Biomedical subjects

G L Chahine

Publications and source records attributed to G L Chahine.

3 recordsLinked to original sources

PubMed1996

Scaling of mechanical heart valves for cavitation inception: observation and acoustic detection.

This paper discusses scaling laws of cavitation in mechanical heart valves based on analysis of leaflet operation and on hydrodynamic theory. It then suggests the laboratory use of large geometric scales and testing at low operating pressures to more easily investigate new heart valve designs. With such scaling, observations and measurements will become easier since the cavitation regions will be larger in dimension and the time scales will be increased due to reductions of bubble characteristic times and leaflet oscillation periods. The paper also discusses cavitation noise and the potential for acoustic detection of cavitation in a mechanical heart valve.

Biophysical Phenomena↗

PubMed1994

Cavitation dynamics at microscale level.

Cavitation in a liquid is known for its deleterious effects, namely erosion, noise and loss of performance. In a mechanical heart valve, stresses generated by cavitation could lead to catastrophic failure. These deleterious effects are directly connected to the dynamics of pre-existing microscopic nuclei in the liquid medium. To highlight this, a selective review of the dynamics of the bubbles at the microscopic levels is considered here; the various aspects of the problem are highlighted and briefly addressed; new areas of research in non-spherical and bubble cloud dynamics are then considered. The importance of the inclusion of these collective and non-uniform flow effects in the dynamics of bubbles in a realistic cavitating flow field is also elucidated.

Heart Valve Prosthesis↗

PubMed1994

Effect of cavitation on pyrolytic carbon in vitro.

It has long been known that mechanical heart valves, when tested for durability using non-physiologic conditions common in accelerated testers, would cavitate. Until recently, cavitation was never observed in vivo. The discovery that a small number of Edwards-Duromedics heart valve explants indicated signs of cavitation erosion prompted a reassessment of the cavitation erosion potential of pyrolytic carbon (PyC). Analyses of the explanted valves indicated that cavitation may be accentuated by porous regions in the pyrolytic carbon coating from which most mechanical heart valves are constructed. Early studies have shown that for PyC (a) the resistance to cavitation erosion is comparable to that of aluminum, (b) the resistance to cavitation erosion is high initially, but with time the erosion rate accelerates, and (c) the cavitation erosion resistance is somewhat variable. In this study, similar experiments were performed utilizing polished pyrolytic carbon as well as microporous surfaces since microporous surfaces have been implicated as accelerating erosion. Within the accuracy of the measurement, we found no contributing acceleration due to the microporous nature of the pyrolytic carbon surfaces tested when compared to the polished surfaces. Examination of cross sections of samples exposed to cavitation conditions revealed the presence of extensive microcracking even without the presence of substantial surface erosion.

Carbon↗