Yamazaki K, Mori T, Tomioka J, Litwak P, Antaki J F, Tagusari O, Koyanagi H, Griffith B P, Kormos R L
University of Pittsburgh Medical Center, Pennsylvania, USA.
ASAIO J. 1997 Sep-Oct;43(5):M567-71.
A critical issue facing the development of an implantable, rotary blood pump is the maintenance of an effective seal at the rotating shaft. Mechanical seals are the most versatile type of seal in wide industrial applications. However, in a rotary blood pump, typical seal life is much shorter than required for chronic support. Seal failure is related to adhesion and aggregation of heat denatured blood proteins that diffuse into the lubricating film between seal faces. Among the blood proteins, fibrinogen plays an important role due to its strong propensity for adhesion and low transition temperature (approximately 50 degrees C). Once exposed to temperature exceeding 50 degrees C, fibrinogen molecules fuse together by multi-attachment between heat denatured D-domains. This quasi-polymerized fibrin increases the frictional heat, which proliferates the process into seal failure. If the temperature of the seal faces is maintained well below 50 degrees C, a mechanical seal would not fail in blood. Based on this "Cool-Seal" concept, we developed a miniature mechanical seal made of highly thermally conductive material (SiC), combined with a recirculating purge system. A large supply of purge fluid is recirculated behind the seal face to augment convective heat transfer to maintain the seal temperature below 40 degrees C. It also cools all heat generating pump parts (motor coil, bearing, seal). The purge consumption has been optimized to virtually nil (< 0.5 cc/day). An ultrafiltration unit integrated in the recirculating purge system continuously purifies and sterilizes the purge fluid for more than 5 months without filter change. The seal system has now been incorporated into our intraventricular axial flow blood pump (IVAP) and newly designed centrifugal pump. Ongoing in vivo evaluation of these systems has demonstrated good seal integrity for more than 160 days. The Cool-Seal system can be applied to any type of rotary blood pump (axial, diagonal, centrifugal, etc.) and offers a practical solution to the shaft seal problem and heat related complications, which currently limit the use of implantable rotary blood pumps.
植入式旋转血泵的发展面临的一个关键问题是在旋转轴处保持有效的密封。机械密封是广泛应用于工业领域中最为通用的密封类型。然而，在旋转血泵中，典型的密封寿命远短于长期支持所需的时间。密封失效与热变性血液蛋白的粘附和聚集有关，这些蛋白会扩散到密封面之间的润滑膜中。在血液蛋白中，纤维蛋白原因其强烈的粘附倾向和较低的转变温度（约50摄氏度）而起着重要作用。一旦暴露于超过50摄氏度的温度下，纤维蛋白原分子会通过热变性D结构域之间的多重附着而融合在一起。这种准聚合的纤维蛋白会增加摩擦热，从而使该过程进一步发展导致密封失效。如果密封面的温度保持在远低于50摄氏度的水平，机械密封在血液中就不会失效。基于这种“冷密封”概念，我们开发了一种由高导热材料（碳化硅）制成的微型机械密封，并结合了循环冲洗系统。大量的冲洗液在密封面后方循环，以增强对流热传递，将密封温度保持在40摄氏度以下。它还能冷却所有产生热量的泵部件（电机线圈、轴承、密封）。冲洗液的消耗量已优化至几乎为零（<0.5毫升/天）。集成在循环冲洗系统中的超滤单元可连续净化和消毒冲洗液，超过5个月无需更换过滤器。该密封系统现已应用于我们的脑室内轴流血泵（IVAP）和新设计的离心泵中。对这些系统正在进行的体内评估表明，密封完整性良好，超过了160天。冷密封系统可应用于任何类型的旋转血泵（轴流、斜流、离心等），为轴密封问题和与热相关的并发症提供了切实可行的解决方案，而这些问题目前限制了植入式旋转血泵的使用。
