MITRAL HEART-VALVE CAVITATION IN AN ARTIFICIAL-HEART ENVIRONMENT

Background and aims of the study: The formation and subsequent collaps e of vaporous cavities in the fluid around mechanical heart valves at valve closure can create stresses large enough to damage both the valv e itself and blood cells. Improved understanding of cavitation mechani sms should lead to a reduction in the cavitation potential of future v alve designs. Materials and Methods: This study compares eight mechani cal mitral valves of two different geometries (Monostrut and Medtronic Hall), occluder housing gaps (tight medium, and leaky), and occluder materials (Delrin and pyrolytic carbon). The valves were evaluated in a model ventricle of I-he Penn State Electric Ventricular Assist Devic e (EVAD) operating within a mock circulatory loop. The EVAD represents one half of a total artificial heart. The mock loop consisted of sili cone tubing connected to elements designed to mimic the compliant and resistant properties of the natural circulation. Cavitation was contro lled by varying the degree of filling of the ventricle: low filling ca used higher valve closing velocities resulting in greater cavitation i ntensities than complete filling of the ventricle. The intensity of ca vitation was quantified using a parameter derived from the high freque ncy fluctuations in the mitral pressure that occur around the valve du ring cavitation events. The shape of the cavitation pressure signature and that of the power spectrum of the cavitation pressure signature w ere used in addition to the cavitation intensity parameter to make com parisons between valves. Results: Of the three valve characteristics s tudied, occluder material showed the most significant influence on cav itation intensity: valves with pyrolytic carbon occluders demonstrated greater cavitation than did those with Delrin discs. Conclusion: It i s hypothesized that the dominant form of cavitation on the valves stud ied is related to vortex formation and that occluder material influenc es the intensity of cavitation through the strength of the tension wav e generated at valve closure, while geometry and gap have only seconda ry effects. Future studies are planned to incorporate this technique i n an in vivo environment.