Sneckenberger D S, Stinebring D R, Deutsch S, Geselowitz D B, Tarbell J M
Bioengineering Program, Pennsylvania State University, University Park 16802-4400, USA.
J Heart Valve Dis. 1996 Mar;5(2):216-27.
The formation and subsequent collapse of vaporous cavities in the fluid around mechanical heart valves at valve closure can create stresses large enough to damage both the valve itself and blood cells. Improved understanding of cavitation mechanisms should lead to a reduction in the cavitation potential of future valve designs.
This study compares eight mechanical 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 the Penn State Electric Ventricular Assist Device (EVAD) operating within a mock circulatory loop. The EVAD represents one half of a total artificial heart. The mock loop consisted of silicone tubing connected to elements designed to mimic the compliant and resistant properties of the natural circulation. Cavitation was controlled by varying the degree of filling of the ventricle: low filling caused higher valve closing velocities resulting in greater cavitation intensities than complete filling of the ventricle. The intensity of cavitation was quantified using a parameter derived from the high frequency fluctuations in the mitral pressure that occur around the valve during cavitation events. The shape of the cavitation pressure signature and that of the power spectrum of the cavitation pressure signature were used in addition to the cavitation intensity parameter to make comparisons between valves.
Of the three valve characteristics studied, occluder material showed the most significant influence on cavitation intensity: valves with pyrolytic carbon occluders demonstrated greater cavitation than did those with Delrin discs.
It is hypothesized that the dominant form of cavitation on the valves studied is related to vortex formation and that occluder material influences the intensity of cavitation through the strength of the tension wave generated at valve closure, while geometry and gap have only secondary effects. Future studies are planned to incorporate this technique in an in vivo environment.
机械心脏瓣膜关闭时，瓣膜周围流体中蒸汽腔的形成及随后的坍塌会产生足够大的应力，从而损坏瓣膜本身和血细胞。更好地理解空化机制应能降低未来瓣膜设计中的空化可能性。
本研究比较了两种不同几何形状（单支柱型和美敦力霍尔型）、封堵器与外壳间隙（紧密、中等和泄漏）以及封堵器材料（聚甲醛和热解碳）的八个机械二尖瓣。这些瓣膜在宾夕法尼亚州立大学电动心室辅助装置（EVAD）的模型心室中进行评估，该装置在模拟循环回路中运行。EVAD代表全人工心脏的一半。模拟回路由硅胶管连接到旨在模拟自然循环顺应性和阻力特性的元件组成。通过改变心室的充盈程度来控制空化：低充盈导致更高的瓣膜关闭速度，从而产生比心室完全充盈时更大的空化强度。空化强度通过一个从空化事件期间瓣膜周围二尖瓣压力的高频波动中得出的参数来量化。除了空化强度参数外，还使用空化压力特征的形状和空化压力特征的功率谱形状来比较不同瓣膜。
在所研究的三个瓣膜特征中，封堵器材料对空化强度的影响最为显著：带有热解碳封堵器的瓣膜比带有聚甲醛圆盘的瓣膜表现出更大的空化。
据推测，所研究瓣膜上的主要空化形式与涡旋形成有关，封堵器材料通过瓣膜关闭时产生的张力波强度影响空化强度，而几何形状和间隙仅具有次要影响。计划在未来的研究中将该技术应用于体内环境。
