Modification of miniature flush surface wall shear probes for biomedical use

A review of the in vitro evaluation of conduit-mounted cardiac valve prostheses

This review concerns the issues affecting the in vitro evaluation of conduit-mounted prosthetic heart valves at the design development stage, and the question of standardisation of testing at the quality assurance stage. Particular attention is given to areas of conduit valve development and research which have been neglected, ambiguously covered or left to the discretion of the researcher in the current standard for conventional prosthetic valves, ISO 5840.

In-vitro wall shear measurements at aortic valve prostheses

Wall shear distributions during the cardiac cycle at the valve rings of Starr-Edwards, Björk-Shiley and Lillehei-Kaster aortic valves are measured and compared with thresholds reported for shear-induced trauma of blood components. Further, for the disk valves, the influence of pulse rate on wall shear stresses is evaluated. Hot film anemometry with flush-mounted wall shear probes is used as measurement technique in a pulsatile flow mock circuit. The experimental systolic data support the better hemodynamic characteristics of the disk valves over the ball valve also with respect to the threshold shear stresses of flow induced blood trauma. These results are confirmed by postoperative clinical studies, where lower LDH-values are found with the disk than with the ball valves. During diastole, however, high shear stresses are measured and calculated at the valve ring of the Björk-Shiley prosthesis, which can be referred to the non-overlapping closing mechanism. This result is discussed with respect to the often observed thrombus formation at the disk downstream of the smaller orifice of the Björk-Shiley valve.