Cox James L, Ad Niv, Myers Keith, Gharib Mortiz, Quijano R C
Division of Cardiothoracic Surgery, Washington University School of Medicine, Barnes-Jewish Hospital, St Louis, MO 63110, USA.
J Thorac Cardiovasc Surg. 2005 Aug;130(2):520-7. doi: 10.1016/j.jtcvs.2004.12.054.
It was hypothesized that native heart valves function as if they were simple tubes with sides that collapse when external pressure is applied. Because "form follows function," this hypothesis could theoretically be confirmed by implanting a simple tube into the anatomic position of any native heart valve and documenting that under the same anatomic constraints and physiologic conditions as the native valve, the tube would assume the form of that native valve. If the hypothesis were thus proved, it would follow that a tissue valve based on a tubular design would have superior flow dynamics and stress distribution and would therefore be expected to outlast currently available tissue valves. Such a tubular tissue valve, the 3F Aortic Bioprosthesis (3F Therapeutics, Inc, Lake Forest, Calif) was designed and tested in vitro against a commercially available stentless aortic bioprosthesis.
With the use of state-of-the-art testing equipment, some of which had to be developed especially to test this truly stentless bioprosthesis in vitro, transvalvular gradients, effective orifice areas, degree of transvalvular laminar flow, finite element analysis of the distribution of leaflet stress, and accelerated wear testing for long-term durability were evaluated for the new 3F Aortic Bioprosthesis in comparison with the St Jude Medical Toronto SPV aortic bioprosthesis (St Jude Medical, Inc, St Paul, Minn).
The valve gradients were lower and the effective orifice areas were greater for the 3F Aortic Bioprosthesis at all valve sizes and under all test conditions, including cardiac outputs ranging from 2.0 to 7.0 L/min, mean perfusion pressures from 40 to 200 mm Hg, and aortic compliances of 4% and 16%. The transvalvular flow across the 3F Aortic Bioprosthesis in vitro was qualitatively smooth, with a minimum of surrounding vortices. Maximum stress occurred in the belly of the leaflets of the 3F Aortic Bioprosthesis, with minimum stress at the commissural posts. The 3F Aortic Bioprosthesis was superior to the Toronto SPV valve in accelerated wear tests.
These in vitro studies show that a tissue aortic valve designed on the basis of the proved engineering principle that form follows function has better hemodynamics, flow dynamics, stress distribution, and durability when compared under identical in vitro conditions with an excellent commercially available tissue aortic valve.
有假设认为，天然心脏瓣膜的功能就如同简单的管道，当施加外部压力时其管壁会塌陷。由于“形式追随功能”，从理论上讲，通过将一个简单的管道植入任何天然心脏瓣膜的解剖位置，并证明在与天然瓣膜相同的解剖限制和生理条件下，该管道会呈现出该天然瓣膜的形态，这一假设便可得到证实。如果该假设得到证实，那么基于管状设计的组织瓣膜将具有更优的血流动力学和应力分布，因此有望比目前可用的组织瓣膜使用寿命更长。这样一种管状组织瓣膜，即3F主动脉生物假体（3F Therapeutics公司，加利福尼亚州莱克福里斯特），已被设计出来并在体外与一种市售的无支架主动脉生物假体进行了测试。
使用了最先进的测试设备，其中一些设备是专门为在体外测试这种真正的无支架生物假体而开发的，对新型3F主动脉生物假体与圣犹达医疗多伦多SPV主动脉生物假体（圣犹达医疗公司，明尼苏达州圣保罗）进行了跨瓣压差、有效瓣口面积、跨瓣层流程度、瓣叶应力分布的有限元分析以及长期耐久性的加速磨损测试评估。
在所有瓣膜尺寸以及所有测试条件下，包括心输出量从2.0至7.0 L/分钟、平均灌注压力从40至200 mmHg以及主动脉顺应性为4%和16%时，3F主动脉生物假体的瓣膜压差更低，有效瓣口面积更大。体外通过3F主动脉生物假体的跨瓣血流在定性上较为平滑，周围涡流最少。3F主动脉生物假体瓣叶的中部出现最大应力，在瓣叶交界柱处应力最小。在加速磨损测试中，3F主动脉生物假体优于多伦多SPV瓣膜。
这些体外研究表明，基于已证实的“形式追随功能”这一工程原理设计的组织主动脉瓣膜，在相同体外条件下与一种优质的市售组织主动脉瓣膜相比，具有更好的血液动力学、血流动力学、应力分布和耐久性。
