Role of computational fluid mechanics in the analysis of prosthetic heart valve flow

Unsteady effects on the flow across tilting disk valves

The present study simulates numerically the flow across two-dimensional tilting disk models of mechanical heart valves. The time-dependent Navier-Stokes equations are solved to assess the importance of unsteady effects in the fully open position of the valve. Flow cases with steady or physiological inflow conditions and with fixed or moving valves are solved. The simulations lead into mixed conclusions. It is obvious that steady inflow cases that account for vortex shedding only cannot model realistic physiological cases. In cases with imposed physiological inflow, the details of the flow field for fixed and moving valves might differ in the fully open position as well, although the gross features are quite similar. The fixed valve case consistently results in safe estimations of several critical quantities such as the axial force, the maximal shear stress on the valve, or the transvalvular pressure drop. Thus, fixed valve simulations can provide useful information for the design of prosthetic heart valves, as long as the properties in the fully open position only are sought.

Development of a ceramic conduit valve prosthesis for corrective cardiovascular surgery

This paper reports some of the ways in which biomaterial considerations have influenced the design, development and construction methods for a prototype conduit valve prosthesis in which the valve body is made from alumina. This material is used principally for its ability to grow and support a thin (< 0.1 mm) tissue covering on the surfaces in contact with the blood. This non-vascular covering does not interfere with the operation of the valve, but is thick enough to camouflage the underlying surface from any further interaction with the blood. This is important for any conduit valve because of the large internal surface area, but would be especially beneficial for children if it could obviate the need for chronic anticoagulation.

Fluid dynamic study of the moving actuator type total artificial heart by image-processing technique

Flow velocity inside the artificial ventricle of a moving actuator type total artificial heart is investigated by the image-processing technique. Optical flow is estimated from two sequential images of flow patterns to find flow-velocity distribution. The region with high velocity inside the artificial ventricle is found from the estimated flow-velocity distribution. Fluid velocity in a simple glass conduit is analysed and can be estimated by calculating optical flow.

Limitations of flow detection by color Doppler: in vitro comparison to conventional Doppler

There is little awareness of the limitations of flow detection with the commercially available color Doppler flow mapping system. The influence of flow velocity, ultrasound attenuation, and penetration depth on flow detection in color Doppler (Toshiba SSH 65A) were therefore studied in vitro and compared with conventional Doppler. The flow model had physiological flow volumes and laminar flow with parabolic velocity profile in a horizontal tube of Lucite with less than 3 degrees of coincidence. Conventional Doppler flow velocity measurements correlated highly with laser Doppler anemometry results (r = 0.99, SEE = 3 cm/sec). Signal strength of color Doppler and pulsed Doppler was semi-quantitatively graded using a scale from 0 to 5. Scale 1 (sparse signals) was useless for any assessment in color Doppler but just allowed velocity measurement in pulsed Doppler. Using 19-dB attenuation, flow velocities greater than 100 cm/sec had good scores with moderate gain, 60-100 cm/sec needed increasing gain, and velocities less than 40 cm/sec were not detectable with color Doppler but readily so with pulsed Doppler. With increasing attenuation (1-29 dB) and also with increasing penetration depth, flow detection was reduced significantly (P less than 0.001) more in color Doppler than in the pulsed technique (P less than 0.01). In conclusion, low flow velocities, high attenuation, and greater than 8 cm penetration depth may hamper flow detection in color Doppler and, thus, diagnostic accuracy. Conventional Doppler with its superior accuracy and sensitivity should therefore consolidate diagnostic ultrasound assessment.