The velocity distributions in the clearance gap of the Kyoto-NTN biocentrifugal ventricular assist device model were measured by laser Doppler velocimetry (LDV) at three inlet flow conditions, namely operating, fully opened, and fully closed conditions. The results obtained have a similar trend as in the earlier measurements using air as medium and the hot-wire probe, a washout mechanism that is a segment of fluids in the gap situated from theta = 60 degrees to 220 degrees, has a larger radial velocity component flowing toward the eye of the pump, as compared to other regions in the gap where the tangential velocity component is dominant. It is essential to have a good washout for the leakage flow through the clearance gap between the stationary casing and the impeller of the pump so that the blood will not keep on circulating in the gap but is washed out to the eye in order to reduce the chances of being destroyed. Although the detailed velocity distributions are not the same, this should be due to the minor fabrication differences between two pump models. The current noninvasive LDV measurements should have a better representation of the actual flow field than the earlier studies due to the blood analog being used as the flow medium. Furthermore, as compared to the methods used in the earlier studies, there is basically no modification of the pump geometry in the present measurement.

This study was designed to examine the effects of the anastomotic angle on the flow and haemodynamic parameter distribution patterns of the proximal anastomoses, with emphasis on identifying site-specific haemodynamic features that could reasonably be expected to trigger the initiation and further development of anastomotic intimal hyperplasia. Particle image velocimetry measurements were carried out with three simplified glass proximal models under a physiological flow condition. The results revealed that the disturbed flow and the induced shear stress patterns including low recirculation flow, stagnation point, high wall shear stress, high temporal wall shear stress gradient, low time-averaged wall shear stress (TAWSS), and high oscillating shear index (OSI) occurred around the anastomotic joints and the flow field at proximal anastomosis was strongly affected by the anastomotic angle. Among the three models investigated, the 45 degrees backward anastomosis is found to have a smaller low-recirculation-flow region along the graft inner wall, non-stationary stagnation, and separation points, a higher TAWSS and smaller high-OSI low-TAWSS and low-OSI high-TAWSS regions.

No abstract

Coronary artery bypass grafting, the major treatment for coronary stenosis, has long-term patency problem due to intimal hyperplasia along the graft and at the graft/artery junction (proximal and distal anastomoses). It is well demonstrated that the hemodynamic factors are linked to the development of intimal hyperplasia and have been hypothesized as a cause of bypass graft failure. Although some researchers had investigated distal anastomosis, further studies upon the proximal anastomosis and even the complete bypass model, including both proximal and distal anastomoses, are still lacking in the literature and it is important and necessary for a better understanding of CABG. Therefore in this project, flow characteristics and hemodynamic parameters (HPs) distributions of proximal anastomosis and the whole bypass model were studied in order to enhance the understanding of the stenosis pathophysiological process and provide useful information for sleeve design and medical doctors. Furthermore, geometrical improvement to the distal anastomosis was proposed to reduce the nonuniformity of hemodynamics and the hemodynamic performance was evaluated and compared with a baseline distal anastomosis model. At the first stage, the effects of proximal anastomotic angle on local hemodynamics were studied to provide useful information for medical doctors and serve as the basis for the design of a whole anastomosis model, with emphasis on identifying site-specific hemodynamic features that could reasonably be expected in triggering the initiation and further development of anastomotic intimal hyperplasia. PIV measurements revealed that the flow fields in the proximal anastomosis were strongly influenced by the anastomotic angle. A large size of flow separation region was found along the graft inner wall just

Local hemodynamics of complete bypass model under steady flow condition was investigated using the instantaneous velocity fields acquired by Particle Image Velocimetry (PIV). At proximal anastomosis a low velocity region was found near the heel along the graft inner wall and a stagnation point was found near the toe. The velocity profile was relatively smooth except slightly skew toward the graft outer wall. Near the occluded end of the distal anastomosis, the fluid was found almost stationary although a weak recirculation occurred. Higher wall shear stress was found to be located at the toe and the artery bed near the toe of the distal anastomosis.