Surface roughness was applied to the cylindrical section. Bovine blood was sheared for 30 min over a set of roughened surfaces of between arithmetic mean roughness (Ra) 0.1 and 0.8 mm covering 10% of the surface area of the cylindrical section (equivalent to 1.8% of the whole blood contact area) at a shear rate of 3750/s. The threshold value thus obtained for rapid increase in hemolysis was between Ra 0.6 and 0.8 mm. When sheared with a roughened surface of Ra 0.8 mm applied to the cylindrical surface at areas between 0 and 100% (equivalent to between 0 and 18% of the whole blood-contacting area), the hemolysis level did not increase from 10 to 100%, but a significant difference was obtained between 0 and 10%. This suggests that red blood cells were destroyed not by fatigue failure caused by rolling on the roughened surface, but due to the high shear stress generated by surface roughness. Moreover, it appears that the shear stress was generated over the entire cylindrical section, regardless of the area of surface roughness.

Computational Fluid Dynamic Analysis of the Flow around the Pivot Bearing of the Centrifugal Ventricular Assist Device

Abstract: Flow mechanisms within a monopivot centrifugal pump were clarified in order to prevent stagnation around the pivot bearing, which may cause thrombogenesis. We focused on the geometric effects of the pump, which included the effects of the washout hole diameter, the pivot friction area and the back gap width of the impeller relative to the washout around the pivot bearing. Flow patterns were carefully examined around the pivot bearing, including the region inside the washout hole and the back gap of the impeller, by computational fluid dynamic analysis. Based on the results from the computational fluid dynamic analyses, we found that a balance relationship between the washout hole diameter and the back gap width of the impeller affected the secondary flow toward the pivot bearing that eliminated the stagnation around the pivot bearing. In addition, while increasing in the pivot friction area eliminated stagnation around the pivot bearing, it also increased hemolysis within the pump.

The pivot wash in two impeller modes for the Baylor/Miwatec centrifugal blood pump.

Abstract: A centrifugal blood pump with a double pivot impeller and an eccentric inlet port is being developed as an implantable artificial heart by the Baylor College of Medicine and Miwatec Co Ltd Flow visualization measurements were conducted to compare the flow around the pivot for two impeller operational modes: the top and the bottom contact modes In the top contact mode, one-way flow in the pivot gap due to the eccentric vortex was observed, and sufficient wall shear rate to prevent thrombus formation was attained around the bottom pivot for over 1,400 rpm Computational fluid dynamic analyses confirmed that the causes of the eccentric vortex were the inlet eccentricity and the pressure imbalance in the volute

P1D-7 Ultrasonic Measurement Systems of Mechanical Properties for Tissue-Engineered Vessel Wall Evaluation

Abstract: Evaluations for biocompatibility and structural integrity of the tissue-engineered vessel wall before and after grafting it are important. These are closely related with mechanical properties. Therefore, in vitro and in vivo ultrasonic measurement systems for tissue-engineered vessel wall evaluation was developed based on the ultrasonic elasticity measurement method suited to the evaluation of mechanical properties, in this study. Based on the pressure-strain loops attained by the ultrasound catheter and pressure sensor, elastic modulus and compliance are measured. Feasibility studies for the measurement systems were conducted by using rubber tube phantoms and canine vein. Experimental results revealed that the developed systems could provide equivalent accuracies to standard tension test

Flow visualization analysis of a monopivot centrifugal blood pump developed by MERA

Abstract: A circulatory assist pump, which can be used for around two weeks after an operation, is under development by MERA. For R&D of a centrifugal blood pump it is important to prevent the thrombus formation caused by low shear stress and the hemolysis caused by high shear stress. Flow visualization analysis was performed around the pivot to prevent thrombus formation. We analyzed horizontal and vertical section around the pivot and enough washout to prevent thrombus formation was verified. In addition, a slight stagnant region was found in the outlet section and a relatively weak jet in the impeller tip region. Hemolysis tests were conducted also under the conditions of 100mmHg-5L/min and 200mmHg-5L/min. Hemolysis index, NIH, was 150% of BPX-80 under the condition of 100mmHg-5L/min, and 80% of BPX-80 under the condition of 200mmHg-5L/min. The hemolysis rate improves for high pressure conditions.